Sedimentary Basins and Petroleum Geology of the Middle East

SEDIMENTARY BASINS AND PETROLEUM GEOLOGY OF THE MIDDLE EAST

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ELSEVIER SCIENCE B.V. Sara Burgerhartstraat 25 P.O. Box 211, 1000 AE Amsterdam, The Netherlands

9 2003 Elsevier Science B.V. All rights reserved.

This work is protected under copyright by Elsevier Science, and the following terms and conditions apply to its use: Photocopying Single photocopies of single chapters may be made for personal use as allowed by national copyright laws. Permission of the Publisher and payment of a fee is required for all other photocopying, including multiple or systematic copying, copying for advertising or promotional purposes, resale, and all forms of document delivery. Special rates are available for educational institutions that wish to make photocopies for non-profit educational classroom use. Permissions may be sought directly from Elsevier's Science & Technology Rights Department in Oxford, UK: phone: (+44) 1865 843830, fax: (+44) 1865 853333, e-maih [email protected]. You may also complete your request on-line via the Elsevier Science homepage (http://www.elsevier.com), by selecting 'Customer Support' and then 'Obtaining Permissions'. In the USA, users may clear permissions and make payments through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA; phone: (+1) (978) 7508400, fax: (+1) (978) 7504744, and in the UK through the Copyright Licensing Agency Rapid Clearance Service (CLARCS), 90 Tottenham Court Road, London W1P 0LP, UK; phone: (+44) 207 631 5555; fax: (+44) 207 631 5500. Other countries may have a local reprographic fights agency for payments. Derivative Works Tables of contents may be reproduced for internal circulation, but permission of Elsevier Science is required for external resale or distribution of such material. Permission of the Publisher is required for all other derivative works, including compilations and translations. Electronic Storage or Usage Permission of the Publisher is required to store or use electronically any material contained in this work, including any chapter or part of a chapter. Except as outlined above, no part of this work may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of the Publisher. Address permissions requests to: Elsevier's Science & Technology Rights Department, at the phone, fax and e-mail addresses noted above. Notice No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made.

First edition 1997 Second impression 2003 Library of Congress Cataloging in Publication Data

Alsharhan, A.S. Sedimentary basins and petroleum geology of the Middle East / A.S. Alsharhan, A.E.M. Nairn. p. cm. Includes bibliographical references and index. ISBN 0-444-82465-0 1. Sedimentary basins--Middle East. 2. Geology, Structural-Middle East. 3. Petroleum--Geology--Middle East. I. Nairn, A.E. M. I1. Title. QE615.5.M628A38 1997 97-48322 553.2'8'0956--dc21 CIP British Library Cataloguing in Publication Data A catalogue record from the British Library has been applied for. ISBN:

0-444-82465-0

O The paper used in this publication meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper). Printed in Hungary.

PREFACE

The wealth of petroleum has made the Middle East one of the most actively explored regions of the world. The volume of geological, geophysical and geochemical data collected by the petroleum industry in the last several decades has been enormous. The Middle East may be a unique region in the world where the volume of subsurface data and information exceeds that based on surface outcrop. Because of the confidential nature of petroleum exploration, however, a large amount of the most sensitive data and interpretations have been kept in oil company files, although other less sensitive information has been published in international, regional and local scientific journals. Unfortunately, however, these published data and information have caused confusion, due to a lack of uniformity and consistency. The problem has been particularly serious in the field of stratigraphy when a regionally accepted stratigraphic nomenclature has not been established. The situation has improved substantially since the 1960s, following a number of regional conferences such as Geo '94 and "96 as well as stratigraphic meetings between the operating companies. As a first step toward solving the problems of lithostratigraphic unification and standardization in countries where they operate, the Union Internationale des Sciences Geologiques in France established seven volumes of the Lexique Stratigraphique International under the direction of L. Dubertret. Published between 1.959 and 1975, they cover some parts of the Middle East, but left the remaining parts without a detailed stratigraphic lexicon. Prior to WWI, there was little in the way of a comprehensive study of the Middle East. Since that time, syntheses of the geology have tended to be of restricted areas, conducted by such pioneers as Powers in Saudi Arabia, Bender in Jordan, Dunnington in Iraq and Glennie in Oman. Comprehensive regional geologic overviews have been left to a few authorities of whom the contributions made by Beydoun are outstanding.. In completing this volume, we are indebted greatly to these earlier workers as well as to the many other geological experts whose detailed contributions have provided the groundwork for further synthesis. The chapters included in this volume cover the main aspects of regional stratigraphic and paleographic history, and of regional hydrocarbon potential. The regional stratigraphy and paleogeography are described on a country-by-country basis. Even through some repetition of description is inevitable by this method, it may be the most informative approach for readers because the many changes of formation names or formation lithology from area to area or from country to country are rather confusing. Furthermore, such repetition may be used as an indicator of stratigraphic similarities or differences. In an attempt to smooth out the differences in the stratigraphic nomenclature, the paleogeographic section at the end of each chapter describes and illustrates lateral facies changes from one part of a basin to another. From the Permo-Carboniferous onward, the cyclicity of deposition is more apparent in the region and an early rampplatform model was proposed by Murris (1980). Subsequently generalised under the influence of ethe ideas of eustatic sea-level change, the model emphasizes both the vertical and lateral variations of facies as clastics swept from paleohighs or older Paleozoic formations onto the platform during sea-level lowstands and renewed transgression restored dominant carbonate sedimentation~

As in the case of most Mesozoic formations of the Arabian Basin, the lithological description based on outcrops around the basin margins is inadequate because coarser clastic facies are commonly replaced in the deeper platform by carbonates and in the basins by argillaceous and fine carbonate muds. Therefore, it has been considered necessary to establish new type and reference sections based on wells as well as on outcrops in different parts of the basin. We have broken away from the traditional system-by-system approach, particularly when dealing with stratigraphy of the Paleozoic sequence, because of the paucity of faunal data that could clearly establish geologic age. Instead, we have applied the sequence stratigraphic terms introduced by Sloss, which emphasize the uniformity of the geologic events of the early Phanerozoic along the northern edge of Gondwana from Algeria to Jordan and beyond. It also emphasizes the diachroneity of the basal clastic features over the unconformity that terminated the late Proterozoic-early Phanerozoic sequence. By contrast, the Mesozoic sequence, so much better known and with a greater complexity, can be more readily handled in the classical manner integrated with the sequence stratigraphy proposed by Sloss for North America. The hydrocarbon potential of the region varies a great deal; in such countries as Jordan and Turkey, there have been relatively few oil/gas discoveries, whereas abundant oil production is known in Saudi Arabia, Iran, Iraq, Kuwait and the United Arab Emirates and the more recent active oil explorationt begun in Yemen. Both the richness of the petroleum resource and the stage of exploration have influenced the abundance and/or availability of critical geologic data. We have attempted to collect and analyze the available data and to tabulate major play types in each area. The principal sources of data are derived from such journals as the Bulletin of the American Association of Petroleum Geologists, Oil and Gas

Journal, Proceedings of the Society of Petroleum Engineers (Middle East Conference), the Arab Petroleum Congress proceedings and the Organization of the Arab Petroleum Exporting Countries (OAPEC) proceedings, as well as some local journals. The discussion of petroleum potential also is made on a country-by-country basis, because most oil statistics have been published by each country and cross-references to the stratigraphic and paleogeographic chapters of this book is madee easier. We believe that an understanding of geology and geologic history is essential for assessing the regional hydrocarbon potential. Many figures and tables drawn from the literature are included. Some of these have been modified, and some have been prepared especially for this volume. The list of acknowledgments is long, not only reflecting the diversity of sources, but even more emphasizing the courtesy extended to the authors of the present work. Inevitably, much has been missed, some of it because it was unavailable, some because it was or still is covered by confidentiality agreements, and some for linguistic reasons. There are gaps in information often reflecting the lack of published data, particularly apparent in the section dealing with hydrocarbon production. The inequality of the treatment is clearly apparent in the data-survey tables. However, errors and other shortcomings are the responsibility of the authors. The ultimate measure of the success of the volume is the use it will be to those interested in the geology of the Middle East in industry and academia. The areas we have not attempted to cover, despite their importance, are those of water, mineral resources and environmental issues.

A. S. Alsharhan, AI Ain, U.A.E. A. E. M. Nairn, Columbia, SC

ACKNOWLEDGEMENT

First and foremost, we would like to acknowledge our deep gratitude and appreciation to our wives and families for their forbearance and support, and their acceptance of the inroads c~ our time which resulted from the preparation of this volume. The book could never have taken shape without the help of many co-workers of whom we would like particularly to express our thanks to Ma. Bonita P. Valdez-Cruzada and Dhabia Bakhit for their help in all phases of writing, drafting and assembly of the book also to Eileen Ross, Jo Render and Connie Bartemus for their assistance in the preparation of the Text and to Rhonda Boyle, Valerie Gray, Joel McGee and Jamil Antar for their help in drafting the figures, and to our colleagues in the Earth Sciences and Resources Institute, especially M. Waddell, for their encouragement and support. We were fortunate to have colleagues such as R.W. Scott, K.W. Glennie, J. St6cklin, A.A. A1Laboun, R.J. Murris, J. Rogers, and K. Magara, who read critically initial rough drafts of some chapters of the book before finalization and whose comments improved the final text, and the long list of fellow scientists who provided copies of their work basic to the geology of the region. We thank our editor, Mrs. Femke Wallien, of Elsevier for her patience and encouragement from the inception of this book to its completion. The editors and publishers of many journals provided permission to reproduce many of the figures, in particular Elsevier Sciences and associate publisher Pergamon Press, American Association of Petroleum Geologists Bulletin, Bulletin of the Geological Society of America, Geological Society of London and associate journal Petroleum Geoscience, Dr. M.I. Husseini of Gulf Petrolink, Bahrain, Canadian Society of Petroleum Geologists, Journal of Petroleum Geology, American Geophysical Union, Schlumberger Middle East Technical Review, Society of Petroleum Engineers, Gordon and Breach (Modem Geology), Micropaleontology, John Wiley and Sons, Analytical Chemistry, Royal Society of Edinburgh, Palynology, Canadian Journal of Earth Science, Balkema, Cambridge University Press and associate joumal Geological Magazine, Chapman and Hall, Journal of Geophysics, International Association of Sedimentologists, Springer-Verlag, Oil and Gas Journal, and Nature. We would like to express our appreciation to His Highness Sheikh Nahyan Bin Mubarak A 1 Nahyan, Minister of Higher Education and Scientific Research and Chancellor of the United Arab Emirates University for his encouragement and support. In attempting to synthesize such a field as the Sedimentary Basins and Petroleum Geology of the Middle East, we have undoubtedly missed many references and under-represented a part of the field of study. We apologize for the pertinent work not cited and for the "gaps" in our text.

vii

DEDICATION

This book is dedicated to my mother and to the memory of my father.

A.S.A.

This book is dedicated to my family and friends.

A.E.M.N.

viii

TABLE OF CONTENTS PART ONE Chapter 1: An Introductory Overview G e o g r a p h i c and G e o m o r p h o l o g i c S e t t i n g ................................................................................. 1 Geologic Setting ................................................................................................................. 4 S e q u e n c e Stratigraphy .......................................................................................................... 7

Chapter 2: The Geological History and Structural Elements of the Middle East Introduction ........................................................................................................................ Geological History ............................................................................................................... Phase 1 T h e C o n s o l i d a t i o n of the A r a b o - N u b i a n M a s s i f ................................................ Phase 2 T e c t o n i c S t a b i l i t y ...................................................................................... Phase 3 T h e H e r c y n i a n E v e n t .................................................................................. Phase 4 T h e T r i a s s i c E x t e n s i o n a l P h a s e .................................................................... Phase 5 J u r a s s i c and C r e t a c e o u s E v e n t s ..................................................................... Phase 6 C e n o z o i c E v e n t s ....................................................................................... M a i n S t r u c t u r a l E l e m e n t s ..................................................................................................... 9 S e d i m e n t a r y B a s i n s .................................................................................................. T a b u k s u b - b a s i n , S a u d i A r a b i a ................................................................................ W i d y a n s u b - b a s i n , S a u d i A r a b i a .............................................................................. S i r h a n s u b - b a s i n , J o r d a n ........................................................................................ R u b A1 Khali and Ras A1 K h a i m a h sub-basins, Saudi A r a b i a - U . A . E ........................... Z a g r o s B a s i n , Iran ................................................................................................ P a l m y r a and Sinjar sub-basins, S y r i a - I r a q .................................................................. T h e M e s o p o t a m i a n s u b - b a s i n , Iraq ........................................................................... R e d Sea and G u l f of A d e n sub-basin, Saudi A r a b i a - Y e m e n .......................................... 9 Arches ................................................................................................................... H u q f - H a u s h i A r c h , O m a n ....................................................................................... H a d h r a m o u t A r c h , Y e m e n ...................................................................................... C e n t r a l A r a b i a n A r c h , Saudi A r a b i a .......................................................................... Q a t a r - S o u t h Fars A r c h , Q a t a r - Iran .......................................................................... H a i l - R u t b a h - G a ' a r a and K h l e i s s a Arches, Saudi A r a b i a - Iraq ........................................ M a r d i n H i g h , T u r k e y ............................................................................................. 9 T r a n s f o r m F a u l t s and N o r m a l Faults ........................................................................... S o u t h e a s t e r n A r a b i a n p l a t f o r m ................................................................................ M a s i r a h T r a n s f o r m Fault, O m a n ........................................................................ M a r a d i F a u l t , O m a n ........................................................................................ S a i w a n - N a f u n F a u l t , O m a n .............................................................................. D i b b a Z o n e , O m a n - U A E ............................................................................... O m a n Line, O m a n .......................................................................................... O w e n F r a c t u r e Z o n e , Y e m e n - O m a n .................................................................. N o r t h e r n A r a b i a n P l a t f o r m : Central Syrian F a u l t Z o n e .............................................. N o r t h w e s t e r n A r a b i a n P l a t f o r m : J o r d a n - D e a d Sea Fault S y s t e m ................................... Fold Belts: T a u r u s M o u n t a i n s , T u r k e y ................................................................... Z a g r o s , M o u n t a i n , Iran ........................................................................ O m a n M o u n t a i n s , O m a n - U . A . E .......................................................... Discussion ........................................................................................................................

15 22 22 36 37 38 38 39 44 46 47 47 47 48 48 50 50 50 52 52 52 52 53 53 53 54 54 54 54 54 54 54 54 54 54 55 58 59 62

TWO Chapter 3: Infracambrian of the Middle East

PART

Introduction ................................................................................................................... S t r a t i g r a p h y of I n f r a c a m b r i a n R o c k s in O m a n : ......................................................................... H u q f Group: ............................................................................................................. A b u M a h a r a F o r m a t i o n ......................................................................................... Khufai F o r m a t i o n ................................................................................................ S h u r a m F o r m a t i o n ............................................................................................... B u a h F o r m a t i o n .................................................................................................. Ara F o r m a t i o n ....................................................................................................

65 69 69 70 70 70 73 73

ix

CONTENTS

Th e A g e of the H u q f G r o u p ......................................................................................... C o m p a r i s o n of the Huqf Group with other Outcrops in Oman ..................................................... M i s t a l F o r m a t i o n ...................................................................................................... Haj ir F o r m a t i o n ........................................................................................................ M i ' a i d a n F o r m a t i o n ................................................................................................... K h a r u s F o r m a t i o n ...................................................................................................... H i j a m F o r m a t i o n ....................................................................................................... C o m p a r i s o n of Oman with other Outcrops in the Middle East .................................................... C o m p a r i s o n with the Republic of Y e m e n ....................................................................... C o m p a r i s o n with the United Arab Emirates .................................................................... C o m p a r i s o n with Saudi Arabia .................................................................................... C o m p a r i s o n with Jordan ............................................................................................. C o m p a r i s o n with Southeast T u r k e y .............................................................................. C o m p a r i s o n with Iraq ................................................................................................. C o m p a r i s o n with Iran ................................................................................................. P a l e o g e o g r a p h y and Geologic History of the Infracambrian .........................................................

74 76 76 76 76 76 76 77 77 78 78 80 81 81 81 84

Chapter 4: The Early Paleozoic Quiescent. Phase in the Middle East: The Sauk Cycle and the Early Part of the Tippecanoe Cycle Introduction ................................................................................................................... The E arl y P a l e o z o i c of O m a n ................................................................................................ 9 The Sauk Sequence in Central and South-central Oman ................................................... H a i m a G r o u p (Cambrian? to earliest Silurian): .......................................................... The Karim and Haradh formations ..................................................................... T h e A m i n F o r m a t i o n ..................................................................................... The M a h w i s / A n d a m f o rm at i o n s ........................................................................ 9 The T i p p e c a n o e Sequence in Central Oman: ................................................................. G h u d u n F o r m a t i o n ............................................................................................... Safiq F o r m a t i o n .................................................................................................. 9The Sauk and Tippecanoe Sequences in Southern Oman (Dhofar Province): ......................... M u r b a t S a n d s t o n e F o r m a t i o n ................................................................................. 9The Sauk and Tippecanoe Sequences in Eastern and Southwestern Arabia ........................... O m a n Mountains (Oman Region): A m d e h Fo r m at i o n ................................................ Oman Mountains (United Arab Emirates Region): R a ' a n Formation .............................. S o u t h w e s t e r n Saudi Arabia: Dibsiyah F o r m a t i o n ....................................................... The Early Paleozoic of Northern Saudi Arabia and Jordan ........................................................... 9 The Sauk Sequence in North and Northwestern Saudi Arabia: ........................................... Y a t ib F o r m a t i o n .................................................................................................. Saq F o r m a t i o n .................................................................................................... 9 T h e Sauk S e q u e n c e in Jordan ..................................................................................... R a m G r o u p ....................................................................................................... S u b s u r f a c e F o r m a t i o n s : .................................................................................. Salib F o r m a t i o n ...................................................................................... Burj and Abu K h u s h e i b a formations ............................................................ A j r a m F o r m a t i o n ..................................................................................... A m u d F o r m a t i o n ..................................................................................... S u r f a c e F o r m a t i o n s : ....................................................................................... Salib Arkosic Sandstone F o r m a t i o n ............................................................ U m m Ishrin S a n d s to n e F o r m a t i o n .............................................................. Disi S a n d s t o n e F o r m a t i o n ......................................................................... U m m Sahm Sandstone F o r m a t i o n .............................................................. 9 The Tippecanoe Sequence in North and Northwestern Saudi Arabia: .................................... T a b u k G r o u p : ................................................................................................ H a n a d i r F o r m a t i o n ..................................................................................... Kahfah F o r m a t i o n .................................................................................... R a ' a n F o r m a t i o n ....................................................................................... Quwarah Formation (and its equivalent Ordovician Formations 1-5) .....................

87 94 94 94 94 95 95 96 96 96 97 97 98 98 100 100 103 103 103 103 108 108 108 108 110 110 110 110 110 111

111 111 111 111 112 112 113 114

CONTENTS

Z a r q a F o r m a t i o n ........................................................................................ S a r a h F o r m a t i o n ....................................................................................... Q a l i b a h F o r m a t i o n .................................................................................... 9 T h e T i p p e c a n o e S e q u e n c e in J o r d a n ............................................................................ K h r e i m G r o u p ............................................................................................... S u b s u r f a c e F o r m a t i o n s : ............................................................................... Sahl as S u w w a n F o r m a t i o n ....................................................................... U m m T a r i f a F o r m a t i o n ............................................................................. T r e b e e l F o r m a t i o n ................................................................................... B a t r a F o r m a t i o n ...................................................................................... A l n a F o r m a t i o n ....................................................................................... S u r f a c e F o r m a t i o n s " . ................................................................................... H i s w a h F o r m a t i o n ................................................................................... D u b a y d i b F o r m a t i o n ................................................................................ M u d a w w a r a F o r m a t i o n ............................................................................. K h u s h s h a F o r m a t i o n ................................................................................ 9 T h e T i p p e c a n o e S e q u e n c e in Iraq: K h a b o u r F o r m a t i o n .................................................... 9 T h e T i p p e c a n o e S e q u e n c e in Kuwait: T a b u k F o r m a t i o n .................................................. 9 T h e T i p p e c a n o e S e q u e n c e in Qatar: ............................................................................. T a b u k F o r m a t i o n ................................................................................................ S h a r a w r a F o r m a t i o n ............................................................................................. 9 T h e T i p p e c a n o e S e q u e n c e in the United Arab Emirates: S h a r a w r a F o r m a t i o n ....................... T h e E a r l y P a l e o z o i c S e q u e n c e in Southeast T u r k e y and Syria ...................................................... 9 T h e S a u k S e q u e n c e in S o u t h e a s t T u r k e y : ..................................................................... S a d a n F o r m a t i o n ........................................................................................... Z a b u k F o r m a t i o n .......................................................................................... K o r u k F o r m a t i o n ........................................................................................... S o s i n k F o r m a t i o n .......................................................................................... S e y d i s e h i r F o r m a t i o n ..................................................................................... 9 T h e S a u k S e q u e n c e in Syria: Zabuk, Burj and Sosink f o r m a t i o n s ...................................... 9 T h e T i p p e c a n o e S e q u e n c e in S o u t h e a s t Turkey" B e d i n a n F o r m a t i o n ......................................................................................... S o r t T e p e F o r m a t i o n ...................................................................................... 9 T h e T i p p e c a n o e S e q u e n c e in Syria: ............................................................................. K h a n a s s e r F o r m a t i o n ...................................................................................... S w a b F o r m a t i o n ............................................................................................ Afandi Formation ......................................................................................... T a n f F o r m a t i o n ............................................................................................. T h e E a r l y P a l e o z o i c o f I r a n .................................................................................................... 9 T h e S a u k S e q u e n c e ................................................................................................... L a l u n F o r m a t i o n ........................................................................................... D a h u F o r m a t i o n ............................................................................................ M i l a F o r m a t i o n ............................................................................................. K a l s h a n e h F o r m a t i o n ..................................................................................... D e r e n j a l F o r m a t i o n ........................................................................................ I l e b e y k F o r m a t i o n ......................................................................................... 9 T h e T i p p e c a n o e S e q u e n c e : ......................................................................................... S h i r g e s h t F o r m a t i o n ...................................................................................... N i u r F o r m a t i o n ............................................................................................. L a s h k e r a k F o r m a t i o n ...................................................................................... Z a r d K u h F o r m a t i o n ....................................................................................... P a l e o g e o g r a p h y and G e o l o g i c History o f the Early P a l e o z o i c ......................................................

114 115 115 115 116 116 116 119 119 119 119 119 119 120 120 120 120 121 121 121 121 122 123 123 123 123 126 126 126 128 128 128 128 128 129 129 129 129 129 129 129 129 130 130 130 130 133 133 133 133 134 134

Chapter 5: The Early-Late Paleozoic of the Middle East: The Kaskaskia Cycle Introduction ................................................................................................................... T h e K a s k a s k i a C y c l e in the M i d d l e E a s t ................................................................................. 9 T h e K a s k a s k i a S e q u e n c e in N o r t h e r n Saudi A r a b i a ........................................................

141 141 141

xi

CONTENTS

J a u f F o r m a t i o n .................................................................................................... S a k a k a F o r m a t i o n ................................................................................................ P r e - U n a y z a h Clastics ( B e r w a t h F o r m a t i o n ) ............................................................... 9 T h e K a s k a s k i a Sequence in Southwest Saudi Arabia: K h u s a y y a y n F o r m a t i o n ....................... 9 T h e K a s k a s k i a S e q u e n c e in Qatar: Tawil F o r m a t i o n ....................................................... 9 T h e K a s k a s k i a S e q u e n c e in the United Arab Emirates: .................................................... O u t c r o p F o r m a t i o n : A y i m F o r m a t i o n ...................................................................... S u b s u r f a c e F o r m a t i o n : T a w i l F o r m a t i o n .................................................................. 9 T h e K a s k a s k i a S e q u e n c e in Oman: M i s f a r G r o u p ........................................................... 9 T h e K a s k a s k i a S e q u e n c e in Kuwait: J a u f F o r m a t i o n ....................................................... 9 T h e K a s k a s k i a S e q u e n c e in Iran: ................................................................................. P a d e h a F o r m a t i o n .......................................................................................... S i b z a r F o r m a t i o n ........................................................................................... B a h r a m F o r m a t i o n ......................................................................................... G e i r u d F o r m a t i o n .......................................................................................... 9 T h e K a s k a s k i a S e q u e n c e in Iraq" . Pirispiki Redbeds K a i s t a F o r m a t i o n ........................................................................................... O r a S h a l e F o r m a t i o n ...................................................................................... H a r u r F o r m a t i o n ............................................................................................. 9 T h e K a s k a s k i a S e q u e n c e in S o u t h e a s t T u r k e y : ............................................................... D a d a s F o r m a t i o n ........................................................................................... H a z r o F o r m a t i o n ........................................................................................... Y i g i n l i F o r m a t i o n ......................................................................................... K o p r u l u F o r m a t i o n ........................................................................................ Kirtas Quartzite and H a s a n b e y l i F o r m a t i o n s ........................................................ 9 T h e K a s k a s k i a S e q u e n c e in Syria: M a r k a d a G r o u p .......................................................... P a l e o g e o g r a p h y and G e o l o g i c History of the Late Paleozoic K a s k a s k i a C y c l e .................................

141 147 148 148 149 149 149 149 150 150 150 150 150 150 150 150 151 151 151 151 151 151 153 153 153 154 154 156

Chapter 6: The End of the Paleozoic and the Early Mesozoic of the Middle East: The Absaroka Cycle T h e L o w e r Part o f the A b s a r o k a C y c l e (Latest C a r b o n i f e r o u s - P e r m i a n ) ......................................... T h e P a l e o z o i c Part o f the A b s a r o k a C y c l e ............................................................................... A b s a r o k a S e q u e n c e South of the Central Arabian Arch ...................................................... 9 A b s a r o k a S e q u e n c e in O m a n ................................................................................ Haushi Group" . ............................................. A1 K h l a t a F o r m a t i o n ............................................................................... G h a r i f F o r m a t i o n ................................................................................... K h u f f F o r m a t i o n ........................................................................................... S a i q F o r m a t i o n ............................................................................................. 9 A b s a r o k a S e q u e n c e in the United Arab Emirates: ..................................................... S u b s u r f a c e F o r m a t i o n s : H a u s h i G r o u p : .............................................................. G h a r i f F o r m a t i o n .................................................. A1 K h l a t a F o r m a t i o n .............................................. K h u f f F o r m a t i o n ................................................... Surface F o r m a t i o n s : A s f a r and Q a m a r f o r m a t i o n s .................................................. R u s s A1 Jibal G r o u p : ................................................ B i h F o r m a t i o n ...................................................... H a g i l F o r m a t i o n ................................................... G h a i l F o r m a t i o n ................................................... 9 A b s a r o k a S e q u e n c e in Qatar: ................................................................................ H a u s h i F o r m a t i o n .......................................................................................... K h u f f F o r m a t i o n ........................................................................................... 9 A b s a r o k a Sequence in southwestern Saudi Arabia:Juwayl M e m b e r " . ......... 9 A b s a r o k a Sequence in the Republic of Yemen: Akbra Shale F o r m a t i o n ........................ A b s a r o k a S e q u e n c e North of the Central Arabian Arch: ..................................................... 9 A b s a r o k a S e q u e n c e in Central and Northern Saudi Arabia ..........................................

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161 161 168 168 169 169 169 171 173 173 173 174 175 175 175 175 176 176 176 176 176 177 178 178 178 178

CONTENTS

U n a y z a h F o r m a t i o n ........................................................................................ K h u f f F o r m a t i o n ........................................................................................... 9 A b s a r o k a S e q u e n c e in Kuwait: K h u f f F o r m a t i o n ...................................................... 9 A b s a r o k a S e q u e n c e in Bahrain: K h u f f F o r m a t i o n ..................................................... A b s a r o k a S e q u e n c e in N o r t h w e s t and Northeast of the A r a b i a n P l a t f o r m ............................... 9 A b s a r o k a S e q u e n c e in J o r d a n ................................................................................. O u t c r o p Section: U m m Irna F o r m a t i o n .............................................................. S u b s u r f a c e Section: H u d a y b G r o u p ................................................................... A n j a r a F o r m a t i o n ........................................................... H u w a y r a F o r m a t i o n ........................................................ B u w a y d a F o r m a t i o n ........................................................ 9 A b s a r o k a S e q u e n c e in Iraq ................................................................................... W e s t e r n Iraq ( H a i l - R u t b a h A r c h area)" Nijili F o r m a t i o n ............................................................................. G a ' a r a F o r m a t i o n ............................................................................ N o r t h e r n Iraq (Northern Thrust Belt Area): Chia Zairi F o r m a t i o n ............................. 9 A b s a r o k a S e q u e n c e in S o u t h e a s t T u r k e y ................................................................ G o m a n i i b r i k F o r m a t i o n ................................................................................... 9 A b s a r o k a S e q u e n c e in Syria" Dolaa F o r m a t i o n ........................................................................................... Heil F o r m a t i o n ............................................................................................. A m a n u s S a n d F o r m a t i o n ................................................................................. 9 A b s a r o k a S e q u e n c e in Iran: .................................................................................. S o u t h w e s t Iran: F a r a g h a n F o r m a t i o n ............................................................ D a l a n F o r m a t i o n ................................................................ N o r t h e r n and C e n t r a l Iran: ............................................................................ D o r u d F o r m a t i o n ................................................................ R u t e h F o r m a t i o n ................................................................ N e s e n F o r m a t i o n ................................................................ J a m a l F o r m a t i o n ................................................................ T h e U p p e r Part o f the A b s a r o k a C y c l e (Triassic) .............................................................. T h e E n d o f the A b s a r o k a C y c l e in Central A r a b i a ............................................................ 9 T r i a s s i c o f S a u d i A r a b i a : ..................................................................................... S u d a i r F o r m a t i o n ........................................................................................... Jilh F o r m a t i o n .............................................................................................. Minjur F o r m a t i o n .......................................................................................... T h e E n d o f the A b s a r o k a C y c l e in E a s t e r n Arabia: ............................................................ 9 T r i a s s i c o f U n i t e d A r a b E m i r a t e s .......................................................................... A b u D h a b i and D u b a i R e g i o n ( S u b s u r f a c e Section) .............................................. S u d a i r F o r m a t i o n ................................................................ Jilh ( G u l a i l a h ) F o r m a t i o n ..................................................... M i n j u r F o r m a t i o n ............................................................... N o r t h e r n E m i r a t e s R e g i o n ( O u t c r o p S e c t i o n ) ...................................................... M i l a h a F o r m a t i o n ............................................................... G h a l i l a h F o r m a t i o n ............................................................. 9 T r i a s s i c o f O m a n ................................................................................................ C e n t r a l and S o u t h e r n O m a n ( S u b s u r f a c e Section) ................................................. S u d a i r F o r m a t i o n ................................................................ Jilh F o r m a t i o n ................................................................... C e n t r a l O m a n M o u n t a i n s ( A l l o c h t h o n o u s Units) ................................................. Mahil F o r m a t i o n ..................................................................................... Sumeini Group" M a q a m F o r m a t i o n ............................................................................. J e b e l W a s a F o r m a t i o n ....................................................................... H a w a s i n a A s s e m b l a g e ............................................................................... H a m r a t D u r u G r o u p : Z u l l a F o r m a t i o n ...................................................... W a h r a h F o r m a t i o n .............................................................................. A1 A y n F o r m a t i o n ..............................................................................

178 182 186 186 186 186 186 187 187 188 188 189 189 189 189 189 189 190 190 190 191 191 191 192 192 192 192 193 193 193 193 194 194 197 198 198 199 199 199 199 199 199 201 201 201 201 201 202 203 203 204 204 204 206 206 206 207 207

xiii

CONTENTS

Halfa F o r m a t i o n ................................................................................. H a l i w F o r m a t i o n ................................................................................ A1 A r i d h F o r m a t i o n ............................................................................ Ibra F o r m a t i o n ................................................................................... H a y b i Complex" ...................................................................................... H a w a s i n a M61ange .............................................................................. Exotic L i m e s t o n e ............................................................................... H a y b i V o l c a n i c s ................................................................................. B a s a l S e r p e n t i n e a n d T e c t o n i c M61ange ................................................... Batinah Complex" B a r g h a h F o r m a t i o n ............................................................................. Sakhin F o r m a t i o n ............................................................................... Salahi F o r m a t i o n ................................................................................ B a t i n a h L i m e s t o n e B l o c k s .................................................................... 9 T r i a s s i c o f Q a t a r ................................................................................................ S u w e i ( S u d a i r ) F o r m a t i o n ................................................................................ G u l a i l a h (Jilh) F o r m a t i o n ................................................................................. M i n j u r F o r m a t i o n ........................................................................................... T h e E n d o f the A b s a r o k a S e q u e n c e in the E a s t e r n A r a b i a n Gulf: . S o u t h w e s t e r n Iran .................. K a n g a n F o r m a t i o n ......................................................................................... D a s h t a k F o r m a t i o n ........................................................................................ K h a n e h K a t F o r m a t i o n ................................................................................... T h e E n d o f the A b s a r o k a S e q u e n c e in the C e n t r a l and N o r t h e r n A r a b i a n Gulf: ....................... 9 T h e T r i a s s i c o f B a h r a i n : ...................................................................................... Sudair F o r m a t i o n ............................................................................................ Jilh F o r m a t i o n ............................................................................................... 9 T h e T r i a s s i c o f K u w a i t : ....................................................................................... Sudair F o r m a t i o n ............................................................................................ Jilh F o r m a t i o n ............................................................................................... M i n j u r F o r m a t i o n ........................................................................................... T h e E n d o f the A b s a r o k a S e q u e n c e in N o r t h and N o r t h e a s t e r n Arabia: .................................. 9 T h e T r i a s s i c o f Iraq: ........................................................................................... M i r g a M i r F o r m a t i o n ..................................................................................... B e d u h S h a l e F o r m a t i o n .................................................................................... G e l i K h a n a F o r m a t i o n .................................................................................... M u l u s s a F o r m a t i o n ......................................................................................... Z u r H a u r a n F o r m a t i o n ..................................................................................... K u r r a C h i n e F o r m a t i o n ................................................................................... Baluti F o r m a t i o n ............................................................................................ 9 T h e T r i a s s i c o f J o r d a n : ........................................................................................ O u t c r o p F o r m a t i o n : ....................................................................................... A b u R u w e i s F o r m a t i o n ............................................................................... U m T i n a F o r m a t i o n .................................................................................... I r q A1 A m i r F o r m a t i o n ................................................................................. M u k h e i r i s F o r m a t i o n ................................................................................... H i s b a n F o r m a t i o n ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ain Musa Formafon ................................................................................... D a r d u n F o r m a t i o n ........................................................................................ Ma'in Formation ........................................................................................ S u b s u r f a c e F o r m a t i o n : R a m t h a G r o u p : ............................................................... S u w a y m a F o r m a t i o n .................................................................................... H i s b a n F o r m a t i o n ........................................................................................ M u k h e i r i s F o r m a t i o n ................................................................................... Salit F o r m a t i o n ........................................................................................... A b u R u w e i s F o r m a t i o n ................................................................................ 9 T h e T r i a s s i c o f S y r i a : .......................................................................................... A m a n u s S h a l e F o r m a t i o n ................................................................................. K u r r a C h i n e F o r m a t i o n .................................................................................... B u t m a h F o r m a t i o n ..........................................................................................

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209 209 209 211 211 211 211 211 211 211 213 213 213 213 213 213 213 214 214 216 217 217 217 217 217 217 218 218 218 218 218 218 218 218 218 219 219 220 220 220 220 220 220 220 221 221 221 221 221 222 222 222 222 223 223 223 223 223 224

CONTENTS

A d a i y a h F o r m a t i o n ......................................................................................... Mus Formation .............................................................................................. Alan Formation .............................................................................................. 9 T h e T r i a s s i c o f S o u t h e a s t T u r k e y : .......................................................................... Cigli Group ................................................................................................... Cudi F o r m a t i o n .......................................................................................... Aril Formation ............................................................................................ B e d u h F o r m a t i o n ......................................................................................... P a l e o g e o g r a p h y and G e o l o g i c History of the A b s a r o k a C y c l e .............................................. T h e L o w e r Part of the A b s a r o k a Cycle (latest C a r b o n i f e r o u s - P e r m i a n ) ............................ T h e U p p e r Part of the A b s a r o k a C y c l e (Triassic) .........................................................

224 224 224 224 224 224 224 224 225 225 229

Chapter 7: The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic Introduction ................................................................................................................... T h e J u r a s s i c S e c t i o n in C e n t r a l A r a b i a ................................................................................... T h e J u r a s s i c o f S a u d i A r a b i a : ....................................................................................... Marrat F o r m a t i o n ................................................................................................ Dhruma Formation ............................................................................................... T u w a i q M o u n t a i n F o r m a t i o n .................................................................................. Hanifa Formation ................................................................................................. Jubailah Formation ............................................................................................... Arab Formation .................................................................................................... Hith Formation .................................................................................................... T h e J u r a s s i c o f B a h r a i n ................................................................................................ Marrat Formation ................................................................................................. Dhruma Formation ............................................................................................... T u w a i q M o u n t a i n F o r m a t i o n .................................................................................. Hanifa Formation ................................................................................................. Jubailah Formation ............................................................................................... Arab Formation .................................................................................................... Hith Formation .................................................................................................... T h e Jurassic Section in Southern and S o u t h w e s t e r n Arabia: T h e Republic of Y e m e n ....................... Kohlan Formation ................................................................................................ Amran Group: ...................................................................................................... Shuqra Formation .............................................................................................. M a d b i F o r m a t i o n .............................................................................................. Sabatayn F o r m a t i o n ........................................................................................... Naifa Formation ................................................................................................ T h e J u r a s s i c S e c t i o n in E a s t e r n Arabia: ................................................................................... 9 T h e Jurassic of the U n i t e d Arab Emirates (Subsurface F o r m a t i o n s ) .................................... Marrat F o r m a t i o n ................................................................................................ Hamlah Formation ................................................................................................ Izhara F o r m a t i o n .................................................................................................. Araej Formation ................................................................................................... Diyab Formation .................................................................................................. Arab F o r m a t i o n and its equivalents (Fahahil and Qatar formations) ................................. Hith F o r m a t i o n and its e q u i v a l e n t s .......................................................................... The Jurassic of the Northern United Arab Emirates (Surface F o r m a t i o n s ) : M u s a n d a m G r o u p 9 T h e J u r a s s i c o f Q a t a r ................................................................................................ H a m l a h F o r m a t i o n ............................................................................................ Izhara Formation ............................................................................................... Araej Formation ................................................................................................ Diyab Formation ............................................................................................... Darb Formation ................................................................................................. H a n i f a and J u b a i l a h F o r m a t i o n s .............................................................................. A r a b F o r m a t i o n and its e q u i v a l e n t s : ........................................................................... Fahahil Formation ...........................................................................................

235 245 245 245 245 248 250 250 250 252 254 254 254 254 254 254 254 254 254 255 257 258 258 258 258 259 259 259 259 261 261 262 263 263 266 266 266 267 267 269 269 269 269 269

XV

CONTENTS

Qatar Formation Arab F o r m a t i o n .............................................................................................. Hith Formation .............................................................................................. T h e Jurassic S e c t i o n in E x t r e m e E a s t e r n Arabia" O m a n ............................................................... 9 T h e Jurassic o f N o r t h e r n Oman" M u s a n d a m G r o u p ......................................................... 9 T h e J u r a s s i c o f C e n t r a l O m a n ..................................................................................... S u b s u r f a c e F o r m a t i o n s : S a h t a n G r o u p : .................................................................... Mafraq F o r m a t i o n ............................................................................................. D h r u m a F o r m a t i o n ........................................................................................... T u w a i q M o u n t a i n F o r m a t i o n ............................................................................... Hanifa Formation .............................................................................................. Jubailah Formation ............................................................................................ S u r f a c e F o r m a t i o n s : S a h t a n G r o u p : .......................................................................... Saih Hatat F o r m a t i o n ......................................................................................... Mayhah Formation ............................................................................................ G u w e y z a S a n d s t o n e F o r m a t i o n ............................................................................. G u w e y z a L i m e s t o n e F o r m a t i o n ........................................................................... ~ T h e Jurassic o f S o u t h O m a n : K o h l a n F o r m a t i o n ............................................................ T h e Jurassic Section on the Eastern Side of the Arabian Gulf: S o u t h w e s t e r n Iran ............................. Neyriz Formation ....................................................................................................... Adaiyah Formation ..................................................................................................... Mus Formation .......................................................................................................... Alan Formation .......................................................................................................... Sargelu Formation ...................................................................................................... Najmah Formation ...................................................................................................... Gotnia Formation ....................................................................................................... Hith Formation ......................................................................................................... Surmah Formation ...................................................................................................... T h e J u r a s s i c S e c t i o n in N o r t h e a s t e r n A r a b i a : ............................................................................ ~ T h e J u r a s s i c o f K u w a i t : ............................................................................................. Marrat Formation ................................................................................................. Dhruma Formation ............................................................................................... Sargelu Formation ................................................................................................ Najmah Formation ................................................................................................ Gotnia Formation ................................................................................................. Hith Formation .................................................................................................... ~ T h e J u r a s s i c o f Iraq ................................................................................................... 1. L i a s s i c S e c t i o n o f Iraq: ..................................................................................... Ubaid Formation ............................................................................................ Butmah Formation' . ............................. Baluti Formation ............................................................................................ Adaiyah Formation ......................................................................................... Mus Formation .............................................................................................. Alan Formation .............................................................................................. Sarki Formation ............................................................................................. Sekhanian Formation ...................................................................................... 2. D o g g e r S e c t i o n o f Iraq: ..................................................................................... Muhaiwir Formation ....................................................................................... Sargelu Formation .......................................................................................... 3. M a l m S e c t i o n o f Iraq (Early S u b - C y c l e ) : ............................................................... Najmah Formation .......................................................................................... G o t n i a ( A n h y d r i t e ) F o r m a t i o n ........................................................................... N a o k e l e k a n F o r m a t i o n .................................................................................... Barsarin F o r m a t i o n ......................................................................................... 4. M a l t a S e c t i o n of Iraq (Late S u b - c y c l e ) : ................................................................ Makhul Formation .......................................................................................... Chia Gara F o r m a t i o n ....................................................................................... K a r i m a M u d s t o n e F o r m a t i o n ............................................................................ Sulaiy Formation ........................................................................................... ~ 1 7 6 1 7 . 6 . 1 . 7 . 6. 1 7~ 6 . . . . . . . . .

xvi

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~ 1 7 6 1 .7 6. .

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~ 1 7 6 1 7 .6 .1 .7 .6 1. 7. 6. .

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~ 1 7 6 1 7 6. . . .

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271 271 271 271 271 273 273 273 273 273 273 274 274 275 277 278 278 279 279 279 279 279 279 279 279 279 280 280 280 280 280 280 282 282 283 283 283 283 283 283 283 283 284 284 284 284 285 285 285 285 285 286 286 286 286 286 286 287 287

CONTENTS

T h e Jurassic Section in N o r t h w e s t e r n and N o r t h e r n A r a b i a n Platform: .......................................... 9 T h e J u r a s s i c o f J o r d a n ............................................................................................... Surface Formations" . ............... D e i r A l i a F o r m a t i o n ........................................................................................ Zarqa F o r m a t i o n ............................................................................................. D h a h a b F o r m a t i o n ......................................................................................... U m m M a g h a r a F o r m a t i o n ................................................................................ A r d a F o r m a t i o n .............................................................................................. M u a d d i F o r m a t i o n .......................................................................................... S u b s u r f a c e F o r m a t i o n s : ......................................................................................... A z a b G r o u p ...................................................................................................... Hihi F o r m a t i o n .............................................................................................. N i m r F o r m a t i o n ............................................................................................. Silal F o r m a t i o n .............................................................................................. D h a h a b F o r m a t i o n ........................................................................................... R a m l a and H a m a m F o r m a t i o n s ......................................................................... M u g h a n n i y a F o r m a t i o n ................................................................................... 9 T h e J u r a s s i c o f Syria: Q a m c h u q a F o r m a t i o n ................................................................. 9 T h e J u r a s s i c o f S o u t h e a s t T u r k e y : Cudi G r o u p ............................................................... J u r a s s i c P a l e o g e o g r a p h y and G e o l o g i c H i s t o r y ..........................................................................

287 287 287 287 287 288 289 289 289 289 290 290 290 290 290 290 291 291 291 291

Chapter 8: The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous Introduction ................................................................................................................... T h e F i r s t Cycle" T h e E a r l y C r e t a c e o u s ..................................................................................... 9 E a r l y C r e t a c e o u s o f Saudi A r a b i a : ................................................................................ Sulaiy F o r m a t i o n ................................................................................................. Y a m a m a F o r m a t i o n .............................................................................................. B u w a i b F o r m a t i o n ................................................................................................ B i y a d h F o r m a t i o n ................................................................................................. Shuaiba F o r m a t i o n ............................................................................................... 9 E a r l y C r e t a c e o u s o f E a s t e r n A r a b i a : .............................................................................. E a r l y C r e t a c e o u s in the U n i t e d A r a b E m i r a t e s .... ....................................................... S u b s u r f a c e F o r m a t i o n s : .................................................................................. R a y d a and Salil F o r m a t i o n s ......................................................................... H a b s h a n F o r m a t i o n .................................................................................... L e k h w a i r F o r m a t i o n ................................................................................... K h a r a i b F o r m a t i o n ..................................................................................... S h u a i b a F o r m a t i o n .................................................................................... S u r f a c e Section: M u s a n d a m G r o u p U n i t 4 ........................................................... E a r l y C r e t a c e o u s in Q a t a r ....................................................................................... Sulaiy F o r m a t i o n ........................................................................................... Y a m a m a F o r m a t i o n ........................................................................................ Ratawi F o r m a t i o n ........................................................................................... Kharaib F o r m a t i o n .......................................................................................... H a w a r S h a l e F o r m a t i o n ................................................................................... Shuaiba F o r m a t i o n ......................................................................................... E a r l y C r e t a c e o u s o f B a h r a i n .................................................................................... Sulaiy F o r m a t i o n ........................................................................................... Y a m a m a F o r m a t i o n ........................................................................................ Ratawi F o r m a t i o n ........................................................................................... Kharaib F o r m a t i o n .......................................................................................... H a w a r F o r m a t i o n ............................................................................................ Shuaiba F o r m a t i o n ......................................................................................... E a r l y C r e t a c e o u s o f O m a n ...................................................................................... W e s t e r n O m a n M o u n t a i n s ( s u b s u r f a c e f o r m a t i o n s ) ............................................... R a y d a F o r m a t i o n ........................................................................................ Salil F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

297 311 311 316 316 317 317 319 319 319 319 319 320 321 321 321 321 324 324 324 324 324 324 324 325 325 325 325 325 325 325 325 325 325 327

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CONTENTS

H a b s h a n F o r m a t i o n .................................................................................... L e k h w a i r F o r m a t i o n ................................................................................... Kharaib F o r m a t i o n ..................................................................................... Shuaiba F o r m a t i o n ..................................................................................... Central Oman Mountains (Allochthonous Units) .................................................. Sidr F o r m a t i o n .......................................................................................... N a y i d F o r m a t i o n ........................................................................................ M a y h a h Formation C M e m b e r ...................................................................... M a y h a h Formation D M e m b e r ...................................................................... Northern Oman Mountains (Musandam Peninsula) ................................................ M u s a n d a m M e m b e r G ................................................................................. M u s a n d a m M e m b e r H and I .......................................................................... 9Early Cretaceous on the eastern side of the Arabian Gulf: southwestern Iran ........................ F a h l i y a n F o r m a t i o n ........................................................................................ G a d v a n F o r m a t i o n .......................................................................................... D a r i y a n F o r m a t i o n .......................................................................................... Garau F o r m a t i o n ............................................................................................ 9Early Cretaceous in the Northern, Northwestern and Northeastern Arabian Platform: ............. Early Cretaceous in Kuwait: ............................................................................. S u l a i y / M a k h u l F o r m a t i o n ......................................................................... M i n a g i s h F o r m a t i o n ................................................................................. Ratawi F o r m a t i o n ..................................................................................... Z u b a i r F o r m a t i o n ..................................................................................... Shuaiba F o r m a t i o n ................................................................................... Early Cretaceous in Iraq: .................................................................................. 1. Southern Iraq: ...................................................................................... Ratawi F o r m a t i o n .............................................................................. Zubair F o r m a t i o n ............................................................................... Shuaiba F o r m a t i o n ............................................................................. 2. Northern Iraq ....................................................................................... Garagu F o r m a t i o n .............................................................................. L o w e r Balambo Formation .................................................................. L o w e r Sarmord Formation ................................................................... Lower Qamchuqa Limestone Formation ................................................. Early Cretaceous in Syria: ................................................................................ Q a m c h u q a F o r m a t i o n ................................................................................ R u t b a h F o r m a t i o n .................................................................................... H a y a n e F o r m a t i o n .................................................................................... Early Cretaceous in Jordan: Kurnub Group .......................................................... Early Cretaceous in Southeast Turkey: ................................................................ M a r d i n Group ......................................................................................... A r e b a n F o r m a t i o n ................................................................................ 9 Early Cretaceous in Southern and Southwestern Arabia: ............................................ The Republic of Yemen: Qishn Formation ................................................................ The S e c o n d Cycle: The Mid-Cretaceous ................................................................................... 9 Mid-Cretaceous in Eastern Arabia: The United Arab Emirates ........................................... S u b s u r f a c e Formations: ........................................................................................ N a h r U m r F o r m a t i o n ....................................................................................... M a u d d u d F o r m a t i o n ........................................................................................ Shilaif/Khatiyah F o r m a t i o n ............................................................................. M i s h r i f F o r m a t i o n .......................................................................................... Outcrop Formations" Nahr Umr and Mauddud formations ............................................ 9 Mid-Cretaceous in Eastern Arabia: Oman ..................................................................... Western Oman Mountains (subsurface formations) ...................................................... N a h r U m r F o r m a t i o n ...................................................................................... Natih F o r m a t i o n ............................................................................................. M a u d d u d F o r m a t i o n ........................................................................................ M i s h r i f F o r m a t i o n .......................................................................................... Central Oman Mountains (Allochthonous Units): Qumayrah Formation .........................

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CONTENTS

N o r t h e r n O m a n M o u n t a i n s ( M u s a n d a m P e n i n s u l a ) ..................................................... O u t c r o p Section" W a s i a G r o u p .......................................................................... S u b s u r f a c e S e c t i o n : ........................................................................................ K a z d h u m i F o r m a t i o n ................................................................................. M a u d d u d F o r m a t i o n ................................................................................. K h a t i y a h / M i s h r i f f o r m a t i o n s ...................................................................... S o u t h e r n O m a n ( D h o f a r R e g i o n ) ............................................................................. Q a m a r F o r m a t i o n ........................................................................................... H a r s h i y a t F o r m a t i o n ....................................................................................... Fartaq F o r m a t i o n ............................................................................................ 9 M i d - C r e t a c e o u s in S o u t h w e s t e r n Iran ............................................................................ B a n g e s t a n G r o u p : ................................................................................................ K a z d h u m i F o r m a t i o n ....................................................................................... Sarvak F o r m a t i o n ........................................................................................... Surgah F o r m a t i o n ........................................................................................... 9 Mid-Cretaceous in C e n t r a l and E a s t e r n Arabia: .............................................................. M i d - C r e t a c e o u s in Central and Eastern Saudi Arabia: W a s i a F o r m a t i o n .......................... M i d - C r e t a c e o u s in N o r t h w e s t e r n Saudi Arabia: W a s i a F o r m a t i o n ................................... M i d - C r e t a c e o u s in K u w a i t : W a s i a G r o u p ................................................................... B u r g a n F o r m a t i o n ........................................................................................... M a u d d u d F o r m a t i o n ........................................................................................ W a r a F o r m a t i o n ............................................................................................. A h m a d i F o r m a t i o n .......................................................................................... M a g w a F o r m a t i o n .......................................................................................... M i d - C r e t a c e o u s in Q a t a r : . W a s i a G r o u p ..................................................................... N a h r U m r F o r m a t i o n ....................................................................................... M a u d d u d F o r m a t i o n ........................................................................................ A h m a d i F o r m a t i o n .......................................................................................... K h a t i y a h F o r m a t i o n ........................................................................................ M i s h r i f F o r m a t i o n .......................................................................................... M i d - C r e t a c e o u s in Bahrain: W a s i a G r o u p .................................................................... N a h r U m r F o r m a t i o n ....................................................................................... M a u d d u d F o r m a t i o n ........................................................................................ W a r a F o r m a t i o n ............................................................................................. A h m a d i F o r m a t i o n .......................................................................................... R u m a i l a F o r m a t i o n ......................................................................................... M i d - C r e t a c e o u s in N o r t h e r n A r a b i a n P l a t f o r m : ................................................................. 9 M i d - C r e t a c e o u s in I r a q ......................................................................................... 1. S o u t h e r n and S o u t h w e s t e r n Iraq: .................................................................... N a h r U m r F o r m a t i o n ................................................................................. M a u d d u d F o r m a t i o n .................................................................................. W a r a F o r m a t i o n ....................................................................................... A h m a d i F o r m a t i o n .................................................................................... R u m a i l a F o r m a t i o n ................................................................................... M i s h r i f F o r m a t i o n ................................................................................... 2. W e s t e r n Iraq: ............................................................................................. R u t b a h F o r m a t i o n .................................................................................... M ' s a d F o r m a t i o n ...................................................................................... 3. N o r t h e r n and N o r t h e a s t e r n Iraq: ..................................................................... R i m S i l t s t o n e F o r m a t i o n .......................................................................... J a w a n F o r m a t i o n ...................................................................................... U p p e r Q a m c h u q a L i m e s t o n e F o r m a t i o n ........................................................ U p p e r S a r m o r d F o r m a t i o n .......................................................................... U p p e r B a l a m b o F o r m a t i o n ......................................................................... Kifl F o r m a t i o n ......................................................................................... D o k a n L i m e s t o n e F o r m a t i o n ...................................................................... 9 M i d - C r e t a c e o u s in J o r d a n ..................................................................................... Ajlun Group: ................................................................................................ N a u r F o r m a t i o n .......................................................................................

347 347 348 348 348 348 348 348 348 348 349 349 349 349 349 349 350 352 352 352 352 353 353 353 354 355 355 355 355 355 355 355 355 355 355 355 355 356 356 356 356 356 356 356 356 356 356 356 357 357 357 357 357 358 358 358 358 358 358

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CONTENTS

Fuheis F o r m a t i o n ..................................................................................... Hummar Formation Shuayb Formation .................................................................................... W a d i As Sir F o r m a t i o n ............................................................................. Khureij F o r m a t i o n .................................................................................... 9 M i d - C r e t a c e o u s in S y r i a ....................................................................................... Judea F o r m a t i o n ............................................................................................. M a s s i v e L i m e s t o n e F o r m a t i o n .......................................................................... 9 M i d - C r e t a c e o u s in S o u t h e a s t T u r k e y ...................................................................... S a b u n s u y u Formation ..................................................................................... D e r d e r e F o r m a t i o n .......................................................................................... M i d - C r e t a c e o u s in Southern and Southwestern A r a b i a : T h e Republic of Y e m e n ....................... Harshiyat F o r m a t i o n ............................................................................................. Fartaq F o r m a t i o n .................................................................................................. T h e T h i r d C y c l e : T h e L a t e C r e t a c e o u s ..................................................................................... Late C r e t a c e o u s in the southern Arabian Gulf:United Arab Emirates ................................... A r u m a G r o u p ......................................................................................................... Laffan F o r m a t i o n .................................................................................................. Halul F o r m a t i o n ................................................................................................... Ilam F o r m a t i o n .................................................................................................... Fiqa F o r m a t i o n .................................................................................................... S i m s i m a Formation .............................................................................................. Muti F o r m a t i o n .................................................................................................. J u w e i z a F o r m a t i o n ............................................................................................... Q a h l a h F o r m a t i o n ................................................................................................ L a t e C r e t a c e o u s in E a s t e r n Arabia: O m a n ........................................................................ 1. W e s t e r n O m a n M o u n t a i n s .................................................................................. L a f f a n F o r m a t i o n ........................................................................................... Fiqa F o r m a t i o n .............................................................................................. Muti Formation ............................................................................................. J u w e i z a F o r m a t i o n .......................................................................................... Qahlah F o r m a t i o n ........................................................................................... S i m s i m a Formation ........................................................................................ 2. C e n t r a l O m a n M o u n t a i n s ( A l l o c h t h o n o u s Units): ................................................... S e m a i l ( O p h i o l i t e ) N a p p e ................................................................................. 3. N o r t h e r n O m a n M o u n t a i n s ( M u s a n d a m P e n i n s u l a ) .................................................. O u t c r o p Section: M u t i F o r m a t i o n ...................................................................... Subsurface Section: L a f f a n F o r m a t i o n .............................................................. I l a m F o r m a t i o n ................................................................... G u r p i F o r m a t i o n ................................................................. L a t e C r e t a c e o u s in Eastern Arabian Gulf: S o u t h w e s t e r n Iran .............................................. I l a m F o r m a t i o n ................................................................................................... G u r p i F o r m a t i o n ................................................................................................. T a r b u r F o r m a t i o n ................................................................................................ A m i r a n F o r m a t i o n ............................................................................................... L a t e C r e t a c e o u s in W e s t e r n and N o r t h w e s t e r n A r a b i a n G u l f ........................................................ 9 L a t e C r e t a c e o u s in Qatar: .................................................................................... A r u m a G r o u p .................................................................................................. Laffan F o r m a t i o n ............................................................................................ Halul F o r m a t i o n ............................................................................................. F i q a / R u i l a t F o r m a t i o n ..................................................................................... S i m s i m a Formation ........................................................................................ 9 L a t e C r e t a c e o u s in Bahrain: A r u m a G r o u p ............................................................... 9 L a t e C r e t a c e o u s in Kuwait: ................................................................................. K h a s i b / M u t r i b a F o r m a t i o n ............................................................................... Sa'di F o r m a t i o n ............................................................................................. Hartha Formation ........................................................................................... Bahrah F o r m a t i o n ...........................................................................................

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CONTENTS

T a y a r a t F o r m a t i o n ..................................................................... ..................... L a t e C r e t a c e o u s in C e n t r a l a n d S o u t h w e s t e r n A r a b i a : ................................................................. 9 L a t e C r e t a c e o u s in S a u d i A r a b i a : A r u m a F o r m a t i o n ................................................... 9 L a t e C r e t a c e o u s in the R e p u b l i c o f Y e m e n " Mukalla Formation ....................................................................................... Sharwain Formation ........................................................................................ Tawilah Group .............................................................................................. Ghiras Formation ....................................................................................... Medj-Zir Formation ..................................................................................... L a t e C r e t a c e o u s in the N o r t h e r n A r a b i a n P l a t f o r m : .................................................................... 9 L a t e C r e t a c e o u s in I r a q ......................................................................................... 1. S o u t h e r n I r a q : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Khasib Formation ..................................................................................... Tanuma Formation ................................................................................... Sa'di Formation ....................................................................................... Hartha Formation ..................................................................................... Qurna Formation ...................................................................................... Tayarat Formation .................................................................................... 2 . W e s t e r n Iraq" D i g m a F o r m a t i o n ...................................................................... 3 . H i g h F o l d e d Z o n e o f Iraq: ............................................................................. Gulneri Formation .................................................................................... Kometan Formation .................................................................................. Shiranish Formation ................................................................................. Bekhme Formation ................................................................................... Hadiena Formation .................................................................................... Tanjero Formation .................................................................................... Aqra Formation ........................................................................................ 9 L a t e C r e t a c e o u s in J o r d a n : B e l q a G r o u p ................................................................... S u r f a c e F o r m a t i o n s : ................................................................................. W a d i U m m G h u d r a n F o r m a t i o n ................................................................ Amman Formation 9 A1 H i s a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M u w a q q a r F o r m a t i o n ............................................................................ S u b s u r f a c e F o r m a t i o n s : ............................................................................ Rajil Formation ................................................................................... Hamza Formation ................................................................................. Hazim Formation ................................................................................. A m m a n a n d A1 H i s a f o r m a t i o n s .............................................................. Usaykhim Formation ............................................................................ M u w a q q a r F o r m a t i o n ............................................................................ 9 L a t e C r e t a c e o u s in S y r i a ...................................................................................... Soukhne Formation .................................................................................. Shiranish Formation ................................................................................. 9 L a t e C r e t a c e o u s in S o u t h e a s t T u r k e y ...................................................................... Karababa Formation ........................................................................................ Karabogaz Formation ...................................................................................... Sayindere Formation ....................................................................................... Korkandil Formation ....................................................................................... Kastel Formation ............................................................................................ T e r b u z e k F o r m a t i o n ....................................................................................... Besni Formation ............................................................................................. Germav Formation .......................................................................................... C r e t a c e o u s P a l e o g e o g r a p h y a n d G e o l o g i c H i s t o r y ............................................................. Tectonic Events .................................................................................................... P a l e o g e o g r a p h y a n d C y c l i c i t y : ................................................................................ E a r l y C r e t a c e o u s C y c l e .................................................................................... M i d - C r e t a c e o u s C y c l e ...................................................................................... Late C r e t a c e o u s C y c l e .....................................................................................

373 373 373 374 374 374 374 374 374 375 376 376 376 376 376 376 376 376 376 377 377 377 377 377 377 377 377 377 378 378 378 378 379 379 379 379 379 379 379 379 380 380 380 380 380 380 380 380 380 381 381 382 382 382 384 384 388 390

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CONTENTS

Chapter 9: The latest part of the Zuni and Tejas cycles of the Middle East: The Cenozoic Introduction ....................................................................................................................... Part 1: The P a l e o g e n e of the M i d d l e East ................................................................................ 9 The P a l e o g e n e of the Central, Eastern and Northeastern Arabian Platform ........................... P a l e o g e n e of Saudi A r a b i a .................................................................................... U m m Er R a d h u m a F o r m a t i o n .................................................................. Rus Formation ...................................................................................... D a m m a m F o r m a t i o n .............................................................................. P a l e o g e n e of Q a t a r .............................................................................................. U m m Er R a d h u m a F o r m a t i o n .................................................................. Rus F o r m a t i o n ...................................................................................... D a m m a m F o r m a t i o n ............................................................................. P a l e o g e n e of B a h r a i n ........................................................................................... U m m Er R a d h u m a F o r m a t i o n .................................................................. Rus Formation ...................................................................................... D a m m a m F o r m a t i o n .............................................................................. P a l e o g e n e o f K u w a i t ........................................................................................... R a d h u m a F o r m a t i o n ............................................................................... Rus Formation ...................................................................................... D a m m a m F o r m a t i o n .............................................................................. P a l e o g e n e of Southern and W e s t e r n Iraq .................................................................. U m m Er R a d h u m a F o r m a t i o n .................................................................. Rus Formation ...................................................................................... D a m m a m F o r m a t i o n .............................................................................. P a l e o g e n e of Southwestern and Southeastern Iran and adjoining areas ........................... P a b d e h F o r m a t i o n .................................................................................. Jahrum F o r m a t i o n ................................................................................. S h a h b a z a n F o r m a t i o n ............................................................................. T a l e h Z a n g F o r m a t i o n ............................................................................ K a s h k a n F o r m a t i o n ................................................................................ Asmari F o r m a t i o n ................................................................................. P a l e o g e n e of the U n i t e d A r a b E m i r a t e s ................................................................... U m m Er R a d h u m a F o r m a t i o n .................................................................. Rus Formation ...................................................................................... D a m m a m F o r m a t i o n .............................................................................. A s m a r i F o r m a t i o n ................................................................................ P a b d e h F o r m a t i o n ................................................................................. P a l e o g e n e o f O m a n ............................................................................................. Central and W e s t e r n O m a n M o u n t a i n s (outcrop formations) ..................................... J a f n a y n L i m e s t o n e F o r m a t i o n ........................................................................ Rusayl F o r m a t i o n ........................................................................................ S e e b L i m e s t o n e F o r m a t i o n ............................................................................ R u w a y d a h F o r m a t i o n ................................................................................... F a h u d F o r m a t i o n ......................................................................................... M u t h a y m i m a h F o r m a t i o n ............................................................................. Southern O m a n (Dhofar Region): (outcrop formation) H a d h r a m o u t G r o u p .................. U m m Er R a d h u m a F o r m a t i o n ........................................................................ Rus Formation ............................................................................................ A n d h u r and Q a r a f o r m a t i o n s ........................................................................... Taqa F o r m a t i o n ........................................................................................... Central and Southern Oman: (subsurface formations) H a d h r a m o u t G r o u p .................... U m m Er R a d h u m a F o r m a t i o n ........................................................................ Rus Formation ............................................................................................ D a m m a m Formation .................................................................................... F a r s Group" T a q a F o r m a t i o n ............................................................................... N o r t h e r n O f f s h o r e O m a n ................................................................................... Pabdeh F o r m a t i o n .........................................................................................

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393 396 408 409 409 411 411 412 412 412 412 414 414 414 414 415 415 416 417 417 417 417 417 418 418 419 419 420 420 420 420 421 421 421 422 422 423 423 423 423 424 425 425 425 426 426 426 426 426 426 426 427 427 427 428 428

CONTENTS

L o w e r F a r s F o r m a t i o n .................................................................................... Guri Formation ............................................................................................. M i s h a n and y o u n g e r f o r m a t i o n s ....................................................................... 9 T h e P a l e o g e n e of Southern, S o u t h w e s t e r n and W e s t e r n A r a b i a ......................................... P a l e o g e n e of W e s t e r n Saudi A r a b i a (Red Sea R e g i o n ) ................................................. Suqah Group: ................................................................................................. Pre-Usfan F o r m a t i o n ................................................................................. Usfan Formation ...................................................................................... Matiyah Formation ........................................................................................... P a l e o g e n e o f the R e p u b l i c o f Y e m e n ....................................................................... P a l e o g e n e of East and Southeast Y e m e n : H a d h r a m o u t G r o u p ................................... U m m Er R a d h u m a F o r m a t i o n ..................... : ............................................... Jeza Formation ......................................................................................... Rus Formation ......................................................................................... H a b s h i y a F o r m a t i o n .................................................................................. P a l e o g e n e o f W e s t and N o r t h w e s t Y e m e n ........................................................... Y e m e n V o l c a n i c s ( A d e n Trap Series) ............................................................ 9 T h e P a l e o g e n e of the N o r t h e r n A r a b i a n Platform: .......................................................... P a l e o g e n e o f N o r t h w e s t Saudi Arabi: Hibr G r o u p ...................................................... P a l e o g e n e o f J o r d a n .............................................................................................. Subsurface Formation: U m m R i j a m F o r m a t i o n .................................................... W a d i S h a l l a l a F o r m a t i o n .................................................. Surface Formation: U m m R i j a m F o r m a t i o n ........................................................ W a d i S h a l l a l a F o r m a t i o n ....................................................... Taiyiba F o r m a t i o n ................................................................ T a q i y e M a r l F o r m a t i o n ......................................................... S a r ' a C h a l k - F l i n t F o r m a t i o n .................................................. M a ' a n N u m m u l i t i c L i m e s t o n e F o r m a t i o n ................................ D h a h k i y e C h a l k F o r m a t i o n ................................................... 9 P a l e o g e n e o f S y r i a .............................. ............................................................... Aaliji Formation .............................................................................................. Palmyra Formation ........................................................................................... K e r m a v F o r m a t i o n ........................................................................................... Sinjar Formation .............................................................................................. Jaddala F o r m a t i o n ............................................................................................. Chilou Formation ............................................................................................ Midyat Formation ............................................................................................ 9 P a l e o g e n e of N o r t h e r n Iraq ................................................................................... Kolosh Formation ............................................................................................ Sinjar Formation .............................................................................................. K h u r m a l a F o r m a t i o n ......................................................................................... Aaliji Formation .............................................................................................. Jaddala F o r m a t i o n ............................................................................................. Avanah Formation ............................................................................................ Gercus Formation ............................................................................................. P i l a Spi L i m e s t o n e F o r m a t i o n ............................................................................ Kirkuk Group: S h u r a u L i m e s t o n e F o r m a t i o n .................................................... S h e i k h Alas F o r m a t i o n ........................................................... Tarjil F o r m a t i o n ..................................................................... B a j a w a n F o r m a t i o n ................................................................. Baba F o r m a t i o n ...................................................................... Anah F o r m a t i o n ..................................................................... A z k a n d F o r m a t i o n .................................................................. Ibrahim F o r m a t i o n .................................................................. 9 P a l e o g e n e o f S o u t h e a s t T u r k e y ............................................................................. Part 2: T h e N e o g e n e of the M i d d l e East .................................................................................. T h e N e o g e n e of the Central and Eastern A r a b i a n Platform: ................................................ 9 N e o g e n e of S a u d i A r a b i a .....................................................................................

428 428 428 428 428 428 428 429 429 429 429 429 429 429 429 429 430 430 430 431 432 432 433 433 433 433 433 434 434 434 434 434 434 434 434 434 434 435 435 435 435 435 435 435 436 436 436 436 436 436 436 437 437 437 437 437 439 439

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CONTENTS

H a d r u k h F o r m a t i o n ........................................................................................... D a m F o r m a t i o n ............................................................................................... H o f u f F o r m a t i o n .............................................................................................. Kharj F o r m a t i o n .............................................................................................. 9 N e o g e n e of Q a t a r ............................................................................................... L o w e r Fars F o r m a t i o n ....................................................................................... D a m F o r m a t i o n ............................................................................................... H o f u f Formation .............................................................................................. 9 N e o g e n e o f B a h r a i n ............................................................................................ J a b a l C a p F o r m a t i o n ......................................................................................... R a s al A q r F o r m a t i o n ........................................................................................ 9 N e o g e n e of the U n i t e d A r a b E m i r a t e s ..................................................................... G a c h s a r a n F o r m a t i o n ......................................................................................... M i s h a n F o r m a t i o n ............................................................................................ H o f u f F o r m a t i o n .............................................................................................. 9 N e o g e n e o f O m a n .............................................................................................. M i o c e n e C o n g l o m e r a t e and Y o u n g e r D e p o s i t s ....................................................... The N e o g e n e o f Southern and W e s t e r n Arabia: ................................................................ 9 N e o g e n e of W e s t e r n Saudi Arabia (Red Sea R e g i o n ) ................................................. Tayran Group: M u s a y r F o r m a t i o n .................................................................... Y a n b u F o r m a t i o n ..................................................................... A1 W a j h F o r m a t i o n .................................................................. Jizan V o l c a n i c F o r m a t i o n .......................................................... Burqan F o r m a t i o n ............................................................................................. M a g n a Group: Kial F o r m a t i o n ....................................................................... J a b a l Kibrit F o r m a t i o n .............................................................. M a n s i y a h Formation ......................................................................................... G h a w w a s F o r m a t i o n ......................................................................................... Lisan Formation .............................................................................................. 9 N e o g e n e of Y e m e n : A d e n V o l c a n i c Series .............................................................. T h e N e o g e n e o f N o r t h e a s t e r n Arabia" 9 N e o g e n e of K u w a i t ............................................................................................ Ghar Formation .............................................................................................. L o w e r F a r s F o r m a t i o n ..................................................................................... D i b d i b b a F o r m a t i o n ........................................................................................ 9 N e o g e n e of S o u t h e r n Iraq .................................................................................... Ghar F o r m a t i o n .............................................................................................. L o w e r F a r s F o r m a t i o n ..................................................................................... U p p e r F a r s F o r m a t i o n ..................................................................................... Zahra F o r m a t i o n ............................................................................................. B a k h t i a r i F o r m a t i o n ........................................................................................ 9N e o g e n e o f S o u t h w e s t e r n Iran ............................................................................. G a c h s a r a n F o r m a t i o n ....................................................................................... R a z a k F o r m a t i o n ............................................................................................ Mishan Formation .......................................................................................... A g h a Jari F o r m a t i o n ....................................................................................... B a k h t i a r i F o r m a t i o n ........................................................................................ T h e N e o g e n e of the N o r t h e r n A r a b i a n Platform: .............................................................. 9 N e o g e n e o f J o r d a n .............................................................................................. S i r h a n - A z r a q - J a f r Basins (Subsurface F o r m a t i o n ) ................................................. Qirma Formation ............................................................................................ Azraq F o r m a t i o n ............................................................................................. Jafr F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N o r t h e a s t e r n and Eastern Jordan (Surface Outcrop) .................................................. T e r t i a r y B a s a l t i c P l a t e a u ................................................................................... Surface o u t c r o p in D e a d S e a - J o r d a n Rift ............................................................... D a n a C o n g l o m e r a t e F o r m a t i o n .................................................................... L i s a n M a r l F o r m a t i o n ...............................................................................

xxiv

439 439 439 439 439 439 439 439 439 439 439 441 441 441 441 441 441 441 441 442 442 442 442 442 442 442 442 442 443 443 443 443 443 443 443 443 443 443 443 444 444 444 444 445 445 446 446 447 447 447 447 447 447 447 447 447 447 448

CONTENTS

9 N e o g e n e of S y r i a ............................................................................................... Dhiban F o r m a t i o n .......................................................................................... Jeribe F o r m a t i o n ............................................................................................ L o w e r F a r s F o r m a t i o n ..................................................................................... U p p e r F a r s F o r m a t i o n ..................................................................................... B a k h t i a r i F o r m a t i o n ........................................................................................ 9 N e o g e n e of the Foothills and High F o l d e d Z o n e of Northern Iraq ................................ E u p h r a t e s L i m e s t o n e F o r m a t i o n ........................................................................ S e r i k a g n i F o r m a t i o n ....................................................................................... Dhiban F o r m a t i o n .......................................................................................... J e r i b e L i m e s t o n e F o r m a t i o n ............................................................................. 9 N e o g e n e of S o u t h e a s t T u r k e y ............................................................................... Part 3: C e n o z o i c P a l e o g e o g r a p h y and G e o l o g i c History ............................................................. P a l e o g e n e P a l e o g e o g r a p h y .......................................................................................... N e o g e n e P a l e o g e o g r a p h y ............................................................................................

449 449 449 449 449 449 449 449 449 449 449 449 451 458 462

PART THREE Chapter 10 : Hydrocarbon Habitat of the Middle East Introduction ....................................................................................................................... S u r f a c e Oil and G a s S e e p s .................................................................................................... Turkey ..................................................................................................................... Iran ......................................................................................................................... Iraq ......................................................................................................................... Kuwait .................................................................................................................... S a u d i A r a b i a ............................................................................................................. Bahrain .................................................................................................................... Yemen ..................................................................................................................... Syria, L e b a n o n and J o r d a n ........................................................................................... H i s t o r y o f E x p l o r a t i o n ......................................................................................................... C u r r e n t Status o f M i d d l e E a s t Oil .......................................................................................... H y d r o c a r b o n P r o d u c t i v i t y ............................................................................................ Source Rocks ............................................................................................................ G e o c h e m i s t r y of Oil and Gas ....................................................................................... R e s e r v o i r R o c k s ........................................................................................................ I n f r a c a m b r i a n to P a l e o z o i c ..................................................................................... T r i a s s i c and J u r a s s i c ............................................................................................. C r e t a c e o u s .......................................................................................................... Tertiary .............................................................................................................. C a p R o c k s ( S e a l s ) ..................................................................................................... Traps ....................................................................................................................... T i m i n g o f T r a p F o r m a t i o n ........................................................................................... T h e G r e a t e r A r a b i a n and O m a n i Basins ..................................................................... T h e Z a g r o s B a s i n ................................................................................................. Potential Plays ...................................................................................................................

467 467 468 468 469 469 469 469 469 469 470 473 489 492 502 510 511 516 516 517 517 520 521 521 521 522

Chapter 11: Hydrocarbon Habitat of the Greater Arabian Basin Introduction ....................................................................................................................... K u w a i t and the K u w a i t - S a u d i A r a b i a Neutral Z o n e .................................................................... S t r a t i g r a p h i c H i s t o r y .................................................................................................. S t r u c t u r a l H i s t o r y ...................................................................................................... R e s e r v o i r R o c k s ........................................................................................................ L o w e r C r e t a c e o u s R e s e r v o i r s ................................................................................. M i n a g i s h F o r m a t i o n ................................................................................... R a t a w i F o r m a t i o n ....................................................................................... Z u b a i r F o r m a t i o n ....................................................................................... M i d d l e C r e t a c e o u s R e s e r v o i r s .................................................................................

525 525 527 528 530 530 530 530 530 531

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B u r g a n F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 M a u d d u d F o r m a t i o n .................................................................................... 531 W a r a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 M i s h r i f F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 U p p e r C r e t a c e o u s R e s e r v o i r s .................................................................................. 531 T a y a r a t F o r m a t i o n ...................................................................................... 531 T e r t i a r y R e s e r v o i r s ............................................................................................... 531 R a d h u m a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 S e a l s a n d Seal F o r m a t i o n s ............................................................................................ 532 G o t n i a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 S a r g e l u F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 R a t a w i F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 Z u b a i r F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 B u r g a n F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 A h m a d i F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 M u t r i b a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 K h a s i b F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 R u s F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 L o w e r F a r s F o r m a t i o n ................................................................................. 532 Oil G e o c h e m i s t r y and S o u r c e R o c k s .............................................................................. 532 M i d d l e C r e t a c e o u s S o u r c e R o c k s ............................................................................ 534 R u m a i l a and M i s h r i f F o r m a t i o n s ...................................................................... 534 A h m a d i F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534 W a r a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534 M a u d d u d F o r m a t i o n ....................................................................................... 534 B u r g a n F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534 L o w e r C r e t a c e o u s S o u r c e R o c k s ............................................................................. 534 S h u a i b a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534 Z u b a i r F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537 R a t a w i F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537 M i n a g i s h F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537 S u l a i y F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537 J u r a s s i c S o u r c e R o c k s .......................................................................................... 537 D h r u m a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537 S a r g e l u F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537 N a j m a h F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537 K u w a i t Oil F i e l d s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537 G r e a t e r B u r g a n F i e l d ............................................................................................. 538 B a h r a h F i e l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540 R a u d h a t a i n F i e l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541 S a b r i y a F i e l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542 M i n a g i s h F i e l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542 U m m G u d a i r F i e l d ............................................................................................... 544 K h a f j i F i e l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544 W a f r a F i e l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544 D o r r a F i e l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547 H o u t F i e l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547 L u l u f i e l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547 U m m G u d a i r S o u t h F i e l d ...................................................................................... 547 S o u t h F u w a r i s F i e l d ............................................................................................. 547 Bahrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548 S t r u c t u r e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549 S t r a t i g r a p h y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551 R e s e r v o i r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551 K h u f f F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553 A r a b F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554 M a u d d u d F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554

xxvi

CONTENTS

Seals ....................................................................................................................... S o u r c e R o c k s and H y d r o c a r b o n M i g r a t i o n and A c c u m u l a t i o n ............................................. P r o d u c t i o n a n d R e s e r v e s .............................................................................................. Qatar .............................................................................................................................. Structure .................................................................................................................. S t r a t i g r a p h y .............................................................................................................. R e s e r v o i r C h a r a c t e r i s t i c s ............................................................................................. T a b u k F o r m a t i o n ................................................................................................. S h a r a w r a F o r m a t i o n ............................................................................................. T a w i l F o r m a t i o n ................................................................................................. H a u s h i F o r m a t i o n ................................................................................................ K h u f f F o r m a t i o n ................................................................................................. I z h a r a F o r m a t i o n ................................................................................................. Araej F o r m a t i o n .................................................................................................. A r a b F o r m a t i o n .................................................................................................. K h a r a i b F o r m a t i o n ............................................................................................... S h u a i b a F o r m a t i o n .............................................................................................. N a h r U m r F o r m a t i o n ............................................................................................ M a u d d u d F o r m a t i o n ............................................................................................. M i s h r i f a n d K h a t i y a h f o r m a t i o n s ............................................................................ S e a l s a n d S e a l F o r m a t i o n s ........................................................................................... T a b u k F o r m a t i o n ................................................................................................. S h a r a w r a F o r m a t i o n ............................................................................................. T a w i l F o r m a t i o n ................................................................................................. H a u s h i F o r m a t i o n ................................................................................................ S u d a i r F o r m a t i o n ................................................................................................. I z h a r a a n d A r a e j f o r m a t i o n s .................................................................................... H a n i f a a n d L o w e r J u b a i l a h f o r m a t i o n s ..................................................................... A r a b F o r m a t i o n ................................................................................................... Hith A n h y d r i t e .................................................................................................... H a w a r F o r m a t i o n ................................................................................................. N a h r U m r F o r m a t i o n ............................................................................................ K h a t i y a h F o r m a t i o n ............................................................................................. L a f f a n F o r m a t i o n ................................................................................................. S o u r c e R o c k s ............................................................................................................ S h a r a w r a F o r m a t i o n ............................................................................................. H a u s h i F o r m a t i o n ............................................................................................... H a n i f a F o r m a t i o n ................................................................................................ J u b a i l a h F o r m a t i o n .............................................................................................. S h u a i b a F o r m a t i o n .............................................................................................. M a u d d u d F o r m a t i o n ............................................................................................. M i s h r i f / K h a t i y a h f o r m a t i o n s ................................................................................. Oil c h a r a c t e r i s t i c s a n d h y d r o c a r b o n m a t u r a t i o n .................................................................. O i l a n d G a s F i e l d s ..................................................................................................... D u k h a n F i e l d ...................................................................................................... I d d E l S h a r g i F i e l d ............................................................................................... M a y d a n M a h z a m F i e l d .......................................................................................... B u l H a n i n e F i e l d ................................................................................................. N o r t h Field ........................................................................................................ United Arab Emirates ........................................................................................... R e g i o n a l S t r a t i g r a p h y ........................................................................................... Reservoirs ........................................................................................................... Haushi G r o u p ............................................................................................... K h u f f F o r m a t i o n ........................................................................................... S u d a i r - G u l a i l a h - M i n j u r f o r m a t i o n s ..................................................................... A r a e j F o r m a t i o n ............................................................................................ D i y a b F o r m a t i o n ............................................................................................ A r a b F o r m a t i o n ..............................................................................................

554 554 558 559 559 559 561 561 562 562 562 562 562 562 563 564 564 564 564 564 564 564 564 564 564 564 564 564 564 564 565 565 565 565 565 565 565 565 565 565 565 565 566 566 566 568 571 571 574 575 575 576 578 578 578 578 579 579

xxvii

CONTENTS

Thamama Group ............................................................................................. Habshan Formation .................................................................................. L e k h w a i r F o r m a t i o n ................................................................................. Kharaib Formation ................................................................................... Shuaiba Formation .................................................................................. Mishrif Formation ......................................................................................... Aruma Group: ................................................................................................ Ilam Formation ....................................................................................... Halul Formation ...................................................................................... Simsima Formation ................................................................................. A s m a r i and G a c h s a r a n f o r m a t i o n s ..................................................................... S e a l s a n d S e a l F o r m a t i o n ........................................................................................ S o u r c e R o c k s a n d Oil G e o c h e m i s t r y ........................................................................ Traps ................................................................................................................ O i l a n d G a s F i e l d s ............................................................................................... Z a k u m Oil Field ............................................................................................ A s a b Oil Field .............................................................................................. B u H a s a Oil F i e l d .......................................................................................... M a r g h a m G a s - C o n d e n s a t e F i e l d ........................................................................ F a t e h Oil F i e l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bab Oil Field ................................................................................................ E1 B u n d u q Oil F i e l d ....................................................................................... S a j a a G a s - C o n d e n s a t e F i e l d ............................................................................. Jordan .................................................................................................................... H i s t o r y of E x p l o r a t i o n .......................................................................................... T h e S e d i m e n t a r y B a s i n s and their H y d r o c a r b o n P o t e n t i a l ............................................. D e a d S e a - J o r d a n V a l l e y B a s i n ........................................................................... Azraq Basin .................................................................................................. Sirhan Basin ................................................................................................. N o r t h J o r d a n i a n H i g h l a n d s ............................................................................... A1 J a f r B a s i n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Risha Basin .................................................................................................. Basalt Plateau ............................................................................................... Saudi Arabia ........................................................................................................ T e c t o n i c and S t r a t i g r a p h i c F r a m e w o r k ..................................................................... H y d r o c a r b o n S y s t e m s ........................................................................................... Source Rocks ...................................................................................................... P a l e o z o i c F o r m a t i o n s ..................................................................................... Jurassic Formations ....................................................................................... C r e t a c e o u s F o r m a t i o n s ................................................................................... Cenozoic Formations ..................................................................................... Reservoir Rocks .................................................................................................. Saq Formation ......................................................................................... Tabuk Formation ..................................................................................... J a u f F o r m a t i o n ......................................................................................... U n a y z a h F o r m a t i o n .................................................................................. Khuff Formation ..................................................................................... Marrat Formation .................................................................................... Dhruma Formation .................................................................................. T u w a i q M o u n t a i n F o r m a t i o n ..................................................................... Hanifa Formation .................................................................................... Jubailah Formation .................................................................................. Arab Formation ...................................................................................... Hith Formation ....................................................................................... Sulaiy Formation .................................................................................... Yamama Formation ................................................................................. Buwaib Formation .................................................................................... Biyadh Formation .....................................................................................

xxviii

579 579 579 579 579 579 580 580 580 580 580 580 580 585 590 590 590 591 594 595 595 595 596 598 602 604 604 605 605 605 607 607 607 608 608 611 613 613 618 621 622 625 626 626 626 626 627 628 628 628 628 629 629 631 631 631 631 631

CONTENTS

S h u a i b a F o r m a t i o n ............................................. 9..................................... W a s i a F o r m a t i o n ..................................................................................... L o w e r A r u m a F o r m a t i o n .......................................................................... T e r t i a r y F o r m a t i o n s ................................................................................. Cap R o c k ...................................................................................................... H a n a d i r S h a l e M e m b e r ............................................................................ R a ' a n S h a l e M e m b e r ................................................................................ Q u s a i b a S h a l e m e m b e r ............................................................................ U n a y z a h F o r m a t i o n ................................................................................ K h u f f F o r m a t i o n .................................................................................... L o w e r S u d a i r F o r m a t i o n .......................................................................... M a r r a t F o r m a t i o n ................................................................................... D h r u m a F o r m a t i o n ................................................................................. H a n i f a F o r m a t i o n ................................................................................... J u b a i l a h F o r m a t i o n ................................................................................. A r a b F o r m a t i o n ..................................................................................... H i t h F o r m a t i o n ...................................................................................... B u w a i b F o r m a t i o n . ................................................................................. B i y a d h F o r m a t i o n ................................................................................... W a s i a F o r m a t i o n ( A h m a d i M e m b e r ) .......................................................... W a s i a F o r m a t i o n ( R u m a i l a M e m b e r ) .......................................................... A r u m a F o r m a t i o n ................................................................................... D a m F o r m a t i o n ..................................................................................... M a n s i y a h F o r m a t i o n ............................................................................... G h a w w a s F o r m a t i o n ............................................................................... S t r u c t u r e and T r a p M e c h a n i s m s .............................................................................. Oil F i e l d E x a m p l e s .............................................................................................. S u p e r g i a n t G h a w a r Oil F i e l d ............................................................................ H a r m a l i y a h Oil F i e l d ...................................................................................... Q a t i f Oil F i e l d .............................................................................................. K h u r s a n i y a h Oil F i e l d ................................................................................... A b q a i q Oil F i e l d ............................................................................................ Yemen .................................................................................................................... S t r u c t u r a l and S t r a t i g r a p h i c F r a m e w o r k .................................................................... H y d r o c a r b o n P a r a m e t e r s ........................................................................................ M a ' r i b - J a w f - S h a b w a - B a l h a f G r a b e n S y s t e m ........................................................... E a s t e r n T a b l e l a n d .............................................................................................. N o r t h e r n F l a n k ......................................................................................... H a d h r a m o u t - J e z a - Q a m a r B a s i n ..................................................................... S a y h u t B a s i n ............................................................................................ R e d Sea C o a s t a l A r e a and the T i h a m a Sub-basin ..................................................... G u l f of A d e n B a s i n ...........................................................................................

633 633 633 633 633 633 634 634 634 634 634 634 634 634 634 634 634 634 634 634 634 634 634 634 634 634 637 637 638 638 639 639 642 643 644 644 644 644 644 647 647 647

Chapter 12: The Hydrocarbon Habitat of the Zagros Basin Introduction

....................................................................................................................... .......................................................................................................... I n t r o d u c t i o n and H i s t o r y of E x p l o r a t i o n .......................................................................... S t r u c t u r e and T r a p s ..................................................................................................... R e s e r v o i r C h a r a c t e r i s t i c s ............................................................................................. Paleozoic ............................................................................................................ B e d i n i a n F o r m a t i o n ........................................................................................ H a n d o f F o r m a t i o n .......................................................................................... H a z r o F o r m a t i o n ........................................................................................... Mesozoic ............................................................................................................ A r i l F o r m a t i o n .............................................................................................. Mardin Group: ............................................................................................... S a b u n s u y u F o r m a t i o n ..............................................................................

Southeast T u r k e y

651 653 653 653 658 659 659 659 659 659 659 659 659

xxix

CONTENTS

Derdere Formation .................................................................................. Karababa Formation ................................................................................. Karabogaz Formation ..................................................................................... Raman Formation .......................................................................................... Garzan Formation .......................................................................................... Germav Formation ......................................................................................... L a t e M e s o z o i c to C e n o z o i c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sinan Formation ........................................................................................... C r u d e Oil G e o c h e m i s t r y ............................................................................................... Source Rocks: ........................................................................................................... Paleozoic Formations" Bedinian Formation ........................................................................................ Dadas Formation ........................................................................................... Triassic-Jurassic Formations .................................................................................. Cretaceous Formations: ......................................................................................... Derdere Formation ......................................................................................... Ortabag Formation ......................................................................................... Kiradag Formation ......................................................................................... Karababa Formation ....................................................................................... Karabogaz Formation ..................................................................................... Kastel Formation .......................................................................................... Tertiary Formations .............................................................................................. Seals and Seal Formations ............................................................................................ Telhasan Formation ............................................................................................. Kastel Formation ................................................................................................. Mardin Group ...................................................................................................... K a r a b o g a z , S a y i n d e r e a n d B e l o k a f o r m a t i o n s .............................................................. Kiradag Formation ............................................................................................... Germav Formation ............................................................................................... Gercus formation .................................................................................................. Oil Field Examples ..................................................................................................... Raman and Bati-Raman fields .................................................................................. Garzan Field ........................................................................................................ Dodan Field ........................................................................................................ Syria ............................................................................................................................... I n t r o d u c t i o n and History of E x p l o r a t i o n .......................................................................... Structure and Traps ..................................................................................................... Reservoir Characteristics .............................................................................................. Kurra Chine Formation ........................................................................................ Mulussa Formation .............................................................................................. Butmah Formation ............................................................................................... Dolaa Group ....................................................................................................... Cherrife Formation .............................................................................................. Qamchuqa Formation ........................................................................................... Soukhne Formation ............................................................................................. Massive Limestone .............................................................................................. Shiranish Formation ............................................................................................ Jaddala Formation ................................................................................................. Chilou Formation ................................................................................................ Dhiban Formation ............................................................................................... Jeribe Formation ................................................................................................. Source Rocks ................................. . ........................................................................... Crude Oil Geochemistry ............................................................................................... Seals and Seal Formations ............................................................................................ Mulussa Formation .............................................................................................. Kurra Chine Formation ......................................................................................... Adaiyah Formation .............................................................................................. Alan Formation ...................................................................................................

xxx

659 659 659 659 659 660 660 660 661 662 664 664 664 664 664 664 664 664 664 664 665 665 667 667 667 667 667 667 667 667 667 667 669 669 670 670 673 673 680 681 681 681 681 681 681 681 681 681 681 681 681 681 683 685 688 688 689 689

CONTENTS

Iraq

S a r g e l u F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 C h e r r i f e F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 S h i r a n i s h F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 A a l i j i F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 J a d d a l a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 D h i b a n F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 L o w e r F a r s F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 O i l F i e l d E x a m p l e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691 I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691 S t r a t i g r a p h y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694 S t r u c t u r e a n d T r a p s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696 R e s e r v o i r C h a r a c t e r i s t i c s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697 K h a b o u r Q u a r t z i t e F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698 A l a n F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698 G o t n i a A n h y d r i t e F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698 N a j m a h L i m e s t o n e F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698 Y a m a m a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698 S u l a i y F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698 R a t a w i F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 700 Z u b a i r F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 700 S h u a i b a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 00 N a h r I m r F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 00 R u m a i l a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 700 M i s h r i f F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 00 H a r t h a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 L o w e r F a r s F o r m a t i o n / G h a r F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 Z a g r o s B a s i n R e s e r v o i r F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 K u r r a C h i n e F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 B u t m a h F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 S a r g e l u F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 C h i a G a r a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 G a r a g u F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 S a r m o r d F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 J a w a n F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 D o k a n L i m e s t o n e F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 U p p e r B a l a m b o F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 K o m e t a n F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 M u s h o r a h F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 S h i r a n i s h F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 A s m a r i F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 K a l h u r F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 S e r i k a g n i F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 E u p h r a t e s L i m e s t o n e F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 J e r i b e L i m e s t o n e F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703 Q a m c h u q a G r o u p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703 K i r k u k G r o u p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703 S o u r c e R o c k s a n d O i l G e o c h e m i s t r y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705 S e a l s a n d S e a l F o r m a t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 06 C a p R o c k s in the A r a b i a n B a s i n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 10 G o t n i a F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 10 R a t a w i F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710 Z u b a i r F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 10 N a h r U m r F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 10 K h a s i b F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710 S h i r a n i s h F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710 L o w e r F a r s F o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 10

xxxi

CONTENTS

C a p R o c k s in the Z a g r o s B a s i n .................................................................................... P i r i s p i k i R e d b e d s ................................................................................................. Baluti F o r m a t i o n .................................................................................................. A d a i y a h F o r m a t i o n .............................................................................................. N a o k e l e k a n F o r m a t i o n ......................................................................................... K h a s i b F o r m a t i o n ............................................................................................... S h i r a n i s h F o r m a t i o n ............................................................................................ Aaliji F o r m a t i o n ................................................................................................. D h i b a n F o r m a t i o n ............................................................................................... Oil F i e l d E x a m p l e s ..................................................................................................... A i n Z a l a h F i e l d ................................................................................................... B u t m a h Field ....................................................................................................... K i r k u k Field ....................................................................................................... Bai H a s s a n Field ................................................................................................... Q a i y a r a h Fields ..................................................................................................... B u z u r g a n Field ..................................................................................................... N a h r U m r Field .................................................................................................... R u m a i l a Field ...................................................................................................... Z u b a i r Field ......................................................................................................... Iran

..................................................................................................................................

Introduction ............................................................................................................... Stratigraphy ............................................................................................................... S t r u c t u r e a n d T r a p s ..................................................................................................... R e s e r v o i r C h a r a c t e r i s t i c s .............................................................................................. Z a g r o s B a s i n R e s e r v o i r F o r m a t i o n s .......................................................................... F a r a g h a n F o r m a t i o n ....................................................................................... D a l a n F o r m a t i o n ( K h u f f e q u i v a l e n t ) .................................................................. K a n g a n F o r m a t i o n ......................................................................................... S u r m e h F o r m a t i o n ......................................................................................... F a h l i y a n F o r m a t i o n ....................................................................................... G a r a u F o r m a t i o n ........................................................................................... D a r i y a n F o r m a t i o n ......................................................................................... B a n g e s t a n G r o u p ........................................................................................... S a r v a k F o r m a t i o n .......................................................................................... I l a m F o r m a t i o n ............................................................................................. A s m a r i L i m e s t o n e ......................................................................................... M i s h a n F o r m a t i o n ......................................................................................... A r a b i a n B a s i n R e s e r v o i r s F o r m a t i o n s ....................................................................... K h u f f F o r m a t i o n ........................................................................................... K h a m i G r o u p ................................................................................................ A r a b F o r m a t i o n ............................................................................................. F a h l i y a n F o r m a t i o n ....................................................................................... G a d v a n F o r m a t i o n ......................................................................................... D a r i y a n F o r m a t i o n ......................................................................................... K a z h d h u m i F o r m a t i o n ..................................................................................... M i s h r i f F o r m a t i o n ......................................................................................... J a h r u m F o r m a t i o n ......................................................................................... G h a r F o r m a t i o n ............................................................................................. S o u r c e R o c k s a n d Oil G e o c h e m i s t r y .............................................................................. A s m a r i F o r m a t i o n ......................................................................................... P a b d e h F o r m a t i o n ............................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G u r p i F o r m a t i o n ........................................................................................... K a z h d h u m i F o r m a t i o n ..................................................................................... G a r a u F o r m a t i o n ........................................................................................... S a r g e l u F o r m a t i o n ......................................................................................... P a l e o z o i c s o u r c e r o c k s ................................................................................................. Oil G e o c h e m i s t r y ........................................................................................................

xxxii

710 710 710 710 710 710 710 710 710 710 710 711 711 712 712 712 713 713 713 716

716 716 718 720 720 720 721 721 721 721 721 721 721 721 721 721 722 722 722 722 722 722 722 722 722 722 722 722 723 723 723 723 724 724 726 726 726

CONTENTS

S e a l s a n d S e a l F o r m a t i o n s ........................................................................................... D a s h t a k F o r m a t i o n ........................................................................................ K a n g a n F o r m a t i o n ......................................................................................... Hith F o r m a t i o n ............................................................................................. G a d v a n F o r m t i o n ........................................................................................... K a z h d h u m i F o r m a t i o n ..................................................................................... G u r p i F o r m a t i o n ........................................................................................... G a c h s a r a n F o r m a t i o n ...................................................................................... Oil F i e l d E x a m p l e s .................................................................................................... P a z a n u n F i e l d ..................................................................................................... K u h - i - M u n d F i e l d ................................................................................................ M a s j i d - i - S u l a i m a n F i e l d ........................................................................................ N a f t - i - S h a h F i e l d ................................................................................................. Lali Field ........................................................................................................... A g h a Jari F i e l d ..................................................................................................... G a c h s a r a n Field .................................................................................................... B a h r e g a n s a r F i e l d .................................................................................................. H a f t K e l F i e l d ..................................................................................................... B i b i H a k i m e h F i e l d .............................................................................................. A b o u z a r ( A r d e s h i r ) F i e l d ....................................................................................... N a f t - S a f i d F i e l d ....................................................................................................

729 729 729 729 729 729 729 730 730 730 730 730 733 733 733 733 734 734 735 735 735

Chapter 13: The Hydrocarbon Habitat of the Oman Basin I n t r o d u c t i o n ....................................................................................................................... T h e O m a n S e d i m e n t a r y B a s i n ................................................................................................ S o u r c e Rocks, Oil G e o c h e m i s t r y and H y d r o c a r b o n G e n e r a t i o n ............................................. Source Rocks ...................................................................................................... Oil G e o c h e m i s t r y ................................................................................................ I n f r a c a m b r i a n H u q f Oil G e o c h e m i s t r y ................................................................ I n f r a c a m b r i a n " Q " C r u d e Oil G e o c h e m i s t r y ......................................................... S i l u r i a n Safiq Oil G e o c h e m i s t r y ....................................................................... U p p e r J u r a s s i c D i y a b Oil G e o c h e m i s t r y ............................................................. C r e t a c e o u s N a t i h Oil G e o c h e m i s t r y ................................................................... H y d r o c a r b o n G e n e r a t i o n and M i g r a t i o n .................................................................... B u r i a l H i s t o r y ............................................................................................... R e s e r v o i r R o c k s ........................................................................................................ I n f r a c a m b r i a n R e s e r v o i r s ................................................................................. C a m b r o - O r d o v i c i a n R e s e r v o i r s ......................................................................... P e r m i a n R e s e r v o i r s ........................................................................................ L o w e r C r e t a c e o u s R e s e r v o i r s ........................................................................... M i d d l e C r e t a c e o u s R e s e r v o i r s ........................................................................... P a l e o c e n e R e s e r v o i r s ...................................................................................... S e a l s and Seal F o r m a t i o n s ........................................................................................... I n f r a c a m b r i a n S e a l s ........................................................................................ C a m b r o - O r d o v i c i a n S e a l s ................................................................................ P e r m i a n and T r i a s s i c Seals .............................................................................. C r e t a c e o u s S e a l s ............................................................................................ P a l e o c e n e S e a l s ............................................................................................. S t r u c t u r e and T r a p s .................................................................................................... Oil F i e l d E x a m p l e s .................................................................................................... F a h u d and N a t i h F i e l d s ................................................................................... A1 H u w a i s a h F i e l d ......................................................................................... L e k h w a i r F i e l d .............................................................................................. Yibal Field .................................................................................................... S a f a h F i e l d ................................................................................................... M u k h a i z n a F i e l d ............................................................................................ M a r m u l F i e l d ................................................................................................

737 738 746 746 747 747 747 747 750 750 750 751 753 755 755 756 757 757 757 757 758 758 758 758 758 758 760 760 762 763 764 766 766 767

xxxiii

CONTENTS

Nimr Field .................................................................................................... 770 Saih Rawl Field ............................................................................................ 770 Qaharir Field ................................................................................................. 771 Rima Field .................................................................................................... 772 Bukha Field ................................................................................................... 772 References ............................................................................................................................ 775-811 Index .................................................................................................................................. 813-843 Appendices ........................................................................................................................... A2-A99

xxxiv

Chapter 1 AN INTRODUCTORY OVERVIEW

GEOGRAPHIC AND GEOMORPHOLOGIC SETTING

The countries of the Middle East (Fig. 1.1), the region reviewed in this book, cover parts of the lands of the eastern Mediterranean and the greater part of Arabia (Arabian Shield, Arabian Platform and Arabian Gulf), and the western Zagros Thrust Zone, an area enclosed between 13 ° and 38 ° N and 35 ° and 60 ° E (Figs. 1.2 and 1.3). Topographically, the higher elevations generally lie to the west in the Arabian Shield and pass eastward into the lower-lying areas occupied by the Arabian (Persian) Gulf and the Tigris-Euphrates Valley. To the east of these lie the Zagros ranges, with the Zagros Crush Zone forming the boundary of the region considered here, although as will appear in the following pages, it makes geological sense to include southwestern Iran in the early Phanerozoic. The Arabian Gulf is a shallowly submerged area, with an average depth of only 60 m (197 ft); even the deepest part, lying at the southeastern end, has a depth of only 240 m (787 ft). Bathymetric charts show a depth asymmetry, with the deeper parts lying closer to the Iranian than to the Arabian shore. At its northern end, the Arabian Gulf gradually is being filled by sediments forming the prograding TigrisEuphrates Delta (Fig. 1.2). At the southeastern end of the Arabian Gulf, there is a sharp change in trend, and the gulf narrows, forming the Strait of Hormuz, where the Musandam Peninsula projects toward the Iranian shore. The submarine continuation of the Arabian Peninsula further restricts open contact of the gulf with the Arabian Sea. However, the greatest depths are found in the Straits. Beyond the Straits (Hormuz and Bab A1 Mandab near the Gulf of Aden), a profound geological change occurs; while the Arabian Gulf lies on continental crust, the floor of the Gulf of Oman and Gulf of Aden is oceanic. The natural boundaries of the Middle East are most easily defined to the north and northeast, where the Taurus Mountains pass eastward to the Zagros Fold Belt (Figs. 1.1 and 1.3). North of the Taurus Mountains lies the Anatolian Plateau, which is bounded to its north by the Pontic Mountains. Topographically, these two ranges combine to the east, although the geological continuation of the Pontian Belt may be sought in the Caucasian province. In a similar manner, their eastward extension also divides to form the Zagros and Alborz Mountains, which together enclose the Iranian Plateau. Topographically, the Zagros is continued to the east by the Makran ranges. The Makran ranges are geologically very young and still in the process of formation; the geological continuation of the Zagros is formed

by the mountains of Oman. The region is bounded by Owen Fracture Zone and Gulf of Aden rifting to the south and by the rift system of the Red Sea and the Gulf of Aqaba to the west. The area enclosed within the boundaries of the region is more than 1,000,000 km e and is sparsely populated, with the exception of the fertile crescent of the TigrisEuphrates Valley. It contains within its borders a major part of the world's known hydrocarbon reserves and a disproportionate number of the supergiant and giant fields. It is the economic importance of these resources that has stimulated an interest in the area that has increased as the extent of the resources has become better established. The northern third of the region is covered by the alluvial deposits from the Tigris-Euphrates River System, which drains the area from the mountains to the north and east. Presently, the Tigris-Euphrates Delta is prograding and gradually filling the Arabian Gulf. The larger area to the south contains two of the world's great deserts: the An Nefud (Nafud) in the north, and the Rub al Khali in the south. Within the Rub al Khali is a large sand sea, with dunes up to 200 m (656 ft) in height; in the Great Nefud, the sand dunes, which cover about 145,000 km e, are up to 300 m higher than the surrounding terrain. Farther north in the Syrian desert, ablation has removed most of the loose sand, thereby exposing extensive gravel-or rock-covered plains, and desert pavements, making crossing the desert difficult. Geomorphology and climate (principally the availability of water) have controlled human settlement and communications in the Middle East. In western Saudi Arabia lies an old pediplane with inselbergs. Although its exact age is not known, it is overlain by early Tertiary lavas. Several erosion surfaces have been defined; the principal surfaces are those at 1,650 m (5,280 ft), 1,200 m (3,840 ft) and 900 m (2,880 ft), the last and youngest of which is known to predate rifting. The whole region lies within the arid subtropical zone, and only a few, very restricted parts of Lebanon and Turkey are not classified as extremely arid. During the summer, the main track of the jet stream that controls the paths of atmospheric depressions passes north of the Pontic Mountains. During the winter, the track of the jet stream moves rapidly southward to cover the northern Arabian Gulf. Few depressions pass south of 30 ° N. Therefore, the area receives little benefit from the depressions during summer, except perhaps the Caspian shores of Iran, or winter; thus, it is not surprising that large areas have a rainfall regime of 100-300 mm/year. In general, the

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changes to sierozems, or gray desert soil in the southwest and northeast. In the north, reddish prairie soils develop, and within the neighboring mountains, chernozem or chestnut soils develop. The natural vegetation is characteristic of desert sand semi-deserts, with scrub woodlands at the higher elevations and steppe in the extreme north. Cultivation is restricted mainly to the flood plains. Along the low, fiat and sandy shores, salt fiats or sabkhas have formed in shallow depressions. Due to the high rates of evaporation, salt crusts develop that, when the salt is relatively free from sand, have been exploited locally. Under storm conditions, these low-lying areas may be flooded by the sea, which can extend miles inland. Under other conditions, aeolian dunes may bury the sabkhas. Agriculture is still important in the economies of many of the countries in the region, not only providing food and export revenue, but a source of employment. For environmental and technological reasons, crop yields generally are low, and crop variety is restricted. Oil revenues have meant that a progressively larger percentage of the food requirements are met by imports as well as fueling economic development. Politically, the area contains a number of large coun-

An Introductory Overview

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political factors have led to the development of an extensive network of pipelines (Fig. 1.4). Other primary minerals exist; but, on the whole, these are poorly known, and even less exploited. Only the chromium and antimony in Turkey is of significance in world trade. There are, however, important phosphate deposits in Jordan and Israel/ Palestine, and Saudi Arabia. The Arabian Shield has good potential deposits of copper, gold, iron, silver, manganese and lead. Yemen has a fair potential in copper, iron and salt. In Oman, occurrences of copper, chromite, asbestos, nickel and lead were reported in antiquity. In the U.A.E., asbestos, chromite and copper have been discovered recently. In Iran, there are potential important mineral discoveries, such as lead, chrome, manganese, coal and copper. In northern Iraq, iron ore, chromite, lead and zinc occur; while in central and western Iraq, sulfur and phosphate are found. In Syria, chromite and asbestos deposits are known in the Lattakiya area, and some deposits of asphalt, iron and phosphate have been developed. Two fundamental reasons have inhibited development: the low level of exploration and the inaccessibility of the potential

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G E O L O G I C SETTING In plate-tectonic terms, the area lies within the Arabian Plate. It covers the Republic of Yemen, Oman, Saudi Arabia, the U.A.E., Qatar, Bahrain, Kuwait, Jordan, the

fertile crescent of Syria and Iraq, southeastern Turkey, and southwestern Iran during the Paleozoic and earliest Mesozoic. The generalized geologic map (Fig. 1.5) and illustrative cross sections (Fig. 1.6) are simplifications of the combined results of field research by governments, academic institutes and detailed hydrocarbon exploration by the petroleum industry. Excluded from consideration here are the continental part of the Levantine Plate and Sinai, that is the areas west of the Levantine Fracture System (Dead Sea Rift).

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form the southeastern and southwestern boundaries of the Middle East area. Both are very young features, and as a result, the development of a coastal plain in both regions is minimal. The agreement of the geological features on both sides of the Gulf of Aden and the Red Sea, which show concordant geological structures, indicates that separation in a geologically very recent time was accompanied by a small, but significant, transcurrent displacement. It is the onshore continuation of shear fractures associated with the

Sedimentary Basins and Petroleum Geology of the Middle East

Fig. 1.5. Generalized geologic map of the Middle East, (modified from CGMW-UNESCO, 1985: USGS- ARAMCO, 1963, Beydoun, 1988) with lines of section of Fig. 1.6. opening of the Red Sea, passing up the Gulf of Aqaba and forming the Dead Sea Rift, to abut against the Taurus Mountains in the north, that complete the periphery of the Middle East. Along the eastern shores of the Red Sea, uplifted Precambrian rocks and their sedimentary and volcanic cover provide greater relief than is seen on the western side; and, in the Asir Mountains of Yemen, elevations of more then 3,700 m (11,840 ft) are reached. This elevation gradually declines to the north and east. The western side of the Jordan rift is overlooked by the Levant uplands, completing the elevated rim of the area. An indication of the underlying geological basis for the limits to the Middle East is shown by the distribution of seismicity (Fig. 1.7). It particularly is marked along the mountain fronts and, to a lesser extent, along the ridge-rift system that forms the southwestern and northwestern limits, lines that are essentially plate boundaries (Figs. 1.2 and 1.3). In the western part of the Arabian Plate, young volca-

nics are abundant; they occur as the Trap Series in Yemen, where they form the "harrats," and extend into Saudi Arabia. They also crop out extensively in Jordan, Syria and Turkey. Thus, the Red Sea and the Gulf of Aden are young ocean basins of the type with which the Neotethys, formed by separation between central Iran and Arabia during the Late Triassic, can be compared. Geologically, the principal features defining the area can be assigned to three causes (Beydoun, 1988): extensional events in southern and eastern Arabia that result from seafloor spreading in the Gulf of Aden and the Red Sea with the generation of incipient ocean basins; compressional folding in the north and northeast in the TaurusZagros-Oman Orogenic Zone consequent upon continentcontinent collision; and strike-slip faulting along the Dead Sea Rift or Levant Fracture Zone (Figs. 1.2 and 1.3). The ability to recognize such features, which were the result of similar events in the geological past, provides the key to

An Introductory Overview

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continuing through the Mesozoic, during the early Paleozoic, the geological history of the whole region so closely parallels that of the Arabian Peninsula that it is reasonable to assume it formed an integral part of the Arabian Platform ( s e n s u s t r i c t o ) for most of the Paleozoic.

SEQUENCE STRATIGRAPHY The lower Paleozoic depositional pattern in the Middle East is relatively simple and has a high degree of correspondence with the sedimentational history of the northern margin of Gondwana from the Maghreb to Iran. This similarity might be expected to manifest itself in the distribution of marine fauna, but marine horizons are few, due to the fact that the lithofacies of the exposed rock sequence were unsuitable for the existence and/or preservation of fauna. In the lower Paleozoic, there are few faunally datable horizons, and reliance has had to be placed on trace fossils to provide most of the stratigraphic control. Gaps in the faunal record also may be due partly to the fact that the

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Fig. 1.7. General distribution of earthquakes in the Middle East in the pre-instrumental period (to 1899) plotted as triangles, and events of magnitude 5 or greater, from 1899-1992, plotted as open circles (after Ambraseys et al., 1994, by kind permission of Cambridge University Press). regions involved have been explored less. The gaps may be filled with more research and with the acquisition of more surface and subsurface data, such as the recognition of Paleozoic faunas in deep wells in Syria (e.g., Sudbury, 1957), Saudi Arabia (A1 Laboun, 1986) and Oman (Hughes-Clarke, 1988). The apparent lack of some horizons, however, may be due to non-deposition, such as the absence of the Ashgillian in much of the region, attributed to glaciation that affected much of northern Gondwana during the Ordovician/Silurian. The late Paleozoic time interval is poorly known, with few surface exposures. During the Mesozoic, deposition over the Arabian Platform remained relatively simple, and the ramp and platform model of carbonate deposition developed by Murris (1981) has proven a very fruitful means of considering intracratonic sedimentary sequences (Alsharhan and Nairn, 1986, 1988, 1990). The principal complication in this simple history is marked by the plate collision accompanying the obduction of ophiolites, the emplacement of the Oman nappes, and the emplacement of the Zagros ophiolites, which mark the beginning of the formation of the Zagros Fold Belt. The closing of the Neotethys completed the process during the Neogene. Although outcrops are few, with so much of the area low-lying and covered with unconsolidated deposits, the dearth of outcrops is counterbalanced greatly by the extensive system of wells drilled in the search for, and the exploitation of, the petroleum wealth of the region. These subsurface data provide an unparalleled three-dimensional picture and permit the recognition of relatively subtle facies changes, which can be traced for considerable distances in the absence of major structural discontinuities. The richness of these data, together with the large numbers

of oil field operators in the area, has resulted in a multiplicity of stratigraphic terms. The consequence is that even before account is taken of facies variability, a single stratigraphic unit may carry the same or different names, may be defined differently even in nearby fields, may have different time limits assigned, or may be ranked differently as a member or formation. The inevitable confusion has been to some extent resolved by agreement between the operating companies, the publication of the Lexique Stratigraphique International (for most countries in the Middle East, except Kuwait, Bahrain, the U.A.E. and Oman), and by a number of syntheses (Saint-Marc, 1978; Murris, 1981; Koop and Stoneley, 1982; Beydoun, 1988). It follows from the above that much is known about the economically important series. Other formations that underlie the oil-beating beds, such as the Paleozoic rocks in Saudi Arabia, are less well-known. The detail available has sometimes resulted in the recognition that the recorded sequences do not always fit into the conventional mode, as, for example, in the Cretaceous, where it is more convenient to make a threefold division rather than the conventional division into the Upper and Lower Cretaceous. The Middle East, as any part of the world, has been affected by major and minor unconformities throughout geological time. Sea-level fluctuation, epeirogenic movement and volcanic activity have all played their part in controlling sedimentation. Therefore, in preparing the geological history of the Middle East, the authors, while retaining the traditional division of the stratigraphic column into systems, series, etc., have found it profitable to use somewhat longer intervals of time during which geological events follow a consistent pattern. That is, use has been made of the ideas of sequence stratigraphy, where the major intervals are bounded by interregional unconformities marking transgressions and regressions that appear to be global in extent (Sloss, 1963). Within the major intervals, there occur many smaller-scale, transgressive and regressive events marking intervals of shorter duration. The calibration of these fluctuations of sea level during geological time has been developed by Vail et al. (1977) and Haq et al. (1987). The basic feature of sequence stratigraphy is that it makes explicit the time-transgressive nature of the unconformities in contrast to the traditional use of unconformities bounding geological systems, where there commonly is an implicit assumption that, at least in limited areas, they represent time horizons. The recognition of the time-transgressive nature of the unconformities makes it difficult to put a precise age on the oldest part of the unconformable surface. The major sequences have names drawn from North American geology. These primary sequences are broken by one or more second-order events, which may be less well-defined and not always apparent on a global scale, but which may be extremely important on a regional scale. The general acceptance of sequence stratigraphy came about through the development of the curves correlating changes in sea level, as developed by Vail et al. (1977) (Fig. 1.9). Figs. 1.10-1.12

An Introductory Overview

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Fig. 1.8. Isopach contour map of the total Phanerozoic sedimentary cover in the Middle East, with contour interval in thousands of feet (based on data from Wilson and Peterson, 1986). are attempts to summarize data from the Middle Eastern countries according to the Vail model. The Sauk sequence covers the beds deposited during the time interval from the Late Precambrian to Early Ordovician (end Arenigian), that is from the oldest transgressive sediments on the pre-Tassilian surface of Beuf et al. (1971) to the youngest, regressive marine sediments. The beds are overwhelmingly clastic, mostly sandstone, and commonly contain a fauna largely restricted to trace fossils. The Tippecanoe sequence extends from the Middle Ordovician (early Llanvirnian) to Early Devonian. Over most of the northern margin of Gondwana, a distinctive base to this sequence is absent, and the top of the sequence is often relatively ill-defined and poorly dated. In most areas, there is an important break; much or all of the Ashgillian, together with parts of the late Caradocian and possibly the earliest Llandoverian, is missing, with the time represented by an important glacial epoch. Glacial deposits of this epoch are best represented by the Sarah/Zarqa

formations of central Arabia. The succeeding argillaceous sediments with their rich graptolite fauna establish the middle Llandoverian as the oldest identifiable horizon over most of North Africa and northern Arabia. The Early Devonian to mid-Carboniferous Kaskaskia sequence is not well-known in Arabia. Although marine limestone of both Middle Devonian and Early Carboniferous age is known in some deep wells, clastics form an important part of the sequence and can be dated by their palynomorphs. The Absaroka sequence spans the time from the latest Early Carboniferous to Early Jurassic. In Arabia, the oldest beds rest upon a well-defined unconformity, the Hercynian unconformity, and mark the resumption of clastic sedimentation in those regions following uplift and deep erosion. The presence of the great Karoo "Dwyka" glaciation is indicated by sporadic deposits in Oman and the southwestern Rub al Khali. Over much of the Arabian Platform, the most significant beds are formed by the Permian Khuff Limestone sequence, the first major marine

Sedimentary Basins and Petroleum Geology of the Middle East

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10

mid-Tertiary; beds above the upper Miocene are poorly represented, and the stratigraphic record has many gaps. In the west, from Yemen north to Syria and Turkey, the extensive volcanic activity found is a reflection of the important tensional events affecting this western margin of Arabia. Within the range of these major, first-order cycles, as stated earlier, onlap and offlap sequences bounded by regional unconformities have been recognized by Vail et al. (1977) and Haq et al. (1987). They have attempted to correlate them in a global sequence of sea-level fluctuations. The onlapping sequences result from rapid deposition during transgression, whereas slower depositional rates mark the offlapping sequences as the seas gradually receded. Vail and Wilbur (1966) believe that the onlap unconformities do not necessarily represent erosional unconformities, and that the onlapping beds sometimes provide the key to discerning the unconformable base of a series. The movement may be the result of orogenic movement or the magnitude of sea-level change. In the Middle East, Caledonian and Hercynian events are identified by their effects on sea-level change, not by their orogenic effects. They are marked mostly during the Late Silurian and Early Carboniferous. However, account must be taken of the effects upon sea level of Late Ordovician glaciation and the Karoo glaciations in the Early Permian. During the Mesozoic, the tectonic effects of the closing of Paleotethys and the opening of Neotethys can readily be identified in the sea-level fluctuations recorded

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An Introductory Overview in the lithofacies changes seen in the stratigraphic record. The first major orogenic activity is not observed until the Late Cretaceous collision, when the Iran Block, which had only separated from the Arabian Plate during the PermoTriassic, collided with it along the Zagros line. Nappes were emplaced from northeast to southwest, as the collision zone closed and the Zagros foredeep formed (Murris, 1981). Across the Dibba Line in the southern Arabian Gulf, ophiolitic nappes were emplaced in northern Oman. In the broadest sense, until these events in the Mesozoic

and Cenozoic, the Arabian Platform was a slowly subsiding continental margin at the edge of the Tethys dominated by facies characteristic of shelf conditions; whereas in Iraq and Iran, miogeosynclinal facies predominated. A major sea-level fall in the late Oligocene-early Miocene is reflected in a major unconformity. This was the time of the tectonic activity related to the opening of the Red Sea and the Gulf of Aden. The final phases of Alpine activity, from the Miocene to Pleistocene, are associated with the uplift and folding of the Zagros.

13

This Page Intentionally Left Blank

Chapter 2 THE GEOLOGICAL HISTORY AND STRUCTURAL ELEMENTS OF THE MIDDLE EAST

INTRODUCTION

the Arabian Shield and the Arabian Platform may mark the suture between plates that were independent units until the end of the Pan-African movements around the beginning of the Phanerozoic. The major tectonic events during the Phanerozoic in the Middle East are summarized in Tables 2.1-2.3, according to their tectonic content in Table 2.4. The present geological boundaries of the region as defined here are the result of the latest phase in a long history of tectonic activity, of which the breakup of the AfroNubian Dome with the separation of Arabia from the Nubian Shield across the Red Sea spreading center is one of the more spectacular events. The southern end of the Red Sea links up with the Gulf of Aden Rift and Transform System through the Afar Depression and is in continuity with the Carlsberg Ridge (Fig. 2.1). The onshore

The boundaries of the Arabian Shield, Arabian Platform and Arabian Gulf and the margins of the Arabian Plate (Fig. 1.1) are all recently formed, dating from midand late Tertiary. In that sense, the region forms a coherent unit relatively easy to define. However, the changing face of the globe over geological time makes it difficult to define a unit that can be treated as such for even as short a time as the Phanerozoic. Consequently, the present boundaries are arbitrary; for example, using the Zagros Mountains and the Zagros Crush Zone as the present limits separates the Arabian Platform from central Iran, although the early Paleozoic history of both is similar. Going one step further, it may be argued that the boundary between

PLATE TECTONIC MAP OF THE MIDDLE EAST

EURASIA

PLATE

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Fig. 2.1. Plate tectonic map of the Middle East. The extent of the convergence zone between the Eurasian, Arabian and Indian plates is based on seismic activity (data from McKenzie et al., 1970; Ben Avraham and Nur, 1976; De Jong, 1982; Hempton, 1987). 15

Sedimentary Basins and Petroleum Geology of the Middle East

Table 2.1. Major tectonic events affecting the Middle East during the Paleozoic Era.

branches of this rift system are the African-Ethiopian riffs and the Gulf of Aqaba-Dead Sea Rift-Transform System. The latter is part of a set of fractures that ends to the north abutting the Taurus Mountains. Although discussion of the African side of the fracture system does not form part of this text, some reference to the area, as well as the region east of the Zagros Crush Zone, is unavoidable in order to better comprehend the geological evolution of the Arabian Plate, the fundament of the Middle East. A minimum twodegree rotation (about a pole near 36 ~ N, 31 o E) is necessary to fit the Arabian Peninsula to the African continent along the 200 m (656 ft) isobath (Delfour, 1976; Fig. 2.2), moving the peninsula 145 km (91 mi) to the southwest along the line of the Gulf of Aqaba shear, although rotation of as much as 6 ~ has been proposed. This returns Arabia to its position at the beginning of the Cenozoic. In a broad sense, the evolution of the Middle East may be considered in terms of two "megacycles," where the consolidation of the northern margin of Gondwana represents the end of the first megacycle (see review in Stern, 1994). The second megacycle covers the events affecting the northern margin of Gondwana and its interrelation with Laurasia, culminating with the collision of the AfroArabian Plate with Laurasia. Beydoun (1991) reviewed the geological history of the Arabian Plate in the context of its hydrocarbon potential.

16

The events of the first megacycle concluded in the early Phanerozoic with the consolidation of the Afro-Arabian Plate, which included Iran. It involved the sweeping together of a system of island arcs and oblique collision during the Late Proterozoic, a three-stage sequence of events according to Behre (1990), with an early phase of rifting at 1200 Ma followed by subduction and island-arc accretion between 975 and 715 Ma to account for the ophiolite belts in the Sudan, Ethiopia and Saudi Arabia, and a final phase of continent-to-continent oblique collision to account for the nappe folds and thrusts in the Mozambique Belt of Africa. In this view, the Mozambique Belt is continued into that part of the Arabian Peninsula and Iran now largely covered by Phanerozoic sediments (Warden and Horkel 1984). According to Kazmin (1988), this phase did not end until the earliest Paleozoic with the crumpling of the Inda Ad Series of Somalia. It seems reason.able to assume that the shear movements in the Najd Fault Belt, and presumably also along the Zagros line-Arabian Gulf area, mark stress release associated with the final collision phase. During the early stages of the second megacycle, conditions of relative quiescence reigned, for the Paleozoic orogenic episodes, upwarp and erosion in Gondwana represented the Caledonian and Hercynian in particular. This deep erosion stripped off Paleozoic sediments down to the

The Geological History and Structural Elements of the Middle East

Table 2.2. Major tectonic events affecting the Middle East during the Mesozoic Era. Age

Major Events • In late Cenoman!an/Early Turonian, major changes in tectonic and depositional regions took place due to collision and partial subduction of the margin of the eastern Arabian crustal block, with a spreading ridge whose axis is centered in theGulf of Oman. • In Late Cretaceous, the Neotethys began to close with the initiation of a number of subduction zones on the northern margin ofTethys, which led to the emplacement of ophiolites, melanges and oceanic sediments on the margin of the Arabian Plate. • The RuEbah and Khleissia paleohighs were separated by the Anah Trough,

S Si

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• The initial subsidence of the Anah Basin and the early rifting in the Euphrates Graben. • In the northern Middle East, subsidence occurred due to tensional slab-pull forces, as the promontory approached the north-dipping subduction zone beneath the Bitlis-Poturge fragments. • Ophiolite emplacement in Oman was preceded by platform emergence, with the development of a peripheral bulge in response to initial loading of the continental margin. This was followed by rapid drowning of the platform.

O

s

• Major regional unconformities divide the Cretaceous of the Middle East into Early, Middle and Late, controlled by sea level and epeirogenic movements.

o 71

• The Khleissia Paleohigh formed an integral part of the Rutbah Paleohigh. • The Paleotethys finally closed with the collision of the Cimmerian Block and Eurasian Plate resulting in the formation of the Pontides in northern Turkey. • The Isfahan Basin was uplifted and deformed. It recorded the collision of blocks in central and northern Iran. •Blockfaultingandseafloor spreading continued, resulting in further separation of the continental fragments between the margin of Arabia and Eurasia. • Major extensional phase began all over Tethys. .2

• Intracontinental rift developed along the northern margin of Gondwana.

E5

• The Paleotethys closed, and the Neotethys started to open, • Subsidence in Palmyra Zone and in Sinjar-Euphrates-Anah troughs.

Table 2.3. Major tectonic events affecting the Middle East during the Cenozoic Era. Age

Major Events • The Hadhramoui Arch started to develop in the Paleocene and attained its present form, approximately at the end of the Eocene.

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• Trap volcanics erupted in Gulf of Aden and the Red Sea during the late Oligocene-early Miocene, • Arabian Plate began to separate from African Plate because of NW progradation of central Indian Ridge spreading center. • Peralkaline granite emplacement in southern Red Sea occurred during the late Oligocene. • The Ha'il-Rutbah-Ga'ara Paleohigh was domed and eroded. • In theearly Eocene, the Proto-Arabian Plate moved northaspart of large African-Arabian Plate. By the late Eocene, the African-Arabian Plate first impinged on Eurasian Plate, resuhing in thrust stacking of stretched northern margin of Arabia.

17

Sedimentary Basins and Petroleum Petroleum Geology Geology of the Middle Sedimentary Basins Middle East

Major tectonic elements with examples from the Middle East (based on information information Table 2.4. Major Robertson, 1994; 1994; Glennie et al., 1974; 1974; Glennie personal communication, 1995; 1995; and and the authors). authors). from Robertson, Tectonic Setting Rift-related

Divergent margin

18

Tectonic Facts

Characteristics

Examples

"Passive" rifts

Basin showing evidence of rifting, faulting and subsidence, followed by flexurally controlled uplift, then magmatism; typically rotated fault-block geometry

Rifting of Neoiethys in Late Permian-Triassic related to breakup of the northern margin of Gondwana prior to spreading from the mid-Triassic onwards; development of early geanticlines (e.g., Helez, and Hazro, southeastern Turkey, suggest flexural uplift)

"Active" rifts

Basin showing evidence of thermally controlled uplift mantle piume and/or more short-lived (upwelling); typically marked by regional unconformity, volcanism, then rift-related faulting

Red Sea?

Failed rifts (aulacogens)

Rift basins do not proceed to spreading stage, but fail and are infilled with shallowing-up ward sedimentary successions; these zones of crustal weakness are easily deformed during later tectonic instability

Euphrates Rift in the Upper Cretaceous (Lovelock, 1984); Jawf-Marib Graben of Yemen?

Intra-platform basins

Pelagic and redeposiied carbonates, floored by volcanics/sediments of stretched continental basement (where exposed); long-ranging successions normally remain above CCD and show gravity input from bordering carbonate platforms; may include condensed deposits on local volcanic highs

?Palmyra Zone, Syria (Lovelock, 1984)

Carbonate platform

Siliciclasttc, volcanic and/or basement overlain by km-thick, shallow-water carbonates, with periodical flooding, giving rise to pelagic carbonates and emergence, with non-sequences, karst and local bauxites

Taurides, southern Turkey, southeastern Turkey and Arabian Platform

Marginal seamount

Basement highs, including small, off-margin carbonate platforms, capped by condensed pelagics, locally including Mn nodules or Fe/Mn deposits; basement either volcanic and/or older, pre-rift-aged units

Hawasina "Exotics" (e.g., at Jabal Kawr, Oman)

The Geological History and Structural Elements of the Middle East

Table 2.4 2.4 continued. continued. Tectonic Setting Spreading ridge

Convergent margin

Tectonic Facts

Characteristics

Examples

Spreading ridge

MOR-type ophiolites, basal, metalliferous sediments, lensional faulting exposing plutonics, with ophicalcite in slow-spreading, rifted ridges; overlying pelagic cartKtnates, then siliceous facies below CCD

Red Sea Kahnu and Daragar ophiolite suite of Inner Makran (Glennie etaf, 1990)

Abyssal plain

Laterally continuous blanket of deep-sea, pelagic and hemipelagic sediments, deposited after subsidence below the CCD; siliceous in upwelling areas, may include inactive ridges and/or within-plate-type volcanics

Deep-water facies of Hawasina {Haliw/Halfa formations of Glennie et al., 1994, Umar Group ofBRGS)inOman

Continental fragment

Fragments of continental crust, where preserved, overlain by siUciclastics and carbonate-pi at form units, showing only limited subsidence; bordered by a small, passive margin passing laterally into oceanic crust

?Soco£ra Island (Yemen); SirjanSanandaj Zone, a Pernio-Trias sic microcontinent (Iran)

Oceanic seamount or oceanic plateau

Thick pile of MORBAVPB-type basalts, locally overlain by rapidly subsiding, carbonate-platform units; pelagic, calcareous or non-calcareous sediment capping; marginal talus, partly within flexural moat

Jabal Kawr, Oman

Supra-subdued on zone ophiolite

Complete ophiolite, with harzburgitedepleied mantle, sheeted dykes and lATtype/bonitic extmsives; locally includes acidic, calc-alkaline extmsives and volcaniclastics

Hatay, Baer-Bassit and Guleman ophiolites of southern and southeastern Turkey; Semail Ophiolite of Oman Mountains

Oceanic arc

Thick piles of basalts and basaltic andesites' subordinate, more fractionated extmsives and volcaniclastics; tuffaceous, where shallow-water and/or subaerial

Neotethyan units in central and southeastern Turkey (not welldocumented); possibly Doragar Zone of Inner Makran (Glennie etal,, 1990)

Subduct ion/ accretion complex

Thick units of structurally repeated, deepsea sediments, often with slivers of scraped-off oceanic crast; succession ideally thickens and coarsens upwards in individual thrust slices and shows downward younging in age of accreted units; many structural complications; often melange units

Hawasina sediments of Oman Mountains; colored melange of Crush Zone and other parts of Iran; Makran Wedge (MaastrichtianRecent)

19

Sedimentary Basins and Petroleum Geology of the Middle East

Table Table 2.4 continued. continued.

Tectonic Setting

Collision-related

20

Tectonic Facts

Characteristics

Examples

Fore-arc basin

Structurally overlies subduct ion/ accretion units; comprises thick, variable sequences of moderately deep- to shallow-marine or subaerial deposits, including carbonates, siliciclastics and/or volcaniclastics; often relatively structurally intact, with only low-grade meiamorphism

Kyrenia Range, Cyprus

Back-arc basin (intracontinenial)

MORB- and/or lAT-type ophiolite overlain by terrigenous and/or volcanogenic sediment shed from both active arc and continental basement; locally siliceous and/or organic-rich sediments

Zanjan-Taftan Zone of Cenozoic volcanics overlying Neotethys 2, but probably acquired volcanics because of late (?) subduction of crush zone (Neotethys I) beneath Sitjan-Sanandaj microcontinent, Iran

Back-arc basin (intra-oceanic)

MOR- and/or lAT-type ophiolite, overiain by mainly volcanogenic sediments, including tuffs; little or no coarse, clastic sediment input; volcaniclastic turbidites and debrisflowsin areas proximal to active arcs

Not specifically recognized, but may include some ophioliterelated units in Neotethys of southeastern Turkey; ? Jaz Murian, southern Iran (overlies Daragar Zone basalts)

Intra-oceanic collision

Structurally complex assemblages of several ophiolitic and/or active marginrelated units {including oceanic arcs) often separated by serpentinitic melange; amalgamation by strike-slip and/or thrusting

None specifically recognized, but may be present, particulariy in Neotethys of southeastern Turkey; start of Hawasina subduction beneath Semail oceanic arc; jump to Makran subduction when Arabian Platform could not be consumed down Semail Trench in Oman

Remnant ocean basin

Ophiolite (where preserved) overlain by deep-sea sediments, then much younger, gravity-deposited sediments, commonly with provenance including emplaced ophiolites and collision zones already sutured along strike; little or no associated arc volcanism

Killan units of southeastern Turkey; Dashl-i-Kavir (northern central Iran) Paleogene salt basin Sebzevar ophiolites/radiolarites north of Lut Block represents closure of that part of Tethys (Paleo-Tethys?) in Iran

Pre-coUisional, extensional basin

Extensional, fault-controlled basins developed on active continental margins (locally including ophiolites), above subduction zones, with litde or no active subduction-related volcanism

Lower Tertiary Hazar Basin of southeastern Turkey; Crush Zone of Iran (Neotethys 1)

Fore deep with emplaced oceanic crust

Collapsed passive mai^ins, overlain by deepening-upwards, sedimentary successions, including hemipelagic, pelagic sediments, debris flows; overthrust by accretionary units and/or ophiolites

Collapse of Arabian margin, related to Late Cretaceous ophiolite emplacement in southeastern Turkey

The The Geological History and Structural Elements of the Middle East

Table Table 2.4 continued. continued.

Tectonic Setting

Strike-siip

Tectonic Facts

Characteristics

Examples

Foreland basin with emplaced continental crust

Collapsed passive margins, overiain by deepening-upwards sedimentary successions, mainly terrigenous turbidiies and mudstone; debris flows locally at the top; ovenhrust by continental thrust sheets; includes piggy-back basins, other complications

Licey^iingiis Basin in southeastern Turkey

Uplift-related, tectonic setting

Varies from regional to local with unconformiies, structural evidence of upUft and/or diapirism; associated sediments deposited in basins, either locally or far-removed

Regional uplift Anatolian Plateau (Turkey); ?Sirjan-Sanandaj Zone, Iran, central Iran/Lut region; diapiricZagros Mountians-Hormuz Zone Oman Salt Basin/South Arabian Gulf decollement diapirs

Transform rifts and passive margins

Passive margin bordered by subsiding basin, outer ridge composed of sediments and/or continental basement stivers; structural evidence of shear, especially near condnent-ocean boundary; reduced subsidence, volcanism relative to "normal" margins

Late Paleozoic-Eariy Me so zoic (n on-em placed) rifted Levant; ?DibbaZone (U.A.E.); mdange sediments at Batain coast of southeastern Oman

Oceanic transform faults

Ophiolites cut by major fault zones showing pervasive strike-sUp, fragmentation of ophiolitic crust; local rotations; fault-control led, sedimentary basins with extrusives and coarse talus intercalations; ophicalcite where submarine exposure of ultramafics

Cutting (and resealed) Semail Ophiolite of Oman Mountains; east of Jabal Raudha? (Oman); ?offset along Wadi Ham (northwest of Kaiba) in U.A.E.; Gulf ofAqaba in western Arabia

Oceanic crust in pull-apart basins

MORB-type ophiolite overlain by relatively proximal terrigenous sediments; possible evidence of strikeslip within ophiolites; bordering margins may show thermal metamorphism related to intrusion/spreading

Probably Black Sea and South Caspian? (pseudo oceanic crust?)

Convergencerelated (pre-collisional)

Sedimentary basin in forearc/backarc locations influenced by oblique subduction and/or strike-slip; hard to recognize as tectonic facies

Neotcthyan fore arc basin (e.g., Hazar, southeastern Turkey)

Strike-slip and rotation (pre-collisional)

Complex and variable settings marked by compression, strike-slip and/or tectonic rotations (about vertical axes); transtensional, pull-apart basins related to oblique collision

Tertiary Lice, "pull-apart" basin in southeastern Turkey; rotation of Kushmandar Metamorphics of Inner Makran along extension of Naiband Fauh (Glennie et al., 1990) (probably post-collisional)

Strike-slip and rotation (post-collisional)

Regions of pervasive strike-slip and distributed shear, including zones of compression, transtension; localized volcanism and deep-level (granitic) intrusion; block rotations; localized melange genesis; strike-sUp, pull-apart basins

South Iran; Crush Zone of Iran; North Anatolian Fault of Turkey; Batain Melange, southeastern coast of Oman, associated with emplacement of Masirah Ophiolite (side-swipe, not normal obduction) (Glennie, 1995)

21

Sedimentary Basins and Petroleum Geology of the Middle East Cambrian over the paleohighs such as the Qatar-South Fars Arch. In contrast, in the northern continents, the Hercynian particularly is important, for it represents the time of the suturing along the north-south line of the Urals of the European Plate with the Siberian. This trend swings eastward through the central Asian Angaran Geosyncline (Nalivkin, 1973). In the Middle East, after these events in the late Paleozoic, a period of tension developed, which culminated in the early Mesozoic with the opening of "Neotethys" and the closing of "Paleotethys" during the Late Triassic. A single plate or several continental fragments of the Iran Sub-plate separated from the northern margin of Gondwana and, as part of the "Cimmeria" of Sengrr (1979, 1987), collided with the Asian Turan Plate along the northern foot of the Alborz Range (Strcklin, 1974; Davoudzadeh et al., 1986). The later closure of Neotethys was marked by the orogenic events during the late Mesozoic and Cenozoic along the line of the Zagros, as the Arabian part of the Afro-Arabian Plate subducted below Eurasia. Attendant tensional effects in the rear of the Arabian Plate then manifested themselves in the Red Sea opening. An excellent review of the entire tectonic history of the Middle East is found in Beydoun (1991), in which he has tried to relate the plate-tectonic history to the hydrocarbon potential of the region. The pre-Hercynian Tethys ocean was characterized by an epicontinental sea, which covered much of Arabia. Water depth gradually increased where this marginal sea or miogeosynclinal zone extended into Iran and Pakistan and became "geosynclinal" in extreme northern Iran, where it approached the former USSR (Fig. 2.3). An early set of Paleozoic-Mesozoic-Cenozoic paleogeographic maps of the region is provided by Wolfart (1981), Murris (1981) and Koop and Stoneley (1982), and the reader can refer to them for more information. G E O L O G I C A L HISTORY Phase 1: The Consolidation of the Arabo-Nubian Massif

The consolidation of the Arabo-Nubian Massif can be regarded as the terminal event of the first megacycle. The second megacycle began early in the Phanerozoic, and its development and history was influenced to some extent by the earlier history; consequently, some attention will be given in this section to the late Proterozoic history. According to Behre (1986), the final consolidation marked the suturing of the Arabian and Iranian extension of the Mozambique Belt with the zone of island arcs of the Sudan and southwestern Arabia. This line, however, is only well- established where Kazmin (1988) indicates its presence in the Horn of Africa (the Inda Ad Zone and its analogues). Over the greater part of the Arabian Peninsula, outcrops of Precambrian are absent. Crystalline basement 22

rocks crop out in the Arabian Shield; the western part of Saudi Arabia; the Republic of Yemen; some of the islands in the southern Arabian Gulf, which lie within the United Arab Emirates (U.A.E.); Oman (the Murbat and Kuria Muria Islands); and some parts of the Saih Hatat area of the Oman Mountains. Outcrops also are known in central and northern Iran, Syria and southeastern Turkey. Their distribution is shown in Fig. 2.4 and modifies the comment of Falcon (1967) that no basement outcrops are known between the Zagros Thrust and the main outcrops of the Arabian Shield. The area of greatest outcrop in Saudi Arabia was relatively poorly known until the detailed mapping and geochronological studies of the United States Geological Survey (USGS) (USGS-ARAMCO, 1963; Brown, 1970), followed by Fleck et al. (1980), whose work concentrated on the southern part of the outcrop area, and the work on the central Arabian Shield by Jackson and Ramsay (1980) and Darbyshire et al. (1983) (Fig. 2.5). The rocks typically consist of deformed, stratified and undeformed to partially mobilized plutonic units intruded by batholithic granites and exposed over an area of 610,000 km 2 (381,250 mi2). The geochronological studies reveal that the oldest of the exposed metamorphic rocks are in the ca. 1000 Ma range and, therefore, are coeval with rocks of Kibaran age in Africa (950-1050 Ma). Brown (1970) recorded three principal age g r o u p i n g s - 720-735, 660-670 and 570 Ma m which can be paralleled with events in Africa. The youngest of these reach up into the Phanerozoic. A number of lithostratigraphic units have been defined and are listed in Table 2.5. The younger of these are discussed more fully in the following chapter on the Infracambrian. Ponikarov et al., (1967) reported outcrops of regionally metamorphosed Precambrian quartzite, schists, marl and amphibolites in the Bassit area of Lattakiya in northwestern Syria. Brinkmann (1976) described two metamorphic massifs in southeastern Turkey: the Bitlis Massif of high- grade gneisses and amphibolites of Late Proterozoic age; and the Poturge Massif, where the metamorphic rocks have a possible early Paleozoic age. The Precambrian basement rocks have affected the Phanerozoic sequence because they provided a source of sediment and minor adjustments along basement faults, which resulted in the local thickening of some sequences. In other cases, they have played a role in the development of structural traps for hydrocarbons. The latter is especially the case in the southern Arabian Gulf fields. Jackson (1980) attempted a preliminary correlation of the Late Proterozoic rocks of northeast Africa and Arabia and showed basically two geographic groupings, around the Tanzanian craton and around the Red Sea-Gulf of Aden area. In this latter area, he remarked on the general lithological and gross structural similarities to an older group of metasediments interbedded with geochemically primitive metavolcanics; a younger group of metavolcanics and metasediments that bore a resemblance to modern back-arc basins, destructive margins or modern island

The Geological History and Structural Elements of the Middle East

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23

Sedimentary Basins and Petroleum Geology of the Middle East

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24

The Geological History and Structural Elements of the Middle East

Table Table 2.5. 2.5. Lithostratigraphic Lithostratigraphic units of the Arabian Shield. Shield. Unit

Age (Ma)

Lithology

Depositional Environment

Jubaylah Group

530

Terrigenous clastic conglomerates, arkosic sandstone and siJt.stone with minor mudstone, shale, chcrty limestone and dolomite. Carbonates with stromatolitic lamellae

Alluvial fan to lacustrine with intertidal carbonates

Sham mar Group

570

Rhyolitc, trachyte, lithic and arkosic arenite. granite and granodiorite, rhyolittc volcanics and dykes

Subaerial to shallowmarine volcanic arc and molasse origin

Murdam Group

570-550

Polymictic basal conglomerate and thin marble and thick arkosic sandstone, polymictic conglomerate and rhyolite above

Deposition during period of uplift and erosion

Halaban Group

600-500

Rhyolitic and irachytic ash flows and pyroclastic rocks. Andesitic flows, agglomerate, tuffand breccia, subordinate basalt. Conglomerate, fine elastics, basalt, agglomerate and breccia

Partly emergent ridge or island arc

AbJah Group

850-750

Conglomerate and coarse graywacke with volcanic clasts. Andesitic to dacitic volcanics and pyroclastic and volcaniclastic rocks. Conglomerate and coarse graywacke with volcanic clasts

Deltaic to shallowmarine near a volcanic source

Jiddah Group

890

Metamorphosed basaltic, andesitic to dacitic volcanic, pyroclastic and volcaniclastic rocks with conglomeratic sandstone, phyllitc, chert and marble

Island arc

Bahah Group

950

Schist formed from silty to sandy graywacke and silty chert, some marble, conglomeratic arkose, and mafic tuffand meta-andesites

Baish Group

1165

Metamorphosed volcanic breccias and volcaniclastics and tuffaceous rocks

Low-energy environment with intermittent turbidity flow deposits near a volcanic arc, may be on oceanic crust

arcs; and a third group of Infracambrian volcano-sedimentary and sedimentary units that were only weakly metamorphosed. This work refined the earlier work of Brown (1970). Geological and geochronological data were combined to produce time-calibrated, stratigraphic columns for the shield. Jackson and Ramsay (1980) then attempted to correlate these across the shield and define a number of Proterozoic stratigraphic sequences in a manner analogous to that of Sloss (1963); that is, three sequences - - A, B and C - - bounded by unconformities, where these can be identified (Fig. 2.6 and Table 2.6). Where sufficient data are available, the consolidation can be broken into a number of sub-phases, although their number and age limits vary

according to author. Behre (1986) and Brown (1970) recognized three sub-phases, but with different age limitations and different again from those of Jackson and Ramsay (1980), whose divisions are shown in Table 2.6. Bentor (1985) provided a variant with four sub-phases, with the principal difference occurring in the handling of the younger-dated events. Bentor's variant is the one described here. The older events basically lie within the same time limits. In the geochronological report of the USGS, the summary of results of the Rb/Sr studies from all the major units, except for the layered gabbros and serpentinites, shows that the Arabian Shield did not consist of reacti-

25

Sedimentary Basins and Petroleum Geology of the Middle East

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Table 2.6. Summary of lithological characteristics of "sequences" A, B and C and the stratigraphic units of the Arabian Shield, Saudi Arabia (after Jackson and Ramsay, 1980, and reproduced by kind permission of the Geological Society, London ).

Age (Ma) @570

Rock Units

Characteristic Lithofacies

Fatima, Afif, Halaban and Hulayfah

1, Subaerial to shallow-marine volcano-sedimentary (volcanic arc/ moiasse type): polymictic conglomerate, Jithic and arkosic arenite, calcarenite and marble interbedded with thick basalt-andesitedaciie-rhyolite lava and pyroclastic deposits (commonly ignimbritic).

Murdama, Jibalah and Ablah

2. Shallow-martne/fluviatile sedimentary (molasse type): fine- to medium-grained arkosic, micaceous and calcareous clastic sediments interbedded with polymictic conglomerate, lithic arenite and marble (sometimes stromatolitic),

Samran, Jiddah, Halaban, Hulayfah and Ablah

3. Volcano-sedimentary (volcanic-arc type): thick basalt-andesitedacite-rhyelite lava and pyroclastic deposits, interbedded with volcaniclastics and subordinate mudstone, chert, quartzite and marble.

Urd-ophioJite complex and equivalents

4. Mafic-uliramafic/volcano-sedimentary (ophiolite type?): serpentinized mafic-ultramafic complexes, associated with basalt (locally pillowed), keratophyre, marble, chert, graywacke, argillite and tuff.

Baish and Arafat

5. Greenstone-amphibolite-greenschisis: greenstone, amphibolite and greenschists with subordinate quartzo-feldspathic schist (mainly derived from mafic to intermediate lava, pyroclastic and volcaniclastic deposits), interbedded with subordinate finegrained pelitic or calcareous schist (derived from sediments).

Arafat, Bahah and Hali

6. Para-schists: fine-grained micaceous quartzite, mica schists, phyllitc, slate, carbonaceous schists, calc-schist, marble, ferruginous quartzite and chert and para-amphibolite.

Ajal

7. Gneiss-schist-amphibolite: ortho- and para-gneiss, amphibolite, calc-schist, marble, quartzite and leptynite.

< u u a u 3

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26

The Geological History and Structural Elements of the Middle East vated Archean crust, and there was no evidence to support the existence of sialic crust much older than 1000 Ma. The oldest plutonics measured were around 900 Ma (Fleck et al., 1979). These trondhjemites, diorites and quartz diorites, young from west to east or southwest to northeast, suggest a general eastward migration of the axis of magmatism and, hence, presumably of the island arc. Jackson and Ramsay (1980) recognized an older andesitic assemblage basically coeval with dioritic plutons and suggested a common genesis at about 900 Ma on the basis of composition and Rb/Sr ratios. The oldest ages recorded were from a basaltic assemblage, which yielded ages of 1165 Ma. Rocks from this assemblage from the southern part of the Precambrian outcrop, they believed, formed in an island-arc environment, remote or isolated from any continental land mass. This island-arc environment persisted from 920-680 Ma and includes numerous tectonic and magmatic phases. Later magmatic rocks, dated in the 610-650 Ma age range, are more evolved petrologically and suggest a source different from the diorites dominated by oceanic lithosphere and perhaps mantle, to one including previously differentiated sialic crust, but juvenile because there is no significant increase in the Rb/Sr ratios. They assign the magmatic activity in the 900-680 Ma age range to the Hijaz Orogenic Cycle and attribute to the Pan-African event the suturing of Arabia to the Gondwana land mass. With the beginning of collision, deformation and metamorphism, granodiorite to granitic magmatism became shield-wide, the result of subduction of an eastdipping plate under the earlier island arc. Bentor (1985) suggested a slightly different variant, a four-phase shield evolution described below: Sub-phase 1: The Oceanic Assemblage, 1100-950 Ma. Represented by oceanic tholeiitic pillow basalts and basaltic andesites that together may total more than 6,500 m (about 21,320 ft), as in the Bidh Volcanics (790 Ma), now found as metavolcanics. The principal intrusives are gabbros with some trondhjemites that cut ultrabasic rocks. They may reach a thickness of up to 7,000 m (in excess of 22,960 ft), as in the Jebel al Wask and Jebel al Ess. The associated volcanogenic sediments, now metasediments, are equally thick and consist of graywackes, breccias and chert, as in the Baish, Bahah and Arafat groups. Sub-phase 2: Island-arc Stage, 950-650 Ma. This phase is represented by a sequence of intermediate extrusives, andesites, dacites and rhyodacites that may total 1,700 m (more than 5,576 ft), as well as volcanogenic clastic sediments, tuffs and agglomerates. The rocks were subsequently metamorphosed to a greenschist facies. Examples of these rocks are Ishmas Volcanics (700 Ma), Halaban/Hulayfah Volcanics (800-670 Ma), Balas and Aqiq Volcanics (750 Ma), Fatimah Volcanics (688 Ma) and Samran and Shayban units (800 Ma). The associated volcanogenic sediments, now metasediments, consist of conglomerate, siltstone, sandstone and graywackes with occasional carbonates, deposited in a shallow-marine envi-

ronment. They may be extremely thick; thicknesses in the order of 13,000 m (more than 42,640 ft) have been reported. Examples are the beds of the Ablah Group (about 760 Ma) and the Abt Formation (850 Ma). The intrusive rocks range from hornblende diorites to quartz diorites, tonalites, trondhjemites, granodiorites and monzo-granites, with ages that range from 900 to 650 Ma for the granodioritic gneiss domes. Sub-phase 3: The Calc-alkaline Batholithic Phase, 650-590 Ma. This phase is dominated by calc-alkaline volcanics, andesites, rhyolites, ignimbrites and basalts. Examples are the Lower Murdama Volcanics (650 Ma), Jahhad Volcanics (615 Ma), Juqjuq Volcanics (612 Ma) and the Arfan Volcanics (608 Ma). The associated shallow-marine to continental sediments consist of continental molasse, arkose, conglomerate and shelf carbonate, as found in the Lower Murdama Group. The intrusives are, in the main part, calc-alkali gabbros to granites, granodiorites and late to post-orogenic granitoids, such as the Wadi Shuwas quartz monzonite or the Taif granite. Sub-phase 4: The Alkaline Batholithic Phase, 590550 Ma. The sedimentary and volcanic rocks of this phase, such as those of the Upper Murdama Group, are separated from the older rocks of the Lower Murdama Group by the Yewfik Unconformity. The 600-4,000 m (1,968-13,120 ft) thick beds of the Jebalah (Jubaylah) Group belong to this phase and are composed essentially of alkali-basalts, andesites, rhyolites, pantellerites, ignimbrites and pyroclastics interbedded in continental alluvial or lacustrine sandstone and conglomerate. The sequence, however, contains some limestone. The Shammar Volcanics, up to 12,000 m (more than 39,360 ft), also belong to this phase of activity. There are some carbonates associated with the volcanics. The intrusive rocks of this phase are mostly alkaline, comenditic and pantelleritic granites, such as the Jebel al Tuwalah riebeckite-aegerine granite and the Hadh Aldyaheen ring complex. Both Beydoun (1988) and Kroner (1985) pointed out in their surveys of the evolution of the Proterozoic Arabian-Nubian Shield that, although there was general agreement on the plate-tectonic origin of the shield through island-arc accretion, there are several interpretations of how this came about. Models suggesting growth by arc suturing and ophiolite obduction, the opening and closing of back-arc basins, or by a combination of arc accretion and continental fragments, have all been proposed (Figs. 2.7 and 2.8). There are even differing views on the polarity of subduction. The presence of the basaltic sequence with ages in excess of 1000 Ma has been interpreted as evidence for an island arc as already indicated, but it also has been suggested that this may represent the incorporation of a microcontinental fragment of unknown origin. Kroner (1985) proposed a model (Fig. 2.8) contrasting the evolution of Arabia and Egypt between 700 Ma and 900 Ma and concluded that subduction-related magmatism in the oceanic domain in the east created the first Pan-African arcs in Arabia, and that the westward-directed subduction may 27

Sedimentary Basins and Petroleum Geology of the Middle East

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.

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~

Passive margin sediments Ophiolitic relics of proterozoic ocean crust Post pan pan-African hot-spot PIutonism and volcanism

Oceanic crust

~

Arc systems and developing Pan-African crust

~

Fig. 2.7. A cartoon depicting stages in the development of the Arabian-Nubian Shield. (a) depicts the situation in the early Pan-African with many immature arc systems. By Middle Pan-African times, (b) the arcs have matured and coalesced, but have not attained continental dimensions. By late Pan-African times, (c) the arcs have coalesced into continents, but these still overlay subduction zones, and magmatic activity had calc-alkaline affinity. Figure (d) depicts the post Pan-African (500-600 Ma) situation. When the continent was fully developed, subduction ceased, and magmatism was per-alkaline and of within-plate affinity (after Gass, 1981).

.

.

.

.

~,

.

-

.

.

.

NUBIAbl D O M A I N

.

~

7,50 Ma

COHTINEICrAL NILE CRATON

MAKKA

EVOLVING ARC

MARGIN

~

.

NW

,,/i,

~,,

Jl,.

LITH TERRAHE

TERRANE

MARGINAL

'

,,

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.

ARABIAN DOMAIN

TF..RRANE A C C R E T I O N A N D O V E R T H R U S T I N G N I L E PASSIVE

~,

,

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AFIF EXOTIC TERRANE

TERRANE

Nil

I

~'~2~_

I ;,#l

~s

"

I

.

.

.

.

.

|

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6 4 0 Ha

E

Fig. 2.8. Hypothetical composite NW-SE cross sections across the southern Eastern Desert of Egypt (Nubian Domain) and the southern Arabian Shield (Arabian Domain) showing suggested evolution at about 750 Ma (top) and about 640 Ma (bottom). The black symbol in the lower section denotes ophiolites and/or an ophiolitic m61ange (after Kroner, 1985).

28

The Geological History and Structural Elements of the Middle East have been the prime cause for the back-arc-related rifting and passive margin evolution farther west in Egypt. Marginal basins in Egypt would represent, therefore, a tensional setting, whereas the compressive deformation in Arabia resulted from arc and terrane collision with the consumption of oceanic crust. In Sudan, the Onib-Sol Hamed Suture, the continuation of the Yanbu Suture of Arabia (see below), is continued farther to the west by the Allaqi-Heiani Suture and displaced somewhat to the north by the Hamisana Shear Zone (Stern et al., 1990). The general absence of high-pressure-low-temperature assemblages on the Arabian Shield suggests that deep trenches did not develop as a result of a thicker crust that favored overthrusting and interstacking during collision or oblique docking. If, as seems reasonable, it can be accepted that simple collision models featuring juvenile arcs are an insufficient explanation for the observations, then it seems probable that plate fragments and oceanic plateaus may be involved in addition to oceanic arcs in a manner similar to the situation in the present Indonesian archipelago. Certainly, seismic data clearly indicate a heterogenous crustal structure. Thus, the process was neither entirely ensimatic, nor ensialic. The most detailed plate-tectonic model of Arabia is 36'

that of Stoesser and Camp (1985), who identified five distinct terranes separated by four ophiolitic suture zones (Fig. 2.9). They claim to have identified three ensimatic island arcs in the western part of Arabia: the Asir, Hijaz and Midyan terranes separated by the east-northeast-striking Yanbu suture in the north and the southerly Bir Umq Suture (Fig. 2.10). The lithostratigraphic units associated with the terranes are shown in Fig. 2.11. These are truncated to the east by the north-south-striking Nabitah Suture. This, and the parallel- striking A1 Amar Suture, separate two terranes with continental affinities. The Nabitah Suture Zone, about 100-200 km (62.5-125 mi) wide, shows that plutonism was active between 680 and 640 Ma and contains ultramafic and mafic rocks interpreted as ophiolite complexes. Stoesser and Camp also believe that the A1Amar suture is the result of convergence, for it separates two terranes of differing composition. More detail is provided by A1 Shanti and Mitchell (1976). Radain et al. (1987) note that within the Asir Terrane west of the Nabitah suture, there are layered metavolcanics and metasediments with intrusive rocks characteristic of a destructive margin. In looking at the timing of the intrusive events, they came to the same basic conclusion: that the two phases of tonalite intrusion, at 854+10 Ma and

44

J

NAI~AH O R ~ BELT

AI.NARstYruRE ARRAYN SUTURE

Fig. 2.9. Tectonic sketch map of the Arabian Shield, showing terranes and suture zones. Northwest-trending solid lines indicate fractures of the Najd Fault System (modified from Stoesser and Camp, 1985 and reproduced by kind permission of the Geological Society of America).

~v-- 7

U~AN

16"~

OROC~N1CBELT

~

ARCTERRANE~0.70OM~

~

ARCTERRANE(,cX~)OM~

tl

1110Rm

29

Sedimentary Basins and Petroleum Geology of the Middle East WESTERN ARC TERRANES

EASTERN TERRANES

'VOLUTIONARY,

,

PHASE 9

EPICONTINENTAL SUBSIDENCE

tNTRACRATONIC

NAJID WRENCH FAULTING

'

GRANITIC PLUTONISM AND CALDERA FORMATION MOLASSIC SEDIHEICrATION

6OO-

9

~ 70o-

~

"I/V/,,

, , , ,

"

I'Q"~

st~ ~ , 9, . -

' ALAMAR ACCRETION

~,

Fig. 2.10. Tectonic evolution of the Arabian Shield. A solid vertical line between terranes indicates time during which adjacent terranes are separated. Vertical lines represent no stratigraphic record (after Stoesser and Camp, 1985, and reproduced by kind permission of Geological Society of America).

I_.~ -J ..J

MICROPLATE ACCRETION "---"

~,~.~

~tJ

- OROGENY

800-

ARC MAGMATISM

~

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~ ~ "1 CONTINENTAL

~. ,, a >1

>1200

Ca^TONIC

i AGE~ . (Ma), 5OO

.

. MIDYAN

WESTERN . .

I

ARC TERRANES . HUAZ

EASTERN

' t

TERRANES

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Asia

AR R A Y N

: UNIT SAQ

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+-F+ 4-+ + A T T E N U A T E D C O N T I N E N T A L .f -I"~ -t- + § § + ~+ +"~ -I- § + * B A S E M E N T --__~'~+++++44§ ~ + UABALKI'iLDAI63KIMal

.t-'t-+-I- + - I " ,.t~§

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~J

Fig. 2.11. Lithostratigraphic units and magmatic arcs of the Arabian Shield terranes. Sedimentary lithologies (S): ST=sub-aqueous (in part turbiditic); SG=sub-aqueous (largely graywacke); SM=shallow marine; SA=sub-aerial to shallow marine (arkosic molasse); CS=continental shelf; EP=epicontinental. Volcanic lithologies (V): LB=low-K basalt; HB=high-K basalt; B=bimodal (basalt/felsic); I=intermediate; R=rhyolitic. Plutonic lithologies (P): GB=gabbro; DI=dioritic; TN=tonalite and trondhjemite; GD=granodiorite; GR=granite; AG=alkali granite and alkali-feldspar granite. Groups are shown in upper case letters and formations in lower case letters. The Farri and Urd groups occur between terranes and represent highly deformed, ophiolite-bearing, accretionary-prism deposits of the Yanbu and A1 Amar sutures, respectively. Oblique lines indicate no stratigraphic record. Units marked with an asterisk in the Midyan Terrane are located in the Eastern Desert of Egypt (after Stoesser and Camp, 1985, and reproduced by kind permission of the Geological Society of America). 30

The Geological History and Structural Elements of the Middle East 815+13 Ma, showed a chemistry indicating oceanic affinities. The detailed study of the lead isotopic dating on rocks from the Zalm area by Stacey and Agar (1985) demonstrated not only that the southern Afif Terrane contained older continental crust with a long upper-crustal prehistory extending back into the Archean, but that it was isotopically different from the northern part. Both concluded that the western margin of the terrane developed an Andean character before 720 Ma, and that the Afif Terrane collided with the Asir Terrane during the Nabitah orogeny between 685 and 640 Ma. They also recognize later intrusions into the suture zone. Thus, the Afif Terrane may be regarded as a microplate, partly continental and partly oceanic, which is incorporated into the Arabian Shield. The simplest outline of tectonic activity in this early phase in the history of the Arabian Shield, as summarized by Stoesser and Camp (1985), is one of the ensimatic-arc developments from about 950-715 Ma. The Asir Terrane may represent multiple-island-arc accretion (Fig. 2.10). From 760 to 715 Ma, at least three contemporary arc systems, the Hijaz, Taif and Tarib, may have developed. From 715 to 640 Ma, through collision and accretion, the Arabian neocraton formed with the suturing of the five terranes along the Yanbu, Bir Umq, Nabitah and A1 Amar sutures. Collision-related, intracratonic magmatism and tectonism continued for another 80 Ma following collision-related orogenesis. The northwest-southeast-striking Najd Shear Fault System, which has a lateral displacement of as much as 200-300 km (125-187.5 mi), occurred during this intracratonic phase and is dated as between 630 and 550 Ma by Stoesser and Camp (1985) and 580 and 530 Ma by Moore (1979). Moore indicated that the Najd Transcu~ent Fault System was made up of a complex of parallel, curved and en echelon faults and, as a result, shows a striking similarity to the approximately contemporaneous shear-fault system bounding the western edge of the Touareg Shield of Algeria (Caby, 1968). Stacey and Agar (1985) indicate that the fault system began as a dextral shear at about 640 Ma, changing to show sinistral strike-slip motion at about 620 Ma. Johnson and Vranas (1984) asserted that the metallogenic cycle they identified in central Arabia was similar to that of other arc-accreted domains. They noted two distinct periods of copper-zinc mineralizations occurring 200 Ma apart, at approximately 900 and 700 Ma, and a tungsten association found in the post-tectonic Pan-African phase. Subsequent work has tended to confirm the broad outline as given here, although there are some changes in the timing of events. Jackson and Ramsay (1980) and Roobol et al~ (1983) limit sequence C to ca. 1000-1200 Ma, sequence B to 650-900 Ma, and sequence A to 570-650 Ma. Clark-Lowes (1985) in the Midyan area of Saudi Arabia and Stern and Manton (1987) in the Feiran region of Sinai interpret data in terms of island-arc terranes, but Clark-Lowes (1985) sees the possibility of accretion against 700 Ma crust lying to the north. Stern and Manton

(1987) point to the general northward movement of intrusive events from 650 Ma in the south to about 600 Ma in the north, although Kazmin (1988) would place the final phase of activity as late as about 500 Ma. After this time, the Arabo-Nubian Massif can be treated as a single unit. The extent of the massif in Egypt is uncertain; widespread juvenile tonalites are lacking in Egypt. Older sialic rocks, however, seem to be restricted to west of the Nile, and the area east of the Nile may be the back-arc and passive margin related to the oceanic arcs of Arabia (Kroner, 1985). A somewhat different interpretation has been presented by Kemp et al. (1982), who adopt a chelagonic evolution model for the Arabian Shield. They regard the Precambrian as primarily the active, early, mobile phase of the cycle, while the Phanerozoic represents the stable, middle part of the cycle. The Precambrian, therefore, represents a period of high heat flow, during which they recognize several subcycles of sedimentary and volcanic activity initiated by faulting and accompanied by first silicic and then basaltic volcanic activity followed by compression and ending with epeirogenic uplift and erosion. These subcycles are regarded as typical of intracratonic activity. There is little evidence for either tectonic emplacement of ultramafic rocks or migration of fold belts over a 600 Ma period. In this model, the Phanerozoic represents a period of crustal cooling leading to increasing crustal strength. There has not been much detailed seismic study. However, Mechie et al. (1986) were able to show significant variations in the depth of the Moho and intercrustal discontinuities from the results of a long refraction line extending across the area from the Farasan Islands (Red Sea) in the southwest, to just west of Riyadh in the northeast (Healy et al., 1982; Gettings et al., 1986). The most obvious change, the jump of 20 km (12.5 mi) in the Moho depth, coincides approximately with the location of the Hijaz Escarpment and marks the edge of the Red Sea Depression and the Arabian Shield. It is a relatively young feature, and it is possible to show a division into three regions that correspond to the general pattern established by Stoesser and Camp (1985). The depth to the Mohorovicic discontinuity exceeds 40 km (25 mi) under the HijazAsir and the Shammar provinces northeast of the A1Amar Idsas Fault, but is less than 40 km south of the fault under what they call the Najd Terrane, corresponding to the Afif Terrane of Stoesser and Camp (1985). Stacey and Hedge (1984) provide evidence for basement rocks with ages in excess of 1638 Ma at the eastern margin of the shield, which had been reset to around 650 Ma, suggesting that east of the Afif Terrane (east of the A1 Amar-Idsas suture), there existed another old terrane that can be correlated with the change in crustal thickness seen on the Saudi Arabian seismic refraction line (Mooney et al., 1985). ClarkLowes (1985) in the Midyan region and Stern and Manton (1987) in Sinai also have indicated the presence of older crust to the north. Thus, there are a number of grounds for supposing the existence of older and topographically more

31

Sedimentary Basins and Petroleum Geology of the Middle East subdued crust to the east and north of the main Precambrian outcrops of the Arabian Shield. In the entire discussion, concern has been paid only to the shield and its relation to that part of the Arabo-Nubian Shield across the Red Sea in Africa. Yet, the shield continues to the east and northeast, becoming more deeply buried beneath Phanerozoic sediments as the Arabian Gulf is approached. The end of the USGS refraction line shows that horst and graben structures can be traced as far as the line continues. However, over the major part of the Arabian Platform, even in those few locations where there has been some deep drilling, there is very little information concerning the nature or the presence of Precambrian rocks. They have been penetrated in one well drilled on the Burgan High in Kuwait and in well Ghadir Manqil-1 in South Oman and in some recent exploration wells in southwestern Saudi Arabia, although no descriptions are available. They indicate either considerable basement relief, which seems unlikely on stratigraphic grounds, or subsequent, post-Infracambrian movement, which seems probable given the history of the late Paleozoic (see Chapter 5). The only age dates available are a handful given by Perfil'yev et al. (1982) from rocks from central Iran. These dates confirm the conclusion reached by Thiele (1966) on tile existence, in this part of Iran of (at least) two phases of Precambrian metamorphism; for while most age dates fall in the 600-1000 Ma range, there are, in the northwestern part of the region, two Rb/Sr ages that are pre-Assyntian lying in the 1800-2300 Ma range. Samani (1988) reported ages from volcanic fragments caught up in the Hormuz evaporites in the range of 560 to 1040 Ma, but also pointed out that on the basis of composition, sedimentary sequences and degree of metamorphism of the other fragments, it was possible to distinguish three different complexes: an early Precambrian (?) granite-gneiss and migmatite complex (Table 2.7), a late Precambrian metamorphic complex up to amphibolite grade, and a greenschist or slightly higher-grade metamorphic series that passes upward into unmetamorphosed facies. Although it could be argued that this region may not represent a continuation of the Arabian Platform, given the existence of the suture on the northeastern sides of the Zagros Mountains, the identity of the early Paleozoic sequences suggests that such continuity did exist. Samani (1988) argued that the consolidation of central Iran conforms to a consolidation during the Kibaran and Pan-African orogenies (1100-550 Ma) as part of Gondwanaland, leaving unresolved the existence of older, nuclear cratonic areas farther to the north. The other principal area where Precambrian rocks can be found is in exposures along the axis of the Huqf-Haushi Axis of Oman, which extends southwestward from Oman at Qalhat, Jebel Ja'alan and Mirbat, and in the A1 Halaniyat Islands (Fig. 2.4). Although outcrops generally are restricted, and radiometric ages are lacking, field mapping of these Precambrian outcrops shows that they are surrounded by Infracambrian strata that are structured dif-

32

ferently. This implies an important break between the two groups of rocks consistent with field observations in the Tabuk Basin of northwestern Saudi Arabia. Gass et al. (1990) have shown that the Precambrian rocks that crop out in Oman (Fig. 2.4) include metasediments of greenschist or even amphibolite facies that have been intruded by dolerites, granodiorites and granites, all cut by doleritic and felsitic dikes. These rocks are dated radiometrically as Late Proterozoic (600-800 Ma range) (Table 2.8); therefore, they are chronologically as well as compositionally within the Pan-African domain, and are not part of an older Early Proterozoic basement series of the type found in the Afif Terrane of Saudi Arabia. Geochemical analysis identifies most of the granites as volcanic-arc granites similar to those in the Pan-African terranes of western Arabia. Outside the Arabian Shield, the Precambrian rocks generally are described in lithological terms and may be assigned to groups and named. They cannot be correlated, except on the highly subjective basis of lithological similarity. Beydoun (1966) has described four principal types of basement rocks cropping out in South Yemen: 1) a series of volcanic rocks, mainly lava flows but with associated tufts; 2) a series of primarily metasedimentary rocks (also containing meta-igneous rocks); 3) a series of virtually unmetamorphosed sedimentary rocks thought to be the equivalents of the preceding group; 4) and a series of intrusive rocks, large and small, basic and acidic. The few radiometric ages available are consistent with the younger dates found in Saudi Arabia and lie within the Phanerozoic close to the Cambro-Ordovician boundary. Very little has been published on the continuation of the Precambrian sequence in northern Yemen; Geukens (1966), in a short account of the geology of Yemen, does not give a single reference. Outcrops are found in the mountains in northern and eastern Yemen, as well as at the base of horst blocks below the Trap Volcanics. There are, for example, extensive outcrops along both sides of the Sa'dah Graben. Lithologically, mica-schists and pink granites predominate, but amphibolites, marble and quartzite also have been described. At one location, the appearance of a conglomerate seems to indicate the presence of two metamorphic series. In Turkey, crystalline rocks have been found in four main areas (Fig. 2.4). The rocks that crop out in the Bitlis Massif of Southeast Turkey are partly of magmatic origin (amphibolite, hornblende gneiss and leucocratic gneiss), and partly consist of metasediments such as sillimanitebearing, foliated gneiss and muscovite-biotite schist (Brinkmann, 1976). All show amphibolite grade metamorphism and are intruded by granitic and pegmatitic rocks. These basement rocks, unconformably overlain by greenschists, quartzites and marble, were subjected to later, Caledonian recrystallization. Both Archean and Late Proterozoic ages have been recorded in the Menderes-Taurus Massif in two different blocks separated by the Karinti strike-slip fault (Kroner and Seng6r, 1990). Not only do

The Geological History and Structural Elements of the Middle East

Table 2.7. Stratigraphy, structural process, magmatism and ore-forming ore-forming stages during tiie Infracambrian-Early Cambrian in Iran (after Samani, 1988). the Infracambrian-Early

Age

'5 o

Orogenic Phase

= '^ = ^

«I

OS

'S M — a rd <5 u c is

< 1

(£

1

Ores

1

c u .2 '•B c

Formation/Lithology

Magmatism

log

u

Epicontinental to platform-type sediments of Rizu, Desu, Bayandor, Soltanieh, Barut and Zaigun formations

^ S

c It E « "S ^

£0

ID

i

*- c •s «

'E

O

i 2£ " £ S o 35

£ 9-

1

S « S S < ^

is a, -a

o "S s:

2o

=3 U

E

Highly volcanogenetic series, carbonates, tuff shale sandstone, limestone, dolomites, evaporitcs and acidic to basic lava flows; Duzakh Darrch Complex and Hormuz Series

Eb n ^ « c ^

D S

-J

*

O

y

1

E 2

•~ o

^^ S .2,

6

IN

-

Z ^

<

EH

I.*

u

E d S. o 5 w

1 ® «'

£^ S ^ is

Rifling and block faulting

£

1

„

E^

E C « w> .S 2 "a <

c u E u •a "o

Greenschist facies metamorphics of Morad, Kahar and Tashk formations mainly flyschoid[ype sediments

High-grade metamorphic complexes of Chapedony, Boneh, Shurow, Sarkund, northwestern Iran

c

'e u a. O a _o ca

1 3

these ages suggest heterogeneous source areas for Paleozoic rocks, but they also suggest the incorporation of Archean fragments during the consolidation of Gondwanaland. There also are a few scattered outcrops of quartzites, marble, schists and amphibolites in northwest Syria, described by Ponikarov et al. (1967), in the Bassit area of Lattikiya. They have been regionally metamorphosed to greenschist facies of early to middle Riphean age. The period of the transition to the succeeding quiet period is one of considerable interest. The basal member of the stratigraphic succession that marks the period of

tectonic stability is a sandstone that has been given different names in different areas. It rests upon an unconformable surface, which in North Africa is referred to as the infra-Tassilian surface and which is poorly dated there. However, in the Tabuk Basin of northwestern Saudi Arabia below the basal Saq sandstone and the unconformity, there is steeply dipping limestone; and if their equivalence with the Fatima limestone is correct, as it seems to be, then these rocks have an Early Cambrian age and pre-date the development of the unconformable surface in that area. The movements, which resulted in the tilting of the beds, must then have occurred within the Cambrian, consistent

33

S e d i m e n t a r y Basins and P e t r o l e u m G e o l o g y of the M i d d l e East

Table 2.8. Tethyan ophiolites in the Middle East (after Lippard et al., 1986, and reproduced by kind permission o f G e o l o g i c a l S o c i e t y , London). See F i g . 2 . 1 3 f o r c o u n t r y and location

Country/ Region

Individual Compltxcs

1. Pontides, Anatolides

Formation

Obduction''/ Emplacement*^ Age

Remarks

J u ras sicCretaceous?

Numerous small complexes, mainly in melange zones. Some high pressure metamorphism Poorly known. Most probably an extension of the Anatolian belt

2. Lesser Caucasus

Vedi zone, SevanAkara

"Pre-Cenomanian"

3. Taurides

a) Marmoris b) Mcrsin-Kersanti c) Anlalya d) Posanti e) Beyshin 0 Hoyran

Middle Cretaceous?

86-104 Ma (metamorphics cut by Campanian, 75 Ma, dykes)

Largely harzburgites. Layered sequence exposed in Antalya. No sheeted dykes or lavas. Metamorphic soles and mantle sequences cut by tholeiitic dykes

4. Cyprus

Troodos

Middle to Upper Cretaceous (79 Ma)

87-89 Ma Pre-Campanian formation

Intensely studies. Recent work on lavas suggests a supra-subduction zone setting

5. NW SyriaSE Turkey

a) Hatay b) Baer-Bassit

Middle Cretaceous

86-89 Ma Post-Campanian-Pre-Maastrichlian emplacement

Complete sequences exposed. Harzburgitic island-arc tholeiite chemistry

6. Zagros Mountains (Iran)

a) Khoy b) Kermanshah c) Neyriz

Middle Cretaceous

89 Ma? Post-Campanian-Pre-Maastrichtian emplacement

Ophiolites strung out along Zagros Fault Zone (2,000 km long). Harzhurgiie at Neyriz cut by low K tholeiite dykes. Islandarc tholeiite lavas in other complexes

7. Oman Mountains

Scmail (Samail)

Cenomanian (98-94 Ma)

96-85 Ma Post-Campanian-Pre-Maastrichtian emplacement

Harzburgitic mantle sequence. Island-arc tholeiite chemistry

8. Southeast Oman

a) Masirah Island b) Ras Madraka

Cretaceous?

Prc-Eocene, probably Late Cretaceous emplacement

Harzburgites, MORB? chemistry. Related to NE-SW "transform" faulting along Masirah Line. Probably a part of the Owen Basin obductcd from the SE

9, Makran (Iran)

a) Makusian-Fanuj b) Iranshah

Upper Cretaceous?

Pre-Paleocene emplacement

Late Cretaceous back-arc marginal basin. Harzburgites. MORB-IAT chemistries

10, East and central Iran

a) Naif b) Baft c) Esrandagheh d) Tchehel-Cureh

Upper Cretaceous?

Pre-Paleocene emplacement

Mainly harzburgites. Small ocean basins around Lut Block. MORB and lAT chemistries.

1 ], North Iran

Sabzevar

Cretaceous?

Pre-Paleocene emplacement

Harzburgite. Small ocean basin between Lut and Asian Block. I AT? chemistry

a "Formation age" refers to isotopic ages of igneous minerals (usually of doubtful validity, except in cases of U-Pb Zircon ages) and the paleontological age of interbedded or conformable sediments. b "Obduction ages" given in Ma in this column, are isotopic ages of amphibolites in metamorphic soles taken to indicate the time of initial oceanic displacement. c "Emplacement age" generally is a minimum age of nappe emplacement bracketed by the age of the youngest rocks involved in the thrusting and the oldest cover sediments, usually continental or shallow-marine beds.

34

The Geological History and Structural Elements of the Middle East with the observation that the limestone are found only within depressions associated with the Najd Fault System, the age of which also lies within the Early Cambrian. They are, therefore, sediments associated with the tensional phase that followed the consolidation of the Arabo-Nubian Plate. Clearly, the age of this infra-Tassilian surface is not the same everywhere, just as the age of the overlying sediments varies from place to place. The dating of the limestone, however, places an upper limit to the age of infraTassilian surface. In sequence stratigraphy terms, the surface is the same as the pre-Sauk surface in American terminology (Sloss, 1963). Stratigraphically, the age of this surface becomes older to the north, as indicated by the progressively more marine nature and older ages that can be assigned to the Sauk sequence in Jordan and Syria. The closest approach to sedimentary continuity across the pre-Tassilian surface is in southern Oman, where the stratigraphy of the Infracambrian is particularly wellknown as a result of petroleum exploration and drilling. Below the oldest formation, the Abu Mahara Formation, a basement trachyte was drilled, from which an age of 654+12 Ma was reported. However, Gorin et al. (1982) regard this merely as a volcanic episode and place the basement age at 858+16 Ma, the date obtained from rocks in Jebel Ja' alan. Although no definitive datum marker has been found within the Huqf Group rocks, there is no doubt that sedimentation there is contemporaneous with at least the last phase of the Pan-African movements and the consolidation of the Arabo-Nubian Shield (a succession described in the next chapter). The deposition of the Ara evaporites, commonly equated with the Hormuz evaporites of the Arabian Gulf, marked the top of the sequence that began during the Infracambrian. The base of the overlying Haima Group in South Oman consists of fine- to coarsegrained sandstone deposited in environments ranging from scree fans to aeolian conditions. The age of these sandstone and of the overlying beds of the Amin and Mahwis formations is not well-established, but they are overlain by beds to which an age as old as Middle Cambrian has been assigned. The evidence of ages predating the Pan-African event in the Arabian Platform, although scattered and disappointingly few, requires modification to the accretion model for the growth of the cratonic area proposed by Stoesser and Camp (1985). Warden and Horkel (1984) hinted at such a modification. The recognition of at least two periods of Precambrian metamorphism and of ages reaching back to 2000 Ma in Iran suggests the existence of older crust that may be compared to the Precambrian cratons of both Madagascar and India. Implicit in this is the recognition of continent-continent collision, with the accretion of the Arabian Platform-central Iranian fragment completing the consolidation of Gondwana. This collision followed the early phase of arc accretion so well-documented by Stoesser and Camp (1985) from the research efforts in Saudi Arabia by the USGS and other groups. It was associated with significant transcurrent movement

analogous to the Cenozoic deformation pattern north of the Himalayan Belt during the Cenozoic. In Saudi Arabia, the most striking example of this strike-slip movement is shown in the Najd Fault System. This system trends northwest-southeast and forms a zone about 400 km (250 mi) wide. Sinistral displacement, which followed an initial phase of dextral movement along the fault system, has been estimated to be as much as 240 km (150 mi) and post-dates the collisional phase (Stern, 1985). Schmidt et al. (1978) interpreted the Najd Fault System as a Late Precambrian, oblique shear zone associated with continent to continent collision. The emplacement of granitic plutons occurred both during and after fault movement, thus providing a means of dating the movement. The whole rock K/Ar date of a pluton intruding the fault system of 530 Ma indicates that the faults had ceased moving by the Late Cambrian. Close to the eastern margin of the Arabian Shield, radiometric ages have been reset, and only through the careful work of Stacey and Hedge (1984) was it possible to detect the presence of older ages on the eastern side of the suture. The Arabian Platform may, therefore, represent the continuation of the eastern branch of the Mozambique Belt, and it is an interesting observation that the limit of the Mesozoic outcrops closely follows this proposed line of suture/junction. As mentioned earlier, the USGS seismic line crosses the shield into the platform for a short distance, and the interpretation of this seismic line shows that the basement in this area is marked by horst/graben faulting. The eastern margin of the shield in Saudi Arabia is also a location marked by the accumulation of significant thicknesses of early Paleozoic sediments (A1 Laboun, 1986; see Chapter 4). This late phase of Najd transcurrent motion forms a striking parallel with the contemporaneous events occurring between the West African Craton and the Hoggar along the Adrar-Tanezzrouft Zone, a zone in which Archean ages have been recorded (Ferrara and Gravelle, 1966), and one in which Caby (1968) reported significant transcurrent movement of the order of 300 km. What makes the Arabian Platform area, particularly in southern Oman, so important is the fact that the tensional effects associated with this last phase of Pan-African activity during the latest Precambrian and early Phanerozoic led to the formation of a series of horsts and semi-grabens, with the latter becoming the sites of active deposition. The sediments deposited have been well-documented as a result of hydrocarbon exploration drilling. Two sedimentary cycles are recognized: the first was an alternating sequence of clastics and carbonates; the second ended with the widespread deposition of evaporites, the Ara evaporites of Oman; their equivalents elsewhere in the Arabian Gulf are the Hormuz salts. The distribution of the Hormuz salts and their equivalents suggests that during the late Precambrian, central Iran, the Arabian Gulf and the Salt Ranges of Pakistan were all part of the same land mass covered by shallow seas (Strcklin, 1968a, b; Gorin et al., 1982). An alternative interpretation proposed here is

35

Sedimentary Basins and Petroleum Geology of the Middle East that the evaporites developed in a series of pull-apart basins and in shallow epicontinental basins, resulting from the tensional and shear movements that closed the PanAfrican event. Samani (1988) suggests two probably interconnected, intracontinental rift structures extending from Iran into southeastern Arabia (Fig. 2.12) separated by the Qatar-South Fars Arch (or its precursor), with which metallogenesis was associated, consistent with this idea. Stern (1985) recognized the Hammamat sediments of Egypt, which appear to be equivalent in age to the Jubailah Group of Saudi Arabia, as a post-orogenic molasse. Means of correlation in the generally uniform sequence are basically absent, and it is only recently that the recognition of horizons containing archaeocyathids has shown that the

formation extends up into the Early Cambrian.

Phase 2: Tectonic Stability Following the consolidation of the Arabo-Nubian Shield and its accretion to the margin of Gondwana, a long period of relative stability supervened, and much of the Paleozoic is dominated by the deposition of widely spread sheets of siliciclastic sediments deposited in epicontinental seas that spread across much of the Middle East (Chapter 4). A major unconformity, represented by the infra-Tassilian surface, formed over late Precambrian-early Phanerozoic rocks. It was upon this unconformable surface that

50" metamorphic exposures [ §

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Fig. 2.12. Late Precambrian-Early Cambrian lithofacies and tectonic map of Iran and the Arabian Peninsula showing major salt basins of Murris (1980) (modified from Samani, 1988). 36

The Geological History and Structural Elements of the Middle East early Paleozoic clastic sheets were deposited. These are assigned to the Cambro-Ordovician (Sauk sequence) and are best exposed in the western part of the Arabian Peninsula. Where sedimentary transport directions have been measured in Saudi Arabia, they indicate a source to the south. The obvious source, the Arabian Shield, does not appear to have been the sediment source, for the sedimentary transport directions in southwestern Saudi Arabia in the Wajid Basin indicate the same transport direction as farther north. The source must be sought farther southeast, possibly from the Haushi-Huqf Uplift or, more likely, a source still farther south in Gondwana. Thus, there is a very close parallel to the situation found along the margin of the Sahara Platform in Algeria. The analogy cannot be drawn too closely, for the development of evaporites found in Oman is not matched in Africa. A number of subsidiary sedimentary sources, such as the Ha'il-Rutbah-Ga'ara Arch in northern Saudi Arabia and western Iraq and the Amanus Arch in Syria and Turkey, also may have played a role. During the Paleozoic, the major unconformities can be related to epeirogenic movements and eustatic sea-level fluctuations. Similar clastic deposits are found in central Iran, which must be considered part of the Arabian Platform at this time, with the margin of Gondwana lying north of the present Alborz Mountains (St0cklin, 1974; Davoudzadeh et al., 1986). Not a great deal has appeared in print concerning the Paleozoic section in Arabia, but the descriptions of the early Paleozoic section in the Tabuk area (Helal, 1964b) and the Devonian of the Jauf area (Helal, 1965a, & b; A1 Laboun, 1986) of northern Saudi Arabia, combined with the recognition of the Late Ordovician glacial horizon, indicate a further parallel with the sedimentary pattern seen on the African Sahara Platform. The end of this period of tectonic calm is not easy to define, because very little information is available concerning the Carboniferous deposits. From Sudan and southern Egypt, the description of grounded glacial deposits of the Carboniferous on the B ir Uweinat-Bir Safsaf Uplift suggest that in Sudan at least, the calm was interrupted by a Hercynian event before glaciation. Care must be taken in discussing the data of Steineke et al. (1958) and Helal (1964a, 1965 a, & b), for they assign a Permian age to the Wajid Formation; whereas most other workers place it in the Cambro-Ordovician based on the occurrence of trace fossils (Alsharhan et al., 1991; Stump and van der Eem, 1995). Silurian and Devonian epicontinental marine deposits are widespread over the Arabian Platform and, in places, may have a great thickness; more than 6,000 m (19,680 ft) is indicated by geophysical data in southeastern Jordan and the TaurusZagros Fold Belt in eastern Turkey. The Devonian deposits include the early part of the Tippecanoe sequence, which ended in the mid-Carboniferous. In northeastern Syria, the late Paleozoic sequence includes metamorphosed graptolitic quartzites; in central and eastern Syria, the sequence

consists largely of shale. As a result of later erosion, Ordovician and Silurian strata are absent over the Sinjar Uplift. Sharief's description (1982) of the depositional environment of the Triassic System in central Saudi Arabia, where broad lagoonal and tidal-flat deposits followed the marine conditions of the Late Permian, again implies a period of tectonic calm (belonging to the Kaskaskia sequence). There is a lack of structural information. Helal (1964a, b, 1965 a & b) indicates that there are numerous NW-SE-trending faults, and his map (in 1965) shows the existence of horst and graben features. He surmises that both these and folds with the same trends resulted from a period of reactivation, but his data are insufficient to indicate whether, as in the Sahara, these faults also were active during the early Paleozoic and affected sedimentary thicknesses. It may be supposed that the coincidence of the axis of the Ha'il-Rutbah Arch with the marginal part of the basement outcrop is not pure coincidence.

Phase 3: The Hercynian Event A Hercynian or Paleotethys ocean can be located north of Iran, but the general lack of surface and subsurface data make the Hercynian event difficult to define. As indicated earlier, it appears that this event, an event seen on the African craton marked by the emergence of the Hoggar Massif and the east-west-trending uplift in southern Egypt and northern Sudan, occurs at the end of the Tippecanoe sedimentary sequence and is a particularly important marker in the history of the Middle East. In Africa, the continuity of the sediment-transport directions and lithologies north and south of the exposed Precambrian massifs indicate that the upwarping of a generally east-west structure was accompanied by the emergence and the erosional stripping of the thick early Paleozoic sequence. The same erosional stripping can be seen in Arabia; however, to this point, the continuity of the Sauk and Tippecanoe sequence sediments across the central Arabian Arch has not been demonstrated. The precise dating of this uplift is hampered by the lack of stratigraphic control. However, south of the central Arabian Uplift, in the depression forming the Rub al Khali Basin, the existence of early Paleozoic rocks at a depth too great to be penetrated by the drill is probable, because sediments of this age have been found over the Qatar-South Fars Arch (Stump and van der Eem, 1995). As in Sudan, grounded glacial deposits also appear, resting on the central Arabian Arch close to the Arabian Shield (Chapter 5), helping provide an indication of the timing of the event. The presence of early Late Permian clastic sediments places a limit on the age of the uplift in Arabia. Recently, the Late Carboniferous to Sakmarian age, based on palynological data suggested for the pre-Khuff Unayzah sediments (A1 Laboun, 1986), has been revised to early Late Permian. Thus, in Arabia, as nearly as can be determined within the limits of

37

Sedimentary Basins and Petroleum Geology of the Middle East the rather imprecise dating available, the boundary between the Absaroka and Kaskaskia sequences is the same as in North America. The sedimentation pattern of the Late Permian reflects a major change in Arabia, marking as it does a shift from a primarily siliciclastic regime to a prolonged phase of carbonate deposition with interspersed clastic episodes. Thus, the Arabian Platform became a shallow carbonate shelf, shallow enough on numerous occasions to become an evaporating pan with the development of gypsum and anhydrite, and halite on occasion. Phase 4: The Triassic Extensional Phase

During the Middle and Late Triassic, a number of tension-related basins and highs began to develop before the extensive Ladinian to Norian rifting events, which are of greater importance in the history of Gondwana than any of the Paleozoic epeirogenic movements, for they provide clear evidence for the beginning of the separation of East and West Gondwana. This major event lies within the Absaroka sequence, as defined by Sloss (1963); consequently, it is more convenient to use the sea-level change sequence of Haq et al. (1987) when considering the stratigraphy of the Middle East. Subsequently, the closing of Paleotethys marked the first collision of part of Gondwana with Eurasia. Collision of the Iranian fragments with the Turan Block north of the Kopet Dagh in Iran occurred during the Liassic. In effect, a split associated with as much as 350 km (219 mi) of shear displacement, according to Christian (pers. comm.), developed along the line of the present Zagros Shear Zone, as the Iranian segment or segments of the Afro-Arabian craton separated and left the narrow Neotethys ocean to the southwest. The effects of this extensional phase in the Middle East can be seen later during the Mesozoic in the formation of the Palmyra, Sinjar and Euphrates-Anah troughs in Syria and Iraq on the Arabian Platform. This split can be traced westward into the Mediterranean and along the line of the Arias in northwest Africa. In the western Mediterranean, this time is marked by the development of extensive evaporitic facies seen, for example, in the Late Triassic-Early Jurassic evaporitic facies in both Algeria and Morocco. In Arabia, however, the Triassic succession shows a development more typical of the so-called Germanic facies, with a lower, mixed clastic/carbonate sequence and an upper clastic unit consisting mainly of siltstone and sandstone separated by a marine carbonate unit. However, to the southeast in Oman, the Middle Triassic is represented by deep-water sediments in the Hawasina Basin. The association of these sediments with the Haybi Volcanics and pelagic carbonates suggests that shallow-water platforms or oceanic islands occurred in this deep basin (Glennie et al., 1974). From this time, the sedimentary and structural developments in central Iran show distinctive differences from those affecting the Arabian Platform. During the Jurassic, the apparently greater mobility and subsidence of the Iranian area, accompanied with continental deposits 38

can be contrasted, with a thinner, but continuous, marine sequence accumulating in the developing Zagros Neotethyan Trough. Phase 5: Jurassic and Cretaceous Events

The first tectonic event of the Jurassic (at the beginning of the Zuni sedimentary sequence of Sloss, 1963) was the closure of the Paleotethys by the collision of the continental microplate or plates of central Iran, which had separated from the margin of Gondwana, with the mass of Laurasia. Simultaneously, Neotethys was opening up along the line now marked by the Zagros Crush Zone, as the microplate or plates migrated away from the rest of Gondwana (Lippard et al., 1986). In Oman, this ocean is known as the Hawasina Ocean of Glennie et al. (1974) or the Oman Tethys of Lippard et al. (1986), and in Iran as the Hercynian Ocean of Berberian and King (1981). Later, in the Jurassic, rifting made itself felt in the Arabo-Nubian Shield, as in Yemen and Somalia. This rifting can be related to the breakup of the northern part of Gondwana, most spectacularly marked by the separation of east from west Gondwana as Madagascar, attached to East Gondwana, pulled away from Africa. Although these events undoubtedly affected the pattern of sedimentation established during the Late Permian, regional changes in sedimentation patterns during the Jurassic and Cretaceous are more readily related to the pattern of eustatic sea-level changes. The marine invasions were characterized by extensive shelf limestone, which continued from the Permian up into the Triassic, where Sharief's (1982) description of the depositional environments indicates the existence of broad lagoonal and tidal fiats passing to the carbonate ramp and platform environments of the post-Toarcian Jurassic and Cretaceous. Murris (1981) described these vast epeiric seas of the Mesozoic, which persisted over the eastern part of the Arabian Platform (see chapters 7 and 8). The Early and Middle Jurassic in the Arabian Gulf then consisted of alternations of relatively quiet, deeper-water carbonates and shale with shallower-water, higher-energy carbonates. The Qatar-South Fars Arch acted as a contemporary positive area off which all units thicken to the east, while a restricted graben existed in the offshore U.A.E., continuing to the onshore and providing more localized deeperwater conditions. To the west, close to the margin of the Arabian Shield, the epicontinental sea shallowed, and marginal clastic facies developed. As the dip eastward was shallow, wide expanses of intertidal and supratidal deposits can be recognized. At certain periods, such as close to the end of the Jurassic, thick and extensive diachronous anhydrites, sometimes associated with halite, can be traced in the Arabian Gulf from the western U.A.E. to southern Iraq. Murris (1981) demonstrated that the Jurassic and Cretaceous carbonate sequence can be split into a sequence of

The Geological History and Structural Elements of the Middle East sedimentary cycles over the Arabian Platform, although differences occur on either side of the Qatar-South Fars Arch. While there is some evidence in the Arabian Gulf for reactivation of roughly north-south basement trends, the most profound changes developed during the Late Cretaceous in the Zagros and Oman, as a result of continued subduction of the Arabian Plate, and culminating in the emplacement of the ophiolites and nappes. The distribution and obduction/emplacement age of the Tethyan ophiolites is shown in Fig. 2.13 and Table 2.8. The associated sedimentary changes show in the development of radiolarites and flysch in the Oman and Zagros mountains (Fig. 2.13), while late Turonian/Santonian sediments were eroded over the bulge that developed in the craton in advance of the subduction front as a result of loading the continental margin. In central Syria and northwestern Iraq, Late Cretaceous subsidence is related to tensional slabpull forces, as the promontory approached the north-dipping subduction zone beneath the Bitlis-Poturge fragments, as suggested by Lovelock (1984). Thus, in the broadest sense, important though the earlier Jurassic and Cretaceous events were, their effects on sedimentation, as seen on the Arabian Platform, were relatively minor until the late Cenomanian or early Turonian, when major changes in the tectonic and depositional regimes associated with the collision and partial subduction of the eastern Arabian Plate margin with a spreading ridge in Oman began. This structural event appears to coincide with a major break in the sea-level curve of Haq et al. (1987) and correlates with the Late Cretaceous global, eustatic, sea-level rise. In eastern Arabia, there was a change from a shallow, stable platform environment to an open-marine, deep-water trough in which turbidites and flysch accumulated. The sedimentary pattern on the platform during most of this time is a reflection of fluctuating sea level. The alignment of many of the oil fields and sub-

ARABIAN

7 ""~~'~se,

S 9

J

i ~0 Sea

Major fault zones

Fig. 2.13. Distribution of Tethyan ophiolites in the Middle East. Data on numbered occurrences are given in Table 2.8 (after Lippard et al., 1986).

surface structures, however, may be explained by basement control. However, it should be remembered that if the general north-south field alignment is assigned to basement control, so, too, is the development of the central Arabian Graben System. Phase 6: The Cenozoic Events

Neotethys closed during the Cenozoic with the collision of the Afro-Arabian Plate with the Eurasian Plate, as the continued subduction of the Afro-Arabian Plate brought the two continental units into contact. The first clear indication of this was the obduction of the Late Cretaceous ophiolite bodies (80-90 Ma) onto the Arabia Plate in Oman, Iran (Kermanshah of Neyriz) and Turkey (Alavi, 1994) (Fig. 2.14A-C). The principal zones of the Zagros part of the Zagros-Taurus Fold Belt are shown on Fig. 2.14E, with an outline of the stages in closure in Fig 2.14D. Although the limit of the Zagros traditionally is set at the Sanandaj-Sinjar Zone, the Arabian continental crust continues beneath that zone, as the Arabian crust descends below the magmatic, ensialic arc, the Urumieh-Dokhtar magmatic assemblage. The southwestern limit of the Sanandaj-Sirjan Zone does not coincide with the Main Zagros Thrust, but lies some kilometers to the west. The Sanandaj-Sirjan consists of numerous overlapping nappes, which have transported various rock sequences southwestwards from the suture zone (Fig. 2.14A-D). These rock units consist of epicontinental, passive continental and shelf facies rocks, which differ only from the lithologies of the units in the Simple Fold Belt in that the Middle Triassic to Lower Jurassic beds show a dramatic change from marine carbonates to non-marine shale and graywacke. A few of the Sanandaj thrust sheets contain pyroclastic and volcaniclastic rocks and minor andesites from forearc sediments formed on the nowdestroyed margin of the Iranian Plate. There are several generations of imbricated sheets and both small and largescale duplexes. The same continuing convergence and associated orogenic events in the Taurus Mountains region of Anatolia (Southeast Turkey) have been documented by Yilmaz (1990), as the ocean that formerly existed along the northern margin of the Arabian Plate was progressively eliminated. During that process, convergence initially led to the collision of an island arc and continent (the Yuksekova Complex and Taurides) at the end of the Early Eocene. This deformed package during the late Middle Eocene to Late Eocene collided with the Arabian Platform. The allochthon, as a package, was then thrust over the autochthon at a later stage in the orogeny in the late Early Miocene. Subsequent post-collisional convergence in post-Middle Miocene time was accommodated along eastwest strike-slip faults reactivating earlier thrusts and by their dissection by high-angle faults. The final phase in the Zagros of Iran involved epeiro-

39

Sedimentary Basins and Petroleum Geology of the Middle East A- PRE-OBDUCHON (EARLY CRETACEOUS) Sedlm~.ntary cover 1\

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Fig. 2.14A-E Tectonics of the Zagros Orogenic Belt of Iran (after Alavi, 1994). A-C=schematic cross sections illustrating pre-obductional and obductional initial collision steps in the Zagros Collision Zone; D=schematic cross-sectional view of the Zagros Orogen, where syn-collisional thrusts have complicated the picture; E=location and simplified Zagros subdivision. 40

The Geological History and Structural Elements of the Middle East genic uplift of the southern and central parts of the folded mountain belt, with the development of gravity-slump features west of the mountain belt in the present-day foreland. Thus, in the Arabian Gulf area, the orogenic events are most apparent and led to the development of structures later tapped for hydrocarbons. The result of these compressional events in the Arabian Gulf Basin was to restrict the basin and shift the trough axis toward the southwest. In recent years, the assumption that the cover sequence of the Simple Fold Belt was detached from basement along a surface formed by the Hormuz evaporites or, to some extent, over the younger Phanerozoic evaporites has been called into question by a re-evaluation of the role of basement tectonics (Ameen, 1991a, b, 1992; McQuillan, 1991). While not questioning the decollement over the Hormuz evaporites in southwestern Zagros in northeastern Iraq, where evidence of diapiric structures is lacking, their extension is not known, and basement block faulting is regarded as a critical factor in the development of the fold belt (Ameen, 1992). Here, a distinction can be made between the northern area (Iraq, Turkey), where basement reactivation is important, and the southern Zagros, where salt decollement plays the larger role. Along the Taurus-Zagros range, Ameen (1992) defines a number of blocks separated from one another by NE-SW lines, which, in the case of the Mosul and Kirkuk blocks, is a fault zone along the line of the Greater Zab River (Fig. 2.15a, b). Each block is divided into a number of zones parallel to the trend of the mountains, but which show changes from block to block. The separation of the two blocks has been determined from the shape and values of the contour lines, surface structural trends, major lineaments recognized on Landsat images and gravity anomalies (Ameen, 1992, Figs. 2 a, b and 3). The boundaries of the blocks were regarded as the surface expression of faults or fault zones in the basement. Expanding this idea, Ameen (1991a) introduced the idea of geowarping for open or gentle composite flexures or folds composed of lesser folds. The geowarps find geomorphological expression and tend to be more intense in the high mountains than in the foothills regions. They are related to the orogenic, crustal movements that led to greater lateral shortening and crustal thickening in the zones closer to the suture between colliding plates and are contemporaneous with the fold belt itself. The relative geowarps provide the conditions favorable to the development of forced folds or buckle folds, which require coherent contact between a thin (less than 10 km), sedimentary cover and a low-temperature, low-pressure environment. Although in southwestern Iran, emergent salt plugs exhibit alignment patterns, McQuillan (1991) shows that the alignment is not that of the Zagros Fold Belt, but considers it to be controlled by basement lineaments, which manifest older, more north-south trends. Thus, recent findings relating to investigations of hydrocarbon accumulations have served to emphasize the importance of basement structure, whether by directly influencing Ceno-

zoic sedimentation, as in northeastern Iraq, or indirectly, as in the northern Arabian Gulf. A further result of the Neogene compression in the northern part of the Middle East was the inversion of the Syrian and northwest Iraqi Palmyra and Sinjar depressions (Fig. 2.16), with the formation in the north of broad, open anticlines that become tighter southward, developing into typical ramp anticlines overturned to the south (Lovelock, 1984). Erosion has cut deeper into the anticlines in the south than in the north, exposing Tliassic rocks, in contrast to the north, where only Cretaceous horizons are exposed. In depth, detachment occurs in these folds at the level of the Triassic and Jurassic evaporites. Associated with these structures in central Syria is a major NE-SW-trending fault zone with the Abba and A1 Furat faults at the northeastern end of the zone (Fig. 2.16) (Lovelock, 1984). The Abba Fault appears to form the western end of the Sinjar Trough, continuing southward to terminate along its southern margin. The A1 Furat Fault appears to be a flower structure associated with the strike- slip zone. The Euphrates Graben (Fig. 2.16) is offset by the east-west-trending Anah Graben. Both of these grabens, which began to subside during the Late Cretaceous, were inverted during the Miocene. The Abu Jir Fault Zone, which can be traced 600 km running parallel to the main Zagros Thrust, extends southeastward from the Euphrates Graben into southern Iraq (Fig. 2.16). In the southwestern and western parts of the Middle East, sandwiched between the two main phases of orogenic activity during the Paleocene-Eocene and the late Miocene-Pliocene, and in part contemporaneous with them, is the evidence of extension most apparent in the Gulf of Aden and the Red Sea, particularly during the Paleogene (Burek, 1969, 1970). The first indications of significant movement in the Gulf of Aden-Red Sea-Arabian Sea area is of Late Cretaceous uplift (Table 2.9). The doming of the Arabo-Nubian Shield, which was followed by rifting in the Gulf of Aden and the Red Sea, culminated near the close of the Eocene (Lowell and Genik, 1972; Peterson and Wilson, 1986). Reactivation of the Hadhramout Arch is dated as beginning in the early Paleocene, with the arch, and the Rub al Khali Depression north of it, reaching their present form by the end of the Eocene. Separation of Arabia from Somalia as a result of rifting of what had been a local depression (Beydoun, 1966; Azzarolli, 1968; Closs, 1939) began in the late Eocene, accompanied by widespread volcanism in the Gulf of Aden. Vertical faulting and uplift of the rift walls by as much as several thousand meters occurred and is recorded on both sides of the rift. This activity continued through the Oligocene, and by the early Miocene, the Red Sea margins had attained essentially their present form. Baker (1970), however, concluded that the main phase of development occurred during the early Miocene with the deposition of early Miocene marine sediments in the proto-gulf, followed in the late Miocene and Pliocene by phases of faulting and seaward warping of Neogene sedi-

41

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 2.15a, b. The regional basement tectonic pattem of northem Iraq showing the borders of the Mosul and Kirkuk blocks and the longitudinal and transverse faults that break the blocks into smaller sub-blocks (lines 1-8). Notice that other longitudinal and transverse faults apart from those shown on the map do occur. (after Ameen, 1992, and reproduced by kind permission of AAPG)

42

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Sedimentary Basins and Petroleum Geology of the Middle East ments. The currently active zone of rifting passes through the Gulf of Tadjura into the Afar. This Gulf of Aden Rift and transform spreading links with the 2,000 km Owen Fracture Zone, which is aligned approximately parallel to the continental margin of the Indian Ocean (Beydoun, 1982). McElhinny (1970) concluded from his interpretation of paleomagnetic data that during the early Tertiary, the fracture zone was a sinistral transform fault separating Arabia-Somalia from India, and Whitmarsh (1979) described the northern part of the transform zone as a relict of earlier sea-floor spreading before the opening of the Gulf of Aden. There are two possible models of Late Cretaceous-Early Tertiary sea-floor spreading involving the Owen Fracture Zone (Whitmarsh, 1972). One, a threeplate model, gives the best fit of the paleomagnetic data from Africa, Madagascar and India, and involves the separation of Madagascar and India near the end of the Cretaceous. The second model, which shows a migration

northward of the spreading ridge with respect to Africa, requires India and the anomalies north of the ridge to spread at twice the speed of the ridge. MAIN STRUCTURAL ELEMENTS As a consequence of the geological history outlined in the preceding section, a number of structural elements may be defined. The following short descriptions of these structural elements outline their geographic location and principal features (Fig. 2.17). It should be recalled that the average crustal thickness in northern Arabia and Iran is about 45 km, and in Turkey (the Anatolian Plate) and the Zagros is about 50 km. The greater thicknesses of the latter two probably is due to the convergence of the African and Eurasian plates (Shaheen, 1977). Shaheen (1977) suggested that the similarity of the crustal structure of northern Arabia (Jordan, lraq and

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Fig. 2.17. Major tectonic elements in the Middle East showing Arabian, Zagros and Oman sedimentary basins and major sub-basins, paleohighs, trends and faults (compiled from A1Laboun, 1986; Murris, 1981; Brown, 1972; Powers, 1968; Beydoun, 1988).

44

The Geological History and Structural Elements of the Middle East

Table 2.9. Time constraints and nature of crust in the evolution of the Red Sea, Gulf of Aden and Afar depressions (compiled from Behre, 1986). Area

Age of Initiation of Rifting

Initiation of Seafloor Spreading

Nature of Crust

Gulf of Suez

a. Pre-Carboniferous b. after late Eocene (37-40 Ma)

No development of spreading axis

a. underlain by continental crust

Gulf of Aqaba

a, early Miocene b. post-early Miocene

No development of spreading axis

continental crust

Red Sea

a. Late Cretaceous b. late Oligocene (30 Ma) c. late Oligocene (22.5 Ma)

Late Miocene (9 Ma)

In the nonhern part of the Red Sea: a. subsided continental crust with dykes b. subsided and attenuated continental crust c. oceanic crust consisting of basalts interlayered evaporites. In the central part of the Red Sea: a. oceanic crust from coast to coast b. limited oceanic crust

Gulf of Aden

a. early Mesozoic b. early Oligocene (30 Ma)

a. Early Oligocene (30 Ma) b. Late Oligocene (23.5 Ma) c. Late Miocene (10 Ma)

a. oceanic crust from coast to coast b. limited oceanic crust c. attenuation of continental crust below the coastal plain

Afar

a. Mesozoic b. Middle-Late Eocene (41-34 Ma) c. Late Oligocene (ca. 25 Ma) d. Middle Miocene (14 Ma)

Development of axial volcanic range 1 -2 Ma

Continental to transitional crust, except in the Erta Ala spreading axis.

Syria) and the Arabian Peninsula resulted from their being part of one plate during most of their geological history. He concluded that there was evidence for a plate boundary between northern Arabia-Iran to the south and Turkey to the north because of the differences in depth to the mantle low-velocity channel and crustal thickness. This conclusion is fully consistent with the stratigraphic history. Morphologically, the main structural features of the Middle East are the Alpine Mountain System, which stretches through Turkey and northeastern Iraq, and through the Zagros Mountains of Iran to the Oman Mountains; the mountainous loop that passes through the Lesser Caucasus and the Alborz of northern Iran, encompassing the central Iran Block; and the Arabian Shield and Platform, with its relatively undisturbed Phanerozoic sedimentary cover. The Levant Platform to the west forms the northwestern margin of the Arabian Block, from which it is separated by the prominent Jordan-Dead Sea (left lateral transcurrent) Fault System with its associated broad

uplifts. The Red Sea Rift Valley, a large, fault-bounded depression that breaks the crest of the Afro-Arabian Shield, a positive element since early Paleozoic time, is linked to the Jordan-Dead Sea Shear System. The region was affected by three major orogenies: the Late Proterozoic-early Phanerozoic Pan-African event, which ended with the consolidation of Gondwana; and the two major Paleozoic orogenies, the Caledonian and the Hercynian, which sutured together Pangea, but had remarkably little effect in the cratonic areas. These Paleozoic orogenies were primarily responsible for upwarping and the absence of the Silurian and Devonian, which is attributed to these movements in some parts of Arabia, Iran, Iraq and Turkey. Interspersed with the compressional events were periods of extension during the early Paleozoic, Cambrian to Silurian, the late Paleozoic, Early Devonian-Carboniferous and again during the Permian. The first and the last were unaccompanied by any volcanic activity, whereas the second was accompanied by basalt

45

Sedimentary Basins and Petroleum Geology of the Middle East magmatism in Iran (Berberian and King, 1981). The principal effects seem to have been the reactivation of basement faults (Berberian and King, 1981). During the Mesozoic-Cenozoic, the disruption of Pangea that resulted from further tensional events brackets two compressional events. The earlier, Cimmerian event (Sengrr and Yilmaz, 1981) began during the Middle to Late Triassic and ended during the Early Jurassic and the later, Cretaceous-Cenozoic Alpine orogenic event. While the effects of the later event are very obvious, the earlier event, related to the disruption of Pangea, is only just being recognized in the Middle East. The first Mesozoic compressional event marked the closure of Paleotethys as a sliver of the Gondwana margin as either a single unit or as a series of small plates (Anatolia, central Iran, Afghanistan, central Tibet) closed against Eurasia. Opening up in its/their wake lay the Neotethys south of the rifted-off fragments of Gondwana and north of the remainder of the Arabian (Gondwana) Plate in the Arabian area. Neotethys does not seem to have formed more than a Red Sea-type oceanic basin; however, it did permit the continued development of the Arabian Platform as a passive margin (Glennie et al., 1974). Later, the basin finally closed because of subduction during the late Mesozoic along the line of the Zagros Mountains. Currently, the northeasterly drift of Arabia away from Africa driven by the active spreading in the Gulf of Aden and the Red Sea is being accommodated in the Gulf of Oman with subduction along a north-dipping subduction plane under the Makran. A result is the deformation of the sedimentary prism in offshore Oman, which may account for the vertical tectonics seen in the Oman

Mountains (Gorin et al., 1982; White and Ross, 1979). Associated with the Cenozoic tensional movements responsible for the Red Sea opening is the reactivation of grabens, particularly in the northern part of the Arabian Plate. This brief comment on the general structural history of the region stresses the necessity to define some of the principal basins and structural elements, arches, faults and folds that may have been active on one or more occasions and to which constant reference will be made during succeeding chapters. With limited data available, many of these elements cannot be described in detail. Sedimentary

In this study, the Middle East is divided into three major sedimentary basins (Fig. 2.17): the Greater Arabian Basin, the Zagros Basin and the Oman Basin. Each basin is further divided into sub-basins, and each of these has its own style and time of origin reflected by differences in thickness and lithology. The megatectonic framework of the Middle East (Fig. 2.17) shows that the area is dominated by the many sub-basins, broad regional highs, anticlines and flexures reflecting deep-seated basement faults and salt diapirisms. From the early Mesozoic onwards, the pattern of sedimentation in the Middle East was influenced by periods of increased activity alternating with quiet intervals. During the late Turonian to the early Campanian, a major change in basin configuration took place, heralding the first phase of Alpine compressive tectonics (Murris, 1981). During the Late Cretaceous orogenic period in Syria, northwest-

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Fig. 2.18. Generalized lithostratigraphic cross section of the Widyan and Tabuk sub-basins in northern Arabia (modified from A1 Laboun, 1986, and reproduced by kind permission of AAPG). 46

The Geological History and Structural Elements of the Middle East ous and Permian sediments (Fig. 2.18). The northern part of the basin is covered by Late Cretaceous and Eocene sediments that have a shallow, northeasterly dip (2.5 m per km; Powers et al., 1966). The deep structure is less wellknown. Sirhan Sub-basin. The sub-basin, which is located in central Jordan and trends NW-SE (Fig. 2.17), developed during the Cretaceous. Subsidence began during the Cenomanian and continued through the Senonian in the northwest. Sedimentation prograded toward the southeastern part of the basin, as indicated by the thickness and sediment facies, with the major subsidence occurring during the Late Cretaceous transgression. The initiation of rifting in the basin coincided with doming and resulted in the Late Jurassic to Early Cretaceous regression (Abu Jaber et al., 1989). In the northwestern part of the sub-basin, the Early Cretaceous sediments are dominated by about 400 m (1,312 ft) of sandstone, with subordinate limestone and shale deposited in an open-marine environment of unrestricted marine circulation (Abu Jaber et al., 1989). This is followed by about 900 m (2,952 ft) of limestone, dolostone and marl of Cenomanian-Turonian age. During the Senonian, compression began to dominate the tectonic setring along the Mediterranean margin (Eyal and Reches, 1983; Abu Jaber et al., 1989). Large areas of the Levant were dominated by chert, bituminous limestone and some phosphorite. Sedimentation in the Early Cretaceous in the southeastern part of the basin was relatively slow. About 700 m (2,296 ft) of sandstone, dolostone and evaporites were deposited during the Cenomanian-Turonian; during the Senonian, about 950 m (3,116 ft) of sandstone, dolostone and coarse clastic sediments accumulated; during the Paleocene-middle Eocene, about 700 m (2,296 ft) of sedi-

ern Iraq and Southeast Turkey, dextral and sinistral strikeslip faults, fault zones and grabens were formed. The grabens were filled by a thick sequence of Sediments, which were inverted during the late Tertiary compressive phase, giving rise to en-echelon fold belts. Tabuk Sub-basin. The Tabuk Sub-basin lies in northwestern Saudi Arabia, west of the Ha'il-Rutbah Arch, with an axis trending and gently plunging in a north-northeasterly direction. Cambro-Ordovician rocks, principally arenaceous, are exposed on the western and southwestern flanks of the sub-basin. On the eastern margin, it is delimited by the Ha'il-Rutbah Arch (A1 Laboun, 1987). Of particular interest in a series that extends from the Cambrian to Devonian is the existence of a faulted graben structure on the western side that contains a rare, marine carbonate sequence (Fig. 2.18). It has a relatively simple structure cut by high-angle, steeply dipping, northwest-trending, normal faults that may reflect deep-seated basement faults. Widyan Sub-basin. This basin lies on the eastern side of the Ha'il-Rutbah Arch in northern Saudi Arabia; during the early Paleozoic, it contained a sedimentary sequence continuous with that in the Tabuk Basin to the west (Fig. 2.18). A general easterly tilt, however, means that the section is more continuous, the Devonian beds are much better developed than in the Tabuk Basin, and it contains Carboniferous beds absent in the latter (A1 Laboun, 1987). The basin also shows a narrow extension southward between the Arabian Shield and the Summan Platform, with a thick early Paleozoic section. In the western part of the basin, deep-seated faulting affects the Cretaceous rocks; on the eastern flank, a segment of the central Arabian Graben and Trough System has vertical displacements of several hundred feet. Following Hercynian warping, the"basin continued to receive Late Carbonifer-

NORTHERN

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Fig. 2.19. Generalized lithostratigraphic cross section in the Ras A1 Khaimah-Northern Rub al Khali sub-basins of Arabia (compiled with modification from Schlumberger, 1981" and reproduced by kind permission of Schlumberger) 47

Sedimentary Basins and Petroleum Geology of the Middle East ments were deposited (Anon., 1986; Abu Jaber et al., 1989). Rub

al

Khali

and

Ras

al

Khaimah

sub-basins.

These sub-basins trend and plunge to the northeast, and although they are thought to be part of the same basin, they commonly are treated as independent basins. Throughout their length, the basins maintain a uniform width of approximately 300 km. The combined basins extend from the Hadhramout High in the south to the Strait of Hormuz and onshore coastal part of southeastern Iran. They contain prolific oil and gas accumulations within a thick Phanerozoic sequence. In the northeast, the Ras al Khaimah Trough apparently extends offshore into the Arabian Gulf almost as far as the coast of Iran (Fig. 2.19) (Alsharhan and Nairn, 1995; Alsharhan, 1989). It is regarded primarily as a Tertiary feature, but has some history of Cretaceous activity. As it is adjacent to foreland areas characterized by different structural styles created after the Triassic, its antiquity may be considerably greater. Tensional block-faulted structures related to crustal extension developed during the Late mid-Cretaceous; asymmetrical anticlines on the hanging walls of thrusts and simple detached anticlines all suggest a more complex history. It has a thick Tertiary section that accumulated in a deep sedimentary trough (foreland basin) in front of the intensely folded Oman Mountains. The Rub al Khali Basin is bounded by the central Arabian Arch in the north, the Arabian Shield in the west, a basement high along the northern coast of the Gulf of Aden in the south, and the Oman Mountains in the east. It formed during and after the uplift of the central Arabian Arch and basically is a Cenozoic depression succeeding a much bigger Mesozoic (and possibly Paleozoic) basin. Based on subsurface information, the Phanerozoic section is very thick, with intervals of erosion and/or non-deposition or unconformities. It is dominated by large, gentle folds of various shapes and sizes related to differential regional subsidence or uplift along basement faults. Salt domes and plugs are irregularly distributed and occur as narrow, emergent plugs or deeply buried, non-emergent pillows. The remoteness and the consequent lack of data make the origin of the basin extremely uncertain, and the possibility that it may be a basin comparable with the Widyan and Tabuk, and equally old, remains only a suggestion with limited support. Zagros Basin, Iran. The late Cenozoic Zagros Basin is a foreland basin that developed on the Arabian Plate as it attempted to subduct beneath Iran (Fig. 2.20). The axis of the basin lies considerably east of the Arabian Gulf. James and Wynd (1965) and Cherven (1986) believed that the thickness pattern indicated that some of the formations are thicker than the same formations penetrated by wells near the Arabian Gulf, with the implication that the eastern part of the Zagros Basin has been cannibalized as the fold belt migrated westward. The basin is located west of the Zagros Crush Zone. Near this zone, the area is intensely folded and faulted, but

48

the intensity of folding gradually decreases away from this area towards the Arabian Gulf. The late Alpine Orogeny was the strongest tectonic movement that occurred, and it produced a series of northwest-southeast parallel structures. Throughout geologic history, the area has been predominantly the site of continuous deposition, although erosion and/or non-deposition and disconformity occur at B AGE

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The Geological History and Structural Elements of the Middle East (Sachun-Jahrum) and basinal marl and marly limestone (Pabdeh Formation). The Oligo-Miocene Asmari and Gachsaran formations consist of shallow-water, neritic limestone (Fig. 2.20). Many authors, among whom may be listed Cherven (1986), Dickinson (1974) and Stoneley (1974), suggest that the change from the shallow-water Asmari Limestone

a few stratigraphic levels (Fig. 2.20), followed by the regressive carbonate-clastic sequence of the Plio-Pleistocene. There is a regional unconformity at the base of the Permo-Carboniferous, and unconformities occur at the top of the Triassic, Jurassic, post-Cenomanian and post-Turonian. The principal Cenozoic sediments consist of Paleocene-Eocene shallow-water limestone and dolomites ,,

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49

Sedimentary Basins and Petroleum Geology of the Middle East to the very shallow, lagoonal-supratidal, evaporitic sequence (Gachsaran Formation) represents a classic sealreservoir sequence and records the restriction and drying up of a basin emerging as a result of the isostatic uplift as the Arabian Plate resisted further subduction. The timing is consistent with the opening of the Red Sea and the intense deformation along the Zagros Crush Zone. Palmyra and Sinjar sub-basins. These two Syrian sub-basins originally were parts of a single aulacogen opening to the Levantine continental margin to the west and extending towards the Tethyan continental margin in the east. The relationship between the two is illustrated in Fig. 2.21. However, the NE-SW trend of the Palmyrides suggests that it follows a basement structural line, and one hypothetical interpretation from McBride et al. (1990) is figured (Fig. 2.22). The age at which the intracratonic aulacogen began to subside between the Aleppo High to the northwest and the Rutbah High to the southeast cannot be defined clearly in the absence of faunal control; it may have begun as early as the latest Carboniferous (Fig. 2.22). Subsidence was rapid, however, and the basal clastic wedge gave way to marine carbonates and clastics. By the early Middle Triassic, sedimentation had spread into the Sinjar Basin. Continuity of sedimentation was broken by a period of uplift and erosion between the late Jurassic and early Cretaceous (Aptian-Albian). It ended in the Paleogene, with inversion beginning in the early Miocene and intensifying during the late Miocene and Pliocene with uplift, folding and faulting in response to stresses transmitted from the plate margins (Chaimov et al., 1992). Neogene sediments are restricted to isolated continental basins (e.g., A1 Daww Depression). The Euphrates-Anah Graben (Fig. 2.17) formed in conjunction with the Palmyra during the late Permian to late Triassic and separate the two sub-basins (south Pahnyra and Sinjar) during the Cretaceous. In the Euphrates Graben, the early period of rifting is late Cretaceous in age, followed by a quiescent period during much of the Paleogene. Gentle compression and inversion took place during the Miocene, producing younger flexures over the deep-seated graben structure (Lovelock, 1984). It also resulted in renewed strike-slip movement on the master fault, the A1 Furat Fault, which controls the course of the Euphrates. The Anah Graben continues eastwards towards the Euphrates Graben at an angle of 60 ~ at the Syria-Iraq border. It formed during the Late Cretaceous as a faultcontrolled trough that also was inverted during the Miocene (Lovelock, 1984). It is marked by the long, broad, gentle arch of the Anah anticline, which brings Oligocene rocks to the surface in few small inliers. The Mesopotamian (central Iraq) Sub-basin. The Mesopotamian Sub-basin (sometimes known as the central Iraq Sub-basin; see Lovelock, 1984) lies between the Abu Jir Zone to the southwest and the Makhul Zone to the northeast (Fig. 2.16). It is formed by depression of the margin of the Arabian Plate, which was overthrust by the Eurasian Plate during the course of the Alpine Orogeny.

50

The sedimentary history was complicated by a series of transgressions, regressions, flysch sedimentation, evaporite sedimentation and even igneous activities. The stratigraphic section from the Cambrian to the present is almost complete. Gravimetric measurements indicate that at its deepest part, the basement has sunk to more than 12,000 m (39,360 ft), and Pliocene sediments up to 3,000 m (9,840 ft) thick have been intersected in drill holes. Breaks are minor, and thickness exceeds thousands of meters of various sediments. Evaporites, including salt, recurred several times from the Cambrian to the Miocene. Salt tectonics may be responsible for some of the local anomalies. Red Sea and Gulf of Aden sub-basins. The basins originated during the late Oligocene-early Miocene, when an episode of diffuse spreading associated with listric faulting and dike intrusion disrupted the continental margin (Cochran, 1981). Magnetic anomaly data, however, indicate that oceanic crust formed in the Gulf of Aden at 10 Ma; but, because the Red Sea oceanic crust is found only in the southern part of the basin, the northern part remains in the process of rifting. Based on kinematic data and plate tectonic theory, however, the Gulf of Aden and the Red Sea are thought to be entirely floored, coast to coast, by newly formed oceanic crust, with the plates on either side remaining perfectly rigid (McKenzie et al., 1970). Tectonic activity in both regions may have begun in the Jurassic or Cretaceous, with separation dating after a phase of Oligocene-Miocene uplift and early middle or late Miocene faulting (Whiteman, 1965; Azzarolli, 1968; Beydoun, 1970; Le Pichon and Francheteau, 1978). Many authors interpreted the Gulf of Aden to be the result of horst and graben tectonics that developed from the fracturing of an updomed Arabian-Nubian Shield and the rifting apart of Arabia and Somaliland (Beydoun, 1986; Closs, 1943; Azzarolli, 1968). The development of the gulf began with late Eocene regional uplift of the margins and the formation of a local depression (Azzarolli, 1968); however, according to Baker (1970), the main phase of development was in the early Miocene, when marine sedirnents were deposited in the proto-gulf, followed by late Miocene and Pliocene faulting with the seaward tilting of the Neogene sediments. The fracture trends in the center of, parallel to and oblique to the gulf may be the result of the collapse of the edges of the plateau uplift and the gradual separation of the two sides of the gulf, accentuating gravitational fracturing along east-northeast and east-west lines (Beydoun, 1982). The Red Sea appears as a large, fault-bounded depression in the crest of the Arabian-Nubian Shield, a shield that had been a positive element since the early Paleozoic (Mulder et al., 1975). The stratigraphic sequence, which has been affected by normal faulting and Miocene salt diapirism, ranges in age from Paleozoic to Quaternary. The thick Miocene succession may reach as much as 3-4 km (1.9-2.5 mi) near the outer margins and in the southern part of the Red Sea, where halokinesis is most intense.

The Geological History and Structural Elements of the Middle East NW

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51

Sedimentary Basins and Petroleum Geology of the Middle East Subsidence in the graben began in the Oligocene-early Miocene, with initial terrestrial deposits followed by evaporites that persisted through much of the Miocene. Late Miocene-Pliocene tectonic activity finally severed the link with the Mediterranean, but an open link with the Indian Ocean was established during the Pliocene. Through the use of geochronological data, correlation of the shield rock across the Red Sea has been established (Fleck et al., 1976).

resulting in the development of a thick sequence of Cretaceous and Tertiary sediments (Gorin et al., 1982). The western flank dips gently westward into the South OmanGhaba salt basins (Tschopp, 1967a, b; Gorin et al., 1982), whose trend may be related to the uplift of the axis of the arch. Hadhramout Arch. In contrast to the Huqf-Haushi Arch, this is a young structure (Fig. 2.17) that began to develop in southern Arabia during the Paleocene and whose present form was attained by the end of the Eocene. The main arch is divided into two by a gentle syncline. The arch is approximately perpendicular to the HuqfHaushi Arch, and it forms the principal highlands of southeastern Yemen. In the early Eocene, thickness variations reflected the development of the arch, until in the late Eocene, when anticlinal warping led to the emergence of the arch. The linear continuity of the structure seems to preclude local effects, and it may reflect deep-seated reactivated fractures. Central Arabian Arch. Although a relatively gentle feature, the central Arabian Arch has a profound effect on the present surface distribution of sedimentary rocks in western Arabia. The arch trends in an east-northeasterly direction across the central part of the Arabian Platform, from the easternmost point of the Arabian Shield to possibly as far

Arches

Several major arches dominate the structural pattern of the Middle East; however, because of a lack of deep wells, their history of activity, particularly their period of activity, is seldom well-known. l-luqf-l-laushi Arch. This NE-SW-trending high is a broad, faulted anticlinal structure, located in eastern Oman (Fig. 2.23), which behaved as a structural high throughout most of the Phanerozoic. It runs approximately parallel to the continental margin of Oman. It was initiated during the Cambrian as a result of block faulting and tilting. As a result of subsequent epeirogenic movements, younger sediments progressively onlap the flanks of the arch (Ries et al., 1990). The eastern flank is fault-controlled, with NNE-trending tensional faults thrown down to the east,

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Fig. 2.23. Major structural elements in southeastern Arabia (Oman Basin) (compiled with modification from Gorin et al., 1982; Murris, 1981).

The Geological History and Structural Elements of the Middle East as Qatar (Fig. 2.17). It separates the northeast-dipping, central segment of the stable shelf from the southern, eastdipping segment and has a complex geological history (A1 Kadhi and Hancock, 1980). Powers et al. (1966) argue that the arch, in its present form, could be a residual high caused by sagging of the regions on either side, and point towards the fault and graben system just north of the arch as evidence for a tensional regime. It controls the curvature of the Interior Homocline and the dip of the beds on the shelf that dips northward or southward from it. The south-dipping beds pass uniformly under the Rub al Khali Basin (Powers et al., 1966). The arch was mildly positive during the early Paleozoic, as the pre-Permian sediments seem to pinch out against it. Strong upwarping occurred during post-Early Devonian and pre-Late Permian times, and older sediments were peneplaned and stripped from the crest of the arch. Later submergence permitted the deposition of the Late Permian carbonates directly upon the basement across the axis and for some distance to the north and south. The central part of the craton gradually subsided during the Mesozoic, resulting in a fairly uniform depositional sequence, the thickest part of which appears to coincide with the present axis of the arch. Only in the mid-Cretaceous are the first traces in the sedimentary record found that indicate that renewed movement of the arch was continued into the Late Cretaceous with the same pattern of sedimentation. Subsidence of the northern part of the arch increased its apparent relief. Movement, however, decreased during the Paleocene and Eocene. Qatar-South Fars Arch. The arch is a positive NNE- to S-SW-trending structure (Fig. 2.17), which became established in the late Paleozoic and divided the Arabian Gulf Basin into two sub-basins. It is a Hercynian structure and has subsequently influenced later sedimentation, for all units thicken away from the high. Southeast of the arch toward the U.A.E., in both onshore and offshore, there is a small basement graben anomaly that formed a localized deep-water, sedimentary basin with Late Jurassic deposition, even as the rest of the region showed signs of progressive shallowing. It may be noted that the onset of Late Jurassic evaporite formation was diachronous. First seen during the Late Jurassic (Kimmeridgian) of southern Iraq, anhydrite deposition moved southward down the trough from Saudi Arabia to the western U.A.E., where extensive evaporites were deposited in a sabkha-like environment during the late Tithonian. l-Ia'il-Rutbah-Ga'ara and Khleissia arches. The longest arch in the Middle East extends from northern Arabia into northern Iraq (Fig. 2.17) and is covered by 4-6 km of Paleozoic clastic sediments (Lovelock, 1984), which were domed during the late Tertiary and eroded. exposing 900 m (2,880 ft) of Permian continental sediments flanking the Ga'ara Depression. The Khleissia High in Iraq, which is the northernmost of this sequence of highs, is marked by its reduced sedimentary thicknesses of less than 1,200 m (3,936 ft) of Mesozoic sediments overlying about 2,600 m (8,528 ft) of Paleozoic resting on the

basement (Bruderer, 1960). The Khleissia was uplifted and peneplaned during the Late Jurassic, remaining above sea level until Aptian-Albian time as an integral part of the Rutbah High, until it was separated by the development of the Anah Trough during the Campanian-Maastrichtian. The Rutbah-Ga'ara-Khleissia highs are marked by prominent positive gravity anomalies indicating the presence of basement at relatively shallow depths. Seismic evidence in northeastern Jordan indicates that the Rutbah Ga'ara Arch is a post-Paleozoic feature that persisted from the Early Cretaceous through the Turonian as the sediment accumulation increased during the Senonian, and from the Paleocene to middle Eocene (Anon., 1986; Abu Jaber et al., 1989). The Ha'il-Rutbah Arch in northwestern Saudi Arabia formed the abutment for the Palmyra Basin during the inversion of the basin in Neozoic time. The southern part of this arch is known in Saudi Arabia as the Ha'il Arch and is located in northwestern Saudi Arabia. It was gently folded along a north to south axis in the Late Cretaceous (Greenwood, 1973); during Late Cretaceous tectonism, three northwest-trending grabens, the Azraq-Sirhan, Turayf and Khor Umm Wail ,were formed (Ahnond, 1986). Of these, the Azraq-Sirhan became an active depositional area during the Cenomanian, continuing until the end of the Cretaceous (Basha, 1982). The time of its formation is the same as that of the east-west-trending central Arabian Graben near Riyadh (Hancock et al., 1981). The Ha'il Arch has a complex history; the lower Paleozoic sediments were deposited across the present axis without a change in thickness or facies. The Upper Cretaceous rocks in northern Saudi Arabia show a change from carbonates on the eastern flank to continental clastics on the crest, proving emergence. The parallel trends of the Cenozoic volcanic belt of the Arabian Shield and the Ha'il Arch led Greenwood (1973) to propose a mantle uplift of deepseated origin for both phenomena. Mardin High, Turkey. The Mardin High is known to have been an important tectonic unit in southeastern Anatolia since the Paleozoic, and Bozdogan and Erten (1990) concluded that sedimentation was uniform in the area until the end of the Cambrian. Sedimentological and stratigraphic gaps and paleogeographic differences can be observed during Ordovician deposition, illustrating tectonic control of post-Cambrian deposition. Early Ordovician deposits overlie the Cambrian deposits with an angular disconformity over the flanks of the high, whereas Late Ordovician deposits overlie the crest of the high, indicating the existence of the Mardin High during the Early Ordovician (Tremadocian). The high continued to control the sedimentation on the platform area until the Cretaceous. The distribution of the Ordovician deposits in southeastern Anatolia indicates that the high extended in a northwest-southeast direction. This high separated two basins in the platform: the Diyarbakir Basin in the east and the Akcakale Basin in the west (Fig. 2.17). In the Akcakale

53

Sedimentary Basins and Petroleum Geology of the Middle East Basin, only the Ordovician and Triassic-Jurassic rocks are preserved; but in the Diyarbakir Basin, the Ordovician, Silurian-Devonian, Permian and Triassic-Jurassic rocks are present. The Hakkari region was separated from the Diyarbakir Basin by another high formed in the Sirt area and active from the Devonian to the end of the Permian. These tectonic elements in southeastern Anatolia seem to be the northern extension of the major tectonic elements of the Arabian Plate. Transform Faults and Normal Faults Southeastern Arabian Platform Masirah Transform Fault. The N-NE-trending Masirah Fault runs parallel and adjacent to the southeastern continental margin of Oman with its sequence of faults (Fig. 2.23) (Murris, 1980; Moseley and Abbots, 1979) and forms the boundary between the continental crust of the Arabian Platform and the oceanic crust of the Owen Basin. Ries et al. (1990) have shown that this is the master fault of a fault zone that can be traced for at least 600 km (375 mi). It shows left lateral displacement. Within the fault zone, there is a pervasive system of both NNE-SSW- and N-S-trending faults, with the age of the last movements demonstrably Cretaceous. Maradi Fault. The fault trends northwest-southeast, parallel to and south of the Oman Mountains, and continues southeastward under the gravel plains of central Oman. It eventually joins the north-south-trending Saiwan-Nafun Fault, which cuts across the Haushi-Huqf area (Fig. 2.23) (Tschopp, 1967a; Gorin et al., 1982). It has a left-lateral slip component (Tschopp, 1967a; Gorin et al., 1982). The Maradi-Nafun Fault, according to Ries et al. (1990), is not a continuous structure; it is more than likely that the Haushi-Nafun Fault is related to the Masirah Transform System, whereas the Maradi Fault is an expression of a basement fracture system related to the Najd Fault System of western Arabia. Saiwan-Nafun Fault. Activated during the Late Cretaceous, this fault had a displacement varying from down to the east in southern Oman to down to the west in central Oman (Fig. 2.23), providing evidence of sinistral rotational movement. It is composed of a sequence of reactivated, en echelon basement fractures, with a combined throw approaching 150 m (492 ft) (Gorin et al., 1982). Dibba Zone. The Dibba Zone is a N-NE- to S-SWtrending lineament in the northeastern U.A.E. (Fig. 2.17) that resulted from the fragmentation and rifting of an eastfacing carbonate platform in the Middle to Late Triassic during the development of a shelf edge (Murris, 1980; Searle et al., 1983; Lippard et al., 1982). The margin collapsed in the mid- and Late Cretaceous and formed the limit of the Oman orogen. There is no evidence of late Mesozoic transform motion, although earlier strike-slip movement may have occurred (Lippard et al., 1982; Searle et al., 1983). The Dibba Fault separates the oceanic crust

54

of the Gulf of Oman-Makran on its eastern side from the continental crust to the west. In all probability, the line acted as an ocean-continent transform fault during the Mesozoic along the boundary between the Arabian Plate and the Tethys Ocean. Oman Line. The line is a long-lived crustal feature of regional importance, probably dating back to the Precambrian, which marks the southeastern end of the Zagros range (Fig. 2.17). It also marks the sudden termination of the post-Paleozoic sequence of the Arabian Gulf and separates two entirely different sedimentary provinces: the carbonate platform to the west and the deep-water flysch and radiolarite facies to the east. Considerable dextral transcurrent motion along the Oman line occurred at the southeastern termination of the Zagros Range. Owen Fracture Zone. The zone is a 2,000 km (1,250 mi) long fracture zone (Fig. 2.17) roughly parallel to the continental margin of southern Arabia (Beydoun, 1982), one which McElhinny (1970) concluded on the basis of paleomagnetic data was a sinistral transform fault during the early Tertiary, separating Arabia-Somalia from India. Whitmarsh (1979) described the northern part of the Owen Fracture Zone as the relict of an earlier seafloor spreading before the opening of the Gulf of Aden, and probably no longer an active fault. Northern Arabian Platform Central Syrian Fault Zone. This major NW-SEtrending fault zone was active during the Tertiary, and possibly also during the Late Cretaceous. The principal faults are the parallel Abba and A1 Furat faults at the northeastern end of the fault zone (Lovelock, 1984). The Abba Fault appears to bound the western end of the Sinjar Trough and continues southward, terminating along the southern margin of the trough. The A1 Furat Fault appears to be a flower structure, typically associated with strike-slip zones. The Anah and Euphrates grabens both began to subside during the Late Cretaceous and were inverted during the Miocene (Lovelock, 1984). The Euphrates Graben, offset by the Anah Graben, continues southeastward as the Abu Jir Fault Zone (Halsey and A1 Sikini, 1983; Lovelock, 1984). These lineaments extend for about 600 km (375 mi) parallel to the main Zagros Thrust from southeastern Turkey to southern Iraq, and they show strike-slip displacement. Northwestern Arabian Platform Jordan-Dead Sea Fault System. This fault system is basically a left-lateral transcurrent (transform) fault, or a sequence of en echelon faults whose movements have opened up a number of rhombochasm (rift) troughs, of which the Dead Sea is the best known (Quennell, 1958; Freund et al., 1970; Garfunkel, 1970). They are associated with the early Miocene extensional movements in the Red Sea. The faults begin at the mouth of the Gulf of Aqaba, a simple rhombochasm, and continue along the Araba Valley (Wadi Araba) as relatively simple strike-slip faults. From

The Geological History and Structural Elements of the Middle East the Gulf of Aqaba, the lateral displacement amounts to 105 km (66 mi), and restoring the displacement matches up the Mesozoic facies on either side of the fault. The projection of the Araba Fault projects into the eastern Dead Sea Fault, and the Jordan Valley Fault lines up with the western rift boundary fault. The Dead Sea rhombochasm between these faults has acquired more than 6,000 m (19,680 ft) of Pliocene and Pleistocene sediments, including the evaporites that now form diapirs. Fold Belts

A fold belt marks the northern and eastern margins of the Middle East. It extends as a continuous belt through Turkey, the northeastern corner of Syria, Iraq and Iran to the mountains of Oman. For geographical reasons and for convenience in description, the continuity of the fold belt may be broken up into three mountain belts" the Taurus, Zagros and Oman mountains. Three zones can be defined: the autochthonous areas to the north and east, including the Anatolian Plateau of Turkey and the masses of central Iran; the fold belt, which can be split into the Foothills Fold Belt, a zone of sharp and asymmetrical folds with southward thrusting; and the Simple Fold Belt, which ends abruptly at the Oman Line east of Bandar Abbas. The Simple Fold Belt has more symmetrical folds as their distance from the collision zone increases and is a zone that contains numerous oil-bearing structures. The sedimentary column in this belt is estimated to be up to 12 km thick in Iran along the axis of the Mesopotamian Foredeep, but probably only half as thick in southeastern Turkey. Exposures of the upper part of this foredeep succession are well-developed in a number of anticlinal cores. There is a difference in structural style in southeastern Turkey due to the absence of younger evaporites, and decollement may take place at the base of Paleozoic shale, contrasting with the disharmonic folding that occurred in Iran due to the thick layer of evaporites between the Tertiary Paleogene limestone and the younger clastic rocks. The fold zones rest on the marginal part of the Arabian Plate. Taurus Mountains. The Taurus Mountains rise along the southern edge of the Anatolian Plateau and extend from west to east from the Aegean Sea to the SanandajSirjan ranges of the Zagros Mountains, which continue the mountain chains to the southeast (Figs. 2.17 and 2.24). The mountains are structurally and stratigraphically complex, with large, low-angle thrusts; nappes emplaced by gravity sliding; and numerous transverse faults. The southern border of the Taurides is marked by a tectonic contact, which can be traced from the Maras area to the Hakkari Mountains in an arcuate line about 600 km (375 mi) long and concave to the south. The surface of this contact is nearly horizontal, dipping gently to the north. The underlying Miocene shale shows only minor tectonic effects in contrast to the allochthonous Elazig Nappe emplaced during the late Miocene, which shows a high degree of tectonism and involves the Malatya, Hazar and Maden units.

There are a number of detailed geological studies, in particular those of Rigo and Cortesini (1964), Ilhan (1967, 1971, 1974) and Brinkmann (1976). These studies are summarized below. The oldest rocks that crop out in the easternmost Taurus, the Malaya Unit, are metamorphosed, recrystallized carbonates locally intruded by acidic, igneous bodies. These rocks are overlain by a Late Cretaceous to Paleocene Hazar Unit of more than 1,000 m (3,280 ft) of flysch-type graywackes and shale; in turn, the Hazar Unit is overlain by the Paleocene to Eocene Maden Unit of basic igneous rocks, marl, siliceous shale and nummulitic limestone. This somewhat enigmatic unit may represent an ophiolitic mrlange intercalated in the flysch. These allochthonous sediments composing the Besni olistostrome and the Kevan Nappe, which now lie on top of the Foothills Structural Belt, may have formed originally in the Taurus Geosyncline. They consist of radiolarites, cherty limestone, siliceous shale and blocks of recrystallized limestone associated with enormous masses of spilites, peridotites and tuffaceous agglomerates. Its emplacement took place during the Late Cretaceous, partly filling the Kastel Formation Foredeep to the south. In many parts of the Taurides, volcanism persisted from the Oligocene into the Pliocene. The autochthonous Mesozoic and Cenozoic sequence of the Western Taurides constitute a single unit over which three major allochthonous systems were emplaced. The Mesozoic up to the Late Cretaceous consist primarily of extensive, shallow-water carbonates, followed by a Late Cretaceous-Eocene flysch. These are overlain by the deposits laid down in a regionally transgressive early Miocene sea. The two major periods of tectonic activity occurred during the Late Cretaceous, predating the flysch, and during the late Miocene, post-dating earlier Miocene marine deposits. Brunn et al. (1971) described three main nappe systems in the western Taurides: the Antalya Nappes, which occur along the southern edge of the autochthonous zone; and the Taurus Occidental and Lycian nappes, both of which occupy a more northerly position. The nappes were emplaced in two phases, during the late Senonian to Paleocene and during post-Burdigalian time. The Antalya Nappes overlie the stratigraphically younger parts (Permian to Senonian) of the autochthonous Taurus. Parts of this sequence were laid down in shallow water. There are deep-water Triassic radiolarites, Carnian pillow lavas and undated peridotites, gabbro and diabase dikes, which form part of an ophiolitic complex. There also are Senonian radiolarites. The Antalya Nappes were emplaced in pre-early Miocene and during a post-Burdigalian phase. The nappes of the western Taurus consist mainly of Paleozoic rocks of Devonian to Permian age, but also may include Mesozoic carbonates, radiolarites and ophiolites. The Lycian Nappes are formed by a sequence of rocks

55

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The Geological History and Structural Elements of the Middle East ranging from Permian to Maastrichtian in age. The lithofacies show the presence of both shallow- and deep-water facies such as the tintinnid limestone of the Berriasian and Maastrichtian wildflysch. The Occidental Tauride Nappes are formed from a sequence of Dogger limestone overlain by Malmian wellbedded, argillaceous limestone and an Early and Late Cretaceous shallow-water limestone sequence. The succession is dominated by shallow- and deep-water, bioclastic limestone of Paleogene age and ends with the appearance of sandstone and marl. The Taurus range separates southeastern Turkey from central Turkey to the north, while the Amanus Mountains form the boundary to the west (Fig. 2.24). Thus, the Amanus Mountains form the marginal zone of the Arabian Shield and contain a sequence ranging from Middle Cambrian to Miocene. Their overall structure is that of megaanticlinorium striking northeast and overturned locally. The fold belt includes a large part of southeastem Turkey and extends from the Foothills Belt to the Syrian Plateau; thus, it includes the folded zone of northeastern Syria, a zone marked by a steep gravity gradient. The characteristic feature of the fold belt is the presence of large, generally east-west-trending, elongate anticlines with amplitudes of 1-10 km and wave lengths of 5-20 km, which resulted from strong tangential pressure. Their length along the axis may be from as little as 5 km to as much as 150 km, and they trend parallel to the mountain front. Both amplitude and wavelength depend upon lithology, tending to be greatest where thick, massive limestone is involved, and least in the thin-bedded, limestone-marl-shale sequences. The symmetry of the folds also is related to their proximity to the line of suture; and in the fold belt, there is a gradual transition from the more strongly folded, asymmetric structures of the Foothills Structural Belt at the southern limit of the Taurus Mountains to the gentler and more symmetric folds of the simple fold zone. Many of the fold structures proved to be productive, with fields such as Karatchok, Rumaila, Suwaidiyah, Musharad and Ain Zalah. Less-competent Tertiary sediments are draped over folded fault blocks in deeper, more competent carbonates, as, for example, the Garzan, Raman and Gercus anticlines. These deeper blocks have been affected by faulting that trends north-northeast, as, for example, that affecting the Mardin and Bozova uplifts. Such structures usually are characterized by strong relief with closures of several hundred meters, a distinct asymmetry and some disharmonic movement. The steep, southern flanks commonly are affected by high-angle, reversed faults, which at depth affect the Mardin carbonate section. The fold belt passes northeastward through the zone of foothills structures, where fold structures are more intense, without a sharp boundary into a narrow zone of thrusts bounded to the northeast by the Main Zagros Thrust. This zone is called the Imbricated Zone by Falcon (1967) and the Zagros Thrust Zone by St6cklin (1968a),

and was divided by Haynes and McQuillan (1974) into an imbricated zone, trench zone and crush zone (Fig. 2.24a). Northeast of the thrust zone, metamorphic rocks, including Precambrian, are exposed; in the southeast, the Precambrian rocks are deeply buried. Thus, the thrust is a major reversed fault that marks the line of collision between the Arabian Plate in the southwest and the Iranian and other plates on the northern side. North and northwest of Diyarbakir, nearly flat-lying Tertiary sediments and Quaternary basaltic volcanics cover a system of small, imbricated sheets thrust to the south. These structures contain numerous producing fields such as Kayakoy, Kayakoy North, Kirkan and Baykan. Practically all the Turkish producing fields occur within the fold belt, a zone that may be linked to the Dezful Embayment of Iran and the Kirkuk Embayment of Iraq. The structures seem to have been outlined during the Late Cretaceous and later rejuvenated by Neogene tectonic movements. The Foothills Structural Belt can be paralleled with the imbricated part of the Thrust Zone of Iran in the sense of Haynes and McQuillan (1974). The Foothills Structural Belt was affected by two diastrophic events, during the Late Cretaceous and late Tertiary. The fold belt can be compared with the Simple Fold Belt of the Zagros Range in Iran and Iraq. It was during the Late Cretaceous that the Besni Olistostrome and the Kevan Nappe were emplaced. The section under the allochthonous slide complex has different structures locally related to the slide itself, such as imbrication, low-angle, thrust faults and extremely complicated structures immediately under the gravity nappe. The late Tertiary tectonic event was accompanied by southward thrusting of the Taurus Range and is apparent mostly in the northern part of the Foothills Structural Belt, where most of the structures relatively close to the Taurus are more complex than in the more southerly simple fold zone. During the late Tertiary, Neogene event, the Palmyra and Sinjar depocenters in Syria and northwest Iraq, in which an anomalous thickness reaching up to 1,500 m (4,920 ft) of Paleocene and Eocene beds had accumulated, were inverted, and the resulting Palmyrides Fold Belt developed. The Palmyrides are characterized by broad, open folds in the north, which become tighter in the south. The folds typically are ramp-anticlines strongly overturned to the south (Lovelock, 1984). To the north, Cretaceous rocks are exposed in anticlinal cores; further south, where erosion has cut more deeply into the structures, Triassic rocks are exposed. In depth, the folds detach along Triassic/Jurassic salt horizons. The details of the structure of the Palmyride Belt are much better known since the release of well and seismic data (McBride et al., 1990; Chaimov et al., 1990; A1 Saad et al., 1992; Seber et al., 1993; Chaimov et al., 1993; Best et al., 1993) and detailed field mapping (Searle, 1994). In the southwestern part of the Palmyrides, short-wavelength, southward-verging monoclines and box folds with overthrusting leading to a crustal shortening of 20 km over a decollement surface formed by the Triassic evaporites, 57

Sedimentary Basins and Petroleum Geology of the Middle East which may be as much as 400 m (1,312 ft) thick. The close similarity in the stratigraphic section, both in lithology and thickness, as well as in structural style, invites continuity with the Negev Fold Belt of Sinai lying west of the Dead Sea Fault. Folding in the northern Palmyride region across the east-west A1Jhar Fault is much less intense; the shortening is no more than 1-2 km; and the belt disappears as a significant feature at the Euphrates Depression, although it is continued in the Sinjar Basin. The cause is presumed to be the thinness of the Triassic evaporites or their patchy di.~tribution. The main unresolved problem is to account for the difference in displacement along the Dead Sea Fault, for whereas 105 km seems fairly certain in the south, a displacement of only 25 km plus the Palmyride shortening of 10 km leaves half the displacement unaccounted for in the north. Zagros Mountains. The Zagros Mountains of Iran commonly are divided into the three principal tectonic

units (Fig. 2.25a) (Falcon, 1969, 1974; St0cklin, 1968a; Coleman-Sadd, 1978; De Jong, 1982): 9 Zagros Fold Belt, a thick sequence (about 12 km, or 7.5 mi) of Paleozoic to Pliocene sedimentary rocks folded into large anticlines and synclines during the Mio-Pliocene. 9 Zagros Thrust faults (Imbricated Belt), overthrusts developed during the Late Cretaceous and Pliocene, when radiolarian chert and ophiolites were emplaced over shallow-water sediments. 9 Zagros Main Thrust, the fault forming the northeastern edge of the Arabian Plate, separating the thrust belt from a strongly deformed zone with metamorphic and volcanic rocks. In the Zagros Thrust Belt, the sedimentary rocks were divided into five units totaling from 12,000 to 14,000 m (39,360-45,920 ft) (Fig. 2.25; O'Brien, 1950; ColemanSadd, 1978; De Jong, 1982) from top to bottom as follows: Unit 5: Incompetent Group (lower/middle Miocene to Pleistocene)" Varies in thickness from 2,000 to ~c~'P

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Fig. 2.25. a=ophiolite zones and main structural trends in southern and southwestern Iran (modified from Strcklin, 1974); b=lithostratigraphic section of the Zagros Fold Belt in Iran (modified from O'Brien, 1957; Coleman-Sadd, 1978). 58

The Geological History and Structural Elements of the Middle East 4,000 m (6,560-13,120 ft) of thin-bedded marl, shale, sandstone and conglomerate with minor anhydrite (early Miocene-Pliocene), unconformably overlain by Plio-Pleistocene conglomerates. Folds are small and disharmonic, and with the Competent Group folds, rest upon evaporites of the Mobile Group that have formed more than 200 diapirs in Hormuz and Gachsaran evaporites (De Jong, 1982). Unit 4: Upper Mobile Group (lower Miocene): Consists mainly of about 2,000 m (6,560 ft) of the middle part of the Gachsaran Formation, mainly Miocene salt, gypsum, anhydrite and marl. Unit3: Competent Group (Cambrian-Oligocene): The thickest unit, 6,000-7,000 m (19,680-22,960 ft) of Cambrian to Carboniferous clastics with subordinate limestone, and Permian to Late Cretaceous carbonates with minor shale, marl and evaporites. The Upper Cretaceous to Oligocene consists of shale and limestone overlain by Asmari limestone and the basal Gachsaran anhydrite. Unit 2: Lower Mobile Group (Infracambrian to Early Cambrian): Is not exposed in places, but is present as numerous salt diapirs, particularly in the Fars Province. The salt is associated with gypsum, shale, carbonates and igneous rocks assigned to the Hormuz Series. Unit 1: Basement Group (Precambrian): Granite, basalt, gabbro and amphibolite brought to the surface in salt diapirs (Kent, 1970). The Zagros Fold Belt (Fig. 2.25) was formed by a combination of flexure-slip and neutral-surface folding mechanisms indicated by bedding-plane slickensides, extensional faults parallel to the axial plane of the anticlines, and compressional features in the synclines (McQuillan, 1974; Coleman-Sadd, 1978; and De Jong, 1982). The belt is the result of the collision of the Arabian Continental Plate with the central Iranian Block to the northeast (Strcklin, 1968a; Falcon, 1969). Seismic data from Jackson et al. (1981) indicate that older faults were reactivated as high-angle thrusts; and Strcklin (1968a, b), Haynes and McQuillan (1974) and Stoneley (1976) show that during the Mesozoic and early Cenozoic, the folded belt of the Zagros was a subsiding, continental margin, where movement began in the Permian preceded by crustal thinning and normal faulting. The Zagros Mountains mark the southern part of the Mesozoic-Cenozoic orogeny, with the relatively stable platform that existed during the Paleozoic affected only by epeirogenic movement (Falcon, 1974). Marine clastics, the dominant lithofacies during the Paleozoic, were replaced by a thick (1,000 m, or 3,280 ft) sequence of shallow- to deep-water carbonates, with only a minor clastic influx from Permian to late Miocene (Strcklin, 1968a, b; Falcon, 1969). During the Late Cretaceous, the proto-Zagros Range developed, but the main phase of movement occurred during a Miocene-Pliocene orogenic episode, during which time

there was the accumulation of synorogenic, continental clastics (Falcon, 1974). Thus, the rocks of the Zagros Thrust Belt consist of radiolarian chert, limestone, ophiolites and some metamorphic rocks emplaced over a shelf sequence during the Late Cretaceous. During the late Cenozoic, the belt was folded and intruded by diapirs with the development of reverse faulting (De Jong, 1982). The different opinions concerning the position of the ultramafic rocks have been summarized by De Jong (1982): those who believe the rocks occur in large overthrust sheets (Gray, 1950; Ricou, 1968; and Hallam, 1976), those who believe that the ultrabasics were autochthonous and emplaced through igneous intrusion (Gansser, 1955; Wells, 1969), and those who suggested high-angle thrusting (Strcklin, 1968 a, b; Falcon, 1969; Haynes and McQuillan, 1974). Berberian and King (1981) claimed that following the Middle Triassic compressional phase, the whole area underwent tensional movements characterized by Late Triassic continental, alkali rift basalts in the Alborz and central Iran. Oman Mountains. The Oman Mountain Chain, which is some 700 km (438 mi) long and 50-130 km (3181 mi) wide, borders the southern side of the Gulf of Oman (Fig. 2.26). The natural subdivision of the overthrust belt is into an external zone, which represents the overthrust belt south and west of the leading edge of the Semail Thrust and the area south and east of the marginal fold and thrust belt (Glennie et al., 1974), and the internal zone of the Oman Mountains Overthrust Belt from the Batinah coast in the Gulf of Oman to the leading edge of the Semail Nappes. Sedimentologically, the external zone consists almost entirely of sediments of the Hawasina Complex (e.g., the Hamrat Duru Range, Jebel Sufra and Jebel Hammah) and structurally of a regular sequence of foreland, propagating thrust slices containing Hawasina and Haybi complex rocks, with the more distal units thrust over the more proximal (Glennie et al., 1974). A large part of the internal zone is covered by the Semail Ophiolite, which, because of its thickness and competent nature, remains relatively undeformed. The ophiolite was carried on the Semail Thrust, which appears to truncate all the lower structures (Glennie et al., 1974). The warping of the Semail sheet has resulted in the formation of a number of tectonic windows or culminations, which are, from northwest to southeast, the Hawasina, Jebel Akhdar, Jebel Nakhl and Saih Hatat windows. Although of variable dimension, the largest has a wavelength of 35 km (22 mi) and an amplitude of 3 km (1.9 mi); all the windows have a box-fold geometry with a horizontal crest and steeply dipping limbs. With the exception of the Jebel Nakhl window, whose axial trace is transverse to the trend of the mountain belt, all the others parallel the trend. Complex duplex structures in the Mesozoic shelf carbonates exposed in the culminations in the internal zone indicate that the shelf sequence was involved in the Late Cretaceous Nappe emplacement (Ries et al., 1990). Thrusts and thrust-related structures have been recognized 59

Sedimentary Basins and Petroleum Geology of the Middle East

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60

onto the Arabian continental margin. Following emplacement, the nappes were covered by shallow-marine Maastrichtian and early Tertiary limestone. The outer part of the Arabian continental margin, together with its cover nappes, was uplifted during the Oligocene and early Miocene to form the Oman Range. Unit 5: Semail Nappe, a huge mass of ultramafic and mafic rocks (ophiolites), comprises spilitic pillow lavas, feeder dikes, hypabyssal gabbroic and gabbroic rocks, a layered transition zone between the gabbros and peridotites, peridotites and serpen-

The Geological History and Structural Elements of the Middle East

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Fig. 2.27. Tectono-stratigraphic relationships of the rock units in the Oman Mountains (after Glennie et al., 1974). tinites that formerly formed part of an oceanic rise, which was the distal limit of the basin in which the Hawasina sediments accumulated. Unit4: Hawasina Allochthonous Unit, several thin, imbricated nappes, each consisting of a sedimentary sequence covering part of the Permian to preSenonian rocks. The Permian and Triassic are represented by shallow-water, carbonate olistoliths. Deeper-water facies, with radiolarian chert, pelagic limestone and carbonate turbidites, developed during the Jurassic and Cretaceous. These beds were deposited in an oceanic basin

northeast of the present Oman Mountains from the Permian to Cenomanian. Unit3: Sumeini Parautochthonous Unit, comprising Permo-Triassic limestone, dolomites, sandstone and marl; Late Triassic coarse boundstone; Triassic calcareous mudstone, boundstone and conglomerates; and Jurassic to Mid-Cretaceous, partly slumped and conglomeratic, calcareous grainstone, mudstone and minor chert. Unit2: Mid-Permian to mid-Senonian autochthonous sediments, composed mainly of shallow-marine carbonates, with part of the shelf stretching into the Arabian Platform and deposited on the continental margin of Arabia. Unit 1" Pre-Permian sialic basement consisting of granites, folded and partly metamorphosed sediments and mafic volcanics from a basement consolidated during a pre-mid-Permian orogeny. Detailed investigation by an Open University team and the USGS reinterpreted and updated the stratigraphy of the area, and the result was published by the Geological Society of London (1986) and in the Journal of Geophysical Research (1981). The geology of the area may be divided into four major tectonostratigraphic units: 1) Pre-Permian rocks (basement rocks and associated sediments): A Precambrian crystalline basement of Jebel Ja'alan, where gneisses and schists are cut by intrusive granites (Glennie et al., 1974). It also occurred in the Dhofar Province of mainly granites and amphibolites (Lippard et al., 1986). The basement is overlain by late Precambrian to Early Permian continental to shallow-water marine sediments, including glacial deposits. 2) An autochthonous succession of mid-Permian to Late Cretaceous Hajar Supergroup and Aruma Group of Glennie et al. (1974). It consists of massive, marine carbonates of shallow-water origin with some openmarine conditions, representing part of a broad, carbonate platform of Arabia. These sediments rest unconformably on late Precambrian to early Paleozoic sediments, representing part of the stable Arabian Platform (Lippard et al., 1986). 3) Allochthonous units, composed mainly of Mesozoic rocks emplaced as a series of thrust nappes in the Late Cretaceous and subdivided into five units (Lippard et al., 1986). The Sumeini Group are mainly poorly fossiliferous, fine-grained limestone, with some shallowwater carbonates and intraformational conglomerates. The Hawasina Assemblage is composed of Mesozoic hemipelagic and pelagic sediments, mostly of turbidite origin (quartz and carbonate turbidite, silicified limestone and radiolarian chert). The Haybi Complex of Searle (1980) includes thrust slices and olistoliths of volcanics, exotic limestone and Hawasina-type sediments contained in a fine-grained, pelitic matrix and a thrust slice of sub-ophiolite, metamorphic rocks and serpentinite. The Semail Nappes of the basal

61

Sedimentary Basins and Petroleum Geology of the Middle East metamorphic sheet (0-500 m, or 0-1,640 ft, thick) is tectonically overlain by ultramafic tectonites (8-12 Ion), in turn overlain by layered peridotites and gabbros (0.5-4 km, or 0.3-2.5 mi), high-level plutonic rocks (10-500 m, or 33-1,640 ft), a sheeted-dyke complex (1-1.5 km, or 0.6-0.9 mi) and, at the top of the succession, extrusive lavas and interbedded, pelagic sediments (0.5-2 km, or 0.3-1.25 mi) (Lippard et al., 1986). The Batinah Complex of Woodcock and Robertson (1982a, b) consists of a lower m61ange, the Batinah M61ange, composed of blocks of the Semail Ophiolite, exotic limestone, Haybi Volcanics, Hawasina sediments, metamorphic rocks and serpentinite (Lippard et al., 1986). 4) A neoautochthonous sequence of Maastrichtian and early Tertiary sediments, composed mainly of fluviatile conglomerates, sand, gypsiferous marl and fossiliferous, marly limestone. The western and southwestern foreland belt of the Oman Mountains is characterized by elongate, usually asymmetric anticlines, in which early Tertiary and Late Cretaceous rocks are exposed. The trend of the folds is approximately parallel to the main axis of the Oman Mountains. Within this belt are the producing fields of Western Oman, such as Natih and Fahud. According to Tschopp (1967b), the Fahud Anticline is fault-formed before and during the deposition of the Albian-Cenomanian limestone, with the principal vertical movements occurring during the Senonian along the Fahud Fault. Renewed folding and uplift occurred during the Tertiary. The structures that existed in that area during pre-Senonian time were low-relief domes formed by Infracambrian salt pillows or fault structures. The emplacement of the Hawasina and Semail nappes transmitted compressional stresses to the bordering sedimentary complexes on the platform and developed foreland folds around the nappe fronts. The uplift of the Oman Mountains during the Tertiary further enhanced the decollement of the pre-existing Cretaceous structures and incorporated Tertiary rocks into the Cretaceous folds, clearly seen in subsurface of the Fahud Field, where the Tertiary rests unconformably on more steeply folded Cretaceous structures (Glennie et al., 1974). DISCUSSION The degree to which the tectonic effects impact upon sedimentation essentially depends upon the scale of the event and the location of the depositional site with respect to the location of the principal tectonic activity. This is easily exemplified by the Mesozoic sedimentation patterns of the Arabian Platform. As indicated earlier, during the Late Jurassic and Cretaceous over the greater part of the platform, the principal facies variation can be attributed to sea-level fluctuation, which itself is attributed to plate activity. This may be contrasted with the Late Cretaceous

62

flysch sedimentation pattern with radiolarites, marl and conglomeratic olistoliths associated with the foredeep that developed in front of, and was enveloped by, the advancing nappe pile in Oman and the adjoining areas. A smallerscale effect, but still related to the general tectonic pattern, is the development of salt domes, a halokinetic result of stresses induced by and in the subducting plate; examples of this are to be seen in the U.A.E. offshore province and in southem Iran. Of an intermediate character are the sedimentation changes associated with the development of broad warps and ridges in the cratonic areas more distant from the subduction zone, as, for example, in southeastern Yemen, where the early Eocene thickness variations reflect the progressive development of the reactivated Hadhramout Arch. This arch was active earlier in the Jurassic, when horsts and grabens developed associated with a major phase in the breakup of Gondwana. The arch is now separated by the Gulf of Aden from its southwestern continuation, which lies within Somalia. The alignment of these structures suggests that the ultimate control may be an old Precambrian feature. One further example is the Ha'il-Rutbah Arch, which extends northward from the margin of the Arabian Shield and which, according to Lovelock (1984), was upwarped in the late Tertiary and eroded to expose a 900 m (2,952 ft) section of Permian continental sediments along the flank of the Rutbah High. There still is discussion about whether this feature was active during the Paleozoic. Thus, the current structural framework of the Middle East is one of an Alpine orogenic system stretching from Turkey in the northwest through Iraq and Iran to Oman in the southeast, which borders on two sides the Arabian Shield and Arabian Platform. The distinction between the shield and platform is the relatively little-disturbed Phanerozoic sediments that overlie the platform; whereas in the shield, the Precambrian is exposed. The western margin of the shield/platform is marked by a left-lateral shear system of the Dead Sea-Jordan Valley at the western edge of the Levant Block, a part of the shield, and the Red Sea Graben at the western margin of Saudi Arabia and Yemen. To the southeast of Oman and Yemen lies the Gulf of Aden and the Arabian Sea, with its system of spreading and transform faults. Strong, tangential stresses in the fold belt of Turkey and Syria formed several asymmetric structures parallel to the Taurus Mountains. The intensity of the stress decreased southward. The dominant feature of the fold belt is the occurrence of east-west-trending, elongate anticlines. Near the edge of the craton in Syria and Turkey, block faulting resulted in the cratonic trend dominated by the Mardin and Bozova highs. The less-competent Tertiary sediments generally are draped over folded fault blocks above the deeper and more competent Mesozoic carbonates. The features are characterized by strong relief and have a closure of several hundred meters and a strong asymmetry. The steep southern flanks commonly are

The Geological History and Structural Elements of the Middle East affected by steep, high-angle (50-60~ reverse faults that affect the Mesozoic succession. In the Palmyra Fold Belt of central Syria (Fig. 2.16), the Paleocene and Eocene sequence reaches an anomalously high thickness of 1,500 m (more than 4,920 ft), giving the appearance of a small foredeep of limited extent and duration. Its origin was due to southward lithospheric thrusting that reached the surface on the southeastern flank of the Anti-Lebanon, so that the trough was formed, filled and deformed during a brief episode in the late Tertiary. The Jordan-Dead Sea Fault System is a series of en echelon breaks that form rhombochasm rift troughs, including the Gulf of Aqaba (Quennell, 1958; Freund et al., 1970; and Garfunkel, 1970). The whole appears basically as a left-lateral transcurrent fault that began in the Gulf of Aqaba as part of the extensional system affecting the Red Sea in early Miocene time, isolating the sequence of simple horsts and grabens of the present Gulf of Suez from the continuing Red Sea extension. Along the Araba Valley (Wadi Araba), the fault is a relatively simple zone of strike-slip faulting. Activity along the Jordan-Dead Sea Fault was at its maximum during the late Miocene and Pliocene. The total left-lateral displacement along the segment from the Gulf of Aqaba to the Jordan Valley is 105 km (66 mi). Restoring the displacement matches up Mesozoic facies as well as east-west right-lateral faults across the Jordan-Dead Sea Fault (Freund et al., 1970). The Dead Sea rhombochasm contains more than 6,000 rn (more than 19,680 ft) with thick Pliocene and Pleistocene salt that forms diapirs. The Araba Fault projects along the eastern side of the rift basin and the Jordan Valley Fault into the western side, with the two joined by a system of northwest-trending faults. The Simple Fold Belt of the Zagros Range extends from southeastern Turkey across northern Syria and Iraq into southern Iran, ending abruptly at the Oman Line east of Bandar Abbas. Within this belt, the sediment thickness may total as much as 12,000 m (more than 39,360 ft) in Iran spanning the whole Phanerozoic, but probably is less than half that in Turkey. The structural style and fold size in the fold belt varies along its length because of the absence of evaporites in Turkey (where the decollement surface is at the base of Paleozoic shale). In Iran and Iraq, the thick evaporites have resulted in disharmonic folding between the Tertiary limestone below and the clastics overlying the evaporites above. The folds usually are asymmetric in the Zagros, with amplitudes of 1-10 km (0.6-6.25 mi) and wavelengths of 5-20 km (3.1-12.5 mi), both dependent to a great extent on lithology. The length along the axis of the folds may exceed 150 km. The strike of the fold axes changes from northwest-southeast along the main Zagros Range to a more east-west trend near

Bandar Abbas in southeastern Iran and in southeastern Turkey and northern Syria at the ends of the fold belt. The Simple Fold Belt passes gradually northeastward into a narrow zone of thrusting, called the Imbricated Zone by Falcon (1967) and the Zagros Thrust by Strcklin (1968a), which extends to the Main Zagros Thrust. This zone has been subdivided by Haynes and McQuillan (1974) into imbricated, trench and crush sub-zones. The bounding Zagros Thrust on the northeastern side of the zone has a remarkably straight northwest-southeast alignment and marks the line of collision between the Arabian and Iranian plates. The folded zone in northeastern Syria is the extension of the Simple Fold Belt of the Zagros Range. Here, the folds are broad and symmetrical, and only minor faulting is seen at the surface. The folds are important structures for producing hydrocarbons. They occupy a zone of steep gravity gradients between the Sinjar Swell and the axis of the Mesopotamian Foredeep. In the south and southwestern Middle East Basin lies the main Arabian Platform, that part of the Arabian Shield/ Craton buried by Phanerozoic sediments extending from the Cambrian to Recent. The thickness of this sedimentary sequence ranges from 5,200 m (17,056 ft) at outcrop to 7,500 m (24,600 ft) or more closer to the folded belt. It is a region that has been subjected only to epeirogenic warping; evidence for orogenic deformation is lacking. Warping due to evaporite flow at depth and structures attributed to reactivation of basement faulting (such as the mid-Cretaceous rifting) are characteristic. However, the prominent sedimentary and erosional break, locally marked by the Hercynian unconformity, indicates the existence of important, late Paleozoic epeirogenic uplift and erosion. In the unfolded areas of Syria and Iraq, there is geophysical evidence of buried structures, a complex structural pattern resulting from the combination of mainly vertical movements with different trends. These movements have resulted in structures that may be traced for tens to even hundreds of kilometers. The inference can be drawn from the phases described above, that although they serve as a framework to which the stratigraphic developments of Arabia may be tied, the duration of the phases increases with increasing age. If any conclusion, however, is to be drawn from the disruption of Gondwana, it is that in all probability, the older events were as complex as the younger; thus, the apparent simplicity of these earlier events is a combination of our inability to discriminate between short intervals of time because of the inadequacies of dating and correlation methods, and the destruction of critical evidence through the ravages of time.

63

This Page Intentionally Left Blank

Chapter 3 INFRACAMBRIAN OF THE MIDDLE EAST

Cambrian beds of the Sauk sequence is in Iran (St6cklin et al., 1964). If more detailed sedimentological studies were available, the region would provide an ideal type section. There is no break across the Cambrian-Infracambrian boundary, and the Infracambrian or "Assyntic" basement basal unconformity appears to be exposed in places. Drilling in Oman, while of inestimable value in providing stratigraphic and lithological information, also serves to highlight some of the weaknesses inherent in the study of the Infracambrian; the base is not exposed and seldom has been penetrated by the drill, and the age of the basal part of the sequence, which can be known only through radiometric dating, is very uncertain. One well bottomed in lava dated as 654+12 Ma, but it may be argued that this merely represents a volcanic horizon within the basal part of the sequence, even if the date is correct. The age of the Ara Salt at the top of the succession is somewhat better known, for the age of the overlying Haima Group rocks is well-established paleontologically. The areas within the Arabian Gulf and surrounding regions where Infracambrian evaporitic rocks are exposed and described from surface outcrop and subsurface based on well data and seismic interpretation is shown in Fig. 3.1. By itself, the presence of folded and tilted Infracambrian carbonates is not an indication of sedimentation contemporaneous with the final phase(s) of the Pan-African movements. However, the dating of the Najd Fault movements in Saudi Arabia and the dating of the Infracambrian of Oman, mentioned above, is consistent with the correlation of the archaeocyathid fauna that provides some paleontological control. In the previous chapter, a case was made for the growth of the Afro-Arabian Shield to be one of island-arc accretion followed by oblique plate collision with which left lateral shear and tensional movement was associated. The preserved Infracambrian rocks represent the sedimentary fill of the pull-apart structures that resulted from these movements. Some years ago, Stern (1985) considered the Hammamat Formation, cropping out in the Eastern Desert of Egypt (Grothaus et al., 1979), as the molasse fill of such a structure. It was only with the recent discovery of a carbonate horizon containing archaeocyathids (Khalifa et al., 1988) that there was a clear indication of the age of the Hammamat Formation and its equivalence to the Infracambrian of the Arabian Peninsula. The Ghaba and South Oman salt basins resulted from the epi-cratonic breakup of the Middle Huqf carbonate platform, which can be correlated with the formation of other salt basins in the area (Husseini, 1988; Visser, 1991). Strike-slip faulting with a strong compressional element reshaped the western and southern margins of the South

INTRODUCTION Historically, before the common use of radiometric methods and the recognition of the value of stromatolites as a means of assigning stratigraphic ages, the term "Infracambrian" was widely used to cover a series of unmetamorphosed or barely altered sedimentary sequences resting upon clearly metamorphosed Precambrian rocks. For the Middle East, the definition of the Infracambrian by St6cklin (1972) was revised by Wolfart (1981), who described it as follows: "In the Middle East, a barren group of cherty dolomites and red or variegated, micaceous shale and sandstone up to 2 or 3 kilometers in thickness, having a wide distribution, is designated Infracambrian. Upward, these rocks pass gradually into biostratigraphically dated Early Cambrian rocks. The Infracambrian is separated from the Precambrian basement complex either by a pronounced angular unconformity or by a less distinct (non-angular) disconformity. The Infracambrian is, thus, more closely linked with the Cambrian System than with the Precambrian basement complex. At least partly, it may still be Precambrian in age."

Although the above is true in the area discussed by Wolfart (Iran and southeastern Turkey), in many other areas, an unconformity caps the Infracambrian succession; in the Arabian region, this generally is the case. While the term lacks precision, and it certainly fails to indicate the presence of clastics both above and below the carbonates, it is a useful descriptive term to cover the earliest, unaltered sediments resting upon Precambrian basement, with the stipulation that no precise duration can be assigned to them, and that they cannot be assumed to cover the same time interval everywhere. Apart from the little-studied sequence in northwestem Africa (Anti-Atlas and Taoudenni Basin), nowhere in North Africa and the Arabian Peninsula is the Infracambrian as well-known and as nearly complete as in Oman (Gorin et al., 1982). In the sense of Sloss (1963), the Infracambrian forms another sequence, with both transgressive and regressive clastics sandwiching a marine carbonate succession. The Oman succession, therefore, serves as a type section against which other, less complete sequences may be compared. It has the advantage of more complete subsurface study because of the economic importance of its hydrocarbon potential. The second area where there appears to be only a slight break between the Infracambrian and the lowermost

65

Sedimentary Basins and Petroleum Geology of the Middle East

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A R A B I A N SEA

Fig. 3.1. Distribution of Infracambrian salt basins in the Middle East (based on surface data from Kent, 1970; and subsurface data from Murris, 1980; and Alsharhan and Kendall, 1986). Oman Salt Basin, with the uplifted areas shedding the clastics that subsequently form the rocks of the Haima Group at the end of the Huqf period. By the Late Ordovician/Early Silurian, this relief had been largely eroded away, and the Huqf Basin had become part of the Rub al Khali Basin (Visser, 1991). The lithotypes assigned to the Infracambrian of the Middle East are listed in Table 3. I. They represent deposits in a predominantly terrestrial to shallow-marine environment with the extrusion of volcanics. At that time, posttectonic, subaerial volcanism was approximately coeval, with continental sedimentation. In central Saudi Arabia and Jordan, continental deposits interfinger with shallowmarine clastics and carbonates. The Arabian Gulf area and Iran were vast, carbonate banks surrounding restricted, evaporitic basins. Ketin (1966) suggested that southeastern Turkey and the central Arabian Shield were parts of a province experiencing block faulting, with sedimentation in intramontane basins that also were receiving volcanics. A lithostratigraphic correlation of these Infracambrian

66

rocks is illustrated in Fig. 3.2 9This will be incorporated in the paleogeographic map at the end of this chapter, where an attempt is made to place the geological history in a regional context. Using the available radiometric and paleontological data, St6cklin (1986) regarded the major part of the Infracambrian-Cambrian evaporite sequence in Oman, Iran and Pakistan as lying within the Vendian. However, this use of Russian terminology, from a different plate and given the uncertainties of correlation, seems inappropriate for Gondwana rocks. The extent to which these Infracambrian beds extend into the lower Paleozoic remains unclear, particularly in the absence of a world standard for the Precambrian-Cambrian boundary, compounded by the inadequacy of the paleontological record.

Infracambrian of the Middle East

Table 3.1. Infracambrian rock units in the Middle East. Asterisks indicate outcrop, and bullets indicate subsurface.

67

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Infracambrian of the Middle East ter 2, Fig. 2.5). The Huqf Group was named from the principal locality and is subdivided into five formations. These are (in ascending order) the Abu Mahara, Khufai, Shuram, Buah and Ara formations (Fig. 3.3). Field observations are supplemented by subsurface data from other areas (southern Oman), because in the Huqf region, the uppermost formation, the evaporitic Ara sequence is found at the surface only in the form of salt plugs, and nowhere is the basal contact of the lowest formation exposed. The stratigraphic succession shown in Fig. 3.3 is compared with the outcrop data from the Oman Mountains described by Glennie et al.

S T R A T I G R A P H Y OF INFRACAMBRIAN ROCKS IN OMAN

Huqf Group The principal exposure of Infracambrian rocks in Oman is associated with the Huqf-Haushi Arch, a structure that strikes northeast-southwest parallel to the Arabian Sea coast of Oman and at a marked angle to the major trends seen in the Precambrian Shield of Saudi Arabia (see Chap-

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Fig. 3.3. Stratigraphic and sedimentologic interpretation of late Precambrian-Early Cambrian Huqf Group outcrops correlated with formations in the Oman Mountains (modified from Gorin et al., 1982, Alsharhan and Kendall, 1986). 69

Sedimentary Basins and Petroleum Geology of the Middle East (1974), Gorin et al. (1982) and Wright et al. (1990) and summarized below. Abu M a h a r a Formation. The formation (about 565 m, or 1,853 ft) is the oldest sedimentary rock unit found in Oman. It crops out also in the hills of the Dhofar Province (southern Oman), where it overlies a metamorphic, crystalline basement. Basement also is found immediately below Abu Mahara clastics in well Ghadir Manqil-1. The best exposures in the Huqf area are in the anticlinal cores of the Khufai and Mukhaibah structures, which are linked to the north-south-trending Saiwan-Nafun Fault (Gorin et al., 1982) (see Chapter 2, Fig. 2.3). The base of the formation was reached in a well drilled at the Khufai Anticline, which bottomed in trachyte. This volcanic rock was dated at 654+12 Ma, but Gorin et al. (1982) consider this a volcanic episode rather than the age of the crystalline basement, which they equate with the 858+16 Ma age in Jebel Ja'alan in east central Oman. A thin dolomite overlies the volcanic horizon, and the rest of the formation is an alternation of sandstone, partly quartz-cemented, and argillaceous siltstone to silty shale. The sandstone is predominant in the upper part of the formation. At the top, finely laminated and dolomitic siltstone alternating with silty dolomites of tidal-fiat origin are locally cut by channels filled with fluviatile sandstone (Fig. 3.4). The beds of the Abu Mahara Formation are regarded as forming in a braided-stream to tidal-fiat regime, probably located between a low-relief land mass to the north and an offshore trough to the east based on their thicknesses in subsurface (Gorin et al., 1982). The thickness of sediments in the trough is great. Shale and siltstone, the shallowwater sediments, commonly are laminated and glauconitic. There is considerable variation in sandstone grain size, sorting and thickness. The sandstone commonly shows sinuous dessication cracks and alternates with red siltstone interpreted as flood-plain deposits. The finely laminated, silty dolomites with mud cracks probably are tidal-flat deposits. Note that in both southern Oman (well Ghadir Manqil-1) and in the Oman Mountains in the Mistal Formation, a glacial episode is reported near the end of Abu Mahara time, although this is not shown in the Abu Mahara section drawn by Gorin et al. (1982) or Wright et al. (1990) (Fig. 3.4). Khufai Formation. This primarily carbonate unit (about 320 m, or 1,050 ft) shows a rapid transition from the underlying Abu Mahara Formation, as the yellow, silty dolomites and dolomitic siltstone at the top of the Abu Mahara are replaced by dark-gray dolomites in the lower part of the Khufai Formation. At the base, there occur collapse structures associated with solution brecciation, anhydrite and traces of halite. The dolomites become very fetid upward. Small-scale folding and slump structures are found in some layers. Chert and diagenetic, spherical dolomite nodules with concentric structure also occur. Stratiform stromatolites are common (Fig. 3.5). In the upper part of the formation, stratiform and linked stromatolites again are common, along with numer-

70

ous chert lenses. Relicts of oncoidal and pelletoidal wackestone to grainstone structure can be identified. There are horizons where brecciation is found. Coarse- and finegrained dolomite may be interbedded. Occasional, current-bedded, fine- to coarse-grained sandstone is found, and siltstone is interbedded locally with dolomites in the upper part. The uppermost bed, a dolomitized, oncoid-ooid-pelletoidal grainstone, forms a good marker throughout the Huqf region. Because it appears to have been lithified before deposition of overlying Shuram sediments, it is interpreted as a hardground. The depositional environment of the formation is interpreted as fluctuating between supratidal to shallow, intertidal conditions. Where the collapse structures and sedimentary breccias are found, these are thought to represent sabkha conditions, with the collapse due to salt solution. The structures are associated with thin anhydrite and layers of coarsely crystalline calcite, which may be secondary replacement deposits. The change from fetid dolomite to subordinate grainstone suggests short, high-energy intervals (storm) under lagoonal conditions. The disappearance of fetid dolomite in the upper part of the Khufai Formation may indicate a return to a more open, lagoonal character. The boundary between the two commonly shows more massive, grainy carbonates, with cross- and graded-bedding and scour and fill structures, possibly barrier or high-energy shoals and/or an intertidal environment. However, the massive grainstone is overlain by low-energy stratiform and linked stromatolites with subordinate intercalations of high-energy grainstone. The association of solution breccias linked to anhydrite, dessication structures in the stratiform and linked algal mounds, numerous chert laminae and nodules, and coarsely crystalline dolomites regarded as diagenetically replaced anhydrite suggests an intertidal to supratidal environment. The interbedded grainstone is thought to be storm wash-over material, within which flakes of the algal mat material may be incorporated. Terrigenous material, rounded silt to fine sand-sized grains, then represents deflation products blown in from the nearby land mass. In the Buah area, sandstone, invariably cross-bedded, commonly cuts the stromatolites at high angles and is interpreted as tidal channel deposits. Higher in the sequence, the sands become laterally continuous, show fine lamination, low-angle cross-lamination and rippled surfaces and give way upward to more fetid, stratiform stromatolites. By the end of the Khufai, however, a rise in sea level had transformed the tidal fiats into a high-energy environment all over the Huqf area. Shuram Formation. The formation, as described by Gorin et al. (1982) and Wright et al. (1990), consists of 270 m (886 ft) of a lower sequence of fissile and slightly calcareous shale and siltstone which, being relatively soft, weather readily, and an upper sequence of alternating siliciclastics, grainstone and calcareous mudstone (Fig. 3.6). The grainstone is ooidal (with both radial and concentric structures), silty and micaceous. Locally, it may be

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Fig. 3.7. Sedimentological interpretation of the Buah Formation in Oman (based on Gorin et al., 1982; Wright et al., 1990).

Infracambrian of the Middle East with scour and fill structures. This grainstone probably formed local shoals or barriers. At the top, the influx of clastics resulted in sandy, crystalline dolomites alternating with sandstone that may be 20 m (66 ft) thick. Stratified and domal stromatolites are common and probably are the result of numerous minor fluctuations in sea level in a very shallow, subtidal to intertidal setting, where moderate to high-energy conditions prevailed (Figs. 3.7 and 3.8). Where sections are more complete, the massive dolomites may be overlain by red-green, silty claystone with anhydrite, within which some sandstone horizons are intercalated. An alternative to including them within the Buah Formation is to regard them as representing a period of post-Buah-pre-Mahatta Humaid emergence, a form of fossil "soil" (Gorin et al., 1982) such as is seen on the western flank of the Huqf axis, where the Mahatta Humaid Formation overlies deeply karstified Buah dolomites. Ara Formation. The formation is not present in the Huqf area, but has been defined from the results of drilling in southern Oman. In subsurface, it is about 1,775 m (5,812 ft) thick and can be shown to consist of a major carb0nate/evaporitic sequence with thick salt (halite) and subordinate anhydrites, shale, siltstone and claystone intercalations (Fig. 3.9). In outcrop associated with the salt plugs, the carbonates, mostly in the form of dolomites, are dark and fetid, locally silty or sandy with chert nodules, and possibly stromatolitic. Similar fetid dolomites are encountered in well Fahud-1 at a depth of about 3,693 m (12,113 ft) before the evaporites are penetrated. The carbonates contain algal mats and stromatolites and are rich in organic matter, which was deposited during periods when normal marine conditions prevailed in a basin setting varying from marginal to deep basinal. The evaporites formed at times when there was restricted marine access to the basin, and under these conditions, thick halites and potash salts were deposited, from which hypersalinity can be inferred (Mattes and Morris, 1990) (Fig. 3.10). The edge of the Ara Salt Basin cannot be established, and Gorin et al. (1982) consider it probable that thick

conglomeratic, with clasts of the same material present as fiat, rounded pebbles. At the top of the formation, the siltstone disappears. There is a disconformity at the base of the formation, as indicated by the hardground found at the top of the Khufai Formation. The break was followed by the influx of fine-grained, clastic material seen forming the shale and siltstone in the basal part of the Shuram Formation. These beds are laterally continuous and suggest deposition in a low-energy, marine environment. Water depth was never great, as suggested by the presence of rippled surfaces, low-angle cross-bedding, and small-scale slump structures. In the upper part of the sequence, the fall-off in clastic input led to the establishment of carbonate deposition. The presence of thinly bedded, oolitic grainstone suggests somewhat higher-energy conditions, which could explain the absence of clay by a winnowing process. These oolitic shoals may have protected shallow lagoons in which storms broke up partially consolidated grainstone that were then redeposited as rounded, fiat pebbles in the succeeding bed, resulting in the intraformational conglomerates that occur. Buah Formation. The progressive diminution of clastic influx, which was never great in the Shuram Formation, continued with the establishment of a more purely carbonate environment, now represented by the Buah carbonates. This finely bedded, argillaceous limestone is about 340 m (1,115 ft) thick and shows a remarkable continuity over the whole Huqf region. Three units may be distinguished (Gorin et al., 1982; Wright et al., 1990); the lowest unit consists of thinly bedded, laminated limestone and dolomites and is overlain by a middle unit of thickly bedded dolomites, with many chert nodules and numerous horizons of solution breccias commonly associated with anhydrite and gypsum pseudomorphs. The upper unit is dominated by thinly bedded, laminated dolomites, evaporites and stromatolites. These were deposited under shallow, supratidal, low-energy conditions, with periodic subaerial exposure. Intervals of massive, coarse-grained carbonates show both cross-bedding and graded bedding

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Fig. 3.8. Idealized block diagram showing the depositional setting of the Buah Formation in Oman. 73

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 3.9. Distribution of the Infracambrian Ara Formation in Oman (modified from Sykes and Abu Risheh, 1989). evaporites never covered the Huqf axis, for the base of the Mahatta Humaid Formation (equivalent to basal Haima Group; Fig. 3.2) shows no signs of disturbance attributable to salt withdrawal. Consequently, if present, the evaporites had to have been completely eroded prior to Mahatta Humaid deposition. They consider a more likely scenario to be that the Huqf axis formed part of the platform bordering the salt basin and that part of the Buah Formation may be a lateral facies equivalent of the Ara Formation. The karstified surface of the Buah Formation also suggests at least temporary emergence of the Huqf axis.

The Age of the Huqf Group Clearly, the sediments of the Huqf Group postdate 74

860 Ma, the radiometric age of the sub-Huqf basement rocks 9The significance of the radiometric age of the volcanic rocks at the bottom of the hole drilled on the Khufai Anticline, 654+12 Ma, is not so clear, and depends on whether these are regarded as within the Abu Mahara Formation or below it (Gorin et al., 1982). No Cambrian fossil or trace fossil has been found within the Huqf Group, although there is an abundance of sheet-stratiform and linked stromatolites, and specimens of Collenia have been reported. Gorin et al. (1982) described two columnar forms of stromatolite, one similar to Acaciella Walter and Aldania Krylov, and the other showing some resemblance to Gymnosolen Steinmann, which have been regarded as Late Proterozoic in Russia, China and Australia. The presence of Claudina in the Ara

Infracambrian of the Middle East z o i< rr" O ii

LITHOLOGY

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Fig. 3.10. Schematic model illustrating variations in environmental conditions and mineralogical facies in the Ara Salt Basin during deposition of a typical carbonate/evaporite cycle. Thickness of carbonate intervals varies from 20 m to 250 m (modified from Mattes and Morris, 1990, and reproduced by kind permission of Geological Society, London). Formation has suggested a possible equivalence with the Ediacara fauna of latest Proterozoic or possibly earliest Cambrian. The calcareous algae reported are insufficiently well-preserved for specific identification and, hence, are of no value for dating. Palynological studies have yielded nothing of stratigraphic value. However, a catagraph (?) Nubecularites antis Zhuravleva, which in Siberia has been assigned to the latest Precambrian-earliest Cambrian, has been found in the Khufai Formation. The oldest sediments of the Haima Group, which

unconformably overlie beds of the Huqf Group, have been dated as Late Cambrian to Early Ordovician; consequently, the top of the Huqf Group may lie somewhere in the Early to early Late Cambrian. An absence of critical fauna can be attributed to the unfavorable hypersaline environment. This time interval also must include time for the erosion associated with the unconformity. If the Ara Salt can be correlated with the Hormuz Series of Iran, where there are some radiometric and paleontological data, then the top may reach into the early Middle Cambrian. A second

75

Sedimentary Basins and Petroleum Geology of the Middle East lithological parallel lies in the existence of glaciogenic diamictites in the Mistal Formation in the core of the Oman Mountains, a formation that has been equated to the Abu Mahara Formation (Fig. 3.2). In the latter formation, the presence of diamictites also has been reported in well Ghadir Manqil-1 of southern Oman. Such glaciogenic sediments commonly have been reported in Late Proterozoic sediments to the extent that Harland (1971) proposed that their presence might be used to define the Cambrian-Precambrian boundary.

COMPARISON OF THE HUQF GROUP WITH OTHER OUTCROPS IN OMAN As might be anticipated, the lithological similarities of the Huqf Group are closest to the outcrops in nearby regions. Two main regions of outcrop in the Oman Mountains and the sequence found in the Jebel Akhdar show the closest resemblances, shown in Figs. 3.2 and 3.3. The formations in the Jebel Akhdar area show such close similarities to the Huqf Succession that basically the same descriptions may be used. Glennie et al. (1974) equated the Mistal Formation in part with the Abu Mahrah Formation. The Hajir Formation was equated with the Khufai, the Mi'aidin Formation with the Shuram and the Kharus Formation with the Buah. In the Saih Hatat area of the Oman Mountains, the Kharus Formation equivalent is called the Hijam Formation. Correlations cannot be readily made with the Ghaba and Fahud salt basins, which have been little penetrated because of their depth. Nevertheless, penetration of surface salt and data from well Fahud-1 suggests that the evaporite sequences are similar to those in the South Oman-Ghaba salt basins. Mistal Formation. The formation, about 1,000 m (3,280 ft) thick, consists mostly of diamictite, with exotic elements in laminated sandstone and shale. The formation is widely distributed in Jebel Akhdar, where Glennie et al. (1974) divided it into three units. The lower unit, about 200-300 m (656-984 ft) thick, is composed of unsorted, argillaceous, silty, sandy conglomerate ranging from granules to small boulders. The pebbles are of shale, siltstone, schist, phyllite and granite. The middle unit consists of about 600 m (1,968 ft) of thick-bedded sandstone, with lenses of conglomerate, thin beds of quartz sandstone with subordinate siltstone, shale and platy, laminated limestone. The main sedimentary structures are parallel laminations, ripple marks and clay drapes. The upper unit is about 100 m (328 ft) of thin-bedded, argillaceous sandstone. The conglomerates and sandstone of the Mistal Formation were deposited in tidal-channels, whereas laminated limestone possibly indicates tidal-fiat conditions. The base of the Mistal is not exposed and is conformably overlain by the Hajir Formation or unconformably overlain by the Permian Saiq Formation. Diamictites also are seen in southern Oman in well Ghadir Manqil-1. Thus,

76

it would appear that the volcanics, in which the well drilled in the Khufai Anticline terminated, must lie well within the Abu Mahara Formation above presumed diamictites. In coastal southern Oman, nearly 1,250 m (4,100 ft) of arkosic sandstone are reported directly overlying basement. If they are Mistal Formation equivalents, they must also be in the upper part of the succession, for no diamictites are reported. Hajir Formation. The formation consists of about 100 m (328 ft) of thickly bedded, hard, black, finely crystalline limestone with minor amounts of chlorite and quartz grains and patches of fine-grained dolomite deposited in shallow-marine conditions. The bedding often shows some structures suggesting current-scoured hollows infilled with lithoclastic grainstone. The formation is conformably underlain by the Mistal Formation and overlain by the Mi'aidin Formation. Mi'aidan Formation. The formation crops out in Wadi Mi'aidin, southeast of the Jebel Akhdar area. It consists of about 500 m (1,640 ft) of a monotonous succession of green, red and gray, thinly bedded, laminated and slightly micaceous siltstone and shale, with fine-grained sandstone and subordinate, thin, recrystallized limestone. It overlies the Hajir Formation and, locally, the Mistal Formation with a sharp but concordant contact and is overlain conformably by the Kharus Formation. Both the Kharus and Mi'aidin formations are unconformably overlain by the Permian Saiq Formation (Glennie et al., 1974). The Mi'aidin Formation tentatively is considered to be a lateral facies change from the Amdeh Formation. Kharus Formation. This formation also occurs in the Jebel Akhdar area and is about 180 m (590 ft) thick. The lower 30 m (98 ft) is thinly bedded, laminated and partly recrystallized mudstone with detrital quartz. It is overlain by about 150 m (492 ft) of massive, yellow-brown, finegrained dolomites with nodular chert at the top. The dolomite is laminated and locally preserved with silicified stromatolites. The formation was deposited in a tidal-fiat environment and is tentatively correlated with the Hijam Formation. In the type area, it overlies the Mi'aidin Formarion with an abrupt contact. The Kharus Formation is unconformably overlain by the beds of the Ordovician Amdeh Formation and may represent the carbonate edge bounding the Ghaba Basin, just as it was suggested that the uppermost beds of the Buah Formation may be the lateral equivalent of part of the Ara Salt Formation. l-lijam Formation. The formation ranges in thickness from 150 to 200 m (492-656 ft) of massive, yellow-brown, fine-grained dolomite of shallow-marine origin. It tentatively is correlated with the Kharus Formation of Jebel Akhdar. The outcrop in Saih Hatat and Hijam normally overlies the quartzite of the Amdeh Formation. The upper surface is truncated either by a thrust plane with quartzite of the Amdeh Formation above or by the Permian Saiq Formation (Glennie et al., 1974).

Infracambrian of the Middle East C O M P A R I S O N OF OMAN W I T H O T H E R OUTCROPS IN THE MIDDLE EAST Although no direct link has been established, there is a strong supposition that the Buah-Ara carbonate-evaporite sequence of Oman is continuous with the better-known Hormuz salt in the Northern and Southern Gulf Salt basins. In the Arabian Gulf, the Qatar-South Fars Arch may play much the same role in separating the Northern and Southern Gulf Salt basins, as the central Oman High separates the Ghaba-South Oman Salt Basin from the Fahud Basin to the north. Continuity is suggested with the late Precambrian carbonate platform of central Iran, which may be the lateral equivalent of the Hormuz Series and at least part of the Huqf Group. The Kerman salt occurs on the eastern side of this carbonate platform. The presence of the Infracambrian Hormuz evaporites in the Arabian Gulf region is known through the occurrence of salt domes attributed to halokinetic movements. Blanford (1872) introduced the name Hormuz Salt Formation for the complex salt and associated sedimentary and igneous rocks that crop out on Hormuz Island in the Arabian Gulf. Subsequently, Pilgrim (1908) applied the term to all salt-plug material of all the salt domes in southern Iran and the Arabian Gulf Islands. St6cklin (1986) proposed using the name Hormuz Complex, a term that conforms to modern nomenclatural rules (Hedberg, 1976,

cited in Stticklin, 1986). Murris (1980) described the distribution of salt domes in four separate basins: the South Oman-Ghaba, Fahud and Southern and Northern Gulf, based upon subsurface data (Fig. 3.1). There are abundant local structures attributable to salt tectonism, including linear, salt-cored ridges, shallow piercement domes and low-relief pillow structures. Kent (1970) described the Hormuz evaporites as a repetition of cycles of halite-gypsum-colored shale and dark dolomites; whereas Wolfart (1981) regarded the evaporites of the Hormuz Formation as consisting principally of halite and gypsum with interbedded, fetid, black, laminated limestone and brown, cherty dolomites, within which some red sandstone, variegated shale and a variety of igneous rocks are intercalated. In Iran, the Hormuz Series rocks grade laterally into the gypsum-beating dolomites, limestone, chert and silty shale of the Soltanieh Formation and were deposited on the carbonate platform separating the evaporite basin from the open sea (Zharkov, 1984). C o m p a r i s o n with the R e p u b l i c of Y e m e n

Continuing southwest from southern Oman, an Infracambrian sequence is found in southeastern Yemen in the Hadhramout, west of Mukalla. It is unmetamorphosed or

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Sedimentary Basins and Petroleum Geology of the Middle East virtually unmetamorphosed. Beydoun (1964, 1966) recognized and briefly described four relatively unfossiliferous formations collectively referred to as the Ghabar Group (Figs. 3.2 and 3.11). They crop out in two main areas" the Wadi Ghabar and Minhamir. Although lithological and thickness changes are seen between the two main areas of outcrop, they bear some similarities to the Huqf Succession in Oman, and correlation is based on lithological arguments (Gorin et al., 1982). Although no equivalent of the Ara evaporite sequence is seen, gypsum is reported in the uppermost, Harut Formation, providing some indication of arid conditions, and the four formations of Beydoun show the same alternation of clastic and carbonate sequences. Acidic and basic rocks intruding the rocks of the Ghabar Group have been dated 590!-_50 Ma, supporting the correlation with the Huqf Group. The most reasonable parallels with the Huqf Group are to equate the Shabb with the Khufai, and the Harut with the Buah, suggesting that a more detailed examination should reveal the presence of stromatolites. The base of the Minhamir Formation rests on a peneplaned, crystalline basement. The formation, which reaches a thickness of 143 m (469 ft), consists of tuffaceous, limey, conglomeratic sandstone, lithic tufts and tuffaceous mudstone containing a variety of lava pebbles, mostly of intermediate character with rare metamorphic and chert pebbles probably of fluvial origin (Greenwood and Bleakley, 1967; Beydoun and Greenwood, 1968). The Shabb Formation (Fig. 3.11), which conformably overlies the Minhamir, is made up of mainly thin-bedded, occasionally sandy limestone, with some chert bands and gypsum occurring parallel to bedding. Sand forms are an increasingly important component in the upper part of the formation. The thickness diminishes from 43 rn (141 ft) in Wadi Ghabar to only 13 m (43 ft) in Wadi Minhamir. Deposition appears to have occurred in a restricted environment, with conditions verging on an evaporitic setting (Beydoun, 1966; Beydoun and Greenwood, 1968). The Khabla Formation shows a gradual transition up from the Shabb Formation and consists of 210 m (688 ft) of dolomites, calcareous sandstone, mudstone, calcareous and dolomitic siltstone with some interbedded dolomite, and gypsum suggesting deposition in a shallow-marine, slightly restricted environment. The Harut Formation also shows a transitional passage up from the underlying Khabla beds. In Wadi Ghabar, it consists of 31 m (102 ft) of well-bedded, sandy dolomites; massive, calcareous quartzites; some platey, shale beds; impure dolomite; and fairly pure limestone. It is somewhat thicker (48 m, or 157 ft) in Wadi Minhamir, where it consists of gypsiferous, sandy and silty limestone. The sand grains within the carbonates are rounded, suggesting the existence of a shallow-marine restricted in arid environment (Beydoun, 1966). In the southern part of the former South Yemen, two metamorphic groups, the Garish and Thaniya groups, 78

appeared correlatable with the Ghabar Group. The first, the Garish Group, found in southwestern South Yemen, consists of a sedimentary sequence of rocks that have undergone metamorphism to an albite-epidote-amphibolite grade, with the grade of metamorphism increasing toward the west (Beydoun, 1964, 1966). The second, the Thaniya Group, crops out in western South Yemen, with the protoliths, sandstone, siltstone, shale and limestone metamorphosed to an albite-epidote-hornblende facies (Beydoun, 1964, 1966).

Comparison with the United Arab Emirates Rocks of the Hormuz Series are the oldest rocks known in the United Arab Emirates (U.A.E.). Exposures in a number of islands such as Das, Dalma, Qarnain, Zirkouh, Arzanah, Sir Bani Yas, Dayina, Sir Abu Nu'air, Tunb, Nabiyu Tunb and Abu Musa, as well as exposures in the Jebel Dhanna Peninsula, reveal them to be a varied suite of shale, dolomites and volcanics in addition to the evaporite members and divisible into four main groups: evaporites, sedimentary rocks, pyroclastics and intrusive igneous rocks (Fig. 3.12). The evaporites consist of a massive, crystalline rock salt with soft, gypsiferous horizons. Massive-bedded, crystalline gypsum with relict anhydrite crystals of varying color predominate. Due to solution, there are numerous deep sink holes and collapse structures. Dolomitic limestone and fetid dolomites with thin, sandymarly beds form the main sedimentary components and commonly are seen as massive blocks. Fine-grained and massive sandstone and siltstone with micaceous, massive, sandy and silty beds also are found. The pyroclastic rocks predominantly are crystal tufts with quartz, feldspar and hydrobiotite phenocrysts. The lithic tufts also contain fragments of acid extrusives. In the offshore islands, fragments of extrusive rocks are common, and although porphyritic rhyolites are the principal type represented by devitrified glass, porphyritic dolerite with orthoclase, carbonatized trachyte and amygdaloidal lava also occurs.

Comparison with Saudi Arabia The sequences described to this point show a considerable degree of similarity. Differences appear when the succession in Saudi Arabia is examined; in any case, the section there appears to be less complete. The earliest descriptions of the Infracambrian are found in the works of Karpoff (1957, 1960), who defined the rocks as the Wadi Fatima Series from the locality of the same name. These rocks can be shown to overlie the more highly metamorphosed, volcanic tufts, breccias and conglomerates assigned to the Medina Series. More modern radiometric and geochemical work of the USGS and groups from Britain has shown now that the older series represents the rocks that were swept up as a series of island arcs in the consolidation of the Arabian Shield (Darbyshire et al.,

Infracambrian of the Middle East

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some of the dolomites, evidence of oolite texture is not obliterated entirely. Where silicification preserved the structures, both spheroidal and columnar, laminated structures are seen. There also is evidence for the preservation of hardgrounds within the succession and of erosional features due to wave action. Intercalated in the carbonates are sand wedges that show evidence of low-angle, planar cross-bedding and graded bedding. Thus, both bed-load and suspension-load transport occurred during deposition. The overlying volcanic series provides evidence of subaerial eruption associated with fluvial and lacustrine deposition. The fossil biota suggest that deposition occurred in a shallow, subtidal environment, probably in tropical to subtropical conditions. Water-energy conditions were sufficiently high to encourage the development of oolitic shoals at times; at other times, conditions were conducive to the development of algal mats. The clastic sediments, varicolored sandstone and siltstone are interpreted as marine, clastic wedges consistent with the presence of annelid burrows. The recognition of fragmentary archaeocyathids and of the stromatolite Conophyton provides evidence on which an Early Cambrian age may be assigned to the Middle Fatima Formation. The recognition of Skolithos in the cherty dolomites interbedded with red siltstone in a sequence 90-130 m (295-426 ft) thick provides support. Unfortunately, no such detailed, lithological analysis has been carried out on the underlying Lower Fatima Formarion, which consists of 10-50 m (33-164 ft) of sand-

79

Sedimentary Basins and Petroleum Geology of the Middle East stone, siltstone, shale, pyroclastics and a basal conglomerate, nor of the 500 m (1,640 ft) of the Upper Fatima Formation made up of reddish siltstone and volcanic rocks. The volcanic rocks indicate subaerial eruption and are associated with clastic sediments interpreted as fluvial and lacustrine deposits, with some dolomites regarded as formed in a hypersaline, subtidal environment. The Fatima Group (Fatima Series of Karpoff) has alternative nomenclatures. Brown and Jackson (1960), based upon outcrops in southwestern Saudi Arabia near the northwestern Yemen border, separated it into the Abla Formation, equivalent to the Fatima Formation, overlain by the Shammar Formation (Fig. 3.2). The Abla Formation, as described by Brown and Jackson (1960, 1979), consists of about 500 m (1,640 ft) of a basal conglomerate grading up into arkose, graywacke and stromatolitic limestone or marble. This sequence contains flows and andesitic, dacitic and minor basaltic tufts and is cut by sills. The rocks rest disconformably on older schist and granite. The Shammar Formation was described by Brown and Jackson (1960, 1979) and consists of more than 2,000 m (6,560 ft) of unmetamorphosed rhyolite, dacite and andesite flows, which may be amygdaloidal and porphyritic, associated with agglomerate and tuff. The sequence also contains thinly bedded, cherty, dolomitic limestone, conglomerates and graywackes. These rhyolite agglomerates may be contemporaneous with the rhyolitic granitic intrusives, which seem to have supplied the mineralization at Mahad Dahab. In general, the interpretation of these beds as a cratonic, rather than a geosynclinal, series, as Karpoff suggested, has been borne out by the work of Basahel et al. (1984), although there are differences in detail. Schmidt et al. (1983) named rocks equivalent to the Abla and Shammar formations in the Arabian Shield of Saudi Arabia as the Jubaylah Group. Comparison with Oman and southeastern Yemen, as mentioned above, has to be based on the age and lithology of the carbonate horizon, which reasonably

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The Infracambrian Huqf rocks have been compared to the rocks of the Saramuj Formation (which takes its name from the locality in Wadi Saramuj) of Jordan. In western Jordan, small outcrops of the Late Proterozoic Saramuj Conglomerate and Slate Graywacke Series rest unconformably upon plutonic rocks. The conglomerate, which is between 60 and 70 m (197-230 ft) thick, consists of epimetamorphic to non-metamorphic, well-rounded, crystalline boulders, predominantly from an alkali-granite, quartz-dolerite, quartz porphyry, porphyry, porphyritic gneiss and quartzite source rocks, in an arkosic matrix. There are a number of fine- to coarse-grained, arkosic interbeds. Above the conglomerate, there follows a slate and graywacke sequence, which may total over 200 m (656 ft) of alternating, gray-green to red-brown, dense, siliceous or sandy shale alternating with sub-graywackes. There are many quartz, porphyry sills up to 30 m (99 ft) thick, as well as dikes and plugs of quartz porphyry and porphyrite that intrude the Slate Graywacke Series. In the south of Gharandal on the northern slope of Jebel az Ziblijje, Mitchell (1955) described a thickness of about 500 m (1,640 ft) of the Saramuj Series resting with clear discordance upon older Precambrian rocks, but separated from them by about 2 m (6.6 ft) of strongly altered and fractured rocks containing fragments of the older formations. Sandstone and arkose are more common in these outcrops of the Saramuj than elsewhere, and thin bands (0.5 m) of stromatolites also occur. The beds, which show numerous overthrusts and decollement, are considered a typical orogenic molasse. In the subsurface of eastern Jordan, the Aqaba Basement Complex (Precambrian)(Fig. 3.13), penetrated in A1 Jafr-1 (20.1 m, 66 ft) and Safra-1 (32 m, 105 ft), is com-

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Fig. 3.13. Surface-subsurface section of Precambrian to early Cambrian (?) rocks in Jordan (based on Powell, 1989a).

80

Infracambrian of the Middle East posed of coarsely crystalline granite at the base, followed by granite wash and sandstone. The granite gives an age of 585+6 Ma (Andrews, 1991) and can be correlated in part with the Arab Complex (630-570 Ma) in southwestern and western Jordan. The Saramuj Formation, in subsurface, has a limited distribution (Fig. 3.13); it is found in wells Northern Highland-1 (79 m, 259 ft) and Safra-1 (420 m, 1,378 ft) and consists of reddish-brown and purple conglomerate, with pebbles and boulders of granitic and metamorphic composition set in a matrix of fine to coarse, angular, arkosic sandstone with beds of shale (Bender, 1974; Andrews, 1991). The top and bottom contacts of the Saramuj Formation are unconformable with the Salib Formation (arkosic sandstone) above and the crystalline basement complex (Aqaba) below (Fig. 3.2). The Saramuj was deposited in an isolated half-graben as a braided, alluvial-fan system in a rapidly subsiding, fault-controlled basin (Powell, 1988; Andrews, 1991).

Comparison with Southeast Turkey The only known, Late Proterozoic, unmetamorphosed, volcanic and sedimentary rocks occur in southeastern Turkey in a single outcrop west of Derik and are reported in a few wells drilled in that area (Ala and Moss, 1979). The total late Precambrian thickness of about 2,300 m (7,544 ft) is divided into 2,000 m (6,560 ft) of andesites, spilites, breccias and tufts, with some intercalated, red sandstone and shale, and is assigned to the Derik Formation, followed conformably by 300 m (984 ft) of polygenetic conglomerates, sandstone and redbeds grouped as the Sadan Formation (Fig. 3.2). The base of the Derik-Sadan sequence is not seen. The age of the Sadan Formation is conventionally considered to be Early Cambrian or Infracambrian (Rigo and Cortesini, 1964).

Comparison with Iraq There are no surface outcrops of Late Proterozoic rocks in Iraq, nor have they yet been recorded, even in the deep wells. Based upon geophysical data, principally gravimetric, the presence of Hormuz Salt equivalents is inferred in eastern and southeastern Iraq, with their distribution controlled by older Precambrian basement faults with trends assumed to be north-south to northwest-southeast. However, the conclusions are somewhat controversial (St6cklin, 1968b; Dunnington, 1958; Powers et al., 1966).

Comparison with lran There exists a thick suite of Infracambrian rocks in Iran that can be found in most parts of the country. The stratigraphic relationships are complex, but two groups of rocks are recognized and described by St6cklin (1986). An upper unit rests disconformably on a very thick series of

green slates and arkosic sandstone (Kahar Formation in northern Iran) or unconformably upon tightly folded clastics of the Morad Series, which form the lower unit in the Kerman area (Fig. 3.2). They may rest on crystalline "Assyntic" basement in eastern Iran. The lower, clastic sequence goes by different names in different areas. The upper unit is a carbonate, generally dolomitic sequence to which the names Soltanieh Dolomite and Barut Formation have been assigned in North and central Iran (Alborz Range and Tabas area). The lowermost unit of the Infracambrian sedimentary cycle is called the Kahar Formation in the central Alborz Mountains and central Iran (north of Isfahan), and the Morad Series in southeastern Iran (in the region of Kerman and Sagand). In the type area of the Kahar Formation, northwest of Tehran, a thickness of 1,600 m (5,248 ft) is unconformably overlain by about 450 m (1,476 ft) of the Bayandor Formation, which crops out near Zenjan farther to the northwest, according to St6cklin (1986). The Morad Series in the Kerman District in southwestern Iran, which totals more than 1,000 m (3,280 ft) northwest of Zarand and is equivalent to the Kahar (Fig. 3.14), is overlain by the sandstone, dolomites and volcanic rocks of the Rizu Series, which passes laterally (eastwards) into the saline Desu Complex exposed in a number of Hormuz-type, highly tectonized, diapiric structures. The Desu Complex is considered to be the equivalent of the Bayandor through Zaigun sequence of northern Iran, where dolomite appears to have replaced the evaporites to a greater or lesser extent. In northwestern Iran, the 2,500 m (8,200 ft) thick succession comprises the clastic Bayandor Formation, in which there are shale and some stromatolitic dolomites; the Soltanieh Dolomite, a cherty and stromatolitic dolomite with the Chapoghlu shale in the lower third; the Barut Formation, of clastics with regular intercalated dolomites; followed by the Zaigun shale, siltstone and sandstone that show an upward passage to the Cambrian Lalun Sandstone. This sequence of lithologies is surprisingly persistent in the Alborz Mountains and most of central Iran. Descriptions of the older successions, the Kahar and Morad, can be generalized; they both are arkosic and quartzose and sometimes micaceous sandstone and quartzites. The finer-grained lithologies, often green or red in color, are interbedded with variegated, argillaceous shale and tuffaceous beds. At the top, the intercalation of black, siliceous shale containing radiolaria indicates deep, openmarine deposition (St6cklin, 1972; Gansser, 1955). The Morad Series is overlain with pronounced unconformity by a clastic of the Rizu Series. St6cklin et al. (1965) and St6cklin (1972) concluded that the Kahar Formation (Precambrian) is the oldest non-metamorphic formation in northern Iran. It is known in the central and western Alborz, the Soltanieh Mountains and southern Azerbaijan. It is formed of about 1,600 m (5,248 ft) of argillaceoussericitic to sandy, micaceous, slaty shale with subordinate intercalations of quartzitic sandstone, dolomite, limestone 81

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82

with the Chinese Precambrian-Cambrian boundary section is reported by Brasier (1989). St6cklin (1986) gave a full discussion of the stratigraphic and age relations of these Precambrian rocks and placed the lower unit in the Riphean and the upper in the Vendian (Fig. 3.14); however, on balance, the evidence suggests that at least part of the Soltanieh Dolomite may lie within the Early Cambrian. The Rizu Series (Vendian) in southeastern Iran, a nonsaline, non-diapiric equivalent of the Desu Complex (Fig. 3.14), does not lend itself to the usual tripartite division. For more than 12 m (40 ft) of a brecciated, conglomeratic base, there are about 100 m (328 ft) of variegated, micaceous shale, sandy dolomite and sandstone followed by about 500 m (1,640 ft) of tufts, tuff-breccias, sandstone, dolomites and cherty beds. The sequence is capped by 150-200 m (492-656 ft) of quartz-porphyritic lava and tuff. In the Alborz region and Tabas area, the dolomites are capped by a clastic succession separated into a lower Barut Formation and an upper Zaigun Formation; equivalents of these two units in the Kerman area seem to form some of the block material in the Desu diapirs. The type area of the Barut Formation lies 18 km (11.3 mi) southwest of Zenjan in northwestern Iran, where it measures 714 m (2,342 ft) of purple, argillaceous to silty or fine, sandy, micaceous shale with thin beds of dolomite that often contain chert. In general lithology, the beds of the formation differ from the lower Kahar and Bayandor formations, principally in the higher percentage of carbonates and the presence of limestone absent in the older for-

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SLATES AND SANDSTONES Fig. 3.15. Lithostratigraphic section of the Soltanieh Formation of the Alburz Mountains, northern Iran (based on data from Brasier, 1989; Zhiwen et al., 1989). mations. The presence of stromatolites has been recorded in some of the dolomites. The type area of the Zaigun Formation lies 35 km (22 mi) northeast of Tehran, where dark, wine-red, silty and micaceous shale with some cross-bedded sandstone in the lower part of a 450 m (1,474 ft) thick sequence crop out. The sequence thins to the northwest and is absent in parts of the Zenjan area because of pre-Lalun erosion (St6cklin et al., 1964). The age of the Barut and Zaigun formations cannot be determined accurately, and the upper age limit basically is set by the occurrence of fossils within the overlying Lalun Formation, indicating an Early Cambrian age. North of Kerman in southwestern Iran, the Infracambrian deposits pass laterally into a diapiric, evaporite formation, the Desu Complex, which correlates, in part at least, with the Hormuz Salt Formation of southern Iran and eastern Arabia (and with the Punjab Saline Series of Pakistan). In outcrop, it consists of a chaotic succession of irregularly distributed and deformed dolomites and gypsum, with some black limestone and thinly bedded, micaceous sandstone and siltstone intercalated with acid, intermediate and basic intrusive rocks. The Infracambrian rocks are spread over a wide area and appear, at least partly, to be coeval with some younger

granite intrusions around 600 Ma (cf. Schmidt et al., 1978; Davoudzadeh et al., 1986). The volcanic rocks found in the Garadash Formation, the Taknur Formation, the RizuDesu Series and the Hormuz Formation all appear to be partly equivalent in age to this granite, the Doran Granite. The age data are all consistent with an end of Precambrian to Early Cambrian age, yet without the possibility of accurately locating the boundary between the two. The sediments of the Hormuz, Rizu and Desu formations were laid down in subsiding basins in which laminated dolomites, evaporites and occasional iron sulfides accumulated. These areas were bounded in central and northwestern Iran by carbonate shelves, which in turn interfinger northward with more clastic sequences that include the older sediments of the Bayandor, as well as those of the younger Soltanieh and Barut formations. The red siltstone and shale of the Zaigun Formation in northern, central and southwestern Iran mark the terminal, regressive phase of the Infracambrian and indicate partly subaerial, arid conditions. Evidence from the northwestern part of Iran suggests the presence of an erosional unconformity above the Zaigun Formation, separating the Infracambrian succession from the Lalun Formation, which forms the basal member of the SauL sequence in Iran. The succession in Iran provides a clear parallel with

83

Sedimentary Basins and Petroleum Geology of the Middle East the Infracambrian found in Oman, despite the differences in the stratigraphy recorded. In both areas, there is a repetition of the clastic-carbonate succession, and both end with the deposition of evaporites. The Abu Mahara Formation of the Huqf Group parallels the Kahar, Bayandor and Morad of Iran; while the threefold division of the Soltanieh Formation, into lower and upper dolomites separated by the Chapoghlu Shale, matches the Khufai, Shuram and Buah formations of the Huqf Group. The Ara salt then may be paralleled with the Barut Formation. There does not appear to be an Oman equivalent to the Zaigun Formation of Iran, which completes the Infracambrian succession and fills most of the time interval prior to the commencement of the Sauk sequence in the Middle East.

P A L E O G E O G R A P H Y AND G E O L O G I C HISTORY OF THE INFRACAMBRIAN Radiometric data indicate that magmafic and metamorphic activity did not end with the Precambrian, but continued well into the Cambrian. Thus, there is no doubt that the unmetamorphosed, sedimentary sequences assigned to the Infracambrian and now known to continue into the Cambrian are contemporaneous with the final phase of the Pan-African event. It is, therefore, possible to derive a structural model consistent with the established sedimentological data and incorporate this in a paleogeographical scheme. One outcome of this is that it puts relatively strict time constraints on the upper age limit of the so-called infra-Tassilian surface. This surface, first defined by the French in Algeria, is known widely across the northern margin of the African Shield, but generally can be dated only within fairly broad limits (Beuf et al., 1971). With their recognition of the Najd Shear Fault System, which can be dated from 630 to 550 Ma, Stoesser and Camp (1985) provide a key to the tectonic model. Moore (1979) shows that this shear fault system is a plexus of NW-SE-trending faults forming a belt as much as 300 km (187.5 mi) wide. Contemporaneous, volcanic activity is found both in Saudi Arabia (Shammar Volcanics of Brown and Jackson, 1960) and in Egypt (Dokhan Volcanics; Stern et al., 1984). Stern et al. (1984) make a connection between the development of sedimentary basins and the Najd Fault. They report on the abundance of northeasttrending dikes, the abundant volcanics, and the sedimentary basins that all have the same trend. The sediments are derived from and deposited in block-faulted domains and indicate a crustal, tensional (extensional) phase directed northwest-southeast. Taking this one step further, Husseini (1988) suggested extension on the northeastern side of the Najd Fault System to account for the Infracambrian salt basins of Oman. In the description of the Huqf Group rocks of Oman that formed in this extensional trough, Gorin et al. (1982) reported that the Huqf Axis was a major structural element that faulted down into the Masirah Trough to the east in

84

the late Precambrian, explaining the rapid, eastward thickening of the Abu Mahara Formation and its gentle, westerly dip under the Ghaba Salt Basin of Oman. The general absence of coarse clastics and unconformities in the Huqf Group suggests that movements on the axis were mild and that there was no high relief or a relatively distant source area for the sediments. However, the Huqf Group clearly is made up of fining-upward, sedimentary cycles, which suggest at least two phases of movement. Following the deposition of the Huqf sediments, there was a further phase of movement, for the unconformable base of the Haima Group clastics in places cuts down to the Khufai Formation. The central Oman Platform to the west may have acted as the platform edge to the GhabaSouth Oman Salt Basin, and Gorin et al. (1982) have suggested a possible lithofacies change to support the hypothesis. In the South Oman Salt Basin, the western edge is marked by the Ghudun-Khasfah Fault, but its northern continuation to the Ghaba Salt Basin is shown by Gorin et al. (1982) as an anticlinal axis pitching northward (Fig. 2.23). There is no information available to discuss the tectonic setting of the Fahud Salt Basin. The available descriptions of semi-grabens indicated previously, however, are consistent with the hypothesis of Husseini (1988). To explain the Hormuz salts and their links to the Oman salt basins, it may be necessary to suggest that the Zagros Zone of Husseini be more akin to the Najd Zone in terms of width and permit a link up through the zone. In this model, the Dibba line is given a much greater age than normally is the case. This can be fitted to the overall paleogeographic picture of the region during the earliest phase of the Cambrian (Fig. 3.16). A general, marine realm seems to have extended from Libya to Jordan, but the presence of a stromatolitic, archaeocyathid-bearing limestone in southwestern Sinai at Abu Durba (Omara, 1972) and the discovery of a similar fauna in the Middle Fatima Formation in Saudi Arabia (Basahel et al., 1984), plus the occurrence of cherty limestone in the Jubaylah Formation (the age equivalent of the Fatima Formation), show the penetration southward of an arm of this sea, presumably along the line of the Najd Fault System. The Fatima Formation does not appear to extend farther to the east, where continental clastics are presumed to have replaced it. G0rin et al. (1982) suggest that most of Arabia may have formed a carbonate platform; but, due to erosional removal from the shield area and non-exposure, this is hard to prove, and there might equally have been an area of subaerial outcrop equivalent to the central Arabian Shelf. Based upon paleomagnetic evidence, Morel and Irving (1978) suggest that during the Early Cambrian, the Arabian Platform formed part of the southern margin of Gondwana, lying at a latitude of about 40~ The widespread occurrence of evaporites and carbonates during the late Precambrian to early Middle Cambrian in the Middle East, covering an area of 4,000 km (2,500 mi) by 2,000 km

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at Abu Durba in Egypt. Other analogous, shear-fault systems are presumed to have existed along, or close to, the suture between the Arabian Shield and Platform, which was present as a distinct trough during the early Paleozoic and along the line of the present Arabian Gulf. The Arabian Gulf hosted a sea with restricted ingress, in which the Hormuz salts were deposited. This sea linked with the Ara Salt Sea in southern Oman and with the Salt Range Basin of Pakistan, connections that have been suggested by a number of authors. The Hormuz Sea may have spread over the Arabian Platform in a manner analogous to the spread of the Triassic Sea over Algeria, and Bou Rabee (1986) in a thesis has suggested the existence of Hormuz salts in Kuwait in her interpretation of the geophysical data. They also underlie most of the southern Iraq oil fields and crop out in a small inlier in Jebel Sanam in southern Iraq. The Infracambrian salts have exerted a major influence on structure throughout the Phanerozoic, but each basin has its own tectonic style. In Oman, salt movements in the basins have resulted in the formation of local structures that have produced hydrocarbons. Edgell (1992) has

85

Sedimentary Basins and Petroleum Geology of the Middle East emphasized the potential role of Proterozoic sedimentary rocks as source rocks charging late Paleozoic reservoirs in the Arabian Gulf region. As a general mechanism, however, this must be qualified given the distinctive geochemical fingerprint of the Proterozoic oil (see Chapter 13). In the southern Arabian Gulf, several islands are the result of salt diapirism, and shallow, piercement structures have been detected in seismic surveys in offshore Qatar and the U.A.E. In many of the Iranian coastal islands and on the adjacent mainland, salt extrusion has been observed. In the northern Arabian Gulf, many large, elon-

86

gate salt pillows and salt swells have been documented in the oil fields of Qatar (Dukhan), Bahrain (Awali) and southern Iraq (Rumaitha). In Kuwait, the Burgan Structure occurs where halokinetic movement was associated with the presence of a basement horst. All the coastal Saudi Arabian oil fields display a circular shape associated with Infracambrian salt-cored structures (Alsharhan and Kendall, 1986). In the area east of the present Arabian Sea, an extensive land mass existed. The fine-grained nature of the sediments in the South Oman Trough suggests that it may have been a low-lying extension of the Mozambique Belt.

Chapter 4 THE EARLY PALEOZOIC QUIESCENT PHASE IN THE MIDDLE EAST: THE SAUK CYCLE AND THE EARLY PART OF THE TIPPECANOE CYCLE

Laboun, 1989; Berberian and King, 1981). The major stratigraphic breaks, which are identified over most of the basin and separated into three mega-depositional cycles (Fig. 4.2), are attributed to a series of tectonic pulses pre-, syn- and post-Hercynian (A1 Laboun, 1989). The first major stratigraphic break is the pre-Late Devonian unconformity, which is related to the early phase of the tectonic movements. The second break is the pre-Late Carboniferous unconformity, which is more pronounced as it corresponds to the maximum phase of the movements. The pre-Hercynian mega-depositional cycle has a

INTRODUCTION The most complete section of Paleozoic rocks is exposed in a great, thin, arcuate belt around the eastern flank of the Arabian Shield (Fig. 4.1). The rocks also are exposed in small, widely scattered inliers in the intensely folded and thrust faulted regions of the Taurus-ZagrosOman Fold Belt. During the Paleozoic, the Middle East went through a series of epeirogenic movements, which resulted in regional structural developments and caused a pronounced stratigraphic break (Husseini, 1988; A1

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400 Km

Fig. 4.1. Generalized Paleozoic sediment outcrop and isopach map of the Middle East (contour interval in thousands of feet) based on data from Wilson and Peterson (1986) and A1Laboun (1990). Outcrop areas outside Saudi Arabia are numbered 1-16 as follows: Oman: l=Haushi, 2=Jebel Jalan, 3=Saih Hatat; Iran: 4=Kuh-e Faraghan, 5=Kuh-e Gahkum, 6=Kuh-e Surmah, 7=Khareh Kat, 8=Kuh-e Dinar, 9=Kuh-e Gereh, 10=Zard Kuh, 1l=Chal-Isheh; Turkey: 12=Hakkari (Zap), 13=Hazro, 14=Derik, 15=Amanus; Syria:16=Jebel Abdulaziz. 87

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 4.2. The mega-depositional cycles and tectonic events of the Paleozoic of Arabia (modified from A1 Laboun, 1990). The global sea-level curve is modified from Vail et al. (1977). threefold division into a Lower Devonian, a SilurianOrdovician and a Cambrian-Ordovician sub-cycle. During the Paleozoic, the Middle East behaved as a relatively stable, passive, continental margin over which terrestrial and shallow-marine sediments accumulated. The total thickness of the Paleozoic sediments in the Middle East is somewhat speculative, for there are many areas where there is little or no control. The greatest thicknesses exceed 4,688 m (15,377 ft) in southwestern Iran, northeastern Iraq, northern Syria and southeastern Turkey, and more than 6,250 m (20,500 ft) in Oman. Fig. 4.1 shows these very general isopach lines, which ignore thinning against the Summan Platform in central Arabia and, therefore, differ considerably from the more detailed isopach maps of the lower Paleozoic in the Tabuk and Widyan basins in northern and northwestern Arabia presented by A1 Laboun (1986). The early Paleozoic of the Middle East was a period of gentle, epeirogenic movement of large and generally rigid crustal units. Widespread transgressions and regressions crossed a shallow, epicontinental shelf mantled with clastic sediments thickening to the north and east. A number of

88

broad basins are recognized, but their detailed history is insufficiently well-known to be able to determine whether there was differential movement of the arches that separate them. Outcrops are seen in the south against the Arabian Shield, and again in southern Jordan and northern Saudi Arabia, but disappear below younger cover to the north and east.Although no lower Paleozoic rocks crop out in Syria, they have been found in subcrop. A more complete section is exposed in southeastern Turkey, where it has been brought to the surface as a result of subsequent tectonic movements. In the Arabian Gulf, lower Paleozoic rocks, if present, are at too great a depth to be penetrated by drilling, except over structural highs. However, they appear at the surface in Iran, and there are limited outcrops in Oman, southwestern Saudi Arabia and northern Yemen. During the early Paleozoic, the sedimentary source areas generally lie to the south, while more open-marine conditions existed to the north. Within this sequence, there are marked unconformities and considerable lateral facies changes. The sedimentary breaks are attributed to movements of a number of basement highs that were particularly active during the late Paleozoic and early Mesozoic. Many wells penetrate the Paleozoic succession, and these sediments have, in some places, an important hydrocarbon and source-rock potential. Over the paleohighs and the platform area of southern Yemen, where the Paleozoic has been removed totally or in part, the Mesozoic rocks may rest directly on basement or on different levels of the Paleozoic. Evidence of Caledonian deformation is totally lacking, but the times at which deformation occurred elsewhere may be represented by times of sea-level change. The evidence of Late Ordovician glaciation is more complete than that found in North Africa, thereby providing a better understanding of the details of that glaciation. The Silurian shale development, the Qusaiba Shale Member in Saudi Arabia, is economically important in North Africa and Arabia and seems to have played the role of a major source-rock horizon (Mahmoud et al., 1992). The isopach maps of A1 Laboun (1986) show changes in the sediment distribution patterns, with lower Paleozoic beds in northern Saudi Arabia filling the Tabuk Basin, but with later Paleozoic sediments confined to the east of the Ha'il-Rutbah Arch (see Fig. 2.17 and compare 4.16 with 5.10). The effects of the late Paleozoic Hercynian Orogeny in the Middle East are reflected by uplift accompanied by erosion and a diversification of topography, much as in North Africa. This event finally was brought to a close by the deposition of the younger Permian Khuff carbonates during the Permian transgression following the clastic deposits of the Late Carboniferous-Early Permian Unayzah Formation and the Carboniferous (?) (informally called the "Pre-Unayzah Clastics" by A1 Laboun, 1986) found in the Widyan Basin of Arabia. The Paleozoic succession in Iran, the whole of which must be considered as lying on the eastern part of the Arabian Plate at that time, consists of a relatively uniform section, with prevailing continental to epicontinental con-

The Sauk Cycle and the Early Part of the Tippecanoe Cycle ditions as in northern Arabia, reflecting epeirogenic uplift further to the west but having some important lacunae. The area lies at the eastern to northeastern margin of Gondwana, with clear evidence of the existence of marine conditions that have a longer duration than in the rest of the Middle East. (See the paleogeographic maps of the lower Paleozoic in this chapter.) Igneous activity is known in central, northwestern and northeastem Iran; it appears to be restricted to the late Precambrian or possibly to dike intrusion during the early Paleozoic. It was only during the Late Triassic that this part of Iran separated from Gondwana as a single unit or, more probably, as a number of individual fragments, opening Neotethys in its wake. It collided later with Laurasia, closing the Paleotethys. The crustal thinning accompanied by rifting that preceded this Triassic separation cannot be dated accurately. Prior to the Late Permian marine invasion in which the Khuff carbonates (or their equivalents) were deposited, crustal thinning and faulted depressions formed in which clastic sediments accumulated. Palynologically, these are dated as Late Carboniferous to Early Permian. The most extensive exposures of Paleozoic sedimentary rocks are in southern Jordan, east of the Dead Sea, and in northern Saudi Arabia, where they lap onto the edge of the Arabian Shield. Discontinuities are found in outcrop sediments of northern Syria, and also in Turkey in anticlinal structures in the Amanus Mountains in the west, in parts of the Taurus Mountains, over the Mardin High, and in the Hazro and Zap anticlines in the southeastern part of the country. They also are found in northeastern Iraq, and in Iran, where they crop out in the Rezaiyeh-Esfandagheh 13lock. In Oman, Paleozoic rocks occur in the Oman Mountains and in the Huqf area in the central and southern parts of the country, where they have been brought to the surface by tectonic movements. The only major Paleozoic outcrops between the Arabian Shield and the marginal fold belt of western Iraq lie over the Rutbah High, where a thick, late Paleozoic (Permian) clastic sequence is preserved. The three main areas of occurrence of the lower Paleozoic rocks lie in northwestern Saudi Arabia bordering the Arabian Shield, in southwestern and central Saudi Arabia. In the latter area, clastic sediments of the Wajid Formation and its equivalents are exposed in Yemen, Saudi Arabia and Oman, where they follow the Infracambrian with what appears to be a relatively short break. In northern Saudi Arabia, the lower Paleozoic can be traced into Jordan, with the change in facies suggesting an approach to more normal-marine conditions. Elsewhere in the Middle East, the lower Paleozoic rocks have been penetrated in deep wells, as in Syria, Qatar, Oman, Saudi Arabia and in Kuwait, but with a frequency sufficient only to permit the broadest of conclusions concerning their regional development. One major unsolved question concerns the activity of ridges such as the Ha'il-Rutbah Arch. Whereas it is clear that the major N-NW-trending ridges were active during most of the early Paleozoic and up into the Devonian in Algeria (Beuf et al., 1971), there is very little indication that the

same can be recognized in the Middle East. This is more likely to reflect a lack of precise data than a confirmation of the stability of the ridges. Contours on the top of the basement in northern Saudi Arabia indicate that the surface defines a north-plunging arch, which has been suggested as continuous with the Rutbah High in Iraq. The lower Paleozoic rocks wrap around the Ha'il Arch without important thickness or facies changes, according to Powers et al. (1966), from which they concluded that the arch represented a paleogeographic feature that began to be uplifted in the Cretaceous, for Cretaceous rocks transgress unconformably over the Paleozoic rocks of the arch. However, Greenwood (1973) pointed out that pre-Permian erosion has removed progressively more of the Paleozoic section in a southerly direction, so that Permian rocks rest unconformably on crystalline basement south of the central Arabian Arch. Presumably, this involved late Paleozoic epeirogenic uplift with which some tilting, and possibly arching, of the Ha'il Arch may be associated. Structural contours drawn on the top of the Permian rocks seem to be discordant with respect to the lower Paleozoic trends. The alignment of Tertiary volcanics on the Arabian Shield with the Ha'il Arch suggests that they follow a fracture within the shield. As it is discordant with the latest Pan-African trend of the Najd Fault System, it must be presumed to be a younger feature, or at least a feature reactivated after the development of the Najd faults. Consequently, an "a priori" case can be made for activity of the arch on at least three occasions. Parallel to the Ha'il Arch and extending close to the Arabian Shield, the Widyan Basin shows a southerly, prong-like extension between the Arabian Shield and the Summan Platform containing relatively thick lower Paleozoic deposits which must somehow be related to the history of the arch. Although seldom stated, the western margin of the Tabuk Basin may be a similar feature. In its present form, it is closely related to the Cenozoic history of the Dead Sea Transform Fault, a feature active in Late Proterozoic and early Phanerozoic (Cambrian) time. In presenting the geological history of the early Paleozoic of the Middle East, it is convenient to consider the sediments of the Sauk and Tippecanoe sequences together. As a basis for reference, the two principal regions, in Saudi Arabia and Oman, will be used. The basal Sauk Sequence, up to and including the Lower Ordovician, can best be considered in Oman where, as stated earlier, the section is most nearly continuous down into the Infracambrian; however, the top of the section, which belongs to the Tippecanoe Sequence, is more complete and better-known in Saudi Arabia and Jordan. Figs. 4.3 and 4.4 show the lithostratigraphic correlation charts of the Paleozoic era in the Middle East for representative formations described in this chapter, with general lithologies and major unconformities indicated. Table 4.1 represents the lower Paleozoic formations in the Middle East, with general lithologies and environment of deposition indicated.

89

Table 4.1. Early Paleozoic rock units units in the Middle East East. Asterisks indicates outcrop and bullets indicate subsurface.

oO

Country Oman

Age

Unit

Lithology

Haima Group:

•*

Cambrian-E. Silurian

Well-sorted sandstone, shale, minor dolomitic stone. It consists of four formations

a. Karim Formation

**

Early Cambrian

Liihic and quartzose sandstone and Micaceou

b. Haradh Formation **

Early Camberian

Quartzose Sandstone

G~

c.Amin Formation

Early Cambrian

Quaft20se, argillaceous and micaceous sands

G~

M, Cambrian lo E. Ordovican

Micaceous sandstone

•*

d, Mahwjs Formation **

~v O'J

e. Andam Formation **

M. Cambrian to E. Ordovican

Clay St one, sandstone, and marl

f. Ghudan Formation **

M, Ordovican

Micaceous sandstone and siltstone

g, Safiq Formation

*

L. Ordovian to E. Silurian

Quari/ose and argillaceous sandstone, silt and

f~

Ordoviciati? *

PolymicI conglomerate, arlcosic sandstone, si and quartzose sandstone

f~

Murbat Formation

Ordovician

Quartzitic and argillaceous sandstone, siltston with minor dolomite

M, Ordovician?

Shale, siltstone and sandstone

O~

Amdeh Formation

United Arab Emirates

Rann Formation

Saudi Arabia

Yatib Formation

*

g~

G~ O ~===, O 0~ O t~

*

E. Cambrian

Conglomerate and micaceous sandstone ~===i

f~

Wajid Formation

*

Cambro-Ordovjcian

Quatzitic sandstone, silty clay and conglomer

M.Cambrian to E. Ordovician

Lithic arkose, quartzose sandstone, thin mica siltstone, shale and intraclast conglomerate

Tabuk Group:

E. Ordovician to E. Silurian

Shale, micaceous sandstone to siltstone and m conglomerate

a. Hanadir Formation *

E. Ordovician

Shale, mudstone, thin siltstone and sandstone

b. Ordovician sandstone

M, Ordovician

Micaceous sandstone, thin siltstone and shale

* Saq Formation

•*

'*

r

N

O

Table 4.1 continued.

Country

Unit

Age

Lithology

**

L, Ordovician

Shale, thin interbedded sandstone and siltstone

d, Sarah Fonnation

**

E. Silurian

Conglomerate, sandstone and minor shale

e. Qusaiba Formation *

E. Silurian

Graptoliiic shale and siltstone

f. Sharawra Formation

E. Silurian

Micaceous sandstone, siltstone and clay stone

91

Qasim Fonnation

**

Ordovician

Shale, sandstone and minor siltstone

Zarqa Fonnation

'*

L. Ordovician

Tillitc, boulder silty claystoneand sandstone

Sarah Formation

•*

E. Silurian

Tillite and sandstone

Qalibah Formation •* (previously Tayarrat)

E. Silurian

Laminated and micaceous shale, siltstone and sa stone

Qatar

Tabuk Formation

E. to L. Ordovician

Micaceous and arkosic sandstone, stltstone, clay and shale.

Kuwait

Tabuk Formation

E. Ordovican loE. Silurian

Micaceous sandstone, hematitic clay, conglomera minor volcanic rocks

Jordan

Ram Croup:

**

Cambrian-E. Ordovician

Sandstone with minor siltstone and shale

a. Salib Formation

'

E.-M. Cambrian

Arkosic and proto-quartzitic sandstone

b. Umm Ishrin Formation

M.-L. Cambrian

Massive brown weathered sandstone

c. Disi Formation

*

E. Ordovician

Massive white weathered sandstone and siltstone

d. Umm Sahm Formation

*

E. Ordovician

Well-soned sheet sandstone

c, Abu Khusheiba Formation

•

E.-M. Cambrian

Micaceous sandstone, clayey in part

f, Burj Formation

*

E.-M. Cambrian

Micaceous siltstones, shales, and limestone

g. Ajram Formation

•

M.-L. Cambrian

Sandstone with streak of shale

L. Cambrian- E. Ordovician

Sandstone and micaceous shale

h. Amud Formation

•

The Sauk Cycle and the Early Part of the Tippecanoe Cycle

c. Ra'an Formation

oH

o

Table 4.1 continued.

92 lO

Country

Age

Unit

Litiiology

**

Ordovician-E. Silurian

Sandstones and shales

a. Hiswah Formation

*

E. Ordovitian

Shale, sandstone with sandy shale and silts

b. Dubaydib Formation

*

M.-L. Ordovician

Sandstone and minor sandy shale

c. Mudawwara Formation

*

L, Ordovician~E. Silurian

Silty sandstone, sandy shale with local gyp

d. Khushsha Formation

*

E. Silurian

Flaggy sandstone, sandy shale, argillaceous

M, Ordovician

Laminated, micaceous siltstone and thin sa

c. Sahl as Suwwan Formation f, Umm Tarifa Formation

'

L. Ordovician

Interbedded sandstone and siltstone

g. Trebeel Formation

•

L. Ordovician-E. Silurian

Shale, siltstone, and sandstone

E. Silurian

Micaceous shale, clay stone, and sandstone

E. Silurian

Laminated, micaceous sandstone and siltsto

E. Cambrian

Orihoquartzite with minor shale

h. Batra Formation i. Alna Formation

*

Syria Zabuk Formation

Burj Formation

*

E. to M. Cambrian

Dolomitic limestone

Sosink Formation

*

M, to L. Cambrian

Quarl/.ose sandstone

E. to M. Ordovician

Shale, shaly sandstone, quartzosc sandston anhydritic limestone

Khanaser Formation

Iraq

Afandi Formation

•

L. Ordovican

Quartzose sandstone, shale, conglomerate

Swab Formation

*

E. Ordovician

Silty shale, black shale and sandstone

Tanf Formation

•

Silurian

Shale and siltstone with subordinate sandy

Khabour Formation

*

M. to L. Ordovician

Quartzitic sandstone, graywacke and silty, shale

Sedimentary Basins and Petroleum Geology of the Middle East

Khreim Group:

Table 4.1 continued.

Country 'Hirkey

Unit

Age

Lithology

Sadan Formation

**

E. Cambrian

Redbed sandstone and siltstone

Zabuk Formation

'

E, Cambrian

Pink quartzitic sandstone

Koruk Formation

•*

M. Cambrian

Dolomite and limestone with minor interbed and sandy limestone

Sosink Formation

**

E, to L. Cambrian

Sandstone, shale, and siltstone

~r r./3

Seydischir Formation

**

L. Cambrian toE. Ordoviean

Shale, quartzitic sandstone to limestone

Sort Tepe Formation

•*

L. Ordovician

Coarse-grained sandstone

Bedinian Formation

•*

L. Ordovician

Shale, subarkosic sandstone

Handof Formation

•*

L. Ordovician-Devonian

Shale with sill and sand intercalation

Dedeler Formation

**

E. Silurian

Interbeddcd siltstone, shale, sandstone with m conglomerate

Lalun Formation

*

E. to M. Cambrian

Quartzitic sandstone with minor silty shale c ate

C3 f'3

Iran

Dahu Formation

E. to M. Cambrian

Quartzitic sandstone with glauconitic sandsto shale intercalation

Ilebeyk Formation

L. Cambrian

Fissile and micaceous shale, sandstone and l

Mila Formation and/or Group

M. Cambrian to Ordovician

Alternating dolomite and marl, glauconitic li shale and sandstone

a. Kalshaneh Formation

M. Cambrian

Mahc volcanlcs. carbonate, shale, and sands

b. Dcrcnjal Formation

M. t o L . Cambrian

Siltstone and limestone interbeddcd with ma silty limestone

c. Shirgesht Fomiation

Ordovician?

Marl, hmestone, siltstone, and sandstone

Lashkerak Formation

E.-M. Ordovician

Sihy shale with siUy nodular limestone

Ordovician-Silurian ?

Shale intercalated with tine sandstone

Silurian to E. Devonian?

Dolomite and limestone interbeddcd with sh

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Fig. 4.3. Lithostratigraphic correlation chart of the Paleozoic in the southern part of the Middle East showing the formations, generalized lithologies and major unconformities. The northwestern Saudi Arabia section has been revised by Vaslet's (1989 and 1990) (see Table 4.2). THE EARLY P A L E O Z O I C OF OMAN The Sauk Sequence South-Central Haima

Group

(Cambrian?

in Central and Oman

to earliest Silurian)

The lower Paleozoic of Oman is referred to as the Haima Group (Figs. 4.2 and 4.3), a name taken from well Haima-I drilled in east-central Oman. Although rocks of the Haima Group are found everywhere in the subsurface in southern and western Oman, outcrop is restricted to the Haushi area in central Oman. The rocks of the Haima Group are predominantly fine- to very fine-grained clastics, well-sorted and coarse- to moderately well-sorted fluviatile sands with some shale and shale clast intercalations, and zones of discontinuous, nodular, dolomitic limestone. Locally, there are sub-horizontal and parallel-bedded, millimeter-thick shale laminations interbedded in thick, sub-arkosic and sub-lithic, calcite-

94

cemented sands (de la Grandville and Howell, 1981; de la Grandville, 1982; Nandyal et al., 1983 Boserio et al., 1995). In southern Oman, a distinct unconformity can be seen separating the lower from the upper part of the group. This was used by Hughes-Clarke (1988) as part of the subdivision of the Haima Group (Fig. 4.5). Because the information is largely derived from subcrop, lithologic descriptions lack detail. The Karim

and l-laradh Formations,

equivalent

to

In central and western Oman, this sequence, named by Hughes Clarke, (1988) as the Lower Haima Formation, consists of coarse to fine, lithic and quartzose, often micaceous sandstone considered to have been deposited in a variety of environments ranging from scree fans to mature fluviatile or even aeolian conditions (Hughes-Clarke, 1988). It is suggested that the range of environments and lithology may relate to a variety of synsedimentary structures resulting from deformation of the underlying evaporites of the

the Lower l-laima Formation

(Early Cambrian).

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Fig. 4.4. Lithostratigraphic correlation chart of the Paleozoic in the northern part of the Middle East showing the formations, generalized lithologies and major unconformities. Ara Formation, such as rim synclines, and turtle backs with intrasalt wall depocenters. The recent division by Boserio et al., (1995) of the Lower Haima into the Karim and Haradh Formations placed into the older, Karim, formation medium to finegrained, moderately well sorted, light grey-red fluviatile sandstone with a variable detrital carbonate content succeeded by red-grey-green, soft, micaceous shales and silts, possibly marine in origin. The Haradh formation consists of fine-grained, well sorted, porous, quartz sandstone which passes upwards into sublithic, cross-bedded, medium-grained sandstone rich in chert fragments deposited as stacked braided channel deposits on an extensive flood plain (Boserio et al, 1995). Stratigraphically, the Lower Haima (Karim and Haradh) Formation is approximately equivalent to part of the Saq and Lalun formations of Saudi Arabia and Iran, respectively. The Amin Formation (Early Cambrian). This formarion consists of about 320 m (1,050 ft) of argillaceous

and micaceous, coarse- to fine-grained sands, with fine silt and variable gravel beds in the upper and lower parts. The middle part is characterized by a clean, quartz-rich, sand body indicative of an aeolian setting, according to HughesClarke (1988). It is enclosed within beds that are partly waterlain, and, by reference to the enclosing beds, placed in the Lower Cambrian. Hughes-Clarke (1988) relates the Amin Formation to the Lalun Sandstone of Iran, which has a similar aeolian character. The

Mahwis/Andam

Formations

(Middle-Upper

Cambrian). In the South Oman salt basin the sequence is referred to the Mahwis Formation. It consists of fine- to medium-grained, micaceous sands, about 376 m (1,233 ft) thick, which spread out as flood sheets in a continental setring mostly in southern Oman (Fig. 4.6). The lower boundary is conformable with, and may be a transition from, the Amin Formation. The upper boundary is followed disconformably by the Ghudun Formation marine beds; however, north of 20 ~ N, the Mahwis Formation rocks show a lateral passage into marine beds, and the Andam facies suggest a

95

Sedimentary Basins and Petroleum Geology of the Middle East

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-

Fig. 4.5. Lithostratigraphic chart of the lower Paleozoic (Haima Group) in Oman showing general lithologies, and unconformities (after Boserio et al., 1995 and reproduced by permission of Gulf Petrolink ,Bahrain) southern source for the clastic sediments (Hughes-Clarke, 1988). The age assigned to the formation is based on the age assigned to the laterally equivalent beds of the Andam Formation. The Andam Formation is well developed in the Ghaba and Fahud salt basins and was divided into three units by Hughes-Clarke (1988): a lower unit of dominant claystone with interbedded, fine-grained sandstone; a middle unit of mainly claystone, fine-grained sandstone, and marl with subordinate, fossiliferous carbonates; and an upper unit of mainly claystone with some prominent channel sands, orthoquartzites and micaceous sandstone. The formation, about 1,113 m (3,651 ft) thick in well Farha-1, was deposited in a coastal-plain to marginal-marine environment in central Oman (Fig. 4.6). The marine influence is most obviously developed in the middle unit, where fossiliferous carbonates yield a fauna of trilobites, brachiopods and monoplacophoran molluscs described and figured by Fortey (1995). The upper part of the Andam Formation has yielded only a single trilobite species characteristic of the latest Cambrian. The fossils span much of the Upper Cambrian (Kushanian, Changshanian and Fengshanian of the standard Chinese record). In a regional sense, the Andam Formation and its

96

equivalents extend into Oman and the marine sandstone and carbonate belt from Iran, where the Mila Formation is similar to the Andam in age and facies. To the southwest lay the purely continental conditions reflected in the facies of the Mahwis Formation. Correlation with the Amdeh Formation in the Oman Mountains is invalid (Fortey, 1995), for the Mahwis/Amdeh Formation contains a Llandeilian-Llanvirnian fauna near the top, and the Andam and Saq sandstone of Saudi Arabiahave yet to yield Ordovician fossils. The Tippecanoe Ghudun

Sequence

Formation

(Middle

in Central

Oman

Ordovician)

(Figs. 4.3

and 4.5). The beds of this formation mark the first deposits of the Tippecanoe Sequence of Sloss (1963). The micaceous sandstone and siltstone are about 1,480 m (4,855 fi) thick in this formation. They are typical deposits of a coastal-plain environment, but the presence of glauconite, a rare acritarch fauna, and bioturbation near the base and the top are suggestive of a marginal-marine setting (Hughes-Clarke, 1988). A Llandeilian-Llanvirnian age is assigned based upon palynomorphs. Safiq Formation

(Late Ordovician-Early

Silurian)

The Sauk Cycle and the Early Part of the Tippecanoe Cycle

ARABIAN GULF

GULF OF OMAN Abu Dhabi

.Jtr UNITED ARAB EMIRATES

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Fig. 4.6. General distribution of the Cambrian Mahwis and Andam formations in Oman (modified from Sykes and Abu Risheh, 1989). Note that according to Fortey (1995), the Mahatta Humaid Formation is equivalent to the Andam Formation, and the Mahwis Formation is the purely continental, lateral equivalent of the Andam Formation. (Figs. 4.3 and 4.5). This formation consists of 515 m (1,690 ft) of mainly coarse- to fine-grained, quartz-rich sandstone, with variable amounts of mica and feldspar interbedded with argillaceous sands, silt and shale in coarsening-upwards cycles. The shale often is organicrich, with a marine acritarch and chitinozoan fauna on the basis of which a Caradocian to Llandoverian age is suggested 9 The sandstone generally is barren and suggests deposition in a restricted, marginal-marine setting 9 South of 20 ~ N, the Safiq Formation is the oldest marine formation in the Paleozoic and rests upon earlier Haima continental clastics. North of 20 ~ N, the formation

rests upon similar clastics assigned to the Andam Formation (Hughes-Clarke, 1988), indicating a southerly transgression (Fig. 4.6).

The Sauk and Tippecanoe Sequences in Southern Oman (Dhofar Province) Murbat Sandstone Formation (Ordovician) (Fig. 4.7). The Murbat sandstone crops out in a restricted area of about 100 sq km around Murbat Village in Dhofar, where it rests upon a Precambrian crystalline basement cut by dikes. The basement has been dated as 604+24 Ma. The sandstone 97

Sedimentary Basins and Petroleum Geology of the Middle East Z

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Fig. 4.7. Simplified stratigraphy and lithological description of the Ordovician Murbat Formation in Oman (based on data fromQidwai et al., 1988). is unconformably overlain by Cretaceous sediments 9 Lees (1928) described the type section and named the Murbat Formation. It consists of more than 1,000 m (3,280 ft) of conglomerates, arkosic sandstone, sandy shale and pebble beds, with pebbles derived from the basement. The formation fines upward, and a number of thinly bedded, brown, green or purple shale beds occur near the top. The beds were regarded as debris-flow deposits formed as an alluvial fan under semi-arid conditions by Davies (1981, cited in Qidwai et al., 1988). The Metal Mining Agency of Japan (1981, cited in Qidwai et al., 1988) reported that the lower part was regarded as a shallow-water deposit, and the middle and upper parts as deposits formed under deeper-water conditions. Allison and Wills (1981, cited in Qidwai et al., 1988) regarded the lower part as fluvial and the middle and upper parts as fluvio-marine. Subsequently, Qidwai et al. (1988) divided the Murbat Formation of southern Oman into three members (Fig. 4.7): the lowest 600 m (1,968 ft) is the Ayn Member; the middle 430 m (1,410 ft) is the Arkahawl Member; and the upper 560 m (1,830 ft) is the Marsham Member. The Ayn Mem98

ber begins with 100 m (328 ft) of matrix-supported, polymict conglomerate, with clasts ranging from clay size to boulders of more than 1 m in diameter, some of which are faceted and striated. They interpreted this as a PermoCarboniferous glacial diamictite, overlain by interbedded, conglomeratic, coarse sandstone and a shale bed containing clasts they regarded as dropstone. The overlying Arkahawl Member oversteps the Ayn Member in the west to rest upon basement. The basal bed is a limestone, or shale in some places, and is overlain by thick, cross-bedded, coarse- to medium-grained, arkosic sandstone and shale. The Marsham Member consists of interbedded shale and siltstone with some fine, quartzose, sandstone horizons. From these lithologies, Qidwai et al. (1988)concluded that Ayn Member beds represented a glacial diamictite. The two overlying members then were deposited as turbidity flows in deeper water within the basin. Although Lees (1928) correlated the Murbat Formation with the Nubian Sandstone of Egypt, Morton (1959), Beydoun (1966) and Beydoun and Greenwood (1968) assigned an Ordovician age. Mercanton and Poll (1968) and Allison and Wills (1981), both cited in Qidwai et al. (1988), regarded the succession as lithologically similar to the Infracambrian Abu Mahara Formation; whereas Wolfart (1981) regarded the Murbat rocks as similar to other Ordovician rocks in Oman. In the report of the Metal Mining Agency of Japan (1981, cited in Qidwai et al., 1988), it was argued that the Murbat Sandstone unconformably overlies dikes they dated as Ordovician-Silurian and suggested a possible Permo-Carboniferous age, making the formation the lateral equivalent of the Bani Khatmah (Sandstone) Formation of Saudi Arabia. Qidwai et al. (1988) also assumed a Permo-Carboniferous age equating the glacial horizon with the A1 Khlata Formation of Oman, as well as with the Early Permian Bani Khatmah Formation of southwestern Saudi Arabia, as described by Alsharhan et al. (1991). In the absence of any paleontological arguments, there is no real basis to assign a younger age to the beds, whether they may be Permo-Carboniferous or are evidence of the Late Ordovician glacial. Detailed palynological study needs to be done to determine the accurate age of the Murbat Formation.

The Sauk and Tippecanoe Sequences in Eastern and Southwestern Arabia Oman Mountains (Oman Region) Amdeh Formation (Ordovician). This formation, exposed in the core of the Oman Mountains (in Saih Hatat, near Muscat) (Fig. 4.6), overlies massive, yellow-brown, fine-grained dolomites of the Hijam Formation. It is composed of up to 3,500 m (11,480 ft) of monotonous quartzites and shale, locally interbedded with green shale and cut by basic dikes (Lees, 1928; Morton, 1959). The beds were deposited as turbidites in a marine environment, where they are associated with basic volcanics. Near the

The Sauk Cycle and the Early Part of the Tippecanoe Cycle top of the Amdeh Formation, acritarchs and trilobites establish a mid-Ordovician (Llandeilian-Llanvirnian) age. Lovelock et al. (1981) subdivided them into five conformable members (Fig. 4.8), which represent a transition from deeper water to a coastal-barrier setting passing into a shallow-marine shelf. These members are briefly described below. Upper Siltstone Member (805 m, or 2,640ft). It consists of greenish-gray siltstone intercalated with quartzitic sandstone, argillaceous sandstone and occasional shale. Bioturbation and cross-bedding are common. It has a depositional environment with a shallow-marine shelf. Upper Quartzite Member (1,677 m, or 5,500 fl).The member consists of gray-brown, well-bedded, quartzitic sandstone interbedded with thin shale. Tabular cross-bedding with oversteepened foresets and bioturbation are common. Skolithos burrows occur. It was formed on a low energy, rapidly subsiding coastal- to shallow-marine shelf 0

environment Middle Shale Member (445 m, or 1,460ft). It consists of poorly bedded shale and siltstone, and shaly to quartzitic sandstone with intense bioturbation. Skolithos and Cruziana trace fossils are found. It has a depositional. environment, with a lower-energy, shallow-marine shelf. Lower Quartzite Member (253m, or 83Oft). It consists of pale-colored, well-bedded, quartzitic sandstone, with parallel bedding, wave ripples and cross-bedding. It was laid down in a coastal barrier environment Lower Siltstone Member (240 m, or 787ft). It consists of greenish-gray, poorly bedded, pebbly siltstone and sandstone, with rounded dolomite boulders up to 1 m. It formed in a deep-water depositional environment infilling a rapidly inundated Hijam paleo-relief with intermittent gravity mass flow deposits and sedimentation from suspension.

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Fig. 4.8. Stratigraphy and lithological description of the early Middle Ordovician Amdeh Formation in Oman (modified from Lovelock et al., 1981). 99

Sedimentary Basins and Petroleum Geology of the Middle East O m a n Mountains (United Arab Emirates Region) Ra'an Formation (Middle Ordovician). The formation takes its name from the type section on Jebel Ra'an, at the southeastern end of Jebel Ramaq southwest of the Dibba Zone in the United Arab Emirates (U.A.E.). Its distribution is confined in outcrop to the Jebel Ramaq-Jebel Qamar areas, where it consists of shale and siltstone with sandstone lenses (Fig. 4.9). The sandstone contains Cruziana tracks. The fauna consists of trilobite debris, small brachiopods and rare cephalopods (Hudson et al., 1954a). Blocks of mature quartz grit and sandstone occur with a mixture of shale, siltstone and nodular or red limestone blocks and are best seen at the southeastern end of Jebel Qamar South in the U.A.E., as described by Hudson et al. (1954a), Glennie et al. (1974), Alsharhan (1989) and Robertson et al. (1990). The Ra'an Formation in Jebel Qamar consists of about 80 m (262.5 ft) of thinly cross-bedded proto-quartzites grading upward into well-rounded, massive, quartzose sandstone and siltstone. The deposits mark current-influenced deposition on a stable siliciclastic shelf, with clastic sediment from a granitic source terrain. If the occurrence of Cruziana tracks is significant, the Ra'an Formation may be equivalent to the Upper Siltstone Member Amdeh Formation in the central Oman Mountains; its occurrence, however, as exotic blocks in the Jebel Qamar

Z

9

sedimentary mrlange in the U.A.E.'s Dibba Zone precludes any more formal assignment. As shown by Glennie (1977), no pre-Permian-post-Huqf Group equivalents are known in the main or central Oman Mountains. Southwestern Saudi Arabia

The ? Late Proterozoic through Paleozoic deposits in Saudi Arabia, formerly assigned to the Wajid, were found to consist of a number of depositional packages, the informal "Supergroups" of Stump et al. (1995), which reflect periods of uplift (Fig. 4.10a). They recognized six such groups, which included the Permian and Triassic (Fig. 4.10b). In southwestern Arabia, the first supergroup is missing, and the sixth includes the Permian and Triassic. Groups II and III belong in the Cambro-Ordovician, and IV and V belong in the late Paleozoic (see Chapter 5). Dibsiyah

Formation

(Middle

Cambrian-Lower

Ordovician, "Supergroup II" of Stump and van der Eem, 1995). The formation crops out in southwestern Saudi Arabia and can be traced in bore holes from 17~ ' N to 20045 ' N and from about 43 ~ E to 45035 ' E (Fig. 4.1 l a). It rests unconformably on the Arabian Shield and is covered unconformably by the Sanamah Formation or a younger formation. In the Wajid Platform areas, it has a thickness of 170 m (568 ft), compared with more than

E t/) td)

DESCRIPTION

LITHOLOGY

tO:

-1-

~1 <

~_

Grey thick bedded or massive sandstone, grey fine grained limestone, with bioclastic intercalations, including Megaiodonts. Shallow carbonate deposition on tilted fault blocks within a basin

_

-

Z:

Pink thin-bedded cak:ilutites, condensed. Brown weathering massive limestone, includes fine grained bioclastic limestones and boundstones;Parafusulina,

e~

Carbonate build-up and back reef on horsts.

Neoschwagerina.

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N

$ -J

Z

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Massive cz~ss-bedded fine to medium grained I quartzose sandstone, becoming thinner bedded and more shaley towards exposed top.

Z <

__ z z<

Grey well bedded fosslliierous fine grained limestones, brachiopods, crinoids, ostracods, echinoderms, algae: open shelf Laterally ~riable ientecubur o~nge_quartzose sandstones anti siliceous bioclastic limestones, , aeolian - derived quartz. Shell b e d s fspiri/ers), paratusulina; shoreline Red ferruginous, muddy, fine - drained ]imstones, orthocones, ostracode, bryozoa, echinoderms, spirobis; condensed shelf deposit. Brown nodular limestones with manganese nodules and crusts, mudstone and bioclastic intercalation, condensed shelf deposit Brown ,..,mudstones and impure fine-grained limestones, ]rarely well ex .Ros~ ~hosphaEic bone bed; / tTansgressive deposff~

O0

Cruziana

9 Current-swept shelf sands

100

Fig. 4.9. Composite succession of the Paleozoic formations exposed in the vicinity of Jebel Qamar, westem Oman Mountains, U.A.E. (modified from Robertson et al., 1990, and reproduced by kind permission from the Geological Society of London).

PERIOD OF DEFORMATION

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Fig. 4.10. a=summary of tectonic events in southwestern Arabia. Fig. 4.10b=eomparative general stratigraphy of the Paleozoic of Southwestern Arabia, (theWajid Outcrop Belt ) and northern Arabia (both figures after Stump and van der Eem, 1995, reproduced by kind permission of Gulf Petrolink, Bahrain).

b~ 9

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NORTH N.ALMIDARAH

ALMIDARAH

[.,_3__..,, [7P2,, J 1 UPPER QUSAIBA x~..

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Dibsiyah Formation Devonian-Carboniferous sediments

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Fig. 4.11a. Outline geological map of the Wajid Plateau area, southwestern Saudi Arabia, showing the locations of the sections of the Khusayyayn and Qusaiba formations figured in 10b, (after Stump and Van der Eem, 1995, and reproduced by kind permission of Gulf Petrolink, Bahrain)

Fig. 4.1lb. The Qusaiba Member in the Wajid Plateau:,southwest Arabia: section localities as follows l=Jebel A1 Qu'ad 17~ N, 44o27'02" E; 2=Jebel Karmah, 18o37'30" N, 44012'45 " E; 3=south of Jebel Ilman, 18o43'43 " N, 44o17'30 " E; 4=AI Midarah area, 19036'38 " N, 44002'20 " E; 5=north AI Midarah area, 19037'36 " N, 44o02'20 " E.(after Stump and Van der Eem, 1995, and reproduced by kind permission of Gulf Petrolink, Bahrain)

The Sauk Cycle and the Early Part of the Tippecanoe Cycle 1,500 m (5,000 ft) for the equivalent succession in the subsurface of Jordan. At the base of the Dibsiyah Formation, there usually is a "paleosol" succeeded by a lower sequence of cobble to pebble conglomerates of highly variable thickness containing rounded quartz boulders in a quartzose matrix cemented by calcite and hematite. It is followed by texturally and compositionally mature quartzarenites containing conglomeratic beds with psammitic intercalations. Sedimentary structures are mainly intense cross-bedding with imbricated clasts within channels. The upper section of the Dibsiyah Formation consists of cross-bedded to intensely Scolithus-bioturbated quartzarenite. The "lower" Dibsiyah was deposited in a braidedstream environment that prograded in a clastic apron downslope from southern Arabia into Jordan. The marine facies in the "upper" Dibsiyah represent deposits in environments from shore-face to tidal-fiat to field-channel. The Sanamah Member (Ashgillian-Lower Llandoverian), about 140 m (459 ft) thick, consists of basal heterogenous conglomerate, followed by a sequence of coarsegrained, conglomeratic sandstone, with an alternation of medium-grained sandstone and fine-grained psammitic sandstone above a ferruginous hardground. The conglomerate clasts of cobble size or smaller are rounded to subrounded with percussion marks and often are imbricated along the channel bases. The absence of poorly sorted, texturally immature sediment in the valley fill is inconsistent with a glacial origin, and the "striated pavements" usually occur at the base of sub-aqueous density or debris flows. The valleys were excavated during the early to middle Caradocian following "Taconic" uplift. The latest Sanamah sediments were marine in origin. No biostratigraphically significant taxa have been found, and the age assigned is based upon lithological similarities with the Zarqa and Sarah formations of Vaslet (1989, 1990; Table 4.2). The unconformities above and below the Sanamah Member were the result of uplift and erosion associated with two phases of Taconic uplift.

THE EARLY PALEOZOIC OF NORTHERN SAUDI ARABIA AND JORDAN The second major outcrop area of lower Paleozoic rocks lies in the Tabuk and Widyan basins of northern Saudi Arabia and extends north into Jordan. A great wedge of generally north-dipping sediments passes from continental environments in Saudi Arabia in the south to progressively more marine conditions in the north (Fig. 4.3). Unfortunately, the succession disappears below younger beds and has not been penetrated by deep drilling to any great extent, but has been penetrated in Jordan. At the base of the sequence, a pebble to boulder conglomerate lies on a peneplaned surface in Saudi Arabia, although it generally is absent in Jordan. Powers et al. (1966), Delfour et al. (1982) and A1 Laboun (1986) regarded this pene-

planed surface to have been generated over rocks of the Assyntic Orogeny, which appears to be the same surface as that referred to as the Infratassilian surface in the Maghreb. Since this relatively low-dipping sedimentary sequence lies on tilted rocks with algal limestone, and which elsewhere contain archaeocyathids and volcanics (dated at 540-&-_18 Ma) of the Jubaylah Group, it is clear that the age of the unconformity lies within the Early Cambrian (Hadley and Schmidt, 1975) in this part of Saudi Arabia. The dating establishes an upper limit for the late Pan-African movements, for the deposition of the Jubaylah Group sediments was contemporaneous with the activity of the Najd Fault System. These faults cut granite bodies Kroner (1985) termed post-tectonic.

The Sauk Sequence in North and Northwestern Saudi Arabia Yatib Formation (Early Cambrian?). The formation was named by Ekren et al. (1987) after Jebel Yatib (27028'38 " N, 41~ " E), 25 km east of Ha'il, where about 21 m (69 ft) of clastics rest with angular unconformity over the Precambrian basement (Table 4.2 and Fig. 4.12). Ekren et al. (1987) and Vaslet (1987a & b, 1990) described the section showing that the basal part of the Yatib Formation consists of conglomerate with a matrix of slightly indurated, granitic sand containing well-rounded boulders and blocks, followed upward by fine-grained, micaceous sandstone and slightly indurated, conglomeratic sandstone, all set in an arenitic matrix. Planar crossbedding of medium- to coarse-grained sandstone ended the sequence. The sediments of the Yatib Formation were laid down in a fluviatile environment, in which the relatively immature and commonly coarse-grained material was deposited, whereas the fine-grained sediments such as siltstone may be attributed to lacustrine environments. Saq Formation (? Middle Cambrian to Early Ordovician) (Table 4.2; Figs. 4.3 and 4.12). The Saq Sandstone was named after the type locality of Jebel Saq (26016'02 " N, 43o18'37 " E) by Burchfiel and Hoover in 1935 (cited in Powers et al., 1966), where the upper part of the unit is exposed. Bramkamp (1952, cited in Powers et al., 1966) raised the unit to formation status, and it was formally recognized by Thralls and Hasson in 1956. Steineke et al. (1958) first published the details of the type section and described it as 600 m (1,968 ft) of white, gray and tan, cross-bedded, quartzose sandstone. In 1983, ARAMCO staff mapped the Saq Sandstone as a broad band of outcrops rising from the broad plain east of Ha'il and extending 500 km (312.5 mi) northwest to southeast along the eastern front of the basement to Duwadimi (24020 ' N) in the Khuff quadrangle (Fig. 4.13). In this area, the Saq Formation consists of moderately wellrounded, coarse- to medium-grained, highly cross-bedded sandstone yellow to brick-red in color. Adjacent to the Arabian Shield, quartz pebbles in a sandstone with a dark

103

Sedimentary Basins and Petroleum Geology of the Middle East

Table 4.2. Stratigraphic correlation chart of Paleozoic rocks in Saudi Arabia (compiled from Helal, 1964 a & b, 1965; Powers et al., 1966; Powers, 1968; Bahafzallah et al., 1981; AI Laboun, 1986; Vaslet, 1989, 1990). 1

.....

"'

I Powers,

~

et al., Helal. 1964, 1965

Bahafzallah

!

at al., 1981 AI Laboun, 1986

1966 Powers, 1968

'

'

"'

'

Vaslet, 1 9 8 9

1990

'

AGE

9 u.

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,

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.

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.

.<

Z Our . --~ ~ Shaiba " I' Tawi]Mix Sandstone ;, '

-- ~ . ~ :~

I

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----

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,

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,

9

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Tawll Formation

9

l

-

.

Mbr

blr.

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,

.......

GEDINNIAN {PRIDOLIAN) LUDLOVIAN

Tawti Formation

u,i 9 ,~.l

WENLOCKIAN 7

,

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.... 9

,

LLANDOVERIAI'

,

oki., ~.

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Upper Tabuk Sandstone

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Member Y / / / .

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Ra'an sh~. ordovic|an Sandstone

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Lower Tabuk

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Cruziana Series

Z o_

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SIg Sandstone =

. . . . . . . . . .

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JUBAYLAH GROUP / BASEMENT ROCKS

matrix are found close to outcrops of basic rocks, in contrast to the light-colored matrix where granite is found. Silty, very fine-grained sandstone also occurs, but shale is thin and rare. The sediments commonly are soft and friable, but are harder when sericitic siltstone is developed. Water movement through the sandstone has resulted in the remobilization of iron and its re-precipitation as Liesegang rings. Using both surface and subsurface information, Delfour et al. (1982) and A1 Laboun (1986) recognized two distinct facies in the Saq Sandstone: a lower fluvial and an upper littoral to shallow-marine facies (Fig. 4.12). Detailed descriptions can be found in Clark-Lowes (1985). The lower facies of the Saq Sandstone consists of a thick sequence of planar and tabular cross-bedded sandstone in

! __ Y ~

0

I D|bsi~h

SAQ F O R M A T I O N

,~

ARENIGIAN [TREMADOCIAN

Sallr.

xD~

FORMATION

104

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Sanamah Mbz I

Hanadir Mbr.

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m

9 ~

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"

X

. ......

PRECAMBRIANEARLY CAMBRIAN

sets 30-50 cm thick. They are well-sorted to poorly sorted, fine- to medium- to coarse-grained, and reddish to whitish in color. The lower bounding surfaces of the planar units invariably are erosional and often sub-horizontal. The foresets commonly are angular and intersect the lower bounding surfaces discordantly. Sets vary in thickness from 5 to 300 cm, with small-scale sets ranging from 5 to 15 cm and medium-scale sets from 30 to 80 cm. Superimposed on the large-scale sets may be small-scale, planar cross-strata; they also may be cut by subhorizontal erosion surfaces. Foresets commonly fine upward, and quartz granules and/ or shale intraclast lags may occur at the toe of the foreset. Quartz pebbles may be found scattered on the foresets rather than concentrated in the lag deposits. Trough crossstratified sands are found in troughs and scours.

The Sauk Cycle and the Early Part of the Tippecanoe Cycle z

~

___._-_

~

LITHOLOGY

~ ~ ~

PALEOENVIRONMENT

ZflOm Fer---ru-9-mous i~aleosurtace "j tlaggy sandstone wit h ~ ~ UpDer intertidal zone. beach .~-Ct~h Greenish macrocongJomeratlc layers lr white,hne-gra0necl.carDonated ~ L ---" Protected =nterticlal fiat

~:~~ "~176176176176176 o,s,,,,,,,uv,,, ~

r(..-u~,l,,, ,-,-,Redsiltstone,microconglomerate

, _..__L o w e r . t e r t K : l a l ---- tntertKtal TK:Ialchannel --

Medium-to fine-grained sandstone (cross-Deridingmthe upper part)

Ul:)Oerintertidal

m Free-grainedmicaceous;ilty sanastone Nestedtroughs,upward fining from " coarse-grainedsandstoneto fine silt , ,

__. Laaoonal?salt marsh

~-115 ;.

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~;

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Coarse-grainedunsorted DeOblysandstone Basalconglomerate

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PRECAMBRIAN~x,,it,,ill

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Fig. 4.12. Facies and paleoenvironmental analysis of Cambro-Ordovician Saq Formation in central Saudi Arabia (from Delfour et al., 1982). Smaller-scale features such as recumbent, folded cross stratification commonly are found in fine- to mediumgrained sandstone and in the cosets of coarse-grained sandstone. Shale clast intraformational conglomerates occur, and clasts also are found at the base of troughs. There are thin, interbedded, micaceous siltstone and varicolored, shaly partings. In these finer-grained sediments, rippled surfaces may occur. There is little in the way of systematic vertical change in grain size, and rather abrupt changes occur between well-sorted, often micaceous, fine- to very fine-grained horizons and poorly sorted, medium- to coarse-grained sand, even in sandstone near the base of the succession. In the coarser-grained beds, including basement schist, pebbles may reach a size of up to 5 cm and may be quite abundant. The lithofacies is regarded as a braided-stream deposit. Argillaceous overbank or flood-plain deposits are absent, and well-organized, fining-upward sequences are rare. The large bedforms represent minor channel fill, unconfined flood stage accretion on mid-channel bars under upper-flow regime conditions, planing off existing bars and depositing horizontally stratified sandstone. The small-scale bedforms then represent waning flood stages when flow was

restricted largely to channels. These channels truncated bars and deposited new bedforms on their flanks. The thick succession of planar, tabular cross-beds of differing grain size, set thickness and sorting is attributed to the preservation of transverse and linguoid mid-channel bars created by recurrent floods. The presence of Cruziana and Rusophycus traces in the finer-grained, intercalated beds indicates that the fluvial facies was subjected to periodic marine influences. The maturity of the sandstone and the rounded rutile, zircon and tourmaline are consistent with a polycyclic history of the detritus. The upper member of the Saq Sandstone consists of fine-grained, cross-bedded, argillaceous sandstone, micaceous siltstone, shale and calcareous sandstone with microconglomeratic bands (Fig. 4.14). The absence of mediumto coarse-grained sandstone and the presence of widechannel-shaped sandstone bodies that cut through bioturbated and rippled, silty sandstone beds are the characteristic features distinguishing this facies from the preceding sandstone. Another difference is the presence of bimodal current bedding, with currents from the north and east. Intraclast conglomerates or mica flakes mark some bedding surfaces. The more flaggy sandstone may have

105

Sedimentary Basins and Petroleum Geology of the Middle East ......

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Fig. 4.13. Lithostratigraphy and isopach map of the Middle Cambrian-Early Ordovician Saq Formation in Saudi Arabia (the thicknesses are modified from A1Laboun, 1986 by permission of AAPG): l=Tabuk; 2=Jebel Sharawra; 3=A1Tawil; 4=A1Jauf; 5=Ha'il; 6=Jal Ab Saqiyah; 7=Jebel Ra'an; 8=Qusayba; 9=A1Hanadir; 10=Buraydah; 1l=Jebel Sarah; 12=Jebel Saq; 13=Unayzah; 14=Khuff; 15=Dawadimi. Note that on Figs. 4.1 and 4.13, the zero isopach line is erosional and not the original depositional thickness. The erosional edge of the Paleozoic sediments parallels the isopach lines, indicating the erosional nature of those isopachs. flute casts on its lower surfaces and scour marks on the underlying beds. The fine-grained units may be intensely bioturbated, obscuring the primary bedding. When not destroyed, ripple lamination and horizontal stratification are apparent 9Such beds may contain reworked and broken brachiopod and bivalve fragments. In this facies, a variety of fining-upward sequences have been described by ClarkLowes (1985). The depositional environment indicates a transition from brackish-water, distal alluvial, to a littoral, shallow-marine setting. The sediments forming the beds of this second facies were supplied by the fluvial streams represented by the deposits forming the first facies; hence, the Cruziana-bearing beds of the first facies merely reflect a temporary development of the second. In subsurface, the Saq Sandstone ranges in thickness from 482 m (1,581 ft) in well AI Qasim to 928 m (3,044 ft) in well Rial Fuhah in the vicinity of Tabuk (northwestern Saudi Arabia) (A1 Laboun, 1986). There is a basal pebble to boulder conglomerate with unsorted, angular to subangular clasts, in a slightly ferruginous, calcitic to clayey, quartzose matrix resting upon a major peneplaned surface,

106

as indicated earlier. The isopach map ofAl Laboun (1986) shows the thickness of the Saq Sandstone increasing to more than 1,000 m (3,280 ft) close to the margin of the Tabuk Basin, but information is lacking for the center of the basin. There is a striking narrow extension southward of the Saq Sandstone along the eastern side of the Arabian Shield (Fig. 4.13), which also is apparent in the distribution of the following Tabuk Group thicknesses along an axis that parallels the Ha'il Arch. These isopach maps show the Saq wrapping around the Ha'il Arch with little change in the contour pattern. At the top of the Saq Formation, as seen west of A1 Hanadir and about 100 km (62.5 mi) to the north, there are typical cross-bedded sandstone and ripple-marked sandstone, with iron-rich phosphatic pebbles up to 1 cm across, overlain by 1 m of conglomeratic beds interbedded with low-angled, cross-bedded sandstone with tippled tops (E1Khayal and Romano, 1988). The conglomeratic elements may measure from 1 to 38 cm and lie with their long axes parallel to the bedding. Within the sand matrix, there are

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Fig. 4.14. Lithostratigraphic section of Lower Cambrian Yatib Formation and Middle-Upper Cambrian, Early Ordovician Saq Sandstone Formation in central Saudi Arabia (compiled from Ekren et al., 1987; and Vaslet, 1989, 1990). broken lingulacean valves, and orthocones are found on the surface of one of the conglomerate beds. The overlying blocky mudstone is regarded as the basal member of the Hanadir Shale Formation of the Tabuk Group. Both Powers et al. (1966) and A1 Laboun (1986) divided the Saq Formation into four members, in ascending order: Siq, Quweira, Ram and Umm Sahm (Fig. 4.13). These members are summarized below. Umm Sahm Sandstone Member. It can be traced almost without interruption from the type locality in Jordan southeast around the margin of the Arabian Shield to where it passes under sand of the Great Nafud. It consists of buff to brown, dark-weathering and cross-bedded sandstone. Quartz pebbles and granules are common, with lenses of sandy shale containing Cruziana tracks. The Umm Sahm appears to have a fluviatile-continental origin, but the presence of trilobite tracks proves at least part of it was deposited in a shallow-marine environment. Ram Sandstone Member. Extending from southeast Jordan to northwestern Saudi Arabia, the member consists of light-colored, whitish to buff-weathering, coarsegrained, eolian cross-bedded sandstone, with common quartz granules and pebbles. Quweira Sandstone Member This is a series of discontinuous exposures extending south from A1 Wuwayrah in Jordan to the A1 Madinah-Tayma Road in Saudi Arabia. The Quweira north of latitude 28 ~ N is composed of reddish-brown, massive to cross-bedded, continental sand-

stone. Conglomeratic zones of quartz and feldspar granules and pebbles are common, and silt occurs locally. South of latitude 28 ~ N, the sandstone of the Quweira is yellow or buff in color, thin-bedded and medium-grained, and contains pebbles of quartz. Siq Sandstone Member. This narrow belt of discontinuous exposures borders the Arabian Shield from latitude 28 23' N southeast to longitude 40~ ' Eo The member consists of medium-bedded to massive sandstone, dark-red in color, and locally conglomeratic, with pebbles from the underlying Precambrian complex. The age of the formation was based on the correlation of the lower part of the unit to a pre-Middle Cambrian Trilobite-bearing Sequence in Jordan (Zerqa area) and from the occurrence of arthropod tracks of Cruziana. As a result, the sandstone commonly was stated to range from the Middle Cambrian to Early Ordovician (Powers et al., 1966; Powers, 1968). E1-Khayal and Romano (1988), in a re-study of the Cruziana beds in the top unit of the Saq sequence, dated a faunule collected from isolated exposures, which they regarded as a horizon near the top of the Saq Sequence. Their material was collected from a site about 20 km west-southwest of Hanadir in a sequence of trough cross-bedded sandstone. The fauna indicated an Early Ordovician age, post-early Tremadocian, and most probably Arenigian. Although didymograptids and some tuning-fork graptolites are known in the top meter of the Saq Sandstone, their poor state of preservation precluding 107

Sedimentary Basins and Petroleum Geology of the Middle East specific identification, E1-Khayal and Romano (1988) suggest that the unit may range up to the late Arenigian. Williams et al. (1986) provided a revision of the type section in the vicinity of Jebel Saq, where about 663 m (2,175 ft) were measured and described. Vaslet (1987a, b, 1989, 1990) subdivided the Saq into two members m the Risha and Sajir m e m b e r s - (Fig. 4.14 Table 4.2) and provided a detailed sedimentological and environmental analysis. The Risha Member, 308 m (1,010 ft) thick, unconformably overlies the Precambrian basement. The lower part of the member consists of conglomerate of centimeter-sized, well-rounded, white quartz pebbles in a sandstone matrix, representing a fluviatile system in which the braided channels intersect one another. The upper part consists of coarse- to fine-grained sandstone of a fluvial and deltaic system, characterized by more rectilinear and more extensive alluvial bodies and by meandering channels. The Sajir Member, about 355 m (1,165 ft) thick, consists of medium- to fine-grained sandstone interspersed with micaceous siltstone and laid down in a shallow-water, pro-deltaic environment in the lower part; the upper part is on a tidal fiat, where well-sorted and fine-grained sediments arranged in prograding subhorizontal bodies are separated by silty intercalations.

The Sauk Sequence in Jordan Ram Group (Early Cambrian-Early Ordovician) The Sauk Sequence can be traced north of Saudi Arabia into Jordan, where it is well-exposed in the Southern Desert. Bender (1968, 1975) has described this sequence, and Selley (1972) has given a detailed sedimentological description of the sequence that closely parallels the descriptions made by Clark-Lowes (1980) in Saudi Arabia. As in the Saq Sandstone of Saudi Arabia, two principal facies have been recognized in the succession that has been termed the Ram Group. It has been divided into four formations in ascending order: Salib, Umm Ishrin, Disi and Umm Sahm (Table 4.1 and Fig. 4.15a & b).Selley (1972) interpreted the depositional environment as a shallow-marine shelf to shallower tidal flat, where cross-bedded shoal sands alternate with rippled and burrowed tidal-fiat deposits. As might be anticipated in such an environment, trace fossils are more abundant, with siltstone surfaces traversed by Cruziana trails and burrows attributed to Sabellarifex (= Tigillites or Skolithos). Near the top, 50 m (164 ft) below the graptolitic beds, is a persistent siltstone horizon with Harlania burrows (the Harlania Shale Member). Along the eastern side of Wadi Araba to the Dead Sea, the Cambrian sediments consist only of about 50 m (164 ft) of basal conglomerates resting with angular unconformity above a pronounced erosional hiatus. In the area east of the Wadi Araba, the conglomerates are absent, but there are about 200 m (656 ft) of bedded arkosic sandstone resting on peneplaned rocks of Precambrian age. These are followed by about 110 m (361 ft) of white, fine-grained

108

sandstone that interfingers with, and farther south and east is replaced by, as much as 350 m (1,148 ft) of the lower part of a massive, brownish, weathered sandstone of continental origin (Bender, 1975), all assumed to be Cambrian. Towards the north and west, the "lower brownish sandstone," a continental and deltaic sequence, is replaced by about 110 m (361 ft) of fine, whitish, marine sands, which are in turn replaced by a 50 m (164 ft) dolomite-limestone and shale sequence well-known in the Dead Sea region (Bender, 1975). In this limestone sequence, a fauna of latest Early to Middle Cambrian age has been described (Blanckenhorn, 1912; Richter and Richter, 1941; cited in Bender, 1974). To the south and east, the fine, white sandstone reverts back to a continental facies. The upper part of the same Cambrian sandstone overlies the carbonate horizon, indicating the end to the short, temporary transgression (from the south) within the Middle Cambrian. In the area near the Dead Sea, the upper part of this sandstone is replaced gradually by white sandstone, which may be as much as 220 m (722 ft) and of marine origin, and, hence, located at the margin of the Late Cambrian sea. The name "Ram Group" was assigned by Powell (1988) and Masri (1988) to formations established by Bender (1968, 1974) and Lloyd (1969) and previously assigned to the Disi Group (Lloyd, 1969). The latter name has been abandoned, as it was also used for one of the component formations. Thus, the Ram Group (Lower Cambrian-Lower Ordovician) incorporates all of the predominantly siliciclastic formations and the marine carbonate wedge unconformably overlying the Precambrian base and conformably overlain by the Khreim Group beds, both at the surface and subsurface, although different formational names are used. Fig. 4.15a shows the lithostratigraphic nomenclature of the Ram Group surfacesubsurface formations.

Subsurface Formations Salib Formation (Early Cambrian). The formation is present throughout Jordan at the surface and in deep wells, except where basement rock crops out in the southwest. The formation has been penetrated in a few wells, with 289 m (948 ft) occurring in A1 Jafr-1, 531 m (1,742 ft) in Northern Highland-1 and 750 m (2,460 ft) in Wadi Sirhan-3. The formation consists of arkosic and conglomeratic sandstone, with some micaceous, sandy claystone stringers, overlain by poorly sorted, feldspathic, pebbly sandstone and sandstone with rare clay stringers and mica and heavy mineral concentrations (Andrews, 1991). The base of the formation in outcrop rests unconformably on the Saramuj Formation. The top of the formation is conformably overlain by beds assigned to the Abu Khasheiba (at A1Jafr), Umm Ishrin (Southern Desert outcrop) or Burj (in subsurface) formations. The Salib Formation was deposited in a continental environment, with minor marine incursions. Selley (1972) interpreted these sediments in southern Jordan as deposited in a braided-stream, alluvial

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Burj Formation and its equivalent, the Abu Khusheiba Formation (late Early Cambrian-early Middle Cambrian). The Burj Formation is distributed widely, except in southwest Jordan, where basement rocks are exposed. At its thinnest, it is up to 61 m (200 ft) in A1Jafr-1, but in a limited number of wells, it may reach as much as 135 m (443 ft), as at Safra-1. Andrews (1991) divided it into five units (A-E), although Shinaq (1990) grouped them into three members as follows: Tayan Member (Unit A), Numayri Member (units B and C) and the Hannah Member (units D and E). Unit A ranges in thickness from 16 to 29 m (53-95 ft) of micaceous siltstone and silty claystone. Unit B ranges from 16 to 24 m (53-79 ft) of interbedded shale and limestone. Unit C ranges from 33 to 45 m (108-148 ft) of massive limestone and dolomite. Unit D ranges from 2 to 15 m (6.5-49 ft) of siltstone/micaceous claystone, with minor limestone/dolomite beds. Unit E ranges from 12 to 34 m (39-112 ft) of oolitic and micritic limestone interbedded with claystone. The formation was deposited in an intertidal-subtidal environment to a coastal (enclosed lagoon) environment (Andrews, 1991). The top and base of the Burj are contbrmable (Fig. 4.15a). The Abu Khusheiba Formation was known by Bender (1974) as the White, Fine-grained Sandstone Formation, but was named Abu Khusheiba by Powell (1989a). It is equivalent to part of the Burj Formation and ranges in thickness from 100 m (361 fl) at the type locality (Bender, 1974) to 50-60 m (164-197 fl) at Wadi Museimir (Powell, 1989 a). The formation, which consists of fine- to mediumgrained, micaceous sandstone, clayey in part, contains scattered clasts of quartz porphyry or rhyolite, probably locally derived. The sandstone may show small-scale, trough cross-bedding and planar or laminated bedding. Foreset-dip measurements indicate a bimodal or polymodal distribution. The base is marked by a sharp junction below with the underlying medium-grained sandstone of the Salib Formation. The top contact with the fine-grained, micaceous sandstone above is erosional in many places (Powell, 1989 a) and rests on the Ajram Formation. Based on the evidence of lithology, trace fossils and sedimentary structures, the formation was deposited in shallow-water, under-marine or brackish conditions, probably in the shoreface zone of a prograding clastic shoreline subjected to oscillating wave action and tidal currents. Ajram Formation (mid- to Late Cambrian). The name of the formation was introduced by Andrews (1991) to describe a geophysically defined rock unit in the subsurface, broadly comparable with what was known as the Umm Ishrin Formation (Powell, 1989 a). The latter term now is restricted to the outcrop section in southern Jordan. The formation has been completely penetrated by only five wells: A1 Jafr-1 (thickness 286.8 m, or 940 fl), Wadi Sirhan-3 (thickness 323 m, or 106 fl), Wadi Sirhan-10 110

(thickness 370 m, or 1,214 fl), Wadi Ghadaf-2 (thickness 226 m, or 741 ft) and Northern Highland-1 (thickness 253 m, or 830 ft) (Andrews, 1991). It consists of argillaceous and very fine- to fine-grained sandstone, with streaks of shale and micaceous claystone. There are local thin limestone interbeds or stringers at the base. The formation was laid down in a fluvial, braided-stream environment, with periodic marine influences (Andrews, 1991; Powell, 1989 a; Selley, 1972; Makhlouf and Abed, 1991). The base of the formation is marked by a thin shale horizon separating it from the underlying Burj Formation (Unit E). At higher levels, the formation contains limestone, and the top is gradational with the Amud Formation.

Amud Formation (Late Cambrian-Early Ordovician). The name of Amud Formation is applied to a subsurface formation by Andrews (1991) and replaces the Disi Sandstone and Umm Sahm formations of Bender (1974) and Powell (1989 a). The Amud has an extensive distribution in subsurface, but has been penetrated totally by only four wells: A1Jafr-1 (1,204.6 m, or 3,949 ft), Wadi Sirhan-3 (1,191 m, or 3,906 ft), Wadi Sirhan-10 (1,249 m, or 4,096 ft) and Wadi Ghadaf-2 (1,270.5 m, or 4,166 ft). Andrews (1991) divided the Amud Formation into two units. The lower unit ranges in thickness from 1,006 to 1,185.5 m (3,300-3,888 ft) of fine- to medium-grained, slightly argillaceous sandstone with thin interbeds of micaceous siltstone. The thickness of the upper unit ranges from 85 to 219 m (279-718 ft) and consists of very fine- to fine-grained sandstone, with secondary quartz overgrowths, a kaolinite matrix, pyrite and other heavy minerals. It includes several thick shale beds. The base of the formation shows a gradational contact with the Burj Formation. The top is easily recognized by the abrupt change from sandstone to the mud and shale of the Sahl as Suwwan Formation. The Amud Formation is interpreted as a deposit from a sinuous river system in the more distal, alluvial plain.

Surface Formations Salib Arkosic Sandstone Formation (Early Cambrian). The formation is the lowest unit and rests on a planar, shallowly dipping unconformity formed over Precambrian igneous rocks. The only location where there is a basal conglomerate is close to the line of the present Aqaba-Jordan Rift, which appears to have been a line of weakness even in the Late Proterozoic. It was active during the Cambrian, as indicated by the occurrence of quartz porphyry volcanics. Continued activity during the Cambrian is shown by the distribution of facies, which indicate a high area east of the southern part of the "rift" or suture (Bender, 1975), where continental beds formed, and a structurally lower Palestinian block west of it, over which marine intercalations can be found within the Cambrian succession. Covering the rest of the area, only a "granite wash" is found, except where a talus develops around local residual relief. Such relief, as in Algeria, is never marked;

The Sauk Cycle and the Early Part of the Tippecanoe Cycle Selley (1972) quotes 35 m (115 ft) as the maximum. The name "Salib" was established by Lloyd (1969) as a synonym of the Basal Conglomerate and Basal Bedded Arkose of Bender (1968, 1974), of the Lower Quwayra series of Quennell (1951) or the Quwayra Sandstone of Wetzel and Morton (1959). It ranges in thickness from 60 m (197 ft) in southern Jordan to up to 220 m (722 ft) south of the Dead Sea. The Salib Formation (Fig. 4.15b) consists of medium- to very coarse-grained, pebbly, cross-bedded, arkosic and sub-arkosic sandstone, and pebble to cobble conglomerates. Sedimentary structures include thin beds of planar to tipple cross-lamination, trough cross-bedding within medium- to large-scale tabular sets, and overturned or convoluted bedding (Powell, 1988,1989 a). The lower boundary is formed by the erosional unconformity above the Aqaba Complex/Saramuj conglomerate, whereas the upper boundary lies at the base of the Umm Ishrin Sandstone. Selley (1972) concluded that conglomeratic and trough cross-bedded sandstone and the absence of macrofossils in the Salib Formation indicated deposition in a braided-stream, alluvial environment. The presence of sedimentary structures such as tabular, erosive trough crossbedding suggests high-energy, high-discharge rivers with medium- to large-scale, subaqueous dunes (Powell, 1989 a). Conglomerate deposited by traction currents along the river beds fill the depressions in the peneplain. The occurrence of trace-fossil horizons near the top of the formation indicate brief marine incursions across the alluvial plain. Umm lshrin Sandstone Formation (Middle to early Late Cambrian). The term was used first by Lloyd (1969) and is equivalent to the Upper Quweira Sandstone of Quennell (1951) and the Massive Brownish Weathered Sandstone of Bender (1968, 1974). The thickest development of Umm Ishrin is in southern Jordan (230-320 m, or 755-1,050 ft), where the full sequence is exposed. Bender (1968) measured a section at Wadi Dana (western Jordan) of about 110 m (361 ft). The formation consists of medium- to coarse-grained quartz arenite, with trough cross-bedded foresets marked by scattered pebbles and pebble lags in the base of the channels (Fig. 4.15 b). Overturned (slumped) cross-bedding is common. Thin beds of finely laminated, micaceous, fine-grained sandstone and siltstone occur (Powell, 1988, 1989 a). The lower and upper boundary contacts are gradationalo The base is defined above a tabular-bedded, pebbly, quartz arenite of the Salib Formation passing to massive, weathering, quartz arenite of the Umm Ishrin. The top is defined below the massive, rounded, pebbly quartz arenite of the Disi Formation. The formation formed in a fluvial, braidedstream environment (Selley, 1972) on the evidence of medium- to large-scale trough, cross-bedded, pebbly sandstone with graded and overturned forests and unimodal paleocurrent flow. Burrowed, tippled or parallel-bedded siltstone indicate brief estuarine or marine incursions across the alluvial plain (Powell, 1989 a). Disi Sandstone Formation (Late Cambrian-Early Ordovician). The term was renamed first by Lloyd (1969)

and later by Selley (1972) for the synonymous Massive White Weathered Sandstone of Bender (1968, 1974). Lloyd (1969) used the same name for the group, but the latter was renamed the Ram Group (Powell, 1989 a), and only the formation name was retained. Ranging in thickness from 300 to 350 m (984-1,148 ft) in the type area at Qa Disi, the formation consists of medium- to coarsegrained, massive, thick-bedded, quartz arenitic sandstone with large-scale trough cross-bedding and planar-bedded sets with eroded bases. In the upper third of the formation, parallel, laminated, micaceous, fine-grained sandstone and siltstone with thin beds of tipple, cross-laminated or smallscale trough cross-bedded sandstone (Powell, 1988, 1989 a) are found. The lower and upper contacts are gradational, with the Umm Ishrin below and Umm Sahm above. Lithology, sedimentary structures and paleocurrent flow suggest that the Disi Formation was deposited as largescale, subaqueous dunes in high-velocity, high-discharge, braided rivers (Selley, 1972; Powell, 1989 a). Umm Sahm Sandstone Formation (Early Ordovician). The term was introduced by Quennell (1951) and used by Lloyd (1969), Selley (1972) and Powell (1989 a). Bender (1968, 1974) clearly defined the characteristics and correlation of the unit, formerly known as the Bedded Brownish Weathered Sandstone. The formation crops out only in southern Jordan and ranges in thickness from 220 to 250 m (722-820 ft) in the Qa Disi-Sahl as Suwwan area. The Umm Sahm Formation consists of medium- to coarsegrained, thick-bedded, quartz arenite, with trough and planar cross-bedding in laterally persistent tabular- or wedgeshaped sets and channel fill with trough, cross-bedded sets Rippled and ripple cross-laminated, micaceous, ripple cross-laminated or planar cross-laminated sandstone also is found (Powell, 1989 a). Trace fossils such as Cruziana sp., Harlania sp. and Sabellarifex sp. are abundant (Bender, 1974; Selley, 1970). The lower boundary is gradational and marked by rounded-weathering sandstone with erosive sets of the Disi Formation, to tabular-weathering, thinner-bedded sandstone of the Umm Sahm Formation.

The Tippecanoe Sequence in North and Northwestern Saudi Arabia Tabuk Group There have been at least three major attempts to establish a stratigraphic nomenclature for the Lower Paleozoic beds of north and northwestern Saudi Arabia. These are summarized in Table 4.2 and involve changes of status, member to formation, formation to group status, fortunately without changed boundaries, except in the case of the uppermost Ordovician beds. Although more complex, the nomenclature of the most recent version (Vaslet, 1989, 1990) seems the more geologically sound and will be adopted here. This means abandoning the well-established

111

Sedimentary Basins and Petroleum Geology of the Middle East Tabuk Formation (or Group) and adapting the Qasim Formation for beds with a Llanvirnian to Caradocian age. The name "Tabuk Formation" was proposed by Bramkamp et al. (1954, cited in Powers et al., 1966) for the sequence of sandstone, siltstone and shale cropping out in northern Saudi Arabia formally defined by Steineke et al. (1958). The formation crops out intermittently along a 300 km strip from the Great Nefud Sand Desert to the town of Unayzah. In the southern two-thirds of the outcrop, this band is about 35 km wide; but, south of Jebel Hanadir, the basal contact is obscured by gravel and sand. The most complete section crops out south of the Great Nefud in the Qusaiba-Er Ra'an area (26055 ' N). It consists of more than 1,700 m (5,576 ft) of rhythmically alternating marine shale and continental- to marginal-marine sandstone, represented in a sequence of marine transgressions and regressions, a complex intercalation of cross-bedded sandstone, shale and siltstone. The presence of three principal shale members results in the outcrop pattern of roughly parallel escarpments, which permitted Powers (1968) to divide the formation into seven informal units and A1 Laboun (1986) to divide it into six. The informal members were raised to formational rank following the suggestion of E1-Khayal and Romano (1988) without any significant changes in lithological interpretations (Fig. 4.16 and Table 4.2). Williams et al. (1986) subsequently introduced the term "Qasim Formation" (Llanvirnian to Ashgillian) to cover the lower part (units 1, 2, 3 and the base of 4) of the Tabuk Formation, such as the part of the succession between the Saq Sandstone and the first late Ordovician glacial erosion surface that crops out east and south of Ha'il (41~ ' E) and throughout the Qasim region. Vaslet (1987a, b, 1989, 1990) revised the sedimentological interpretation using established names for the units" Hanadir, Kahfah, Ra'an and Quwarah members. If these are regarded as formations, as has been done here to correspond to the terminology for the Ashgillian and younger beds, then the Qasim must be raised to group status. Descriptions of the individual formations that follow have been drawn from the work of Powers et al. (1966), Powers (1968), Helal (1964a, 1968), A1Laboun (1986) and ClarkLowes (1980).

l-lanadir Formation (middle to upper Llanvirnian and possibly early Llandeilan). The Hanadir Shale is a distinctive unit that replaced as the first formation of the Tabuk Group, the Didymograptus Shaly Member, which A1 Laboun (1986) regarded as Arenigian in age and the unit 1 of Powers et al. (1966). Subsequently, E1-Khayal and Romano (1988) revised the description and dating of the unit, upgraded it to formation rank, and established a type section west of Jebel A1Hanadir, about 53 km west of Buraydah in the A1 Qasim Province. The type sequence consists of about 22 m (72 ft) of pale-fawn to buff weathering shale and mudstone, occasionally gypsiferous, with relatively rare, thin siltstone, sandstone, and conglomeratic bands. These coarser clastics tend to be thin (about 10 cm) 112

and lenticular, wedging out along strike. They also may show hummocky cross-lamination. A middle to upper Llanvirnian age can be assigned (Fortey and Morris, 1982) based on the presence of graptolites in the shale. However, there still is a question of how much of the lower Llanvirnian is present. Where the Hanadir Formation is thicker (42 m, or 138 ft), Fortey and Morris (1982) identified a fossiliferous sequence with reworked trilobites (Neseuretus). At Jebel Shammar, brachiopods, crinoids, ostracods and conodonts have been found, which may indicate an extension up into early Llandeilian. Cruzianid trace fossils are relatively common, with indeterminate horizontal trace fossils in both shale and sandstone. There is a local phosphatic and bioclastic (fish debris) conglomerate at the base. The transgressive, subtidal episode represented by the shale is recognized over much of the northern margin of Gondwana, as in Tunisia and Algeria. It marks the end of the Sauk Sequence and the beginning of the Tippecanoe Sequence. The argillaceous sediments above the Saq Sandstone have a low-diversity fauna, poor in articulate brachiopods and dominated by trilobites. The assemblage was deposited on an offshore shelf below normal wave base, and accumulated during a rapid transgression. Selley (1970) considered the broadly equivalent mud sequence in Jordan to have formed in an offshore mud zone passing up through fine-grained turbidites into a cross-bedded, channel-sand complex. He later described it as a high-slope, turbiditic, delta sequence (Selley, 1985). In central Arabia, however, the sandstone horizons found in the upper part of the Hanadir Formation are regarded as the result of storm events. The sudden incursion of thick, cross-bedded sands argues for a rapid environmental change with the appearance of strong bottom currents, which can be correlated with a sea-level fall during the Llandeilian. Kahfah Formation (Llandeilian). This sequence of 104 m (341 ft) of fine- to medium-grained, micaceous sandstone with thin siltstone and shale intercalations is the Lower Tabuk Sandy Member of Helal (1964a), the Scolithus Sandstone of Powers (1968) and the Ordovician Sandstone of A1 Laboun (1986). Lithologically, ClarkLowes (1985) described four subfacies. One sub-facies consists of greenish to gray shale interbedded with purple shale. This contains cone-in-cone structures and may have a development of fibrous gypsum parallel to the bedding. In the lower parts of each unit, a fauna of trilobites and graptolites may be found; and a horizon with winnowed bivalve fragments occurs immediately above the Hanadir Shale. Ripple-laminated siltstone becomes increasingly abundant upwards. This siltstone, which averages about 30 cm in thickness, shows small-scale trough cross-bedding, which may pass up into climbing ripples and horizontal, laminated shale. The shale may have Skolithos and Bifungires as trace fossils. A second sub-facies consists of bioturbated and rippled siltstone alternating with shale, which becomes less abundant upwards and generally is barren, and coarser sands. The base of the sand and siltstone com-

The Sauk Cycle and the Early Part of the Tippecanoe Cycle

Fig. 4.16. General lithostratigraphy and isopach map of the Early Ordovician to Early Silurian Tabuk Group in northwestern Saudi Arabia (the thickness contours are modified from A1 Laboun, 1986 and reproduced by kind permission of AAPG). monly is scoured with scour-and-fill cross-beds. Flute and prod markings occur in the finer-grained beds, and smallscale load casts increase in frequency upwards. Flaser bedding indicates a two-directional current system. The third sub-facies consist of fine-grained sandstone, which normally possesses trough cross-bedding. They may also display channel fill cross-stratification, low angle crosslamination but completely lack biogenic structures. The fourth sub-facies consists of a medium- to coarse-grained, poorly sorted sandstone with a channelled base, which contain coarser lag deposits and in which biogenic activity generally was minimal, although the beds may contain U tube and Skolithos burrows near the top. The current directions generally are directed to the east or east-northeast, consistent with asymmetrical ripples that trend south or southeastward, and channel and scour axes directed to the east or southeast. The depositional environment suggests shallowmarine conditions above and below the wave base, with no indication of emergence. The fauna, made up of suspension and sediment feeders, is one appropriate to such an environment, and some beds show marked bioturbation indicative of relatively quiet water conditions. However, these conditions were intermittently interrupted by higher velocity currents carrying the coarser clastic sediments and resulting in channelling, with the development of

scour and sole markings. The ripples indicate wave action driven by winds oblique to the shore and directed obliquely onshore or alongshore toward the southeast. There is little evidence of significant tidal currents in the absence of recognizable tidal sand ridges. It is suggested that the coastline ran roughly north-south to northwestsoutheast with the sea to the northeast and fluvially derived sediments entering from the west through fluvially dominated deltas. Depending upon the balance between the rate of sediment supply and subsidence, the fluvial sediment resulted in progradation or the maintenance of stable, shallow-water conditions (Clark-Lowes, 1985). Ra'an Formation (Upper Caradocian, at least in part). In the Tabuk Basin, this shale, the Diplograptus Shaly Member of Helal (1964 a & b) and unit 3 of Powers (1968), ranges in thickness from 14 to 100 m (46-328 ft). It consists of gray-purple and green, graptolitic shale, with thin, interbedded sandstone and siltstone deposited in an outer-shelf environment influenced by deltaic conditions. It is dated by the occurrence of graptolites, conodonts and trilobites. The presence of palynomorphs and chitinozoans found in subsurface samples confirm the age (cf. McClure, 1978; AI Laboun, 1986). At a few localities, as at Khashim ar-Ra ~an and Jal as Saqiyah, the Ra'an Shale is capped by a 1-3 m (3.3-10 ft) thick tillite in which there are large, elongated sandstone, igneous and metamorphic, angular to

113

Sedimentary Basins and Petroleum Geology of the Middle East sub-rounded clasts, which may be striated, grooved, polished or faceted, in an argillaceous matrix 9The tillite also may contain tip-up clasts of the underlying Ra'an Shale. However, the tillite is discontinuous and may interfinger with proglacially deposited sandstone (McClure, 1978). There also are sporadic outcrops of finely varved, siltstone rhythmites in which dropstones are rare. In the Jebel Sarah area, a deep channel or paleovalley cuts through the Ra'an and Hanadir shale and is filled with torrentially deposited cross-bedded sandstone that, at the eastern end of the valley, appears to merge into the Lower Silurian sandstone (McClure, 1978). The geometry at the eastern end suggests a fluvio-glacial outwash fan. A close analogue is found in Algeria.

Quwarah Formation (late Caradocian-?Ashgillian). About 87.5 m (287 ft) thick, it corresponds to the basal part of unit 4 described by Powers (1968) and the bioturbated sandstone (Facies 4) described by ClarkLowes (1980). It consists of an alternation of fine-grained sandstone, micaceous siltstone and claystone. The sandstone is bioclastic in places, containing fragments of orthoceratids, lingulids and fish debris. The depositional environment probably was proximal infralittoral. The Quwarah is truncated everywhere by the first glacial erosion surface. 9 Quwarah Equivalents (Ordovician formations 1-5) (late Caradocian to Ashgillian). Recently, a north-dipping trough that cuts though all the beds from the Ra'an Shale Member to the Precambrian basement has been discovered in central Saudi Arabia. It contains a clastic, predominantly sandstone fill, which is the age equivalent of the Quwarah but cannot be correlated with it lithologically. Connally and Wiltse (1995) provided a summary lithological description and figures (see Fig. 4.18 p.117). The upper formations all show the influence of the central Arabian Arch. Formation 5: Feldspathic sandstone deposited in a ma104 m(340fl) rine, tidal environment composed of reworked sediment from the Saq and Qasim units. In some wells are approximately equal amounts of silt and poorly sorted sandstone, sometimes bioturbated. Formation 4: Compositionally and texturally mature 91-122m reworked quartz sandstone probably from (300-40Oft) the reworked Saq Formation. sands are either intensely bioturbated, massive with relict cross-stratification or high-angle cross-bedded sands with little or no bioturbation. The proportion of each changes, with bioturbation most common in the east and decreasing westwards. Herringbone cross-bedding is common, with bioturbation due to Scolithos. It is a middle cobble and pebble conglomeratic unit. Formation 3: An upward-coarsening, lithic, quartz sand315 m(1,032 fi) stone with erosional upper and lower contacts. Many low-angle cross-beds and bio-

114

turbation (Scolithos) are common. Beds coarsen towards the western depositional margin of the basin. It has a deltaic/shoreline facies, with current features trending south. Formation 2: Basal conglomerate followed by a range of 122m (60Oft) siltstone, fine sand and coarse conglomerate in a coarsening-upwards section. Has low-angle cross-bedding and rare bioturbation. It was deposited in an alluvial-fan environment trending upwards toward fandelta and marginal-marine beds. Formation 1: Clear, well-sorted quartzarenites with 122m (40Oft) steep cross-bedding. With no biogenic or trace fossils, it is considered an aeolian deposit. On the geological map of northwest Arabia, Bramkamp et al. (1963) showed an unconformity within the Tabuk Formation, marked by brown or beige sandstone transgressive over the lower and middle parts of the Tabuk Formation. This transgression occurs within unit 4 of Powers et al. (1966) and Powers (1968). Vaslet (1987a) regarded this unconformity as associated with the Late Ordovician glaciation and agrees with McClure (1978), who had earlier demonstrated that these transgressive sequences belong to glacial formations and dated this glacial phase as late Caradocian. The Upper Ordovician glacial deposits in central Arabia were subdivided into two formations, each underlain by strong glacial unconformities (Table 4.2 and Fig. 4.10 b): the Zarqa Formation below and the Sarah Formation above. Vaslet (1987a, b, 1990) provided detailed sedimentological and depositional settings, which are summarized below.

Zarqa Formation (Late Ord~ The Zarqa Formation crops out in central Saudi Arabia between Unayzah (27055 ' N, 42007 ' E) and A1 Qara (26023 ' N, 43050 ' E) and unconformably overlies the Quwarah Formation. It consists of a complex alternation, about 115 m (377 ft) thick, of siltite and clayey silt containing blocks (boulder clay) of tillite and of fine-grained, micaceous sandstone very commonly deformed by slumping. Vaslet's detailed sedimentological studies reveal that it consists of three main facies" 1) The Tillite Facies, which occurs as localized pockets ranging in thickness from 2 to 9 m (6.5-29.5 ft) of glaciogenic detrital rocks with basement blocks, sandstone and boulder blocks and claystone blocks. 2) The Boulder-Clay Facies, which ranges in thickness from 2 to 20 m (6.5-65.5 ft) of dark-green, silty claystone, commonly sandy and very micaceous, and contains variable quantities of gravel, boulders, and blocks of varied lithology. 3) The Sandstone Facies, which ranges in thickness from 1 to 10 m (3.2-33 ft) of fine-grained, micaceous sandstone intercalated within the boulder clay. The sedimentary structures show lamination, slumping, frost

The Sauk Cycle and the Early Part of the Tippecanoe Cycle wedges and polygonal ground cracks typical of a glacial environment. The Zarqa Formation is dominated by glacial features and a continental environment succeeded by sub-aquatic deposits, except in the uppermost part, where laminated sandstone is interpreted as intertidal of marine character. Sarah Formation (Early Silurian-Lower Llandoverian). The Sarah Formation crops out in central Arabia between the southeastern Great Nafud and Wadi ar Rimah. It ranges in thickness from 90 to 300 m (295-984 ft) of medium- to fine-grained sandstone (characterized by cross and oblique bedding structures), accompanied by a tillite facies of glacial to marine origin. The formation shows a variety of morphologic features such as continental tillite and reworked tillite in a sub-aquatic environment and polyphase episodes (alternation of tillite and sandstone) that represent stages of periodic advance and retreat of the ice; a glacial floor with parallel striations and grooves as well as concave pluck structures and crescent-shaped fractures; rockslides and large-scale slumping; and erratic and laminated, varve-like rocks. The lower part of the Sarah was interpreted as glacial paleovalley deposits, followed by ttuvial-marine sediments and ending in the upper part with subaquatic sedimentation in which the traces of a periglacial, lacustrine environment persist locally but have become increasingly marine in character. Qalibah Formation (Early Silurian). In Saudi Arabia, McClure (1978, 1988) reiterates that the Silurian Sequence was preceded by a major glaciation in the latest Ordovician. Powers (1968) described the important unconformities and geological processes associated with the Tabuk Formation. Bahafzallah et al. (1981) and A1 Laboun (1986) redefined the upper boundary of the Tabuk to account for the disconformity associated with the Late Silurian hiatus. Helal (1964 a & b, 1968) defined the Silurian Sequence as a separate formation named the Sharawra Formation. Powers et al. (1966) introduced the term "Qusaiba" for the Lower Silurian Shaly Member of the Tabuk Formation, but Powers (1968) favored using units numbered from 1 to 7 of the Tabuk and discarded the term "Qusaiba" Member. A1 Laboun (1986) reintroduced the terms "Qusaiba" and "Sharawra" members of the upper Tabuk Formation. Based on Vaslet's (1987a, b, 1989, 1990) new lithostratigraphic study, the Lower Silurian Sequence was named the Tayyarat Formation, which begins in the middle Llandoverian (Qusaiba Member) and ends in the late Llandoverian (Sharawra Member). Mahmoud et al. (1992) renamed the Tayyarat Formation the Qalibah Formation, but retained the same members (Table 4.2; Figs. 4.11 and 4.17). The Qalibah Formation crops out at the town of A1 Qalibah between 27~ N, 38033'57 " E and 28005'57 " N, 38022'26 " E, and consists of about 499 m (1,637 ft) of fine-grained, thin, well-bedded sandstone, and greenish to gray shale (Mahmoud et al., 1992). The lower boundary of the Qalibah conformably overlies the Sarah Formation, and the upper boundary is overlain, possibly disconformably, by the Late Silurian and Early

Devonian Tawil Formation or unconformably by the Carboniferous Unayzah Formation. Surface and subsurface sections of the Qusaiba and Sharawra members of the Qalibah Formation were described by Vaslet (1989, 1990) and Mahmoud et al. (1992), as summarized below: a) Qusaiba Member (Llandoverian). At the surface, it consists of 256 m (840 ft) of organic-rich, laminated shale with some interbedded tippled siltstone, abundant graptolites at the base, and micaceous siltstone and sandstone in the upper part, all deposited in a marine, outer-shelf environment. The thicker subsurface section may reach up to 762 m (2,500 ft) in the west to more than 1,828 m (6,000 ft) in the east (Aoudeh and A1 Hajri, 1995) in the vicinity of A1AurayyatYurayf-A1 Jauf in NW Saudi Arabia. It consists of well-bedded to laminated alternations of micaceous shale and siltstone, with thin sandstone intercalations and micaceous partings. The lower part is characterized by very thin (10 ft), black shale, rich in organic matter, the "Hot Shale" of Aoudeh and A1 Hajri (1995). It is the most important source rock of the Paleozoic (and equivalent to the Tannezzuft of Libya) as well as a seal to the underlying Ordovician reservoir. The Hot Shale has an outer-neritic origin, but, as the Qusaiba, youngs from the west and southwest towards the northeast. It is not present everywhere (Fig. 4.19). In those areas, the influence of continental deposits increases. b) Sharawra Member (Wenlockian). About 243 m (790 ft) thick in outcrop, it is dominated by alternating silty, micaceous shale and fine-grained, well-bedded sandstone. It is characterized by phosphatic, conglomeratic sandstone of an infralittoral, marine environment in the lower part, and highly burrowed and bioturbated beds of a marine-strand environment intercalated with beds of shore-face type in the upper part. In the subsurface, the member reaches a thickness of about 352 m (1,155 ft) in a coarsening-upward sequence of siltstone and sandstone with a few intercalations of shale.

The Tippecanoe Sequence in Jordan The Tippecanoe Sequence is found only in south and southeastern Jordan, where it consists of a deltaic sequence alternating with deltaic-marine beds. It is not recorded in the Jordan Rift, but it probably is present as a clastic, marine facies of Silurian and Ordovician age (Fig. 4.3 and Table 4.1) in West Jordan and may be present in North and Northeast Jordan, according to Bender (1975). Although the sequence lacks distinctive argillaceous units, the arenaceous units can be correlated with the section described in Saudi Arabia. There appears to be no indication of the glacial horizon that overlies the Ra' an Shale of Saudi Arabia and is used to explain the absence of the Ashgillian.

115

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 4.17. General lithology and log characteristics of the Lower Silurian Qalibah Formation subsurface in central Saudi Arabia (based on two wells, Udaynan-1 and stratigraphic well-39) (after Mahmoud et al., 1992 and reproduced by kind permission of AAPG). Khreim Group (Ordovician-Silurian) The name is taken from Wadi Khreim in southern Jordan and was first used by Lloyd (1969) for the formations defined by Bender (1974) and named in upward sequence the Graptolite Sandstone, Sabellarifex Sandstone, Conularia Sandstone and Nautiloid Sandstone. The group ranges from 592 to 634 m (1,942-2,080 ft) and predominantly consists of alternating cycles of fine- to medium-grained, micaceous sandstone (quartz arenite) and micaceous siltstone with subordinate mudstone. It is considered to have been deposited in alternating, shallow inner-shelf and deeper mid-shelf zones of a broad epeiric sea, with periodic offshore mud deposition in the outer-shelf zone (Powell, 1989 a & b). Work by the Natural Resources Authority (NRA) led to the subdivision of the group in outcrop into four formations (Hiswah, Dubaydib, Mudawwara and Khushsha) (Powell, 1989 a) and in subsurface into five for116

mations (Sahl as Suwwan, Umm Tarifa, Trebeel, Batra and Alna) (Fig. 4.15).

Subsurface Formations Sahl as S u w w a n F o r m a t i o n ( L l a n v i r n i a n ) . The formation was introduced for the subsurface unit that equates with the lower half of the exposed Hiswah Formation. The thickness increases from 127 m (417 ft) in Wadi Sirhan-10 to 189 m (620 ft) at Risha-3. It consists mainly of shale and micaceous, silty shale, intercalated with claystone and micaceous siltstone, followed by dark-grey siltstone interbedded with very fine- to fine-grained, micaceous sandstone (Andrews, 1991). The lower boundary of the formation represents a major sequence boundary, with the transgression of marine shale over dominantly continental clastics (Amud Formation). The upper boundar 3, is taken at the base of the first sandstone beds at the base of the Umm

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Sedimentary Basins and Petroleum Geology of the Middle East i

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The Sauk Cycle and the Early Part of the Tippecanoe Cycle Tarifa Formation. The Sahl as Suwwan Formation records the first occurrence of widespread, fully marine environments. The lower part is characterized by basinal shale with restricted circulation and a reducing bottom environment, followed by a distal, outer sublittoral depositional environment constituting the entire succession (Andrews, 1991).

Umm Tarifa Formation (Llandeilan-CaradocianAshgillian). The term was introduced by Andrews (1991) for the subsurface Ordovician strata that lie between the Sahl as Suwwan and the Trebeel formations.They are completely penetrated by eight deep wells and ranges in thickness from 546 rn (1,791 ft) at A1 Jafr-1 to 1,114 m (3,654 ft) at Risha-3. In outcrop, it is equivalent to the upper Hiswah and lower Mudawwara formations. Andrews (1991) divided the Umm Tarifa Formation into three informal units. The lower ranges from 90 to 241 m (295-790 ft) of thin-bedded, very fine- to fine-grained sandstone, followed by grey to dark-grey, micaceous siltstone. The middle ranges from 451 to 266 m (1,480-872 ft) of interbedded, micaceous siltstone and very fine- to fine-grained, silica-cemented, silty sandstone. The upper unit has a thickness ranging from 74 to 420 m (243-1,378 ft) and consists of very fine- to fine-grained sandstone interbedded with thin beds of shale. The base of the Umm Tarifa Formation is clearly defined by a basal sandstone unit At the top is an unconformity on which rests the Trebeel Formation. The formation was deposited in a shallow-marine shelf environment influenced by tides and periodic storm events (Powell, 1989 a; Andrews, 1991). Trebeel Formation (Ordovician-Silurian). This formation was named by Andrews (1991) for a subsurface unit well-developed in the Risha, Wadi Sirhan and A1Jafr areas. It ranges in thickness from 67 to 132 m (220-433 ft) in Risha Field to 30 m (98 ft) in Wadi Sirhan. Lithologically, the formation is divided into four units (Andrews, 1991) as described below. Unit A is a shale and siltstone sequence, about 23 m (75 ft),in which are dispersed very fine-grained sand to pebble-sized clasts. Unit B ranges in thickness from 18 to 55 m (59-180 ft) of trough cross-bedded, coarse sandstone. Unit C ranges from 13 to 55 m (43-180 ft) of interbedded mudstone, burrowed argillaceous siltstone, and very fine to fine-grained, sandstone interbeds. Unit D ranges from 20 to 53 rn (66-174 ft) of planar/trough cross-bedded, fine- to medium-grained sandstone. The Trebeel Formation rests unconformably on the Umm Tarifa Formation; the top is gradational and shows the change from the Trebeel sandstone to the Batra shale. The Trebeel Formation in Jordan suggests a close association of glacial deposits with clean, pre- and post-glacial sandstone. Wadi Sirhan was a glaciomarine environment in which was deposited submarine till, distal glacial laminites and ice-rafted dropstones. In the Risha area deposition was characteric of a marine shelf, where the sea level was controlled by glacio-eustatic influences. Batra Formation (Llandoverian-Wenlockian). The formation is developed inA1Jafr (234-343 m, or 768-1,125

fl), in Wadi Sirhan (360-602 m, or 1,181-1,975 ft) and in Risha (872-1,544 m, or 2,860-5,064 ft). Lithologically, the formation is composed of three units (Andrews, 1991). The Lower Hot Shale Unit ranges from 9 to 18 m (30-60 ft) thick black, fissile, micaceous and highly graptolitic shale, rich in organic material, with TOC of up to 7 wt%. The Middle Hot Shale Unit is dominated by micaceous claystone, with stringers of very fine-grained sandstone and has a low organic content (0.4-1.5 wt%). The Upper Hot Shale Unit is about 50 m (164 ft) thick consisting of micaceous shale, with an organic content of 0.8-2.0 wt%. The Batra Formation base overlies the Trebeel with a minor break. The top of the Batra is a gradational boundary with the Alna Formation. The upper and lower units were deposited in a pelagic to hemipelagic setting under anoxic bottom conditions and high organic productivity. The middle unit was deposited in an open-marine shelf of low energy.

Alna Formation (Late Wenlockian to Ludlovian). The formation was introduced by Andrews (1991) to describe the dominantly arenaceous sequences that conformably overlie the Batra Formation shale in the subsurface. The maximum recorded thickness is 710 m (2,329 ft) in the Wadi Sirhan area and 919 m (3,014 ft) in the Risha area.The differences in thickness in the subsurface everywhere were due to variations in the amount of Hercynian erosion products. The formation consists of very fine-, medium- and coarse-grained, argillaceous sandstone with interbedded claystone. Glauconitic sands, limonitic ooids and sucrosic dolomite also are described. In some wells drilled in the Wadi Sirhan, a major 74-92 m (243-302 ft) dolerite intrusion is found at the base of the formation. The dolerite consists of labradorite, augitee, biotite, olivine, opaque and heavy minerals. The basal contact of the formation is gradational marking a change in lithology from shale of the Batra Formation to the interbedded sandstone and claystone of the Alna Formation. The upper boundary is marked by a major erosional unconformity over which lies Permian, Triassic or Cretaceous strata. The Alna Formation was deposited in a shallow-marine, outer to inner sublittoral environment.

Surface Formations Hiswah Formation (Llanvirnian). The term was first introduced by Abu Lihie (1989) and is equivalent to the lowermost part of the Khreim Formation of Lloyd, (1969) and synonymous with the Graptolite Sandstone of Bender (1974). It ranges in thickness from 57 to 70 m (187-230 ft) of predominantly laminated shale, micaceous siltstone, and fine-grained, micaceous sandstone with hummocky crossbedding, trough cross-bedding, ripple cross-lamination and planar lamination. Silty mudstone beds also are present. The base is taken at the contact of the trough cross-bedded sandstone of the Umm Sahm Formation and fine-grained, micaceous and graptolitic sandstone of the Hiswah Formation. The top is taken at the base of the first sandstone with abundant Sabellarifex burrows (Powell, 1989 a). The sedi-

119

Sedimentary Basins and Petroleum Geology of the Middle East ments were deposited as storm- and fair-weather sediments in a shelf environment, ranging from mid-shelf to outershelf and at the top to the inner shelf.

Dubaydib Formation (Llandeilian to Caradocian). The formation was introduced by Abu Lihie (1989) and is equivalent to the upper part of the Khreim Formation of Lloyd, (1969) and the Sabellarifex Sandstone of Bender ( 1974). The formation ranges in thickness from 120 to 150 m (394-492 ft) and divided into three informal members by Powell (1989 a). The lower member consists of thick beds of fine-grained, micaceous sandstone, with thin, micaceous siltstone. The sandstone is rich in Sabellarifex and intensively burrowed and bioturbated. The middle member is a non-burrowed, finely laminated sandstone interbedded with micaceous siltstone. The sedimentary structures found are low-angled cross-stratified, lensoid channels,and massive-bedded, intercalated and ripple-bedded units The upper member is a micaceous, fine-grained, thin-bedded sandstone with extensive ripple cross-lamination intercalated with micaceous siltstone. The base is defined by the first appearance of thin-bedded sandstone with abundant Sabellarifex. The top is taken below a varicolored shale bed in the lower part of the Mudawwara Sandstone. The lower member of the Dubaydib Formation was deposited in a nearshore, shallow-water sand bank or middle shoreface zone colonized by suspension-feeding worms. The middle member was deposited in high-energy, high-sedimentation conditions in a mid-shelf zone, with alternating storm- and fair-weather conditions. The upper member is dominated by shallow-water, upper and lower flow regime units, followed by shore-face or shallow subtidal conditions with a low rate of sedimentation (Powell, 1989 a).

Mudawwara Formation (Caradocian-upper Llandoverian). The termwas first used by Lloyd (1969) for the rocks equivalent to the Canularia Sandstone (Bender, 1974) and was adopted by Masri (1988) and subdivided into three members, from base to top: the Tubeiliyat Sandstone, Batra Mudstone and Ratiya Sandstone. The formation varies in thickness from 220 to 250 m (722-820 ft) and consists predominantly of alternating, finely laminated, fine- to medium-grained, micaceous sandstone, and very fine, micaceous sandstone or micaceous siltstone. Tubeiliyat Sandstone Member consists of about 105 m (344 ft) thick of varicolored, ripple cross-laminated, micaceous siltstone and very fine-grained sandstone. The sediments contain Skolithos, Sabellarifex, Harlania and sparse Cruzenia traces. Bedforms in sandstone include ripple cross-lamination, low-angle cross-bedding, planar bedding, and oscillation interference and ladder-back ripples. The Batra Mudstone Member has a thickness of about 85 m (279 ft) of mudstone with thin, red siltstone laminae, overlain by medium- to coarse-grained, trough cross-bedded, quartz arenite sandstone. The Ratiya Sandstone Member is about 60 m (197 ft) of finely laminated, micaceous sandstone intercalated with micaceous siltstone and

120

silty mudstone. Gypsum occurs as thin laminae and infilling joints. The sediments contain Diplograptus sp., Glyptograptus sp., Monograptus cf. Sedgwicki and undetermined trilobites and brachiopods. The base is gradational and taken between the sandstone of the Duba);dib Formation and the overlying varicolored siltstone of the Mudawwara Formation. The top also is gradational, from thinly-bedded, micaceous siltstone and sandstone of the Dubayib Formation to varicolored sandstone of the Khushsha Formation. The formation was deposited in an inner to mid-shelf environment, with periodic deeper water, open-marine conditions indicated by a higher proportion of siltstone, fine-grained sandstone and thick mudstone (Powell, 1989 a). Khushsha Formation (lower Llandoverian). The formation was introduced by Masri (1988) replacing the Nautiloid Sandstone of Bender 1974). It ranges from 33 to 160 m (108-525 ft) of thin-bedded, micaceous siltstone and fine-grained, wavy, cross-bedded sandstone, grading upwards into thick-bedded, varicolored, micaceous siltstone and fine-grained sandstone with an abundant fauna. The bedforms include hummocky cross-stratification. The basal contact is gradational, from thinly laminated, micaceous siltstone and fine-grained sandstone of the Mudawwara to thick-bedded, alternating sandstone and siltstone of the Khushsha. The top is marked by the Kurnub, Cretaceous unconformity in a wave-dominated region with brief storm events (Powell, 1989 a).

The Tippecanoe Sequence in Iraq Khabour Formation (Middle to Late Ordovician?). In northern Iraq, in the thrust zone, a single formation represents the Tippecanoe Sequence. Wetzel (1950, cited in Bellen et al., 1959) first defined this formation and named it the Khabour Quartzite (Fig. 4.3 and Table 4.1). In the outcrop, it has a thickness of more than 800 m (2,624 ft), and in subsurface, in well Khleisia-1, as much as 1,250 m (4,100 ft) was penetrated without reaching the base. It consists of thinly bedded, fine-grained sandstone (quartzites and graywackes) and silty, micaceous shale. However, the presence of dolomite and limestone intercalations found in the Khleissia well indicates more marine conditions. The depositional environment initially was an intertidal-mud-flat setting that graded into the deeper-water conditions in which the turbidites were deposited (Buday, 1980). The sediment-transport directions swing from northeast to easterly, but are more nearly southerly in the uppermost part of the succession. Detailed studies of the trilobite, brachiopod and molluscan fauna indicate an age ranging from the Llanvirnian to Caradocian. Dittmar (1971, cited in Buday, 1980) attributed the lower part of the sequence to the Middle Ordovician, and the presence of a conglomeratic layer may mark a boundary between the Middle and Late Ordovician (Llandeilian-Caradocian), according to Buday (1980).

The Sauk Cycle and the Early Part of the Tippecanoe Cycle However, given the recognition of a glacial level elsewhere in the Middle East, it is not impossible that the conglomerate might represent some part of the Caradocian-Ashgillian succession, but more detailed data are essential if this is to be resolved. Clearly, an equivalence of the lower part of the succession to the Hanadir Shale and Ordovician Sandstone horizons of Saudi Arabia is established for the lower part of the sequence. No direct evidence exists for the presence of any Cambrian horizon.

Tabuk Formation of Saudi Arabia.

The Tippecanoe Sequence in Qatar Tabuk Formation (Early-Late Ordovician?). It is recorded in the deepest wells (Matbakh-2 and Ras Qirtas1) drilled in the northern part of the country (Figs. 4.3 and 4.21). The beds consist of about 198 m (650 ft) of an alternating sequence of micaceous and arkosic sandstone, siltstone and shale (Hamam and Nasrulla, 1989). The sandstone units are well-laminated to cross-bedded and show a fining-upward trend. This sandstone most probably was storm-surge deposits or was reworked by gently pulsating traction currents in a shallow-marine environment. The siltstone and shale are intensely burrowed and bioturbated, and sedimentary structures are almost obliterated. The sediments are rich in trace fossils indicative of tidal influence in a shallow-marine environment. Sharawra Formation (Silurian). It rests unconformably on the Tabuk Formation and is overlain by the Devonian Tawil Formation. It has a thickness of about 665 m (2,182 ft) and is divided into two members. The Lower Shaly Member, Llandoverian in age, is composed of gray, blackish, micaceous siltstone and claystone. These darkcolored beds have sapropelic materials and, therefore, are potential source beds. They are overlain by the Upper

The Tippecanoe Sequence in Kuwait Tabuk Formation (Early Ordovician-Early Silurian?). The deepest well, Burgan A-l, encountered 473 m (1,500 ft) referred to the Tabuk Formation (Fig. 4.20), which consists of fine- to coarse-grained, micaceous sandstone, with a reddish-brown clay matrix containing hematite- stained pebbles of volcanic rocks, and quartzite with grains of felspar alternating with sub-rounded pebble and cobble conglomerates. The pebbles and cobbles consist of both intrusive and extrusive igneous rocks in a finegrained, hematite-stained, argillaceous sandstone matrix (Khan, 1989). The formation is unconformably overlain by the Jauf Formation and underlain by the quartz and claystone-shale intercalations of Precambrian age. Based on its lithologic character, it has been correlated with the

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Sedimentary Basins and Petroleum Geology of the Middle East Sandy Member of Wenlockian to Ludlovian age (Fig. 4.21), consisting of alternating sandstone and fine-grained, micaceous siltstone and claystone (Hamam and Nasrulla, 1989). The sandstone shows rippling and flaser bedding and contains varying amounts of K-feldspar, volcanic rock fragments and clay minerals. The sedimentological interpretation of the Sharawra Formation indicates deposition in a shallow-mariine environmment.

S h a r a w r a F o r m a t i o n (Silurian): Only the upper part of the Silurian was reached by a deepest well in offshore Abu Dhabi and we named it as the upper Sharawra Sandstone Member because of its similarity in lithology and age equivalent to the unit found in well Matbakh-2 in Qatar reported by Hamam and Nasrulla (989). This member consists of about 22.5m (730 ft) of sandstone with minor interbeds of claystone (Fig. 4.22). This unit has been recently described by Hassan et al. (1995) as follows: 46

T h e T i p p i c a n o e s e q u e n c e in the U n i t e d A r a b E m i r a t e s

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Fig. 4.21. Lithostratigraphy of the Silurian Sharawra Formation in Qatar (based on data from Hamam and Nasrulla, 1989). Note that Aoudeh and A1 Hajri (1995) restrict the Sharawra Member to the Wenlockian and the Qusaibah to the Llandoverian in Saudi Arabia. 122

The Sauk Cycle and the Early Part of the Tippecanoe Cycle m (150 It) of sandstone (light grey, quartzitic, fine to very fine-grained, argillaceous, micaceous, pyritic and slightly dolomitic). 120 m (390 ft) of claystone is grey, blocky, occasionally fissile, silty and noncalcareous. Claystone and shale (grey, silty, pyritic and non-calcareous). 15 m (59 ft) of very fine grained, argillaceous and pyritic and non-calcareous sandstone. 42 m (139 ft) of grey shale, silty, micaceous with occasional pyrite, and very thin interbeds of sandstone and siltstone. Hassan et al. (1995) reported the presence of Eisenackia cf lagenomorpha Leiosphaeridia sp., Lophosphaeridium sp., Dictyotifium sp. and Angochitina sp. Eisenackia wihich gave the age of the sequence as mid/late Ludlovian to ?Pridolian. These sediments were deposited in an open marine conditions under normal salinity.

THE EARLY PALEOZOIC SEQUENCE IN SOUTHEAST TURKEY AND SYRIA

disehir beds are found in the Hakkari area (Fig. 4.23 b). However, in some areas, the overlying beds range from the Devonian to as young as Permian? or Triassic. The sequence is more complete in the Amanos Mountains (Fig. 4.24) and extends into the Early Silurian, although there is a potential break during the Ordovician between the Seydisehir and Bedinan formations (Cater and Tunbridge, 1992). Fig. 4.23 b shows a general strike section from Seydisehir in the west to the Turkish border, with Iraq-Iran in the southeast with the principal locality names. It particularly points to the existence of a north-south-trending graben in the Amanos Mountains of south-central Turkey. Figures drawn from Cater and Tunbridge (1992) show the facies distribution (Fig. 4.24 A-F). The currently accepted names of the four formations that bridge the Cambrian are shown on the stratigraphic column (Fig. 4.24). Formation names now have replaced the older letter terminology established by Dean and Krummenacher (1961).

Saran Formation (Late Infracambrian-early Early The Sauk Sequence in Southeast Turkey During the early Paleozoic, the northern margin of ancient Gondwana lay close to northern Syria and Turkey; consequently, the known sections show facies differences when compared with those of Jordan, Iraq and Saudi Arabia farther to the south. The sequences generally are fine grained and more argillaceous, with more and earlier evidence of marine conditions existing during the Cambrian. In the far western Anatolides, an Early Cambrian marine sequence has been described in the Gray Limestone Member of the Cal Tepe Formation (Dean, 1975), overlain by shale of the Seydisehir Formation, which contains a Middle Cambrian fauna. As the top of the formation extends into the Early Ordovician, the Seydisehir Formation in this part of Turkey is equivalent to the Koruk (in part?) and Sosink formations in the Mardin area (Fig. 4.23a). Since there are no outcrop data in Syria, and there are few deep wells, the section is not well-known; however, the well data generally show fair agreement with the field observations in Turkey. In southeastern Turkey, as a result of tectonic movements, Paleozoic rocks from the Cambrian to Permian crop out in a number of inliers, providing information supplementing data from wells drilled during the course of hydrocarbon exploration. The succession contains a number of discontinuities and possible diachronous situations. There are two principal areas involved" the Amanos Range in central southern Turkey and the Derik-Mardin area of southeastern Turkey (Fig. 4.23 b). The basic stratigraphic data are drawn from the works of Dean (1975), Janvier et al. (1984), Dean and Monod (1985) and Dean et al. (1986), and the review by Cater and Tunbridge (1992). In southeastern Turkey, the Late Cambrian succession is terminated by an erosional surface, above which lie the Late Ordovician Bedinan beds in the Derik-Mardin area, although unconformable Late Cambrian to Early Ordovician Sey-

Cambrian). In the Zap Anticline at Derik and Tut (Fig. 4.23), and in well Akcakale-1, Early Cambrian rocks of the Sadan Formation, formerly called Formation A by Dean and Krummenacher (1961), have been recognized at the surface and in the subsurface. Rigo and Cortesini (1964) proposed the name of the formation for rocks Kellogg (1961, cited in Dean, 1975) originally assigned to the Telbesmi Formation. It is approximately equivalent to the combination of the Sadan Redbeds Formation and the Zabuk Quartzite Formation of Schmidt (1965). In the type locality, the formation begins with a basal conglomerate and volcanic clasts, followed by a continental redbed sequence of coarsely bedded sandstone, with shale and sandy limestone. The formation may exceed 1,700 m (5,576 ft) in thickness, and the fluvio-deltaic sandstone forms an obvious parallel with the beds of the Saq Sandstone of Saudi Arabia. The base of the formation is not seen in the Zap Anticline, but the top of the formation can be observed passing up into pink, quartzitic sandstone (Zabuk Formation). The base of the succession is seen in the Derik inlier, where a basal breccia-conglomerate overlies volcanic rocks of the Derik Formation assigned to the late Infracambrian. The Sadan Formation here is only 480 m (1,575 ft) thick and consists of a continental redbed series of sandstone and siltstone. If the correlation with the Sadan Formation in the Zap Anticline is correct, there must be a significant facies transition between the two areas. Zabuk Formation (Early Cambrian). Dean and Krummenacher (1961) previously called this formation Formation B. It crops out in the Amanus area (south-central Turkey) (Fig. 4.24). It has a thickness of about 600 m (1,968 ft) of pink, quartzitic sandstone and conglomerate with thin inclusions of ferruginous, micaceous shale (Table 4.1). The formation is the facies equivalent of the top of the Sadan Formation (Zap Anticline) in southeastern Turkey. Pebbles of pale quartzite, dark schist and igneous 123

Sedimentary Basins and Petroleum Geology of the Middle East

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124

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The Sauk Cycle and the Early Part of the Tippecanoe Cycle

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125

Sedimentary Basins and Petroleum Geology of the Middle East rocks occur throughout the formation, where cross-bedding is common. The beds become more ferruginous and shaly at the top, culminating in a horizon of ferruginous shale a few meters thick. The formation passes upward into the Koruk Formation. Koruk Formation (Middle Cambrian). In the Hakkari area (Fig. 4.24), the Koruk Formation consists of about 350 m (1,148 It) of primarily carbonate beds (Dean, 1982 a). An initial dolomitic member is followed by an alternation of interbedded shale and sandy limestone. The top of the formation passes by transition into the sandy and shaly Sosink Formation. However, in the Zap Anticline, an unconformity (Fig. 4.23) marks the top of the formation, above which lies the Late Cambrian-Early Ordovician Seydisehir Formation where the Sosink Formation is absent (Fig. 4.23). In the type section near Derik in well Akcakale- 1, the basal unit is formed by 200 m (656 ft) of sucrosic dolomite above the redbeds at the top of the Sadan Formation.The beds of the Koruk Formation were deposited during the first major marine transgression of the Phanerozoic in southeastern Turkey. In the northern limb of the Zap Anticline, the Lower Dolomite Member ranges from 300 to 350 m (about 9841,144 ft) and consists of alternating, fine-grained, black and white, stromatolitic dolomites with occasional packstone, shale and coarse dolomites indicating low-energy, peritidal conditions (Dean et al., 1981). These rocks pass up into the 38.4 m (about 126 ft) Limestone Member. Dean et al. (1981) identify six units within the Limestone Member, each ranging in thickness from 1.8 to 13.5 m (about 6-45 ft). Units A, B and C contain trilobites that indicate a Middle Cambrian age. Towards the top, clastics become more important, while units D, E and F contain varying amounts of shale, with mudstone and siltstone in the uppermost units (Unit F). In the Zap Anticline area, the depositional environment indicated changes in water depth deepening from peritidal to pelagic. Conformable above the youngest nodular limestone of the Koruk Formation in this area is a thick detrital unit of at least 2,500 m (8,200 ft), equivalent to the Seydisehir Formation in the western Taurus Mountains. Exposures of the Koruk Formation in the Amanos Mountains show considerable similarities with the outcrops in the Zap Anticline described by Dean et al. (1986). Sosink Formation (early Late Cambrian). In the type section near Sosink (Figs. 4.23 and 4.24), Kellogg (1960, cited in Dean et al., 1981) described the Sosink Formation in the Derik area, where it is about 1,057 m (3,467 ft) thick, and divided it into two members. The lower, Shale Member, which is about 192 m (630 ft) thick and contains some thin limestone and siltstone, is followed by a 865 m (2,837 ft) Sandstone Member. The sandstone commonly is cross-bedded and contains some shale in a coarsening-upward unit formed in a deltaic complex. The base of the formation has been defined where the shale with thin sandstone succeed the dolomites at the top of the Middle Cambrian Koruk Formation. According to Dean

126

(1982b), much of the type Sosink may be a facies equivalent of the higher part of the Koruk Formation found east of Derik in southeastern Turkey. The top of the succession is marked by an unconformity, over which lies the shale at the base of the Caradocian Bedinan Formation. Dean (1982b) reported that the thin limestone in the shale member may include locally abundant glauconite and fossil debris with trilobite and brachiopod fragments. Lithologically, this limestone may be lime mudstone, wackestone or a whitish, sparry limestone. In the Tut area of south-central Turkey (Fig. 4.24), the formation, described as mostly shaly with an occasional fine-grained sandstone succession totalling about 350 m (1,148 ft), formed in a delta-front to pro-deltaic environment. It is here overlain by Cretaceous limestone. In subsurface, a thickness of 600 m (1,968 ft) was penetrated in well Akcakale-1. In the Bakuk and Girmeli wells southeast of Derik that penetrated the formation, it shows a return to the facies developed in the type section. Here, the formation is characterized by an upwards-coarsening sequence passing from shale to sandstone-dominant lithologies. In the southern Amanus Mountains, the Sosink Formation has a basal 8 m (26.3 ft) of shale with Middle Cambrian trilobites passing up into 2 m (6.6 ft) of pink, nodular limestone that gives way to 50 m (164 ft) of well-bedded, bioturbated, trilobite shale. The Sosink's great thickness variations are attributed to its deltaic depositional environment. Westward toward the Tut area, the thinner sequence probably was deposited in deeper water.

Seydisehir Formation (Late Cambrian-early Arenigian). This 2,500 m (8,200 ft) sequence is found in the Hakkari region (Fig. 4.23a), where it comprises a series of shale and thin, to medium-bedded sandstone with occasional intercalated dolomite beds deposited upon a wave-swept shelf. The formation's upper half consists of a monotonous, flysch-like alternation of black shale and finely laminated quartzites with abundant trace fossils (especially trilobitic Cruziana traces). Unconformably overlying the formation is the Caradocian-Ashgillian Sort Tepe Formation (Dean et al., 1981), equivalent to the Derik region's Bedinan Formation (Figs. 4.23 b and 4.24). In the Taurus Mountains, the Sort Tepe is unconformably overlain by the Late Devonian dolomites with molluscan debris, red sandstone and shale of the Yiginli Formation or younger Mesozoic beds (Janvier et al., 1984). On the northern limb of the Zap Anticline, Dean et al. (1981) and Dean (1982a) described a sequence of thick clastics and assigned them to the Seydisehir Formation beds formerly placed in the Gira Formation by Altinli (1966). They made two informal divisions into lower and upper sequences, which were subdivided further. The lower 970 m (3,182 ft) consists of shale and silty shale interbedded with gray and white quartzites and graywackes with Cruziana trace fossils. There are occasional bands of dolomitic limestone and limestone with a fauna suggesting affinities with Iran's Mila Formation. The upper sequence is a 300 m (984 ft) thick sequence of dolomites and shale,

The Sauk Cycle and the Early Part of the Tippecanoe Cycle

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MIDDLE CAMBRIAN (Koruk Formation)

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127

Sedimentary Basins and Petroleum Geology of the Middle East with the latter containing a fauna that includes Saukia and Niobella and trilobite fragments indicating a Tremadocian age. The Seydisehir Formation is present in both the Amanos Mountains and the Zap Anticline of southeastern Turkey. The absence of the formation between these latter two localities (Figs. 4.23 and 4.24) was interpreted as an indication of Early Ordovician emergence, with the emergent area possibly having acted as a local sedimentary source (Dean et al., 1986). The above formations complete the Sauk Sequence in Turkey. Fig. 4.24, shows the facies distribution from Early Cambrian to Early Ordovician, clearly illustrating the Cambrian marine phase. The lower part of the Tippecanoe section apparently is absent, for the lowest member of the Tippecanoe appears to be no older than Caradocian in age.

In Syria, the projected thickness of Cambrian beds, based upon the thicknesses found in southeastern Turkey, is in the order of 800-1,000 m (2,624-3,280 ft). The Early Cambrian Zabuk Formation of orthoquartzites and siltstone of continental origin is followed conformably by the Middle Cambrian Burj Formation of shallow marine dolomitic limestone with thin shale intercalations, which were penetrated in well Khanasser-1 in northeastern Syria, where only 62 m (203 ft) were recognized. The Late Cambrian Sosink Formation measures about 700 m (about 2,296 ft). The lithology of the Late Cambrian rocks, in which well Swab-1 in eastern Syria bottomed, consisted of shale, sandy limestone and orthoquartzitic sandstone and shaly sandstone of continental origin resting conformably upon Middle Cambrian Burj carbonates (Ala and Moss, 1979; Labadidi and Hamdan, 1985) (Fig. 4.4 and Table 4.1).

to the upper member of the Bedinan Formation (Dean et al., 1981). Therefore, the upper shale member is equivalent to the Dadas, according to Kellogg (1960, cited in Dean et al., 1981). The age of the lower shale is assigned to the late Caradocian based on correlation of the contained fauna with that of Bohemia (Dean, 1983). Correlation of the highest beds suggests that they are probably still within the upper Caradocian. Cretaceous redbeds and sandstone rest unconformably on this sequence. The presence of the formation has been proved in numerous wells. In the Akcakale, Harran and Girmeli wells, the Bedinan Formation sediments are lithologically similar to the deltaic facies of the type section, but there is a marked thinning and a decrease in the amount of sandstone present immediately north of the Girmeli well, seen also in the Bakuk and Gercus wells. Sort Tepe Formation (Ashgillian). Dean et al. (1981) introduced a formation of as much as 25 m (82 ft) of clastics, principally shale and siltstone, above the Seydisehir Formation and below the Devonian in the Cukurca area of the southern Zap Valley. Dean (1980) and Dean et al. (1981) divided the section in the type area into five beds. Above is a thin (0.75 m, or 2.5 ft) bed of high-energy grainstone and ferruginous oolite with reworked quartzite, with graptolitic shale of 1 m (3.28 ft), bioturbated siltstone of 1.5 m (5 ft) and shale of 5 m (15.5 ft), followed at the top by 2 m (6.6 ft) of siltstone with graptolites, trilobites and brachiopods. The beds represent the deposits laid down in a regressive shoreline environment. They are equated with 50 m (164 ft) of shelf-facies shale and sandstone below the Devonian in the Zap Anticline. The overlying beds, which are the transgressive Tiginli red sandstone and the Kaprulu shale, are assigned to the upper Paleozoic, (Devonian to Carboniferous). The sandstone has been compared to the Pirispiki Formation in Iraq (Chapter 5). Thus, the Silurian generally is lacking in the Taurus Mountains (Janvier et al., 1984).

The Tippecanoe Sequence in Southeast Turkey

The Tippecanoe Sequence in Syria

In Turkey, the Tippecanoe Sequence consists of two formations - - the Bedinan and the Sort T e p e - which are approximately equivalent in age (Fig. 4.24).

Ordovician rocks have been penetrated in several places in northern, central and eastern Syria (Fig. 4.4). Lithologically, the succession is made up of fine-grained, thin-bedded, micaceous shale, with intercalations of finegrained sandstone. The presence of the trilobites Colpocoryphe arago and Pseudobasilicus cf nobilis in the lowest 23 m (84 ft) of the shale in well Abba-1 is diagnostic of Llandeilian (Sudbury, 1957); and, as the remaining 300 m (960 ft) of shale is unfossiliferous, it may extend as high as the Silurian. In well Tanf-1, 2,000 m (about 6,560 ft) of Late Ordovician rocks, primarily sandstone, rest on Early Ordovician sandy limestone. A thick section also is found in well Khanasser-1. Thus, the evidence points to a fairly wide Ordovician distribution in subsurface, with sediments in the lower part of the section generally indicative of a shallow-marine shelf environment. The section

The Sauk Sequence in Syria Zabuk, Burj and Sosink formations (Cambrian).

Bedinan Formation (Caradocian-eady Ashgillian) Near the village of Bedinan, 20 km south- southeast of Derik and southwest of Mardin, about 680 m (2,230 ft) of shale and sandstone crop out and were named Bedinan in a 1960 unpublished report by Kellogg (cited in Dean et al., 1981). They consist of a dominant lower member of greenish shale, 502 m, or 1,647 ft thick, followed by 121m (397 ft) Of fine-grained, well-sorted sandstone passing up into poorly sorted, brown, medium- to coarse-grained, subarkosic sandstone. These are capped by 87 m (285 ft) of dark-green shale and dark, silty sandstone assigned to the Dadas Formation and regarded as Early Silurian. A more recent modification has removed the sandstone from the Dadas Formation, and the remaining shale unit is assigned

128

The Sauk Cycle and the Early Part of the Tippecanoe Cycle appears to coarsen upwards, with an increase of sandstone with respect to the lower shale and limestone. It is interpreted as the distal facies to the shoreline and deltaic facies found in Jordan (Sudbury, 1957; Bender, 1974). In 1985, Lababidi and Hamdan divided the Syrian Ordovician-Silurian sediments into four formations: the Tremadocian-Arenigian Khanasser Formation (from wells Khanasser- 1, Swab- 1 and Tanf- 1); the Swab Formation, from Llanvirnian to Llandeilian, found in eastern Syria (in Swab-1 and Khanasser-1); the Llandeilian-Ashgillian Afandi Formation (type section in well Afandi-1 in northeastern Syria) and the Tanf Formation (Silurian). These sediments were deposited in environments ranging from continental to continental/marine to nearshore setting.

Khanasser Formation (Tremadocian-Arenigian). The formation consists of quartzitic sandstone, with some interbedded shale that contains acritarchs and chitinozoans of continental origin. The formation is conformable with the beds below (Sosink Formation) and above (Swab Formation) in central Syria, but disconformable in eastern Syria (Fig. 4.4). The thickness varies from well to well, from 625 m (around 2,050 ft) to 381 m (about 1,250 ft). The age of the formation essentially relates it to the Sauk Sequence, but it is included here in dealing with well information. Thus, the formation is equivalent to the Seydisehir Formation in southeastern Turkey. Swab Formation (Early Ordovician, LlanvirnianLlandeilian). The Swab Formation is well-developed in eastern Syria, where it reaches a thickness of 932 m (about 3,057 ft) in Swab-1 and drops to about half that amount in the central part of the country (Khanasser-1). It is made up of silty shale, black shale and sandstone of both marine and continental origin, with graptolites, acritarchs and chitinozoans.

Afandi Formation (Late Ordovician, LlandeilianAshgillian). The formation is named from well Afandi-1 in northeastern Syria, where the formation has a thickness of about 450 m (1,476 ft), which increases toward central Syria, to where in well Tanf-1 it reaches 1,140 m (about 3,739 ft). Lithologically, the succession is made up mostly of continental sandstone and siltstone, with rare intercalations of limestone. The upper and lower contacts are confonnable in central Syria, and disconformable in the eastern part of the country. Tanf Formation (Silurian). Silurian rocks have been found in several wells in Syria and have been assigned to the Abba Group, although the term "Khabour Beds" has been used (Ala and Moss, 1979). Lababidi and Hamdan (1985) introduced the term "Tanf Formation." The strata may reach a thickness of 500 m (1,640 ft), with the dominant lithologies consisting of shale and siltstone with subordinate sandy beds and a rich graptolitic fauna. These beds undoubtedly represent the distal, deeper-water facies of the neritic to fluvial deposits found in Jordan and Saudi Arabia. According to Berry and Boucot (1972), the shale and siltstone of the Tanf Formation and its equivalent covered wide areas of Syria, Jordan and Saudi Arabia,

although the sediments reflect nearer-shore environments in the latter two areas. The formation is capped by an unconformity, and most of the Late Silurian up to the Late Devonian is absent over most of Syria. The beds also rest unconformably upon the Afandi or Markada formations.

THE EARLY P A L E O Z O I C OF IRAN

The Sauk Sequence Where the Infracambrian Zaigun Formation is welldeveloped, there is no obvious sedimentary break between the Zaigun and Lalun formations (Figs. 4.4 and 4.25). The Lalun Formation, on the basis of trace fossils such as Cruziana, is assigned to the Early Cambrian, the lowest member of the Sauk Sequence. Near the top of the Lalun Formation, the presence of Redlichia trilobites provides evidence not only of an Early to Middle Cambrian age, but of the beginning of the late Early Cambrian transgression. This transgression, which persisted into the Late Cambrian, is marked by carbonate sediments (the limestone and dolomites of the Mila and equivalent formations), which replaced the Lalun clastics. In some places, the Zaigun clastic sediments may be missing, as in the Zenjan area in northwestern Iran, because of pre-Lalun erosion, but only in the region north-northwest of Tehran are conglomeratic horizons found intercalated in the Lalun Formarion.

Lalun Formation (Early to Middle Cambrian). Assereto (1963) named the Lalun sandstone to replace the older term "Old Red Sandstone," which became obsolete when the unit was recognized as Cambrian in age. The unit is persistent and easily recognized by the coarser size of the particles as compared to the underlying beds of the Barut and Zaigun formations. In the type area, about 40 km northwest of Tehran, the formation is about 600 m (1,968 ft) thick and made up of thick beds (approximately 80-100 cm thick) of light- to wine-red, ripple-marked and cross-bedded, moderately well-sorted, medium-grained sandstone. The top of the formation is marked by a persistent, white, well-rounded quartzite (Fig. 4.25). The lower sandstone units tend to be reddish-brown, well-bedded, compact arenites with angular grains. In the lowest 70 m (230 ft), there are interbedded, fine, red, sericitic, silty shale with sandstone that may include conglomeratic bands in which the conglomeratic components may be up to half a meter in diameter and consist of porphyritic rhyolite, quartzite and chert. As indicated earlier, the age is established by the presence of Cruziana and redlichiid trilobites (cf. Stticklin, 1972). The sandstone can be compared with the purple sandstone of the Salt Range in Pakistan, the Saq Sandstone of Saudi Arabia or the Lower Quweira Sandstone of Jordan. Dahu Formation (Early-Middle Cambrian). In the Zagros Basin of southern-southwestern Iran, Setudehnia

129

Sedimentary Basins and Petroleum Geology of the Middle East (1975) described a composite section of up to 1,000 m (3,280 ft) of fine- to medium-grained and occasionally coarse-grained, laminated sandstone, which is assigned the same age and referred to the Dahu Formation. The latter sandstone is occasionally cross-bedded and may be greenish, glauconitic and include shale intercalations, and grade up to medium- to coarse-grained, strongly cross-bedded sands. At these higher horizons, the sandstone is occasionally pebbly and, more rarely, micaceous. The clasts consist of basic igneous and volcanic rocks with some quartz pebbles.

Mila Formation (Early Cambrian-Early Ordovician). The type area for the Mila Formation at Mila Kuh lies about 230 km east-northeast of Tehran (St6cklin et al., 1964), where it has been subdivided into five members ranging in age from Early Cambrian to Ordovician (Table 4.3). While it is largely a carbonate succession, occasionally there was an ample supply of clastic sediment. The type section has a thickness of 585 m (1,919 ft), but the thickness of the Mila Formation exceeds 2,000 m (6,560 ft) in the depocenters in northeast central Iran, (north of Tabas); elsewhere in the southeast central Alborz, thicknesses range from 500 to 700 m (1,640-2,296 ft). In southwest Iran,( southwest of Golpaygan, Figs. 4.25 and 4.26), the Mila Formation has a thickness of more than 1,000 m (3,280 ft). Table 4.3 shows the subdivision and correlation chart of the Mila Formation in Iran. In northern Iran, the Mila Formation has been divided into five members (St6cklin, 1972). The lowest (Member 1) consists of alternating dolomites and marl. Member 2 is made up of limestone with subordinate marl and siltstone. Member 3 is composed of glauconitic limestone. Member 4 consists of siltstone, sandstone, glauconitic limestone and marl. The final member (5) is a clastic sequence of Ordovician shale and well-bedded sandstone. The faunal assemblage of trilobites and brachiopods provides the dating. From this dating, it is clear that members 1-4 (Kalshaneh and Derenjal formations) belong to the Sauk Sequence, but member 5 (Shirgesht Formation) belongs within the Ordovician part of the Tippecanoe Sequence, although no precise age is given (Table 4.3 and Fig. 4.26). According to Assereto (1963), who reported on the Karadj and Djadjerud valleys, where about 400 m (1,312 ft) of the Mila Formation are exposed, a lithologic division can be made into four units. Here, the Mila Formation is unconformably overlain by quartzites forming the lower part of the dominantly calcareous Late Devonian to Early Carboniferous Geirud Formation (see following section on Kaskaskia Sequence). Thus, there was a widespread regression and emergence between the latest Cambrian or Early Ordovician and the Middle to Late Devonian; consequently, the Tippecanoe Sequence is not represented here. The lower part of the Mila is conformable with the Upper Lalun quartzite. Setudehnia (1975) described and divided the Mila Formation in southern and southeastern Iran (Zagros Basin) into three distinct members (Fig. 4.25 and Table 4.3) as

130

follows: Member A:

(Early-Middle Cambrian). About 71.5 m (235 ft) of red, silty shale grading up into an alternation of red, silty shale and gray and yellow dolomites and limestone, followed by more coarsely crystalline, massive, saccharoidal dolomite and gray, thin-bedded dolomites; the member ends with fine- to coarse-grained dolomites interbedded with red shale. Member B: (Middle Cambrian). Its thickness, ranging from 25 m (82 ft) at Kuh-e Dinar to 138 m (450 ft) at Zard Kuh, consists of red, silty shale with salt pseudomorphs. Member C: (Middle-Late Cambrian). This unit, which reaches a maximum of 350 m (1,148 ft), consists of interbedded limestone and shale with minor sandstone. The limestone is light- to dark-gray, well-bedded with some ripple marks, and rarely brecciated. It is fossiliferous and overlain by a succession of shale and sandstone assigned to the Ilebeyk Formation. The Mila Group of eastern Iran is the exact stratigraphic equivalent of the Mila Formation of northern and south-southeastern Iran. Because of the considerably greater thickness and greater differentiation, it was found useful to raise the formation to group status (St6cklin, 1972). The component formations of the group are, in ascending order, the Kalshaneh and Derenjal formations (Sauk Sequence) and the Shirgesht Formation (Tippecanoe Sequence), which in turn correspond to the five members in the type section in northern Iran (Table 4.3). Kalshaneh Formation (Middle Cambrian). In the western Derenjal Mountains of eastern Iran, Ruttner et al. (1968) described a thickness of about 1,000 m (3,280 ft) of mafic volcanics and dark-gray, fine-bedded dolomites, with some chert; black, fetid limestone; and red-green and yellow shale with interbedded quartzites. There is a sharp lithologic break between these beds and the overlying Derenjal Formation. The lower contact generally is disturbed by basic intrusions.

Derenjal Formation (late Middle to Late Cambrian). The type section in eastern Iran is 862 m (about 2,827 ft) thick (Ruttner et al., 1968). The basal 195 m (640 ft) of yellowish and reddish-gray siltstone, marl and dolomite intercalation is followed by flaggy limestone interbedded with marly and silty beds and ends with 20-30 m (66-90 ft) of fossiliferous, gray, massive limestone. The beds can be dated by their brachiopod and trilobite fauna. Both overlying and underlying contacts are conformable and transitional.

llebeyk Formation (Late Cambrian, equivalent to the Derenjal Formation). Setudehnia (1975) first introduced the name Ilebeyk Formation (Late Cambrian) for a sequence of about 280 m (918.5 ft) of predominantly shale and sandstone exposed along the Zard Kuh Range (Fig. 4.26). The shale is greenish-gray, fissile and micaceous,

The Sauk Cycle and the Early Part of the Tippecanoe Cycle

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21

Fig. 4.25 Composite stratigraphic sections of Cambro-Ordovician sediments in the High Zagros Belt (compiled with modification from Setudehnia, 1975). enclosing minor, thin, fossiliferous limestone. The sandstone is green-gray, micaceous, laminated and slightly cross-bedded. Berberian and King (1981) show the Ilebeyk as equivalent to the top part of the Mila Formation, but show the Zard-Kuh as post-Mila, occupying most of the Ordovician and extending into the Early Silurian. This is presumably an error, as the graptolitic shale and sandstone succession recorded by Davoudzadeh et al. (1986) consists of up to 800 m (2,624 ft) of Ordovician to Silurian shale north of Bandar Abbas and is known as the Shirghest Formation in northeast and central Iran. In the Zeber Kuh range in eastern Iran, a Late Cambrian shale and sandstone succession has been described by

Sahandi et al. (1984) as overlain by white, conglomeratic and feldspathic meta-sandstone to which an Early Ordovician age is tentatively assigned, one which would fit with the base of the Tippecanoe Sequence if the age can be established. Further to the north from the Taknar inlier, Muller and Walter (1984) collected a fauna from the Mila Formation (here raised to group status, with three subdivisions named and given formational rank), which indicate the presence of rocks of Late Cambrian to Early Ordovician (Arenigian) ages. The presence of Late Ordovician, middle Ashgillian forams also has been reported, indicating the presence of Tippecanoe Sequence rocks. Within the inlier, there is dark limestone (Niur Formation) that contains

131

Sedimentary Basins and Petroleum Geology of the Middle East

LITHOLOGY

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132

The Sauk Cycle and the Early Part of the Tippecanoe Cycle

Table 4.3. Division of the Cambro-Ordovician Mila Group/Formation in Iran (compiled from Stiicklin, 1972; Setudehnia, 1975). South & Southeast Iran

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yielded conodonts of late Llandoverian to early Wenlockian, as well as Late Silurian to Early Devonian, age. As the brachiopods found indicate correlations with late Llandoverian to Pridolian strata, it may be that most of the Silurian, hence, the upper part of the Tippecanoe Sequence, is preserved in the sequence found in the Taknar inlier (Berry and Boucot, 1972). In northern, southwestern and eastern Iran, a number of formations have been identified that occupy the interval from the Early Ordovician to Late Silurian (Ludlovian). The oldest of these are the Lashkerak Formation in northern Iran ,the Shirgesht and Niur formations in eastern Iran (Ruttner et al., 1968, in Wensink, 1992; Stticklin, 1972), and Zark Kuh Formation in southwest Iran

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uppermost Silurian and possibly Early Devonian species, but its stratigraphic relation to the Mila succession has not been established (Muller and Walter, 1984). In this part of Iran, the Tippecanoe Sequence is incomplete, but ranges from Early Ordovician to Early Devonian.

The Tippecanoe Sequence The stratigraphic gap that eliminates much of the Ordovician-Silurian succession (Fig. 4.4), and the age uncertainties of much of the rest of the Tippecanoe Sequence sediments in Iran, make the history of the period difficult to decipher. One major distinction from Arabia during the deposition of the Sauk Sequence sediments is the prominence of marine carbonate platform deposits that appear early in the Cambrian. In terms of timing, a minor marine transgression into Jordan also occurred, but did not persist into the Late Cambrian. The shelf edge, therefore, may be supposed to follow a west-northwest-east-southeast trend. Sub-parallel to it was the pre-Zagros swell, which appears to have acted as a sedimentary source. The change from the Sauk Sequence to the Tippecanoe in Early Ordovician is not apparent in the northwest; although, towards the northeast, there appear coarse clastic sediments overlying the carbonates of the Late Cambrian-Early Ordovician, implying a period of uplift with the rejuvenation of erosional processes. Although there is a thick succession of Zard-Kuh sediments in the southwestern part of Iran, there generally is little information for the central and eastern parts of the country. In the Taknar inlier, however, there are isolated but datable Late Ordovician and Silurian black limestone and marl, which seem to indicate a formerly more extensive marine coverage. The limestone and sandstone intercalations in the Niur Formation have

Shirgesht Formation (Early to Middle Ordovician) of the Upper Mila Group. The Shirgesht Formation, in eastern Iran (northern Tabas) is well-developed and is lithologically more varied and subdivided into three members or units. The basal unit consists of argillaceous beds passing up to carbonates. The middle unit consists of fossiliferous, red, sandy limestone and marl and the upper unit of marl, shale and siltstone. The Shirgesht is thicker, in excess of 1,200 m (nearly 3,936 ft). The Shirgesht is conformably underlain by the Derenjal Formation and overlain by sandy limestone of the Niur Formation (Silurian) in the type section, while the basal part is disturbed by basic igneous intrusions in other localities.

Niur Formation (Silurian-Early Devonian?). In eastern Iran (Fig. 4.25), however, an Early to Late Silurian succession, which has an exposed thickness of 446 m (about 1,463 ft) to more than 628 m (2,060 ft), is found in the Ozbak-Kuh Mountains (Ruttner et al., 1970). The succession consists mostly of carbonates, principally dolomites and coral limestone, with some interbedded shale. Between the towns of Kerman and Sagand, outcrops of dolomites and limestone with a fauna indicative of an Ordovician-Silurian age have been described by Huckriede et al. (1962, cited in Stocklin, 1972). The contact with the underlying Shirgesht Formation is disturbed by igneous intrusions, but it is entirely conformable in some outcrops. The upper contact with the overlying Padeha Formation is conformable and transitional. St~cklin (1972) believes that an important part of the Niur Formation is the numerous diabase-dykes cutting through the lowermost part of the formation and older rocks and merging in a flow-sheet of olivine basalt intercalated in the Niur Formation about 70 m (230 ft) in the lower part. Lashkerak Formation (Early to Middle Ordovician). The Lashkerak Formation (Fig. 4.4) consists of shale, sandstone and cherty dolomite (59 m, or 194 ft) overlain by 25 m (82 ft) of fossiliferous, reddish, nodular limestone and ended by 55 m (180.5 ft) of sandstone, shale and a few thin limestone beds and is assigned an Early to Middle Ordovician age. The quartzite of the Lalun Sand133

Sedimentary Basins and Petroleum Geology of the Middle East stone contacts conformably with the Lashkerak. The formarion is separated by a considerable sedimentary gap (non-angular disconformity) from the Carboniferous Mubarak Formation. Zard Kuh Formation (Ordovician). Setudehnia (1975) introduced the name Zard Kuh Formation, which is a sequence of predominantly shale intercalations with beds of fine-grained sandstone exposed only in the Zard Kuh Mountain Range in the Zagros Crush Zone (Fig. 4.4). He divided it into two members (Fig. 4.25). The lower member (Early Ordovician) is about 93 m (305 ft) thick and consists of basal, fissile, micaceous shale overlain by thin beds of limestone containing trilobites followed by four cycles of interbedded, fissile, micaceous shale and finegrained, micaceous sandstone. The upper member, about 250 m (820 ft) thick, is composed of shale with thin layers of fine-grained, micaceous sandstone and thin beds of conglomerates in the middle part of the member. The lower boundary of the Zard Kuh Formation is sharp and conformable with the underlying Ilebeyk Formation, whereas the upper boundary disconformably contacts the sandstone and shale of the Permo-Carboniferous Sequence. The Zard Kuh clastics in southwestern Iran cannot easily be linked to a general pattern. They may represent a deep embayment extending across central Iran, whose continuity is broken by the metamorphism of the intervening lower Paleozoic sediments. Alternatively, as Davoudzadeh et al. (1986) suggest, if the pre-Zagros swell separates the area of southwest Iran from south central Iran, to what sediments do the Zard Kuh relate in Arabia?

PALEOGEOGRAPHY AND GEOLOGIC HISTORY OF THE EARLY PALEOZOIC During the Cambrian, conglomerate, arkosic sandstone and siltite of continental origin covered much of central and northwestern Arabia. A continental influence also dominated in southeastern Arabia. A transgressive facies that corresponds to marine carbonate containing trilobite faunas characterized the Middle Cambrian. In southeastern Turkey, dolomite and limestone and, in turn, a thick, flysch-type sequence overlies the Early Cambrian, which consists of conglomeratic sandstone and shale. The Early Cambrian in the Zagros Basin of southwestern Iran generally consists of detrital sandstone, shale and conglomerate showing limestone intercalations. While the Middle Cambrian comprises limestone, shale and trilobitebearing marl (Setudehnia, 1972), the Late Cambrian is poorly preserved. In central Iran, dolomite and quartzite dominated in the Early Cambrian, and basic volcanic rocks in the Middle Cambrian are interbedded with dolomite, evaporite and limestone. In the Late Cambrian, sedimentation alternated from siltstone to dolomite to limestone to sandy limestone (St6cklin, 1972). St6cklin (1972) reported that in northern

134

Iran, the Early Cambrian consists of arkosic sandstone, shale and quartzite, followed by Middle Cambrian clayey and silty carbonates that extend until the basal Ordovician. In the Late Cambrian-Early Ordovician (Tremadocian-early Arenigian), coarse-grained sandstone incorporating conglomeratic beds laid down in an alluvial braided-stream type deposition dominated southern and central Arabia (Dabbagh and Rogers, 1983; A1 Laboun, 1986). These sediments may extend as far as Jordan (Selley, 1972). In the Arenigian, a marine influence that appears as alternations of sandstone and siltite characterized central Arabia. Graptolite- and trilobite-beating clays of marine origin dominated central and northwestern Arabia during the Llanvirnian. Bender (1975) and Wolfart (1981) described a graptolite-bearing sandstone from the Llanvirnian in Jordan. Tigillites formed in a shallow, relatively calm sea and were reported from the late Arenigian and Llandeilian and early Caradocian in Jordan (Vaslet, 1987b). During the late Caradocian and possibly part of the Ashgillian, sandstone and clay of shallow-marine origin covered central Arabia. In the Llandeilian, fine-grained, detrital sediments consisting of graptolite were found in Syria (Wolfart, 1981; Flugel, 1963). In southeastern Anatolia, clay and sandy clay of continental origin overlain by quartzite and black shale dominated the Caradocian and Arenigian (Dean, 1975; Frontaine, 1981). In central Iran, a thick sequence of shale, tuffaceous sandstone and carbonate overlies the ArenigianLlanvirnian, which consists of limestone and sandy-clayey sediments (St6cklin, 1972). In northern Iran, marine sediments rich in trilobites and overlain by a thick carbonate sequence of limestone, marl and siltite are characteristic of the Tremadocian-Llanvirnian and Llandeilian. In southwestern Iran during the Ordovician, thick marine sediments comprising shale, silt and sandstone containing graptolite and trilobite fauna were deposited (Setudehnia, 1972). In eastern Arabia during the Devonian, fine-grained sandstone was deposited in southern Oman. In the Huqf region, sandstone contains clayey intercalations, whereas quartzitic sandstone and shale rich in Scolithus is found in northern Oman (Lovelock et al., 1981; de la Grandville, 1982; Morton, 1959). A marine regression dominated the Late Ordovician following Caledonian orogenic movements and the extension of glacier ice sheets over a major portion of Gondwana. McClure (1978) described this ice sheet, which extends to central Arabia. Vaslet (1989, 1990) provided detailed lithostratigraphy of the glacial and periglacial deposits and their extension in the Paleozoic outcrops of Saudi Arabia. In central Arabia, glacial episodes left evidence such as tillite, striations, roches moutonn6es of continental origin and reworked tillite, clay containing dropstone, bedded sandstone with slump structure and varves of marine and/or lacustrine origin (Vaslet, 1989, 1990). No glacial episodes are reported from Jordan, but

The Sauk Cycle and the Early Part of the Tippecanoe Cycle Vaslet (1987a) believes that this glaciation affected at least the south of the country as far as the border between it and Saudi Arabia. Clayey-sandy, graptolite-bearing sediments appeared in the middle and early Llandoverian in northwestern Arabia and middle Llandoverian in Jordan (Wolfart, 1981; Bender, 1975). In eastern Arabia, the Silurian is poorly preserved. In southern Oman, it is comprised of sandy clays; in the northern Arabian Platform (southern Turkey), it is comprised of shale, clay and calcareous shale containing graptolites. Marine deposits with marked terrigenous influences, such as limestone with coarse-grained sandstone and shale, represent the Llandoverian and Pridolian in the northern part of the Middle East. In northern Iran, carbonate and sandy facies dominated the Wenlockian; in central Iran, from the early Llandoverian to the end of the Silurian, marine, calcareous-sandy, calcareous and clayey-sandy sediments are dominant (Wolfart, 1981; Strcklin, 1972). In the Zagros Basin of southwestern Iran, the Llandoverian displays a marine facies of shale and sandstone rich in graptolites. The Wenlockian is not reported from southwestern Iran (Setudehnia, 1972). Throughout the Middle East, the paleogeography of the entire Infracambrian and Cambrian was governed by the existence of the Arabian Shield to the south and west and by large swells or highs in the central and northern parts of the Middle East. The paleogeographical maps (Figs. 4.27-4.29) show the shield surrounded by a belt of clastic, terrigenous sediments (Wolfart, 1981). During the earliest Cambrian, short marine regressions occurred, accompanied by the development of lagoonal, evaporitic sediments. Later, during the Early, Middle and Late Cambrian, marine conditions became increasingly more general, with the development of carbonates, although clastic sediments continued to be deposited over many parts of the region (see paleogeographic maps Fig.4.27). The conditions during the earlier parts of the Ordovician (Fig.4.28) were basically similar with lower Tremadocian limestone and marl covering most of Iran; although thick sequences of conglomerates and quartzites (Fig. 4.27) are indications of local, marked relief in northern Iraq and adjacent parts of Turkey. Over northern and southern Iran, northeastern Syria and southern Turkey, the deposits consist mainly of graptolitic shale, sandstone and quartzites (Wolfart, 1981). The paleogeographic maps of the Silurian (Fig. 4.29) show that the beds of Llandoverian and Ludlovian age are predominantly marine sandstone and shale laid down with the presence of corals and brachiopods indicative of shallowwater conditions in eastern Iran. These marine conditions were interrupted by emergence during the Early Silurian (Wenlockian) and again in the Late Silurian, when continental conditions were reestablished. It should be recalled that during the earliest Silurian, the area was recovering from a period of glaciation. Thus, tectonically, the lower Paleozoic seems to have been a relatively quiescent period, during which vast sheets

of clastic sediments spread across the Middle East, much as in the North African part of the northern margin of Gondwana. Only in south-central Turkey, in the Amanus Range, is there evidence of contemporary graben formation (the Karasu Graben) (Cater and Tunbridge, 1992), suggesting that the same may hold true for the Middle Cambrian of Jordan. The occurrence of conglomeratic beds and emergence during the Late Silurian marks the regressive phase of the Tippecanoe Sequence, evidence of uplift and emergence, at least on a local scale. It is difficult to estimate the time interval between the close of the Infracambrian sedimentation and the basal deposits of the Sauk Sequence. This time interval, during which the Infratassilian surface developed, appears to be shortest in Oman, placing Oman in closest contact with the marine realm, where sedimentation was presumably continuous. Even here, erosion of the Infracambrian sediments in places cut down into horizons of the Khufai Formation near the base of the Infracambrian Huqf Group. In northern Saudi Arabia and Jordan, the predominantly clastic Sauk Sequence rests on a gently dipping erosional surface. Below that surface is steeply dipping, archaeocyathid limestone, which is presumed to be a record of the presence of Early Cambrian beds. The rocks of the Sauk sequence, as seen in Saudi Arabia and Jordan, consist overwhelmingly of vast aprons of mature, terrestrial to shallow-marine sandstone, with subordinate shale and siltstone. In their lower part, they are described as braided-stream-fluvial deposits (Delfour et al., 1982; A1 Laboun, 1986); overbank or flood-plain deposits are absent, and fining-upward sequences are rare, although large bedforms representing minor channel fill and unconfined accretion on mid-channel bars are recognized. The upper part is characterized by transitional facies marking the change from fluvial-stream to brackish and shallow-marine, littoral settings. In contrast to the lower sandstone, which indicates transport from a southerly quadrant, bimodal current patterns are seen in the upper sandstone. The change also is consistent with the biological evidence. Whereas in the lower part of the sandstone, trace fossils such as Cruziana and Rusophycus found in the finergrained beds are evidence suggesting occasional marine incursions, bioturbation may be intense enough to obscure primary bedding in the upper part; in such beds, reworked, fragmentary, bivalve and brachiopod debris may be found (Clark-Lowes, 1985). The top of the Saq Sandstone Sequence is not well-defined everywhere; and, west-southwest of Hanadir, a meter-thick conglomerate, which rests on a ripple-marked sandstone with iron-rich phosphatic pebbles, contains separated lingulacean shells in the matrix. E1-Khayal and Romano (1988) collected a faunule at the top of the Saq Sandstone, dated as post-early Tremadocian and most probably Arenigian. In Oman, the Andam Formation was deposited under coastal-plain to marginalmarine conditions. The marine conditions are best developed in the middle member of the formation and have yielded a Tremadocian to Arenigian fauna. Therefore, they 135

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still about 1,000 m (3,280 ft) thick. Of the five members of the Mila Formation//Group, the lower four belong paleontologically to the Sauk Sequence. However, it must be noted that in the Zagros Basin, the Early Cambrian also shows evidence of a shallow-marine transgression, as indicated by the presence of red-green shale, dolomites with Cruziana traces, and white quartzites, conditions which persisted into the Ordovician. The general paleogeographic picture is incomplete, because so little is known of the region south of the central Arabian Arch. The isopach maps ofA1Laboun (1986) show two basins - - the Tabuk and Widyan basins m separated by the Ha'il-Rutbah Arch. The latter, usually considered a younger feature, deepens towards the northeast with the gradual filling of the more westerly Tabuk Basin during the early Paleozoic quiescent period. Towards the end of the Paleozoic, the isopachs generally trend east-west, parallel to the northern edge of the Summan Platform, and northsouth, parallel to the Ha'il-Rutbah Arch, as will be discussed later. It usually is stated that no thinning occurs across the feature, but it is arguable whether this can be sustained given the paucity of data points. It certainly is clear that a deep trough extends southward along the continuation of the eastern side of the arch between the Arabian Shield and the Summan Platform. At this point, therefore, based on an analogy with a similar structure in Algeria, syndepositional movement during the early Paleozoic should not be ruled out. The Tippecanoe Sequence covered much of the same area in the Middle East that was covered by beds of the

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The Sauk Cycle and the Early Part of the Tippecanoe Cycle Sauk Sequence, and both the Ordovician and Silurian were times of relative tectonic quiescence. Following the general subsidence of the area, clastic marine sediments cover wide areas in the Middle East, particularly in Saudi Arabia and Jordan, during both periods (Figs. 4.28 and 4.29). Outcrops of Ordovician rocks follow the same general pattern as those of the Cambrian, which they conformably overlie. The general absence of coarse-grained deposits indicates sources more distant than during the Cambrian. A significant reversal of the trend occurred during the Late Ordovician, which may be more attributable to a glacial sea-level lowering than to any major tectonism. The source of the clastic deposits is to be sought in the Arabian Shield. Only in the more mobile parts of the shelf in northern Iraq and Turkey are thick sequences of conglomerates and quartzites found, whose origin is to be sought in local swells. In contrast, in the more distal parts of the Middle East shelf, in northern and southern Iran, eastern Syria and southern Turkey, graptolitic shale and calcareous sandstone and quartzites occur (Wolfart, 1981). There are some breaks in the Ordovician succession resulting from epeirogenic uplift, for there are no verified Middle Ordovician strata in southeastern Turkey; in the Zagros Range, clastic sedimentation is dominant. In northern Iraq, there is a shift at this time in the sediment transport patterns from northerly to southerly. Paleogeographically and climatically, the most important event of the Late Ordovician was the occurrence of glaciation, the same event as widely recognized in North Africa (Tucker and Reid, 1973; Wolfart, 1981). McClure (1978) has identified the presence of glacial deposits, such as glacial boulders and tillites in the Late Ordovician, extending a considerable distance eastward and marking the margin of the ice sheet. The glaciation appears to have begun in late Caradocian and continued through much of the Ashgillian. Although a diamictite has been recognized, it is thin and may interfinger with proglacially deposited sandstone (McClure, 1978). A glacial valley cut through the Ra' an and Hanadir shale, with a clastic fill that has been described. Both Beydoun (1988) and McClure (1.978) indicate ice movement toward the northeast, toward the shallow shelf. Thus, the northern Afro-Arabian part of Gondwana marked the margin of the southern polar ice cap, forming a striking analogy with the events in eastern Algeria (McClure, 1978). A second feature, based upon analogy with the situation in Algeria, concerns the Wajid Sandstone of southwestern Saudi Arabia and Yemen. Dabbagh and Rogers (1983) published an excellent sedimentological study of the Wajid. Their descriptions of the depositional environments match those of the clastic sequence in northern Saudi Arabia. They assigned an Ordovician age based on the occurrence of trace fossils. Complications have arisen because a Sakmarian age has been assigned to beds assigned to the top of formation. However, as the two sequences are from different areas, the suggestion has been made that there are two formations separated by an uncon-

formity that cuts out most of the Paleozoic (Alsharhan et al., 1991). On this basis, it would follow that the Wajid outcrop, s e n s u stricto, was isolated from the beds to the north in the present Tabuk and Widyan basins by the Hercynian uplift of the central Arabian Arch. Consequently, the original source of the Sauk Sequence must lie south of the Arabian Shield, much as the French have demonstrated that the lower Paleozoic clastics of the Saharan Platform had a source south of the Hoggar. The Tippecanoe Sequence closes out under the relative quiet of the Late Silurian regression, although there are very few places where a gradational transition into the Devonian can be followed. There are no reported post-middle Llandoverian rocks in the Zagros Basin of southern Iran; but, according to Ala et al. (1980), this may be a result partly of subsequent erosion, which in places may have removed all rocks from as old as the Middle Ordovician to Late Carboniferous. Wolfart (1981) indicates that the region of the Turkish-Iraqi-Iranian border was emergent during most of the Silurian. The depositional environment for the Silurian as a whole ranges from littoral to a probable outer neritic, as shown in Fig. 4.29.

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Chapter 5 THE EARLY-LATE PALEOZOIC OF THE MIDDLE EAST The Kaskaskia Cycle

INTRODUCTION

wide continental clastic sequence covered much of the Arabian Platform. In northern and eastern Saudi Arabia, the succeeding Kaskaskia Cycle is represented by the beds of the Jauf and pre-Unayzah (Sakaka and Berwath, Figs. 5.1 and 5.4) formations. The Jauf Formation equates with the transgressive part of the cycle and is followed by the regressive part of the cycle as clastics prograded eastward and northeastward. The transgressive part of the cycle was relatively short, for the two limestone members occur during the Siegenian-Emsian-?Eifelian, when sediment input was low. The Sakaka Formation was regarded by Powers (1968) and Sharief and Moshrif (1989) as a transition to the Berwath sandstone. The distribution of the beds of the Kaskaskia Cycle is controlled by their generally easterly-northeasterly dip and by the extensive Hercynian erosion.

The late Paleozoic-early Mesozoic includes two sedimentary megacycles that follow the end of the Tippecanoe Cycle in the Early Devonian; the Kaskaskia Cycle, which extends from the late Early Devonian to latest Mississippian (Early Carboniferous); and the early part of the Absaroka Cycle, which extends from the post-late Mississippian to Early Jurassic (see Chapter 6). The break between the Kaskaskia and Absaroka cycles is quite distinct and marks the end of a long period of platform subsidence that had persisted since the early Phanerozoic consolidation of Gondwana, the result of uplift and erosion. Thus, the first Absaroka deposits overlie an unconformity referred to as the Great Hercynian Unconformity.

Jauf Formation (Early Devonian, Pragian-eady

THE KASKASKIA CYCLE IN THE MIDDLE EAST

Emsian). Berg et al. (1944, cited in Powers et al., 1966) named the Jauf Formation from the town of A1 Jauf (29049 , N, 39052 ' E), where the complete formation is exposed. Steineke et al. (1958) reported the description of the type section, and Helal (1965a & b) recorded a sequence consisting mainly of varicolored, silty shale with numerous thin beds of limestone and dolomite in the upper third of the sequence, which follows a sequence of continental sandstone. The total thickness of the carbonates and continental sandstone may reach 600 m (1,968 ft) (Fig. 5.3). Bahafzallah et al. (1981) described the stratigraphy and facies of the Jauf Formation. Hemer and Nygreen (1967) provided some palynological information from well S-462 (30030 ' N, 40025 ' E) approximately 80 km (50 mi) north of the location of the type section at A1 Abd (in the A1 Jauf region). They recognized four palynological zones in sandstone and shale samples, ranging in age from middle Frasnian to early Givetian, and recorded minor amounts of coal in the sequence. They did not record the presence of any marine microplankton, nor did they report the presence of any limestone. Consequently, it must be assumed that their section must lie largely within the preUnayzah Clastic sequence of A1Laboun (1986)(seep. 144). Bahafzallah et al. (1981) reported that fossils are scarce due to dolomitization, but Helal (1965 a & b) described some of the limestone beds in the Jauf sequence as richly fossiliferous. R. J. Murris (pers. comm., 1993) believed that all over the Paleotethys, in Europe as well as in Morocco-Algeria-

As a type area for the development of sediments of the Kaskaskia sequence, the least well-represented cycle in the Middle East, the Widyan Basin near A1 Jauf in Saudi Arabia is chosen as the region where the most complete sequence has been penetrated by the drill. The beds dip gently eastwards to northeastwards, and, as a result, in the eastern part of the basin, the beds generally lie at too great a depth to be penetrated by drilling. In the Middle East, Paleozoic rocks, which are not removed by post-Hercynian erosion, commonly are encountered either as a result of drilling over uplifts or highs, as in Oman and over the Qatar-South Fars Arch, or are brought up tectonically as exotic blocks in mrlange, as in the mountains of the United Arab Emirates (U.A.E). In the thrust zone in northern and central Iraq and over the Rutbah Uplift, there is a more complete section than that seen in the Arabian Gulf area. Over much of Iran, the stratigraphic situation parallels that seen in the Arabian Peninsula, for much of the Carboniferous and Late Devonian sequence appears to have been removed by erosion. The correlation of the Paleozoic rocks is shown in Figs. 5.1 and 5.2, and a listing of the formations is presented as Table 5.1.

The Kaskaskia Sequence in Northern Saudi Arabia During the course of the early Paleozoic, the Tabuk Basin was progressively filled with continental clastic deposits until by the end of the Sauk Cycle, a platform-

141

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The Early-Late Paleozoic of the Middle East

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Fig. 5.3. Generalized stratigraphy and isopach map of the Early Devonian (Jauf Formation) in northwestern Arabia (thickness map after A1 Laboun, 1986 and reproduced by kind permission AAPG). Note that the zero isopach line is erosional and not the original depositional isopach. Turkey-Iran, the maximum Devonian subsidence occurred in the Middle Devonian. Based on detailed studies of invertebrate faunas by Boucot et al. (1989) and Forey et al. (1992), the Jauf Formation represents shallow- and marginal-marine deposits of Pragian to early Emsian age. The formation consists of five members (Figs. 5.1 and 5.3) overlain by the "pre-Unayzah clastics," which are regarded as a separate unit (A1 Laboun, 1986). The sediments of the Jauf Formation and its equivalent were deposited on a wide, stable platform bordering Paleotethys and stretching from Morocco to Saudi Arabia. In Arabia, the Jauf Formation sediments were deposited in a subsiding area, with a considerable influx of clastics from a source area to the west and south maintaining shallow-water, marine conditions. Carbonates formed when the clastic supply diminished. The carbonates are almost invariably argillaceous and contain an appreciable sand component. When the water depth exceeded wave base, shaly beds such as the Sabbat Shale Member accumulated. Bahafzallah et al. (1981) recorded in the shale-limestone alternation the presence of two cycles, each beginning with a lagoonal or brackish, intertidal phase passing up into a marine, beach phase represented by the two main limestone members, each ending in a dolomitic phase initiated

by increasing salinity.

Tawil Sandstone Member (inferred age: Early Devonian, Gedinnian). The clastic lithologies of this continental deposit crop out only in the vicinity of A1 Tawil and A1 Jauf in the Tabuk Basin. They have a thickness that ranges from 50 to 189 m (164-620 ft) and consist of fine- to coarse-grained, thick, cross-bedded units, and frequent gravelly or pebbly sandstone beds, with occasional interbedded shale beds. The lithological character of the Tawil Sandstone indicates rapid erosion and deposition. The maximum thickness of the unit is not well-known, but may exceed 200 m (656 ft). No diagnostic fossils have been recovered from the unit in the Jauf area. The Tawil was deposited in a fluviatile environment of a braided-stream system, showing a fining-upward sequence with the development of flood-plain type facies and the formation of paleosoils with plant debris at the top (Vaslet, 1987 b). Shaibah Shale Member. An alternating sequence of about 50 m (164 ft) of shale, sandstone and dolomitic mudstone rests upon a reddish, weathered limestone at the base. Sandstone, the dominant lithology of the unit, may range from fine- to coarse-grained, although most commonly are medium-grained. They vary from well- to

145

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 5.4. Generalized stratigraphy and isopach map of the Middle Devonian to Early Carboniferous (Sakaka-"pre-Unayzah-Berwath Formation") in northwestern Arabia thicknesss(modified from A1Laboun, 1986 and reproduced ky kind permission AAPG). poorly sorted, are commonly calcareous and may show cross-bedding. Some detrital carbonate beds also are recorded. The dolomitic mudstone may contain glauconite granules. The Shaibah Shale, which forms a striking lithological contrast to the underlying Tawil Sandstone Member, is believed to have been deposited in a predominantly fluvio-deltaic to lagoonal or flood-plain environment. Qasr Limestone Member. This distinctive, 18 m (59 ft) thick member is made up of dark-gray to brown, massive and dolomitic limestone with minor shale and sandstone interbeds. However, recrystallization has not obliterated primary structures, and, in some places, the formation is highly fossiliferous with many spiriferid brachiopods and corals as well as some rare gastropods, disrupted crinoid debris and broken pelecypod shells. Calcitic dolomites, biorudites and biomicrites have been identified (Bahafzallah et al., 1981). This member was deposited in a shallow-nearshore-marine environment. The limestone can be traced several kilometers in outcrop north of A1 Jauf. The Qasr Limestone Member marks a distinctively more marine facies, with carbonates formed in a proximal sub-tidal to intertidal domain. This is the first carbonate shelf to form in central Arabia in the Paleozoic (Vaslet,

146

1987 b). Sabbat Shale Member. A shallow-marine to continental sequence of about 100 m (328 ft) of red to green shale with occasional medium- to fine-grained sandstone and siltstone, particularly in the lower part of the member. Gypsum laminae and lens are common. The Sabbat Shale Member shows a return to continental influences in a flood-plain to lagoonal environment typified by the presence of coaly beds containing plants, and meandering fluviatile channels. Marine influences persist, with tidal facies at the top of the member (Vaslet, 1987 b). Hammamiyat Limestone Member (Siegenian?Emsian). This consists of about 106.3 m (349 ft) of darkgray to brown, sparry limestone, which may be fossiliferous and usually thin bedded and alternates with gray and green, silty shale. Large corals have been found, and the faunal assemblage with brachiopods, algal and crinoid remains suggests a normal, offshore-marine environment (Helal, 1965 a & b) in which the alternating carbonate and silty shale indicate a lagoonal-marine to intertidal setting. Lithologically, several carbonate types can be recognized, including fossiliferous biomicrudites, sparitic biomicrite, dolomicrites and pelmicrites. A high percentage of the cal-

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Fig. 5.5. Lithostratigraphic section of the Devonian sediments cropping out in northern and northwestern Saudi Arabia, showing the Sakaka sedimentary facies with a general description and presumed depositional environments (modified from Sharief and Moshrif, 1989 and reproduced by kind permission of Journal of Petroleum Geology). cite in the limestone is syngenetically brecciated, but in the coarse-grained calcareous matrix, the dark fragments of platy limestone do not show preferential orientation, although the fragments commonly are parallel to the bedding. The fragments belong to beds that show intraformational slumping. Dolomitization, which caused volume shrinkage, has led to the development of bird's-eye structures. In some beds, bioturbation has occurred, and burrows parallel to the surface indicate infaunal activity. Sakaka Formation (?Eifelian to ?Frasnian). Sandford (1950, cited in Powers et al., 1966) first applied the term "Sakaka Sandstone" to cover a thick, siliciclastic sequence (sandstone interbedded with siltstone and shale) that crops out in the A1 Jauf area east of the Ha'il Arch in the Widyan Basin. Sharief and Rogers (1980) and Sharief and Moshrif (1982) carried out a detailed, sedimentologi-

cal and stratigraphic examination of this formation. It forms the lower part of what A1 Laboun (1986) termed the "pre-Unayzah clastics" (Fig. 5.4), the sequence found in northwestern Saudi Arabia in subsurface lying above the Hammamiyat Siegenian and the pre-Serpukhovian (Mississippian) Unayzah Formation. However, Powers (1968) had recognized a Transition Zone of sandstone, shale and siltstone with several platy, impure limestone and dolomite bands and an upper unit of fine- to coarse-grained sandstone interbedded with siltstone and shale that he named the Berwath Formation. Later, Sharief and Moshrif (1989) confirmed the subdivision of A1 Laboun's pre-Unayzah clastics into Powers' two formations. If the palynological identifications of Hemer and Nygren (1967) can be applied, the Sakaka (Transition) Unit has an ?Eifelian to ?Frasnian age. The Sakaka Sandstone Formation in out-

147

Sedimentary Basins and Petroleum Geology of the Middle East crop consists of about 210 m (689 fi) of complex, interbedded sandstone, siltstone and shale of a bay to fluvial environment. Sharief and Moshrif (1989) recognized three facies (Fig. 5.5): 1) silty shale and fine-grained sandstone; 2) highly variably bedded sandstone; and 3) sandstone and shale in a fining-upward sequence. The paleoenvironment of the lower units changed from bay to fluvial, while the upper unit represents fluvio-deltaic conditions with some shallow-marine influence. The Sakaka unconformably underlies the Middle Cretaceous Wasia Formation (cross-bedded, moderately to well-sorted, quartz arenites). The lower contact is conformable and sharp above the uppermost limestone of the Hammamiyat Member of the Devonian Jauf Formation (Sharief and Moshrif, 1989). "Pre-Unayzah Clastics (Berwath Formation) (Early Carboniferousn). A1 Laboun (1986) introduced the term pre-Unayzah as an informal name for a clastic section known only in subsurface in northwestern Saudi Arabia bracketed by the the Hammamiyat Member of the Jauf Formation and the basal, well-developed shale unit of the Unayzah Formation previously named the Berwath FormatiOn by Powers (1968). As the formational name problem is not yet resolved they will be referred to as the' Berwath/pre-Unayzah Formation" The clastics are approximately 413 m (1355 ft) thick (Fig. 5.4) and consist of continental sandstones, fine- to SOUTH

coarse-grained, interbedded with shales and siltstones. The sequence thickens towards the northern part of the Widyan area. The continental environment apparently extended beyond the Carboniferous into the Early Permian in the north and northeast of central Arabia but in a more claysandy facies.

The Kaskaskia Sequence in Southwest Saudi Arabia Khusayyayn Formation (Lower-Middle Devonian). Although included in "Supergroup IV" of Stump and van der Eem (1995), the base of the Khusayyayn Formation rests upon deeply eroded beds of the Qalibah Formation, following a period of uplift and erosion between the Silurian and Early Devonian (Fig. 5.6). It lies, therefore, within the Kaskaskia Cycle and should be separated from the late Tippecanoe Qalibah Formation. The formation has a thickness of about 200 m (656 fi) and locally may be divided into upper and lower parts, which may be separated by an unconformity (in the Bani Khurb region). The two interfingering facies in the "lower" Khusayyayn Formation consist of sandstone of a marginal-marine to upper-shoreface type and shallow, lagoonal claystone, which have yielded early Devonian fish near the base, and middle Devonian megascopic plants from the upper part. No fossils have been recovered from

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The Early-Late Paleozoic of the Middle East the high flow regime fluvial, ?lacustrine and aeolian beds. Sediment transport directions in the "lower" Khusayyayn show a northerly or northwesterly paleocurrent, but the upper unit has a more easterly component. The Kaskaskia Sequence in Qatar Tawil Formation (Devonian-Early Carboniferous?). Below the Permian Khuff carbonates in Qatar, a sequence of pre-Khuff sediments including Paleozoic beds is penetrated in the deepest wells, Matbakh-2 and Ras Qirtas-1 (Hamam and Nasrulla, 1989). The units of the Jauf Formation, to which the general name "Tawil Formation" has been applied, overlie the Tippecanoe sequence of the early Paleozoic beds (Fig. 5.7 and the following discussion). The succession consists of about 479 m (1,570 ft) of a repetitive alternation of thinly bedded sandstone, argillaceous sandstone, siltstone and shale beds. The greater part of the formation consists of quartzose to slightly arkosic sandstone, commonly cross-bedded with a varying amount of K-feldspar, plagioclase, plant debris and mica flakes and a cement ranging from quartzose to sideritic to gyp-

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Fig. 5.7 Sedimentological interpretation and gamma-ray-FDC logs of the Devonian-Permian (Tawil and Haushi formations) in Qatar (based on data from Hamam and Nasrulla, 1989; Schlumberger, 1981).

sum. The lithological description of the upper part of the Tawil Sandstone suggests deposition under alluvial conditions, most probably in a braided-stream environment. In the lower part of the formation, about 100 m (328 ft) of good-reservoir-quality rocks consisting of dark, shaly sandstone and subordinate carbonates alternate with white to brown, coarse- to medium-grained, quartzose to arkosic sandstone. The lower part of the sequence is regarded as having formed in a shallow-marine to sublittoral depositional environment. The Hercynian unconformity truncates the top of the succession. Without faunal information or detailed descriptions of the lithologies, parallels with the Jauf Formation are necessarily suspect; however, the presence of limestone horizons suggests that there may be Hammamiyat or Qasr limestone marine equivalents, and the sequence's arenaceous upper part may represent the pre-Unayzah clastics of Saudi Arabia. The Kaskaskia Sequence in the United Arab Emirates

Outcrop Formation Ayim Formation (Devonian?). Robertson et al. (1990) have described allochthonous blocks found in the Dibba Zone sedimentary mrlange in the northern U.A.E. These have been assigned to the Ayim Formation of Devonian age (Fig. 4.9). About 12 m (40 fi) crop out in Jebel Qamar; the lower 0.15 m (0.5 fi) consist of a phosphatic limestone and well-rounded sand grains in a siltstone matrix that grade up into 5 m (16.5 fi) of finely laminated shale, argillaceous lime mudstone and siltstone. Above this is a stylolitic, concretionary limestone with bioclastic limestone (0.25 m, or 0.8 ft) and 3 m (10 ft) of nodular limestone with a manganese crust and nodules, evidence of sedimentation break. The remaining 3.5 m (12.5 ft) of the section is made up of argillaceous, micritic limestone and hematitic shale. These sediments contain base material, fish teeth, broken fish scales, preferentially oriented Orthocones, echinoderm fragments, cephalopod remains, ostracods and polyzoans. The Ayim Formation sediments were deposited on a stable, shallow-shelf environment.

Subsurface Formation Tawil Formation (Middle Devonian-Lower Carboniferous?). In the subsurface, ony the deepest wells in onshore and offshore Abu Dhabi penetrate about 300-430 m (984-1410 ft) of the Tawl Formation. The sediments encountered in the deepest offshore well in Abu Dhabi range from Lower Carboniferous to Middle Permian and have recently been described by Hassan et al., (1995). In this study they are referred to the Tawil Formation (Fig.4.22) for they are identical to the sequence described by Hammam and Nasrulla (1989) in well Matbakh-2 in Qatar. They have been divided into two units following All and Silwadi (1989) and Alsharhan (1994). The upper unit ranges from ?late Upper Devonian into Lower Carboniferous consists of 201 m (660 It) of

149

Sedimentary Basins and Petroleum Geology of the Middle East fine to very grained, occasionally medium-grained, quartzitic sandstone, moderately to well-sorted and pyritic, and commonly with a silica cement. Minor thin shale and siltstones bands also occur and the sediment is interpreted as a delta distributary channel deposit. The basal unit of the sequence is of marine origin and contains glauconite (Hassan et al., 1995). The lower unit, ranging from Middle to probably Upper Devonian, consists of 229 m (750 ft) quartzitic, fine to very fine-grained occasionally medium-grained sandstone. The quartz grains are angular to subangular to subrounded and moderately to well-sorted. Interbedded claystone/shale and siltstone are present. The claystone/ shale constitutes about 15-20% of this section and is greenish grey, silty, occasionally pyritic and non-calcareous. The siltstone is brown to green grey, argillaceous occasionally micaceous. The sequence was deposited in a sub-littoral marine environment of normal salinity (Hassan et al. 1995). These sediments were dated from Middle Devonian to Lower Carboniferous based on the occurrence of Crassispora sp. and Cristatisporites sp., Cymbosporites cyathus Dibolisporites cf echinaceus and D.cf gibberosus (Hassan et al. 1995)

The Kaskaskia Sequence in Oman Misfar Group (Early to Middle Devonian). The Early Silurian to Late Carboniferous period is represented by a major unconformity between sediments that often are difficult to distinguish seismostratigraphically. Isolated well data record the presence of Devonian Misfar clastics resting unconformably upon Ordovician and covered by Early Carboniferous beds in south-central Oman (Figs. 4.5 and 5.1). Definite proof of the existence of the Devonian sediments comes from only three wells" Misfar-1, where there is about 44 m (145 ft); Batha-1, with a thickness of 278 m (912 ft); and Ghufos-1, of questionable thickness (Hughes-Clarke, 1988). Lithologically, the beds consist of a sequence of shale, quartzose sandstone and sandy limestone. They contain ostracods and stromatolite-like structures and were deposited in a terrestrial environment, but one in which there were some marine influences. HughesClarke (1988) assigned them to the Devonian. The Kaskaskia Sequence in Kuwait Jauf Formation (Middle-Late Devonian). Burgan well A-1 in the Burgan Oil Field, the deepest well in Kuwait untill 1990, fully penetrated the Jauf Formation, which had a thickness of 835 m (2,740 ft). Khan (1989) recognized two members (Fig. 4.17): a lower 138 m (445 ft) of thick limestone with ostracods and algal debris; and an upper 700 m (2,295 ft) of brown, light-green and darkgray, silty and sandy shale, occasionally pyritic, with occasional silicified, anhydritic, dolomitic and limestone inter150

beds. The upper and lower contacts are conformable, and because no faunal data are available on which to assign ages, correlation with the Jauf Formation of Saudi Arabia is based solely upon lithological similarities.

The Kaskaskia Sequence in Iran Padeha Formation (Early Devonian). The formation in central Iran consists of about 492 m (1,614 ft) of clastics that conformably overlie the Niur Formation. The sandstone shows cross-bedding, ripple marks and other sedimentary structures and has an argillaceous, dolomitic or calcareous cement (Ruttner et al., 1968). There is intercalated, red shale and a single 3-5 m (10-16 ft) band of well-bedded dolomite. The contact with the overlying Sibzar Dolomite is unconformable. Sibzar Formation (Middle Devonian). This formation consists of about 100 m (328 ft) of calcareous dolomites, dolomitic limestone and sandy, recrystallized limestone (Stocklin, 1972). The contact with the underlying Padeha is conformable, and it passes by transition into the Bahram Formation above. Bahram Formation (Middle-Late Devonian/ Givetian-Frasnian). Found in central Iran (Fig. 5.2), the formation consists of more than 300 m (984 ft) of gray and black, well-bedded, partially dolomitized limestone interbedded with green shale. It contains a fauna of corals, brachiopods, gastropods and crinoids (Stocldin, 1972) and shows a conformable relationship with the underlying Sibzar Formation and the overlying Shishtu Formation.

Geirud Formation (Late Devonian-Early Permian). The Geirud Formation crops out in the Alborz Mountains (Fig. 5.2) and was divided by Assereto (1963, 1966) into four members, from top to bottom, as follows: Member D: Black, oolitic, sparry limestone: 300 m (984 ft) Member C: Light-gray, massive dolomites: 170 m (558 ft) Member B: Black limestone, clay and marl: 220 m (722 ft) MemberA: Sandstone, black marl, sandy limestone and basalt flows: 290 m (951 ft) The Geirud beds rest with a sharp, disconformable contact on the Mila Formation limestone and are overlain disconformably by the clastic of the Dorud Formation.

The Kaskaskia Sequence in Iraq There are three principal areas in Iraq where Paleozoic sediments are known; in the north in the thrust zone, over the top of the Rutbah Uplift in western Iraq, and in deep wells between Khleissia and Mosul in central northern Iraq. These sections have been described by Buday (1980). While the Kaista and the succeeding formations can be established as Famennian or younger in age, for the

The Early-Late Paleozoic of the Middle East presence of Spirifer verneuilli is found in the upper part of the formation, there has been considerable discussion concerning the stratigraphic position of the Pirispiki Formation. Initially regarded as Ordovician or Ordovician/ Silurian (Bellen et al., 1959), a Late Devonian age was established by Seilacher (1963). The Devonian-Carboniferous Succession in Iraq is made up of the following units (Fig. 5.2): 9

Pirispiki Redbeds (Devonian) (including the Chalki Volcanics);

9

Kaista Fm. (L. Devonian, Famennian);

9

Ora Shale Fm. (L. Devonian-E. Carboniferous);

9

Harur Fm. (E. Carboniferous-Tournaisian); and

9

Khabour Quartzite-Shale Fm. (Ordovician).

The presence of the Tournaisian and Visean in somewhat different facies has been reported in Syria, suggesting that in western and northern Iraq, other Kaskaskia sequence beds may remain to be discovered. Pirispiki Redbeds (Devonian). Wetzel (1950, cited in Bellen et al., 1959) introduced the formation name for beds that crop out in the northern thrust zone in Iraq. There are no records of their subsurface crop. The formation is made up of massive, cross-bedded quartzites, marly sandstone, siltstone and rare shale with lenticular intercalations of conglomerates containing green, igneous rocks deposited in a continental environment (Buday, 1980). In outcrop, the thickness is about 80 m (262 ft), and no fossils have been recorded. It seems reasonable to assign a Devonian age to this formation, because the beds grade up into the basal Kaista beds with the same lithology. However, a precise age cannot be determined. Correlation has been suggested with variegated clays and sandstone alternating with fossiliferous, marly limestone, which provides an early Middle Devonian (Eifelian) age and crops out near Hazro in southeastern Turkey, or with terrigenous-marine clastic formations of Devonian age in the Alborz Mountains of Iran (Buday, 1980). Thus, the age question is far from settled. The Chalki Volcanics are an integral part of the upper Pirispiki beds and, therefore, can be considered only a member, not a formation. The volcanics consist of altered, olivine basalt flows with ash, shale and siltstone intercalations and a thickness of only 20 m (65.5 ft) (Buday, 1980).

Kaista Formation (Late Devonian-Famennian). The type section of the formation in the northern thrust zone, which is only 70 m (230 ft) thick, consists of siltstone, silty shale and some quartzite in the lower part that grades up into argillaceous limestone. The depositional environment ranges from continental to shallow marine (Bellen et al., 1959). In well Khleissia-1, beds assigned to the Kaista Formation differ in lithology and age from those in the outcrop section. The thickness of the formation in the Khleissia area increases to 257 m (843 ft). A basal conglomerate is present, and there is a more com-

plete gradation from the coarse-grained, conglomeratic sandstone, through fine-grained, dolomitic mudstone to limestone (although limestone is not reported in the well; Buday, 1980). These beds are overlain by glauconitic, dark-gray, silty shale, followed by gray marl with silty intercalations capped by marl with argillaceous laminae (Gaddo and Parker, 1959, cited in Buday, 1980) that passes up gradationally into the shale of the Ora Formation. According to Buday (1980), the formation cannot be widely recognized outside the type area.

Ora Shale Formation (Late Devonian-Early Carboniferous, upper Famennian-lower Tournaisian?). This formation, introduced by Wetzel (1952, cited in Bellen et al., 1959), is based on outcrop data from northern Iraq, where as much as 220 m (722 ft) are reported. In subcrop, twice that thickness of gray, gray-green, organic-rich shale and siltstone, with lenticular, biodetrital limestone and fine-grained, limestone interbeds, is recorded in Khleissia-1. The shale contains relatively abundant brachiopod and anhydrite nodules. Glauconite is common throughout the section (Ibrahim, 1978; Buday, 1980). This unit, which grades upward conformably into the beds of the Harur Formation, was laid down in a marginal-marine and supratidal to inner-neritic setting. Harur Formation (Early Carboniferous-Tournaisian). The name was given by Wetzel and Morton in 1952 (cited in Bellen et al., 1959) to a sequence of about 60 m (197 ft) of biodetrital limestone with thin, micaceous shale interbeds in the type section. As in the case of the Ora Shale, twice this thickness is recorded in well Khleissia-1, where silty and shaly interbeds are more common. The lower part of the sequence, made up of dark-gray siltstone with subordinate sandstone, dolomite and limestone, grades up into saccharoidal dolomite, fossiliferous glauconitic, marly limestone and peloidal, dolomitized limestone, capped by soft, carbonaceous and somewhat calcareous shale with rare siltstone horizons (Ibrahim, 1978; Buday, 1980). The formation, laid down in a marine, neritic reef to fore-reef environment, is conformable upon the Ora Shale Formation consistent with the assigned Tournaisian age. It is the youngest of the Kaskaskia sequence beds preserved in the area. The Kaskaskia Sequence in Southeast Turkey The Kaskaskia sequence in Turkey does not form a readily identifiable sequence, primarily due to the limited and sporadic outcrops. Published information is limited.

Dadas Formation (?Late Silurian-Early Devonian). The Dadas Formation (Figs. 5.2 and 5.8) is a sequence of more than 200 m (656 ft) of deltaic, coarsening-upward sandstone and shale found in outcrop in the Dadas and Zeynala areas and, according to TPAO (Turkiye Petrolleri Anonim Ortakligi), in restricted outcrops north of Diyarbakir and the Mardin High. The base of the sec-

151

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The Early-Late Paleozoic of the Middle East fion is faulted out, and the top of the formation is marked by brown, oil-stained, cross-bedded sandstone of the Hazro Formation, which succeeds the greenish sandstone of the Dadas Formation. The Dadas equates to the Tawil and Sharawra of Saudi Arabia and overlies the Silurian Handof shale. The Dadas Formation also is exposed in the core of the Hazro anticline situated in front of the southeastern Anatolian Thrust Zone. According to Guvenc et al. (1982), the formation ranges from Late Silurian to Early Devonian. It consists of about 142 m (466 ft) of lower shale, grading upward to interbedded sandstone, sandy limestone, shale and marl that indicate deposition in a shelf environment and represent a shallowing-upward sequence. Hazro Formation (Early-Middle Devonian). The formation originally was dated as Permian, but this dating has been revised recently to Early-Middle Devonian (R. J. Murris, pers. comm., 1993). It occurs in outcrops in the Hazro Uplift and in wells in the Diyarbakir area (Katin-6 and Kayayolu-1). It consists of sandstone, shale and dolomitic limestone and, thus, resembles the Jauf Formation. It unconformably overlies the Dadas or Handof shale formations. In subsurface, its Early to Middle Devonian age is based on sporomorphs. The Hazro Formation (Fig. 5.2) is found in surface outcrop in the Dadas section, where it is 125 m (410 ft) thick, and in the Zap area, where only 15 m (49 ft) has been recorded. The succession consists of fluvio-deltaic, cross-bedded, oil-stained sands and shale. The top of the section lies immediately below a dolomitized wackestone at the base of the Gomaniibrik Formation. The thin sequence at Habbur in the Zap area consists of a ferruginous, oncoidal packstone followed by sandstone and plant-bearing shale. The Hazro Formation crops out in the core of the Hazro anticline, where about 124 m (407 ft) of cross-bedded sandstone, siltstone, marl, shale, coal seams and dolomites were deposited on a clastic tidal fiat (Fig. 5.8). Guvenc et al. (1982) have carried out a detailed sedimentological study of this section, in which they conclude that the deposition of the Hazro Formation commenced under transgressive conditions, but developed as a regressive unit. Under these conditions, they identified five sedimentary facies (F-1 to F-5) (Fig. 5.9) deposited in environments ranging from lower-sand fiat, barrier-bar and tidal-inlet, lagoon and inner-tidal-fiat, coastal-barrier, coastal-plain and delta-front. In the subsurface north, northeast and southeast of Diyarbakir, the Hazro Formation ranges in thickness from 100 to 150 m (328-492 ft). It again is composed of deltaic shale, thin sandstone and marl with occasional thin limestone. The thickness of sandstone and shale appears to decrease to the south and southeast away from the Dadas-Hazro area. The reduced thickness of the formation in the Habbur section suggests that the far southeast of Turkey may reflect accumulation in a sub-basin related to the main deltaic development in the Diyarbakir district~ Yiginli Formation (Early-Middle Devonian). This

formation, found only in the region of Zap in the Hakkari area (Figs. 4.23a and 5.8), consists primarily of fluvio-deltaic, red sandstone and shale, but has limestone developing near the top of the section. A dolomite at the base serves as a marker horizon. The beds of the formation rest unconformably over the Seydisehir quartzites. They are lithologically comparable with the beds of the Pirispiki Formation, which lie just over the border in Iraq, and to similar beds in Iran's Geirud and Koshyayla groups, which have yielded a rich fish fauna (Janvier, 1980). Janvier et al. (1984) described a section of about 300 m (984 ft) from the northern limb of the Zap anticline (from top to bottom) as follows: d) dolomites containing ostracods and mollusc fragments indicative of a brackish-water environment; c) quartzite-siltstone alternation, with brown to red, thick-bedded, commonly well-sorted and cross-bedded sandstone; yellow, red or purple siltstone; and possible deposition in a fluvial environment; b) siltstone-sandstone-dolomite alternation, with the dolomite possibly with rare molluscan debris; and a) dolomite forming a 2 m (6.6 ft) marker horizon. The peritidal carbonates (dolomites) toward the top of the formation probably are related to sea-level rise and the ensuing transgression, which resulted in the development of the more open-marine conditions during the deposition of the overlying Koprulu Formation (Janvier et al., 1984).

Koprulu Formation (Late Devonian-Early Carboniferous). The Koprulu (Figs. 4.23a and 5.8) is another formation only seen in the Zap area. It comprises a sequence 260 m (853 ft) thick of dark-gray shale with thin limestone conformable upon the Yiginli Formation. The base is placed at the first limestone, which follows above the highest dolomitic beds of the Yiginli Formation. Janvier et al. (1984) described a section of the Koprulu Formation that was characterized by a rich, fish fauna from the Cukurca anticline (from top to bottom) as follows: f) limestone with locally developed patch reefs in generally dark, sandy, detrital limestone known locally as the Belek Facies; e) black shale, which includes rare limestone intercalations and abundant ostracods and brachiopods indicative of a Tournaisian age; d) limestone and shale with Late Devonian vertebrate remains; c) black, sandy limestone; b) shale; and a) black packstone and mudstone with abundant mollusc and ostracod debris and well-sorted, quartz grains alternating with yellow siltstone with latest Devonian vertebrate fragments. With the gradual increase in the proportion of limestone and a concomitant decrease in the thickness of shale, the formation passes upward into limestone known locally as the Belek Facies. The latter unit, 130 m (426 ft) thick, is a sequence of medium- to thick-bedded, bioclastic limestone named by Schwan (1971). The vertebrate fauna in 153

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 5.9. Depositional models of facies association (F1 to F5) of the Hazro Formation, Hazro region, Southeast Turkey (modified from Guvenc et al., 1982). tion with the underlying Ordovician rocks, in contrast to tile Koprulu Formation is unique and indisputably Gondthe age assignments of Schwan (1971). wanan, and it contains forms that reputedly are Devonian R. J. Murris (pers. comm. 1993) believes that throughand others that uniquely are Carboniferous. out southeastern Turkey, Silurian shale (Handof) passes Kirtas Quartzite and Hasanbeyli Formation (Midinto sandstone and shale (Dadas, Late Silurian-earliest dle-Late Devonian). In the Amanus Mountains, more than Devonian) and is overlain unconformably by basal Devo400 m (1,312 ft) of Devonian sediments crop out. They nian sandstone (Kirtas, basal Hazro and Yiginli), followed consist of red and green sandstone; fossiliferous, calcareby Devonian to Lower Carboniferous limestone, shale and ous sandstone; limestone; dolomites and shale (Schwan, minor sandstone (Hazro, Yiginli and Koprulu formations). 1971). The succession is split into an underlying Kirtas Sandstone and the overlying Hasanbeyli Formation (Figs. 5.2 and 5.8). According to Schwan (1971), this sequence The Kaskaskia Sequence in Syria conformably overlies rocks of a Silurian age. Deposition, Markada Group (latest Devonian-Carboniferous). which occurred on an irregular surface with local highs, is It is composed of 300 m (984 It) to 1,500 m (4,920 ft) of marked by the variable lithologies seen in the southern sandy shale and minor terrigenous carbonates, which were part of the Amanos Mountains. Dean et al. (1986) placed previously called the Markada Formation and have been the formations in the Middle to Late Devonian and indicalled the Doubayat Group. They overlie lower Paleozoic cated an unconformable contact below the Kirtas Forma-

154

The Early-Late Paleozoic of the Middle East (5,222 ft) in well Sayad-1 (Lababidi and Hamdan, 1985; A1Youssef and Ayed, 1992). The lithologies recorded consist of sandstone and shale, with which are intercalated some calcareous or dolomitic intervals in the lower part. Both spores and brachiopods have been found, and palynological analyses (Ravn et al., 1994) indicate the presence of three assemblages. The youngest assemblage is characterized by Aratrisporates, a taxon essentially confined to Visean beds in North Africa. The affinities of an older Carboniferous assemblage are less clear, with a mixture of Tournaisian and Visean taxa, but the third and oldest assemblage has clearly latest Devonian affinities, with

sediments with a slight angular unconformity. The Upper Silurian is missing in Syria 9This unconformity may represent a more extensive loss of section than the low angle implies, or the region may have been structurally higher during the Late Silurian and/or part of the Devonian, with these rocks never deposited (Best et al., 1993). The Strunian-Tournaisian-Namurian Markada Formation (Fig. 5.2) takes its name from well Markada-101 in eastern Syria, where a thickness of about 1,090 m (3,575 ft) has been encountered. The same formation is as much as 1,500 m (4,920 ft) thick in well Swab-1,700 m (2,296 ft) in well Tanf-1, 1,589 m (5,212 ft) in well Doubayat-2 and 1,592 m

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Sedimentary Basins and Petroleum Geology of the Middle East

Retispora lepidophyta a key indicator of later Famennian (Strunian) strata. The basal contact with the Tanf Formation is disconformable, but the overlying Amanus Formation seems to rest conformably upon beds of the Markada Formation. The lithological description suggests that the beds were deposited in a fluvio-estuarine environment. Early Carboniferous rocks are relatively widely spread in Syria and reflect a eustatic sea-level rise through the Late Devonian, as shown in Haq et al. (1987). They exceed 600 m (1,968 ft) in thickness in northeastern Syria, thinning to half that total in the southwest. Part of the thinning may be attributed to Hercynian erosion, because an unconformity at the top of the Carboniferous occurs throughout Syria. Facies variations show that the transgression proceeded from northeast to southwest, from black argillites with dolomite intercalations to a section of sandstone and shale with fragments of coal and fossil wood in wells Swab-1 and Tanf-1 (Husri and Austin, 1985). Presumably, the Carboniferous section continues without a break into Jordan, where nearshore sediments have been recorded in wells Suwailah-1 and Safra-1. Conodont studies by Husri and Austin (1985) indicate that much of the Syrian Carboniferous is Toumaisian to late Visean in age; consequently, these can be considered the terminal members of the Kaskaskia sequence. Ala and Moss (1979) use Iraqi equivalents when referring to the Syrian section. Dubertret (1967, cited in Buday, 1980) recognized that higher Carboniferous rocks belong to the early part of the Absaroka sequence. A1 Youssef and Ayed (1992) described the late Paleozoic sequences that deep wells have penetrated (Fig. 5.10). The Carboniferous succession was renamed the Markada Group. The Markada Group consists predominantly of fine-grained sandstone interbedded with gray-black, calcareous shale, within interbeds of limestone and siltstone deposited in shallow-marine to deltaic environment. The group is underlain disconformably by the shale of the Early Silurian Tanf Formation and is overlain disconformably by the Permian Amanus Group. A1Youssef and Ayed (1992) divided the Markada Group into five formations, which are listed below from base to top: a) Sayad Formation, which consists of about 358 m (1,174 ft) of siltstone and silty shale; b) Athar Formation, which is composed of about 230 m (755 ft) of predominantly sandstone and siltstone; c) Halul Formation, which consists of about 125 m (410 ft) of limestone and dolomitic limestone; d) Sawanet Formation, which is composed of about 740 m (2,427 ft) of sandstone, siltstone and shale; and e) Najeeb Formation, which consists of about 412 m (1,352 ft) of interbedded sandstone and sandy shale. P A L E O G E o G R A P H Y AND GEOLOGIC HISTORY OF THE LATE PALEOZOIC KASKASKIA CYCLE

At the beginning of the Devonian (Gedinnian), the Arabian Shelf was dominated by coarse, clastic sediments

156

deposited in a continental environment, continuing with cyclic deposits in a fluviatile-deltaic to lagoonal environment during the Siegenian. In the Emsian, the deposits were characterized by an alternation of marine siltstonesandstone and fossiliferous carbonates indicative of the continuing transgression. Local unconformities are indicative of the effects of the final Caledonian phase, which has been identified in southern Turkey by Brinkmann (1976). Sedimentation continued in the Anatolia, Taurus and Hazro regions dominated by sandy shale and calcareous quartzite and rare carbonates. In the foothills north of Diyarbakir, the Devonian is represented by shallowmarine shale, dolomites and deltaic, sandy limestone, while in the Hakkari region, it is characterized by intertidal to deltaic dolomites and sandstone (Cater and Tunbridge, 1992). The Devonian in central Iran began with sandy limestone containing conodonts and stromatoporoids of continental origin, followed by a sequence of sandstone, dolomite and gypsum of lagoonal-marine facies with an evaporitic trend. The principal Middle Devonian lithology is dolomitic limestone of a shallow-marine origin (Wolfart, 1981 and Stocklin, 1972). In central Arabia, the Middle and Late Devonian sediments, which consist mainly of clayey, detrital sediments of paralic-continental origin, are reported from the subsurface (Powers et al., 1966; A1 Laboun, 1986). In northwestern Arabia, the Middle-Late Devonian crops out as continental sandstone and shale with plant remains (Sharief and Moshrif, 1989). In Southeast Turkey (Hazro region), the Middle-Late Devonian is dominated by shale, limestone and sandy dolomites and characterized by marine facies with some continental influence. In central Iran, the Middle-Late Devonian is characterized by very fossiliferous carbonates with minor shale of a shallow-marine origin, while in northern Iran (Elburz), the Late Devonian is dominated by a transgressive sequence of sandstone, shale and locally phosphatic, fossiliferous limestone (Stocklin, 1972). In northern Saudi Arabia (Widyan Basin), a thick, clastic sequence of sandstone, siltstone and shale was deposited during the Carboniferous and continued into the early Permian in a continental to tidal-marine environment (A1 Laboun, 1986; Powers, 1968). In southern and southwestern Arabia, the Khusayyayn Formation is the lithological equivalent of the Tawil and Berwath formations of central Arabia. It rests unconformably upon the Qusaiba (Silurian) Member. Sedimentation terminated in the early Namurian, and uplift and erosion ensued. The Khusayyayn is a generally coarsening-upwards, cross-bedded unit. Locally, an unconformity separates a lower early to middle unit from an upper late Devonian-Carboniferous unit. In southeastem Turkey (in the Hakkari area), the dominant Carboniferous lithology is brackish to marine, black shale and shallow-marine limestone. No evidence of these deposits is reported in the Amanus and Diyarbakir regions, where they probably were eroded during tectonic uplift (Cater and Tunbridge, 1992). During the Permian, marine limestone, deltaic clastics and coals were deposited in the

The Early-Late Paleozoic of the Middle East northern part of Diyarbakir, while the Late Permian is dominated by marine facies of sandstone and limestone in the Hakkari area. In northern Iran (Elburz region), the Early Carboniferous is dominated by a marine transgression of fossiliferous limestone. The Late Carboniferous was eroded, and the Early Permian red sandstone, siltstone and shale rest unconformably over the Early Carboniferous, followed by the Late Permian carbonates (dolomite and limestone) (Chateauneuf et al., 1978). In central Iran, sedimentation continued from the Carboniferous to Early Permian, dominated by shale, quartzitic sandstone and fossiliferous limestone (Stocklin, 1972). In southwestern Iran, detrital sandstone and quartzite with plant debris were deposited from the Early Carboniferous to Early Permian. The remains of the Permian-Carboniferous glaciation that affected all of southern Gondwana can be found in the southern and southeastern Arabian Peninsula, characterized by glacial deposits from the Early Carboniferous to Early Permian, as described by McClure (1980), Braakmann (1982), Kruck and Thiele (1983) and Alsharhan et al. (1993). The tillites and periglacial sediments were described both from outcrop and in subsurface in central and southern Oman. Tillite and boulder clay thatrest upon striated floors also are found in northwestern Yemen. In summary, the paleogeographic development of the Middle East from the Silurian to the end of the Kaskaskia sequence is hard to establish because of the lack of information. Essentially, the principal outcrop data are derived from northern Saudi Arabia, with some information from Iraq and Iran, supported by a limited amount of data derived from deep wells. The reasons appear to be: (1) during the Late Devonian, much of the Middle East was emergent; hence, strata of that age were not deposited or represent deposits laid down in fluvial or near shore environments (Fig. 5.11); and (2) extensive erosion took place during the Hercynian upheaval, with the removal over wide areas of Early Carboniferous and Devonian strata. With a rise in sea level, marine conditions became more widespread during the later part of the Early Carboniferous (Fig. 5.12). The distribution of lithologies suggests that the clastic sediments had their origin in the Arabian Shield. Local highs also persisted, because estuarine conditions seem to have continued into southeastern Turkey, and Early Carboniferous strata are missing in northern Syria. Nevertheless, the general pattern of depositional environments seems to have been one in which terrestrial conditions predominated in the south, with paralic-deltaic conditions occurring in southern Syria and passing to shelf and reef conditions in northern Syria and Iraq. In northern Saudi Arabia, which may be taken as the type area, the Kaskaskia sediments assigned to the Jauf Formation span the time range from the Gedinnian to Siegenian, although diagnostic fossils are absent in the Jauf area, and the pre-Unayzah clastics probably represent the Upper Devonian and Lower Carboniferous. The zero isopach of the Jauf Formation includes only the eastern-

most part of the Tabuk Basin, and by the time of the deposition of the pre-Unayzah clastics, the western limit of the depositional basin coincided with the Ha'il-Rutbah Arch (Fig. 5.5). The depositional environment, which changed from continental to nearshore, is marked by the change from continental/transitional clastics (Tawil Sandstone Member and Shaibah Shale Member) to one dominated by two carbonate members (Qasr and Hammamiyat Limestone members) separated by an interval of continental to lagoonal, red and green shale and red sandstone (Subbat Shale Member). The principal areas of outcrop of the Kaskaskia sequence beds in Iraq lie over the Rutbah Arch and in the thrust area of northern Iraq are found in deep wells between Khleissia and Mosul. There, some distinctive differences are found in the succession when compared to that in Saudi Arabia. The lowest beds are continental redbeds, to which no definite age has been assigned. The beds, however, grade up into a sequence that passes from continental to shallow-marine, as indicated by the appearance in the upper part of the succession of argillaceous limestone that can be dated as Famennian. Marine conditions also continue to a higher horizon, for the topmost formation, a biodetrital limestone deposited in a neriticreef to fore-reef environment, is dated as Tournaisian. Above the beds of the Jauf Formation in Saudi Arabia lie the pre-Unayzah clastics of the Sakaka and Berwath formations, which are a northward-thickening, continental sandstone and shale. They show a transition down into the beds of the Jauf Formation. While they are not dated with any degree of confidence, they are usually considered ?Middle to Late Devonian non-marine clastics and, therefore, coeval with the marine horizons found in northern Iraq. There is a distinct break between the pre-Unayzah clastics and the overlying Unayzah beds, which contain palynomorphs said to be as old as late Carboniferous in age, although the formation is now regarded as early late Permian in age. Not surprisingly, the Devonian-Early Carboniferous succession recorded in southeastern Turkey shows a strong resemblance to that found in northern Iraq, with an initial sequence of clastics and carbonates of Early to Middle Devonian age, followed by Middle and Late Devonian clastic sequence, giving way to marine carbonate conditions that persist into the Early Carboniferous. In Syria, only "probable" Early Devonian shale with sourcerock potential was encountered in well Meskene-1, where it appears to rest conformably upon the Silurian Tanf Black Shale sequence. Unconformable Early Carboniferous rocks have been found fairly widely in the subsurface, and a NE-SW transgression is inferred as the black argillites and dolomites in the northeast pass to sandstone and shale with coal fragments in the southwest. The thinning found in the sequence, however, is attributed to erosion preceding the Hercynian Unconformity. In eastern Arabia, surface information is restricted to some allochthonous blocks found in the sedimentary m61ange found in the Dibba Zone of the Oman Mountains. 157

Sedimentary Basins and Petroleum Geology of the Middle East ._,

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The Early-Late Paleozoic of the Middle East The deepest wells in the U.A.E., however, penetrate at least 430m (1410 ft) of Late Devonian sandstone, siltstone and subordinate shale dated palynologically as Strunian/ Famennian. The presence of reworked Silurian foraminifera near the top of the Devonian provides evidence of contemporaneous erosion. In Qatar, in wells Matbakh-2 and Ras Qirtas-1, over beds of the Tippecanoe sequence, lies a sequence of thinly bedded, argillaceous sandstone and cross-bedded sandstone with variable amounts of plant debris, siltstone and shale referred to the Tawil For-

mation. The top of the sequence is capped by the Hercynian unconformity. Further evidence for the presence of the Devonian is given by the presence of rocks assigned to the Misfar Group in three wells in south central Oman (Misfar-l, Batha-1 and Ghufas-1). Lithologically, although these rocks are primarily clastic and formed in a continental environment, beds of sandy limestone provide a clear indication of periodic marine influences.

159

This Page Intentionally Left Blank

Chapter 6 THE END OF THE PALEOZOIC AND THE EARLY MESOZOIC OF THE MIDDLE EAST The Absaroka Cycle

THE LOWER PART OF THE ABSAROKA CYCLE (LATEST CARBONIFEROUS-PERMIAN)

a small ocean, the first signs of the breakup and dispersion of Gondwana, a process that continued during the rest of the Mesozoic and Cenozoic. Climatically, changes occurred from the glacial conditions developed during the early Permian in southern Saudi Arabia, Yemen and Oman, when the region was in latitudes about 50 ~ S to the arid and evaporitic conditions found during the Triassic, by which time the region had migrated into lower altitudes. Sedimentologically, during the Absaroka Cycle, the Permian seas transgressed over the continental beds of the Unayzah Formation, until the basal sandstone and shallow platform carbonates of the Khuff Formation came to rest upon the Precambrian of the shield. By the end of the Permian, regression occurred, and in the marginal areas clastic deposits again covered Saudi Arabia. The nuclear regions, the United Arab Emirates (U.A.E.) and Qatar, however, remained sites of carbonate deposition through the Middle Triassic, when, as a result of further transgression, carbonate deposition returned to eastern Arabia and parts of central Arabia, where the classic, three-fold division of the Triassic is recognized. Table 6.1 lists the formations within the Absaroka Cycle.

There is a major break between the Kaskaskia and Absaroka cycles marked by an unconformity sometimes referred to as the "Great Hercynian Unconformity." With the end of the Kaskaskia Cycle, there ended a long period of subsidence that was followed, in the Arabian Peninsula, by the so-called "Hercynian Orogeny," a period of uplift and erosion. Thus, over the western part of the central Arabian Arch, Permian glacial deposits may rest directly upon the Precambrian, whereas the Tawil Sandstone (early Devonian) and lower beds still are preserved below the Mesozoic sequence in Qatar. As a result of uplift, erosion stripped off considerable thicknesses of Paleozoic sediments, reducing still further the apparent poor representation of the beds of the Kaskaskia Cycle. In Arabia, there is little evidence of orogenic activity. Only in the vicinity of Mashhad in northeastern Iran is the presence of ultrabasic lava flows and metamorphosed lower Carboniferous rocks direct evidence of an orogenic event. Some evidence of its protracted duration is provided by Wensink (1983), in his interpretation of Devonian paleomagnetic data, and by Weddige (1984). However, there is evidence of a clear change in the sedimentation pattern; for example, see the isopach maps of A1 Laboun (1986) for the Middle Devonian to early Carboniferous (Fig. 5.5) and the late Carboniferous to early Permian and late Permian (Figs. 6.1 and 6.2), which reflect upwarping associated with extensional fracturing and the development of basins trending in a more east-west to northeast-southwest direction as the regional stress field changed. The upper part of the Absaroka Cycle was marked by a regression in the marginal areas of the platform and the area of carbonate platform contracted in the marginal areas such as Saudi Arabia, to expand again during the Middle Triassic, and retreat again in the Upper Triassic as the cycle came to an end during the Hettangian. An examination of the chart of global cycles of sea-level change (Fig. 1.9) marks it as the lowest Phanerozoic sea level since the Cambrian. The time covered by the Absaroka Cycle encompasses major tectonic and climatic change. Paleotethys closed as part of the Afro-Arabian Plate collided with Laurasia along a line following the eastern slopes of the Alborz Mountains of Iran. In its wake, the Neotethys opened up as

THE PALEOZOIC PART OF THE ABSAROKA CYCLE Over the greater part of the Arabian Peninsula, the mid-Carboniferous was a time of considerable erosion. The uplift and erosional event is related to the initial stresses in Gondwana, marking the onset of the processes leading to the disruption of that supercontinent. The importance and timing of this event, in the Middle East generally, is overlooked, perhaps because it is difficult to define with real precision. The sedimentary succession of this closing phase of the Paleozoic can be readily summarized as a clastic sequence followed by a widely spread carbonate event that marks the first major transgression over much of the Middle East since the beginning of the Phanerozoic. The earlier Silurian graptolitic shale, which occurs along the northern part of the Saudi Arabia outcrop belt and is found in the subsurface as far south as the Dhofar region of southern Oman, and the Devonian limestone of the Jauf Formation are not as extensive as those recorded in North

161

Sedimentary Basins and Petroleum Geology of the Middle East

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162

The End of the Paleozoic and the Early Mesozoic of the Middle East Table 6.1. 6.1. Absaroka rock units units in the Middle Middle East. East. Table Asterisks indicate outcrop, and and bullets indicate subsurface.

Saudi Arabia

Age

Unit

Country

••

E.-M. Triassic

Shale with subordinate siltstone, sandstone, occasional gypsum bands and carbonates

Fkwd plain imcrtidal flat

Jilh Formation

•*

M.Triassic

Sandstone alternating with siltstone, shale and limestone

Shallow marine

L. Triassic

Sandstone with minor conglomerate and shale

Continental

Unayzah

*

L. Carbon iferous-E. Permian

Sandstone, siltstone, claysione

Swampy delta plain

Juwayl

•*

L. Carboniferous-E. Permian

Sandstone with conglomeratic horizons

Fluvial passing to shallow marine

Khuff

**

M.-L. Permian

Limestone, dolomite, shale, anhydrite

Littoral to shallow sublitloral

Sudair Formation

•*

L. Triassic

Limestone interbedded with dolomite, minor shale and anhydrite

Supratidal to subtidal

Jilh Formation

*

M. Triassic

Anhydritic, dolomitic limestone

Shallow marine

M injur Formation

*

L. Triassic

Interbedded. argillaceous sandstone and mudstone

Continental to marginal marine

Milaha Formation

*

M. Triassic

Argillaceous, dolomitizcd limestone

Sheltered lagoonal to inner shelf

Giialilah Formation

*

L. Triassic

Sandstone and marly grain stone and calcareous shale

Continental to subtidal

Khuff Formation

•*

E,-L. PermianE. Triassic

Shale to dolomite, dolomitic hmestone, anhydrite

Tidal flat

•

L. Carboniferous

Quartzitis sandstone, claystone, Shale

Fluvial

Al Khlata Formation Gharif Formation ' * Exotic Limestone Formation

E. Permian

Intertwdded sandstone, siltstone .shale

Fluvial

PcrmoTriassic

RccrystaUized limestone and sandstone

Shallow marine

Bih Formation

M. Permian

Dolomite and dolomitic limestone

Tidal flat

L. Permian

Argillaceous, shaly and dolomitic limestone

Tidal flat

E. Triassic

Massive, sucrosic dolomite

Tidal Hat

E. Triassic

Anhydrite, dolomite with marine shale

Lower energy, marginal

M, Triassic

Dolomite and oolitic-peloidal grainstone

Tidal flat

Hagil Formation

*

Ghail Formation Oman

Environment

Sudair Formation

M injur Formation

U.A.E

Lithology

Sudair Formation

•

Jilh Formation Mahil Formation

*

M.-L. Triassic

Sucrosic, dolomitic with minor chert bands

Ver)' shallow lagoon

Maqam Formation

*

L, PcrmianE. Triassic

Dolomitized limestone with breccia conglomerate and calcareous shale

Shallow to deep water

163

Sedimentary Basins and Petroleum Sedimentary Petroleum Geology Geology of the Middle East

Table Table 6.1 6.1 continued. continued. Country

Unit

Age

Environment

Jebel WasJa Formation

M.-L. Triassic

Recrystallized and fossiliferous limestone

Fore reef to talus slope

Zuila Formation

Trias sic

Shale with subordinate, turhiditic and radiolarian limestone, quartz arenitc and chert

Deep marine turbidite

Wahrah Formation

L, TriassicCenomanian

Tiirbiditic limestone and radiolitic chert

Deep marine

AI Aya Formation

E. Permian-M. Triassic

Turbidttic sandstone, limestone, shale and chert

Deep marine

Haifa Formation

L. TriassicM. Cretaceous

Radiolarian chert, siliceous shale and siliceous limestone

Deep marine

Haltw Formation

L, TriassicE. Cretaceous

Radiolarian chert, silicified limestone and chert

Deep marine

M. Jurassic

Conglomerate, lithoclastic limestone and chert

Deep marine turbidite

Ibra Formation

TriassicE. Jurassic

Limestone with some shale, sand-stone and igneous rock fragments

Shallow marine

Haybi Complex

TriassicE. Cretaceous

Mega-breccia, conglomerate, oceanic, island-arc sandstone, limestone, basalt. agglomerate and serpentinite

Exotic blocks of deep and shallow water sediments pillow lava

Batinah Complex

TriassieCretaceous

Ophiolite, exotic, deep-water, submarine limestone, volcanic, metamorphic, siliceous and calcareous sediments

Passive margin deep water sediments pillow lava

Al Khlata Formation

WestphalianSakmarian

TiUitc, outwash fans and fluvial sand

Glacial to fluvio-glacial

SakmarianArtinskian

Arkosic sand, silt, and silty shale

Braided stream

Khuff Formation

M.-L, Permian

Dolomite, limestone with minor anhydrite and shale

Shallow marine

Saiq Formation

M.-L. Permian

Limestone and dolomite

Moderately open marine

Bih Formation

M. Permian

Dolomite intercalated with dolomitic limestone

Intenidal to supratidai

Hagil Formation

L, Permian

Dolomitic and argillaceous limestone with minor shale

Intertidal to supratidai

A star Formation

PermoCarbon iferous

Siliciclastic

Glacial

Qamar Formation

Permian

Carbonate

Shallow marine

At Aridh Formation

Gharir Formation

164

Lithology

•*

The End of the Paleozoic and the Early Mesozoic of the Middle East

Table 6.1 6.1 continued. continued. Table Country Qatar

Iran

Unit

Age E, Triassic

Micaceous shale, siltstone. dolomite, anhydrite and marl

Shallow marine

Gulailah(Jilh) Formation

M.Triassic

Limestone, anhydrite, calcareous and argillaceous dolomite

Shallow marine

Minjur Formation

L. Triassic

Quartzitic sandstone, siltstone, shale

Continental

Haushi (Unayzah) Formation

PermoCartioniferous

Sandstone, conglomerate and sandy shale

Alluvial

Khuff Formation

L. Permian

Limestone dolomitic limestone, anhydrite

Shallow marine

*

Kangan Formation

•*

E. Triassic

Dolomitized limestone, shale, dolomite and anhydrite

Shallow marine

Dashtak Formation

•*

E.-M. Triassic

Shale and silty shale interbedded with dolomite and anhydrite

Shallow marine

L. Triassic

Argillaceous limestone, dolomite and shale

Shallow marine

Dalan Formation

L. Permian

Limestone, dolomite, minor evaporiie and sandstone

Restricted to open shelf

Faraghan Formation

E. Permian

Sandstone with minor variegated shale

Littoral, partly deltaic

EJonid Formation

E. Permian

Clayey marl, marly limestone and sandstone

Littoral

Nesen * Formation _ * Jamal Formation

L, Permian

Sandstone, marly shale, chert and sandstone

Littoral

L. Permian

Fossiliferous, dolomitic limestone

Shallow marine

Wajid Formation

Stephanian-Sakmarian

Quartz arenite, minor conglomerate

Fluvio-deltaie

E. Permian

Shale with tillite. shaly mudstone

Glacial lake

E. Triassic

Shale with subordinate siltstone, sandstone and gypsum

Shallow marine

M.Triassic

Argillaceous dolomite with streaks of anhydrite and shale

Shallow marine

PermoCarboniferous

Silty, shaly sandstone

Fluvio-deltaie

L. Permian

Dolomitized limestone and minor anhydrite

Shallow marine

E. Triassic

Microcrystalline and argillaceous, dolomitic limestone

Shallow marine

M. Triassic

Argillaceous dolomite, anhydrite and shale

Shallow marine

Akbra Formation Bahrain

Sudair Formation

* * *

Jilh Formation Unayzah Formation

•

Khuff Formation Kuwait

Environment

Suwei (Sudair) < Formation

Khanckhai Formation

North Yemen

Lilhology

Sudair Formation Jilh Formation

*

165 165

Sedimentary Basins and Petroleum Geology of the Middle East

Table 6.1 6.1 continued. continued. Country

Iraq

Environment

*

L. Triassic

Sandstone interbedded with shale and limestone and argillaceous dolomite with fossil shale

Shallow marine

Khuff Formation

«

L. Permian

Dolomite with minor anhydrite, shale and limestone

Very shallow marine

E, Triassic

Limestone, shale and rare sands

Marine

* Mirga Mir Formation Beduh Formation

«

E, Triassic

Shale with marl and subordinate, thin limestone

Shallow marine

Cell Khana Formation

*

M. Triassic

Shale, limestone and dolomite

Nearshore to lagoon

*

M.-L, Permian

Limestone, dolomite, minor shale and sandstone

Mixed shelf to reefal shelf

PermoCarboniferous

Sandstone, shale, minor marl and coal

Fluvio-lacustrine to littoral

L. Triassic

Limestone alternating with dolomite and shale

Lagoon

L. Triassic

Shale with bands of dolomilic, silicified and oolitic limestone

Lagoon

M.- L, Triassic

Limestone often dolomitized with intertiedded marl, marly limestone

Shallow to deep marine

L. Triassic

Cypsiferous marl interbedded with marly limestone

Lagoon

*

L. Triassic

Alternating saccharoidal dolomite, anhydrite, argillaceous limestone, shale and halite

Nearshore to supratidal

•*

M. Triassic

Limestone and dolomites with interbedded shale

Low-energy shelf setting

*

M. Triassic

Intertwdded, dolomitic limestone and mariy clay

Tidal flat

M. Triassic

Sandstone, marl, shale and laminatedstromatolitic limestone

Low-energy shelf setting

M, Triassic

Sandstone, claystone, siltstone and argillaceous limestone and shale

Non-marine to marine periods in paralic setting

M. Triassic

Limestone with marl/shale intercalations, dolomite and dolomitic limestone

Low energy shallow marine

E,-M. Triassic

Alternation of sandy and shaly limestone, shale and shaly sandstone

Fluvial and channel hll

Ga'ara Kurra Chine Formation Baluti Formation Mulussa Formation Zor Hauran Formation Abu Ruwcis Formation Salit Formation

* * * * *

Um Tina Format ion IriiAlAmir Formation

* *

Mukheiris Formation Hisban Formation

,*

Ain Musa Formation

166

Lithology

Minjur Formation

Chi a Zairi

Jordiin

Age

Unit

The End of the Paleozoic and the Early Mesozoic of the Middle East

Table 6.1 continued. Country

Age

Unit

Lithology

Environment

Dardun Formation

*

E. Triassie

Thinly bedded, dolomitic iimestone, laminated shale and marl, bioturbated sandstone and intraformational conglomerate

High energy inner shelf

Ma'in Formation

*

E. Triassic

Alternating thinly bedded sandstone, siltstone and clay

Tidal nat

E. Triassic

Sandy, giauconitic, bioclastic limestone, sandstone and shale

High energy inner shelf

L. PermianE. Triassic

Sandstone with laminated silt and clay

Terrestrial

E. Permian

Micro-conglomerate, giauconitic sandstone, interbedded with shale

Shallow marine

E.-M. Permian

Shale, argillaceous, pyriiic, fossilif'erous limestone and argillaceous dolomite

Shallow marine with periodically anoxic conditions

L, Permian

Fine- to medium-grained sandstone, ferruginous, argillaceous sandstone

Fluvial

E. Triassic

Sandstone and siltstone with argillaceous limestone

Marine with influx of elastics

M. Triassic

Massive to thinly bedded, argillaceous and evaporiiic dolomite

Shallow marine

L, Triassic

Dolomite with minor limestone and anhydrite

Shallow marine

L. Triassic

Anhydrite with intercalations of dolomite and shale

Shallow marine

L. Triassic

Anhydrite with minor, dolomitic anhydrite and argillaceous dolomite

Shallow marine

L. Triassic

Dolomite, some anhydritic dolomite

Shallow marine

•

M. CarboniferousL. Permian

Siltstone, shale and limestone

Alluvial plain to deepwater, mixed shelf

**

E. to M. Triassic

Carbonate and shale

Marginal marine to non-marine

L. TriassicE. Cretaceous

Massive limestone dolomite and shale

Peritidal

Triassic?

Limestone;dolomitc;evaporiie: subordinate, pyriiic shale; sandstone

Shallow marine

Triassic?

Shale and sandy limestone

Shallow sublittoral

Hazro Formatio.,

M, Permian

Sandstone, siltstone, shale and coal

Deltaic paralic

Gomaniibrik Formation

L, Permian

Limestone, shale and minor sandstone

Littoral to shallow sublittoral

Suwayma Formation Um [ma Anjara

*

Huwayra * Buwayda Syria Amanus Formation Kurra Chine Formation

* *

Butmah Formation « Ada!yah Formation Alan Formation

•

Mus Formation Amanus Formation Turkey Cigli Group Cudi Croup Aril Formation Beduh Formation -

•

•

*

167

Sedimentary Basins and Petroleum Geology of the Middle East toral, sandy, basal Khuff beds (Senalp and A1 Duaiji, 1995). For descriptive purposes, the Absaroka sequence can be divided into sections north and south of the central Arabian Arch; however, continuity occurs around the eastern end of the arch in Qatar and Iran.

Africa. Most of the available information is from subsurface, but because of the importance of the Late Permian Khuff Limestone and its equivalents as a gas reservoir, much more is known about its lithology and distribution than is available for the older rocks. Outcrop data apart from that available from Oman generally are restricted both in the time span represented and in areal distribution. The importance of the Late-Carboniferous and Permian in Oman is that the outcrop data can be supplemented from subsurface. These data illustrate the stratigraphic relationship of the Permo-Carboniferous glaciation to the betterknown Late Permian limestone sequence. The Oman Succession (Fig. 6.3) provides the most complete section southeast of the central Arabian Arch; the best section, north of the arch in the Widyan Basin, is known through boreholes. Although it was initially thought (A1 Laboun, 1986) that there was no break between the Unayzah and the overlying Khuff Formation, recent studies have demonstrated the existence of a paleosol horizon separating the fluvial Unayzah from the lit-

Absaroka Sequence South of the Central Arabian Arch Absaroka Sequence in Oman The beds immediately overlying the Hercynian unconformity in Oman are assigned to the Haushi Group. Although they are exposed in the Haushi-Huqf Uplift, the beds in the group are defined and subdivided from well data in Dhofar Province of southern Oman (HughesClarke, 1988). The succession of late Paleozoic formations (Fig. 5.2) is as follows:

2)

Khuff Formation (equivalent to Saiq Formation in the Oman Mountains) (mid-Late Permian)

ARABIAN GULF GULF OF OMAN

Abu Dhabi

UNITED ARAB EMIRATES.

Muscat

l 9

.

~

9 ~3 : - " ..: ~

.

~ ~176 .

~176 ~

SAUDI ARABIA

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~. .'

,"

,

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,

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.

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9 .._.:.,

__- . . . . , , . . = . ~ . -----.r ." .

.

.

.

~

9 ~

. ..

.

._

- .. ~

9

.-

:._,_.~___._

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, ,....=._"

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[ VErosion/Non-

depos.ition .

~. Kuria Muria

B o . u . n . d a r y oT t h e s a l t Daslns

Erosional limit ARABIAN SEA

[

Ol

i

801

,

160 ~1200km

Fig. 6.3. Distribution of Carboniferous glacial facies (A1 Khlata Formation) in Oman (modified from Sykes and Abu Risheh, 1989). 168

The End of the Paleozoic and the Early Mesozoic of the Middle East 1) Haushi Group (Late Carboniferous-Early Permian) b) Gharif Formation (Sakmarian-Artinskian) a) A1Khlata Formation (with the Rahab Shale Member) (Westphalian-Sakmarian)

Haushi Group (L. Carboniferpus-E. Permian) A. AI Khlata Formation (Westphalian to Sakmarian). This formation is known throughout southern Oman and as far north as the Fahud Oil Field. The glaciogenic sequence in Oman is similar to that in Yemen and southwestern Saudi Arabia and has yielded four palynological assemblages from subsurface samples, which amplify the surface sample data of Besems and Schuurman (1987) and date the A1 Khlata as late Westphalian-early Stephanian to Asselian-Sakmarian (Love, 1994), closely parallel to assemblages from North Africa to Australia. In the southern Oman oil fields region, three distinct lithological types are found in the A1 Khlata Formation: tillites, outwash fans and fluvial sands interpreted as a sequence of glacial and fluvio-glacial deposits. The top of the formation marks the end of glaciation in Oman. The tillites consist of discontinuous, unstratified mixtures of sand and clay containing striated pebbles and boulders with local intercalations of poorly laminated and contorted sandstone (de la Grandville, 1982; Nandyall et al., 1983; Teauw et al., 1982) representing the morainic deposits left by the retreating glaciers. The outwash sands, which interfinger with the tillites, represent glacial outwash material 3-21 m (10-69 ft) thick of coarse- to finegrained, cross-bedded sand, thin conglomerate and gravel layers. They are thought to represent the reworking of tillite by glacial meltwaters. The fluvial sands form the more continuous and thicker units and are more commonly friable to unconsolidated, coarse-grained sands with thin, conglomeratic layers containing well-rounded pebbles and pebbly sandstone horizons. They represent the deposition of the glacial material and the outwash sands in braided streams in a pro-glacial delta. There also are finingupward, shaly intercalations (de la Grandville, 1982; Nandyall et al., 1983). In the type section at A1 Khlata, in the wadi of the same name in the Huqf-Haushi area, the formation consists of a 4-6 m (13-20 ft), internally structureless diamictite containing granitic and acid volcanic clasts, shale and some chert clasts overlying a glacial pavement cut on the Khufai Formation of the Huqf Group. The diamictite is overlain by sandstone showing large-scale, planar crossbeds. In other areas, there may be three to four diamictites separated by yellowish-red sandstone, which also has large-scale, planar cross-beds indicating transport toward the northeast (Wright et al., 1990), consistent with the direction of ice movement determined by Braakmann et al. (1982). In places, the sandstone is followed by channelled gray shale (the Rahab shale of Levell et al., 1988) and several meters of thick, varved silts, with each varve about 2 cm thick, containing occasional dropstone (Wright et al.,

1990). Love (1994) points out that although the base of the Rahab Shale appears to be synchronous, the top is not. The basal diamictite is regarded as a basal till, whereas the succeeding diamictites represent local readvances. The cross-bedded sandstone is interpreted as large sand and gravel bars of a braided, fluvio-glacial outwash system in which the varves indicate glacio-lacustrine conditions (Fig. 6.3). The base of the formation is unconformable upon Misfar, Haima or Huqf group rocks, whereas the top of the formation grades into the overlying Gharif Formation. The shale at the top of the A1 Khlata Formation (the Rahab shale), which ranges from 3 to 20 m (10-66 ft), was formed in brackish to fresh water. It commonly is burrowed and, so far, has proved to be unfossiliferous (Levell et al., 1988). Besems and Schuurman (1987) carried out a detailed sedimentological investigation, which determined the age and depositional environment of the A1 Khlata Formation in Oman. A sequence of seven stratigraphic sections forming nearly continuous outcrops are found in east-central Oman (Fig. 6.4). The lithologies are: 1) a diamictite; 2) a polymict conglomerate with granite pebbles and boulders, as well as chert, dolomite and diamictite that grades up into a mixed succession of diamictite, pebble sands, sands and siltstone. Dropstone is recorded in the laminated siltstone in the upper part of the section; 3) poorly sorted, gray, silty diamictite in the lower part, passing to clast-rich conglomerate and pebbly sandstone with large-scale cross-bedding in the upper part; 4) a base dominated by siltstone, which is overlain by a sequence of cross-bedded sands, pebbly sands and sandy conglomerates; 5) a series of conglomerate, siltstone with contorted bedding, and sands with small-scale cross-bedding capped by a sandy conglomerate section above a basal diamictite; 6) conglomerate overlain by sandy diamictite, which contains lenses of conglomerate; and 7) mainly sandy and silty diamictites with sand lenses at the top. The authors considered that in sections 1, 2, 6 and 7 in Fig. 6.4, the diamictites were deposited as lodgement tills, whereas the diamictites in sections 3 and 5 were true tillites. The laminated siltstone that contains dropstone in sections 4 and 5 and the cross-bedded sands were regarded as deposits laid down in a fluvio-glacial environment. B. Gharif Formation (Sakmarian-Artinskian). Beds of the Gharif Formation crop out in western and northern Huqf area and in subsurface as far north as the Fahud Field in the western Oman Mountains (Hughes-Clarke, 1988). It probably is either continuous with, or the lateral equivalent of, the pre-Khuff clastics known elsewhere in the ArabianGulf region (e.g., Unayzah Formation of Saudi Arabia) (Fig. 5.1). The formation is made up of 175 m (574 ft) of alter169

Sedimentary Basins and Petroleum Geology of the Middle East

CORRELATION DIAGRAMS OF THE SECTONS

|

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...-37".9.

.. -..

:

9

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??-3 ." r :J

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UII

-t

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LOCATION MAP LEGEND

~

~

Sand(crossbedded) ~

~

r ~

/

E"C'C'I Pebblysand !\?0"01 (crossbedded)

~

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I

o.~ ) 7e~ - [

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(1-7) AI Khlata 9 outcroparea with sections 1-7

Conglomerate Dolomite(Khufai)

['~-~ Dropstonelaminites ~ = ~ Diamictite i V/l

Sandyconglomerate (crossbedded)

f:;!:i.l Cements,,e~ ,.., HHA

- Haushi-Huqf

Arch

Fig. 6.4. Correlation diagram of the Late Carboniferous-Early Permian glacial deposits in outcrop area of eastern central Oman (modified from Besems and Schuurman, 1987, and reproduced by permission of Palynology). nating arkosic sands, silt and silty shale capped by thick, red, lateritic clays (de la Grandville, 1982), divided into three informal members (Fig. 6.5) by Hughes-Clarke (1988). The basal member, a bioclastic limestone (the Haushi Limestone Member of Hughes-Clarke), subsequently has been renamed the Saiwan Formation and dated as Early Permian (Sakmarian-Artinskian) on the basis of its macrofauna and ostracod assemblage, and separated from the Gharif by an unconformity. The clastic sediments of the two remaining members of the Gharif Formation (of Hughes-Clarke, 1988) are regarded as having been deposited in a braided-stream, lacustrine and shallow-marine-

170

coastal environment, particularly in the lower part, and continental, mottled siltstone, claystone and stacked channel sands in the middle and upper parts. The laterites suggest sub-tropical conditions The succession is as follows (de la Grandville, 1982; Nandyall et al., 1983), despite their location above glacial beds. The composition of the Gharif clastics shows that they probably are derived from the varied material of the A1 Khlata glacial phase (HughesClarke, 1988). The palynological assemblage Kingiacolpites subcircularis has been recovered from lacustrine siltstone and shale and from shallow-marine, coastal deposits in the

The End of the Paleozoic and the Early Mesozoic of the Middle East HASIRAH FIELD

JAWDAH FIELD

MEMBER

DESCRIPTION

[

I LITHOLOGYI

SHALLOW MARINE ~ [ ~ = ~ [ ~ LIMESTONES

RED-BED CLAYSTONES / J

J

t~r--.L-~

I

CONTINENTAL

LITHOLOGY

! DESCRIPTION

SHALLOW MARINE LIMESTONES

I .,...

j,, J

f

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SAND POOR FLUVIAL SYSTEMS

iSOLATED. STACKEE AND MULTILATERAL 9 ' :~FLUVIAL CHANNELS IN RED PALAEO 9. SOLS AND LACUS

~

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TRINE MUDSTONES

I RENEWAL OF CLASTIC SEDIMENT SUPPLY

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GLACIOFLUVIAL SEDIMENTS AND LACUSTRINE SHALES

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Fig. 6.5. Summary of lithostratigraphy and sedimentology of the Early Permian Gharif Formation, in Oman. On the eastern flank of the South Oman Salt Basin oil is found mainly in the Lower and Middle Gharif, whereas in the Ghaba Salt Basin oil occurs mainly in the Middle and Upper Gharif (after Mercadier and Livera, 1993, and reproduced by kind permission of International Association of Sedimentology) lower Gharif Formation, suggesting an Artinskian age. Assemblages from higher in the Gharif succession continue into the Khuff Formation. From the uppermost silty shale intercalated in the channel sands, a rich and diverse pollen and spore assemble has been recovered (Le Metour et al., 1995) that is very similar to that of the lower part of the Upper Permian succession with a Murghabian age. Thus, although the lower unit might be considered time-equivalent to the Unayzah, the uppermost beds that pass into the Khuff gradually and conformably must be regarded as Late Permian in age. The lower boundary is placed at the base of the basal sand, which rests conformably upon the Rahab Shale Member of the A1 Khlata Formation. The upper limit is either conformable with the base of the overlying Khuff

carbonates or overlain unconformably by younger units (the Albian Nahr Umr beds). Khuff Formation (mid- to Late Permian). The beds of the Khuff Formation are widespread through central and southern Oman and are lacking only in the southeast, where they have been removed by Cretaceous erosion (Fig. 6.6). The lithology of the formation is dominated by about 670 m (2,198 ft) of dolomites and fossiliferous limestone with only minor shale horizons, and a single interval marked by disseminated, nodular anhydrite (Fig. 6.7). Toward the southeast, the carbonates are invaded by fine clastics, and the formation becomes dominated by finegrained red beds eventually. The Khuff carbonates were deposited in a shallowmarine environment ranging from subtidal, tidal-fiat to supratidal, marking a regional marine transgression over

171

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0

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UNITED (ARAB ) EMIRATES / " ~ ' ~ .

and coastal plain claystone

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SAUDI ARABIA o

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LEGEND

Shallow marine bioclastic and dolomitic packstone/ grainstone (top) and bioclastic lime-wackestone (bottom)

LLi -J I:~

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Jilh Formation

~

SudairFormation

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OMAN

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~

AkhdarGroupEroded Ero$ioul Limit

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m

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o o

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80 I

160 2 0 0 k i n I

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Fig. 6.7. Summary of the Late Permian-Early Triassic Khuff Formation in Oman (after Mercadier and Livera, 1993, and reproduced by kind permission of the International Association of Sedimentology)

Fig. 6.6. Generalized distribution of tile Late Permian-Middle Triassic sediments) of the Akhdar Group in Oman (modified from Sykes and Abu Risheh, 1989).

09

The End of the Paleozoic and the Early Mesozoic of the Middle East

ILl <

co LU z LITHOLOGY O R -r-

DESCRIPTION

DEPOSITIONAL

FOSSILS

ENVIRONMENT r'

Shallow marine

9Coarse-crystalline dolomite

Dolomite, grey to dark-grey, with textures of packstone, pelletal, oolitic, some boundstone, and probably much lime mudstone. Fusulinid foraminifera.

Gladochonous,

z

<

Dolomite, grey, with r e l i c textures of pelletal and oolitic 9l i m e s t o n e

uJ 13. Iii ....J

E

grey to black, with relic 9 textures of packstone/ "wackestone, bioclastic, "pelletal, foraminifera, and grainstone 9 :Dolomite,

i

s

Cosafera sp. indica brachiopoda. Debrya granotis. Caninia aft. liangshanensis

Massive dolomite

dendroides corwenia chihsiaenis. lvanophyilum carcphyloides Ivanophyilum splend Lophophyilum splendens multiseptum Michelinia Micheli $~enszszoaagenophy siyangensiswaageno~ ilum lourdriwaagenojourdriwaagem phyilum persicum wertzeiella persica zventzeiella cf. timorca.

A shallow marine carbonate with dark open-marine limestones at the base, becoming progressively more restricted marine facies upwards, and progressively lagoonal dolomitic limestones and black dolomite at the top

Fig. 6.8. Sedimentological interpretation of the mid-Late Permian (Saiq Formation) in the Oman Mountains (modified from Glennie et al., 1974).

Wackestone, bioclastic, and lime 9 packstone,pelletal, , bioclastic

Lime wackestone, black, i bioclastic and packstone Dolomite black and quartz sandstone, grey. Packstone/ wackestone, foraminifera, peUetal, bioclastic conglomerate, sandy, pebbly. ;Varied .brachiopod assemDla~les

the margin of an Arabian subcontinent with low relief and a minimal clastic supply (Hughes-Clarke, 1988). They are described more fully in the section on Saudi Arabia. In the Oman Mountains, the equivalent beds, referred to as the Saiq Formation, are in fully marine facies (Fig. 6.8). Saiq Formation (mid- to Late Permian). The Saiq Formation has a thickness of about 500 m (1,640 ft) in outcrop of the Oman Mountains. The lower part is made up of black, fetid limestone and dark-gray, medium-grained, bioclastic wackestone with intercalated zones of shell hash. The succeeding section consists of black- to brownish-gray, fetid dolomites, which are well-bedded and finely crystalline, with well-preserved, relict textures varying from wackestone to grainstone and containing some shell horizons (Glennie et al., 1974). The deposits were formed in deeper water than the Khuff in Oman, but the succession shows an upward shallowing (Fig. 6.8), and lagoonal, coal-bearing shale occurs at the top. In Saih Hatat, volcanic rocks, several hundred meters of rhyodacite and lava, are incorporated in the lower Saiq Formation in an extensional graben. They are progressively overlain by northward-prograding, shallow-shelf, reefal limestone. Over the Musandam Peninsula in northern Oman, two Permian formations have been described that, in age and general lithology, represent conditions similar to those in

which the Khuff formed. They comprise the B ih and Hagil formations in the Rus al Jibal Group of Glennie et al. (1974), a group developed better in the U.A.E.

Absaroka Sequence in the United Arab Emirates In the U.A.E., there are two main areas from where late Paleozoic rocks have been reported: from the mountainous areas adjacent to Oman, and from the lower-lying areas bordering and within the Arabian Gulf, where the stratigraphic succession is known from deep wells.The succession is as follows 9 2. Khuff Formation (Late Permian-Early Triassic) 1. Haushi Group (Late Carboniferous-Early Permian) b) Gharif Formation (Late Carboniferous) a) A1 Khlata Formation (Early Permian)

Subsurface Formations Haushi Group (Late Carboniferous-early Late Permian). The group (formerly the pre-Khuff or Wajid or Unayzah Formation) is penetrated by a few deep wells in the U.A.E. The thickness recorded in offshore Abu Dhabi varies from about 206 m (675 ft) in the west to 256m (842 ft.) in the central part of Abu Dhabi. The clastic sequence

173

Sedimentary Basins and Petroleum Geology of the Middle East described by Alsharhan (1994) as the Unayzah formation, consists of fine- to medium- and occasionally coarsegrained, quartzose sandstone, moderately to poorly sorted, with sub-angular to sub-rounded grains and either a siliceous or calcareous cement ). There also are shale laminae and dark-gray, pyritic and slightly dolomitic siltstone. Based upon published and unpublished information in the UAE and a comparison with published data from Oman and Qatar the term Haushi Group was introduced and divided into two formations described below. Gharif Formation (lower Permian) A formation of 118 m (388 ft) of interbedded sandstone, siltstone and shale of fluvial origin. The sandstone is fine to very fine-

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grained, subangular to subrounded and moderately well sorted. The siltstone is grey in colour becoming brown in depth and is argillaceous and non-calcareous (Fig. 4.22). The shales are grey to brow, soft to moderately hard, blocky to semi-blocky and non-calcareous. Hassan et al., (1995) reported that the sandstones contained plant remains and rootlets and fining upwards sequences are typical typical of fluvial channel-fill posits in a meandering to braided channel depositional system. The siltstones formed as levee or crevasse splay deposits whereas the shales were laid down on flood plains or in oxbow lakes.The age of this formation is Early Permian based on the occurrence of Apiculatisporites cornutus together with

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Shelfal, lagoonal

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.

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. . . .

Fig. 6.9. Sedimentological interpretation and gamma-ray-FDC/CNL log characteristics of the Late Permian (Khuff Formation) in the U.A.E.: M.A.=Middle Anhydrite. 174

The End of the Paleozoic and the Early Mesozoic of the Middle East

Vittatina sp. (Hassan et al., 1995). AI Khlata Formation (Upper Carboniferous). The formation consists of 138 m (454 ft) ofquartzitic, fine-to, moderately to well-sorted, coarse-grained sandstone, in which the grains are sub-angular to sub-rounded with secondary quartz overgrowths and shale/claystone which is grey to reddish grey, silty non-calcareous but occassionally carbonaceous, and grey or brown argillaceous, micaceous and pyritic siltstone. There is also a 2 m (7 ft) (Fig. 4.22) coal seam. The Upper Carboniferous is interpreted as fluvial in origin with stacked channel sands and overbank deposits with the coal formed from swamp vegetation and containing a flora which includes

Apiculiretusipora multiseta, A. semisenta, Reticulatisporites cf cancellatusl Raistrickia sp. and Vittatina sp. Khuff Formation (Late Permian-possibly Early Triassic). The Khuff Formation, as reported in the Abu Dhabi and Dubai oil fields, may range from a thickness of 650 m (2,132 ft) offshore to nearly 1,000 m (3,280 ft) onshore. It is a complex of limestone and dolomites with anhydrite in Abu Dhabi, with dolomites the dominant lithology in Dubai. There, the Khuff can be subdivided into only two major carbonate units separated by anhydrite beds, the so-called Middle Anhydrite Marker (Fig. 6.9). Based on detailed sedimentological interpretation, the Khuff section in Abu Dhabi was subdivided from the base upward into four major lithostratigraphic units (Fig. 6.9) (Alsharhan, 1993b). The KhuffA Unit is about 220 m (722 ft) thick and consists of lime mudstone and wackestone to packstone representing deposition within a shallow-water and relatively quiet open-marine setting. At the base, the sediments are argillaceous dolomites with minor terrigenous mudstone and thin-bedded shale. They grade upward to microcrystalline and rhombic dolomites with scattered relict peloidal/oolitic/bioclastic wackestone to packstone and grainstone and also patches and nodules of anhydrites. These sediments formed in an open-marine setting with some restricted marine influences in the upper part. The Khuff B Unit, with an average thickness of 188 m (617 ft), is dominated by dolomicrite, microcrystalline dolomites, nodular anhydrite and subordinate grainstone, lime mudstone and wackestone. Anhydrite is common, and sedimentary structures are mainly planar and ripple cross laminations. Excellent porosity is related to rhombic dolomite development, with good intercrystalline and vuggy porosity. The Khuff C Unit has a maximum thickness of 470 m (1,542 ft) and is composed of foraminiferal, oolitic and dolomitic grainstone and packstone, dolomicrite, stromatolitic mudstone and microcrystalline anhydrites. This unit consists mostly of microcrystalline dolomite with varying degrees of anhydritization. The rhombic dolomite has good intercrystalline and vuggy porosity. The Khuff D Unit has a maximum thickness of about 147 m (482 ft), dominated by oolitic, dolomitized grainstone, dolomicrites, mudstone, peloidal packstone and subordinate anhydrite interbeds. The unit is characterized

by low- and high-energy, oolitic grainstone (shoal environment). Khuff D is made up of rhombic dolomite with intercrystalline and vuggy porosity and grainstone that is strongly recrystallized and characterized by interparticle and vuggy pores. The Khuff is similar to other subcrops in the Arabian Gulf, with deposition occurring in an environment varying from an unrestricted shallow-marine setting to restricted shoal-lagoonal and supratidal conditions (Fig. 6.9).

Surface Formations This part of the U.A.E. close to the Oman Mountains provides further information on late Paleozoic rocks. Asfar and Qamar formations (Permian). Throughout the Oman Mountains, large detached blocks of poorly bedded, white, recrystallized limestone of Permian and Triassic age are found in the sedimentary mdlange between the Hawasina Thrust sheets and the Semail Ophiolite. In the U.A.E., these olistoliths in the Dibba Zone form the Jibals A1 Qamar (North and South), which are both blocks of carbonate and clastics several kilometers across in which several different units can be recognized (Hudson et al., 1954b; Robertson et al., 1990). The Early Permian Asfar Formation comprises up to 25 m (82 ft) of sandstone and limestone (Fig. 4.9), passing up from fine- to medium-grained siltstone and sandstone to lenticular, cross- and wavy bedded, fossiliferous limestone, which in turn give way upwards to recrystallized, bioclastic limestone. The top of the formation consists of alternating bioclastic sandstone, quartzose sandstone and stylolitic, micritic limestone. The Asfar sandstone and limestone contain fossils such as productids, spiriferids and fenestellids of Early Permian age. The sandstone appears as the fill of channels cut into the shallow-water carbonates. The Qamar Formation of Late Permian age ranges in thickness from 60 to 100 m (197-328 ft) of brown, weathering, mainly fine-grained limestone, which generally is recrystallized (Fig. 4.9). Massive to weakly or rubbly bedded boundstone is interpreted as patch reefs developed on fault blocks. The limestone rests disconformably over the beds of the Asfar Formation. The Qamar limestone was laid down in a shallow-marine setting and contains fusulinids, corals and brachiopods of Late Permian age.

Russ al Jibal Group (mid-Permian to Early Triassic). Glennie et al. (1974) proposed the term "Russ al Jibal Group" for three Permo-Triassic formations described by Hudson (1960) that together form the Russ al Jibal Group in the northern U.A.E. The type locality is Jebel Hagab, where about 1,500 m (4,920 ft) of gray, dolomitic, karstic limestone collapse breccias with stromatolites, fenestral structures and edge-wise conglomerates indicating original deposition in intertidal to supratidal settings. Three formations have been recognized and have been described by several authors, including Hudson et al. (1954a), Hudson (1960), Glennie et al. (1974), Searle et al. (1983) and

175

Sedimentttry Basins and Petroleum Geology of the Middle East

I

I

I'Z

DESCRIPTION

LITHOLOGY

Massive-bedded dolomites, fine to medium-grained crystalline limestones, Porcellaneous limestones and oolitic limestones. Thin dark-green shale.

i E

Alternations of fine-grained argillaceous limestones with occasional shales and fine-grained dolomitized limestones. Cross-laminated towards the top weak select pelletai structure.

FOSSILS

Zonotrichites iissavensis, Trocho/ina, Hemigordius, Agathammina, Giomospira and Ciimacammina

Hemigordius, Agathammina pusilla, Ciimacammina, Glomospira and Robuloides

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supratidal.

c~

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Calcitome//a, Geinitzina, Postcarbonica,

Globivaivulina graeca, G/omospira,

Hernigordius, Parafusu/ina, Pseudovermiporel/a soda/ica

and Anthrocopore/ia spectabilis

Fig. 6.10. Sedimentological interpretation of the mid-Permian-Early Triassic (Bih, Hagil and Ghail formations) in the northern Oman Mountains, U.A.E. (modified from Hudson, 1960). Alsharhan and Kendall (1986). Below are brief descriptions derived from the preceding authors (Fig. 6.10). Bih Formation (mid-Permian). In Jebel Hagab, the formation consists of about 200 m (650 ft) of gray to darkbrown, medium-grained, burrowed, saccharoidal dolomites, occasionally interbedded with fossiliferous and partly oolitic, dolomitized grainstone and some minor porcellaneous, dolomitic limestone (Fig. 6.10). The sediments display the characteristics of shallow-water, moderate- to high-energy deposits laid down in a subtidal to supratidal environment, and the age is assigned based on the occurrence of fusulinids and algae. Hagil Formation (Late Permian). This formation contains a sequence of about 260 m (853 ft) of alternating fine, gray, argillaceous limestone, often cross-bedded with shaly partings or partings of shale and fine, dark-gray, dolomitized limestone with slightly oolitic limestone containing a stromatolitic and foraminiferal assemblage from which the age of the formation can be derived (Fig. 6.10). It crops out on the eastern and southern side of the Hagil window on the extreme southern side of the Musandam Peninsula. The formation is interpreted as deposited in a shallow-water, supratidal to subtidal environment. Ghail Formation (Early Triassic). The boundary between these massive dolomites of this formation and the Hagil Formation is placed above a dark-gray, limestone

176

breccia containing prominent fragments of light-colored, porcellaneous limestone. The formation consists of 500 m (1,640 ft) of massive, sucrosic dolomite interbedded with dolomitized limestone. Relict peloidal and bioclastic structures can be distinguished, particularly in the upper half of the succession. In the lower part, large-scale current bedding is apparent. Solution breccias, cavernous weathering, fracturing and buckling of strata also are features of the beds of this formation, which was laid down in an intertidal to supratidal environment. Occasional marl can be found in the lower and middle parts of the formation. The formation has a sparse ostracod, algal and foraminiferal assemblage (Fig. 6.10).

Absaroka Sequence in Qatar Haushi Formation (66Unayzah-equivalent 99 clastics) (Late Carboniferous-early Late Permian). Below the Khuff Limestone in Qatar lies a sequence of about 213 m (700 ft) of fine-grained, pebbly sandstone with subordinate conglomerates, siltstone and variegated, sandy shale. Within these clastic beds, occasional thin beds of anhydrite, lignitic and silty coal have been found (Schlumberger, 1981; Hamam and Nasrulla, 1989). The assignment to the Haushi Formation and its equivalence to the Unayzah Formation are based on lithological similari-

The End of the Paleozoic and the Early Mesozoic of the Middle East

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1500 1600

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Fig. 6.11 Sedimentological description and log characteristics of the Late Permian (Khuff Formation) in Qatar (compiled with modifications from Schlumberger, 1981" Hamam and Nusralla, 1989; ): U.A.=Upper Anhydrite; M.A.=Middle Anhydrite. ties, for no paleontological data are presented. In the lower part of the succession, the sandstone consists of oligomictic to polymictic, fine-grained to pebbly sandstone with some conglomerate or breccia horizons. The sandstone either is parallel-bedded or shows low-angle cross-bedding with carbonaceous plant debris concentrated along the bedding planes or occurring as discontinuous laminae. Thin, red, silty to clayey interbeds may occur. An alluvial, braided-stream to wadi-type environment has been suggested, where flash floods transported debris into the depositional basin. In the uppermost part of the succession, the sandstone is texturally and mineralogically very mature and cross-bedded and laid down in a shallow, nearshore environment. Khuff Formation (Late Permian). The Khuff Formation in Qatar, which is about 550 m (1,800 ft) thick, consists lithologically of massive, tidal-fiat, oolitic, peloidal, dolomitic grainstone and packstone forming cycles terminated by the development of subtidal and supratidal, dolomitized mudstone, wackestone and anhydrites deposited in very-shallow, semi-restricted to open-marine envi-

ronments (Schlumberger, 1981). These depositional facies show a change from the present onshore into the offshore, where more open-marine conditions replace the supratidal-dominated environment. With very low relief, small fluctuations in sea level resulted in considerable shifts in the location of the ancient shoreline. Five megacycles are recognized in the Khuff carbonate reservoirs (K1-5) (Fig. 6.11), of which two are placed within the Triassic. In contrast, four are described in Saudi Arabia (Alsharhan and Nairn, 1994). The lowest cycle (K5) consists of tight, slightly argillaceous dolomites and occasional interbedded anhydrites, terminated by the thick Median Anhydrite that forms a useful marker horizon. Each of the succeeding four cycles (K1-4) can be broken down into subcycles and has basically the same lithologies: tight, dolomitic mudstone or wackestone; thinly bedded, dolomitic packstone or grainstone; and subordinate, porous, dolomitic grainstone. Interbedded anhydrite is not uncommon, but undolomitized limestone is rare.

177

Sedimentary Basins and Petroleum Geology of the Middle East

Absaroka Sequence in southwestern Saudi Arabia.

Juwayl "Member" (Stephanian-late Early Permian). In southwestern Saudi Arabia near the Yemen border, there are outcrops of sandstone, first assigned to the Wajid Formation, then informally named the Bani Khatmah Formation by Alsharhan et al. (1991), and now referred to as the Juwayl "Member" Wajid Formation of Kellogg et al. (1985) or the Supergroup V Juwayl "Member" of Stump and van der Eem (1995). The Juwayl is equivalent to the Unayzah Formation in central to northeast Saudi Arabia. The unit rests on a Hercynian erosional surface and is covered by the basal Khuff flooding surface. The upper part of the section was measured by Bramkamp in 1950 (cited in Powers et al., 1966), who documented a 150 m (492 ft) section in Wadi Bani Khatmah. The lower part of the formation, which is well-exposed in the hills and mesas along 19051 ' N, was measured by Steineke et al. (1958), and the 365 m (1,197 ft) middle section was pieced together at Bani Kur. Other exposures of the formation have been recorded in Jebel Umm Ghiran and Bani Ruhayyah. The sedimentological descriptions of the Juwayl sandstone and the Wajid Formation sandstone (Hadley and Schmidt, 1975; Dabbagh, 1981; Dabbagh and Rogers, 1983) are similar. Alsharhan et al. (1991) re-interpreted and described these sediments in southwestern Arabia and differentiated between the two formations. They are fluvially transported, light-gray, yellow, buff-brown or red, coarse-grained sandstone commonly including coarse pebbly sandstone and pebble conglomerates throughout the section. The sandstone is mature, polycyclic deposits in fining-up sequences that may end in a fine sandstone or siltstone band. The grains are subangular to sub-rounded and show moderate sphericity values. The repeating fining-upward units are observed most clearly in the southern part of the outcrop area. The beds thin from south to north in the direction of sedimentary transport, as determined from the cross-bedding of both tabular and trough crossbedded units and from ripple trends. Toward the north, the transport trend may swing from north to northwesterly to a more northeasterly direction. The sands have been interpreted as deposits of northerly flowing streams from a glaciated region. The lower part of the deposits is fluvial, but towards the northeast, the deposits may have been in a shallow-marine setting resembling fjords (Stump and van der Eem, 1995). The Khuff carbonates gradually grade into a siliciclastic series, and although limestone stringers are still interbedded at 22036 ' N, limestone stringers become less frequent as the beds thicken and become more clastic. By 19012 ' N at Khashm Sudayr and 18024 ' N at Jebel Umm al Ghiran, the sequence is entirely clastic. Thus, the Juwayl Member is regarded as a lateral facies of the Unayzah Sandstone Formation. Palynological data indicate that the Juwayl Member (previously the Bani Khatmah Formation is Late Carboniferous to Early Permian in age (Powers et al., 1966; Alsharhan et al., 1991). Therefore, it is a direct

178

correlation of the Unayzah Formation north of the central Arabian Arch (A1 Laboun, 1990).

Absaroka Sequence in the Republic of Yemen The late Paleozoic section in Yemen was assigned to the Wajid sandstone and Akbra shale formations, with the latter formerly considered part of the Jurassic sequence (the Liassic Kohlan Formation), but now known to be the equivalent of part of the A1 Khlata Formation of southern Oman. More recently, a modification has been proposed that would confine the term "Wajid Formation" to the early Paleozoic beds.

Akbra Shale Formation (Early Permian). The formation, which ranges in thickness from 40 to 110 m (131361 ft), is restricted to the northwestern part of the Republic of Yemen (North Yemen), where it rests unconformably upon sandstone. Where the sandstone wedges out, the shale comes to rest directly upon the Precambrian basement; it is, in turn, unconformably overlain by beds of the Kohlan Formation (Kruck and Thiele, 1983). The base of the Akbra shale is a tillite containing Precambrian basement boulders and pebbles (Fig. 6.12). The boulders are well-rounded to subangular and may be grooved and striated. The overlying varves, like shaly mudstone, have many of the characteristics of glacial varves and most probably are seasonal deposits laid down in a glacial lake with ice-rafted dropstone. Absaroka Sequence North of the Central Arabian Arch Absaroka Sequence in Central and Northern Saudi Arabia The most complete section of the Absaroka sequence north of the central Arabian Arch is found in the Widyan Basin. It is the simplest introduction to the late Paleozoic sequence in northern Arabia, for only two formations are to be considered, the Unayzah and Khuff. South of the central Arabian Arch, the Juwayl (previously part of the Wajid Formation) is equivalent to the Unayzah Formation, which contains lithological equivalents of the Permo-Carboniferous Haushi glacials so well-established in Oman and southern Arabia. Unayzah Formation [lower Upper Permian (Kazanian)]. The Unayzah Formation is a thick, continental red bed sequence of varied facies (Fig. 6.13), named after the town in the al Qasim District near the edge of the Arabian Shield where it is exposed in road cuts and in an escarpment as a thin band paralleling the outcrop of the Khuff limestone. It is unconformable over various formations from the Precambrian to Devonian and is, in turn, unconformably overlain by the lowermost clastic beds of the Khuff Formation. The greatest thickness recorded in outcrop is 36.3 m (119 ft) in Wadi A1 Shajarah, although in well Hawtah, 88 m (285 ft) have been recorded.

The End of the Paleozoic and the Early Mesozoic of the Middle East

AGE

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Fig. 6.12 Lithologic log of Early Permian Akbra Shale located northeast of Hajjah at 15o44'26 " N, 43~ " E, Yemen (modified from Davison et al., 1994 and reproduced by kind permission of the Geological Society of America).

~SUBGLACIAL

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179

Sedimentary Basins and Petroleum Geology of the Middle East A1 Laboun (1986) described the formation and formally defined the stratotype the following year (A1 Laboun, 1987), although the term was used previously for the lowermost member of the Khuff Formation (Delfour et al., 1982) for about the same rocks, and E1 Khayal and Wagner (1985) published a formal definition based on the section in Unayzah town. The latter were able to demonstrate a brief erosional break separating red, fluvio-lacustrine mudstone and sandstone from the overlying channelfill sandstone, gray shale and dolomite streaks of marginal-marine or shallow-marine origin, using it as the Unayzah-Khuff contact. This boundary was placed where the first transgressive shale unit of the Khuff Formation appeared, emphasizing the importance of the marine flooding surface and marking a significant environmental and climatic change from the Unayzah arid alluvial fan to the marine or marginal marine of the basal Khuff clastics. The type-section described by A1 Laboun (1987), located at 26055 ' N, 43o34 ' E and extending about 100 m (328 ft) along a north-south-trending escarpment was reinvestigated by Senalp and A1Duaiji (1995), whose results are summarized in Fig. 6.14. Note that at the type locality, the base of the Unayzah is not exposed. The principal distinction between the two accounts is the recognition by Senalp and A1 Duaiji of a pre-Khuff unconformity that restricts the Unayzah to deposits of a meandering-fluvial-system and flood-plain facies. The SR-RAY

facies distribution in the A1 Hawtah-Hazmiyah Field area is illustrated in Fig. 6.14a, b and c. The mudstone contains silt laminae, and there are well-preserved root structures. Plants are found in the sandstone. There is poorly sorted sandstone with lateral thickness and grain-size changes, lateral accretion surfaces and soft sediment deformational structures, small-scale festoon, cross-bedded and tippled surfaces. Paleocurrent directions indicate sand transportation toward the southeast, north and northeast. Overall, in the better-preserved sections, the Unayzah shows a thinning- and fining-upwards sequence with a decrease in debris-flow and mud-flow facies. The formation was formed from coalescing fans dominated by braided streams with point bars and crevasse channels grading downslope to playa lakes under arid to semi-arid conditions. Eolian conditions are inferred, and although no dunes have been identified, the image log from well Hawtah-1 supports this interpretation. The age for differently defined Unayzah units ranges from late Carboniferous to late Permian, based upon the interpretation of the floral evidence. On balance, current thought assigns an early late Permian Kazanian age, consistent with a late Permian (Tatarian) age based upon a mixed allochthonous plant assemblage found in the basal Khuff clastics. Ferguson and Chambers (1991) described the lithology of the Unayzah Formation in the vicinity of the oil

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The End of the Paleozoic and the Early Mesozoic of the Middle East

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181

Sedimentary Basins and Petroleum Geology of the Middle East fields in central Saudi Arabia, where it consists of about 180 m (590 ft) of siliciclastic, fluvial, coastal plain, deltaic and shallow-marine facies. It was subdivided into three members, of which the C Member recorded the first postHercynian marine incursion, while the A and B members recorded a second transgressive-regressive cycle. The Unayzah C Member (Fig. 6.14c) is characterized by a poorly sorted, fine silt to medium-grained sandstone with floating granules and pebbles of marine origin, and represents the earliest known post-Hercynian marine inundation of central Arabia. A withdrawal of this sea at the end of C Member deposition indicates that the member is capped by a sequence boundary. As the C Member is bounded top and bottom by sequence boundaries, it is considered to be a lower depositional sequence within the Permian siliciclastic succession. The Unayzah B Member consists entirely of fine to pebbly, cross-bedded sandstone of alluvial origin, deposited during a post-Hercynian relative sea-level rise, when the non-marine environment was aggrading. The sandy and conglomeratic sediments support river interpretation. The member is part of a transgressive systems tract, and

the maximum extent of flooding and the culmination of the transgressive system is in the red siltstone bed of the lower A Member. The Unayzah A Member consists of a thin, transgressive lag followed by a regressive pulse of offshore marine siltstone, shoreface sandstone and mixed clastic, coastalplain sediments in the lower part. The member records a progradational cycle, with offshore siltstone grading upward into paralic sandstone. The lowermost marine siltstone is red, none to moderately bioturbated and contains an increasing upward percentage of thin, sandstone storm beds. The paralic sandstone consists of a variety of facies, including shoreface, foreshore and distributary-channel. The importance of the Unayzah as well as the basal Khuff clastics (Ash-Shiqqah Member) lies in the fact that they are the principal reservoirs of the more recently discovered fields in central Arabia. Sedimentological descriptions of these beds in the Abu Jifran/Farhah oil fields have been given by King (1995). Khuff Formation (mid-Late Permian). The Khuff Formation takes its name from Ayn Khuff (24055 ' N, 44043 ' E) near the Riyadh-Jiddah Road. The term was

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Fig. 6.15. Khuff Formation (Permian) isopachs in the Arabian Gulf region (after A1Jallal, 1995, and reproduced by kind permission of Gulf Petrolink, Bahrain). 182

The End of the Paleozoic and the Early Mesozoic of the Middle East

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Table 6.2. Khuff Formation divisions (various authors). Powers et al., 1966 (outcrop)

Delfour et al. (1982) (outcrop)

Khartam Member Midhnab Member

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Unayzah Fm.

Lower Khuff

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183

Sedimentary Basins and Petroleum Geology of the Middle East from the open-marine and deep-water slope facies by a coral-algal reef barrier (Fig. 6.16). It is the intertidal and sabkha facies with mudstone and anhydrite that provide the reservoir seals over most of Arabia. In central Saudi Arabia, the Khuff is unconformably overlain by the Triassic shale of the Sudair Formation, but in the Widyan Basin to the north, the early Mesozoic beds and the Khuff Formation are progressively truncated by Early Cretaceouspre Wasia erosion. As a result of this erosion, the strata of the late Paieozoic cannot be traced into Jordan. The limestone beds of the Khuff Formation follow conformably above the basal clastics and thin, argillaceous limestone. The Khuff Formation was considered by Steineke et al. (1958) to be probably Late Permian in age, but some have doubted this age assignment because only a few, poorly preserved brachiopods and nautiloids were found. Other fossils, such as pelecypods and gastropods, are nondiagnostic. However, microfossils extracted from well

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cores near the top of the formation, such as foraminifera and algae, spores and pollen, all support a Late Permian age. The fossil assemblage collected from the outcrop in the lower part of the Khuff Formation, while containing different species, yielded mainly the same genera. The microfauna from the Khuff limestone in the U.A.E. suggest that the age range may extend into the Early Triassic (Scythian). In the Saudi Arabian outcrops, the Khuff/ Sudair formational boundary is older than further to the east (Qatar and U.A.E.) because of the increasingly marine conditions from west to east. Delfour et al. (1982) divided the Khuff Limestone Formation into five informal members (Table 6.2), of which the lowest, first separated as a distinct formation by A1 Laboun (1986, 1987), has been restored as a result of studies by Senalp and A1 Duaiji (1995) and E1 Khayal and Wagner (1985). The reference section figured by Powers et al. (1966) shows three divisions. In some areas, however,

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184

The End of the Paleozoic and the Early Mesozoic of the Middle East distinctions are hard to make because of dolomitization. Descriptions of the individual members (Fig. 6.17) are based on outcrops in the Ad Dawdimi Quadrangle at the eastern edge of the Arabian Shield by Delfour et al. (1982) and are summarized below, with the addition of the basal Khuff clastics from Senalp and A1 Duaiji (1995).

succeeded by yellow, dolomitic clay with a few bioclastic, dolomite interbeds and capped by blue-gray, blocky and clayey dolomite beds terminating with a bioturbated, burrowed and algal layer (Fig. 6.17). These sediments were deposited in an intertidal to subtidal setting. Duhaysan Member. The unit is 13.5 m (45 ft) thick, and a sequence of three lithofacies has been recognized within it. The lowest consists of gray, bioclastic dolomites and white, bioclastic, pelletoidal dolomites with intraclasts, followed by a middle unit of white, gypsiferous, dolomitic clay. The upper unit is made up of gray, flaggy, fine-grained and bioturbated limestone overlain by white, clayey dolomite (Fig. 6.17). The depositional setting of these sediments was subtidal. Midhnab Member. This 58 m (190 ft) thick member also comprises three lithofacies, with a basal succession of conglomeratic and lithoclastic, dolomitic limestone. Above follows an alternation of laminated, clayey, dolomite and yellow or bluish, gypsiferous, dolomitic claystone. The upper lithofacies consists of light-gray, lacustrine limestone with remains of charophytes (Fig. 6.18) deposited in an intertidal to supratidal setting. Khartam Member. It is made up of two lithologic types with a thickness of 27 m (89 ft). The lower sequence of bioclastic, lumachellic limestone is overlain by blue, laminated, dolomitic clay rich in pellets and terrigenous material at the base. Upward, the dolomitic clays become yellowish and pass upward to more ochreous and ferruginous, bioclastic dolomite. The upper sequence is made up

Basal Khuff clastics (Ash-Shiqqah Member of Senalp and Al Duaiji, 1995, or Khuff-E of Al Jallal, 1995). These succeed an erosional break observed by E1 Khayal and Wagner (1982). Resting directly on the unconformity marked by a doliche and paleosol surface is one meter of interbedded marl, argillaceous limestone and sandstone (Fig. 6.15a, b), which is intensely bioturbated, and one meter of grayish-brown, bioturbated, dolomitic limestone. The remainder of the sequence consists of marl and shale that incorporate a channel-fill sandstone (King, 1995). The channel sandstone has reactivation surfaces, herringbone cross-bedding and current tipples. Gypsum layers show parallel bedding or form satin spar veins. These basal clastics mark a marine transgression (flooding surface), the onset of the massive Khuff limestone interval with thin limestone, shale and some channel sandstone totalling from 5 to 21 m (16.5-70 ft). Huqayl Member. The measured thickness of 34.2 m (112 ft) is divided into a lower unit of bluish, silty, bioclastic dolomite followed by greenish or yellowish, gypsiferous clays with blue-gray, blocky, fine-grained dolomites at the top; and an upper unit consisting of bluish, granular, bioclastic dolomites and fine-grained, laminated dolomite

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Fig. 6.18 Sedimentological interpretation and suggested nomenclature of the Late Permian (Khuff Formation), Saudi Arabia (modified from A1Jallal, 1995, and reproduced by kind permission of Gulf Petrolink, Bahrain). 185

Sedimentary Basins and Petroleum Geology of the Middle East of beige, powdery, calcitized dolomite with microcrystalline limestone containing occasional stromatolitic patches overlain by silty, clayey, flaggy dolomite and lumachellic dolomite and oolitic limestone (Fig. 6.17) laid down in a subtidal to intertidal setting. In eastern Saudi Arabia in the vicinity of the oil fields, a five-fold division of the Khuff Formation also is possible (A1Jallal, 1995) (Fig. 6.18); however, Delfour et al. (1982) note that there is no indication of whether these correlate with the divisions just described. The first unit (Khuff E) consists of basal, carbonaceous sandstone, followed by interbedded carbonaceous shale and argillaceous limestone with some sand deposited in a marine to marginalmarine setting. The second unit (Khuff D) marks a shallowing-upward succession from a muddy carbonate-anhydrite facies in which there are a few stringers of grainstone into a widespread supratidal anhydrite. The third unit (Khuff C) consists of cross-bedded grainstone and packstone interbedded with burrowed mudstone and wackestone and includes intercalations of intertidal mudstone and wackestone. The fourth unit (Khuff B) is a sequence of dolomitic and anhydritic, ooidal-peloidal packstone and grainstone interbedded with mudstone and wackestone. The fifth unit (Khuff A) consists of packstone/grainstone and dolomitized mudstone and anhydrite. The similarities in the lithofacies of central and eastern Saudi Arabia and the predominance of tidal-flat environments passing to supratidal suggest that the Khuff Sea transgressed over a broad, peneplaned surface virtually devoid of relief. The differences in the lithofacies are related simply to the greater proximity to the source area of central Saudi Arabia. The cyclic nature of the succession is a continuation of the cyclicity observed in the Unayzah Formation, reflecting the arbitrary nature of the selection of a boundary between the two formations.

Absaroka Sequence in Kuwait Khuff Formation (mid-Late Permian). In Kuwait, the deepest well drilled over the Burgan High penetrates through the Khuff limestone into the underlying clastic sediments. There is less information about the pre-Khuff clastics in Kuwait, although a relatively thick section was penetrated in well Burgan A-1 (in the Burgan Oil Field). Intercalations of limestone, dolomite and thin anhydrite beds appear as precursors of the conditions that succeeded during the deposition of the Khuff. A thickness of 587 m (1,925 ft) of the Khuff Formation was penetrated in Burgan A-1. The succession can be divided into three distinctive, lithological units (Khan, 1989). The lower member consists of 143 m (470 ft) of massive, buff-gray dolomite with rare, thin interbeds of shale, which may grade to siltstone. In the upper part, thin, anhydrite beds are present with traces of pyrite and some quartz grains. The middle member is 151 m (495 ft) thick and consists of alternating anhydrite and dolomite with thin, green-gray shale. The upper member, the thickest at 293 m (960 ft), is made up

186

of massive, buff-gray, sucrosic dolomite with thin, green or orange, shaly interbeds that may grade into brick-red siltstone in the lower horizons. The shale is more uniformly dark-gray in the upper part. Traces of glauconite, anhydritic dolomite and thin, dolomitized, oolitic grainstone occur. The formation was deposited in very shallowmarine conditions with high-energy shoals before the advent of low-energy conditions marked by the onset of argillaceous facies of the Triassic Sudair Formation. The lower boundary of the Permian carbonates is well-defined by a pronounced unconformity that marks a major depositional hiatus in Kuwait. The unconformable upper limit is of unknown duration. The Late Permian age is assigned from the presence of well-preserved foraminifera and algae, a fauna that includes Globovalvulina vonderschmitti, Pachyphloia cf. ovata, Hemigordius cf. ovatus and Mizzia velebitana, algae, echinoids, bryozoa, gastropods and ostracods (Khan, 1989).

Absaroka Sequence in Bahrain. Khuff Formation (mid-Late Permian). The Khuff Formation in the Awali Field lies at a depth of +2,750 m (9,020 ft). It is reported to unconformably overlie a silty, shaly sandstone attributed to the Unayzah Formation. There are insufficient data to establish whether this assignment is reasonable. Although the Khuff Formation contains the major gas reserves in Bahrain, there are only very brief descriptions of the Khuff limestone although the thickness is considerable, as much as 700 m (2,296 ft) having been reported. The carbonates are described as dolomitized, microsucrosic, oolitic, peloidal packstone and grainstone with anhydritic interbeds that pass up, without unconformity, into the beds of the overlying Triassic Sudair Formation. Absaroka Sequence in Northwest and Northeast of the Arabian Platform Absaroka Sequence in Jordan As indicated by Bender (1975), no Devonian rocks are exposed in Jordan, although they may be present in subsurface in the extreme southeast of the country in the A1 Azraq-Wadi as Sirhan and A1 Jafr basins. Carboniferous beds are unexposed, although the presence of the Carboniferous in subsurface is known from the presence of early Westphalian A-Namurian-late Visean palynomorphs in a sequence of clastics and impure limestone from well Safra-1.

Outcrop Formations Um Irna Formation (Tartarian-early Scythian). A small outcrop, about 85 m (279 fi) thick, on the shore of the Dead Sea was reported by Bandel and Khoury (1981). These clastic rocks were known as the Um Irna Formation.

The End of the Paleozoic and the Early Mesozoic of the Middle East

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Fig. 6.19 Lithofacies interpretation and depositional model of the Um Ima Formation in Jordan (after Makhlouf et al., 1991). The formation Consists of both thin- and thickly bedded siltstone and silty shale, together with thick-bedded sandstone, siltstone and silty shale, and can be divided into six units. The sediments in each cycle represent terrestrial deposits eroded from the nearby Precambrian basement. A detailed study carried out by Makhlouf et al. (1991) reported that the Umm Irna is well-exposed along the Dead Sea between Wadi Mukheiris and Wadi Atun and reaches a maximum of 60 m (197 ft). The formation unconformably overlies upper Middle Cambrian sandstone of the Umm Ishrin Formation and is conformably overlain by the Triassic Ma'in Formation. Makhlouf et al. (1991) divided the formation into two sedimentary facies that correspond to the informally designated lower and upper members (Fig. 6.19); these are summarized below. The lower member (Facies 1) consists of about 10 m (33 ft) of interbedded sandstone and siltstone and silty shale arranged in up to five fining-upward sequences. Each sequence comprises a lower erosion surface overlain by tabular to lenticular sandstone units (moderately wellsorted quartz arenites), passing vertically and laterally into siltstone and silty shale with subordinate mudstone containing small, carbonaceous plant fragments. This facies is laid down in shallow, low-sinuosity, sand-bed--dominated channels draining the distal reaches of a low-gradient alluvial plain, which probably extended northwards into a shallow, marginal-marine environment (Bandel and Khoury, 1981; Makhlouf et al., 1991). The upper member (Facies 2) consists of 50 m (164 ft) of sandstone, siltstone and silty shale. The succession is composed of five well-defined, fining-upward sequences ranging from 4 to 14.5 m (13-476 ft) in thickness. Individual sequences comprise an erosionally based, coarsegrained, pebbly sandstone grading up through mediumand fine-grained sandstone into siltstone and silty shale. The sandstone is tabular and laterally persistent, internally complex units structured by erosively bounded trough

cosets. The siltstone, silty shale and silty mudstone are lacking sedimentary structures, except for a few ripples. These sediments show characteristics of both meandering and braided-stream deposits.

Subsurface Formations

Hudayb Group (Permian). The distribution of the Permian rocks in Jordan is restricted to the northern part of the country, where they range from 200 to 226 m (656-741 ft) in thickness in wells Ajlun-1 and Northern Highlands-2, to about 3 m (10 ft) in well Risha-1. Sunna et al. (1988) used the term "Hudeib Sandstone Shale Formation" for the Permian sediments in outcrop and subsurface; subsequently, Andrews (1992) introduced the term "Hudayb Group" to cover all the Permian rocks of Jordan. Andrews (1992) divided the group into three formations - - the lower: Anjara Formation, the middle: Huwayra Formation and the upper: Buwayda Formation with ages ranging from late Early to early Late Permian. There is little published information on these formations, and the following summary and Fig. 6.20 are based on Andrews (1992). Anjara Formation (Early Permian). This formation represents the initial deposits of the post-Hercynian sequence that rests unconformably on earlier Paleozoic strata. The name was taken from the town of Anjara. The type section is in well Ajlun-1, where the formation has been fully penetrated, and about 74 m (243 ft) of sediment were recorded. In well Northern Highlands-2, the thickness of Permian sediments is only about 45 m (148 ft), separated by 97 m (243 ft) of dolerite. The formation consists of two units: a lower unit of about 18 m (59 ft) of micro-conglomerate, with subangular to sub-rounded, clay-cemented, quartz grains; and an upper unit of about 27 m (89 ft) of fine- to medium-grained sandstone. The sandstone is glauconitic and locally pyritic and kaolinitic and is interbedded with dark-grey and black, and occa187

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig 6.20 Lithostratigraphy of the Permian Hudayb Group in Jordan (modified from Andrews, 1992). sionally reddish, silty, bituminous and pyritic shale. The basal Anjara rests unconformably on medium- to coarsegrained sandstone and the red-brown shale of the Cambrian Salib Formation. The upper unit grades upward into the carbonates of the Huwayra Formation. The formation marks the first shallow-marine incursion of the Early Permian, a transgression over the eroded landscape of Jordan. Huwayra Formation (Early-Mid Permian?). The formation has been penetrated in three wells in northern Jordan: Northern Highlands-2 (about 83 m, or 272 ft), Ajlun-1 (about 91 m, or 298 ft) and Er Ramtha-lA (about 37 m, or 121 ft). The first two wells fully penetrated the formation. The Huwayra Formation in Northern Highlands-2 consists, in the lower part, of a thin, radioactive shale followed by a sequence of finely crystalline, argillaceous, pyritic and fossiliferous limestone containing streaks of microporous (chalky) limestone and thin beds of grey shale. A similar lithology was found in well Er Ramtha-lA, with a black to dark-grey, sandy, argillaceous dolomite in the middle. In well Ajlun-1, the formation is composed of a mixture of shale (grey, dark-grey to black in color and silty, occasionally sandy, pyritic and micaceous), limestone (crypto- to finely crystalline, occasionally oolitic, argillaceous and chalky), dolomites (brownish-grey to black, argillaceous and light-brown to buff) and sandstone (white to grey, fine- to mediumgrained and occasionally glauconitic and argillaceous). The basal contact with the Anjara Formation is gradational and conformable. The top contact also is gradational and is 188

placed between the carbonates and shale of the Huwayra Formation and the sandstone of the Buwayda Formation. The Huwayra beds were deposited on a shallow-marine, carbonate shelf with anoxic conditions affecting the bottom waters, as indicated by the presence of the basal, radioactive shale and the interbedded, dark-grey to black shale. Buwayda Formation (early Late Permian). The formation has been fully penetrated in three wells in northwestern Jordan, with thicknesses of 63 m (207 ft) in well Ajlun-1, 74 m (243 ft) in well Northern Highlands-2 and 78 m (256 ft) in well Er Ramtha-lA. Thin units about 3 and 10 m (10 and 33 ft) have been penetrated in wells Risha-11 and 2, respectively. The formation has two lithological components (pure sandstone and mixed sandstone). The pure sandstone is grey, pink, white or translucent and fine- to medium-grained. The mixed sandstone is fine-grained, red-brown, ferruginous, argillaceous, dark-grey, lignitic sandstone with coaly fragments and woody material forming an abundant kerogen component. This sandstone is interbedded with black to dark-grey siltstone and silty shale. In well Er Ramtha-lA, the formation is composed of shale interbedded with fine- to mediumgrained sandstone, with streaks of grey, argillaceous and glauconitic limestone. This formation conformably overlies the Huwayra Formation in northwestern Jordan, whereas in the western Risha area to the northeast, the thin equivalents of this formation lie directly on Lower Paleozoic strata. The uppermost Permian sediments are absent,

The End of the Paleozoic and the Early Mesozoic of the Middle East and the Buwayda clastics are unconformably overlain by the Early Triassic Suwayma Formation carbonates. In outcrop and in the Risha area of northeastern Jordan, the clastics of the Buwayda Formation are unconformably overlain by the clastics of the Ma'in Formation or their subsurface equivalents (Suwayma Formation). The sediments of the Buwayda Formation formed in a fluvial environment.

Absaroka Sequence in lraq There are two areas in Iraq where late Paleozoic beds are found: over the Ha'il-Rutbah Arch in the western part of the country bordering Jordan, and in the Northern Thrust Belt in the border region with Syria, Turkey and Iran.

Western Iraq (Ha'il-Rutbah Arch Area) The Permo-Carboniferous sediments crop out in the western part of the country over the crestal part of the Ha'il-Rutbah Arch in the Ga'ara Depression. They have been found in well Akashat-2 drilled in the western desert of Iraq. In the outcrop and subsurface, two units were recognized: the lower unit, or Nijili Formation, of Dunnington (1954; in Buday, 1980); and the upper unit, or Ga'ara Sandstone Formation, of Boesch (1938, in Buday, 1980). Nijili Formation. About 100 m (328 ft) thick, this formation was described from well Alkashat-2 in the Western Desert of Iraq (A1 Gailani and Ala, 1984). It consists of lower, sandy, micaceous claystone, which grades up into dolomite-cemented quartz arenites, ferruginous claystone, dolomite-cemented quartz siltstone and darkred claystone. In turn, these pass up into light-gray siltstone capped by a dolomite-cemented quartz arenite. The base of the formation has not been penetrated, and the formation is unconformably overlain by the Ga'ara Formation. The Nijili is dominated by sandy deposits of continental origin, with intervals of lacustrine or swampy deposits, with abundant Sigillaria sp. stems, some in a position of growth. These are dated as Late Carboniferous to possibly Early Permian. Ga'ara Formation. This formation has a known thickness of about 150 m (492 ft) of complex, multicolored, medium- to coarse-grained, cross-bedded sandstone alternating with varicolored, sandy and kaolinitic clays containing lenses of limonitic or partly hematitic ores and thin, light-colored quartzite and siltstone interbeds with streaks of coal (Buday, 1980). The sandstone has an openframe fabric partially cemented by dolomite. The base of the formation is unconformable with the Nijili Formation. It is overlain by the Mulussa Limestone Formation, from which it is separated by a hiatus. The formation was deposited in a continental, fluviatile to lacustrine environment, but in which littoral marine influences are included. The age assignment, based upon the recognition of plant remains, is Permo-Carboniferous; however, in Wadi Dwaiklah, the presence of Lobatannularia and Pla-

giozamites suggests an age ranging up into the mid-Permian. The exact stratigraphic position of the formation, its lithological character and faunal content remain to be established (Buday, 1980).

Northern Iraq (Northern Thrust Belt Area) Chia Zairi Formation (mid-Late Permian). Originally described by Wetzel (1950, cited by Bellen et al., 1959) in the Northern Thrust Belt area of Iraq, the formation has a thickness of 750-810 m (2.,460-2,657 fi). It consists of three units described by Bellen et al. (1959) and Buday (1980). The lower unit ('Darari Formation" ) consists of 340390 m (1,115-1,279 ft) of alternating thin-bedded, biodetrital limestone, dark-blue limestone and massive, cliffforming, silicified limestone. The middle unit (Satina Evaporite Member) is made up of 60-80 m (197-262 ft) of dolomites, with solution and recrystallized breccias and marl. The upper unit ("Zinnar Formation"), which is 300320 m (984-1,050 ft) thick, consists of thin-bedded, biodetrital and sometimes cherty limestone with some silicified limestone. The uppermost limestone is partly oolitic and may contain some clastic admixture (Buday, 1980). However, these divisions are seldom recognizable in the field and, hence, are seldom used. In the same general area, the beds have been partly penetrated by well Atshan1 (west of Mosul), where the lithological succession, except for the uppermost part, is somewhat different, with a clastic admixture throughout the lower part of the succession consisting of silty, argillaceous limestone, silty dolomites and some shale and sandstone in the lowermost part. The Chia Zairi Formation is rich in fossils in the type area, and, according to Hudson (1960), the coral and algal fauna indicate a mid- to Late Permian age. The uppermost beds also contain forams with an Early Triassic affinity, suggesting a transition up into the Triassic. Therefore, the formation is the time equivalent of the Khuff Limestone of Arabia, but, although the formation is essentially a carbonate sequence, there are some distinct facies differences. The formation, however, is easy to correlate with the Permian limestone formations of southern Turkey. Absaroka Sequence in Southeast Turkey There appears to be a major gap until the deposition of the Middle Permian fluvio-deltaic beds above the Koprulu and Hazro/Yiginli formations in southeastern Turkey. North of Diyarbakir (Hazro area), the Devonian sediments are unconformably overlain by Permian limestone and deltaic clastics (Kas and Gomaniibrik formations)(Fig. 6.21)., followed by Triassic sandstone and limestone of the Goyan Formation. The Goyan Formation records the northward progradation of shallow-marine, deltaic facies (Cater and Tunbridge, 1992). In the Hakkari

189

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Fig. 6.21. Lithostratigraphy of the late Paleozoic sequence in the Hazro region, Southeast Turkey (modified from Guvenc et al., 1982). area, the Devonian shale rests unconformably and is overlain by the beds of the Permian Alan Yayla Formation, which consist mainly of coarse, alluvial clastics overlain by a coal-bearing sequence (Cater and Tunbridge, 1992). G o m a n i i b r i k F o r m a t i o n (Late Permian to Triassic?). The formation ranges from about 175 to 290 m

(574-959 ft) and crops out in the Dadas-Hazro area (Fig. 6.21) and in the Hakkari region, where 1,000 m (3,280 ft) can be recognized. In both areas, there is a clear break between the sandstone and shale of the Hazro Formation and the carbonates at the base of the Gomaniibrik Formation~ Three subdivisions of the formation can be recog-

190

nized in the Dadas-Hazro area. The lower and upper members are composed of carbonates, while the middle member is made up of clastics (Guvenc et al., 1982). The A Member consists of 38 m (125 ft) of micrites and biomicrites, followed by the 90 m (295 ft) B Member of siliciclastic, deltaic facies of sandstone and coaly shale. The C Member marks a return to carbonate deposition, with 161 m (331 ft) of medium- to coarse-grained biomicrites. This sequence suggests that deposition corresponds to one regressive and two transgressive episodes.

Proceeding still further to Syria, the section usually is incomplete. Dubertret (1967, cited in Buday, 1980) identified clastic and carbonaceous rocks of lacustrine and marine origin overlying marine Early Carboniferous strata in wells E1 Barde-1 and E1 Bouab-1 and overlain, in turn, by Triassic rocks. Ala and Moss (1979) regarded these reports as speculative and preferred to assign the rocks to an informal Doubayat Group of Permo-Carboniferous age, based upon their lithological resemblance to Late Permian rocks of the Northern Thrust Belt area of Iraq. Permian marine beds are found in Syria (Arak-1, and possibly in other wells in the Palmyra-Sinjar Trough). A total thickness of more than 600 m (1,968 ft) of marine carbonate and fine-grained, clastic sediments eventually accumulated in this depression. Southeast and north, the trough sediments grade into shallow-marine clastics, and fluvio-deltaic beds shed from the flanks of the Rutbah, Khleissia and Mardin highs. Sharief (1982) suggested that more open-marine conditions may have existed to the northwest, as represented by the black shale and limestone found in well Khanasser-1. A1 Youssef and Ayed (1992) revised the stratigraphy of the late Paleozoic in Syria and defined the Amanus Group (Fig. 6.22), which extends from Lower Permian to Lower Triassic and consists of three formations: Hell, Amanus Sand and Amanus Shale. The Amanus Shale is assigned to the Triassic (Fig. 6.22). The thickest Permian section was reported in the Palmyra Trough. The Permian deposits are underlain disconformably by the Carboniferous and overlain conformably by the shale of Early Triassic. The Late Permian to Early Triassic period represents one phase of continental deposition, with a gradual change from dominant siltstone and shale interbedded with sandstone to dominant micaceous shale and silty shale. Dolaa Formation (Permian). The Permian Dolaa Formation is present throughout Syria. In central Syria in well Azar- 1, it consists of some 50 m (164 ft) of bioclastic and massive-bedded, pale-gray limestone containing corals, brachiopods, gastropods and foraminifera. Farther south in well Soukne-1, the thickness increased to 90 m (295 ft) of bioclastic and argillaceous limestone, which grades upward into argillaceous, thin-bedded limestone, marl and minor silts with occasional bands of quartzitic sandstone. In well Markada-1, the lower part consists of

The End of the Paleozoic and the Early Mesozoic of the Middle East

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stone 9The lowest consists of 170 m (558 ft) of silty, calcareous claystone with minor thin streaks of dolomite and quartzitic sandstone. Amanus Sand Formation (Late Permian). The formation takes its name from the Amanus Mountains in Turkey, but the type section is defined in well Rasafa-1. The formation ranges in thickness from 97 to 125 m (318-410 ft) and is composed mainly of interbedded sandstone and shale of continental origin. The sandstone is fine- to coarse-grained, poorly sorted and occasionally silty, cemented by silica (quartz overgrowth) and, in places, well-to sub-rounded, glauconitic grains. The shale is calcareous, finely laminated, fissile to sub-fissile and pyritic.

Absaroka Sequence in Iran Separate formational names are used to define the Permian rocks in different areas of Iran. According to Setudehnia (1975), the lithological section in the Zagros Basin in the southwestern part of the country most closely resembles that of Saudi Arabia and the Arabian Gulf. In northern Iran, different formational names describe a sec-

191

Sedimentary Basins and Petroleum Geology of the Middle East tion in which marine influences are apparent even in the Early Permian (Assereto, 1966). u:

GAMMA LITHORAY LOGY [API UNITS

9 C9

SONIC LOG

GENERAL DESCRIPTION

Southwestern Iran

Faraghan Formation (Early Permian-Artinskian). In southwestern Iran at Zard Kuh and Kuh-e Dinar in the Zagros Basin, Setudehnia (1975) has described a clastic sequence (Faraghan Formation) below and a carbonate sequence (Dalan Formation) above, although exposures are poor. The formational name of the clastics was assigned by Szabo and Kheradpir (1978) from the locality at Kuh-e Faraghan north of Bandar Abbas, where exposures are good. There, 311 m (1,020 ft) of clastics with minor carbonate bands rest upon Silurian graptolitic shale of the Gahkum Formation. At other localities in the basin, the base of the formation may rest upon either Ordovician or Cambrian rocks. This widely recognized, angular unconformity is the Hercynian Unconformity and suggests that Hercynian orogenic activity included at least part of the Zagros Basin. The subsurface type section is in well Kuh-e Siah-1, where about 112 m (367 ft) were encountered (Szabo and Kheradpir, 1978) (Fig. 6.23). The clastics of the Faraghan Formation consist of coarse quartz conglomerates with sub-rounded pebbles in a finer sand matrix. They grade up into medium- to coarse-grained, cross-bedded quartz arenites, which are poorly cemented and friable. The sequence ends with variegated shale interbedded with fine- to medium-grained quartz arenites. In outcrop, some shale horizons are found, but the shale component is dominant in subsurface. The Faraghan Formation essentially is a transgressive, lower-coastal-plain, clastic sand, probably deposited during progressive, oscillatory, shallow-marine transgressions of the Permian Sea. There is a gradational contact with the overlying Dalan carbonates. Dalan Formation (Late Permian). The carbonates of the Dalan Formation take their name from well Dalan-1 110 km south-southwest of Shiraz, where the sequence was penetrated in an anticlinal structure. In the subsurface type section in Kuh-e Siah, a maximum thickness of 748 m (2,453 ft) was penetrated. Edgell (1976) subdivided the succession into one formal unit (Nar Anhydrite Member) sandwiched between two informal carbonate units" the lower and upper carbonates (Fig. 6.23). The Nar Member consists of massive, bedded anhydrites, anhydritic dolomite and oolitic dolomites. Both the lower and upper carbonate units consist of fossiliferous limestone and dolomites grading up into oolitic, peloidal and partly dolomitized limestone~ Some oolitic horizons are completely dolomitized (Szabo and Kheradpir, 1978). Oolitic limestone also is known at the base of the upper carbonates, where it is overlain by micritic limestone and dolomite with a few stringers of anhydrite and anhydritic dolomite. The Dalan Formation was deposited on a restricted carbonate shelf of low to moderate energy with occasional evaporites. It grades upward into a fossiliferous carbonate

192

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Fig. 6.23. Sedimentary description and gamma ray-sonic log characteristics of the Permian (Faraghan and Dalan formations) in southwestern Iran (modified from Szabo and Kheradpir, 1978, reproduced by kind permission of Journal Petroleum Geology) bank, which accumulated under medium- to high-energy marine conditions, and ended in an open-marine carbonate formed in a low- to medium-energy environment. The upper boundary of the Dalan Formation shows evidence of a minor unconformity with emersion and erosion. Micropaleontological data indicate that the Dalan Formation is Late Permian in age (Kazanian-Kungurian and possibly early Dzulfian; Szabo and Kheradpir, 1978). Northern and Central Iran

Dorud Formation (Early Permian). Assereto (1963) described the 180 m (590 ft) sequence, which crops out in northwestern Iran as Early Permian, and subdivided it into four units (Fig. 6.24). The Dorud disconformably overlies the Geirud Formation and is overlain by the Ruteh Limestone. It is dominated by carbonate rocks in the eastern

The End of the Paleozoic and the Early Mesozoic of the Middle East part of the central Alborz Mountains, but it becomes clastic-dominated to the west. It significantly increases in thickness from south to north, ranging from 63 m (206.6 ft) in Arruh to 490 m (1,607 ft) in the Chalus Valley (Okhravi and Lahijani, 1994). Okhravi and Lahijani (1994) studied the Dorud Formation and divided it into two distinct types. The lower part, characterized by sandstone, oncolitic limestone, dense limestone and siltstone, represents a marine, subtidal to intertidal environment and includes different suites of microfacies: a mud-supported calcarenite with a calcilutite matrix; a grain-supported biocalcarenite with a calcilutite matrix; a grain-supported biocalcarenite; a grain-supported, oncolitic calcirudite; dolomitized, arenaceous calcarenite; and a grain-supported, pelletoidal calcarenite. The upper part comprises rhythmically alternating sandstone and siltstone. The sandstone is medium- to well-sorted, medium and finegrained, or quartzarenite to chert arenite, matrix-free rocks

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consisting of poorly to well-sorted and rounded grains with a silica overgrowth. This part represents a marine to fluvio-deltaic environment. Ruteh Formation (Early-mid-Permian). This widely distributed, predominantly carbonate succession, about 232 m (761 ft) thick in northern Iran also was described by Assereto (1963). He subdivided it into three units (Fig. 6.24) based on changes in the carbonate lithologies consisting of a basal unit of black, thin-bedded limestone with thin, black marl partings; a middle unit of wellbedded, biogenic, massive limestone; and an upper unit of light-gray, massive limestone locally containing chert, alternating with black, well-bedded limestone. Nesen Formation (Latest Permian). The latest Permian sequence in northern Iran, according to Glaus (cited in Wensink, 1991), takes its name from the village of Nesen, where two lithofacies are found. The lower unit, 149 m (489 ft) thick, consists of dark, schistose, calcareous sandstone followed by gray, schistose, marly limestone that sometimes is micritic. These beds are followed by an upper unit, about 144 m (472 ft) thick, of black, finegrained, fine- to medium-bedded, micritic limestone with dark shale, marl and chert bands or lenses. Jamal Formation (Late Permian). In central Iran, the latest Permian beds are placed in the Jamal Formation. They represent the deposits that formed in a shallow, transgressing sea, with a thickness that may reach 490 m (more than 1,607 ft). The basal, relatively thin (10 m, or 33 ft), fossiliferous limestone, the main, middle part of the formation, consists of partly dolomitic limestone (350 m or 1,148 ft) capped by an upper unit dominated by 130 m (426 ft)of black dolomite.

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THE UPPER PART OF THE ABSAROKA CYCLE (TRIASSIC) As much as 915 m (3,000 ft) of late Absaroka Cycle sedimentary rocks of Triassic age are present throughout Arabia and the Arabian Gulf region, except in southwestern Arabia, Yemen and southern and central Oman. In the Zagros Basin, the maximum deposits are about 1,220 m (4,000 ft) thick. In northern Iraq, northwestern Iran, northern Syria and southeastern Turkey, the Triassic totals more than 1,525 m (5,000 ft) (Fig. 6.25). Figures. 6.26 and 6.27 are lithostratigraphic correlation charts of the Triassic in the Middle East for representative formations described in this chapter, with general lithologies and major unconformities indicated. Table 6.1 lists the Triassic formations in the Middle East, general lithologies and environments of deposition. The classic three-fold division of the Triassic is recognized in Saudi Arabia in the central and eastern regions, where clastic lower and upper sequences bracket a mainly carbonate mid-Triassic. In the Arabian Gulf, however, this division is not obvious. As in Oman and the U.A.E., the Early and Middle Triassic were times of mainly carbonate 193

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dominantly continental beds at outcrop, passing eastward to more marginal-marine conditions during the Early Triassic, giving way upward to shallow-marine conditions with marine sandstone and limestone and passing to continental clastics at the close of the Triassic. From west to east, there also is an environmental change with a progressively greater marine influence. Three lithological divisions of the Triassic sequence in Saudi Arabia cropping out in the low Jilh al Ishar escarpment in central Arabia were initially proposed by Bramkamp (1945, cited in Powers et al., 1966) and later assigned formational names by ARAMCO geologists (Powers et al., 1966; Fig. 6.26); 9 Upper Es Sirr Sandstone (now Minjur Sandstone Formation);

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assic offshore province. Sudair Formation (Early-Middle Triassic, Scythian-?Anisian). The type locality for the Sudair shale is at Khashm Sudair (19012 ' N, 4506 ' E), where the lower part of the formation is well-exposed. Bramkamp (1945, cited in Powers et al., 1966) originally designated the lower member of the Triassic sequence as the Es Sirr Formation. The term is now abandoned, and the unit was renamed the Sudair and raised to formation rank by Gierhart and Bramkamp (1951, in Powers et al., 1966). At the same

197

Sedimentary Basins and Petroleum Geology of the Middle East time, they established the A1 Arid escarpment as the type locality). Formal publication of the type section did not appear until the following year in Steineke and Bramkamp (1952) with more detail (Fig, 6.28) provided by Sharief (1986). In outcrop, the Sudair Formation (Fig. 6.28) is composed of about 116 m (382 ft) of brick-red and green shale with subordinate siltstone, sandstone, gypsum bands and several carbonate lenses. North of the type locality, the outcrop along the A1 Arid escarpment retains its lithological identity, where fine clastic elements, evaporites and rare dolomites become more significant. To the east in subsurface, similar lithofacies are identified, although they are darker in color, and evaporites and carbonates are more common than in the outcrop. By the time the coastal area in eastern Saudi Arabia is reached, most of the red beds have been replaced by shallow-marine sediments, although some of the red beds persist up to the coastal region. This extensive red-bed unit, with its evaporitic and dolomite interbeds, has been interpreted as deposits laid down on a flood plain to a lagoonal and tidal-flat environment, which reached across Saudi Arabia at a time when the sediment supply from sources to the west and south were low. The age of the unit is based upon its stratigraphic position and by correlation with well-dated, subsurface equivalents (Powers, 1968). It is regarded as Late Permian (Tatarian) to Early Triassic CBuntsandstein") in age. The upper contact of the Sudair Formation with the Jilh Formation is transitional, marked by the passage from the brick-red shale to the green shale and fine-grained, friable sandstone of the Middle Triassic Jilh Formation (Sharief, 1984, 1986). Further to the south (south of 20o30 ' N), the Middle Triassic thins, and Middle to Upper Jurassic sediments progressively overlap onto the Lower Triassic Sudair Shale (Sharief, 1984). Surface and subsurface data show that the Sudair Shale conformably overlies the Khuff Limestone, and in turn is conformably overlain by the Middle Triassic Jilh Formation, marking a coarsening upward transition from red-gray, silty shale to ferruginous siltstone and sandstone. Jilh Formation (Middle Triassic). The name of the formation was first proposed by Steineke (1937, in Powers et al., 1966) from that given to a low escarpment, the Jilh al Ishar, which extends from 24o03'48 " N, 45o46 ' E to 24 ~11'6" N, 45~ E. In the type section, the Jilh Formation consists of 326 m (about 1,069 ft) of fine- to medium-grained, cross-bedded marine sandstone with prominent limestone and purple shale interbeds capped by a sandy, oolitic limestone (Powers, 1968). The formation, however, shows remarkable lateral facies variation, ranging from continental sands at A1 Haddar (22 ~ N) through marine sandstone at the type locality to limestone with gypsum further north at Safra al Asyah. In the description of the Jilh Formation between A1 Melhah (25o17 ' N) and A1 Haddar (22 ~ N), Sharief (1984, 1986) identified two main units. The lower

198

unit consists of fine- to very fine-grained, thin- to mediumbedded sandstone (sub-arkosic to sub-graywacke type) that grades up into an alternation of siltstone, shale and lime mudstone, with some gypsum, very fine sand and calcareous sandstone (Fig. 6.28). At several horizons, fossil wood, gastropod fragments, brachiopods and echinoderms, as well as evidence of burrowing, have been found. The upper unit consists of friable, fine-grained, moderately sorted and strongly cross-bedded and rippled sandstone. Scour and fill structures, burrows and mud cracks also are found. There are several horizons of slabby, weathering lime mudstone and oolitic/peloidal packstone and grainstone with poorly preserved fossils. To the east, in subsurface, the lower unit is mostly carbonate, with dolomitic or anhydritic limestone, limestone, some shale interbeds and occasional sands, while the upper unit is a sequence of shale, impure limestone, dolomite and anhydrite. According to Powers (1968), faunal identification permits the age to be established as "Early and Middle Triassic" (Buntsandstein and Muschelkalk). The Jilh Formation, deposited in an ancient non-marine (continental) and nearshore to shoreline complex, displays a great diversity of siliciclastic and carbonate facies (Sharief, 1986). Minjur Formation (Late Triassic). The formation takes its name from Khashm al Minjur (23~ N), where the upper part of the sequence is exposed. The type section extends from the eastern edge of the dip slope at the top of the Jilh Formation (23o34'24 " N, 46~ " E) to the base of the Marrat Formation in the face of Khashm al Khlata (23~ " N, 46o10'36 " E) (Powers et al., 1966). The Minjur Formation in its type area is essentially a littoral to continental sandstone with small conglomerate and shale amounts. It usually consists of a white to brown, medium-grained, poorly sorted, cross-bedded quartz sandstone. Conglomerate lenses occur at several horizons, and there are some thin intercalations of red and purple shale. Ripple marks, mud cracks and sand bars are common sedimentary structures, and fossil dunes have been recognized near the top of the section (Powers et al., 1966). The Minjur Formation between A1 Jilan (20 ~ N) and Dalqan (25 ~ N) is described by Sharief (1984, 1986) as showing cross-bedded sandstone with conglomeratic lenses and subordinate shale, only differing in description from that given in Powers et al. (1966) by the presence of fossil plants. Still further north, north of 25o20 ' N, from East Unayzah to Ash Shamah, a similar type of moderately well-sorted, cross-bedded sands incorporates intercalations of varicolored shale, gypsiferous shale and platy, bedded marl. Fossil plant material, which includes tree trunks, silicified wood and poor limb impressions, is present again (Fig. 6.28). The Minjur Formation represents thick, continental, siliciclastic sediments deposited over a broad area during the Late Triassic. It marks a significant change in sedimentation from intricately mixed, siliciclastic carbonate to a mostly uniform, repeated sequence of siliciclastic, finingupward beds (Sharief, 1986).

The End of the Paleozoic and the Early Mesozoic of the Middle East Over most of the area of outcrop, the Minjur Formation can be seen to rest conformably on the Jilh Formation and to be unconformably overlain by the red shale of the Marrat Formation (Sharief, 1984, 1986). To the east in the subsurface in the Abqaiq and Ghawar oil fields, the Minjur Formation forms a wedge of continental clastic sediments below the overlying pre-Marrat unconformity, which records a prolonged period of emergence affecting much of the Arabian foreland. The formation was dated by Powers (1968) as Late Triassic-Early Jurassic (Keuper-Liassic). However, E1 Asa'ad (1983 a & b) gives the Upper Minjur Sandstone a pre-early Toarcian, and probably Hettangian-Pliensbachian, age.

THE END OF THE ABSAROKA CYCLE IN EASTERN ARABIA In Saudi Arabia, the facies of the Triassic sequence become progressively less arenaceous as distance from the Arabian Shield increases, a change that continues to the east, as can be seen from the subsurface data available in the U.A.E. (Loutfi and Sattar, 1987; Alsharhan, 1993). In onshore Abu Dhabi in the more central part of the basin, all three Triassic formations have been identified, with the lower two formations predominantly consisting of carbonate lithologies overlain by an upper clastic formation (Fig. 6.26). The clastic content of the lower formations is represented by argillaceous sediment, for sand is seldom present, and, when found, is described as fine-grained horizons in the Sudair and Jilh formations. Evidence of the existence of north-south-striking marginal highs bounding the Rub al Khali Basin is provided by lithofacies changes and by the less complete sections found in Qatar on the western side and in Oman to the east and northeast.

Triassic of the United Arab Emirates Abu Dhabi and Dubai Region : (subsurface section) Sudair Formation (Early Triassic) This formation consists of carbonate mudstone and terrigenous mudstone that can be divided into three units (Fig. 6.29). The lower unit consists of limestone interbedded with mudstone and minor dolomites. The main lithology of the middle unit consists of massive dolomites with occasional shale breaks, whereas the upper unit is made up of shale and cryptocrystalline dolomite, which is invariably anhydritic and argillaceous. The thickness of the formation ranges from 178 to 297 m (584-974 ft).Towards Dubai, the Sudair Formation is mostly an alternation of dolomites and shale with thin anhydrite bands. The top part of the formation is marked by the presence of streaks of halite (Alsharhan, 1989). The top of the Sudair is conformable with the overlying Jilh/Gulailah and is picked at the first appearance of variegated shale. The base of the Sudair is conformable with the Khuff and is placed at the contact of an interbed-

ded shale/dolomitic limestone sequence overlying thick, massive, dolomitic limestone at the top of the Khuff. Jilh (or Gulailah) Formation (Middle to ?early Late Triassic). This sequence of 253-528 m (830-1,732 ft) of anhydritic, dolomitic mudstone and fine, terrigenous sediments rests conformably upon beds of the Sudair Formation (Fig. 6.29). The top of the formation in the offshore area appears to be marked by an unconformity, over which lie the massive dolomites of the Early Jurassic. However, in onshore areas a Late Triassic continental facies is preserved (Minjur Formation). The gamma-ray logs show several intervals within the Jilh/Gulailah Formation where there are broad variations in argillaceous content over thicknesses of a few hundred feet. In the middle part of the formation, a series of well-defined, fining-upward cycles, each from 31 to 62 m (102-204 ft) thick, have been identified. Each cycle begins with gray or red, terrigenous mudstone, occasionally with some fine sand or lime mudstone, in which nodular anhydrite is common, passing to anhydritic, dolomitic, mudstone beds that commonly form the top part of the cycle. In the offshore, the lower part of the Jilh is predominantly dolomitic with some anhydrite beds (equivalent to the Khail Anhydrite Series of Qatar). The middle part of the succession equally consists of dolomite, but contains several well-defined anhydrite horizons, two of which can be correlated across most of the offshore. The upper part of the formation, once again largely dolomite, contains some thin shale and white anhydrite bands (Fig. 6.29). In Dubai, the Gulailah Formation (=Jilh) largely consists of tan dolomites with minor, dark-gray, bituminous shale, calcareous shale and thin salt at the top (Alsharhan, 1989). The age of the formation is late Middle to early Late Triassic (Ladinian to Carnian). In the offshore region, the upper contact of the Gulailah is marked by an unconformity and is picked at the base of a massive dolomite forming the base of the Hamlah Formation. In contrast, in the onshore area, the contact is conformable with the overlying Minjur Sandstone. The base of the Gulailah also is conformable and picked at the contact between dolomites of the Gulailah and the first appearance of variegated, non-calcareous shale of the underlying Sudair. Minjur Formation (Late Triassic). In onshore Abu Dhabi, it was deposited as a sequence of continental clastics characterized by a highly distinctive sequence of interbedded, argillaceous quartz sandstone and red or varicolored mudstone (Fig. 6.30). The formation has a thickness of about 188 m (617 ft). There are some thin coals near the base and some carbonates at the top. The formation indicates an abrupt transition from the predominantly carbonate sedimentation that characterized the lower two formations. From the gamma-ray logs, three coarsening-upward, clastic cycles can be recognized within this formation, of which the lowest is defined best. The lower cycle consists of interbedded, thick mudstone, siltstone and sandstone that grade up into a thick sandstone unit. Thin coals have been recognized in the lower 199

Sedimentary Basins and Petroleum Geology of the Middle East

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The End of the Paleozoic and the Early Mesozoic of the Middle East

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Fig. 6.30. Lithology and log characteristics of the Late Triassic Minjur Formation in the U.A.E., (example from onshore Abu Dhabi). part of this basal cycle. The middle cycle, although welldefined, is relatively thin and consists of sandstone and, in the lower part, bands of carbonaceous shale. The upper cycle is much less well-defined, and is made up largely of mudstone with only some thin sandstone bands. However, an argillaceous and dolomitic limestone horizon sometimes is present at the top of this upper cycle. Where developed, it marks an unconformity over the entire region. The base is conformable with the Jilh Formation. Northern Emirates Region: outcrop section

The Early Triassic is absent in the mountainous areas of the U.A.E., but two younger Triassic formations m the Milaha and Ghalilah formations - - ranging in age from the Middle to Late Triassic, are found (Fig. 6.31). The mid-Triassic Milaha Formation is made up largely of carbonates, whereas the sediments of the overlying Ghalilah Formation mark the culmination of a basinwide clastic influx that accompanied the Late Triassic regression. Milaha Formation. In the type area, in the Wadi Milaha of the northwestern Oman Mountains (Fig. 6.31), the formation of that name is about 180 m (590 ft) of argillaceous, partly dolomitized lime mudstone (Fig. 6.32). Hudson (1960) distinguished three members: 50 m (164 ft) of thin-bedded, dolomitized limestone alternating with silty marl, siltstone and argillaceous dolomites, followed by 75 m (246 ft) of peloidal, bioclastic limestone and light-brown or buff dolomites. The sequence is completed by 55 m (180 ft) of dark, skeletal wackestone or grainstone with thick-shelled lamellibranchs, megalodonts, bryozoa and algae. The beds were deposited in a sheltered, lagoonal, inner-shelf setting with periodic

influxes of argillaceous sediments. There is a gradational upward passage into the overlying clastic succession of the Ghalilah Formation (Late Triassic-Early Jurassic). The base of the Ghalilah Formation is a 2 m (6.6 ft) band of ferruginous quartz sand, above which follows limestone, quartz sandstone, shale and dolomites. Ghalailah Formation. The type locality of the Late Triassic-Early Jurassic Ghalilah Formation is in Wadi Bih in the northern U.A.E. (Figs. 6.31 and 6.33), where the beds have been described in some detail by Searle et al. (1983) and Alsharhan (1989). A three-fold division of the total thickness of 250 m (810 ft) follows. The lower 105 m (344 ft) of reddish quartz sandstone and marl, is followed by 80 m (262 ft) of flaggy grainstone and interbedded marl and capped by 65 m (213 ft) of ferruginous quartz sandstone alternating with buff and gray marl and calcareous shale is recognized. It has a fauna of lamellibranchs, gastropods, brachiopods and ostracods. In Wadi Ausaq in the northern U.A.E. (Fig. 6.31), the Ghalilah Formation is reduced to 5 m (16 ft) of buff, algal lime mudstone and, only 1 km to the north, by 20 m (66 ft) of limestone overlying a 1 m basal quartz sandstone. In these limestone developments, evidence of frequent emersion is provided by leached, bird's-eye textures, mud cracks and Neptunian dikes. Triassic of Oman Central and Southern Oman (Subsurface Section)

In the subsurface of interior central and southern Oman on the opposite flank of the Rub al Khali Basin, once again, only the lower two formations have been rec-

201

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Fig. 6.31. Simplified geological map of the northern parts of the U.A.E. and Oman (from Alsharhan, 1989; and Searle et al., 1983). ognized (Fig. 6.26). Sudair Formation (Scythian). It consists of about 270 m (885 fl) of anhydritic, finely crystalline dolomite with red and green shale developed near the top and base

202

of the formation (Fig. 6.34). The formation yields molluscan shell debris and some palynomorphs from beds deposited in a low-energy, marginal-marine-tidal-fiat setting (Hughes-Clarke, 1988). It conformably overlies the Khuff

The End of the Paleozoic and the Early Mesozoic of the Middle East

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Fig. 6.33. Lithostratigraphy of the Norian to Liassic (Ghalilah Formation) in the northern Oman Mountains (modified from Glennie et al., 1974). carbonates and is, in turn, conformably overlain by the continuous dolomite sequence of the Jilh Formation.

Jilh Formation (Anisian). The formation is composed of about 112 m (367 ft) of finely crystalline dolomites and shows relict, ooidal-peletoidal textures. It contains a few meter-thick beds of greenish-gray, dolomitic shale (Fig. 6.34). The formation was deposited in a marginal-marine to tidal-fiat environment. The disconformity at the top of the formation is overlain everywhere by Jurassic sediments, while the lower boundary is conformable with the beds of the Sudair Formation (Hughes-Clarke, 1988).

Central Oman Mountains (Allochthonous Units) The allochthonous units of the central Oman Mountains comprise a complex sequence of thrust slices or nappes. The allochthon was divided by Lippard et al. (1986) into five units. From base to top, they are the Sumeini Group, the Hawasina Assemblage, the Haybi Complex, the Semail (Ophiolite) Nappe and the Batinah Complex. In each of these allochthonous units, several different formations and units that cover variable, but often considerable, intervals of time can be recognized. Because they form tectonically separate units up to the present time, little attempt has been made to con'elate the different

203

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 6.34. Lithology and log characteristics of the Early and Middle Triassic succession (Sudair and Jilh formations) in Oman (modified from Hughes-Clarke, 1988, and reproduced by kind permission from the Journal of Petroleum Geology). units stratigraphically or paleogeographically, and each is treated separately here. Mahil Formation (Middle Triassic). The sucrosic Triassic dolomite found in the major wadis in the mountains of northern Oman in the Akhdar, Nahkl and Saih Hatat areas are the lowest recorded Triassic rocks. Where the Early Triassic succession is absent, the carbonates are referred to the Mahil Formation (Anisian-Norian) and have been described in detail by Glennie et al. (1973, 1974; Fig. 6.35). They vary in thickness from as little as 50 m (164 ft) in the northeastern part of Jebel Akhdar to 1,200 m (3,936 ft) in eastern Saih Hatat and 1,500 m (4,920 ft) in Wadi Mijlas. These sucrosic dolomites also contain chert bands and horizons of porcellanous dolomite commonly showing poorly preserved, stromatolitic structures. The succession was deposited in a very shallow, lagoonal setting influenced by continental conditions based on the evidence of ferruginous beds indicating periods of subaerial exposure. The Mahil Formation is unconformably overlain by beds of the Sahtan Group (Norian to early Tithonian)

204

and conformably overlies dolomites of the Saiq Formation (Late Permian-Early Triassic).

Sumeini Group (Late Permian-Mid-Cretaceous) In the Oman Mountains, the Sumeini Group (Late Permian to Cenomanian) consists mainly of poorly fossiliferous, fine-grained limestone, shallow-water dolomites and limestone with local reef facies and intraformational conglomerates. These represent deposits on a Mesozoic outer shelf and continental slope that lie to the northeast of the Arabian Continental Platform (Glennie et al., 1974). Three formations make up the Sumeini Group: the Maqam (Late Permian-Triassic), the Jebel Wasa (Late Triassic) (Fig. 6.28), and the Mayhah formations, ranging in age from Late Triassic to Cenomanian. Description of the first two formations follow.

Maqam Formation (Late Permian to Early Triassic). This formation in the central Oman Mountains was described from outcrops in the wadi of that name in the

The End of the Paleozoic and the Early Mesozoic of the Middle East

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Fig. 6.36. Composite lithostratigraphy of the Triassic (Maqam Formation) in the central Oman Mountains (modified from Watts and Garrison, 1986).

I Deep (?) manne, adjacent bioherm

Jabal Sumeini by Glennie et al. (1974). The succession, made up of nearly 1,000 m (3,280 ft) of shallow-water, dolomitized limestone with breccia and conglomerates,

passes upward into fine-grained, deeper-water sediments; calcareous shale; fine, rhombic dolomite; and chert with breccias and turbidite horizons. A more detailed descrip205

Sedimentary Basins and Petroleum Geology of the Middle East tion was published by Watts and Garrison (1986) and Watts (1988), with a subdivision into six members as shown below (see also Fig. 6.36):

Member F:

175 m (574 ft) of terrigenous shale, some lime mudstone and minor quartz sandstone of Late Triassic age representing slope or proximal basin deposition of sediments moving across a mostly emergent shelf; Member E: 101 m (331 ft) of thin-bedded intercalations of pelagic, bivalve limestone and radiolarian chert overlain by peloidal, pelagic, bivalve calcarenite, calcilutite and lenticular, intraformational calcirudites. The latter are overlain by coarse, skeletal calcarenite that is graded and highly stylolitic. They mark a return to slope carbonate sedimentation. The member was deposited during the Ladinian; Member D: 84 m (276 ft) of green shale and red and tan siltstone with minor quartz sandstone marking a period of clastic influx possibly related to platform emergence deposited in the Early to Middle Triassic; Member C: 456 m (1,496 ft) of platy limestone and abundant marl. In the lower part of the sequence, there are oolitic calciturbidites and intraformational conglomerates. At the top is a thin dolomite interval. The sediments mark a shelf to basin transition from peri-platform carbonates and shale to carbonate, submarine-fan deposits of Early Triassic age; Member B: 376 m (1,233 f t ) o f predominantly thin to massive dolomites with numerous indistinct breccia and conglomerate intervals. Near the base, silicified colonial and single corals (Wentzellites and Lonsdaleiastraea), brachiopods and bryozoa have been found. Argillaceous material is not common, but the presence of breccia and conglomerate suggest slope deposits. The coral species of the Middle Permian indicate that the lower part of the B member is of Permian age; and Member A: 79 m (259 ft) of thin, medium-grained lime mudstone to wackestone and marlstone with brachiopod, crinoid, bryozoan and coral coquinas. The coral debris suggests the vicinity of reefs, while the marl and wackestone suggest deeper-water conditions. Productid brachiopods indicate an Early Permian age for this member. The thick accumulations of carbonate debris derived from both shallow-marine and deeper-water, marine environments suggest a relatively abrupt shelf break and steep slope adjacent to the platform margin. This peri-platform debris apparently formed a base of escarpment apron, which then passed laterally into deep-marine radiolarites. Jebel Wasa Formation (Norian-Rhaetian). At the

206

western end of Jebel Sumeini of the Oman Mountain Ranges is a Late Triassic succession named by Glennie et al. (1974) from the type locality on Jebel Wasa. The formation was first described as consisting of massive recrystallized limestone, originally skeletal grainstone with fossil debris, massive boundstone with corals, calcisponges, encrusting algae and foraminifera, but it subsequently was reinterpreted by Watts and Garrison (1986) as a clast-supported calcirudite with cobble-sized coral fragments and coralline limestone interclasts. The skeletal calcirudites commonly have a matrix of skeletal packstone. The rich fauna includes stromatoporoids, scleractinian corals, hydrozoans, algae, bryozoa, foraminifera and gastropods. A Norian to Rhaetian age was assigned from these forms. At the top of the formation, there is possibly an unconformable contact with the overlying Mayhah Formation, which forms the basal member of the succeeding cycle. The Jebel Wasa Formation is interpreted as having been deposited upon a forereef talus slope. Thus, there is evidence for a rather complex paleogeographic pattern existing during the Triassic, with non-negligible tectonic movement in the Early and Late Triassic.

Hawasina Assemblage (Middle Triassic to MidCretaceous) The Hawasina was defined by Glennie et al. (1974) as a complex of quartz sand and carbonate turbidites. Silicifled limestone, radiolarian chert and shallow-marine limestone are associated with deep-water sediments or have a substrate of sheared basalt pillow lavas. It has an age range from Late Permian to Cenomanian. It crops out in the southern and western Oman Mountains and in a number of inliers in the central part. The term was first used by Lees (1928) as the Hawasina Series, and Glennie et al. (1974) named it the Hawasina Allochthonous Unit. Lippard et al. (1986) used the term Hawasina Assemblage following the definition of Williams (1975) for the term assemblage. The Hawasina Assemblage consists of the following units: the Hamrat Duru Group, the Wahrah, A1 Ayn, Halfa, Haliw, A1-Aridh and Ibra formations. Detailed biostratigraphic studies were carried out by Glennie et al. (1974).

Hamrat Duru Group (Early Triassic-Cenomanian). Consisting of about 1,000 m (3,280 ft) of turbiditic quartz sandstone, siltstone, shale and redeposited limestone with some chert, it was divided into five formations: Zulla, Guweyza Sandstone, Guweyza Limestone, Sidr and Nayid. Only the Zulla Formation (Triassic) is described in this chapter. Zulla Formation (Triassic). Glennie et al. (1974) named the formation from Wadi Zulla in the central Oman Mountains, where it is exposed in the Hawasina window. Cooper (1987) re-examined the formation and recognized four units (Fig. 6.37): Unit 4: (Halobia Limestone of Bernoulli et al., 1990): 35 m (115 ft) of lime mudstone with subordinate grainstone containing abundant thin-shelled,

The End of the Paleozoic and the Early Mesozoic of the Middle East

z:

A

LEGEND:

E ~

C ) u.,

'

~

Lime mudstones and subordinate IV : z ,_~ -_. _-. -_.- grainstones 200: " -q--' ;" !

i

!

~

Silicified limestone

~. i.. i.: Quartz-bearing l'-i,'l , [,.~.~ limestones

~

Partly s i l i c i f i e d ~ limestone

lJ

! :i

150-

~

ca

O')

...-,

.---.

~"

E F--.

i

:-

iRi-i'

-

"--" ' "

chert

AGE

GROUP

N

~,, - -

-':~

r-'r--z--~

I

5o-i

~....n 0 - ~" - . r..~ r..)

i

~,-,-,-.- ~. i,

!

i !

!

!

l

l

Sid'r

f

....

Shales with subordinate fine-grained turbiditic limestones

r ,,._. cO

<

l

E _"r"

Guweyza

limestone

Guweyza sandstone

1~

[ ~-, -, :-,-~

0

FORMATION

Nayid

iL.Z-a,-,l-z ~

_

Limestone with chert nodules

Radiolarian li:L!;I S.n,,o.

SHicified radiolarian wackestone turbidites, radiolarian chert, quartz silts Shales, fine-grained quartz arenite and silts

., 100-

ii

l-q-L-r] Limestone

LOGY

ro I -~-

i!

,J

Shale

DESCRIPTION

,~:._- _7~-4

TRIAS SIC

Zuila

........

Fig. 6.37. Lithostratigraphic interpretation of the Triassic Zulla Formation in the Oman Mountains (modified from Cooper, 1987). bivalve and echinoid debris; Unit 3: (radiolarian chert of Bernoulli et al., 1990): 30 m (98 ft) of silicified radiolarian wackestone turbidites, radiolarian chert and rare quartz silts; Unit 2: (sandstone and shale of Bernoulli et al., 1990): 47 m (154 ft) of gray-green shale, and thin-bedded green, fine-grained quartz arenites and silts; and Unit 1" (turbiditic calcarenites and shale of Bernoulli et al., 1990): 100 m (328 ft) of shale with thin, subordinate, fine-grained, turbiditic limestone. According to Glennie et al. (1974), the lower part of the Zulla Formation is in tectonic contact with highly sheared shale of the Upper Cretaceous Muti Formation. In turn, these overlie sheared, conglomeratic limestone thought to represent the parautochthonous Mayhah Formation. The upper limit of the formation is defined by the sharply conformable contact of limestone of the Zulla with sandstone and shale of the Guweyza Formation. The sediments of the Zulla Formation seem to have been deposited as deep-water, pelagic shale and calcareous muds with silts from turbidity currents. Sedimentation was interrupted by a phase of rifting and basin subsidence. Uplift of the carbonate platform in the hinterland may have been driven by the thermal response to widespread alkaline volcanism both in the Haybi Complex and within the Hamrat Duru Group itself. The depositional model of the Zulla Formation in the Oman Mountains is shown in Fig. 6.38. Wahrah

Formation

(Late

Triassic-Cenomanian).

The formation, occurring in the central and southern

Oman Mountains, consists of about 200 rn (656 ft) of limestone turbidites and chert divided by Glennie et al. (1974) into five informal members (Fig. 6.39). These are listed (from top to bottom) below. Upper Limestone Member. In this member, about 40 m (131 ft) of oolitic grainstone with interbedded cherty, peloidal and radiolarian lime mudstone. Chert lenses, well-developed ripples and sole marks are common. Upper Chert Member Up to 50 m (164 ft) of centimeter-bedded radiolarian chert make up this member. Calcareous Mudstone Member This has a thickness of about 30 m (98 ft) of decimeter-centimeter thick beds of gray, radiolarian mudstone. Lower Limestone Member. This member is up to 100 m (328 ft) of mostly graded, meter-thick beds of oolitic grainstone and lenses of silicification. Sedimentary structures such as flute, groove casts and ripples are observed. Lower Chert Member. It consists of about 50 m (164 ft) of radiolarian chert. The basal contact is always tectonic, while the upper limit is either tectonic or erosional. The sediments of the Wahrah Formation were deposited in a turbiditic, deepmarine environment. The rocks generally are finer-grained and more siliceous than the Hamrat Duru sediments of equivalent age and more probably deposited further from the shelf edge as described by Glennie et al. (1974), Graham (1980) and Lippard et al. (1986). AI Ayn Formation (Early Permian to Middle Triassic). The formation occurs in Wadi A1 Ayn, north of Jebel Kawr, where it is composed of about 150 m (492 ft) of tur-

207

Sedimentary Basins and Petroleum Geology of the Middle East

Unit !

Unit !i

Source of basement clasts _, !nc~176

Sea Level

Outer shelf acting

/ \\~'~

/'~', ~ ~ /, ~\ ~

/ I

Erosion of the ~ ~ / . . . . . . . . . -'-.... ,)1 platform resulted r ./.~..'~. /I in the influxof ./.~ J / ~ \ ~ ~ / I terripenous ~":,'~C~. /':,~\\)II~, \

channeledby oollUc

"~:~

discontinuous

~

tuurbidttes(slopesediments)

I

~

X

IX X x

X

"X

X

~

'*" ** 9~ ~

X

X

X X ~

1

\

~.X

..,'

-.'.

"

*9 *9*

X ~

l.

Unit !il

Unit IV R e - e s t a b l i s h m e n t of m i n o r carbonate production

Platform

..'# ...,.~

emergence

..~

, /,

: ~

\

~

x

/,/]

Carbonate ~ platform : / . o.

~~..gSlllcifledrnarls/#

,- 1~ .r .

X

.~

.......

~/~k,~,~___.

t

~176

/ --

:-" ~,~~

/

_

x

xXx x x ~ x

Fig. 6.38. Model of the sediment deposition patterns of the Triassic Zulla Formation in the central Oman Mountains (after Cooper, 1990, and reproduced by kind permission of the Geological Society, London).

Z 0

~

~

~ Z-- LITHOLOGY

C3

LU

otl

DESCRIPTION

FOSSILS

~ I-,-rRed radiolarian chert

Z

o

,~

"-

z

Nauticolilna, Valvulinidae, Calpionella Sp., Tintinopsella sp., Nannoconus steinmanni. Gray-brown pelletal grainstone turbidites, N. bermudezi. lithoclastic flute casts and ripples are Protopenroplis striatus, well cleveloped Pfenderina salnitana. P. trochoidea. Kun~ubia sp., Pseudocvclammina cf lituus, 7:rocholina 9alastiniesis. Dic~.'oconus caveuxi

eq

=

Red-brown radiolarlan chert

vvv ~ v LU

o~ ,

,

Light gray partly

silicified lime mudstone

,

o

Light brown, oolitic grainstone turbidites, flute and groove casts, silicified lenses

_J

208

Fig. 6.39. Lithostratigraphy of the Late TriassicCenomanian (Wahrah Formation) in the central Oman Mountains (modified from Glennie et al., 1974).

The End of the Paleozoic and the Early Mesozoic of the Middle East

F ~i a" ~< ~ 7_,,.,

L~

0

DESCRIPTION

__ ~ E LITiiOLOGu

FOSSILS

O I1

|

i 9

~ 9 ~

9

o

9 9

~ ~

o

~

~

9

9 9

~

Dark gray, coarse-grained, quartz sandstone turbidites with sole marks and current-rippled upper surfaces

9

i

-

Ir 9

e=

Radiolarians, filaments, Huarania cL amiji, Varistoma, Duostomina, Mesonodosarioids

<:

9

.

~ ' io iol! ~+' ' !~ ~'11 ~1] [ -I~.e~" i ~:[ /

Pale brown oolitic grainstone

l ~ t

Pale brown to gray-green packstone/ wackestone, micropelletal, burrowed with minor carbonaceous streaks

l

~ l l+ ~')

:

Fig. 6.40. Lithostratigraphy of the Middle Triassic-Early Jurassic (A1 Ayn Formation) in the central Oman Mountains (modified from Glennie et al., 1974).

Pelagic lamellibranch mudstone Shale and green-shaly chert Red chert

"-' " -" "'" "I--it ceousWhite'greensandstonefi tonemedium-grained, mica_ '

~_

Greenish-red, shaly chert t

biditic quartz sandstone followed by 200 m (658 fi) of peloidal wackestone and packstone turbidites and ended by shale and chert with minor quartz sandstone (Fig. 6.40). The sandstone covered by desert varnish gives a black surface coating (Glennie et al., 1974; Lippard et al., 1986). Both the upper and lower contacts of this formation are tectonic.

Halfa Formation (Late Triassic-mid-Cretaceous). The formation is distributed in the area of Wadi Bani Khalid, near the village of Halfa, north of the Wahiba sands. It consists of about 130 m (426 ft) of red and green, centimeter-to-decimeter-bedded chert. It contains abundant radiolaria and Halobia cf. moluscana (Wanner). Sometimes, the chert is separated by siliceous shale often only a centimeter thick. The uppermost part contains decimeter-bedded, peloidal wackestone and packstone (Fig. 6.41) (Glennie et al., 1974). The succession is unusual in being intruded by dykes and sills, along which planes show slight movement. Near the top, and close to the contact with the overlying Semail Nappe, there is a sharp change from gently folded to contorted bedding (Glennie et al., 1974). The Halfa Formation was deposited at a very slow rate in the deeper parts of an ocean basin.

Haliw Formation (Late Triassic-Early Cretaceous). Outcrops are widely spread between Jebel Sumeini in the north and the Ibra area in the southeastern

Oman Mountains. The formation consists of about 60 m (197 ft) of centimeter-bedded, red, radiolarian chert and silicified packstone and grainstone of filaments, small, pelagic lamellibranchs related to Halobia. At the base of the formation, fine-grained, basaltic pillow lavas are common with volcanic lithoclasts (Fig. 6.42) (Glennie et al., 1974). Both the upper and lower boundaries are tectonic. The high degree of silicification and the high content of red shale reveals deposition in a deep-marine environment. The presence of associated basaltic pillow lavas and volcanic lithoclasts indicate that the sediments probably were deposited on oceanic crust, and the limestone and lithoclasts probably were derived from an area of shallowwater deposition.

AI Aridh Formation (Triassic-Middle Jurassic). Occuring in widely scattered areas in the Oman Mountains, it consists of 125 m (410 fi) of coarse conglomerates, lithoclastic grainstone, turbidite and chert. Fragments of basic igneous rocks are common (Fig. 6.43). The upper and lower contacts of the formation are always tectonic where clearly seen. The presence of red radiolarian chert suggests a deep-water origin, while carbonates imply the presence nearby of a shallow-water source area for the turbidites. The occurrence of igneous fragments with limestone boulders suggests that the main source of detrital material was a shallow-water shelf with which volcanic

209

Sedimentary Basins and Petroleum Geology of the Middle East

m

0

~,~ LITHOLOGY =

DESCRIPTION

FOSSILS

7. r~

M g . L ~ _ $ilidfi~ limemudstone,manganesedendritesgraimto~ Halobia cf.

~, ~,~, ~,= ! ,=~..,~~, ,,.,, RedGhert ~ w _ ~ =,.

~~~

W

P , ~

W

Darkgray,silidfied wackestone,micropelletal,filament= Siliceousshale

moluccana, radiolarians Sponge spicules and filaments

, Darkgray,micropelletalpackstone Olivegree~shale

W |

Fig. 6.41. Lithostratigraphy of the Late Triassic-Mid Cretaceous (Halfa Formation) in the central Oman Mountains (modified from Glennie et al., 1974). Z

LITHOLOGY

DESCRIPTION

g

"=

Red radiolarianand silicifiedwackestone and packstone.

X X X X X X X X X

FOSSILS

Ouostomina, Lituosepta, Nautiloculina, Labyrinthia, Valvulinidsand Nautiloculina

Basaltic pillow lavas.

Fig. 6.42. Lithostratigraphy of the Late Triassic-Early Cretaceous (Haliw Formation) in the central Oman Mountains (modified from Glennie et al., 1974). ~=

g LITH0LOGY

.<

DESCRIPTION

FOSSILS

Red chert

~J ,,u r~ t...

~____g~'

~z

~;~

:=:z:=o';'~,'"

==t

,s=S

! r .=m

oil= I..

[.=

.=~ =~=~.

Haurania. Lituosepta, Boueina hochstetteri Green chert with pale gray-brown lithoclastic liassica, limestone beds Uragiella iiassica, Pale gray-brown lithoclastic grainstone containing Zonotrichites, igneous grains and occasional conglomerate with Diplopora, Involutina, large boulders of exotic limestone (Ex) Duostomina Limestone conglomerate with rounded boulders of exotic limestone Pale gray-brown, slightly oolitic pelletal grainstone

Fig. 6.43. Lithostratigraphy of the Triassic-Middle Jurassic (A1Aridh Formation) in the central Oman Mountains (modified from Glennie et al., 1974).

210

The End of the Paleozoic and the Early Mesozoic of the Middle East rocks were associated (Glennie et al., 1974). Ibra Formation (Triassic-Early Jurassic). The formation is well-developed near the town of Ibra in the southeastern Oman Mountains. It consists of about 220 m (722 ft) of boulder beds of recrystallized limestone, lithoclastic grainstone with some igneous clasts, peloidal grainstone, shale, mudstone and some brown sandstone (Fig. 6.44). Both the upper and lower boundaries are tectonic. The formation may overlie the formations of the Hamrat Duru Group, and the Wahrah and A1 Ayn formations.The formation was deposited in an area that was more distal from the source of coarse limestone components and possibly in deeper water (Glennie et., 1974).

Haybi Complex (Triassic to Early Cretaceous) In the Oman Mountains allochthonous rocks, tectonically sandwiched between the thrust sheets of the Hawasina sediments below and the Semail Ophiolite Nappe above, have been named the Haybi Complex by Searle and Malpas (1980). The complex is highly deformed with numerous thrust slices and imbrications (Fig. 6.45). The rocks are, in part at least, equivalent to the Oman M61ange of Glennie et al. (1974) with thrust slices and olistoliths of volcanic rocks (Haybi Volcanics of Searle et al., 1980), the Exotic Limestone of Searle and Graham (1982), the Hawasina Sedimentary M61ange and a metamorphic thrust slice and serpentinite of Lippard et al. (1986). They are briefly described below. Hawasina M61ange. It consists of slightly deformed limestone turbidites with red shale and sheared mudstone interpreted as olistostromes, together with deep-water, radiolarian chert probably of mid-Cretaceous age. The Haybi Volcanic sands, mega-breccias and conglomerates contain large blocks of exotic, shallow-water limestone. Z

!

i

'-'

!

r.d .,==

=

DESCRIPTION

Brown quartz sandstone and grainstone with igneous clasts Gray-brown grainstone, lithoclasticwith ~ ~ ) igneous clasts

'7 = .

~ ~:

The Batinah Complex represents a passive margin on the northeast side of the Semail Ocean Basin. This margin was probably narrow and stratigraphically condensed relative to the Arabian passive margin. The Batinah Complex

' Grainstorm to coarse, lithodastic limestone t~iconglomerate

.u!

~

Batinah Complex (Triassic-Cretaceous)

"~

LITHOLOGY !

Exotic Limestone. It consists of massive blocks of mid-Late Permian to Late Triassic coral-algal boundstone and shallow-water, fusulinid limestone. Some of the limestone is associated with deep-water, pelagic sediments with numerous chert nodules and thin, siliceous radiolaria or pillow basalts. They are interpreted as carbonate buildups on oceanic islands (Glennie et al., 1974) or a continental platform or shelf prior to Triassic rifting. Haybi Volcanics (Triassic). A major component of the Haybi Complex, these may reach 700 m (2,296 ft) in thickness. The lower part is trachytes, ankaramites and alkali basalts with abundant agglomerates and tufts formed subaerially or as a result of shallow-marine eruptions (Searle et al., 1980). The upper, entirely submarine in origin, is dominated by tholeiitic basalts, breccias and tuff hydrothermally altered to spilitic greenstone. Basal Serpentine and Tectonic Mrlange. Rocks derived from the base of the Semail Ophiolite during nappe emplacement, it consists of a thin unit of sheared and ductilely deformed, serpentinized lherzolite, harzburgite and dunite (Searle et al., 1980). The basal serpentine is usually darker in color than the less serpentinized peridotites of the mantle sequence and is continued downward by the disruption of a metamorphic sheet to form a tectonic mrlange. The metamorphic blocks may reach sizes measured in hundreds of meters and form competent rafts within the ductile-deformed serpentine in which phacoidal cleavage is developed (Searle and Malpas, 1980).

FOSSILS

Involutina spp., Duostominidae, Mesonodosariids.

Green calcareous shale

_~ -"

~

Gray, coarse-grained, oolitic grainstone

=:

Gray, bruwn g~ain.~one I Gray, pelletal, radiolarian wackestone

..., t_.

I ~ i

[-.

I

I~, I

1

I Gray, pelletal, lithoclastic grainstone

. . . . .

Silty shale with minor lithoclastic grainstone/

packstone

. . . . . ~

.

~ 9

.

~

.

~

.,,.

Fig. 6.44. Lithostratigraphy of the Triassic-Early Jurassic sequence (lbra Formation) in the central Oman Mountains (modified from Glennie et al., 1974).

211

Sedimentary Basins and Petroleum Geology of the Middle East

ROCK UNITS

o~ ~ ~ LITHOLOGu

DESCRIPTION

l

~ "~ ~

'"

I |,,

~'~ ,~

I ,~ "

t~ ~ ~ - ~ / ---.. ~ --"~ ---- -'-- -~ . 9 ~ ..... ~.~~ --J u ~ ~~__~r ~~~ ~ ~~-----~

,

A

:~t, ~ ~.'Z'

i i

,. ~ _~"~

,~o ~

....

'

B'anded unit fabric due to shearing superimposed on compositionally banded peridotites semail thrust p.lane "" ' Amphibioietes and green'schist facies metamorphic blocks enclosed in basal serpentinite matrix to form tectonic melange

.

.

'"

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Fig. 6.45. Generalized tectonic stratigraphy of the Haybi Complex in the Oman Mountains (modified from Searle and Malpas, 1980,-and reproduced by kind permission of the Royal Society, Edinburgh).

, ,

="=~' ~ a ~~ I-9'.r..1-- ,~ .. u.v." ~ ' Q

Alkali besalts and Ankaramites (200-218 m.y.) . Trachytic laves and tuffs A _'. . . . . . . . . . . . . .

i~/

~...../

Exotic white limestone (Late Permian-

L=~Tna=ic)

C)O= ,,. C::::).~ . q-"

olistoslrome flows

,.".~

Volcanic blocks

I

9

I 0."i , . ~: ". ~ 0.:.o:/" ;J ;"

Hawesina limestone and sandstone blocks in sheared red mudstoneshale

' ~ (~:; ; e : ' ~ : ~., ~,- .L..~

..~.~..~ 4..

=,

"""

Exotic white limestone with marble-breccia. . at base (Late PermianLate Tnassnc) Intrusive sills of alkali peridotite and kaersutite gabbro (92 m.y.) Tholeiitic pillow lavas, pillow breccias, tuffs end agglomerates

, ~(~'-~) q,"=" I,~ 9~ . . t ~ p r ,, ~~ ~'~ ; ,, i ,", J . . J ~ ~9J ~~ = = E ~ 9 ,'~ 9 ,, t , ~ ~ ,, ~,,j

rr

'

Harzburgites anddunites of mantle sequence

(~

X

'

r)

~..o

Q(

~ ~ \ N~NN\ ~ X N x ]

A -

,

.

.

.

.

.

.

Radiolarite - shale- turbidite

C a l c a r e o u s sheets

Upper Batinah Complex .

Siliceous sheets X

.

.

.

.

Calcareous sheets

9

. . . . .

I I

Jurassic

Salahi l Formation I 1 Lower i Limestone I Unit

U Barghah Formation M

0 _J

L

....

I

Semail Ophiolite Upper Cretaceous

Triassic _

i. . . . .

Cretaceous

; L

..

U M L

Limestone blocks

Upper Chalk Unit

I

Sakhin Formation

"-Li-m~stone Units

a b Fig. 6.46. a=informal tectonostratigraphic units of the Triassic-Cretaceous Batinah Complex in Oman; b=lithostratigraphy of the upper Batinah Complex (from Woodcock and Robertson, 1982b, and reproduced by kind permission of the Canadian Journal Earth Sciences).

is composed of large (10-100 km2), tabular or lenticular units and lies structurally between the Semail Ophiolite and its overlying autochthonous, uppermost Cretaceous to

212

Tertiary, sedimentary cover. These sediments are exposed in the east-central Oman Mountains near the Batinah coastal plain. Its detailed description by Woodcock and

The End of the Paleozoic and the Early Mesozoic of the Middle East

Batinah Limestone Blocks (Late Triassic). These are of two types: a) several detached limestone blocks up to 300 m (984 ft) in diameter (lime mudstone, chalcedonic chert, wackestone and packstone) resting depositionally on Upper Triassic mafic pillow lavas; and b) detached limestone masses more than 15 km 2 around Sohar Peak in tectonic contact with serpentinite below. This limestone is a recrystallized lime mudstone, bioclastic packstone and minor coral and algal boundstone.

Robertson (1982 a,b) is summarized here. These authors divided the complex into the Lower Batinah Complex, or Batinah M61ange, and Upper Batinah Complex, or Batinah Sediment Sheets (Fig. 6.46). The Batinah M61ange is composed of blocks of the Semail Ophiolite, exotic limestone, Haybi Volcanics, Hawasina sediments, metamorphic rocks and serpentinite, which locally has a depositional contact with the top of the ophiolite. The Upper Batinah Complex consists of siliceous sheets (Barghah Formation), calcareous sheets (Sakhin and Salahi formations) and Batinah limestone blocks. Barghah Formation (Late Triassic-Cretaceous). This formation consists of two units. The lower is thinly bedded, with siliceous and calcareous sediments, including fine-grained, quartzose siltstone. The upper is a radiolarian chert and calcilutite locally floored by Late Triassic mafic pillow lavas. Sakhin Formation (Late Triassic-Early Jurassic). It is composed of heterogeneous assemblages of quartzose sandstone and siltstone, redeposited limestone, calcilutites, mudstone, clays and radiolarites. The texturally immature, turbiditic sub-litharenites presumably were eroded from locally exposed basement, whereas the more mature sandstone underwent more prolonged reworking, possibly involving both aeolian and alluvial transport. Radiolarian chert were deposited above the carbonate compensation depth in a deep-water environment. Salahi Formation (Early-Middle Jurassic to MidCretaceous). The formation consists of two units. The lower unit is made up of calciturbidites intercalated with partly silicified, finely laminated lime mudstone. Many of the calciturbidites show Bouma sequences and sole marks, particularly flutes and grooves. Bioturbation is extensive. The upper unit comprises intercalations of pink, off-white or green, porcellaneous lime mudstone; white, finely laminated, unsilicified chalk; and brown-weathering calciturbidites. These sediments were deposited as a deep-sea carbonate fan.

DESCRIPTION

.

W/I/1/,

CARN-

,.l_ _ _ I ~ L

LhJI)IN-

.

.

.

Quartzitic sandstones in western part of the country only [

,~,

C.mlail~

.

_#__ hv/,.-ir~...- 7,m - I -.rO'A

A

91#% I

Jilh

1

Z

I

1

A A

I%

1

9

9 I

I'

1

l !

r "^._.7_^~

&NISIAN l . v

In Qatar, both Early and Middle Triassic rocks are present, although they have been named differently; the Suwei Formation is equivalent to the Sudair Formation of the UAE, and the Gulailah Formation is the Jilh equivalent (Fig. 6.47). They have been described by Sugden and Standring (1975) and Alsharhan and Nairn (1994). An abbreviated account is presented here. Suwei/Sudair Formation (Early Triassic). The type location of the Suwei Formation is in well Dukhan-65 in western Qatar, where the complete formation is penetrated, although it was first recognized in well Kharaib-1 in central onshore Qatar. It was named after a village near that well. The formation, about 220 m (722 ft) thick, consists of micaceous shale and siltstone, dolomite, nodular anhydrite and marl deposited in a lagoonal-subtidal setting with an upward increase in the flux of fine-grained, argillaceous clastics. Both the base and top of the formation show conformable relations, with the base passing down into the Khuff and the top grading up to the Gulailah. Gulailah/Jilh Formation (Middle Triassic). The type locality of the formation is from well Kharaib-1, where it consists of 160 m (525 ft) of mainly limestone, anhydrite, calcareous and argillaceous dolomite and authigenic quartz and carbonates. The finely crystalline dolomites locally contain thin beds of silty, gray marl and anhydrite and may grade into tightly cemented, slightly

ONSHORE OFFSHORE LITHOLOGY

AGE

i

Triassic of Qatar

.

.

.

.

.

.

.

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Fig. 6.47. The Triassic formations of Qatar. (after Schlumberger, 1981, Alsharhan and Naim, 1994) 213

Sedimentary Basins and Petroleum Geology of the Middle East argillaceous lime mudstone. The basal part of the formation tends to be the more argillaceous, with more frequent marl intercalations and anhydrite beds laid down on a shallow, restricted, shelf environment. There is an erosional unconformity at the top of the Gulailah Formation, which is overlain everywhere by the Hamlah Formation of Early Jurassic age,with the exception of the extreme western onshore area, where it is overlain by the Minjur Formation. Minjur Formation (Late Triassic). The Minjur Formation is absent in offshore U.A.E. and most parts of Qatar (Fig. 6.26). It occurs only in a few wells in the southern part of the Dukhan Oil Field in western Qatar, where the formation is about 30 m (98 ft) thick and dominated by fine- to medium-grained, quartzitic sandstone and siltstone with shale of continental origin. During the Late Triassic, the Qatar-South Fars Arch was actively uplifted, leading to non-deposition and erosion and restricted distribution of the Minjur Formation to westernmost onshore Qatar (Alsharhan and Nairn, 1994). R. J. Murris (pers. comm., in Alsharhan and Nairn, 1994) believes such a possibility, because the sequence of Rhaetic sandstone, shale and siltstone reappears on the other

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The three formations on the eastern shore of the Arabian Gulf in southwestern Iran described by Szabo and Kheradpir (1978) are summarized below. Although they do not extend in stratigraphic range beyond the lower Middle Triassic, they serve to demonstrate the continuing reduction in the clastic content of the Lower Triassic. The Triassic into Jurassic passage usually is represented by an unconformity in the Zagros Basin. The Triassic stratigraphic relationship is shown in Fig. 6.3, and the map (Fig. 6.48) and section (Fig. 6.49) show the facies distribution. Several cycles of sedimentation have been observed within the Triassic sequence in the Zagros Basin, each beginning with shallow-marine carbonates and terminating with anhydrites of a sabkha environment (Setudehnia,

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THE E N D OF THE A B S A R O K A S E Q U E N C E IN THE E A S T E R N A R A B I A N GULF: SOUTHWESTERN IRAN

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Peloidal-oolitic

grainstones and lime mudstones dolomitic

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1978). As shown in Fig. 6.48, the isopach map of the Triassic in this basin indicates the presence of two thin areas separated by a thick area. The general thinning is associated with greater uplift, as in the Fars Platform, or due to non-deposition of the lowermost Triassic interval and truncation by the pre-Jurassic unconformity in the northwest immediately southwest of the Crush Zone (Setudehnia, 1978)o The lithofacies distribution shows that the Lower

Triassic succession consists mainly of limestone with thin beds of anhydrite and terminates with shale, followed by an accumulation of anhydrites and dolomites during the Middle and Late Triassic. The pattern of sedimentation is of shallow-water deposition of dolomite in the northeastern part of the Zagros Basin and sabkha-type deposits through southwestern Iran and the Arabian Gulf, with a general shallowing toward the Arabian Peninsula. 215

Sedimentary Basins and Petroleum Geology of the Middle East

Kangan Formation (Early Triassic, Scythian). The Kangan Formation (Scythian) takes its name from a village in the Fars Province located near the Arabian Gulf. The formation has a thickness of about 178 m (589 ft) in subsurface to 140 m (459 ft) in outcrop and is made up of three principal lithofacies (Fig. 6.50). It incudes a basal, clean, pelletoidal with oolitic grainstone and mudstone all partly or completely dolomitized and including minor

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evaporites with sand and silt grains (Fig. 6.50). The second lithofacies consists of the basal, shaly facies with shale, argillaceous limestone and dolomite. The pelecypod Claraia is abundant at some horizons. The final lithofacies is made up of evaporites and carbonates, dolomitic limestone, dolomite and anhydrite (Fig. 6.50). From this description, the role of the carbonate sediments is dominant in contrast to the major role of clastics in the outcrop

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Fig. 6.51 Lithology and log characterisitics of the Early-Middle Triassic Dashtak Formation in Iran (modified from Szabo and Kheradpir, 1978, and reproduced by kind permission of Journal of Petroleum Geology) 216

The End of the Paleozoic and the Early Mesozoic of the Middle East sections in Saudi Arabia. The formation rests disconformably on the Permian Dalan Formation, but passes upward into the Aghar Shale Member of the Dashtak Formation. Dashtak Formation (Early-Middle Triassic). The Dashtak Formation takes its name from well Dashtak-1 drilled on an anticline about 75 km west of the city of Shiraz. A thickness of about 814 m (2,670 ft) was encountered in well Kuh-e Siah-1, although only 660 m (2,165 ft) was measured in outcrop at Kuh-e Surmeh. The eight members of the formation are illustrated in Fig. 6.51. Above the basal shale and silty shale and occasional interbedded dolomite and anhydrite stringers of the Aghar Member, there are evaporite units A-C, separated from the topmost evaporite Member D by the Sedifar Dolomite Member. Evaporites B, C and D mainly comprise anhydrite with variable amounts of dolomite and occasional shaly or silty horizons. In the evaporite A Member, the proportion of argillaceous dolomite and limestone interbedded with anhydrite is higher than in the other units. The Sedifer Dolomite Member is a distinctive, featureforming, dark-brown, coarsely crystalline dolomite in which chert is developed near the top. The carbonate members overlying and underlying the B evaporite are argillaceous dolomites, limestone with shale stringers and anhydrites. The upper boundary of the Dashtak Formation is marked by a major pre-Jurassic unconformity, which has removed, to a varying degree, the upper part of the Triassic Dashtak Formation. Conformable contacts are observed between the base of the Aghar Shale Member of the Dashtak Formation and the top of the Kangan Formation (Szabo and Kheradpir, 1978). Khaneh Kat Formation (Early-Middle Triassic). The Khaneh Kat Formation is a term introduced by James and Wynd (1965) for the upper part of the Triassic carbonate succession cropping out near the village of Khaneh Kat, about 110 km east of Shiraz; the term was redefined later by Szabo and Orbell (1975, in Szabo and Kheradpir, 1978). It is the lateral facies equivalent of both the Kangan and Dashtak formations, differing from them in the absence of distinctive evaporite horizons (Fig. 6.52). It consists of about 550 m (1,805 ft) of carbonates and minor shale. The lower part of the formation is mostly argillaceous carbonates and shale, whereas the upper part is shallow-water, stromatolitic limestone and dolomites showing mud cracks, solution breccias and gypsum pseudomorphs, and rare gypsiferous shale. The top of the formation was designated by James and Wynd (1965) at the top of the Sefidar Dolomite. The base was picked where finely laminated limestone overlies the carbonateS of the Permian Dalan Formation. The lateral contact with the Dashtak and Kangan formations is a gradational facies change.

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Fig. 6.52. Lithological interpretation of the Early-Middle Triassic Khaneh Kat Formation in Iran (modified from Szabo and Kheradpir, 1978, and reproduced by kind permission of Journal of Petroleum Geology).

THE END OF THE ABSAROKA SEQUENCE IN THE CENTRAL AND NORTHERN ARABIAN GULF: BAHRAIN AND KUWAIT West of the Qatar Arch, the late Paleozoic to early Mesozoic section is known in Bahrain, Kuwait and southern Iraq. Lithologically, a parallel can be drawn between the sequence seen in Kuwait and southern Iraq and that in Abu Dhabi, and between Bahrain and Qatar. Beds thicken away from the Qatar Arch, while at the same time, the clastic content decreases as the carbonates increase.

Triasic of Bahrain To the west of the Qatar Arch in Bahrain, the Sudair and Jilh formations have been recorded. The Jilh is terminated by an unconformity with the Minjur Formation, removed by erosion, as in most parts of Qatar, and the partial erosion of the Jilh Formation (Figs. 6.26, 6.53). Sudair Formation (Scythian). This formation is dominated by clastic sediments, red or green shale, with subordinate silts, sandstone, gypsum and carbonate lenses. Jilh Formation (Anisian-Ladinian). The formation ranges from 244 m (800 ft) on the crest to 420 m (13,878 ft) on the flanks of the Bahrain Field and is composed mainly of gray and partly argillaceous dolomite with streaks of anhydrite and gray-green shale. Mohamed and Khalaf (1991) subdivided the Jilh Formation into lithostratigraphic units A through E. (Fig. 6.53.) 217

Sedimentary Basins and Petroleum Geology of the Middle East

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Triassic of Kuwait Sudair Formation (Early Triassic). The formation is mainly a shale and microcrystalline, argillaceous, dolomitic limestone sequence (Fig. 6.54) that reaches a maximum thickness of about 500 m (1,640 ft) in northern Kuwait (Khan, 1989). It is Tatarian to Scythian in age, based upon subsurface correlation and the identification of pollen and spores. The formation thins southward, and the thickness in the southern Kuwait oil fields decreases to 400 m (1,312 ft). Jilh Formation (Middle Triassic) . It is predominantly a carbonate sequence from 260 to 330 m (853 to 1,082 ft) thick (Fig. 6.54). Two subdivisions can be made. The lower unit consists of argillaceous dolomite; microporous, white anhydrite; and gray-green, sub-fissile shale with a thick bed of anhydrite. The upper dolomite unit is interbedded with anhydrite and salt and occasional shale partings (Khan, 1989). The occurrence of Myophoria sp. suggests a Ladinian to Anisian age range. Minjur Formation (Late Triassic). This formation consists of three units beginning with pyritic sandstone interbedded with dark-brown shale and limestone stringers (Fig. 6.54). These beds are followed by the middle unit composed of thick, argillaceous dolomites with some thin shale bands. The upper unit consists of slightly fissile 218

Triassic of Iraq

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THE END OF THE ABSAROKA SEQUENCE IN NORTH AND NORTHEASTERN ARABIA:

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shale with some thin bands of dolomite and anhydrite (Khan, 1989). It ranges in thickness from about 310 m (1,017 ft) in southern Kuwait to about 330 m (1,082 ft) in northern Kuwait. A Carnian to Rhaetian age range has been assigned, because the formation yielded Estheria minuta Alberti and Lingula tenuissima var. zenkeri Alberta.

In southern Iraq, the standard Triassic formations found in Kuwait can be traced in subsurface in southeastern Iraq with little change in facies. However, in the northeastern part of the country in the thrust zone and in western Iraq, a quite different series of formations and lithological conditions defines the Triassic. There are three formations within the Lower and Middle Triassic, and four are described in the Upper Triassic succession by Bellen et al. (1959), Owen and Nasr (1958) and Buday (1980), as summarized in the stratigraphic chart (Fig. 6.27). Mirga Mir and Beduh formations (Early Triassic). The two formations are known in outcrop in the Northern Thrust Zone of h'aq and in subsurface in the Atshan well in central northern Iraq. The Mirga Mir Formation. This formation consists of 200 m (656 ft) of thin-bedded, gray to yellowish limestone and shale and rare sands. Some of the limestone is peloidal, and low to moderate energy, lagoonal, oolitic limestone and some anhydrites have been recorded in subsurface (Buday, 1980; Bellen et al., 1959). An Early Triassic (early Werfenian or Scythian) age has been assigned to the formation, based upon the fauna reported from these beds by Bellen et al. (1959). The Mirga Mir develops gradationally from the underlying Chia Zairi Formation. The upper boundary also is gradational and conformable with the overlying Beduh (Shale) Formation. Beduh (Shale) Formation (Early Triassic). It crops out in the Northern Thrust Zone and is found in subsurface in the Atshan well in central northern Iraq. Lithologically, the formation consists mainly of 60-70 m (197-230 ft) of red-brown to purple shale and marl with subordinate, thin limestone and sandy streaks laid down in a shallow-marine environment (Buday, 1980; Bellen et al., 1959). The top of the formation conformably contacts the beds of the Geli Khana Formation. Geli Khana Formation (Middle Triassic). The formation crops out in the Northern Thrust Zone and in subsurface has been recorded in the Ibrahim, Alan, Atshan and Mileh Tharther wells. It is dated as Anisian-Ladinian, based upon the fauna contained in the 200-375 m (6561,230 ft) of shale, limestone and dolomite. Two units are recognized" a lower sequence of bluish, grayish and yellowish shale and thin-bedded limestone, followed above by an upper sequence of dark, massive dolomite and thick-

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bedded limestone with subordinate shale and marl (Buday, 1980). The lithologies indicate a change from a lower, nearshore to lagoonal, evaporitic environment to a neritic, basinal setting. The top of the formation is marked by an unconformity, with evidence of weathering and hematization and silicification of the uppermost beds (Bellen et al., 1959). Mulussa Formation (Middle to Late Triassic). The formation crops out on the Rutbah High in western Iraq and is not known in subsurface. It reaches a maximum thickness of 160 m (525 ft). It passes laterally into the Kurra Chine Formation toward northern and northeastern Iraq, and into the continental littoral Minjur Sandstone Formation of Saudi Arabia to the south. The lowest part of the formation consists mainly of limestone, sometimes sandy, oolitic and peloidal, or conglomeratic and fossilif-

erous, and often dolomitized. The upper part is dominated by a higher proportion of marl and marly interbeds of limestone (Buday, 1980). The formation is essentially neritic, with occasional shallow- to deep-marine environments. The lower part is in disconformable contact with the Paleozoic Ga'ara Formation, but the upper contact shows a transition to the Zor Hauran Formation. Zor Hauran Formation (Rhaetic). The formation crops out in western Iraq on the Rutbah High, where it is from 23 to 30 m (75-98 ft) thick. To the north and northeast, it passes laterally into the Baluti Shale. It is replaced toward the south by continental deposits of the upper part of the Minjur Formation of Saudi Arabia. The formation is characterized by gypsiferous marl interbedded with marly limestone and dolomitized limestone. At the upper boundary, a conglomeratic horizon with an indurated, ferrugi-

219

Sedimentary Basins and Petroleum Geology of the Middle East nous crust indicates a period of post-Rhaetic emergence following deposition (Bellen et al., 1959). The deposits are those of a lagoonal environment and were formed during the time of regression with which the evaporitic horizons are associated (Buday, 1980). Kurra Chine Formation (Late Triassic). In western and northern Iraq, the Kurra Chine Formation, which rests on the GelS Khana Formation, has a Carnian-Rhaetic age and is composed of a monotonous series of dark-brown and black limestone alternating with thick, fetid dolomites and thin, papery shale. The formation has a thickness of as much as 850 m (2,788 ft) in outcrop, although the subcrop thickness is reported as 600 rn (1,968 ft) (Buday, 1980; Bellen et al., 1959). It formed in a lagoonal environment with euxinic and neritic influences. The lower contact is marked by an erosional break, while the upper contact with the overlying Baluti is conformable and gradational. Baluti (Shale) Formation (Rhaetic). The top of the Kurra Chine Formation in central and southern Iraq lies within the Norian (Fig. 6.27), grading upward conformably into late Norian-Rhaetic Baluti shale in central and southern Iraq. The shale crops out in the Northern Imbricated and High Folded zones, with a thickness of 35-60 m (115-197 ft) in outcrop and 25-80 m (82-262 ft) in subcrop. Intercalated within the shale are thin (up to 10 cm), dolomitic, silicified and oolitic limestone bands. Buday (1980) interpreted the depositional environment as lagoonal-estuarine to lagoonal-evaporitic. The formation's lower and upper contacts are conformable and gradational.

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Triassic of Jordan

In Jordan, Cox (1924, 1932) gave the original description of the Triassic sequence and provided faunal lists. Until very recently, this was the best data available. He indicated a succession with the beds wedging out southward and coming to lie on progressively older horizons of an early Middle to Late Cambrian age. This basal, erosional contact often is poorly developed, contrasting with the easily identifiable upper contact with the dominantly coarse-grained, pebbly, white Cretaceous sandstone. The Triassic sediments are exposed in northern Jordan along the Dead Sea to WadS Hisban in the Najr az Zarqa Valley and in WadS Na'ur. Bandel and Khoury divided the succession into nine formations (see below). This division generally has been accepted in subsequent mapping and sedimentological studies (Fig. 6.55). Abu Ruweis Formation (Carnian). This youngest Triassic formation is about 200 m (656 ft) thick. It is dominated in outcrop by dolomitic, laminated marl and limestone, clays and laminated anhydrite and anhydrite intraclasts in a marly matrix. The sediments indicate a nearshore, supratidal-sabkha environment. Um Tina Formation (Ladinian). This is about 70 m

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Drift wood

Fig. 6.55. Composite lithological interpretation of the Triassic succession cropping out in Jordan (modified from Bandel and Khoury, 1981). (230 ft) thick. It consists of interbedded, dolomitic limestone and marly, gray clays. The carbonates are characterized by parallel or wavy, stromatolitic structures particularly in the uppermost. Anhydrite usually is distributed in most parts of the sequence. The sediments were laid down in a tidal-fiat environment. Irq AI Amir Formation (late Anisian). The formation is made up of sandstone, marl and limestone capped by the laminated, stromatolitic carbonates. The Irq AI

The End of the Paleozoic and the Early Mesozoic of the Middle East Amir Formation was subdivided into three members, which are listed below. Shita Member. This member is 25 m (82 ft) of gray shale and marl with 2 m of dense limestone at the top. The marl and clays are bioturbated and rich in marine fossils. The limestone is intraclastic and burrowed with an algal and marine fauna. Abu Yan Member This is a 32 m (105 ft) thick unit consisting of four carbonate bands. The lower (8 m or 26 ft) consists of very fossiliferous, bioturbated, nodular limestone and marl, with layers rich in sand and glauconite. This is followed by 9 m (30 ft) of coarse-grained limestone with coquina and oolite horizons. The third 10 m (33 ft) thick unit, consists of bioturbated, silty, shelly sandstone with thin intercalations of fossiliferous limestone. The top is formed by 5 m (16.5 ft) of massive, locally dolomitized limestone. Bah Hath Member. The member is a 26 m (85 ft)unit of fine sandstone, silt and clay, including two massive, bioturbated, nodular limestone bands 1.5 and 2.8 rn (5 and 9 ft) thick, respectively. The sandy and silty beds may be channelled, laminated, cross-bedded or strongly bioturbated. Oyster shells, drift wood and plant fossils are preserved. Mukheiris Formation (middle Anisian). This formation is a 90 m (295 ft) section split into three members of equal thickness. The lowest member consists of crossbedded, channel-fill sandstone in a sequence of silt and clay, followed by calcareous sandstone with intercalated sand and clay. A marine depositional environment is indicated by strong bioturbation, the presence of glauconite, and a fauna that includes reptilian bones, bivalves and cephalopods. The middle member of green and purple, silty shale and clays contains fossils of Lingula in the lowest few meters. The upper member comprises cross-bedded or bioturbated sandstone, claystone and siltstone. There are layers of quartz conglomerate, and fossilized drift wood and plant fragments are found. Hisban Formation (early middle Anisian). The Hisban Formation is a35 m (115 ft) limestone with marly intercalations and calcareous burrows lithified in situ prior to consolidation of the marly matrix. The marl contains glauconite sand and a fauna of oysters and brachiopods.

Air Musa Formation (late Scythian-early Anisian). This formation is a 70-80 m (230-262 ft) sequence, with a massive sandstone at the base capped by the Hisban Limestone above. In the subsurface (well Suweilih-1), the formation is composed of an alternation of sandy and shaly limestone, shale and shaly sandstone, with glauconite present at several levels. It has been split into three members, as follows: Siyale Member This member is 30 m (98 ft) of clay and gray, green or purple marl with three fossiliferous, bioturbated, calcareous beds at the base, the upper two of which yield much glauconite. Sand-filled channels are found in the upper part of the member. Jamala Member. The Jamala Member is 18 m (59 ft)

of intercalated siltstone, claystone and sandstone. Near the base of the member is a limestone containing glauconite and an intraformational conglomerate with silt, shale and cross-bedded sandstone pebbles. Muhtariqa Member It is 45 m (148 ft) of medium- to coarse-grained, white, flaser-bedded, intertidal or shallowwater sandstone in the lower part and larger-scale crossbedding in the upper horizons, with the individual crossbeds separated from one another by silty partings. The unidirectional transport indicated in the upper beds and the presence of layers of quartz pebbles or of clay balls and drift wood are consistent with the effects of fluvial transport in these upper beds. Dardun Formation (early Scythian). This formation is 60 m (197 ft) thick, with its base formed by carbonates and its top marked by the first bioturbated, silty layers at the base of the Ain Musa Formation. There is a four-fold division of the formation. The lowest unit consists of 11 m (36 ft) of thinly bedded, dolomitic limestone intercalated with commonly bioturbated, laminated shale and marl. Above lies a 15 m (49 ft) cross-bedded, white sandstone unit, with an upper part consisting of a dolomitic layer with marly intraclasts. An upper, 23 m (75 ft) carbonate unit of laminated, dolomitic limestone is interbedded with shale and mud-cracked laminites. Bioturbation is present. The topmost part of the unit consists of finely laminated marl with layers of bioturbated limestone containing clay pebbles. The final, 12 rn (39 ft) sandy unit is made up largely of bioturbated sandstone and intraformational conglomerate with limestone and shale pebbles. The carbonate beds often are thin and show rippled surfaces with bivalves commonly distributed on the bedding planes. Ma'in Formation (middle Scythian). Two members totalling 35-40 m (115-131 ft) were deposited within the tidal zone or in very shallow water. Himara Member. The member is 15 m (49 ft) thick -r NORTHWEST JORDAN RHAETIAN -'NORIAN :

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Fig. 6.56. Lithostratigraphic correlation of Permo-Triassic strata in Jordan and adjacent countries (compiled from Andrews, 1992, Jordan; Bebeshev et al., 1988 ,Syria, and Bellen et al., 1959, Iraq). 221

Sedimentary Basins and Petroleum Geology of the Middle East and made up of alternating thin-bedded sandstone, siltstone and clay. The bedding surfaces commonly are rippled and mud cracked. Burrows are common, and bivalve shells are abundant. Nimra Member This member reaches a thickness of 20-25 m (66-82 ft) It consists of a lower horizon of flaserbedded sandstone with some silt and clay partings and an upper level of fine, white, cross-bedded sandstone in which bioturbation can be observed.

Subsurface Formations The Triassic sediments in subsurface include an unconformity-bounded sequence of carbonates, clastics, shale and evaporites. It is found mostly in wells drilled in the Northern Highland area of northern Jordan and the Risha and Hamza areas of northeast Jordan. Andrews (1992) integrated all the available subsurface data in northwest Jordan into a new, lithostratigraphic framework of five formations combined into what he termed the Ramtha Group (Fig. 6.56).

Ramtha Group (early Scythian-Carnian) In the Azraq Basin, sediments of the Ramtha Group have been penetrated in seven wells, including some in the Hamza Oil Field. In this region, the succession cannot be differentiated into formations, but two units can be recognized. The lower unit consists of siliceous, cemented, fineto coarse-grained sandstone with thin streaks of silty shale, followed by an upper unit of fine-grained, pyritic and silty dolomite; and silty, pyritic and glauconitic shale and sandstone, which may be fine- to medium-grained, pyritic and glauconitic. The total thickness ranges from 265 m (869 ft) in well Hamza-13 to 443 m (1,453 ft) in Fuluk-1. In this area, the Ramtha Group unconformably overlies Lower Paleozoic strata of the Umm Tarifa Formation. The Kurnub Sandstone beds rest unconformably the Ramtha Group. The beds were deposited in a shallow-shelf (subtidal) to intertidal environment. In northeastern Jordan, Risha area, the Ramtha Group is thinner, but also undifferentiated, with a thickness ranging from 121 m (397 ft) in well Risha-6 to 197 m (646 ft) in Risha-8. The lower part of the succession is composed of fine- to medium-grained sandstone interbedded with thin claystone and occasional dolomites, followed by finely crystalline, saccharoidal, pyritic and glauconitic dolomite and thin beds of shale or claystone. The Ramtha beds unconformably overlie the Silurian Alna Formation (claystone and silty shale and fine-grained sandstone) and are unconformably overlain by the claystone and friable sandstone of the Kurnub Group. The Ramtha Group in the Risha area was deposited in a shallow-marine littoral to a possible inner, sublittoral environment. Andrews (1992) was able to subdivide the Ramtha Group in northwest Jordan into five formations, introducing some new formational names, in ascending order: Suwayma, Hisban, Mukheiris, Salit and Abu Ruweis. The

222

following summary description of the formations is based on his data.

Suwayma Formation (early Scythian-early Anisian). The formation is regarded as the lateral equivalent to the combined Ma' in, Dardun and Ain Musa formations seen in outcrop and described by Bandel and Khoury (1981). The Suwayma has been penetrated in 12 wells in northern Jordan, where it ranges in thickness from 25 m (82 ft) in well Risha-19 to 309 m (1,137 ft) in Er Ramtha1A. The formation is characterized by two main lithofacies units. The lower unit is a limestone-shale facies composed of sandy, glauconitic, bioclastic and oolitic limestone and dolomites overlain by fine- to medium-grained sandstone interbedded with shale and silty clays. The upper unit is an arenaceous facies, composed of light-grey, argillaceous limestone and shale beds overlain and underlain by colorless, white and light-grey, fine- to medium-grained, glauconitic and partly argillaceous sandstone and interbedded, thin, green-grey shale, brown siltstone and grey-brown limestone. The basal Suwayma carbonates rest unconformably on the clastics of the Permian Buwayda Formation. The upper boundary is gradational, and the limit is placed at the appearance of the first massive limestone of the Hisban Formation. The lithology of the formation indicates deposition under high-energy, inner-shelf conditions. However, the presence of woody kerogen in claystone at the top of the formation suggests some subaerial exposure and possibly a continental influence. Hisban Formation (Mid to Late Anisian). The formation is widely distributed across northern Jordan and ranges in thickness from 32 m (105 ft) in well Risha-14 to 155 m (508 ft) in Qitar el Abd-1. In northeastern and northern Jordan, the formation is composed of interbedded limestone and shale; whereas in northwestern Jordan, the formation consists of massive, fossiliferous limestone that is partly oolitic and includes subordinate beds of fossiliferous, argillaceous limestone. Towards the top of the formation, there is a small amount of vuggy, saccharoidal, fossiliferous dolomite and anhydritic dolomite. The base of the Hisban Formation is in sharp contact with clay and shale of the Suwayma Formation. The top is placed at the limit where the argillaceous limestone of the Mukheiris Formation conformably overlies the carbonates of the Hisban Formation. The formation probably was deposited in a low-energy, shallow-marine environment interspersed with periodic intervals of agitated, high-energy conditions. Mukheiris Formation (late Anisian-Ladinian ?). This formation is widely distributed in northern Jordan and is recognized in all the Northern Highlands and Risha wells. It ranges in thickness from 98 m (321 ft) in well Ajlun-1 to 31 m (102 ft) in Risha-14. The formation consists of silty shale and claystone with beds of fossiliferous, argillaceous limestone at the base and in the middle. In well Northern Highlands-l, there are several dolerite sills totalling 35 m (129 ft), and in well Suweileh-1 north of Amman, the formation consists of shale overlain by varicolored shale and marl with very little sandstone. The

The End of the Paleozoic and the Early Mesozoic of the Middle East lower contact is defined where the thick limestone beds of the Hisban Formation are conformably overlain by the argillaceous limestone and shale of the Mukheiris Formation. The upper contact is defined at the boundary between the argillaceous beds of the Mukheiris Formation and the conformably overlying limestone of the Salit Formation. The formation was deposited in a non-marine to marine, paralic setting over most of northern Jordan, whereas in the Risha area of northeastern Jordan, restricted, anoxic conditions prevailed in a quiet-water environment, as indicated by the high content of thick, bituminous, amorphous, organic matter. Salit Formation (late Anisian-early Carnian ?). The formation is found in the Northern Highlands, al Harra and west Risha areas of northern Jordan, where it varies in thickness from 118 m (387 ft) in well Risha-14 to 421 m (1,381 ft) in Northern Highlands-2. The Salit Formation is partly equivalent to the Irq A1 Amir and Um Tina formations in outcrop. The Salit Formation is composed of limestone and dolomites with interbedded shale. The limestone varies from microcrystalline to medium crystalline and commonly is argillaceous, often grading to calcitic dolomites. The limestone may be micropyritic, peloidal, ooidal, bioclastic, carbonaceous and glauconitic in places and frequently grades into wackestone and occasionally grainstone. The dolomites are fine- to coarse-grained with a saccharoidal texture. The shale is fissile, non-calcareous to calcareous or dolomitic and micropyritic, and has organicrich intervals. Near the top, the shale and thin limestone interbeds range from 20 to 30 m (66-98 ft) thick and form good marker horizons. The base of the formation is picked where a thick sequence of limestone with interbedded shale (Salit Formation) comformably overlies the redbrown shale of the Mukheiris Formation. The top is taken below the first thick anhydrites of the Abu Ruweis Formation. The Salit Formation was laid down in a low-energy, carbonate-shelf setting, with periodic intervals of highenergy conditions indicated by oolitic, bioclastic and peloidal limestone, or of restricted circulation indicated by the presence of organic-rich laminites. Abu Ruweis Formation (Carnian). The formation is well-developed in northern Jordan and varies in thickness, especially in the Risha area, where the greatest and least thicknesses were recorded. In well Risha-1, it attains a thickness of 505 m (1,656 fi), but decreases to as little as 152 m (499 fi) in Risha-14. In Risha-2, a thickness of 492 m (1,614 ft) was recorded, but this included 110 m (361 ft) of intrusive dolerite. The formation consists of fine- to medium-grained, crystalline, saccharoidal dolomite, anhydrite, argillaceous limestone and shale. White, colorless halite interbedded with beds of shale, anhydrite and partly anhydritic dolomite 22 to 57 m (72-187 It) thick have been recorded in wells drilled in the A1 Harra and Risha areas. The Abu Ruweis beds have a conformable and gradational contact with the Salit Formation, marking the change from the Salit carbonate-shale to the thick anhydrite of the Abu Ruweis Formation. The top is selected where the anhy-

drites of Abu Ruweis are unconformably overlain by the Jurassic limestone of the Azab Group. The formation was deposited in a marginal sabkha environment, and a salt pan developed in northeast Jordan, based on the presence of the thick halite found in many wells.

Triassic of Syria The successions in the Iraq-Jordan frontier area indicate the effects of movements of the Ha'il-Rutbah Arch. In Syria, however, the Triassic is more complete, and despite the changed formational names, the lithofacies sequence shows features similar to those found in the Arabiab Gulf. There is no general scheme correlating the Triassic throughout Syria. Although there are individual correlations for small areas, they do not incorporate the facies variations, making it difficult to correlate succession on a broader scale. The thickness and facies of the Triassic beds indicate that there were uplifts bordering the older central Syrian and Mesopotamian depressions throughout the Triassic. The information is derived from a number of deep wells and presented by Bebeshev et al. (1988, 1989) and Lababidi and Hamdan (1985), as summarized in Fig. 6.27. Amanus Shale Formation (Early Triassic). The Early Triassic Amanus Formation in the Dolaa well northeast of Palmyra was first described by Syrian geologists who recognized a Lower Amanus suite of sandstone (Late Permian) overlain by an Upper Amanus suite of shale (Early Triassic). The Amanus Shale in central Syria (about 150 m, or 492 ft) is composed of intercalated sandstone and argillite, grading upward into alternating limestone and carbonized argillites with rare carbonized plant fossils and ending in dolomitized limestone. In northeastern Syria (in wells Aoda-106 and 107), this sequence changes through the incoming of greater clastic influx, gray quartz sandstone and siltstone with an increase in the plant fossils found in the argillites. The lower unit in central Syria, as seen in wells Azar-1 and Habari-1, consists of interbedded red and green quartz sandstone and lenticular siltstone. To the northeast, in Markada-101, facies changes similar to those marking the lower unit occur as red and green sandstone and argillites with rare coalified plant fossils appear. However, to the southeast on the evidence from well Kari1, the presence of red argillaceous limestone and of algal limestone suggests a continuation of the marine conditions found in central Syria. The age of the formation is Early Triassic (Scythian) based on the presence of foraminifera and ostracods. Kurra Chine Formation (Middle Triassic). The Middle Triassic is represented by the Kurra Chine Formation, which is made up of about 500 m (1,640 ft) of a lower dolomite unit and an upper anhydrite unit. The dolomite unit ranges from fine- to coarse-grained, massively to thinly bedded, and argillaceous to anhydritic. The anhydrites are massive, very homogeneous and contain thin bands of dolomitic argillites and anhydritic dolomites with minor salt. In central and northeastern Syria, the dolomites

223

Sedimentary Basins and Petroleum Geology of the Middle East are generally uniform, but may be argillaceous or relatively pure and grade up into an alternation of pure and anhydritic dolomite. They range from 250 to 350 m (8201,148 It) in wells Aoda- 103 and 107, Rumelan-6, Jibisi208 and Tishrin-5. West of the Euphrates River, this formation ranges in thickness from 100 to 550 m (328-1,804 ft) in wells Racca-1, Habari-1 and Azar-1, and consists of two units. The lower microcrystalline dolomites are interbedded with calcareous dolomite grading up into more uniform dolomite. In some wells, as in Soukne, rock salt has been encountered. The upper anhydrite unit has interbedded anhydritic dolomites in the north, whereas it contains shaly and clayey dolomitic anhydrites in central Syria. The Middle Triassic age assigned to this formation is based on palynology. The formation is separated from the Amanus Formation by a disconformity, but it is conformable with the overlying Butmah Formation. Butmah Formation (Late Triassic). In central Syria, the Late Triassic Butmah Formation found in wells Sfae-1, Amara-1 and Zidan-1 consists of uniform dolomite. However, in the Souedie-Roumeila and Jebissa fields limestone and anhydrite also are found. The thickness varies from 100 m (328 ft) to some tens of meters. The amount of anhydrite increases in the upper part of the formation, and at Jebissa may form bands 5-10 m (16-32 ft) thick intercalated in the dolomite and limestone. In this region, a 25 m (82 ft) intercalation of shale occurs in the middle of the formation. Near Soukne-1, the succession is less clastic and contains more sulfates. The sequence is composed of up to 30% anhydrite interbedded with dolomite. The proportion of sulfate reaches as much as 50% in well Didi-1. Over the Rutbah High, the carbonates give way to a succession made up of about 20 m (66 ft) of argillites, siltstone and sandstone. The presence of foraminifera, spores and ostracods permits a Carnian age to be assigned to the Butmah Formation. The contacts with the underlying Kurra Chine and the overlying Adaiyah are conformable. Adaiyah Formation (Late Triassic). It occurs in east, north and central Syria, where the thickness varies from a few tens of meters up to 100 m (328 ft) of anhydrite with intercalations of dolomite and shale laid down in lagoonal-evaporitic conditions. In wells Soukne-1, Hol-1 and Nora-l, pure anhydrite is found enclosing beds of fine argillite. In wells Racca-1, Sfae-1 and Zidan-1, the anhydrite encloses dolomitic anhydrite, and in Amara-1 and Sirom-1, the succession consists of argillite with fine interbedded dolomite and anhydrite. Contacts with the underlying Butmah and overlying Mus are conformable. Mus Formation (Late Triassic). The formation occurs in eastern and northeastern Syria. It ranges in thickness from 40 to 100 m (131-328 ft) and is a sequence of uniform, light-whitish dolomites with occasional anhydritic dolomite. In the southwest in well Kariaten-1, it becomes a succession of calcareous dolomites and dolomitic and algal limestone, and the carbonate is present as limestone in the Golan Heights. The contacts with the underlying Adaiyah and overlying Alan are conformable.

224

Alan Formation (Late Triassic). In northeastern and eastern Syria, this formation ranges from 40 to 50 m (131164 ft) in thickness of medium- to fine-grained anhydrite grading up into an alternation of argillaceous anhydrites, dolomitic anhydrites and argillites deposited in a lagoonal environment. In the Karatchok-Souedie area, anhydrite prevails, whereas the Jebissa area is distinguished by interbedded dolomite. The formation is conformably overlain by the Sargelu Formation and rests conformably on the beds of the Mus Formation. Toward paleohighs, there is facies replacement of the anhydrites successively by anhydrite-bearing dolomite and dolomitic argillites (Aoda-107, Shamu- 1, Sirom- 1, Gbebi- 101 and Markada- 101). Triassic of Southeast Turkey Cigli Group In southeastern Turkey, the Triassic crops out in the Zap anticline and in the Mardin and Hazro areas. On the flanks of the Zap Anticline, Early and Middle Triassic rocks occur, represented by up to 1,000 m (3,280 ft) of marginal-marine to non-marine carbonates and shale of the Cigli Group (Fig. 6.27). Cudi Formation. A 2,000-3,000 m (6,560-9,840 ft) sequence of Late Triassic to Early Cretaceous rocks (Cudi Formation) overlies the beds of the Cigli Group. They grade upward from peritidal limestone and dolomites into a pelagic accumulation of thinly bedded, parallel, laminated and often slumped, argillaceous limestone, shale and massive, crystalline dolomites. The sequence is completed by shale and argillaceous limestone. Aril Formation. In the Mardin-Diyarbakir area, however, the Triassic sequence begins with a 5-20 m (16-66 ft) basal sandstone followed by 650 m (2,132 ft) of marine carbonates and evaporites with subordinate, pyritic shale to which the name Aril Formation has been applied (Ala and Moss, 1979). The formation has been detected in the subsurface from well Aril-1 near Gaziantep. The lower part of this sequence belongs to the Triassic-Jurassic, where the upper part belongs to the Cretaceous. Triassic strata are missing from the crest of the Diyarbakir-Mardin swell, but to the north and northeast of this area, the sequence consists of about 170-200 m (558-656 ft) of red shale and sandy limestone (Beduh Formation) that rest unconformably upon older sediments (Ala and Moss, 1979; Rigo and Cortesini, 1964). Beduh Formation. In the Hazro area, the Beduh Formation is about 90 m (295 ft) thick, while it is up to 2,000 m (6,560 t ) in the Hakkari region. Arikan (1975) subdivided the Beduh Formation into three members, from older to younger: a Lower Marly Limestone Member consisting of about 130 m (426 ft) of alternating, thin-bedded lime mudstone, silty or sometimes dolomitic with intercalations of brachiopod-bearing limestone, followed by a varicolored Shale Member consisting of about 50 m (164 ft) of claystone and shale with subordinate lime mudstone

The End of the Paleozoic and the Early Mesozoic of the Middle East and sandstone. The third member is the Upper Marly Limestone Member, which consists of about 150 m (426 ft) of alternating laminated, argillaceous lime mudstone, with calcareous, marly shale and conglomeratic sandstone streaks in the middle. P A L E O G E O G R A P H Y AND G E O L O G I C H I S T O R Y OF T H E A B S A R O K A C Y C L E

The Lower Part of the Absaroka Cycle (latest Carboniferous-Permian) An interval of extraordinary importance in the history of the Middle East separates the sedimentary sequences of the Kaskaskia and Absaroka cycles. During the Late Car-

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boniferous, a sea-level fall, resulting from the buildup of the Permo-Carboniferous ice sheets, amplified a period of uplift and erosion (Hercynian activity). One result in Arabia, was the removal of considerable thicknesses of sediment, as a result of which Late Permian limestone rests upon rocks of diverse ages from the Precambrian, Cambrian, Early Devonian to Carboniferous (Powers, 1968). This unconformity commonly is referred to as the "Hercynian Unconformity." The so-called "Hercynian Uplift" generally is described as an epeirogenic movement, but it is hard to avoid the suggestion that it may not have been accompanied by some crustal (tensional) thinning, potentially even graben formation, as in southern Africa, where Permian fracturing signalled the beginning of the disruption of Gondwana. One consequence of such movement is that the Permian sediments were not laid down on an even

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Sedimentary Basins and Petroleum Geology of the Middle East floor, which does appear to be the case. The central part of the Arabian Shield appears to have undergone the greatest amount of uplift, and grounded Permian glacial deposits are found resting upon the Precambrian there. Tillites, outwash conglomerates and periglacial, fluvial sands deposited in southern Arabia during the Late Carboniferous and Early Permian are described by de la Grandville (1982), McClure (1978) and Alsharhan et al. (1993) (Fig. 6.57). The glacial influences decrease northward, and coastal deposits correspond in age to the glacial beds in Iran and eastern Turkey (Szabo and Kherapir, 1978). The distribution of depositional environments of the Late Carboniferous and Early and Late Permian are shown in Figs. 6.58, 6.59 and 6.60. The result of the erosional stripping of Paleozoic sediments from over the arch also led to isolation of the early Paleozoic sediment of the Republic of Yemen (North Yemen) and southwestern Saudi Arabia from the much more extensive outcrops found to the north. North of the central Arabian Arch in the Widyan Basin, the oldest sediments overlying the Hercynian unconformity, assigned to the Unayzah Formation (A1 Laboun, 1987), initially were thought to form a transition into the Khuff Limestone; however, as a result of hydrocarbon exploration, this is now known to not be the case (Fig. 6.15b). The isopach map of the thickness of the Unayzah Formation shows the changes in basin development caused by the Hercynian movement, with the isopachs now running parallel to the margin of the Summan Platform in contrast to the north-south orientation of the axis of the basin in which the pre-Unayzah clastics accumulated (Figs. 5.5 and 6.1). The western edge of the Widyan Basin now coincides with the Ha'il-Rutbah Arch, with only a thin tongue of sediment penetrating southward between the Summan Platform and the Arabian Shield. In the northern Widyan Basin, the early Mesozoic section and the Khuff Formation are progressively truncated by Early Cretaceous, pre-Wasia erosion (A1 Laboun, 1986), and Late Carboniferous and Permian strata cannot be traced into Jordan because of this. In Iraq, however, fluviolacustrine to presumed deltaic conditions represented by the sediments of the Nijili Formation reflect the extension of the continental, shallow-marine, sedimentary environments of the Unayzah Formation. It has been suggested that these beds owe their existence to the emergence of the Rutbah High (Ibrahim, 1979). The age of the Unayzah sediments in Arabia cannot be closely defined, although it appears that they extend across the Carboniferous-Permian boundary. Late Carboniferous to Early Permian palynomorphs have been identified, and forms diagnostic of Westphalian, Stephanian and Sakmarian-Artinskian occur, but older Carboniferous and younger Permian also are known, possibly reflecting inadequate control over drill cuttings rather than such an extended age range. Sediments found south of the central Arabian Arch (in the western Rub al Khali Basin) in North Yemen and southwestern Saudi Arabia are interpreted as

226

having formed in a marginal-marine environment, marginal to the sea in which the Khuff was deposited. Current opinion is that the Unayzah beds are early Late Permian. In the Haushi-Huqf and Haima-Ghaba areas of eastcentral Oman, the Early Permian is represented by conglomerates of glacial origin, which grade into terrigenous clastics deposited in lagoonal or marginal-marine conditions, which give way upward to limestone (Tschopp, 1967a). Even in an area that must have been close to the meltfront of the ice sheet, it is hard to avoid the implication of the rapid climatic change resulting from the disappearance of the ice, for glacial deposits are followed in rapid order by the development of the warm-water, carbonate-platform sequence of the Khuff Formation. Thus, in southern Arabia during the Permian, a vast epeiric sea developed, with a marginal belt of clastics supplied from the emergent shield. In central Arabia, shale replaced sands as the dominant clastic. The clastics were supplied from the emergent shield to the west (Murris, 1980; Saint-Marc, 1978). However, the principal sediments in this sea, which extended over the entire Arabian Gulf, including the zone now occupied by the Zagros Thrust Belt, were carbonates with some evaporites (Murris, 1980; Alsharhan and Kendall, 1986). A passive margin sequence of platform carbonates accumulated in the subsiding Isfahan Basin, east of the present Zagros Thrust Belt, created a shallow-water carbonate bank that can be traced into Oman. In places, reefoidal limestone formed, and the shelf marginal facies also is recognized in Oman (Sharief, 1983). It is apparent that a considerable part of western Iran was emergent during the Late Carboniferous and Early Permian (Szabo and Kheradpir, 1978), and this area was the source for the turbiditic flysch that, together with basaltic flows and tufts, was laid down over Early Carboniferous and older rocks in southeastern Iran (Cherven, 1986) in the newly opened Neotethys. This phase of siliciclastic deposition was succeeded by carbonates during the subsequent major transgression of the Late Permian. Toward the end of the Early Permian, during the Artinskian, transgression appears to have reached the area of the High Zagros, and the basal Permian deposits of the Faraghan Formation represent marine sands deposited during a progressive, if oscillatory, advancing sea. The source of the sand was reworked, older Paleozoic sediments or deltaic deposits from near the Zagros Thrust (Szabo and Kheradpir, 1978). Later in the Permian, with the continued rise in sea level, carbonate deposition prevailed (Dalan Formation). Four carbonate facies have been recognized, with the first three indicating the progress of transgression from a restricted, low-energy shelf to a medium- to highenergy shelf and to an open-marine, low-energy setting. The final facies, characterized by nearshore carbonates and clastics, mark a return to shallower-water conditions. As shown by Szabo and Kheradpir (1978), most of the clastic material is reworked Paleozoic sediments deposited in a deltaic environment at a site near the location of the

The End of the Paleozoic and the Early Mesozoic of the Middle East

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The End of the Paleozoic and the Early Mesozoic of the Middle East Main Zagros Thrust (Fig. 6.61). Although carbonates were deposited over the top of the Zagros High, the feature seems to have continued to influence sedimentation in the sense that it acted as a barrier restricting the free circulation of sea water in the area to the west. Carbonates built up over the high, and reefs may have developed in places. To the east of the high and north of Oman lay the developing Neotethys, in which deeper-water sedimentation occurred. A general regression at the end of the Permian was marked by the deposition of thick, siliciclastic sediments that continued to be deposited into the Early Triassic, for there are more than 1,100 m (3,608 ft), with only a few limestone beds in the Zagros Basin (Edgell, 1976). In central Arabia, the continental clastics of the Sudair Formation were formed during this time interval. However, it must be noted that carbonates continue to form in some parts of the region, making the lower Sudair facies equivalent to the upper part of the Khuff limestone facies. The changing depositional environments reflect the tectonic activity in the region, and, as previously indicated, the Permian marks the first major marine transgression in the Middle East. Although earlier transgressions have been recorded, they appear to have been of shorter duration and associated generally with clastic sediments. The carbonates of the Late Permian are a precursor of the carbonate sedimentation that dominated the later Mesozoic. In the tectonic sense, the end of the Permian is the time of the precursory events leading to the formation of the Neotethys, which formed along the Zagros line in the wake of the diminishing Paleotethys and eventually closed around the end of the Triassic, coinciding with the end of the Absaroka Cycle.

the stratigraphic succession through the use of the formational names given to the different facies. However, in discussing the paleogeography in an attempt to integrate these changes, a sequence of facies are defined that can be applied to the whole region. Formation names may be introduced where necessary for the purpose of clarity in discussing local variations in the overall paleogeographic history. This history has been discussed by Murris (1980) and Sharief (1983) and Berberian and King (1981), although the latter authors restricted their attention mainly to Iran and the areas immediately to the southwest. The maps illustrating this account generally are similar. During the Early Triassic (Fig. 6.62), the influx of clastics from the paleohighs and the Arabian Shield increased, and the carbonate platform became restricted to a narrow, NW-SE-trending belt in the region of the Arabian Gulf. This influx decreased during the Middle Triassic (Fig. 6.63), and a carbonate evaporitic platform showing the influence of minor, open-marine conditions in the north occupied much of the basin. The Late Triassic was dominated by fluviatile and coastal clastics (Fig. 6.64). No deposition was recorded over the Qatar Arch which extended from Qatar to the Central Arabian Gulf, and coastal Iran. Restricted, arid conditions prevailed in the northern part of th Middle Easte basin. ARID FLOODPLAIN ARID CLASTICPLATFORM ARID MIXEDPLATFORM EVAPORITICPLATFORM EVAPORITIC/CARBONATE PLATFORM SHALLOW CARBONATE SHELF .--.-9 EROSIONAL

The Upper Part of the Absaroka Cycle (Triassic) The Lower Absaroka sequence was followed in the Triassic by the upper part of the sequence, which actually ended in the early Jurassic (Hettangian). Thus, the greater part of this history is the history of the Triassic. Within the Triassic of the Middle East, although not recognizable everywhere, the three classic divisions of an early regressive phase are distinguishable: the Bunter of European terminology, a transgressive phase equivalent to the Muschelkalk and a final regression equivalent to the Keuper as the Absaroka sequence ended. The phases in this paleogeographic history can be recognized through the expansion and contraction of a sequence of facies belts across the Arabian Platform. During the regressive phases, facies dominated by clastics expanded eastward and northward from the Arabian Shield, only to contract during transgression. Although the shield was the principal source of clastic sediments, conditions were such that the sediment supply was restricted, and coarse material generally is absent. In the preceding section, an account has been given of

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Fig. 6.63. Paleogeographic map of the Ladinian-Camian sediments in the Arabian Gulf region (modified from Murris, 1980, and reproduced by kind permission ofAAPG).

Fig. 6.64. Paleogeographic map of the Rhaetian sediments in the Arabian Gulf region (modified from Murris, 1980, and reproduced by kind permission ofAAPG).

Nine principal lithofacies belts are recognized, although the differences between some of the facies are small. Because one facies grades into the next, identification of the small differences and the location of boundaries between belts can pose problems (Fig. 6.65)(see Sharief, 1982): Lithofacies 1: non-marine, fluvial deposits consisting essentially of thick, cross-bedded or sheetlike clean sands, poorly laminated and highly bioturbated sandstone with minor shale and conglomerates were deposited. Lithofacies 2: a restricted-shelf, lagoonal, tidal-flat complex of sandstone, unfossiliferous, varicolored shale with some gypsiferous horizons, siltstone and mudstone. Ripple marks, micro-cross laminations, burrows and rare desiccation cracks occur in the finer-grained lithologies. Fossil wood and plant material occur. Lithofacies 3: contains restricted-shelf, lagoonal, tida-flat and shoreline deposits; and cross-bedded, well-sorted quartz arenites and quartz wacke with some intercalated micritic and peloidal limestone. Lithofacies 4: contains restricted lagoonal and supratidal deposits; varicolored and crystalline, gran-

ular or nodular anhydrite, some unfossiliferous lime mudstone, shale, siltstone and occasional sandstone. Lithofacies 5: contains shallow-shelf carbonates, limestone and dolomite, with some anhydrite, unfossiliferous shale and mudstone. Characteristically, the beds contain a shallow marine fauna. Lithofacies 6: contains shelf-margin sediments, fossiliferous limestone and dolomites intercalated with marl and shale. Lithofacies 7: contains deeper-marine, shelf-basin deposits., Fossiliferous, argillaceous limestone and black shale with some interbedded marl. Lithofacies8: contains terrigenous to shallow-marine deposits, richly fossiliferous sandstone, dark-gray to green shale with thin, sandy to black limestone with a diverse stenohaline fauna. Lithofacies 9: contains a flysch-like sequence in deeper basins, interbedded, varicolored shale and sandstone with layers of conglomerate and abundant volcanic rocks and tuff. The regressive sequence of the Early Triassic is marked by the replacement of the Permian deposits, which

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Sedimentary Basins and Petroleum Geology of the Middle East were dominantly carbonates, by unfossiliferous sandstone, siltstone and mudstone intercalated with carbonates that spread across the Arabian Platform as far east as the northern Arabian Gulf. They continue a trend established in the Late Permian. The facies show, through the occurrence of occasional plant remains, sedimentary structures and the presence of gypsiferous shale, that continental clastic sediments passed into lagoonal and tidal-fiat deposits (lithofacies 1 and 2). To the south and north, these lagoonal, tidalfiat, shoreline deposits present a higher proportion of sandstone (lithofacies 3). Around Qatar and central Oman, where there was shallow water, but in an area more remote from a sediment source, the proportion of lime mudstone and anhydritic limestone in the lithofacies increased (lithofacies 4). The remainder of the platform, including much of Iran, was an area of shallow-marine-shelf carbonate deposition. The more open environment was characterized by carbonates with an open-neritic-marine fauna (lithofacies 5); closer to the continental region, under slightly shallower-water conditions, some marl and shale are intercalated, and some of the limestone is dolomitic (lithofacies 6). The deeper, basinal parts of the carbonate shelf are characterized by thinly bedded, argillaceous limestone and black shale (lithofacies 7 and 8). In northeastern Iran, the occurrence of thick, interbedded shale, sandstone and volcanic debris, a typical Tethyan flysch trough facies (lithofacies 9), mark the rapidly subsiding basin between the closing Iranian segment of the Arabian Plate and the Eurasian Plate. Geographically, these lithofacies translate into a change from broad lagoonal and tidal-flat deposits in central Arabia northward through supratidal and lagoonal conditions into restricted, very shallow, platform deposits where shelf carbonates were formed (Sharief, 1986). Eastward into the United Arab Emirates, the Early Triassic shows a progression from a shallow-marine environment subjected to a variable energy regime gradually passing up to shallow-marine, sabkha conditions. In Oman, the lowenergy, shallow-marine environment shows the influence of tidal-fiat and even coastal-plain conditions, suggesting the approach to a local high (Hughes-Clarke, 1988). In the northern part of the Arabian Platform, the sedimentation pattern identifies the influence of a number of highs: the Mardin, Rutbah and Khleissa. The latter two were separated by a trough, the Euphrates-Anah Trough, during the Triassic. The Mardin and Khleissa highs rose above sea level and were subjected to erosion, with the erosion products abundant in both the Lower and Middle Triassic beds deposited in the large Mesopotamian Basin that fringed the highs to the north and northeast (lithofacies 7). This basin extended from southeastern Turkey into central Iran. West of the Rutbah-Khleissia highs, clastic deposits also are abundant in the Early Triassic, accumulating in the Palmyra-Sinjar Trough, a feature that connected with the Mediterranean Tethys further to the west. In Syria and Lebanon, these Early Triassic sediments appear as shale in

232

the more central part of the trough and as fluviatile to deltaic sands near the trough margins. They are capped by evaporites of Early to Middle Triassic age. The succession of fine-grained clastics with associated carbonate-evaporites formed under restricted-shelf-lagoon and tidal-fiat conditions (lithofacies 2) in a NW-SE-trending belt into eastern Iraq and Saudi Arabia (Buday, 1980). With the onset of the Middle Triassic transgression, the clastic facies belts of non-marine and intermittent nearshore and shoreline deposits and very shallow-marine, high-energy shoal conditions (lithofacies 5) became more restricted to central and southern Saudi Arabia. In northern Arabia, a mixed carbonate-clastic, restricted-shelf-tidalflat-lagoonal-shoreline complex developed. Nowhere does there appear to be any evidence of anything but shallowwater conditions, and thin, platy limestone with poorly preserved lamellibranchs and worm tracks ("Calcaires vermicules") is a very characteristic carbonate type. In the U.A.E., the conditions that developed during the Early Triassic continued into the Middle Triassic, with a sabkha bordering a restricted basin into which there were small incursions of more normal-marine waters. Toward the northern part of the U.A.E., sheltered lagoonal-inner shelf conditions dominated, but the evidence of periodic influxes of argillaceous sediments suggests a nearby sediment source, presumably to the northeast in Oman (Alsharhan, 1993). In the northern part of the Arabian Platform, the Rutbah-Khleissia High was less important as a topographic feature, and shallow-water shelf carbonates formed to the east (Murris, 1980). In general, a belt of carbonates and evaporites characteristic of a shelf-lagoonal-tidal-flat environment occupied the central part of the Arabian Platform, the Palmyra-Sinjar and Euphrates-Anah troughs. These facies grade into carbonates, and shale formed in a shallow-marine to shelf-margin environment in southern Turkey, most of Syria, Jordan, northern Iraq and Iran. In northern and eastern Iran and northeastern Iraq, however, major mixed carbonate buildups of shallow to shelf margin origin are found. The transition to more open-marine conditions is seen in Iraq in the passage from the carbonate ramp sequence in the Lower Triassic, the argillaceous limestone and shale of the Mirga Mir Formation, through the shale and marl of the Beduh Formation, to the variegated shale and thick-bedded limestone of the lower Geli Khana Formation (lower Middle Triassic) into the massive limestone and dolomites of the upper Geli Khana Formation. This sequence ends with development of a regional unconformity above the upper Geli Khana Formation. The transition from the Middle to Late Triassic was marked by sharp changes in the depositional environments, as the lowered sea level that followed the deposition of the limestone and dolomites of the upper Geli Khana Formation in Iraq and their equivalents in Iran led to an increase in the detrital clastic component in a region stretching from central to northeast and eastern Arabia. This Late Triassic unit is characterized by clastic sedi-

The End of the Paleozoic and the Early Mesozoic of the Middle East ments (lithofacies 1 and 2) consisting essentially of alternating sandstone, shale and siltstone in fining-upward sequences. The sandstone is varicolored and commonly forms thick, cross-bedded units of mature, moderately well-sorted quartz arenites and quartz wackes. The interbedded shale also is generally unfossiliferous, but may be highly bioturbated and burrowed. Ripple marking and the presence of fragments of fossil wood and plant remains are not uncommon. A continental, non-marine, fluvial to deltaic to a nearshore-marine depositional environment has been proposed for these beds with the progradation of delta lobes into interdistributary bays. The occasional presence of coal emphasizes the continental aspect of the continental-marginal-marine nature of the deposits. Toward Iran, the clastic content increases, and the sequence is dominated by richly fossiliferous sandstone and dark-gray to greenish shale with layers of thin, sandy, black limestone with a diverse, stenohaline fauna (lithofacies 8) formed under shallow-marine conditions, but an environment that received a discrete clastic input. In Iraq, the Late Triassic limestone of the Mulussa Formation transgresses over the Middle Triassic beds onto the Permian Ga'ara Fo~xnation of the Arabian Platform. However, the overlying lagoonal marl and limestone of the Rhaetic Zor Hauran Formation indicate the onset of an end to the Triassic regression. In northern Iraq, the equivalent Late Triassic formations are the Kurra Chine, a formation consisting mainly of dark limestone, and the Baluti Formation, made up of lagoonal and estuarine sediments in the Overthrust Zone, but passing to lagoonal evaporitic sediments in subsurface. Further to the east in central Iran, the presence of dark-gray, well-bedded, fossiliferous limestone intercalated with marl and shale (lithofacies 6) shows the increasingly marine nature of the shallow shelf. In the extreme northeast of Iran, terrigenous, flysch-like deposits with shale, sandstone and conglomerate as well as tuff and volcanics occur (lithofacies 9), a continuation of the conditions established during the Early and Middle Triassic, as indicated by the occurrence of volcanism in the BassitAmanos areas of Turkey and Cyprus (Ponikarov et al., 1967). These are a reflection of this most tectonically active portion of the Arabian Plate. Tectonic movements were more widely felt during the Late Triassic than at any other time in the Triassic; these movements, which resulted in a complex of horst and graben structures, are responsible for rapid lateral facies variations seen in western Iran and southeastern Turkey. This intensified tectonic activity opened the Mesozoic or Neotethyan seaway (the

Taurus-Zagros Trough of Sharief, 1983), which cut through the Afro-Arabian Block separating central, eastern and northern Iran from the rest of the Arabian Plate. It is reflected also in the intrusion of dikes and volcanic activity and, in places, metamorphism in northeastern Iran. In southeastern Turkey, carbonate deposition in this Neotethyan Seaway continued throughout most of the Late Triassic and up until near the end of Jurassic. More than 1,000 m (3,280 ft) of carbonates and evaporites were formed (Cordrey, 1971). The lithologically similar succession that accumulated in the Palmyra and Sinjar troughs of central and eastern Syria also continued to be deposited until the Late Jurassic (Druckman et al., 1975). The shoreline of the Neotethyan Seaway lies in northern Saudi Arabia. Over the stable Ladinian-Carnian Shelf of Iraq, calcareous rocks formed mostly under conditions of a reduced clastic influx (Buday, 1980). Near the shoreline, intermittent clastics are present as alternating, finingupward sequences of cross-bedded sandstone and shale. These latter beds tend to be highly bioturbated and contain plant fragments and fossils such as gastropods, ostracods and algae (lithofacies 3). At the top of the succession, gypsum, anhydrite, shale, mudstone and dolomite formed in a tidal-flat environment (lithofacies 4), which dominated in northern and eastern Saudi Arabia and in the Arabian Gulf. Marine carbonates that formed on a very shallowmarine shelf cover a wide area in the Middle East, extending from eastern Arabia, over Iran, Iraq, central western Syria and Jordan (lithofacies 5). These include lime mudstone, peloidal grainstone and massive, microcrystalline, dolomitic limestone and dolomites with intercalated marl and some anhydrite. The contained fauna consists of gastropods, ostracods, green and blue algae, echinoderms, corals, brachiopods and ammonites. In western Jordan, southeastern Turkey and Iran, mixed clastic-carbonate facies occur (lithofacies 6), with dark-gray, well-bedded, fossiliferous limestone and dolomitic limestone with intercalations of soft marl and shale deposited on the shelf edge. These pass to very fossiliferous, thin-bedded limestone and black shale with interbedded chert and silicified limestone (lithofacies 7) deposited in the zone transitional to deep-water basins. Lithofacies 9, deposited in deeperwater basinal conditions, consists of the terrigenous, flysch-like sequence that, with interbedded shale, sandstone, conglomerates, volcanics and tuff, occurs in northeastern Iran (Fig. 6.64), continuing a depositional sequence that began in the Early Triassic.

233

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Chapter 7 THE LATE MESOZOIC PART OF THE ZUNI CYCLE IN THE MIDDLE EAST: THE JURASSIC

thickens from an erosional limit along the borders of the Arabian Shield and southern and southeastern Arabia, toward the Arabian Gulf, where thicknesses of the order of 1,220-1,525 m (4,000-5,000 ft) are common (Peterson and Wilson, 1986). These values increase to more than 2,300 m (7,544 ft) in the Fars Province Iran (Zagros Crush Zone) (Setudehnia, 1978). In Jordan, the exposed Jurassic sediments range in thickness from 430 to 450 m (1,410-1,475 ft), the same order of magnitude found in well Ramtha-1 (370 m, or 1,214 ft) (Bandel and Khoury, 1981), whereas about 660 m (2,165 ft) were encountered in Souedie Field

INTRODUCTION During the Jurassic, the Middle East was, for the most part, covered by shallow-shelf seas that showed periodic fluctuations in level. Although the transgressions and regressions were relatively small in terms of absolute sealevel change, they induced major changes in the sedimentological environments. The open Tethyan (or Neotethyan) Sea lay to the north and northeast, as indicated not only by facies distribution, but also by significant changes in the sedimentary thicknesses recorded (Fig. 7.1). The sequence

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Sedimentary Basins and Petroleum Geology of the Middle East in northeastern Syria (Ala and Moss, 1979). A progressive, worldwide, eustatic rise in sea-level began during the Sinemurian, the middle part of the Early Jurassic, as shallow seas spread over the eastern and northeastern parts of the craton, ending a period of regression and emergence that had characterized the latest Triassic and earliest Jurassic. The Mardin Paleohigh in southeastern Turkey remained a positive feature and constituted a barrier separating the shallow open seas of the northern margin of Arabia from the regiori to the east, resulting in the formation of clastics and evaporites in parts of the northern and eastern margins of the Arabian Platform. In northeastern Iraq and western Iran, deep-water sediments accumulated in an intrashelf basin. Later, in the Jurassic, movements led to differential vertical uplift over southeast Turkey, western Jordan and southern Arabia, accompanied by the erosion of the older part of the section from many of the paleohighs. With this uplift and erosion, Late Jurassic sediments were removed from much of central Syria and, to a lesser extent, from the Syrian coastal region and parts of Lebanon. Further to the southeast, Sinemurian transgressive seas (forming the beginning of the Zuni Cycle of Sloss, 1963) advanced from the northeast toward the southwest to lap against the positive areas forming the southeastern, southern and southwestern margins of the Rub al Khali Sub-basin of the Arabian Basin. This transgression coincided with crustal thinning and transgression over other parts of the Afro-Arabian Craton, and in the development of the thick Early Jurassic sequence in the coastal regions of the Somali Embayment, which marks the inception of the breakup of Gondwana in that region. Over the northern Arabian Plate in Jordan, Iraq, Syria and southeastern Turkey, conditions were much the same as further south. By the end of the Early Jurassic, a shallow-marine platform formed, upon which carbonate and evaporitic facies were deposited according to sea-level conditions. This Early Jurassic transgression continued into the Middle Jurassic, again marked by short-lived still stands and/or minor transgressions and regressions. Over the vast carbonate platform covering most of eastern Arabia, these minor events were recorded by Murris (1980) as the alternation of shallow carbonate platform and open-marine (slightly deeper-water) limestone and minor clastics. The sea-level fluctuations marked by relatively small but distinctive facies changes can be traced for large distances across Saudi Arabia and correlated with similar events in Iran. Westward, the carbonate platform or shelf graded into a mixed carbonate-clastic facies that recorded passage to nearer-shore, shallower-water environments in which evaporites periodically formed. By the Bathonian, a major intrashelf basin, the Lurestan Basin, which had begun to form as early as the late Liassic, developed in Iraq, Kuwait and parts of Iran in the northern Arabian Gulf. A major transgressive pulse occurred during the Callovian, the early Late Jurassic, coinciding in timing with the onset of

236

the southerly drift of Madagascar, as part of eastern Gondwana broke away from Africa and the rest of western Gondwana. By late Oxfordian to early Kimmeridgian time, a second intracratonic basin in which euxinic sediments accumulated had formed over the United Arab Emirates (U.A.E.), partly onshore and partly offshore, and extending into Qatar. At this time, southern Iran, including part of the Arabian Gulf, was a positive area. The features were comparatively short-lived, for the basin had disappeared, and the positive area was reduced to less than a quarter of its size by the Tithonian. This was part of a general shallowing process in the Lurestan Basin, which thenbecame an area of evaporite deposition in common with the greater part of the Arabian Platform. Although the sea level generally continued to rise during the Late Jurassic, sedimentation rates appear to have more than kept pace with, and finally exceeded, the rate of flooding, with the consequent development of extensive shoal and sabkha environments where extensive evaporites accumulated. Because of the extraordinarily great economic importance of these rocks in the Arabian Gulf region, their subsurface distribution, thickness and lithofacies changes are well-known, and relatively minor sealevel changes can be documented and traced great distances. Under these conditions and given the greater paleontological control, it is more convenient to follow the numerous and varied changes that occur within the Zuni Cycle, a cycle that did not end until the middle Paleocene, through an appreciation of the second-order cycles of sealevel change than in terms of the primary cycle. This applies equally to the Jurassic and the Cretaceous. As typically is the case in stratigraphy, initially type sections were established in the areas of outcrop, and as these in general lie close to the former basin margins, the sediments described are far from typical. Subsurface information shows that in proceeding further from the margin toward the open sea, the clastic component diminishes in thickness and commonly is replaced by finer-grained clastics, from sand to silt or mud, and these in turn disappear to be replaced by carbonate sediments. As the clastic sediments commonly are unfossiliferous or contain non-diagnostic fossils without an abundance of wells, correlation of the so-called type sections with the subsurface becomes difficult or impossible. To this must be added the difficulty in correlation imposed by the recognition of the numerous small lithofacies changes across the Middle East (Figs. 7.2 and 7.3 and Table 7.1), which is a function of the greater abundance of data. In order to present a coherent account, an initial description will be given of the original type sections in central Arabia; subsequently, lithofacies changes will be traced basinward, and new subsurface type sections will be established.

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The Late Mesozoic Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic Table 7.1. Jurassic indicate outcrop, outcrop, and and bullets bullets indicate indicate subsurface. Table 7.1. Jurassic rock units units in in the the Middle Middle East. East. Asterisks Asterisks indicate subsurface.

Area Saudi Arabia

Unit

Age E. Jurassic

Argillaceous limestone, sandstone, siltstone and shale

Tidal flat, lagcKmal and ncrilic

Dhruma Formation

M. Jurassic

Gypsifcrous clay-shale, wackestone and argillaceous limestone

Tidal flat, lagoonal and neritic

Tuwaiq Mtn. Formation

M. Jurassic

Bioclastic, peloidal wackestone and packstone

Low-energy shelf

Hanita Formation

L. Jurassic

Calcareous shale, peloidal-bioclastic limestone and argillaceous limestone

Shallow to moderate water

Jubailah Formation

L. Jurassic

Gypsiferous shale; dolomitized, peloidal. oolitic limestone

Shallow-water shelf

L, Jurassic

Interbedded wackestone, argillaceous pack stone/grain stone, dolomite and anhydrite

Tidal flat

L. Jurassic

Nodular anhydrite with interbedded dolomite, minor pcloidal-oolitic limestone

Lagoonal supratidal

E. Jurassic

Dolomitic limestone, calcareous dolomite and shale

Tidal flat

Dhruma Formation

M. Jurassic

Dolomitic limestone and calcareous shale

Shallow lo moderately deep marine

Tuwaiq Mtn, Formation

M. Jurassic

Dense, dolomitic, bioclastic limestone and calcareous shale

Low energy deeper water

Hani fa Formation

L. Jurassic

Microporous argillaceous limestone, shale and peloidal limestone

Moderate to low energy

Jubailah Formation

L. Jurassic

Argillaceous lime muds ton e/wackestone with subordinate dolomite and packstone

Shallow-water shelf

Arab Formation

L. Jurassic

Argillaceous and dense limestone, dolomitic limestone and anhydrite

Tidal flat

Hith Formation

L. Jurassic

Massive anhydrite with some dolomite and limestone

Supratidal

Kohl an

E. to M. Jurassic

Conglomerate shale and marl interbedded with sandstone

Deltaic

Am ran Group

M, to L. Jurassic

Interbioclasiic limestone, dolostoneand siliciclastic sediments

Low-energy shelf

a. Shuqra Formation

M. to E. Jurassic

Well-bedded, fossilifcrous limestone at times interbedded with shale and marl

Shallow neritic

b. Madbi Formation

L. Jurassic

Shaley-silty, gypsiferous marl and marly limestone

Open marine

•*

Hith Formation

Yemen

Environment

Marrat Formation

Arab Formation

Bahrain

Lithology

Marrat Formation

**

239

Sedimentary Basins and Petroleum Geology of the Middle East

Table 7.1 continued. continued. Area

United Arab Emirates

Qatar

240

Unit

Age

Lithology

Environment

c, Sabatayn Formation

L. Jurassic

Restricted succession of cvaporites with elastics

Shallow marine

d. Naifa Formation

L, Jurassic

Porcellanous limestone, marl, shaly marl and fossiliferous limestone

Open marine

Marrat Formation

E. Jurassic

Bioclastic, peloidal limestone, dolomite and dolomitic limestone

Tidal flat flood plain

Hamlah Formation

E. to M. Jurassic

Micro-crystalline dolomite; lime mudstone; peloidal, dolomitized packstone/ grain stone

Nearshore marine/quiet water

Izhara Formation

M. Jurassic

Microporous, doJomitized limestone, peloidal limestone and calcareous shale

Quiet-water shelf

Araej Formation

M. Jurassic

Peloidal pack stone/grain stone wackestone and argillaceous lime mudstone

Moderate- to quiet-water marine shelf

Diyab/Dukhan Formation

L. Jurassic

Lime mudstone containing abundant organic matter and minor packstone, grainstone and sucrosic dolomite

Intrashelf, anoxic basin

Fahahil Formation

L. Jurassic

Lime mudstone graded upward to wackestone and packstone containing dolomite and minor nodular anhydrite

Shallow marine

Qatar Formation

L, Jurassic

Dense dolomite, lime mudstone and bioclastic wackestone with anhydrite and dolomite

Shallow to intenidal

Arab Formation

L. Jurassic

Oolitic-pcloidalpackstone/grainstone, wackestone, anhydrite dolomite

Tidal flat

Hith Formation

L. Jurassic

Massive anhydrite with minor dolomite and dolomitic limestone

Very shallowwater supratidal

* Mil sand am Group (U.A.E. outcrop)

Jurassic to E. Cretaceous

Dolomitic lime mudstone and intraclastbioclast grainstone, argillaceous mudstone, oncolitic/peloidal packstone and carbonate sands

Lagoon to subtidal/in tenidal

Hamlah Formation

E. to M. Jurassic

Sandy marl, glauconitic sandstone, shale, limestone, saccharoidal dolomite and nodular to anhydrite

Nearshore to shallow marine

Izhara Formation

M. Jurassic

Dense, argillaceous limestone and dolomite with minor shale and marl

Shallow-water shelf

Araej Formation

M. Jurassic

Lime mudstone/wackestone with interbedded peloidal-bioclastic packstone/ grainstone

Low to high energy, lagoon to shallow open marine

Diyab Formation

L. Jurassic

Argillaceous, silty, slightly dolomitic limestone and dense lime mudstone

Open-marine shelf (outer shelO

The The Late Mesozoic Mesozoic Part of the the Zuni Cycle in the Middle Middle East: East: The Jurassic

continued. Table 7.1 continued. Area

Oman

Age

Unit

Lithology

Environment

Hanifa Formation

L. Jurassic

Bituminous, argillaceous lime mudstone and shale

Shallow open marine

Jubailah Formation

L. Jurassic

Argillaceous lime mudstone/wackestone and peloidaj pack stone/grain stone

Shallow shelf

Darb Formation

L. Jurassic

Argillaceous lime mudstone with thin, pyritic and peloidal limestone and minor dolomite

Open marine (outer shelf)

Arab Formation

L. Jurassic

Pcloidal-bioclasticpacksione/grainstone intercalated with lime mudstone, sucrosic dolomite and anhydrite

Sheltered lagoonal, broad tidal flats

Fahahil Formation

L. Jurassic

Alternating dolomitic lime mudstone and dolomite graded to bioclastic packstone and grainstone and anhydrite

Lagoon

Qatar Formation

L. Jurassic

Dense, dolomitic-anhydritic limestone and peloidal, oolitic limestone

Intertidal

Hith Formation

L. Jurassic

Nodular, chicken wire and massive anhydrite with stringers of dolomite and limestone

Shallow marine to supratidal

Musandam Group

Jurassic, E. Cretaceous

Cyclic nature of massive lime mudstone, graded to thinner bedded, oolitic grainstone and bioclastic limestone and dolomite

Tidal flat

Mafraq Group

E. Jurassic

Continental elastics and ferruginous, oolitic limestone

Shallow marine high energy

Dhruma Formation

M. Jurassic

Argillaceous mudstone/wackestone, dolomitic packstone and marly limestone

Shallow shoalintertidal

Tuwaiq Mtn. Formation

L, Jurassic

Lime mudstone, biociasiic/oolitie packstone and grainstone and dolomite

Subiidal-shoal

Hanifa Formation

L, Jurassic

Argillaceous lime mudstone and wackestone, fossiliferous packstone and grainstone

Low to high energy shallow marine

Jubailah Formation

L, Jurassic

Slightly argillaceous lime mudstone and wackestone with some dolomite

Low energy marine

E. JurassicM, Cretaceous

Lime mudstone/wackestone, martstonc graded upward to bedded chert and thin beds of chert-clast breccia and thin-bedded lime mudstone/wackestone

Passive continental margin slope

M. Jurassic

Grainstone turbidites with quartz grains, lime mudstone and marly shale

Turbidity currents

May hah Formation

Guweyza Sandstone Formation

*

241

Sedimentary Basins and Petroleum Geology of the Middle East

continued. Table 7.1 continued. Area

Age

Unit Guweyza Limestone Formation

Thick-bedded, oolitic grainstone with turbiditic wackestone and lime mudstone

Shelf edge deep water

E. to M. Jurassic

Arkosic sandstone, conglomerate, siltstone, sandy marl and calcareous, dolomitic, ferruginous sandstone

Deltaic

Neyriz Formation

E, Jurassic

Dolomite, brecciated to finely laminated, argillaceous shale; dolomitic limestone; silty shale; siltstone and sandstone

Shallow water

Adaiyah Formation

E. Jurassic

Anhydrite intcrbcddcd with dolomite and dark shale

Shallow water

E. Jurassic

Limestone

Shallow water

Alan Formation

M. Jurassic

Bedded anhydrite with subordinate limestone

Shallow water

Sargelu Formation

M. Jurassic

Shale and argillaceous limestone

Deep water

Najmah Formation

M. to L. Jurassic

Pellety, algal limestone

Shallow water

Gotnia Formation

L. Jurassic

Anhydrite with subordinate dolomite and shale

Shallow-deep water

Hith Formation

L. Jurassic

Anhydrite and gypsum with interbcdded dolomite

Supratidal

Surniah Formation

E. to L. Jurassic

Thick-bedded to massive, fine-grained dolomite followed upward by thin to massive-bedded and fine to coarse, crystalline dolomite and limestone

Shallow water

Marrat Formation

E. Jurassic

Alternation of argillaceous limestone, anhydrite, dolomite and dolomitic limestone

Tidal flat

Dhruma Formation

M. Jurassic

Calcareous shale with occasional limestone interbeds

Inner shelf

Sargelu Formation

M. Jurassic

Argillaceous limestone, calcareous and carbonate shale

Marginal marine

Najmah Formation

L. Jurassic

Argillaceous limestone containing interbedded, bituminous and calcareous shale

Outer-neritic shelf

Hith Formation

L. Jurassic

Massive anhydrite with minor limestone and shale

Sabkhalagoon

Gotnia Formation

L. Jurassic

Anhydrite with halite layers inlerbedded with argillaceous limestone and anhydrite

Supersaline lagoon

Ubaid Formation

E. Jurassic

Argillaceous sandstone with tnterbedded marl, sandy limestone with abundant chert

Shallow littoral lagoonal

Mus Formation

Kuwait

Iraq

242

Environment

L. Jurassic

Kohl an Formation Iran

Lithology

*

*

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic

Table 7.1 continued. continued. Area

Unit

Age

Lithology

Environment

Butmah Formation

E. Jurassic

Limestone with intcrbedded anhydrite, bioclastic and argillaceous limestone with some shale and sand

Lagoon

Balutt Formation

Rhaetic

Shale with thin, intercalated, dolomitic limestone

Lagoon cstuarine

Adaiyah Formation

E. Jurassic

Bedded anhydrite, calcareous shale and marl

Evaporitic lagoon

Mus Formation

E. Jurassic

Doiomitized and recrystallized limestone and calcareous shale

Normal marine

Alan Formation

E. Jurassic

Bedded anhydrite with thin, oolitic limestone

Evaporitic lagoon

Sarki Formation

E. Jurassic

Thinly bedded, cherty and dolomitic limestone, cherty dolomite with thin shale and marl

Evaporitic lagoon

Sekhanian Formation

E. Jurassic

Etolomite and dolomitic limestone with some chen

Shallow lagoonal e vapor ite

Muhaiwir Formation

M. Jurassic

Marly, oolitic, sandy limestone

Neritic

Sargclu Formaiion

E. to M. Jurassic

Thinly bedded, bituminous limestone, dolomitic limestone and shale

Euxinic

Najmah Formation

L. Jurassic

Alternating fine-grained, recrystallized limestone and oolitic, pcloidal packstone/ grainstonc

Shallow marine lagoon neritic

Gotnia Formation

L. Jurassic

Bedded anhydrite with subordinated intercalations of calcareous shale, limestone and shall

Supersaline lagoon

Naokelckan Formation

L. Jurassic

Thinly bedded, highly bituminous dolomite and limestone intcrbedded with shale, sbaly limestone and dolomite

Euxinic

Barsarin Formation

L. Jurassic

Sequence of limestone, dolomitic limestone and cherty, brecciated carbonate

Lagoonal e vapor ite

MakhuJ Formation

L, Jurassic

Argillaceous and calcareous limestone with minor silty sandstone

Lagoon neritic

Chi a Gara Formation

L. Jurassic to E. Cretaceous

Thinly bedded limestone, calcareous shale, marly limestone and marl

Open marine

Karimia Formaiion

L, Jurassic

A sequence of monotonous calcareous muds tone

Euxinic

Sulaiy Formation

L. Jurassic

Detrital limestone some oolitic and recrystallized limestone with rare interbeds of sandy shale

Neritic

243

Sedimentary Basins and Petroleum Geology of the Middle East Table 7.1 7,1 continued. continued. Area

Unit

Age

Lithology

Environment

Deir Ala Formation

E. Jurassic

Claystone, thinly bedded limestone, bioturbated sandstone followed by sandy limestone

Marine with fluvial influence

Zarga Formation

E. Jurassic

Massive, cross-bedded sandstone, conglomeratic sandstone, bioturbated and flaser-bedded sandstone with minor ferruginous limestone and dolomite

Shallow marine tidal flat

Dhahab Formation

M. Jurassic

Fine-grained, bioturbated limestone

Shallow shelf

Umm Maghara Formation

M. Jurassic

Dolomite and dolomitic limestone, cross-bedded and bioturbated sandstone, marl and siltstone

Shallow marine tidal flat

Arda Formation

M. Jurassic

Cross-bedded and flaser-bedded sandstone and ferruginous limestone

Fluviatile

Muaddi Formation

L. Jurassic

Finely laminated shale, dolomitic sandstone, claystone, marl and some limestone

Terrestrial to shallow marine

Hihi Formation

E. Jurassic

Silty claystone interbedded with thin beds of limestone and sandstone

Shallow marine with strong continental influence

Nimr Formation

E. Jurassic

Microcrystalline, dolomitic limestone with intercalations of oolitic, sandy limestone

Shallow shelf with slight clastic influx

Silal Formation

E. to M. Jurassic

Interbedded sandstone, silty to sandy, calcareous shale and oolitic, argillaceous limestone

Shallow marine with clastic influx

Dhahab Formation

M. Jurassic

Argillaceous dolomite, slightly anhydritic, with thin streaks of limestone

Shallow-marine shelf

Ram la and Ham am Formations

M. Jurassic

Basal shale followed by interbedded, macrocrystalline dolomite and dolomitic limestone with fine- to medium-grained sandstone and shale

Shallow marine andfluvial or tidal channel

Mughanniya Formation

M. to L. Jurassic

Dolomite and patches of massive anhydrite, followed by argillaceous, glauconiiit limestone with thin beds of claystone

Marginal marine to sabkha

Syria

Qamchuqa Formation

E. to M. Jurassic

Packsione, dolomitic limestone and shale

Lagoon

Southeastern Turkey

Cudi Group

L. Jurassic toE. Cretaceous

Perilidal limestone, anhydrite and dolomite; thinly bedded, laminated, argillaceous lime mudstone and minor shale

Shallow marine

Jordan

244

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic THE JURASSIC SECTION IN CENTRAL ARABIA All the formations of the Jurassic in Saudi Arabia were named after locations found between 18~ and 25 ~ N and 45 ~ and 47 ~ E. The principal outcrops of these formations in the vicinity of Riyadh are shown in Fig. 7.4a, b. The sequence of formations is shown in Figs. 7.5-7.7. The detailed descriptions of Powers et al. (1966), Powers (1968), Okla (1984, 1986, 1987) and Moshrif (1987) are summarized below. Since all the formations described in Saudi Arabia are used without chamge in Bahrain the two areas are described together.

The Jurassic of Saudi Arabia Marrat Formation (Toarcian-Aalenian). The formation takes its name from the town of Marah (25004 ' N, 45029 ' E) in central Saudi Arabia, where it has a maximum thickness of 111 m (364 ft). Prior to 1945, the strata of the Marrat Formation were regarded by ARAMCO geologists as forming the basal member of the Tuwaiq Mountain Formation. The beds subsequently were raised to formational rank by Bramkamp and Steineke (1945, cited in Powers et a1.,1966), and the Tuwaiq was given formational status by Powers et al. (1966). The formation crops out as a series of discontinuous exposures from the A1 Taysiyah Plateau (28003 , N) south to Khasm Mawan (22050, N), a distance of more than 550 km (344 mi); however, the outcrop area narrows, and the topographic expression of the formation becomes less distinct at Khashm adh Dhibi (24o15 ' N). Moshrif (1987) traced the formation from Wadi Birk (23 ~ N) to Khashm Furuthi (25046 ' N) (Fig. 7.4). A detailed lithological description of the formation was provided by Powers and McClure (1962, in Powers et al., 1966) along latitude 24013 , N from Khashm adh Dhibi. They defined three members (Fig. 7.5): 9 U p p e r M e m b e r (24.2 m, or 79.4 ft): the basal, thin, shale beds grade up into thin alternations of brown, microporous wackestone/packstone with gastropods and shale. The top is formed by microporous, argillaceous limestone; 9 M i d d l e M e m b e r (41.8 m, or 137 ft): red, green and yellow siltstone and shale grading upward into finegrained, cross-bedded, calcareous sandstone containing thin bands of argillaceous limestone and wackestone/packstone; and 9 L o w e r M e m b e r (21.5 m, or 70.5 ft): brown, mediumgrained, crystalline dolomite sometimes interbedded with partly dolomitized, argillaceous limestone. These grade up into red-brown, microporous and argillaceous, limestone intercalations, followed by interbedded, red and green sandstone, siltstone and shale with thin beds of argillaceous limestone and wackestone. The top of the member is formed by red-brown,

medium to coarse-grained, angular, calcareous sandstone. The formation was dated as Toarcian-Aalenian, based on the ammonites and other fauna, and deposited in a tidal-fiat, lagoonal and neritic environment. It rests unconformably upon the Late Triassic Minjur Formation. (Powers et al., 1966, show that the Rhaetic is cut out.) It passes conformably up into the Dhruma Formation. Dhruma Formation (Bajocian-Callovian). The formation, first defined by Steineke (1937, cited in Powers et al., 1966) as a member of the Tuwaiq Formation, but subsequently raised to formation status by Bramkamp (1945, cited in Powers et al., 1966), takes its name from the town of Dhruma (24~ ' N, 46007 ' E). The first published description of the formation appeared in Steineke and Bramkamp (1952), although a type section was not presented until later (Steineke et al, 1958). The type section was composed from a series of outcrops between Khashm adh Dhibi (24012'24 " N, 46007'30" E) and Khashm al Mazrui (24019'00 " N, 46019'36 " E). A three-fold division is recognized (Fig. 7.5), as had been earlier established by Holm (1947, in Powers et al., 1966): 9 U p p e r D h r u m a : a) Hisyan Member: tile lower unit of the Upper Dhruma, consisting of about 64 m (210 ft) of tan to green, calcareous shale interbedded with white, microporous limestone; b) Atash Member: consisting of about 25 m (82 ft) of wackestone/packstone interbedded with argillaceous limestone; 9 M i d d l e D h r u m a : about 165 m (541 ft) thick, consisting of cream to tan wackestone grading up to compact, thin packstone and ending with lime mudstone and subordinate marl intercalations and brownish, oolitic limestone; and 9 L o w e r D h r u m a : about 121 m (397 ft)thick, consisting of green to olive clay-shale with thin, interbedded wackestone, sandstone and gypsum bands grading upward into interbedded, microporous limestone and gypsiferous clay-shale and ending with wackestone and dense, creamy lime mudstone and interbedded shale. A thin gypsum band lies at the base. The limestone near the top (known as the Dhibi Limestone) may form cliffs. The maximum thickness of the Dhruma Formation, 375 m (1,230 ft), occurs at Khashm adh Dhibi, from where it thins southward to 264 m (866 ft) at Wadi Birk and 200 m (656 ft) at Khashm al Juwayfah (22032 , N), to finally wedge out near Khashm az Zifr (19030 ' N) (Powers et al., 1966). The top of the formation is unconformably overlain by the Tuwaiq Mountain Formation. The age of the fbrmation ranges through Bajocian to Callovian. Arkell (1952) assigned a Bajocian age to the Lower Dhruma based on the occurrence of a D o r s e t e n s i a and E r m o c e r a s fauna. The Middle Dhruma was given a Bathonian age and the Upper Dhruma a Bathonian-Callovian age, based on ammonites. In the north, the sediments of the Dhruma were formed under progressively more marine conditions, beginning

245

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic

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Fig. 7.5 Lithostratigraphy of the Early Jurassic (Marrat Formation) and Middle Jurassic (Dhruma Formation) in Central Saudi Arabia (composite outcrop section based upon descriptions in Powers et al., 1966, and Moshrif, 1987). Location of the formations shown in Fig. 7.4 247

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Fig. 7.6. Stratigraphic sections showing the general lithology and sedimentary structures of the Middle Jurassic (Bajocian-Callovian (Dhruma Formation in the E1 Arid Escarpment of central Saudi Arabia. The location of the sections is shown in the map on the right modified from Bramkamp et al., (1963) (after A1Aswad, 1995, and reproduced by kind permission of Gulf Petrolink, Bahrain) with tidal flats and lagoons followed by shallow-marine to moderately deep-marine conditions. The facies of the Dhruma Formation, however, show a change southwards from the mixed siliciclastics and carbonates in the north to exclusively siliciclastics in the south (Fig. 7.6). The sandstone generally is mature, friable and cross-bedded. The transport is towards the north, accompanied by decreasing grain size. Fine- to mediumgrained, the sandstone shows fining-upwards sequences. Compositionally, it ranges from the most common sublithic arenite through feldspathic litharenite; subarkose, quartzarenite, lithic arkose; and litharenite with a mature, heavy mineral suite of opaques, zircon, rutile and tourmaline with minor garnet, epidote mica and hornblende. Examination of the quartz grains suggests a derivation from plutonic rocks and middle- to high-grade metamorphics. A1Aswad (1995) interpreted these data as an indication of a southerly provenance from the Hadhramout Arch, rather than from the shield to the west. The presence of fossil wood and the increasing proportion in higher horizons of kaolinite over illite suggests a climatic regime becoming less arid with time~

Tuwaiq Mountain Formation (middle CallovianOxfordian). The limestone that forms a nearly parallel sequence of west-facing scarps takes its name from Jibal A1 Tuwaiq in central Arabia. Initially named and described by Steineke (1937, cited in Powers et al., 1966) as the Tuwaiq Mountain Limestone Member of the Tuwaiq For-

248

mation, it was raised to formational rank by Bramkamp (1945, cited in Powers et al., 1966). The description of the type section along the Riyadh-Jiddah Road through the Hisyan Pass (between 24~ N, 46007 '10" E and 24056'30" N, 46012'32 " E) was provided by Arkell (1952), where a total thickness of 215 m (705 ft) was measured. A thickness of 200-215 m (656-705 ft) also was recorded at Darb al Hijaz-Wadi Nisah (24015 ' N) by Powers et al. (1966). Okla (1984, 1987) described a section of 193 m (633 ft) along a new road between Riyadh and A1-Mizhmia (24038 ' N, 46043 ' E), which he divided into an upper and a lower division (Fig. 7.7). The lower division (103.3 m, or 339 ft) is made up of light-colored biomicrites with abundant sponge spicules and molluscan fragments, thin pelmicrites and pelletiferous biomicrites. The upper division (89.7 m, or 294 ft) is a gray, ledge-forming biomicrite with abundant corals (Amphiastraea and Microsolina), stromatoporoids and Kurnubia spp. and abundant dasycladacean algae in pelbiomicrites. The formation lies disconformably upon the Dhruma Formation below and is followed conformably by the Hanifa Formation. In central Arabia, the lower part of the formation is characterized by sediments laid down in the lowenergy part of a carbonate shelf or homoclinal ramp, which grades upward into high to moderate-energy deposits in a water depth ranging from 20 to 30 m (66-99 ft), as indicated by abundant corals and algae. Deeper-water conditions typical of a restricted, intrashelf basin are found in

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic

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Z.....

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LITHOLOGY

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LEGEND

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{_ ~ . T ~

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180-

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W 0"

Light {,,ellm~, hard btomtcrtte with a ~ n t

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249

Sedimentary Basins and Petroleum Geology of the Middle East the vicinity of the oil fields in eastern Saudi Arabia. Hanifa Formation (Early Kimmeridgian). The type section lying in Wadi Hanifa near 24056 ' N was described by Powers et al. (1966). It was regarded originally as a member of the Tuwaiq Mountain Formation by Steineke (1937, cited in Powers et al., 1966), but was raised to formational status within the Tuwaiq Mountain Group by Bramkamp (1945, in Powers et al., 1966) and used in this sense by Kerr (1953). The formation was described in detail by Steineke and Bramkamp (1952a, b) and Steineke et al. (1958). It crops out in a narrow and somewhat irregular arc from Nafud ath Thuwayrat (26032 ' N) to Bani Khatmah (17~ ' N), a distance of nearly 1,100 km (688 mi), with the outcrop ranging from 0 to 25 km (0-15.6 mi) in width (Powers et al., 1966). It has a thickness of 101 m (331 ft) of argillaceous limestone, wackestone/packstone and shale containing Pseudocyclammina jaccardi (Schrodt) in the lower part and Kurnubia morrisi (Redmond) in the upper part. A similar thickness (101.5 m, or 333 ft) was described by Okla (1986) from near Jabal A1 Abakaya 60 km (37.5 mi) northwest of Riyadh, where a two-fold division again can be made (Fig. 7.7). Okla described the lower 52.7 m (173 ft) as yellow to light-gray, friable, gypsiferous and calcareous shale and soft, yellow, argillaceous limestone with interbedded, fossiliferous intramicrites, coral-bearing biomicrites and micrites grading up into ledge-forming intrasparites and pelsparites, biomicrites and micrites. The upper division consists of 48.8 m (160 ft) of calcareous shale, spicular biomicrite and pelmicrite capped by more pelmicrites, pelsparites, oosparites and oncolitic limestone. The sediments of the Hanifa Formation generally were deposited under deep to moderately deep, quietwater conditions with the formation of argillaceous limestone and appreciable thicknesses of shale (Okla, 1986). The presence of gypsum bands indicates that the water depth on some occasions was shallow enough to permit the formation of evaporites and associated thin limestone. The presence of oolitic and peloidal limestone also provides indications for the existence of shallow, more turbulent, high-energy conditions. At the top of the Hanifa Formation is a sharp discontinuity separating the formation from the limestone of the overlying Jubailah Formation (Okla, 1986). Jubailah Formation (early Kimmeridgian). Originally named as a member of the Tuwaiq Formation (Steineke, 1937, cited in Powers et al., 1966) and raised to a formation within the Tuwaiq Mountain Limestone Group (Bramkamp, 1945, in Powers et al., 1966), the Jubailah Formation was named in 1952 (Steineke and Bramkamp, 1952 a & b), although the detailed definition did not appear until the publication of Steineke et al. (1958) and Powers et al. (1966). The type locality lies in the Wadi Hanifa, where the lower part of the formation, about 85 m (280 ft) thick, lies between 24o53'48 " N, 46019'36 " E and 24~ N, 46o19'36 " E near the town of A1 Jubaylah. The upper 25 m (82 ft) of the succession was measured

250

between A1 Jubaylah and Riyadh in the same wadi (Powers et al., 1966). The formation has a total thickness there of 110 m (361 ft) and is made up of shallow-water carbonates, mostly argillaceous limestone, wackestone and packstone with some dolomite (Steineke et al., 1958; Powers et al., 1966). Okla (1986) reported a thickness of 103.8-117.6 m (340-386 ft) of the Jubailah Formation in Wadi Nisah, about 60 km (37.5 mi) south of Riyadh, and made a threefold division into three units of almost equal thickness (Fig. 7.7). The lower unit is dominated by light-gray, gypsiferous shale with thin beds of pelsparites grading upward into thick, dolomitized biomicrites and peloidal wackestone followed by pelsparites and pseudo-oolitic grainstone. The middle unit is composed of biomicrites interbedded with pelsparites, and the upper unit is mainly thinly bedded, dolomitized and brecciated, fossiliferous biomicrites with thin beds of pure dolomite and conglomeratic micrite. Meyer et al., (1996) identified lithofacies different from the Jubailah Formation in the Ghawar Field which show a stacking order from muddy and massive carbonate sands passing upwards through burrowed mud, stromatoporoids and platy mudstone (Fig. 7.8) The Jubailah Formation beds were deposited in an extensive but complex, shallow-water-shelf environment, with evidence of high-energy, shoal-water conditions and quiet-water, carbonate deposits. In some parts of the basin is an indication of a deeper-water influence. Although separated by a sharp disconformity at the base, the top of the formation passes conformably up to the Arab Formation.

Arab Formation (early Kimmeridgian-Tithonian). The Arab Formation was included initially in the Riyadh Member, the uppermost member of the Tuwaiq Mountain Formation (Steineke, 1937, cited in Powers et al., 1966). Subsequently, Bramkamp (1945, cited in Powers et al., 1966) raised the Riyadh Member to group status and divided it into two formations - - a lower Arab Formation and an upper Hith Formation (Powers et al., 1966). The first usage as a formation was in Steineke and Bramkamp (1952), although a formal description did not appear until several years later (Steineke et al., 1958; Powers, 1962). Because of poor outcrop, the type sequence was defined in well Dammam-7 in the Dammam Field (Powers, 1968; Steineke et al., 1958). The formation has a thickness of 127.5 m (418 ft) comprising interbedded wackestone, argillaceous limestone, dolomites and anhydrites. Four Carbonate units A-D, each separated by a thick anhydrite sequence, were defined from top to bottom (Fig. 7.8): 9 Arab A Member: about 16.8 m (55 ft) of tan to brown, dense, argillaceous limestone with thin beds of brown calcarenite and minor anhydrite near the top; ~ Arab B Member: about 10.7 m (35 ft) of tan to brown, dense, argillaceous limestone with thin, interbedded, brown wackestone/packstone in the lower part grading up into massive anhydrite;

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Massive nodular and chicken-wire anhydrite with some interbeds of dolomite and limestone Argillaceous limestone, minor wackestone and anhydrite Anhydrite,doiomltized,argiilaceous limestone and calcarenlte Massive anhydrlte,partially dolomitized Packstone and thin partially dolomitized argillaceous limestone and wackestone Massive anhydrite complexly interbedded with finely crystalline dolomite. Peloidal packstone Dolomitized argillaceous limestone.

Fig. 7.9. Stratigraphy and log characteristics of the Late Jurassic (Arab-Hith Formation) in Saudi Arabia (modified from Wilson, 1985). about 41.5 m (136 ft) of tan to brown, fine-grained wackestone with some thin beds of partially dolomitized, argillaceous lime mudstone to wackestone and packstone. It grades up into massive anhydrite with minor bands of dolomite and packstone/grainstone; and 9 A r a b D M e m b e r : about 58.5 m (192 ft) of tan to brown, partially dolomitized lime mudstone with interbedded, clean, porous packstone and grainstone and some dolomite. It grades up into massive, white anhydrite with thin, interbedded dolomite or dolomitized packstone. Hughes (1996) described the Arab-D Member as composed of a series of high frequency paleobathymetric changes superimposed upon extensive carbonate platform deposits. Gradual shallowing resulted from either from a reduction in the subsidence rate, a fall in sea-level or a rise in the carbonate productivity rate or a combination of such event.s The latest in this series of events, the deposition of very shallow water marine carbonates terminated the deposition of Arab-D evaporites. The textural characterisitics and lithofacies assemblages of the Arab-D Member were described by Meyer et al., (1996) and are illustrated in Fig. 9

252

Arab C Member:

7.10. The carbonate-evaporitic cycles of the Arab Formation represent the most restricted Jurassic sedimentation. The deposits mark progressive basin infilling ending in regressive sabkha deposits. The cycles contain minor transgressive episodes, during which carbonates formed. These reflect the control of sedimentation by epeirogenic subsidence and eustatic sea-level change. The Arab D marks the final upward shoaling, basin-fill phase, whereas the Arab C, B and A are transgressive. In general, the depositional setting from Arab D marks progressively more restricted conditions as the proportion of lagoonal and intertidal sediments culminated in the supratidal, evaporitic conditions (Wilson, 1985). The Arab Formation passes conformably up into the Hith Formation, with the boundary between the two taken at the boundary between the argillaceous limestone and minor anhydrite below and the massive anhydrite above. The lower boundary with the Jubailah Formation is taken at the change from porous packstone/wackestone below to tight, argillaceous limestone above. l-lith Formation (Tithonian?). The Hith anhydrite is

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic

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253

Sedimentary Basins and Petroleum Geology of the Middle East named after Dahl Hit (24~ " N, 47~ E). The outcrop of the Hith lies in a solution pit 15 km (9.4 mi) southwest of Riyadh, where an apparently complete sequence is seen (Powers et al., 1966). The Hith's thickness was measured originally by Bramkamp and Burger (cited in Powers et al., 1966) and defined in a publication by Steineke et al. (1958) as 71.2 m (233.5 ft) of bluishgray anhydrite, but Powers (1968) described about 90.3 m (296 ft) of massive, white anhydrite with some lime mudstone, wackestone or dolomite occurring toward the base of the formation laid down in supratidal, evaporitic conditions. In subsurface, the Hith consists of about 140 m (459 ft) of nodular anhydrite with interbedded dolomite capped by peloidal-oolitic grainstone and stromatolitic mudstone (known as the Manifa reservoir) (Fig. 7.9). The base with the Arab Formation already has been defined. The top of the Hith may have a disconformable relation with the overlying Early Cretaceous Sulaiy Formation, with the boundary placed at the change from a solution, collapse, limestone breccia below to oolitic, peloidal packstone above.

The Jurassic of Bahrain Marrat Formation (Toarcian-Aalenian?). About 76 m (250 ft) thick, the Marrat Formation represents a sequence of Toarcian-Aalenian dolomitic limestone, calcareous dolomite and shale deposited over a broad, intertidal fiat. These sediments rest unconformably upon beds of the Middle Triassic Jilh Formation and are overlain by the Dhruma Formation. Since the passage is conformable, the foMaation must be diachronous, because the Dhruma Formation is described as containing Aalenian forms. Dhruma Formation (Bajocian-Bathonian). About 305 m (1,000 fi) thick, this formation consists of a sequence of fine-grained, white, dolomitic limestone and black, calcareous shale deposited in shallow-marine to moderately deep-marine environments. The formation is dated as Bajocian-Bathonian, based on Rigadnella sp., Pseudomarssonella sp. and Pfenclerina trochoidea. Although the contact with the underlying Marrat is sharp, the beds are conformable and pass by transition into the overlying Tuwaiq Mountain Formation, as in Saudi Arabia. Tuwaiq Mountain Formation (Callovian-Oxfordian?). About 87 m (285 ft) thick, the formation consists of fine-grained, dense, dolomitic limestone with abundant corals, with black calcareous shale and thin, well-bedded, microporous limestone in the lower part of the succession. The contacts with the overlying Hanifa Formation and underlying Dhruma Formation are conformable. The sediments were laid down in low-energy, deeper-water conditions. Hanifa Formation (lower Kimmeridgian). About 87 m (285 ft) thick, this formation consists of lower, microporous, argillaceous limestone, wackestone/pack-

254

stone, shale and gypsiferous shale commonly containing corals. These grade upward to peloidal and oolitic grainstone interbedded with fossiliferous packstone. Jubailah Formation (early to middle Kimmeridgian). About 87 m (285 ft) thick, the Jubailah Formation is composed of an alternation of argillaceous limestone and dolomite with subordinate wackestone and packstone deposited in shallow-water-shelf conditions. The contacts with the overlying Arab Formation and underlying Hanifa Formation are conformable. Arab Formation (Kimmeridgian-Tithonian). About 168 m (550 ft) thick, the Arab Formation hosts major oil accumulations and was divided into four members. The lower part of the Arab D Member consists of fine to microcrystalline, dolomitic limestone that is argillaceous and tight. This grades upward into anhydritic limestone and dense dolomite, which pass to packstone with some oolitic limestone and dolomite layers. The C Member consists of massive, white to tan anhydrites and finegrained, tan to brown packstone. The Arab B Member has massive, white anhydrite with intercalated, thin, dolomitized, argillaceous limestone and wackestone/packstone. The Arab A Member consists mainly of white lime mudstone and thin wackestone with minor anhydrite horizons. The Arab Formation was laid down in a tidal-fiat setting ranging from supratidal to subtidal-intertidal. The contacts with overlying and underlying formations are conformable. Hith Formation (Tithonian). About 91 m (300 ft) thick, the Hith Formation is composed mainly of massive anhydrite with some interbeds of dolomite and limestone. It is conformably overlain by the beds of the Early Cretaceous Sulaiy Formation and in conformable contact with the underlying Arab Formation.

THE JURASSIC SECTION IN SOUTHERN AND SOUTHWESTERN ARABIA: THE REPUBLIC OF YEMEN The Permian beds (Akbra shale), formerly regarded as part of the Wajid section in the former North Yemen, are the only Paleozoic sediments of post-Ordovician age preserved in the Republic of Yemen. The oldest rocks found resting upon the erosional unconformity surface of these beds are clastics assigned to the Kohlan Formation (Fig. 7.2 and 7.11). The sediments have been assigned broadly to the Liassic, based on the description of preserved plant fossils found in the former North Yemen (Lamare and Carpentier, 1932). The sequence is nowhere very thick and represents channel-fill deposits laid down upon an irregular surface in a continental to marginal-marine environment. Above the sandstone is a dominantly carbonate section referred to as the Amran Group (Fig. 7.2 and 7.11). The beds of the group, however, show considerable lithofacies variation from lagoonal and evaporitic facies to more open-marine limestone.

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quartzites with some foliated chert from the Precambrian basement, fills channels and is followed by 30 m (98.5 ft) of coarse-grained, cross-bedded, fining-upward sandstone beds. The base of these units usually is erosional. The beds are tightly cemented and sutured with bedding-parallel stylolites. The remainder of the succession is made up of about 33 m (108 ft) of coarsening- and thickening-upward sequences of sandstone with abundant tippled surfaces and wave-rippled, lateral accretion units with trough crossbedding and climbing, rippled lamination. The top of the formation shows much burrowing and passes conformably upward into the shallow-marine units of the Amran Formarion. Braided, fluvial depositional environment~ are proposed for the sandstone, giving way to conditions of a lower delta plain with the reworking of laterally accreted, meandering channel fill. The coarsening-upward units and the sandstone with climbing ripples at the top probably are deltaic mouth bars (Elanbaawy, 1985). In the southern part of former North Yemen, where the thickness drops to the order of 20-30 m (65.6-98.5 ft), the beds are entirely clastic. West of Taizz in the southern part of the country, the formation is more than 25 m (82 ft) of medium- to coarse-grained, well-sorted, porous sandstone. The sandstone is laterally continuous and thick-bedded and shows abundant medium-scale, trough cross-bedding, including herringbone cross-beds and wave-rippled surfaces. The cross-beds dip north and south, but internal cross-ripple lamination builds up to the south in places.

255

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic the Kohlan Formation provided evidence of storm deposits in a normally quiet, muddy environment below the fairweather wave base. The herringbone cross-beds suggest tidal influences with a coastline oriented roughly eastwest, with the sands accumulating on an unstable, southdipping slope. In former South Yemen, the Kohlan sediments are still unfossiliferous, but, in contrast to the orthoquartzitic sandstone further north, are described as light-colored, arkosic sandstone with basal conglomeratic layers that include fragments of basement rocks; in further contrast to the Kohlan in the former North Yemen, they contain interbedded, green and purple marl of remarkable lateral extent. The beds pass conformably to the beds of the Amran Group (Greenwood and Bleakley, 1967; Beydoun and Greenwood, 1968). Although depositional conditions appear to be unchanged, passing from fluvio-lacustrine to deltaic, the source of sediments cannot be the same as those from North Yemen, given the conclusions derived concerning composition and coastline orientation.

Amran Group (? late Callovian/Oxfordian to Tithonian). The broad lithofacies distribution of the Middle and Late Jurassic suggests the existence of an early phase of lagoonal and shallow-shelf environments, which later gave way to evaporitic sabkhas. Paleogeographically, there was a broad, coastal/sabkha margin fringing the southern and southwestern side of the Arabian Shield, deepening to offshore, open-marine conditions south and west of the Yemen coastal margin (Dainelli, 1943; Leeder and Zeidan, 1977), where the equivalents of the Amran carbonates are placed in the Antalo Limestone Formation of Ethiopia or the Sa Wer Formation of Somalia. The evaporitic facies is more extensively developed in central Yemen and automatically invites correlation with the Hith evaporites in eastern Arabia. Clastics and evaporites accumulated in local grabens, such as in the Marib, A1 Jawf and Shabwa grabens. Locally, the Amran pinches out over pre-existing basement highs with an east-west orientation such as the Hadhramout Arch. The fossil assemblages in both former North and South Yemen provide indications of an age range from the Bajocian to the end of the Tithonian. However, in a recent micropaleontological biozonation (Simmons and AI Thour, 1994), which narrowed the time range, none of the published lithofacies zonations, including the one adopted here, were used, as the lithostratigraphic equivalents of units is only approximate. The group generally follows conformably above the Kohlan Formation, but generally is unconformably overlain by the elastic beds of the Late Cretaceous Tawilah Formation (Fig. 7.11). Davison et al., (1994) divided the Amran Group in northwest Yemen into two formations (Fig. 7.13). The lower formation, known as the Rayadh Formation consists of a coarsening upward sequence of laminated fossiliferous limestone with intercalated shale deposited in a regressive shallow marine shoal setting, alternating with intraplatform muddy limestone. The upper, Wadi A1 Ahjur

Formation, is made up of fossiliferous, ferruginous limestone and massive sandy limstone, part of a shallow marine siliciclastic/carbonate regressive sequence. In the former North Yemen, the carbonate sequence has not been separated into different units, despite the recognized vertical changes in depositional environments. The Amran Formation described by Geukens (1966) in Wadi La'ah, where about 380 m (1,246 ft) are exposed, comprises fossiliferous, calcareous shale (20 m, or 66 ft) overlain by thick-bedded limestone (170 m, or 558 ft), which in turn are overlain by thick-bedded limestone (50 m, or 164 ft) capped by a 90 m (295 ft) thick shaly-marlylimy complex. The best exposed sequence, about 275 m (902 ft), occurs at Jabal Faliafilah, where the lowest 70 m (230 ft) of the succession is dominated by intrabioclastic limestone generally passing upward from mudstone to packstone fabrics on a 1-2 m (3.3-6.6 ft) scale. The bioclasts are mainly oyster and echinoid fragments at the base, with gastropods, brachiopod and echinoid fragments becoming more common higher in the sequence. The carbonates show evidence of abundant horizontal and vertical burrowing. The larger intraclasts, along with siliciclastic grains, are more common at the base, whereas fetid mudstone and smaller clasts are more common higher in the sequence. This shallow-marine sequence consists of episodic, progradational cycles imposed over a gradually deepening trend. The larger intraclasts indicate nearshore conditions at the bottom of the sequence, marking a transgression over the sandstone of the Kohlan Formation. These beds are followed by about 25 m (82 ft) of black, fetid lime mudstone and thin wackestone that lack burrows, along with 15 m (49 ft) of coarsening-upward, vertically burrowed, fetid, black wackestone with rare mudstone and intraclastic packstone. Above, the succession gives way to a 55 m (180 ft) sequence of dolostones containing calcareous nodules and calcite-lined vugs. In turn, these are overlain by about 100 m (328 ft) of interbedded, bioclastic packstone, wackestone and mudstone with chert bands and nodules. The lime mudstone commonly is black and fetid. Burrowing is common in some beds (including Thalassinoides). Some of the coarser of these beds show dewatering structures. The top 10 m (33 ft), which consists of thinly bedded, bioclastic packstone, has abundant oyster and brachiopod shells. Reworked wackestone and packstone were spread over a quieter-water, fetid, mudstone facies during repeated progradational cycles, with the mudstone becoming predominant as the water depth increased. They record less energetic, poorly oxygenated water conditions that inhibited the growth of burrowing organisms. The overlying, laterally continuous dolostones have a high porosity related to the dolomitization of former grainstone and packstone, and they still retain trough cross-bedding. The lower contacts of some of these units show evidence of erosion. The bioclasts generally are poorly preserved, but the former presence of corals is still detectable. The coral debris, particularly abundant near the top, indicates the

257

Sedimentary Basins and Petroleum Geology of the Middle East presence of nearby reefs supplying debris to shoal bars that may be of tidal or longshore drift origin (Beydoun, 1966; Beydoun and Greenwood, 1968; Elanbaawy, 1985). The shoaling was followed by a minor transgressiveregressive event, because low-energy muds, which show the effects of loading by coarser packstone, are preserved above the dolostone and capped by repeated, minor, progradational cycles of alternations of low-energy shelf muds and probable storm deposits, and reworked, oysterrich packstone sheets formed as a nearshore facies. The Amran in the extreme eastern part of the Republic of Yemen (former South Yemen) has been raised to group status and has been divided into four formations, although the second and third are diachronous (Fig. 7.11). It is a sequence that may range from as little as 35 m (115 ft) to as much as 733 m (2,404 ft), depending upon local depositional conditions and subsequent erosion. According to Beydoun and Greenwood (1968), the fossil assemblage suggests that the group may extend into the Berriasian. The base of the group here, however, is dated as Callovian and, therefore, begins in the Late Jurassic, not the Middle Jurassic, as in south and west Yemen.

"Top" Naifa Formation (Tithonian-?Berriasian)

Amran Group Sabatayn Formation/Madbi Formation (upper Oxfordian-upper Kimmeridgian)

"Base" Shuqra Formation (Callovian-Oxfordian) Toland et al., (1995) have recognised four disconformity bounded 3rd order depositional sequences in the Upper Jurassic of southern Yemen: UJ 40 Late Tithonian-?Berriasian (Saar Formation?) of shallow water oolitic grainstones which reflect basin inversion. UJ 30 Early-mid Tithonian, hybonotum-early microcanthum Zone (Naifa Formation) comprise of pelagic lime mudstone and claystone and represent a half-graben fill. UJ 20 Mid-Late Kimmerdigian, divisum-beckeri Zone (Madbi Formation) comprised of pelagic lime mudstone and claystone with initial rifting occurring in the mid-Kimmerdigian and followed by an important phase of footwall uplift. UJ 10 Late Oxfordian-Early Kimmerdgian (Shuqra Formation) represents shallow water transgressive-regressive carbonate shelf succession.

Shuqra Formation. This formation, which may be 60-80 m (196-262 ft) thick, consists of well-bedded, fossiliferous limestone, at times sandy and oolitic, with interbeds of

258

shale grading up into yellowish, fossiliferous marl and back into shallow, neritic limestone (Beydoun, 1964,1966; Beydoun and Greenwood, 1968). Toland et al. (1995) interpreted the Shuqra Formation as a Transgressive Systems Tract (TST), followed by a Maximum Flooding Surface (MFS) and an aggradational-progradational, shoaling-up Highstand Systems Tract (HST), bounded above and below by disconformities. It represents the late early Oxfordian-early Kimmeridgian pre-rift, transgressive-regressive, carbonate-shelf sequence. It rests upon 20 m of sandy lime mudstone dated as Late Callovian and, thus, is the basal part of the Amram described near Sana'a by Simmons and A1Thour (1994). Madbi Formation. Conformable above the Shuqra limestone, the Madbi Formation consists of a sequence of about 233 m (764 ft) of gray, rubbly, shaly, silty and gypsiferous, bituminous and fetid marl interbedded with thin bands of marly, fossiliferous limestone. These were deposited in a more open-marine environment, according to Beydoun (1964, 1966) and Beydoun and Greenwood (1968). They are overlain unconformably by the beds of the Naifa Formation. As defined, the formation is equivalent to the UJ20 depositional sequence of Toland et al. (1995). The basal contact is a flooding surface with a thin floatstone, above which is a deepening-upward, progressively more argillaceous to a MFS attributed to the development of a halfgraben system. The sequence closes with a shoaling-up, pelagic, claystone-lime mudstone succession interpreted as a HST. The biota is similar to the Arab D in eastern Arabia. Sabatayn Formation. This formation is a laterally restricted, facies equivalent to the open-marine facies represented by the beds of the Madbi Formation. It varies in thickness from 70 to 300 m (230-984 ft) and has been divided into four members (from older to younger): the Shabwa, Layadim, M'qah and Ayad (Beydoun, 1964, 1966; Greenwood and Bleakley, 1967, Beydoun and Greenwood, 1968;). The Shabwa Member consists of about 30 m (98 ft) of halite with some bituminous streaks, although the base has not been observed. Mobilization of the salt has occurred, resulting in the development of halokinetic structures. It is conformably overlain by the Layadim Member, about 63 m (207 ft) of variegated and black, bituminous shale with alternating thin bands of marl, limestone and dolomite. The member interfingers laterally up to the 150 m (492 ft) thick M'qah Member, which consists of coarse-grained sandstone and marl with abundant plant remains. There are shaly limestone and dolomite bands and gypsum at some levels, and some of the beds are fetid and bituminous. At the top of the succession is the Ayad Member, which may be up to 230 m (754 ft) thick and consists of gypsum with more thin, interbedded, fetid dolomite and bituminous, limestone bands. Naifa Formation. This formation overlies both the Madbi and Sabatayn formations, forming the top of the

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic Amran Group in extreme eastern Yemen (former South Yemen). The entire section thickens eastward and ranges from as much as 446 m (1,463 ft) to 126 m (413 ft). The lower part of the succession is made up of fine-grained to porcellanous limestone and marl; gray to pink, shaly marl, which may be partly gypsiferous or silty, occurs in the upper part. There also is interbedded, fossiliferous or bituminous limestone. In the west, the upper part of the formation usually is absent. The presence of intraformational breaks associated with the occurrence of evaporitic beds indicates the erosion of local (partial) barriers resulting from the development of the Mukalla High along a northsouth axis. In general, the formation represents the spread of open-sea conditions into extreme eastern Yemen, conditions absent in southern and northern Yemen. This has suggested to Beydoun (1964, 1966), Beydoun and Greenwood (1968) and Greenwood and Bleakley (1967) that from the Tithonian to Berriasian, western and northern Yemen was emergent. The formation overlies the Madbi Formation with slight, angular discordance and is overlain unconformably by the Cretaceous Qishn Formation. According to Toland et al. (1995), there are two depositional sequences (UJ30 and UJ40) in the Naifa, defined as extending from the early mid-Tithonian to ?Berriasian. The lower sequence (UJ30) has the same interpretation as UJ20 (Toland et al., 1995). These two sequences are regarded as broadly equivalent to Arab C and B, respectively. The upper sequence (UJ40), however, marks a basin inversion that occurred during the late Tithonian and is interpreted as a Transgressive Shoreface Succession (TST). It is truncated by coarse clastics, suggesting a second inversion in the early mid-Cretaceous of the Qishn Formation.

THE JURASSIC SECTION IN EASTERN ARABIA Although the lithofacies changes in the Arabian Gulf area, compared to the outcrops in Saudi Arabia, are relatively slight during the Jurassic and are a response to small fluctuations in water depth, there is a critical depth range over which a particular lithofacies may persist unchanged. The result is that while a small depth change may cause a lithofacies change in one area, the depth change is not critical in another; hence, no change is recorded. Consequently, although the lithofacies change may be sufficient to lead to the assigning of a different formational name in the one instance, no name change is made in the other; as a result, there is some confusion and mis-correlation. This commonly occurs when age and name assignments have to be based on subsurface data. In contrast, the same formational name may be applied to quite different lithofacies believed to be of the same age. When paleontological information is poor, the possibilities for confusion seem boundless, which is a situation increasingly common in the Jurassic and Cretaceous of the Arabian Gulf area. Here the increasing amount of information from subsurface sec-

tions has to be fitted to a very imperfect stratigraphy. For this reason, it is difficult to simplify the stratigraphy, while at the same time providing an account using present terminology. For example, in Bahrain, the same formational names are those used in Saudi Arabia, whereas a completely distinctive terminology has been established in Qatar. Some of these latter formational names are used in the U.A.E. mixed with names retained from the Saudi terminology (Fig. 7.2). To reduce confusion, the country of origin and where the term is used will be included with the formation name.

The Jurassic of the United Arab Emirates Subsurface Formations Marrat Formation (Early Liassic). Although Qatar, the U.A.E. and Oman lie several hundred kilometers east of Jibal AI Tuwaiq, where the Jurassic type sections of Saudi Arabia crop out, in onshore Abu Dhabi, the name for the Early Jurassic deposits used in Saudi Arabia, the Marrat Formation, is retained for a mixture of terrigenous clastics and limestone. The formation is divided into two units (Fig. 7.14), rather than the three units in Saudi Arabia, and it has a thickness of about 100 m (328 It). The lower unit consists of bioclastic packstone and grainstone; intraclastic, peloidal and oolitic packstone and grainstone; and very fine, dolomitic lime mudstone interbedded with quartzose sandstone and silty claystone deposited in a marginalmarine environment under variable energy conditions. The upper unit is composed of dolomitic, oolitic grainstone; micritic sandstone and sandy limestone forming a complex of carbonates, mudstone and dolomitic sandstone that probably represents a tidal-fiat-flood-plain environment (Alsharhan, 1989). This formation is not present in Qatar and offshore U.A.E. due to non-deposition or erosion; therefore, whereas the Marrat Formation passes up conformably to the Hamlah Formation in onshore Abu Dhabi, the Hamlah Formation in these latter areas rests unconformably on the Middle Triassic Gulailah Formation (the local Jilh equivalent). Hamlah Formation (Early-Middle Liassic). In Abu Dhabi, this formation has a thickness ranging from 56 to 240 m (184-787 ft). It has a higher dolomite content than in Qatar, being formed by massive, gray, microsucrosic dolomite with only traces of anhydrite in the basal part deposited in a nearshore marine environment. The beds pass up into bluish-green, pyritic shale interbedded with streaks of black, organic-rich shale with argillaceous dolomite. The upper part of the formation is dominated by white to light-brown lime mudstone with traces of pellety, dolomitized packstone and grainstone and pale-gray, noncalcareous shale deposited under quiet but well-oxygenated, water conditions (Fig. 7.15). Toward Dubai, the per-

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Fig. 7.15. Lithological interpretation and log characteristics of the Early-Middle Jurassic (Hamlah and Izhara formations) in the U.A.E. 260

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic centage of dolomite increases, and the formation becomes dominated by dark-gray to brown dolomite with thin, black to dark-gray shale streaks. In offshore Abu Dhabi and Dubai, as in Qatar, the Hamlah Formation is unconformable over the Gulailah Formation (Jilh Formation equivalent), but only in the onshore Abu Dhabi region does it follow conformably over the Marrat Formation. Identification of Pseudocyclammina liasica, Thaumatoporella parvo vesicularis, Lithiotis sp. and Glomspira sp. leads to the suggestion of a middle Liassic age. Note that the age of the Hamlah in the U.A.E. is greater than in Qatar. Izhara Formation (Bajocian-Early Bathonian). The Izhara Formation is assigned a late Liassic to Bajocian age and has a thickness ranging from 86 to 148 m (282485 ft). It is, therefore, potentially older than the same formation in Qatar. It contains soft, microporous lime mudstone and occasionally dolomitized mudstone and wackestone that grade up into more lime mudstone and calcareous shale, followed by peloidal packstone and grainstone interbedded with highly organic lime mudstone and calcareous, non-fissile and slightly pyritic, black shale (Fig. 7.15). The formation was deposited in quiet-water shelf settings, as suggested by the argillaceous limestone and high-energy fluctuations in the depositional regime indicated by the grain-supported sediments (Alsharhan,

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1989). The formation is regarded as the lateral equivalent of the Lower Dhruma Formation. However, in the UAEbased upon the occurrence of Bositra sp. and Lenticula sp. as well as echinoid and pelecypod debris, a late Liassic to Bajocian age has been suggested. The top of the Izhara, which is picked at the top of a clean packstone, is presumed to be conformable with the overlying Araej Formation, while the base is conformable with the Hamlah Formation. Araej Formation (Bathonian to Callovian or Oxfordian). The same three members of the Araej Formation of Qatar have been identified in Abu Dhabi and Dubai. The lithologies and thicknesses (about 188 m, or 616 ft) of the three members (Fig. 7.16) are, however, slightly different from those found in Qatar (Alsharhan and Whittle, 1995). The Lower Araej Member has a thickness of about 127-91 m (417-300 ft) and contains bioclastic-intraclastic and peloidal lime mudstone with significant amounts of clay and pyrite and less wackestone of open-marine origin. The Uwainat Member, about 40-54 m (120-178 ft) thick, shows a gradation from peloidal lime mudstone to bioclastic-intraclastic, dolomitic grainstone, packstone and wackestone. The Uwainat was deposited in a shallow to very shallow, subtidal lagoon and barrier-bar or shoal setting of a remarkably stable, marine-shelf environment. The Upper Araej Member, about 39-102 m (128-325 ft) thick, shows

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Fig. 7.16 Lithological interpretation and log characteristics of the Middle Jurassic (Araej Formation) in the U.A.E.

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tiloculina oolithica, Pfenderina trochoides, Pseudocyclammina maynci and Iranica slingeri suggests an age range from Bathonian to early Oxfordian. The lower contact of the Araej is believed to be conformable. The upper contact is seen on a regional scale to be unconformable with the overlying Diyab Formation. Diyab

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Kimmeridgian). Cycles in the Diyab Formation are not recognized in Abu Dhabi, although three members can be distinguished (Fig. 7.17). The formation is equivalent to the Hanifa Formation and part of the Jubailah Formation of Saudi Arabia. The thickness ranges from 260 to 313 m (853-1,027 ft), but thins to less than 16 m (50 ft) near the basin margin in offshore Abu Dhabi in the Tini Field (de Matos and Hulstrand, 1995). The lower member consists of two highly radioactive/clean lime mudstone separated

262

by a thin band of chicken-wire anhydrites (de Matos and Hulstrand, 1995) interbedded in massive and fissile lime mudstone containing abundant organic matter that gives off a sulfurous odor. The middle member is made of tight, dense lime mudstone with minor grainstone, packstone and brown, sucrosic dolomites. The upper member comprises organically rich limestone with rare interbeds of peloidal, pyritic grainstone (Alsharhan, 1989). The Diyab Formation was deposited in an anoxic, intrashelf basin whose eastern edge is located in the central offshore Abu Dhabi and passes westward into offshore and onshore Qatar. The age assigned to the Diyab Formation in Abu Dhabi is Oxfordian based upon stratigraphic position as it is followed by the conformably overlying Arab Formation. As the Fahahil Formation of Qatar also is regarded as early Kimmeridgian and equivalent to the Arab D, it is clear that the top of the Diyab Formation in the U.A.E. is not the same as, but higher than, the top of the Diyab of Qatar and must include the Darb Formation. In Abu Dhabi, the lower contact with the Araej Formation, while conformable in the east, is unconformable in the west.

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic

Arab Formation and Its Equivalents (OxfordianTithonian) Arab Formation (Oxfordian-early Tithonian). As indicated in the discussion of the section in Saudi Arabia, the division of the Arab Formation in the Arabian Gulf into four members by Powers (1962) was based upon the sequence of alternating cycles of carbonates and evaporites. Minor disconformities are common throughout the Arab Formation, separating major cycles and sub-cycles within individual cycles. They represent breaks in sedimentation due to local shallowing, and some may be erosional surfaces. Short-duration immersion and increased current activity also are potential causes. Within each cycle, environmental conditions show a progressive upward restriction with an increase in anhydrite and dolomite toward the top (de Matos, 1994). This formation is well-developed in offshore Abu Dhabi, where it is equivalent to the Fahahil (Arab D) and Qatar (Arab C, B and A) formations in the onshore, and there appear to be only small differences in the lithological composition of the individual members when compared with that section in Saudi Arabia. The intervening dense intervals, Lower Anhydrite and Dense Limestone (between Arab D and C), the Middle Anhydrite (separating Arab C and B) and the Upper Anhydrite (below Arab A), are composite units in which the proportion of anhydrite to carbonate increases from east to west (Fig. 7.18). In offshore Abu Dhabi, the formation has a thickness ranging from 180 to 285 m (590-935 ft). The Arab D Member is the main reservoir of the western Abu Dhabi offshore fields. It consists of brown to darkbrown, well-sorted, oolitic, peloidal packstone and grainstone passing up to dolomite and dolomitic limestone, whereas in Saudi Arabia, the limestone tends to be wackestone and passes up into massive anhydrite. In the latter region, the C Member again shows a greater development of anhydrite toward the top, whereas only in the Arab B and A members is anhydrite common in Abu Dhabi. In the carbonates, oolitic packstone and grainstone replace the lime mudstone, wackestone and packstone as the common carbonate facies. The sequence of lithologies in the Arab A-D members in the western U.A.E. comprise a shelf-lagoon-tidal-flatsabkha sequence similar to the depositional model proposed by Alsharhan and Whittle (1995) and A1 Silwadi et al., (1995) for the Qatar Arab Formation (Fig. 7.19). The Arab D Member represents a regressive sequence from shelf through offshore bars to lagoon with tidal fiats as the final phase. The Arab C Member represents a continuum of the net regressive sequence with dominant intertidal/ shallow-lagoon environments and numerous periods of subaerial exposure within a sabkha environment. The Arab B Member is dominated by sabkha environments with a minor transgression giving rise to a suite of intertidal sediments, whereas the Arab A Member represents the culmination of a net regression with dominant supratidal

environments. The deposits of the Arab Formation indicate a gradual shallowing of the depositional basin, for lagoonal lime mudstone predominates in the west and is replaced laterally by packstone and grainstone formed under shoal conditions. In the central part of Abu Dhabi, the interfingering of shoal, lagoonal and supratidal sediments is indicative of a regressive cycle. However, further to the east, openmarine shelf sedimentation persisted (Fig. 7.19). The sedimentary cycles of the Arab Formation in offshore Abu Dhabi represent a series of regressive intervals, as each begins with shoal lime-sand (grainstone) and passes upward into lagoonal dolomites followed by intertidal, stromatolitic dolomite to terminate in supratidal anhydrites and dolomites (Fig. 7.19). The lower and upper contacts of the Arab Formation in offshore Abu Dhabi are conformable with the Diyab, which here must include equivalents of the Fahahil and Qatar formations; the presence of Trocholina cf. alpina, Kurnubia palastiniensis and Nautiloculina oolithica suggests an Early Kimmeridgian-Early Tithonian age range.

Fahahil Formation (Arab D Member) (early Kimmeridgian). This formation is well-developed in western onshore Abu Dhabi, but it cannot be recognized in wells drilled in eastern and southeastern Abu Dhabi, due either to non-deposition or to a slight erosional unconformity. Its thickness ranges from 137 to 147 m (450-482 ft), and it consists in the lower part of lime mudstone that grades up into wackestone and packstone containing dolomite. However, anhydrite appears to be present only as nodules and not as discrete beds, and the basic environment remained shallow-marine, subtidal to supratidal. The formation is in conformable contact with the overlying and underlying formations. Qatar Formation (Arab A, B and C members) (late Kimmeridgian). In onshore Abu Dhabi, it is composed of 90-125 m (300-400 ft) of mainly dense, dolomitic lime mudstone and fossiliferous wackestone interbedded with anhydrite and dolomite. The common dolostone is interpreted as deposits formed in an extremely shallow to intertidal environment. The contacts are conformable with the Hith and Fahahil formations.

Hith Formation and Its Equivalents (Asab, Mender and Fateh Members) Hith Formation (Tithonian). This formation forms the terminal member of the Jurassic sequence, extending from Saudi Arabia to Bahrain-Qatar and the western part of the U.A.E. In western Abu Dhabi, the formation consists of 72-148 m (236-485 ft) of massive beds of anhydrite showing chicken-wire texture. Interbedded with the anhydrite and light- to dark-colored, sucrosic dolomites are brown to dark-brown, pellety wackestone and packstone that occasionally replace the dolomites (Alsharhan and Kendall, 1994).

263

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 7.18. Lithological interpretation and log characteristics of the Late Jurassic (Arab-Hith Formation) in the U.A.E. In the general absence of fossils, the age of the Hith is taken as Tithonian. It is conformable with the Arab Forma tion or its equivalent below, and with the limestone and dolomites of the Berriasian Habshan Formation above. Here, the boundary is placed abitrarily above the last major anhydrite bed (Fig. 7.19) and assumed to be the Jurassic-Cretaceous boundary. Parallel and close to the edge of the Hith, this usage is not possible (de Matos, 1994), and the faunal content of the lowermost Habshan beds does not provide the exact stratigraphic positioning of the boundary. The formation thins to the east and is not found in eastern Abu Dhabi or Oman, due either to facies change or erosion (de Matos, 1994). In some wells in the onshore region of Abu Dhabi, the distinction between the Qatar Formation and the overlying Hith Formation is not easily made, for the two formations may grade into each other both laterally and vertically. The gradation is the only reflection of changes in depositional 264

environment that, in eastern and southeastern Abu Dhabi, lead to the distinction of the Asab Oolite Member and the Mender Glauconite Member as facies equivalents of the Hith Formation. Asab Member. This member, about 94 m (308 ft) thick, consists mainly of dolomitic lime mudstone grading upward into oolitic grainstone and peloidal, bioclastic wackestone and packstone and represents oolitic bars (shoal lime sand) corresponding to the more open-marine edge of a very shallow platform. Under more protected conditions, some of the grains are coated. Passing from central Abu Dhabi toward Dubai and the northern U.A.E., the Kimmeridgian-Tithonian sequence is controlled by sea-level fluctuations and shows rapid facies changes compared with central and eastern Arabia. In Dubai, the Late Jurassic formations consist of the Hith equivalents (Fateh and Asab members), where the Asab Member found in onshore wells again consists of clean, oolitic grainstone and packstone underlain by thin

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Sedimentary Basins and Petroleum Geology of the Middle East mudstone and dolomite with traces of anhydrite. Traced into offshore Sharjah, the Asab Oolite is represented by packstone and wackestone with subordinate chert, silicifled limestone, glauconite and thin dolomite. Thus, the formation becomes progressively less dolomitic and more limey as it is traced eastward across Dubai into the northern U.A.E. offshore area. It is the facies equivalent of both the Qatar and Hith formations and, thus, covers a time range from the early Kimmeridgian to the end of the Tithonian. An 87Sr and 86Sr analysis of belemnites from the Asab oolite and the Arab A anhydrite from well Bu Tini-3 shows they are identical, and a seismic study of northeast Abu Dhabi reveals a lateral equivalence of the uppermost Arab, Hith and Asab oolite. Therefore, there remains considerable uncertainty on the precise correlation of these uppermost Jurassic beds and their age range (de Matos, 1995. Mender Glauconite Member This member, about 60 m (197 ft) thick and found mainly in the extreme southeast (Mender area) of Abu Dhabi, is composed of more bioturbated, bioclastic lime mudstone with rounded glauconite grains of fine sand size grading up into bioclastic, peloidal packstone. The interpreted environment is a deeper, offshore, low-energy environment, which became shallower and developed a somewhat more energetic regime. Fateh Member It is found in offshore Dubai, where the type section defined in well Fateh-1 reaches up to 300 m (984 ft) in thickness and passes from grain-rich, pelletal and skeletal wackestone/packstone and dolomitic packstone to coarsely crystalline, saccharoidal dolomite. It is equivalent to the Arab and Hith formations of western Abu Dhabi. Conformable contacts also are seen in this member. It is interpreted as deposited in a shallow, subtidal to supratidal setting (Alsharhan, 1989).

The Jurassic of the Northern United Arab Emirates Surface Formations Musandam Group (Jurassic-Early Cretaceous) The term "Musandam Group" was introduced by Lees (1928) for the group of limestone that ranges from the Jurassic into the Cretaceous and covers the major part of the Musandam Peninsula of Oman. At the type locality in Wadi Hagil and Milaha in the northern U.A.E., Hudson and Chatton(1959) divided the Musandam Limestone succession into a series of units generally of formational rank, lettering them from A to P). In 1960, Hudson raised the Musandam Limestone to Group status. De Matos et al (1994) and Toland et al. (1993) studied the Jurassic section cropping out in the northern United Arab Emirates providing detailed record of relative sea level change and yielding vital clues to understanding the biostratigraphy and sequence stratigraphy of the Jurassic. The basal Liassic beds are occasionally sandy and form a condensed interval with crinoids, abundant phosphatic

266

particles, fish debris and bivalves. There is no clear, visible break in sedimentation between the Triassic and Jurassic in the carbonates of Wadi Naqab. If there was interruption in the sedimentation, the hiatus was certainly minor. In their study de Matos et al. (1994) described 366 m (1200 ft) of Lower Jurassic carbonates of Wadi Naqab (Fig. 6.31) and concluded that the Liassic starts with a transgressive, coarse cross-bedded ooidal grainstone and continues with cyclic shallow carbonate sediments composed of multiple peritidal cycles. The base of each cycle is commonly bioturbated and rich in lituolids, algae and oncoids representing a lagoonal subtidal environment. The top of the cycle frequently shows disrupted supra to intertidal laminations locally displaying birdseye structures. Cyclicity is on the meter-scale and, in the Lower and Middle Liassic, cycle tops are commonly marked by paleoexposure surfaces (paleokarst) with dissolution features, calcretes, dolomitization and meteoric cements indicating sea level oscillations. The Middle Jurassic is not studied in detail but represented a thick sequence of shallow water carbonates mainly mudstone, grainstone and packstone containing bioclastic and oolitic, peloidal and oncoidal intraclasts. Toland et al. (1993) studied the Oxfordian succession at Wadi Hagil (Fig. 7.20) and concluded that: the Oxfordian about 102 m (335 ft)thick is equivalent to the Lower Musandam Limestone unit F of Hudson and Chatton (1959). It is made up of three distinct members. The lower member, 16 m (52 ft) thick comprises regressive, thin bedded, fine to very fine sand grade cortoid packstones, characterized by hummocky cross stratification, wave ripple laminae and occasional intraclast lag deposits. This is interpreted as a storm dominated offshore succession deposited above storm wavebase. The middle member is 14 m (46 ft) thick and comprises regressive thin to medium bedded peloidal packstones and grainstones with common partly silicified branching stromatoporoids and dasycladacean algae. The upper member 72 m (243 ft) thick comprises resistant thick-bedded peloidal packstones and grainstones with occasional coral-stromatoporoid floatstone units.

The Jurassic of Qatar Hamlah Formation (Early-Middle Liassic). The name of this formation was first used by Sugden (cited in Sugden and Standring, 1975) in an unpublished report to the Qatar Petroleum Company from the type locality on the west coast of Qatar. The type section proposed by Sugden and Standring (1975) is in well Dukhan-65, where about 75 m (246 ft) was described. The formation consists in the lower part of sandy marl with dark limestone and dolomites with occasional anhydrite streaks interbedded with green shale and gray marl (Fig. 7.12). In the middle of the formation is a zone of shale with subordinate marl

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Fig. 7.20 Sequence stratigraphy of the Jurassic-Early Cretaceous in Wadi Hagil area, northern UAE (compiled from Toland et al., 1993 and reproduced by permission of Society of Petroleum Engineers) and glauconitic sandstone. The upper part of the formation is dominated by dark-colored, saccharoidal dolomites with nodular anhydrite deposited in a nearshore to shallowmarine environment (Alsharhan and Nairn, 1994). Because the formation is unfossiliferous, an Early Jurassic age is assigned based upon regional correlation with adjoining areas. The formation is followed conformably by the Izhara Formation, but rests unconformably on the Triassic dolomite of the Gulailah Formation. lzhara Formation (Bajocian-Early Bathonian). The formation, introduced by Sugden in an unpublished report for the Qatar Petroleum Company and described by Sugden and Standring (1975), was named from a location in central Qatar, where it is regarded as equivalent to the Lower Dhruma Formation in Saudi Arabia. The type section was chosen in well Kharaib-1 in central onshore Qatar. It consists of about 137-150 m (449-492 ft) of a

sequence that begins with fine-grained, dense, argillaceous limestone and dolomite grading up into dolomites that vary from calcareous to dense, porous or saccharoidal and may include dark-gray shale or marl and thin siltstone intercalations(Alsharhan and Nairn, 1994). The formation ranges in age from Bajocian to possibly early Bathonian and was deposited in a shallow-shelf environment. In central Qatar, the Izhara Formation rests unconformably over the Gulailah Formation, while the formation is in conformable contact with the Hamlah Formation in western Qatar. It also is conformable with the overlying Araej Formation. Araej Formation (Bathonian to Callovian or Oxfordian). A third formation, introduced by Sugden and Standring (1975) was named the Araej Formation taken from Jebel Araej in southern Qatar. The type section was established from the records of well Kharaib-1 in central

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic Qatar. From the fauna, Sugden and Standring (1975) assigned the age as Bathonian to Oxfordian and, thus, claimed the formation was equivalent to the middle and upper parts of the Dhruma Formation in Saudi Arabia. The Araej contact is conformable with the underlying Izhara Formation. It is overlain disconformably by the Diyab/ Hanifa Formation (Fig. 7.21). The Araej, which reaches a thickness of 180-200 m (590-656 ft), is divided into three members (Alsharhan and Nairn, 1994): 9 Upper Araej Member: about 47 m (155 ft) of foraminiferal grainstone and packstone with interbedded wackestone and lime mudstone. There are some argillaceous horizons. Pellets often are black and pyritic. It was deposited in a low- to moderate-energy, shallow, open-marine setting; 9 Uwainat Member: about 55 m (180 ft) of buff, medium to coarse-grained, bioclastic peloidal, fossiliferous grainstone and packstone with foraminifera and stromatoporoid algae, deposited under moderately high-energy conditions with occasional returns to low-energy, marine, lagoonal conditions; and 9 L o w er Araej Member: about 100 m (328 ft) of gray lime mudstone and wackestone with some interbedded, peloidal packstone and occasional grainstone in the lower part and dense, light- to dark-gray limestone, and pyritic, peloidal grainstone and packstone in the upper part. It was deposited in a low- to moderate-energy, shallow-marine to lagoonal setting.

Diyab Formation (Oxfordian to Possible Early Kimmeridgian). This formation was named by Sugden and Standring (1975) based upon an earlier report of Sugden prepared for the Qatar Petroleum Company. The name is taken from a locality on the southern part of the Dukhan anticline in western Qatar, and the type section was chosen from the record of about 110 m (361 ft) in well Dukhan51. The formation is made up of three cycles, with each cycle beginning with black, argillaceous, silty and slightly dolomitic limestone grading up into fine-grained, dense lime mudstone and white anhydrite. In the type section, the anhydrite at the end of the third cycle is not recognized. The age of the formation, based on the microfauna identified in the Qatar section, is given as Oxfordian to possible early Kimmeridgian. The formation is followed conformably by the Darb Formation, which is regarded as the age equivalent of the lower Kimmeridgian Jubailah and Hanifa formations of Saudi Arabia and offshore Qatar. It was deposited in an open-marine, outer-shelf setting. Darb Formation (early Kimmeridgian). The formation was proposed by Sugden and the description later included in a publication by Sugden and Standring in 1975. It was named after a solitary sand dune in southern Qatar at Taas al Darb, which marks an ancient track to Mecca. The formation is well-established as a separate formation only in onshore Qatar. The type section was selected in well Dukhan-51, where a thickness of about 230 m (754 ft) is recorded. The formation consists of dense, dark-gray, argillaceous lime mudstone with numer-

ous thin beds containing scattered, large, pyrite-stained pellets. These grade up into more lime mudstone and dolomites, which pass conformably up into the predominantly lime mudstone of the Fahahil Formation. The fauna indicates an early Kimmeridgian age and deposition in an open-marine, outer-shelf setting.

Hanifa and Jubailah Formations (Oxfordian-early Kimmeridgian) These formations are well-developed in offshore Qatar, and both are equivalent to the Diyab and Darb Formations in the onshore area. Hanifa Formation (late Oxfordian). The formation shows significant lateral variation in both thickness and lithology and ranges from 15 to 90 m (50-300 ft),. In the central part of Qatar, the formation consists of thinly laminated, bituminous lime mudstone grading upward into basin-fill shelf carbonates, bioturbated wackestone and peloidal packstone capped by massive, nodular, mosaic anhydrite. Toward the eastin the extreme offshore (e.g., Maydan Mahzam and surrounding areas), the formation becomes much thinner, but the basal, bituminous limestone and the upper anhydrite still are present, indicating that the stratigraphic unit still is complete. The formation was deposited in a relatively shallow-marine environment, mostly below wave base, with only minor differences in depth between the somewhat deeper, organic-rich units and the shallower, bioturbated and evaporitic units (Droste, 1990; Alsharhan and Nairn, 1994). The shallowwater, high-energy carbonates of the Araej Formation are sharply overlain by laminated, dark, bituminous mudstone of the Hanifa. The contact is a hardened, bored and sometimes erosional surface, considered by Murris (1981) to be diachronous (lithoclines). The upper contact is conformable with the Jubailah Formation. Jubailah Formation (early Kimmeridgian). The Jubailah Formation consists of about 100 m (328 ft) of argillaceous, organic-rich lime mudstone and wackestone that grade upward into progressively higher-energy deposits of peloidal packstone and grainstone and minor dolomitic limestone and evaporites deposited on a very shallow shelf bordered by sheltered lagoons and broad tidal flats. The Jubailah overlies the Hanifa and underlies the Arab with a sharp but conformable contact.

Arab Formation and Its Equivalents (Fahahil and Qatar Formations) (Oxfordian-Tithonian) The combined Qatar and Fahahil formations are lateral equivalents of the Arab Formation (Fig. 7.22). The lower part of the Arab Formation in offshore Qatar (Arab D Member) equates to the Fahahil Formation in onshore Qatar). The upper part of the Arab Formation (Arab C to A members) is equivalent to the Qatar Formation in the onshore area. Fahahil Formation (Oxfordian). It was established in Qatar by Sugden in Qatar Petroleum company reports, 269

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic from a location in the Dukhan Anticline near the Dukhan Field.. In the type section, chosen by Sugden and Standring (1975) in Dukhan-66, 60 m (197 ft)of alternating dolomitic lime mudstone and dolomites grade up into grainstone interbedded with packstone, wackestone and skeletal grains in a lime mudstone matrix and end with the formation of anhydrite (Fig. 7.2). The overlying Qatar Formation and the underlying Darb Formation contacts are conformable with the Fahahil Formation. The formation was deposited in an evaporitic, lagoonal and sabkha setting.

Qatar Formation (Kimmeridgian-eady Tithonian?). In onshore Qatar, this formation was named by Sugden (1953) in an unpublished report to the Qatar Petroleum Company and was chosen because it was the first commercial oil reservoir in the Dukhan Field. The type section chosen by Sugden and Standring (1975) in well Dukhan-28 has a thickness of about 89 m (292 ft). Lithologically, the succession consists of light-brown or gray anhydrite and anhydritic dolomites at the base, which grade up into a cyclic, carbonate-anhydrite sequence. The carbonate units of the sequence generally consist of dense, dolomitic, anhydritic limestone and lime mudstone; and oolitic, peloidal grainstone and packstone with minor lime mudstone. The cycles end with massive anhydrite and dolomitic anhydrite. Dolostones that formed in extremely shallow, intertidal conditions are common. The lime mudstone, either laminated or brecciated, associated with the dolostone corresponds to slight variations in a similar tidal-fiat setting. Foraminiferal determinations give an age range of Kimmeridgian-Early Tithonian. Arab Formation (Oxfordian-early Tithonian). This formation in offshore Qatar constitutes the thickest of the numerous depositional cycles of the Late Jurassic (Alsharhan and Nairn, 1994) (Fig. 7.22). The Arab D Member marked a regression from the shallow, open-marine shelf lime mudstone and wackestone with occasional peloidal, tidal-current, shoal grainstone and packstone in the lower and middle parts through subtidal and intertidal, wellsorted, oolitic, peloidal grainstone and packstone, with occasional wackestone extensively dolomitized and leached. The Arab C Member, marked by the deposition of thick, dolomitic packstone and grainstone deposited in an intertidal, channel complex, is followed upward by dolomitized, restricted, lagoonal, algal boundstone, subtidal lime mudstone and wackestone, and laminated, often peloidal packstone and wackestone with occasional intervening, open-marine, shoal grainstone. The Arab B and A members were deposited in depositional sedimentary cycles in a shallow, subtidal to supratidal environment. Each cycle began with algal stromatolite boundstone in a shallow, subtidal-intertidal environment overlain by oolitic, peloidal grainstone/packstone predominantly representing shallow, subtidal to intertidal deposits that often show some evidence of small channels. The cycle was ended by a thick sequence of chicken-wire anhydrite of supratidal origin.

Within the Arab A-D units, low- to medium-energy facies of algal, desiccated or brecciated mudstone, bioturbated mudstone and locally laminated, bioclastic mudstone are interbedded with high-energy, oolitic and peloidal packstone and grainstone often dolomitized and with nodular anhydrite layers. They show trough and oblique cross-bedding. Transitional between the anhydrite and carbonate zones are massive chicken-wire anhydrites. Mainly shallowing-upward sequences are seen culminating in burrowed, desiccated or brecciated surfaces (Bouroullec and Meyer, 1995). The greatest sea-level fall occurred in the Upper Arab D, with an abrupt transition from an offshore to lagoonal backshore environment, but there were numerous local, short flooding events throughout the Arab Formation. l-lith Formation (Tithonian). The reference section of the Hith Formation (Tithonian?) in Qatar was defined in well Dukhan-25, where Sugden and Standring (1975) described about 150 m (492 ft) of white, nodular, chickenwire or massive anhydrite. The succession here includes numerous stringers of brown dolomite and some thin beds of oolitic or dolomitic limestone. Here, the formation formed in a shallow, hypersaline, supratidal setting. The Hith Anhydrite marks the final shallowing and infilling of the long-established Jurassic sea, in which vast thicknesses of carbonates were deposited over much of Arabia (Sugden and Standring, 1975). It is conformable with the overlying and underlying formation.

THE JURASSIC SECTION IN EXTREME EASTERN ARABIA: OMAN In the United Arab Emirates, the Musandam Group has been divided into units 1-4, but the subdivision into AI members (Ricateau and Riche, 1980) is used on the Musandam Peninsula of northern Oman (Fig. 7.23). In central Oman, the term Sahtan Group has been used for surface and subsurface whereas only one formation was described from outcrop in southern Oman which has not been raised to group status.

The Jurassic of Northern Oman Musandam Group (Jurassic-Lower Cretaceous). Over the Musandam Peninsula in northern Oman, the monotonous succession consists of dark-gray, shallowwater limestone,occasionally dolomitic or sandy near the base, and porcellanous, radiolarian mudstone known as the Musandam Group. The thickness is not as great (about 600 m, or 1,968 ft), and nine members (A to I) were recognized by Ricateau and Riche (1980)(Fig.7.23). Members A to F are Jurassic in age (Fig. 7.16) and described below, while members G, H and I are Early Cretaceous in age and will be described in Chapter 9. Mem-

271

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 7.23. Lithostratigraphy of the Jurassic-Early Cretaceous (Musandam Group) in the northern Oman Mountains, (Musandam Peninsula), (modified from Ricateau and Riche, 1980 and reproduced by kind permission of Journal of Petroleum Geology)

Thick banks of lime mudstones,often bioturbated with algae L Argillaceous nodular, limestone Massive dolomite and dolomitic limestone Alternation of lime mudstone and wackestone with brachiopods and algae Massive bioclastic limestone. Shaly sands intercalated with limestones rich in corals and large iamellibranchs

bers A-D are middle Liassic; Member E is middle-late Liassic; and Member F is from Dogger to Maim in age. The limestone in this group shows a generally cyclic nature, with each cycle beginning with massive lime mudstone grading to thinner-bedded, oolitic grainstone, first skeletal then cross-bedded, succeeded by thin, burrowed, bioclastic limestone grading up into mudstone of the next cycle (Glennie et al., 1974). The repeated transgression and regression also mark an overall shallowing of the depositional cycles. This description was expanded by Ricateau and Riche (1980), who described members A and B (270 m, or 864 ft) as regular alternations of fossiliferous,

272

algal lime mudstone and wackestone grading up into dolomites formed from bioturbated limestone in which valvulinids were abundant. Member C (37 m, or 121 ft) is an argillaceous, nodular lime mudstone; members D and E (480 m, or 1,574 ft) are thick banks of bioturbated, algal lime mudstone passing up into rhythmically bedded, marly, lumachelles and algal limestone. The latest Jurassic Member F (370 m, or 1,214 ft), consists of algal lime mudstone with gastropods giving way to packstone with corals. The Liassic was marked by subcontinental sedimentation close to the tide-line and by low-energy carbonate sedimentation, whereas very low-energy sedimentation

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic continued in the Dogger and Malm, and lacunae and condensation mark this active margin of the Arabian Platform. It is clear that the Lower Musandam Group is a facies equivalent of the Sahtan Group in central Oman and of the Marrat to Hith formations in eastern Saudi Arabia.

The Jurassic of Central Oman Subsurface Formations. Although the most distant from the outcrop sections in Saudi Arabia, the Lower and Middle Jurassic succession in Oman more closely resembles the Saudi section than that in onshore U.A.E. Glennie et al. (1974) introduced the teI~ "Sahtan Group" (Fig. 7.2) for the predominantly shallow-marine carbonates that range in age from the late Liassic (Sinemurian) to Oxfordian-Kimmeridgian. The name was derived from the area chosen for the type sections in Wadi Sahtan on the northern flank of the Jebel Akhdar, where about 300 m (984 ft) crop out. Northward, there is a transition from the Sahtan facies to that characterizing the Musandam Group in the Musandam Peninsula. The base of the Sahtan Group rests disconformably over rocks of the Permian Akhdar Group following a brief period of emersion and erosion at the end of the Triassic. Basically, the succession consists of thin sandstone, conglomerates and ferruginous oolites in the lower part, passing up into sandy, fossiliferous limestone; dark-gray mudstone; bioclastic wackestone alternating with thickerbedded, skeletal and peloidal packstone and grainstone; and beds of dolomite. The succession is completed by small depositional cycles of mudstone that grade to grainstone, capped by intertidal stromatolites. The Sahtan Group was divided by Hughes-Clarke (1988) into five formations based upon subsurface sections in western Oman. The lowest, known as the Mafraq, is equivalent to the Marrat of Saudi Arabia, while the remaining four (Dhruma, Tuwaiq Mountain, Hanifa and Jubailah) are terms used in Saudi Arabia and are directly comparable in age

.Sahtan Group (Sinemurian-Early Tithonian). In subsurface, Hughes-Clarke (1988) subdivided the Sahtan Group (Butabul Group of Gorin et al., 1982) into five formations: Mafraq, Dhruma, Tuwaiq Mountain, Hanifa and Jubailah (described above). The group is equivalent to the lower six informal members (A-F) of the Musandam Group of the Musandam Peninsula of northern Oman. Mafraq Formation (Sinemurian-Bajocian). The formation, proposed by Hughes-Clarke (1988), incorporates beds formerly assigned to the Marrat Formation. It occurs throughout Oman, except in those locations where the entire Sahtan Group has been removed by erosion. The type section in well Mafraq-1 has a thickness of 63 m (207 ft) and consists in the lower part of a continental clastic unit laid down during the retreat phase at the end of the Triassic. It grades up into an upper part mainly of ferrugi-

nous, oolitic limestone of a shallow-marine, high-energy environment (Fig. 7.24). This basal unit previously was described in outcrop in the Jebel Akhdar area (Wadi Sahtan) by Glennie et al. (1973, 1974) as a sequence of sandstone, ferruginous oolites and conglomerates, often alternating with limestone and fossil hash. The base rests with a low-angle unconformity on rocks of the underlying Akhdar Group, while the top is followed conformably by the Dhruma Formation. Dating is through the occurrence of relatively rare palynomorphs and microfossils.

Dhruma Formation

(late Bajocian-Callovian).

Beds assigned to the Dhruma Formation crop out frequently in the Huqf and Oman Mountains and in all wells in interior central Oman. When they are missing, it is due to either non-deposition or removal by Cretaceous erosion from over paleohighs. In central Oman, Hughes-Clarke (1988) designated a reference section in the Yibal Field (well Yibal-85), where about 223 m (731 ft) were encountered. The lower part consists of argillaceous mudstone and wackestone with interbedded, marly limestone. The latter contains molluscan and echinoid debris and thinshelled, pelagic lamellibranchs that accumulated in a subwave-base, shelf environment. A change in depositional environment to a shallowshoal to intertidal setting in the upper part of the formation is indicated by the appearance of slightly dolomitic packstone and wackestone and marly limestone (Fig. 7.24). The lower and upper boundaries are conformable with the Mafraq and Tuwaiq Mountain formations, respectively.

Tuwaiq Mountain Formation (late CallovianOxfordian). Less widely distributed than the Dhruma Formation, rocks of this unit are absent from the Huqf region and central Oman Mountains, while beds of the Tuwaiq Mountain Formation are truncated by unconformities in eastern Oman. The formation is known only in the subsurface of the oil-producing areas, where it consists of 128 In (420 ft) of deeper-shelf lime mudstone with pelagic lamellibranchs in the lower beds, overlain by bioclastic to wellsorted, ooidal packstone and grainstone ending with coarsely crystalline, euhedral dolomites. It contains a fauna of corals, foraminifera and algae forming a regressive sequence from a low- to moderate-energy, shallow subtidal setting to moderate- to high-energy, shoal conditions, to an emergent sabkha setting. (Fig. 7.25) (HughesClarke, 1988). It is underlain conformably by the Dhruma Formation and overlain conformably by the Hanifa Formation. Hanifa Formation (early Kimmeridgian). This formation also has a restricted occurrence, for it is found in subsurface only in the westernmost part of interior Oman, where it follows conformably the Tuwaiq Mountain Formation and is succeeded conformably by the Jubailah Limestone Formation (Fig. 7.25). It consists of about 65 m (213 It) of argillaceous lime mudstone and wackestone in the lower part, grading up into fossiliferous packstone and grainstone deposited in a low- to high-energy, shallowmarine setting (Hughes-Clarke, 1988). 273

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 7.24 Lithological interpretation and log characterisitics of the Middle-Late Jurassic (Mafraq, Dhruma and Tuwaiq Mountain Formations) in Oman (modified from Hughes-Clarke, 1988, and reproduced by kind permission of Journal Petroleum Geology).

Jubailah Formation (late Kimmeridgian-early Tithonian). This formation is present only in the subsurface in extreme western Oman, where it is truncated by Lower Cretaceous beds of the Kahmah Group. The formation is made up of 79 m (260 ft) of fine-grained, slightly argillaceous lime mudstone and wackestone with some fine-grained, dolomitic bands formed under low-energy, marine conditions (Fig. 7.25). In the Lekhwair Field in the western Oman Mountains, the formation is represented by deep-water, argillaceous limestone that may be a precursor to the depositional conditions of the Rayda Formation (Hughes-Clarke, 1988). The lower boundary is conform-

274

able with the Hanifa Formation, and the upper boundary always is marked by a hiatus or disconformity, followed by the Kahmah Group.

Surface Formations Sahtan Group (middle Liassic-Oxfordian) Glennie et al. (1974) described the group as consisting of more than 415 m (1,361 ft) of shallow-water carbonates, sandy at the base, which crop out in Wadi Sahtan on the northern flank of Jebel Akhdar. The lower part is composed of thin sandstone alternating with fossiliferous lime-

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic J

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stone. The middle part is dominated by mudstone and bioclastic wackestone alternating with thicker-bedded, peloidal-bioclastic packstone and grainstone. The upper part consists predominantly of mudstone grading to grainstone at the top. The group disconformably overlies the Mahil Formation (Triassic) and is conformably overlain by the Kahmah Group (Early Cretaceous). Saih Hatat Formation (Middle Jurassic). Pratt and Smewing (1990) show that the Middle and Late Jurassic

sections on Saih Hatat are relatively deep-water deposits overlying shallow-water, mixed carbonate-siliciclastic deposits of the Lower Jurassic. They termed the deepwater unit the Saih Hatat Formation and designated the type section in Wadi Qurr off Wadi Tayin on the southern side of Saih Hatat, where about 207 m (679 ft) crop out. They divided it into 10 units, from top to bottom: 9 argillaceous lime mudstone and peloidal-bioclastic packstone: 35 m, or 115 ft; 9 calcareous shale: 5 m, or 16 ft;

275

Sedimentary Basins and Petroleum G e o l o g y o f the M i d d l e East

9 9

9 9 9 9 9

and argillaceous lime mudstone and thin-bedded, peloidal packstone: 11 m, or 36 ft. The lower and upper contacts of the Saih Hatat are conformable. The lower part rests on thick-bedded, oolitic and intraclastic grainstone, and the upper part is in contact with dark-colored, thin- to medium-bedded, argillaceous lime mudstone, shale and fine-grained, peloidal-bioclastic grainstone. Both the lower and upper sediments belong to the undivided Sahtan Group (Pratt and Smewing, 1990). The Saih Hatat Formation is equivalent in subsurface to the Dhruma, Tuwaiq Mountain and Hanifa formations.

peloidal grainstone: 6 m, or 20 ft; calcareous shale, argillaceous lime mudstone and thin-bedded (locally bioturbated), peloidal-bioclastic grainstone: 50 m, or 164 ft; lime mudstone and peloidal-intraclastic-bioclastic grainstone: 30 m, or 98 ft; argillaceous lime mudstone and thin, lenticular-bedded, locally bioturbated grainstone: 40 m, or 131 ft; peloidal, partly silicified grainstone: 3 m, or 10 ft; thin-bedded, argillaceous, locally bioturbated lime mudstone: 24 m, or 79 ft; medium-bedded, peloidal grainstone: 3 m, or 10 ft;

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Fig. 7.26. Lithostratigraphic interpretation of Jurassic-Cenomanian (Mayhah Formation) in the central Oman Mountains (modified from Watts and Blome, 1990, and reproduced by kind permission from the International Association of Sedimentology).

276

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic

Ai OOID SHOALS

RAMP MARGIN RARE LOCALIZED SLUMPS

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THIN-BEDDED, BIOTURBATED LIME MUDSTONE AND WACKESTONE COMPOSED OF PELOIDS, SPONGE SPICULES AND RADIOLARIANS, RARE OOLITIC PACKSTONE/GRAINSTONE

BI DROWNED PLATFORM (RAMP)

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"DISTAL" MARGINAL BASIN SILICIF1ED LIMESTONE AND RADIOLARIAN CHERT

Mayhah Formation (Liassic-Cenomanian). In eastern Arabia, Mesozoic slope facies about 750 m (2,460 fi) are coeval with the Arabian Platform carbonates. These slope facies are assigned to the Liassic-Cenomanian Mayhah Formation (Fig. 7.26) of the Sumeini Group and are exposed in thrust-bound slices in several places along the western edge of the Oman Mountains (Glennie et al., 1974; Watts and Garrison, 1986). The succession of deeper-water sediments deposited in the Hawasina Basin of Oman also occurs as allochthonous, successively underplated, thrust-bound packages along the western and southern Oman Mountains, where they comprise the Hamrat Duru Group (Triassic-Middle Cretaceous). Several lithologic units within the Mayhah Formation were mapped and described by Watts and Garrison (1986) and Watts and Blome (1990); the lower part of the sequence, the Middle and Late Jurassic Member A, is coarse, redeposited limestone that passes upward into fine-grained lime mudstone and marlstone. Tithonian to Valanginian members B and C are bedded chert and thin beds of chertclast breccia, respectively. The Valanginian to Cenomanian Member D is thin-bedded lime mudstone and wackestone. Only members A and B are described in this chapter. Member A (Liassic-early Tithonian). The 400 m

(1,312 ft) thick Member A consists of thin-bedded lime mudstone and peloidal wackestone with channelled and lenticular calcirudites and oolitic calcarenites (Fig. 7.27). The upper part of Member A contains most of the thick, lenticular, coarse-grained, peloidal and intraclastic packstone (Watts and Garrison, 1986) showing numerous amalgamation surfaces and graded bedding. The thinly bedded lime mudstone appears to have formed on a deep marine periplatform, with the finely laminated, peloidal packstone deposited by turbidity currents. Watts and Garrison (1986) concluded that the thick apron of thinly bedded, periplatform limestone of Member A accumulated on the continental slope, which was cut by numerous gullies now filled with lenticular wackestone/packstone. Rotated limestone slump blocks and slide scars in associated thin-bedded calcilutite also indicate a carbonate slope environment (Watts and Blome, 1990). Ooids in packstone and grainstone facies were derived from ooid shoals at the platform margin, while coralline limestone suggests that reefs also existed at the shelf edge (Fig. 7.27). Member B (Tithonian-Valanginian). It ranges in thickness from 15 to 34 m (49-112 ft) of chert representing silicified, radiolarian lime mud that is extensively recrys-

277

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 7.28. Lithostratigraphic interpretation of Middle-Late Jurassic (Guweyza Sandstone Formation) in the central Oman Mountains (modified from Cooper, 1987).

Fig. 7.29. Lithostratigraphic interpretation of Middle-Late Jurassic (Guweyza Limestone Formation) in the central Oman Mountains (modified from Cooper, 1987).

tallized. The chert of Member B may have formed in response to platform submergence and the concomitant reduction in the supply of shelf-derived carbonate (Fig. 7.27) (Watts and B lome, 1990).

Duru Group and is composed of 208 m (682 ft) of three packets of meter-thick, bedded, oolitic grainstone separated by two intervals of graded, turbiditic wackestone and lime mudstone with only minor, oolitic, grainstone intercalations. At the top of the formation is a fining-upward sequence that has a well-developed, conglomeratic limestone at its base (Fig. 7.29) (Cooper, 1987). The sediments were deposited in high-energy, oolitic shoal grading laterally into discontinuous, channel-fed, carbonate fans. The lower boundary is marked by oolitic grainstone above quartz-bearing, lithoclastic grainstone or quartz-arenites and shale of the Guweyza Sandstone Formation. The upper boundary is marked by rapid transition to the chert and silicified limestone of the Sidr Formation. In the southern Oman Mountains, large volumes of oolitic sediments accumulated at the shelf edge were emplaced into deeper-water environments during distinct episodes to form large, unconfined sheet deposits superimposed on turbidity-current and hemipelagic deposits. In the central Oman Mountains, the input of carbonates by turbidity currents and as hemipelagic deposits were greatly reduced. Widely developed conglomerates at the top of the Guweyza indicate regional destabilization of the shelf

Guweyza Sandstone Formation (early Middle Jurassic). The second rock unit in the Hamrat Duru Group, the formation consists of about 200 m (656 ft) of decimeter- to meter-bedded grainstone turbidites containing quartz grains and forming bands a few tens of centimeters to a meter thick. Interbedded with the grainstone are lime mudstone and marly shale. These beds are succeeded by about 50 m (164 ft) of silicified, radiolarian wackestone and a capping of limestone conglomerates and quartzbearing grainstone (Fig. 7.28) (Cooper, 1987). Quartz sands were admixed with shelf-edge carbonate sands transported by turbidity currents into a deep-water environment. A conformable transition from the Zulla Formation (Triassic) is seen in the Sumeini area and Hawasina window. The top of the formation is marked by a rapid reduction in sandstone and an increase in oolitic limestone of the Guweyza Limestone Formation.

Guweyza Limestone Formation (mid-Late Jurassic). The formation is the third rock unit in the Hamrat 278

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic

AG E

LU RESTAN GOTNIA~

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The Jurassic of South Oman Kohlan Formation (Early-Middle Jurassic). This contains the only Jurassic sediments recorded from South Oman (Dhofar). They crop out near Ras Sajar, where they again consist of coarse- to medium-grained, multi-colored, arkosic sandstone with intervals of green and purple siltstone and shale, and conglomerate bands of quartz pebbles that may pass into sandy marl and calcareous or partly dolomitized, ferruginous, indurated, lagoonal sandstone. According to Hawkins et al. (1981), a local high may have sourced these sediments. The variations in thickness from 17 to 81 m (56-266 ft) reflect topographic irregularities of the basement on which the sediments rest and are consistent with a restricted origin.

THE JURASSIC SECTION ON THE EASTERN SIDE OF THE ARABIAN GULF: SOUTHWESTERN IRAN The Jurassic sediments on the eastern side of the Arabian Gulf are represented by two different facies, one in Lurestan Province and the adjacent part of Khuzestan Province (SW Iran) and the other in the coastal and interior of Fars Province (Figs. 7.30). They have been described in detail by James and Wynd (1965) and Setudehnia (1972) and summarized below. This brief overview of the eastern side of the Arabian Gulf clearly shows a continuity with the sequences seen to the west. Facies changes are small and mostly indicate an increase in carbonate content with a corresponding decrease in clastic content. There does not appear to be much of an increase in water depth, as indicated by the high proportion of dolomites, even after excluding secondary dolomitization. Neyriz Formation (Liassic).A Liassic formation was named by James and Wynd (1965) after the town of Neyriz in Fars Province, Iran,. It has a thickness of about 350 m (about 1,148 ft) and consists in the lower part of thinly bedded rubbly dolomites, followed by shale, dolomites and medium to thick, locally brecciated dolomite. The upper part of the section begins with dolomite and dolo-

mitic limestone, siltstone, silty shale and sandstone that are capped, in turn, by thinly bedded to finely laminated, argillaceous dolomites (Fig. 7.30). The sediments are characteristic of shallow water marine conditions. Both contacts are conformable, but whereas the lower is a sharp lithological break, the upper is gradational to the Adaiyah Formation. An early Liassic age usually is assigned to the formation, and it is correlated with the Marrat of Saudi Arabia and the Baluti Shale of Iraq. Adaiyah Formation (Early Jurassic). According to Setudehnia (1972), the formation consists of about 63 m (206 ft) of shallow marine, subtidal to supratidal environments where anhydrite is interbedded with dolomite and dark shale (Fig. 7.25). It is conformably overlain by the limestone of the Mus Formation and rests conformably upon dark-gray shale and limestone. Mus Formation (Early Jurassic). The Mus Formation comprises about 56 m (184 ft) of shallow marine limestone (Fig. 7.25), in part correlated with the Mus Formation of Iraq (Setudehnia, 1972). It is underlain by the anhydrites and dolomites of the Adaiyah Formation and overlain by the anhydrites of the Alan Formation. Both contacts apparently are conformable. Alan Formation (Middle Jurassic). This formation consists of about 90 m (295 ft) of bedded anhydrite with subordinate limestone deposited in a restricted supratidal to intertidal setting (Fig. 7.30). Sargelu Formation (Bajocian). The thickness of the formation ranges from 160 to 220 m (525-722 ft) of deeper water marine shale and argillaceous limestone. It is disconformably overlain by the Najmah Formation (Fig. 7.30). It occurs in subsurface and in outcrop in northern Lurestan Basin. The age is given as Bajocian, which, if correct, means that only part of the formation is present compared with areas on the other side of the Arabian Gulf. Najmah Formation (?Middle-Late Jurassic). This formation has been found only in wells that also penetrate the Sargelu Formation. It is made up of about 19 m (62 ft) of shallow marine, pellety, algal limestone (Fig. 7.30). It is underlain disconformably by the Sargelu Formation and overlain by the anhydrite of the Gotnia Formation. Gotnia Formation (Late Jurassic). The Gotnia Formation, which crops out in northern Lurestan at Tang-e

279

Sedimentary Basins and Petroleum Geology of the Middle East Haft, has also been found in wells in the Emam Hasan and Masjid-e-Suleiman Fields. It has a subsurface thickness of about 141 m (462 ft) of anhydrite with subordinate dolomite and dark-gray shale (Fig. 7.30). It is considered primarily a relatively deep-water anhydrite. Dolomite solution breccias occur in outcrop. A disconformity may be found at outcrop at the top of the Gotnia, where it lies under the Garau Formation. l-lith Formation (Late Jurassic). It consists of evaporites, (anhydrite and gypsum, with interbedded dolomite totalling 75-94 m (246-308 ft) in subsurface areas of coastal Fars near the Arabian Gulf. It was deposited mainly upon intertidal fiats or in supratidal conditions with penecontemporaneous replacement phenomenon. In the Kuh-e Sunneh, the formation is made up of 24 m (79 ft) of brecciated dolomite, with the evaporites having been removed in solution. In the interior Fars Province, the evaporites give way to a dolomitic facies, and the formation pinches out toward Bandar Abbas (southeastern Iran). The precise age determination of these anhydrites is not possible due to the lack of fossils. A Late Jurassic age, however, has been assumed for this formation. The Hith Anhydrite overlies the limestone and dolomites of the Surmah Formation and underlies the limestone of the Fahliyan Formation. Both the upper and lower contacts seem to be conformable. Surmah Formation (Early to Late Jurassic). The formation name is taken from Kuh-e Surmah in the Fars Province, where it is best developed. It also is found in the northeast Khuzestan and northeast Lurestan provinces. As described by James and Wynd (1965) and Setudehnia (1972), it consists of about 689 m (2,260 ft) of shallow water carbonates, dominantly thick-bedded to massive, fine-grained dolomites succeeded by thin- to massive-bedded, fine to coarsely crystalline dolomite and limestone that is partly cherty (Fig. 7.30). Both the upper and lower contacts are conformable and transitional. Toward Iraq, the beds of the formation become better differentiated and are replaced gradually by shale, limestone and anhydrite assigned to the Adaiyah, Mus, Alan, Sargelu, Najmah and Gotnia formations (Setudehnia, 1972). This is consistent with the fauna retrieved from the formation, which indicates that its age spans from the Early to Late Jurassic.

T H E JURASSIC SECTION IN NORTHEASTERN

ARABIA Northeast from the Saudi Arabia type area, the principal source of information on the Jurassic succession is from Iraq (Fig. 7.3); the data from Kuwait, mainly from Owen and Nasr (1958), Bou Rabee (1986, 1996) and Yousif and Nouman (1995), are more-or-less complete and substantially modify the basic pattern of facies distribution (Fig. 7.31). In Iraq, where the basic information is taken from Bellen et al., (1959) and Buday (1980), there is a thick Lower Jurassic section, which generally indicates a

280

lower Liassic transition toward to northeast from a shallow, littoral environment into a shallow, lagoonal setting. In the upper Liassic in the northern Foothills Zone of Iraq, there is evidence of the existence of a normal, marine environment. Over much of this northern area during the Dogger and into the Maim, an intrashelf basin that had begun to develop as early as the late Liassic is distinguishable. Although it is not possible to specify the depth of the basin, it was sufficient for euxinic conditions to develop. It persisted until the Tithonian, when shallow-water, evaporitic conditions (Gotnia Formation) developed over the entire area (7.32).

The Jurassic of Kuwait In Kuwait, all the oil discoveries relate to Cretaceous and Tertiary reservoirs, and only a few wells have been drilled to test for oil potentially trapped in Jurassic formations in the Minagish, Sabriyah, Burgan, Magwa, Ahmadi, Umm Gudair, Abduliyah and Dharif fields. The total thickness of Jurassic sediments ranges from 550 to 6,616 m (1,800-21,700 ft). An ideal section of the Jurassic sediments in Kuwait is chosen in the Minagish Field (Fig. 7.31), where the stratigraphic sequence is composed of six formations, as described by Alsharhan and Kendall (1986), Bou Rabee (1986), Yousif and Nouman (1995,1996) and Ali (1995) and summarized below. Marrat Formation (l-lettangian-Toarcian?). The name "Marrat Formation" has been retained for an early Liassic sequence, which has a maximum thickness of 550700 m (1,800-2,300 ft) in the Burgan Field. The formation is thinnest (as far as is known) in the Sabriyah Field. The succession consists of a lower alternation of argillaceous limestone and soft, microporous anhydrite with dolomite, followed by an upper section of partly dolomitized limestone and microcrystalline dolomite. The Marrat Formation was subdivided into five units (from top to bottom): A, B, C, D and E. Unit C is considered the most important and is the deepest oil trap known so far in Kuwait. The formation was deposited under restricted, supratidal to intertidal-subtidal conditions. The overlying conformable beds are assigned to the Aalenian (Dhruma Formation). Marrat is the age equivalent of the Butmah (limestone), Alan (anhydrite), Mus (limestone) and Adaiyah (dolomite) formations of southern Iraq.

Dhruma Formation (Aalenian-early Bajocian). The formation varies in thickness from 30.5 to 61 m (100200 ft), consists of calcareous shale with occasional limestone interbeds and is considered an excellent cap rock over the Marrat reservoir. It shows a thinning section occurring at the central portion of Kuwait and trending north-south from the Magwa to Sabriyah fields, abrupt thickening at Ahmadi and gradual thickening toward western Kuwait from Abduliyah to Rugei. Here, the limestone tends to be lime mudstone and contains a few bioclastic wackestone and packstone intercalations with radiolaria.

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic

GENERAL DESCRIPTION

Anhydrite interbedded and intermixed with limestone and minor shale

Salt and anhydrite interbeds with occasional limestone and shale streaks

Interbedded packstone, argillaceous limestone and bitumen Interbedded wackestones, muds tones,grainstones and bitumen Shale with limestone lamination Interbedded limestones, wackestones and calcareous

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Limestone with occasional packstones and grainstones and minor shale, dolomite and anhvd~

Interbedded lime mudstone, dolomite, anhydrite and shale

Interbedded limestone, dolomite and anhydrite

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Fig. 7.31 Lithostratigraphic units of the Jurassic section of Kuwait (modified from Yousif and Nouman, 1995, 1996 and reproduced by kind permission of Gulf Petrolink, Bahrain). AN anhydrite units 1-4, ST salt units 1-4 281

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Fig 7. 32 Jurassic - Cretaceous lithostratigraphic correlation in Iraq. Formations and ages based on Bellen et al., 1959, Owen and Nasr, 1958 and Buday, 1980 Locally, some of the limestone is impregnated with a kerogen-like material. These sediments were deposited in an outer-neritic environment (Marrat and Sargelu formations, respectively). Sargelu Formation (Bajocian-Bathonian?). The thickness of the formation varies from 76.22 m (250 ft) in the Burgan Field to about 33.54 m (110 ft) in the Sabriyah Field. Lithologically, the Sargelu beds show an increased proportion of argillaceous limestone. The calcareous and carbonaceous shale may contain occasional plant remains. Intercalations of oolitic limestone are found in the lower and upper parts of the formation, indicating deposition in a marginal-marine environment. The entire Sargelu Formation represents a stage in the evolution of a new regressive cycle, where intertidal, peloidal packstone overlies subtidal, argillaceous lime mudstone. The formation possesses oil potential in some areas. The formation is conformably overlain by and conformably underlies the Dhruma and Najmah formations, respectively.

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Najmah Formation (Callovian-Oxfordian). The formation consists of argillaceous limestone and locally contains from 24 to 104 m (80-340 ft) of interbedded, bituminous and calcareous black shale. The formation thins in central Kuwait and trends north-south from the Magwa to Sabriyah fields. There is an abrupt thickening at Ahmadi and a more gradual thickening towards western Kuwait (from Abduliyah to Rugei), where the limestone tends more towards lime mudstone with a few bioclastic (radiolarian) wackestone and packstone intercalations. Locally, some of the limestone is impregnated with a kerogen-like material. These sediments represent deposition in an outerneritic environment. Deep-water, euxinic conditions are inferred from the presence of black, ammonitic, radiolarian limestone. As reducing conditions are favorable for the accumulation of the organic materials, the formation currently is considered the best source rock for oil generation in the entire Jurassic section, and there is some oil production from the fractured limestone of the Najmah Formation

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic in some areas within Kuwait. The top of the Najmah Formation has been considered an unconformity, and the top is identified easily below the Gotnia evaporites. Gotnia Formation (Kimmeridgian). The formation has a thickness ranging from 229 m (750 ft) in eastern Kuwait close to the axis of the Kuwait Arch to more than 457 m (1,500 ft) on the western side of the arch in the Minagish Structure. The Gotnia Sequence is complete in the southern and western areas of Kuwait, but shows a remarkable thinning towards northeastern Kuwait across the crest of structures such as the Raudhatain, Sabriyah and Dhabi arches. The Gotnia Formation consists of the cyclic alternation of four salt and four anhydrite-limestone units. The salt is white to clear and crystalline, whereas the anhydrite is light- to dark-grey or white, earthy or argillaceous. The anhydrite interbeds are mostly interbedded with fossiliferous, argillaceous limestone, shale and some bitumen. Deposition occurred in a supersaline lagoon, so fossils are rare and consist of some ostracods and small gastropods of little stratigraphic value. The Jubailah, Hanifa and Arab formations of Saudi Arabia are the equivalents of the Gotnia Formation of Kuwait; however, the Gotnia Formation in South Iraq is equivalent to both the Gotnia and Hith formations of Kuwait. Ali (1995) demonstrated that the variations in thickness of salts across the Kuwait arch, the absence of the first unit in the north and the disappearance of three units in the south between Umm Gudair and Wafra was consistent with penecontemporaneous growth of the arch and a northward tilt. The more uniform thickness of the upper units implies growth of the Kuwait Arch ended in the upper Gotnia. The Gotnia Formation formed in an evaporitic basin in the northern Arabian Gulf, which extended from the Euphrates River in Iraq to the onshore northern Wafra Field and also includes the offshore Lulu Field in the Kuwait-Saudi Arabia Divided Zone. Hith Formation (Tithonian). The formation varies in thickness from 61 m (200 ft) at Dhabi to 335 m (1,100 ft) in the Rugei fields. Southwestern Kuwait was a very mobile zone at the end of the Jurassic, and during the deposition of the Hith, it received a much thicker sequence of sediments than the rest of Kuwait. The Hith consists of a sequence of massive anhydrites interbedded and intermixed with argillaceous limestone and minor shale. In southwest Kuwait, the Hith consists of a thick sequence of interbedded lime mudstone, anhydrite and shale deposited in a sabkha-lagoonal setting. The Hith conformably overlies and underlies the Gotnia and Sulaiy formations, respectively. It act as an effective and excellent cap rock for the pre-Gotnia reservoirs.

The Jurassic of Iraq 1. Liassic Section of Iraq Ubaid Formation ("Liassic"). This formation, first described by Dunnington (1940, cited in Bellen et al., 1959), crops out in the western desert of Iraq in an area of outcrop restricted to the Rutbah uplift. The formation is not known elsewhere. Two members are recognized: the lower 25-30 m (82-98.5 ft) consist of coarse-grained and argillaceous sandstone with interbedded, variegated marl. The upper 40-50 m (131-164 fi) consist of recrystallized, oolitic-peloidal, sandy limestone with abundant chert and some minor beds of shale. The fauna, identified by Bellen et al. (1959), gives a Liassic (unspecified) age and indicates a shallow littoral to lagoonal environment. The lower contact of the formation proves to be disconforrnable. The formation rests on the eroded surface of the Zor Hauran Formation and is clearly of transgressive character. The upper boundary is unconformable and marked by beds of the Middle Cretaceous Rutbah Sandstone Formation. Butmah Formation (early Liassic). The Butmah Formation does not crop out, although it is found in nearly all subsurface sections from the Foothills Zone to the Mesopotamian Zone. As described by Bellen et al. (1959) and Buday (1980), it consists of three units: a lower 120 m (or about 394 ft) succession of limestone with some interbedded anhydrite, followed by a middle unit of about 180 m (590 ft) of oolitic and peloidal limestone, argillaceous and detrital limestone, which include some sands, shale, dolomitic limestone and glauconite. The upper unit, 200 m (656 ft) thick, consists of oolitic-peloidal limestone, some detrital limestone with shaly interbeds, and some anhydrite. The Butmah Formation was laid down in a lagoonal environment with some clastic input, substantially less, however, than that found in the beds of the Ubaid Formation. The macrofaunal debris, ostracods and forminifera indicate a Liassic age. The basal contact is conformable with, and grades down into, the underlying Baluti Shale. The top contact is abrupt, marked by the thick-bedded anhydrites of the Adaiyah Formation. Baluti Formation (Rhaetic). The formation is made up of 35-80 m (115-262 ft) of gray-green and gray shale with thin, intercalated, dolomitic, silicified, oolitic limestone and recrystallized breccias formed in a lagoonal to estuarine environment (Buday, 1980). The lower and upper contacts of the formation are conformable and gradational. The formation is confined to the outcrops on the High Folded, Imbricated and Northern Thrust zones. Adaiyah Formation (late Liassic). The Adaiyah Formation, found in the Mesopotamian and Foothills zones of Iraq, was named by Dunnington from well Adaiyah-1 (Dunnington, 1953, cited in Bellen et al., 1959) for a sequence of 30-100 m (98-328 ft) of bedded anhydrites with subordinate inclusions of brownish limestone; black,

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Sedimentary Basins and Petroleum Geology of the Middle East calcareous shale; greenish marl; and an occasional salt bed, an almost pure, evaporitic, lagoonal facies. Fossils are rare, mainly gastropod, echinoid debris and small ostracods. The age, therefore, is based on regional stratigraphic considerations. It shows a gradational passage up into the carbonates of the Mus Formation.The formation is distributed throughout the Foothill and Mesopotamian zones of the mobile shelf and along the edge of the stable shelf in Iraq and Syria to the north of, and around, the Euphrates River. Mus Formation (early Toarcian). The formation was first defined in well Butmah-2 in Iraq, which lies in the Foothills Zone, by Dunnington (1953, cited in Bellen et al., 1959). In the wells that penetrate the formation, it has a thickness in the 30-40 m (98-131 fi) range, made up of recrystallized and dolomitized limestone interbedded with marly limestone and subordinate, calcareous shale in the lower part, passing into the upper section of peloidal, slightly dolomitic limestone with intercalations of marly limestone (Bellen et al., 1959). According to the relatively abundant fauna, the age of the formation is late Liassic, although the fauna does not suffice for precise age identification, and the probable early Toarcian age assigned (Bellen et al., 1959; Buday, 1980) was based on faunal and facies comparison with the Sekhanian Formation in the thrust area of Northeast Iraq and Southeast Turkey. The formation has roughly the same distribution as the underlying Adaiyah (anhydrite) Formation in the Foothills and Mesopotamian areas of the unstable shelf and may occur on the stable shelf north of the Euphrates River. It also has been recognized in the adjacent areas of northeastern Syria, and it is represented to the north by the middle "Lithiotis Limestone" Member of the Sekhanian Formation. The Mus Formation was deposited in a normal marine environment and, thus, represents an interval of more normal salinity between two intervals marked by the development of evaporitic lagoons. The upper and lower limits of the formation usually are conformable and gradational; however, in well Mileh Tharthar-1, the overlying Alan has a basal, sandy conglomerate over an erosional unconformity (recognized by Bellen et al., 1959; but not by Dittmar et al., 1971, in Buday, 1980). Tentatively recognizing this break, it has been correlated with an "intra-Liassic break" indicated in the Butmah Formation by a clastic incursion, and with the break between the Ubaid and Muhaiwir formations in the Rutbah-Ga'ara area of western Iraq. Alan Formation (latest Liassic). The formation is found on the western parts of the unstable shelf and stable shelf area and has the same areal distribution as the underlying Mus Formation. It is composed of bedded anhydrites with thin, pseudo-oolitic limestone, and halite also may occur in some areas. In thickness, the formation ranges from 0 to 60 m (0-197 ft), with the anhydrites frequently wedging out. The formation is unfossiliferous; hence, its assigned age, latest Liassic, depends upon its stratigraphic position. The formation is a typical product of an evapor-

284

itic stage of sedimentation at the end of the Liassic cycle. The evaporitic lagoons were not present throughout the entire basin, and in some areas such as Ain Zalah, they were replaced by calcareous, lagoonal or neritic sediments (Buday, 1980; Bellen et al., 1959). The formation has conformable and gradational contact with both the underlying and overlying formations. Sarki Formation (early Liassic). In the High Folded, Imbricated and Thrust zones of northern Iraq, the Liassic sequences have different formational names. The Sarki Formation was first named and described by Dunnington (1952, in Bellen et al., 1959). It is widely distributed and has two divisions. The lower 120 m (about 394 ft) consists of thinly bedded, cherty and dolomitic limestone, alternating with shale, saccharoidal dolomite, shell breccias, microconglomerates and oolitic limestone. The thicker upper unit (180 m, or about 590 ft) is made up of soft, cavernous dolomite and cherty dolomite, alternating with thin shale and marl. The fauna it contains suggests an early Liassic age. The formation maintains a generally dolomitic character throughout, although there is considerable thickness and lithological variation, and the two-fold division described can be maintained only in the type area of northern Iraq. The formation can reach a thickness of the order of 500 m (1,640 ft) in the northern ranges. The generally accepted interpretation of the depositional environment is of a lagoonal evaporitic setting, but as evaporites are few, and recrystallization breccias do not form an appreciable thickness, more accent may be placed on shallow, neritic conditions with frequent lagoonal intervals (Buday, 1980). The fauna, which contains small gastropods and non-diagnostic foraminifera in addition to fish and algal debris, establishes a Liassic age, while the early Liassic age depends upon stratigraphic position between the well-dated Late Triassic (Kurra Chine Formation) and the topmost Liassic and Bajocian Sargelu Formation. It probably is closely correlative with the Butmah Formation and with the upper part of the Dolaa Formation of Syria. Sekhanian Formation (late Liassic). The Sekhanian Formation has a distribution similar to that of the Sarki Formation in the High Folded and Thrust zones of northeastern Iraq. First named and described by Wetzel and Morton (1950, cited by Bellen et al., 1959), the formation has been divided into three members discernible only in the type area; elsewhere, the potential divisions are obscured by intensive dolomitization. The lower member consists of 85 m (279 ft) of dark, sucrosic dolomite and dolomitized limestone with some solution breccias. The middle member of about 44 m (144 ft) is made up of fossiliferous and peloidal limestone; the so-called Lithiotis Limestone Member often is dolomitized and contains chert. The upper member has about 51 m (167 ft) of dark, fetid, saccharoidal dolomite and dolomitic limestone again containing some chert. The upper and lower boundaries of the formation are clear and conformable; however, the upper boundary with the Sargelu Formation is obscured by dolomitization in some places.

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic In the Northern Thrust Zone, although a three-fold division can be recognized, there are some facies differences, and dark, fetid dolomites and dolomitic limestone predominate. However, the fauna recovered shows close resemblances to the Lithiotic limestone fauna, and a local formational name, Zulam Formation, has been applied to these Sekhanian equivalents (Buday, 1980). The formation may equate to the Mus-Alan-Adaiyah formations of the Mesopotamian and Foothills zones and to the middle and upper parts of the Marrat Formation of Saudi Arabia (Buday, 1980). The formation was deposited under neritic conditions, but occasionally shows lagoonal-evaporitic influences in the lower part, with the incoming of more euxinic conditions in the middle and upper parts.

2. The Dogger Section of Iraq The Dogger in this section north from Saudi Arabia is represented by only two formations: the Muhaiwir, which occurs over that part of the stable platform lying south of the Euphrates River; and the Sargelu Formation, which replaces it north of the river. Muhaiwir Formation (Bathonian). The Muhaiwir Formation was first described by Wetzel (1951, in Bellen et al., 1959). It is distributed in outcrop and subsurface sections over the stable shelf of Iraq south of the Euphrates River only. Surface sections are of the order of 50 m (about 164 ft) in thickness. It is a persistent of relatively heterogeneous assemblage with the dominant lithology being marly, oolitic and sometimes sandy limestone. Interbedded with the carbonates are alternating sandstone and soft, marly and fine-grained limestone. The uppermost part is a purely carbonate section of limestone and marly limestone. The formation was deposited under neritic conditions in a sea of normal salinity. It contains an abundant fauna that clearly indicates a Bathonian age, but no evidence has been found to indicate the presence of Bajocian either in the type area or in wells. At the top of the formation, there is a clear unconformity with the overlying Cretaceous Rutbah Sandstone. Because of poor outcrop, the lower boundary cannot be clearly defined. Sargelu Formation (Liassic-Bathonian). The formation, which crops out in the High Folded and Imbricated and Northern Thrust zones, is widely distributed in subsurface south as far as the Euphrates River. It was first recognized and described by Wetzel (1948, in Bellen et al., 1959) in the High Folded Zone, where it ranges in thickness from 20 to 125 m (66-410 ft). However, over the Foothills Zone and in the unstable shelf part of the Mesopotamian Basin, the thickness increases to 250-500 m (820-1,640 ft). Lithologically, it is a fairly uniform formation consisting of thinly bedded, black, bituminous limestone, dolomitic limestone and thin, papery shale. Streaks or lenses of black chert are found in the succession's upper part (Bellen et al., 1959). Although the depositional environment was generally euxinic, the degree of aeration var-

ied, and some layers show a higher degree of oxygenation. The relatively abundant fauna in the Sargelu beds indicates an age ranging from the latest Liassic to Bathonian. However, as a possible Middle Jurassic age has been assigned to Posidonia faunas found in the underlying Sekhanian Formation, there must either be an error in the age assignment, or the boundaries between the two formations may be diachronous or simply facies-controlled. The depositional environment provides evidence of the development of an intracratonic, euxinic basin, so the appearance of aerated conditions and the similarities of the fauna would suggest that the basin never reached any great depths, although the thickness changes show that the total subsidence reached several hundred feet. The base of the formation is not well-defined and appears to be both conformable and gradational, but it is obscured by dolomitization, as remarked earlier. The top of the formation is an erosional unconformity, and much of the Callovian may be absent (Bellen et al., 1959).

3. The Maim Section of lraq (Early Cycle, Oxfordian-early Kimmeridgian) As Buday (1980) pointed out, the break that can be recognized in Iraq at the beginning of the Dogger is related to the proximity of parts of the region to the continental margin where Kimmerian tectonic activity was occurring in the internal part of the Alpine Geosyncline. The very existence of the intrashelf basin, which developed during the Dogger, is related to these events. The effects of the tectonic movements are felt very little in the stable shelf area. Within the Maim, there are two sub-cycles separated by a minor sea-level fall at the end of the Kimmeridgian (Haq et al., 1988). The upper sub-cycle continues into the Berriasian (Early Cretaceous). Both formations of the lower sub-cycle, the Najmeh and Gotnia, are assigned the same age limits, as it appears clear that the Gotnia anhydrites may be both underlain and overlain by Najmeh carbonates. Thus, the "Gotnia Formation" merely represents an evaporitic lithofacies, and the two facies appear to interfinger in the Kirkuk section. In the High Folded and Northern Thrust zones, the time-correlative beds are the Barsarin and Naokelekan formations. Both formations are condensed and may have numerous breaks in sedimentation, but despite this, the depositional environments indicated do not differ significantly from those found in the Lurestan Basin.

Najmah Formation (Callovian-early Kimmeridgian). The early Late Jurassic sub-cycle includes the Najmah and Gotnia formations, which extend from the stable shelf over the southern part of the unstable shelf. The Najmah Formation consists of the shallow-water, calcareous, neritic and lagoonal lithofacies that developed over the stable shelf and the southern part of the unstable shelf during the early part of the Late Jurassic and is equivalent to the Tuwaiq Mountain, Hanifa and Jubailah formations and the

285

Sedimentary Basins and Petroleum Geology of the Middle East lower part of the Arab Formation in Saudi Arabia. The type section was established in the Foothills Zone (well Najmah-29) by Bellen et al. (1959), and the description was completed by Kadhim and Nasr (1971 in Buday, 1980). In the type area, the succession consists of alternating fine-grained, recrystallized limestone and oolitic and peloidal limestone (Bellen et al., 1959). The maximum thickness of the formation reaches 330 m (about 1,082 ft). The formation has yielded abundant foraminifera and is assigned a Callovian-early Kimmeridgian age (Fig. 7.3). The lower contact is unconformable with the Dogger, but the upper contact is conformable. To the north, the formation is replaced by the condensed and carbonaceous Naokeleken and Barsarin formations.

Gotnia (Anhydrite) Formation (Callovian-early Kimmeridgian). The Gotnia Formation in the Mesopotamian Basin is made up of bedded anhydrites with subordinate intercalations of brown, calcareous shale; thin, black, bituminous shale; and recrystallized and oolitic limestone. In extreme southeastern Iraq, rock salt is found (Bellen et al., 1959). The thickness of the formation is about 200 m (656 ft) in the type area. The formation was deposited in a supersaline lagoon and has very rare fossils with some ostracods and foraminifera such as Helisaccus dunningtoni and Glomospira sp. The contacts of the formation at its type locality with the underlying Najmah and the overlying Makhul formations and in other subsurface sections are usually conformable.

Naokelekan Formation (late Oxfordian-early Kimmeridgian). The lower of the two condensed formations found in the High Folded, Imbricate and Northern Thrust zones of Iraq, the Naokelekan Formation was first described by Wetzel and Morton (1950, in Bellen et al., 1959). It ranges in thickness from 10 to 30 m (33-98 ft) of thinly bedded, highly bituminous dolomites and limestone interbedded with black, bituminous shale in the lower part passing upward into fine-grained, thinly bedded, fossiliferous, dolomitic limestone; shaly, bituminous shale; and fine-grained limestone (Buday, 1980). The fauna found particularly in the fossiliferous, dolomitic limestone ("Mottled Bed" and "Coal Bed") provide a late Oxfordian age; there is no indication of the existence of the Callovian or early Oxfordian or the presence of the middle-late Kimmeridgian, yet both contacts of the formation are said to be conformable. The beds were deposited in a euxinic environment in a slowly subsiding basin. Barsarin Formation ("Late Jurassic"). The Barsarin Formation, the second condensed formation, occurs in the High Folded Zone of northeastern Iraq. It has a thickness ranging from 20 to 60 m (66-197 ft). It was described by Wetzel (1950, in Bellen et al., 1959) as a sequence of limestone, dolomitic limestone and cherty, contorted and brecciated carbonates where brecciation is attributed to the solution of a former evaporite content. In the absence of fossils, the age cannot be precisely determined, except by stratigraphic position. It is distributed over the same area as the underlying Naokelekan Forma286

tion. The Barsarin Formation is believed to have been deposited, at least in part, in a lagoonal-evaporitic environment, partially indicated by the presence of anhydrite and oolitic limestone interbeds in some sections, and partly by the presence of brecciated and crumpled beds (Buday, 1980). The contacts of the formation are conformable above and below.

4. The Maim Section of lraq (Late Sub-cycle, Tithonian-Berriasian) Widely distributed over the more northerly part of the unstable shelf is the Chia Gara Formation, which interfingers with the Makhul Formation and the Karima Mudstone Formation in the Foothills Zone of Iraq. Over the stable shelf and the southwestern part of the unstable shelf in Iraq, the upper sub-cycle is represented by the Sulaiy Formation. The formation as used in this sense includes both the Tithonian and Berriasian, unlike Saudi Arabia, where it is restricted to the Early Cretaceous (Buday, 1980). Makhul Formation (Tithonian). This formation was first established by Dunnington (1935, in Bellen et al., 1959). In the type section, in well Mukhul-1, it consists of 300 m (more than 984 ft) of argillaceous limestone and calcareous mudstone, sometimes dolomitized or recrystallized. Near the base of the formation, peloidal limestone and nodules of anhydrite are found, and peloidal limestone reappears near the top. In general terms, the formation is relatively heterogeneous, but essentially neritic and calcareous in character, with clear signs of a pellet and silty sandstone supply. The existence of periodic lagoonal intervals is shown by the occurrence of oolite and anhydrite as well as infrequent pelagic incursions. The formation has a local character and developed at the margin of the stable shelf in central Iraq. It is considered a somewhat more shallow-water, nearshore facies. It grades laterally into the pelagic Chia Gara Formation. The lower boundary of the Makhul Formation with the Gotnia anhydrites usually is sharp but conformable; the top contact apparently also is conformable, but involves a break that can be erosional in some places.

Chia Gara Formation (middle Tithonian-Berriasian). The formation is widely distributed throughout the mobile shelf and the Mesopotamian Zone, where it intertongues with the Mukhul Formation of the High Folded Zone. The type locality lies in the High Folded Zone, where it was first described by Wetzel (1950, in Bellen et al., 1959) from a location in the Chia Gara Anticline. Lithologically, the formation is uniform throughout Iraq, consisting of two basic lithofacies types" thinly bedded limestone and calcareous shale in the lower part of the section, followed by an upper part in which marly limestone and marl predominate. In the type section, a thickness of 230 m (754 ft) was recorded, but the thickness may range from 30 to 300 m (98-984 ft). Based on ammonites, common in a formation depos-

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic ited in an open sea, the age ranges from the middle Tithonian to Berriasian. There remains, however, some doubt concerning the relation of the formation to the underlying and overlying beds. The interfingering with the Makhul Formation in the area of the Foothills Zone and the presence of occasional silty layers are an indication both of the shallowness of the sea and of uplift in the adjoining continental area, extending roughly from west of the Tigris and linked to the Mardin Uplift in southem Turkey. The basal contact of the formation in the type section with the underlying Barsarin Formation is said to be conformable, although a break in sedimentation is suspected. The upper contact is much less certain, but in the type area in the southeastern part of the High Folded Zone and in the Imbricated Zone, a gradational, conformable transition to the lagoonal, oolitic limestone beds of the Valanginian Garagu Formation generally is accepted. However, in areas north of the type area, in the Northern Thrust Zone, an erosional contact exists, and a conglomerate may form at the base of the Valanginian Garagu beds.

Karima Mudstone Formation (Tithonian-Berriasian). This formation is a sequence of monotonous, darkcolored, calcareous mudstone that, according to Bellen et al. (1959), was first described by McGinty (1953, cited in Bellen et al, 1959) in well Kirkuk-109 in the Foothills Zone. It has a relatively restricted extent (until about 1980, it was only recorded in one well), but reaches a considerable thickness (610 m, or about 2,001 ft). It is presumed to have been deposited in a narrow, rapidly sinking local basin in which, on occasion, euxinic conditions developed. It contains a fauna of ostracods, some radiolaria, small gastropods and rare, small, pyritized ammonites (Deptoceras sp.). The relation of the formation to the more widely distributed Makhul and Chia Gara formations is not clear, but the basin is presumed to be the result of local movements that began during the deposition of the upper part of the Chia Gara Formation; hence, the upper part of the Karimia Formation is younger than both of the latter formations. The movements are regarded by Buday (1980) as the first indications of an intra-Berriasian break. Sulaiy Formation (Tithonian-middle Berriasian?). According to Powers (1968), the formation was first defined on the stable shelf in Saudi Arabia. In southern Iraq, it has a thickness ranging from 100 to 400 m (3281,312 ft) of neritic, detrital limestone, some oolites and hard, recrystallized limestone, and rare interbeds of sandy shale (Bellen et al., 1959). The age is based upon its microfaunal content, but evidence is insufficient at this point to determine whether the formation extends only through the middle, or whether the entire Berriasian may be present. The formation is in apparent conformable contact with the overlying Ratawi Formation. In places where it is followed by the Zubair Formation, the boundary may be slightly unconformable or disconformable. At the lower boundary, some arenaceous layers indicate a possible short uplift or time break. Passing to the northeast through the Mesopotamian

Basin and the Foothills Zone to the High Folded and Northern Thrust zones, the equivalent formations are the combination of the Makhul and Chia Gara formations with some or all of the Karima Formation.

THE JURASSIC SECTION IN N O R T H W E S T E R N

AND NORTHERN ARABIAN PLATFORM The information available from Syria and southeastern Turkey, as in Jordan, is not very detailed, both from the lack of outcrop, the small amount of accessible subsurface data lacking in good micropaleontological control, in addition to losses through post-Jurassic erosion.

The Jurassic of Jordan Surface Formations Wetzel and Morton (1959) and Bender (1963, cited in Bender, 1974) provide an early record of Jurassic outcrops in Jordan in their description of a section in Wadi Huni on the northern side of the Zerga River. Subsequently, a more detailed account was provided by Bandel (1981), who recognized six Jurassic formations (Fig. 7.33). The following brief descriptions are based upon his account. Deir Alia Formation (early Liassic). The formation consists of a lower Huni Member and an upper Nimr Member, with a total thickness of 30-35 m (98-115 It). The Huni Member, about 15 m (49 ft) thick, is composed of purple clay, with abundant hematitic pisolites, followed upward by thinly bedded, fossiliferous limestone of marine origin and bioturbated sandstone and claystone containing fossil plant roots. In subsurface, sandy intercalations are lacking, and pisolitic clays are overlain by ferruginous oolite and limestone. The Nimr Member, 17-18 m (56-59 fi) thick, includes sandy limestone intercalations, layers of quartz gravel and some conglomeratic bands. The sand and gravel are indications of the proximity of shoreline and fluvial influences. Commonly, the sands and gravel have become intermixed with the marl and limestone as a result of bioturbation. The limestone may be oncolitic and contains a rich marine fauna. Zarga Formation (late Liassic). The formation, which ranges in thickness from 35 to 70 m (115-230 ft), consists of three members (in ascending order): the Humra, Um Butma and Farush members. The lowest, Humra Member, measures some 25 m (82 ft)in thickness and consists of three massive, cross-bedded sandstone units separated from one another by channel and flaser sands and capped by a bioturbated sandstone which is overlain by a dolomite unit. The sediments show the characteristics of shallow-marine deposits on intertidal fiats. The Um Butma Member is 25 m (82 ft) thick and composed principally of an 11 m (36 ft) sandstone with a conglomeratic base that overlies 12 m (39 ft) of bioturbated and flaser-bedded sandstone grading upward to parallel-

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288

arenaceous unit, showing both cross-bedding and gradedbedding, with only a limited number of flaser-bedded units showing traces of bioturbation. However, ferruginou~ hard grounds, dolomitic cement and some dolomite beds are present. The depositional environment indicates a shallowmarine environment with tidal fiats and channels now filled with sand. Dhahab Formation (early Middle Jurassic). This principally limestone unit (Fig. 7.33) ranges from 43 m (141 ft) in thickness in Wadi Um Butma to 54 m (177 ft) in

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic Wadi Zarqa. The limestone usually is fine-grained and totally bioturbated, with a pattern characteristic of a noncompacted, crab tunnel system. The limestone contains a rich fauna of bivalves, echinoids, crinoids, brachiopods, corals and calcareous algae. The formation is divided into four units (in ascending order): a first unit of 6-7 m (20-23 ft) of interbedded marl and limestone, a second unit of 1011 m (33-36 ft) of marl and clay, a third unit of dolomitized limestone 29 m (95 ft) thick, and a fourth unit of 7 m (23 ft) of interbedded marl and limestone. The sediments are laid down in a well-illuminated, shallow-shelf sea with abundant organic activity. Umm Maghara Formation (middle Dogger). The Umm Maghara Formation has three members - - Dafali, Mintar and Ramad - - which together total about 85-125 m (279-410 ft). The Dafali Member, the lowest member, consists of 35 m (115 ft) of cross-bedded sandstone with about half showing large-scale cross-beds, conglomerate horizons and trunks of driftwood, and the remainder has flaser bedding and is weakly to strongly bioturbated. It is somewhat thicker than in well Ramtha-1. Some of the arenaceous beds have a dolomitic matrix and may be completely churned up by bioturbation, and such beds may be capped by ferruginous oolites. The lower two thirds of the Mintar Member, which is 41-44 m (134-144 ft) thick, consist mainly of sandstone, with the upper third consisting of limestone and marl. As in the underlying Dafali Member, the basal, flaser sands contain driftwood trunks and some quartz conglomerates overlain by bioturbated, argillaceous, flaser-bedded sands associated with ferruginous oolites. There is a fauna of brachiopods, gastropods, crinoids and bivalves in the upper part of the member. The Ramad Member is 45 m (148 ft) thick and is composed totally of sandstone with some silty partings. Where the sands have been channelled, the channels are filled with cross-bedded sand. Signs of bioturbation are lacking. Conglomeratic horizons with quartz pebbles up to 1 cm occur in the channels. The general depositional environment of the formation is shallow-marine and tidal-fiat with fluviatile influences and overbank, silty and clay-rich deposits becoming more important upward. Breaks in sedimentation are suggested by the occurrence of ferruginous crusts and oolites found in the middle member, the Mintar Member. Arda Formation (late Dogger). The 55-70 m (180230 ft) Arda Formation consists of a lower Bin Fa'as Member and an upper Ain Khuneizir Member. The base of the Bin Fa'as Member is marked by the appearance of crossbedded sands that contain abundant driftwood. Large, lenticular sand bodies fill channels cut into the silty intercalations within the sand sequence, and these are overlain by flaser sands. The latter pass up into dolomitic sands overlain in turn by ferruginous oolites. The top of the member is primarily a sandy dolomite to dolomitic sandstone. This member was deposited as fluviatile sands. The Ain Khuneizir Member consists in the basal part of silty shale with thin, sideritic intercalations. Plant remains and amber are

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Fig. 7.34. Stratigraphic chart of the Jurassic formations compiled for Jordan, Syria and western Iraq. present throughout. Above the silty shale and cutting into them are cross-bedded sands. Dolomite and ferruginous oolite followed by claystone overlie the shale. In the Arda area, the lower terrestrial facies have been replaced by marly and sandy beds with a rich marine fauna, whereas the middle sandstone and upper limestone are in much the same lithofacies. Muaddi Formation (Maim). The formation is terminated by the conspicuous Late Jurassic-Early Cretaceous unconformity, and only 55-80 m (180-262 ft) are exposed. Two members, the Shaban and Tahuna members, are recognized. The lower, the Shaban Member, is about 40 m (131 It) thick and consists of finely laminated shale overlain by dolomite and dolomitic sandstone deposited in a transitional zone between non-marine and marine environments. The Tahuna Member is about 35 m (115 ft) thick. The lower 15 m (49 ft) consists of non-bioturbated claystone with intercalated, sideritic bands and passes upward into marl and shale with some intercalated limestone. The limestone is partly oncolitic, partly fine-grained and always fossiliferous. The top of the member is formed by a 20 m (66 ft) of fossiliferous, fine-grained limestone, which commonly is dolomitized for a few meters below the unconformity. The sediments were deposited in terrestrial to shallow-marine environments. Subsurface Formations The Jurassic is found in subsurface in northwesternmost Jordan (north of Amman) and in the north and northeast in the A1-Harrat and western Risha areas. The term "Azab Group" was introduced for the Jurassic strata in northern Jordan by Khalil and Muneizel (1992, in Andrews, 1992). The group is dominated by limestone, dolomite, dolomitic limestone, sandstone, clayey siltstone and marl and ranges in thickness from 28 m (92 ft) in well 289

Sedimentary Basins and Petroleum Geology of the Middle East Risha-12 to 598 m (1961 ft) in Ajlun-1. The basal rocks of the Azab Group unconformably overlie the Triassic Ramtha Group, and the upper boundary is a prominent unconformity surface overlain by the Lower Cretaceous Kumub Sandstone. Andrews (1992), based on available outcrop and borehole data, subdivided the Azab Group in northwest Jordan into six formations (Fig. 7.34), which are summarized below. In the Risha and A1-Harra areas, where the Jurassic is thin and lacks the characteristic subdivisions, beds dated as Jurassic are assigned to the Azab Group, with an age ranging from the Bathonian to mid-Callovian, and are bounded by unconformities above and below (Andrews, 1992). The thickness ranges from 28 m (92 ft) in well Risha-12 to 144 m (472 ft) in Qitar el Abd-1. The group is composed of finely crystalline limestone, partly argillaceous, vuggy, oolitic, pyritic, bituminous and glauconitic, with some thin, pyritic shale. In some wells, the basal Jurassic is composed of claystone overlain by medium- to coarse-grained sandstone.

Azab Group (Hettangian-Oxfordian) Hihi Formation (late Hettangian-Sinemurian). The formation originally was assigned as the Huni Member of the Deir Alla Formation (Bandel, 1981), but was raised to formation status by Khalil and Muneizel (1992) based on lithology. The formation is found in only four wells (Ajlun-1, Er Ramtha-lA, Northern Highlands-2 and S-90). The thickness ranges from 51 m (167 ft) at Ajlun-1 to 6 m (20 ft) in Er Ramtha-lA. The formation is composed of silty claystone (silty to sandy, calcareous and limonitic) interbedded with thin beds of oolitic, peloidal, slightly argillaceous limestone and fine- to medium-grained sandstone. The base of the Hihi Formation rests unconformably on the underlying anhydrite, claystone and limestone of the Abu Ruweis Formation. The top is gradational and marked the change from shale to the thick limestone of the Nimr Formation. The formation was deposited in a shallow-marine environment with strong continental influence and a nearshore lagoon. Nimr Formation (Pliensbachian-mid-Toarcian). The formation is the upper member of the Deir Alla Formation of Bandel (1981) and was raised to formation status by Khalil and Muneizel (1992). Found in the same four wells that penetrate the Hihi Formation, it ranges from 14 m (46 ft) in Er Ramtha-lA to a thickness of 35 m (115 ft) in Northern Highlands-2. The formation is composed of shale and is overlain and underlain by thick beds of oolitic, dolomitic limestone. In Er Ramtha-lA, no shale has been reported, and the Nimr Formation here is composed of microcrystalline, slightly dolomitic limestone with intercalations of oolitic, sandy and limonitic limestone at the top. The Nimr Formation rests conformably on the underlying Hihi Formation. The top is gradational and placed where the limestone of the Nimr passes into the interbedded sandstone, limestone and shale of the Silal Formation.

290

The Nimr Formation was deposited on a shallow, warmwater, carbonate shelf into which there was a low influx of clastics probably derived from rivers. Silal Formation (mid-late Toarcian-Aalenian). The formation was known previously as the Zarqa Formation (Bandel, 1981) and renamed the Silal Formation by Khalil and Muneizel (1992) to avoid confusion with the originally defined Zarqa Group. It also is found in the same four wells that penetrate the Hihi and Nimr formations and ranges in thickness from 57 m (187 ft) in well Ajlun-1 to 25 m (82 ft) in Northern Highlands-2. The Silal Formation consists of interbedded, medium- to coarse-grained sandstone; coarse-grained, silica-cemented sandstone; and silty to sandy, slightly calcareous shale interbedded with black, oolitic, argillaceous limestone. No sandstone was reported in well Northern Highlands-2, where the formation is dominated by the interbedded, oolitic limestone and shale. The lower contact is picked where the thick-bedded limestone of the Nimr is overlain by the interbedded sandstone, limestone and shale of the Salil Formation. The top is where the clastic Silal Formation is overlain by the more massive Dhahab carbonates. The formation was deposited in northwestern Jordan in a shallow-marine environment with an influx of clastic material indicated by the minor transgressions and regressions that affected this area. Dhahab Formation (Bajocian). The formation is found in the same wells as the other Jurassic formations of northwest Jordan. It ranges in thickness from 101 m (331 ft) in well Northern Highlands-2 to 77 m (253 ft) in Er Ramtha-lA. Lithologically, the formation consists of microcrystalline to macrocrystalline, slightly argillaceous dolomite with thin streaks of limestone. The dolomites are fractured, but cemented by slightly anhydritic and locally argillaceous dolomite. The lower contact is taken where the interbedded, mixed limestone/clastics of the Silal Formation are overlain by the thick limestone of the Dhahab Formation. The upper contact is placed between carbonates of the Dhahab and an interbedded shale/limestone sequence of the Ramla Formation. The Dhahab Formation was laid down on a shallow-marine shelf.

Ramla and l-lamam formations and equivalents (Bathonian). These mainly carbonate beds with only a minor clastic component were assigned to the Ramla and Hamam formations by Khalil and Muneizel (1992). In subsurface, the two formations are indistinguishable. They are equivalent to Um Maghara and Arda formations of Bandel (1981). They occur only in the same four wells in northwestern Jordan, with a thickness ranging from 71 m (233 ft) in well Northern Highlands-2 to 57 m (187 ft) in Er Ramtha-1A. The Ramla and Hamam formations consist of a basal shale followed by interbedded, macro-crystalline dolomite and dolomitic limestone with fine- to medium-grained sandstone and shale. The lower contact is gradational and conformable, marking the lithological change from the limestone of the Dhahab Formation to the thick shale of the basal Ramla and Hamam formations. The upper contact again marks a lithological change from

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic the mixed lithologies of the Ramla/Hamam formations to the uniform limestone of the Mughanniya Formation. The sediments were deposited in shallow-water (inter- to subtidal) and fluvial or tidal channels.

Mughanniya Formation (CaUovian-Oxfordian). The formation, the youngest Jurassic formation in Jordan, is partly equivalent to the Muaddi Formation of Bandel (1981). It is found in northwest Jordan, ranging in thickness from 83 m (272 ft) in well S-90 to 304 m (997 ft) in Ajlun-1. The formation consists of finely to coarsely crystalline dolomite (carbonaceous or highly bituminous in places) and patches of massive anhydrite, followed upward by argillaceous, glauconitic limestone with thin beds of claystone. The lower contact is placed where the Ramla/Hamam limestone is succeeded by the dolomite of the Mughanniya Formation. The upper contact of the formation is marked by an unconformity over which rests the sandstone of the Lower Cretaceous Kurnub Sandstone. The Mughanniya indicates a marginal-marine to sabkha environment of deposition. The Jurassic of Syria

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Fig. 7.35. General lithostratigraphy of the Late Triassic-Jurassic? (Cudi Group) in southeastern Turkey (modified from Arac and Yilmaz, 1990). several hundred meters of shallow-water dolomite and limestone are found. In the West Hakkari area, where the sequence is largely dolomitized and contains numerous thick-bedded, coarse to medium-grained, sucrosic dolomites, stratigraphic and paleontological control is poor. At the base and near the top of this section are slightly recrystallized mudstone and minor dolomicrites, while near the middle of the section, there is a sequence of highly weathered, concretionary ironstone with hematitic, goethitic and limonitic pisolites and oolites. Shallow-water deposition under normal-marine salinity conditions is proposed for this succession.

JURASSIC PALEOGEoGRAPHY AND GEOLOGIC HISTORY On the most general scale, the paleogeography of the Jurassic is essentially the history of the progressive flood291

Sedimentary Basins and Petroleum Geology of the Middle East ing of the Arabian Peninsula from the Neotethys that lay to the north and east. This process began early in the Jurassic, but by the end of the Jurassic, some 45-50 Ma later, regression had reduced the former carbonate platform to the state of a large evaporating pan. The thickness of the Jurassic is variable; it may be as little as 500 m (1,640 ft), as in central and southern Oman; more commonly, it reaches a thickness of the order of 800 m (2,624 ft) in the western Arabian Gulf region. The thickest sections are in the Musandam Peninsula area of northern Oman, where the thickness increases to more than 1,800 m (5,904 ft), and in the Fars Province of Iran, where it increases to more than 2,300 m (7,544 ft) (Setudehnia, 1978; Peterson and Wilson, 1986). Within that general pattern, several minor phases of sea-level change can be recognized. The general rise in sea level, which began early in the Jurassic, is seen first in Iran (St6cklin, 1968). During the Sinemurian, it is represented by the beds seen in the eastern and northeastern parts of the Middle East, flooding across the Qatar-South Fars Arch, which had become exposed during the Late Triassic, and spreading progressively across the craton to lap up against the more positive areas forming the southeastern, southern and western margins of the Rub al Khali Basin. This is borne out by the Early Jurassic age of the outcrops in the Musandam Peninsula of Oman and the Fars Province of Iran. By the end of the Early Jurassic, a nonevaporitic carbonate platform had been established across the eastern and southeastern parts of the Middle East, flanked to the west by an arid clastic-carbonate shelf (Murris, 1980) (Fig. 7.36). In the northern part of the Arabian Plate, the shelf-supported carbonates and evaporites form an arcuate zone around an emergent land mass that extended northward from Saudi Arabia. By the beginning of the Middle Jurassic, the Tethyan Sea had transgressed far over the shelf in Iraq, with a shoreline that reached into northern Saudi Arabia. In the north, the shallow, differentiated, carbonate-evaporite shelf that dipped gently northeastward was separated from the open-marine shelf by a ridge or high that may be the extension southeastward of the Mardin High. The open-marine shelf north of the Mardin High continues into southeastern Turkey (Cordey, 1971; King 1973). Beyond the open shelf, deep-marine conditions existed in central Anatolia and central Iran, where the sequences are made up of clastic-calcareous and volcaniclastic sediments deposited in a deep-water environment (Altinli, 1966; St6cklin, 1968a). This transgression, with minor still stands (or minor, short-lived regressions) continued into the Middle Jurassic as a wide carbonate platform covered much of the Arabian Plate. It became the setting for the development of a vast carbonate ramp grading southward and westward through a zone of mixed carbonate and clastic sediments into the clastic sediments of the shallow, marginal sea bordering the continental zone. Correlation of the carbonates from Saudi Arabia to Iran is possible indicating the continuity of the depositional environments, but by the middle part of

292

the Dogger (Bathonian), a major intrashelf basin, the Lurestan (or Mesopotamian) Basin, occupied the northwestern part of the Arabian Gulf region (Fig. 7.37). In the early Callovian in the southwestern Arabian Gulf, depositional conditions were established in which broad sheets of pelletoidal and oolitic packstone and grainstone alternated with pelletal and skeletal mudstone and wackestone. Economically, there is considerable oil production from these horizons, and it would seem that the hydrocarbons were derived from the kerogens within the rich, muddy limestone facies or from earlier, Bajocian, units. By late in the Callovian, a major transgressive pulse, marking an eustatic sea-level rise, inundated the eastern Arabian Platform. It stepped over the earlier Dogger sediments and came to rest upon the Arabo-Nubian Shield or onto the interior homocline of Arabia. The euxinic Lurestan Basin was bordered to the north by a ridge covered with shallow-marine carbonates (Buday, 1980) and to the southwest by fine-grained, shallow, neritic carbonates, including oolites, against the edge of the Rutbah-Khleissia High of Iraq. Westward, the euxinic basin continued into Syria through the Palmyra-Sinjar Trough. Shale deposited in the trough was interspersed with lagoonal evaporites. The same facies are recorded in the Euphrates-Anah Trough. In southwestern Syria and adjacent areas, shallow, oxygenated water conditions during the early and middle Callovian gave way to deeper water in the late Callovian (Walley, 1983). The deepening reached its maximum during the early Oxfordian, when restricted, basinal conditions were established with water depths ranging from 100 to 200 m (328-656 ft). However, shallowing began during the middle Oxfordian and culminated in the shallow, oxygenated waters of the Kimmeridgian-Tithonian. These changes in water depth, however, are related to local tectonic movement. This minor regression, which marked the end of the Middle Jurassic, was related tectonically to two major events: the final closure of the Paleotethys and the separation of east and west Gondwana. In response to the final closure of Paleotethys, uplift is recorded in Iraq. Not only is there a reduction in thickness of the euxinic sediments, but erosion associated with the uplift removed much of the Middle Jurassic in the eastern Zagros Mountains and in central Anatolia in Turkey, where Late Jurassic sediments are clearly unconformable upon the Early Jurassic. In eastern Syria, even the Triassic sediments deposited close to the margins of the Sinjar and Palmyra troughs were subject to erosion, and the Cretaceous may directly overlie Paleozoic beds on the southern flanks of these troughs. A sea-level rise was reestablished, and subsidence of parts of the craton continued during the Late Jurassic, resulting in the continued differentiation of the intracratonic Lurestan Basin from the shelf and the differentiation of a second, smaller basin centered in western Abu Dhabi in the southern Arabian Gulf (Fig. 7.38). Although the center of the Lurestan Basin may have become as deep as a

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Fig. 7.36 Paleogeographic map of the Middle East during the Late Liassic (modified from Murris, 1980, and reproduced by kind permission of AAPG)o

Fig. 7.37. Paleogeographic map of the Middle East during the Bathonian (modified from Murris, 1980, and reproduced by kind permission of AAPG).

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Fig. 7.38 Paleogeographic map of the Middle East during the late Oxfordian-eady Kimmeridgian (modified from Murris, 1980 and reproduced by kind permission of AAPG).

Tithonlan Fig. 7.39Paleogeographic map of the Middle East during the Tithonian (modified from Murris, 1980, and reproduced by kind permission of AAPG).

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Jurassic few hundred meters, the depth of the southern Arabian Gulf Basin never exceeded a few tens of meters. These intrashelf basins are extraordinarily important economically, as they were areas in which euxinic conditions developed leading to the preservation of kerogen-rich, bituminous lime muds and marl, which later became the source for the hydrocarbons trapped in the Late Jurassic Arab reservoirs (Murris, 1980; Alsharhan and Kendall, 1986). In the eastern part of the Arabian Gulf, the continental margin that separated the carbonate-evaporite platform from the open ocean was exposed during the OxfordianKimmeridgian, and little or no sedimentation occurred east of this margin, and only the rising sea levels of the Late Jurassic restored pelagic sedimentation. To the west over the main lagoonal-evaporitic basins, more openmarine conditions developed, with the consequent absence of clastics and the deposition of carbonate sediments under euxinic conditions in the intrashelf basins. During the Tithonian (Fig. 7.39), the climate became more arid, thus aiding the development of the extensive evaporites deposited on the very shallow platform that existed over much of the Arabian Gulf and in the Lurestan Basin in the northern Arabian Gulf, where basinal salt and laminated anhydrite interbedded with shale were formed.

In the northern part of the Arabian Plate, late Dogger tectonic movements continued to be felt in eastern Iraq, Kuwait and eastern Saudi Arabia generally, as uplift affected the divides between basins. This is reflected in the differences in lithofacies and the consequent lithological variety found in the Late Jurassic, particularly during the Kimmeridgian, effects not apparent in the southern part of the Arabian Plate where neritic conditions reigned. In the High Folded and Thrust zones of northeastern Iraq, the effects are shown by the occurrence of sections of reduced thickness, sequence breaks and sediments that show some euxinic influences in the lower units and lagoonal-evaporitic influences in the upper units. In the opinion of Buday (1980), the northern promontory of the Arabian Platform acted as a shallow marginal ridge whose northem margin is still unknown. North and northeast of that ridge in southeastern Turkey (Altinli, 1966; Strcklin, 1968), there is a relatively thick, clastic, lagoonal section, and a partly lagoonal, partly molasse sequence in northwestern Iran, indicating the presence of a more northerly, rapidly subsiding Maim Trough (Ftirst, 1970). The southwestern boundary of that ridge coincides with the edge of the Rutbah-Khleissia High, which now extends into the Foothills Zone west of Mosul in Iraq.

295

This Page Intentionally Left Blank

Chapter 8 THE LATE M E S O Z O I C PART OF THE ZUNI CYCLE IN THE M I D D L E EAST : THE C R E T A C E O U S

INTRODUCTION

change in sea level also is the explanation of the ramp and platform stages of carbonate deposition described by Murris (1980). During low sea-level stands, clastic sediments from the Arabian Shield to the west pushed eastward, restricting carbonate development to the region closer to the present Arabian Gulf. It is of interest that during this time period, it is hard to see any systematic, easterly shift in the shoreline position. Consequently, it must be assumed that the western part of the Afro-Arabian Plate must have been undergoing concomitant uplift, both preserving the location of the shoreline and maintaining the grain size of the clastic sediments prograding eastward. The southern and northern parts of the Arabian Platform are better treated as discrete units or areas, because their histories are somewhat different. The tectonically active "geosynclinal" area (northern Iraq and northwestern Iran) also requires separate treatment. During the Cretaceous, in the northern part of the Arabian Plate, the Lurestan Basin maintained its integrity; while in the southern Arabian Gulf, additional, smaller, intracratonic basins developed [the Abu Dhabi and Shilaif/Khatiyah intrashelf basins of the United Arab Emirates (U.A.E.) and western Oman. The principal effect on the sedimentary regime of the Late Cretaceous tectonic movements, which closed the Neotethys, was the restriction of the basins in which the Cenozoic sediments were subsequently deposited. The final phase in the history of the area is dominated by the Neogene phase of tectonism and the filling of the Mesopotamian Trough of Iraq along its axis, a process still in progress. The chapter will begin by providing some general introductory information concerning the development of terminology, followed by type-section descriptions for each of the three divisions. Subsequently, sections from other parts of the Arabian Platform will be compared against the type sections, balancing the utility of first establishing a type section, regardless of area, against the repetition of describing the section country by country. In this manner, the lithofacies changes can be related to the changing tectono-stratigraphic environments. The lithostratigraphic correlation of the southern and northern parts of the Middle East is shown in Figs. 8.3, 8.4 and 8.5. All the Cretaceous formations mentioned in the text are listed in Table 8.1.

There are two distinct phases in the geological evolution of the Cretaceous of the Middle East that reflect its tectonic history. For the greater part of the Cretaceous, the depositional environment conditions of a shallow carbonate shelf persisted over the region, continuing the pattern established during the Jurassic. During this time, the subduction that was occurring under the zone of the present Zagros had very little effect on the Arabian Platform. However, by Campanian time sediments were being deposited into a developing foredeep, which marked the closing of the Neotethys and the emplacement of nappes and ophiolites in Oman and Iran. The ophiolites are dated at about 90 Ma and extend from Iran (Kermanshah region) to Oman. From this time onward, the latest Cretaceous and the following Cenozoic are characterized by the gradual exhumation of the Arabian Platform and the progressive restriction of the marine area leading to the form of the present Arabian Gulf. The imposition of the foredeep over the eastern part of the Arabian Platform is apparent in the thickness of the Cretaceous sediments. Peterson and Wilson (1986) reported that over the Arabian Platform, parts of central Saudi Arabia, western Iraq, Oman and Yemen, the Cretaceous thickness generally is less than 900 m (2,950 ft); whereas in Iran, northeastern and southeastern Iraq, Kuwait and southeastern Saudi Arabia, the southern Arabian Gulf region and eastern Oman, thicknesses may exceed 2,450 m (8,036 ft) (Fig. 8.1). Over the Arabian Platform, three regional unconformities can be recognized below the Albian, Coniacian and Paleocene. These unconformities divide the Cretaceous into lower, middle and upper divisions, rather than the internationally recognized two-fold division. The sediments of the Lower Cretaceous (Berriasian to Aptian) Cycle are referred to the Thamama Group; the mid-Cretaceous (Albian to Turonian) Cycle belongs to the Wasia Group; and the Upper Cretaceous (Coniacian to Maastrichtian) Cycle is referred to the Aruma Group (Harris et al., 1984; Alsharhan and Nairn, 1986) (Fig. 8.2). Each division can be subdivided further into two subcycles, although the subdivisions are not clearly recognizable everywhere. This subdivision seemingly can be attributed to sea-level change and minor epeirogenic movements (Alsharhan and Nairn, 1986; Scott, 1988)o The

297

Sedimentary Petroleum Geology Geology the Middle Middle East Sedimentary Basins Basins and and Petroleum of the M Middle Table 8.1. Cretaceous rock units of i d d l e East. Asterisks indicate outcrop, aand n d bullets indicate subsurface. subsurface. Area Saudi Arabia

298

Unit

Age

Lithology

Environment

Thamama Group

E. Cretaceous

Limestone, dolomite, sandstone and shale

Shallow marine to continental

a. SuJaiy Formation

BerriasianValanginian

Inlerbedded lime mudstone, peloidal and detrital packstone/wackeslone and oolitic grainstone

Subtidal to intcrtidal

b. Yamama Formation

Valanginian

Peloidal, bioclastic packstone with thin interbeds of lime mudstone and wacke stone

Open platform shelf lagoon

c. Buwaib Formation

Hauierivian

Complex of interbcdded shale, dolomite, packstone and lime mudstone

Shallow marine lagoon

d. Biyadh Formation

Hauierivian

Cross-bedded, quartzose sandstone with some variegated shale

Continental to shallow marine

e. Sbuaiba Formation

BarremianAptian

Massive, often porous and vuggy dolomite with occasional limestone

Shallow marine

Wasia Formation

M. Cretaceous

Quartzose sandstone, sandy shale and some siltstone and limestone

Fluvial to shallow marine

a. KhaQi Member

E. Albian

Interbcdded sandstone, siltstone and shale

Fluvial and flood plain

b, Safaniya Member

M. Albian

Sandstone and shale with some interbcdded, sandy marl limestone

Fluvial and flood plain

c. Mauddud Member

L. Albian

Laminated, crystalline limestone

Shallow marine

d. Wara Member

Cenomanian

Shale interbcdded with sandstone and some limestone

Shallow marine lagoon

e. Ahmadi Member

E.-M. Cenomanian

Shale, sandstone and argillaceous limestone

Lagoon

i". Rumaila Member

M. Cenomanian

Limestone interbcdded with marly and sandy limestone complex

Restricted shelf, lagoon and tidal Hat

s2, Mishrif Member

L. CenomanianE. Turonian

Limestone interbcdded with shale

Very shallow to shallow, open marine

Arum a Formation

L. Cretaceous

Limestone (nodular, dolomitic and argillaceous), subordinate sandstone and shale

Shallow marine

a. Lina Member

L, CretaceousMaastriebtian

Dolomite, calcareous shale with interbcdded limestone

Shallow marine

b. Upper Atj Member

Dolomite with some limestone

Shallow marine

Maastrichtian

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

8.1 continued. continued. Table 8.1 Area

Unit c. Middle Atj Member

Age *

Environment

Campanian

Calcareous shale and microporous limestone

Shallow marine

TuronianE. Campanian

Wackestone with impure and sandy dolomite

Shallow marine

E. Cretaceous

Porous and dense limestone, dolomite and shaie

Shallow to deep open marine

a. Rayda Formation

L. Tithonian?E. Berriasian

Silica-rich, radiolarian calpioneJIid lime mudstone

Oxygen poor deeper oceanic water

b. Salil Formation

M. BerriasianHauterivian

Argillaceous lime mudstone

Density current deposits

d. Lower A [j Member United Arab Emirates

Lithology

Thamama Group

*

c. Habshan Formation

'

BerriasianValanginian

Peloidal, bioclasiic, intraclastic, dolomiiic and anhydritic limestone

Bank marginal shoal lagoon

d. Lekhwair Formation

*

HauterivianE. Barrcmian

Peloidal, bioclastic, oolitic packstone and argillaceous lime mudstone/wackestone

Subtidalintertidal

e. Kharaib Formation

Barremian

Microporous, dense lime mudstone/ wackestone to peloidal, imraclastic packstone

Shallow, epeiric shelf

f. Shuaiba Formation

Aptian

Algal-rudisttd limestone, argillaceous and shaly limestone

Shallow marine, subtidal to intertidal

Musandam Group Unit 4

BerriasianAptian

Radiolarian lime mudstone, siliciclasticcarbonatc turbiditcs, grainsione and packstone

Deep water turbiditcs to shallow water

M. Cretaceous

Argillaceous and bioclasiic limestone and shale

Shallow deep open marine

L. Aptian to E,-M. AJbian

Variegated shale, occasional thin beds of marl and sandstone

Shallow, subtidal shelf

L. Albian

Skeletal, peloidal packstone and wackestone

Shallow shelf

L. Albian-E. Cenomanian

Argillaceous, bituminous, lime mudstone/ wackestone and minor packstone

Open marine deep basin

M. to L, Cenomanian

Bioturbated, bioclastic packstone/ wackestone and rudistid packstone/ grainstone

Shallow marine

L. Cretaceous

Calcareous shale, marly limestone, sandstone and bioclastic limestone

Shallow deep open marine

Coniacian

Laminated, flaky and sometimes calcareous shale with occasional intercalated marl

Open marine

Wasia Group a. Nahr Umr Formation b. Mauddud Formation

• *

• *

<*

c. Shilaif/ Khatiyah Formation d. Mishrif Formation

*

Aruma Group a. Laffan Formation

*

299

Sedimentary Basins and Petroleum Geology the Middle East

Table 8.1 continued. continued. Area

Unit

Age

b. HaluJ Formation

ConiacianSantonian?

Marly limestone and marl with minor biocJastic limestone

Shallow water, low to moderate energy

*

L. ConiacianE. Santonian

Shaly, argillaceous lime mudstoney wackestone, marl and skeletal packstonc

Deep water hemipclagic

d. Fiqa Formation

*

Coniacian to m idMaastricht i an

Calcareous shale, argillaceous lime muds ton c/wackes tone and marl

Deep marine

e. Muti Formation

*

ConiacianSantonian

Radiolarian lime mudstonc, chert and conglomeratic limestone

Deep sea

L. Campanian to Maastrichtian

Sandstone, conglomerate, shale and fragments of igneous and metamorphic rocks

Deep sea of basinal, lurbiditic elastics

L. Campanian toE. Maastrichtian

Ophiolitic breccia, ophiolitic conglomerate

Fluvial and marine

M. to L. Maastricbiian

Foraminiferal, rudisiid packstonc/ wackestone

Shallow marine shelf

E, Cretaceous

Argillaceous and peloidal limestone, shale and marl

Shallow to slightly deep open marine

Berriasian

Argillaceous lime mudstone with thin, peloidal, oolitic limestone

Subtidalintertidal

VaJanginian

Microporous limestone with occasional peloidal, oolitic, intraclastic limestone

Open platform shelf lagoon

c. Ratawi Formation

Hauterivian

Dense, argillaceous limestone with intraclast and pellet interbeds, marl or marly limestone

Shallow slightly deep open marine

d. Kharaib Formation

Barrcmian

Microporous limestone, peloidal wackestone, shale and marl

Shallow marine shelf

c. Hawar Fonnatinn

L. Barremian to E. Aptian

Marl and shale

Open marine

E. to M. Aptian

Bioclastic, peloidal packstonc/ wackestone; microporous, bioturbated, limemudstone/wackesione

Shallow to slightly deep marine shelf

M. Cretaceous

Limestone and shale with minor marl and sand

Fluvial shallow to deep marine

AJbian

Marly sand, quart/itic/argillaccous sand and shale with few bands of limestone

Fluvial and lower coastal plain to shallow marine

• *

q. QahJah Formation

h. Simsima Formation Thamama Group

• *

*

a. Suiaiy Formation b. Yamama Fonnaiion

t. Siiuaiba Formation

*

*

Wasia Group

a. Nahr Umr Formation

300

Environment

c. Ham Formation

r. Juweiza Formation

Qatar

Lithology

*

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

Table Table 8.1 8.1 continued. continued. Area

Unit

Age

Environment

b. Maud dud Formation

'

Albian

Dense, foraminiferal, lime mudsione; peloidal, bioclaslic, packstonc/ wackestone and shale

Shallow to slightly deeper shelf

c. Ahmadi Formation

'

Ccnomanian

Shale (with thin sand), limestone and numerous thin marl and shale

Shallow open marine

Cenomanian

Dense, microporous, lime mudstone, wackestone and packstonc

Slightly deeper marine

d. Khatiyah Formation e. Mishrif Formation

'

Cenomanian

Bioclastic wackestone and packstonc

Shallow marine

Aruma Group

*

L. Cretaceous

Argillaceous and bioclastic limestone, shale and marl

Shallow lodeep open marine

a. Laffan Formation

ConiacianSantonian

Shale (pyritic/calcareous)

Open marine

b. Halul Formation

SanionianCampanian

Argillaceous limestone; dense, partly silicified, bioclastic wackestone, marl and shale

Shallow water, low to moderate energy

Campanian

Shale and bioclaslic packstonc and wackestone

Shallow open marine

Maastrichtian

Argillaceous limestone, dolomttizcd, bioclastic wackestonc/packstone and calcareous shale

Shallow marine shelf

c. Fiqa/Ruilat Formation

'

d. Simsima Formation Bahrain

Lithology

Thamama Group

*

E, Cretaceous

Argillaceous and peloidal limestone, shale and marl

Shallow to slightly deep open marine

a. Sulaiy Formation

'

Bcrriiisian

Dense, dolomitic mudstone inicrbedded with peloidal-ooliiic packstonc/ grain stone

SubtidaU intenidal

b. Yamama Formation

BcrriasianValanginian?

Wackestone, mudstone and packstonc

Open platform shelf lagoon

c. Ratawi Formation

Hauterivian

Argillaceous limestone and tKcasional wackestone interbedded with marl

Shallow to slightly deep open marine

d. Kharaib Formation

Barremian

Crystalline to microporous limestone with some marl

Shallow marine shelf

e. Hawar Formation

L. Barremian

Shale and marl

Shallow to slightly deep open marine

Apttan

Argillaceous microporous limestone, occasionally dolomitic

Shallow marine

M, Cretaceous

Bioclastic, peloidal limcsionc, shale and sandstone

Fluvial-shallow to deep marine

f Shuaiba Formation Wasia Group

*

301

Sedimentary Basins and Petroleum Geology the Middle East

Table 8.1 continued. Table 8.1 continued. Area

Environment

•

Albiati

Shale interbedded with sandstone and layers of arenaceous limestone

Fluvial and lower coastal plain

b. Mauddud Fonnation

'

Albian

Peloidal, bioclastic wackestone/pack stone

Shallow marine

c. Wara Formation

Ce Romanian

Shale and numerous linear sand bodies with thin limestone

Shallow marine lagoon

d, Ahmad! Formation

Cenomanian

Shale with ihin, finely crystalline limestone

Lagoon

e. Rumaila Formation

CenomanianE, Turonian?

Bioclastic, peloidal wackesionc/ packstone and some microporous, argillaceous limestone

Restricted shelf to tidal flat

L. Cretaceous

Pyritic shale, dolomitic and argillaceous limestone and dolomite

Shallow marine

Kahmah Group

E. Cretaceous

Porcellanitc chert and marl; bioclastic, peloidal, argillaceous limestone

Deep to shallow marine

a. Raydii Fonnation

Bcrriasian

Thin-bedded, porcellaneous mudstone and wackesionc with chert

Deep marine shelf

b, Salil Fonnation

Valanginian toE. Hauterivian

Thin- bedded, argillaceous mudstone/ wackestone and marl

Sub-wave base marine

c. Habshan Formation

Hauterivian

Coarsening-upward sequence of wackestone to grainstone

High-energy tidal flat

L. Hauterivian

Argillaceous limestone, bioclastic wackestone and peloidal, bioclastic packstone/grainstone

Shallow restricted marine

Barremian- E, Aptian

Limestone with thin, argillaceous material

Shallow marine

E. to M. Aptian

Algal and rudistid limestone with argillaceous material

Shallow to slightly deep water

BerriasianBarremian

Chcrty and silicitied radiolarian limestone, wackestone turbidite with shale partings

Deep water or just below CCD

BarremianCenomanian

Lithoclastic, peloidal, turbiditic grainstone with subordinate, intcrbedded lime mudstone, marl and silicified marl

Close to the CCD

PreCenomanian

Megabrcccia containing clasts of chert and lime mudstone

Submarine debris flow

d. Lekhwair Formation c, Kharaib Formation

*

•*

•*

t. Shuaiba Formation Sid'r Formation

*

Nayid Formation Mayhah Formation C Member

302

Lithology

ii. Nahr Umr Formation

Aruma Group Oman

Age

Unit

*

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

continued. Table 8.1 continued. Age

Lithology

May hah Formation D Member

Valanginian to Cenomanian

Thinly bedded, argillaceous lime mudstone, gravity-flow slumps and slides and redeposited, oolitic, intraclastic packs tone

Debris flows from slope and shelf edge

Musandam * Group (Members G, H, I)

BerriasianAptian

Radiolarian, tintinntd limestone; argillaceous, nodular and bioturbatcd limestone

Deep to shallow

Wasia Group

M. Cretaceous

Bioclastic, peloidal limestone, calcareous shale-marl, argillaceous limestone

Shallow deep open marine

a. Nahr Umr Formation

Albian

Calcareous shale and marl, some argillaceous limestone

Shallow marine

b, Natih Formation

L. Albian-L, Cenomanian to E, Turonian

Peloidal, intraclastic packstone/ wackestone, rudisiid-algal packstone/ g ra i n St o n e/w ackes ton e

Open marine, shallow, quiet shelf

c. Mauddud Formation

Latest AlbianM. Cenomanian

Microporous, dolomitized limestone; bioclastic, peloidal packs ton e/wacke stone

Shallow protected shelf

d. Mishrif Formation

M. Cenomanian or E. Turonian?

Bioclastic, peloidal packstone/grainstone; microporous, argillaceous wackestone and rudistid, algal limestone

Elongated islands and highenergy shoal

Qumayrah Formation

Cenomanian to Coniacian

Chert, siliceous mudstone, fragments of rudist bivalve and other fossil fragment

Synorogenic deposits

Qamar Formation

AlbianCcnomanian

Intcrbedded, bioclastic lime mudstone/ wackestone, glauconitic calcareous sandstone, pyritic shale

Shallow open marine with terrigenous flooding

Harshiyat Formation

Cenomanian

Laminated lime mudstone and siltstone with thin beds of sandstone

Shallow marine with terrigenous flooding

Limestone, marl and thin shale

Shallow marine lagoon

Unit

Area

Fartaq Formation

Cenomanian

Environment

marine

A rum a Group

L, Cretaceous

Bioclastic limestone, calcareous shale, marl and sandstone

Shallow to deep open marine

a, Laffan Formation

Coniacian

Calcareous shale and minor limestone

OpM:n marine

b. Fiqa Formation

SantonianCampanian

Hcmipelagic shale; argillaceous, peloidal wackestone

Deep to shallow

c. Muti Formation

ConiacianCampanian

Conglomeratic limestone, calcareous mudstone, shale and marl

Rysch-like deposits

d, Juweiza Formation

L. CampanianMaastrichtian

Marl, shale and conglomerate and rare, argillaceous limestone

Flysch-like deposits

marine

303

Sedimentary Basins and Petroleum Geology the Middle East Table 8.1 Table 8.1 continued. continued.

Area

Age

Lithology

E. Maastrichtian

Lithic sandstone, mudstone, chert, basalt and marly limestone

Non-marine fluviatile

t. Simsima Formation

Maastrichtian

Microporous lime mudstone/wackestone; peloidal packstone and dolomite

Shallow marine

ScinaiJ Ophioliie Nappes

L. Cretaceous

Peridotite, gabbro diabase, pillow lava and pelagic sedimentary rocks

Oceanic lithosphere origin on the Arabian continental margin

Unit c. Qahlah Formation

a. Tec ionized Peridotite

Harzburgite and duntte

h. Layered Gabbro

Olivine, chromite, clinopyroxene and plagioclase

c. High-level Gabbro

Iran

*

Plagioclase. clinopyroxene, orthopyroxene, Fe-Ti oxides I olivene, and horn blende gabbro

d. Sheeted Dike Complex

Diabase and basalt dikes

e. Pillow Lavas

Basaltic, volcanic rocks

Fahliyan Formation

Ben^iasianValanginian

Massive, oolitic, peloidal limestone

Shallow carbonate shelf

Gadvan Formation

BarremianE. Aptian

Bioclastic limestone interbedded with marl, shale or argillaceous limestone

Shallow marine to neritic

Danyan Formation

Aptian

Thick-bedded, massive limestone

Shallow marine lagoon

Garau Formation

NeocomianConiacian

Shale, thinly bedded limestone and chert

Deep marine

Kazdhumi Formation

Albian to E. Cenomanian

Bituminous shaie with subordinate, argillaceous limestone

Deep water neritic

Sarvak Formation

AlbianTuronian

Argillaceous, nodular-bedded limestone, bioclastic limestone and nodular chert

Deep marine

Surgah Formation

TuronianE. Santonian

Pyritic shale interbedded with limestone

Deep marine

Ham Formation

SantonianCampanian

Well-bedded, argillaceous limestone

Shallow marine back reef

Gurpi Formation

*

SantonianPaleocene

Marl and shale with subordinate, argillaceous limestone

Deep water neritic

Tarbur Formation

*

L.Campan tanMaastricht ian

Anhydride and reefal limestone

Shallow marine

MaastrichtianPaleoccne

Thin-bedded limestone, silisionc, sandstone and local conglomerate, chert and marl, sandy limestone

Flysth-typc sediments

Amiran Formation

304

*

Environment

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

Table 8.1 continued. continued. Table 8.1 Area Kuwait

Iraq

Age

Unit

Lithology

Environment

Makhul Formation

L. TithonianBcrriasian

Argillaceous limestone, occasionally dolomitic, interbedded with marl and chert

Shallow marine

Minagish Formation

Valanginian

Dense lime mudstone/wackestone and peloidal, bioclastic, oolitic limestone

Low- to highenergy shoal

Ratawi Formation

Hauterivian

Bioclastic, peloidal limestone, shale and sandstone

Shallow marine shelf

Zubair Formation

Barremian

Sandstone with some shale intercalation and minor limestone

Littoral and partly deltaic

Shuaiba Formation

Apt i an

Coarsely crystalline, dolomitized limestone

Low-energy shallow lagoon

Burgan Formation

E.-M. Albian

Sandstone intercalated with shale

Deltaic

Mauddud Formation

L. Albian

Packstone/wackestone containing interbedded, dense limestone and some thin sand and marl

Shallow marine

Wara Formation

E. Cenomanian

Glauconitic sandstone and siltstone with some shale

Subaqueous (marine to nonmarine)

Ahmadi Formation

E.

Limestone, shale alternation

Outer neritic

Magwa Formation

M. CenomanianE. Turonian

Pyritic, argillaceous, fossiliferous limestone and thin shale

Quiei to slightly agitated neritic marine

Khasib (Murriba) Formation

Coniacian

Dense, detrital limestone with minor shale

Deep lagoon

Sa'di Formation

SantonianE. Campanian

Fossiliferous lime mudstone/wackestone with few shale and dolomite

Neritic with open sea influence

Hartha Formation

L. CampanianE. Maastrichtian

Detrital limestone, some dolomite, shale and marl

Marginal marine

Marginal marine

Cenomanian

Bah rah Formation

Maastrichtian

Detrital and oolitic limestone with shale and chert

Tayarat Formation

L. Maastrichtian

Dolomitic, locally anhydritlc limestone with minor pyritic shale

Marginal marine

Ratawi Fomiation

Valanginian to Hauterivian

Shale, slightly pyritic, with interbedded stringer of peloidal, bioclastic limestone

Partly euxinic lagoon

Zubair Formation

Hauterivian to E, Aptian

Alternation of shale and sandstone with intercalation of siltstone

Littoral, partly deltaic

305

Sedimentary Basins and Petroleum Geology the Middle East Table Table 8.1 8.1 continued. continued.

Area

Age

Unit

Environment

BerriasianValanginian

Sandy, oolitic limestone with marl and sandstone and minor limestone

Lagoon

Lower Balambo* Formation

ValanginianAlbian

Thin-bedded limestone intercalated with marl and shale

Deep water

Lower Sarmord Formation

HauterivianBarremian

Marl with alternations of marly, neritic limestone

Deeper neritic marine

Lower Qamchuqa Formation

Aptian

Massive, bioclastic, neritic limestone with minor silt and other terrigenous admixture

Neritic marine

Shuaiba Formation

Aptian

Argillaceous, microporous limestone with some partly glauconiiic limestone

Shallow to moderate marine

Nnhr Umr Formation

Albian

Sand and sandstone with amber and pyrite

Deltaic and continental

Albian

Detrital, peloidal limestone with occasional shale

Shallow shelf

E. Cenomanian

Shale and siltstone with thin band of sandstone

Shallow marine deltaic

E. Cenomanian

Shale with some limestone

Shallow marine with terrigenous flooding

Rumaila Formation

Cenomanian

Microporous and oligosteginal limestone and marl

Deep water subsiding

Mishrif Formation

CenomanianE. Turonian

Fossiliferous and detrital limestone

Shallow marine

Cenomanian

Fine- to course-grained sandstone

Continental

M'sad Formation

Cenomanian

Reefal limestone, detrital and microporous limestone with some marl, sandy marl and sandstone

Shallow marine

Rim Siltstone Formation

E. Albian

Silly, pyritic mari, marly siltstone, thin sandstone and marl

Nearshore lagoon

Jawan Formation

Albian

Marly, peloidal limestone; marly dolomite and anhydrite

Neritic and semi-lagoon

Upper Qamchuqa Formation

Albian

Dolomite and fossiliferous limestone

Neritic

Upper Sarmord ' Formation

Albian

Marl and hmestone

Neritic to semi-bathyal

Upper Balambo' Formation

CenomanianTuronian

Thinly bedded, globigerinal marl and radiolarian limestone

Deep marine bathyal

Garau Formal ion

Mauddud Formation

•

*

Wara Fo mi alien Ahmadi Formation

Rutbah Formation

306

Littiology

*

*

The The Late Mesozoic Part of the the Zuni Cycle in the Middle Middle East: East: The The Cretaceous Cretaceous

Table 8.1 8.1 continued. continued. Table Area

Unit Kifl Formation

•

Lithology

Environment

Cenomanian

Anhydrite, peloidal oolitic limestone, dolomiiic limestone

Hypersaline lagoon

Dokan Limestone Formation

Cenomanian

Oligosteginal limestone

Open marine

Khasib Formation

L. TuronianConiacian

Shale alternating with marly limestone

Lagoon

U. Senonian

Shale with microcrystalline, marly and detrital limestone

Nearshore basin

Sa'di Formation

U, Senonian

Chalky, marly, globigerinal limestone and marl

Neritic

Hartha Fomnation

L. Campanian to Maastrichtian

Organo-detrital, glauconitic limestone with shale interbeds

Marginal marine

Qurna Formation

Maastrichtian

Limestone, argillaceous and locally dolomitic with marl intercalation

Deep open sea

Maastrichtian

Phosphatic, glauconitic and locally silicified marl

Shallow marine, littoral-neritic

Gulneri Formation

E. Turonian

Black, bituminous, laminated, calcareous shale

Basinal euxinic condition

Kometan Formation

E. TuronianSantonian

Thinly bedded, globigerinal and oligosteginal limestone, and bands of chert

Deeper neritic

Shiranish Formation

L. Campanian to Maastrichtian

Thinly bedded, mariy limestone and marl

Deep open marine

Bekhme Formation

L. Campanian toE. Maastrichtian

Bituminous dolomite and detrital limestone and some limestone conglomerate

Shallow marine

Hadiena Formation

L. Campanian toE. Maastrichtian

Dolomitic limestone; silty, detrital, calcareous marl and conglomeratic limestone

Rapidly subsiding basin

Tanuma Formation

Digma Formation

Syria

Age

*

*

Tanjero Formation

*

L. Campanian to Maastrichtian

Pelagic marl, silt, marl and sandy limestone

Flysch and open marine

Aqra Formation

*

Maastrichtian

Reefal limestone, locally dolomitizcd

Neritic

Qamchuqa Formation

Barremian to Apt Ian

Dolomitized and recrystallized limestone, sandstone and shale

Neritic

Ruibah Formation

Barremian to Albian

Silisione, shale and sandstone with volcanic fragments

Continental

307

Sedimentary Basins and Petroleum Geology the Middle East

Table 8.1 continued. continued. Unit

Area

Age

Gypsum, dolomite and intercalated anhydrite

Shallow marine lagoon

Judea Formation

CenomanianTuronian

Bioclastic limestone, microporous and dense limestone, dolomite and chert

Shallow marine

Massive Limestone Formation

Cenomanian to Campanian

Wackcstonc, porcellaneous limestone, argillaceous and dolomitic

Shallow to slightly deep marine

ConiacianCampanian

Alternation of marly and cherty limestone and glauconitic sandstone

Deep open marine

CampanianMaastrichtian

Marl and marly limestone and recfal, argillaceous, porous limestone

Deep open marine

HauterivianAlbian (?)

Glauconitic sandstone; lenticular, channelled sandstone; lignitic sandstone and conglomerate with thin, sandy dolomite and dolomitic limestone

Braided to meandering river

L. AlbianE. Coniacian

Limestone, dolomite and marl with tongues of sandstone, siltstone and mudstone

Shallow to deep marine

L. Albian-E. Cenomanian

Nodular limestone and dolomite intercalated with marl, sandstone and siltstone

Nearshore to shallow intertidal

Cenomanian

Calcareous marl, siltstone and thin, marly limestone

Open marine to outer shelf

L. Cenomanian

Massive limestone, dolomitic limestone and dolomite with few intercalations of marly limestone

Shallow subtidal lagoon

E. Turonian

Alternating limestone, marly limestone and argillaceous shale

Open marine outer shelf

Turonian

Dolomitized limestone and thin, marly limestone

Shallow marine

ConiacianCampanian

Chalk and marly chalk rich in foraminifera with minor limestone, chert and dolomite

Outer neritic to bathyal marine

Coniacian

Marl, clayey micrite and limestone

Shallow marine

Bclqa Group

ConiacianEocene

Chalk, marl, chert and phosphate

Deep open marine

Muwaqqar Formation

U. MaastrichtianL. Eocene

Argillaceous, phosphatic, chalky and marly limestone

Deep water outer shelf

Soukhnc Formation

'

*

Shiranish Formation Kumub Group

•*

Ajlun Group Na'ur Formation Fuheis Formation

<*

•*

Hummar Formation Shuayb Formation WadiAsSir Formation Wadi Umm Ghudran Formation Khureij Formation

308

Environment

Aptian to Cenomanian

Hayane Formation

Jordan

Littiology

**

** **

•*

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

Table 8.1 continued.

309

Sedimentary Basins and Petroleum Geology the Middle East

Table 8.1 continued.

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

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THE FIRST CYCLE: THE EARLY CRETACEOUS As indicated earlier, the fundamental simplicity of the Arabian Platform carbonate sediments has been complicated by the number of different stratigraphic schemes developed. Alsharhan and Nairn (1986, 1988, 1990) attempted to correlate the different units and provide an account of the variety of terminologies used in the Arabian Gulf region. The basic formational names in general use are those that Steineke et al. (1958) and Powers et al. (1966) established from type areas in Saudi Arabia. They cannot be used without some qualifications, however, because of lithofacies changes basinward, especially evident in the mid-Cretaceous Wasia Group. The Middle East, and especially the Arabian Platform, must be one of the few parts of the world where the information from the subsurface outweighs the outcrop data. The basic formational descriptions from Saudi Arabia provide the initial starting point for the consideration of the platform sequence of the Cretaceous. However, because of strong facies changes that affect the mid-Cretaceous, Alsharhan and Nairn (1986) proposed subsurface type sections based upon data from the UAE (Abu Dhabi region), following

the methods used by Bellen et al. (1959), Powers (1968) and Sugden and Standring (1975).

Early Cretaceous of Saudi Arabia Powers et al. (1966) reported that as early as 1935, Burchfiel and Hoover had assigned all the strata above the Marrat Formation and below the top of the Jubailah Formation - - that is, below the pre-Wasia unconformity, to the Tuwaiq Mountain Formation; however, in 1937, Steineke included the Riyadh chalk and limestone, which lie above the Jubailah Limestone. Bramkamp and Burger (1938, cited in Powers et al., 1966) raised the Riyadh chalk and limestone sequence to formational rank and included within it the Lower Riyadh, Hith Anhydrite and Yamama Limestone members. Subsequently, the Sulaiy and Yamama members were separated from the Riyadh Formation and named the Thamama Formation, the name taken from Khashma ath Thamama, a location about 150 km (94 mi) south of the city of Riyadh. Before 1940, beds now included in the Thamama Group were regarded as Jurassic, and it was their recognition as Cretaceous that prompted Steineke (1940, cited in Powers, 1968) to establish the Thamama Formation. Later, in 1952 (Steineke and 311

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The Late M e s o z o i c Part of the Zuni Cycle in the Middle East: The Cretaceous

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous Bramkamp, 1952), the formal three-fold division of the Early Cretaceous limestone into the Buwaib, Yamama and Sulaiy formations was incorporated into the Thamama Group. This group subsequently was redefined by Powers et al. (1966) to include the Biyadh Sandstone at the top of the sequence. Thus, the redefinition included within the Thamama Group all the strata between the Late Jurassic Hith Formation and the mid-Cretaceous Wasia Formation -that is, all the Lower Cretaceous, the Sulaiy, Buwaib, Yamama and Biyadh formations as seen in outcrop. In subcrop, the upper part of the Biyadh Formation is replaced by another carbonate sequence, that of the Shuaiba Formation, because both are in continuous sequence with the underlying beds. In places, however, the vertical extent of the sandstone of the Biyadh Formation may extend beyond the assigned limits of the Thamama Group,

for they may be the lateral equivalent of beds as young as the mid-Cretaceous Mauddud Formation. A brief description of the formations included in the Lower Cretaceous in the type areas follows. The distribution of these sedimentary rocks in outcrop of central Arabia is shown in Fig. 8.6, and the sedimentary analysis of the available type and reference sections of the Early Cretaceous carbonate sequence in central Saudi Arabia has been described by Shebl and Alsharhan (1994) and is shown in Fig. 8.7. In brief, the depositional environment of the early Cretaceous was of a shallow-marine, carbonate platform dipping gently eastwards, forming a ramp over the Jurassic (Hith) evaporites. Locally in Abu Dhabi, shallow, oolitic limestone passes to pelagic mudstone. Vertically, an early Hauterivian unconformity separates carbonate deposition into two sub-cycles. The upper sub-cycle is marked by the

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Fig. 8.6. Distribution of Cretaceous outcrop in central Saudi Arabia (based on Powers et al., 1966).

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Sedimentary Basins and Petroleum Geology the Middle East

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spread of clastics from the west and northwest (Biyadh Formation), reaching as far east as Qatar (Ratawi Formation). Towards the end of the cycle, shallow-water carbonate deposition was reestablished (Shuaiba Limestone). An intrashelf basin in Abu Dhabi and western Oman contains deeper-water, argillaceous limestone, and rudist and algal mounds became established at the shelf break. The Gotnia Basin in the north persisted through the first cycle with clastic sediment sources from the northwest (Shebl and Alsharhan, 1994). Sulaiy Formation (Berriasian-Valanginian). The formation takes its name from a gravel-filled channel, the Wadi as Sulaiy in central Arabia. The type section was measured in a cliff above Dahl Hit at 24~ N, 47000'06" E, where about 170 m (about 558 ft) are exposed. In subsurface, the formation thickness ranges almost everywhere from 152 to 185 m (499-607 ft). Lithologically, in outcrop, the formation consists mainly of interbedded lime mudstone, peloidal and detrital packstone and wackestone. Coquinal and oolitic grainstone, often recrystallized, show an abundance of oyster and

316

other shell fragments. Near the base, there are several brecciated levels and scattered quartz grains (Powers, 1968; Shebl and Alsharhan, 1994); all sediments were deposited in subtidal and intertidal, shallow-water environments. In subcrop, the lower part of the formation is a greenish-tan, fine-grained to finely crystalline, compact and dense limestone. The upper part consists of more porous wackestone and packstone. The contact with the underlying Hith Anhydrite is a possible disconformity. The top contact with the Yamama Limestone is gradational. The basis of the age assignment is the occurrence of a fauna that includes Pseudocyclamina sulaiyana, Nautiloculina sp., Trocholina sp., Spirocyclina sp., Liebusella sp. and Bramkampella arabica (Steineke et al., 1958; Powers et al., 1966; Powers, 1968), suggesting a Berriasian-Valanginian age range. Y a m a m a F o r m a t i o n ( V a l a n g i n i a n ) . The formation takes its name from the town of A1 Yamama (24 ~ N). As defined by Steineke et al. (1958), the formation consists of 58 m (190 ft) of limestone between the dense Sulaiy limestone below and the Buwaib or Biyadh Formation above.

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous The formal type section and its description were provided by Powers et al. (1966). In outcrop, the section is made up of 45.5 m (149 ft) of golden-brown, peloidal, bioclastic packstone with common, but thin, interbeds of lime mudstone and wackestone deposited in an open-platform, shelf lagoon (Shebl and Alsharhan, 1994). In subsurface, the formation expands to a thickness of about 150 m (492 ft) and can be divided into two distinct units. The lower unit typically consists of light-gray, fine-grained, dense limestone with numerous arenaceous, pelletized foraminifera commonly set in a fine-grained, translucent limestone matrix. The upper unit consists of light-cream to light-buff lime mudstone to wackestone with a few streaks of porous packstone (Powers, 1968). The formation is in gradational contact with the underlying Sulaiy Formation. The contact with the Buwaib Formation is conformable in subsurface, whereas it is unconformably overlain by the Biyadh Sandstone in outcrop. The fauna includes Everticyclamina eccentrica, Pseudocyclammina cylindrica and Pseudocyclammina sp. Buwaib Formation (Hauterivian). The Buwaib Formation is named from Khashm al Buwaib at 25015'03 " N, 46~ E in central Saudi Arabia, where the type section is from about 11 to 18 m (36-59 ft) thick; but in subsurface, the section thickens to a minimum of 55 m (180

fl) in the Dammam Field in eastern Saudi Arabia and up to a maximum of 112 m (367 ft) in the Ghawar Field. It incorporates all the beds carrying Cyclammina greigi, which would place the base of the formation at the horizon of the stratigraphic break formed by the pre-Biyadh unconformity both in the surface and subsurface. The surface exposures consist of a complex of interbedded, argillaceous limestone/marl, dolomite, bioclastic wackestone/packstone and lime mudstone, with occasional thin bands of quartz sandstone (Powers et al., 1966; Moshrif, 1981) (Fig. 8.8). The beds are interpreted as being deposited in a very shallow-marine environment, where both wave and current activity ranged from low- to high-energy (Shebl and Alsharhan, 1994). In subsurface, the lower part of the formation consists of massive limestone, which grades upward into interbedded limestone and shale followed by thin, buff-colored, finely crystalline, dense limestone. The limestone carries a fauna that includes the highspired Trocholina sp., Chrysalidina arabica and Cyclammina greigi. The Buwaib appears to overlie the Yamama Formation with complete conformity, even in the oil field areas, except in the Khurais Field, where there is evidence of a basal disconformity. The top of the formation grades conformably into the Biyadh Formation. Biyadh Formation (Barremian-Aptian). The Biy-

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Sedimentary Basins and Petroleum Geology the Middle East adh Formation takes its name from the extensive, gravelplain A1 B iyadh, where sandstone crops out. The beds originally were included by Koch and Brown (1934, cited in Powers et al., 1966) as part of a large, unnamed, clastic series of presumed Cretaceous age, which Burchfiel and

consists of black weathering, cross-bedded, quartzose sandstone with some interbedded, variegated shale. Variations in the depositional environment are indicated by several horizons of conglomerates, which suggest increased

Hoover (1935, cited in Powers et al., 1966) called the

erosion and uplift? in the source area, and by thin beds of ironstone, which probably represent pauses in the rate of

Nubian Sandstone. The unit is diachronous, and sandstone of the same lithological type is found in outcrop representing the Wasia Group, at least in part (Alsharhan and Nairn, 1986). The name Biyadh Sandstone was introduced by Thralls and Hasson (1956), but the formal description appeared in Steineke et al. (1958). In outcrop, the Biyadh Formation, approximately 300-400 m (984-1,312 ft) thick, is divided into lower, middle and upper parts (Fig. 8.9) of roughly equal thickness. It

deposition and possibly the development of temporary lakes or soils. The section ends with cross-bedded, quartz sandstone with abundant quartz pebbles (Powers et al., 1966; Moshrif, 1980a, b; Moshrif and Kelling, 1984). The bulk of the Biyadh Formation appears to be of alluvial, channel-fill origin, mainly point-bar sands, and alluvial, flood-plain origin. At the top of the formation, there is a disconformable contact between the coarse, pebbly, quartz sands of the Biyadh with ferruginous, silty sandstone

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Fig. 8.9. Lithostratigraphy of the Lower Cretaceous Biyadh Formation in central Saudi Arabia (modified from Moshrif and Kelling, 1984). See Fig. 8.6 for distribution of these sediments. 318

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous belonging to the Wasia Formation. This erosional surface probably resulted from local changes and a brief time interval of the type to be anticipated in a fluvial sequence. In subsurface (as in the Ghawar Field), the Biyadh Formation is bracketed between the Buwaib (HauterivianBarremian) below and the Shuaiba (Aptian) above; consequently, the formation is assigned an age range from the Barremian to Aptian. The section, as much as 625 m (2,050 ft) thick, appears to be richer in shale and argillaceous mudstone and may mark a marginal-marine environment, an interpretation strengthened by the appearance of two relatively thin limestone members containing orbitolinids within the sequence of predominantly green shale in the eastern Arabian oil fields (Dammam and Qatif). Toward Qatar and the U.A.E., the Biyadh Formation in subsurface is mostly replaced by limestone. In outcrop in Saudi Arabia, the base of the Biyadh is placed at the top of the highest thin limestone of the Buwaib Formation and the top at the disconformable contact between coarse, quartz sand with quartz pebbles below and the ferruginous, silty sandstone in the Wasia Formation above. Shuaiba Formation (Aptian). The Shuaiba Formation is known only in subsurface in Saudi Arabia, where it consists of massive, often porous and vuggy dolomite with occasional limestone in the Khurais and Ghawar fields (Powers, 1968). Some levels containing orbitolinids have been found in both the Abqaiq Field and well Jauf-1. The thickness ranges from 25 to 110 m (82-361 ft). In the Khurais Field, it is overlain by sands that form the basal part of the Wasia Group, but it is capped elsewhere either by shale or an alternating sand-shale succession rich in lignitic fragments and, locally, pieces of amber. The contact with the underlying, greenish-gray shale and sandy shale attributed to the Biyadh (Fig. 8.3) is sharp, but conformable. In the Rub al Khali Basin (Shaybah Field), the Shuaiba thickness ranges from 90 to 120 m (295-394 ft), where it consists of porous wackestone and packstone with abundant rudistid, other shell debris and algal growth. The formation is much better developed in the U.A.E., where it has been studied in detail because the rudist facies is an important reservoir (Alsharhan, 1993); the description will be expanded when variations occurring on the carbonate platform are discussed.

Early Cretaceous of Eastern Arabia There is a strong lithological similarity in the Thamama Group succession in the countries lying immediately east of the Saudi Arabian sections. The formational names used are essentially the same; the principal change is the replacement of the Buwaib by the Ratawi Formation in Bahrain and Qatar, and by the Habshan and Lekhwair formations in the U.A.E. and Oman (Fig. 8.3). There is a lithofacies replacement of part of the Biyadh sandstone by the Hawar shale and Kharaib limestone in Qatar and the U.A.E. The stratigraphy of Oman recognizes the Early

Cretaceous Kahmah Group rather than the Thamama Group. Although the basic lithologies of the two are not much different m that is, the Early Cretaceous is characterized by shallow- and deep-water carbonates B the lower part of the Kahmah Group consists of thin- to thickbedded, microbioclastic mudstone and wackestone and fine, thin-bedded, porcellaneous limestone succeeded in the upper part of the Kahmah Group by thick-bedded, bioclastic and pelletal wackestone and packstone alternating with bioclastic mudstone and skeletal, oolitic and pelletal, fossiliferous grainstone. The succession of lithologies points to a progressive shallowing sequence on the Arabian continental margin, from the slowly deposited porcellanites in a deeper-shelf environment at the base to shallow, open-marine, shelf deposits at the top. The age range of the deposits is listed as latest Tithonian to Aptian, based upon the shallow-water fauna.

Early Cretaceous in the United Arab Emirates.

Subsurface Formations Rayda and Salil formations (late Tithonian?-early Valanginian). In eastern and southeastern onshore Abu Dhabi and passing toward Oman, a basinal, radiolarian, carbonate mudstone, the Rayda Formation, is equivalent in part to the Habshan Formation of western Abu Dhabi. The Rayda facies in Oman consist of deep-water, ramp mudstone and wackestone, whereas the facies give way to grain carbonates to the west into Abu Dhabi. The basal, Cretaceous Rayda Formation has been encountered only in a few wells, where it is represented by more than 125 m (410 ft) of radiolarian and tintinnid lime mudstone with minor amounts of micropelloidal material (Hassan et al, 1975; Connally and Scott, 1988; Alsharhan and Kendall, 1991). de Matos (1994) reported a glauconitic, pyritic, detrital, packstone-to-grainstone layer at the base of the Rayda Formation in Abu Dhabi. Simmons (in de Matos, 1994, p. 98) interpreted this as a local hardground (possible disconformity) at the top of the Jurassic, or a maximum flooding surface of the lowermost Cretaceous associated with the Thamama transgression. The age of the Rayda Formation is Early Berriasian, based on the presence of Calpionella alpina and Calpionella elliptica in Oman and onshore Abu Dhabi (Simmons and Hart, 1987; Connally and Scott, 1988; de Matos, 1994). The Salil Formation, which overlies the Rayda Formation, is absent in the eastern Abu Dhabi area (Hassan et al., 1975). The best records of the two formations are found in subsurface in the onshore, northern U.A.E. (Sajaa Field, Sharjah), where the Rayda Formation consists of lightgray, silica-rich, radiolarian-calpionellid lime mudstone with dolomitic patches totalling 46 m (151 ft). These grade up into the Salil Formation, which consists of gray, argillaceous mudstone 183 m (600 ft) thick (Connally and Scott, 1988). The Rayda sediments were deposited in oxygenpoor, deeper oceanic water, whereas the Salil was laid

319

Sedimentary Basins and Petroleum Geology the Middle East down in deeper water by bottom currents, as indicated by density-current deposits. The base of the Rayda Formation, at the Jurassic-Cretaceous boundary in the Sajaa Field, is placed below the lime mudstone and above the underlying, coarsely crystalline dolomite with peloids and intraclasts. The Rayda Formation shows an upward passage into the Salil, with the lithological boundary placed between medium-bedded limestone below and argillaceous, wavy, laminated limestone above, a boundary that can be picked out on gammaray curves (Connally and Scott, 1988). The age assigned to the Rayda Formation is Tithonian-Berriasian, based on calpionellid zones B and C of Remane (1964), and the Salil Formation is middle Berriasian-Hauterivian. The presence of Calpionellites darderi in well cuttings from the upper Salil Formation suggests a late Valanginian or

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Fig. 8.10. General lithology and log characteristics of the Lower Cretaceous Thamama Group in the U.A.E.

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous shore location. The formation formed updip on a vast carbonate ramp that developed during the initial flooding of the stable cratonal platform and prograded over, and subsequently filled, the Jurassic cratonal margin depression (Alsharhan and Kendall, 1991). Lekhwair Formation (Hauterivian-early Barremian). The formation, which ranges from 215 to 365 m (705-1,197 ft) in thickness, is the equivalent of the Ratawi Formation in Qatar and the Buwaib Formation in Saudi Arabia. The lithofacies in the lower part of the Lekhwair Formation consist of fine-grained, pelleted, argillaceous wackestone and minor lime mudstone grading to peloidal, bioclastic, oolitic packstone followed by bioclastic and intraclastic packstone; pyritic, argillaceous wackestone; and more lime mudstone. In the upper part of the formation, the percentage of argillaceous lime mudstone and subordinate, bioclastic, glauconitic wackestone and packstone increases at the expense of the other lithofacies (Hassan et al., 1975; Alsharhan, 1989). The formation as a whole is characterized by alternating cycles of shallow, subtidal, turbulent water, and grain-rich limestone with deeper-water, subtidal, mud-rich carbonates (Alsharhan, 1989) (Fig. 8.10). Kharaib Formation (Barremian-Lower Aptian). The formation has a thickness of 88-110 m (289-361 ft) and represents porous and dense, carbonate, sedimentary cycles. Porous, grain-supported limestone (peloidal-oolitic packstone and grainstone), representing a regressive phase formed in very shallow, epeiric-shelf seas above the wave base, is followed by tight, non-porous, mud-supported limestone that represents the succeeding, marine transgressive phase. The sediments themselves range from dense, microporous, lime mudstone and laminated wackestone to peloidal, intraclastic packstone (Alsharhan, 1989) (Fig. 8.10). The carbonate cycles may have occurred during a period of substantial fluctuations in the rate of production and deposition of carbonate sediments on an extremely low-relief, depositional surface. Shuaiba Formation (Aptian). The formation records the differentiation of an intrashelf basin and shelf margin within the stable craton. In the basin, a typical, basinalslope facies of relatively dense and argillaceous lime mudstone/wackestone and shale with some grain-supported sediments were deposited, forming the Bab Member (Alsharhan, 1985). Around the basin margin, different lithofacies range from 100 to 145 m (328-475 ft) in thickness and include microporous, slightly argillaceous lime mudstone and wackestone; boundstone with abundant green algae; peloidal, bioclastic wackestone and packstone; coarse-grained packstone and grainstone with abundant rudists; and peloidal wackestone/packstone with corals and orbitolinids (Fig. 810). In the Bu Hasa Oil Field, for example, the rudist buildups developed upon algal mounds, the growth of which provided a basl topography. The combination of the elevated basin margin and the stable conditions is reflected in the vertical and lateral growth and the control exercised on their distribution

(Alsharhan, 1987, 1993, 1995). The two formations, Kharaib and Shuaiba, forming the top part of the Thamama cycle in the U.A.E. contain important oil reserves, giving the beds particular importance. Boichard et al. (1995) investigated the development of porosity. By applying sequence-stratigraphy techniques to the two formations, they were able to identify five sequences, two in the Kharaib succession and three in the Shuaiba. Fig. 8.11 (Boichard et al., 1995) gives a sequence-stratigraphy interpretation and indicates the principal facies and environments. The first two (K1, K2) developed the carbonate ramp, whereas the last two ($2, $3) developed within the Abu Dhabi Intrashelf Basin. (The third developed during the initiation of the basin.) Meteoric leaching of the sequence boundary beds during the highstand before being covered by transgressive deposits was responsible for the high porosity, whereas the tops of sequences ($2, $3) were never exposed.

Surface Section Musandam Group Unit 4 (Berriasian-Aptian). In the mountainous areas in the northern U.A.E., the Early Cretaceous Thamama Group equivalents in outcrop are known as the Musandam Group Unit 4 (BerriasianAptian) and are best developed in the Wadi Hagil area (Fig. 6.7) (in the Ras A1 Khaimah region) (Fig. 8.12). The Hauterivian-Aptian is dominated by mixed siliciclasticcarbonate turbidites with burrowed, muddy sediments and impressive, intraformational unconformities, passing upward into grainstone with rudists, corals and gastropods and terminated by thick-bedded, nodular and argillaceous lime mudstone with rudists, Textularids and Orbitolina (Fig. 8.12). Toland et al. (1993) studied the Berriasian-Early Valanginian succession at Wadi Hagil (Fig. 7.20) and concluded that: the Early Berriasian about 35 m (115 ft) equivalent to Upper Musandam Limestone unit G (in part) of Hudson and Chatton (1959). The base of the sequence is marked by a planar erosion surface locally overlain by up to 5.5 m (18 ft) of stratified clastsupported conglomerates with well rounded cobbles and small boulders. It is overlain by 29.5 m (97 ft) of clinostratified thin-bedded pelagic lime mudstones characterized by calpionellids and planktonic crinoids. The planar bounding surface at the base of sequence marks a significant erosional hiatus (?Kimmeridgian-earliest Berriasian) and an abrupt change in depositional environment from shoreface to platform slope. The basal conglomerate is interpreted as a transgressive lag deposit, the clinostratified lime mudstone sequence represents a highstand progradation of a carbonate foreslope into a starved deepwater basin. The base is a prominent downlap surface. The Latest Berriasian-?Early Valanginian, in excess of 66.5 m (218 ft) in thickness, is equivalent to Upper Musandam Limestone unit G (in part) to unit H (in part) of Hudson and Chatton (1959). The Lower 46 m (151 ft) of

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Early Cretaceous in Qatar The Yamama and Sulaiy formations (Berriasian-Valanginian) are equivalent to the Habshan and lower Lekhwair formations, while the Ratawi (Hauterivian) is equivalent to the upper Lekhwair Formation of the U.A.E. The Kharaib-Hawar (Barremian-early Aptian) is equivalent to the Kharaib Formation of the U.A.E., while the Shuaiba is similar in both countries. Detailed studies of these formations can be found in Sugden and Standring (1975) and Alsharhan and Nairn (1994). A composite, lithostratigraphic section is shown in Fig. 8.13. Sulaiy Formation (Berriasian). The formation consists of about 140 m (518 ft) of argillaceous lime mudstone, with thin beds of peloidal and oolitic limestone near the base and fine-grained, dolomitic wackestone with rare grainstone in the upper part. The formation is underlain by the Hith Formation (Tithonian), with the conformable contact placed at the top of a limestone containing anhydrite nodules of the Hith. It is overlain by the Yamama Formation, and the conformable contact is placed where porous, peloidal limestone of the basal Yamama rests on finegrained lime mudstone assigned to the underlying Sulaiy. Yamama Formation (Valanginian). The formation is about 120 m (444 ft) thick and consists in the lower part of light-gray, microporous limestone with fine-grained, peloidal and oolitic-intraclastic limestone, locally passing upward into peloidal wackestone and lime mudstone. The formation is overlain by the Ratawi Formation, and the contact appears conformable. The boundary is placed where porous limestone of the Yamama is overlain by argillaceous limestone of the basal Ratawi. It rests conformably on the Sulaiy Formation.

324

Ratawi Formation (Berriasian). The formation consists of about 145 m (536 ft) of a cyclic sequence (about five to six cycles) of fine-grained, dense, argillaceous limestone with intraclasts and pellets interbedded with gray and blue marl or marly limestone. The marl in each cycle does not exceed 7 m (23 ft) in thickness. The contact with the overlying Kharaib Formation is erosional. The surface is lithified in places, and boring of that surface can be seen in core samples. These borings are filled with marl, reinforcing the suggestion that the boundary is a hardground. The contact with the underlying Yamama Formation is apparently conformable, placed where argillaceous, peloidal limestone of the basal Ratawi overlies lime mudstone of the upper Yamama. Regionally, there is evidence of possible elimination of some beds at this boundary, which could, therefore, be unconformable (Sugden and Standring, 1975). Kharaib Formation (Barremian). It is about 85 m (279 ft) thick and consists of microporous limestone grading upward into an alternating sequence of shale and marl, continuing with peloidal, orbitolinid wackestone. The lithofacies of the Kharaib Formation suggest that it represents deposits on a shallow-marine shelf influenced by currents and slightly higher-energy conditions than those affecting the Ratawi beds. The contact with the underlying Ratawi Formation apparently is conformable, but regionally, considerable cutout and condensation of beds beneath the Kharaib Formation can be demonstrated over the Qatar Arch. The contact with the overlying Hawar Formation also is conformable. Hawar Shale Formation (late Barremian-early Aptian). This formation, which rests upon the beds of the Kharaib Formation, consists of some 15 m (49 ft) of bluegreen marl and shale rich in Choffatella decipiens and is conformable with the Kharaib below and the Shuaiba above. Although the unit is present throughout onshore Qatar, it gives way in the offshore to bioclastic, peloidal packstone, wackestone and argillaceous, glauconitic lime mudstone. This limestone can be traced eastward through the U.A.E. and is placed as a top unit in the Kharaib Formation. In the U.A.E., the name is redundant. Shuaiba Formation (early to mid-Aptian). This formation in offshore Qatar is particularly prominent because of its economic importance and the variety of lithofacies identified. The formation reaches a thickness of about 132 m (433 ft). In onshore Qatar, it consists of microporous limestone containing fine-grained, calcareous, organic debris strongly recrystallized in part and occasionally dolomitized. In the offshore, four units that represent a single depositional cycle have been described (Alsharhan and Nairn, 1994). The first unit consists of basal, algal boundstone deposited in shallow water, grading up into bioturbated and burrowed, microporous lime mudstone formed on an open-marine shelf. A second unit follows, consisting of microporous, argillaceous, densely cemented, stylolitic lime mudstone and wackestone with the mixed benthonic and pelagic fauna of a fairly deep shelf. This, in turn,

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous grades into a third unit of microporous, bioturbated lime mudstone and wackestone, with calcareous foraminifera and echinoid fragments formed in a quiet, open-marine environment. The fourth unit, deposited in water of variable depth and, consequently, higher energy, has a typical reef-like heterogeneity, with large, gray patches of algal, encrusted corals, rudist fragments and gastropods. It is presumed to have been somewhat elevated above the local sea floor, standing close to sea level. The formation rests conformably upon shale of the Hawar Formation and is disconformably overlain by the shale of the Nahr Umr Formation.

Early Cretaceous of Bahrain The Lower Cretaceous succession here consists of six formations, which have not received the detailed study made in the neighboring countries. A general description follows below and is shown on Fig. 8.3. Sulaiy Formation (Berriasian). The formation is represented by dense, dolomitic lime mudstone interbedded with peloidal-oolitic packstone/grainstone and peloidal, bioclastic, detrital wackestone. The contact between the Sulaiy and Yamama formations is conformable. Yamarna Formation (late Berriasian-Valanginian?). The formation is mainly wackestone, lime mudstone and packstone. Ratawi Formation (Hauterivian). The formation is composed of fine-grained, argillaceous limestone and occasional wackestone interbedded with soft, white marl. Kharaib Formation (Barremian). The formation is characterized by crystalline to microporous limestone and recrystallized limestone with some associated shale. Hawar Formation (late Barremian). The formation consists mainly of blue-gray shale and marl. Shuaiba Formation (Aptian). The formation consists of gray, argillaceous limestone at the base, passing up into microporous, fine-grained limestone. In part, the limestone may be strongly recrystallized and occasionally dolomitic. It is capped by microporous limestone at the top.

Early Cretaceous of Oman

Western Oman Mountains( Subsurface Formations) The Early Cretaceous in Oman is known as the Kahmah Group, a name given from Wadi Kahmah on the southern slopes of Jebel Akhdar of the Oman Mountain Range and may be used instead of the Thamama Group. It is a thick, carbonate sequence ranging from deepermarine, porcellanitic lime mudstone, chert and marl in the lower part to shallow-marine carbonates in the upper part. At the base, almost everywhere, there is a major sedimentary break, typically between the shallow-marine, Jurassic Sahtan carbonates and the pelagic facies of the basal Cretaceous Kahmah Group. There is a sedimentary break at

the top of the Kahmah Group, where marl and shale of the mid-Cretaceous Wasia Group rest on the karstified surface of the Kahmah Group (Hughes-Clarke, 1988). In the Oman Mountains, the thickness of the Kahmah Group reaches 750 m (about 2,460 ft), thickening toward the west and thinning toward the east. The stratigraphy, shown in Fig. 8.4, has been detailed by Morton (1959), Tschopp (1967a), Wilson (1969), Glennie et al. (1973, 1974), Simmons and Hart (1987) and Hughes-Clarke (1988). The Kahmah Group in subsurface is split into a lower Kahmah consisting of the Rayda, Salil and Habshan formations, and an upper Kahmah of the Lekhwair, Kharaib and Shuaiba formations, terms used in the U.A.E. (Alsharhan and Nairn, 1986; Hughes-Clarke, 1988). The presence of porcellanitic lime mudstone in the lower Kahmah reveals that deposition occurred in a deep basin with slow sedimentation during the Berriasian to early Valanginian. The presence of echinoid and molluscan fragments, the abundance of dasycladacean algae, and oolitic-peloidal packstone all point to shallow-shelf environments, from winnowed, oolitic, shelf-edge shoals to lagoonal or backshoal and lagoonal-channel conditions during the later Valanginian, conditions that persisted through the rest of the Lower Cretaceous. The rocks in the upper part of the Kahmah Group were deposited under shallow-water conditions, continuing the shallowing process indicated in the lower part of the group, and display numerous shallowingupwards cycles of the ramp interior (Simmons, 1994). The carbonate lithologies include abundant bioclastic wackestone; burrowed, peloidal grainstone; oolitic, peloidal packstone; and argillaceous limestone. Marl, sometimes pyritic, commonly is interbedded in the limestone. The upper part of the Shuaiba limestone, peloidal packstone and grainstone, may be locally enriched with rudist remains (Simmons and Hart, 1987; Hughes-Clarke, 1988; Alsharhan and Nairn, 1993; Pratt and Smewing, 1993). Rayda Formation (Berriasian). The formation takes its name from the Irq Rayda locality in the Lekhwair Field in the western Oman Mountains, where the thickness of the type sections is 152-168 m (499-551 ft). In subsurface, it is about 55 m (180 ft) thick, mostly of thin-bedded, porcellaneous lime mudstone and wackestone with thin chert and synsedimentary fractures (Fig. 8.14). At Wadi Miaidin, Simmons and Hart (1987) described the lower part of the formation as characterized by micritic, calcified radiolarians and small, benthonic and planktonic foraminifera; the upper part also is micritic with abundant calpionellids and microbioclasts. At Jebel Akhdar, the formation ranges in thickness from 30 to 83 m (98-272 ft) and consists of thin-bedded, cherty lime mudstone to wackestone and rare packstone containing pelagic microfossils (Pratt and Smewing, 1993). These represent slowly accumulating deposits on a deep-marine shelf below wave base. The base of the formation rests upon bored hardground at the top of the Sahtan (Jurassic) Limestone in northern Oman and the eastern U.A.E. (Pratt and Smewing, 1993) but pinches out in Sharjah, suggesting local paleotopography 325

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous (Scott, 1990). However, the possibility that the unit may be partly equivalent to the Hith, with only the top representing the Berriasian (Hughes-Clarke, 1988; Simmons and Hart, 1987) cannot be excluded. Salil Formation (Valanginian to earliest Hauterivian). The formation takes its name from Wadi as Salil near the Lekhwair Field. In the type section, it has a thickness of 192-212 m (630-695 ft), but the thickness increases to about 256 m (840 ft) in subsurface. It is a succession of thinly bedded, argillaceous mudstone, wackestone and marl with bioclasts, suggesting a continuation of the facies developed in the beds of the Rayda Formation (Fig. 8.14). The presence of silicified radiolaria, rare planktonic foraminifera and fecal-pellet grainstone suggests that part of these sediments probably were derived from shallower regions of the carbonate ramp and deposited in a subwave-base setting. The succession of lithofacies also suggests a progressive reduction in water depth (HughesClarke, 1988; Simmons and Hart, 1987). Pratt and Smewing (1993) described the Salil Formation from Jebel Akhdar and adjacent areas and concluded that the formation varies considerably in thickness, from 110 m (361 ft) at Jebel Madar to 485 m (1,463 ft) in Wadi Sahtan. It consists of thin- to medium-bedded, locally wavy and nodular-bedded, argillaceous lime mudstone with interbedded, calcareous shale; rare, fine-grained, peloidal grainstone; and, toward the top, bioclastic wackestone and packstone. Habshan Formation (Hauterivian). The formation is characterized by about 174 m (570 ft) of a coarseningupward sequence of wackestone to grainstone, with commonly occurring ooidal and algal, oncoidal and shell debris providing evidence of a high-energy setting (Fig. 8.14). The Habshan Formation at Jebels Akhdar and Madar ranges from 65 to 85 m (213-279 ft) and is composed of medium-bedded, locally cross-stratified, oolitic, oncolitic, peloidal and bioclastic grainstone and packstone (Pratt and Smewing, 1993). Lekhwair Formation (late Hauterivian-Barremian). The formation, 320 m (1,050 ft) thick, is dominated by sedimentary cycles, in which argillaceous limestone to marl with pyrite and some quartz silt grade upward into microporous, algal-skeletal wackestone terminating with peloidal-skeletal packstone and grainstone (Fig. 8.15). The Lekhwair at Jebel Madar consists of about 140 m (459 ft) of interbedded, thin to thick and rarely massive-bedded lime mudstone and bioclastic, peloidal wackestone to grainstone with local, finely crystalline, argillaceous dolostone. Bioturbation is common, while burrows; microbial laminites; laterally linked, hemispheroidal stromatolites; cross-lamination and small-scale channeling occur locally (Pratt and Smewing, 1993). The Lekhwair sediments reflect a shallow, probably restrictedmarine environment with a minor clastic input. Kharaib Formation (Barremian-earliest Aptian). The formation is composed of 103 m (338 ft) of mudstone, with oncoidal and binding algae in the lower part giving way upward to packstone and grainstone with common

rudists to end with thin, argillaceous limestone (Fig. 8.15). The Kharaib Formation at Jebel Madar is about 65 m (213 ft) thick. According to Pratt and Smewing (1993), it is composed mainly of massive limestone units of bioturbated, bioclastic and peloidal packstone and wackestone with local concentrations of oysters, rudists and corals. The formation is a shallow-water deposit throughout. Shuaiba Formation (Aptian). The formation consists of shallow- to deeper-water deposits with a return to shallow-water environments at the top. It has a thickness in subsurface of 95 m (312 ft). The lower part is dominated by Bacinella algal-skeletal wackestone and boundstone, passing upward into argillaceous limestone and foraminiferal, rudistid wackestone and packstone (Fig. 8.15). The Shuaiba in outcrop is lithologically more homogenous than the underlying Kharaib, ranging in thickness from 40 to 125 m (131-410 ft) and consisting of massive beds of bioturbated, bioclastic and peloidal packstone with local rudstone and grainstone. Oysters and rudists, foraminifera and algae are common. At the top of the formation at Jebel Madar is a thick sequence about 10 m (33 ft) of requienidcaprinid, rudist biostrome (Pratt and Smewing, 1993). In northern Oman, Shuaiba sedimentation continued later than further south in the U.A.E. The sea-level fall at about the Early/Late Aptian boundary did not affect the deeper parts of the basin. Consequently, the Shuaiba escaped the leaching developed prior to the deposition of the Nahr Umr in other areas..

Central Oman Mountains (Allochthonous Units) Sid'r Formation (Berriasian-Barremian). The formation is the "upper chert member" of the Dhera and Wahrah formations, the "chert member" of the Dibba Formarion of Glennie et al., 1974, and the fourth rock unit in the Hamrat ad Duru Group of Cooper (1987). It consists of about 140 m (460 ft) of thin-bedded, moderately to extremely cherty and silicified, radiolarian wackestone turbidites with shale partings (Fig. 8.16). The lower 25 m (82 ft) show an increase in fine-grained, silicified, peloidal packstone and grainstone (Cooper, 1987; Glennie et al., 1974). The occurrence of Cuneolina sp. and tintinnid microplankton confirm the Early Cretaceous age. The Sid'r Formation is thought to have been deposited in relatively deep water at, or just below, the carbonate compensation depth (CCD) (Glennie et al., 1974). Stratigraphically, the Sid'r Formation unconformably overlies the Guweyza Formation, and the top is conformably overlain by the beds of the Nayid Formation. Nayid Formation (Barremian-Cenomanian). The formation is the "Upper Limestone Member" of the Dhera and Wahrah formations, the "Upper Member" of the Dibba Formation (Glennie et al., 1974) and the last rock unit in the Hamrat ad Duru Group of Cooper (1987). The Nayid is about 50 m (164 ft) thick of decimeter-bedded, lithoclastic and peloidal, turbiditic grainstone with subordinate, interbedded lime mudstone, marl and silicified marl (Fig.

327

Sedimentary Basins and Petroleum Geology the Middle East

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L,THOLOGY

GENERAL DESCRIPTION

RADIOLARIAN ~ O N E , ~ T L Y OR COMPLETELY SIUCIqED OOLITIC GRAINSTONE WITH ABUNI~NT LITHOCLASTIC AND MICROCLASTIC ALTERNATING WITH LIME MUDSTONE, SlUCIFIED SHALE AND CHERT

LITHOLOGY

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GENERAL DESCRIPTION SILICIFIED AND RADIOLARIAN LIME MUDSTONE AND R~CKSTONES

' LITHOCLASTIC, SKELETAL PACK.STONE AND GRAINSTONES CONTAINING ~ENTS OF RUDISTID LAMELLIBRANCH AND DEBRIS OF FORAMINIFERA. TURBIDITE GRAINSTONE

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8.17). These sediments were deposited in a protected environment proximal to the position inferred for the paraautochthonous Sumeini Group, as described by Glennie et al. (1974). The base of the Nayid Formation is marked by an abrupt reduction in silicification. The top contact generally is tectonic, except in the Hawasina Window area, where the contact with the Muti Formation is conformable. Cooper (1990) concluded that the Nayid Formation was deposited close to the CCD and that the preservation of coarse-grained carbonate reflected the reduced silicification potential of these allochems, rather than a significant rise in the CCD.

Mayhah Formation, C Member (pre-Cenomanian?). The member is composed of megabreccias up to 190 m (623 ft) thick. The breccias contain clasts of chert apparently derived from the underlying B Member and a matrix consisting of granular wackestone/packstone (Watts and Garrison, 1984). Breccia beds are up to 5.5 m (18 ft) thick and typically have a clast-supported fabric with clasts oriented sub-parallel to bedding. The thick megabreccias of the C Member represent extensive, submarine-debris, avalanche deposits; such large mass flows (similar to the one described by Mutti et al., 1984) may

328

have originated due to tectonic steepening of the slope and could have been emplaced by movements triggered by seismicity (Watts and Garrison, 1986) (Fig. 8.18a). Watts and B lome (1990) reported that the age of the megabreccia is poorly known (pre-Cenomanian?), so it may correlate with calcirudite in the D Member. Alternatively, the underlying B Member chert may have formed an inherently unstable substrate, leading to its repeated failure and downslope movement as debris flows.

Mayhah Formation, D Member (Valanginian to Cenomanian). The member ranges in thickness from 60 to 105 m (197-344 ft). The lower part is dominated by a thick interval of thinly bedded, argillaceous lime mudstone, whereas numerous gravity flows, sediment slumps and slides in the upper part indicate a steepening of the slope prior to basin closure. It also contains numerous thin to thick, lenticular beds of redeposited, oolitic and intraclastic wackestone/packstone (Watts and Blome, 1990) (Fig. 8.18b). The coarse-grained deposits are interbedded with moderately bioturbated, thinly bedded lime mudstone, which locally is interlaminated with wackestone. The wackestone contains rare ooids and peloids and abundant radiolaria, pelagic foraminifera and sponge spicules.

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

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Intraformational debris sheet with numerous folded slabs Fig. 8.18. Facies models for the C and D members of the Mayhah Formation, Oman Mountains (from Watts and Garrison, 1986; Watts and Blome, 1990): A=the Member C facies model; in the Early to mid-Cretaceous (pre-Cenomanian), slope instability led to the cataclysmic erosion of much of the platform margin and the resulting thick accumulation of debris or megabreccia; slope instability could be related to tectonic steepening of the slope and seismicity that led to instability of the margin of the carbonate platform; this steepening of the continental margin slope may have accompanied approach to a northward-dipping subduction zone prior to the closing of the Hawasina Basin (South Tethys Sea) in the Late Cretaceous; alternatively, sediment loading due to progradation of thick, shallow-marine carbonate over a previously drowned platform (shown above) may have initiated the collapse; B=the Member D facies model; in the pre-Cenomanian upper part of the Mayhah Formation, the sudden onset of slumps and sediment gravity flows signify steepening of the slope resulting from tectonic downbowing of the continental margin. The member also contains minor chert and interbedded shale and mudstone. The upper contact of the Mayhah Formation (top of the D Member) with the Qumayrah Formation is sharp and conformable, but it sometimes may be gradational where siliceous, radiolarian-bearing limestone of the basal Qumayrah rests on the calcareous chert of the top Mayhah. The sediments of D Member were deposited in various environments, according to Watts and Blome (1990). The bedded lime mudstone and wackestone, largely composed of pelagic faunas and carbonate mud, marked the return to monotonous, basinal, carbonate sedimentation. Slumps and sediment gravity flow could signify steepening of the slope resulting from tectonic downbowing of the continental margin. Widespread debris sheets containing clasts of folded, slope limestone originated as mass movements and evolved into debris flows, whereas the occurrence of thick, lenticular beds of oolitic packstone/grainstone were derived from shallow-water, ooid shoals at the shelf edge.

In the northern Oman Mountains (Musandam Peninsula), the Lower Cretaceous Thamama Group equivalents lie within the Musandam Group (Jurassic to Lower Cretaceous); thus, they are equivalent to the Sahtan and Kahmah groups of Glennie et al. (1974). A division into nine members (A to I) has been made (Ricateau and Riche, 1980) (Fig. 7.16), of which only members G (BerriasianValanginian), H and I (Barremian to Aptian) are Thamama Group equivalents and, consequently, the only ones described here. Musandam Member G (Berriasian-Valanginian). This member is about 295 m (968 ft) thick. The lower 15 m (49 ft) is represented by light-gray, radiolarian lime mudstone with tintinnids, and siliceous and ferruginous nodules and bands on an unconformable surface of fractured, Tithonian biostromal limestone. Above is about 110 m (361 ft) of a mixed facies of siliciclastic/carbonate turbidites with burrowed, muddy tops and impressive, intraformational unconformities followed by thick, argillaceous limestone with rare ammonites and belemnites (about 110 m, or 361 ft), overlain by about 170 m (558 ft) of lime mudstone, wackestone, packstone and grainstone with a rich microfauna containing Calpionella dardei, C. incinata and Haplophragmoides catenui. A few intraformational conglomeratic horizons are interbedded within the limestone sequence. Musandam Members H and I (Barremian to Aptian) are about 300 m (984 ft) thick, beginning with alternations of thick-bedded, argillaceous, nodular limestone and bioturbated limestone containing bryozoa, solitary corals, lamellibranchs and gastropods. The limestone grades up into lime mudstone and wackestone, with orbitolines, algae and foraminifera and a macrofauna of rudist and gastropod debris concentrated in shelly horizons. The top is an irregular and bored surface. The presence of orbitolinids suggests an Aptian age.

Early Cretaceous on the Eastern side of the Arabian Gulf : Southwest Iran In Iran the Jurassic to Early Cretaceous carbonates are known as the Khami Group, ae name originally assigned by Strong and Falcon (cited in Setudehnia, 1972) to massive and thin-bedded limestone forming the high cliffs at Kuh-e Khami northeast of the Gachsaran Oil Field in southwestern Iran. The group was divided into a sequence of five formations by James and Wynd (.1965) - - the Surmah, Hith, Fahliyan, Gadvan and Dariyan m of which the lower two are Late Jurassic in age (described in Chapter 7), while the upper three are Early Cretaceous.(see James and Wynd, 1965, Setudehnia, 1972) Fahliyan Formation (Berriasian-Hauterivian). The lowest of the Early Cretaceous formations, it is named after a village in the Fars Province. Like the rest of the

329

Sedimentary Basins and Petroleum Geology the Middle East region, the carbonate lithologies and fauna (including corals and algae) are consistent with a shallow, carbonateshelf depositional environment and have a thickness of 366 m (1,200 ft) of massive, oolitic and peloidal limestone with contemporaneous brecciation in the lower part (Fig. 8.19). The formation is conformably overlain by the marly limestone of the Gadvan Formation. From Fars toward southwestern Lurestan and northeastern Khuzestan provinces, the Fahliyan Formation grades into, and intercalates with, the Garau Formation (Fig. 8.5). Gadvan Formation (Barremian-early Aptian). The formation, which also has a type locality in the Fars Province at Kuh-e Gadvan, is a sequence of limestone about 107 m (350 ft) thick, consisting of dark-gray, argillaceous, bioclastic limestone interbedded with gray, green to brownish-yellow marl (Fig. 8.19). Lateral facies changes occur; the formation in the Khuzestan Province consists of dark shale and argillaceous limestone, whereas in the Lurestan Province, the limestone passes to the dark to black, argillaceous limestone of the Garau Formation (Neocomian-Coniacian) and ranges in deposition from a shallowmarine to neritic, inner-shelf, low-energy environment. Toward the Arabian Gulf, the shaly component diminishes and disappears. The Gadvan grades up into the succeeding Dariyan Formation. Dariyan Formation (Aptian). Named after a village in the Fars Province, this formation is 286.5 m (940 ft) thick at the type locality and consists of thick-bedded, massive limestone with abundant orbitolines deposited in a shallow-marine to lagoonal environment (Fig. 8.19). It is present throughout southwestern Iran, with the exception of central and southern Lurestan, where it is replaced by the Garau Formation. It has been correlated with the Shuaiba Formation on the opposite side of the Arabian Gulf. Garau Formation (Neocomian-Coniacian). The formation takes its name from Tang-e Garau, Kabir Kuh in the Lurestan Province. Eight lithological units of deepmarine origin (Fig. 8.20) have been recognized by Setudehnia (1972) (from top to bottom): Unit 8:9.8 m (65 ft) of sandy limestone with chert nodules Unit 7:73 m (240 ft) of sandy, glauconitic shale and limestone Unit 6 : 1 2 2 m (400 ft) of alternating gray shale and thin-bedded, fine-grained, shaly limestone Unit 5 : 5 8 m (190 ft) of light- to dark-gray, very fine-grained limestone with chert nodules Unit 4 : 1 1 3 m (370 ft) of gray and brown fossil shale with bands of limestone Unit 3:143 m (470 ft) of dark-gray to buff, very fine-grained, thinly bedded limestone Unit 2 : 2 9 6 m (970 ft) of black, carbonaceous shale with interbedded, dark, very fine-grained, thinly bedded limestone Unit 1 : 9 m (30 ft) of black, carbonaceous shale with concretions The Garau is overlain by the beds of the Albian-Turo330

nian Sarvak Formation, but there is a diachronous relationship, because in the deeper part of the basin, the lower part of the Sarvak Formation is a lithofacies equivalent to the top of the Garau. Where the boundary between the two is seen on the shelf, the presence of a sandy, glauconitic interval suggests the presence of a nonconformity.

Early Cretaceous in the Northern, Northwestern and Northeastern Arabian Platform The transit across Kuwait and Iraq extends across the platform to the deeper-water basin lying off the edge of the platform in northern Iraq. Uplift during the Late Jurassic and Early Cretaceous affected the region; the region was one of tectonic stability for the rest of the Cretaceous. The depositional environments in Kuwait during the Berriasian-Valanginian grade laterally from a shallow-shelf to outer-neritic environment found in Iraq. By facies transition, the Ratawi Formation (Valanginian-Hauterivian) passes laterally and vertically to the Zubair Formation (Hauterivian). From the age, it is clear that the transgression arrived later in Saudi Arabia; the Sulaiy Formation, deposited during the late Tithonian to Valanginian interval, is overlain by the Valanginian Yamama Formation, with its characteristic bioclastic packstone separated from the Buwaib (mid-Hauterivian to mid-Barremian) above by an unconformity, at least in places; in Iraq, the Zubair (Barremian), the equivalent in part of the Buwaib, passes down without break into the Ratawi (Hauterivian) (Alsharhan and Nairn, 1986).

Early Cretaceous in Kuwait The Lower Cretaceous section is dominated by neritic limestone in the lower part and is overlain by shale containing stringers of limestone and sandstone, followed by thick sandstone interbedded with shale and minor siltstone. The section is completed by limestone and dolomitic limestone (Fig. 8.3).

Sulaiy/Makhul Formation (latest Tithonian-Berriasian). The lowest formation in the Cretaceous of Kuwait, it ranges in thickness from about 140 m (459 ft) in northern Kuwait to about 300 m (984 ft) in the south (A1 Refai, 1967). It consists of dense, brown, cryptocrystalline, argillaceous limestone, which is locally dolomitic and anhydritic and is interbedded with marl and silt and contains chert nodules in the lower part (Fig. 8.21). The beds, which contain radiolaria, sponge spicules, bivalve debris, miliolids, ostracods and algal remains, formed in a slightly deeper-marine environment with unrestricted circulation. Although sedimentation was continuous, the basin floor appears to have had an undulating topography seen as slight changes in sequence thickness along strike from the northern to southern parts of the country.

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The name of the formation was adopted by the Kuwait Oil Company from well Minagish-8 in the Minagish Oil Field

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in central Kuwait, where the thickness is about 325 m (1,066 ft) and ranges up to 360 m (1,181 ft) in northern Kuwait (Fig. 8.21). A1 Refai (1967) recognized three subdivisions: the Upper and Lower Dense "members" separated by an oolite member. These are easily recognizable in the southern part of Kuwait, but a distinction between the other two members cannot be made where the oolite member is missing. The oolite member is a peloidal, bioclastic, locally dolomitic, medium- to coarse-grained, oolitic grainstone. The hard, dense members above and below tend to be micritic (lime mudstone and wackestone) with low porosities, but with oil staining along the bedding planes. The Minagish contains benthonic foraminifera, miliolids, ostracods, echinoderms, calpionellids and skeletal fragments. Ratawi Formation (Late Valanginian-HauterivJan). The formation varies from about 290 m (951 ft) in northern Kuwait to 130 m (426 ft) in the south. The facies in the lower part of the formation all over the country is primarily carbonate (bioclastic, peloidal limestone), while in the upper part, it ranges from shale and sandstone in the west to shale and limestone in the east. These sediments, which contain benthonic foraminifera, algae, calpionellids and other skeletal fragments, were deposited on a shallowmarine, shelf environment. Zubair Formation (Barremian-Aptian). The formation ranges in thickness from 353 m (1,158 ft) in the south to about 450 m (1,476 ft) in the north. A dominantly sand-

332

Fig. 8.21. Lithostratigraphy of the Late Jurassic-Early Cretaceous Sulaiy/MakhulMinagish formations in Kuwait (modified from A1 Rifaiy and Lemone, 1987).

stone succession with some shale intercalations and minor limestone, it represents littoral and partly deltaic sediments derived from the erosion of the Arabian Shield. The age of the formation in Kuwait is reported as Barremian, based upon microfossils identified by Owen and Nasr (1958). In depositional environment and age, it is almost identical to the Biyadh Formation in Saudi Arabia. The sandy sequence, which contains some interbedded marl and marly limestone, crops out on Jabal Abd el Aziz in Syria (Ponikarov et al., 1967) and has a wider age range, Valanginian-Barremian. It is roughly equivalent to the lower and middle parts of the Zubair Formation in Iraq (Buday, 1980) and to the Zubair Formation in Kuwait. Shuaiba Formation (Aptian). Ranging in thickness from 60 m (197 ft) in the south to 80 m (262.5 ft) in the north, this formation consists of coarsely crystalline, porous, heavily fractured and cavernous, dolomitized limestone with rare thin shale deposited in a low-energy, shallow, lagoonal environment. Early Cretaceous in Iraq

I Southern Iraq The Berriasian-Aptian cycle is represented by many formations, most of them occurring on the platform area on both the stable shelf(south and central areas) and unstable shelf (northern areas). The formations laid down in those areas were relatively well-investigated by Bellen et

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Ratawi Formation (Valanginian to Hauterivian). The formation was first described in the Ratawi Field in southern Iraq. It is well-developed in subsurface in southern Iraq only and consists of between 220 and 300 m (722984 ft) of dark, slightly pyritic shale. It includes interbedded stringers and beds of buff, pyritic, peloidal and fossiliferous limestone in the lower part (Bellen et al., 1959). The sediments are interpreted as deposits in a partly euxinic lagoon fringing the shore of the transgressing Cretaceous sea. The lower and upper boundaries of the formation are conformable. The upper part passes gradually into the Zubair Formation. The lower part of the formation can be correlated with the Buwaib Formation of Saudi Arabia (Buday, 1980).

Zubair Formation (Hauterivian to early Aptian). The formation was introduced to designate an interval of predominantly terrestrial clastics that preceded the deposi-

tion of the oil-bearing sequences in the southern Iraqi oil fields. Lithologically, the formation consists of an alternation of shale and sandstone with intercalations of siltstone and has a total thickness of 380-400 m (1,246-1,312 ft). The beds formed in a littoral, partly deltaic, sedimentary environment as regressive phases of prodelta, delta front, swamp and marsh and ended as a shelf setting developed (All and Nasser, 1989). The five members recognized (Fig. 8.22) are summarized below from older to younger: 9 Upper Shale M e m b e r : greenish black, hard, fissile shale enclosing a sandstone-siltstone zone 9 Upper Sandstone Member: predominantly sandstone with subsidiary siltstone 9 Middle Shale M e m b e r : black, or greenish black, hard, fissile shale with occasional sandstone streaks 9 L o w e r Sandstone Member: mostly sandstone with subsidiary shale and siltstone 9 L o w e r Shale Member: fissile shale, including two dis-

333

Sedimentary Basins and Petroleum Geology the Middle East the beds of the Lower Qamchuqa Group, which form one of the major reservoirs, recently have been studied by A1 Shdidi et al. (1995) with data from wells in an anticlinal structure 60 km long by 5 km wide lying west of Kirkuk. Of the four megasequences, the Cretaceous Qamchuqa/ Sarmord/Balambo formations developed during the phase of basin extension (Figs. 8.23 ). The Qamchuqa Group includes the upper and lower Qamchuqa Formation, the upper and middle Sarmord Formation, and the Balambo Formation. Their facies relations are shown in Fig. 8.24. The upper and lower Qamchuqa carbonates are equivalent to the Mauddud and Shuaiba, and the shaly upper and middle parts of the Sarmord Formation are equivalent to the Nahr Umr and Ratawi formations. The megasequences are bounded by discontinuities, and although only the lowest is regional, marking an abrupt change in sedimentation from shallow-shelf carbonates to deeper-shelf marls, the other two m the intraAptian Shuaiba/Nahr Umr break and the Mauddud/Wara contact m are well-known within the Arabian Platform. The megasequences are subdivided by local discontinui-

tinct sandstone zones and minor amounts of siltstone. The contacts of the upper and lower formations are mostly gradational and conformable In southern Iraq and Kuwait, the deposition of the Zubair Formation was contemporaneous with, but of shorter duration than, that of the Biyadh Formation in Saudi Arabia (Ali and Nasser, 1989). Shuaiba Formation (Aptian). In the type area in the Zubair Field, southern Iraq, the Shuaiba is composed of about 80 m (262 ft) of argillaceous, microporous and crystalline limestone with some peloidal packstone with some partly glauconitic limestone in the upper part (Bellen et al., 1959). The carbonate was deposited in a shallow- to moderate-marine environment with a restricted terrigenous supply. The lower contact with the Zubair Formation usually is conformable and gradational, whereas the upper contact with the Nahr Umr Formation is unconformable.

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Sedimentary Basins and Petroleum Geology the Middle East ties into mesosequences (two in SM1, and four in SM2) and represented by variations in sedimentation (Fig. 8.23). Garagu Formation (Berriasian-Valanginian). The formation is found over the unstable shelf in northern Iraq close to the shelf edge. It contains a more complete marine section than that found closer to the Arabian Shield and averages from 200 to 230 m (656-754 ft) in thickness, although this may vary considerably because of facies changes. The formation consists of sandy, oolitic limestone with marl and sandstone in the upper and lower parts and thick, bioclastic-detrital limestone in the middle (Bellen et al., 1959). It represents a lagoonal depositional environment beyond the reach of a major clastic supply. The top contact, as a rule, is conformable with the overlying Lower Sarmord Formation. Exceptionally, local unconformities may occur. The lower boundary is unconformable. The formation is widely spread and typical of the basal Lower Cretaceous in northern Iraq, where it is present in outcrop and in the subsurface of the unstable shelf. In the Kirkuk area, the Garagu Formation forms a tongue within the Lower Sarmord only. Further north in southeast Turkey, it may be represented within the Cudi Group. The deep-water equivalents are included in the Balambo Formation, which occupies much of the Cretaceous. Lower Balambo Formation (Berriasian-Albian). In northern and northeastern Iraq, the formation represents the deeper-water, bathyal Cretaceous sediments deposited during much of the Cretaceous. The Balambo Formation commonly is divided into lower and upper divisions, which correspond to the Early Cretaceous (Thamama Group) interval and the mid-Cretaceous (Wasia Group) interval in southern Iraq and Arabia. The Lower Balambo (Berriasian-Albian) consists of about 280 m (918 ft) of thin-bedded, blue, ammonitic limestone intercalated with olive-green marl and dark-blue shale (Bellen et al., 1959). The fauna lacks typical neritic forms and is characterized by pelagic elements. The lower boundary appears to mark a non-sequence, while the upper boundary is gradational.

Lower Sarmord Formation (Berriasian-Barremian). The formation in its type locality in the High Folded Zone of northeastern Iraq consists of about 455 m (about 1,493 ft) of monotonous, brown and bluish marl with alternations of marly, neritic limestone (Bellen et al., 1959) laid down in a deeper-neritic, marine environment. The limits of the formation generally are transitional and conformable, although an unconformity exists in one small region of the Foothills Zone, where it is overlain by the Albian (Jawan Formation).

Lower Qamchuqa Limestone Formation (AptianAlbian). The formation is found in the High Folded Zone in northern and northeastern Iraq as a 250-300 m (820-984 ft)-thick layer of massive, rather argillaceous, fossiliferous, neritic limestone with some disseminated silt and glauconite. The limestone often is dolomitized and interbedded with dolomite and may contain a subordinate, ter-

336

rigenous admixture (Fig. 8.23a) (Buday, 1980; A1 Shdidi et al., 1995). The lower contact of the formation usually is conformable, while the upper contact is unconformable, corresponding with the intra-Aptian discontinuity.

Early Cretaceous in Syria In eastern central Syria, where the Palmyra and Sinjar troughs occur, the Lower Cretaceous sediments were confined largely to the troughs. The branching Euphrates Anah Trough received Lower Cretaceous deltaic, clastic sediments only at its confluence with the Palmyra Trough. By the Aptian-Albian, carbonate-evaporite platform sedimentation was reestablished in the troughs. Deltaic, clastic sediments accumulated on the flanks of the RutbahKhleissia High, and neritic carbonates and evaporite sediments were deposited northward away from the high (Fig. 8.4). Qamchuqa Formation (Barremian to Aptian). This formation is found in Syria, where it rests unconformably over the late Jurassic Sargelu Formation. Dolomitization and recrystallization of the limestone is common here, as in Iraq. Toward northeastern Syria, the upper part of the Qamchuqa Formation is replaced by the Ghona Formation (Aptian-Albian), an alternation of limestone and dolomite; whereas in eastern Syria, the Ghona gradually is replaced by clastic sediments (sandstone and shale) and argillaceous limestone deposited in a neritic environment. The Ghona Formation is in disconformable contact with the overlying Soukhne Formation (Coniacian-Campanian). The lithology of the Qamchuqa, excluding the facies variation in eastern and northeastern Syria, is very similar to that of the contemporary Shuaiba Limestone found in southern Iraq. Rutbah Formation (Barremian-Albian). The formation is well-developed in central and eastern Syria and ranges in thickness from 40 to 247 m (131-810 ft). It is composed of a sequence of siltstone, shale and sandstone with some volcanic deposits, followed unconformably by the Hayane Formation. It overlies disconformably the Qamchuqa Formation. Hayane Formation (Aptian-Cenomanian). The formation is well-developed in the Palmyra region in central Syria, passing from gypsum in the lower part upward into dolomite with intercalated anhydrite. It rests disconformably upon the lower Qamchuqa Limestone, but is followed conformably by the bioclastic limestone of the Cenomanian Judea Formation.

Early Cretaceous in Jordan Kurnub Group (Berriasian-Albian). This clastic group represents the Lower Cretaceous deposits of central and southern Jordan. The group was first described by Bender (1967, cited in Bender, 1974). Subsequently, Abed (1982) provided detailed lithofacies descriptions from northwestern Jordan. The group replaces the earlier division into a lower Massive White Sandstone and an upper

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous (Albian-Cenomanian) is conformable and gradational. In northern Jordan, the upper part of the Kurnub, the Subeihi Formation, rests unconformably on a Permian to Jurassic sequence; in the southern two-thirds of the country, where the Hercynian and base Cretaceous unconformities merge, the sandstone overlies Lower Paleozoic sediments (Andrews, 1992).

Variegated Sandstone used by Bender. It is a sequence of about 300 m (984 ft) of varicolored, fining-upward, friable, quartz arenites of dominantly fluvial-channel fill with intercalated, shallow, tidal-fiat beds, as indicated by ripple marks and reversal of current bedding directions in southcentral Jordan with marine intercalations (dolomite and marl) in north-central Jordan (Bender, 1974; Abed, 1982). Powell (1989b) divided the Kurnub Group at Wadi Karak into two formations and six lithological units" the lower Arada Formation (units 1 and 2) and the upper Subeihi Formation (units 3-6) (Fig. 8.24). There, the Kurnub overlies the Cambrian Umm Ishrin Sandstone and is overlain by the Naur Formation. The Kurnub Group is widely distributed in outcrop along the rift margins and in subsurface. The maximum thickness in outcrop is more than 350 m (1,148 ft) and varies in subsurface from 238 m (781 ft) in well Northern Highlands-1 to 25-60 m (82-197 ft) in the Risha and Sirhan areas. At outcrop, the Kurnub Group generally is assigned a Hauterivian-Albian age, and in subsurface, where dating is imprecise, the age ranges from Aptian to Albian-early Cenomanian? (Andrews, 1992) (Figs. 8.4 and 8.25). The contact with the overlying Naur Formation ~) ~. C) F<~ ~:r ~ ~ ~':::>

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erately deep water in an open-marine environment (Cordey, 1971). The group is unconformably overlain by the upper Campanian Karabogaz Formation. The Mardin Group consists of four formations: the Areban (Upper Barremian-Upper Albian), Sabunsuyu (Upper Albianlower Cenomanian), Derdere (Middle Cenomanian-lower Turonian) and Karababa (Upper Coniacian-Lower Campanian). Unconformities are developed at the tops of the Sabunsuyu and Derdere formations (Figs. 8.5 and 8.26). The Lower Cretaceous, discussed here, is represented by the Areban Formation. Berriasian-Barremian strata are absent because of non-deposition or erosion. Block-faulting in the Late Jurassic and Early Cretaceous created some high and low areas (horsts and grabens), with the high areas not transgressed until the Aptian (Ala and Moss, 1979; Temple and Perry, 1962; Celikdemir et al., 1991). Duran and Aras (1990) observed the existence of a sedimentological break between the Sabunsuyu and Derdere formations° The Sabunsuyu Formation shows karstic fea338

tures caused by subaerial erosion and solution at the uppermost part and is overlain by transgressive, shallowmarine, bioclastic, carbonate facies of the Derdere Formation. Areban Formation (Aptian). The formation ranges in thickness from 3 to 50 m (10-164 ft) of pale-yellow to pale-brown sandstone; sandy limestone; very fine-grained, sandy dolomite; yellowish-brown shale; marl; and shaly limestone of a shallow-marine, nearshore environment with an influence of clastic supply from the paleohigh areas nearby. It unconformably overlies the Cudi Group (Celikdemir et al., 1991) and is overlain by the Sabunsuyu Formation. The Areban Formation is one of the clastic units of the southeast Anatolian autochthonous sedimentary sequence. Based on dinoflagellate assemblage studies by Ertug (1990), the lower part of the formation is of ?Late Barremian-Aptian age, the middle part is Early Albian, and the upper part is Middle-late Albian.

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Early Cretaceous in Southern and Southwestern Arabia: The Republic of Yemen A regional unconformity separates the Cretaceous section from the Jurassic rocks. The Cretaceous rocks are included in two groups" the Tawilah Group in the west and the Mahra Group in the east. The rocks of the Mahra Group are developed best in southern and southeastern Yemen (the former South Yemen) and southern Oman (Fig. 8.5), where five formations have been recognized that range in age from Barremian to Maastrichtian: the Qishn, Harshiyat, Fartaq, Mukalla and Sharwain formations (Beydoun and Greenwood, 1968), similar to the names adopted in the stratigraphy of South Oman (Fig. 8.4). In the west, continental and nearshore facies are the dominant lithofacies; whereas the dominant lithologies in the east represent nearshore to shallow-marine environments. The Qishn Formation (Barremian-Aptian) is described here, because it is the only Lower Cretaceous sedimentary unit in the Mahra Group. Due to a major unconformity in western and northwestern Yemen (the former North Yemen), the Lower and mid-Cretaceous beds were removed by erosion. The Tawilah is dated as Late Cretaceous to Paleocene (El Nakhal, 1988). Qishn Formation (Barremian-Aptian). The forma-

tion is the most regionally developed basal unit of the Cretaceous system and reflects the return to marine conditions after the terminal Jurassic phase of uplift and erosion. It onlaps earlier deposits from east to west (Beydoun, 1991; Beydoun et al., 1993). This is the lowest formation in the Mahra Group of southern Yemen, where it is recognized as a distinct cycle of marine sedimentation. The top is marked by a regression followed by the basal Albian clastics of the Harshiyat or Fartaq formations. The formation crops out in several localities in the coastal region of Yemen and is found in deep wells as a prolific oil producer in the former South Yemen. Its thickness in the outcrop may range from a low of 32 m (about 105 ft) in the west to the high of 411 m (1,348 ft) in the east, and it ranges from 300 to 450 m (984-1,476 ft) in subsurface. In the west, it is made up of a basal conglomerate followed by shelly sandstone, with bands of oolitic and fossiliferous limestone capped by shaly marl and sandy limestone (Greenwood and Bleakley, 1967). To the east, the section thickens, and the basal, conglomeratic sandstone rests disconformably on the Jurassic Naifa Formation. It is succeeded entirely by shaly and oolitic limestone, with alternating marl bands containing marly limestone and thin, shale stringers (Beydoun, 1964, 1966; Beydoun and Greenwood, 1968) in the upper half. In subsurface, as in outcrop, the sequence starts

339

Sedimentary Basins and Petroleum Geology the Middle East with a basal conglomerate resting unconformably on the Upper Jurassic Naifa Formation, followed by shallowwater carbonates and interbedded sands, marl and shale in the middle, and limestone in the upper part (Beydoun et al., 1993). THE SECOND CYCLE: THE MID-CRETACEOUS The term "Wasia Formation," used by Powers et al. (1966) in Saudi Arabia for the Mid-Cretaceous sequence, is inappropriate in the Arabian Gulf region; formations must be based upon subsurface cores and well-log data, where paleontological control makes it possible to give initially purely lithostratigraphic data a chronostratigraphic significance. The suggestion to upgrade the Wasia Formation to group status and the units to formational rank was made by Owen and Nasr (1958), based upon studies in southern Iraq and Kuwait. The Wasia Group, in these terms, covers the interval from the Albian to Cenomanian and locally early Turonian time. The excellent quality of the subsurface data available to the authors from the U.A.E. and recent published information from Saudi Arabia, Qatar and Oman make the U.A.E. an ideal region in which to establish a type section for the mid-Cretaceous, and further suggests the possibility of subdividing the Wasia Group into two sub-cycles: the lower, predominantly clastic Nahr Umr-Mauddud Subcycle; and the upper, more predominantly carbonate WaraMishrif Sub-cycle (Alsharhan and Nairn, 1988). In Saudi Arabia, the Nahr Umr Formation usually is considered in terms of two members, the Khafji and Safaniya. The upper sub-cycle consists of the Wara, Ahmadi, Rumaila and Mishrif formations and their equivalents. If there is a disadvantage to the subsurface data, it is that units commonly were defined for the convenience of the operating company concerned; hence, there are problems in the selection of units and horizons used in defining sequences. To overcome this, however, at a liaison meeting, the operating companies in the Arabian Gulf area established type sections for the Lower Cretaceous units, but as no such agreement exists for the mid-Cretaceous, except in Qatar (Sugden and Standring, 1975), Alsharhan and Nairn (1988) proposed a set of type sections from wells drilled in the U.A.E. There are no obvious breaks in the succession; hence, it is possible to present a composite section against which other areas of the platform may be compared. In Saudi Arabia, the marginal sediments belonging to the Wasia Group generally crop out as brown to black, weathering sandstone with some red and green, interbedded shale, particularly in the lower part. The upper contacts are disconformable everywhere, and a strong disconformity occurs in subsurface at the contact with the succeeding Aruma Group sediments over some structures. The base of the Wasia is equally marked and steps over progressively older formations (Powers, 1968). The beds present a highly variable succession of sediments of continental and shallow-marine origin, reflecting the rapidly

340

changing and widely shifting depositional patterns of transgressive and regressive cycles. Redbeds, coastalplain, tidal-fiat, delta-lagoonal and paludal environments are all represented within the stratigraphic succession. In subsurface, the seven formally identified members of the Wasia Group "Formation" recognized in Saudi Arabia are, in ascending order, the Khafji, Safaniya, Mauddud, Wara, Ahmadi, Rumaila and Mishrif members (Powers, 1968; Sharief et al., 1989). As discussed earlier, the Wasia is raised to group status in southern Iraq, Kuwait, Qatar, U.A.E and Oman. In southern Iraq, Bahrain, Qatar, U.A.E. and Oman, the Khafji-Safaniya Member of Saudi Arabia and the Burgan Formation of Kuwait are equal to the Nahr Umr Formation, and the Rumaila and Mishrif of Saudi Arabia are equivalent to the Magwa Formation of Kuwait. Alsharhan and Nairn (1988) have attempted to illustrate the relationships of the carbonate-shelf deposits see also (Fig. 8.3). Distinctions between similar lithofacies of different ages are virtually impossible to make, and no better example can be given than the mass confusion that exists over the mid-Cretaceous clastic sediments in central Arabia. Thus, at the continental margin, unless there is a fortunate intercalation with identifiable fauna, distinctions between the sandstone deposited at different intervals tend to be difficult. The extraordinary coincidence of so much sandstone within a short distance spatially has an important geometrical implication, because the steady subsidence of the continental margin must be balanced by uplift in the source area to enable the coastal zone to remain in approximately the same position. The generally restricted thickness of the clastics suggests either a mature source area or conditions that did not favor mass wastage, as would characterize a region of low relief and rainfall. The mid-Cretaceous Wasia Group in Arabia was deposited over a period of 21 Ma from the late Aptian until earliest Turonian. During that time, an upward change from shallow-shelf clastics to shallow-shelf carbonates can be traced. Mid-Cretaceous in Eastern Arabia: The United Arab Emirates

During the Middle Cretaceous cycle, compression at the Oman margin resulted in the reactivation of basement structures. During this time, the shallow Abu Dhabi Basin lacked a deep-water connection with Neotethys. Sequences of different scales can be recognized in the succession. Six intermediate-scale sequences are recognized in the Wasia interval, but higher-frequency cycles within them are apparent during the Mishrif/Khatiyah/Shilaif (Pascoe et al., 1995). The predominance of bioturbated over wave-dominated traction deposits, the tendency of the basins to anoxia, and the macrofaunal dominance of rudists suggest a low-energy basin periodically isolated from the ocean, with water depths no greater than a few tens of meters.

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous Within the basin, the sequences are characterized by rapid, basinward shifts in the ramp-platform facies in an overall progradational setting. Major platform-drowning events are absent, and transgressive deposits are recognized as thin, muddier, but faunally richer, horizons.

Subsurface Formations Nahr Umr Formation (late Aptian to early-midAlbian). The formation has a thickness of 170 m (557 t ) and consists predominantly of argillaceous rocks laid down in a shallow, subtidal, shelf environment. The lithology comprises thick beds of variegated shale, red-brown to green or brownish-gray, with thin, interbedded limestone and occasional thin beds of marl and sandstone in the middle. Near the base, the shale contains phosphatic concretions and pyritic and glauconitic, limestone horizons (Fig. 8.27a) (Alsharhan and Nairn, 1988; Alsharhan, 1991, 1994). The age is based upon a foraminiferal assemblage, which includes abundant Orbitolina concava and Hemicyclammina sigali, and ostracods recovered from the drill samples. Locally, the base can be shown to be late Aptian based on nannoplankton, slightly older than the age proposed in the type area in southern Iraq. The formation is separated from the underlying Shuaiba Formation by a regional erosional unconformity of late Aptian age. The upper contact with the Mauddud limestone is conformable, and the boundary is placed between the base of the lowest well-developed limestone and the underlying brownish-gray shale. Mauddud Formation (late Albian). With a thickness of 60 m (194 ft), this formation is composed of shallowshelf, skeletal and peloidal packstone and wackestone, which locally may contain rudist fragments (Fig. 8.27a). The conditions of deposition during the accumulation of sediments that form the Mauddud were relatively uniform over much of the Arabian Gulf area with the accumulation of predominantly shallow-shelf carbonates. It marks the end of the first clastic-carbonate sub-cycle in the Arabian Gulf. Shilaif/Khatiyah Formation (late Albian-early Cenomanian). In Abu Dhabi, the term "Shilaif Formation" was introduced in drilling reports from the Abu Dhabi marine areas, where it is developed best. In Dubai, the Dubai Petroleum Company used the term "Khatiyah Formation." For convenience, Alsharhan and Nairn (1988) recommended the term "Shilaif/Khatiyah Formation," because both have similar lithological and age characteristics; however, to be consistent with the nomenclatural code, the older term is preferred. The formation has a total thickness of 171 m (560 ft). The sediments were deposited at a time in the late Albian when the combination of sealevel rise and mild, differential subsidence over parts of the craton led to the establishment of open-marine conditions over the intrashelf basin. The Shilaif/Khatiyah Formation consists of a sequence of shallowing-upward cycles that range in thickness from about 15 to 50 m (49-

164 ft) and are clearly recognizable in logs and cores. The total number of cycles found varies locally from six to eight. Each cycle consists of fine-grained, dark-brown to almost black, bituminous lime mudstone/wackestone/ packstone grading up into fine-grained, argillaceous, brown, slightly bituminous limestone with abundant Pithonella spp. The bedding is an alternation of lightercolored, burrowed and cemented limestone and thinner, darker and stylolitized limestone. Bioturbation and burrows are present throughout the section (Jordan et al., 1985; Burchette and Britton, 1985; Alsharhan and Nairn, 1993). An abundant fauna with Pithonella spp., planktonic and benthonic foraminifera, calcareous nannofossils and some molluscs from different wells traversing the stratigraphic interval establishes the age (Alsharhan and Nairn, 1988). The contacts above and below are gradational.

Mishrif Formation (middle to upper Cenomanian). The generalized stratigraphy of the Mishrif Formation shown in Fig. 8.27a is somewhat deceptive, for as it appears in Fig. 8.27b, the Mishrif, at least partly, is a facies equivalent of the Shilaif. The formation has a thickness of about 101-125 m (330-410 ft) and is well-developed in the offshore area of the U.A.E. Lithologically, two units are recognized. The lower unit consists of open-marine, slightly deeper-water, fine- to very fine-grained, bioturbated, bioclastic packstone and wackestone with calcispheres. Foraminifera and pyrite occur near the base. Micro-stylolites are developed between some of the beds. The upper unit is made up of shallow-water carbonates, medium- to very coarse-grained packstone and grainstone with large rudists and bivalve fragments, and interskeletal lime mudstone. Brecciated, conglomeratic limestone and black, organic-rich limestone also are present. Locally, there may even be some coal seams. The formation shows coarsening-upward cycles (Alsharhan and Nairn, 1993). Burchette and Britton (1985) and Burchette (1993) described six lithofacies associations in the Mishrif (Fig. 8.28). These are briefly described as follows: 1) Basin: silt to fine sand grade, organic-rich packstone and wackestone with a pelagic fauna. The limestone is well-bedded with abundant microstylites and shows cyclicity (in units 10-40 m thick) from dark, organicrich to fine-grained, light, bioclastic limestone and becomes more argillaceous in the northern gulf. It formed in an open-marine, basinal environment in water depths generally less than 100 m. The dark, organic-rich intervals interbedded with bioturbated beds indicate a periodically restricted environment. 2) Slope: well-bedded, silt to fine sand grade bioclastic wackestone with a sparse, pelagic foraminiferal fauna and poorly bedded, friable, coarse, bioclastic packstone. Grains are micritized, but are largely of molluscan and echinoderm origin. The middle and upper parts have a diverse infaunal and semi-infaunal molluscan assemblage, extensively bioturbated, with small, abraded rudists. Formed in a coarseningupward environment as the slope prograded, the

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Sedimentary Basins and Petroleum Geology the Middle East absence of slumps indicates a low-gradient slope. Shoal: poorly sorted, bioclastic packstone, grainstone and rudstone, abundant small, rolled rudists. Bedding poorly defined, although locally cross-stratified. Reflects deposition under conditions of low-energy shoals and banks. Pervasive bioturbation has destroyed most sedimentary structures. 4) Rudist Biostrome and Patch Reef: coarse, shelly, bioclastic rudstone and floatstone. A diverse and intact fauna like the shoal fauna, but more diverse, dominated by rudists. Found in scattered patches up to 15 m thick, it consists of biostromes and small bioherms within a prograding margin sequence. 5) Back Shoal: thin-bedded, fine to very coarse, bioclastic packstone, wackestone and grainstone. Extensive bioturbation, Callianassa-type burrows and small rudist clusters. It is a zone of mixing between shoal and interior lagoon. 6) Lagoon: indistinctly bedded, benthonic, foraminiferal and peloidal lime mudstone and wackestone, with a characteristic nodular character in places. Molluscan debris, echinoderm and ostracods locally important. Usually, the uppermost unit of the Mishrif succession formed on broad, shallow, sheltered platform interiors. The coarser intercalation probably is back-shoal sand fiats. Tuwayil Member The sedimentation of the Mishrif Formation was initiated over a broad carbonate shelf bordering a linear foreland basin (Burchette, 1993). Within that shelf, an intraplatform basin developed in which first the Shilaif facies limestone and then, during the latest Cenomanian, the more varied facies of the Tuwayil were deposited. As sea level fell, the lower Tuwayil foraminiferal and bioclastic unit gave way to an upper clastic unit, with the cyclic development of siltstone and fine sandstone corresponding to the 94 Ma Lowstand Systems Tract. The Tuwayil is a uniquely basinal unit, 106 m (350 ft) thick, overlying the Shilaif basinal limestone, but less than 3 m (10 ft) over the marginal Mishrif (Fig. 8.27b). The Tuwayil, about 125 m (410 ft) thick, consists mainly of clastic, dark-gray shale and siltstone followed by fine- to medium-grained and moderately well-sorted, quartzitic sandstone, with glauconite grains common and some layers rich in plant remains. Very fine-grained, subangular to sub-rounded, moderately well-sorted, quartzitic, glauconitic and calcareous sandstone also is found. The sands are believed to be from an exposed platform to the south and transported by north-flowing streams, despite the lack of transport directions, and distributed by wave and current action indicated by abundant sedimentary structures seen in core samples (Azzam, 1995). Ruwaydah Member As sea level recovered in the early Turonian, the Lowstand Systems Tract gave way to a Highstand Systems Tract at 90 Ma. In this more openshelf, sedimentary regime, the limestone of the Ruwayda was deposited. It is about 119 m (390 ft) thick and consists of deeper-water, argillaceous lime mudstone and wacke3)

344

stone, slightly silty marl and pyritic dolomite, with rare phosphate and glauconite grains and irregularly distributed grainstone that may contain very fine quartz particles in a shaly matrix. They contain burrows and small, planktonic forms such as Heterohelix spp. and a relatively poor fauna of miliolids. Outcrop Formations The mid-Cretaceous Wasia Group in the northern U.A.E. represents the youngest carbonate-shelf sequence resting disconformably upon the upper Musandam Group (Unit 4). It is, in turn, disconformably overlain by either the Aruma Group sediments or by yellow or red marl tentatively assigned to the Cenozoic Pabdeh Formation. Two formations were identified: the Nahr Umr and Mauddud (Alsharhan, 1989). The Nahr Umr Formation is only 40 m (131 ft) thick and consists of three units. The lower is a dark-gray grainstone; the middle is an argillaceous, orbitolinid packstone showing karstic, emergent features; the upper unit, the thinnest, is composed of red marl. The Nahr Umr is in conformable contact with the Mauddud limestone. The Mauddud Formation is about 60 m (197 ft) thick and consists of orbitolinid, gray packstone with less argillaceous material than the Nahr Umr Formation. Both formations are regarded as shallow-water deposits. Mid-Cretaceous in Eastern Arabia: Oman Western Oman Mountains Nahr Umr Formation (Albian). This formation in the western Oman Mountains is about 158 m (518 ft) thick and consists of calcareous shale and marl and some argillaceous limestone and micritized, orbitolinid wackestone and packstone (Fig. 8.29). The sediments reflect shallow-marine conditions with a high clay influx (Hughes-Clarke, 1988). The formation lies unconformably upon the Aptian Shuaiba Limestone in western Oman, but in the oil fields of South Oman, it may rest upon various older units down to the early Paleozoic Haima Group. The beds form an excellent seal (de la Grandville, 1982). The upper boundary is conformable and transitional up into the lower carbonates of the Natih Formation (Hughes-Clarke, 1988). Natih Formation (late Albian-late Cenomanian). The Natih Formation, sometimes called the Wasia Limestone, ranges from 344 to 450 m (1,128-1,312 ft) of dominantly open-marine carbonates deposited near wave base. The beds include basal, nearshore, terrigenous clastics. The principal lithologies are peloidal, intraclastic packstone; rudist packstone; and foraminiferal, algal wackestone/packstone formed under high-energy conditions near the platform margin or under shallow, quiet-water, shelf conditions. The formation is truncated by the Coniacian regional unconformity (Alsharhan and Nairn, 1988; Glennie et al., 1974; Scott, 1990). In the vicinity of the oil fields in the western Oman Mountains, seven lithological

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Fig. 8.29. Lithostratigraphy and log characteristics of the Middle Cretaceous Wasia Group in Oman (compiled and modified from Harris and Frost, 1984; Hughes-Clarke, 1988).Subdivision of th Natih Formation based on Tschopp (1967a) and Alsharhan and Nairn (1988) members of the Natih Formation have been differentiated based on log and lithological considerations (Tschopp, 1967a). They are (from younger to older): MemberA: 61 m (200 ft) of microporous wackestone/ packstone and peloidal packstone with skeletal fragments and benthonic foraminifera Member B: 85 m (280 ft) of bituminous, argillaceous packstone and wackestone with pelagic foraminifera and lamellibranchs Member C: 49 m (160 ft) of slightly bituminous, microporous, argillaceous wackestone with abundant pelagic foraminifers; thin, shaly intercalations; and tight, partly dolomitized limestone in the lower part Member D: 43 m (140 ft) total, consisting of bioclastic, pelletoidal, microporous packstone (38.5 m, or 126 ft) grading up into 4.5 m (15 ft) of bioclastic wackestone with rudist debris Member E: 165 m (540 ft) of pelletoidal lime mudstone with some chert grading upward to uniform, pelletoidal wackestone Member F: 30.5 m (100 ft) of microporous and dolomitic wackestone, with some argillaceous intervals Member G: 17 m (55 ft) of slightly dolomitized, microporous lime mudstone increasing in

bioclastic and pelletoidal content up-section to wackestone and packstone at the top The lower boundary is conformable and transitional. The upper boundary represents a regional hiatus, with generally shaly units of the Aruma Group lying disconformably upon Natih carbonates (Hughes-Clarke, 1988). Harris and Frost (1984) recognized three carbonate units in the Natih Formation: shallow-shelf limestone equivalent to the Mauddud and Mishrif formations and intrashelf, basinal facies equivalent to the Khatiyah. Based on biostratigraphic control, they show that the Mauddud is equivalent to Natih members E-G of Tschopp (1967a) and was deposited from the latest Albian through middle Cenomanian. The Mishrif is equivalent to Natih members A-D of Tschopp (1967a) and was deposited during the later Cenomanian and early Turonian (Scott, 1990). Mauddud Formation. It consists of about 212.5 m (697 ft) of microporous, dolomitized, bioclastic and peloidal wackestone/packstone deposited on a protected carbonate shelf without major wave or current agitation. The beds are associated with the local development of radiolitid, rudist bioherms or packstone of rudist rubble (Fig. 8.30). Because of subaerial leaching, porosity has been enhanced through the preferential solution of the rudistids. Mishrif Formation. It consists of 238 m (781 ft) formed in a depositional setting controlled by the extensional block faulting related to the formation of the Oman 345

Sedimentary Basins and Petroleum Geology the Middle East hiE CARBONATE SHOAL SKELETAL SANDS

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Fig. 8.30 Depositional model of the Middle Cretaceous Mishrif Formation (Natih Members AD) in Oman. The lower figure is an enlargement of the area nearshore carbonate shoal environments (modified after Harris and Frost, 1984 and reproduced by kind permission from AAPG). foredeep. Tilted, closely spaced, fault blocks resulted in a series of elongate islands or shoals on the upthrown blocks where grainstone and peloidal packstone were formed (Fig. 8.30 a & b). These beach and nearshore deposits graded seaward into mud-rich carbonates with lithoclasts of broken, radiolitid rudists, which apparently resulted from the destruction of rudists patches growing in slightly deeper waters offshore. Carbonate mudstone and wackestone were deposited in the deeper parts of the depressions formed on the downthrown side of the fault blocks (Harris and Frost, 1984; Alsharhan and Nairn, 1993). Thus, the mid-Cretaceous sediments in the western Oman Mountain oil fields are considerably thicker than in the southwestern part of the country or on the Musandam Peninsula to the north. The intrashelf basin that began to form in the late Albian in the southern part of the Arabian

346

Gulf filled with sediments that have proven to have a good source-rock potential (within the Shilaif/Khatiyah Formation; Murris, 1980). In Oman, local depressions within the shallow, carbonate shelf were common during deposition of the Mauddud and Mishrif formations. Water depths in these depressions may have been only a few tens of meters deeper than on the adjacent shelf (Harris and Frost, 1984). The intrashelf, basinal, limestone sediments known here as the Khatiyah Formation are typical microporous, pelagic lime mudstone with Pithonella and rare globose, planktonic foraminifera and calcareous nannoplankton.

Central Oman Mountains (Allochthonous Units) Qumayrah Formation (Cenomanian to Coniacian). The formation was previously described by Glennie et al. (1974) as a facies of the Muti Formation, but detailed

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous field mapping and the interpretation of Watts and Blome (1990) raised it to formation status. The Qumayrah Formation ranges in thickness from less than 10 m (33 ft) to more than 125 m (410 ft) of chert, siliceous mudstone and redeposited, conglomeratic limestone and wackestone conformably overlying the Mayhah Formation (D Member) (Figs. 7.26 and 8.4). The Cenomanian section contains purple, siliceous mudstone and radiolarian chert with thin beds of wackestone that contain a variety of platformderived material including Orbitolina and bioclastic, rudist and bivalve fragments and slope-derived intraclasts of radiolarian lime mudstone. The Coniacian part of the section is composed of chert containing radiolarians, and conglomeratic limestone containing clasts of slope-derived lime mudstone, bioclastic wackestone and fossil fragments (Watts and Blome, 1990). As described by Robertson (1987) and Watts and Blome (1990), the Qumayrah Formation represents synorogenic deposits that formed in response to the closing of the Hawasina Basin. These sediments accumulated immediately prior to the emplacement of the Semail Ophiolite over the Oman continental margin. The abrupt transition from the limestone of the Mayhah Formation into the siliceous sediments of the Qumayrah Formation may be due to the rapid rise of the CCD and/or

tectonic subsidence of the continental margin slope below the CCD. The well-rounded, skeletal fragments probably were abraded in high-energy, wave-agitated environments. Abundant Orbitolina with encrusting, calcareous algae and fragments of rudist apparently were derived from coeval or older rudist banks at the platform margin-peripheral bulge (Watts and Blome, 1990) (Fig. 8.31).

Northern Oman Mountains (Musandam Peninsula) Outcrop Formations (Fig. 8.4)

Wasia Group (Albian-Lower Cenomanian). The group consists of marl with orbitolinids (Orbitolina cf. concava and Orbitolina sp.) and yellow, stained, shell limestone with echinoid and rare algae (Lithcodium aggregatum) resting above the bored, erosion surface of Aptianage sediments. Ricateau and Riche (1980) believe that the thickness of the Wasia is much greater, and only the lower part of this unit, about 130 m (4,227 ft), has been recognized on the Musandam Peninsula, with erosion having removed the younger horizons.

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347

Sedimentary Basins and Petroleum Geology the Middle East

Subsurface Formations (Fig. 8.4) In subsurface in offshore Musandam (wells Khassab1 and Bukha-1), Ricateau and Riche (1980) describe the sequence as follows: Kazhdumi Formation (Albian). The formation attains a thickness of about 130 rn (427 ft) of shale with orbitolinids and Hemicyclammina sigali deposited in a neritic environment. Mauddud Formation (Upper Albian). The formation is a transgressive sequence about 40-50 m? (130-164 ft?) thick of lime mudstone/wackestone with green algae, gastropods, ostracods and orbitolinids deposited in an intertidal to open-marine environment.

Khatiyah/Mishrif formations (upper Albian-Cenomanian). These sediments attain a thickness of 200 rn (656 It). It is a regressive sequence beginning with wackestone/packstone containing pelagic foraminifera, followed by grainstone with rudist, alveolinids and much organic debris, and ending with limestone containing green algae, ostracods and gastropods.

Southern Oman (Dhofar Region) Qamar Formation (Albian-Cenomanian). The formation ranges in thickness from 235 to 600 m (771-1,968 ft) of interbedded, gray, bioclastic lime mudstone/wackei

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stone showing brown-green, glauconitic, calcareous, finegrained sandstone and pyritic shale. The limestone may show minor dolomitization (Hawkins et al., 1981). The formation is divisible into five members, based on the presence of green sandstone (glauconitic and calcareous sandstone with minor shale) and dark shale within the typical, thinly interbedded sequence of limestone and shale (Fig. 8.32). Harshiyat Formation (Cenomanian?). The formation, as described by Hawkins et al. (1981), consists of around 100 m (328 ft) of green, gray, laminated mudstone and siltstone with sporadic thin beds of gray-brown, fineto medium-grained sandstone (Fig. 8.32). The section is rich in foraminifera Orbitolina cf. concava, Pecten quadricostasa and Salenia scutigera, indicating a Cenomanian age. Fartaq Formation (upper Cenomanian). The formation ranges in thickness from 100 to 215 m (328-705 ft) and is divided into three members. The lower Limestone Member consists of biosparite and biomicrite with shell and skeletal debris and rare dolomite. The middle MarlShale Member is a very thin, persistent unit. The Upper Marl Member is composed of marl and argillaceous lime mudstone (Fig. 8.32).

I 100M ~

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

Mid-Cretaceous in Southwestern Iran Bangestan Group (Albian-lower Campanian). The group was proposed by Slinger and Crichton (1959) to cover the limestone unit that variously had been called the mid-Cretaceous Limestone, Rudist Limestone, Hippuritic Limestone and Lashteag Limestone. James and Wynd (1965) raised the term to group status to include the Kazhdumi, Sarvak, Surgah and Ilam formations because of the more local development of the Surgah and the restricted development of the Kazhdumi in some areas (Fig. 8.4). The group, therefore, includes not only the Wasia equivalents, but also the Aruma Upper Cretaceous equivalents in the ?Surgah and Ilam formations. The name is derived from Kuh-e Bangestan in the Khuzestan Province. Kazhdumi Formation (Albian to early Cenomanian). The formation consists of 210 rn (689 ft) of dark, bituminous shale with subordinate, dark, argillaceous limestone. Glauconite is common, especially in the lowest 91 m (298.5 ft). Oxidation zones are common in the lowest 30.5 m (100 ft). In the Iranian offshore fields such as the Darius Field, the formation consists of shale/marl and limestone formed predominantly in a neritic environment, although minor, thin sandstone beds may be present. In contrast in the Cyrus Field, the proportion of sand increases considerably, and about 40 m (131 ft) of sand facies occur between a lower and an upper shale-limestone unit (Mina et al., 1967). The basal contact with the underlying Dariyan Formation is associated with a zone of rubification, suggesting either a shallowing or a possible diastem. The upper contact shows a gradational transition to the basal part of the Sarvak Formation (James and Wynd, 1965; Stocklin, 1972) (Fig. 8.19). The formation is present throughout the Fars Province, but it passes into the black shale and limestone of the Garau Formation in central and southwestern Lurestan. Southwest of Khuzestan, the Kazhdumi Formation interfingers with the sandstone of the Burgan Formation of Kuwait and the Nahr Umr Formation of southeastern Iraq. Sarvak Formation (Albian-Turonian). The formation is named after Tang-e Sarvak, Kuh-e Bangestan in the Khuzestan Province. In the type section, it consists of three limestone units totalling 832 m (2,729 ft) from top to bottom (Figs. 8.20 and 8.5) (James and Wynd, 1965; Setudehnia, 1972): Unit 3 : 4 2 m (138 ft)of bedded, rubbly, weathering, iron-stained and brecciated limestone Unit 2 : 5 3 5 m (1,755 f t ) o f massive, tan, microporous limestone with rudist fragments and abundant brownish-red chert nodules. Large-scale crossbedding occurs in the middle part of the unit Unit 1 : 2 5 5 m (836 ft) of dark-gray, fine-grained, argillaceous, nodular-bedded limestone with impressions of ammonites and some thin, dark, marl partings The formation conformably overlies the Kazhdumi Formation with a transitional contact. The upper contact

with the marl and shale of the Gurpi Formation is sharp. The unit is widely distributed in the Khuzestan and Fars provinces. In northwestern Lurestan and toward Iraq, it interfingers with the Garau Formation (Fig. 8.5). In the coastal Fars Province, the Sarvak Formation has affinities with the equivalent units of the mid-Cretaceous Wasia Group in Arabia and is divided into two members. The lower, the Mauddud Member, consists of 61-122 m (200-400 ft) of thick-bedded, gray to brown, Orbitolinarich limestone. The upper, the Ahmadi Member, consists of 30.5-61 m (100-200 ft) of gray- to-green shale and thinbedded limestone. Its contact with the overlying Ilam Formarion is disconformable. Extending the use of lithostratigraphic names beyond their type region creates chronological problems, particularly apparent in the use of the terms "Sarvak" and "Garagu" formations. Superficially, it makes no sense that a Neocomian-Coniacian formation is overlain by one that is Albian-Turonian in age, especially when there appears to be evidence of disconformity at the observed contact. The explanation lies in the fact that the formational names are lithofacies terms; hence, the facies of the Garagu Formation in the type area in the southwestern Lurestan Province underlie a facies assigned to the Sarvak Formation, while in the vicinity of the oil fields (Emam Hasan Field) in the same province, the facies of the Sarvak grade laterally into the dark shale and limestone facies of the Garagu Formation, which extends into the Late Cretaceous (Fig. 8.5). At the top of the Sarvak Formation is a significant disconformity in the Fars and Khuzestan provinces, one which is less apparent in the Lurestan Province, where the formation has a deep-water character. The facies at the base of the Sarvak in the Lurestan Province extends down into the Albian, with the disappearance of the facies characterizing the Kazhdumi Formation. In the coastal Fars Province, only the lower part of the Sarvak Formation is present, with the top having been removed below the postCenomanian-Turonian disconformity (Fig. 8.5).

Surgah Formation (Turonian-?early Santonian). A local formation whose outcrop is restricted to Lurestan (Fig. 8.5), takes its name from Kuh-e Surgah in Lurestan Province. It consists of 176 m (576 ft) of mainly light- and dark-colored, pyritic shale interbedded with yellow weathering, fine-grained limestone. The lower contact with the Sarvak Formation is a weathered zone, with potholes and limonitic clay indicating a minor disconformity. The top of the formation shows a similar disconformable relation with the overlying Santonian-Campanian (Ilam Formation) (Setudehnia, 1972).

Mid-Cretaceous in Central and Eastern Arabia The developments discussed so far have centered around the carbonate platform in the U.A.E. and adjoining areas, its differentiation during the late Albian and Cenomanian into an intrashelf basin over parts of that carbonate plat-

349

Sedimentary Basins and Petroleum Geology the Middle East form, and an approach to deeper-shelf conditions in Oman. In tracing the history toward the northwest and west, a new paleogeographic situation becomes apparent: the transition toward the continental margin. In Saudi Arabia, the beds that formed in the littoral, elastic zone bordering the carbonate shelf are exposed; and in the gentle arc around the Jurassic in central Saudi Arabia, to Qatar, through Bahrain, Kuwait and into southern Iraq, the transition from littoral/ coastal conditions into the relatively sediment-poor regimes of the carbonate shelf can be traced. It is a pattern of transgression, when shallow seas swept across vast expanses of low-lying shelf, establishing a broad area of carbonate deposition alternating with periods of regression when elastic sediments flooded in from the Precambrian Arabian Shield areas and pushed the sea back toward its earlier confines. These exchanges occurred on several occasions and appear to be modulated by sea-level fluctuations. The details of the movements are not easy to chronicle, for the exposures are most commonly of the nearshore elastics, which, unfortunately, are seldom richly fossiliferous. A major compensatory factor is that because of the economic importance of the region, more detailed subsurface data are available than from almost any other part of the world, and many countries and companies have shown a remarkable willingness to release data, without which the understanding of these relatively minor, but extraordinarily complex events, would be impossible when examined in detail. In the following presentation of the Wasia Group and its equivalent rocks, therefore, it is convenient to examine the elastic sediments in central Arabia and trace their replacement progressively from the basin margin out onto the carbonate platform toward the Arabian Gulf.

Mid-Cretaceous in Central and Eastern Saudi Arabia Wasia Formation (Cenomanian-?lower Turonian). In central and eastern Saudi Arabia, the name "Wasia"was initially applied by Steineke (1938, cited by Powers et al., 1966) to sandstone lying between the Buwaib and Aruma limestones from the locality Khashm Wasia (23 ~ N, 24 ~ E) approximately 100 km (62.5 mi) southeast of Riyadh, Saudi Arabia replacing the imprecise term "Nubian Sandstone." Steineke and Bramkamp (1952) restricted the term to a sequence of 42 m (138 ft) of quartzose sandstone and sandy shale containing some thin siltstone and limestone intervals. It was delimited below by an unconformity within the elastic sequence and capped by the Aruma Limestone. The remaining lower elastics were assigned to the Biyadh Formation placed at the base of the Wasia Formation, but regardless of nomenclature, as Moshrif and Kelling (1984) pointed out, there are strong similarities between the Biyadh and Wasia sandstone, not only in terms of lithology and depositional environment, but also in terms of sediment-transport directions. They further indicated that the stratigraphic break with conspicuous erosional surface is visible only at Khashim al Malala (in

350

central Arabia); elsewhere, there is continuity of sedimentation, which argues against a terminology involving two formations. The age of the Wasia Formation was given as Cenomanian by Steineke et al. (1958) based on the occurrence of Neolobites vibrayeansis (d'Orbigny), although Powers et al. (1966) considered the formation to include the Turonian. The early Turonian age was based upon poorly preserved foraminifers in Kuwait (El Naggar and A1-Rifaiy, 1972) and needs better documentation. The Wasia Formation in outcrop generally consists of brown to black, weathering sandstone with interbedded red and green shale in the lower part. It is a highly variable succession of sediments of continental and shallow-marine origin, representing deposits of rapidly changing and widely shifting, transgressive and regressive cycles. The base of the formation in outcrop is a profound unconformity, and the basal beds overstep progressively older beds (Powers, 1968). The upper contact is disconformable everywhere and is present in subsurface as a strong, angular discordance (the pre-Aruma unconformity). Traced eastward into subsurface, the Wasia Formation thickens and undergoes a rapid facies change until, near the Saudi Arabian oil fields, the Wasia Formation, as originally defined by Steineke, can be divided into seven (lithofacies) members (Fig. 8.3). Alsharhan and Nairn (1986) pointed to the potential confusion when a facies change can be identified as a "member," as in Saudi Arabia, whereas in neighboring countries where the facies transition is not seen, the lithofacies are identified as "formations." Redbeds, coastal-plain, tidal-fiat, marsh, deltaic and shallow-marine lithofacies have been recognized within the sequence (Powers, 1968). The same seven can be recognized in the Rub al Khali and are described below (Powers, 1968; Soliman and A1 Shamlan, 1975; Sharief et al., 1989) (Figs. 8.3 and 8.33). Khafji Sandstone Member (lower Albian). It consists of fining-upward cycles of complexly interbedded sandstone, siltstone and shale about 274 m (899 ft) thick. It rests on the Shuaiba Limestone with a contact that may be unconformable and marks a sharp change from limestone to a silty, shale unit, depending upon location. The finingupward trend, the abundance of lignite and nearly equal amounts of sandstone and shale may indicate a complex environment (Sharief et al., 1989) with high-energy conditions for the meandering-channel, fluvial system of the sandstone and low-energy conditions for the overbank flood-plain origin of the siltstone and shale). Safaniya Sandstone Member (middle Albian). It is a well-developed, important reservoir in the Safaniya Field, where it is about 130 m (426 ft) thick. The sandstone thins southward to 85 m (279 ft) in the Manifa Field and 55 m (180 ft) in the Qatif and Abqaiq fields. The sandstone is clean, has good porosity and alternates with shale. In the upper part, the shale is lenticular and contains Hemicyclina whitei and ostracods. It is in conformable contact with the Mauddud Limestone (upper Albian), which,

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

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therefore, provides a limiting date. The coarsening-upward trend of grain size and the abundance of glauconite in the sandstone and pyrite in the shale suggest a marine environment (Sharief et al., 1989). Mauddud Limestone Member(upper Albian). Also called the Orbitolina Limestone, it is a wedge of shallowwater limestone that spreads far into the central Rub al Khali, where it is still about 60 m (197 ft) thick. Along its western margin in central Arabia, the limestone is dolomitic, pyritic or glauconitic with some interbedded shale or silty sandstone. Basinward toward the Arabian Gulf, the limestone becomes cleaner as the percentage of shale decreases and sand disappears (Powers, 1968). Sharief et al. (1989) show that the Mauddud is represented by finegrained limestone containing some interbedded, pyritic shale, and may have accumulated in a very shallow-water, reducing environment of a restricted-shelf or lagoonal and tidal-flat complex. Wara Member (lower Cenomanian). It is heterogeneous and exhibits rapid, lithological change both laterally and vertically, with an average thickness of about 45 m (148 ft). Continental sandstone in the west passes eastward toward the Arabian Gulf into sandstone and shale and is replaced completely by limestone east of Qatar. Coastal-

plain redbeds and tidal-flat and subaerial, deltaic deposits are dominant in the central Arabian Ghawar Field and extend as far north as the Khurasaniyah and Manifa fields in eastern Saudi Arabia. Green shale forms the submarine part of the delta in the Dammam and Safaniya fields, and shallow-water, marine shale forms a band around the delta front, blanketing the region from near Riyadh through Qatar into the Rub al Khali. East of Qatar, the Wara Member is present entirely in a limestone facies. A vertical change also can be seen; e.g., in the Ghawar Field, the Wara passes upward from coarse-grained sand to silty shale to shale, whereas the change in the Dammam Field is from sandy limestone to shale. Sharief et al. (1989) concluded that during the Wara depositional time, the sea level partly transgressed into eastern and central Arabia, and clastic sediments such as glauconitic sandstone and pyritic shale were accumulated. During this time, lignitic sandstone and shale facies of fluvial-channel and flood-plain origin formed in the west. Ahmadi Member (lower-middle Cenomanian). It is characterized by about 70 m (230 ft) of limestone interbedded with sandstone and shale). Sediments of the Ahmadi are represented by different facies, including pyritic shale in the east, glauconitic sandstone and shale in

351

Sedimentary Basins and Petroleum Geology the Middle East

the central area, and lignitic sandstone and shale to the west. This variation indicates a gradual transgression of the sea during the early Cenomanian. Sharief et al. (1989) concluded that the member varies from restricted-shelf, lagoonal and tidal-flat conditions in eastern and central Arabia to non-marine deposits in the west. Rumaila Member (middle Cenomanian). It consists of about 80 m (262 ft) of limestone and shale. The lower part, sometimes referred to as the Prealveolina Limestone, is composed of a succession of limestone, dolomite and shale. The upper part of the Rumaila is predominantly grayish-green and black shale containing Ammobaculites sp., Crusella gregoria, Nezzezata cf. N. simplex, Valvulina sp. and Prealveolina sp. The sediments, laid down in a shallow-marine setting, range from deposits in restrictedmarine, lagoonal conditions to hypersaline lagoon (Fig. 8.33). The top of the unit normally is conformable, although it has been eroded over the top of structures such as the Ghawar, Abqaiq and Safaniya domes during preAruma exposure.

ments known as the Sakaka Formation; and an upper unit consisting of clastic and mixed, fine-clastic and calcareous, shoreline-shallow-marine deposits considered part of the mid-Cretaceous Wasia Formation. This Wasia Formation in northwestern Saudi Arabia then was divided by Sharief and Moshrif (1989) into two units (Fig. 5.6). The lower, about 65 m (213 ft) thick, consists of medium- to fine-grained, sub-rounded, moderately to well-sorted quartzarenite, with several conglomeratic horizons. The sedimentary structures exhibit several types of cross-bedding, mostly small to moderately large-scaletabular with some trough cross-bedding, and were deposited as a clastic, shoreline facies. The upper unit, about 28 m (92 ft) thick and composed of varicolored sandstone with variable grain size and alternating beds of variegated siltstone, mottled clay-shale and some calcareous sandstone, was deposited in a shallow-marine environment. The formation rests unconformably upon the underlying Devonian Sakaka Formation and is unconformably overlain by the Upper Cretaceous Aruma Formation.

Mishrif Member (upper Cenomanian-lower Turonian). Characterized by a carbonate-clastic succession, it

Mid-Cretaceous in Kuwait

varies in thickness from 30 to 140 m (98.5-479 ft). The lower part is predominantly limestone, ranging from freshwater below to stylolitic, densely fractured, algal limestone, above which there occur poorly preserved, inconspicuous foraminifera, Bulmina sp., Discorbis sp., Pyrgo sp., Rotalia sp. and Stensioina sp. The thickness varies from 25 m (82 ft) (as seen in the Uthmaniyah Field) tO 50 m (184 ft) (as seen in the Abu Hadriya Field). The upper part of the Mishrif usually consists of gray shale with thin limestone and minor amounts of very fine sand. The sediments were deposited in a transitional environment between shallow, open-marine and restricted-marine and vary considerably in thickness from 5 m (16.5 ft) at Fadhili to more than 90 m (295 ft) in the Rub al Khali Basin. In places, over the Ghawar, Abqaiq, Safaniya and Khurasaniyah domes, pre-Aruma erosion may have completely removed the Mishrif Member, or left only the lowermost beds.

Mid-Cretaceous in nothwestern Saudi Arabia

Wasia Formation. In northwestern Saudi Arabia In the A1 Jawf region of northwest Saudi Arabia, a thick, siliciclastic sequence crops out, named in 1950 by Sandford (cited in Powers et al., 1966) as the Sakaka Sandstone. The age is controversial. According to Powers et al. (1966), the sandstone and minor siltstone are a lateral continuation of the Wasia Formation in central Arabia. Based on a detailed surface-subsurface study utilizing palynological and lithological data of Sharief and Rogers (1980) and Sharief and Moshrif (1989), the sequence was divided into two units: a lower unit of Middle-Late Devonian non-marine, clastic sedi-

352

Wasia Group (Albian Turonian) This group has been divided into the five formations described below. Burgan Formation (lower-middle Albian). In the type area in the Burgan Field, is a sandstone unit that may reach a thickness of 351 m (1,150 ft), of which intercalated shale may represent only 10% of the thickness. It consists of well-bedded, well-sorted, littoral sands deposited near a delta front on a gradually sinking shelf. The shale is estuarine and contains abundant plant remains (including amber), but foraminifera are absent (Owen and Nasr, 1958; Adasani, 1965; Brennan, 1990; Alsharhan, 1994). The former authors recognize two divisions of the Burgan: the "Third" and "Fourth Sand" units (Fig. 8.34). The "Third Sand Unit" (equivalent to the Safaniya Member) is about 145 m (476 ft) of glauconitic sand in the lower part, with an upper part of interbedded, dark-gray shale. The middle section is nearly pure quartz sand with very little secondary cementation and contains amber and lignite remains. The "Fourth Sand Unit" (equivalent to the Khafji Member), which accounts for about 206 m (675 ft) of the total thickness, is a clean, well-sorted sand, with little secondary cementation and some traces of lignite, amber and plant remains. The sandstone contains no microfossils and is dated by its apparent time equivalence with the Nahr Umr Formation in Iraq. Mauddud Formation(upper Albian). The limestone forms a single band from as little as 2 m (6.6 ft) thick at Umm Gudair in the south to 12 m (39 ft) at Burgan in the east and 98 m (321 fi) at Radhautain in the north. It is composed mainly of packstone/wackestone and contains interbedded, gray to buff, dense, finely crystalline beds and soft, porous, brown limestone and some thin, interbedded, fine, greenish-brown sands and dark-gray marl near

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the base (Adasani, 1967). Detailed study by A1 Shamlan (1975, 1980) recognized nine microfacies associations: Orbitolina-Trocholina biomicrite; Orbitolina-Trocholina pelsparite; Ovalveolina-miliolid biomicrite; shelly biomicrite; argillaceous biomicrite; dolomitic biomicrite; dolomite; sandy, dolomitic, Orbitolina biomicrite; and carbonaceous siltstone. These sediments are considered to have been deposited in a shallow-marine environment with scattered shell banks. Wara Formation (lower Cenomanian). The formation consists of thick, glauconitic sandstone and siltstone with some gray shale in the upper and lower parts (Owen and Nasr, 1958). The thickness of the formation ranges from 46 m (150 ft) in southern Kuwait to about 91 m (299 ft) in northern Kuwait. It represents the influx of sand from western Arabia into a subaqueous environment (marine to non-marine) in Kuwait and extending into southern Iraq. Ahmadi Formation (lower Cenomanian). The formation consists of two discrete members with a thickness ranging from 62 to 81 m (203-266 ft). The lower, the caprock limestone, is a typical limestone-shale alternation containing Cytherei bahreini. The upper, the Valvulina shale, is primarily pyritic, brick-red to reddish-brown to

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Crusella intermedia, Trocholina lenticularia, Haplophragmoides spp., Flabellina spp., Vaginulina spp., Gumbelina spp., Lenticulina spp., Exogyra conica, E. columba, Neolobites sp. and Ammobaculites sp. Magwa Formation (middle Cenomanian-lower Turonian). The term was introduced by Owen and Nasr (1958) to include the youngest mid-Cretaceous unit found in well Umm Gudair-1, where it consists of 104 m (341 ft) of hard, dense, gray, finely crystalline, pyritic and fossiliferous limestone, with thin, greenish, shale bands at the base. In the type section, it contains abundant alveolinids and is the product of an outer, neritic, marginal, deep-basin environment (Fig. 8.35). The formation appears to be equivalent to the Mishrif and Rumaila formations of northern Kuwait. E1 Naggar and A1 Rifaiy (1972 a & b, 1973) retain the terms "Rumaila" and "Mishrif" and include them as members of the Magwa Formation. E1-Naggar and A1-Rifaiy (1972 b, 1973) concluded that the Rumaila Member is equivalent to the lower part of the Magwa and is represented by three microfacies associations: a lower, pyritic, argillaceous limestone with abundant arenaceous foraminifera and rare planktonic remains; an upper associ-

353

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ation of skeletal, micritic limestone with pyritic shale partings characterized by abundant remains of the planktonic foraminiferal and rare benthonic remains; and a middle section of an intermediate, mixed character. The Rumaila ranges in thickness from 43 m (140 ft) in southeastern Kuwait to about 137 m (450 ft) in northern Kuwait. The Mishrif Member is equivalent to the upper part of the Magwa Formation and is typified by white-colored, alveolinid, coralline, rudistid, algal and reefoidal limestone. This is readily distinguishable from the underlying, relatively deep-water, dark-colored, shaly, marly, pyritic limestone and calcareous shale of the Rumaila Member, which forms the lower part of the Magwa Formation. The Mishrif Member is represented by a lower alveolinid, dicyclinid, shaly limestone with minor intercalated, reefal, bank facies with local pyritization or dolomitization, followed upward by coralline, algal, rudistid, microporous lime-

354

stone. The facies shows variability, forming marly limestone in the west and central Kuwait areas, but shale in the east. This member has a thickness of about 76 m (250 ft), but in some areas such as the Burgan Dome, both it and the Rumaila Member may have been completely removed by pre-Aruma erosion. The depositional environment of the Magwa Formation has been postulated to represent a quiet to slightly agitated, infralittoral to circalittoral, marine environment for the Rumaila Member, with intermittent, partial restriction from the open sea and temporary anoxic, anaerobic conditions This was followed by a continuous regression to near-emergence during the deposition of the Mishrif Member under littoral or even supralittoral conditions. Mid-Cretaceous

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous Wara Unit, known in Bahrain and Saudi Arabia, is not recognized in Qatar, where the rocks are assigned to the Ahmadi Formation in the onshore, and to the Khatiyah Formation in the offshore, as in Dubai (U.A.E.) (Fig. 8.13). In the onshore region, the Ahmadi beds occupy most of the rest of the mid-Cretaceous up to the Mishrif Formation, which caps the mid-Cretaceous succession. It should be stressed that the Ahmadi, Khatiyah and Mishrif in Qatar are partial lateral equivalents to the Wara, Ahmadi and Rumaila in Bahrain. The Wara/Ahmadi represents a more coastal, clastic-rich facies; the Khatiyah represents an open-marine, low-energy shelf; and the Mishrif represents the higher-energy, shelf/reefoidal (rudistid) facies. The mid-Cretaceous succession has been divided by Sugden and Standring (1975) and Alsharhan and Nairn, (1994) into the five formations that follow. Nahr Umr Formation (Albian). The formation ranges in thickness from 47 to 170 m (154-582 ft) and is composed of clastic sediments divided into three units (Alsharhan and Nairn, 1994). The lower unit consists of gray, marly sands and quartzitic, argillaceous sands with many thin, marl and shale bands. The influence of the continental deposits is reflected by the presence of local thin lignites, phosphatic concretions and ferruginous oolites. The middle unit is predominantly a shale sequence, but has ferruginous oolites and thin, marly, glauconitic sandstone. The upper unit is composed of marly, glauconitic sandstone associated with numerous bands of gray shale and marl and a few beds of gray limestone. During the deposition of the Nahr Umr, Qatar was situated in a transitional zone between a continental, depositional environment in the west (fluvial and lower coastal plain) and a shallow-marine environment with shale and minor sandstone in the east. Mauddud Formation (Albian). Containing the first spread of carbonates in the clastic-carbonate cycles that affect the Wasia Group sediments, this formation reaches a thickness of 56 m (184 ft) and represents the spread of shallow-shelf carbonates over a wide area . In onshore Qatar, the formation consists in the lower part of limestone, which alternates with green-gray shale and passes up into a more continuous limestone succession. A vertical gradation can be seen from gray, dense, foraminiferal lime mudstone to peloidal, bioclastic packstone and wackestone. The limestone contains Trocholina sp., Orbitolina sp., echinoid spines, textularids, small gastropods and molluscan debris. In the offshore areas, and on occasion in a somewhat deeper-water environment, the lithofacies give way to dense, microporous lime mudstone, wackestone, packstone and grainstone. In the upper part of the Mauddud, there are local concentrations of skeletal rudists, and the presence of erosion surfaces provides an indication of the shallowness of the water conditions. Ahmadi Formation and its equivalents (Cenomanian). This formation, about 200 m (656 ft) thick, is well developed in the onshore where it consists of a succession of shale with thin, argillaceous sands in the middle, and

porous packstone and wackestone, followed by shale and marly shale and capped by packstone and wackestone with numerous beds of thin marl and shale, deposited in shallow, open-marine conditions. Khatiyah Formation. The offshore facies equivalent to the lower part of the Ahmadi Formation, from which it differs by the occurrence of dense, microporous lime mudstone, wackestone and packstone. This formation contains foraminifera and codiacean algae. The shallow-water depositional environment was deeper than that characteristic of the nearshore area however, the presence of hardgrounds with bored surfaces is indicative of non-depositional intervals, and the extensive bioturbation equally suggests relatively shallow-water conditions. Mishrif FormationThe Mishrif is the offshore facies equivalent of the upper partAhmadi Formation, about 80 m (262 ft) thick, is a reefoidal facies composed of shallowwater, bioclastic wackestone and packstone with rudist debris. The overlying Laffan Formation is unconformable on the Khatiyah or Mishrif formations.

Mid-Cretaceous in Bahrain Wasia Group.The mid-Cretaceous succession consists of five formations, which have not received the detailed study found in neighboring countries. A general description is given below and is illustrated in Fig. 8.3. Nahr Umr Formation (Albian). This formation is about 219 m (718 ft) thick and consists of black shale interbedded with sands and sandstone, lignite, pyrite and amber with a fauna of shallow-marine origin. It also contains several thin layers of glauconitic, silty sandstone, siltstone and arenaceous limestone. Mauddud Formation (Albian). It is composed of gray, bioclastic limestone and peloidal-bioclastic wackestone and packstone. Wara Formation (Cenomanian?). It is a predominantly arenaceous facies (shale and numerous linear, sand bodies) with some thin limestone developed in the upper part, in which Orbitolina qatarica is found. Ahmadi Formation (Cenomanian). This is a greater development of blue and greenish, pyritic shale rich in Trocholina sp., but includes two thin, finely crystalline, fossiliferous, limestone horizons. Rumaila Formation (Cenomanian-lower Turonian?). This formation consists of shallow-water, bioclastic, peloidal wackestone and packstone rich in algae, rudists and corals, and some microporous, argillaceous limestone. It is, therefore, poorer in argillaceous materials than the same formation in Saudi Arabia. Mid-Cretaceous in Northern Arabian Platform The following information provided on the mid-Cretaceous in the Zagros Basin, Syria, southeastern Turkey and northeastern Iraq clearly is inadequate to do justice to a region complicated by Alpine folding and a later cover of

355

Sedimentary Basins and Petroleum Geology the Middle East younger sediments. It is possible only to indicate the complexity of the platform area and point to the varied depositional environments of the shelf margin and deep-water deposits of the Zagros Basin. Westward from Iraq toward Jordan, the mid-Cretaceous, when present, is in a largely continental facies. The top part of the Kurnub Sandstone of Jordan, in all probability, formed as late as the mid-Cretaceous, but exact equivalence with the clastic facies of Saudi Arabia is hard to establish. However, the presence of the marine Cenomanian is well-established. There is considerable facies change in these areas, and the lithofacies changes in many of the formations may be diachronous, resulting in the problem of interpreting conditions of deposition based upon formational names in the absence of precise locations of sections.The mid-Cretaceous, on the whole, is very poorly represented in northeastern Syria and southeastern Turkey.

Mid-Cretaceous in lraq. 1 .Southern and Southwestern Iraq The lithofacies of the formations of the mid-Cretaceous Wasia Group in southern Iraq are similar to those of the northern Arabian Gulf states (Figs. 8.3 and 8.33). Nahr Umr Formation (Albian). The formation is lithologically consistent with the facies described in Kuwait because sand and sandstone with lignite, amber and pyrite (Bellen et al., 1959) occur but in some places, shallow-water, littoral, neritic, fossiliferous limestone have been reported. The formation, however, is predominantly deltaic, with continental, terrigenous deposits (Ibrahim, 1983; Alsharhan, 1994). It has a relatively uniform thickness of 100-120 m (328-394 ft), but gradually thickens to the south to reach 150-180 m (about 492-590 ft). Mauddud Formation (Albian). The formation is well-developed in southern Iraq, where it reaches a maximum thickness of 152 m (500 ft), but decreases to about 37 m (121 ft) in northern Iraq (in well Makhul-1). It consists of organic, detrital, sometimes peloidal limestone, with occasional green or bluish, shale streaks. It conformably overlies the Albian Nahr Umr Formation and is unconformably overlain by the black, silty shale and siltstone of the Wara Formation (Fig. 8.36). Wara Formation (lower Cenomanian). This formation is well-developed only in southern Iraq and is not recognized north of the Basrah oil fields (e.g., Rumaila and Ratawi fields). It consists of 15-18 m (50-60 ft) of black, silty, unfossiliferous shale and siltstone and contains thin bands 2-3 m (7-10 ft) thick of fine-grained sandstone. The existence of a disconformity between the Wara and the Albian Mauddud, and the conformity of the boundary with the overlying Cenomanian Ahmadi Formation, support a lower Cenomanian rather than Albian age for the Wara Formation (Bellen et al., 1959). Ahmadi Formation (lower Cenomanian). This for-

356

mation was introduced by Owen and Nasr (1958) in southern Iraq to cover the deposits in a marine basin that have a strong, terrigenous component. The formation consists of 150-170 m (492-558 ft) of shale (grayish at the base and greenish to brownish near the top), with a limestone in the basal part known as the Cythereis bahraini limestone (Bellen et al., 1959). In a paleogeographic sense, the bedsfringe the huge Wasia Delta of Saudi Arabia (including, therefore, the Rutbah of western Iraq) and pass conformably up into the Rumaila Formation. Rumaila Formation (Cenomanian). Widely distributed in southern Iraq, it is a predominantly carbonate formation ranging from 100 to 200 m (328-656 ft) in thickness, with a lower unit of fine-grained, microporous limestone and an upper unit mostly of fine-grained, oligosteginal limestone and marl. The term was introduced by Rabanit (1952, cited and subsequently presented in Bellen et al., 1959). The formation was deposited in the deeper parts of a subsiding basin, although variations in the rate of subsidence led to the local development of lagoonal conditions. The upper boundary is conformable with other Cenomanian units. Towards the east and northeast, the formation is progressively replaced by the carbonates of the Mishrif Formation, finally wedging out along the northeastern margin of the Mesopotamian Basin (Buday, 1980). The formation is present in Kuwait, but is replaced toward the southeast of that country by the neritic limestone of the Magwa Formation. Mishrif Formation (Cenomanian-early Turonian). The formation, about 162.5 m (533 ft) of a complex of bioclastic-detrital limestone in places, including algal, coral and rudist bioherms, was described by Rabanit (1952, cited in Bellen et al., 1959; Buday, 1980). At the top in the Zubair Field are freshwater, limonitic carbonates.

2. Western Iraq Rutbah Formation (Albian). It consists of about 23 m (75 ft) of white to varicolored, fine- to coarse-grained, locally ferruginous sandstone that shows cross-bedding. These beds are mostly continental and only exceptionally littoral or marine. They represent the sediments marginal to the mid-Cretaceous transgression over the stable shelf and were described first by Foran and Keller (1937, cited in Bellen et al., 1959). The base is unconformable with the Mulussa Formation, and the top is unconformable with the overlying Mishrif or M'sad formations. Therefore, it is comparable to the Albian clastic facies in Saudi Arabian outcrops. Elsewhere to the south and southeast, the formation grades into the Nahr Umr Formation. M'sad Formation (Cenomanian?). It has a thickness of 150-160 m (492-525 ft), but thins to the north and west (Bellen et al., 1959). As the Mishrif is traced to western Iraq onto the slopes of the Rutbah uplift, the littoral facies influences of the M'sad Formation take over. The facies consist of alternating, shallow-water, reefoid limestone; shell breccias; microdetrital and microporous limestone

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

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3. Northern and Northeastern Iraq In the Foothills Zone of the Zagros in northeastern Iraq, a number of mid-Cretaceous formations have been described that are difficult to relate to one another. Because the ages generally are poorly defined and often wide-ranging, their interrelationships are not easy to determine. Most descriptions tend to draw comparisons with southern Iraq. Bellen et al. (1959) and Buday (1980) defined the seven Albian-Turonian formations in the Foothills Zone. These formations are described below and illustrated in Figs. 8.3 and 8.5. Rim Siltstone Formation (lower Albian). It was described by Dunnington (1953, cited in Buday, 1980) from a section in well Alan-1 in the Foothills Zone of northwestern Iraq, where the thickness is between 55 and 60 m (180-197 ft). Lithologically, the formation consists of silty, pyritic marl, marly siltstone, thin sandstone and anhydritic marl (Bellen et al., 1959). It is a deposit formed in a nearshore, lagoonal environment without any evidence of deltaic influence. The lower contact is gradational with the Qamchuqa Formation, while the upper is conformable with the Sarmord Formation. Jawan Formation (Albian). This formation, defined by Dunnington (1953, cited in Bellen et al., 1959) in well Jawan-2 in the Foothills Zone, consists of 50 to 300 m (164-984 ft) of marly, peloidal and recrystallized lime-

APTIAN BARREMIAN

stone, marly dolomite and anhydrite. The sediments, laid down in a neritic, semi-lagoonal environment, rest unconformably over the Lower Qamchuqa Formation (Shuaiba equivalent of southern Iraq) or upon the Lower Sarmord Formation. The upper contact is conformable. The formation intertongues with other Albian formations.

Upper Qamchuqa Limestone Formation (Albian). The formation in the High Folded Zone of Iraq is separated as an independent formation from the Lower Qamchuqa Formation (Aptian) and consists of dolomite that replaces neritic, bioclastic-detrital limestone and nondolomitized, detrital, locally argillaceous limestone (Fig. 8.23a) (Bellen et al., 1959; A1 Shdidi et al., 1995). It was deposited in a neritic, sometimes high-energy, shoal environment. The average thickness ranges from 50 to 250 m (164-820 ft), depending upon structural position and whether there has been erosional removal of some of the formation. Towards the south, the formation is equivalent to the Mauddud, as the base of the formation grades up from the Nahr Umr Formation, and the basal layers commonly contain some silt and shale admixtures. The upper contact is unconformable and is overlain directly by Late Cenomanian or Turonian formations. Upper Sarmord Formation (Albian). Also found in the Foothills Zone of Iraq, it contains neritic to semibathyal sediments, mainly marl and neritic limestone up to 100 m (328 ft) thick. The lower contact is gradational in the High Folded Zone. The upper limit is conformable and gradational with the Upper Qamchuqa Formation (Fig. 8.23b) and its equivalent. In some places (in southern and 357

Sedimentary Basins and Petroleum Geology the Middle East southwestern Iraq), it appears to be replaced by the Upper Qamchuqa (Mauddud equivalent) and is, thus, a facies of the latter (Buday, 1980); however, in all other cases, the upper boundary is marked by the pre-Cenomanian break, which explains the absence of the formation in areas of extensive denudation. Upper Balambo Formation (Cenomanian-Turonian). This formation in northern Iraq is a monotonous sequence of thinly bedded, globigerinal marl, which passes downward into radiolarian limestone (Bellen et al., 1959). The thickness normally ranges from 170 to 350 m (557-1,148 ft), but it exceeds 900 m (2,952 ft) in well Naft Khaneh-1. The sequence was deposited in a deep-marine, bathyal environment and contains a pelagic fauna. The lower boundary is conformable; thus, part of the deepwater Balambo Formation may be included in the midCretaceous. The upper contact is presumed to be a nondepositional unconformity, because the overlying beds belong to the upper Campanian Shiranish Formation (Bellen et al., 1959). K i t Formation (Cenomanian). This formation in northern Iraq is thin, 15-20 m (49-66 ft), and is composed of anhydrite, peloidal and oolitic limestone. In some areas, dolomitic limestone, marly limestone and subordinate shale are found. The depositional environment reflects a relict, hypersaline lagoon, replaced by freshwater deposits in some places. While the lower contact is gradational, the top is covered by transgressive late Turonian-early Senonian sediments (Buday, 1980). Dokan Limestone Formation (Late Cenomanian). Developed in the High Folded Zone in northeastern Iraq, the formation ranges in thickness from 4 to 150 m (13-492 ft). It consists of light-colored, gray and white, locally rubbly, oligosteginal limestone, with glauconite coated on pebble-like masses. The sediments were deposited in an open sea, as indicated by the abundant pelagic fauna. It is bounded by unconformities above and below.

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Ajlun Group (upper Albian-Coniacian) The Ajlun Group (Figs. 8.25 and 8.37) is equivalent to the carbonate Judea Group on the West Bank and the Negev. It crops out in northern Jordan and along the margins of the rift in the Dead Sea-Gulf of Aqaba region. The group ranges in thickness from 610 m (2,000 ft) in northern Jordan and the Azraq Hamza Basin to 101 m (331 ft) in Wadi Sirhan. In subsurface, it reaches 658 m (2,158 ft) in well Wadi Rahil-1 to 380 m (1,246 ft) in well Hamza-1 (Powell, 1989 b). The Ajlun Group is dominated by limestone, dolomite and marl, with tongues of siliciclastics occurring south of the country. The sediments were laid down in a shallow, warm-water, carbonate platform. Fluvial sandstone and subsidiary lenses of shallow-marine clastics are sourced from the Arabian Shield. The lower and upper contacts are disconformable on the Kurnub Sandstone below and with the Belqa chalky and pelagic limestone above. The Ajlun Group was subdivided into six formations (Powell, 1989 b). These are, in upward sequence: Naur, Fuheis, Hummar, Shuayb, Wadi As Sir and Khureij (Fig. 8.37). The Ajlun Group has been studied in detail by Abu Ajamieh et al. (1988), Powell (1989 b) and Andrews (1992) because of its importance as a reservoir, an aquifer and a source of clay for cement. The following summary of the Ajlun formations was based mainly on these references. Naur Formation (upper Albian to lower Cenomanian). The formation is synonymous with the basal Cenomanian shale and limestone (Burdon, 1959, cited in Bender, 1974), the lower part of the Nodular Limestone Unit (Bender, 1974) and the lower Calcaire Neritiques of Wetzel and Morton (1959). The formation predominantly consists of fossiliferous and dolomitic limestone, dolomite and marl with sandstone interbedded with siltstone and marl in the lower part. The formation ranges in thickness

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous from 150 m (492 ft) in central Jordan to 40 m (131 ft) at Ras En Naqb in the south. This Naur sequence is divided by Powell (1989 b) into four members from base to top. The Wadi Jubeira Member (Member A) ranges from 56 m (184 ft) to 8 m (26 ft) at Wadi Hisa. It consists of glauconitic, bedded sandstone and interbedded siltstone, mudstone or marl. The sediments have small-scale crossstratification, bioturbation and simple vertical or horizontal burrows. The member was deposited in an alluvial plain at the coastal margin. Member B ranges in thickness from 15 m (49 ft) at Wadi Shumahk (south of the Dead Sea) to 42 m (138 ft) in Wadi Mujib. It is composed of dolomite, dolomitic limestone and limestone, with sparse chert nodules with abundant burrows which impart a distinctive, nodular texture. Burrow-fill is preferentially dolomitized. These sediments were deposited in a shallowwater, tidal-flat setting. Member C has a thickness of 20 m (66 ft) at Wadi Esh Shita (Amman), to 40 m (131 ft) at Abu Khusheiba, to 41 m (135 ft) at Wadi Rustani. It is composed of dolomite, dolomitic limestone and limestone, with chert nodules deposited in a uniform, shallow-water (subtidal) environment. Member D is missing. In subsurface, the Naur Formation ranges in thickness from 22 m (72 ft) at well Siwaqa-1 to 76 m (249 ft) at well Wadi Rijal-4. It consists in the lower part of interbedded dolomite, limestone, shale, anhydrite and sandstone, followed by argillaceous limestone and shale and ending with anhydritic dolomite and fossiliferous, oolitic limestone. The sediment was laid down in a restricted-shelf environment with normal, marine waters and graded to an intertidal environment in the upper part, as evidenced by anhydrite, dolomite and oolitic limestone. Fuheis Formation (Cenomanian). The formation was introduced by Masri (1963, cited in Powell 1989 b) and is broadly equivalent to the middle part of the Nodular Limestone Unit of Bender (1974). The thickness ranges from 55 m (180 ft) at Wadi Khusheiba to 90 m (295 ft) at Irbid. The Fuheis consists of marl; calcareous siltstone; thin-bedded, nodular limestone; lime mudstone and shelly wackestone. The lower part (marl and calcareous siltstone) suggests deeper-water conditions on the inner shelf, while oyster limestone deposited in a subtidal to intertidal environment. The lower and upper parts of the formation gradationally contact with the Naur and Hummar formations, respectively. In subsurface, the Fuheis Formation ranges from 26 m (85 ft) at well Siwaqa-1 to 36.5 m (120 ft) at well Hamza5 and consists of thin beds of argillaceous, pyritic and glauconitic sandstone, followed upwards by a thick sequence of slightly calcareous shale with streaks of argillaceous limestone. These sediments deposited in an open-marine to outer-shelf environment. I-Iummar Formation (upper Cenomanian). The name was first assigned by Masri (1963, cited in Powell 1989 b); it is partly equivalent to the lower Echinoid Limestone Unit (Bender, 1974). Ranging from 10 m (33 ft) in thickness at Wadi Mujib to 76 m (250 ft) at Azraq, the for-

mation consists of limestone, dolomitic limestone and dolomite, with distinctive, thin-bedded, clayey micrites and circular, sub-horizontal burrows at the lower part. The formation was deposited in a warm, shallow-water, subtidal to lagoonal environment; the lower and upper contacts are gradational. In subsurface, the formation ranges from 60 m (197 ft) at well Dabikiyeh-1 to 91 m (299 ft) at well Wadi Rajil4. In the lower part, it consists of argillaceous and chalky limestone followed by fossiliferous, fine, crystalline, fractured, pyritic limestone. The upper part consists of dolomite with anhydrite-filled fractures and argillaceous, pyritic limestone with thin shale. These sediments are interpreted as deposits on a shallow shelf with an occasional skeletal, shoal complex, followed by shallow-shelf carbonates interbedded with calcareous, marine shale. Shuayb Formation (Lower Turonian). The name was established by Masri (1963, cited in Powell, 1989 b). The formation ranges from 36 m (118 ft) int Wadi Es Shita to 72 m (236 ft) in Wadi Abu Khusheiba. It consists in the lower part of thinly bedded, porcellaneous limestone, shelly in part, with marl intercalation. The upper part is crystalline, massively bedded, dolomitic limestone and limestone with shell debris. An inner-shelf setting was proposed for the lower part; subsequently, the sea level fell, and dolomite and laminated limestone were deposited in a shallow, lagoonal to supratidal environment. The lower contact is defined at the transition from thick-bedded, dolomitic limestone of the Hummar Formation to thin-bedded, silty limestone and marl of the Shuayb Formation. The top is placed at the junction with massive bedded limestone of the overlying Wadi As Sir Formation. In subsurface, the Shuayb Formation ranges from 80 m (262 ft) at well Hamza-2 to 131 m (430 ft) at well Wadi Ghadaf-2. It consists of three lithological units. The lower is argillaceous shale overlain by argillaceous lime mudstone and wackestone rich in planktonic foraminifera. The middle unit is shale overlain by pyritic, glauconitic, oolitic limestone that is slightly argillaceous and marly. The upper unit is glauconitic, argillaceous sandstone with shale and marly limestone. The lower unit was deposited in an open-marine to outer-shelf environment, while the middle and upper units represent shallowing from a marine to nearshore environment. Wadi As Sir Formation (Turonian). The name was introduced first by Masri (1963, cited in Powell, 1989 b) and is equivalent to the upper part of the Echinoid Limestone Unit, the Massive Limestone Unit and the Sandy Limestone Unit of Bender (1974). The formation ranges from 16 m (53 ft) at Zakimat A1Hasah to 146 m (479 ft) at Wadi Mujib. It consists of well-bedded, massive limestone, dolomitic limestone and dolomite, with subsidiary, sandy limestone and marl; beds of gypsum are present locally near the base, and beds of chert nodules are common in the middle and upper parts. The formation was deposited in a shallow, subtidal to intertidal environment. The basal contact is defined at the 359

Sedimentary Basins and Petroleum Geology the Middle East junction between marl, mudstone and siltstone of the Shuayb Formation and dolomitic limestone of the Wadi As Sir Formation. The upper part is unconformable with the chalk of the basal Belqa Group. In subsurface, the formation ranges from 327 m (1,073 ft) in well Northern Highlands to 50 m (164 ft) in wells Wadi Sirhan-1 and 2. The lower two-thirds of the Wadi As Sir Formation are composed of glauconitic, slightly argillaceous, pyritic, and locally, oolitic dolomite and limestone interbedded with shale and marl. These sediments were deposited in an upper, intertidal environment with evidence of a tidal-fiat and supratidal, sabkha setting. Khureij Formation (Coniacian). The formation is only developed locally at outcrop, taking its name from Jabal Khureij (Powell, 1989b). It conformably overlies the Wadi As Sir Formation at Jabal Khureij (central-southern Wadi Araba); the top is the base of the overlying Wadi Umm Ghudran Formation. It ranges in thickness at the type section (on Jabal Khureij), from 100 to 120 m (328394 ft), to only 16 m (52 ft) and 26 m (85 ft) repectively at Wadi Abu Khusheiba and Zarqa Main. The Khureij consists of marl, clayey micrite, thin-bedded, shelly wackestone/packstone with subordinate oolitic and dolomitic limestone and calcareous siltstone; beds of small chert nodules also are present. Dolomitized, clayey micrites and calcareous siltstone in the lower part of the sequence suggest low-energy, slightly deeper water. Periodic shallowing of the area, shown by oolitic-peloidal packstone rich in echinoid-gastropod and oysters, suggests a shallow, subtidal to intertidal setting developed during a low sea-level stand. The upper part of the formation is dominated by clayey micrites with diverse fauna, suggesting a prevailing shallow-water, low-energy setting.

Mid-Cretaceous in Syria Judea Formation (Cenomanian-Turonian). This formation ranges in thickness from 104 m (341 ft) in the Palmyra Mountain Range to more than 250 m (820 ft) in central Syria. It consists mainly of bioclastic limestone, microporous and dense limestone, and granular dolomite. Chert nodules occur throughout the section. It is underlain by the Hayane Formation (Barremian to Aptian), which rests on clastics of the Rutbah Formation, and is unconformably overlain by the dolomite and glauconitic sandstone of the Soukhne Formation. Massive Limestone Formation (Cenomanian to Campanian). The formation has been correlated with the Judea Formation, in part, in northeastern Syria. It is supposed that only the lower part is, in fact, mid-Cretaceous, and that the upper part should be coeval with the Soukhne Formation. There is no indication in the description of the succession whether there is a break in sedimentation between the two, as is found in many other areas. Lithologically, the Massive Limestone Formation consists of 280-400 m (918-1,312 ft) of wackestone, porcellaneous limestone, argillaceous and dolomitic limestone and dolo-

360

mite. There is, however, considerable lithological variation in the formation, depending upon location; in central and eastern Syria, more marly limestone seems to be present, and in northeastern Syria, the lower part is a marly limestone grading upward to porous, argillaceous, reefal limestone showing some similarities to northeastern Iraq. It lies unconformably on the Ghona Formation and grades up into the Campanian-Maastrichtian Shiranish Formation.

Mid-Cretaceous in Southeast Turkey Sabunsuyu Formation (upper Albian-lower Cenomanian). This formation is best developed in the Derik Mazidagi Road, where about 215 m (705 ft) are exposed. It has been subdivided by Cater and Gillcrist (1994) into the following four members(Fig. 8,38): Member I is 60 m (197 ft) thick and consists of lime mudstone with echinoids and planktonic foraminifera. Bioclastic packstone becomes more common upwards. The member was deposited in a shallow-marine setting, with pelagic lime mudstone and bioclastic storm deposits that accumulated in a low-energy setting. Member 2 is about 80 m (262 ft) thick and records a return to basinal lime-mudstone-dominated facies deposited in a gravitationally unstable submarine slope. Member 3 is 44 m (144 ft) thick. It starts with intraclastic and bioclastic grainstone containing large indigenous echinoids and shows large-scale tabular cross-bedding. It grades upwards into bioclastic wackestone and lime mudstone that are vuggy and heavily burrowed. This member was deposited in an offshore ebb-tidal or stormebb-tidal setting. Member 4 consists of 31 m (102 ft) of cherty wackestone in fining-upward sequences with intrabioclastic, cross-bedded grainstone and abundant oyster shells. The uppermost part is dolomitized and heavily burrowed and contains gypsum pseudomorphs. The member records deposition as shallow-marine bioclastic sands.

Derdere Formation (middle Cenomanian-lower Turonian). This formation was divided by Cater and Gilicrist (1994) into the five members (Fig. 8.38) described below. Member 1 consists of 27.6 m (91 ft) of dolomitized calcarenites and chertified, bioclastic limestone. This member records a return to open-marine conditions with ammonites. Progradation of shallow-marine bars is recorded in the coarsening-upward units, but regression at the end of this time led to complete dolomitization. Member 2 comprises 23 m (75 ft) of vuggy dolostone with complete pectinid bivalves. Concentrically zoned chert nodules within this sequence contain relict inclusions of dolomitic mudstone cut by bedding-parallel stylolites. This member may have been deposited in shallowmarine conditions. Member 3 is 14 m (46 ft) thick and consists of massive, vuggy dolostone and greenish, argillaceous marl in a shallow-marine setting.

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Sedimentary Basins and Petroleum Geology the Middle East Member 4 is composed of about 30 m (98 ft) of limestone with abundant solution vugs. The basal 12 m (39 ft) of this sequence coarsens upwards initially from marly limestone to vuggy, intraclastic and bioclastic wackestone followed above by 18 m (59 ft) of marl to heavily karstifled, dolomitic, bioclastic wackestone and packstone, which display large-scale collapse fills, red, sandy crackfills between meter-scale blocks and abundant, block calcite-filled veins. This member records two phases of progradation of bioclastic sands, either driven by shoaling after initial transgressions or by autocyclic means. Member 5 is 20 m (55 ft) thick of vuggy, stylolitic dolostone with bivalve and foraminiferal bioclasts. Dedolomitization is common close to joints and fissures. These features are all cut by later stylolites. It records another marine transgression in the formation.

Mid-Cretaceous in Southern and Southwestern Arabia: The Republic of Yemen In the former North Yemen, as will be argued in the succeeding section, the Cretaceous Ghiras Sandstone Formation should be treated as Upper Cretaceous because of its transition into beds dated as Paleocene, so that only in the former South Yemen is there any representation of the mid-Cretaceous. There, two formations are dated as Albian to Cenomanian: the Harshiyat Formation, which conformably follows upon the Qishn Formation (and which itself may extend into the lowermost Aptian), and the Fartaq Formation further to the west, which succeeds the lower part of Harshiyat found to the east (Fig. 8.4). Harshiyat Formation (Albian-Cenomanian). The formation has a thickness of 200-300 m (656-984 ft). The lithofacies changes from predominantly arenaceous in the western part of the former South Yemen, where it consists mainly of sandstone and conglomerates with some interbedded shale, marl and siltstone, to about 100 m (328 ft) of interbedded shale and marl, with some current-bedded sandstone, marl and shale in the eastern part of the former South Yemen and toward South Oman. The arenaceous component increases toward the top of the formation. The formation contains two well-defined limestone members (Beydoun, 1964, 1966; Beydoun and Greenwood, 1968; Mateer et al., 1992). The lower, the Rays Member, about 95 m (312 ft) of clastic beds which comprise about 9 m (30 ft) of thick-bedded, coarsely recrystallized, ferruginous, dolomitic limestone that is sandy in places. The upper, the Sufla Member, is a 188 m (617 ft) thick sandstone sequence capped by about 6 m (20 ft) of massive, fossiliferous, dolomitic limestone (Greenwood and Bleakley, 1967). The formation is conformably underlain by the Qishn Formation, and apparently conformably overlain by the Mukalla Formation. Fartaq Formation (Albian-Turonian). This formation passes laterally into the lower clastic part of the Harshiyat Formation in the eastern part of the former

362

South Yemen, but it is absent in the west. It represents a marine-facies equivalent of the upper part of the Harshiyat Formation. It reaches a thickness of 510 m (1,672 ft) and is composed of shale and limestone, followed by fossiliferous, marly, crystalline limestone that sometimes is oolitic. Interbedded marl, silt and shale appear near the top of the succession (Beydoun, 1964, 1966; Beydoun and Greenwood, 1968). The formation rests conformably on the Qishn Formation and is overlain, apparently conformably, by the Mukalla Formation.

THE THIRD CYCLE: T H E LATE C R E T A C E O U S In Arabia, deposition of the Late Cretaceous Aruma Group, which occupied a period of 15-20 Ma (Scott, 1990), followed the end of a period of major emergence and erosion during the Turonian. In the U.A.E., Oman and Iran, the sediments of the Late Cretaceous vary in thickness and lithology, because they include the sedimentary response not only to events affecting the platform, as during the earlier parts of the Mesozoic, but also the response reflecting the tectonic developments associated with plate collision and subduction, the nappe emplacement in Oman and the development of the foredeep. Therefore, the description of the successions in areas such as the U.A.E. provides an excellent starting point for the examination of the Late Cretaceous sequence in the Middle East. To the west, there is a gradual transition across the shelf to the continental deposits that bordered the shelf sea; and in the opposite direction toward Iran, the facies, where preserved, mark deeper-water conditions and the effects of collision/subduction. This complex interaction of plate-tectonic activity, collision and partial subduction, regional subsidence and eustatic sea-level change is reflected in the variety of sediments laid down. Upper Cretaceous sediments are widely distributed in the Oman Mountains (Glennie et al., 1974), where beds of the group disconformably overlie the midCretaceous sediments or still older units. They are, in turn, unconformably overlain by formations of early Tertiary age. Therefore, the Late Cretaceous was the time when thrust sheets were emplaced over the Arabian continental margin, and when some of the more distal equivalents of the Aruma Group were, in fact, caught up in the allochthon and emplaced along with the thrust sheet (Searle 1980; Graham, 1980). Thus, in the more south-southwestern parts of the U.A.E., in Dubai and the Abu Dhabi region, four principal formations have been recognized: the Laffan, Ilam (or Halul), Fiqa and Simsima. In the northern U.A.E., five have been identified (Glennie et al., 1974; Alsharhan, 1989). Three of them m the Muff, Fiqa and Juweiza formed in a foredeep on the continental margin immediately before and during the emplacement of the thrust sheets. The remaining two - - the Simsima and Qahlah

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous formed along the flanks. The Muff represents the products of erosion of the shelf carbonates on the oceanward flank of the foredeep prior to the arrival of the thrust sheets on the continental margin during the Coniacian to Campanian. It is a lateral lithofacies equivalent of the shale and marl of the Fiqa Formation during the Santonian, although the Muti Formation in Oman (Scott, 1990) is assigned a longer duration (Coniacian to Campanian). The Juweiza Formation is composed of flysch sediments derived from the erosion of the Hawasina sediments and Semail Ophiolite Thrust sheets. It is equivalent to the Qahlah Formation, which occurs on the eastern side of the allochthon and is characterized by a similar lithofacies. Again, however, the time ranges are not exactly the same. The Juweiza is assigned a time range of upper Campanian to Maastrichtian, whereas the Qahlah appears to be restricted to the lower Maastrichtian. Both formations grade westward into the shale of the Fiqa Formation, which occupied the central and continental marginal part of the foredeep. There are exposures of the Juweiza Formation of the Aruma Group along the western Oman Mountain Front in the Musandam Peninsula; in the Dibba Zone, three facies crop out that are particularly interesting to hydrocarbon exploration, for they have source-rock and seal capabilities. For the northern part of the Middle East region, it is convenient to use the succession in southern Iraq as a starting point, because it is similar in many ways to that of southern Arabian Gulf. One would then radiate from there in a broad sweep from the northeast, which includes the Foothills and Folded Zone of northeastern Iraq and Iran, through northeastern Syria and Turkey to the northwestern to western sections of Syria and Jordan, where the influences of relatively simple uplift have had important sedimentological effects.

Late Cretaceous in theSouthern Arabian Gulf :United Arab Emirates Aruma Group. The Aruma Group in subsurface in the Abu Dhabi/ Dubai region consists of transgressive and regressive cycles recorded by beds assigned to four formations. In ascending order: these are the Laffan, Halul (Ilam), Fiqa (Aruma Shale) and Simsima (Fig. 8.39). In outcrop in the western Oman Mountains and northern U.A.E., where the Oman Foredeep (Aruma Basin) developed during the Late Cretaceous, the facies pattern is more complex and the formations recognized are the Fiqa, Muti, Juweiza, Qahlah and Simsima (Fig. 8.40). Laffan Formation (Coniacian). This formation is about 27 m (90 ft) thick and consists of three units. The basal unit forms a sequence of light, olive-brown or greenish to gray shale, which may be finely laminated, papery or flaky shale. The middle unit consists of off-white or yellowish-gray lime mudstone, which sometimes is marly and contains scattered pyrite. The upper unit of the succession comprises finely laminated, olive-gray or dark-yel-

low-brown shale, sometimes calcareous or very calcareous, with traces of pyrite and occasional intercalated marl. Although the basal Laffan deposits are of deltaic origin, sourced from the west, the major part of the formation was laid down in an open-marine setting (Alsharhan, 1989). The Laffan Formation can be shown to rest unconformably upon mid-Cretaceous carbonates where they form the basal deposits of the advancing Late Cretaceous Sea (Alsharhan and Nairn, 1990; Harris et al., 1984). Halul Formation (Coniacian-Santonian.9). In Abu Dhabi the formation consists of a 400-500 m (1,311-1,640 ft) thick sequence beginning with light, olive-gray to yellowish-gray, marly limestone and marl speckled with fine, calcite grains. These are followed by lime mudstone, wackestone in part, with colors ranging from yellowishbrown to olive-gray near the top. They contain slightly argillaceous, bituminous seams with scattered, silt-sized, pyrite crystals. The formation ends with pale-orange to yellowish-orange beds of coarse-grained, bioclastic carbonates (wackestone, packstone or grainstone). The overlying contact with the Fiqa Formation is apparently conformable, but there is some evidence that suggests that there probably is a widespread unconformity of short duration. The underlying contact with the Laffan Shale is conformable. The greater part of the Halul is the product of shallow-water deposition under low- to moderateenergy conditions (Alsharhan, 1989). There was little influx of clastic material into the depositional basin, and the conspicuous increase in fine-grained clastics is, in eastern Abu Dhabi, indicative of relatively greater water depths. Ilam Formation (late Coniacian-early Santonian). The Ilam Formation, introduced by the Dubai Petroleum Co. in the Dubai region (Schlumberger, 1981), is equivalent to the Halul Formation, and consists of 7 m of lime mudstone to wackestone, shaley and argillaceous beds and deep-water, hemipelagic, terrigenous rocks with abundant Pithonella calcispheres. These grade upward into mediumgrained marl with abundant calcareous nannofossils and planktonic foraminifera, and end with skeletal and peloidal packstone containing abundant small, miliolid foraminifera (Alsharhan, 1989). The beds of the Ilam Formation represent sediments deposited on a shallowshelf updip from a clastic-carbonate ramp configuration and platform slope representing deep-water, hemipelagic conditions (Alsharhan and Kendall, 1995). Fiqa Formation (Coniacian-mid-Maastrichtian). The formation ranges in thickness from 61 to 1,220 m (200-4,000 ft) and is divided into two members: the lower Shargi Member and the upper Arada Member (Alsharhan, 1995). The Shargi Member consists of dark-gray, fissile, platy and slightly calcareous shale with abundant pyrite filling the tests of foraminifera, and some phosphatic and glauconitic grains. These grade up into dark-gray, argillaceous lime mudstone with rare pyrite. There are abundant Heterohelix sp. and common Globotruncana sp. The 363

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous Arada Member is composed of white-to-buff, microporous, argillaceous mudstone to wackestone with pyrite, and dark-gray, argillaceous, silty mudstone and shale. The member is completed by dark-gray, argillaceous mudstone to marl and light-gray marl and contains orbitoids, textularids and Globotruncana sp. The depositional environment is interpreted as moderate- to deepmarine, with a fauna suggesting a deep-shelf setting (Alsharhan, 1989, 1994, 1995).

Simsima Formation (middle-upper Maastrichtian). The thickness of the formation in subsurface is about 80 m (262 ft), while it ranges from 24 to 61 m (79200 ft) in outcrop. In outcrop in the western Oman Mountains (Sharjah region), the basal part of the Simsima Formation consists of packstone with Orbitolidea tissoti, which reflect an open, shallow-marine environment, followed by a normal, warm, marine, dolomitic packstone and wackestone sequence with orbitoids and a thick sequence of Lepidorbitoides packstone and rudist packstone laid down in a semi-restricted to restricted shallowmarine shelf. In subsurface, the Simsima is indicated by the appearance of a sequence of black, argillaceous shale with rudist and bioclastic packstone of a subtidal to intertidal type followed by intertidal, muddy, dolomitic limestone grading upward into algal, bioclastic lime mudstone and wackestone (Alsharhan and Nairn, 1993; Alsharhan, 1995). These are associated with hardgrounds suggesting a semi-restricted, marine environment accompanied by sealevel changes that resulted in the development of non-depositional conditions presaging the unconformity atthe end of the Cretaceous. Muti Formation (Coniacian-Santonian). The 15 m (50 ft) thick formation is exposed in northern U.A.E. and consists of autochthonous, radiolarian, deep-sea lime mudstone and chert; conglomeratic limestone; and carbonate lithoclasts containing shallow, shelfal fossils (Alsharhan, 1989). The sediments represent the uplift and erosion of the carbonate of the old cratonal margin, which lay to the east of the subsiding U.A.E./Oman Foredeep. Juweiza Formation (late Campanian-Maastrichtian). The type locality of the Juweiza Formation is well Juweiza-1 in Sharjah, and the formation is found in wells Remah B-1 and Remah-2 (Dubai) and Menidies-1 (Abu Dhabi), all within the Oman Foredeep Basin (Aruma Basin) close to the western Oman Mountains. It ranges in thickness from 152 to 1,220 m (500-4,002 ft) and consists of sandstone, shale and conglomerate which contain igneous and metamorphic rocks. The sandstone is composed of silty to very fine, sand-sized graywacke containing angular to subangular, quartz grains. The conglomerates contain pebble-sized quartz, chert and limestone clasts. The shale is light- to dark-gray, greenish-gray and brownish-gray. The sediments were deposited as deep-sea facies of basinal, turbiditic clastics. Qahlah Formation (late Campanian-early Maastrichtian?). The formation crops out in the western Oman Mountains (in the Dubai-Sharjah region) and ranges in

thickness from 40 to 70 m (131-230 ft). It is characterized by the dominance of clast-supported breccia and conglomerates, which can be grouped into four facies from bottom to top (Fig. 8.41): 9 lateritic, ferruginous mudstone formed in situ or in proximal location and transported for a short distance over the ultrabasic rocks 9 ophiolitic breccia, where fragments vary from pebbles to boulder size and are subangular to angular, suggesting very short transportation and rapid accumulation 9 ophiolitic conglomerate, sub-rounded to rounded and very poorly sorted, with no preferred orientation or structure 9 lithic sandstone, fine to medium-grained, moderately sorted and immature, and composed predominantly of quartz, olivine, serpentine, pyroxene and iron oxides The conglomerate and breccia were depositedas alluvial fanglomerates and wadi deposits, while the lateritic and lithic sediments were deposited in a fluvial and marine environment. The Qahlah Formation rests unconformably over the Coniacian-upper Campanian Semail Ophiolite and may be conformably or unconformably overlain by the Maastrichtian Simsima Formation.

Late Cretaceous in Eastern Arabia: Oman The basic developments of the Aruma lithologies in the U.A.E. are repeated in the Oman autochthon, where the Coniacian to Maastrichtian sediments were deposited in the foredeep that developed west of the Oman Mountains during the Late Cretaceous orogen on the eastern margin of the Arabian Platform. Except for the non-recognition of the Ilam Formation in Oman, the lithofacies and formational names in Oman generally are the same as those in the region of the U.A.E. With the arrival in the foredeep of flysch-type sediments, additional formational names were added, and their correlation with the established formations was determined. The lithofacies of the Laffan, Fiqa and Simsima formations are nearly identical to those in the U.A.E., and if a difference can be detected, it is that they may represent deposition under slightly greater water depths (e.g., deposition a little further from the continental margin of the foredeep). More detail on the stratigraphy of the Late Cretaceous in Oman can be found in Wilson (1969), Glennie et al. (1973, 1974), Hopson et al. (1981), Lippard et al. (1986), Hughes-Clarke (1988), Nolan et al. (1990), Searle (1980) and Scott (1990).

1.Western Oman Mountains Laffan Formation (Coniacian). The formation represents the basal Coniacian transgressive deposits in the Late Cretaceous Sea. It consists mainly of calcareous brown and gray shal, with minor limestone, unconformably overlying mid-Cretaceous carbonates. A yellow paleosoil and calcareous shale immediately overlie the unconformity. In outcrop at Wadi Miaidin, a thin sequence of interbedded ironstone and hematitic carbonates may

365

Sedimentary Basins and Petroleum Geology the Middle East

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous represent the same basal deposits of the advancing Late Cretaceous Sea or a period of stagnation of the Late Cenomanian Sea. Fiqa Formation (Santonian-Campanian). The formation consists of hemipelagic, fissile, pyritic shale, capped by soft marl and gray, argillaceous, microporous, pelletoidal wackestone (Tschopp, 1967a, b; Wilson, 1969; Glennie et al., 1974) deposited in the western and central area of the Oman Foredeep Basin at the time of maximum subsidence of the trough (Fig. 8.42). This was the time of the westward advance and emplacement of the Hawasina sediments and Semail (Ophiolite) Nappe. The beds contain planktonic foraminifera and calcareous nannoplankton within dark-gray or brownish marl, which is about 70% carbonate with clay minerals, of which kaolinite is more abundant than montmorillonite or illite. In the vicinity of the west-central Omani oil fields, the beds of the Fiqa Formation are about 418 m (1,372 ft) thick and are divided into two members: the lower Shargi Member, a mainly shaly facies of deep-marine, pelagic, depositional environment; and the upper carbonate Arada Member, made up of shallow-marine, limestone facies. HughesClarke (1988) believed that the lower boundary of the Fiqa is always sharp, with age and facies changes evidence of a hiatus. The upper boundary generally is sharp, with evidence of disconformity between the Fiqa and Simsima or Tertiary sediments (Fig. 8.43). Muti Formation (Coniacian-Campanian). Based on lithological criteria, the formation, about 340 m (1,115 ft) thick, is divided into two parts (Fig. 8.44). The lower part of the succession, about 100 m (328 ft) thick, contains conglomeratic limestone (coarse-grained packstone/grainstone) with a matrix of argillaceous, calcareous mudstone. The upper part of the formation, about 240 m (787 ft) thick, consists of indurated marl, calcareous shale and minor limestone conglomerates (Glennie et al., 1974). It forms a flysch-like sequence and constitutes the main part of the Aruma Group in Oman. The upper beds of the Muti Formation pass laterally into the shale and marl of the Fiqa Formation. The Muti is overlain by the Juweiza, with a contact believed to be a major thrust plane. Glennie et al. (1974) believe that the Muti Formation may be overlain tectonically by various units of the Hawasina other than the Juweiza Formation. It also can overlie various autochthonous formations from the mid-Cretaceous Wasia Group to the Permian Mahil Formation. Juweiza Formation (Upper Campanian). The beds of the Juweiza Formation are proximal, synorogenic deposits consisting of allochthonous clastic sediments localized in the central and eastern portions of the foredeep (Fig. 8.42). Rocks of this formation have been encountered in well Suneinah-1 and in outcrops on the Musandam Peninsula and in Wadi Mi'aidin (Wilson, 1969; Glennie et al., 1974). The clastic sediments in the wells are mostly silt to very fine, sand-sized graywacke, but there are occasionally medium- to coarse-grained beds. The Juweiza outcrops on the Musandam Peninsula have been

described by Glennie et al. (1974) as a flysch-like sequence of marl and shale with conglomerate and sandstone containing basic igneous components and abundant chert debris. These siliciclastics probably are distal turbidites deposited on submarine fans in the Oman Foredeep from sources in the thrust slices of the nappes to the east. Qahlah Formation (early Maastrichtian). This formation consists of 140 m (459 ft) of shale and marl with coarse, polygenetic conglomerates from the Oman allochthon. It occurs on the eastern side of the exposed allochthon (Coffield, 1984; Glennie et al., 1974; Nolan et al., 1990). It also contains lithic sandstone, clasts of red mudstone, chert, marly limestone and basalt. The Qahlah was deposited in a non-marine, fluviatile to shallow-marine environment. It unconformably overlies the Hawasina or Semail Ophiolite and is overlain conformably by the Simsima Formation, but locally, it may be covered disconformably by early Tertiary sediments (Fig. 8.45). Simsima Formation (Maastrichtian). The Simsima in Oman, as in the U.A.E., is composed of shallow-water limestone deposited after the cessation of orogenic activity and consists here of 137 m (450 ft) of white, microporous mudstone/wackestone interbedded with skeletal, pelletoidal packstone-wackestone and coarse, saccharoidal dolomite (Nolan et al., 1990; Glennie et al., 1974). In subsurface, the Simsima consists of about 148 m (486 ft) of highly fossiliferous, shallow-water limestone, dolomite and dolomitic limestone. The formation either unconformably overlies the Hawasina sediments or Semail Ophiolite or conformably overlies the Santonian to Campanian Fiqa and Maastrichtian Qahlah formations (Glennie et al., 1974). It is conformably overlain by the Umm Er Radhuma, although a hiatus encompassing the latest Maastrichtian to early Paleocene can be shown to be present (Hughes-Clarke, 1988) (Fig. 8.45).

2. Central Oman Mountains (Allochthonous Units) Semail (Ophiolite) Nappe (Upper Cretaceous). These rocks in Oman and the U.A.E. were emplaced on the thick, autochthonous, Permian to Cretaceous shelf-carbonate section that characterizes the Arabian Peninsula. This ophiolite represents a thick, allochthonous sequence of peridotite, gabbro, diabase, dike swarms, and pillow lava (basaltic intrusive) associated with pelagic, sedimentary rocks (Fig. 8.47), and forms an arcuate belt approximately 400 km (250 mi) long (Glennie et al., 1974). The Semail Ophiolite thrusts over the Haybi Complex and Hawasina sediments and contains one of the best-preserved examples of oceanic lithosphere. It represents a large fragment of the Arabian continental margin during the closure of the Tethys Ocean in the Late Cretaceous (Glennie et al., 1974; Chen and Pallister, 1981). It has the classic, ophiolite stratigraphy and consists of five stratigraphic units (Fig. 8.46), which were described in detail by Glennie et al. (1974), Hopson et al. (1981) and Lippard et al. (1986) and are summarized here (from bottom to

367

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Fig. 8.45. Lithostratigraphy of the Qahlah Formation, near Qalhat, eastern Oman Mountains (modified from Nolan et al., 1990, and published by kind permission of the Geological Society, London).

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368

nopyroxene). The harzburgite and dunite are pervasively serpentinized with lizardite, clinochrysolite and brucite. The peridotite tectonite exhibits a banded appearance, but grades into massive zones. The banding consists of concentrations of orthopyroxene-rich zones, 3 to 10 cm thick, interbanded with oli-

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369

Sedimentary Basins and Petroleum Geology the Middle East

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vine:rich zones. The peridotite-gabbro transition is a heterogeneous zone that marks the transition from uppermost mantle rocks (harzburgite and dunite) characterized by tectonic fabric to oceanic, crustal rocks represented by cumulate, ultramafic rocks and gabbro and lacking any tectonic fabric. Layered gabbro: Layered gabbro (about 3-5 km, or 1.9-3.1 mi, thick) generally has a narrow (0.5 km, or 3.1 mi) zone of two-phase olivine and chromite cumulates at the base, which overlies several kilometers of three-phase cumulates of olivine, clinopyroxene and plagioclase. It has megasopic features such as ratiolayering, size-layering and orientation of cumulus phases, particularly plagioclase and clinopyroxene. These features result in the sedimentary-like appearance of the layered, gabbro outcrop (Hopson et al., 1981). High-level gabbro: This gabbro varies in thickness (<1 km, or 0.6 mi, thick) and always occurs as a horizon sandwiched between the overlying sheeted-dike complex and underlying layered gabbro. The highlevel gabbro is texturally complex and lithologically ranges from fine-grained to coarse-grained rocks. The finer-grained rocks usually are plagioclase-clinopyroxene-Fe-Ti oxides, olivine, orthopyroxene and hornblende gabbro. The coarser-grained rocks typically are plagioclase-hornblende, clinopyroxene, FeTi oxides, quartz gabbro and diorite. Sheeted dike complex: The dike complex is composed of parallel to sub-parallel diabase and basalt dikes. The diabase is hydrothermally altered, exhibiting zeolite to upper greenschist facies assemblages, with metamorphic grade increasing downward. The dikes overlie high-level gabbro and penetrate upward into and locally feed pillow lava. The estimated stratigraphic thickness of the dike complex is 1.2-1.6 km (0.75-1 mi) and is discontinuous. Pillow lavas: Basaltic volcanic rocks, discontinuously exposed, reach a thickness of more than 700 m (2,296 ft). The rocks are intensely altered, yet original igneous features have been preserved. The basalts are aphyric and vesicular, and most vesicles are lined or filled with secondary minerals.

3. Northern Oman Mountains (Musandam Peninsula)

Outcrop Formation (Fig. 8.4) Muti Formation (Coniacian-Lower Santonian?). The formation sediments consist of yellow and green shale and marl with intercalations of quartzitic sandstone resting with strong discordance on a karstified hardground developed on the substratum (which may be the pre-Senonian discordance; Ricateau and Riche, 1980)o

Subsurface Formations (Fig. 8.4) The subsurface section was studied by Ricateau and Riche (1980) in wells Khassab-1 and Bukha-1 and is sum-

370

marized below: Laffan Formation (Coniacian?). This is about 1 m (3.3 ft) of black to red shale deposited in an open-marine environment. Ilam Formation (Coniacian-Santonian?). The formation is made up of 20-25 m (66-82 ft) of bioclastic packstone and grainstone with echinoids, rudist debris and Rotalia skourensis, Dicyclina sp., Valvulammina and Mont-charmontia appennica. Ricateau and Riche (1980) reported that in well Bukha-1, the Ilam has not been differentiated, and it may have been by erosion prior to theg deposition of the Gurpi Formation. Gurpi Formation (Santonian-Maastrichtian). This formation presents a cycle of basinal, argillaceous, carbonate sedimentation (argillaceous limestone and dark shale) and attains a thickness of about 600 m (197 fi). Ricateau and Riche (1980) divided it into two parts. The lower part is Santonian-Campanian in age and consists predominantly of argillaceous limestone and shale with a mixture of pelagic foraminfera (globigerinids), Heterohelix and arenaceous foraminfera deposited in an outer platform environment. The upper part, Campanian-Maastrichtian in age, is a rhythmically bedded series of sandy limestone, sometimes silicified, with arenaceous foraminifera and argillaceous limestone containing pelagic foraminifera (Globotruncana fornicata, G. wiedenmayeri and G. magdalensis). The beds are a carbonate flysch facies.

Late Cretaceous in Eastern Arabian Gulf: Southwestern lran Cretaceous rocks are found in the Lurestan Province, where most of the local formational names were established, and in the Khuzestan and Fars provinces. One feature of the stratigraphic sequences described is that some formations are assigned relatively long time ranges and cross boundaries marked by unconformities elsewhere in the Middle East, as is the case with the Garau Formation (Neocomian-Coniacian); the Bangestan Group (AlbianCampanian) and the Surgah Formation (Turonian-lower Santonian), which include parts of both the middle and Late Cretaceous; and the Gurpi (Santonian-Paleocene), Amiran (Late Maastrichtian-Paleocene) and Sachun (Upper Maastrichtian) formations, which cross the Maastrichtian-Paleocene boundary. The data available to this point do not permit a determination of whether such formations actually show continuous sedimentation or whether unconformities exist that have not yet been recognized. The general, lithostratigraphic interpretation of Late Cretaceous formations can be found in James and Wynd (1965) and Setudehnia (1972) and is summarized below and in Figs. 8.5 and 8.48 Ilam Formation (Santonian-Campanian). The formation was named from Ilam, a town in the Lurestan Province, where 190 m (624 ft) of well-bedded, gray to lightgray, white, weathering, fine-grained, argillaceous limestone with grayish-black, shale partings is exposed (Setudehnia, 1972). The basal bed of the formation is a silty

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limestone with hematite nodules and pipes. The formation rests on the Surgah Formation in the Lurestan Province and upon the Sarvak Formation (Ahmadi Member) in the Khuzestan Province. In both cases, the sedimentological descriptions of the boundary suggest the existence of a disconformity. The top contact of the Ilam with the Gurpi Formation is described as being apparently conformable in the Lurestan Province. However, in the interior of the Fars Province, part of the Ilam appears to be replaced by the marl of the Gurpi Formation. Gurpi Formation (Santonian-Paleocene). The type locality for the Gurpi Formation is Kuh-e Gurpi in the Lurestan Province. The formation has a thickness of 320 m (1,050 ft) and consists mainly of soft, weathering, bluishgray marl and shale with subordinate, argillaceous limestone bands (Setudehnia, 1972). It overlies thellam Formation with minor disconformity, and underlies the Tertiary (Pabdeh Formation) with the contact placed at the base of sandy, silty, purple shale forming the lowermost Pabdeh. In the Lurestan Province, two prominent limestone units are included in the Gurpi Formation: the Emam Hasan Limestone and the Lopha Limestone members. The Emam Hasan Limestone Member (Maastrichtian) may reach a thickness of as much as 114 m (374 ft) of fine-grained,

argillaceous, thinly bedded limestone alternating with blocky, gray marl and limestone. The member can be identified in the Lurestan Province and parts of the Khuzestan Province. The Lopha Limestone Member (Campanian), about 206 m (676 ft), is present only in the Lurestan Province, where it is a shallow-water, shelly limestone with an abundant megafauna and is named after the most commonly occurring species. The Gurpi Formation is found throughout most of southwestern Iran, but the age range of the formation is variable; it extends from the Santonian to Maastrichtian in the Fars Province and parts of the Khuzestan Province and from the Campanian to Paleocene in the Lurestan Province. This period of time was marked by considerable basin differentiation, with the development of facies variants that may be of considerable thickness, but of restricted extent. The presence within the Gurpi Formation of the two limestone members is one example; two others are thick and have been accorded formational status: the Tarbur and Amiran formations. The lower is a predominantly limestone unit (late Campanian to Maastrichtian in age); the other is a predominantly clastic unit of siltstone; and sandstone is younger in age (Maastrichtian to Paleocene).

371

Sedimentary Basins and Petroleum Geology the Middle East

Tarbur Formation (upper Campanian-Maastrichtian). Named after the village of Tarbur in the Fars Province, this predominantly local formation is well-developed in the Interior Fars Province, from where it can be traced southwestward to interfinger with the marl and shale of the Gurpi Formation. It consists of 527 m (1,730 ft) of resistant, shelly, cliff-forming, anhydritic limestone (Setudehnia, 1972). The basal contact with the Gurpi marl is sharp, but clearly diachronous. The top of the formation, at the contact with the gray and green marl of the Paleocene (Sachun Formation), is marked by the appearance of ferruginous nodules and concretions suggesting an erosional interval between the two. Paleontologically, the Tarbur Formation can be correlated with the Hartha Formation of southern Iraq and the Hartha-Bahra and Tayarat formations of Kuwait. Amiran Formation (upper Maastrichtian-Paleocene). This local formation takes its name from Kuh-e Amiran in the Lurestan Province, where it consists of 817 m (2,680 ft) of dark, olive-brown siltstone and sandstone, with local conglomerates containing mainly chert boulders and shelly limestone (Setudehnia, 1972). The lower contact with the Gurpi Formation is gradational; the upper contact is conformable, followed by the lenticular limestone of the Taleh Zang Formation. From the central Lurestan Province to the south and southwest, the beds of the Amiran Formation interfinger with marl of the Gurpi and Pabdeh formations. Late Cretaceous in Western and Northwestern Arabian Gulf The Aruma Group in Qatar retains the same formational names used in the U.A.E., except that the Fiqa Formation, used in offshore Qatar, is replaced by the term "Ruilat Formation" in the onshore. The Aruma Group is marked at both top and bottom by regional unconformities, and, as might be expected, the succession has much in common with that of nearby UAE, with the offshore section almost identical. The principal trend observed in Qatar is the thickening of the sequence from onshore to offshore, which accompanies a change in facies. No formational division was made for the Aruma of Bahrain, and the group is described as one unit. The general, lithostratigraphic description of Upper Cretaceous formations in these countries can be found in Lababidi and Hamdan (1985), Sugden and Standring (1975), Bou Rabee (1986), Owen and Nasr (1958) and Alsharhan and Nairn (1994) and are summarized below and in Fig. 8.3.

Late Cretaceous in Qatar Aruma Group (Coniacian-Maastrichtian) The Upper Cretaceous section is made up of the following four formations: Laffan Formation (Coniacian-Santonian). The Laf372

fan Formation is primarily a shale formation rich in marine ostracods conformably underlying the Halul Formation, but separated by a basal unconformity from the underlying mid-Cretaceous. It is described as having a thickness of 30.5 m (100 ft), but there is no indication of the shale being either pyritic or calcareous (Sugden and Standring, 1975; Schlumberger, 1981). Halul Formation (Santonian-Campanian). The offshore section, which, with a thickness of 73 m (240 ft), is five times thicker than the onshore section, is divided into four lithofacies units. The lithofacies following a basal, gray, microporous and slightly marly limestone pass to a marl and shale followed by partly brown, microporous to partly gray, microporous, bioclastic wackestone with some pyrite, and are completed by gray, microporous, bioclastic wackestone. The onshore section is a mere 15.3 m (50 ft) of gray, argillaceous limestone grading up into light-gray, dense, partly silicified lime mudstone and wackestone (Sugden and Standring, 1975; Alsharhan and Nairn, 1994). Fiqa/Ruilat Formations (Campanian). The Ruilat Formation is the onshore equivalent of the offshore Fiqa Formation in Qatar. The offshore Fiqa succession has the same subdivision as in Abu Dhabi and Oman, into the Shargi and Arada members. The lower, the Shargi Member, is about 61 m (200 ft) of blue-gray shale with planktonic foraminifera. The upper, the Arada Member, is about 18 m (60 ft) thick, consisting of bioclastic packstone and wackestone. Chert nodules are found at the top of the unit. The implication is that during the early stages of development of the Fiqa Formation, somewhat deeper-water, muddier conditions existed in Qatar than in Abu Dhabi, but more uniform conditions were established by the time of deposition of the Arada Member (Alsharhan and Nairn, 1994). The Ruilat Formation in the onshore, as described by Sugden and Standring (1975), has a total thickness of about 69 m (225 ft) of limestone. The basal 3 m (10 ft) is light-gray limestone with common glauconite nodules developed above the unconformity with the Halul Formation, followed by about 66 m (215 ft) of dense, gray lime mudstone and wackestone containing fine, elongate spicules, recrystallized foraminifers and calcareous silt with chert nodules at the top. The contact with the overlying Simsima Formation is conformable. Simsima Formation (Maastrichtian). The Simsima Formation, 115-205 m (380-672 ft) thick, has been subdivided to a greater degree than in Abu Dhabi. There are two members, the lower Jana'an and the upper Salwa (Sugden and Standring, 1975), which yield three and two further subdivisions, respectively: Salwa Member (21-33 m, or 68-110 ft) 9 argillaceous limestone grading up into slightly microporous, bioclastic packstone; and 9 green-gray, calcareous shale sometimes containing pyrite, small foraminifera and ostracods.

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous Jana'an Member (95-180 m, or 312-590 ft): 9 argillaceous limestone grading up into alternating, dolomitized wackestone and gray, microporous, bioclastic packstone; 9 dolomitized, bioclastic wackestone; and 9 light-gray, partly microporous limestone and slightly dolomitized, bioclastic packstone.

Late Cretaceous in Bahrain Aruma Group (Coniacian-Maastrichtian). In Bahrain, the Aruma Group has not been formally differentiated, although, based on lithological criteria, can bedivided into three units. The lower is greenish-blue, pyritic shale. The middle is fine-grained or granular, dolomitic limestone and saccharoidal dolomite interbedded with shale. The upper is black, pyritic shale with argillaceous limestone. The Aruma contact with the underlying Cenomanian Mishrif Formation is disconformable, and the contact with the overlying Paleocene Umm Er Radhuma also is unconformable. Late Cretaceous in Kuwait The Upper Cretaceous succession has been divided into the following formations: Khasib/Mutriba Formation (Coniacian). This formation, also known as Mutriba Formation, ranges from 283 m (928 It) in northern Kuwait to about 24 m (79 fi) in southern Kuwait. It consists of white to gray, dense, detrital limestone, locally glauconitic, with an intercalation of shaly horizons near its base. The age is based on Globigerina sp. and Gumbelina sp., and calcispheres are present. Sa'di Formation (Santonian-lower Campanian). It ranges in thickness from 12 m (39 ft) in southern Kuwait to about 304 (997 ft) in northern Kuwait. The formation consists of fossiliferous lime mudstone with few intercalations of shale and dolomite.

Hartha Formation (upper Campanian-lower Maastrichtian). It consists of an organic-rich, detrital limestone with some dolomite, shale and marl intercalations, particularly near the top, deposited in a marginalmarine environment. The thickness ranges from almost zero over a structural high (e.g., Burgan High) to about 274 m (899 fi). Bahrah Formation (upper Maastrichtian). The formation is named after Bahrah on the northern side of Kuwait Bay with a type section defined in well Burgan-10. It ranges from about 18 m (59 ft) in southern Kuwait to 85 m (279 It) in northern Kuwait. Lithologically, it can be divided into two units, with the lower containing detrital and oolitic limestone and black shale with some small foraminifera, and the upper containing predominantly white, dense, microcrystalline limestone with some chert (Owen and Nasr, 1958; Alshamlan, 1975). Tayarat Formation (upper Maastrichtian). The type section for the formation is in well Burgan-10 in

southeastern Kuwait. Thicknesses range from about 200 m (656 ft) in the south to about 350 m (1,148 ft) in the north. It consists of brownish or dark-gray, granulaa', dolomitic and locally anhydritic limestone with minor, interbedded, black, bituminous and pyritic shale. Owen and Nasr (1958) indicate a fauna that includes Omphalocyclus macropora, Lofiusia and Lepidorbitoides.

Late Cretaceous in Central and Southwestern Arabia 1. Late Cretaceous in Saudi Arabia Aruma

Formation

(Turonian-Maastrichtian).

Steineke and Bramkamp (1952) applied the name Aruma to an upper Cretaceous sequence of rocks cropping out at the A1-Aramah Plateau in central Arabia. Detailed lithostratigraphy was carried out by Powers et al. (1966) and E1Asa' ad (1983a & b). As the region closest to the continental margin, the hiatus between the Wasia and Aruma formations in Saudi Arabia is at its greatest, and the formation here is assigned a Campanian to Maastrichtian age (that is, the unconformable break stretches through the Coniacian and Santonian). In outcrop, the Aruma rests on varicolored clastics of the Wasia and is overlain by the Paleocene Umm Er Radhuma Formation. Within the sequence, a break permits the division of the Aruma into an upper shale and impure, carbonate succession and a lower, cleaner, carbonate succession. Everywhere east of the outcrop of Aruma sediments toward the Arabian Gulf, the stratigraphic break can be recognized in the subsurface. In some places, there are indications of angular discordance in some structures; in others, there is little evidence of discordance. The thickness increases eastward and reaches as much as 670 m (2,198 ft) in the vicinity of the Abu Hadriya Field in eastern Saudi Arabia. Four members have been identified in Saudi Arabia by Powers et al. (1966), while E1-Asa'ad (1983a & b) identifies three. These are, from top to bottom (Fig. 8.49): 9 Lina Member (33-37 m, or 108-121 ft): dolomite and calcareous shale, olive shale and argillaceous dolomite with interbedded limestone; 9 Upper Atj Member (or upper Hajajah Member of E1Asa'ad, 1983a & b) (27.6 m, or 92 ft): dolomite, with some limestone in the upper part; 9 Middle Atj Member (or lower Hajajah Member of E1Asa'ad, 1983a & b) (41-46 m, or 134.5-151 ft): basal, olive-green, calcareous shale grading up into finegrained, microporous limestone; and 9 Lower Atj Member (or Khanasir Member of E1Asa'ad, 1983a & b) (30-40 m, or 98-131 ft): finegrained wackestone with impure and sandy layers and beds of red-brown, vuggy dolomite.

373

Sedimentary Basins and Petroleum Geology the Middle East

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The Yemen section, likewise, is incomplete, with the Campanian to Maastrichtian Mukalla Formation overlying with apparent conformity the Harshiyat and Fartaq formations in the former South Yemen. The Upper Cretaceous formations in Yemen was described in Beydoun (1964, 1966), Beydoun and Greenwood (1968), Greenwood and Bleakley (1967), Geukens (1966) and E1 Nakhal (1988) and is summarized next. Mukalla Formation (Campanian-Maastrichtian). The formation crops out in the Hadhramout in former South Yemen, where the type section is 165 m (about 541 ft) thick in outcrop to 558m (1830 ft) in subsurface, and consists of a lower section of current-bedded, medium- to coarse-grained sandstone separated by a marl band from the upper part of fine- to coarse-grained, ferruginous sandstone with silty partings. The section is capped by interbedded marl, siltstone and sandstone.The formation records a transgressive phase during which widespread continental, deltaic to marginal marine deposits accumulated. Sharwain Formation (Maastrichtian). The forma-

374

This formation was introduced as the Tawilah Series in the northern part of Yemen (former North Yemen) by Lamare et al. (1930) to cover the sandstone sequence lying between the Middle-Upper Jurassic and the Tertiary, which inferentially might include Cretaceous beds of uncertain age. The beds were studied by Geukens (1966) at their type locality at Jabal al Tawilah, about 50 km (31 mi) northwest of Sana'a, where they consist of 180 m (about 590 ft) of continental, coarse-grained, white, crossbedded sandstone and conglomerate. Subsequently, E1 Nakhal (1988) raised it to formation status and divided the sequence into two members, one of which he regarded as Cretaceous (Ghiras Member) and the other as Paleocene (Medj-Zir Member). A1 Subbary et al. (1993) raised it to group status, and the two members to the formation rank as they are mappable units (Fig. 8.50). This redefinition is in accordance with the stratigraphic code (American Commission on Stratigraphic Nomenclature, 1983). Ghiras Formation (Middle-Upper Cretaceous). It attains a thickness of 315 m (1,033 ft) and is composed mainly of sandstone interbedded with thin, lenticular layers of channel conglomerate, siltstone and mudstone. The sandstone is coarse- to medium-grained and contains matrix-supported, intraformational sandstone clasts, some mud clasts and small quartz pebbles. The sedimentary structures are mainly trough cross-bedding arranged in cosets, tabular cross-bedding, graded bedding, and ball and pillow structures, occasional ripple cross-lamination and a few silicified wood fragments. The sediments were deposited in a braided, fluvial-channel environment. The contact with the overlying Medj-Zir Formation is conformable. Medj-Zir Formation (Paleocene). The formation attains a thickness of about 70 m (230 ft) of fine-to medium-grained sandstone interbedded with mudstone and siltstone with very rare, channel-conglomerate layers. Well-developed, large-scale cross-beds represent submarine-bar deposits. Burrows, clasts and a very thin horizon of fossiliferous claystone occur in the lower part. The formation is characterized by the presence of the concretionary, iron-rich zones, burrows, casts and siltstone. The formation was laid down in a shallow-marine to coastalplain environment. The contact with the overlying Tertiary

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous a.

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basalt, andesite, trachyte lavas and tuff is conformable. Late Cretaceous in the Northern Arabian Platform It seems generally true that in the northern part of the Middle East region, Jordan, Syria, northern and western Iraq and southeastern Turkey, it is more difficult to identify two possible sub-cycles, as has been attempted in the southeastern part on the Arabian Platform area (in the U.A.E. and adjoining areas). There is, however, a tendency for a stratigraphic break to be apparent between the lower Coniacian-Santonian and the upper Campanian-Maas-

trichtian. Over the platform area of western Iraq-Jordan, the sequence usually is thin and consists of carbonates and some marl. The common presence of phosphate and glauconite suggests a sediment-poor regime. Several formations are described that cross boundaries between major divisions (e.g., across the MiddleUpper Cretaceous or the Maastrichtian/Paleocene breaks), where unconformities or disconformities occur elsewhere in the region. It cannot be established whether the continuity is real or only apparent, whether either or both sedimentological and paleontological detail is sufficient to

375

Sedimentary Basins and Petroleum Geology the Middle East warrant any firm conclusion. It is a region where surface detail is often hard to obtain, but this is more than compensated by the wealth of subsurface data, so that an attempt to unravel the stratigraphic knots and resolve a lot of the confusion arising from the tendency to introduce (and seldom clearly define) local formational names can and should be attempted (Figs. 8.3-8.5). The Upper Cretaceous formations over the shelf areas of western Iraq, Jordan and Syria generally are thin and, despite some lithological variety, generally typify a shallow, carbonate shelf on which deposition was not always continuous, as indicated by the common occurrence of both glauconite and phosphate.

Late Cretaceous in Iraq 1. Southern Iraq

Khasib Formation (late Turonian-Coniacian). The Khasib Formation was first described from well Zubair-3 in southern Iraq by Owen and Nasr (1958), who noted a thickness of about 50 m (164 ft). The formation consists of a lower section of dark-gray and greenish shale alternating with gray, fine-grained, marly limestone. The upper part is made up of only gray, fine-grained, marly limestone (Bellen et al., 1959). The deposits are interpreted as lagoonal with a prevailing oligosteginal fauna. The lower contact is disconformable, but without a hiatus (Owen and Nasr, 1958), while the upper contact is gradational and, thus, conformable. Tanuma Formation (upper Senonian). The Tanuma Formation in the Zubair Field also was described by Owens and Nasr (1958) as about 30 m (nearly 98.5 ft) of black, fissile, sometimes pyritic shale with streaks of gray, microcrystalline, marly and detrital limestone that sometimes is glauconitic. An oolitic band appears in the upper part of the succession. Therefore, the depositional environment inferred is that of a nearshore basin, with apparently restricted communication with the open sea; hence, partly euxinic and partly lagoonal influences (with the formation of oolites) are recorded. Both the upper and lower contacts with the Khasib and Sa'di formations are gradational. Sa'di Formation (upper Senonian). The Sa'di Formation was assigned the same time range and described from the same well (Zubair-3) by Owen and Nasr (1958). The formation consists of 300 m (984 ft) of relatively monotonous, white, chalky, marly, globigerinal limestone with a single well-developed marl band 60 m (197 ft) thick in the middle (Bellen et al., 1959). The formation wedges out nearly completely toward western and northwestern Iraq. The sediments are typical of a neritic, sedimentary environment with a commonly occurring, planktonic, foraminiferal fauna. The lower contact of the formation with the Tanuma Formation usually is gradational and conformable, whereas the top contact usually is marked by an unconformity.

376

Together, the three formations (Khasib, Tanuma and Sa'di) show a transition across the Zubair Field from lagoonal, and sometimes restricted, environments into open-marine conditions. Not surprisingly, the formation in which open-marine conditions occur is the one most readily correlated with the Sa'di Formation of Kuwait.

l-lartha Formation (Upper Campanian-Maastrichtian). The Hartha Formation was identified first in the Zubair Field by Rabanit (1952, cited in Bellen et al., 1959). The formation is composed of 200-250 m (656-820 ft) in thickness of bioclastico-detrital, glauconitic limestone with green or gray, shaly interbeds. In places, the limestone is strongly dolomitized (Bellen et al., 1959). The formation intertongues with, or forms a single tongue within, the Shiranish Formation found in the High Folded Zone in northern Iraq. The formation was deposited for the greater part in a marginal-marine, fore-reef, neritic, shoal environment, but back-reef facies are found locally. The lower contact of the formation is unconformable and often is marked by the development of conglomeratic beds (Buday, 1980). Qurna Formation (Maastrichtian). In southeastem Iraq, the formation consists of 76-137 m (250-450 ft) of commonly argillaceous and locally dolomitic limestone with a few marly intercalations, some with a rich globigerinid microfauna (Owen and Nasr, 1958). Buday (1980) recommended that the term "Qurna" be abandoned in southem Iraq and the beds regarded as a tongue-like member of the Shiranish Formation, but the name still is used. It is disconformable with the underlying Hartha Formation and conformable with the overlying Tayarat Formation. Tayarat Formation (Maastrichtian). In southeastern Iraq, the formation ranges from 92 to 274 m (300-900 ft) of brownish and dark-gray, crystalline, dolomitic and sometimes anhydritic limestone and whitish limestone interbedded with minor, thin, black, bituminous, pyritic shale (Owen and Nasr, 1958). The formation was laid down in a shallow-marine setting. It conformably overlies the globigerinid marl and marly limestone of the Qurna Formation and unconformably underlies the Umm E r . Radhuma Formation (Paleocene).

2. Western Iraq

Digma Formation (Maastrichtian). On the stable Iraqi shelf, an independent stratigraphic unit of Maastrichtian age was described from the Anah Trough. The Digma Formation was first described by Bellen et al. (1959) from well Anah-1. The thickness of the formation in western Iraq ranges from 30 to 90 m (98-295 ft) of locally phosphatic, glauconitic and locally silicified marl. The beds were deposited in shallow-water, littoral-neritic conditions during the late Maastrichtian transgression. The top of the formation has suffered erosion, and the transgressively overlying sediments are of Paleocene age (Umm Er Radhuma or Aaliji formations). The base of the formation in the type section is gradational and conformable (Buday, 1980).

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

3. High Folded Zone of lraq

Gulneri Formation (lower Turonian). The position of the Gulneri Shale Formation is somewhat equivocal; it is a very thin unit, only 1 or 2 m (3.3-6.6 ft) thick, consisting of black, bituminous, finely laminated, calcareous shale with some glauconite and collophane in the lower part. It was deposited in a basinal, euxinic environment and is separated from the underlying Dokan Formation and the overlying Kometan Formation (Turonian-Santonian) by unconformities (Buday, 1980). It may, thus, be regarded as the deposits laid down in a relict basin following the retreat of the Cenomanian seas, and prior to the advance of the Late Cretaceous seas in which the Kometan Formation was laid down. Kometan Formation (Turonian-Santonian). This is the most widespread formation in central and northern Iraq. First described by Dunnington (1953, cited in Bellen et al., 1959), it reaches a thickness of 100-120 m (328-394 ft). The formation includes beds of a deeper, neritic, globigerinal, open-sea facies, as well as the calcisphere facies. The gray, thin-bedded, globigerinal limestone may be silicified locally and contain bands of chert concretions. Near the base, the beds may be glauconitic (Bellen et al., 1959). The lower contact is unconformable (as with the Gulneri Formation). The upper limit has varied relations, often unconformable or disconformable; it sometimes is seemingly in a conformable succession with the overlying beds. Shiranish Formation (upper Campanian-Maastrichtian). The formation, first described by Henson (1940, cited in Buday, 1980), is the most widely developed within the High Folded Zone. It is almost identical lithologically with the Hartha Formation of Rabanit (1952) and the Qurna Formation of Damoian (1975, both cited in Buday, 1980). It has a thickness range of 100 to 400 m (328-1,312 ft) of thinly bedded, marly limestone overlain by blue, pelagic marl and occasional marly limestone beds. The marl sometimes is dolomitic. There is a rich microfauna (Bellen et al., 1959; Owen and Nasr, 1958), supporting the interpretation of the depositional environment as deep, open marine. In the type area, the lower contact is conformable, but the upper boundary usually is erosional or at least non-sequential.

Bekhme Formation (upper Campanian-lower Maastrichtian?). The formation, distributed in the High Folded Zone, consists of 300-500 m (1,014-1,640 fi) of bituminous, secondary dolomite. The dolomite is a replacement of bioclastic-detrital limestone and overlies reef-detrital limestone, alternating with reef-shoal limestone and a basal breccia conglomerate (Bellen et al., 1959), with which they make an unconformable contact with the overlying and underlying formations.

Hadiena Formation (upper Campanian-lower Maastrichtian). It is well-developed in the High Folded Zone and may total as much as 750 m (2,260 ft). It was deposited in a rapidly subsiding basin in the Northern

Thrust Zone. It, too, has a basal unconformity. The formation overlies mostly the Chia Gara, but sometimes the Barasarin or Neokelekan formations are the underlying beds. The upper limit is conformable and gradational with the Aqra Formation. The Hadiena can be divided into the following three units, from top to bottom (Buday, 1980) Unit3: conglomeratic and fragmental limestone with angular fragments of hematite and quartz grains set in a ferruginous, limestone matrix Unit 2: silty, detrital, calcareous marl and sandy, marly limestone containing detrital hematite, phosphatic and chert grains, as well as conglomeratic and fragmental interbeds Unit 1" dolomitic limestone with vestiges of conglomeratic and fragmental elements

Tanjero Formation (upper Campanian-Maastrichtian). The formation finds its maximum development in the Imbricated Zone of the High Folded Zagros, where it may reach a thickness of 1,500-2,000 rn (4,920-6,560 ft). However, the formation thins to the southwest and, probably, to the northeast. It consists of two units: a lower unit of pelagic marl with rare, marly limestone and silt (the silt content diminishing toward the base of the sequence), and an upper unit of silt, marl and sandy or silty, bioclasticdetrital limestone (Bellen et al., 1959). The bulk of the formation represents flysch sediment deposited in a rapidly subsiding trough. Only in the lower part of the section do the sediments have an open-marine origin, only slightly affected by a terrestrial, terrigenous influx (Buday, 1980). The lower boundary usually is conformable with the Shiranish Formation. The upper commonly is marked by a break in deposition and covered by Paleogene sediments. Aqra Formation (Maastrichtian). The formation in the High Folded Zone, about 740 rn (2,427 ft) thick, consists of a reef limestone complex with massive rudist reefs, shoal reefs and fore-reef, detrital limestone. The limestone is locally dolomitized or silicified and may be impregnated with bitumen (Bellen et al., 1959).

Late Cretaceous in Jordan

Belqa Group(Coniacian-Eocene) The Belqa Group, predominantly pelagic sediments (chalk, marl, chert and phosphate), rests disconformably over the Ajlun Group (lower-Middle Cretaceous). It crops out from the Yarmouk River in the north, to the Eas En Naqh-Batn E1 Ghul in the south. It also is present in central-southern Wadi Arab (Powell, 1989b). The most complete sequence has been penetrated in boreholes. The group, whose name was taken from the Belqa District of northern Jordan, was first named by Quennell (1951). Different nomenclatures have been used since that time, and the present study follows the classification of Powell (1989 b) for surface outcrop formations and Andrews (1992) for subsurface data (Figs. 8.4 and 8.23).

377

Sedimentary Basins and Petroleum Geology the Middle East

Surface Formations The Belqa Group ranges in age from Late Coniacian to Late Eocene and forms the greater part of the Jordan Plateau. The typical sections are found in northern Jordan, between the Yarmouk River and Amman, but there is no complete, continuous section through the group. The thickness is 450 m (1,476 ft) and 520 m (1,706 ft) at Edh Dhira and Dana, respectively (Powell, 1988). The group was divided into the following formations, in ascending order: Wadi Umm Ghudran, Amman, A1 Hisa and Muwaqqar (which extended to the Eocene). The following is a summary of each formation, based on the work of Powell (1988, 1989b).

Wadi Umm Ghudran Formation (Coniacian-Campanian?). The formation was named for Wadi Ghudran ed Dib, southeast of Irbid, by Parker (1970, cited in Powell, 1989b) and is equivalent to the B 1 unit of Wolfart (1959, cited in Bender, 1974), to the Bla, Bib and Blc units of MacDonald and partners (1965 cited in B, cited in Bender,1974)), and to the upper part of the Massive Limestone Unit of Bender (1974). The formation ranges from 32 m (105 ft) at Jabal Waqf as Suwwan to 87 m (285 ft) at Wadi Mujib. Based on lithological descriptions, MacDonald and partners (1965 a & b, cited in Bender, 1974) and Powell (1988) divided it into three members: the Mujib Chalk, Tafila Chalk and Dhiban Chalk. The lower and upper members are massive chalk, rich in detrital fragments, with thin beds of dolomitic, marly chalk present in the upper part. The middle member is dolomitic, marly chalk, with chert nodules and marl laminae and large limestone concretions with chert laminae and stringers and dolomite lenses. The lower contact is gradational and conformable, where basal, detrital chalk of the Wadi Umm Ghudran Formation rests on the carbonate of the Ajlun Group. The top is taken at the base of the first massive chert of the basal Amman Silicified Limestone Formation. The sediments were deposited as normal, pelagic chalk resulting from a change in the configuration of the shelf from platform to ramp, and a concomitant rise in sea level associated with the late Coniacian transgression, as described by Flexer et al. (1986). Amman Formation (Campanian). Its name is taken from the capital city of Jordan, where it forms a large part of the bedrock. Bender (1974) reported that the formation is equivalent to the lower B2 of Wolfart (1959), the middle (cherty) part of the Amman Formation (Masri, 1963), the lower part (B2a) of the B2 Silicified Limestone and Phosphate Formation (MacDonald and partners, 1965a & b) and the lower part of the Amman Formation (northern Jordan) of Parker (1970, cited in Powell, 1989b). It ranges in thickness from 13 m (43 ft) at Zakimat A1Hasah to 100 m (328 ft) at Qatrana. The formation consists of thin- to medium-bedded, heterogenous lithologies. These are predominantly gray, white or brown chert exhibiting a variety of textures ranging from homogenous to brecciated, gray, microcrystalline

378

limestone (as beds and concretions); dolomitic, chalky marl; thin chalk; and thick-bedded, locally cross-stratified, oyster-coquinal grainstone. Phosphate (granules and peloids) is rarely present, usually occurring at the top of individual chert or limestone beds in the upper part of the sequence. The base is defined at the boundary between the underlying chalk or marly chalk (Wadi Umm Ghudran Formation) and the first massive, thick-bedded chert above. In southern Jordan, the first thick chert above the green-gray silt and sand of the Fassua Formation marks the base of the Amman Formation. The upper boundary is gradational and is marked by an increase in phosphate, marl and limestone and a decrease in thick-bedded chert, producing a marked break of slope with the softer beds above. Chert-carbonate facies rich in ostracods and siliceous microfossils were deposited in the mid-shelf (northern and central Jordan), while chalk rich in calcareous nannoplankton and pelagic foraminifera was deposited on the deeper-water, outer shelf (present Mediterranean coast). Shallow-water conditions on the mid-shelf are substantiated by the cross-bedded, coquinal oyster banks and laterally equivalent grainstone in central Jordan. The water depth must have been about 10-20 m. The paucity of a shelly, benthonic macrofauna within the chert (particularly the brecciated cherts) indicates that at the bottom, there may have been an anaerobic, basal water layer in a stratified ocean (Powell, 1989).

AI l-lisa Formation (Campanian-Maastrichtian). The name derives from the town of A1 Hisa in the main phosphate mining area of central Jordan (El Hiyari, 1985; Khalil, 1986). It is equivalent to the Phosphorite Member (Bender, 1974), the upper B2 of Wolfart (1959, cited in Bender, 1974), the upper part of the Amman Formation (Masri, 1963, cited in Bender, 1974), the upper part (B2b) of the B2 Silicified Limestone Phosphorite Formation (MacDonald and partners, 1965a & b, cited in Bender, 1974) and the upper part of the Amman Formation (northern Jordan) of Parker (1970, cited in Powell, 1989b). It ranges in thickness from 12 m (40 ft) at Zakimat A1 Hasah to 70 m (230 ft) at Siwaqa. It consists of thin- to medium-bedded chert, marl, chalky marl, phosphorite, microcrystalline limestone and oyster-coquinal grainstone. The latter are locally crossstratified and pass laterally to in-situ, biohermal banks. The carbonates are locally dolomitized; phosphate is present as granules and peloids in the limestone (calcareous phosphate) and chert, and as lens of soft phosphorite. The base is gradational and is marked by a break of slope reflecting the higher proportion of softer chalk, marl and phosphorite beds, compared to the hard chert in the underlying formation. The top is defined at the base of the thick, tan, pink and yellow marl and chalky marl of the Muwaqqar ChalkMarl Formation. The A1 Hisa phosphorite was deposited on the mid- to inner parts of the broad shelf sea rich in organic matter

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous derived from necktonic fauna and phytoplankton. A concentration of phosphate in this unit is assumed to be due to high organic productivity in the Tethys Ocean. This initial concentration may have been due to oceanic upwelling of nutrient-rich water close to the shelf break, with further concentration by winnowing on the shelf (Powell, 1989 ).

Muwaqqar Formation (Upper MaastrichtianLower Eocene). Widely distributed and reaching a maximum thickness of 332 m (1,089 ft) in extreme northwestern Jordan, in the vicinity of the Yarmouk River the formation consists of chalky marl, marl, chalky limestone, chert and occasional phosphate and highly bituminous marl (Powell, 1989b; Shawabkeh, 1991) deposited in an inner to outer shelf environment.

Subsurface Formations The time range of the Belqa Group in subsurface extends from the Upper Coniacian to Lower Eocene and contains the Rajil, Hamza, Hazim, Amman-A1 Hisa/ Usaykhim, Muwaqqar, Umm Rijam and Wadi Shallala formations (Fig. 8.26). In this section, the first six formations will be described, based on work by Andrews (1992). Rajil Formation (upper Coniacian?). The formation ranges from 175 m (574 ft) in well Wadi Ghadaf-1 to 551 m (1,807 ft) in well Hamza-3 and can be divided into a lower sandstone unit and an upper claystone-limestone unit. The "Sandstone Unit" is about 155 m (508 ft) thick and consists of poorly sorted, argillaceous sandstone interbedded with claystone and shale with minor, chalky limestone and dolomitic limestone bands. The "Claystone-Limestone Unit," about 260 m (853 ft) thick, consists of silty claystone; pyritic shale; slightly argillaceous, chalky limestone; and pyritic, dolomitic limestone with nodular chert and lenses of anhydrite towards the top. The Rajil Formation conformably overlies the Wadi As Sir Formation, and the top conformably overlies the Hamza Formation. The Rajil was deposited in a transgressive regime in a nearshore environment with a fluctuating sea level.

l-lamza Formation (Upper Santonian to Campanian?). The formation is restricted to the Hamza Graben and Azraq Basin and ranges in thickness from 221 m (721 ft) in well Heavy Oil-1 (in Wadi Rajil) to 940 m (2,755 ft) in well Hamza-4. It is composed mainly of finely crystalline, recrystallized and saccharoidal dolomite with abundant beds and nodules of chert and siliceous, argillaceous and marly limestone. The Hamza Formation overlies the Rajil Formation with minor unconformity, and major sedimentary change is represented at this boundary. The lower, dolomitic Hamza is overlain by the upper Hazim limestone. The Hamza Formation was deposited in a shallowmarine, carbonate-shelf setting. Hazim Formation (lower Maastrichtian). This formation is restricted to the Hamza Graben and Azraq Basin and ranges in thickness from 136.5 m (448 ft) in well

Adla-1 to more than 608 m (1,994 ft) in well Heavy Oil-2. It is composed of finely crystalline limestone, which is variously argillaceous, marly, chalky, dolomitic, pyritic and glauconitic with thin beds of anhydrite toward the top. The contacts are conformable. The lower boundary is placed between the cherty and dolomitic limestone of the Hamza and the argillaceous and marly limestone of the Hazim. The upper boundary is taken where carbonates with chert of the Amman Formation overlie the marl and limestone of the Hazim Formation. The Hazim was deposited in a shallow-water, marine, lagoonal to supratidal environment.

Amman and AI Hisa formations (Maastrichtian). These formations together constitute an important stratigraphic and economically important unit. The boundary between the Amman and A! Hisa formations is gradational, with an upward increase in phosphate, marl and limestone and a decrease in thick-bedded chert. Powell (1989b) suggested a division of the sequence into two units: the lower called the Amman Silicified Limestone Formation, and the upper called the A1 Hisa Phosphorite Formation. The Amman and A1 Hisa are found throughout Jordan, with thicknesses ranging from 20 m (66 ft) in well Risha17 to 138.5 m (454 ft) in well Hamza-11. The Amman Formation is composed of siliceous, saccharoidal dolomite, with chert and minor intercalations of argillaceous and chalky limestone. The A1 Hisa Formation is composed of argillaceous, phosphatic and bituminous limestone. Asphalt and chert occur in patches only in the lower part. In subsurface, the Amman Formation rests unconformably on the Wadi As Sir Formation (in the Northern Highlands), the Hazim Formation (the Azraq area) or the Kurnub Group (the Wadi Sirhan area). The top of the A1 Hisa Formation is defined as a sharp contact between chert, limestone and phosphate and thick, chalky marl of the Muwaqqar Formation. The Amman and A1 Hisa formations were deposited in a mid-shelf, shallowwater, carbonate environment. Usaykhim Formation (Maastrichtian). The formation is restricted to the A1 Harra area northeast of the Azraq Basin and is found in seven wells only: Fuluk-1 (72 m), Hamad-1 (100 m), Qitar A1Abd (37 m), Risha-2 and 19 (12.47 m), Smeica (100 m) and Wadi Hazim-1 (87 m); in outcrop, no more than 30 m is found. In subsurface, the Usaykhim is composed of a mixture of sandstone, microconglomerate and siltstone with chert. In most wells, the Usaykhim rests unconformably on the Ajlun Group and is overlain by phosphatic shale and limestone of the Amman and A1 Hisa formations. The formation was deposited in a shallow-marine environment.

Muwaqqar Formation (Upper MaastrichtianLower Eocene). The maximum thickness of the formation is reached in well North Highlands-2 (322 m, or 1,056 ft) (Andrews, 1992). In subsurface, due to the unconformity between the Cretaceous and Paleogene, two informal units can be recognized. The lower is argillaceous, phosphatic, 379

Sedimentary Basins and Petroleum Geology the Middle East locally fossiliferous and partly marly limestone, with chert nodules. The upper is soft marl interbedded with partly fossiliferous, argillaceous and chalky limestone(Andrews, 1992). The base of the Muwaqqar Formation is taken as the sharp junction between marl of the Muwaqqar and chert, limestone and phosphate of the A1 Hisa Formation, while the top has been defined on the first appearance of hard, chalky limestone of the Umm Rijam Formation overlying marl (Andrews, 1992). The lower unit (Maastrichtian) was deposited in a low-energy, broad-shelf environment, while the upper unit (Paleocene-Eocene) was laid down in a relatively deep-water, outer-shelf environment (Andrews, 1992).

Late Cretaceous in Syria The following two formations, ranging in age from Cenomanian to Maastrichtian, occur in eastern, central and northeastern Syria: Soukhne Formation (Cenomanian-Carnpanian). In Syria, two age ranges are given depending upon location: the first (Cenomanian-Campanian) for the beds found in central Syria, and the second (Santonian-Campanian) for beds in eastern Syria (the Euphrates Depression). The sequence ranges in thickness from 30 to 91 m (98-298 ft) and is composed mostly of an alternation of marly to cherty limestone and glauconitic sandstone. The formation generally is conformable both below and above in central Syria, but the base is unconformable over the Cenomanian-Turonian Judea Formation in eastern Syria.

Shiranish Formation (Campanian-Maastrichtian). The formation is well-developed in eastern, central and northeastern Syria, where the facies changes from area to area and the thickness ranges from 90 to 250 m (295820 ft). In central and eastern Syria, it is characterized by marl and marly limestone; while in northeastern Syria, the upper part is missing due to unconformity, and the lower part consists of gray, marly limestone grading upward to reefal, argillaceous, porous limestone. It contacts conformably with the underlying formation and disconformably with the overlying formation.

Late Cretaceous in Southeast Turkey Good data sources on the geology of Southeast Turkey are few. The seminal work is that of Rigo and Cortesini (1964) followed more recently by Cater and Gillcrist (1994). After deep-water sedimentation in the early part of the Late Cretaceous (Karababa, Karabogaz, Sayindere formations), the depositional environment changed as a result of late Campanian early Maastrichtian tectonic movements with the formation of the Kastel Intracratonic Basin and the syndepositional emplacement of the Karadur and Kocali complexes (Fig. 8.51). The final middle Maastrichtian to early Paleocene phase was marked by shallow, high-energy, nearshore and lower-energy, shallow-shelf and basin environments.

Karababa 380

Formation

(upper Coniacian-lower

Campanian). This formation was divided by Cater and Gillcrist (1994) into the following two parts: The lower part is 23 m (75 ft) thick, fining upwards from 1 m (3.28 ft) graded beds of quartz-bearing, bioclastic wackestone with reworked and indigenous clam shells, to a sequence of finer-grained, bioclastic limestone. It was deposited by storms above wave base. Deepening conditions resulted in muddier carbonate sedimentation below storm wave base. The upper part is 37 m (121 ft) thick of cherty, karstifled limestone. The lower 13 m (43 ft) is a fining-upward sequence passing from echinoids, bivalve and gastropodbeating bioclastic packstone into marl. Above this is an 8 m (26 ft) thick sequence of normal-graded, clam-bearing, bioclastic wackestone showing bedding and lamination overlain by a collapse breccia. The top of the formation consists of bioclastic limestone with chert and carbonate nodules. The upper part records a deepening marine setring within storm influence. Karabogaz Formation (middle Campanian). This formation overlies the Karababa Formation with an erosional unconformity and consists of about 20-30 m (66-98 ft) of heavily chertified limestone rich in phosphatic vertebrate fragments with clast-supported chert-pebble beds in the basal part of the formation. Chertification occurred after burial compaction and the fracturing of brittle clasts. The formation was probably developed during an interval of transgressive flooding, perhaps during a period of oceanic upwelling (Cater and Gillcrist, 1994). Sayindere Formation (Upper Campanian). The formation rests conformably upon the Karabogaz Formation and is overlain unconformably by the Korkandil or Germav formations. The formation itself is relatively thin, about 50-250 m (164-820 ft) of thin to medium-bedded, dark-gray to black, highly argillaceous limestone and marly limestone rich in planktonic foraminifera, radiolaria, calcispheres and sponge spicules indicating a deepwater, pelagic, depositional environment (Fig. 8.26). Korkandil Formation (lower Maastrichtian). The thickness of the Korkandil limestone is about 100 m (328 ft) and consists of thick-bedded, recrystallized, bioclastic packstone with rudists and conglomeratic limestone deposited in a shallow-marine environment. Near the base of the formation are thick-bedded, lithic limestone and wackestone. It rests unconformably on the Sayindere Formation, is conformably overlain by the Germav Formation and is a local equivalent of the Kastel Formation. Kastel Formation (Campanian-Lower Maastrichtian). The formation consists of alternating shale and sandstone with planktonic foraminfera deposited in a basin formed by tectonic activity in southeastern Anatolia. Contemporaneously, two allochthonous units from the Taurus Belt were emplaced into the basin by gravity slides: the lower Karadur Complex of Cenomanian-early Turonian shale, limestone and turbiditic conglomerate; and the upper Kocali Complex of submarine, spilitic lava and dia-

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

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intercalations. The conglomerate pebbles are from the Kocali Complex. Fossils generally are sparse, occurring in five or six sandy limestone lenses, the lower two of which are rudist biostromes associated with large benthonic foraminfera, hermatypic corals, lamellibranchs and algae that provide age control. The formation is diachronous with both the Besni and Germav formations. B e s n i F o r m a t i o n ( M i d d l e to U p p e r M a a s t r i c h t i a n ) .

381

Sedimentary Basins and Petroleum Geology the Middle East There are two units in the Besni Formation: a lower yellow to gray sandstone 3-20 m thick and an upper medium- to thick-bedded limestone 10-25 m thick that contains some dolomite bands. The sandstone contains benthonic foraminifera and some lamellibranchs, and although rudists are rare, they occur in a single sandy limestone. The overlying limestone contains, in addition to rudists, foraminifera, lamellibranchs, echinoids, gastropods, corals and red algae dating the formation. Germav Formation (Upper Maastrichtian-Paleocene). The 50-200 m thick formation is made up of alternating gray-green shale, sandstone and local conglomerates, with some locally persistent 1-10 m limestone bands characteristically containing, in addition to rudists, fragmented corals, lamellibranchs, gastropods and benthonic foraminfera. No rudistids are found in growth positions. It has been subdivided into the following three informal members: Germav 3: 1,500 m (4,920 ft) typical flysch, dark-gray and green shale and graywacke with gray, pelagic limestone and coarser, lithic limestone. The graywacke and lithic limestone form the base of turbidite flows, which grade up into shale and pelagic limestone. Germav 2: 70-90 m (230-295 ft) of alternating marl, shale, sandstone and limestone. The latter contain broken bivalves, gastropods and rudists. The limestone occurs as lenticular bioherms within fine, clastic sequences, deposited on a shallow-marine shelf flooded periodically by terrigenous clastics. When the clastic influx decreased, rudists and corals could developed reefal buildups. Germav 1: 150 m (492 ft) of red, lithic conglomerates, sandstone and siltstone. The sandstone is thin and parallel-laminated and interpreted as deposits from periodic currents that swept across silty plains. Pebble and cobble conglomerates developed within the channels, and gravel bars formed. Clasts of ophiolite and chert occur in the conglomerates. The depositional environment of the unit is interpreted as a silty flood plain with debris flows and low-sinuosity braided streams. The three formations were deposited on a ramp on the northern margin of the Arabian Plate under conditions of nearshore, high-energy conditions (Terbuzek conglomerates) to lower-energy, shallow-marine, rudistid limestone contemporaneous with the high-energy clastic influx. No typical rudist reefs are found. The shelf was clastic-dominated because of the influx of material derived from the adjacent Taurus Orogenic Belt. When the terrigenous influx ceased, carbonate-rich deposits formed. Small floatstone beds are interpreted as slope turbidites rather than downslope buildups (Ozer, 1993).

382

CRETACEOUS P A L E O G E O G R A P H Y AND GEOLOGIC HISTORY Tectonic Events

The stratigraphic history of the Middle East during the Cretaceous can be understood in terms of the superposition of a sequence of tectonic events of different orders of magnitude. The three orders of events are described below. Third-order Cretaceous events are recognized through the evidence of sea-level change. Three principal cycles can be recognized that form the basis for the threefold division of the Cretaceous (Fig. 8.2) adapted as the standard for the Arabian Peninsula and Arabian Gulf Basin. The first, the Early Cretaceous (Thamama Group), extends from the Berriasian to the mid-late Aptian; the second is the mid-Cretaceous (Wasia Group) time interval from the earliest Albian to Turonian; the third, Late Cretaceous (Aruma Group) time interval extends from the postTuronian into the Maastrichtian. Each of these cycles appears to be further subdivided into two (Alsharhan and Nairn, 1986, 1988, 1990). The oscillation in sea level expressed in the lithofacies was interpreted by Murris (1980) in terms of his carbonate ramp and platform hypothesis. Second-order events are related to extensional movements most characteristic of the northern part of the Middle East, the continued movements in the Sinjar-Palmyra and Euphrates-Anah Trough and the uplift of the RutbahKhleissia High through Iraq and Jordan. This high separated a Mediterranean domain in the west from a Mesopotamian domain in the east (Buday, 1980) until as late as the Late Berriasian. Evidence of this intra-Berriasian movement is confined to areas relatively near the platform margins in central Iran and the Levant. On the Saudi Arabian stable shelf, sedimentation was relatively unaffected by these movements, but unconformities are evident in eastern Iraq, southwestern Iran, Kuwait and easternmost Saudi Arabia. The Rutbah-Khleissia High uplift affected Saudi Arabia at the Valanginian/Hauterivian boundary. First-order events that affect the stratigraphic history of the Cretaceous culminated in the emplacement of ophiolite bodies along the Sernandaj-Kermanshah Crush Zone in Iran and the emplacement of the Semail Nappe in Oman at about 90 Ma. This event was one of the latest phases in the sequence of first-order tectonic events affecting the Middle East, because following crustal thinning during the late Paleozoic, a fragment of the southern paleo-Tethyan margin separated during the early Mesozoic. This separation left in its wake a small oceanic basin, the Neotethys, analogous to the present Red Sea. The continental fragment, which now includes present-day central Iran, may have undergone significant lateral displacement and rotation. The basin reached its widest extent when the northeastern margin, the continental leading edge of the

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous separated fragment, reached the subduction zone against the Eurasian margin during the Early Jurassic. This line, along which the collision occurred, lies between the Alborz and the Kopet Dagh (that is, between the massif of central Iran and the Turan Plate). It should be remarked that the area was close to the pole of the spreading motion, for a much greater opening is seen in the east than in the west. Subduction ended during the Jurassic, and closure of the Neotethys Ocean began as the Arabian-Nubian Plate continued to advance toward collision with Eurasia, which began during the Late Cretaceous along the line of the present Zagros, a line that marked the location of the new subduction zone. On a regional scale, the timing of the ophiolite emplacement postdates the ridge jump in the ?late Cenomanian that isolated Madagascar and resulted in a fragment separating from northeastern Somalia (which now may be incorporated into Eurasia as the Afghanistan Block?) and the appearance of oceanic conditions close to the present Indian Ocean shoreline of the Horn of Africa. In a stratigraphic sense, the effects of these tectonic events, as reflected in the sedimentation history of the region, is remarkably limited. The most clearly defined signs are the development of an intra-Berriasian unconformity seen in eastern Iraq and the first clear indication of the impending collision, the development during the Turonian of a bulge or flexure on the Arabian Plate, whose effects are seen in the successions in eastern Arabia (the U.A.E. and Oman). As obduction of the ophiolite nappes developed, this bulge of the continental plate in the U.A.E. and Oman migrated westward, which can be determined through the dating of the unconformity that youngs progressively to the west. It has been calculated that the time lapse represented by the duration of the unconformity may be as much as 15 Ma in the west close to the Arabian Shield, but as little as 3 Ma in the east in the U.A.E. (Harris et al., 1984). Although a foredeep developed in Oman, in which there accumulated the thick, flysch sequence of the Campanian (Fiqa Formation) over the greater part of the Arabian Peninsula, the Cretaceous is characterized by a carbonate platform that shows very little evidence of the tectonic event that so affected the Oman margin (Alsharhan and Nairn, 1990; Scott, 1990; Alsharhan, 1994). The effects of the intra-Berriasian unconformity are not observable in Arabia, where there is no break between the Berriasian and Valanginian, although a late effect is noted at the Valanginian-Hauterivian boundary. During the Early Cretaceous of southeastern Turkey and southwestern Iran, the deep-water slope and basin deposits, the "eugeosynclinal sequence," were distinguished by radiolarian marl and very fine-grained sediments. In northern Iraq, the passive margin sediments and the basinal deposit zones were separated by a mid-basinal, ophiolitic zone, which gave way upward to a sequence of volcanogenic, sedimentary rocks. The passive-margin sedimentary wedge (miogeosynclinal zone) subsequently was overridden by Cretaceous and Tertiary thrust sheets; thus, its eastern boundary is speculative. Although less spectac-

ular, the results of vertical movements of the craton, both positive and negative, control sedimentary thicknesses, with thinning against the Ha'il-Rutbah-Khleissia High and the thickening in the associated transverse troughs, the Anah and Sinjar grabens. The intracratonic, Mesopotamian Basin, which developed on the central Iraq Platform, continued to subside (Murris, 1980). In the southern section of this basin, in the vicinity of the Arabian Gulf, the Cretaceous section can be described in terms of the Murris ramp carbonate model (Koop and Stoneley, 1982), as the shelf built out into the Tethyan Ocean. Against the Arabian Shield (in eastern Arabia) in the supratidal and subtidal flats, lagoonal and open-shelf environments, shoals, biohermal accumulations and an intrashelf basin can be identified through their lithofacies associations (Alsharhan and Nairn, 1986, 1988, 1990, 1993 a & b). Each of the three divisions of the Cretaceous, following the system of subdivisions used in the Middle East, is capable of being subdivided into two sub-cycles. The ramp model also can be applied in Iraq to the sequence on the eastern flank of the Rutbah-Khleissia High, as well as in southern Turkey against the Mardin High, although there is a thinning and partial wedging out to the northwest where the exposed ridge reaches close to the marginal sedimentary prism, periodically interrupting the continuity between the Taurus and Zagros ranges. The Mardin and Khleissia paleohighs were exposed during the Early Cretaceous, but both were inundated during the Albian; yet, by the end of the Turonian, the Rutbah-Khleissia High was fully exposed. Sedimentation in the bordering troughs was sourced from the exposed highs that supplied deltaic sediments (mainly sands and shale). The branching Euphrates-Anah Trough received clastic sediment during the Early Cretaceous only at its confluence with the Palmyra Trough; but, by Aptian-Albian time, with the gradual submergence of the highs, a carbonateevaporite sequence became established. Movement in the troughs was largely fault-controlled. On the western flanks of the Khleissia High in Syria and the Levant, sedimentation was not confined to the immediate area of the Palmyra Trough, but spread over the entire area. Against the high, deltaic sands formed, and neritic carbonates and carbonate-evaporite sequences developed away from the high. In one of the few areas of volcanicity, lavas occurred in western Syria and Lebanon during the Early Cretaceous. The waxing and waning of the carbonate and clastic sediment deposition across southern and eastern Iraq, Kuwait, and Saudi Arabia, the third-order events, were due to the interaction of sea-level change and the initiation of subduction in the Taurus-Zagros region in southeastern Turkey, northeastern Iraq and northwestern Iran. Folding in this region, dating from the late Albian-early Cenomanian, continued with increasing intensity into the early Turonian. The passive margin still was a region of subsidence and uninterrupted sedimentation. One effect associated with this activity was the reactivation of the older highs already noted. From the Turonian to Coniacian, stronger

383

Sedimentary Basins and Petroleum Geology the Middle East pulses of tectonic activity developed, and uplift of the high was recorded on the unstable shelf as rapid facies change or breaks in sedimentation. A foredeep formed in Iraq along the line of the developing orogen, which, after an initial fill of calcispherid, marly limestone during most of the Senonian, received a thick sequence of flysch clastics until the late Campanian, when carbonate deposition was reestablished. One result of the Turonian-Campanian uplift was the erosional removal of Turonian-Campanian sediments from considerable areas adjacent to the foredeep, although within the foredeep, as previously remarked, sedimentation continued unabated. The late Campanian-Maastrichtian began with a major transgression over the shelf, which intermittently covered the Rutbah-Khleissia High. The foredeep, however, continued to subside in northeast Iraq, with continuing flysch deposition with sediments supplied from the uplifted areas. As in earlier periods, the foredeep was separated by a ridge from the intracratonic basins on the shelf. Along the orogenic front, nappes were emplaced that tended to over-run their own debris. By the late Maastrichtian, the orogenic upheaval abated, ophiolitic nappes were emplaced, and a quieter depositional regime returned to northern Arabia. The Cretaceous ended with a minor regression. The next major tectonic activity involved uplift of the Zagros ranges to the east and can be observed in the flood of clastic sediments that poured into the Mesopotamian Basin during the late Miocene-Pliocene. Thus, the events that controlled deposition are the events critical to the appreciation of the paleogeography. As subduction progressively closed the gap between the Arabian and the Eurasian plates, premonitory disturbances are reflected in the development of unconformities accompanied by greater diversification in depositional environments, with rapid local changes in lithofacies and thicknesses seen earlier in the Mesozoic. Although compressional forces are dominant, sight should not be lost of the tensional forces affecting the Arabian Plate; the tensional grabens of Syria and Iraq already are well-known, although less attention has been focussed on the graben system of central Arabia.

Paleogeography and Cyclicity Paleogeographic reconstructions result from the natural integration of all the events and, therefore, require a somewhat different style of presentation. The principal tool is the presentation of a sequence of paleogeographic maps providing a view of the entire region in a series of time slices. The choice of the time slices to depict, to explain the tectonic history of the slices adopted here, is based on the development of the regional unconformities. As will become increasingly apparent, the three orders of events mentioned earlier are an oversimplification, because there are sub-orders of events that involve changes of a more local importance overprinted on events of

384

regional or global scale. For example, unconformities that can reflect tectonic events of a more local nature occur in the Zagros region within the thick sedimentary sequence overlying the platform edge. The succession shows a great degree of variability in lithology and thickness, resulting from the greater tectonic instability of the platform edge. In general, the northern part of the Middle East, in terms of the definition used in this work (that is, in the ZagrosTaurus Zone of Northwest Iran, Northeast Iraq, Syria and Southeast Turkey) has more variability and develops more local sequences than found in the more stable parts of the platform. It also must be admitted that it is a region where less detail is available because of the combination of tectonic complexity and poor exposure. Nonetheless, the three-fold division of the Cretaceous recognized in the field can be applied to the region as a whole. In stratigraphic terms, the sediments of each division are assigned to three groups: the Thamama, Wasia and Aruma equivalent groups of Arabia, justified by their general applicability. The sediments in the groups do not entirely encompass the Cretaceous everywhere; near the platform margin in the Levant, tectonic instability at the end of the Jurassic is shown by the development of an intra-Berriasian unconformity that is seen in Iraq, one which is not apparent in Saudi Arabia. At the end of the Cretaceous in the region adjoining the Zagros, the Maastrichtian is incomplete, and deposits at the end of the Maastrichtian and the earliest Paleocene are missing in many areas. Within the platform itself, note must be taken of regional structures, particularly highs resulting from the reactivation of basement lines of weakness periodically throughout the geological history of the region. One of the more obvious is the Rutbah-Khleissia High in Iraq, which served in the Early Cretaceous to separate a Mediterranean sedimentary domain from the Mesopotamian to the east (Buday, 1980), but which was largely submerged before the end of the Cretaceous. Thinning over the crests of other anticlines or arches, the Ghawar-Burgan anticlines and the Qatar-South Fars Arch, provides evidence of relative uplift during the Cretaceous; even if movement was generated over rising Infracambrian salt, the prime cause still is assigned to movement of basement fractures. Each of the three divisions generally can be regarded as composed of two sub-cycles. They are not clearly recognizable everywhere, even on the stable Arabian Platform, but enough of an argument can be made to believe that their ultimate cause was sea-level fluctuation modified by movements predominantly local in character and discussed in detail by Murris (1980), Harris et al. (1984), Alsharhan and Nairn (1986, 1988, 1990), Alsharhan and Kendall (1991), Scott (1990), Lenindre et al. (1990) and Kendall et al. (1991 ).

Early Cretaceous Cycle The Early Cretaceous sediments in Saudi Arabia near

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous the exposed Precambrian massif are characterized by littoral and continental sands. The sands usually are thin and local, but they occasionally push far out onto the shelf, suggesting that the terrestrial environment was one of presumed low relief and low rainfall, much as at the present time, such that the sediments accumulated in the continental area were flushed through wadis onto the shelf by flash floods at irregular and relatively rare intervals. The general consistency of the shoreline position throughout the Cretaceous suggests a hinge-like movement; otherwise, the location of the littoral zone might be expected to migrate with time (Connally and Scott, 1985; Alsharhan and Nairn, 1986). Toward eastern Arabia and the Arabian Gulf, the deposits were laid down in tidal-fiat (intertidal, subtidal flats and lagoonal) and open-shelf environments. Within these environments, facies indicate the presence of shoals, biohermal accumulations with somewhat deeper intrashelf basinal sediments characterized by their lime muds. The most obvious subdivision of the Early Cretaceous in the Arabian Peninsula and adjoining areas on the platform is in terms of two sub-cycles, as already indicated. The lower generally is uniform and extends into the early Hauterivian; the upper extends into the Aptian (Alsharhan and Nairn, 1986; Scott, 1990). The distinctive feature of the second sub-cycle is the clastic influx from western Arabia, which by the mid-late Barremian occupied the western half of the basin, pushing the carbonate realm with its coral, algal and rudist limestone far to the east. These latter beds hold extensive gas and oil accumulations in the southern Arabian Gulf, sealed by interbedded marl, argillaceous limestone and shale. Further to the north, the coastal clastics also form important reservoirs and are sealed by later shale deposited in a nearshore environment and charged from euxinic Late Jurassic to Early Cretaceous deposits in the Arabian Gulf and Mesopotamian basins. Murris (1980) and Alsharhan and Nairn (1986) concluded that the Berriasian-Valanginian in Arabia shows essentially a narrow strip of deeper-water carbonates stretching across Oman, which gives way to an equally narrow intermediate zone, passing to a broad area of shallow-water carbonates (Fig. 8.52). The Hauterivian-Barremian interval was characterized by a vast carbonate ramp sloping from the Arabian Shield in the west eastward toward Oman (Fig. 8.53). The persistence of the broad, shallow, intraplatform, carbonate ramp, modified in the east by renewed, gentle movement of the Lekhwair Uplift (Oman), resulted in a broad, north-south-trending, intermediate zone through Oman. In later Barremian time, the influx of coarser clastics from the Arabian Shield increased, pushing the zone of shallow-water, carbonate deposition eastward (Fig. 8.54). The carbonates further out on the shelf bear witness to an increasing proportion of argillaceous sediments. During the Early Aptian, the area of shallow-water carbonates increased, expanding at the expense of the coastal-plain environment (Fig. 8.55). Early

Cretaceous deposition was terminated here by mid-Aptian regression, resulting in an unconformity that can be traced across the Arabian Peninsula (Alsharhan and Nairn, 1986; Harris et al., 1984; Scott, 1990). In northern Oman, the basal interval contains starved porcellanites deposited on a deeply submerged shelf, which progresses upward into shallow, open-marine, shelf limestone at the top. The interior portions of central and southern Oman appear to be characterized by low to moderate energy and restricted, shallow-marine carbonates close to, or along, the shelf-slope break of an intrashelf basin. In southern Oman (Dhofar region), shallow-marinecarbonate deposition was interrupted sporadically by minor clastic influxes. On the platform in central Iraq, the intracratonic Mesopotamian Basin (Fig. 8.55) continued to subside. In its southern part in the vicinity of the Arabian Gulf, the succession, which developed consistent with the ramp carbonate model of Murris (1980; Koop and Stoneley, 1982), was established by the Aptian. Here, Cretaceous rocks overlie a Jurassic sequence generally capped by evaporites. The ramp carbonates are related to the slow recovery of sea level, an event coeval with the development of a new sub-basin in the Khuzestan Province of Iran. The carbonates prograde out into the Tethyan Sea to the east, with an apron of Tintinnid slope and basinal marl. By the Early Cretaceous, evaporite deposition had ceased in southern Iraq, and the depositional pattern reflected that of the Late Jurassic. Uplift of the Arabian Shield resulted in a strong, clastic source emerging to the southwest, producing an overall eastward shift in the facies pattern. In northern Iraq, uplift and erosion resulted in the breaching of earlier hydrocarbon accumulations and the local deposition of sedimented bitumen (Dunnington, 1958). This area was not covered by sediment again until the Barremian. Intrashelf basins with euxinic, pelagic conditions were related to a more distal position of the basins in northern Iraq; marine transgression followed during the Aptian, leading to the deposition of carbonates over earlier deposits. Northwest of the Arabian Platform, toward Syria in the direction of the Rutbah-Khleissia High, the ramp carbonates thin, and the eastern flanks of the high itself became the site of deltaic, clastic sediments. Farther to the north into southern Turkey were shallower-water conditions; the ramp carbonates thin and partially wedge out where the ridge approaches to the platform edge. Here, the Rutbah-Khleissia High intermittently separated the shelfmargin sedimentary wedge (the Geosynclinal Trough of some authors) of the Zagros from that of the Taurus (Buday, 1980). Early Cretaceous sediments generally were absent over the Mardin High in southern Turkey until the late Barremian, but the structure was not submerged until the mid-Cretaceous. The Aptian is dominated by sandstone, shale, sandy limestone and sandy dolomite of a nearshore environment. During the Early Cretaceous, the Mardin 385

Sedimentary Basins and Petroleum Geology the Middle East

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The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

Fig. 8.54. Paleogeography during the Middle to Late Barremian in the Middle East (modified from Murris, 1980 and reproduced by kind permission of AAPG.

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Riyadh

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Fig. 8.55. Paleogeography during the Middle Aptian in the Middle East (modified from Murris, 1980 and reproduced by kind permission of AAPG).

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387

Sedimentary Basins and Petroleum Geology the Middle East High acted as a separation between the Syrian Sinjar and Palmyra troughs to the south from the deeper-water, pelagic sediments to the north. In east-central Syria, Early Cretaceous sediments are confined largely to the Palmyra and Sinjar troughs, which lie between the Mardin High and the Rutbah-Khleissia High. From as early as the Early Jurassic, sedimentation was restricted to the eastern end of the Palmyra Trough; here, Early Cretaceous beds are unconformably overlain by mid-Cretaceous sediments. Deltaic sands and shale poured into the trough from the exposed flanks of the high. Shale that accumulated in the axial part of the trough is a potential source rock for the flanking deltaic sands. The Euphrates-Anah Trough only received deltaic, clastic sediment during the Early Cretaceous in the region of their confluence with the Palmyra Trough, sedimentation that extended southeast of the Syria-Iraq border; but, by the end of the Early Cretaceous, in the Aptian-Albian, carbonate-evaporite conditions were established in the troughs. In southeastern Turkey, northeastern Iraq and northwestern Iran, the Early Cretaceous lithofacies consist of radiolarian marl and very fine-grained, clastic sediments (Buday, 1980) that suggest deep-water, bottom-of-theslope deposits (the eugeosynclinal deposits of some authors) separated from the shallow-water sediments by a mid-basinal, ophiolite zone, subsequently replaced by a volcano-sedimentary sequence of rocks known as the Gimo Suite of Buday (1980). As Tertiary overthrust sheets cover the zone, the location of the boundary is uncertain. The trough was filled mostly with deep-water, pelagic sediments to the northwest and shallow-water sediments to the southeast. The continuation of the Mardin High separates these neritic sediments to the northwest from the shallow-platform carbonates to the southeast (Buday, 1980). In western Syria, Early Cretaceous sedimentation was more extensive, spreading beyond the immediate surrounds of the Palmyra Trough, with deltaic clastics lapping up against the flanks of the Rutbah-Khleissia High and neritic carbonates and carbonate-evaporites occurring further from the uplifts. In central and western Syria, volcanogenic conglomerates and basalts are interbedded in the clastic succession. Lateral and vertical facies changes are apparent in this sequence, and near the Lebanese coast, the neritic carbonates grade into deep-water, radiolarian marl and argillaceous limestone. During the Late Jurassic, there was widespread epeirogenic uplift, but no igneous activity is known in Jordan. The persistent, slow, tectonic tilt, which elevated areas in South and East Jordan and depressed those in the north and west, was still active. The fluviatile, sandy sediments interdigitate with marine, sandy marl and limestone roughly along the site of the old Jurassic shoreline (Daniel, 1963, Bender, 1975).

388

Mid-Cretaceous Cycle In Arabia, the mid-Cretaceous began with widespread sheets of clastic sediments that resulted from the erosion of the Arabian Shield following the late Aptian uplift. Northwest of the Arabian Gulf, a deltaic system developed, covering southern Iraq and spreading into Kuwait, Saudi Arabia and Bahrain with the presumed delta front in Iran (Fig. 8.56). In the southern part of the region, a wide area of alluvial and lower-coastal-plain sediments give way eastward to littoral sands and a vast, shallow, shalecovered platform (Alsharhan and Nairn, 1988; Alsharhan, 1994). The sediments thin southeastward due to progressive onlap. Transgression in the late Albian rapidly ended the clastic depositional phase, and carbonate platform conditions were reestablished and persisted until the latest Cenomanian and early Turonian. Evidence of differentiation within the region is marked by the occurrence of a minor unconformity, a brief pulse of clastic sedimentation and the development of a large, intracratonic basin (Fig. 8.57). During the Cenomanian, the ramp model of carbonate sedimentation proposed for the Early Cretaceous remained valid. The depth of water had a profound effect, controlling the location and development of rudist assemblages on the platform (Fig. 8.58). The sedimentary phase lasted until the Turonian, as the carbonate and clastic realms waxed and waned across the area. Post-Turonian erosion removed part of the section not only over the regional paleohighs, but also along the Zagros Crush Zone (Murris, 1980). In Oman, shallow, open-marine, carbonate sedimentation, often within the wave base, continued through the Albian-Cenomanian. A basal, terrigenous, nearshore interval in central and northern Oman gave way up section to a series of shoaling-up, carbonate cycles but in southern Oman, (Dhofar) these sequences are interrupted by clastic influxes. The late Aptian rise in sea level, with the concomitant expansion of the carbonate platform in the northern part of the Middle East, was brought to an abrupt halt by the most pronounced regression since the Late Triassic. By the midAlbian, a clastic regime had spread over the Mesopotamian Basin, except for a small region in the northeast (Murris, 1980). However, to the northeast in Iraq and in southeastern Turkey, at the platform margin and in the deep-water basin, sedimentation was continuous with uninterrupted, pelagic sediments, without significant facies change, through the Albian. The neritic belt was slightly broader, compared to its Valanginian-Aptian predecessor, but still appears as the southeastern extension of the Mardin High (Buday, 1980). In southern Iraq during the Albian, clastic, deltaic sediments were deposited, and carbonate-shelf facies and a euxinic basin persisted in the north and northeast. In northern central Iraq, evaporite facies were deposited during the Cenomanian, with shelf carbonates deposited to the north and east. There was a further regression after Cenomanian

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

of man

Fig. 8.56. Paleogeography during the Early to Middle Albian in the Middle East (modified from Murris, 1980; Alsharhan and Nairn, 1988). Arabian Sea

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389

Sedimentary Basins and Petroleum Geology the Middle East

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Shallow Shelf Mixed Clastic '~ AlluvialPlain ~1 and Carbonates ~ Lower,Coastal Plain ~ Shelf Margin Buildup Shallow Shelf Clastic I~ Intrashelf Basin Fig. 8.58. Paleogeography during the Cenomanian in the Middle East (modified from Murris, 1980; Alsharhan and Naim, 1988). deposition, when the Zagros Basin entered the collision phase of its development. Structural units of large dimensions were uplifted, and erosion accompanied regression. The regression left the Rutbah-Khleissia High completely emergent during the mid-Albian. Coastal and alluvial sands and interbedded shale deposited on the flanks of the high and were charged from the Early Cretaceous euxinic shale in the northern basin or laterally from southwestern Iran. These are very important reservoirs in the northern Arabian Gulf. Following the mid-Albian regression, advancing seas submerged most of the Rutbah-Khleissia High (Wolfart, 1967). The Mardin High was completely submerged, and neritic and reefal carbonates occupied that entire region of Turkey (the Mardin Group). The late Aptian-early Cenomanian, dominated by dolomite with evaporite lenses, fossiliferous biosparite and biomicrite, was deposited in a tidal-fiat setting including supratidal and intertidal environments. The middle-late Cenomanian is characterized by relatively deeper-marine conditions and pelagic, foraminiferal-bearing biomicrite indicating slow sedimentation under anaerobic conditions. The Turonian is dominated by peloidal and fossiliferous packstone and grainstone of a shallow-shelf edge and lagoonal environment (Celikdemir et al., 1991). Over the entire area, which includes western Syria to Jordan, the fluvial sands and shale gave way to neritic chalks and carbonates, as a primarily carbonate regime became established. The carbon-

390

ates surrounded a reduced, and now isolated, Khleissia High and advanced up the flanks of the Rutbah High. The waxing and waning of this sea led to the alternation of carbonates and elastics in the Mesopotamian Basin. The intrashelf basins typically were filled with calcispherid marl and radiolarian lime mudstone, which form excellent source-rock beds in the deeper parts of the basin. Over the shallower-shelf areas, the foraminiferal-algal, wackestone and packstone, rudist packstone and grainstone were formed and now are reservoir horizons. The cause of these changes is considered to be the initiation of subduction in the Taurus-Zagros region of Turkey and Iran. Folding began during the late Albian and continued with increasing intensity during the Cenomanian and Early Turonian, gradually encroaching on the shelf margin and causing it to subside. Consequently, the sedimentation on the unstable shelf margin of eastern Iraq became more diversified with the rapid alternations of elastic and carbonate sediments. South from Turkey to Syria in the Sinjar-Palmyra and Euphrates-Anah troughs, thick, carbonate-marl sequences accumulated. Open-marine marl, intercalated with finegrained, organic carbonates m potential source rocks for the flanking, shelf-carbonate reservoirs - - formed in the troughs, while high-energy carbonates characterized the flanks. Trough subsidence was rapid and fault-controlled. The sediments subsequently were covered by the deposits of the transgressing Late Cretaceous sea. In Jordan, marine transgression came from the west and northwest during the Albian-Turonian with the deposition of limestone alternating with thinner beds of marl, beginning in western Jordan. In eastern Jordan, small tongues of fossiliferous, sandy limestone were laid down. Marine transgression gained slowly upon the land, finally reaching almost to the southern and eastern parts of the country in the Late Cenomanian (Daniel, 1963). Neritic limestone and marl were dominant in eastern Jordan. Toward the end of the Cenomanian, the sea shallowed, and some swells developed in eastern Jordan. Contemporaneously, submarine volcanicity in western Jordan occurred. The Turonian strata are of shallow-water facies dominated by lagoonal limestone with occasional gypsum, but sand and sandy marl increase toward the south and east of Jordan (Daniel, 1963).

Late Cretaceous Cycle Over the Arabian Platform, the Wasia-Aruma break was followed by a Coniacian transgression, which continued into the Early Campanian (Alsharhan and Nairn, 1990). In eastern Arabia, the Coniacian was characterized by a shallow, open-marine-shelf environment, in which the predominantly argillaceous sediments were deposited. The process continued during the Santonian, with the clastic contribution progressively diminishing as a bioclastic carbonate of shallow-marine environment became established. Within this area, local highs remained emergent,

The Late Mesozoic Part of the Zuni Cycle in the Middle East: The Cretaceous

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to reactivate structures such as the Rutbah-Khleissia and Mardin highs or arches, resulting in non-deposition and erosion during late Turonian and Coniacian time. The pulses of activity were repeated at shorter intervals than formerly and were more intense. Erosion removed some of the mid-Cretaceous sediments not only from the highs mentioned, but also from the Zagros Crush Zone, where slope erosion may have occurred along the continental margin fronting the encroaching ocean. It was at this time that the Rutbah-Khleissia High extended beyond Mosul in northern Iraq to form a uniform ridge trending roughly northwest-southeast and separating the western Mediterranean Tethys from the eastern Indo-Pacific Basin, which covered Saudi Arabia, Iraq and Iran. The common characteristic of the Late Cretaceous cycle was the progressive shifting of the sedimentary basin southeastward (toward eastern Arabia), with progressively younger transgressions in the same direction. The Maastrichtian ended on a rather quiet note, with some sedimentation in the Ras al Khaimah Trough (in the southern Arabian Gulf), but with a relatively short, non-depositional interval characterizing much of the rest of the region. Paralleling the rising orogenic front in Iraq, a NWSE-trending foredeep first received a Turonian-Coniacian fill of calcispherid, marly limestone through the Coniacian; however, during the later part of the Senonian until the late Campanian, these were replaced by a thick, fiysch sequence. Calcispherid marl also occupied the western part of the Mesopotamian Basin toward the RutbahKhleissia High, but was replaced in the center of the basin by globigerinal marl and marly limestone. The area west of the high was completely submerged, and the sequence over the high itself is represented by reefal-neritic limestone. The only part of the high still emergent lay in westernmost Iraq. In the troughs that cut through the high, the Euphrates-Anah and Palmyra-Sinjar early Senonian, calcispherid, shaly marl, shale and bituminous limestone (potential source rocks) accumulated, with phosphatic and cherty beds near the base of the succession. Through the remainder of the Senonian in the Syrian troughs, thick, globigerinal marl and marly limestone showing abrupt thickness variations characteristic of sediments deposited in fault-controlled basins are found. The basins remained active into the early Tertiary. Away from the troughs throughout eastern Syria, the deposits consist of neritic limestone with lagoonal, phosphatic and cherty beds near the base. In western Syria and Lebanon, neritic marl and marly limestone were laid down. To the north in southeastern Turkey, Senonian marl and reef carbonates onlapped onto the Mardin High from the south. In the northern part of the Middle East at the end of the Turonian-early Campanian, the stable-unstable shelf and the shelf margin were uplifted, initiating a major regression that resulted in the removal of much of the sediments that had accumulated earlier. The sedimentary wedge along the plate boundary, including the unstable part of the shelf, did not emerge, and sedimentation con391

Sedimentary Basins and Petroleum Geology the Middle East tinued, marked only by facies change. However, by the end of the Campanian and into the early Maastrichtian, widespread transgression occurred, profoundly affecting the paleogeographic history of the northern part of the Middle East. The subsiding foredeep received a thick, flysch sequence derived from the erosion of earlier-deposited, deep-water sediments in northern Iraq, now emplaced in nappes along the orogenic front. The nappes were thrust from the northeast to the southwest, where synorogenic sediments close to the nappe front consisted of boulder clays and conglomerates and olistostromal masses (Buday, 1980). At greater distances from the thrust front, a regular flysch succession of sandstone, shale and silts accumulated. During the late Campanian-Maastrichtian in northeastern Iraq, the foredeep trough was separated from the

392

intracratonic basins of the platform by a submerged ridge, as it had been during earlier Cretaceous time. One effect of the Maastrichtian transgression was the covering of the Rutbah-Khleissia High with a thin veneer of mostly phosphatic, sandy sediments, reworked in postMaastrichtian time. It also resulted in the thick accumulations of marly, neritic limestone in the Sinjar Trough, and the mixed, open-marine, marly and neritic limestone and lagoonal sediments of the Euphrates and Anah troughs. The most active subsidence of these troughs was close to the margin of the Rutbah-Khleissia High; subsidence of the Palmyra Trough was much less dramatic. The effect in southern Syria and all of Jordan was the deposition of phosphatic, neritic, shoal carbonates and of mixed, openmarine, marly and neritic limestone in northwestern Syria.

Chapter 9 THE LATEST PART OF THE ZUNI AND TEJAS CYCLES IN THE MIDDLE EAST: THE CENOZOIC

(Kermanshah) and Oman, which mark the early phase in the collision process that closed the Neotethys. There was, however, a widespread regression at the turn of the Mesozoic-Cenozoic, at which time much of the Middle East was emergent and exposed to erosion. Only in the basinal areas of the Arabian Basin (the Ras al Khaimah Sub-basin of the northern United Arab Emirates) and the Zagros Basin of Iran, where the sediments of the Paleogene Pabdeh Formation accumulated, does sedimentation appear to have been continuous. As there generally is little clastic material in the basal Paleocene beds, this MaastrichtianPaleocene break is presumed to be of short duration and not marked by major uplift and erosion, although it can be shown that the uppermost Maastrichtian and the Danian are missing in southern Iraq. Early during the Paleogene, transgression reestablished extensive marine conditions over most of the northern part of the Arabian Shelf, persisting until the late Eocene. In the Ras al Khaimah Sub-basin, the thick Paleogene flysch sequence (Pabdeh Formation) is the continuation of sedimentation in the old Cretaceous foredeep extending from Oman into the onshore and offshore of the northern part of the United Arab Emirates (U.A.E.) and into the Fars Province of southeastern Iran. As a result of this transgression, only those parts of the Middle East such as western Saudi Arabia, Syria, parts of Iraq (including the Ga'ara Arch) and, in extreme eastem Arabia, areas as the Huqf Arch, the Semail (Ophiolite) Nappe and Hawasina sediments of Oman remained exposed (Fig. 9.4). The Zagros Trough shallowed as the depocenter migrated southwestwards, and that part of the trough northwest of the Fars Platform developed into a broad basin. A widespread transgression occurred between the Paleocene and lower Eocene, and the distinction between the Zagros Basin and Ras al Khaimah Sub-basin gradually diminished during the course of the Eocene. A single broad, but shallow, basin extended southwest of the Ras al Khaimah Sub-basin, in which shallow, open-shelf carbonates accumulated, as reflected in the deposition of the limestone, dolomite, marl and evaporites referred in Arabia to the Hasa Group. More restricted conditions developed as the sea level fell during the Oligocene, culminating in a late Paleogene hiatus, during which all the Oligocene and late Eocene beds were removed by erosion from over much of Arabia. This break is found nearly everywhere, and sediments appear to be continuous only in coastal Iran, the northern U.A.E., parts of northern Iraq and in some isolated areas in southern Oman and Yemen.

INTRODUCTION The varied tectonic events of the Cenozoic exerted a profound control over the paleogeography and, hence, the stratigraphic history of the Cenozoic. Even if the rate at which the events occurred is not greatly accelerated with respect to the preceding Mesozoic events, there nevertheless appears to be greater diversity in those events than was apparent during earlier epochs. In the eastern and northeastem parts of the Middle East, the Neotethys closed, while the Gulf of Aden and the Red Sea opened to their rear in the south, southwest and west. Associated with this opening, the Gulf of Aqaba-Dead Sea and Gulf of Suez Shear and Rift System developed. The location of these tectonic events defines the current boundaries of the region (Fig. 9.1). A parallel may be drawn between these events and the split, as a result of which the Neotethys was born. As a consequence of major tectonic events, it is possible to distinguish several provinces: the relicts of the Arabian carbonate platform, the flysch foredeep trough west of the Zagros extending all the way from Turkey to Oman, and the newer rift troughs of the Gulf of Aden and the Red Sea. The Cenozoic sediments reached a thickness of more than 5,000 m (16,400 ft) in the fold belt of southwestern Iran and thin westwards to the zero line in central Saudi Arabia (Figs. 9.2 and 9.3). In the Red Sea Basin, the sediment thickness ranges from 915 m (3,000 ft) to 4,575 m (15,000 ft) (Fig. 9.2). The differentiation of a molasse trough in the Paleogene extending from southern Iraq through Kuwait and northeastern Saudi Arabia to the coastal Fars Province of Iran was associated with the closure of the Neo-tethys and the rise of the Zagros Mountains. Sediments derived from the erosion of the newly formed mountains poured into this trough during the late Neogene. In southwestern Arabia, there were extensive outpourings of lavas and the development of granitic intrusions linked with the developing split between the Nubian Shield and Arabia. In the northern part of the region, south of the Taurus Suture Zone, the fracturing of the northern part of the Arabian Plate accompanied the development of the tensional Sinjar and Euphrates grabens in Iraq and Syria. An important second-order control on the sedimentation patterns was the development or reactivation of arches such as the Hadhramout and the Qatar-South Fars arches (Fig. 9.4). The initiation of these developments dates back to the Late Cretaceous and is essentially synchronous with the emplacement of the ophiolite bodies, such as those of Iran 393

Sedimentary Basins and Petroleum Geology the Middle East 5'0"

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The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

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Fig. 9.4. Approximate location of the Zagros Basin and Ras al Khaimah~ub al Khali sub-basins. It began as early as the late Eocene in places from southern Iraq to Abu Dhabi, and lasted through the Oligocene and locally even into the early Miocene until the Neogene marine conditions became fully established. During this time, the carbonate shelf retreated towards the Indian Ocean, and the Ras al Khaimah Foredeep was reduced to a shallow remnant in which shoal carbonates formed. Concurrently, the Zagros Trough also shallowed, and the depocenter migrated southwestwards, but was separated from the Ras al Khaimah Trough by the Fars Platform, which was covered by shallow-water limestone and supratidal

evaporites. In eastern Arabia, southern and southwestern Iraq and parts of the Arabian Gulf, uplift and erosion seem to have removed most of the latest Middle Eocene, Late Eocene and Oligocene. The late Paleogene hiatus over the Arabian Platform corresponds to a period of active extensional tectonics in the Gulf of Aden-Red Sea area. In the Gulf of Aden, extension resulted in the formation of WNW-ESE depressions or synrift basins separated by NE-SW-oriented ridges (Fig. 9.5a). The ridges mark the projection into the continent of oceanic fracture zones and correspond to transfer zones present in the continental margin. The depressions are located over the projections into the continent of oceanic ridges and correspond to the Oligo-Miocene synrift basins dated by the synrift sediments that established a Rupelian-Chattian, Oligocene age (about 27 Ma) (Fantozzi, 1995). It should be noted that the synrift basins, therefore, were accumulating sediments 10-11 m.y. before the appearance of oceanic crust in the gulf (anomaly 5). The restoration of the two sides of the Gulf of Aden demonstrates an asymmetry in the central part of the gulf. Whereas east of Boosaaso, the Mesozoic and Tertiary sediments are roughly equally distributed (Fig. 9.5b), there is an asymmetry to the west. Paleozoic and pre-Paleozoic rocks crop out in Somalia; in Yemen, the synrift sequences crop out extensively along the coast, and inland Paleocene and Cretaceous deposits are exposed as a result of E-W faulting. This asymmetry is consistent with the Wernicke model, with the development of a low-angle detachment surface leading to the exposure of structurally deeper horizons on the lower plate and moderately rotated half grabens and intense vulcanicity on the upper plate. An analogous model for the Red Sea was presented by Voggenreiter et al. (1988), and for the Red Sea-Gulf of Aden by Bohannon (1989). The onset and duration of the extensive OligoceneMiocene volcanics of Yemen and Ethiopia are dated in the same time range (18-20 Ma; Davison et al., 1994) as the tensional depressions in the Gulf of Aden. The lavas of the youngest, fault-rotated Yemen Volcanic Group, dated at 18 Ma, are unconformably overlain by flat-lying Miocene sedimentary rocks and younger lavas (10 m.y.). Although Red Sea rifting began in the Late Oligocene with extension, the main period of Red Sea extension, between 18 and 10 Ma, is estimated at 4.5 mrn/yr, with an extension factor of 1.7. However, the oceanic crust in the central Red Sea Rift is only 5-6 Ma old and, thus, is younger than the oceanic crust in the Gulf of Aden. Surface uplift was contemporaneous with the main extension. The advance of the Neogene sea was far less extensive than that of the preceding Paleogene. Consequently, Neogene rocks form a less extensive, relatively narrow and poorly exposed band of outcrops midway between the Paleogene outcrops and the shores of the present Arabian Gulf, one further step in the gradual restriction of marine conditions to more closely approximate the present Arabian Gulf. The lithostratigraphic correlation of the Middle

395

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PART 1: THE P A L E o G E N E OF THE MIDDLE EAST As a result of the widespread regression at the end of

396

the Cretaceous, virtually all of the Arabian Peninsula became emergent, except for the relatively restricted basinal areas in the northern U.A.E., where the Pabdeh Formation was deposited. There is little clastic material in the basal Paleocene beds of eastern Saudi Arabia; consequently, the Tertiary-Cretaceous boundary often is lithologically indistinct. The Maastrichtian-Danian hiatus is presumed to be of short duration, although, as indicated above, there is evidence that part of the Maastrichtian and Danian are missing. Thus, early during the course of the Paleocene, a major transgression reestablished widespread marine conditions that covered eastern Arabia and the entire northern part of the Arabian shelf, extending over

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

Table 9.1. Cenozoic rock units of the Middle East. Asterisks indicate outcrop, and bullets indicate subsurface.

397

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Table 9.1 continued.

398

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Table 9.1 continued.

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407

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Fig. 9.8. Lithostratigraphic correlation chart of the Cenozoic formations in Iran (modified from James and Wynd, 1965) and Southeast Turkey. the Taurus-Zagros Trough (Buday, 1980). These conditions prevailed until the early to middle Eocene. The Early Tertiary was a period of tectonic calm following the completion of deformation in the Oman Mountains and mild folding in the Zagros Foothills Belt. The paleogeography varied but little once marine conditions were reestablished. A stable landmass to the west, the Arabian Shield, was bordered by an extensive, shallow carbonate shelf that deepened towards the two eastern troughs adjacent to the tectonically active areas in Iran and Oman. These two principal troughs, the Zagros Trough and the Ras al Khaimah Sub-basin (previously known as the Pabdeh Foredeep Trough), were continuations of the older Cretaceous troughs and were separated by the shallowwater Fars Platform. The latter basin, the Ras al Khaimah Sub-basin, is known only in the subsurface, and it probably was separated from the Rub al Khali Sub-basin further to the west by a ridge joining the stable area around the Mender-Lekhwair Paleohigh to the stable area of offshore UAE (Alsharhan and Nairn, 1995) (Fig. 9.4). The Ras al Khaimah Sub-basin margin to the southeast is formed by the Oman Mountains, while the Zagros Basin extended to the northwest into the Taurus Trough. The only part of the Arabian Shield to be submerged lay in central Yemen, where a narrow sea formed, if the Paleocene to lower Eocene limestone found in the Gulf of Aden and the Red Sea regions is excluded. The clastics deposited in these seas suggest that the deposits were derived from a tropical landmass undergoing lateritic weathering. These climatic conditions are consistent with the evaporitic conditions during the Ypresian in the eastern shelf area of Arabia. The folding and uplift of central Iran during the lower Tertiary, which preceded the main orogenic phase of the late Tertiary, displaced the axis of sedimentation in the Zagros Trough to the southwest. In this southwesterly direction, the sequence thins as water depth decreased. The sediments that accumulated consist of basinal shale, marl and argillaceous limestone. However, towards the northeastern margin of the Zagros Trough in Lurestan, thick, flysch-like accumulations replace these deposits and reflect the rapid erosion of the uplifted Late Cretaceous

408

radiolarites originally deposited in the deep trough marginal to the mountains in the northern part of Iraq (Fig. 9.4). The fiysch sediments are succeeded by red molassic sediments that coarsen upwards (James and Wynd, 1965). This deep basin was separated from the main Zagros Basin to the southeast by a local northwest-southeast high (the Fars Platform), over which lagoonal and reefal limestone accumulated. The Paleocene deposits in the Ras al Khaimah Sub-basin are lithologically similar to those in the Zagros Trough. Shallow seas in the northeast lay over the Rutbah-Khleissia Ridge in southern Syria and northeastern Jordan, as well as over the Fars Platform between the Zagros Basin and the Ras al Khaimah Sub-basin and the southwestern margin of the troughs in the latter two areas. As indicated by the outline of the stratigraphy of the Paleogene given above, the geological and sedimentological history of the Middle East can be described most easily by traverses from the Central Arabian Platform into the Zagros and Ras al Khaimah basinal area, which will illustrate the change from shallow-water platform deposition in the southwest (Hasa Group) to deeper-water sedimentation in the flysch basins to the northeast (Pabdeh Formation). From southern Iraq to the U.A.E., the Paleogene platform deposits are represented by three formations m the Umm Er Radhuma, Rus and D a m m a m - which together make up the Hasa Group (Powers et al., 1966; Bellen et al., 1959), while the Jahrum and its time equivalent, the Pabdeh Formation, developed in the Zagros Basin in the Fars Province of Iran (Fig. 9.8) (Setudehnia, 1972) and the Ras al Khaimah Sub-basin of the United Arab Emirates.

The Paleogene of the Central, Eastern and Northeastern Arabian Platform A variable thickness of Paleocene-Eocene rocks crops out over much of western Iraq and central Saudi Arabia; the maximum recorded in the western part of the basin is about 330 m (1,082 ft), but more than double that thickness has been drilled in the deeper, more easterly part of

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic thick sequence of neritic and nummulitic limestone and evaporites in the shallow-water areas and thicker, calcareous flysch in the deeper water where the older Cretaceous foredeep basin continued to subside. In the extreme eastern part of Abu Dhabi near Dubai, reefs rim the Ras al Khaimah Trough, which had almost disappeared as a distinctive feature by the end of the Eocene, for the upper two-thirds of the succession merge with the bordering shelf sediments.

the basin in South Iraq. In the onshore of Abu Dhabi (in well Minedis-1, close to the mountains), more than 1,220 m (4,000 ft) of turbiditic and conglomeratic sediments have been drilled. Over southern Iraq, Kuwait, Saudi Arabia, Qatar and the southwestern U.A.E., the shallow-water, Paleogene platform deposits generally are assigned to three formations: the Umm Er Radhuma, Rus and Dammam (Powers et al., 1966). Originally termed the "Bahrain Series" by Pilgrim (1908) based on the occurrence of Paleocene to Eocene rocks in Bahrain, it subsequently was renamed the Hasa Group (or Series) by Sander (1951, cited in Powers, 1968) from the rocks that crop out in eastern Saudi Arabia. This division of the series, subsequently raised to group status by Owen and Nasr (1958), was described in detail by Powers (1968) and Tleel (1973) from type sections in the Hasa Province in eastern Saudi Arabia. The formational names have been applied to rocks of similar lithology from southern Iraq to UAE. The platform and peri-reefal carbonates of the Asmari Formation (Oligocene-Early Miocene) are similar to those of southwestern Iran. The Fars Group of the U.A.E. and Qatar consists mainly of marginal to non-marine coarse clastics and associated evaporites similar to those of Iran and Iraq (Jones and Racey, 1994). The undifferentiated Oligo-Miocene clastics of Qatar and the U.A.E. presumably correlate partly with the Asmari and partly with the Fars, linking the Paleogene and Neogene. In contrast to the younger Neogene sediments mostly buried under recent deposits, the Paleogene sediments crop out over wide areas of eastern Arabia (Fig. 9.9) as a

Paleogene of Saudi Arabia

Hasa Group (Paleocene.Middle Eocene) In central, northern and eastern Saudi Arabia, the Paleogene sequence shows a characteristic, shallow-platform lithology bordering the continental margin further to the west. The successions in Qatar and Bahrain have some similarities not obscured by differences in local nomenclature. From Saudi Arabia to Bahrain, Qatar and the western U.A.E., the Paleogene is calcareous, with typical shallowwater lithologies. Lithologic changes are hard to identify, but passing through Kuwait and southeastern Iraq, the edge of the platform is approached, with thickness increases implying greater subsidence. On the slope into the basin, an increase in the clastic component from silty to sandy seems to imply a source of clastics generally to the northeast, from the direction of the Zagros Mountains. Umm Er Radhuma Formation (Paleocene-early Eocene). The name of the lowest Paleocene formation dates back to Henry and Brown (1935, cited in Powers et

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The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic al., 1966) and was taken from the Umm Er Radhuma water wells (28~ N, 44~ E) in eastern Saudi Arabia. It was applied initially by Steineke and Hoover (1936, cited in Steineke et al., 1958) to about 243.1 m (798 ft) of platform carbonates containing fossiliferous lime mudstone, wackestone/packstone, dolomitic limestone and dolomites from a type section in Wadi al Batin. Two subdivisions of the formation were recognized by Powers et al. (1966) at outcrop. The lower division is about 102.7 m (337 ft) of partially dolomitized and commonly fossiliferous, microporous (chalky), aphanitic limestone in which there may be rare siliceous horizons and rare foraminifera, gastropods and pelecypods. The upper division, of 140.4 m (460 ft) of interbedded, partly dolomitized and alternately microporous (chalky) and silicified, pelletiferous wackestone/packstone, has a similar fauna to the lower part. Based on faunas identified by Powers et al. (1966), Elkhayal (1974), Hasson (1985) and Jones and Racey (1994), the age range represented is Paleocene to Early Eocene, but the Early Paleocene appears absent or condensed in some areas. In subsurface, the Umm Er Radhuma Formation is strongly dolomitized and has a fauna suggesting a shallow-marine setting. It was subdivided by Hasson (1985) based on planktonic foraminifera zonation (Fig. 9.10). The formation rests disconformably over the Late Cretaceous Aruma Formation, but the contact with the Rus Formation is conformable. Rus Formation (Early Eocene). The formation takes its name from a small hill, Umm Er Ru'us, on the eastern flank of the Dammam Dome in eastern Saudi Arabia (26019 ' N, 5008 ' E). The term was first used by Bramkamp (1946, cited in Powers et al., 1966) to replace the older descriptive term "Chalky Zone" earlier applied to Lower Eocene beds. Its formal use was proposed by Thralls and Hasson (1956). A detailed description of the type section appeared two years later in Steineke et al. (1958), with Sander (1962) providing some paleontological data. The formation lacks age-diagnostic foraminifera, and the assigned age is based on regional evidence (Jones and Racey, 1994). The formation basically consists of microporous (chalky) limestone with irregular masses of crystalline gypsum, geoidal quartz, finely crystalline anhydrite and minor amounts of dolomitic limestone and shale. In eastern Saudi Arabia, Tleel (1973) redefined the Rus Formation, dividing it into three informal units (Fig. 9.11). The lower unit ranges from 20 to 23 m (66-75 ft) of fine- to coarse-grained, white, chalky (microporous), aphanitic, dolomitic limestone, and limestone with bands of gypsiferous shale at the top. The middle unit, about 10 m (33 ft) thick, consists of calcite geodes and, less commonly, wafer-like mud balls in grayish, microcrystalline, massive limestone. The upper unit consists of about 21 m (69 ft) of quartz geodes and chert nodules probably formed by ground-water percolation after the formation of the Dammam Dome. Tleel (1973) interpreted the depositional environment as restricted lagoonal to supratidal sabkha with occasional marine incursions. The contact

with the shale of the Dammam Formation is conformable. Dammam Formation (Middle Eocene). The formation is named after the Dammam Dome in eastern Saudi Arabia. The type section was designated by Bramkamp along the old Dhahran-A1 Alah Road at 26~ N and 5004'50" E (Powers et al., 1966). The description was published in Steineke et al. (1958) from the Rim Rock of the Dammam Dome, 7.2 km north and 85 km west of Jebel Umm Er Rus, where about 28 m (92 ft) of light-colored i

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Sedimentary Basins and Petroleum Geology the Middle East limestone, marl and shale are exposed. The succession comprises platform carbonates with subordinate, fine clastics and locally pelagic carbonates. Powers et al. (1966) recognized the following five members described below (from younger to older) (Table 9.2 and Fig. 9.11). The Alat Member consists of about 9.6-15 m (31-49 ft) of chalky (microporous), dolomitic limestone underlain by light-colored, dolomitic marl with a Dictyoconus sp. fauna. The Khobar Member is dominated by 9.5 m (31 ft) of dolomitic marl passing up into partly recrystallized, nonporous, nummulitic limestone followed by marly limestone and capped by more nummulitic limestone with abundant Nummulitic somaliensis. The Alveolina Limestone Member consists of about 0.9-2 m (3-6.5 ft) of pale-orange to yellow-gray, microcrystalline, partially recrystallized, dolomitized or silicifled limestone. Alveolina elliptica, var.floscula and Lunica pharoins are common foraminifera. The Saila Shale Member ranges from 2 to 4 m (6.5-13 It) of dark-brown to yellowish, sub-fissile clay and shale underlain by impure, fossiliferous, calcarenitic limestone. An abundant fauna includes Alveolina sp. A. decipiens, N. globulus, Coskinolina batlasiliei and Dictyoconus sp. The Midra Shale Member, formerly the Shark Tooth Shale, the basal member of which consists mainly of 3 m (10 It) of yellow-brown, fissile, thinly laminated shale with minor gray marl and limestone. The presence of Ostrea turkestanensis in beds of this age in Bahrain is reported by Cox (1936) and from eastern Saudi Arabia by Tleel (1973) The Midra and Saila members were deposited in a more turbid, open-marine environment in which homogenous mud was deposited; however, during deposition of the Alveolina, Khobar and Alat members, the water depth was shallow (14-20 m, or 46-66 ft), and the energy was low to moderate (Tleel, 1973). The contact with the overlying Lower Miocene (Hadrukh Formation) is unconformable and marked by the change from the clean limestone of the Dammam Formation to the sandy limestone of the Hadrukh Formation.

Paleogene of Qatar

ttasa Group (Paleocene-Middle Eocene) Umm Er Radhuma Formation (Paleocene-Early Eocene). The formation, which forms the lower part of the Bahrain Series, initially was called the Busaiyir Formation by Sugden (1953, cited in Sugden and Standring, 1975), then renamed Umm Er Radhuma (Henson, 1940, cited in Cavelier, 1970; ). The formation is found only in deep wells in thicknesses generally ranging from 270 to 370 m (886-1,214 ft) of limestone, dolomitic limestone, locally porous and vugular, with minor gypsum and anhydrite, and basal, pyritic, blue marl intercalations (Fig. 9.6). These sediments were laid down in a shallow, dominantly quiet, warm-water marine environment with markedly

412

reduced detrital influx, which may be attributed to predominantly low relief in the source area or the prevalence of arid climatic conditions (Abu-Zeid, 1991). Rus Formation (Early Eocene). The use of the term "Rus" for beds that constitute the main part of the informal Lower Limestone Group of Williamson and Pomerol (1938, cited in Cavelier, 1970) was formalized by Sugden and Standring (1975). Abu-Zeid and Boukhary (1984) recognized two distinct units in the Rus of western Qatar (Jebel Dukhan), an older, A Member, 19 m (62 ft) thick, and a younger 12.5 m (41 ft). In a recent study by Boukhary and Alsharhan (in prepn) of surface and subsurface data three new members were established from base to top : 1. Abu Samra Member; grey, dolomitic, occasionally slightly argillaceous limestone with quartz grains and some gypsum interbeds with a thickness at the type locality (western Qatar, water well P29) of about 40m (130 ft). It probably rests unconformably on the Umm er Radhuma and is conformably overlain by the chalky Sulaimi Member. It is assigned to the LateYpresian 2. Sulaimi Member.; a white, beige, dolomitic, chalky limestone with some fragmentary chalcedony in the middle and lower beds with molluscs, mainly Cardium, Corbula and Cerithidae, found in the type Suaimi well in northern Qatar. It is conformable with beds above and below and is dated as Late Ypresian. 3. Doha Member. A greyish yellow to light brown, dolomitic and marly with various foraminifera Lituolidae, Verneuilinidae and Eggerellidae and molluscs. The type locality is in westernn Qatar at Fhailhil (Jabal Dokhan). The base is conformable but it has an unconformable relationship with the overlying Dammam Formation members. The thickness at the type locality is 8.5 m (28 ft) and the assigned age Late Ypresian. A1-Hajari and Kendall (1992) recognized three lithofacies units in subsurface based upon lithology, sedimentary structures and well logs. Their lithological units are described below" The Dolomitic Unit is gray to buff, compact, crystalline, dolomitic limestone and white, chalky, porous limestone in the lower part. The sediment accumulated in a shallow sea in which there is evidence of a transition zone between an open-marine and protected setting where interbedded evaporites accumulated. The Evaporite Unit consists of abundant evaporites (locally gypsum) and gray marl interbedded with limestone and greenish clay, with some geodal quartz nodules present at several levels. These sediments were deposited in a typical sabkha to lagoonal transition. The Chalky Limestone Unit consists of light-colored, soft, porous, chalky limestone intercalated with thin layers of marl and calcareous claystone and fossiliferous, laminated limestone beds at the top. These sediments suggest a gradual change from a more restricted and isolated environment to one with an open-marine influence. Dammam Formation (Middle Eocene). The forma-

Table 9.2. Lithostratigraphic correlation of the Eocene formations of the Arabian Gulf. --

AGE

FORMATION i

MIOCENE

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EASTERN SAUDI ARABIA (Powers et al. 1966; Tleel 1973) Dam Formation Hadrukh Formation

BAHRAIN (Doornkamp et al. 1980) Jabai Cap Formation

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Sedimentary Basins and Petroleum Geology the Middle East tion ranges in thickness from 30 to 50 m (98-164 ft) and was deposited in a shallow-marine, subtidal setting. The subdivision of the Dammam Formation differs in part from the formation in Saudi Arabia (Table 9.2). Cavelier (1970) recognized upper and lower subdivisions, each further subdivided into members, not all of which are recorded in Saudi Arabia, and subsequently revised by Abu-Zeid (1991) (Table 9.2). The lower division has two subdivisions, or members. The lowest member is the Midra (Saila) Member of shale, shaly and marly clay and limestone with lenticular, phosphatic nodules. The difference is that the basal limestone in Qatar is separated as a member, whereas it is included in the Midra Member in Saudi Arabia. However, the uppermost member of the Lower Dammare (Dukhan Alveolina Limestone) appears to equate to the Alveolina Bed of Saudi Arabia (and the Middle Eocene Alveolina Limestone of Smout, 1954) and consists of massive limestone and dolomite. The upper division has two subdivisions. The lower, known as the Umm Bab Dolomite and Limestone Member, was formerly the Simsima Chalk Member of Stevenson (1959, in Cavelier, 1970) and was equivalent to the Khobar Member. It consists of crystalline and dolomitic limestone with local intercalations of chert. The Alat Member is equivalent to the Abarug Dolomitic Limestone and Marl Member (the Abarug beds, Abarug limestone and Abarug chalk of Williamson and Pomeyrol, 1938, cited in Cavelier, 1970). It consists of clayey, dolomitic, chalky marl followed upward by bioclastic-detrital limestone that is slightly dolomitized. The Midra Shale Member accumulated in a fairly shallow-marine environment and marked the peak of a period of less arid climatic conditions. The limestone of the Dukhan-Umm Bab and Abaruq members was deposited in a quiet, partly protected basin under more arid climatic conditions. The lower contact of the Dammam with the Rus is conformable, but the contact with the overlying Dam Formation (Mio-Pliocene) is unconformable.

Paleogene of Bahrain

Hasa Group (Paleocene-Middle Eocene) Umm Er Radhuma Formation (Paleocene-Early Eocene). In the lower part of the succession, the proportion of shale is higher than in Qatar. The upper part of the formation consists of limestone and calcareous dolomites, which tend to be vuggy and porous. The formation is rich in foraminifera such as Smoutella arabica, Sakesaria cotteri, Nummulites lahirii, N. fraasi, Lockhartia concliti, L. aiversa and L. haimei. Although thinner, it is otherwise lithologically little different from Qatar and is believed to have been deposited in an intertidal to subtidal setting. The lower contact is disconformable with the Aruma Formation, but the upper contact is conformable with the Rus. Rus Formation (Early Eocene). Of the seven "formations" recognized by Doornkamp et al. (1980), two, the

414

Awali and Hafirah, are regarded as members of the Rus Formation; the others are referred to the Dammam Formation. These represent two subtidal cycles, each marked by a deepening of water followed by a regressive rhythm of carbonate accumulation for a total thickness of 103 m (317 ft). The beds accumulated in water depths of-3 to -32 m, but with some indications of intertidal and occasionally of supratidal conditions. Environmental interpretation of the Awali and Hafirah carbonate members are given in Fig. 9.12 from Doornkamp et al. (1980). The most distintive fabrics are the bivalve-bored hardgrounds, the low-diversity shell banks and callianassoid shrimp burrows. Dammam Formation (Middle Eocene). This formation consists of five carbonate lithofacies associations, all formed in water depths of a few meters, the details of which are illustrated in Figs. 9.12 and 9.13 and are briefly described below (from Doornkamp et al., 1980) in descending order. Jabal Hisai Member. The carbonate seen in a restricted outcrop consists of about 6 m (20 ft) of a white or grey, slightly quartzose dolosiltite formed in water with good open circulation. It contains a grass-bed assemblage rich in epi- and in-faunal elements, including current sensitive echinoderms and acroporid corals. West Rifa Flint Member. This member is an assemblage distinguishable from the underlying A1 Buhayr carbonate by the presence of layers of brown or black chert parallel to the bedding. It has a thickness of about 7 m (23 ft) and rests unconformably upon the A1 Buhayr or upon the Foraminiferal Carbonate, an indication of erosion of the older beds above the crest of the Dukhan Dome. Al Buhayr Carbonate Member. The unit consists of six regressive cycles laid down in water depths never exceeding 7m (23ft) and generally about half of that depth. The facies is highlighted by the development of crustacean burrows, some of which show evidence of considerable reworking. The member has a thickness of about 15 m (49 ft) of laminated, yellow-orange, argillaceous dolosiltite with gypsiferous layers. It rests upon a hardground, dessication-cracked surface of the Foraminiferal Carbonate. Foraminiferal Carbonate Member. This member ranges in thickness from 5 to 8.5 m (16.5-28 ft) of dolosiltite separated by impersistent bands of softer, shaly, friable dolostone. It was deposited in waters more than 2 m deep of normal or near normal salinity. The base rests upon oyster beds, algal-baffled mounds and well-winnowed, bioclastic sand hollows. The foraminiferal assemblage variety has been reduced by dolomitization. Dil 'Rifah Carbonate Member. The member is a sequence of eight cycles succeeding the Hafirah Member formed at water depths ranging from supratidal to 2 m (6.6 ft) deep. Of variable thickness, it may exceed 20 m (66 ft) of dolosiltites and attapulgite-rich shale or clay.

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

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Further to the north in the Arabian Gulf, the formation thickens, reaching as much as 400-650 m (1,400-2,130 ft) in southern and central Kuwait, but thinning to half that amount further to the north. Lithologically, the section is more anhydritic, but it does not differ greatly from that described in Qatar. The limestone tends to be dolomitic and anhydritic, particularly in the middle of the sequence,

and contains relatively few fossiliferous horizons. In the southwestern part of the state, the intrusion of sand with lignitic debris implies proximity to an emergent area (Owen and Nasr, 1958; Omar et al., 1981). In extreme southern Kuwait toward Saudi Arabia, the formation is made up of an upper and lower dolomite and calcarenitic limestone section separated by an alternating anhydrite and anhydritic limestone. Bou Rabee and Burke (1987) divided the formation into three members (Fig. 9.14) as follows (in ascending order):

415

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Fig. 9.13 Sedimentological and environmental interpretation of the Middle Eocene (Foraminiferal Carbonate, A1 Buhayr Carbonate and West Rifai Flint members of the Dammam Formation) in Bahrain (modified after Doornkamp et al., 1980). See Fig. 9.31 for the legend. The Arhayia Member, about 220 m (722 ft) thick, is dominated by dolomitized limestone with a considerable amount of intercalated anhydrite deposited in a shallowmarine, intertidal environment. The Jalib Member, about 31 m (101 ft) thick, is a sequence of alternating anhydrite and limestone formed in a shallow-marine, supratidal setting. The Wafra Member, about 169m (555 ft) thick, consists of calcarenitic and dolomitized limestone. Anhydrite is present as thin, nodular beds intimately mixed with limestone and marly horizons, which may form up to 10%

416

of the sequence. These sediments were deposited in a shallow-marine, supratidal to subtidal setting. Rus Formation (Early Eocene). In contrast to the preceding areas (Saudi Arabia, Bahrain and Qatar), the Rus Formation is a prominent subsurface unit in Kuwait, where it consists of alternating massive, hard, dense anhydrite and unfossiliferous limestone with a few shale and marl beds (Owen and Nasr, 1958) deposited in a shallowmarine environment (Fig. 9.14). From a thickness of 80 m (250 ft) in the central area, it expands to 150 m (450 ft) in the northern area and to 200 m (650 ft) in the offshore and

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

GENERAL DESCRIPTION

tnd minor ~ L i m e s t o n e , dolomitized ~bands towards the ~top and shelly at base. ~Shallow marine setting. ;x~xx~xt AAAAAAA| Anhydrite with ....... ~limestone intercalation

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evaporite towards

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Fig. 9.14. Lithostratigraphy and depositional setting of the Paleocene-Eocene (Hasa Group) in Kuwait (modified from BouRabee and Burke, 1987). southwestern regions. As in the case of the Radhuma Formation in southwestern Kuwait, the facies again changes and indicates an approach to nearshore, supratidal conditions (Omar et al., 1981) composed mainly of limestone that is soft, chalky, marly and gypsiferous with minor sand and anhydrite. Dammam Formation (middle Eocene). The beds of the Dammam Formation are the oldest rocks seen at the surface (13 m, or 43 ft, exposed in the A1Ahmadi quarry). The following three lithological units are recognized by Omar et al. (1981) in subsurface (see also Table 9.2): Unit 3 is a shelly, microporous (chalky) limestone with hard, siliceous limestone at the top. Unit 2 is a siliceous limestone with sand beds at the base and microporous (chalky), shelly, thin, siliceous limestone at the top. Unit 1 has a persistent, gray-green, waxy shale at the base, which may contain scattered dolomitic rhombs, some pyrite, shark teeth and phosphate nodules, grading up into green shale and dense, dolomitic limestone; nummulitic, dolomitic limestone; and thin, anhydrite beds. The thickness of the formation ranges from about 122 m (400 It) in southwestern Kuwait to as much as 305 m (1,000 It) in the offshore in BuNyan Island. The nummulitic limestone is readily recognizable over much of the area and carries a suite of large Middle Eocene (Lutetian) foraminifera: Lockhartia hunti var. pustolosas and Dictyoconoides kohaticus. The formation was deposited in a shallow-marine environment with the

marine-continental boundary between units 2 and 1. The Dammam Formation, which underlies all of Kuwait, overlies the Rus Formation, upon which it rests with a possible minor disconformity.

Paleogene of Southern and Western Iraq Hasa Group (Paleocene-Upper Eocene)

Umm Er Radhuma Formation (Paleocene-Lower Eocene). In the southern Iraq oil fields, the Umm Er Radhuma is described as up to 500 m (1,640 ft) of anhydritic and dolomitic limestone, with chert in the upper part of the formation (Fig. 9.7). Buday (1980) regarded the formation as forming in a general shallow-marine environment periodically influenced by lagoonal conditions. Towards the north and northeast, the carbonates show a progressive transition to the basinal globigcrinal beds of the Aaliji Formation. The base of the Umm Er Radhuma Formation is unconformable, but the top is conformable where the Rus Formation is developed. In western Iraq, west of the Rutbah High, the Umm Er Radhuma Formation is between 50 and 120 m (164-394 ft) thick, but it wedges out on the southern and southwestern slopes of the Rutbah uplift. It shows marked lithofacies changes, both in the type and distribution of lithofacies, as the limestone becomes phosphatic and incorporates marly intcrbcds and cherty horizons. A conglomeratic and/or sandy and oolitic phosphoritc unit is prominent in the lower part of the succession (Bcllcn ct al., 1959; A1 Naqib, 1967). The phosphatic facies formed in a more shallow, ncarshorc, partly lagoonal setting. The faunal evidence confirms that the phosphatic limestone facies is Palcoccne in age (Ctyroky and Karim, 1971; A1 Hashimi, 1973), but the presence of Lower Eocene horizons cannot be excluded. The lower contact of the phosphatic facies of the Umm Er Radhuma Formation is transgressive and unconformable. The upper contact is erosional and may be transgressively overlapped by the Dammam Formation where the Rus Formation is missing. Rus Formation (Early Eocene). The formation is found in wells drilled in southern Iraq (Owen and Nasr, 1958" Bellen et al., 1959), where it sometimes is difficult to distinguish the Rus Formation from the beds of the Umm Er Radhuma Formation (Fig. 9.7). The formation reaches a thickness of up to 100 m (328 fi) and is predominantly anhydritic, with some unfossiliferous limestone, blue shale and marl. It is assigned to the Early Eocene based on stratigraphic position and generally can be successfully correlated over the entire South Iraq-KuwaitSaudi Arabian region. It was formed in a lagoonal, evaporitic environment in local basins. Where seen, the base is conformable, but the upper contact is unconformable where overlain by freshwater chalk and shaly limestone beds at the base of the Dammam Formation.

Dammam Formation (middle-upper Eocene). A reference type section was described by Owen and Nasr

417

Sedimentary Basins and Petroleum Geology the Middle East (1958) in the Zubair Field for southern Iraq. There, the Dammam Formation, which was regarded as Middle Eocene by Owen and Nasr (1958), consists of 225-290 m (738 to 951 ft) of whitish-gray, porous, dolomitized and microporous (chalky) limestone, within the lower part of which some green-gray shale interbedded (Fig. 9.7). It was deposited in a shallow, neritic environment. In outcrop, Huber and Ramsden (1945, in Bellen et al., 1959) recognized about 10 informal lithological units; in 1973, A1 Hashimi identified 11 biostratigraphic units m five larger foraminiferal assemblage zones, three planktonic foraminiferal concurrent zones and three local benthonic foraminiferal zones in the western desert on the slopes of the Rutbah U p l i f t - and was able to show the presence of the Upper Eocene. The upper and lower contacts are unconformable. Towards the northeast, where open-marine conditions prevailed, it passes into the contemporaneous Jaddala Formation. The middle and upper Eocene facies of central Syria are identical with those recognized in the Dammam of southern Iraq. Other correlative beds are the beds of the Midyat Formation of Turkey and the Jahrum and Pabdeh formations (in part) (Fig. 9.7 and 9.8) of the central Fars Province of southwestern Iran.

Paleogene of Southwestern and Southeastern Iran and Adjoining Areas In southeastern Iran, approaching the northern part of the U.A.E., the border between the typical platform conditions described up to this point and those of the Pabdeh or Ras al Khaimah Trough is crossed. The typical sequence (the Pabdeh Formation) shows a sudden increased thickness of predominantly elastic beds in contrast to the elastic-carbonate sequence of the platform.

The beds of the platform-to-basin transitional sequence are assigned to the Jahrum Formation. They consist mainly of carbonates, which are, however, considerably thicker than those of the platform. The lithostratigraphy and facies variation in Iran is shown in Fig. 9.8, and the type-section localities of these formations are shown in Fig. 9.15.

Pabdeh Formation (Paleocene to early Miocene). The formation is named after Kuh-e Pabdeh in the Khuzestan Province, where James and Wynd (1965) and Setudehnia (1972) described the type section at Tang-e Pabdeh, 32025 ' N, 49~ E. The formation is known in outcrop and in subsurface in the provinces of Khuzestan, Fars and Lurestan of Iran. The section, northeast of the Lali Oil Field, has a thickness of about 870 m (2,620 ft) and is divided into the following five units (Fig. 9.16), in ascending order: Unit 5 : 4 5 9 m (1,505 ft) of thin-bedded, argillaceous limestone interbedded with shale Unit 4 : 8 2 . 3 rn (270 ft) of dark shale with rare, thin limestone in the lower part Unit 3: about 42.6 m (140 ft) of thin-bedded, argillaceous limestone with chert nodules (assumed to be the deep-water facies equivalent to the Taleh Zang Member of Lurestan) Unit 2: about 74.7 m (245 ft) of gray shale with bands of argillaceous limestone Unit 1: 140 m (460 ft) of blue and purple shale marl with thin, interbedded, argillaceous limestone The fauna contained in the beds of the Pabdeh Formation indicates that the age of the formation may extend beyond the commonly assigned Paleocene-Oligocene age range into the Neogene (Lower Miocene), at least in the Khuzestan Province, thus providing evidence of the contiROCK STRATIGRAPHIC UNIT

KERMANSHAH 1 TALEH ZANG 2 KASHKAN 3 SHAH BAZAN 4 JAHRUM 5i ~ ~ 6 ASMARI 6A A H W A Z SST. MBR. 6B KALHUR MBR. 7 FARS G R O U P 7A ~ S A R A N 7AI ChlEHEL MBR. 7A2 C H A M P E H MBR. 7A3 M O L MBR. 7B RAZAK 7C MISHAN 7CI C.dJRIMBR. 7D A G H A JARI 7D1 LAHBARI MBR.

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Fig. 9.16. Lithostratigraphy of the Pabdeh, Asmari and Gachsaran formations (Paleocene-Lower Miocene), compiled from the type localities at Kuh-e Pabdeh, Kuh-e Asmari and Kuh-e Namaki, respectively (modifed and compiled from James and Wynd, 1965). nuity of sedimentation from the Paleogene (James and Wynd, 1965). However, the location of the boundary requires more complete faunal information, particularly because in the extreme northwestern and southeastern parts of the basin, there is a lateral facies transition into carbonates of the Jahrum Formation. The Pabdeh Formation everywhere overlies beds of the Gurpi Formation. In the type section, the contact is conformable, but a disconformity is found in the Fars Province where the purple shale (unit 1) is missing. Here, the contact is placed at the base of a bed of cherty limestone, which contains shark teeth, glauconite and an occasional pebble conglomerate (Setudehnia, 1972) indicating a disconformity. The top contact of the Pabdeh Formation with the Oligocene (?early Miocene) Asmari Formation is conformable (Setudehnia, 1972). J a h r u m Formation (Paleocene-Late Eocene). The formation takes its name from the type locality at Kuh-e Jahrum in the Fars Province, where the type section was described by Setudehnia (1972). It is divided into three units (from older to younger) (Fig. 9.17) that, taken together, form the equivalent in Iran to the Hasa Group in Arabia and, with the exception of the absence of evaporite, show a considerable degree of lithological identity with

Fig. 9.17. Lithostratigraphy of the Jahrum Formation (Middle Eocene to Paleocene) at Tang-e Ab on the northern flank of Kuhe- Jahrum, Iran (modified from James and Wynd, 1965). the succession known in Southern Arabian Gulf: Unit 3 : 2 9 5 m (968 ft) of massive buff to tan, dolomitic limestone; Unit 2: from 175 to 180 m (574-590 ft) of thin- to medium-bedded dolomites; and Unit 1: about 38 m (124 ft) of massive, gray and brown weathering dolomites. This predominantly dolomitic succession in the central Fars Province, the shallow-water equivalents of the Pabdeh Formation, is found in the offshore Arabian Gulf wells Suru-1 and Farur B-1. On the Fars Platform, there is a transition between the Jahrum and Pabdeh facies. In the Khuzestan Province, the Jahrum Formation is known only in subsurface. In the central and northern Lurestan Province, the equivalents of the Jahrum Formation are the Taleh Zang and the Shabbazan formations, which are split by the conglomerates and sandstone assigned to the Kashkan Formation. The Jahrum Formation normally rests conformably upon the silty marl, dolomites and evaporites of the Sachun Formation. Where the latter is absent, it overlies either the Pabdeh or Gurpi beds. The upper contact is with the Asmari Formation and is equivalent to, and almost identical with, the lithologies of the Umm Er Radhuma and Dammam formations of the Arabian Platform. In the coastal Fars Province, the age range probably is middle to late Eocene, which is somewhat younger than in the type area. Rocks of the Jahrum facies were deposited on the northeastern margin of the Zagros Trough as it was being uplifted, with the southward displacement of the depocenter, and a mixed Pabdeh-Jahrum facies overlies Pabdeh facies in well Sirri A-1 in the southern part of the Arabian Gulf. Shahbazan Formation (Middle to Late Eocene). The type section of the formation was measured at Tang-e Do in the Lurestan Province, where the thickness is 338.3 m (1,110 ft) (Fig. 9.18). The formation consists of whiteand brown-weathering, 1-3 ft beds of porous, saccharoidal

419

Sedimentary Basins and Petroleum Geology the Middle East glomeratic constituent of the rocks. The Kashkan overlies the biohermal limestone of the Taleh Zang Formation. ~' LITHOLOGY G E N E R A L DESCRIPTION AGE ~: ~ Where the Taleh Zang is not present, the Kashkan rests directly on the Amiran Formation. It underlies the doloOLIGOMIOCENE _ A_ S _~. I ~: Mi I li i _~ ~tt ~i F O S S I L I F E R O U S L I M E S T O N E mites of the Shahbazan Formation. From central Lurestan m - 'L-*! - ~* \ ~ ' i ~ MBD~'M- mmor~D, ~:~ous. s,~o:H.~(:~towards the southwest and southeast, the clastics of the o,,;5, mo \ x Kashkan are replaced by the limestone of the Taleh Zang u.l "I" and Shahbazan formations (Setudehnia, 1972). Asmari Formation (Oligocene-Early Miocene). The :--c.Z.. . . . . - , , ~ = . ~ ' ~ OI:}IMtSENII'~ ~ ~-~EJ COLORED type section of the Asmari Formation at Tang-e Gele Tursh ~ i< .: . . . . . . . . atasror~ S~BSXOr~ANDCONGLOMB~TE o_~,.,~___ ~ , . ~ , lies on the breached southwestern flank of an anticline in .~~ ~ %.~.-'"-~. the Kuh-e Asmari Range in the Khuzestan Province of o i X X X Iran. In the type section, only the middle and upper parts z z LI I I i~EDIL~-BEDI)ED ~ ~: . 1 I l of the limestone are exposed. The lower part of the forma0__1,--I, -r 67O ! I 1 tion is represented by a laterally equivalent shaly facies ' generally assigned to the Pabdeh Formation. There is no ~ ' . ' . - ~ . ' . ' ~ . " : " .-~.'I SILl%"1E)NE A N D SANDSIOI'4E w r r H L O C A L .................. l ~ O F ~ CONGL~I"E unconformity between the two lithofacies. The thickness is .................. A N D SHELLY L ~ E s r o ~ SHELLY L ~ E S r O N E i " ."~'. "" .-: "" "~.. /Id~E) I~M~ L Z; iI u~ m.. quite variable and may range from a few feet to more than 0 < ::":"-:"'": " ' " ' " : 518 m (1,700 ft). The formation consists of creamy- to ~: , brown-colored, well-jointed limestone with shelly intercalations (Fig. 9.16). The limestone is dense with little priMAASTRI-i ! ' .................... CHTIAN J GURPi AND 'i -I- I - - i ' S t ~ . L Y ~ N E mary porosity, although it is a prolific reservoir where fracture porosity is well-developed. In the Ahwaz and Mansuri fields, the basal few hundred feet of the Asmari Fig. 9.18. Lithostratigraphy of the Amiran, Taleh Zang, Kashkan limestone is represented by calcareous sandstone and and Shahbazan formations (Paleocene-Upper Eocene) compiled sandy limestone with minor shale (the Ahwaz Sandstone from different type localities at Kuh-e Amiran and Tang-e Do in Iran (modified and compiled from James and Wynd, 1965). Member of James and Wynd, 1965). The Ahwaz Sandstone Member can be considered a facies continuation of dolomite and dolomitic limestone. The Kashkan Formathe Ghar Formation of Kuwait and southeastern Iraq. tion underlies this formation with apparent conformity, as While the base of the Asmari Formation is conformthe contact is gradational. The upper contact with the limeable with the Pabdeh Formation in the Fars Province, it is stone of the Asmari Formation is disconformable. The diachronous in the Lurestan and Khuzestan provinces. In Shahbazan Formation is developed best in central and the southwestern Lurestan Province, however, the lower northeastern Lurestan. Towards the southeast and southpart of the Asmari Formation consists of evaporites, maswest, it becomes thin-bedded and argillaceous and eventusive and bedded gypsum, marl and some thin-bedded limeally passes into the shale and marl of the Pabdeh stone near the base and at the top for a total of 120 m (394 Formation. From central Lurestan towards the northeast, ft). Towards the northeast, this facies rises in the series to the Shahbazan is replaced progressively by the conglomerinterfinger with the Middle Asmari limestone. In contrast, ates and sandstone assigned to the Kashkan Formation the upper contact with the Gachsaran Formation is con(Setudehnia, 1972). formable in the latter two areas, but is diachronous in the Taleh Zang Formation (Paleocene to Middle Fars Province, where it passes into, or interfingers with, Eocene). The type section was measured at Tang-e Do in beds of the Razak Formation. To the southeast, the Asmari Lurestan, where the thickness appears to be 204. m (670 grades into the marl of the Pabdeh Formation, as seen in ft) and consists mainly of medium-bedded to massive, the wells on Qeshm Island (James and Wynd, 1965). resistant, gray and brown, fossiliferous limestone. The The Lower Asmari Formation has been correlated Taleh Zang conformably overlies the sandy marl and sandwith the Chattian-Rupelian (Oligocene) by Eames et al. stone of the Amiran Formation. The upper contact with the (1962),and the Middle and Upper Asmari with the early overlying Kashkan Formation apparently is conformable Miocene. (Setudehnia, 1972). From central Lurestan towards the southwest and southeast, the Taleh Zang interfingers with Paleogene of the United Arab Emirates and passes into the shale and limestone of the Pabdeh ForIn the U.A.E., both basinal and platform sequences mation. occur. As in Iran, transition from the platform into the Kashkan Formation (? Paleocene-Middle Eocene). basin is marked by an increased thickness, although the The type section was measured at the northeastern flank of traditional formational names still can be used. SedimenKuh-e Amiran in central Lurestan, where the formation is tary continuity with the Neogene is indicated by the about 370 m (1,215 ft) and is composed mainly of red conAsmari limestone (Figs. 9.6 and 9.19). glomerate, sandstone and siltstone. Chert is the main con--

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about 100 m (328 ft) thick, is well-developed in western Abu Dhabi. It is uniform in lithology, but thins to the northeast of Abu Dhabi, where it loses its identity. It shows evidence of deposition in very shallow water to a supratidal environment with dolomitic and argillaceous limestone at the base, grading up into thick, massive anhydrites capped by cream or gray, bioclastic limestone and interbedded anhydrites. The presence of the middle evaporite unit provides evidence of a regressive phase within the formation. In outcrop, the Rus Formation, about 184 m (604 ft) of alternating marl or marly limestone and limestone, is characterized by extensive dolomitization and chertification (with associated glauconitization). These carbonates were deposited cyclically in a shallowwater environment. The cyclic nature of sedimentation suggests that deposition was eustatically driven (Whittle and Alsharhan, 1994). The Rus Formation has conformable contacts with the overlying and underlying formations in subsurface, but in outcrop the base of the formation is not exposed. Dammam Formation (middle-upper Eocene). The Dammam Formation consists of three lithological units about 229 m (750 ft) thick in subsurface and 1,098 m (3,602 ft) in outcrop. The lower comprises light blue-gray

421

Sedimentary Basins and Petroleum Geology the Middle East lime mudstone; soft, marly limestone; and porous, calcareous shale. The middle unit is formed by porous, well-bedded, nummulitic grainstone and packstone and is capped by an upper unit of argillaceous limestone and shale. The lithologies provide evidence of the reestablishment of normal-marine shallow-shelf conditions. These sediments imply cyclic deposition of predominantly shoal-water and open-marine, bioclastic, grain-supported limestone and quiet-water, lagoonal and outer-shelf, mud-supported limestone with short periods in a supratidal setting driven by high-frequency, sea-level oscillation (Whittle et al., 1995). The Asmari limestone follows conformably over the Dammam Formation in eastern Abu Dhabi; however, further to the west, post-Eocene erosion has removed beds down to the top of the Dammam Formation, and, consequently, there is an unconformable contact between the Dammam and Gachsaran formations. To the northeast and east of Abu Dhabi where the Rus Formation disappears, the Dammam overlies the beds of the Umm Er Radhuma and/or Pabdeh. The Dammam thickens to the east into the Ras al Khaimah Sub-basin, where the limestone passes into a more argillaceous facies, equivalent in part to that of the Pabdeh. Asmari Formation (early-middle Oligocene to Early Miocene?). The late Eocene regression persisted into the early Oligocene and led to the exposure of a large part of the region, as the carbonate platform shrank towards the Indian Ocean, although not all of the Ras al Khaimah Trough was exposed. This time period was marked by the appearance of the Oligocene Asmari sediments, limestone, clastic sediments and evaporites, which filled the trough with shallow-water deposits laid down in a restricted marine environment. The facies variations seen in this Oligocene interval in and around the Ras al Khaimah Trough are related to a gradual shallowing combined with a paleogeographic position related to proximity to the shoreline. Shallow-water, high-energy shoal carbonates of Oligocene Asmari facies are encountered in subsurface in offshore U.A.E. They crop out in Jebel Hafit close to the Oman Mountains and have a thickness ranging from 435 m to 481 m (1,427-1,578 ft). The formation is composed of silty and gypsiferous marl with conglomeratic limestone in the lower part. It grades upward into thickly bedded, algal, coral and nummulitic limestone and is completed by poorly bedded, marly, foraminiferal limestone and marly, oolitic and bioclastic limestone. These sediments and the fauna they contain suggest deposition in a deep, outer shelf. A quiet-water lagoon supplied peloids to the back-reef, reef and fore-reef facies as well as to the shallow, open-marine facies of the inner shelf (Whittle et al., 1995). In offshore Abu Dhabi and Dubai, where more information has been garnered from subsurface, the Asmari Formation ranges in thickness from 54 m to 108 m (177354 ft) and can be divided into three lithological units. The lower unit consists of nummulitic and dolomitic limestone, dolomites with silty mudstone and anhydritic nod-

422

ules. The middle unit is mainly intraclastic and nummulitic packstone and grainstone and calcareous mudstone, whereas the upper unit is composed of silty dolomite, pellety and dense in part, interbedded with pellety limestone. The Asmari is overlain conformably by early Miocene sediments, and the base rests conformably on the late Eocene Dammam Formation. Pabdeh Formation (Paleocene to Oligocene?). The Ras al Khaimah Sub-basin represents a still-subsiding part of the old Cretaceous Basin, which extends from Oman through both the onshore and offshore parts of the northern U.A.E. into the Fars Province of southeastern Iran. In southeastern Iran and off the Musandam Peninsula, a virtually continuous Paleocene to Oligocene bathyal sequence of rhythmically bedded, argillaceous limestone and chert, the Pabdeh Formation, was formed. Towards the top of the formation, there is a progressive change to depositional environments more characteristic of an external platform with open-marine conditions (Ricateau and Riche, 1980). The Pabdeh Formation of the Ras al Khaimah Subbasin is similar to the section in the Zagros Trough, except that the basal purple shale is absent and is replaced by marl and argillaceous limestone. The formation reaches a thickness of about 1,500 m (approximately 4,920 ft), but thins and is less complete in offshore Ras al Khaimah and towards Dubai and Abu Dhabi. About 500 m (1,640 ft) of calcareous flysch, consisting of interbedded hemipelagic, biogenic limestone, marl, calcareous shale and clay, is found between eastern offshore Abu Dhabi and Umm al Qaiwain. In central and western Abu Dhabi, this basinal, calcareous flysch sequence shows a facies change that marks the transition back to shallow-shelf carbonates (e.g., Umm Er Radhuma and Rus). The eastern margin of the Ras al Khaimah Sub-basin against the mountains of northwestern Oman is steep; near this margin, where the basin was deepest, it received submarine mud-flow conglomerates and turbiditic deposits, and limestone and shale were deposited during the Paleocene and middle Eocene. The flysch is exposed near Sha'am at the Oman-Ras al Khaimah border and has been drilled in that region. The well section of PaleoceneEocene flysch is repeated by faulting, but bathyal, black, calcareous, pyritic shale interbedded with clastics still was present at a depth of more than 3,660 m (12,000 ft) when drilling was terminated. The composition of the flysch, the moderately rounded, coarse, variegated sand with chert, volcanic and probable serpentine material, suggests that the stripping of the Semail and Hawasina nappes provided the likely source and, thus, is a continuation of the Late Cretaceous Juweiza facies. At the edge of the Ras al Khaimah Sub-basin, there appears to be a conformable, lateral transition to the Eocene (Dammam) shelf limestone. The passage is diachronous, and away from the basin, the upper part of the Pabdeh Formation is Oligocene in age, and the beds are unconformably overlain by the Gachsaran evaporites.

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

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Paleogene of Oman Two distinct regions can be recognized: the central and western Oman Mountains and southern Oman (Dhofar region) (Fig. 9.6).

N

,.,~ /

Outcrop Formations Central and Western Oman Mountains The existing Paleogene lithostratigraphic framework of central and eastern Arabia cannot be applied directly to the Oman Mountains, as this would demand changing the original descriptions of the existing formations; consequently, a new, local lithostratigraphic framework for the Paleogene was presented by Nolan et al. (1986, 1990). This is summarized below and in Fig. 9.20. Jafnayn Limestone Formation (late Paleocene to early Eocene). About 126 m (413 ft) of carbonate platform limestone occurs in the type section at Wadi Rusayl, west of Muscat, Oman. It consists of 3-4 m (10-13 ft) of basal, nodular, crystalline limestone with reworked chert and ophiolite clasts, followed above by about 69 m (226 ft) of marl and marly wackestone. These are overlain by about 53 m (174 ft) of thickly bedded packstone and wackestone with grainstone and rudstone towards the top (Fig. 9.27). At the base of the Jafnayn Formation is a low-angle unconformity. The upper boundary with the Rusayl Formation appears conformable, but a non-sequence or disconformity may be present. The Jafnayn Formation formed in a shallow-shelf environment. The lower part is interpreted as having formed in low-energy conditions, whereas the upper division appears to have formed in a higher-energy environment. Rusayl Formation (Lower-Middle Eocene). A thickness of 144 m (472 ft) was measured at the type sec-

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tion near Rusayl village west of the Oman Mountains. The basal unit consists of 52 m (171 ft) of poorly indurated, multicolored shale and marl with occasional thin, microcrystalline limestone. It lacks age-diagnostic foraminifera, but does contain questionable Early Eocene ostracods and microspores. Above is a 6 m (20 ft) thick, resistant, microcrystalline limestone bed followed by 37 m (137 ft) of soft, multicolored shale and marl. It contains probable Middle Eocene larger benthonic foraminifera including Somalina (Jones and Racey, 1994). The beds, in turn, are overlain by 12.5 m (41 ft) of interbedded multicolored shale, sandstone and conglomerate. Towards the top of the formation are 18.5 m (61 ft) of multicolored shale and marl, 18 m (59 ft) of interbedded marl, shale and well-

423

Sedimentary Basins and Petroleum Geology the Middle East

GENERAL DESCRIPTION

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130 m (426 ft) of nodular-bedded packstone with abundant nummulitic foraminifera (Fig. 9.21). Based on at study by Jones and Racey (1994), the Seeb Formation in the eastern Oman Mountains contains foraminifera of Middle Eocene Nummulite obesus and Assilina spira abradi zones of Schaub (1981), and the index species of the Late Eocene Nummulite perforatus zone was found at Alkhawd (30 km from Wadi Rusayl). In the western Oman Mountains, the formation is of Middle Eocene to Early Oligocene age. The contact with the underlying Rusayl Formation is sharp but conformable. The top of the Seeb Formation is not exposed. A regional unconformity occurs on the Arabian Peninsula between Eocene and Oligo-Miocene strata. Such a feature may occur at the top of the Seeb Formation. Racey (1994) provided a detailed depositional facies and environmental analysis of the Seeb Limestone along the Batinah coastal area of Oman. Overall, it presents a range of environment from quiet-water, restricted-innerramp to deeper, outer-ramp conditions. Biofabrics repre-

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Fig. 9.21. Lithostratigraphy of the Late Paleocene-Middle Eocene (Jafnayn, Rusayl and Seeb formations) from the type locality at Wadi Rusayl, southern Batinah coast, near Muscat, Oman (after Nolan et al., 1990, and reproduced by kind permission of the Geological Society, London). laminated grainstone and bioclastic limestone, which contains definite Middle Eocene larger benthonic foraminifera including Linderina rajasthanensis (Fig. 9.21). The basal contact between the Rusayl and Jafnayn formations is a sharp non-sequence. The upper contact with the Seeb Formation is sharp but conformable. The formation formed in littoral to inshore environments and ranges from conglomeratic beach and peritidal facies, through restricted lagoonal and mud-fiat facies, tidally influenced gravel bars and foraminiferal limestone, to shallow, submergent, storm-bedded, sandstone barrier complexes. Seeb Limestone Formation (Middle Eocene-Early Oligocene). The formation is approximately 356 m (1,168 ft) thick in the type section in Wadi Rusayl, where the lower 30 m (98 ft) of the formation consists of thick to moderately well-bedded wackestone/packstone with cross bedding, overlain by 51 m (167 f t ) o f medium-bedded, bioturbated, nodular packstone. Above this follows a 145 m (476 ft) limestone with thin marl partings overlain by

424

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Fig. 9.22. Lithostratigraphy of the Eocene (Ruwaydah Formation) at Wadi Sakhin, northern Batinah coast, near Saham, Oman (after Nolan et al., 1990, and reproduced by kind permission of the Geological Society, London).

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic senting original life assemblages, generally restricted to low-energy, often protected environments, contrast with sequences rich in sand and shallow-marine foraminifera interpreted as storm sheets, shoals or low-amplitude banks. Ruwaydah Formation (Eocene). The formation is approximately 900 m (2,952 ft) or more in thickness in the type area, near Wadi Sakin on the northern Batinah coast. The lower 60 m (497 ft) consists of tabular, well-bedded, hard crystalline biosparites with chert nodules, shale and marl. Overlying them are 800 m (2,624 ft) of thinly interbedded, tabular, fine-grained, chalky (microporous) limestone, shale and marl followed upwards by about 50 m (164 ft) of chalky (microporous) limestone, marl and shale with occasional coarse, bioclastic horizons (Fig. 9.22). Neither the top nor the bottom of the formation is exposed. The Ruwaydah Formation formed in a submarine slope environment and consists of turbidity-current/debris-flow, apron-fan deposits flanking the eastern side of the northcentral Oman Mountains. Fahud Formation (Middle Eocene). About 160 m (525 ft) of thin-bedded, chalky (microporous) wackestone, shale and marl are present in Jebel Fahud (Fig. 9.23). The

formation usually appears poorly fossiliferous, although occasional horizons rich in alveolinid foraminifera or echinoids and gastropods occur. The base at the type locality appears to be conformable, but the top of the underlying Jafnayn Formation is irregular. The Fahud beds are mostly of low-energy shelf facies.

Muthaymimah Formation (Paleocene to Eocene). The formation consists of a sequence, about 300 m (984 ft) thick, which occurs on the northwestern side of Sayh Muthaymimah. The lower 37.5 m (123 ft), which consists of shale, marl and thin, flaggy, argillaceous limestone, is overlain by 18 m (59 ft) of thickly bedded limestone con-

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L. CRETA-

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Fig. 9.24. Lithostratigraphy of the Paleocene-Middle Eocene (Muthaymimah Formation) from the type locality at Jebel Muthaymimah, western central side of the Oman Mountains, near Buraymi and A1 Ain (after Nolan et al., 1990, and reproduced by kind permission of the Geological Society, London). 425

Sedimentary Basins and Petroleum Geology the Middle East glomerate. On top of this follows 56 m of thin, platy and flaggy bedded, splintery, argillaceous lime mudstone and marl with occasional thin, lenticular, conglomerate bands, succeeded by 2-3 m (6.6-10 ft) of conglomerate with chert, ophiolite and limestone pebbles. Above are 42 m (138 ft) of thin, flaggy, interbedded, argillaceous limestone and marl. Overlying these are 88 m (289 ft) of interbedded shale and marl with thin, graded, lithic sandstone and limestone bands containing occasional nummulites and lenticular conglomerates. The succession is continued by 40 m (131 ft) of thickly bedded to massive limestone conglomerate containing reworked clasts of nummulitic limestone, ophiolite and chert debris (Fig. 9.24). The formation rests with a sharp contact upon the Semail Ophiolite. This boundary appears to be unconformable, but has acted as a slip plane during later tectonic movements. The lenticular conglomerates were deposited by a variety of unconfined or semi-confined debris flows in a proximal, submarine-slope environment. Interbedded with these are graded calcareous, lithic sandstone and limestone in which units of a typical Bouma cycle can be recognized, indicating deposition from turbidity currents.

Southern Oman (Dhofar Region) The first sediments deposited over the late Maastrichtian unconformity surface are assigned to the Hadhramout Group and include four formations (Fig. 9.6), which are described by Beydoun and Greenwood (1968) and Hawkins et al. (1981) and summarized below.

Hadhramout Group (Paleocene-Middle Eocene) Umm Er Radhuma Formation (Paleocene-early Eocene). In South Oman, in outcrop, the facies of the lower unit consist of a 200-330 m (656-1,082 ft) basal alternation of carbonaceous dismicrites, black shale and green mudstone. These are overlain by partly dolomitized limestone interbedded with chalky (microporous) horizons and rare marl. The unit is completed by dark, fossiliferous and partially dolomitized biosparites with numerous thin bands of black shale, greenish mudstone and marl. This upper part consists of 200-320 m (656-1,050 ft) of pale biomicrites with subordinate beds of marl, black shale and dark limestone (Hawkins et al., 1981). The depositional environment is interpreted as shallow-marine, intertidal to supratidal. Rus Formation (Early Eocene). In outcrop, the formarion consists of 100-180 m (328 -590 ft) of bedded gypsum and chalky (microporous) limestone with occasional bands of chert, marl, gypsiferous chalk and dolomitic limestone deposited under restricted subaerial to supratidal conditions (Hawkins et al., 1981). Beydoun and Greenwood (1968) concluded that in southern Oman, evaporite deposition did not begin until relatively late, and the Rus is believed to be mainly of middle Eocene age. Towards the central Oman Mountains, at the edge of the evaporite basin, the Rus thins and either pinches out or passes later-

426

ally into more open-marine deposits; in other parts of the basin, facies changes occur locally within the formation, resulting from variations in currents, salinity and proximity to more open-sea conditions.

Andhur and Qara formations (Dammam Equivalents) (Middle Eocene). In southern Oman, the Dammam Formation equivalents are named the Andhur and Qara formations. In outcrop, the lithofacies essentially are the same as those of the Habshiya Formation of South Yemen, where the Andhur is the shaly formation, and the Qara is the carbonate formation. The Andhur Formation is about 43 m (121 ft) thick and consists of fossiliferous, yellow shale and chalky marl with interbedded, argillaceous limestone. It is underlain conformably by the Rus Formation and overlain conformably by the Qara Formation. The Qara Formation, about 194 m (636 ft) thick, consists mainly of fine- to medium-grained, gray to creamy limestone, sometimes porous, nodular or dolomitized, alternating with marly and chalky (microporous) limestone. Based on their fauna, both formations are dated as Middle Eocene and are facies equivalents, as one passes into the other across northern Dhofar. The depositional environment is interpreted as a shallow-water, normal marine environment (Beydoun and Greenwood, 1968; Hawkins et al., 1981). Taqa Formation (Oligocene-Miocene). The Taqa Formation rests unconformably upon the youngest beds of the Hadhramout Group, although the contact is not always angular. It is overlain by Miocene conglomerates or younger deposits. It ranges from 1,100 to 1,400 m (3,6084,592 ft) in thickness. It is developed mainly in Dhofar and along the southeastern coasts of Oman. The lowermost beds consist of calcareous and slightly glauconitic, greengray silt and fine sand. The upper part of the formation provides evidence of slightly deeper-water, open-marine conditions, as the sand and silt are replaced by thin-bedded, crystalline micrites and sparites with minor marl. As the formation post-dates late Eocene faulting, it only occurs south of the Jebel Qara boundary faults (Beydoun and Greenwood, 1968; Hawkins et al., 1981). Post-Oligocene movements are responsible for the tilting and disturbance of beds of the Taqa Formation and older deposits.

Subsurface Formations Central and Southern Oman

Hadhramout Group (Paleocene-Late Eocene?) The Umm Er Radhuma, Rus and Dammam formations have been referred to as the Hasa Group in the Arabian Peninsula. Use of the term "Hadhramout Group" in Oman reflects the rather wider lithological variation found in subsurface.

Umm Er Radhuma Formation (Paleocene-Early Eocene). The formation, totalling about 341 m (1,118 ft), has a basal shale/marl unit (Shammar Member) (about 15-

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic < GAMMA I ~_ RAY LITHO ==~ (APIUNIT) LOGY

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30 m, or 50-100 ft), followed by a thick sequence of dolomitized limestone with only minor argillaceous breaks (Fig. 9.25) indicating a shallow-marine, probably partly intertidal, environment. The lower boundary is a hiatus or disconformity, and the upper boundary is conformable and transitional into the marl and evaporites of the Rus Formation (Hughes-Clarke, 1988). Rus Formation (Early Eocene). This formation is about 130 m (426 ft) thick, consisting of gypsum or anhydrite, with associated variable dolomite or dolomitic marl, silica geodes and secondary silicification common in South Oman. The formation probably is deposited in a restricted lagoon, playa or sabkha setting (Fig. 9.25) (Hughes-Clarke, 1988). The upper and lower boundaries are conformable and transitional into the Dammam and Umm Er Radhuma carbonates, respectively. By its widespread occurrence, the formation must reflect a regional sea-level fall from a stable shelf. The southern silicification possibly is derived from an influx of volcanic tufts and ashes. The formation occurs throughout Interior Oman, except to the southeast and where it is eroded and

i

overlain by younger outcrops (Hughes-Clarke, 1988). Dammam Formation (Middle-Late ? Eocene). The formation is formed by about 142 m (464 ft) of limestone with some variability in dolomitization and minor marl interbeds, which were deposited in shallow-marine environments (Fig. 9.25). The lower contact is conformable, while the upper contact is a hiatus overlain by Fars carbonates or clastics (Hughes-Clarke, 1988).

Fars Group (Oligocene-Pliocene) In Oman's oil-producing areas, the Fars Group is divided into two parts. The lower, known as the Taqa Formation (Oligocene-Miocene), is mainly carbonates, while the Upper is post-Miocene unnamed of varied clasticevaporite sequences. Taqa Formation (Oligocene-Miocene). The formation, about 500 m (1,640 ft), is dominated by carbonates (microporous and porous, reefal limestone) deposited in a shallow-marine to lagoonal setting (Fig. 9.26) (HughesClarke, 1988). The formation overlies with hiatus the

427

Sedimentary Basins and Petroleum Geology the Middle East

GAMMA (API

PAY

Units)

LITHO-

LOGY

600 m (1,968 ft) thick (Ricateau and Riche, 1980).

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GENERAL

DESCRIPTION

The Paleogene of Southern, Southwestern and Western Arabia

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Paleogene of Western Saudi Arabia (Red Sea Region) A dominantly carbonate sequence, including chalky and porous marine .o sometimes reefal limestone. Shallow marine including reefal and lagoonal environment

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Fig. 9.26. Lithostratigraphy and log characteristics of the OligoMiocene (Taqa Formation) in Oman (modified from HughesClarke, 1988, and reproduced by kind permission of Journal of Petroleum Geology). Hadhramout Group and passes up with transition into undifferentiated Fars clastics and evaporites. The Taqa is developed mainly to the south (Dhofar Province) and along the southeastern coasts of Oman, and in Yibal Field and adjacent areas, reflecting areas with the most marine influx during the Oligo-Miocene (Hughes-Clarke, 1988).

Northern Offshore Oman

Pabdeh Formation (Paleocene-Oligocene). This is an argillaceous carbonate series, 1,500 m (4,920 ft) thick, with a base formed of rhythmically bedded, argillaceous limestone with chert and shale. The bathyal environment is dominant at the base and changes progressively towards the external platform, with open influence towards the top (Ricateau and Riche, 1980). Lower Fars Formation (Upper Oligocene to Lower Miocene). The thickness of the formation ranges from 650 to 750 m (2,132-2,460 ft) and consists of an evaporite episode comprising a basal, saliferous unit overlain by an anhydrite unit (Ricateau and Riche, 1980). Guri Formation (Upper Miocene). The formation consists of about 50 m (164 ft) of dolornitic shale and bioclastic limestone (brachiopods, crinoids, corals and lamellibranchs).

Mishan and younger formations (Upper Miocene to Quaternary). These are a series of shale wth sandy marl interbedded with a bank of shelly limestone about

428

In southwestern Saudi Arabia, Paleogene volcanic episodes several million years long have been recognized (Voggenreiter et al., 1988). The greatest extrusive activity with the effusion of alkali olivine basalts began as little as 2 Ma ago in southwestern Saudi Arabia and Yemen, postdating the development of the Red Sea rifts. The pre-rift sequence in western Saudi Arabia consists of freshwater to shallow-marine deposits dated as Campanian to Early Eocene. The presence of sediments of Middle to Late Eocene and of late Oligocene age has not been confirmed. The sequence was divided into a number of formal lithostratigraphic units (Fig. 9.27), which are summarized below, described by Hughes and Filatoff (1995). Suqah Group (Campanian-Middle Eocene). A prerift sequence in the Red Sea region of Saudi Arabia known as the Suqah Group is present in the Jeddah and Midyan areas; in exploration well Jeddah-1, it rests unconformably at the underlying basement. It can be divided into the following two formations (in ascending order):

1) Pre-Usfan Formation (Campanian-Lower Maastrichtian). The formation occurs at the surface and in subsurface in exploration well Jeddah-1 and consists ,j

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The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic of poorly sorted, locally kaolinitic, pebbly sandstone with minor interbedded siltstone. The sediments were deposited in a braided-river complex, grading in its upper part into a succession with marginal-marine incursions.

2) Usfan Formation (Maastrichtian-Lower/Middle Eocene). The formation is present in the Jeddah region and consists of black shale and light-colored siltstone and interbedded mature sandstone, with rare bioclastic limestone, coals and oolitic limestone. It is locally intruded by basalt in the upper part. The Usfan rests conformably, but may be locally unconformable, upon the pre-Usfan Formation. The sediments were deposited in shallow, nearshore-marine environments, deltaic and estuarine at the base, grading to non-marine, low-energy fluviatile at the top. Matiyah Formation (Early Oligocene). This formation, in the Jeddah area, is separated unconformably from both the Suqah Group below and the Tayran Group above. It consists of purplish-red to variegated and weathered siltstone and fine-grained sandstone with intervening basalt flows. The sediments were laid down in a low-energy, oxidizing, fluvio-lacustrine regime with volcanic episodes.

Paleogene of Yemen Paleogene of East and Southeast Yemen The Early Cenozoic was a tectonically quiet period in Yemen, and the interval was characterized by the widespread deposition of shallow-marine carbonates with significant dolomitization. There are many evaporitic intervals in southern Yemen and clastic sediments in northern Yemen. In southern Yemen, the principal Paleogene deposits are the Paleocene to middle Eocene sediments, equivalent to the Hasa Group in the Arabian Gulf and are assigned to the Hadhramout Group (Fig. 9.6).

Hadhramout Group The group consists (in ascending order) of four formations m Umm Er Radhuma, Jeza, Rus and Habshiya which can be compared to the sequence in the South Oman (Dhofar) region. There are significant facies variations in the Umm Er Radhuma and Habshiya that point to a more proximal coastal location of the South Oman deposits as compared to those in Yemen. This trend is more apparent in the latter part of the Paleogene, where the sequence is completed by the beds of the Shihar Group. The Shihar Group is distinctive because of its variable lithologies and sporadic occurrence. Both groups reflect the proximity of uplifted, emergent areas, restricted basins and shallow seas. In northern Yemen, an area that remained primarily continental, the preserved Paleogene rocks are, consequently, poorly dated and include abundant volcanics, of which only some have been radiometrically dated. Umm Er Radhuma Formation (Paleocene). In the

former South Yemen, the Umm Er Radhuma Formation lies disconformably on the Cretaceous section and presents a Paleocene transgressive facies. The type section is 215 m (705 ft) thick and is fairly continuous throughout South Yemen. A basal dolomite is overlain by a shale interval and then fine-grained, nodular and marly limestone beds that give way to a massive, fine- to coarse-grained limestone with calcite veins and chert vugs. The top of the section consists of fossiliferous, massive, gray limestone with dolomitic, chalky (microporous) lime mudstone and shelly horizons. The section thins to the west to a Paleocene shoreline, which is no longer preserved (Beydoun, 1964, 1966; Beydoun and Greenwood, 1968; Greenwood and Bleakley, 1967). A fairly abundant microfauna, on which the Paleocene is based, was identified by Beydoun and Greenwood (1968). The formation is apparently conformably underlain by the Mukalla Formation and conformably overlain by the Jeza Formation. Toward northern Yemen, the formation thins and is regarded as partly equivalent in age to the volcanic trap series. Jeza Formation (Lower Eocene). In the former South Yemen, the formation is composed of 133 m (436 ft) of yellow and pink, partially silicified, papery shale and beds of marl alternating with gray, silicified and chalky (microporous) limestone (Beydoun and Greenwood, 1968). The formation conformably follows the Umm Er Radhuma Formation and is overlain conformably by the Rus Formation; thus, it must be considered a facies equivalent of part of one or the other formation. Rus Formation (Early Eocene). This formation, in the former South Yemen, is 138 m (about 453 ft) thick of bedded gypsum with occasional bands of chert, marl and gypsiferous, chalky, dolomitic limestone (Beydoun and Greenwood, 1968). It apparently is conformable with the underlying and overlying beds. Although the Rus Formation has a wide areal extent, it is considered to have been deposited in a restricted basin, where local conditions resulted in lithological variations. Habshiya Formation (Middle Eocene). In the former South Yemen, this formation is regarded as equivalent to the Dammam Formation. It consists of about 224 m (735 ft) of green, gray, yellow and pink, papery shale and yellow, chalky, gypsiferous limestone, alternating with chalky and dolomitic limestone. The Habshiya Formation apparently is conformably underlain by the Rus Formation and normally marks the end of the Paleogene succession. Locally, it may be overlain unconformably by the Shihar Group or younger deposits.

Paleogene of West and Northwest Yemen Most of the onshore Tertiary sequence in Yemen is made up of volcanics, both lava and pyroclastics, cut by dikes, sills and granitic intrusions. The granites are concentrated along a north-south-oriented band extending along the eastern edge of the Tihama Coastal Plain.

429

Sedimentary Basins and Petroleum Geology the Middle East Two main groups of volcanic rocks occur: the Oligocene flood volcanic rocks intruded by granite, and the Pliocene-Holocene alkaline, intraplate volcanics (Davison et al., 1994). Chiesa et al. (1983) indicate that the oldest radiometric ages of the lavas in northern Yemen are 29 Ma, whereas the granites are 28-21 Ma, and the dikes are 26-20 Ma (Capaldi et al., 1987). The Oligocene-Miocene Volcanic Trap Sequence in northern Yemen covers an area of 40,000 sq km and may be up to 2 km thick, thinning eastwards (Chiesa et al., 1983). The basal flows commonly are basaltic ignimbrites, sometimes amygdaloidal, and ash-fall tufts. The volcanics are characterized by a high ferric-iron content. Yemen Volcanics (Aden Trap Series) (OligoceneMiocene). The term "Yemen Volcanics" was introduced by Grolier and Overstreet (1978) in the northern province of Yemen, while the term "Aden Trap Series" was introduced by Greenwood and Bleakley (1967) in the southern Province of Yemen. This widespread volcanic activity occurred during the Late Cretaceous and Early Tertiary and is believed by many authors (e.g., Gass, 1970; Chiesa et al., 1983; Almond, 1986; Camp and Roobol, 1989; A1Kirbash and A1-Hibshi, 1992) to be associated with the vertical uplift of the Afro-Arabian Dome and rifting of the Red Sea. The volcanic rocks cover almost 45,000 sq km in Yemen and are a result of fissure-erupted and calderaeruptive centers with dykes and volcanic flows (A1-Khirbash and A1-Hibshi, 1992). The volcanics have a thickness ranging from 700 m (2,296 ft) several kilometers northeast of Sana'a, to 1,500 m (4,920 ft) in the Sana'a region, to 2,000-3,000 m (6,560-9,840 ft) to the west of Sana'a (Fig. 9.28). They consist of basal volcaniclastics (tufts, shale, coal interbeds, fossiliferous limestone, basaltic pillow lavas with a paleosol at the top of the sequence), followed upwards by alternating sequences of basin and acidic volcanics. The basic volcanics are mainly alkali-olivine basalt with phenocrysts of pyroxene and olivine flood basalt; ash; gabbroic, sill-type intrusions; magmatic breccias; agglomWEST (RIFT MARGIN)

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The Paleogene of the Northern Arabian Platform

The northern part of the Middle East region is tectonically more diverse than the area further to the south. There are no equivalents in Arabia of the Euphrates-Anah grabens, and lithologies are more varied. To the northeast, the platform is replaced by the deep basin bordering the TaurusZagros Belt, and deposits equivalent to the flysch of the Pabdeh (Ras al Khaimah) Sub-basin are found in this basin. Thus, descriptions of the Paleogene in Jordan and Syria, excluding the northeastern extremity, parallel those of the Saudi Arabian region, whereas the descriptions of the sedimentation and thicknesses in Southeast Turkey, Northeast Syria and northern Iraq parallel those in the Ras al Khaimah and Pabdeh sub-basins of the U.A.E. and Southeast Iran, respectively. Paleogene of Northwest Saudi Arabia

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erate; conglomerates; and basaltic and composite dikes. The acidic volcanics are composed mainly of xenolithic, alkalic, layered ignimbritic rhyolites; pyroclastics; agglomerate; ash; lapilli tuff; flow-banded, contorted and unlayered ignimbrites; obsidian, rhyolitic and composite dikes; and sandy, tuffaceous intercalations and peralkaline pyroclastics. In the southern provinces of Yemen, these rocks usually crop out and are not covered, but in a few places, they lie below a cover of Pliocene deposits. In the northern provinces of Yemen, the rocks are unconformably overlain by the Aden Volcanic Series. These early Tertiary volcanics resulted from the development of a hot spot or mantle plume in the Afar triangle. This area of high heat flow became the site of crustal rifting and spreading during the Oligocene (Girdler and Styles, 1974). Subsequent thermal subsidence led to the deposition of thick, non-marine sediments within the Red Sea Basin, during which time complex half grabens and transfer faults developed along the borders of the Red Sea (Hutchinson and Engels, 1970; Voggenreiter et al., 1988). Volcanism ceased along the Red Sea margin during the Neogene about 14 Ma ago, possibly caused by, or related to, the initiation of the Gulf of Aqaba Strike-slip System (Voggenreiteret al., 1988).

Hibr Group (Paleocene-Upper Eocene). The term was first introduced by Berg and Owens (1946, cited in Powers, 1968) to embrace Tertiary rocks exposed in the vicinity of Tall A1Hibr (31051' N, 3808 ' E) in northwestern Saudi Arabia. The group is partially equivalent to the Umm Er Radhuma, Rus and Dammam formations of central and eastern Saudi Arabia. The formation has a thickness ranging from 150 to 485 m (490-1,590 ft) and is composed of thinly bedded, microporous, cherty limestone and marl. Partial dolomitization is common. Much of the chert is present as lenses, platy masses and flat and spheroidal nodules within the microporous limestone (Fig. 9.29). The Hibr Group was deposited in a shallow to

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

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Although the Tertiary of Jordan is known only in a broad outline, there is sufficient information to relate it to the rest of the Middle East. Bender (1974, 1975) has summarized the available data, from which it is clear that a distinction can be made between the Paleogene and Neogene. The Paleocene and Eocene over most of Jordan consists of limestone and marly limestones laid down in a neritic environment. Thickness variations show that the floor of

the shallow, epeiric sea in which the Paleocene sediments were deposited had a local topography of swells and depressions. Bender (1974, 1975) adopted lithofacies terms in descriptions of sections and placed reliance on faunal identifications. He indicated a pattern of calcareous sedimentation continuous from the Cenomanian until late Eocene. He described the lithofacies that cover much of the country as phosphorites, oyster lumachelles, chert nodular bands associated with bituminous marl and chalky limestone. Lithofacies terms are used to identify sequences dated micropaleontologically. Lithostratigraphic studies were undertaken by the Jordan Natural Resources Authority (NRA) and the British

431

Sedimentary Basins and Petroleum Geology the Middle East Geological Survey to establish a correlation between the outcrop and subsurface successions and to reduce the confusion caused by the misuse of formal names. The newly established stratigraphic nomenclature was published by Powell (1989 b) and Andrews (1992) and is summarized below and shown in Fig. 9.6.

Subsurface Formations Umm Rijam Formation (Early-Middle Eocene). The formation in the Azraq and Wadi Sirhan sub-basins is penetrated by wells and ranges in thickness from 137 m (450 fi) in well Wadi Sirhan-7 to 311 m (1,020 ft) in Hamza-1. The Umm Rijam Formation is composed of light- to dark-brown, argillaceous, silicified limestone with thin beds and nodules of dark-brown chert and phosphatic limestone (Andrews, 1992). The base of the formation is defined between massive, hard, chalky limestone and the underlying marl and chalky marl of the Muwaqqar Formation (Powell, 1989b). The top of the formation is between

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the interbedded limestone and chert of the Umm Rijam and overlying chalk (Fig. 9.30). The formation was deposited in an outer-shelf, deep-water, pelagic environment. Wadi Shallala Formation (upper Early to Middle Eocene). The thickest subsurface succession is found in the Hamza Graben (well Hamza-16, about 428 m, or 1,404 ft). It consists of soft, buff, grayish-buff and light-brown, marly limestone, and marl with occasional dark-brown chert nodules. In Wadi Sirhan, it is composed of a fossiliferous, marly, partly limestone-chert sequence, argillaceous, marly and siliceous limestone with chert nodules (Fig. 9.30) (Andrews, 1992). The lower contact of the formation is at the change from interbedded limestone and chert to chalk and nummulitic limestone. The top is unconformably overlain by the unconsolidated and arenaceous beds of the Miocene Qirma Formation. The formation was deposited in a mid- to outer-shelf, pelagic environment.

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The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

Surface Formations The differences between the outcrop geology of the Paleogene interval and its subsurface character can be placed in a consistent stratigraphic framework. With a large and scattered outcrop area and varied rock types, a description of this stratigraphic interval is essential and will form a quick reference for those working in the field. Umm Rijam Formation (Middle Paleocene to Middle Eocene?). The formation crops out along the rift margins in southern Jordan, but it is exposed in the Edh Dhira Faulted Monocline in central Jordan. The formation thins from 220 m (722 ft) at Irbid to 122-145 m (400-476 ft) in isolated outcrops along the southern rift margin. It consists of chalky limestone, chalk, chert and microcrystalline limestone. Black chert as beds and laterally coalescing nodules is conspicuous in the lower part. Glauconite and limonite are present locally at the base of the formation (Powell, 1989 b). The base is defined at the junction between the marl and chalky marl and the overlying massive, chalky limestone of the Umm Rijam Formation. The top is marked by the present-day erosion surface or by a regional erosional unconformity at the base of the Oligocene-Miocene Dana Conglomerate. The absence of a shelly, benthic macrofauna, the predominance of planktonic and benthic foraminifera and calcareous nannoplankton, and uniform lithologies suggest a deep-water, pelagic environment. Wadi Shallala Formation (Middle to Late Eocenelate ?Oligocene). The term "Wadi Shallala Formation" was introduced by Parker (1970) for the youngest division of the Belqa Group that crops out in the area of the Yarmouk River. The formation is about 35 m (115 ft) thick in Wadi Shallala and about 130-140 m (426-459 ft) in the Yarmouk Valley, and about 55 m (180 ft) are exposed in the Azraq area (Powell, 1989 b). At Wadi Shallala, the formation is composed of chalk and chalky marl with thin beds of marly limestone that are locally bituminous. In the Azraq area, it consists of 60-70 m (197-230 fl) of marl, 30 m (98 ft) of limestone with concretionary chert and again by dominantly marly strata. The marl is locally bituminous, and there are thin beds containing glauconite and phosphate (Powell, 1989b). The formation was deposited in a pelagic environment. The lower contact of the Wadi Shallala Formation is based on the upward increase in marl and a decrease in bedded chert from the underlying Umm Rijam Formation. The top is overlain by the Oligocene limestone of the Taiyiba Formation. Taiyiba Formation (Oligocene). The Taiyiba sedimentary sequence is well-exposed in Wadi Taiyiba west of Irbid in northwestern Jordan. They also are found in water wells northeast of Azraq. They have a measured thickness of 40.5 m (133 ft) in the three units below, according to Daniel (1963): Upper Unit: 21 m (69 f i ) o f massive limestone with glauconite Middle Unit: 11 m (36 ft) of marl with limonitic

nodules 8.5 m (28 ft) of glauconitic marl, sandy near the top They represent deposits in freshwater lakes that occupied the rift areas. The Taiyiba Formation rests unconformably with an erosional contact upon the Wadi Shallala Formation below. It is overlain unconformably by the sands of the Neogene. Taqiye Marl Formation (Paleocene). The formation reaches a thickness of about 52 m (170 ft) in southeastern Jordan (Edh Dhira Syncline), where two units are identified. The lower unit consists of foraminiferal marl about 27.5 rn (90 ft) thick. The upper unit, about 24.5 m (80 ft) thick, begins with thin beds of chalky limestone with globigerinids, followed by thick, clayey marl with concretions of iron sulphate and veins of gypsum. It is a conformable sequence with the Ghareb Chalk and the overlying Sar'a Chalk-Flint Formation. It also is present as patches in the Jordan Rift Valley and in northwestern Jordan towards the Lebanese border. A similar marl is found in the Beka'a between the Lebanon and anti-Lebanon Mountains. The Paleogene Aaliji Marl closely resembles the Taqiye Marl (Daniel, 1963). Sar'a Chalk-Flint Formation (Lower-Middle Eocene). The formation occurs in the Rift Valley, near Azraq and in northwestern Jordan. The best section is exposed in southeastern Jordan and has been described by Wetzel and Morton (1958) and Daniel (1963), where a thickness of about 247 m (810 ft) is divided into the six units below (from older to younger) Unit 6 : 2 m (6.5 ft) of glauconite and bands of thick, chalky limestone Unit 5 : 1 0 m (33 ft) of chalky limestone with nodules and bands of black flint Unit 4: 108 m (354 ft) of poorly bedded, chalky limestone, some gypsum and calcite veins Unit 3 : 6 4 m (210 ft) of chalky limestone with thin flint beds Unit 2 : 4 2 m (138 ft) of chalky limestone Unit 1 : 2 1 m (69 ft)of thin-bedded, chalky limestone-flint nodules The formation rests conformably over the Taqiye Marl Formation. Ypresian beds are found in the Beka'a Valley and in patches along the Lebanese coast. The equivalent beds in Syria belong to the Jaddala Formation and contain numerous beds of flint. Based upon detailed micropaleontological studies by Koch (1968), the Chalk-Chert Formation covers the Paleocene to Middle Eocene interval. The overlying Ma'an Limestone beds represent the Middle and Upper Eocene. The horizons of nummulitic limestone may range through the Eocene; at the Ma'an outcrops, the beds probably are lower and middle Eocene in age; in the Gharandal outcrop (both locations about 100 km south of the Dead Sea), the age range extends into the Upper Eocene. The ?OligoceneLowermost Miocene Lower Syntectonic Conglomerate occurs above the Upper Eocene beds.

Lower Unit:

433

Sedimentary Basins and Petroleum Geology the Middle East

Ma'an Nummulitic Limestone Formation (uppermost Lower to Middle Eocene). The formation is known

tion, respectively).

in eastern Jordan and in the Wadi Gharandal in the rift valley. The type section was described by Wetzel and Morton (1959) in eastern Jordan, where some 50.5 m (165 ft) of exposed limestone were divided by Daniel (1963) into three units. The lower unit, about 19 m (62 fi) thick, consists of thick, dense, saccharoidal limestone with thin flint bands and rare chalky limestone bands towards the top. The middle unit is a 3.5 m (11.50 ft) clay with coprolites and some plant impressions. The upper unit is 28 m (92 ft) of dense, well-bedded limestone, slightly sandy towards the top, with intercalations of marl in the lower part. The lower part of the formation is conformable with the Middle Eocene Sar'a Formation, but the upper limit generally is an exposed erosional surface.

The formation is found in the Mesopotamian Foredeep in northeastern Syria and is correlated with the Aaliji Formation of central Syria, Iraq and Jordan, as well as with the lower part of the overlying Palmyra Formation. Lithologically, it comprises an alternation of marl, marly limestone, fossiliferous limestone and shale. Asphaltic masses also are encountered. As with the Aaliji Formation, it rests conformably upon the Shiranish Formation and is conformably overlain by the Sinjar Formation. The age of the formation is Montian-Thanetian, based on the foraminifera Globigerina velascoensis, G. pseudomenardi, G. pusilla, G. angulata, G. uncinata, G. trinidadensis and G.

Dhahkiye Chalk Formation (Upper Eocene?Lower Oligocene). The formation is exposed in the

is a partly fossiliferous sequence of sucrosic and calcareous dolomites and limestone rich in Globigerina formosa and Globigerina rex. The formation is well-developed in central Syria, the Euphrates Depression and the Mesopotamian Foredeep. Jaddala Formation (Middle-Upper Eocene). As defined in northeastern Syria and in the Euphrates Depression, this formation consists of about 277 m (900 ft) of microporous and nummulitic limestone with chert nodules in northeastern Syria and marly limestone and marl in the Euphrates Depression. It is conformably overlain by beds of the Upper Eocene-Oligocene Midyat Formation in the Mesopotamian Foredeep, and the Chilou Formation in central Syria and the Euphrates Depression. It also is conformable with the underlying Sinjar Formation. The fossils found in this formation are mainly Globigerina carroazulensis, G. lehneri, G. kugleri, G. formosa and G. rex.

Azraq area, where it was first described by Wetzel and Morton (1958). Later, Daniel (1963) divided the formation into the three units below: Unit 1" 18 m (59 It) of well-bedded chalk and gypsiferous marl Unit 2: 14 m (46 ft) of chalk with glauconite and phosphate nodules Unit 3 : 5 . 5 m (18 ft) of bituminous marl The base of the formation is not exposed. The top, however, is unconformably overlain by beds of the Neogene Dana Formation.

Paleogene of Syria Lying further to the north is the Paleogene section found in Syria, where, as might be anticipated, the sequence closely parallels that described in Jordan, although it often is much thicker and has other formational names (see the following and Fig. 9.8).

Aaliji Formation (Paleocene to Lower Eocene). This formation occurs in central Syria, has a thickness of about 645 m (2,100 ft) and is composed almost entirely of olive-green to dark-gray or dark-blue marl with few thin, marly limestone bands deposited in an offshore, openmarine environment. It rests conformably over the Shiranish Formation, but is covered unconformably by the Tyron Lens, which is part of the Jaddala Formation (Lababidi and Hamdan, 1985). The age of the formation is DanianThanetian, based on the foraminifera Gumerlina-Glo-

botruncana, Globigerina bulloides, G. pseudobulloides, G. triloculinoides and Globoratalia spp. Palmyra Formation (Paleocene to Oligocene). The formation is found in central Syria, where it reaches a thickness of 770 m (2,525 ft) of glauconitic chalk, reefoidal limestone, chalky marl and argillaceous marl with numerous flint beds. Thus, the lower part is equivalent to the Aaliji Formation, as well as to the Chilou and Jaddala formations of eastern Syria. The upper and lower contacts are conformable (Dahek Limestone and Soukhne Forma-

434

Kermav Formation (Paleocene-Lower Eocene).

daubjergensis. Sinjar Formation (Lower Eocene). This formation

Chilou Formation (Upper Eocene-Lower Miocene). The formation is well-developed in central and eastern Syria (Euphrates Depression) and is composed of marly limestone, marl and thin beds of shale and dolomite. It can be divided into two units by the occurrence of a thick (5-8 m, or 16.4-26.3 ft) bed of anhydrite. It is conformable on the Jaddala Formation and is overlain with a sharp contact by the Dhiban Anhydrite. The age of the formation ranges from Bartonian to Aquitanian, based on the foraminifera Globigerina trilobus, G. keugleri, G. ciper-

oensis, G. opima, G. angulisuturalis, G. anguliofficinalis and G. ampliapertura. Midyat Formation (Upper Eocene-Oligocene). In the Mesopotamian Foredeep in northeastern Syria, this sequence, 254 m (830 ft) thick, consists of anhydritic dolomite with thin beds and nodules of anhydrite. Cavities in the beds are filled with green clay. The dolomite may be calcareous and oolitic in places, and it may be more chalky in other areas. It is unconformably overlain by the Jeribe Formation, but rests conformably on the underlying Jaddala Formation.

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

Paleogene of Northern Iraq Different formational names have been adopted for the distinctive facies developed in the deeper parts of the Zagros Trough (Fig. 9.8). Kolosh Formation (Paleocene). Dunnington (1952, cited in Bellen et al., 1959; and Buday 1980) designated a type section of the Paleocene Kolosh Formation in the High Folded Zone of the Zagros. The formation is a succession about 704 m (2,307 ft) thick, beginning with blue shale and green, sandy limestone, which contain Saudi labyrinthica, miliolids and rotalid limestone, and shale grading upward to red shale and sandstone with Lockhartia sp., valvulinids and miliolids. These are followed by more ostracod limestone with Dictyokathina simplex, Lockhartia sp. and valvulinids, and the succession ends with ostracod limestone and marl with Miscellanea miscela, ostracods and miliolids. The Kolosh Formation contains flysch-type clastic beds with planktonic foraminifera in the lower part and larger, benthonic foraminifera in the upper part, which establish a Paleocene age (Kassab, 1976). The lower and upper contacts of the formation are unconformable. The formation is correlated with the Aaliji and the Umm Er Radhuma formations, which are typical of the platform area. Beyond Iraq, the formation continues into Turkey as the clastic facies of the Kermav Formation. In the other direction, into southwestern Iran, the equivalents are in the Amiran Formation and the lower part of the Pabdeh Formation (cf. Buday, 1980).

Sinjar Formation (late Paleocene-early Eocene). The formation is named after the area in Jebel Sinjar where the beds were first described by Keller (1941, cited in Buday, 1980). The recrystallized carbonates of the Sinjar Formation range in thickness from 100 to 200 m (328656 ft) and comprise several different facies, algal, reefal, a lagoonal, miliolid and nummulitic facies. They were deposited in a fore-reef (shelf margin) carbonate environment. Both the lower and upper contacts of the formation are unconformable. The formation found in Syria (Buday, 1980), is equivalent to the Becirman Formation in Turkey and can be correlated with the Taleh Zang Formation of Iran.

Khurmala Formation (Upper Paleocene-Lower Eocene). The Khurmala carbonate section in 1 Kirkuk, about 185 m (607 ft) thick, is partly peloidal and dolomitic and partly finely crystalline limestone, also, there may be relatively abundant anhydrite, gypsum and pyrite with associated intercalated marl and chert. It was deposited in a back-reef (tidal-flat and lagoon) carbonate environment and contains a fauna of miliolids, valvulinids, alveolids, clavulids, small gastropods and algae. There is a gradational contact with the underlying formation, usually the Kolosh, with the facies of the two formations interdigitating, suggesting a potentially diachronous relationship. The top of the formation is an erosional unconformity. Accord-

ing to Buday (1980), there are no proven equivalents outside Iraq, but it would appear to be equivalent to part of the Jahrum Formation of southwestern Iran in age and lithology.

Aaliji Formation (upper Paleocene-lower Eocene). Bellen (1950, cited in Bellen et al., 1959) introduced the name "Aaliji Formation" for a sequence of about 150 m (492 ft) of gray and light-brown, argillaceous marl, marly limestone and shale with fine-grained chert and associated rare glauconite, in the type section designated in well Kirkuk-109. Towards the north and northeast of the type section, a lithological change occurs as the terrigenous admixture becomes first silty, then arenaceous. Towards the southeast and west, more limey, globigerinal mud and chalky, argillaceous limestone developed. Buday (1980) interpreted the formation as typical offshore marine sediments lying between the neritic shoal area on the platform slope in southwestern North Iraq and a series of marginal uplifts with reefs in northeastern North Iraq. The upper and lower contacts of the formation are unconformable. It is an age equivalent of the lower Pabdeh Formation of the Iranian Zagros, the Kermav Formation of southern Anatolia and the Taqiye Marl Formation of Jordan.

Jaddala Formation (late Lower Eocene to Upper Eocene). The formation was described first by Henson (1940, cited in Bellen et al., 1959) as consisting of 350 m (1,148 ft) of marly and microporous (chalky) limestone and marl with occasional thin intercalations of oolitic, peloidal grainstone. It represents deposits laid down in an open-marine environment lying between neritic shoal zones in southwestern and northeastern northern Iraq. The latter zone is over the ridge that separates the platform area from the subsiding Gercus Molasse Trough in the foredeep (Buday, 1980). The formation is bounded by unconformities above and below. The upper parts of the Hibr Formation in northwestern Saudi Arabia are facies- and age-equivalent to the Jaddala, while the equivalent in Iran is the middle part of the Pabdeh Formation (Buday, 1980). Avanah Formation (Middle-Upper Eocene). The formation was first described by McGinty (1953, cited in Bellen et al., 1959) in well Kirkuk-116, where it consists of dolomitized and recrystallized limestone of shoal type with high-energy facies and occasional intercalations of dolomitized, lagoonal limestone, particularly in the lower part (Bellen et al., 1950). The beds formed over the barrier that separated the Gercus Molasse Trough from the open, more marine (Jaddala Formation) to lagoonal (Pila Spi Formation) carbonates lying on the platform to the southeast (Buday, 1980). The lower contact of the Avanah Formation is unconformable, and unconformable Middle Miocene beds rest above. According to Buday (1980), the formation is almost identical in facies and age to the Dammam Formation, with the qualification that an Upper Eocene age has been clearly proven in the beds of the Avanah Formation, whereas the presence of the Upper Eocene has not yet 435

Sedimentary Basins and Petroleum Geology the Middle East been established in the Dammam. The Midyat Limestone of Syria might be partly equivalent to the Avanah, which is correlated also with the Jahrum Formation of the southeastern Zagros (Buday, 1980). Gercus Formation (Middle Eocene). The formation was first described in southern Turkey. In the Iraq High Folded Zone, the formation is about 850 m (2,788 ft) thick, but it decreases towards southeastern northern Iraq where, near the Iranian border, the thickness has diminished to 100 m (328 ft). Bellen et al. (1959) described the formation as consisting of red and purple shale, mudstone, sandy and gritty marl with some soft sandstone and conglomerates. Toward the top, gypsum lenses are found, and rare lignite and sandstone occur towards the base of the sequence. The formation is a typical molasse, deposited in a relatively broad, subsiding foredeep trough. According to Buday (1980), the formation is diachronous, with a Late Paleocene-Lower Eocene age in Turkey and a Lower Eocene-Early Upper Eocene age in southeastern Iraq with no break at the base; however, Bellen et al. (1959) consider that there is an unconformity between the Gercus and the underlying Paleocene Kolosh Formation in the High Folded Zone of the Zagros. There is a break at the top of the formation where it is covered by Miocene deposits, but none where it is overlain by the Pila Spi Formation. The formation can be correlated with the Kashkan Formation of Iran.

Pila Spi Limestone Formation (Middle-Upper Eocene). This formation was described first by Lees (1930, cited in Bellen et al., 1959) from the Pila Spi area of the southeastern margin of the High Folded Zone, where it varies in thickness from 100 to 200 m (328-656 ft). Bellen et al. (1959) describe the formation as consisting of well-bedded, hard, porous, bituminous, algal limestone in the lower part and well-bedded, bituminous, chalky and crystalline limestone with bands of chalky marl and nodular chert in the upper part. It is an inshore, lagoonal sequence filling a marginal, slightly subsident foredeep basin. The lower boundary of the formation usually is gradational, whereas the upper boundary is unconformable everywhere. It has been correlated with the Dammam and Avanah limestone formations, with the Midyat Formation of northeastern Syria, with the Pila Spi Formation in southern Turkey, and with the Jahrum Formation of southwestern Iran (Buday, 1980).

Kirkuk Group (Oligocene) The Oligocene sediments in northern Iraq have been assigned to the Kirkuk Group and divided into numerous formations with relatively restricted distribution and thickness. The group is bounded by unconformities above and below. The individual formations are identified in presumed stratigraphic order and show a progression from reef and back-reef facies into offshore and basinal conditions.

Shurau Limestone Formation (Lower Oligocene).

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The formation was described first by Bellen (1956) from well Kirkuk-109. It ranges in thickness from 18 to 60 m (59-197 ft) and is composed of porous, coralline, reefal limestone in the lower part, grading upwards into gray, dense, black, reefal limestone. The formation follows conformably over the Sheikh Alas Formation and is unconformably overlain by the Baba Limestone Formation. Facies correlatives of the formation in other areas of Iraq are the Anah and Bajawan formations, the Oligocene reefal limestone of Syria and the lower Asmari of Iran (Buday, 1980). Sheikh Alas Formation (Lower Oligocene). The formation was described first by Bellen (1956) from the outcrop area in the northern dome of the Qara Chaug Dagh (North Iraq), where it ranges in thickness from 18 to 50 m (59-164 ft) and consists of porous and occasionally rubbly, dolomitic and recrystallized limestone. In subsurface, the formation consists of fore-reef and reef, marly limestone and organic-detrital limestone with some conglomeratic beds at the base (Hay and Hart, 1959; cited in Buday, 1980). The formation is the oldest of the Oligocene reef and fore-reef facies and may be equivalent to the limestone of the northeastern Syrian Oligocene and of the Oligocene Jahrum and Lower Asmari of Iran (Buday, 1980). It is conformably overlain by the Shurau Limestone, but the basal contact is unconformable. Tarjil Formation (Lower Oligocene). The formation was first described by Bellen (1956) from well Kirkuk-85, where the formation consists of up to 100 m (328 ft) of slightly dolomitized, globigerinal, marly limestone and represents the offshore, basinal deposits of the lower Oligocene. It rests unconformably on the Upper Eocene, but is conformably overlain by beds of the Baba Formation (Middle Oligocene) and is, thus, apparently the facies equivalent of the Sheikh Alas and Shurau formations. The formation may be correlated with the marly limestone sequences in the lower part of the Syrian Oligocene and the marly limestone of the Upper Pabdeh Formation of Iran (Buday, 1980). Bajawan Formation (Middle Oligocene). The formation was described first by Bellen (1956) from well Kirkuk- 109. It consists of about 40 m (131 ft) of tight, reef or back-reef, miliolid limestone, alternating with porous, partly dolomitized, rotalid, algal, coral and reefal limestone with thin, marly interbeds (Bellen, 1956; Bellen et al., 1959; Buday, 1980). The formation was laid down in the reef and partly back-reef area of the shallow Oligocene sea. It follows the Baba Limestone Formation conformably, but transgresses to the northeast and southwest, overlapping pre-Oligocene beds, and is unconformable there. It is unconformably overlain by the Miocene Lower Fars. The formation is correlated with the organic clastic and reefal limestone of the Syrian Oligocene (Ponikarov et al., 1967).

Baba Formation (Middle Oligocene-early Upper Oligocene). The formation was first defined by Bellen (1956) from well Kirkuk-109, where it is 20 m (66 ft)

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic thick. The maximum thickness of 60 m (197 ft) is reached in well Anah-2. The formation consists of porous, dolomitized limestone deposited in the fore-reef area on both the northeastern and southwestern margins of the Oligocene Basin of northern Iraq. It unconformably overlies the Shurau Limestone Formation in the type area, or the Sheikh Alas Formation in the Anah region. Where overlain by the Bajawan Formation, the contact is conformable. The Baba Formation can be correlated with similar facies along the Euphrates in Syria (Ponikarov et al., 1967) and with the Jahrum and Lower Asmari formations in Iran. Anah Formation (Upper Oligocene). The formation, 40-60 m (131-197 ft) thick, was defined first by Bellen (1956). It crops out widely and in subsurface sections and is primarily a reef deposit alternating with back-reef, miliolid facies. It is composed of gray, brecciated, recrystallized, detrital and coralline limestone (Bellen et al., 1959). The lower contact is conformable, and the upper always is unconformable. The formation is correlated with the calcareous Oligocene of Syria and the Jahrum-Lower Asmari oflran (Buday, 1980). Azkand Formation (Upper Oligocene). The formation was introduced by Bellen (1956) for fore-reef facies, usually about 100 m (328 ft) thick, very similar in lithology to the Baba Limestone Formation, with which it is in unconformable contact. It consists of massive, dolomitic and recrystallized limestone (Bellen et al., 1959). The regional correlation of the formation is the same as that of the Anah Limestone Formation (Buday, 1980), which conformably overlies it. Ibrahim Formation (Upper Oligocene). The formation was introduced by Bellen (1956,) from well Ibrahim-1 in the Foothills Zone for 56 m (184 ft) of globigerinal, marly limestone, slightly dolomitized, with minor pyrite and occasional glauconite (Bellen et al., 1959) whose distribution is very little known. It is the offshore, deeperwater facies equivalent of the Upper Oligocene reef facies. It lies unconformably on the Tarjil Formation and is unconformably overlain by the Euphrates Limestone Formation. Paleogene of Southeast Turkey As in many other areas, there appears to be a hiatus between the Late Cretaceous and the Early Tertiary; however, Brinkmann (1976) states that the Cretaceous-Tertiary boundary lies within a thick sequence of marl. The marl is overlain by the equivalent of the red beds found elsewhere in the region. The stratigraphy and facies changes of southeastern Anatolia during the Cenozoic (Fig. 9.7) reflect its proximity to the tectonically active zones. During the first part of the Paleogene, a deep, new oceanic trough, one that had come into existence before the end of the Cretaceous, developed. It received flysch sediments including conglomerates (Germav Formation) derived from the erosion of massifs that had first emerged during

the late Cretaceous. The trough was bordered by Paleocene reefoidal deposits (Sinan Formation) as it shallowed southwards into a shelf sea. As a result of an early Eocene regression, red-bed complexes (Gercus Formation) developed with sediment derived from the north and east. Reefs intercalated and overlain by the red beds also are recorded (Beciram Formation). A regional transgression in the middle and late Eocene resulted in the formation of a broad but shallow carbonate shelf over the entire area, with only the Kirsehir and Menderes massifs remaining unsubmerged. The 200 m (656 ft) shelf carbonates and interbedded, thin, shaly layers of the Midyat (Hoya) Formation, laid down in this shallow sea, are regarded as a partial equivalent of the lower part of the Asmari Formation. They intercalate locally with, and are overlain by, mainly evaporite beds of the Germik Formation that pass laterally into a chalky marl facies. The Oligocene of Anatolia was mainly a continental period, and there was marine deposition only in limited areas and for short times. Early Miocene uplift in southeastern Anatolia separated the Mediterranean Province from the Indo-Pacific region.

PART 2: THE NEOGENE OF THE MIDDLE EAST Eastern Arabia appears to have undergone uplift and subaerial erosion from the late Paleogene until the early Neogene, and the mountains and the foothills region of northern Oman have been emergent since the Miocene. As a result of erosion, extensive gravel pediments of late Cenozoic conglomerates, sandstone and shale molasse developed at elevations of 4,000 m (13,000 ft) (Morton, 1959; Glennie et al., 1974). Even today, a continental desert environment with sabkha deposits persists in the area. Deposition was continuous only in the Ras al Khaimah Trough, where deeper-water sedimentation was replaced by shallow-water carbonates of the later Dammam and Asmari limestone formations. The Asmari limestone is the main reservoir unit in much of southwestern Iran and northern Iraq, where it has been described as massive, dense limestone with rather poor primary and secondary porosity, but which, as a result of fracture porosity, are prolific reservoirs in both areas. As the formation provides continuity between the Neogene and Paleogene in the Ras al Khaimah Sub-basin, a description already has been given. In the northern Arabian Gulf, in Kuwait, southeastern Iraq, Saudi Arabia and parts of Iran, the equivalent deposits are largely clastic. These are late Oligocene-early Miocene sediments that represent the sand transported out of an easterly directed wadi system onto a carbonate shelf. They probably followed the same trend as the modern wadi system, and similarly also were probably intermittent deposits that may have been carried far out onto the carbonate platform during major flood stages. There is some

437

Sedimentary Basins and Petroleum Geology the Middle East confusion as to whether they should be regarded as equivalent to the Asmari or Gachsaran formations of the southern Arabian Gulf; for example, the Ahwaz Sand of Iran progressively replaces only the "Middle" and "Lower" Asmari and not the Lower Miocene "Upper" Asmari, whereas the Ghar Sand of Kuwait, the lateral equivalent of the Ahwaz Sand, is overlain by a sandy unit of early Miocene age (Owen and Nasr, 1958). Clastics of the same age are recognized only in the western, onshore part of Abu Dhabi. Close to the shore line in Saudi Arabia, the shallow-marine component dies out altogether, and the sequence is replaced by a non-marine unit (Powers et al., 1966; Powers, 1968), whereas the sands interfinger with the Asmari limestone in southwestern Iran. Because of a lack of age-diagnostic fossils, correlation with some Neogene formations in the northern Arabian Gulf is based on the lithological and general stratigraphic character with varying degrees of confidence and accuracy. In southern Iraq and Kuwait, the Ghar and Dibdibba formations comprise essentially marginal to non-marine, coarse clastics, which also lack age-diagnostic fossils. The coarse clastics of the Hadrukh Formation of Saudi Arabia are presumed to correlate with those of the Ghar Formation. The Dibdibba Formation is presumed to correlate with the Hofuf and Bahr formations of Saudi Arabia. The Jeribe Formation of northern Iraq is presumed to correlate with the Dam Formation (carbonates and evaporites) of Saudi Arabia. During the early and Middle Miocene, the ridge separating the marine molasse basin persisted. It extended through southeastern Turkey into Iran to form the broad but relatively shallow basin in Syria and Iraq, disappearing only during the late Miocene-Pliocene. The fill of the early Miocene Basin resting on the shelf can be treated as two sub-cycles. During the lower sub-cycle, the basin occupied the region now occupied by the Imbricated Zone, High Folded Zone and the northeastern part of the Foothills Zone. The deeper parts of the basin lay in the zone of the present folded part of the Foothills Zone, over the stillsubmerged Khleissia Uplift and stable shelf and over the Mesopotamian Zone. South of the Euphrates, the stable shelf also was submerged and folded, but remained a relatively shallow, littoral area. Sedimentation began with clastics followed by calcareous deposits over the broad, shallow littoral zone, whereas in the deeper parts, the initial sediments were calcareous and marly, later passing to lagoonal evaporites (e.g., Dhiban Formation). Continuing movement during the early Miocene in the northern part of the Middle East led to the formation of local north-south-oriented basins isolated from the open sea. During this sub-cycle, the transgression did not reach the former intraplatform, basinal area (Buday, 1980). However, the extension of the basin southeast into Iran was extensive, and the subsiding basin was filled with deposits of the Gachsaran evaporite facies. Further slight relaxation of stress during the late-Early Miocene was reflected by renewed transgression, which reached the

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former intraplatform basin, which had the character of an intermontane molasse trough (Buday, 1980). The configuration of the Miocene Basin changed, and although the sea no longer reached the stable shelf to the south, it did transgress the entire Foothills Zone and much of the High Folded Zone. The sediments deposited were similar to those of a rapid sub-cycle, a short, calcareous, shallowwater reef phase followed by a lagoonal phase at a time when block movements had again resulted in separation into individual lagoons. The lagoons were once again the site of evaporite deposits, and some units, such as the Lower Fars Formation, are notably thick. The sub-cycle was ended by a progressively greater influx of clastic sediments eroded from the uplifted northeastern folded areas in northern Iraq and northwestern Iran, marking a typical foredeep basin west of the Iranian accretionary wedge or west of the subduction zone that brought Tethys sedimentation to a close. The late Miocene and Pliocene in the northern part of the Middle East were times of paroxysmal thrust movements and orogenic uplift of the Thrust, Imbricated and High Folded zones (that is, of the late Tertiary foredeeps) and of the uplift of the entire stable shelf, signalling the deposition of a thick, terrigenous molasse in the still-subsiding foredeep. By the end of the Pliocene, uplift reached the former foredeep, and molasse sedimentation ended. The early Miocene to Pliocene sediments generally formed in a series of elongated basins parallel to the Zagros and Oman ranges, separated from each other and from the open sea to the southeast by shallow "sills." In the Arabian Gulf, the Qatar Arch was a positive area separating basins to the northwest and southeast. In the northern basin, the Upper Asmari limestone was deposited, whereas the southern basin, partly cut off from the open sea (as indicated above), became the site of deposition of the Gachsaran evaporites. The Arabian Gulf basins are asymmetrical with the steep flank on the northeastern side, while to the south and west, the shallowly dipping flank sediments transgressed over the margins of the Arabian Shield. The clastics deposited on this shallowly dipping limb gave way to pelagic marl and shale in the more central parts of the basin, where subsidence was more rapid. These restricted basins, which became progressively more saline during the early Miocene with the development of density layering as a result of restricted inflow and high evaporation rates, culminated in the deposition of gypsum, halite and, in extreme cases, even potash salts. Subsequently, a marine influx from the southeast returned the region to normal-marine-environment conditions, with widespread carbonate deposition characteristic of the middle Miocene. During the Late Miocene, there was a period of general regression, marked by the development of continental clastics whose deposition continued through the Pliocene. In southern Iraq and onshore Qatar, the Late Miocene is represented by the Upper Fars, giving way to the non-marine Bakhtiari Formation in the Pliocene.

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

The Neogene of the Central and Eastern Arabian Platform

The only fossils recorded by Powers et al. (1966) are

Corbicula sp. and Melania sp. in sediments deposited in a freshwater, lacustrine environment.

Neogene of Saudi Arabia (Fig. 9.6) Hadrukh Formation (Lower Miocene). The formation takes its name from the type locality at Jabal al Haydarukh (2704'36" N, 49~ E) in Saudi Arabia, where there is a sequence of about 84 m (260 ft) of sandy limestone and calcareous sandstone with chert and gypsum present in minor amounts. The base rests unconformably upon Dammam limestone. The top of the formation is placed at the contact of the calcareous sandstone below and the basal, Echinocyamus limestone of the Dam Formation (Powers et al., 1966) above. Rocks of the Hadrukh Formation are non-marine, except for a few thin layers near the top of the formation, which contain poorly preserved, marine molluscs. The Ghar Formation of Kuwait and southern Iraq (Owens and Nasr, 1958) is regarded as the time equivalent of the Hadrukh Formation. Dam Formation (Middle Miocene). The type section lies in Saudi Arabia at Jebel al Lidan (26~ N, 49027'42" E) and consists of 91 m (298 ft) of pink, white and gray marl; red, green and olive clay with minor sandstone interbeds; and microporous (chalky) limestone and coquina containing common marine fossils (Powers et al., 1966) of shallow-marine origin. The base cOnformably overlies the Hadrukh Formation, and the top lies at the contact between the marl and marine limestone of the Dam with the argillaceous sandstone and gravel of the basal Hofuf Formation. Hofuf Formation (Late Miocene-Early Pliocene). The formation is named after the Saudi Arabian town of A1 Hofuf (25o22 ' N, 49~ ' E), where the beds are continental and consist of 95 m (312 ft) of a lower sequence of greenish-gray marl, red conglomerate and white boulder and pebble limestone. The upper sequence of white, chalky and sandy limestone alternating with red and white, argillaceous sandstone is capped by gray, marly limestone, with limestone boulders in a marly, quartz-sand matrix. The formation is unconformably overlain by Quaternary and Holocene surface deposits such as terrace sands and conglomerates, marly sandstone, sandy limestone and sabkha deposits over most of Saudi Arabia, except in the northwest, where there are basic volcanic flows. Kharj Formation (Plioeene). The formation takes its name from A1 Kharj in central Saudi Arabia, where the type section recorded by Bramkamp et al. (1956, cited in Powers et al., 1966) at 23034 ' N, 47~ ' E measured 28.1 m (92 ft) and is described below (Powers et al., 1966): 9 3.4 m (11 fi) of botryoidal limestone (suggestive of algal origin) 9 1.8 m (6 ft) of coarse limestone conglomerate (rectangular clasts) 9 22.9 m (73 ft) of poorly sorted sand, gravel and conglomerate with irregularly bedded, limestone pebbles and a calcareous cement

Neogene of Qatar (Fig. 9.6) Lower Fars Formation (lower to middle Miocene). These Miocene sediments are a marginal development of the thicker and more typical Fars deposits, which can be traced in a continuous development to the type area in Iran. The formation has a thickness of about 79 m (260 ft) and was divided by Sugden and Standring (1975) into two units. The lower unit, 25 m (82 ft) thick, consists of partly sandy marl interbedded with sandy limestone, sandstone and shale. There are thin, limonitic beds and nodules in the marl near the base. The upper unit, 54 m (177 ft) thick, is composed of chalky (microporous) limestone and marl, followed by marl with thin beds of gypsum in the middle of the succession and capped by sandy limestone. Dam Formation (Middle Miocene). The formation is subdivided into lower and upper units. The lower unit consists of 30 m (98 ft) of marine limestone and clay containing Echinocyamus, large foraminifera and bryozoa. Large, secondary gypsum crystals occur, and fissures are halite-filled. The upper unit, some 48 m (157 ft), is made up of limestone and clay containing a lagoonal fauna. The vertical and lateral change in facies, marked by the diminution of clastics and the increase in carbonates, indicates a lateral change to a more marine environment in Qatar than in Saudi Arabia. The lower unit was deposited in a shallow-marine environment with a relatively high rate of terrigenous sedimentation, normal salinity and alkaline chemical character. The upper unit formed under relatively highly evaporitic conditions in a shallower, more saline environment (Hilmy et al., 1987).

Hofuf Formation (Late Miocene-early Plioeene). The formation is compositionally similar to that in Saudi Arabia with the predominance of clastic sediments, sometimes pebbly (pebbles of quartz, jasper and limestone), but considerably thinner, a mere 10 m (33 ft) thick. The conglomerate at the top of the unit has a calcareous cement. The sediments were deposited in a continental environment and rest conformably upon the Dam Formation.

Neogene of Bahrain (Fig. 9.6) Jabal Cap Formation (Miocene). This formation is about 122.4 m (400 f t ) o f massive, dolomitic limestone with a finely laminated structure. It contains fragments of corals and algae and is interbedded with cross-bedded sands. The sand contains mud clasts, coated carbonate grains, ooliths and shell fragments, reflecting deposition under very shallow-water conditions (Fig. 9.31). Ras al Aqr Formation (Pleistocene). This very thin (3.5 m, or 11.2 ft) Pleistocene unit consists of fine- to medium-grained limestone; slightly leached, shelly, oolitic limestone with cerithiid gastropods; quartzose sandstone; massive, often conglomeratic, dolosiltites; muds; and 439

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440

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic thinly bedded, fine- to very fine-grained, dolomitized calcisiltites with many bivalve shells of coastal sabkha and beach origin.

Neogene of the United Arab Emirates(Fig. 9.6) Gachsaran Formation (Early Miocene). The formation essentially is early Miocene in age and consists of three units totalling 481 m (1,580 ft): Unit 3: upper, massively bedded anhydrite with interbedded, bioclastic dolomite, dolomitic limestone and gray-green to brown mudstone Unit 2" middle sequence of interbedded, dolomitic limestone; limestone, calcareous mudstone and marl that may be variously sandy, silty or bioclastic; and interbedded, calcareous sandstone and siltstone with thin, nodular bands of anhydrite Unit 1: lower anhydrites with interbedded, sandy dolomite and mudstone and thin beds of sandstone The lithological and faunal data are consistent with deposition in a shallow-marine to brackish-water environment, and the presence of plant debris suggests an influx from a nearby continental area. The Gachsaran is overlain conformably by the Mishan Formation and conformably overlies the Asmari Formation. Mishan Formation (Early to Middle Miocene). In the Ras al Khaimah Sub-basin, the formation is divided into three units. The lower unit is a microporous, bioclastic limestone with bands and nodules of gypsum, thin, calcareous sandstone and mudstone overlain by green-gray mudstone grading upwards into the middle unit of soft marl containing gypsum nodules and becoming silty towards the top. The uppermost unit consists of light-gray, porous, shelly limestone with thin marl that again contains gypsum nodules. In the eastern Abu Dhabi offshore areas, only two members are recognized in the Mishan Formation, which is there some 290 m (951 ft) thick. The lower member, about 132 m (432 ft) thick, consists of chalky, fossiliferous limestone with thin beds of argillaceous limestone and thin beds of calcareous quartz sandstone. The upper member, about 157 m (516 ft) thick, consists of lime mudstone with thin beds of calcareous shale or anhydritic limestone, followed upwards by foraminiferal limestone with thin, silty clays and calcareous shale. The Mishan is overlain unconformably by sandy, conglomeratic PlioPleistocene deposits. The base is conformable over the Gachsaran Formation. Hofuf Formation (? Miocene). This formation, sometimes called the Oligo-Miocene Clastics or Miocene Clastics by Alsharhan (1990) or the Baynunah Formation by Whybrow (1989), is known only in the central and western parts of onshore Abu Dhabi. It has a thickness of about 110 m (360 ft) and consists of poorly consolidated, non-marine to marginal-marine, quartzitic and calcareous sandstone with marl, thin beds of lacustrine limestone and nodules and microcrystalline gypsum. The clastics probably were deposited as continental to marine beds built out

by an easterly flowing wadi system, one that presently is followed by the modern wadis. The stream probably flowed intermittently, but during major floods carried clastic sediments far out onto the carbonate shelf. Plio-Pleistocene sediments in the U.A.E. are widespread and characterized by cross-bedded, calcareous sandstone, sandy limestone and miliolites. Recent deposits are dominated by carbonate sands and lagoonal dolomitic muds, intertidal algal mats and supratidal sabkha gypsum, anhydrite and halite.

Neogene of Oman Miocene Conglomerate and Younger Deposits

In South Oman, the Miocene clastic and carbonate sequence lacks age-diagnostic fossils and is composed of an alternation of limestone conglomerates, pink, marly limestone with subordinate amounts of chalk and yellowish marl. The rounded pebbles and cobbles are in a calcareous sand and clay matrix (Beydoun and Greenwood, 1968; Hawkins et al., 1981). As the mountains and foothills region of central Oman have been emergent since the Miocene, extensive sheets of gravel have developed in the foothills and valleys (Morton, 1959). Drilling in the Gulf of Oman has shown the presence there of up to 4,000 m (13,100 ft) of late Cenozoic molasse, conglomerate, sandstone and shale (Glennie et al., 1974). The post-Miocene deposits consist of raised beaches, river terraces, fanglomerate and lacustrine deposits, alluvial gravel, silt and aeo, lian deposits resting unconformably on older formations (Beydoun, 1964; Hawkins et al., 1981). Fanglomerates are the dominant lithofacies in southern Oman.

The Neogene of Southern and Western Arabia Neogene of Western Saudi Arabia (Red Sea Region) As a result of late Oligocene to early Miocene movements, two sub-basins developed in the Red Sea: the Midyan Sub-basin in the northernmost Red Sea at the junction of the Red Sea and Gulf of Aqaba, and the Jaizan Sub-basin in the southern Red Sea just north of the Saudi Arabian/Yemen border. Both sub-basins received a predominantly coarse clastic fill, but there were intervals of carbonate and evaporite deposition and some shale horizons in both. Drilling in the Midyan Sub-basin has revealed commercial quantities of condensate, wet gas and minor oil, whereas drilling in the Jaizan Sub-basin has been less successful, although waxy, paraffinic oil and drygas shows were recorded (Mansiyah well). The lithostratigraphy of these Neogene sediments summarized here was described by Hughes and Filatoff (1995) (Fig. 9.27). The basal Miocene, of marine and marginal synrift sediments, is unconformably overlain by Lower Miocene deep-marine siliciclastics and Early to

441

Sedimentary Basins and Petroleum Geology the Middle East Middle Miocene interbedded evaporitic, siliciclastic and carbonate deposits with deep-marine gypsum and halite in the middle Miocene. Freshwater to marginal-marine beds occur in the Late Miocene, and the Pliocene to Pleistocene sequence is dominated by carbonates and siliciclastics resting unconformably on the underlying sediments. Tayran Group (Lower Miocene). The group is widespread along Red Sea coastal areas, although largely replaced by volcanics in the south. It can be divided into the following four formations: 4) Musayr Formation (Lower Miocene). The formation, which occurs in the Midyan area, rests unconformably on basement, overlapping the A1 Wajh Formation siliciclastics and Yanbu Formation evaporites. It can be divided into two units. The lower is a predominantly siliciclastic unit laid down in an intertidal environment. The upper unit is dominated by bioclastic carbonates with a rich macro- and microfauna deposited in a shallow, inner, neritic carbonate platform. 3) Yanbu Formation (Lower Miocene). The formation, present in exploration wells and up-holes north of and including the Yanbu area, overlies siliciclastic beds of the A1 Wajh Formation. It consists of laminae and crystals of anhydrite disseminated in a thick halite sequence, the deposits of a hypersaline, marginalmarine environment, sabkhas and salinas. 2) AI Wajh Formation (Lower Miocene). The formation is widespread in the Red Sea coastal basins, resting unconformably on older stratigraphic units. It consists of interbedded, coarse- and fine-grained, siliciclastic deposits and a fluvio-lacustrine facies with marginal-marine (estuarine) pulses. 1) Jizan Volcanic Formation (Lower Miocene). These volcanics and intrusive rocks in the Jizan and Ghawwas regions also are found in exploratory well Jizan North-1 and intrude the beds of the Tayran and Burqan formations. The formation is made up of basalt, dolerite flows and intrusions and volcaniclastic deposits, as well as shale. Burqan Formation (Lower Miocene). Present throughout the Saudi Arabian Red Sea area, it rests disconformably upon the beds of the Tayran Group. It consists of calcareous shale and claystone with interbedded sandstone and thin limestone, grading laterally into thickly bedded sandstone. The sediments of the Burqan Formation were deposited in a deep-marine, upper bathyal to deep, outerneritic environment based on the presence of rich and diverse, planktonic foraminifera with deep-marine, benthonic foraminifera (Hughes and Filatoff, 1995). Magna Group (Lower to Middle Miocene). Widely distributed in the Saudi Arabian Red Sea area, these siliciclastic and carbonate beds have a more localized distribution. This group is divided into the two formations below: 2) Kial Formation (Middle Miocene). The formation rests conformably upon the Jabal Kibrit Formation and consists of a thinly bedded, fine-grained, silici-

442

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clastic-evaporitic association, deposited in a moderately deep-marine environment with shallow carbonate platform facies locally developed. Two episodes of deep-marine extreme hypersalinity caused precipitation of gypsum in deep-marine conditions. Jabal Kibrit Formation (Lower to Middle Miocene). It consists of a lower part of interbedded shale and anhydrites, which grade upward to thick beds of calcareous shale and mudstone. It rests unconformably over the Burqan Formation. These sediments were laid down in a deep-marine, outer-neritic to possibly upper-bathyal environment. Hughes and Filatoff (1995) concluded that the evaporitic unit in the lower part of the Jabal Kibrit is the result of deepmarine precipitation from an extremely hypersaline environment, and that the coarse siliciclastic and carbonate components are the products of penecontemporaneous, downslope transport from a shallowmarine-shelf source. Kamal and Wyn Hughes (1995) recognized the carbonates as a separate member, the Wadi Waqb Member, and assigned it to the base of the uppermost Lower Miocene.

Wadi Waqb Member (basal uppermost Lower Miocene): The carbonate reservoir member of the Jabal Kibrit Formation consists of 51 m (168 ft) of a yellowish-gray wackestone/packstone sequence in which 14 local, informal, biostratigraphic zones are recognized by Kamal and Wyn Hughes (1995). Dolomitization is restricted to the mud component, and the porosity of the beds can be related directly to their dolomite content. The major part of the packstone component consists of shallow-marine detritus emplaced by carbonate debris flows in an outerslope-upper-bathyal environment (-200 m). This interpretation is consistent with the mixing of benthonic and planktonic foraminifera, rhodoliths not in a growth position, and the absence of shallow-water, sedimentological criteria. It is regarded as equivalent to the Jabal Kharamoul Member of the Kareem Formation in the Gulf of Suez. Mansiyah Formation (Middle Miocene). The formation is distributed widely along the Saudi Arabian coast of the Red Sea. It rests conformably on the underlying Kial Formation. Faulted or unconformable contact relationships are present in areas adjacent to halokinetic glide planes. The formation consists of halite and anhydrite with scattered, thick beds of fine-grained siliciclastics, deposited in moderately to very deep-marine, and extremely hypersaline, conditions. Hughes and Filatoff (1995) determined that the marine environment was indicated by the presence of dinoflagellate cysts in the interevaporitic shale; anoxic conditions are suggested by an abundance of pyrite-impregnated, amorphous kerogen.

Ghawwas Formation (Middle to Upper Miocene). The formation is distributed widely along the Saudi Red Sea region, where it rests conformably upon the Mansiyah Formation. It consists of coarse- to fine-grained, siliciclas-

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic tic beds, containing scattered layers of anhydrite, which were deposited in an intertidal to shallow, inner-neritic environment. Sabkha conditions developed periodically. Lisan Formation (Pliocene to Pleistocene). The formation is distributed widely along the Saudi Arabian Red Sea coast, where it rests disconformably and possibly unconformably upon the Ghawwas Formation. It consists of coarse- and fine-grained siliciclastics and carbonates. The depositional environment ranges from supratidal, through intertidal and shallow-marine, carbonate platform to upper bathyal, based on the variable character of the foraminifera.

Neogene of Yemen Aden Volcanic Series (latest Miocene-Holocene). The sequence in the southern provinces of Yemen, exposed from the Bab al Mandab eastward to the Sayhut area, consists of basaltic flows and pyroclastics with numerous cinder volcanic cones. The basaltic lava is associated with ash and agglomerate, and the basalt varies from scoriaceous, vesicular and ropy lava mixed with pyroclastics, to a massive and columnar type (Greenwood and Bleakley, 1967; Beydoun and Greenwood, 1968). These volcanic flows rest upon basement rocks or Jurassic and Cretaceous sedimentary rocks. In the northern provinces of Yemen, the Aden Volcanic Series consists of basic volcanic ash and lapilli, vitrophyric basalt, basaltic lava flows with phenocrysts of plagioclase, acidic and welded ignimbrite, trachyte, minor olivine and pyroxene and peralkaline obsidian These rocks rest unconformably on the Precambrian basement, Tawilah Group (Cretaceous-Paleocene) or Yemen Volcanics, but are not covered by any other rock units. The Quaternary intraplate, alkaline magmatism is about 100-250 m (328820 fi) thick of basaltic, plateau lava peppered with many scoria cones of strombolian and phreatomagmatic eruptions (Davison et al., 1994).

The Neogene of Northeastern Arabia Neogene of Kuwait (Fig. 9.8) Ghar Formation (Early Miocene). The outcrop thickness is only 33 m (108 fi), but it increases in subsurface and ranges from 195 to 260 m (640-853 ft) of marine to terrestrial, coarse-grained, unconsolidated sandstone with a few thin, sandy, limestone, clay and anhydrite layers. At the formation's base, above the eroded top of the Dammam Formation, is a brown, marly, coarse-grained sandstone with subordinate, fine, white, crystalline limestone resting unconformably over the Dammam Formation and in gradational contact with the Lower Fars Formation. Lower Fars Formation (lower Middle Miocene). This formation is equivalent to the upper part of the Dam Formation in Saudi Arabia. Ranging in thickness from 61 m (200 ft) in the west to more than 183 m (600 ft) in the

eastern area into the offshore, it is absent in the south. It consists of fine- to coarse-grained, conglomeratic sandstone, variegated shale and thin, fossiliferous limestone. In northern Kuwait and southern Iraq, anhydrites, gypsum, clays and marl, as well as marine, shallow-water limestone indicative of shallow, offshore conditions, become more common. Clay balls at the base of the sandstone suggest erosion and redistribution of bottom sediments (Owen and Nasr, 1958). The depositional environment suggested is that of a relatively rapidly sinking basin frequently separated from open-marine conditions by rising ridges. The basal contact of the formation is conformable, but the upper contact is gradational and probably diachronous. Dibdibba Formation (Late Miocene-Pliocene). The term was first used by MacFadyen (1938, cited in Fuchs et al., 1968) and applied to a type locality A1Dibdibba Plain, which extends from Basra to the northern part of Kuwait. The formation reaches its maximum thickness of about 220 m (600 ft) in Kuwait. Lithologically, the formation consists of a fluviatile, ungraded and often cross-bedded sequence of sands and gravels accompanied by subordinate intercalated beds or lenses of sandy clay, sandstone and conglomerate carbonate or evaporite, cemented siltstone. The contact of the lower part with the Lower Fars Formation is gradational. It is overlain by unconsolidated Recent and sub-Recent sediments of varying lithologies.

Neogene of Southern Iraq (Fig. 9.8) Ghar Formation (Early Miocene). The Ghar Formation ranges in thickness from 100 to 150 m (328-492 ft) and was described first by Owen and Nasr (1958) in well Zubair-3 in Iraq, where it consists of sands and gravels with rare anhydrite, clay and sandy limestone interbeds (Bellen et al., 1959). The Ghar Formation was deposited in a littoral environment and most likely was partly deltaic in the type area. The lower contact is unconformable with the Dammam Formation, and the upper contact is a gradational passage into the Lower Fars Formation. Lower Fars Formation (Middle Miocene). It consists of more than 900 m (about 2,952 ft) of anhydrite, gypsum and salt interbedded with limestone and marl and relatively fine-grained clastics (Owen and Nasr, 1958; Bellen et al., 1959). The formation represents the deposits of a relatively strongly subsiding basin, with sparse fossils because of the hypersaline character of the basin. The lower contact of the formation is conformable with the Jeribe Formation, and the upper contact is gradational. The formation is distributed widely in Iraq and Syria and extends to the Syrian-Turkish border (Weber, 1963). Towards the southeast, the formation extends into Iranian territory, and in Turkey, its age and facies equivalents are included in the molasse. In Kuwait and Saudi Arabia, the formation has its equivalents in the Lower Fars and Dam Formations respectively. Upper Fats Formation (Upper Miocene). In Iraq,

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444

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thin-bedded limestone and marl 116 m (380 ft) of salt with anhydrite and thin, limestone intercalations Member 1: 40 m (130 ft) of interbedded anhydrite and limestone with associated bituminous shale. In the Fars Province, the formation is clearly diachronous, younging from southeast to northwest, and evaporites gradually replace limestone in the upper part of the Fars Formation. Razak Formation (Early Miocene). The Razak Formation is named after a village in the Fars Province, where it consists of 805 m (2,639 ft) of variegated red, gray and green, silty marl interbedded with subordinate silty limestone and minor sandstone (Fig. 9.34). It rests conformably upon the Asmari Formation and is conformably overlain by the limestone of the Guri Member of the Mishan Formation; both contacts are transitional. The formation is developed best in the interior Fars Province and to the south and southwest, where it interfingers with the Gachsaran evaporites. Mishan Formation (Middle to Late Miocene). The formation takes its name from the village of Mishan in the Khuzestan Province of Iran, where about 752 m (2,825 ft) of marl and limestone are found. The basal part of the formation is made up of 62 m (203 ft) of alternating limestone and gray marl followed by 690 m (2,622 ft) of gray marl alternating with more resistant, shelly limestone (Fig. 9.35) (James and Wynd, 1965; Setudehnia 1972). The basal contact of the limestone and marl of the Mishan Formation with the gypsum of the underlying Gachsaran Formation is sharp. Locally, the basal beds show a facies change, passing laterally into a massive, reefal limestone, the Guri Limestone Member. The upper contact with the Agha Jari Formation is transitional and diachronous. The beds of the Mishan Formation were deposited in a linear, marine trough trending northwest to southeast in the Zagros Basin; in this trough, the diachronous replacement of the carbonates of the Mishan Formation by the clastics of the Agha Jari Formation can be observed in Lurestan Province, southeastern Iraq, Kuwait and Saudi Member 2:

A A A A A AAAAj

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Fig. 9.34. Lithostratigraphy of the Razak Formation (Lower Miocene) at the type section on the northern flank of the Kuh-e Jahrum, Iran (modified from James and Wynd, 1965). ~

=r

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I

Fig. 9.33. Lithostratigraphy of the Gachsaran Formation (Lower Miocene) from the type section in the Gachsaran Oil Field, Iran (modified from James and Wynd, 1965). tion was named in Iran from the Gachsaran Oil Field, where it is best developed. The name was applied to a thick and extensive development of evaporitic sediments with marine intercalations of varying importance. It is economically important as the seal over Asmari reservoirs. The formation, as described by James and Wynd (1965) and Setudehnia (1972), consisted of interbedded anhydrite and limestone associated with bituminous shale, subordinate salt and red and gray marl. The Gachsaran Formation is a tectonically incompetent unit highly subject to solution effects and is characterized by extreme mobility in response to differential pressure. Because of these characteristics, a complete sequence seldom is found (Setudehnia, 1972). Watson (1960, cited in Setudehnia, 1972), compiled the following composite section for the Gachsaran Formation based on well data from Gachsaran Field (from youngest to oldest) (Fig. 9.33): Member 7: 140 m (460 ft) of alternating anhydrite; gray, marly and argillaceous limestone Member 6: a lower unit of about 104 m (340 ft) of alternating marl and limestone, followed by a middle unit of about 121 m (397 ft) of salt and anhydrite, and ending with an upper unit of 61 m (200 ft) of anhydrite with gray to red, marl intercalations Member 5: 323 m (1,060 ft) of red to gray marl alternating with anhydrite Member 4: 874 m (2,780 ft) of salt with gray marl, limestone and anhydrite Member 3: 229 ,m (750 ft) of thick anhydrite and subordinate salt overlain by alternating anhydrite,

445

Sedimentary Basins and Petroleum Geology the Middle East eastern Fars Province. Z~

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Bakhtiari Formation (late Pliocene-Pleistocene). The Bakhtiari Formation takes its name from the mountains in the northeastern Khuzestan Province. The name "Bakhtiari" was first applied to the chert and limestone conglomerates interbedded with sandstone that lie unconformably upon the Fats sediments of the Lurestan and Khuzestan provinces (Pilgrim, 1908; James and Wynd, 1965). It is an almost wholly terrigenous, clastic unit ranging in grain size from a silt grade to boulder conglomerate, with a thickness of about 518 m (1,700 fi). The lower 83 m (600 ft) of the formation consist of massive conglomerate interbedded with coarse, cross-bedded sandstone and grit followed by 335 m (1,100 ft) of massive, cliff-forming conglomerates with lenticular, cross-bedded sandstone and grit derived from the erosion of the folded Miocene-

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Agha Jari Formation (Late Miocene-Pliocene). The formation, which takes its name from the Agha Jari Oil Field in the Khuzestan Province, consists almost entirely of terrigenous clastics ranging from silt sizes to boulder conglomerates between 650 and 3,250 m (2,132-10,660 fi) thick. The principal lithology consists of gray, calcareous sandstone with veins of gypsum, red marl and siltstone. As indicated above, the basal contact with the Mishan Formation is both transitional and diachronous. The upper contact with the conglomerates of the Bakhtiari Formation is unconformable. In the Lahbari Syncline in the Khuzestan Province, a facies equivalent of the upper part of the Agha Jari Formation consists of 1,576 m (5,170 ft) of buff, weathering, gypsum-veined siltstone and silty marl with interbedded sandstone, and the upper 773 m (2,535 It) is formed by pebbly sandstone and siltstone assigned a locality name, the Lahbari Member (Fig. 9.36). The conglomerates of the Bakhtiari Formation rest on this member, which finds its principal development in southwestern Lurestan. In Lurestan and Khuzestan, the formation was deposited in a lacustrine to estuarine environment. Partly marine in the Fars Province, it passes into the Hofuf Formation of Saudi Arabia and the Dibdibba Formation of Kuwait.

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Fig. 9.36. Lithostratigraphy of the Agha Jari Formation (Upper Miocene-Pliocene), Iran. The lower part is taken near the Agha Jari Oil Field, while the Lahbari Member is measured at Tang-e Tukab on the northeastern flank of the Haft Kel Anticline (modified from James and Wynd, 1965). 446

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Fig. 9.37. Lithostratigraphy of the Bakhtiari Formation (PlioPleistocene) at the type section north of Masjed-e Sulaiman, Iran (modified from James and Wynd, 1965).

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic Pliocene Orogenic Fold Belt (Fig. 9.37). The basal contact with the Agha Jari Formation is an angular unconformity or disconformity; the top of the unit is an erosional surface and is covered by alluvial material. The formation was deposited in a strongly subsiding foredeep and, thus, can be considered a freshwater molasse. The Miocene-Pliocene Zagros Orogeny was followed by the erosion of folded and uplifted materials producing a great quantity of coarse clastics that deposited to form the Bakhtiari Formation (Setudehnia, 1972).

The Neogene of the Northern Arabian Platform Neogene of Jordan (Fig. 9.6)

and consists of flood lavas, dyke systems and pyroclastic sediments. Some volcanic centers have been identified. Many of the fissures still can be recognized as long rows of cones. Bender (1974) recognized major phases of intrusion, of which the lower three are restricted to Jordan, and the others are seen in both Jordan and Syria. The flows overlie middle and upper Eocene limestone, and individual flows may be distinguished through the preservation of soil horizons. The youngest of the flows are post-Miocene, and activity may have persisted beyond the middle Pleistocene into historic time. However, no distinction can be made either mineralogically or chemically between flows of different age. Ibrahim (1993) named these basalts the Harrat Ash Sham Basaltic Group, with an assigned age range from Miocene to Pleistocene.

Subsurface Formations Dead Sea-Jordan Rift Sirhan-Azraq-Jafr Basins The Neogene beds of Jordan show a considerable variety of lithofacies, which fit within the general lithofacies patterns of the area despite their sporadic occurrences. Qirma Formation (Miocene). This formation is found in subsurface in the Azraq and Sirhan basins. In the Hamza Field, the sequence, about 211 m (692 fi) thick, is encountered and consists of a mixture of fine- to mediumgrained sandstone, loose sand, chalky limestone and marl with nodules of chert and thin, dolerite beds (Andrews, 1992). The Qirma is thought to have been deposited in a brackish-water lake. Basalt crops out extensively in the A1 Harra area of North Jordan and reaches about 500 m (1,640 It) in thickness. In subsurface, in well Qitar el Abd1, about 469.5 m (1,540 It) of flood basaltic lavas with dykes, pyroclastic sediments and other volcanic products (Andrews, 1992) were drilled. Azraq Formation (Pliocene-Pleistocene). The formation occurs in the central part of the Azraq Basin, where it consists of about 20 m (66 ft) of interbedded gypsum, gypsiferous marl, claystone and fenestrated micrite with a few unconsolidated sand and gravel deposits that formed in a lacustrine environment (Andrews, 1992). Jafr Formation (Pleistocene). The formation occurs in the Jafr Basin, where it reaches a thickness of 18 m (59 It) in outcrop, whereas the thickness ranges from 21 m (69 It) in Jafr-1 to 53 m (174 It) in Jafr-2 in subsurface. It consists of poorly bedded, locally sandy, lacustrine limestone with chert pebbles (Andrews, 1992).

Surface Outcrop Northeastern and Eastern Jordan

Tertiary Basaltic Plateau (Miocene-Pleistocene). In eastern Jordan, Late Cenozoic and Quaternary volcanics cover a strip 50-170 km (31-106 mi) wide that extends over a distance of more than 180 km (an area of 11,000 sq km), representing an enormous volume of plateau basalt. The basalt is a classic, intraplate, continental basalt type

Dana Conglomerate Formation (Late OligoceneMiddle Pleistocene). This formational name was used first by Parker (1970) for localized sequences of conglomerates, limestone and marl consisting of local bedrock clasts and deposited in subsiding basins adjacent to the proto-Dead Sea-Gulf of Aqaba Rift. Bender (1974) refers to this unit as the Syntectonic Conglomerate and subdivided it into lower and upper units. The formation is restricted in outcrop in the northwestern part of the Jordan Rift, where the total thickness is at least 250 m (820 ft). A field study was carried out by Powell (1989 b), who subdivided it into two lithological members (Fig. 9.38). The lower member (late Oligocene-Early Miocene) consists of thick beds of pebble-boulder conglomerate with wellrounded, poorly graded clasts of chert and limestone. The conglomerate is interbedded with fine- to medium-grained chalk, limestone and quartz sand. Scoured and rippled surfaces and small-diameter, inclined and horizontal burrows are common. The upper member (Middle Miocene-Middle Pleistocene) has thick beds of clast-supported, wellrounded, poorly sorted, pebble-boulder conglomerate with a calcarenite/siliciclastic matrix. The clasts are of microcrystalline limestone, chert, phosphatic chert and chalk. The lower contact is unconformable on the bedded chalk and chalky limestone and chert of the Umm Rijam Formation. The Lisan Marl Formation (Late Pleistocene) unconformably overlaps the Dana Conglomerate Formation. The alternation of conglomerate beds with scoured bases and finer-grained, burrowed calcarenites and siliciclastics with sparse, micritic limestone suggests periodic deposition of alluvial-fan deposits into a subsiding lake basin. Rare, sand-filled, fining-upward channels point to channelized flow on parts of the alluvial fan. The finergrained calcarenite and the silty limestone probably were deposited in a deeper part of the lake at the distal margins of the fans. The alternating nature of the beds and the presence of synsedimentary faults in the coarse deposits demonstrate that periodic tectonic activity, manifested in the uplift of the lake hinterland and subsidence of the basin,

447

Sedimentary Basins and Petroleum Geology the Middle East 03 ~ ~"

LITHOLOGY

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was the major controlling factor in the sedimentation of the formation (Powell, 1989 b). Lisan Marl Formation (Late Pleistocene). This formation is present only in western Jordan adjacent to the Dead Sea, where it rests unconformably on strata ranging in age from the Late Proterozoic-Early Cambrian to Neogene. The largest outcrops occur on the Ed Dhira Plain and the western margin of the Lisan Peninsula, where the unit, about 100 m (328 ft) thick, overlies the Dana Conglomerate east of the Dead Sea Fault. The formation name is taken from the Lisan Peninsula and was first named the Lisan Deposits by Lartet (1869, cited in Powell, 1989 b). It is equivalent to the Lisan Series of Burdon (1959, cited in Bender, 1974) and to the Lisan Beds of Bender (1974). Based on detailed sedimentological study, Powell (1989 b) divided the Lisan Formation into the following three lithofacies units: 1) Upper Unit: The Lisan Marl Gravel Facies consists of fine- to coarse-grained siliclasts, sand and pebblesized gravel with thin intercalations of laminated marl. Sedimentary structures include large-scale, west-dipping, Gilbert-type cross-stratification, smallscale trough cross-bedding and channel-fill with contorted bedding and slump structures at the channel

448

BURROWS

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LENSES, CHALK,

margin. Middle Unit: The Lisan Marl Beach-rock Facies consists of trough cross-bedded lenses of carbonatecoated, quartz sand interbedded with marl and overlain by grainstone cemented by aragonite. 3) Lower Unit: The Lisan Marl Facies consists mainly of millimeter to centimeter, laminated, varved, alternating clay-rich and clay-poor, aragonite marl and small gypsum crystals with an accicular, aragonite content. The base of the formation rests unconformably on rocks ranging from Late Proterozoic to Holocene in age. The top is the depositional surface of the former lake or is covered by Holocene alluvial gravel. The nature and distribution of the Lisan lithofacies indicate deposition of a saline or hypersaline, pelagic facies in the central portion of the lake, fed by streams flowing from the rift margins. Periodic variation in the sediment volume entering the lake and salinity produced varved, laminated marl. Lacustrine deltas built lakeward by periodic accretion of large-scale foresets, and instability on the depositional surfaces possibly due to seismic activity, resulted in slumped, rotated blocks moving downslope. Beach rock comprising cross-bedded, lowangle, lakeward-dipping, carbonate-coated grains devel-

2)

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic oped on shallow-shore margins (Powell, 1989 b).

Neogene of Syria (Fig. 9.8) The principal areas of outcrop are in northeastern Syria, where the Miocene-Pliocene section is relatively complete and can be tied to the section in the Foothills and High Folded zones of Iraq. Dhiban Formation (Lower Miocene). The formation, developed in the Euphrates Depression, consists of about 170 m (558 fi) of anhydrite and halite in very thin layers, with occasional beds and streaks of silt. It grades up into massive, bedded anhydrite with thin layers and streaks of buff to gray limestone and blue-gray silt with Pecten sp., Chausinella sp., rotalids and miliolids. The contacts with the overlying Jeribe Formation and underlying Chilou Formation are gradational. Jeribe Formation (Middle Miocene). The formation, first defined in the Foothills Zone of Iraq, is welldeveloped in northeastern and eastern Syria and consists of 52 m (170 ft) of shelly and detrital, algal-reef and crystalline, porcellaneous, foraminiferal limestone with occasional thin beds of marl. It is followed conformably by the Lower Fars Formation, but rests disconformably upon the Dhiban Formation in the Euphrates Depression and the Midyat Formation in the Mesopotamian Foredeep.

Lower Fars Formation (Lower-Middle Miocene). The formation, well-developed in northeastern Syria and the Euphrates Depression, is about 750 m (2,500 fi) thick of anhydrite, gypsum and salt, with interbedded limestone, marl and shale. It is conformably overlain by the Jeribe Formation and grades up into the Upper Fars Formation.

Upper Fars Formation (Upper Miocene-Lower Pliocene). The formation is well-developed in eastern and northeastern Syria, where it consists of more than 425 m (1,394 ft) of alternating reddish-brown to gray, finegrained, current-bedded sandstone with reddish-brown siltstone and blue-gray clay. Beds of grit appear towards the top. There are occasional veins and crystals of selenite. Whereas the contact with the underlying Lower Fars Formation is unconformable, the overlying Bakhtiari Formation rests conformably on the Upper Fars. Bakhtiari Formation (Pliocene). The Bakhtiari Formation is well-developed in eastern and northeastern Syria, where the thickness totals around 2,000 m (6,500 fl) of alternating clay, silt, siltstone and conglomerate deposited in a fluvio-lacustrine environment. The formation rests conformably over the beds of the Upper Fars Formation, but is overlain with angular unconformity.

Neogene of the Foothills and High Folded Zone of Northern Iraq (Fig. 9.8) Euphrates Limestone Formation (Lower Miocene). The formation was described originally by Boekh (1929, in Bellen et al., 1959) at the type locality in the Anah Trough. In outcrop, it consists of well-bedded, recrystallized, shelly and chalky (microporous) limestone.

In subsurface, however, the formation also contains sand, marl and marly limestone. The formation reaches a thickness of 100 m (328 ft) (Buday, 1980). The limestone formed under shallow-marine, reef and lagoonal conditions, for there are local coral and lithophyllid reefs, with fore-reef facies on the one side and lagoonal conditions on the other. The basal contact of the limestone usually is unconformable, whereas the upper contact is marked by an erosional termination, where the presence of an overlying basal conglomerate indicates an emergent phase. Serikagni Formation (Lower Miocene). This basinal, non-evaporitic sequence was described first by Bellen (1955, cited in Bellen et al., 1959) at Jebel Sinjar in the Foothills Zone. The formation is made up of globigerinal, chalky (microporous) limestone with a few additional calcareous bands totalling 150 m (490 ft). The environment of deposition was that of a typical offshore basin (Buday, 1980). The lower contact generally is an unconformity, whereas the top is conformable. Dhiban Formation (late Lower Miocene). These evaporitic sediments represent the final evaporites of the lower Miocene. The formation was described first by Henson (1940, in Bellen et al., 1959) in the Jebel Sinjar area in the Foothills Zone. It has a thickness ranging from 10 to 150 m (32-490 ft) and consists of thick beds of gypsum interbedded with thin beds of marl and recrystallized limestone. The formation was deposited under lagoonalevaporitic conditions after local movement or the effect of a global fall in sea level. The lower contact probably is gradational, but the upper contact is regarded as unconformable. Formations of equivalent age are either continental clastic sequences such as the Hadrukh and Hofuf formations of Saudi Arabia (Powers et al., 1966) or a molasse facies as found in southeastern Turkey.

Jeribe Limestone Formation (Lower Miocene). Bellen (1957, cited in Bellen et al., 1959) first described the formation at a type locality in the Jebel Sinjar region in the Foothills Zone, where it consists of 70 m (230 ft) of generally massive, recrystallized and dolomitized limestone. In subsurface, the limestone becomes more marly. According to Bellen et al. (1959), it was deposited in a lagoonal, back-reef and reef environment with some indications of more offshore facies. In the type area, the lower contact of the formation is conformable, as is the contact with the overlying Lower Fars Formation. The formation in Syria is transgressive and has a basal conglomerate. The equivalent beds in northwestern Iran are assigned to the Kalhur Limestone in the oil field belt, and to parts of the Upper Asmari and Mishan formations (Buday, 1980).

Neogene of Southeast Turkey (Fig. 9.7) The Lower Miocene beds in southeastern Turkey rest unconformably upon the Midyat and Germik formations. They consist of foraminiferal marl and flysch sandstone, which contain lenses of conglomerate and pass into gypsiferous marl and sand towards the foreland (Firat For-

449

Sedimentary Basins and Petroleum Geology the Middle East

Table 9.3. Summary of the tectonic events affecting the Middle East during the Cenozoic. Estimates of the timing and intensity of tectonic events ranges from precise in some areas to very approximate in others (modified after Boote et a1.,1990, and reproduced by kind permission of the Geological Society, London

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1. South Zagros folding increasing tectonic intensity from (d) to (a) 2. Oman Mountains uplift a) Minor uplift b) Tectonic activity c) Unconformity d) Tectonic activity e) Unconformity 3. Makran Subduction a) Subduction b) Increased tectonic activity c) Subduetion d) Increased tectonic activity e) Subduction

1. Dead Sea Transform a) 40kin T r a n s c ~ t Major Grabens b) 65kin Transcurrent local Rhornb c) Transfer d) Initiated e) Dike injection 2. Gulf of Suez a) Slow subsidence b) Strong axial subsidence c) No subsidence d) Unconformity e) Rapid subsidence f) Unconformity g) Subsidence h) Unconformity i) Dike injection j) Initial faulting 3. Red Sea a) Sea floor spreading b) Major subsidence possible

(cont.) c) Major subsidence (extension) d) Major extensional faulting e) Major subsidence f) Major extensional faulting g) Major subsidence (extension) h) Major extensional faulting i) Initial faulting 4. Gulf of Aden a) Sea floor spreading b) Possible sea floor spreading c) Major subsidence d) Major extensional faulting e) Initial faulting 5. East Africa Rift a) Major extensional faulting b) Dormal uplift c) Major extensional faulting d) Dormal uplift

1. Anatolian Conversion Zone a) Lateral extrusion b) Uplift c) Initiation 2. Bitlis Suture and S.E. Turkey a) Foreland folding b) Terminal suturing c) Shortening/restocking of continental margin d) Initial suturing 3. Syrian Mobile Zones (Palmyrids/Sinjar) a) Culmination b) Early deformation initial folding c) Initiation of inversion

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

Table 9. 4 Physiographic features of the Red Sea (compiled from Sestini, 1965; Cochran, 1983; Bohannon, 1986; Dixon et al., 1989).

mation). To the north, Silvan Formation reef carbonates develop and separate this subcontinental platform lying to the south from the intradeep basin to the north where the Lice Formation flysch was deposited. The flysch deposits continued to be deposited until the end of the Miocene, when nappes were introduced into the basin as a result of gravity slides. Renewed nappe activity occurred during the Plio-Pleistocene, and continental clastics formed (Selmo Formation). Strong tensional movements terminated deposition as basalt intrusions covered much of the region.

0

ARABIA PART 3: C E N O Z O I C P A L E O G E O G R A P H Y AND G E O L O G I C HISTORY The collision of the Afro-Arabian Plate with Eurasia marked the closing of Neotethys and the emplacement of nappes and ophiolites over the margin of the Arabian Plate in the late Cretaceous fundamentally changed the paleogeography of the Middle East. During the Cenozoic, as during the late Cretaceous, there is clear evidence of a major clastic contribution from the erosion of these emplaced nappes. That volume increased significantly towards the end of the Neogene following the Miocene-Pliocene orogenic events in the Zagros and related mountains as flysch and molassic sediments poured into the foredeep. The tectonic events, timing and intensity that affected the Middle East during the Cenozoic are summarized in Table 9.2. The magnitude of these events, and the struc-

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Fig. 9.39. Sketch map showing the approximate amount of oceanic crust beneath the Red Sea and possible locations of transform faults. Vertical shading represents oceanic crust created during an early spreading phase; horizontal shading represents oceanic crust created during a recent spreading phase (after Hall et al., 1977). 451

Sedimentary Basins and Petroleum Geology the Middle East tures developed, have tended to obscure the effects of sealevel fluctuations that dominated the sedimentation pattern throughout the Mesozoic. The fracturing and spreading that opened the Red Sea and Gulf of Aden still are sufficiently young, so their effects on sedimentation, while profound locally, are not widespread. The age and development of the opening of the Red Sea, the physiographic features of which are summarized in Table 9.3, have not been unambiguously determined in the absence of well-defined, magnetic anomalies close to both margins, although the presence of oceanic crust in the central trough or spreading center in the southern Red Sea (Thompson, 1976) generally is accepted (Fig. 9.39). The marginal areas are covered by a thick sequence of Miocene evaporites determined as a result of deep drilling and seismic-refraction studies (Fairhead, 1973; McKenzie, 1970). Based on kinematic data, these evaporites, in some views, are believed to rest upon oceanic crust, which would, therefore, be taken as stretching from coast to coast, or more likely upon thinned continental crust as in the Gulf of Aden (Fantozzi, 1995). Opening as part of a two-phased event was suggested by Girdler and Styles (1974) and others, with the first phase beginning during the Oligocene and the second (Plio-Pleistocene) phase represented by the present central trough. Le Pichon and Francheteau (1978) concluded that the total separation found by matching opposing coastlines

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Fig. 9.40. Distribution of pre- and synrift Red Sea volcanism (after Bayer et al., 1988). 452

(McKenzie et al., 1970) correctly predicts the trends of the currently active transform faults in the central graben between 19~ and 23 ~ N. Between 19 ~ and 15.5 ~ N, the opening of the southern Red Sea has been about a pole situated to the south and opening 5-10 cm per year over the last 2 m.y. Left-lateral motion along the Levant Shear Zone has been estimated to total 105-110 km (66-69 mi), of which the first 65 km (41 mi) occurred during the Miocene and the last 45 km (28 mi) after that during the Plio-Pleistocene. The strike-slip movement in the southern part of the Levant Shear Zone is accommodated along enechelon faults within the sedimentary fill of the graben oblique to the trend of the graben itself (Garfunkel, 1970). The Trap Series, the enormously thick and extensive sequence of volcanic rocks, covers much of the bordering areas of Ethiopia, southern Saudi Arabia and northern Yemen (Fig. 9.40). Although the initial activity may have begun as early as the Late Cretaceous, the major extrusive activity took place during the Oligocene and Miocene (Davison et al., 1994). The basaltic trap flows, extruded through tensional fractures preceding the opening of the Red Sea (Mohr, 1983; Chiesa et al., 1983), cover much of southwestern Yemen (Geukens, 1966 a & b). In the southern part of the Red Sea Province, late Oligocene peralkaline granites dated at 22 Ma indicate that the phase of diffuse extension extended as far as the Afar (Almond, 1986). The granite, dated at 27.7 Ma in North Yemen by Grolier and Overstreet (1978), generally is associated with this event. Late Oligocene and Eocene sediments are absent as a result of regression or uplift. The lavas and associated ignimbrites extruded during the Oligocene and Miocene (Geukens, 1966 a& b; Chiesa et al., 1983; Civetta et al., 1978) blanket pre-existing structures. Stratigraphic and facies data support the idea that extrusion preceded the uplift of the Ethiopia-Arabian Dome (Whiteman, 1968; Coleman, 1977; Almond, 1986) and was related to a prerift phase of crustal extension (Mohr, 1983; Chiesa et al., 1983; Davison, 1994). This pre-rift phase of extension in the Red Sea and Gulf of Aden basins preceded opening in the Oligocene, as extension in the Red Sea and Gulf of Aden basins, accompanied by listric faulting, disrupted the Afro-Arabian Plate. Gass (1970) and Burke and Whiteman (1973) attribute the rifting and volcanicity of the AfroArabian Dome to one or more mantle plumes, but Almond (1986) attributes it to a more passive mantle-rifting process. A second phase of volcanic activity, marked by widespread basaltic lavas, occurred during the Neogene, forming the "harrats" of North Yemen and Saudi Arabia. Volcanics of the same age are developed as far away as Turkey, Syria and Jordan (Brown, 1970; Almond, 1986). These second-phase volcanics postdate the initial formation of the Red Sea and much of the uplift of Arabia, but are roughly coeval with the post-rift volcanics of Ethiopia. The structure of the Red Sea north of 19 ~ N can be explained by a three-stage e v o l u t i o n - an early stage of continental extension, followed by two intervals of sea-

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic

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Fig. 9.41. The evolution of the Red Sea, based on marine geophysical data from the Red Sea and regional geological data, especially from the Suez and Aqaba-Dead Sea rifts: a=Early "Gulf of Suez-Red Sea Rift Valley" stage in the Oligocene, 30 Ma; b=the extended lithosphere at the beginning of the Miocene, 25 Ma; cracks propagate NNE to form the early Gulf of Aqaba-Dead Sea Rift; c=after the first major episode of sea-floor spreading (shown with stipple) and 62 km of shear along the Dead Sea Transform, 15 Ma; d=the present Red Sea after the second phase of sea-floor spreading (closer stipple), which was initiated at the end of spreading (closer stipple), which was initiated at the end of the Miocene 5 Ma ago, together with a further 45 km of shear along the Dead Sea Transform (after Girdler and Southern, 1987, and reproduced by kind permission of Nature). floor spreading (Girdler and Styles, 1974) (Fig. 9.41). In the Red Sea, oceanic crust is recognized only in the southern part, between 19~ and 23 ~ N, with the northern Red Sea still rifting. The development of the Gulf of Aqaba Transform arrested the rifting process in the Gulf of Suez, which subsequently developed into an important petroleum province. The Aqaba Transform can be traced northward past the Dead Sea to where it ends at the Taurus Mountains. Although Freund (1965) dates the earliest movement on the Dead Sea faults as Late Cretaceous, the main phase of left-lateral movement occurred in the early to middle Miocene with a displacement totaling 62-65 km, followed by a further displacement during the Pliocene to Recent, according to Quennell (1984). It was during the late Miocene and Pliocene that the Arabian Platform finally collided with the Iran and Van plates along the Bitlis Suture Zone (Dewey and Seng6r, 1979; Scott, 1981), leading to the development of the Border Fold Zone of Turkey and the Fold Zone of Iraq, from which the thick flysch deposited on the Arabian Platform was derived. The formation of the Gulf of Aden began in the late Eocene with the uplift and subsequent fracturing and rifting of a depression that developed on the eastern margin of a bulge of the Arabo-Nubian Shield (Azzarolli, 1968; Beydoun, 1966; Closs, 1939). The main phase, according to Baker (1970), occurred during the late Oligocene-early Miocene and is reflected in the deposition of marine sediments in the proto-gulf. Later Miocene and Pliocene faulting was accompanied by the seaward warping of Neogene sediments. Magnetic anomalies show that the oceanic crust dates at 10 Ma, and oceanic crust still is in the process of formation in the Gulf of Tadjura. Laughton et al. (1970), Girdler and Styles (1978) and Cochran (1981) consider the formation of the Gulf of Aden to have occurred in two discrete phases m an initial phase of diffuse extension over a zone approximately 100 km wide in

a rift-valley environment during the late Eocene, followed by concentrated extension about a single axis with the beginning of true sea-floor spreading in the Oligocene and early Miocene. Crustal extension of 65-200% of the original rift valley occurred before the establishment of the oceanic ridge. The northeastern drift of Arabia is being accommodated in the Gulf of Oman by the subduction of the Arabian Plate below the Eurasian. This has resulted in the deformation of the Makran sedimentary prism at the continental margin and may account for the vertical movements in the Oman Mountains (Gorin et al., 1982; White and Ross, 1979). The fractures are both parallel and oblique to the Gulf of Oman. The southeastern coast of the Arabian Sea is formed by a major sinistral transform fault, the Owen Fracture Zone, which separated Arabia-Somalia from India before the opening of the Gulf of Aden (Beydoun, 1982; Whitmarsh, 1979; McElhinny, 1970). In southern Oman and southeastern Yemen, the dominant structural element is the Hadhramout Arch (Fig. 9.42). It is divided into two sub-parallel culminations by a broad, gentle syncline and is bordered to the north by the complementary Rub al Khali Depression. The arch began to develop during the Paleocene and culminated in the Eocene (Beydoun, 1969). Gentle, easterly tilting of Dhofar reactivated what had been an area of low relief since the Jurassic, and it is suggested that the A1 Helaniyat Islands may represent the extension of the basement core of this arch. Normal block and step faulting has occurred along the southern flank of the Hadhramout, resulting in prominent fault scarps (Fig. 9.43). In the fault zones, shattered and mylonitized debris may form zones 100 m (328 ft) wide. The formation of the faults was initiated during the Eocene (Hawkins et al., 1981) and, therefore, belongs to the sequence of events associated with the opening of the Gulf of Aden. The intersection of major fault systems has

453

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resulted in the formation of step-like features, and tilted fault blocks are seen in the Salalah Plain (Fig. 9.43). Hempton (1987) summarized the tectonic evolution of the Arabian Plate during the late Paleogene and Neogene. During the middle late Eocene (Fig. 9.44), block faulting, accompanied by the first phase of rifting in the Red Sea, was preceded by thermally driven uplift, presumably a result of the reorientation of the central Indian Oceanic Ridge (spreading center) to a northwestern trend consequent upon the collision of the Indian and Eurasian plates (Patriat and Achache, 1984; Hempton, 1987). Stresses associated with rift propagation were large enough to allow Arabia to separate from Africa, even though part of the northern margin was undergoing compression (Hempton, 1987). Convergence of the northern margin of the Arabian Plate and Eurasia took place during the late Oligocene and early Miocene (Fig. 9.45), and the rapid movement away from Africa may have caused thinning and extension in the Red Sea region, resulting in the development of block faulting and the beginning of continental-rift-type volcanicity (Schmidt et al., 1983; Hempton, 1987). Diabase

454

dikes intruded into the fault zones, defining pull-apart basins, plateau basalts in the Afar and Yemen, and ophiolites in Saudi Arabia, which all date from this time (Schmidt et al., 1983; Coleman, 1984; Hempton, 1987). Bartov et al. (1980) provide evidence for left-lateral movement along the Dead Sea Transform Fault beginning at about 18-22 Ma. The Oman Mountains were not uplifted into a mountain range until the late Oligocene-early Miocene. This uplift may have been in response to crustal shortening caused by the opening of the Red Sea. By the middle Miocene (Fig. 9.46), Arabian Plate motion had slowed, and crustal extension ended. The Red Sea Trough had flooded, and evaporites had begun to accumulate. Isostatic movements uplifted the Red Sea Rift shoulders, and rhyolitic volcanics were erupted in Yemen (15-11 Ma; Schmidt et al., 1983; Coleman, 1984; Hempton, 1987). In the Dead Sea (pull-apart) Basin, extension and subsidence ended, and the basin was filled with sediment (Zak and Freund, 1981). At the northern margin of the Arabian Plate are indications of uplift in the Bitlis Zone and reactivation of deformation processes in the Palmyra Trough. Throughout eastern Anatolia, calc-

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Fig. 9.45. Tectonic reconstruction from the Late Oligocene to early Miocene in the Middle East, illustrating the opening of the Red Sea, Gulf of Aden and Dead Sea transform faults (after Hempton, 1987, and reproduced by permission of Tectonics).

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Fig. 9.47. Tectonic reconstruction of the early Pliocene, illustrating the westward escape of the Turkish Plate, renewed independent motion of Arabia to the north and renewed extension in the Red Sea (after Hempton, 1987, and reproduced by permission of Tectonics).

455

Sedimentary Basins and Petroleum Geology the Middle East alkaline volcanics began to erupt (Dewey and Burke, 1973; Dewey et al., 1973; Dewey and Sengtir, 1979; Sengrr and Yilmaz, 1981). Renewed extension occurred in Arabia during the early Pliocene as the plate resumed its northward movement. This movement involved the reactivation of the Dead Sea Transform (Fig. 9.47) and the northern and eastern Anatolian faults bounding the Turkish microplate, which responded by escaping westward. The continuing northward movement of Arabia led to the accumulation of 45 km of left-lateral displacement as the Dead Sea (pullapart) Basin continued to elongate and subside (Zak and Freund, 1981). In Iran, the Lut Block moved eastward with right-lateral movement along the Zagros Fault, while numerous left-lateral faults developed in northern Iran. Thus, most of the convergence was accommodated by the lateral extrusion of microplates. Economically, too, the effects of the Cenozoic event have been far-reaching; the charging of the good reservoirs with their excellent seals, and the magnitude and extent of the relatively simple structural traps present have made the region a dominant force in the world of petroleum. Proven reservoirs in Arabia and Iran are in the carbonates of the Umm Er Radhuma, Dammam, Jahrum and Habshiya formations (Paleocene to Eocene), in northern Iraq in the carbonates of the Kirkuk Group (Oligocene); and in Iran in the carbonates and clastics of the Asmari Formation (Oligo-Miocene). Potential reservoirs occur in the carbonates of the Habshiya Formation (Eocene) of Yemen, the Sinjar and Avanah formations (Eocene) of northern Iraq, and the Euphrates Formation (Miocene) of northern Iraq and eastern Syria. Excellent seals are evaporites developed in the Rus, Dammam, Dhiban, Gachsaran and Lower Fars formations and the Kalhur Member of the Asmari Formation, while fine clastic seals are developed in the Middle Fars and Mishan formations. In the Arabian Peninsula and Iran, non-deposition or erosion associated with major inversion occurred in the Early Paleocene. A sag basin was developed in the Late Paleocene-Early Eocene, and a foreland basin formed in response to a collision between the Arabian and Eurasian plates in southwestern and northeastern Iran and northern Oman. Flysch and molasse, coarse and fine clastics and pelagic carbonates were deposited in northern and northeastern Arabia, and platform carbonates were deposited everywhere else. Evaporites were deposited widely during the early Middle Eocene, while at the end of the Eocene, regional uplift and erosion may have been caused by isostatic rebound following earlier thrust-loading in northern and eastern Arabia, or by Red Sea rifting in southern and western Arabia (Jones and Racey, 1994). Local unconformities at the Paleocene-Eocene boundary, at the EarlyMiddle and the Middle-Late Eocene boundaries, provide the basis for the distinction of four subsequences. The contraction of the Tethyan Seaway (presumably floored by a Tertiary sedimentary sequence) connecting the Indian Ocean to the east with the Mediterranean to the

456

west resulted from uplift of its floor at the end of the Eocene. Peri-reefal and pelagic carbonates of the Oligocene occur as a narrow, linear belt running through Syria, Iraq, Iran and the Arabian Gulf. There also are some isolated outcrops of Oligocene rocks in southern Oman and Yemen, but these are absent elsewhere because of either non-deposition or uplift and erosion associated with a sea-level low or Red Sea rifting at the end of the Oligocene. Local unconformity with the Oligocene occurs in some parts of the Middle East (e.g., northern Iraq, Yemen and southern Oman). To discuss the paleogeography of an area as large as the Middle East, it is essential to break it down into manageable entities, both in time and space, and a manageable framework into which the various pieces can be related. The pieces are labeled APC 1-4 (Arabian Peninsula Cenozoic). In a time sense, this is achieved relatively simply by using the major sedimentary break between the Paleogene and the Neogene engendered by the late Oligocene to early Miocene fall in sea level. This break point is the boundary between "megasequences" APC 2 and 3. The break between megasequences APC 1 and APC 2 is located at the unconformity at the base of the Oligocene; each megasequence then is subdivided further by local unconformities (Jones and Racey, 1994). Although this regression is in evidence nearly everywhere, sedimentary continuity is preserved in the two principal troughs, the Zagros Trough and the Ras al Khaimah Sub-basin, which remained active sedimentary sinks although reduced in size. The regression at the end of the Cretaceous, which persisted into the early Paleogene, was neither sufficiently great nor long in duration to serve as more than a convenient introduction to the Tertiary. The early to middle Eocene regression and the widespread development of evaporites provide a useful break point during the Paleogene cycle comparable to similar break points during the Cretaceous. Because the tectonic events with which they may be linked are sufficiently remote, except in the immediate Zagros Province, it is a deceptively simple pattern to handle. The end of the Paleogene cycle is roughly coincident with the Oligocene-Miocene boundary, but sedimentary continuity can be established in the trough regions. At the trough margins, the presence of clastic sediments provides evidence of the break. Complications arise when discussing the paleogeography of the Neogene, for despite the reduction in the area of sedimentation, the increasing pace of tectonic activity resulted in the division of the Middle East region into a number of quasi-independent, small basins separated from one another and, in many cases, from the open sea, by ridges or arches, with the consequent diversity of lithofacies. Therefore, the key element that makes it possible to link together the seemingly endless diversity of stratigraphic histories of the different areas is the tectonic history. Consequently, it is of no little importance to recapitulate the principal events in the Cenozoic tectonic history of the Middle East and the sedimentational effects

The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic that may be directly attributed to them. In the preceding chapters, an attempt was made to present the regional geology in terms of a number of traverses from the stable Arabian Platform towards the margins of the Arabian Plate. The technique was and is successful when the subduction margin was sufficiently distant to permit the continental plate and its offshore sedimentary wedge to be treated as a whole, and the plate history is a simple one of rise and fall of the sea level under these circumstances. This was the case during the Paleogene when the site of the lower Cenozoic folding lay in central Iran. The virtual elimination of Neotethys by the subduction of the Arabian Plate below the Eurasian, and the folding, uplift and emplacement of the sedimentary wedge at and over the plate margin, require a less generalized treatment. The tectonostratigraphic framework units that need special attention are those associated with the Zagros folding and nappe emplacement. The elevation and erosion of the newly formed Zagros folds provided a source of clastic, flysch and other debris, as the emplaced nappes tended to be buried under their own debris. The sedimentary rocks of the continental marginal wedge

involved in these movements include the deep-sea radiolarian beds as well as slope sediments formerly described as the eu- and miogeosynclinal beds. They were separated from the cratonic sediments during the Van Phase of the Paleogene Orogeny (Buday, 1980) by a ridge in northern Iraq and most likely were connected with the former "miogeosynclinal" ridge in the area of what is now the Northern Thrust Zone (Buday, 1980). The Arabian Platform, the tectonically stable area bordering the Arabian Shield, continued to be affected relatively little by the Zagros events, particularly during the Paleogene, although by the Neogene, the area of marine deposition was very much restricted, associated with the process of gradually infilling the Neotethys. The unstable shelf area, that part of which incorporates Iraq and Syria, is marked by the continued history of the Euphrates-Anah and Palmyra-Sinjar troughs, in which sediment filling was fault-controlled. The new element in the regional, tectono-stratigraphic framework was the opening of the Gulf of Aden and the formation of the Red Sea, which linked the Dead Sea-Jordan Rift Transform System with the Taurus Trough. The emergence of the western Arabian Highlands and

Shallow carbonates over deep marine Deeper mixed shelf Erosional limit ~Coastal plain . ~ P OPEN MA.,NE" S.ALLOWSHE.F " I I ; ~ CarbO~ Garbonllte nates Mixed ~ Cllrbonate/EvaDorite Clastics ~

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250km

Fig. 9.48. Depositional setting of the Paleocene-Early Eocene sediments in the Middle East (modified from Murris, 1980 and Alsharhan and Nairn, 1995).

RIYADH

-....

457

Sedimentary Basins and Petroleum Geology the Middle East the closure of the western end of the Tethyan Seaway occurred because of tectonic activity during the OligoMiocene. During the Miocene, the wide spread of marginal, non-marine sediments (evaporites and coarse clastics) occurred in the eastern and western parts of the Middle East; marine sediments were restricted to the Tethyan Seaway (Jones and Racey, 1994). During the Miocene, the Red Sea was intermittently connected to the Gulf of Aden and the Indian Ocean, as indicated by the occurrence of the Indo-Pacific benthonic, foraminiferal biofacies Ammonia and Pseudorotalia (Jones and Racey, 1994). Continental sedimentation continued over most of the Middle East during the Pliocene, except in the Red Sea, where marine sedimentation occurred following the opening of the Strait of Bab A1 Mandeb. At the end of the Pliocene, the final Zagros collision took place, causing extensive deformation of earlier sediments. Many local unconformities occurred during the Neogene in many parts of the Middle East at the Early-Middle Miocene boundary, within the Middle Miocene, at the Middle-Late Miocene boundary and at the Miocene-Pliocene boundary. Within the scope of the tectono-stratigraphic elements and the regional history, a number of time segments summarize the overall pattern through the presentation of a GERCUS SINAN

number of paleogeographic maps.

PALEOGENE

PALEOGEOGRAPHY

The paleogeography of the Paleogene is summarized in Figs. 9.48 and 9.49. It was a brief period of relative tectonic quiet following the completion of deformation of the Oman Mountains and the mild folding in the Zagros Foothills Belt. The geography shows a stable landmass to the west bordered by a shallow, eastern shelf gradually deepening into foredeep troughs marginal to the aforementioned recently emplaced, tectonic masses. The short regression at the end of the Mesozoic left virtually all of the gulf area above sea level. The foredeeps were areas where sedimentation was continuous from the Late Cretaceous. The Zagros and Ras al Khaimah foredeep basins were separated by the shallowly submerged Fars Platform. There is little clastic material in the basal Paleocene, and the Maastrichtian-Tertiary hiatus often is lithologically indistinct, so the break appears to have been of short duration with little erosion. The ensuing early Paleocene transgression reestablished marine conditions, leaving only western Saudi Arabia, Iran, parts of Iraq (the Ga'ara N

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The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic High) and Oman (the Huqf Swell and the Hawasina and Semail nappes) above water. The Arabian Shield area in Saudi Arabia and Yemen and the northern parts of Oman remained exposed throughout the Paleogene, excluding only those parts in which a shallow sea spread over central Yemen and the Dhofar Province of southern Oman. Of the two foredeeps, the Zagros Trough and the Ras al Khaimah Sub-basin, the latter had all but disappeared as a distinctive feature by the end of the Eocene, whereas the Zagros Trough shallowed, and the depocenter migrated southwestwards. In the Ras al Khaimah Sub-basin during the Paleocene, a carbonate flysch was deposited (Pabdeh Formation), and there are turbidites and mud flows against the eastern margin of the basin (against the Musandam Peninsula). The deepest part of the main Ras al Khaimah Sub-basin lay close to the eastern margin of Oman and the U.A.E., where there are thick, flysch-like sediments, as exposed near Sha'am on the Oman-Ras al Khaimah border and in well Maaridh-1 (onshore northern U.A.E.), where there are more than 1,859 m (6,100 ft) of interbedded flysch and black shale presumed to be derived from the Semail and Hawasina nappes. Their distribution probably is restricted to near the basin margin, as flysch is not found further offshore in Ras al Khaimah (well Trucial Offshore1), where the recorded facies consist of basinal marl. At the southern margin of the Ras al Khaimah Subbasin (in extreme southern Abu Dhabi and southeastern Dubai), a late Paleocene reef facies developed on the shelf break to deep, open water. The reef facies may be 200 m (656 ft) thick in the east, with corals whose growth forms indicate growth in very shallow water. Around the basin margin was a shallow, carbonate shelf upon which carbonates continued to be deposited until the early Eocene (Umm Er Radhuma Formation). There is a suggestion that the southern Ras al Khaimah Sub-basin was separated from the Rub al Khali by a ridge extending from the Lekhwair-Mender High in onshore Abu Dhabi to the stable area of offshore Abu Dhabi (Fig. 9.4). Adjacent to the northern Oman Mountain Belt along the steep eastern slope of the Ras al Khaimah Sub-basin, a sequence of Paleogene interbedded, submarine, debrisflow conglomerates, turbiditic sandstone, limestone and shale accumulated. Deposition of the basinal facies continued into the Oligocene off the northwestern coast of the Musandam Peninsula (Ricateau and Riche, 1980; Nolan et al., 1990). In the northeastern and southwestern parts of the central Oman Mountains, shallow-marine limestone of late Paleocene to early Eocene age is present (Nolan et al., 1990). During the early Eocene, the central Oman Mountains probably were emergent, but a transgression dominated by an open-shelf, limestone facies rich in benthonic foraminifera became established in the Middle Eocene. While southwest of the central Oman Mountains, highly fossiliferous limestone and marl developed to the northeast, late Eocene-Oligocene limestone with fine-grained, less fossiliferous limestone and marl with coral patch reefs developed, marking a late Eocene regression that termi-

nated the transgression begun in the Middle Eocene. During the early Eocene, Oman still lay within the tropical belt in a position similar to that it held during the late Cretaceous, but probably was in a rain shadow because of the northward drift of the Indian Plate across the line of the prevailing paleowind (Nolan et al., 1990; Smith and Briden, 1977). The lower Eocene succession in the central and northern Oman Mountains contains less evaporites than in central Arabia and southwest of the Oman Mountain Belt, probably further reflecting the paleoclimatic influence of the mountain belt (Glennie et al., 1974, Nolan et al., 1990). The shallower-water conditions, which existed over the Fars Platform, are marked by carbonates interspersed with supratidal dolomites of the Jahrum Formation and the predominantly Paleocene supratidal evaporites of the Sachun Formation (James and Wynd, 1965). Reefs also developed over this platform. To the southwest, the platform passed by transition into the epeiric seas covering the continental shelf of Saudi Arabia, where the Umm Er Radhuma Formation was deposited during the Paleocene and into the Early Eocene, before a regression brought the return of the evaporites of the Rus Formation. In Iraq during the Paleocene, the Zagros Trough was a broad trough separated from the marginal foredeep by a high over which reefs and lagoonal deposits developed (Dunnington, 1958). The deep trough and barrier high gradually disappeared, forming a broader, shallower basin by the Upper Eocene. Southwestward, the basin passed to the carbonate succession of the Arabian Shelf (the Umm Er Radhuma Formation). The northeastern margin of the Zagros Trough in Lurestan and northern Iraq, as well as the Lurestan Province of Iran, saw the accumulation of thick, flysch-like deposits (of the order of 1,000 m, or 3,280 ft), which persisted until the Lower Eocene (James and Wynd, 1965; Dunnington, 1958). The main source of these flysch deposits was the erosion of the uplifted Cretaceous radiolarites. The fiysch was succeeded by 330 m (1,082 ft) of molasse-type red beds. The flysch was confined to a deep trough marginal to the mountains in northern Iraq and separated from the main Zagros Basin by a local northwest-southeast high, over which lagoonal and/ or reefal limestone was deposited (Dunnington, 1958). In the main basin, thin-bedded, globigerinal marl formed a sequence notable for the number of breaks in sedimentation. The marl is more glauconitic and phosphatic in the southwest towards the Ga'ara High, where it intercalates with the littoral and neritic limestone of the Paleocene and lower Eocene. The distinction disappeared in the middle and upper Eocene when globigerinal marl and limestone covered all of northern Iraq. The history of the early Paleogene continental shelf of most of Arabia mirrors that of much of the Mesozoic, with its extensive shallow-water carbonates (Umm Er Radhuma) giving way to evaporites (Rus Formation). The evaporites were replaced by more normal-marine conditions at about the turn of the lower to middle Eocene, 459

Sedimentary Basins and Petroleum Geology the Middle East when the beds of the Dammam Formation were deposited. The Early Paleogene, even if a generally quiet interval tectonically, nevertheless was one during which evidence of irregularities in the ocean floor from diapirism and structural movement was developed, now observed in terms of thickness and facies variations (Fig. 9.50). The lower Eocene Rus is a relatively thin sequence of restricted, shallow-water dolomites, marl and evaporites that rim the Oman Mountains and thicken towards offshore Abu Dhabi. Passing into the Ras al Khaimah Subbasin and the open-shelf margin, the formation loses its definition in onshore and offshore Dubai; in onshore Abu Dhabi (Jabal Hafit), the Rus is represented by a sequence a few tens of meters in thickness consisting of tidal-fiat and shallow, subtidal limestone with sparse anhydrite nodules (Whittle and Alsharhan, 1994). This sedimentary pattern appears to be out of phase with the main sequence of sealevel fluctuations envisioned by Haq et al. (1987), for the latter proposes a slow sea-level rise in the late Paleocene and early Eocene. However, as open, carbonate-shelf conditions were reestablished by the middle Eocene, indicated by the thick, nummulitic shelf carbonates and shale of the Dammam Formation, the cause of this brief intermission with its evaporite deposition can be assigned to mild tectonic warping in eastern Arabia. The main phase of Paleogene uplift and erosion was initiated during the latest Middle Eocene to late Eocene and continued into the Oligocene, when the carbonate shelf shrank towards the Indian Ocean and, perhaps, the last remnants of the Ras al Khaimah Sub-basin. Erosion associated with the regression led to a major truncation of the Dammam Formation in the western Arabian Gulf, with progressively less erosion eastwards. Although in parts of Iraq, Iran and the southern Arabian Gulf, there are indications that a transgression was reestablished in the early Oligocene, some parts of Iraq, Iran (Fars Province) and probably most of Oman remained emergent until covered during the late Oligocene (Bellen et al., 1959; Setudehnia, 1972 ; Powers et al., 1966). Only in the remnants of the Ras al Khaimah Subbasin does there appear to have been continuity of sedimentation into the early Miocene. Not only do the younger, calcareous flysch beds of the Pabdeh Formation grade westwards into the shelf-equivalent Umm Er Radhuma, Rus and Dammam formations, but they persist into the early Miocene in the trough, until they are replaced by the thick, evaporitic facies of the Gachsaran Formation (the term used in the Zagros Fold Belt in western and northwestern Iran and equivalent to the Lower Fars Formation or Fars Group in southeastern Iran) in the deeper parts of the former basin. This restriction of the Pabdeh Trough resulted from a prograding, submarine-fan system filling the trough from its eastern side and displacing the depocenter westwards (Figs. 9.49 and 9.50). The evaporite sequence may be as much as 1,219 m (4,000 ft) thick in the near offshore areas of Abu Dhabi and Dubai, where the halite thickness accounts for about 25% of the

460

total. The salt grades from almost pure halite in the center of the basin with very few beds of shale or marl, into mixed salt and anhydrite, and finally to predominant anhydrite at the basin margin, followed above by nearly 305 m (1,000 ft) of mixed shale, marl and anhydrite. During the Oligocene and into the earliest Miocene (Fig. 9.51), shallow shoal carbonates, approximately equivalent to the Asmari limestone of western and northwestern Iran and offshore U.A.E., were formed over the Fars Platform, so these, too, are facies equivalents of the upper part of the Pabdeh Formation. The Asmari limestone is considered to reflect the Oligocene to early Miocene eustatic sea-level rise over the previously emergent platform. It tends to be thickest along the western margin of the Oman Mountain Belt and on the shelf of southeastern Iran. In its characteristic development, the formation is a massive, dense limestone deposited in a subtidal-intertidal environment. However, in the central areas of the carbonate shelf, a distinction sometimes is made between the Lower Asmari, where the limestone is interbedded with shale and marl, and the Upper Asmari, which generally is a clean limestone unit (Fig. 9.51). The formation has a low primary porosity, and the Asmari limestone in the Zagros Basin is famous as the carbonate reservoir facies of Iran, largely because of production from fracture porosity. Products of the erosion of the Arabian Shield during the time of deposition of the Asmari limestone transported into the Zagros Trough led to the formation of the Asmari clastics in Kuwait and southeastern Iraq (Ghar sands) and the Ahwaz sandstone of Iran (Fig. 9.52). In southwestern Abu Dhabi, the equivalent clastics are the Late OligoceneMiocene clastics and, in Saudi Arabia, part of the Hadrukh Formation. The Ahwaz Sands of southwestern Iran and the Ghar Sands of southeastern Iraq and K0wait can be shown to be derived from the Arabian Shield to the southwest (Murris, 1980; Buday, 1980; Powers et al., 1966), as deltaic sand was built out northeastwards by an eastwardflowing wadi system probably very similar to the present. Sediment transported periodically by major floods was carried far out onto the carbonate platform. In southern Kuwait, the deposits are thin and non-marine and are overlain by early Miocene clastics. In southwestern Iran, the clastics are marine and interfinger with the Asmari limestone (James and Wynd, 1965). In Abu Dhabi, these (?) Oligo-Miocene clastics are recognized only in the central and western parts of the onshore, but are presumed to have a similar origin to the Ghar Sands of Kuwait. Closer to the source area, the marine element, represented mostly by anhydrites, dies out until the entire formation is continental and is referred to the Hadrukh Formation in Saudi Arabia (Powers et al., 1966; Powers, 1968). There is some confusion concerning the exact age of these clastics, whether they are equivalent to the Asmari limestone or the Gachsaran Formation. In Kuwait, however, the Ghar Sands (the lateral equivalents of the Ahwaz Sands) are dated as early Miocene by an overlying sandy bed (Owen and Nasr,

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Sedimentary Basins and Petroleum Geology the Middle East 1958), and an analogous situation appears to exist in southwestern Abu Dhabi. The Paleocene transgression covered the entire northern Arabian Platform and extended over the Taurus-Zagros Trough. The deep-water zone (the "eugeosyncline" of earlier authors) that lay along the Iran-Turkey border received a sequence of clastic and volcanogenic sediments, which continued into the Eocene. Subdivision of the area distinguishes a strongly subsiding central belt that was the site of extensive volcanism. The outermost belt was the site of flysch deposition that persisted into the Oligocene, and the inner belt next to the craton was the location of volcanicfree, carbonate sediments. The appearance of another belt of flysch-molasse and variegated sediments has given rise to the suggestion that these were deposited in a trough separated by a ridge from the preceding area (Buday, 1980). As the trough filled, the depocenter migrated to the southwest. The location of the ridge is well-established and is the successor of the Cretaceous Ridge (Buday, 1980), although it is not well-developed in southeastern Turkey, where Paleogene orogenic movements were relatively minor when compared to the stronger late Cretaceous movements. It is assumed that deformation of the deepwater sediments began sometime before the end of the Eocene, because conglomerates occur in the Uppe Eocene and proven Upper Eocene and Oligocene beds are absent, although they are present closer to the shelf margin. The trough is bordered to the southwest by an openmarine shelf, on which reef and backreef limestone formed, extending southeastwards from southeastern Turkey into Iran. The other side of the shelf is formed by a zone of deeper-water sedimentation of the Palmyra-Sinjar Trough. The trough, in turn, is bordered by the RutbahKhleissia High, which formed a partial barrier separating the Mediterranean from the Indo-Pacific Bioprovince (Ponikarov et al., 1967; Powers et al., 1966). The area, bounded to the north by the troughs and to the east by the Rutbah-Khleissia High, was a shallow, carbonate, evaporite platform extending across southern Syria and Jordan, where phosphatic carbonates were deposited in shoalwater conditions. This platform at the end of the Paleocene, and particularly during the early Eocene, shows the replacement of the limestone by lagoonal evaporites, sediments that are part of the Rus Formation of Saudi Arabia. In Jordan, the deposition of calcareous sediments of exclusively marine origin continued without interruption from the Danian through the Eocene. In northern and northwestern Jordan, it is represented by microporous limestone in which chert nodules and layers are intercalated, whereas the succession in southeastern and eastern Jordan is dominated by nummulitic and marly limestone with layers of concretionary chert (Bender, 1974). This limestone and marl sequence with chert of PaleoceneEocene age is an indication that the area was subject to marine conditions until the Eocene; however, during the Oligocene, tectonic movements resulted in uplift and erosion in many parts of Jordan. The eroded sediments accu-

462

mulated under deep-marine conditions in zones that resulted from structural subsidence, such as the Wadi Araba-Jordan, the Azraq-Wadi Sirhan, E1Jafr, the northern part of the Jordan Graben and the eastern margin of the Jebel ed Drouz (basalt) Plateau. The deposits range in age from Oligocene to Miocene, with the sediments dominated by glauconitic sands, limey marl and sandstone.

NEOGENE PALEOGEOGRAPHY Although the sea level recovered after the PaleogeneNeogene transition, the effects are largely masked because of Late Miocene-Pliocene tectonism. Thus, the Agha Jari Formation, for example, consists of a rapidly deposited, non-marine, clastic wedge of molasse built out from the rising Zagros Mountains with estuarine and lacustrine conditions predominating. The formation is strongly diachronous, younging away from the mountains. During approximately the same time limits, the Dibdibba Formation of Kuwait (Owen and Nasr, 1958) and the Hofuf Formation of Saudi Arabia (Powers et al., 1966; Powers, 1968) were deposited (Fig. 9.52). The Hofuf Formation is a relatively thin sequence of aeolian and fluvial clastics. It probably extends into southern Abu Dhabi, where clastic sediments usually appear above the Asmari or its equivalents. These clastics, however, appear to have been sourced from the slowly rising Arabian Shield. By the end of the Aquitanian (Early Miocene) (Fig. 9.53), subsidence in the slowly sinking "normal" marine basin extending from northwestern Iraq to southeastern Iran had become more rapid in some areas and had ceased in others, resulting in the formation of a series of small, elongated basins separated from one another and from the open sea to the southeast by a number of shallow sills. These basins existed from the early Miocene into the Pliocene parallel to the present Zagros and Oman Mountain trends. The basins were asymmetric, with their steeper flank to the northeast. The central parts of the basins show the greatest subsidence rate and the thickest sediments in the Arabian Gulf area. To the south and west, the basins transgressed over the margins of the Arabian Shield. Clastic sedimentation dominated at the margins of the basins, with pelagic shale and marl in the central parts of the basins and shelf carbonates elsewhere. The Qatar-South Fars Arch is an example of a positive area separating a southern basin, partially cut off from the open sea and consequently becoming progressively more saline, from the basin in northeastern Iraq-southwestern Iran in which the Asmari limestone formed. The onset of evaporite deposition in the southern basin was essentially synchronous, although there was some overlap at the basin margins. In the Iraq-Iran Basin, however, evaporite deposition did not begin until the late early Miocene, and as late as the Middle Miocene in northern Iraq. In a region with little net inflow and high evaporation, density layering developed with halite precipitating in the cooler waters in

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The Latest Part of the Zuni and Tejas Cycles in the Middle East: The Cenozoic the deeper parts of the basin and the less soluble gypsum forming around the basin margins. Under extreme conditions, even potash salts were precipitated. The Gachsaran Formation accumulated under such conditions, although the stage of potash deposition was not reached. The onset of deposition of the Gachsaran Formation was essentially synchronous, and only at the basin margins is there evidence of onlap. On the northeastern side of the Arabian Gulf, the Burdigalian Upper Asmari limestone was deposited from southwestern Iran to northeastern Iraq. Diachronous evaporites are associated with it, ranging from the late early Miocene in southwestern Iran (James and Wynd, 1965) to the middle Miocene in northern Iraq (Bellen et al., 1959). The Gachsaran Formation is largely evaporitic and, hence, forms a good cap rock to the Asmari reservoirs. The cap-rock properties deteriorate in the coastal Fars Province of Iran and over the Qatar Arch to the Abu Dhabi boundary with Saudi Arabia, but the formation may contain carbonates with moderate to good porosity, and these contain small amounts of gas in Abu Dhabi (Alsharhan, 1989). During the Miocene and Pliocene, farther from the Arabian Shield margin toward the Arabian Gulf, a widely distributed sequence of non-marine to marine clastics, lacustrine marl and carbonates was deposited. An influx of argillaceous material from the northwest resulted in the spread of marl and clays over the Fars Platform in offshore Iran and the basin area; however, these give way to Pliocene carbonates further to the south (Fig. 9.54). These sediments also are found in onshore Qatar as a sequence of marl, chalk, shelly limestone and gypsum resting on the Lower Fars (Sugden and Standring, 1975). The beds resemble the sediments of the Mishan Formation, particularly in the presence of gypsum beds. With the exception of minor subsidence during the early Miocene, when sediments of the Lower Fars were laid down, the late Tertiary of Qatar has been one of regional uplift, erosion or nondeposition (Sugden and Standring, 1975). Widespread emergence of the Arabian Platform in the middle Eocene reduced Tethys to a relict sea. Since that time, emergence has persisted, and continental conditions have obtained over central and eastern Arabia, with the exception of intermittent, minor flooding of the present coastal area in the middle Miocene (Powers et al., 1966). More than 600 m (1,960 ft) of sandstone, sandy marl and

sandy limestone filled and levelled the Rub al Khali Depression during Miocene-Pliocene time (Fig. 9.55). Only rare non-marine fossils have been recovered from this clastic section to date, and despite numerous wells, the first few hundred meters are poorly sampled and little studied (Powers, 1968). The vast lava fields over the shield areas and in northwestern Arabia attest to considerable volcanic activity during the Mio-Pliocene and later. The paleogeographic evolution of the northern Arabian Platform during the early and middle Miocene is marked by transgression, which resulted in the formation of a broad, relatively shallow basin extending from eastern Syria southeastwards into Iran. The filling of this basin took place in two phases: an earlier phase of calcareous and marly sediments, followed by lagoonal evaporites with a peripheral rim of clastics (in Iran and Saudi Arabia). At the end of this interval, progressive uplift began, signalling a further stage in the development of the Zagros-Taurus Mountain System. As a result, the late Miocene and Pliocene sediments form part of a coarsening-upwards sequence, ending with massive conglomerates and molassic sandstone filling the foredeep. These sediments are contemporaneous with the late-stage orogenic events. The beginnings of the Zagros Pliocene folds and nappe emplacement may date back to the late Miocene in Kurdestan and the northern High Zagros (Berthier et al., 1974); certainly, the intensity of the movements increased from the Miocene into the Pliocene. On the eastern side of the Arabian Gulf, by the end of the Pliocene, uplift reached the foredeep basin, and molasse sedimentation came to an end as the basin underwent mild block faulting. The present successor foredeep basin has shifted further west and coincides with the axis of the Arabian Gulf and its northern extension, the Mesopotamian Depression. In the central part of the Jordan-Wadi Araba Graben, a thick series of evaporites formed during the MiocenePliocene, deposition continuing into the lower Pleistocene. These evaporites reached a thickness of approximately 4,000 m (13,100 ft), while a clastic facies such as shale, marl, sand and gravel accumulated marginal to the evaporite (Bender, 1974). This clastic sedimentation of fluviatilelacustrine type continued in the graben during the PlioPleistocene, accompanied with some volcanic intercalations in the northern part of the graben (Bender, 1974).

465

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Chapter 10 HYDROCARBON HABITAT OF THE MIDDLE EAST : AN OVERVIEW

INTRODUCTION

is, along the Taurus-Zagros Belt), shows have been reported from most countries in the Middle East (Fig. 10.1). Many of the fields in southwestern Iran (NaftKhaneh and Masjid-i-Sulaiman) and northern Iraq (Kirkuk and Qaiyarah) were discovered through their proximity to surface oil seeps. The visible evidence of the "oiliness" of the Middle Eastern countries has been known and described throughout the centuries, and reference to it can be found in Lees, 1951, 1934; Link, 1952; Iraq Petroleum Co., 1956; British Petroleum Co., 1956; Fox, 1956; Dunnington, 1958; Temple and Perry, 1962; Langozky, 1963; Mostofi and Paran, 1964; Ahmed, 1972; Lebkuchner et al., 1972; and Gansser, 1955. Since the early '50s, however, most of the discoveries have come as a result of geophysical exploration as structures that could be determined from surface outcrop, with or without surface seepage data, have been tested. As this facet of hydrocarbon study has seldom attracted much attention, a brief review follows to rectify this omission. It is implicit in the review that the process of oil leakage has gone on through time, and it may be a fair assumption, since it cannot be verified, that as much or more oil has been lost as has been preserved. In an excellent review, Beydoun et al. (1992) point out that not all losses are to be attributed to Miocene tectonics; some are due to earlier

The presence of hydrocarbons in the Middle East has been known since historic times, and they have been used in a variety of ways. Pitch is reported to have been used to waterproof the Ark, and was used by the Sumerians not only for waterproofing, but as a bonding material in construction. Both the ancient Persians and Alexander the Great created incendiary weapons and used them in warfare. In Iraq, Sennacharib (704-682 B.C.) used them in the construction of a canal. Large-scale commercial exploitation of liquid hydrocarbons is, however, a 19th-20th century phenomenon. At the end of 1948, the Middle East provided only 4.9% of the world's production, but that had grown to 15% one year later. The estimated reserves in 1944 were 18 B.bbl, but that figure had increased to 32 B.bbl four years later; and, only one year later, the discovery of the Nahr Umr and Zubair fields (Iraq) and the Fadhili and Ghawar fields (Saudi Arabia) added significantly to that total. The magnitude of the petroleum potential in the Middle East is so well-known that little documentation is required. The only areas with production and potential approaching that of the Middle East are in the Pricaspian Basin and the West Siberian Basin of the former USSR. Saudi Arabia ranks second in proven reserves and first in exporting oil, replacing the former Soviet Union with its rapidly declining production. Exploration in the producing areas of the Arabian Gulf and in the Zagros generally is in the mature phase; after many years of increasing reserve estimates, the figures are beginning to decline, despite the dramatic increase in reserve estimates of gas. However, there still are major untested areas, particularly in Iraq, Jordan and Yemen, and new play concepts and the introduction of new technologies may reverse the decline, at least temporarily. The combination of a number of factors, such as the accumulation of a thick sequence of sediments; the presence of excellent reservoir rocks (mainly carbonates); the wide, regional distribution of seals; the close association of reservoirs with the intrashelf, basinal source rocks; and the excellent, large anticlinal traps with extraordinarily wide closure all have contributed to the hydrocarbon richness of the Middle East.

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SURFACE OIL AND GAS SEEPS

Although most of the information on the occurrence of hydrocarbon shows relates to Turkey, Iran and Iraq (that

Fig. 10.1. Middle East map showing the location of oil and gas seepages (triangle).

467

Sedimentary Basins and Petroleum Geology of the Middle East events such as the late Cretaceous to (locally) early Paleocene collision event associated with ophiolite obduction. The Upper Cretaceous impregnation with bitumen of the outcropping reef limestone in the Kurdish Mountains in northeastern Iraq is one example of a pre-Zagros Basin hydrocarbon loss. The presence of water-born, bituminous pebbles in Paleocene-Lower Eocene conglomerates in northeastern Iraq, the impregnation of Lower Fars sediments deposited on top of the Lower Miocene Jeribe and Euphrates limestone and the presence in the Pliocene Bakhtiari beds of detrital bitumen provide ample evidence of the loss of hydrocarbons over a protracted period of time. As the following review will emphasize, no simple generalization concerning the source of the oil seeps can be made. While most are related to late Mesozoic or Cenozoic sources, the source of the oil may be derived from Paleozoic rocks in some areas. Structurally, the greatest number of shows are in the Zagros Fold Belt, in the mountains and foothills belt, where the Cenozoic folds and faults provide easy migration paths. These shows, consequently, are not necessarily good indicators of the location of the structures from which the hydrocarbons are escaping. In contrast, in regions where deformation is less intense, a more direct relation between seep and structure is possible, as in the Burgan Field in Kuwait.

Turkey Asphaltic substances in southeastern Turkey were systematically mapped and described by Lebkuchner et al. (1972). Vein-like deposits originated from the filling of deep, open tensional cracks above and below thrust faults and in faulted anticlines, where masses of asphaltic material were squeezed toward the surface. The source rocks were black, bituminous shale diagenetically altered to asphaltic pyrobituminous, black shale. They occur from near the middle of the Middle Triassic to Upper Cretaceous in a calcareous and dolomitic limestone sequence. They were examined by the Turkish government, not as an indicator of the presence of hydrocarbons as might first be thought, but as an alternative solid fuel. Temple and Perry (1962) reported that the Permian Hazro Formation, mainly littoral sandstone in southeastern Turkey, was impregnated with asphalt. The sandstone overlies hydrocarbon-rich Siluro-Devonian shale, and the prospect that the asphalt impregnation may have been an early expulsion product from this shale and later transformed to asphalt cannot be excluded in the absence of geochemical data. Asphalt also is found in mid-Cretaceous rocks, which are exposed in an extension of the Taurus Fold Belt into the Kurd Dag and Amanos Mountains in both southeastern and northwestern Turkey. The hydrocarbon shows, and the active oil seeps on the shore of the Gulf of Iskenderun in southern Turkey, which may be related to either Tertiary

468

reservoirs in the fold belt or to oil generated in the Neogene Basin in the Gulf of Iskenderun, are witness to the oil-generating capacity of these younger sediments. Despite the seeps and a belief that there must be important oil accumulations in Turkey, Mason (1930) was pessimistic about prospects; however, Eyoub (1931), who examined prospective areas based upon oil shows, was more optimistic, especially concerning the Mardin area. However, as late as 1939, drilling in the Mardin area, although finding pockets of gas and asphalt and viscous oil shows, had not uncovered any commercial prospects (Tasman, 1939).

lran The Mountain Belt and the Foothills Zone of the Zagros in Iran and Iraq are rich in oil and gas shows (Lees, 1934, 1951), and numerous small veins and pockets of asphaltite occur in the Eocene, Cretaceous and Jurassic marlstone and limestone. Surface seepages are much less common than the solid residues occurring in the rocks; nevertheless, they are distributed widely from north of Mosul in Iraq to Bandar Abbas in southeastern Iran. For the most part, the seeps are small, but some may yield several gallons a day; since the beginning of the Tertiary, at such a flow rate, this could amount to as much as 50 MM.bbl, assuming a fairly constant flow. The most prolific oil and gas seepages occur in the Foothills Zone. Many are close to the Tertiary Asmari limestone outcrops and represent the final phase of exhaustion of former oil accumulations resulting from exposure of the reservoir. In these instances, oil is contained in linked fractures that provide easy migration paths, as porosity of the Asmari Limestone itself is low (Lees, 1933). Other seeps are found in the Lower Fars (Miocene), where erosion has weakened the cover rocks over reservoirs sufficiently to permit leakage to the surface. In the fold belt, leakages generally are the result of escape along fracture zones, faults or thrusts which occur above the Miocene anhydrite cap rock. Where they occur within the Asmari Limestone or older rocks, they may indicate eroded oil fields or mark old migration paths. In the Masjid-i-Sulaiman Field, where the young fold is intact and final structural adjustment still is incomplete (Link 1952), in the absence of major faulting and in the presence of a good cap rock, the seeps occur at the turnover of the crest, where it is assumed there was enough minor fracturing of the cap rock to allow upward passage of the oil. In the Makran area of southeastern Iran, three oil seeps are known (Mostofi and Paran, 1964), with the oil coming from limestone and serpentinites of the ophiolitic melange. There also are several gas seeps associated with salt-water springs and many mud volcanoes, some no longer active. The seeps are found mainly in the Middle Makran Formation, but do occur in the Upper Makran For-

Hydrocarbon Habitat of the Middle East mation (Miocene to Pliocene) and the flysch sediments. The most spectacular of the mud volcanoes is Napag, which erupts gas and mud, possibly containing blocks of Middle Makran sandstone, every five to ten seconds. In the main central basin of Iran, oil indications occur in Eocene shale and Oligo-Miocene limestone and marl. Gas is indicated in sour gypsum and in the sulfur mines over a somewhat wider area (Mostofi and Paran, 1964). In the Qum area, traces of oil were found in a khanat (a subsurface water channel) cut in marine Oligo-Miocene limestone in 1934, and a second was discovered in the Mil area some 25 km to the west in 1951. In 1956, well Alborz-5 on the Alborz structure in the Qum area had a spectacular blowout (Gansser, 1955). In the southern part of the Caucasus Province and Caspian Tertiary Province of Iran, oil and gas seepages are known in the Moghan, Rasht and Mazanderan basins (Mostofi and Paran, 1964); in the Gorgan Plain, two large mud volcanoes occur over anticlinal trends, one of which still has good gas and oil indications.

lraq It is clear from the oil and/or gas seeps in Iraq that the seeps are not over the subsurface structure. In the Naft Khaneh Field, oil and gas escaping through fractures in the cap rock of the field migrate along a thrust fault to the surface (Link, 1952). The thrusts resulted from late Neogene compressional folding with d6collement and flow of the evaporites. The surface seeps are not, therefore, good indicators of the exact location of the structure that was the source of the seep. In the Hit area in western Iraq, about 150 km west of Baghdad, there are extensive seeps of heavy sulfurous oil (Staff, Iraq Petroleum Co., 1956), which form small asphalt lakes all the way from Hit to the Euphrates River, a distance of 40 km. The seeps are found in porous Lower to Middle Miocene limestone and are believed to be due to upward migration along buried north-south faults. A well drilled at Awasil found heavy oil (10~ in sands at the base of the Middle Cretaceous and in limestone streaks in probable Upper Jurassic anhydrites. Most of the bitumen found in Iraq generally is considered to be of Late Jurassic age, although the reservoirs now being drained are much younger (Dunnington, 1958). In some of the very heavy, sulfurous seeps, the bitumen may be derived from the Upper Fars limestone (Upper Miocene) after being resedimented following escape into the Middle Miocene (Lower Fars) sediments.

Kuwait Surface exploration following the granting of a concession to the Anglo-Iranian Oil Company and Gulf Oil Company located three oil or gas seepages in positions that suggested they may be above the crest of a Tertiary uplift (Fox, 1956). The first of these, Bahrah, was drilled in 1936/1937 without encountering oil in commercial

quantity. Preceding the discovery of the Burgan Field in 1938, an extensive bitumen lake was found by shallow drilling and the excavation of shallow pits. Development of the field itself was delayed by the advent of World War II, and production did not begin until mid-1946.

Saudi Arabia A 5-cm stringer of bitumen in anhydrite overlying the Arab producing horizons is one of two known occurrences of oil in sediments pinching out above the Upper Jurassic Arab Formation. A second, a tar seep, was found at Dahl Hit in a small solution cave near Riyadh (Link, 1952). Along the Red Sea coast, especially in the Farasan and Dahlac islands, there are scattered oil seeps that have attracted the attention of many companies, as they suggest the generation of oil at some time in the history of the Red Sea Basin (Ahmed, 1972). Many of the seeps seem to indicate migration along fault planes.

Bahrain A small gas seep was found above the Bahrain structure, and the first well drilled struck oil (Link, 1952).

Yemen In the former South Yemen, bituminous occurrences are associated with Jurassic salt, with bitumen and oil in shale and limestone. Gilsonite is reported as a result of very early oil expulsion.

Syria, Lebanon and Jordan In the central Syrian Jebel Bishri Anticline, asphalt is found in Upper Cretaceous and Miocene rock and along the boundary faults of the structure. The source of these shows may lie in the Euphrates Depression to the east. Asphalt shows also are recorded in rocks in the faulted Palmyra Fold Belt, occurring mainly in Middle and Upper Cretaceous rocks. It is believed that this represents oil generated in these organic-rich rocks as a result of deep burial during the early Tertiary. Large quantities of asphalt also are found in Senonian rocks in the southern Bekaa Valley; in particular, the deposits near Hasbaya are well-known and have been exploited since ancient times. The Hasbaya deposits have been related to those along the Jordan-Dead Sea Rift in the Dead Sea Valley 300 km to the south. Lebanon, too, has asphalt in the Middle Cretaceous rocks in the northwestern corner of the country, which, although not abundant, may signal the dissipation of oil accumulations exposed to Tertiary erosion. In the Jordan Valley-Dead Sea area, large amounts of asphalt and heavy oil are found in Paleozoic sandstone, in fractures in Jurassic and Cretaceous limestone, in Neogene

469

Sedimentary Basins and Petroleum Geology of the Middle East alluvial sands and as large masses floating in the Dead Sea. The probable origin is the Danian oil shale or, more accurately, dolomitic marl, which crops out in the Dead Sea Rift (NRA,1989). Escape is mainly along the margins of step-faulted blocks. The asphalt and oil are immature and sulfurous, and it has been assumed that the asphalt occurrences point to mature oil at depth in the rift (Langozky, 1963). In the 1920s, there was a report of flowing mature oil along one of the eastern border faults consistent with this interpretation.

HISTORY OF EXPLORATION

Although the first concession was granted in the 1890s, it was abandoned after several years of unsuccessful exploration drilling. The first oil discoveries in the Middle East were made by the D'Arcy Company, which was granted a concession in 1901 for work in southwestern Iran. The company was attracted to the Masjid-iSulaiman Anticline by copious seeps and gas escapes from the crest of the structure. Drilling led to the discovery of the Masjid-i-Sulaiman Field in 1908, the first field to be discovered in the Middle East. In 1909-1910, a pipeline was constructed from Masjid-i-Sulaiman tO Abadan, and the refinery constructed there began operations in 1914. The fact that all subsequent fields discovered in Iran, up to 1938, were associated with surface oil or gas seeps underlines the importance of surface shows in the early exploration efforts. The pace of discovery, at first relatively slow, increased rapidly in the 1930s and '40s. Heft Kel began production in 1928. The Bahrain Field was discovered in 1932 and oil in commercial quantities in 1938. In Saudi Arabia, the Dammam Field was the first oil field discovered in 1938, the Abu Hadriya Field was found in 1939, and the Abqaiq Field was discovered in 1940. In Iran, the Gachsaran Field was found in 1941, and the Agha Jari Field was found in 1944. In the same year, the Qatif Field was found in Saudi Arabia. The Lali fields were discovered in Iran in 1948 (Lees, 1950), and the Fadhili, Ain Dar and Haradh fields (now known as the Ghawar Supergiant Field) of Saudi Arabia were found in 1948-49 (Steineke and Yackel, 1950). As a result, as early as 1944, de Golyer (1944) could underline the growing importance of the Middle East oil fields and a shift away from the United States-Caribbean as the center of production. Initial exploration in the Middle East was carried out by companies with very broadly based, long-term concession agreements. These subsequently have been modified to resolve questions of inequity, and to take into account the national aspirations of the host country in the light of changing economic and political conditions. The companies that today hold major oil interests in the Middle East m British, Dutch, French and American m generally are those with a long history of activity in the region. However, the explosion in the demand for hydrocarbons after World War II, combined with increasingly sophisticated

470

exploration methods and the introduction of new techniques, resulted in an increase in the number of companies seeking concessions. The present summary of the history of exploration is based upon the publications of ARAMCO (1960), Tiratsoo (1984) and Beydoun (1988), as well as the annual summaries provided in the American Association of Petroleum Geologists Bulletin, World Oil, the Oil and Gas Journal and other, more industry-related sources. Following the early exploration phase, which began early in the century, Iran changed the operating rules in 1954. The operating concession to the Anglo-Iranian Oil Company (AIOC) was taken over by the National Iranian Oil Company (NIOC), which was given the right to carry out all oil exploration and production in an area designated as the Agreement Area. This was an approximately linear belt in southwestern Iran stretching a distance of 1,392 km (870 mi) with a width of 192 km (120 mi) covering parts of the Lurestan, Khuzestan, Fars and Kerman provinces. The area closely approximates that of the original AIOC operating area. In 1957, NIOC signed a number of jointventure agreements with various companies, agreements principally in the offshore region and in the Zagros outside the foothills and fold belt. In 1973, the Iranian Oil Exploration and Production Company (IOEPC) became the oil service company of Iran, leaving to the National Iranian Oil Company (NIOC) the responsibility for production operations, in return for discounts on liftings. Discoveries were made, some of which rapidly came on line, as others remained undeveloped. Most of the onshore fields lie in the Dezful Embayment in the southern province of Khuzestan, where intense folding has resulted in a number of long, sinuous anticlines paralleling the Zagros Mountain Belt. Twenty-two of the onshore fields account for 92% of crude production. The remaining 8% is derived from 13 fields discovered in "recent" years (Tiratsoo, 1984). Iran was the first country in the Middle East to export gas; in the 1970s, vast reserves were discovered during the development of fields such as Marun, Ahwaz, Agha Jari and Gachsaran. Other discoveries were made in the central Iranian Basin, as in Sarajeh (near Qum), Tange-Bijar near the Iraq border, and the Khangiran Field (Khorasan Province). In neighboring Iraq, the first concession was awarded in 1914 to the Turkish Petroleum Company, a British/German group; however, after independence in 1918, the company was renamed the Iraq Petroleum Company (IPC). In 1922, the composition of the company changed to include Dutch, French and American interests. The concession agreement was revised in 1931. The Kirkuk Field was first discovered in 1927; its reserves were estimated at 4 B.bbl in 1944, but they were upgraded to 7.5 B.bbl three years later. The Anglo-Persian Oil Company was granted a small concession in which the Neft Khaneh Field was discovered near the Iranian border (that part extending into Iran is called the Naft-i-Shah Field) in 1923. The major discovery of the Kirkuk Field was made in 1927 in northern Iraq by the Turkish Petroleum Company four years after the

Hydrocarbon Habitat of the Middle East granting of the concession, but the company name subsequently was changed to IPC. Then, the Bai Hassan (1953) and Jambur (1954) fields were discovered. In the concession in southern Iraq awarded to IPC, the Zubair Field was discovered in 1948, and the Rumaila Field was discovered in late 1953. The Iraq National Oil Company (INOC), formed in 1964, took over exploration fights to the rest of the country outside of the producing fields. The company also operated the Qaiyarah heavy-oil accumulation discovered near Mosul by British Oilfield Development in 1927. INOC entered into a service agreement with the French Company Elf-ERAP, and the Siba Field near Basra was discovered in 1969, with Jabal Fanqi in 1970 and Abu Ghurab in 1971. Buzurgan (1969) also was found in the former Basra Petroleum Company exploration area. Following agreements reached with the Indian Oil and Natural Gas Commission and Braspetro, the Ma'jnoon Field was discovered by the latter in 1976. INOC became the sole exploration and production agent in Iraq. Exploration activity in other parts of the Arabian Gulf picked up in the 1930s. In 1932, the Bahrain Petroleum Company (BAPC) began exploration and struck oil in the Jebel Dukhan structure, which subsequently was developed as the Awali Field. Since that time, despite extensive exploration efforts, no further discoveries have been made in Bahrain. In Qatar in 1935, a concession was granted to the Anglo-Iranian Oil Company, which subsequently transferred it to an IPC affiliate, Petroleum Concessions Ltd. They, in turn, formed a subsidiary operating company, Petroleum Development (Qatar) Ltd. Exploration began in 1937, and oil was struck in 1940 in well Dukhan-1, but oil production was delayed by World War II until about 1949. The company changed its status to become an affiliate of Petroleum Concessions and, subsequently, changed its name to Qatar Petroleum Company in 1953. The concession granted in 1949 to Superior Oil Company and the Central Mining and Investment Corporation was relinquished in 1952 after failure to find a structure. An offshore concession to Shell in 1952 was transferred to Shell Oil Company of Qatar in 1954. They began the exploration in mid-1953, which led to the discovery of the giant fields, Idd el Shargi (1960) and Maydan Mahzam (1963). Another offshore field (El Bunduq) was discovered in UAE waters by Abu Dhabi Marine Areas Company (ADMA) in 1964, but it now straddles the boundary between the Emirates and Qatar because of a border adjustment. The Bul Hanine Field discovered in 1965 was not developed until 1970, following the border adjustment agreement with the Emirates in 1969. In 1971, Shell (Qatar) discovered the supergiant gas field, North Field (previously known as the Northwest Dome Field), which extends from the onshore into Qatar waters as far as the Qatar-Iran boundary. On December 23, 1934, the Kuwait Oil Company was granted a concession. Their first well north of Kuwait Bay, drilled in 1936, was unsuccessful, but their second, drilled in the Burgan area, found oil in April 1938. Magwa was

discovered in 1951, Ahmadi in 1952 and the major find at Raudhatain, northwest of Kuwait Bay, in 1955, then Sabriya in 1957 and Minagish in 1959. Together, these made Kuwait one of the major producers of crude oil in the Middle East, and Kuwait ranked fourth among the world crude-oil producers by 1966. Production peaked in 1973. In 1950, the Kuwait National Oil Company was formed; initially a products marketing and refining company, it subsequently entered the exploration field working in expired concession areas with the aid of foreign companies, but failed to make any new discoveries. In 1975, Kuwait acquired full control over the assets of the Kuwait Oil Company, which then became the sales company. Kuwait and Saudi Arabia share equal rights in the Neutral Zone lying between the two countries. In 1948, Kuwait granted oil rights to Aminoil, and Saudi Arabia granted similar rights to Getty Oil Company the following year. Aminoil discovered the Wafra Field in 1953. The Japanese-owned Arabian Oil Company, which obtained a concession in 1958 in the offshore Neutral Zone, found the Khafji Field in early 1960 and the A1 Hout Field in 1963. Two onshore producing fields, Fuwaris (1961) and South Umm Gudair (1966), were discovered, and two small and undeveloped offshore fields (Lulu and Dorra) were found in 1967. The year 1933 saw the Turkish government create the Petroleum Exploration and Exploitation Administration, which became the department of Mining Research and Exploration Institute of Turkey (MTA) in 1935. The first well spudded in Turkey in 1934 was at Bashirin, followed soon after by several wells drilled by MTA. The first commercial field, dating back to q940, was Raman in southeastern Turkey, where a second MTA discovery,the Garzan Field, was made in 1950. In 1954, the government formulated the Petroleum Law, which permitted private companies to explore in Turkey and encouraged several European and American companies to begin exploration. In the mid- 1950s, the existing oil fields were transferred to another government agency, the Turkish Petroleum Corporation (TPAO). Revision of the petroleum laws in 1983 renewed exploration interest, and several foreign companies are engaged in joint ventures with TPAO, with most of the interest concentrating on the southeastern part of the country. There presently are some 58 producing fields, but production is low on the whole. American exploration in Saudi Arabia began with systematic, geological field work combined with geophysical exploration (gravity, magnetic and seismic). The government of Saudi Arabia granted the first exploration concession in 1933 to Standard Oil of California (now Chevron). The first well drilled on the Dammam Dome in 1935 was dry, but drilling on the structure continued until well Dammam-7 proved oil in 1938. Exploration and development continued during the war years, with further discoveries during 1940. After the discovery of the Dammam Field, the California Arabian Standard Oil Company was renamed the Arabian-American Oil Company

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Sedimentary Basins and Petroleum Geology of the Middle East (ARAMCO), and ownership was expanded to include Exxon and Mobil. Over the years, the outline and structure of the supergiant Ghawar Dome gradually was blocked out by the combination of gravity and magnetic mapping supplemented by structural drilling after oil was discovered at Ain Dar in 1948, at Haradh in 1949, at Uthmaniya in 1951 and at Shedgum in 1952. Several relinquishments reduced the original ARAMCO concession to about one-fifth its original size, but no new discoveries were made, despite onshore and offshore exploration of the relinquished areas by Phillips and Agip. Over the years, the Saudi government has taken an increasing number of shares in the ARAMCO concession until it is now a state-owned company, with ARAMCO reduced to the status of a service company. Exploration in the United Arab Emirates (U.A.E.) (previously known as the Trucial Coast) began in 1936 in Abu Dhabi with the founding of the Petroleum Development Trucial Coast (PDTC) as a subsidiary of IPC. Following a geological reconnaissance, PDTC signed an agreement in 1939 for exploration in the Trucial Coast. Gravity and magnetic surveys were completed onshore in 1947-48 and offshore by 1954. Seismic surveying began in late 1949 and continued into early 1950. In 1953-54, the Murban/Bab structure in the onshore was discovered. The company was renamed the Abu Dhabi Petroleum Company (ADPC) in 1962 and the Abu Dhabi Company for onshore operations (ADCO) in 1982. The company is responsible for the discovery of the Bab, Bu Hasa, Asab, Sahil, Shah and Jarn Yaphour fields, as well as other onshore fields. Parts of the areas relinquished by the company have been granted and explored by other companies. Rights to offshore exploration were granted to the D'Arcy Exploration Company in 1953, which subsequently were reassigned to the Abu Dhabi Marine Areas Ltd. (ADMA). The original agreement was amended in 1966 to cover periodic relinquishments after the discovery of two giant fields (Umm Shaif in 1958 and the Zakum field in 1964). In 1971, the Abu Dhabi National Oil Company (ADNOC) was formed, acquiring 60% of ADCO in 1974 and 60% of ADMA in 1978. Other companies have obtained concessions in the areas relinquished by ADMA, such as the Umm A1 Dalkh Development Company and the Abu Dhabi Oil Company of Japan. In the other emirates, the Dubai Marine Areas (DUMA) was formed by Compagnie Francais des Petroles and Hispanoil; in 1961, when PDTC relinquished their concession, CONOCO took over the onshore area as Dubai Petroleum Company and acquired a 60% share of DUMA to become the offshore operator. This ultimately resulted in the discovery of four fields, the Fateh (1964), Southwest Fateh (1970), Rashid (1976) and Falah (1976) fields. ARCO later took over the onshore concession and discovered Margham (1981). In Sharjah, PDTC drilled onshore unsuccessfully in the 1950s, followed by MECOM and Shell. In 1970, an offshore concession was granted to the Buttes Group, which found the Mubarak

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Field in 1972. AMOCO took over the onshore concession in 1978 and made a major discovery of the Sajaa Oil/Condensate Field in 1980. Union Oil Company began exploration drilling in Ras al Khaimah in 1969 and discovered commercial oil and gas in 1971. Gulf Oil obtained an offshore concession in 1981 and discovered light oil in the Saleh Field in 1983, with initial recovery of 200 MM.bbl oil and 1.2 TCF gas. Mecom and Shell began exploration drilling in Umm al Qawain in the 1960s without success, and not until 1976 did the United Group, with Zapata as operator, bring in gas and condensate in well Umm al Qawain-1. In Ajman, only a small discovery, the A1 Hamidiyah Field, was made by Landoil. The company surrendered the concession, which now is operated on a small scale by the Ajman Emirate. In Oman, the beginning of exploration dates back to 1937, with the granting of a concession to Petroleum Development (Oman) Ltd., which covered the country. After drilling a number of dry holes, Iraq Petroleum Company (IPC) relinquished their interest, leaving Shell, Partex and other partners. In 1953, City Services and Atlantic Richfield began extensive exploration in South Oman (Dhofar) and discovered abundant heavy oil in 1955, leading to the discovery of the Marmul Field one year later. Continued exploration by Shell and Petroleum Development Oman (PDO) led to the discovery of commercial oil quantities in the Yibal (1963), Natih (1963) and Fahud (1964) fields. The Compagnie Francais des Petroles joined the Shell Group in 1964 and participated in several discoveries in northern and central Oman. As a result of an extensive drilling and development program in southern Oman during 1969, a number of commercially exploitable pools of relatively light oil were made by PDO. The government of Oman opened several new areas in northern and central Oman, which led to the signing of concession agreements with Occidental, Elf Aquitaine and Japex. The 1970s then turned out to be the decade in which fields in northern and central Oman were brought on line, and 33 of the 50 known fields currently are on stream. Exploration in Jordan and Syria dates from the 1950s. In Syria, IPC pulled out in 1950, after drilling several unsuccessful exploration wells; however, the Menhall Oil Exploration and Exploitation Company had better success, for after being granted a concession in 1955, they found heavy sulfurous oil at Karatchok in 1956. The German Concordia Company, whose concession had been granted in 1956, discovered the Souedie Field in 1959. The Syrian General Petroleum Company, later the Syrian Petroleum Company (SPC), discovered the Rumaila Field in 1962. The company was the sole operator from 1964 to 1975 and made a number of discoveries in the northeastern part of the country, including the discovery of light oil in the A1 Jebissa and Ghouna fields in 1979. Concessions in the eastern part of the country awarded to the Romanian State Oil Company, the Syrian American Oil Company and Deminex subsequently were relinquished without any discovery. However, the Pecten Group discovered the

Hydrocarbon Habitat of the Middle East Thayyam Field in 1984; and, Marathon, whose concession lay in the Palmyrides region, had two gas and condensate discoveries, Cherrife (1981) and Ash Shaer (1985). The most prospective regions still lie in the northeastern and north-central parts of the country, and many companies have been awarded blocks. SPC continues to explore and develop new discoveries. Between 1957 and 1978, exploration in Jordan attracted Phillips, Pauly, Total, Mecom and the Yugoslav company INA. Fifteen wells were drilled, but although significant shows were found in three wells, none were found to be commercial prospects. The Jordanian State Natural Resources Authority (NRA) drilled many wells in the decade 1963-1974, two of which encountered oil and gas shows in Turonian sediments. Later, during the 1980s, NRA shot a number of seismic lines and drilled about 18 exploratory wells, leading to the discovery of the Hamzeh Field in 1984. The field now is in the stage of production testing several producing horizons. In 1987, the Risha Field was discovered near the Iraqi border, producing gas from Silurian sediments. Exploration in Yemen began in 1954, when Amoco drilled some dry holes in former South Yemen. Subsequently, the South Yemen Petroleum Company, Sonotrach and the Russian Technoexport drilled many wells and evaluated some areas for bidding. Later, Mecom drilled unsuccessful exploration wells in 1961 in the Red Sea littoral of their North Yemen concession, followed by an equally unsuccessful Shell program between 1976 and 1980. In 1976, AGIP obtained a production-sharing agreement for an offshore concession in the Gulf of Aden, an area that yielded a discovery at Sharmah in 1982. The first success onshore in the former North Yemen was that of the Hunt Oil Company, which was awarded an onshore concession in 1981 and discovered oil in the Alif Field in 1984. Further exploration results in the Marib Graben indicate that other discoveries have been made.

CURRENT STATUS OF MIDDLE EAST OIL In 1910, the world output of crude oil was only 327.8 MM.bbl, and the Middle East contribution was negligible, because the first oil field (Masjid-i-Sulaiman) to be found in Iran was discovered only in 1908 and was not yet producing (Tiratsoo, 1984). By 1920, Iran was contributing, for the first time, an appreciable proportion of oil m about 1.8% of the world's total production. The oil production in the Middle East increased when Iraq became a producer, and the Middle East output had attained 4.8% of the world's total production by 1940. Gradually, in 1946, the Middle East contribution increased to 8.9% of the total world production, as Saudi Arabia became a world-scale oil producer. Following years of continuous growth, when output approximately doubled each decade, the Middle East accounted for nearly 39% the world's production by the end of 1974. It then slipped to about 22.6%. The steady

growth in the volume of ultimate recoverable oil equivalent from 1908 through 1980 is summarized in Table 10.1. Table 10.2 shows the annual production of each country in the Middle East from 1918 through 1994. The observed fluctuations in the published production figures partly reflect the dominant position of the former USSR, which developed rapidly as new areas were opened up after the disruption and destruction caused by the Gulf War. Other contributing factors were the reduced production of the leading producing countries during the Gulf War, OPEC's decisions linked with the maintenance of crude oil prices, and production from new countries or regions such as China, the North Sea and South America. About two-thirds of the world's ultimate recoverable oil lie in the Arabian Gulf region, of which about half lies in the elongate anticlinal folds of the Simple Fold Belt of the Zagros Range. About two-thirds of the proven gas reserves are associated gas (that is, gas associated with oil). The remaining third, the non-associated gas, mostly is trapped in Upper Permian reservoirs. About two-thirds of the proven remaining gas lies within the Simple Fold Belt of the Zagros Range, with most of the remainder in traps on the Arabian Platform, where retention of both oil and gas is excellent due to the lower degree of fracturing of reservoirs and seals in comparison with the Zagros. The remaining proved reserves, including all additions due to secondary and Tertiary recovery, field expansion or drilling to deeper reservoir horizons (that is, the expanded remaining reserves of Grossling, 1976) are considered to be about 150% of the proved reserves. As the deeper reservoirs of the Middle East often prove to be quite rich in hydrocarbons, the estimated factor of 1.5 probably is on the low side for gas, but on the high side for oil. The estimated range for undiscovered resources in traps so far undrilled is between 20 and 50 B.bbl, with a 55% chance that the amount lies between these limits. Most undiscovered oil is expected to lie in conventional traps. The most promising area for exploration is Iraq, which is only partially explored and where there is a 60% chance that another 10-25 B.bbl may be found. The next most attractive area is in the U.A.E., where the chance factor of discovering another 10-20 B.bbl is rated at 75%. In Iran, where the estimate is for potentially an additional 210 B.bbl and Saudi Arabia with 3-10 B.bbl more to be found, the chance factors are 50% and 51%, respectively. In Syria, there is a 50% chance for a future potential of 0.5 to 4 B.bbl. Oil in smaller amounts may yet be discovered in Kuwait, the northern part of the U.A.E., the Republic of Yemen and Oman, where the discovery of giant fields cannot be excluded. The least promising areas for further discoveries are Bahrain, Jordan and Lebanon. Expectations are high for future discoveries of large volumes of associated and non-associated gas in known fields, especially in deeper horizons. There is a chance factor of 75% that fields with 500-1,500 trillion cu ft will be discovered, and it is anticipated that much of this will be in Iran, especially in the Simple Fold Belt of the Zagros

473

Sedimentary Basins and Petroleum Geology of the Middle East Range along the Arabian Gulf, where Permian rocks are one of the main reservoirs. Other countries with a high gas potential are Iraq (100-500 trillion cu ft potential with a 50% chance factor) and in offshore Qatar, where there already are major finds in the North Field (Grossling, 1976). Non-associated gas discoveries in the 2-10 trillion cu foot range can be anticipated in the U.A.E., Saudi Arabia, Syria and Turkey, although the chance factor associated with each is different. Potential resources in the 10-50 trillion cu foot range in Bahrain and Oman have chances of 12 and 20%, respectively. The range of associated gas with volumes of 20-60 trillion cu ft in new structures is rated more or less in proportion to the oil to be found. The main hydrocarbon production and reserves in the Middle East, as indicated from the preceding, lie in the Arabian Gulf Basin, the Arabian-Iranian province that extends from southern Oman to the Arabian Gulf region, eastern Arabia and southwestern Iran as far as the northeastern Syria-southeastern Turkey border, including northwestern Iraq. There also is production from a number of small basins or sub-basins such as the Marib-Shabwa Basin of Yemen, the Red Sea in the maritime regions of Saudi Arabia, the Palmyride Basin of Syria and the AzraqSirhan Basin of Jordan. There also is a small number of basins immediately outside the area discussed, such as the Gulf of Suez Basin, central-western Turkey and the maritime Levant, Sinai and the southern Palestinian coast and Dead Sea areas. Total recoverable reserves in the Middle East were estimated at the end of 1993 by World Oil (1994) to be 632.5 B.bbl of oil and 1239.046 TCF of gas. According to Tartir and Shamlan (1990), at the end of 1988, Saudi Arabia's reserves accounted for 255 B.bbl of oil, or 27% of the worldwide reserve; and 181 trillion cu ft of gas, or 5% of the world's gas reserves. These figures may be compared with the estimate by the Oil and Gas Journal in 1983 of 135.7 B.bbl of oil and 775 trillion cu ft of gas, and with Riva's 1984 figures of 290.8 MM.bbl and 624.9 trillion cu ft of gas. The latter inferred reserves of 86.9 B.bbl of oil and 275 trillion cu ft of gas, and calculated the undiscovered oil at 174.5 B.bbl and 849.5 trillion cu ft of undiscovered gas. In 1981, the Department of Energy (USA) estimated reserves of 439 B.bbl, whereas Tiratsoo in 1984 made estimates of 347.2 B.bbl of oil. Although these figures clearly indicate the uncertainties in reserve estimates and the parameters on which the calculations are based, they show that discoveries have exceeded expectations, at least over this time interval. The figures should not be regarded as absolute, because actual production figures are not published in many countries. There is less uncertainty about the importance of the Middle East. Production was from only about half of the 475 fields, with the other half being relatively new and as yet non-producers or unassessed discoveries. Total present production from the main Arabian oil basin actually is derived from some 170 fields, of which 107 are rated as supergiants and giants (Table 10.3), and others are classed

474

as large fields. In Saudi Arabia alone, production at the end of 1987 was from 60 fields (39 wholly onshore, 17 offshore and four partly onshore-partly offshore). What is clear is that the major producers in the Middle East m Saudi Arabia, Kuwait, the U.A.E., Iraq and Iran have a disproportionally low output compared to their reserves (26% of world production with 63% of the reserves), but it is to these countries that the world must look for the additional 1.5 MM.bbl per day required by expanded use. Expanded production will require major capital expenditure at a time when the capital reserves of the countries in question have been severely eroded. To compensate for the capital shortfall, joint ventures with foreign participants could be undertaken, and this is already taking place to some extent. However, it is not clear that the countries involved necessarily feel that expansion to meet world demands is in their own best national interests. St. John (1980) estimated the ultimately recoverable (EUR) oil and gas, and also the barrel oil-equivalent (BOE) (converting gas to oil-equivalent at 6,000 cu ft of gas equalling 1 barrel of oil). He counted 390 supergiants and giants in the world, which have a total BOE of about 1,169 B.bbl, out of which the Middle East region has 92 supergiants and giants, with their total BOE at about 590 B.bbl (about 50% of the world). Carmalt and St. John's (1986) updated assessment shows an increase in the number of supergiant and giant fields in the world to 509, containing a total of about 1,400 B.bbl. Of this total, the Middle East region contains 107 fields (about 20.8%) and about 606 B.bbl (about 43.3%) of the world totals (Table 10.4). Using Carmalt and St. John's (1986) supergiant/giant field data for the Middle East (Table 10.3), Fig. 10.2 was constructed by assigning the estimated ultimate recoverable barrel oil-equivalent (EUR, BOE) of each field to its discovery year, and computing the five-year running averages of the reserve addition, number of fields and field size. The solid curve in Fig. 10.2 shows the historical change of the oil-equivalent reserve addition. There are significant fluctuations of the reserve additions; the two periods of low discovery are related to the Great Depression in the early 1930s and World War II. The historical cumulative frequency plot of oil reserve additions also was made on probability paper and is shown in the upper half of Fig. 10.3, while the frequency plot is shown in the lower half of the same figure. On the cumulative plot, the trend is shown as a nearby liner, suggesting that the fluctuations caused by economical and political reasons had only a small effect on the eventual cumulative discovery of petroleum in the region. The plot on the lower half of Fig. 10.2 shows the fiveyear averaged number of supergiant/giant discoveries, with a dramatic increase in the 1950s and early '60s. Since the late 1960s, however, the number of discoveries has declined continuously. The upper half of Fig. 10.4 shows the historical cumu-

Hydrocarbon Habitat of the Middle East Table 10.1. Rate of discovery of ultimate recoverable oil equivalent by year in the giant fields of the Middle East (based on data from Carmalt and St. John, 1986).

475

Sedimentary Basins and Petroleum Geology of tthe Middle East

Table 10.1 continued.

476

Hydrocarbon Habitat of the Middle East

Table 10.1 continued.

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Table 10.2. Annual Middle East crude production in thousands of barrels. Sources: Various issues of American Association of Petroleum Geologists, Oil and Gas Journal, World Oil & International Petroleum Encyclopedia. Note figures may vary according to source, selection has been made of the more conservative estimates.

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485

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486

Hydrocarbon Habitat of the Middle East

Table 10. 3 continued.

487

Sedimentary Basins and Petroleum Geology of tthe Middle East

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Hydrocarbon Habitat of the Middle East

Table 10.4. Statistical summary by size of the world's giant and supergiant fields (based on 509 fields) and the Middle East (based on 106 fields). Data based on ultimate recoverable oil-equivalent from Carmalt and St. John (1986).

lative frequency plot of the number of supergiant/giant fields discovered in the Middle East. The nearly linear trend in the rate of discovery (in terms of number of fields) shows an upturn in the 1950s. Extrapolating the trend may be useful in predicting the discovery rate, at least in the near future, assuming no major changes in the exploration effort. However, the broken line in Fig. 10.2 shows the average size of supergiant/giant fields discovered by year, an average that has declined significantly since 1950. The giant and supergiant field data show the same pattern for both the world and the Middle East, but a histogram shows that the Middle East fields generally are larger than in other parts of the world (Fig. 10.5). In both, the number of fields is 4-8 B.bbl less than the log normal distribution trend predicts. It should be emphasized that the data of Carmalt and St. John (1986) is for supergiant and giant fields only; hence, any field smaller than 0.5 B.bbl (or 500 MM.bbl) recoverable oil-equivalent automatically is excluded from this analysis. The distribution of Middle East oil and gas fields by size is shown in Tables 10.4, 10.5 and 10.6. According to Ivanhoe and Leckie (1993), in the Middle East, the average field size (e.g., median field is 100 MM.bbl) is about 20 times larger than in Latin America, and 1,000 times larger than in Eastern Europe, where the median field holds 100 M.bbl (Fig. 10.6).

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489

Sedimentary Basins and Petroleum Geology of the Middle East Table 10.5. Giant and supergiant fields of the Middle East (based on information up to 1990).

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Sedimentary Basins and Petroleum Geology of the Middle East hydrocarbon accumulations occur in the subtidal to intertidal lithologies. Primary porosity and permeability tend to be low, but may be enhanced by a system of fractures, thus making the Khuff Sequence a good to very good reservoir (Alsharhan and Nairn, 1994). For oil, the most prolific reservoirs are the Upper Jurassic Dhruma and Arab formations (in Saudi Arabia, Bahrain, Qatar and Abu Dhabi) . The Middle Jurassic Tuwaiq Mountain Formation in Saudi Arabia and the Areaj Formation of Qatar and the U.A.E. are important reservoirs. The Albian Nahr Umr/Burgan Sandstone (in Kuwait and southern Iraq); the Lower Cretaceous Zubair Sandstone in southern Iraq; the Lower Cretaceous Thamama carbonates in the U.A.E., Qatar and Oman; the Cenomanian Wara Sandstone in Kuwait; and the Mishrif Limestone in the U.A.E., Qatar, Oman and southern Iraq are important producers. The Upper Permian Khuff limestone in Saudi Arabia, Bahrain, Qatar, the U.A.E., Oman and Iran is an important reservoir of nonassociated gas, probably sourced from Silurian basinal shale and marl (Alsharhan and Nairn, 1994). The traps primarily are structural either along north-south-trending Paleozoic structural arches, or in structures associated with mobilization of the Infracambrian-Lower Cambrian Hormuz and equivalent salts, or along the fold belt collision in the Zagros Basin (Fig. 10.8 and Table 10.7). Increasingly, productivity is being enhanced through the use of 3-D seismology to detail subsurface structural and facies patterns (Fig. 10.9) as well as discover new fields (A1 Husseini and Chimblo, 1995). Production in northern Iraq, Syria and southeastern Turkey generally is confined to late Tertiary structures of the Zagros-Taurus Fold Belt. The most important reservoirs lie in the Cretaceous Mardin carbonates in southeastern Turkey, the Upper Cretaceous "Massive Limestone" or Soukhne Formation, the Shiranish Limestone in Syria, and the Oligocene Kirkuk Limestone, an Asmari equivalent in Iraq. There are other producing horizons in the Triassic, Lower Jurassic, Middle Cretaceous and Miocene. The major source rocks are the Middle Jurassic Sargelu Formation, the Upper Jurassic Neokelekan shale, with other sources such as the ?Silurian, Permo-Triassic and Cretaceous. The seals are Middle Jurassic shale, Upper Cretaceous marl and Miocene evaporites. Trapping is mostly within complex compressional folds, often overturned and thrust over evaporites at shallow levels, associated with the Late Tertiary folding in Iraq and southeastern Turkey and the rejuvenation of block-faulted structures in Syria. In Iran, the greatest productivity is from the Oligocene-Miocene Asmari and the Cenomanian Sarvak (Bangestan) limestone. Other reservoir rocks occur in the Upper Cretaceous Ilam, Lower Cretaceous Fahliyan, Middle Jurassic Surmeh and the Permian Dalan (Khuff equivalent) carbonates. The structural traps are primarily asymmetrical, NW-SE-trending anticlines, commonly truncated and thrust at the level of the Upper Miocene (Table 10.7). The primary source rocks are the Middle Jurassic Sargelu, the Aptian Gadven, the Albian Kazhdumi 492

and the ?Silurian Gahkum Shale. The principal seals are the Miocene Gachsaran evaporites and the Cretaceous Gurpi and Kazhdumi shale. A summary of geological and production data of Permian, Jurassic, Cretaceous and Tertiary reservoirs in the Middle East countries is given in Tables 10.8 to 10.13. The fortunate combination of a number of factors has contributed to the hydrocarbon richness of the Middle East. These can be summarized as: 1) the accumulation of a thick sedimentary pile throughout the Phanerozoic with a few major interruptions and, until the late Neogene, without volcanicity; 2) excellent carbonate reservoir rocks with both primary and secondary (fresh-water leaching) porosity and fracture porosity; 3) wide regional distribution of seals, anhydrite (Upper Jurassic Hith and Gotnia formations and Miocene Gachsaran Formation) and shale (Cretaceous Nahr Umr and Laffan formations) and seals of intermediate quality (argillaceous limestone); 4) reservoirs in extensive shelf areas closely associated with the intrabasinal anoxic source rocks rich in organic matter; 5) traps that are anticlinal with extraordinarily wide closures, gentle growth structures on the Arabian Platform associated with the flow of Infracambrian salt or deep-seated basement faults and traps associated with the tectonically active Taurus-Zagros-Oman Mountains; 6) enormous storage capacity of the unbreached traps; 7) the substantial release of oil and gas from large zones of mature source rocks; and 8) the formation of traps preceding migration. In the following sections, these factors will be discussed in more detail. Source Rocks

Over the Arabian Platform, the Phanerozoic, which thickens to more than 12 km in the Arabian Gulf region, can be broken down relatively simply into Paleozoic, Jurassic, Cretaceous and Lower Tertiary source rocks; upper Paleozoic, Mesozoic and Tertiary reservoirs; PermoTriassic and Upper Jurassic evaporitic seals; and Cretaceous shale seals. To this Phanerozoic grouping, however, should be added the Infracambrian, which is so important in Oman. In addition to this almost ideal vertical succession, there is the lateral gradation from carbonate platform into a deeper basin environment towards the northeast. Significant erosional or non-depositional breaks are present in all parts of the section, particularly during the Paleozoic, Cretaceous and Oligocene on the Arabian Platform and during the Paleozoic in parts of the Zagros region, so that probably nowhere in the region is a complete stratigraphic section present. The Middle East was affected by several episodes of tectonic activity, including

Hydrocarbon Habitat of the Middle East Table 10.7 Trap genesis, time of formations and examples of oil and gas fields in the Arabian Gulf region. The location of these fields is shown in Fig. 10.8.

493

Sedimentary Basins and Petroleum Geology of tthe Middle East Table 10.7 continued.

494

Hydrocarbon Habitat of the Middle East

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Fig. 10.8 Structural trends over the major oil and gas fields in the Arabian Gulf region (compiled mainly from Murris, 1980; Klemme, 1984; Alsharhan, 1989). See Table 10.7 for oil field names as numbered on this map.

the Late Precambrian, early Paleozoic (Caledonian Orogeny), late Paleozoic (Hercynian Orogeny), Late Cretaceous-early Tertiary and late Tertiary. Each of these events exerted a profound influence on regional and local tectonic patterns, paleogeography, sedimentary facies distribution

and the processes of petroleum generation, accumulation and preservation (Mun'is, 1980; Wilson and Peterson, 1986; Beydoun, 1991). The structural pattern is equally favorable. Haloki-

netic movement of the Infracambrian salt, which began in the late Paleozoic and continues to the present day, has resulted in the formation of flat, salt-based domes. This in conjunction with basement-induced faulting from the Mesozoic onward has served to create large drape folds over the basement blocks. There is a wide age range of source rocks within the Middle East, and their relative importance changes with geographical location. Under the circumstances, it is simpler to review the source-rock

495

Sedimentary Basins and Petroleum Geology of the Middle East

IC

i ,//

0 "" L

A!

I!

B

....

lKm. n

_

-"

I

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OO

i

II Uthmaniyah area 9 Well control -,=9 Fault

--6000-

Contour interval

9

/

I i

Fig. 10.9. Examples of the increased detail through application of 2D and 3D seismology. Top=Idd A1Shargi Field (Qatar): A=early discovery; B=2D seismic; C=3D seismic. Bottom= Ghawar Field, Uthmaniyah area (Saudi Arabia)" A=location; B=2D seismic; C=3D seismic.(after A1 Husseini and Chimblo, 1995, and reproduced by kind permission of Gulf Petrolink, Bahrain potential country by country. Table 10.14 shows the general distribution of the source rocks through the Phanerozoic in the Middle East. The sequence in the Zagros Fold Belt is in many ways similar to that of the Arabian Platform, with the exception of the very thick and lithologically varied Tertiary sediments, a reflection of the Alpine events that left the Arabian Platform virtually untouched. Oil is housed in Cretaceous and Oligo-Miocene carbonate reservoirs, although it probably began migrating and accumulating in Jurassic and Cretaceous salt-based and stratigraphic traps in the Late Cretaceous. The late Miocene to Pleistocene orogenic event created the elongated anticlinal traps, into which oil then migrated. The presence of evaporites accentuated the pre-existing structural features, which had a growth history extending back into Paleozoic times, and aided the migration of oil already trapped into OligoMiocene reservoirs capped by a very effective Miocene evaporite seal. This seal was preserved in areas of major

496

axial depressions by the synorogenic, molasse-type sediments deposited on top of it. Beydoun et al. (1992), in their review of the Zagros Basin, summarized the results of geochemical typing, which included sulfur isotope studies (Thode and Monster, 1970), vanadium-nickel ratios (A1 Shahristani and A1 Atyia, 1972) and physico-chemical dating of oils by Young et al. (1977), and indicated two principal results. First, that oils in reservoirs of different ages, despite some compositional differences, were derived from a common source, emphasizing the importance of vertical migration; and, secondly, geochemical differences in oil composition in contemporaneous reservoirs in different fields, which presumably reflects differences in source-rock deposition, also indicates the relatively minor importance or absence of lateral migration. Five potential source rocks have been identified by Ala et al. (1980) in the Zagros Province of southwestern Iran. They range in age from the Paleocene-Eocene to the

Hydrocarbon Habitat of the Middle East Table 10.8. Geologic and production data for Permian reservoirs in the Arabian Gulf and adjacent areas (modified from Klemme, 1984; Alsharhan and Kendall, 1986).

Table 10.9. Geologic and production data for Jurassic reservoirs in the Arabian Gulf (modified from Klemme, 1984; Alsharhan and Kendall, 1986).

497

Sedimentary Basins and Petroleum Geology of the Middle East

Table 10.10. Geologic and production data for Lower Cretaceous reservoirs in the Arabian Gulf (based on data from Klemme, 1984; Grantham et al., 1988 Alsharhan, 1989; Alsharhan and Nairn, 1994).

Silurian. The formations are the Eocene-Paleocene Pabdeh, Maastrichtian-Campanian Gurpi, Neocomian-Coniacian Garau, Albian Kazhdumi and Silurian Gahkum. The organic matter in these formations is almost exclusively of marine algal origin. The Kazhdumi is the major source of the hydrocarbons in the Asmari and Sarvak reservoirs. The source-rock potential of the U.A.E. has been reviewed by many authors (Alsharhan, 1989; ADNOC, 1984). The major sources appear to be the Oxfordian-early Kimmeridgian Diyab/Dukhan Formation and the late Albian-Cenomanian Shilaif/Khatiyah Formation. The gas in the Khuff Formation is either from the Lower Khuff sediments or from the Lower Silurian shale. Other minor potential source rocks have been identified in the stratigraphic section and will be described in detail in the succeeding chapter. Grantham et al. (1990) identified five groups of source rocks in Oman. The Precambrian Huqf Group, the Silurian Safiq Formation, the Upper Jurassic Diyab Formation and 498

the mid-Cretaceous Natih Formation all are considered potential source rocks. Although the source of the "Q" crudes in the Infracambrian Huqf Group reservoirs is not clearly identified, the oils contain a series of compounds characteristic of the group. The main sources of oil in southeastern Turkey are the dark, bituminous, marine shale of the mid-Maastrichtian Germav Formation. Other potential source rocks are the shale of the Cambrian Sosink Formation, the Late Devonian Bedinian Formation, the Silurian-Devonian Handof Formation, the Early Carboniferous Koprulu Formation and the bituminous sandstone of the Late Permian Hazro and Inbirik formations. The Triassic-Jurassic Aril Formation also is regarded as a potential source rock. The Santonian-lower Campanian Karababa A Member and Karabogaz Formation are good to excellent source rocks with widespread kitchen areas with total organic contents (TOCs) ranging from 6.76 to 7.8% (Soylu, 1991). The shale and silt of the Middle Ordovician Swab

Hydrocarbon Habitat of the Middle East Table 10.11 Geologic and production data for Middle Cretaceous reservoirs in the Arabian Gulf (based on data from Ala et al., 1980, Klemme, 1984; Grantham et al., 1988; Alsharhan, 1989; Alsharhan and Nairn, 1994).

Table 10.12. Geologic and production data for Upper Cretaceous reservoirs in the Arabian Gulf, Southeast Turkey and Northeast Syria (based on information from Klemme, 1984; Beydoun, 1988).

499

Sedimentary Basins and Petroleum Geology of the Middle East

Table 10.13. 10.13. Geologic Geologic and production data for Tertiary reservoirs in Southwest Iran (based on informatiom 1984, Beydoun Beydoun et et al, al, 1992). 1992). information! from Ala, Ala, 1982, 1982, Klemme, Klemme, 1984, Reservoirs

Asmari Formation (OJigo-Miocene); 95% ol IKL- reservoir consibis of fractured limestone, reef and reef debris; 5% consists of sandstone in three fields (Ahwaz, Mansuri and Marun). Carbonate pay zones arc characterized by poor primary reservoir properties, and production is dependent on fracturing.

Sources

Argillaccou.s limestone and shale of the Pabdeh Formation (Paleoccne-Eocene), Source from below leakage from the shale of the Albian Kazhdumi and Garau (Ncocomian-Turonian) and Gurpi (Maasirichtian) formations.

Time of Maturation

Middle to Late Tertiary

Time of Trap Formation

First phase was during Campanian-Senonian, and second phase was during Late Miocene lo Recent,

Mode of Trap Formation

Plate collision and wrench movernent along the Zagros suture

Time of Migration

Upper Tertiary to Recent

Mode of Migration

With intense folding, vertical migration occurred, and oil migrated from Cretaceous to Tertiary; e.g., the Asmari accumulations arc secondary and have been derived from the underlying Cretaceous successions by vertical migration through thousands of feel of intervening fractured limestone.

Expulsion Efficiency

15-20%

Formation and the Silurian Tanf Formation in Syria probably are the most important Paleozoic source rocks. Also important are the Triassic Kurra Chine, which consists of carbonates; the bituminous marl of the middle Jurassic Sargelu Formation; and the bituminous, marly limestone and shale of the Campanian-Maastrichtian Shiranish Formation, the Maastrichtian-Paleocene Germav Formation and the middle-Upper Eocene Jaddala Formation, a sequence consisting mainly of bituminous, marly limestone. The Miocene source rocks are immature, and the oil found in the Miocene Jeribe Limestone of the A1 Jebissa Field might stem from Mesozoic source rocks. In Iraq, the Upper Devonian-Lower Carboniferous Ora Formation contains organic-rich shale and marl. Other formations with source-rock potential are bituminous marl, shale, argillaceous limestone and dolomites of the Kurra Chine and Sargelu formations. Cretaceous source rocks such as the Valanginian to Turonian Balambo Formation and the Maastrichtian Shiranish Formation also may play a role in northern Iraq, but this depends entirely on the level of organic metamorphism to which they have been exposed~ In southern Iraq, bituminous shale in the Valanginian-Hauterivian Ratawi and Zubair formations is potentially important. In Saudi Arabia and adjoining regions in the Middle East, the early Silurian Qusaiba Formation is the principal Paleozoic source. Maturity calculations based on geohis-

500

tory analysis (Bishop, 1995) indicate that it generated hydrocarbons throughout the Mesozoic and in the Cenozoic. Post-Hercynian (early Permian) subsidence created the accommodation space in which the regional reservoir, the Khuff Formation (and, to a minor extent, the underlying Unayzah Formation) and the regional seal, the Triassic Sudair Formation, accumulated. Significant oil generation began during the Triassic in the Arabian Gulf area, migrating into the Rub al Khali region by the late Cretaceous. The rate of oil generation declined during the mid late Jurassic and temporarily ceased with the uplift of the southern end of the Arabian Plate, but gas continued to be generated in areas not previously exhausted following the Neogene collisional event, and it was this late-phase gas that charged the compressional traps in the Zagros (Bishop, 1995). The early generated gas charged the Khuff traps existing prior to the formation of the Zagros. An organic-rich source rock has been identified in the Jurassic of Saudi Arabia (Ayres et al., 1982). The sediments are thermally mature, with amorphous alginite mostly of blue-green algae. These organic-rich sediments accumulated in an intrashelf basin during the CallovianOxfordian and are referred to the Tuwaiq Mountain and Hanifa formations. The Sulaiy Formation (Berriasian-Valanginian) beds are the only Cretaceous sediments that can qualify as source rocks. The Toarcian Marrat, the Bajocian-Bathonian Lower and Middle Dhruma formations

Jurassic

Muwoqar

Ccrmav

Wadi Essir Kaur

Karabogaz Karpbaba Derdene Sayindere

Marib M^bi/ Sabatayn

Aril

Triassic

Chilixi iaddala Aalljl

Jnidd^kla

Shiranish SouVhnc Qiunchuq;) Rulbah

Shi rani sh

Khasib

Undambo

Wara

Pabdch

Raiuwi

[lam Gurpi Khazhdumi Gadviu)

Kumaila Mishrif Ahamdi Wara Mauddud Burgan Shu Alba Zubair Katawi Minagish Sulaiy

Sulajy

Surmeh

Sar^elu Dhrunia Najmah

Hanifa Tuwajq Dhruma Marrat

ChiaGara Zubair

Satgehi

Kurra Chine

Mansjynh Burqan Yanbu Alwajh

Aahji

Nahr U m r

Saudi Arabia

S^irgelu

Najmah

Naolcclckan

Sargdu

Kurra C h i n e

Baluij

Minjiu^ Jilh

[Jeduh

Khuff Unayzah

A nun us ^'ermjon

InbiriV Kilzro

Carbomferous

Najteb Sawanet

Devonian

Jauf

Koprulu

Silurian

Mudawarra

Handof l>ada,^

Tanf

Ordt'vician

Hiswa

Bcdinan

Sav^ab

Can)brian Infracambnan

So^tink

Gahl^ijm

Qu^aiba

Hanadir Pit'Saq

Hydrocarbon Habitat of the Middle East

F-grt Saar Nalfa

Sinan

t~

Mukalla

Taqiya

e~

Oetaceoui

1aqa

Kuwait

om

Tertiary

Iran (Zagros Basin)

O

Age

o Im

South I r a q

om

o

North Iraq

r

Syria

om

Stiuibeut Turkey

o

Jiird^n

o

Yrmfn

&

Country

.=.

oH

O ra~

Table 10.14. Source-rock formations of the Middle East (compiled from various sources, cite

501

Sedimentary Basins and Petroleum Geology of the Middle East and the Devonian Jauf Formation's organic-rich shale member have a lower source-rock potential. The Silurian shale is the major source rock for the Paleozoic reservoirs in central Saudi Arabia (Abu-Ali et al., 1991). Most of the oil trapped was generated from rich, mature source rocks in the Gotnia Basin in the north and the Arabian Basin in eastern Saudi Arabia . The two basins are separated by the Arabian shelf (Tartir and Shamlan, 1990). The basins originated in the Middle Jurassic and persisted until the Late Jurassic (CallovianKimmeridgian) in the south and until the Early Cretaceous (mid-Bathonian-Hauterivian) in the case of the Gotnia Basin. The source-rock facies is black to brownish-black, laminated limestone, generally uniform in total composition. Some dark laminae, which may have a TOC of as much as 50%, were derived from primarily planktonic or algal remains. They were preserved under anoxic conditions existing within these restricted basins. The earliest time for oil maturation of the Jurassic source rocks probably is the Late Cretaceous, but the timing of migration is Tertiary, probably late Tertiary, and in all probability still is incomplete. The reservoirs retain much of their charge simply because of the absence of strong compressional tectonics, with little fracturing having occurred to destroy their integrity. In Qatar, Frei (1984) and Alsharhan and Nairn (1994) identified two source-rock horizons in the Jurassic/Cretaceous sequence: the Late Jurassic Hanifa and Lower Jubailah, and the Albian Lower Mauddud formations. There is minor source-rock potential in the Aptian Shuaiba and Cenomanian Khatiyah formations. These sediments were formed in an extensive, starved basin during an increase in sea level. They contain sapropelic, liptodetrinitic and algal organic matter with a 1-6% TOC. In Bahrain, analytical data show that the organic carbon content is adequate to characterize the Dhruma, Tuwaiq Mountain, Hanifa, lower part of the Jubailah, lower part of the Sulaiy, Ratawi and Nahr Umr formations as possessing source potential for Jurassic-Cretaceous oil. The rocks of the lower part of the Khuff Formation indicate fair to good source quality. The Ordovician graptolitic Qusaiba shale is sufficiently rich in organic matter and is sufficiently mature to have sourced both the Khuff and Unayzah formations (Samahiji and Chaube, 1987). The Jurassic and Cretaceous carbonates and clastics in Yemen are major source rocks in the Marib-Jauf-Shabwa areas and have sourced major fields. Thin Lower Cretaceous coals and shale in the Qishn Formation have fair to good potential for generating minor to fair quantities of oil and gas (Barnard et al., 1992). The thin shale in the Mukalla Formation has significant oil and/or gas source potential. The thin shale/limestone in the Jurassic Kohlan Formation has a fair source potential. In Jordan, geochemical study on asphalts and heavy oils in the Dead Sea Rift indicates that the source material of the bacterially reworked algae lies in bituminous marl of Late Cretaceous age (Nissenbaum and Goldberg, 1980;

502

Wilson et al., 1983). In the Azraq-Wadi Sirhan Basin, the potential source rocks are the Upper Cretaceous bituminous marl, while the marine sediments of the Paleozoic and lower Mesozoic are possible source rocks in the northern Jordanian highlands (Beydoun et al., 1994). G e o c h e m i s t r y of Oil a n d G a s

Dunnington (1967), in an analysis of the age distribution of the approximately 250 commercial fields known at that time, indicated that 200 were in rocks of Cretaceous and Jurassic age. A second group of 32 were Miocene to Oligocene in age, occurring mainly in the Asmari Limestone of southwestern Iran and northern Iraq. Thus, the remainder of the stratigraphic column accounts for very few fields. A more recent analysis would modify this to some extent, given the Permian gas and oil discoveries and the presence of the lower Paleozoic in the Arabian Basin and the Infracambrian discoveries in southern Oman. The geochemical analysis of source rocks and oil to establish their relationships requires the determination of TOC, Rock-Eval pyrolysis (where the S 2 peak in an immature rock suggests a maximum for potential productivity), total soluble extract (TSE) and kerogen S13C isotopic composition. To determine the source-rock potential, the hydrocarbon type [either from a calculated hydrocarbon index (HI) or derived from a cross plot of S 2 and percentage of TOC] and the maturity of source rocks in the sedimentary section must be known (Fig. 10.10). An example of such a study that concentrated on Jurassic source rocks and oils was made by Cole et al. (1994a). Their result of geochemical typing establishes the identity and parent

80 70

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60

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6

8

10

12

14

16

18

20

% Total Organic Carbon Fig. 10.10. S2 pyrolytic yield (in mg HC/g rock) versus % TOC for the Tuwaiq Mountain Formation source rock in the Arabian Basin. This plot shows a slope-derived HI of 665 for this source rock where immature (after Cole et al., 1994a, and reproduced by kind permission of Canadian Society Petroleum Geologists).

Hydrocarbon Habitat of the Middle East

I00

-65O

I'

9

o

-1150 -

9

n I".

Do

I

-1650 --

Thamama

9 OlD 9

9

9

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IS,s,,IPldlplts o oo oe

v

I .-'.::"

-{

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9

i"

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i"

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j,

%

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%TOC

S1 Yield

$2 Yield

Hydrogen

Index

Fig. 10.11. % TOC, S2 pyrolysis yield (in mg HC/g rock) and hydrogen index (HI; in mg HC/g TOC) distributions in the Jurassic section for a representative well from the Khurais Field. Note that the thick Tuwaiq Mountain section that is enriched in organic carbon has excellent pyrolysis yields and is highly oil-prone (after Cole et al., 1994 a, and reproduced by kind permission of Canadian Society of Petroleum Geologists). source of oils from different fields (and different levels within a field) in eastern Saudi Arabia. They could further establish something of the nature of the source organic carbon and demonstrated its value by comparing it with oil found in Permian reservoirs with their Silurian source rock. Clearly, as the maturity of the source rock increases and hydrocarbons are expelled, the hydrocarbon potential of the remaining organic potential of the source rock falls. To determine the original source potential, immature material is needed; when the HI of the immature and mature samples can be compared, the potential of the residual organic kerogen may be estimated. Fig. 10.11 shows the geochemical parameters based on samples from a deep well in the Khurais Field in Saudi Arabia, which penetrates the Mesozoic section where the source rock is thickest and immature (Cole et al., 1994a). Moderately organic-rich intervals (TOC greater than 1%) occur throughout the Jurassic section, with the highest values from near the base of the Tuwaiq Mountain Formation to the base of the Hanifa Formation; a second interval of rich source rock extends from the upper Hanifa Formation into the base of the Jubailah Formation. The source rocks in the first group are the lamalginitic, thinly laminated, dark-gray to black, peloidal carbonates, with subordinate vitrinite and inertite, and in the latter group, calcareous shale and limestone, where the shale has the higher TOC values. A cross plot of TOC and S2 analyses from the Hanifa source rock shows differences attributable mostly to differences in maturity and, in some small measure, to a

more variable kerogen assemblage. The use of gas chromatography, gas chromatographymass spectrometry and carbon isotopes more clearly demonstrates gross oil family relationships and demonstrates the sub-families, showing facies and maturity changes across a basin, ignoring potential long-range migration. The similarities of four samples of Arab and Hanifa oils are apparent in Fig. 10.12. The pristane/phytane relationship shown in Fig. 10.13 illustrates a single trend from immature to more mature Jurassic oils, as does comparisons of specific biomarkers as norhopane-hopane. The steranes recognized are indicative of a marine, algal, carbonate source. For comparison, chromatograms from Khuff reservoirs (Fig. 10.14) show their derivation from a distinctly different source, with a different sulfur content. The Permian reservoir oil in Saudi Arabia has a low sulfur-high saturate content, pristane/phytane ratios greater than 1:2 and biomarkers indicative of a marine, clastic setting. Their carbon isotopic signature is consistent with an origin from the organic-rich shale at the base of the Silurian Qusaiba Member of the Qalibah Formation (Cole et al., 1994a). The narrow range of API gravity values from 20 to 40 ~ and the sulfur content range between 1 and 4% (Fig. 10.15) suggest similar organic facies, source material and thermal history for most of these crude oils, or taken one step further, a common source (Dunnington, 1967; Kent and Warman, 1972). But, although the Middle East crude

503

Sedimentary Basins and Petroleum Geology of the Middle East

Central Ghawar Arab-Reservoired Oil

Mazalij Arab-Reservoired Oil

Fig. 10.12. C15+ gas chromatograms of representative Arab oils from Saudi Arabia (Cole et al., 1994 a, and reproduced by kind permission of Canadian Society of Petroleum Geologists

m

Imp_~ . it3

U3

Safaniya Arab-Resevoired Oil

I

Abu H a d r i ~ ~ Arab-Resevoired Oil

J 1.2

Crude 9 Oils oSourceRockExtracts

1.0 O.8-

Fig. 10.13 Pristane/nC17 versus phytane/nC18 for Jurassic oils and Hanifa and Tuwaiq Mountain source rocks in Saudi Arabia. Note that the oils and immature and mature extracts plot along a single trend, indicating a single group of oils derived from a single source-rock type (after Cole et al., 1994 a, and reproduced by kind permission of Canadian Society of Petroleum Geologists).

o

v-I

lu IX,

0.6. 0.4

Mature Source Rocks

0.2

L

0.0

9

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w

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~ o

I

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H y d r o c a r b o n Habitat of the Middle East

B Khuff Reservoired Condensate

Khuff Reservoired Oil

1

m/z 191 (hopane * tricyclics)

C30 Hopane E

Triyclics

_

o-

Extended HopanesMature pattern

z

Diasteranes C27

Co-elution of C27 p B 20R and C29 p 0,20S diasterane

f

diasterane

C28

m/z 217 Isteranes)

C29

9

Fig. 10.14. C15§ gas chromatograms of representative Permian Khuff reservoir oils from Saudi Arabia. (after Cole et al., 1994a and reproduced by kind permission of Canadian Society of Petroleum Geology

505

Sedimentary Basins and Petroleum Geology of the Middle East

o0

TERTIARY 9 OILS SW IRAbl OCRETACEOUS OIL, KUWAIT A JURASSIC OIL. SAUDI ARABIA

o

o

A A o~ o

Oo

9

o o Oo

Fig. 10. 15 The relationship between API o gravity and sulfur content (weight%) in some reservoirs in the Middle East.

Agg o A oA

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~

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go

AM" CdRAVITY

oils appear remarkably uniform in the C15+ hydrocarbons and gross fractional composition, as well as in the C4-C 7 gasoline range hydrocarbons, detailed geochemical analysis of the C15 + fraction revealed subtle differences that may reflect variations in oil maturity and possible differences in the source beds or source material within the source beds. Thode and Monster (1970) presented evidence based on sulfur isotopic composition of several oils from northem Iraq that suggested that the oils from two small fields may have been derived from a Paleozoic source rock. They also analyzed 42 oil samples from Tertiary and Cretaceous reservoirs in Iraq and Iran and found the sulfur isotopes from these crudes to be very uniform, despite the age differences between the reservoirs. The average value, 5.4%, was distinctly different from the average of three crudes from Triassic age reservoirs (average 2.4%). They also looked at the variations in the sulfur isotopes of oils from different depths in the same field to show that these, too, were uniform. In the Kirkuk Field in Iraq, oils from four horizons m Tertiary and Upper, Middle and Lower Cretaceous m were identical within the limits of reproducibility of the determinations (S34=5.5%). In the Bai Hassan Field in Iraq, $34 values from oils of the same four levels were 7.25%, a finding that strongly supports Dunnington's (1967) contention of a single, common source for all the major oil accumulations in Cretaceous and Tertiary traps. Using their sulfur isotope data, Thode and Monster (1970) tried to determine the most likely source for the oils by a comparison with evaporites of Jurassic, Cretaceous

506

and Tertiary age. They concluded with the Jurassic as the most likely age and the Tertiary as the least likely. Sulfur isotope data for the Upper-Middle Cretaceous crudes from the offshore in the U.A.E. are nearly identical with the average reported from the Bai Hassan Field (Iraq), data for the combined Tertiary, Upper, Middle and Lower Cretaceous reservoirs and, coincidentally, from oil produced from Middle-Upper Cretaceous horizons. Sulfur isotope data may be useful in interpreting the source of H2S in natural gas. The two principal mechanisms are bacterial activity and thermo-chemical breakdown of anhydrite. Although bacteria can exist at temperatures as high as 100~ their activity is greatly reduced above 60~ that is, during the first stages of burial and diagenesis, whereas the thermo-chemical breakdown of anhydrite cement and nodules requires temperatures variously estimated in the 130-170~ range (Orr, 1974; Machel, 1987). H2S will be removed by reaction with iron and normally will affect the first bacterially produced gas. Thermo-chemically produced H2S forms at greater depths, of the order of 4,600 m (15,000 ft), where light carbon calcite replaces the anhydritic cement or nodules. The amount is controlled by temperature (a function of depth), age and anhydrite availability, with the sulfur having a 34S composition similar to the anhydrite from which it was derived and, thus, is heavy. In contrast, H2S biotically formed at shallower depths tends to be isotopically light (Orr, 1975). However, some caution is necessary in interpretation, for in the case of the Khuff reservoir in the Dubai Fateh Field, Videtich (1994) suggested a sul-

Hydrocarbon Habitat of the Middle East phate source from an evaporite other than late Permian seawater. A potentially useful application of sulphur-selective flame photometric analysis with high-resolution gas chromatography of the thiophene organo-sulphur compounds, the benzo- and dibenzothiophenes, may provide an empirical means of distinguishing between oils derived from carbonate and siliciclastic sources (Hughes, 1984). A study of oils from a variety of sources in the western United States, Kuwait, Dubai, the North Sea and Alberta showed similarities related to the type of source rock, regardless of the source-rock age or location (Table 10.15). A comparison of Ilam oil and a Khatiyah source-rock extract (Fig. 10.16) illustrates the comparison. A comparison of crude oils derived from a common source rock but produced from reservoirs of different lithology showed them to be essentially similar. With increasing maturity through the reduction in benzothiophenes, the differences between carbonate- and siliciclastic-derived oils diminishes, but the changes do not destroy the distinction (Table 10.15). Source-reservoir relations in the Middle East were studied by Young et al. (1977), who calculated the ages of the reservoir oil using the gasoline range and heavy hydrocarbon analyses, and compared these with ages derived paleontologically for the producing reservoir rocks in Iran, 1

2

Iraq, Saudi Arabia and the U.A.E. (Table 10.16). The information necessary to calculate the hydrocarbon ages includes detailed chemical analysis of the oils, stratigraphic information for the section with which the oils were associated and temperature information from which geothermal gradients may be determined. The results show a generally good agreement with the geologically interpreted ages. The agreement commonly is better with oils from Cenozoic reservoirs than from older reservoirs, and it is better for oils from clastic reservoirs than it is for oils from carbonate reservoirs (Young et al., 1977). These limitations must be kept in mind when evaluating the results of oil reservoir ages. Eight Miocene reservoirs in the Zagros Fold Belt of Iran have calculated gasoline range hydrocarbon ages greater than 120 Ma, and the remaining six have an average age calculated as 104 Ma. Taken as a group, these oils in Miocene reservoirs may be interpreted as having an Early or Middle Cretaceous origin. Dunnington (1967), using geological and geochemical evidence, concluded that the oil in the Asmari Oligocene-Miocene reservoirs in Iran had migrated along fractures from the underlying Cretaceous and Jurassic source rocks, consistent with the interpretations made by Young et al. (1977). Similarly, the calculated ages of five oils from Lower Cretaceous reserILAM OIL

A

g

~3

2313- 2388 m

26.9 API 2.3

I [

2.3% S

lil r

13

5

1

l! ;

't 'I

,I I , :

I KHATIYAH E X T R A C T Z I

i

I I

: i , ,, :

2533 - 2540 m

I1

I

,

,,

13

lo

I

14

9

l I

II

i

RETENTION TIME Fig. 10.16. Comparison (A) FPD gas chromatogram and (B) m/z 217 mass fragmentogram of a crude oil from the Ilam Formation, Southwest Fateh Field, Dubai, and a rock extract from the Khatiyah Formation, Fateh Field, Dubai.(after Hughes, 1984, and reproduced by kind permission of AAPG)

507

Sedimentary Basins and Petroleum Geology of the Middle East

Table 10.15 Changes in the compositional parameters of oil from carbonate and siliciclastic sources for non-biodegraded oil of comparable maturity (Hughes, 1984, and reproduced by kind permission of AAPG). Carbonate Source

Parameter

Siliciclastic Source

Tc^l Sulphur

High

Low

Gravity

Low to medium

Medium to high

n-alkanes (CPL or OEP)

Even to no predominance

Odd to no predominance

Pris tan e/Phy lane

Very low

Low to high

Stcranes

High aquatic lo mixed aquatic/ terrestrial

High terrestrial to aquatic/terrestrial

Disteranes

Low (to medium)

Medium to high

Thiophenic Sulphur

High in benzothiophenes Fairly equal distribution of benzothiophenc/dibenzothiophene

Low in benzothiophenes Decreasing amounts of dibenzothiophcncs

Maturation Change

Redistribution of ihe mcthylbcnzoihiophenc isomers generally uniform

Reduction of the methylbenzodithiophenes show decreasing amounts of dimethyl- and trimethyt-dibenzothiophcncs relative to methyl-dibenzothiophenes

voirs in the U.A.E. (Abu Dhabi region) average 131 Ma, which is in good agreement with the paleontological age assigned; four of the six Middle Cretaceous oils in Iran have hydrocarbon ages of 107-120 Ma, consistent with the paleontological determination of the reservoir age. The 18 oils from Saudi Arabia produced from Middle and Upper Jurassic reservoirs have calculated gasoline range hydrocarbon ages averaging 174 Ma and clearly suggesting oils generated from Jurassic source rocks. The correlation of the age of oil reservoirs with the oil produced clearly can have a significant impact on sourcerock-oil correlations. The studies reported here based on data of Young et al. (1977) strongly suggest that the Middle East oils were sourced from rock sequences slightly older than the producing reservoirs, except for the Asmari of the Zagros Fold Belt. The evidence also indicates that the published oil source rocks in Saudi Arabia and the U.A.E. are Cretaceous and Jurassic in age (Ayres et al., 1982; Alsharhan, 1989). Fig. 10.17 shows lateral thermal gradient variations in the Arabian Gulf region. Present-day geothermal gradients may act as a guide to the thermal regime controlling the generation of oil and gas in the basin. The mechanism of hydrocarbon generation and accumulation in this region has been treated by many authors and divided into three categories: a) Catagenetic origin and long-distance migration (Murris, 1980; Ayres et al., 1982; Hassan and Azer, 1985;

508

Alsharhan, 1989; Higuchi, 1994). The idea is based on studies of argillaceous rocks where possible source sediments at a depth and over a sufficient geological time generate petroleum through the "kerogen" stage. b) Diagenetic origin and short-distance migration (Wilson, 1982, 1990; Taguchi and Mori, 1992, Higuchi, 1994). The idea is that the carbonate rocks have the capability to generate hydrocarbon directly from organic matter within them without passing the "kerogen" stage. c) Early migration and accumulation, or the "Protopetroleum Theory" (Dunnington, 1967; Kamen-Kaye, 1970; Higuchi,1994). The basis of this theory is that oil that has not yet reached a mature stage may be generated in a shallower zone than usual for oil generation. After the premature migration and accumulation, it finally matures in the reservoir. Middle East crude oils generally are considered to be derived from marine organic matter in carbonate/evaporite-associated source rocks. They are high in sulfur and rich in C13 to C20 alkanes and have low pristane/phytane ratios (0.6 to 1.0). They show even carbon predominance. Statistical analysis of saturated hydrocarbons by Tissot et al. (1977) clearly demonstrates that the combination of even carbon predominance, and low pristane/phytane ratios (less than 1.0) occur only in oils and extracts associated with carbonate/evaporite-associated source rocks. The parameters indicate highly anoxic depositional envi-

Hydrocarbon Habitat of East Hydrocarbon Habitat of the the Middle Middle East

Arabian Gulf Table 10.16. 10.16. Calculated ages of gasoline-range hydrocarbons in oils, Arabian 1977, reproduced reproduced by by permission permission of AAPG). AAPG). (after Young et al., 1977, Country

Iran

U.A.E.

Qatar

Saudi Arabia

Field

Reservoir

Reservoir Age

(ft)

Estimated Temp.

Calculated Age

Assigned Reservoir Age

Depth

Chashmch

Asmari

MifKCne

Khush

Asmari

MitKtnc

11,300

265

>120

20

Par-e Siah

Asmari

Miocene

7,500

200

99

20

Haft Kc!

Asmari

Miocene

2,900

125

101

20

Marun

Asmari

Miocene

10,700

265

106

20

Agha Jari

Asmari

Miocene

8,700

280

102

20

Ramshir

Asmari

Miocene

9,100

250

109

20

Rag-e-Safid

Asmari

Miocene

8,350

285

106

20

Kharg

Asmari

Miocene

6,350

195

>136

20

Ab Teytnur

Bangestan

M. Cretaceous

11,200

260

>120

100

Ahwa?,

Bangestan

M. Cretaceous

11,100

260

109

100

Marun

Bangestan

M. Cretaceous

11,600

275

107

100

Bibi Hakimeh

Bangestan

M. Cretaceous

6,500

190

107

100

Kilur Karim

Bangestan

M. Cretaceous

10,700

270

>65 (90?)

100

Binak

Bangestan

M, Cretaceous

10,600

270

21

100

Ruwais

Shuaiba

E, Cretaceous

S,(KX)

225

97

120

Bu Hasa

Shuaiba

E. Cretaceous

7,800

280

146

120

Bab

Kharaib

E. Cretaceous

8,400

252

147

120

Sahil

Kharaib

E. Cretaceous

8,930

250

131

130

Asab

Kharaib

E. Cretaceous

9,300

266

132

130

Dukhan

Arab-C

L, Jurassic

5,700

193

211

155

Dukhan

Arab-D

L. Jurassic

6,350

205

211

160

Dukhan

Uwainat

M. Jurassic

7,200

219

174

174

Marjan

Khafji

M. Cretaceous

6,930

180

211

100

Ghawar-Ain Dar

Arab-D

L. Jurassic

7,300

215

167

145

GhawarHaradh

Arab-D

L. Jurassic

7,400

215

166

155

GhawarUthmaniyah

Arab-D

L. Jurassic

7,400

215

165

155

509

Sedimentary Basins and Petroleum Geology of the Middle East

Table 10.16 continued.

Country

Field

Reservoir

Reservoir Age

Estimated Temp. (°F)

Calculated Age

Assigned Reservoir Age

Dammam

Arab-B

L. Jurassic

4,650

206

164

145

Qatif

Arab-C

L. Jurassic

7,240

220

173

145

Qatif

Arab-D

L. Jurassic

7,375

226

170

145

Abu Safah

Arab

L. Jurassic

6,700

189

181

145

Berri

Arab-A

L. Jurassic

7,400

218

175

145

Berri

Arab-C

L, Jurassic

7,430

220

173

145

Khursaniyah

Arab-A

L. Jurassic

7,110

183

209

157

Khursaniyah

Arab-B

L. Jurassic

10,140

240

148

145

Abu Hadriya

Arab-A

L. Jurassic

8,260

250

162

150

Abu Hadriya

Arab-B

L. Jurassic

8,370

250

150

155

Abu Hadriya

Arab-C

L. Jurassic

8,550

250

161

158

Abu Hadriya

Arab-D

L. Jurassic

8,710

250

166

160

ronments for the source rocks. Thus, within a carbonate sequence, oxygenated, shallow-water facies and subaerially exposed, sabkha facies are unlikely candidates for source-rock formation. The most likely depositional environment to contain organic matter capable of producing the Middle East oils is in a starved intrashelf basin with an oxygen minimum zone above the sediment-water interface. The late Oxfordian to early Kimmeridgian provides one such example (Fig. 10.18); the sediments were then covered by a Tithonian evaporitic facies. East of the Qatar Arch, Cretaceous deep-water, intraplatform basins developed, giving rise to the Apfian basinal facies (the Bab Member) of the Shuaiba Formation, and the Cenomanian Khatiyah/Shilaif pelagic facies, each of which has been invoked as a source rock (Fig. 10.19). Pym et al. (1975) identified seven individual sterane/ triterpanes in Middle East oils and were able to demonstrate that the southern Arabian Gulf oils had different relative abundances than those of oils from the northern Arabian Gulf (Fig. 10.20). The most probable cause of this difference is a small difference in depositional environment of the source beds (isolated sub-basins?) in the different parts of the Arabian Gulf.

Reservoir Rocks The most important oil-reservoir rocks are presented in Table 10.17; at least 80% are carbonate, and the remainder are sandstone. Reservoirs in which gas is trapped are at

510

Depth (ft)

least 95% carbonate, and the remainder are sandstone. The estimates are based on the ultimately recoverable oil and do not include undrilled potential. The age range of the reservoirs with regard to the ultimately recoverable oil and gas in the main producing countries shows that Cretaceous rocks host 51% of the recoverable oil, and Paleozoic rocks 50% of the gas. Distribution of hydrocarbons within any multiple reservoir in the stratigraphic column is controlled by a variety of reservoir parameters. The Arabian Platform and the Zagros Fold Belt together constitute a basin downwarping into a small oceanic basin in the Klemme (1980) basin classification. From the Late Carboniferous until the late Miocene, sedimentation was dominated by carbonate formed on a stable platform that passed eastward into the Tethys Ocean. To the west, the carbonates are replaced, as a rule, by marginal, arenaceous clastics derived from the continental Arabian-Nubian Shield. Murris (1980) recognized two basic states of this broad carbonate platform, which he described as a carbonate ramp and differentiated carbonate shelf. The carbonate ramp is characterized by a cyclical alternation of more or less argillaceous units, coinciding with periods of increased clastic influx from the highlands of the Arabian Shield to the west onto the Arabian shelf. The differentiated shelf conforms to the more standard carbonate platform of Wilson (1975) when, during periods of high sea-level stand, the source of clastics was displaced far to the west. The best carbonate reservoirs occur within the high-energy, ooidal grainstone terminating the carbonate cycles (e.g., the Upper Jurassic Arab Formation

Hydrocarbon Habitat of the Middle East

49"

53"

51"

0 l

I

|

OIL AND GAS FIELDS -.~... TEMPERATURE GRADIENT IN "F/lOOft 111 112

% 114

!18 I

"31"

" 121

i

~98 i..\

/ / /

KUWAIT g

\

Z~ \

IRAN 149

BAHRAIN 0162

i,,.U'IqrT'ED ARAB ,~. ~ l s

i.9! j

-N~!o

9

OMAN

'

,

N 9

,,"~. . . . . . . . . .

i I .sO ~ _ _ / ~ . . ._. . . . . . . 70),~

SAUD! ARABIA

47" |

|

49" |

!

,

D~

\ 51" |

,

53" t

i

515"

,,.P / as / I

Fig. 10.17. Lateral thermal gradient variations in the Arabian Gulf region (based on Clarke,1975, Klemme, 1984,) and other sources). Numbers refer to fields and are listed in Table 10.7 of Saudi Arabia, Qatar, Bahrain and offshore Abu Dhabi). Porosity of the limestone may be enhanced by leaching or diminished by cementation and even subaerial exposure during the sea-level fall during the carbonate-ramp phase (Alsharhan, 1987). Purser (1978) has suggested that early lithification plays an important role in the preservation of porosity, by reducing compaction and consequently reducing the pressure solution that provides the sparite cement filling pore spaces. Early dolomitization similarly is useful, as it is more resistent to lithostatic and tectonic pressure and, with less stylolitization, has less carbonate solution available for pore infilling. The regressive clastics

formed at the same time also provide good reservoirs (e.g., Cretaceous Zubair and Nahr Umr/Burgan formations in Kuwait and southern Iraq). Other good carbonate reservoir types are the biohermal buildups such as the rudists and algal boundstone along the shelf margins (e.g., Cretaceous Shuaiba and Mishrif formations in the U.A.E. and Oman). In the following paragraphs, the principal reservoirs are reviewed briefly in stratigraphic order. lnfraearnbrian to Paleozoic. The oldest producing horizons in the Middle East are the carbonate (mainly dolomite) and sandstone horizons of the Infracambrian to Early-Middle Cambrian Huqf Group in Oman, though oil,

511

Sedimentary Basins and Petroleum Geology of tthe Middle East

1 ~ BJXliXlC h~'I'RABI'Fe2~ BASIN

~ O W

"~" ~

CARBONATE SHELF

LIMITS

Q ~e~sa~ ,'O. SO[2[HWEST ARABIAN CRJI.FBA

O~

,~OiRm

Fig. 10.18. The principal Jurassic intrashelf basins of the Arabian Gulf which sourced the Jurassic-Cretaceous reservoirs of the area (modified after Murris, 1980, Alsharhan and Kendall, 1986)

[ .?_-~ LOWER COASTAL PLAIN

~

~.SI-~.~.OW SHELF

tzt..t~t~;,~

Iz'/77~MIXED SHALLOW

IT-"IISHALLOWSHELF

F 9JCARBONATES

~ B A S I N MARGIN

CARBONATES

-

BASINAL CARBONATES (~

I

l|

EROSIONAL LIMIT

Fig. 10.19. The principal Cretaceous intrashelf basins, A) during Aptian, B) during Crenomanian. Illustration of the rudist build ups around the basin margins which form the prolific reservoirs of the Arabian Gulf (modified after Murris, 1980, Alsharhan and Nairn, 1993, Alsharhan, 1995)

512

I

Hydrocarbon Habitat of the Middle East

AHWAZ FIELD-IRAN D BANGESTAN GROUP MIDDLE CRETACEOUS)

~SMAR! FORMATION TERTIARY)

30%

.30%

20%

.20%

N

N B

B

.10%

"10%

H

U V

I

MURAN FIELD-IRAN ASMAR! FORMTION [TERTIARY)

30%

BIB-~-ffA-~MAHFIELD-IRAN ASMAR! FORMATION TERTIARY)

D

! 30%

D

N

N

,20%

B

10%

G

20%

C

U

'10%

V " - - "

BURGAN FORMATION

I :(MIDDLECRETACEOUS) I

I !

KHARAIB FORMATION | LOWER CRETACEOUS) ~

| /

N

......

B

.

,

80

. 20

MINUTE

,,

.

~

lO%

.

BH

.

"

_

~

~-'

'"

~

~V

4-1

,

6-0

~

7-8

~9

~ 2-7

1

~

!~

ENT ~

PEAK

,

'

~

10 S

I

~'

~

~ 4

-

9

Fig, 10.20 Average relative proportion of triterpane in some Middle East oils (after Pym et al., 1975, reproduced with kind permission of Analytical Chemistry) 513

514 Farit^ Jeribe, Dhibann Chilou, Jaddala

Main Limestone^ Jaddala/Avanab, Aaliji, Jenbe, Euphrates

Gcrniav, Garian, Beloka, Raman^ Kambogaz, Sayiixlerc, Karabaha, Dcrikre

Shiranish, Massive Limextones Qamchuqn, Rulbah

Shi rani :(h/Pikner Komeian/Dokan, QaiTtt htiqa, Sarmord, Garagu

lluimah

Sar^lu

Aril

Kuira Chine, Ooba (Mulussa)

Kurra Chine Baluti

T^cfmian

Hazro

Amanus Sand

Cart>oiiiferou!t

Koproulu

Najeeb.SawancL HalDul

De^'onian

Hajidof

Silurian

Dadas

Triasjtic

Main

Or
Kliarcini

Cambrian

Ram

Enfracambiian

Saramuj

Ik'ainan

Sedimentary Basins and Petroleum Geology of tthe Middle East

Gercus, Sinan

oml

Zerqa

North Iraq

r~

Masilah, Marib. Shuqra^ Kohlan

O r~ r~

Jurassic

O

Airaq, Ajlun. Kumub

E

Sbarwnyn, Mukal!a« Harshi^at* Qishn. Furl, Sarar. Naifa

Syria

O

CrcUkC«ous

olml

Sarar, HEuni, Ghaydah^ Hadhranioul

E

Southeast l\irkey

Age Tertiary

O

Jordan

r~

O

O

o~

Yemen

E

ojq

O

t< Country

oH

m

O

Table 10.17 continued. Country South Iraq

Kuwait

Qatar

Saudi Arabia

Age

United Arab Emirates

Tertiary

Ghar^ Lower Pars

Ghar, Lower Knrs, Radhuma

Ghawwa^K Damnum, Yanbu, Matisiyah, Alwajih

Cectaccou*

Hartha^Mlshrif. NahrUmr^ Shuaiba, Zubalr, Ratawi, Sulai^'

Mishrif, Tayaryl, Wara, Mauddud^ Btirgan, ZuhuJr. Minagiiih,Ratawi.

Aruma, MishriF. Rumaila^ Ahmodi, Wara. Mauddud, Safaniyah, Khpfjj. ShuaJba, Biyadh^ Buwaibn Yamama^ Sulaiy

Miiihrif, Ahmudi. Khatiyah, Mauddud, Nahr Umr, Shuaiba. Ratawi. Yamama

Sim'tima, llam^ Mishhf, Halul. Mauddud, SliuaJha, Kharaib, Lx^khwyir. Habshan

JurassJc

Najmah

Marrai. Sargeko, Najmah

Hith, Arab, Jubailah^ Hanifa, l u w o i q Mountain, Dhruma. Marrai

Arab, Ju1>ai1ah, HaniTa. Araej, Izhara

Arab. Diyab, Aracj, Marrat

Khuff.

Khufr Una^zah

Minjut. Jilh

Permian

Khuff^ Unayzah

Hau^hi Carboniferous Devonian

Jauf

Tawil

Silurian

Sarah

Sharawra

OrJoviirifin

Zarqa

Tabgt

Cmnbriitn LnfnK:4Uiibnan

Hydrocarbon Habitat of the Middle East

Tfiiissic

Pabdch, As man

515

Sedimentary Basins and Petroleum Geology of the Middle East gas and condensate production from these horizons is relatively small-scale. The depositional environment of these rocks is interpreted by Gorin et al. (1982) as shallowmarine to supratidal. They are capped by the Ara evaporites. Some of the carbonates have source-rock capabilities. The pre-Permian, mainly clastic, reservoirs in the eastern part of the Arabian Peninsula (Saudi Arabia, Qatar and the U.A.E.) and in northern Arabia (Jordan and Syria) usually are gas-bearing and contain unspecified amounts of condensate, but the rocks have been explored insufficiently apart from those in southern Oman. Only in southern Oman have the Cambro-Ordovician fluvial sediments and the Carboniferous-Early Permian terrestrial (and partially glacial) sandstone proved to contain heavy oil in appreciable amounts. Thus, the Lower Paleozoic clastic rocks potentially are of major importance as reservoirs for non-associated gas, but apparently of lesser importance as oil and condensate reservoirs. In southern Turkey, the Paleozoic sandstone has been shown to carry gas and oil. The most important reservoirs for natural gas in the Arabian Basin and the Zagros Fold Belt of southwestern Iran are the carbonates of the Upper Permian Khuff Formation and equivalent formations. The carbonates are predominantly shallow-marine to lagoonal facies and are generally dolomitized. The reservoir quality reflects rapid changes in depositional environment and dolomitization that has resulted in the development of secondary porosity. The source of the gas may be from Silurian shale or lie within the Khuff itself; however, the pristane/phytane ratio (1.5 to 2.36) and carbon isotope values (from -28.0 to -29.1) suggest a terrestrial source rock, which may favor a Permian source. There is as yet no satisfactory explanation for the origin and evolution of the methane and condensate in the carbonates or of the reaction kinetics described by Welte et al. (1981). The transformation into methane with source-rock temperature increasing at only one degree per m.y. does not readily release gas at maturity, and it is a transformation that takes place only when temperatures correspond to late maturity or over-maturity, at which time the gas and condensate may be expelled and so explain the lack of an oil phase. Triassic and Jurassic. Triassic and Lower Jurassic carbonate reservoirs are of only minor importance in Middle Eastern countries. There is some gas in the mainly dolomitic, Upper Triassic Kurra Chine Formation of northeastern Syria. Minor amounts of hydrocarbons also are found in the Lower Jurassic Marrat Formation of Saudi Arabia and Kuwait, the Safiq Formation of Oman and the Liassic Butmah Formation of northeastern Syria. The main reasons for the hydrocarbon scarcity are the low leakage from the Permian because of the effective Lower Triassic evaporite or argillaceous dolomite and limestone seals combined with the lack of a source rock, whether of local or regional extent. The changed depositional environment conditions that developed toward the end of the Early Jurassic (Murris, 1980) resulted in the deposition of widespread sheets of

516

peloidal-ooidal packstone and grainstone in cycles alternating with argillaceous, peloidal-bioclastic mudstone and wackestone. These conditions, which persisted from the Bathonian to the Albian, were accompanied by the tectonic differentiation of the Arabian Basin. In the central part of the basin, higher-energy carbonates were deposited, which subsequently became hydrocarbon reservoirs (Bathonian Dhruma Formation), followed by the formation of euxinic sediments (late Oxfordian to early Kimmeridgian). This close association of source and reservoir rocks makes this period so important for hydrocarbons. The Late Jurassic concluded with four such alternations four depositional cycles, each with an anhydrite seal occurring at the top of the cycle (Arab A, B, C and D). Above lies a regional anhydrite seal (Hith Anhydrite), which prevented upward migration of oil once oil generation had begun. This unique source-reservoir-seal in the Upper Jurassic makes it the world's largest single oil habitat, with some 50,000 MM.bbl of ultimate recoverable oil. Cretaceous. The wide carbonate platform continued to exist during the Early Cretaceous, with the difference that ramp-type, carbonate-shelf conditions replaced the differentiated carbonate shelf (Murris, 1980), and anhydrite ceased to be a member of the depositional cycle. During the course of the Early Cretaceous, the influx of detrital clastics progressively increased, until they occupied the western half of the Arabian Basin, displacing the carbonates eastward, by the late Barremian. The extensive sheets of peloidal, bioclastic packstone and grainstone, representing the high-energy part of each cycle, form the excellent reservoir rocks of the southern Arabian Gulf, trapped and sealed by the interbedded marl and argillaceous limestone. The clastic sand facies in the northern Arabian Gulf (Zubair Formation) also are sealed by interbedded shale. In the southern Arabian Gulf, a second intrashelf basin developed; and a rudist facies developed around the shelf margins of this basin (buildups, scattered patches, rudist meadows and grainstone of rudist fragments), forming the prolific Shuaiba reservoirs. Alluvial and coastal sands in the northern Arabian Gulf deposited during the mid-Albian regression subsequently became the reservoirs of the Nahr Umr/Burgan Formation and the Khafji and Safaniya members. They were charged from the euxinic Lower Cretaceous deposits in the Lurestan Basin and sealed by interbedded shale. The rudist buildups form good-quality reservoirs in the Cenomanian Mishrif Formation of the U.A.E. and Oman (Fig. 10.19). The source of the Mishrif oil lies in the contemporaneous Albian-Cenomanian Shilaif/Khatiyah Formation, which has reached maturity only in the more deeply buried areas (Alsharhan, 1995). In southwestern Iran, the Sarvak Formation (late Albian-Cenomanian) is a reservoir charged from the underlying bituminous shale and argillaceous limestone of the Albian Kazhdumi Formation (Ala et al., 1980). The Sarvak Limestone, one of the more important carbonate reservoirs in the Zagros Fold Belt in Iran, is made up of

Hydrocarbon Habitat of the Middle East foraminiferal-algal wackestone and packstone and rudist packstone and grainstone. Other reservoirs of lesser importance are the Mishrif Formation in southern Iraq and the Mardin Group of southern Turkey. Reservoirs of the uppermost Cretaceous are known in the Zagros Fold Belt of Iraq and Syria (Shiranish Formation), and southeastern Turkey (Raman and Garzan formations). These are not found in the southern Arabian Gulf, for this was a period of erosion, except in the U.A.E., where some production is obtained from Maastrichtian carbonates (Simsima Formation). Tertiary. The Paleocene-Eocene of the Arabian Basin was a time during which there developed a series of successor basins and wide, shallow, evaporitic shelves. The Sinan Formation of late Maastrichtian-Paleocene age is an important carbonate reservoir in southeastern Turkey, and the Lower Eocene dolomitic and anhydritic limestone of the Radhuma Formation are productive in the Wafra Field in southern Kuwait. During the latest Oligocene to early Miocene at the northern tip of the Arabian Gulf, a major influx of sand formed the Ahwaz Delta; these sands, together with the Asmari limestone and the beds of the Kirkuk Group, are the major reservoirs for the giant fields of the Zagros Fold Belt in Iraq and Iran. The Ahwaz and Ghar sands are poorly cemented. They have porosities of 20-30% and a permeability of the order of 1 darcy. The Asmari Formation and Kirkuk Group reservoirs are predominantly peloidal-oolitic packstone and grainstone. The Asmari Limestone has a thickness of 100-800 m (328-2,625 ft), with matrix porosities of 5-15% and permeability ranging from one to a few millidarcies, except where a reef trend progrades obliquely across platform facies. With such parameters, it is clear that the high yields (20,000-25,000 BOPD) are the result of fracture porosity. Geochemical data suggest that they are sourced from the Middle Cretaceous Kazhdumi Formation. During the Plio-Pleistocene, when the major anticlines were formed, tectonic movements fractured the Campanian-Oligocene marl and shale that had been an effective seal to the Cretaceous reservoirs until that point. This permitted oil migration into the Asmari and Kirkuk traps capped by the Gachsaran and its equivalent evaporites, which form an efficient seal. Gas deposits of unknown volume occur in the Miocene of the Saudi Arabian northern Red Sea area. Heavy oil and condensate have been discovered in the Oligo-Miocene Asmari carbonates and the PaleoceneEocene Pabdeh Formation of the U.A.E. (Alsharhan and Nairn, 1995).

Cap Rocks (Seals) The principal cap rock in the Middle East is anhydrite, which formed during several different epochs. Shale, mostly Cretaceous, however, performs the same function. The most representative cap rocks are tabulated (Table 10.18). The age range of most seals is Permian to early

Miocene; the most effective in terms of hydrocarbon production are the Late Jurassic Hith Formation anhydrites sealing the oil in the reservoirs in the Arab Formation (Murris, 1980; Alsharhan and Kendall, 1994), the early Miocene Gachsaran (formerly the Lower Fars) anhydrite and thinly bedded limestone capping the prolific reservoirs in the Dezful Embayment in Iran (Ala, 1982), and the Cenomanian shale over the crest of the Burgan Field in Kuwait, despite their thickness over the anticlinal crest of a mere 30 m (96 ft) (Kent and Warman, 1972). The latter seal is imperfect, as indicated by heavy oil shows over the crest of the structure. The Early Triassic argillaceous dolomite and shale probably cap the Permian Khuff carbonate reservoirs in the Arabian Gulf. The position of the cap rock in the sedimentary sequence, together with its effectiveness, determines the level of stratigraphic entrapment. In the Fold Belt of the Zagros Range, most pre-Miocene cap rocks fail by fracturing, which resulted from the Plio-Pleistocene fold movements, thereby allowing the upward migration of hydrocarbons until their movement was arrested by the lower Miocene cap-rock anhydrite (Gachsaran Formation). The cap rock could, however, be effective only in the areas where it was spared from erosion, as in the axial depressions of foreland folds in the Dezful and Kirkuk embayments. In direct consequence, in those areas of the Zagros Fold Belt where the cap rock has been removed or where the development is thin, very few economic accumulations of hydrocarbons are known. Exceptional in this respect are three small High Zagros fields found by SIRIP, where apparently the cap-rock efficiency in the lowermost Mesozoic over uppermost Permian was not destroyed and where gas has been found in the Permian carbonates. In the Arabian Gulf region, the Tithonian Hith Anhydrite (the Gotnia in Kuwait and southern Iraq) is the most important and effective seal/cap rock (Murris, 1980). It has a variable thickness and can reach thicknesses of a few hundred meters; but the thickness is about 150 m (492 ft) in eastern Saudi Arabia in the Ghawar, Dammam and Qatif fields. More importantly, for its function as a seal in the southern Arabian Gulf, it was unaffected by the Zagros Orogeny (Alsharhan and Kendall, 1994). In the southern part of the Arabian Gulf, the Albian Nahr Umr Shale and the Coniacian Laffan Shale and occasionally tight limestone in the Lower Cretaceous Thamama Group act as effective seals to reservoirs containing oil and gas (Murris, 1980; Alsharhan, 1989). The cap rock in the prolific Dezful Embayment of southwestern Iran is the lower part of the lower Miocene Gachsaran Formation (formerly the Lower Fars), an alternating sequence of 40 m (131 ft) of thick-bedded anhydrite and thin-bedded limestone and bituminous shale (James and Wynd, 1965). Sometimes just called the Cap Rock, it is overlain by the remainder of the Gachsaran Formation. The seal has been breached or destroyed on a large scale in the Zagros Simple Fold Belt as a result of young folding and development of migration paths, traces of which are

517

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Country

Yemen

Jordan

Age Sarar, Hadhramout

Cretaceous

Sharwayn, Mukalla, Fartaq, Qishn, Furt, Saar, Naifa

Belqa, Kurnub

Jurassic

Marib, Shuqra Kohl an

Zerqa

North Iraq

Gere us

Pars, Dhiban, Aa!iji,Chilou, Jaddala

Lower Fars, Jaddala, Dhiban, Aaliji, Euphrates

Mishan, Gachsara Jab ram

Kasiel, Germ a V Sayindere

Shirbanish, Soukhne, Qamchuqa

Shiran ish, Qamchuqa, Sarmord

Gurpi, S Kazhdum Gad van

Sargelu, Alan, Mus, Adniyah

Naokelekan, Adaiyab,

Hith

Baluli,

Dashtak

Triassic

Telhasan

Kurra Chine, Amanus

Permian

Gomaniibirik

Heil

Carboniferous

Najeeb, Sawanct

Devonian

Koprulu

Silurian

Khushisha

Ordovictan

Hiswa

Cambrian

Salib

Infracambrian

Sou I

Syria

Handof

Dalan

Sedimentary Basins and Petroleum Geology of tthe Middle East

Tertiary

Southeast Turkey

O

m

Country

Qatar

South Iraq

Kuwait

Tertiary

Loower Pars, Rus

Ghar/Lower Pars, Rus, Radhuma (basai shale)

Rus, Dam, Mansiyah, Burqan,

Cretaceous

Shirhanish, Tanuma, Nahr Umr, Zubair, Ratawi, Yamama

Sadi,Khasib,Wara Ahmadi, Burgan, Zubair, Ratawi

Aruma, Rumaila, Ahmadi, Wara, Safaniya,Biyadh, Buwaib, Yamama

Laffan, Ahmadi, Mauddud, Nahr Umr, Hawar,Raiawi,

Laffan, Halul, Nahr Umr, ThamamaGroup (dense limestone)

Jurassic

Gotnia

Gotnia, Sargelu Hilh, Marral

Hith, Arab, Jubailah, Hanifa, Dhruma, Marral

Hilh, Arab. Jubailah, Hanifa Araej, Izhara

Hith, Arab, Areaj, Izhara

Khuff, Haushi

Khuff, Unayzah

Age

Saudi Arabia

M injur, Jilh, Sudair,

Permian

Kbuff, Unayzah

Carboniferous

Berwath

Devonian

Jaaf

Silurian

Sarah

Ordovician

Qusaiba, Ra'an, Hanadir

Cambrian Infracanibrian

Hofuf, Umm er Radhuma (basal shale)

Tawil

Tabuk

Hydrocarbon Habitat of the Middle East

Triassic

United Arab Emirates

519

Sedimentary Basins and Petroleum Geology of the Middle East marked by asphalt and heavy oil stains (Kent and Warman, 1972). Seal destruction by faulting is common, occurring in both the Red and Dead seas, and can be observed in some Arabian Gulf fields such as Idd E1 Shargi in Qatar. Traps The tectono-stratigraphic provinces of the Middle East are four in number; they become progressively younger and less stable toward the north and northeast. They are the Precambrian Arabian Shield, the stable shelf covered by a relatively thin (3,000 to 10,000 m, or 9,600 to 32,000 ft) layer of Phanerozoic sediments, the unstable shelf, with a vastly greater thickness of generally shallowly dipping Phanerozoic sediments that include all the major Saudi Arabian fields, and the zone of marginal troughs that stretches from northeastern Iraq to southern Iran and includes the northern margin of the Arabian Gulf. This latter is the domain that developed in Cretaceous or earlier times as intrashelf basins. To these must be added a fifth zone, the allochthonous nappes of the Oman Mountains, which are the remains of an island arc obducted over the normal Arabian sedimentary sequence. The term applies only to the obducted mafic and ultramafic rocks of the Oman Mountains that end along the Hawasina Nappe front. In discussing the hydrocarbon province of the Mid-

dle East, the concern is with the stable shelf and the zone of marginal troughs. In discussing the trap-forming mechanisms, a distinction can be made between these two zones. In the Arabian shelf region, sometimes called the basement uplift province, the principal trap-forming mechanisms are linked to the system of north-south-striking basement fractures and to halokinetic effects. The basement structures are part of a system of north-southstriking highs and lows, of which the better known are the Ha'il-Rutbah Arch, the Tabuk and Widyan basins and the Burgan-Wafra-Khurais highs. Movements of the evaporites can be split into those affecting the Upper Proterozoiclower Phanerozoic (Cambrian) Hormuz (and Ara) evaporites and those of the younger evaporitic sequences (Mesozoic and Cenozoic). The basement uplifts (Fig. 10.21) operate in two ways: there may be horst-like uplifts recognizable by the presence of positive gravity anomalies or by movement along basement fractures. They may have triggered upward movement of salt to produce salt domes, growth structures that may have begun to form during the Jurassic and continued their movement during the remainder of the Mesozoic and Cenozoic. Such salt-cored structures are characterized by the presence of negative gravity anomalies. These anticlines include the Ghawar, Khurais and

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Fig. 10.21. The subsurface contours show the approximate base of the Mesozoic. The dotted lines are part of an old parallel system of lineaments in eastern Arabia that have controlled movement, creating large oil fields (modified after Alkhatieb and Norman, 1982; Edgell, 1987). 520

~

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200 Mi

Fig. 10.22 Tectonostratigraphic provinces or zones in the Arabian Gulf and adjacent areas (compiled from Murris, 1980; Alsharhan and Kendall, 1986; Edgell, 1987).

Hydrocarbon Habitat of the Middle East Dukhan structures and are related to the development of salt walls. The Infracambrian Hormuz salt movements also may be associated with piercement domes (Fig. 10.22). A salt dome province is recognized in the Arabian Gulf with which many of the major fields are associated, such as the Khafji, Safaniya, Dukhan, Bahrain (Awali), Zubair and Rumaila. The trends of similar structures change to a northeasterly direction east of about 53 ~ E. The change has been associated with the existence of southwest-trending, left-lateral basement shears, a change exemplified by the Bab Dome of Abu Dhabi and, in a more general sense, by the trend of the Rub al Khali and the Huqf-Haushi Axis in Oman. Zagros Fold Belt and Foreland Basin traps are dominated by Neogene compressional folds that vary greatly in size. The anticlines are arranged in long en e c h e l o n trends, with folds that often are box-shaped and asymmetrical, as in the Gachsaran (Iran) and Kirkuk (Iraq) fields. The folds show no effects of deep-seated evaporite movement, although they do show d6collement over the Gachsaran (Lower Fars) evaporites, which permitted disharmonic folding. Stratigraphic traps are unknown in this area. In Oman, dissolution drape is important in the formation of the heavy oil accumulations (A1 Marjeby and Nash, 1986), as in Amal Field in southern Oman. The fields in Syria occur in transtensional and transpressional structures. This, associated with shear fault motion, seems to be responsible for fields such as Rumailan and Souedie. Combination traps (plays in which stratigraphic pinchouts and unconformity traps may develop with growth structure) are important in the mid-Cretaceous Khatiyah and Mauddud formations in the Qatar North Field.

Timing of Trap Formation Greater Arabian and Omani basins. In the Arabian Platform, the sediment-covered part of the northeastern extension of the Arabian Shield (Falcon, 1967) has remained unaffected by orogenic deformation since the end of the Pan-African event in the Early Cambrian. Since that time, it has been subjected to epeirogenic warping, salt flowage at depth and drape folding over basement faults that have been reactivated on several occasions, although this is not always easy to document. The literature is full of references to the Hercynian and Caledonian orogenies, which are better represented by vertical movement than by compressive events. Several north-south structures have been ascribed to reactivation of basement structures, as differential subsidence initiated non-compressional domes, the growth of which is linked to the development of oil fields in eastern Arabia. Dunnington (1958), discussing the unfolded part of Iraq, concluded that the pre-Miocene tectonic pattern was complex due to the interaction of vertical faults with different trends (north-south, east-west, northeast-southwest, northwestsoutheast), with ages of movement yet to be unraveled.

According to Trusheim (1974), halokinetic movements on the Arabian Platform began when the sedimentary overburden on the Infracambrian evaporites reached 1,000 m (3,280 ft). A series of pillow structures may have developed as early as the Late Cambrian. These continued to grow through the Paleozoic and Mesozoic, with continued, if restricted, growth through the Cenozoic. In addition to halokinetic activity, periodically reactivated basementcontrolled fault patterns controlled the location of highs and lows from early in the Phanerozoic (see Chapter 2). Fault-controlled structures may have begun to form from the ?Paleozoic onward. It has been suggested that the Silurian and Permian source rocks released their hydrocarbons, oil and/or gas, from the Late Jurassic onward, and the Jurassic source rocks beginning in the Late Cretaceous. Cretaceous to Eocene source rocks matured and released their hydrocarbons from the early Tertiary to recent. It seems likely that hydrocarbons, once trapped, remained in the same structure during its prolonged period of growth in the Mesozoic and Cenozoic (Dunnington, 1958). The structures apparently could accommodate hydrocarbons from both Paleozoic and Mesozoic sources until Cenozoic tectonism reactivated faults and oil migrated, as described by Dunnington (1958). The mechanism responsible for forming the transpressional and transtensional structures was associated with strike-slip along the Levant Fracture and secondary fractures branching from it. Zagros Basin. The Zagros Simple Fold Belt was the product of the latest Alpine orogenic phase (MioPliocene), which culminated in the Pliocene, to be followed by pronounced post-orogenic uplift still in progress. These movements caused the Cretaceous-Eocene release of hydrocarbons, which then migrated into still younger structures, a phase that does not appear to have affected the platform hydrocarbons. It seems reasonable to assume that the quantity of hydrocarbons trapped before the latephase movements was many times greater than that which now exists in the fold belt and that the late-phase orogeny destroyed many of the pre-existing accumulations. Earlier tectonic phases are largely obliterated or overprinted by the late tectonic movements. The preceding Late Cretaceous phase, which had manifested itself in the Zagros Thrust Zone and the Zagros Imbricated Belt, almost certainly had an impact on the Simple Fold Belt. General conclusions concerning the early formation of traps indicated for the Arabian Platform are regarded as valid for the Zagros area, too (e.g., facies and fault-controlled traps almost certainly existed from the early Mesozoic onward). To what extent the halokinetic concept can be applied to the Simple Fold Belt of Iraq is uncertain, as the regional distribution of the Infracambrian evaporites is unknown. What is clear is that evaporites were not deposited in southeastern Turkey. Southeastern Turkey lies in the northern segment of the Zagros-Taurus ranges and contains sediments that range in age from Paleozoic to Tertiary. Since the Meso-

521

Sedimentary Basins and Petroleum Geology of the Middle East zoic, deposition has occurred in an asymmetrical basin whose axis trended northwest through northeastern Iraq and southwestern Iran, shifting progressively westward through geological time (Temple and Perry, 1962). Orogenic compression in the late Tertiary resulted in the uplift of the basin and impressed on it the present structural pattern. The folded belt consists of a series of elongate, asymmetric, east-west-trending anticlines. The structures are similar to, and continuous with, the large oil-producing structures of Iran and Iraq.

POTENTIAL PLAYS The occurrence of hydrocarbons throughout the Phanerozoic strata of the Middle East is related to a variety of factors tied to the juxtaposition of source-reservoir-seal, migration history and trapping mechanism. While each may share some characteristics, each may also be unique. Critical variables controlling the geographic occurrence of hydrocarbons in the region include original facies variations over the depositional shelf or basin and movements of basement faults and halokinetic activity. The evaluation and integration of these critical variables, together with the appreciation of maturation, migration history and trapping mechanisms, must form the basis of the search for new fields. The discovery of new fields is ample proof that the region has not yielded up all its treasures and stimulates continued exploration. Jurassic rocks still contain the most attractive hydrocarbon potential, especially in eastern Saudi Arabia and the southwestern Arabian Gulf, where the principal objectives are the Middle and Upper Jurassic units. These units contain the near-ideal association of source rocks, excellent oolitic limestone reservoirs, with high porosities and permeabilities, below excellent cap rocks and form broad open structures giving way to very large accumulations. Cretaceous reservoirs still may hold some potential in northeastern Syria. Deeper Mesozoic plays (e.g., the Triassic Kurra Chine Formation) and Paleozoic plays have been inadequately tested. The deep structures within the stable shelf have not been examined. Further attractive prospects in Syria are the folds in the Palmyra Belt, the Sinjar Trend and the fault blocks in the Homs area to the west. In southeastern Turkey, severe Early Cretaceous uplift and erosion militate against the discoveries in the stable platform area and the Taurus foothills and, thereby, confine exploration to the post-Lower Cretaceous, where productive zones have been found in the Middle-Upper Cretaceous Mardin Limestone and the carbonates of the Upper Cretaceous Raman and Garzan reef facies. These reservoirs are sourced from the Upper Cretaceous Germav and Kiradag marine shale (back-reef facies). The seals consist of Upper Cretaceous shale (Table 10.17). Some potential still exists for moderate to smaller discoveries in the Cretaceous of southeastern Turkey. The extensive Neogene volcanics in that region may conceal attractive struc-

522

tures not yet tested. In the Turkish, Adana Offshore Basin, there is a thick marine Neogene section capped by Messinian salt with unknown potential, and similar conditions exist in the Antalya Basin. Of the interior, onshore basins, the most attractive are the Tuz Golu, Van Mus and SivasMalatya. The first of these basins, the Tuz Golu, has a thick Tertiary marine-lacustrine section capped by salt and contains well-developed traps, but the greatest potential may lie in the northeastern Van-Mus Basin under a volcanic cover. The Black Sea coast and the Pontid foothills with Neogene fault blocks and Lower Tertiary-Mesozoic faulted anticlines, which potentially are of considerable interest, lie outside the scope of the Middle East, as defined here. Although the Zagros Fold Belt, with its many giant and supergiant oil and gas fields, has been intensively explored, there still remains the potential for the discovery of medium-sized Asmari fields. In the west, the Asmari sandstone equivalent, the Ahwaz Sandstone, is untested. In the southeastern Zagros, where the fold belt appears to be more gas-prone than oil-prone, many salt-induced structures remain to be tested both onshore and offshore. In the onshore, the Tertiary Guri Limestone Member of the Mishan Formation has good potential. The Cretaceous Mishrif play may extend into Iranian waters in the Arabian Gulf; and more Alborz-type Oligo-Miocene structures may be anticipated to bear oil onshore in the interior Kavir Basin. The accretionary wedge of Tertiary sediments in the Makran Fold Belt may be regarded as an attractive frontier province with gas prospects. Further gas prospects lie in the Caspian Neogene sands and the Triassic marine sediments on the Tabas Block. Less inviting is the potential of the Tabriz, Isfahan, Meshad and Kerman post-orogenic basins, the Paleozoic Lut Block and the complexly folded Eocene flysch of the Sefidabeh Trough in eastern Iran. The greatest potential for new discoveries lies in Iraq, where there are many large, insufficiently tested structures in the Zagros Folded Zone; the region could wind up with a field density similar to neighboring Iran. Also within the stable platform part of Iraq, block-faulted structures may be found, although the Hit-Awasil area with its tar and asphalt seeps west of Baghdad appears to be only marginally interesting. The discovery of the East Baghdad Field, with about a 30 B.bbl potential, underlines the attractiveness of Jurassic salt-induced structures in the lower Euphrates depocenter. In the northern Arabian Gulf area (Mesopotamian Sub-basin), a potential play involves updip sands of the Cretaceous Nahr Umr Formation. Along the Ha'il-Rutbah Arch in central and western Iraq and eastern Jordan, there may exist the possibility of Paleozoic stratigraphic and combination traps. In Jordan, the recent discovery in the Sirhan Basin, which tested 400 BOPD, has opened a new area of the Arabian Platform to exploration, but the Lower Cretaceous sandstone reservoirs in both the Sirhan and A1 Jafr fault-bounded basins are only marginally attractive. The Jurassic carbonates in western Jordan only offer the prospect of small quantities

Hydrocarbon Habitat of the Middle East of gas. In Kuwait, all the major structures have been tested to the Cretaceous level. Pre-Cretaceous plays in the producing zones conceivably could add a few billion barrels to the reserves, and there remain small, untested stratigraphic traps. The greatest potential, however, lies in the virtually untested offshore area and western onshore area. In Oman, production is associated with two play concepts. One involves production from the InfracambrianCambrian Huqf Group, the Cambro-Ordovician Haima Group and the Permo-Carboniferous Haushi Group in central and southern Oman (Dhofar), sourced by the Infracambrian algal limestone and trapped in structures associated with Cambrian salt mobilization and solution, and sealed by Permian Haushi beds or Albian Nahr Umr shale. The second play in the Omani foreland concerns production from the Middle Cretaceous Wasia Group and the Lower Cretaceous Thamama Group carbonates. Permian Khuff equivalent dolomites and lower Jurassic Marrat sandstone and limestone units were sourced primarily from Natih (Wasia) bituminous shale and sealed by the Albian Nahr Umr to Coniacian Laffan shale. The carbonate reservoirs are located on block faults, and Cambrian salt-related highs have secondarily enhanced porosities. Most of the Mesozoic structural features in northwestern Oman already have been tested, and future potential may be limited to delineating porosity trends in established reservoirs. The most attractive areas are the Infracambrian salt basins of central and southern Oman, especially along the basin flanks where the shallow, salt-induced anticlines and dissolution features are best developed. One such interesting play involves dissolution along the eastern flank of the Marmul Field. Infracambrian pre-salt plays may exist, but are difficult to detect seismically. The possibility in southern Oman of Jurassic pinch-outs beneath the Cretaceous and Tertiary cover and Neogene gas plays along the Batinah coast of Oman, and complexly folded anticlines off the Musandam Peninsula and adjacent offshore areas are other attractive plays. The Masirah Basin, tested by a few wells, appears to lack source rock. In Yemen, the still relatively recent discovery of oil in the Jurassic sands of the Mukalla-Mar'ib Graben in the northeastern part of the former North Yemen has spurred considerable interest. The graben contains a number of salt-induced structures, and a discovery (Sharmah) has been made in the Eocene carbonates in the offshore part of the graben. There also is interest in possible Jurassic-Cretaceous plays in the Fartak or Hadhramout synclines to the northeast. The onshore part of the Mukalla Graben is of little interest because of Cretaceous uplift of the Mukalla Arch and thinning of the Jurassic section. Associated with these structures is the deep Amran Graben. In offshore Qatar, the odds of finding new, moderately sized oil fields in Mesozoic carbonate reservoirs are slim, but other structures containing Permian Khuff non-associated gas may be present. However, given the enormous

reserves of the North Field, there is little incentive to explore, and onshore drilling of the Paleozoic Qatar-South Fars Arch to this date has been disappointing. In the U.A.E., favorable conditions exist for condensate and non-associated gas within the Mesozoic-Paleozoic sequence, in particular within the Permian Khuff Limestone. In the offshore and along the thrust belt of the Oman Mountains, a number of promising structures have yet to be tested in the Ras al Khaimah Sub-basin, follow. ing the trend of the Margham-Sajaa-Saleh fields. In Saudi Arabia, the frontier areas are defined as sedimentary basins lying outside the Concession areas. For ease of reference, they can be divided into four regions: the northern, central, southern Saudi Arabia and Red Sea zones. In the eastern Province of Saudi Arabia, all the major structures down to the Jurassic have been tested, for due to favorable reservoir-source relations, even small closures can contain major accumulations. The greatest potential for new discoveries, therefore, may lie in finding non-associated gas in the Permian Khuff carbonates in the eastern Province and in the Arabian Gulf and in the preKhuff clastics in central Saudi Arabia. Prospects in the northern province probably lie around the southern margin of the Gotnia Basin, where reservoirs may have accumulated oil migrating from the basin. Prospects in the central and western areas of Saudi Arabia are influenced by the central Arabian Arch, a lowangle, easterly plunging structure with a surface expression. The recent discovery of the A1 Hawtah and other fields south of Riyadh in Paleozoic clastics, of light oil in the Wadi Birk well geochemically similar to that in the Tinat Field 300 km to the east, opens up a new frontier province. The source of the oil is unknown. Whether it derives from the Silurian Qusaiba shale, which is mature and widely distributed, or whether it is from the basal Khuff shale, it points to a considerable exploration potential. The Rub al Khali Sub-basin, mainly a Tertiary-Late Cretaceous feature, has a thick Paleozoic section in its western half that is largely untested. In the eastern part of the basin, Lower Cretaceous oil has been found in the Shaybah Field and Upper Jurassic oil and gas in the Ramlah and Kidan fields, respectively. Historically, exploration has concentrated on testing large structures along the Paleozoic north-south trends, and stratigraphic pinch-outs and truncations that exist within the Paleozoic and Mesozoic sections have been largely ignored. The potential of the interior homocline is doubtful due to the lack of structure, severe erosion and probability of hydrocarbon migration into larger structures to the east. The Red Sea coast holds a good potential for the discovery of gas in commercial quantities. Future exploration will tend to concentrate on the discovery of smaller structures and upon the search for subtle traps. Although the stability of the shelf for a long period, which influenced the development of the giant oil pools, reduces to some extent the stratigraphic trap potential, it does not eliminate the potential of smaller structures.

523

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Chapter 11 HYDROCARBON HABITAT OF THE GREATER ARABIAN BASIN

INTRODUCTION

bia, Bahrain or the Qatar Arch, with N-S, N-NE/S-SW or NE-SW trends. Traps also are related to salt structures as in Yemen, or with domal structures with either east-west or north-south trends in the Cretaceous of the United Arab Emirates (U.A.E.) and offshore Qatar. A few stratigraphic traps are found in UAE, Kuwait and Saudi Arabia and combination traps occur in the U.A.E. and Jordan. The principal reservoirs in the Arabian Basin are the sandstones of the Upper Jurassic and Cretaceous in Yemen; Upper Jurassic Arab carbonates of Saudi Arabia, Bahrain, Qatar and U.A.E.; Lower Cretaceous carbonates in U.A.E., Qatar, Kuwait and Saudi Arabia; Middle Jurassic carbonates in Qatar and U.A.E.; Middle Cretaceous sandstones and carbonates in U.A.E., Bahrain and Saudi Arabia; Permian carbonates in Saudi Arabia, Bahrain, U.A.E. and Qatar; Pre-Permian sandstones in Saudi Arabia; and Lower and Middle Cretaceous sandstones in Kuwait. The main source rocks are the argillaceous, bituminous limestone in the Upper Jurassic, Lower and Middle Cretaceous, and the shale in the Lower Paleozoic. Seals are mainly anhydrites and shale, but the dense limestone also may act as a seal.

There is an obvious subdivision of hydrocarbon habitats in the Middle East into those basins lying primarily on the Arabian Platform and those in the Zagros Basin. This also generally translates into the age of the fields. On the Arabian Platform, concern is primarily with Jurassic and Cretaceous source rocks and reservoirs and secondarily with Paleozoic sources and reservoirs; in the Zagros Trough, the traps and reservoirs are mostly Cenozoic and are the result of late Cenozoic tectonism. As the Cenozoic tectonic activity resulted in the formation of the Zagros Foredeep/Basin, it is not surprising that this resulted in the implanting of younger basins over the edges of the Arabian Platform. This gives rise to the generalization that Mesozoic basins and fields occur on the Arabian Platform, and Cenozoic fields and basins occur in the Zagros Trough, with an intermediate group containing elements of both in Syria and Iraq. They are included in the Zagros Basin for the convenience of the reader. Standing somewhat apart from these, a third group can be established to consider the Oman oil basin with Infracambrian, Paleozoic and Cretaceous source rocks and reservoirs. Within the limitations of this grouping, the hydrocarbon habitats are treated here on a country-by-country basis to be consistent with the stratigraphic treatment in earlier chapters. As petroleum basins are no respecters of political boundaries, the fields that cross state boundaries will be discussed under the country where the field is best developed. The number of plays compared with the number of fields is small; consequently, to avoid repetition, detailed field descriptions will be limited to providing examples from the different countries and referring other fields to the appropriate type, relying on a tabulation of field data to provide more detail when required. There is a price to pay for this style of presentation, but an attempt is made to minimize duplication. The greatest proportion of the Middle East oil and gas reserves and resources are found in the Arabian Basin (Fig. 11.1), which, according to Klemme (1980), constitutes a type 4 basin (downwarp into small ocean basin). Other oil and gas deposits are linked to rift-type basins (e.g., Red Sea). The Paleozoic to Middle Miocene sequence in the Arabian Basin is the world's richest hydrocarbon province. Large volumes of non-associated gas also are housed in the Paleozoic sequence of central and eastern Arabia. Structural, mainly anticlinal, traps are the most common. They may be associated with basement-controlled structures, as in offshore Abu Dhabi, Kuwait, Saudi Ara-

KUWAIT AND THE KUWAIT-SAUDI ARABIA NEUTRAL ZONE Kuwait has an area of 17,818 sq km (6,000 sq mi). It lies at the head of the Arabian Gulf, forming part of the Lower Mesopotamian Flood Plain on its western shore. It is bordered by Saudi Arabia and Iraq. The Kuwait-Saudi Arabia Neutral zone which lies south of Kuwait was jointly administered until the 1970s, when the area was divided between the two countries although oil production is still jointly administered. Topographically, it is a relatively featureless area, with slightly undulating, sandy or gravelly desert. It rises gently to about 274 m (900 ft) in the southwest, a topographic feature that reflects recent geological structure. The surface is covered by clastic sediments of the Kuwait Group ranging in age from Miocene to Recent. In the Jal az Zor Escarpment, several calcrete horizons are exposed within the beds of the Kuwait Group. They commonly occur near the upper surface of argillaceous sandstone, about 2-3 m below the surface, and are developed diagenetically. According to Khalaf and E1Sayed (1989), the host fluviatile, argillaceous sandstone may have been deposited during a humid climatic cycle and the calcrete during the succeeding period of semi-aridity. The calcrete host sandstone usually is capped by a thin layer of red mudstone resembling terra rossa, which may

525

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 11.2. Location map of Kuwait and the Kuwait-Saudi Arabia Neutral Zone showing the major oil and gas fields and some exploration wells. Since 1922, the zone has been jointly administered by Kuwait and Saudi Arabia, but in the 1970s, it was divided between the two countries and subsequently referred to as the Divided (Neutral) Zone. Oil and gas production has continued to be administered and shared by the two countries. The main onshore and offshore fields of the zone are: Wafra, Umm Gudair South (Umm Gudair extension), South Fuwaris, Khafji (Safaniyah extension), A1 Hout, Dorra and Lulu (Esfandiar extension). 526

Hydrocarbon Habitat of the Greater Arabian Basins have been developed from the leaching of the top part of the calcrete profile. The landscape is controlled by the development of duricrust, silcrete and calcrete in the south and a gypsiferous crust in the north. The desert zone is covered by residual gravels, playa and aeolian deposits such as wadi fill, active sand sheets and dune fields (both fixed and mobile). There is a positive sediment budget in the north and west, with sediment transported by northwest winds from the muddy plains of Mesopotamia and southern Iraq, but active deflation is occurring in the south and east (Khalaf, 1989). The climate is hot and dry, with temperatures ranging from 12.7 ~ C (January) to 37.4 ~ C (July) with a diurnal range of up to 17 ~ C. Rainfall is light, with a mean annual value of 100 mm. Oil seepages have been known for a considerable time near Bahrah, north of Kuwait Bay, and at Burgan, where oil in commercial quantity was first struck by KOC (a joint Anglo-Persian and Gulf Oil development) in 1938 and remained undeveloped until after World War II. Surface geological exploration carried out early in the century before the granting of the first concession suggested the existence of large Tertiary uplifts, with the presence of oil or gas seepages suggesting that these may have been located on or near the crests of the structures. Drilling of Bahrah, the first of these, began in 1936 and reached a depth of 2424 m (7,950 ft) without penetrating any commercial hydrocarbon accumulations. While this was in progress, drilling had begun on the Burgan structure, where an extensive bitumen lake had been penetrated by shallow drilling. Well Burgan-1 was begun in 1937, but it was not completed as a producing well until 1963 because of wartime delays. Between 1938 and 1942, eight additional wells were begun on the Burgan structure, but were plugged because of wartime conditions. Magwa-1 was spudded in 1951 on a suspected subsidiary structure, which subsequently proved a substantial extension to the Burgan Field. Drilling of Ahmadi-1 began in 1952 and was completed as a producer in the Wara Sands and the Mauddud Limestone, demonstrating that the Ahmadi Ridge structure was later than the development of either the Burgan or Magwa fields (Fox, 1956). In 1954, the considerable hydrocarbon potential of the Umm Gudair structure, a seismically defined feature some 13 mi. west of Burgan, was discovered in the Wara Sandstone reservoir. In 1955, the rich oil potential of the Raudhatain Field was found, and with continued exploration several new fields were discovered in Kuwait and in the Neutral Zone. Initially all production came from shallow Tertiary and Cretaceous reservoirs, however following further seismic exploration oil was discovered in Jurassic beds. In 1975, the State of Kuwait assumed full control over the Kuwait Oil Co. assets and now is the sole company in Kuwait onshore and offshore (with the exception of the offshore part of the Kuwait-Saudi Arabia Divided Zone). In 1977, Kuwait took over the Aminoil company operation in the Neutral Zone by the nationalized Kuwait Oil Co., while Texaco (previ-

ously Getty Oil) and Arabian Oil Co, operations remained unchanged (Beydoun, 1988). By 1966, Kuwait had become the fourth largest producer in the world, although conservation policy decisions have constrained production (Beydoun, 1988) since 1973. In 1979, the total recoverable oil was estimated at 65.4 B.bbl, which was increased to 92.7 in 1984, with 36.3 TCF of natural gas. As Adasani (1985) pointed out, however, there still remains a group of virtually untested anticlines in western Kuwait. The country ranked among the world's oil producing countries with supergiant and giant oil fields (Fig. 11.2).

Stratigraphic History The geology of Kuwait and the Neutral Zone is known primarily from wells and geophysical data, especially seismic, in the virtual absence of surface outcrop. The overall structure is generally simple consisting of a series of roughly parallel, N-NW-trending anticlinal uplifts. Hydrocarbons both onshore and offshore are found in combination structural-stratigraphic traps usually elongated north-south. For most of the Mesozoic, Kuwait occupied an intermediate position between the Arabian Shelf and the thicker, passive margin sediments of the Arabian Gulf. Marine carbonate deposition predominated, interspersed with the incoming of deltaic sands during parts of the Cretaceous and clastic continental deposits during the postEocene period. A lithostratigraphic column showing the principal source rock, reservoir and seals is shown in Fig. 11.3. There were several intervals of evaporite deposition" the formation of the Jilh during the Triassic, the Gotnia of the late Jurassic, the Rus of the Eocene and the Miocene evaporites of the Miocene Lower Fars. Detailed stratigraphic and lithofacies descriptions of some of the Mesozoic formations have been provided by A1 Shamlan et al. ( 1981) and Adasani ( 1965, 1967, 1985). Precambrian basement has been reached as a result of deep drilling in the Burgan structure. The Paleozoic is believed to contain mainly continental clastics with intercalated shallow shelf carbonates and may reach 2,000 m (6,560 ft) in thickness. The Mesozoic section consists of deposits over the hingeline between platform sedimentation in Saudi Arabia and deeper basinal deposits in Iraq and may reach a thickness of about 5,000 m (16,400 ft) in Kuwait and the Neutral Zone. The Triassic section passes from marine and lagoonal shale in the lower part, returning to a middle section of shallow-marine carbonates, to more continental clastics at the top. The Jurassic section comprises mostly carbonate beds with evaporitic horizons in the lower and upper parts and is followed by a Cretaceous of shallow-marine limestone interspersed with deltaic sandstone. Similar conditions prevailed during the Paleocene-Eocene, however in the Miocene there is a transition from limestone deposition to the predominantly continental clastics which continue through the Plio-Pleistocene.

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these do not contain oil, although they may have in the past, some of the structures may have experienced growth subsequent to oil migration and are dry for this reason. The main structural elements of Kuwait are shown in Fig. 11.4. These elements include structural arches, regional highs and lows, anticlines, synclines and faults. The Burgan-Magwa-Ahmadi structural complex can be regarded as a single complex, although each part may have experienced movements individually short but collectively spread over a long time period. Figs. 11.5 and 11.6 provide cross-sections and lithostratigraphic correlation across Kuwait and southern Iraq. It is probable that the time from the end of the Jurassic to the end of the deposition of the Middle Cretaceous Mauddud Limestone and from the close of the Cretaceous until the end of the Middle Miocene was represented by stable, subsiding conditions. Following the deposition of the Mauddud to the end of the Cretaceous and from the Middle Eocene to Miocene, the elevation of parts of the Burgan-MagwaAhmadi anticlinorium changed considerably (Fox, 1959), with local stratigraphic thinning and even washouts and erosion occurring over the uplifted parts of the structures, dating this structural growth from a beginning in the Cenomanian. Further structural growth, of the order of 152 m (500 ft), occurred during the interval from the Maastrichtian to Middle Eocene, followed by a pause in deposition, because rocks of this age are overlain by Miocene or younger sediments. Rejuvenation of older structures con-

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The geology of Kuwait is known only from wells and geophysical, particularly gravity and seismic, exploration in the absence of surface outcrop. The structure generally is very simple, consisting of a series of roughly parallel, shallow-dipping (2-3~ anticlinal uplifts trending generally N-NW-S-SE, with a few having a more north-south to north-northeast-south-southwesterly trend clearly shown on the Bouguer anomaly map (Warsi, 1990). The most prominent is the Kuwait Arch, extending from the border near Wafra in the southwest to the northern border near Abdali, with which most of the major oil fields are related (Burgan, Magwa, Ahmadi, Bahrah, Sabriya, Raudhatain and Wafra). The other major gravity structure is the NWSE-trending gravity high in western Kuwait that reflects the position of the Dibdibba Arch. The wells drilled in this structure between 1959 and 1962 were dry. As some of

528

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529

Sedimentary Basins and Petroleum Geology of the Middle East tinued, however, with the main uplift concentrated in the region of the eastern flank of the Ahmadi Ridge, at which time the Burgan-Magwa-Ahmadi structure reached its present state of development. The offshore fields (Hout, Khafji-Safaniya and Dorra) are located on the same broad north-south structural trend. The Hout field is the most tightly folded of the three structures. East of the Hout field there is a large closed syncline, which in size is almost equivalent to that of the entire Hout field indicating that it was the source of the salt flowage into the Hout structure (Behbehani, 1980). Reservoir Rocks

The principal hydrocarbon production in Kuwait and the Neutral Zone stems from Cretaceous reservoirs, and although deep drilling has established new Lower Jurassic (Marrat Formation) and Middle Jurassic (Sargelu Formation) limestone reservoirs it has failed to prove the existence of Permian, Khuff, gas. In North Kuwait, an important Miocene heavy oil reservoir occurs in the Lower Fars of the Ratga Field. The Jurassic reservoirs account for 11% and 20% of the ultimately recoverable oil and gas reserves. Only 1% is found in the Miocene, the rest is in the Cretaceous. However the Jurassic discoveries open up the prospect for further discoveries in Kuwait, and the offshore potential in the Cretaceous has not been fully tested. In a preliminary simulation of primary oil migration (onedimensional fluid-flow model), Ozkaya (1991) simulated migration from the Burgan and Sabriya fields of hydrocarbons generated in the Middle Jurassic Sargelu Formation, concluding that maximum oil saturation was never reached in the Burgan area, but that the critical value was reached on expulsion begun during the Eocene in the Sabriya area. How realistic a model it is cannot be fairly judged in the absence of many of the (assumed) parameters. In the Neutral Zone, the Eocene limestones provide an additional Tertiary reservoir which accounts for 8% of the ultimately recoverable oil reserves. A summary of the characteristics of the main producing horizons, in stratigraphical order, follows. Lower Cretaceous Reservoirs.

Minagish F o r m a t i o n . This formation consists of three members. The Lower Member is peloidal-bioclastic, occasionally dolomitic limestone with fine-grained, peloidal limestone, a 22% porosity and a nearly 500 md permeability. The Middle Member is composed of medium- to very coarse-grained, oolitic grainstone with occasional pellets, bioclastic leaching and the common development of vugs. The uppermost part of this member is mainly well-cemented, peloidal limestone and calcareous, argillaceous limestone. The porosity is about 30%, while the permeability is nearly 500 md. The Upper Member (known also as the Minagish Oolite Member) is a massive, oolitic,

530

fossiliferous limestone cemented with varying amounts of lime mud and sparry calcite. The porosity of about 22% is controlled by diagenetic processes, mainly calcitization and dolomitization, while the average permeability is 450 md. The Minagish Oolite Member is a prolific oil horizon in the Minagish, Umm Gudair, Burgan, Magwa and South Umm Gudair fields and is well-developed in southern Kuwait oil fields. This oolite member is absent in northern Kuwait, where the formation commonly consists of fractured limestone, with some of the fractures filled with calcite. Near the oil-water contact is a zone of heavy and dark, tarry oil known as tar mat in the Minagish Field, which varies in thickness from 10 m (33 ft) in the northeast to 33 m (100 ft) in the north of the field. This tar mat is continuous throughout the reservoir, and it initially forms a seal isolating the oil zone from the aquifer. Ratawi Formation. The formation consists of two shale members with intercalated sands and limestone. The formation ranges in thickness from about 152 m to more than 366 m (500-1,200 ft). The central part of Kuwait has received the greatest thickness of the formation along the NW-SE basinal axis; this thickness also increases toward the offshore area. The Ratawi Shale Member contains three separate sandstone beds deposited as isolated sand bodies of limited extent in a shallow-marine setting. The limestone is poorly interbedded with dense intervals of about 20% shale. The average porosity is about 15%, while the water saturation is between 16 and 32%. Oil with 45 ~ API was produced from two thin sandstone zones (about 10-15 ft thick) in the Ratawi shale in the Sabriya and Raudhatain fields. The formation produces in the Umm Gudair, with oil gravity from 24 to 28 ~ API. It does not produce commercial oil in the Minagish Field. The pay thickness in the Wafra Field averages about 61 m (20Oft). It has a tight, oolitic facies and is fractured Ratawi limestone. The average porosity of the pay zone is 2023%, with 24.5 ~ API oil having a sulfur content of 3.6%. The productive area for this reservoir is estimated at 20,000 acres (Nelson, 1968). The Ratawi Formation is the principal reservoir in the Lulu field with 30-40 API gravity oil and 1.7% sulfur content. At Fuwaris (also known as South Fuwaris) the Ratawi reservoir has 23 -26 API gravity oil and 3.5% sulfur content. At al Hout the oil has 35.3 API oil and 1.4% sulfur. The Ratawi Formation also yields oil in the Dorra Field. Zubair F o r m a t i o n . This formation thickens from south to north, and the shale/sand ratio increases from a clean sand interval in the southwest to 45% sand/shale in the north and northeast. The Zubair consists of about 415427 m (1,360-1,400 ft) of alternating sandstone, siltstone and shale, subdivided into three shale units interbedded with three sand units. The formation contains the main oil reservoirs at Raudhatain occurring in the well-developed sand horizons, but many of the thin sand zones within the predominantly shale section also contain hydrocarbon. In the Sabriya Field, the oil occurs only in thin sand stringers

Hydrocarbon Habitat of the Greater Arabian Basins in the upper Zubair shale and in the thin sands of the lower Zubair and, in the Bahrah Field, some oil from the Lower Cretaceous Zubair Formations in the sandstone section.

Middle Cretaceous Reservoirs Burgan F o r m a t i o n . Called the Fourth and Third sands, this formation is composed of well-sorted, rounded, medium- to coarse-grained sandstone, grading upward into alternating fine-grained sandstone and siltstone. Lignite, amber and glauconite are present throughout the sequence (Adasani, 1965, 1967). The Burgan Formation is the producing reservoir in the Burgan, Ahmadi, Bahrah, Minagish, Raudhatain and Sabriya fields. The Third Sand member consists of interbedded glauconitic sands and dark-gray shale with a middle unit of pure quartz sand and may reach a thickness of 110 m (361 ft). The Third Sand has an average porosity of 20% and a permeability between 380 and 605 md, with interstitial water saturation of 25-31%. The oil has a 28 to 24 ~ API gravity, and near the oil-water contact, the hydrocarbon system changes very rapidly to heavy, viscous and highly undersaturated oil. The Fourth Sand Member consists of a thin (6 m, or 20 r ) basal, shaly unit, succeeded by 210 m (700 r ) of pure quartz sandstone, medium- to coarse-grained, well-sorted, very clean and soft, containing little in the way of secondary cementation. The Fourth Sand has an average permeability of 4 darcies, a porosity averaging 23% and an interstitial water saturation of 4%. The oil has a gravity from 29 to 32 ~ API, with very heavy oil at the bottom. The sulfur content and viscosity increase with depth, while the solution gas/oil ratio decreases with increasing depth. Mauddud Formation. The formation is a compact, even dense, calcarenitic, locally detrital and peloidal limestone 5 to 10 m (20-30 ft) thick that contains abundant microfossils. Although it commonly is oil-stained, the Mauddud in the Greater Burgan produces only locally in the Burgan and Magwa fields and is not considered a significant reservoir because of its generally low permeability (average 10-15 rod). Oil was produced in the Bahrah Field, which had a 30 ~ API oil gravity; at Raudhatain, with a 29 ~ API oil gravity; Sabriya, with a 28 ~ API oil gravity; Dorra, with a 27-28 ~ API oil gravity and 2.9% sulfur; and Khafji, with a 28.5 ~ API oil gravity and 2.8% sulfur. Wara Formation This formation, consists of sandstone and interbedded shale. In south and southwest Kuwait shale is dominant whereas carbonates are developed in the upper part of the formation in the north and northeast. The average porosity in the Wara sand in the Minagish Field is 23%, with an average water saturation of 22%. The Wara sands have permeabilities from a fraction of a millidarcy to several darcies. In the Wafra Field, the Wara Formation consists of 4961 m (160-200 r ) of sand, siltstone and shale. The average porosity of the pay sand is 29%, yielding 24 ~ API oil with a 3.0% sulfur content. The productive acreage is estimated at 14,000 acres (Nelson, 1968). In the Greater Burgan

Field, the Wara Formation ranges in thickness from 40 to 50 m (140-180 ft), of which up to 60% of the total thickness comprises reservoir sand. Porosities in the cleaner sand sections of the Wara reservoir reach 30% and average about 24%. Permeabilities vary in magnitude from a few to thousands of millidarcies. Interstitial water saturation varies widely, with an 18-20% average (Brennan, 1990). Oil accumulation was proved in the Minagish, Burgan and Khafji fields. The hydrocarbon system was undersaturated, and no gas cap was present, whereas the Magwa and Ahmadi fields had small gas caps on top of the Wara reservoir. The sandstone sequence in the Minagish Field generally is much finer-grained and has a poorer development than in the other Kuwaiti fields, resulting in a lower productive capacity, for they contain much interbedded siltstone and shale and have more cementation by glauconitic, lignitic and carbonaceous materials. Mishrif Formation. This formation consists of crystalline limestone with rare thin shale intercalations forming 7 to 8% of the total thickness, which averages 58 m (190 fl). Porosity varies from 15 to 21%, and the water saturation is between 18 and 48%. Significant oil accumulation occurs in the Minagish Field, and test results indicate that this reservoir has low productivity and relatively poor reservoir characteristics. At A1 Hout, 35 ~ API oil with a 1.4% sulfur content also was produced from the Mishrif Formation dolomitic limestone.

Upper Cretaceous Reservoirs Tayarat Formation. The formation consists of granular, calcarenitic limestone with some shale stringers between 9 and 22% of the total thickness. Oil-bearing in the Umm Gudair Field, the net pay thickness reaches a maximum of 37 m (120 ft) in Umm Gudair west, and 49 m (160) in south Umm Gudair. Water saturation is between 27 and 45%. The porosity value varies from 15 to 25%, with a pronounced porosity decrease on the northeastern flank of the east lobe of the Umm Gudair Field. Tertiary Reservoirs Radhuma Formation. This formation ranges in thickness from 424 to 500 m (1,390-1,640 r ) and is divided into three members. The Wafra Member (First Eocene Limestone, reservoir 1), Jalib Member (Second Anhydrite, seal 1) and Arhaiya Member contain Eocene Limestone (seal 2), Second Eocene Limestone (reservoir 2) and Third Eocene Limestone (seal 3). The Wafra Field is the only field that produces from this formation. The Wafra Member "First Eocene" pay zone, 61-70 m (200-230 r ) thick, lies in the upper part of the Radhuma Formation. The limestone tends to be marly and shaley and often has considerable amounts of anhydrite infilling the porosity and contaminating the limestone. Porosity is from 30 to 35% and generally becomes poorer to the north and west. The oil averages 19~ API and contains 4.43%

531

Sedimentary Basins and Petroleum Geology of the Middle East sulfur. The total possible productive acreage is approximately 23,000 acres (Nelson, 1968). The Arhaiya Member "Second Eocene" pay is only about 30-37 m (100-120 ft) and contains some limestone interbeds with varying amounts of marly limestone and gypsiferous limestone with a 25 to 30% average porosity. The oil gravity is 20 ~ API, with a 4.43% sulfur content (Nelson, 1968).

Seals and Seal Formations The seal for nearly all of Kuwait's huge oil and gas reserves in Mesozoic reservoirs is shale. The most important cap rock shale is interbedded within several Lower and Middle Cretaceous reservoir sandstones (particularly the Albian Burgan sands and the Cenomanian Ahmadi shale), which seal about 88% of the country's oil reserves and about 80% of its gas reserves. The remainder is contained in Jurassic limestone reservoirs sealed by Middle Jurassic shale and Upper Jurassic evaporites. Only a small amount of oil (mostly heavy oil), representing less than 1% of Kuwait's total oil reserve in the northernmost part of the country, is retained in the Miocene Ghar sandstone and the Lower Fars limestone, where Lower Fars evaporites are still marginally developed. The Ghar/Lower Fars heavy oil represents a residue after strong seepage, which indicates that the sealing capacity of the Lower Fars evaporites in this area is imperfect. The formations that can act as seals follow. Gotnia Formation: It consists of anhydrites, salts and subordinate limestone and shale. This formation is the local cap rock for the major oil and gas reservoirs in the underlying Sargelu limestone. Thinning indicates activity of the Kuwait Arch at this time. Initially, northern Kuwait was a structurally higher platform, later tilting to the northeast with thick late Gotnia anhydrite and salt (Ali, 1995). Sargelu Formation. It consists of shale and argillaceous limestone. The shale forms seals for oil and gas accumulations in interbedded Sargelu limestone reservoirs and in underlying limestone of the Marrat Formation. Ratawi Formation It consists of shale and limestone. The shaley unit in the upper part seals off major oil and gas accumulations in the lower Ratawi limestone and the underlying Minagish limestone reservoirs. Zubair Formation. The formation consists mainly of sand and shale. The shale forms a good seal for the major oil and gas reservoirs in interbedded Zubair sands. Burgan Formation It is composed of sandstone and shale. Interbedded shale units form the seals for important oil and gas accumulations in two major sandstone reservoirs. Ahmadi Formation. It is composed of red to brown shale and limestone. The shaly unit in the upper part of the formation acts as the cap rock for oil and gas reservoirs in the lower Ahmadi Limestone Member and in underlying

532

sands of the Wara Formation. The Ahmadi Formation is the principal cap rock for the giant oil and gas accumulations in the Burgan sandstone, which probably represents the world's largest single sandstone reservoir. Mutriba Formation. It consists of calcareous shale and subordinate limestone. The shale unconformably overlaps various formations of the Wasia Group and acts as a partial seal for the Mishrif and Ahmadi limestone reservoirs included in this group. Khasib Formation. It consists of shale and marly limestone. This formation seals the local oil and gas reservoir in the Mishrif limestone. Rus Formation. It consists of anhydrite, subordinate limestone, shale and marl. This formation is a highly effective cap rock for the major oil accumulation in the Radhuma Formation in the Wafra Field, the only field in the southwestern part of the Arabian Gulf producing from Eocene rocks. Lower Fars Formation. It consists of anhydrites and intercalations of siltstone and shale. As a cap rock, this formation has a very limited effectiveness in Kuwait, but seals an important heavy oil reservoir in the interbedded Lower Fars and in the underlying Ghar sandstone in the Ratga Field.

Oil Geochemistry and Source Rocks Analytical results of stable carbon and sulfur isotope distributions in oil and extract fractions and kerogen were described by Robinson et al. (1991). Some of the values for the sulfur content of Kuwait oils at 2.1-4.2 wt% are higher than the 2.3-3.3 wt% commonly recorded. The crudes are of a very similar isotopic composition; the isotopic ranges of total oil are only 0.6%0 and 3.4%0 for carbon and sulfur, respectively. The carbon isotopic results of Robinson et al. (1991) are in full agreement with the observation of Ayres et al. (1982), that the Cretaceous crudes of the northern part of the Arabian Platform are isotopically lighter than -26.5%o. However, for sulfur isotopic compositions, Kuwait crudes are enriched in 532S with respect to Tertiary and Cretaceous oil from northern Iraq showing -8.7%o<534ScDT<-1.9%o (Thode and Monster, 1970). The high extract yields (>3 wt%) of oil from the Burgan and Raudhatain fields indicate the non-indigenous character of the extracted hydrocarbons. Oil-kerogen pairs showing closest 513C values are those from the Mauddud, Minagish and Ratawi formations (Fig. 11.7), and pairs showing good 534S correlation were obtained from the Mauddud, Zubair Lower Shale and Ratawi. A poorer 534S correlation was found in samples from the Minagish and Ratawi formations, having sufficient kerogen to be considered potential source rocks (Robinson et al., 1991) (Fig. 11.7). Only oil samples from Mauddud and Minagish are pyritic, and as the organic sulfur is similar in isotopic composition, it probably indicates a common origin. The higher rates of accumulation of organic matter in the sedi-

Hydrocarbon Habitat of the Greater Arabian Basins

AGE

FORMATION

BGIRA 9

O

x.z. 34~

a. z3 r.2 9.§

/534 S (%o)CDT

-2q -is -19 -5

. ,-z,a

..-:

19 1~

9- . . .

27

MAUDDUD

,~

9 .;

. . . . . . . . .

O~!

WARA D

Extract l~rogen Carbonate Iwt%) (wt%) ~13C(~o)PDB~513C(%0) PDB

Well N u m b e r L ~

/

/ / ~

.'... ..

/

//

/

:::~i}

:

9 .

.

9

Oil 160

BURGAN

!

,,

.

25

~

o

..~

..;

SHUAIBA

Ir

27

:::4 ::'.:D i..'!

,I / I

A

:;...: ....

9 .

!:t~.~ .. 9

.: 1

,"

tO

ZUBAIR

0 Oil

II

::

:

2:

G

i.i i 9..

:~

9 ..,,

-~

RATAW! 399A' 1 L~

,

MINAGISH 399A !

i

:.:~'; : .....

.,,

. ,

,

O Extract

G:"'Good oil/extract type curve fit Trend lines for Raudhatain Zi.i..;:i Oil range samples only

L!i

9

i

L

r

~ Kerogen

~

,,,-:-,. : - .

o

l w w;. ~i,o: Pyrite

0 A

-

Main trend line for all samples

Fig. 11.7. Geochemical analysis of crude oil from the Burgan (BG) and Raudhatain (RA) oil fields, Kuwait (after Robinson et al., 1991). .

.

.

.

,

,,

,,

,

,,

L.

I

BURC.~N / m

4

.

r

"1

MINAGISH

i

RETENTION

TIME

Fig. 11.8. The sulfur-selective flame photometric detector (FPD) gas chromatograms of aromatic fractions of carbonate source rocks of the Burgan (sandstone) Formation in the Sabriya Field and the Minagish (limestone) Formationin the Minagish Field (after Hughes, 1984 and reproduced by kind permission of AAPG). Peak identification: 1=C2 Benzothiophenes, 2=C3 Benzothiophenes, 3=C4+ Benzothiophenes, 4=Dibenzothiophene, 5=Methyldiobenzothiophenes 6=Dimethyldibenzothiophenes, 7=Trimethyldibenzothiophenes.

"~

533

Sedimentary Basins and Petroleum Geology of the Middle East ments result in 13C enrichment of carbonates. In this figure, the dashed lines through all data points show similar trends for the amount of kerogen ("immobile" organic matter) and stable carbon isotopic composition of carbonates. Since sulfur in rock extracts and kerogen usually is 16 wt%, it is very unlikely that it is derived from the original biomass, but more likely is from bacterial reduction of seawater sulfate, as is the case for samples from the Mauddud and Minagish formations. Many authors such as Dinur et al. (1980), Thode (1981) and Orr (1986) explained that when the available Fe is limited, leading to a high ratio of organically bonded sulfur to pyritic sulfur, the first-formed pyrites may be significantly enriched in 32S. This may be the case with the Ratawi Formation in the Raudhatain Field and the Minagish Formation in the Burgan Field, although the ratios of organic to pyrite sulfur are fairly low with these samples (0.33 and 0.12, respectively), especially when compared to the ratios in the Raudhatain Field samples from the Mauddud Formation (23.71) or the Burgan Formation (1.17). In most of the samples, the pyrites are isotopically heavy; their sulfur is not cogenetic with the organic sulfur (Robinson et al., 1991). Only the 534S value of sulfates of samples from the Burgan Formation is indicative of seawater sulfate; the other samples are all isotopically lighter. This may be interpreted by the formation of secondary sulfates. Kuwait crude oils from the Burgan and Raudhatain fields are very uniform in stable carbon and sulfur isotopic composition, thus forming one oil family probably derived from a single source rock (Robinson et al., 1991). Mauddud source rocks strengthen the model of a close association of reservoir and source for the Burgan Field (Kamen-Kaye, 1970), but in the case of the Raudhatain Field, oil from this source would have to migrate into older formations, which could only really occur by invoking a large lateral component during updip migration from deeper-buried sections under the Arabian Gulf. Minagish source rocks would accord with a common Cretaceous source of Middle East oils, as suggested by Dunnington (1967). The excellent isotopic correlation of the Middle Cretaceous rocks to crudes as impregnation effects by the reservoir oil argue for Lower Cretaceous source rocks in the Ratawi and Minagish formations (Robinson et al., 1991). To determine if the carbonate source rock introduce distinctive organosulfur compositions Hughes (1984) selected two groups of oils in reservoirs of different ages in Kuwait to study evidence of carbonate source. Crude oil in the Burgan Sandstone Formation and the Minagish Limestone Formation is believed to have it source in argillaceous micritic carbonate mudstones of the Lower Cretaceous Ratawi Formation. The carbonatederived oils are characterized by significant amounts of benzothiophenes (Fig. 11.8). In the Burgan and Minagish oil, the benzo- and dibenzothiophenes are comparable and C4 + derivatives are more abundant than the C3 + derivatives. A summary of the characteristics of the main source

534

rock formations is given below. The source rock potential of the Lower and Middle Cretaceous, and geochemical analyses recently reported by Abdullah and Kinghorn (1996) are listed in Tables 11.2 and 11.3. Middle Cretaceous source rocks Rumaila and Mishrif Formations. The Rumaila Formation is composed of fine grained marly limestone intercalated with calcareous sh. The rocks of the Mishrif Formation are a complex of bioclastic limestone containing algal, rudist or coral-reef debris. TOC (average 0.4% weight) and pyrolysis reuslts indicate that the formations constitute a poor source rock. T max and kerogen color imply the immaturity of both formations. In the Minagish Field petrographic analysis show the presence of marine amorphus, apropelic Type II organic matter whereas in the Umm Gudair Field the organic matter is more of Type IIIII type (Abdullah and Kinghorn, 1996). Ahmadi Formation. The sequence of limestone and shale has TOC values of less than 1% wt, Density fractionation and pyrolysis results indicate the presence of type III kerogens.The rare preserved spores and vitrinite show a TAI of 1 and Ro of 0.34 which indicate immaturity (Abdullah and Kinghorn, 1996). Wara Formation. The formation is compoed of interbedded fine-grained sandstone and siltstone withlignitic, thinly laminated shale. Elemental and petrographic analysis indicate the presence of Type III kerogen due to the oxidation and biodegradation of organic matter which probably was originally of higher quality (Abdullah and Kinghorn, 1996). The spore color and low vitrinite reflectance values show the formation to be immature. Mauddud Formation. The calcarenitic and marly limestones of the Mauddud contain 0.72% TOC which analysis shows to be immature Type II kerogen. The organic matter is low density amorphus, marine sapropel (Abdullah and Kinghorn, 1996) Burgan Formation.The formation is made up of well-sorted sandstone intercalated with black, laminated shale in which there are abundant plant remains and some resin nodules and lenticles. The TOC values are in the range 0.64-3.4 % wt, fair to good at the top and good to very good in the lower part. The results of kerogen elemental analysis and pyrolysis indicate Type II-III and Type III kerogen. T max and elemental analysis (Abdullah and Kinghorn, 1996) indicate maturity, however much of. the formation is generally immature. Lower Cretaceous source rocks Shuaiba Formation. The sequence of dolomitic, crystalline, porous and cavernous limestones have TOC's ranging between 0.67-1.29% wt. with marine, amorphous, partially degraded kerogen (Type II-III OM). The kerogen is lighter in color (greenish-yellow) in the Minagish Field than in the Raudhatain and is relatively immature.

Hydrocarbon Habitat of the Greater Arabian Basins Table 11.1 The results of TOC, pyrolysis and elemental analyses of kerogens from some of the oil fields of Kuwait (After Abdullah and Kinghorn, 1996 and reproduced by kind permission of Journal of Petroleum Geology) Formation

Oil Field

Sulaiy Minagish

Ratawi Limestom Ratawi Shale Zubair

RAUDHATAIN

Shuaiba Burgan Mauddud Ahmadi Sulaiy Ratawi Shale Zubair RIQUA

Buraan Wara Ahmadi Mishrif Minagish Ratawi Shale ASH-SHAHAM

Zubair Burgan Ahmadi Sulaiy Minagish

Ratawi

TOC

H/C

O/C

Sl

$2

1.55 1.91 1.38 0.53 0.4 0.43 0.36 0.88 0.55 0.8 0.38 1.86 2.84 2.83 0.94 0.88 0.61 1.29 2.18 1.64 0.64 2.02 0.72 0.38 2.68 1.5 .2.69 1.1 1.6 1.79 2.37 1.16 0.97 0.55 1.3 2 84 1.33 1.28 2.27 3.25

0.67 1 1.01 0.94

0.042 0.057 0.069 0.076

1.33 1.54 1.27 0.39

1.24

0.097

1.11 0.97 1.22 0.91 0.85 0.72 0.91 0.99

0.189 0.128 0.16 0.113 0.196 0.177 0.163 0.149

1.22 0.97 0.77

0.1 0.183 0.172

0.092 0.119 0.094 0.109 0.071 0.132 0.095 0.262 0.125 0.280 0.13 0.111 0.191 0.076 0.099 0.099

1.01

1.01

0.164

2.46 3.36 0.89 0.62 0.4 0.36 1.29 1.96 0.54 0.51 0.22

1.19 1.29 1.54 1.27 1.05

0.09 0.112 0.080 0.118 0.066

1.09 1.24 0.99

O.118 0.117 0.132

1.21

0.166

HI

2.89 5.34 5.49 2.12

471 449 443 418

186 280 398 400

0.32 0.22 0.19 i 0.16

0.04 0.03 0.09 0.02 i0.13 0.11 0.08

0.19 0.28 0.61 0.27 4.49 3.9 2.89

425 428 434 429 429 435 430

22 51 77 70 241 137 102

0.18 0.10 i 0.13 0.05 0.03 0.03 0.03

0.07

1.07

430

!122

0.06

4.34 5.77 3.7 1.71 16.25 2.86

429 423 429 412 418 405

336 265 226 267 804 397

0.04 L0.04 0.05 0.07 0.29 0.07

0.18 0.22 0.21 0.13 16.65 0.21

1.65 1.55 1.14 0.99 0.92 0.99 1.07 0.96 i 1.15 1.35 1.43 1.04 1.73 1.37 1.46 1.01 1.12 0.9

i Tmax

SI/SI+S2

l

]

!

0.11

0.73

435

181

0.1.3

0.998 4.36 0.01

8.5 8.7 0.84

429 431 419

660 444 164

0.11 0.33 0.01

231

0.05

i

Limestone Ratawi Shale

L

MINAGISH

!Zubair Shuaiba Burgan I

iMauddud iWara Ahmadi Rumaila Mishrif Rumaila Mishrif

UMM GUDAIR

0.8 0.39 0.44 0.64 3.09 0.67 3.41 3.36 1.82 4.05 0.56 2.43 0.5 2.1 ....1.38 0.4 0.22

0.09

1.85

423 ,

' 1.16 0.8 0.89 1.22 , 1.02 0.87 0.81 1.44 0.87 1.21 0.96 I 1.29 ,' 1.27 ! 0.9 F 1.19

' 0.146 0.128 0.202 0.241 , 0.182 0.078 0.188 0.206 0.233 0.137 0.16 0.13 ' 0.137 , 0.177 0.167

!

..... 0.03 i0.22 !0.75 l 1.89 11.68 0.16 2.29 0.08 12.16 0.07 5.27 i 3.42 , 0.01

, ]

1.17 12.7 2.25 , 12.31 14 4.2 27.1 1.8 4.8 0.88 6.9 ' 8.8 , 0.73

,

, ' ,

417 426 413 421 428 431 416 422 416 423 398 412 422

, , ,

, '

182 409 336 361 418 230 669 314 199 176 329 637 183

, ,

' ,

0.02 0.02 0.25 0.13 0.11 0.04 0.08 0.04 0.72 0.07 0.43 0.29 0.02

535

S e d i m e n t a r y B a s i n s and P e t r o l e u m G e o l o g y o f the M i d d l e E a s t

Table 11. 2 S u m m a r y of source-rock potential of Lower and Middle Cretaceous ( T h a m a m a and Wasia Groups) for some of the oilfields of Kuwait (after Abdullah and Kinghorn, 1996, reproduced by kind permission of Journal of Petroleum Geology). Formation Sulaiy

Minagish

Field Name

Richness

Type

General

Raudhatain

Good to very good

II Marine

Mature

Minagish Riqua

Fair Excellent?

II Marine II Marine

Very early mature Mature

Raudhatain

!Fair to good

II-III, III Marine

Minagish Fair to good Ash-Shaham Very good?

II-III, III Marine I-II Marine

Very early mature Very good source rock in AshShaham, the oolitic and deeper parts in Raudhatain is also good Very early mature Mature

Good source rock in northern parts of Kuwait, becomes fair in Minagish Field

Ratawi Raudhatain Limestone Minagish

Fair

III Marine

Very early mature Poor source rock

Fair

III Marine

Immature

Ratawi Shale

Good

III Marine and terrestrial

Immature

Poor to fair Minagish Good to very good Riqua Ash-Shaham Good to very good

III Marine and terrestrial II-III Marine and terrestrial II-III Marine and terrestrial

Immature Mature Mature

Raudhatain

III Marine and terrestrial

Very early mature Rich source rock but of low quality organic matter Immature Mature

Zubair

Shuaiba

Burgan

Mauddud

Wara

Raudhatain

Fair to very good

Very good Minagish Fair to good Riqua Ash-Shaham Good

III Marine and terrestrial II-III Marine and terrestrial II-III Marine and terrestrial

Raudhatain

Good

II Marine

Immature?

Minagish

Fair to poor

II-III Marine

Immature

Raudhatain

Very good to fair

III Marine and terrestrial

Immature

Very good to good Minagish Very good to good Riqua Ash-Shaham Very good

II-III,III Marine and terrestrial II Marine and terrestrial II Marine and terrestrial

Immature Very early mature Very early mature

Raudhatain

Good?

II Marine

Immature?

Minagish

Good?

II Marine

Immature?

Minagish

Poor

III Marine and terrestrial

Immature

II-III Marine and terrestrial

Very early mature

Riqua

Ahmadi

Rumaila and Mishrif

536

Maturity

Raudhatain Minagish Riqua Ash-Shaham

Poor Poor Fair Poor to fair

i

Rich source rock but with low quality organic matter and mature only in Riqua and Ash-Shaham

Marine type organic matter rich in Raudhatain and poor in Minagish. More samples required

Rich in organic matter but of gas type in both Raudhatain and Minagish. Oil and gas type in Riqua and Ash-Shaham

Immature but very good organic matter quality. More samples needed

Poor source rock. More samples needed

i

II-III Marine and terrestrial III Marine and terrestrial I-II? Marine

Immature

Poor source rock

Minagish

II Marine

Immature

Marine organic matter but partially biodegraded

9 Riqua Umm-Gudair Poor

III Marine II-III, III Marine

Immature Immature

l

Hydrocarbon Habitat of the Greater Arabian Basins

Zubair Formation. The formation is composed of interbedded sandstone and gray to black, thinly laminated shale. The TOC ranges between 0.5-3.09 % wt indicative of a very good source rock. The lower part of the formation contains Type III kerogen in the Raudhatain Field, but is Type II-III in the Riqua area. The maturity level in both the Riqua and Ash Shaham areas lies at the earliest stage of oil generation (Abdullah and Kinghorn, 1996). Ratawi Formation. This formation consists, in the lower part, of a planktonic-skeletal wackestone facies of argillaceous and lime mud-rich wackestone, where the intermictite micropores contain organic remains deposited in a relative deep-marine basin. This was followed by a massive, hard green-grey shale with a middle sandstone unit. In the Neutral Zone fields the lower part of the section consists of bioclastic, pelloidal limestone and interbedded mudstone. The upper part of the section consists of a combined facies of boundstone/grainstone sequences of interbeds of highly leached, algal boundstone and bioclastic grainstone. Most of the Ratawi sedimentation took place on a carbonate ramp setting with scattered lenses of algal biostromes. The oil in the Khafji and Hout fields of the Neutral Zone were classified as paraffinic-napthenics, while in the Wafra Field, the oils were classified as aromatic-intermediates. Lower Cretaceous carbonate facies of planktonic wackestone and Upper Jurassic evaporite and argillaceous limestone facies constitute the sources of Ratawi oils. Oils in the Hout Field followed a longer migration pathway than those in the Khafji Field. Oil from the Wafra Field in Ratawi oolite also may have accumulated in the Ratawi limestone intervals. The Hout and Khafji crudes (31-35 ~ API, 0.6-0.7% sulfur) were classified as paraffinic-naphthenic oils, and both Wafra oils (2126 ~ API, 1.2-1.6% sulfur) were classified as aromaticintermediate oils. The predominant source rocks of the Ratawi oil are carbonates with evaporites and shale or shaly source beds. The Ratawi crude samples can be categorized into marginally mature oils in the Wafra Field to mature oil in the Hout and Khafji fields. Hout crudes followed longer migration pathways than those in Khafji, and the Wafra oils likely migrated from the Ratawi oolite of the Wafra Field (Behbehani, 1988). In the Kuwait oilfiields Abdullah and Kinghorn (1996) concluded that the total organic carbon (TOC) in the carbonate section in the lower part of the formation is relatively poor to fair with values of 0.44-3.2% wt. There are slight differences in the level of maturity with depth, and in the deeper parts of the Riqua and Ash Shaham fields samples are mature. Minagish Formation. The limestones of the Minagish Formation are divided into three parts, the upper and lower parts are non-oolitic limestone enclosing an oolitic unit with high porosity and permeability. Abdullah and Kinghorn (1996) Reported Toc values of 0.3-0.54 for the non-oolitic limestane and 1.29-1.95 % wt. for the oolitic unit. Pyrolysis results show the presence of Ty II-III, III and even Type IV kerogens in the shallowest part of the

formation. The hydrogen index calculated for the oolitic limestone in the Minagish field averaged 552mg HC/g organics but falls to 355 mg HC/g, with amorphous marine-algal content having an average Tmax of 435 C indicating the onset of the oil-generation phase. Organic matter in the non-oolitic limestone shows the effects of biodegradation which increases with increasing depth and hence shows reduced kerogen quality. The distinctive kerogen typesfound in the Ash Shaham area is marked by well-preserved filamentous algae mixed with sapropelic, fluffy amorphous particles of low density Type II kerogens (Abdullah and Kinghorn, 1996) Sulaiy Formation. The TOC values for the thin, dark gray argillaceous limestone and shale of the Sulaij Formation range between 0.4-2.68 % wt. The presence of dark colored kerogen suggests that the formation is over-mature in the deepest parts of the Raudhatain Field, shallower levels may be at the peak of oil generation and in the Minagish Field, the formation is at the beginning of the oil generation phas (Adullah and Kinghorn, 1966).

Jurassic source rocks Dhruma Formation (Bajocian). The formation is composed of dark-grey shale, soft, slightly hard or blocky, and calcareous with frequent streaks and thin beds of limestone toward the base. The maximum development of source potential, the maximum of organic matter, is towards the south. The volume of organic matter has been determined and mapped (Fig. 11.9). Sargelu Formation (Bathonian). This formation is dense limestone interbedded with shale. The shale is calcareous, black at the top of the unit, but mainly grey in the rest of the section. The source-rock thickness was calculated as shown in Fig. 11.9. The source potential seems to increase to the west, with a maximum thickness of 12 m (39 ft). The average volume of organic matter calculated from density logs is 3.3%, whereas the average values of 4.3% and 4.5% were obtained by sonic and gamma-ray logs, respectively. Using the minimum values for each location, the organic matter content contour map (Fig. 11.9) indicates the increase in organic matter towards the west of Kuwait (Hussain, 1987). Najmah Formation (Callovian-Oxfordian). The formation is composed of dense limestone, black shale and oolitic, pellety limestone. It is organically rich and has distinctive wireline log characteristics. A map of source-rock thickness (Fig. 11.9) shows an increase in the source-rock potential to the east of Kuwait, where the thickness of organic richness reach 60 m (197 ft). Kuwait Oil Fields The hydrocarbons in Kuwait and the Neutral Zone are widely distributed in Cretaceous and Tertiary rocks and have recently been found in the Jurassic (see Fig. 11.3).

537

Sedimentary Basins and Petroleum Geology of the Middle East

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Greater Burgan Field The field consists of three giant fields (Burgan, Magwa, Ahmedi) located near the crest of the Kuwait arch. The discovery well of the Burgan Field, the second exploration well in Kuwait, was drilled in 1938 and flowed at rates of up to 4,343 bbl/d of 32.5 ~ API oil. By 1942, when further exploration was suspended, another eight wells had confirmed the magnitude of the discovery. Work was resumed in 1945 and the field went on stream in 1946. Magwa was discovered in 1951 by a well drilled near a 538

known gas seep and the field went on stream in 1953. In 1952 the Ahmadi discovery well was drilled and it too went on stream in 1953. The Greater Burgan dome is over 750 km 2 in area with an aspect ratio/ellipticity of 0.5 with minor tensional faulting cutting the crestal zone. Development drilling has established that the Burgan, Magwa and Ahmadi fields form a single major accumulation, with the latter two forming a subsidiary domes separated from the main Burgan structure by small grabens. The graben is 11.5 km wide and has two pronounced NW-SE-trending bounding faults with throws of 30-150 m (98-492 ft) and approximately 22 km in length. The three fields - - Burgan, Magwa and Ahmadi - - can be regarded as a single complex, although each may have experienced individual short periods of movement spread collectively over a long

Hydrocarbon Habitat of the Greater Arabian Basins time and superposed over a general subsidence from the end of the Jurassic to the Albian and from the end of the Cretaceous until the end of Middle Miocene. The period from Albian to the end of the Cretaceous and from Middle Eocene up to the end of the Middle Miocene was a period of structural growth, marked by local stratigraphic thinning and even washouts and erosion of the structurally highest parts. The Greater Burgan Field is an ovate dome of some 500 km 2 with a high ellipticity of 0.7 and a slight elongation striking north (Fig. 11.10). The structural depth of the dome are uniformly about 1~ The Burgan structure is cut by nearly 30 faults mapped as straight, in part radial and commonly 3-4 km in length with throws generally less than 15 m (49 ft) with the largest fault having a 73 m (239 ft) throw (Carman, 1996). The Magwa Field has an area of186 km 2 and an ellipticity of 0.75. The structure is cut by over 20 faults 3-6 km in length and trending NW-SE.

MAG~ SECTOR

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Carman (1996) reported that the northern flank of the Magwa dome is cut by a pair of NW-trending faults, which define a small graben about 10 km in length, causing a net 15 m (49 ft) upthrow to the north with axial offset. The Ahmadi Field has an area of 144 km 2 containing four major en echelon which trend N-NW with lengths of 2025 km and a spacing of 500 m (1640 ft). The fault throws are of the order of 15 m (49 ft) with the largest throw recorded of 106 m (348ft) on the northern plunge of the structure (Carman, 1996). The west flank dips of the Greater Burgan Field are seldom more than 2.5 ~ and the east flank dips are locally as high as 10 ~ The reservoirs are the Wara and Burgan Sandstone formations of the Middle Cretaceous Wasia Group separated by the limestone of the Mauddud Formation, which seldom is more than 11 m (35 ft) thick. The Burgan Sandstone grades upwards from a near perfect reservoir sand through the incoming of shale into the competent caprock shales of the Ahmadi Formation. The sandstone reservoir is fine to coarse-grained and porous (22%) with low interstitial water and oil saturated. The permeability ranges from less than 1 md to as much as 30 darcies, averaging some 380 md. The vertical closure on the reservoir may exceed 305 m (1,000 ft). The Burgan sand in the Kuwait area is divided into the Third and Fourth Sands based upon the recognition of regional marine flooding events, the tops defined by limestone or equivalent beds. Each sand unit is composed of a number O ~

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Fig. 11.10. Structure contour map of the top of the Burgan Formation (Albian), the main producing horizon in the Greater Burgan Field of Kuwait. The structure contains three fields Burgan, Magwa and Ahmadi. The approximate locations of the discovery wells are points 1-3, which were drilled between 1938 and 1952 (after Brennan, 1991, and reproduced by kind permission of AAPG).

Fig. 11.11. Depth structure map of the Bahrah Field derived from multi-fold 2D seismic data and well data. Closed circles are oil wells, and open circles are dry wells (after A1-Anzi, 1995, by permission, Gulf Petrolink, Bahrain). 539

Sedimentary Basins and Petroleum Geology of the Middle East of parasequences whose bounding surfaces with their higher shale and mudstone tends to restrict vertical reservoir communication. Attempts are being made to model sub-parasequence scale flow units (Kirby and A1 Hamoud, 1996). The presence of lignite, amber and glauconite in the Third and Fourth Sands suggests deposition in lagoonal to littoral conditions. The Wara and Burgan formations share a common oil-water contact, with an areal extent of nearly 300 sq mi. An oil-saturated section of 372 m (1,221 ft) of Jurassic horizons penetrated in deep test wells has proven non-productive, flowing salt water and some gas (Adasani, 1965), but there may be another 3050 m (10,000 ft) of Paleozoic that have not been fully penetrated. Deeperdrilling at Greater Burgan was successful in proving additional reserves of light oil (31-38 ~ API) in Early Cretaceous (Neocomian) Minagish Formation and the late Early Jurassic (? Toarcian Marrat Formation). The recoverable oil in the Greater Burgan Field appears to be at least 75 B.bbl, perhaps half of what was originally in place.

Bahrah Field This field has an area of about 160 sq km. It lies on

the northern side of Kuwait Bay along the Burgan-Sabriya Axis. Topographically, it is cut by the southeast-facing Jal az Zor Escarpment, which has an elevation of up to 80 m (262 ft) and is cut by many steep-sided wadis. The surface geology defines a north-plunging anticline exposing sands and gravels of Oligocene to Holocene age (A1-Anzi, 1995), subsequently confirmed seismically. The area first attracted attention in 1914, as a result of surface oil and gas seeps on the Bahrah alluvial flats and on areas of gas seeps about 2 km apart.The field was discovered in 1956 and went on line in 1960. Nine wells drilled into the Cretaceous between 1937 and 1983 and the further nine wells after 1983. These well data, together with approximately 500 km of multifold seismic (shot in 1979, 1982 and 1987), cuttings, cores and electric logs, provide a basis for details of stratigraphy and reservoir characteristics. Oil shows were found in the Lower Fars, Mauddud, Burgan, Zubair, Ratawi and Minagish formations, but no economic production was found in the Zubair and deeper formations. The structure of the Bahrah Field is that of a lowangle, plunging anticline (A1 Shammari, 1983) with a

Table 11.3. Summary of reservoir fluid characteristics in the Cretaceous formations of the Raudhatain Field (after Adasani, 1967).

540

Hydrocarbon Habitat of the Greater Arabian Basins ssI

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number of faulted culminations (Fig. 11.11). At the level of the top of the Mauddud, the width of the structure is about 10 km, with individual pools of the order of 5 sq km. The structure has grown steadily since the Cretaceous and, possibly, since the late Jurassic. Oil is produced from the Miocene Lower Fars Limestone, the Middle Cretaceous Mauddud Formation and the Burgan Formation. Most wells drain a single formation, but some tap two reservoirs. The occurrence of multi-level oil-water contacts in the Burgan Formation (Fig. 11.12) and sporadic production from the Lower Fars and Mauddud Formations suggests that the oil distribution may be controlled by a combination of faulting and stratigraphic features (A1 Anzi,1995). The Burgan sands may yield up to 3,000 bbl/d immediately below the porous Mauddud Limestone which has a yield of 500-1000 bbl/d. The Lower Fars which is a highly porous and permeable unconsolidated sand reservoir yields u p to 300 bbl/d of undersaturated, 8-14 ~ API oil. The Ahmadi Shale, which usually acts as a cap rock, has been found to have a porosity of 15-18% may yield 27-29 ~ API oil. Ultimately, recoverable oil reserves are estimated at about 930 MM.bbl. Raudhatain

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.

Field

Raudhatain and the adjacent Sabriya fields lie in northern Kuwait north of the Bahrah Field. A gravity and magnetic survey in 1936-37 gave no indication of structure either on the Bouguer, second derivative or magnetic maps; however, seismic surveys carried out in 1949 in an attempt to trace the northward continuation of the Burgan uplift outlined a smaller but good NW-SE-trending structure by following a reflecting horizon close to the top of the Mauddud formation, although no velocity data from closer than Southeast Kuwait were available (Milton and Davies, 1965). By early 1955, the Mauddud, Burgan and Zubair formations were all producing, and the field went on stream in 1960.

The Raudhatain Field has a slightly elongated faulted, domal structure, with flank dips seldom greater than 3 ~ and covers an area of 17,800 sq km (6,953 sq mi). Steep near-vertical faults have been identified in several wells. Eleven faults were mapped by Carman (1966) with a quasi-radial fault pattern. The average throw is 15 m (49 ft) with the largest fault which has a throw of 45 m (148 ft) intersected in a well in the Mutriba Formation above the Mishrif. The structural closure is a minimum of 152 m (500 ft) at the level of the Mauddud Limestone. To the north, closure in not defined, but there is no evidence of dip reversal. The structure is faulted, with faults that have throws of 9-12 m. (30-40 ft) and exhibit a quasi-radial pattern suggestive of a primary uplift origin due to Precambrian-Cambrian salt movement in depth. Structural growth began during the Cenomanian, and all subsequent formations show a crest-to-flank thickening, with the greatest during Rumaila and Mishrif times. The trap formation probably was complete by the mid-Late Cretaceous. The pre-Tertiary isopachs show the NE-SW-trending crest axis; the swing to the north in post-Eocene time coincides with Zagros folding. Stratigraphic information from the Raudhatain Field, which lies in a position intermediate between Basra and southeastern Kuwait, suggests that the correlations of Owen and Nasr (1958) seem possible, because the section generally is similar to that of the Rumaila Field in southeastern Iraq. The entire interval from the base of the Zubair to the top of the Mauddud averages 880 m (2,900 ft) in thickness and contains nine separate oil reservoirs (Table 11.3 and Fig. 11.13), four within the Zubair Formation, two within the Ratawi Formation and two within the Burgan Formation all separated from one another by shale interbeds. The remaining reservoir within the Mauddud Formation is capped by marine shales of the Ahmadi Formation (Brennan, 1990). The Zubair reservoir averages 420 m (1,380 ft) in thickness and contains three potentially productive zones

541

Sedimentary Basins and Petroleum Geology of the Middle East

19 37 33

1

36

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Fig. 11.13. Generalized cross-section showing the main oil accumulations (in black) in the Raudhatain-SabriyaBahrah oil fields in Kuwait (modified from Adasani, 1967). with many sand pools separated by shale. The reservoir sands are a clean orthoquartzite with an average 20% porosity and a variable but high permeability, whereas the aquifer rocks below the oil-water contact are diagenetically altered with silica, carbonate and secondary pyrite, reducing the porosity to less than half. The Mauddud reservoir is approximately 55 m (180 ft) thick with porosities in the range 16-22% and permeabilities averaging 22 md. The Burgan reservoir is about 207 m (680 ft) thick with an average porosity of 24% and average permeability of 1035 md. The original recoverable reserve of the Raudhatain Field has been estimated at 8.8 B.bbl of crude oil plus 13.19 TCF of natural gas. With a recovery factor of 39%, this translates into an oil-in-place reserve of 11 B.bbl plus 33.8 TCF of gas (Brennan, 1990).

Sabriya Field The Sabriya Field is an elongate, faulted anticlinal structure with flank dips ranging from 8~ to the east to approximately 4 ~ to the west. The structural plunge is about 2-3.5 ~ to the north and south. Eleven faults were mapped by Carman (1996) one with an approximate 38 m (125 ft) throw, three faults have throws exceeding 20 m (66 ft). The majority trend MW-SE while the others trend NE-SW or NNE-SSW. The field was discovered in 1956 and went on stream in 1967. Production is from the Burgan Sandstone and Ratawi Limestone, which yield a 2832 ~ API oil with a 2.5-3.4% sulfur content. The Mauddud Limestone in the Sabriya Field is essentially dry (A1-Rawi, 1981). This is interpreted as due to the reservoir being higher than in the Raudhatain Field at the time of oil migration, presumably during the Early Cretaceous prior to diagenesis (A1-Rawi, 1981; Ibrahim, 1983). Diagenetic

542

sealing of the pore spaces in the aqueous zone occurred prior to the structural growth in the Sabriya Field. Subsequent structural growth in Raudhatain permitted vertical migration into the Burgan and Mauddud reservoirs, but inhibited lateral migration into the Sabriya Field (A1Rawi, 1981). The field produces mainly from the Middle Cretaceous Mauddud and Burgan formations (Fig. 11.13). The Mauddud Formation contains hydrocarbons in the middle section with a 28.5 ~ API gravity. The porosity ranges from 10-22%, but at the southern end of the field deterioration of porosity may be sufficient to prevent the mass escape of the hydrocarbon over the structural spill point of the Mauddud. Logs and pressure data indicate that the oilwater content of the Mauddud may be tilted to a greater degree than that in the Burgan sandstone and that oil escape through the structural saddle at the south end of the field (Adasani, 1967). Oil accumulation in the thin sand stringers of the Upper Zubair shales is somewhat of a paradox in the scheme of oil migration. This oil could be primary, but the similarity in gravity and sulfur content to that of the Zubair at Raudhatain make this premise unlikely (Adasani, 1967). The oil in the Ratawi Formation occurs in the uppermost shale-sand stringer and in the porous thin limestone. The Upper Burgan sand reservoir averages nearly 37 m (120 ft) in thickness with average porosity varying from 27-20% from crest to flank as a result of vertical changes in the section. The elevation of the oil-water contact is controlled by the structural elevation of the spill point or the saddle of the fold.

Minagish Field The Minagish Field in southwestern Kuwait, about 40

Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.14. Structural contour map of the top of the Lower Cretaceous Minagish Formation in the Minagish oil field (after Adasani, 1985).

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543

Sedimentary Basins and Petroleum Geology of the Middle East km west of the Burgan Field, was discovered in 1959. Minagish-I flowed at 10,000 bbl/d of 34 ~ API crude with 2.1% sulfur from the Minagish Formation and went on stream in 1961. The field is an elongated anticline trending almost due north-south with a maximum length of 13.5 x 6.7 km (8.5 x 4 mi) (Fig. 11.14), the flanks dip 5-7 ~ and there are about 10 faults radiating from the crestal area which have steep hades and normal displacements generally less than 20 m (66 ft). The east and west flanks dip 3 ~ while the north and south flanks dip 2 ~. Although there are radiating faults present in the crestal area, they have little influence as controls on the hydrocarbon accumulation. Oil (20 ~ API) was found in the Mishrif Limestone, the Wara Sandstone and the Burgan Sandstone, all belonging to the Wasia Group (Fig. 11.15). Cun'ently, the Minagish Limestone is the main producing formation. The limestone is a massive, porous, detrital, oolitic and fossiliferous limestone averaging 92 m (300 ft) in gross thickness with a porosity between 15 and 21% and a permeability of 40 md. The presence of a tar mat near the original oil/water contact (El Aouar and Rasool, 1970) has reduced its reservoir properties. The principal production is from the middle part of the section where the Wara sand with a porosity of 22% contains an oil accumulation producing 85-360 BOPD. The Burgan sandstone has a gross thickness of 40 m (132 ft) with an average porosity varying between 1624%. It produces oil at a rate of 1117 BOPD from Minagish- 10 (Adasani, 1985). By 1970, 23 wells had been drilled, of which eight were producing from the Minagish oolite (Thamama Group) and four were being used for gas injection, a process begun in 1967 to counter the rapid decline in reservoir pressure of 400 psi (an average production drop from 50,000 bbl per psi drop), which had resulted in the field being shut-in between 1963 and 1966 because of poor reservoir performance and by 1980 it had produced 255 MM.bbl. The Minagish oolite is the largest and most productive of the reservoirs in the field, and is the producing horizon in the Umm Gudair Field. It is the lowest economic oil-producing horizon in Kuwait. The other reservoirs of the Middle Cretaceous Wasia Group, in order of importance, are the Burgan, Wara and Mishrif. The ultimate recoverable oil reserves are estimated at 2.1 B.bbl (Beydoun, 1988).

Umm Gudair Field The first well drilled in 1954 was to test the potentialities of the Wara, Burgan and Zubair formations was dry. In 1962 well-2 was drilled and oil was discovered in the Minagish Formation leading to discovery of the Umm Gudair Field. The Umm Gudair structural is composed of two elongated domes separated by saddle (Umm Gudair West and Umm Gudair East). West Gudair is on the smaller structural closure trending almost north-south. It had commenced structural growth during the Late Jurassic. The

544

East Umm Gudair structure extend southwards as a broad structural high. The structural development postdates the Jurassic (Adasani, 1985). The field went on production in 1962 from the main Minagish reservoir (Fig. 11.15) which consists of about 91 m (300 ft) of massive peloidal-oolitic limestone (average porosity 21%, permeability from 41500 md). The oil has 25 ~ API gravity with sulfur content of 3.8%. There is also minor production from the Tayarat Formation (Maastrichtian) which consists of limestone with a net pay thickness of 37-49 m (120-160 ft) and a porosity varying between 15-35%. By 1980, the field had produced 172 MM.bbl of oil and had initial recoverable reserves estimated at 4 B.bbl (Beydoun, 1988).

Khafji Field The Khafji Field was discovered in 1959 and went on stream in 1961. The structure is a broad, elongated nose (Fig. 11.16), which is a northward extension of the huge Safaniya structure in offshore Saudi Arabia. This structural trend is regionally located on a northeast-trending arch and is more than 250 km long from Safaniya at the southwest to Hendijan at the northeast in Iran. The crest of the structure appears to be broad and relatively undeformed with some high closures. A few small, normal faults were detected in some sections near the crest (Behbehani, 1980). The Khafji Field is structurally higher than the Hout Field and was subjected to considerably more erosion. The Rumaila and Mishrif formations do not exist over the crest of the field and on the northwestern flank only a limited section of the Mishrif Formation is found (Behbehani, 1983). The oil occurs in multiple reservoirs of Middle and Lower Cretaceous age (Fig. 11.17). The Rumaila Limestone has 27-28 ~ API oil and 2.8% sulfur. The Wara Sandstone, Mauddud Limestone and Burgan Sandstone have 26-28.5 ~ API oil and 2.8% sulfur, while the Ratawi Limestone has 33-35 ~ API oil and 1.7% sulfur. The average field production in 1979 was 405,000 bbl/d which dropped to 243,000 bbl/d in 1985, by which time the field had produced 2.17 B.bbl. Initial recoverable reserves were estimated at 6.43 B.bbl (Beydoun, 1988).

Wafra Field In the Wafra Field, the first well was drilled into the Wara Formation in 1949 on the basis of this a gravity survey. Two later wells proved dry, but the fourth well found oil in the Wara and Radhuma formations. This well was discovered in 1953 and went on stream in 1954. The Wafra structure is a gentle, elongated, anticlinal fold about 10 x 4 mi, with a closure of about 23 m (75 ft). A smaller fold, about 3 x 1.5 mi, lies to the southwest and is separated from the main structure by a shallow saddle about 23 m (75 ft) deep. This western area is associated with the strong, linear Fuwaris Fold, which trends northwest-southeast just west of the Wafra Field (Nelson,1968).

Hydrocarbon Habitat of the Greater Arabian Basins

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545

Sedimentary Basins and Petroleum Geology of the Middle East

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A Fig. 11.19. A) Structural contour map (depth in feet ) on top of micritic limestone zone 3 of the Ratawi Formation in the Umm Gudair South Field. B) cross -section correlation using porosity-resistivity logs showing the three micritic limestones zones (1-3) in the Umm Gudair South Field (compiled from Johnson et al., 1996). Note that the average depth of the producing horizon is 8200 feet subsea and the average oil-water contact is 8400 ft. subsea.

546

Hydrocarbon Habitat of the Greater Arabian Basins Four of the reservoirs are responsible for most of the production from the field (Fig. 11.18)" the Radhuma formation (First and Second Eocene "Limestone" with 19-20 ~ API oil and 4.4% sulfur), the Wara Formation (Middle Cretaceous) with 24 ~ API oil and 3.4% sulfur and the Ratawi Formation (Lower Cretaceous) with 24.5 ~ API oil and 3.6% sulfur and the Tayarat Formation (Maastrichtian) with 18~ API oil (Danielli, 1988). The Eocene reservoirs of the Wafra Field produce from dolostone with porosities reaching 45% and permeabilities exceeding 1000 md in places. The original sediments were deposited in coastal environments ranging from shallow subtidal to supratidal sabkhas with mainly high-water salinities. On the history of production Beydoun (1988) concluded that in 1979 the field produced 114000 b/d oil which dropped to 85000 b/d in 1985. By mid 1985 the field had produced a total of 1.25 B.bbl of oil despite a lengthy shutdown while desulfurization facilities were built in 1960's. The original recoverable oil reserve was estimated to be 1.7 B.bbl. Dorra Field The field was discovered in 1967 largely on the basis of seismic evidence and then conformed by well data. The Dorra is an oval-shaped domal structure northeast of the Hout Field lying on the Hout anticlinal axis. It measured 10 x 7 km in size. A synclinal saddle, determine mainly from seismic data, lies between the Hout and Dorra fields (Behbehani, 1980). Well Dorra-1 found sour oil, Dorra-2 encountered oil and gas and Dorra-3 is a commercial well with proven gas reserve. The reservoir is the Albian Mauddud limestone with 27-28 ~ API oil and 2.9% sulfur. There is minor production from the Lower Cretaceous Ratawi limestone. Ultimate recoverable oil reserves are estimated to be 163 MM.bbl while recoverable gas reserves are 35 TSF (Beydoun, 1988). Hout Field This field was discovered in 1963 and went on stream in 1969. The structure, about 10 x 5 km, is a narrow, tightly elongated, symmetrical anticline, with a hinge running almost north-south. The presence of many faults affects the Mishrif and Rumaila producing zones. The seismic study clearly indicated a graben below the crest of the Hout structure. The apparent syncline on the crest of the structure results from this deeper-seated graben (Fig. 11.17). Almost all of the faults encountered are normal faults, with steep dips and variable throws; however, some encountered on the western flank have low dips. Most of the faults occur along the structural axis and on the western flank of the structure. The faults are more common in the Lower and Middle Cretaceous sections than in the deeper formations (Behbehani, 1980). The Hout area was

stable until the Cenomanian with a thick accumulation of sediment. During Turonian time an intense tectonic event in the form of rapid local uplift, particularly in the northeastern part of the field, occurred. Upper Cretaceous-Tertiary sedimentary deposits in the Hout area plunge toward the north-northeast (Behbehani, 1980). There are two producing carbonate reservoirs in the Middle Cretaceous (Mishrif and Rumaila formations) and one in the Lower Cretaceous (Ratawi Formation). Oil gravity is 35.5 ~ API with 1.4% sulfur. The field averaged 8000 bbl/d in 1979, rising to 2300 bbl/d in 1985, by which time the field had produced a total of 248 MM.bbl. Initial recoverable reserves were estimated at 197 MM.bbl (Beydoun, 1988). Lulu Field The field was discovered in 1967 as a small extension of the Iranian Esfandiar Field with the main reservoir in the Lower Cretaceous Ratawi Formation. It yields 34 ~ API oil with 1.7% sulfur. Beydoun (1988) reported that the field has as little as 1 MM.bbl of recoverable oil reserves. Umm Gudair South Field The field is a large anticlinal structure (Fig. 11.19a) an extension of the Umm Gudair Field discovered in 1966 and went online in 1968. Production is from the Lower Cretaceous Ratawi Formation with 24.5 ~ API oil and 3.5 sulfur. The reservoir lies in about61-91 m ( 200-300 ft) of wackestones and packstones with a porosity range of 21% and a 245 md permeability. Three micritic zones inhibit vertical flow and can be correlated across the field (Fig. 11.19b). The vertical permeability is one to three orders of magnitude less thanthat of the oolitic limestone reservoir. Primary recovery has declined from an initial value of 41000 bsi to the current value of 3300 bsi. Field observations and simulation studies have determine that edge water is more important than bottom water (Johnson et al., 1996). The initial recoverable oil reserves were estimated at between 420-500 MM.bbl. After the second Gulf war the drilling of twelve wells and workover of existing wells in the field drove daily production from 3200 bbls in1994 to 115,000 bbls by the end of 1995. New drilling and advanced field management techniques have increased ultimate recovery from 29% to about 41% of the field's estimated 1.8 B.bbl of oil in place. South Fuwaris Field The field was discovered in 1961 and went on stream in 1964. It produced from the Lower Cretaceous Ratawi Formation with 23-26 ~ API oil containing 3.5% sulfur. Initial recoverable reserves were estimated at 35 MM.bbl with accumulative production by 1985 of 21 MM.bbl but no more recent figure is available.

547

Sedimentary Basins and Petroleum Geology of the Middle East June 1, 1932, oil was discovered on this structure, which became the Awali Field (renamed later to Bahrain Field). Oil flow was tested from the Wasia Group (Middle Cretaceous) at 6,120 m (2,008 ft) at a 9,600 bbl/d rate of 38~ crude oil. The first geophysical survey in the Bahrain area, an offshore reconnaissance reflection survey, was carried out by Geophysical Services Incorporated from September 1939 to June 1940 between Manama and Fasht Jarim Island to the north. The only structural information obtained was the suggestion of a high to the south of Fasht Jarim. Later, a marine survey was begun in November 1948 and completed in March 1950, revealing a paleohigh at Fasht Abu Saafa, north of Fasht Jarim. Subsequently, a refraction survey was carded out in 1961. The Bahrain government signed a participation agreement with BAPCO in 1952. Then, in 1974, the government established the Bahrain National Oil Company (BANOCO), a state company that acquired a 60 share in BAPCO. The complete takeover of petroleum operations was completed in 1974. Since then, no other new fields or discoveries have been made in Bahrain, despite extensive exploration efforts by national and international companies. Fig. 11.20 locates the Bahrain Field and some of the exploration wells that have been drilled in Bahrain on sev-

BAHRAIN

The State of Bahrain has an area of 678 sq km and consists of a group of islands located on the northeastern edge of the stable Arabian Platform between Qatar and the east coast of Saudi Arabia in the Arabian Gulf. The first concession granted for petroleum exploration in the Arabian Gulf was in Bahrain in 1925. There were three main reasons behind the choice of Bahrain for oil exploration; the pattern of surface outcrop on the main island, which indicated the presence of an anticlinal feature, the known presence of oil seeps in the Jebel Dukhan area, and the political stability of the country all served to reduce the financial risks inherent in oil exploration (A1Rawi, 1983). Although Gulf Oil Company was the first to show interest in Bahrain, its operations were barred by the terms of the Red Line Agreement. Therefore, it sold its rights to Standard Oil of California (SOCAL, and now Chevron). They successfully negotiated an exploration agreement with the Bahrain government and established the Bahrain Petroleum Company (BAPCO) in 1929. The first exploratory well was spudded in 1931 on the crest of a dominant surface anticlinal feature, near an old seepage, and was given the name of Jabal Dukhan (mountain of smoke). On I

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Fig. 11.20. The location of the Bahrain Field and the principal onshore and offshore exploration wells

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Hydrocarbon Habitat of the Greater Arabian Basins eral delineated structures. Field descriptions and hydrocarbon parameters are summarized in Appendix Table. Structure

The Bahrain Field is fairly large and elongate, north-south anticline some 30 miles long and 11 miles wide. It is slightly asymmetrical, with dips on the western flank of 4" and 2 ~ on the eastern flank. Its structural closure increases from 4,877 m (1,600 ft), 7,315 m (2,400 ft) and 10,973 m (3,600 ft) at the level of the Mauddud, Arab to Khuff formations, respectively. Based on the Bouguer and residual gravity maps, the field is inferred to be a saltinduced feature with a salt swell underlying the structure at a depth of the order of 5,905 m (18,000 ft). Pressure instability in salt in subsequent periods caused accelerated growth interrupted by periods of relative quiescence (Samahiji and Chaube, 1987). Samahiji and Chaube (1987) and Chaube and Sama-

hiji (1995) show that the, simplified, structural-contour maps (Fig. 11.21) present, step by step, the development and growth of the structural closure from the time of deposition to the present day. Growth of the Bahrain structure can be seen as early as the Ordovician, although as a result of uplift and erosion, several hundred feet of sediment was stripped from the crest of the structure at the end of the Silurian. A gradual onlap of sediments onto the slowly subsiding high occurred during the Devonian. There are signs of post-Hercynian stripping from the crest of the arch. The growth of the field has been traced through a series of paleo-structural maps (Figs. 11.22-11.24), with the aim of dating the earliest time of hydrocarbon emplacement, assuming the emplacement could not have occurred until the Paleoclosure on the pay zone at least equal to the present hydrocarbon column (Samahiji and Chaube, 1987; Chaube and Samahiji, 1995). The three key horizons mapped, top Ahmad, top Hith and top Khuff closely track the structural history of the Cretaceous Jurassic and Permian pay zones respectively. Since post Her-

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Cl.--100~t

Fig. 11.21. Structural contour map of the Bahrain Field: a=top of the Khuff Formation; b=top of the Arab Formation; c=top of the Mauddud Formation (from Chaube and Samahiji, 1995, reproduced with permission from Gulf Petrolink, Bahrain). 549

Sedimentary Basins and Petroleum Geology of the Middle East

PRESENT KHUFF STRUCTURE

MAASTRICHTIAN

KIMMERIDGIAN

TITttONIAN

TURONIAN

BATHONIAN

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UPPERTRIASSIC-. LOWER JURASSIC

APTIAN

LOWERTRIASSIC 0

PRESENT

MAASI'RICH'I1AN

PRESENT

550

TIJRONIAN

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1URONIAN

Fig. 11.22. Paleostructural maps of the Permian (Khuff Formation) showing closure development in the Bahrain Field. Note that the top Khuff structural surface at present has a closure over 1,098 m (3,600 ft) (after Samahiji and Chaube, 1987; reproduced with kind permission from Society of Petroleum Engineers).

0

10 km

10kin

lOkm

Fig. 11.23. Paleostructural maps of the Tithonian (Hith Formation) showing the development of paleoclosure at important geologic times in the Bahrain Field. The Hith forms the seal over the Arab reservoirs and tracks the Arab structural development. Note that the closure at each geologic time is shown in meters and feet (after Chaube and A1 Samahiji, 1995, reproduced with permission from Gulf Petrolink, Bahrain).

Fig. 11.24. Paleostructural maps of the Cenomanian (Ahmadi Formation), showing closure development in the Bahrain Field at important geologic times. The pattern is considered typical of the multiple Cretaceous reservoirs. Note that the closure at each geologic time is shown in meters and feet (after Chaube and A1 Samahiji, 1995, reproduced with permission from Gulf Petrolink, Bahrain).

Hydrocarbon Habitat of the Greater Arabian Basins

AGE

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GROWTH INCREMENT

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CUMULATIVE GROWTH FACTOR

ALL NUMBERS REPRESENT % OF PRESENT CLOSURE

Fig. 11.25. Growth history of the Bahrain Field during specific periods and cumulative growth factors at specific instants of time (after Samahiji and Chaube, 1987, reproduced with permission from the Society of Petroleum Engineers). cynian time, the structure has continued to grow from the Permian-Recent as shown in Fig. 11.25. The principal growth pulses occurred during the Upper Triassic-Lower Jurassic, Turonian, Maastrichtian and Eocene-Miocene, as reflected in major erosional unconformities caused by the flow of salt into the present crestal areas and withdrawal from the surrounding areas (Samahiji and Chaube, 1987). Stratigraphy

During the geologic history of the Arabian Basin, thick sequences of sedimentary rocks were deposited. Subsequently, folds of different types and sizes resulting from epeirogenic movements caused large oil traps (reservoirs) to form. The known stratigraphic section totals more than 6,000 m (19,680 ft), with rocks ranging from Paleozoic to Recent (Fig. 11.26). General descriptions are found in Chaube and Samahiji (1995), Samahiji and Chaube (1995) and Mendeck and A1 Madani (1995). In summary, the Lower Paleozoic sequence is made up largely of continental clastics (sandstone, siltstone and shale), subordinate shallow-marine or lacustrine carbonates, and marine, darkgrey to black shale. A number of unconformities testify to long periods of emergence and erosion. Following the Hercynian unconformity, Permian sedimentation was dominated by minor clastics and widespread shallow-marine and lagoonal carbonates and evaporites and the Lower-Middle Triassic by beds that include continental clastics and carbonates capped by an unconformity from the Carnian to Pliensbachian. During the Lower and Middle Jurassic, the cyclic sequence of alternating shallow-marine carbonates and clastics (mainly shale) includes some deeper, subtidal, basin facies. The Upper Jurassic consists of an upwardshallowing, regressive facies in which each cycle of car-

bonates is capped by anhydrite. The Berriasian-Valanginian dark mudstone facies formed in an intrashelf, basinal setting along with shallow-shelf limestone. Cyclic sedimentation, with shallow-shelf carbonates alternating with shallow-marine to non-marine, regressive clastics, occurred during Hauterivian to Turonian time. Shallowwater carbonates with a few clastic beds dominated the Coniacian through Maastrichtian interval. During the Tertiary, shallow-marine carbonates and clastics were widespread across the country. Reservoirs

The Bahrain Field has been producing continuously for 60 years, with production coming mainly from the Middle Cretaceous (Wasia Group) beds primarily from the Ahmadi, Wara, Mauddud and Nahr Umr formations, which contain 87% of the field accumulation. The rest of the oil production comes from the Lower Cretaceous Kharaib Formation and the Upper Jurassic Arab Formation. Additionally, there is minor production from the Cretaceous Aruma, Mishrif and Rumaila formations and Middle Jurassic Dhruma Formation. Significant gas reserves have been discovered in the Arab and Khuff formations, with gas that has been injected directly into the Mauddud reservoir to maintain reservoir pressure since as early as 1938. Reservoir rocks are found in 12 formations (24 reservoirs in all; Fig. 11.27, with the major production from the Upper Permian Khuff carbonates, Upper Jurassic Arab limestone (Arab B and D zones have oil and gas caps, while the C and A zones have free gas) and the Middle Cretaceous Wasia Group clastics and carbonate (Nahr Umr, Mauddud, Wara and Ahmadi). The Wasia Group, also known as the Bahrain Zone, is divided into the First Pay (three zones) and the Second Pay (five zones). The

551

Sedimentary Basins and Petroleum Geology of the Middle East

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552

Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.27. Diagrammatic N-S section showing the interrelationship of source rocks, reservoirs, seals and hydrocarbon accumulations in Bahrain (from Chaube andSamahiji, 1995, reproduced with permission from Gulf Petrolink, Bahrain). First Pay A and B zones also are known as the Ahmadi Formation, the First Pay Zone as the Wara Formation, the Second Pay Limestone B Zone as the Mauddud Formation, and the Third Pay Siltstone A, B, C and D zones as the Nahr Umr Formation. The reservoirs range in depth from 450-830 m (1,476-2,723 ft) in the Cretaceous, 1,2651,753 m (4,150-5,751 ft) in the Jurassic, and 2,660 m (8,727 ft) in the Upper Permian. Oil shows have been recorded in the Marrat, Tuwaiq Mountains and Hanifa formations, and a minor oil accumulation is present in the Fadhili Member of the Dhruma Formation. The Hith Formation has minor gas reserves in carbonate stringers. In the Cretaceous, heavy, tarry oil shows occur within the Yamama Formation, and minor, relatively light oil is found in the Kharaib Formation. Several thin, carbonate layers in the Rumaila and Mishrif formations hold heavy oil, and there are considerable reserves in the porous, carbonate beds in the Aruma Group. Tar has been recorded during

drilling in the Eocene carbonates (Chaube and Samahiji, 1995). K h u f f F o r m a t i o n (Upper Permian). The formation contains very large and highly prolific gas reservoirs. The gas was discovered in 1948, when crestal well 52 was deepened. Wells 88 and 128 also penetrated and evaluated the Khuff, proving the major extent of Khuff gas accumulation (Shehabi, 1979). Because of the lack of a market, the reservoir was not developed until 1969. The porosity is largely interparticle, resulting from solution removal of earlier mineral cement during late diagenesis (Shehabi, 1979). There are four principal Khuff reservoirs (K0-K3) (Janahi and Mirza, 1991; Alsharhan and Nairn, 1994; (Alkhayat and Mohammed, 1987). The upper reservoir, K0, has an average net pay thickness of about 38.1 m (125 ft), with 14% porosity and 295 md permeability. Reservoir K1 has a net pay of 12.2-61 m (40-200 ft), with porosity averaging 17% and permeability averaging 54 md. Reser-

553

Sedimentary Basins and Petroleum Geology of the Middle East voir K2 is the principal gas zone, with a net thickness averaging 47.2 m (155 ft), a porosity of 16% and a permeability of 83 md. Reservoir K3 has an average net pay of 6.1 m (20 ft) and low porosity and permeability, about 2.5% and 1 md, respectively. Arab Formation (upper Jurassic). Oil was first discovered in the Arab D reservoir when well 58 was completed as an oil producer in July 1938. Development drilling of the reservoir was slow until 1970, but has increased since then. The reservoir contains a major oil accumulation, overlain by a thick gas cap and underlain by an active aquifer. It produces by a combination of gas-cap expansion and water drive, with a slight contribution from solution gas. Arab D contains fine-grained, partially dolomitized calcarenite and is slightly anhydritic. Murty et al. (1983) divided it into four distinctive layers, based upon the lithology and porosity, formed as a result of the variable degree of dolomitization and the development of vugs and/or fractures, as follows: 9 The lower tight interval, which consists mainly of fine to microcrystalline, dolomitic limestone and is very tight and muddy. 9 The lower porous interval, which is dolomitic limestone with an average porosity of 26% and an average permeability of 150 md. 9 The upper tight interval, which is anhydritic limestone and dolomite with an average porosity of 10% and an average permeability of 2 md. 9 The upper porous interval, which is mainly packstone/ grainstone with some oolitic and dolomitic layers and has an average porosity of 24% and an average permeability of 88 md. Mauddud Formation (Middle Cretaceous). Oil production from the Mauddud reservoir began in 1933 and ended in 1936, when the pressure/production showed that water influx was insufficient to maintain production. The injection of gas from Arab zones was initiated in April 1938 and was used until injection was switched to lean gas from the Khuff reservoir. Continued gas injection resulted in the formation of a secondary gas cap, which covered 63.5% of the entire Mauddud reservoir by September 1992 (Wolff et al., 1993). The gas cap divided the reservoir into two zones separated by a resistivity marker. This zonation is apparent and influences the movement of the gas cap downward and laterally across the structure ( Samahiji and Kolluri, 1987). The Mauddud Formation consists of bioclastic packstone, grainstone and wackestone formed in a shallowmarine environment. The average pay thickness is 27.7 m (91 ft). The reservoir is dominated by vuggy and leaching porosity ranging from 20 to 35% and a permeability ranging from 10 to 1110 md.

Seals The Hith anhydrite and the basal Aruma shale form

554

extensive and equally important cap rocks. Other seals are provided by tight, intraformational carbonates and shale. Gypsiferous shale in the lower Triassic is particularly important as a seal for the important accumulation of nonassociated gas in the Permian Khuff carbonates. The three major anhydrite members of the Arab Formation form the cap rocks for the Arab Limestone reservoirs B, C and D, respectively. The Hith anhydrite is the overall cap rock for oil and gas accumulations in the limestone reservoirs of the Arab Formation, sealing the mainly gas-bearing upper Arab reservoirs A and B. Shale of the Nahr Umr Formation seals four major, interbedded siltstone members (A, B, C and D), which contain oil that constitutes the Third Pay of the Bahrain Zone, the main oil producer. Shale of the Ahmadi Formation is the principal cap rock for the upper two pays of the multiple reservoir. The pay zones sealed by Ahmadi shale correspond to Ahmadi limestone intercalations (First Pay A and B zones), the underlying Wara Sandstone (First Pay C Zone) and the Mauddud Limestone (Second Pay).

Source Rocks and Hydrocarbon Migration and Accumulation Source rocks for Khuff non-associated gas are thought to be either Silurian shale or indigenous to the Permian carbonates. Source rocks for the hydrocarbons in the Jurassic and Cretaceous reservoirs are the Middle Jurassic and Lower Cretaceous carbonates and shale (Fig. 11.28a, b). Detailed studies on source rock and hydrocarbon migration were made by Samahiji and Chaube (1987), Chaube and Samahiji (1995) and Mendeck and A1 Madani (1995) and are summarized below. The Hanifa Formation consists of dark-grey to black, organic-rich, laminated, lime mudstone/packstone and peloidal grainstone and is considered to have the best source potential, with TOC values ranging from 0.36 to 1.72 wt%. The Tuwaiq Mountains Formation, with a TOC of 0.49 wt%, the Dhruma Formation, with a TOC of 0.560.88 wt%, and the Marrat Formation have local, thin layers of dark-colored, organic-rich carbonates that may be significant sources. The TOC of the Jubailah Formation ranges from 0.12 to 0.51 wt% and has an uncertain source potential in Bahrain. The lower part of the Sulaiy Formation consists of dense, dark, lime mudstone, with a TOC of about 0.19 wt%, which also could qualify as a likely source. The organic-rich, carbonate intervals in the Cretaceous sequence have a low to moderate TOC (0.21-1.22 wt%) or Bitumen-free Organic Carbon values (0.24-0.41 wt%), and a general lack of oil prone kerogen (10-90%), low hydrogen indices and hydrocarbon yields (Chaube and Samahiji, 1995). Based on burial history curves of a few exploratory wells in Bahrain (Fig. 11.29), (Chaube and 1 Samahiji, 1995) concluded that the source rocks of the Dhruma-Hanifa formations (Callovian-Oxfordian) are

Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.28a. Isopach map (in feet) of the potential Berriasian (Lower Sulaiy Formation) source-rock facies in Bahrain (after Chaube and Samahiji, 1995, reproduced with permission from Gulf Petrolink, Bahrain). mature in the Bahrain area with the onset of oil generation in Paleocene to Middle Eocene time, and the main generating phase occurred between the Middle Eocene and Oligocene. However, Rock-Eval analysis of samples from exploration wells in northern offshore Bahrain (e.g., Fasht A1 Jarim-1) show that the organic carbon appears to be marginally mature for main oil generation, but the Thermal Temperature Index (TTI) values are low, and the sequence is immature. Source-rock analysis from the lower part of the Sulaiy Formation (Berriasian) shows that over most of the Bahrain area, the onset of oil generation was reached only in the Upper Miocene and has not reached the onset of a major yield. Source-rock evaluation of the lower part of the Khuff interval indicates fair to good source quality, with TOC that averages 0.5 wt% and that may reach 1.7 wt% certain

5- BU AMAMA 6- FASHTAL JARIM-I

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Fig. 11.28b. Isopach map (in feet) of the potential Oxfordian (Hanifa Formation) source-rock facies in Bahrain (after Chaube and Samahiji, 1995, reproduced with permission from Gulf Petrolink, Bahrain). intervals. The Qusaiba graptolitic shale (Silurian) is sufficiently rich in organic matter (0.3 to 1.1 wt%) and is sufficiently mature to have been the source of both Khuff and pre-Khuff gas. In the Arabian Gulf, Alsharhan and Nairn (1994) reported that the Khuff gas accumulations may have an indigenous Khuff source. In the Bahrain Field, the level to which the Lower Khuff beds would have subsided by the end of the Cretaceous would have taken them below the main oil-generation zone, and, during the Tertiary, the Lower Khuff would have been sufficiently mature to source the gas in the Khuff reservoirs (Samahiji and Chaube, 1987). The Khuff gas was emplaced in the field in its present trap around the early Tertiary. A geochemical analysis of oils in the Bahrain area shows that the oil in the Cenomanian-Turonian reservoirs in the Rumaila and Mishrif formations are heavier, more sulfurous and more paraffinic in contrast to the Middle Cretaceous (Wasia Group) oils, which are, as a whole, of medium gravity, moderate paraffinicity and moderate sulfur content. The oil found in the Wasia Group can be dis-

555

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 11.30 Gas chromatograms of saturated and aromatic C 15+ fractions of Jurassic (Arab) and Cretaceous (Mauddud) oils in Bahrain (after Chaube and Samahiji, 1995 and, reproduced with permission from Gulf Petrolink, Bahrain).

Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.31. The Bahrain Field daily production rates (after Mendeck and A1 Madani, 1995, reproduced with permission from Gulf Petrolink, Bahrain).

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Fig. 11.32. Reservoir contributions to field production in the Bahrain Field (after Mendeck and A1 Madani, 1995, reproduced with permission from Gulf Petrolink, Bahrain). tinguished from that in the Arab Formation, which has lower gravity oils, a higher sulfur content, a lower paraffinicity index and a higher porphyrin content. These oils had a common source at the time of primary migration, and the differences in maturation are due to deeper burial and a consequently elevated temperature and accelerated chemical reaction rates. Geochemical analyses carried out on Mauddud and Arab oils by Cities Services (1986, cited in Chaube and Samahiji, 1995) show that both oils have identical pristane/phytane (Pr/Ph) ratios, suggesting a genetic relationship. An even-odd carbon number preference in the nparaffins, naphthenic-aromatic, the medium gravities and gas chromatograms of the saturate and aromatic C15+ fractions of the Jurassic (Arab) and Cretaceous (Mauddud) oils are very similar, suggesting a common origin (Fig. 11.30). The migration of oil into the Arab zones could com-

mence at any time in the post-Aptian, and there has been no post-emplacement leakage from the Arab reservoirs. The probable sources in the Callovian-Oxfordian could not have subsided sufficiently to begin generating oil before the Maastrichtian, and the hydrocarbon migration into the large Arab reservoirs took place during the end of the Cretaceous and into the Early Tertiary. The hydrocarbon emplacement into the Ahmadi reservoir could not have predated the early Tertiary, and the inferred source may be valid for the other Cretaceous accumulations. The conversion of hydrocarbons generated from CallovianOxfordian sources into Jurassic and Cretaceous oils had commenced by the end of the Maastrichtian and charged the paleo-Arab structure to a greater extent than is presently seen. During the Early Tertiary, the form of the structure was accentuated, with crestal tightening, faulting and fracturing resulting in the breaching of the Hith anhydrite seal, and the charging of the Cretaceous reservoirs during

557

Sedimentary Basins and Petroleum Geology of the Middle East a phase of hydrocarbon remigration. The multiple, large, Cretaceous reservoirs and the very low volume of the charge found in the Arab reservoirs seen at the present time strongly support a remigration mechanism. Northwest of Bahrain (at Umm Nassan), the onset stage was reached during the Oligocene, with the start of major oil generation occurring during the Miocene. The Callovian-Oxfordian source rocks attained maturity by the Paleocene-Eocene and charged the Jurassic reservoirs. That some of the Jurassic oil migrated into the multiple Cretaceous reservoirs through the Hith anhydrite seal due to intense post-Eocene structural growth suggests a common source rock. Although there are some potential intervals in the Cretaceous sequence, good Cretaceous source rocks are lacking, but they may contribute to minor oil and gas accumulation in the Cretaceous reservoirs. Production and Reserves

The production of oil and gas since discovery is shown in Fig. 11.31, which shows periods of decline and increase in production through the years, increases attributable to an active program of field development. Contribution from different formations to total production, and

558

percentages of current and cumulative production figures are shown in Fig. 11.32. The Upper Permian Khuff reservoir accounts for all the producing, non-associated gas and condensate. Most of the Khuff gas is used for re-injection into the higher reservoirs. The condensates account for 5% of the ultimate recoverable oil reserves. The Jurassic limestone reservoir accounts for 36% of the recoverable oil reserves. The Cretaceous clastic and carbonate reservoirs are the most important oil reservoirs in Bahrain, accounting for 59% of the recoverable oil reserves (Mendeck and Madani, 1995). Up to 1994, more than 510 wells have been drilled in the field, producing from 12 formations, with the majority of production from the Ahmadi, Wara, Mauddud, Nahr Umr, Arab and Khuff formations. Cumulative production for the field up to 1994 was 885 MMBO and 4.5 TCFG. The ultimate recoverable oil (+NGL), and gas reserves are 1,100 MMBO and 10,500,000 MMCFG, respectively. Production rates during the first half of 1996 were approximately 7,068,000 barrels of oil at an average daily rate of 38,833 barrels, and 176 billion cubic feet of gas at an average of 966 million cubic feet/day (A1 Hayat Newspaper in 13.8.1996).

Hydrocarbon Habitat of the Greater Arabian Basins

QATAR Qatar, between latitudes 24~ ' N and 26~ ' N, has an area of about 12,000 sq km and projects about 170 km northwards into the Arabian Gulf (Fig. 11.32). The history of hydrocarbon exploration and production in Qatar, covering both onshore and offshore concessions, was summarized by Dominguez (1965), Sugden and Standring (1975), Owen (1975), Beydoun (1988) and Alsharhan and Nairn (1994) and is outlined below. The first concessionary fights from the ruler of Qatar were given to the Anglo-Iranian Oil Company in May 1935. The company then transferred the concession contract to an Iraq Petroleum Company (IPC) affiliate and the operating company Petroleum Development (Qatar) Ltd. Exploration began in 1937, and the long, narrow anticline on the west coast that forms Jebel Dukhan was delineated as the best prospective oil structure. In October 1938, well Dukhan-1 was spudded and became a discovery well after reaching a depth of 1,777 m (5,829 ft) in January 1940. Oil was found in the Upper Jurassic Number 3 Limestone Member of the Qatar Formation (equivalent to the Arab Formation in Saudi Arabia). Subsequently, oil was discovered in the Number 4 Limestone Member and in the Middle Jurassic Uwainat Member of the Araej Formation. Gas was found in the Permian Khuff Formation. In November 1952, an offshore grant was awarded by the ruler to Shell Overseas Exploration Company, which became the Shell Company Qatar in August 1954. A gravity survey was begun in June 1963, followed by seismic-reflection surveys six months later. The structural interpretation of the seismic record showed that the eastern area was dominated by salt-tectonic structures, whereas the northern area was fiat and featureless. In January 1956, the first offshore well was drilled on the crestal part of the elongated, hourglassshaped Idd E1 Shargi structure. It reached a depth of 3,714 m (12,182 ft), but was dry. A second well drilled on December 1959 (Idd E1 Shargi-2) to a depth of 2,600 m (8,528 ft) into the northern dome of the structure proved oil in the Middle Jurassic Araej Formation and in the Upper Jurassic Arab II and Arab IV reservoirs of the equivalent Qatar Formation in onshore. In March 1961, well No. 4 on the southern dome discovered oil in the Lower Cretaceous Shuaiba Formation. In 1964, a second and more prolific offshore discovery, Maydan Mahzam, was developed some 30 km northeast of Idd E1 Shargi. A discovery well, drilled in July 1963 to a total depth of 2,811 m (9,220 ft), encountered oil in the Upper Jurassic Qatar (Arab) Formation; and the E1 Bunduq Field, straddling the Qatar-U.A.E. boundary, was discovered in the following year by Abu Dhabi Marine Areas Company (ADMA). In July 1970, the E1 Bunduq Company was formed following a border agreement between Qatar and the U.A.E. All ADMA rights in the field were assigned to the new company, with a 50-50 production-sharing agreement

between the two states. In March 1969, the Bul Hanine Field was discovered, the latest and most prolific of all the offshore oil fields in Qatar. It is producing from the Middle Jurassic Araej and the Upper Jurassic Qatar (Arab) formations. The North Field, discovered by Shell Qatar in 1971 with well NWD-1, contains gas and condensate in the carbonate series of the Permo-Triassic Khuff Formation, with oil in the thin, Albian Nahr Umr clastic reservoir. The major oil and gas field of Qatar are shown in Fig. 11.33a,b. According to World Oil (1994), crude production at the end of 1993 averaged about 413 M.bbl/d from 290 wells, and 35,000 BCPD, for a total liquid output of 448,000 BPD. Estimated reserves at the time totaled 3.4 B.bbl crude, 755 MM.bbl condensate and 165 TCF gas.

Structure A post-Oligocene northerly tilt of the Qatar-South Fars Arch in the northern offshore area of Qatar occurred as the proto-Arabian Gulf began to form as a foreland sag. Due to a Miocene-Pliocene compressional event in the Arabian Gulf, the minor northward tilt of the Dukhan structure may have been responsible for late filling of the southernmost culmination and the trapping of oil in the early Upper Jurassic section. In Qatar, the Infracambrian salt was sufficiently deeply buried to begin a diapiric rise during the Jurassic. The oil fields in offshore Qatar and Abu Dhabi were formed in association with the rise of salt anticlines, whose location is related to deep-seated faults such as those found in the Dukhan Field and some fields in Abu Dhabi and Saudi Arabia. The Qatar-South Fars Arch (Fig. 11.34), which has been a prominent structural high during much of geological time, divides the Arabian Gulf into the Western Gulf Basin in the northwest and the Eastern Gulf Basin to the southeast. The presence of the arch greatly influenced the structural evolution of the region and, consequently, the sedimentation patterns. The movement of the deeply buried salt formations caused uplifting and on occasion pierced the overlying beds (Fig. 11.34). Thus, in the Eastern Gulf Basin, salt "pillows" of various shapes, but limited areal extent, are thought to underlie the producing oil fields of Qatar (Bul Hanine, Idd E1 Shargi, Maydan Mahzam) (Fig. 11.33a,b). In the Western Basin, a large, elongated salt pillow underlies the Dukhan Field.

Stratigraphy Qatar is part of the Arabian Interior Platform, over which a thick sequence of sediments has accumulated since the Paleozoic to a thickness estimated by geophysicists to exceed 10 km. The sedimentary section shows minor lithological variations and a relative thinning in the Mesozoic section over the Qatar-South Fars Arch. The occurrence of major and minor unconformities in the 559

Sedimentary Basins and Petroleum Geology of the Middle East

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Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.34. Onshore-offshore structural cross-section of in Qatar Arch (modified from Qatar Petroleum Company Staff, 1981). stratigraphic sequence indicate continuing epeirogenic Reservoir Characteristicss movements and structural growth as well as relative sealevel fluctuations throughout the Phanerozoic. Prolific oil reservoirs, source rocks and regional seals Paleozoic sediments (mainly sandstone and shale) at are found in Middle and Upper Jurassic rocks, and fair to least 3,000 m (9,840 ft) thick are thought to have been good reservoirs, source rocks and seals in the Lower to deposited in Qatar, although little is known of the pre-Perbasal Upper Cretaceous beds. Prolific gas is found in mian sequence, except from the few wells drilled to the Upper Permian (Khuff) carbonate reservoirs. The depth at Ordovician (Fig. 11.35). The Middle-Upper Permian shalwhich the reservoir rocks are found range from below low-marine shelf and lagoonal carbonates and supratidal 3,400 m (1 1,152 ft) in the Ordovician-Permian clastics to evaporites range in thickness from 500 to 850 m (1,6402,500-2,900 m (8,200-9,512 ft) in the Upper Permian 2,788 ft), with the maximum thickness of the Permian Khuff carbonates. Most of the oil in Qatar is produced Khuff carbonates and evaporites over the Qatar Arch. from Jurassic carbonate reservoirs (Araej and Qatar/Arab Shelf conditions continued during the Triassic and Jurasformations) at depths of 1,400 to 2,750 m. Oil and gas sic. The Triassic section (Fig. 11.36) is about 500 m (1,640 accumulations found in the Cretaceous reservoirs as the ft) thick and comprises shelf carbonates and subordinate Shuaiba and Kharaib carbonates, lower Nahr Umr sandmarl capped by supratidal evaporites. The Jurassic section stone and Khatiyah/Mishrif carbonates occur at depths (Fig. 11.36) consists of about 900 m (2,953 ft) of shelf carranging from 940 to 1,875 m. bonates overlain by supratidal evaporites. Deeper-marine The Pre-Khuff clastics contain 0.6% of the ultimate conditions seem to have prevailed during the Cretaceous, recoverable gas reserves; the remaining 96.4% of the ultiwhen about 1,200 m (3,937 ft) of chalky and marly limemately recoverable gas reserves lies in the Permo-Triassic stone, shale and carbonate were deposited in eastern and Khuff carbonates. The Jurassic carbonates contain 98% western Qatar, thinning to 900 m (2,952 ft) over the Qatar and 4.8% of the ultimate recoverable oil and gas reserves, Arch. A marked unconformity separates the Tertiary from respectively. The Cretaceous limestone contains only 2% the Cretaceous (Fig. 11.36). The Tertiary section is about of the ultimate recoverable oil reserves and has negligible 850 m (2,788 ft) thick in eastern Qatar, thinning to about gas reserves. 300 m (984 ft) in western Qatar. The succession includes The following general review of the reservoir characPaleocene shelf limestone and dolomites, and shelf carteristics was given by the Ministry of Finance and Petrobonates with supratidal evaporites deposited during the leum, Qatar, (1977), Murris (1981), A1 Kawari (1983), Eocene. The Oligocene is missing. The Eocene and MioFrei (1984), Alsharhan and Kendall (1986), Hamam and Pliocene rocks are partly exposed in onshore Qatar. They Nasrulla, (1989). Wilson (1991) and Alsharhan and Nairn consist of carbonates, evaporites and shale with conglom(1994) (Figs. 11.35 and 11.36). erate on top. Tabuk Formation (Ordovician). The formation con-

561

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'

Hydrocarbon Habitat of the Greater Arabian Basins The Arab IV (Member D) comprises four main reservoir types, whose porosity and permeability are shown in Fig. 11.37. Sucrosic dolomites in the eastern offshore fields form very good reservoir units, with the high permeability of these rocks due to the idiotopic and sucrosic texture and well-developed, good, intercrystalline porosity and permeability. The dolomitized lime mudstone and wackestone, often argillaceous and bioturbated, generally have a moderate to good porosity (10 to 30%) and a permeability of generally less than 10 md. Good porosity may be found in peloidal packstone and grainstone due to the occasional occurrence of interparticle, vuggy and moldic pores. Porosity ranges from 10 to 30%, and permeability is from less than 10 to more than 100 md. The oolitic grainstone shows that the porosity and permeability increase with increasing grain size, and, as a result of the wellrounded and well-sorted nature of these sediments, the porosity is up to 30%, and permeability ranges from 100 to more than 5000 md. The lower part of the Arab III-C reservoir consists of dolomitic grainstone and represents a major reservoir unit in some of the offshore fields such as the Idd E1 Shargi North Dome. The grainstone commonly is leached and has moldic porosity. The upper part of the Arab III-C is the most variable interval and consists of a complex of dolomitized, algal boundstone, mudstone/wackestone and peloidal packstone with occasional grainstone. The pore types are mainly moldic and interparticle, and these sometimes have been totally leached and cemented by calcite cement. The porosity in the Arab III-C reservoir ranges from 1 to 30%, with permeability from less than 1 up to 1000 md. The Arab I (A Member) and II (B Member) reservoirs consist of algal boundstone and oolitic grainstone. Often, this grainstone has been leached, and a common moldic

contains significant reserves in the Dukhan, Bul Hanine, Maydan Mahzam and Idd E1 Shargi fields (see Appendix Table C). The Uwainat limestone reservoir generally has good, moldic, vuggy and solution-channel porosity with related permeability enhancement, but the overall permeability is rather poor. In the Dukhan Field, with an average porosity of 18%, the permeability is only 15 md, but in the Idd el Shargi North Dome, the reservoir has a porosity of 5-20% and a permeability of 1-1600 md. In the Maydan Mahzam and Bul Hanine fields, the comparable porosity and permeability figures for the Uwainat reservoir are 1023% and 2-300 md and 5-21% and 500 md, respectively. With increasing depth of burial, the thin reservoir zones suffer from compaction and pressure solution. A tar mat is present within the present oil zone in the Idd E1 Shargi Field and also in the gas cap of the Bul Hanine Field. The tar mat is interpreted as the result of the accumulation of tar close to the initial free-water level during an early stage of oil migration. Subsequent stages of hydrocarbon migration may have extended the oil column in the Idd E1 Shargi Field and added a gas cap in the Bul Hanine Field. The Upper Araej reservoir has a low to moderate porosity and low to very low permeability. In the better packstone and grainstone reservoir zones, the porosity ranges from 8 to 14%, while permeability may reach some tens of millidarcies. The reservoir is gas-bearing in the Maydan Mahzam and Bul Hanine fields. The presence of producible oil was established only recently in Maydan Mahzam. Arab Formation (Upper Jurassic). The most prolific reservoirs of Qatar in all the fields mentioned previously lie within the Arab Formation. These reservoirs contain the largest oil accumulations in the world, with best porosity and permeability characteristics in peloidal oolitic limestone.

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563

Sedimentary Basins and Petroleum Geology of the Middle East porosity is developed. Porosity ranges from 7 to 30%, with a permeability ranging from less than 1 up to 800 md. Kharaib Formation (Lower Barremian). The Kharaib Formation is oil-bearing in the North Field, but has a poor reservoir quality. The microporous, peloidal packstone and grainstone have matrix porosity and minor moldic porosity, which resulted from the leaching of algal fragments. The porosity ranges from 15 to 30%, but permeability is low (up to 12 md). The microporous, bioturbated wackestone shows well-developed, moldic and matrix porosity, with total porosity ranging from 16 to 28%, but permeability is very low (up to 12 md). Shuaiba Formation (Aptian). The formation is oilbearing in the Idd E1 Shargi North Dome, where it consists predominantly of microporous lime mudstone. The Bacinella algal boundstone and rudist fragments in the basal part of the Shuaiba possess moldic porosity in the leached algae and have a fair permeability (up to 15 md) and an average porosity of about 10%. The microporous lime mudstone, the dominant rock type, is bioturbated, compact and stylolitic, with a very low permeability (up to 3 md) and a porosity ranging from 6 to 25%. The coral boundstone at the top of the Shuaiba reservoir has a moldic, vuggy porosity of 16 to 30% and a permeability that ranges from 25 to 50 md, but may sometimes reach 1000 md. Nahr Umr Formation (Albian). The formation includes a good but relatively thin 3-5 m (10-16 ft) sandstone reservoir containing oil and gas in the North Field. It is a clean, well-sorted sand, unconsolidated to slightly cemented and interbedded in well-cemented, quartzitic sandstone. The cement consists of calcite and siderite, quartz overgrowths and clay minerals. Porosity is around 21%, with permeabilities from 3 to more than 1000 md. Mauddud Formation (Albian). The carbonates are moderate to poor reservoirs in the North Field. Although the microporous, peloidal wackestone and grainstone; foraminiferal, peloidal wackestone and grainstone; foraminiferal, peloidal packstone; and local, rudist-skeletal packstone and grainstone have interparticle porosity and some leached, vuggy porosity ranging from 12 to 24%; the permeability is low, from 0.1 to 70 md. Mishrif and Khatiyah formations (Cenomanian). The carbonates of these formations in the North Field generally are poor reservoirs as a result of lithification and extensive bioturbation. Moldic porosity resulting from leaching ranges from 8 to as high as 28%, but permeability is very low, from 0.1 to 5 md.

Seals and Seal Formations The principal gas reservoirs in the Permian carbonates in Qatar are sealed by evaporites and the overlying Triassic shale; and the Middle-Upper Jurassic carbonates, which contain most of the oil in Qatar, are associated with evaporites providing the reservoir/cap rock combinations.

564

The reservoirs and related cap rocks typify the platform cover sequence in the Arabian Gulf region, but there is a certain distinction between the northern and southern gulf sub-basins on either side of the Qatar Arch. Middle Jurassic and Lower Cretaceous shale seals, which are found in the Qatar Arch and the Southern Gulf Sub-Basin, though of minor importance, are of negligible importance in the Northern Gulf Sub-Basin. The Permian and Upper Jurassic evaporites are, however, the most important cap rocks in all three sub-basins of Qatar. The anhydrites of the Permian Khuff Formation and the Lower Triassic gypsiferous shale seal about 95% of Qatar's established, non-associated gas reserves contained in Khuff carbonates and, subordinately, in underlying Permo-Carboniferous clastics. The most important Mesozoic cap rocks are anhydrites of the Upper Jurassic Arab and Hith formations. They seal about 75% of the oil and associated gas reserves of Qatar. Marl and shale in the Middle Jurassic and, to a lesser extent, the Lower Cretaceous sequence in the Qatar Arch and the Southern Gulf Sub-Basin form the cap rocks for the remaining 25% of the oil reserve with its minor associated gas. The following are some details of individual seals (see also Figs. 11.35 and 11.36). Tabuk Formation (Ordovician). The sandstone of the Tabuk Formation appears to provide the seal for the small gas accumulation encountered in well Matbakh-2. Sharawra Formation (Silurian). The siltstone of the Sharawra is a good seal for the gas accumulation found in the same formation in the North Field and well Matbakh2. Tawil Formation (Lower Devonian). The Tawil quartzose sandstone, which has extensive quartz overgrowths, seals the underlying gas column found in the same formation in well Matbakh-2. Haushi Formation (Lower Permian). The strongly cemented sandstone appears to seal the gas reservoir in wells Ras Qirtas-1 and Matbakh-2. Sudair Formation (Lower Triassic). The dense, microcrystalline dolomites, sandy-silty shale and anhydrite form an excellent seal for the Khuff gas reservoir in the North Field, Bul Hanine, Idd E1 Shargi and Dukhan fields. Izhara and Araej formations (Middle Jurassic). The dense lime mudstone and marl in these formations form seals for the oil found in them and in the Dukhan Formation. Hanifa and Lower Jubailah formations. The dense, argillaceous limestone in the Hanifa and lower Jubailah formations seal minor oil accumulations in Bul Hanine and the Idd E1 Shargi North Dome. Arab Formation. Anhydrite layers between the Arab I (A Member) to IV (D Member) act as intraformational seals for oil found in the Dukhan, Idd E1 Shargi and Bul Hanine fields. Hith anhydrite. This has proved to be the regional seal for the large oil and gas accumulations found in the Arab reservoirs in the Qatar area and elsewhere in the Ara-

Hydrocarbon Habitat of the Greater Arabian Basins bian Basin.

Hawar Formation (Barremian). The marl and shale of this formation seal the oil column in the Kharaib reservoirs of the North Field and the Idd E1 Shargi South Dome fields. Nahr Umr Formation (Albian). In the Idd E1 Shargi Field, the seal for the Shuaiba reservoir is provided by the regional shale of the Nahr Umr Formation. It also caps the oil in the basal sandstone reservoir of the Nahr Umr Formation in the North Field. Khatiyah Formation (Cenomanian). The shale and argillaceous limestone in the lower part of the Khatiyah Formation act as a seal for the Mauddud reservoir in the North Field. Laffan Formation (Coniacian). The shale of Laffan seals the Mishrif reservoir in the North Field.

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Source Rocks Prolific source rocks occur in the Middle and Upper Jurassic sequence, and fair source rocks are found in Middle Cretaceous. Good source rocks for the non-associated gas and condensate in the Khuff Formation occur in the shale of the Paleozoic sequence. These source rocks are discussed in detail by Frei (1984), Hamam and Nasrulla (1989), Beydoun (1988), Droste (1990) and Alsharhan and Nairn (1994). The source rocks of hydrocarbons found in Jurassic and Cretaceous reservoirs are Middle Jurassic and possibly also in some Cretaceous carbonates. Below are descriptions of individual formations. Sharawra Formation (Silurian). The shale in the lower part of the Sharawra is a marginal to excellent source rock with predominantly sapropelic matter and a total organic matter content ranging from 0.5 to 7 wt%. The shale has a low pyrolysis yield, indicating a postmature stage for oil generation that is still favorable for gas. Haushi Formation (Lower Permian). The shale in the lower part of the Haushi Formation is a marginal to fairly good source rock for gas and some oil. The sapropelic organic matter may reach a total organic content of up to 2.5 wt%. The vitrinite reflectance values range from 0.97 to 1.01. Hanifa Formation (Upper Jurassic). The major inundation of the Arabian Platfor~ at the end of the Middle Jurassic resulted in the development of an intrashelf basin across Qatar. In this basin, the laminated, bituminous lime mudstone and marl of the Hanifa Formation were deposited, which form the prolific source rocks for the oil in most of the Jurassic and Cretaceous reservoirs of Qatar. Fig. 11.38 shows the regional isopach map of the Hanifa Formation and also indicates the approximate northeastern limits of its well-developed source facies. Organic matter varies from 1 to 6 wt% total organic carbon (TOC) and consists predominantly of sapropel, which is partly bacterially degraded. Geochemical correlation between the oils

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Fig. 11.38. Isopach map of the Hanifa source rock in Qatar (modified from Frei, 1984; and Alshahan and Naim, 1994). Contoured gross thickness is measured in feet. trapped in the various reservoirs and the Upper Jurassic source rock is excellent, and it is therefore believed that virtually all the oil that accumulated in the Qatar fields originated from the Hanifa and the immediately overlying Jubailah source rocks. Jubailah Formation (Upper Jurassic). The lowermost part of the Jubailah Formation contains organic-rich, dark-grey, laminated, silty, lime mudstone with a TOC content of 0.5-3.5 wt%. The laminated, sapropelic matter is classified as mixed to kerogenous, indicating a source for both oil and gas. Shuaiba Formation (Aptian). The formation in southeastern offshore Qatar has organic-rich intercalations where the TOC content is up to 12.6 wt%. The amount of pyrolysible, organic matter varies from insignificant to excellent. A high proportion of the organic matter is partly micritized, with some liptodetrinites and algae making it strongly oil-prone. This source-rock horizon, as well as all younger ones, is immature over the Qatar Arch because of shallow burial, but may be sufficiently mature in the surrounding areas where it was more deeply buried. Mauddud Formation (Albian). In eastern and southeastern Qatar, the formation consists of interbedded, globi-

565

Sedimentary Basins and Petroleum Geology of the Middle East gerinal marl and calcareous shale with laminated, organicrich intercalations. The TOC content of the organic rich intercalations ranges from 3 to 8.3 wt% and is mainly sapropelic with minor amounts of liptodetrinites and algae. The organic matter is classified as kerogenous to mainly kerogenous and is an excellent, potential oil-source rock. Mishrif/Khatiyah formations. The argillaceous limestone of the Mishrif/Khatiyah in the offshore area has organic matter, but presents only a minor source rock potential.

Oil Characteristics and Hydrocarbon Maturation The crude oils accumulated in the various Mesozoic reservoirs described by Frei (1984) and Alsharhan and Nairn (1994) have a sulfur content ranging from 1 to 3 wt% and an API gravity from 26 to 43 ~ API. A plot of API gravity versus C29 degree of organic metamorphism (DOM) by Frei (1984) is shown in Fig. 11.39 and indicates a rather narrow range of DOM for such a wide range of API gravity. In other words, these oils may be considered to have had a similar thermal history, and their wide variation of API gravity is due probably to biodegradation, water washing or evaporation of the lighter fractions. Primary, light Jurassic crudes with gravities of 36 ~ API and above occur in the Maydan Mahzam, Bul Hanine and Idd E1 Shargi fields (Fig. 11.40). They contain high percentages of normal alkanes (saturated hydrocarbons), as shown by the triangular plot of C 7 alkanes ("Primary" in Fig. 11.39). In contrast, the crude oils with API gravity of less than 30 in the Cretaceous reservoirs of the North Field, which plot in another region of the figure ("Transformed"), probably reflect bacterial degradation of similar, primary, light crudes. Some crude oil in Jurassic reservoirs near the Qatar Arch that are heavier than those of the Cretaceous are possibly the result of the evaporation of the lighter fractions. Fig. 11.41 shows the C15/C30 ring distribution of Qatar crudes and source rocks. The data of the Idd E1 Shargi, Bul Hanine, Maydan Mahzam and North Qatar Arch crudes plot in a small area of the triangular graph, suggesting a common source. They are most likely derived from structureless organic matter (SOM) and/or algal matter, mixed with other types. In addition, the plot shows the Hanifa and lower Jubailah to be the most likely source rocks, because of their closeness to the crude oil populations (Fig. 11.42). The stable carbon isotope ratio varies by less than 1% about a value of 26.5%, further suggesting a common source for these crude oils (Frei, 1984; Alsharhan and Nairn, 1994). A comparison of the gas chromatograms of the saturated hydrocarbons from a typical Arab IV (D Member) oil and extracts from the Hanifa and lower Jubailah source rocks (Fig. 11.42) demonstrates their close relationship. The shape of the gas chromatograms and the sterane-

566

triterpane distributions corroborate an origin from bacterially reworked phytoplankton. The low pristane/C17 and phytane/C18 ratios (0.2 to 0.4) in all of the crudes indicate that the oils were expelled from mature source rocks deposited in a reducing environment (Frei 1984; Alsharhan and Nairn, 1994). The Upper Jurassic source rocks probably began yielding oil beneath an overburden of about 1,750 m (5,740 ft) equivalent to a vitrinite reflectance of 0.62 R o. The distribution of the Jurassic accumulations is controlled by the distribution of the mature Hanifa-lower Jubailah source rocks and the regional Hith anhydrite seal. Geographically, most of Qatar lies within the oil-generation zone, whereas the southeastern offshore area lies in the gas-generation zone (Fig. 11.43). Over most of the axis of the Qatar Arch, maturity of the Upper Jurassic source rocks was barely reached, while the structurally highest, northeastern part remained immature; it is ironic that the thickest Hanifa source rocks should occur over the Qatar Arch (Fig. 11.4 3). The small number of Jurassic and Cretaceous oil discoveries over the arch is due at least partly to the scarcity of mature sections within the drainage area and partly to the lack of structural closures. Oil maturation in southeastern offshore Qatar was first reached during the Late Cretaceous. The Cretaceous source rocks are still immature everywhere in Qatar.

Oil and Gas Fields Five commercially significant, hydrocarbon-bearing structures and one shared with the U.A.E. (El Bunduq), not described here, have been discovered in Qatar since 1940 (Fig. 11.43). One, the North Field, is one of the world's largest known gas fields. The hydrocarbons in Qatar are widely distributed in the stratigraphic column, occurring in Ordovician clastics to Cenomanian carbonates. All the fields have more than one pay zone. The following summary descriptions are based on information from the Ministry of Finance and Petroleum, Qatar (1977), A1 Kawari (1983), Beydoun (1988), Wilson (1991), Jubralla and Hammam (1991), and QGPC and AmocoQatar (1991) and included in the Appendix table which summarises field data and the relevent hydrocarbon parameters. Dukhan Field. The field was discovered in 1940 and went on stream in late 1949. The structure of the field is that of a long, salt anticline with a gentle, north-south trend and an overall teardrop shape. It is about 70 km (43.5 mi) long and from 4 to 6 km (2.5-3.7 mi) wide. The field has low structural relief and was recognized from the surface distribution of Tertiary rocks. At the surface, the limbs of the structure have dips of 2-10 ~ The anticline is asymmetric, and four culminations along strike have been recognized at the level of the Jurassic Arab reservoirs. This broad fold configuration at the Arab level gives way to an axial graben at the deeper Permian Khuff level as a result

Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.40. Plot of C7 alkane distribution of Qatar crude oils (after Frei, 1984; Alsharhan and Naim, 1994).

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Fig. 11.42. Gas chromatograms of saturated hydrocarbons from Upper Jurassic (Hanifa and lower Jubailah) source rocks and Arab D Member oils of Qatar (after Frei, 1984; Alsharhan and Naim, 1994).

Fig. 11.41. Plot of C]5/C30 ring distribution of source-rock extracts and crude oils from Qatar (after Frei, 1984; Alsharhan and Naim, 1994)" SOM=structureless organic matter.

567

Sedimentary Basins and Petroleum Geology of the Middle East

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Oil Field

Fig. 11.43. Estimated maturity zones of Hanifa source rocks in onshore and offshore Qatar (modified from Frei, 1984; Alsharhan and Naim, 1994). of early extension above the rising salt ridge (QGPC and Amoco-Qatar, 1991). At the Arab and Khuff levels, a pronounced inflection or change in strike towards the southeast in the southern portion of the field was recognized. Up until the end of 1990, the deepest well was Dukhan DKG27, which reached a total depth of 4,975 m (16,318 ft)and ended in Ordovician clastics. Thus, the Dukhan Field is an anticlinal trap, with a 488 m (1,601 ft) structural closure at the Arab level and 641 m (2,102 ft) at the Khuff level. It is a giant oil and gas field in which all the reservoirs are in carbonate rocks, with the main producing zones in the Arab, Araej (Uwainat Member) and Khuff beds. The initial recoverable oil reserves are estimated to be 2.3 B.bbl, and the recoverable gas reserves exceed 1.2 TCF. The Jurassic-Cretaceous geological sequence with the relative position of the reservoirs is shown in Fig. 11.44. The No. 3 Limestone (C Member) reservoir of the Arab Formation lies at an average depth of 1707 m (5600 ft) SS. The formation is a sequence of limestone and dolomite. The reservoir is about 85 ft thick with an average

568

porosity of 15-20% an average permeability of 30 md containing undersaturated oil with 37 ~ API gravity, 200-500 ppm of H2S and 1.8% sulfur. The No. 4 Limestone (D Member) reservoir of the Arab Formation lies below the No. 3 Limestone, being separated by some 18 m (60 ft) of anhydrite. The reservoir rock consists of limestone and dolomite and is about 56 m (185 ft) thick with average porosity and permeability of 19% and 70 md respectively. The reservoir has a large gas cap. The oil has 42 ~ API gravity with 130-300 ppm HzS and 1.1% sulfur. The Uwainat reservoir of the Araej Formation lies at an average depth of 2149 m (7050 ft) has a mean porosity of 18% and a mean permeability of 15 md with almost no permeability and low porosity in the basal 12 m (40 ft). The reservoir contains a relatively thin oil rim with an overlying gas cap. The Khuff reservoir containing non-associated gas was discovered at Dukhan in 1960 and development started in 1976. The top of the formation lies at about 2835-3262 m (9300-10,700 ft). The formation varies in thickness from 448-564 m (1470-1850 ft). Gas production from the Khuff Zone started in 1978. The formation consists of predominantly dense dolomite with some beds of limestone and anhydrite. Five lithological units (K1-K5) have been distinguished and can be correlated. The gas consists of approximately 80% methane, 14% nitrogen, 4% carbon dioxide and less than 2% hydrogen sulfide. ldd El Shargi Field. The field consists of two elliptical, faulted domes, aligned approximately north-south, whose origin is thought to be a result of salt pillowing active since the Triassic. The Idd E1 Shargi North Dome is elongated NE-SW over a halokinetically induced dome that measures some 12 x 7 km at the level of the Shuaiba Formation. Dips along the flanks of the structure are 5 ~, but decrease to the southwest (Jubralla and Hamam, 1991). Discovered in May 1960, and the field went on production in 1964 from the Shuaiba, Araej and Arab reservoirs, this field is the oldest offshore field. The Jurassic-Cretaceous geological sequence in the North Dome with the relative position of the reservoirs is shown in Fig. (11.45). The Shuaiba reservoir lies at an average depth of 1362 m (4470 ft). The reservoir is about 99 m (325 ft) thick. The reservoir contains mainly chalky lime mudstone, wackestone with porosity varying between 22-30% and permeability between 0.2-5 md, with the exception of a restricted area at the crest, where higher permeabilities (about 200 md) have been observed. The oil is approximately 27 ~ API gravity containing 100-200 ppm of H2S and 2.8% sulfur. The Arab-III (C Member) dolomitic packstone and oolitic dolomitic packstone reservoir, lies at an average depth 2070 m (6790 ft). The reservoir is about 30.6 m (100 ft) thick with a porosity varying between 10-23% and permeability between 50-200 md. The oil has 27 ~ API gravity and contains about 100-200 ppm H2S and 3% sulfur. The driving mechanism of the reservoir is the gas cap with pos-

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Hydrocarbon Habitat of the Greater Arabian Basins sibly a minor aquifer influx. The Arab-IV (D Member) lime mudstone and packstone reservoir lies at an average depth of 2104 m (6900 ft). The reservoir is about 102 m (335 ft) thick, porosity varying between 10-38% and permeability between 1-300 md. Oil with 32 ~ API gravity containing 100-200 ppm H2S and 1.8% sulfur. The reservoir driving mechanism is gas cap drive. The Upper Araej peloidal packstone/wackestone reservoir lies at an average depth of 2378 m (7800 ft). The reservoir is about 46 m (150 ft) thick with porosity varying between 5-20% and permeability between 0.1-20 md. The oil contains 100-200 ppm H2S and 1.2% sulfur. The Uwainat wackestone/packstone and grainstone reservoir lies at an average depth of 2424 m (7950 ft). The reservoir is about 55 m (180 ft) thick with porosity varying between 5-20% and permeability between 1-1600 md with oil of 36 ~ API gravity containing 100-200 ppm H2S and 1.2% sulfur. The Jurassic-Cretaceous geological sequence in the South Dome with the relative position of the reservoirs is shown in Fig. (11.46). The Shuaiba and Kharaib reservoirs lie at an average depth of about 1524 m (5000 ft), and are very similar lithologically to those in North Dome, although much higher. Both reservoirs are known to contain oil with 29 ~ API gravity, 200 ppm H2S and 2% sulfur. The Arab reservoir in the South Dome have been subjected to considerable tectonic disturbance which has led to collapse of the crest of the structure, and a number of distinct fault blocks have been resulted. The Arab reservoir is similar to the Arab reservoir in the North Dome but is generally higher. It produced oil of 25 ~ API gravity, somewhat similar in properties to the Arab crude of the North Dome. Production from the Shuaiba reservoir in the North Dome is characteristically low, usually around 300 bbl/d; this has been increased using horizontal drilling normal to the open NE-SW fractures. The enhanced permeability has increased production to around 4,000 bbl/d. The NW-SEtrending fractures are closed (Cosgrove and Jubralla, 1995). Production uses a gas cap drive. The field has regional oil in place of about 4.4 D/bbl. Maydan Mahzam Field. The field is a flat, domal structure about 8 x 5 km in size, with a maximum dip of about 8 ~ on the flanks. It was discovered by Shell-Qatar in 1963. The crest and the northern flank of the reservoir appear to be faulted, but the faults have minor throws (up to 15 m or (50 ft) and do not act as barriers to flow. The main reservoir is in Arab D carbonates with porosity and permeability values of 12-13% and 5-4000 md, from which production began in 1965. The Arab C reservoir, which began producing in 1966, exhibits good reservoir qualities and low water saturation. The best reservoir development is found at the crest of the structure, which has 20-30% porosity and 100-1000 md permeability. The energy for these two reservoirs is provided mainly by dump flooding assisted by natural aquifer influx. The Uwainat reservoir has a porosity ranging from 10 and 23%

and a permeability from 2 to 300 md. Reservoir energy is supplied by gas cap drive.The field is produced from the Jurassic formations with 84% of the oil in the Arab C and D, with oil in place recoverable of 44% and ultimate recovery placed at 55% beyond which an additional 5% is targeted for enhanced oil recovery. The Jurassic-Cretaceous geological sequence with the relative position of the reservoirs is shown in Fig. 11.47. The Arab-III (C Member) dolomitic limestone reservoir lies at an average depth of 2195 m (7200 ft). The reservoir is about 26 m (85 ft) thick with porosity varying between 10-30% and with permeabilities up to500 md. The oil has 39 ~ API gravity containing about 100-200 ppm H2S and 1.3% sulfur. The driving mechanism of this reservoir is water dumpflood assisted by natural aquifer influx. The Arab-IV (D Member), sucrosic dolomite and limestone reservoir, lies at an average depth of 2226 m (7300 ft). The reservoir is about 99 m (325 ft) thick with porosity varying between 10-30% and permeability varying between 5-100 md. The oil has 39 ~ API gravity containing 100-200 ppm H2S and 1.3% sulfur. The driving mechanism of this reservoir is water dumpflood assisted by natural aquifer influx. The Uwainat wackestone/packstone reservoir lies at an average depth of 2669 m (8750 ft). The reservoir is about 58 m (190 ft) thick with porosity varying between 10-23% and permeability between 2-300 md. The oil has 38 ~ API gravity. Reservoir energy is supplied by gas cap drive. Original recoverable oil reserves were estimated at 1.1 B.bbl. Bul l-lanine Field. The field is an elliptical dome elongated north-south with dimensions of 8 x 16 km. The field was discovered in 1965 by well BH-1 drilled in the northwest part of the field by Abu Dhabi Marine Area (ADMA); however, the first development well was not drilled until 1971 after the demarcation of the marine boundary with Abu Dhabi in 1969. The first production came in June 1972 as the last, and most prolific, of the three Shell-Qatar offshore fields. The original recoverable oil reserves were estimated at 680 MM.bbl. The Arab D is the most prolific reservoir and contains a STOIIP of 2.4 B.bbl. The reservoir was developed by crestal production, with pressure support provided by peripheral dump flooding. The porosity and permeability vary from 5 to 32% and 1 to 6000 md, respectively. Production from the Arab C reservoir, where the porosity and permeability vary from 5 to 20% and 50 to 500 md, respectively, is by gas cap drive, possibly aided by aquifer influx. The Jurassic-Cretaceous geological sequence with the relative position of the reservoirs is shown in Fig. 11.48. The Arab-IV (D Member) reservoir lies at an average depth 2332 m (7650 ft) and is about 91 m (300 ft) thick. The porosity and the permeability vary between 5-32% and 1-600 md respectively. The oil has 36 ~ API gravity. The driving mechanism in this reservoir is water dumpflood supplementing the aquifer influx. The Uwainat reservoir lies at an average depth of 571

Sedimentary Basins and Petroleum Geology of the Middle East

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Hydrocarbon Habitat of the Greater Arabian Basins NWD-2

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Fig. 11.51. Hydrocarbon and tilling history of the North Field (Qatar) showing the timing of trap elements, source rock, reservoir, seal ,trap growth and maturation of the Lower Silurian (Qusaiba Formation potential sources sources (Bishop 1995) reproduced by permission of Gulf Petrolink Bahrain.) trap growth and maturation of the Lower Silurian (Qusaiba) potential sources (Bishop, 1995, reproduced by permission of Gulf Petrolink, Bahrain) 573

Sedimentary Basins and Petroleum Geology of the Middle East 2706 m (8875 ft). The reservoir is about 53 m (175 ft) thick with porosity and permeability varying between 521% and 50-500 md respectively. The oil has 37 ~ API gravity. The driving mechanism in this reservoir is gas cap drive, possibly assisted by aquifer influx. North Field. The field was discovered in 1971 by Shell Qatar when discovery well NWD-1 was drilled. It is considered to be the largest, single, non-associated gas reservoir in the world, with proven reserves of more than 300 TCF and estimated total reserves of 500 TCF. The field is an enormous, gentle, dome-shaped anticline trending north-south, at least 130 km, with a width of 75 km and an area of more than 6,000 sq km, nearly half the area of Qatar. The main reservoir lies in the carbonates of the Permian Khuff Formation, from which gas and condensate are produced. The Khuff Formation has a thickness of about 854 m(2,800 ft), in which five reservoir units, K1-K5, separated by layers of anhydrite, are recognized. It comprises a rapidly alternating sequence of carbonate rock types with reservoir seals consisting of either bedded anhydrite or replacement anhydrite and tightly cemented dolomites and limestones. Two conspicuous markers are provided by beds of massive anhydrite designated as the Upper and

574

Median Anhydrites (Fig. 11.49). The formation has been divided into four major reservoir groupings and numerous subgroups based on gamma ray markers. Facies changes occur between the wells, and marked differences can be seen in porosity development in gamma ray correlatable units.The best reservoirs are found in grainstone with a high moldic and interparticle porosity. Intercrystalline porosity in the dolomite and dolomitic grainstone reservoirs may exceed 30%, with permeabilities around 300 md. Oil has been discovered in some of the Cretaceous reservoirs (Mishrif and Khatiyah carbonates, Nahr Umr sandstone, Shuaiba, Kharaib and Lekhwair carbonates) (Fig. 11.50) in the North area. In an attempt to explain why the North Field contains gas not oil in the Khuff, Bishop (1995) developed a diagram (Fig. 11.51) to illustrate the timing of trap growth and hydrocarbon expulsion for the Silurian and Carboniferous source rocks. The major point seems to be that the source rocks could yield only gas during the latest Miocene period of trap growth. This later gas has presumably displaced earlier reservoired oils.

Hydrocarbon Habitat of the Greater Arabian Basins UNITED ARAB EMIRATES

The U.A.E. is situated in the southeastern part of the Arabian Basin between latitudes 22040 ' and 26000 ' and longitudes 51 ~ and 56000'. The seven E m i r a t e s - Abu Dhabi, Dubai, Sharjah, Ajman, Umm al Qawain, Ras A1 Khaimah and F u j a i r a h - vary considerably in size, from Abu Dhabi, the largest (area 66,000 sq km), to Ajman (260 sq km), the smallest. With the sole exception of Fujairah, all are oil-producing, giving the U.A.E. a production rate of 2.2 MM.bbl/d. In tectonic terms, the U.A.E. lies within the interior platform of the Arabian Shield (Fig. 11.52), bounded on the northwest by the Qatar-South Fars Arch, and on the east and northeast by the foreland basin and adjacent foreland fold and thrust belt of Oman. The sedimentary section reaches a thickness of about 6,500 m (21,320 ft) in the southwest and thickens toward the basin depocenter in the north. It is subdivided into a number of major cycles, each characterized by a predominant lithology, and is bounded by major unconformities. Exploration activities for hydrocarbons in the U.A.E. began in 1936 with surface geologic reconnaissance, grav-

ity, magnetic and seismic surveys. The first test drilling began in 1950 (Ras Sadr RS-1), but without discovery oil, the commercial hydrocarbon discoveries in 1959 were in the Abu Dhabi Umm Shaif Field in the offshore and the Murban Field, now "Bab" Field, in 1960 in the onshore. A series of discoveries followed, so the U.A.E is now one of the richer oil-producing areas in the world (Fig. 11.52). Economic hydrocarbon deposits are found in two types of traps of regional importance: structural (anticlinal) and combined structural/stratigraphic (usually carbonate platform and unconformity). They are related to structural growth of the basement during and after sedimentation or related to structural growth of the Infracambrian salt.

Regional Stratigraphy

The Late Paleozoic to Recent section encountered in the deepest wells of United Arab Emirates has a maximum thickness of about 6506 m (21,000 ft) (Fig. 11.53). A feature of sedimentation since the beginning of the Late Permian has been the dominance of shelf carbonates, with

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Fig. 11.52. Location map of UAE showing the major oil and gas fields 575

Sedimentary Basins and Petroleum Geology of the Middle East evaporites of only secondary importance. There are minor influxes of argillaceous and arenaceous clastics, but these are rare. The first sediments laid down after the Hercynian orogeny were the continental clastic sediments assigned to Permo-Carboniferous. During Late Permian time, a marine transgression occurred and a carbonate platform was established over the area and during this time, the limestone/dolomite and minor anhydrite beds of the Khuff Formation were deposited. The carbonate platform was maintained throughout Early Triassic times with the deposition of shales, limestones and dolomites of the Sudair Formation, followed upward by the Gulailah (Jilh) Formation of alternating sequences of anhydrites, dolomites, limestones and minor shales. During late Triassic time, the climate was less arid and a relative drop in sea level preceded the deposition of the continental sandstones and siltstones of the Minjur Formation. The Early and Middle Jurassic, epeiric carbonates were deposited across the Arabian Gulf region. Deposition commenced with a mixture of terrigenous clastics and carbonates of the Marrat Formation, followed by the deeper water argillaceous limestones and dolomites of the Hamlah and Izhara formations, and ending with the shallow water, moderate- to high-energy limestones of the Araej Formation. During Late Jurassic, there was a gradual transition from deep water in western United Arab Emirates to shallow shelf conditions to the east that graded through shoal and lagoonal facies and culminated in supratidal facies. In early Late Jurassic time, intrashelf basinal sediments (the Diyab/Dukhan Formation) which consisted largely of argillaceous limestones, were deposited to the west, whereas to the east a cleaner limestones facies was deposited. These was followed by the cyclic deposition of limestones, dolomites, and anhydrites of the Arab Formation.The Tithonian anhydrites of the Hith Formation which were deposited in the west graded eastward into carbonates. The earliest Cretaceous sediments are the dominantly mixed oolitic, dolomitic limestones and lime mudstones (the Habshan Formation). These were followed by a long period of cyclic carbonate sedimentation with alternating shelf limestones and deeper water limestones of the Lekhwair and Kharaib formations. In central Abu Dhabi an intrashelf basin was formed in Aptian time where argillaceous limestones and shales (Bab Member) accumulated, and at the fringes or rim of this basin, rudistid and algal buildups were deposited (Shuaiba Formation). Collectively, these formations make up the Thamama Group. The deposition of the Wasia Group ("Middle" Cretaceous), started with Nahr Umr, the transgressive shales. Toward the end of Nahr Umr sedimentation, shale deposition diminished to the point that marine carbonate deposition commenced again across the area, beginning with the Mauddud Formation in which a transition occurred from shallow-marine sedimentation to somewhat deeper water conditions. A basin then developed in central Abu Dhabi in which the Pithonella limestones of the Shilaif/Khatiyah

576

Formation were deposited. At the basin margins, shallow shelf sedimentation led to the development of the foraminiferal-algal-rudist wackestones/packstones/grainstones of the Mishrif Formation. At the end of Cenomanian time, a major period of emergence and erosion terminated the deposition of the Wasia Group. Deposition of the Upper Cretaceous Aruma Group began with the transgressive Laffan Shale, which unconformably overlies the Wasia Group in all parts of the basin. The Halul Formation is characterized by shallow shelf carbonates. Following their deposition, renewed subsidence and the associated transgression in Campanian times resulted in the deposition of the basinal shales and limestones of the Fiqa Formation. A shallowing of the basin led to the deposition of the shallow shelf carbonates of the Simsima Formation. In late Maastrichtian time, a regressive facies developed over a large part of the Arabian Gulf region, resulting in non-deposition at the end of the Cretaceous. A widespread transgression occurred during the Paleocene, which resulted in deposition of thin basal shales, followed by the shallow shelf limestones of the Umm Er Radhuma Formation. In the early Eocene, restricted shelf conditions prevailed and the carbonate/evaporitic sequence of the Rus Formation was deposited, followed by the widespread nummulitic limestones of the Dammam Formation. During late Middle Eocene time, widespread emergence of the Arabian platform occurred; however, in the east, the Asmari Formation (Oligocene), consisting mainly of shelf limestones was deposited. It is overlain by a thick, Miocene sequence of interbedded carbonates, salt, anhydrite, shales and clastics. Reservoirs

U.A.E. reservoir rocks are developed entirely in carbonate facies (11.53). Several deep-pool tests in onshore and offshore oil fields in Abu Dhabi and Dubai have proved the existence of large, non-associated gas accumulations in the Upper Permian Khuff Formation. Oil and gas are found in Middle and Upper Jurassic limestone in offshore Abu Dhabi only. The most important oil-producing horizons are the Thamama Group Lower Cretaceous carbonates. There also is oil production from the Middle Cretaceous and Upper Cretaceous carbonates. Important, but small, accumulations are found in the limestone of the Upper Cretaceous Halul Formation in the offshore areas. A small, heavy-oil accumulation occurs in both the Oligocene Asmari Formation in the Mandous Structure and in the Paleocene Pabdeh Formation in the Hamediah Structure. The depth of the reservoirs is variable. The Khuff reservoir in Abu Dhabi occurs at depths between 4,300 and 5,456 m (14,108-17,900 ft), and Jurassic reservoirs are found at depths between 2,300 and 3,300 m (7,546-10,827 ft). The Cretaceous reservoirs in Abu Dhabi and the other Emirates range in depth from 1,500 m (4,921 ft) in Abu

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577

Sedimentary Basins and Petroleum Geology of the Middle East Dhabi to about 4,350 m (14,272 ft) in Sharjah, and to more than 4,700 m (15,420 ft) in Ras A1 Khaimah. The Lower Cretaceous reservoirs were not tested in the other northern Emirates, where they lie at great depths. Tertiary reservoirs occur at depths of about 1,000 m (3,280 ft) in offshore Abu Dhabi. The best reservoirs in the U.A.E. occur in shelf carbonates. Clastic reservoirs also are known, but exhibit poor reservoir characteristics in comparison.

Haushi Group (Late Carboniferous-Early Permian). This formation consists of quartzitic and micaceous sandstone interbedded with siltstone and shale. Some gas shows were encountered in the sandstone and siltstone sections of the Haushi Group in the Zakum, Nasr and Bu Haseer fields (Fig. 11.52). Gas was tested in the Satah Field. Some gas shows (mainly methane) were reported during the drilling of the Haushi Group in the Shah Field. The Hair Dalma Field is the only field producing gas from reservoir units 1 and 3 of the Haushi Group, with production rates between 1.70 and 4 MM.scf/d (approximately 48,000 and 116,000 m3/day) per well. The gas is composed of 21-23% N 2, 8.5-8.7% CO 2 and 6769% methane, and it contains no H2S (Alsharhan, 1994).

Khuff Formation (Late Permian-Early Triassic). Khuff reservoirs in offshore Abu Dhabi have proved the presence of large volumes of gas, composed predominantly of methane with small volumes of nitrogen, carbon dioxide and C2-C 5 gases. The reservoirs occur in thick sequences of dolomite, peloidal-oolitic packstone and grainstone sealed by interbedded or nodular anhydrite. Porosities are mainly interparticle, intercrystalline and fractured. In the upper Khuff reservoir, the main bulk of porosity ranges from 1 to 7%, with an average of 5%; while in the lower Khuff reservoir, porosity ranges from 2 to 20%, with an average of 10%. Permeabilities vary widely, from less than 1 md to several tens of md. Several discoveries have been made in salt-cored domal and anticlinal structures that proved gas and condensate, the Umm Shaif, Zakum, Hair Dalma, Hail, Satah, Nasr, Sath A1 Raaz Boot, Arzanah, Abu A1 Bukhoosh and Fateh fields (Loutfi and E1 Bishlawy, 1986; Alsharhan and Nairn, 1994). The gas composition in these fields consists of hydrocarbon gases (C 1 and C2) associated with varying proportions of H2S, CO 2 and N 2. The Zakum and Fateh fields produce appreciable amounts of H2S (33%), CO 2 (20%) and N 2 (7%) in association with hydrocarbon gas. The gas in these fields is highly sour and probably is formed due to the high-temperature reaction between methane and anhydrite or via a thermochemical sulfate reaction at relatively low temperatures (Videtich, 1994), rather than microbiological reduction at sulphate. It is believed that the Khuff Formation contains approximately 19% of the estimated total gas in place in the U.A.E. Condensate/gas ratios are highest in the northwest corner of offshore Abu Dhabi; dry gas is found in southeast onshore and central/western off-

578

shore Abu Dhabi, eastern offshore Abu Dhabi, offshore Dubai, and central and western onshore Abu Dhabi. Dry gas also occurs in eastern onshore Abu Dhabi and in the Falaha Syncline (located between the Shah-Asab-Sahil and Bu Hasa-Bab trends).

Sudair-Gulailah-Minjur formations (Triassic). No hydrocarbon production has been reported from this sequence in the U.A.E., but gas shows occur in offshore Abu Dhabi. Porosity is generally poor to fairly good (59%), with some reduction in porosity due to depth of burial and diagenesis. Loutfi and Sattar (1987) and Alsharhan (1993) reported that maturation profiles of the entire Triassic in the Umm Shaif and Abu A1 Bukhoosh fields are in the oil zone, while in the Satah, Hair Dalma, Bu Hasser, Zakum and Nasr fields, only the upper part of the Triassic is in the oil zone, with the remainder of the sequence within the wet-gas zone. At Ghasha, the entire sequence is in the wet-gas zone, but at Hail, Bab and Bu Hasa, it extends from the wet- to dry-gas zone; and in the Jarn Yaphour Field area, it is in the dry-gas zone. The maturation history, the burial sedimentation and the well-developed structures formed during the Triassic in the northern part of Abu Dhabi suggest these areas are promising in terms of potential hydrocarbon accumulation. Generally, however, the hydrocarbon potential of the Triassic is due to the leaks in the regional seal, in contrast to the Jurassic or Cretaceous formations, where the seals are better. Araej Formation (Middle Jurassic). The Araej reservoir characteristics were described by Alsharhan and Whittle (1995a) and are summarized below. The Lower Araej shows very little reservoir development, with very low porosity (about 8%) and low permeability (less than 10 md) due in a large part to extensive calcite cementation and the predominance of mud-supported textures. Secondary porosity is poorly developed as rare interparticle and vuggy pores and to a lesser extent, intraparticle and mouldic pores. The Uwainat Formation is characterized a reservoir by contrasting upper and lower parts with varying permeability due to highly stylolitized and compacted sediments. The lower part of the Uwainat shows poor reservoir characteristics, the porosity being mostly less than 7% and permeability less than 1 md. Porosity increases in the upper part of the Uwainat Formation, to between 7 and 15%. The permeability is moderate for the majority of the values are less than 10 md, though some intervals are as high as 100 md. The Upper Araej reservoir has moderate to good porosity (up to 16%) and good permeability (up to 100 md). The grainstones and well-cemented packstones have a porosity from 5 to 16% and a permeability from less than 1 to 100 md. The argillaceous lime mudstones and wackestones are characterized by lower porosity (ranging from 3 to 9%) and very low permeability (less than 1 md). Hydrocarbons occur in the Araej Formation, shallowwater shelf carbonates with good reservoir quality. Light oil (35 ~ API) is found at Umm Shaif in all Araej members,

Hydrocarbon Habitat of the Greater Arabian Basins and oil in this formation also occurs at the Yasser, Belbazem, Alpha-l, Umm al Dholou, ADNOC (I-A, 1-B and lC), Jarnain and Hair Dalma fields. Gas-condensate is found in the Ghasha, Satah and Zakum fields and CC Structure (Hassan and Azer, 1985; Loutfi and E1Bishlawy, 1986). Diyab Formation (Upper Jurassic). In addition to being the major source rock for the Jurassic and Lower Cretaceous reservoirs, it also is a good reservoir unit in the porous, oolitic-peloidal packstone-grainstone. Oil has been produced at this zone at wells Bu Dana-l, ADNOC 1-B and ADNOC 1-C (Loutfi and E1 Bishlawy, 1986; and Alsharhan, 1989). Arab Formation (Upper Jurassic). The Arab Formation comprises four units cyclically deposited as transgressive and regressive carbonate-evaporite units (Arab A to D or I to IV). The Arab D Member is the most prolific hydrocarbon reservoir, characterized by mudstone and wackestone in the basal part of the section, grading upward into bioclastic, dolomitic packstone/grainstone and sucrosic dolomite (Alsharhan and Whittle, 1995b). The highest porosity in the Arab C occurs in dolomitic grainstone due to a decrease in the anhydrite cementation. Mud-supported lithologies within this member have low porosity. The dolomites at the base and top of the section have poor intercrystalline porosity due to anhydrite cementation. The Arab B consists of dolomitic and dolomitized grainstone with much greater anhydrite cementation than in the Arab C or D members. The Arab A consists of anhydrite and dolomitic limestone with very low porosity. The formation is the principal oil reservoir, with porosities of up to 30% and permeabilities exceeding 100 md. The Umm Shaif Field contains the largest oil accumulation (with a well-developed gas cap) in this formation, with 38 ~ API oil. Other important Arab Formation oil accumulations occur in the Ghasha, Nasr, Bu Tini, Saath A1 Raazbooth, Abu A1 Bukhoosh, Satah, Jarnain, Dalma, E1 Bunduq, Arzanah, Hair Dalma, Hail, ADNOC l-A, ADNOC l-C, Umm al Dholou, Umm A1 Salsal and Belbazem fields. In the Bab, Mubarraz and western Mubarraz fields, the Upper Jurassic has proved to be gas-bearing, mainly methane, but with as much as 28-32% hydrogen sulfide. Thamama Group (Lower Cretaceous). The Lower Cretaceous stratigraphic sequence has been divided into four formations (Fig. 11.53).In the U.A.E., the greatest oil accumulation occurs in the carbonate sequence of the Thamama Group. The Thamama hydrocarbon-producing zones occur in a number of structures in the U.A.E., such as the Bu Hasa, Bab, Asab, Sahil, Ruwais, Jarn Yaphour, Mender, Qusahwira, Hudairat, Shanayel, Rumaitha, Zubbaya, Zararra and Huwaila field in onshore Abu Dhabi. Offshore fields (Zakum, Umm Shaif, Mubarraz, Abu A1 Bukhoosh, Nasr, Belbazem, Umm al Dholou, Umm al Salsal, Delta, Mandous and Umm Lulu) also produce from the Thamama, as do the Fateh, southwestern Fateh, Rashid

and Margham fields in Dubai. The Mubarek and Sajaa fields (Sharjah) and Saleh field (Ras A1 Khaimah) also produce from Thamama zones (Alsharhan, 1994). Habshan Formation. This formation is mainly characterized by microporous lime mudstones/wackestones and dolomitic peloidal and bioclastic packstones/grainstones. Reservoir studies of this formation indicate that the best porosities and permeabilities are present in dolomitic grainstones. The porosity in these rocks occurs predominantly as interparticle and intercrystalline types. In some lime mudstones and wackestones porosities were improved by leaching processes associated with subaerial exposure. Lekhwair Formation. The grainstones and packstones usually have the best permeabilities and porosities (25-120 md and 20-26%, respectively), because they are characterized primarily by interparticle porosity, but these textures are not always permeable when they occur within the vicinity of stylolites. The interparticle porosity tends to be filled with calcite or dolomite. Lime mudstones/wackestones that occur contain moldic and vuggy porosities, in which the pore network is partly or irregularly continuous depending on the degree of solution of the rocks, with the consequent ranges in porosity from 15-23% and permeability from 9-11 md. Kharaib Formation. The mud-supported rocks have both good porosity and permeability due to the abundant interparticle pore associated with dissolution. The grainstones show higher permeability peaks due to the association of the interparticle pores and solution vugs. The slight decrease in the porosity is probably the result of compaction. Some porosities in the grainstones are high (2030%), although permeabilities are rather low (1-10 md). The low permeability values closely match those of mudstones and are probably due to more complete calcite cementation. The lowest porosity and permeability values are due to the numerous stylolitic partings and laminations. Shuaiba Formation. Reservoir quality of the Shuaiba Formation depends upon two parameters" (a) texture and depositional setting; and (b) porosity modification by diagenetic processes. The original sedimentary composition and texture strongly influence the effect of diagenesis upon these sediments. The diagenesis through an interplay with porosity and permeability may either improve or degrade original reservoir quality. Porosity ranges from 527% and permeability from less than 1 md to more than 120 md. Good porosity and high permeability are found in the reefal sediments due to subaerial exposure and leaching. Mishrif Formation (Middle Cretaceous). The Mishrif Formation is composed of rudistid and algal buildup carbonates and exhibits very good reservoir characteristics; porosity ranges from 20 to 30%, but permeabilities are only moderate to low, with an average of 25 md. The principal oil accumulations in the Mishrif occur at Umm A1 Dalkh (Abu Dhabi), Fateh, southwestern Fateh and Rashid (Dubai). Good oil shows have been found in 579

Sedimentary Basins and Petroleum Geology of the Middle East Abu Dhabi in the Hair Dalma, Sadiyat and Hudairat fields (Alsharhan, 1995). An integrated study of the low-angle, platform-ramp facies of the Mishrif Formation, using seismic, well-log, sedimentological and field production data, was made by Pascoe et al. (1994) to determine the generation and distribution of the reservoir facies as an aid to exploration. Using sequence-stratigraphic concepts, they identified six Mishrif cycles in which the bioclastic shoal facies were the major reservoir, and the subaerial to lacustrine platform and dysoxic platform lagoon facies were the potential seals. The regional seal was the overlying Lafan Formation shale. The clastic sediments in the Tuwayil Member exhibit moderate reservoir characteristics, with porosities of 327% and permeabilities of 0.17-28 md. The member has tested heavy to medium oil from the Mushash well, and heavy oil from the Dhafra wells (Loutfi et al., 1987; Azzam, 1995). Aruma Group (Upper Cretaceous). Commercial hydrocarbons in the Upper Cretaceous are confined to the Simsima, Halul and Ilam formations, which are the best potential exploration targets, particularly in the northeastern Emirates offshore in a belt parallel to the Oman Mountains. llam Formation (Santonian). The formation contains hydrocarbons and is a secondary reservoir in the Fateh field, although in the SW Fateh it contains non-commercial oil. The oil is very similar to that reservoired in the Mishrif Formation and probably migrated upwards from the Mishrif along fault zones. Halul Formation (Santonian). The limestone of the Halul Formation exhibits low to moderate reservoir characteristics, with moderate porosity and low permeability. Heavy oil accumulations occur in the Mandous and A1 Khair fields (Schlumberger, 1981). In Dubai, the Ilam (Halul) Formation has fair to good porosity. It is a secondary reservoir in the Fateh Field and contains only noncommercial oil in southwestern Fateh. Simsima Formation (Maastrichtian). The limestones of the Simsima in the subsurface commonly contain interparticle fracture, moldic and vuggy porosity while the dolomite has good intercrystalline porosity, especially in the Shah Field. Shallow-water carbonate sediments, associated with secondary porosities and good permeabilities are the only oil-bearing strata in the Shah Field of onshore Abu Dhabi. The beds may also have potential in the offshore of the northeastern U.A.E., where local buildups occur at the edge of the basin. Asmari and Gachsaran formations (Upper Tertiary). The dolomitic limestone of the Asmari and Gachsaran formations in the Mandous Field contain heavy oil.

Seals and Seal Formations The anhydrite cap rocks in the hydrocarbon-bearing

580

reservoir of the Jurassic offer excellent sealing qualities. Shale seals are present in Middle Jurassic and Cretaceous sequences (Fig. 11.53). The dense limestone within the Thamama Zones is an intraformational seal for the Thamama reservoirs. The shale of the Nahr Umr Formation is the regional seal for the Shuaiba carbonate reservoirs. The bituminous lime mudstone of the Shilaif source rock is a lateral seal for the stratigraphically-trapped Mishrif and Halul oil in the Umm al Dalkh and Hudairat fields. The Laffan shale forms the regional top seal for the Mishrif hydrocarbons in the U.A.E. (Hassan and Azer, 1985; Jordan et al., 1985; Loutfi and E1Bishlawy, 1986; Alsharhan, 1989). The Simsima oil in the Shah Field is sealed by the shale and argillaceous limestone of the basal Umm er Radhuma Formation. The anhydrite and dolomitic limestone in the upper part of the Asmari Formation act as a seal for this formation in the Mandous Field. The prolific Upper Permian Khuff carbonate reservoirs contain non-associated gas effectively sealed by interbedded anhydritic layers. The argillaceous limestone and shale of the basal Sudair Formation act as a top seal for the gas accumulation in the Upper Khuff Formation. Upper Jurassic shale and argillaceous lime mudstone of the basal Diyab Formation, reported from the offshore part of Abu Dhabi, seal the major oil and gas accumulations in carbonate reservoirs of the Middle Jurassic Araej Formation. The Upper Jurassic evaporites occur in both the Arab and Hith formations and seal the major oil and gas accumulations of the Arab Formation in western Abu Dhabi. The anhydrite units between each zone (zones AD) in the Arab Formation act as intraformational seals in the same field, and the Hith Anhydrite has proved to be a regional seal for the upper Arab reservoirs. Where the facies in the Hith is breached through faulting (as at Abu A1 Bukhoosh) the Arab oil can migrate upwards. Paleocene-Eocene Pabdeh shale is found only in the subsurface of the northeastern U.A.E. and offers some additional sealing capacity. Lower-Middle Miocene anhydrite and rock salt and minor dolomite of the Gachsaran Formation cover the whole offshore area ofAbu Dhabi and are an excellent regional seal for all the underlying hydrocarbon- accumulations, especially for the Oligocene Asmari Limestone reservoirs.

Source Rocks and Oil Geochemistry

The main source rock levels in the UAE have been identified by ADNOC (1984), Hassan and Azer (1985), Loutfi and E1 Bishlawy, (1986), Alsharhan, (1989), Mohamed and Ayoub (1992), and are summarized in Table (11.4 ) by Lijmbach et al. (1992). Mohamed and Ayoub (1992) carried out the oil and source-rock geochemistry on rocks from Abu Dhabi which is summarized below. The pristane/phytane ratios of the

Hydrocarbon Habitat of the Greater Arabian Basins Table 11.4. The Main Source Rock Horizons in the United Arab Emirates (after Lijmbach et al., 1992). Age Late Permian

Formation Khuff

Ansian- Ladenian Carnian - Rhaetian

Jilh Miniur

Callovian Oxfordian - Early Kimmeridgian

Uweinat Dukhan

Berriasian- Early Valan~inian Berriasian - Aptian

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Aptian

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Ccnomanain

Tuwayil Shilaif Laffan Fiqa

Albian- Cenomanian Coniacian Campanian

Jurassic Dukhan source rock and the oils in the onshore Abu Dhabi fields have values of less than one, indicating a similar and carbonate origin. The most prominent differentiating criteria between the oils and the Dukhan source rocks as compared to the other source rock candidates are the nickel/vanadium values which are extremely low. The Dukhan nickel/vanadium ratios are different from all the other source rocks (Fig. 11.54a). A plot of the carbonate isotope ratios vs pristane/phytane ratio (Fig. 11.54b) shows similarities between the oils and the Dukhan source rock, supporting the nickel/vanadium variation values and the biomarker results. The sulfur content of the oils and the extract of the Dukhan also show great similarities and are clearly different when compared with the other source rock candidates (Fig. 11.54c). The oils of Abu Dhabi exhibit a very mature character indicated by the high API ~ values, isomerization, VRE% and the mature chromatographic character. The Dukhan Formation shows a highly mature to post mature status and it is interpreted that the oils of onshore Abu Dhabi were sourced mainly from the mature Dukhan Formation. The Maastrichtian Simsima oil of Shah Field, although slightly heavier (relatively less mature) than the rest of onshore Abu Dhabi oils, is still considered fairly mature. Its gas chromatography shows a smooth, even and mature character. The sterane isometrization is near completion. The calculated vitrinite reflectance equivalent is approximately 1%. Therefore, it is not likely that such a mature oil (at this shallow depth + --000 ft) would have been generated from a source rock of low maturity like the Shilaif. The Shilaif Formation, unlike the Shah Simsima oil, contains vanadium in the range of 724 to 2200 ppm, nickel in the range of 62 to 162 ppm and sulfur in the range of 3.3% to 3.9%. In the almost all of the main fields of onshore Abu Dhabi there are strong indications of potential vertical communication. It is possible to explain the vertical and areal distribution of the oils in onshore Abu Dhabi as due to seals becoing progressively more effective with burial. In Shah Field and at the time of

Type of Source rocks Probably good Type II SR for oil postmature Post-mature 1I Marginal Type II/llI SR for gas and some oil; post-mature post-mature II Excellent Type II SR for oil postmature Good II (post-mature) Fair II (mature in different dense intervals) Good to excellent Type ]1/I SR for oil mature m-iv and II-1II(mature) Excellent Type ]Yl SR for oil mature Good II (mature) m-IV (mature)

early oil expulsion (which was relatively earlier than the rest of Abu Dhabi), the succession of seals from the Nahr Umr, and the dense zones aove the Thamama interval were penetrated all the way to the Simsima, at which point oil wss barred from further migration during the Tertiary time. The Nahr Umr Formation, which was not an effective seal in Shah area in southern Abu Dhabi ,d became an effective seal in central Abu Dhabi. It is believed that the Dukhan Formation constitutes the main source rock for the major oil accumulations in onshore Abu Dhabi. The generation of oil commenced towards the beginning of the Tertiary and reached its peak during the Eocene. Most of the structural growth of the main fields in Abu Dhabi took place during the Late Cretaceous providing timely traps for hydrocarbon accumulation. Most of the variations in the oils in onshore Abu Dhabi can be attributed to differing maturity levels and minor facies change within the Dukhan source rock. Rock-Eval analysis has been carried out by Lijmbach et al (1992) on suitable samples from Abu Dhabi onshore oil fields Fig. (11.55 ) shows that the mature Shuaiba/Bab and Shilaif source rocks type are Type I-II source rocks with HI=400-800. The Dukhan, Minjur and Khuff source rocks have only a low HI <100 remaining, asoil from these post-mature source rocks has already expelledl. All the oil analyzed probably has a similar source,whatever environment it is now found. The original biomass is thought to consist of bacterially reworked algal matter, deposited in shaly, marly or carbonate environment respectively. The organic matter contained in the thin and argillaceous siltstone and shale interbedded within the Unayzah sands is probably the source of gas, although these clastics are incapable of generating a significant gas volume. (Geochemical analysis shows that the total organic carbon content ranges from 0.94 to 1.4%.) It seems most likely that, as in Saudi Arabia, the principal origin of the Unayzah gas is to be sought in the Silurian shale. In the U.A.E., this shale occurs at a great depth but has been pen581

Sedimentary Basins and Petroleum G e o l o g y of the Middle East

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Fig. 11.54. Oil-source rock correlations in the UAE oi field a)Porphyrin vs. stable carbon isotopes. Note that most of onshore Abu Dhabi oils correlate vert well with theUpper Jurassic Dukhan (Diyab)source rock. b) Pristane/Phytane ratio vs.Stable carbon isotope ratio. Note that the oils of onshore Abu Dhadi cluster around the Dukhan (Diyab) source rock. c) Sulfur content vs. stable carbon isotope ratio. Note that the close correlation between the oils and the Dukhan (Diyab) source rock. (after Mohamed and Ayoub, 1992). I000OIL-PRONE

Shuaiba 9Formation (Bab Member) AShilaif Formation Simsima, Fiqa, rl Tuwayii Formations O Dukhan, Minjur, Khuff Formations

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Hydrocarbon Habitat of the Greater Arabian Basins etrated in four wells. The total organic carbon (TOC) of the Sudair Formation is about 1% by weight. The Gulailah (Jilh) Formation contains a TOC ranging from less than 0.5 to about 2 wt%, and the organic content ranges from less than 1 to 3 wt% in the Minjur Formation. The TOC of the Triassic section gradually increases towards the central part of the U.A.E. The main organic types of sapropelic kerogen are amorphous organic matter and algal remains; humic matter has been recorded, but is a minor component. Palynomorphs studied indicate that the thermal alteration index (TAI) varies across the oil fields. At Mender and Umm Shaif (down to a depth of 4,000 m), thermal indices range from 2.75 to 3; and in the Hail, Hair Dalma, Bab and Mender fields (down to a depth of 5,000 m), thermal indices are 3 to 3.5. The hydrocarbon generation potential of the Minjur Formation is about 1.15 kg/ton and of Sudair Formation about 2.41 kg/ton (Loutfi and Sattar, 1987; Alsharhan, 1993 a & b; Whittle and Alsharhan, 1995). The Diyab in offshore is the equivalent to the onshore Dukhan Formation. The Diyab in western offshore Abu Dhabi was deposited in an intrashelf basin setting. There is a facies change in the source beds that thin to the eastern offshore Abu Dhabi toward Dubai and where dark-gray, finely laminated, argillaceous lime mudstone and wackestone with calcareous shale give way to dolomite and dolomitic limestone with some peloidal packstone and grainstone. This marks the change from a euxinic intrashelf basin to a shallow-water, subtidal lagoon to the east and a change from source-rock to non-source-rock facies. Geochemical typing, gas chromatography and sterane-phytane fingerprinting identified the Diyab Formation as the source of the hydrocarbons found in the Arab and Thamama reservoirs. The formation lies mostly below the oil window, so the main phase of oil generation was during the early Miocene. TOC of the Diyab Formation ranges from 0.72 to 1.8 wt%, with sapropelic, oil-prone kerogen sometimes mixed with sapropelic-humic, and pyrolysis gives a yield of 0.55.0 kg/ton. TOC values range from 0.5 to 0.82 wt% in the onshore, but are higher in western offshore Abu Dhabi (0.3-5.5) and generally less than 2%, with the highest TOC values in the basal organic layer. The highest pyrolysis values (90.5-5.0 kg/ton)occur in the northwestern offshore. The onshore areas generally are characterized by low TOC values (<1 wt%) and low pyrolysis values, with only the Mender and Qusahwira areas showing moderate source potential (TOC as great as 1.2 wt%). Gas chromatography, mass spectrophotometry of the sterane and triterpane fingerprints and carbon isotope values of Diyab/Dukhan source-rock abstracts indicate that they were the single source for the Arab and Thamama oils. The distribution of the oils was controlled by the distribution of the Hith seal facies, for oil in Thamama reservoirs occurs only east of the Hith edge or where the Hith seal was not wholly anhydrite, where facies change or where the integrity of the seal was broken by faulting per-

mitting vertical migration (Alsharhan and Kendall, 1995). Thermal modelling, when applied to known source rocks in Abu Dhabi (Thompson, 1995), show the Diyab Formation reaching oil maturity and then gas maturity during the late Cretaceous (Turonian-Campanian), with a hiatus in gas generation during the early Tertiary and the Shilaif, becoming during the Miocene less than oil mature over the most northern onshore Abu Dhabi. As with potential gas cracking in the Arab D Member, both are more deeply buried. However, to get the simulated maturity to simulate the observed maturity, it is necessary to modify the assumption of constant heat flux and insert two intervals of increased flux during the late Cretaceous and late Miocene. These intervals of increased flux are attributed to contemporary tectonic events, ophiolite emplacement during the late Cretaceous and the late Miocene-Recent Zagros collision, although there is no direct evidence of this. The Diyab-Dukhan Formations are possible source rocks in parts of western and SE Abu Dhabi, in the Falah and Sir Abu Nuair synclines, and NE Abu Dhabi (Fig. 11.56). Oil generation in a the Diyab-Dukhan Formation started 73 MM yrs ago, and peaked in central, SW and NE onshore Abu Dhabi 56 MM yrs ago. At the same time gas generation was taking place in the Se and NW regions. At present, only the latter two areas have some oil-generation potential, while the rest of the Diyab-Dukhan Formation has potential only for gas (Alsharhan 1989). In the lower part of the Arab Formation at Hair Dalma and Umm Shaif, there is an organic enrichment corresponding to an increase in argillaceous content. In this basal unit, there is the possibility of minor oil source potential being developed in the Arab D member. The Lower Cretaceous Thamama Group forms the most important reservoir in the U.A.E. The geochemical analysis and oil characteristics of the Thamama is shown in Fig (ll.57).The dense argillaceous units interbeds between the various reservoirs have been considered as a possible source for the Thamama oils, and in particular the Shuaiba basinal facies (Bab Member) which is thought to be a good source rock by Alsharhan (1989) and Lijmbach et al. (1992). These basinal facies consists of argillaceous lime mudstone and wackestones, dominated by pelagic and planktonic faunas, in which the TOC content ranges between 1-6 wt% and pyrolysis yields reach 16 kg/tonne. Volumetric calculations for Shuaiba source rock by Azzam and Taher (1995) indicate that most of the Upper Thamama oils have been generated and migrated from a mature Shuaiba source. The beginning of hydrocarbon generation from the Shuaiba source rock was as early as Eocene time. The Shilaif Formation, which was deposited under anoxic basinal conditions, contains sediments that include highly bituminous, pelagic, shaly lime mudstone-wackestone and Pithonella limestone. There is an increase in maturity from offshore to onshore Abu Dhabi-Dubai, with an area of lower maturity in southeastern Abu Dhabi 583

Sedimentary Basins and Petroleum Geology of the Middle East

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Hydrocarbon Habitat of the Greater Arabian Basins (ADNOC Staff, 1984; Loutfi and E1 Bishlawy, 1986). Most of the offshore area is immature or has just reached the oil-generation threshold. There is an area of more mature Shilaif to the east, where rapid subsidence in the Ras A1 Khaimah Basin has led to deeper burial" the Shilaif in this area is now approaching the maximum oil-generation phase (ADNOC staff, 1984; Alsharhan 1989) (Fig. 11. 58a). The Shilaif Formation has TOC values ranging from 1 to 6%, and in some intervals may reach up to 15%; pyrolysis results show that P2 values range from 3-47 kg/ tonne confirming that the formation is a good to excellent source rock (Hassan and Azer, 1985) (Fig. 11.58b). Visual kerogen typing indicates a preponderance of oil-prone sapropelic material. Vitrinite reflectance values range from 0.21-0.53%, showing that the formation is immature or at best marginally-mature, while in extreme eastern offshore Abu Dhabi the formation is just approaching maturity (Hassan and Azer 1985; Loutfi and E1 Bishlawy, 1986; Alsharhan, 1989). Jordan et al. (1985) reported that the Khatiyah (Shilaif Formation) in Dubai is an oil-prone source rock lying within the oil window, with respect to kerogen maturity. The TOC in the Shilaif ranges between 1 to 7% and in some intervals reaches up to 15% (Fig. 11.

59). The organic geochemical results from carbonate rocks of the Shilaif and Mishrif formations of the Umm Addalkh Field determined by Taguchi and Mori (1992), after examining the relationship between thermal maturation and bitumenffOC ratios in these carbonates, showed that the vitrinite reflectance does not delineate the oil window indicating that the carbonates are thermally immature. The elemental analysis of kerogens showed that most samples from the Shilaif Formation plot in the zone of Type I and/ or Type II kerogens on a van Krevelen diagram, while samples from the deeper Mishrif Formation plot in the zone of Type II and/or near Type III kerogens. The kerogen data also indicate that all samples from the Shilaif Formation fall within the principal zone of oil generation (Taguchi and Mori 1992). The sulfur content of kerogen isolated from these carbonate samples is much higher than those in shale. This tendency is confirmed by comparing the sulfur contefits of kerogens in carbonates with those of kerogens in a shale and a thin cool seam samples (Taguchi and Mori 1992). The kerogens in the Shialif and Mishrif are considerably richer in organic sulfur than typical kerogens from argillaceous rocks where the high content of sulfur and kerogen of carbonate rocks seems to be in common with that in the rest of the world. Hughes (1984) used the thiophenic organosulfur compound in characterizing the Upper Cretaceous Ilam crude oil of the SW Fateh Field which was derived from the Cenomanian Khatiyah (Shilaif) carbonates. He concluded that the Khatiyah samples have TOC content of 2.88 wt% and the Khatiyah extract has an odd-even predominance (OEP) of 1.07 and a pristane/phytane ratio of 0.69, which are similar to an OEP of 0.97 and pristane/phytane ratio of 0.66 for the Ilam oil. As seen in Fig. 11.60 the similarity in

sterane is seen as evidence that the Khatiyah Formation is the source of the Ilam oil. Fig. (ll.60b) shows the comparison between the Khatiyah extract and Ilam oil using sulfur-selective flame photometric detector gas chromatograms of the aromatic fraction and the m/z 217 mass fragmentograms of the saturate fractions. They concluded that the distribution of thiophenic-sulfur compounds are similar and have many of the features associated with oil from carbonate sources. The generation of oil in the Shilaif Formation began 22.5 Ma years ago, and peak oil generation in the central, west and northeast of Abu Dhabi occurred some 3 Ma years ago. At present, the Shilaif Formation is immature in the northeast and northwest onshore areas. There are two principal areas offshore Abu Dhabi-Dubai in which oil generation from the Shilaif took place: the Sir Abu Nuair syncline and the Ras al Khaimah Basin (Fig. 11.61). Oil generation from the Shilaif was initiated during Oligocene times in southem offshore Dubai. In these ares, the occurrence of a free oil phase in fluid inclusions demonstrates that the oil had migrated from the Shilaif source rock during the Late Oligocene to Mid-Miocene. To the NW, oil generation commenced at progressively later times (late Miocene and early Pliocene), while in the Sir Abu Nuair syncline, oil generation was initiated during late Miocene. The extensive presence of argillaceous material in the Fiqa Formation precludes the development of reservoirgrade porosity. Some of the less argillaceous limestone has traces of leached porosity, and minor intercrystalline porosity occurs in the fine dolomitic limestone developed in the lower part of the Fiqa (Alsharhan, 1995). In some wells, the Fiqa contains immature humic vitrinite with no source-rock potential, but in other exploratory wells in northeast offshore Abu Dhabi, the formation contains more sapropelic organic matter that has reached moderate maturity levels and may have sourced some oil (Alsharhan, 1989). Lijmbach et al. (1992) reported that some potential source-rock intervals (type III-IV) exist as relatively thin, but kerogen-rich, layers in the Asab Field, Abu Dhabi, but with vitrinite reflectance values of about 0.43% R o, the kerogen is immature.

Traps The U.A.E. encompasses parts of the Southern Gulf Sub-basin, the Rub A1 Khali Sub-basin, the Ras A1 Khaimah Sub-basin and the Oman Foreland Basin. Folds are mostly periclinal in style with flank dips generally less than 5 ~. The main structural trends are shown in Fig. 11.62. Basement structures in the Arabian Basin have exerted some control over the deposition and subsequent structural growth of the sub-basins. The Rub A1 Khali and Ras A1 Khaimah sub-basins cover a large part of the U.A.E. and lie in a primarily Tertiary depression, for during the Mesozoic, the region was part of the Interior Arabian Platform. Sediments thicken towards the Arabian Gulf, along a NE-SW regional structural trend. The sedi585

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 11.60. Comparison of flame photometric detector (FPD) gas chromatograms and B) m/z 217 mass fragmentograms of a crude oil, from the Upper Cretaceous Ilam Formation, and of a rock extract from the Middle Cretaceous, Khatiyah Formation, SW Fateh Field, Dubai, UAE (after Hughes, 1984, reproduced with permission from AAPG). Identification key for peaks 1-14 are as follows : 1. C2 Benziothiophenes, 2. C3- Benziothophenes, 3. C4+ - Benzothiophenes, 4. Dibenzothiophene, 5. Methyldibenzothiophenes, 6.Dimethyldibenzothiophenes, 7.Trimethyldibenzothiophenes, 8. Benzonaphthothiophenes, 9. 1313(H), 17a(H),20(R +S)-diacholestanes, 10. 5a(H), 14a(H), 17a(H),20R-cholestane + 24-ethyl-1313(H),17a(H), 20R-diacholestane, 11. 24-methyl-5a(H), 14a(H), 17a(H),20Rcholestane, 12. 24-ethyl-5a(H),14a(H),17a(H),20S-cholestane, 13. 24-ethyl-5(H), 148(H), 1713(H),20(R + S)-cholestane, 14. 24-ethyl5(H), 14(H), 17(H), 20R-cholestane.

587

Sedimentary Basins and Petroleum Geology of the Middle East mentary fill usually is fiat-lying, with a few gentle structural undulations. The Southern Gulf Sub-basin is a depression with an Infracambrian salt sequence at the base. Salt plugs are known in the offshore islands, and salt structures with varying trends are responsible for the major fields in the offshore U.A.E. All hydrocarbon accumulations discovered so far in these sub-basins are contained in structural traps, although combined stratigraphic-structural or stratigraphic traps exist in some areas. In western Abu Dhabi, most of the oil and gas is in Jurassic reservoirs; in the central areas, most of the oil is in Lower Cretaceous reservoirs; and in the eastern offshore of Abu Dhabi to Ras A1 Khaimah, oil reservoirs are Middle Cretaceous in age. In western Abu Dhabi, structural traps can be shown to have started developing in the Upper Jurassic, but the initiation of structural trap formation eastward seems to become progressively younger. In the Oman Foreland Basin, the Sajaa and Margham structures (which produce gas and condensate) are below the buried frontal thrust of the Oman Mountains Over-

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thrust Belt. There, the structural traps are faulted anticlines that began developing in the Upper Cretaceous and Miocene, were related to the uplift of the present-day Oman Mountains, and were reactivated by pre-existing faults in the area. The Gulf of Oman part of the basin is poorly explored, and only four dry wells have been drilled in offshore Fujairah. The sub-basin is a trough formed during the Upper Cretaceous. The explored sequence is argillaceous and detrital throughout, and the base of this series of large ridges parallel to the coast, which seem to be due to clay diapirism (domes of high-pressure shale of Upper Cretaceous age or older), occur. Most, if not all, traps are halokinetic growth structures induced by Infracambrian salt controlled by basement growth structures. The eastern part of the Emirates is situated in the foreland belt of the Oman Mountains of the Ras A1 Khaimah Sub-basin. Faulted anticlines and fault-related folds are expected in this area. Salt movement and trap formation may have started in the Paleozoic and continued into the Tertiary. The foreland folds of the Oman Mountains in the Ras A1 Khaimah Sub-basin are Tertiary in age and very likely had an earlier structural history.

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Fig.11.62,Structural trend of oil and gas fields at the top of the Lower Cretaceous level in the UAE.

589

Sedimentary Basins and Petroleum Geology of the Middle East Retention is thought to be excellent in structures capped by evaporites and shale, but is expected to be worse in the foreland belt of the Oman Mountains because of a higher degree of deformation. Migration from Mesozoic source rocks is thought to be mostly of Tertiary to Recent age, depending on local burial history and temperature gradients. The timing of migration from Paleozoic source rocks remains speculative, but is anticipated to be Mesozoic, most probably Upper Mesozoic. Oil and Gas Fields Despite the number of oil and gas fields in the U.A.E. (Fig. 11.52), the majority are structurally very simple anticlinal structures, virtually unfaulted, attributed to ?basement- and structure-activated salt domes. In some cases, the field parameters are enhanced by facies changes, which themselves may be attributed to changes in the depositional environment as a result of depth changes either through sea-level change or subsidence rate. In the following selection of fields, the choice has been made to illustrate the influence of the variety of geological parameters, from the simplest structure (Zakum and Umm Shaif) to the influence of a basement structure and/or reactivation on a number of fields (Asab and Bab), to a demonstration of the effects of compaction and thickness of evaporitic seals (Umm al Anbar, Neewat al Ghallen and Hail fields). The inclusion of the Bu Hasa and Fateh fields shows the detail of a structural and stratigraphic trap (rudist reef reservoir). Close to the Oman Mountain Fold and Thrust Belt in the northern Emirates, anticlinal structures are faulted and overthrust and can be illustrated by the geology of the Margham and Sajaa fields. Appendix table. D summarizes some of the oil and gas fields of the U.A.E. Zakum Oil Field The giant offshore Zakum Field, discovered in 1963 when Zakum-1 found oil in all zones of the Lower Cretaceous Thamama Group, went on stream in 1967, producing 50,000 bbl/d. The field has an area of about 500 sq kin, measuring 45 km along the east-west axis and 25 km at its maximum width towards the eastern end of the field. It overlies a west-plunging asymmetrical anticline with dips of 2-5 ~ on the steeper, northern flank, and less than 2 ~ elsewhere (Fig. 11.63). It developed as a result of ?basementtriggered diapiric salt movement, although the Cretaceous was not pierced by the evaporites. The crest of the anticline originally lay N-NE of the present crest, migrating south to its present position during the Eocene. Structural growth continues, for a topographic high is observed on the sea floor (Hassan et al., 1979; and Alsharhan, 1990).The anticline is essentially unfaulted, only near the eastern limited is there evidence of about 3 m (10 ft) of the lower part of the Lekhwair cut out, no other faults have been detected seismically or in recent wells drilled into the

590

structure. Declining well pressure to the point that free gas being evolved created a secondary gas cap led to dumpflooding in 1972-73 and margin injection wells between 1976 and 1979 to maintain production at 1,000 bbl/d per well. As of 1979, the field had produced 667 MM.bbl of 40 ~ API with a 1% sulfur content. The main production is from Zone IV, the lower part of the Lekhwair Formation, and is known as the Zakum Member (Hassan et al., 1979 and Alsharhan and Nairn, 1986) (Fig. 11.58), but production from Zone I, the uppermost unit (Shuaiba Formation), has been described by Aldabal and Alsharhan, 1989) and from Zone II (Kharaib Formation) by Alsharhan (1990). The oil/water contact in Zone IV is at a depth of 2,770 m (8,860 ft) sub-sea and 289 m (950 ft) below the crest of the structure, which has a structural closure of 328 m (1,000 ft). The greatest porosities and permeabilities (maxima 31.8% and 62 md in the case of the Shuaiba) are found over the crest, decreasing down the flanks and with depth. Porosity enhanced by leaching is interparticle, intraparticle, vuggy or moldic, but is reduced by diagenetic calcite cementation that may range from 10 to 100%. In the Kharaib Formation there are several reservoirs in each of the zones, but no hydraulic continuity. Each is underlain by dense, argillaceous limestone. They occur in the clean, well-sorted, shallow-water, oolitic, biodetrital packstone/grainstone of cyclical deposits. The cycles consist of progressive changes from deep-water facies in the west to shallow-shelf and shoal facies in each and mark a true shelf edge to the intracratonic Abu Dhabi Intrashelf Basin. The cycles are regarded as the result of sea-level fluctuation due to eustatic or effects. The top of the Thamama is a regional unconformity over which the Nahr Umr shale forms an excellent seal. Asab Oil Field The giant Asab Field is the central field of three onshore fields m the Shah, Asab and Sahil - - lying along an anticlinal trend and flanked by the Falaha Syncline to the west. The field was discovered in 1965 and went on stream in late 1973. The elongated, anticlinal structures of the fields (Fig. 11.64) is due to salt doming and growth faults, which have an aerial extent of 229 sq km with 183 m (600 ft) of structural relief at the top of the Kharaib Formation. Formation of such structural traps began in the late Jurassic in western Abu Dhabi, but developed somewhat later in eastern Abu Dhabi where the Asab Field is located. The structure is a simple, faulted elongate anticline. It is asymmetric with the northwestern flank slightly broader than the SE (Alsharhan, 1993 b) and a structural relief of 183 m (600 ft) at the top of the lower Cretaceous. Dips are all less than 5 ~. The faulting is late Middle Cretaceous to Campanian in age, and maximum uplift in the Maastrichtian occurred when the faults were no longer active. Although there is no evidence of effective communication

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Fig. 11.63 East-West structural cross-section across Zakum Field, Abu Dhabi, United Arab Emirates showing oil accumulation and regional seals. between reservoirs, faulting may have permitted lateral migration, and eastward migration was enhanced by the gradual facies changes from basinal to shelf lithologies in that direction. The reservoirs of the Kharaib Formation are located in zones B and C and consist of about 56 and 25 m (180 and 80 ft), respectively, of lime mudstones/wackestones and peloidal packstones/grainstones with porosity of 20-30% and permeabilities of 1-700 md. These sediments are sealed by overlying dense lime mudstones. The Zone B reservoir is estimated to contain 8.8 MMBO, while zone C contains 1.4 MMBO (Johnson and Budd, 1975). Sulfur content is 0.94 wt%. In its initial conditions, the reservoir crude was undersaturated by about 1800 psi. Differential degassing at the reservoir temperature of 120~ (250~ gave a solution GOR of 997 scf/bbl and a crude of 38.4 ~ API at standard conditions (Mallinson and Sharp, 1975; Alsharhan, 1993). In 1975, the recoverable reserves in the Kharaib zone B were estimated at 3 billion stock tank barrels (B STB), with an initial rate of production of 400,000 bbl/d, while in Kharaib zone C, reserves were estimated at 0.6 B STB, with an initial production rate of 60,000 bbl/d (Mallinson and Sharp, 1975; Alsharhan, 1993 b). Bu Hasa Oil Field

Oil in commercial quantity was discovered in the Bu Hasa Field in 1962, which was considered at that time an extension of the Bab Field. The field is a gentle, broad structural high formed over a reactivated basement feature. The discovery well (BH-2) bottomed in the dense unit

below the Thamama Zone B at a depth of 2,709 m (8,667 ft), encountering 39 ~ API oil in the Shuaiba Formation and in the Kharaib Formation Zone B. The Bu Hasa Structure is filled to spill point over the saddle between Bu Hasa and the Huwaila structure to the south (Fig. 11.65). The Bu Hasa-Huwaila axis is an anticline, and the Bu Hasa Field stretches 35 km (22 mi) north-south and 20 km (12.5 mi) east-west. It is broadest at the northern end and plunges to the south (Fig. 11.65). Structural relief on the field is of the order of 250 m (800 ft), with an areal closure of 538 sq km (207 sq mi). The flanks dip at 1-2 ~ No faults have been identified. Field growth began during the Albian, with most structural uplift during the Campanian-Maastrichtian and further moderate growth up to the end of the Eocene. The beds of the Shuaiba Formation, 146.6 m (480 ft), are the main oil-bearing horizon sealed by the overlying Nahr Umr shale. The Shuaiba Formation displays pronounced vertical and lateral lithologic variations generated by the development of a rudist reef complex over an algal platform (Fig. 11.66). Nine distinct petrophysical/reservoir subzones (A to I) have been identified (Harris et al., 1968; Twombley and Scott, 1975; Alsharhan, 1985a, b, 1987, 1993; Hulstrand et al., 1985) that significantly affect the reservoir mechanics. The nine distinctive units were defined by their porosity, permeability and lithology. The formation is composed mainly of rudistid and algal sediments and rudistid mounds which overly and have built up the topography on an algal platform. The position and elevation of the platform edge, combined with rising eustatic sea level, created a tendency toward both vertical and lateral growth,

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Fig.11.67 East-west structural-stratigraphic cross section in the Margham Field, UAE (modified from Mount et al., 1995 and reproduced with kind permission of Gulf Petrolink, Bahrain). and regulated the form and distribution of the rudist accumulation. The Shuaiba Formation has good reservoir quality ranging in porosity from 18-25% and with average permeability exceeding 100 md. The trap is structural-stratigraphic in the sense that although the trap is stratigraphic, with oil contained particularly in rudist buildups, the buildups occurred over basement-controlled highs. The Shuaiba rudist buildups, which show considerable facies variation, formed over an algal platform bordering an intrashelf euxinic basin. They have a rough NW-SW alignment (Fig. 11.66), and the belt includes fields in Qatar (Idd el Shargi) and Iran (Reshadat) at one end and the Yibal and Huwaisa fields in Oman at the other. In the U.A.E., in addition to Bu Hasa, the Shuaiba yields appreciable oil in the Huwaila Field.

Margham Gas-Condensate

Field

Close to the deformation front between the essentially unfolded foredeep and the complexly deformed northern

594

Oman Mountains Fold and Thrust Belt, which extends the length of the Musandam Peninsula into Oman, there occur a number of fields, including the Sajaa, Moveyeid, Kahaif, Khubai, Margham and Remah, controlled by frontal structures. As an example, the Margham Field, which was discovered in 1982 by Arco when Margham-1 flowed 34.4 MCFg/d and 2,330 bbVd of 50 ~ API of condensate from a Thamama reservoir at a depth of more than 3,860 m (10,000 ft), lies at the leading edge of a late Cretaceous through mid Tertiary west-vergent thrust front. The gas produced from the field is partly re-injected and partly used by industry. Because of seismic modelling in conjunction with data from 17 wells, the original interpretation of the field as a fault-bounded "pop-up" wedge with the Mauddud involved in the faulting, has been replaced by the idea of an east-vergent fault propagation fold (O'Donnell et al., 1995; Mount et al., 1995) created over a wedge structure propagating out of the fault belt (Fig. 11.67). The structure

Hydrocarbon Habitat of the Greater Arabian Basins is considered by O'Donnell et al. (1995) as the product of two compressional events: first, the development of a fault propagation fold, initially generated during the Late Cretaceous in response to the obduction of the Semail ophiolite, followed in the middle late ?Miocene by a tightening of the fold and thrusting of the entire overlying sedimentary section that accompanied Alpine compressional movements. The Margham anticline is cut by a number of forelimb and backlimb thrusts, and a north-northwest trending shear fault. The reservoir is located within the Lower Cretaceous Thamama Group at depth of more than 3,860 m (12,661 ft), lying at the leading edge of a Late Cretaceous through mid-Tertiary west vergent thrust front. The Shuaiba consists of shallow-shelf limestones mainly wackestones, packstones and intercalated rudist and algal bioherms. The Kharaib and Lekhwair consist of limestones deposited on a broad regionally extensive, carbonate ramp. They contain alternating cycles of shallow-water subtidal grainstones and somewhat deeper-water, mud-rich deposits. The Shuaiba is the main reservoir with porosity mostly confined to the matrix and permeability controlled by the presence or absence of natural fractures (Ernster et al., 1988). Hydrocarbon entrapment is believed to have occurred during the Late Cretaceous, although the Tertiary deformation was primarily responsible for the present geometry of the anticline. Fateh Oil Field The field was discovered by Dubai Petroleum Company (DPC) during 1966 and oil production commenced in 1969. The Fateh field is an anticlinal domal structure trending NE-SW caused by salt movement during the Cretaceous. The field is elliptical in shape measuring about 15 km (9 mi) by 10 km (6 mi) and has vertical closure of about 275 m (900 ft) (Fig. 11.68). When the production began the field had a weak water-drive, and water injection began in June 1974. The productive area of Fateh Field is about 18,000 acres (71.6 km 2) with 71% of the production from the porous Middle Cretaceous carbonates of the Mishrif Formation, and 20% coming from Lower Cretaceous carbonates of the Thamama Group and the rest from the Upper Cretaceous Ilam Formation. The Permian Khuff Formation containes H2S natural gas.The Mishrif Formation is the main reservoir and lies at about 2,440 to 2,600 m (8,000-8,500 ft). Reservoir facies in the Mishrif Formation are fine-grained, mollusk-fragment grainstones and packstones deposited in a mainly forereef environment, in which porosities average 20 to 25%, and permeabilities average 15 to 50 md. The trap at Fateh is stratigraphic and structural, formed by truncation of reef, near-reef, and forereef carbonate facies beneath a post-Cenomanian unconformity over a salt structure (Jordan et al., 1985). The superior quality of Mishrif reservoir is attributed to the effects of post-Cenomanian diapiric salt movement, whereby considerable secondary porosity developed as a

consequence of exposure to fresh water. Erosion resulted in a major unconformity, which completely removed the Mishrif from the crest of the field (Videtich et al., 1988). The overlying Laffan Shale provides the seal for the Mishrif reservoir. The Khatiyah Formation, which is the basinal equivalent of the Mishrif, is a primarily organic rich limestone and is the main source of hydrocarbons. Bab Oil Field Bab Field is an elongated unfaulted anticline, 45 km long and 28 kms wide (Fig. 11.65). The structure is symmetrical with gentle dips (less than 2 ~) throughout the field. The southem flank is wider than the northem flank, and has structural relief of about 268 m (880 ft) at the top of the Shuaiba Formation. It has an areal closure of about 1,077 sq km at the top of the Kharaib Formation. The field was discovered during 1953 by Abu Dhabi Petroleum Company (ADPC), the first well drilled in January, 1953 was dry but the drilling the second well in 1958 proved oil. The field came on production in 1963 at an initial rate of 130,000 bbl/d, but due to an increase in the gas/oil ratio with time this production rate has decreased. A water injection scheme along the gas rim and along the oil pool periphery was started in March, 1974. The main production is from the Lower Cretaceous Kharaib Formation which is characterized by transgressive and regressive carbonate cycles reflecting different depositional facies. Reservoir development and hydrocarbon accumulation in Bab Field are primarily controlled by the structural flexure, depositional setting and diagenetic porosity development. Reservoir porosity ranges from 1120% and permeability from less than 1 to 700 md. The main factor controlling porosity distribution is dissolution which is very strong on the top of the structure but decreases towards the flanks of the field. The permeability distribution is very strong at the top of the structure. The Kharaib Formation has 40 ~ API oil and a sulphur content of 1.07%. The reservoir temperature is 250 ~ F, and the initial pressure was 4,178 psig at 8,300 ft subsea. The saturation pressure in the upper part of the Kharaib (Zone B) generally decreases with depth as measurements indicate a 4157 psig at gas-oil contact, 3,850 psig average in existing producers and 2,800 psig at water-oil contact. The producing gas/oil ratio is 1,200 SCF/STB, and the formation volume factor is 1.73 RB/STB. El Bunduq Oil Field E1 Bunduq field was discovered during 1965 by Abu Dhabi Marine Areas. It is owned equally by the Govemments of Abu Dhabi and Qatar. The structure has a typical dome shape and has an areal extent of 9,300 acres above the oil-water contact. The dome is approximately 6 by 11 km trending northeast to southwest (Fig. 11.690) and is related to deep diapiric movement of Paleozoic salt, although the salt has not been penetrated by any of the field wells. Production was established in early November

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Fig. 11.68 Fateh Field, Dubai (A Stratigraphic cross-section of the Middle Cretaceous Mishrif and Khatiyah formations showing reef development (B) Structural contour map on top of the Middle Cretaceous Mishrif Formation in Fateh oil field, Dubai, UAE. (C) Schematic structural cross section (D) Regional development and depositional facies setting of the Middle Cretaceous Khatiyah and Mishrif Formations in UAE (compiled from Jordan et al., 1985 reproduced by kind permission of Springer-Verlag). 1975 from the Arab-D reservoir with approximately 30,000 bbl/d of 39 ~ API gravity oil and 1% sulphur and continued until July of 1979 when the field was temporarily shut-in between 1979 and 1984 due to excessive gas production. A water injection scheme was developed in 1984 aimed at improving recoverable oil reserves to 125 MM.bbl (Beydoun, 1988). 3D seismic data has provided a more detailed and accurate horizon and fault interpretation. A greatly increased number of faults were identified on both of new 3D seismic sections and time slices at the Thamama to the Uwainat horizons. The graben fault system at the crestal area was clearly recognized, comprising 3-4 steps faults. The maximum fault throw is about 100 ft. Several faults running NW-SE direction with throws a few tens of feet were newly encountered on the NW and SE flank areas of the field (Honda et al., 1996). The fault patterns at the Thamama, Hith, Arab, Diyab and Araej Formations are similar, since the same faults are interpreted as cutting each event (top of Thamama V, top of Arab D, top of Uwainat), terminating beneath the top Uwainat but not penetrating the Triassic section. Oil and gas accumulations were found in the Arab and Araej formations. The Arab Formation contains the most important hydrocarbon reservoirs. It is divided into four members, the lowest being the primary oil reservoir. The three upper members contain gas. The A, B and C mem596

bers are relatively thin intervals of dolomite and dolomitic limestone separated by beds of anhydrite. The D member is mainly dolomitic limestones, grading upward, from the shelf limestone of the basal Arab through lagoonal and intertidal sediments. The thickness of the Arab D reservoirs are 104 m (340 ft) and 85 m (280 ft), respectively. Sajaa

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The field was discovered in 1980 by AMOCO Sharjah when the well Sajaa-1 was tested and proved to be capable of producing 50 million cubic ft (1.4 million cubic meters) of gas and 5,000 bbl (800 cubic meters) of condensate liquids per day from Lower Cretaceous and Upper Jurassic carbonates, which form a single reservoir, sealed by the Middle Cretaceous Nahr Umr Shale. The field went on stream in 1982. The field is a retrograde gas condensate reservoir with an average porosity of 10% and permeability of 1 millidarcy. The net pay within the field ranges from 80-925 ft (24-282 m). The Sajaa structure, which is about 10 by 8 km in size, is a large north-south oriented anticline bounded on west and southwest by a major thrust faults which seal the reservoir against the Upper Cretaceous Aruma shale. The Sajaa field is not a salt induced structure but is part of the buried frontal thrust of the Oman overthrust belt (Fig. 11.70). Two major periods of thrusting were responsible

Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.69 E1 Bunduq Field of Qatar and U.A.E. (A) Structural contour map on top of Upper Jurassic Arab D reservoir (B) Major fault trends at the field (after Honda et al. 1996).

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for the evolution of the Sajaa structure. During the first episode in the Upper Cretaceous some 80 million years ago, compressional forces from the east led to the thrusting of Semail, Hawasina, Sumeini nappes and the shelf carbonates. The normal stacking order in this thrusting from bottom to top is shelf carbonate, Sumeini, Hawasina and Semail napps. The of Semail, Hawasina and Sumeini thrust sheets which involved several hundred kilometers of movement, never reached the Sajaa structure. As a result of this thrusting episode, a wedge of Upper Cretaceous and Lower Tertiary sediments were deposited in front of the thrust sheets. The second and final episode of thrusting took place during Miocene, some 35 million years ago, causing the uplift of the present day Oman mountains reactivating some of the pre-existing faults. It was during this time that Sajaa attained its present day elevation. In 1983 output increased to 52,000 bcpd and 500 million cfgpd reaching 60,200 bcpd in 1985. Production started to decline in 1986 and by 1989 it was reduced to 27,900 bcpd, 7,750 bpd LPG and 260 million cfgd (Beydoun 1988; Arab Oil and Gas Directory, 1996). In 1989, 15 wells were producing at Sajaa and in 1992, 3 more wells were completed. These encountered productive intervals of 215 and 890 ft at depths below 10,000 ft. In 1992, these intervals were brought into production yielding 15,000 bcpd and 100 million cfgpd boosting total production to 38,000 bcpd and 580 million cfgpd at which level it is currently maintained (GeoArabia, 1996). Original recoverable reserves are estimated to be as low as 109 MM.bbl condensate and 1.56 TCF gas, or as high as 400 MM.bbl condensate and 6 TCF gas.

Fig. 11.70 Sajaa gas-condensate Field, Sharjah. (A) East-west structural cross section showing gas-condensate accumulated in the Lower Cretaceous carbonate reservoir; (B) Structural contour map on top of the Lower Cretaceous Thamama Group (after Blinton and Wahid, 1983). 597

Sedimentary Basins and Petroleum Geology of the Middle East JORDAN

edge of the Arabia Sub-plate, the edge defined by the Dead Sea Rift and Shear Fault System. Despite the progress of the last few decades, the geology of the country still is relatively poorly known. Essentially, it may be divided into three broad zones: the A1 Jafr, Wadi Sirhan and Azraq

Jordan has an area of 90,650 sq km, of which sedimentary areas cover 86,000 sq km. It lies at the western

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Hydrocarbon Habitat of the Greater Arabian Basins Table 11.5. Exploration wells drilled in Jordan until 1990. Compiled from OAPEC, 1985; NRA Jordan, 1989; Andrews, 1991 (see Fig. 11.73 for well locations).

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Table 11.7. Source-rock potential in different sedimentary basins in Jordan (compiled and modified from Abu Ajamieh et al., 1988; NRA, Jordan, 1989; Beydoun et al., 1994).

basin areas, characterized by east-west striking shear faults. These are truncated to the west by the Cenozoic Dead Sea Shear Zone and cut obliquely by a sequence of northwest-southeast-striking faults (Fig.11.71), of which the most clearly defined are those of the Azraq-Sirhan Basin trend and the A1 Karak-Wadi Fiha Fault Zone, leading one to suspect that the fault bounding the Risha Basin also may be complex and that all may have an original late Proterozoic-early Phanerozoic origin from their parallelism with the Najd Fault System, and have been subsequently reactivated. Precambrian crystalline rocks crop out in the southwest, but most of Jordan is covered by a Phanerozoic mantle of sediment; an appreciable area is covered by relatively young lava flows. It is only as a result of extensive geological and geophysical mapping and the drilling of numerous exploration wells that subsurface data has helped clarify the structural and stratigraphic problems. The stimulus for the exploration was the search for both water and hydrocarbons, which led to the drilling by Pauley and Phillips of Safra- 1 in 1957. In the absence of the numerous established fields and

the more abundant data accumulated since their discovery in adjoining countries, the treatment of the hydrocarbon habitat in Jordan has had to take a different format, with the brief examination of the defined sedimentary basins, and not an examination of hydrocarbon parameters. However, this procedure does permit the identification of potential areas of interest. The generalized lithostratigraphic sequence of the Phanerozoic sediments in various parts of Jordan, shown in Fig. 11.72 reflects the sediment deposited and preserved, the dominant sedimentary facies, and the major unconformities recorded. (For more detail, see Bender, 1974; and Beydoun et al., 1994.) The Infracambrian-lowest Cambrian is dominated by volcano-sedimentary coarse clastics, over which Cambrian continental clastics lie unconformably. They consist of alternating red-brown sandstone, micaceous sandy siltstone, micaceous sandy shale, and local carbonates. During the Ordovician-Silurian, a sequence of marginal marine, fine-grained clastics, and argillaceous sediments was deposited. Major unconformity terminated Silurian deposition, but Devonian rocks are not known either in exposure or in subsur-

601

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602

nental-lacustrine deposits and rare, intermittent, marine sediments. Extensive volcanic activity took place in the north Jordan valley and in northeast Jordan during the Plio-Pleistocene. History

of Exploration

Direct natural evidence for the existence of oil in Jordan is provided by surface occurrences of oil and gas seepages, bituminous calcareous sediments, asphalt, and tar sands. Blake and Ionides (1939, cited in Bender, 1974) described a seep of liquid petroleum at Ain Umma, which is situated on the east side of the Dead Sea. Asphalt occurs in and near the Dead Sea as blocks, concretions, veins (including ozocerite veins), and cavity and fissure fillings. Oil shale is distributed widely both in outcrop and in many boreholes. The most important oil shale occurs near the base of the Upper Cretaceous Chalk Marl Formation, which crops out across much of north-central and southcentral Jordan (Abed and Amireh, 1983). Exploration mapping in Jordan was begun in 1947 by the Transjordanian Petroleum Co., Ltd., and by Pauley Oil Exploration and Phillips Petroleum from 1956 to 1960. A reinterpretation of the available geophysical, petroleum geological, and exploration-drilling results carried out by

Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.73 Location of exploration wells in Jordan. Note the concentration of wells in the Risha and Hamzah fields. this partnership led Pauley Oil Exploration and Phillips Petroleum Co. to drill six wildcat wells (four east of the Jordan and two to the west) (Fig. 11.73). From 1964 to 1966, exploration activities were resumed by MECOM Oil Co., who deepened one existing well and drilled three others, but with no positive results (Bender, 1969, cited in Bender 1974). Later, Industrija Nafte Zagreb Yugoslavia (INA) drilled four wells between 1968 and 1972. The Natural Resources Authority (NRA) drilled over 60 wells in the years 1980-1990 (Fig.11.73 and Table 11.5). The following summary of exploration drilling is based on Bender (1969, cited in Bender 1974, 1975), Abu Ajamieh (1985), OAPEC (1985), NRA Jordan (1989) and Beydoun et al. (1994). Phillips Petroleum Co. and Pauley Oil Exploration in 1957 drilled Safra-1, a dry hole on a SE-NW-striking structural high. They followed by drilling Ramailah-1 in

1958 on the structurally highest part of a broad north-25 ~ east-striking anticline lying north of Jerusalem. Slight oil and gas shows were recorded in Triassic sediments in the latter well. Suweileh-1 was drilled in 1959, 20 km northwest of Amman on a N-NE-striking structural high in the Lower Cretaceous sandstone, mapped as a symmetrical, closed anticline. Some gas shows in the drilling mud and slight oil shows in an open-hole drill-stem test at 685 m (2,247 ft) were reported. Jordan Valley-1 was drilled in 1959, on a site about 15 km east-southeast of Jericho, on the eastern side of the Dead Sea Graben. No oil or gas shows were recorded, and Halhul-1, drilled in 1959, also was found to be dry. Lisan-1, drilled in 1960 approximately in the center of the Lisan Peninsula in the Dead Sea region, had some oil shows, but was abandoned after penetrating a 3,672 m (12,048 ft) section of Tertiary rock salt without reaching its base.

603

Sedimentary Basins and Petroleum Geology of the Middle East In 1964, MECOM Oil Co. drilled Mar Saba-1 on the upper western flank of the Mar Saba anticline and found a slight oil show in the calcareous-sandy Lower Cretaceous sequence. In 1965, Azzun-1 was drilled on the flat crest of the Azzun anticline, about 20 km west-southwest of Nablus. The well was abandoned at a depth of 518 m (1,699 ft) in the Upper Cretaceous limestone, due to drilling difficulties. MECOM Oil Co. also drilled Jericho-1 in 1965 on a narrow block bordered by faults, at the western side of the Jordan Graben, and abandoned it at a depth of 1,649.7 m (5,410 ft) without oil or gas shows. In 1967, NRA drilled the test well E1 Lisan-1. The strongest oil and gas shows were recorded, even though the drilled sequence consisted of an almost impermeable alternation of salt-shale-marl, the base of which could not be penetrated. The Industrija Nafte Zagreb Yugoslavia (INA) drilled four wells between 1970 and 1971; in one, there was good to strong oil show regarded as residue after incomplete flushing of a breached Middle Cretaceous. From 1963 to 1990, about 63 wells were drilled by NRA. These finally resulted in the discovery of the small Hamzeh Oil Field in Cretaceous beds and Risha Gas Field in Ordovician clastics, both of which currently are producing. The initial production rate was 2,000-2,500 bbl/d in 1985 (Beydoun, 1988) but this has dropped to about 200-500 bbl/d (Beydoun et al., 1994). The trap in the Hamzeh Field is seismically defined, with faulted closure the principal MidCretaceous reservoir in carbonates of thin sand. Light oil was found in the Ordovician sandstone of the Wadi Sirhan area. From 1972 to 1985, no foreign company was active in Jordan; however, between 1986 and 1989, three Production Sharing Agreements (PSAs) were signed with Amoco, Hunt, and Petro-Fina, respectively, and each company drilled one well. Based on extensive, if irregular, geological and geophysical data (which includes seismic, aeromagnetic, local gravity, and magnetic survey and complete landsat imagery) technical aid assistance agreements were signed with RNA, Petro-Canada International Assistance Corporation (PCIAC), Japan National Oil Company (JNOC), and the Austrian firm OMV for evaluating this data. Amoco, with OMV, drilled two wells, but despite encouraging leads, the permits were allowed to lapse in view of economic conditions. Hambo Energy Company (South Korea) currently is active in Jordan. In 1991, the total production of oil was 146,000 bbl, and gas was 7,300,000 MCF. Output from the Hamzeh Field averaged an estimated 400 bbl/d in 1991 from the two main Cretaceous reservoirs (Hummar and Shueib formations). An average 20,000 MCFD of gas is produced in the Risha Field from the Risha Member of the Ordovician Dubaydib Formation. In 1992, four gas wells and one dry hole were reported to have been drilled in Jordan. PetroCanada continued to provide financial and technical help to NRA to develop additional gas reserves. The estimated reserves of oil is 4 MM/bbl and 215 BCF of gas (World Oil, 1993). 604

In 1996, Trans-Global Co, signed a production sharing agreement with NRA-Jordan for a 6,675 km 2 block in the Dead Sea region, Wadi Arab and Karak. It was planned to drill four wells over an initial period of four years, followed by two successive wells in two year periods. Another and similar agreement was signed by NRA-Jordan and Anadarko in 1996 coming the 16,800 km 2 Safawi block in northeast Jordan and plan to drill six wells during eight and half years.

The Sedimentary Basins and Their Hydrocarbon Potential The basis of the basin studies are the stratigraphic syntheses of Bender (1974, 1975), Abed (1982), Gilbert (1983) and Powell (1989 a & b) and are summarized in Fig. 11.71. Each basin has its individual tectonic and geologic history. The six basins identified by Bender (1974, 1975), Basha (1982), Gilbert (1983), Daher et al. (1988), NRA, Jordan (1989), Powell (1989, a & b), Abu Ajamieh et al. (1989), Andrews (1991) and Beydoun et al. (1994) are described briefly. Most have oil and gas shows, but some areas have received relatively little attention when compared with the area south of Amman where thick oil shale is known to occur. From our study and the work of previous authors listed above, it seems there generally is good to fair quality reservoir levels in the stratigraphic column of Jordan. The sandstone reservoirs occur in Infracambrian, Paleozoic, Lower Cretaceous, and Neogene beds, while the carbonate reservoirs occur in the Mesozoic and Paleocene. Paleozoic seals are claystone and shale; the Triassic seal is evaporite; the Jurassic-Cretaceous are sealed by thin shale at the source-rock level and by Pliocene salt. Horsts and tilted fault blocks and drape structures over deep-seated fault blocks are the principal hydrocarbon traps. The Ordovician, Silurian, Triassic, Cenomanian-Turonian, Maastrichtian and Paleocene are the most significant proven sourcerock units. Tables 11.6and 11.7 show the hydrocarbon habitat parameters in each basin in Jordan.

Dead Sea-Jordan Valley Basin The Dead Sea-Jordan Valley Rift Basin is part of the Levant transform fracture system made up en echelon, sinistral strike-slip faults of varying length. Although most of the movement was Neogene, it has been suggested by both Bender (1983) and Quennell (1983, 1984) that the system either overlies a late Proterozoic suture or a major basement fault. Subsidence and fill in the Dead Sea has resulted in a synrift sequence exceeding 12,000 m (47,230 ft) in thickness; the Pliocene evaporites alone may total 5,000 m (19,680 ft) (Powell, 1988). It has been known as a hydrocarbon province throughout historical times, but despite the many wells drilled in the rift valley, no major commercial hydrocarbon accumulations have been found. Indications of solid and liquid hydrocarbons are known

Hydrocarbon Habitat of the Greater Arabian Basins throughout the Dead Sea Basin from seepages and drilling results. Geochemical studies by Nissenbaum and Goldberg (1978, 1986) on asphalts and heavy oils indicate a source material of bacterially reworked algae and a calcareous source rock poor in clay minerals. Maturity depth is about 5,000 m (16,680 ft) (Abu-Ajamieh, 1985). Low to normal heat flow gradients are characteristic of the region (20-22~ but there are anomalously high values when there has been volcanic activity (40-45~ or where there is a thick Neogene salt succession as on the Lisan Peninsula where 37~ was reported. Bituminous rocks are found at different stratigraphic levels in several areas. The highest bitumen contents are in the Upper Cretaceous, euxinic facies deposits of chalk and marl. In the Lajjun area, Speers (1969, cited in Bender, 1974) described a bituminous deposit approximately 15 km wide, having a very homogeneous character and an average hydrocarbon yield equivalent to an oil shale. Asphalt has been found floating in the Dead Sea and collected in small quantities along its shores. According to Ionides and Blake (1939), a block of asphalt measuring 150 m (492 ft) thick was salvaged. A fault breccia impregnated with asphaltic residual oil was observed in the area southeast of the A1 Lisan Peninsula, where a north-northeast-striking major fault zone separates the echinoid limestone (Cenomanian-Santonian) from Cambrian shale and sandstone. Potential reservoir rocks include the Lower Cretaceous fluvial Kurnub sandstone, fractured Middle Jurassic carbonates, Triassic shallow marine clastics and carbonates and fluvio deltaics. Potential traps are associated with subsided fault blocks along the rift margins. Migration via fault planes is probable as asphalts and oil seeps are known to be associated with faulting. The structural setting of the rift is one of throughgoing N-NE-trending wrench faults intersecting northwest-trending cross faults, genetically related to the Red Sea spread center which intersects the valley at closely spaced intervals. The structure results in a series of horsts and grabens formed by subsidence accompanied by block faulting (Fig. 11.74) and forming sedimentary basins with a section which can be up to 8 km in thickness and sub-basins within the Jordan Valley-Dead Sea Rift. The grabens of the Jordanian side are generally narrower and deeper than those on the opposite side of the Dead Sea. Flanking the valley are abundant oil and gas seeps from rich Upper Cretaceous source shale and marl known on both sides. Hydrocarbons generated from these mature source rocks may have migrated upward and outward to supply the potential traps within the valley. The local structural pattern is one of en e c h e l o n folds, wrench faults, horsts, and swells and pillows in the Tertiary salt.

Azraq Basin The Azraq-Sirhan graben system in central and southeast Jordan lies southwest of the plateau basalt region. It is

a Late Cretaceous-Early Tertiary structure trending NWSE in which drilling has confirmed the presence of a thick sequence of Lower Tertiary, Cretaceous, Triassic and Lower Paleozoic clastics, the latter 2,000-4,000 m (6,56013,120 ft) thick. In that part of the basin, which extends into Saudi Arabia, Devonian follows the Silurian, however, considerable erosion preceded deposition of the Early Cretaceous which may rest upon Triassic or Lower Paleozoic. The Azraq and Sirhan elements of the basin are separated by the east-west-trending, dextral, Sawaqa Shear Fault. Possible reservoirs in the Azraq Basin occur in the Triassic sandstone, Lower Cretaceous Kurnub sandstone, Cenomanian-Turonian fractured carbonates and the Campanian Azraq sandstone. A known source rock is marl of the Cenomanian and Turonian. The Triassic and some Paleozoic rocks also may have source potentials. The geothermal gradient varies from 28 to 40 ~ km. Maastrichtian sediments contain early-matured, asphaltic oil that has suffered some biodegradation. Growth faulting is the main structural feature responsible for the development of a NW-SE-trending asymmetrical graben. The traps are structural closures controlled by the faults (Fig.11.75). A series of compressional anticlines also are found in the downthrown/northern block that trends east-west at the southern margin of the Azraq Block.

Sirhan Basin The Sirhan Basin is less productive mainly because the known Tertiary and Cretaceous fill is relatively thin and geochemically immature. The potential source rock is the Upper Cretaceous bituminous marl. Well-known as a source rock is the thick, widespread Silurian shale, which tends to thicken toward the southern and eastern parts of the basin. The lower Paleozoic sandstone may provide reservoirs in which porosity and permeability have been secondarily enhanced. Potential traps are those associated with basement fault control and synsedimentary faulting, and their types are horsts and arches formed by intersecting fault trends, together with drape and rollover features in the overlying sedimentary rocks. Growth faults of modest size fringe the northern and eastern margins of the basement-controlled block. A typical trap thus would be a structural closure controlled by drape or fault sealing, and a stratigraphic-fault combination trap on the downthrown side of the fault block. Petroleum migration can be envisaged in such a location from the Upper Cretaceous source rocks in structural lows to the traps.

North Jordanian Highlands Surface mapping and geophysical surveys have established the presence of numerous structures controlled by basement faults with a variety of orientations. Flexuring and tilting commonly is associated with the faulting, and comparatively complex structures have developed. The

605

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606

Hydrocarbon Habitat of the Greater Arabian Basins regional north plunge is interrupted by horst blocks, anticlinal structures, and marginal swells. The northern highlands are characterized by a broad arch, where the generation of oil is shown by the existence of oil seeps in spring waters in the area flanking the Ajlun Dome. Reservoirs are present in the Triassic, Jurassic, and Lower Cretaceous sequences, and slight oil and gas shows have been reported from the Jurassic Zerqa Group. The Triassic section consists of an alternating sequence of carbonate reservoir rocks and shale/anhydrite source and seals. Upper Cretaceous bituminous shale and limestone overlain only by relatively thin recent sediments are not likely to have reached geochemical maturity. AI Jafr Basin

The present A1 Jafr Basin is a wide, roughly circular depression with a Quaternary alluvial fill surrounded by Mesozoic/Cenozoic deposits. This basin is superimposed upon an Early Paleozoic or Late Proterozoic NNW-SSEtrending graben that received a thick sequence of early Paleozoic shallow-water clastics. Within this sequence, there is a widely spread, thick development of early Silurian shale that forms an excellent source rock. Early Mesozoic uplift and erosion removed all of the late Paleozoic sediment and Late Cretaceous and early Tertiary marine sediments rest unconformably upon the early Paleozoic succession (Fig. 11.71). Risha Basin

The Risha Basin area of northeast Jordan (Fig. 11.75) located on the western side of the Rutbah Arch is a late Paleozoic inverted basin, partly stripped of sediment before being buried under a Mesozoic uniformity. The Paleozoic clastic sequencethickens eastwards up to 6,500 m (21,320 ft) and includes rich Silurian source rocks. The

presence of Triassic evaporites provides an effective seal. Th discovery of the Risha Field was made following detailed seismic and interpretation of the 16 wells drilled by the NRA. Horsts with gentle dip reversals were identified within the generally eastward dipping section (Fig. 11.75). Large-scale stratigraphic pinchouts and probable sand lenses within the shale section, which may form suitable traps, also exist. Geothermal gradients rise from 30~ to 50~ The higher figure is regarded as the more typical. Thus, although discoveries and production in the Risha Field are small, this may be more a reflection of the exploration effort to date. What is now needed is more exploration, primarily seismic, to select potential areas and structures. The region, however, seems unlikely to have the potential of the surrounding areas largely because of its paleogeographic history. Basalt Plateau

Large areas of the northeast Jordan Plateau are covered by Mesozoic rocks overlain by no more than 100 m (328 ft) of basalt. On the eastern flank of the basalt cap, a gentle regional dip towards the west is seen in the Mesozoic section, which also thickens in the same direction. On the western flank, the Mesozoic is cut by a series of northtrending normal faults, down throwing to the west, with east-dipping tilted Mesozoic fault blocks disappearing under the basalt cover. As the region is underlain by a Mesozoic section, there is a possibility that high-quality Cretaceous source rocks may be feeding oil into Cretaceous and perhaps Jurassic carbonate and sandstone reservoirs. The heat of the basalt may have helped mature the Cretaceous oils during basalt emplacement in the Quaternary times (NRA, Jordan, 1989).

607

Sedimentary Basins and Petroleum Geology of the Middle East

SAUDI ARABIA Saudi Arabia has an area of 2,240,000 sq km. It consists of the shield area to the west and the lowland bordering the Arabian Gulf to the east. The climate is a typical desert climate with relatively few oases. The eastern edge of the shield, which served as the type area for many formations, is bordered by a scarp where the principal Mesozoic exposures are found, including type areas for many formations. Central Arabia is a topographic high that separates the better-known northern basins, the Tabuk and Widyan, from the large desert wastes of the Rub A1 Khali, the "empty Quarter." The first concession was made to Standard Oil of California in 1933 (Beydoun, 1988) and was due to run for 66 years. The first well was drilled in 1935. Texas Oil acquired a 50% share of the concession in 1937. Early in 1938, Dammam-7 struck oil in Jurassic rocks, and exports began the following year. During the same year, the concession agreement was extended to cover virtually the entire sedimentary area, although subsequently, the area was scaled back through relinquishments. Further discoveries were made in 1940, and development continued through the years of WWII. The company was renamed ARAMCO in 1944 and was joined in 1947 by Standard Oil of New Jersey (Exxon) and Standard Oil of New York, Socony Vacuum (Mobil). The 250 km long supergiant Ghawar Field was discovered in 1948, and subsequent discoveries made the country one of the largest producers in the world. The Saudi Arabian government subsequently awarded a 60-year onshore concession to Getty covering its undivided half-interest in the Neutral (now the Divided) Zone, which is shared with Kuwait, and an offshore concession was awarded to the Japan Arabian Oil Company in 1957-58. A subsequent change in oil policy led the Saudi government to acquire a 25% share of ARAMCO in 1973, increasing to a 60% share the following year; in 1980, it took 100% control backdated to 1976 and retained ARAMCO as the operator. The country has the world's largest known hydrocarbon reserves, even excluding the most recent finds in central Arabia. According to one estimate made before the central Arabian finds had been evaluated, the reserves stood at around 170 B.bbl with 126 TCF of gas, excluding the Permian non-associated gas. The principal production, from rocks of late Jurassic age, exceeded 3 B.bbl in 1976, but was scaled back in accordance with OPEC requirements. In 1994, production averaged 7,973,360 BOPD from an estimated 260 B.bbl of recoverable oil (World Oil, 1995). Husseini (1996) reported that due to global energy demand Saudi ARAMCO production grew from 38 B.bbl of oil equivalent in 1974 to over 54 B.bbl of oil equivalent during 1994. Over 10,000 km 2 Of 3-D seismic were shot since 1990 together with hundreds of exploration and development wells drilled including numerous horizontal

608

wells. Since 1990, Saudi ARAMCO has replaced its cumulative oil production and added new reserves and has increased its gas reserves by 20.7 TCF of which 9.7 TCF are non-associated. The principal oil production is from a few giant/supergiant fields; although many smaller fields are known, they remain to be developed. The principal source rocks for this oil are Jurassic, and it is convenient to treat the Saudi Arabian oil fields in three categories, the Mesozoic and the more recently discovered Paleozoic and Cenozoic fields. The location of Saudi Arabia and the major fields is shown in Fig. 11.76.

Tectonic and Stratigraphic Framework The basic tectonic controls of the Arabian Plate have been related to the events occurring at the tectonically active margins; there are compressional terrains along the northern and eastern margins of the plate, specifically the Simple Fold Belt of southeastern Turkey and the ZagrosOman Fold Belt. The Arabian Platform, which now forms northeastern Saudi Arabia, remained relatively undisturbed throughout most of the Phanerozoic and received widespread clastic and shallow-marine carbonates, which can be correlated across the entire platform with varying degrees of certainty. An examination of the individual major stratigraphic sequences indicates that the uplift and subsidence patterns and lithologies were controlled by the tectonic deformation active at the plate margin. For the purpose of a consideration of the Mesozoic hydrocarbon development, the history may begin with the final amalgamation of the Pangea during the Hercynian, a time marked by the development of a major unconformity on the Arabian Plate, the Great Hercynian Unconformity. Grabowsky and Norton (1995) have illustrated the location of the Arabian Plate by means of paleogeographic maps for the late Permian to the middle Eocene time interval. Although the history of the Arabian Platform is relatively simple in overall pattern during this time interval, it is marked by the development of sequences separated from one another by periods of nondeposition. Each eustatic sequence is marked by a basal transgressive succeeded by highstand deposits often capped by a non-depositional surface where there may be signs of erosion or karstification. The sequences can be arranged into stacks separated by regional unconformities. The trend of the facies belts changed from approximately east-west in the late Jurassic to NW-SE during the deposition of the latest Tithonian anhydrite to a more nearly north-south trend during the early and middle Cretaceous (Grabowsky and Norton, 1995), reflecting a change from the northward tilt of the Arabian Platform to a tilt in an easterly direction prior to Turonian plate collision. The collision marked a fundamental change in the history of the region more clearly evident during the Cenozoic history of the region. The sedimentary section in central and eastern Arabia reaches a thickness of more than 8,000 m (26,240 ft) and

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Fig. 11.77b, Phanerozoic lithostratigraphic section and hydrocarbon parameters in the Mesozoic-Cenozoic sediments of Saudi Arabia.

610

Hydrocarbon Habitat of the Greater Arabian Basins can be subdivided into major cycles (Fig. 11.77). Each cycle is characterized by a predominant lithology and is bounded by major unconformities that disappear toward the basin center in the east, where sedimentation was continuous. The Cambrian-Carboniferous is dominated by the fluvial, lacustrine and deltaic sedimentation that prevails in most of the sequence, excluding the early Silurian marine shale and the Devonian lagoonal carbonates. Permian and Triassic rocks consist of alternating marine and nonmarine clastics with a thick carbonate section in the lower and middle parts. Lower and Middle Jurassic rocks comprise marine shale interbedded with shelf carbonates and thin layers of sandstone. The Upper Jurassic and early Lower Cretaceous rocks form a sequence of shelf carbonates with alternating evaporite and cyclic marine deposits near the end of the Jurassic. Late Lower Cretaceous rocks are represented by coarse fluvial clastics in the north and marine shale and limestone in the south. The Middle Cretaceous beds consist of thick deltaic and shallow-marine clastics in the north, alternating with marine carbonates and shale in the east. In the south, shale predominates with thin, interbedded carbonates and clastics. Upper Cretaceous to Eocene rocks are shelf carbonates with evaporite intervals. Miocene and Pliocene layers are formed by shoreline calcareous sandstone with subordinate sandy limestone interbedded with fluvial and eolian sandstone. The Red Sea Basin s e n s u stricto began with the formation of a gulf north of Jeddah during the Upper Cretaceous, presumably along an older fracture in the basement of the African-Arabian Shield. Sedimentation began during the Eocene with the deposition of clastic beds in a marine and littoral environment. Tectonic movements during the Oligocene and Lower Miocene formed the Red Sea Graben, enabling transgression, first from the Mediterranean and later from the Gulf of Aden. The Miocene sediments in the north, marine sandstone and shale correspond to the Infra-Evaporite Series found in the southern Red Sea. After the Middle Miocene, the Red Sea Basin became restricted and isolated, and thick evaporite and salt layers (Evaporite Series) were deposited. Finally, the cycle terminated with a continental sequence of Pliocene and Pleistocene age (Fig. 11.78).

Hydrocarbon Systems The greater part of the Arabian Basin is located in Saudi Arabia and is one of the world's major oil-producing areas, holding approximately 26% of the known oil reserves, of which two-thirds are found in Jurassic carbonate reservoirs. Production is drawn mainly form Jurassic and Cretaceous rocks on the northeastern flank of the Central Arabian Arch. The arch appears as a well-defined structure that originated during the Precambrian and influenced all subsequent sedimentation. Most fields in Saudi Arabia are in large anticlinal structures that strike north-south and probably developed as drape folds over reactivated base-

ment uplifts (Fig. 11.79. The exceptions are structural highs with a more circular pattern in the eastern part of the producing area, which probably are related to halokinetic movement of the Infracambrian salt (Edgell, 1992). Optimal conditions for oil generation and preservation, thick, oil-prone source rocks, extensive reservoir and excellent seals, existed during the late Jurassic. Most of the oil is derived from the thermally mature Jurassic (Callovian and Oxfordian) carbonate rocks that charged late Jurassic reservoirs by vertical migration. Extensive migration was prevented by the overlying evaporite seals such as the Hith evaporites. The limitation of the Cretaceous clastic and carbonate reservoirs in the northeastern part of the area probably is a reflection of the restriction of thermally mature Cretaceous source rocks or the lack of locally subjacent evaporite seals that allowed charging from Jurassic sources. The source-rock sediments accumulated in three basins, the Gotnia, Arabian and the southern Arabian Gulf (Fig. 11.80), which developed over the passive margin of the Arabian Plate. The Arabian Basin, shallower than the Gotnia, was separated from it and from the southern Arabian Gulf Basin by highs that restricted circulation within the basin. This allowed the development of anoxic conditions under which large quantities of organic matter, mostly algal, were preserved. Water depths within the basin were never great, probably in the order of a few tens of meters. Cyclic changes in sea level allowed the accumulation of high-energy shallow-water grainstone shoals and dolomitic limestone facies (the reservoir facies) near the basin margins, passing into organic-rich lime mudstone towards the center of the basin. The shallowing-upwards sequence led to the formation of evaporites completing the source-reservoir-seal sequence. Four such sequences are reported in the Arab Formation; the evaporitic facies formed the seal for the hydrocarbons that accumulated in the high-energy shoal deposits charged from the organicrich shale and mudstone in the basin center. The several elements of the Jurassic hydrocarbon system have received individual treatment (Ayres et al., 1982; Alsharhan and Magara, 1994; Cole et al., 1994 a & b). The base of the Tuwaiq Formation to the base of the Hanifa, and the top of the Hanifa to the base of the Lower Jubailah Formation, provide the thickest source-rock facies of thin, laminated, dark-grey to black, organic-rich, peloidal carbonates with dominant lamalginite and subordinate vitrinite and inertite. The most important reservoirs are to be found in the Arab Formation, where they are lettered A to D from the top down. Each reflects a shallowing-upwards cycle from grainstone to an evaporite cap. In the Jurassic, the evaporitic sediments provide the best seals. Although not as important as the Jurassic system in northeastern Saudi Arabia, the Cretaceous system is an important contributor to the overall hydrocarbon yield. The only sediments that qualify as source rocks are the rocks of the Berriasian-Valanginian Sulaiy Formation in the northeastern part of the area, an area in which significant oil accumulations are found. The reservoir and source rock potential is to be 611

Sedimentary Basins and Petroleum Geology of the Middle East

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found in the carbonate and clastic sediments of the Wasia Group. The Cenozoic history of rifting in the Red Sea-Gulf of Suez, with the associated sedimentation, created the potential for the development of hydrocarbon resources. Although this has been fully realized in the Gulf of Suez, discoveries in the Red Sea region are much more scanty, despite numerous surface oil seeps indicative of oil generation. The syn- and post-rift Neogene sequences containing source, reservoir and seal rocks are widely distributed, but pre-Neogene rocks occur less frequently. Thus, hydrocarbon plays are mostly in Neogene rocks, with traps provided by rotated basement fault blocks and horsts in the pre-evaporite sequence and by stratigraphic pinchouts in the post-evaporitic beds. Four undeveloped gas/condensate and dry gas accumulations have been discovered in the Midyan Sub-basin. Since the stratigraphy of the Gulf of

612

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11.78, Lithostratigraphic section for the Red Sea basin of western Saudi Arabia. Petroleum system events are plotted for source rocks, reservoirs and seals. The source rock geochemical analysis of the Jaizan and Midyan subbasins are also plotted (complied from Cole et al. 1995, w i t h permission from Gulf Petrolink,Bahrain).

POTENTIAL - (SR,R, S)

Suez is similar to that of the Red Sea, the potential for significant finds cannot be ignored. The Saudi Arabian side has the wider shelf, but it is poorly explored. Two Red Sea sub-basins (Midyan and Jizan) are attractive from the exploration point of view. Despite their separation, the Midyan Sub-basin at the junction of the Red Sea and Gulf of Aqaba in the north and the Jizan Subbasin in the southern Red Sea close to the Yemen border, the regional geology of the two is similar. The relative lack of published data makes it convenient to treat the two areas together. Reported seepages are recorded in two areas: in the vicinity of Barqan in the north and around the Darsan and Farasan islands and the adjacent onshore basin margin in the south. In other areas of the Saudi Arabian coast, reports of seeps are few and seldom confirmed. Seeps on the islands led to the drilling of a number of shallow wells in the 1920s and 1930s.

Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.80 Location of the Jurassic intrashelf basins (left) showing the Arabian basin (A) the southern Arabian Gulf basin (B) and the Gotnia basin (C) (see Murris, 1980; Alsharhan and Kendall, 1986). Source rock isopach map (fight) showing thickness of source rock having greater than 1% TOC (contours in meters) (modified from Ayres et al., 1982) ",,

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Fig. 11.79 Simplified geologic map of central and eastern Saudi Arabia showing the main structural trends of oil fields.

Paleozoic Formations

Throughout North Africa and the Middle East, the organic-rich early Silurian shale, the Tannezufft of Libya and the Qusaiba Shale of the Qalibah Formation in Arabia, have proven to be a majo r source rock, particularly the basal "hot shale." By means of their contained graptolite and chitinozoan fauna, the regional stratigraphy of this time interval is well-established and indicates the rapid transgression of the post-glacial seas over the Arabian Plate in early Rhuddanian time. However, it is only in the last two decades that the importance of this horizon as a petroleum source rock has become as fully appreciated in the Middle East as it is in North Africa, for it is regarded as the source of the non-associated gas in the North Field of Qatar and of the oil in central Saudi Arabia. This consideration has been established from the high degree of similarity in the isotope and biomarker distribution between the Paleozoic reservoir oils and the Qusaiba source rock, which show much closer correlation than with extracts of other potential source rocks. Arabian super-light crude, 43-45 ~ API oil with low sulfur, was discovered in Unayzah and basal Khuff clastics in 1989, where it is trapped in structural closures controlled by faults or drape over underlying fault blocks (McGillivray, 1994). Eleven oil and gas fields have been discovered between 100-200 km south of Riyadh and 100 613

Sedimentary Basins and Petroleum Geology of the Middle East km east of the margin of the Arabian Shield. Geochemical analysis of the black to dark-gray shale from the Hanadir, Ra'an, Qusaiba, Jauf, Unayzah and Khuff formations indicates that the Qusaiba Member ("hot shale") of the Silurian Qalibah Formation has a maximum TOC of 6.15%, followed by the Jauf with 3.7, the Unayzah with 2.10, the Khuff with 1.34, the Hanadir with 1.13 and the Ra'an with 0.68%. The maturity of the analyzed rock samples was high (2.29-2.47% R o) (Mahmoud et al., 1992). Gas chromatography-mass spectrometry selectedion monitoring techniques for detecting sterane, terpane and monochromatic and triaromatic steroids showed that all biomarkers were in very low concentrations in these high-gravity oils. Only steranes and diasteranes, analyzed by metastable-reaction-monitoring gas chromatographymass spectrometry, were present in sufficient concentrations to be used for correlation. As shown in Fig. 11.81,

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Fig. 11.81 Biomarker distribution of Paleozoic oil and source rock bitumen extracts from Saudi Arabian fields (after Mahmoud et al. 1992, reproduced with permission from AAPG).

614

the Qusaiba "hot shale" showed a correlation with the Paleozoic oils based on C27-C29 steranes and diasteranes. Historically, the Qusaiba Member was treated as a homogeneous sequence, until high-resolution, biostratigraphic data and detailed source-rock analysis of samples from the northwestern part of the Nafud Basin, where the unit is only about 3 m (10 ft) thick, show it to have been formed under repeated anoxic and oxic conditions (Aoudeh and A1-Hajri, 1990, 1995). However, where the unit exceeds 31 m (100 ft) in thickness, only anoxic conditions were recorded. The Qalibah Formation shale as a whole is a thick sequence of massive, dark-grey shale widely distributed over the Middle East. An isopach map of the Qusaiba Member indicates it was formed in two subbasins surrounding a local high (Fig. 11.82), and the same pattern can be seen in the distribution of glacial channels in the pre-Qusaiba rocks, where the basal Qusaiba shale is missing. The general paleogeographic pattern is of a major, rapid transgression during the early Llandoverian, followed by a regressive phase of a prograding delta, where the succession of facies pass from outer-neritic Qusaiba, inner-neritic Sharawra and nearshore to fluvial conditions of the Tawil sandstone (Aoudeh and A1-Hajri, 1995). Studies by Cole et al. (1994b) on the basal Qusaiba Member shales of the Silurian Qalibah Formation from northern Saudi Arabia which were summarized here have shown that these shales are organic-rich and have excellent oil-generating potential. Based on the gamma-ray log response (Fig. 11.83), the Qusaiba Member of the Qalibah Formation was divided by Cole et al. (1994b) into three distinct zones. The low gamma-ray response, or cool zones, is not considered a source rock. Most shales within this zone were deposited under oxic conditions. The moderate gamma-ray response, or warm zone, contains moderate to excellent source rock quality. The shales from this zones were deposited under primarily dysoxic conditions, but source rock quality in the basin. The hot shales were deposited under dysoxic to mainly anoxic conditions, but again, source rock quality is controlled by position in the basin. Table 11.9 summarizes the % TOC and $2 yields for the gamma-ray response zones. Fig. 11.84a shows the distribution of the total source rock package in northern Saudi Arabia (Nafud basin) assuming that the entire warm plus hot zones represent the source rock package and that all shales with greater than 1% TOC would contribute some hydrocarbons to the system. A thick source rock package developed west of the Jawf Sub-basin during early Silurian time. Fig. (11.84b) shows regional distribution of the hot gamma response zone and the area where TOC exceeds 3%. Again, a thick source rock package developed west of the Jawf Sub-basin, with the depocenter located in the Tayma area. Most of the basal Qusaiba source rock has mixed oil/gas-prone to oil-prone potential, except for the southeastern part of the Nafud Basin. The basal Qusaiba shale in this locality is mostly gas-prone. A regionally extensive basal Silurian source rock exists in the northern region of Saudi Arabia. The thickest interval

Hydrocarbon Habitat of the Greater Arabian Basins

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Sedimentary Basins and Petroleum Geology of the Middle East

Table 11.8 Source rock summary data of the Silurian Qusaiba Member in northern Saudi Arabia (after Cole et al., 1994b). Immature Qusaiba Member Shales: Cool Gamma-Ray Response Zone %TOC $2 Yield average: maximum" minimum" number of samples:

0.72 2.85 0.25 240

Warm+HotGamma-Ray Response Zones %TOC 4.17 20.17 0.42 206

1.22 11.60 0.01 240

$2 Yield 19.93 86.78 1.00 206

Mature Qusaiba Member Shales: Cool Gamma-Ray Response Zone average: maximum: minimum: number of samples:

%TOC 0.70 3.33 0.22 149

Warm+Hot Gamma-Ray Response Zones %TOC $2 Yield

$2 Yield 0.58 5.93 0.00 149

5.25 11.91 0.50 24

6.78 17.62 0.15 24

% T O e = total organic carbon (wt.%) $2 yield = $2 yield (mg HC/g rock) from Rock-Eval pyrolysis Total Organic Carbon (%) >5%

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Fig. 11.84 Isopach maps (in feet) for the Silurian basal Qusaiba shales in Nafud Basin of northern Saudi Arabia. (A) Isopach map showing the regional distribution of total organic carbon (wt%) (after Cole et al. 1994b). (B) Isopach map showing the overall potential as based on hydrogen indices using a minimum of 3.0% TOC (after Cole et al. 1994b). 616

Hydrocarbon Habitat of the Greater Arabian Basins gest deposition occurred under varying anoxic to dysoxic conditions. Similarity between the Tayma-2 and Tabuk-1 are apparent in the fragmentogram fingerprints and in specific ratios. The isopach thickness distribution of the warm plus hot basal Qusaiba source rock package and is annotated to show the regional depositional environments (Fig. 11.86). The Qusaiba shale in the Tayma area was deposited under

is located west of the Jawf Sub-basin and thins in the graben itself. This thinning is caused by the environmental and structural conditions during deposition. Tricyclic and hopane data (Fig. 11.85), from representative Qusaiba extracts from the Tayma-1, Tabuk-1 and Kahf-1 wells, and the saturate fraction GC-MS fragmentograms, show that the basal Qusaiba source rocks were derived from the same type of organic matter, but specific biomarkers sug'

m/z 191 Hopanes Tabuk--1 W e l l

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Tricyclics

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~. '

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Low Molecular Weight Steranes

i

i

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~ 1

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SAUDI ARABIA \.,

yma

~,- - - --\ ~'._".._".-.:-.:-:N

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Dysoxic to Anoxic black shale and oxic grey shale I----'_--~Mostly,Dysoxic and ' - --" Anoxicin lower part (Grey vs. Black shale}

Fig. 11.85. Representative rn/z 191 (hopanes + tricyclics) and m/z 217 (steranes) fragmentograms determined from the saturate fractions of total soluble extracts of the Silurian basal Qusaiba shales from the Tabuk- 1, Tayma- 1 and Kahf- 1 wells in Nafud basin of northern Saudi Arabia (after Cole et al. 1994b).

~

Oxic to Dysoxic shale

~'~

Mostly Dysoxic shale

Fault 0

Fig. 11.86. Map showing the regional distribution of depositional conditions for the basal Silurian Qusaiba warm + hot shales in Nafud basin of northern Saudi Arabia (after Cole et al. 1994b).

50 km

617

Sedimentary Basins and Petroleum Geology of the Middle East

EAST !

WEST

GHAWAR

ABQAIQ~ FORMAT{ON

" ^ ^ ^ ^ ^ ^ ^ ^ ~" ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ X' ^ ^ ^ ^ ~ ^ ^ ^ ^ ^ ^ ^ ^ ^ A ^_~__^_ ^ ^A ^_^_^^ ^ ^ A ^_^.^ ~,^.^.^ 0_A_ ^_^_^ 0^^^^^^^^^^^^^~ A h.^_ . . . . . . . . . . . . . . . ^. .^^^^ .. ^^~^^^,~^^^^^^^^^^^^^^^^^^^^^^^^ ~ X,,X^,C-,~%-",~-"x -^- ^ ,, ~-^ ,, "^ ",,."-,~"^^",~"-~,--,,---,,--,,--,,--,,-,,---a- -,,- -.,- ~ - ~ - - ~ - - ~ ~ , - - , ~ - - , C - - - , = ~ - - ~ - ~ i~1':.?', .~.".Y.XI"j ~i~"i' ~.ii i/,I'L'X~"".'.X.L'./"ji"~<.'i"j~'.'J'~':'.J~l"..:'.J"i jI~C J..x~.".6~.c". '.j~ii~::','~.i.i.h.' i I'XL'.~ii.-j~"X=J.ih.'ji'.x. 'l.xJJ~-'.".i:'.~j'-jJ.~~'.!1~

HITH ARAB

........... """" "" ""-" """"'""'" """. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ='~" " """"" ;'"" '""- - ~ - " : - '" " ....JJUBAILAH i.:.." ":'.'."..'i.'..':.':-.: ".'.-~"".:." ~ ..-..-:--77.::".." " ; i ' ; ' " "'"'"' :"-"~""""'"" : "'""':"'"" " : ' " ' " " ~ : " " ' . ' " : " ~ HANIFA , ///f, / ! ! ! ! I !1/_l./_l~1111111111 I I I ! / / 9/ / / z ~ TUWAIQ

DHRUMA {AAAAA]Anhydrite

~ 7 ~ Source rock facies

1}i".::'i:]Porous grainstone facies

~

Non-reservoirs

-~ Well 9 Oil accumulation

Fig. 11.87, Diagrammatic cross section showing stratigraphic position of reservoir, source rocks and seal facies within Jurassic of Saudi Arabia (after Ayres et al. 1982, reproduced with permission from AAPG). essentially uniform anoxic to dysoxic conditions in a highly productive possibly sediment-starved sub-basin of the greater Nafud Basin. The high TOC content and very oil-prone HI confirm that the immature basal Qusaiba "hot" shale represents high-quality Type II source rock. Toward the proximal edges of the basin, the source interval generally decreases in thickness and quality. Tabukl towards the west, the source interval remains thick, but source quality has significantly decreased. The depositional environment has shifted from anoxic at Tayma to dysoxic at Tabuk (Cole et al., 1994b). The Qusaiba shale generated hydrocarbons throughout the Mesozoic and again during the late Tertiary, interrupted by Eocene uplift of the southern part of the Arabian plate. Oil generation began during the Triassic in the region of the present-day Arabian Gulf, moving south into the Rub A1 Khali by the late Cretaceous. The rate of oil generation declined through the Mesozoic prior to the major growth in trap capacity during the Tertiary. Gas saturation presumably occurred as the rate of oil generation declined and continued to form during the phase of increasing trap capacity during the late Tertiary, resulting from the Arabia-Eurasia collision, presumably displacing previously reservoired oil (Bishop, 1995).

Jurassic Formations The Mesozoic source-rock facies in eastern Saudi Arabia may reach a thickness of 152 m (499 ft) and extend from the base of the Jurassic Callovian-Oxfordian Tuwaiq Mountain Formation to the base of the Hanifa Formation and from the top of the Hanifa to the lower Jubailah Formation. These basinal facies consist of laminated, organicrich lime-mud wackestone that grades up into organicpoor, bioturbated lime wacke-packstone. The Dhruma Formation passes conformably up into the Callovian-Oxfordian Tuwaiq Mountain limestone, an organic-rich carbonate source rock in northern Saudi Ara-

618

bia with a TOC content averaging from 2 to 5%. The strati graphic position and isopach is shown in Figs 11.80 and 11.87. The depositional environment is interpreted as a restricted intrashelf basin separated by carbonate grainstone shoal from the open-marine environment of the Tethys Sea to the east. The presence of coccoliths, ammonites and fine shell debris shows that the bottom water of the basin was not toxic to many organisms. Because the thicknesses of the basin facies are little greater than those of the grainstone shoal, the differential subsidence rate cannot have been important, and the presence of disrupted and reworked beds suggests that weak currents were occasionally important, presumably at times when open sea contact was less restricted. The bitumen content of the Tuwaiq Mountain Limestone is high and may exceed the kerogen, "which may indicate mobilization and migration of bitumen within a highly oil-prone source rock" (Ayres et al., 1982). The kerogen in the source rock is predominantly amorphous alginite, and maturation follows the type II path (Fig. 11.88a). The area within the Arabian Basin where oil generation can be expected on the basis of maturation calculations is shown in Fig.11.88 b. Maturation and migration occurred in the early Tertiary (Ayres et al., 1982). The geochemistry of the Jurassic source rocks was described by Cole et al. (1994) based upon TOC, RockEval pyrolysis, total soluble extract and kerogen 813C isotopic composition of more than 600 samples from the Khurais, E1 Haba, Ghawar and Abu Hadriya fields. These fundamental source-rock data for samples from the Hanifa, Tuwaiq Mountain and Dhruma formations are summarized in Table 11.9 of these, the Tuwaiq Mountain Formation is the thickest and most extensive. As with increasing maturity, the hydrocarbon potential of the remaining organic matter decreases; analysis of relatively immature samples provides a better estimate of the hydrocarbon potential of the source rock. Data from

Hydrocarbon Habitat of the Greater Arabian Basins

g

.

N

/g

IRAQ IRAN

/kUWAi;

5

i 9

~~

100

""...

~

9. /

"% ~..~...~:

il

'""

Fig. 11.88 Maturation of hydrocarbon in the Callovian-Oxfordian source rocks in Saudi Arabia. A. Probable thermal-maturation path (after Tissot et al. 1974) for kerogen source rock. B. Maturation levels based on Lopatin's time-temperature index ('ITI) for source-rock facies (after Ayres et al. 1982, reproduced with permission from AAPG).

% 9l . . ~ / ' . . .

~

~

I'-"~ t.

..-..'.

\ SAUD! ARABIA

I''~ % I

0

80 km

"x,

........ isorank 9/o Ro

I I

Oil field

0.O5

12 25

50 1oo

0.1

0.15

02

025

200

Table 11.9. Comparison between the Jurassic Hanifa and Tuwaiq Mountain source rocks, the Arab and Hanifa reservoired oils, and the Permian reservoired oils in Saudi Arabia using selected chromatographic, carbon isotopic, and biomarker parameters (after Cole et al. 1994a, and reproduced by kind permission of the Canadian Society of Petroleum Geologists). Khuff Formation

Source Rocks

Arab and Hanifa Formation Oils

API Gravity Sats. vs. Aromatics vs. Resins vs. Asphaltine pristine/phytane sulfur (%)

not measured S1.0%

25-35 S=A>R~A <1.0 >1.0%

>40 S>A>R>A

Carbon isotopes

-25.3 to-26.7 -26.6 to-27.8

-26.1 to -27.8

-28.0 to-30.5

Most

Most

No

No

No

Yes

Most

Most

Rare

Hanifa and Tuwaiq Parameter

Mountain

Oils

1.8-2.2 <0.2%

Biomarkers: C29 norhopane ~C30 hopane abundant 17 ct(H)diahopane Full Extended Hopane Range 2a-methyl- 17a(H).2113(H)-hopane Hexahydrobensohopanes Present C24 Tetracyclic >>> C25 or C26 Tricyclics Extended Norhopanes Present Extended Tricyclics Present Sterane distribution Diasteranes

Yes

Yes

No

Yes Yes

Ues Yes

No No

Yes

Yes

No

No

No

Occasional

C293C27>C28 Low to High

C29>C27>C28 Low to High

C29'C27>C28 Moderate to High

619

Sedimentary Basins and Petroleum Geology of the Middle East

u~

FORMATION

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9

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Sl YIELD

$2 YIELD

' 460 ' 860

HYDROGENINDEX

Fig. 11.89, Total organic carbon (%TOC), $2 pyrolysis yield (in mg HC/g rock) and hydrogen index (HI; in mg HC/g TOC) distributions in the Jurassic section for a representative well from the Khurais field. Note the thick Tuwaiq Mountain section that is enriched in organic carbon, has excellent pyrolysis yields and is highly oil-prone (after Cole et al. 1994a, reproduced with permission from Canadian Society of Petroleum Geologists). BO' '

9

~o~

10-

3sJ

60-

#

50-

o/

a,O-

~o9

30-

2010-/

3025-

9Baker lker tba 9Haba Jaham 9Khurais-A o Khurais-B QGhawar 9Abu

,r

7~

l

y

i

tO-

9

~olff,.* 9

15-

~

9Haba ~ daham Khurals-A : Khurais-B

~

10

Abu Hadriya 0

i~,~~, TOC %

3

4'

s'

6

~

TOC %

Fig. 11.90. $2 pyrolytic yield (in mg HC/g rock) versus %TOC for the Jurassic source rock interval in the Arabian Basin. (A) The plot shows a slope-derived H1 of 665 for this source rock where immature (after Cole et al. 1994a). (B) Hanifa Formation, this plot shows a slope-derived H1 of 640 for the oil-prone, organically-enriched source rock where immature. However, as shown in the diagram, the Hanifa is much more variable in source rock quality than the thicker source rock package analyzed from the Tuwaiq Mountain Formation (after Cole et al. 1994a, reproduced with permission from Canadian Society of Petroleum Geologists). samples in the Khurais Field, which cover the entire Jurassic section, show that the Tuwaiq Mountain Formation, 142 m (466 ft) thick, is the most organically enriched source rock, with a 3.15% TOC (Fig. 11.89) The cross-

620

plot of TOC against $2 is a further indication of the oilprone nature of the source rock (Fig. 11.90). Source-rock quality may be cyclical, resulting from sea-level fluctuations during the course of deposition. The upper Hanifa-

Hydrocarbon Habitat of the Greater Arabian Basins Lower Jubailah, the second source rock, is thinner, about 33 m (108 ft), and has a mixed oil- to gas-prone character. The similarity of the gas chromatographic analyses of crude-oil and source-rock extracts (Fig. 11.91) establish the Tuwaiq Mountain-Hanifa as the source of the Jurassic reservoired oils. Burial history and thermal modeling indicate increasing maturity from the western rim of the basin in central Saudi Arabia to the northeast (toward Safaniya) and southeast (toward Qatar). The Tuwaiq Mountain Formation source rock reached early-stage maturity at about 75 Ma, with many areas reaching peak-expulsion maturity by the late Cretaceous and Early Tertiary as the fill of broad, gentle structures began. By 25 Ma, most of the Tuwaiq Mountain and Hanifa formations north and south of the basin center had attained expulsion maturity (Cole et al., 1994 a & b), and the filling of basin margin structures was underway (Cole et al., 1994 a). At the present day, kitchens in

part of Ghawar Field and to the east as well as those in the northeast past the oil expulsion window (Fig. 11.92) In gross compositional terms, the Arab and Hanifa reservoir oils are high-sulfur (1-4%), aromatic-intermediate oils consistent with a marine-carbonate source. The oils all have similar hydrocarbon chromatograph characteristics, but are significantly different from Permian condensates; because the difference cannot be attributed to greater maturity, it suggests intrinsic source-rock differences. The primary difference between the mature and immature source rock may be attributed to maturity and minor facies variations that are likely to occur at the edges of the basin rather than in the source-rock depocenter.

Cretaceous Formations Source-rock analyses in the Cretaceous show that the large oil accumulations in the northeastern offshore fields

SOURCE ROCK EXTRACTS

Immature",n,,,

E

iF

RESERVOIRED OILS

'

,mm~,u.~

IA

M~..,,, A.~b O,,

B

c..,.., Gh..~. A.~b o,,

9.

I)

,

I

,o

D

Fig. 11.91 C15+ gas chromatograms of representative of oils from the Upper Jurassic Arab Formation from Mazalij (A) Central Ghawar (B) Safaniya (C) and Abu Hadriya (D) fields. Cls+ gas chromatograms of representative source rock extracts. E and F from immature Hanifa and Tuwaiq Mountain and from Khurais and E1 Haba fields, and G and H from mature Tuwaiq Mountain-Hanifa source rock interval from Ghawar field (after Cole et al. 1994a, reproduced with permission from Canadian Society of Petroleum Geologists).

621

Sedimentary Basins and Petroleum Geology of the Middle East

IRAN

- .

ARABIAN GULF .

i

-_~

" -

ARABIAN GULF

~

.

.

.

.

i

.

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T

/

%

-----

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- -I- - : SAUDI ARABIA

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~

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iRAN

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phase oil expulsion ~

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'

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9

" " i'."...i :. ' . i . -" [ 7 ~ immature to I:.arly ~ g e n e r a t i o n mature

:. ......~.:.

End otl expulsion to oil preservation

~

Oil field

0

100 km

J_

Fig. 11.92.Maturity maps of the Jurassic top of the Hanifa Formation at 75,50, 25 and 0 Ma time slices in Saudi Arabia and adjacent areas based on the generation and expulsion classes (after Cole et al. 1994a, reproduced with permission from Canadian Society of Petroleum Geologists). could not have been generated within the sequence. Although the sediments are sufficiently organic-rich locally, the thermal maturity is too low, and the kerogen quality is poor because of related continental sedimentation, and too gas-prone to be the oil source. There are sufficient geochemical and physical similarities with the Jurassic oils for the source to have lain within source rocks in the Gotnia Basin. Alternative sources lie in the Albian Kazhdumi Formation present to the north and east, and in the Safaniya Member of the Wasia Formation in the Rub A1 Khali Sub-basin, comprised of a 9-18 m (30-60 ft) sequence of dark, organic-rich, laminated lime mudstone with up to 14.0% TOC of primarily sapropelic or amorphous, oil-prone, Type II organic matter (Fig. 11.93). The Mishrif Member, 91-122 m (300-400 ft) of grey to darkbrown, organic-rich, fine-grained limestone, commonly contains more than 10% organic carbon, mostly as oilprone, sapropelic material similar to that present in the Safaniya Member (Newell and Hennington, 1983).

622

Cenozoic Formations

In the Red Sea Basin, the Cenozoic source-rock geochemistry of both the Midyan and Jizan sub-basins has been reviewed by Cole et al. (1995), who also attempted to assess the extent of the hydrocarbon kitchens. Fig. 11.94 is a histogram showing the distribution of TOCs and pyrolytic yields in the principal units in the Midyan and Jaizan sub-basins, respectively. No thick or regionally extensive oil-prone source-rock units, with the exception of the Maqna Group in the Midyan Sub-basin, have been identified. However, some thin, organic-rich shale and carbonate units have the potential to be better-developed distally. To evaluate their potential, a series of cross-plots of the $2 yield against TOC as shown in Fig. 11.95. The plots show considerable scatter. All the sedimentary units tested show that the kerogen consists of heterogenous assemblages. Samples of the Maqna Group mostly follow the oil-prone trend; however, the thickness of the richest horizons does not exceed 20 m (66 ft) in the Midyan Sub-basin and only

H y d r o c a r b o n Habitat o f the G r e a t e r A r a b i a n B a s i n s

~

'

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Fig. 11.93, Log characteristics of the Albian Safaniya Member source rock in Rub al Khali basin of Saudi Arabia (modified from Newell and Hennington 1983, reproduced with permission from Society of Petroleum Engineers). MIDYAN BASIN SOURCE ROCK

70

JAIZAN BASIN SOURCE ROCK

50, a,O30 20 1

I

I

I

0 I O-OJ

I

'

' _~,

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TOC %

TOC % 70 60-

50" 40"

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I

1 I 1-;

10' 2-3 i 3-5 ' 5-10'10-20'

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w 1-2 i 2-3 I 3-5 ' 5-10 '10-20

$2 YIELD (mg Hc/g rock) ~

Ghawwas Formation i~ Mansiyah Formation

$2 YIELD (mg Hc/g rock)

I • Maqna • Group

~

[~~

['. .... ~!.i;] P r e - r i f t / B a s e m e n t

Burqan Group

Tayran Group sediments

Fig. 11.94. Histograms showing the distribution of total organic carbon (%TOC) and RockEval pyrolytic yields ($2 yield in mg hydrocarbons per gram rock) for each of the Tertiary sedimentary sequences in the Midyan (left) and Jaizan (fight) sub-basins in the Red Sea of Saudi Arabia (after Cole et al. 1995 reproduced with permission from Gulf PetroLink,Bahrain). 623

Sedimentary Basins and Petroleum Geology of the Middle East 2-3 m (6.5-10 ft) in the Jaizan Sub-basin. Overall, samples in the Burgan Group appear to have moderate source richness and are the probable source of the wet to dry gas reservoired in the lower to middle Miocene sands in the Jaizan and the limestone of the Midyan Sub-basin. Maturity levels within the thin, organic-rich shale in the Infra-Evaporite Group of the Red Sea Basin may have passed the oil window because of an abnormally high thermal gradient (Ahmed, 1972). Maturity levels increase

slowly in the shallow, post-rift section, but increase rapidly where exposed to the syn-rift gradient. Maturity trends at the top of the Tayran Group in the Midyan area and at the top of the Burqan Group in the Jaizan are shown in Fig. 11.96. Wells away from the rifting center or located on continental crust generally display linear and low-maturity gradients (Barnard et al., 1992). The depth to the top of the oil window is highly variable, depending upon both the thermal and burial histories, specifically the loss of section

~

m

-Q

(B/~H 15tu)(r"131A gs

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!.

.o

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624

(B/~H l~tu) (]q~IA gS

(15/~H 15tu)(]"I~IA gS

Hydrocarbon Habitat of the Greater Arabian Basins

.

.

".. g

~

..

.'d

//.

Immature (< 0.5% VRe)

9

~ ~

.

.

.

Oii window (0.5-1.0% VRe) Oil preservation

onset gas

(1-1.3% VRe) Wet gas w i n d o w ~ (1.3-1.8% VRe) Dry gas to thermallyspent (> 1.8% VRe) generation

~_

k

. o

.

9 '

Z ~'~

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Rahfax,. . . .

Z SEA

X XX XXXXx ..X 0 l

SUDAN Z m <

/

/ /

/ ETHIOPIA

|

Z < N

/ i

15 km

Fig. 11.96. (A) Location map of the Midyan and Jaizan sub-basins in the Red Sea Region of westem Saudi Arabia. (B) Map of Midyan basin showing the maturity trends drawn on the top of the Tayran Group. (C) Map of Jaizan basin showing the maturity trends drawn on the top of the Burqan Group (after Cole et al. 1995 reproduced with permission from Gulf PetroLink,Bahrain).

0

200 km

<

.~.

-

-- RED SEA -

due to faulting and/or erosion. In general terms, the top of the oil window follows the trend in geothermal gradient and becomes shallower in the southern Red Sea, lying between 2,000 and 3,000 m (6,560-9,840 ft) in the Egyptian offshore to 1,000-2,000 m (3,280-6,560 ft) in the central and southern Red Sea. At the basin margin, the oil window occurs at relatively shallow depths due to faulting and erosional loss of section. In the southern Red Sea, there is a tendency for pre-rift and pre-salt, syn-rift Miocene beds to be over-mature due to the high heat flow in all but the most immediate basin-margin settings (Mitchell et al., 1992). Lopatin modeling, using presentday gradients (and therefore giving conservative results), indicates that the lower to middle Miocene pre-salt succession reached the oil window about 10 Ma years ago and the post-salt Upper Miocene reached the top of the oil window about 5 Ma years ago in the southern and central Red Sea. The Pliocene in that area that is not in structurally high positions is still in the early-mature stage.

Reservoir

Rocks

Reservoir rocks in Saudi Arabia are present throughout the entire stratigraphic record (see Figs. 11.77, 11.78). Several deep-pool tests in proven oil fields penetrated the pre-Khuff Paleozoic clastics. Cambrian-Ordovician sediments of the Saq Formation and Ordovician-Silurian beds of the Tabuk Formation were found to be oil- and gasbearing, and gas and light-gravity oil were discovered in the Devonian Jauf Formation for the first time. The largest deposits of non-associated gas were discovered in the Khuff Formation of Upper Permian age. Light-gravity oil was discovered in the Lower Jurassic Marrat Formation only in the Maharah Field, offshore northeastern Saudi Arabia. Oil-bearing rocks in the Middle and Upper Jurassic are mainly limestone. The most important oil-producing horizons in the Saudi Arabian oil fields lie in the Upper Jurassic Arab Formation, particularly the Arab D Member. Cretaceous oil bearing rocks, sandstone and limestone of the Wasia Formation, occur in the offshore fields of north625

Sedimentary Basins and Petroleum Geology of the Middle East eastern Saudi Arabia. Sandstone in the Dammam Field are gas-bearing only. The depth of the reservoirs is variable. Upper Permian and older Paleozoic reservoirs are much deeper, which explains the presence of gas and light oil (condensate). The Jurassic reservoirs lie at depths from 1,400 to 3,750 m (4,592-12,300 ft), and the Cretaceous reservoirs at depths ranging from 1,400 to 2,540 m (4,5928,331 ft). In the northern Red Sea, important gas and condensate discoveries were made in Miocene sandstone in the Barqan Field. In the southern Red Sea, oil and gas shows were reported from massive salt with shale beds belonging to the Evaporite Series of the Upper Miocene. The depth of reservoirs is about 2,000 m (6,560 ft) in the northern Red Sea and 2,500 m (8,200 ft) in the southern Red Sea. The ages of producing reservoirs range from Lower Paleozoic to Upper Cretaceous in central and eastern Saudi Arabia and are Miocene in the Red Sea. Lower Paleozoic reservoirs are mainly in clastic sediments and subordinate carbonates. Jurassic reservoirs are almost exclusively calcarenite, calcarenitic limestone and, to a larger degree, dolomite. Cretaceous reservoirs are mainly sandstone and, subordinately, limestone. Miocene reservoirs of the Red Sea are exclusively clastics. In central and eastern Saudi Arabia, 94% of the ultimate recoverable non-associated gas reserves are located in Upper Permian Khuff carbonates, and 6% in CambrianDevonian clastics and carbonates. Of the ultimate recoverable oil reserves, 76% are found in Upper Jurassic Arab carbonates, 5% in Lower and Middle Jurassic carbonates, and 19% in Cretaceous sandstone and limestone. Of the ultimate recoverable associated gas reserves, 84% are found in Upper Jurassic Arab carbonates, 6% in the Lower and Middle Jurassic carbonates, and 10% in Cretaceous sandstone and limestone. In the Red Sea Basin, gas and condensate reserves cannot be estimated at this stage. Attractive reservoir potential is found in the Cambrian, Ordovician and Silurian clastics and Devonian carbonates, which are still in the early stage of exploration. In the existing oil fields, particularly those in the central Arabia, the pre-Permian reservoir potential is excellent. Potential source rocks are Ordovician, Silurian and Carboniferous shale. The Upper Permian Khuff carbonates have an excellent reservoir potential in almost all the existing fields of the eastern Arabian Platform, provided structural closures are found. Source rocks are probably mostly pre-Permian in age. No hydrocarbon discoveries have been made in Triassic rocks of Saudi Arabia. This is due to the absence of indigenous source rocks and the effectiveness of the Upper Permian evaporite seal on top of the Khuff Formation, with the overlying Lower Triassic Sudair shale acting as an additional seal preventing hydrocarbons from migrating into the Triassic sequence. The Jurassic shelf carbonates are considered the best reservoirs in many existing fields and have an excellent potential in undrilled traps and structures. Cretaceous sandstone and limestone are favorable reservoirs in northeastern Saudi

626

Arabia. Reefal limestone of the Aptian is an excellent reservoir for oil and gas in the Rub A1 Khali Sub-basin, if areas of favorable structural/stratigraphic relationship can be located. However, gas may be expected towards the center of the Basin (Suhul and Kidan fields) and oil with or without a gas cap towards the basin margin (Shaybah Field). The short description of the principal reservoir formations which follows is based upon data from OAPEC (1985, 1989), Beydoun (1988), various proceedings of SPE-Middle East Oil Shows, Middle East Geoscience and other local publications. Saq Formation (Carnbrian-Ordovician). This formation consists of fluvial sandstone and siltstone. The oil and gas reservoir is unspecified. The Saq Formation partly correlates with the Wajid Formation in southwestern Saudi Arabia.

Tabuk Formation (Ordovician-Lower Devonian). The formation consists of sandstone, siltstone and shale deposited in a terrestrial to marine setting. It is locally a minor oil and gas reservoir. Gas is produced in the Mazalij fields. The formation partly correlates with the Wajid Formation in southwestern Saudi Arabia. Jauf Formation (Devonian). This formation consists of carbonate and siltstone and is an unspecified oil and gas reservoir. It probably correlates partly with the Wajid Formation in southwestern Saudi Arabia. Unayzah Formation (Early-Late Permian). The Unayzah Formation consists of sandstone with a variable content (0-6%) of detrital mud, lithic fragments, mudstone intraclasts and feldspars. The sandstone shows a considerable variety in cement, with quartz overgrowths, dolomite, calcite, anhydrite and some minor authigenic clays. It was deposited in an alluvial-fan to playa environment under arid to semi-arid conditions (Senalp and Al-Duaiji, 1995). Diagenesis was controlled by depositional features that determined flow paths and rates of movement of migrating fluids; consequently, diagenesis of similar clean sandstone is essentially the same. Compaction, which reduced pore volume with the expulsion of interstitial formation water, was offset to some extent by early carbonate and anhydrite cement in the sands. However, secondary porosity (415%) due to the dissolution of cements and unstable grains prior to oil emplacement plays a major role in the total porosity (Fig. 11.97), for the dissolution of frame-forming cements and grains may cause hole instability and the migration of clays can cause pore throat plugging. The absence of significant felspar in the macroporous sands points to its removal by corrosive solutions that preceded hydrocarbons, both derived from the gradual maturation of the Qalibah Formation in the deeper parts of the basin lying to the east. The Unayzah acted as both a reservoir and a potential carrier to transport hydrocarbons from mature areas of the basin to areas of structural and stratigraphic closure. The basal shale and anhydrites of the Khuff Formation provide a regional vertical seal for the Unayzah. Gas was tested in the Unayzah Formation in the Ghawar, Abu Safah, Berri and Qatif fields of Saudi Arabia.

Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.9% Burial history diagram illustrating influence of source rock maturation in Uddayan-A on digenetic evolution of Unayzah and basal Khuff sandstones in A1 Hawtah Field. Clay transformtion in Uddayan Field shales started around 240 Ma resulting liberation of Si, Ca, K, Fe, Mg and interlayer H20 for silica and carbonate cementation in A1 Hawtah reservoir rocks. Qusaiba shales in Uddayan Field entered oil window around 160 Ma (see Abu-Ali 1991 ). Gradual organic matter maturation caused generation of organic acid and C02 which migrated into Hawtah reservoir rocks generating substantial secondary porosity prior to main phase of oil emplacement (after Aktas and Cocker,1995,and reproduced with permission from Gulf PetroLink, Bahrain).

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Ferguson and Chambers (1991), McGillivray and Husseini (1992) and Alsharhan (1995) reported that oil and condensate were produced from some new discoveries in central Saudi Arabia, such as Nuayyim, Hazmiyah, Hawtah, stratigraphic well-39, Talhah, Dilam, Hilwah, Raghib, Hamzah, Udaynan and Tinat. Hydrocarbons were encountered in six reservoir facies, viz. braided-river, shorefaceforeshore, delta-channel, coastal-plain channel, valley-fill channel and transgressive lag (Ferguson and Chambers, 1991). Khuff F o r m a t i o n (Permian). The Khuff Formation contains the earliest major transgressive carbonates deposited over the shallow continental shelf of eastern Saudi Arabia. The formation, about 510 m (1,670 r ) thick, has been divided into four carbonate reservoir units, Khuff A to D, and a fifth and lowest clastic unit, Khuff E, in an upward sequence (A1 Jallal, 1995), each formed during a

different depositional cycle. The cycle commences with mainly subtidal carbonates and shallows upward into a regressive phase of mainly intertidal and sabkha sediments deposited on a carbonate-evaporite shelf (see Chapter 5). Reservoir quality is controlled by lateral continuity or discontinuity of the facies and also by diagenesis. High porosity and permeability is usually associated with primary interparticle pore spaces (A1 Jallal, 1987, 1995; Alsharhan and Nairn, 1994). Khuff gas from the Saudi fields is sour, containing hydrogen sulphide and carbon dioxide. Production is accompanied by water (1.5-2 bbl per million standard cu ft of gas) and moderate amounts of heavy condensate (API gravity 47.5 ~ 30-50 barrels per million standard cu ft of gas) (Kasnick and Engen, 1989). Analysis of the gas shows that it contains approximately 20% non-hydrocarbons, of which H2S forms about 4.1 mole%, CO 2 3.7

627

Sedimentary Basins and Petroleum Geology of the Middle East

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Dhruma Formation), and the lower part of the Upper Fadhili Zone (the upper part is included in the Tuwaiq Mountains Formation). Oil is produced in Fadhili, Faridah, Khurais, Mazalij, Samin and Sharar fields.

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Tuwaiq Mountain Formation (Callovian-Oxfordian). It consists of calcarenite and limestone deposited in a

.

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Fig. 11.98,Anhydrite total footage ranges in feets in the Permian carbonates of the Middle East (after A1 Jallal, 1995, reproduced with permission from Gulf PetroLink, Bahrain). mole% and N 2 12.3 mole% (Kasnick and Engen, 1989). The condensate has 0.81% sulfur and significant quantities of heptanes and heavier components. In a regional sense, A1 Jallal (1995) demonstrated a relationship between a low anhydrite content and a high porosity. The higher porosity in the grainstone facies coincides with a high-energy shelf break marking the opening to open-marine conditions in Oman and Iran. The SaudiKuwait area, however, belongs to the zone of the restricted carbonate-evaporite shelf (Fig. 11.98). Significant gas production was reported from the Khuff Formation in the Dammam Field in 1957, and gas reserves of great significance have been discovered since then in other major fields such as Ghawar, Abu Safah, Berri, Harmaliya, Khurais and Qatif. In the Abu Jifan and Farhah oil fields, King (1995) showed that the lower part of the Khuff (Unit E clastics) had excellent reservoir characteristics, with permeabilities of more than 3 darcies, and where the initial discovery well Abu Jifan-23 flowed 8,200 bbl/d of 42 ~ API oil with 4 million cu ft of gas from Permian, Siluro-Ordovician and Ordovician sections. Marrat Formation (Toarcian-Lower Jurassic). It consists of argillaceous limestone, shale and sandstone deposited in a shallow marine shelf setting. The formation is locally a minor oil reservoir in the Maharah Field. Dhruma Formation (Bajocian-Callovian). It consists of limestone and shale deposited in a shallow-marine shelf. The Dhruma Formation is divided into three units: Lower, Middle and Upper Dhruma Formation. It consists of four reservoir units" Faridah Zone and Sharar Zone (Middle Dhruma Formation), Lower Fadhili Zone (Upper 628

shallow-marine shelf setting. The formation includes two reservoir units, the Upper Fadhili Zone (the lower part is with Dhruma Formation) and the Hadriyah Zone. Oil and gas is produced in Abu Hadriyah, Berri and Qatif fields.

Formation

(Oxfordian-Kimmeridgian).

The formation consists of shallow-marine shelf carbonates and argillaceous bituminous mudstone and shale and is an excellent reservoir-source rock facies unit. The Hanifa reservoir occasionally shows exceptionally high permeability caused by high-angle fractures, which are less than 1 mm in width, containing calcite cement and hydrocarbon residue. These fracture occurrences are closely associated with high-amplitude stylolites, but seem to be related to stratigraphic positions. Figure 4 compares the porosity-permeability plot for Hanira with that of Arab D in the same field. While the porosity ranges of these two reservoirs do not differ greatly, the permeability range of Hanifa (less than 10 md) is much less than that of Arab D (up to 8,000 md). The reservoir in the Abqaiq Field was described by Grover (1993) as mud-supported limestone, having micropores of 2-5 micron size with relatively high porosity (5-32%) and low permeability (about 10 md) (see Fig. 99). The microporosity is considered to reflect retention of primary intercrystalline spaces within the original lime mud sediments. The Hanifa is separated from the overlying Arab D reservoir by more than 137 m (449 fi) of fine-grained carbonates of the Jubailah Formation, which seems to have acted as a seal for hydrocarbons. However, this seal is a leaky one, probably because of the presence of microfractures. Further to the north in the Berri Field of Saudi Arabia, the Hanifa changes its facies to skeletal grainstone and stromatoporoid boundstone complexes (Kompanik et al., 1993). In the vertical direction, the Hanifa is a large-scale, coarsening/shallowing-upward, carbonate platform sequence (about 150 m, or 490 ft, thick), consisting of a lower non- reservoir unit of organic-rich, laminated lime mudstone and low-porosity skeletal wackestone, and an upper reservoir unit of grain-rich carbonates that include skeletal packstone, grainstone and coral/stromatoporoid boundstone. The skeletal sands and stromatoporoid/coral bioherm complexes dominate the outer ramp and ramp margin environment. They grade southward of the field into skeletal packstone and wackestone along a ramp margin slope, and finally into tight lime mudstone in the basin (Kompanik et al., 1993; Fig. 11.100). The best reservoir facies lie in the conglomerate and grainstone, with a permeability reaching as high as 10,000 md and a porosity greater than 30%.

Hydrocarbon Habitat of the Greater Arabian Basins

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Fig. 11.99 Porosity-Permeability cross plot data A) Comparison of porosity and permeability cross plot data from Arab D and Hanifa reservoirs of Abqaiq Field, Saudi Arabia. The two reservoirs have a similar porosity range, but Arab-D permeabilities range from 0.1 to 8,000 md while Hanifa permeabilities are less than 10 md, a difference of three orders of magnitude between these two reservoirs. B) Cross-plot of core-plug porosity and permeability data from the Hanifa reservoir in Abqaiq Field, Saudi Arabia (after Grover, 1993, reproduced with permission from Society of Petroleum Engineers).

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The formation is a major oil and gas reservoir. Oil is produced in Khurais Field and oil and gas is produced in Abqaiq, Abu Hadriyah, Berri, Ghawar (Ain Dar Area), Harmaliyah, Khursaniyah and Mazalij fields. Jubailah Formation (Kimmeridgian). It consists of calcarenite and bituminous limestone deposited in a shallow-marine shelf setting. The formation consists of two pay zones, Lower Jubailah and Upper Jubailah Members. Oil is produced in Khurais and oil and gas is produced in Abqaiq, Ghawar fields.

Arab

Formation

(Kirnmeridgian-Portlandian).

This formation consists of calcarenite, dolomite, bituminous limestone and anhydrite deposited in a shallow-

marine shelf setting (lagoonal deposits and supratidal). It is a major oil and gas reservoir in the Interior Platform and Northern Gulf Sub-basin. Oil is produced in the Khurais, Manifa and Marjan fields, and oil and gas are produced in the Abqaiq, Abu Hadriyah, Abu Safah, Berri, Dammam, Fadhili, the supergiant Ghawar), Harmaliyan, Khursaniyah and Qatif fields. This reservoir includes the Arab A, B, C and D zones. The reserves include all of the Arab A, B, C and D, Arab D/Jubailah reservoirs and the Jubailah and Hith formations. The reservoir has oil and gas accumulations in the Mazalij Field and oil accumulations in the following non-producing fields and discoveries: Abu Jifan, Dhib, Dibdibba, Duhaynah, E1 Haba, Faridah, Habari,

629

Sedimentary Basins and Petroleum Geology of the Middle East Hamd, Harqus, Jaham, Jaladi, Jana, Jawb, Juraybiat, Jurayd, Karan, Kurayn, Lugfahim Qirdi, Ribayan, Sadawi, Salsal, Samin, Sharar, Suban, Tinat, Wariyah and Watban. Petrographic and petrophysical properties of the Arab D reservoir, which is the most prolific in Saudi Arabia, -I -.

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Fig. 11.101 Composited effect of mud-size matrix (0-100%) and dolomite percent (0-75%) on porosity and permeability of Arab D reservoir in Ghawar Field (after Powers, 1962).

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Fig. 11.102 Effect of % dolomite (75-100%) on porosity and permeability of an Arab 'D" Reservoir in Ghawar Field, Saudi Arabia (Powers, 1962).

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Fig. 11.103 Semilog plots of average porosities and permeabilities. (Left figure) Arab-C reservoir facies in several wells, showing the isopachouly cemented and sparsely cemented zones of the ooliticOmoluscan grainstone facies to have the best reservoir quality. (Right figure) Arab-D reservoir facies in several wells. Grain-selective dolomitization in the fine grainstones comprising much of the Arab-C reservoir improves permeability. Most dolomitized fine grainstones are more permeable than undolomitized grainstones with similar porosities. Grainstone facies intervals (both undolomitized and dolomitized) with lower average porosities and permeabilities were more compacted or are lower in the reservoir and near the transition (after Wilson 1985 reproduced with permission from Springer-Verlag).

630

Hydrocarbon Habitat of the Greater Arabian Basins were studied extensively by Powers (1962), Wilson (1985) and Mitchell et al. (1988). A large number of core analysis results of the Arab D at Ghawar is presented (see Fig. 11. 105). Porosity ranges from a few percent to more than 30% and permeability from 1 to more than 1,000 md. As for the effects of mud-size matrix and dolomite, Powers (1962) presented his summary graph (Fig. 11.101), which shows that an increasing matrix percent reduces both porosity and permeability and that increasing dolomite up to 75% also reduces porosity and permeability. Changes of porosity and permeability for the 75-100% dolomite range are shown in Fig.11.102, which depicts drastic increases of both porosity and permeability in the dolomite content between 80 and 90% dolomite, suggesting that a complete dolomitization would destroy the pore spaces. The preservation of the relatively high primary porosity in the Arab D reservoir, due to the early migration of oil that formed an inert insulating medium, seems less likely than the preservation of pore space due to early diagenesis. The investigation of Ibrahim et al. (1981) suggests that primary migration into the reservoir is unlikely to be much earlier than the late Turonian, supporting Purser's (1978) suggestion that primary porosity was retained through the development of early diagenetic fabrics. The pore spaces show signs of secondary enlargement (dedolomitization); hence, in the case of the Arab D reservoir, the primary porosity persisted without evidence of any major compaction from the Kimmeridgian through Cenomanian, prior to hydrocarbon entrapment in a structure that became closed only during the Turonian. Computer modeling of reservoir facies using sequence stratigraphic concepts as well as facies geometry to distribute porosity permeability and initial water saturation (Kompanik et al., 1995) demonstrated that fluid flow, permeability and porosity are controlled by both primary depositional fabric and diagenesis. This type of study has been applied in the Berri Field to control water flooding and design techniques to extract large volumes of unswept oil. Wilson (1981 and 1985) studied the Arab C and D reservoirs at the Qatif Oil Field in Saudi Arabia, where porosity ranges from 1 to 30% and permeability from about 0.1 to over 5,000 md in Arab C, while porosity in Arab D ranges from 5 to 25% and permeability from about 0.1 to 1,000 md (Fig. 11.103). Wilson (1985) concluded that the Arab C reservoir's sparsely cemented zones of ooliticmolluscan grainstone have the best reservoir quality, while selective grain dolomitization in fine grainstone of the Arab D reservoir improved permeability without significantly affecting porosity. Porosity-permeability values from core analysis reported by Wilson (1981), plotted as black dots in Fig. 11.104, are compared with well-log analysis results by Magara et al. (1993) shown as open circles. This figure shows a good match between the core and well-log analysis results in the Qatif Field, with ranges of porosity and permeability resembling those found in the Ghawar Field (Fig. 11.105), except for some low perme-

ability measurements less than 1 md in the former. Magara et al. (1993) extended their study of porosity vs. dolomite percentage in the Arab A, B, C and D reservoirs to other fields (C, D, E, F and G) in central and eastern Arabia (Fig. 11.106). In the Arab A, B and C reservoirs, the percentage of dolomite tends to increase westward and southwestward, but at the same time, porosity (and thus probably permeability) decreases in the same direction, suggesting that dolomitization does not necessarily improve porosity (and permeability) in their study area. According to Broomhall and Allan (1985), dolomitization may have been caused by a supersaline brine moving vertically from deeper sections (e.g., the Triassic Jilh halite) or laterally (from the Late Jurassic Gotnia halite). Wilson (1981) observed that coarse grainstone in the Qatif Field was undolomitized, and interpreting this as evidence that the dolomitizing fluids moved quickly through rocks of relatively high permeability, whereas where fluid movement was slower through peletic micrite, oolitic micrite and micritic limestone, dolomitization in the Qatif is common. However, in contrast to this, Powers (1962) and Magara et al. (1993) showed that selective dolomitization took place in lime mudstone, whereas grainstone, regardless of its grain size, usually was not affected by dolomitization. Hith Formation (Portlandian). This formation consists of limestone, dolomite and anhydrite deposited in a shallow-marine shelf and supratidal setting. It is locally a major oil and gas reservoir. Oil is produced in the Manila and Rimthan fields. The Hith Formation contains two reservoir units: the upper, Manila (limestone) in the Manila Field and the lower, Rimthan (limestone) in the Rimthan Field. Non-commercial quantities of oil were also detected in the Abu Hadriyah Field. The tar seep, which was discovered at the Hith outcrop in 1938, was of great regional significance and later proved the existence of large quantities of oil in the region. Sulaiy Formation (Berriasian-Valanginian). The formation consists of limestone, calcarenite and calcarenitic limestone deposited in a shallow-marine setting. It is also known as the Lower Ratawi reservoir. Oil is produced in the Marian and Sharar fields, and oil and gas are produced in the Manila Field. Yamama Formation (Valanginian). This formation consists of calcarenite and limestone deposited in a shallow-marine shelf setting. It is also known as the Upper Ratawi reservoir, Oil is produced in the Dawl, Hamur, Jubah, Manila, Marian, Sharar and Zuluf fields. The formation thickens basinward. Buwaib Formation (Hauterivian). The formation consists of sandstone and shale deposited in a shallowmarine and deltaic setting. It is locally a minor oil reservoir. Oil is produced in Sharar fields. Biyadh Formation (Barremian). This formation consists of sandstone and shale deposited in a marine and deltaic setting. It is known as the Zubair reservoir in the 631

Sedimentary Basins and Petroleum Geology of the Middle East 7

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40

50

(%)

Fig. 11.105. Plot showing core analysis results of porosity and permeability of Arab 'D' Reservoir at Ghawar Field, Saudi Arabia, reported by Powers,1962) (after Alsharhan and Magara, 1995).

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Hydrocarbon Habitat of the Greater Arabian Basins offshore, northeastern Saudi Arabia and contains oil and gas in the Safaniya Field. Shuaiba Formation (Lower Cretaceous). The formation consists of limestone deposited in a marine setting (organic reef deposits). Oil is produced in the Ramlah Field, and oil and gas are produced in the Shaybah Field. The formation produced gas in the North Kidan, South Kidan and Suhul discoveries.. Wasia Formation (Albian-Turonian). This formation consists of shallow-marine limestone, sandstone and shale. It is a major oil and gas reservoir in the Northern Gulf Sub-basin. It includes seven reservoir units: the Mishrif (limestone), Ahmadi (limestone), Wara (limestone), Mauddud (limestone), Rumaila (limestone), Safaniya (sandstone) and Khafji (sandstone) members. Oil is produced in the Hamur, Hasbah and Dawl fields, oil and gas are produced in the Safaniya, Marjan and Zuluf fields, and gas is produced in the Dammam Field. Lower Aruma Formation (Coniacian). The formation consists of calcarenite deposited in a shallow-marine setting. It is locally a minor oil reservoir. The formation also is known as the Lawhah reservoir, where it is oil-bearing in the Lawhah Field.

Tertiary Formations. The only known Tertiary reservoirs are in Miocene sands in the Red Sea Basin, which are assigned to the Maqna and Burqan Groups and. consist of sand and sandstone. The area has only recently been explored, but adequate reservoirs have been found in structural or combination traps. Drilling in the Midyan and Jizan sub-basins of the Red Sea has met with mixed success. The groups contain locally minor gas and condensate reservoirs. Gas and liquids are produced in the Barqan Field. The formation tested 11,650 M.CFD gas and 650 bbl/d condensate through a 1/2 inch choke from a 41 m perforation in well Barqan-2. The calculated absolute open flow is 100,000 M.CFD gas. Reservoir data refer to the tested interval in well Barqan-2. Six wells tested structures in the Midyan Sub-basin, and good results were found in the Burqan structure, where commercial quantities of gas condensate were found (but as yet undeveloped; Mitchell et al., 1992). Up to 50 MM.cf/d gas and condensate have been recorded from Barqan-1 and 2, with flow rates of 1,200 bbl/d of oil from Barqan-3. Renewed drilling in the Midyan Sub-basin in the early 1990s led to the discovery of condensate, wet gas and minor black oil in three wells; 42 ~ API oil was found in several sandstone reservoirs encountered at depths between 1,400 and 4,300 m (4,59214,104 ft) and the Burqan Field was declared commercial in 1992. In the Jizan Sub-basin in the southern Red Sea close to the Yemen border, three wells in the northern part of the area tested a waxy, paraffinitic 42 ~ API oil and dry gas; in the Mansiyah-1 well, 34 ~ API oil and gas shows were reported from a limited reservoir within the Evaporite Group at 2,500 m (8,200 ft).

Cap Rocks The cap rocks of Saudi Arabia range in age from Lower Ordovician to Miocene/Pliocene for the Arabian Basin and from Lower to Upper Miocene in the Red Sea Basin (see Figs. 11.77, 11.78). They consist of evaporites, shale and occasionally tight carbonates. Shaly cap rocks are distributed over the entire Arabian Basin sedimentary sequence, both laterally and vertically. Tight carbonate seals are restricted to the Jurassic sequence. Upper Permian evaporites are very effective seals for the huge nonassociated gas accumulations and Upper Jurassic Hith anhydrites for the major oil in eastern Saudi Arabia. Cap rocks of the Cretaceous reservoirs are shale and marl. Miocene anhydrite and rock salt overlie the reservoir sequence of the Red Sea Basin. Oil retention in central and eastern Saudi Arabia is excellent. Upper Permian-Lower Triassic and Upper Jurassic evaporites and shale and Cretaceous shale form impermeable regional seals. Upward seeping through these caps may have occurred in rare cases, only because of faulting or lateral thinning or wedging. Migration of hydrocarbons from early Upper Jurassic and Lower Cretaceous source rocks is mostly Tertiary, usually Late Tertiary to Recent in age, depending on burial depth and local temperature gradients. Lower Paleozoic source rocks may have reached maturity during the Mesozoic and over maturity during the Cretaceous-Lower Tertiary. Shaly sequences are reported from the Paleozoic section. They are either Ordovician/Silurian or Carboniferous in age. Upper Permian evaporites effectively seal the nonassociated gas of the Khuff carbonate reservoirs. The Lower Triassic Sudair shale improves the sealing capacity of the underlying Khuff in the Arabian Basin. Lower Jurassic shale of the Marrat Formation and Middle Jurassic dense limestone of the Dhruma Formation are cap rocks for some minor reservoirs. Upper Jurassic Hanifa and Jubailah shale seals the corresponding carbonate reservoirs. Anhydrite beds of the Upper Jurassic Arab Formation, together with the overlying Hith anhydrite, form an excellent regional cap rock for the main oil and associated gas accumulations in the Arab carbonates. HauterivianBarremian shale and marl of the Buwaib and Biyadh formations are reported from northeastern Saudi Arabia only. They seal both interbedded sandstone reservoirs and the underlying Berriasian-Valanginian limestone beds. Upper Cretaceous shaly members of the Wasia Formation (Ahmadi and Rumaila members) offer excellent regional seals for the main Cretaceous reservoirs in northeastern Saudi Arabia, together with the Coniacian Lower Aruma shale. Neogene Dam Formation shale and marl, probably with limited sealing capacity, are known from northeastern Saudi Arabia. The only known reservoirs are Red Sea Basin Miocene sands that are sealed by a thick evaporitic sequence of the age-equivalent. The principal cap rocks are briefly listed below.

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Member

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Formation)

633

Sedimentary Basins and Petroleum Geology of the Middle East

(LoWer Ordovician, Llanvirnian). This member consists of sandy shale deposited in a deltaic to very shallowmarine setting. The sand content generally increases to the south. It is a possible cap rock for the Saq Formation sandstone reservoir. Ra'an Shale Member (Tabuk Formation) (Upper Ordovician, Carodician). The member consists of shale deposited in a deltaic to shallow-marine setting. The sand content increases to the south. This is a possible cap rock for the sandstone reservoir in the lower part of the Tabuk Formation.

Qusaiba Shale Member (Tabuk Formation) (Lower Silurian, ldwian). The shale is a possible cap rock for the sandstone reservoirs in the upper part of the Tabuk Formation. Unayzah Formation (Lower-Middle Permian). The formation consists of shale and sandstone deposited in a continental to shallow-marine setting. The shale forms a cap rock for the sandstone reservoir within the formation. The Unayzah Formation was previously known as the preKhuff clastics and is equivalent to the Haushi Group of Oman and the Arabian Gulf region. Khuff Formation (Upper Permian). This formation consists of evaporite, limestone and dolomite deposited in shallow-marine, lagoonal deposits and transitional marine, tidal-flat deposits. Lower Sudair Formation (Upper Permian). The formation consists of shale with some sandy and limey intercalations at the base. Marrat Formation (Toarcian). This formation consists of shale, argillaceous limestone and sandstone deposited in a shallow-marine setting. Dhruma Formation (Middle Jurassic). The formation consists of dense limestone deposited in a shallowmarine setting. Dense limestone seals several minor reservoir sequences.

Hanifa

Formation

(Oxfordian-Kimmeridgian).

This formation consists of shale, limestone and sandstone deposited in a basinal, euxinic setting. It also is a source rock. Jubailah Formation (Kimmeridgian). The formation consists of shale interbedded in a carbonate reservoir sequence deposited in a shallow-marine shelf setting. Arab Formation (Portlandian-Tithonian). This formation consists of evaporite and limestone deposited in a very shallow-marine, lagoonal setting. Each member of the formation (Arab D-Arab A) consists of a carbonate reservoir sequence overlain by sealing evaporites. Hith Formation (Tithonian). The formation consists of evaporite, limestone and dolomite deposited in a shallow-marine, lagoonal setting. Buwaib Formation (HaUterivian). This formation consists of shale and sandstone deposited in a shallowmarine shelf setting.

Biyadh Formation (Upper Hauterivian-Barremian). The formation consists of marl, argillaceous limestone and carbonate deposited in a coastal to shallow-

634

marine setting (west to east). Wasia Formation, Ahmadi Member (Cenomanian). This formation consists of shale, limestone and sandstone deposited in a marine setting. It is the same formation as the Nahr Umr shale of Kuwait and the U.A.E. Wasia Formation, Rumaila Member (Cenomanian). The formation consists of shale and limestone deposited in a marine setting. The interbedded limestone acts as reservoirs.

Aruma

Formation

(Coniacian-Maastrichtian).

This formation consists of shale and carbonate deposited in a shallow-marine setting. Dam Formation (Miocene-Pliocene). The formation consists of shale, marl, sandstone and limestone deposited in a molasse-type sedimentation. It is important as a cap rock for Tertiary reservoirs in some onshore and offshore fields.

Mansiyah

Formation

(Burdigalian-Helvetian).

This formation consists of evaporite (anhydrite and rock salt) and shale deposited in a shallow-marine, lagoonal setting. The evaporitic sequence of the Ras Malaab Group provides a most efficient seal. Ghawwas Formation (Helvetian). The formation consists of evaporite (anhydrite and rock salt) and shale deposited in a shallow-marine, lagoonal setting. The evaporitic sequence of the Ras Malaab Group provides a most efficient seal.

Structure and Trap Mechanisms Oil and gas production in Saudi Arabia is entirely from the Arabian Basin, apart from a small gas and condensate discovery in the Red Sea Basin. Saudi Arabia covers a large part of the Arabian Basin, which extends from the Arabian Shield in the west towards the Zagros Fold Belt to the east. Basement structures beneath the Arabian Basin have controlled deposition and subsequent structural growth to a certain extent. The Interior Homocline constitutes a belt of Paleozoic, Mesozoic and Cenozoic rocks of unusual tectonic stability. The Interior Platform comprises the area between the basin hinge line to the west and northern Arabian Gulf Sub-basin to the east and the Oman Basin to the southeast. Sedimentary rocks usually are fiat with few gentle structural undulations. Several major north-south-trending anticlinal axes presumably are related to the basement (e.g., Ghawar Field). The northern Arabian Gulf Sub-basin constitutes a depression with an Infracambrian-Early Cambrian salt sequence at the base. Salt structures differ in trends and constitute mechanisms in the major offshore fields in northwestern Saudi Arabia. The Rub A1 Khali Sub-basin is primarily a Tertiary depression devoid of Infracambrian salt structures. Economic hydrocarbon deposits are found in two types of traps of regional importance. Traps are of the structural (anticlinal) and combined structural/stratigraphic (facies) type and trend north-south. These structures are related to basement structural growth during sedimentation. Anticlinal traps

Hydrocarbon Habitat of the Greater Arabian Basins trend NE-SW and are related to the Infracambrian salt structural growth. The central Arabian oil fields have a north-south trend, which was established during the Precambrian. A NW-SE trend parallel to the Najd Fault trend is recognized, but is subordinate to the north-south trend (Fig. 1 I. 107). The central part of the Arabian Plate is cut by the central Arabian Arch, a low-dipping, east-plunging regional high that forms a culmination for migrating hydrocarbons. The arch has low relief, as the flank dips range from 1 to 20 ~ and significantly influenced the deposition and distri4T.

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Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 11.108 Regional tectonic elements in the vicinity of central Arabian oilfields (after Simms 1995, reproduced with permission for Gulf PetroLink, Bahrain). gravimetric and magnetic data indicate a 400 km bifurcating fault system on the western side of the arch, with the westernmost segment of the fault system along a probable suture on the Arabian Plate reactivated during the Hercyntan (mid-Devonian). Many shear faults active between the late Carboniferous and Jurassic were initiated (Simms, 1995). The right-lateral strike-slip movement has been related to periods of active rifting and subduction associated with the opening of Neotethys and with the Alpine closure of the Tethys Ocean. Many reversed faults are associated with the growth of oil-producing structures, and Mesozoic rocks are draped over the faults (Simms, 1995). A north-south horst block shows a gravity high almost exactly underlying the fields. Basement faults are located at a depth bordering this underlying horst, as well as some oblique, cross-cutting faults, which apparently are left-lateral, strike-slip faults in the basement. Ghawar, Qatif, Harmaliyah, Wari'ah, E1 Haba, Rimthan, Dibdibba, Jaham, A1 Hawah, Dilam, Hilwah, Ragibh, Nu'ayyim, Mazalij, Abu Jifan, Tinat, Khurais, Bakr and Fardiah fields are all underlain by uplifted basement blocks coinciding with positive gravity anomalies. The crestal stratigraphic sequences in these fields indicate repeated rejuvenation of their underlying basement uplifts and show major elongated anticlines. Karan, Abu Sa'afah, Abu Hadriyah, Dammam, Harqus, Ribyan, Maharah and Lawhah fields have the typical circular shape of diapiric structures, and all are marked by 636

distinctive negative gravity anomalies. This is because basement faulting has also penetrated the Upper Precambrian halite beds of the Hormuz Series, triggering deepseated salt diapirism and producing domal oil-field structures. Safaniya, Khafji, Kurayn, Jana, MarjanfFereidoon, Zuluf, Berri and Jurayd fields are elongated, doubly plunging structural anticlines along a general NE-NNE direction. These are due to left-lateral, strike-slip faulting in the basement, which has also penetrated the salt beds of the Hormuz Series, causing diapiric salt-wall structures at depth that have uplifted the overlying strata in elongated anticlines (Edgell, 1991). The Manifa Field is an elongated structure trending NW-SE, a doubly plunging anticline exhibiting a strong negative gravity anomaly interpreted as originating from basement faulting along a northwestern trend that has also cut the Upper Precambrian salt beds of the Hormuz Series. This allowed the lighter salt to move upwards as a broad salt wall, pushing up overlying Phanerozoic strata (Edgell, 1992). The Habah Field is clearly developed along an eastwest structural alignment. It is also an elongated, doubly plunging anticline with a negative gravity anomaly due to basement faulting and rupture of the Hormuz Series salt beds, which caused deep-seated diapirism and consequent structural growth. The Khursaniyah and Fadhili oil fields are domal structures and are considered to be due to deepseated salt diapirism. Structural traps of Paleozoic oil

Hydrocarbon Habitat of the Greater Arabian Basins fields discovered in central Saudi Arabia have a moderate relief, with generally 30-100 m (98-328 ft) of vertical closure. Horsts and tilted, asymmetric fault blocks were developed due to "Hercynian" structural movement. Extensional faulting developed regional north-south aligned axes during the Triassic (to Early Jurassic).

Oil Field Examples Most of the data on Saudi oil fields is confidential and restricted by major oil companies, such as Saudi ARAMCO and the Arabian Oil Company. A small amount of information has been published (OAPEC, 1985, Beydoun, 1988), and limited information has been released in open meetings such as the SPE Middle East Oil Shows and Middle East Geosciences. Data from some of the major fields are summarized in the Appendix tables E.

Supergiant Ghawar Oil Field The Ghawar Oil Field is a simple anticlinal structure, with a length of nearly 200 km (140 mi), a width of 16 km (10 mi) and uniform flank dips of 5-8 ~ There are six culminations (which are, from north to south: Farzan, Ain Dar, Shedgum, Uthmaniyah, Hawiyah and Haradh) (Fig. 11.109). 0

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Its presence was first indicated through the discovery of the E1 Nala anticlinal axis during the course of surface mapping in 1935. Widely spaced structural holes drilled in 1941 confirmed the existence of this major anticlinal axis, which has a total length of 400 km (250 mi). Oil of 33-36 ~ API and an oil column of 396 m (1,300 ft) was found in the Arab D reservoir and the uppermost Jubailah Formation as early as 1948 in the Ain Dar area. The next discovery in 1949, in the Haradh area was followed by Uthmaniyah in 1951, Shedgum in 1952 and Hawiyah in 1953, by which time it was evident that the total constituted a single oil structure. The Fazan culmination was discovered in 1957 (Beydoun, 1988). Production from the Ain Dar began in 1951, followed by Uthmaniyah in 1953, Shedgum in 1954, Farzan in 1962, Haradh in 1964 and Hawiyah in 1966. The first review of the field was presented by ARAMCO in 1959. Except for two small Eocene outcrops, the field is blanketed by Miocene-Pliocene continental deposits that are hard to correlate. Drilling data suggest that the effect of the E1 Nala Axis on the Miocene-Pliocene deposits was on the initial depositional dip, which became progressively less as the thickness of the accumulated sediments increased. Gravel plains cover the eastern and western sides of the structure. The structure of the Ghawar Field is well-known as a result of drilling and gravity survey (see Bouguer and structural contour maps, Fig. 3a, b, ARAMCO). It is simplest in the south, where it has a simple anticlinal form to as far north as the Huiya area, where the eastern flank shows an offset of 10-15 km before resuming the general north-south trend. An offset is apparent on the western flank, but detailed information is not available; further to the north, a central depression bordered by marginal elevations is developed. In the Uthmaniyah areas, the western elevation is only 15.2 m (some 50 ft), in contrast to a 137 m (450 ft) elevation in the east, but between the Ain Dar and Shedgum areas, the elevation on both sides of the depression is similar and of the order of 122 m (400 ft). The depression appears to be a reflection of an older structure, for it is apparent in paleostructural maps of the Aptian-Albian succession. The trend on the south Ain Dar and Shedgum structures is N 15~ E, parallel to the trend of the Abqaiq structure, and it is probably not accidental that the trend of the eastern flank sediments is nearly in line with the western flank of the Abqaiq structure. Flank dips on both the Ghawar and Abqaiq structures flatten and merge, with the synclinal axis closer to the Ghawar structure. Faulting in the Ain Dar structure appears to be smallscale and without effect on the overall structure. The evidence of growth of the Ghawar structure can be seen only in thickness variations, for no lithological changes have been detected. The paleostructural map of the Arab D shows the beginning of the Ghawar structure, which was clearly developed by the time of the WasiaAruma unconformity, although relief was still low. There was further growth during the Eocene, and further devel-

637

Sedimentary Basins and Petroleum Geology of the Middle East opment is evident during the interval represented by the Eocene-Miocene unconformity. However, by the Miocene, the development of the anticline was largely complete, and the dips in the Miocene-Pliocene continental rocks are either initial dips or due to solution collapse. Of the four Arab Formation fining-upwards cycles, only the lowest, the Arab D Member, is oil-bearing in the Ghawar Field. The range of depositional environments at the top of the Jubailah and in the lower part of the Arab D Member are little different. The general depositional environment is considered to be similar to that of the presentday Arabian Gulf. In the Arab D, however, there is a gradual transition from carbonate to evaporite deposition. Note that the Arab D Member thins from north to south as the C-D anhydrite thickens. There is a facies trend apparent in the same direction from the predominantly calcarenites in the northeast to the mixed calcarenite and fine-grained limestone to the southwest. All the carbonates in this interval are shallow-water and include types with sediments whose grain size ranges from silt or an even finer grade through sand size to conglomeratic. High oil productivity usually is associated with the calcarenitic limestone, which generally lacks a finer-grained component, implying formation under conditions under which finer material was sifted out. The gravity of the highly undersaturated Ghawar crude oil increases from north to south, in the 32-36 ~ API range; at the same time, the oil-water contact rises by nearly 137 m (450 ft). Well productivity decreases progressively from north to south, due to a reduction in reservoir thickness, the corresponding reduction in porosity and permeability (with the porosity roughly proportional to the proportion of calcarenites present in a given section) and the increasing viscosity of the oil. The average output for the whole field in 1979 was 5.09 MM.bbl\d, and total oil production had reached 19.0 B.bbl by 1979. Total estimated original recoverable oil reserves for the whole field are 80.3 B.bbl (Beydoun, 1988).

Harmaliyah Oil Field The Harmaliyah Field is in a relatively simple asymmetric anticline with few faults illustrated (Fig. 11.110), about 40 km long by 15 km wide, with the steeper, southeastern flank showing dips of 1.5~ ~. It lies east of the Ghawar Field (Fig. 11.77) and has no significant surface expression. Oil was found in 1971 in the Arab D reservoir below the C-D evaporite seal. The field went on line in 1973 and was shut down temporarily in 1980. It produced 35 ~ API oil with a 1.65% sulfur content and a 740 gas/oil ratio. Through a series of paleostructural maps, Ibrahim et al. (1981) were able to demonstrate the absence of significant structural closure during the Jurassic. A gently plunging structural nose was apparent during the BerriasianValanginian, with a 15 m (50 ft) closure somewhere northeast of the present field, which was replaced by a N-NE-

638

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Fig. 11.110 Structure contour map on top of Upper Jurassic Hith Anyhydrite of Hammaliyah oilfield of eastem Saudi Arabia (after Ibrahim et al. 1981, reproduced with pemmission from AAPG). trending, closed anticline during the ?late Albian-early Coniacian interval (most probably Turonian) caused by a potential gravity slide toward the E-NE along a pre-Upper Jurassic bedding plane. The structure adopted a more dome-like structure during the Coniacian-Maastrichtian, subsequently changing to the present anticlinal form during the course of the Tertiary. Assuming Jurassic marine source rocks and a geothermal gradient of 3-4.5 ~ C/100 m, neither the source rock nor the Arab D reservoir rocks were buffed deeply enough for primary oil migration to have occurred. Suitable generation and trapping conditions, however, existed by the Turonian-Maastrichtian, a process aided and speeded by the increased depth, compaction and hydrodynamic head resulting from late Cretaceous plate collision (Ibrahim et al., 1981). By mid 1979 the field had produced a total of 133 MM/bbl. The original recoverable oil reserves were estimated at about 1 B/bbl (Beydoun, 1988).

Qatif Oil Field The Qatif Field was discovered in 1945, after surface geology and gravity surveys had indicated the presence of a major north-south anticlinal structure. Qatif is interpreted as a low-amplitude, "banana-shaped" shear fold, convex westward, probably formed by fight-lateral displacement along basement faults and possibly enhanced by deep movement of salt from the Cambrian Hormuz Salt (Wilson, 1985). The field is an enormous structural trap measuring approximately 44 km long by 5-7 km wide (27

Hydrocarbon Habitat of the Greater Arabian Basins mi x 3-4.4 mi) and contains several Jurassic carbonate reservoirs of which two, the Arab C and Arab D members of the Upper Jurassic, are the most important, with initial production beginning in 1945. Arab C and D seals are widespread units of bedded to nodular anhydrite, and, in the Arab C Member, a lime mudstone in the middle of the reservoir separates productive intervals over part of the field (Fig. 11.111). Core-plug porosities and permeabilities are clearly associated with very sparse cements. Porosities in the upper Arab C tend to be slightly higher, but are associated with substantially lower permeabilities because the upper reservoir has poorer secondary porosity. Porosities and permeabilities generally are lower in the Qatif Arab D. Only a few of the reservoir rocks have porosities above 20% and permeabilities above 100 md (see Wilson, 1985; and Fig. 11.107). High porosities and permeabilities in the reservoirs are due to preserved primary porosity or early diagenetic secondary porosity. The average API gravity of produced oil is 39 ~ for Arab C and 38 ~ for Arab D with initial sulfur content of 2.4% and 1.6%, respectively. The initial and continuing production mechanism is a water drive. Other producing oil reservoirs are Arab A in 1948, Arab B in 1962 and Fadhili in 1963 and gas reservoir is discovered in the Permian Khuff Formarion. In 1979, the field averaged 150,000 bbl/d and total of 620 MM.bbl. The original recoverable oil reserves were estimated at 4.7 B.bbl (Beydoun, 1988).

Khursaniyah Oil Field The Khursaniyah Field is an anticlinal, domal structure whose major axis trends in a NE-SW direction. The angle of dip varies from about 4 ~ on the northern nose to about 9 ~ on the southwestern flank. Figure 11.112 is a structure contour map of the top of the Arab C reservoir with a structural cross-section of the Upper Jurassic reservoir. Khursaniyah well-1 was spudded on March 4, 1956, and during June of that year, it discovered sour oil in all four "members" of the Upper Jurassic Arab Formation and in a porous calcarenite section of the Jubailah Formation. Petrophysical characteristics were first described by Millam (1963) are summarized below. Average porosities are 23% for Arab A, 25% for Arab B, 26% for Arab C and 23% for Arab D, while the Jubailah has an average porosity of 21%. Permeability averages are 900 md for Arab A, 200 md for Arab B, 300 md for Arab C and 80 md for Arab D. The average thickness of each producing zone is 11 m (37 ft) for Arab A, 11 m (37 ft) for Arab B, 32 m (104 ft) for Arab C, 23 m (74 ft) for Arab D and 2,050 m (6,725 ft) for Jubailah. The proved oil column of the Arab A is slightly more than 366 m (1,200 ft); that of Arab B is 355 m (1,163 ft); Arab C has an oil column of 335 m (1,100 ft); Arab D is 274 m (900 ft); and the Jubailah is 102 m (336 ft). The proved areas of each producing zone are 15,500 acres for

Arab A, 14,200 acres for Arab B, 12,800 acres for Arab C, 11,300 acres for Arab D and about 300 acres for the Jubailah Formation. The gravity of the oil from the four Arab members and the Jubailah Formation is 31 o. The percent weight of sulfur varies from 2.31 to 2.55%. The original solution gas-oil ratios of the five producing zones from the Arab A in sequence through the Jubailah are 390, 360, 390, 380 and 320 cu ft/bbl. The average productivity index of each of the Arab members is 29 for Arab A, 10 for Arab B, 50 for Arab C and 53 for Arab D. The original reservoir pressure of Arab C was 3,284 psig at 1,982 m (6,500 ft) subsea. The average depth necessary to penetrate all four members of the Arab Member is about 2,134 m (7,000 ft). The estimated original recoverable oil reserves for the field was 2.2 B.bbl, reported by Beydoun (1988).

Abqaiq Oil Field The Abqaiq Field is approximately 51.2 km (32 mi) long, averaging more than 9.6 km (6 mi) in width. The Abqaiq structure consists of a long, relatively narrow anticline, with its major axis oriented N-NE-S-SW. The southern area contains an anticline of this anticline (Fig. 11.113) unusually large closure; the northern area, approximately three-fourths as long as the southern, forms a broad, relatively low extension of this anticline (McConnell, 1951). In the Arab D reservoir, the vertical distance from the top of the oil accumulation in the main anticline to the oil-water contact is approximately 457 m (1,500 ft), whereas the oil column in the northern area seldom exceeds 73 m (240 ft). Abqaiq oil is obtained from limestone of the Upper Jurassic (Arab and Hanifa formations). The layers of anhydrite divide the Arab Formation into four members, known from top to bottom as A, B, C and D. Commercial production in the Abqaiq Field is found only in the C and D members. The oil-bearing limestone, the major portion of which is either oolitic or dolomitized, extends through a total interval averaging 64 m (210 ft). Permeabilities are extremely high. Average oil gravity for Arab C is 29 ~ API with 2.7% sulfur, and for Arab D and the Hanifa is 37 ~ API with a 1.4% sulfur content. The Hanifa Formation at the Abqaiq Field consists of organic rich carbonates overlain by up to 100 m(3 50 ft) of porous, fine-grained limestone and lesser dolomites of the Hanifa reservoir facies. Core-plug porosities for the Hanifa reservoir range from 5% to more than 30%, while permeabilities range from 1 to less than 10 md (Grover, 1993). Gas was present in the Permian Khuff Formation. In 1979, the output oil from Abqaiq averaged 667,000 b/d, and had produced by mid 1979 a total of 6.03 B.bbl of oil. The field has estimated recoverable oil reserves were 8.44 B.bbl (Beydoun, 1988).

639

Sedimentary Basins and Petroleum Geology of the Middle East

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Hydrocarbon Habitat of the Greater Arabian Basins

Fig. 11.113 Structural contour map on top pf Arab-D Member in Abqaiq oil field, eastem Saudi Arabia (after McConnell, 1951, reproduced with permission from Oil and Gas Journal).

641

Sedimentary Basins and Petroleum Geology of the Middle East YEMEN

where Yemen-Hunt delineated three potential structures, Alif, Meem and Lam, based upon 1,845 km of seismic. Drilling of the first wildcat began in 1984; in July 1984, it became a discovery well, with the first oil flowing at 7,800 bbl/d, and it was declared a commercial prospect the following year. The pace of exploration quickened. Construction of a 10 M.bbl/d refinery was begun in 1985; the next year, work commenced on a pipeline from the Alif Field to an offshore oil terminal at Ras Isa, using a converted tanker for initial storage. By the end of 1987, nearly 130 wells had been drilled, only 20 of which were dry, and the Azal Field had been found and a tie made to the Alif pipeline. Production had reached 175 M.bbl/d, with most exported to Japan and Korea (Abraham, 1988). By the early 1990s, the Shabwa-Balhaf Graben and the Tertiary tableland had yielded additional discoveries, all associated with the Mesozoic sequence, and a significant Tertiary find was made in the Gulf of Aden. It is curious that the region that attracted the most attention and for which most information is available has not yielded any discoveries. In 1996,

The Republic of Yemen lies in the southwestern part of the Arabian Peninsula. It is bounded to the west by the southernmost part of the Red Sea, to the south by the Gulf of Aden, to the east by Oman and to the north by Saudi Arabia. Exploration for oil began in the 1950s, prior to the union of the Republic of North Yemen and the Peoples Democratic Republic of South Yemen. Early exploration concentrated on the Red Sea coastal region and the Tihama Basin. Two German firms, Prakla and Deilmann, focussed on the area around Salif made attractive by the presence of an oil seep and a salt mine. They carried out geological, gravimetric and magnetic surveys. A decade later, Mecom drilled and abandoned five wells after discovering only non-commercial oil and gas shows. Subsequently, more attention was given to the offshore, and in the 1970s, Shell and Hunt shot several thousand kilometers of seismic and drilled a few wells without any notable discovery. In the 1980s, exploration switched to the Ma'rib-Jawf Graben,

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Fig. 11.114 Location map of Yemen showing the major oil and gas fields discovered. The name of the fields is numbered from 130 as follows: 1. Shammah, 2. Tawila, 3. Heijah, 4. Camaal, 5. Sunah, 6. Hemiar, 7. Hemiar North, 8. Ayad East, 9. Ayad West, 10. Amal, 11. Sabatayn/Halewah (gas), 12. Jabal Habah (gas), 13. Jabal Huqum, 14. Mawza (gas), 15. A1Wihdah (oil/gas), 16. Shaharah (oil/gas), 17. A1Raja Jannah/Dostour A1Wahdah (gas), 18. A1Sa'idah (gas), 19. As'ad A1Kamil (oil/gas) 20. Saif Bin Yazin, 21. A1 Shura (gas), 22. Azal, 23. Alif, 24. Ma'eeh (gas), 25. Lam (gas), 26. Wadi Bana, 27. Meem, 28. Raydan, 29. Jabal Samadan (gas), 30. A1Tahreer (gas). 642

Hydrocarbon Habitat of the Greater Arabian Basins British Gas drilled two exploration wells on the Socotra offshore license (Block 38) which was dry. The company in late 1995 withdrew from Hood license (Block 35) after acquiring a seismic survey of 1,050 km and drilling three exploration wells. Block 10 East Shabwa operated by Total is expected to go into production in early 1997 from Atuf, Kharir and Wadi Taribah Fields, add about 20,00025,000 bbl/d of oil to Yemen production. Nimir Petroleum Co. planned to run 500 km seismic lines and drilled on well in Block 16 (Qamar) and Block 4 (Ayadh) and are exploration well in Block 33 (A1 Furt). In 1996, after completing the drilling of one dry well, Qinab-1 at Block 11 (Sirr Hazar), Elf Aquitaine relinquished the block. The major oil and gas fields discovered in Yemen, some of which are still underdeveloped, are shown in Fig. 11.114. Little detailed information is available in the literature outside of the Red Sea Province (Beydoun, 1989; Doornenbal, et al., 1991; Beydoun and Sikander, 1992; Crossley et al., 1992; Barnard et al., 1992): a short article on the Ma'rib-Jawf Basin (Abraham, 1988), one on the former South Yemen (Paul, 1990) and on the Gulf of Aden (Bott et al., 1992; Barnard et al., 1992; Crossley et al., 1992). As no detailed field studies or production figures have appeared, the hydrocarbon potential can only be discussed in regional terms.

Structural and Stratigraphic Framework The number of elements in the structural framework of Yemen depends upon the author cited, but basically the simplest is that of Beydoun et al. (1993) and Ellis, et al.,

(1996), in which a western, elevated Precambrian province with a partial cover of Tertiary volcanics is separated from what they have called an eastern tableland by a complex, NW-SE-trending graben complex. The eastern tableland is broken up by two highs. The more important of the two, the North Hadhramout High, separates the northern flank, which dips gently under the Rub A1 Khali, from the southern flank, step-faulted towards the Gulf of Aden. A southern high, the Fartak High and the South Hadhramout High isolate the Hadhramout-Geza-Qamar Basin from the narrow offshore Sayhut Sub-basin; the basin also breaks through between the Mukalla and Hoowarin highs to link with the Shabwa Basin, where a number of fields have been found (see Fig. 11.115). As a result of the Najd Orogeny in the Late Precambrian in Arabia, isolated basins were formed in basement depressions. The initial Paleozoic sedimentation in these basins in Yemen took place in continental to shallowmarine environments and consisted of conglomerates, sandstone and limestone. The Upper Cambrian-Ordovician consists mainly of continental deposits. The Permo-Carboniferous clastics were deposited in a fluvio-glacial system of sedimentation. The Upper Triassic-Lower Jurassic clastics were deposited on the unconformable surface over the Permo-Carboniferous and represent an extensional stage prior to the Middle Jurassic rifting. The Middle Jurassic is a sequence of deepwater sediments consisting of black, bituminous shale, sandstone, marl and limestone. Prior to the Tithonian, block-faulting and tilting occurred, followed by a

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11.115 Major Mesozoic-Tertiary structural elements and the location of the basins, grabens and paleohighs of Yemen (after Ellis et al. 1996, reproduced with permission from Petroleum Geoscience).

643

Sedimentary Basins and Petroleum Geology of the Middle East sequence of clean sands and evaporites. However, although an unconformity has been recognized between the Tithonian and Kimmeridgian in the northwest, marine sedimentation was continuous in the south. The Cretaceous is mainly a sandstone succession with some limestone in the south and changes facies to sandstone in the northwest. The variable Tertiary sequence consists of shallow-marine carbonates, evaporites and sandstone. Neogene volcanics cover most of northwestern Yemen. A lithostratigraphic chart of the Jurassic, Cretaceous and Tertiary with hydrocarbon parameters in the vicinity of the oil and gas fields is given as Fig. 11.116.

Hydrocarbon Parameters Ma'rib-Jawf-Shabwa-Balhaf Graben System The Ma'rib-Jawf-Shabwa-Balhaf sub-basins developed along the line of a fracture zone formed during the Precambrian Najid Orogeny (Husseini and Husseini, 1990). They reach the coast of the Gulf of Aden east of Balhaf. This system initially was thought of as a simple aulacogen with a continuation into Somalia, but now is known to be a more complex structure. The Ma'rib-Jawf Graben itself may be a series of minor grabens or half grabens and is apparently separated from the rest of the basin to the north by a younger lineament (Fig. 11.117), see also Bott et al., 1992). It contains salt domes, a line of oil seeps (Paul, 1990), and a number of oil pools. (Fig. 11.116). Prior to the mid-Jurassic rifting, there accumulated approximately 2,134 m (7,000 ft) of predominantly clastic late Precambrian to early Jurassic sedimentary rocks, which also covered most of the Arabian Peninsula. During the middle Jurassic, a like thickness of deep-water, black shale, marl and limestone were deposited and covered by 610 m (2,000 ft) of late Jurassic, Cretaceous and Tertiary deposits and a further 305 m (1,000 ft) of Quaternary sand and gravel. The single source rock is the bituminous black shale of the Middle Jurassic Amran Group, which has TOCs up to 2.9%, with the reservoir, the Tithonian Sabatayn sandstone, sealed by late Jurassic evaporites. Where the Kohlan sandstone is faulted against rocks of the Am Dubbah Group, it forms a secondary reservoir sealed by the shale of the Am Dubbah Group. The Shuqra Formation fractured limestone also is a proven reservoir in the East Ayad Field, sealed by non-fractured limestone of the same formation. Since 1984, twenty fields have been discovered in the Ma'rib-Jawf Sub-basin in Upper Jurassic sediments. The fields produce from depths as shallow as 790 rn (2,600 ft) to as deep as 2,960 m (9,700 ft). The total hydrocarbon column thicknesses of the discovered fields vary from a few meters (tens of feet) to more than 975 m (3,200 ft) of vertical relief. The fields also vary in areal size from 0.4 sq km (100 acres) to approximately 57 sq km (14,000 acres). All major hydrocarbon accumulations are structurally trapped due to extensional tectonics; some minor strati-

644

graphic hydrocarbon accumulations are associated with the major structural traps. The traps are rotated fault blocks with Tithonian sandstone draped over the blocks during structural growth (Fig. 11.118). Although the basin is still in the early stages of development, more prospects have been identified in the Ma'ribJawf part of the basin. There are another three fields in the Shabwa extension of the basin, along with three more potential fields and four new discoveries (Beydoun et al., 1993). The Shabwa production was reported by Paul (1990) to be from 3 M.bbl/d to 10 M.bbl/d. The estimated reserves, all in Jurassic sandstone, exceed 3 B.bbl of oil and 20 trillion cu ft of gas. Within the Sabatayn Group (Tithonian), the evaporites provide a regional seal, and gravity-induced salt movement provides a variety of traps. The lowstand clastic fan in this group represents important proven and potential clastic reservoirs. The distal mudstone also was deposited during this lowstand and delta progradation and provides important source rocks (Ellis et al., 1996). The Qishn sandstone locally has very good reservoir quality and forms the main reservoir facies in the area. Intraformational mudstone and shale provide laterally extensive regional seals for these clastic reservoirs. The Alif Field reserves are estimated at 500 MM.bbl. The Asa' ad A1 Kamil Field, which was discovered in 1988 and covers an area of about 60 sq km, has recoverable reserves of about 140 MM.bbl of oil and 2.7 TCF of gas. The Azal Field, discovered in 1987, is 9 km long and 5 km wide, with a discovery well that produced 5400 bbl/d oil of 39 ~ API. Other discoveries in the Ma'rib-Jawf-Shabwa area includes Saif, Jabal Nuqum, Raydan, A1 Wihdah, A1 Shura, A1 Raja and Dostur A1Wihdah (Fig. 11.114).

Eastern Tableland For convenience, the region is described in three parts. Northern Flank. Dipping gently under the Rub A1 Khali, the Northern Flank consists of a relatively thin shelf sequence of Mesozoic and Tertiary beds overlying a northwards-thickening wedge of pre-Jurassic clastics (Paul, 1990). The schematic cross-section (Fig. 11.119) shows its relationship to the step-faulted zone of the HadhramoutJeza Trough and the Sayhut Basin. The summary stratigraphic chart (Fig. 11.120) indicates that oil shows have been found in pre-Jurassic, Jurassic and Cretaceous beds. The source of hydrocarbon here is potentially from the Paleozoic beds down dip. Few wells have been drilled, so conclusions are provisional at best. Hadhramout-Jeza-Qamar Basin. This basin lies on the southern flank of the North Hadhramout High/Arch and is bounded to the south by the Fartak High and the South Hadhramout Arch, which separates it from the Say hut Basin. Because the trough contains a sedimentary section of up to 3,000 m (9,843 ft) that can be broadly correlated with the section in the Omani and Saudi fields, there is interest in Jurassic and Cretaceous oil prospects (with

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645

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 11.118 Carbonates, shales and evaporites are the dominant Jurassic fill in the Iyad sub-basin which lies in the central part of the Marib-Shabwa graben. The reservoirs in the Iyad and Amal fields are primarily in the dolomite and limestone intervals which are found both above and below the Jurassic salt sequence (Amla'ah Group) (modified from Schlumberger 1992, reproduced with their permission ).

646

Hydrocarbon Habitat of the Greater Arabian Basins the Tertiary regarded as non-prospective here). As the Mesozoic onlaps the North Hadhramout Arch, there is a potential for the development of stratigraphic traps. A few wells have been drilled near the crest of the arch, and the Tarfayt well flowed oil on a drill stem test, but the three wells drilled by Braspetro in the Jeza Trough were dry. Greater success was recorded in wells drilled between the Mukalla and Howarime highs. The Cretaceous Tawilah Group in eastern Yemen consists of fluvial-deltaic, shallow-marine and turbidite sandstone providing potential reservoirs, probably sourced from Upper Cretaceous oil-prone coals developed in eastern Yemen and sealed by transgressive mudstone and carbonates. Potential traps are stratigraphic as well as closure, resulting from drape over structural highs developed during rifting. Tarfayt well bottomed at 1,753 m (5,750 ft) in basement; 7 b/d of 32 ~ API oil were recovered during testing of the Qishn carbonates (Paul, 1990). This oil could have been generated only from a "kitchen" in the bordering Jeza Trough to the south, either from a Qishn source level or from Upper Cretaceous source levels. The Upper Cretaceous Mukalla Formation in Qamar Bay contains shale that has significant oil and/or gas potential in the offshore A1 Fatk well (Beydoun et al., 1993). This well reached a total depth of 4,300 m (14,083 ft) without penetrating the entire Mukalla Formation; TOC values of 1.18 up to 8.79 wt% (marine sapropel?) were recorded with good to very good petroleum potential and with predominantly type II organic matter (Barnard et al., 1992; Bott et al., 1992). Sayhut Basin. Extending from the Mukalla High eastwards to the Oman border, this basin occupies the narrow continental shelf (no more than 60-70 km wide) and out to the 1,000 m isobath in the Sayhut-Ras Sharwayn area (Fig. 11.119). Based upon eight wells drilled by AGIP, it is regarded as a prospective area for oil and gas (see Fig.ll.121. An important discovery was made in Sharwayn 1X, where a production test yielded 300 bbl of 40.5 ~ API oil from the Oligocene Ghadyah Formation. After production casing was run, 1,800 bbl of 43.6 ~ API oil was obtained from the Eocene Habshiya Formation, rising to 3 M.bbl/d after acidization. The well subsequently was abandoned, but it can be reentered. There, the reservoir rocks were Paleocene-Eocene limestone with the source rock in evaporitic shale and the seal evaporitic shale, anhydrite and local shale. The traps are fault-related. Ellis et al. (1996) reported that the Tertiary Hadhramout Group provides proven and potential reservoirs developed from fracturing or subaerial exposure and dissolution of the carbonate during lowstands. The seals are an impermeable, transgressive facies. Anhydrite of the Rus Formation provides an ideal seal for interbedded dolomites and underlying carbonate reservoirs. Red Sea Coastal Area and the Tihama Sub-basin

The Tihama Sub-basin, coastal plain and offshore

region is bounded to the east by the Yemen Escarpment, and has a maximum width of 150 km and a length of 350 km. As indicated earlier, exploration began in the 1950s, based upon the general similarities with the oil-rich Gulf of Suez province. Despite more than 15,000 mi of seismic and the handful of exploration wells drilled, no commercial prospects were found, although there were good oil and gas shows. The structures sought were diapirs, rim synclines, salt walls and collapse structures. In the Cenozoic sequence, good to very good source rocks have been reported in Seidiyah- 1, A1 Auch- 1, Abbas- 1 and Kathib- 1, with TOCs that may reach from 1.3 to 2.9% in the interbedded, bituminous, black shale. The components varied from sapropelic (oil-prone) to humic (gas-prone). In Zeidiyah-1, Hoideidah-2 and Kathib-1, sandstone interbedded in the overlying marine shaly section shows porosities of 12.8 to 27.6% and permeabilities of 2.0 to 24 md. Hydrocarbons in the Pre-evaporite Group are thought to be possible because of lateral facies changes and faulting, bringing the source beds in contact with more porous beds. There is even the possibility of Miocene source beds being in contact with the Mesozoic reservoirs, creating the possibility of migration to older formations. Traps may be expected in the Tihama Sub-basin and offshore southern Red Sea, where block faulting in the pre-Neogene may have created structural traps, and the reservoirs here might be tilted against a shale seal. Traps also formed by the salt structures. Anticlines with fourway dip closure can be found above pillows, reservoirs can be truncated and sealed against diapirs, and faulting induced by the halokinesis may lead to other structural traps. Stratigraphic traps may result from the influence that halokinesis has on sedimentation. There is the possibility of carbonate buildups and sandstone lenses (Doornenbal et al., 1991). Gulf of Aden Basin

In the Gulf Of Aden, although the rifting mechanisms are similar to those in the Red Sea, the exploration targets are different, reflecting the difference in stratigraphic history. In 1982, AGIP discovered black oil in well Sharmah1, where tests produced 3,700 bbl/d of 43 ~ API oil from a Middle Eocene carbonate reservoir at about 2,100 m (6,868 ft) (Beydoun, 1986, 1988) and two barrels of heavy 12~ API oil from the synrift Oligocene. The entire Paleogene and Mesozoic marine successions are present, including those in a series of subsidiary, oblique grabens in the coastal plains on either side of the Gulf of Aden (e.g., the Balhalf Graben). Several occurrences of free oil are found in the Cretaceous Harshiyat Formation in Sarar1, and 38 ~ API oil occurs in Ras Ghashwah-1 in Eocene rocks below the pre-Oligocene unconformity. The Jurassic Madbi Formation has good source-rock potential, as it is rich in organic and bituminous matter. It has been encountered in three wells at depths of less than 4,000 m (13,120 ft), suggesting that it may now be in the

647

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 11.121 Composite columnar section and hydrocarbon parameters in the Sayhut Basin (compiled with modification from Paul, 1990).

late- or post-mature phase, with earlier expulsion, before attaining present-day levels of maturity. Faulted pre-Oligocene sediments provide a good hydrocarbon habitat (source, reservoir and seal), with basin geometry controlling the sediment distribution of the overlying Oligocene and Neogene, which in turn controls the source and reservoir distribution and provides a subordinate exploration

play where the sequence is buried adequately and is mature enough to generate hydrocarbons (Beydoun, 1991). For the Infra-Evaporite Group, prospective traps are formed mainly by basement block faulting, rotated fault blocks and horsts. In the Supra-Evaporite Group, traps form by salt diapirism and salt flow, together with the structuring associated with basinward sliding and salt-

648

Hydrocarbon Habitat of the Greater Arabian Basins withdrawal draping over older horst or tilt blocks (Beydoun, 1991). Combination structural-stratigraphic traps involving an erosional unconformity parameter have a proven hydrocarbon trapping potential, as seen in the Sharmah Field, and the stratigraphic trap component has significant exploration potential elsewhere. Thermal modeling has identified a number of offshore kitchen areas in Cretaceous rocks, with excellent source potential with plays that principally lie in reasonable water depth and within the oil-generation zone (Bott et al., 1992). Potential Oligocene source rocks are immature, and lateral source, seal and reservoir facies vary rapidly. The primary structural traps are rollover anticlines associated with listric growth faults (Bott et al., 1992). In the Gulf of Aden, significant oil- and gas-prone source rocks in generally iso-

lated occurrences have been identified in the Lower and Upper Jurassic, Lower and Upper Cretaceous and the earlier Paleogene formations of offshore Yemen (Beydoun and Sikander, 1992). Source rock, about 20 m (66 ft) thick, in the Qishn Formation was reported in the Hami well in the offshore east of Mukalla, where the TOC values are between 6.0 and 12.0 wt.% of type II kerogen. The depth at which this occurs in the well is within the oil window (Bott et al., 1992). At the western end of the Gulf of Aden lies small basin known as the Abyan Basin. Its existence was the result of seismic work that showed a closed, fault-bounded structure with a sedimentary section thickening southwards. More work is required to fully establish the potential of the basin.

649

This Page Intentionally Left Blank

Chapter 12 THE HYDROCARBON HABITAT OF THE ZAGROS BASIN

INTRODUCTION

Traditionally, the Zagros is divided into three zones: the Zagros Thrust Zone, which forms the eastern margin; the Imbricated Zone, which is about 80 km wide; and the Folded Belt, in which the degree of folding decreases southwestwards (Ala, 1990). The Zagros Thrust is characterized by its nearly straight-line outcrop, suggesting that it has the nature of a sub-vertical, reversed fault separating central Iran from the Afro-Arabian Plate. The Imbricated Zone consists of a series of thrust-bound imbricated slices, which provide the highest topography of the Zagros Mountains and in which there is no basement involvement. Although there are exotic blocks of Permo-Triassic and Upper Cretaceous limestone, there is no chert or ophiolific material. The Fold Belt contains numerous anticlinal and synclinal structures, many of which may be 100 km long, with a few more than 250 km long. Their amplitudes are of the order of 1-10 km, and their increasing structural elevation is towards the northeast. The folds are asymmetric and commonly en echelon, with the southwestern limbs vertical or overturned, diminishing in intensity of deformation towards the southwest. The folds may be separated from one another by dextral strike-slip faults, reflecting an older structural trend. A very characteristic feature is the disharmonic folding that occurs above the Cenozoic evaporites. The fold belt can be divided along its axis into basins separated by swells such as the Qatar-South Fars Arch, which separates the Dezful Embayment in the center, with its concentration of the major fields, from the Pabdeh Trough to the southeast, where fields are associated with piercement domes developed over rising salt domes. The domes have dimensions of 3-10 km, with the Hormuz salts (Late Proterozoic-Early Cambrian age) rising up through as much as 3,658 m (12,000 ft) of strata. The fold belt terminates in the southeast, north of Oman at the ZendanMinab Fault Zone. In the southeast, the principal fold axes show a change in trend to a more W-E or WSW-ENE orientation. North of the Dezful Embayment is the Kirkuk (or Sirwan) Embayment, which terminates against the Ha'ilGa'ara Arch in the Syria-Turkey-Iraq border zone. Liquid oil and solid or semi-solid bitumen have been known in the area since antiquity. The first discovery was made in 1903 in Chia Surkh (Iraq), and a major oil accumulation in Iran at Masjid-i-Sulaiman was discovered in 1908; however, not until 1927, with the discovery of the Kirkuk Field in northeastern Iraq, was a major discovery found outside Iran. The largest gas discovery was made in 1966 in Pars (Iran). Most of the oil and gas fields occur within the Dezful Embayment (Fig. 12.1), which includes most of Khuzestan, the southern part of the Lurestan Prov-

The Zagros Basin is the second largest basin in the Middle East, with an area of about 553,000 sq km (213,500 sq mi). It extends from Turkey, northeastern Syria and northeastern Iraq through northwestern Iran and continues into southeastern Iran. In Klemme's 1980 classification, it constitutes a type 4A (downwarp/closed) basin. For the purpose of this discussion, the Zagros Foreland Basin is bounded to the east by the High Zagros Mountains and the Crush Zone. The western limit is less welldefined, but in a broad sense, it laps onto the Arabian Plate. In the southeast, the limit lies offshore in the Arabian Gulf; in the northwest, it lies west of the Euphrates Valley up to the Turkish-Syrian border, where the Ha'ilRutbah-Ga'ara Arch converges with the Zagros Mountains. It encompasses an area containing two-thirds of the world's oil and one-third of its gas in a narrow belt some 2,500 km long and 5-700 km wide (1,555 x 435 mi). The Tertiary collision imposed a NW-SE fold trend, which contrasts with the pre-Neogene north-south trend characteristic of the western Arabian Gulf region. All of the Tertiary reservoirs have been sourced from rocks that accumulated on the passive margin of the Arabian Craton and predate the late Eocene onset of collision. Despite a brief period of extension during the Permo-Triassic, this craton has been essentially stable since the late Proterozoic as a result of which a thick sequence of Phanerozoic sediments accumulated. The foreland basin developed with the disappearance of Neotethys as suturing began in the northwest and migrated southeastwards during the mid- to late Eocene. The suturing was accompanied by crustal thickening arid movement along the originally passive margin of the Arabian Plate and is related to the spreading movements in the Red Sea-Gulf of Aden (Hempton, 1987). Until at least as late as the early Miocene, evidence for a deep seaway along the line of the Zagros Suture is provided by the presence of Maastrichtian and Paleocene limestone exotics in a Miocene matrix, until continental collision finally gave definition to the northeastern Arabian Foreland Basin. The downwarping of the outer shelf and the uplift of the inner shelf restricted the area of deposition of upper Eocene and lower Oligocene tropical carbonate-shelf sedimentation. These conditions persisted into the early Miocene. It was in the shallower parts of the shelf in the northeast that the Asmari and Kirkuk main limestone developed, and the upper Pabdeh pelagic marl accumulated in the deeper parts.

651

Sedimentary

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Hydrocarbon Habitat of the Zagros Basin ince and the southwestern part of the Fars Province. Characteristically, the long axes of these anticlinal fields are oriented northwest-southeast, parallel to the Zagros trend. Oil was found outside the Tertiary Zagros Belt in Bahrain (1932), Saudi Arabia and Kuwait (1938) with the discovery of the Awali, Dammam and Burgan fields, respectively, in Cretaceous (Bahrain and Kuwait) and in Jurassic rocks (Saudi Arabia), followed in 1939-1940 by a Jurassic discovery in Qatar. Many other fields have been discovered in the post-World War II period. These fields have a more north-south trend, as in the Burgan and Ghawar fields, and reflect older structural trends. According to Kent and Warman (1972), many of the exposed anticlines in the easternmost Zagros either never contained oil, or late migration allowed escape at the surface. Nevertheless, the Zagros Orogeny presumably destroyed a number of pre-existing accumulations (Beydoun et al., 1992), and there are many signs in northeastern Iraq as well as in southeastern Iran of surface loss from the Late Cretaceous onwards in the form of bitumen-impregnated reef limestone and water-born bitumen pebbles in some Paleocene, Eocene and Pliocene conglomerates. The age of the reservoirs in the Zagros Basin ranges from the Permian carbonates (Iran), Triassic and Jurassic carbonates (Syria) and Triassic carbonates (northern Iraq and southwestern Iran), to the most prolific reservoirs in the fractured carbonates of the Cretaceous and Tertiary (Iraq, Iran, Southeast Turkey and Syria). The reservoirs are sourced principally from the Cretaceous. There have been several major reviews of the Zagros Basin, primarily from the point of view of hydrocarbon exploitability; of these, the works of Dunnington (1958, 1960, 1967), Lees (1933, 1953), British Petroleum (1956), Falcon (1958), Lees and Richardson (1940), Beydoun (1991) and Beydoun et al. (1992) are the most comprehensive. The post-Carboniferous subsidence history of the basin following the Hercynian phase of block faulting was described by Koop and Stoneley in 1982. Because parts of some countries such as Syria and Iraq are located in the Greater Arabian Basin also, the hydrocarbon habitat of Southeast Turkey, Syria, Iraq, Iran and some fields in the Arabian Basin are included in this chapter as a matter of convenience.

SOUTHEAST TURKEY

Introduction and History of Exploration As specified by the Law Relating to Petroleum (Act numbers 6326 and 2808), Turkey is divided into 18 licensing areas (Fig. 12.2) (Goktekin, 1989). In each area, a company can acquire up to eight concessions, each with a surface area of 5 sq km, for a period of four years, which can be extended for two additional years. Exploration for oil has had the greatest success in the

Bitlis-Zagros Zone of southeastern Turkey, a zone formed in response to the collision of the Arabian Platform with Eurasia (Sengrr and Yilmaz, 1981). From the first discovery of oil at Raman (Southeast Turkey) in 1940, until the middle 1950s when concessions were opened to foreign companies, the State Minerals Exploration Institute (MTA) and the Turkish Petroleum Cooperation together have controlled all exploration activity. Most of the companies that took concessions subsequently have relinquished them because of poor results. Only Turkish Shell has made regular, if small, discoveries. In 1983, changes were made to the petroleum laws to provide more incentives for foreign companies to explore, but the changes have had only limited success. Virtually all of the petroleum-producing fields in Turkey are located in the southeast near the Syria and Iraq border (Fig. 12.2). Table 12.1 provides a listing of the oil and gas fields in Southeast Turkey. Although some natural gas is produced in the Thrace Basin in European Turkey, it is of minor significance. The reservoir ages range mostly from Ordovician to Tertiary (Paleocene) (Fig. 12.3). Lithologically, the majority of reservoirs occur in carbonate rocks. Oil of two types has been found: heavy-gravity (with high sulfur) and medium-gravity oils. The estimated recoverable reserves are about 297.5 MM.bbl of oil and 633.4 B.cf gas (World Oil, 1992). The regional stratigraphic succession is shown in Fig. 12.3. The Lower Paleozoic beds generally comprise volcanics and clastics, while the Upper Paleozoic rocks consist of clastics and carbonates. The Triassic and Jurassic are formed of shallow-marine carbonates and evaporites. The Early and Middle Cretaceous consist of clastics in the lower part passing upward into alternating limestone and dolomite. These carbonates are deposited under shallowmarine (subtidal to intertidal) conditions. During the Late Cretaceous, neritic limestone and flysch-type, calcareous shale were deposited. The Tertiary is characterized by open-marine conditions of glauconitic shale and local reeftype beds developed under shallow-marine conditions.

Structure and Traps Structural deformation in southeastern Turkey formed in response to the continental collision of the Arabian and Eurasian plates when, during the Upper Cretaceous (Campanian-Maastrichtian), an Early Alpine Orogeny created an elongated foredeep. The late Alpine Miocene-Pliocene Orogeny resulted in further crustal shortening, reactivating earlier fault systems and creating the present tectonic regime (Fig. 12.4). The Taurus-Zagros Mountains have been subjected to regional metamorphism, large-scale uplift and nappe emplacement. The foothills are characterized by imbricate structures and disharmonic folding. The fold belt is characterized by large surface anticlines, which often are bounded by steep reverse faults. Much of Tur-

653

Sedimentary Basins and Petroleum Geology of the Middle East Table 12.1. Major oil and gas fields in Southeast Turkey l\irkey (compiled from Tiratsoo, 1984; Beydoun, 1988; various issues of Oil and Gas Journal and AAPG annual review from 1950-1990).

Year

Company

Reservoir

Age

Apr

Cumulative Production

1. Adiyaman

1971

TPAO

Karababa

Turonian

27.6

7.45 MM.bb)

2. Adiyaman South

1977

TPAO

Karababa

Turonian

20.4

115,836 bbl

3. Adiyaman North

1977

TPAO

Karababa

Turonian

32

59,000 bbl

4. Alcik

1983

TPAO

Karababa

Turonian

34

27,908 bbl

5. Barbes

1972

Shell

Karababa

Turonian

30

14.005 MM.bbl

Katin

Devonian

45-55

1,500 bbl/d lOMM.cf gas 1.700 bbl/d Condensate in Barbes Deep-1

Field

6. Deycayit

1976

TPAO

Beloka

C am pan i an

26.1

146,886 bbl

7. Beykan

1964

Shell

Karababa

Turonian

33.2

55-58 MM.bbl

8. Bolukyala

1977

TPAO

Karababa

Turonian

35.3

167,663 bbl

Karabogaz

C am pan i an

7

7

Camurlu

Triassic

Gas

1.5 BCF gas 569,686 bbl oil

Si nan

Maastricht! an

7

12.2

9. Camurlu

1975

TPAO

lO.Celikli

1964

TPAO

Beloka

Campanian

35.2

92,320 bbl

11. Cemberlitas

1983

TPAO

Derdere

Albian

30.5

2.104 MM.bbl

12. Cobantepe

1975

Shell

Karababa

Turonian

32.8

152,034 bbl

IS.Cukurtas

1985

TPAO

Karababa

Turonian

36

36,694 bbl

14. Dincer South

1981

TPAO

Karababa Camurlu

Turonian Triassic

16,7 gas

3,478 MM.bbl

15, Dodan

1965

TPAO

Sinan

MaastrichtianPal eocene

36

1,403 bbl

i6. Garzan

1951

TPAO

Garzan

Maastricht! an

25

31,65 M.bbl

17. Germik

1958

TPAO

Garzan

Maastricht! an

19

2.93 MM.bbl

18, Ikiztepe

1976

TPAO

Sinan

MaastrichtianPaleocene

11.3

88,051 bbl

19. Kahta

1958

Amoseas

Karabogaz

ConiacianSantonian

11.5

3.945 MM.bbl

20. Konaltepe

1982

TPAO

Karababa

Turonian

3!

435,260 bbl

654

Hydrocarbon Habitat of the Zagros Basin

Table 12.1 continued. 12.1 continued. Year

Company

Reservoir

Age

Apr

Cumulative Production

21. Katin

1971

Shell

Karababa

Turonian

29.5

3.59 MM.bbl

22. Kayakoy

1961

Shell

Karababa

Turonian

38.2

26.57 MM.bbl

23. Kayakoy South

1976

TR\0

Karababa

Turonian

30.4

1.67 MM.bbl

24. Kayakoy West

1964

Shell

Karababa

Turonian

34.70

18.1 MM.bbl

25. Kervan

1983

Shell

Karababa

Turonian

30

6,033 bbl

26. Kock

1972

Shell

Karababa

Turonian

27.4

12,422 bbl

27. Kozluca West

1985

TR\0

Karababa

Turonian

12

2,033 bbl

28. Kurkan

1963

Shell

Karababa

Turonian

31.4

45.617 MM.bbl

29. Kurkan South

1967

Shell

Karababa

Turonian

34.5

6.197 MM.bbl

30. Kurtalan

1961

TPAO

Garzan

Maastrichtian

33.2

214.278 bbl

31. Magrip

1961

TPAO

Garzan

Maastrichtian

18.4

14.194 MM.bbl

32. Magrip North

1969

TPAO

Carzan

Maastrichtian

27

84,285 MM.bbl

33. Malahermo

1965

Petropar

Sinan

MaastrichtianPaleocene

33

3,077 bbl

34. Maiatepe

1970

Shell

Karababa

Turonian

32.7

6.137 MM.bbl

Shell

Karababa

Turonian

33.9

502,861 bbl

31

141,475 bbl

Field

35. Maiatepe West 36. Mehmetdere

1982

TPAO

Karababa

Turonian

37. Moila

1974

Aladdin

Mardin

Cretaceous

38. Oyuktas

1972

TPAO

Garzan

Maastrichtian

31

592,005 bbl

39, Piyanko

1968

Shell

Karababa

Turonian

35.5

1.409 MM.bbl

40, Raman

1945

MTA

Beloka

C am pan i an

18.8

44.280 MM.bbl

TPAO

Garzan

Maastrichtian

13.3

31.875 MM.bbl

41. Raman West

2,801 bbl

42. Sahaban

1966

Shell

Karababa

Turonian

33.2

12.36 MM.bbl

43. Sahaban South

1978

TPAO

Karababa

Turonian

34.50

1.474 MM.bbl

44. Saricak

1973

TPAO

Karababa

Turonian

31.50

2.3 MM.bbl

45. Saricak South

1973

TPAO

Karababa

Turonian

31.5

3.34 MM.bbl

655

Sedimentary Basins and Petroleum Geology of the Middle East Table Table 12.1 12.1 continued. continued.

Field

Year

Company

Reservoir

Age

Apr

Cumulative Production

46. Sebyan

1973

Shell

Karababa

Turonian

33,4

60.380 bbl

47. Selmo

1964

Mobil

Sinan

MaastrichtianPaleocene

34.4

60.75 MM,bbl

48. Selmo West

1981

TPAO

Sinan

MaastrichtianPal eocene

34

274.864 bbl

49, Sezgin

1970

TPAO

Garza n

Maastrichtian

17

87.559 bbl

50. Silivanka

1962

TPAO

Garza n

Maastnchtian

25

6.85 MM.bbl

Beloka

Campanian

7

51, Sincan

1980

Shell

Karababa

Turonian

31.2

1.97 MM.bbl

52. Sivritepe

1977

TPAO

Karababa

Turonian

33.4

456.434 bbl

53,Yatir

1973

Shell

Karababa

Turonian

31.1

65,000 bbl

54.YatirWest

1974

Shell

Karababa

Turonian

30.9

4.57 MM.bbl

55.Yenikoy

1973

TPAO

Karababa

Turonian

31.3

7.35 MM.bbl

56. Yenikov East

1974

TPAO

Karababa

Turonian

31.3

3.49 MM.bbl

57. Yolacan

1970

TPAO

Raman

Upper Cretaceous

19

23,473 bbl

58. Akpinar

1985

TPAO

Karababa

Turonian

7

7

59, Bekias

1985

Shell

Karababa

Turonian

7

7

60, Firat West

1984

TPAO

Karababa

Turonian

7

7

61,KahtaWest

1985

Aladdin

Karabogaz

ConiacianSanionian

7

7

62. Kucukpirin

1985

TPAO

Karababa

Turonian

7

7

63, Yasince

1974

Aladdin

Mardin

Cretaceous

29

7

656

Hydrocarbon Habitat of the Zagros Basin

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Fig. 12.3. Stratigraphic correlation of rock units in Southeast Turkey, showing the distribution of source rocks, reservoirs and seals in the Phanerozoic of Southeast Turkey (modified from Soylu, 1987).

657

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 12.4. Main structural elements with dominant structural trends of oil and gas fields in Southeast Turkey. key's producible, high-quality oil has been found in the foothills and fold belt, which form in an extremely narrow rim of less than 10 km in width and 200 km in length (. Much of the present hydrocarbon production in southeastern Turkey is from structurally controlled traps in hanging-wall anticlines elongated east-west or in footwall cutoffs associated with northerly dipping thrusts in the inner zone between the Diyarbakir-Mardin High and the southern limit of the allochthonous thrust sheets (Ala and Moss, 1979; Rigo and Cortesini, 1964; Temple and Perry, 1962) (Fig. 12.4). Many of these structures are up to 50 km long and up to 10 km wide, and have a few hundred meters of closure. Most have some surface topographic expression, and Landsat interpretation shows numerous apparently closed structures that have not yet been tested (Livaccari and Merin, 1986). These promising possibilities must be tempered by the demonstration of Tasman and Egeran (1951) that there are major discordances between the surface geometries and that of subsurface structures. The folds affecting the Cretaceous rocks are tighter and discordant with respect to those in the overlying Tertiary rocks, implying that the Late Cretaceous structures have been tightened by the Tertiary structural events. The less competent Tertiary sediments generally are draped over fault blocks, as in the Garzan, Raman and Gercus anticlines. In the southern trough, extending to the Syrian border, the structures are more open, the terrain has low relief, and many of the important oil-bearing structures have been detected only through gravity anomalies and seismic mapping (Temple and Perry, 1962). The Bati-Raman (West Raman) and Garzan group of fields belong to this zone. The main producing fields of southeastern Turkey lie 658

within the foothills structural belt and the folded foreland. Small imbricate anticlines occur in the Diyarbakir trend, and elongated anticlines occur in the folded belt. Both are asymmetrical and probably consist of Paleozoic shale horizons. Many of the structures and faulted uplifts in southeastern Turkey seem to have been outlined during the late Mesozoic and rejuvenated by subsequent movements, with the strongest movement corresponding to late Tertiary (Miocene-Pliocene) tectonism. Most Upper CretaceousTertiary basins have been affected by at least two deformational phases. The dominant features in the fold belt are the large east-west-trending, elongated anticlines. The transition from the fold belt to the imbricated structures of the foothills is gradual. In the area north and northwest of Diyarbakir, almost flat-lying Tertiary sediments and Quaternary basalts cover a system of rather small, imbricated folds thrust to the south (Tasman and Egeran, 1951; Rigo and Cortesini, 1964; Ilhan, 1967, 1971). The dominantly extensional tectonics of the early Paleozoic was replaced in later Paleozoic times by compressional tectonics that may have created inverted fault traps (Cater and Tunbridge, 1992). Reservoir Characteristics

The principal petroleum reservoirs in southeastern Turkey occur primarily in the Middle to Upper Cretaceous and Paleozoic, but there also are younger reservoirs (Fig. 12.3). The characteristics of the principal reservoirs are outlined below.

Hydrocarbon Habitat of the Zagros Basin

Paleozoic Bedinian Formation (Ordovician). This formation was found to contain producible gas (3 MCF/d) in the Hazro High area. This formation offers potential stratigraphic traps, because the shale contains sand bodies that form excellent reservoirs (Erdogan and Akgul, 1981). Handof Formation (Upper Ordovician-Devonian). The formation consists of about 900 m (2,952 ft) of shale containing silty-sandy intercalations with locally developed, bituminous, black-shale intervals. In well Handof-1, 1.7 MMCF/d of gas and 36 bbl/d of condensate were tested from the Silurian sediment (Bozdogan et al., 1987),~ and light oil and gas also were recovered from sand bodies in this formation. Hazro Formation (Permian). This formation is characterized by massive, cross-bedded, orthoquartzitic sandstone near the bottom, coal seams in the middle, and shale and siltstone in the uppermost part. Oil-impregnated sandstone is seen exposed in the core of the Hazro Anticline. Well Katin-6, which produces oil from the Cretaceous Mardin Group, penetrated the Hazro sandstone that was found to yield economical amounts of gas (6 MMCF/d) (Erdogan and Akgul, 1981; Cater and Tunbridge, 1992). Well Hazro-1 tested oil from the sandstone unit, and well Barbed Deep-1 tested 1600 bbl/d oil. Minor gas discoveries in the Permian Gomaniibrik Formation in the Selmo Field (west of Diyarbakir) are rich in CO 2 and probably are sourced from intercalated coals and carbonaceous shale (Bozdogan et al., 1987; Cater and Tunbridge, 1992). Mesozoic Aril Formation (Triassic). This formation consists of about 1,000 m (3,280 ft) of carbonates (limestone and dolomites) and evaporites. Minor gas reservoirs were found locally in the Camurlu dolomite unit of this formation in the Camurlu and Dincer South fields (Beydoun, 1988) (Table 12.1). The Camurlu hydrocarbon gas reservoir and a CO 2 gas reservoir are found in the Camurlu Oil Field, where it constitutes the gas cap of the oil field. The quantity of recoverable gas is estimated at 950 million m 3, out of which only 40 million m 3 had been produced before the end of 1985 (Goktekin, 1989). Mardin Group (Aptian-Lower Campanian). About 700 m (2,296 ft) thick, the Mardin Group consists of the clastic Areban Formation at the base, followed by a thick sequence of alternating limestone and dolomite of the Sabunsuyu, Derdere and Karababa formations, which contain potential reservoir, source and seal rocks (Figs. 12.3 and 12.5). These sediments were deposited under shallowmarine (subtidal to intertidal) conditions. Tasman and Egeran (1951) have suggested that the occurrence of the large hydrocarbon accumulations in these late Cretaceous carbonates is due to a structuring event that postdated the deposition of the Mardin Group. This resulted in the uplift and subaerial exposure of the upper part of the Mardin car-

bonate sequence, enhancing porosity through fracturing, leaching and dolomitization. The porosity ranges from 4 to 30%, with a permeability commonly from less than 1 to 16 md, although fracture permeability may reach up to 750 md. In places, the Mardin Group is overlain unconformably by shale of the Germav Formation (Senonian-Paleocene), which acts as a seal. The Mardin Group is the main producing horizon in southeastern Turkey, with more than 70% of the total oil production of Turkey from the Karababa Formation, and minor production from the Derdere and Sabunsuyu formations (Erdogan and Akgul, 1981). Sabunsuyu Formation. This formation is characterized by dolomite and sandy dolomite. Porosity is mainly intercrystalline and enlarged intercrystalline ranging from 5 to 15%, and permeability is more than 10 md. Derriere Formation. The formation consists of peloidal-bioclastic packstone/grainstone and dolomites, with interparticle porosity sometimes enlarged through dissolution. Dolomitization locally increases porosity and provides intercrystalline porosity. Porosity ranges from 5 to 15%, and permeability is higher than 10 md (Celikdemir et al., 1991). Karababa Formation. The Karababa C Member consists of fossiliferous packstone (algae, mollusk and echinoid) with porosity between 1 and 10% and permeability between 5 and 10 md. The following is a list of the most important fields that produced oil and gas from the Mardin Group, which provides about 70% of the crude oil produced from the Phanerozoic of southeastern Turkey (Table 12.1 and Fig. 12.2; Rigassi, 1971; Ala and Moss, 1979; Erdogan and Akgul, 1981; Beydoun, 1988): Adiyaman, Barbes, Beykan, Cemberlitas, Dincer South, Katin, Kayakoy, Kayakoy South, Kayakoy West, Kurkan, Kurkan South, Malatepe, Raman, Sahaban, Sahaban South, Saricak South, Sincan, Yatir, Yatir East, Yenikoy and Yenikoy East. Karabogaz Formation (Middle Campanian). The formation consists of argillaceous, bioclastic limestone, chert and marl, with an average porosity and permeability of about 12% and 21 md, respectively. The formation has source-rock potential (Wagner and Pehlivan, 1987) (Fig. 12.5) and contains subordinate or minor reservoirs in the Adiyaman, Adiyaman North, Adiyaman South, Bolukyayla, Kahta and Piyanko fields (Fig. 12.2 and Table 12.1). Raman Formation (Campanian-Maastrichtian). This formation is composed of fractured, reefoidal limestone that sometimes is dolomitic. Porosity was enhanced by leaching, fracturing and jointing before the deposition of the overlying Germav shale (Tasman and Egeran, 1951; Ala and Moss, 1979). Porosity averages 17%, and permeability averages 130 rod. It is an important reservoir rock in the Beycayir, Molla, Raman and Silivanka oil fields (Table 12.1 and Fig. 12.2). Garzan Formation (Late Maastrichtian). The formation is a fractured, bioclastic to reefal limestone of shallow-marine origin (Fig. 12.6). As a reservoir, it has an 659

Sedimentary Basins and Petroleum Geology of the Middle East

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660

Late Mesozoic to Cenozoic Sinan Formation (late Maastrichtian to Paleocene). Equivalent in part to the Germav Formation of reefoidal and dolomitic limestone, this formation is considered to have been deposited under shallow-marine conditions. The reservoir has a thickness ranging from 15 to 65 m (49 to 213 ft), with an average porosity of 5% and permeability less than 5 md. The formation is an effective reservoir in such fields as Camurlu, Dodan, Ikiztepe and Selmo (Beydoun, 1988; Ala and Moss, 1979; Fig. 12.2 and Table 12.1). The analysis of natural solid bitumen (impsonite) from an asphaltic vein (Seridahli vein) and five crude oils from different reservoirs (including the Garzan and Raman fields) in Southeast Turkey by gas chromatography and gas chromatography-mass spectrometry has been interpreted by Mueller et al. (1995) as indicating that the two have no relationship with one another in terms of source materials. This conclusion must be qualified by the recognition of the low concentration of biomarkers and the degree of alteration of the highly mature bitumens. The Southeast Turkey oils are sourced from immature, mostly anoxic, marine carbonates, in which terrestrial plant material plays an insignificant role. Based upon the n-alkane

Hydrocarbon Habitat of the Zagros Basin

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BI

SUB'rlD~ ENVIRONMENT IX)MINATED BY MIcRrI'E AND A R ~ O U S

REEFTALUSAND hNTERREEFENVlROINId~NT~ T E D OCCASIONALINTRACLASTS(BICX21.ASllE~ '~

M]CRITE

BY Sili:']_l FR/M:IMEIr AND

~ ISI.ANDIX)MINATEDBY Fll~ GRAINED,TIGHT~ FLATSi~IMENTS IOCCASK)NALLYCAN ~ U D E BC/]IACLASTSAI~ Si-IglJ_ ! ~ RESULTING FROMSTORMACTIONS,OR D O L ~ ~ FROM~ ALTERATIONS)

0

Fig. 12.6. Depositional models of the Garzan Formation (Maastrichtian) in the Raman/Bati-Raman field area (A) and in the Garzan Field area (B) (after Salem et al., 1992, and reproduced by kind permission of AAPG). distribution, the source material appears to be algalderived. The oils do not appear to have been extensively biodegraded and, with the predominance of even-numbered n-alkanes and a low pristane/phytane ratio, show the characteristics of oils sourced from deposits in a carbonate and/or evaporitic environment. Crude Oil Geochemistry

Crude oils produced in southeastern Turkey may be

grouped as medium or heavy. The frequency distribution of API gravity (Fig. 12.7) based upon Table 12.1 data, shows a bimodal distribution, one centered around 30-35. API and another at 10-12 ~ API. An exception is condensate in the Barbes Field Devonian reservoir (40-450 API). The frequency diagram of both medium and heavy oil versus geological age shown in Fig. 12.8 suggests that most of the Middle Cretaceous oils are of medium gravity, whereas the younger oils (Late Cretaceous-Paleocene) are

661

Sedimentary Basins and Petroleum Geology of the Middle East

MEDIUM

Fig. 12.7. Histogram showing the bimodal oil gravity and frequency relationship of the number of fields in Southeast Turkey.

,il

i

.11j ! 9 i/111 f//jq w"1 i" ,/~ / / / / ~

HEAVY

CONDENSATE 9

.

,

lo

/Jr/

4O

2o

API" GRAVITY

FREQUENCY AGE

9~---.-- HEAVY-~ (

1,o TERTIARY

I

,s

~

MEI~

s

PALEOCENE MAASTRICHTIAN

UPPER CRETACEOUS

CAMPANIAN

1,o

1,s

~

--~

~

3o Fig. 12.8. Histogram showing the reservoir ages versus the frequency for types of oil in southeastern Turkish fields.

SANTONIAN TURONIAN

MIDDLE CRETACEOUS

CENOMANIAN ALBIAN

LOWER CRETACEOUS (PART)

APTIAN BARREMIAN

either heavy or medium. A typical heavy oil (9.7-15.1~ API) from the BatiRaman Field is produced from a very shallow depth (1,300 m or 4,300 ft) at a low temperature (150-160 ~ F). Although complete analytical data are unavailable, the oil is considered to be geochemically immature on the grounds of the possibility of water washing and biodegradation is low because of the high formation water salinity (180,000 ppm), (Genca et a1.,1979).

Source Rocks Before 1985, there were few, inadequate organic geochemical analyses to use to determine the potential source rocks for various kinds of oils. A deep test in the Raman Field showed that the underlying Triassic-Early Cretaceous carbonates contain abundant asphalt and light oil. Tasman and Egeran (1951) and Ala and Moss (1979) reported that the heavy oil (18.5 ~ API) in the Raman Field was most likely the residue of an

662

accumulation in a pre-Raman reservoir flushed during the Late Jurassic-Early Cretaceous structural event. As mentioned earlier, however, other heavy oils in younger horizons are considered to be immature. In well Handof-1, locally developed black shale is known in the Handof Formation, which Rigo and Cortesini (1964) described as bituminous. The Maastrichtian dark, bituminous, marine shale of the Germav Formation is regarded as the best source rock in southeastern Turkey; Ala and Moss (1979) argued that following the Late Jurassic-Early Cretaceous structural event, the only potential source rocks are restricted to the Upper Cretaceous. Most of the early sequence consists of neritic carbonates, and it was not until the increased rate of subsidence during the Maastrichtian allowed the deposition of finer, organic-rich, clastic material in a deeper- marine environment that source rocks were deposited. In the Beykan, Kurkan, Kayakou and Katin fields, the flysch sediments of the Kastel Formation separate the Mardin carbonate pay zones from the Germav shale. In this area, the Mardin Group is underlain directly by Paleozoic sequences, so Ala and Moss

Hydrocarbon Habitat of the Zagros Basin

TRIASSIC-JURASSIC FORMATIONS

PALEOZOIC FORMATIONS

I0 9 8 ~SILURIAN FM.}

7 6

A

o~

5

6

~

5

[_

3

43 2

FERM~

I

2

1

1 0

0

576 READING

2 0 4 ~

CRETACEOUS FORMATIONS

TERTIARY FORMATIONS

u~

6

16

m t<~ m+

1.4 1.2 10

i t'u<x:

N

O.8 0.6

t,,t,1

++ +t+ +,

2

+

I~~

h dJi'

ill

I ! I i1 III

~o

l,I]L,111 ,,,,,pijl+l,j] 9 6 ~

796~

Fig. 12.9. Total organic carbon of Phanerozoic formations in Southeast Turkey (after Harput and Erturk, 1991). A

B

C28

TYPE I

90o

29

0

700

9

,5o0

/: :.:o.. :o._;

o

o~176 .~

3o0

r

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./

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,o

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9

o

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o

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w +

"o

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-27

70

99

......:oo. 9

m dlll m TYPE .

,

9

~

,

60

,

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II

l C

W'

2,

9

9o

"

'

70

~

.

so

.

.

.

3o

.

~

1o

C

2'

~10

31

n3CSATURATES(O/O01

0 ~

I

9 I~DAS II

9DADAS []

Fig. 12.10. Source-rock analysis of the Dadas Formation (Upper Silurian-Lower Devonian) in Southeast Turkey (after Soylu, 1987, reproduced by kind permission of Balkema): A=hydrogen-oxygen index plot; B=triangular diagram showing relative amounts of (~7, C28 and C29 steranes; C=isotopic data (saturates versus aromatics). 663

Sedimentary Basins and Petroleum Geology of the Middle East (1979) suggested long-range migration from a Germav source to the southwest, where the Kastel Formation pinches out and the Germav shale is unconformably overlain by the Mardin Group.

Cretaceous Mardin Group were generated from source rocks within the Silurian to Devonian Handof and Dadas formations, and the Lower Paleozoic hydrocarbons are likely to have the same source (Cater and Tunbridge, 1992).

Paleozoic Formations The Cambro-Ordovician sediments of southeastern Turkey have low source potential for the total organic carbon content (TOC) ranges from 0.05 to 0.6%. The alternating shale, siltstone and limestone of the Devonian to Permian (Koprulu and Hazro Formations) have moderate source rock potential and a TOC content ranging from 0.5 to 0.6%, but may reach more than 2% in some thin intervals (Fig. 12.9a) (Harput and Ertuk, 1991). Bedinian Formation (Upper Ordovician). This formation contains dark-colored, marine shale with high source potential and, through a process of continuous migration, can account for all of the oils in southeastern Anatolia of varying API gravities found at different stratigraphic horizons (Erdogan and Akgul, 1981). Based on phytoplankton evolution and sterane carbon distributions presented by Gurgey and Harput (1990), the source rock of southeastern Turkey can be divided into two groups. Group I oils (Sinan, Germik, Garzan, Silivanka, Beycayiri, Bati Selmo, Cemberlitas and Adiyaman fields) were derived possibly from Cretaceous source rocks. Group II oils (Raman, Bati-Raman, Magrip, Camurlu, Bail Kozluca and Guney Saricak fields) are the mixture of oils generated from both Cretaceous and Paleozoic source rocks. Fig. 12.3 shows the source-rock distribution from the Cambrian-Paleocene.

Dadas Formation (upper Silurian-lower Devonian). The formation was divided into three members (Dadas I-III) (Soylu, 1987). Dadas I has a thickness ranging from 49 to 101 m (161 to 331 ft) of shale, with argillaceous limestone bands and source-rock potential (TOCs ranging from 1.74 to 5%), a mixture of type II and HI kerogens (Fig. 12.10a) and significant amounts of C25 alkanes characteristic of terrestrial organic matter. The abundance of C29 steranes relative to C27 steranes (Fig. 12.10b) indicates a terrestrial source. The carbon isotope values for the alkanes are from-28.2 to-30.1 per mil (Fig. 12.10c). These kerogens reveal the presence of abundant sapropelic material (Soylu, 1987). Dadas II has a thickness ranging from 5.5 to 317 m (18-1,040 ft) of shale, with limestone and sandstone intercalations (Soylu, 1987) and few significant source potential of type II kerogen (Fig. 12.10a). Dadas III consists of shale and sandstone intercalations, with thin dolomite, limestone and marl interbeds that have an excellent source-rock potential. They range in thickness from 22 to 113 m (72-371 ft). The TOCs of about 5% contain type II kerogen and some type III of terrestrial organic matter (Fig. 12.10a). The amount of C29 steranes is greater than the amount of C27 steranes (Fig. 12.10b) and carbon isotope values ranging from -28.8 to -29 per mil (Fig. 12.10c) (Soylu, 1987). The light, low-sulfur oils in the

664

Triassic-Jurassic Formations The Triassic-Jurassic sediments of southeastern Turkey, composed of dolomite and marl, generally have a low TOC content (0.01-0.5%), but may contain a few intervals of high organic content rising to 8% (Fig. 12.9b), according to Harput and Erturk (1991). They concluded that the Cretaceous sediments have good to moderate source-rock potential.

Cretaceous Formations Derdere Formation (Cenomanian-Lower Turonian). This formation, consisting of bioclastic-pelagic lime mudstone and wackestone, was deposited in a reducing environment in a partly closed basin. The maturity of this formation ranges from immature to late mature, with an average TOC content of 1.5% (ranging from 0.3 to 2.2%) (Celikdemir et al., 1991). The organic matter is composed of type II and mixed type II and type III kerogen (Sengunduz and Soylu, 1990). Ortabag Formation (Coniacian-Campanian). The formation has a TOC content of around 1% in black carbonate and clayey carbonate with amorphous-herbaceous organic matter. Kiradag Formation (Maastrichtian). This formation has a very high TOC content from 0.5 to 7.5% (Fig. 12.9c) of woody organic matter and ranges from immature to early mature; however, the shale layers of the Germav and Kastel formations (Maastrichtian-Paleocene) have very low source-rock capacity, with TOCs ranging from 0.3 to 0.5%, despite some thin beds with a TOC of as high as 4%. Karababa Formation (Santonian Karababa-A Member). The lower part of this formation is a dark, muddy carbonate (bioclastic-pelagic lime mudstone and wackestone) with a good source-rock quality, with TOCs of between 0.76 and 7.65% (Table 12.2). The type of organic matter is mainly amorphous, sapropelic kerogen of Type I or Type II (Fig. 12.11); in some wells, there are minor amounts of coaly, organic matter (Soylu, 1991; Wagner and Pehlivan, 1987). The unit also shows different levels of maturity based on spore-color index (SCI), ranging from early mature (SCI=3.5) at well Sahabe-1 to over mature (SCI=8) at well Karadag-1 (Table 12.2 and Figs. 12.11 and 12.12)(Soylu, 1991). Karabogaz Formation (Campanian). Of dark, muddy carbonates (bioclastic lime mudstone and wackestone with chert and pelagic foraminifera), the formation has a TOC content ranging from 0.53% to 7.88% (Table 12.2), with typical marine, organic matter composed of Type I or Type II kerogen (Fig. 12.9) (Soylu, 1991; Wag-

Hydrocarbon Habitat of the Zagros Basin

A

1 12 9 J 800,

J. 7.1

800

i,/TM 71,/

....

~

1

8 o

50

.~

150

250

,

,

,

50

350

OXYGEN INDEX

,

,

150

,

35o

250

OXYGEN INDEX

Fig. 12.11. Hydrogen index-oxygen index graph for the Upper Cretaceous Karababa A Member (left) and Karabogaz Formation (right) of Southeast Turkey (after Soylu, 1991). The names of the wells plotted here are listed in Table 12.2. 37130

20

N

1~..7.5 7

ERNENEK

J

9

GLOBASi

ozo:/)N

llt,

654 GAZIANTEP m

11

f i

BIRECIK

37" o

~24 -~

|

9s i

.

.

.

.

.

.

I.,

....

t

j

i

.

ao~ "

I

i

Fig. 12.12. Maturity distribution of the Cretaceous Karababa A Member and the Karabogaz Formation in the Adiyaman area, District XII, Southeast Turkey (after Soylu, 1991). See Fig. 12.2 for the location of the area and Table 12.2 for the name of the wells (1-26). ner and Pehlivan, 1987). The spore-color index (SCI) is from early mature (SCI=3.5) in well Sahabe-1 to over mature (SCI=9) in Gedik-1 (Table 12.2 and Fig. 12.12).

Kastel

Formation

(Campanian-Maastrichtian).

The formation is well developed in the Kastel Basin and includes marls, argillaceous limestone and organic-rich black shale with TOCs of 1.5-2.4.

Tertiary Formations

tiary sediments (carbonates and conglomerates) generally is very low (0.1 to 0.5), but some high TOC readings occur in dark-gray limestone (TOC 1.2 to 1.8%) (Fig. 12.9d). They are immature in District X, but over mature in the eastern part of District IX of southeastern Turkey (Harput and Ertuk, 1991). The Germav shale most likely is the source of the hydrocarbons reservoired in the laterally equivalent Sinan Formation at the Selmo Field (Ala and Moss, 1979).

The TOC content and source-rock potential in the Ter-

665

Sedimentary Sedimentary Basins and Petroleum Geology of the Middle East Table 12.2. data for the Cretaceous Cretaceous Karabogaz Formation Formation and 12.2. Source-rock-quality data and Karababa Karababa A Member Member from wells in Southeast Turkey (compiled from Soylu, 1991). The location of the the wells is shown in Fig. 12.10. The

WELL

KARABOGAZ FORMATION

KARABABA A MEMBER

TOG

HI

SGI

TOG

HI

SGI

1. Adiyaman-2

3,35

709

7.0

-

-

-

2. Alidag-2

t.90

250

7-7.5

-

-

-

3, Avsar-l

3.23

811

4.5

6.11

750

4.5

4. Bakrachi-2

1.21

618

4.5

-

-

-

5. Bcsni-t

2.16

764

5.0

1.91

766

4.5-5

6. B. Piriii-l

1.50

239

-

1.5

239

7. Calgan-1

2.10

338

6.5

'

-

-

8. Cemberlitas-5

-

-

-

1.63

225

4.5-5

9. Cukurtas-2

-

-

-

1.12

173

7.5

10. Dudcre-1

1.17

439

5.5

1.05

407

5.5

-

-

-

2.47

732

5.5

12. Firai-2

0.99

472

5.5-6

0.95

488

5.5-6

13. Gedik-1

1.07

29

8-9

1.05

121

8-9

14. Gokviran-l

2.96

787

4.5

7.65

498

4.5

15. Karadag-1

-

-

-

2.16

326

8.0

16. Karakopru-1

1.13

474

5-6

-

-

-

17. Karahoyuk-1

3.74

774

5.0

-

-

-

18. Kayaicpc-1

0.66

68

5.0

0.70

52

5.0

19. Kinik-1

0.95

304

-

-

-

'

20. Kocali-1

0.53

43

7.0

0.76

40

7.0

21.Mutlu-l

1.18

107

8.9

-

-

-

22. Sahabc-1

3.48

577

3.5-4

1,11

578

3.5-4

23. Samsat-1

3.20

670

6.5

4.10

712

6.5

24. Sa2gin-2

7.88

709

5.0

-

-

-

25. Suvarli-2

2.00

430

7-7.5

2.01

613

5-6

26. Tumay-1

-

-

-

0.83

227

-

11. Durukaynak-2

TOC=Total organic carbon; HI=Hydrogen index; SCI=Pore color index.

666

Hydrocarbon Habitat of the Zagros Basin

Seals and Seal Formations The bulk of the oil reserve in southeastern Turkey is contained in Aptian-Lower Campanian shelf carbonates (Mardin Group) and in Upper Cretaceous-Paleocene reef limestone deposited on the crest and flanks of the Mardin high, sealed by thick shale sequences overlying and interfingering downflank with the carbonates. The open-marine shale of the upper Germav (Maastrichtian-Paleocene) and the Gercus shale (lower Eocene) of a continental to marginal-marine environment supplement the Upper Cretaceous shale as seals for the important Cretaceous carbonate reservoirs. Significant hydrocarbon shows in the epicontinental Paleozoic sequence indicate the presence of potential reservoir and seal. Their distribution is controlled by Mesozoic erosion. The lower Paleozoic Handof shale acts as an effective seal for underlying or intercalated reservoirs. The lower Koprulu carbonates form a seal over Handof gas reservoirs, and the tight, upper part of the Hazro sandstone seals the Hazro oil and gas reservoirs. Gas reserves exist in the Triassic dolomites (Camurlu Dolomite Unit) under evaporite seals, even though both the reservoir and seals are of limited extent. The main cap-rock formations over oil and gas reservoirs in southeastern Turkey are indicated below; others are shown in Fig. 12.3. Telhasan Formation (Triassic). This formation consists of lagoonal evaporites and is the probable seal for significant gas accumulations in Triassic Aril dolomites in the Camurlu and Dincer South fields (Ala and Moss, 1979).

Kastel

Formation

(Campanian-Maastrichtian).

About 200 m (656 ft) of shale, marl and argillaceous limestone, the formation is a good seal for hydrocarbon reservoirs in the underlying Karabogaz and Karababa formations (Temple and Perry, 1962; Rigo de Righi and Cortesini, 1964; Rigassi, 1971). Mardin Group (Aptian-Lower Campanian). About 700 m (2,297 ft) thick, this formation is a shallow- to deep-water, carbonate sequence with minor clastics. There are three distinct reservoir intervals, separated by source and seal rocks. The basal unit of the Derdere Formation (pelagic lime mudstone) seals the Sabunsuyu reservoir, while the basal unit of the Karababa Formation (pelagic lime mudstone) forms a seal over the Derdere Formation.

Karabogaz, Sayindere and Beloka formations (upper Campanian). These formations consist mainly of pelagic limestone of a deeper shelf to basinal setting. They are transgressive in character and form good seal rocks over the Mardin Group. Kiradag Formation (Maastrichtian). The formation, consisting of a thick sequence (about 200 m, or 656 ft) of shale with occasional sandstone, partially seals the Mardin limestone's major oil and gas reserves and the Maastrichtian Raman limestone's oil accumulations (Ala and Moss, 1979; Rigassi, 1971; Temple and Perry, 1962).

Germav

Formation

(Maastrichtian-Paleocene).

With a maximum thickness of 850 m (2,788 ft), the formation consists of open-marine, argillaceous sandstone, limestone, shale and marl intercalations. It is the most important seal unit in southeastern Turkey. The shale of the lower Germav is the main seal for major oil accumulations in the Raman and Garzan limestone reservoirs, whereas the shale of the upper Germav acts as a lateral seal for subordinate oil reserves in the higher Sinan limestone (Ala and Moss, 1979; Rigassi, 1971; Rigo and Cortesini, 1964). Gercus Formation (lower Eocene). This formation consists of a few hundred meters of shale, mudstone and minor sandstone, conglomerate and gypsum deposited in a coastal-mud-fiat to marginal-marine environment. It is a top seal for local oil accumulations in the Sinan reefal limestone (Ala and Moss, 1979).

Oil Field Examples To illustrate the typical fields, brief outlines of the Rami, Bati-Raman, Garzan and Dodan fields are given here and summarized in the appendix. Raman and Bati-Raman fields. These structures are two separate closures, which appear to form one very long, E-SE-trending to W-NW-trending surface anticline (Salem et al., 1992). The closures are separated by major cross fault or fault systems. The western part of the structure is the Bati-Raman Field, and the eastern part constitutes the Raman Field (Fig. 12.13). The Raman Field is an east-west-trending, narrow, elongated, double-plunging anticline, bordered by a major reverse fault in the south with a length of 12 km, an average width of 2.75 km and an approximate vertical closure of 150 m (492 ft). The field was discovered in 1946 and went on stream in 1958. The field is half dome, gently dipping on the northern flank (18~ steeply dipping to the south and bounded by high-angle reverse faults on the south side (Fig. 12.14). The form of the structure developed as a result of the Savic phase of the Alpine Orogeny; the final folding and eastwest-trending reverse faults formed following the major compressional movement, pre-dating the pre-Maastrichtian normal step-faulting (Sener and Bakiler, 1989). The main producing zones are the Cretaceous Mardin Group and the Garzan Formation. The Mardin Group is overlain unconformably by Lower Maastrichtian terrestrial clastics, shallow-marine shale and limestone intercalations of the Kiradag Formation, followed by the Maastrichtian Garzan Formation. The Garzan and Kiradag formations fail to cover the paleohighs of the underlying Mardin Group (rudist buildup). The field produces mainly from Mardin carbonates, with an oil-water contact (OWC) encountered at 3,000 m (9,840 ft), and from the Garzan Formation to the north and east, usually with the same OWC as the Mardin. The field contains more than 611.4 MM STB oil inplace. The oil gravity varies from 15 ~ to 19 ~ API areally. Appendix tables include the basic geological and reservoir

667

Sedimentary Basins and Petroleum Geology of the Middle East

~THRUST F A U L T ,"

C' --" ,0M

BAT'RAMAN

"

~

/

~.,.~----,aRAMAN__.~r.~.~_______. " - ' - - - ' ' ~~fO l~i , ~ ) .

~~-"__~~10~%~.

Fig. 12.13. Structural map showing the top of the Garzan Formation (Maastrichtian) in the Raman/Bati-Raman field area (after Salem et al., 1992, and reproduced by kind permission of AAPG).

120(:1 100(

800

~-:.:-".i:ii:-:"!::::...::;::.":::: ~9

:.:"" :-2 ' : - - ' ~

-

6013 9

"-"

-

- -z_---L---_-

---I-"----------

-i--

. 20o -.

--

--

-- -I ' -- r - . .

- F

.

9. -

-. -

1

.

.

.

_-_r_

200. - - _ - -

.

-

.

.

I- -

FZ_--__->:

"

F----

-.

---I I -

--

_- - I

L

---

Fig. 12.14. Structural cross-section across the Raman Oil Field, Southeast Turkey (modified from Tasman and Egeran, 1951).

"-

I - ~ -'- - ~ - ~ "-~ t - -- - - - ----- --:

--

I'I-

-

_

--1 F

F .

"

-------

I

o, . --

. . . . .

I. . . . . 1- - -

-

.

- -----'----I-

.

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Ii t ...----- ...... ----..... ............... 9 ......... .-..-- ~

=

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.:

~

_ --I-f

RE-

-

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.k_-~.

-

4OO

6OO

[.[.U.~ UPPF_.RbtlDYAT(UPPERHI:HA)FORMATION

~

GERMAVFORMATION

E~ ~

~

GARZANFORMATION

......

KIRADAGKARABABAFORMATION

LOWF_..RbtlDYAT(LOWERHOYA)FORMATION GERCUSFORMATION

500 mi.

0 t.

D

l

J POSSIBLEACTIVEFAULTSDURING / ~DEPOSITIONOFGARZANFORMATION

D --

i

__

u 1.

\',=

D JD

"/••

fi+aJLT

"~Ti-~UST FAULT

u/D

C.!

= 25M

Ul D ~ : z l ~ l IKnl

Fig. 12.15. Structural map on top of the Garzan Formation (Maastrichtian) in Garzan Field (after Salem et al., 1992, and reproduced by kind permission of AAPG).

668

Hydrocarbon Habitat of the Zagros Basin data for the Raman Field. The areal variation of temperature is related to the formation depth. The structurally lower parts of the reservoir to the north and northeast contain lower API oil at higher temperatures (155 ~ F), whereas higher parts contain higher API oil at lower temperatures (140 ~ F). The Bati-Raman Field was discovered in 1961 by TPAO and is the largest oil field in terms of size of structure and reserves. It is an elongated, partly asymmetrical anticline approximately 18 km long (Fig. 12.13) and 3.5 km wide, with an average structural closure of 160 m (525 ft). It produces from the Garzan carbonates, which form a stratigraphic trap. The formation in both the Raman and Bati-Raman fields is composed of agglomerations of small, reefoidal buildups surrounded by shell detritus and capped by shallow-marine lime mudstone (Fig. 12.6). The Garzan limestone is a reef that exhibits rather pronounced heterogeneities both areally and vertically. In the eastern half, the formation is chalky, clean and porous, but low in permeability; in the central and western parts, a welldeveloped system of secondary porosity and permeability is believed to exist. In these areas, the existence of a secondary vugular porosity interconnected by fissures appears to be superimposed over a low primary porosity (Genca et al., 1979). The reservoir limits are the water-oil contact at 600 m (1,968 ft) subsea to the north, a fault system in the southwest and a permeability pinchout to the southeast. The reservoir and fluid characteristics are summarized in the appendix. The oil column is 180 m (590 ft) long and consists of very heavy crude oil (having an API gravity ranging from 9.7 ~ to 15.1 ~ high in sulfur (5.7%) (Genca et al., 1979). There are some 2 B.bbl of oil in-place, but because of oil gravity and a permeability barrier, only a relatively small amount is recoverable under primary and secondary recovery methods (Beydoun, 1988).

Garzan Field. This field was discovered in 1951 and went on-stream in 1956. The field lying northeast of the Raman Field is a structural anticline that measures 11.5 km long and 1.5 km wide. It consists of three separate closures (Fig. 12.15); the two eastern closures constitute the Garzan Field, and the small westernmost one constitutes the Germik Field. Oil is produced from the Garzan Formation with accumulations in a small oyster bank that proliferated in bays and estuaries or nearshore lines (Fig. 12.6). The formation is the main producing horizon in the Garzan Field. The Garzan Formation was divided into three members from base to top m A, B and C. Garzan B and C contain hydrocarbons with API gravity of 24 ~ oil and viscosity of 6.75 cp undersaturated (Table 12.3). The Garzan structure is a double-plunging anticline bordered by a major reverse fault extending along the southern flank (Fig. 12.15). To the north, the reservoirs (Garzan B and C) are defined by a lateral thinning of the porous limestone interval as the facies wedge out (Warren et al., 1987). Dorian Field. Located approximately 55 mi. from the Bati-Raman Oil Field (Fig. 12.2 and Table 12.1), this field was discovered in 1965 by TPAO. The Dodan structure is a NW-SE-trending anticline, with a length of 5.5 mi and a width of 1 mi. The field contains a large volume of CO 2, with a gas potential found in three formations m Upper Sinan, Garzan and Mardin limestone m at depths of about 854 m (2,800 ft), 1799 m (5,900 ft) and 2226 m (7,300 ft), respectively. With the latest development wells drilled since 1980, a total gas reserve of 250 MMSCF is estimated to exist in the zones. The composition of the natural gas contained in each formation is similar, predominantly consisting of CO 2 and an API gravity of about 36 ~ The reservoir pressure of the Dodan Field varies from 1650 psig to 2400 psig with depth.

669

Sedimentary Basins and Petroleum Geology of the Middle East

SYRIA Introduction and History of Exploration Syria occupies an area of 185,180 sq km (71,498 sq mi) in the eastern Mediterranean (Fig. 12.16). The principal crude oil pipelines that link the Syrian Petroleum Company fields in northeastern Syria with the port of Tartus and supply the Homs refinery are shown in Fig. 12.16. An Iraq Petroleum Company (IPC) pipeline crosses the country from Iraq to Homs, with branches to Baniyas and Tripoli. A new line links the Shell fields in central Syria near Deir Ez Zor through the IPC line to Homs. Refined products from the Homs refinery supply Damascus, Aleppo and Latakia. In the southwestern extremity of the country, the Saudi Arabian pipeline crosses from Jordan to Lebanon, but has not been used since 1988. The generalized stratigraphic column of Syria, showing the distribution of reservoirs, source rocks and seals, is shown in Fig. 12.17. The Paleozoic section consists of alternations of shallow-marine sandstone, shale and minor carbonates. The Triassic and Jurassic rocks comprise lagoonal carbonates and evaporites alternating with continental sandstone. The Cretaceous is comprised of marine limestone, dolomites, marl and subordinate sandstone. The Paleogene section is formed of marine carbonates and marl, while the Neogene is dominated by shallow-marine and lagoonal limestone, evaporites and clastics. Accounts of the history of exploration in Syria have been published by OAPEC (1985); and Beydoun (1988) N

~.

'

provides the basis for the following discussion. The first exploration efforts accompanied with geological field work were carried out between 1934 and 1937 in northeastern Syria, and deep exploration drilling began in 1939 shortly before the outbreak of World War II. The IPC, in association with the state-owned company that later became the Syrian Petroleum Company, discovered gas at Jebissa and Ghouna in the late '30s and '40s, but these fields were not developed until much later. Exploration lapsed during World War II and did not pick up until the '50s; between 1939 and 1965, only 18 wells were drilled. The first major discovery, the Karatchok Field, was made in 1956 by the American independent Menhall Company, followed by a second discovery of the Suwaidiyah (Souedie) Field in 1959 by Concordia. Subsequently, in 1962, the discovery of the Rumailan Field by the Syrian Petroleum Company followed the nationalization of all oil operations. Exportation of hydrocarbon began in 1968 with Soviet help in the completion of the pipeline to Tartus. Only in 1975 did the Syrian government begin to award production-sharing contracts to foreign operators. Significant discoveries were made in the mid-1980s, when the existence of the Euphrates Graben (Fig. 12.18) was confirmed by the drilling of A1 Furat-9, which bottomed in Upper Cretaceous argillaceous limestone at 2,960 m (about 9,700 ft) after penetrating through mature Upper Cretaceous source rocks. The subsequent drilling of Thayyem (Fig. 12.18) on a prominent, tilted fault block a few miles west of Deir Ez Zor in the Rasafa contract area discovered a pool of light (33 ~ API), sulfurous oil in the Jeribe limestone (Miocene) and a much larger pool of sweet, light (36.7 ~ API) oil in the Lower Cretaceous Rut-

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670

Hydrocarbon Habitat of the Zagros Basin

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671

Sedimentary Basins and Petroleum Geology of the Middle East SW

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672

Hydrocarbon Habitat of the Zagros Basin bah sands. Subsequently, exploration expanded eastwards into the Ash Sham contract area, where 26 of the 28 commercial pools are located. The Euphrates Graben generally is about 50 km wide, but is a complex of many smaller grabens (Fig. 12.19). Rifting began early, with the syndepositional Derro sandstone, and had largely ended by the deposition of the Upper Shiranish limestone in Campanian-Maastrichtian time. Sabkha and proximal marine carbonates dominated the sequence until the late Miocene-Pliocene collision with the Eurasian Plate, after which time the deposits were entirely continental. Presently, there are a number of producing fields (Fig. 12.16 and Table 12.3), although many of the newly discovered fields are small, and production data are not available for all fields. The principal reservoirs are in rocks Carboniferous to Tertiary in age, with most production from Cretaceous carbonates and minor production from sandstone (Table 12.3). Most fields have multiple producing reservoirs and more than one type of hydrocarbon (medium and heavy gravity oil, condensate and gas). The Paleozoic sequence, while it holds some potential with some minor oil-prone source rocks, currently is not a potential future target. The major traps occur in elongated, asymmetrical anticlines that continue into Turkey (Fig. 12.19). They often are controlled by pre-Miocene basement block-faulting and may be involved in two phases of folding. The seals tend to be either shale or evaporites. The evaporites are common in the shallow-marine or transitional Triassic, Jurassic and Neogene, whereas shale tends to form the cap rocks in Permian, Cretaceous and Paleogene marine sequences. Estimated producing wells in Syria total 106. The proven recoverable oil reserves of Syria are estimated at about 3 B.bbl, and about 8 TCF of gas (World Oil, 1993). In the following sections, an attempt will be made to characterize the nature of the variety of the most important traps, reservoirs, source rocks and seals in Syria and to summarize the available geochemical characteristics of the known crude oils. To illustrate the principal features, accounts of, or references to, typical fields will be included. Thus, attention will be concentrated on the characteristics important from the petroleum standpoint rather than on the lithological or environmental aspects presented in earlier chapters. They are based upon data presented by Weber (1963, 1964), Metwalli et al. (1972, 1974), Wetzel (1974), Ala and Moss (1979), Syrian Petroleum Company (1981), Beydoun (1988) and OAPEC (1989).

Structure and Traps The comparison between the location of the major fields in Syria (Fig. 12.16) with the map showing the principal tectonic units shows the clear relationship between the hydrocarbon traps and the structural elements. In fact, the commercial hydrocarbon deposits occur in anticlinal

traps particularly in the northeastern part of the country (Fig. 12.19). A distinction can be made between this anticlinal zone and the more stable shelf and basin elements such as the Sirhan Basin (Jordan) and the Rutbah Uplift (Iraq). The two are separated by the Palmyra Mountain Fold Belt, which is characterized by closely spaced folds and steep, tilted blocks. To the southwest, the folds converge and merge into the north-south--oriented Anti-Lebanon Range, which extends southwards into the Judean Mountains. To the northeast, the fold axes diverge and form a system of en echelon structures in which important discoveries have been made. The folds were formed during the Cretaceous to Pliocene Alpine Taurus-Zagros Orogeny (Weber, 1963, 1964; Wolfart, 1967 a & b; Metwalli et al., 1974; Ala and Moss, 1979; Lovelock, 1984; Beydoun, 1988; and Best et al., 1993). Halokinetic movements of Infracambrian salt, if present, are not significant. Syndepositional movements were active through the Oligocene, with the main uplift in the Mio-Pliocene, at which time many of the high-relief, closed anticlines were formed. The folds extend northeastward into the Mesopotamian Foredeep as broad, open folds that became steeper towards the northeast. This area includes the Tuwal AbbaSinjar Swell (Fig. 12.20) with the Karatchok, Rumailan and Souedie fields, and the smaller Ulayyan and Hamzah fields in a narrow trend near the Turkish border. Major updip oil migration from Permo-Triassic source rocks probably occurred during the Eocene, charging the Jurassic reservoirs in the Ramadan and Souedie fields. Thus, the downdip Karatchok Field was bypassed. Later migration into Cretaceous reservoirs probably occurred during the Pliocene, accompanying the intense folding and fracturing of the broader structures in Syria.

Reservoir Characteristics Although Paleozoic rocks may yet be found to provide potential source rocks and reservoirs, the majority of commercial reservoirs are in fractured carbonates and sandstone of Mesozoic and Tertiary age (Fig. 12.17). Table 12.4 provides a list of the principal reservoir horizons and Table 12.5 reservoir characteristics of fields with the reservoir information available. In a general sense, the fractured carbonates of the Triassic Kurra Chine Formation are important gas and heavyoil reservoirs in eastern and northeastern Syria, and the Triassic Mulussa limestone produces in the Aleppo area. The rocks of the Lower Jurassic Butmah Formation are oil- and gas-producing in eastern and northeastern Syria, along with minor production from the Cretaceous Qamchuqa, Shiranish and Soukhne carbonates. The most important sandstone reservoir is the Lower Cretaceous (Cherrife Formation) of the Thayyem Field in southeastern Syria. In central Syria, the Triassic and Jurassic Dolaa (Mulussa) Group, equivalent to the Kurra Chine Forma-

673

Sedimentary Basins and Petroleum Geology of the Middle East NE

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Ritib.ih

L. Cretaceous

37

Oil

6. Al Kharrata

Rutbah (Cherrife)

Barremian-Aptian

7

Oil

Jeribe

Miocene

7

Sulphurous oil

8. Al Ward North

Rutbah

L. Cretaceous

9. An Nishan

Jeribe

3. Al-Hawi

7. Al Mahash

lO.Aoda

ll.Ash-Shaer

IZAsh-Shoia

1976

1985

1979

1985

1985

on

36,6

Oil

Miocene

,T

Oil

Shiranish

Maastrichtian

15

Heavy oil

Kurra Chine

U. Triassic

30

Light oil/gas

Butmah

L. Jurassic

28

Light oil

Mulassa

Triassic

Soukhne

CampanianConiacian

T

7

Jeribe

Miocene

7

Sulphurous oil

Rutbah (Cherrife)

Barremian-Aptian

Soukhne

Campanian* Coniacian

56-62

•)

33.5

Condensate and gas

'J

Oil

13. Babassi

1978

Shiranish

Maastrichtian

15

Heavy oil

14. Bad ran

1979

Massive Limestone

CampanianSantonian

16

Heavy oil

Shiranish

Maastrichtian

T

Oil

Shiranish

Maastrichtian

7

Oil

Chilou

L. OligoceneE, Eocene

7

Gas

Mulassa (Dolan)

U. Triassic

7

Gas

Mulassa (Dolan)

U. Triassic

60

Condensate

Qamchuqa

L.-M, Cretaceous

7

.7

15. Barde

1950

16. Bishri 17. Cherrife

1982

675

Sedimentary Basins and Petroleum Geology of the Middle East 12.3 continued. continued. Table 12.3 FIELD

YEAR

FORMATION

GEOLOGIC AGE

REMARKS

API° GRAVITY

18. Derik

1965

Massive Limestone

CampanianSantonian

18

Heavy oil

19. Derro

1977

Jeribe

Miocene

30

Light oil

Chilou

Oligoccne

7

Gas

Jaddala

M. Miocene

7

7

Shiranish

Maastrichtian

35

Light oil/gas

Chilou

L. OligoceneU. Eocene

7

7

Chilou

L. Oligocene

2'i 2

20. Gbeibe

21. Ghouna

1976

1979

U. Eocene 22. Habbari

23. Hamzah

1976

1963

24. Hasw

T

Gas/condensate 7

Aasafir (HayancJ

Albian-Aptian

20.1

Oil and gas

Mulassa (Dolan)

U. Triassic

7

T

Kurra Chine

U. Triassic

7

7

Massive Limestone

CampanianSanionian

20

Butmah

L. Jurassic

7

Chilou

Oligoccne

7

Oil and gas

Light oil/gas

•,'

2S. Jeribe

1978

Soukhne

CampanianConiacian

•)

Gas

26, Jehissa

1968

Jeribe

Miocene

?

Gas

Jaddala

Eocene

17

Heavy oil

Shiranish

Maastrifhtian

21

Heavy oil

Soukhne

Camp;ini^inCcmiacian

30

Light oil/ 1.8% sulfur

Butmah

L. Jurassic

32

Light oil

Kurra Chine

U. Triassic

41

Light oil/gas and condensate

Soukhne

CampanianConiacian

7

Gas

Kurra Chine

U. Triassic

7

Oil/gas

Shiranish

Maastrichtian

T

Oil

Massive Limestone

CampanianSantonian

Shiranish

Maastrichtian

Butmah

L. Jurassic

27. Jido

28. Kahlaniyah 29. Karatchok

676

1956

19-21 ') 28

Heavy oil/ 4.2% sulfur Gas Light oil

Hydrocarbon Habitat Habitat of the Zagros Basin Table 12.3 12.3 continued. continued. FIELD 30. Khirbah

YEAR 1963

31.Kotba

FORMATION

GEOLOGIC AGE

REMARKS

A P P GRAVITY

Kurra Chine

U. Triassic

25

Butmah

L. Jurassic

7

Massive Limestone

CampanianSantonian

?

Oil

Shiranish

Maastrichtian

7

Oil

17

Heavy oil

Light oil

32. Leiac

1962

Massive Limestone

CampanianSantonian

33. Markada

1974

Chilou

Oligocene

T

Oil/gas

34. Maiiout

1979

Jeribe

Miocene

7

Gas

Kurra Chine

U. Triassic

7

Oil

7

Oil

35. Nabaj

1981

Mulassa (Dolan)

U. Triassic

36. Najecb

1980

Mulassa (Dolan)

U. Triassic

Rutbah (Cherrife)

Barremian-Aptian

Mulassa (Dolan)

U. Triassic

Rutbah (Cherrife)

Barremian-Apiian

Massive Limestone

CampanianSantonian

23

Light oil/ 3.9-4.6% sulfur

Shiranish

Maastrichtian

22

Light oil

Kurra Chine

U. Triassic

35-48

Light oil/ condensate

40. Salhieh

Chilou

Oligocene

7

Oil and gas

41.Sarhit

Rutbah (Cherrife)

Barremian-Aptian

?

Oil

37. Omar

38, Ratka 39. Rumaitan

1962

Gas/condensate

• '

•)

Oil T

T

Oil

42. Sfaiyeh

1979

Mulassa (Dolan)

U. Triassic

18

Heavy oil

43. Sheikh Mansour

1978

Chilou

Oligocene

17

Heavy oil

Jeribe

Miocene

T

Gas

44. Sheikh Said

1977

Shiranish

Maastrichtian

13

Heavy oil

Massive Limestone

CampanianSantonian

T

Oil shows

45. Sheikh Sulaiman

Soukhne

CampanianConiacian

7

Gas

46. Sijan

Judea

L. Cretaceous

'J

Gas/condensate

Rutbah (Cherrife)

Barremian*Aptian

T

'J

677

Sedimentary Basins and Petroleum Geology of the Middle East

Table 12.3 12.3 Continued Continued FIELD 47. Souedie (Suwaidiyah)

48, Soiikhne

YEAR 1959

1968

49, Tanak

SO. Tanak North

1992

51. Tayyani 52. Thayyem

53. Tishreen

54. Ulayyan

1984

1976

1962

FORMATION

GEOLOGIC AGE

REMARKS

A P P GRAVITY

Massive Limestone

CampanianSamonian

25

2.5-3.7% sulfur

Shiranish

Maastricht! an

24

Light oil

Kurra Chine

U. Triassic

32

Low sulphur, gas and condensate

Butmah

L. Jurassic

36

Light oil

Mulassa (Doian)

U. Triassic

Mulassa (Dolan)

U. Triassic

Massive Limestone

CampanianSan Ionian

Rutbah (Cherrife)

Barremian-Aptian

Mulassa (Dolan)

U. Triassic

Jeribe

M. Miocene

Rulbah (Cherrife)

Barremian-Aptian

Jaddala

M. Eocene

18-20

T

Shiranish

Maastrichtian

18-20

7

Chilou

L. OligoceneU. Eocene

IS

Kurra Chine

U. Triassic

Massive Limestone

Cam pan i anS anion Ian

17-19

Shiranish

Maastrichtian

17

Heavy oil

12

Heavy oil

55. Wahab

1978

Mulassa (Dolan)

U. Triassic

56, Zurabeh

1979

Shiranish

Maastrichtian

Massive Limestone

CampanianSamonian

Gas/condensate ?(•>

Oil

Oil shows 36,5

Oil Oil

36.5

•)

Oil 7

Oil Gas

18.3

Heavy oil, 2.5% sulfur

Oil and gas

7

Most of the fields were discovered by the Syrian Petroleum Co., except for: (29) Karatchok by Menhall Co.; (7) A1Mahash, (12) Ash Shola, (36) Najeeb and (52) Thayyem by Pecten; (15) Barde by Marathon Oil Co. Cumulative production in some fields, as reported in Beydoun (1988), were as follows: Hamza 3.385 MM.bbl, Jebissa 2.65 MM.bbl, Karatchok 76 MM.bbl Rumailan 40.51 bbl, Souedie 618.25 MM.bbl, Tishreen 3 MM.bbl and Ulayyan 5.46 MM.bbl.

678

t~ o~

e,i

Markada

Carboniferous

150-250

Bioclastic limesiotie. fine sandstone, shale

Shallow-marinedeltaic

Kuira Chine

Upper Triassic

92

Argillaceous limestone and sandstone dolomite

Miilus$a (Dolan)

Upper Triassic

90

Butmah

Lower Jurassic

Cheirife (Rutbah)

Lithology

Environment

Porosity (%)or Type

Permeab (md

8-17

Fractu

Lagoona I

Fracture

Fractu

Limestone, minor sand-terrestrial stotie

Lagoonal

2-12

200

Fractured dolomite

Lagoonalshallow shelf

14

15-90

B arte mi an Aptian

no

Sandstone, carbonate, shale

Shallow marine

7

7

Qamchuqa

Middle Cretaceous

480

E>olomitic limestone, linnestone

Shallow shelf

7

7

"Massive Limestone"

Campania I) Santonian

180 (580 ft)

Limestone, dolomite, glaueonitic sandstone, cherty limestone

Shallow shelf

2-13

26-43

Shi rani sh

Maastricht! an

265

Bituminous, marly limestone

Shallow marine

Moderate

Fractu

iaddala

MiddleUpper Eocene

385

Marly limestone and marl

Shallow marine

3

Fractu

Chitou

Oligocene

22-100

Limestone, dolomite

Shallow shelf

17

SO

Dhiban

Lower Miocctie

46

Marly sand, limestone, anhydrite and halite

Lagoonal to supratidal

6-15

Fractu

Jeribe

Middle Miocene

25-70

Etolomite. dolomitic limestone, mudslone, anhydrite

Shallow marine shelf (organic shelf)

5-30

too

Low (less tha

Hydrocarbon Habitat of the Zagros Basin

Reservoir Thickness (m)

om

Age

Im

0 o~

Formation

t~ 0

Table 12.4. Major reservoir formations in Syria.

0

o~

o~

"0

0

o~

oO ~

0

0

0

0

0

0

o~

679

Sedimentary Basins and Petroleum Geology of the Middle East Sedimentary Basins and Petroleum Geology of the Middle East

Table Table12.5. 12.5.Reservoir Reservoircharacteristics characteristicsininsome someSyrian Syrianoil oilfields. fields. (53)* Tishrean

(26) Jebissa

(54) Ulayyan

(29) Karatchok

(39) Rumailan

(47) Souedie

Average

3

1

17

18-23

11

12

12.5

78,4

78,4

60,5

175

185

180

173 (initial)

72

72

60.5

28

61

87

48

Saturation Pressure

0.937

0,946

0.931

0.933

0,934

0.927

0.916 (surface)

Sp.WL

0.907

0,924

0,905

0,895

0,875

0,837

0.846

Oil Viscosity

3,547

7,543

1.527

625

445

137

bed

81

72

62

17

9

3

surface

Water Viscosity

0,5

0.5

0,5

0.4

0.4

0,4

0.4

Formation Volume (RB/STB)

40

35

33

68

81

80

78

Temp. CO

7

80

100

140-110

80

150-1400

110-150

Fermeabil' ity (md)

7

18

20

18.5

18.5

24-24

24

Specific Gravity (API)

7

32-18

35-21

174

80

185

Gas/Oil Ratio

7

4

4.5

4,2

3.25

3-2.5

Parameter Porosity Saturation Initia) Pressure (psig)

2,5

, -

* The numbers refer to the corresponding numbered fields given in Table 12.3.

tion, has proved to contain good reservoirs sourced by Paleozoic shale. The fractured Tertiary carbonates of the Jaddala, Chilou, Dhiban and Jeribe Formations are important as reservoirs in central and northeastern Syria. In the Euphrates Graben the principal production is from pre-rift beds, the Triassic Mulussa Sandstone with a 200 m (656 ft) oil column and the Early Cretaceous Turbah Sandstone. Both formations have porosities of up to 20% and permeabilities of the order of a darcy ore more. In contrast, the Ordovician and Carboniferous reservoirs are tight. The source rocks are the late Cretaceous lime

680

mudstone, the richest, at the base following the Derro Sandstone, is the beds of the R'Mah Chert Member of the Soukhne Formation. Most of the rifting ended in the Late Cretaceous and the Late Cretaceous Upper Shirhanish Limestone forms a good, tight seal. Only minor production is found in Cenozoic beds, which may be sealed by Tertiary anhydrites (de Ruiter et al., 1995). The principal reservoirs are briefly summarized in the following paragraphs and in Tables 12.4 and 12.5. Kurra Chine Formation (Triassic). A thickness of approximately 500 m (1,640 ft) of dolomite, limestone,

Hydrocarbon Habitat of the Zagros Basin evaporite, sandstone and shale in which the reservoir thickness amounts to 90 m (295 ft). In Jubaissah-5 the reservoir shows fracture permeability and is a minor gas producer. Gas is also produced in the Judaissah (Jebissa) and Tishreen (October) fields, and oil and gas is recovered in the Hamzah, Rumailan, Suwaidiyah (Souedie) fields and in the Khirbah discovery. Mulussa Formation (Triassic). The 500 m (1,640 ft) of transitional marine limestone, sandstone and gypsum is a primary reservoir with a 2.5% porosity and low permeability. Oil and gas are produced from the Habbari Field, and it is also oil bearing in the Wahab and Safeeh fields. Butmah Formation (Liassic). The dolomite, dolomitic limestone anhydrite and shale of the formation were laid down in a transitional marine to shallow marine shelf environment. Oil and gas is produced in the Jubaissah (Jebissa), Hamzah, Karatchok and Suwaidiyah (Souedie) fields. Dolaa Group (Triassic-Jurassic). A sequence of 80 m (262 fi) of limestone, sandstone and gypsum deposited in a transitional marine to continental environment. The beds within the group yield gas and condensate in the Cherrife and Soukhne fields.

Cherrife Formation (Upper Jurassic-Lower Cretaceous). Oil and gas is produced from this formation in the Thayyem Field. Lithologically it consists shallow marine sandstone, shale and limestone 125 m (410 ft) in thickness. Qamchuqa Formation (Albian). The formation consists of 800 m (2,624 ft) of dolomitic and marly limestone deposited on a shallow-marine shelf. Gas is produced in the Ghouna Field.

Soukhne Formation (Coniacian-Santonian). A thickness of 150 m (492 ft) of sandy limestone, dolomite, shale and sandstone deposited on a shallow marine shelf. Oil and gas is produced in the Jubaissah (Jebissa) Field and oil and gas from the A1 Hol and Jeribe fields. Massive Limestone (Campanian). The formation consists of 200 m (656 ft) of marly dolomitic limestone and dolomite deposited on a shallow marine shelf. Primary porosity and fracture porosity is in the 1-13% range with matrix and fracture permeability of 27 md. The reservoir yields 0il and gas in the Hamzah, Karatchok, Lelac, Rumailan, Suwaidiyah (Souedie) and Ulayyan (Aliane or A1 Hayane) fields and in the Kirbah discovery and has produced gas in the Karatchok Field.

Shiranish Formation (Campanian-Maastrichtian). A sequence of 80-2,000 m (262-6,560 ft) of marly and bituminous limestone deposited in s shallow marine environment. It has a gross reservoir thickness of 265 m (869 ft). Oil and gas are produced in the Gbeibe (Kubebe), Rumailan, Sheikh Said, Suwaidiyah (Souedie) and Ulayyan (Aline or A1 Hayane) fields, oil in the Zurabeh Field and oil and gas in the Karatchok Field.

Jaddala Formation (Middle Eocene-Upper Eocene). A thickness of 600 m (1,968 ft) of marly marine limestone with a gross reservoir thickness of 384 m (1,260

ft). Secondary porosity is of the order of 3% with fracture permeability. Oil and gas are produced in the Gbeibe (Kubebe) and Tishreen (October) fields. Chilou Formation (Lower Oligocene). The formation consists of 350 m (1,148 ft) shallow marine shelf limestone and dolomite with a gross reservoir thickness of 320 m (1,050 fi). It has medium porosity and fracture permeability. Oil and gas are produced from the Gbeibe (Kubebe), Ghouna, Salhieh (Salihiya) and Sheikh Mansour fields and gas from the Margada Field.

Dhiban Formation (Upper Oligocene-Lower Miocene). These transitional marine to supratidal deposits are 250 m (820 ft) thick and consist of marly and sandy limestone, anhydrite and halite deposits.The gross reservoir thickness is 45 m (148 ft). Secondary porosity ranges from 6 to 15%. Permeability is mainly fracture permeability. Oil and gas are produced in the Jubaissah (Jebissa) Field. Jeribe Formation (Middle Miocene). A thickness of 250 m (820 ft) of dolomite, dolomitic limestone, mudstone and anhydrite deposited in a shallow-marine shelf setting of which the reservoir thickness totals 60 m (197 ft). Primary and secondary porosity are in the 6-28% range. Oil is produced in the Derro Field and oil and gas in the Jubaissah (Jebissa) Field.

Source Rocks Potential source rocks have been recognized in a number of formations ranging in age from Ordovician to Eocene (Table 12.6). The most likely sources for the hydrocarbons trapped in the Carboniferous Markada Group and the Triassic Kurra Chine Formation is the Paleozoic shale of Ordovician, Silurian and Carboniferous (both middle and upper) age, as well as the Permo-Triassic Amanus Formation. It is conceivable that some hydrocarbons also may have been generated by Kurra Chine beds. The Cretaceous reservoirs may have been charged with hydrocarbons stemming from the Middle Jurassic bituminous marl of the Sargelu Formation or the bituminous, shaly intercalations in the Qamchuqa limestone of the Upper Cretaceous Shiranish marl and shale. The Miocene rocks generally are immature; hence, oil in the Jeribe limestone may have had a different source, as previously indicated. The potential source rocks have been discussed by Metwalli et al. (1972, 1974), Ala and Moss (1979), the Syrian Petroleum Company (1981) and A1 Youssef and Ayed (1992). The Paleozoic source rocks may have released hydrocarbons from the Jurassic onward, depending upon the depth of burial and the temperature. The earliest release of Jurassic hydrocarbons probably was during the early Tertiary, whereas oil probably was not expelled from Cretaceous sources before the Neogene. Potential source rocks of Syria are listed in Table 12.6 and Fig. 12.17.

681

Sedimentary Basins Basins and and Petroleum Petroleum Geology Geology of of the the Middle Middle East East Sedimentary Table 12.6. 12.6. Major Major source-rock source-rock formations formations in in Syria. Syria. Table FORMATION

AGE

LITHOLOGY

THICKNESS

ENVIRONMENT

(m)

SOURCE ROCK Richness

Type

LOM

Middle Ordovician

Bituminous shale, siltstone and finergrained sandstone

ISO

Open marine

Fairgood

Lipid

10-12

Silurian

Shale and marl

120

Open marine

Good

Lipid

10-12

3. Sawanet

Middle Carboniferous

Shaly sandstone

130

Shallow-marine to deltaic

Fair

Humic

9-12

4. Najeeb

Upper Carboniferous

Shaly sandstone

130

Shallow-marine to deltaic

5. Amanus Shale

LowerMiddle Triassic

Pyritic shale

150

Marine restricted

Excellent

Lipid

8-12

6. KurraChine

Upper Triassic

Argillaceous dolomites, anhydrite, calcareous laminated shale

220

Marine restricted

Good

Lipid

8-12

7. Sargelu

Middle Jurassic

Bituminous limestone with shale intercalations

280

Marine restricted

Fair

Lipidhumic

8-11

8. Cherrifc (Rutbah/ Ghouna)

BarremianAptian

Sandstone, shale and carbonate

500

Shallow marine

Fair

Lipidhumic

6-10

9. Qamchuqa

Lower Cretaceous

Argillaceous limestone, shale and dolomite

290

Marine restricted

Fair

Lipidhumic

8-10

10. Soukhne

ConiacianCampanian

Sandy limestone, dolomite, shale and sandstone

100

Shallow marine

Goodexcellent

Lipidhumic

6-10

11. Shiranish

Maastricht! an

Marl and marly limestone, often bituminous

100

Marine restricted

Fairgood

Lipidhumic

6-10

Paleocene

Limestone and dolomite

50

Shallow marine

Good

Lipidhumic

6-9

n.Jaddala

MiddleUpper Eocene

Bituminous marly limestone

140

Marine

Fair

Lipidhumic

8

I4,ChiIou

Oligocene

Argillaceous shale

50

Shallow marine

Fair

Lipidhumic

6

1. Sawab

2. Tanf

12. Aaiiji

.....

682

Hydrocarbon Habitat of the Zagros Basin In the Sinjar-Palmyra and Euphrates-Anah troughs (Figs. 12.19 and 12.20), the basal Triassic sequence includes shale deposited in the central part of the trough, and fluviatile and deltaic sands deposited on the southern flanks. The basinal shale and other shale in the underlying Paleozoic section may have acted as sources for oil now found in the sands deposited on the southern margins of the troughs. The overlying Triassic evaporites would have acted as an effective seal for the hydrocarbon accumulations. The Paleozoic Swab Formation (Ordovician) and Tanf Formations (Silurian) consist of graptolitic rich shales interbedded with siltstone and sandstone. The organic rich horizons are seldom more than a few meters thick scattered throughout the section, somewhat richer in the Tanf than in the Swab Formation. Rock eval and pyrolysis indicate that the Hydrogen index is low, T max is high and the organic matter mature (especially in the Swab Formation). Maturity maps based on these data and the results of the application of the Lopatin method are illustrated in Fig. 12.21. The Lower Triassic, Amanus, shale and the organic rich shales and mudstones of the Middle Triassic Kurra Chine Formation, which range in thickness from 20-50 m (66-164 ft) and 15-40 m, respectively, contain principally Type 1 and 2 lipids with a minor humic component. The maturity map of the Triassic (Fig. 12.21c) shows the gradation from wet gas-dry gas-heavy oil-natural oil in eastern northeastern and central Syria. The Upper Cretaceous mudstones and occasional interbedded packstone-wackestone contain organic rich cherts, 30-40 m (98-131 ft) thick in the Soukhne Formation and 20-50 m (98-131 ft) thick in the Shirhanish Formation, with Type 2 lipids. According to their maturity group (Fig. 12.21d) these rocks are largely immature, and oil and gas condensate occur only in eastern and northeastern Syria (Serryea, 1990).

Crude Oil Geochemistry Syrian oil was classified by Serryea (1990), who divided them into the following three categories based upon oil gravity and metal content (Fig. 12.22): 1) Heavy Oil, which covers 17 oils produced from Triassic, Jurassic, Upper Cretaceous and Tertiary reservoirs from fields in northeastern Syria; 2) Normal Oil, which covers 12 oils produced from Triassic, Jurassic, Upper Cretaceous and Tertiary in the Rumailan Field and an Upper Cretaceous reservoir in the A1 Hol, Thayyem al Furat and Ash Shola fields and from Tertiary reservoirs in the Derro and Ghouna fields; and 3) seven light oils, two from Tertiary reservoirs in the Jebissa and A1 Hol fields, four from Lower Cretaceous reservoirs in the Thayyem, A1 Isharra, A1 Ward North and A1 Ahmar fields and one from the Tertiary reservoirs in the Syraum Field. The geochemical characteristics of crude oils in some fields analyzed from Miocene, Cretaceous and Triassic oil-

bearing rocks are given by Metwalli et al. (1972) and shown in Tables 12.7-12.9. The specific gravity of the crudes generally decreases downwards both stratigraphically and structurally from Miocene reservoirs (0.935) to Cretaceous (0.876) and Triassic (0.722) reservoirs. The sulfur-weight percent figures are 4.80% (Miocene oil), 1.87% (Cretaceous oil) and 0.62% (Triassic oil) (Table 12.12). Although not shown in the tables, the light-fraction weight percent increases downwards from 21.0% (Miocene oil), 34.0% (Cretaceous oil) and 55.0% (Triassic oil), according to Metwalli et al. (1972). The weight percent of asphaltenes is 7.40% (Miocene oil), 0.10% (Cretaceous oil) and 0.30% (Triassic oil). All of these changes suggest that the increase in petroleum maturation is related to either higher temperatures or geologic age. Secondary factors such as biodegradation and water-washing could have changed shallow oils into heavier types, but there are insufficient data to prove this point. Analysis of Syrian asphaltene oil on the Van Kreveling curve (Fig. 12.23) indicates that the source of the Triassic oils is from Type 1 organic matter (lipid 1), whereas the source of the Cretaceous and Tertiary oil is from Type 2 (lipid 2) and Type 3 (humic). The relationship between pristane and phytane is used to compare the Syrian oil with its source rock environment as plotted on an Orr cross-plot (Fig. 12.24). This shows that the environment of the organic matter was that of a marine regressive to transitional setting). The vertical distribution of different crude types is influenced not only by maturation, biodegradation and water-washing, but also by migration, the natural chromatographic effect. During migration, a given crude becomes lighter (higher API gravity), less sulfurous and less asphaltic and loses such heavy trace metals as nickel, vanadium, copper and iron (Table 12.7). Silverman (1965) added more changes to this list due to oil migration, such as an increase of paraffinic hydrocarbons, a decrease in resins and a decrease in the C13:C12ratio. To demonstrate the possibility of upward oil migration, Metwalli et al. (1972) compared crude oils from the Souedie (Upper Cretaceous) and Karatchok (Upper Cretaceous) fields (Table 12.7). Because of the systematic decrease in the abovementioned factors from Karatchok to Souedie (Table 12.8), Metwalli et al. (1972) proposed that oil migrated northeast-southwest from the former to the latter field. In contrast, the Miocene oil in the Jebissa Field is heavier, more sulfurous and more asphaltic and has a higher content of heavy trace metals than the Souedie (Upper Cretaceous) crude (Table 12.8). Consequently, Metwalli et al. (1972) concluded that the relatively immature Miocene oil has a different source than those of older oils. Bitumen extracted from Triassic reservoirs in the Suwaidiyah, Rumailan, Naur, Khirbah Aoda, Fahedah, Safiyah, Wahab and Amalah is similar in composition to the oil extracted, a result confirmed by carbon isotope analysis comparing Triassic oil with Triassic source rocks 683

684

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i ~~~ 9

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t.

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to

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.

,~

,,." ,,'

\.~

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Sedimentary Basins and Petroleum Geology of the Middle East

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Seals and Seal Formations The cap rocks of the hydrocarbon-bearing structures of Syria range in age from Permian to Miocene (see Syria Petroleum Company, 1981; Ala and Moss, 1979; A1 Youssef and Ayed, 1992). They consist either of evaporites (mainly anhydrite) or shale. The evaporites prevail in the shallow-marine to transitional Triassic, Jurassic and Neogene sequences. Shaly cap rocks are found in the Permian, Cretaceous and Paleogene marine series that consists of carbonate, marl, shale and subordinate sandstone. Upper Triassic cap rocks consist of anhydrite and subordinate gypsum, which seal the underlying Kurra Chine carbonate reservoir. Several Lower and Middle Jurassic anhydrite layers, forming parts of the Adaiyah, Alan and Sargelu formations, appear to be excellent seals for Jurassic reservoirs. Shale interbedded in the Rutbah (Cherrife) 685

Sedimentary Basins and Petroleum Geology of the Middle East

SOURCE ROCK ENVIRONMENT 20,

Fig. 12.24. Source-rock environment of Syrian oil on an Orr diagram (after Serryea, 1990). The histogram showing the relationship between Pr/Ph and frequency in a number of Syrian fields is shown on the fight. The numbers refer to the fields as follows: l=Amalah (Middle Triassic oil); 2=Wahab; 3=Rumailan (Tertiary oil); 4=Fahdah; 5=Rumailan (Cretaceous oil); 6=Naur; 7=Aodah; 8=Suwaidiyah; 9=Gbeibe; 10=Zurabeh; l l=A1 Hol (Cretaceous oil); 12=A1 Hol (Jurassic oil); 13=Amalah (Lower Triassic oil); 14=Jebissa; 15=Khirbah; 16=Ghouna; 17=Derro; 18=Ash Shola; 19=Syroum; 20=Thayyem; 21 =Amalah (Upper Cretaceous oil); 22=Ash Shaer.

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686

Hydrocarbon Habitat of the Zagros Basin Table 12.7. A geochemical comparison between Miocene and Cretaceous Syrian crude oils (after Metwalli et al., 1972).

P=paraffinic, I=intermediate, N=naphthinic, Ni=nickel, V=vanadium, Fe=iron.

Table 12.8. Chemical analysis of two Syrian crude oils of the same reservoir age (Shiranish Formation, Maastrichtian) (after Metwalli et al., 1972). Note that the two crudes are different in their geochemical characteristics as a result of migration maturation in a proposed NE-SW direction.

687

Sedimentary Basins and Petroleum Geology of the Middle East

Table 12.9. Geochemical characteristics of crude oils from the Jebissa Oil Field, Syria (after Metwalli et al., 1972).

Formation (uppermost Jurassic-Lower Cretaceous) form seals for gas accumulations in the carbonate reservoirs of the Dolaa Group. Marl of the Shiranish Formation (uppermost Cretaceous) unconformably overlies the Upper Cretaceous reservoirs. Paleocene and Eocene shale and marl are widely distributed and also may seal the Upper Cretaceous Massive Limestone reservoir. Both Neogene anhydrite and rock salt seal major reservoirs in the Tertiary carbonate series. The major sealing zones of Syria are listed in Table 12.10 and Fig. 12.17. In eastern Syria, a suitable reservoir/source/seal combination within the Triassic-Jurassic sequence is a prime consideration for future oil exploration. The Mulussa Formation, for example, may become very attractive if its reservoir facies either unconformably overlie the OrdovicianSilurian shale or if it has been thrust over the Cretaceous shale, and if the entire sequence is covered by an effective seal such as the evaporites within the Triassic-Jurassic sequence (Kurra Chine, Adaiyah and Alan formations). In the Palmyra-Sinjar and Euphrates-Anah troughs (Fig. 12.19), most source rocks have reached a sufficient depth of burial to generate oil, which then could have migrated along the southern flanks of the trough. The Jurassic dolomite reservoirs are sealed by the

688

Alan anhydrite and the Sargelu anhydritic shale. The Lower and Middle Cretaceous limestone and dolomites are covered by the Shiranish marl. Oil, which had migrated primarily into the Qamchuqa (Lower Cretaceous) or related formations, probably moved further upwards into the Senonian reefs of the Massive Limestone Formation. In the Souedie and Qamishliyeh fields, the Chilou and Jeribe reefal limestone (Oligo-Miocene) generally is capped by anhydrite. The lack of oil or gas in these reservoirs probably means that the seals on the older reservoirs have been more effective and have not let oil leak upward to the Oligocene and Miocene limestone. The Lower Fars evaporite of Miocene age is salt in the central part of the Euphrates Basin, but it is anhydrite around the edges. A short account of the principal cap rocks follows. Mulussa Formation (Upper Triassic). The formation consists of 500 m (1,640 ft) of evaporite, mainly gypsum, carbonate and sandstone deposited in a transitional lagoonal environment. It is the lateral equivalent of the Kurra Chine Formation. Kurra Chine Formation (Upper Triassic). A thickness of 500 m (1,640 ft) of evaporite, shale, dolomite, limestone and sandstone deposited in a transitional

Hydrocarbon Habitat of the Zagros Basin

Table 12.10. Major seal formations in Syria.

evaporitic, lagoonal environment. Adaiyah Formation (Lower Jurassic). A sequence of 175 m (574 ft) of anhydrite deposited in an evaporitic lagoonal environment. Alan Formation (lower Jurassic). A further 50 m (165 ft) of shallow marine evaporitic anhydrite. Sargelu Formation (Middle Jurassic). A formation of 300 m (984 ft) of anhydrite, shale and carbonate deposited in a shallow marine and evaporitic setting. It is the lateral equivalent of the Dolaa Group carbonate. Cherrife Formation (Lower Cretaceous). The formation, 80-120 m (262-406 ft) thick, consists of shale, sandstone and carbonate deposited in a shallow marine

setting.

Shirhanish Formation (Maastrichtian). This 200 m (565 ft) of marl and argillaceous limestone was deposited in a marine environment. Aaliji Formation (Paleoeene-Lower Eocene). The formation is made up of 300 m (984 ft) of marine shale. Jaddala Formation (Middle-Upper Eocene). A thick (600 m, or 1,968 ft) marine marl and limestone. Dhiban Formation (Lower Mioeene-Burdigalian). A formation of 260 m (853 ft) of anhydrite, halite and marly limestone deposited in transitional lagoonal and supratidal environments. Lower Fars Formation (Tortonian). Shallow marine

689

Sedimentary Basins and Petroleum Geology of the Middle East evaporitic gypsum, anhydrite, clayey marl, clay and siltstone deposited in a shallow marine environment.

et al., 1974). The eastern part of the field is a doubly plunging anticline with dips of 1-3~ on the west, the dip increases to about 10~ Shallow faults are recognized seismically on top of horizon B (Fig. 12.26); some of these faults were transversed in deep drill holes. The evaporites overlying the Jeribe Formation act as a plastic cover and prevent many of the deep faults from reaching the surface. The major uplift of the Cretaceous-Jurassic-Triassic reservoir section in the Jebissa Field occurred during Neogene-Recent times, which helped entrapment of oil generated from the Carboniferous or older source rocks. Oil probably migrated into broad/regional uplifts first, and later to anticlinal structures and fault blocks genetically unrelated to the late folding and thrust structures. Heavy oil staining has been found in the Soukhne and Ghouna formations (Upper Cretaceous) and in the Oligocene Chilou Limestone. Metwalli et al. (1972) have stated on the basis of petroleum geochemistry that the oil in the Miocene Jeribe Limestone is derived from a Miocene source rock.

Oil Field Examples

Most of the oil and gas fields found today occur in anticlines, typical examples are given below and are summarized in Appendix E. The Karatchok Field, the first field discovered in Syria in 1956, went on stream in 1969. It produced oil from the Massive Limestone Formation (Coniacian-Santonian), with oil gravity of 19-21 o API oil with a sulfur content of about 4.2%. Dry gas has been discovered in the Late Cretaceous Shirhanish Formation and 28 ~ API oil in the Triassic Butmah Formation. Recoverable oil reserves are estimated at 800 MM.bbl and 150 BCF gas (Beydoun, 1988). The Jebissa Field is in a simple anticlinal structure cut by a few faults (Fig. 12.26) trending east-west and NESW. The structure is 13 km long and 5 km wide (Metwalli

Fig. 12.26. The Jebissa Oil Field: A=structural map of the dome; B=cross-section based on seismic data (after Metwalli et al., 1972, reproduced with permission from AAPG).

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Hydrocarbon Habitat of the Zagros Basin IRAQ

former presence of gas escapes may be marked by the partial or wholesale replacement of gypsum or anhydrite by porous crystalline aragonite or "secondary limestone," a process believed to have gone on in subsurface under reducing conditions, or the replacement of limestone or marl by a mixture of earthy matter including gypsum crystals and associated with sulfur, free sulfuric acid and occasionally jarosite and chalcedony (Gach-i-turush, sour gypsum). In places, the escaping oil and gas have ignited, leaving behind burned rock with marl baked red to a hard, tile-like or even glassy consistency (Lees and Richardson, 1940). Where overthrusting occurs, escaping fluids have migrated some miles along the thrust planes to emerge at points distant from their fold source. However, locating the source is complicated by the incompetent folding that has occurred in the Lower Fars rocks. The two principal reviews of the hydrocarbon potential of Iraq are both fairly old, that of Dunnington (1958) concerning northern Iraq

Introduction

Iraq, with an area of 438,317 sq. km comprises part of the Arabian Basin west of the As Fold Belt to the western desert near the border of Syria and Jordan, including the Mesopotamian Plain and part of the Zagros Basin in the northwest, northeast and southeast near the borders of Syria, Turkey and Iran. The principal oil fields lie within the Zagros Basin, although there are important fields in the Arabian platform area. Geologically Iran can be divided structurally into the Mesopotamian zone which is part of the Arabian Platform, the Foothill Folded zone passing to the highly folded and overthrust zone (Fig. 12.27). In many parts of Iraq, active seepages of liquid oil and gas escapes occur, as well as bitumen deposits, veins and impregnations of porous or shattered rock. The presence or

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Sedimentary Basins and Petroleum Geology of the Middle East k.

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Hydrocarbon Habitat of the Zagros Basin and that of Ibrahim (1983) on southern Iraq. The Zagros Folded Zone of Iraq, which is about 160 km wide, contains the majority of the oil fields. The northern part is made up of two blocks the Kirkuk and the Mosul, with the line of separation coinciding with the Zab River. The northern basin, the Mosul Block, was the less stable of the two, and the result is seen in the relatively poor development of the Middle Jurassic-Upper Cretaceous source rocks. On the other hand, a more complete section is found in the larger Kirkuk Block (Ameen, 1992), where as much as 4,505 m (15,000 ft) of Middle Jurassic to Middle Miocene sediments accumulated and where the favorable development of grabens and semi-grabens enhanced the preservation of Jurassic-Cretaceous source rocks. Oil fields are found in four main regions in northern Iraq" the principal fields of the Kirkuk area (Kirkuk, Bai Hassan Jambur and Pulkhana), the fields NNW of Mosul (Ain Zalah and Butmah), a group west of Kirkuk (Kaiyarah, Najmah, Jawan and Kasab) and a fourth grouping in the southern part of the embayment (Naft Khaneh). Synorogenic differential movements on longitudinal basement faults (fault stacking) associated with the formation of the Zagros folds had a major effect on hydrocarbon generation, migration and trapping. There is a fifth group of fields closely linked to the fields of Iran in the southeastern part of the country (Abu Ghurab, Jabal Fauqui and Buzurgan) that belong to the Dezful Embayment. On the Arabian Platform in the southeastern part of the country are a number of fields, such as Rumaila, Zubair and Nahr Umr, whose structures are not related directly to the Zagros Fold Zone, but are most probably related to halokinetic movement of Infracambrian salt. In 1956, the Iraq Petroleum Company (IPC, 1956) reported on the history of exploration up to that time, which they divided into three stages. The first stage, from 1926 to 1931, consisted of the mapping of surface anticlines and reconnaissance work in the Kurdistan Mountains and western Iraq. Twelve structures were tested, with limited success because of drilling problems. However, the period was marked by the discovery of the Kirkuk Field. During the second stage, from 1930 until halted by World War II in 1940, there was considerable drilling of surface anticlines and the discovery of a number of fields such as Qaiyarah and Ain Zalah. Extensive air photo surveying and stratigraphic studies in the Kurdish Mountains marked the third stage of development when the Butmah (1952), Bai Hassan (1953) and Jambur (1954) fields were discovered. In the Basra concession in southern Iraq, geological field surveys were replaced by geophysical surveys in 1945, and in the western desert region in 1954. By 1956, practically the entire prospective area had been covered by reconnaissance gravity and magnetic surveys, with seismic surveys of the more prospective areas. In northern Iraq, in addition to the known fields, there is widespread evidence of the dispersion of formerly extensive oil accumulations in the folded belt, and some seepages are still active. Extensive bitumen impregnations

occur at Berat Dagh, Pila Spi and Pir-i-Mugram. In the Berat Dagh area, the suggestion that oil was generated and dissipated from Upper Cretaceous sediments runs contrary to the general lack of Upper Cretaceous oils in the active fields, and it is suggested that the oil was generated in Lower-Middle Cretaceous beds and migrated under the heavy loading of younger sediments. The same interpretation holds for the Pir-i-Mugram impregnations. This view is supported by the pebble-coated bitumen balls in the Upper Cretaceous section; but, in the absence of a potential source in the basinal Middle Cretaceous sediments at Pila Spi, a source in the late Cretaceous flysch or the immediately underlying beds seems more likely. There appear to have been three main phases of active seepages and oil loss in the highly folded mountain zone. During the Middle-Upper Cretaceous transition, seepage occurred through windows in the sediment seal, at the end of the Cretaceous through regression and erosion and fracture of the seal, and finally during the phase of main anticlinal folding through the destruction of primary porosity traps and the breaching of low-quality seals (Dunnington 1958). These periods of seepage and loss are not apparent in the Foothills Belt. Two other episodes of widespread dissipation affected the Foothills and Foreland Zone and resulted in the loss of Upper Jurassic oil: during the period of uplift and erosion at the Jurassic-Cretaceous boundary, and again at the onset of Lower Fars sedimentation when surface losses are estimated to run into hundreds of millions of tons (Dunnington, 1958). Southwestern Iraq covers an area of more than 82,000 sq km and lies south of 32 ~ N and west of the Euphrates River. Geological interest in the area began with reconnaissance surveys of the areas of seepage between the Tigris and Euphrates rivers in the early 1920s, but more attention was paid to the western regions (A1Naqib, 1967) for potential exploration targets. However, the decision to concentrate upon the development of the Kirkuk Field led to a cutback in exploration in the late 1920s, until a concession was awarded in 1938 for the area of southern Iraq bordering Iran, Kuwait and Saudi Arabia. With World War II, however, exploration was temporarily suspended, to be renewed in the early post-war period with Zubair the first area investigated; by 1950, the transition from exploration to development of the Zubair Field had been accomplished. Inauguration of production from the field occurred in 1952, and the discovery of the Rumaila Field was made a year later. The major oil and gas fields in Iraq are shown in Fig. 12.28, and a summary of the status of exploration is given by Ibrahim (1966) which shows that of the 400 structural prospects delineated so far, 150 have been drilled to yield more than 66 commercial fields, 8 commercial gas discoveries, 17 oil discoveries, 19 holes of unknown status and 40 dry wells. The estimated volume of the oil discovered in Tertiary reservoirs is about 33.8 B.bbl, in Cretaceous reservoirs around 107.1 B.bbl and in Paleozoic reservoirs about 1 B.bbl (Fig.12.29). 693

Sedimentary Basins and Petroleum Geology of the Middle East

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Fig. 12.29 The relative maturity of the main exploration play formations in Iraq. (after Ibrahim, 1996, reproduced by Kind permission of the Oil and Gas Journal). The main exploration plays in the Phanerozoic rocks of Iraq were defined by Ibrahim (1996) as maturing, immature and frontier plays, none is mature inside Iraq. The distribution of field sizes in Iraq, figure in Fig. 12.30 shows several gaps between 3-4, 10-15, and 15-25 B.bbl. oil field sizes, is an indication of the sizes of the giant fields which remain to be discovered. Oil production has varied through the years from 3.5 MM.bbl/d during 1979 to more than 3.5 MM.bbl/d prior to the Iraq/Iran war and again reaching that figure immediately preceding the Gulf War in 1990. By 1995, the production figure was around 600,000 bbl/d (Oil and Gas Journal). Stratigraphy

The stratigraphy of the Iraq part of the Arabian and Zagros basins is shown in Figs. 12.31 and 12.32. The Arabian Basin in Iraq comprises the area west of the Zagros

694

Fig. 12.30 Field size distribution in Iraq (after Ibrahim, 1996, and reproduced by permission of the Oil and Gas Journal). Fold Belt to the Western Desert near the border with Syria and Jordan, including the Mesopotamian Plain. Paleozoic rocks are known in the Western Desert (Rutbah High) and in a well in the Khleissia Block in northwestern Iraq where they attain a thickness of about 2,400 m (7,872 ft) forming three depositional cycles, each separated by a depositional hiatus or unconformity. The Cambro-Ordovician cycle, which consists primarily of transitional sandstones and shales, is followed by the Devonian-Lower Carboniferous cycle with its continental and shallow marine sandstone, and shallow marine limestone and shale. The Upper Carboniferous-Middle Triassic cycle although it also contains continental beds shows a marked change basinward into shallow marine limestone and shale. The much greater thickness of the Mesozoic

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Fig.12.32 Lithostratigraphy and hydrocarbon potential (sourcerocks, reservoirs and seals) distribution in the Mesozoic-Cenozoic sediments of northern part of Iraq of the Zagros Basin.

section (3,000-6,000 m, or 10,840-16,400 ft) encompasses six cycles which contain a much greater proportion of marine beds, limestone, shale and lagoonal evaporites together with deltaic sandstones on some occasions (the Barremian-Albian, and the Cenomanian-Lower Campanian cycles). The Upper Jurassic-Lower Cretaceous, Cenomanian-Lower Campanian, and Paleocene-Lower Eocene cycles consist mainly of shallow shelf carbonates and lagoonal to supratidal evaporites. The Middle Eocene cycle has a basal and top section of clastics with an intervening section of shallow marine and lagoonal limestone. The uppermost Miocene-Pliocene cycle marks a return to continental sandstone, gravel and conglomerate.

Southeastern, northeastern and northwestern Iraq lie within the Zagros Basin (Fig. 12.1). The depositional cycles recognized in the Arabian Basin show thickness and lithological variations in the Zagros Basin (Fig. 12.32). Deep intrashelf basinal sedimentation prevailed during the Mesozoic, resulting in the deposition marls surrounded by narrow belts of shelf carbonates. The recognition of volcanic rocks at different intervals during the Paleozoic and Mesozoic can be related to early phases of deformation. The Cenozoic alpine deformational phases are marked by great paleogeographical change as illustrated by the succession from reef limestones of the Lower OligoceneLower Miocene to the Middle Miocene salt and evaporite

695

Sedimentary Basins and Petroleum Geology of the Middle East sequence in turn giving way to the Pliocene-Pleistocene clastic sediments.

Structure and Traps The geographical distribution of the known oil fields has been controlled by the paleogeographical conditions in the depositional basins and the gradients and loads subsequently imposed upon them. Primary accumulations have resulted from lateral migration, but vertical migration played the dominant role in the subsequent development of all the known accumulations, as well as loss through dissipation at the surface. If correct, the vast majority of the oil in the Foothills Zone has originated as a result of migration across bedding, in marked contrast to the situation in the southern Iraqi fields in the Basra area and in the Arabian fields. Tectonic influences on sedimentation in Iraq began with the closing of the Tethys Ocean. Prior to the Alpine Orogeny, the Arabian Platform was a long-lived, subsiding continental margin (Jackson, 1980) at the edge of the Tethys Ocean and was covered by a thick sequence of typical shelf sedimentary facies. Associated slope facies were deposited in what is now Iran and the extreme northeastern part of Iraq. Major orogenic influences on sedimentation are first seen in the Late Cretaceous as the Arabian Platform collided with the Iran Block and the Zagros Foredeep formed (Murris, 1981). Compression resulted in the formation of a ridge separating the trend of the flysch basin from a depressed molasse basin at the edge of the Arabian Platform during continuing sedimentation (Buday, 1980). During the Paleogene, tectonic activity greatly decreased, but shelf sedimentation continued, primarily influenced by eustatic sea-level fluctuations. From the Miocene through the Pleistocene, renewed tectonic activity resulted in uplift and folding of the outer Arabian Platform into what is now the Folded Zone, reversing the movement on earlier normal faults in many instances. Iraq exemplifies the wide range of petroleum habitat found in the Middle East. The southern oil fields are dominated by large, halokinetically formed arches, while the Folded Zone encompasses a series of complexly folded and overthrust anticlines. The Overthrust Zone has a variety of thrust and imbricate structures, with a small regional extent and a lack of petroleum potential. Sedimentary cycles provided alternating sequences of potential source and reservoir rocks for the Arabian Platform. These cycles constitute the broad pattern of deposition over Iraq, but do not exclude localized cycles due to local movements and environmental changes, the details of which can be found in earlier chapters (see also A1Naqib, 1967). At the margin of the Arabian Platform, local movements were of less relative importance. The primary source of sediment was the Arabian Shield and emergent highs such as the Ga'araKhleissia High. The Arabian Platform is characterized by

696

mildly warped strata with folds increasing in magnitude approaching the Folded Zone, and often by extensive preMiocene faulting. The relatively simple structural regime is complicated by extensive facies changes and unconformities throughout the stratigraphic section. The Simple Folded Zone of the Zagros can be subdivided into a narrow zone of intensely faulted, imbricated folds accompanied by the development of thrusting near the Zagros Border Fault Zone, and a wider, simply folded zone with smaller, less disrupted folds where asymmetric anticlines are separated by narrow synclines towards the northeast and pass to a wider zone of smaller, narrower anticlines separated by wider synclines to the southwest (Fig. 12.27). The difference in intensity of deformation is seen in an estimated 20-24% shortening of the surface rocks close to the Taurus-Zagros Suture Zone, compared to a 3-4% shortening away from the suture (Ameen, 1992). Within both the Kirkuk and Mosul blocks, seismic and Landsat data on lineation provide evidence of basement extensional faults (grabens or semi-grabens; Ameen, 1992), which pre-date the late Cretaceous and are inferred to date from the initiation of, or have been reactivated during, the initiation of Tethyan rifting. The extensional movement created sub-basins in which there are variations in stratigraphic thickness apparent in gravity measurements. The basement faults trend parallel to the long axes of the basins and permit the distinction of four or five subblocks in the Mosul Block and six in the Kirkuk Block. Recent seismic data indicate that movement in the region is still occurring at depths as great as 33-69.9 km (Ameen, 1992). Movement along the basement faults during the period of extension resulted in the formation of sub-basins/troughs (grabens or semigrabens), apparent as thickness changes in the sedimentary cover rocks. In the Mosul Block, the grabens tend to be short, narrow and arranged en echelon, in contrast to the wider, longer grabens in the Kirkuk Block that do not overlap (Fig. 12.27). The faults were subsequently rejuvenated and inverted during the Mio-Pliocene, accompanied by strike-slip motion along transverse faults. This converted the sub-basins or troughs into anticlines in the folded zone, with the cumulative effect of the differential fault movement producing monoclinal "geowarpings" in the surface sediments. The upwarped geowarps face south and southwest, with amplitudes of the order of 1.9-7.3 km; in contrast, the downwarped part of the structure shows less frequent and less substantial fault stacking, with a greater depth of burial favoring hydrocarbon maturation, particularly in the Kirkuk Block. There is a substantial thinning of as much as 1,200 m (approximately 4,000 ft) in the Middle Jurassic-Middle Miocene sediment thickness in the Mosul Block compared to the Kirkuk Block as the result of Berriasian-Albian tectonic uplift of the less stable northern Iraq Basin/Block. During this time, a considerable thickness of potential Middle Jurassic source rocks was removed, as well as all the Tithonian-Berriasian and the non-deposition or erosion

Hydrocarbon Habitat of the Zagros Basin of the Valanginian-Hauterivian succession that resulted in the reduced hydrocarbon potential of the Mosul Block. The Kirkuk Block remained continuously submerged during this time. The Mosul Block was not completely submerged until the Campanian. The Zagros Folded Zone of Iraq, which is about 160 km wide, contains the majority of the oil fields in two basins or blocks, the Kirkuk and the Mosul. The line of separation coincides with the Zab River. The northern Basin, Mosul block, was the less stable of the two, the result of which is seen in the relatively poor development of the Middle Jurassic to Middle Cretaceous source rocks. On the other hand, a more complete section is found in the larger Kirkuk block (Ameen, 1992), where as much as 4,505 m (15,000 ft) of Middle Jurassic to Middle Miocene sediments accumulated and where the favorable development of grabens and semi-grabens enhanced the preservation of the Jurassic-Cretaceous source rocks. Syn-orogenic differential movements on longitudinal basement faults (fault stacking) associated with the formation of the Zagros folds had a major effect on hydrocarbon generation, migration and trapping. Oil fields are found in four main regions in northern Iraq: the principal fields in the Kirkuk area (Kirkuk, Bai Hassan, Jambur and Pulkhana), the fields N-NW of Mosul (Ain Zalah, Moshorah and Butmah), a group west of Kirkuk (Qaiyarah, Najmah, Jawan and Kasib) and a fourth grouping in the southern part of the embayment such as the Naft Khaneh Field. There is a fifth group of fields closely linked to the fields of Iran in the southeastern part of the country (Abu Ghurab, Jabal Fauqui and Buzurgan) belonging to the Dezful Embayment. The growing folds provided hydrocarbon traps sealed by the middle Miocene evaporites of the lower Fars Formation. Many of the fold traps resulted from inversion over the pre-existing extensional basement faults. The distribution of the evaporite seal was controlled by the geowarping that began to develop during the Oligocene; in the upwarped areas, the deposits of the lower Fars consist of sand, silt and marl, with only subordinate development of limestone and an insignificant amount of gypsum or anhydrite. This lack of a cap rock led to a substantial hydrocarbon loss from the uplifted regions. In contrast, the more abundant limestone, gypsum, anhydrite and halite, silty marl and shale form an effective seal, trapping the hydrocarbons in the downwarped regions~ The structures on the Arabian Platform part of the southern Iraq oil fields include extremely large, elongate salt swells and pillows with few piercements and are nor related to the Zagros Zone. The Rumaila, Zubair, Tuba, Luhais, Nahr Umr and West Qurnah fields are attributed to assumed salt tectonic structures that have undergone intermittent structural readjustment (Ibrahim, 1983). Drape structures over deep-seated fault scarps in southern Iraq, probably accentuated by the growth of Infracambrian salt pillows, are the main trap type in this region of the Iraq basin.

Reservoir Characteristics A1 Gailani (1996) identified about forty seven reservoirs ranging in age from Ordovician to Miocene (Table 12.12). All the fields discovered have multi-plays with two to four pay zones in each field. The Arabian Basin accounts for 60% and 65% of the ultimate recoverable oil and gas reserves, respectively. The Zagros Basin accounts for 40% and 35% of the ultimate recoverable oil and gas reserves, respectively. In the Arabian Basin, Jurassic oil and gas reserves account for less than 1% of the ultimate recoverable oil and gas reserves. Cretaceous sandstone and limestone are the most important reservoirs. They account for 98.2% and almost 100% of the ultimate recoverable oil and gas reserves, respectively. Tertiary heavy oil reserves account for about 0.8% of the ultimate recoverable oil reserves. In the Zagros Basin, the Triassic reservoir accounts for less than 0.6% of the ultimate recoverable oil and gas reserves, the Jurassic reservoirs account for only 0.8% and 0.6%, and the Cretaceous reservoirs account for 20% and 8% of the ultimate recoverable oil and gas reserves, respectively. The Tertiary rocks are the most important reservoirs in the Zagros Basin, as they account for 85% and 95% of the ultimate recoverable oil and gas reserves, respectively. The Triassic carbonates are considered to offer excellent potential for further discoveries of oil and gas in northwestern Iraq in both the Arabian and Zagros basins (Sadooni, 1995). Potential reservoir rocks in Lower and Middle Jurassic carbonates may be found in northwestern Iraq in both the Arabian and Zagros basins. Reservoir rocks of moderate potential may be found in Upper Jurassic limestone in southern Iraq. Excellent potential reservoirs for further discoveries of oil and gas occur in the Cretaceous sediments of Iraq. Fractured PaleoceneMiocene carbonates offer excellent reservoir potential in undrilled structures along the Zagros Fold Belt from southeastern to northern and northwestern Iraq. Potential reservoir rocks for heavy oil may be found in Miocene sandstone and sandy limestone in southern Iraq with oil and gas migrated from Cretaceous reservoirs. Significant gas shows in the Ordovician sandstone in northwestern Iraq (Arabian Basin) highlight the potential of Paleozoic reservoir rocks in that region. Reservoir rocks in the Arabian Basin (southern and central Iraqi fields) are found in the Ordovician sandstone, Jurassic limestone, Cretaceous sandstone and limestone (which represent the major reservoirs) and in the Middle Miocene calcareous sandstone and sandy limestone. The depth of the reservoir rocks varies considerably within the basin. The Paleozoic gas reservoir in the Khleissia Block in northwestern Iraq occurs at a depth of 3,490 m (11,447 ft) and the Lower Jurassic reservoir at 3,400 m (1,115 ft), whereas the Middle and Upper Jurassic reservoirs range in depth from 2,700 to 3,000 m (8,856-9,840 ft). Lower Cretaceous reservoirs occur at depths from 2,500 to 3,850 m

697

Sedimentary Basins and Petroleum Geology of the Middle East (8,200-12,628 ft), and Middle-Upper Cretaceous reservoirs at depths from 800 m to 3,000 m (2,624-9,840 ft). The Miocene reservoirs in the southern fields occur at an average depth of 300 m (984 ft). Minor reservoirs in the Zagros Basin occur in Upper Triassic, Lower Jurassic, Middle Jurassic, Lower Cretaceous and Middle and Upper Cretaceous carbonates. The major reservoirs are found in the Tertiary carbonates. Depths to the reservoir rocks in the Zagros Basin of Iraq are variable. Triassic reservoirs reach an average depth of 3,050 m (10,004 ft) in northwestern Iraq, and Jurassic reservoir depths range from 1,500 to 3,000 m (4,920-9,840 ft). The Cretaceous reservoirs occur at depths varying from 1,125 to 3,800 m (3,690-12,464 ft), with Tertiary reservoirs ranging from 300 to 2,900 m (984-9,512 ft). The producing formations in the Arabian Basin are briefly described below (see also Beydoun, 1988; OAPEC, 1989; Dunnington, 1967; Beydoun and Dunnington, 1975) and summarised in Table 12.11. Khabour Quartzite Formation (Ordovieian). This formation consists of quartzose sandstone and shale deposited in a terrestrial and shallow-marine setting. The formation is locally a minor gas reservoir with a gross reservoir thickness of 150 m (492 ft). Non-associated gas was tested in well Khleissia-1. Alan Formation (Liassie). It consists of evaporite, (sometimes anhydritic), and limestone deposited in a supratidal and transitional-marine and lagoonal setting. The formation is locally a minor oil and gas reservoir in Samawa-1. The hydrocarbons may be sourced from the overlying Sargelu Formation.

ing Yamama deposition, resulting in facies differentiation within the structures, reefal facies in the higher parts with higher porosities, and lagoonal facies in the depressions. Argillaceous mudstone formed on the outer ramp in the deeper part of the basin provided permeability barriers. The best production is from the oolitic shoals and the cleaner reefal facies. Sulaiy Formation (Portlandian-Berriasian). This formation consists of detrital, sometimes oolitic, limestone deposited in a shallow-marine setting. It is locally a minor oil reservoir with a gross reservoir thickness of about 300 m (984 ft). The Ratawi Field produced oil from this formation. -'-IRAQ

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698

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Najmah Limestone Formation (Callovian-Oxfordian). Consisting of oolitic limestone, dolomite and anhydrite deposited in a shallow-marine and transitionalmarine setting (lagoonal and shoal deposits). Oil and gas. were tested in Samawa and gas in Fallujah discoveries. Yamama Formation (Valanginian). The rocks of the Yamama Formation, about 315 m (1,033 ft) thick, are the principal reservoir rocks in southern Iraq. Sadooni (1993) subdivided the formation into three reservoir units separated by two barrier units, which make correlation possible over southern Iraq. Within the depositional basin, two principal environments are recognized: the western, which is part of the stable Arabian Platform; and the eastern, which is part of the unstable Mesopotamian Foredeep (Fig. 12.33). Along the hinge line between these two areas, an oolitic shoal belt developed. The main structures (West Qurna, Rumaila and Zubair) were probably growing dur-

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Hydrocarbon Habitat of the Zagros Basin Table 12.11 Reservoirs and oil characteristics in Iraqi Fields (compiled from AI Gailani, 1996 and reproduced by kind permission, Oil and Gas Journal)

Age Miocene Miocene Miocene Lower Miocene Lower Miocene Middle Miocene Lower Miocene Mid,die Oligocene Oligocene Oligocene Lower Oligocene Lower Middle Upper Eocene Middle Upper.Eocene Paleocene-Eocene Upper Senonian-Maastrichtian Upper Senonian-Maastrichtian Maastrichtian-Upper Campanian Upper Senonian Upper Campanian-Upper Senonian Upper Campanian-Lower Senonian Lower Campanian-Lower Senonian Turonian V alanginian-Turonian Cenomanian Cenomanian Cenomanian Turonian Cenomanian ~ Albian Albian Albian Albian Albian-Aptian Aptian-Albian Lower Aptian-Hauterivian Lower Aptian-Hauterivian Hauterivian-Valanginian Hauterivian-V alanginian Berridsian-Valanginian Tithonian-Berriasian Upper Jurassic-Callovian Upper Jurassic LBath~ Jurassic i Lower-Middle Liassic Upper Triassic Rhaetic Upper Permian 0rdovician-Llandeilo ....

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Sedimentary Basins and Petroleum Geology of the Middle East

Ratawi Formation (Valanginian-Hauterivian). It consists of limestone deposited in a shallow-marine setting. The formation is locally a minor oil and gas reservoir in The Samawa discovery with a reservoir gross thickness of 300 m (984 fi).

Shuaiba Formation (Aptian). It consists of oolitic limestone sometimes dolomitic limestone and dolomite deposited in a shallow-marine setting. The formation is locally a minor oil reservoir in the Majnoon Field. Nahr Umr Formation (Albian). This formation includes the Kifl-1 and Rachi-1 discoveries and the Majnoon, Nahr Umr and Ratawi fields. It thins and pinches out against the Ha'il-Rutbah Arch in western Iraq. It has a thickness of 193 m (633 ft) to a maximum of nearly 355 rn (1,100 ft). It was deposited in a continental, flood-plain to delta-plain environment to inner-neritic marine conditions. Lithologically, it ranges from a fine-grained, unfossiliferous, rounded to sub-rounded sandstone with clear frosted grains and some shale and siltstone horizons, to a mediumto coarse-grained, angular to subangular, poorly sorted, argillaceous to carbonaceous sandstone with black, fissile, carbonaceous shale. In the absence of the Shuaiba, it is difficult to distinguish it from the Zubair. The area containing producible oil lies within a zone where the sandstone/ shale ratio lies between one and eight in shallow-marine sheet sands. As almost all the producing traps are above beds of the Zubair Formation, it is assumed that the two units were sourced by the same underlying Lower Cretaceous source rocks, with vertical migration during the late Paleocene to early Eocene in the southwest and during the Miocene in northeastern Iraq. Rumaila Formation (Cenomanian). The formation consists of foraminiferal limestone, dolomitic limestone, marl and shale deposited in a shallow-marine to deepmarine setting. This formation is locally a subordinate oil and gas reservoir in the Fallujah discovery well.

Zubair Formation (Upper Valanginian-Barremian). This formation is an important oil-bearing formation in central and southern Iraq. It consists of alternating coarse- to fine-grained sandstone and shale up to 389 m (1,277 ft) thick. The sedimentological features have been described by Ali and Nasser (1989), who show that the most important reservoirs are in the low-sinuosity distributary lobes, distributary mouth bars and shallow-marine sheet sands. The distribution of the formation in central and southern Iraq is shown on an isopach map (with a changing sand/shale ratio) illustrated by Ali and Nasser (1989). Formed in a fluvial environment, the Zubair is the deltaic equivalent of the Biyadh Formation of Saudi Arabia. Basically, the Zubair Formation in southern Iraq consists of two main sandstone horizons sandwiched between three shale units. Four principal lithofacies were identified by Ali and Nasser (1989): the products of prodelta, delta front, swamp and marsh, and shelf environments (Fig. 12.34). The porosity ranges from 19 to 28% and permeability from 80 to 500 md. The formation is locally a basinwide minor oil and gas reservoir with a reservoir gross thickness of 150-250 rn (492-820 ft) and a net thickness of 90-170 m (295-558 ft). The formation produced oil from the Abu Khaimah and Kifl discoveries and the Luhais, Majnoon, Qurna West, Ratawi, Siba and Tuba fields. Oil and gas are produced from East Baghdad, Nahr Umr, Rumaila North and South and Zubair fields.

Mishrif Formation (middle to late Cenornanian). The Mishrif reservoirs are Widely developed at several

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Fig. 12.34. Three-dimensional model of the Lower Cretaceous Zubair Formation in Southern Iraq (after Ali and Nasser, 1989, and reproduced by kind permission of Gordon and Breach Science Publishers) 700

Hydrocarbon Habitat of the Zagros Basin The best reservoir characteristics are found in the high-energy barrier sequence and in the shoal deposits (Fig. 12.35), where, in the absence of micrite, porosities are in the 20-25% range and permeabilities range from 10 to more than 1000 md. The porosity in the moderateenergy deposits drops to 10-15%, with permeabilities about 10 md, to porosity of 0.5% and a permeability of 0.1 md in the low-energy micritic-mudstone deposits. The formation's gross reservoir thickness is 110 m (361 ft). Oil is

locations in the Middle East, especially in Iraq. The overall Mishrif is a regressive sequence that can be subdivided into two sub-cycles, and each in turn into subsequences related to the instability of the shelf. The early sub-cycle shows a trend from outer-shelf--open-marine to restricted lagoonal conditions, and the later sub-cycle shows a passage up from outer to inner shelf, with a barrier between the two (Fig. 12.35). The two sub-cycles are separated by a sedimentary discontinuity (Reulet, 1982).

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Sedimentary Basins and Petroleum Geology of the Middle East produced in the Abu Ghiran, Buzurgan, Jabal Fauqui, Halfayah, Luhais, Majnoon, Qurna, western Ratawi, Rumaila North and South, Tuba and Zubair fields and also in the Dujaila discovery well.

Hartha Formation (Upper Campanian-Lower Maastrichtian). This formation consists of organic-detrital, occasionally dolomitic, limestone deposited in a shallow-marine setting. It is locally a minor oil reservoir with a reservoir gross thickness of 200-350 m (656-1,148 ft). The Majnoon Field and the Fallujah discovery produced oil in this formation.

Lower Fars Formation (Ghar Formation) (Middle Miocene). It consists of sandstone, calcareous sandstone, sandy limestone and evaporite deposited in a shallowmarine and terrestrial setting. The formation produced oil in the Nahr Umr Field and oil and gas in the Zubair Field.

Zagros Basin Reservoir Formation The following formations are the producing formations in the Zagros Basin (Dunnington, 1967, Bellen et al., 1959; Beydoun, 1988). Kurra Chine Formation (Rhaetian). It consists of limestone, dolomite, anhydrite and shale deposited in a shallow-marine and transitional-marine setting. The Sufaya Field and the Alan discovery produce oil in this formation but minor production is recorded from the Butmah Field only. Butmah Formation (Lower Liassic). This formation consists of dolomitic limestone, sometimes argillaceous, deposited in a shallow-marine and transitional-marine setting. With a reservoir gross thickness is 540 m (1,771 ft), it is locally a minor oil and gas reservoir. The Sufaya Field produced oil in this formation. Sargelu Formation (Middle Jurassic). It consists of bituminous, dolomitic limestone and shale deposited in a deep marine setting. The formation is a minor oil reservoir producing oil in the Hamrin Field and oil and gas in the Alan- 1 discovery.

Chia Gara Formation (Middle Porflandian-Berriasian). The formation consists of limestone and shale deposited in a deep-marine setting. It is locally a minor oil reservoir for a small quantity of light (47.5 ~ API) oil was tested from this formation in the Kirkuk Field. Garagu Formation (Valanginian Hauterivian). It consists of oolitic, sometimes sandy and ferruginous, limestone deposited in a transitional-marine and shallowmarine setting. The formation has a reservoir gross thickness of 90-230 m (295-754 ft) and is locally a minor oil reservoir in the Bai Hassan Field. Sarmord Formation (Valanginian-Aptian). This formation consists of dolomitic and argillaceous limestone deposited in a shallow to deep-marine setting. Oil is produced in the Sassan Field and oil and gas in the Kirkuk Field. Jawan Formation (Albian). It consists of oolitic limestone, dolomite and anhydrite deposited in a shallow-

702

marine and transitional-marine setting. The formation has produced oil in the Sassan Field. Dokan Limestone Formation (Cenomanian). The formation consists of foraminiferal, sometimes glauconitic, limestone deposited in a deep-marine shelf. The Bai Hassan Field produced oil, and the Jambur Field produced gas.

Upper Balambo Formation (Cenomanian-Turonian). It consists of foraminiferal limestone deposited in a deep-marine setting. With a reservoir gross thickness of 550 m (1,804 ft), the formation is locally a minor oil reservoir in the Injana discovery.

Kometan Formation (Turonian-Lower Senonian). This formation consists of foraminiferal limestone deposited in a shallow- and deep-marine setting. It has a gross reservoir thickness of 40-250 m (131-820 ft) and is a subordinate oil and gas reservoir. The formation produced oil in the Injana discovery and the Jawan, Kirkuk, Najmah, Qasab and Sufaya fields; oil and gas in the Qaiyarah Field; and gas and liquids in the Chemchemal Field.

Mushorah Formation (Lower Senonian-Lower Campanian). It consists of foraminiferal limestone and dolomite deposited in a shallow-marine setting. The formarion has a 0.3-1.2% porosity and a fracture permeability and is locally a minor oil and gas reservoir in the Ain Zalah Field.

Shiranish Formation (Upper Campanian-Maastriehtian). The formation consists of marly, foraminiferal limestone and marl deposited in a deep-marine setting. It has primary and secondary (vuggy) porosity ranging from 2 to 18% and a matrix and fracture permeability. The formation is a major oil and gas reservoir; it produced oil in the Ain Zalah, Kirkuk, Pulkhana and Sufaya fields and oil and gas in the Injana-5 discovery and the Bai Hassan, Butmah and Sasan fields. Asmari Formation (Lower Oligocene-Lower Miocene). Consisting of carbonate deposited in a shallowmarine setting, this formation is the lateral equivalent of the Kirkuk Group in northern and northeastern Iraq. It is a subordinate oil reservoir in the Abu Ghirab, Buzurgan and Jabal Fauqui fields. Kalhur Formation (Lower Miocene). It is a lateral equivalent of the Jeribe Limestone Formation (Middle Miocene) in northern and northeastern Iraq. This formation consists of dolomitic, sometimes foraminiferal, limestone, with a fracture porosity averaging 13%, deposited in a shallow-marine setting. It has a gross reservoir thickness of 70 m (230 ft) and is a subordinate oil reservoir in the Chia Surkh discovery and the Naft Khaneh Field. Serikagni Formation (Lower Miocene). This formation consists of marly, foraminiferal limestone deposited in a deep-marine setting. It has a gross reservoir thickness of 150 m (492 ft) and is locally a minor oil reservoir in the Pulkana Field.

Euphrates Limestone Formation (Lower Miocene). It consists of coral, dolomitic, sometimes

Hydrocarbon Habitat of the Zagros Basin chalky limestone deposited in a shallow-marine setting. Oil is produced in the Jawan, Najmah and Qasab fields, and oil and gas are produced in the Jambur and Qaiyarah fields. Jeribe Limestone Formation

(Middle Miocene).

The formation consists of dolomitic limestone deposited in a shallow-marine setting. It has a gross reservoir thickness of 55-70 m (180-230 ft) and is locally a minor gas reservoir in the Jambur Field. Q a m c h u q a Group (Hauterivian-Albian). The Qamchuqa Group is one of the major reservoirs in the Zagros Basin. In the Kirkuk region, facies changes in the Qamchuqa Group are related to water-depth changes from about 50 to 200 m. This permits the division of the reservoir in the anticlinal structure into three zones (A-C, see Fig 12.36): a northwestern zone, in which neritic facies dominate; a central zone, where basinal facies play a greater role; and a southeastern zone, which contains basinal mudstone facies (Fig. 12.36). The Qamchuqa is the lateral equivalent of the Nahr Umr, Mauddud, Shuaiba, and Ratawi formations of southern Iraq). The beds in zones A and B consist mainly of rudist-bearing platform carbonates with increasing basinal facies present in zone B to the southeast, passing finally into zone C, where the deepwater facies equivalent to the Qamchuqa are referred to the Balambo Formation. The regional paleogeography and stratigraphy of the group has been discussed by A1 Shdidi et al. (1995) in sequence-analysis terms. The relatively high primary porosity (early to late post-sedimentary) with inter- and intra-particular, mold and fenestral pores has been enhanced by secondary diagenesis with a major phase of epigenetic dolomitization and the creation of vuggy porosity between the Cenomanian and Senonian, and the development of fracture porosity and surfacewater action during the Miocene. The formation is a subordinate oil and gas reservoir. Oil is produced in the Ain

Zalah, Bai Hassan and Kirkuk fields, with oil and gas in the Jambur Field. Kirkuk Group. Because of the complex interfingering of the different Tertiary carbonate facies and their effects on the local stratigraphy, Majid and Veizer (1986) found it convenient to base their interpretation of the local paleogeography on the facies distribution (Fig. 12.37). The group is known and described in the Kirkuk Field and produces from carbonate reservoirs of late Paleocene to early Miocene age in which primary, intergranular and intraskeletal porosity have been enhanced by secondary dissolution and fracture porosity. The carbonates were deposited on a shallow-marine shelf in a complex biogenic buildup, one in which 18 major lithological facies were identified by Majid and Veizer (1986). The reservoirs are associated with the biohermal and foreslope facies. The basic paleogeographic pattern is one of a homoclinal ramp evolving into a rimmed carbonate shelf. Drowning of the shelf in the late early Eocene initiated the first depositional cycle, which was terminated by late Eocene regression. During the Oligocene in the southeastern part of the Kirkuk Block, two basin-to-platform cycles developed, whereas the northwestern part was largely exposed at this time. Exposure in the southeast did not occur, except perhaps marginally, until the late Oligocene. Each cycle was characterized by lime mudstones formed in an open basin passing landwards through foreslope, bioherm to mud-fiat facies. Two stages of carbonate diagenesis are recognized: an early stage of micritization, submarine cementation, dissolution and early dolomitization; followed by a later phase of ubiquitous cementation in the presence of meteoric water, with further dissolution and dolomitization. Selective solution is characteristic of the biohermal and foreslope facies, and the result of more intensive diagenesis present in the nearshore facies, resulting in

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Sedimentary Basins and Petroleum Geology of the Middle East

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Hydrocarbon Habitat of the Zagros Basin higher original and secondary porosity. Geochemical studies confirm that the diagenesis reflects a mixed meteoric surface water and marine water. Stylolites developed in the basinal carbonates (Majid and Veizer, 1986). The formation has good primary and secondary (vuggy) porosity ranging from 5 to 35%, and the fracture permeability exceeds 100 md. The formation is locally a major oil, gas and condensate reservoir. Oil and gas were produced in the giant Kirkuk and Bai Hassan fields, with gas and liquids produced in the Kor Mor discovery.

Recently, attention has been given to the potential of the late Triassic Kurra Chine Formation as a source rock (Sadooni, 1995). The formation was deposited under a variety of continental and nearshore, shallow depositional environments ranging from carbonate-shelf and lagoon to sabkha and evaporitic tidal-flat. The formation contains black, pyritic, carbonate mudstone and algal carbonates It may have potential as a source rock. Although most of the primary porosity has been destroyed by diagenesis, there is some solution porosity. Fracture porosity is difficult to estimate given the paucity of cores. Pore spaces do contain residual hydrocarbons and bitumen in the northern part of the basin; however, the formation does not yet have commercial potential (Sadooni, 1995). A1 Habba and Abdulla (1989) and A1 Habba et al. (1994) indicated that there are numerous, prolific source rocks in the northern and western Iraqi fields (see Table 12.12). The results of the geochemical analysis of nearly 300 oil and rock samples from fields in northern Iraq of Late Cretaceous Balambo Formation and the Jurassic Chia Gara, Barsarin, Gotnia, Neokelekan and Sargelu formations from six wells in northern and northeastern Iraq were reported by A1 Habba and Abdullah (1989) (Figs. 12.3912.41). They demonstrated that the rocks examined had good source-rock potential and that the hydrocarbons

Source Rocks and Oil Geochemistry The principal source rocks were deposited during the late Jurassic to early-middle Cretaceous, and the weight of evidence suggests that it is oil from these two sources that is responsible for charging most of the Iraqi reservoirs. Maturation of the Upper Jurassic source-rock formations began around 90 Ma, with peak generation from 85 to 13 Ma, a peak not yet attained for lower Cretaceous source rocks. Rapid maturation followed the heavy loading by a Mio-Pliocene molasse that raised the thermal gradient. Fig. 12.38 shows the different stages in the formation, tapping and maturation of the hydrocarbons in the Qamchuqa reservoir.

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705

Sedimentary Basins and Petroleum Geology of the Middle East

Table 12.12. Analysis of some source rocks from northeastern and western lraq (compiled by AI Gailani, 1996 from AI Habba and Abdullah, 1989, and AI Habba et a|., 1994) Age

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Formation

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TOC % 1.18 7 9.6 7.8 5.34 1.17 5

Average TOC

2.19 3.09 4 4.95

1 1.48 16.62 0.9-5

began generating in the lower part of the Balambo Formation some 15 Ma ago, and the weight of evidence suggests it is oil from the Late Jurassic and Early Cretaceous formations which charged most of the Iraqi reservoirs. The oil migrated horizontally under the Sarmord seal and was trapped in reservoirs in the Kirkuk, Jambur and Khabaz formations. Oil maturity was reached in the Jurassic formations 37 Ma ago, generating an estimated 18 B.bbl. Studies made during the 1970s by A1 Shahristani and A1 Atiya (1972) and A1 Shahristani and Hanna (1974) on vanadium, nickel and bromine concentrations in oil provide information not only on oil migration, but on the potential common origin of the oil. Trace amounts, from a few parts per million to a few parts per billion, of vanadium and nickel are found incorporated in soluble organic complexes, the metallo-porphyrins associated with the asphaltic fractions. In the Kirkuk fields, the vanadium/ nickel ratio in oil samples drawn from the same level in different wells remains fairly uniform, suggesting that the oils have a common origin or similar source environments. There are, however, significant differences in samples drawn from oils at different levels in the same field, which is interpreted as reflecting slower migration of the asphaltenes and resins because of their high molecular weight. Thus, the decreasing gradient due to the retention of the asphaltenes and resins is an indication of vertical migration. This decrease also can be observed along the axis of the migration path. A1 Shahristani and Hanna (1974) suggests that the behavior of bromine shows a positive correlation with that of vanadium/nickel, but it may prove to be a more sensitive indicator of oil migration despite its low concentrations. The results from this geochemical work support Dunnington's (1958) contention of significant vertical migration, and A1Shahristani and Hanna (1974) go so far as to suggest that oil drawn through fractures is continuously being replaced from below. Although the results from the northern Iraqi fields

706

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around Kirkuk sound very convincing, it must be recorded that in the Rumaila and Zubair fields in southern Iraq, a different pattern emerges, with the vanadium and nickel in the hydrocarbons in the older reservoirs appearing to contain lower concentrations. In these fields, there is a much greater variation in the vanadium content from different wells at the same level. There also is a tendency for lower vanadium values to occur in the vertex of reservoirs, so the interpretation of vanadium/nickel ratios may not have yielded all their secrets.

Seals and Seal Formations Where the oil is trapped in the Asmari Limestone and its equivalents, the seal is the evaporites of the Lower Fars Formation. This seal is very effective in most cases, but sometimes oil and gas seeps have been detected. The seal formation for the reservoirs in late Cretaceous rocks is formed by basinal marl, which resulted from a eustatic rise in sea level during the late Cretaceous. In the Arabian Basin (Fig. 12.31), the main reservoirs are Lower Cretaceous sandstone under a seal of interbedded shale, and Upper Cretaceous limestone beneath shale caps. The Miocene and Jurassic evaporites play only a minor role as cap rocks in the Iraqi sector of the Arabian Basin. In the Zagros Basin, the main reservoirs are limestone of the Oligocene Kirkuk Group under a cover of Lower Fars evaporites, and several Upper Cretaceous limestone units under shale seals. Additional but minor hydrocarbon accumulations were discovered in Lower Cretaceous, Jurassic and Upper Triassic limestone reservoirs mostly sealed by shale. The cap rocks for all Mesozoic reservoirs are interbedded and/or overlying shale, including the PaleoceneLower Eocene Aaliji shale of the Zagros Basin (Fig. 12.32). Faulting (partly synsedimentary gravity faults) has reduced the seal efficiency of some of these Mesozoic

Hydrocarbon Habitat of the Zagros Basin

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Sedimentary Basins and Petroleum Geology of the Middle East

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Sedimentary Basins and Petroleum Geology of the Middle East shales, as in the case in the Zagros Basin in the Ain Zalah Field, where oil and gas from reservoirs as old as Hauterivian (Qamchuqa Formation) are leaking along fractures to higher reservoirs as young as Maastrichtian (Shiranish Formation). The distribution of hydrocarbon accumulations in the Zagros Basin coincides with the maximum development of the Miocene Dhiban and/or Lower Fars evaporites, which clearly shows the important sealing effect of these evaporite deposits. The Lower Fars evaporite facies rapidly changes to a purely clastic facies, and the oil still retained by the Lower Fars Formation represents less than half a percent of the country's total oil reserve.

Cap Rocks in the Arabian Basin Gotnia Formation (Upper Jurassic). It consists of 200 m (656 ft) of an anhydrite with subordinate shale and limestone. This formation is a tight seal for local oil and gas accumulations in underlying Najmah limestone and minor oil in interbedded limestone. Ratawi

Formation

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Consisting of about 200 m (656 ft) of dark shale with minor limestone, it represents a seal for significant local oil and gas accumulations in lower Ratawi limestone and oil in underlying Sulaiy limestone reservoirs. Zubair Formation (Valanginian-Barremian). This formation consists of 350 m (1,148 ft) of alternating sandstone and shale. The shale provides fair seals for major oil and gas accumulations in interbedded sandstone reservoirs. Nahr Umr Formation (Albian). It consists of 160 m (525 r ) of alternating sandstone and shale and represents an important seal for major oil reservoirs in the interbedded sands. Khasib Formation (Turonian). This formation consists of 60 m (197 ft) of shale and marly limestone and is a fair seal for major oil and gas reservoirs in underlying Mishrif limestone. Shiranish Formation (Maastrichtian). It consists of 120 m (394 fi) of marl and marly limestone and is a fair seal for important oil accumulations in underlying Hartha limestone in the Majnoon and Fallujah fields. In the Zagros Basin, it is an extensive cap rock of limited efficiency and a partial seal for substantial oil and gas accumulations in underlying limestone reservoirs (Kometan, Mushorah and Qamchuqa formations). A restricted connection by fracturing between the underlying QamchuqaMushorah reservoir and the overlying limestone reservoir of the Shiranish Formation exists in the Ain Zalah Field. Lower Fars Formation (Middle Miocene). The formation consists of more than 800 m (2,624 It) of anhydrite and salt with intercalations of limestone and siltstone. Evaporites of the Lower Fars form seals for significant local oil and gas accumulations in interbedded limestone and in sands of the underlying Ghar Formation. The Lower Fars evaporites in the Zagros Basin are the principal cap

710

rock for the large underlying limestone reservoirs ranging in age from Paleocene to Lower Miocene, particularly for the limestone of the Oligocene Kirkuk Group.

Cap Rocks in the Zagros Basin Pirispiki Redbeds (Ordovician). These beds form the seal over small gas discoveries found in the Khabour quartzite in Khleissia-1. Baluti Formation (Rhaetian). This formation consists of 80 m (262 ft) of calcareous shale with intercalated limestone. The shale represents limited oil and gas accumulations in underlying Kurra Chine carbonates. Adaiyah Formation (Liassic). It consists of 30-100 m (98-328 ft) of anhydrite with subordinate limestone and shale. The anhydrite represents a tight seal for local oil and gas accumulations in Butmah limestone in the Sufaya Field. Naokeleken Formation (Upper Jurassic). The formation consists of a few tens of meters of bituminous shale and dolomitic limestone. Locally, it is an important seal for the Sargelu limestone reservoir at the Hamrin Field. Khasib Formation (Turonian). It consists of 60 m (197 ft) of shale and marly limestone, where it forms the cap rock for major oil accumulations in underlying Mishrif limestone reservoirs. Shiranish Formation (Upper Campanian-Maastrichtian). Consisting of about 230 m (754 ft)of marl and marly limestone, this formation is an extensive cap rock of limited efficiency and forms a partial seal for substantial oil and gas accumulations in underlying limestone reservoirs (Kometan, Mushorah and Qamchuqa formations). A restricted connection by fracturing between the underlying Qamchuqa-Mushorah reservoir and the overlying limestone reservoir of the Upper Shiranish Formation exists in the Ain Zalah Field. Aaliji Formation (Paleocene-Lower Eocene). The formation consists of 150 m (492 ft) of alternating shale, marl and limestone. It is an extensive seal for major oil and gas accumulations in the underlying Shiranish limestone reservoir and in the Ain Zalah Field and also for deeper (Qamchuqa and Mushorah) reservoirs communicating with Shiranish limestone. Eocene-Oligocene marl overlying the Aaliji Formation adds to its seal efficiency. Dhiban Formation (Lower Miocene). It consists of 70-100 m (230-328 r ) of anhydrite with subordinate marl intercalations. This formation forms a high-quality seal for major oil and gas accumulations in Euphrates/Serikagni limestone in the northwestern part of the Zagros Basin.

Oil Field Examples A summary of data for some of the Iraqi fields is given in Appendix 12. Ain Zalah Field. This field was discovered in 1939 by a combination of surface geology and gravity measure-

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Fig. 12.42. Structure on the top of the Middle Cretaceous Qamchuqa Formation in the Ain Zalah oilfield (From E1Zarka and Ahmed, 1983, reproduced by kind permission of Journal of Petroleum Geology). ments in a prominent surface anticline exposed as a series of ridges of limestone and gypsum in beds of the lower and middle Miocene Euphrates and Lower Fars formations, reflecting the anticlinal structure located some 60 km northwest of Mosul. E1 Zarka and Ahmed (1983) described the structure of the Cretaceous section as a bicrestal, double-plunging anticline whose east-west axis is affected by a major east-west fault (Fig. 12.42). The discovery well initially produced 1,500 bbl/d, but this was lost when the well was deepened, and it has yielded only 200 bbl/d since completion. Production from the field was put on line in 1958 from 28 wells. Production from the upper reservoir, which was replenished by oil from the lower pay zone, continued until 1969. The appendix provides a summary of the field characteristics. The reservoir has all active water drive, resulting in the volumetric replacement of oil by water. There are reservoirs in the fractured limestone of the late Campanian-Maastrichtian Shirhanish Formation and in the Albian Qamchuqa Formation. The oil in the two pay zones is so similar in gravity (32 ~ and 29 ~ API, respectively) and chemistry that derivation from a single source seems inescapable, even though the two pay zones are separated by some 610 m (2,000 ft) of barren, marly, globigerinal limestone, similar in lithology to the reservoir rocks of the first pay zone. During World War II, the field was shut down between 1941 until 1947, when drilling recommenced. Thirteen wells were completed in the Shiranish limestone between then and 1950. Oil was discovered ill the porous, fractured Albian Qamchuqa limestone in 1957. The net pay zones in the two reservoirs are 91 m and 100 m (298 and 330 ft), respectively, out of total gross reservoir thicknesses of 704 and 165 m (2,305 and 540 ft) for the Shiranish and Qamchuqa formations, respectively, with an estimated 37 and 158 MM.bbl in the upper and lower reservoirs. The cumulative production at the end of 1976 was 20 and 146 MM.bbl, respectively. Reservoir data indicate that the Shiranish reservoir contains more oil, but the recoverable reserves are less (El Zarka, 1993). Primary production is from the western part of the field, especially from the upper pay zone. A pressure drop during production from the Shiranish reservoir was offset by water injection in the northern flank of the structure.

The trap is a faulted anticline with two reservoirs. Oil was initially trapped in the crest of the downfaulted southern anticlinal block in the fractured limestone of the Qamchuqa Formation, but migration along and across the fault (Fig. 12.43) led to entrapment in the crest of the northern, upthrown block in the Shiranish limestone. The shale and limestone form imperfect seals, for migration has occurred from the lower to the upper reservoir, and oil has even moved into the sands of the Aaliji Formation, which overlies the Shiranish limestone. Oil migration began in the late Cretaceous along fractures and along the unconformity between the middle and upper Cretaceous. The unconformity separating the seal from the late Cretaceous "first pay" had little effect on the reservoir, for no significant secondary porosity developed, and oil was not in place at that time. In contrast, the unconformity above the second pay was associated with leaching and the development of secondary porosity (Dunnington, 1958). As shown in Fig. 12.41, the oil-water contact is tilted and may reflect hydrodynamic effects in the eastern section of the field. The source rocks are thought to be the black, bituminous shale of the Qamchuqa and Mushorah shale of the middle and upper Cretaceous; however, there are no available data on TOC, kerogen type or maturation level. The oil is paraffinic, 31.5 ~ API for the Shiranish oil and 30.7 ~ API for the Qamchuqa oil, with sulfur levels of 2.6% and 2.5%, respectively. Butmah Field. Adjacent to the Ain Zalah Field, this field is in one of two inline domes of the Butmah Anticline (Fig. 12.44). It yields 30 ~ API oil, which has migrated into fractured late Cretaceous Shirhanish marly limestone, equivalent to the first pay of the Ain Zalah Field. The limestone equivalent to the second pay of Ain Zalah, while oilstained, is water-logged. The structure of the field is illustrated by Fig.12.44. As in the case of the Ain Zalah Field, there is an active water drive yielding oil very similar to Ain Zalah oil. There also is a small production of light oil (35 ~ API) from the Triassic Kurra Chine limestone (Beydoun, 1988). K i r k u k F i e l d . The Kirkuk Field lies in a sinuous anticline stretching some 96 km (60 mi). It is broken into three major anticlinal culminations separated by two prominent saddles overthrust from the northeast with decollement

711

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712

reef shoal and main reef facies; the backreef facies of porcellaneous limestone is impermeable. The field produces 36-44 ~ API oil. The potential source sediments lie to the southwest and south of the present field and form part of the southeastern dome (Dunnington, 1958). By analogy with the Ain Zalah Field, it is presumed that the oil has, in fact, migrated upwards from a Lower or Middle Cretaceous sequence. Dunnington's (1958) account of the origin of the Kirkuk oil involves primary accumulation in Middle Cretaceous traps at about the end of the Cretaceous, followed by secondary migration into the developing Kirkuk structure during the early stages of Mio-Pliocene folding. Rupture of the Turonian and upper Cretaceous cap rocks permitted migration into an upper Cretaceous reservoir, then later migration into the "main limestone" following the fracturing of the Paleocene-lower Eocene seals. The capping Lower Fars evaporite sequence also contains porous limestone, which is oil-bearing but volumetrically insignificant. The seal is not complete, for extensive gas and oil seepages are known at the surface. The Eocene and Oligocene depositional cycles prograde northeastwards from basinal limestone to nummulitic limestone shoals. Bai l-lassan Field. This field lies parallel to the Kirkuk Field and about 6 km (3.75 mi) to the southwest. There are, however, no oil or gas seeps. The reservoir unit is equivalent to the "main limestone" of Kirkuk and contains saturated 32 ~ API oil, similar to the Kirkuk oil, with an extensive gas cap. The oil also is presumed to have migrated upwards from a middle Cretaceous reservoir in neritic limestone, with a potential origin in the MiddleLower Cretaceous basinal sediments (Fig. i2.47 see p. 560)i Additional production is possible from the Upper Cretaceous Shirhanish limestone and the Middle Cretaceous Qamchuqa limestone (Beydoun, 1988). Qaiyarah fields. There are three fields in a series of anticlinal structures in the Qaiyarah structure (Figs. 12.48 and 12.49 see p.561) m the Qaiyarah, Najmah and Qasab - - w i t h two productive reservoirs. The upper and more productive reservoir is in the lower Miocene neriticlagoonal Euphrates limestone, and the lower is in upper Campanian-lower Maastrichtian neritic limestone. The oils in both reservoirs are similar, with gravities between 11.5 and 19 ~ API; all are sulfurous (6.5-8% sulfur) and density stratified with the heaviest oil in the deeper parts of the structure. The oil-water contact is tilted and is highest in the northwest. The Euphrates limestone is sealed by the anhydrites, marl and limestone of the Lower Fars Formation, which lacks the presence of halite in this area. The seal between the two reservoirs is formed by thin, globigerinal marl of Upper Cretaceous to Oligocene age. Dunnington's model for the charging of the reservoirs is shown as Fig. 12.49. Buzurgan Field. This is a low-relief, smooth anticline with two culminations running NW-SE. It is about 60 km long and 12 km wide, with each culmination about 30

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Fig. 12.44 Schematic sections across the Ain Zalah and Butmah fields illustrating the probable mode of accumulation of the oils. A) shows thefirst pay with secondary accumulation of oil in fractures in marly globigerinal limestones of Upper Cretaceous age, fed by vertical migration from 2nd pay. B) shows the second pay residual primary accumulation in neritic Middle Cretaceous limestone (after Dunnington, 1958, reproduced by kind permission of AAPG). km long (A1-Ani, 1975). The field lies northeast of Amarah close to the Iraq-Iran border. The main pay is in the Mishrif Formation from wells drilled in the southeastern culmination, with non-commercial oil in the Jeribe-Euphrates and Upper Kirkuk formations in the northwestern culmination. Three complete sedimentary cycles are recognized in the Mishrif and a fourth terminating at an unconformity. The cycles end in biostromal accumulations (reservoirs) and begin with lime mudstone (potential seals). Nahr U m r Field. Nahr Umr is a domal anticline with a NNW-SSE axial trend about 20 km long. Drilling and seismic survey showed evidence of crestal faulting. The field has a negative residual gravity anomaly (Sayyab and Valek, 1968). The main pay lies in the Nahr Umr Formation, from which 41-46 ~ API oil was produced on test. Rumaila Field. This field lies in an asymmetrical anticline in which the western flank is the steeper. It has no clear surface expression and is 100 km long by 18 km wide lying about 50 km west of Basrah. The field produces 35 ~ API oil from the Zubair Formation (and some heavier oil from the Mishrif Formation). Oil with a 24-28 ~ API that has a relative high sulphur content also can be produced from the Mishrif Formation, but economics preclude exploitation through the same producing network as that which drains the "Main Pay." For political reasons, the northern structural culmination was considered a separate field (called Rumaila North), but it is well-known that both the northern and southern structural culminations share the

same oil-water contact. On that basis, the ultimate recoverable oil of the Rumaila Field is of the order of 18,600 M.bbl (Halbouty et al., 1970), which qualified it as the sixth largest oil field in the world (Halbouty et al., 1970). Zubair Field. This anticline is 60 km long and 8 km wide, with a flank dip of 2-3 ~ and a NNW-SSE axial strike. The structure has two culminations: the southern, the Rafidiya Dome; and the northern, the Hammar Dome. Oil and gas were found in the Lower Fars, Ghar, Mishrif and Zubair formations. The main production is from two sand members in the Zubair Formation: the Upper Sand Member, which produces 36 ~ API oil; and the Lower Sand Member, with 42 ~ API oil.

713

Sedimentary Basins and Petroleum Geology of the Middle East

NW

SE K H U R M A L A DOME

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Fig. 12,45. The three major anticlinal culminations of the Kirkuk Field, Iraq. (after Dunnington, 1958 and reproduced by kind permission of AAPG). 6O MILES

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Fig. 12.47. Schematic section illustrating the probable mode of oil accumulation in the Baba dome (Kirkuk) and the Bai Hassan Field, Iraq a) secondary accumulation in the porous main limestone, fed vertically from primary accumulation in Middle Cretaceous reservoir. b) secondary accumulation in fractured Upper Cretaceous marly limestone fed vertically from primary accumulation in Middle Cretaceous reservoir. c) residual primary accumulation in Middle Cretaceous reservoir (after Dunnington, 1958, and reproduced by kind permission of AAPG).

Hydrocarbon Habitat of the Zagros Basin

QASAB

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Fig. 12.48. Schematic map and cross-section of the Qaiyarah, Najmah, Jawan and Qasab fields showing the disposition of the two superposed culminations (Upper Cretaceous and Oligocene). The oil-water surfaces in both reservoirs slope down to the southeastern pitch of the Qaiyarah Field (after Dunnington, 1958 reproduced by kind permission of AAPG).

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Fig. 12.49. Schematic section across the Jawan, Najmah and Qaiyarah structures showing the probable mode of accumulation of the oils and major source beds and seals. Note that in the Qaiyarah secondary accumulations due to upward migration along and across the fault from primary accumulation in Upper Jurassic reservoirs (after Dunnington, 1958, reproduced by kind permission of AAPG).

715

Sedimentary Basins and Petroleum Geology of the Middle East these fields were temporarily shut down during the IraqIran war since 1980, and a number of known fields have been renamed since the Iranian Revolution.

IRAN Introduction

Iran has an area of 1,648,000 sq km, with its major oil and gas resources concentrated in the Zagros Fold and Thrust Belt, an area extending from the Iraq/Iran frontier in the northwest to the Omen line in the southeast, a distance of 1,300 km. The zone in Iran is 200-300 km wide, limited to the northeast by the Zagros Thrust Zone and to the southwest by the Mesopotamian Plain and the Arabian Gulf (Fig. 12.50). The oil and gas resources are found in reservoir rocks from late Paleozoic to middle Cenozoic in age. The major reserves are in the Oligocene-Miocene Asmari Limestone of the Khuzestan Province, although an important reservoir is found in the more deeply buried Cretaceous sandstones and carbonates and in the Jurassic carbonates. Most of the gas is found in the Permo-Triassic carbonate-evaporite sequence of the Deh Ram Group, an equivalent of the Khuff Formation of Arabia. '~.....~ "~ r"

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Fig.12.50 Location map of the Zagros basin showing the Khuzestan (A), Lurestan (B) and Fare (C) provinces with major structural trends. Although the working of small surface deposits goes back to antiquity, the first exploration well was not drilled until 1903 (Chia Sarkh-1). It proved to be a dry hole, as was the second drilled in 1906 at Mamtain in the Khuzestan region; however, the well at Masjid-i-Sulaiman struck oil in 1908 (Schlumberger, 1991). The continuous development of fields was interrupted by the war years of World War II, when an effort was concentrated on production. From 1957, exploration turned to the offshore area until the advent of the Iraq-Iran war in 1978, when a number of fields were shut-in and some discoveries remained undeveloped. Production then dropped from 5.68 MM.bbl/ d to 2.58 MM.bbl/d, but has since recovered to about 3.7 MM.bbl/d in 1994 (World Oil, 1995). The ultimate recoverable reserves of Iran are about 59 B.bbl of oil and about 620 trillion feet of gas. The location of Iran and its major oil and gas fields is shown in Fig. 12.51. A number of

716

Stratigraphy

The sediments composing the Zagros Fold Belt are up to 12,000 m (39,360 ft) thick, and, except for the Devonian and Carboniferous systems missing throughout the belt, the section is a nearly continuous, conformable sequence from the Infracambrian to the Pliocene. Sedimentation began with important Infracambrian (Vendian) evaporites, followed by the shallow-marine carbonate and clastic deposits of the Lower Paleozoic. From the Permian and throughout most of the Mesozoic and up to Lower Miocene, the area was part of a broad, shallow carbonate platform. Subsequently, thick evaporites followed by continental red beds characterize the Mio-Pliocene. Folding accompanied by syntectonic and post-tectonic molasse took place in Plio-Pleistocene time. A composite lithostratigraphic section including the hydrocarbon parameters in the main producing fields of Iran is shown in Figs. 12.52 and 12.53. The Paleozoic has a thickness of about 2,400 m (7,872 ft) and embodies three depositional cycles, each separated by a depositional hiatus or an unconformity. The Cambro-Ordovician and Silurian cycle consists of transitional-marine sandstone and shale. The Devonian-Lower Carboniferous cycle is comprised of continental and shallow-marine sandstone and shallow-marine shelf carbonates and shale, whereas the Upper Carboniferous-Middle Triassic cycle is composed of continental clastics that change basinwards into shallow-marine limestone and shale. The Mesozoic section ranges from 3,000 to 4,000 m (9,840-16,400 ft) in thickness and is better known as a result of better exposure and its economic importance. The distribution and variation of the observed facies patterns is evidence that the Arabian Platform was subject to broad epeirogenic uplift and depression with the development of swells or arches that accounted for the formation of large basins. Sedimentation in these basins can be broken up into a number of depositional cycles, each separated by an unconformity or a depositional hiatus. The Upper TriassicMiddle Jurassic cycle consists of shallow-marine shelf carbonates and lagoonal evaporites, shale and limestone. The Upper Jurassic-lowermost Cretaceous cycle is composed of shallow-marine shelf carbonates and lagoonal evaporites (Jurassic) and shallow-marine limestone (lowermost Cretaceous). The Barremian-Albian cycle is comprised of shallow-marine limestone and shale, with deltaic sandstone. The Cenomanian-Lower Campanian cycle consists of shallow-marine and deltaic sandstone and alternations of shallow-marine limestone, shale and marlstone. The Upper Campanian-Maastrichtian cycle is composed of shallow-marine limestone and marlstone. The Tertiary section is more than 1,350 m (4,428 ft) thick, comprising a

Hydrocarbon Habitat of the Zagros Basin

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Fig. 12.51 Major oil and gas fields of Iran. The names of the fields are as follows: 1. Veyzenhar, 2. Sarkhan, 3. Valeh Kuh, 4. Halush, 5. Samand (gas), 6. Delhuran, 7. Danan, 8. Kabud. 9. Qaleh Nar, 10. Lab-e-Saif, 11. Chashmeh Khush, 12.Paydar, 13. Zeloi, 14. Lali, 15, Karun, 16. Masjid-e-Sulaiman, 17. Par-e-Siah, 18. Naft Safid, 19. Haft Kel, 20. Kupal, 21. Ramin, 22. Marun, 23. Ahwaz, 24. Susangerd, 25. Ab-e-Teimur, 26. Dorquan, 27. Mansuri, 28. Shadegan, 29. Khavizi, 30. Kuh-e- Bangestan, 31. Pads, 32. Karanj, 33. Agha Jari, 34. Ramshir, 35. Pazanan, 36. Rag-e-Safid, 37. Kuh-i-Rig, 38, Doudrou, 39. Shurom, 40. Gachsaran, 41. Garangan, 42. Bibi Hakimeh, 43. Siah Makan, 44. Hedijan, 45. Bahrgansar, 46. Nowruz, 47.Abouzar (Ardeshir), 48. Soroush (Cyrus), 49. Esfandiar/Lulu (Iran/ Kuwait), 50. Ferouzan/Marjan (Iran/Saudi), 51. Darood (Darius), 52. Binak, 53. Kilurkarm, 54.Gulkhad, 55. Sulabedar, 56. Chilingar, 57. Rudak-Milatun, 58. Narges, 59. Sarvestan, 60. Aghar (gas), 61. Dalan (gas), 62. Bushgan, 63. Kuh-eKaki, 64. Kuh-i-Mand, 65. Pars (gas), 66. Kangan (gas), 67. Nar (gas), 68. Varvi (gas), 69. Assaluyeh (gas), 70. Balal (Bahram), 71. Reshadat (Rostam), 72. Resalat (Rakhsh), 73. Salman (Sassan)/Abu A1 Bukhoosh (Iran/U.A.E.), 74. Sirri (A-D), 75. Nas (Sirri-E), 76. Salakh (gas), 77. Gavarzin (gas), 78. Sum (gas), 79. Sarkhun (gas)

717

Sedimentary Basins and Petroleum Geology of the Middle East O')

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Fig. 12.52. Lithostratigraphic section of southwestern and northwestern Iran (Khuzestan and Lurestan provinces) showing the distribution of the major reservoirs and seals

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Paleocene-Lower Eocene cycle of shallow-marine shelf carbonates and lagoonal/supratidal evaporites, a Middle Eocene cycle of continental clastics at the base followed by shallow-marine and lagoonal limestone, marl, evaporites and sandstone in a subsiding basin on top, and a Miocene-Pliocene cycle of continental sandstone, conglomerates and gravels. The depositional cycles recognized in the Arabian Basin appear as thickness and lithological variations in the Zagros Basin, where deeper intrashelf basinal sedimentation prevailed during the Mesozoic and resulted in the deposition of basinal marl surrounded by belts of narrow shelf carbonates. Volcanic rocks are found at different intervals in the Paleozoic and the Mesozoic and can be related to early phases of deformation. The Cenozoic alpine deformational phases are marked by great changes in the paleDgeography of the region. The reefal limestone of the Lower Oligocene-Lower Miocene Asmari Formation were overlain by a Middle Miocene salt and evaporite sequence, which in turn is overlain by Pliocene-Pleistocene clastic sediments.

n.

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Fig. 12.53. Lithostratigraphic section of the Fars Province, Iran, showing the major reservoirs, source rock and seal distribution. Structure and Traps

The position of the Arabian Gulf and Zagros basin together formed a major part of the vast Arabian Platform and its northeastern margin which were affected by gentle but steady subsidence since the Permian. Extensive, uniform shelf carbonates were thus the main product of sedimentation and reef limestones were relatively rare. The platform environment with its frequently restricted circulation favored the deposition and preservation of large amounts of organic matter. In late Jurassic and Miocene time thick evaporites formed which subsequently acted as very efficient seals. Subsidence, though gentle, was hardly halted or reversed, thus preventing the early erosion and dissipation of hydrocarbons generated. Folding in the Zagros occurred as a final phase in the Plio-Pleistocene creating numerous large anticlinal structures which acted as ideal traps. It also caused extensive fissuring and frac-

Hydrocarbon Habitat of the Zagros Basin turing and thus provided the necessary porosity and permeability in the limestone whose primary porosity was generally low. As indicated earlier, the Zagros Foreland Basin traps are dominated by the results of Neogene-Quaternary folding (Fig. 12.51), with the development of open or complex, monoclinal flexures or folds that may be anticlinal (anticlinoria) or synclinal (synclinoria) and on which are superposed lesser folds. These result from lateral orogenic stresses rather than from vertical uplift. The anticlines vary in size up to the largest (Kabir Kuh), which is 190 km (120 mi) long with amplitudes that may reach 6-10 km (3.7-6.2 mi). In many areas, the folds appear to be concentric in style, with the implication of diminution of size with depth. According to Ameen (1991 a & b), a traverse across the fold belt shows the existence of large-scale "geowarps," which are monoclinal with maximum dips of 13 ~ and which developed contemporaneously with the anticlinal folds. They are regarded as the result of differential uplift due to shortening and thickening of the underlying crust. The geowarps underlie the entire fold zone and extend parallel to the main chain. The style of the individual anticlines is due to the presence of thick, rigid carbonates of the Asmari Formation. One consequence of the folding is detachment from basement along a surface at the top of the underlying Hormuz evaporites. Consistent with this, complexities such as salt thrust cores have been encountered in some deep wells. Detachment also occurs above the Asmari Limestone, with deformation accommodated by movement in the overlying Fars evaporite beds. Outside the fold belt, the Arabian Platform and Basin were practically unaffected by compressional movement, and gentle elongated to oval drape structures over deep fault scarps or salt pillows of Eocambrian salt are the common traps. These structures, however, do not attain the major dimensions found in the offshore and onshore fields of the Arabian Gulf states. Asymmetric "whale-back" anticlines, several tens of kilometers long and several kilometers wide, are the most common trap type in the Zagros Fold Belt. Folding was facilitated by decollement above the pre-Middle Cambrian evaporites. On the other hand, disharmonic folding and thrusting of Neogene surface sediments above the Gachsaran evaporites pose a major exploration problem in that they often obscure the structure at the Asmari and deeper levels. Upwarping has had an effect on the hydrocarbon resources of the area, for uplift served to inhibit oil production; the downwarped zones, which were protected from erosion and received a substantially thicker sequence of Miocene-Pliocene deposits, enhanced oil generation and migration under a evaporitic (Fars) seal (Ameen, 1991 a & b). Purely stratigraphic traps do not occur; however, thinning over growing anticlines and even pinching out introduces a stratigraphic element into the structural traps, but these are not thought to contribute greatly to field reserves (Beydoun et al., 1992).

Many of the giant fields are multi-reservoired, producing from fractured carbonate pay zones, of which the most prolific are in the Oligo-Miocene Asmari Limestone Formation and the carbonates of the Late Cretaceous Bangestan Group. The north-south-trending Qatar-South Fars Arch, a major flexure probably related to a deep basement fault, divides the Zagros Fold Belt into two segments that strongly differ in their hydrocarbon potential. The bulk of the oil reserves is contained in the Dezful Embayment, situated to the northwest of the Fars Arch, which is known locally as the Kazerun Line. The embayment represents a Neogene foredeep in front of the rising High Zagros, characterized by strong subsidence and correspondingly rapid accumulation of thick Neogene Fars sediments. Here, extensive preservation of the Gachsaran evaporite seal has favored the retention of Asmari oil. In contrast, the Fars Arch, to the southeast of the Kazerun Line, represents a relatively uplifted sector of the Zagros Fold Belt. Here, conditions for the accumulation of hydrocarbons in Asmari reservoirs are less favorable; moreover, the fold pattern is complicated by numerous diapiric intrusions of Infra-Cambrian salt. Whereas oil production in the Fars Arch is insignificant, important deposits of non-associated gas have been found in Jurassic and Permian carbonate reservoirs. A shallow gas reservoir was also discovered in a local reef development of the Miocene Guri Limestone, a carbonate intercalation in the Upper Fars of the southeastern Fars Arch. Structures of the Iranian fields in the Arabian Gulf are dominated by numerous salt domes, both buried and emergent, of pre-Middle Cambrian salt. Progressive doming took place from Early Mesozoic through Neogene time and has caused changes in formation thickness, lithology and diagenetic characteristics in the sediments surrounding the diapirs. Gentle domal drape structures over salt pillows and buried salt domes are the dominant trap type in this part of the Arabian Gulf. Trap density is rather high, but the average trap size is relatively small. The important structural changes in the area date from the Neogene, when the Zagros Zone became the most unstable element in the Middle East (Koop and Stoneley, 1982). Accepting the geochemical data that indicate that the source rocks were Early Cretaceous, there was no significant oil generation before about the Eocene, and little or no expulsion until the deposition of the Asmari Formation (e.g., some time in the early Miocene, and most probably penecontemporaneous with the Zagros folding). Such a scheme provides for vertical migration and avoids the necessity of proposing some intermediate reservoir where oil could accumulate until it migrated into its final storage place. Migration occurred through fractures, for oil in the Asmari Limestone occurs only in pores in direct communication with fractures, and impregnation of the micritic matrix of the limestone is lacking (Ala, 1982). Earlier matured oil, as from Jurassic source rocks, may have been trapped in growth folds within the Dezful Embayment, as 719

Sedimentary Basins and Petroleum Geology of the Middle East well as some on the more stable Arabian Platform (Ghawar, Burgan, etc.). The emplacement pattern of salt domes in Iran, both emergent and subsurface, is unique to the Fars Province and is related to basement tectonics (McQuillan, 1991). There are more than 100 active emergent domes, with diameters in the 3-15 km range and with evaporites that have penetrated thousands of feet of strata. The Infracambrian Hormuz evaporites, the source of the salt, and basement crystalline rocks are nowhere seen in situ. The regional location of the salt domes is not related to Tertiary folding, although most active plugs are associated with Zagros fold axes and appear to have "inflated" the anticlines in some cases (McQuillan, 1991). A recti-linear pattern of salt-plug emplacement can be detected, for the preferred orientation corresponds to major basement lineament trends. The consensus opinion is that significant oil generation in the Zagros sector did not occur until the Eocene and that no significant oil expulsion took place before the Miocene; the entry of oil into reservoirs was geologically recent, post-dating the formation of the traps that resulted from the Miocene-Holocene orogeny.

Reservoir Characteristics The importance of fracturing to production was first established in the Neogene reservoirs of the Zagros fields, where it could be established that the high production rates and reservoir communication could be explained only by fracturing. Field observation also showed that a field could be drained by fewer and more widely spaced wells. Fracture communication across 610-915 m (2,000-3,000 ft)of marl and shale also provided the explanation for the presence of oils of early Cretaceous origin in deeper Cretaceous reservoirs and in the Asmari reservoirs. Further evidence of this communication is provided by the movement of the oil-water contact in two separated reservoirs in unison when only the Asmari is being produced. Where the oil-water contacts do not move in unison, other differences, such as the specific gravities of the oils, are found. The oil produced was also derived in part from the intrinsic limestone porosity, although this is low. Orientation and the type and age of fractures are important, and flow anisotropy has been observed. Although there are two main periods of fracture, these may overlap in time but differ in orientation, when both are present in an anticline. Type 1 fractures seem to develop prior to type 2 fractures that parallel the anticlinal axes (McQuillan, 1973, 1985). Each fracture system may be associated with two conjugates shears and two tensional fractures, and techniques now exist for determining the width, length and fracture density. The primary porosity of the carbonate reservoirs is controlled by the depositional facies. Significant backbank carbonate reservoirs are found in the Asmari Forma-

720

tion in a belt 1,200 km long and 200 km wide, extending from northeastern Iraq into southeastern Iran, an area that coincides with the thickest accumulations of Cenozoic sediments. The absence of reservoirs in the Paleocene is attributed to the absence of frame-forming organisms. Reservoir enhancement by diagenesis (karstic dissolution) and/or dolomitization reflects the strong effects of tectonoeustatic control (Goff et al., 1995.). The large oil and gas accumulations of the Zagros Fold Belt are all associated with carbonate reservoirs. Most important are the Asmari Limestone of OligoMiocene age, followed by the limestone of Albian-Campanian Bangestan Group. The Bangestan and Asmari reservoirs are often in communication in spite of thick marl and shale layers between the two. Deeper reservoirs occur in the limestone and dolomite of the Jurassic-Lower Cretaceous Khami Group and in Permian carbonates (Dalan Formation). The primary porosity of all these carbonate reservoirs is generally poor, but improves locally in oolitic and bioclastic varieties. The enormous storage capacity is, however, mainly related to secondary porosity due to fracturing recrystallization and dolomitization. Fracture density in the Asmari Limestone has an inverse relation to bed thickness (McQuillan, 1973). Many of the carbonates consist of a dual system, with oil predominantly in the matrix and with fractures acting as channels. Other factors are the excellent cap-rock conditions, particularly the high sealing efficiency of the evaporitic Gachsaran Formation above the Asmari Limestone, and the large average size and high density of favorable structural traps. The Iranian part of the Arabian Gulf comprises sediments representing a typical platform cover, in which shallow-water limestone alternates with coastal sands and which includes several important evaporitic intervals. The sequence totals 8-10 km in thickness and ranges from Infracambrian to Recent, encompassing, however, many sedimentary gaps. Carbonates under cover of Triassic, Late Jurassic and Miocene evaporites are the main seals. Interbedded shale provides additional seals for Cretaceous limestone and sandstone reservoirs. Oil-prone source rocks have been recognized in Middle-Upper Jurassic and Lower Cretaceous intra-platform basinal shale, and deep-seated Silurian shale probably is a major source for gas.

Zagros Basin Reservoir Formations The following are the major reservoir formations in the Zagros Basin of Iran (Fig. 12.52), (see also Schlumberger 1976, 1991; Ala, 1982; Beydoun, 1988; Beydoun et al., 1992). Faraghan Formation (Lower Permian). The formation consists of sandstone, conglomerate and shale, with intergranular porosity, deposited in a fluvio-deltaic to marginal-marine environment. The formation is a subordinate gas reservoir in the Zagros Fold Belt, and gas is produced from the Pars Field.

Hydrocarbon Habitat of the Zagros Basin

Dalan Formation (Khuff equivalent) (Upper Perw.. mian). It consists of limestone, dolommc limestone, dolomite and anhydrite deposited in a shallow-marine environment with partly restricted circulation. The reservoir has a gross thickness of about 700 rn (2,296 ft). The formation has fair primary porosity in oolitic and bioclastic varieties, with secondary porosity through dolomitization and fracturing. The Dalan is a major gas reservoir in many fields such as Nar, Fats, Kangan, Aghar and Samand, as well as some discovery wells, produce from this formation. Kangan Formation (Lower Triassic). This formation consists of dolomitic limestone, occasionally evaporitic, with shale and argillaceous limestone deposited on a shallow-marine shelf. The reservoir has a gross thickness of about 200 m (656 ft) and secondary porosity due to dolomitization. It produces gas in the Pars and Kuh-e Mand fields. Surmeh Formation (Middle-Upper Jurassic). It consists of limestone, dolomitic limestone and dolomite and has secondary porosity due to dolomitization and fissuring. The formation has an average porosity of about 9% and net reservoir thickness of about 150 m (492 ft). It produced oil and gas from the Chillingan and Garangan fields and gas from the Suru and Kuh-e-Mand fields. Fahliyan Formation (Lower Cretaceous). The formation consists of massive oolitic and peloidal limestone of shallow-marine origin. It has a fracture porosity ranging from 9 to 12%. The net reservoir thickness is about 275 m (902 ft). The formation produced oil in the Doudrou Field and the Dorquain discovery, oil and gas in the Chillingar, Garangan and Kharg fields, and gas in the Suru Field. Garau Formation (Neocomian-Coniacian). It consists of argillaceous and marly limestone and shale of marine euxinic origin. It has a gross reservoir thickness of about 160 m (525 fi). A minor gas reservoir locally, this formation produced gas in the Emam Hassan Field. Dariyan Formation (Aptian). This formation consists of thick-bedded limestone of shallow-marine origin and has a gross reservoir thickness of 156 m (512 ft). It acts as a subordinate oil and gas reservoir. It produced oil and gas in the Kuh-i-Rig Field and oil in the Khaviz discovery. Bangestan Group (Albian-Campanian). The group is made up of three formations: Kazhdumi, Sarvak (Surgeh) and Ilam, but in some areas is collectively referred to as the Bangestan Group. It is composed of a thick sequence of shallow-marine, massive limestone has secondary porosity mainly from fissuring and, in southwestern Iran, forms an important secondary reservoir in the Dezful Embayment. The net reservoir thickness ranges from 70 to 630 m (230-2,066 fl), while the gross reservoir thickness ranges from 220 to 980 m (722-3,214 ft), with 415% porosity. The group represents a major oil and gas reservoir; oil is produced from the Zeloi, Danan, Jufeyer, Maleh Kuh and Sarkhan fields; oil and gas are produced from the Agha Jari, Bibi Hakimeh, Dehluran, Gachsaran,

Kupal, Lab-e-Safid, Lali, Marun, Naft-E-Safid, Rag-ESafid, Bahrgansar and Ramshire fields; and gas is produced from the Karun, Mamtain and Veyzenhar fields. Sarvak Formation (Cenomanian-Turonian). This formation consists of argillaceous limestone in the lower part graded upward to massive microporous limestone and nodular chert with secondary porosity from fissuring with 7-14% porosity. It has a gross reservoir thickness of 24790 m (79-2,591 ft) and a net reservoir thickness of 5-285 m (49-935 ft). The Sarvak Formation has a major oil and gas reservoir; oil is produced in the Bibi Hakimeh Field; from Dalpiri, Kuh-e-Mand and Shakeh discoveries, oil and gas are produced in the Ahwaz, Binak, Hendijan and Mansuri fields and in the Bahrain, Kabud, Kilhur, karim, Satvestan and Siah Makan-i discoveries; and gas liquids are produced in the Tang-i-Bijar Field and in the Babgir-1 discoveries. Ham Formation (Santonian-Campanian). It consists of argillaceous limestone and shale of a shallow to deep open-marine environment. This formation has a gross reservoir thickness of 25-170 m (82-558 ft) and a net thickness of 110 m (361 ft). The reservoir has secondary porosity due to fissuring, with porosity ranging from 9 to 20%. The formation is a minor oil and gas reservoir, oil and gas are produced from the Ab-E-Teimur, Ahwaz, Emam Hassan and Mansuri fields; gas is produced from the Halush Field and oil from the Darquain and Sirri A fields. Asmari Limestone (Oligo-Miocene). The Asmari Limestone Formation is one of the most prolific reservoirs; within the Dezful Embayment in the Zagros area, at least 63 oil and gas fields have been discovered, of which four are supergiant fields, and 12 qualify as giant fields. In the early days, most drilling concentrated on the crests of Gachsaran anticlines, until it was recognized that these did not correspond to the crests of the deeper Asmari structures. Where the formation is exposed, it is seen in huge whale-back anticlines. The Asmari Formation in the Khuzestan Province has a thickness from 320 to 488 m (1,0501,600 ft) of well-indurated wackestone and packstone carrying a rich late Oligocene-early Miocene foraminiferal fauna. Of this thickness, the net reservoir thickness ranges from 10 to 280 m (33-918 ft). The formation is subdivided into a lower section of shelf sediments, with the larger foraminifera forming 50-75% of the grain content, followed above by the middle and upper sections of muddy wackestone, where the percentage of grains drops to 25-50%. The top third of the formation is thin-bedded, but passes to more massive, locally dolomitized units in the lower part. Towards the southwest near the head of the Arabian Gulf, the formation becomes sandier; the Ahwaz Sandstone Member, which represents sands derived from the Arabian Shield interfingering in the limestone in the middle part of the formation, considerably enhances the quality of the Asmari reservoir. In northwestern Lurestan, at the same horizon, evaporites of the Kalhur Member interfinger in the limestone. The conformably overlying Gachsaran

721

Sedimentary Basins and Petroleum Geology of the Middle East evaporites, anhydrites and halite with marl and limestone stringers form an incompetent cap rock (McQuillan, 1985). Despite the low intrinsic porosity of the Asmari Limestone, seldom more than 5%, with permeabilities of a few millidarcies, because production rates can exceed 80,000 bbl/d, an appeal was made to the importance of fractures where porosity reached 25% and permeability exceeded 100 md. However, variations from well to well within the same field that bear no relationship to theoretical concepts of fracture distribution on anticlinal folds require more detailed analysis of large- and small-scale fractures. Analysis showed that whereas the large-scale fractures were related to major structure, the small-scale fractures failed to show the same relationship.McQuillan's (1985) maps show the density of fracture distribution following three major trends: 10~ N-20 ~ W, 20 ~ N-30 ~ E and N 80 ~ E. The density of fractures was greatest where the zones of enhanced fractures intersect the N 20 ~ W trend of the Bibi Hakimeh and Gachsaran fields and this is the location of the high producing wells. The implication is that the small-scale fractures were present in the rocks since early in their diagenetic history and can be related to basement structure. Oil is produced from the B ibi Hakimeh, B inak, Chashmeh Khush, Dehluran and Naft-i-Shah fields and Kaki, Kuh-i-Mand, Mamtain Namak-e-Kangan Nargesi, Paydar, Qualeh Nar, Rudak, Siah Makan and Tangu undeveloped fields and discoveries. Oil and gas are produced from the Agha Jari, Ahwaz, Gachsaran, Haft Kel, Karanj, Kupal, Lab-E-Safid, Lali, Mansuri, Marun, Masjid-iSulaiman, Naft-E-Safid, Par-E-Siah, Paris, Pazanan, Bahrgansar, Hendijam, Kharg, Bushgan, Danan, Gulkhari, Kabud, Karun, Kilhur Karim, Mulla Sani, Shadegan and Susangerd fields. Gas is produced from the Gavarzin Field and in the Bangestan-1 discovery. Mishan Formation (Middle Miocene). This formation consists of fossiliferous limestone, conglomeratic marl and marl deposited in a shallow-marine platform to reefal setting. It is a minor gas reservoir, and gas was produced from the Sarkhum Field.

Arabian Basin Reservoirs Formations The following are the major reservoir formations in the Arabian Gulf Basin of Iran (Fig. 12.53) (Ala, 1982; Beydoun, 1988; Schlumberger, 1976, 1991). Khuff Formation (Upper Permian). It consists of shallow-shelf limestone, dolomitic limestone, dolomite and anhydrite characterized by poor to fair interparticle porosity and secondary porosity through dolomitization and fracturing. The formation is well-developed in the Arabian Gulf and corresponds broadly to the Dalan Formation. It produced gas in the Varavi, Aghar, Bandubast, the "G" structure and West Namuk fields.

Khami Group (Upper Jurassic-Lower Cretaceous). It consists of 1,500 m (4,920 ft) of limestone and

722

dolomite. The limestone is generally tight, with secondary porosity characterized by dolomitization and fracturing. The porosity ranges from 7 to 18%, and the net reservoir thickness ranges from 25 to 150 m (82-492 ft). The group produced oil and gas in the Darius (Darood), Gashu and Suru fields. Gas was produced from the Mamtain, Milatun, Qishn, Rudak, Sarkhum and Sulabedar discoveries. Arab Formation (Upper Jurassic). This formation consists of dolomitic limestone, dolomite and anhydrite, with a gross reservoir thickness of 105 m (344 ft). The formation contains a subordinate oil and gas reservoir in the offshore Iranian fields. The formation correlates with the Upper Surmeh Formation in the Zagros Fold Belt. It produced gas in the "G" structure discovery, oil in the Fereidoon (Foroozan) and Reshadat (Raksh) fields and oil and gas in the Sassan (Salman) and Resalat (Rostam) fields. Fahliyan Formation (Berriasian). It consists of calcarenitic limestone with good interparticle porosity, but tight aphanitic limestone interbeds are present. The reservoir gross thickness is about 45 m (148 ft). The formation correlates with the Fahliyan Formation of the Zagros Fold Belt. It produced oil in the Fereidoon (Foroozan) Field, oil and gas in the Darius (Darood) Field, and gas in the "G" and "F" structure discoveries.

Gadvan

Formation

(Hauterivian-Barremian).

Consisting of about 100 m (328 ft) of limestone, marl and shale formed in a euxinic marine environment, the formation produced oil in the Esfandiar Field. Dariyan Formation (Aptian). The formation consists of thick-bedded limestone of shallow-marine origin, with 150 m (492 m) of reservoir gross thickness. It produced oil in the Alpha and Reshadat (Raksh) fields, and oil and gas in the Resalat (Rostam) Field. Kazhdumi Formation (Albian). It consists of sandstone and shale of a terrestrial to marginal-marine environment. The formation has a gross reservoir thickness of 65200 m (213-650 ft) and a net reservoir thickness of 30 m (98 ft). It produced oil in the Fereidoon (Foroozan), Hendijan and Nowruz fields and oil and gas in the Cyrus (Soroosh) and Bahregansar fields. Mishrif Formation (Cenomanian). It consists of dense to detrital limestone and shale of shallow-marine origin. The porosity is low, mainly interparticle, and the permeability is about 15 md. The formation correlates with the Sarvak Formation of the Zagros Fold Belt. It produced oil and gas in the Resalat (Rostam), Sirri C and Sirfi D fields and oil and gas in the Nosrat (Sirri E) Field. Jahrum Formation (Eocene). This formation consists of medium-bedded to massive limestone and dolomite with a gross reservoir thickness of 345 m (1,132 ft) and a net reservoir thickness of 30 m (98 ft). It produced oil and gas in the Bahregansar Field and gas in the T-1 discovery. Ghar Formation (Lower Miocene). It consists of sand, sandy limestone, clay and anhydrite of terrestrial and lagoonal deposits. The formation is correlated with the upper part of the Asmari Formation. It has a gross reser-

Hydrocarbon Habitat of the Zagros Basin voir thickness of 5-90 m (16-295 ft) and a net reservoir thickness of 45 m (148 ft). The average porosity in sandstone is 30%, and the average permeability is 2500 md. The formation produced oil in the Hendijan Field, oil and gas in the Ardeshir (Abouzar) and Darius (Darood) fields and gas in the Bahregansar Field.

Source Rocks and Oil Geochemistry With the advent of modern geochemical techniques (Young et al., 1977; Ala et al., 1980), it has been possible to show that of the potential source rocks, the EocenePaleocene Pabdeh Formation, the Maastrichtian Gurpi Formation, the Neocomian-Turonian Garau Formation, the Albian Kazhdumi Formation, the Middle Jurassic Sargelu Formation and the Silurian Gahkum Formation The bulk of the oil in the Zagros Foreland Basin in Iran and Iraq was derived from Early Cretaceous source rocks containing marine, oil-prone, algal type II kerogen. Over most of the basin, the Pabdeh and Gurpi formations are immature, and the Silurian may have sourced the non-associated gas in the Permian reservoirs, but it is the maturation of the organic matter in the Kazhdumi Formation during the late Eocene that became the major source, with lateral contributions from the Garau and Sargelu formations that reached the oil window during the late Cretaceous (Ala, 1990). Evidence for this early maturation, attributed to the late Cretaceous deformation and obduction overburden, is found in the presence of bitumen pebbles in Upper Cretaceous-Paleogene clastics (Dunnington, 1958; Kent et al., 1951). The principal reservoirs are contained in carbonate rocks, of which the Asmari Formation carbonates are the most important, for although the formation has poor intrinsic porosity, it is highly fractured as a result of Zagros tectonics and, consequently, is a prolific reservoir. The Bangestan Group, the Ilam and Sarvak formations (Santonian-Coniacian), the Khami Group (Jurassic to Neocomian) and the Deh Ram Group (Permo-Triassic Kangan and Dalan formations) also provide potential reservoirs, especially where they contain clastic tongues. As all the oil accumulations are structurally controlled, the time of folding provides a clue to the earliest charging of the reservoirs (i.e., hydrocarbon generation and migration were contemporaneous with the Zagros Orogeny during the late Tertiary), because prior to the late Tertiary event, there was neither sufficient structural closure nor the presence of the effective migration channels, provided by the fault and fracture communication, between the Cretaceous source rocks and the Asmari reservoir. However, as a number of the producing structures give evidence of pre-Miocene syndepositional fold growth as early as the Cretaceous and Paleogene, there is the additional potential for beds thinning and even wedging out against incipient highs, implying growth-related stratigraphic traps. Initially, it was conjectured that the Zagros Asmari oil

was derived from a variety of sources from the Jurassic upwards; a considerable body of evidence however, both geochemical and field data, has been assembled since then which supports a pre-Tertiary source for the oil. Thus, in the Masjid-i-Sulaiman Field, although Richardson (1924) and Weeks (1952) considered that the source of the oil lay in the Asmari Limestone itself, in contrast the views of Lees (1934) and Dunnington (1958) were that the oil was derived through vertical migration from mainly Lower and Middle Cretaceous sources, a conclusion supported by geochemical and isotopic data (Thode and Monster, 1970). Source rocks appear to have been deposited intermittently throughout the Jurassic-Early Cretaceous-Early Tertiary in Khuzestan and Lurestan, but their extent and pattern of distribution are varied (Said, 1987). The following short descriptions of the potential source rocks are derived largely from Ala et al. (1980), Ala (1982), Dashti (1987) and Bordenave and Burwood (1990 and 1994). Of all the potential source-rock formations, the Kazhdumi Formation is regarded as the best in both quality and quantity. Asmari Formation (Oligocene-Miocene). More recently, Kashfi (1984) has argued quite persuasively that the Asmari Formation still qualifies as a source-rock formation, claiming that although not organically rich, it compares favorably with other source beds proposed. The maximum estimated burial of the Asmari Limestone ranges from 3,772 to 4,086 m (12,380-13,410 ft) and has an estimated thermal gradient of I~ per 30 m (99.5 ft). The formation in the early Pliocene would have been within the oil window. Migration, consequent upon further burial and late Pliocene fracturing, would have resulted. The absence of blackened forams and palynomorphs indicates that the temperature was never high enough to destroy the oil content. However, in the southeastern Zagros, subsidence failed to place the Asmari in the oilproducing zone. Pabdeh Formation. This formation is made up of argillaceous sediments deposited in the Dezful Embayment and Fars Province through the Paleocene and Eocene and until the end of the Oligocene in the Lurestan Province. Anoxic conditions during the Middle to Late Eocene occurred in a SE-NW-trending trough from the northern edge of the Fars Province through the Dezful Embayment and Lurestan into Iraq (Fig. 12.54a). In the most bituminous samples in Lurestan, TOC values are between 3 and 4%, but reach as high as 5.5% in northern Fars to as much as 11.5% in southwestern Lurestan. The kerogen is primarily of algal origin with only limited terrestrial organic matter. Geochemical analysis shows that the rocks still contain appreciable quantities of convertible, light-colored kerogens and, hence, are relatively immature in Khuzestan and Lurestan. Only in the northeastern part of the Dezful Embayment has there been much hydrocarbon generation. Gurpi Formation. The Campanian to Maastrichtian marl generally has low TOCs, except in two areas in northern Fars and the northeastern Dezful Embayment. Despite its greater thickness (100 m, or 330 fl), its source contribu723

Sedimentary Basins and Petroleum Geology of the Middle East

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tion is probably small. Surface samples that have been analyzed appear to be immature. Kazhdumi Formation. The Kazhdumi marl and argillaceous limestone in Iran are laterally equivalent to the Burgan sands on the western side of the Arabian Gulf. During the Albian, anoxic conditions developed in the shallow Dezful Embayment, which was separated by a high from the Garau Depression restricting marine influence and facilitating the development of anoxia. Over the high, the Kazhdumi is organically lean and relatively thin. Up to 300 m (--1,000 ft) of bituminous marl, with TOCs in the 3-6% range, were deposited, and the largest fields in Iran are in the regions of thick, organically rich Kazhdumi marl (Fig.12.54b). Following the Albian, more normalmarine conditions with limestone deposition were reestablished (Bordenave and Burwood, 1990). In Khuzestan and the Fars Province, the limestone was deposited in more oxygenated water, and its organic content is low; the overlying marl, however, has a high organic content with organic material of continental origin. 724

All the available geochemical data point to the Kazhdumi Formation as the dominant source rock for the accumulations found in the main fields (Ala et al., 1980). The best evidence is the similarity between the chromatograms of the saturated alkane components and those of the corresponding fractions in crude oils (Fig. 12.55). In the Fars Province, the Kazhdumi Formation is generally less bituminous, and its source-rock potential is dramatically reduced because of facies transition that occurs close to the boundary between the Fars and Khuzestan provinces. Garau Formation. The facies of the Garau from the Valanginian to the Aptian (even to the Coniacian in some areas) consisted of dark-brown, anoxic, radioactive, laminated, pyritic marl alternating with fine-grained limestone. The TOCs are high in the marl (2-9%) and as much as 12% in the limestone. The Garau facies also extended into northern Fars, where it is referred to the Gadvan Formation, but there it is only locally rich in organic matter. In the absence of regional geochemical sampling, conclusions are applicable only to central Lurestan, where the

Hydrocarbon Habitat of the Zagros Basin

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725

Sedimentary Basins and Petroleum Geology of the Middle East kerogens show thermal alteration and where the organic matter has a dark-brown color so that it must be considered a likely source for the Asmari and Bangestan oils. Sargelu Formation. The anoxic conditions under which the Sargelu shale was deposited developed during the Middle Jurassic in a basin established in the early Jurassic over northeastern Iraq and Lurestan and extending into the Dezful Embayment. In Lurestan, this consists of 100-200 m (330-660 ft) of black Posidonia paper shale with TOCs varying from 1.5 to 4.5%, which is reduced to about half in the northeastern Dezful. Although potentially a good source rock, its value is reduced in Lurestan and northern Dezful, where it is often isolated from good reservoirs by thick evaporites. Paleozoic source rocks. Information on Paleozoic source rocks is sparse, because outcrops are widely separated, well penetration has not been frequent, and only recently have the Paleozoic fields in Saudi Arabia been discovered. The late Ordovician-early Silurian shale, which crops out at Kuh-e-Farghun and Kuh-e-Gahkum and contains graptolites indicating an Early Silurian age, has a relatively high TOC (about 3%) and is, therefore, a potential source rock; however, pyrolysis indicates that it has undergone strong evolution (Said, 1987). The relative abundance of gas supports this view. The late Paleozoic sediments generally have a very low organic content; the thick Permian limestone in the Surmeh and Gahkum sections, despite its color and smell of oil when freshly broken, has a low organic content and is not a potential source rock. Oil Geochemistry Crude oil-source rock extract correlations carried out by Ala et al. (1980) show the following results: the kerogen is a marine, type 2, algal and oil prone; the organic matter in the Pabdeh and Gurpi formations is generally immature and therefore incapable of generating significant quantities of hydrocarbons, and finally, the three oldest formations contain major. Of these latter three, the Kazhdumi was identified as the mature source of hydrocarbons in the Asmari and Bangestan reservoirs. Fig. 12.55 presents a series of chromatograms showing the distribution of n-alkanes in Kazhdumi and Bangestan solvent extracts and the corresponding fraction in a crude oil sample from the Karandj Field in which there is good peak to peak correlation.organics properties. The Kazhdumi source rock, which consists of up to 300 m (984 ft) of black, low energy marl and argillaceous limestone, was deposited in an intrashelf basin. It has a large, type 2, algal content with TOCs reaching 11% and S1 + $2 of up to 40 g HC/kg. The source rock potential indices are in excess of 20 t/m 2. Sulfate reducing bacteria were extremely active as indicated by the sulfur rich crudes derived from it (Fig. 12.56) The Kazhdumi had reached the oil-producing window over most of the Dezful Embayment by late Miocene or Pliocene. Maximum overburden on the Kazhdumi in most of

726

the main structures in SW Iran was reached by the end of the Pliocene. The fracturing of the limestone and marl which resulted from the Zagros folding, facilitated the expulsion of the hydrocarbons from the source rocks and its migration into the Bangestan and Asmari reservoirs. The post-Kazhdumi geological history (Fig. 12.57) has favored not only the high productivity of the source rock but also the retention in reservoirs of about 73.5% of the world's reserves (Bordenave and Burwood, 1994). PETROLEUM SYSTEM EVENTS |

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Fig. 12.57 Albian Kazdhumi Formation : petroleum generation in Iranian oilfields (after Bordenave and Burwood, 1994, reproduced by kind permission of Springer Verlag). The typical crude-oil properties listed in Table 12.13 and illustrated in Fig. 12.58 suggest the existence of two generic families of oil in the Zagros Basin of Iran, for although all the oils are paraffinic, in the main field area in the Dezful Embayment where the oil gravity ranges from 24 to 32 ~ API in the Asmari and Bangestan Group rocks, the vanadium-nickel and sulfur ratios are consistently higher than those found in the northeastern Dezful area, where the API gravity is around 37 ~ (Fig. 12.59). Although the pristane/phytane ratios are less than one, and the carbon isotope cross plots are all indicative of a marine carbonate source, the stable carbon and sulfur isotope profiles clearly differentiate the oils into two compositional types (Fig. 12.59), with some oils of intermediate isotopic composition suggesting mixed provenance. The presence of a hopanoid biomarker (Fig. 12.60) restricted to northeastern Dezful, which suggests the presence of a terrigenous angiosperm plant contribution from a source no older than

Hydrocarbon Habitat of the Zagros Basin Table 12.13. Summary data of Iranian crude oils (extracted from Fallah et al., 1972.)

727

Sedimentary Basins and Petroleum Geology of the Middle East

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N.E. DEZFUL TYPE

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Fig.12.60 Terpane m/z 191 fragmentograms for typical Main Fields (Ahwaz-Asmari) and N.E. Dezful (Par-e-Siah-Asmari) oils. Note the conspicuous 18 (H) oleanane peak in the Par-eSiah oil (after Bordenave and Burwood, 1990).

728

Hydrocarbon Habitat of the Zagros Basin the Late Cretaceous, indicates a younger source. Sourcerock-oil profiling reveals an excellent correlation of this potential younger oil with the Pabdeh Formation (Fig. 12.55a) and a Kazhdumi source (Fig. 12.55b) for the main field hydrocarbons. It was the rapid deposition of the 1,500-2,000 m (4,912-6,550 ft) of the Gachsaran Formation that resulted in the maturation of the Kazhdumi oils and the deposition of the 2,000-2,500 m (6,550-8,188 ft) of the Agha Jari Formation synchronous with the development of the Zagros folds, which provided the depth of burial and temperature increase that permitted the northeastern Dezful oil to reach maturity. Fluid connection between the source rocks and reservoirs was facilitated by fractures developed during the main orogenic phase of Zagros folding (Bordenave and Burwood, 1990).

Seals and Seal Formations From the Permian to the Early Miocene, the Zagros basin had the characteristics of a steadily subsiding shelf with deposition of an almost uninterrupted sequence of carbonates, in part interbedded with, and laterally passing into, intrashelf basinal marl and shale. Subsidence accelerated in the Late Miocene-Pliocene and converted the basin into a foredeep in front of a rising orogen in the Zagros hinterland. This foredeep received the molasse-type evaporitic and clastic deposits of the Mio-Pliocene Fars Group, in which a thick basal unit of salt and anhydrite (Gachsaran Formation) played a paramount role as seal for a major portion of the hydrocarbon reserves of the basin. Subsidence of the foredeep was the greatest in the Dezful Embayment in the northwestern part of the fold belt, where the thickness of the Fars Group attains 5,000 m (16,400 ft), equaling the thickness of the underlying Permian through Lower Miocene carbonate section. The bulk of oil reserves in the Dezful Embayment is contained in the Oligo-Miocene Asmari Limestone and in limestone of the Cretaceous Bangestan Group. The Bangestan and Asmari reservoirs are often in communication with the Gachsaran evaporites serving as the common seal. In the Arabian Gulf Basin, where the Gachsaran thins and the evaporites are gradually replaced by clastic sediments, its importance as a cap rock diminishes rapidly. Evaporites play a predominant role in the hydrocarbon habitat in the Zagros and Arabian basins, where practically all of the known oil reserves and more than 95% of the gas reserves of the country are located. The persistent platform character of the Arabian and Zagros basins throughout their Paleozoic, Mesozoic and Early-Middle Tertiary history offered ideal conditions for the repeated formation of evaporites in lagoonal and supratidal shelf environments. Shale seals formed in intrashelf basins are found mainly in the Cretaceous but are of comparatively minor importance. More than 50% of the huge Iranian gas reserves are contained in Permian carbonates in the Arabian and

Zagros Basins and owe their retention to Triassic evaporite seals, mainly anhydrite. The Late Jurassic Hith anhydrite is the cap rock for major gas reserves in Upper Jurassic carbonates in the Fars Province and for important local oil and gas accumulations in the Dezful Embayment and the Arabian Basin. Towards the northeast, where the Hith anhydrite wedges out, its role as cap rock is taken over by Lower Cretaceous shale, particularly the Albian Kazhdumi shale, which overlies the thick limestone reservoir of the Jurassic-Lower Cretaceous Khami Group. The shale of the Nahr Umr or its equivalent in the Arabian Basin is the equivalent of the Kazhdumi shale of the Zagros and serves as a seal for interbedded sandstone and underlying limestone reservoirs. The seal effectiveness of Upper Cretaceous shale, particularly the Gurpi shale above the Bangestan limestone reservoirs, is limited by fracturing, so that the Cretaceous Bangestan and Oligo-Miocene Asmari reservoirs are in open communication with each other. The descriptions that follow are of the major seal formations over the main producing reservoirs (see also Figs. 12.52 and 12.53). Dashtak Formation (Lower-Middle Triassic). This formation consists of 1,000 m (3,280 ft) of dolomite, anhydrite and shale. It represents a cap rock for other gas reservoirs in Permian carbonates. The anhydrite intercalations in the formation provide a good seal for major gas accumulations in the Dalan (Permian) and Kangan (Lower Triassic) carbonate reservoirs in the coastal belt of the Zagros. The basal Aghab Shale Member adds to the seal efficiency of the unit. Kangan Formation (Lower Triassic). The Kangan Formation consists of 150 m (492 ft) of dolomite, anhydrite and red shale. It is a good seal for the major Permian Khuff limestone in the Kangan Field of the coastal Fars. The formation correlates in part with the Triassic Dashtak Formation. Hith Formation (Tithonian). Consisting of 50-150 m (164-492 ft) of anhydrite and minor dolomite, it is a very efficient seal, mainly for gas accumulations in the Surmeh Formation. Gadvan Formation (Hauterivian). This formation consists of tens of meters of tight limestone interbedded with shale and sand. the shale serves as a partial seal for oil and gas in a Lowermost Cretaceous limestone reservoir in the Darius Field and for oil in the Fereidoon (Foroozan) Field. Kazhdumi Formation (Albian). The formation consists of several tens to a few hundred of meters of shale and some argillaceous limestone.The shale is a fair seal for important oil and gas accumulations in the Darius, Fereidoon (Foroozan), Cyrus (Soroosh), Nowruz, Hendijan and Bahregansar fields of the northeastern Arabian Gulf and for subordinate oil reserves in the southern Arabian Gulf. Gurpi Formation (Upper Cretaceous). It consists of marl and shale with subordinate marly limestone. Fracturing limits the seal efficiency of this formation, allowing partial communication of the underlying Albian-Campa729

Sedimentary Basins and Petroleum Geology of the Middle East nian Bangestan reservoirs with the Oligo-Miocene Asmari reservoir. Gachsaran Formation (Lower Miocene). This formation consists of several hundred meters of salt and anhydrite with minor limestone and shale. It is an excellent evaporite seal for major oil and gas accumulations in Asmari Limestone reservoirs. The evaporites often flow as a result of the late Zagros tectonic movements, but nevertheless remain an important seal, despite the fracturing that affected the more brittle rocks. It fails when removed by late erosion, as evidenced by the leakage along rejuvenated faults as a result of Pliocene or subsequent erosion.

Oil Field Examples Structurally, the majority of the Iranian fields in the Asmari Limestone are sealed by evaporites within the Lower Fars succession. As a result of decollement, structures in the overlying beds may be highly complex. The Asmari Limestone is non-reefal, and as much as 75% may be non-productive. In the northwest, the limestone may consist of as much as 50% sand, sometimes unconsolidated. Except where sandy, the porosity is generally low, and the high productivity is due to fracturing, which accounts for the generally good permeability averaging 10 md (as much as 20 md in some places). Below about 6101,220 m (2,000-4,000 ft), the intense fracturing of the Asmari and pre-Asmari strata results in a complete fluid connection. The Asmari has four fields with more than 10 B.bbl and 12 fields containing more than 500 MM.bbl. The amplitude of the Asmari folds is variable; however, in several places, the crest-to-trough amplitude may be 6,000 m (20,000 ft) over a lateral distance of only 8-16 km (5-10 mi). Closure on the anticlines are on the plunging ends of the structures, which because of the northwest tilt of the area, the critical closure is on the southwestern end of the structures, where the vertical difference between the spill point and the crest may be between 1,220 and 2,140 m (4,000-7,000 ft). The oil is asphaltic, with gravities in the 30-38 ~ API range with the higher gravity values in the more northerly fields. Generally, the oil composition does not vary greatly, presumably due to good fracture connection via the fissure systems. This fracture connection appears to be good between the Asmari Limestone and the rocks of the Bangestan Group, in some areas across the 610-915 m (2,0003,000 ft) of separating shale and marl, as the oils are essentially identical in composition and type (Hull and Warman, 1970). Where the connection does not exist, the two units act as independent reservoirs, with differing gravity values and other properties. There is no evidence for the formation of tar mats or heavy basal segregations (Hull and Warman, 1970). Fields are typically filled to spill point. Sulfur percentages range from about 1% to 3.5%. Associated gas varies non-systematically in composition, and gas caps vary from very large to small. A sum-

730

mary of some of the oil and gas fields is presented in the Appendix. Pazanun Field.The field lies 15 miles southeast of Agha Jari on the same anticlinal axis, but separated from it by a deep saddle. The surface fold is long, narrow and asymmetric. Lower Fars rocks are exposed on the southwest flank with Middle Fars and Upper Fars and Bakhtiari on the northeast. The southwest flank is disrupted by a thrust fault (Fig. 12.61). Drilling of the first well began in 1926 but was suspended in 1930 without reaching the Asmari. The No. 2 well, begun in 1935, became the discovery well the following year when it struck a gas cap with a proven gas column of 600 m (1,968 ft), evidence of a major gas accumulation (British Petroleum Co. 1956). The field went on stream in 1963. The main reservoir, the Asmari Limestone has aa average porosity of 7%. No production history is available, but Beydoun (1988) reported that the field produced 81,000 bbl/d in 1978 and a cumulative production up 1978 of 205.8 MM.bbl. Gas reserves are estimated to be 50 TCF and the ultimately recoverable oil reserves of 1 B.bbl. Kuh-i-Mund Field. The field lies over 100 mi south of Gachsaran and extends for almost 60 mi along the Arabian Gulf coast southeast of Bushirelt is in a gentle, almost symmetrical anticline in Fars rocks and has rleatively few, normal faults, in a range which trends north northwestsouth southeast. There is a sudden change in trend of the anticlinal axis which runs northwest-southeast in the southern two thirds of its length to almost north-south in the northern third. A small "gach-i turush" crust is found at the anticlinal crest. Drilling began in January 1931, and although shows of very heavy oil were found in Eocene rocks, drilling was abandoned in 1932 (British Petroleum Co., 1956). Subsequently, in 1974 major reserves of heavy oil were in lightly fractured zones in the Khami Group (Jurassic-Lower Cretaceous) and deep drilling into the Permian carbonates established the existence of large gas reserves (Beydoun, 1988). Masjid-i-Sulaiman Field. This field is the oldest in Iran, for the first producing well was brought in 1908. The field was located on an anticlinal crest in an area defined by surface gas and oil seepages, but it became apparent during drilling that the subsurface structure did not coincide with the surface crops because of disharmonic folding over the evaporite horizon. The surface outcrop shows a broad anticline in rocks of the Lower Fars with steep surface folds and shallow thrust sheets. Fig. 12.62 is a simplified cross-section that ignores structure above the Asmari Limestone. Initially, it was thought that the reservoir was in sandstone in the Fars series, until drilling proved the oil was in limestone, but it was not until 1919 that the limestone was determined micropaleontologically as the Oligo-Miocene Asmari Limestone. The Asmari reservoir has a length of 32 x 6 km (20 x 3.75 mi) and reaches to within about 150 m (600 ft) of the surface. It has a thickness of about 330 m (1,000 ft). It yields 39.4 o API oil with a 1.13 % sulfur content. Porosity

H y d r o c a r b o n Habitat of the Zagros Basin

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Hydrocarbon Habitat of the Zagros Basin is primarily fracture porosity of the order of 6%. There is a little production from the underlying Eocene marl and marly limestone, which has the same oil-water contact as the Asmari Limestone but with a slightly different gravity. Beydoun (1988) reported that the field is now over 95% depleted but has produced over 1.48 B.bbl since it was discovered. Naft-i-Shah Field. This field, formerly known as the Naft-i-Shahand, continues into Iraq, where it is called the Naft Khaneh Field. It was discovered in 1927 by AIOC, but not developed until 1937. At the surface, it appears as a sinuous, elongated, asymmetrical, faulted anticline (Fig. 12.63) trending NW-SE for an observable distance of 80 km (50 mi) with a width of 8 km (5 mi). At the surface, Upper Fars, Lower and Upper Bakhtiari rocks are exposed, and Lower Fars rocks are exposed at the fold culmination. The southeastern flank of the anticline has dips of up to 75-90 ~ and is associated with a thrust fault that disrupts the anticline parallel to and southwest of the axis, with displacement of the Lower Fars of up to a kilometer. The anticline pitches 3-5 ~ in both directions from the crest maximum. Seepages were recognized in 1903; the surface structure was mapped by 1918; drilling began the following year; and this first well was a discovery well in the Iraq sector. The main reservoir was found in the thick Miocene Kalhur Limestone member of the Asmari Formation underlying the Lower Fars with which it is in free connection. In subsurface, the Kalhur Limestone is a simple asymmetrical anticline, with flank dips of 16-17 ~ on the northeastern flank and about 60 ~ on the southwestern flank. The limestone has a thickness of 66.5 m (215 ft) and lies at a depth of 731 m (2,400 ft). It has ultimately recoverable reserves of about 180 MM.bbl (Beydoun, 1988) with lower gravity (43 ~ API) and sulfur content (0.6%) than most southwestern Iranian fields. Lali Field. The Lali Field is divided into two zones by the deep gorge cut by the Karun R i v e r - the Lali Plain on the right bank and Lali Ambal on the southwestern (left) b a n k - and lies about 40 km (25 mi) northwest of Masjidi-Sulaiman. It underlies two synclines in the Upper Fars/ Bakhtiari rocks (Fig. 12.64). The field is 24 km (15 mi) in length and 6.4 km (4 mi) in breadth; typically, it is asymmetrical, with the steeper, southwestern limb locally overturned. Despite surface indications, several unsuccessful wells were drilled until 1938, when based upon a seismic refraction survey, two wells, Lali 1 and 2, proved oil in the Asmari Limestone although production did not begin until 1948. As early as 1918, the area had been determined to be prospective, aided by gas seepages along the fault separating the two surface anticlines, but difficulties had been experienced in locating the crest of the structure. Deepening one of the wells in 1949-1950 proved a deeper, low porosity, Middle Cretaceous, Sarvak, limestone reservoir. This reservoir is separated from the Asmari by intervening Upper Cretaceous/Eocene marl and marly limestone; however, although the oil is somewhat heavier (35.6 ~ API) and

has a slightly higher sulfur content (1.19%, in contrast to 0.69-0.95%), the oil is very similar to that trapped in the Asmari Limestone. By the end of 1966 the field had produced 57 MM.bbl of oil but by 1972, production had dropped to 900 bbl/d, and the field was shut down in 1973.The ultimately recoverable reserves were estimated at 580 MM.bbl in the Asmari and 156 MM.bbl in the Sarvak Formations. Agha Jari Field. The Agha Jari Field lies on the edge of the Folded Foothills Zone, where the thrust front of the fold rises 180 m (600 ft) out of the coastal plain (Fig. 12.65) some 126 km (80 mi) east of Abadan City. At the surface, it appears as a 30 km (19 mi) asymmetrical, faulted anticline in the Upper and Middle Fars, with lower Fars appearing in the crestal culmination (British Petroleum Co., 1956). In subsurface, the crest of the fold in the Asmari Limestone lies considerably northeast of the thrust outcrop, resulting in delays in discovering the structure from the first well drilled in 1926 until gas was discovered in a well drilled in 1936. Only in the post-World War II period, in 1945, was the axis of the Middle Cretaceous structure defined by the first large-scale refraction study. The field has consistently yielded 1 MM.bbl/d from 40 wells, each averaging 40,000 bbl (80,000 bbl from exceptional wells). The crest of the Asmari structure lies at a depth of 762 m (2,500 ft), and the thickness of the limestone is more than 457 m (1,500 ft); however, the limestone has not been fully penetrated. Although the porosity of the limestone is not high (7.6%), a good lateral connection exists, for equal drops in the datum pressure have been found in two wells 12 km (7.5 mi) apart. Commercial production from the Asmari Limestone began in 1945 of 34.6 ~ API oil with 1.42% sulfur, with individual wells capable of producing 40 M.bbl/d. In 1956, a second producing zone was developed in the Sarvak Limestone (Middle Cretaceous) where oi with a gravity of 34.6 ~ API and a sulfur content of about 1.38% was found at a depth of 2,000 m (6,560 ft). Pressure measurements indicate that a free connection exists with the Asmari Limestone although they are separated by 670 m (2,197 ft) of non-productive strata. Production in 1978 was 634 M.bbl/d, with a cumulative total production of 6.857 B.bbl. The oil-water interface has not yet been penetrated (British Petroleum Co., 1956), so it is not known if a water drive is in operation. Gachsaran Field. In 1956, Gachsaran was the most southerly of the fields, producing from the Asmari Limestone lying near the border of the Fars Province. Its had dimensions of 22.4 by 6.4 km (14 by 4 mi), its structure is shown in Fig. 12.66. It occurs in a region of numerous gas seeps, and burnt rocks are present. The area was surveyed in 1921-1922, but the wells chosen for test drilling in two synclines were either dry or contained oil in non-commercial quantities. A decade later, with the availability of better seismic data, drilling led to discoveries of commercial oil in 1937. The average porosity of the Asmari Limestone is esti-

733

Sedimentary Basins and Petroleum Geology of the Middle East ronment that occasionally was locally restricted. This changed during the early Cretaceous with the evidence of thicker limestone and marl suggesting somewhat deeperwater conditions in the offshore, whereas the shallower environments were restricted to the nearshore area, up until near the end of the Neocomian, when shallow-water conditions were reestablished and persisted for the remainder of the lower Cretaceous up to the Thamama-Wasia Unconformity. During the Aptian, uniform carbonates (Shuaiba equivalents) formed a uniform regional cover, followed by a regional Aptian-Albian unconformity. The Sarvak reservoir formed during the succeeding Middle Cretaceous interval, following the deposition of the Upper Nahr Umr beds. A widespread regional regression after the deposition of the Sarvak Formation, exposed the formation which was partially to totally removed by erosion. The remains were subsequently covered by late Cretaceous Globotruncanid marl and argillaceous limestone. The other principal reservoir, the Oligo-Miocene Asmari Limestone, formed under mainly shallow-marine, epicontinental and near-reef limestone conditions, grading to the brackish-water and lagoonal conditions of the Ghar Formation. The overlying Gachsaran brackish to lagoonal beds give way in turn to the evaporitic clay and marly beds of the Agha Jari Formation, which acts as a seal. Field production from seven wells has declined from an initial production of 3,600 bbl/d in 1961 to 2 M.bbl/d in 1968 (Prosdocimo and Aftabrushad, 1968). In 1979, production averaged 12,334 bbl/d with a total production by mid 1979 of 120.94 MM.bbl. The initial recoverable reserves were estimated to be 180 MM.bbl, but revised to 150 MM.bbl in 1977 (Beydoun, 1988). Haft Kel Field. The field lies about 35 miles southsoutheast of Masjid Sulaiman. The field is in a 25 by5 km asymmetrical anticline in Tertiary, Fars, rocks. The Lower Fars Formation covers a wide expanse of the southwestern flank of the anticline and is believed to form a thrust sheet overlying the northeastern flank of an Upper Fars/Bakhtiari syncline. There is a small, thick oil show, a patch of

mated at 9% of which a large proportion consists of large pores. Fissuring is variable. The limestone has a thickness of about 457 m (1,500 ft). The crude oil has a 32 ~ API and a relatively high sulfur content of 1.6%. By mid-1978, the field had produced 4.45 B.bbl, a little more than half of the total recoverable oil. In 1956 a second reservoir was found in the Sarvak Limestone and the presence of a gas-bearing zone in the Khami Group (Jurassic-Lower Cretaceous) was discovered in the same well. The oil water contact is tilted from 2,255 m (7,400 ft) on the northeastern flank to 2,468 m (8,100 ft) on the southwestern flank. The wells in the northwest zone have a very high production (more than 80,000 bbl/d dry oil) whereas the wells on the southwest flank have a lower production rate of about 40,000 bbl/d (McQuillan, 1985). Gachsaran is one of the supergiant fields of Iran, withultimately recoverable reserves estimated at 8.5 B.bbl of 31.3 ~ API oil with a 1.7 % sulfur content. Bahregansar Field. Bahrgansar was the first offshore discovery in the Arabian Gulf. Drilling followed an offshore seismic survey by Western Geophysical in 1958 and oil was discovered in 1960 by SIRIP (the Agip-AIOC partnership) andthe field went on stream in 1961. The initial discovery of oil in the Asmari (31 ~ API) and in the Sarvak (25 ~ API) formations in a symmetrical anticline was made in well Bahrgansar-1 and subsequent wells proved the Nahr Umr, Yamama and Sulaiy formations to also be oil-bearing. Gas is present in the Middle-Upper Eocene Jahrum limestone and gas with some oil are present in the Ghar Sandstone A brief description was reported by Prosdocimo and Aftabrushad (1968). The field and the subsequent Nowruz discovery lie on a N-NE-S-SW trend. The generalized field structure that illustrates the unconformity trap is shown in the cross section (Fig. 3). The sedimentary column shows a recurrent Jurassic sequence of sedimentary cycles that are predominantly carbonate, with clastics more common in the lower part of the cycle and evaporites at the end of the cycle formed in an overall lagoonal to shallow-marine depositional envi-

NE

SW Many gas seepage 9

.

. 9

.

.

o

9 §

9

9

§

§

~

[.'.~..':.!'i] Upper Fars

i

Basal Lower Fars-1 (Seal)

~

LowerFars-i

~

Lower Fars-ii

~

.

~

'

A

~

J

9

N

9

N

9

. .

.

.

N

~--"7.-1

Lower Fats-Ill

Middle-Lower Cretaceous

A'smari limestone (Reservoir)

Eocene-Oligocene ~

Middle Fars Upper Cretaceous

Fig. 12.67 Fig.12.63 .Schematic stratigraphic- structural cross-section inHaft Kel Field, Iran (modified from British Petroleum Co. 1956).

734

w .

9

§

b,

.

.

.

Hydrocarbon Habitat of the Zagros Basin bitumen impregnated gypsum, and at the southeast pitching end of the structure is an active gas escape (British Petroleum Co., 1956) (Fig. 67). Drilling began in 1926, well HK-1 was abandoned in the Lower Fars Formation, whereas HK-2 penetrated the Asmari limestone and in 1928 became the discovery well. Commercial production began at an initial rate of 5,500 bbl/d in 1929. The structure of the Asmari in the Heft Kel Field is fairly symmetrical although the southwest flank is slightly steeper than the northeast. The reservoir thickness, 274.4 m (900 ft), is fairly uniform. There are two separate domes each a gas cap. The southeastern dome is the shallower, some 365.8 m (1,200 ft) higher that the northeastern dome. The limestone is extensively fissured and has a porosity of 9.5 %. The oil has an API gravity of 37.8 and a 1.22% sulfur content. The Eocene beds are oil-bearing, but the Middle Cretaceous limestone, though showing plentiful traces of oil, are water-bearing. The Eocene and Cretaceous reservoirs at Heft Kel are in fluid connection with the Asmari and are drained by production from the Asmari. The Eocene reservoir however is of little importance because of its exstremely low porosity (British Petroleum Co., 1956). The field is almost depleted for in 1978 it produced only 4,000 bbl/d with the cumulative total production of 1.69 B.bbl (Beydoun, 1988). Bibi l-lakimeh Field. The field is a long surface anticline which was discovered, and went on stream, in 1964. It lies 15 mi (24 km) southwest of, and parallel to, the Gachsaran Field. It has a length of about 54 mi (24 km) and an average width of 3 mi (4.8 km) (Fig. 12.66). The main reservoir, about 487 m (1,600 ft) thick with a large gas cap, is contained in the Asmari Formation. The matrix porosity is in the 4-11% range containing low gravity crude (30 ~ API) with 1.6% sulfur. According to McQuillan (1985) the original gas-oil contatc is at 925 m (3,035 ft), with the oil-water contact is tilted from 1,890 m (6200 ft.) on the northeast flank to 1965 m (6450 ft.) on the southwest flank. The Sarvak limestone is a second reservoir in the Bibi Hakimeh Field and contains 29.9 API oil and 1.6% sulfur. The Asmari and Sarvak are in fluid connection through fractures. The 1966 production from the field was 320,00 bbl/d falling to 220,000 bbl/d of good quality oil and associated gasin 1978. The total production from the field reached 2.5 B.bbl of oil and 8 TCF of gas in 1978 (Beydoun, 1988). Abouzar (Ardeshir) Field. This offshore field is located in a water depth of 36.6 m (120 ft). Ater drilling six mud-line suspesion, delineation wells it was declared commercial in December 1970. The structure is 24 km (15 mi) long by 8 km (5 mi) wide gently dipping (about I ) anticline which has an oil column of 45.7 m (150 ft). It produces a viscous, sour, crude (3.4 cp) of 27 ~ API from unconsolidated sand of the Ghar Formation (Lower Miocene) (Fig. 12.68). The trend of the field is parallel to, is the same age as, the structures in the Asmari oil fields onshore.The sand is the lateral equivalent as the Ahwaz member of the Asmari Formation, which is productive in

y

Lower Fat's

N(

Ghar Sandstone F i ~ Asmari Limestone Gas Oil Water 0

Fig.12.68 Schematic structural cross-section and isopach (in feet) of the Miocene Ghar Sandstone in the Abou Zar (Ardeshir Field), Iran (modified from Creamer et al., 1979) southwest Iran onshore. Porosities of about 25% and permeabilities averaging 2.5 darcies have been recorded. The oil zone is overlain by an initial 18.3 m (60 ft) gas cap over the crest and underlain by an aquifer expected to be active and with a large areal extent (Creamer et al., 1979). Production began in November 1976, and by December 1978 the field was producing at the rate of 200,000 bbl/d. The Ghar Sandstone, found at a subsea depth of 853 m (2,500 ft), underlies most of the Abouzar Field, is sealed by the thick anhydrite shale sequence of the overlying Fars Group. The sandstone is a nearshore to neritic deposit filled to spill point. Naft-Safid Field. Formerly known as the White Oil Springs, the field lies 10 mi northwest of Haft Kel, of which structure it is a lower culmination and from which it is separated by a deep saddle to the southeast (Fig. 12.69). The surface structures is a long narrow asymmetrical anticline in Tertiary Fars rocks. It begins southwest of Haft

735

Sedimentary Basins and Petroleum Geology of the Middle East

SW

NE

Light oil and gas seepage I

k

~

;" .

9

~ 9 9

. ~

Upper Fars

~ . . '

9

~

Lower Fars-Ili

~

l..i .. ! Upper Cretaceous ~

Middle Fars

~

Basal Lower Fars-1 (Seal)

~

~

Middle-LowerCretaceous

Kel in the Lower Fars Formation and is strongly overthrust to the southwest. There is a gas and light oil seepage with Gach-i-turtush developed in the crestal region near the thrust fault. Drilling began in 1913 with two wells which were later abandoned and the field shut down until 1934 when renewed drilling yielded gas in 1935. The fourth well also entered the gas cap, but the fifth entered the oil column in the Asmari limestone and was declared commercial (British Petroleum Co., 1956). The Asmari reservoir is long and narrow with a length of about 17 miles and a two mile width. There are two gas

736

, , . . . ,

".

9

9 ~

Lower Fars-i

9

9

9

~

Eocene-Olig~:ene ~

~._.~.f.o. 0_.~

.0

~

. . ~

9

~'~

.

..

.~

.

.

9

.

.

..

.. ...~

" ".

9

Fig. 12.69 Schematic stratigraphicstructural cross-section of the Naft Safid Field, Iran (modified from British Petroleum Co. 1956).

Asmari limestone (Reservoir) Lower Fars-ii

domes of which the more southwesterly is the main one Although the gas discovery dates to 1934, commercial production of oil did not begin until May 1945 with a production rate of 11,400 bbl/d. The crude oil has an API gravity of 35.4 ~ and a sulfur content of 1.5%. In 1963 a second producing horizon in the Sarvak limestone was tapped with oil gravity of 35.3 ~ API and a sulfur content of 1,45%. In 1978 the output from the field amounted to 22,000 bbl/d yielding a total, production of 38.7 MM.bbl. The ultimate reserves are in the order of 3 B.bbl (Beydoun, 1988).

Chapter 13 THE HYDROCARBON HABITAT OF THE OMAN BASIN

Late Cretaceous, coeval with the emplacement of the Hawasina and Semail Thrust Complex, and in the Early Tertiary during the growth of the Oman Mountains (Glennie et al., 1974; Graham, 1979; Sykes and Abu Risheh, 1989). The Maradi Fault Zone is a wrench-fault lineament with sinistral movement in the Late Cretaceous. The Oman (Sedimentary) Basin, the area of interest in petroleum exploration, has an area of about 170,600 sq km (65,850 sq mi) (Fig. 13.2) and is classified by Klemme (1984) as a downwarp into a small, closed ocean basin (type A4).

INTRODUCTION The Sultanate of Oman lies in southeastern Arabia, with an area of about 300,000 sq km (115,830 sq mi) and an estimated population of around two million. The country is dominated by high mountains running N-S to NESW. The mountains are formed from obducted ophiolites and thrust sheets and associated ocean-floor and sedimentary rocks. Fig. 13.1 shows the main structural elements in Oman. The dominant structural trend is NE-SW, as exemplified by the sub-basins. This is, at least in part, due to the uplift of the eastern Arabian Plate margin during the late Paleozoic, Mesozoic and Tertiary. In northern Oman, the major tectonic phases of deformation took place in the ~',~ ,,

: 9. . ~

N

ARABIAN GULF

i "/"~. ) ~ N ~ G U L F OF OMAN

.A. E:.~.~ G U L F

UNTEDARABEMIRATES/ f i

.:.'. -~o~t~ ..

i

I" ~"'~. ~....~

UNT~ AR/~ ENIt~TF.S

i ,-.... -... , ,.,,../x.\

!

!.io"! ' 9: ' .' '.'. . . . .. "'.i"'.,.- " . .

~

\

.22

~ ::...... 9. .~.. ......,.

SAUDI ARABIA

i

SAUD! ARABIA

//!

~ J/:

~.~-~"

.~"

OMAN

q

. ~ . ,~; !, ,

..~.,./

I"

I " I~_.~"'-....." ', - - - -

I :1 I

'1.1 I,l;ii'Z/I/~ .... ''1.11. / ......

ARABIAN SEA

/.1 i /

. t" " .---------

2JS_

" ~ r19

F !

o j II "'

i

o

~

N~C,~mltlANSEi~EI~I'S

~SkLT

" " "DtRUSTF~dJI.TE~

I

' u

z ooltm I

IOOUi

Fig. 13.2. The Oman (Sedimentary) Basin: A=South Oman Subbasin; B=Central Oman Sub-basin; C=West Oman Sub-basin; D=Oman Foreland (Northern) Sub-basin; E=Huqf Sub-basin; F=Masirah Sub-basin; G=Gulf of Oman Sub-basin; H=Offshore Musandam Sub-basin. The numbers identify some of the fields in the sub-basins: l=Bukha; 2=Natih; 3=Fahud; 4=Safah; 5=Lekhwair; 6=Yibal; 7=A1 Huwaisah; 8=Sahmah; 9=Ghaba North; 10=Saih Wihayda; 1l=Qam Alam; 12=Saih Rawl; 13=Habur; 14=A1 Ghubar; 15=Jalmud; 16=Rima; 17=Nimr; 18=Amal; 19=Marmul; 20=Birba.

__ . . M/dOR RM.~.TZOI~E A- MARADI.

B,a~5

SEA

JP

,,,

Fig. 13.1. Simplified map showing the main structural elements of Oman (compiled from Glennie et al., 1974; Gorin et al., 1982; Murris, 1980). The salt basins emphasize the NE-SW structural trend. 737

Sedimentary Basins and Petroleum Geology of the Middle East As early as 1924-25, geological reconnaissance surveys had been made along the Batinah coast and in the Jebel Akhdar, although detailed mapping of the surface features in the desert west of the Oman Mountains did not begin until 1954, with field observations in the Oman Mountains and Oman Foothills and in the Haushi-Huqf area. The first exploration license was granted to the Iraq Petroleum Company (IPC) in 1924; although the initial oil exploration in Oman by Petroleum Development (Oman), a subsidiary of IPC, dates to 1937, the first well was not spudded until 1955 (Dhofar Cities Service, Marmul-1) to test a mapped structure. The first discovery made in the Oman Basin was the Marmul Field in 1956. The deepest producing well, Lekhwair-70, reached a depth of 5,913 m (17,033 ft), but a dry exploration well, Ghubbali-1, reached nearly the same depth (5,193.6 m, or 17,035 ft). During the 1960s, Petroleum Development Oman (PDO) and Shell discovered commercial oil prospects in the Yibal Field in 1962, the Natih Field in 1963 and the Fahud Field in 1964. Construction began in 1966 on a 175 mi pipeline from Fahud to Mina al Fahal near Muscat, and exports through the terminal began the following year. Subsequently, Sun, Amoco, Quintana, BP, Cluff, Japex and Occidental acquired concessions and/or exploration fights in Oman. Exploration rights for all of southern Oman (Dhofar region) were acquired by the Dhofar Cities Service Company in 1953, representing Cities Service and Richfield Oil companies, and exploration was begun with air-photo, geophysical and stratigraphic studies. Mecom acquired the Dhofar interests of Cities Service in 1962, and Pure Oil in 1963 and Continental Oil a year later signed agreements with Mecom, but returned their interests in 1967 before Mecom relinquished their interest in 1969. Acreage formerly held by PDO in different parts of the onshore has been acquired by various groups of companies, and a number of small discoveries have been made in northern Oman, western central Oman and northern central Oman. There are 64 fields (Fig. 13.3), with a total production of around 500,000 bbl/d, all concentrated in the onshore area. Little attention was given to activity in offshore Oman, and few wells were drilled (Table 13.1). The first offshore concession in the Gulf of Oman was awarded to Wintershall and partners in 1965. They carried out marine seismic surveys and geological, gravity and magnetic studies and drilled two dry holes before relinquishing their interest in 1974. Placid and BHPP drilled two dry wells that did not penetrate rocks older than the Cretaceous on the eastern side of the Musandam Peninsula. A group led by Elf Aquitaine acquired exploration rights in the Arabian Gulf near the Strait of Hormuz in 1974 and made a discovery in 1976. The occurrence of both oil and gas wells and the presence of numerous shows and undrilled structures mark the Strait of Hormuz as a future exploration area. Currently, the only producing field in the region is the Bukha Field, discovered in 1979, which has potential reserves of 40

738

MM.bbl of condensate in the Middle and Lower Cretaceous limestone. By January 1, 1989, a total of 417 exploration and exploratory appraisal wells had been drilled throughout Oman during the 1956-1989 period, 57 of which had been drilled to depths of more than 3,600 m (11,808 ft). Thirtytwo of them were drilled into Paleozoic and Infracambrian strata. Crude oil production in 1994 averaged an estimated 815,182 bbl/d and 448 MM.CF/d of associated gas. Total reserves by the end of 1994 were estimated to be 5.183 B.bbl of crude and 25.32 TCF of gas (World Oil, 1995).

THE OMAN (SEDIMENTARY) BASIN This basin was initiated in the Infracambrian, and the southern part went through a complicated depositional and structural history during the Paleozoic. The Paleozoic sediments subsequently were deformed by folding and faulting, primarily due to salt withdrawal (dissolution) on the southern flank of the South Oman Sub-basin and salt piercement elsewhere prior to the deposition of the Mesozoic beds. From the Upper Permian onwards, it essentially was part of the Arabian Basin. The greater part of the Oman Basin constituted part of the Arabian Shelf. The Oman Mountains and the area of the Gulf of Oman were part of the Oman-Zagros-Taurus Trough, which was affected by Upper Cretaceous and Tertiary orogenic events. The tectono-depositional history of the Oman region is summarized in Table 13.2. The stratigraphy of the Oman (Sedimentary) Basin can be divided into a number of discrete units bounded by major unconformities (Fig. 13.4). The more distinctive of these include a well-defined Late Proterozoic clastic and carbonate/evaporite shelf (Huqf Group) and the CambroOrdovician clastic succession of the Haima Group. These are separated by a relatively long interval from the primarily continental late Paleozoic Haushi and Akhdar groups, which thin northwards and contain a number of intraformational unconformities indicating the contemporaneous uplift and erosion of an area overlapped by the present Oman Mountains. Stratigraphic data suggest that continental rifting and oceanic development began during the Permian and resulted in the formation of the deep-water sediments. The early Mesozoic was characterized by the development of a carbonate platform that included some thin sandstone beds near the base. The carbonate platform continued into the Late Mesozoic, until it was overridden by the tectonic emplacement of the obducted sequence of the Oman Mountains during the latest Mesozoic. The Tertiary sequence consists of shallow-marine shelf carbonates and lagoonal-sabkha evaporites. Thus, the hydrocarbons reside mainly in pre-Mesozoic clastic reservoirs and Mesozoic-Tertiary carbonate reservoirs. The Oman (Sedimentary) Basin comprises eight units (Fig. 13.2): the Huqf Sub-basin, the South Oman Subbasin, the Central Oman Sub-basin, the Oman Foreland

Results of exploration wells drilled in offshore Oman until 1992 (compiled (compiled from from OAPEC, OAPEC, 1985; 1985; Pauker Table 13.1. Results Pau and Hemer, 1991). Well

Date

Company

Gas/

Dry

I'roduiring F o r m a t i o n / A g e

CondctLsalc

A^e/Formu Total D e

Batinah Marine-1

l%8

WinterKliall

«

Upper Cretac

BarinahB-1

1971

Wintcrshall

*

Upper Cretac

M.iMrqh-l ( S M P A - ! )

4 - 1975

Sun

•

7

9 - 1975 Htinjam-l

1975

SNEA ( F I O

*

7

7

4 - 1976 Soulh Masirah-B

12 - 1976

fSMra-[)

1 - 1977

Bukha-I

12 - 1978

SNKA (KIO

5 - 1979

GuirOil

•

Sun

7

Thainama Gp. { L o w e r Crclaccous)

*

Miffhrif h^m. ( M i d d l e Cretaceous)

Lower Cret (Thainama

ClufroilLid Khasab-I

1 - 1977

SNKA (KH)

Lower Cret

6 - 1977 Sawquirah B a y ]

2 - 1979

O C~

O

(Thainama Amoco

7

Amoco

7

5 - 1979 K u n a Muria-1

5 - 1982

O ~=~ G~

9 Ghutibali-1

S - 19K2

SNEA (Elf)

Lower Cretac

1 2 - 19K2 Motmum-l

^-

19K4

Amoco

Infriicamh

4 - 1984 Musandam-1

6 - 19B6

(HuqfG Placid

Upper Creta

1 0 - 1986 BLikhn-2

1 - 1986 4 - 1986

WestBukha-l

Diba-1

International

«

Pclrok'um Co.

1 2 - 1986

Intcrnatiunal

7 - 1987

Pelruleuni Co.

1 2 - 1988

B H P Pclrnleuin

•

Thamama Gp. (L,owcr Cnclaceous)

Lower Creta

M i s h r i f Fm. (Middle Cretaceous)

(Thainama

M i s h r i f Fin. (Middle Cretaceous)

Lower Cret

Thainama Gp. (Lower Cretaceous)

•

(Thainama Teniary

5 - 1989 BukJia-3

7

SNEA ( K I D

«

Thamama Gp. (Lower Crelaccous) Mishrif Fm. (Middle Cretaceous)

Sawquirah Hay .Soulh-1 --d t~

•}

Armvo

•

Lower Cret (Tliarnaina 7

b=.ao

Sedimentary Basins and Petroleum Geology of the Middle East Table 13.2. Summary of the tectono-depositional history of Oman from Permian time to Late Tertiary (Glennie et al, 1974)

740

Hydrocarbon Habitat of the Oman Basin

('

ARAB

qP60

---....__.-....,... / \i. 9 ~.,,.

~61

\

59jI

\

a58

11157

56~

\ \

\.

SAUDI ARABIA /

/

\

/

/

~)

/ b51

Q50

~,52

1149 ~z,8

47t

/

/ / /

/ / /

/

Fig. 13.3. Location map of Oman showing oil and gas fields. All fields are oil-producing, except where indicated O/G (oil and gas) or G (gas). The field names are numbered as follows: l=Diyab; 2=Murrud; 3=Rahab; 4=Thuleilat; 5=Qaharir; 6=Qata; 7=Marmul; 8=Birba; 9=Thamoud; 10=A1 Dhabi; ll=A1Burj; 12=Ihsan; 13=Jameel; 14=Mawhoob; 15=Amal; 16=Amal South; 17=Amin; 18=Karim West; 19=Warad; 20=Zahra; 21=Simsim; 22=Nimr West; 23=Nimr; 24=Runib; 25=Rima; 26=Rasha; 27=Jalmud; 28=Jawdah; 29=Mukhaizna; 30=Zareef; 3 l=Sayyala; 32=Bahja; 33=Suwaihat; 34=Wafra; 35=Zauliyah Northeast; 36=Hasirah; 37=Sahmah; 38=Anzauz; 39=Barik; 40=A1 Ghubar; 41 =Mahjour; 42=Habur; 43=Saih Rawl; 44=Alam; 45=Qam Alam; 46=Saih Nihayda (O/G); 47=Ramlat Rawl; 48=Ghaba North; 49=Qarat A1 Milh; 50=Burhaan South; 51=Burhaan North; 52=Mussalim; 53=A1 Huwaisah; 54=Yibal (O/G); 55=Fahud; 56=Fahud West (G); 57=Natih; 58=Shibkah; 59=Natih West (O/ G); 60=Daleel; 6 l=Dhulaima; 62=Lekhwair; 63=A1 Barakah; 64=Safah.

5/.,

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20KM 10MI

"_.__5 .-..."~LA-'LAH

(North Oman) Sub-basin, the offshore Musandam Subbasin, the Gulf of Oman Sub-basin, the Masirah Sub-basin and the West Oman Sub-basin. Of these, only four (sub-basins A-D) have been explored extensively and are the major producers of oil and gas. The Huqf Sub-basin, controlled by the Huqf Arch, is a belt of uplifted Late Proterozoic and Paleozoic rocks, with beds tilted to the northwest and southeast on either side of the arch. The South and Central Oman sub-basins include

ARABIANSEA zoo,,

the area of Infracambrian salt deposits of southern and central Oman and have a northeast-southwest trend. In this basin, the major traps with accumulations of heavy oil are related to salt dissolution on the southern flank of the basin. The Oman Foreland (North Oman) Sub-basin extends from central Oman, where it is underlain by evaporites that sometimes reach the surface in salt domes, to the Musandam Peninsula in the northeast, and it parallels the trend of the Oman Mountains.

741

Sedimentary Basins and Petroleum Geology of the Middle East

FORMATION

CLASTICS/ EVAPORATES

I LITHOLOGY

I

... . . . ~ ' ....

Z:r

UMMER

FK~A NATIH (]M~SHRIF/ M A ~

~ ff'

SOURCEROCK

e

o~

laJARAIB LEKHWP4R

"RJ'dUP~lbrrN. DHRUI~ CONDENSATE

CARBONATE RESE.RVOIR CLAs'rlc RESERVOIR

N O N - ~ N

KHUFF UNCON~

GHARIF AL~I~

-

CONtORNABI.E

C O ~

Alia SHURAN KHUFAI ABU MAHRA

Fig. 13.4. Generalized stratigraphy and hydrocarbon occurrences in Oman (compiled and modified from Grantham et al., 1988; Hughes-Clarke, 1988, reproduced by kind permission from Journal Petroleum Geology).

742

Hydrocarbon Habitat of the Oman Basin The Gulf of Oman Sub-basin is bounded by the Makran to the north and the Oman Mountains to the southwest. It is the convergent region at the northeastern margin of the Arabian Plate, with the crust below the gulf consisting of a 6 km thick oceanic crust overlain by 7 km of normally compacted sediments (White and Louden, 1982). The offshore Musandam Sub-basin surrounds the Musandam Peninsula and extends to the entrance of the Arabian Gulf, Strait of Hormuz and the northern Gulf of Oman. The paleo-structural and paleo-sedimentational reconstruction of both sub-basins has been described by Ricateau and Riche (1980) and Ross et al. (1986) and is shown in Fig. 13.5. The eastern edge of the Arabian platform in Oman was uplifted at the end of the Middle Cretaceous, resulting in halokinetic activity, with the emplacement of the Hawasina oceanic sediments and the Semail (Ophiolite) Nappe over the edge of the Arabian plate during the late Cretaceous. The imbrication of the substrate by thrusts and reversed faults persisted into the Paleocene with the continued growth of the Oman Mountains. The Gulf of Oman is regarded as a trough formed during the Upper Cretaceous with an argillaceous fill. Geophysical data indicate that the base of the sequence was formed of coast-parallel ridges that resulted from Upper Cretaceous or older clay diapirism. The sedimentary fill between the ridges consisted of Paleocene to Lower Miocene turbiditic, deltaic and coarse conglomeratic beds overlain by an Upper Pliocene to Quaternary deltaic complex of rhythmic alternations of silt, shale or sandy shale and conglomerates. The sediments were derived from the erosion of the uplifted Oman Mountains. The Masirah Sub-basin is a graben structure believed

to be part of a Mesozoic rift system associated with the Neo-Tethyan southern margin. The western margin of the graben is a major normal fault. The Huqf Uplift to the west and the Masirah Fault Zone at the eastern margin of the sub-basin have controlled sedimentation that reaches a thickness of 4 km, accumulated possibly from as early as the Cambrian (Fig. 13.6). The occurrence of several phases of sedimentation and tectonic activity, however, has resulted in complex stratigraphic relationships. The general structural style is illustrated in Fig. 13.7A. Wells drilled in the Masirah Graben indicate that either Cambrian-Triassic rocks were not deposited or subsequently were removed by erosion (Fig. 13.7B). One of the thickest Infracambrian Huqf Group sequences in Oman was found in Sun well Masirah-1 (SMPA-1) drilled in the southern Masirah Graben and may indicate the presence of another Infracambrian basin east of the Huqf Uplift or of a general eastward thickening (Beauchamp et al., 1995). Sourcerock studies of samples from these wells by Beauchamp et al. (1995) gave TOC values of the order of 0.67%, indicating the absence of a true source rock. The hydrogen indices show that no oil potential remains because maturity levels were high. A few wells penetrate reservoir-quality Cretaceous sedimentary rocks in the southern part of the graben. The absence of X compounds in oil from the Infracambrian suggests that the oil was derived from a Mesozoic rather than an Infracambrian source (Beauchamp et al., 1995). Despite the absence of direct well ties and seismic data on sediments below the allochthonous sheets, further exploration of the graben seems worthwhile. The Huqf Sub-basin (known also as the Huqf Arch) is a major NE-SW-trending structural element along the southeastern edge of the Arabian Peninsula (Fig. 13.8). Its

g

i

Fig. 13.5. Simplified tectonic map of the Gulf of Oman and adjacent areas (modified from Ross et al., 1986).

ARABIAN GULF

/UNITED j~ SAUDi "~.")",/L. x.

<;~

o

NEOGENE FOLD BELT

~

FOREJ.AND FOLD BELT

1777-1] EXPOSED N ~ N E

FSc~iAuroctm~t~us ~ ~ U P P E R CRET.DIAI~IC SHALES AND

PALEOCENE-Is ~"~BURIED N ~ N E

~OPHIOLITE

~

I N - - A N

~a.~~us

SALT SEDIMENTS

oea,osrrs

ITI']Tn 7~u,,J~ CRUSH ZONE MIOCENETURB[XTE~. . . . . . . . . . . ,SEDIMENTS ~ uPPER~ AND YOUNGER SEDIMENTS

9 9THRUSTFAULT

743

Sedimentary Basins and Petroleum Geology of the Middle East

PERIODI E P O C H

GROUF HUQF UPLIFT

MASIRAHGRABEN

GROUP PERIOD!

OUGOCENE

~

-

EOCENE

I-, -

--~-MAASTRICH-~ TIAN

-_~ ~

i~

~ ---- ~ '

_.._.

"

.

~

~

,re.mAre I

'

~

:

i

~

~

.

- ~ .

Fig. 13.6 (left). Stratigraphy of the Masirah Graben and Huqf Uplift of Oman (after Beauchamp et al., 1995, reproduced by kind permission of AAPG).

~

.

~ Z =, 7 . , "I - 7,.,l~ ' + -. 4~ ~~ ~- --, , ~ ~ " ' ~ +z++,

AVrlAN-

~,~

<

o~ H.+,UrmvL+.~ "

m

"T'--'-~I;~'..'.""',',w~.-a ~ ~ ~ ~ '

PE-RM~ /IdITINSKI~N" CARBON , M - -----I USHI ~

'

' I I ~ ~ J

~

!I~ROUS ~..SI'PI-I~L!.~i~ _ _ 3RDO-

<

--------' ~

......

~s_,+,,, lr_o+_+,,,o'r,,.,, +__+__ .............. " --

. . . . . . . . . . . . . .

+<.

.~A,++-,~-SSIC

~

,ii........."

,

+'

++ +

i+

+8

ii

,MUSCAT

60

B

C

m

A

17 K M

31

.~EA FLOOR ,.

.

+-=- : : :: :_ t._:--_--'E

OMAN

EA R S

~

~

:" - -- --:---:-

~

~

'

~

KM

..... ---" -=: -- --: :_

-

-

:

"

-

DAHMAM

<

RUS

i:------'---~ 7---"---.-'i ;'------i

7~ r.= :I

_---_~

,,,,,

_~ ~ _ ! _ . I L ~ j . . ,

~ F - ' -'_--.':ARABIAN

~''--

:

L__ i-~---~ t

SEA

TD 3056 m 0

IOOKM

TO3450m ~;~

O M A N MOONTAINS

[~ I N D I A N / PA L I E O T $ ~ SEDIbIF_N~

~

I~EC~MBRIAN BASEMENT

Fig. 13.7. Left=principal tectonic features of eastern Oman, showing the location of the three wells drilled in the Masirah Graben; Right=stratigraphic logs of wells A, B and C (after Beauchamp et al., 1995, reproduced by kind permission of AAPG).

744

Hydrocarbon Habitat of the Oman Basin '."::

:~:.

SAiWAN- 1

i.;...'. .......

;::i

.~...

~o : " , ."

.':.'.~.~ .':i". "i': ~,

" , ", ". . . "i'

,.:...,. .,

:-i" .: .:' ......:

...":'.::i~i

/J

INDIAN OCEAN

A

,oo:

MASIRAH-1

.....

zo o o ~ l l l ~ 4 r ~ x x

-

'

'

" "

-

x . x x t xx, ....

B

-

"

~

(

~

~

-

-

I~l"

CENOZOIC [ ] BUAH FORMATION ~ FAULT 9BASALTINTRUSION SEDIMENTS MESOZOIC ISHURAM ~ ANTICLINAL AXIS H A HUQF AXIS SEDIMENTS ~ FORMATION SN F SAIWAN-NAFUN ~CARBONIFEROUS -~'ff~ FAULT TRIASSIC SEDIMENTS t'~'~KHUFAI FORMATION . - ~ SYNCLINAL AXIS []CAMBRIAN-EARLY I'~ABU MAHARA [ ' ~ OPHIOLITE ORDOVIClAN " = FORMATION d~" DIP SEDIMENTS k'~ BASEMENT

a

Fig. 13.8. Simplified geological map of the Huqf Sub-basin of Oman (after Gorin et al., 1982, reproduced by kind permission of AAPG). eastern flank is faulted down to the Masirah Sub-basin, whereas the western flank dips gently down towards the Ghaba Salt Basin, where the Buah carbonates are at a depth of 6.5 km. The Huqf Axis is dominated by basement block faulting, and most of the folding is a consequence of block movement. Throughout its history, the area has remained a high and has never been subjected to major orogenic movement. The rapid thickening of the Abu Mahara Formation east of the Huqf Axis suggests that these block movements may have begun during the late Precambrian; however, during the deposition of the younger Huqf Group sediments, movements appear to have been oscillatory, and no angular unconformities have been found. In addition, following the deposition of the Huqf Group, a phase of tectonic activity occurred during the early Paleozoic, and Hercynian movements during the Late Carboniferous affected the entire Middle East. Mesozoic and Tertiary activity that affects the Cretaceous sediments seems to have been concentrated in the region of the Saiwan-Nafun Fault (Fig. 13.8), a continuation of the

Maradi Fault Zone of central Oman (Gorin et al., 1982). Evaporites of the Huqf Group are absent over the Huqf Axis, but are thick over a large part of central and southern Oman. The evaporites, which locally pierce the surface, are largely involved in most of the oil fields. The Huqf Group rocks over the axis penetrated by the deeper wells are not productive, and production is restricted to the shallower wells where the Huqf Group sediments are not deeply buried (Saiwan- 1, Masirah- 1 and Dharir- 1). Along the southeastern flank of the South Oman Sub-basin, well Ghadir Manquil-1 was found to be dry. The South and Central Oman sub-basins make up most of interior Oman south of the Oman Mountains and extend south into the Dhofar Province. It is made up of two b a s i n s - the Ghaba and South Oman salt basins - which contain major oil discoveries in Oman. The structural development of these sub-basins is characterized mainly by mild deformation within the basin, but major tectonic activity at the margins has shaped and reshaped the basin margin (Fig. 13.9) and has influenced the sedimentation patterns during different geological periods (Visser, 1991). The succession consists of a Late Proterozoic-early Cambrian platform clastic-carbonate-evaporite beds (Huqf Group) succeeded by Cambro-Ordovician clastic beds (Haima Group). A long period marked by erosion and/or non-deposition was followed by the terrestrial clastic and associated carbonate-platform sequence of the late Carboniferous-Permian. Further erosion and/or nondeposition during the Triassic and early Jurassic preceded a carbonate-platform sequence that persisted from the early Jurassic into the Tertiary. The hydrocarbon traps formed are all related to salt removal, large turtle-back anticlines resulting from the inversion of former rim synclines, truncation traps rimming eroded turtle-back anticlines, small anticlines draped over residual masses of dolomite and shale, and porous and fractured dolomites within such residual masses after salt removal (A1 Marjeby and Nash, 1986). The dominant structural trend in the South and Central Oman sub-basins is from southwest to northeast, which partly is a product of the uplift of the eastern Arabian Plate margin in the Late Paleozoic, Mesozoic and Tertiary and of the subsidence of the Rub al Khali Sub-basin, which began during the Ordovician after rapid subsidence had allowed the accumulation of at least 5,000 m (1,640 ft) of Cambro-Ordovician sediments. Significant oil generation had already occurred before the end of the deposition of Haima Group sediments. The thickness of post-Carboniferous sedimentary beds may not exceed the thickness of sediments eroded before the basal Haima unconformity; consequently, there was no later expulsion of hydrocarbons.

745

Sedimentary Basins and Petroleum Geology of the Middle East

I

NORTH

OMAN

r.J' ~

GULF

N

l

'~r \

~.

~

1

"!I" 1

NW

SE/

UN~rED^~B

_

"'-

~,~.

~L.-

~"~

'

1

!~ ^ ~

I

,.~

~'-=:r:i:=:~'.=.-*:_::T'.~*.::~e2::-'.~:.':

9

"':'"

. 9

".

.

"

"

9 ."

~L~....~e-.+~ ""':" ~' ' ~ o

I

"

9 9" " 7 . " * ?. . ",;,,... , -~- .

12.

"" ~ ' . ' - : - ' - - ' " 9. . . .

9

9

KM

9

9

9

3:" .'-"

"." " . ".'. "" . " " -,,.~. 9 . 9~ -9.~ . . . .- : . . . . " - "9'.I . " . -.. ."--".-.

9 9

9

9

9

9

9

9

9

9

#

,'~"

"

"--.I~-"

9 . 9

9

~,~m,~.~[

! 9

9

~

F

~l/~ TE

NW

SE

RUB

,,eLl.. K H . , M J BASIN

G l f J [ X J N ~ HIGH

SOUTH SALT

~ BASIN

EASTERN

..

FLANK

TER'rL, MtY

BASIN

KURIA MURIA ISLANDS

..

O"TJJJiJ,~/-------

2

.

9

s-.

9

•

ABU NNtRA FORMATION

~

ARA CARIg3~TES

~ARA

SALI'S

9 9 .

" o " "'-:/

. .:'~.

4-

~

~

~.'~.. 3..'." "":

/

[

x.

~,,

/~//"

r

. .o

.~.

SOUTH OMAH

Trr

r

. .

:'7-a~,~moup

9

9 ~

9

.--O'... "".

§

' -;-'; 9

~ 4.

9

~.

9

KHUFF FORMATION

I s~x~c~up

9

~ 7-

HN.ISH GROUP

~

GROUP

9

, ,

. - . , ; . - . * . ; : ~ . - ~ ; . . : . . . -

.-

-

" 9

9

9

9 ,i. 9

9

-.

9 9

9

9

9

9

9

A

4.

9

9

9

9

9

4,

9

9

9

-..:

:

. ,i,

9

9

9 9

9

,,

I

. . . . . . 9

9 .

9 9

[~,~maAGRot~

l 9

9

9

~

R4ULT

Fig. 13.9. Geological cross-sections in northern and southern Oman. The tectonic events that affected the basin gently deformed the sediments, creating traps. The location of the sections appears on the inset map: A=Fahud Salt Basin; B-Ghaba Salt Basin; C=South Oman Salt Basin (modified from Visser, 1991).

Source Rocks, Oil Geochemistry and Hydrocarbon Generation Source Rocks Investigation of the potential oil and source rocks in Oman shows that there are several source-rock horizons ranging from late Proterozoic (Infracambrian) to mid-Cenozoic (Fig. 13.4), with the principal oil reserves stored in reservoirs Permian to Cretaceous in age. Except in southern Oman, the oils generally are low-sulfur, low-wax, light oils derived from structureless, marine, sapropelic organic matter with no contribution from land plants (Grantham et al., 1990). The main source-rock horizons identified in Oman are shown in Fig. 13.4. Their main geochemical characteristics are summarized in Table 13.3, (see also Grantham et al., 1990). The three principal types are linked to late Proterozoic (Huqf), Silurian (Safiq) and Cretaceous (Natih) source rocks; the fourth probably is derived from an Upper Jurassic (Diyab) source. The characteristics of the fifth group ("Q" crude oil) are distinctive and most closely related to the Huqf oils, so although a Proterozoic age seems the most probable, the actual source-rock horizon has not yet been identified. Geochemical analysis suggests that the Proterozoic

746

oils are derived from salt-related, kerogenous rocks and, as such, show similarities with oils in Siberian and Australian Proterozoic rocks. The high 813C values recorded in the Proterozoic Khufai carbonate rocks suggest that high organic productivity was associated with widespread anoxia and/or rapid burial. It is a pattern that can be traced 800 km across Oman and matches the pattern found in the Oman Mountains. The low ;513C values found associated with the early Silurian Safiq source rocks reflect either a deglacial water composition or a change to a well-ventilated ocean. The results suggest the continuity of the source rocks of Oman with similar rocks in the Rub al Khali Sub-basin of Saudi Arabia. The only potential source rocks in the pre-Permian belong to the Infracambrian Huqf Group. Although generally deeply buried, they are exposed along the HaushiHuqf Axis, where the Huqf Group is seen to consist of an alternating sequence of siliciclastics and carbonates. The two carbonate units, the Khufai and Buah formations, are similar, consisting of low-energy, bituminous, sub-tidal beds overlain by prograding shoal deposits and capped by peri-tidal or lagoonal, evaporitic sediments. Diagenetic studies indicate that the residual hydrocarbons postdate early-phase dolomitization but pre-date subsequent silica replacement. The Ara Formation, with its evaporites, is

I

Hydrocarbon Habitat of the Oman Basin

Table 13.3. Main geochemical characteristics of Oman crude oils (after Grantham et al., 1988, 1990).

assumed to contain significant source-rock potential in the form of stromatolitic, algal mats in dark, laminated, calcareous shale or dolomites with a high to very high clay content. The best source-rock intervals (TOC>2%) contain layered or structureless (type II) organic matter probably of cyanobacterial origin. The deeper-water parts of the Ara Formation periodically were anoxic, and the beds contain alternating kerogen-rich and kerogen-poor carbonates and shale interspersed with evaporites.

Oil Geochemistry Infracambrian Huqf Oil Geochemistry Edgell (1991) has emphasized the importance of Proterozoic oil in the Arabian Gulf area and its potential contribution to the oil resources in the Middle East as a result of migration into younger strata. The Huqf oils generally are heavy and sulfur-rich (Table 13.4). Characterized by a low pristane/phytane ratio (generally less than 1), there are a predominance of C27 steranes and a relatively high concentration of tricyclic terpanes (Grantham et al., 1990). Geochemical analysis shows an absence or relatively low content of rearranged steranes and highly negative carbonisotope values. These carbon isotope values are among the most negative crude oil values known. A further characteristic of the Huqf and Q oils is the presence of branched hydrocarbons, isomers of methyl and dimethyl alkanes, the so-called "X" compounds for which no source has been found to date. They also have been found in Siberian Proterozoic oils. The projected source is at a lower, and presumably more restricted, Huqf level. The crude oils correlate very well with extracts of the Huqf source rock

(Table 13.5). These oils are found in fields such as Bahja, Fayyadh, Sayynia and Zareef (Edgell, 1991).

Infracambrian "Q" Crude Oil Geochemistry The pristane/phytane ratio, in contrast to the Huqf oils, is greater than 1, and there is a preponderance of C27 steranes and a relatively high concentration of tricyclic terpanes (Grantham et al., 1990). The sterane concentrations are roughly equivalent to those found in the Huqf oils. The level of sterpane rearrangement is moderate, and the carbon isotope value is around 30.5 0/00 (Table 13.4). The Xbranched hydrocarbons are found only in these Q oils and in the Huqf oil, and no source rock has been identified in Oman. The projected source is at a lower and presumably more restricted Huqf level not yet penetrated.

Silurian Safiq Oil Geochemistry In the upper Paleozoic clastics, a distinctive oil type is found with geochemical characteristics (Tables 13.4 and 13.5) suggesting a derivation from the basal shale of the Safiq Formation. The sulfur content is low, and API gravity values are moderate. The pristane/phytane ratio (1.6 to 1.7) is higher than in the Proterozoic oils, and there is a relatively high proportion of rearranged steranes (30 to 39%). The naphthenic, low sulfur content of the oil is indicative of a marine setting with a restricted, continental, clastic influx in keeping with the global, transgressive cycles of the late Ordovician and early Silurian of the Afro-Arabian Craton.

747

-..! 4~ oo

Table 13.4. Geochemical data: Crude oils derived from various source rocks (compiled from Grantham et al., 1988, reproduced by kind permission from Journnal of Petroleum Geology).

Sourer Rocks

Crude Oil

Reservoir

API Gravity

i

c»

)i!ilrilHilion

CM

VRIi

« o

'•2

Kuqr

t^is Disiribution

IsDprenotds

Ciross C o m p o s i t i o n

Z

.SatK

Arom

Ik't

£c pii

SI 17

18

1R

2R

3K

3R

4R

5R

AimlS-l

Ghiu^r

24.4

47

2.3

33

37

12

0,6

03

07

61

30

9

20

48

32

073

Nkiham-l

Al Khlam

100

0.0

2.6

22

32

11

0.6

06

1,3

48

39

13

21

46

33

069

H4

7.0

1,3

38

26

5

0.9

0,3

0,5

62

30

6

26

52

22

085

r.,o ~..to

Rirnp-7

-Q-

Runib-I

NaUh

25,0

0.3

1.4

42

50

R

0.8

1.2

1.7

53

36

11

27

46

27

0,80

Sayyala-1

Cjharif

.mi

17.9

0.3

76

5

19

1.2

07

0,7

4fj

37

16

40

36

24

1.04

Bahja-1

48.7

14.3

0,1

49

7

2

I.I

0,5

05

4X

43

9

37

46

17

1.00

Biilija-]

42 .,S

9.7

0.2

63

10

3

1.0

0.5

0.6

56

35

9

45

37

18

1,04

ZoreeM

4f,.y

1,3,S

0.2

50

K

3

I.I

0.8

O.S

53

40

7

41

3S

2]

1,00

t~

Fayyadh- ]

27.?*

0.9*

04

70

17

4

.*

.•

_•

39

46

15

3S

44

19

0,92

39.6

9

0.1

65

32

3

1.7

0.5

0,4

56

32

12

35

37

28

0.96

r o

Suhmah-1

36.5

6

0.4

64

33

3

1.7

0,6

04

56

3

13

32

38

30

0,92

Shamah- L

364

6

0.3

56

41

1

1,7

0.5

0.4

60

29

II

35

36

29

0,96

34.7

10.3

06

55

37

S

I.I

0.:!

a3

48

37

15

37

40

23

1.00

35.8

6,7

0,7

51

42

7

1,1

03

a3

51

35

14

30

44

26

0,92

29,3

5.7

1.9

-

0.8

0.3

a4

50

33

17

20

54

27

0,85

30.1

7 7

2.3

-

08

0.3

a4

39

43

18

26

46

28

0,92

26,4

9.0

l.."j

33

27

K

1.0

0,4

0.4

52

36

12

31

40

29

1.00

16.2'

16.0

1,7

23

27

14

1.0

0.5

0,6

52

34

14

25

42

33

092

13.2

1.7

1.0

33

48

19

1.0

0.4

0,4

59

31

10

24

48

28

092

go ~..l~

go

Safiq

Diyab

Sahmah-l

|j^1chwair-8

Charif

Shuaiba

[^fchwaJr-3.S [^khwair-27

Tuwaiq Mountain

lMiulaima-1 Natih

Shibkah-I

Natih

Suqun-1 NaUh W-57

% Lt. Frac.=% light fraction boiling below 120~ % S=% organic sulphurSats=% saturates; Arom=% aromatics; Het=% heterocompounds Isoprenoids: Pr=pristane; Ph=phytane; 17=nC 17; 18=nC 18 C15 and C3o Distribution=Cl5 and C30 ring distributions (Lijmbach et al., 1983): 1R=l-ring saturates; 2R=2-ring saturates; 3R=3-ring saturates; 4R=4-ring saturates; 5R=5-ring saturates C29 VRE=vitrinite reflectance equivalent based on the C29 ring distributions (Lijmbach et al., 1983) Sterane Type=stereocherrdcalcomposition of C27-C29 steranes: Iso=5o~ (H), 14~(H), 1713(H)steranes; Nor=-5~ (H), 14~(H), 17t~(H) steranes; Rear=-1313(H), 17o~(H)rearranged or "dia" steranes *parameters affected by bacterial degradation.

O 0"Q ,.< O

~.,~~

go

Table 13.5. Geochemical data: Precambrian Huqf, Silurian Safiq and Mid-Cretaceous Natih source rocks (comp reproduced by kind permission of Journal of Petroleum Geology).

Source Rocks

Sourcirock Extracts

RmiToIr

ft

%

Extract

Organic Curbon

GrtKS Composition

Situ

Huqf

Safiq

NiUih

Arom

Net

C j j Distribution

IsoprtiMtds

a.

Cj^ Distribution

^2, VRE

IR

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3R

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5R

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61

33

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57

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47

28

20

32

47

0.71

Hasiiah-:!

009

1.0

29

39

30

0.9

0.9

OS

51

18

11

16

48

36

0.84

U Sjillq

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0.5

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29

51

0.9

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29

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11

12

37

1.08

Jebcl Qusaybah CH-.l

Nauh " l i '

0.3

1,9

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06

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% Extract=% ethyl acetate extract of source rocks; Sats=% saturates; Arom=% aromaucs; Het=% heterocompounds Isoprenoids: Pr=pristane; Ph=phytane; 17=nCi7; ISsnCjg C;5 and Cjg Distribution=Cij and C30 ring distributions (Lijmbach et al., 1983): lR=I-ring saturates; 2R=2-ring saturates; 3R=3-ring saturates; 4R=4-ring saturates; 5R=5-ring satu C29 V/f£=vitrinite reflectance equivalent based on the C29 ring distributions (Lijmbach et al., 1983) Sterane r>pe=stereochemical composition of C27-C29 steranes: Iso=5a (H), 14P(H), 17P(H) steranes; Nor=5a (H), 14a(H), 17a(H) steranes; Rear=l 3p(H), 17a(H) rearranged or "d

Sedimentary Basins and Petroleum Geology of the Middle East Upper Jurassic Diyab Oil Geochemistry

In northwestern Oman, in the Upper Jurassic Lekhwair and Dhulaima fields, oil is produced from BarremianAptian (Shuaiba-Kharaib) and Tuwaiq Mountain reservoirs (Table 13.3). Geochemically, the oil is identical to oil found in the Upper Jurassic Arab Formation and Lower Cretaceous Thamama Group reservoirs of the U.A.E. and Qatar. No good source rock has been identified in Oman, but by analogy with the U.A.E. and Qatar, the source is considered to lie within the Hanifa/ Diyab formations, with the oil migrating from sources outside Oman.

i

MAIN PHASE !

CUMULATIVEG s

OF TRAP FORMATION

CRET~

o

zo I

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% 60 I

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Cretaceous Natih Oil Geochemistry

-300

The Natih Formation hosts oil in many of the northern oil fields and also contains two organic-rich intervals that are potential source rocks. The sterane distribution is similar to a worldwide range of steranes derived from Cretaceous carbonates (see tables 13.4 and 13.5)

/!o.

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Hydrocarbon Generation and Migration Visser (1991) modeled the hydrocarbon-generation history of the Oman Basin and presented typical temperature, vitrinite reflectance equivalent (VRE) curves and generation curves for each of the sub-basins (Figs. 13.10 and 13.11). He demonstrated that on the eastern flank of the Ghaba and South Oman salt basins, the Middle Huqf (Khufai-Shuram-Buah) source became mature and generated hydrocarbons as early as the late Ordovician, ceased generating during the early Devonian, recommenced during the late Permian-early Triassic and became postmature for oil by the end of the Jurassic. The upper Huqf (Ara) source has an even more complex generation history, entering the gas window by the end of the Cretaceous. In contrast, in the axial parts of the basin and on the eastern flank of south Oman, the calculated VRE increased rapidly until the end of the Haima and thereafter remained at about the same level, becoming post-mature for oil and gas in the first location and at present only just reaching maturity for oil in the second area. As most of the oil reserves are found in Haima and Haushi reservoirs sealed by Haushi, Akhdar or Wasia shale, the hydrocarbons were generated before the traps were formed; consequently, some form of intermediate storage and remigration has to be invoked. In the West Oman Sub-basin, such as in the Sahmah and nearby fields, however, the oil in the Gharif Formation reservoirs is a mixture of Huqf and Q oils in virtually any proportion, but potential contributions from a Safiq (Silurian) source are difficult to identify because of low biomarker concentrations (Fig. 13.12). Differences in the proportion of Q oil in the lower reservoirs and Huqf oil in the higher reservoirs in the northern fields have been interpreted as due to the more restricted distribution of Q source rocks and sub-recent faulting that has allowed the migration of the Huqf oils (Fig. 13.13). The potential for the successful exploration for Gharif reservoirs in the West 750

AriaS,~T H Y R ~ ~

~-~

r ..~~~ON

~

50O UNITED ALIAS..!./ ...EbI~IAI~.S . :: : .:-:.

RUBAL KHAUFLANK

SOtrlH OMAN AND GklM~

SALTBAS~

Arabian Sea

"0 ,| '

Fig. 13.10. Average cumulative generation curves for the middle Huqf (lines A, B and C) and upper Huqf (lines D, E and F) source rocks (upper figure). The areas of hydrocarbon generation in Oman are shown in the lower figure (after Visser, 1991). Oman Sub-basin will require high-quality seismic data to define low-relief structures, as incised valley fills and fault identification as well as a consistent model for Gharif reservoirs to help overcome poor sand development and reservoir discontinuities. Reservoir risks can be reduced by drilling horizontal wells (Guit et al., 1995). Fields in the South and Central Oman sub-basins have hydrocarbons originating from local or regional kitchens of Infracambrian source rock, which, by local and longrange migration, charge shallow, anticlinally structured Paleozoic clastics draped over a core of sediment (Fig. 13.14). Geochemical analyses show that oils originate from Infracambrian salt-related, kerogenous source rocks found at depths of between 1,200 and 4,500 m (3,93614,760 ft) in South Oman. The hydrocarbons generated are thought to have migrated beneath the salt for long distances and, due to periodic subsidence, may have been available to charge traps over a long time period. A local

Hydrocarbon Habitat of the 9

)

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I 9 J9 9

9

UNITED ARAB EMIRATES / .) 9 /'0 :..!..":.."" I..~'..'~"": ~'~"~'~-.~.

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OMAN

U N I T E D A R A B EMIRATES

./ / 9

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9

_ . _ _

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ARABIAN SEA

ARABIAN SEA

~CAMBRIAN LATE ORDOVICIAN/SILURIAN

~

~ / , I U ~

~ M A ~ , ~ AREA . W i n

CRETACEOUS

~

co.r~OL

sO~CE.OCKS AaE ~ S m T

200Km l

OR ONL~E LY TO BE PRESENT

Fig. 13.11. Time of the main oil-generation phases (Cambrian-Cretaceous) of middle and upper Huqf source rocks in 9 ser, 1991). charge may immediately "fill" the overlying trap or be diverted updip if an overlying salt cover is present. Preferential charging includes a location close to a major salt edge, the early disappearance of an effective salt barrier and, particularly effective in the case of the Haima cores, a large core for recapturing "charge" in the eastern flank of the South 9 Sub-basin (A1 Marjeby and Nash, 1986).

Burial History Well information, depositional/erosional isopach maps and seismic data were used to establish the burial graphs for the source rocks in different areas. The overburden removed during the formation of regional unconformities is estimated from regional geological data, compaction trends and fission-track analyses. The burial history of the South 9 Sub-basin (Fig. 13.15) shows rapid subsidence in the Cambrian, which allowed the accumulation of up to 5,000 m (16,400 ft) of CambroOrdovician Haima sediments. Significant oil generation already had taken place by the end of the Haima, dating a major uplift of the Huqf source-rock sequence to the same time. Deposition since the Carboniferous may not have exceeded erosion above the base of the Haushi unconfor-

(after Vis-

mity, and no later expulsion of hydrocarbons has taken place (Sykes and Abu Risheh, 1989). ; The burial history of the Central 9 Sub-basin (Fig. 13.16) shows that the Huqf Group was buried to a great depth (up to 8,000 m, or 26,240 ft) by the Early Silurian, followed by erosion of less than 1,500 m (4,920 ft) during the Devonian. Subsidence was slow during the Mesozoic and Cenozoic and had some periods of limited uplift. The amount of uplift and erosion changes from north to south in the Central 9 Sub-Basin, but these differences are of subordinate importance in the hydrocarbon-generation history (Visser, 1991). Subsidence in parts of the North 9 Sub-basin has been more continuous throughout the Mesozoic and Tertiary. Huqf source rocks may have continued to generate oil and gas throughout this period and now may be at or near their maximum burial depth (Fig. 13.17). Several structures showed a continued growth history and normal faulting, possibly reactivated several times, allowing vertical migration of Huqf-sourced hydrocarbons into all reservoirs from the Permian (Gharif) below 3,600 m (11,808 ft) to the Cretaceous at 1,200 m (3,936 ft) (Sykes and Abu Risheh, 1989).

751

STERANE D I S T R I B U T I O N S

TRITERPANE DISTRIBUTION

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0.2

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Fig. 13.12. Source-rock analysis and oil characteristics of Oman (after Guit et al., 1995, reproduced with permission from Gulf Petrolink, Bahrain).

Hydrocarbon Habitat of the Oman Basin S 0

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L._

=./

w

,

~

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groupings: (1) the primarily clastic-carbonate Infracambrian Huqf Group; (2) the lower Paleozoic Haima Group and the late Paleozoic Haushi Group reservoirs, which are fluvio-deltaic or fluvio-glacial in origin; and (3) the Mesozoic primarily carbonate reservoirs of the Shuaiba and Natih formations. There are minor reservoirs present in the Triassic carbonates, the Jurassic sandstone and carbonates and the Paleocene-Eocene Umm Er Radhuma limestone. In central Oman, the principal reservoirs are contained in Late Paleozoic clastic and lower and middle Cretaceous carbonate rocks. In the Haushi-Huqf area, the dolomitized grainstone of the Infracambrian Huqf Group provided potential reservoir rocks in which both primary and secondary porosity can be recognized. The value as reservoirs of the ?Ordovician Haima Group clastic sediments, found concentrated around the periphery of the South Oman and Ghaba salt basins, lies in the amount and quality of the clay content. Authigenic kaolinite and montmorillonite may vary in quantity from 1 to 31%, with the higher content inhibiting permeability and porosity. The oldest exploited reservoirs consist of the glacial diamictites and fluvio-glacial along the northwestern flank of the Huqf-Haushi Axis. Reservoirs are of variable quality due to the rapid facies changes in depositional environments. The Permo-Triassic platform carbonates of the Khuff Formation play a much larger role in the United Arab Emirates (U.A.E.) than in Oman, but they are represented at Yibal in northern Oman. Normally, these rocks are tight, and the hydrocarbon plays are linked closely to halokinetically generated highs that permitted subaerial exposure and the resulting development of secondary porosity.

N

9

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Fig. 13.13. Central and western Oman charge concepts and Huqf Q oil fairways: H=area of Huqf source-rock kitchen; Q=area of Q source-rock kitchen (modified from Guit et al., 1995, reproduced with permission from Gulf Petrolink, Bahrain). Reservoir

Rocks

The reservoir rocks of Oman fall into three distinct

FORMA~ TION / GROUP

-

I

AGE

DAMMAM

RUS U M M ER RADHUMA

NATIH

~...~.--.~.

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9

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iCEOUS

.. . - . ." . . - '

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o ~

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HUQF

INFRACAMBRIAN

t| Fig. 13.14. Hydrocarbon accumulation and trap mechanisms in southern Oman. The arrows indicate migration pathways: A=long-range migration; B=short-range migration; C=remigration; F=faults (modified from A1 Marjeby and Nash, 1986; Alsharan and Kendall, 1986). 753

Sedimentary Basins and Petroleum Geology of the Middle East

670

600

o

505

286 246 213

406 360

430

144

65

2MA

I-RTiARY

ITE 1000~u

p. ~u 2000X

032 2462

0.62 3: F~~J

H~iM~

|

HUQF

| J

3000,

\

Fig. 13.15. Typical burial curve for the South Oman Sub-basin (after Visser, 1991). The heavy lines are the upper and middle Huqf source-rock levels used in the calculations. The dashed lines are the iso-VRE curves for the base and top of the oilgeneration window (0.62 and 1.2) and the top of the main gas-generation window (2.4).

4000

~_o 670 o.

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600 .

, 505 ,

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MA TERTIARY ]

1 Fig. 13.16. Typical burial curve for the Central Oman ~KHt~R l Sub-basin (after Visser, ! HAUSHI 1991). The heavy lines are the upper and middle Huqf source-rock levels used in the calculations. The dashed lines are the iso-VRE curves HAIMA for the base and top of the oilgeneration window (0.62 and 1.2) and the top of the main gas-generation window (2.4). WASIA

k_\\ \

~ 62-~kX \

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=

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Sq5

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286 248 213

l&&

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I I I

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AKHDAR HAUSHI

~u

HAIMA 5000

'

g ~ - " "'~:4-500

HUQF

6000 7000

754

j

Ill

Fig. 13.17. Typical burial curve for the North Oman Sub-basin (after Visser, 1991). The heavy lines are the upper and middle Huqf source-rock levels used in the calculations. The dashed lines are the iso-VRE curves for the base and top of the oil-generation window (0.62 and 1.2) and the top of the main gas-generation window (2.4).

Hydrocarbon Habitat of the Oman Basin The Lower-Middle Cretaceous (Kahmah and Wasia groups) carbonates provide important reservoirs in both northern and central Oman. The relevant formations include the Kharaib, Shuaiba, Natih and Mishrif formations. The most prolific reservoirs are the rudist biostromes in the Shuaiba, Natih and Mishrif formations. The biostromes may have formed as a chain of localized, prograding, rudist mounds with porous fore-reef facies over a halokinetically induced, bathymetric high with secondary, moldic porosity enhanced by sub-aerial leaching. The late Cretaceous rocks of Oman are not prolific anywhere. Some notes on the reservoirs of different ages follow. lnfracambrian Reservoirs The Huqf Group contains few beds with good reservoir potential. The sands of the Abu Mahara Formation generally show porosities of less than 5%, and all the potential carbonate reservoirs in the Middle Huqf seldom are out of the 5-10% porosity range. The principal reservoirs are the limestone and dolomite stringers within the Ara evaporite sequence at the top of the Huqf. Although the Buah Formation lies immediately above the source

rock, all the wells demonstrate porosities below 10%. The Abu Mahara and Khufai formations lie beneath the main source rock within the Shuram Formation and, therefore, are charged from potentially deeper sources within the Abu Mahara Formation. Much of the porosity preserved in the Ara carbonates is either primary porosity slightly modified by early leaching or cementation, or porosity generated early in the diagenetic history of the source rocks by dolomitization and leaching. Cambro-Ordovician Reservoirs The typical configuration of potential reservoir and seal pairs is shown in Fig. 13.18. Good reservoirs are present throughout the Haima sequence and contain oil in the Karim, Haradh, Amin, Mahwis, Ghudun and Safiq formations on the eastern flank of the South Oman Sub-basin (Fig. 13.19). Their reservoir character depends upon depth and lithofacies. The lowest porosity is found in the Karim Formation (5-15%); the Haradh Formation has average porosities (10-20%), whereas the highest values (15-30%) are found in the Am 9 Mahwis, Ghudun and Safiq formations (Boserio et al., 1995). -i

SE

NW

"////,//////,LL

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. 9

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it

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Fig. 13.18. Hydrocarbon accumulations in Paleozoic strata of the South Oman Sub-basin (modified from Boserio et al., 1995, reproduced with permission from Gulf Petrolink, Bahrain). 755

Sedimentary Basins and Petroleum Geology of the Middle East deposits. The overlying Mahwis Formation contains shaly, sheetflood sands as part of an alluvial apron probably sourced from the southeast.

I SOUTH O M A N SALT BASIN AND ua

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The Khuff Formation in the western Oman Mountains contains five carbonate reservoir zones (Bos, 1989; Abu Risheh and A1 Hinai, 1989). In the Yibal Field, where sour gas was tested, a fault separates two areas with different fluid distributions: a western 100 m (333 ft) oil column with a relatively small gas cap on the downthrown side; and a 60 m (203 ft) oil column with a thick gas cap on the eastern upthrown side. The carbonate reservoirs have porosities in excess of 20%, but show significant lateral variations both in thickness and reservoir porosity properties. Porosity is primarily moldic, partially enhanced by intercrystalline porosity. Permeabilities range from 1.0 to more than 100 md (Alsharhan and Nairn, 1994). Reservoir quality in the Haushi Group is essentially depth-dependent, with increasing quartz overgrowth reducing porosity and permeability to below 4,000 m (13,120 ft) (Fig. 13.20). The A1 Khlata Formation sandstone may have porosities in the 20-30% range, with permeabilities of 0.1 to 15 md. Locally, the reservoirs are fractures, probably as a result of salt withdrawal. The reservoirs often show considerable lateral inhomogeneities and unconformities reflecting the rapid lithological changes within the glacial deposits (Heward, 1990). The sand reservoirs generally are massive and interpreted as glacio-lacustrine, deltaic or subaqueous fan deposits. The Gharif Formation fluvial-channel and shallowmarine sandstone reservoirs have porosities ranging from 11 to 19% in western and central Oman. The channel sands are cross-stratified and commonly fine upwards, and many of the sand bodies appear to be composite, stacked channel sands (Focke and Popta, 1989; Heward, 1990).

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Fig. 13.19. Stratigraphic subdivision of the Cambro-Ordovician Haima Supergroup in southern Oman (modified from Boserio et al., 1995, reproduced by permission from Gulf Petrolink, Bahrain). The formations are numbered as follows: l=Ara; 2=Karim; 3=Haradh; 4=Amin (conglomerate-sandstone member); 5=Amin (sandstone member); 6=Mahwis (sandstone-conglomerate member); 7=Mahwis (sandstone-siltstone member); 8=Ghudun; 9=Hasirah; 10=Haushi Peneplain: U=unconformity, G=gradational change, UDH=unconformable-disconformable hiatus, R=reservoir, S=seal. Lithologically, the Karim sandstone is fine-grained, whereas tile Haradh sands formed part of a prograding, alluvial apron sourced from highland west of the South Oman Sub-basin. The sands of the Amin are clean, quartzose, aeolian sands with a predominance of horizontally stratified or low-angle, cross-stratified dune or interdune 3O

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Hydrocarbon Habitat of the Oman Basin The sandstone in the lower part of the Gharif Formation is made up of coarsening-upward, deltaic sands replaced upwards by mottled sandstone and siltstone with local calcrete soil profiles in association with the channel sands. The Gharif contains some 23% of the remaining oil reserves in Oman. The oil properties vary widely, with API values ranging from 12 to 53 ~.

cating that high porosities are not necessarily associated with high permeabilities. High permeabilities generally are found in the upper part of the reservoirs. Pressure data suggest that the reservoirs probably have a common freewater level, and it is assumed that communication exists between them, although the oil-water contact (OWC) may range from 15 to 30 m (50-100 ft) within and between productive zones attributed to lithological variation.

Lower Cretaceous Reservoirs The Kahmah Group contains several good carbonate reservoirs in the Yibal, A1 Huwaisah, Ghaba North, Qarn Alam and Saih Nihayda fields, of which the most important is the Shuaiba Formation. In the Yibal Field, the Shuaiba Formation has a thickness of 288 m (975 ft). The porosity in the porous, chalky limestone ranges from 25 to 42%, with matrix permeability of less than 1 md to 50 md. The Biyadh sandstone, the major reservoir of the Marmul Field, is a medium-grained, well-rounded, quartz sand 49 m (160 ft) thick in Marmul-1. In the extreme south of the South Oman Basin, this basal sand reservoir rests unconformably on Murbat Formation Paleozoic clastics.

Middle Cretaceous Reservoirs It is from reservoirs of this age that the major oil and gas production of Oman is derived. The reservoirs lie in the Natih Formation, which has been divided into seven members, lettered A to G from the top down; all are productive, with the A, C and E members particularly important (Table 13.6). The maximum gross thickness of the oil column is 457 m (1,500 ft), above which is a 110 m (360 ft) gas cap. Table 13.5 shows the porosities and permeabilities of the different members of the Natih Formation, indi-

Paleocene Reservoirs The lower part of the limestone in the Umm Er Radhuma Formation acts as a reservoir, but is found only in the Marmul Field in the eastern interior of the Dhofar Province at depths between 566 m (1,857 ft) and 606 m (1,988 ft) below ground level. The oil is viscous and 18 ~ API and rose in the well to some 91.5 m (300 ft) of the ground elevation. The presence of the reservoir is due to updip closure of the Marmul anticline and the porosity from diagenesis and partial replacement by dolomite replacement. Dead oil occurs in some of the formation's upper limestone.

Seals and Seal Formation Substantial heavy oil deposits in Infracambrian carbonate and sandstone reservoirs are sealed by the Ara evaporites. About one-third of the oil in the Oman Basin is trapped in Paleozoic clastic rocks, for which the Carboniferous-Lower Permian shale of glacial and fluvial origin acts as partial lateral and/or top seals. The Nahr Umr shale that overlaps various older formations acts as an important partial cap rock for some Paleozoic reservoirs, particularly

Table 13.6. Petrophysical characteristics of the Middle Cretaceous Natih Formation in Oman.

757

Sedimentary Basins and Petroleum Geology of the Middle East in the South Oman Sub-basin. Triassic shale and a fossil soil coveting an earlier erosion surface are responsible for the retention of some gas and condensate in the Upper Permian Khuff Formation carbonates. Reservoirs in Paleocene-Eocene carbonates that contain residual oil leaked from Cretaceous reservoirs are sealed by marl and anhydrites of the Eocene Rus Formation. Fig. 13.4 shows the major seal formations in Oman. Infracambrian Seals The dominantly argillaceous beds of the Mahwis Formation could form seals to intercalated reservoir rocks, along with the regionally extensive Shuram Formation; however, it is the Ara Evaporites that are the principal seal for the underlying Buah carbonate beds. Cambro-Ordovician Seals The most important seal within the Haima Group is the shale of the Karim Formation, where thicknesses of up to 300 m (984 ft) have been recorded. The thick, silty shale in the upper part of the Haradh Formation has a good sealing potential in at least one Haima "turtle-back" (Boserio et al., 1995), and even where the shale is thin, it is known to have la'apped oil. In the Marmul area, thin, laminated, calcareous shale in the Mahwis Formation potentially could form seals. Permian and Triassic Seals Intraformational seals within the Haima Group include the Rahab shale at the top of the A1 Khlata Formation and the shale units within the Gharif Formation. The shale or argillaceous limestone at the base of the Khuff Formation provides a regional top seal. The basal, reddish and grayish-green, laminated, anhydritic shale of the Sudair Formation provides a good seal over the Khuff limestone (Hughes-Clarke, 1988). Within the Khuff Formation itself are good seals such as the claystone-anhydritic dolomite and anhydrite at the base of K-4 or the intra-K-5 tight, anhydritic dolomite horizon. Cretaceous Seals In the Yibal Field, the compact, non-porous limestone in the Kharaib and upper Shuaiba formations act as seals. In the Middle Cretaceous, the "B" Member of the Natih Formation has a low permeability and may act as a partial seal; however, it is the shale and laterally equivalent green shale and argillaceous limestone of the basal Nahr Umr that are the most important seal for the hydrocarbons trapped in Shuaiba reservoir rocks. The Middle Cretaceous reservoirs are sealed by the Late Cretaceous Fiqa Formation shale that lies unconformably above. Paleocene Seals Interbedded, thin, dark shale seals the limestone reser-

758

voirs within the Umm Er Radhuma Formation. Structure and Traps In southern and central Oman, structural deformation was relatively minor, with major restructuring occurring at the platform margin through the process of salt withdrawal, forming rim synclines at the eastern flanks of the South Oman and Ghaba salt basins (Visser, 1991) created by Middle Huqf epi-cratonic rifting. Both the Ghaba and South Oman salt basins retain evidence, seen in seismic lines, of their rift origin (Boserio et al., 1995). Their formation coincided in time with the formation of salt basins on a regional scale. The extent of the original carbonate platform in which the basins developed is unknown. During the Cambrian, and subsequently, as a result of halokinetic activity that was the dominant structural influence during the Paleozoic, salt-cored and turtle-back structures were created, and rim synclines received a fill of early Paleozoic sediments (Fig. 13.16). The increased sedimentary overburden in the northeast resulted in increased salt movement in that direction, and movement induced by basement adjustments resulted in the formation of substantial pillow structures by the end of the Permian. The early Paleozoic surface during the Carboniferous was levelled as a result of erosion following Carboniferous uplift of the Arabian Craton, and the West Oman Sub-basin opened northwestward into and became a part of the Rub al Khali Sub-basin. During the Permian, the Tethyan margin lay to the north, down the slope of which turbidites flowed into the deep proto-Indian Ocean Basin. An epi-continental, carbonate shelf developed over the Rub al Khali Sub-basin, with sediments generally thinning southeastward. The closure of the Tethys Oceanic Basin during the Cretaceous with the obduction of the Semail ophiolites was accompanied by deformation of sediments south of the Oman Mountains and the formation of the main oil traps in northern Oman. The offshore Masirah Graben was formed at about this time (Beauchamp et al., 1995). It is limited to the east by a large wedge of stacked, imbricate thrusts, which may conceal a rift sequence below. In the North Oman Sub-basin, continuous subsidence throughout the Mesozoic and Tertiary reactivated salt movement, and salt domes locally pierce the surface, but only pillowing is observed in many structures. Major tectonic activity, coeval with the emplacement of the Hawasina and Semail nappes, reactivated structures; therefore, as the Huqf source rocks continued to generate oil, vertical migration into all reservoirs from the Gharif Formation, below a depth of 3,600 m (11,808 ft) to the Cretaceous at 1,200 m (3,936 ft), could occur. The West Oman Sub-basin spans the region between the South and Central Oman sub-basins and the Rub al Khali Sub-basin to the west. It is a little-explored region of low relief covered by sand dunes. Structural deformation generally is not severe, but continued structural growth

Hydrocarbon Habitat of the Oman Basin took place during the Mesozoic and Tertiary, and the major fields in this r e g i o n - Yibal, Lekhwair and A1 Huwaisah are essentially low-relief, dip-closed structures with throws on the faults, where present, less than the thickness of the sealing formation. The fields contain oil in the Shuaiba and Natih carbonates sourced from the Diyab and Natih formations. The structural development of the Proterozoic South and Central Oman sub-basins is a distinctive development in the hydrocarbon history of Oman. Both show their origin as rifts formed during a middle Huqf phase of epi-cratonic rifting (Boserio et al., 1995), which can be correlated with similar events in the Arabian Gulf region. Subsequently, the basins were characterized by mild deformation in the center of the basins, but with major tectonic reshaping of the basin margins (Visser, 1991). This is evidenced by the significant lack of hydrocarbon accumulations in Paleozoic (Haima Group) sedimentary rocks within the South Oman Sub-basin, in contrast with the 20 B.bbl in place in similar reservoirs along the eastern flank of the basin (Boserio et al., 1995). Four types of hydrocarbon trap occur in the South and Central Oman sub-basins, all related to salt removal: large, turtle-back anticlines resulting from the inversion of former peripheral synclines; truncation traps rimming eroded, turtle-back anticlines; small anticlines draped over residual masses of dolomite and shale; and porous and fractured dolomite and shale, and porous and fractured dolomites within such residues after salt removal (A1 Marjeby and Nash, 1986). Combinations of various types of trap are common. Extensive truncation traps rim many of the inverted pods of Haima strata (Fig. 13.21). They comprise dipping Gharif sands sealed laterally by A1 Khlata, Gharif and Khuff claystone or capped by the Nahr Umr shale (de la Grandville, 1982). Their fluid contacts may be shallower, similar to or deeper than the adjacent main Haima/A1 Khlata accumulation, and the oil commonly is

slightly heavier and more viscous. Small anticlines consisting of A1 Khlata and Gharif reservoirs draped over Ara remnants occur particularly with the pre-Nahr Umr and Late Cretaceous dissolution synclines (Fig. 13.22). The reservoirs are separated by intraformational shale seals and charged with oils of varying density (Heward, 1990). Ara remnants comprise structurally jumbled arrangements of dolomite, organic-rich shale and anhydrite, which represent concentrations of residual lithologies after salt dissolution. Production has been obtained in the Simsim Field from a porous and fractured dolomite interval sealed by the fine-grained clastics of the Karim Formation (Fig. 13.23) (Heward, 1990). In northern and western Oman, the reservoirs may be structurally deformed blankets (e.g., the Natih Formation in the Natih and Fahud fields) (Fig. 13.24), or a large, stratigraphic trapping element is involved in the form of the accumulation of rudist limestone (e.g., the Shuaiba Formation, A1 Huwaisah Field). Evidence for the former existence of salt along the eastern flank of South Oman is provided by chaotically structured masses of dolomite, shale and anhydrite originally interbedded with the salt. The peripheral sinks created by the salt withdrawal subsequently were filled by Cambro-Ordovician continental sands. Late Paleozoic erosion left salt pillows or ridges at or close to the surface, separated by the Haima sands deposited in the peripheral sinks. Later salt solution by Permo-Carboniferous glacial meltwaters under glacio-lacustrine conditions resulted in shaly and sandy sequences capping the Haima sands, which became traps for migrating Infracambrian oil. Further periods of salt withdrawal occurred during the Mesozoic. Clearly, many aspects of the petroleum geology of the province are related to salt movement and solution, which have influenced sedimentary geometries and facies distributions. The reservoirs may be in Cambro-Ordovician (Haima Group), Permo-Carboniferous (A1 Khlata Formation) or Permian (Gharif Formation) rocks.

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(H~A~OUP) Fig. 13.21. The hydrocarbon trap in the Marmul Field occurs in the Haima and A1 Khlata reservoirs at the crest of a truncated, turtleback anticline. The flanking Gharif truncation traps have deeper and shallower oil-water contacts than the main accumulation (modified from Hughes-Clarke, 1988, reproduced by kind permission of Journal of Petroleum Geology). 759

Sedimentary Basins and Petroleum Geology of the Middle East

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~1 1Kin

Oil Field Examples

ACC~TION

Fig. 13.23. The hydrocarbon trap in the Simsim Field comprises a pod of the Haima draped over remnant Ara lithologies. Ara remnant lithologies are oil-producing (modified from Heward, 1990, reproduced by kind permission of Geological Society, London)).

Data from some of the major fields are summarized in Table 13.8, and the descriptions that follow illustrate the major geological features that characterize these fields. F a h u d a n d N a t i h F i e l d s in t h e F o r e l a n d Sub-basin

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years. Together, they flank an uplifted, fault-controlled block with deep, sedimentary troughs on either side. They produce 33.6 ~ and 31.3 ~ API oil, with about 1-1.13% sulfur from multiple Middle Cretaceous Wasia Group carbonate reservoirs. The Fahud Field in northern Oman lies in a plain dissected by wadis that extend southwestward from

(North Oman)

The giant Fahud and Natih fields, the two major fields, lie parallel in northwestern Oman (Fig. 13.3). Less than 30 km apart, they were discovered in successive

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Fig. 13.24. A hydrocarbon trap in the Fahud Field, where the Natih and Shuaiba reservoirs are draped over faults (after Hughes-Clarke, 1988, reproduced by kind permission of Journal of Petroleum Geology).

760

Hydrocarbon Habitat of the Oman Basin the Oman Mountains towards the Rub al Khali. Morphologically, it is an uplifted, anticlinal block, with the crest rising 180 m (590 ft) above the plain. It was recognized from the air and structurally surveyed in 1954. The first well, Fahud-1, was spudded in 1956 and abandoned at a depth of 3,730 m (12,235 ft) in Paleozoic salt, with indications of producible oil in a relatively thin Wasia limestone section. In 1962, commercial oil was found in the Natih limestone in well Fahud-2, where the oil column was of

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the order of 457 m (1,500 fi) in thickness. The small thickness recorded in Fahud-1 (27 m, or 90 ft) was the result of intersected fault cutout. The field went on-stream in 1967. The oil is trapped in a faulted, WNW-ESE, asymmetrical anticline (Fig. 13.25) ,~plunging gradually at both ends, with maximum dips on the flanks of 17~ and 19~ The structure is truncated by a fault zone with an aggregate displacement of 1,220 m (4,000 ft) dipping at 45 ~ and probably related to basement movement (Tschopp,

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Fig. 13.25. A=structural contour map of the top of the Middle Cretaceous Natih Formation in the Fahud Field (depths below sea level in ft); B=structural cross-section of the Fahud Field in Oman showing reservoirs and seals (modified from Tschopp, 1967b ) 9AD=Mishrif Formation and E-G=Mauddud Formation (after Alsharhan and Naim, 1988). 761

Sedimentary Basins and Petroleum Geology of the Middle East 1967b). The closure measures 27 x 4 km, with the top of the culmination occurring 229 m (750 ft) below ground level. Structurally, the Fahud structure compares closely with the Natih Uplift some 30 km to the northeast. The early structural history is not known; the first positive indications of structural growth occurred during the AlbianCenomanian, and growth continued into the SantonianCampanian. The Natih limestone is divided into seven members, A to G; of these, the source of the oil is presumed to be the Natih B Member, with the oil generated in the deeper depressions north and south of the Natih-Fahud Horst. Oil migration into the Wasia reservoirs is presumed to have occurred shortly after deposition of the formation (Tschopp, 1967 a & b) during the Santonian-Campanian. All the Natih members are productive, with porosities around 30%, but with a considerable range in permeabilities (Table 13.6). Primary interparticle and moldic porosity appears to be dominant, and dolomitization and fracturing, important elsewhere in the Middle East, play only a minor role. Secondary moldic porosity, formed during subaerial exposure, is more common than primary porosity, especially in the thicker stratigraphic units (Harris and Frost, 1984). The B Member is mainly a bituminous, non-reservoir facies, and because it is productive only in some wells, it is not regarded as a completion prospect. There is an overlying 110 m (360 ft) primary gas cap. The Natih Field was discovered in 1963 by well Natih-1, with oil in the Natih and Shuaiba reservoirs. The Natih, which lies in the Fahud Salt Basin, is a 10 x 6 km, NW-SE-trending anticline bounded to the north by reverse

faults. The top of the Natih Formation structural map (Fig. 13.26) shows that two fault sets dominate in the Natih Field, one set roughly NE-SW-trending and the other NW-SE- to WNW-ESE-trending (Mercadier and Makel, 1991). The Natih reservoir is a heavily fractured, tight, chalky limestone with a tight, low-permeability matrix; consequently, production depends greatly upon the number and orientation of fractures intersected by the wells, where porosities range from 15 to 27% and permeabilities from 2 to 500 md. A 3-D seismic survey was made in 1992 to locate small-scale flexures and faults with displacements as low as 3 m (left), with which the fracture orientation is linked, for the optimum location of wells (Whyte, 1995). Experience has shown that an average improvement of 30% can be achieved by means of the Gas Oil Gravity Drainage technique aided by gas injection. The Natih Field has 475 million m 3 of 32 ~ API oil in place (Whyte, 1994) and an estimated original recoverable oil reserve of 660 MM.bbl. AI Huwaisah Field in the West Oman Sub-basin

The A1 Huwaisah Field lies in northwestern Oman about 300 km southwest of Muscat. Discovered in 1969, it went on-stream in 1971 and measures about 10 x 7 km. It produces oil with 33 ~ API and 1.5% sulfur under strong water drive from the rudist-bearing Shuaiba (Aptian) limestone sealed by Albian Nahr Umr shale (Fig. 13.27). In 1993, there were 72 wells in the main field, an eastern extension and two satellites (in which there is considerable heterogeneity in the reservoir parameters). The result is

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Hydrocarbon Habitat of the Oman Basin

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, KHARAI~

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that although the pool is considered a single accumulation, it is difficult to derive a comprehensive reservoir model; to avoid the danger of leaving significant oil, a 3-D computer model was developed by Vahrenkamp and Grotsch (1995). Basically, the early Aptian Shuaiba limestone was subjected to late Early Aptian subaerial erosion, with the consequent enhancement of porosities during emergence, which lasted a few million years before the deposition of the early Albian Nahr Umr shale. Within the Shuaiba limestone, reservoir types have been defined based upon depositional facies, porosity and permeability and capillary characteristics (Vahrenkamp and Grotsch, 1991). Examination of well cores demonstrates the existence of shallowing-upward trends measurable on a scale of meters. Using 3-D modelling, a 75 m (246 ft) NW-SE strip, 11 x 5 km wide, was presented in six time slices depicting the establishment of patch reefs on a pre-existing carbon-

0

0. SKin

ate shelf, with the gradual development of a barrier separating lagoonal and back-reef facies from more openmarine facies. The program's parameters include lithology, permeability, porosity and capillary pressures. This model allowed a structurally contained facies model to be translated into a hydrocarbon saturation model under virgin conditions (Vahrenkamp and Grotsch, 1995). In 1985 the field had an average production of 19,250 bbl/d with a cumulative production of 150 MM.bbl so that the field is probably more than half depleted (Beydoun, 1988). Lekhwair Field in the West Oman Sub-basin

The Lekhwair Field, approximately 140 km northwest of Fahud, was discovered in 1968 and brought on-stream in 1976. After several dry holes were drilled, due to a reservoir that was partly dry because of intermittent structural

763

Sedimentary Basins and Petroleum Geology of the Middle East

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The Yibal Field is a large, domal feature developed primarily by deep-seated salt movement. It measures approximately 15 x 20 km and has a NE-SW axial elonga-

764

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growth, a field was established in 1969 (Beydoun, 1988). In the field, late Cretaceous uplift and erosion have resulted in the removal of much of the Cretaceous sequence. The major Fiqa and Nahr Umr seals were breached, so the seal for the accumulation in the lower Shuaiba and Kharaib reservoirs is the shale facies of the Upper Shuaiba backed up by the basal Tertiary Shammar shale. The field consists of two low-relief domes: the main, or "A," area with 80% of the STOIIP; and the structurally lower "B" area to the northwest (Fig. 13.28). Light, low-viscosity oil is produced from two low-permeability, chalky limestone reservoirs - - the lower Shuaiba and Kharaib. These reservoirs are separated by a tight, argillaceous and laterally continuous layer assumed to prevent cross flow. Injection rates seem to be controlled more by local, small-scale faults than by permeability or porosity trends. Stock tank oil initially in place (STOIIP) is estimated to be 1311 MM.bbl. Well production rates typically are 630 bbl/d. The initial reservoir pressure in the A area of 1987 psi is some 73 psi above the bubble-point pressure. Production during the 1976-1979 period at rates of up to 28,300 bbl/d resulted in the reservoir pressure declining by some 160 psi below bubble point, with an accompanying sharp rise in the producing gas-oil ratio to 1,400 ssf/bbl from the solution gas-oil ratio of 525 scf/bbl (Willets and Hogarth, 1987). Consequently, production from the lower Shuaiba was shut in to conserve reservoir energy, while the Kharaib production fell to 3,150 bbl/day net.

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Fig. 13.28. Structural crosssection and structural-contour map of the top of the Shuaiba Formation in the Lekhwair Field of Oman (compiled from HughesClarke, 1988; Willetts and Hogarth, 1987).

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tion and flank dips of 4-5 ~ The structure is complicated by extensive tensional faulting, which affects the trapping mechanism in the oil reservoir. All the faults are highangle, normal faults. Many of the prominent fault traces trend either SE-NW or NE-SW. These preferred alignments are thought to be related to the influences of regional tectonics (Fig. 13.29a) (Litsey et al., 1983). The Yibal Field was discovered in November 1962, when well Y-2 penetrated the oil column near the crest of the structure, tested 40 ~ API oil at 3,500 bbl/d and was put onstream in 1969. Original oil in place in the Shuaiba was estimated in 1983 to be about 2.85 B.bbl of stock tank oil (Litsey et al., 1983). The Shuaiba Formation, the main reservoir, is about 122 m (450 ft) thick and demonstrates thickening in the central part of the Yibal Field. Interval thicknesses between various correlation points in the Lower Shuaiba are constant, but thickening does take place in the Upper Shuaiba, defined as that section of the Shuaiba above the highest gamma-ray-log response (Fig. 13.29b). Abrupt variations in layer thickness are attributed to faulting. Thickening in the Upper Shuaiba implies some growth mechanism, due either to deposition in a basin or biologic buildup on a sea-floor high, or possibly greater off-structure compaction. The Shuaiba Formation was deposited in a low- to moderate-energy, pelagic environment. Shallowwater fauna probably were transported downslope periodically from a higher-energy environment to the south. The porosity in the Shuaiba upper oil-bearing portion of the reservoir is generally from 25 to 42%. It has a lower porosity zone usually between 14 and 22% above the OWC at the crest of the structure. Matrix permeability in the Shuaiba generally ranges from less than 1 md to 50 md

Hydrocarbon Habitat of the Oman Basin

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Fig. 13.29b. Lithostratigraphy and log characteristics (gamma ray/neutron) of the Yibal Field of Oman. The location of the cross-section is shown in Fig. 13.29a (modified from Litsey et al., 1983, reproduced by kind permission of Society of Petroleum Engineers). (Grant, 1981; Litsey et al., 1983). One suggested reason for the unusually high porosity in the main chalk reservoir is its preservation from chemical compaction by the early accumulation of oil. This mechanism also contributed to the greater reservoir thickness in the center of the field. In 1977, sour gas was tested in the Permo-Triassic rocks of well Y-85. The structure map of the field at this level shows a NE-SW-trending fault dividing the structure into two areas with different fluid distributions (Fig.

13.29c). On the western downthrown side, there is a 100 m (328 ft) oil column with a relatively small gas cap, whereas a 60 m (197 ft) oil column on the eastern upthrown side has a large gas cap (Bos, 1989). These Khuff carbonates contain five reservoir zones (K1-K5) (Bos, 1989; Abu Risheh and A1 Hinai, 1989; Alsharhan and Nairn, 1994). Carbonate reservoirs K1-K5 generally have porosities of more than 20%, but show significant lateral variations in both thickness and reservoir properties.

765

Sedimentary Basins and Petroleum Geology of the Middle East EAST

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Porosity primarily is oomoldic, partially enhanced by intercrystalline porosity, and permeability ranges from less than 1 to more than 100 md. Well Y-192 was drilled in 1985 and tested oil in the K2, K3 and K4 beds and gas and condensate in K1 and K5. In 1986, Y-212 and Y-214 were drilled, and oil shows were found in K1 from well Y-212. Well Y-230 tested oil at the rate of 1,250-1,890 bbl/d in the low-permeability K2 bed. Well Y-236, drilled near the end of 1987, found gas in K1 and the upper part of K2. The lower part of beds K2 and K3 were found to be in the oil column (Bos, 1989; Alsharhan and Nairn, 1994).

Safah Field in the West Oman Sub-basin The Safah Field, which was discovered in 1983 and went on-stream in 1984, covers approximately 25,000 acres and contains more than 650 M.bbl of oil and 54 B.CF of gas. The trap is a combination of structure and stratigraphy on a northward-plunging nose dipping off the Lekhwair High. The nose provides three-way dip closure, with the updip seal provided by facies change. Structural dip averages less than 1~ down the crest of the nose. The reservoir, the Shuaiba Formation (Aptian), consists of micritic lime mudstone. A change in facies to tight, argillaceous lime mudstone to the south and west provides the updip seal. Reservoir porosity varies from 12 to 30%, with an average of 22%. Permeability generally ranges from 3 to 5 md, with pore throats of less than 5 microns. The reservoir is overlain by tight limestone of the Shuaiba Formation, which is overlain by Nahr Umr shale. The field is divided into laterally equivalent east and west lobes separated by a narrow structural low and a stratigraphic barrier of tight, argillaceous limestone (Fig. 13.30a). The lobes have a different reservoir-fluid quality ; the West Lobe generally has a poorer net-to-gross pay ratio and increased argillaceous content and is more variable in lithology than the East Lobe (Vadgarna and Ellison, 1991). 766

Fig. 13.29c. Subdivision and hydrocarbon distribution within the Khuff Formation in the Yibal Field of Oman (modified from Bos, 1989).

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The East Lobe is subdivided into northeastern and southeastern zones based on PVT properties (Table 13.7). The mechanism separating the reservoir is suspected to be a low-amplitude, normal fault (Fig. 13.30b). The Northeast Zone contains saturated oil with a gas-oil contact at 1,834 m (6,015 ft) subsea depth and an OWC (40% water saturation) at 1,864 m (6,115 ft) subsea. The Southeast Zone has undersaturated oil with an OWC at 1,867 m (6,125 ft) subsea (Chen, 1995).

Mukhaizna Field in the South Oman Sub-basin The field was discovered in 1975 with well Mukhaizna-1, drilled some 50 km north of the Rima Field in the South Oman Sub-basin. The field consists of two structures covering an area of some 350 sq km. The northern structure, which is controlled by dip closure, is separated by a saddle from the second structure, which has

Table 13.7. Reservoir fluid properties of the Shuaiba Formation in the Safah Field of Oman (after Vadgama and Ellison, 1991).

Hydrocarbon Habitat of the Oman Basin

e64

fault-bound closure in the south at a depth of some 800 m (2,624 ft) (Fig. 13.31a). Oil was found in the Upper and Middle Gharif reservoirs separated from each other by a 510 m (16-33 ft) thick shale that can be traced over the entire field (Fig. 13.3 lb). The Gharif Formation consists of coarse- to medium-grained fluvial sediments deposited during the early Permian on a broad E-W-oriented, lowgradient, alluvial plain that grades into monotonous, alluvial mudstone with few medium- to fine-grained, fluviatile channel sands that generally are highly unconsolidated, with 25-35% porosities and a corresponding permeability of 0.1-4 darcies (Bouvier et al., 1995). The net-to-gross ratio in both the Upper and Middle Gharif in the area exceeds 50%, allowing far full 3-D pressure communication within each reservoir. All wells encountered net oil pay in the Gharif, most commonly in the Upper Gharif, and produced on test on average at the marginally economic rate of some 30 m 3 per day or about 190 barrels of dry oil per day with a gravity of 15 ~ API and a viscosity of 1600 milli-Pascal/second (mPa/s). The total oil in place in the Upper and Middle Gharif reservoirs was calculated at 265 million m 3 with reserves of 5.3 million m 3 (33 M.bbl) on the basis of a 2% recovery factor (Bouvier et al., 1995).

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Marmul Field in the South Oman Sub-basin This oil field was discovered in 1956 and was declared non-commercial at oil prices then operative upon the recommendation of DeGolyer-McHaughton of Cities Services Petroleum Company. It contains a heavy, viscous oil of 18 ~ API in a Paleocene Umm Er Radhuma reservoir. This oil is found at shallow depths of the order of 576 m (1,890 ft), but will not flow to the surface, rising to 91 m (300 ft) below the surface in open hole tests. A second reservoir occurs in the Lower Cretaceous Biyadh sandstone in the Marmul Field at depths from 854 to 976 m (2,8003,200 ft) and contains oil of 20.8 ~ API gravity with a gasoil ratio of 100 CF/bbl. The production capacity of Marmul-2 was rated 1,000 bbl/d. On a production test from August 23, 1957 to February 21, 1958, Marmul-2 produced 38,715 bbl of oil. It originally was reported in discovery well Marmul-1 that the gravity of oil from the Lower Cretaceous Biyadh sandstone reservoir was 22 ~ API with a low sulfur content. In 1956, the heavy oil accumulation that had an essentially unpredictable reservoir distribution was considered noncommercial, and the concession was relinquished after five wells were drilled. In 1978, the decision was made to develop the Greater Marmul area, which then was put on-stream in October 1980 (de la Grandville, 1982). The Marmul Field is a large, 17 x 20 km anticline on the eastern flank of the South Oman Sub-basin. The field now produces 5,880 m 3 per day from the Permian Gharif and A1 Khlata sands and Cambro-Ordovician Haima sands. The Gharif reservoirs consist of a stacked sequence of sheet-like sands, interbedded with thinner silt and shale. The A1 Khlata reservoirs are a complex sequence of later-

767

Sedimentary Basins and Petroleum Geology of the Middle East

0

ally variable sand, shale and diamictites deposited in a glacial setting. The Haima reservoir consists of massive, finegrained sands and shale. The reservoirs are truncated and sealed by the Cretaceous Nahr Umr shale (Binbrek, 1994) (Fig. 13.32). In this field, the 100 m (328 ft) gross oil column significantly exceeds the vertical relief of the Nahr Umr dip closure, demonstrating the effectiveness of the intra-A1 Khlata seals. The primary accumulations experienced tilting and leakage leading to the migration of the hydrocarbons into the overlying strata, and large volumes of this migrated heavy oil, highly transformed, are present in Tertiary and Mesozoic carbonates. The structural trapping element is provided by a NE-SW-trending anticline developed in the pre-Cretaceous section as a result of salt withdrawal and solution. The hydrocarbon charge must originate from deeply buried late Precambrian (Huqf) kerogenous source rocks downflank in the salt basin northwest of Marmul. The source rocks appear to have reached maturity only recently. Remigration of part of the charge took place into the Tertiary. Carbonate rocks probably resulted from late Tertiary tilting and/or faulting. The main characteristics of the Marmul crude oil are an average gravity of 21.5 ~ API, a viscosity of the order of 300 centistokes at 100~ and a sulfur content of 2%. The Haima consists mainly of fine- to very fine-grained, well-sorted, loose to moderately consolidated sands. It contains a few shale intercalations and shale clasts; some calcite-cemented, tight streaks and sub-horizontal, parallel, micrometer to millimeter shale laminations are common. Porosities range from 13 to 39% and permeabilities from 5 to 1,110 md. The Gharif Formation consists of three reservoir facies: tillites, outwash and fluvial sands. The tillites consist of a homogenous, unsorted mixture of clay, sand and pebbles, with boulders of metamorphic and sedimentary origin. They are non-stratified, although they are intercalated in places with contorted, vaguely laminated sandstone. The porosity of the tillites ranges from 1 to 25%, but they are of a non-reservoir to very poor reservoir quality, with permeabilities ranging from 0.2 to 35 md. They are likely to act as partial seals within the lower Haushi reservoirs and

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Hydrocarbon Habitat of the Oman Basin

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Fig. 13.32. A=structural-contour map of the base of the Albian Nahr Umr Formation in the Marmul Field of Oman; B=generalized structural cross-section showing the Paleozoic reservoir (Haima-A1 Khlata-Gharif) and seal (Nahr Umr) in the Marmul Field of Oman (from de la Grandville, 1982; Binbrek, 1994; Ishak et al., 1995). locally between the Haima and Haushi reservoirs. The outwash deposits are relatively thin (3-20 m, or 10-70 ft) bodies of coarse- to fine-gained sands, thin conglomerates and gravel layers interbedded with tillites. They are interpreted to be periglacial deposits in close association with the tillites, and they represent disaggregation products of the tillites. The reservoir quality of the outwash sands varies from very low to very good (permeabilifies higher than 10 darcies). The fluvial sands consist of thick bodies of sands, pebbly sands, thin conglomerates and shaly intercalations. The sands show mega-cross-bedding with some overturned foresets. The fluvial sands probably accumulated in channels in the fluvioglacial delta. The porosities of the fluvial sandstones range from 12 to 35%, with an average

of 22%. Their permeabilities are from 0.7 to 3,000 md, with an average of 300 md (de la Grandville, 1982). The Gharif reservoirs subcrop unconformably under the Nahr Umr shale, which constitutes the lateral seal of the stratigraphic trap. The stacked reservoirs are overlain conformably by thick Gharif clays, which represent the bottom seal of the stratigraphic trap. In addition, the stacked sands may be separated (at least locally) from each other by intraformational shale layers. The basal, varved Rahab shale forms the seal separating the A1 Khlata from the Gharif. Along the northern rim of the field, viscous oil of some 100 to 300 centipoise is found mainly in the Permian Lower Gharif units 1 and 2, which consist of a stacked sequence of sheet-like sands interbedded with

769

Sedimentary Basins and Petroleum Geology of the Middle East thinner silt and shale. The sediments are coastal, deltaic deposits (Mercadier and Livera, 1993). The average porosity is 30%, with a permeability of 1-5 darcies. The maximum gross thickness is 75 m (246 ft), depending on the distance from the subcrop edge, with a net/gross of 60%. The Gharif beds dip at 6 ~ and are truncated by the base of the Nahr Umr Unconformity (Albian), which dips at 2 ~ in the same direction as the Gharif Formation. At the northern rim of the Gharif Field, the initial oil in place is 54.3 million m 3. The reservoir produces under a strong-edged water drive and is developed by 26 vertical wells (Ishak et al., 1995).

Oil production in the Nimr Field comes from Cambro-Ordovician and Permo-Carboniferous elastics (locally called Haima and Gharif, respectively) (Fig. 13.33). Oil in the reservoir is underlain by an extensive water aquifer of the Haushi Group; hence, the production mechanism is a bottom water drive that has a mobility several hundred times greater than that of the oil. The reservoir is characterized by relatively high viscosity (21~ API, 400 cP) oil. The total reserve was estimated by A1 Rawahi et al. (1993) to be about 428 x 106 m 3 STOIIP. Saih R a w l Field in the C e n t r a l O m a n S u b - b a s i n

In May 1974, PDO announced the discovery of a new oil field at Saih Rawl in southern central Oman 40 miles east of the Ghaba North Field. The field went on-stream in 1975 and should add another 30 M.bbl/d of high-gravity, low-sulfur crude to Oman's production from both the Lower Cretaceous Shuaiba limestone and Permo-Carboniferous A1 Khlata sandstone reservoirs. In 1978, commer

N i m r Field in the S o u t h O m a n S u b - b a s i n

The Nimr Field, about 35 x 8 km, is located on the eastern flank of the South Oman Province. It was discovered in 1980, and, due to its complexity, some 50 appraisal wells were required before it was brought on-stream in 1985 with production of 860 bbl/d.

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Fig. 13.33. Reservoir development in the Nimr Field of Oman. Upper figure: A=Gharif reservoir of shale/sand alternation; B=Amin reservoir (eastern slope) of homogeneous, clean, aeolian sand cut by A1 Khlata valleys; C=A1Khlata reservoir of heterogeneous and unpredictable deposits in paleovalleys; D=Amin reservoir (western slope) of homogeneous, argillaceous sandstone dissected by A1 Khlata valleys (after AI Zarafi, 1993). Lower figure: Cross-section of wells over part of the Nimr Field illustrating the irregular unconformities beneath and within the A1 Khlata Formation (modified from Heward, 1990, reproduced by kind permission, Geological Society of London). 770

Hydrocarbon Habitat of the Oman Basin

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cial oil was established in the Lower Jurassic Marrat Formation sandstone reservoir. In 1985, the average daily production of 41 ~ API oil was 9,693 bbl/d, and the total production had reached 78.5 MM.bbl in 1985. The Shuaiba reservoir contains a thin column of undersaturated, light oil (less than 25 m, or 82 ft) underlain by water, trapped in a flat but slightly undulating structure (Fig. 13.34). The reservoir extends over an area of 50 sq km and consists of fine-grained, chalky mudstone and wackestone. The predominant porosity is intergranular matrix porosity, with the occasional development of vugs due to selective leaching towards the top of the reservoir (A1 Zarafi, 1993). Reservoir data are shown on Table 13.8. No evidence of fractures/faults has been observed to date, either in core samples or from pressure transient analysis. Also, there is no strong evidence of faulting from the 3-D seismic, although sub-seismic faulting always is possible. Q a h a r i r F i e l d in t h e S o u t h O m a n

Sub-basin

The Qaharir Field is located on the southeastern margin of the South Oman Sub-basin, discovered in 1978; it produces from the Permian Gharif and A1 Khlata and the Cambro-Ordovician Haima sands at a rate of about 1,445 m3/d, with oil gravity of 30 ~ API. The field has a domal

771

Sedimentary Basins and Petroleum Geology of the Middle East

Fig. 13.35. A=structural-contour map of the top of the Cambro-Ordovician Haima Group in the Qaharir Field of Oman; B=structural cross-section of the Qaharir Field of Oman (modified from A1Kharusi and Binbrek, 1994).

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structure bounded by faults and cut by NW-SW-trending faults (Fig. 13.35). Two major faults predicted by 3-D seismic were encountered and shown to define a graben structure, but the seismic imaging shows complex Haima faulting. Three additional disturbed zones within the A1 Khlata Formation have been interpreted as minor faults between the two major faults. Some of the interpreted faults appear as conductive features. This conductivity may be because the fault was open and filled with water or mud filtrate at the time of logging (A1 Kharusi and Binbrek, 1994). The 3-D seismic was imaging complex Haima faulting. The production rate in 1985 averaged some 7,500 bbl/d, and the total production at the end of the year was 14.5 MM.bbl. R i m a F i e l d in t h e S o u t h O m a n S u b - b a s i n

The Rima Field was discovered in 1979 and brought on-stream in 1982. The Rima structure covers a relatively small surface area of 17 sq km at the OWC and is one of a

772

number of turtle-back anticlines created by the withdrawal of older salt formations. In the field, 33 ~ API oil is produced from the Ordovician Mahwis and Permo-Carboniferous A1 Khlata sandstone reservoirs. The fine-grained, homogenous sands of the Haima Group are interpreted as sheet-flood deposits in the distal portions of semi-arid alluvial fans. The heterogeneous A1 Khlata Formation was deposited in deep (at least 250 m, or 820 ft) and narrow (12 km), fault-controlled valley systems that cut the Haima Group in a north-south direction. The A1 Khlata/Gharif boundary is taken at the top of the Rahab shale regarded as a lacustrine deposit, probably representing a large, lowlying, peri-glacial and post-glacial water swamp area. The A1 Khlata and Mahwis formations form one single reservoir complex sealed by the regionally extensive Rahab shale (Fig. 13.36). The A1 Khlata/Mahwis reservoir complex has a common OWC at 878 m (2,880 ft) and a maximum oil-column height of 130 m (426 ft) at the crest of the structure (Van Kossem et al., 1993). The field contains a STOIIP of approximately 150 million m 3 (950 M.bbl). B u k h a F i e l d in t h e O f f s h o r e M u s a n d a m

Sub-basin

The offshore Musandam and Gulf of Oman sub-basins have been explored much less than the other Oman sub-basins. However, the discovery of gas/condensate by Elf and Mobil in Lower and Middle Cretaceous reservoirs raises the exploration potential of the sub-basins (Pauken and Hemer, 1991). The only producing field in this region is Bukha, discovered in 1979. The Bukha Field lies in the West Musandam Peninsula, an elongated anticline about 11 x 2.5 mi bounded by reverse faults on the

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Fig. 13.36. Geological cross-section of the Rima Field of Oman. The Permo-Carboniferous A1Khlata is the main reservoir, as indicated by the arrows. The formation here fills a deep, narrow graben system within the Mahwis Formation (modified from Meyer et al., 1995, reproduced by kind permission of Society of Petroleum Engineers ). southeastern and northwestern flanks. The Bukha-1 discovery was drilled in December 1978 by a consortium led by Elf Aquitaine, and production was tested in the Middle Cretaceous (Sarvak/Mishrif limestone). In May 1979, Elf tested 2 M.bbl/d of 52 ~ API condensate and 22 MM.CF/d gas from this well. Bukha-2 flowed 48 MM.CF/d of gas and has an initial deliverability of more than 7 M.bbl/d of condensate. Two production tests of the Lower Cretaceous and Middle Cretaceous limestone in Bukha-2 flowed a total of 4.3 M.bbl/d of 50 ~ API condensate. Well Bukha-3 reached the Lower Cretaceous and produced gas/condensate from Middle and Lower Cretaceous limestone. TheBukha Field came on-stream in April 1994 and was

producing 6 M.bbl/d of condensate and some 50 MM.CF/ d of gas from two wells by July. Production from this field was transferred to UAE (Ras A1 Khaimah) where the processing facilities are located. The field has 40 MM.bbl of condensate reserves (Oil and Gas Journal, 1987). In 1995 the International Petroleum Corp. produced 5000 b/d of condensate and 1100 bbl/d of liquified petroleum gas. The organic-rich rocks of the Tertiary and Late Cretaceous Pabdeh and Gurpi formations typically are too shallow to be thermally mature, but the Middle Cretaceous Kazhdumi/Khatiyah Formation is thought to contain the source rocks. The reservoir is sealed by the Ilam chalk.

773

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SUBJECT INDEX A Aaliji Formation 433, 689, 710 Iraq 376, 435, 435 Syria 434 Aaliji shale 706 Abarug beds 414 Abarug chalk 414 Abarug limestone 414 Abba Fault 41, 54 Abla Formation Saudi Arabia 80 Ablah Group 25, 27 Abouzar (Ardeshir) Field 735 Abqaiq Field 199, 470 Abqaiq Oil Field 639 Absaroka Cycle Latest Carboniferous-Permian 161 paleogeography and geologic history 225-233 Paleozoic 161-193 the end in eastern Arabia 199-214 Triassic 193-199 Absaroka rock units Middle East 163-167 Absaroka sequence 9 Bahrain 186 Iran 191-193 Iraq 189 Jordan 186-189 Kuwait 186 Oman 168-173 Qatar 176-177 Saudi Arabia 178, 178-186 Southeast Turkey 189-190 Syria 190-191 the end in northeastern Arabia 218-225 the end in southwestern Iran 214-217 the end in the central and northern Arabian Gulf 217218 United Arab Emirates 173-176 Yemen 178 Abt Formation Saudi Arabia 27 Abu Dhabi Upper Thamama sequence stratigraphy interpretation 322 Abu Dhabi (Intrashelf) Basin 297, 321 Abu Ghurab Field 471 Abu Hadriya Field 352, 373,470 Abu Jir Fault Zone 41, 54 Abu Khusheiba Formation Jordan 110 Abu Mahara Formation 70, 76 Iran 84 Oman 35, 84, 745, 755 Abu Ruweis Formation Jordan 220, 223, 290

Adaiyah Formation 689, 710 Iran 285 lithostratigraphy 279 Iraq 283-284 southwestern Iran 279 Syria 224 Adana Offshore Basin 522 Aden Volcanic Series 430 Yemen 443 Afandi Formation Syria 129, 129 Afar Depression 15 Afif Terrane 31, 32 African-Ethiopian rifts 16 Afro-Arabian Craton crustal thinning 236 Afro-Arabian Plate 39, 451 consolidation 16 Afro-Nubian Dome 15 Agha Field 732 Agha Jari Field 470, 733 Agha Jari Formation 462, 446 lithostratigraphy 446 Ahmadi Field 471 Ahmadi Formation 532, 534 Bahrain 355 Iraq 356 Kuwait 353 lithstratigraphy and log characteristics 353 Qatar 355 Saudi Arabia 340 Ahwaz Delta 517 Ahwaz Field 420, 470 Ahwaz Sand Iran 438 Ahwaz Sandstone 460, 522 Ain Dar Field 470, 472 Ain Musa Formation Jordan 221, 221 Jamala Member 221 Muhtariqa Member 221 Siyale Member 221 Ajlun Group 358-360, 377, 378, 379 lithostratigraphy 358 Ajram Formation Jordan 110 Akbra Formation Saudi Arabia lithologic log 179 Akbra Shale Formation 254 Yemen 178 Akhdar Group 273,738 Akhdar shale 750 A1 Amar Idsas Fault 31 Suture 29 A1 Aridh Formation 813

Sedimentary Basins and Petroleum Geology of the Middle East Oman 209-211 lithostratigraphy 210 A1 Ayn Formation Oman 207, 211 lithostratigraphy 209 A1 Daww Depression 50 A1 Furat Fault 41, 50, 54 A1 Halaniyat Islands 32 A1 Hamidiyah Field 472 A1 Helaniyat Islands 453 A1 Hisa Formation Jordan 378, 379 A1 Hout Field 471 A1Huwaisah Field 757, 759 structural-contour map of Shuaiba Formation 763 West Oman Sub-basin 762-763 A1 Jafr Basin 522, 607 A1 Jawf Graben 257 A1 Jebissa Field 472, 500 A1 Jhar Fault 58 A1 Khlata Formation Carboniferous glacial facies 168 glacial and fluvio-glacial deposits 169 Oman 169, 756, 758, 759, 767, 769, 770, 771,772 A1 Wajh Formation Saudi Arabia 442 Alan Formation 689, 698 Iran 279, 285 lithostratigraphy 279 Iraq 284 Syria 222 Alborz Mountains 1 Aleppo High 50 Alif Field 473 Allaqi-Heiani Suture 29 Alna Formation Jordan 119 Alveolina Bed 414 Alveolina Limestone 414 Areal Field 521 Amal South Field hydrocarbon traps 760 Amanus Formation Syria 191 Amanus Group 190 lithostratigraphic section 191 Amanus Mountains 57, 89, 126, 135 Amanus region 156 Amanus Sand Formation Syria 190, 191 Amanus Shale Formation Syria 190, 223 Amdeh Formation, Oman 76 Lower Quartzite Member 99 Lower Siltstone Member 99 Middle Shale Member 99 stratigraphy and lithological description 99 Upper Quartzite Member 99 Upper Siltstone Member 99 Saudi Arabia 98 Amin Formation Oman 35, 95, 755 Amiran Formation

814

Iran 370, 372, 420, 435 lithostratigraphy 420 Amman Formation Jordan 378, 379 Amran 257 Amran Graben 523 Amran Group 254, 257-259 Amud Formation Jordan 110 An Nefud 1 Anah Formation Iraq 437 Anah Graben 41, 54, 383 Anah Trough 376, 392 Anatolian Plateau 1 Andam Formation Oman 95-96 Andhur Formation Oman 426 Anjara Formation Jordan 187 Antalo Limestone Formation Ethiopia 257 Antalya Nappes 55 Aqaba Basement Complex 80 Aqiq Volcanics 27 Aqra Formation Iraq 377 Ara evaporite sequence 78, 520, 755 Ara Formation Oman 73-74, 746, 747, 759 evaporites 757 Ara Salt 65 Ara Salt Sea 85 Arab Complex 81 Arab Formation 510, 517, 554, 563, 564, 579, 629, 634, 722, 750 Bahrain 254 Arab A-D members 254 Qatar 269, 271 Arab A-D members 271 lithogical interpretation 270 Saudi Arabia 250-252, 286 Arab A-D members 250-252 United Arab Emirates 263 Arab A-D members 263 Araba Fault 63 Arab-Hith Formation Saudi Arabia stratigraphy and log characteristics 252 United Arab Emirates lithological interpretation 264 Arabia and Eurasia tectonic reconstruction 455 Arabian Basin 516 Arabian Basin of Iraq Cap Rocks 710 Arabian Basin Reservoir Formations 697 Arabian Basin Reservoirs Formation Iran 722-723 Arabian Block 45, 391 Arabian Continental Platform 204 Arabian Craton 758 Arabian Foreland Basin 651

Index Arabian Graben System 39 Arabian Gulf 1, 7, 279, 330, 351,363, 382, 462, 465, 474, 759 boundaries 15 calculated ages of gasoline-range hydrocarbons in oils 507-508, 509 Jurassic production data 497 lithostratigraphic chart of Eocene formations 413 Lower Cretaceous production data 498 Middle Cretaceous production data 499 paleogeographic map of Early Triassic sediments 229 paleogeographic map of Ladinian-Carnian sediments 230

paleogeographic map of Rhaetian sediments 230 Permian production data 497 tectonostratigraphic provinces or zones 520 Upper Cretaceous production data 499 Arabian Gulf Basin 41,474 Arabian Gulf region lateral thermal gradient variations 508, 511 structural trends over major oil and gas fields 495 trap genesis, time of formations and examples of oil and gas fields 493-494 Arabian Peninsula 382, 456, 743 lithostratigraphy of the Cretaceous 311 rotation 23 Arabian Plate 13, 15,233,382, 3835, 384, 393,454, 500, 743,745 geological setting 4 motion 454 rotation 16 subduction 457 Arabian Platform 1,295, 297, 375, 384, 390, 395, 453, 457, 465, 473,496, 510, 521 boundaries 15 Arabian Shield 1, 31,358, 457, 459, 460, 462, 521 boundaries 15 geochronological studies 22 geological map 24 lithostratigraphic units 25 lithostratigraphic units and magmatic arcs 30 stratigraphic units 26 tectonic activity 31 tectonic evolution 30 tectonic sketch map 29 uplift 387 Arabian-Nubian Plate 383 Arabian-Nubian Shield 510 development 28 refraction line 31 Arabo-Nubian Massif fold belts 55--62 Phase 1, consolidation 22-36 Phase 2, tectonic stability 36--37 Phase 3, Hercynian event 37-38 Phase 4, Triassic extensional phase 38 Phase 5, Jurassic and Cretaceous events 38--39

Phase 6, Cenozoic events 39--44 Arabo-Nubian Shield refraction line 32 Arada Formation Jordan 337 Araej Formation 562, 564, 578 Qatar 267-269 Lower Araej Member 269 Upper Araej Member 269 Uwainat Member 269 United Arab Emirates 261-262 lithological interpretation 261 Lower Araej Member 261 Upper Araej Member 261 Uwainat Member 261 Arafat Group 27 Arda Formation Jordan 289, 290 Ain Khuneizir Member 289 Bin Fa'as Member 289 Areban Formation Southeast Turkey 338, 338 Aril Formation 659 Southeast Turkey 224, 498 Aruma Formation 634 Bahrain 414 Saudi Arabia 352, 373, 373 Lina Member 373 Lower Atj Member 373 Middle Atj Member 373 Upper Atj Member 373 Aruma Group 61,297, 344, 363,372, 373, 382, 384, 580 lithostratigraphy 364, 374 lithostratigraphy and log characteristics 364 Aruma limestone 350 Asab Field 472, 590 Asab Oolite 266 Asfar Formation United Arab Emirates 175 Ash Shaer Field 473 Asir Terrane 29, 31 Asmari Formation 580 Asmari Formation 438, 460, 465, 702, 723 Asmari carbonates 517 Iran 49, 419, 420, 445 lithostratigraphy 419 reservoirs 456, 507 Kalhur Member seal 456 Southeast Turkey 437 United Arab Emirates 420, 422, 422, 441,462 Asmari limestone 517, 721 Asmari Limestone Formation Iran seeps 468 Avanah Formation Iraq 435, 436 815

Sedimentary Basins and Petroleum Geology of the Middle East reservoirs 456 Awali Field 471,653 Ayim Formation United Arab Emirates 149 Azab Group 289, 290 Azkand Formation Iraq 437 Azraq Basin 379, 447, 605 Azraq Formation Jordan 447 Azraq Hamza Basin 358 Azraq Sub-basin 432 Azraq-Sirhan Basin 474 Azraq-Wadi Sirhan Basin 502

B Bab A1 Mandab Strait 1 Bab Field 472 Bab Oil Field 595 Baba dome (Kirkuk) 714 Baba Formation Iraq 436 Bahah Group 25, 27 Bahja Field 747 Bahr Formation Saudi Arabia 438 Bahrah Formation Kuwait 373 Bahrain Burial-history curves 556 Field 549 Gas chromatograms 556 Jurassic section 254 mid-Cretaceous 355 Neogene 439 Paleogene 414 Production and Reserves 558 Stratigraphy 551 surface oil and gas seeps 469 the end of the Absaroka sequence 217 Upper Cretaceous 373 Wara Unit 355 Bahrain Field 470 daily production rates 557 Reservoir contribution 557 Bahrain Series 409 Bahram Formation Iran 150 Bahregansar Field 734 Bai Hassan Field 471,506, 712, 714 Baish Group 25, 27 Bajawan Formation Iraq 436 Bakhtiari Formation 438 Iran 446 lithostratigraphy 448 Iraq 446 Syria 449 Balambo Formation 702 Geochemical analysis and interpretation 707 Iraq 334, 336, 500 Baluti Formation 710 Iraq 220, 233,283 Bangestan Group 349, 370, ~721 Bani Khatmah Formation Saudi Arabia 178, 183

816

Barghah Formation Oman 213 Barsarin formation 705 Geochemical analyasis 709 Iraq 285,286 Barut Formation Iran 81, 83, 129 Basal Serpentine Oman 211 Basalt Plateau 607 Batinah Complex 62, 203 Oman 211-213 tectonostratigraphic units, lithostratigraphy 212 Batinah Limestone Blocks Oman 213 Batra Formation Jordan 119 Lower Hot Shale Unit 119 Middle Hot Shale Unit 119 Upper Hot Shale Unit 119 Bayandor Formation Iran 81, 82, 84 Baynunah Formation United Arab Emirates 441 Beciram Formation Southeast Turkey 437 Bedded Brownish Weathered Sandstone Jordan 111 Bedinan Formation 659, 664 Southeast Turkey 123, 128, 498 Beduh Formation Iraq 218, 232 Southeast Turkey 224 Bekhme Formation Iraq 377 Beloka formation 667 Belqa Group 377-380 lithostratigraphy 358 Berwath Formation Saudi Arabia 141, 156 Besni Formation Southeast Turkey 381-382 Besni olistostrome 55 Bibi Hakimeh (oil) Field 732, 735 B idh Volcanics 27 Bih Formation Oman 173 United Arab Emirates 176 Bir Umq Suture 29 Bitlis Massif 32 Biflis Suture Zone 453 Bitlis Zone 454 Biflis-Zagros Zone 653 Biyadh Formation 631, 634 Oman 767 sandstone 757 Saudi Arabia 315, 316, 317-319, 350 lithostratigraphy 318 Biyadh sandstone 319 Border Fold Zone 453 Bozova High 62 Bu Hasa (Oil) Field 321,472,591, 593 Buah Formation Buah carbonates 745 Iran 84 Oman 73, 80, 746, 755 Bukha Field 738 Musandam Sub-basin 772-773

Index Bul Hanine Field 471,571 Buntsandstein 198 Burgan Anticline 384 Burgan Field 471, 517, 527, 663 Burgan (Sandstone) Formation 531, 532, 534 Kuwait 340, 352 Khafji Member 352 lithstratigraphy and log characteristics 353 Safaniya Member 352 Burgan High 32, 391,520 Burgan structure 527, 538 Burgan-Magwa-Ahmadi anticlinorium 528 Burj Formation Jordan 110 Hannah Member 110 Numayri Member 110 Tayan Member 110 Syria 128 Burqan Formation Saudi Arabia 442 Butabul Group 273 Butmah Field 711 Butmah Formation 681, 702 Iraq 283, 284 Syria 224, 516 Buwaib Formation 631, 634 Saudi Arabia 315, 316, 317, 321,330, 333 lithostratigraphy 316 lithostratigraphy and depositional setting 317 Buwayda Formation Jordan 187, 188, 222 Buzurgan Field 712

C Cal Tepe Formation Southeast Turkey 123 Gray Limestone Member 123 Caledonian Orogeny 495 Cambro-Ordovician cycle 694 Cap Rocks 517 Arabian Basin of Iraq 710 Zagros Basin of Iraq 710 carbonate ramp 510 Carlsberg Ridge 15 Cenozoic paleogeography and geologic history 451--458 Central and Eastern Arabian (Platform) 770 mid-Cretaceous 349-355 Neogene 439-441 Central and South-central Oman Sauk sequence 94-96 Tippecanoe sequence 96-97 Central and southwestern Arabia Late Cretaceous 373--375 Central Arabian Arch 52, 226, 523 Central Arabian Graben and Trough System 47 Central Arabian Platform Paleogene 408--428 Uplift 37

Central Oman Sub-basin 738, 745 burial history 751 hydrocarbon trap 759 Saih Rawl Field 770-771 structural development 759 typical burial curve 754 central Saudi Arabia distribution of Cretaceous outcrop 315 lithostratigraphic and sedimentological interpretation of Triassic sediments 197 lithostratigraphy of Lower Cretaceous 316 central Syrian Fault Zone 54 Chalky Zone 411 Chapoghlu Shale Iran 84 Cherrife Field 473 Cherrife Formation 681, 689 Chia Gara Geochemical analysis 709 Chia Gara Formation 702 Iraq 286--287, 377 Chia Zairi Formation Iraq 189, 218 Satina Evaporite Member 189 Chilou Formation 681 Syria 434 Cigli Group 222-223 Coal Bed 286 commercial oil discovery 3 Conularia Sandstone Formation Jordan 116 Cretaceous lithostratigraphy in Iraq, Kuwait, Saudi Arabia, Bahrain, Qatar, United Arab Emirates 312 lithostratigraphy in the Arabian Peninsula 311 lithostratigraphy of southeastern Turkey, northern Iraq, southwestern Iran 314 lithostratigraphy of Syria, Jordan, Saudi Arabia, Yemen, Oman 313 paleogeography and cyclicity 384-392 paleogeography and geologic history 382-392 reservoirs 516 Cretaceous Hajar Supergroup 61 Cretaceous Ridge 462 Crude Oil Geochemistry southeastern Turkey 661 Syrian 683 crystalline basement 22 Cudi Formation Southeast Turkey 224 Cudi Group 291, 336, 338 general lithostratigraphy 291~ " Cyrus Field 349

D Dadas Formation 664 Source-rock analysis 663 Southeast Turkey 128, 151 Dahek Limestone Formation Syria 434 Dahu Formation Iran 129 Dalan Formation 721

817

Sedimentary Basins and Petroleum Geology of the Middle East Iran 192, 192, 217 Nar Member 192 sedimentary description 192 Dam Formation 634 Qatar 439 Saudi Arabia 438, 439, 443 Dammam Dome 411, 471 Early Eocene-Miocene succession 411 Dammam Field 317, 319, 470, 471,517, 653 Dammam Formation 437, 460 Bahrain 414 A1Buhayr Carbonate Member 414 Dil 'Rifah Carbonate Member 414 Foraminiferal Carbonate Member 414 Jabal Hisai Member 414 sedimentological and environmental interpretation 416 sedimentological and environmental interpretations 415 West Rifa Flint Member 416 Iraq 417--418, 435,436 Kuwait 417, 443 units 1-3 417 Oman 426, 427 Qatar 412-414 Abarug Dolomitic Limestone and Marl Member 414 Alat Member 414 Khobar Member 414 Midra Shale Member 414 Simsima Chalk Member 414 Umm Bab Dolomite and Limestone Member 414 reservoirs 456 Saudi Arabia 408, 409, 411-412, 430 Alat Member 412 Alveolina Limestone Member 412 Khobar Member 412 Midra Shale Member 412 Saila Shale Member 412 seals 456 United Arab Emirates 421-422 Dana Conglomerate 433 Dana Conglomerate Formation Jordan 447 lithological section 448 Darari Formation Iraq 189 Darb Formation Qatar 269 United Arab Emirates 262 Dardun Formation Jordan 221 Darius Field 349 Dariyan Formation 721 Iran 330, 331,349

818

Dashtak Formation 729 Iran 217 Aghar Shale Member 217 lithofacies distribution 215 lithology and log characteristics 215 Sedifer Dolomite Member 217 Dead Sea Basin 456 Dead Sea Fault 58 Dead Sea rhombochasm 63 Dead Sea Rift 6, 5024 Dead Sea Transform 454, 456 Dead Sea-Gulf of Aqaba Rift 447 Dead Sea-Jordan Rift 447 Dead Sea-Jordan Rift Transform System 457 Dead Sea-Jordan Valley 62 Dead Sea-Jordan Valley Basin 604-605 Deir Alia Formation Jordan 287 Huni Member 287 Nimr Member 287 Dense Limestone 263 Derdere Southeast Turkey 338 Derdere Formation 659, 6644 Southeast Turkey 360 members 1-5 360 Derenjal Formation Iran 130 Derik Formation Southeast Turkey 81, 123 Desu Complex 81, 82, 83 Devonian-Lower Carboniferous cycle 694 Dezful Embayment 57, 470, 517, 651 Dhabi Arch 283 Dhahab Formation Jordan 288, 290 Dhahkiye Chalk Formation Jordan 434 units 1-3 434 Dhera Formation Oman 327 Dhiban Anhydrite 434 Dhiban Formation 438, 681, 689, 710 seals 456 Syria 449 Dhibi Limestone 245 Dhofar Province 745, 757 Dhruma Formation 516, 537, 628, 634 Bahrain 254, 502 Kuwait 280 Oman 273 Saudi Arabia 245-248, 248, 269 Atash Member 245 Hisyan Member 245 lithostratigraphy 248 Lower Dhruma Member 245 Middle Dhruma Member 245 Dhulaima Field 750 Dibba Formation Oman 327 Dibba Line 13

Index Dibba Zone 54, 157, 175, 363 Dibdibba Formation 438 Kuwait 443, 446, 462 Dibsiyah Formation Saudi Arabia 100--103 Sanamah Member 103 differentiated ramp 510 Digma Formation Iraq 376 Disi Sandstone Formation Jordan 111 Diyab Formation 579, 750 Oman 498, 759 Qatar 269 United Arab Emirates 262 lithological interpretation 262 Diyab oil geochemistry Upper Jurassic 750 Diyab/Dukhan Formation United Arab Emirates 498 Diyab-Dukhan Formations 583 Diyarbakir High 151 Diyarbakir region 156 Diyarbakir trend 658 Diyarbakir-Mardin High 658 Dodan Field 669 Dogger tectonic movements 295 Dokan Formation Iraq 377 Dokan Limestone Formation 702 Iraq 358 Dokhan Volcanics 84 Dolaa Formation Syria 190-191, 2844 Dolaa Group 681 Dorra Field 547 Dorra Field 4711 Dorud Formation Iran 192 sedimentary description 193 Doubayat Group 190 Dubaydib Formation Jordan 120 Dukhan Alveolina Limestone 414 Dukhan Anticline 521 Dukhan Field 568

E Early Cretaceous Cycle 384-388 Iraq 332-336 Jordan 336 Kuwait 330-332 northern, northwestern and northeastern Arabian Platform 3302-338 Southeast Turkey 337-338 Syria 336 Early Paleozoic Iran 129-134 northern Saudi Arabia and Jordan 103 paleogeography and geologic history 134-138 Early Paleozoic sequence Southeast Turkey and Syria 123-129 Early Pliocene tectonic reconstruction 455

East Baghdad Field 522 Eastern and southwestern Arabia Sauk and Tippecanoe sequences 98 Eastern Arabia Mid-Cretaceous 340--348 Tertiary formation outcrops 409 Thamama Group 319-329 Upper Cretaceous 3724-373 Eastern Arabian Platform Paleogene 408-428 Edh Dhira Monocline 433 E1 Bunduq Field 471 E1 Bunduq Oil Field 595 Emam Hasan Field 349 Epeirogenic movement 8 Es Sirr Formation Saudi Arabia 197 Ethiopia Oligocene-Miocene volcanics 395 Ethiopia-Arabian Dome 452 Euphrates Depression 58, 434, 449 Euphrates Formation Iraq reservoirs 456 Euphrates Graben 41,393, 670, 673 Structural cross-section 672 Euphrates Limestone Formation 702 Iraq 437, 449 Euphrates River 285 Euphrates Trough 392 Euphrates-Anah Graben 41, 50, 54 Euphrates-Anah Trough 38, 230, 290, 380, 381,378,388, 391,457 Eurasian Plate 39 Exotic Limestone Oman 211

F Fadhili Field 472 Fahahil Formation Qatar 262, 263, 269, 269 United Arab Emirates 263 Fahliyan Formation 721, 722 Iran 280, 329-330, 331 Fahud Anticline 62 Fahud Fault 62 Fahud Field 472, 738, 759, 760 Foreland (North Oman) Sub-basin 760-762 hydrocarbon trap 760 structural-contour map of Natih Formation 761 Fahud Formation Oman 425 structure 762 Fahud Salt Basin 76, 762 Falah Field 472 Faraghan Formation 720 Iran 192, 226 sedimentary description 192 Farasan Islands 31 819

Sedimentary Basins and Petroleum Geology of the Middle East Fars Group 427 460 Fars Platform 215, 391,395,408,419,458,459, 460, 465 Fars Province 330, 349, 393, 408, 418, 420, 422 stratigraphic sequence 48 Fartak Syncline 523 Fartaq Formation Oman 348 Limestone Member 348 Marl Member 348 Marl-Shale Member 348 Yemen 339, 362, 374 Fassua Formation Jordan 378 Fateh Field 472, 507 Fateh Oil Field 595 Fatima Formation Saudi Arabia 79, 80, 85 Fatima Group 80 Fatima limestone 33 Fatimah Volcanics 27 Fayyadh Field 747 Fiqa Formation Oman 367, 758, 764 Arada Member 367 lithofacies 365 lithostratigraphy and log characteristics 368 Shargi Member 367 Qatar 372 Arada Member 372 Shargi Member 372 United Arab Emirates 362, 363,363 Arada Member 363 Shargi Member 363 First cycle Early Cretaceous 311-340 first-order cycles 10 Fold Zone 453 Folded Belt 651 Foothills Structural Belt 57 Foothills Zone 285, 286, 287, 438, 444, 449 oil and gas seepages 468 Foreland (North Oman) Sub-basin Fahud and Natih fields 760-762 Fuheis Formation Jordan 359 Nodular Limestone Unit 359 Fuwaira Field 4711

G Ga'ara Arch 393 Ga' ara Formation Iraq 233 Gach-i-turush 691 Gachsaran 733 Formation 582 Gachsaran evaporites 422, 438 Gachsaran Field 470, 733 Gachsaran Formation 438,460, 465, 517, 730 evaporites 517 Iran 50, 420, 422, 444--445, 460 lithostratigraphy 419, 445

820

members 1-7 445 seals 456 United Arab Emirates 441,441 units 1-3 441 Gachsran oil field 7322 Gadvan Formation 722, 729 Iran 330, 330, 331 Gahkum Formation Iran 192, 498 Garadash Formation Iran 83 Garagu Formation 702 Iran 349 Iraq 287, 336 Garau 721 Garau Formation 721, 724 Iran 330, 330, 349, 498 lithostratigraphic units 331 units 1-8 330 Garish Group 78 Garzan Anticline 57 Garzan Field 473, 669 Garzan Formation 517, 659 Geirud Formation Iran 130, 150 members A-D 150 Geli Khana Formation Iraq 218, 218, 232 Geochemical analysis Late Jurassic 708, 709 Geochemical analysis C 15+ fraction 506 geochemical typing parent source of oils 502 Geochronological studies Arabian Shield 22 Gercus Anticline 57 Gercus Formation 667 Iraq 436 Southeast Turkey 437 Gercus Molasse Trough 435 Germav Formation 660, 667 marine shale 522 Southeast Turkey 380, 382, 437, 498 members 1-3 384 Syria 500 Germik Formation Southeast Turkey 437, 449 Ghaba North Field 757, 770 Ghaba Salt Basin 52, 65, 84, 85, 745, 750, 758 rift origin 758 Ghabar Group 78 Ghaba-South Oman Salt Basin 77, 84 Ghail Formation United Arab Emirates 176 Ghalilah Formation United Arab Emirates 201 lithostratigraphy 203 Ghar Formation 438, 722 Ahwaz Sandstone Member 420 Iraq 420, 443

Index Kuwait 420, 439 443 Ghar sands 460 Ghareb Chalk 433 Gharif Formation lithostratigraphy of Safiq South- 1 171 Oman 169-171, 750, 756, 756, 757, 755, 766, 767, 768, 769, 770 Haushi Limestone Member 170 reservoir facies 766 structural-contour map 766 Ghawar (Supergiant) Field 199, 315, 319, 351,470, 517 Ghawar Anticline 384, 520 Ghawar Dome 472 Ghawar High 391 Ghawwas Formation 634 Saudi Arabia 442 Ghiras Formation Yemen 374 Ghona Formation Syria 336, 360 Ghouna Field 472 Ghudun Formation Oman 96, 755 Ghudun-Khasfah Fault 84 Gilsonite 469 Gimo Suite 388 Glaciation Late Ordovician 139 Gomaniibrik Formation Southeast Turkey 153, 190 members A-C 190 Gotnia Anhydrite Formation 698 Gotnia Formation 517, 532, 705, 710 Geochemical analysis 708 Iran 279 lithostratigraphy 279 Iraq 280, 283, 285, 286 equivalents 283 Graptolite Sandstone Formation Jordan 116 Great Hercynian Unconformity 161 Great Nefud 183 Greater Arabian Basin 523, 528 Hydrocarbon Habitat 527 Gulailah Formation 578 Gulailah Formation Qatar 267 United Arab Emirates 259, 261 Gulailah/Jilh Formation Qatar 213-214 United Arab Emirates 199 Gulf of Aden 1, 5, 46, 393, 395, 452, 453,457 formation 453 volcanism 41 Gulf of Aden Basin 452, 647 Gulf of Aden Rift 44 Gulf of Aden Sub-basin 50-52 Gulf of Aden-Red Sea area extensional tectonics 395 Gulf of Aqaba l., 6, 63 Gulf of Aqaba Strike-slip System 430 Gulf of Aqaba Transform 453

Gulf of Aqaba-Dead Sea 393 Gulf of Aqaba-Dead Sea Rift-Transform System 16 Gulf of Iskenderun 468 GulfofOman 1, 46, 441,453, 738, 743 simplified tectonic map 743 Gulf of Oman Sub-basin 741,772 Gulf of Suez 453 Gulf of Suez Basin 474 Gulf of Suez Shear and Rift System 393 Gulf of Tadjura 453 Gulneri Formation Iraq 377 Guri Formation Oman 428 Gurpi Formation 723, 729 Iran 349, 370, 371,419, 498 Emam Hasan Limestone Member 371 Lopha Limestone Member 371 Oman 370, 773 Guweyza Limestone Formation Oman 278 lithostratigraphic interpretation 278 Guweyza Sandstone Formation Oman 278 lithostratigraphic interpretation 278

H Ha'il Arch 89, 147 Ha'il-Ga'ara Arch 651 Ha'il-Rutbah Arch 37, 53, 62, 88, 189, 520, 522 Saudi Arabia 137 Ha'il-Rutbah-Ga'ara Arch 37, 53, 651 Ha'il-Rutbah-Khleissia High 383 Habshan Formation 579 Oman 325,327 lithostratigraphy 326 United Arab Emirates 264, 319, 320-321 Habshiya Formation reservoirs 454 Yemen 426, 429 reservoirs 456 Hadhramout 77, 372 Hadhramout Arch 41, 52, 246, 391, 451 schematic cross-section 454 Hadhramout Group 426, 429 Hadhramout High 48 Hadhramout Syncline 523 Hadhramout-Jeza-Qamar Basin 644 Hadiena Formation Iraq 377 units 1-3 377 Hadrukh Formation Saudi Arabia 412, 438, 439, 449, 460 Haft Kel Field 734 Hagil Formation Oman 173 United Arab Emirates 176 Haima Group 35, 65, 94-95, 745, 753,758, 759, 767, 768, 770, 771,772 Clastic succession 738

821

Sedimentary Basins and Petroleum Geology of the Middle East play concept 523 Haima sequence 755 Haima Supergroup stratigraphic subdivision 756 Hajir Formation 76 Halaban Group 25 Halfa Formation Oman 209 lithostratigraphy 210 Haliw Formation Oman 209 lithostratigraphy 210 Halobia Limestone 206 halokinetic movement 495 Halul Formation 580 Qatar 372 United Arab Emirates 363 Hamam Formation Jordan 290-291 Hamisana Shear Zone 29 Hamlah Formation Qatar 214, 266 United Arab Emirates 259, 259-261 lithological interpretation 260 Hammamat Formation Egypt 65, 85 Hamrat ad Duru Group 327 Hamrat Duru Group 206-211, 277 Hamrat Duru Range 59 Hamza Field 447 Hamza Formation Jordan 379 Hamza Graben 379, 432 Hamza Oil Field 222 Hamzeh Field 473 Hanadir Formation Saudi Arabia 112, 139 Hanadir Shale Member 633 Handof Formation 659 Southeast Turkey 498 Hanifa Formation 566 Hanifa Formation 565, 628, 634, 750 Bahrain 254, 502 Oman 273 Qatar 269, 502 Saudi Arabia 250, 285, 500, 503 lithostratigraphy 249 United Arab Emirates 262 Haradh Field 470, 472 Haradh Formation Oman 755, 758 Harmaliyah Oil Field 638 Harrat Ash Sham Basaltic Group 447 Harshiyat Formation Oman 348 Yemen 339, 362, 374 Rays Member 362 Sufla Member 362 Hartha Formation 702 Iraq 372, 376, 377 Kuwait 373 Hartha-Bahra Formation Kuwait 372 Harur Formation Iraq 151 822

Harut Formation Yemen 78 Hasa Group 393, 408, 409--412, 412-414, 415-417, 417-418, 419, 421-422, 426, 429 lithostratigraphy and depositional setting 417 lithostratigraphy and log characteristics 427 Hasanbeyli Formation Southeast Turkey 154 Haushi Formation 562,564, 565 Qatar 176 Haushi Group 169, 738, 7535, 756, 768, 77000 play concept 523 porosity-depth relationship 756 Haushi shale 752 Hawar Formation 565 Bahrain 325 Qatar 325 Hawar (Shale) Formation 319 Qatar 326 Hawasina Allochthonous Unit 61 Hawasina and Semail Thrust Complex 737 Hawasina Assemblage 61,203, 206-211 Hawasina Allochthonous Unit 206 Hawasina Basin 38, 347 Hawasina Complex 391 Hawasina M61ange Oman 211 Hawasina Nappe 422, 459, 520, 758 Hawasina Ocean 38 Oceanic sediments 743 Sediments 3933 Series 206 Hawasina Thrust sheets 175 Hawasina Window 59, 328 Hayane Formation Syria 336, 360 Haybi Complex 61,203, 211 tectonic stratigraphy 212 Volcanics 38, 62 Oman 211 Hazar Unit (Taurus Mountains) 55 Hazim Formation Jordan 379 Hazro Anticline 89 Hazro Formation 659 depositional models of facies association 154 Southeast Turkey 153, 498 Heft Kel Field 470 Heil Formation Syria 190, 191 Hercynian Orogeny 161,495 Unconformity 192, 225 Uplift 225 Hibr Formation lithostratigraphic sections 431 Saudi Arabia 430 High Folded Zone 285,286, 287,358,376, 377, 380, 449 High Zagros fields 517 Hihi Formation Jordan 290 Hijam Formation Oman 76 Hijaz Escarpment 31 Hijaz Orogenic Cycle 27 Hijaz Terrane 29

Index Hijaz-Asir Province 31 Hippuritic Limestone 349 Hisban Formation Jordan 221, 222 Hiswah Formation Jordan 119, 119-120 Hisyan Pass 248 Hith (Anhydrite) formation 316, 517, 564 Hith Formation 519, 631, 634, 729 Bahrain 254 Iran 280, 327 Iraq 283 Qatar 271 Saudi Arabia 250, 252, 273 United Arab Emirates 263-266 Asab Member 264-266 Fateh Member 266 Mender Glauconite Member 266 Hofuf Formation Qatar 439 Saudi Arabia 438, 439, 439, 444, 446 44, 462 United Arab Emirates 441 Hormuz evaporites 32, 41, 77, 520 salt movements 521 salts 35, 651 Hormuz Formation Arabian Gulf 77 Iran 83 Iraq 81 Hormuz Sea 85 Hormuz Series 75 Hout Field 547 Hudayb Group 187-189 Hudeib Sandstone Shale Formation Jordan 187 Hummar Formation Jordan 359 Echinoid Limestone Unit 359 Huqf Arch 393,741,743 Huqf Axis 84, 745, 746 Huqf Group 84, 169, 498, 743, 745, 746, 753, 755 age 74-76 clastic and carbonate/evaporite shelf 738 Iran 84 Oman 84, 135 play concept 523 rocks 35 Yemen 78 Huqf Megacycle 85 Huqf oil geochemistry Infracambrian 747 oils 750 source-rock sequence 751 Sub-basin 743, 745 simplified geological map 747 Swell 459 Uplift 743 stratigraphy 744

Huqf-Haushi Arch 52, 69 Huqf-Haushi Axis 32, 521 753 Huwayra Formation Jordan 188 Hydrocarbon generation and accumulation mechanism 508 Hydrocarbon Systems SAudi Arabia 611

I Ibra Formation Oman 211 lithostratigraphy 211 Ibrahim Formation Iraq 437 Idd E1 Shargi Field 522, 568 Idd el Shargi Field 471 Ilam Formation 580, 721 Iran 349, 370-371 Oman 3700 United Arab Emirates 362, 363 FPD gas chromatogram and m/z 217 mass fragmentogram of Southwest Fateh Field 507 Ilebeyk Formation Iran 130 Imbricated Belt 5211 Zone 287, 3777, 438, 651 Inbirik Formation Southeast Turkey498 Infracambrian lithostratigraphic chart 68 Middle East 65-86 reservoirs 511, 758 rock units 67 salt basin distribution 66 Infracambrian salt halokinetic movement 495 salt basins 523 salt pillows 62 infra-Tassilian surface 36 age 35 Interior Fars Province 372 Iran Absaroka sequence 191-193 Arabian Basin Reservoirs Formations 722-723 Asmari OIigocene-Miocene reservoirs 507 distribution of Late Permian carbonate facies 228 Early Paleozoic 129-134 Kami Group 329-330 Kaskaskia sequence 150 lithostratigraphic correlation chart of Cenozoic formations 408 lithostratigraphic correlation of the Precambrian to early Paleozoic 132 oil and gas 717 Reservoir Characteristics 720 Sauk sequence 129-133 Source Rocks and oil Geochemistry 723 Stratigraphy 716-718 Structure and Traps 718 surface oil and gas seeps 468ff-469 Tippecanoe sequence 133-134 Zagros Basin Reservoir Formations 720 Iran B lock 13 Iran Plate 39, 453 823

Sedimentary Basins and Petroleum Geology of the Middle East Sub-plate 22 Iraq Absaroka sequence 189 Early Cretaceous 330-336 Field size distribution 692 hydrocarbon potential 691 Jurassic section 283-287 Kaskaskia sequence 150-151 Late Cretaceous 376-377 lithostratigraphic correlation chart of Cenozoic formations 407 major fields 692 mid-Cretaceous 356-358 oil seepage 691 Seal and Seal Formations 706-710 surface oil and gas seeps 469 the end of the Absaroka sequence 218-220 Tippecanoe sequence 120-121 Zagros Folded Zones 693 Iraq-Iran Basin 462 Irq A1 Amir Formation Jordan 220-221, 223 Abu Yan Member 221 Bah Hath Member 221 Shita Member 221 Isfahan Basin 226, 524 Ishmas Volcanics 27 IIzhara Formation 562, 5646 Qatar 269 United Arab Emirates 261 lithological interpretation 260

J Jabal Cap Formation Bahrain 439 sedimentological and environmental interpretation 440 Jabal Fanqi Field 471 Jabal Hafit 460 Jabal Kibrit Formation Saudi Arabia 442 Wadi Waqb Member 442 Jaddala Formation 681 Iraq 418, 435 Syria 433,434, 500 Jafnayn Formation Oman 425 lithostratigraphy 424 Jafnayn Limestone Formation Oman 423 Jafr Basin 447 Jafr Formation Jordan 447 Jahhad Volcanics 27 Jahrum Formation 459, 722 Iran 408,419, 435,436 lithostratigraphy 419 units 1-3 419 reservoirs 456

824

Jaizan Sub-basin 441,622 Jamal Formation Iran 193 Jambur formation 7066 Field 471 Jarn Yaphour Field 472 Jauf Formation 626 Kuwait 150 Saudi Arabia 141-147, 502 Hammamiyat Limestone Member 146 Qasr Limestone Member 146 Sabbat Shale Member 145 Tawil Sandstone Member 145 stratigraphy and isopach map 145 United Arab Emirates 149 Jawan field cross-section 715 Jawan Formation 702 Iraq 336, 357 Jawan, Najmah and Qaiyarah structures 715 Jebalah (Jubaylah) Group 27 Jebel Akhdar 76, 204, 274, 325, 327 Window 59 Jebel Dukhan structure 471 Jebel ed Drouz Plateau 462 Jebel Hafit 422 Jebel Nakhl Window 59 Jebel Sinjar 449 Jebel Wasa Formation Oman 204, 206 Jebissa Oil Field, Syria geochemical characteristics 688 Jeribe Formation 6813 Iraq 438, 449 Syria 4491 Jeribe (Limestone) Formation, 500, 703 Jeza Formation Yemen 429 Jibal A1 Tuwaiq 259 Jiddah Group 25 Jilh Formation Bahrain 217 lithostratigraphic units 218 Kuwait 218 Oman 203 lithology and log characteristics 204 Saudi Arabia 198 United Arab Emiratesm lithology and log characteristics 200 Jilh Limestone Formation Saudi Arabia 197 Jizan Volcanic Formation Saudi Arabia 442 Jordan Absaroka sequence 186-189 Early Paleozoic 103--111 Exploration wells 599 exploration wells 603 Jurassic section 287-291 lithological interpretation 220 lithostratigraphy of Cretaceous-Lower Tertiary formations 338 major sedimentary basins598

Index mid-Cretaceous 358-360 Neogene 447-4499 Paleogene 431-434 Sauk sequence 108 Source-rock potential 601 stratigraphic chart of Jurassic formations 289 surface oil and gas seeps 469--470 the end of the Absaroka sequence 220--223 Tippecanoe sequence 115-120 Traps, reservoirs and source rocks 600 Jordan Graben 462 Rift 447 Jordan Valley Fault 63 Jordan Valley-Dead Sea-asphalt and heavy oil 469 Fault System 45, 54, 63 Jordan-Wadi Araba Graben 465 Jubailah Formation 565, 6291, 634 Bahrain 254, 502 Oman 274 Qatar 269 Saudi Arabia 250, 285, 311, 5033 lithostratigraphy 249 Jubailah Limestone 311 Jubaylah Formation Saudi Arabia 84 Jubaylah Group 25, 80 Judea Formation Syria 336, 360 Juqjuq Volcanics 27 Jurassic paleogeography and geologic history 291-295 Jurassic Chia Gara formation 705 Jurassic production data Arabian Gulf 497 Jurassic section eastern Arabia 259-271 northeastern Arabia 280--287 northwestern and northern Arabian Platform 287-291 Oman 271-279 Saudi Arabia and Bahrain 245-254 southwestern Iran 279-280 Yemen 254-259 Juweiza facies 422 Formation Oman 367 United Arab Emirates 362, 365

K Kahar Formation Iran 81, 82, 84 Kahar or Morad Series 82 Kahfah Formation Saudi Arabia 112-113 Kahmah Group 319, 7555 Oman 325-329 Kahwah Group reservoirs 759 Kaista Formation Iraq 151 Kalhur (Limestone) Formation 539, 702 Kalshaneh Formation Iran 130 Kangan Formation 721, 729 Iran 216-217 lithofacies distribution 215 Kaprulu shale 128 Karababa Formation 659, 664

Karababa A Member Source-rock-quality 666 Southeast Turkey 498 Southeast Turkey 338, 380 Karabogaz Formation 659, 664, 667 Source-rock-quality 667 Southeast Turkey 338, 380, 498 Karasu Graben 135 Karatchok Field 472, 670 Karim Formation Oman 755, 758, 759 Karima Mudstone Formation Iraq 286, 287 Karoo glaciations 10 Kashkan Formation Iran 419, 420, 436 lithostratigraphy 420 Kaskaskia rock units 144 Kaskaskia Cycle Middle East 141-159 paleogeography and geologic history 156--159 Kaskaskia sequence 37 Iran 147-148 Iraq 148-149 Kuwait 147 northern Saudi Arabia 137-144 Oman 146-147 Qatar 145-146 Southeast Turkey 149-152 southwestern Saudi Arabia 144-145 Syria 152 United Arab Emirates 146 Kastel Formation 665, 667 Southeast Turkey 380 Kastel Formation Foredeep Saudi Arabia 55 Kavir Basin 522 Kazhdumi Formation 516, 517, 722, 724, 7291 Iran 331,349, 349, 498 Oman 348, 773 Kerman Basin 522 Kermanshah Ophiolite 393 region 297 Kermav Formation Southeast Turkey 435 Syria 434 Kevan Nappe 55 Khabaz formation 706 Khabla Formation Yemen 78 Khabour Formation Iraq 120 Quartzite 120 Quartzite Formation 698 Quartzite-Shale Formation Iraq 151 Khafji Field 471,544 Khafji Member 516 Khail Anhydrite Series 199 Khami Group 722 Iran 329-330 Khanasser Formation Syria 129

825

Sedimentary Basins and Petroleum Geology of the Middle East Khaneh Kat Formation Iran 217 lithofacies distribution 215 lithological interpretation 217 Khangiran Field 472 Kharaib Formation 564, 579 Bahrain 325 Limestone 319 Oman 325, 327, 755, 758, 764 lithostratigraphy 326 Qatar 324, 324 United Arab Emirates 321 Kharj Formation Saudi Arabia 439 Kharus Formation Oman 76 Khasib Formation 532, 710 Iraq 376 Khasib/Mutriba Formation Kuwait 373 Khatiyah Formation 564, 565 Qatar 355, 502, 521 United Arab Emirates FPD gas chromatogram and m/z 217 mass fragmentogram, Fateh Field 507 Khatiyah/Mishrif formations Oman 348 Khleissia 694 Arch 53 High 53, 190, 232, 383, 390 Paleohigh 383 Uplift 438 Khreim Group 116 Khufai Anticline 70, 76 Carbonate rocks 746 Khufai Formation Iran 84 Oman 70, 135, 169, 746, 755 Khuff carbonate reservoirs 517, 765 KhuffFormation 516, 553, 562, 578, 627, 634 7224, 753 Bahrain 186, 502 Kuwait 186 Oman 168, 171,171, 226, 756, 758, 759, 765 carbonates 758 Qatar 177 sedimentological description and log characteristics 177 Saudi Arabia 161, 180, 182-186, 500 Ash-Shiqqah Member 185 Basal Khuff clastics 185 Duhaysan Member 185 generalized stratigraphy and isopach map 162 Huqayl Member 185 isopachs 182 Khartam Member 185 major environments and regional facies 183 Midhnab Member 185 sedimentological interpretation and suggested no-

826

menclature 185 United Arab Emirates 175, 498 Khuff A-D units 175 sedimentological interpretation 174 Khuff Limestone 226, 523 Saudi Arabia 168, 189 Khuff Limestone sequence 9 Khurais Anticline 520 Khurais Field 317, 503, 620 % TOC, $2 pyrolysis yield and hydrogen index 503 Khurais High 520 Khurasaniyah Field 351 Khureij Formation Jordan 360 Khurmala Formation Iraq 435 Khursaniyah Oil Field 639 Khusayyayn Formation lithostratigraphy 148 Saudi Arabia 148-149 Wajid Plateau 102 Khushsha Formation Jordan 120 Khuzestan Province 330, 349,371,385, 418,419, 420, 446,470 Kial Formation Saudi Arabia 442 Kidan Field 523 Kifl Formation Iraq 358 Kimmerian tectonic activity 285 Kiradag Formation 664, 667 marine shale 522 Kirkuk formation 706 Kirkuk (or Sirwan) Embayment 651 Kirkuk Block 41, 42 dome 714 Embayment 57, 517 Field 470, 506, 711, 714 Group 436-437, 517, 703, 706 reservoirs 456 Kirsehir Massif 437 Kirtas Formation Southeast Turkey 154 ~Kohlan Formation Oman 279 Yemen 178, 254, 255-257, 257, 502 lithostratigraphy 256 Kolosh Formation Iraq 435 Kometan Formation 702 Iraq 377 Kopet Dagh 38, 383 Koprulu Formation Southeast Turkey 153-154, 498 Korkandil Formation Southeast Turkey 380 Koruk Formation Southeast Turkey 126 Limestone Member 126 Lower Dolomite Member 126 Kuh-i-Mund Field 730 Kurdestan 465 Kurnub Group 336 lithostratigraphy 337, 358

Index Kurnub Sandstone 290, 356, 358 Jordan 222, 291 Kurra Chine Formation 680, 683, 688, 702 Iraq 218, 231,284, 500 Syria 221, 500, 516, 524 Kuwait Absaroka sequence 186 Early Cretaceous 330-332 Jurassic section 280-283 Kaskaskia sequence 150 lithostratigraphic correlation chart of Cenozoic formations 407 lithostratigraphic correlation of Triassic sediments 219 lithostratigraphy 121 mid-Cretaceous 352-354 Neogene 443 Paleogene 415--417 Reservoir Rocks 530 source-rock potential 536 Stractural History 528 surface oil and gas seeps 469 the end of the Absaroka sequence 218 Tippecanoe sequence 121 TOC, pyrolysis, kerogens 535 Upper Cretaceous 373 Kuwait and the Neutral Zone Mesozoic lithostratigraphy 528 Kuwait Arch 526 Kuwait major oil fields 529 Kuwait-Saudi Arabia Neutral Zone 526

L Laffan Formation 565 Oman 365, 370 lithofacies 365 Qatar 372 shale 5253 United Arab Emirates 362, 363 Laffan Shale 517 Lahbari Syncline 446 Lali Field 470, 732, 733 Lalun (Sandstone) Formation 81 Iran 83, 129, 129, 137 Lashkerak Formation Iran 133, 133 Lashteag Limestone 349 late Aptian sea-level rise 388 Late Carboniferous-Early Permian glacial deposits correlation diagram 170 Late Cretaceous central and southwestern Arabia 373-375 Iraq 376-377 northern Arabian Platform 375-382 Oman 365-370 Saudi Arabia 373 Southeast Turkey 380-382 Syria 380

United Arab Emirates 363-365 Yemen 374-375 Late Cretaceous Cycle 390-392 Late Cretaceous global, eustatic, sea-level rise 39 Late Ordovician glaciation 10, 88 Late Paleozoic paleogeography and geologic history 156--159 Latest Carboniferous-Permian Absaroka Cycle 161 Lebanon surface oil and gas seeps 469-470 Lekhwair Field 325, 750, 759 structural cross-section and structural-contour map of Shuaiba Formation 764 West Oman Sub-basin 763-764 Lekhwair Formation 579 Oman 325, 327 lithostratigraphy 326 United Arab Emirates 319, 321 Lekhwair High 766 Uplift 385 Block 62 Fracture (Zone) 6, 521 Platform 45 Levant Shear Zone 452 Levantine Fracture System 4 Levantine Plate 4 Lice Formation Southeast Turkey 451 Lisan Formation Saudi Arabia 443 Lisan lithofacies 448 Lisan Marl Formation Jordan 4480-449 lower unit 448 middle unit 448 upper unit 448 Lisan Peninsula 448 Lower Anhydrite 263 Lower Aruma Formation 633 Iran 436 Lower Brownish Sandstone Jordan 108 Lower Cretaceous Yemen 339-340 Lower Cretaceous Cycle 297 Lower Cretaceous production data Arabian Gulf 498 Lower Dhruma Formation Saudi Arabia 267, 500 United Arab Emirates 261 Lower Fars seeps 468 Lower Fars Formation 438, 517, 6891, 702, 710 Iran 460 Iraq 443 Kuwait 443 Oman 428 Qatar 439, 465 seals 456 Syria 449, 449 Lower Haima Formation Oman 94-95 Lower Jubailah Formation 564 827

Sedimentary Basins and Petroleum Geology of the Middle East Lower Jubailah Formation Qatar 502 Lower Limestone Group 412 Lower Mauddud Formation Qatar 502 Lower Murdama Volcanics 27 Iraq 357 Lower Qamchuqa Group 334 Lower Sudair Formation 634 Lulu Field 471,547 Lurestan 408 Lurestan Basin 236, 292, 297, 51666 Lurestan Province 349, 370, 371,372, 418, 419, 420, 446, 4591 Lut Block 456, 522 Lycian Nappes 55

M M'sad Formation Iraq 356 Ma'an Nummulitic Limestone Formation Jordan 434 Ma'rib-Jawf-Shabwa-Balhaf Graben System 644 Ma'in Fonnation Jordan 185, 187, 219 Himara Member 219 Nimra Member 220 Ma'jnoon Field 471 Madbi Formation Yemen 258, 259 Maden Unit (Taurus Mountains) 55 Magna Group 442 Magwa Field 471 Magwa formation Kuwait 340, 353-354 lithostratigraphy 354 Mishrif Member 354 Rumaila Member 354

Mahatta Humaid Formation Oman 74 Mahil Formation Oman 202, 203 lithostratigraphy 203 Mahra Group 337 Mahwis Formation Oman 35, 95, 137, 755, 756, 758, 772 Main Zagros Thrust 51397, 63, 229 Major oil and gas fields in Southeast Turkey 654 Makhul Formation Iraq 286 287 Kuwait 330 lithostratigraphy 332 Makhul Zone 50 Makran area, Iran oil seeps 468 Fold Belt 522 ranges 1 Malaya Unit (Taurus Mountains) 55 Malm Trough 295 Manifa Field 351 Mansiyah Formation 634 Saudi Arabia 442 Mansuri Field 420 Maqam Formation Oman 2024-204

828

lithostratigraphy 205 members A-F 206 Maradi Fault Zone 54, 737, 745 Mardin Group 337-338, 517, 6591, 667 lithostratigraphy 339 Mardin High 53-54, 62, 151, 190, 292, 385, 388, 391 Mardin Paleohigh 236, 383 Uplift 287 Margham structure 588 Margham Field 472 523 Gas-Condensate Field 594 Marib Graben 257, 473 Marib-Shabwa Basin 474 Markada Formation Syria 129 Group 154 Marmul Anticline 757 Marmul Field 472, 523, 7380, 757 hydrocarbon trap 759 South Oman Sub-basin 767-770 structural-contour map of Nahr Umr Formation 769 Marrat Formation 516, 628, 634 Bahrain 254 Kuwait 280 units A-E 280 Oman 771 Saudi Arabia 245, 273, 285, 311,500 Lower Member 245 Middle Member 245 Upper Member 245 United Arab Emirates 259, 261 lithological interpretation 260 Marun Field 470 Masirah Basin 523 Masirah Fault Zone 743 Masirah Graben 743, 758 stratigraphy 744 Masirah Sub-basin 741,743 Masirah Transform Fault 54 Masirah Trough 84 Masjid-i-Sulaiman 716 Masjid-i-Sulaiman Anticline 470 Masjid-i-Sulaiman Field 468, 470, 473,730, 731 Massive Limestone Formation 681 Syria 360 Massive White Sandstone 338 Matiyah Formation Saudi Arabia 429 Mauddud Formation 315, 531, 534, 564, 565 Bahrain 355 Iraq 356, 357 Kuwait lithstratigraphy and log characteristics 353 Oman 345, 348 Qatar 355, 521 United Arab Emirates 341, 344

Index Mauddud Limestone 528 Kuwait 352 Mauddud Wara contact 334 Maydan Mahzam Field 471,571 Mayhah Formation Oman 204, 277, 3280--329, 341 C Member 328 D Member 328 facies model 277 facies models for C and D members 329 lithostratigraphic interpretation 276 Member A 277 Member B 277-278 Medina Series 78 Medj-Zir Formation Yemen 374 Menderes Massif 437 Menderes-Taurus Massif 32 Mender-Lekhwair Paleohigh 408 Meshad Basin 522 Mesopotamian (central Iraq) Sub-basin 50, 522 Mesopotamian Basin 285, 384, 385, 388, 390, 391 Mesopotamian Foredeep 55, 63, 434, 449 Mesopotamian Trough 297 Mesopotamian Zone 438 Metallo-porphyrins 706 Mi' aidan Formation 76 Mid-Cretaceous Yemen 362 Bahrain 355 central and eastern Arabia 349-355 Cycle 388-390 Iraq 356-358 Jordan 358-360 Kuwait 352-354 northern Arabian Platform355-362 Oman 344-348 Qatar 355 Saudi Arabia 350-352 Southeast Turkey 360-362 southwestern Iran 349 Syria 360 United Arab Emirates 340-344 Mid-Cretaceous Cycle 297 Middle Anhydrite 263 Middle Anhydrite Marker 175 Middle Cretaceous production data Arabian Gulf 499 Middle Dhruma Formation Saudi Arabia 500 Middle East Absaroka rock units 163-167 annual crude production 478-481 averaged oil reserve addition 477 cap rocks (seals) 517 Cenomanian paleogeography 390 Coniacian-Santonian paleogeography 391 Cretaceous rock units 298-310

crude oils marine organic matter 508 cumulative percentage-frequency plot by number of fields 482 cumulative percentage-frequency plot by reserve 482 current oil status 473--522depositional environments of Late Carboniferous sediments 227 depositional setting of Early Carboniferous sediments 158

depositional setting of Early Miocene 463 depositional setting of Late Permian sediments 228 depositional setting of Paleocene-Early Eocene sediments 457 Early Paleozoic Quiescent Phase 87-138 Early Paleozoic rock units 90-93 Early to Middle Albian paleogeography 389 Early to Middle Valanginian paleogeography 386 facies distribution of Early Earliest Middle Miocene 463

facies distribution of Late Miocene-Holocene 464 facies distribution of Middle-Late Eocene 461 facies distribution of Oligocene 461 facies distribution of Paleocene-Early Eocene 458 five-year averaged number of giant/supergiants 482 oil reserve addition of giants/supergiants 482 frequency and cumulative-frequency plots of giants/ supergiants 482 geochemistry of oil and gas 502-510 giant and supergiant field data 489 giant and supergiant fields 490 history of exploration 470--473 hydrocarbon habitat 467-470 hydrocarbon productivity 4891-492 Infracambrian 65-86 isopach map 87 isopach map of Cenozoic sediments 394 Cretaceous sediments 310 Jurassic sedimentary rocks 235 Jurassic lithostratigraphic correlation chart of the northern part 238 the southern part 237 Jurassic rock units 239-244 Kaskaskia Cycle 141-159 Kaskaskia rock units 144 Late Albian-Early Cenomanian paleogeography 389 late Mesozoic part of the Zuni Cycle 297-392 Late Valanginian to Early Barremian paleogeography 386

Latest part of the Zuni and Tejas cycles Cenozoic 393-408 Lithofacies distribution of Triassic sediments 231 Lithostratigraphic chart of the Triassic (northern part) 196

Lithostratigraphic chart of the Triassic (southern part) 195

Lithostratigraphic correlation chart (southern part) 406

829

Sedimentary Basins and Petroleum Geology of the Middle East Lithostratigraphic correlation chart of the Paleozoic (northern part) 95, 143 Lithostratigraphic correlation chart of the Paleozoic (southern part) 94, 142 major tectonic elements 44 major tectonic events 16, 17 map of oil and gas seepages 467 Middle Aptian paleogeography 387 Middle to Late Barremian paleogeography 387 Neogene 437--451 Paleogene 396-437 paleogeographic map of Late Liassic 293 Bathonian 293 Cambrian 136 Ordovician 137 Oxfordian-early Kimmeridgian 294 Silurian 138 Tithonian 2964 paleogeographical interpretation of Early Permian sediments 227 paleogeographical setting of Late Devonian sediments 158

paleogeography 456 petroleum potential 467 producing formations 513-514 sealing formations 518-519 potential plays 522-523 present-day mega-tectonic framework 394 reservoir rocks 510-517 sedimentary basins 46 source rocks 492-502 source-reservoir relations 507 source-rock formations 501 statistical summary of giant and supergiant fields 489 summary of tectonic events during Cenozoic 450 supergiant and giant oil and gas fields 483-488 surface oil and gas seeps 467-470 tectonic history review 22 tectonic reconstruction from Late Oligocene to early Miocene 455 Tethyan ophiolites 34 timing of trap formation 521 total recoverable reserves 474 total thickness of Triassic sediments 194 traps 520-521 ultimate recoverable oil rate of discovery 475-477 Middle Fars Formation seals 4568 Middle Fatima Formation Saudi Arabia 79, 84 Middle Miocene tectonic reconstruction 455 Midyan sub-basin 622, 441 Midyan Terrane 29 Midyat (Hoya) Formation 437 Southeast Turkey 449 Syria 434, 436, 449 Turkey 418 Midyat Limestone Formation Syria 436 Mila Formation Iran 82, 126, 130, 131,137 830

members 1-5 130 members A-C 130 Mila Group/Formation division of the Cambro-Ordovician 133

Milaha Formation United Arab Emirates 201 lithostratigraphy 203 Minagish Field 330, 471,542-544 Minagish Formation 530, 537 Kuwait 330-332 lithostratigraphy 332 Minhamir Formation Yemen 78 Minjur Formation 578 Kuwait 218 Qatar 214 Saudi Arabia 198, 245 United Arab Emirates 199, 199 lithology and log characteristics 201 Minjur Sandstone Formation Saudi Arabia 219 Miocene Basin 438 Miocene Clastics 441 Miocene-Pliocene cycle 695 Miocene-Pliocene orogenic events 451 Mirga Mir Formation Iraq 218, 232 Misfar Group 150, 159 Mishan Formation 428, 449, 522, 722 Guri Limestone Member 522 Iran 445, 446 Guri Limestone Member 446 lithostratigraphy 446 Qatar 465 seals 456 United Arab Emirates 441 Mishrif Formation 516, 531, 534, 5646, 579, 700, 722 Bahrain 373 Iraq 3568, 356, 517 Kuwait 353 Oman 345, 755 Qatar 355 Saudi Arabia 340, 341-344 United Arab Emirates lithofacies 341-344 lithofacies analysis 343 Mishrif/Khatiyah formations 566 Mistal Formation Oman 76 Mohorovicic discontinuity depth 31 Morad FormationIran 84 Morad Series 81 Mosul Block 41, 42 Mottled Bed 286 Mozambique Belt 86 Muaddi Formation Jordan 289, 291 Shaban Member 289 Tahuna Member 289 Mubarak Field 472 Mudawwara Formation Jordan 119, 120

Index Batra Mudstone Member 120 Ratiya Sandstone Member 120 Tubeiliyat Sandstone Member 120 Mughanniya Formation Jordan 291 Muhaiwir Formation Iraq 285 Mukalla Arch 523 Mukalla Formation Yemen 339, 374, 374, 429, 502 Mukalla Graben 523 Mukalla High 259 Mukalla-Mar'ib Graben 523 Mukhaizna Field lithostratigraphic cross-section and hydrocarbon distribution of Gharif Formation 7680 South Oman Sub-basin 766-767 structural-contour map of Gharif Formation 768 Mukheiris Formation Jordan 221, 222 Mulussa Formation 681, 688 Iraq 219, 233, 356 Murban/Bab structure 472 Murbat Formation Oman 97-98, 757 Arkahawl Member 98 Ayn Member 98 Marsham Member 98 stratigraphy and lithological description 98 Murdam Group 25 Mus Formation Iran 287 lithostratigraphy 279 Iraq 284 southwestern Iran 279 Syria 224 Musandam Group 266, 271-273, 329 Oman members G-1329 Musandam Group Unit 4 321 Musandam Peninsula 1,292, 346, 363, 367 422, 459, 523,738, 741,743 Musandam Sub-basin 741,743 Bukha Field 772-77333 Musandam Unit- 4 composite stratigraphic section 323 Musayr Formation Saudi Arabia 442 Mushorah Formation 702 Muthaymimah Formation Oman 425-426 lithostratigraphy 425 Muff Formation Oman 207, 328, 367, 370 lithostratigraphy 368 United Arab Emirates 365 362 Muwaqqar Formation Jordan 379, 432

N Nabitah Suture 29 Naft-i-Shah Field 470, 731,733 Naft-Safid Field 735 Nahr Umr Field 713 Nahr Umr Formation 522, 564, 565 700, 710 Bahrain 355, 502

Iraq 334, 356, 357 Oman 344, 758, 759, 762, 763, 766, 769 shale 757 Qatar 355 Saudi Arabia 340 Khafji Member 340 Safaniya Member 340 shale 517 523 United Arab Emirates 341, 344 Nahr Umr Unconformity 770 Nahr Umr/Burgan Formation 516 Nahr Umr-Mauddud Sub-cycle 340 Naifa Formation Yemen 258 Najd Fault System 35, 65, 85, 89 Najd Shear Fault System 84 Najd Zone 84 Najmah field cross-section 715 Najmah Formation 537 Iran 279 lithostratigraphy 279 Iraq 285-2868, 286 Kuwait 282-283 Najmah Limestone Formation 698 Naokelekan Formation Iraq 285, 286 Naokeleken Formation 710 Geochemical analysis 708 Natih Field 472, 738, 759, 760, 762 Foreland (North Oman) Sub-basin 760-762 structural-contour map of Natih Formation 7622 Natih Formation Oman 344-345, 498, 753,755, 757, 758, 759, 761 lithological members 345 members A-G 345, 762 petrophysical characteristics 757 shale 523 Natih oil geochemistry Cretaceous 750 Natih Uplift 762 Naur Formation Jordan 337, 358 Calcaire Neritiques Unit 358 member A-D 359 Member B 359 Member C 359 Nodular Limestone Unit 358 Nautiloid Sandstone Formation Jordan 116 Nayid Formation Oman 327 lithostratigraphy 328 Neff Khaneh Field 470 Negev Fold Belt, Sinai 58 Neogene Bahrain 439 central and eastern Arabian Platform 439-441 Jordan 447-449 Kuwait 443

831

Sedimentary Basins and Petroleum Geology of the Middle East Middle East 437-451 northeastern Arabia 443--447 northern Arabian Platform 447--457 northern Iraq 449 Oman 441 paleogeography 462-4657 Qatar 439 Saudi Arabia 439 Red Sea region 441-443 Southeast Turkey 449 southern and western Arabia 441--443 southern Iraq 441-444 southwestern Iran 444--447 Syria 449 United Arab Emirates 441 Yemen 443 Neokelekan formation 705 Neotethyan Sea 235 Neotethyan Trough 38 Neotethys 5, 6, 7, 382, 393,451,457 opening 38 Nesen Formation Iran 193 Neyriz Formation Iran lithostratigraphy 279 southwestern Iran 279 Nijili Formation Iraq 226 Nimr Field reservoir development 770 South Oman Sub-basin 770 Nimr Formation Jordan 290 Niur Formation Iran 131,133, 133 Non-associated natural gas 3 North and northwestern Saudi Arabia Sauk sequence 103-108 North Field 471,474, 521,523 North Oman Sub-basin Mesozoic and Tertiary subsidence 758 subsidence 751 typical burial curve 754 Northeastern Arabia Neogene 443--447 Northeastern Arabian Platform Paleogene 408-428 Northeastern Syria structural traps 674 Northern Arabian Platform Late Cretaceous 375-382 mid-Cretaceous 355-362 Neogene 447-451 Paleogene 430-437 Northern Iraq Neogene 449 Paleogene 435-437 Northern Oman geological cross-sections 746 Northern Saudi Arabia Early Paleozoic 103-111 Kaskaskia sequence 137-144

832

Northern Thrust Zone 285, 377, 457 Northern, northwestern and northeastern Arabian Platform Early Cretaceous 330--338 Northwest Dome Field 471 Northwestern Saudi Arabia generalized geological map 431 Paleogene 430 Nubian Sandstone 350 Nubian Shield 393 O Oil and gas fields in Southeast Turkey 653 Oil concentration bromine 706 nickel 706 vanadium 706 Oil Geochemistry and Source Rocks Kuwait 532 Oil seepages phases 693 Oligocene flood volcanic rocks 430 Oligocene-Miocene Volcanic Trap Sequence 430 Oligocene-Miocene volcanics Ethiopia 395 Yemen 395 Oligo-Miocene Clastics 441 Oman Absaroka sequence 168--173 central and western charge concepts 753 dissolution drape 521 geochemical characteristics of crude oils 747 geochemical data of crude oils 748 geochemical data of source rocks 749 hydrocarbon generation 750 Jurassic section 2713-279 Kahmah Group 325-329 Kaskaskia sequence 150 Late Cretaceous 365-370 lithostratigraphic chart of the lower Paleozoic (Haima Group) 96 lithostratigraphy of Middle Eocene (Fahud Beds) 425 lithostratigraphy of the Simsima Formation 3691 lithostratigraphy of the Wasia Group 345 location map of oil and gas fields 741 main structural elements 737 mid-Cretaceous 344-348 nappes 8 Neogene 441 offshore exploration wells 739 oil-generation phases (Cambrian-Cretaceous) 751 ophiolites 10 Paleogene 423--428 source rocks 498 source-rock analysis 752 source-rock horizons 746 southern hydrocarbon accumulation and trap mechanisms 753 stratigraphy and hydrocarbon occurrences 742 stratigraphy of Infracambrian rocks 69-76 the end of the Absaroka Cycle 201-213

Index Oman (Sedimentary) Basin 737, 738-773 Oman Basin 521, 738 Cambro-Ordovician reservoirs 755-756 Cambro-Ordovician seals 758 Cretaceous seals 758 hydrocarbon generation and migration 750--751 hydrocarbon habitat 737-773 Infracambrian reservoirs 755 Infracambrian seals 758 Lower Cretaceous reservoirs 757 Middle Cretaceous reservoirs 757 oil field examples 760-773 oil geochemistry 747-750 Paleocene reservoirs 757 Paleocene seals 758 Permian and Triassic seals 758 Permian reservoirs 756-757 reservoir rocks 753-759 seals and seal formation 757-760 source rocks 746-747 structure and traps 758-759 Oman Foredeep lithofacies distribution of Upper Cretaceous in the northern part 366 Oman Foredeep Basin 367 Oman Foreland (North Oman) Sub-basin 7438, 741 Oman Foreland Basin 588 Oman Line 54, 55, 63 Oman Mountains 59-62, 206, 362, 408,454, 460, 737, 741,743, 745, 746, 758, 761 allochthonous nappes 520 Belt 459, 460 deformation 458 facies model for the Cenomanian-Coniacian 347 lithostratigraphy of Paleocene-Eocene rocks 423 Overthrust Belt 59 United Arab Emirates sedimentological interpretation of the mid-Permian-Early Triassic 176 units 1-6 60--61 Oman Ophiolite 393 Oman-Zagros-Taurus Trough 738 Onib-Sol Hamed Suture 29 Ophiolites 297 Ora (Shale) Formation Iraq 151, 151,500 Orbitolina Limestone 351 Ordovician formations central Arabia 117 Ordovician formations 1-5 Saudi Arabia 114 Ortabag Formation 664 Owen Fracture Zone 1, 44, 54, 453

P Pabdeh Foredeep Trough 40 8 Pabdeh Formation 460, 723 Iran 49, 371,393,418, 419, 420, 435, 498 lithostratigraphy 421 units 1-5 418

Oman 428, 773 United Arab Emirates 344, 396, 408, 422, 517 Padeha Formation Iran 150 Paleocene littoral and neritic limestone 459 reef facies 459 Paleogene 417 Bahrain 414 central, eastern and northeastern Arabian Platform 408-428 Jordan 431-434 Kuwait 415-417 Middle East 396--437 molasse trough 393 Northern Arabian Platform 430-437 northern Iraq 435-437 Northwest Saudi Arabia 430 Oman 423-428 paleogeography 458-462 Qatar 412--414 Saudi Arabia 409--412 Southeast Turkey 437 southern and western Iraq 415--418 southwestern and southeastern Iran 418--420 Syria 434 United Arab Emirates 420--422 western Saudi Arabia 428-429 Yemen 429-430 Paleogene Orogeny Van Phase 457 Paleogeography Cenomanian of Middle East 390 Coniacian-Santonian of Middle East 391 Early to Middle Albian of Middle East 389 Early to Middle Valanginian of Middle East 386 Late Albian-Early Cenomanian of Middle East 389 Late Valanginian to Early Barremian of Middle East 386 Middle Aptian of Middle East 387 Middle to Late Barremian of Middle East 387 Neogene 462-465 Paleogene 458-462 Paleogeography and cyclicity Cretaceous 384-392 Paleogeography and geologic history Cenozoic 451-466 Paleogeography of the Aptian-Albian in northern Iraq and western Iran332, 389 Qamchuqa Group 333 Paleotethys closing 38 final closure 292 ocean 37 Paleozoic Absaroka Cycle 161-193 glacial and periglacial deposits 134 mega-depositional cycles 88 Paleozoic source rocks 7268 Palmyra Basin 53,474 Palmyra Belt 522 833

Sedimentary Basins and Petroleum Geology of the Middle East Palmyra Depression 41 Palmyra Fold Belt 63 Palmyra Formation Syria 434 Palmyra Mountain Range 360 Palmyra Sub-basin 50 Palmyra Trough 190, 383, 388, 392, 454 Palmyra-Sinjar Trough 190, 232, 292, 391,457, 462 Pazanun Field 730, 7311 Permian production data Arabian Gulf 497 Permian-Carboniferous glaciation 157 Permo-Carboniferous ice sheets 225 petroleum reservoirs southeastern Turkey 658 Pila Spi Formation Turkey 436 Pila Spi Limestone Formation Iraq 436 Pirispiki Formation Iraq 128 Pirispiki Redbeds 712 Iraq 151 Pontic Mountains 1 pre-Unayzah Formation Saudi Arabia 141 Pre-Usfan Formation Saudi Arabia 428 principal reservoirs Cretaceous 516 Infracambrian to Paleozoic 511 Tertiary 517 Triassic and Jurassic 516 Proterozoic oils geochemical analysis 746 proto-Indian Ocean Basin 758 Protopetroleum theory 508 Punjab Saline Series 83

Q Q crude oil geochemistry Infracambrian 747 Q oils 750 Qaharir Field South Oman Sub-basin 771 structural-contour map of Haima Group 772 Qahlah Formation Oman 367 lithostratigraphy 366, 368 United Arab Emirates 362, 3657 Qaiyarah field 712 cross-section 715 Qalibah Formation Saudi Arabia 115, 115, 148, 503 general lithology and log characteristics 116 Qusaiba (Shale) Member 88, 115, 503 Sharawra Member 115 Qamar Formation Oman 348 United Arab Emirates 175 Qamchuqa Formation 681 Iraq 334, 336 Syria 291,336 Qamchuqa Group 703 lithofacies cross section 335 Qamchuqa Limestone 336 Qara Formation Oman 426 Qarn Alam Field 757 834

Qasab field cross-section 715 Qasim Formation Saudi Arabia 112 Qatar Absaroka sequence 176-177 Early Cretaceous 324-325 Jurassic section 266--271 Kaskaskia sequence 149 lithostratigraphy of Sharawra Formation 122 Neogene 439 Oil and Gas Fields 566--574 oil and gas fields 560 Oil Characteristics and Hydrocarbon Maturation 566 Paleogene 412--414 Paleozoic stratigraphic 562 Reservoirs 561 Simplified geological map 560 Stratigraphy 559 structure 559 the end of the Absaroka Cycle 213--214 Tippecanoe sequence 121-122 Triassic formations, onshore and offshore 213 Upper Cretaceous 374-373 Qatar Arch 217, 229, 438 465 Qatar Formation Qatar 263, 269, 271 United Arab Emirates 263, 264 Qatar-South Fars Arch 7, 22, 37, 38, 53, 77, 141,214, 292, 384, 393,462, 5235, 559, 651 Qatif (Oil) Field 319, 470, 5179, 638 Qirma Formation Jordan 432, 447 Qishn Formation Yemen 259, 339, 339-340, 502 Qumayrah Formation Oman 329, 346 facies model 347 Qurna Formation Iraq 376, 377 Qusaiba Formation Bahrain 5024 Saudi Arabia 500 Wajid Plateau 102 Qusaiba shale 5233 Qusaiba Shale Member 636 Quwarah Formation Nafud Basin 118 Saudi Arabia 114 Quweira Sandstone Jordan 129

R Ra'an Formation 139 Saudi Arabia 113 Diplograptus Shaly Member 113 United Arab Emirates 100 Ra'an Shale Member 6344 Radhautain 352 Radhuma Formation 517, 531 Kuwait 415-416 Arhayia Member 416 Jalib Member 416 Wafra Member 416

Index Rahab Formation Oman 758, 769, 772 Rahab shale 169 Rajil Formation Jordan 379 Claystone-Limestone Unit 3791 Sandstone Unit 379 Ram Group 108 Raman (oil) Field 471,653 Raman and Bati-Raman fields 667 Raman Anticline 57 Raman Formation 517, 659 Ramlah Formation Jordan 290-291 Ramlah Field 523 ramp and platform model of carbonate deposition 8 Ramtha Group 222-223, 290 Ras al Aqr Formation Bahrain 439 Ras al Khaimah Foredeep 395, 458 Ras al Khaimah Sub-basin 48, 393, 408, 422, 430, 437, 456, 459, 460, 523 approximate location 395 Ras al Khaimah Trough 48, 391,409, 418,422, 437 Rashid Field 472 Ratawi Field 333 Ratawi Formation 530, 532, 537, 700, 710 Bahrain 325, 502 Iraq 287, 333, 334, 500 Kuwait 330, 332 Qatar 321,324 Raudhatain Field 471,527, 533-534 Raudhatain Arch 283 Rayda Formation Oman 325-327 lithostratigraphy 326 United Arab Emirates 319-320 Razak Formation Iran 445 lithostratigraphy 445 Red Sea 5, 46, 382, 393, 452 evolution 453 oceanic crust 451 opening 452 physiographic features 451 pre- and synrift volcanism 452 rifting 454 structure 452 Red Sea Basin 430, 452 Red Sea basin, Lithostratigraphic section 612 Red Sea Depression 31 Red Sea Rift 454 Red Sea Rift Valley 45 Red Sea Sub-basin 50--52 Red Sea Trough 454 Reservoir Rocks 618-626 Kuwait 530-5324 Reservoirs Bahrain 551 Rezaiyeh-Esfandagheh Block 89 Rim Siltstone Formation Iraq 357

Rima Field 766 geological cross-section 773 South Oman Sub-basin 772 Risha Basin 601,607 Risha Field 473 Riyadh chalk and limestone 311 Riyadh Formation Saudi Arabia 311 Hith Anhydrite Member 311 Lower Riyadh Member 311 Yamama Limestone Member 311 Rizu Series 81, 82 Rizu-Desu Series 83 Rub al Khali 1,350, 500, 521 schematic cross-section 454 Rub al Khali Basin 37, 66, 292, 319 Rub al Khali Depression 453,465 Rub al Khali Sub-basin 48, 236, 523, 745, 746, 758, 761 approximate location 395 Rudist Limestone 349 Ruilat Formation Qatar 372 Rumaila Field 471,472, 713 Rumaila Formation 534, 700 Bahrain 355 Iraq 356 Kuwait 353 Saudi Arabia 340 Rumailan Field 521,670 Rus al Jibal Group 173 Rus Formation 460, 532 Bahrain 414 sedimentological and environmental interpretations 415

Iraq 417 Kuwait 417-417 Oman 426, 758 Qatar 412 A Member 412 Chalky Limestone Unit 412 Dolomitic Unit 412 Evaporite Unit 412 Saudi Arabia 408, 409, 4113, 430, 459, 462 seals 456 United Arab Emirates 421 Yemen 429 Rusayl Formation Oman 423 lithostratigraphy 424 Russ al Jibal Group 175-176 Rutbah Formation Iraq 356 Syria 336, 360 Rutbah High 50, 89, 190, 230, 390, 417 Rutbah Sandstone Formation Iraq 283, 285 Rutbah Uplift 141, 418 Rutbah-Khleissia High 232, 292, 382, 384, 385,388, 391, 835

Sedimentary Basins and Petroleum Geology of the Middle East 392, 462 Rutbah-Khleissia Ridge 408 Ruteh Formation Iran 193 sedimentary description 193 Ruwayda limestone 344 Ruwaydah Formation Oman 4257 lithostratigraphy 424

S Sa Wer Formation Somalia 257 Sa'dah Graben 32 Sa'di Formation Iraq 376 Kuwait 373 Sabatayn Formation Yemen 258 Ayad Member 258 M'qah Member 258 Shabwa Member 258 Sabellarifex Sandstone Formation Jordan 116 Sabkhas 2 Sabriya Field 471,542 Sabriyah Arch 283 Sabunsuyu Formation 459 Southeast Turkey 338, 360 members 1-4 360 Sachun Formation 459 Iran 370, 37 2 Sadan Formation Southeast Turkey 81,123 Sadan Redbeds Formation Southeast Turkey 123 Safah Field oil distribution in Shuaiba Formation 763 reservoir fluid properties of Shuaiba Formation 764 structural-contour map of Shuaiba Formation 765 West Oman Sub-basin 764 Safaniya Member 516 Safiq Formation Oman 96--97, 498, 516, 755 source rocks 746 Safiq oil geochemistry Silurian 747 Sahil Field 472 Sahl as Suwwan Formation Jordan 116--119 Sahmah Field 750 Sahtan 274 Sahtan Group 204, 273, 274-279, 329 Sahtan Limestone 325 Saih Hatat 204 Saih Hatat Formation Oman 275-277 Saih Hatat Window 59 Saih Nihayda Field 757 Saih Rawl Field Central Oman Sub-basin 770-771 reservoir data from Shuaiba Formation 771 structural-contour map of Shuaiba Formation 771 Saiq Formation Oman 76, 173, 204 sedimentological interpretation 173 Saiwan Formation Oman 170

836

Saiwan-Nafun Fault 54, 743 Sajaa structure 586, 594 Sajaa Field 317, 521 Sajaa Gas- Condensate Field 594 Sakaka Formation Saudi Arabia 141,147-148, 350 Sakaka Sandstone 350 Sakhin Formation Oman 213 Salahi Formation Oman 213 Salalah Plain 452 Saleh Field 470, 521 Salib (Arkosic Sandstone) Formation Jordan 81,108, 110111 Salil Formation Oman 325, 327 lithostratigraphy 326 United Arab Emirates 319-320 Salit Formation Jordan 221 Samran Unit 27 Sanandaj-Sinjar Zone 39 Saq Formation 624 facies 104-107 Saudi Arabia 103--108 lithostratigraphic section 107 lithostratigraphic section and isopach map 106 Quweira Sandstone Member 107 Ram Sandstone Member 107 Risha Member 108 Sajir Member 108 Siq Sandstone Member 107 Umm Sahm Sandstone Member 107 Saq Sandstone Saudi Arabia 33, 129, 135 Sar'a Chalk-Flint Formation units 1-6 Jordan 433 Sarah Formation Saudi Arabia 115 Saramuj Conglomerate 80 Saramuj Formation Jordan 80, 81 Sargelu formation 705 Geochemical analysis 708 Sargelu Formation 532, 537, 689, 702, 726 Iran 279 lithostratigraphy 279 Iraq 284, 285 500 Kuwait 282 Syria 336, 500 Sarki Formation Iraq 284 Sarmord Formation Iraq 334, 336, 702 Sarvak Formation 516, 721 Iran 330, 349, 349, 371 Ahmadi Member 349, 371 lithostratigraphic units 331 Mauddud Member 349 units 1-3 349 Oman 773 Saudi Arabia Tectonic and Stratigraphic Framework 608 Source Rocks 606-625 Saudi Arabia

Index Absaroka sequence 178, 178-186 C 15+ gas chromatograms of representative Arab oils 504

C 15+ gas chromatograms of representative Permian Khuff reservoir oils 505 Cap Rocks 633--634 Hydrocarbon Systems 611 Jurassic section 24564-256 Late Cretaceous 373 major oil and gas fields 609 mid-Cretaceous 350-352 Neogene 439 Paleogene 409-412 Paleozoic correlation chart 104 Phanerozic lithostratigraphic section 610 Phanerozoic lithostratigraphic section 610 pristane/nC 17 versus phytane/nC18 for Jurassic oils and Hanifa and Tuwaiq Mountain source rocks 504

Red Sea region Neogene 441--443 Reservoir Rocks 625-633 Seals 554 Source Rocks 613-625 Source Rocks and Hydrocarbon Migration 554 Structure and Trap Mechanism 634-637 surface oil and gas seeps 469 Thamama Group 311-319 Tippecanoe sequence 111-115 Wara Unit 357 Sauk sequence 9, 37 Jordan 135 Saudi Arabia 135 Sayhut Basin 647 Sayindere formation 667 Southeast Turkey 380 Sayynia Field 747 sea-level change 297, 383 sea-level fluctuation 8, 10, 236 Seals and Seal Formations Iran 729 SE Turkey 667 Syria 685 Second cycle mid-Cretaceous 340-362 Seeb (Limestone) Formation Oman 424-425 Sefidabeh Trough 522 seismicity distribution 6 seismology 2D and 3D 496 Sekhanian Formation Iraq 284-285, 285 Selmo Formation Southeast Turkey 451 Semail (Ophiolite) Nappe 59, 60, 62, 175, 203,209, 211, 365, 367, 382, 391,393, 422, 426, 459, 743, 758 composite columnar section 369 Oman 365-368 Semail (Ophiolite) Thrust 59,363 sequence stratigraphy 7 Serikagni Formation 702 Iraq 449

Sernandaj-Kermanshah Crush Zone 382 Seydisehir Formation Southeast Turkey 123, 126, 126 Shabb Formation Yemen 78 Shabwa Graben 257 Shah Field 472 Shahbazan Formation Iran 419, 420 Shammar Formation Oman 764 Saudi Arabia 80 Shammar Group 25 Shammar Province 31 Shammar Volcanics 27, 84 Sharawra Formation 562, 564 565 Qatar 121-122 Lower Shaly Member 121 Upper Sandy Member 121 United Arab Emirates 122-123 Shark Tooth Shale (Dammam Formation) 412 Sharwain Formation Yemen 339, 374 Shaybah Field 319, 523 Shayban Unit 27 Shedgum Field 472 Sheikh Alas Formation Iraq 436 Shihar Group 429 Shilaif Formation United Arab Emirates lithofacies analysis 343 Shilaif/Khatiyah Basin 2977 Shilaif/Khatiyah Formation 516 United Arab Emirates 341, 3468, 498 Shiranish Formation 517, 702, 710 Iraq 358, 376, 377, 500 Syria 360, 380, 500 Shirgesht Formation Iran 130, 133, 133 Shirhanish Formation 681, 683, 689 Syria 434 Shuaiba Formation 510, 534, 564, 565, 579, 633, 700 Bab Member 510 Bahrain 325 Iran 330 Iraq 334 Kuwait 332 Oman 325, 327, 753,755, 757, 758, 759, 763, 764, 766, 770 lithostratigraphy 326 Qatar 324-325, 502 Saudi Arabia 319 United Arab Emirates 321 Bab Member 321 Shuaiba Limestone 316, 336, 350 Shuaiba sedimentation 327 Shuayb Formation Jordan 359 Shuqra Formation Yemen 258 Shuram Formation 70-73 Iran 84 Oman 755 Shurau Limestone Formation Iraq 436 837

Sedimentary Basins and Petroleum Geology of the Middle East Siba Field 471 Sibzar Formation Iran 150 Sid'r Formation Oman 327 lithostratigraphy 328 Silal Formation Jordan 290 Silicified Limestone and Phosphate Formation Jordan 378 Silvan Formation Southeast Turkey 451 Simple Fold Belt (Zagros) 57, 473, 517, 521 Simsima Field 759 hydrocarbon trap 760 Simsima Formation 517, 580 Oman 367 lithofacies 365 lithostratigraphy and log characteristics 369 Qatar 372-373 Jana' an Member 373 Salwa Member 372 United Arab Emirates 362, 365 Sinan Formation 517 Southeast Turkey 437 Sinjar Basin 58 Sinjar Depression 41 Sinjar Formation Iraq 435 reservoirs 456 Syria 434 Sinjar Graben 383, 393 Sinjar Sub-basin 50 Sinjar Swell 63 Sinjar Trend 522 Sinjar Trough 388, 392 Sinjar-Palmyra Trough 390 Sirhan Basin 447, 522, 605 Sirhan Sub-basin 47 Sivas-Malatya Basin 522 Slate Graywacke Series 80 Slirt Series 444 Soltanieh Dolomite 81 Soltanieh Formation Iran 82, 83, 84 Sort Tepe Formation Southeast Turkey 128 Sosink Formation Southeast Turkey 126, 126, 498 Syria 128 Souedie Field 472, 521,670 Soukhne Formation 681, 683 Syria 336, 380, 434 Source Rocks southeast Turkey 662 Syria 681 geochemical analysis 502 Oman 498 potential in United Arab Emirates 498 potential in Zagros Province 496 Source Rocks and Oil Geochemistry Iran 723 Iraq 705-706 838

South Fuwaris Field 547 South Oman Salt Basin 52, 65, 84, 745, 750, 758 rift origin 758 South Oman Sub-basin 738, 745, 755, 758, 766 burial history 751 hydrocarbon accumulation 755 hydrocarbon trap 759 Marmul Field 767-770 Mukhaizna Field 766--767 Nimr Field 770 Qaharir Field 771 Rima Field 772 structural development 759 typical burial curve 754 South Umm Gudair Field 471 Southeast Turkey Absaroka sequence 189-190 Early Cretaceous 337-338 Early Paleozoic sequence 123--129 facies distribution of Early Cambrian to Early Silurian sediments 127 facies distribution of Late Silurian-Permian sediments 152

Jurassic section 291 Kaskaskia sequence 151-154 Late Cretaceous 380---3822 Main structural elements 658 mid-Cretaceous 360--362 Neogene 449 Paleogene 437 Sauk sequence 123--128 source rocks 498 Southeast Turkey oil and gas fields 652 Stratigraphic correlation 657 structural sketch map 381 the end of the Absaroka sequence 224-225 Tippecanoe sequence 128 Total organic carbon 663 Crude Oil Geochemistry 661 petroleum reservoirs 658 Seal and Seal Formations 667 Southern and western Arabia Neogene 441-443 Southern and western Iraq Paleogene 417-418 Southern Iraq Neogene 443--444 upper stratigraphic correlation diagram of Albian rocks 357 Southern Oman Dhofar region structural cross-section 454 geological cross-sections 746 lithostratigraphy of Cretaceous 348 Sauk and Tippecanoe sequences 97-98 Southwest Fateh Field 472 Southwestern and southeastern Iran Paleogene 418--420 Southwestern Iran composite lithostratigraphy section of Late Cretaceous-Early Tertiary formations 371 Jurassic section 279-280

Index mid-Cretaceous 349 Neogene 444--447 source rocks 496 Tertiary production data 500 the end of the Absaroka sequence 214-217 Triassic lithofacies map 214 Upper Cretaceous sequence 370-372 Strait of Bab A1 Mandeb 458 Strait of Hormuz 1, 48, 738, 743 Stratigraphic History Kuwait 527 striated floors 157 Structural History Kuwait 528 Structure Qatar 559 Structure and Traps Iraq 696 Subeihi Formation Jordan 337 Sudair Formation 564, 578 Bahrain 217 Kuwait 218 Oman 202-203, 758 lithology and log characteristics 204 Saudi Arabia 184, 197-198, 500 United Arab Emirates 199 lithology and log characteristics 200 Sudair Shale 198 Sulaiy Formation 537, 631, 698 Bahrain 325, 502 Iraq 286, 287 Qatar 324 Saudi Arabia 254, 315, 316, 318, 320, 330, 500 lithostratigraphy 316 sulfur isotope data 506 Sumeini Group 61,203,204, 277, 328 Sumeini Parautochthonous Unit 61 Summan Platform 137 supergiant and giant fields 474 Supergiant Ghawar Oil Field 637 Suqah Group 428 Surface oil and gas seeps Bahrain 469 Iran 468-469 Iraq 469 Jordan 469-470 Kuwait 469 Lebanon 469-470 Saudi Arabia 469 Syria 469-470 Turkey 468 Yemen 469 Surgah Formation Iran 349, 349, 370, 371 Surmah Formation Iran 280, 280 Surmeh 721 Surmeh Formation 721 Suwaidiyah Field 670 Suwayma Formation Jordan 189, 222 Suwei/Sudair Formation Qatar 213 Swab Formation 685 Syria 129, 498

Syria Absaroka sequence 190-191 Early Cretaceous 336 Early Paleozoic sequence 123--129 Generalized stratigraphic column 671 Jurassic section 291 Kaskaskia sequence 154 Late Cretaceous 380 lithostratigraphic section of late Paleozoic sediments 155 Major oil and gas fields 675 Major structural elements 672 mid-Cretaceous 360 Neogene 449 oil and gas fields 670 Paleogene 434 Sauk sequence 128 Seals and Seals Formations 685 surface oil and gas seeps 469-470 the end of the Absaroka sequence 223--224 Tippecanoe sequence 128--129 Syrian Crude Oil Geochemistry 683 Syrian oil Source-rock environment 686 Syrian oil fields Reservoir characteristics 680

T Tabas Block 522 Tabriz Basin 522 Tabuk area Paleozoic section 37 Tabuk Basin 32, 47, 88, 141,157, 520 Saudi Arabia 137 Tabuk Formation 115, 564, 626 Kuwait 121 Qatar 121 Saudi Arabia 112 Lower Silurian Shaly Member 115 Qusaiba Member 115 Sharawra Member 115 Tabuk Group general lithostratigraphy and isopach map 113 Tabuk Sub-basin 47 Taiyiba Formation Jordan 433 lower unit 433 middle unit 433 upper unit 433 Taknar inlier 133 Taknur Formation Iran 83 Taleh Zang Formation Iran 372, 420 lithostratigraphy 420 Tanf Formation Syria 129, 500, 683 Tanjero Formation Iraq 377 Tanuma Formation Iraq 376 Taqa Formation Oman 426, 427 lithostratigraphy and log characteristics 428 Taqiye Marl Formation Jordan 433, 435

839

Sedimentary Basins and Petroleum Geology of the Middle East Tarbur Formation Iran 372 Tarjil Formation Iraq 436, 437 Taurus 393 Taurus Mountains 1, 6, 55-57, 453 Taurus Occidental Nappes 55 Taurus Orogenic Belt 382 Taurus Suture Zone 393 Taurus Trough 457 Taurus-Zagros-Oman Fold Belt 87 Taurus-Zagros-Oman Orogenic Zone 6 Tawil (Sandstone) Formation 562, 564 Qatar 149, 159, 161 Saudi Arabia 156 Tawilah Formation Yemen 257, 339 Tawilah Group 374, 443 lithostratigraphy 375 Tawilah Series 374 Tayarat Formation 531 Iraq 376 Kuwait 372, 373 Tayran Group 429, 442 Tayyarat Formation Saudi Arabia 115 Tectonic and Stratigraphic Framework Saudi Arabia 608 Tectonic Mrlange Oman 211 Tejas sequence 10 Telhasan Formation 667 Terbuzek Formation Southeast Turkey 381 Tertiary reservoirs 517 Tertiary Basaltic Plateau 447 Tertiary production data southwestern Iran 500 Tethyan margin 758 Tethyan Ocean 383, 510 Tethyan Sea 292, 385 Tethyan Seaway 458 contraction 456 Tethys 465 Tethys Oceanic Basin 758 Thamama Formation Saudi Arabia 311 Sulaiy Member 311 Yamama Member 311 Thamama Group 297, 311,315,336, 382, 384, 517,579, 750 Eastern Arabia 319-329 Geochemical analysis and oil characteristics 584 lithology and log characteristics 320 play concept 523 Saudi Arabia 311-319 Thamama transgression 319 Thaniya Group 78 Thayyam Field 473 Thermal gradients 508 Third Cycle Late Cretaceous 362-382 Tiginli red sandstone 128 Tigris-Euphrates Delta 1 Tigris-Euphrates River System 1 Tihama Coastal Plain 429

840

Tihama Sub-basin 647 tillite and boulder clay 157 Tippecanoe sequence 9, 37 trap formation, timing 5213 Trap Series Yemen 6, 452 Trap Volcanics 32 Trebeel Formation Jordan 119 units A-D 119 Triassic Absaroka Cycle 193--199 reservoirs 516 Trilobite Sequence 137 Turan Block 38 Turan Plate 383 Turkey Structure and Traps 653 surface oil and gas seeps 468 Tuwaiq Mountain Formation 628 Bahrain 254, 502 Oman 273 Saudi Arabia 245, 248, 250, 285, 311,500, 503 lithostratigraphy 249 $2 pyrolytic yield 502 Tuwaiq Mountain Limestone Member 248 Tuz Golu Basin 522

U United Arab Emirates oil and gas fields 590 Traps 585 Margham Field cross section 594 reservoir rocks 574 Seals 580 Source Rocks and Oil Geochemistry 580-590 Structural trend of oil and gas fields 591 Traps 585-590 Ubaid Formation Iraq 285 Um Irna Formation Jordan 186-187 Um Maghara Jordan 290 Um Tina Formation Jordan 218, 221 Umm Er Radhuma Formation 460 Bahrain 373,414 Iraq 3768, 417, 435 Kuwait 417 lithostratigraphy 410 Oman 367, 426, 753, 757, 7580, 767 Shammar Member 426 Qatar 412 reservoirs 456 Saudi Arabia 373, 408, 409--411, 430, 459 United Arab Emirates 421, 460 Yemen 374, 429 Umm Gudair Field 544 Umm Gudair South Field 547 Umm Gudair structure 527 Umm Ishrin (Sandstone) Formation Jordan 111, 187 Umm Maghara Formation Jordan 289

Index Dafali Member 289 Mintar Member 289 Ramad Member 289 Umm Rijam Formation Jordan 432, 4335, 447 lithostratigraphy and log characteristics 432 Umm Sahm (Sandstone) Formation Jordan 107, 111 Harlania Shale Member 108 Umm Shaif Field 472 Umm Tarifa Formation Jordan 119 Unayzah beds 157 Unayzah Formation 578, 626, 634 Bahrain 502 Saudi Arabia 88, 147, 161,178, 178-182, 500 detailed measured section 179 generalized stratigraphy and isopach map 162 logs and core description 180 stratigraphic cross section 181 Unayzah A-C members 182 United Arab Emirates 226 Regional Stratigraphy 575 Absaroka sequence 173-176 Early Cretaceous 319-324 Jurassic section 259-266 Kaskaskia sequence 137-152 Late Cretaceous 363-365 lithostratigraphic correlation of Tertiary formations 421

lithostratigraphy of the Qahlah Formation 366 mid-Cretaceous 340-344 Neogene 441 Paleogene 420-422 Source Rock Horizons 581 source-rock potential 498 the end of the Absaroka Cycle 199-201 Upper Anhydrite 263 Upper Asmari Formation 449 Upper Balambo Formation Iraq 358,702 Upper Carboniferous-Middle Triassic cycle 694 Upper Cretaceous Bahrain 373 eastern Arabia 372-373 Kuwait 373 lithofacies 366 Qatar 372-373 Upper Cretaceous Cycle 297 Upper Cretaceous production data Arabian Gulf 499 Upper Cretaceous sequence southwestern Iran 370-372 Upper Es Sirr Sandstone Formation Saudi Arabia 194 Upper Fars Formation Iraq 443 idealized vertical sequence 444 Syria 449 Upper Murdama Group 27 Upper Pabdeh Formation Iran 436 Upper Qamchuqa Limestone Formation Iraq 357 Upper Sarmord Formation Iraq 357

Urumieh-Dokhtar magrnatic assemblage 39 Usaykhim Formation Jordan 379 Usfan Formation Saudi Arabia 429 Uthmaniya Field 472 Uthmaniyah Field 352

V Van Mus Basin 5224 Van Plate 453 Vanadium-nickel ratios 496 Variegated Sandstone 337

W Wadi As Sir Formation Jordan 359, 379 Echinoid Limestone Unit 359 Massive Limestone Unit 359 Sandy Limestone Unit 359 Wadi Fatima Series 79 Wadi Ghabar 78 Wadi Miaidin 365 Wadi Sahtan 274 Wadi Shallala Formation Jordan 432, 433 lithostratigraphy and log characteristics 432 Wadi Sirhan Sub-basin 432 Wadi Umm Ghudran Formation Jordan 360, 378 Dhiban Chalk Member 378 Massive Limestone Unit 378 Mujib Chalk Member 378 Tafila Chalk Member 378 Wafra Field 471, 517, 544 Wafra High 520 Wahrah Formation Oman 207, 211,327 Calcareous Mudstone Member 207 lithostratigraphy 208 Lower Chert Member 207 Lower Limestone Member 207 Upper Chert Member 207 Upper Limestone Member 207 Wajid Formation Saudi Arabia 37, 89, 178 Juwayl "Member" 178 Khusayyayn Member 156 Qusaiba Member 156 Supergroup V Juwayl "Member" 178 Wajid Outcrop Belt 101 Wajid Sandstone 139 Wara Formation 531, 534 Bahrain 355 Iraq 356 Kuwait 353 lithstratigraphy and log characteristics 353 Saudi Arabia 340 Wara Sandstone reservoir 527 Wara-Mishrif Sub-cycle 340 Wasia Delta 356 Wasia Formation 633

841

Sedimentary Basins and Petroleum Geology of the Middle East central and eastern Saudi Arabia 350-352 Saudi Arabia 315, 340, 373 Ahmadi Member 351 Khafji Sandstone Member 350 lithostratigraphy and depositional setting 351 Mauddud Limestone Member 351 Mishrif Member 352 Rumaila Member 352 Safaniya Sandstone Member 350 Wara Member 351 Ahmadi Member 634 Rumaila Member 634 Wasia sandstone 350 Wasia shale 750 Wasia Group 297, 311, 318,336, 340, 344, 347, 352-354 356, 384, 382, 755, 760, 761 lithostratigraphy 342 lithostratigraphy and log characteristics 345 play concept 523 time-stratigraphic relationships of sequence boundary 342

West Musandam Peninsula 772 West Oman Sub-basin 741,750, 758 A1 Huwaisah Field 762-763 Lekhwair Field 763-764 Safah Field 766 Yibal Field 764-766 western Oman Mountains Paleozoic formations 100 western Saudi Arabia Paleogene 428--429 western Saudi Arabia (Red Sea region) lithostratigraphy and paleoenvironment of the Cenozoic Formation 428 Widyan Basin 88, 89, 141,147, 156, 168, 184, 226, 524 Saudi Arabia 137 Widyan Sub-basin 47

Y Yamama Formation 631, 698 Bahrain 325 Qatar 324 Saudi Arabia 315, 316-317, 317, 330 lithostratigraphy 316 Yamama Limestone 316 Yanbu Formation Saudi Arabia 442 Yanbu Suture 29 Yarmouk River 377, 433 Yatib Formation Saudi Arabia 103 lithostratigraphic section 107 Yemen Absaroka sequence 178 Hydrocarbon Parameters 644 Jurassic section 254--259 Late Cretaceous 374-375 Lower Cretaceous 339-340 major oil and gas 642 mid-Cretaceous 362 842

Neogene 443 Oligocene-Miocene volcanics 395 Paleogene 429--430 surface oil and gas seeps 469 Yemen Volcanic Group 395,443 lithostratigraphy 430 Yewfik Unconformity 27 Yibal Field 472, 7388, 756, 757, 758, 759, 764 lithostratigraphy and log characteristics 765 structural-contour map of the Shuaiba Formation 765 subdivision and hydrocarbon distribution in Khuff Formation 766 West Oman Sub-basin 764-766 Yiginli Formation Southeast Turkey 153, 153

Z Zabuk Formation Southeast Turkey 123, 123 Syria 128 Zabuk Quartzite Formation Southeast Turkey 123 Zagros Basin 48, 135, 214, 229, 355 390, 393,408,459, 521, 651 approximate location 395 extent 652 geochemical typing, sulfur isotope studies, vanadiumnickel ratios and physico-chemical dating 496 isopach map of Cenozoic sediments 395 reservoirs 655 Zagros basin Location map 716 Zagros Basin of Iraq Cap Rocks 7100 Zagros Basin Reservoir Formations 702-705 Zagros Crush Zone 1, 7, 15, 16, 38, 50, 235, 391 Zagros Fault 456 Zagros Fold Belt 8, 41,496, 510, 516 517, 521 522 Miocene reservoirs 507 Zagros Folded Zone 522 Zagros Foothills Belt 408 folding 458 Zagros Foredeep Basin 458 Zagros Foreland Basin 521 Zagros Foreland Basin traps 719 Zagros Mountain Belt 470 Zagros Mountains 1, 58--59, 393,462 units 1-5 58-59 Zagros ophiolites 8 Zagros Orogeny Miocene-Pliocene 447 Zagros Range 63, 473 Zagros (Shear) Zone 38, 84 Zagros Suture 651 Zagros Thrust Belt 59, 226, 521, 651 Zagros Trough 393 395,408, 422, 456, 459, 460 Zahra Formation Iraq 444 Zaigun Formation Iran 82, 83, 84, 129 Zakum Field 472, 590 Zap Anticline 89, 126 Zard Kuh Formation Iran 134 Zareef Field 747

Index Zarga Formation Jordan 287-288 Farush Member 287, 288 Humra Member 287 288 Um Butma Member 287, 287 Zarqa Formation Saudi Arabia 114 Zendan-Minab Fault Zone 651 Zinnar Formation Iraq 189 Zor Hanran Formation Iraq 219, 233, 283 Zubair Field 334 376 417, 471,713 Zubair Formation 516, 530 532, 537, 702, 710 Iraq 287 333 500 lithostratigraphy and log characteristics 333 Lower Sandstone Member 333

Lower Shale Member 333 Middle Shale Member 333 Upper Sandstone Member 333 Upper Shale Member 333 Kuwait 330, 332 Zulam Formation Iraq 285 Zulla Formation Oman 206 lithostratigraphic interpretation 207 sediment deposition 208 units 1-4 206 Zuni Cycle Late Mesozoic part 235-244 Zuni sequence 10

843

This Page Intentionally Left Blank

APPENDIX

Summary of some of the oil and gas fields in the Middle East

Sedimentary Basins and Petroleum Geology of the Middle East

APPENDIX Data summaries of some oil and gas fields* A. Kuwait and the Kuwait-Saudi Arabia Neutral Zone B. Bahrain C. Qatar D. United Arab Emirates E. Saudi Arabia E

Southeast Turkey

G. Syria H. Iraq I.

Iran

J.

Oman

*for more information, see chapters 11 (A-E), 12 (F-I) and 13 (J). The data, summarized in the following tables, were collected from many published papers and reports (cited in chapters 11-13) of these the most importan sources were Tiratsoo (1984), OAPEC (1985), Beydoun (1988), Carmalt and St John (1986), Society of Petroleum Engineers, Middle East Oil ShowProceedings 1979-1997, Alsharhan and Kendall (1986) and Petroconsultant's Monthly Scouting Reports. In fields where there is a single reservoir horizon the summary data are presented in single column format, where there are several reservoir horizons the general field data are summarised at the beginning and end and each reservoir is separately numbered. To avoid confusion blank columns in the table are shaded. By contrast where information is not available to us, whether because it is confidential or unpublished the revelent entries are indicated by question marks.

A2

A. Data from some oil and gasfieldsof Kuwait and the Kuwait-Saudi Arabia Neutral Zone.

njWARtS SOUTH

FIELD NAME GENERAL . DESCKlPnON

(

;•.•;

U M M GUDAIR

U M M GUDAIR SOUTH

FIELDNAME

^

F M d S i n Ibni^l

Dtptli t o T D i i o f h r l l l )

^

T I l l c k H I l Dl Par ZODC Ift)

B^ly U 1 . VHJ Kienune 2CA

CIii»iaaitl« Anbiin PUtfonn

Ambijin PUiibnn

l,ii()at.laix>

M*2rN.4r5rE

2 9 ' J r N, ^T'SS' E

irso's-N.ir+ria'E

RESERVOIB FAKAMETERS

]M1

l%2

1966

RtacrruJr Pan^ty

R^wmi £ou(h^2

UmmGuduf^Z

Umin Gudiir South-3

>

230 1

(%)

PtnnnbUitr (nd)

T

23

22

7

3OO-I20O

)ao

I n l t i i l P t t m n (pri[)

y

680-1120

330(M100

^

t

TI9

656

7

250-J90

BolUHq H o k T c m p c n t m

1

7

ITl

FiimiflU«i VaJanK Factor IRBATBl

7

1.18-1.27

112

21.6-26

27.!

24-?7

!

IM-1J6

I7S

)J

3.8

].]

I S 74

4.3

7

•

40

WiiHdriw

Wuer dnw ^ M>lui]un g u

W]Ur drive

l%4

1962

1968

Producer

Prtiduar

9 n9m

35(I9S4)

lfla97B)

PndiKn'Willi

&il97i}

3I(I9M)

I6{I97B)

^ ^

T

O b K m r lYplli

1

liOccliDD Wdls V

*

-^ - •

^

OaUtJc uid, bioclulK ItmslcKie

UtlH4ao

l*7^»

TUckH<m

LJEC 6cTniiti>n-H«mcnvitit

AKt -

.

- •

• • . ; •

• - '

•

:

•

-

FomtlDD

RMiwi

Litbokicr

Shile, undsione tnd |jmcvt[?nc LtfC BfmuLui'Hiutcn^ k«ji

Ad SOURCE

CMfOURatlafoct^STB) Sultur CaatcDl (%) VtocoBty (CP)

•.f:.'-

RUlwi

FonualkHt

•

RltlW! Ai:

pUKcAtt w d bitumimiu limsuone 600 LUC Beniniin-HhiienviAn Structunl vvicliw

>

^

nxmucnoN PARAMETERS R«omry Factdrt*) DiHrt McchanitiB

7

t

7

Doll; Production (dau)

llMliMAJall

21.222 bbVd ( I M ) )

9MMci/d(ain«^) >43M.bbVili>il(l98)1

TvUI PnHluclioa ldatc>

16MM.Wilal t7.J8.cf»M(l976)

iMMMb)>l(l9M)

3 ; M M bbl

7

JOO MM.Mil

7

7

7

KKvrtnbitOU

7

MOOMM.bM

42Q-M0 M M b M

Ricavtrablc G u

1

'

7

Iqjcctkpa StatiH

Eftimalcd RcaerYtx RKOvrrablt Rfocrrcj —

Formitlin

•

1

« .

PROOUCINC. H O U Z O N

•

CHL P A R A M E T E R S OH U r t T l l j CAP!)

Av

300 ] 7 M l K n

B v h M i Point P n a n n

Produccr

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-

7

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•

8,778

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T o M WtUa D r i l k d ( d m )

Ulboloo'

•

1

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•

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Seismic sufwy

EBemioBift)

SBAL

-

a.i>a

Seismic survey iini

I M i d Dtpdi (ft) P b o t t t r r Mctbod

200

U M M GUDAIR SOUTH

Anbiin nacfmn

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UHE^nTT' "CU

a.403

T

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U M M GUDAIR

^

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i '

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33.6BJ:IIII(197S)

t287MMMilDil(l«SS)

E<|IIITII«UOU

ft 3

o.

>

A. continued

> 4i-

AHMADI

FIELD NAME GENERAL DESOUPnON FVW S i n I k m ' l

Laoikn

FIELDNAME

• •

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"

,

•

13.7 I 10 km

CUHfAciiktn

Billy :21 KIcmiTK^Ci

» ^ N . 4 r r E

Arahjan Platlomi

Atmwt)

1H2

kESEkVOlB MRAMETERS

1

r

3

4

RcHTVoJr pDrHi[j<%)

2^

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13-19

30

100.500

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^

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T

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U4

JUIMADI

-

•

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([»iKI

Q.

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IM)

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79 1483

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2

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1

2

3

4

raODtJCING HOBIZONS

neUSIHIM

TbulHub DiUkd(dilt)

DWiof Production

FDrnuUoii

Wan

MAuddud

Buixui

Burgan

LMbatotf

SinddDnc

LiRVHW

3nl5aaltione

4 t h SHnd^CE^fV

IBO

25

*73

«75

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SEAL FnrmBCiDn LUbntoiy

1

2

3

4

AhmnJi

MAuddud

Burfin

Bui^n

Sluk

1

2

3

4

Simcuiml teilied mticline. Thit field 13 a K-S^rencbng culmiutiDnonthc rrujor Burjan •LinKLiuc.

1

2

3

4

Deptli (oTo|i oip>r(tt)

3.670

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15

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7

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W o k wMcr dnvT + B>3CAp

7 Sbtu

7

37

Rmff u

AlbiAn

An

OTHER rAKAMETERS

•J

Recovrrr Factor

1

700

TbkkwKn)

7

137

PRODUCTION PARAMETERS

ArgilUccoui limmonr And bitumiTHui t l u k

UUmtiio

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n

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7

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3

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7 G H

w

A. continued

BAHKAH

HELD NAME

-

GENERAL DBSCWFTIOW FkUSInlkA)

LocaHoa

I b t e l Depth
FIELDNAME

RAHRAH

^

7

T

7

^E^ESSS^ 8SE-, .^

3

4

5

Amo(

1

PtvduetkM (kMr')

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ftlTBiepm Ptnvliice

A n b i m Plufonn

I9'33'4S- N, 41*H'4S'' E

Dill if

1956

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TO

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IS

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7

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7

7

7

7

7

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7

7

7

7

7

7

7

7

7

7

30

17-11

N

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7

7

7

1

7

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7

7

7

7

7

vltmHylCP)

1

7

7

7

InltU] PrrMurt Dflltof FrpdiKdon fVDdlKcr Wclb

ntODtJciNc BOKOCyHS Fomutlon UOtatotj

mduHscni Ap

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8(1M1)

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4
t

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1

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MtutUtK]

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faOeOWm Welb

r

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4

5

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Smdslone I / K I thale

Limntone. ihtle

IJT

160

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late Bemaiian^ HalLcnviwt

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SEAL

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(pilU

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t

OIL ^ M H MRAMKinS^I OU U m i c y <°API)

ft B O.

>

7

ihile ACT

SOURCE

LanshimScmvAliui

OenDminian

1

2

Barmniinnrly Aptiin

HautcriiniiAEntiy BsrremLir

3

4

5

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Rmwi

UtboloKr

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700

600

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I m Beiriaiian-Hmuienvian

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1

2

3

Dtptfa to Top

^

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a.160

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19

OTHER rARAMETERS

*>

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4

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PRODUCTION PARAMETERS Rccorery Factor

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IS

5 9JM

13S

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7 Reatnt* — E^aWalnlOU

•

.

f.

on

4»MMbbl

^

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MOOMMbblDil * 175DB.crpa

RtCAwaUt

7

A. continued

>

FIELD A n or

REStJtVOUl MRAMETES5

96J6»

7

1

7

3

4

3

HeMSlBlbio'l

Locatkn (latloBU

7

IS

23

24

^ii

100-iOO

10

itiuooa

4cca

1200

?

T

7

ims

7

T

7

7

7

7

?

7

7

U7

7

Fonntktt VUunw F K I O T (RgySTB)

7

7

1

7

7

OIL PARAMEISRS

1

tnlctol P i T n u r r

SuUurConuiit

2 4 1 16

Total D c r t k t n )

Aratnir Ptallorm

Diuof Macmtry

1»38

Mattwtty

Bufftn-I

7

Dbcover^ Method

S a i m k md lurface survey

BmtlamW)

239

I94«

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413 ( 1 » M )

Pn&tat

rnoDuciNc

J

OteemrWilb

3

2

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.

.

:.s

.

HORIZONS '. '

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313

1

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T

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7

3

4 ».8

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3M

M6

17

M

2.«

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t

7

7

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3fdS»ditone

4thSiMblofie

IM

25

rJ5

*73

(l«S3)

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Weak wucr <Jnvf

l8B.tibl(l»M)

liyKlioil Statu

bdnalid Rcitrvct

2

3

Ahiruili

Mtuddud

Rui^ar

FormatiiHi

Shftk

Dnue limntonc

unditone

7

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,

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fill

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.

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3

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Formation

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fiitumiiBux ihale ind vp^lacout linerion

Argillxxoui

a.

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Albiin

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BUilG\N

FIELDNAME

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H/iME

iVipTypf

Gently N'Scllipiical dome *ithiTurwfawsE-W. Dipt rtrely exceed jr^. Mauddud, Burgan knl MirdgjthrcKrv«niefMntedt>raNNWfiuhrmrnM«g^kaand AhiTudi.TNc Winittff>«pir itironunuDiu. 4

5

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1

2

3

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),42S

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IM

20

OTHER MRAMETERS

•

A. continued

FIELDNAME

MAGWA

HELDNiiME

"3~F—T-n—"^—

GINOAL : DeWTTION

RESGRVont PAKAMriEKS

^

F k U S i n (km)

^

Clurillcilkiii

Btlly m Klcmmc 2Ci

T

Dttt<<

19)2

A n b i ^ Pljitromi

Mifwt-I

f

DtacttHrT MHhsd

Stiuctunl (kilbng

Dcntii>i(n)

7

l«]

FMd.SIMu

Ftoduoer

ToulWcUi D r i l M (diU)

II6(I«M)

10! (79 ckMKi)

ObKmrWcUa

4

I^Jcctfon Wttb

7

IMtot

WcUi / ,

h'ormaUoii

1

2

3

Wio

HiLi^jri

bur>;4iri

SinlflafK

3nJ SartdJiont?

•UNSwidilDnc

176

•HS^

MO

.

-

*

-

.

.

3

•

IT.T

23.29

K

hniHbUlt]r(iAd>

250

HOC-WOO

1000-3000

UdilPniBm

T

7

1

BubMc P O I B I

1

7

^

7

T

7

7

1

7

1

1

3

BottaBiH
fT)

FormaliHi

PRODUCINa HOIUZO^(!i .

1

ktatmir

WeU Ttabl DfftUi
MAGWA

(RBSTB)

on. MRAMETSRS

LHbsbKr TUcknostn)

aw

'i^'-' • •.v > / .

Fmadon

A *

«>«™CE FonbatlDit LltbollIC

TUckDCH (ft) Atl

^

• • ; ' ; i 3 . ; -

BurgJIfi

Bufsan

ShAle

Shalv landslcmc

Shale

CdKHTuniin

AJ^inn

AJbim

3 .^r

2

r%'

Kuhdumi

BiEiiimruui iluie, Umestoftc

•

K^LLfHluiri

kA^^tlumi

BituininoLih

Biiuminouj

700

700

Albian

AltHin

1

- 2

-1

11

479

125

SalAir CvotcDt

1.3

13

24

1

1

1

3

(») ViKHlly(CP)

ntoDucnoN PARAMETERS Recovery Ffedor

T

Drivi

(1981)

lilUI PniducdoB llUtil

111

Daily P r n l u c l k n Idalil

RHfrttrabIc

T OW

3

3,58J

).7BH

4.L^N

ThdckuHof h j Zincing

l«

3J0

MO

7

t

7

Pniductiofl I k n ' )

.VI :

S87

Efiuiralcnl Oil

IVpUl UN Top

Anaof

]J)

TOO Aibiin

SuuCTUflJ riUllHl UlllCl nf

Tnplypt OTBEK MXAMETERS

AJbtin

2

Ahmidi

LHb«)i>ty

>

Al^i^n

Cemrwufrn

A f

Oil ( i r i T i t r I ' A F l ) UH^OUKltl* licVSTB)

Water invc + gis cipwiucHi v*i (BCip

laj«ti«i SbtiB

^

.»

EiUnalid

7

r

RKD^raMf

T

a. >

A. continued

> oo

FIELDNAME

MINACISH

GENEKAL DESCRIrriON

.-

F M d Slic (lim)

Locfitiofl

?

29'5" N, ATiY

E

ClBKflcStlDII

Bally : : i Klcmme 2Ct

lytnilriim

Arahikn PljEfomn

DUcif M«c«vtrT

1>»

Dteflwry

Miiufjib'l

Sdtinic Hirvcy

Eknu« (ft)

iTT

IS(1978)

Mtthod 1961

FMdSUItu

Producer

ToUIWdli Drilkd ((••It)

14 1I97e)

Ottrrtr WcUi

(1978)

Wtib

1

1

3

4

PradocbiM nvdimr WUb • HORIZONS Foniudon

Miilinf

Win

BuFj>n

Minjp^

UUuloiy

LimHtone

SindslonCK stulc

Sindnonc. vhik

OaliLic limtiHKM

450

ISO

I.ISO

450

L I U CcwKluniui

Esly Ccmnunivi

Alhiin

Eviy VilAnfinian

1

2

3

4

'nkknostn)

Av SSAl. Fomutfan

Tvtuma

AhmiLli

Burgan

KMtwj

Ulbolac

Shale, iiurl

Sbik

Shalf

Shale

Aft

SinloruHl

Mid'Cenomuuvi

Alhiwi

Haulcnvitj^

1.

z

3

4

SOURCE FonuUiHi Ulbaioc

AiKilLiDooui ituty liiiic$(Dnc

LMe

fiemuiU'

2

3

4

D*ptll ki Top

4.641

J.MO

J.64S

9,4»

TfatdUKBOf

IW

7

l»

KW

IT,M4(cta

•?

7

T

Anaf PiudiRtlon

14

16-14

25-40

h r a a M U t r (nd)

7

300

lOOO-ITDD

W300

M t U I PI mure

T

7

1

4764

BubMc Point P n a v n (p>t(t)

T

^

T

7

BotlnnUD)! IbiDfHnlHR r F )

T

T

7

7

^

7

7

1.1-1.3

OIL FAKAMKTERS

1

2

3

4

OUGraTlir<°API)

1

T

m

».14J

CuHMlRMto (icCniTBI

1

1

•>

147616

StUAir C o U t M

•?

T

4J

2JH40

Vhcoailp (CP)

-

t

1

0.54-1 86

,3

4

00 ft Cu

(P^t)

4 (i9T»)

FamUoB Vdluini F K I D T (RB/STBI

B

13 01

I c

3

(»)

O CD

PRODUCTION FARAMErCRS DtHn MtClUBiSBI

Rewvrry Fictvr

Rccovrrvtik RCHfVH E q i U n l t n l Oil

WitCT(irvc+8 U CKpiruion

IiVKcUaD StabB

G u tnjccbon 1 too MM.cf in MtniKiih

6J3tptpl/d(IOT3>

Tout pFOdUCtlOB Matil

U 8 M M Mil (1984)

Eidnalcd

7

1

RrAttcnMc Oil

2.1 Bbbl

RccwfnUc

T

Hiutenviui

StnKtunU vi[i< lir# ifTected by bolt) piC' and pCKt-Enccrx rnkJingcvcnls

1

orrOEft PARAMETERS

\i-ia

Rucrrnr P m s i t r (%)

Daily PraductloA (dAKI

6O0

Alt lyipiypr

2

<«)

Ritiwi

TUckncHift)

1

RESERVOIR MRAMEIERS

».152

T s u i DtltUi
MINAGISH

FIEI.D NAME

00 CD

5.' & m

A. continued

RAUDHATAIN

FIELD NAME GENERAL DESCRimaN n e M Slat (kiB)

Loatfoa (bttloaiJ

R E S E R V O I R "• '^ MRAMETERS '

T

Oawhcatkiis

Bally 221 KIcnunc ICa

FVlrokiim FYoviDCt

Aiabian Platfonr

WS^N,

Dateaf DficwerT

IWJ

DbcAvtry Wdl

Raudhauin-I

Raermir

PtnDHbiJily 1 md)

Datror PrvducUoo Prvduccr WclU PRODUCINC BDRIZONS

7

IMO

DlicvTcrr MtUud

Seismic survey

FkM Statu

Piwliicer

ToWWdli

58 [I9K4I 2 [19S4I

Otwemr Willi

(14M)

litiectlaa Wrila

1

2

3

4

Mauddtid

BuF^Aft

Zubur

Rplawi

Ulbokcr

LiiKtionc

Sandstone

Sind$uHV. ihAk

Sindslone.shak. Litneunne

30O

575

IJBO

110

SEAL FornHlJoii

Lower CreticHHit

Albiin

t

2

Ahrudi

BuT^an

Ap SOURCE

CenoirAnitfi

Albian

t

2

TUckiMU in> A|<

Dtpth la Top

P m l w U H llun')

Riuwi

25

..•, 3

7-24

20

IJ

401-500

4XMia()

ICO-MO

14713761

2500-4280

4060.4280

BubMePoliil

7

7

7

7

BMtonHdtt T^mpcrmtiiRCT)

1

^

7

7

M

1.4-1.7

U-Z7

z

. 3

3

Fannatim VaJome Factor IKB/STB)

]J

OK. • "'Vt MRAMeiERS

4

4

J'>^

>: 1

. ; i . i^

4l>.-l-l

r.aa/Oil RaMo iKf/STB)

6] J

737-80S

M«-14a0

2260-2770

Suinir CotttfDt

1.7

2.7

10

10

7

7

nU C r i r i l T [°AP1I

700

600

Abin

Lower CreiKCQUi

1

2

3

4

7.400

7J97

9.036

10,300

7

T

^

0

7

^

?

m 3

a.

(») V b n a j t y (CP)

7

>

^

"^ al^^^^H

P R O D U C T I O N "I P A R A M E T E R S ';>

Lower Creticeoui

Slfucoiral. tlijhUy tlonpcal NNE-SSW domt «ilth JOinc fiuhing The t « f i « f dips i n atxHH 3^. TtM dome is t h o u ^ la be due lo u l l al deplh.

?

IS

,'

Rtcot*ry Factof

7

Drin Mecfaaal^

Wiicr^vc + ^eipansion

hlactloa Statai

G o injection HO MMct/dinUtc Zulwr rctervoir}

Daltr Pnidoction Idatcl

9l,«42Mil/d (1M3)

llHal Pnductlaai (4«»)

1 1 B.hbl(l«g4)

EMiiaalMl

7-5Bhbl

7

Ri«r*«nhla OU

7

RemttiaMt Gai

?

Rjuwi

rtyZaatltl) A n a of

Zutuir

Af^llKHHii bituminou dule and limaUKE

LillHlDU'

OTHER nuuMEirERS

4

Kuhdumi

Fomstkia

TrapTypt

3

Shtk

[JtbDlacf

z

7

DrlllMl
Ap

1

(ft)

Fomutkia

TlitckiicB
>

EkrattDD

.'

2240.2305

Initial Pr^Bura TiiUII>cpth
RAUDHATAIN

FIELDNAME

RecaTTraW* Rcatma — E q u l n k n t Oil

A. continued

> o

FIELD NAME

SABRIYA

FIELDNAME

':- "^-r - - ^ M

Dsscjumofo' FMilSiK(kB')

n*»t|h^rt^m

I d 7

Loutlai

A n t u n Pkdfomi

Date of

Tsui iviiiti inj

Kkmmc^Ci

Pmrim

1957

DtscovHT WcU

Sitoiya-I

P t n W b W t r (Bd)

SABRIYA

I

2

IB

19

7

lOO-lKU

T

1

7

U

-3

1

Intllil P u s B n

7

7

7

Bubblt Polat

T

t

1

7

Bottom Hole l^mpcnturT {*F)

7

1

7

7

Formafion

T

7

7

7

C/3

ft

(ft)

MMksd FWd s t a t u

4

IW

SennDcniT'cy

T

i»ei

RBSEftVOIK MRAMETEttS

PTDduor

Total WeOi

5l(l»M)

P r a « « v r f (p«4B)

D H U n l Idalal

Produqr WeUs PKOD(JClN( BOUZONS

Ulhdlofjf

WEBI

1

l«.

Formatkiii

4 (1«M)

Ototrvtr

45 (IM4)

I

Iq^cctlDii

7

i

F

*

VoluniF Factor

•••••.

1RB/?tTBt

»'a«^-^l* V - H B ^

Mtutlttutl

BLtrf;3ji

Zubiir

RjLaw]

UmctuMK

^wtuonCv sfiale

SindxUmCv stuk

SaiKhJcmc.. lime

OtL RUlAMrTeilS o n C r a i l t y CAPIl

IMckaHtcft)

1300

573

795

An

130

FonB^dofi

UlbolDo

2

1 ^^ar-j

J*

Hi,[^jn

SAAdsuHU, shile

SindsLone. i h i k

Il—J¥i—

SsMir CoDUBl

iflJuiat'.TMMI - " ^ - » ~ lUiiwi

Shiiutu

Sbk

DokHnitk

viiaHy(CP) •

SOURCR

CcnDfTHIUVl

• l i

• - - .

ApUaji

2

3

Hiutmviia

Af.

• r

,

-

J}«

no

f

T

1.4

J.5

7

7

^

•>

C3

3 a.

1

-)

O Ctq

7

DUn

47JI6tlbl/ll

Total Prodvctkia

(l9Mt

WaLwaierdnvc

7

+ g u injccttnn

l4|«11oa Statw

3a7MM.tibl (1984)

bdaatcd Jtcacrvt*

t)(7) BbM

T

KacotcnUtf

7

IllMlf)

RecovtrmUc

700

MO

AfciiA

U BsTutbU-Hiutenviin

EquiTiltiil ( M

2

3

4

1.100

7.415

7

7

Tiikliaaior

197

UM

7

1

t

7

7

\10SntaB,

•'

(») Plodurtian M M i )

D«f III to Tuf) of Pi]' (Hi

A n a of

>;.4

RK13WL

Smictur*! N^S-irending viuclinc

IVapTypc

4

FSODUCTIQN nUUMETERS

4 ' T ^

BitufniPAu o r f » c ncli ihtlt and lirncstcHic

Udllllllf!' Tl^duuttin)

OTHES PAKAMETEJU

AlbiLir

^pjhilitmi

Formitisii

- fi^PI

; : A

vi

Rcoonrr Factor

An

1

ItcOSTBI

Alhiui

&Ap«M S K A L ' ^ - ' ^

t3

tVtlta

0

Rccovarabk CM

a. &5

A. continued

FIELDNAME

ALBOUT 'I ,t»;

G E N E K A L *• DKSCMmON F k M SUt

•

[LIB'I

Locadoa

^

FIELDNAME

-•••

^^^^^^H^^^^Kj

^

lit! ?

Clm^flcaEHHi

RaJly331 Kltinine2CA

i r 4 6 ' N, V)V E

D«l»ar

1W3

|TI iTtwf mn

T

Sainuc HHvey

5.500

A] Haul 1

TUckiKaitf

?

DktCDf Pradudioa

WtUi ntODUCLVG HORIZONS

'=

PIT

•mbaa

T

1M»

FWUSuEu

ProfkKH

IWdWdb Drilled (date)

]7(in2)

)6 1 lyKli

Ohiirnr Will

•?

bjKtiaa

T

1

FornuttoD

Mi%hn1

RMHUA

RMWI

Ltlholofgr

LiTnolDnc dolonubc linHtHK

LimatDiK

Oolitic bmalDiK

MO

145

ntckKmri) An

SEAL

Z « I

(ft)

Anasf rrDdiictiofli ntSERVOIR TAKAMETKftS

c«™™

CeimninunTUmuu

: r

1

3)0 L BecTiuimHwieriviKl

^E^.1t>^

woo

5.750

^ H ^ ^ H

11.J0OKIB

7

7

T

T

T

T

1

hntrvutr Piv<»lty(%l

;3;(!

Ptnn«l>Ult7 i B d )

7

1

7

Inldd pRHiir* (prit)

?

7

7

•sbbbfWiM

^

T

7

B«taaiH<4t Thmpcntar* (*F)

T

7

7

ForiHIIsa VtJunir FBCIOT IRB/STB)

1

7

7

^

2

Fl M M t ( P ^ l )

'*s9

i^H

Dcp41i ioTof>

m

MCOHHI

^'

AjibiAn PIBISKTII

Wen I k u l Dfpth (ft)

MKAMEISaS

ALHOUT

> 3

FonHdan

Taniiiiu

Rumvia

EUiiwT

UdHtocr

MirLuid x h i ^

ArpUaceous liimcflEnc

Stele and unddone

SuLaruan

(Jawmuum

LBemuianHiutenviAii

GaiNMRaHa (KCSTB)

1000

yH<j

990

^^SHR''^'-'

SstftirCoatia

1.3

1.3

a4

-

T

7

Af

scxmcE YJ.

1

SK

^ ^ • 2

Fomuliiin

k«u^t

RALJ^I

Ulbaltcr

ArpLlaceout

ArpLlionu

on. ,-,, '• MKAMKTEXS OUCnrltrrAPI)

600

35,3

ji

AjplUcoom

600

6Q0

BcrriuivV HjuLcnviin

l^Bemtiiu-

FKODUCnON MKAMETEKS R K O t t r 7 factor

A«t

TnpTrf

Bcmuisn^ HwlcnvLMi

SinictunI wiuclirte wii^t npnni 1 faut[]n^

;%-.3

(») Vbnji(tT(CP)

TUdcBHiCri)

"-;

Dnilr PnditcUoa Idatt)

KHv^Fnnc EquhnicBt OH

T

VAMcdrivi

<»)

Stem }.4«)liiil/iliiil
TMll Prvdvctton

4*IMIM.IM«U JOB.cfiB (19W)

EadiiHlcd

:ooMiu.bbi
1

•iLUHIlbll Oi

197IMM.litil

BKIFfmDifl G«

T

& >

A. continued

DORKA

n r i D NAME GVODtAL DESCKimON

^

F k U SItt I k m ' )

Lmttoa

20 « 10

ClmsiflcilloQ

Billy 221 Kleiiunc2Ci

18*56'S«-N.

Palc
1»*7

7

T D U I DrpUi ( I D

'

-

•

ScUniciwvey

DORRA

H E L D NAME !

?

-

,

•

-

••

A n b i u i P]d[fcrmi

^cnituiD

Dom-I

T

Ekntioa

40.100 a n a

7

BESEKVOtK PAXAMEIEBS

1

2

Rt«rvt)if

24

^

Anaef Productioo

^

Initial P I I M I I I I DrnMUt

WtUs

T

FWd^latiii

F^nkKcr

T

OhtfTtr W,ll,

1

Totd Willi DrUMhtet)

9(1MZ)

?

pDmBtlan

MJUJJNJ

Bj;.rii

UdiatDcr

LimeslDne

(k)liLK hmejcoTc

MO

3S0

LjCcAlbi*n

Lj£e Boritfivi HAULrnvian

TUduai
SEAL

• '

RaU^i

Win

T

FDmvlioa Voliimt Factor IRB/STBI

7

on,

1

-

;

•

I

2

PAKAMETERS

2

^SBfc--;'«>:

Fomudofl

a.

^

-

BubMt PDlnl Prranm [ p ^ l Bottom HoJt Tctn(Kratun<^n

1

'^

ft

Wflh

1

ntODUONG HORIZONS

on

1

PtroMBliULty ( m l )

Mitbixl

17-18

o a (iratily rAP[) G H f O i l Ratio (•cUSTH)

7

Sulfur CoDtcnl

3

Vlicd^ty (CP)

'

• '

ft

'

c 3 O

^

*-<

•

Utlki)otr Air

SaiditofK. shtic

SmdiUinc. ih«ic

Eirty CenomAnL^

1 J i f PfmAiiBn-

UMtM-*l

KJLJ«I

H JLi [ f n V1 .iji

Forma lion

uuutotr

L Dcmuuuv Hiiiceriviin

DttptktoTop

,

'

2

J.wa

T

RicoTfrablf

1

EqoinlmOU

olfirim ThkduKiiof FarZoHini

0

Drin Mtcbaniun

Wicer dnve

Total FrvdvctiaA Idalcl

?

RtcOTfnbl*

l6)MM.bM

on SlrucIunU vniitiJinc

IkiplVpt

DaUy Prwluctlan (dalel

MO

600

Ap

OIBSB PAlAMeTFJCS

R««iv«r7 Factor

LiniQlDne

TUckncnim

o

PBODUCnON FARA^fK^EICS

2

SOUBCE

o"

7

OQ

"^

Slacm

*> MOMM.bblal + 3ST.cfEU

fT

tn 3ST.cf

S3

A. continued

FIELDNAME GvsatAi. .' DescRiFTiar

F R L D

KHAFJI

* - •

( U i

FVUSlBlW

-

"

•

"

•

•

. .

OTHER

AjafaiAa P l u l o r m

L o a l k n

M*23'N, 48'M'E ?

Total D n x k (A)

1961

Date or

IVpdiioTbf^

Khagi-I

IMmcmtry

19J9

Xlftitof

n e U

Ana

7

E l m t t H

Seiinucturvey

"55:3

li](l9M)

FrcHkKa

Statu

of

4,900

T

7

330

470

1

7

1

1

3

4

5

26-28

26-2t

10^30

0

20O

130,000 K I H

HESERVOIK

(19M)

"

Pamdly

(19M)

> 17-JO

RcKrv(4r

t

OtatrvH

(19M}

•

•:' •

'

l»-33

(%1 300<WOOO

^rM

f

^

7

3606

7

7

7

7

7

7

lU

1 ID

7

i.i;

IJ5I

2S0

PemknbMil^f I m d ) PROOUCINC r

4.700

4,100

•:••;:•

ProdufliDa

fAKAMETIXRS

147

4030

4.01(1

^ 3

h l Z o o i t n )

Pradncttoa

Wrlli

. 'fft

3

o(PiJ(ft)

K 1 « I I K 2 C I

am, toot)

4

1

FAKAMETERS

Prln4euin

BalllUI

11

KHAFJI

N A M E

•

HOBIZONSJ

^ ^

1 i r i ' i V Tta^Fi

Inittd

'.

FortiudOD

I t M l I t

«ta

MaddHl

Bunjin

Ktfnri

Utbubcr

Umnione

SAnditafK-H i h i J e

LJiKton

SvidiuiK

CikfRnitic

Pravun

B u b U t PnliM Pnfnm
v»

343

53t

MHl^Cenommun

LatcAlbiui

F^rFv A l h i a n

t jEr RrmaJAn-

1

-^f3.-'V:t::

IB

'nitckKB
*r

130

BofCooi K o f f

>

T e m p t m u r e (*F>

Hjij:c-ivian

F n a U o B

"a ft 3

V d K H F K U r S E U .

' . ^-1,

'

Ruiiiiuk

Fornwttcui

ArxillKtcHU

UtbuloD

. -r-i Ahir.j.i,

Wija

.4 burx^n

K(ttJ*«

Stutk

Sink

s^ui.^LiiiK. s h i l e

Sink

. 5

• * ' "

limstone

An souxcE

Mid-CencHniniin

Hmtenvisn

.^ r^^ -

FinBttsD

uuuiotr T U d u i ^ ( n )

Ate iVi^Typc

UEknuiiin-

EirtyAJbisn

Mid-Cawmaiuin

2 • ^

,. 3 . JtMirwi AifilUceoiH btnimilMou LmHUHK

too

..4

.


a.

1

Z

3

4

s

OUGriWty("APIi

;7

2i

:e

;*-;»

))

GutfOtlttitla

140

7

7

IZ)

ISS

SaMirCaataat

}

3

2.1

2,9

1.U

V b n t t r (CF)

3.9

f

7

J

091

^^^as drive

ljO«ti«

Ui 1 9 B 1 , d u m p -

(ML i.-/ MRAMEIBU

^'

>

<>drSTB)

FRODUCnON FAKAMETERS

'•• 1

Lite B o n u a n - HHUenviui

Ditn

Statw

•

Rood WVlll Jumped wtter tt

S m c t u n l anicUne

n H o f about 29.000 B W P D

217t)MM.M4

iMir ProductioB (date)

(1981)

rtUUlKUIII

(l»U)

ftcacrvH

—

EqulTalentOU

7

R#«vrrab4c OH

7^00 M M . b M M l + 3000-5000 B-CffH

(ilatt)

RKQTvrabltf

E H I I H I H I

630aMMtitil

?

f.

A. continued

>

FIELDNAME GENERAL DESCRirriON nrySlxtkm)

1 *

' ' ^ '

•'•

(Mkntt

FIELDNAME

"V'^^-^.-v.

OTHER •'i''.MBAMSTEBS

<.'l*Adft«tion

Bally 221 KIcmmtiCA

Dutof

1933

M*34' N, 47*5*'E

LocirttH

WAFRA

FttnUvm

A n b i K i Pljit(£ifTn

Wt(r»-4

•

4:i)

\^^t>

30O-1M

i«a-iKi

77.[»0icici

7

Mrihod

Scitmic ninwy oDfchoiet

FWU Stadia

PmkiceT

JAW

^XV610

ElmtttB (It)

}aO(19M) DrUciKdab)

P I wluLuui 7

Produnr

>

Obarw

RAdhuctu [2nd Eocene)

(IflEoccn)

LimexiDne and dotomitK limcHooe 700-750

Tbkkawm)

40(M50

PtkcrtfltEirty Eocene

A(t

tlHcr>«ir FiiiH
4

P m n b U i r ) ' (md)

Wu-i

RjUtki

Lnnmaie

SjDditDne

Unetlone

(50-200

IW-WO

600-70)

MautncliOiA

CeaDnuBiiD

LvBenufitD-

1

1

. '

Tayar^ic

:

. 3

.;.v^

nnHi«

Radhumt

Rui

RKlhunu

Ahnudi

Rauwi

I Mill p

Dolcmile

Anhydrite

Dolonutkr linrntonc

Sluk

Sandtfone, ihtlc

Mid-CciiAnuniin

1_ BeTTi»i»HauEfl-rviui

*«• savmcf.

KBSBBVOIR MRAMEnSS

I .UJ i^

PileDCFfK-EAriy Eocene

1

^

.

3

^.^

HjJl^iO'-'^^J kalawi

Fsmtkm

th.no

7

7

L70

7

7

7

*

3

4

Iti-lit

:v

10-23

"»

7

7

7

7

7

7

7

BubMt Point PiriMiiFT [p
-J

t

t

7

M70

BstUD Hok l^Bkfwntuft <*F>

7

7

7

7

,51

Fomiailoa Vgtuinr Fuctw {RB/VrB»

T

7

7

7

1,125

2

3

4

OIL MKAMETERS

1

400

MD

Scnomm

Bemotiw- Hiulerivitn

NW-SEekirtpiKlirticliiie WTUI tubsidingfotdloSW [HwJvciivt l i Eocene tcvcli. A pcnMtbiliry btmef M H C O ( ^ Eocene limcuoM \mi h u mulLed in u i iccumulitiDn pluriBinf SE to ^3rm * t q w i i e TBervoir.

13-*!

OUCrtvitjCAFI)

19

»

IS

M

24.5

GurOURuiD

7

7

7

215

7

«»

tA

7

3,37

3,6

t

'

1

1

c 3 O o_

(Kir^TB) Siittir CoitfcBt

(»)

?

AcgiilAoeous iinieflonc

Ulkatocy

3

(pil)

V l K « i t ] l ICPI

TWduBiin)

;5 .it)

fncture

UtWPmBR

Foraiallaa

Lttbulocr

3

A r t s of PradiKtlan

7 Mrib

2

1

PBODUCINC BORIZONS

t*»»iyp«

1.95«

Pay Z o H (ft)

WtU

IM3

Otlnl

Ap

3 .

; i

00

Tblil Diplb m j

SEylL

[>tp4ii uiTbii of P>r ifl)

WAFKA

t. . .-.

FKOIHlCnON MKAMETXKS

•

,

'

•

\d'

' -• DHn

• ^

{») EMIT PndiKttoa « l * t t )

ttaevnrmbit RocrvH — E4u*nl»tOU

M M cerd g u (1978) * 8 i M.bbVdoil (198!)

a. a.

ToUl Fnddctt«n <^MI)

OH

T

EjdmalBl

172a M M . M

HKUTtralHe

7

(1978) <- 1250 M M .Mil Oil (1985) 7

1

llOcCttOQ .Statu

G H

tn

ell

m

emml m

FIELD NAME

1

BAHRAIN

L

4

t

4

1934

Reld slaw Obrncr Wdb

O

B. Data from the Awali oil field, Bahrain.

L

4

t

I

10.1100

10.1600

1240

I240

?

7

?

7

?

?

32 1944

21

I

3-25

I

lm

I

Appendix A

. ,'4 . ?*

10.3100

A15

C. Data from some oil and gasfieldsof Qatar

>

FIELDNAME

Btll, ItANtVE

GnVMAL DBsnuFnON

FIELDNAME

•3

'

BITL H A M \ E

OIHEK KARAMETERS

I

2

TJm

B.liJU

.

F M d S i n lluB^I

Locickn iLpt, lAO^ IbulDerihltl) IMiof PradHctMA R n s H T HnHt

n.ii6itri

ClBHiflCjUOfl

Billy J : 1

P^troiFum Provlsc*

Artbi»n

Depth ta Top

Z l - M - N. S r W E

Difc of D b c w t r r

l%9

DtKtrver^WeU

Bui Haiuw-2

7.700

DiKovery MeLbod

Seismic

FJerntlod m

7

ThldUHKdf Pl]> Z « K (fl)

)3

4 (1911])

1973

TkMStatai

Producer

TbulWtllj Drilkd IfUlcl

11 (IM])

OtHrrtrHUk

1 (l«i>

IttftctlaB WtUi

of h r im m-ina

ITJ

16.640 a c m

1

C/3

A m of PniduclioD

RISKRVODI nUtAMETERS

1

Ruuiuir PRODUCING HOMZONS

-

3 B

2

J.30

i-ii

2-1000

SO-SOO

JK5

4373

:062

7

111

227

LSI

7

CO

2

•

1

&3 ?RiiKibtUlr (mdl

Formation Anfa- D MemtKr Utbotui;

Dolominic. pctoidii

Initial P i w n Pelcii
liinauHie with anhydntK ilnngcr Thlckumni An

SEAL

45CM:K)

200

KmitKuipiPE. TiThdm>n

Balhoniui

2

1 Arab< Anb-C nwmber)

Aratj | U Araej Mbr>

LHhttoc

Anh)nlhlf i l haul Anblll

LimcmubuoM

Kiirmendgiin' ETitlKHiiArt

BMhoniin

1

2

Hanifa

Horufa

SOURCE FoniuliDA Ulbokcr

TMckawItt) Afl

Laminitsl. bituminout bmmonc onJ »h*le

PRMUIT

•

Limiiuied, bitU' miiHui limcitone w J (tdlt

90-300

90-300

Oxtordim

Oxf[ifdian

3

Ip^)

ft

BAttoBiHal* TcDipcntuR

FormaUiHi

Aft

I^D

B u b U i Point

FvnnatloB Voluii>iFicti>r
O ft

OIL FARAMETEKS

, -

2

o_ o" O

• • « —

<)U (;r»»iti CAPlt

-ij

"

Gu^lRada (KltSTB)

T.W

7

Sulfur C o a t n l ( « >

2.2

2.1

V l K w i l j
0.11

0.4

ft

FKODUCmON PARAMETERS R i u o n r j Factor < » )

t>ail> Productkn (datcl

W &5 li

Drive MKhaniun

Water (lumped irvo ih« praducing lonnaiioa

Iq^ectloa Stntv*

WdCf iirjccimr

170.000 WlAi oil (148)1

l^«al Pradttctlaa ()

389 MM.Mri
bdBBtcd

6S0MM.bbltf cariy lUgeof ditwvffy

Rccovrrabtc Oil

1250 M M btll

Rennrenbk

1

jaMM.criai 11??'*)

THplVve

Amkline r t l ited lo u l l movement tt depth Rcn^nbk Equivminii oil

lUOMM.MI

C. continued

DUKHAN

FIELD ^ \ M E

NJKHAN

FIELDNAME

GENERAL IXSCRDnON

U

183

ItO

JJ.ODOicni

7 I 6 km

IJCO

rkrZaK(ft) I7i4lun

1

•2

3

4

lj-20

l»-28

19

IB-22

w-:oa

70(avt)

lHvii.)

U

»l]-33}0

3300

an

7

24$0

i66i

3360

7

BonomHolc TnupcmtiiTi

193

u

:!i»

2S0

FormatiDtt VolvnK Factor (RB/^TBI

14

L»7

[^

7

OB, .'••' PARAMETERS

1

2

3

4

OU ( i r a i l t y CAPD

37

42

42.5

las

Gai/(MI Raiki

73J

1070

loeo

'

Aftaof FtVdKtkA Klcnunc 1 Ca L o u d e n (lit. loat)

M-OC N. W * r E

t

R E S E R V O I R -"x PARAMETERS

DottofDlxovtTT 1

TaMDep DmUot

SwfMX rnififnng

5,M5

ReierToIr Po«wlty(»)

TbulWelk Di'Ulid (ilile)

Prvductkn

ObHrm-WiOi

15 ilWJ-i

Pcnneibitlly (md)

[4>ectioii W t i k

Initial P r a n t r t II9H4)

ntODUCINO

Bubble FWal PnauR(priK) Anfa Anb-CMbr

Anej (Uwainu Mbr)

Anb-DMbr

Dolonute ind l i i w w n e wilh thin liyer of Anhydrite

UtlHlnt;

([••ill

Oolilic m l peloid dill

Doloniivud limHtone with thin layer of jah)rdhle

Kirnmcod^wi-TiiSDruui

Ap

•^r^

(K*STRI

Anil Ar^BMbr

Anh AfitvCMbr

Ant) (U- AjKj Mbr)

ti AM.!

Anhyikict between eitxh mcniber

Denie limestone

DokKiule inif;

bnUed wirh u n d y shiJr Aft

"a ft

1^00

T U c k K M (ft)

B- TnAilit:

KinunentlBiiri - -TLthAniui

T't^^

SOURCE

SulAarConliu(«)

IJ

1.1

O.B

0-2

Vtocoaily I C P l

03

04

03

t

FRODUCnON PARAMETERS RecoveTy Factor

K..

••

•'

t

:

^

^

;

_

•

-

_

(*)

^maax^Bi^m

E

«

_

>

(1M3)

ToCal PrsdilctillB Idatel

IStNMM.bbloil

RKD>*raUe Ol

32(lDMM.litil

(I9S4)

a.

•

I d j t f tion StatUA

Wa[cr ]n>ctt]0n in Afril ttt. [V

EiUmtcd Rtttrrt*

2400 MMbbloil and 1.1 T C F

wauf tlfive. jaiiap

"SE Daily Pmductlfla (dale)

_

Dllve Mrchmnljnn

£3

LvninMed, bitununout Limeslone, mArl li¥l i h ^ 90-3CO An TVipType

oniFJi PARAMKItHS • v p l h to Top of P I T (ft)

> -J

SymniHriMl, l o o j . ( n m w M S uDcline (urallel to iht C related to decp-xCMOl u l l nioveinenl

Rcconrabte ReeervH — EquinltntUU

37i3 M M bM

330 TCF Gm

C continued

> 00

FIELDNAME

n w EL SHASCI

CSffiftAL ' DISCKIFTtOM

m o EL SHARCI

riEUlNAME Aiva «f P m l i K t k n

,

— —^ . ' ^

'kESEXvon PASAMETERS

Fldd Sin ikm')

Rocmlr PDniitrt^)

7

-

4

5

13-24

3)1

ISl

W-HO

I-500

1-16(»

1-20

00

MKI

3«W

4010

4010

a.

3000

»ao

J»0

)5M

JOS

112

230

130

T

1

-)

1

1

z

3

4

5

16

17

32

36

36

1330

1

27.300 » c m

T

1

1

t

3

13-30

1IV20

40-100 23«0

2000

'.

LacBtkn <1BL ID^>

521*'are

P n K a b m i y
aj2()

-IMlIt Deptb IR)

(MO

Dali gf Prodoctiiv BibUiPidal PnHDR(pdc)

11 (19B?)

lit l^mpcnluR

nUXMJCING HOKOONS

( ^

-i^ FArnulion VIJIIIEK FKUT

Arah [ A n b - C Mbl)

Anfe {An*-Dl«br)

•>

IRB/STB)

oa

'

3

MRAMETERS

CluUi m l bioclu-

F^Lotdil dDjonutic Upieiionc and minor ubydritf

OU U n v J I f <°API)

Kjmmcn(]][iu-tl Ti[hofl!W> SEAL Anb (Anb-BMbr)

Anti (Afit>-C Mbt)

Adhrdiie ba««ai och fwnbcr

Uttttotr

AlKj (U AlK) Mbt.) Denu limntone

KjmiTtcndjlian • "n LhKsni iji

Ate

J^'^^'.

Utboloo

SvlfiirCaatnt l « )

it

re

l»

12

11

viHoiur (Cp)

2.i

1.0

0!

02

02

Scivciw*). Fkmfited ind bitobitc uBcline: l«o dofw (Ttlacnl to HII movCfKflO Hptnted by I uddlf f-Aicnsi^ ndiAl fiulitjnf ii presfln m the norrheni dorrtr :

Dkpth ID T o p of Par

(ft)

u

1

DfffTC M u . n l u u i u

(»»

RfCarrrmble RrtMT« — FjgulnlcDt (HI

Apdm

TnpTVpc

ft«(«wf>FK(or

O ft

.

PKOODcnON rARAMETEKS

Ljnuiuled, bHumuxHU UmoUKK md thak

im Aft

TWckuMof Pk; Z a « (ft)

750

(ihu)

Df^HK nch inicf-

MBAHETEBS

1130 (KffSTB)


SCMBCE

7»

2-

17,000 bbl/d (m3),29.S M M cCTd ( s (1*76)

(dale)

G a expuuKHi wiltt rninor wllcr dnvf and ^ o p

IqMkuiSutui

7

l6»MMbblal

EHllUtHl Rorrrs

2100 MM.Milaii u the atiy sUfeof dlKOvgir

RKWcnbtc

T

()9a3). loau

ft

MM.cffH (1976)

IDOOMMMll

lOOOMMbbt

OU

aM fa

C. continued

F I E L D NAIUE

MAVDANMAHZAM

IGEHERAL DBSCBIPnON FMd Sin Iknl

FIELDNAME

i . i i (1

trmj

Uuijfludai)

PVUriteam

Dalf d T P t a m i T

Lecsttoa
MAVDANMAHZAM 7,M0

1963

Anhian

T M i t i i m iif fkjr Z a H 1(1)

80

A n a gf FrDdBcOfld

D i K i P n ^ '•^B

H.MOKIB

^'i^?9

Mihmn-I TidMi Dtpth in^

»,9»3

DtacDvcrr Mttkad

CktvityieUmic

Dale or P m l i K t f M

IMS

FWMStBdH

Produccr

15

ObHmrWdk

7

PrudmrWilb

PRODUCING HtMtZONS

I

•,

'

1

QprAtkiAin)

3J(I9S3)

LL < 19(15)

Wdb .J • ^ t-^Vrl

KESEKVOIk MKAMETEJtS

2

3

Fonkudon

Anb Anb-CMbi

Arah Ant>- U Mbr

1 '^jjruE Mhr

Ulkiili«y

Dolomitic UTIKitoiK with mhy-

DukHnibc Ume^ MDOC with inh>^ dfite H f i j i ^

Pekndil "Otitic iim^ ixant

13D

360

IS5

Kimmehil^inE. Tlthoiuan

KJmmcndparR T"i 1N iniiin

BaUlDniir

TUckKB
*95

ft«*nrair

FOfUBtioa

utbolocr

Av

1

2

3

Ai-ih

•\r.n-| i\j Aratj Mbrt

\nhynlc 'vtween e*ch member

Kimmendgiiin-

Kirnmendiiin

IVnie Umc-

Bathofuui

2

3

Hiiufa

Huufa

LuninMHl. tiiLuminoui li rnm«ie ind

L^iiminuHl. biiu-

LiminMHl. bilurninpus iLmriUiACtAj ihale

Oxfonitin

UIHJUt PAKAMETEXS

>

Oifordun

I

1 -

'

^

•

?

1

7

2-300

i(H;

p K n e a U U I ; (md)

30400

;-soo

1

3«30

36£t

1 4^w

Bubhlt PQIDI PrcMUft Ipd^)

1772

IM)

1

4210

BatUmKoli

XU

106

1

n]

FimliiiaVdBW F»«iir(RB«TB)

1.41

1.33

1

2

JS

IK ^

I.I

OIL ^ ; MXAMETEBS

:

«7

VIHMIIT

(CPI

a.

Ml

II.TO)

O.SI

048

1.1

1 i

1 2ft

I.I

(KTOTB)

SvNiir C o a u u ( « )

:M

r

Stcorvtry Fjhctor

;o

t > h n MKiuruMn

..VLi[( 11 n}CL'Lj.in

1lO«ti(M Statu*

Mtly tbon tip nxkof Anit una IMtr PndKUoa hutcj

Si.OOOMiloil (IMJ)

T«UI PnducllDO Mtt)

1100 MM.bbI

90-300 Onfordiui

3

W ^ uOectiDn

wufce i n u n ^ -

ElhptitlAl dome wiih ifvcTil ^nulJ, unfCFrnefli fiutti L^iticJ by a dcep-scilcd u l l

TVipTVpt

1

wich w n e r

1

An

140

(Jump noodiji^

Hinifi

90-300

1

FBODUCntW nUAMETEKS

ForaaUiiii

9O-3O0

IM

lO-VI

Gii^OUKitki

SOUKCE

TUckDcsini

1

1

'•'^

UAtlotr

t.^x

3

Anb Anb-BMbr

Anhydriic bdween each Tncmbw

1

PwTMicy

OUGnvin'rAPIi SKAL

T-'<*>

1 .

(10

'•

Rcatrvci ^ E ^ i l n l n t Oy

170 M M M l oil

1 I W MM.bbI (M

Eitlmirtnl

ll(WMMt>t>l

RKDmblc

7

(19S31

GH

C. continued

> o

MUBARKAZ

HELD ^AME

FkldSlic

ClHikllllKl

•>

ntFDimin Prvrlm

: 2 I B>tly/ 1 C t Klcmmc

1

^3

4

5

«

Alibitn

EUnsct tmm 12 u> 25

ROFfYatr PHiidri'(%)

Mub«rru-I

R m j e i rrom 1 to 30

PcrmeiibUllj (ind)

on a.

Wdt

DbCOtMTT

MMUSO}

«03-«5M

4Ml-i646

4883-4980

MCU-JIU

S26«-3361

Bubble Polat

i7J7

18S0

1830

1424

1330

tVM

Etotlom Hole TtmptratuiT

T

?

7

T

1

7

IJI3

I.30S

1.305

I.Ul

i.m

1.432

t

2

3

5

6

Initial Prt^urE l(U3«

DteMwiy

Seumk nirver

WiltrDcptli

1973

rMilSiitiii

Piwlucer

TvUl WfQl DrlUtd (dlttr

P m d u n r WcUf

U

QtiHrvtr

1

bvlcctlon Wtlb

PRODUCING BORIZONS

1

2

3

4

-fbUlDtplkdl)

2

PHRAMmRS

IW»

Loardan (Ittt h«c^

MUBARRAZ

FIELD NAMF

BEsutvont

-

GENERAL DBSCRimON

100

(R)

Productkn

3)(I«S4)

t

5

upper

Fonutloa Volume Feetor (RB/ST6)

'

Hituhin

Khusb

F^madgn

• - • . , - "

kHHT

14VCT

kwer

upper

OIL MRAMETERS

kiwcr

Uimtone

Ulkilaof TUckncsfll)

MO

3M

1

SEAL

Z

4

3 LeLhwair

Khinib

FvnuOoo

5

'

*

t

Hkqhwi

Dense lin^fniithtHK^uchfoncKtlAlfrwn top indbotlom by denx LimesiQMJ

uthoiofr An

1

SOURCE

B e r n u i i n to Vikinginiui

Hwicnviui

BuTemiin

2

4

3

Focniitlcin

Oyab^Dukrun)

Ulbii4iici>

AjiilLHHUi. ihlly. bitutniiKHU licnalone

s

6

OaCmttrCAPI)

37

35

)i

37

39

43

GuKMRuio

4tl

Me

400

217

315

119

StOTur C a m t n l

I

1.1

1.1]

1.1

1.3

1.2

ViKdelty (t:P>

0.}4«

05M

osw

njso

0 432

0.320

O^rofdiin

Ajt

I c

O ct

•

PKODVCnON FARAMZTERS

•

'

o,

•

:i

Drive HeckHiDiBii

WiUT and iDluuon f u

Iq^edlDB SlalBi

Daily PnductlDfi {date)

22X100 bbUd (1484)

TuUI Prttduetion Idatcl

74 MM.bM (19841

EidiBated Rcavma

162 M M M l

Recpvmble IteHTHe — EquiTakDt OH

lOOMHbbl

Rce«*rmbk

7

Retonrehie

1

RccDttry Fkclor

1$00

ThiduKasfft)

3

(•ecnvi

Hi-fri—iM m ^hli mijMM

H«u(enviui

Btrrenun

Aft

lOOD

• 4

13CO

& cT W

oa

TVo m i ^ oricicliul tnntU icvintud by u^Nlc M d d i s

TnpTypc OTHER MBAMEmS Depth la Top

1

2

3

4

s

6

iJOO

9/100

9,i}a

),M0

lOJOO

ia«oo

?

7

irfPiJim Raifet fRiin «a ID 1 SO

tUcimot Fir

Z M *

in)

Areisf

1

t

1

f

PniAiclliii I k a * )

1

D. Data from some oil and gasfieldsof the United Arab Emirates

BUTIBI

FIELDNAME

DESCRIFTKMf

:,;,";!

FVWSlitlkm') CUniAaitliiii

PctrolciiiB P i w i i i c e

Locmtian

Zamn

Arxuub

• . - • • j / A ^ - - :i^-- '••• ^ ^ . ' • . i : : ^ - - ^ : r - ^

mgm

UmnAlDulkb

••••-

• .^••••••':

FiUah

FIELONAME

UmmAlDalkh

FUtota

Dnkhan (DiytA)

SUIiif (Khatiyat))

KlmUyah (Sbilaif)

»isly, arenaceous limestone

Shaly, arenaceous limestone

Shaly. aT{;illaceOLi& limestone

Shaly, aisillaceous Lmestonc

1,450

1,500

Arranab

Diyab

Diyab

1

. . ' : f . - r '

FormalloD

1

15»5

7

IS I 7

7 I 10

22^ Bally/ ^CatCleiniDC

221 Bally/ 2CaKleratfc

22i Bally/ 2 C t Kleimne

221 Billy/ 2CaKlcninK:

T i l BiOly/ 2CaKlemnie

Anbian PUifDfin

ArsWan Platfotni

Arabian FlBtfomi

Aiabiiul PUtfonn

Arabian Platfonn

?

24'4n7'N 52*34'04'E

7

7

2S*JgWN 34'1 I ' l l ' E

Shaly. ar^liaceois limcstEHic

UttKliiKr

nudum (ft)

1,500

Age

Qxfordian

IVvpT^

1979

1*73

1970

I96S

l»76

DbcnvcryWeU

BuTJni-l

ATEBIUII-I

Zsm»^L

UimnAlDalkh-l

Pdlifa-1

TMalDtpthfrt)

12,150

12J92

SJCO

7

»,«5

Seumic survey

Seismic: sufvey

Seismic aurvey

Sdaniic survey

Seisnuc survey

DfllcDfiyiscvnry

Zamrm

BvUni

300

300

AlbianCenonunJan

AlbianCenonurutn

Dcmal stfuctura

DomnI slrucniR

Structursl anticline

Structural anticline

DomaU gentle sttucnire

lo.sno

10.750-10,550

3,700

SO0(W30O

9,000

HO

95-153

130

150

4O0

7

75

7

7

• OTHER M J u i r f E T F R S ' DipUi to I b p or Pay (HI D b c o v c r y MclbDd

T h k k i K s i of Pay Zone (ft) W i t e r Depth (ft)

77

50

2M

7

7

A n a of PnidiHtioii (liiil^ DiteofFtodiictkiD ncUS^atm TtiulWtUillTiycd (dill) Piwtucer W i l b

T

ISM

1978

Producer

?

Producer

PlDdtKCl

32

?

7

11

?

1979

7 3(1^^5)

?

7

20

Wdli

1

7

7

7

7

Iiyectton Well9

?

3

7

7

7

tibscntr

^

•

-

^

-

^

•

.

.

^

.

Anb

Arvib

ShLuiba

Mishrif

MiEbrif

Liine stone/ dokunitic litne&tone

!ludist/al^ liiiKstofie

Rudiat/al^ limeslone

Rudist/ilgal UnKslOfte

KiiruneridgianE.TlihOfvifln

Age

SEAL

•

220-250 KimnKTidgtan' ETlthonian

Aptlan

•-

.•^-••••^•:

.•••

mo Cenomantui

500 <;>ncifTianiBn

• : ^ ^ , • • ^ • • ^ . * • >

Nahr Umi

Laifan

Laffan

F«rni4tiun

Hiih

Hicli

LiUiDtoEr

Anhydhie

Anhydrite

Slule

Shik

Shale

Tithonian

Albiui

Coniictui

Coniacian

Agt

Tlthaniw

19

18

10-12

18

20-25

20-130

6-lK

SO

1530

16

[nltiat Pressure (psig)

4490

53B3-5423

24«0

1

3980

Bublilt PoUM p R u i m

1721

1936-3659

2244

7

1321

2S0

7

110

7

210

1.3i-1.41

7

144

7

1.14

i%)

(psIO

Limestone/ dcJofnitJc limestDne 450

f^^;

F»riiKiiliaity(iiHl)

LIlliiiliiu

-IM)

.

tUstnoivFonelly

FaraudDfl

TUckiKHdl)

>

^ PARAMETERS

«

7

70 E.;i,;.-.:.vj;'.i^^mm»

.

•

ButbiDl HAlt IbmperahiTe Fornwlkin Volume F^Lor (Rfi/STB)

.•'^^;?vlr • 39

41.6-»5.3

43.7

30

n^^H

1EE-36S

554-3729

374

)

323

SulDur CAtitent (%)

0.79

O.OS

OJK

1.6

1,1

Viscosity (CP)

0.33

7

0.35

7

1.12

OtLPARAMEIERS

'"•'••'•

Oil Gravity (°API) Gas/CHI R a t k ( H t « T B )

25-47

a a

>

D. continued

>

to to

BuTini

FIELDNAME PROTWCnOff PAKAMKTERS

•

Arzanah

ZarrflTA

UmmAJDalkh

Fftilah

1

0

^

•'•_

•

-

20

34

7

Waicr injectinn

A^iler drive

?

?

7

Ii^cctiDD Staliu

7

37.000 bhl/d

?

T

7

Daily Prvductivn

f

lOnOOObbl/d (1984)

7

MIObbl/d (1979)

1

2.372 MM.Iltll (19TO)

R«i:<>vc^ Fat^bir(%) Drive Mechjinisiu

T d t ^ Producdon (date)

•-'

•-'

23 MM.bbL

7

Estlnutcd Reserves

•1

87 M M bbl

7

7

524MM.Ilbl

Recwcrahte Reserves — Equivalent Oil

7

7

•>

1

7

Recoverable OJI

T

•>

7

l6SMM,bbt

7

RecQVf rftble Uas

7

7

•?

^

.

^

^

in

?

ft

o OQ

CD

a. a. cT W

D. continued

FIELD NAME

Sdiil

^^

tKSCKlPnON FttMSbtdiB')

Cl.^k.d^ M m ^ B B n vf IDCC

160

Sbih • T

5li7

FJ Buoduq

Runuitha

lluwaila

FTFXD NAME

^

SOURCE }ftl 7

lOll

i

211 Baity/ ICiKlcmmc

111 Bally/ 2 Ca Kknune

211 Bally/ 2CaKlcinnic

221 Bally/ 2CaKleiiiiiK

Anbim PUtform

Anbian PlMform

AntiiiD

Anbian PtaifOftn

Anbian PlitfanB

'.-. Shilaif

"""*"

Arpllaceoua liiiKSIQiK/ihale

Ar^llaccoui limcsigA^hale

ThlckKaaini

2(ia«M

1,300

IJOO

IJOD

" iflllllM

Oxfofdian

Oxfofdian

Sinictunl faulted antKlinc

Ekangalcd umcTure

Dvmal

StriKtuimJ intklinc

Suuctural

e.soo

4.070

I96T

19U

1963

1!I6»

1%]

MwmrWiU

Sul-I

Sliih-1

El Bimduq' 1

Rumailfia^l

Hi»aitM4

' OtBER PAKAMEIEBS

iMidDip
I0.4M

13 J H

1IU3]

I0.7M

10^7

DvptfatoTupiirPay

SetMnic f g r t y

5cuouc$un«T

Seiuiuc lunfry

SeismK wrvcy

Seiimk lurvey

T h l d u K B al Pay Zaac ftt)

I4S

7

KS

1

f

440

A n a of Pr«lucti«HBcn*>

110

lOTi

\9n

1915

T

7

7

T

RESEKVOtR ^^ FAKAMETEBS - -^ '\

5(1»M1

T

TkipTyri

Dkir af PradHctioB ncMSunii

Pmlucc/

Pmkicer

Pn^HH

Ikxal WcUi DriUid

»{W4)

19<1WS)

Vt(\9i*)

P i o l m r Wtlk

la

OkHntrWtOl

4

liUtctlHWiJh

ft

IIOUZON

« «

SirEuinu

Utbotoi;

fV>roui Umcslvnc

DotOftalic linwslonF

TlkkDHsOt) Ap

.-

--•,<-:••,

»J31

S.060

230-3W

2«0

143

230

133

»J00

40

T

20-;;

14-21

9-20

1520

»-:\

PamtuMUty ( n 4 l

Ml

40-330

6-SO

1 «0

3-130

>

7

Initial P i m u R (paii)

Uli

1»70

4420

4690

4M2

2

T

7

tw

417)

2I1M

1344

1

7

Bubble Po44t r i i a a i i i i <patD

1323

1!

BouoaiHok T^Diftfralurr

223

170

ZM

110

IN

FomatkHi V'oliuQc F M I D T I RR/STB>

12(7

101

l.»

1.4«

1.36-1.41

Oil Grarlly I'API)

40

30

39

4:1

3S.3

Gaa/OU RaUo (acVSTB)

3*3

33

ISHI

433

370

Snk^irCant»ai{%l

Ml

2.7-1.4J

2.6

D.U

077

13S-2.74

7

0.27-0 33

OJJ

Ajih

dokinulic limaunc

Klu/Aib

Shu^td

Pwou* lijimmx

Rudiit/ilgxt

1}(M00

)40

150

420

BtfTcmtin

Muitnchtim

KimmendgianTllhofuan

Barmiuan

Aftian

.••

OILPAKAMEIEHS

Vbc«My
'*"

Fonnatiaa

Khinib

Umin Ef Radhuma

Hitli

Khanib

Litb>>4i>i;

DtnfC lifneuorte

ShakAimestone

Anhydnu

Dcnic liincMLSiiC

Sruic

BtfiemUn

I^kooene

TVihonian

BaiTCTTuan

Afeiisn

An

. . J i ; i<'.^.-

7

l«0

SEAL

:

14

• , . - .

Kh.iriuTi

• -'<

«.3aa

R c a c m i r PDroairy (%>

-

Fniatiaii

Diyab Sbair, vtillacoom Umatone

LavAlbianOcntnnanun

7

O e t i t k w (fl)

Divah Stialy. Hfillaceciu bmcstone

IJOO

*t

D b c o n f T MHbod

l>1>a(i Shalr. tft^llatxna limslofie

OatDfdim

W W N i2*}3'E

DmuottMtaintry

Honila V .adHIMri

Oukhan ll>iyab>

warE

Zl-WN

Biinnilha

F i BundtH)

?

U l Btlly/

I3*4
Lootkia

Sbah

K^nulkHi

A*,

>

SahU

NahrUirv

,i ^

y

3

9>

D. continued

nnjuum

Sahll

Shah

ntoiKJCTior* PARAMETERS

Rl BuDduq

Rumaitha

HnwaiU

' U

30

))

20

1

^A^tcr i d j K w n

Wucr injection

GtsuucitKd

Water injcclwn

?

T

1

Daily Prwluctioa
:axiooMiiou

MJtOO Mil oil (IH84)

Total Praducllsa

]1 MMbblDil

R K V T H T Factor 1 % ) DHwMerlinjmi IqKctlaa S u i v t

(*««*l

t

t

30.CC0tiN

7

7

IMMbblnl

le.J MM.bbI (I9KI)

?

7

•»

WHO

3 (IMJ) 2 ] I IWSTB

637MM.bM

UiMMbbI

StcovtraMc t t t j e r w i —

M l M M bb(

K»MM.bH

1

->

T

RKonrmMcOU

SOOMMMil

WOMMbbl

7

T

7

7

t

^

7

EMtinalid R o n r a

RccflrvtraMc (^ja

00

^

T

P5

&3

3 CI.

IS*

o ft

a! a.

D. continued

5»kfa

H E L D NAME GENERAL i DESODTION

i '

M.nk«

S^|u

-;, V'

FMdSlH
1^(1 (jHun n c v i B c t

• - '

-^^•1

^

7 Z2I Billyh 2CilCtcmmc

221 Billy' 2ClKkmnK

Anbiui Ptafonn

Anbtvi nnfofn

S4M)-I

SiJH-L

hUrtbwi-l

Tbtal Dtptb (ft)

0

t

7

^eumic l u m y

t

Sonnic lurvev

&5

T

T

I9M

1M2

1M4

Ptoduccr

Ftofcfcr

Aoduccf

7

T

lt{tVM)

ToulWdbDiilkd

TbMucs(ft)

TV»»Typt

PndiiccrWrili Otwrm->Vrili

^ '

li«)KttoaWcUt

T

D>|itli u IV); Hi Fur (ft)

FonnaliH

ThlltlUMlftl Act

X.

RESERVOIR FARAMinXKS

An

Bubblt M i l P m u R

7

.J

>

T

(P4)

1,«»

Qsununiiin

Beniuim

-

•••

CtjntMC\ aI^

If)

7

2.7W

Sh*ie

^

i m t i i l P r t i m (pi
«0

Lttboloo

lOJtO-11.000

I

r.utQiiala

L^Tvi

ii.ono

IM

1

ClrtNHUtt^

FonpailDn

Rultf^ tmkline

PcmnUUty (ad)

SUL I

StniciunI fmlua

1

rhairtfnu (4fv.

Ulbokir

Sirucnmi'

7

A n a of ProducthH

Tlunuma tjf

Mishnr

W) OxAndiiii

1

•i"

"'^^

Sink AlbiKi

BatbnHdk T^Bpcrmturt

7

7 F»rti>r(RB«TB) OtL PARAMETER

-r^.^.

NdirUDir

\.L.-,; 1 :'•.;

cKbomitec

.UK]

f

"

:-

AlbiuCemmantui

I*,I75

T U d u t e H oTPiT Z « (ft)

^^^>^> .

PRODUCING- V/^'?-' HORIZON

siutr. vpllftceoui

7 r"

7

OTHEH PAKAMETERS

S*Mmir?tinMtj[%\ T

Shdy, u^llKAKd linKitonc

Ap

1

LNiunci J Vffu

FMdSUIui

Maifhun

Uirib

Ulbdloc;

1482

Date i f Prsducttm

fon^mtitm

ICiJUemiDC

•no

Eiemtiixi ini

S«tH

(Shiliin

IW3

D l K c m r ^ MeUMd

SuMi

T

1

PaleirDtKcvcrT

FIELDNAME •BdOlCE

j^^^H

^^^H

^Ei

7

1

10

0I» 7W» 7

^Biw

;1

90-980

r

1,900 7

(3ulky

1 J

i

T 711J 7

173

IM

7

7

OH Grerlty CAPI)

4).)

51.J

V)

Gi^OUKalladdrSTB)

4T01

II!

7

SaUiu'Ci>MtM(«)

7

0.1 1

7

VtocHitT (CP)

7

7

7

"a ft s

D. continued

>

FIELDNAME

am^

S^tdi

'

Marf^kv

^^^^^^^^^^H

•

t

RccovHT Ftclor {% > DrinMccba^n

1

1

O i l mjecfion

iDJecttOB *JUtltl

t

y

1

DkUy Produdiaa

?

4a000bblld

U/XMbbVd (1M4)

(IM3) 7

tl,9njb33

bbl

00 CD

3'

ft 3

T

ca

ASOMMbM

05

ISATCFp. I09MM.UI

4300 M M cC

^;9 Rccmtnble W m r w i — Equlvsfenl Oil

0

IMOMMbbI

7

RMFwrahli on

7

300MM.Mil

T

ft«cnt*rkMc Gam

T

tTCF

1

ft ly •

'T^^^

Q fS

a. fT

tn &5

D. continued

FIELDNAME

H E L D NAME

"iffleNERAL. • i "

RESKltVUItt MRAMETUtS

DescanawM 221 BiII^/ 2CtKlemiw

FMilSiK'l

ASAB

1

RcHrro^r

:_

lO-M

12-30

•*r*i

h m n U H t r ^B^l

n^io^

• *

1

WIJ'E

0.J-TO0

1

ima

1

rai

ItiuIDttMbdl)

IS6
BubUc Point Pft^prT

1

o.)-wa

1

39«a

aw

IMUcdte) Bottam Ho4<

MO

1 ^"

'*

'

'nu^rvuirr

'^

Wetb ' FoFmatkifi VaJmuc Fictor (RH/STD)

PRODUCING HORIZONS kf'Ji;iiti f/i>r>rt'

on.

!.6

>^ '

PAKAMETots ;

>

-'1

VlKflrity ICP>

RtcgTCTT Factor

AffiUiceouL, thity, btniminoui limoinx

no

WO

ft 3

au

>4

CuKNJ Rilio (•d/^TBI

PRODUCTION PAHAMt:TFJU VUVftCET^

•a

« T

Sulfur Contml

Dnuc tinvuortc i jhdvr
.1

Oil C n i H l y l APi>

a. >

T

•)

*' , 43

Drin MediBBiun

WwrMt^t

l^l.cdiB

Saa>

14D.45S MlIM wtter

DuU)! Pmhtctiofi

IM.OWbbVd

IMal

l.l4«MMbfal (l»MI

EilliDaud

4.64 B.MI

Rcnrcnblc RMtrf — EqurivaWm OU

4J33 MM.bbI

RuBttiibh OB

4.000 M M . t M

Rccavcnbit

lOTCF

IJOO

ElongilHl. itructunl fiulted snticbne

> to

C M

D. continued

>

FIELDNAME

?5as? DESCRIFTION FMiSlB(kK^

BAB

FIELDNAME

Ul Bill;/

tR teUKVn rlM^kAMFiRirs

1

..»

l>.M6

P t r m i i N U l r (md i

)*-3:

o.i-«a

U l t k l PrcMun

*17i

T

^

T

B«U(MiHo)e T^Bpcntun

130

?

Ftjrnmtioii Volume Fodor iftB/;rrBi

l.TJ

?

IV41V4«1B

jet*

(UkliHiU 1MM Depth in)

(HO

^ i m j c hirvey

BBbbk Point ittdfM)

Dmtint PTttdufHoa

HORlZON§

1

(Ml C n i i l T I ' A P I I

m AK

?^

G u m i Rolio (HirSTB)

•

^^^^^

'H»niir
5: 7

lOT

O.IS

*

•

•

;

-

•

•

-

•

•

;

•

o CD

^

• '

o

PRODU(TI0M FARAMKTERS

At, 90U>CE

Jiiri

lan-two •

Sulfiir Cofileitt

(»)

CO 05

OIL - ^'~ . PARAMETEKS

SEAL

00 CO

^

ffl) At> T n f fypr OTHER MBAMKtKKS DtTlkla'RiF •fPirim

Pij z « irt) (km")

SlKt/*try Foctor

(*)

IB

DpUj ProdudiDn {dalcl

1SOMM tibVi

RKOwcnblf RtHrm — Eiiiiinleiu OK

UjaMMbM

DH't Meduainn

op

nvnKDOB

640MM.bbl
liUictlaa Sutui

111.705 bbl/d

53
a. w

(t4K)) lUcvTtnkblc Oil

).MOMM.Mil

1tK0*tr*bl» G B

4.S4TCF

03

D. continued

BUHASA

Fm^DNAME GENERAL DESCUniQN FlddSlK

LocalteB

T D U I DtpUi (fl)

FIELD NAME

' ISi,67Jtaet

73'WN 53*10fE

niMiiiiiliii

Dale of

121 Billy/ ^CaKtemmc

Pwrlnrt

Anbtui PUlfont)

Rncmir Pmntri^)

146}

DbanrrT

Muitani:

IVnu&hUlly

Sciiauc

1

BUHASA

RESERVOIR PARAMETERS

vwty

BcndoBlA)

T

imit

1

2

3-2T

I]

0 II20

JO

laltidFrnHin

J»6

WTO

Bobbk Poini p T H i u n Ipslitl

U U

2)22

BoMoaKnli

ua

UO

rontiBtiofi

1.73

l.«0

1

2

(NlGmltyl'API)

39!

41

CHTOUROCHI

TM

90)

Sulfur Coflttnt

095

D>.7a

Vtamtllf (CF)

o.:a

T

^—^

MIOHII

196!

fMdSUIw

PraiucCT

-nMalWeb

M4(I9M)

Ill

ObKmrWtOt

12

Iqiccttoo WtUi

94

pTDducttofl PnduccrWdb

PRODUCING HOKUONS Fonnatkn

1

z

Shuatt*

Khimb

iRB/SrBj OIL MRAMETKRS

L.iirttuDfv

LMulDtr Limestone T b k k n im Ap

4«Q

170

AplUD

Binrmian

SEAL

-^

UtlulOflf

> •

Ap

sotntcE

ALhi^

BidTcimin

r

2

FnHltDP

Dukhin IDiyib)

Ulkolacr

A r f i l l m o u i , ihilf, khUimiiuui limHiDM 1,M0

TUcklHMlft)

Oifofdiin

Ai>

SttuctunL^tinti^fAphic uticlinF

T*»pTrpt

I

2

Dcptta to Toil ofPMj<m

7.500

8.100

TkiduBoT Far Z o H (tl)

yo-.i:«

Idll

Amot

I O l «

19 I « . }

OTHER PARAMOatS

Pndianlaa (kH*)

> to

a a. ><'

L X

Dense lini«Eiinc

Shdlr

ft

iKfr^TB)

Khanih

FonBitiiin

> "a

.

.

.

-

i'»

PRODUCTION PARAMETERS

ti^-JaUUt

n-'iA

DriTt Meckuium

Wucr and j ^

Iq^cdkHl StORB

19.»0ObblAJ waut

Dalll EVodudion Idilfl

210.000 bbl/d

Total Pnductloa (date)

M 2 0 M M bM (19M)

Eulnulnl Rocrrn

20i

(l»M)

Rrcorri^blF Rcstrvct — E q i ^ i l e n l CM

9,1X1 MM.bbl

K u v n i BDH

1.000 M M .bU

RccovcnUc

Recovery rkctor

G H

\
6.71 TCF

D. continued

-

GSteftAL DESCRipncm fWd Slacks')

Linlt« ,kat) I M d D i p l k (ri)

i

liilO

ChwUadii*

U l Billy/ 2CiKleinme

7

Daw of

IM3

JAKNYAPHOUB

FIELDNAME

JARN VAPHOUH

H E L D NAME

tvtxiAtum.

RESQIVOIR FARAMFfKIIS

AntHin PIstTonn

*-I3

r(»)

JmYlftBv-l WiH

lawv

S a l i n e nirvey

Elmlti>a<m

1

ai-i3a

1

3160

H2

Mtlbdd 1971

FWU S t a t u

PrDducif

T

O h H r m Willi

•J

TbUIWtlk

BubtJc Point Pr^Burr (pslg)

WW

DdlMllltttI

PmliKtlsii r r o d u a r WtUi

»(l»«8)

U)Kltaa

1 7

2

FwTHtlofi

^huQiba

KhmibZofKlB)

UlkatDcr

ftiHkit/alga^ limcfiooe

Uritcilont

240

lU

Apfian

Butfcni^n

1-

3

Nihrt'rni

K^ur^ih

Liltmloif;^

Shilr

iViue LiiTKStDnc

An

Albim

Birremiin

1

1

TUckncBini An SEAL Pocmttoa

SOUKCE

pyklun<[>iyab)

Ulboloir

ATftUKCouiH ihiJy, bituimnoia iineitDne

TUckmin)

'>

Fwhcd (lAicnml Aiuitliv

TVipTViK

1

2

Depth to Top ofPlTini

10.050

10.360

lUckHof T*1 Z s a i ( d )

MO

t«0

A m of

90

T

OTHEK M R A M E m U

Pndiicttin<Wl

3

3

a.

PAKAMrrEits ]v

CWMKM RlUll {•cf/STB>

lew

Sulfur Cwil4nt

(WJ

fT c

O o*

Vlicarit} (CP)

aio

ai3 O

PRornjcrroN PARAMFiyjlS G u m|«UDn

Rcewtry factor

IqjKtiaB

ft

1*1

Rn Rnrrn — frj|iiiTilent Oil

Oiro<xb*n

Ate

§•

2.01

•jL z

on,

[MiT Pn4i (dattl

1J0O

ft

03

Voigm* pBCItir (RB/STBf

(MKinrll.i rAPIl

PomHtiaa

oo

170

1 1

1

rKOMJCINC H0UZ(»4S

1

a. CL

Mm)

trl P5

D. continued

CENEKAL " DESCRIPTION ntUStitlka')

LHsttao

;

••^...;-..i,..-

] i 10

LluHAcacioa

U l Billy/ 2 C i KlcmrTK

T

DllKll

1974

Pttniieuitt

USEKVOIR. nUAMETERS

7.137

Etcnbuacni

»7

Mcltiad Dot I '

T

FMdSUUaa

Producer

IWalWcOi I>rUkd
6(19M)

P r a d m r Wclk

T

ObKTKrWtdt

T

IIOKIIMI

f

PKODUCmC BOBIZONS

2

';^^^^P

Fomutioa

ami.

Lfihv-^ir

Lltbolocr

LiAKtlOW

Limestone

MO

WO

A()tilll

Haulfn^iir-.

TUckaniin) \ f

^AL~^^^H tUxVai

uibolocr

Stik

«1

1-30

>

JJIO

BabUc Point pRamlpiiB)

F 1

IMO

1)«0

EtotlouHol* l^miicnturT

t

140

140

1,27

I.2B

r

:^1. -'^-^^SM^ OIL MRUfXTEU

.^1

>

OilCnrltyrAPFl

M.i

I M

< ra^Oil Riiig Isd/STB)

»L

)»

OL7

Olt

0.M

a«i

Sulftir Cofllml

a.

ig

L^kJlwair Vbmitr (CP) Dccuf iimcilitnc FRODIJCTLON'

Alwi

An ' '"^ SOURCE

0.1-*

2t70

LaidvlPiHHn

Fomtotiao Vohimc F i d o r (RB/STRI

H

"-. 1

Fwntk*

I-IJ

P c n H M U l T (mil)

QuuhwuV'L

Soinuc *urvty

^ ^ ^ ^ ^ ^ ^ ^ ^ 4 '.r

,

Rmnwrir

Anbun PlMTonB

wui

TM^Dipttdl)

guuinmtA

FIELDMAME

QtJSAHWIRA

riELDNAME

'iUL ^

HnJtcnviJJi

PARAMfrruis

2

RccvTtrf F k c t v

1

Fonnatloo

DuUiin <[hy>h)

utboiotr

AitiLlKtouL %ii^y. htumiiKiullimcsuMV

Oxfor^tn

Alt

StnictunI inbchnc

Tnpiypt

R-;-"- 1

2

DnXkuTop tdfmyM

3JS)

(..(*<)

TUckMHtf

15

5?

Am
M

PndacUaa (kB>)

IMn

1

yMd SUM

[MIy PndBcfkn

6.000 bblfd oil 0J]3MM.<:«Iis

R«anrBbk WtWITM —

7

nui

T

Pr»J»H*»a

Evtimstod R^rrt*

1

IJOO

T ^ A M W

OTHER PARAMETEB5

-v

7

oi

7

D. continued

FIELDNAME

FIELD ^AME

DKSCXIFnOW

BeSXRvniR RUUMrrEKS

RASHTD

I

FliM Sin (kMI*!

i

;o

11

LootlDa (lit, liat>

riijmlillllj (ud.

ao

M

7

T

Ibul DtfOt in)

WtMPna»R (I-ID Bubble Polat

7

•7

BonoaHolt

7

7

FomliiHi VgluiH F K U T (RBfSTB)

7

1

OIL pAKAMrreRS

t

OV G m i t r ('API)

)}

»

GH/OURlUa

7

fl

7

7

Sejuniciufvey

(1) TMilWclk

00 ft

a. §• 3

P n a H R Ipiit)

DIUIHI (datel

InjKtiai Wtib

td

•'

2

(•ctSTBI Sttthij ConltBt

1

<«) 7

V U n d t r (CP)

Drln

Factor

(*) I.WOUiM (19W)

ttacawrjblt

7

1buJ PndiKtiDa Idiu)

A m of

Slitw OJMM.Uil (IMO)

7

oy

>

• '

MCCSUIIIIB

Pivduclion

Equivalent Od

^^^^^K;

I^^^^H'

MRAMETEKS

IMIT

W^^^^^^^^m^

• '

PRomjcnor* VtKvrtT^

^^^^^^^^^^^H,

g-**"-*"*

ST

c

3 O o* *< OQ

o 3-

7

7

m 03

D. continued

S O U T H W E S T FATEM

FIELDNAME GENERAL DESCtllTJON r M d S i n nun')

LOCBUOD ( b l ,

.

•

1

kof)

^

* • : •

"—.»—u—

•a 1 Billy/ ICiKloniH

DMcif

Win

•

Pitn^uftt

ILDW

. . •

-

Anbiin

5ou(hwsl taeh-l

54*irM- E

Tbul Deptk ini

^

.

Seiinuc urvey

WtltrDt^tn)

109

M(lMa)

Mitbod [tateof Pndvrtion PtodiKir WiUa PKODUCIMG

1971

FVUSUtsi

F^oduccr

TbulWtUi Drilkd (dilc)

27

O l w m r WEUS

1

[itj«U«t Wtib

I

•

^

2

aoRizoNs Shuiutu

Mithnf

Funudoo

Linvstonf

IJtIigliiof

>

kimotcKM TMdtiiM«(ft)

An

100^ WO Onomxnian

-

l » Aptidn

1

1

FomwCKHi

UtFu

NihiUmi

UthsloD

Stialc

Stuk

ConiaLnaji

Albian

SEAL

Ap

2

1

SOURCE

Shuaiha

Fomation (ShiUiD

Ajfilliceoui, shil> limestone

Uthotoir sluly liin«tone

TblduKom) Alt

Z«0

IM

AlbUnCemmvuvi

Apliin

DDITUI stiucruTT

T n f Ty|K

OIHER nutAMEiEas DcpUi b> Tup nifty yn\

PIT Z O K

1

2

7J0O

mooo

lOCMOQ

K)


A n * of PndiHUnnui'l

'>

7

•a

m 3

D. continued

FIELDNAME

FATTJI

GENERAL DESCHIPnON F M d S l u (iua'l

-

riMriiriTinn

9ili

Daunt

L o a d o a (lar. l i B ( ) WM'WE ItiulDtpditrt)

RF.SKmOIR PARAMtrtE>£

•

121 Gaily/ ICjKlemmt

PHr«l*iiaL

IM6

DlKvnrT Wd

Arabtm

HtaarHrir

Fuh-I

Sdiinc wrtvy

W i l e r Otiflh (It)

IM

Total Wrlli DrlUei) Idatil

lOOdWt)

liOtcUan Wclb

^

nddStatia

ftDducer

ProdimrWiUi

'

O b K r r r r Wdls

• '

niODUCING HORRdNS

'

1-1!

17-22

^

3 10

*

7

M(n

«0

4230

MM

BuMfe Point r i i M M i i fiiiiii

7

l«36

7

BAttOfuHole Temfieratiirv

7

210

7

FurmilJDn ^DluiiK I'aclor iRBftTBI

7

T

T

on.

1

1

3

JS

11

31

<:aWOii R i l k i

7

3S0

7

Stiinir ConltBt

14

O

t

Vlace^lT ICP)

1

Initial P r c m i n

IM9

2

*\U

K n H a b l l i t r (Bd)

00

(pall)

MMbod l>ftt«Of

1

Platform

DbcwfTT

12,111

FATEH

FIELDNAME

•

^- 2

ShuLuM

Mijhnf

lUm

ForiHIiaB

3

Limc^CEint

UmsiocK

UlkotDCT

Jimnl4>nr TlilrlrMMtn)

SEAL

t^:

Fomwdoa Ulbolcc]' Ad SOUSCE

',*

Aptiui

CancHiuniin

Slot Hu An

Ate

1

2

3

Lower Aruma

LaHaii

Skhf Liju

Shxk

Shale

Sha^

Curpintaji

CCKILKTIU1

Albiin

••i.'-'i

2

'-.-.

•"

y

..•.-•.•<

Konnadon

Khj[]>:ir» i?)hiUiEh

Shu^ha

UflHlai]'

AjpliicKnu oli^DtiepiuI limesumc ind th«ie

Ar^illacmu, ^haly limestone

2A0

W

T I l l l t H M fttl

AlJianCenaintiuin

Aft

OTHER ) * . i . MRAMrms DeiHtitgTiir

1

AjfitB

Dvmil. (IHpttciI sinj^ri ic

Tnpiypi

I

1

3

7.):o

s.ono

<).[»0

lOO-SCO

70

116

7

oiParini 2U

' Area gf Pradadtoa O B ' )

7

MRAMETEKS OU l\twnty

80

2iO-MXI

300

0= B

i'AFI)

0.6-0 i

a

•'•

PRODtlCnON PARAI^hHERS Kvee/nfTi Factor

*}

Dl+r»

Wu£r drive

blectfo*

83, KB bbl/d watH

l7:.M]bbl (1978)

T
J ] ] MM.Uil (197S>

Ertlia*tt4 Raacrvta

2.3«B1*1

l.iaOMIUIbtil

Rccflrnrablc Ol

1.200MM.bbl

RacDverable

7

1%) Dailf Pntductiufl (dale) RtcflfvcraUc Rcaerfca — EiiahFakatM

s 5.' m

D. continued

MVBAREK

FIELDNAME

''.

GENEKAL DESCRIFTTON F M d S l i i Ikm'l

LoolioB (Lat, loaf)

^

H E L D NAME

1

221 Billy/ 2 C i KJcmiTK

Date of

1

RESEBVOIk nUUMETEKS

' ClttMiOcalkpo

MVBAftEK

htnlvuiD

2

'*

^

Anbim FUtfonn

7

l^>nMltT(%t

Mubuck A-1

1*71

, ..

t

T

7

1M7

IT6S

1SI«

BsbUtMu P l L I I H lpi
1

T

7

BofloiaHolc TfrnprntHTT

7

7

7

FocnliiKi Volume Fictor (Rfi/^TBI

T

7

7

OIL nUCAHETEU

1

z

Otl (;niniy I'API)

35.6

Jti.4

GmiKMKMaa (Mf«TB)

100

7«1

7I«0

7

7

7

J

7

r^raHblllCT (mdl

Will iBldal F r c d u n Toul Deplli (ft)

DKtgf PnxlactlDi PradKtrWtlb

KJM

DtKffTWT Method

SajiTDC lurvey

Wii«'DtpUi
XO

191*

FIridSiktuj

ProduCff

IbulWtUi DrilM(iliU)

lOdfM)

1

tiOfilkioWrUi

7

7

#^>

**>-**-

(P^D

uncTTCr n v n i PBODVCING HOKIZONS FonnaltDa titholafjf T b l d u H (ft) Ar SEAL KDmutioo UtfantiiD Ap SOURCE

1

1

llun lupiXTi

llun (kirwer>

MiiJmf

Lim&ionc

IjniC^[(irc

Rcclil Limcs[Dne

3

L«0

|}«J

2«a

SviEoniui

Sarloruui

CenDnuntin

1

2

3

Lower AAifna

ll^rri

Lirf^

Shtie

Dense Lifncuane

Stuic

Cunpifiian

Sninmfiian

ConiKun

2

3

1

Sotfiu- CootcBt

(») viKsdtriCPi MiODUtrnoN KABAMETKKS

3

7 •

•'

•'

lOuUyiri (S^l*in

Farmadoa

•

Drin

OWDCtlK

TMil Pmhictioa (Mt)

eOMMbU (1980)

Kocrrca

7

K«c«»«nMc

(*)

li^tftloa Stihu

7

AjplUceouiKbihimirKHiK LLmrsinnc u ^ t l u l t

UUHlofjf

DttUy Praductiaa

260

TblckacM (ft)

6J)00MilM {IW4)

7

Albi>n-CeiK>iiunin

Alt

Scnieturvl. iJomAl aniictine

T^mpTyp.

1

2

3

DipUi to Tvp i>fl^r(ft)

I2.M)U

i:.7fto

12,W0

TfaktjKKof

llj

IIU

1

7

OTHCJI PAKAMETERS

F I T £ ( « Iftl A n

,,(j.

if

Pnductlan (km')

M

RecmrmMc RcKTva — e i | i i i n k i U tm

7

oa

7

a.

D. continued

FIELD NAME

ABUALBtnUtOOSH

FIELDNAME

^

GENERAL DESCRIPTION S t i

nHdStH
n m i i i t
Dattor

L K S U M dirt, lootl

T D U I Diplli (ft)

Pttmkvia

u i eiiir'

AtwA) BuUKMhl

IM9

9.810

Anbun PlMfonn

Sainuc urvey

WiiwDepUi
MQ

ABUALBUKHOOSH

RESERVOIR PARAMETERS

1

3

Reatrroir

10

a

»

•._•••:-

3

"

;

•

'•<.'4

10-12

N :^

•;?.;:

PmwltTI^I M

s

20

15-100

bytU Pmnin

US]

3wa

3960

MOO

Bubbk Polnl PnMtlE*(psi£}

]MU

•una

l5on

7

7

7

1

1.3

1.6

l«

!.-»

PnHUIitr(Bd)

t/2 Q.

§• 3

^(Hbod 1OT4

FkU Statu

Pnjducer

TDtdWrib DriURllitatel

»(19M)

P r a d m r WtUi

2i

Otacrrer Weill

4

InjKUon Welb

7

PBODllCINO HORIZONS

•

T

3

4

Anb Anb-BMbr

Anb AnM^Mti

Anb Anb-DMbr

Dktcaf PiDdactioa

LcUiwair

FATUHliDB

LimmoiK

Ulholacy Tiiiitiim rrp

220

ljfiv$tOfic, ^tomitic iirmtonc jm] uihytlntc 2»-lU

2»-lU

Hauteriviui

Af

I

SEAL

Lck^wiir

Fvniialkn

-..^91mBSKm,im* Anb Anb-BMbi

D R I K limextcme

Aohydfiit

HfLLtenviui

Kimmcndciin - Tilhocuin

Att

1

SOURCE

3

2: '^"^

rorandai

DiyalVDukhin

UtlHkio

AriiUACttuL duly, biivminoui limakme

Anb Anb-CMbr

4

SmmunJ

.

' Wl!

TUckHof

>

Oil ( i n T i t y <°API)

SslAir C o n t n l

^^^1^1 37

M

»

36

4M

law

IMD

ZJMOO

f

7

7

T

D M

OLM

040

06-1-1

anikliM

1

3

4

S.OtJU

B.OW

i.200

u

110

SCO

M

7

7

t

C

3 O ft

o_ o"

(») VbndlyiCP)

Recovery FiKtor

"<: o

'.

Ml

7

Dri«t MgcbHiton

TOMObtll'lS (I9M)

Ibtal PndKtIoii (iblil

12» M M M I (l»<4)

7

R«cvHnUt OB

t

l«)

RccoHnbtc Ratrrn — Eiiiilnfcnt o a

P I T Z O O I (ft)

PrvdiKtioa fluv'l

PARAMETERS

OIIIT PinjduciiDft (ilatc)

otPilffl)

Amur

3 G-

'^^9

PROOi;CT10N PARAMt:TERS

Oxfordiin

A d

tWiiTypi

DtpUi 10 Top

OIL

CO

&3

1,300

lUckmsCft)

OI'HER •"^-" MRAMEIER5

ForApbon VoluDK Faclor (RaSTB)

G u / O l l Rilio (icBSTBI

KimmerH%un-T1tt»niin

Anb-AMtw UlbulocT

SIO

BvttiniHii4c Tempera t u n

loa-iita

sohjrtlOd SM

lAjtcthH Sunn

t

Eitiiutcd

4TS M M bbj

Srt a. a. m

! Ga

D. continued

I I E L D NAME ••ORAL ' DBSOUFDON rkUSiii

U M M SflAIF

:;, .

• ' ^

1 ll.OOO a i K i

VwaUnii (iw, looo

i:iajuAco(ioa

: : i Biiij/ 2CaKkinine

Date of

IMS

hlnknuD

Arabian P1H^(l^n UnunShaif'l

LTMM S H A I P

RESERVOIR PARAMETERS

1

2

3

RCSCTVOU' PorattTl^)

IS

tl-j2

y-13

FyranblUtr (irf)

- 4

Saimic lurvey

Wotir Dtptk in)

110

Producer

ToUl Weill DrlllHl m i l t l

I37(19»(»

Injfftion WtUl

44

• ;"•

li

20-100

60-3 SO

4»I20

W

laMtlPrtbun

2900

4400

4880

6900^000

Rubble tVWnt P m i i T (p>iK)

llfiO

36004X0

4S20

J

ButtomKolt TtB|Hraturt

IS«

in

330

320

Fomatliiii Vohune F K I O T (RH/STB)

I.2B

I.6T

I.U

7

1

2

3

4

Wtl

IJSS

T b u l Dcplk (ft)

• ' .

DlKdrvtry

J3'(3'E

nEI.BNAMK

MMkad 1961

neMStarui

P r a l m r WHb

77

ObHmrWtUi

nUMWCING HOKIZONS

1

2

PrHtiKdon

^ 3

4

Fonnackn

Shiuibi

Alob

Aracj

Khufl

UtbDloET

LifKlVW

Limeuone/doto nblic limestone

Limeslone

OCpkHnitic liinolone

IM

TtO

770

2,800

TMckiM-dtl

SBAL FurmaUiH

•

1 NitrUmr

CtUovitn

LAIC Peniuvi

3

4

Hilh

AJKJ

SiMlair

Kimmendgiin' E.TllwitUn

Aptim

Air

^

;.?.'• J '

•.•

Anhydntc

Dense bmntoiK

5hxk

Athim

Tithonjui

Callovivi

EirJjrTriusk'

SOUBCE

1

2'

3

4

FflmulloD

Shu^bi

Di>ab

Quuihi

Ulbalatgr

ArvllacAut UmeuHie

AffilLKxau, ihily UmsioM

Sttile

TMtkum (ft)

1JO-2I0

1.300

100

An

Aptian

Oifonbin

Silunin

Utbuloir Ad

OwJ. [tenul tmxturc

TnfTtvc CITHER nUtAMETERS Depth tt> Top of F i j t n i

1

2

3

4

J.SOO

a.sQO

f.ICO

12.*Q0

IBD

J73.|J)«)

*x

MO

1

HO

7

T

l>ijZai>t
> -J

on.

. • *'''.';iT

rAKAMETERS :)i!

19

17

45

(luTOII R i l l s (K*STBI

MO

130(>

1120

7

Sulfur CoDlcBt

15

l.»

1.0

0.9

1

-

7

I

Oil C r l Y l t r CAPl)

3

>

(1) Viscocilr 1 t'P)

PROOtJCTION PARAMETCRS Recwery Factor

(*)

Daily PmlurtiDfl (dutil Recwenbic Raerra — EqiinlemOl

"[

?^H

mMIMMoil

Watermiation

2Q

(1984) UOjnObbl/iloil (1980)

To**) I*roductlaa I4ili>

909 M M . M I oil
Esdouled Retrrvs

1.2 B.bbl

i.JOOMMbbl

kocovcrabk OB

1.300 MMbN

Rcc04tr*blt

t

D. continued

>

MU8ARRAZ

nELDNAMK GEHEKAL DcsCHornoN

^

FMdSIn

RESERVOIR PARAMETERS

I9M

DtaCdMry

Mubarru-I

4503-4598

4511-4M4

4U5-4M0

5028-5121

1366-1362

W«terDnilh

100

tnillal PrvMurE (pal[)

M0«-«M3

Sdinuc wrvcy

Bubbk PnlBI Praasiu* (pric)

1757

1850

lUO

1424

!330

19)4

7

>

7

7

7

7

1.231

1 297

1,412

Produ«f

ToulWclU DrilMdIitt)

33(19841

25

Obacmr WHb

1

hjKtioi

7

2

1

4

3

s

upper

lower

upper

B e m u i i n to Vituigimin

Hautoivttn

Birmniin

Z

4

3

< ^

5

Lckhwur

Kiunib

Ulhnlofy

Dense lin«frLii(ltlane(acli7onc(c4ledrn)m Lop And tHJltom by (lenK tiine$i6ne)

SOURCE

I

2

3

4

s

«

A i j i i l u c u s . ihil>. bitununoui limobiUK

mtnlip

IKO

TMcfciMiUni

OTIIEk nUtAMETTEBS Dtpth tvTop

t

1

2

3

4

S

8.S00

9,000

9,150

9,900

lOJOO

10,600

7

t

R w f O frtnn M lo 110 r i r Z o H (11) A m of rradBcltsa (km')

7

7

7

7

*V'\.^,

jjf^;*-.^'^

5

•• X

6

3!

35

37

39

45

400

287

325

519

SalhrCsamt

1

1.1

1.15

1.2

1.2

).:

V t o n d t r ICP)

054«

0564

0564

0.580

0.4)2

0.330

21

I>rtvT

Waiaand ioluli«i ^

Mcctiulw

7

a 5'

161 MM.bbl

(19M)

7

Rauiiuanc

7

22flOO»ilM (19M)

IMal PHrdBctioa
74 M M bbl

Ktcmtrrabk

lOOMM-Hrl

RacDwcnUr OU

13

O

13" fO

SlalH EiUiaatnl Rcavma

Dally PrudiKlkin (dale)

EqiilvakulOll T\vo major mciclrful tnndi leplrverl try tuU Iciaddlet

TnpTVpt

2

40«

RHCTVS —

Onfonliaii

Ap

I J7

(*)

§• ft 3

P

412

Racmcrr Paclor

Di^ab iDukhin)

rinMrtni

1.305

PRODVCnON PARAMETERS

B e r n u i i r to Vikings nim

HwEtfivim

Birremian

1 313

1305

(%)

Hit)«hH

Fomufiwi

ACT

00

Cu^OURaUir (adlSTB)

0
800

310

1

RaiiKH fiTjfn 1 ti> 20

OIL PAKAMEIERS

kiwcT

LJmetnMK

Ulkohicjr

Aft

Prmcablllcy (md)

Formabon Volumr FHrlDT |RB«T6)

6

Hibshir

Lekhwiir

Khanib lower

RanBH Tmn 12 to 25

BouooaHDlt Trmpfnturf

'

upper

ReacrTolr

(ft)

Pndvctfofl

SEAL

6

Data of

FMdSlilM

ThkkiKKim

5 . *'^

11'..

Anbian Plarlorrri

1973

Fomwlkia

^3

htnrtnm

Mtttud

ntODUCING BOWZONS

2

211 Bally/ 2CaKlcinmc

1(U3«

hsdwxrWclb

1

ClHtUodan

Locutoa l l u . l o ^

T s u i Dtpdi (ft)

MVBARRAZ

FIELD NAME

a.

£: fT m

D. continued

ZAKUM

FIELDNAME GENESAL DESCRIPTION Ftdd !tlic (km')

•

»»30

audttcaUoD

H E L D NAME

-

^trvtciun

221 Bally/ 2CiKlRiirne

Anbiui Plurwrn •

DMior IMSCOfHf^

T t i m — (111, l i l t ]

I9M

DlKovtry

I

2

-3

4

5

tf<

Rdcrrok

24

29

i»

11

10

n

- • •

Zakum]

l-J

15-30

10-26

60-150

1-30

1-33

3773

3T2J

3801

42CO

41«0

7

Bubbk FUnt Pnsiurv lpilR>

1000

600-lKlO

lOOO-IHO

KXXMKIO

1M&4200

7

Bottom Holt TtmpFraturc

215

2»

222

22a

232

US

ForimiloD VolujUH Factor

12

1 22

1.15

1.6

1.5

1.54

3

4

s

6

f V r r m M U t T lOri) Liiitul p T w u n

I b u l DcfUk (H)

11.676

DtActrrcry

Sdiniic survey

WalirDiptt

BO

l^t)

m) Dt«it«f Pmhictldn PmhicirW^Ui

PKOOUCING HORIZONS Fomudoa

Utbokiir Tlilitiimin) Aft SEAL

1M7

FleMSunii

Pwductr

m

ObiirTcr WiIU

7

1

1

3

4

5

<

SttuAiba

Khamb

Lekhwiif (upperj

Lekhvur < tower)

Habahin (upper)

HabUiin

OIL MRAMTren.s

Utwvtum

LimestocK

limestDne

Umeitone

Limatone

Limslone

o i l Ccavitif CAPIl

ISO

310

SOO

1000

Aptiar

Bvrrmian

Hautenv;an

BcTTi»iv^TO VaUn^niin

TWalWiUi DrUM(«>(t)

13) (1W9I

110 Wdb

1 IVihr LTnnr

UlbolsD

Shik

Att

Albiin

,

2:

Khvub

.

3

4

5

<

Lck^wwr

Lekhwair

Hubshjii

Hibitun

Dnue L^rv muditone ( o c h zone leiled froir U>p mi tvnDm b^ dense I j m o v n f ) Utntmitm

z

Huiurivian

3

Bflnuian ID VaUmginivn

4

s

50VBCE

1

Formttiofl

Shuutu

Piy«b (Duihui)

UdialsD

Ajpliaceoil

Affillieeoui, ihij^. bilunnnoui limestone

l$0

1,500

A».

«

ScnieturiL. domal. elorygaifd in i r eut^v^il dLrecTiDn

1

3

4

5

«

Dcplh I D Top airmyttl)

6,950

7.130

7J70

«uOoa

t.zw

Bj6«0

ThkkacHor

I7i

14)

740

»o

440

IIS

7

67]

7

7

7

1

pTwhictlaD (kal')

Sulfur C o a b n l

t

2

436

•Hi

35.6

40

39

38 3

700-1200

950^1250

90&I300

2W.30O

230-3SO

3»400

1

1.2

1.3

I.T

1.9

2.1

1

1

7

^

7

DHve McdunUai

W^tcrtlnvc.

litiectlaa Slatuf

243.236 bbVll witei

I.OOOMMtibl

EMiqaatod RtatffTca

1613 B.biil

(*) Vbcoriti
7 r.

rKODUcnoN MKAMETERS Rfcotvry Factor

• ' ^ • .

U-Jl

(»l

RcmvtnbW Rmrrcj — F j i i d n U m <)il

1

A n a of

CavCHI Ratio (KflSTB)

DaUr Pt^uctfoa tdatal

Oxfordiin

Apiiui

TnpTypt OTBEK PAKAMCTEKS

'


Fonnatlon

Thkkiia((m

ZAKUM

ȣ.SERVOIK PARAMirrFNS

237.000 bbl/d

18,400 MMbM

PrDdiKtloa

(loao)

Oil

IB.4O0 MM. M l

7

••

E. Data from some oil and gasfieldsof Saudi Arabia.

> O

HARMALIVAH

FIELDNAME

SHAVBAH

FIELD NAME

^ t o S K A L DESCUFIUM

'Ot^HBG^SB •

n e U SlB

nuriiiilliia Petrvlnm

L o o l l o a [!•(*

Antiaa W i t

knt)

331 BftUy/lCi Kiemiix type

F^tfonn N. 4 9 T r

29V3afl

P * ( t of PmdiKtkia

1913

7

4,500

^^-

nt r i j Z « w

{ft)

(%)

pHiuabUitr

7

xo

^.7i>J

itt)

of PrtidyftiaD

R c j c r r n r EXfoMly

(|iri(l

iBjIial P r a s u n

Seiimtc sumvy

E>ndaain>

SHAYBAH

140

»0

'

76,CXt> j L i T S

25

i3

T

15-100

?

7

?

?

T

7

T

7

))

41

ItESERVODI PARAMEHXS

^haytnh'l

Hmtttmrnr

Mcdwd

A m

19(ift

1

T b u l Dcplh in)

T h k t w

22*35' N, M-Or E

E

HAnruliyih-1

WcU

I>ejitb to T o p of P i y

Ar^iiu PlKform (Rub iJ Kbib)

l»T3

[Mtc d( DIXQVIT7

Dtacwtry

4H ( ^ ^

lij

Z 2 I B ^ y / 2 C t K l c i m n c type

Fro*lfKt

DtKsnrr

^

1 I

dinl')

H A R M A 1.1 Y A H

CTKBft nUUMETERS ^^

B a U 4 c Pdtiil I V « R B o w

(fiii)

Hole I k n f w r o t w T

Pormorioii

Vohuw

00

a. 3

6d

FocurlRB^TB) R e l d ^tiul d o w n in ewiiy

FMdSlilBi

ReJd ™ t y a i ^

L9B0

down

OIL R U t A M E J E K S ' ^ ^ H 'nxd Wtib D T U M

(date)

JT(I«80)

40(1981)

14

7

Oil GnrriH' CAP!) Pnidmr

WtUi

O t u r i r Ii0«tkia

WtOt WtUi

7

T

|1

7

G u f O D Rolio ( K l f S T K )

740

7

SulfbrCoiUcttt^it)

IM

0.7

RORtZON

•

: , - /

• • -

-

•

•

r

^ •%*•-. .' .

. , . ; „ . ; . . 1::

FomiaUan

Aiik> AnbDMbr

ShuAib*

uibobKr

Caicirtnite mt otommc limenDW

O u l i y u i d Tudistic L m e i t o n e

7

440

K i n u n e n d ^ m - £.T1thoiuv>

Aptiui

Tldrtnnfttl Ate SEAL

A rah

Sink

KfJ)

^

^

—

-

^

^

^

—

tf^liAccDui,

bituiuimui

Lime-

JOO

TWckBHsdt)

1k«I^

4 ^ .

Huufi

Hani rJ LinunKeiL

L i i r u F u l e d , i r r i l l x c O i u . h i m m i D o u i liniedone

Av

Water d n ^

7

1

7

U 2 I

T b u l Praluctlofl (dale)

IMMM.ttiH197l)

RcocrvH —

bbVd ( t ! r 7 i )

QkfOfdiwE

KJnuiKftdgiHi

A t^nunetnc N N E - S S W - m i k i n g u u c L n e w i U l i t ! steeper f l w k d i p p i n g t t 1 . ^ - 2 . $ ^ La the H H i i h e * ^ - T V

n « i c l i n e i i b r o k e r by M

k u t rive t n n i v e n c f i u h i .

»0 QifordLin-E. KJirnnendsiiA SlTuCtufkl u i t i c U a e

Recoverable Goo

3 O ft

Oq

•>

7

iXIMMM.Mii

],7IOMMbbloil

1

U B M I

a. & m 05

EqulTikfil Oil R e w r m h k O t l

o, fT c o^

7

•

rornKtiDn

Ulbeko

'

Doll; PnxliKtloD <dou)

R M f t r m b l r Rc9crvrt .•

SOURCE .

MccboBlmi

CcttHutHl

AEbiin

KirnrTifri;1eian

A p

T T T > = K ^ ^ B r

^

•

NihrUmr

Eviponte (iirinfonnibaMl

Uikokifr

''^'

:

Rcorvcfy Fortor 1 % )

•

l-'DmiitlDn

iigwi

IqJtCtkia 54Atl4 • • • • * . • :

-

1.

PAKAMETEBS

DHvc

'

7

Viicoiity (CP) ntODVCING

a.

l.a B.bbi

2JB.btil

7

7

E. continued ABU SAFAH

HEI.D NAME

n i U SlK I k m ' )

201 la

2J1 Billy/ 2ci KlemnKiyrv

f^trokum Pnpvlaca

Arttiin Ptatfonrd

Depth La T«i» •(Paj(ri)

Dwtcof

1963

Dbcwvr7 WcU

AtiuSarth-l

IlikkBaaiatf FarZ«ii
DUmvcrr

Sdimk nwey

WilB-Diplll

JMJ

TJSi

(ft) DAItoT pTHtucdon PradmrWdb

IKODUCINC HORIZONS FcwrnatlDIt

IMS

nddStitui

EVoduccr

I t (197])

ObKi-rcrWeUi

T

1^

Ctlcirenite lod caicimbtic Umctune

CakiRmieAnd calcaieiutic Lmeslone

too

160

L KiniincndKikn E-Ttihoniu

l^KJniinend^inF TlthnrJMi

SEAL FormadDn

1

Kirr-mrnLi^TLaji

Kpm[llc^L^lpian

Formation

SVv.jnIjjri

Lllbah>fr

L^ininviHl. bit^iminoui Limestone

Lamiiutnl bitufninoui linwslDiK

MO

500

LClUiniinE- Kimmeridgian

LCdVivilDI: KifirijTifndpan

Av

TWrnx

i 1

KcKTmr p<»™((j(*)

1 - t

>

t , .

• • ^.

woo

t

T

11,100 K m

T

1

1

Slrvccurml ui[it:]irK

?

i

•

P i n n o M U t r (md)

7

Initial P n a n n

7

BubMi Paint PrisiirT
7

T

BottDOdHfOe Temperature

T

T

^^VHI

*

a.

1530 70

3J

»

(»)

" 7

7

i 1

" (»1

Reeoverable Reacrvet — EqulYaienl iV\

CD 3

7

>

Sulhir Cvfltent

Daily PtDdiKtion Idartil

>

'

Gai/OURatIa (•eOSTB)

PRODUCTION PAftAMETEKS

7

.(?

J

Formatkn VflJume Factor (RB/STB)

OIL

^

Ta

VbndtrCCn

1

Hj:l>t.t-lii*.iki Miiunljin

TUckMsini

ME^RVOnt PAKAMETEBS

uoo

O i l C n . i l j f ("APli

AnhytlnLc (intnfDrmilJocuJ j

-

Artaof ProducdaA

MKAMETEia

AjihydhLe (liUnforniA' thHttI)

SOUKCE

4^

2 iSI

Anb An CMhi

Att

>

.-^.-rn/Vi-

:

E^>

Utbolacf

'•.

U(I»T!)

t

Anb Ant^DMti.

TWckmrn) An

TeUIWdlt [MUcd (dau)

Anb Artb^Mbf

UOHlaci

ABU SAFAH

1

OTHEft PAKAMFTEXS

Qudflaaaa

Lacsttaa

Ttiul Dtpth (ft)

FIELDNAME

-

GENEKAL DESCRIPTKW

140.000 MUd (1980)

4B.U>I

Drive MRJuniim TMai ftvdiictkn (date) RecomraM* OH

t

Iq^ectioa Staliu

T

450MMbtlt

EfUmabd Reaem

4^39 M M bbl oil

ftacweralilc Gm

7

(imo) 4Bbbl

E. continued

>

HELD NAME GENHUI. J^(^ DESdUPTHXt ^ F k M S4H (km^l

14 I 6

LluuflciikHi

-Vr.L:v..Lf r.113

Dhlttf

[.ccitloa

huihUl^l IMI

10/41}

Seiunk and

ElrmfcuOt)

100

TblalWcUi

l(l»73)

MeUMl 1«U

FMdStftbH

PrttduccT

ProducHon

DrilMdItIO

PradiHCT WcOi

«(IWS)

2fl971>

OtjMnrrW*!!*

OtpUi ID Top

t.2M

9.6M

ofr«rin>

Provion

1949

W I I W E

T D U I Depth
rADfUU

f / ' l p a ^ ^ M-^7d??^lg!^^^-* P>'^^^^^pS»U^'^ Klcminc type

(••(.kn^

FIELDNAME

FADHIU

TbkzklXBlf h j ZoM (It)

40 GO ft CL

7

A n a of PmductEcHi

3

USEKVOIK MRAMETEHS

ft 3

Ifcr^z

I

7 Wtlli

rROHICING HOUZONS Formadon

'

•• -^T"TW-j;*I.T

•I Arak ArtfaDMbr

Aft SEAL FiniBtiiHi Litbolofy

Aft

7

Ltmesione

Calcafcnite m d olcoRiutic UnKtune

150

ISO

t J,:r..-.M.

M . f unxuc

Anhydrite ' LTitnfcinnBUDnah

Dtwuru •J,

c 3 O

' ,

KimmendgiAnTithofiian

'

Limmone

40

BtjociuvCllkiviiD

•

ronKdiH

Hmuit

Dhrumi

LI*bs«Di;

Arpibceom. bicuminout ttmnlorc

ArfillKeaui linmtone

500

1»

OKfonJiU'E. Kimmcndgiv)

Cillovtin

-•>*«> Type

-g1 .n

o*

\rJ^

t

A«t

CD

1

SOUSCE

TUdcBKin)

7

Phnimi

UdnlDi;

TMckantim

w 1

2 'll

1

^

\ ft

5.' a.

-

tn ntoDucnoN.

05

MKAMKTKKS Urix

RccefvH7 Factor

UJ(t«H

(») Mly Prodi (date

46/100 bbl/d (197»)

ToM VodiKUlli (date)

StnKtunI •JXKIIIIC 0(1

219 MM.MH (1979)

}5T M M tiki oil

E. continued

HELD NAME GKHEIUL D^OUPnON F k M Sin IkH*)

uitii 25*!S'30" N.

dudicalloa

22IB»lly/2Ci Klenunttype

Data of

194S

1

2

Anttinn Plaironti

DrpthioToii

ii.ixxy

6J0O

AJrDvl

TUdnKHof P*J ZAAf (ft)

40

lU

MWOO

7

1

2

47(V1,Q$0

Gtwiity uirvey ind itnKture ikillinf

ElCTKtkMirt)

M«kod

i»;i

ncMStalw

ProdDoer

T««AlWrili DriUtd {date)

IJ44(1^6)

)8I(I97«)

OkMnrrWtM

^

Iqjtctlod

7

PndncliDii P r a d m r WiUt

htrolrtun

WtU •>

GHAWAR

OTHER PARAMETERS

-

OM,II>^ I t e a l DilHli (11)

FIELDNAME

GHAWAR

Prtpductiod RESERVOIR RiRAMETERS

;«

Rntrvolr lN>r«it¥ 1 % 1

^

P e n a n billty ^n^l

1

2

FvuAlioa

Arab Arab C Mhi

ArabAnib D Mhr

UUukitr

CalcKEiutcs

nODUCING BORIZONS

IDIUAI P r a u r c

Bubble Potoi

bmcslonc T b l d u i i i i in) Ap

SEAL

lOO KJmnKndsiviE. Tutwrnan

1

K1 m mend p 1 an E Ti(h^»niin

2 Anb AnbDMbr

[^UkDlDcy

Anh^rdnie (LnmrarmiiJDnii)

Anhydrte {mlrafoniufionaO

E, Tithoniin

Aft

1

4^

^

1

• ^

f

Fwmalion VoluDtf Fkftar

^RB/STB) OtL FARAMEnnS

3 7

^1

KimmendgMJ^ E,Tnhw»in

SulTkir Coolf nt

7

1.9

z

v)icfKii> (c:n

"

Huii\i/ Ijimculed. bilu-

Umiiuifd biiumincui limuuHK

500

500

C>llowi«n-EKimmendgiui

C A I I D V I U I - E.

Rccovtrr Factor

Daily PndiKtion

-v

RrcovfTiiblt

7

DiiH ^CipSIUKHI

Statu

i.09 MM.MilId (1979)

Tbul PrwIucliDB (ditel

18,980 M M MM (19T9)

ElttluKd ttaatwyta

«0.}WMMM>l

7

RccoTcnUc OR

•I

RKtmraMf Gu

7

Kimmcnid^ui

Sinifiiml. Fton Bitcd N/S uticline c ipsoflhe flinks niife front 3* lo 5*

>

z

i

3iO

PRODUCTION RARAMETZX5

en

7

7

EqulnkfllOfI

>

7

a

LUbotoiT

Ttviyf

y

GH/OURatta ixC'STB)

For^lioa

Ap

1500-^900

Oil G n r i t j ( * A n i

Huiifi

TUckiicB(n>

Bollon Hole TrmpcrmlurF

270

Farmadon

SOURCE

paTTKib*lili^> 4

E. continued

>

GEh4EIUL IKSCKn^ION F U d s i n Ikm')

CUHifkalioa

LncadiHi W4I I k U l Dc|Hll (II)

D o t or Praduclion PrndiKiT Weill

PROPUriNR HORIZONS Fonbalion UtiKtaa

nikkmim) At.

amEK PARAMETEKS

SJi6-»

I'E

Aritnin Plolfonn

221 BaHy/X:Kltnunrtype

Prvvincc

1941

DtacAvtry

Ibpo^gnphic relief, core bolei i i K v L Eocene

1941

Field SiBlH

Pfod«tr

M(1978)

04wrvn-WfUi

7

Drilkd <de(c> *t

Idjcvrtioo

3

3

ArtbCMV

Arah D .Mhr

Dhmnu

Limnumc, dokhmiEic limatonc and vihydritc

E.irTkc^tQDC. H>ol£i-

tirncHDne

»'IM

70-190

225

KimmcrKlfiBn

Kimin«idf[t>n

BtthoniinBijocivi

ind uitiydnlc

2 A.nt

Dtifumi

Ulhohic

Anhydrite (imnTDnTutionil)

Anhydrite

Umcuooe

Kimmeridpui

KiiTiTTtcndpui

$(XJBCE

1

z

Fomllon

Hinifi

Hanifi

[JUHIOH'

•

• : ^

TrapTypt

lU

3i

w.(no

1

7

1

2

3

RcacrYDlr Poroaily <%)

12 31

5 26

io-;<

PenHabllil]' (md)

Hitb

7

7

[oilial P m a m

1

7

7

Bubble h d B I P r a w n (prif]

1

7

7

BollamHaU Tcnpcniun

T

7

7

Fonudflo VoJiinK Factor (RH/STB)

•J

^

7

on.

1

2

3

BtJQCiinCalboviu

3

lARAMETERS

,:

31

3e

37

860

MO

Sulfur CvDLtnt

173

I.M

T

T

7

(«) noDucnoN MBAMETXRS RrcoYTry Factor

(»)

500

500

300

L^ CallovTin^ E. KimmcniJ^ui

U CillovtnE. Kintmcndljln

Ba)ocimCdkirin

Stnictunl AidiclJiK

'%

130

Dtmmt

PndKtiDa (dMtl Rftwrnblt Raatm* — E i i u t n l n i l Oil

ft 3

05

n

I

CD

c

3 O

GH^OURitla (icCSTB)

Arfillaoout Umeitonc

ro o. §•

ITS

Oil C r t H I ; CAPI)

vbc«itr(CP)

00

CO

FARAMETERS

mtnoui limcnuK

Aft

M

RESERVOIR 213(197S)

1

TUdcBtHiri)

6JW

PndKltiia lacni)

Anb

Aft

3

3,7i7

70-262

ElcnOoam)

FvniHt^

SEAL

,2

h i Z a n i Itl)

McOud

t

1 5^2

DcpUi tg Top 4f Pay ((tk

Abqiiq-I

Dtmrrvr;

«,<»a

ABQAiq

FIELDNAME

ABQAIQ

FIELDNAME

•>

ft

o, o* era 3ft

a. & cn &3

Drln

G u cnponiiur and WHcr drive

litjcclioD Statiu

G u injection in ihe louth, water irvfcclitHi in the

1M^ PndactlDa
6,165 M M . U I

EmoalBl

9J0a MM.Wil

(1979)

13.133 MM.bN

ReL4'tTlMC

IIWDMM.bbl

Reco4tnblt G«

2TCF

35 (mnury uv] 14 secondary with gas injection

on

(1979)

E. continued

GENERAI, DESCSIPnON H e u S L H tliiii')

221 Billy 12 Ca KJenuTKCyFe

Date of

1967

DlKovrrj VUI

MKJW-I

«.767

DUKHII J MeUml

Satmic Hffvey

Etcnttoam)

1

l»7)

ncMSutui

Pnxkicer

2«(IW2)

OlHmrWcUi

t

^ T M * I Diptta (H)

ATlbiin Plalfomi

LtUHflcftbOD

1« I I J

DrillKKlUU)

PRODUCING HORIZONS FoniBltDO Ulbakiir ThMuHHin) Alt

IqiKdiHi Weill

t

2

3

KluTji

VviumH

Minifa Mbr

Smdilonc

CirbDiulc

CirtxHute

1

yto

240

BO

Abitn-Cownu^ nun

Vilinprii«n

TiUmiiu

3

^•1

.2'

Fonuatkpn

5>fiiu)rt

Buwiih

HiLh

UtbDlocx

Sandy ) M e

Sl»k

Anhydriie

AJbian-

KiulcnvinTL

TtthDiuui

1

2

3

SEM.

Atf..

-

RESEKVOIS FARAMCIERS

I

Rntrvnir PnnHlty < % 1

7

PerriKptiiJItT [milt [nltUpRSBR

M<19B2)

Praduction P n d u c t r WeUi

MARJAN

FIELDNAME

MA M A N

n E L D NAME

BstiMi P D I D I P n a a u n (pnK>

^2

. -j;.

^

^

^ T

•!

^

"!

T

1

7

7

BolloiD Hoie t^mpfnlun

1

•>

Fornutkut Volumt FnctDT (RB/STB)

1

7

1

OIL PARAMOTRS

1

2

3

OU ( i r . v i l j T A P I )

n

M

3! -J

Gu/OllRitta

Sulfur Content

2J1

2.1

i«

(*l 7

ViKOCily (UP)

Aft

sointcE

V

FomudDn

Sulsiy

SuUij

Kiruri

Lmotone

CAlcvcnitic Limestone

Ltntiiulfids argillaceous timetioiK

2«0

260

MO

Bernuur

Bffnuiui

SiructunI viticLinc

cLtiK

Slnicturtl tniiciiiK

1

2

3

i.eOD

s.ooo

^

1

Utbii)d(r

TUckDcis
aiBER PAKAMKrEBS Dtplh to I n p of P i y t n i

t . KimnvrKlgiAn •

^ 0

Pi]fZaiK
266

1

7

ntoDucnciN MRAMEIERS R t f l n t r y Factor

T

(») Dmilr Pndudiaa (itnti) R*cD>Tf*bk Rncrm — EqBtnWat (Ml

Drin Mcciujilnd

67W)W>l/il Pnducbon (ditt) •!

ReconnUt

W n a dnve

IIOKUO

7

Sunn IMMM.btil (1980)

EiUnalnl

6TJ M M b b l

7

RiUHCi aMc

1

Co

CD B

>

E. continued

^

GDffiKAL DBSCMPnON

•.

488

Ftold S I K ikmr^I

'

221 Bally':u:a Klcmnvm type

PttmtruiKI

Anbian PlatTorm

Dklrof

I9S7

MtnwT

Khunu-I

iiKmi

Saimic Hirvc^r

tMvmUmattH

l>10-MT6

T«tBlWclb

«(197J)

MHbDd [ M I

J*-"-

10(1975)

P n d m r Wells

I-

PBODUCINC HOUZONS

ftoduor

FMdStetB

19«

of

,

•

- • -

••'-—-

" ••-: ^

.

V.

2(WTO

3F\

1nJ4¥tkHi Welb

4.760

5J95

6,490

12.280

J

-J

'

^

fl

7

t

1

3

4

18

T

H i ^ (fdution penmbilitv)

y

1

T7

7

7

Bubble PDldl

^

7

1

BtAiomHoit Tempera rure

1

7

1

7

7

DrpUi ID Top

16119751

AiuoT ^ndvrliDD BESKRVOIK FAKAMKIERS ReacrviWr

Hniufa

Dhmnu

Khuir

Cafbocvic

Cikuenibc iinv-

CtkvcnitF-

in

150

Ap

yx>

IS5 L-

Kimavvlpan

^rmiiJi

Otfocdiin

4

. . : j -• •

\X,XOKm

1 22

18

00

a-

I' E3 «—^

Cd Finiv>blll(]r(iad)

AntiDMbr

nitctUKStft)

, 3

Id)

IDIIUI Prnturt IJtlulacf

^.

4

CilcireniLe ind cilcimutk IjmoiocM

FormacfDn

z

Par Z «

4«TH'E Totd DttMh ((11

1

OIHER RARAMETKSS

CUHifialiaD

LiK*ttai< 111. tool)

KHURAIS

FIELD ^AME

KHURAIS

FIELDNAME

65

13 G.

IpxiKJ

C

3 O

Cilkmui SKAL Foraatfwi

1

2

3^

4

Anil

Hiiufi

Dtinima

Sudflir

uikoUfr

Anhydrile (intnTormMioniU)

[jmHtcne

Ai^lliceous UmnlDfic

Shile

Ate

L. Kimmcnd^m

Oxfofditn

CalloviAn

E.TIiuik

SOURCE

1

1

3

4

FormadDii

Hinifi

Dhrumi

Quuibi

[Jthalati

Luninna), u f i l l K C O u . pckiidil linwsione

Cilcirmttic UmcxuHv

Skuk

5«a

150

400

L. ClllovruE, Kimmcndfiui

Bi>ociaiCtllovixi

Sihirun

TUckHHtrt) Ad

Th^T^ft

Stiuctuni Jtmicbne

FomrutJoA Volume Fador (BIUSTH) OIL rAItAMETER$

7

ft

o, 1

z

-

3

4

Oil C r a ' i t ] ' I ' A F I )

JI

33

36

42

Ga«OaKalla (BC0STB)

280

JTO

MO

T

Sulfur Cofitciil

1.8

19

7

7

7

7

7

•>

7

Drin MechaBln

7

macttas Sttta*

7

3].oaotitii/ij (1979)

TMal PraluctlDii (datal

H I MMbM 119791

Eadnaud

4.400 M M .Mri oil

7.65 B.bbI

RteAHfAbIc

7

a.

(«l Vbcoaity
63

PRODUCTION PARAMETERS l U c o H r y FaclDr

(*> DiUr ProducUoa (dale) RecoT*r8b4t RcatrvH — E^Bivalcnl Oil

7

KttfttnMt Oil

G H

E. continued

GENERAL ' DBSCUFTION f M d S l u ikno'l

FIFXDNAME

KHURSANIYAH

FIELD NAME

OTHER nutAMEitxs

r I3i:

UusiAcalian

I\|IUHIIID

221 bti\yr2CA

Anbiin Plulofm

DtpthuiTDfi

KHURSAMVAH

4

5-

6.035

6.220

6,1140

3»

lU

7i

24

17.000 K m

-v

7

7

*t

1

2

i.WO

5.9JO

}7

_ 3


IMilDcptbm)

DMii>r

Dale of

I9M

DtKVTfrr

KJiunuiiyah-1

S d i m k survey •nd gnvimctnc

B c n t i i n (ft)

0-50

Mrikod 1960

FWldStuia

Pnhkicer

TMdUUb I>rtlM
J2 (W7S)

KESEKVOnt lARAMEIStS

1

z

3

4

5

»(I»7S0

OlwmrWiUi

1

IqiKtiaa WcUi

7 (1T78)

Rncnolr

U

iS

26

2J

21

1

2

3

4

5

AnbAMbi

AnbBMto

AnbCMbr

ArabDMbf

Kini(>

2rM'N. 4
fndacttott PrHluiTr WcUi PRODUCING HORIZONS Fonuttott

Ap

ClUcvrrutc U H I c^iT^niLic limeitone 4S

IW

2

FomtiiHi

Hilh

Artb

uuukir

Anh)rdhle

IIX

4

Anb

Anb

I

2

3 Huufa U m i u i t d . bituirdiwui cvtiontu

T^^TX*

3 JubtilVi

Anhjrdrile (intntornuitonil)

Ulkoloo'

Apt

OxfonJiin

3

FomliDB

TUckiKH<m

20D

30O

80

80-280

7

7

1

)28)7

7

BubbttPnlDI PUJIIIH f|M
7

T

1

7

T

7

7

7

7

7

FwnBtiin Vghuot F K U r
T

1

^

T

1

OIL MRAMETKCS

1

z

3

4

OU G r » « t r CAPD

31

t

7

7

?

G u f O i l Racls

310

)6D

390

ita

310

1.4

:,s

3.)

j-«

u

7

1

7

160

2M

limnlonc Kinunend^in

L. Kimmcndgian-E. Tithcmitn

Alt SOURCE

900

Initial PrtMUR

Umolone

L. KifnTTKndf^ikn'E. Tlthoniin

Hlhomtr

1

SXAL

A m ot

l^nnntHUty (mdl

UMtaticr llikkHiiin}

TUckiKHof P i ; Z o o i (ft)

" 4

-5

3

TcmpnvtuR

{ K K T B I

SuUiir CoalcDi

(»)

500

V l x n t t r IC'PI

t- C*lk»viui'E Kimniendgian

^-^

R«WTf7FKt«r

-J

DrtTt Mcduninn

(1979)

ProductkM (diu)

Dallr Pniductkia (4att) Rtfo^trablt Rnrrm —

7

^

(V

>

•>

PRODUCmm MRAMETCRS

Stfuounl jtmiclinc trending NE-SW:dip3 nnge fmm

.

>

TSUI

?

on

691 M M . M l (1979)

IqlccUoo SUtan

*t

Eulmauil

2JOOMMM>loit

RKOHnMc

J

G H

& >

E. continued

>

GEHEHAL DESCBIFTION FfeU S t u tkm')

L « t k H t 0 * t , hHK)

^'•/:

4Ult>

21 Bal1y/2Ci

Petnkuo

2 3 ' 3 : ' N,

Put If Macovcry

IW!

DlKonry

n

79

36

7

iS.OQOKrs

T

7

y

T

KESEKVOIR KAKAMEIBU

I

2

3

4

5

UtatmiT PimiiilT (%)

^

1

13-31

^-ib

T

PinDoblllly ( n d )

7

1

ll-iOOO

4-500

44

Dhmmi

[nfliBi P r a n i r t

1

''

^

T

J

dlcirenilic LmestoAC

Bubble Poltil Prr^tifT (palt)

1

1

^ .

T

7

T

1

7

•>

1

^

QwM Pay Z a a t (ft)

E k v i d g a 111

IIMi

M I C at ProdlKlinn

194$

FVMSLAtm

t*mductr

ToUIWiUt Dritlnl ( d i t i )

«(1*T»)

30(I9T»)

( l l « m r WcUi

3(1918)

[i^t«
S(19^)

1

2

3

4

5

Arab [AnbAMtn)

Anb (Anb B Mbr>

Arab lAnbCMtn

Anb ( A n b D MbiJ

Calcoicrucei wtiti lome dakxriiiei

LMwiotJi

Forma lion

IM

360

1

2

3

4

5

Hiih

Anb (Anb-A Mbil

Anb (Anb-B)Mbrl

Anb lAnbCMbi)

Dhnimt

Anhydhie

3

2

1

^

Fonnaam VQIHDW Factor (RBffiTB)

on.

4

5

H

}|

3»

43

»70

7

CallcFviin

)»

SvVtir Cddicat

^9

).)

3,«

1.1

0.9

T

T

-

1

7

tJiholoicr

300

160

CiltortrtinE. Kjfnfnendgian

BajocimCalktviir)

(*)

Vlacnlly ICPI

c l i v rtlmed la rif hl'luenl dip itong buciTtenl faulL in ptn dunn J Ihe Juruuc.

& P5

1

Drtn Mtcbamhin

Waler drive

b^tectkM SUhH

1

IW.OCObbKd (1979)

tbul

633.J M M Mil (19)0)

EadiBaleil ReHFVH

3.300 M M bbl Oil

6.800 M M bbl

Rccovtrabk

6M)0 MM.bbI

kccDvtnblc G«

4.79TCF

<») IMIy PmSuclion Idaltl RKOVVI^MC

Rtatrm — EquinlcntOU

(B

o" ere v: o en

PttODUCnOK PARAMETERS Rtcovrrjr Factor

o,

3 O

IW

ArgillKeotu limmone

EkMtxe

3

fT B

37

Umiiuled. art<Ma»ou>, pck>»dtl limttione

A^

2

t

230

Dhnimi

TMckBBXft)

1

05

T

G^OURlOo (actlSTB)

Muufi

3

ITS

OH GraKltjf ("API)

5

a. §•

CT

LinwtbiK

Fomutton

T^pTrpc

Bofl«nHo4e TriBpcrvtun

00

dd

MRAMETERS

Kjmincr>dp»rt- E-Tiirwoiin

An

Atvant PrDdiKtion

Bijod4n-

Kiirmendgian-E. Tlthonian

[JtbolOfty

SOURCE

IW

31

2S

Ap

SEAL

30

8,360

SdiniK. snrfKC imlogy

TWcksBXri)

6.!(()6

7,(775

Df ptb to Tbp

, 3

i>(P»rtft>

Macovcry Mclbod

Formtiaii

6.736

6.930

Anbiin Platform

7J2i

Produnr W t l b

2

5

T o u l Dcfilh ( d )

PRODUCING HORIZONS

1

4

QIHEK MRAMETXRS

1 * -

ClunAcxttiMi

QATIF

FIELD NAME

QATIF

HELDNAME

<4Mt)

nu

E. continued

ZULVF

HELD ^AME GENERAL DESCXUnON

<

'

F k U SiK i k B * )

FIELDNAME :

30 I IT

Oa^flcAtiofli

T

Dttbof

Jr" - ?

IVtmiemn

Antnvi PI^Erurm

PimvcrT WcU

ZuluM

KJcmmciypC L d a « t « lint, ) ( • • )

L%5

«jao

T o t i l OtpUi (11)

Setimic Hirvry

ElCTBtkH (A>

?

PmdiKcr

-nulWrib

4a(i»»i)

RESERVODt rARAMCTERS

1

z

RoemilT I'oradt)'(«)

7

"^

1

t

P c n D n M U t j (mdl

?

•y

1

7

*

T

7

7

F M d Status

Bubble PMnt

1

t

7

7

P n d a n r Weill

14

O b K m r Weill

FKOMJCING HORIZONS

1

2

Fonnitiim

Nfauddikl

SiisliiyA

lilteUtr

Cirtjonxc

7

4

5

BiyMili

Yimamfl

SindHOA«

Cirbonile

KhlTii

413

sen

»0

Baircmiin

VilAiigintui

M»

ALbitn

Aft

IiOHtkia W d b

3

StndilDnc md ih«ie

200

TiiiitMnfn)

t

BvtUHn Hole 'ntupEnturT

?

^

7

7

Fomialioa Volumt FictDT (RB«TB)

7

1

7

?

on.

1

2. _

3

4

5

3

3

FvmatkM

Win

MiiKkluit

Saliniyi

Sihuwba

Buwub

UtbdDD

Shale

Lunslme

Shdy und

DohHiuiic UmcsiafW

Sbite

Aptiui

H*JtHiviin

?*,'

Av

somcE

'

Alt Nin

CenDmuiiiA

/

1

1

3

FormiillDd

Suiujf

Litbslocy

Cilcirenilic UriKvlonc

4

"''•

' i";:

':• •

5

5

5

1

3

4

^

^

^

"*

7

7

7

7

1

JIO

7

T

?

1

1

•

h f Zaoc (ft)

>

•"

30.7

ill

31.2

?

7

1

7 CD 3

Sulfur Cantinl

2.30

2.31

i4i

2.40

2.41

7

7

7

7

7

Drift McduBiiiii

Witerdrivf

li^tclJon Stmuu

7

TbUI PndsctkM (ibitt)

7IM MM.Mil (I9W)

EiUmted Rocrvrt

I 0 . 6 M MM.btil

Rccovtnble OH

T

RKOwmb4e

7

(*) VlndtT(CP) PKODUCTION FARAMETERS Krcattry

Factor

RKtnmbk Rdcrrei — E q u l n l e r l Oil

tf rti (til

Preductiwi (km'l

30.J

T

itttlSTB)

Praductkn

Stnitnifil mticline

TrtHyjn

An*«r

-•

30.7

•

*!*V'^' •.. ^ ^ • - v . ^ V -

^

(%)

BCTTiHun

Av

DepUi la Tup

4.

CuvnuitiiiKi


500

l l i i c l L H U
OTHER PARAMETERS

•

:

PARAMETERS Oil ( i n v l l r C A F I )

1

SEAL

4

- . ' > ' •

DriDnlliUUI

PndKtion

^ 3


MMhDd

iim

D M O T

ZULUF

•t

E. continued

GENEBAL DKSCXIPnON F k U S l a (kBi^)

LocBdoa H a t >«kf)

llM^Diptfcm)

lUI

::.

••••

' ' • • ' " • • ;

1940

Dnuof

9.97S

J-

'

OTBES nUtAMETEXS

•

Df pill td Top ofPinri)

Arahtm

CU^Ocitloa

PluTcnn

Klenmctypc ITTTN,

Atu Hadriyi-1

DbcoTvry Wril

A n * at Pnulurtinn

X

Seunucturvey

Elcntt(U(fl)

hoduccf

lUriWtUl

U (1976)

Tqjrctkn Wdli

T

tMkad I%2

nddSUOH

t

OtHmr WtUi

Pnducdaa P n i d m r Wrlli

PRODUCING HORIZONS FsraMka

1 Anb (Artb-A MbrI

2

3

Arab -BMbt)

Anb (Aiil>-CMbi)

^

4 Anb (Anb-DMbi)

U

lot

OxfDT^UI

1

2

3

4

s

Fornulkpa

HiUl

Anb

Anb

Arab

Dhfumi

UlbotocT

Anhydriie

A«t

TlthDnim

soimcE

1

Anhj^te

Anttydriie

Z

1

3

Utbolotr

LAminiuid. u^llaccDiu lifnatonc

Tv^iyp*

Anhydrite

Kinunend^iiE TiUtonim

H v u f A ^ w i i q MountAin

An

•'

•

«.490

J3

25,000

taa

4

5

6

8^70

U50

9J83

7

U

W

44

)(10

7

?

1

7

T

7

3

4

5

6

1

1

00

RESERVOIR PARAMETEXS

I

2

Rc^TMrir

'!

?

?

P m n u b i l i t T (md)

7

1

7

7

7

7

^

7

T

7

8iiMtiPi4iU t * » « i n (pidc>

7

7

7

7

7

Botloai HaU Ttdifwrttturt

7

7

7

7

7

Fonutiiio VvliuK Factor (RBKTBl

7

1

7

7

7

OIL PARAMETERS

•

OUGnrltT<°APII

a.

txi

(P4)

2

3

4

s

«

JJ

33

2S

33

31

7

ITS ft

c

3 O m

o_ o*

>

MounUin

FonHtlsa

TTilrlmiM I W

400

150

HI

O M

_

LifnestoiM

Limeilone •ndnunor

KimmcndgitfE- Tiihoniui

Ate

SEAL

Tuviiq MouAtfin

(

46

2

1

&3

6

Dhmmj

-

3

V n ^

5

Cak:ircniie. dDkunile ind inhytbiic

Ulboktr

TUckm(n)

"^

ABtl H A O R I V A

FIELDNAME

ABU HADRIYA

FIELD NAME

60

60

T

100

?

Limestone

Co'CHI Ratio (KtlSTB)

tc

LimaUme Bijoctir-

OiFordiui

SMlAu-Conmu

1.:

t.l

2.4

1.7

1.7

T

«

VUcoBtjfCP)

1

'

1

7

1

1

I^Jrctloa Statu!

•)

i.O]BMM bbi oil

fT 4

'

5 Dhninu

tun Umoionc

130

Calloviin GJoopud ttructuraJ aiuiclme

400 OKfofdim

. CUlDvun-E KitmcridfilA

FAKAMETERS Recovtfy Factor

?

DaUr Prodvciliio (data) Rcumci abfC RHtrwa — E q u l n l m t Oy

EMTC

•)

MrcfauUaa

(*1

limcflone WO

ntoDucnoN

M.OaOt>bl/d (1979)

TUal ProductiDO (datil

U « M M Mil (i9M)

ErtiBOtd

1

R««THabk OU

7

RuuiuaDH Cm

Rarrvfl

7

E. continued F I E L D MA M E GENERAL DESCRVnON

DAMMAM

A n a of ^

•

•

Dalf of

U n r U o B (Ixt, k n f )

Afibiafi PUtfonn

14M

Durunun-7

Otmarrwy

RESERVOIR PARAMBTERS

JOWE TM>I OepMl (K)

Mcdmil I9J«

moDuciNG HORIZONS

FfaMSUlH

U

;; '

FomialMKi

''^

1

2

Anb (Afib-AMbrI

Saitniyi

Suffice inlOfif

340

Eknti«i(n)

b^KdoB WiUi

3

'5

1

1

2

3

4

s

6

20-25

:o

30

23

21

7

*

fiO-2QO

MO

190

230

eo

7

T

t

7

T

1

T

BubMEPoliil

1

7

7

7

7

?

s '"-'

4

Battom Hole

7

1

7

7

7

7

tmb ( A n b - BMbc)

Anb (Anb- C Mbrj

Anb (Anb-DMbr>

FuriDiitiaii VoJmtH F K I A T (RB/STB)

7

7

7

T

7

7

•

I

3

4

5

6

PARAMETEttS Oil C;r«*il^ (-API)

)S

51

?"i

34

]!

'

7

7

7

U

M

7

7

7

Prcivirc (ptic)

'-6 Kliuff

^tolDinicic mhydrile

340

TlilituMmi Aft

W

,'.:^ '

2

.".• 1

Kilh

Win

FonuUm

LltbolocT Ap

SOl/RCE

^

100

3)

Anb (Anb-AMbi)

(Anb-BK(ti()

Shile ETnuuc

•

S

.' ' ^ 6

Htnjl'ik/TLiw^Lj Monjit^n

<]^uibi

UibotDo

Shale

Lainjiiud. irtJUiccau limatone

Shtlc

BoTiuiin

500

40D

CMlkiviiD-E, ICimmCiSdgiiA

Sihihin

Circul »f. donul u n i c n i n 1; fiullcd donif pnibiMy c i u e d by iJeet>-teited lah intTUiion.

OTHER £ MRAMETEIU^ Drplii l a Tofi

I l.lit]

2

3

4

4.280

4J40

4JI0

4,340

iW7

40

}l

93

Iff)

7

'^J^^^^^^H

(ft) 1

(ft)

1

T

1

Drin MKkuiaa

Gucx[>uisk£]n

23.«Mbtil/d (1579)

IMil

$73MM.bM (1979)

Eitinntcd RtHTm

IXISOMMbU oil

1

RccoTtraM*

647MM bbl

XKOvmbK

7

RKonry pKtor (»l

^

-^

7 Statu

'

Sulit>

Alt

I.J

PROoucnoN PARAMETERS

lotnfonnitioiul Hhyrhle

TtipTypi

1 J

VlHtMJLy ICP)

L. Ktinirttritl^ati-Tiihoruan

SOO

1.4

Sudur

FwiMtton

T h l d u H M (ni

Sulfur C o q t c n l

Anb < A n b ^ Mbc)

Ti[hofl]ut

•r-4

3»

(*)

Anhydritf

'3

390

6

5Kilc

2

GWOaRiUa (KfSTB)

7

s

Alb] anIVmni&n

"' 1

on,

Lite Pwmi«n

. 4

3 .

3»

237

Kimrwrripan-R TnjKiflUTi

Alhisn ':,'

FIT Z O H

7

47(I97B)

PnducH

UDddone

PIT

7

[nidAlPntfvn

PcmmbiUtr |B^I

C i l c m n i l e , doloinite, dolomitic limciiHic pAd tnhydriie

UUnlocr

of

t

DrHlnKdau)

FndwxrWilu

SEAL

7

Ponidll(%>

4^11

Dmtiif fnAucHtm

7

PnidiKUiiii (liiii')

^

KlemoK type

ClB^ficaHwt

7»*

7

•

•

FMd StK dun')

DtAMMAM

FIELDNAME

i

D«UT Productloa

(Mt)

(4ite) RccDTcnblc RntTTH E a g n l n l n l Oil

G H

^

a

>

E. continued

HELD NAME

MANIFA

OTHER FAKAMETERS

GENERAL DGSCRimON 4011;

niMSEslkill')

CllHl«»ti«

2:1 RaJly/2Ci KkTTUiK l y ^

l^trDltuni FniTliict

AntMU PlAEform

f

MUDf Dbcovcrr

1M7

DbcvTVTT

Mwfl-t

9^10

DtomvtTT MHlMd

Scuink RifTCy

WiitrDepUi

IJ-50

196*

FMdStiDii

Pmtuttf

IMalWen*

l)(ira)

rradawWtUt

7

ObfHTrr WcUi

7

FKODUCING BOMZONS

I

2

3

Loculsa < k l , liiBt)

TDIHI I V I H I I

Ifl)

Outal

Suliij^i

Vunum

CaldfcniR Hid calcvtnitic linestone

Lilhslacy

TUduHKtrt) Alt

SEAL Fomttea

limnlone

240

MO

to

BcmtiLUiValuipiniui

E>emuiHi

TillKini«n

1

I

3

Buwub

Yinwmt

HiUi

Arab (MbflAnb- B

&

Lllkatao

UmCHHH

Shike

An ;

Anhydrite

H4ui£nvi«n

Wtingiruon

'nthonim

1

2

3

'.4

100

rP

Hilh

Anhydrlie

•?

60

lU

Tl

10

X

m.oootciet

7

7

1

RESERVOIR FAKAMETERS

1

2

3

Refcrvoir PonBilj(*)

23

2J

T

>

T

00

4

5

6

a. B

22

16

[9

21

1

^

1

^

•J

7

tsilUI PTHHFt

7

*t

7

7

7

1

Bubblt pDliu Prttxtirr ( p d ^

7

T

1

1

t

1

Botlon Ffol* TrmpHstun

7

•J

7

t

7

1

T

t

1

'I

1

7

FtrnmUIIlT
•

6

Anb (Aiib-BMbil

OIL FARAMFTERS

K inimendp»n-Tiihofiii»n

.*

4

SuUigr Ctkamutic limexlDnt tTKj ttalt

LuninaLecL ^ l o i d j l c v t n n j t s

«

I

1

500

Bcmuiir

. d J I o v i u - E . KJmmcndpiD

3

4

5

6 26-31

1«

27

;7

28

26-31

GH«UR*tk>
1»

W

140

230

160

sa

Rffijet f m n

7

1

7

7

7

T

-)

1

7

7

I c

3 O

1 B 3 *

v i H H i r T 1CP}

SCO

&3

Tl

OU GnvtiT <*APn

SuUW C v o t M l

n>

CD

Anhydnle MntnformilKHU^)

Utboloc;

•M*T>pe

6

Vohinc Factor (RH/STB)

Fonuftlae

Aft

5 8.962

KimmeridEiin'Tthaiun

HwiifftTuwait^ Mmntun

TUcklHKtrt)

4 S.749

Arab (Anb- C Mbcl

to

40

,

8.222

A m of Pndurtkifl

CfelctftniEC. {Jdlomiic. dolcmitk limatDiK md dDlonutic Anhydrite

(Anb-A Mbr)

-80URCX

I

5

A^J^ ( A n b - A Mbf>

3

7.«I

TWckHoT Pay Zoat i m

WcUi

Hilh

2.

7J81

[>tpliiU)Ttop

T

4

1

iifP.j(fl)

r

ForimltiHi

MANIFA

FIELDNAME

7

FRODUCTION FARAMTTBRS Ktcmtrf

Factor

C5 t

7

DriTc Mcduaiiai

23,000 bWd (I9rr9)

TaUl PnHhKtIOB Maul

147 M M bbl (1979)

Etflioaud RmnfM

7

Rccorrrvblc OU

7

RccovcraMc

T

Slalaa

Scnictunl Wliclific [>a% Pradactiaa

HfCQvtn He RcBenm — E^uJVBlaat Oil

8M0MMbbl oil

E. continued

SAFANIYAfi

FIELD NAME CENERAL DESOUFTION

'

:

-

•

•

14

M I

F k l d S l u tkm^l

25

25

7

570

fi2I

MO

7

2400

2430

7

1

7

7

T

7

7

7

T

7

T

?

7

1

0

7

t

7

2

3

4

5

6

1

a

?

PtnwuMlltr (ail)

7

lit)

InItU P n s u n

7

1

Bubblt Pojnt P n s n i n {pslc)

T

2

Ek>»oaH<4f TvmpcrvturT Forauckn VnliidH F K t w (RR*TB1

3.,

19S7

PwdDWrWclb

2IB

FRODUCING HOklZCH4S

1

-

I3-IXI

WuirDcptb

I30(197»)

OiUpnxkKer

FltUStaiut

41.

Mdbod D*ltt( nuducDOB

•

<-

'St

Si/iniyah-1

Seiiinic lurvey

7.460

16

RtwrnUr l>i>ndty(%)

MUl IMdDc^dl)

"•- 6

1

Anbiin PUEform

l»l

DwlCDf

L o d d o n yUl, lonct

^truinub

2^ t Btllyr2Ci Kl«(nnv [ype

Clp^kAdoo

J

2.

RF.SERVOIR PARAMETERS

«•

%

SAFANIYAH

FIELDNAME

DrUlHl (dau) 7 V/fXh

Ahrnddi

Formalion Lltliiilaf]! ThickjKKfft)

3

4

s

Mkuldufl

Safaniyah

KKaTji

Biyidh

SuKmone

SandUonc

JW

BO

••^•'

Wnni

UmcsiOrtt

^indiLone

LJincucrK

Sandsloix

230

100

200

7S0

"^l;••

•-•.\v2r-

;*•

•••;

..

:'•

3-

•

•

.

"

^

•

:

*

-

Birremiin .

6

5

Ahnudi

Win

Win

SATuujrih

Khifji

SttLUlhl

Utbulocr

Stuk

Arviilt(4«vt liOBttoie

Shik

Sluly und

Sluly Hnd

Linttuone

SOUKCS

I.

2

3

4

romtiaa

SuUiy

Uibokcr

Shillaw-ininnc cvbofutd wiiti t l u i i f influence

•

5

>^*"

'

27

=7

]i

240

110

190

u

SuiAir C « i t « (

7

l.J

7

7

t

u

Vtocmlt!'(CP)

7

T

7

itt

].l

T .i

1.4MM.bbl/d (UTO)

T

Drtn MHfaulsiD

Wiierdnve

TotiJ Pndnctldo

).061 M M bbl (1»7111

Eidmalid Rtntf

34.100 MM.bbI

G«

Stitui 30300 M M bbl oil

«ali) RKO>trtMt Rncrvca —

OTHES MRAMETERS

1

2

3

4

5

Dtpdi(aTb|i

1

4JC0

7

4,700

i,2t»

i.100

ThickDaKir

100

40

•J

1»

440

60

lAJnOOOKm

7

1

T

7

7

AnaT Pniacttaa

27

TO

Daily PtwtlKtiOB

Stfuciunl iniicliAc

TYipTXn

27 f.

T

BflTTuitn 10 E- V i l m f i n i u i

An

27 HO

Gu/Oil Riba

;6

500

TkldiaH((n)

-•; .': I

PRODLTL-nON PARAMETERS

AfMian

Albiin

CenomuiiAn

OIL >*^ PARAMETERS CHI G n r t c y ('AP[)

Fimttin

* P

>

.^iife

Albiin

Ccnodtuniui

Ac .SEAl.

. • ; r

•

Rccdvmbli MM.bbI

1I.79TCF

> T)

CD B

Q. ><' >

E, continued

BEftkl

riFXDNAME GBNERAL ; ^ . DCSCKIPT10N

FIELDNAME

-

FMdSlittksr')

.*

L a a l l f l i i (lal, lose)

7

BERRI

1

i

PAKAMETEKS

OanAntiaD

n\ billy ';Ca Klemmelype

FMrokum

• 4

AntMAn PliUDmn

XVptkcvTop ottmr (fl)

7.ia)

7,170

7J70

74^

Bcni-l

TUdcBHsof Pi;ZaiK
42

«

»e

l »

T

I

7

7

I

:

3

?

1

'

"^

1»M Writ

Dbkum J

. 3

3" =3

IttUlDc^UttR)

Ml<

Hunrr MMbod

SeiunkMitfvey

DumT

1967

nMStana

RrDduKT

Eknttoairt)

T

TMilWdti

13I{19T«)

Ana at

.issnivoiR '^i

Diai«l(iUlt)

nutAMRTRS .

O t H n t r Wril]

4

[qJccUiiD HVtK

1

2

3

4

( A n b -A Mbr)

Anti (Anb-BMbr)

Ant (Anb-CMtn)

Allfc (Anti -D Mbr}

Pradanr Wtlb

^H'.

nHWUCING ^ HOSIZOriS. .?" FonnaUon

Utttatoff

Mkutdil-ootdil limaunc md dolomibc limtMorK

An ^^;>'

Fonnadon

r

KimrnendgiAn-lL V i r . " L:-

fi

mm

<"

• 2

3

•

ArHh (Anb-BMbl)

Anh (Anb-AMtK)

• * . -^'i Arab lAnb-CMlK)

1:

1 1

Anhydnte ( i r m f H t n w c M l )

UlkDktT

ijj

Fomattan Uihoticr iM±KH(n>

1H»1>pi

C9

PtmcabUitT ( n l )

T

T

7

7

Initial r i i ^ u T T

•J

1

7

7

Bubble Pi4at

T

7

7

t

BMIDaiKpk l^mpcntBrt

T

?

7

7

1

FwnBUna Vdhunc F K I O T (RBffiTBl

^

7

7

7

1

1

2

3

(MJ ( . r . y i i j (-API)

12

31

Ji

CutWRulD

1

7

7

T

1

M

1!

7

7

1

7

7

7

7

1

on.

. ^ *ii-^--

f 2

3

4

I

1

c 3 O m

LuninMed. I T ^ U K C O I H . iMtuiiuncHU lirn«lone 500 Bi^fKi>n-E. Kimmcndfun Smictunl wcicliw umc 43 km lonf on i H-S irend

. ^


HiniEvTuwaiq MmnlHiJv'DhruirLi

Vlmi^(CR Ac

CO

4

•

PAkAMETKRS Kimmendpin'C' TiiboaiiA

An SOURCE

T:

MS

TUeksHxn)

SEAL

.. j i

•IB

^

1

..

.

.

• -5

&5

^^^^^TK?

E. continued

BERR]

FIELDNAME PftODCCING HORIZONS , .

6

5;

^

m

B

7

1

rormatlan

Kuula

Dhnirru

'HjV'tK)

KhufT

Lilkilocr

ctrtoute

Ckbnite

^^t^mjlf

UmesUHic Jim: doloinite

^ioa

1»

}W

TUckasim)

IIELDNAME

BERRI

BottSHEfofo Icfnpti'Atui 1

?

SEAL

BathoiuAn-Bi><s cian

0(f«di*fi

•

3F

.

6

'

3000

^^;

fe

PARAMSmS'

^ 7.

^ •

•

Formacion

Htmra

Dhninu

Tuwaiq Mounlun

CJuuitu

Utbotof;

Dense limbiOH

Limestone

LimenoK

Shakt

OAfordian

BiiocimCftllnvian

OtfordifTt

E.TriBtic

•

SOURCE Fomialion

LUb(4((r TMck—a
*••

,3 Hanih Argllliceoiu limexlDne

ft Dhruim AjjiliiceDui limestone

,..,.. 7

••

TuwBtq Moufiuin AiyilUccDut

»

J

GuTOil R i t i a (KfSTBI

J

T

t

7

Sulfur CooltBt

t

7

I

7

7

1

VbcsdH'(CPI

Recovtrj Ftcicr

1

400

200

Oxf«diin

Silunui

EqulnlcBtOil -.1

N-S irendi ig innclinc

s

8.290

1

?

•>

1

7

Amur Pn4«ctt«i

7

7

1

1

SESERVri[R PAKAMtliiRS

5

laMUIfriin

i.no

•

«

7

s

^

T

T

?

7

7

1

1

7

7

f

7

7

1

7

7

(P

>

1

R*C«rt*f*U*

WO

6

P t r i K a U U t r (aid)

4 J I M ^ B

...^ ^ .^

PrwtlkCtion

Bithonian-Bajocian

.!!

Drt«

Water drive

M i e r in)ecb«i Stilui

ISUUMETERS

RcKrroir Ponnlty | 1 t l

'

•'

-,..-

Shik

5 Dtp
8

rT^^^^^^^H

IlIJMtiUtd (1979)

500

7

7

Quuitid

OUrodiia

1VipT>pe

;

37 9

PRODifcnoN PARAMtTERS

^

« .'• J7 8

:J •

Ap

7

.)«

OxTonliin

• , .

_ 7

FacUr|RB/^TB)

on,

(HI ( . n r i l y C A P I I A(r

7

f

TMd ProducttoB (ibtc)

I432MM.HII (1979)

EidMutcd

T.MOMMbM

lt*Mr*«raM« ON

7

Rscfwcrabic

T

G B

> ft 3

F. Data from some oil and gasfieldsof Southeastern l\irkey

> ON

FIELDNAME

GARZAN

BATI-RAMAN

FIELDNAME

GENERAL DESCRIPTION

BATI-RAMAN

90VRCS KlnlyigAj 1« 1 : ^

FliM StH (ktf')

11 I 1 PeUgic

Ji Hajiy;:rj

riMiilrtiliiii

00 300

(ft) P H n l c w n Province

'

Lwptlon Uat, Lod]^ D i l e of D t K v w r

7

B«i-R-»-1

TbUI Depth i n )

i

1Wi>p<

I9SS

I'Jt.l

DkwtrrWdl

ConiiciuiCa

A«r

[>iyA;t>jkir

i

1

OTHKR nUUMETERS

Girzin^2

MTJ

2.400

SarfiaffiOtafy

SurfKX B«c4ofy

'

7

1961

1955

Prodiito

Pnducts

H3 11W3)

101 (1«I)

PcOltk

hioniKTiiei

41 e t l l y / 2 C l Klemine type

FKiUedlidr dovnr

ft 3

CO

I>cpUi1oTbf> I N K Q Y H 7 MciDDO Elfviilaalft)

1

DudpfPraduttlmi ••a

ntMSunu

tffmylll) 130 ]S13

tmfj

§

A n a 4 f ProdiKtion

fT c

i, TbbJ Wrili DrUkd itmu)

J

»• ur_n_ I^ riHiunr vfw

1(11

ObRTTCr tViUl

T .J

IqKctiwWfUl

^

ft Rcwrvoir Piiraijtr<%)

' ^

•biUt; (ad I 1,750

•••r'

PRODUCING HORIZON

7

Ml)

'^

Pomutiufl

GiTutfi

GEVTATI

LUtaokir

BKK.'IJ^[K

Biocliiiti:

IpilD lirnfin>w ThkkDCHin) Ate

5JJ

530

^tjustnrKtian

Mumhcrhiian

l^'ATF rpcrmjv

l.^i*Ti Cicrmjv

ShAk.

Shm\c.

MuscncKtiui

Ntiutnchtiwi

SEAL Ponpfttfoa UlkokiT

t I

aa-

Tenpcnitun TF) F o m t l H i Votumt >BclorlRB/STHl OIL PARAMETEIU 0«JGnTltr<°API) Gia/OURatla (KC«TB)

A(i

3 O

RESEKVOm PARAMETERS

SulTur CAdteul f%) Vbn^tTtCP)

tn

F. continued

FIELD NAME

BATl-RAMAN

PSODtJCnCHN PAJUMETERS

-

fttcortry

^

K K I O T [ %)

Dti^t Mfchaniflll

L ' O ; IIIJCL[|iJri

[qfcctkn Suiv«

•'

Diudved B U and wMcf 7 3»5Ull

Datljr Production

(I9«)

•

J : MM.bbl (IOT21

3:)MM btsi
iOO MM.bbl

7 a M M Mil

RecoTcnUt (Nl

1

1

Rcconrcnbk G K

t

7

Tdtd PmductlM

Ettiouttd R H H T C I RKOvervbic RtMIXl ^

.J

GARZAN

t

•

^

•

'

••

•

I

> n> s a.

F. continued

> 00

FIELDNAME

RAMAN

H E L D NAME

GENERAL

-

OTHEK PAttAMETERS

FfcM Sin (km)

17)

H I

djuifkabon

"!

L n U o D
41 BiUy/2C> KlemiTK type

1946 DtKOttfJf

PnpTuicc

Dhtmtty Wtii

4,KI2

E U r n f Pmductlaa

193B

PnHhKn-Welb

M

rsoDUciNG BOUZONS

1

Dbcwcr;

Surface

MMbod

»Ml<«y

FWUStaliu

Products

ObHmrWrlli

-

Elentlaa (ft)

TktaJHUi DitUoKditt) Iqiectkn W^Bi

4.202

3,T7J

Thickntm al Pay Zoot Ift)

IM

230

Raman-)

y

T

T

122 (IWI) •»

1

Gifzar

Mifdjn^jfoup

Umcslont

Utbotof; limotoiM

Prodtiellon (kin^>

Af

328

Aptian^Ewly Cunptmui

^fuH^c)l(ia^

1

*

FwnMdwi

MirdjnGriHjp

Lower Gerrnav

Utbstoi;

Linv muditorv in Mirdin Gnup

Shak. calcarHHii shale

ApliU'EArty Campvuin

MaaunchEian

SEAL

A f

.

SOUKCE

1

Fonaltsa

Denltrt

UUHtSfT

Ate

IHpT^pi

1 .

RESERVOIR FAKAMETERS

1

Rcacryoir Fnronty 1 % 1

12

IS

hrmeabUIfy (md)

50

5»

IJOO

7

325

7

133

140

1 061

l.Ml

=

2

3

l^dfjluha

Kanbosli

Pelagic lim«iorc

Pelagic limestone

320

jOO

100

Cenonunim'hiimian

ConiacimCamptman

Campanian

AI^ILKCDUI

BottOfD HAir TVinpenturc CT) Fomt^tiaA V D I U H H Faetor
3

&5

cr o

o o" 15

19

55.2

la

Sulftir Csnunt <%)

Si

Si

VtaeodtrlCF)

J3

:i

GaafOil Ralhi

a. §•

ft

OlLPARAMirreRS OtI Gravity CAFF)

CO

S3 3

(1>»D BuhMePnlnl

00

(KOSTBI

IJIMUMK TUcksmR)

'

PmnirT(psJx>

2J0O

TUduisfft)

2-

Depth to Tup stPa/irt)

Initial P r e s u r t ftitiiiMiiaa

1

ZiigiTM: Dirartakir

Amsf

IMriDepttim)

RAMAN

pKODOcnoN FARAMETERS RetoYiryFMtiir<»)

Dally Fndoctiag liUtil

m 1

Dtht Mccfaanfam

Ruidc:(pamioD udwiter

li^teiikie Slattti

?

4,707 M l
TUal Pndactlcn (dale)

JOJ<X).(»Ot*l (1990)

EMtnuted Rcatrvta

7

lOOMM.bbl

RcnntnhltOU

RccottraMt

7

Strucural half-dome R«overablc RMeTT«^ E i ] i i i n k i i t [HI

a. &

(1992)

7

G. Data from some oil and gasfieldsof Syria

n C L D NAME

HAMZA

RUMAILAN

ULLAYAN

GENXBAL DESdtlPnON FfcldSbetkni)

SOifEDIE

KARATCHOK

FIELDNAME

HAMZA

ULLAVAN

' t

T

T

UUutlli;

•oiocniuc hmotooc 330

Z^gfot A|> 7

1

1

1

Cnuciui'SifilDnuD

7 Anticline

FHtlnd enufline

Adbdine

Bnud uibcltnf

AnbcUiK

Dtplh to Top olFnyini

4.7»

4^10

]J)IS

4J7I

4A11

ThkkDCHof

M

M

50

XW

10(

U

34

]]1

«4

-IV*|.lT|H DmuotDfaor/wj

IWl

1962

1462

IW9

I9M

tMaa>nf> W i l l

1

Ul^tyin-I

RumAilan-l

SouedieO

KMMchDk-l

T o o l Dcplk (ft)

7

6^22

9.90«

8.308

10J16

Seiinuc lumry

Sciunk WTfcy

Seiuiuc lurvey

Sdtmic turvcy

SdimK Hirvcy

^

7

1

1

1

1975

1916

1969

|96»

\9M

Pnxfaicer

Producer

ftoduccr

Producer

hHluccr

7

0

1

7

7

nwtuciT WcUi

^

7

7

7

7

ObHmrWctli

1

1

7

1

7

IqiKUon W t l l i

^

1

1

1

1

D i t t of PrDducUoa ritldStalut T a u l W i D i Drilled (dm)

OTHER fAKAMeTEMS

-)

A m or PrtKluclion lkiii^> KESERVOUt rfAKAMSIERS

n>

'"

LinKslone

Muuvc UmmoiK

Muiive U r n s lone

Miuive Umnlonc

Msuivr Limcuonc

dolomitic UmeuDfK

M u u v e bmc^ itone. ddkiftiiiic limntDCic

do to mi be limcslone

LiinestDiKH dDlDmitK linHlone

Do k) mi lie liinestonc biMVOW.

FwnwtiQ*

UtboUiT

ylUKCHIIliC

iHduow !fiO

»0

»a

i»a

5S0

ConiicuiV'

ConiKunStmoniui

CofitKiinSmtoniAn

ConiiCiMV Santonian

ConuciinSsntHiiui

SEAL FormAlkA

Shmniih

Shiraniih

Shinnifh

Stunniih

Shirv)i»h

lJftl<«l]l

LimnConc. m v l ^ litneucme

LimHlDiK,

Umeuone. miri> limcMDW

UnrntofK, marly bmmonc

Limolonc. nvH jr limHone

Cinicnniin' MitotndvtA

CiRipiniAi^Miutrichiiin

Mutthchijui

CimpuunMiuthctitian

MuHfichtiui

>

•I

1 :

11

3

>

43i

110-140

140-110

II0-1M

10

7

7

IBO

1IB7

IN

7

7

91

49

»

BMtoatHok l^iaptntun

7

7

T

7

7

Fvmtdort

7

7

7

7

7

VWuwFWUr (RB'STB)

' V^i^^^l

:

OUGnittrrAPI)

Id.)

Id.)

«-i4

24-J)

l«-11

G«IO
17*

7

M

\K

174

SaUlirC«aUM

4.1

IJ

3.04*

7

7

3.3

ti-yi

4J

(») VbcadtT
Aft

"

InJlUI PrtMttTt

MRAMETRSS Av

.!

PttmethmtjtmA}

FRODUCmG HORIZON

TWdiaHiini

:•

41 B i l l y / ^ C i Klcmmctypc

huvkum Piwjnct

ElenttnlRI

KARATCHOK •v*^:

Soilkhu

TWcknaiCn}

DiKAVcrr Mtthod

/ ^ • • • .

• '

Cb^Aadan

Loalka

50UEDIE • •

Fannrntioa

"

KDMAOAN

'MHJRCB

13-3.7

»

G. continued

> o

FIELDNAME niODUCTION MRAMETERS

HAMZA

ULLAYAN

;

RUMAILAN

SOVEDIE

KARATCHOK

1

33

'^* T ^ ^ ^ l

:^

-'*

00 Dttn

7

• i U « t t » Stanu

0

WuQmjoaKHi

T

Wiicf And g u

WttCTHldBH li^tection

7

7

7

IWly FradacttiH Idiitil

r

1,170 bWltay (1M5)

t.imbMldty

(i»ai)

I 0 7 > « l btoVdi; (19Si)

14.700 bbVilir (1M5)

T«4«l PrwIiKtion (daui

«.} MM.bbI (1979)

;.4« MM.bbI (1M1)

40.11 M M bU (1081)

«l8.UMMbU (l«S))

7a MM.bbI (1981)

1

7

7

7

T

:2MMMMM>1 (1988)

100 MM.bbI

m > M M bbl (IMS)

I-2BMII (]M«>

7

RasntiMcOa

7

7

T

7

WO MM.bbI (IMS)

R a n m r m b k tJiA

7

7

7

7

IJOBCF (l«SS)

EiUmlcd

KvunciAHc

a. B o

I

EqutTukatnu

c

3 O

CTQ

a. W 05

G. continued

FIELDNAME

^

iCINERAL,' fiESCKIFTION

LscMtaa tlM, losf} I M t l Depth m )

7

OTHER

- . {.laMiSntioo

•11 MaJlv'X'j Klcmmc lypc

P i K a w f y Dilc

196a

FWM S l H ( k n )

V

.

nUUMETCKS

'

: 1

I

'

1

•

t

1,797

2J9*

7

I0.4W

n

WO

32a

W4

7J

36

7

14

L«

IT

T

14

100

BD

T

15-M

7

7

7

7

BubMlFtthll PnsBRlptit)

7

7

T

7

BouanHiik

7

T

7

1

Fonitttkn VoJuflw Factor (RIVSTB)

7

T

7

7

OIL ^^ FARAMFTERS

1

1

3

Dtpth to Top

z^.

l^crolnun PrrrvlDR UtK^^t^f

Seiunk t u r t y

8J)]

JEBISSA

FIELDNAME

JEBISSA

WtM

ofP»T(fl) ThkkKBiif

Wkm-l

Wdl

^

• • • . ^ 1 *

•

Fki Zo«(ni

ekndoBin)

1

Ans(

MdBM

Prwluctna tkK^) l»7J

FfcMSUM

1

OlMcrvtr Wtlli

Producer from •bur honrons

PnHliKlioa PradmrWtUt

l ^ U l Weill

T

]lljKbDDWc4b

-•

RESERVOIK ' ^ H nUtAI^KTEBS T Rnrr^oir

•

^FRODUCING HORIZONS .

'•"^•1:

• " " • ->

•

1

;

'^

• ..J

P t m a b U I I ; (md) Jenbt

Fniut«

Chilo

Buimih

Ja)l>

[nilid PnoHirr

Limawvud

LHhDlotr

LiDKSfeHieuid

dolonule TlktiaMtfll A »

.SEAl.

V

F-.i.bUDHlafi

Atr

LMnhn ThlduHMdO A f

•RmfTyrt

Do k] mice P

330

l.2«>

UO

MkkUc M k x S K

LjteOUgDceiK

Middk-LlK Gooeoe

Liuiic

I

3

4

• l i k ) (u()per)

OiikiOiwerl

LilDWOfV

LiniHtone

MiiUlc-Liic

Late Qti^ocene

LilF Oli£Dcerv

tei

Aduy^

nurl

i

'2

.

3

•

•,..

IP>il)

Lfiuic

n s o.

'!•

*

Itijlu

JiU:iJj

AlLjl

KumChiiK

Limotone

AipllKfiOUt timaton

Shik

t>alDnuie. irpiltceoui limolDne

400

400

JOO

400

LMe OljBCictne

Middlc-Lltt Eocene

PiJeoceiK

LueTriiuic

> *

20

11

17

40

11-3!

1)-32

100

ISO

Suitor C o i l n i l

4.J

4X)

7

7

vtKOBij i r p )

-

•>

1

T

Ott Crnttjf C A M ) Uu/OilRntia (•cC«TB)

'^^

•

PRODlKTnON PAKAMTTERS Rnrcncry I'ai^tor

Anbctine IMI)f m d n c t t M (dolt)

7.600 MilTdiy

I>riTe MKhanbD

?

LigfcTion StotlH

TobU PndwtloB (ilott)

21.6JMM.Mil (IMJ)

EidniMtll

7

Recovrnblc Goo

135-140 MM.bbI Rcocmo — EqolnkatOtt

>

•a

T^mpcnlBR

, .

Aiihydnle and Umextone

1

Fonnalioii

Mvly Umolofie

rw

1

5^^^^^^^

oa

- •

7

Rcotnv 7

^ i - -

H. Data from some oil and gasfieldsof Iraq.

>

NAFTKHANEH

H E L D NAMK GKNKXAL D r a C B O T I O N

• 1

.

• •

FIELDNAME •••*-:•

-f.-

Olftb

i

NlftKhuKli-l

7%tl«l Dttpth (ft)

7

DtocmrrMiUKNl

O M t DT PrmliKtlHi

-v-.SStV^:.*Hfc*^SifiSL1) FnduR

Penn<*b4lj[y ( n d l I n M U P n s B R (prill

t

Bubble PojBt Prefliuiv (pelg)

T

J70

battoD Hole 'nmpceatttrc

T

W3J

F o r m ban Votumc FKUe IRB/STI)

T

SurfKC fcolocy m d KCV«fft

E>«[tiaB1h1

zta

RuerKrtr PofltMlly (%l

19W

DiKDTrrj' Wril

^^SSB

I.MO

1

KESEKVOn PAKAMETUtS

32M*'30'N,«*jrE

DmU9i(l>iMcirwwry

^^i^^lHK;'.

(11)

A f t * vT Prud iKtIcw

Z l f r a Fold BtH

** *" L a o t l a i ( l i t . k>af>

UTmpmfrmj

T U c k i H i or h y Z i m (A)

^ l Billy/ 2Ci Klmunc type

CI^Molt..

MAFTKHANEH

OTBER MKAMETEKS

4018

rWdStxIka')

raUiiliiiM ti

v.- i * : t -

GO

ft

& 3 fO i3

P5

jHDduccr

FMdSunn

OIL PAHAHEIKHS

, .

•

-

.-

?

Tottl Wtlfa DrlUcd UMU)

41 j

o i l r ^ m l l y CAPI) 0

PrwIanrWilla

Gi>miltitli>
MO^gSO

T

OtocmrWcUi

OM

SaltarCDii(e«(%l

J?

I c

T

b U e n k n WcUi

VIsriHity ICPI

• '

P K O D U C I N G HORIZCIM

O

psoDucnoN fcritic

Foraaaan UUwJofy IMttw(H) Ap

ftHHbfana,

PARAKfETERS

dolomiljc tnd ODlitk bneflonc 140

Pri«M.r«,..l-.

Miocene

II.SCONilAI(tn])

I b u l PrwItKtloa (dalcl

115 MM.bMoU (1973)

Lc»wtTl=iirt

LMHiot;

Evaponle

Eidnioleil R m r » e «

An

Mioufie

Ricorenble Ktmrrti

soURCx: Shinnith

utboiocr

Mvl v¥l mvLy limesione

TlkkKHtrt) AV

TWIVp*

40O ruTi;i«ni«n While-bwk anticliiw'

30tMMbbt C9

• J 4 -•

FsTBaOiHi

o

7

Dolly Produetlaa (dale)

Fomdon

era

W m r drive + f H expansion

[qtecthxi S t a l H

•'^S^"

SEAL

-

Reeovcry Factor ( ^ >

-~ E q u l n l c i u Oil

7

Reconeoble OtI

7

RecDTFTible <jafl

7

H. continued

ABUGHUKAB

FIELDNAME GENERAI. DKSCKIFT10N

FIELONAME

LacMtH

' . " :

W i 7

CluMflatkHk

221BlU/lCt KJeminetypc

12*i4'3CrN.

Dil*<^

I9TI

FIcU S i n Ikm')

1

RESERVOIR rARAMETERS

j #

•

ABUGHURAB

IVtrokum

ZAgraR^Bclt

AtuChunb-l

7

DbcoTcry Mtttod

S a u n c survey

1976

IMdSlalui

1

1

OkHTfcrWilk

T

T

^

bdlbl Pnaaun

1

BubMt pDliit

•'

••

BouaaHoli

^

7

.;

TMdVMk DriUadMiu)

1](I»7U

t

FArmalion VaJuaif F i d o r (BH«TBl

HOBIZONS

iS^^

Forniack>n

Li,p.lrs]tJ

Lltbaiofr

LJmKione

FauiLfemu liinalone

100

500

^>L:l;^• M K - . f : i P

TuriHiiui

TWckBHini A p

SEAL .

.-,.2

1

,

Fonnabon

"**" A r

DhlNil

Tinum

£v>ponlc

Mifly-ir^lld

;.-.^,M,..nK

r4»iii.iL.'ijji

r- *

FornialkHi

Sttir^ni^h

ShFTijii^h M4H]r-ufillAceout linKstonc

Litbolaof

•

•

400

• ' • 1

4W

CunpaniBn

Ciinpwiivi

Act

SLnK'lursJ an[]c]inr

tntViVt

2

I

OTHEK PAKAMEIEBS

i:.i'-;

Dtplhtatbp

^

•

•

"

"

7

?

hrZoHini

iia

A n a at P n i d K l l i n (kai')

>

J

./•

OIL nUtAMETESS ( H I C r a v i l r ("API)

9

^^^^B9

GH/OilRada (icOSTB)

1

2

;:.:

-

7

•••. ^

±1^

CD

7

• '

Q.

Sulfiir CoDttnt

f

37

(») vbc«Mr(CP)

7

••

FRODLICnOW PARAMKTERS RMvTTrjFKfair

t

Dttn

^

1

SOUSCE

"

7

T

: |

1

T

{«)

FrvdiKlkifi

ntoiwciNG

Elmlln

7

PemMMIliT (BKII

WtU

TM>I Dcplk (11)

2

r

Dally

7

StBtlU

T

TcM PtadHclkfl

T

EitlBalHl

7

T

R*c*Hr«lilt OU

7

RccDTcnnc

7

Idutl Rnffvcnblc RtarmA — E i l i i l n l i a l Oil

H. continued

>

AINZAIJUI

HELD NAME O N B U L

DraoumON Held s i n (ka^

• • • • ; • •

' ^

19.2 » 4 H

;

•

•

•

*

•

•

"

LlHSsiAfAtfon

7

>

41 BAliy / 2C.1

AIN ZALAH

FIELDNAME

l>tn4ruiD PnHDcr

«.179

IMI

Dkmwtry Mrthod

T

w«a

FMdSlala*

pmhKCf

P t r a d M (ft)

TttUlWrib

13

OtwrrrrXVdb

PRODUCLMG HOKIZONS Komutton UUwkxr

2

' S^imnish

g.LFTH hiJsJ.l

Marly limeslonc

Dolonutic Umslone

260

5S0

rvnotnivi

Albtvn-Htuten V1 ar

Tlikkixutrtl At,

Iqimtw WvUt

1

s&a

Fnctuic

P m s n U l l t ; (mdl

Fonuliaii

SOintCE Fonnalloii Lltbotofj

Limeicone

Shjif

UlkoloD' *t«

Qunchuqi

A1 hiAJi - H ^ u Lcn ^ 1JJ1

PaLff x-c Rp

'

2

I

Shinriih

Shiniuih Mvl^uid ar^illKHHll limc-

>4^

Mirly And argilla ceout limatDTK

ItOfK

TWckHwih) An

Cam pom in

Dttpth to Tap

CtmptniAii Stru:tunl/>tmtKnp4iht: ^mtrliM

THpTnx OTKCR PABAMETERS

Aoa

4O0

1

2

3jn

sj«a

7

T

91.25

?

PiirZiaiin) A m of Prodortton [kiu'l

J

• ^

T

T

7

7

^

7

t

1

00 ft

y

33(1974)

P n ^ n i r * Ip^ft)

ft

I

ButlooiHo^ l^mptmun Fornwliofli VotuiDc r*c«ar IRB«TB)

6d &3

-

on,

.

.

•

•

-

1

2

.ll.tt

;•;

178

T

.1.11

166

FARAMETERS (Hi C n i i t j l°AP11

ft

cr

(KtlS-TBi

o,

Sulfur Coolcnt •VaJi;-.

-•.

:

f

11

PfUUlHUDB

Praductir W d l i

; * i . ^

p«wMr(%)

tnltUl P r f i A i n Ibtal Eteplk (11)

: •

ZigrcB Fold Bell

AiaZiUh-l

IW7 IMK«vtf7

1

KESERVOnt nUtAMFIEKS

t

fT

c

(*> VkcHltv ICP)

3 O ft

->

•

o, o"

PRODI : t m o N PARAMETERS Rpco*fr> Factor

?

JMYt MKluabm

(1975)

Pnducdsa
1

RcnvrnU* OU

(*) DiUy Pr«lufa«i (dilcl RKnvrnMc Rcscrvti — Equlvniint Oil

W M A drive + ^ CKpifuiDn

liliicttan Suiai

7

lUMMbbl

bdmalid lUnrm

l^MM.bbl

(1MJ)

7

RccoTf n m c

T

Oq

& fT W

H. continued

FIELDNAME

FIELD NAME

^ •II Biij>'.:(.'j (type

naUSiiillur'l

BLTTMAH

USEXVOW MRAMETERS

I

2

10

''

Pnnwnf (%>

DMtd

L o i lAvi 2

^ r a H M I i t y Indt

1

(IM.lMt)

• mi

TMalDrpthirt)

lalUolPmnin

\.A&

t

IJM 1

I4(l«7])

ObHrm W
PKXHiCING HORIZONS

(ft)

w

T

BonaatHsh l^Hpirsliin

Act

^

OD. DARAMTnCRS

I

2

oa (inriir CAPli

30

35

t

1

SaMW CimlrBl

T

t

VboiMrtCP)

-

-

t

IKtffiTBi 3

>

PRODUCTION PARAMETERS R«trttrJ F K I O T

r%i

MrrfaMoAdU

tnpvmon + f u injection

1Md

35MM.U>I

?

Atr

1

VahinwFKbH(RB/STBI

(»)

SOURCE

T - • ' -

n i i H i ipflio

Dd^ PiWiKtfa«

StAttU

ffmrm

T

7

«ili) Ttt^Trt* Rtfo^rratitc PARAMFTERS I V p t k ID Top ofPrnrlfti

Pift Zoat ifl)

TfuukKtwn

>

OS

1 KquJnlnitOII

Oi

?

?

H. continued

>

FIELDNAME CIHKKAL DBSaUFTION f k U S i a Ikm'l

FIELDNAME

BUZURGAN

•

'

-

/

•

,

•

' " —» Clmx^BcstkiD

soii:

....

41 B«l])f/2Ci KlenuiK type

•

-

-

•

• - • • • •

.

Z i g r a Pdlil Bell Pnivlou

1 ' B-l!

RtHnvtr

Diattirtfy 7

UIMpTHBin Scismk wrrt]r

Ekntkncm

7

produccf

T«UI W d b DiiltHKdui)

11 ( i M n

PrvlKbm P r w l u n r WeBi

7

O l w m r WiUi

t

PSomiciNa HORIZONS

T

1

3

FoniHIkn

Ainlkn

Mi^hnr

Ulbolofy

LimolcvK

Ucnalone

400

4«a

T h l c k i H s < ri)

(.>tigi>MkJccnc

Alt

"njTwiiir

1

1

Kirfcuk

Khuib

SAMUcne, ih«k

(tialkv hmnlflix

Aquitiriui

TuMvniJfi

SOUBCE

1

2

FomalliHi

Kiriiuli

RumniU

Ulboloci

Mirl

CTialky, mirly limtsicnc

SEAL Fomllon

Babble Point P r e t M R Ipi^B]

1

BoaoD Hole l^wpenthirr

t

FAmation Vuliime Factor IRB/?iTH}

1

OIL MKAMETERS O i l ( ; r a T l t ) rAPEI

Aff

• '

4

'JEii

C:aiN)ll Ralki lactlSTB)

CO CD

' ^

a. ft

''

1

2

IS-20

2»

65 3

a. fD

^

7

n

4

-)

VhcoiltTlCP) Utboloci

'

(P^LI

MHbod fWidMittH

197«

7

0 1 -1:4D

h m u M U l T (mdl •,

I M a l D t f U i (01

2

•^^

ftiintltr(%) Bkuuifin^l

1969 (UUItac)

• V" - -i-'

BUZURGAN

RaSEKVODC-' MKAMETERS

O m

1

PRODUCTION MRAMETUtS R f c m t f T Factor

OQ

^

Drift Mecfaaaiim

^

Injcclkm

7

EvttmalHl

1.H0 MM.bU

ft

ThkliKsiini

•

500

IM

Cenonunian

Av

A<)uiUlfiiVL

TrtpTyjw

Low-relief, muctunl uiticlinc with iwoculmiiulKini niniung NW-SE

t

2

I>rplb ta Top

9.120

12/«K)

TUckimtDr

1

y

OTHER MKAMETEItS

A n a of Ptaducilan (liHi't

M

7

Dall; Pniducdoa (dalt) Rm^fnble RcxFrvn —, f^ulvaltnt O d

lO.OJO UsI/d

Talal rMdKHoa (dali)

'J

7

RKonrablc Oil

7

a. 7

& fT

H. continued

N O R T H RLrMAILjt

FIELDNAME CEr(ERAL DKSCBIPTION F M d Slit Ikm^t

VaaUaa (lu.)<>i«) T o u l D t p * i i IflJ

NORTH RUMAILA

FIELD > A M E

I

RESERVOIR FARAMRTERS

•>

CUnHallon

221 Billy^^Ca

JOrMCN. ^T-IS'E

Dutof

1970

D4w.wmj

Artbiwi Plitfonn

Itt*tT*olr

^

^

North ftuimtiltl

fkratsbUI; (ad)

1

7

lAilUJ I N v H u r r

t

f

f

7

BMt«H«lt Tkapcnur*

1

T

FsniiiltiiD

1

T

1

2

WiL

T

Difcffwrrj

Saimic lurvey

EVnttaa

7

197?

nddsiMtiH

fioduccf

IbUlWdk DrUM(dui)

W(I1"5)

(pXll B«bMtPi4lll

DMCof

PrDdanr WcUi

7

T

ObwrrerWeili

2

ir

7

•

P n a K ( p ^

Wrlis

PIHMXKTNG HORizons

1

2

Fataattoti

MilJint

Zubur

LHMfr

Umeslone

Suid

VoluHV Factor

on, MRAMETESS

160

TUduHBirtl

:;,

(NI t ; n r l l y I'API)

4oa

G W O I l Rutfo Si a r m n t a rt • H au •

T^inniMi

Aft

37

3i

MO

700

1.9

L9

>

(KCSTB)

s

LciTni.m

Sulfur CAnkol SEAL ForiHlliHi

UtiHiotr

1

I

TanujTLa

Zubair

Mul> timutone

Shik

(%l S ^ ^ ^ ^ H f •

VIK«ICJ (CPI

t

••

pRom'cnoN RARAMETEKS

ConjKian

Aft

lerivitn

SOUKCE

'

1

•> J

Ffmudtioit

ZAi^kr

Zuhur

Ulhalscy

Sandy i h i i e

Sandy Umk

TMckHH^rt)

400

400

toiviin S l r ^ K l u r q t £ji Lie Line

TrapTni. OTHER PARAMETERS Dvpth Lo Tof)

lO.iKXi

7.WXJ

irffijm) TUckfUHof

2

1

-

•

1

7

T

1

r i T Z o o r irt)

AnsT Praluction llun^i

ON

7

(*)

Drin

ISOXXXIbtiUll

TMil

Productkn

(191 J)

Pradactliio

Rttottrftblt

1

•AcwcnHc

t

7 Suiiu

MeriuniiBi

laO M M b M (IW)

Eftinuttd

$.000 M M bbl

( M t )

R H t r m

—

EiilUn)™) Oil

Act

>

Rccovtry FkctDT •

ou

7

T

>

H. continued

00

BAl HASSAN

FIELD NAME

FIELDNAME

OIHER

DESCIUFTION

PAftAMETEKS I S l l

ncMsiK(kB')

Quiiaatiot!

Loothn t i l l , k n i )

41 B ^ ] > / X : «

ZAgxoi

m e m m e type

PnnitK*

1^51

tMicatcry

PMC or

Fold B e l l

BAI HASSAN

1

GENERAL ""f; " '

^ . 2

3

•

. '<J'

DtpthtoTtop

HittBn-3

1.750

1

1

?

»

7

7

7

Far Zwi in) Tkul DtfMh (lt>

I

ElrrntkiD^n) MtcbDd

md

7

npkmtion

M

Am
RBSERVOW 1960

FWdScMH

pcDducer

12

O t w r n r t ^ U k

7

2i(IV7i)

a. ^

Prmliictliia IbB*)

^^

.;v2 • ' V

•

PARXMETeRS

GO

P TI nI KDon

RcHfYofr Frodunr

WcUi

?

•i

^^^E. - '

1

.PRODUCmG

IiOKlJcnWriti

.HORIZONS ForniBtion

^ l a i n Ljmc^liwiF

Shiraiti&h

UUuHofl

R « f i L limolcKV

M v l y hmcslDnc

Doloituiic

10

P o m i t y 1 %>

aw

hranbiUtTlmd^ laltUI

7

' Bsbblt

Ftdu

7

UracHane

TkMUHBdl) An

*75

4O0

550

Olijocmc

ramp«nLvi

AltiSh

1

BolLDmHolf Trmpcnhin FonnBtioa

SEAL

^

--

Foniubon

(RR«TBt (^JUKKIU^J

Dhituji

UllK4«f]r

limc$uHK>niJ

EvtpcntH

dolonule Lower M i o c m e

Aft SOURCE

"

•

'•'.-ii

••'•'

F'jkiXL-iK

on.

T"*

.S h 1 n n i i h

UhokfT

M s r i y kimestHK

Mtrly limolonc

4O0

400

Cunpuiui

Cunptiuin

1

PARAMETERS OH C n r l l f

rAFI)

GH^OIIRada

ShJnniiJi

1

11

•

^

7

7

: 1 • •

7

.Tf^, NaL^LrLri:tn

-A :

o_ fT c

3 O n> Oq

Jia

Ib.H

T

600

7

1

M

1

•

7

1

(icC'STB) SulAir CoiMfPt

(»)

n

Q.

*

Muiuidilolomiu

Vltnulty (CFI

7

-

20

PRODUCTION

OifordiinKinuncndjiui

R c c w r r j F(Ki*r

:*

Drivt

Iqfedla

T

EMbatted

OaOMM.bbl

McchiiuHn TkxpTypi

cr

o_ o"

2

PARAMETERS At<

•T3 ft

i;pp«- Jurmic

'•

2

FomalkiD

T U d u B i l R )

7

Volume Fkclor

1

1.

-*

Pii—re

S t r u c t u n J an l K k n c c o f u i s l i c v o f i w a d o m n Dniir

34.000 bbl/d

Ibul

U ) MM.Mil

Romn*

P n d K t l M

Pniducdaa (ilili) R«(p^nbtc R « « T m — Eiguinltnt (Nl

7

RcvffTcrvUc Oil

7

7 GB

&

H. continued

FIELD NAME CENEBAL DESdUFTION FWM S l u
Laciitiaall#t«)OBt)

FIELDNAME

JAMBUR

assKRVon MKAMEmtS

" Wl 3

^

CUv^Ociitkn

DklCAf

41 Boll^/ X ^ Kleenv lype

JAMBUR

Z

3

?

f

7

hranbUitjf ( B 4 )

7

'

T

M M P l i M i

0

f

T

BuMkPidiit P n t n i R Ipitl)

T

?

7

Ekrilooillatc l^BfKnlaR

?

• '

ZAKPH Foitl Bell

I

PnmiKC ijtinbuf-2

I9M WeU

?

AMbad

Geoktgicfnd u r f t c f mipping

i 9 n

FtaU.Sunti

producef

Pnillimr WtUi

t

OtiwrrtrWrib

PRODUCING aOKIZONS

1

ItaulDt^tft)

^

tlrvaEfaa (fl)

T

ToblWdb DriUrdldatcJ

L«

UjvtlaaWeUi

'\

2

Jerihe

Euphntes

Qt^nchuf^

Ulbalifgr

Mu1> limmonc

DoWicnilic limnlone

Cutionitn

l«0

250

i.eoQ

lUckBHItrt) Aft

Eirly MtocFiK

OUfCicertt

Abian-Haulcnv-

I

2

Lower K m

Dhibui

Mui^onh

Anhyflriic

Denie limnlDnc

Mid-Mkxxne

C- MJDCOK

Camp*rti*A

SOUBCE

1

2

3

F
Shinnish

^hinrkii^

NKkcldkwi

Mirly lirwHone

Mvly limcuiw

Msriy doktmite

400

«n

SEAL FomatiDn Utbalotl'

LMlolOBf TMitiimlfri

Ar

C«np«iii»n

OTHEK rAKAMETEU OipUl la Tap i^Piltri) TIlklUHBOf h]'ZaBi
> VO

1 l.*X

OIL fARAMETERS

. > \,

I

OU Unrvlcjf CAP!)

41^7

GHff)lIRlU«(> (KtfiTR)

IJOO

3

T

>

'i

o 3

a.

Sulfur CDMCBt

13

V t a n ^ q iCP)

-

J

t

Cunpuim

Drin

RKttV*T7 FlWtW

MOObbVd (197))

20

OiFortiinKimmcndipin

2

3

i^OO

^.iyl

7

t

i.<no

nsxtitcia

7

7

lion 4 loLution

' Frotfuctbv

RKAwnUt Riwrwt — E^ulnlcnl OIL

,

1

• ^

MBAME7ER5

Ninnw itrvcmnJ uticline [rmdme NWrSW

T^ipTlf^

Vahmc Fictor (RHA-TB)

3.

mirty ihilc A p

T

T

3

FomBlloa

T

•!

Lnjcctioa Stittft

63 MM.bbI

•?

Rstrm

Produrtwa

RmrwrlkMc OU

t

T

T

H, continued

> o

FIELDNAME GCNEIUL DKSCMPnON FMd S I K Ikm*) L a n l k B (lit, ItBtl

FIELDNAME

KIRKUK

OTHER MKAMETCRS

100*403

CUiiiScilliHi

41 BiIly/3Ci Kjccmc rype

1

Diuif

IWI

PmntUiim

1

Sccpa^ ind

Elmllsadl)

IJ75

3.04(1

4j)ao

Kiduikl

TUckncatof F i ^ ZoiK (ID

-v

^

7

00

7

§• 3

'i

FMdStAtiB

producer

TbUlWclb DrUMIilut)

304(1971)

P n i d u R r %^'tUt

47

O b H m r Wrili

ss

Iiv|«llcv Weill

!)

ntOOUCINC HORIZONS

1

2

3

FornutbHi

M i i n UmntDiK

Shiranish

Qimchuqi

UUmtoij

R « r t l Ijme^une

Marly timeitone

DDlonuuc limestDne

U€0

4«)

«40

Eocene' Early

Campanian

Atbim- Hawrivian

1

2

3

Fomtiiiii

Lpwcr r^r^

Aaliji

Qanx:>iLjqa

LilbDlatJi

Eviiponle

&hale

Dokrtnitk: Limestone

Aft

MioceiM

WcooHie

Alhian- HHiterivian

t

2

3

A|>

Aft«f^

40.300

• '

Pmliicllaa dun')

1934

TbkkBoiin)

RESERVOUt PARAMETERS ReMrToir

Penmbilltjrdnd) Inltid P n a u R

1

2

3

i-yii

le

T

^KJXJ

••

^

?

7

7

souscE rnalkm

Shinnith

Shinnish

Naokc^ir

UUHloty

Mfrly liiiKuone

Mirty linKfUnc

M*rly ddonutc

400

400

20

Cimpuusn

Cimpinian

OifnrdianKiittnwrJrdgiar

lUckatBdl) Ap

Ttvf iy»t

Very IAT;^ ind iinuoui umourtl fhilied uilif line fcpmunsone oi^ntZi^fiA Rwihill uyimneuSc foldi uid ccriuiiu of iNre domo: Bab. Avwuh and Ktunnali

OS

&3

a.

(l»»t) BubblrFWat Pnnn(|idtl

7

?

7

lon«BH<de Ttnpmtun

7

?

7

fT c

FontiBtion

1

7

3 Q ft

-

Miocene SXAL

3

,J

Dtp(lilaT)tp •frijdi)

MHIWII Dale of Pradiicdon

1

Z l f i t a Fold Bch

Well TbuJ Dwpth (ft)

KIRK UK

OIL PARAMETERS OH C r ^ l j CAM) GH(OIIRallD {trtrsTBi Sslliir CoMcnt

o^ o*

^

(RB/STB)

1

I

3

»Jt4

•

213

^

1

:.34-i.is

T

T

'

7

7

7

Waccrdhvc*-

•'

a. a. fT

<») Vbcoitty ICP) FRODUCnON FARAM^fEftS Rccv*vrr Facfor

• . ' " • ' ^

7

gufipHiHon

IniKtigti Sialic

WO.OOObbKd (I97S)

1k>tal hvdwikn (date)

7.14) M M bbl (1975)

Ectlinatnl RcKTvai

9.847 MM bbl Oil

T

kacewrab4i OH

7

Rcnvtrablc Gaa

7

(») Dayjf Productkn
cn

H. continued

ntlM

*

••

DBSCumoN niMstit<Wi

LaculiH ( l i t k i ^

FIELDNAME

RVMAILA

NAME

CENERAI.

ISO l i e

W W N ,

CteaUciiliia DMX'

•

•

^

^

-

-

^

Z

^ 1 Ball^^Ci Kkmmciype

>. a«!i j^UUKVtf

pf»:, Arthitn Platform

RunuilA-1 Wdl

T b U I Dt|ith (rt)

lOJOO

Sdirnknwqr

E]m«»m)

1

19M

FkMStibii

pTO^kW

TDUlWclb D r i l M (4(lt)

9(1»7«>

Prwluctlon ProdmrWiUi

•'

1 HORIZONS

Olwrrcr

Wdk

•>

IqtKttoa W d b

^

^

1

7.600

10.000

lOJOO

T h k J U H f «f Fky Z o H (ft)

•J

K»

630

l73«WiCTB

•t

-J

B£SEKV(HR FARAMETEKS Rcscr>oJr h > r « i t r (%>

' 1

1 IM«

25

PtrmnliMItT (md)

1000

1000

loillAl P n o w t

noo

T

1

1

Miihnf

Zuhur

/ u h Jt r

Ulbaitcr

Ltnrvitone

Intcrbecklal

SAIKUtODC

Babbfe Pnhil

SEAL Formadoa UthotDtl'

400

4W

"nwoniw

Hjuirnvun

Hautcriviffk£. Aptiin

Khuib OuUty lilDSiDIK

Bottom Hi4c

FnrDialioB

Zuhur

Zuhmr

[nierbhlikij

SwdsiofU

OIL rARAMETERS OU C n i l t y ( ' A m G u / O i l Ratio <>cC(STB)

E. Ap4iut

KHitenviAn^ E- Apiinn

1

3

;3

Rumiila

Zubur

RMAWi

ChiUty. iMTly

Shik

state

KtODUCnON FARAMETYRS RKDVtn' Factor

Coni>fi>n

HBUtEnvun-

'i nihil T i i l i i M

SOURCE FqrtttAtiHl

Udutocr

..

liRHtDIK

TUck»(n> Att

TnpTypt

140

400

WO

CenDnuiiiAii

Hiutcnvian-

VAJvifiiuan-

C e n U d i r ucmnl Anticline mUi IwodQfTVi

i

7

7

1

7

T

^

7

t

1

1

269

}2 2

^ '^

R i n ^ from TOO 10 800

?

7

].M

:.7?

2.1

3

Thupcrmtim

VdJumr F i c t w IRR/STB)

• 2

SUHJSUKtC

Al>

lOOD-MOO

•

4M

1-

3 »-M

( P «

and (^^tc

An

'

.. . 3

FdnnAtkHi

TMckBMm)

3'

(ft)

A r t * of Pnductloa

Milbiid

^

MKAMETERS

rfPlJ

IM3

RITMAILA

t-

(*)

Vlinidn'(CP)

3

-> 7

(%) PnHUCtHlB.

>

SOOjnobbird <197S)

•>

Drtit Mtrtlllii™

lj(jK(lon

1

driven wluuon

StillB

1M^ MM.bhl

EtUmmUi Rmrwi

11.800 M M bM

*t

RKonraMc Gu

T

PndKtloa

(duo) Rfcovcnblo EqdnfealOU

>

7

Roconrobk (Ml

H. continued

> to

ZUBAIR

FIELDNAME

cratERAL ' DESCBIPTION FMdStielbill')

Ldcadoa 4UU loot)

CluNftcalioa

MiB

221 B>ll>'^Ci Klenuneiype

fto*Ujc(

Oulf B u i n Zutwi-I

1948

7

7

producer

Eknltaidl)

1

2

^ 3

Rflscmir P«naitrl%>

?

?

1>

10.20

P t m n M U t r (ml)

7

T

I »

KMOO

loJlUI P m n i R

^ '

7

7

7

BaUkPilal F r t f H i n (pf4|)

J

7

7

7

BouowHiile

T

7

7

7

FomwUoa VUuBK F>f tor lRfiA~rBI

1

1

•!

7

OIL PARAMETERS

1

2

3

4

Oil c . n t i t i ' T A P I )

10

28 1

( i u / O i l RiOo (•cBSTBI

MO

Sulfur Content

a

T

FkUStatH

IMl

E>nilll>«r VVdll

3J

ntoDuciNG HOIUZONS

1

*^*

-

Ur_M_

•

^2.

=••••

?

ToUlWiUi DriDnl Idatcl

4

b O H t k n Wctli

3

4

FoniBtkHi

Lower Fjtfi

MithHf

Ziitwr

Ziibur

UthotsD

LimotonCv undsunt

Limoiou

SitndtUHie

Stult

710

160

400

4ff>

TMrtiiinlfri Af

SEAL

1

^HHlcnviiuiE. Aptiir

CeiHiiuniin

Mioocnc

-.2

.

E-AptlATL

4

.

F«niBlivn

Lower Fir^

Khukh

Zutvir

Zubair

LMulDcr

Anhydnte

a u U i > limaKrtK

Intertjoldcd undHQiv uid ihile

SmdiUine

Hiuunviaii' E, Apliin

•HwlcnviviE. Apuan

Av

MMXAK

ConiacivT

1

FomulMi

Kirku^ Group

Rumiiii

Zubwrwid RjiLiwi

Uiholscr

LimnlDnC; unduone

Chilky, mirly Umolonc

Stute

5O0

240

TCO

OUfDccne

Ttironiin

^^laifimui-E, Apiiin

iWckiHin) Aft

iHrTypt

cnsnt niRAMrrexs DvpLli ID Tofi i t P I T (fi) TVAmtmut PtiZ*iK
• '•

3

<m> 7

191

.

1

DO

P B

36

40

a.

t

WO-BOO

«(M

ft

3)

i.«

7

1

7

c O ft

ft

l») Vbcmttr ICP)

•>

7

t

PROKUCnON PARAMETERS

o* oq

7 McduDism

Waicf drive, ^ u npiiuion +

7 Stitut

.......y...;:

ft

E q u i n l t n l <>ll

4

6,880

lO.IW

ID.SSU

128

IM

IM

t

7

t

Ttaupcnuin

Produdwn 4d«(ck

Slructunl ml Klmc w^th X link dipof 1 r ind NNW SSE u i a l «n!ic

1

••.

a.

4

M>UKCE

.-•1

}9(19M)

00

ft

MeCbod D o t at

4

KtSERVOIR PAItAMFTEBS

WUi T s u i Diplti in)

ZLBAIR

FIELDNAME

112,000 titil/d (197 J)

TUal

^

RCKHCI flUH Oil

T4) MM.tibl (WJ)

Ettliiulcd

7

Rcetnci lull'

JJOOMMHll

a. a. 7 CO

I. Data from some oilfieldsof Iran.

FIEUirUME

H H a r u

HlAKH

Ksnqj

N™.

Nlftl-Shlll

FTEU3ISAME

Bd Hiind

KanqJ

HitlKd

* ™

.SUUIDUI

^

SEAL

PBSCUfnoM

t'Dmudaa

fMinxkaa*}

n

1

7

m II

7

1

'

ZA^HF^OAUI

FgUBch

Utbolocr

FDMBCII

ZlfTM f^HHlUJ FnUBtlt {KtlU«9tU

R>ldBcli (KhuzcHU

AnfaiiaGuir BuiD

DbcnvrWid

j r w i ' N. *rii'E 1774

ll*«rN. 45^2'E IMT

IW}

7 •»9121
BclHuns-l

KlItKcM

Kmij-I

Msjid-iSvUirnu-i

t

7

7

1

Sauruc u i r t y

SeUnuc lod

SdBk reftsciion

314

IJOO

I.MO

KWvD^ttim

?

T

PufcrfPllillMH

7

T

Pn»u«

I U M I DipU im

L9U ttoimal

19U Ntn-i-Sh^l

•t

Sfavnc H^fCy

Oeoldgicil auppintud HqHfS

1,200

7

t^OOO

T

7

140

7

7

^

7

Prxkn

ftDduca

T^Odwttl

2(I»TJ1

*»(IWi)

I I IIV7})

] 14 (1973)

1!(1975)

7

PIWIHRWIII

1

l« nil, 1 ^ 1

t

31 oil 1 9 ^

14

7

OkHmrHMi

1

a

3

IS

]

7

IIOR*IHWMI

T

7

1

10

'

-•

urvey BMlKiri)

FMdStmi

PmiiKW

- &

Aviun

Fnarntollon

*»•

•

-

.

ihile

utiythtc mU tnd i h i k

ihilc

JHtJ'VIIC, UH

Lo»er MioctiK

Albiui

E w l y Miocene

UUUIUTTII

Uufpi

Kluzdunu

•htk

.IMU

ihik

200

3»

3ca

320

AltUD

L.Creuooui

Albiin

L-CntKcnn

AiynuncoK

?

• •-

A^mMTi

FitHlKll c«tionit«

^^W^ Auiuft

Hint

I.Tn

WO

l,KXI

1.000

Mid' 10 Lilc CretKHNU

OUfP-MlQCCfK

Olii^Mkicnie

difD-MioceiK

Airnunctnc uMiclinc

AAjmmcbic,

i '^UI\^^ •tM>

AijmiBKtnc upucluic

dome, widi ft«pdip4D«i dKSwniiit lod f H l k r CHS CM die NE.Pi(diuiD ibeSE

HticluK ia Annan (lUlhir) bOKtlDIM Vrtlh Lowcf F u l (L.Mnaoe> cvifnrilE cifi nek

.Cl^."^-'• • ll.WO

»D0

4M0

230

6.713

IJ3I

463

675

304

300

••

11]

<:,-..-J,-f,

^MOOurrs

34.400 KTH

;S.400«ra

7

1

L2

T

13

Z4tti
K^Jhur L L'pprr

Atman «qurvilrtiil

limBtonc

Whik-bKt uiticliiic. SW flutk d i ^ 4 V : NEnukdipt W DixhKTiunK: (WVTf of LwcT Pin pfiftwila. IWQfH Ctfit •ml

rABAMETEKS

m ADnui

FofiiBiaifent daknubc UmeuMK 233 E, M K K V K

LU

Jb

(«l 7

0.015-16

U

7

•t

7

tl*lll PlIUMl

6TT5

IIH

7

lU

'1

7

SikkkriM rn—nlpJll

T

IJJ

3300

7

1

7

247

7

7

IDl

7

7

7

1

\m

7

?

7

ftMtUMT

(Mi)

BMWuHoti

FxtorlRS/imi

>

• '

RESUVOIR nUUHETIBS

Onuii

Aft

TWckMa
DvfMk 10 Tof> of

HOROO^^^I

TM^Hm)

' * •

Gachutrtn

Mid LUC C n ueccut

^Odiicff

(dull

Lmiim

"^••nr

Ttif Tn» 7

Dtow*Cf7 Mrthwl

^ '

Kuhduini

^aoORCX Forma U«a

DMa rf D k c n R T

Githufin

1

•

ZitnMFraeul (Khuttau

Locattoa (liClosfl

Ruige^LAn (j^

41 BiUy r i C i K k m i e lypc AP

Prtrvlmn Prrvtoct

N>ft-Jv<$h4ai

SoWmu

; •

> •a ft 3

/. continued

FIELDNAME

BtlHtini

IbflKtl

N™.

KumI

fWN-Si^

SvMnaB

'^-

OIL nUUMETERS 0«Gnr»l«jCArT)

1

7

}].«

» •

7 7

7

7

T

7

S^)tvC,muat(%)

^

T

1.1

IJ

7

VlHHitT (LT)

T

7

7

7

7

T

7

7

7

7

GuupuHion + wuHdnve

7

CHnp«w4

+ waierdnvv

00

ft

PJtODlICTlOM FlUMMETTja

lh*™M-k-h-

InjirtlM S U M

7

7

^

7

7

IM>r PnxliKtto* (dMt)

7

7

7

7

7

7

7

7

7

7

1

7

7

7

7

7

7

7

7

7

ITS

I CD

rnliiMIr il B i i i i i M

c o"

RK»inli4tOII

1

7

T

•t

7

ItKgTgTiW* C^i*

T

7

7

7

7

o

a. W 05

/. continued

rVLDNMHE

Pu^E-SWi

Pirii

nMStalkm')

Dkk oTINioTcrT

Srns

H E L D NAME •SOURCE

-

VttamOaa

'

Z*tr»R«iul pDldBclt

Z i p ™ RDHIMI RlUScIl (KhuiAun Piovince>

FoUBcll (KJuuolin

Souitierrt AAbiiACuir B*iin

7

•>

?

W3V2I'N,

29»0J'a7"N, 4919'jrE

l%fi

I9M

iw:

1962

OTHER FAKAMEmS

CIS-1

SynH-lA

DtpttbTdtlDr r.jm)

?

» i 6

"**" AnbiuGulf

l^4ai Dnftk lft^

T

Prt^l

Puuiu-2

?

7

9.481

Tjn

Rcfncuo* lurvey

Sviimif tnd

Seiimic utrvcy

Setsmk Hirvejr

1273

1.700

1,190

1

7

Wnur [>e|>(h (R)

1

T

7

W

r

Data nf P V v d K d H

7

?

^

7

7

FMdSUtui

Produocf

PrnkKcr

Produor

^Dducer

Producer

T D U I Wtlb DrUk*

1(19TJ)

13 <1973)

2TU973>

21(1974)

I*(I9TJ)

DbCDvtf^ Mcttod

TUekBHitAI Aft

1961 toi1> PBS'I

TnipTrtw

T V l c k s m of Par

A m «f PnHtKtlHi EknUaalft>

Pvy

P n -

s»»

STTVI

Gwpi

Lows SlUTTKh
KAzhdumi

Italic

Affillacenn

**^

)»

120

200

SuHonun-F^tHKCDC

B.1HU..

***"

t

41 B«llr^ 2Ci K^fliuiM type

tHninryWdi

tki^E-Slili

;;•;'-

'

OMtMatiom

Fr*>tu

s«.

PBUTVD

GmtKM, K9CBIFITON

AaiicluK

AtynwiAK: antKllAc

NW-SE Ayrnmctric dome

AntKlinc

Anuclintf

4.37!

;,ooo

4.700

7.! 2:

7.l4d

230

770

76B

7

100

laSOO Krtt

42,«0aKm

19.260 K I S

^

4 i iOLm

>

aESERVOIR M R A METERS 10

7

7

7

7

T

T

7

30t]'31U

26)1

422]

7

7

7

7

7

7

7

14]

I4e

lU

7

7

1

t

7

t

T

a.l

I

?

t

T

7

7

7

S^lfiir('iiineiil<%l

7

13

7

»

IJ

V l H ^ t y (CF1

7

1

7

1

llc«*rvalr P H H M T

(*)

PcmuflHUty liudh

6

12

(IBIII nvBKvr W H H

1

31

4 «|. 4

^

20

10

ObBTHTWim

1

3

2

I

1

BablikrMit PnHBnlprii)

I I O K U S I I Wrtb

t

^

1

t

T

BotHHlMa

Arab

Bufgui (Kuhdtuiu)

DoloinKic tywoc piCUlO'ODlilk UmoiDiK

UnoHwilidiin] HIKl Utd inlcfuljdEd ititk

HtODUCING HOaiZCM FoniHilQa

"**" 'nickHBin) Ar

AlfTdci

^uiun

Fiuund CUtHHUlO

* ™ " Fiuufcd cMbouiet

I.IOO

MOO

t.2O0

M6

210

OlifD-Miocenc

CM^MiooiK

Oli|a-Mia«ne

KJmiiKodtiin

Albiin

nu. Fonstlaa

Gachufui

Hilh

Bgrfui

t Mtilrmr

Anhydrite vnd u l i

Mhjn^tc

—dMOK

Evly MioceiK

Tldni.

Atiia

Av

>

-J

Factor CRO/yTBI ML.

= ••

MKAMETESS (NIGmtqfl'APl)

M.2

HM 7


T

n 3

a. >

/. continued

> OS

riBLONAME

PkT-E^lAb •

nuCAHETERS

-

'

'

.

•

'

PkHi

Piraiwn J-

•

..^

^

. ,

•. f

S H H / • '

-w

'

•

'' [MT,M.k-l-

"

^

^

^

C u rTDHiiioit +

C u cipu]u«] t

T C/2 CD CI.

[^iKttoaSutii

1

1

1

7

DyiT FinductiDB

1

1

7

7

§• m

Ttotal rrwtwcHas

?

7

!

T

3

EctllHtHi RtMTHI

7

7

t

7

RHOvtfvMc Raatrvta — EqvlTslHiMHl

7

7

1

RaconnbtrOa

7

1

T

7

ftiHvtnbtrGii

T

7

T

7

I

dd

' •13 CI

I CD S

3 O O, O*

m &5

/. continued

ACHA JARI

FIELD NAME

OTHEft PARAMEintS

GENERAL

pescumON TicM Siie I k m ' j

\jxMtion t1*l, lonil 1bu)Dtplk(nj

Dnitgr Praduccjon Prnductr W d l i PRODlfCLNG HORIZONS FariiBlJpa

A1 B i U y ^ * KlHiuiH lypc''

Pro vine*

Zi^roi Frontil Fokl Bcl[

Dattet

193*

Disco re r^i'

A f r4 l t n - 2

DlKOVtTV Micb«l

Svismtc and

1

FleMStltia

ProdiKer

69DiL. 21 p u

ObMmrWtUt

16

7

« ' 4 8 ' N.

-»

auiUlotkn

A**

SEAL

139(1^75^

Injefliof) Well?

l,J50

RESERVOnt FAftAMETERS HMtf>oir Ponsllir 1^)

:

3,100

6X100

J90

::o

61.000

3S.0Qt>

1

2

IJ-li

6

--

t

3190

Initial P j * s u r t

il-ii,

Bubb^Poim PmxuTT(puet

?

'*

]JJ

173

1,700

Bollom Holt TtmpfriCuiT

CfOuS

ForinatiDn VolunH FacUtr
T

OtL PARAMETERS

1

Ohpj-Miocene

1

2

UlbatDC

ilule

Ar

Lciwcr M i m i E

mitj-ljie Creia-

OiKJraviiyrAPlt

> CD 3

'> 2

• >

'* •

2

SOURCE

1

FoririBtion

Gurpt

Khudumi

littwJcic?

shak

shiie

:(;o

200

Sintoniv>PiJcDccnc

Altuin

TnpTrpc

A n a ol Prvduriion C*cr« i

FVrmtmbililT (mdj

Fissured culxtnitn

Pan;ctUj; Gp

Ap

T h i d i n t u of

1

Bui jtUAti GrtHi^i

A^min

Cachsjtrvi

TliickAKS
T

2

1

inhydnif ^ ult

FDrnttt^on

>

700 (Ml

Ulbok>c

TtuduxHlRI

AG HA J A R I

FIELD NAME

Lon£. nuTD^r mticbnc running >rW-S£. \i xi. more neepfy foklpJ Of! i)tc SW ihin oo Uw NE

Suirur Coiwltnl

"*

V u f A l t y iCP)

••

•

PRODUCTION PARAMETERS R f « i t * n Fad or

..:..-.,.

^ '

Drin McduiunD

Dai)> ProducUva Ldate \

0

Totd Pn>ducl»n (daltl

RKOvTrtNr Rner>Tfc — Eouivplrni Oil

t

ktcovtnblc OiJ

G»e:fpiumDn-i-

'F

IqiKtion Slaluf

t

EdiiuiMl Reserves

7

RrcorcraMr

t

/. continued

> -J

BIBHAKIMAH

FIELD NAME GKNEML DBSCROTtON

RESERVOIR rXRAMETERS

Field S l i t i W l

7

CliHlllatiaa

41 B i l l y ' X j K}enime lypc

PftrolfuA

Zj}n»

Locitloa

7

DiUoT Di«o*efy

IMl

Discovery

BibH)klnu^-i

Scitmicuid ^eoioficr survey

Eltvaliaft (Ft)

:.ooa

Itat. I a i t > T g u l Depth itt)

Dalitf Frwliicdop Prwliinr Wtllt

ntODUCING BOUZONS Famutfoo

BIB HA K I M A H

FIELD NAME

^ T

34 cnl, 3 I K

RtKfYoir Poniut> (%l PrnnatHlltydHl)

Fitid S u n i i

O b K m f f Wflli

pioiJuMr

«

Total W d b Driticd (dale; itl^tlOB Wdli

1

2

Asmin

Sarvak fi 14 u m l carbon-

LilbatDir

TUckBemri) Af>

SEAL

1.400 Oligo-MloccM

Mid

1

1

CKThsAnn

Ulboivcr

Anhydnlc. u l l

Aft

Ijcnc^lonc,

\it3[t

CtnoinuuinTun>ni>n

1

2

Formation

G
KazdliuRU

Liltiokdf^

liulc

il»lc

TfiickiKulfl)

330

MO

S^filontvi-

Albiui

Paieoceoc A ymclnc. tniicliful fc Id 1

2

DtpUi lo Toji

soo

3,9no

Tliicfcwtt or

470

470

T:JOO

j;.OD0

OTHEIt FARAl^ETEKS

Ptj Zoiw rrti A n * of Produdlon ( K m l

T

7

;ioo

Eloll«n Ho(f Trmprnturt

|4i6

171

C/3

a. ft

«T( 19751

•>

w

FormaUoa VoJitmc Fictor (Rfi/STB)

T

OIL PARAMTTERS

1

2

C3 3

:99

30

;?

:<]

55

o

16

] ft

1 • '

IlillViJl

E. Mioonw

TYnpTVpt

1

Q ft

SOURCE

A f

6

labbkPoJDt

VlKtMilJ fCP) Fvntvboo

*»

1

f]]L i ; » n t y l^APT> 1.750

z

^ 5

lBJ(i*l P r t w i R MctlkDd

1

PRODUCTION PARAMETERS Rec4vtry FHtor

t

Drln

G j 3 CipAnSL^HI -»-

MKIUIUSIII

Diily Produrdna Mate)

Rcscrtts — EquiT*lrnl Oil

f

t

Total ProdudkHi idalfl RKDvtrable Oil

'

injection Stfthu Ejdnuted Rncrvn

CD t

& Rccovfriblc

1

1

W

/. continued

FIELDNAME

BINAK

GENERAL DESCXIPTION FMdSiKtka')

BINAK

2

1

T *

rAXAMETERS ?

?9'«*N.

LocBtkM

FIFJ.D N A M E • '..-^Jv:

ClMm ftcj lion

Diicdr

hinitum

221 B^Jy/iCi KleiTvnc lypc

Z l f n n Fnintti FiitilBell ff^rt PKPVIOCC) Binak-I

1*59

w.ua

ijm

Drpdi to Tofi • f F i r (ft)

2gi

TUckiHsiif Pty Zvat i n i

»4

WcU

Tool DipUi (H)

T

Seiunicuid

Elcntlaalft)

ZJO

Ehoduccr

l^ulWiUi DiilM(ihli)

4(I»7J)

A n * of PraductiOD (BcTTir

3.iOO

MMbod T

DMCIT

P n d m r Weill

J

neMStniiB

OhwrnrWdh

7

IqiKttoaWilb

2

I

TKOOVCIHG HORIZONS FarBaOin

Asimn

BvignUn On]U[}

Uthslaiy

Ruurcd

Ftuund urbOfUfcf

340

2^00

OljgO-MioCCTK

Mbd-Lm

TfaiduKHint

Av SEAL Fornvtiiin Lllhiitou

A(l

i;

1

/

^ J lb.' hzr'jn Ajihyikilt tad

^1

2

B u g a l a n Group Shile

Mid'Lite CreticeDus

EJJWCT Miocene

1

2

PornHbun

Gurpi

Kjiilhumi

IJUmtiiir

ShAk

Shilc

SOURCE

TMckaHKri)

Av

•

RESEKVOUt PARAMETERS

1

2

Referral

a

7

T

7

laHMPrHDin

MOO

4700

BubMiPobU P m n u n 1 [H^t)

1

7

170

»0

1

1

P t t i m b i l i r ] ' (mdl

Bvttwn Hull TrmpEtstim

>

> m 3

fit

Formation VoluDK r H t o r (RlVSTBl

on.

>

2

MRAMETERS

•

OUGnillrCAPII

:s

J:

7

7

Suinir Coatcut (»l

7

7

vtHHitr (cp)

^

(KOSTB)

330

100

PRODUCTION PARAMirTERg

Sutcimui-

ARHm

RHdrttTT FaetDT

DonuJ AiKKbne

m

•?

'

•;.;•/:?•%,

7

(%) TtmrTyrt

31.600

if.-

Drin McdunlnD

Dili; PnductkA (
?

RHO¥tnbl» Rtacftti — EQHJrvalnt Gfl

T

G u cipiMion + wi(er
? SMIus

7

F^uimalHl Rcstrvn

•7

7

R*cff*vnMc

1

nuuuciHHi

/. continued

>

oo

o

KHARG

FIELDNAME GCNeXAL DESOIPTION r v u Sin llun')

HELD NAME

r

' ?

QwticitKHI KJemme rypc

KHARG ,.iV;

.-

'

•/ . 1

1

.'••

MRAMETESS ZagnH R o n u l Fold Belt

Dtt^laToy

iJ60

Ptwincc)

ThkkHHof

Mt

IU,UUU

P I ; Z O O I
Locabnt (laLknc) Taut Derlh IR)

M»24'N. 7

-> Produnr Wrib

6

ScUrvC lAd geologic uirvcT

Eimtjoo (n>

ISO

Mribod FWMStalui

F^ntuco

IkxalWcUi [ M l k d [dmltl

9(1975)

ObKTTvrWflte

1

InjKtlvn

7

EHKWTTT

Ftmalkn

1

1

2

&3

16

"

03

7

1

naa

4M0

But>Mt Point

't

7

BouomHolc TVuptnturt

in

M«

Fivmalion VoJumt K*rtor

7

1

on.

1

2

"

.i-i

RESERVOIR PARAMTTERS

2 Fihiiyin

cartx»nal?^ and ^4ind

TUduHscn)

*»•

350

900

O l i ^ Miocene

BernuiinViianginiui

1

2

Farancjon

Gachunin

iJaJvan

Utbutoi;

Anhydnle. u l l

ihile

E. Miocene

Vftlut^niv

SOURCE

1

2

FoniHliDit

Gurpt

Godvan

Lilbohicr

ihAle

ahi^

SEAL

3

a. 3

cirbDnata

Ulbalatr

CO

a.

(piW A&man

00

20.600

PtnnnMUtT ( m l * PRODUCING HORIZONS

lHHi.-''°''

i.iou

A m of PmliKtkia < K m j

WcU

50"lg'E

"

Kluri-I

1963

(T c

3 O

ft

o_

'.''

'MRAMETERS Oil G n v t t ; (*APII •

7 (KIISTBI

Aft

TMckKHim

SitlAiT CoBtefit

320

600

SintoniinPilcoccne

Vaitn^nim

1V*p1>pt

CentJy folded, sotncwtul ^ymmelnf amictinc >t»Ul u i arckute u i i ek>ng>icd in a NNE-5SW diiectton

i

•Htft

¥lo»i*tylCP> PRODUCTION FARAMEIXRS Rfcorwrr foctAT

Aft

7

Dili; Productioa (ilotil

7

RocwtnUc

1

RAHTYB —

EqidnkfUOU

7

3.1

(*1

tn

t

Iqjcction SUtui

1

water driw 1

bducd

7

Dritt

FndwOoa Idiu) HACDVC nblfl OU

T

T G H

/. continued

FIELDNAME

KUPAL

41 iil\ynCi KIcmnv [ypc

ncUsiBiidn')

KUPAL

FIELD NAME

GENERAL DESCRIFTION Z l f r o i FlTHItol FiiMBflt (Kh

ftESERVOn PARAMETERS

1

2

Rwervoir Pondt]' 1%)

i:

i;

^

PensHbiUCT \mi\ Lwsdoti

ToUI Dcinh
31'li'N.

Diniir

Ducwfr; Milboil

PrvdtKtlffi

Kuptl-l

5«iim(Csn(J

'

ii3o

7450

dtnttoain)

B D M I I Poliil

1

1

TsulWcUi DTIUH) (ditr)

Botlocn Hole Tcmpentun

248

2M

1

7

JnjrcllaD

Prmliinr Weill

Initiii P n R U T t

?RODtJC!NG BORIZONS

FarnuOon Volvinr Factor IRB/STBI OIL PARAMETEKS

'

OU (irnTlty I ' A P I !

W

2

Uar^ntui GrMjp Utbolac

Fiuured

35

^

>

1

(stOSTB) T h i c k i K n (rt) Sulfur Content A(t

t>liea-MiD«iK

Mid-L. Cretaceous

-^

vuoKitr icpi pRomicnoM rALhoiDU'

AnhvdniF. iilt

Bui^f stftn Gp.

PARAMETERS

^hak

R K f f v r n Fictof

1

M-L.CretKCDUs SOUKCE <]urp<

T^ipTrpi OTHEIt PARAMETERS [>f plii to Top of Piy (ft) T h k k n w of Piy Zont rrt) A m of PnducHoa I K m )

SanKHiiaTbPalfticerw

Diiic Mrchanism

Daily ProdiKtion «la((l

1

Tolal ProducttoB idatti

RKOTvnMe

1

RecQvfrvtilf CM

RH«I>« —

E^uiratent Oil

TIllclUKSfn) Air

Ban^stanCp. shile

LlthoJoD'

a.

1 £

l.-l

(*P

lajtction

1

water tlnve

^

?

/. continued

> 00

LAB-E^AFID

FIELDNAME

FIELDNAME

.,

PboupnoN

r.-.|S

LAR-E-SAFID

KESEBVOIB nUUMETEKS

Cluiinciiiofl

TMdSlKdun'l

41 E i i N y / X j

MrTjkuni

K i t m m c type

PrtjTiiic*

9

IanH*MIH;(^) Losttaa n i l . kH()

i2'W

N.

L96S

Lib-E-Si6d4 WcU

I M d D
•!

Diltof

7

'^S^Z'

SeiiiucAiii]

neMSMto

ftoduco-

uoo

EkntlHidl)

4(1979)

PrnlucrrWcUi

4

T

O f a v m r WeUs

1

7

iiirtiiini—iii (prat) B i i b U i Pobu

BaaaraHok

7

2«70

3M0

7

7

IM

194

C/5

TfDifHratuH

DHUnKdiU)

PrTHtliCllon

4

Reiki B e l l

Iqjecboa U>Us

1

FarmliQii

t

7

VdJumt P a d o r

K: 1'

PROOtJCINGflM BOKIZON.S ] ^ |

2

(RB/VTB)

_2^J^^^^^^H

Fomttm

Anxn

LUbgkcr

Fiuund

cirbonato

CVtPOtWO

1.400

3,000 Mid-L.

OUgo-MwcH

Aff

G^hunn

UlkoHcr

Anhydnte. u h

31

?

C^OaRalta (KfiSTB)

7

7

SoUar CoBlHil

7

7

viic«itr(CP)

T

7

(«)

- I _ ,^

S H

r m t t «

FRODUCnON rARAMEWS }lt
ACT

SOURCE F<mtt
i^^:^

^

UtkoloD TlilckKHm) Ap TrmpTypt OIHER PARAMETERS D t p t b to Tov if PI;

Gurpi

Kuhdumi

ihflje

ittik

320

200 AlbitA

L^CRtKWUt

P™l"«Wh»

>5

J.J50

8.H0

504

T»

2^.000

U.«W

(fl)

TfakkamoT

Par Z « i (D) AnasT

1

(%)

Fmctnr

DaBr

3

aITS

(I

«-^ •-t o, fT c

3 O

o"

T^^^^^^^^^H^^^^

»

IMn —wAlw

"SSr

?

7

TMd Frodacda* MattI

7

EftLoutfed

7

7

RccDvtrabic OH

7

RccvTvnbk

7

((Ute) RcTDwnbU

,-

Oq

niHlactl40

Eqiiivmlnt OU

'3

if"' ^

O i l CiroTJl; <°API)

rmaLnms

SEAL

»5

'W?-''

KAKAMETEW r

IHckHHitl)

OIL

/. continued

FIELD NAME GEKERAL DESCRIFnON 41 Billy/ICl KJdiuiK type

ndd !llii ( W )

L o m i a a llal, loat)

T b u l Di|Mb ((11 rcfnction

Producer W>11>

4« inl. ! I j t u

OtiHmrWElii

muwctNG HCHUZOKS

.

FuurAd cailxmits

(")

ft 3 '.1 lio-M H HTfnc

Act

a. > Vnhydnlc. ^alf

Ap SOtiSCE

•^ V -

1*»pT>i»

MSAHFTERS DcptkuiTop

of P^Zninj

/. continued

> 00

NAFT-E-SAFID

FIELDNAME

'

DESCRIPnON [ » i l Sin 1 km')

Lscilloii lUl> loaf)

FIELDNAME

7 y

CluitnatloD

DMt<'

•

41 BtIly/2Cl KJnniiif type

.

^ImJvuiii

-

-

,

-

•

.

NAFT-E-SAnD

USERVfHR PAJtAMETEKS

t

I^gfOl

I9M

NilD-E-SiAd-J

PHwaMIHr Ind) laHWPnw*

•t

X

2

1}

6

-

t

2«M

2790

P*n™tty(»(

Well TouJ I V p i h m )

V

G u ind oil

E l n i U i i a (ft)

MMMIt

FkUSuw

FVwjMcer

Tot^ Wdli DHUnt l
M{197S)

OtecmrWdli

4

liOirUaii WcUi

1

Mctbad BubbkPotol y

Pndaction rniaar

V/tUi

\boti.2fMl

1

2

FormiltDa

Avrnin

HATL^&un Group

Lmwlocx

Fiuuicd

PRODUCING BDBIZONS

nrtxHuta

900

H d c k H S

Oli^MiDceiK

Aie

SSAL

V

FomAllMi Ulbalotf

1

1

BAngaLin Gp.

.-

Fuured cvboiuta M^LCreuceoui

1

z

Forttiatioit

Gurpi

B i n g n u n Gp.

utkolocr

ArLhydhiF. u l t

itHle

330

200

SanlDniAnPllcocmc

Albiui

lUckDCHin^

TniiTrpc

OI'UKK PAKAMIOTJU

l»

FonMlkm Volume Fftctor IRBKTBl

1

T

on. MRAMKTERS

1

, . 2

-:^ 'r

]!..)

7

%

"?

SwlfUr CoatcM

1.4

l.«

>T«iidiT(CPl

7

1

(«)

DvpUl l
i,4ca

4,TO0

TVdLBCdOr PiirZoDclfl)

:T9

320

umo

I4,<XX)

p 3 CD

Q o"

PRODUCTION MRAMETUIS

Crq

:*

Dkllr PrvductiaB (did)

?

RtcDHrabk

T

DriTi Meciunum Toul Productkia (ditii

Cai CKpiiuion + wner drive

•>

1

Stitui EolmalHl

•*

Recffrenlilc

7

a. T

Ull

,t

w

(KC^STBI

RecDvcry Factor

A>)rinm«nc Anl>cUnc. boi^ in tmv-^cction u d k>nii[iHliuJly-Pilch«iDlheSE,

H

a. 3J.0

E4u*nleii>OU

1

A m of

116

Bsttam H<4t "Rapgrmtitrt

C u m i RaUo

M-L.Cr7tKcou»

L. Miocene

Att

aouKCE

• '

0 « CruTilj C A P I I

2.000

€tnL h h jj~.ui

Anhydnlc. u l l

• ^

PrniTt<pria)

ft*

m 6!

/. continued

RAG-I-SAFID

FIELD NAME

Fltld S i x ikin'l

J4i;}.6

Cl«ifthatk>n

41 B t l i y i C a Ktefnmf type

Pflrokum Fronoct

ZagiQt Fronul Fold Bell (Khuicsun

xrzru.

Oiuaf Wtcvtftty

IW4

tUscmery WcU

lUi-E-StM-l

Elcntkn(ll)

40O

3<«WE ToUI DtpUl (It)

t

PnductT Wctli KUHWCING BOUZONS

"t

FVMSuiui

:s

O t H t m r Wclb

t

:

ToWWtlli DiiUnl lilau>

'

6

T

Initial P r e m i n

•>

J9TO

39;;

'Kit)

^

Biibblt Pojnt

^

Bottom Holt Ttmpcntim

30(I97S)

IM

IM

2

OH. PA1UMETERS

1

2

Oil Gravity I^APII

30

Ji

7

t

J

33

SjnjJi

Udiotaij

tatoonacti

^:artfindt«

1,200

^,000

OlntQ-Miocfnt

CcnomuuAnTuroniin

1

2

GacK&dnn

Sirvak

SEAL

12

Formalioa VoluDK FtclDT IRB/STB)

•njKUiMi WcJIi

A^man

Ar

2

Pt4mre(|Htt>

formmtian

TWdUKsO)

Rufrvolr

PFrmtAblUry Imdl

VkUnd E>lltnf PrwIiKliDn

1

lARAMEIERS

fiovincci Lootioo 1l>t, IDDBJ

RAG-t-SAFID

FIELD NAME

Buntvont

GENERAL DESCKIFnOM

•'

ft 3

(wKiTJtl SnJFur Conttnl 1*1

LiUu4i«!>

Anhydnte. SJII

firtNHUle

PRODUCTION PARAMETEKS

Aft

(Jli?o-Wioccrtt

Cenomanian^ TuiXHIIdfl

R t c w t r y Ftclor It)

SOURCE

1

2

FormBtion

Gurp*

Kozhftumi

LiU»4ocr

ihik

shAl«

':o

:t»

Sdnlonidn' Pikeoccne

AKilKl

Thickiwu (fl> A(t

I "

AS ^mmeirc. dnticlinai 1Dtd

TVttnVp.

1

2

Dtplh 10 Toil of P I T (fl)

4.400

4,;oo

ThkkDHiot PljrZDfW{rt)

924

I3M

OTHER PARAIttETEItS

Area oi

30.400

& >

'

Vlicoiity (CP) FormBEion

>

^

Dritt VttcfatniiiD

Datl; ProdiKtkHi Idlltl

1

TMia Produdkn

Rtcovrnblt Rpstr>« ^ F q u i t i l t n t (HI

T

Rtcovtrabit Oil

UHiter dnvt

li^ltcHoii Stitiu

1

CitlniMttd Rtstrvet

t

Rtcovtnbtc

T

->

Idliti)

GJU

1

I. continued

> oo o

FIELD NAME

r n

GENERAL DBSCBiPnoN FteMSIndtBi')

•

• ^ ' .

tixb

.

.

,

'

:

•

.

•

-

•

•

.

;

•

hUulcuDi

•

/

*

:

•

••

SouUicm

nSERVCHR PARAMKTERS

r

2

Rnrrrolr

T

1

h r m a b U l t y (iHl»

7

t

tnilblPmirT

1

7

Bubble Polnl

7

NERo«ttin-l

DtoMFttry

WcD

1

RAKASH

AnbunCuir Buin

19W 52'W50'E

:

•

221 BillynCi KJcnuzKiypc

OuilSalliHi

Lacxtlga ( b l . laB()

Total Dttpth (ft)

FIELDNAME

RAKASH

S«Uabciun(VT

Wiln- D « ^ m

JJO

Prodimr

TotklWrili DriUrd ld«tc)

14(197})

MMlod 7

P t o d m r Wclb

11

FBODVCING HURIZONK

FWtdSbbH

ObwrTcrWilli

U * * ^

t- *

2

t»

Ap

AptlAII

KimmfrnJetBT

SEAL

:

^

.

•

IJUKOOK;

Ap it-

riimlloii Utbolofy

An

ihilc

•ntiydfiif

Albiin

THhoniir

.;;i::"

Lower Surmch

ihik

VXllLKCOUt

)30

^K]

Vkltn^nian

^•ihonun

StniL Turc f c l i i c i ^ !•' 'H.III - I : . r ; - : f

1

2

5.4iK.

T.ii:

ThickDHiDf Paj'ZoHini

M

u

A n * at PnducHoa

7

y

OTHER J, PAKAMETERS

T

3 B5

OIL PARAMETERS

1

OU G n v i l ; ( ' A P l I ;

7

7

G u / U l l RiUo (•tOSTBI

7

7

Sulfur CofUCDt

7

7

VliflKity [ C n

•'

:

•••

- 3

ft

c

(*)

3 O CO

7

o" (TO

PROouciKm MRAMETEKS Rtcovrry

Factor

7

Drln Mcdujuini

^

Tool Pnducdofl (4«lt)

7

RKOversblc <>U

7

7 Stitui

ft

2

GKIWI

TrtpTyjw

t

Hith

liTTic^[[ine

T i h t i i i i ihl

>

.2

_

Khudufni

Formalkin

T

Votmnt K*ctor (RBWTBJ

Anb

330

T

6d

-

Cirttonila

Tiikt—uni

Dtptta Lo Top

^

lnJKUoaWeUi

ShuulH

FwnHlian

SOUBCT:

-)

DouaoHci* Tempcntun

7

'

P«>Mn(Inll) X>mljtot PmdKlian

00

ofPirfft)

i

D*U7 pTDductlaa

Rfcormbk Rncrm — EqutnlenlOa

7

7

EdllMLHl RcKTva

7

RtvffTvnMc

7

ofT 65

/. continued

FIRLD N4ME

SULABEDAR

GENERAL DCSotimoN

H E L D

.

ClusiflciiiDn

Field Slic ( k m ' )

'

22\ Bi
N A M E

SULABEDAR

MESBKVOtR MftAKRIERS

• . : • . , • .

Prinlnm

Z j g n n Fronlil

P I W U K C

FMJBtil

Dattof

b m )

I9TI

1

^

Dale of

7

''

T

DtiCO**f7

Scitmicifid

Mftbod

geolofk; survey

FMd

Statu

nvduccr

[oilial

ElcTatlaa Ift)

1.S70

Total Weill

)(I97J)

»)i

Pnsnir*

B u b M c PoiDt

BoUomHok

DnMedldate)

Pndwthw

?

SullbcduO W U

IkKd Drplh ini

2

( F i n Province) P e n M a > i U i * 7 ^ittd>

Locmdan I I M .

1

•?

?

150

T

1

1

1

2

Tcmpcnturt l l h « m r

P r o d u t t r W»ll5

li^tcdon Weill

Wills

• '

ForoHlion

ntoDucDM BORIZONS

1

2

K4fhdiifTj

Kiiamj Groap

Shltc

Cs^OfUiet

200

1300

Voluotf Kiclor
Fsnnalkiii

OIL ;

Uttalifir

PAIUMFTERS

j O i l O n i v i t x r*API> TUckacnlti)

^

42

(K S

t A p

Alhun

Tithoftian-

1

2

Kl/CJUuTTu

K h j n i j
(scfSTB)

ForoBlkia

itutc

UtkokcT

PARAMETERS

-)

TLchcHiiin^

Albiin

Apt] an

I

1

SOUBCE

Utholiiti' T h l c k D C H (rtl A p

Kuhduiiu

K h i m i Gpr

ihile

shik

:oa

1300

Albiui

Tichonian^

omtK

-

AniicLinc

2

1

PARAMETERS Dcpcli l a Top of P « f

;.t)aa

y

f

^

Par Zone i n i

> 00

J

i m W i

A f u o f Producttoa Iserts)

I2.D00

G u CKpuisicm + waicr d n v e

'>

^

'i

Esdnutcd

T

idatFh

rdBKk t

rj|UL*aknt

• ^

Production

Rrcot^rabk Oil

Aption

TnpT>p<

Drive Mcfluninii

1

Duly PndurtioB

Fannadon

>

'

"

1

PRODUCTION i n d Limestone

An

V i m s i i T rCP)

S".

1

1

S£ 4 L

Oil

^

/. continued

FfeM S l H (km')

FIELD NAME

AHWAZ

FTEI.D N \ M E

CDtERAL ; DESaumON

. /'"^^

^r •y

PttTAlruni

ClualAcmliDa

AHWAZ

MSEKVOn nUtAMETERS

1

Uiatryoir

17

•

,2

3

14

s

Fold Bell

Wril T i u l D t p t h
Elmboalft)

J fcfncliDn 7

FkUSIUu

Producer

PndKcrWdb

Ti

O b H n r r Wf Ui

4

PRCKWCUVG BOMZONS

1'

»

I I I J K U I M WtUi

.. I Swvak

Fiuured cvtnnun

ihak

1.190

SOO

2,«QD

OUfo-MkKvnc

SamonUii'

1

2.

Formatkifl

Oachunr

<^ijrfn

Utkalafi

Anh^rdnie. u l i

ihxk

iluk

E Mioctnc

SuittoniAii'

rcnonuiuin^

"**" TMrtani (H) Av "s«*i.;

'-'$•:;

Alt

Bnbbfe P o l u P n H u n (pilt)

7

1

7

1U

TK

I4S

FvmuKina VDlaiH FicUir (RB/STB)

7

OIL PARAMEma

>

OH Crwrlty t ' A P n

.;3!B

GafOHRaU* (HlfiTB)

CcDDiniAtiUTUn">ruafi

..-

3

.

SuUW CoDtiiil (»l V l w B i t y
^aivLiJi

1

r

Fimliiiii

Gurfii

KutKlumt

K.ulxJumt

Ulkalasr

thik

itulc

•hale

320

30O

20O

Albiin

ADMAII

^ i ,

TUckMsirt)

*v

L CrdKeoui

L i r ^ vyirLTiKtfic. ArniclmaJ [ok]

TVipTypt

I

1

3

Dcpfh IvTnp

TJOO

101.000

lO.tOII

TUckncHoT P i j ZoDc < ri)

aid

lU

BIO

70,000

70.487

141.7M

HUMMETEBS

A n a of P n d K b o n Imtrtti

7

a

u

7

7

1^

ttifh

IJ

V

DaUr PradBdtoa

*>

• -

RecffvrrtWe RcKrrcs — Equl*alcnt OtI

T

ft

s

»5

Drive MfduAtmi

.'

liO^ction Stenn

Tbtal horfucikM

•>

bdnlcd

Kccff^nMc

7

ou

O era

bV. -

^ '

B

1

PRODUCTION MRAMETEBS RKOvtr7 Factor

on o.

2

t

316

(») 3

"SOURCE

uoo

•MtoniHiile TVmpcntur*

llun

Atfn*n

ForiHtliH

7

59S3

M(1WJ) Dfilkd ( d i u )

'

1

3995

7

Mttbod

Dabar Ptvdactton

1

laitiml P m n i t

rcimcablUtr (iHl)

AhwU'd

19S8

LacatioBlla(,knt)

*

fc

T

R H W H

RacDTHmbk G H

T

trl 0=

/. continued

Held S l H (km')

Locallan l l i l , k a i )

TtUl Dtpth irt)

Area of Pnductiofl (kcnal

^^

GINEIUL DESaUFTION 7

dHrikalkiii

41 B i l l r / : C l KtcRunf type

30^2" N. W)TE

Dmuot

ins

1

Zagn» Fnjnul Fold Belt

hrtmlttun

Saimicind

tnimtr

WcUi

'noouciNG

T

IMiSUMl

43 oil, 3 g u

O b K m r Wrfh

"^ 9

1

2

eicvaiiofi (n^

Aimin

rj arjic !ii iin tjroiip

T D U I Weill DrilMliUtil

U(I97S)

[qlKtloii WeUi

t

.

3

.

Khuni Grouf) Cuteaue>

Ulkokir ihile TMduiBiini

Aw SBiU. Foraadon UMHlatT

Av SOURCE

1.600

>

3

1 GKhunn

BAngmw Cmup

Khuiu Crvup

Anhrdfilcind

Shile

Settle u d Umenonc

Lower MiocHV

Mid-Llic

1

2

Apiian

UlbolocT

Sbik

Stale

320

:!(»

Upper C t d K t m i

I

3

Id

6

s

-

^

Mfi.^

)M5

Bvbtili Point PnamvlpdKJ

J

7

7

no

14U

1«

BotlomHt^ TcmpenluR

0.1-16

Fsmtioii Vollunc Factor (RB/STBI

T

1

7

on,

1

2

3

>

31.1

31

^

n 3

7

1

1

a.

1.7

1.7

7

>

-

T

PAKAMFTEKS

Altnin

Cu^lRntls (KtSTB) StUhu' CtHileiM (*1 VbnHlty
PRODtlcnOM pAkAMrrERS

3 KhwTu Gcftjp CMborMa

^

I3O0 'HLtnniaAApciin

Atyimnflnc inbcUne

•ftipiyp*

00

1

Apcim

'

1.

Ki^hdufTU

I

2

3

Dvptfa toTDp o(h]fm)

4U

3,400

5.S50

TUdUHUof Pk^Zwirt)

718

4«:

493

OIBER PARAMICTEIU

23.000

2190

OaGmltyCAPII

O U ^ Miocene

Cilfpi

Aft

IWO

:joo

ForutkHi

Thidiaaxtt)

is.ooo

Initial P n a i u R

F » n t » M U t 7 (mdl

2,170

BOKIZONS FuiMttWI

142.1X10

Pondty(«)

*«*)I>CB"vey D i l l or FnductiHi

BESKRVODt PABAMETCKS

Gachunn'J HUl

Wttvivy

CACHSARAN

HELD NAME

GACHSARAN

nELDNAI»E

"TirV^. ,;- , 'f

Mwt»nl«ft

(»1 Dsiir Productioa ((••ti) RccDVTTBblr Racrre* — E^uhnlHlOU

•>

Total PmduclkHi (dalil

7

RMo«™Wa Oil

water drive

7

It^litn Statu

7

EidiiBtHl Riatrrtj

T

RennvraUt

7

/. continued

> O

ROSTAM

FIELDNAME

FIELDNAME

ATH

of

1

DssoupnoN 2JI BalJy/ 2Ca Klcmmc

neUSinika'}

ArtbiinGuir

LocMivKlal, laoo Sdinuc lurvey

lUttl Dtpth (ft)

PndDction (J^PWTT WnM

navts)

IqjKtkriiWiU*

WmzoNS Mtsttnf (^djv^ I

(ft)

1

PcimnMUtr iBd)

7

7

7

'

3

7

7

n>

1

I—^

f

BcttiniHgk Ttmpcrvturt

7

FtraitiDn VoJuBvFKlar (RS/STB)

T

OB, MSAMETEKS

1

(NI CnTltj rAPIl

-

T

1

•>

'F

T

7

7

t

t

^1 •

;•

'

1

3

1

^

^ 1

a3 a>

-)

T

OS

7

['

7

7

a.

«

fT c

1 %

• '

3 O o_ o"

. . ^^. -jjJB

t

• --^-Jt^-A

Ate

• i :

ft

PAKAMTTEKS ^OUVCF:

CO

•

BabbkPDlDl

(») i*-^(cn

Utbnlocr

'2

.-..•^.J

(KiSTB)

^

<»

Rannatr P(>nirili<«)

witcr PvpUi rrt) T«toJWtIh

29 DiJ. I g u

RESERVOIB MKAMTTESS

J- -.1 jvi:i'«s ""

j(t^ 1

Ditn

7

ejection 5t«te*

7

1

-n>ui

7

EMnnlH

7

(%1

Pnductioa (ilatt) (0) T

RcotmUt

oy T™»iypi

EpIBES '^ RUAHETEaS DtplilaTap «(Pij(n>

nrzaatdi)

Slrt'rrtalcd sSruL-Cuic LrcnJir;^ ^criijully H-W withlubudjng lAf

[hf rmirTof 2»afl.

W 0=


7

/. continued

MANSURl

FIELD N A M E

FIELD NAME

GENERAL

DesaoFTton FWUI Sax Lknr}

1

QuHfialHHi

Pttfvlwm

41 B i l l y / : C 3 Klenune [ype

F^MBcll

MAN.St'Rl

RESEKVOIK rARAM£TeitS

1

2

3

4

Rhcn^oir

u

13

9

11

P o r a i t r (% 1

(Khuzesun 9mvintx) Lonttoii (1*t, loncl 48-5
Dice of [Hicmfrr

1962

D4an>nrr WcU

Mimun-1

Discovtrv Mithud

SeiiTnic

Etetitkm (ft)

40

?

ttmttot Prodtittioo

1

FtiUSuiiii

producer

TsuJWclb D r i l M (due)

S(I975)

P r o d u n r WcUi

5

O b H T i i r Wrlls

^

tiO«U>D WrUi

1

noooanG

1

2

3

4

AiFiun

llun

Upper Sflivak

Lo*CT Simak

Cvtwiutn

Carbofiitex

CirtKmBCti

Forma lion

carbofwn T U c k I K U [Ft) Aet

SEAL

Babble FUnt F*r«niiv (psifl BoflomHolc Temperature Formation Volume Facuir

420

SSO

930

630

Oliso-^liocciie

Conuciui

T\m>niari

CenonofL-ian

3-

4

1

2

•••.;

Guhurui

Gurpi

llam

LiUiakitT

Aniiydhte JJHI

Shale

Shile

Lo^erMiocFTK

SantoniW'

CtMiiacidn

SOURCE

1

2

For n u lion

Gurpi

Gurpi

Kudhurm

Litholof)^

Sluk

Sh)Ue

Shsic

Oil C r a r i l ) r A f l l

330

320

Afc

OTHEH PARAMETERS Depth to Tdfi DTFft^irti Thtckncnof (ft>

;oo

AiynHPCtnc uiiiciiiw

1

1

3

4

7.100

IO,2JO

10.900

i:.o»

M3

JS8

377

I0.M6

44.Mn

MJSO

U9

PMJ 2 W K

>

Area of Prvdiiclkn ( K R J l

17.649

ISO

22]

23S

1

245

t

t

1

2

3

4

30

:o

29

:i9

1

?

2.3

23

•>

1

Sulfur Coottiu

2

> 3

J

a-

(»l 1 • '

Drin Mcrbaiunn

t

InJKtiDa

•Y

•J

Total ProdiKtKHi

1

Ed^matnl

t

7

Recorerablc OU

t

HnownUc

T

•'

Pr«dlictlofl (date) RenrertMe RtMrwa — EqulTalenl Oti

Altiiin

SuilDitiin Ptkccenc

"fr»p1>p*

•*

t

DaUr

Thkl[iMu4fl>

1

PKODUCTtON PARAMETERS

4

3

T

Uai/Oil RaUo (seVSTB)

R«:itver> Kactor Aft

t 6 2 ^

FAKAMETEItS

Vlitmuty (CP) Pwnudon

1

5750


on,

UtiMl\OKf

?

:9eo

(pX«>

T o u l Dcplli (ft)

HORizora

•J

3511

pH-iDabilIlT
/. continued

>

FIELDNAME

BAII]tAGA^SAR

GENEKAL 1 DCSCMPnON F M i SIK (kB>)

-.

• ^

S.t> 1 J. 6

CUinAalkv

FIELDNAME

41 B i l l ; 1 ^CiKkinme

-^'^^'fsS?

PnMncc

FDUBCU

DtKvrcrr WtN

B«hrminHr-l

BAHRAGANSAR •

50

T

t

*

RESEnvom PARAMETERS

1

2

3

4

5

Rocm^r

1

20-15

7

7

li

Ptrrmbility tndl

*t

7

7

7

Initial f i f u t T

7

7

7

7

7

T

7

7

T

T

7

7

Formallan VdHiwFtKiar (kB/STBI

T

7

T

7

on-

i

3

4

5

1

Pnsductioa Iku^}

trpc D a d of

LocmllDD
IMO

10.971

DbnnrT

Seiimic leflecbwi

BentlHidl)

7

1

FMdStatia

tndaca

I k u l Willi D I I U H I Idatt)

I0(1»T5)

FFDomr nvfli

10

O b K m r Weill

••

•qtKdoaVMb

T

P R O D V C T i G , "• HOtttZONM .1' :

1

2

3

4

Fmialkin

Ghtr

Annan

lihrum

Bkn^sE&n

Nihf Unu

LMiilaij

Swid

Fiuured Ckftwfuws

nrtmmiri

Qntpofluti

Sjnd

142

?60

1.130

720

4)

Olifocene

Obgo-MioccDc

PltwC^nc-

Mid-Lue CrctKCDtu

Albun

1U>1 I>iii<>> IR)

Producllai

C/3

ft

Pnaaunfp^ BOUUDHDIC

IWckowdl) Ap

gXAL

;_,'.

1

•

3

1 J * t f FlTi

Jahructi

Anhjrcknieand u k

Shile

F^wmatfon LMblllVT

z

Lijwcr MuxTflt

Aft

:

4

TtfBfwratuiv

-'

3

. 2

1

i'

Kudhumi

Shile

Shale

Mid U i e

AUnui

4

5

FormadiHi

i^nirpi

llutl

Kjud^utFii

LMulair

Stale

CaibcHu[c3

Sb^

TMckawini Act

330

200

200

Suiiontu^Piieooene

Coniidin

AINU

OTHEn MRAMETEX5 DcpdiloTop

I

2

3

4

h,:iftji

6,810

7,+ti

S,77S

v.fi.U)

T

MO

lOT

IM

4]

v

5

ml P i r (01

r^ZoKtn)

C

t

OdGnrrln'rAPli

• '

»

t

r

J

J

SsllurCoaUH

7

T

?

7

7

Vi>c«il;
^

^

^

T

ntoDucTibN FARAMETEX

3

Q ft

O ft

^

t

Drin

Dall^ FrDductlaa (ilatil

T

1Mal FndactlH (llMtl

7

ftteotrraW* Rmnu — EqidnfenlOtl

T

KCUIVCIBHC ON

0

(*1

Gently fDMcdKViCiJM.stighlJrelonBiled in • SSW.NNE d i i u k i n . #ith imximum closure or 330 fiuid clo SAl vea af 9 iq mi

nxriypt

2

TAKAMEinn

GaalOyitalio

Eocene SOUBCE

CD

;;'

' , ^ J

BuiK^T'^iiii 1 '•

CI

3 a-

bitctiin SMOa

7

EidniatBl IUM.rvta

7

a.

7

J. Data from some oil and gasfieldsof Oman.

FIELD NAMF

RAHAB

QAHARIR

,GKVt:ftAL, DESCRIFTTON rWdSlnnui^^

AMAL

•

-

•

••

7

7

ZSa(35illkin)

7

1

SoulhOmin

SouUiOmtfi SikBuin

•>

SoulhOiun ^iltBuin

South OmiD Stlieuin

SJ'40'E ICI^N

S!'6'3rE IB'irWN

1973

I97S

1977

1978

1980

DiKDTCTy W n l

Klhlb-I

(Muni-l

Himr-l

Amti-l

I M a l DtiHh (ft)

7,407

7J»I

1^74

iX)7

DiKO'VCTy MtthHl

lurvey

ScismK survey

EkrratliHi (ft)

Ml

1.107

Date of PrvdiKtkHi

ivai

i»sa

OmmFvId BcD

Sdunic Mirxty

IMS

BirtM-l lUll

mud-:

FAHUD

-^

Huqf GcDup

llut^f Gruup

Huqf Gmup

Huqt Group

M^tjh

Clulicx.

CUuici. cvbufiitcs. evtp«i(H

CUtba, cutoiuiei, ffviponto

Clutm^ C4f1»uva, evipohtet

Clutin. catouico, eviporita

CtHlky, irt
S.DOO

3,000

i,sao

TIllltMlftl

i^OOO

].ax)

[ufnabriu.

T n f lypt

5tiuctunl

AnbcUne

,(inuat

500 Albiin-evly CJeKHiuniifl

Struciunl

Stniciunl

Fwlted

Edited inffjflirte

•r

nUEAMKTEIS

• • ^ ^ ^ . -

7 1,100

5,1U0

;,400

J,OUU

S,J20

750

lW-200

2»

130

300

120

120

7

T

%

^

7

7

Orpih ID Top

Saunic tufvcy

Seimuc

lurvey Ul

70

1.D00

rayZoKini

IMO

I9«3

I«67

A m of

CD

E>rcdixtton Ikm^t Pralucn'

Pndiiotr

PmdiKtf

Pmkicer

1

35 (I9M)

(IWl)

11 (1«tl)

ProdiKcr

Fiwluotr

4 (19M)

t3

•>

7

7

O t H t m r Wrlli

T

7

7

1

7

*

->

•'

^

7

1

3

^

RESERVOnt PAXAMETGR5

74

27

29

PerttkAblllty Inul)

U-35

20-33

S-IOO

Inlii*! PnMDre

IJ40

1,81]

I.4K

T

•t

II4-I1BT

13*1=

113T

isa

106

\S&

Ruuiuir

T

37

PRMUR

Ghanf,

A mill

Kunu Gnw;>.

Ar»

Nuih

FluviogUcill

Pluvioglaciil

Awliia

Fluviuile

Cirbcnitc ineviporjte

Shelf ctftenatet

4W-610

•tgO^lD

:»

za

l«0

IJOO

Cvbonifoout

PefmoCirtnniferaui

C»inbn>' OrJovictM

CunbroOnktviciin

Eirly Cinihnsn

Lue Alb(wiCcnomi^in

Ap

SEAL NthrUmr

NitirUinr

NlhrUmr

25-32

7

T

5lii>20,0aa

1,750

33,200

7

4.700-31J20

7

I36*F

70^:

7

1.039-1.04}

1.U

1

An

T

(pdf)

BatUHuHale

FonHdoii VoluiK F K U T

OIL MSAMETERS

'

.•

30

20

JO-IB

31

33.6

77

120

S

7

7

120

SaltarCsMM

1-1

3

IV7

3-4

7

1.1J

Vbadrtr(CP)

TOJua

10-133

490-570

;4-;69

0.65

7

LifTu GmM/tm R i t i a

UOmiof}

Shtle

Shtk. fnwiy LjfnstoiK

Shik. n w l

Shale^mvl

Evif*ofi(e

Shilc. iluly nurl

Aft

Albun

Atbitn

A Mm

Albiin

Elrty

ConiacUn

• • '

'rr 2D-10

OilC™vi(jCAPI1 NthiUmr

0.120

2}

ilD Bubble PollH

Ghan(

- !

•fPlj(ft)

umcy

FRUDtlCING HORIZON

>

BIRBA

b o u n d e d hy faults

7

FarmatkH

AMAL

E^CwnbrUn 1962

->

Tlikkiits(ft)

, •. .-. -. -

Ace

PrndiKcrH^li

UtlKAocr

NIMR

hluL^I (jnHjp

evipontct SoultiOfiun SiltBaiin

QAHARIR

27i4 Lllhidatr

Dale at DbooTfTT

Furnulioa

RAHAB t^

UlBiHy/lCiKlemmclype

SS'IJ'E ICOCCN

[zOKtidfl W H l i

•

FIELD NAME

aotxcK ForrnfllJnn

JJ'06'OT' E IS"00r4r N

T D U I W d l i DriUnl (dlU)

FAHUD .

LocatioD

FVMSunn

BtRBA

-

ClMltflLlti*ll

Pnpvincr

MMR

(KC'STBI

Cunbritn

J. continued

>

FIELDNAME MMMWCnON RUtAMnUtS

RXHAB ^ *.

QAHAMH

r i';-. .*!;.;_ .' ':.;;'.• '-V.V.,

NIMB

AMAL

BIKBA

FAHUD

^^^^^^^^1

1

v7

?

! 10

?

JO

7

DriTC

7

7

Wvcrikiw

7

Gnoifi

Gitcip

Ijljecliuii Status

7

7

Withwfter

T

7

»*1H iaiKtion evly 19701

Z.l»M>l

T.42t Mil (I9U)

MXnObbl

4.000 bbl
6.900 bbl (19S1)

66.014 bbl aOBc.

l4.2MM.t>bl

t

0.6 MM.bU

6M.1 M M M l ?9.M)BCF (1983)

3

0.14bm'((t

Rccwciy PKIor

00 CD

(I9M)

Total PrndnctkHi (diui

2.}l M M t M

(19931

l.7MM.titil

(I9M)

CD

s W SB

1

lOO-JCOMM.bbl

lilB.bM

2TMMUil

UMM.tM

l.lMMMMil

ft

22-150 MMtM

7

7

1

7

7

c

R K W t n b k Oil

t

WMM.bN

1

7

7

1

RanxTCffvblf G u

1

1

7

7

7

7

EiUmalnl Rncrvs Rec«vent>lc Rewr^a — EquivBlHI Oil

O

o

a. & fT 05

J. continued

GENERAL DESCRIPTION

7.1D

F k M SJa Ikm)

OwlAatkn

221 Bdty^ 2 C l KJenuiKtype

I

OIBER ^^^^ nUtAMETGRS

•^

V

hlrv^ifi

r.

. 2

i.OWJ

} I.7!0

TfakkDCHof PajZmini

300

7

A m oi

TO

Pvplh lA Top

Hkhixl EUain

!

AL HlIWAtSAH

H E L D NANfE

A L HITWAISAM

FIELD NAME

•fPkyim • • , - * '

A l Huwiiiah-l

I9W

7

L K * M «

DbcoTtry Smmic survey

7^7)

I t i U I D194I1 (ft)

Elcmknm)

30O

1971

rwystetM

ProAmJ

3)(1M3)

ObHTTcrWdlt

1

TbUlWdb

7

RESERVDIR PABAMFTFJI5

7

Rcacrrvlr

Pradncttofl

..*

1

ntODUCLNG HORIZONS

1 Line $1 one

A*«

SEAL

.VVJ

KOO

Aptiiin

PtrrtHJ-

1

2

Nah[ ^'mr

Al KhlA^

• • '

l-omuUno

'^htk m l

LMkalgfr

Aft

SOURCE IW—dH

[ninformaiLonaL

nurl

Wrmo-

Mtnon

2

j.:-»

200 1

Bubbk M M P T H H R (psit>

7

7

BollAiBHalt TVnpcrmlun

7

7

ft 3

Formatiiin V O I U H H Fictor (RH/STTBl

1

7

a.

OIL rARAMETERS

1

2

OU Crarily T A P I )

:i.i

GH/OUR>tl«

7

T

l-l.j

1

^

7

>

VO

tJ

• '

(*1

Cluuci PRODUCTION PARAMKI'ERS i.Boa

200

llM»Hry f •cur

7

Drin Mtdvnba

1

Total PndiKtiiia Idatt)

149 7fi MM.bbI (IMS)

Eidnilcd RcKtirH

J00-2!a MM.bbt

R«VTVr«U»

7

R*cvttnbl»

7

7 Sbbii

OxFonliaii Unfiutot
Did7 PndiictkM (dil<)

ISOJObbl (19U)

->

>

11

7

Sulfur CunMM . - k

H^iin^

Diyib

hiiuminout

•mfTyv

19-23

M-J.OOO

Vl>carity{CP)

Alt

2

•'

Ud-oo

TUckBMdl)

I

tiddal h w u n

P t n m N U t T (nd)

LltlialDD

T i i i i b i i m rni

:

Al KhUti

Stuubt

Fbrnatioa

J '

Production 4kdl')

Mrtbod

P r o d u o r X^Uk

V

oa

G B

J. continued

>

YIBAL

FIELD NAME GBNERyU. OBSCRIFITON

.-

FMdXlulknil

^UPB

':"': lSi20

221 Billy/2La

UUjHOatloa

riBAL

FIELD NAME

htmJnuA

1

1

v3

MKAMETESS " [>t|rtll I n Tftp

- • • • ' '

(Pihud) 1 lllllf

L4e2

IIMEI4

VkKtfnsy

Yibal-l

3»

7

70

t

00 ft)

Pljf Z a « (ft) I M i l D i p l k (11}

Sajmiciunvy

7.M8

ElenM«ga(ft)

2»-«I]

Ananl

Melboil ig«9

f l d d Statu

Producer

IMalWdb DrHVed ( d i u )

1»T(I9«])

RESEItVOIH PAftAMETERS

95(t9«ll

O b H m r WeDi

?

liOecdofi Weill

j^diBi)

RHtrniir

Piwluctldit Frnduor Wttb

rtCODUCING HORIZONS FonnadiiD Litbo4acr Tlili t III •

mi

^F SEAL

1

2

Sh,:.,,u

Khuff

>t:..,LH,..,.».„.

(^aibu(UI»

im

;,;t«j

•S^itljr-.

Lite Permiin

2

1 NiJir U r m

FAniKtiDn

Stialc. n i j r i .

UUiiitatr

'

AlhiiJl

SOm.CE

"•:'

Formation UdmliiKr

' •

1.

... •

Suliif

AV IViplVpt

1-30

7

Initial P n a u n

IJ30

^

BabUalNiliil

I.)J7

7

BMUmHolt TmiptratuiT

7

T

v-t

7

?

1

1

Fomaliati V W u i H Factor

3

o

^ ^ ^ ^ ^ ^ H

(H

[•jrly Tri»sic

2

DiVBh

S^riiui t.']ftHLi:i

OUGnnty('APl>

3*

1.60(1

OKfordidn

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I

7

&

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(*> PRODUCTION PARAMETERS 33Enmar>and Kcondary

Owin Macfaa^HD

Dall; Production (dala)

l2S,l»Mil

Total ProdoctioB (^Ul

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670 Ml^.btil

RacovcnMc

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(*> J t v e toped

«i

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ponul intichnc through u l t irtDvcmciH. fniking

if-

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RCUHCI A N C '

J. continued

*

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f TfT»«tlf

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TOUI Dt^

FIELDNAME

MARMUL

FSLONAME

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1956

Scunuc MiTvty

9Z)2

(11)

OJUUt PARAMETERS

eicndoafAl

2

3

South Onuri SihBuin

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l.L9i

2J7i

1.930

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14)

*

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7

1

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1

2

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7

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MARMUL

1

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1-

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320-l,9BO

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OTHER F A K A M INTERS

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FIELD ^ A M e

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OIL PARAME'l'BRS

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PRODUCTION PAAAMETEKS Rfcorvrry Vmctar <»1 IMIT

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>

1

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