Phosphorites on the Sea Floor: Origin, Composition and Distribution (Developments in Sedimentology)

DEVELOPMENTS IN SEDIMENTOLOGY 33

PHOSPHORITES ON THE SEA FLOOR Origin, Composition and Distribution

FURTHER TITLES IN THlS SERIES VOLUMES 1, 2, 3, 5 , 8 and 9 are out of print

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4 F.G. T I C K E L L T H E TECHNIQUES O F SEDIMENTARY MINERALOGY 6 L. V A N D E R P L A S THE IDENTIFICATION O F DETRITAL FELDSPARS 7 S. D Z U L Y N S K I and E.K. W A L T O N SEDIMENTARY FEATURES O F FLYSCH AND GREYWACKES 10 P.McL.D. DUFF. A . H A L L A M and E.K. W A L T O N CYCLIC SEDIMENTATION 11 C.C. R E E V E S Jr. INTRODUCTION T O PALEOLIMNOLOGY 12 R.G.C. B A T H U R S T CARBONATE SEDIMENTS AND THEIR DIAGENESIS 13 A.A. MANTEN SILURIAN REEFS O F GOTLAND 14 K . W. G L E N N I E DESERT SEDIMENTARY ENVIRONMENTS 15 C.E. W E A V E R and L.D. P O L L A R D THE CHEMISTRY O F CLAY MINERALS 16 H.H. R I E K E 111 and G . V . C H I L I N G A R I A N COMPACTION O F ARGILLACEOUS SEDIMENTS 17 M.D. PICARD and L . R . HIGH Jr. SEDIMENTARY STRUCTURES OF EPHEMERAL STREAMS 18 G.V. C H I L I N G A R I A N and K.H. W O L F COMPACTION O F COARSE-GRAINED SEDIMENTS 19 W. S C H W A R Z A C H E R SEDIMENTATION MODELS AND QUANTITATIVE STRATIGRAPHY 20 M.H. W A L T E R , Editor STROMATOLITES 21 B. V E L D E CLAYS AND CLAY MINERALS IN NATURAL AND SYNTHETIC SYSTEMS 22 C.E. W E A V E R and K.C. BECK MIOCENE O F THE SOUTHEASTERN UNITED STATES 23 B.C. HEEZEN. Editor INFLUENCE O F ABYSSAL CIRCULATION ON SEDIMENTARY ACCUMULATIONS IN SPACE AND TIME 24 R.E. GRIM and N . G U V E N BENTONITES 25A G. L A R S E N and G.V C H I L I N G A R I A N . Editors DIAGENESIS IN SEDIMENTS AND SEDIMENTARY ROCKS 26 T. SUDO and S. SHIMODA, Editors CLAYS AND CLAY MINERALS O F JAPAN 27 M.M. M O R T L A N D and V.C. F A R M E R INTERNATIONAL CLAY CONFERENCE 1978 A . NISSENBAUM. Editor 28 HYPERSALINE BRINES AND EVAPORITIC ENVIRONMENTS 29 P TURNER CONTINENTAL RED BEDS 30 J.R.L. A L L E N SEDIMENTARY STRUCTURES I AND I1 31 T . SUDO. S. SHIMODA, H. Y O T S U M O T O and S . AITA ELECTRON MICROGRAPHS O F CLAY MINERALS 32 C.A. N I T T R O U E R , Editor SEDIMENTARY DYNAMICS O F CONTINENTAL SHELVES

DEVELOPMENTS IN SEDIMENTOLOGY 33

PHOSPHORITES ON THE SEA FLOOR Origin, Composition and Distribution G.N. BATURIN The P.P. Shirshou Institute o f Oceanology, Academy o f Sciences o f the U.S.S.R., Moscow, U.S.S.R.

(Translated by Dorothy B. Vitaliano, U.S.Geological Survey)

ELSEVIER SCIENTIFIC PUBLISHING COMPANY AMSTERDAM - OXFORD - NEW YORK 1982

ELSEVIER SCIENTIFIC PUBLISHING COMPANY 1, Molenwerf P.O. Box 211, 1000 AE Amsterdam, The Netherlands Distributors for the United States and Canada: ELSEVIER SCIENCE PUBLISHING COMPANY, INC. 52,Vanderbilt Avenue New York, N.Y. 10017

L i h r a r \ or ('onyrr** ('alaloyinL: i n I'ublivalion D a t a

B a t u r i n , G . N. (Gleb N i k o l a e v i c h ) P h o s p h o r i t e on t h e s e a f l o o r - o r i g i i : . (Developments i n s e dirne ntoloc y : v . 33) T r a n s l a t i o n of F : ) s f o r i t y n a dne okeanov. I n c l u d e s b i b l i o g r a p h y and i n d e x . 1. Phos phat e rock. 2 . Marine m i n e r a l res?lirces. I. T i t l e . 11. Series. QE471.15.Pk8B3713 553.6'4 81-Ult71 IifiCR?

ISBN 0-444-41990-X (Vol. 33) ISBN 0-444-41238-7 (Series) 0 Elsevier Scientific Publishing Company, 1981

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Scientific Publishing Company, P.O. Box 330, 1000 AH Amsterdam, The Netherlands Printed in The Netherlands

FOREWORD Baturin’s book is a summary of recent data on the distribution, conditions of occurrence, composition, geochemistry, and origin of phosphorites on the ocean floor. In it main attention is paid to shelf phosphorites, includingvery young ones - Late Quaternary and Holocene; information also is given on phosphorite on seamounts, which has been studied in less detail. The most voluminous and most important part of the factual data given by Baturin were obtained by him and other investigators in working up material collected in recent years by numerous Soviet oceanographic expeditions (on the ships “Vityaz’ ”, “Academician Kurchatov”, “Dmitriy Mendeleyev”, “Mikhail Lomonosov”, and others) in the Atlantic, Pacific and Indian Oceans. This material - samples of bottom sediments, phosphorite, phosphatized rocks, and also interstitial waters pressed out of the sediments -was investigated by a number of chemical and physical methods, and as a result several thousand determinations of individual components and parameters were obtained. In addition the author used numerous data pertaining to problems of oceanic phosphorite formation published in the foreign literature. The work contains a review of the principal material on the specific group of oceanological factors governing the facies environment of oceanic phosphorite formation. Such a review is timely. Since the time when phosphorite was found on the ocean floor by the British “Challenger” expedition (1873-1876), it has commanded the attention of geologists as a possible key to an understanding of the origin of phosphorite deposits. As is known, current hypotheses of phosphorite formation are based on the use of oceanographic as well as geologic data; they are the biolithic hypothesis of J. Murray (Murray and Renard, 1891), the chemogenic hypothesis of Kazakov (1937), and the biochemical hypothesis of Bushinskiy (1963). But none of these hypotheses was based on direct observations on the actual processes of recent oceanic phosphoritization, the existence of which remained problematic. This gap was not filled until after 1969, when on the third cruise of the scientific research vessel “Academician Kurchatov” Baturin succeeded in finding numerous and diverse definitely Recent phosphorite concretions on the shelf of southwest Africa, and in following in detail the processes and conditions of their generation and formation. Subsequently Baturin participated in the finding and investigation of phosphorite formed in similar conditions on the shelf of Peru and Chile. In analyzing these data, which are new in principle, Baturin essentially has made more precise and more specific a number of earlier ideas on the for-

VI mation of phosphorite which depend on the interaction of hydrological, biological, and geological processes. It has turned out that oceanic phosphorite formation actually is caused by upwelling, as Kazakov believed. But it is not accomplished as a result of chemogenic deposition of dissolved phosphate from the ocean waters, but rather, in a complex way with other processes participating. These are: consumption of dissolved phosphate by organisms, deposition of biogenic phosphate-containing detritus on the bottom, diagenetic concentration of phosphate in the form of concretions in sediments, and subsequent reworking of the sediments. The importance of these factors for the formation of phosphorite beds was also stressed earlier (Murray and Renard, Bushinskiy), but was largely unrecognized. Now their role has been demonstrated with the help of direct oceanological observations in zones of recent upwelling, and this undoubtedly is a convincing argument in favor of the concept of phosphorite formation on the ocean shelves developed by Baturin. Therefore Baturin’s book, devoted to one of the pressing problems of the geology of the oceans, is a t the same time a contribution to an understanding of the origin of phosphorite in marine sedimentary rocks on land. P.L.BEZRUKOV

FOREWORD TO THE ENGLISH EDITION The publication of this book in the English language apparently is evidence of the increasing interest of the world’s scientific community in problems of the mineral resources of the ocean and in such quite specific questions as the origin of marine phosphorites and the role of upwelling in geology. The discovery of Recent and Upper Quaternary phosphorites on the ocean shelves was the incentive for writing this book, as it made it possible t o ascertain for the first time the actual rather than the presumed facies setting of their formation. The author, being a geologist by training, began his scientific activity with the investigation of Tertiary marine deposits of the southern U.S.S.R. and was more than once a witness of and a participant in flaming and fruitless scientific debates over the conditions of formation of the deposits related t o these formations, inasmuch as there never were any unambiguously interpretable geological facts available t o the disputants. This aroused his interest in Recent processes of sedimentation, especially those going on in zones of upwelling, the existence of which he first learned of from sources of such different character as the works of A.V. Kazakov (1937) and M. BrongersmaSanders (1957). The author’s practical acquaintance with a zone of upwelling came about in 1968 on the shelf of Namibia, which he visited on the research vessel “Academician Kurchatov”. The first samples of diatomaceous oozes brought on board there, which were unlike any other marine or oceanic sediments, filled him with the presentiment that unusual geochemical processes must be connected with them. Therefore the phosphate concretions of various forms and consistency that were found when these oozes were washed away immediately suggested Recent phosphorite formation, which was confirmed by subsequent investigations. It is natural that in describing these results the author tried t o throw light on the question of the composition and distribution of all other phosphorites known on the ocean floor and on the marine geochemistry of phosphorus as a whole. A number of additions to the Russian edition of 1978 have been introduced in the English edition, but it was impossible to encompass all the new literature pertaining t o the subject, and the author begs the reader’s indulgence in advance. The basic idea of the book is that upwelling, in conjunction with biological, diagenetic, and hydrodynamic factors, is the driving force not only of Recent but also of pre-Quaternary marine phosphoritization. Many d o not

VIII agree with this, considering it intolerable interference by oceanology in geology and an excess of the possibilities of the method of actualism. But these disagreements and controversies are in no position to overshadow the fact that the advances in the field of oceanology and the impressive discoveries of a number of geological processes on the ocean floor, including ore processes, that have been made in recent years also are having an undoubted effect on the development of modern geological science as a whole. G.N. BATURIN

CONTENTS Foreword

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

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VII

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1

Foreword to the English edition INTRODUCTION

V

CHAPTER 1 . PRINCIPAL FEATURES O F THE MARINE GEOCHEMISTRY OF DISSEMINATED PHOSPHORUS . . . . . . . . . . . . . . . . . . . . . . . .

5

Sources of phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phosphorus in waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phosphorus in suspension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phosphorus in organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recycling of phosphorus in water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deposition of phosphorus from waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disseminated phosphorus in sea and ocean sediments . . . . . . . . . . . . . . . . . . . . Phosphorus in interstitial water of marine and oceanic sediments . . . . . . . . . . . . . Release of phosphorus from sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 17 23 24 27 30 36 45 50

CHAPTER 2. PHOSPHORITE ON THE OCEAN SHELVES . . . . . . . . . . . . . . . .

55

East Atlantic province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . West Atlantic province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . California province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Peruvian-Chilean province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Local accumulations and isolated finds of phosphorite on the ocean shelves . . . . . .

55 107 115 125 153

.

CHAPTER 3 PHOSPHORITE ON SEAMOUNTS. . . . . . . . . . . . . . . . . . . . . . .

163

Pacific Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Atlantic Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indian Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . On the origin of phosphorite on seamounts . . . . . . . . . . . . . . . . . . . . . . . . . . .

163 177 181 181

CHAPTER 4 . FACIES SETTING OF RECENT OCEANIC PHOSPHORITE F O R M A T I O N * . * - - .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

185

Winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Currents and water masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Upwelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydrochemistry of the waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Primary productivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biota . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mass mortality of fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

185 188 188 191 195 196 201 201 206 207

X CHAPTER 5. STAGES OF LATE QUATERNARY PHOSPHORITE FORMATION 219 ON THE OCEAN SHELVES. . . . . . . . . . . . . . . . . . . . . . . . . . . Supply of phosphorus to the shelf by ocean waters . . . . . . . . . . . . . . . . . . . . . . Consumption of phosphorus by organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deposition of phosphorus on the bottom . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagenetic redistribution and concentration of phosphorus . . . . . . . . . . . . . . . Reworking of phosphatic sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CHAPTER 6. SOME FEATURES O F THE BEHAVIOR OF ELEMENTS ASSOCIATED WITH PHOSPHORUS IN THE COURSE O F OCEANIC PHOSPHORITE FORMATION. . . . . . . . . . . .

..

......

Organic matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbon and oxygen isotopes of COz and PO4 . . . . . . . . . . . . . . . . . . . . . . . . . Amorphous silica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fluorine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Iodine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uranium isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thorium isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rare earth elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rare and disseminated elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CHAPTER 7. ON THE SIMILARITY O F THE PROCESSES OF RECENT AND PRE-QUATERNARY PHOSPHORITE FORMATION . . . . . . . .

231 231 235 240 242 244 245 255 256 265 266

..

279

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293

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297

CHAPTER 8. CONCLUSIONS References

219 219 220 221. 223

Subject Index

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329

INTRODUCTION The purpose of this work is to clarify the voluminous factual data accumulated recently on the marine geochemistry of phosphorus and on all the oceanic phosphorites now known, their composition, age, combination of concomitant facies conditions, and genesis. Main attention has been paid to phosphorite on the submerged margins of the continents (mainly on the shelves) as being the most widespread, best studied, and closest to concretionary phosphorite on land. The phosphorite discovered relatively recently on seamounts and differing essentially from shelf phosphorite has been less studied so far and is described only in general features. Phosphorite was discovered on the ocean floor more than a hundred years ago, at the time of the first joint oceanographic expedition on the “Challenger” (1873-1876). On the basis of what was known of their composition and conditions of occurrence, J. Murray (Murray and Renard, 1891) suggested one of the first versions of the biogenic-diagenetic hypothesis of the origin of phosphorite on the ocean floor and of the concretionary phosphorites from marine sedimentary rocks on land, which are similar to them in morphological features. Recent achievements in the field of oceanography have been used repeatedly to substantiate other hypotheses of the origin of phosphorites, both similar to Murray’s scheme (the biochemical hypothesis of Bushinskiy, 1963) and different in principle (the chemogenic hypothesis of Kazakov, 1937). In recent years marine geology and chemical oceanography have developed a t especially rapid tempos in connection with the overall intensification of the mastering of the oceans. As a result there has been a considerable expansion and renewal of the whole arsenal of data, which on the one hand concern the behaviour of disseminated phosphorus in marine and oceanic sedimentation, and on the other the distribution, composition, age, and conditions of occurrence of phosphorite on the ocean floor. Especially noteworthy are the results of determination of the age of oceanic phosphorites, which have made it possible to dispel the long-standing fallacy of identifying any oceanic phosphorites as Recent. As had been ascertained, phosphorite formation in the ocean occurred in a wide time interval from Cretaceous to Holocene, but its recent manifestations are limited mainly to the areas of the shelves of southwest Africa (Namibia and the northern part of the South African Republic) and Peru-Chile. The undeniable evidence of recent phosphorite formation occurring in

2 the ocean, obtained with the help of mutually consistent geological, geochemical, and geochronological data, permits a new approach to the problem of the origin of phosphorite from the standpoint of the method of actualism, the importance of which in geology has been recognised since the time of Lyell. To accomplish this purpose it was necessary to examine a wide circle of phenomena and trace the Recent paths and forms of migration of phosphorus from its sources of supply to the ocean to the phosphorite occurrences being generated on the ocean floor. Previously such attempts could not be crowned with success as only the initial (phosphorus in the ocean water) and final (phosphorite deposits) links in the chain were open to the eyes of investigators. Its main central part - the transition from Clarke contents of phosphorus t o ore concentrations was left to the fate of hypotheses, formulated on the basis of ambiguously interpretable indirect data. Now that this gap has been filled it has become possible not merely to reconstruct, but also to observe the whole complicated combination of phenomena making up the process of oceanic phosphorite formation. The main source of phosphorus in the present ocean is run-off from the continents; the contribution of a volcanic source is of minor and local significance. The greater part of the total mass of phosphorus arriving in the ocean in the composition of suspended detrital matter is geochemically inert and settles relatively rapidly without taking part in the process of phosphorite formation. The relatively smaller geochemically active part of the phosphorus reaches the ocean in dissolved form. The fate of dissolved phosphorus is decided by its role as one of the most important biogenic elements. Its movement toward the bottom is complicated by repeated use in food chains, beginning from phytoplankton and ending with fish and marine mammals. The main path of extraction of dissolved phosphorus from sea water is biogenic. Being deposited on the bottom in biogenic detritus together with other sedimentary material, geochemically mobile phosphorus is usually disseminated in bottom sediments where its bulk composition fluctuates within the Clarke range usual for sedimentary rocks as a whole. But in those cases where phosphorus-rich biologic detritus accumulates on the floor, relative concentration of phosphorus also occurs. The active process of deposition of geochemically mobile phosphorus is typical only of the near-shore biologically productive zones where upwelling of phosphorus-rich waters occurs; the largest of these zones are located off the coast of southwest Africa and off Peru-Chile. The next stage in the concentration of geochemically active phosphorus - the diagenetic - is related to redistribution of the elements in the upper layer of sediments rich in organic matter and leads to the formation of phos-

3

phate grains, nodules, concretions, phosphate cement, and phosphatization of carbonate detritus, bones, and coprolites. But all these formations, scattered in the sediments, are only the formal elements of a potential phosphorite deposit, which can be produced only by way of concentration of the phosphatic material. For this the final stage of phosphorite formation is necessary - mechanical sorting or redeposition of sediment, which occurs periodically in the zone of the ocean shelves throughout their whole geologic history due to the action of waves and currents. That seems to be the general trend of Cenozoic phosphorite formation on the shelves of the oceans in the light of recent oceanological, geochemical, and geological data, summarized in this book and indicating the multistage nature of this process and biogenic-diagenetic essence of its main links.

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Chapter 1 PRINCIPAL FEATURES OF THE MARINE GEOCHEMISTRY OF DISSEMINATED PHOSPHORUS

SOURCES OF PHOSPHORUS

Phosphorus is supplied to the ocean from several sources: from the continents in the composition of atmospheric precipitation and dust, and from river, underground, and glacial run-off; by abrasion of the shores; from the depths of the earth in volcanic and hydrothermal activity; and in the composition of cosmic material. Let us consider the data characterizing the share of each of the enumerated sources in the introduction of phosphorus into the World Ocean.

Atmospheric precipitation and dust Every year 1~324,000km3 of water fall on the ocean surface in the form 0 on land (Table 1-1). of atmospheric precipitation, and ~ 9 9 , 0 0 km3 Every year about 38,000 km3 of water are supplied from the ocean to the land in the form of atmospheric precipitation, and from the land t o the ocean, not more than 8000 km3 (Defant, 1961; Horn, 1972). The content of dissolved phosphorus in pure atmospheric precipitation (rain, snow, hoarfrost) over the continents ranges between 0.0003 and 0.006 mg/l. In contaminated rain water the phosphorus content may rise to 0.02-0.06mg/l due to the water-soluble part of dust (Bashmakova et al., 1969). In fresh snow contaminated by dust, in particular in the snowfields of Kazakhstan and the Altay, the content of dissolved inorganic phosphorus is still higher - in isolated cases up to 0.8 mg/l (Table 1-2).

TABLE 1-1 Water balance of the earth (Defant, 1961) Surface

Atmospheric precipitation ( km3/ur)

Evaporation (km3/ur)

Oceans Continents

324,000 99,000

361,000 62,000

Earth as a whole

423,000

423,000

TABLE 1-2 Phosphorus content of atmospheric precipitation Reference

Object of investigation

Time of observation

Baikal area

rain water

Aug. 1951 Jul. 1953 Sep. 1951 Feb. 1952 Jan. 1953

7.8-8.7

tr.4.008

Votintsev, 1954

7.6-8.7

0.00 5-0 .O1 0

Votintsev, 1954

Nov. 1957 Mar. 1958

0.9-5.4

0.003-0.006

Voronkov, 1963a

Nov. 1957 Mar. 1958 Jan. 1958 Mar., Apr. 1958

1.1-15.2

0.009-0.135

Voronkov, 1963a

5-8 11.4-53.2

0.003-0.005 0.0003-0.786

Voronkov, 1963a Voronkov, 1963a

snow water hoarfrost Lowland Altay

new-fallen uncontaminated snow new-fallen snow rime packed snow at end of winter

Mineralization (mg/l)

P( mg/l)

Area

5.4

tr.

Votintsev, 1954

Northern Kazakhstan

packed snow at end of winter

Mar., Apr. 1955-1957

4.0-1 11.3

0.0003-0.786

Voronkov, 1963a

Left bank of Ishim River

packed snow at end of winter

Mar. 1955

4.6-11.5

0.003

Voronkov, 1963b

Various areas

rain and snow waters rain water

1965,1966

-

0.010-0. 120

Semenov et al., 1967

0.0 1 0 4 . 0 30

Bashmakova et al., 1969

of U.S.S.R.

Stavropol’ area Antarctica

snow

Jun.-Nov. 1966

18.09-50.92

Oct. 1961 Jan. 1962

40

n.d

Angino et al., 1964

7 To calculate the balance of dissolved phosphorus in atmospheric precipitation it can be assumed that its average content in the moisture evaporated from the ocean surface is 0.003 mg/l, and in the moisture evaporated from the land surface (taking into account contamination by dust) is 0.010-0.015 mg/l. In that case, 3 t/km3 x 38,000 km3 = 114,000 t is supplied annually by the ocean to the land, and 10-15 t/km3 x 8000 km3 = 80-120 x l o 3 t P from the land to the ocean, which indicates that the role of atmospheric precipitation is relatively small in the exchange of dissolved phosphorus between the ocean and the continents. In addition to moisture, solid particles of dust are present in the atmosphere over the oceans, in concentrations ranging from 0.003 to 10 pg/m in various areas, and f r o m < 2 to 20pm, rarely up to 4 0 p m , in size. The predominant components of the mineralogic composition of the dust usually are illite, chlorite, kaolinite, less often plagioclases and quartz. With strong winds dust is carried for hundreds and thousands of kilometers over the oceans, in particular from the Sahara to the West Atlantic (Barbados island). The results of investigation of the dust collected over the oceans have been described in many works (Aston et al., 1973; Chester, 1972). The total amount of atmospheric dust supplied to the ocean from the land is estimated at 1.6 x lo9 t/yr (Lisitsyn, 1974). In some areas it plays an appreciable role in the total balance of sedimentation, which is confirmed by the presence of minerals of eolian origin in deep-sea bottom sediments (Arrhenius, 1966; Griffin et al., 1968; Rex et al., 1969). Atmospheric dust collected over the tropical part of the Pacific Ocean (Prosper0 and Bonatti, 1969) is similar in composition of the main chemical components to the average composition of the rocks of the earth’s crust (Vinogradov, 1956, 1962; Turekian and Wedepohl, 1961). Apparently this also pertains t o the phosphorus content; thus, in atmospheric dust from the northern Caspian area the phosphorus content ranges from 0.04 to 0.10% (Bruyevich, 1949; Bruyevich and Gudkov, 1953) and averages ~ 0 . 0 7 %Thus . the amount of phosphorus reaching the ocean in the composition of atmospheric dust approaches 1.6 x l o 9 (7 x ) N 1.1x l o 6 t.

River discharge The rivers of the earth which flow into the World Ocean drain an area of about 100 X lo6 km2 (Chebotarev, 1953). Their total annual discharge is 36 x l o 3 km3 of water, 3.3 x lo9 t of dissolved and 13-18 x lo9 t of suspended matter (Alekin, 1966; Lisitsyn, 1974; Lopatin, 1950). The intensity and composition of river discharge depend on the climate, relief, and composition of the rocks and soils in the catchment area (Strakhov. 1960).

8

Phosphorus occurs in the river waters in solution and in suspension, in inorganic and organic forms.

Dissolved inorganic phosphorus. The first data on the content of dissolved inorganic phosphorus in rivers were summarized by Clarke (1924), but as was ascertained later, they were much too high (0.11-0.66 mg/l). Usually the dissolved inorganic phosphorus content in river waters is 0.001-0.08 mg/l (Table 1-3) and only in rare cases 0.1-0.2 mg/l (Almazov, 1955; Yeremenko, 1948; Golterman, 1973). In a natural regime of discharge the maximum phosphorus content in the rivers of the European part of the U.S.S.R. is observed at the time of freezeup, due t o regeneration from dead aquatic organisms, and also at the time of the spring floods due to washing out from the soils. During the growing season the phosphorus content drops t o minimal values (Konenko, 1952). The soils of many areas are substantially depleted in phosphorus compared to argillaceous sedimentary rocks. In the podzol loams of the European part of the U.S.S.R. the phosphorus content averages 0.024%, in podzol sandy loams 0.01% (Zonn, 1967), which dictates the extensive use of inorganic phosphate fertilizers. It is because of this that a local high concentration of dissolved inorganic phosphorus in river waters may occur, particularly at the time of spring floods and after rain (Butkute, 1966; Veselovskiy e t al., 1966). The sharpest fluctuations in concentration of dissolved inorganic phosphorus are characteristic of streams and brooks draining the surface soil layer of tilled fields. At the very beginning of the spring thaw the phosphorus concentration in the streams of northern Kazakhstan and the lowland Altay can reach 0 . 1 4 . 2 m g / l , which is related to enrichment in dissolved phosphates of the uppermost soil layer ( t o 3-5cm), which is characterised by low pH values (‘~5.5-6.5). A few days after the beginning of the thaw the content of phosphorus, and also of nitrates, in the streams decreases t o the background values; at the same time the pH increases t o 7-8 (Voronkov, 1963b; Voronkov and Zubareva, 1963). The phosphorus content of river and brook waters varies with fluctuations in the total mineralization. In the dry inorganic residue of river waters the phosphorus content is within 0.002-0.11% (Table 1-3), averagmg 0.023%. The coefficient of aqueous migration of phosphorus, i.e. the ratio of its content in the inorganic residue of river waters and in rocks of the catchment area (Perel’man, 1961), is 0.2-0.3 on the average, which is an indication of the relatively slight geochemical mobility of phosphorus in the supergene zone. On the basis of degree of mobility in river waters, Strakhov (1960) puts phosphorus, iron, and manganese in the same subgroup. On the basis of the data given in Table 1-3, the average content of dis-

9 solved inorganic phosphorus in rivers, calculated taking into account the annual discharge of the rivers*, is 0.015 mg/l. According to other estimates it ranges from 0.010 (Vinogradov,l967) to 0.100mg/l (Clarke, 1924); in particular, for the rivers of the Black Sea basin the phosphorus content is 0.019 mg/l (Volkov, 1975). Dissolved organic phosphorus. The content of dissolved organic phosphorus in the waters of Kuban’, Don, and Volga ranges within 0.005-0.280 mg/l and in most cases is 1.5-3 times greater than the content of dissolved inorganic phosphorus (Barsukova, 1971; Datsko and Guseynov, 1959,1960; Yeremenko et al., 1953). Obviously this is due t o the fact that river waters are often rich in dissolved organic matter, including organophosphorus compounds. The organic matter content in the dry residue of the waters of the Dnieper, Pripyat’, Ob’, and Ket’ is 7-24% (Glagoleva, 1959; Nesterova, 1960), and in the dry residue of the waters of tropical rivers (La Plata, Rio Negro, Uruguay), up to 50-6096 (Clarke, 1924). On this basis it can be presumed that the average content of dissolved organic phosphorus in river waters is -0.030 mg/l. Suspended phosphorus. The phosphorus content in suspended matter in rivers is within 0.02-0.296. In the subcolloidal fraction of suspended matter it is higher - 0.09-0.37% (see Table 1-3). The ratio of inorganic and organic forms in the composition of suspended phosphorus is very variable and depends mainly on the season and drainage condition of the soils. In the waters of the Don the content of suspended inorganic phosphorus varies from 0.06 t o 0.330 mg/l, of suspended organic phosphorus from 0.000 t o 0.212 mg/l, with mean annual values fluctuating within 0.045-0.142 and 0.030-0.063 mg/l, respectively. In the waters of the Kuban’ the average content of suspended inorganic phosphorus in 1949--1950 was 0.438 mg/l, and of suspended organic phosphorus 0.265 mg/l (Datsko and Guseynov, 1959,1960; Yeremenko et al., 1953). The total amount of suspended phosphorus in river waters is usually much higher than that of dissolved - from a ratio of 9 9 : l t o 1:l.Sharp predominance of suspended phosphorus is characteristic of turbid river waters (Table 1-3). According to most available data, the average phosphorus content in river suspensions is 0.06-0.07% (Bruyevich and Solov’yeva, 1957; Glagoleva, 1959; Gorshkova, 1961; Lubchenko and Belova, 1973; Nesterova, 1960; Pakhomova, 1959). For a turbidity of 360-500 mg/l the content of sus-

* According

t o the data of Alekin (1948,1949,1953), Lopatin (1949,1950,1952),and L’vovich (1945,1953).

F

0

TABLE 1.3 Dissolved and suspended phosphorus in river waters River. point

Water NnOff (km’lyr)

Mineralization (mg/l)

Turbidity (mgll)

Phosphorus dissolved (mK/l)

P ratio suspended (mg/l)

in inorg. residue

in suspension

Reference

(%)

imclll

coarse

tine

SUSP.

diss.

0.06

0.23’

45

55

Glagoleva, 1959

-

-

-

Glagoleva. 1959 Almazov, 1955

-

-

-

Glagoleva. 1959

0.370 0.240

67.1 61.6 69.3

32.3 38.4 30.7

0.011-0).192 (av. 0.073) 0.038 0.120 0.036 0.090

94.2

5.8

Yeremenko e t al., 1953

92.7 97.1

7.3 2.9

Glagoleva, 1959 Glagoleva. 1959

Europe

Dnieper Kherson. 1956 Verkhnedneprovsk. 1956 Kakhovka. 1951

53 180 180 184-357

Ripyat’

13.4

Don Aksay. 1940 Aksny. 1956 Donskaya, 1956

28

Ku ban’ Krasnodar, 1950

11

Danube Reni, 1949

113-350 154 176 201

Izmail. 1956

0.027

-

0.018

0.025-0.116 0.051 0.037

0.0254.330 0.082 0.083

0.005-0.059 0.016 0.021

0.008-0.084

0.008-1.175

0.002-0.072

0.026 0.018

0.330 0.630

0.017 0.011

179

0.021

0.066

132 122 182b

25 1 65 102=

0.017 0.017 0.034

0.088 0.029 0.10

0.013 0.014 0.019

-

431

26347

52.7

-

0.023 0.006-0.045

233

-

RhBne

31-1347 970 1626

-

0.006 0.068 0.009

Rivers of Baltic basin

-

78 155

0.018

0.043 0.020-0.105

0.015-0.180

Kuma

Loire Blois Nantes

-

-

-

13 8.6 255

7.9

5

0.032

257-349

Rioni, 1956 Chorokh, 1956 Volga

Seine Corbeil Pont d e Sevres

24 -

149 184-647 322 177

Krasnodar, 1956 Temryuk, 1956

27

2415‘ -

-

-

-

-

0.0014.074 0.006-0.060

-

-

0.002-0.044

-

0.072 0.052

0.033

-

0.040 0.120 0.045 0.110 0.06-0.28 0.02-0.04d -

-

-

-

-

Yeremenko, 1948 Glagoleva, 1959 Glagoleva, 1959

Almazov, 1955

75

25

Glagoleva, 1959

83.8 63.0 75

16.2 37.0 25

Gkgoleva. 1959 Glagoleva, 1959 Strakhov, 1948,1954

-

-

-

Veselovskiy e t al., 1966 Matisone, 1961

0.025 0.115

0.019 0.107

-

-

-

43 48

57 52

Demolon and Marquis, 1961 Demolon and Marquis, 1961

-

-

-

89 14.5

11 85.5

Demolon and Marquis, 1961 Demolon and Marquis, 1961

-

65

35

Demolon and Marquis, 1961

95.2 90.9 72.8 64.0

4.8 9.1 27.2 36.0

Nesterova. Nesterova. Nesterova, Nestcrova,

-

-

-

-

0.006 0.130

0.049 0.022

-

-

0.024

0.039

97.31 96.48 88.20 83.18

512 259 63 44

0.020 0.023 0.025 0.027

0.397 0.231 0.067 0.048

Ash Ob’, 1958 Barnaul Kolpashevo Sugut

Salekhard

394 0.021 0.024 0.028 0.032

0.075 0.085 0.111 0.114

0.111 0.143 -

-

1960 1960 1960 1960

Ket'. 1958 Syr-Dar'ya Amu-Dar'ya Yenisey Chu

-

65.87 432b 421b 140'

14 42 548 1.5

500a

47 1160' 2510E 19c 65gE

70

168'

1250

590 3187

146' 53

1200

-

0.087 0.757 3.750 0.034 0.340

-

0.476

-

0.750

0.031 0.008e 0.010=

-

0.047 0.002 0.002

-

0.200 0.13.0.07e 0.21.0 . 0 P -

73.7 99 99.8 -

26.3 1 0.2

-

Nesterova. 1960 Strakhov. 1948,1954 Strakhov. 1948,1954 Strakhov, 1948.1954 Straknov. 1948.1954

Apia

Nile

Shakhov. 1948,1954

America MisJissippi Amazon

-

0.0034.08 (av. 0.013)

-

-

0.008-0.11 (av. 0.024)

'

'Strakhov, 1948. Alekm, 1953. Lopatm, 1948. Pakhomova, 1959, Bruyevlch and Solov'yeva, 1957. Clarke, 1924

Strakhov, 1948,1954 Gihbs, 1972

12 pended inorganic phosphorus in river ‘waters is 0.200-0.350 mg/l or 8090% of the total phosphorus in rivers. On the basis of these estimates it can be concluded that ~ 0 . million 5 tons of dissolved inorganic and ~1million tons of dissolved organic phosphorus and 10 million tons of suspended, chiefly inorganic, phosphorus reach the ocean every year in river discharge. Other authors have estimated the total amount of dissolved phosphorus brought t o the ocean each year by rivers in figures from 0.7 to 1.9 million tons (Holland, 1971; Riley and Chester, 1971; Stumm, 1972).

Underground discharge A substantial part of the waters draining the continents goes through a stage of underground discharge and then reaches river arteries and becomes part of the river run-off (Makarenko and Zverev, 1970). In addition t o this, there are centers of discharge of ground water in the seas and oceans, sometimes at a considerable distance from the shore (Buachidze and Meliva, 1967). The mineralization of ground waters from different areas ranges from 1 or 2 to 100-200 g/l, and the phosphorus content from traces to a few milligrams per litre (Clarke, 1924). In Caucasus mineral waters the phosphorus content is from 0.003 mg/l (Smirnovskiy spring, Zheleznovodsk) t o 0.053 mg/l (Yekaterina spring, Borzhomi); in the waters of the Polyustrov and Rakhmanov springs i t is 0.13 and 0.4 mg/l, respectively (Alekin, 1953). In the reservoir drainage and ground waters of the Rostov district the phosphorus content ranges within 0.055-0.071 mg/l, and in well waters there, within 0.001-0.014 mg/l (Alekin e t al., 1969). The usual phosphorus content in the inorganic residue of ground waters is thousandths and hundredths of a percent, in isolated cases tenths of a percent . The phosphorus content in ground waters does not depend on their total mineralization or hydrochemical type. Apparently i t is determined primarily by the overall composition of the rocks being drained and by the aggressiveness of the waters with respect to inorganic phosphate compounds, i.e. it is ultimately related to the whole complicated geochemical evolution of ground waters. At present it is impossible t o suggest any criteria for estimating the average phosphorus content in ground waters. Determination of the volume of underground discharge into the seas and oceans is a very complicated matter. A typical example is the underground discharge into the Caspian Sea, which has been investigated for many years using hydrogeological methods. In the opinion of Kudelin

13 (1948), ' ~ km3 3 of water, or 1%of the total volume of river discharge, reaches the Caspian Sea annually from underground discharge. Other estimates give from 0.3 to 49.3 km3 /yr, i.e. the data diverge 160-fold (Apollov, 1935; Zektser et al., 1967; Ulanov, 1965). From the example of several seas of the U.S.S.R. it has been ascertained that some ions (Ca2+,Mg2+,SO,"-, HCOj ) reach them chiefly in the composition of river discharge, others (Na+, Cl-, I-, B-, Br-) in the composition of underground discharge (Glazovskiy , 1976). Phosphate ion apparently belongs to the first group. Glacier discharge At the present time, continental and sea ice occupies about 20%of the area of the earth; its load of sediment reaches 1%,and the total amount of this material reaching the ocean is about 1.5 x lo9 t/yr (Lisitsyn, 1974). For an average phosphorus content of -0.07% in the composition of the detrital material of glacier discharge, about 1 million tons of phosphorus is deposited on the ocean floor annually.

Coastal a brasion The coasts of the World Ocean, the length of which amounts to about 400,000 km, are subject to wave and ice action which is most intensive in the humid zones. The amount of abraded material is estimated at 0.3 X lo9 t/yr (Leont'yev, 1963), and the amount of phosphorus in it, ' ~ 0 . 2million tons.

Volcanism The role of volcanism in the formation of the water mass and salt content of the ocean is tremendous. The ultimate source of all the main anions of ocean water is acid fumes of volcanic eruptions, liberated in degassing of the mantle (Vinogradov, 1959, 1964, 1967). In present conditions, -66 km3 of volcanogenic hot springs (Rubey, 1951) and 2-3 x lo9 t of volcanics (Lisitsyn, 1974) reach the surface from the depths of the earth annually. The phosphorus content in thermal waters (Table 1-4) fluctuates exceedingly widely - from traces t o 111 mg/l. I t is not related to the total mineralization of the hot springs, but shows a slight positive correlation with iron. In the dry residue the phosphorus content ranges from 0.001 t o 0.63% and in the deposits precipitated from thermal waters, from analytical zero in siliceous material from the flank of Mendeleyev volcano (Kunashir Island) to 12.6%in the iron phosphate from Tjiater spring (Central Java) (Zelenov,

TABLE 1-4 Phosphorus in thermal waters and geysers Sampling site

Uzon caldera, Kamchatka Lower Mendelevev spring, Kunashir Island Upper Doctor spring, Kunashir Island Biryuzovoye Lake, Simushir Island, 1933 1958 Crater lake of Kawah IdjenNolcano. East Java Tjiater spring, Central Java Cameron spring, Rotorua, New Zealand Hot Lake, White Island. New Zealand Yellow Crater lake, Taal volcano, Philippines Green Crater lake, Taal volcano, Philippines Yellowstone geysers, U.S.A. Teterata geyser, New Zealand Caldera of Santorin volcano. Aeaean Sea Atlantis I1 basin. Red Sea, metalliferous brine interstitial brine a

2.124.35

674-3778

0-85.2

0-152

0-2.0

0-0.026

04.026

Lebedev, 1975

1.70-2.06

2747-4027

0.7-1.8

60-95

7.8-1 1.6

1.1-1.9

0.044.07

Lebedev. 1975

5.03-12.58

0.7-1.5

0.03-0.04

Lebedev, 1975

0.05

-

0.28 0.884.91

0.007 0.023

Zelenov, 1972 Zelenov, 1972

-

9

0.009

Zelenov, 1972

0.43-0.97

0.007

Van Bemmelen. 1949

tr.

1.8-2.1

1890-4330

0.5-7.5

6.8 3.30

3768 3616-4008

0.05 4.99-6.56

0.02

106.336

2.32-2.81

361.42

850-1018 1862

-

158,051

9448

-

26,989

1444

6-8

60,023 1336-1388 2064 ca. 37,000

5.61'

256,840b

6.1-6.5'.'

250,000

-

-

1496.54

1.4-2.0

4.00-16.65'

-

-

15.7-89.0

5.94

3330

-

-

-

tr.

210 618 tr.-2.0=

0.001

Clarke, 1924

987

0.63

Clarke, 1924

-

111

0.42

Clarke, 1924

-

143

0.14 0.002

Clarke, 1924 Clarke, 1924

0.001

Clarke, 1924

tr.

tr.

2.9=

-

tr.

0.36-2.0

0.05-2.05

0.004-0.04

60-95 b'e (total) 4(t174"' (total)

70-98b'e

5.89d

60-274'.'

0.03-8.48'

'

t o 0.0001

0.002 to 0.003

Hartmann. 1969; Brewer et al.. 1969;' Brewer and Spenser, 1969; Dietrich and Krause. 1969;' Brooks et al.. 1969; Hendricks et al.. 1969

Pushkina, 1967

TABLE 1-5 Distribution of absolute amounts of elements (in geograms, or lo2' g) in sediments, waters, and igneous rocks weathered during the geologic history of the earth (Horn and Adams, 1966) Element

Sediments continental

1

c1 S B Br I Mo Mn Na K Ca Fe P U

38.7 3.17 0.130 0.00571 0.00444 0.00192 0.573 38.3 44.6 159 69.3 1.50 0.00774

Connate water

Ocean water

oceanic shelf

2 116 8.96 0.429 0.0108 0.0149 0.00594 1.44 104 151 208 228 4.85 0.0235

hemipelagic 3

74.5 9.20 0.346 0.200 0.000186 0.0223 27.2 170 203 210 355 10.1 0.0153

Weathered igneous rocks

Difference (1i2 3 i4 + 5+6)-7

pelagic

4 45.6 5.52 0.206 0.124 0.000114 0.0137 16.1 102 120 155 210 5.99 0.00912

5 27.8 1.32 0.00703 0.0953 73.3 X 14.7 X 22.93 X 15.4 0.557 0.586 14.7 X 103 X 44 X

6 267 12.6 0.0673 0.912 0.000701 0.00014 28.1 X 147 5.33 5.61 0.00014 0.000982 0.000421

7 9.79 10.6 0.245 0.0639 0.0102 0.0306 22.4 572 524 739 862 22.4 0.0561

559 30.2 0.940 1.28 0.00102 0.0134 22.9 0 0 0 0 0 0

16 1972). The phosphorus content in iron ore precipitates from the Atlantis I1 basin in the Red Sea is 0.3--0.4% (Hendricks et al., 1969; James, 1969),from the caldera of Santorin volcano in the Mediterranean Sea 0.25-1.6495 (Butuzova, 1968), and in the ore precipitates of steam vents in New Zealand, up to 3%(Weissberg, 1969). There is no correlation between phosphorus and iron in these precipitates. Evidently phosphorus and iron can migrate either together or separately at different stages of the hydrothermal process. High, although not very much so, phosphorus contents related t o submarine eruptions have been observed in the waters off the shores of Japan (0.05-4.06 mg/l) (Okada, 1936) and in the Tyrrhenian Sea (0.013 mg/l; buljan, 1954, 1955). The dissolved hydrothermal phosphorus coming into the ocean is in part disseminated in the water layer, in part deposited along with the accompanying iron. It has been established that the sediments of the Red Sea, Pacific and Atlantic Oceans that are rich in hydrothermal and volcanogenic iron are also rich in phosphorus, but its source may not be hot springs so much as sea water with a background content of phosphorus sorbed by iron hydroxides*. The origin of the elements in the ocean can be judged from their absolute amounts liberated in the weathering of igneous rocks during the geologic history of the earth and entering into sedimentary rocks, ocean sediments, and water. The results of such calculation suggest that the main anions of sea water are undoubtedly volcanogenic, but on the whole volcanogenic sources play a secondary role in the balance of phosphorus, and also of iron and several other cations (Table 1-5).

Cosmogenic material The amount of cosmic dust falling on the earth’s surface amounts t o -10 x l o 6 t/yr (Lisitsyn, 1974). The phosphorus content in cosmic material can be judged from the composition of meteorites. Stony meteorites contain 0.04-0.38% P, stony-iron meteorites 0.006-0.2% P, iron meteorites 0.02-0.94% P, and the samples of lunar rocks collected by “Apollo 11” 0.04-0.32% P (Moore, 1973). For an average content of 0.2-0.3%, the total amount of phosphorus reaching the ocean from cosmogenic material is not more than 30,000 t/yr. On the basis of the data given it can be concluded that 15-20 million tons of phosphorus reach the World Ocean annually in the solid phases and more than 1.5 million tons in solution (Table 1-6).

* See sections below dealing with deposition of phosphorus from waters and phosphorus in sediments.

17 TABLE 1-6 Introduction of suspended and dissolved phosphorus into the World Ocean Source

Phosphorus in solid phases Eolian River suspensions Glacial discharge Coastal abrasion Volcaniclastic Cosmic dust

Dissolved phosphorus River discharge Volcanic exhalations Underground discharge*

Amount of material ( l o 9 t)

Average P content

(%I

Absolute mass of P(106 t )

1.6 13-18 1.5 0.3 2-3 0.01

0.07 0.07 0.07 0.07 0.1 0.3 ( ? )

1.1 9-1 4 1 0.2 2-3 0.03

36 X l o 3 km3 66 km3 -

0.045 mg/l 1 mg/l -

1.5 0.066

-

* Volume of underground discharge and its phosphorus content not established. PHOSPHORUS IN WATERS

Phosphorus dissolved and suspended in sea and ocean waters occurs in inorganic and organic forms. The ratio between them varies considerably depending on the season, depth, and local conditions in the basin.

Dissolved inorganic phosphorus In the surface waters of the seas the content of dissolved inorganic phosphorus ranges from 0.1 to 40pg/l (Table 1-7). At a time of intensive proliferation of phytoplankton it drops to analytical zero, and before the growing season it reaches a maximum. In the deep waters of the seas the phosphorus content as a rule is considerably higher and relatively constant. In aerated basins the maximum phosphorus content in deep waters reaches 100-130pg/l (Sea of Okhotsk and Bering Sea), in the waters of stagnant basins 300 pg/l (Black and Baltic Seas, Norwegian fjords). In the surface layer of the waters of the open ocean the phosphorus content varies widely, from analytical zero to tens of micrograms per liter (Table 1-8). In a period of proliferation of phytoplankton it is minimal, as in the seas, but after the growing season it rises to 3 - 6 p g / l in the tropics and 60-68 pg/l in polar regions. In intermediate layers of water the content of dissolved inorganic phosphorus reaches a maximum, and in different parts of the

18 TABLE 1-7 Content of dissolved inorganic phosphorus (pg/l) in sea waters Sea

Surface waters

Deep waters

Aral

0.7-3.1

0.0-17

Blinov, 1956; Bruyevich and Solov’yeva, 1957

Caspian North Central South

0.0-35 0.1-15 0.1-17

8-7 5 7-78

Bruyevich, 1937 Bruyevich, 1937 Bruyevich, 1937

Black

7-40

107-299

Azov

0.0-22

4-200

Mediterranean

0.0-6.5

2.2-13

Bernard, 1939; McGill, 1961; Thompson, 1 9 3 1

Adriatic

0.2-20

-

White Baltic Gotland basin Landsort basin h a n d basin Barents Bering Okhotsk Japan Norwegian fjords

Reference

Bruyevich, 1953; Datsko, 1959; Dobrzhanskaya, 1960; Skopintsev, 1975; Fonselius, 1974 Bronfman, 1972; Datsko, 1959

.2-30

to 46

5.5-14 7 .l-7.8 9-10

28-309 13-8 5 10-20

ErcegoviE, 1934; Scaccini-Cicatelli, 1972 Bruyevich, 1960, Trofimov and Golubchik, 1947 Chernovskaya et al., 1965 Chernovskaya e t al., 1965 Chernovskaya e t al., 1965

20

Bruyevich, 1948

20-87

80-130

Ivanenkov, 1964; Mokiyevskaya, 1959; Wardani, 1960

0.0-20

60-100

Bruyevich e t al., 1960; Mokiyevskaya, 1958

5-20 -

5 0-6 0

Bruyevich e t al., 1960

6

to 300

Strom, 1936

ocean this maximum occurs at different depths (Fig. 1-1).In the northeastern part of the Pacific Ocean the maximum phosphorus content (105 pg/l) is characteristic of depths of about 400 m, and in the southwestern part in the Coral Sea region, it is -60pgll and is observed at a depth of about 2200 m. Below the layer of the maximum the phosphorus content decreases somewhat, and in deep waters it again reaches about the same values as in the intermediate layer. The average weighted concentration of dissolved inorganic phosphorus is: in the Atlantic Ocean 55pg/l, in the Indian 68, in the Pacific 77, and the average of the waters of the World Ocean 72. Dissolved inorganic phosphorus

19 TABLE 1-8 Average content of phosphorus (pg/l) in the meridional strip 150-160' hemisphere, summer, Pacific Ocean (Chemistry of the Pacific Ocean, 1966) Depth (m)

50-40'

0 25

37 46

N

E, northern

4C+3Oo N

30-20'N

20-10'N

10-O'N

0-10's

7 5

1.5 1.5

2 2

1 1

3 5

constitutes %90%of the total content in the ocean (Chemistry of the Pacific Ocean, 1966). The proportions of the forms of dissolved inorganic phosphorus depend on the salinity, temperature, and pH of the water (Fig. 1-2). In ocean water of normal salinity (35Yo0)at 20°C and pH of 8 the proportions of the forms are as follows: H,POi = 1%,HPOi- = 87%;and PO:- = 12%;99.6%of the phosphate ions form single-charge complexes with Ca2+and Mg2+ (Kester and Pytkowicz, 1967). The complete spectrum of the forms of phosphorus in sea water has the following aspect (5%) (Atlas et al., 1976): MgHPOi

HP0:-

NaHPO:

Cap040 CaHP0:

MgPO;

H2P04 NaH2P0i

41.4

28.7

15.0

7.6

1.5

0.9

4.7

0.1

MgH2PO; PO:-

NaPO:.

CaH2POr

0.1

0.01

0.01

0.01

The average residence time of dissolved phosphorus in the waters of the World Ocean is estimated as 160,000 (Ronov and Korzina, 1960) t o 270,000 years (Vinogradov, 1967). Starting from an amount of water in the World Ocean of 2/14 x lo" t (Vinogradov, 1967; Poldervaart, 1955), an average % P in it, and an average content of dissolved inorganic content of 7.2 x phosphorus in river discharge of 1 . 5 x %, we obtained a figure close to those given above -200,000 years. If the organic phosphorus in river discharge is taken into account, this figure is halved. However, it cannot be taken as the average value, inasmuch as the present epoch is characterized by maximum development of land areas with relatively high relief and correspondingly high rates of erosion (Ronov and Korzina, 1960). In addition, the anthropogenic factor, which causes an acceleration of erosion of soils and contamination of rivers by organic phosphorus from industrial and agricultural waste, must be taken into account.

Dissolved organic phosphorus The content of dissolved organic phosphorus in the surface waters of the seas ranges from 6 to 60 pg/l; at depth it gradually decreases. In most cases the maximum content is observed in shallow-water areas, especially near the shore (Datsko, 1959; Mokiyevskaya, 1958).

20

6C

63

4c

40

20

20

I

<

6

3

20

2.0

40

40

60

50

Fig. 1-1. Depth of layer of maximum concentration of phosphorus in the Pacific Ocean (Chemistry of the Pacific Ocean, 1966).

In the surface layer of ocean waters the dissolved organic phosphorus content ranges from 0 t o 40pg/l; the maximum values here are recorded in the spring in cold waters in the zone of the Oyashio current, minimum values in subtropical regions (Chemistry of the Pacific Ocean, 1966). In deep waters the dissolved organic phosphorus content usually decreases

21

60 PH

80

70 PH

90 PH

Fig. 1-2. Forms and proportions of dissolved inorganic phosphorus in waters (Kester and ; K3 = 4.80 X ; K z = 6.23 X Pytkowicz, 1967). (a) Fresh water ( K , = 7.52 x ; K ; = 0.10 X ;K ; = 0.41 X 10-13). ( b ) 0.68M solution of NaCl ( K ; = 2.83 x ; K ; = 1.37 X lo-'). ;K ; = 0.88 x 1 0 - l o ) . (c) Sea water ( K ; = 2.35 x

t o analytical zero, but in isolated cases it has been found a t depths of ?J 1000 -2000m in amounts up to 40--68pg/l, which is higher than its concentration in surface waters (Strickland and Austin, 1960). The reason for this is not yet clear. A general regularity is characteristic of the distribution of the forms of dissolved phosphorus in the waters of the seas and oceans: in the surface waters organic phosphorus usually predominates, and at depths below the 50-100 m horizon, inorganic (Fig. 1-3). On the whole, dissolved organic phosphorus constitutes 5-796 of the total phosphorus content in the ocean (Chemistry of the Pacific Ocean, 1966). It is assumed that it occurs in the form of phospho- and nucleoproteins, phospholipids, and products of their decomposition (Armstrong, 1965). S i x unidentified organophosphorus compounds were secreted from sea water containing phytoplankton (Watt and Hayes, 1963).

Extent of saturation of sea and ocean waters with calcium phosphate The question of the saturation of sea water with calcium phosphate was first raised by Kazakov (1937, 1939), who advanced the idea of chemogenic deposition of phosphates. Subsequently many investigators determined the extent of saturation of sea waters with phosphates using thermodynamic calculations and model

22 P, r g - o t / l 04

08

1.2

16

2.0

QOOt 1 2000

24

\

f

4000

Fig. 1-3. Vertical distribution of dissolved inorganic and organic phosphorus in the equatorial zone of the Pacific Ocean (Chemistry of the Pacific Ocean, 1966).

experiments which, however, did not yield unequivocal results. Thus, according to Mikhaylov’s (1968) calculations, the phosphorus content in equilibrium with hydroxylapatite in sea water is 0.02 mg/l, i.e. sea water is supersaturated with phosphorus by three- to four-fold on the average. According to other data, sea water is in equilibrium with or undersaturated in calcium phosphate (Skopintsev, 1972; Kester and Pytkowicz, 1967). The opinion was also expressed that because of the complex composition of sea water any attempts to determine the extent of saturation with calcium phosphate are open to question (Pytkowicz and Kester, 1967). According to experimental data, when calcium phosphate is precipitated from artificial sea water the equilibrium concentration of phosphorus ranges from 0.11--0.15mg/l (Smirnov, 1972; Smirnov et al., 1962) to 2.13-7.97 mg/l (Rozhkova et al., 1962), and from natural sea water, from 0.12-0.7 to 11 mg/l (Ayvazova and Fedosov, 1972; Dmitrenko and Pavlova, 1962). In the experiments by Smimov, who obtained the lowest figures for the

23 solubility of calcium phosphate, he used artificial sea water containing no magnesium, the presence of which increases the solubility of phosphates (Martens and Harris, 1970; Nathan and Lucas, 1977). Thus on the whole the experiments indicate that sea water is undersaturated in calcium phosphate. It should also be kept in mind that hydroxylapatite and fluorapatite are less soluble in sea water than fluor-carbonate-apatite (Atlas and Pytkowicz, 1977; Kramer, 1964), which represents the greater part of marine phosphorites. This shows that the formation of phosphorites is not produced by chemogenic precipitation of calcium phosphate from sea water, but by other factors. These conclusions are confirmed by some new calculated and empirical data obtained at a much higher theoretical and experimental level than before, which fully take into account the form of phosphorus in sea water and are based on new data on the ion activity ratios and thermodynamic model of sea water (Savenko, 1977a,b, 1978a,b, 1979). According t o these data the solubility of calcium phosphate in sea water and interstitial waters is determined mainly by their alkalinity, and the total concentration of dissolved inorganic phosphorus theoretically is expressed by the formula (Savenko, 1979): [ZP] = 3.6 X

[Alk] 0.72

Calcium phosphate is precipitated directly from sea water when the phosphorus concentration is of the order of a few milligrams per liter. A t the same time, the solubility of natural calcium phosphates in sea water depends on their aggregate state, density and degree of crystallinity. The equilibrium concentration of phosphorus in seawater leaching samples of Khibiny apatite and Yegor’yev phosphorite is 0.1-0.2 mg/l; of a Recent phosphorite concretion of the dense variety from the shelf of Namibia, up to 0.5 mg/l; and of freshly precipitated phosphates, 4-37 mg/l. These results completely rule out the possibility of chemical precipitation of phosphate from ordinary sea and ocean waters under natural conditions (Baturin and Savenko, 1980). PHOSPHORUS IN SUSPENSION

The phosphorus content in marine and ocean suspensions ranges from 0.1 to 0.87% (Table 1-9) and averages -0.3%. The highest contents are observed in the peripheral areas of the ocean and in zones of upwelling. A correlation is often observed between the P and Corg contents, which indicates that suspended phosphorus is related to living and dead organic matter. This also is confirmed by data on the granulometry of suspended

24 TABLE 1-9 Phosphorus in suspension in the upper horizons of ocean waters (Bogdanov et al., 1971)

P content, in % of dry substance Frequency of occurrence (%) P content (pg/l) Frequency of occurrence (%)

<0.1 1.7 <1

29.0

0.1-0.2

0.2-0.4

0.4-0.8

20.1

37.4

39.1

1-2

2-4

4-8

24.6

27.4

15.1

>0.8

1.7 >8 3.9

matter. In the 0.01-mm fraction, in which whole valves with plasma are concentrated, it is appreciably higher (Bogdanov et al., 1971; Lisitsyn, 1964). The C:P ratio by weight in suspended matter from the upper layers of ocean water ranges from 10 (occasionally lower) t o 53 and on the whole is close to the C:P ratio in total plankton. In suspensions from deep horizons this ratio is substantially higher due t o the relatively greater mobility of phosphorus and averages % l o 0 (Bogdanov et al., 1971; Lisitsyn, 1964; Menzel and Ryther, 1964). In the productive areas of the ocean, in high latitudes, the amount of phosphorus in suspension in surface waters is 6-30 times less than that of dissolved phosphorus. In subtropical and tropical zones these amounts are comparable, which is evidence of the limited effect of dissolved phosphorus on the development of phytoplankton. As a whole, suspended phosphorus, which is mainly organic, constitutes 3-596 of its total content in the ocean (Chemistry of the Pacific Ocean, 1966). In individual areas, for instance in the northern part of the tropical Atlantic in the 200-1000 m horizons, appreciable amounts of suspended inorganic phosphorus have been found (Volostnykh, 1973), apparently related to clastic particles. In investigating suspended matter collected in the Pacific, Indian, and Atlantic Oceans, including the zones where phosphorite occurs, no chemogenic calcium phosphate has been found (Bogdanov and Lisitsyn, 1968; Klenova, 1964; Lisitsyn, 1964, 1974; Lisitsyn et al., 1973; Pustel’ nikov, 1973). PHOSPHORUS IN ORGANISMS

Phosphorus plays a very important role in the genetics and metabolism of

25 living matter, inasmuch as it is a structural element of enzymes, adenosine triphosphate, ribonucleic acid, desoxyribonucleic acid, nucleic acids, and phospholipids, from which cell membranes are made. In the form of organophosphorus compounds it takes part in various biochemical energy-transfer reactions in the tissues of plants and animals (Matheja and Degens, 1971). The phosphorus content in the tissues of terrestrial organisms usually ranges between 0.1 and 1%of dry weight. Higher contents (up to 3-5%) are characteristic of some bacteria and viruses, in whose cells there are many phospholipids and nucleic acids (Altman and Dittmar, 1964; Matheja and Degens, 1971; Spector, 1956). Among marine phytoplanktonic organisms, the richest in phosphorus are the green, golden, and diatomaceous algae - u p to 2-376 by dry weight (Table 1-10). A weight ratio of C:P = 2 4 : l is typical of diatomaceous plankton, 60:l of the peridiniums (Lisitsyn, 1964). On the average it is 42:l for phytoplankton and 40:l for zooplankton (Sverdrup et al., 1946). The average atomic ratio C:N:P is 106:16:1 for marine plankton (Redfield et al., 1963). TABLE 1-10 Phosphorus content (% b y dry weight) in marine plants Organisms

P

Reference

Diatoms

0.83 0.66 0.4-2.0 0.31-1.2 7 1.03-2.17 0.57 0.57 1 .l--1.3 2.7 1.0-2.0 3.3 0.23-0.54 tr.-O.21 0.04-0.28 0.O38-0.247 1.2-3.0 1.4 0.8 0.57

Ketchum and Redfield, 1949 Riley et al., 1956 Parsons e t al., 1961 Vinogradov, 1953 Vinogradov, 1953 Brandt and Raben, 1920 Riley e t al., 1956 Parsons et al., 1961 Ketchum and Redfield, 1949 Krauss, 1956 Parsons et al., 1961 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Parsons et al., 1961 Parsons et al., 1961 Vinogradov, 1953 Gorshkova, 1961

0.3-5 .O

Vinogradova and Koval’skiy, 1962; Vinogradova and Petkevich, 1967

Diatoms, in ash Peridineans Green algae Bluegreen algae Calcareous algae Brown algae Red algae Golden algae Mixophytes Phytoplankton of Sea of Azov Ash of Black Sea phytoplankton

TABLE 1-11 Phosphorus content (% by dry weight) in marine animals Organisms Stomatopod and amphipod tests Decapod tests* Copepods Euphausiids-Mysids Chaetognaths Polychaete tubes Siphonophores Pteropods Medusae Medusae* Black Sea zooplankton* Sponges* Corals* Bry ozoa* Echinoderms Echinoderms, skeletons* Starfish* Ophiura* Crinoidea* Tunicates Crustacea lobster shells* flesh of crustacea Mollusks (whole) mollusk shells* soft tissues flesh of mollusks Carbonate brachiopods Phosphatic brachiopods Lingulas * Fish (whole) flesh soft tissues soft tissues* scales bones

* In ash. ** Average values.

P 0.80-1.2 6 3.60-9.9 1 0.88-5.2 0 0.37-1.03 0.69-0.87 (0.79)** 1.39-1.60 (1.48) 0.46-0.71 (0.63) 0.44-1.80 (0.99) 2.84-9.38 0.05-0.18 (0.14) 0.23-0.38 (0.30) 0.12-0.44 (0.17) 0.08-1.40 u p to 10 tr.-3.9 5 tr.-3.7 3 tr.-0.53 0.14-2.66 tr.-0.80 tr.-0.16 tr.-0.23 tr.-0.22 0.51 0.10-2.35 2.34-6.15 0.8-1.7 0.29-0.46 tr.-1.59 0.55-2.55 0.7-1.7 tr.-0.12 15.8 7-1 7.16 14.9 5-1 8.7 4 0.94-1.84 (1.40) 0.7-3.2 0.1 1-1.1 1 5.96-1 8.92 6.5-8.3 u p to 1 6

Reference Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Beers, 1966 Beers, 1966 Beers, 1966 Beers, 1966 Vinogradov, 1953 Beers, 1966 Beers, 1966 Beers, 1966 Vinogradov, 1953 Vinogradova and Petkevich, 1967 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Kizevetter, 1973 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Kizevetter, 1973 Vinogradov, 1953 Vinogradov, 1953 Vinogradov, 1953 Beers, 1966 Kizevetter, 1973 Vinogradov, 1953 Vinogradov, 1953 Kizevetter, 1973 Kizevetter, 1973

27 In the tissues of marine animals phosphorus is most highly concentrated in chitin, scales, and bones (up to 6-16%), and also in the shells of some brachiopods. In the soft tissues the phosphorus content is much less - from 0.5 to 3.2%(Table 1-11). The phosphorus content in marine organisms depends strongly on the conditions of growth and food supply. Thus, when water is depleted in phosphorus, the phosphorus content of phytoplankton may be reduced five-fold compared to normal for a given species (Ketchum, 1939a; Ketchum and Redfield, 1949). On the other hand, in the case of a high phosphorus content in the water it accumulates to excess in phytoplankton; with the onset of prolific cell division this excess phosphorus is liberated and used for their growth (Goldberg et al., 1951; Ketchum, 1939b; Matsue, 1949). The greater part of phosphorus in phytoplanktonic organisms occurs in the form of organophosphorus compounds, much less in the form of inorganic polyphosphates ( Amon, 1956). Inorganic phosphorus predominates in the scales and bones of fish and marine animals. In most organic compounds the phosphorus occurs in the form of phosphoric acid derivatives. In addition, compounds with a phosphorus-carbon bond also are found in marine animal organisms (Quin and Shelburne, 1969). On the basis of the degree of biochemical mobility in organisms, labile and firmly bound phosphorus are distinguished. The phosphorus in phytoplankton is chiefly labile, but in diatomaceous algae there also is present firmly bound phosphorus which does not go into solution even after prolonged storage of samples (Goldberg et d., 1951). In the shells of Culunus, firmly bound phosphorus constitutes 94-99% of its bulk content in these organisms (Conover, 1961).

RECYCLING O F PHOSPHORUS IN WATER

Along with other biogenic elements in the ocean, phosphorus takes part in an intensive biological cycle (Table 1-12). According to the estimates of a number of investigators, in the course of primary productivity oceanic plankton creates 1-7 x 1OI6 g C,,,/yr (Vinogradov, 1967; Koblents-Mishke et al., 1970; Nielsen and Jensen, 1957; Ryther, 1959, 1970). Up to 1.7 x 10'' g of phosphorus, which is equivalent to its content in the whole photic layer of the ocean, is required for this. Thus, if the phosphorus entering into the composition of living matter were completely removed from the biologic cycle after the organisms die, its reserves in the ocean would be exhausted in a few hundred years. But this

TABLE 1-12 Biomass and productivity in the ocean (according to maximum estimate)

Phytoplankton Bacteria Zooplankton

~~

~~

~~

Organism

Biomass (8)

Productivity (g/yr)

wet wt.

Corg

P

wet wt.

Corg

P

1.0 X 10l6 1.4 x 1014 1.5 X 10l6

1.0 x 1015 1.4 x 1013 1 5 x 1015

2.5 x 1013 3.5 x 10" 3.75 x 1013

7.0 x lo1' 1.4 x 1017 5.0 X 10l6

7.0 X 10l6 1.4 X 10l6 5.0 x 1015

1.75 x 1015 3.5 x 1014 1.25 x 1014

Wet weight and Corg, after Vinogradov (1967);P, from ratio C:P = 40:l.

29 does not occur, due to the fact that phosphorus is again included in the biologic cycle. By far the greatest part (more than 99%) of organic matter produced in the ocean, including organophosphorus compounds, is completely mineralized and dissolved (recycled) with the help of bacteria in the water layer and does not reach the bottom (Bruyevich, 1953; Skopintsev, 1950). The rate of recycling depends on many factors, in particular on temperature, content of biogenic elements and productivity of the waters, which in tum are subject to substantial seasonal fluctuations. The lower the content of dissolved phosphorus and the larger the populations of phytoplankton and bacteria in the water, the more rapidly the cycle is completed. In some productive lakes the tum-over time of dissolved inorganic phosphorus is only a few minutes (Pomeroy, 1960; Rigler, 1956), and in productive near-shore ocean waters it is 1.5 days (Watt and Hayes, 1963). In the waters of the Sea of AZOV,according t o Datsko’s (1959) calculation, total phosphorus “turns over” 8 times a year. The recycling of phosphorus in productive waters can be traced specifically only with the aid of the radioactive phosphorus isotope 32P, inasmuch as this element is utilized instantly and phytoplankton can develop even in water with analytically undectectable traces of phosphorus (Harris, 1957; Pomeroy, 1960; Redfield et al., 1963). Thus its consumers-marine organisms-play the main role in the recycling of phosphorus. The total amount of phosphorus released every day to the surrounding waters by phytoplankton in the course of its life activity is 50--100% of its total content in organisms (Pomeroy et al., 1963; Satomi and Pomeroy, 1965; Watt and Hayes, 1963). In the region of the Peruvian current zooplankton yields from 0.1 t o 3.1 mg P/m2 day, and the anchovy more than 350 mg P/m2 day (Whitledge and Packard, 1971). The atomic ratio N:P decreases in each succeeding link of the food chain: in phytoplankton it averages 16:1, in the feces of zooplankton 7:1, and in the feces of the anchovy 4:1, which indicates more complete and more rapid release of phosphorus by higher organisms (Ketchum, 1962; Whitledge and Packard, 1971). In laboratory tests of the decomposition of diatomaceous plankton (Grill and Richards, 1964) the relationship between the forms of phosphorus changed repeatedly in connection with the activity of microorganisms; at the end of a year 64% of the total phosphorus was in dissolved inorganic, 4% in dissolved organic, and 32% in suspended form. In another analogous series of experiments the ratios of biogenic elements in solution increased: AN:AP from 5:l to 1 6 : l and ASi:AP from 1 O : l to 62:l. Thus in the first stage of decomposition phosphorus is characterized by a relatively high rate of recycling, and in the next, silica (Calvert and Price, 1971b).

30 DEPOSITION OF PHOSPHORUS FROM WATERS

The deposition of phosphorus dissolved in the waters of the seas and oceans takes place via several paths the importance of which is not equal, and may vary depending on local conditions. Deposition in the composition of biogenic detritus and coprolites Phosphorus is closely related to organic carbon in the biologic cycle. To a considerable extent this relationship is inherited over different stages of decomposition of organic matter, as indicated by the regularities of the C:P ratio and the correlation of these elements in living matter, biogenic suspensions, and also in bottom sediments. Owing to this, an estimate of the amount of phosphorus deposited on the bottom and buried in sediments in the composition of biogenic detritus can be made on the basis of the Corg balance. The total value of the primary productivity of the ocean is -20 x lo9 t C,,,/yr (Koblents-Mishke et al., 1970), but only 0.5% of this material, or about 100 x lo6 t Corg(Uspenskiy, 1970), is buried in bottom’ sediments. Taking into account the fact that the C:P ratio in near-bottom suspensions averages 100:1, the amount of phosphorus buried along with organic matter can be estimated at 1 x lo6 t, which is only a little less than the absolute mass of dissolved phosphorus reaching the ocean annually with river runoff. Evidently this is the main way in which phosphorus is removed from sea water. Some phosphorus reaches the bottom in the composition of bone detritus - fish bones and scales, bones of marine mammals. . According to the data of Marti and Martinsen (1966) production of fish in zones of high biologic productivity is 6-8 t/km2 yr. The area of the most productive zone in the Atlantic off the coast of southwest Africa is about 30,000 square miles (Wooster and Reid, 1963), and in the Pacific Ocean off the coast of Chile and Peru, from 25,000 to 400,000 square miles according to different estimates (Wooster and Reid, 1963; Cushing, 1969; Zuta and Guillen, 1970). If the area of both zones is taken as 200,000 square miles on the average, and the average phosphorus content in raw fish as 1%(Kizevetter, 1973), then in the case of assumed equilibrium between the production and mortality of fish, up to 50,000 t P/yr is supplied to the bottom sediments in these zones as bone detritus, and for the ocean as a whole apparently at least 100,000 t/yr or up to 5-6% of the amount of dissolved phosphorus brought by rivers. According t o the estimate by Strakhov e t al. (1973), the percentage of bone-detritus phosphorus coming into pelagic sediments on a profile across the northern part of the Pacific Ocean reaches 30% of its total amount.

31 The process of deposition of phosphorus as part of fecal material eliminated by zooplankton, fish, and marine mammals also plays a certain part. The feces of organisms are substantially richer in phosphorus than the average composition of animal tissues. This is true to the greatest extent of animals that feed on fish: the phosphorus content of the coprolites of sea lions and seals reaches 5 4 %(Hutchinson, 1950). Large coprolites of marine animals and fish sink to the bottom in a few minutes on the shelf zone. The rate of sinking of small coprolites excreted by zooplankton ranges from 36 t o 862 m/day (Fowler and Small, 1972; Osterburg et al., 1963; Smayda, 1969). The scale of this process can be judged from the fact that, for instance, in the zone of the Peruvian current zooplankton and the anchovy each consume 1 x l o 7 t of diatomaceous phytoplankton per year, containing about 2-3x l o 5 t of phosphorus (Ryther et al., 1971; Whitledge and Packard, 1971). Microbial and enzymatic deposition The possibility that microbes take part in the deposition of calcium phosphate from sea water was first suggested by Kassin (1925) in a discussion of the problem of the origin of the Vyatka phosphorite. Subsequently, formations similar in size and shape to bacterial cells were found in phosphorites from various parts of the world (France, U.S.S.R., U.S.A., North Africa) during microscope investigations (Vologdin, 1946, 1947; Vologdin and Korde, 1945; Sokolov and Mashkara, 1938; Cayeux, l935,1936a,b). However, inasmuch as a few morphological features alone cannot be proof of the microbiological origin of phosphorites, this hypothesis was subjected in due course t o valid criticism by Vinogradov and Strakhov. In recent years supposed bacterial structures have again been found in sedimentary deposits of different age, including phosphorites, by means of electron microscope technique (Khvorova and Dmitrik, 1972; Shopf et al., 1965). In recent phosphorite concretions and the oozes containing them, numerous microscopic and ultramicroscopic organogenic formations of the type of bacteria and viruses have also been found (Mishustina, 1973). Marine bacteria actively assimilate dissolved inorganic phosphorus at a rate of 0.5 to 30pg P/1 day and fix it relatively firmly (Sorokin and Vyshkvartsev, 1974; Fedorov and Sorokin, 1975; Johannes, 1964, 1965). In laboratory modeling of the processes of bacterial fixation and deposition of phosphates it has been established that living bacterial cells extract up to 19% and dead up to 8% of dissolved inorganic phosphorus from an aqueous environment; it penetrates the bacterial cytoplasm by diffusion. The greater part of the phosphorus extracted from solution (about 70%)

32 goes into nucleic acids, less into phospholipids and phosphoproteins (Guelin and Lbpine, 1960,1961). Ennever (1963) showed that when cells of the bacterium Bacterionerna rnatruchottii were placed in a salt solution containing 0.55 g/l of sodium hydrophosphate, hydroxylapatite was secreted in 10 days. An analogous result was obtained when bacteria of various species were introduced into the abdominal cavity of white mice (Rizzo e t al., 1963).In both cases the presence of hydroxylapatite in the bacterial cells was demonstrated with the aid of X-ray structural analysis and electron microscopy. Coccous bacteria isolated from diatomaceous oozes in which Recent phosphorite concretions are forming grow actively on nutrient mediums. In a 10- to 12-day test, the formation of round concretions giving a positive reaction for phosphorus was observed on the surface of an agar medium (Mishustina, 1973). In the bacterial decomposition of organic matter in natural unsterilized sea water, phosphatic precipitates also were obtained in several cases. The first such experiments were made as early as the last century by Murray and Irvine (1889), who introduced urea and feces of crustaceans into sea water. Later, analogous experiments were made by other investigators, with the introduction of bacterial nutrients into sea water (Berkley, 1919; Molish, 1925, Malone and Towe: 1970). In actively aerated water, struvite (NH4MgPO, *6H, 0) precipitates out, in an anaerobic setting without active aeration, struvite and monohydrocalcite, and in anaerobic conditions struvite and highly magnesian calcite (Malone and Towe, 1970). From these experiments it follows that deposition of phosphate can occur in an evironment rich in organic matter which is in a stage of active decomposition under the influence of microorganisms. However, the conditions under which the experiments were carried out (isolated volume of water, high content of organic matter) are comparable to a natural environment which exists in interstitial waters rather than in sea water. Moreover, there is no direct evidence that microbes take part in the deposition of phosphorus. Possibly their role is more passive and indirect (adsorption and partial fixation of phosphorus by bacterial cells, change in pH of the environment). In the opinion of Malone and Towe (1970), the struvite in their experiments was deposited chemogenically ; the role of microorganisms came down to the fact that due t o their activity the sea water was enriched in ammonia, inorganic phosphorus, and carbon dioxide, which led t o supersaturation of the solution. The absence of struvite in natural phosphorites apparently is explained by the fact that it is an unstable intermediate compound which is converted to carbonate-apatite. Struvite has been found in marine sediments only in an anaerobic fjord (Boggild, 1911).

33 Enzymes and stimulants, with the help of which bones, teeth, phosphatic shells, and chitin are formed, play a leading role in the deposition of calcium phosphate in biochemical processes. The importance of such processes was clearly demonstrated by experiments on the deposition of carbonatehydroxylapatite from saliva with the participation of the enzyme carbonanhydrase, under conditions where purely chemical precipitation was impossible (McConnell et al., 1961, 1962). From this it was concluded that in natural environments the presence of enzymes, stimulants, and also inhibitors performing the opposite function, affect deposition of phosphates to an immeasurably greater extent than purely physicochemical conditions (McConnell, 1965, 1966). Enzymes undoubtedly are present in marine sediments rich in organic matter and phosphorus, as indicated by selective phosphatization of coprolites and worm casts in sedimentary strata (Bushinskiy, 1966a, 1967). But the action of enzymes and stimulants capable of abiogenic deposition of calcium phosphate (like that of microorganisms) is manifested to full extent on the bottom during diagenesis of sediments rather than in the water. Sorption of phosphorus One of the active mechanisms of extraction of trace elements from ocean water is their sorption and coprecipitation with iron and manganese hydroxides (Goldberg, 1954). Laboratory experiments (Hingston et al., 1967) and also examples of the ratio of phosphorus to iron in suspended matter and sediments of the seas and oceans indicate the possibility of deposition of phosphorus in that way. Thus, phosphorus in suspended matter from the upper horizons of the waters of the Baltic Sea is sorbed on iron-humate coagulants ( Y urkovskiy, 1972). In iron- and phosphorus-rich sediments of the East Pacific Rise, a direct P-Fe correlation in the absence of a P-Ca correlation has been established (Berner, 1973). In Berner's opinion, it follows from this that phosphorus is related to volcanogenic iron which trapped it during deposition from sea water. The phosphorus-trapping mechanism is produced either by chemical sorption on the surfaces of iron hydroxide particles formed when the Fe2+ is oxidized, or by formation of iron phosphate, the solubility of which in sea water is not more than 0.001-0.002 mg/l according to Bruyevich (1944). In estimating the scale of the process of deposition of phosphorus with volcanogenic iron in the zone of the East Pacific Rise (10-30"s and 100130°W), Berner obtained the impressive figure of ~ 1 x 6lo4 t/yr (Table 1-13), which is about 10%of the annual supply of dissolved phosphorus to the ocean from the surface of the continents. Deposition of phosphorus also occurs due t o its sorption by clay minerals.

34 TABLE 1-13 Deposition of phosphorus with volcanogenic iron in the East Pacific Rise (Berner, 1973; Fe, after Bostrom, 1970) Rate of deposition of Fe (kg/km2 yr)

50-100 100-150 150-300 300-4000

Area of zone ( lo6 km2 )

4 1.5 0.5 1.5

Rate of deposition of P (lo4t / w )

3-6 2-3 1-2 10

-

-

c7.5

c16

Weight ratio P:Fe = 0.15 k0.05

According to Olsen’s (1958) data, in a marine environment fine-grained sediments are in sorptional equilibrium with water containing 0.022-0.028 mg P/1. According t o other data, desorption of phosphorus occurs when its content in the water is below 0.030, and sorption when the content is more than 0.09-0.12 mg/l (Rochford, 1951). The role of the latter process has not been estimated for the ocean as a whole, but in comparison to other mechanisms of deposition of phosphorus it seems t o be secondary.

Phosphatization of carbonates Phosphorite often is associated with carbonate rocks. Numerous examples also are known of complete or partial phosphatization of mollusk and gastropod shells, corals, sea urchins, and carbonate detritus in phosphorites both on land and on the ocean floor (Bezrukov et al., 1969; D’Anglejan, 1968; Dietz et al., 1942; Hamilton, 1956; Heezen et al., 1973; Marlowe, 1971; Murray and Renard, 1891; Pevear, 1966; Reed, 1952). On the question of whether metasomatic replacement of carbonate ion by phosphate ion occurs in the sedimentary layer or at the water-bottom interface, the opinions of investigators diverge. Murray and Renard (1891), who discovered and investigated the phosphorites of Agulhas Bank, believed that phosphatization occurred in the sedimentary pile. To support this point of view they cited the results of the first laboratory experiments on phosphate metasomatism: when coral limestone was in contact with a dilute solution of ammonium phosphate for several months about 60% of the carbonate was replaced by phosphate (Irvin and Anderson, 1891). Subsequently a series of experiments on the replacement of carbonates by calcium phosphate were conducted by other investigators. Best known are the works of Ames (1959, 1960; Ames et al., 1958). By passing an alkaline

35 solution of sodium phosphate through a tube filled with ground calcite he obtained carbonate-apatite containing about 10% COz. The reaction in this case occurred according to the scheme: NaOH + 3Na3P04 + 5CaC03 + CaS(P04)30H+ 5Na2C03 The carbonate-apatite obtained had the composition [ Cag.,] Nal. 12 ] [(PO, )5.26 (CO, ] (H, 0)2.00. Solutions with a phosphorus concentration of 1.5 g/l and more and p H % l 1 were used in the experiments, but by extrapolation Ames determined the threshold parameters of the reaction given above - a phosphorus concentration of -0.1 mg/l and pH of 7-8. On the basis of these results it was suggested that phosphatization of limestone occurs due to its contact with sea water (Ames, 1959, 1960; D’Anglejan, 1968, Marlowe, 1971; Pevear, 1966, 1967). However, the actual conditions under which such experiments are made (high phosphorus content in the solution, high pH, low salt background) are very far from the environment typical of ocean waters. On the ocean bottom in different areas there are numerous exposures of ancient carbonate rocks and carbonate detritus (shell, coral) that have been in contact with sea water for a long time but have not undergone any phosphatization at all. Meanwhile, Recent phosphorites on the shelf of southwest Africa are formed in sediments which are practically carbonate-free (Baturin, 1969; Baturin et al., 1970). From this it follows that marine phosphorite formation is independent of carbonate accumulation and that in the present ocean phosphate-carbonate metasomatism does not occur at the water-bottom interface, but below, in the sedimentary. layer, due t o phosphorus reserves contained in interstitial waters rather than in sea water. Other ways of depositing phosphorus Another hypothetical way of extracting phosphorus from ocean waters would be deposition of phosphate ions and colloidal phosphate particles carrying an electrical charge, on electrically active solid surfaces protruding above the bottom surface, including earlier-formed concretions (Mero, 1969). This idea was suggested by analogy with a suggestion concerning the formation of iron-manganese nodules and has not been supported by any experiments. The question of the behaviour of phosphorus in submarine weathering of basalt also is of interest. In the opinion of Corliss (1971), phosphorus passes from basalt to sea water. At the same time Hart (1970) showed that during submarine weathering of tholeiitic rift basalts, their outer layers

36 were enriched in iron and phosphorus due to extraction of these elements from sea water. According to his calculation, 1cm3 of basalt extracts g of iron and 0.3 x lo-’ g of phosphorus per year in the course 1.2 x of hydration. In this case enrichment in iron is observed in an outer layer of basalt up to 100 cm thick, and in phosphorus in a layer up t o 10 cm thick. DISSEMINATED PHOSPHORUS IN SEA AND OCEAN SEDIMENTS

The disseminated phosphorus content of sea sediments ranges from 0.01 to 0.90% (Table 1-14). The highest phosphorus concentrations have been established in the sediments of the northern seas, which contain up t o 0.20.9% P. Sands as a whole are poor in phosphorus compared t o other types of sediments. They are somewhat enriched in phosphorus only in those cases where they contain volcanogenic material of basic or intermediate composition, as for example on the shelves of Kamchatka and the North Kuriles (Bezrukov and Ostroumov, 1957). In some basins or parts of them, a tendency is observed toward an increase in phosphorus content on passing from coarse to fine sediments. This tendency is most clearly manifested in the White Sea, less definitely in the Baltic, Aral, and Caspian Seas (Table 1-14), and also in the western part of the Sea of Okhotsk and Anadyr’ Gulf of the Bering Sea (Bezrukov and Ostroumov, 1957; Lisitsyn, 1966). In the Sea of Okhotsk, Bering Sea, and also in the Kara, Mediterranean, and Arabian Seas, on the whole a relationship between the phosphorus content and granulometric composition of the sediments is slightly expressed or absent. A t the same time the average phosphorus content of the main granulometric types of marine sediments on the whole form a systematic series and are: 0.5% in sands, 0.06% in coarse silts, 0.075% in fine silty oozes, 0.08% in silty pelitic oozes, and 0.10% in pelitic oozes. Marine calcareous sediments (Black Sea) contain: shell sand, an average of 0.03% phosphorus and clayey coccolithic oozes, 0.055% (Glagoleva, 1961). The average phosphorus content in sea sediments as a whole is 0.07%. A common feature is observed in schemes of the areal distribution of phosphorus on the bottom of most intracontinental and shelf seas phosphorus is concentrated in the sediments of the deep-sea basins; in the shallow-water parts high phosphorus concentrations are encountered sporadically. In the sediments of deep-water open seas (Bering, Okhotsk), on the contrary, relatively high phosphorus contents are typical of the shallowwater zones (Fig. 1-4). In the former case the phosphorus is concentrated in the sediments due

TABLE 1-14 Phosphorus content (96) in the top layer ofmarine sediments Sea Barents Kara Kara Baltic Baltic (south part) White NonvegianGreenland basin Norwegian fjords Okhotsk Bering Aral Caspian Black Azov Mediterranean Arabian Average

Sands

0.035 0.045 (0.01-0.07) 0.037 0.03 0.09 (0.014-0.25)**

Coarse silts

Fine silty oozes

Silty pelitic oozes

(0.0534.160)* (0.075-0.160) 0.058 (0.050.068) 0.66 (0.02-0.14) 0.050 0.03

(0.0674.240) (0.0584.117) 0.121 (0.036-0.84) 0.07 (0.03-0.08) 0.068 0.05

(0.070-0.250) (0.0774.115) 0.180 (0.032-0.90) 0.07 (0.01-0.16)

-

-

-

0.075 (0.017-0.135) 0.05 (0.01-0.09) 0.063 0.032 0.043 0.05 (0.034.06)

-

0.10 (0.064.15) 0.05

-

0.12 -

0.073 0.090 (0.043-0.109) (0.0654.117) 0.07 0.09 (0.04-0.12) (0.054.15) 0.10 0.048 0.063 0.052 0.045 (0.0364.07) 0.04 (0.05-0.065) 0.10 (0.05-4.15) 0.06

0.075

Pelitic oozes

(0.1300.220) 0.156 (0.094-0.217) 0.08 (0.034.18) 0.080 0.20

0.11 (0.06-0.16) 0.057 (0.039--0.130) 0.06 (0.024.08)

0.068 (0.035-0.148) 0.07 (0.034.16) 0.16 0.072 0.078 0.040-0.059*** 0.05 (0.03-0.07) (0.035-0.065) (0.04-0.06) 0.10 0.12 (0.07-0.13) (0.08-0.16) 0.08

Number of samples

Reference

214

Klenova and Budyanskaya, 1940

42

Gorshkova, 195713

168

Blazhchishin, 1972

110 250

Pechenewski, 1973 Kalinenko, 1973

97 9

Gorshkova, 1972 Strom, 1936

142

Bezrukov and Ostroumov, 1957; Bezrukov, 1960 Lisitsyn, 1966

19 113 180 38

Brodskaya, 1952 Budyanskaya, 1948 Glagoleva, 1961 Gorshkova. 1961

12 57

Yemel’yanov, 1973a Baturin, 1969

132

0.10

* Limits of variation ofcontents.

** Sediments as a whole. *** Calcareous clayey ooze.

w

4

38

46

44

42

Fig. 1-4. Distribution of phosphorus in marine sediments. (a) Black Sea (Glagoleva, 1961). 1 = 0.025;2 = 0.025-0.05; 3 = 0.05% P. (b) Bering Sea (Lisitsyn, 1966): 1 =<0.05;2=0.05-0.07;3=0.07-0.1;4=>0.1%P.

<

>

39

6(

5E

52

4E

44

Fig. 1-4 (continued). (c) Sea of Okhotsk (Bezrukov, 1960): 1 = < 0.04: 2 = 0.04-0.06; 3 = 0.06-0.09; 4 = 0 . 0 9 4 . 1 2 ; 5 = > 0.12%P.

to organic matter (Black and Caspian Seas) or trivalent iron. The phosphorus-rich sediments of the Kara Sea basin contain up to 18.88% F e z 0 3 (Gorshkova, 1957b). In the Caspian Sea a very high phosphorus content (0.21%) also has been ascertained in the fenuginous sediments of the Apsheron sill, which are enriched in F e z 0 3 up to 8.46--17.92% (Budyanskaya, 1948). In the latter case the distribution of Corg affects the distribution of phosphorus, i.e. ultimately the high biological productivity and shallow depth of the corresponding parts of the basins. In the Sea of Okhotsk the maximum phosphorus content is typical of fine-grained diatomaceous sediments on the northwestern shelf, in the Bering Sea, of the sediments of Anadyr' Gulf. In the central and southern Caspian the fine-grained sediments occurring at depths of not more than 100-300 m are distinguished by a high phosphorus

40

Fig. 1-4 (continued). ( d ) Caspian Sea (Budyanskaya, 1948): 1 = 3 = 0.07-4.04; 4 = 0.04%P.

<

> 0 . 1 ; 2 = 0.1-0.07;

content; in sediments of similar granulometric composition from the shallow-water North Caspian zones the phosphorus content likewise is high (Budyanskaya, 1948). The enrichment of fine-grained shallow-water marine sediments in phosphorus is explained mainly by the fact that a substantial part of it, contained in dead plankton, reaches the bottom. This is indicated by the similarity of the schemes of distribution of P and Corg in shallow-water (up to 200 m) sediments of the Bering Sea (Lisitsyn, 1966). In ocean sediments the phosphorus content ranges from 0.01 to 1-3% and according to the data of El-Wakeel and Riley (1965) the average for the ocean is 0.0776, i.e. it corresponds to its average in argillaceous rocks0.077% (according to Vinogradov, 1956). The average phosphorus content in the main types of ocean sediments is between 0.04% in diatomaceous

41

Fig. 1-4 (continued). (e) Kara Sea (Gorshkova, 1957): figures on contours=P concentration, %.

oozes and 0.146% in red clays (Table 1-15), according to the estimates of a number of authors. In individual areas of the ocean the phosphorus content in the main types of sediments may deviate considerably, in either direction, from the average values given above. In an investigation of about 100 samples obtained during traverses in the eastern Indian Ocean, the following average phosphorus contents in the sediments were established: in foraminiferal, 0.025%; coccolithic, 0.46%; ethomodiscan, 0.033%; radiolarian, 0.057%; miopelagic, 0.118%; eupelagic, 0.214% (Sevast’yanova and Sval’nov, 1978). Taking into account new data obtained in recent years (Table 1-16) the following more precise figures can be given for the average phosphorus content in the main types of pelagic sediments of the World Ocean: 0.07%

42 TABLE 1-15 Average phosphorus content (%) in the main types of pelagic oceanic sediments Clastic sediments

Red clays

0.09 0.09

0.13 0.09 0.13 0.06 0.1460

-

0.0632

Calcareous sediments

0.13 0.09 0.07 0.0421

Cherty sediments -

0.04 0.13 0.12 -

Reference Clarke, 1924 Sujkowski, 1952 Poldervaart, 1957 El-Wakeel and Riley, 1965 Horn and Adams, 1966

in clastic sediments, 0.11% in red clays, 0.06% in calcareous sediments, and 0.04% in siliceous sediments. In calculating these average values the data of Landergren (1964) for seven Pacific cores were not taken into account, as they all were obtained from the same equatorial area where the sediments are considerably enriched in phosphorus. In oceanic, as in marine sediments, the distribution of phosphorus is controlled by its relationship to clastic material, organic matter, biogenic bone detritus, and iron. By far the greatest part of suspended clastic material reaching the ocean from the continents is deposited on the submerged margins of the continents (Vinogradov, 1967; Lisitsyn, 1974), and that pertains completely to suspended clastic phosphorus. In some inshore areas near river mouths small sectors of sediments enriched in clastic phosphorus (up t o 0.1- 0.2%) related to apatite are encountered (Rajamanickam and Padmanabha, 1973). Along with clastic material, the greater part of the absolute amounts of organic matter is deposited on the submerged margins of the continents (Gershanovich et al., 1974; Romankevich, 1974; Strakhov, 1960), including phosphorus extracted from sea water by organisms. Evidently deposition of dissolved phosphorus also occurs mainly on the submerged margins of the continents. This is demonstrated by the similarity of the schemes of distribution of P and Corg or their correlation in sediments enriched in both elements in near-shore zones of upwelling (Yemel’yanov and Senin, 1969) and the border zones of the ocean as a whole (Volkov et al., 1974; Lisitsyn, 1966). According t o the calculations of Horn and Adams (1966), the absolute amount of phosphorus included in shelf and hemipelagic sediments is -15 x l O I 4 t, and in pelagic, 6 x 1014 t. Biogenic phosphatic detritus (whole and broken bones, teeth, scales) also occurs locally in the pelagic and shelf sediments of the ocean (Baturin, 1974a; Belyayev, 1959; Saidova, 1971; Arrhenius, 1959; Boggild, 1916; Murray and Philippi, 1908; Murray and Renard, 1891; Neeb, 1943). It also

43 TABLE 1-16 Phosphorus content (7%) in pelagic oceanic sediments* Clastic

Red clays

Calcareous sediments

8e d i m e nts

P

N

N

P

Cherty sediments

P

N

(tr.4.55)

10

P

Reference N

Pacific Ocean (tr.4.14) -

0.035 -

0.052 -

(tr.4.69)

0.078 0.10 (0.04-0.33) 0.56 (0.037-1.96) 0.126 (0.020-0.360) 0.135 0.059-0.300' 0.138 (0.0804,.174)b

-

11

-

Murray and Renard, 1891 Sverdrup e t al., 1946 El-Wakeel and Riley, 1965 Landergren, 1964

26

-

-

-

Cronan. 1969

-

-

-

0.044

13

-

-

-

Strakhov et al.. 1973; Volkov et al., 1974 Glagoleva et al., 1975

9

(tr.-0).56)

13

-

111

-

9 10

-

-

9

-

0.10

284

0.52 (0.154.94)

Athntic Ocean (tr.4.28) -

0.045 (0.014.08) -

0.13 (0.104.16)

(tr.4.42) 0.093' (0.070-0.172) 0.045 (0.03-0.07) 0.074 (0.019-9.13) 0.13 (0.124.14)

7 2' 4 99

0.067 (0.021-0.117) 0.05 (0.03-0.07) 0.05

(0.0354.055) 3

-

Murray and Renard, 1891 Correns. 1937

5

0.04

3

-

El-Wakeel and Riley, 1965 Landergren, 1964

-

-

Baturin. 1972

Murray and Renard, 1891 El-Wakeel and Riley, 1965 Landergren, 1964

Indian Ocean -

0.05 (0.02-0.06) 0.05 (0.044.06)

0.42 0.65 (0.05-0.09) 0.06 (0.018-0.15) 0.08 (0.05-0.12)

-

1

0.35

1

0.08

3

0.04

1

-

12 5

-

0.047 (0.0354.074) 0.043 (0.03-0.07) 0.04 10.02-0.06\

11

9 -

0.046 (0.018-0.074) 0.03 (0.01-0.06)

-

-

Kuznetsov et al., 1968 Dvoretskaya and Pushkina, 1974

Limits ofvariation ofcontents, combined data o n surface layer and on cores, given in parentheses. a Clays with zeolites; total number of samples of all types of sediments is 204. Clays; red, hemipelagic and transitional types. Red clays and clastic sediments.

has been found in deep-sea drill cores (Nayudu, 1973).In the silt fraction of red clays of the Pacific Ocean the amount of bone fragments locally reaches 40-70%, due t o which the phosphorus content in the sediments is increased to tenths of a percent and in individual cases to 1-3% (Baturin and Kochenov, 1973;Volkov et al., 1974).Scattered fish bones and scales are often encountered in shelf sediments, and in some areas, for instance on the

44 shelves of southwest Africa and Chile, substantial accumulations of bones (Baturin, 1974a). The phosphorus content in iron-rich oceanic sediments depends on their composition and genesis. Volcaniclastic iron-rich sediments in the Atlantic contain only 0.09-0.20% P, recalculated to carbonate-free substance, but glauconitic and hydrogoethite-chamosite sediments on the Atlantic shelf of Africa contain u p to 0.15-2.02% (Yemel’yanov, 1975). Enrichment in phosphorus is characteristic of sediments in which colloidal iron of hydrothermal-volcanogenic origin is present. In the metalliferous muds of the Red Sea the P content reaches 0.22%(James, 1969), in the ironrich sediments of theEast Pacific Rise, 1.47%(Berner, 1973), and in the ironrich sediments obtained by drilling of the Atlantic Ocean floor, 1.6%(Bostrom et al., 1972). The phosphorus enrichment of sediments of this type is especially prominent when recalculated to mineral matter (Fig. 1-5). In most cases ferromanganese nodules also are enriched in phosphorus: they contain 0.02-3.55% P (Table 1-17). In marine nodules, and also in the Pacific nodules that were investigated by Skornyakova and Andrushchenko (1970) a P-Fe correlation is observed. In the Pacific nodules investigated by Mero (1969) there is no such correlation. The marine nodules are substantially richer in phosphorus that the oceanic. The average ratios of

4ooE

80

120

160

150

120

80° w

Fig, 1-5. Distribution of phosphorus (recalculated to mineral matter) in sediments of the Pacific and Indian Oceans (Bostrom et al., 1972). 1 = 0.2;2 = 0 . 2 - 0 . 4 ; 3 = 0.4-0.8; 4 = 0.8-1.6; 5 = 1.6-3.2; 6 = 3.2% PzO5.

>

<

45 TABLE 1-17 Phosphorus content (%) in ferromanganese nodules and crusts Basin

Kara Sea Black Sea (oxygen zone) Baltic Sea Atlantic Ocean Indian Ocean Pacific Ocean

Pacific Ocean as a whole**

P

Reference

range of values

average

N

1.48-3.55 0.83-1.58

2.66 1.10

5 15

1.94-4.08* 0.028-0.1 69 tr.-0.18 tr.-0.04 tr.--1.44 0.22-1.97 0.084.14 0.02-0.43 0.074.28

0.098 0.54 0.22 0.11 0.13 0.18

5 3 3 27 33 1 3 29 31

0.0854.271 0.23-0.59

0.18 0.40

9 5

0.02-1.97

0.28

-

Senov, 1937 Volkov and Sevast’yanov, 1968 Varentsov et al., 1973 Mero, 1969 Murray and Renard, 1891 Murray and Renard, 1891 Murray and Renard, 1891 Goldberg, 1954 Dietz, 1955 Riley and Sinhaseni, 1958 Mero, 1969 Skornyakova and Andrushenko, 1970 Volkov et al., 1974 author’s data

* Recalculated to clastic-free, silica-free, and carbonate-free substance. ** Except data of Murray and Renard (1891). enrichment of the nodules compared to the enclosing sediments are: in the oxygen zone of the Black Sea 6.9 (P) and 7.6 (Fe), and in the northwestern part of the Pacific Ocean 2.5 (P) and 3.3 (Fe) (Volkov and Sevast’yanov, 1968; Volkov et al., 1974). PHOSPHORUS IN INTERSTITAL WATER OF MARINE AND OCEANIC SEDIMENTS

The phosphorus content in the interstitial water of sea and ocean sediments ranges from analytical zero* to 20 mg/l (Table 1-18). The minimum phosphorus content in interstitial waters is characteristic

* In connection

with the small volume of the samples the sensitivity of determination is often limited to within 0.01-0.02 mg/l.

TABLE 1-18 Phosphorus content (mgll) in the interstitial waters of marine and oceanic sediments Reference

Basin

Type of sediment

Range of values

Average

N

North Caspian

oozes silts and sands shell sands

0.22-8.42 0.004-0.148 0.024-0.062

1.24 0.036 0.037

34 39 5

Bruyevich and Vinogradova, 1940a.b; 1947

Central Caspian

oozes oozes with shells shell sands

-

0.10-0.1 1 9 0.010--0.037

0.20 0.15 0.024

1 5 4

Bruyevich and Vinogradova, 1940a.b; 1947

South Caspian

oozes oozes with shells shell sands

0.18-0.55 0.023-0.028 0.024-0.052

0.36 0.025 0.034

2 2 3

Bruyevich and Vinogradova, 1940a,b; 1947 Aleksandrova and Bronfman, 1975

Sea of A w v

oozes

0.275-3.660

Sea of Azov

oozes

tr.-4.80

0.92

18

Gorshkova, 1955, 1961

Taganrog Gulf

oozes

0.02-1.10

0.47

25

Gorshkova, 1955, 1961

Black Sea, northeast part

oozes

0.01-0.27

0.15

-

Black Sea, oxygen zone

oozes: recent old Black Sea new Euxine

0.08-0.74 0.27-1.57 0.55-1.16

0.26 0.92 0.84

8 5 6

Volkov and Sevast'yanov, 1968

1.0-5.0 0.2-1.3

2.3 0.86 0.23

7 5 1

Gorshkova, 1957a. 1975

sediments : tan gray greenishgray

0.036-0.36 0.037-0.66 0.14-1.33

0.095 0.26 0.40

14 9 10

Gorshkova, 1960

Barents Sea, littoral

littoral sands beach sands

0.04-0.53 0.096-0.99

0.20 0.29

17 18

Chernovskaya, 1955

Bering Sea

muddy sediments sandy sediments

0.14-7.48 0.06-1.62

0.36

133 44

-

0.24

-

-

0.25 0.20 0.28 0.18

-

6.76

24

Baltic Sea

Norwegian Sea

Sea of Okhotsk

Saanich Inlet (British Columbia)

oozes silts sands

pelitic diatomaceous ooze silty pelitic diatomaceous ooze fine silt coarse silt sands diatomaceous oozes

-

-

1.08-13.02

-

Zaytseva, 1959

Zaytseva, 1954a,b; Bruyevich and Zaytseva, 1958 Bruyevich, 1955, 1956

-

Nissenbaum e t al., 1972

-

Chesapeake Bay

oozes

0.01-20

90

Bray e t al., 1973

Pacific Ocean, northwest part

gray clastic oozes

0.004-1.96

0.33

99

Bruyevich and Zaytseva, 1960

Pacific Ocean, northwest part

clastic sediments red clays

0.02-2.79 tr.-0.67

-

80 43

Valyashko e t al., 1973

Pacific Ocean, western tropical and subtropical zones

diatomaceous oozes calcareous oozes clastic oozes red clays

0.12-0.92 0.00-1.44 0.07-0.12 tr.4.29

8 37 4 5

Bruyevich and Zaytseva, 1964

0.10 0.10

calcareous oozes clastic oozes red clays

0.012-0.050 0.010-0.021 0.005-0.050

0.030 0.016 0.024

6

Bruyevich and Zaytseva, 1964

9 10

Pacific Ocean, central part

9 33 69

Bruyevich and Zaytseva, 1964

32 36

Rittenberg et al., 1955 Brooks e t al., 1968; Sholkovitz, 1973

oozes

0.643-6.014 0.20-7.30 0.49-3.16

oozes oozes oozes

0.09-0.24 0.61-1.95 0.09-0.12

0.16 1.33 0.10

2 4 2

diatomaceous oozes of shelf pelitic clastic oozes

0.25-8.76 0.0084.4'70

2.5 0.107

30 22

0.467-0.475

0.473

3

1.10-1.72

1.472

6

0.4384.846 0.143-6.04

0.663 0.304

10

0.0064.285

0.115

37

0.006-0.074

0.025

47

calcareous oozes clastic oozes red clays

Pacific Ocean, California Basin

oozes oozes

Atlantic Ocean, southeast part Caribbean Sea, deep-sea drilling: Cariam Basin, hole 147, depth 883m hole 147A, depth 883 m

foot of Aves Swell hole 148. depth 1223 m Venezuelan Basin, bole 149, depth 3972 m

-

-

Pacific Ocean, northwest part

Pacific Ocean, southeast part off Chilean coast off Peruvian coast deepaea zone

0.52

reduced oozes horizon 8.5m horizon 28-32 m reduced oozes, horizon 2.5-4.8 m clastic sediments: horizon 5.1-21 m horizon 51-176111 calcareous clayey oozes horizon 5-232 m horizon 4-374 m


-

Shishkina, 1971

Baturin, 1972 Shishkina and Baturin, 1973

-

6

Gieskes, 1973

TABLE 1-19 Average phosphorus content (mg/l) in interstitial waters in zones of different depth in basins Basin

Depth (m)

P

Reference

North Caspian

0.5-14

1.24

Bruyevich and Vinogradova, 1947

Central Caspian

9-9 2

0.20

Bruyevich and Vinogradova, 1947

26-97 170 460 960

0.36 0.28 0.485 0.225

Bruyevich and Vinogradova, 1947

Black Sea

0.50 50-100 200-4 00 1000-2000 > 2000

0.09 0.27 0.17 0.11 0.01

Zaytseva, 1959

Bering Sea

0-200 200-3 000 > 3000

0.49 0.31 0.25

Zaytseva, 1954a,b

Sea of Okhotsk

0-200 200-1000 1000-3000 > 3000

0.20 0.25 0.23 0.27

Bruyevich, 1955

Pacific Ocean, Peru-Chile region

50-176 500-1020 3200-4160

1.58 0.33 0.10

Shishkina, 1971

Atlantic Ocean, southeast part

75-128 750-2570 5200-5 500

2.5 0.115 0.085

Baturin, 1972

South Caspian

of pelagic sediments, the maximum of sediments of the biologically productive shallow-water zones. The phosphorus content of interstitial waters depends on the granulometric and mineralogic composition of the sediments, depth and hydrodynamic regime of the basin, and depth in the sedimentary layer. The phosphorus content in the interstitial waters of coarse-grained sediments usually is lower than that in fine-grained from the same depths. Thus, in the interstitial waters of clay sediments of the North Caspian the phosphorus content

49 is 0.22-8.42mg/l, and in the interstitial waters of shell sands 0.0240.062 mg/l, i.e. ten times less. In the interstitial waters of deep-sea sediments the phosphorus content in most cases is lower than in shallow-water sediments of the same granulometric composition, which appears, for example, on passing from shelf oozes of the biologically productive zones t o pelagic oozes (Table 1-19). In the interstitial waters of sediments of the Sea of Okhotsk the phosphorus content on the whole is lower than in those of the Bering Sea at comparable depths (Table 1-19). Bruyevich (1956) explains this by the strong tidal currents in the Sea of Okhotsk. The disproportionately low (compared to ammoniac nitrogen) phosphorus content in the interstitial waters of the Sea of Azov could be caused by its leaching (Bruyevich and Zaytseva, 1958) or by diffusion. One of the main factors determining the phosphorus content in interstitial waters is the amount of organic matter and intensity of its mineralization. Thus, on the scheme of the distribution of phosphorus in interstitial waters of the Sea of Okhotsk (Fig. 1-6), two sectors with high phosphorus content stand out -in the north (shallow) and in the south (deep-sea basin). The sediments of both sectors are rich in organic matter (Bezrukov, 1960). In the pelagic zone of the ocean the maximum phosphorus content in interstitial waters is observed in diatomaceous oozes (up to 0.92 mg/l), including the diatomaceous oozes from the Mariana Deep (0.49-0.58 mg/l) from a depth of 8,000-10,000m; these oozes as a rule contain much more organic matter than other types of pelagic oceanic sediments (Bruyevich and Zaytseva, 1964). In the lower horizons of the cores the phosphorus content in the interstitial waters increases on the whole, but this increase is uneven (Fig. 1-7). The high phosphorus content of the interstitial waters of deep horizons of the cores of marine and oceanic sediments is caused not so much by the absolute content of organic matter as by the processes of its mineralization (Rittenberg et al, 1955). Of the components of the solid phase of the sediments, Corg primarily correlates with dissolved phosphorus, and to a lesser extent P. Apparently this is related to a combination of factors, including mineralization of organophosphorus compounds, deposition of calcium phosphate, and sorption of phosphate by iron hydroxides and clay minerals (Baturin, 1972; Bruyevich and Zaytseva, 1958; Senin, 1976; Bray et al., 1973). In interstatial waters rich in phosphorus the pH and Eh values usually are low. High phosphorus contents (up to 3-4 mg/l) in interstitial waters have also been established in three sediment cores with positive Eh values in the California basin (Brooks e t al., 1968). In interstitial waters from sediments with low organic matter content

50

Fig. 1-6. Distribution of phosphorus ( p g / l ) in the interstitial waters from the upper layer of sediments in the Sea of Okhotsk (Bruyevich, 1956).

phosphorus occurs chiefly in inorganic form, but from sediments rich in Corg it is in the form of organophosphorus compounds to a substantial extent (Baturin, 1972). RELEASE OF PHOSPHORUS FROM SEDIMENTS

When in contact with sediments, the bottom waters may be enriched in phosphorus to a certain extent under the influence af various factors: roiling of the sediments, decay of organic matter, diffusion, desorption, and leaching. Enrichment of near-bottom waters in phosphorus due t o roiling occurs in shallow basins. In this case the process of phosphorus exchange, in which the interstitial waters take part, is reversible and depends on the pH, salinity,

51

Fig. 1-7. Distribution of phosphorus in the interstitial waters from cores (540, 615, and 619) of Bering Sea sediments (Bruyevich and Zaytseva, 1958).

phosphorus content in solution, and buffering properties of the water and sediments (Pomeroy e t al., 1965). Release of phosphorus during mineralization of organic matter in sediments has repeatedly been demonstrated by laboratory experiments and experiments in situ, in particular in the Sea of Azov and Black Sea and in New York Bay (Pirogova, 1953;Rowe et al., 1975). Bacteria and enzymes of phosphatase type play a definite part in dissolving organic and inorganic phosphorus compounds. As illustrated by the sediments of the Vellar River estuary off the coast of India, the amount of bacteria capable of putting phosphorus in solution depends on the content of organic matter, which in turn determines the activity of phosphatase (Ayyakkannu and Chandramohan, 1971). The release of organic phosphorus from sediments takes place mainly at the water-bottom interface.

52 According t o Romankevich’s (1977) calculations, in the surface film of sediments of the ocean, 1-3 x lo9 t of Corg and correspondingly 1-3 x lo7 t of Porg are mineralized every year. For the ocean this amounts to 27-81 mg P/m’ yr, on the average. According to the data of Volkov et al. (1974), 25% of the phosphorus originally contained in the upper layer of the reduced sediments of the continental shelf of Japan goes into the water near the bottom (in absolute percentage, 0.019%).With the sedimentation rate of the order of 100 mm/ 1000 yr in this area (Lisitsyn, 1974), this amounts t o 50 mg P/m2 yr. As a result of investigations of water extracts, Datsko (1948) concluded that 8000 t of phosphorus, or -200 mg/m2 yr, are released every year from the sediments of the Sea of Azov. Judging from the biochemical consumption of oxygen and from experiments in situ, %lo00 mg/m2 yr of phosphorus are supplied to the water from the sediments of New York Bay (Rowe e t al., 1975). Judging from the exceptionally steep gradients of phosphate concentrations on the interstitial and bottom waters, even more intensive flux of phosphates from sediments takes place in the zones of maximum biological productivity on the shelves of Namibia and Peru-Chile, which come under the influence of upwelling (Baturin, 1972; Shishkina, 1971; Shishkina and Baturin, 1973). Manheim’s (1976) formula can be used to determine this flux:

Q

=

Ac . AtS Ax

D-

where Q = phosphorus flux, Ac = difference in phosphate concentration between interstitial and bottom water, Ax = thickness of sediment layers, S = area, t = time, and D = diffusion coefficient. A calculation of the phosphate flux from sediments off the coast of Peru using this formula gave the following values: for station 1654 on the continental slope (depth 1650 m, diffusion coefficient 1.29 x cmz /s) - 20.5 pg-at/day, or about 230mg/mZ yr; for station 1639 on the shelf (depth 30m, diffusion coefficient 5.9 x cm2/s) -612 pg-atlday, or about 690 mg/mz yr (Bordovskiy e t al., 1980). Phosphorus included in the deeper sedimentary layer apparently takes little part in exchange with bottom waters. At a sedimentation rate of more than lo-” cm/s, or about 3 mm/1000 yr, diffusion of ions from interstitial waters into the near-bottom waters is virtually suppressed (Tzur, 1971). According t o Shishkina’s (1971) calculation, the amount of phosphorus released from the sedimentary pile on the shelf of Chile is only 0.065 mg/mZ yr despite the steep gradient of phosphorus concentration in the interstitial (1.95 mg/l) and bottom waters (0.09 mg/l).

53 Desorption of that part of the phosphorus which is bound in sediments with iron and manganese hydroxides occurs when oxidizing conditions are replaced by reducing. In an oxidizing environment phosphorus is fixed by hydroxides, and in a reducing environment, when ferric forms are converted to ferrous, it is released as indicated by examples of the behaviour of phosphorus in lacustrine, marine, and oceanic sediments (Volkov and Sevast’yanov, 1968, Volkov et al., 1974;Datsko, 1948;Hutchinson, 1969; Yurkovskiy, 1972, Bonatti et al., 1971;Nriagu and Dell, 1974;Patrick and Khalid, 1974). At the times when the Sea of Azov is polluted by hydrogen sulfide, as is often observed in the summer, the phosphorus content in water extracts from the sediments usually is 2-4 times lower than in the winter and spring (up to 1.6 mg/kg of sediment), when the waters are well aerated and an oxidized film is formed on the bottom (Datsko, 1948). The boundary conditions of the process of phosphorus exchange in the system waterbottom set in when Eh of the sediments is about 20 mV (Aleksandrova and Bronfman, 1975). In the sediments of the Pamlico River estuary (North Carolina, U.S.A.) the phosphorus content, originally (in fluviatile suspensions) related mainly to iron, decreases from 0.16 to 0.03% as the mouth is approached (Upchurch et al., 1974). Evidently this is explained by intensification of reduction processes in the sediments. Thus release of sorbed phosphorus from sediments, like that of organic phosphorus, occurs under the influence of the decay of organic matter. The preponderant part of the absolute mass of this matter is deposited on the submerged margins of the continents (Gershanovich et al., 1972, 1974; Romankevich, 1974, 1977). There too, by far the greater part of dissolved phosphorus returned to the oceanic cycle from sediments gets into the water, due to biochemical and related reduction processes.

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Chapter 2 PHOSPHORITE ON THE OCEAN SHELVES Phosphorite and phosphatic sediments are known on the floor of the Pacific, Indian, and Atlantic Oceans (Fig. 2-1). They occur in a number of inshore areas (the shelves and upper part of the continental slopes) and in the pelagic zones, chiefly on seamounts (Baturin and Bezrukov, 1971,1976). In addition, there are deposits of guano and metasomatic phosphorites, some of which are being worked, on a number of islands in the tropic zone and on coasts (Zanin, 1975, Hutchinson, 1950). Most of the shelf phosphorites are localized in four very large oceanic phosphorite provinces - the East Atlantic, West Atlantic, Californian, and Peruvian-Chilean.

EAST ATLANTIC PROVINCE

In the East Atlantic province phosphorites occur in the form of a discontinuous belt from the shelf of Portugal on the north to Agulhas Bank on the south (Fig. 2-2). The phosphorites of three regions of this province (submerged margin of South Africa, Morocco shelf, shelf of southwest Africa) have been studied and described in relative detail, but there are only brief mentions concerning the others in the marine geological literature.

Submerged margin o f South Africa The first samples of phosphorite from the ocean floor were obtained from the submerged margin of South Africa (Agulhas Bank area) by the British “Challenger” expedition (1873-1876). Subsequently more diverse and more representative material was collected by several other expeditions : German (“Gazelle” and “Valdivia”), Soviet (“Ob”, ‘.‘Academician Knipovich”, scientific exploration expeditions of the Atlantic Scientific Research Institute of Fisheries and Oceanography), and South African (expeditions of the South African National Committee on Oceanographic Investigations and Capetown University). Due to the integrated geological and geophysical investigations made in recent years, the geology of this area has now been studied much more completely than in other marginal zones of the oceans (Dingle, 1970, 1971, 1973a, b, 1974; Emery et al., 1975; Rogers 1971).

56

Fig. 2-1. Distribution of phosphorite o n the ocean floor (Baturin and Bezrukov, 1971). Legend: 1-4 = phosphorite on the submerged margins of continents; 5-7 = phosphorite on seamounts ( I = Holocene; 2, 5 = Neogene; 3, 6 = Paleogene; 4, 7 = Cretaceous).

The lower structural level of Agulhas Bank consists of a Paleozoic folded basement, on which lie Meso-Cenozoic deposits up to 6.2 km thick (Dingle, 1973a,b). Beneath a thin layer of Quaternary sediments (they are entirely absent over a substantial area) pre-Cretaceous (apparently Jurassic), Cretaceous, and Tertiary deposits occur on the shelf and continental slope (Fig. 2-3). The unconsolidated sediments on the bottom surface are quartz sands with shell detritus, glauconite sands, muddy sediments, and oozes proper (Fig. 2-4). Most of these sediments are characterized by a phosphorus content higher than the Clarke (more than 0.25%P, O5 ). Sediments containing more than 0.75%P,O, occur in four places: west of Cape Agulhas at depths of 200500 m (mainly glauconite sands, containing up t o 10%P, 0, ); south of Cape Agulhas (sands containing shells and in part oozes with fecal pellets, containing 0.75-2.0% P, 0, ); southeast of the mouth of the Gourits River (two belts parallel to the coast, chiefly of glauconite sands on the shelf and upper part of the continental slope, containing up to 7.8%P, O 5; Fig. 2-5). The high content of phosphorus in all types of sediments is related to the presence of phosphate grains, glauconite, or fecal pellets (Summerhayes, 1973). The phosphate grains are angular or semi-rounded and identical in composition to phosphorite concretions. The glauconite consists of black pellets containing 1.6-11.5% P, O5 and light-green grains containing 0.263.0% P , 0 5 , eroded from rocks of different composition. According to the

57

Fig. 2-2. Distribution of phosphorite and phosphatized rocks on the western shelf of Africa (Kharin and Soldatov, 1975). Phosphorite: 1 = brecciated; 2 = conglomeratic; 3 = fine-grained;4 = mammal and fish bones. Phosphatized rocks: 5 = carbonate; 6 = clastic; 7 = limestone; 8 = marl; 9 = dolomite; 10 = siltstone and mudstone; 11 = sandstone; 12 = 200-m isobath. Phosphorite basins of the African coast: 13 = Paleogene; 14 = Upper Cretaceous.

data of X-ray diffractometer investigations, the phosphorus in the black pellets, which were eroded from phosphorites, enters into the composition of carbonate-apatite (Birch, 1971). The muddy sediment fractions, rich in fecal pellets, contain up to 3.25%

58

Fig. 2-3. Geology of Agulhas Bank (Summerhayes, 1973). Rocks: 1 = pre-Cretaceous; 2 = Cretaceous; 3 = Tertiary; 4 = sampling point.

P, 0 5 ,but the form of occurrence of the phosphorus in them has not been established. The phosphorites in the Agulhas Bank area occur mainly a t depths of 100-500 m. Their form is nodular (concretionary), sheeted or irregular, their size from 1cm to 1.5 x 0.3 m. According to the description by Murray and Renard (1891), the first phosphorite samples they investigated from this area consisted of dense round or angular nodules 1 4 c m in size. The surface of the nodules is glazed, brown, with a thin film of iron and manganese hydroxides. Irregularities produced by inclusions of heterogeneous material cemented by phosphate are often encountered on the surface of the nodules. The composition of the non-phosphate component of the nodules is governed mainly by the composition of the enclosing sediments, which indicates that the phos-

Fig. 2-4. Sediments of Agulhas Bank (Rogers, 1971; Summerhayes, 1973): I =shell and quartz sands; 2 = glauconite sands; 3 = muddy sediments; 4 = oozes.

59

Fig. 2-5. Distribution of phosphorus in the unconsolidated sediments on Agulhas Bank (Summerhayes, 1973): 1 = < 0 . 2 5 ; 2 = 0.25-0.8; 3 = 0.8-2; 4 = 2-4; 5 = 4% P z 0 5 .

>

phorites were formed in situ. Concretions from shallow depths, containing grains of glauconite and tests of foraminifera, themselves occur in glauconitic or foraminiferal sands. Concretions from greater depths contain more organogenic remains and fewer mineral grains. Replacement of particles of mud and foraminifera tests by phosphate is often observed in them. The phosphorites consist mainly of phosphate cement enveloping small grains of phosphatic and non-phosphatic material. The phosphate in the cavities of foraminifera is purer than that which cements the grains. Individual samples of phosphorite from Agulhas Bank are also described in several other works (Cayeux, 1934; Collet and Lee, 1905; Murray and Philippi, 1908). In recent years geologists at Capetown University have collected and investigated in detail a new representative collection of phosphorites (Parker, 1971, 1975; Parker and Siesser, 1972). According to their classification, phosphorites are divided into non-conglomeratic (which can be called nodular) and conglomeratic. The nodular phosphorites consist of phosphatized limestones and glauconite-quartz sandstones. Ferruginized and nonferruginized varieties are distinguished among the phosphatized limestones. A glazed surface is typical of the former, a rough surface of the latter. The phosphatized limestones consist of whole and comminuted tests of foraminifera, chiefly planktonic ( 4 0 - 6 5%);fragments of mollusk shells and bryozoan colonies (1-10%), occasional spines and plates of echinoderm skeletons (Fig. 2-6). The clastic components - quartz and feldspar - occur in the form of angular grains of silt dimensions (1-5%). In the non-ferruginized phosphorites the cement is micrite-collophane; its color varies from yellow (collophane) t o gray (micrite); sometimes brown patches of goethite are encountered. The chambers of foraminifera are filled with phosphate-carbonate cement, less often with glauconite or goethite.

60

Fig. 2-6. Organogenic structure of foraminifera1 ooze of phosphorite from Agulhas Bank. White = calcite, dark = phosphate cement. Thin-section, X 140, 11 nicols.

The ferruginized phosphorites differ from the non-ferruginized in that their cement is much richer in finely dispersed goethite. There are no fragments of macrofauna in the ferruginized phosphorites. Some nodules of phosphatized limestone are coated with a discontinuous layer of secondary phosphate up to 1cm thick. Inclusions of glauconite and quartz grains, foraminifera, and fragments of carbonate rocks are present in it (Parker and Siesser, 1972). The nodules of phosphatized glauconite-quartz sandstones consist of grains of glauconite (20-60%), whole and broken tests of foraminifera (130%), quartz grains (5-20%), and fragments of mollusk shells (1-776). The cement is collophane-micrite. The size of the glauconite grains varies from fine to coarse sandy; their shape is equidimensional or irregular. Within some grains there are inclusions of pyrite, which also occurs in the phosphate cement. Rounded and angular

61 grains also occur among the quartz grains, which are from sand to silt size. In some samples semi-rounded collophane pellets are found, some of them homogeneous and others containing inclusions of non-phosphatic material in the nucleus. In samples with a high quartz content, isolated grains of zircon, feldspar, garnet, and tourmaline are observed. Micrite and small inclusions of irregular shape consisting of organic matter or goethite are irregularly disseminated in the collophane cement. Some of the grains of glauconite and quartz are coated with dahllite. The pores of the rock are filled with secondary acicular calcite. The conglomeratic phosphorites, which are most common in this area, consist of pebbles of phosphatized limestone (up to 50% of the rock) held together by a cement similar in composition to the phosphatized glauconitequartz sandstones described above. In many samples of this type two or three conglomerate layers are clearly seen, differing in size of pebbles and content of glauconite grains in the cement. Bedding planes separating layers with denser or less dense packing of grains are also distinguished in the cement. The surface of these planes is glazed and brown due to the higher content of iron hydroxides and organic matter. Upon impact the rock breaks along the planes. In addition, irregular microerosion surfaces are observed in the conglomeratic phosphorites which cut across grains of glauconite, shells, and bedding planes. In the rock there are irregularities and traces of pholad borings, filled with white non-phosphatized micrite with isolated grains of glauconite and foraminifer tests. In some samples of conglomeratic phosphorite there are casts of shells of bivalve mollusks consisting of phosphatized foraminiferal sediment; typical of such samples is a lower content of glauconite, high content of goethite, and the presence of fragments of macrofauna and bones. On the whole, rocks of the last two types are characterized by one common feature: the closer they occur to the shore and the smaller the width of the shelf, the higher the content and the larger the size of the quartz and glauconite grains in them. Study of hand specimens and thin sections has shown that the phosphate in the phosphorites of this area occurs only in the collophane-micritegoethite cement and does not replace. the carbonate remains of organisms, not even the thin-walled tests of foraminifera. In this case the phosphate mineral of the phosphorites is francolite with a high C 0 2 content - up to 5.7% (Parker, 1971, 1975;Parker and Siesser, 1972). Kharin and Soldatov (1975)distinguish brecciform, conglomeratic, and fine-grained varieties among the phosphorites of the submerged margin of South Africa (and the shelf of West Africa as a whole). The first two are charact.erized by the presence of fragments and pebbles of phosphate rock

62

63

Fig. 2-7. Microstructure of phosphorite from Agulhas Bank; electron microscope, X 20,000 (Baturin and Dubinchuk, 1974b). (a) Gel-like phosphate; (b) microgranular phosphate; (c) fibrous (top) and ultramicrocrystalline (bottom) phosphate (microdiffraction pattern of phosphate in upper left corner); (d) ultramicrocrystalline phosphate; (e) contact of carbonate (right) and phosphate; ( f ) crystals of fluorcarbonate-apatite in cavity of a carbonate grain (upper left: microdiffraction pattern of phosphate).

(phosphatized foraminifera1 limestones, calcareous-ferruginous phosphorites), held together by phosphatic-calcareous or phosphatic-calcareous-ferruginous cement. Phosphatized limestones and sandstones of psammitic texture, consisting of grains of phosphate, glauconite, quartz, and feldspar (rarely of monoclinic pyroxene, zircon, apatite, and ore minerals) cemented by a clayey-calcareous-phosphatic mass, belong to the fine-grained group. The following varieties of phosphate were distinguished in investigation of the microstructure of the phosphorites under the electron microscope (Baturin and Dubinchuk, 1974a); (1)Gel-like (Fig. 2-7a). (2) Microgranular, forming solid masses and globules 1-3 pm in diameter (Fig. 2-7b, top). The rough surface of the phosphate is caused by the fact that it consists of granules less than 0.1 pm in size.

64

(3) Fibrous, constituting the inner parts of the globules (Fig. 2 - 7 top). ~~ Microdiffraction investigation on particles extracted on replicas (Fig. 2-7c) suggests that the crystal structure of the phosphate is defective. (4) Ultramicrocrystalline phosphate, forming a “jacket” on the surface of globules of amorphous phosphate. The size of the tabular hexagonal crystals of apatite is 0.1-0.3 pm (Fig. 2 - 7 ~bottom; ~ 2-7d). In particular, apatite crystals are formed at the carbonate phosphate contact as a result of metasomatic replacement of carbonate (Fig. 2-7e, right) by phosphate (Fig. 2-7e, left). (5) Microcrystalline phosphate consisting of crystals 1-3 pm in size (Fig. 2-7f). Euhedral crystals are often formed in the cavities within carbonate grains (Fig. 2-7f, center). Microdiffraction of extracted particles (Fig. 2-7f, upper left corner) confirms that the phosphate consists of fluorcarbonateapatite. ( 6 ) Multiphase microgranular cement consisting of carbonate, phosphate, quartz, and layered silicates, according to microdiffraction data. According to the data of chemical analyses (Parker, 1971; Table 2-1), the P, 0, content of the phosphorites and phosphatized rocks of the submerged margin of South Africa ranges from 0.3 to 2476, CaO from 17.7 to 50%, Fez O3 from 0.60 to 50%, and SiO, from 0.9 to 27.4%. The insoluble residue consists, as is typical of all phosphorites, chiefly of SiO, and Al,03 (Table 2-2). In Parker’s (1971) thin-section investigation it was observed that in some samples phosphatization becomes weaker from the periphery of the concretions toward the center. This observation is confirmed by the results of chemical analysis (Table 2-3). The phosphatized and ferruginized limestones are similar to the nonphosphatized and non-ferruginized limestones in structure, composition of microfauna, and clastic components, differing only in the composition of the cement - micrite, collophane-micrite, and goethite-collophane-micrite (Parker and Siesser, 1972). This suggests that the carbonate, phosphate, and ferruginous rocks of Agulhas Bank are genetically related, and that the phosphatization and ferruginization, t o which primarily the carbonate cement of the original rock has been subjected, was diagenetic in nature. The presence of phosphate pebbles, phosphate cement, and the external phosphate coating indicates at least three stages of phosphatization. The question of the age of the phosphorites of Agulhas Bank was first raised by Murray and Renard ( 1891) who, noting their similarity to Tertiary phosphates on land, nevertheless concluded that they are Recent. The basis for that conclusion was the identical composition of the non-phosphatic components (glauconite, foraminifera) in the phosphorites and in the enclosing sediments. However, it has now been established that the glauconite in these sediments is derived from Tertiary deposits which were eroded twice

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66 TABLE 2-2 Composition (%) of insoluble residue (IR) of phosphorite from Agulhas Bank (Murray and Renard, 1891) Component

Station 142, depth 274 m (IR = 17.34%)

Station 143, depth 3480 m (IR = 11.93%)

77.43 12.40 1.07 1.02 7.91

76.58 13.85 1.27 1.18 7.93

99.80

100.81

- in the Oligocene and at the Pliocene/Pleistocene boundary. As a result of these erosions the shelf belt has been displaced 15 miles toward the shore since mid-Tertiary time (Birch, 1971; Dingle, 1973a). The age of the foraminifera from the non-phosphatized limestones of this area has been determined as Middle Miocene (Parker and Siesser, 1972). Coccoliths of Oligocene age, identified by S.I. Shumenko as Coccolithus cf. primalis Roth, CycloTABLE 2-3 Variation in composition (%) of concretions from station 43 from periphery t o center (Parker and Siesser, 1972) In natural substance

Recalculated to silica-free substance

outer part

nucleus

outer part

1.77 0.06 0.82 0.54 0.01 1.09 51.33 0.38 0.28 11.32 30.90

-

-

pz 0 s LO1

3.88 0.06 1.34 0.93 0.01 0.39 49.53 0.53 0.40 13.93 26.69

0.06 1.39 0.97 0.01 0.93 51.50 0.55 0.42 14.50 27.77

0.06 0.83 0.55 0.01 1.11 52.25 0.39 0.29 11.52 31.46

Total

98.19

98.50

98.50

98.47

Component

SiOz Ti02 Ah 0 3 Fez 0; MnO MgO CaO Naz 0

Kz 0

* Total iron

nucleus

67

Fig. 2-8. Oligocene coccolith (Cyclococcolithus sp.) in phosphorite concretion from Agulhas Bank; X 15,000 (identified by S.I. Shumenko).

coccolithus sp., and Prinsins sp., have been found in the phosphorites themselves (Fig. 2-8). Data on the isotopic composition of uranium in the phosphorites shows that they are more than 1Ma old (Kolodny and Kaplan, 1970a). Finally, the coincidence of the zones of occurrence of phosphorite with outcrops of eroded Tertiary rocks (Fig. 2-3) unequivocally indicates their Tertiary (Oligocene/Miocene) age. Detailed investigation of the fractions of the surface layer of sediments on Agulhas Bank has shown that no phosphatization of carbonates at the waterbottom interface is occurring under present conditions (Summerhayes, 1973). The total reserves of phosphorite and phosphatized rocks (> 1%P, O5) on Agulhas Bank, estimated on the basis of their presumed thickness of 1m, are 140 million tons of PzO,. Some of these rocks are easily beneficiated, by and represent a potential means of mechanical fractionation, to 16%P, 05, reserve of phosphate raw material. Agricultural experiments carried out by the South African company “Fertilizer Development Corporation’’ on the use of ground phosphorites from Agulhas Bank as fertilizer showed that the availability of the phosphorus they contain is at the level of the availability of commercial superphosphate (Summerhayes, 1973).

68

However, the prospects for commercial development of the phosphorites are dim until detailed exploration is done, for the weight of the rocks brought up in dredging is highly variable (< 1 to > 100 kg) (Parker, 1975). Shelf of northwest Africa The shelf of northwest Africa includes the shelves of Morocco and the Sahara. Phosphorites were first found on the Morocco shelf by the “Dacia” expedition (1883). However, this did not become known until 40 years later, when the samples were chemically analyzed (Murray and Chumley, 1924). Subsequently phosphorites were found on the Morocco shelf and also on the Sahara shelf by several other expeditions (Baturin et al., 1973; Kharin and Soldatov, 1975; Summerhayes, 1970, 1972; Tooms and Summerhayes, 1968). In its geological structure the shelf of northwest Africa constitutes a single whole with the adjacent land areas (Lavrov e t al., 1969; Summerhayes et al., 1971). The unconsolidated deposits on the Morocco and Sahara shelves consist chiefly of carbonate sands and silts from < 2 to 10 m thick, rarely 20-35 m. Their main constituents are biogenic carbonates (shell, coral, and bryozoan detritus, foraminifera) and clastic material (mainly quartz, less often feldspar, hornblende, epidote, magnetite). Glauconite occurs locally in the form of grains and fillings of foraminifera tests (Summerhayes et al., 1972). The phosphorites are represented by slightly phosphatized calcareous sands, phosphorite conglomerates, and phosphatized limestones. Phosphate sands occur on the outer shelf of Morocco (between Agadir and Rabat) and of the North Sahara, in the central part of the Morocco shelf (between Safi and El Jadida), and at several points on the inner shelf near the shore (Fig. 2-9). The sands richest in phosphate grains (in the El Jadida region) contain up to 7.9%P2 0 5 ,or up to 20% P, O5 when recalculated to carbonate-free substance. In all the rest of the shelf area the P2 O 5 content in the sediments ranges from 0.11 to 4.6% (per carbonate-free substance) (Summerhayes et al., 1972, 1976). Among the phosphorites proper, conglomeratic varieties predominate; they occur at depths of 150-300 m in the form of concretions of irregular shape, angular fragments and blocks. According to the data of Kharin and Soldatov (1975), the texture of the phosphorites is psephitic, the structure massive or indistinctly bedded. The gravel is from < 1 to 6-8 cm in size and not sorted; in composition it consists of glauconitic sandstones with fragments of granular phosphorite, phosphatic cores of foraminifera, and grains of quartz, feldspar, and pyrite. The cement of the rock is calcareous-phos-

P

.

l

O

R

O

C

C

0

I

Fig. 2-9. Distribution of phosphorus in Morocco shelf sediments (Summerhayes et al., 1 9 7 2 ) : 1 = > 1 ; 2 = 0.5-1; 3 = 0.2-0.5; 4 = < 0.2%P 2 0 s . 5 = sampling localities.

70

Fig. 2-10.Contact between phosphatized fine-silty cement (left) and phosphate gravel with inclusions of foraminifera tests, glauconite and quartz grains (right), in a concretion from the Morocco shelf. Thin-section, X 60, 11 nicols.

phatic with the inclusion of isolated grains of calcite, quartz, glauconite, rhombohedra of dolomite, tests of foraminifera, and iron hydroxides. On the whole the gravel and cement are similar in composition but differ in the size and amount of inclusions (Fig. 2-10). Investigation of samples under the electron microscope (Baturin and Dubinchuk, 1975) showed that the phosphate, which occurs in the form of solid spots, is mainly amorphous (Fig, 2-lla), but in some cases it is microcrystalline, with crystallites -0.5 pm in size (Fig. 2 - l l b ) . Euhedral crystals of fluorcarbonate-apatite are developed mainly at the contact between the cement and the carbonate material, which may be completely replaced by phosphate (Fig. 2 - l l c , d). Typical of the chemical composition of the phosphates of the North African shelf (Table 2-4) are substantial variations in P 2 0 5 content (1023%), related t o unevenness of phosphatization and high content of F e 2 0 , (6-21%), which is fixed in goethite, and of MgO (2.9-3.7%), which is fixed in dolomite. According to the data of MacArthur, the phosphatic matter of these phosphorites is distinguished by a high C 0 2 content - 6.0% on the

TABLE 2-4 Chemical composition of phosphorites 1%) from the shelf of northwest Africa Coordinates

Depth

Sample'

PIOq

CaO

MgO

Si02

TiO,

AI,O,

Fe,O,

FeO

MnO

CO,

C,,

F

LO1

F/P>O,

a a

1888 23.0 19.10 21.90 1084 19.70 10.60

39.76 4020 3680 37.80 38.81 42.7 42.0

3.7

6.85

0.03 0.OH 0.15 0.15 0.25

1.53

6.86 12.50 15.20

0.46 -

0.04 0.03 0.03 0 03 002 0.01 0.05

13 71

0.52 -

1.88 -

15 95 -

0.100 -

(m) 31'55". 9'48'W 31'49". 10°12'W 31'43". 10'09'W 31'34". 10'13'W 33'19". 9'04'W 25'59". 16O16'W 28'23'N. 12'Il'W

150 210 290 275

250 240 55

a a a

b C

-

2.89 -

-

1.41

-

0.52

-

0.15

-

-

0.25

-

* a = conglomeratic phosphorite: b = brecciform phosph0rite.e = fine-grained phosphorite

15.45 14.75

6.15 21.10

-

-

-

-

-

-

-

26.03 -

(first sample ( I 5 0 m depth), from Baturin, 1975a.the others. from Kharin and Soldatov. 19751

72 average (Parker, 1975). The question of the age of the phosphorites on the shelf of North Africa has been fairly definitely answered (Kharin and Soldatov, 1975; Summerhayes et al., 1972). The results of Summerhayes’ investigations on fragmental shell material and glauconite and the details of granulometric composition of the sediments (median diameter, sorting coefficient) showed that the sands, including the phosphatic sands, are relict. The Recent and pre-Quaternary biogenic carbonate detritus found on the bottom surface (fragments of shells, corals, foraminifera) contains 0.080.1% P, O 5 all told, i.e. under the present conditions, no phosphatization is taking place at the water-bottom interface. On the basis of comparison of the geology and petrography of the rocks of the shelf and of the adjacent land it has been established that the phosphorites on the shelf were eroded from rocks of different age: Upper Cretaceous (phosphatized limestones), Eocene (phosphate grains, conglomeratic phosphorites), and Miocene (glauconitic and conglomeratic phosphatized limestones). In particular, calcareous phosphate-bearing rocks of Middle Miocene and Lower Pliocene age are the source of the phosphatic material in the unconsolidated sediments of the Sahara shelf.

73

Fig. 2-11. Microstructure of phosphorites from the Morocco shelf; electron microscope, X 7 0 (Baturin and Dubinchuk, 1975). (a) Amorphous phosphate (in center); (b) microcrystalline phosphate; (c) growth of crystals of fluorcarbonate-apatite at contact of carbonate grain (white in center) with phosphatized cement; (d) replacement of carbonate material by crystalline phosphate.

The absolute age of three samples of glauconite grains associated with the phosphates from the Sahara shelf (Essaouira area, shelf and upper part of continental slope), determined by the potassium-argon method, is from 10.6 k0.5 to 14.4 k0.5 Ma, i.e. Miocene (Summerhayes et al., 1972). According to the identification by V.A. Krasheninnikov, foraminifera in two phosphorite samples from the Morocco shelf (32'N) and Sahara shelf (25'N) also prove to be Middle Miocene (Kharin and Soldatov, 1975). The area of occurrence of the phosphate sediments (with a content of > 1%P2O5) on the shelf of northwest Africa is estimated as 3300 km2,the thickness as 5 m, and the P205 reserves as 430 million tons (Summerhayes et al., 1972). But the existence of vast reserves and high quality of the phosphorite on the adjacent land makes the practical utilization of the phosphorite of the shelf of northwest Africa very remote.

74 Shelf of southwest Africa The shelf of southwest Africa includes the Namibia shelf (from the mouth of the Cunene River, 16'S, to the mouth of the Orange River, 28'30's) and the northwestern part of the shelf of the South African Republic to the Cape of Good Hope (34's). In the northern part of this zone the shelf is narrow and steep, and south of 20's it is relatively wide (100-200 km) and flat; the slope of the bottom in the Walvis Bay area (23's) is 0'14'. On the whole the shelf of southwest Africa is asymmetrical and includes a flat inner shelf, a relatively clearly expressed scarp at a depth of 140-160m, a steeper, often concave outer shelf, and a bend marking the boundary of the shelf and continental slope (at depths of 270-400 m). Here the rocks of the Precambrian/Paleozoic crystalline basement lie at great depth; in the Capetown area they dip toward the ocean at an angle of 2-3". The basement is overlain by presumably Cretaceous rocks, on which lie Tertiary rocks consisting of four members of the same type separated by erosional surfaces. The total thickness of the sedimentary cover in the zone of the shelf and continental slope reaches 3-4 km, and the thickness of Tertiary rocks on the shelf reaches 0.8-1.3 km (Bryan and Simpson, 1971; DuPlessis et al., 1972;Van Andel and Calvert, 1971). On top of the shelf floor and upper part of the continental slope of southwest Africa there occur siliceous (diatomaceous), calcareous, clastic, and glauconitic sediments (Fig. 2-12).The sediments of each of these types are locally enriched in phosphorus due to the presence of phosphate grains, fragments of phosphate rocks, and biogenic detritus. An investigation of 900 samples (Summerhayes et al., 1973) has established that the most extensive zone of high phosphorus contents in the sediments (up to 23% P,O,) occupies the shelf and upper part of the continental slope north of 26's to Walvis Bay. Farther south, phosphatic sediments containing up to 9% P,05 occur in the form of isolated patches (Fig. 2-13). The phosphorites on the shelf and upper part of the continental slope of southwest Africa consist of phosphate sands, sheets, blocks, and large concretions of dense phosphate rock, unconsolidated and compacted phosphate nodules in diatomaceous oozes, phosphatized coprolites, bones of fish and marine mammals. Phosphatic medium and fine sands, containing 6-23s P, 0, , occur among the clastic slightly calcareous and biogenic calcareous sediments (Table 2-5). According to the data of an investigation of eight samples of the sands, their median diameter lies between 0.15 and 0.31mm, the coefficient of sorting between 1.52 and 2.86,and the content of phosphate grains between 29.5 and 74%.

75

Fig. 2-12.Types of sediments on the shelf of southwest Africa (Yemelyanov and Senin, 1969). (a) Granulometry of the sediments: 1 = stations; 2 = sands and coarse silts; 3 = fine-grained sediments; 4 = mud-sand interface; 5 = 200- and 4000-m isobaths; 6 = boundary of humid and arid zones. (b) Sediments: 7 = clastic; 8 = calcareous; 9 = siliceous; 10 = glauconitic; 11 = chamositic. (c) Distribution of fecal, chamositic, and glauconitic pellets; percent by weight of sediments: 12 = 1; 13 = 1-10; 14 = 10.

<

>

34"

32"

33O

31'

30'

29"

28"

27'

26'

25'

24'

U1

17' Q0

[14 2

B3

10O

4

130

R '41

34O

33 O

32'

31'

30'

28O

27'

26'

25'

Fig. 2-13. Distribution of phosphorus in the sediments on the shelf and continental slope of southwest Africa (Summerhayes et al., 1973): I = 0 - 0 . 5 ; 2 = 0.5-1.0; 3 = 1.0-2.5; 4 = 2.5-5.0; 5 = 5-15; 6 = 15%P205.

>

24'

5 6

77 TABLE 2-5 Phosphorus content in the sediments of the outer shelf of southwest Africa (Senin, 1970) Sediment

Depth (m)

CaC03 (%)

N

p 2 0 5 (%)

range of values

average

-

6.84 4.38 6.79 3.75

range of values

average

-

0.60 0.29 1.26 0.28

1 2 11 1

19.02 8.44 0.74

1 7 7

5.27 0.46 0.39

6 1 1

0.46 2.29 2.53

1 11 4

Clastic medium sands fine sands silts fine silty muds

151 113-124 99-3 12 360

Clastic slightly calcareous medium sands fine sands silts

172 110-2 12 12.40-2 5.74 118-380 10.26-25.1 3

28.28 19.90 20.03

Biogenic slightly calcareous fine sands silts fine silty muds

150-285 370 310

41.37 32.30 48.49

Biogenic calcareous medium sands fine sands silts

130 160-305 305-470

51.42-6 8.69 57.21-69.40

68.20 63.29 64.20

Biogenic highly calcareous fine sands silts fine silty muds

150-3 52 71.66-8 4.81 295-382 70.99-7 4.25 420

76.54 73.00 74.20

0.14-2.60 0.25-3.45

0.80 1.85 0.51

10 4 1

Glauconitic fine sands silts

142-3 10 230

4.48 12.88

0.36-4.18 1.77-2.13

1.65 1.95

5 2

3.50-5.2 7 2.16-8.83 -

36.05-48.33 -

0.32-7.5 1 8.47-1 7.30

0.25-0.31 0.25-6.62 -

-

0.21-2 2.9 0.32-2.14

0.39-15.00 -

0.23-6.46 0.37-6.3 5

-

N = number of samples.

The size of the phosphate grains in these sediments usually is 0.05-0.25 mm, the shape round or slightly oval, the color black, the surface shiny or rough (Fig. 2-14), the specific gravity usually 2.50-2.89 (sometimes somewhat more or somewhat less), and the average P , 0 5 content about 32.3%. The grains consist of yellowish-brown amorphous or cryptocrystalline phosphate with abundant black flocs of organic matter. Under the microscope in transmitted light they are opaque or transparent only at the edges. Semi-

78

Fig. 2-14. Phosphatic sand from the outer shelf of southwest Africa (grains of phosphate, quartz, and foraminifera tests); X 30 (Baturin, 1971b).

transparent and transparent phosphate usually is isotropic, with a refractive index of 1.579-1.610. In some grains the phosphate is crystalline and characterized by anisotropy with weak birefringence (0.002-0.005) and its refractive index is higher than that of the isotropic phosphate (1.610-1.630), but there are no clean-cut boundaries between these two modifications of the phosphate. Judging from the results of X-ray analysis, the phosphate of the grains is fluorcarbonate-apatite with unit cell parameters of a = 9.32, c = 6 . 8 7 a (Senin, 1970; Yemel'yanov, 1973a). Grains of this type occur in foraminifera tests, phosphate nodules, and coprolites, as well as in phosphatic sands. Sheets, blocks, and large concretions of dense phosphorite occur in the northern (18-26"S, depths of 115-335 m) and southern parts (30-33'S, depths of 250-1000 m) of the region in question in reworked clasticcalcareous sediments and consist chiefly of fine-grained, to a lesser extent of brecciform and conglomeratic, varieties (Fig. 2-15), The last two varieties are similar in composition to the phosphorites of Agulhas Bank and the Morocco shelf. Phosphatized limestones and sandstones containing more than 10% P, O5 belong to the fine-grained phosphorites. Rocks of similar composition but with a lower P, O5 content are also known.

79

Fig. 2-15. Conglomeratic concretions from the outer shelf of southwest Africa (Walvis Bay area); X 0.5.

The fine-grained phosphorites consist of various grains, chiefly of sand-silt dimensions, and a cementing matrix. The phosphate grains are round, oval, or irregular in shape. The phosphate of the grains is slightly anisotropic and differs from the phosphate cement in the more intense yellow color. Often the grains are surrounded by a thin (0.01mm) rim of crystalline phosphate and are pyritized, sometimes to complete replacement of the phosphate by pyrite. In some grains tiny bone fragments are observed. Inclusions of elongated and angular bone fragments are also observed in the cementing matrix; usually they are surrounded by a rim (0.3mm) of finely crystalline phosphate and are pyritized. Microglobules of pyrite and clusters of them are concentrated on the periphery of the bone fragments, but sometimes also inside them and in the Haversian canals. Glauconite occurs in the form of angular and semi-rounded grains, sometimes fractured and in part broken. The glauconite is often pyritized. Micro-

00 0

TABLE 2-6 Chemical composition (9%) of phosphorites from reworked sediments o n shelf o f southwest Africa (Kharin and Soldatov, 1975) Coordinates

Depth (m)

Sample*

P,O,

CaO

17"25'S, 11'29'E 25'31'5, 14'02'E 31°53'S, 16'16'E 3lo15'S, 16'08'E 32'45'S, 16'55'E 3Zo45'S, 16'55'E 33'21's. 17'39'E 33'28'S, 17'38'E 33"28'S, 17'38'E 33'33'S, 18°21'E 18'35'S, 11'45'E 18'35'S, 11'45'E 18'35'S, 11'45'E 18'35'S, 11'45'E 30'35'5, 15'06'E

150 215 465 490 430 430 245 238 238 318 185 185 185 185 470

a** b b b

21.77 10.67 13.70 10.58 15.10 19.95 11.97 11.79 15.22 16.68 19.23 24.37 23.90 28.99 25.40

34.27 33.64 41.10 36.05 26.37 40.54 24.81 22.25 25.36 30.08 37.71 46.59 36.32 49.37 53.90

b b b b

b b*** c c d d d

1.80 13.22

-

1.51 1.68 1.14 3.74 2.61 1.75 2.22 4.71 0.90 12.04 0.80 -

SiO,

TiO,

Al,O,

19.13 1.53

0.34 0.07 0.05 0.12 0.22 0.10 0.11 0.27 0.05

1.92 0.63

-

7.16 10.06 10.61 30.07 39.97 38.79 26.70 2.65 2.30 0.56 0.17 -

-

0.15 0.08 0.06 0.03 0.05

-

0.95 1.17 2.16 2.10 1.47 2.33 7.51 0.42 1.16 tr. 0.78 -

MnO 4.60 2.03 10.40 2.49 2.47 2.73 12.32 5.23 4.81 5.34 1.74 2.04 0.99 0.78 2.50

0.013 0.01 0.06 0.01 tr.

0.76 1.23

-

-

-

0.59 0.63 -

0.01 0.03

2.40

0.52 0.45

-

-

1.75 -

0.01 -

0.01

= dense uniform concretion; b = fine-grained phosphorite; c = brecciform phosphorite; d = conglomeratic *** aAfter Baturin et al. (1970). *** After Murray and Philippi (1908).

-

0.66

-

phosphorite.

27.97 13.15 15.90 8.82 5.19

-

-

1.11

0.112

-

-

-

0.01

7.61 30.54

-

2.40 -

2.62 -

12.33 14.89 11.33 11.69 -

-

0.088 -

0.098

-

0.090 -

81 globules of pyrite are situated on the periphery, in the center, and in fractures in the glauconite grains. Clastic material consists of angular grains of quartz, sometimes with mosaic extinction, and to a lesser extent of grains of feldspar, rarely of monoclinic pyroxene, zircon, and ore minerals. Other components are the following: finely dispersed calcite, foraminifera tests with brown phosphate cores, fragments of mollusk shells, dolomite, flocculent inclusions of organic matter. All in all, the amount of inclusions contained in the cement ranges from 5 to 50%in different places. The cement of the rock is clayey-calcareous-phosphatic, sometimes with an admixture of iron hydroxides. The phosphate of the cement is grayish yellow, mainly amorphous, with a refractive index of 1.592-1.600 (Baturin et al., 1970; Kharin and Soldatov, 1975). According to the data of chemical analyses (Table 2-6), the P, O5 content in the slabs and blocks of phosphorite on the shelf of southwest Africa ranges from 10 to 22% in the fine-grained and from 19 to 29% in the brecciform and conglomeratic varieties. The extent of ferruginization of the phosphorites varies widely (0.8--12.3% Fe, O3 ). The fine-grained phosphorites from the southern part of the area (31-33”s) are the most ferruginized. Phosphate concretions in diatomaceous oozes consist of a number of varieties representing a gradual transition from unconsolidated to lithified formations. The main types of these concretions are the following: (1)Phosphatized soft clots of diatomaceous ooze from fractions of a millimeter to 1-4 mm in size. They occur in the form of round, lenticular, tabular, and also incrusting and shapeless formations. They differ from the enclosing dark green semi-liquid diatomaceous oozes in the yellowish-white color and somewhat denser consistency (Fig. 2-16). Wet clots are easily smeared, and dry ones crumble with slight pressure. (2) Unconsolidated phosphatic concretions, white, light yellow, or yellowish-gray in color, round or flattened in shape, and from fractions of a millimeter to 1-4 cm in size (Fig. 2-17). In thin-section and under the scanning microscope it is seen that concretions of this kind are of phosphatized diatomaceous ooze (Fig. 2-18). The diatom valves are 0.05-0.25 mm in size and in many cases are covered with a blue coating of iron sulfide. In some of them small pyrite globules are observed. Fusiform segregations of phosphate (probably microcrystals), mainly 1-3 pm in size, are formed on the surface of the valves (Fig. 2-19). In some of the valves the opal wall is replaced by slightly polarizing phosphate. The mineral grains are fragments of feldspars, quartz, pyroxenes, hornblende, and ore minerals. They are angular, within 0.01-0.25 mm in size. The matrix consists of light yellow microgranular phosphate, in some places cryptocrystalline (non-polarizing), but mainly

82

Fig. 2-16. Phosphatized areas (white) in cores of diatomaceous oozes on the shelf of southwestern Africa (Veeh et al., 1974).

microcrystalline (faintly polarizing) and contaminated by pelite, tiny fragments of valves and spines of diatoms. In the phosphate there occasionally are encountered microglobules of pyrite, both solitary and in intergrowths of several individuals. The maximum size of the globules is 0.02 mm. (3) Granular (globular, up to 0.1-0.3 mm in size of globules) nodules of

83

Fig. 2-17 . Unconsolidated phosphatic concretions from diatomaceous oozes of the shelf of southwest Africa; natural size.

Fig. 2-18. Microstructures of unconsolidated phosphatic concretions. (a) Structure of diatomaceous ooze; scanning microscope, x 130. ( b ) Phosphate filling pores in diatom valve; scanning microscope, X 4000.

84

Fig. 2-19. Fusiform segregations of phosphate on the surface of diatom valve in uncon. solidated phosphate concretion; scanning microscope, X 12,000.

yellowish-gray color, with a hardness of 3 on Mohs’ scale, brittle, chiefly round or lozenge-shaped, up to 3-4 cm in size (Fig. 2-20). Nodules of this type are of three varieties: highly phosphatized diatomaceous ooze, chiefly amorphous concretions, and concretions mainly of finely crystalline phosphate. In the phosphatized diatomaceous ooze 40-6076 of the field of view in thin-sections is occupied by diatom valves, leaving rectangular cavities in transverse section (Fig. 2-21). Most of the valves are covered with a blue coating of iron sulfide which, as is seen in transverse sections, in some cases forms an easily discernible layer on the walls. In some valves intergrowths of pyrite microglobules are observed. The opal valves are replaced by slightly polarizing phosphate, the crystalline elements of which are oriented perpendicular t o the surface of the

85

Fig. 2-20. Dense granular phosphate nodules from diatomaceous oozes on the shelf of southwest Africa; natural size.

valve. The cavities of the valve sometimes are partially filled with pure yellowish phosphate. Angular grains of quartz, feldspars, pyroxenes, hornblende, biotite, and saussurite, and also acicular and columnar grains of calcite up to 0.10 mm in size, occupy 1-5% of the field of view. The diatom valves and mineral grains are embedded in a matrix (35-6096) of grayishyellow microglobular finely crystalline phosphate, contaminated by clayey and in part by carbonate pelite. The structure of the phosphate is fairly unconsolidated, as it consists of an aggregate of round clots of different size, the centers of which are more contaminated by pelite than the periphery. The phosphate microcrystals are mainly randomly oriented, but at the edges of some clots they are radially arranged. Microglobules of pyrite occur in places in the phosphate mass. Phosphate nodules of the second kind consist of microglobular isotropic phosphate (Fig. 2-22) with rare diatom valves (or cavities from them), an admixture of clayey pelite and angular grains of feldspars and calcite 0.010.05 mm in size (2-4% altogether). Intergrowths of pyrite microglobules tend to be associated with some diatom valves. In the phosphate mass rare and tiny irregular cavities and a large number of inclusions of nearly pure light yellow and yellow phosphate (up to 30%) are observed. Some of the

86

Fig. 2-21. Granular phosphatic concretion with cavities from diatom valves; thin-section, X 30, I( nicols.

inclusions are round or oval and consist of isotropic phosphate. They apparently are the filling of various cavities, including the cavities of diatom valves, produced in the formation of the phosphate concretions. In some cases the phosphate fills only part of these cavities. Intergrowths of pyrite globules are sometimes seen at the edges of the filling. Some other inclusions also are round or nearly oval in shape, but they consist of finely crystalline phosphate. These inclusions apparently were present in the sediment before formation of the nodules, in the form of isolated phosphate grains of an early generation. Phosphate nodules of the third variety consist of grayish-yellow microgranular, in part finely crystalline and in part (locally) isotropic phosphate with rare irregular cavities and fragments of bones (up t o a few millimeters in size) and with a small number of pyrite microglobules restricted mainly to the walls of the cavities. The cavities and bone fragments sometimes constitute 10-2096 of the thin-section area. In addition to these there occur isolated grains of clastic material, 0.01-0.10 mm in size. They are a deeper yellow color, sometimes striated (fibrous) and contaminated with a white opaque substance concentrated mainly in the middle of the inclusions, forming indistinct clots. The inclusions are phosphatized coprolites (see below).

87

Fig. 2-22. Globular microstructure of phosphate in granular phosphate nodule; scanning microscope, X 6000.

(4)Dense massive tannish-brown nodules, round, lozenge-shaped, elongated, and irregular in shape (Fig. 2-23).Their size varies from fractions of a millimeter t o 5-6 cm. Their color is due to the presence of a matte film on their surface which disappears on calcination. Beneath the brown film the material of the nodules is yellowish-gray in color; its hardness on the Mohs scale is 4-5. The nodules consist of fairly pure light yellow phosphate, chiefly microgranular and finely crystalline, in the mass of which rather many (5--15%) diatom valves are observed, sometimes coated with blue iron sulfides. The opal of the walls of the valves is replaced by finely crystalline phosphate. Pyrite in the form of solitary or clustered microglobules (up to 5%) is usually present in the phosphate and diatom valves. In addition, iso-

88

Fig. 2-23. Dense massive phosphate nodules from diatomaceous oozes on the shelf of rn southwest Africa, natural size.

lated angular grains of quartz, feldspars, and pyroxenes of silt size are encountered. Sometimes round and oblong opaque cavities (up to 2-3 mm long) are encountered. Rare radial aggregates of highly elongated flat colorless phosphate crystals with wedge-shaped, sometimes asymmetrical terrninations, 10-30 pm in size, with parallel extinction and positive elongation, are observed in the large cavities (Baturin et al., 1970). In electron microscope investigations of this type of concretion, several forms of secretion of the phosphate were established: fusiform crystals -1 pm long, aggregates of microglobules -0.1 pm in diameter with faint signs of crystallization, and also globules from one to several microns in diameter. The large globules are crystalline only on the periphery (Fig. 2-24a, lower left), but some small globules are completely crystalline (center of lower half). A t a magnification of x 20,000 it is seen that the crystallites constituting them are aggregates of relatively ordered st.acked filiform crystallites of second order, which in turn consist of still tinier crystalline elements (Fig. 2-24b). At the time of detailed sampling of the sediments of the shelf of Namibia during the 26th cruise of the research vessel “Mikhail Lomonosov” (1972), about 10 kg of phosphate concretions were washed out of the diatomaceous oozes, which made it possible to classify them in more detail lithologically and increase the number of varieties from 3 t o 6: soft, unconsolidated, compacted granular, compacted massive, dense gray, and dense brown (Baturin, 1974b).

89

Fig. 2-24. Globular microstructure of dense phosphate concretion. (a) Aggregates of phosphate microglobules; electron microscope, x 7000 (photo by V.T. Dubinchuk). ( b ) Crystallization of microglobules; electron microscope, x 20,000 (photo by V.T. Dubinchuk).

(5) A t the lower boundary of the zone of distribution of diatomaceous oozes, in diatom-shell sediments, there are no phosphate concretions of the varieties described above, but dense black phosphate grains of irregular shape with glazed surface and phosphate casts of gastropod shells (Fig. 2-25) are encountered. Some of the grains are fragments of completely phosphatized bones. Coprolites are diverse in morphology and composition and occur in sediments of various types. In the clastic and calcareous sediments of the shelf of southwest Africa both soft and lithified coprolites are encountered; they consist of elongated oval grains from 0.05 to 1-3 mm long, gray, greenish, or yellowish in color, opaque, fine-granular, with rough surface. In individual samples coprolites constitute up to 50-70% of the weight of the sediment. Coprolites of this type consist of fine-grained carbonate shell detritus and a yellow-brown flocculent mass of organic matter with inclusions of grains of clastic material and diatom valves. A high phosphorus content (up to 2%) is characteristic of

90

Fig. 2-25. Dense phosphate grains and phosphate cast of a gastropod from carbonate sediments near the lower boundary zone of diatomaceous oozes (depth 148 m); x 6.

the sediments rich in coprolites. Round phosphate grains 0.03-0.13 mm in diameter have been found in some coprolites (Senin, 1970). Beyond the shelf of southwest Africa, in the Niger delta area, coprolites of similar morphology consisting of clay material and glauconite are known in clastic sediments (Allen, 1965; Porrenga, 1967). Phosphatized coprolites from 1-2 mm to 5-6 cm in size, from fish and marine animals, are encountered in the diatomaceous oozes of the shelf of southwest Africa. Unlithified and lithified varieties are distinguished among the coprolites. White and gray unconsolidated coprolites (Fig. 2-26a) consist of isotropic phosphate of irregularly patchy color. The color of the spots is from pale yellowish gray to deep brownish yellow. In the phosphate mass there are many irregular elongated, sometimes branching cavities (up to 50% of the field of view), relatively rare inclusions of fragments of bones, scales, and teeth of fish (not more than 2-3% altogether), and also single and coalescing pyrite globules (not more than 1%). A typical feature of the structure of the material is the clearly manifested fibrous nature of many parts of it. Aggregates of fibers of different thickness sometimes bend in different directions. Also typical is contamination of the

91

Fig. 2-26. Phosphatized coprolites from diatomaceous oozes on the shelf of southwest Africa, natural size: (a) unconsolidated; (b) dense.

phosphate by a nearly opaque or opaque white substance, accumulations of which are situated in large indistinct areas of irregular shape, sometimes elongated in the direction of the fibers. The nearly opaque parts of this substance have a dark brown color in strong transmitted light.

92 No microgranular structure is detected in the phosphate; it resembles a glassy mass, the cracks in which have pink edges and often are curved as is typical of conchoidal fracture. Brown compacted and dense coprolites (Fig. 2-26b) consist of light grayish-yellow or yellow irregularly colored finely crystalline phosphate, with a multitude of round and highly elongated, sometimes branching cavities (up to 50%of the field of view). In places the phosphate is pure, in places contaminated to different degrees by an opaque brown or white finely dispersed substance. The latter is irregularly distributed, forming indistinct clusters of curved bands and spots, bounded by veinlets of purer phosphate (reticular structure). In many cavities radial aggregates of flat colorless crystals of phosphate and single or coalescing microglobules of pyrite are observed. In the phosphate mass, fragments of fish bones and pyrite microglobules are encountered. The phosphate is not microgranular but solid, with sharp edges where there are cracks. Bones of fish and marine mammals are encountered everywhere on the shelf of southwest Africa, but mostly in the northern part of the area (1723'S), where in places they form substantial accumulations (Baturin, 1974a).

Fig. 2-27. Bones of recent fish from diatomaceous oozes on the shelf of southwest Africa, natural size.

93 In diatomaceous oozes there are present relatively fresh white bones of recent fish - sardines, mackerel, hake (Fig. 2-27);on some of them phosphorite concretions are growing (Fig. 2-28).In calcareous and clastic sediments the bones usually are fossilized (brown or black, dense, brittle). Dense bones are phosphatized to some extent or other. The phosphatization is manifested in the filling of cavities in the bone tissue with phosphate, and in the crystallization of fibrous amorphous bone phosphate and its conversion to microgranular finely crystalline phosphate, with simultaneous transformation of hydroxylapatite into fluorcarbonate-apatite. The refractive index of the phosphate increases as the extent of crystallization increases, from 1.56-1.57 t o 1.600-1.630. In the outer layer of fossilized bones from the outer shelf iron hydroxides are often observed, in the form of dendritic segregations up to a few centimeters in size. The tiny cavities in the structure of the bone tissue are filled with microglobular pyrite (globules up t o 0.015 mm in size). The large cavities of porous bones are filled with diverse clastic-carbonate materials of sand and silt size, from the enclosing sediments (from 3-5 to 25% of the field of view in thin-section). Biogenic calcareous detritus, tests of foraminifera, angular grains of quartz and less often of plagioclases, monoclinic pyroxenes, and epidote predominate in this material; sometimes grains of glauconite are encountered, and also round or oval phosphate grains 0.10.25mm in size, consisting of relatively pure yellow finely crystalline phosphate.

Fig. 2-28. Phosphate concretions growing on fish bones; X 2.

94 Chemical composition of the phosphorites. Chemical X-ray structural and thermogravimetric methods were used in addition to optical in investigating the composition of the phosphate concretions, phosphatized coprolites and bones described above and also phosphate fractions isolated from them. According to the results of chemical analyses, the P,Os content in the soft lumps of phosphatized diatomaceous ooze ranges from 3 to 11%, averaging 5%(Table 2-7A,B). In morphologically shaped unconsolidated concretions the P , 0 5 content rises to 20-25%, and in compacted ones to 3133%. Thus lithification and phosphatization of the concretions in question take place simultaneously. The content of CaO, COZYand F increases in that order in parallel with P , 0 5 , while the content of H,O, Corg, SiO,, Al,03, TiO2, and S decreases. A similar picture is observed when the results of analyses of phosphatized coprolites are examined (Table 2-7). In tiny soft coprolites, apparently from fish, the P 2 0 5 content is 1-2% (Senin, 1970), and in natural coprolites of marine animals and birds feeding on fish, 4-1696 (Hutchinson, 1950) ; in phosphatized unconsolidated coprolites from shelf sediments, 25.8% on the average; in compacted coprolites 28.7%, and in dense coprolites 32.4%. By means of X-ray structural investigations on natural samples of phosphatic concretions and phosphatized coprolites it has been established that the phosphate mineral constituting them belongs t o the apatite group (Table 2-8). The isotropic phosphate of the unconsolidated concretions and coprolites is X-ray-amorphous. In samples of granular concretions with intermixed areas of isotropic and cryptocrystalline phosphate, the structural features of apatite are slightly manifested. In dense massive concretions and coprolites these features are quite clearly manifested. The unit cell parameters of the phosphate ranges in these limits: a. = 9.304-9.314, co = 6.868-6.876 8. The chemical composition of bones depends on their mineralization and contamination by non-phosphatic material from the surrounding sediments. Relatively fresh bones contain up to 10-20% of organic matter impregnating the bone tissue and several percent of water. Mineralization of bones is manifested in removal of water, decay of organic matter, phosphatization, and pyritization. The P,Os content in unmineralized porous bones of cetaceans is 18-24%, in bones of living fish 26-28%, and in mineralized bones 29-3276. To investigate the phosphatic material in concretions, phosphatized coprolites, and bones the raw material was ground to 0.075-0.15mm and centrifuged in heavy liquids. The specific gravity of the phosphate fraction

TABLE 2 - I A Average chemical composition (%) of Holocene phosphate concretions, coprolites, and bones from diatomaceous oozes on the shelf of southwest Africa (Baturin, 1970; Baturin et al., 1970) Sample Phosphatized diatomaceLOUS ooze Unconsolidated concretions Compacted concretions Dense concretions Unconsolidated coprolites Compacted coprolites Dense coprolites Unidentified fish bones Lithified bones*

P,O,

CaO

MgO

SiO,

TiO,

A1103

Fe2O3

MnO

C02

Corn

S,,

F

LO1

1R

F/P,O,

5.10

6.96

2.50

49.18

0.08

2.00

1.24

0.001

2.16

3.40

1.46

0.46

19.44

50.09

0.090

23.85 28.66 32.74

35.92 43.12 46.42

1.70 1.47 1.70

14.82 6.06 0.17

0.005 0.005 0.005

0.45

0.80 1.23 0.20

0.001

tr. n.d.

0.001 0.002

5.52 5.54 6.33

1.80 1.03 0.92

0.83 0.90 0.73

2.25 2.87 3.02

14.00 12.41 12.20

15.23 6.32 0.15

0.094 0.100 0.094

25 85 28.72 32.40

35.67 42.11 46.13

2.90 2.55 2.12

1.56 0.20 0.16

0.003 0.016 0.003

0.02 0.10 0.02

0.14 0.52 0.10

0.003 0.004 0.001

5.90 5.34 6.37

2.86 0.88 0.60

1.06

1.50 5.01

-

2.59

0.058 0.168 -

27.88 31.07

37.85 43.68

1.10 0.2

0.93 0.66

0.14

0.50 1.59

n.d. n.d.

4.51 4.92

7.20 1.10

1.28

~~

~

LO1 = loss o n ignition; IR = insoluble residue; n.d. = not detected. * Bones from elastic sediments of outer shelf.

tr.

-

-

-

-

11.35

-

2.16 2.80

23.20 9.36

0.93 0.66

0.077 0.090

TABLE 2-7B Results of partial chemical analysis southwest Africa (Baturin, 1974b)

(a)of

a complete series of phosphate concretions and coprolites from the diatomaceous oozes of the shelf

co2

PlO5 2046* Diatomaceous ooze Phosphatized ooze Concretions soft unconsolidated compacted granular compacted massive dense gray dense brown Phosphatized coprolites unconsolidated compacted dense gray dense brown *

Station locations

- 2046:

2047

cow

2046

2047

2048

2046

2047

2048

2046

2047

2048

2.62 2.86

5.31 3.97

4.37 3.10

5.54 4.02

59.32 38.00

57.00 41.32

58.90 27.26

-

2.25 1.28

1.41 1.13

14.24 0.21

7.70 4.00

1.21 4.16

0.82 11.28

1.28 1.07

1.66

19.51 29.53

25.81 27.24

4.32 5.90

4.94 5.01

5.29 5.92 9.19 6.14

29.60 30.31 31.94

30.36 30.36 30.62

20.68 25.69 30.24 30.23 31.56 32.41

29.50 29.60 30.61 30.00

26.79 30.49 31.13 30.87

27.66 29.91 30.87 31.19

-

Amorphous SO:!

2048

1.33 3.56

-

Of

-

6.21 6.39

-

5.16 5.78 6.10

5.28 5.94 5.76 6.34 6.36

4.33 5.47

-

5.66

6.36 6.21

-

-

-

1.05 0.97 0.98

1.06 1.01 0.88

2.10 1.18 1.21 1.03 1.02 0.87

1.51 1.18 0.88 1.08

1.35 0.90 0.91 0.91

1.56 1.00 0.79 0.71

-

-

0.11 tr. tr.

0.04 tr. 0.03

10.00 5.02 2.08 0.10 0.10 tr.

0.17 tr. tr. 0.04

0.10 0.07 0.17 0.08

0.15 0.15 0.35 0.12

22O40’S, 14O15.6’E, depth 8 7 m ; 2047: 22’27’s. 14’10.5’E. depth 7 8 m ; 2048: 22OO8‘S, 13’58.4’E, depth 85 m .

97 'TABLE 2-8 Results of X-ray structural analysis of phosphate concretions and coprolites from the inner shelf of southwest Africa (Baturin e t al.. 1970) Station Coordinates

Depth (m)

Sample* PzO, (%)

Unit cell parameters

Clarity of lines

(A) Qo

209 161 152 152 152 152 152 160 144

22'59'5, 14'11'E 21'49'S, 13'45'E 22'41'S, 14'20'E 22'41'S, 14'20'E 22'41'S, 14'20'E 22'41'5, 14'20'E 22'41'S, 14'20'E 21'59'S, 13'51'E 22'56'5,13'48'E

120 97 76 76 76 76 76 91 148

a b c b b d e e f

27.53 3 1.08 27.88 30.18 29.62 31.64 32.74 31.16 -

9.314 9.314 9.309 9.309 9.314 9.314 9.304

co

6.868 6.876 6.872 6.874 6.872 6.868 6.876

very weak weak well expressed well expressed well expressed well expressed well expressed well expressed well expressed

* a = unconsolidated coprolite; b = granular phosphate nodule; c = unconsolidated phosphate nodule; d = dense lithified coprolite; e = dense brown concretion; f =phosphatized gastropod mold. ranges from 2.2-2.5 (bone) t o 2.7-2.8 (phosphate concretions). There are no free grains of non-phosphate minerals in the material of this fraction. An insignificant amount of quartz, glauconite, and iron hydroxides is observed only in the form of films and inclusions in the phosphate grains and aggregates (Bliskovskiy et al., 1975a). The data of chemical and thermogravimetric analyses show that the phosphate mineral of the concretions and coprolites is fluorcarbonate-apatite with a P , 0 5 content of -32%, 3% F, and 4% C 0 2 (Table 2-9). In thermogravimetric investigations it was established that the phosphatic substance of the compacted granular nodules from diatomaceous oozes on the shelf of southwest Africa contains an unusually large amount of adsorbed water (3.77%), which is given off in the temperature range of 80-300°C. In the phosphate of commercial phosphorite deposits the content of adsorbed water is much less, of the order of 0.6% (Bliskovskiy et al., 197513). The exothermal peak of the phosphate of the granular nodules, with a maximum at 377°C and the kink in the DTG curve corresponding t o it (Fig. 2-29a) are related to oxidation of organic matter, the content of which is determined from the TG curve in the 300-499°C range and is 1.48%. The loss of bound water is localized in a very narrow range. Beginning at 500°C it takes place mainly in the 650-750°C range, which is manifested in the sharp kink in the DTG curve. The process of dehydration is accompanied by a small but dis-

TABLE 2-9 Chemical composition of phosphatic material of concretions, coprolites, and hones from diatomaceous oozes on the shelf of southwest Africa (Bliskovskly e t al.. 1 9 7 5 a ) Material

Thermogravimetric analysis

Chemical analysis (%) PlOS (total)

p10:

CaO

MgO

AI1O,

Fe20:*

K I O Na,O

CO,

F

SO3

IR

C,

H20 adsorbed

(maximum dissolved

Hi0 hound

PI

O=F

911

organlc matter

Dense phosphatic concretion

31.70

12.60

47.32

0.50

2.68

0.20

046

1.97

4.26 (4.04)

2.85

1.30

0.41

0.92

377

2.R3

1.48

101.73

108

100.65

Phosphatized coprolite

3 1 70

13.16

45.92

1.20

n.d.

0.19

0.10

1.44

4.22 (3.51)

3.22

154

0.15

0.71

4.48

3.36

102

99.25

1.22

98.03

Unlithified whale hone

24.10

14.35

36.68

1.10

-

0.40

0.60

1.44

3.64 (3.50)

1.40

1.08

0.37

8.67

8 80

3.20

15.60

9 8 38

0.53

97.85

Figures in parentheses indicate CO, content determined thermogravimctrically Not included in total. *** Total Fe.

99

!a)

!b)

!C)

Fig. 2-29. Thermograms of phosphorites from the shelf of southwest Africa (Bliskovskiy et al., 1975a). (a) Dense massive nodule: rn = 670 mg; DTG = 1/3; DTA = 1/3; TG = 100 mg; atmosphere - air. (b) Dense phosphatized coprolite: rn = 670 mg; DTG = 1/3; DTA = 1/3; TG = 100 mg: atmosphere - air. (c) Slightly fossilized whale vertebra: rn = 500 mg; DTG = 1/5; DTA = 1/5; TG = 200 mg; atmosphere -air.

tinct exoeffect. The exothermic effect of recrystallization of fluorcarbonateapatite into fluorapatite practically coincides with the end of dehydration. Most of the C02 is removed right after it (kink in the DTG curve with a maximum at 820°C). A small amount of C 0 2 is given off in a highertemperature region (beginning at 946°C); this process is not finished even at 1035°C. The thermogram of the phosphatic substance of phosphatized coprolite (Fig. 2-2913) is similar to that described above and differs from it only in details - the temperatures of all the reactions here are 10-40" lower. Removal of C 0 2 ends at 1005°C. Thus a characteristic feature of the phosphatic material of phosphate concretions and coprolites is a high content of water in adsorbed and structurally bound forms. Nearly all apatite-like calcium phosphates contain more bound water than expected from the stoichometry in the case of isomorphism of PO:- 5 C 0 3 0 H , i.e. CO, : H 2 0 = 5 : l (Bliskovskiy et al., 1975b). This difference is especially large for two of the samples examined. The behavior of these minerals when dehydrated (accompanying exoeffects and final recrystallization to fluorapatite) suggests possible differences in the structural positions of the hydroxyl ions in these oceanic phos-

100 TABLE 2-10 Optical and X-ray structural characteristics of phosphatic material (Bliskovskiy et al. 1975a) Samples

Refractive index

Unit cell parameters (A)

(k0.002) a0

Phosphate concretion Phosphatized coprolite Whale vertebra

1.586 1.591 1.568

CO

9.334 6.89 9.330 6.89 X-ray amorphous

phates compared to the phosphatic material of economic phosphorite ores on land. The phosphate fraction of bone includes more organic matter and adsorbed water and less fluorine than other phosphates; the most characteristic features of its thermic behavior are the narrow localization of the regions of liberation of bound water and coincidence of the exothermic reaction of reorganization of the phosphate lattice with the end of the dehydration state. Decarbonation is finished at 87OoC (Fig. 2-29c). An excess of sodium, which is present in greater amount than needed to compensate for the substitution of P5++ S6+by the substitution CaZ++. Na', is characteristic of the chemical composition of the phosphatic material of all the samples investigated. Apparently, the Na' ions are in firmly sorbed form inasmuch as all the easily soluble sodium salts were removed in the course of preliminary treatment of the material, by repeated washing with distilled water. The refractive index of the phosphates investigated is 1.568-1.591, and the unit cell parameters are a. = 9.33, co = 6.89 (Table 2-10). The refractive index and a. parameter of the unit cell of the phosphate depends on the extent of isomorphic substitution of carbon for phosphorus (Maslennikov and Kavitskaya, 1956; McClellan and Lehr, 1969). In the samples examined the CO2/PZO5ratio is 0.13-0.15. Usually with such a C02/P2 O5 ratio the refractive index of the phosphate of economic ores is much higher than 1.591. The discrepancy established between these characteristics in oceanic phosphates is related to their high water content. The specific gravity of oceanic phosphate is relatively low for the same reason (2.7-2.8). Age of the phosphorites. The diversity of morphology, composition, and

10:. conditions of occurrence of the phosphorites of the shelf of southwest Africa suggests that they are of different ages, which is confirmed by a number of direct and indirect data. Judging from their structural and textural features, the sheets and blocks of phosphorite from the coarse-grained sediments of the outer shelf (brecciform, conglomeratic, and fine-grained varieties) were formed in several stages and eroded from pre-Quaternary deposits. The equilibrium relationship of the activities of the uranium isotopes contained in such phosphorites shows that their absolute age is greater than 1Ma (Baturin et al., 1974). The foraminiferal microfauna contained in phosphorites of this type belongs to the Middle Miocene, according t o identifications by V.A. Krasheninnikov (Kharin and Soldatov, 1975). The dense glazed phosphate grains, accumulations of which locally form phosphate sands in the clastic and clastic-calcareous sandy-silty sediments of the outer shelf, likewise are not Recent (pre-Holocene). The good sorting of these sands and similar median diameters of the phosphate and quartz grains indicate that the sands were formed by reworking and concentration of the grains at a time when sea level was lower, at the expense of pre-Holocene deposits no longer preserved. The equilibrium of uranium isotopic activities = 1.00 kO.01, sample from 225m in the phosphate grains (234U/23gU depth) shows that the age of the sands is more than 1Ma (Veeh et al., 1974). The youngest of all phosphate concretions known on the ocean floor It was shown occur on the inner shelf of sourthwest Africa (20-23's). above that these concretions are genetically related to the enclosing diatomaceous oozes. The latter could have been deposited on the inner shelf, at depths of 60--120m, only in the Holocene, when sea level rose by about 100 m after the end of the last glaciation. Any pre-Holocene fine-grained sediments accumulated in this zone inevitably would have been eroded when the sea level was low. All the diatoms constituting the diatomaceous oozes in question are exclusively Recent species (Mukhina, 1974). The same pertains to most of the fish bones which occur in abundance in the diatomaceous oozes (V.M. Makushok, personal communication). The absolute age of the diatomaceous oozes (samples from layers from 0-10 to 160-203cm), determined by radiocarbon, fall within contemporary to 6600 years old (Table 2-11). The following facts indicate the Recent and Holocene age of the phosphate concretions themselves, in the diatomaceous oozes. The gel-like and unconsolidated phosphate clots are nothing but phosphatized diatomaceous ooze, analogous in all characteristics (except phosphate content) t o the enclosing diatomaceous oozes. The gel-like phosphate fills the cavities in the valves of Recent diatoms and coats relatively fresh bones of Recent species of fish. In turn, the gel-like and unconsolidated phosphate

102 TABLE 2-11 Absolute age (from 14C) of diatomaceous oozes on the shelf of southwest Africa (Veeh et al., 1974) Station (core) CIR 175

CIR 177B CIR 179B CIR 189B

K 153* K 160*

Horizon (em)

Dated material

Age (years)

Sedimentation rate (cm/103 yr) (g/cm2

0-10 0-1 0 70-75 70-75

CO, CaC03 CO, CaC03

730 f60 Recent

-

43

34

15

-

0-3 0 100-1 30 0-30 80-1 10 0-30 0-3 0 60-84 60-84

CO, CO,

340 f150 1470 f310

-

CO, CO,

410 f 140 1470 fllO

-

CO, CaC03

1770 f70 2750 f150 3770 f100 6610 f80

-

-

95-135 160-203

COX

1790 f360 1400f420

53 114

CO,

CaC03 CO,

-

103

1380 f80 1980 f 130

88 65 29 15

lo3 yr)

-

-

38 -

32 -

12 6

-

22 47.5

* According

to determination by I.V. Grakova and V.A. Andriyevskiy (Institute of Oceanology of the Academy of Sciences of the U.S.S.R., personal communication).

concretions grade gradually into dense phosphate grains and nodules; both usually occur together in dredge and core samples. The number of diatoms in the phosphate concretions ranges from 0.4 million valves per gram (compacted varieties) to 120 million valves per gram (unconsolidated varieties). The composition of the diatoms on the whole is the same as in the diatomaceous oozes. The species Actinocyclus ehrenbergii Ralfs, Hercotheca peruviana f. nervosa Mertz, Thalassiosira decipiens Jorg. are encountered most frequently (Table 2-12). The uranium disequilibrium method, described in detail in the works of Cherdyntsev (1969) and Chalov (1968), was used in determining the absolute age of the phosphate concretions. To use this method, a combination of the following conditions is necessary: (a) the isotopic composition of uranium in sea water remained constant during the last million years; (b) the source of the uranium in the phosphorite was sea water; (c) the time of accumulation of uranium in the phosphorite was short compared to their age; (d) after they were formed, the phosphorite concretions were a closed system with respect to uranium.

103 TABLE 2-12 Relative abundance (9i of total number) of the main species of Recent diatoms in phosphate concretions from the diatomaceous oozes of the shelf of southwest Africa (according to identification by Mukhina, 1974) Diatom species

Phosphate concretions unconsolidated

Actinocyclus ehrenbergii Ralfs A . divisus Kiss. Actinothychus undulatus (Bail.) Ralfs Biddulphia alternans (Bail.) Van Heurck Chaetoceros lorenzianus Grun. Ch. subsecundus Hust. Chaetoceros spp. (spores) Coscinodiscus asteromphalus Ehr. C. curvatulus Grun. C. gigus Ehr. C. janischii A. S . C. perforatus Ehr. C. radiatus Ehr. C. stellaris Roper Coscinodiscus sp. Hercotheca? peruviana f. nervosa Mertz Melosira sulcata (Ehr.) Ktz. M. italic0 Ktz. Planctoniella sol (Wall.) Schutt Pleurosigma normanii Ralfs Rhaphoneis simonseni Mertz Rh. wetzeli Mertz Rhizosolenia styliformis Brightw. Stephanopyxis nipponica Gran and Jendo Thalassio ne m a n itzsch io ides Grun . Thalassiosira decipiens Jorg. Th. lineata Jouse Dictyocha fibula - silicoflagellate Sticholoncha zonea - radiolarian spines

5.04 3.4 0.3

-

-

0.8 3.6

-

3.6 0.3

-

3.1

-

2.2

-

34.4 1.2 -

0.3 0.3 0.8 8.1 0.3 0.3 3.6 9.6 17.4

+ +

slightly cemented

compacted

43.20 -

1.4 1.4

-

1.4 6.5 0.7 7.2 13.7 10.1 2.2 2.2 0.7 1.4 -

0.7 0.7

-

0.7

-

5.8

-

+ = present Data on the marine geochemistry of uranium as a whole and on its behavior during phosphorite formation on the shelf of southwest Africa show that in this case all these conditions are fulfilled (Baturin et al., 1974). The content and isotopic composition of uranium in sea water are fairly stable. Uranium is introduced into the phosphate concretions from surrounding sediments rich in this element, and into the latter from sea water, with a

TABLE 2-13 Uranium isotopes in phosphate concretions from diatomaceous oozes on the shelf of southwest Africa Station (core)

152 CIR 175,117B 179B, 189B 152 CIR 186A, 188A 157 152 2048 152 2048

Coordinates

20°48'S, 14'19'E

Depth (m)

76 119-1 34

2Oo48'S, 14'19'E 22'28'5, 14'14'E 2Oo48'S, 14'19'E 22'08'5, 13'58'E 2Oo48'S, 14'1 9% 22'08'S, 13'58'E

76 75-93 75 76 89 76 89

Sample* a* *

***

b* * b*** C**

d* * d* * e* * e* *

p2

O5

(%I

U

Activity ratio %)

1.38

16

0.09-0.6 8

10-30

234u/238u 1.171 f0.009

8.52

6

1.13 f0.02 1.16 f0.02 1.169 f0.013

-

78 29 62 52 86 30

1.16 f0.02 1.160 fO.O1O 1.165 f0.009 1.148 kO.009 1.163 kO.009 1.145 f O . O 1 l

23.85 29.62 31.56 32.74 32.41

from to

CIR 175P (40-50 cm)

134

f***

-

158

0.87 f O . O 1

CIR 175P (90-1 00 cm)

134

f***

-

117

0.96 f O . O 1

* a = enclosing diatomaceous ooze; b = phosphatized diatomaceous ooze; c = unconsolidated concretion; d = compacted granular concretion; e = dense brown concretion; f = dense gray concretion. ** After Baturin e t al. (1972b,c; 1974). *** After Veeh et al. (1974).

105

very insignificant portion of terrigenous uranium in the concretions (not more than 1%). The uranium is accumulated in the concretions at the same time as the phosphorus, and the process of formation of the concretions usually ended in several hundred or a very few thousand years. Compaction and dehydration of the concretions, crystallization of the phosphate and its residence in a reducing environment promoted the closure of the system after formation of the phosphate concretions. The uranium isotopic activity ratio 234U/238Uin the diatomaceous oozes containing the concretions ranges from 1.13 k0.02 to 1.171 k0.009, in the phosphatized diatomaceous oozes from 1.16 k0.02 to 1.169 k0.013, and in morphologically shaped unconsolidated and dense concretions from the upper layer of oozes from 1.145 kO.011 to 1.164 kO.009 (Table 2-13). The uranium isotopic activities in the waters of the World Ocean range within the same limits (Cherdyntsev, 1969). Inasmuch as the difference between the 234U/238Uratios in the diatomaceous oozes (or sea water) and in the concretions falls within the limits of error of determination, the results obtained make it possible to calculate tentatively only the possible upper age limit of the concretions. For this we use the formula of one-time introduction of uranium into the concretion (Chalov, 1968):

where yo is the initial 234U/238Uratio in the concretions, y t is the 234U/ l s a U ratio at the present time, h is the 234U decay constant, and t is the absolute age. Taking the maximum value of 234U/23EUin the diatomaceous oozes (1.171 kO.009) as yo and the average 234U/23*Uratio in the concretions as y t , we find that the maximum age of the concretions from stations 152 and 157 (Table 2-13) is 45,000 years (17,000 k28,OOO years), and from station 2048, 88,000 years (54,000 k34,OOO years). Taking into account all the determinations of 234U/23*Uwe find that the average value of yo in the diatomaceous oozes (1.15 kO.01) is identical to yt in the concretions from the upper layer of oozes (1.155 k0.008), which indicates that they are of the same age. In the deeper layer of diatomaceous oozes, old phosphorite concretions were also found in which the 2MU/238Uactivity ratio was in equilibrium from 0.87 kO.01 to 0.96 kO.01 (Table 2-13). Their age is more than 1Ma. Apparently these concretions are redeposited, and formed in now-eroded sediments (probably diatomaceous oozes) deposited on the shelf earlier.

TABLE 2-14 Chemical composition (%) of phosphate rocks from the western shelf of central Africa Sample

Coordinates

Ferruginized conglomerate* 06'56'S, 12'01'E Fine-grained limestone**

13'43"

17°02'W

Depth (m) 160

20

* After Baturin (1975a). ** After Kharin and Soldatov (1975).

P20,

8.98

10.0

CaO

MgOz SiO,

Ti02

1 4 . 4 9 2.60

19.25 0.02

35.60 4.79

1.33 0.06

LO1

IR

A1,03

F e 2 0 3 FeO

MnO

CO2 C,

F

3.69

37.01

0.57

0.01

2.27 0.57

0.75 10.61 20.2

-

0.02

tr.

1.32

-

1.90

-

27.17

-

107 Western shelf of central Africa Phosphorite and phosphate rocks are found at several points on the western shelf of central Africa - on the shelves of Guinea, Ghana, Gabon, the Congo, and Angola (Baturin, 1975a;Kharin and Soldatov, 1975;Cornen et al., 1973;Giresse and Cornen, 1976). The phosphorites are mainly phosphatized limestones and sandstones, less often phosphatized coprolites. Among the phosphate rocks on the Gabon and Congo shelves there are distinguished: (a) calcareous ochers with carbonate-phosphate cement, containing 20-40% phosphate grains and 510% glauconite; (b) brown sandstones with clay or calcareous cement, containing less phosphate but more quartz; (c) ferruginous organogenic sandstones with abundant quartz grains. Cylindrical coprolites occurring in this same area consist of fluorapatite (Cornen et al., 1973). A phosphatized fermginous conglomerate from the Angola shelf consists of rounded and angular quartz grains up to 3-5 mm in size, usually fractured, with mosaic extinction. The quartz grains are cemented by reddish brown hydrogoethite, including hydrogoethite ovoids 0.1-0.8mm in diameter with concentric-shell structure. The phosphatic part of the rock is the light yellow, microgranular, finely crystalline cement filling the numerous cracks in the mass of hydrogoethite and quartz grains. In the phosphate there are encountered grains of quartz up to 0.5 mm in size, angular fragments of the hydrogoethite cement, and isolated rounded grains of light green glauconite 0.1-0.2 mm in size. Judging from the results of the few analyses, the P,O, content in the phosphatized limestones, sandstones, and conglomerates is low, 9-13%. The fermginized rock varieties contain up to 37% Fe203 (Table 2-14). According to the conclusions of French investigators, the age of the phosphorites from the Gabon and Congo shelves is Neogene (Cornen et al., 1973). Probably the phosphatized conglomerate from the Angola shelf also is Neogene; its absolute age, according to the uranium isotope ratio, is more than 1 Ma (Baturin et al., 1974).

-

WEST ATLANTIC PROVINCE

The West Atlantic phosphate province extends from the southern tip of Florida on the south to Georges Bank on the north, for a distance of more than 1400 km, and includes several areas where phosphate sands, phosphorite concretions, sheets, and various phosphatized rocks have been found (Emery, 1965, 1968; Emery and Uchupi, 1972). Phosphorite was first found in this region (Straits of Florida) by expeditions of the American

108 research vessel “Blake” (1877-1880) and was described by Murray (1885) and Agassiz (1888).

Blake Plateau The Blake Plateau is a vast, relatively flat part of the continental slope east of Florida, situated at a depth of 300--800m. There are practically no unconsolidated sediments on the plateau. The phosphorite occurs on the shallower northern and western parts of the plateau. Farther east there is a zone where the phosphorite is covered by manganese crusts which sometimes coalesce into a continuous sheet. Ferromanganese nodules without phosphorite occur on the deep-water southeastern periphery of the plateau (Fig. 2-30). Phosphorite and manganese nodules occur on the cemented globigerina sand (calcarenite), sometimes are buried in it. In the northern and northwestern parts of the plateau the phosphate material consists of grains, concretions (Fig. 2-31), and blocks weighing up to 56 kg and in the center of the plateau, also of bands of phosphate in iron-manganese crusts (Hathaway, 1971; Hawkins, 1969; Manheim, 1965; Milliman et al., 1967; Pratt, 1963, 1968; Pratt and Manheim, 1967; Pratt and McFarlin, 1966; Sheridan et al., 1969; Stetson et al., 1962). In an investigation of samples obtained in the northern part of the plateau on the seventh cruise of the scientific research vessel “Mikhail Lomonosov” (1960) it was established that the phosphorites are phosphatized limestones. The carbonate material (40-50% of the field of view in thin-section) consists mainly of tests of planktonic foraminifera. Glauconite grains 0.1-0.45 mm in size are present in substantial amounts (5-10%). Pyrite is occasionally encountered; it is partially oxidized, with the formation of brown iron hydroxides. Clastic material (-5%) consists mainly of angular grains of quartz, less often of K-feldspars and plagioclases. The carbonate detritus, glauconite grains, and clastic material are cemented by finely crystalline phosphate, which also fills chambers in foraminifera tests (Fig. 2-32). Pelitomorphic calcite is disseminated in the phosphate. According to the data of chemical analyses (Table 2-15), the P , 0 5 content in the concretions ranges from 20.26 t o 23.53%,CaO from 33.32 to 52.15%,and insoluble residue from 0.52 to 15.37%,which is due both to the extent of phosphatization of the original limestones and t o the variable amount of clastic material included in the concretions. Judging from the eroded surface of the bottom, the phosphorites on the Blake Plateau originated by way of residual concentration when phosphate deposits on the coastal plain were eroded (Pratt and Manheim, 1967). This idea is confirmed by data on the composition of the microflora of

109 79OOO'

78OOO W

3'00' N

2aoo'

f00'

0"00' N 79'06

78OOO'W

Fig. 2-30. Bathymetxy and rocks on the Blake Plateau (Pratt and McFarlin, 1966): 1 = zone of iron-manganese crusts; 2 = zone of phosphorite concretions; 3 = zone of ironmanganese concretions; 4 = submarine photography stations; 5 = dredging stations.

coccolithophorids included in the phosphorites; according to the identification by S.I. Shumenko, these belong to the Late Cretaceous ( Watznaueria deflandrei No&l;Ahmuelerella mirabilis Perch-Nielsen) and Oligocene (Chiasmolithus sp. cf. oamarnensis, Fig. 2-33;Sphenolithus sp.). Submerged Pourtales Terrace The Pourtales Terrace is a levelled erosional bench of the continental shelf at the southern tip of the Florida peninsula. The terrace is 115 nautical miles

110

Fig. 2-31. Phosphorite concretions from the Blake Plateau; reduced to half size.

long and up t o 17 nautical miles wide, and consists of dense Miocene limestones (Jordan, 1954; Jordan and Stewart, 1961; Jordan et al., 1964). Phosphorite has been found at seven stations (Table 2-16) in a zone 70 x 5 miles in area. It consists of concretions, conglomerates, fragments of phosphatized limestone with concentrically layered and dendritic structure, and phosphatized bones of marine mammals. The phosphorite conglomerate consists of dark gray rounded fragments of phosphatized foraminiferal limestone, held together by a lighter-colored cement in which there is no microfauna, which indicates that there were at least two stages of phosphatization. The concentrically layered structure of some concretions apparently reflects rhythmic accumulation of phosphate, taking place over a long period of time. The phosphate of these rocks is francolite; using the X-ray fluorescence method, 1-10s iron and up t o 1%manganese were found in them. Correlation of the geology of the Pourtales submerged erosional terrace with the land part of Florida shows that the phosphorites on the terrace are

111

Fig. 2-32. Structure of phosphorite concretion from the Blake Plateau. Foraminifera tests, grains of clastic material and glauconite with phosphate cement. Thin-section, X 80, I1 nicok.

analogs of the Miocene phosphorites of the Bone Valley Formation. The evidence for this is the Miocene foraminifera microfauna included in the phosphorites (Gorsline and Milligan, 1963).

Shelf of Georgia and North Carolina The phosphorites off the coast of Georgia and North Carolina have been studied by numerous investigators (Gorsline, 1963; Hersey et al., 1959, Lutenauer and Pilkey, 1967;Milliman et al., 1967,1968;Mooreand Gorsline, 1960;Pevear and Pilkey, 1966; Pilkey and Lutenauer, 1967; Pratt, 1969; Pratt and Thompson, 1962;Weinstein, 1973). Chiefly slightly phosphatic quartz-calcareous sands occur on the shelf (Table 2-17);according to all signs they are relict. The phosphatic material consists of hard black and brown nodules, up to 8 cm in size, and well-sorted rounded grains. The size of the phosphate grains is the same as that of the quartz grains in the enclosing sediments. In places the concentration of phosphate grains reaches 14-40%. The phosphorite sands usually lie at depths up t o 30-40 m and are concentrated in individual

112 TABLE 2-15 Chemical composition (%) of phosphorite concretions from the Blake Plateau ~~

~

~

~~

~~

Component

Station 317: 31'57" 78'13'W depth 607 m (Murray, 1885)

Average, 18 samples (Hathaway, 1971)

Station 540: 32'10" 77'52'W, depth 590 m (Baturin, 1975a)

Sample without precise tie-in (Burnett, 1974)

p205

23.53 52.15 1.01 tr.

22.7 46.4

20.26 33.32 1.10 15.37 0.10 7.29 7.06 0.27 0.11

25.80 51.33 1.02 0.20

CaO MgO Si02 Ti02 A12 O3

tr.

Fez 0 3 FeO MnO Na2 0

tr.

-

-

4.0

}

5.5

-

tr.

F CI

so3 CO,

LO1

IR

-

0.58 0.45

K2 0

CO2

0.51 2.80

15.56 2.28 0.16 2.29 -

3.15 0.52

13.2 3.1

6.39 2.00

-

3.25 1.52

0.41 8.86 15.37

-

15.20

* Organic matter. places (Fig. 2-34), from which they are carried by wave action into the neighboring zones. According to the results of the drilling of two exploratory boreholes on the shelf of Georgia southeast of the mouth of the Savannah River, it has been established that the Upper Miocene phosphorite sands are 7.3m thick and overlain by a layer of non-phosphatic sands 1.2 m thick. The reserves of phosphorite sands on the shelf apparently are greater than in the deposits of the same age on the adjacent land (Furlow, 1969). Phosphate grains have been found in drill cores in Miocene rocks and at many points on the Atlantic shelf of the U.S.A. (Bunce et al., 1965; Hathaway e t al., 1970; Nesteroff, 1966). In the opinion of American investigators, the origin of the phosphorite sands is related to transportation of phosphate grains from the shore by rivers in the Pliocene, and to erosion and secondary enrichment of Miocene deposits exposed on the bottom (Pevear and Pilkey, 1966; Lutenauer and Pilkey, 1967).

i13

Fig. 2-33. Oligocene coccolith Chiasmolithus sp. cf. oamarnensis in phosphorite concretion from the Blake Plateau; electron microscope, X 15,000 (identification by S.I. Shumenko).

TABLE 2-16 Points where phosphorite has been found on the Pourtales Terrace (Gorsline and Milligan, 1963) Station

Research vessel

Coordinates

6 9 10 19 6 7

“Gerda” “Gerda” “Gerda” “Gerda” “Explorer” “Explorer” “Blake”

24’17‘N, 24’15‘N, 24’13’N, 24’18‘N, 24’15‘N, 24’15’N, 24’20’N,

-

81’11‘W 81’19’W 81’24%’ 82’21‘W 82”OO’W 82’00’W 82’0O’W

295 327 513 237 491-510 73-437 227

114 TABLE 2-17 Phosphorus content (%) in phosphate-bearing sediments on the Atlantic shelf of the U.S.A. (Goodell, 1967) ~~

PzO5 content

Sediment

N

range of values Sorted foraminiferal sand Foraminiferal and bryozoan sand with grit Foraminiferal muddy sand Glauconitic foraminiferal sand Foraminiferal-quartz muddy sand Quartz sand Quartz sand with shells (15%) Quartz sand with shells (25%) Muddy fine-grained quartz sand Quartz sand with shells and phosphate grains Quartz gravel with shells

average

3.27-6.20

4.61

7

3.28-6.57 3.71-6.47 3.62-3.95 3.18-6.34 0.76-5.93 < 0.01-5.94 < 0.01-5.64 < 0.01-5.81

4.41 4.37 3.79 4.55 3.95 1.43 2.39 2.23

12 8 2 5 22 19 20 18

7.37 5.69

20 14

3.58-4 2.60 3.58-10.81 ~~

N = number of samples

34

I

. _...*. ..

/

5

70

Fig. 2-34.Distribution of phosphatic sands on the Carolina shelf (Lutenauer and Pilkey, 1967): 1 = 0-1;2 = 1-3; 3 = 3-7; 4 = 7-14; 5 = 14% P ~ 0 5 .

>

115 Georges Bank On the northern periphery of the phosphate zone, on Georges Bank, diagenetic concretions with phosphate grains (2-19s) and glauconite (14%) have been found in relict sediments. The microcrystalline calcite, phosphate grains, and fragments of fauna in these concretions are embedded in a ferruginous clay cement (Stanley e t al., 1967). CALIFORNIA PROVINCE

The California phosphate province extends along the west coast of the U.S.A. and Mexico from Point Reyes (north of San Francisco) to the southern tip of Baja California, a distance of more than 2000 km. Accumulations of phosphorite were first found off the coast of California during geological work by the research vessel “Scripps”. Later the phosphorites were traced south along the Mexican part of the California peninsula (D’Anglejan, 1967; Emery and Dietz, 1950;Uchupi and Emery,

1963). Shelf and continental slope o f California (U.S.A.) The phosphorites off the coast of California have been studied in most detail in the area of Los Angeles and San Diego (Dietz e t al., 1942;Emery, 1952, 1960, Emery and Dietz, 1950; Emery and Shepard, 1945; Hanna, 1952;Mero, 1961;Uchupi and Emery, 1963). The submarine relief in the region of southern California is very complex. Beyond the narrow shelf belt, in the upper part of the zone of the continental slope, there is a series of trenches 1500-2200 m deep separated by rises which in places emerge as small islands (Fig. 2-35). Phosphorites occur on the outer part of the continental shelf, on the island shelves, on the summits and slopes of submarine banks and hills, and on the flanks of the trenches and submarine canyons. As a rule the accumulations of phosphorite occur on parts of the bottom where sedimentation is slow or zero and are absent on the bottom of the trenches. The depths at which phosphorites have been found range from 80 to 2800 m, but in 95% of the cases they do not exceed 330 m. The enclosing sediments usually are quartz-mica and glauconite sands and silts, less often silty muds, in which phosphate grains and oolites 0.1-0.3 mm in size are often present. The.P, O5 content in these sediments usually is not more than 0.3-0.5%. The phosphorites consist of grains, sheets, and concretions of various

116 120"

119O

118O

0

10

20

30

40

50

34

33

32

Fig. 2-35. Map of the sea floor in the Southern California area: 1 = stations where phosphorite concretions have been found; 2 = possible occurrences of phosphorite. M, P = samples containing Miocene and Pliocene foraminifera, respectively (Emery, 1960).

shapes (Figs. 2-36, 2-37), usually with a flat bottom side and convex upper side. The maximum dimensions of the phosphorite concretions are 60 x 50 x 20 cm, the average size 5 cm in diameter. At some stations the dragnets brought up hundreds of concretions. Judging from individual estimates and underwater photographs, the concentration of phosphorite ranges from a few kilograms to 100 kg/m2. The phosphorites are hard compact rocks; in color they are tan, brown or black. Their specific gravity is 2.62, the hardness on the Mohs scale -5. The surface is smooth and polished. Concretions from greater depths are coated on top with a film of manganese oxide, which indicates that phosphate

117

Fig. 2-36. External view of phosphorites from the California basin: (a) concretion; ( b ) phosphorite breccia; ( c ) phosphatized sea-lion bone; ( d ) layered phosphorite nodule (Dietz et al., 1942).

deposition has ceased. In places phosphorite conglomerates and breccias consisting of fragments of phosphorite and other rocks bonded by phosphate cement, and also bones of marine mammals and fish, are encountered. Often corals, bryozoa, brachiopods, sponges, and serpulids are attached to the upper surface of the phosphorites. The presence of fauna growing on the concretions indicates that they occur on the bottom in a fixed state. In some concretions tracks of burrowing organisms are observed, filled with calcium carbonate or phosphate. Thin-section investigations have shown that the phosphorites contain phosphate oolites with nuclei of foraminifer tests, glauconite grains, or clastic material. In addition, angular and semirounded fragments of various sedimentary, volcanic, and metamorphic rocks, and grains of quartz, feldspars, pyroxenes, micas, and other minerals are present in the phosphorite sheets and concretions. Abundant glauconite forms round grains and fills chambers in foraminifer tests. The insoluble residue obtained by treating the concretions with hydrochloric acid amounts to 6-30%. Besides clastic

118

Fig. 2-37. Structures of phosphorites from the California basin (Dietz et al., 1942). (a) Phosphate oolites with nuclei in the form of foraminifer tests and mineral grains; thinsection, X 28, 11 nicols. ( b ) Holes bored by pholads, filled with phosphatized ooze (indicated by arrows); polished surface, X 3.5.

material, it contains amorphous silica, remains of diatoms, radiolaria, and sponge spicules (Dietz et al., 1942). According to the results of semiquantitative X-ray-structural mineralogic analysis, the phosphorite concretions contain 72% apatite, 18%potassium feldspar, 5%quartz, 3%kaolinite, and 2%pyrite (Burnett, 1974). Petrographic investigations of the phosphorites have shown that the phosphatic material consists of an isotropic phosphate - collophane - and an anisotropic one - francolite; the latter forms the fibrous concentric layers of the oolites, and replaces foraminifera tests and other calcareous particles. The data of X-ray structural and chemical analyses indicate that the phosphate of the California phosphorites, like that of most phosphorite deposits of old sedimentary formations, is similar in composition to fluorapatite or fluorcarbonate-apatite. The phosphorite concretions contain 20-30% P2 0 5 ,37-47% CaO, 0.34%R2 0 3 ,up to 10%SiO, ,4-5.5% C 0 2 , 2.47-3.9876 F, up to 21%insoluble residue. The F/P20, ratio ranges from 0.096 to 0.130, C 0 2 / P 2 0 5 from 0.1373 to 0.2060 (Table 2-18). When the California phosphorites were investigated, it was originally suggested that they are Recent or Upper Quaternary (Dietz et al., 1942), although the foraminiferal microfauna in them is chiefly Middle Miocene (Table 2-19). Later, after new data on the marine geology of the area and on

TABLE 2-18 Chemical composition (7%) of phosphorites off the coast of California ~

Station

P,Os

CaO

69' 106' 127* 158* 162* 183* 14415** 14002**

29.56 20.19 28.96 29.09 22.43 29.66 30.61 30.65 30.0

47.35 45.43 45.52 46.58 37.19 47.41 44.78 44.18 47.8

Unnumbered***

*** Dietz et al. (1942).

MgO

R2O3

AI203

Fe203 Si02

N a 2 0 KzO

-

0.43 0.30 2.03 0.70 3.93 1.40

-

-

-

-

-

0.64 0.78

-

1.06 1.71

1.00 0.99

8.17 9.70 9.5

0.80 0.87

0.64 0.56

~

-

3.3

(1974). *** Burnett Inderhitzen e t al.. (1970;average of 20 samples).

-

-

-

-

-

CO,

,C ,

F

3.91 4.01 4.30 4.54 4.63 4.87

0.10 1.90 2.25 0.44 0.35 1.50

3.31 3.12 3.07 3.15 2.47 3.36 2.95 3.98 3.4

~-

5.5

-

-

SO3

LO1

-

-

0.85 0.90 2.1

9.34

~-

IR

C

F/P2 0,

C 0 2 /P, 0,

2.59 3.57 4.45 3.57 20.99 2.12 -

100.2

0.1120 0.1069 0.1060 0.1082 0.1099 0.1133 0.096 0.130 0.113

0.1323 0.1373 0.1486 0.1560 0.2060 0.164

-

87.25 87.52 90.58 88.07 91.99 90.32 100.33 -

-

0.183

120 TABLE 2-19 Main foraminifera1 species in the phosphorites off the coast of California (Dietz et al., 1942) Foraminifera species

Age

Anomalina salinasensis Kleinpell Siphogenerina branneri Bagg Biggina robusta Kleinpell Valvulineria californica Cushman Bolivina advena Cushman Bolivina girardensis Rankin Nonion costifera Cushman Nodogenerina advena Cushman a. Laiming

Middle Miocene

Buggina californica Cushman Bolivina imbricata Cushman B. sinnata Galloway a. Wissler Cassidulina crassa d’Orbigny Plum bina ornata d’Orbigny Pullenia miocenica Kleinpell Uvigerinella cf. obesa Cushman

Middle-Lower Miocene

Bolivina californica Cushman Bulimina uvigerinaformis Cushman a. Kleinpell B. ovula d’Orbigny Cassidulina monicana Cushman a. Kleinpell C. modeloensis Rankin Eponides healdi Stewart a. Stewart Cassidulina su bglo bosa Cushman a. Hughes C. californica Cushman a. Hughes Cassidulina spp.

I

Lower Miocene

Pliocene-Recen t

the Miocene/Pliocene phosphorites on the adjacent land had been obtained, that idea had to be rejected. According to Emery’s (1960) data, there were two stages of phosphorite formation in the basin. The first stage went on from the Middle Miocene to the beginning of Late Miocene, the second from Late Pliocene to the beginning of the Pleistocene. In the time interval between these stages (end of Late Miocene/Middle Pliocene), no phosphate sediments were deposited. A t the time of the second stage the Miocene phosphorites were recemented by phosphate. Beginning from the Late Pleistocene, the process of phosphorite formation ceased. The last conclusion is confirmed by data on the isotopic composition of uranium in the California phosphorites. In the 22 samples investigated, from different zones in the basin, the 234U/23*Uactivity ratio is between 0.95 k0.05 and 1.02 k0.05, i.e. close to equilibrium, which indicates an age of more than 1Ma (Kolodny, 1969a, b; Kolodny and Kaplan, 1970a).

121 Western shelf o f Baja California (Mexico) According to D'Anglejan's (1967) data, phosphorites occur on the western shelf of the California peninsula in a belt up to 80 km wide, between 24' and 26'N latitude (Fig. 2-38).The area occupied by phosphorite-bearing sediments is about 13,000 km2. The shelf, which in its origin is an erosional 30" 20" .

115'

I

f

\

/

2c

21

Ilt

.. ..

:... , /

.:I

110'

Fig. 2-38. Area of occurrence of phosphate (hatched) off the coast of Baja California (D'Anglejan, 1967).

122 platform developed on the west flank of the California syncline, is characterized by relatively gentle relief. It is separated from the continental slope by a narrow basin and a series of banks at depths of 50-100 m. The phosphorites occur mainly at depths up to 100 m, often on beaches and in lagoons, and consist of well sorted grains of sand size, the amount of which reaches 15-4076 by weight of the sediment in places. The thickness of the phosphate sediments, penetrated by sediment samplers, is 125 cm. Two types of phosphate grains are distinguished: (1) black ovoid grains predominate in the 0.125- to 0.250-mm fractions, (2) biogenic detritus predominates in the larger fractions; the biogenic particles are flat or platy in shape and are fragments of the valves of phosphatic brachiopods (Disciniscus cumingii Broderip). The surface of the phosphate grains usually is uneven, bumpy (Fig. 2-39). In thin-section it is seen that they are unstructured; sometimes concentric coats are observed, due to contamination of the phosphate by organic matter. The phosphate grains that occur in the reducing zone (middle part of the shelf) are black in color; grains from the oxidizing beach zone are brownish.

123

Fig. 2-39. Phosphate grains from the western shelf of Baja California (D’Anglejan, 1967). (a) Uneven surface of grains; 0.125- to 0.250-mm fraction. (b) Opal coatings of phosphate grains, left after dissolving the phosphate in hydrochloric acid; X 250. (c) Microstructure of phosphate grain. Areas of crystalline and amorphous phosphate alternate with black inclusions of organic matter; thin-section, X 1500, nicok.

+

One of the components of the phosphorites is amorphous silica, which fills cavities in the grains or coats them with a thin film (Fig. 2-3913). About 90% of the field of view in thin-section is occupied by phosphate and -10% by amorphous silica. In some phosphate grains, diatoms are found. Opal, pyrite, inclusions of organic matter, and finely dispersed calcite also are present. The phosphate of the grains corresponds in composition to carbonate fluorapatite and is represented by two varieties: anhedral crystals a few microns in size and a cryptocrystalline amorphous groundmass in which these crystals are embedded (Fig. 2-39c). The crystals often are grouped around inclusions of organic matter. Isolated grains of clastic material scattered in the phosphate mass represent the same mineral assemblage as in

124 the surrounding sediments - quartz, feldspar, less often hornblende, magnetite, epidote, hypersthene, zircon, sphene, and garnet. The P,05 content of the phosphate grains averages 30.2%, the F content 2.8%, and COZ 1.25--1.75%. The concentration of phosphate grains in the sediments is controlled by their granulometry. In fine muds and in coarse-grained carbonate sediments the content of phosphatic material is less than 5% (up to 2% in the < 0.062 mm fraction). Closer’ to the shore, phosphate grains are encountered in dune sands, both Recent and old, that are buried in lagoonal mangrove swamps. Here the content of phosphatic material reaches 10-20% by weight of the sediments. The phosphate grains are very similar in granulometry to the enclosing sediments, which suggests that they were transported and eroded by the same processes. The coefficient of sorting of the grains, both of phosphate and of sediment, is less than 0.5 (i.e. the sorting is good). The origin of the phosphate sands apparently is related to a substantial extent to erosion of pre-Holocene deposits. In particular, this is indicated by the sharp boundary of the phosphorus-rich sediments, which corresponds approximately to the 100-misobath, i.e. to sea level at the time of the last glaciation. Thus the phosphate sands may be remnants of completely eroded Pliocene and Pleistocene deposits. Sands of that type occur on land and lie unconformably on eroded Miocene rocks. In D’Anglejan’s opinion, the unordered structure of the grains indicates that the phosphate did not accumulate around any centers of crystallization, but rather in pore space. The clustering of apatite crystals around shapeless opaque organic segregations indicates that the source of the phosphorus is organic matter. In this respect a typical feature also is the close association of phosphate with amorphous silica, inasmuch as both components could have reached the bottom with remains of phytoplankton, intensively developed in connection with upwelling. And finally, the presence of silica coatings on the phosphate grains suggests that the material apparently was deposited in the course of diagenesis. Besides the phosphate grains described, phosphatic material of other types occurs in the near-shore zone of the southern part of Baja California. Phosphate nodules have been found on the flat tops of underwater banks, at depths of 100-200 m. Thin-section study indicates that they were formed by replacement of carbonate rocks by phosphate. Among unaltered fragments of dolomite, some are found which have phosphate developed on the periphery or along cleavage planes. N o apatite is associated with fragments of non-carbonate rocks (phyllites, basalts). In other parts of the same banks a large number of fragments of phosphatized foraminiferal limestone with a Miocene microfauna were obtained

125 by dredging. Fragments of phosphate rock also were found in dredging the bottom near the cliffs of Bahia San Juanico. Probably some of this material reached the floor as a result of erosion of Tertiary deposits. No aggregates of phosphate grains have been found in phosphorites of this type. Partially phosphatized foraminifera, including Recent benthic and planktonic forms, have been found on the upper part of the continental slope at depths of -750 m. In one core the phosphate content increased from 5% at the top to 12% in the 6 0 c m horizon, while the CaC03 content decreased. In thinsection it is seen that phosphate replaces both the calcite of the tests and the clay-carbonate material in them; glauconite, which often fills the chambers of the tests, is associated with the apatite. Silt grains covered with a fragile apatite crust also are found in the sediments of the phosphorite zone. Apparently in this case the apatite is secondary and was produced due to redistribution and redeposition of phosphorus, inasmuch as that phenomenon is not observed outside the phosphorite zone. In an attempt to determine the absolute age of the phosphate grains from the upper part of the shelf of the area in question by the radiocarbon method, from CO, , values within 9860 +200 to 26,640 +600 years were obtained. However, the possibility of using this method to date phosphorites is doubtful inasmuch as there is no guarantee that all the C 0 2 given off was originally part of the fluorcarbonate-apatite molecules, and is not a secondary younger biogenic or chemogenic impurity. In the dating of phosphatic brachiopod shells which occur along with the phosphate grains, it was ascertained that their age falls beyond the limits of resolution of this method, i.e. it is more than 50,000 years. In ionium dating of two fractions from the same sample of phosphate grains, an age of 230,000 years was obtained. However, the reliability of this result is inadequate in connection with the lack of data on the total ratio of all the uranium and thorium isotopes in the samples. Evidently the age of the phosphorites off the coast of Baja California on the whole is Miocene-Pliocene, except for isolated cases of phosphatization of the tests of Recent species of foraminifera. The area of occurrence of phosphatic sediments with a content of more than 5% apatite is estimated as 1800 km2 ; according to the data of exploratory drilling the thickness of these sediments is about 20 m, and the total reserves of P, 0, are from 1.5 to 4 billion tons (D’Anglejan, 1967,1968). PERUVIAN-CHILEAN PROVINCE

Phosphorite occurs off the coasts of Peru and Chile on the shelf and upper

126 part of the continental slope, chiefly at depths of 100-450m, in a belt -1000 miles long, from 5' to 21"s latitude. The geology of this zone is determined by the conjunction of the structures of the Andes mountain system and the Atacama deep-sea trench, with the greatest amplitude of heighbto-depth drop on Earth (up to 14,700 m). The west flank of the Andes, closely approaching the coast, consists of rocks of various compositions, mainly granitoids of different age and Tertiary sedimentary and volcanogenic rocks. Some peaks of the Andes are active volcanoes, the lavas of which have an andesitic, andesitic-dacitic, and andesitic-basaltic composition. In the Cenozoic there were intensive block movements accompanied by accumulation of substantial thicknesses of clastic deposits in graben-like depressions (Gerth, 1959; Jenks, 1959; Khain, 1971; Lomnitz, 1962). The Pacific shelf of South America is a terrace from 3-5 (off Antofagasta) to 10-20 miles wide (south of Valparaiso). The knee of the shelf is clearly expressed, at depths of the order of 150 m. Below that begins the near-continental slope of the Atacama trench, which is one of the steepest and narrowest in the ocean. The average steepness of the slope is 5-6'; individual scarps of it (for instance, in the region of 21's) are up to 700 m high and up to 45' in slope (Fisher and Raitt, 1962). The surface of the near-continental slope of the trench is complicated by benches, scarps, ridges, and furrows. Along the axis of the slope and at an angle of -30" to its strike there are short low ridges; the depressions between them usually are not closed, but open on the ocean side (Udintsev, 1972). Transverse to the slope submarine valleys and canyons have been cut, most numerous off the coast of Peru in the region of 15-16's. The largest of these is incised 800 m deep and its channel is 1.5 miles wide. On the basis of the character of the bottom relief, thickness of unconsolidated sediments, and geophysical characteristics, main (8-32's) and marginal (north and south) provinces are distinguished (Agapova, 1972). Depths of -6000 m, V-shaped transverse profiles, a narrow and in places flat floor, and maximum values of gravity (up to -259mgal) and magnetic anomalies are typical of the main province. The south marginal province is in the form of a depression up to 4000 m deep, filled with unconsolidated sediments up to 2000m thick. In the northern province the depths do not exceed 3500 m, and the thickness of the unconsolidated sediments is 5001000 m (Ewing, 1963; Ewing et al., 1969). In the main province the thickness of the sedimentary cover is minimal at depths up to 8100 m (a very few hundred meters). On the surface of the floor of the shelf and upper part of the continental slope of the Peruvian-Chilean region, chiefly clastic and to a lesser extent biogenic (slightly siliceous and carbonate) and glauconitic sediments occur

127

Fig. 2-40. Principal types of Recent sediments on the shelf and upper part of the con(Gershanovich and Konyukhov, 1975): 1 = tinental slope of Peru and Chile, 4-18's sands; 2 = fine silty muds; 3 = clayey muds; 4 = foraminifera1 sands; 5 = diatomaceous oozes; 6 = glauconite sands; 7 = outcrops of old deposits.

128

Fig. 2-41. Distribution of phosphorus in the surface layer of sediments of the shelf and in the upper part of the continental slope of Peru and Chile, 4-18's (Gershanovich and Konyukhov, 1975): 1 = 0 . 1 ; 2 = 0.1-0.3; 3 = 0 . 3 - 0 . 5 ; 4 = 0.5-0.7; 5 = 0.7% P.

<

>

129 (Fig. 2-40). Most of these sediments are characterized by a high content of disseminated phosphorus compared to the Clarke (0.1-0.5%). In slightly phosphatic and phosphatic sediments which occur in the form of relatively small areas, the phosphorus content reaches 2-18% (Fig. 2-41, Table 2-20). The phosphorite occurs mainly in clastic-diatomaceous and foraminiferal sediments of diverse granulometric composition - from silty pelites to sands. Samples of phosphorite were first obtained in this region at the time of the “Challenger” expedition (Murray, 1898), and in later years by a number of Soviet and American expeditions (Baturin et al., 1975; Baturin and Petelin, 1972, Gershanovich and Konyukhov, 1975; Logvinenko et al., 1973; Logvinenko and Romankevich, 1973; Saidova, 1971; Bumett, 1974, 1977; Manheim et al., 1975; Niino and Chamberlain, 1961). Lithology and mineralogy of the phosphorites

The phosphorites on the submerged margin of Peru and Chile are represented on the whole by the same complex of formations as on the shelf of southwest Africa - soft, unconsolidated, compacted, and dense phosphate grains and concretions, phosphatized coprolites, bones of fish and marine mammals (Fig. 2-42). The size of the grains and concretions varies from 0.3-0.5 to 5-10 cm. Their shape is diverse - isometric, flattened, irregular; some platy concretions have been perforated by boring organisms. The color of the concretions is from whitish to dark gray and black, sometimes greenish; the surface is rough, less often smooth, but not glazed. Usually there is no internal zoning or structure in the concretions. In every area of occurrence the unconsolidated and dense concretions are similar to each other in mineralogic composition and differ chiefly in the proportions of the major components - phosphatic, biogenic, and clastic. Most of the concretions are phosphatized clastic-diatomaceous sediments similar in composition to the non-phosphatic material from the surrounding sediments. The soft pellet-like phosphate concretions found in diatomaceous and diatom-foraminiferal sediments of the upper part of the continental slope of Peru are of the order of a few millimeters in size. Judging from the results of semiquantitative X-ray mineralogic determinations, the main components of their crystalline fraction are phosphate (20-40%), quartz (5-30%), carbonates (up to 38%),plagioclases (up to 22%),and less often dolomite, Kfeldspar, and augite (Burnett, 1974). Unconsolidated, compacted, and dense concretions are found at several points off the coast of Peru (phosphatized diatomaceous and clastic-diatom-

CI

TABLE 2-20

w

0

Phosphorus content (%) in sediments of the submerged margin of Peru and Chile (Manheim et al., 1975) ~~

~

~~~

~

Station

Depth (m)

Type of sediment

22a 22b 23

2400 1400 1400

clay pellets

28

197

37 38 39 40

144 315 500 1000

206 207 208 209 210

203 700 1660 135 160

211 212 215 216 217 218

350 300 300 1025 2200 100

220

510

clay pellets medium- and coarse-grained glauconite sands with admixture of mud, quartz grains, and diatom remains silt with admixture of diatom and carbonate detritus as above, with admixture of glauconite grains limestone with inclusions of phosphate grains, shell detritus, sand, and diatoms silt with diatom detritus and sand grains (about 5%) diatomaceous silt diatomaceous clayey-silty ooze with soft greenish aggregates and compacted pellets silty sand with diatom and carbonate detritus and phosphate grains silty sand with diatom and carbonate detritus and phosphate grains clayey silt with admixture of diatom detritus silty sand with diatom detritus and phosphate grains sand with shell fragments, admixed silty-pelitic material, and partially phosphatized foraminifera sandy-silty-clayey sediment with diatoms and phosphate grains (up to 5%) sand with foraminifera and phosphate grains of the same size calcareous silt with admixture of diatom detritus silt with shell fragments silt without diatoms and foraminifera diatomaceous silt well-sorted, slightly diatomaceous silt

p205

H2°

0.05 0.03

56.0 64.6

0.04 0.17 0.32 1.10 0.17 0.05

48.0 82.6 93 4.2 84.4 88.1

0.42 0.75 0.82 0.05 0.71

65.1 59.0 56.6 72.3 27.4

0.85 4.80 18.50 0.04 0.08 0.09 0.18

41.0 71.5 37.4 88.1 76.1 79.6 78.2

1.91

61.8

221 223

1000 3350

224

85

225

750

226

1450

pebbles of schist and phosphorite well-sorted silt with slight amount of diatom and carbonate detritus

23.7 0.09 0.05

20.1 82.5 71.7

slightly sandy silt with glauconite, foraminifer tests, and isolated phosphate grains

0.43

59.6

glauconitic silt with rare diatom valves

0.32

49.8

silt with diatom detritus and mica flakes

132

Fig. 2-42. Phosphorites from the Peru-Chile shelf. (a) Unconsolidated concretions (Chile shelf), reduced by 1.5 times. ( b ) Dense concretion perforated by burrowing organisms (Peru shelf), reduced to half size. ( c ) Unconsolidated concretion (light) developed on a dense one (gray) (Chile shelf), X 3. (d) Dense phosphatized sea-lion coprolites (Chile shelf), natural size.

133 aceous sediments) and Chile (phosphatized clastic-diatomaceous and clastic sediments). Concretions off the coast of Peru usually contain 4 W O % clastic material of sand-silt size; represented mainly by grains of quartz, basic and intermediate plagioclases, and subalkalic pyroxenes (Fig. 2-43).The feldspars are highly chloritized and sericitized. The non-phosphatic component second in its relative importance is biogenic silica, the amount of which reaches 20-30’36. In most samples, especially unconsolidated ones, the organogenic structure of diatomaceous ooze is observed. Carbonate material occurs in subordinate amount and consists of dolomite (rhombohedra) and calcite (grains and aggregates of irregular shape). Pyrite also is present, in the form of spherules (about 0.01 mm in diameter) and accumulations of spherules. The phosphatic part of the rock consists of a homogeneous cement which fills the interstices between grains of clastic minerals and the cavities of diatom valves. The phosphate, which has a refractive index of 1.585, is for

Fig. 2-43. Microstructures of phosphorite from the Peru shelf (Burnett, 1974). (a) Angular grains of quartz and other clastic minerals in dark collophane cement; sample PD-15-13, thin-section, 11 nicols. (b) Phosphate-rich area (in center); sample KK-71-161, thin-section, 11 nicols.

134 the most part amorphous. Partial crystallization of the phosphate is observed only in dense concretions. The unit cell parameters of the phosphate are: a. = 9.329, co = 6.889 (Baturin et al., 1975). Fig. 2-44 gives an X-ray diagram of the phosphate. White unconsolidated concretions off the coast of Chile are phosphatized fine silty mud and consist mainly of angular particles of clastic and volcanogenic material bonded by phosphate cement (Fig. 2-45a). These particles, which are 0.01-0.05 mm in size (rarely 0.05-0.5 mm) occupy 50-60% of the field of view of thin-section and consist of plagioclases (71%), quartz (ll%), colorless volcanic glass (6%), magnetite and titanomagnetite (6%), monoclinic pyroxenes (3%), basaltic hornblende (2%) and blue-green hornblende (1%). Organogenic components consist of diatom valves, fragments of skeletons of calcareous organisms, and fish bones up to 1.2 mm in size. About 4% of the field of view is pyrite and phosphate of early generations. Pyrite occurs in the form of microglobules up to 0.01 mm in size, rarely 0.02mm. In places the microglobules are concrescent or clustered around diatom valves. The cement consists of light-yellow isotropic glassy phosphate. In some places cementation is not complete, and round (0.1-0.5 mm in size) or ramifying cavities are left, irregularly distributed and occupying up to 5%of the field of view. On the whole, the lightrgray compacted concretions are analogous in composition to concretions of the first type, but they are unevenly phosphatized. The amount of clastic and volcanogenic material amounts to 2035% to 80% in different places. The cavities (up to 2.5 mm in diameter) are

400

5

-

Eb

-

26

g

-

v1

:

0-

-C I

1

I

I

I

I

I

I

1

I

I

Fig. 2-44. X-ray diagram of phosphorite from the Peru shelf; sample PD-15-13 (Burnett, 1974).

135

Fig. 2-45. Microstructures of phosphorite from the Chile shelf (Baturin and Petelin, 1972). (a) Grains of clastic minerals in phosphate cement; thin-section, X 200, I ( nicols. (b) Cavity filled with isotropic phosphate, thin-section, X 80, (1 nicols.

often filled with yellow isotropic phosphate (Fig. 2-45b), in which in turn smaller round and irregular cavities (0.05-0.2 mm) are observed. The light-gray and gray dense concretions also are phosphatized clastic ooze, in places with amorphous and in other places with microcrystalline phosphate cement. The composition of the non-phosphatic components in them is the same as in the first two varieties. Cavities partially or completely filled with phosphate occur in the concretions, occupying 2-10% of the field of view. In some of the cavities coalescing coatings consisting of finely crystalline phosphate are observed. The phosphate microcrystals are arranged perpendicular to the surface of the coatings. The interstices between the coatings are either empty, due to which a spongy texture is created, or filled with isotropic phosphate, in places contaminated with pelitic material. The inner walls of some cavities are coated with a thin layer (0.005mm) of finely crystalline phosphate. In other cavities there is no crystalline phosphate, but pure yellow glassy isotropic phosphate is present, with occasional cavities (up to 0.12 mm) and small cracks.

136 The refractive index of the phosphate is 1.584 k0.003 in the unconsolidated concretions, 1.587 k0.003 in the compacted ones, and 1.593 k0.003 in the dense ones. According t o the data of X-ray-structural analysis, the unit cell parameters are as follows: u0 = 9.330, co = 6.880 (unconsolidated concretion); uo = 9.335, co = 6.880 A (dense concretion). On the Chilean shelf solid black concretions in sheet form also occur; they consist of phosphatized finegrained arkosic sandstone, partially coated with a layer of finely crystalline phosphate. The boundary between the sandy and finely crystalline phosphate is clear everywhere. The phosphatized sandstone consists 60% of angular particles 0.01-0.6 mm in size. Plagioclases predominate among them (up to 78%); quartz (-lo%), K-feldspar (6%), monoclinic pyroxenes (5%), epidote (l%), and isolated grains of blue-green hornblende are also present. The particles of clastic minerals are cemented by light-yellow isotropic phosphate, in places contaminated by fine fragmental clastic material. Microglobules of pyrite up to 0.07 mm in size are often encountered in the cementing mass. The finely crystalline phosphate is mottled in color, due t o the alternation of dark- and light-yellow areas. The light parts occur in the form of spots or bands intersecting at various angles, and are more strongly polarizing. Valves and fragments of spines of diatoms are occasionally encountered in the phosphate, and also microglobules of pyrite up to 0.01 mm in size. There is noticeably less pyrite here than ir. the phosphate cementing the sandstone. Up to 3-4% of the field of view in thin-sections of the finely crystalline phosphate is occupied by round and irregular cavities (up to 0.3 mm; Baturin and Petelin, 1972). Tests of foraminifera, some of them completely replaced by phosphate, are often encountered in the phosphorite concretions (Fig. 2-46). Probably they were phosphatized before the formation of the concretions, in which phosphatized and unphosphatized foraminifera were included along with grains of clastic material (Bumett, 1974). Phosphate grains (round, oval, and irregular in shape) up to 0.7 mm in size and fragments of phosphorite are constant components of the phosphorite concretions of all types. The grains consist of yellow, dark-yellow, yellowishgray, or brown phosphate, usually isotropic, less often slightly anisotropic, in some cases pure and in others contaminated by pelitic material. The grains have no internal structure. Some of the grains are uniform in composition (Fig. 2-47), others have nuclei in the form of particles of feldspar, quartz, or glauconite (Fig. 2-48). On some particles the phosphate coating is not fully developed, and only thin (ab0v.t 0.02mm) phosphate crusts are formed, coating individual parts of their surface (Fig. 2-48a). Some of the phosphate grains apparently were formed by cavity-filling, secretion or accretion of

a

13’7

Fig. 2-46. Tests of foraminifera in phosphorite from the Chile shelf (Burnett, 1974). (a) Calcitic, with n o signs o f phosphatization; (b) completely phosphatized ; thin-section, 11 nicols.

Fig. 2-47. Homogeneous phosphate grains in concretions from the shelf of Chile: (a) in phosphatized silty-pelitic ooze; thin-section, x 200, II nicols; (b) in phosphatized sandstone; thin-section, X 80, 11 nicols.

138

Fig. 2-48. Phosphate grains with nuclei in concretions from the shelf of Chile (Burnett, 1974). Composition of nuclei: (a) feldspar, (b) quartz, (c) glauconite. Thin-section, 11 nicols.

139 phosphate on the surface of non-phosphatic particles in the concretions themselves before they were completely lithified, others are phosphate of previous generations which was present in the enclosing sediments before the concretions began t o form. In addition to phosphate concretions and bones, phosphatized coprolites have been found in trawl samples from the Chile shelf. They consist either of yellowish-brown microgranular isotropic phosphate, or of light-yellow, glassy, finely crystalline phosphate. There are many voids in the phosphate (from 5 to 25% of the field of view), usually in the form of cracks from 0.1 to 4-5 mm long. In samples of both types there are a large number of fragments of fish bones from 0.1 to 2-4 mm in size (Fig. 2-49). Accumulations of microglobules and individual microglobules of pyrite up to 0.01 mm in size are often encountered in the phosphate and also in the crack-like voids. In some coprolites consisting of isotropic phosphate, numerous phosphatized remains of unidentified organisms, usually elongate and angular, are observed in addition to fish bones. They consist of non-polarizing isotropic phosphate and are either colorless or in part (and sometimes completely)

Fig. 2-49. Fragments of fish bones in phosphatized coprolite from the shelf of Chile; thinsection, X 80, 11 nicols.

140

141 yellowish-brown or reddish. In many cases they are coated with thin films (0.001 mm) of polarizing phosphate consisting of elongated microcrystals arranged perpendicular to the surface of the coating. In most cases the coprolites are structureless; locally, areas of phosphate contaminated by pelitic material, alternating with elongated cavities, are arranged in bands. Using the electron and scanning microscopes, amorphous, globular, and crystalline phosphate with several mutual transitions have been clearly identified in the phosphorites from the shelves of Peru and Chile (Figs. 2-50, 2-51). The amorphous phosphate consists of a homogeneous mass with no signs of granulation or crystallization (Fig. 2-50a). The globular phosphate consists of microglobules up t o 2-5 pm in size and aggregates of them (Fig. 2-50b), or of relatively larger globules (10-30 pm) with a bumpy surface in which radial crystallization of phosphate has occurred locally (Fig. 2-5Oc). The crystalline phosphate consists of hexagonal flakes and prismatic crystallites from fractions of a micron to 1-2 pm in size, which occur in the form of discrete segregations against a background of an amorphous groundmass (Fig. 2-51a, unconsolidated concretion) or form relatively compact accumulations (Fig. 2-51c, dense concretion). In many unconsolidated and dense concretions, elongated fusiform particles with rounded or splintery tips, up to 1-2pm in size, are encountered (Figs. 2-50b7 2-51b). The results of microdiffraction investigations of these particles indicate that they belong to the group of apatite-like minerals in their make-up. In some of those particles signs of crystal form are detected. The fusiform particles usually form pockets or stellate (rosette) accumulations and intergrowths on the surface of diatom valves, in association with mineral grains or in the interpore space (Figs. 2-50d, 2-51c, d). Probably these particles are an intermediate stage between amorphous and crystalline phosphate. Semiquantitative X-ray-structural mineralogic analysis, with subsequent computer processing of the results, also was used to investigate the overall composition of the phosphorites of the Peru-Chile region. The main components of the crystalline phase of the phosphorites are: apatite (8-76%), quartz (4-25544, plagioclases (11-25%), micas, including glauconite (017%),and pyrite (0-7%) (Table 2-21).

Fig. 2-50. Ultramicrostructures of phosphorite from the shelf of Peru. (a) Amorphous phosphate; sample PD-15-13, scanning microscope, x 1100 (Burnett, 1974). ( b ) Aggregates of microglobules and fusiform segregations of phosphate, sample 553-20, electron microscope, x 10,000 (photo by V.T. Dwbinchuk). ( c ) Radial crystallization of phosphate globules, sample 546, electron microscope, X 10,000 (photo by V.T. Dubinchuk). (d) Microcrystals of apatite on the surface of a diatom valve, sample PD-12-05, scanning microscope, X 14,450 (Burnett, 1974).

142 Chemical composition of the phosphorites

The chemical composition of the phosphorites was investigated using classic wet chemistry and the X-ray emission method (Tables 2-22, 2-23). All the investigated samples of concretions except the first (Table 2-23) are phosphate rocks with a P z 0 5 content between 12.7 and 29.0%. In the bones of fish and marine mammals from the sediments on the Chile shelf the P, 0, content is 27.3-29.5%, in phosphatized coprolites 30.7%(amorphous phosphate) and 32.3%(finely crystalline phosphate) (see Table 2-22). To a substantial degree the chemical composition of the concretions correlates with the extent of their lithification. On passing from unconsolidated to dense varieties their P z 0 5 content increases (from 13-24 to 1929%),likewise CaO (from 15-30 to 31-42%), COz (from 2-3 to 3-3.5%), and F (from 1.3-2.1 to 2.0-2.6%). At the same time the content of nonphosphatic components, related to clastic and biogenic siliceous material, decreases: SiOz from 19-44 to 10-3076, AlZO3 from 4.4-9.0 to 2.0-5.7%. N o clear-cut tendencies are observed in the behavior of manganese, iron, sodium, potassium, and sulfur.

143

Fig. 2-51. Ultramicrostructures of phosphorite from the shelf of Chile. (a) Crystallization of apatite in amorphous mass in unconsolidated concretion; sample 250-1 ; electron microscope, x 10,000 (Baturin and Dubinchuk, 1974a). (b) Fusiform segregations of phosphate in unconsolidated concretion: sample 250-1; electron microscope, X 16,500 (photo by V.T. Dubinchuk). (c) Microcrystalline phosphate in dense concretion; sample 250-3; scanning microscope, x 7500. (d) Rosette aggregate of microcrystalline phosphate; sample PD-19-37; scanning microscope, x 11,000 (Burnett, 1974).

TABLE 2-21 Composition of crystalline fraction of phosphorite concretions from the submerged margin of Peru and Chile, according to data of semiquantitative X-raystructural mineralogical analysis (Burnett. 1974) Station

Coordinates

Depth (m)

Mineralogic composition (96) apatite

micas kaolinite

quartz

K-feldspar

plagioclase

10

25 23 12 12 19 11

0 10

Peru shelf KK-7 1- 161 553 A-183 PD-12-05 PD-15-13 PD-15-17

5"09'S, 9'13's. 12'26's. 1Z05'S, 15'13'5, 15' 17's.

81O25'W 79'39'W 77'32'W 77'46'W 75O22'W 75'23'W

299-257 260-340 446 330-360 117-123 350-389

8 33 81 54 43 67

4 12 0 17 3

0 4 0 4 2

0

2

25 24 7 13 16 13

Chile shelf PD-18-30 PD-19-30 PD-19-33 PD-19-37 PD-21-25

18'30'S, 19O3O'S, 19'33'S, 19'37's. 2lo25'S,

70'36'W 70'19'W 70'23'W 70'26'W 70'22'W

346-423 127-132 341-370 430 100

63 67 76 66 61

0 0 0 12 0

0 0 0 3 0

10 5 4 4 8

0

0 0

15 0

0

0 8

23 14 15 12 20

tremolite

calcite

dolomite 28 2

0 0 0 0

pyrite

TABLE 2-22 Chemical composition (90)o f phosphorites from the submerged margin of Peru and Chile, from the data of chemical analyses Sample'

P205

CaO

MgO

Si02

AI,O,

FelOl

FeO

17.70 21.10 21.80 17.28 22.26

30.52 34.02 34.72 34.60 41.50

2.00 2.60 2.20 2.23 2.67

24.91 20.33 19.42 26.62 12.22

6.50 5.48 4.01 3.59 3.59

2.79** 1.89** 2.09** 2.30 0.30

15.73

24.90

1.8

22.23

6.11

20.64 25.62

24.92 38.64

1.2 1.6

31.60 12.30

6.00 3.31

26.45 29.51 27.36

35.01 39.55 41.38

LO1

IR

K20

CO,

COm

SO3

F

-

-

-

3.15 3.57 4.04

-

0.98 0.99

0.70 2.59

0.70 0.35

-

-

2.79

0.48

-

2.31

0.65

-

1.00

7.26

27.01

0.102

2.98 1.79

0.36 0.40

-

3.02 3.01

-

-

0.60

-

2.06 2.55

7.20 8.65

39.17 14.95

0.100 0.100

0.55 0.29

3.56 3.41 4.00

-

-

-

1.62 5.27

-

2.45 2.80

9.11 14.02

13.90 0.79

0.097 0.095

-

-

-

-

-

MnO

Na20

FtP2Os

Peru shelf

Unconsolidated concretions Compacted concretions Dense concretions Dense phosphatized rock Dense phosphatized rock Chile shelf Unconsolidated white concretions Compacted light gray concretions Dense gray concretions Dense black platy concretions Fish bones Whale vertebra Phosphatized coprolite. black Phosphatized coprolite. gray

30.67

-

32.33

-

0.8 0.5 0.69

10.80 0.79 2.98

2.55 n.d. ~

-

2.39 1.59 -

-

-

1.70 2.02 2.30

-

2.49 4.95

-

-

-

9.87 9.89

-

6.00 6.76

32.71 26.27 23.62 -

-

-

5.63

1.39

-

-

-

-

4.51

0.92

-

-

-

-

0.096 0.096 0.106 -

-

-

* Peru shelf: all samples are from Baturin e t al. (1975). except for the frrst o f the dense phosphatized rock samples which is from Gershanovich and Konyukhov (1975). Chile shelf: all samples are from Baturin and Petelin (1972). ** Total iron.

TABLE 2-23

Chemical composition (5%) of phosphorite concretions from the submerged margin of.Peru and Chile, according to the data of X-ray emission analyses (Burnett, 19741 P,Os

CaO

MgO

SiOl

A1203

Fe203 (total)

Na10

K20

S

F

LOI**

ZI

-0

Peru shelf KK-71-161 546 553 A-183 PD-12-05 (a) PD-12-05 (b) PD-15-13 (a) PD-15-13 (b) PD-15-17 (a) PD-15-17 (b)

5.95 21.96 19.80 29.00 24.54 28.82 12.76 18.96 19.03 22.14

19.10 34.60 30.34 42.35 36.32 41.45 21.37 31.17 29.00 33.94

4.87 1.48 1.13 0.88 1.09 1.02 0.68 0.86 1.05 1.36

41.40 22.62 27.89 10.17 18.86 12.41 44.48 30.37 25.77 21.21

8.20 5.11 6.75 1.99 4.82 3.27 9.08 5.76 4.43 4.80

3.68 1.69 1.71 1.42 1.39 1.26 2.09 1.53 6.05 3.27

0.75 0.77 0.91 0.70 0.85 0.80 1.00 0.90 0.88 0.83

1.65 1.12 1.47 0.78 1.11 0.85 2.01 1.48 1.11 1.22

0.05 0.15 0.15 0.09 0.04 0.12 0.27 0.16 0.32 0.14

0.59 2.46 2.18 2.61 2.36 2.63 1.35 1.95 2.09 2.36

15.60 9.77 8.20 10.28 10.24 7.80 4.73 7.52 11.73 11.06

101.84 101.73 100.53 100.27 101.62 100.43 99.82 100.66 101.46 102.33

Chile shelf PD-18-30 (a) PD-16-30 (b) PD-19-30 PD-19-33 PD-19-37 PD-21-25

16.02 22.30 25.06 28.71 22.43 27.67

25.09 32.97 36.02 40.01 33.79 40.51

1.34 1.24 0.85 1.11 1.23 0.74

33.89 23.59 17.99 12.86 16.67 13.31

9.82 6.15 5.07 3.10 3.74 3.39

2.68 2.84 2.69 1.75 6.34 2.39

0.98 0.86 0.86 0.76 0.75 0.90

2.11 1.56 1.27 0.76 1.78 0.81

0.06 0.01 0.39 0.12 0.09 0.23

1.62 2.22 2.25 2.57 2.24 2.49

6.12 8.60 7.43 9.27 10.21 8.69

Average***

22.61

33.93

1.07

22.13

5.15

2.85

0.85

1.30

0.16

2.22

8.78

Station (sample)*

* Samples: a = light-gray concretions; b = dark-gray concretions. ** At 1000°C. *** Not counting first sample.

XI1

CaO/P2Os

F/PzOs

0.25 101.59 1.03 100.70 0.92 99.61 1.10 99.17 0.99 100.63 1.11 99.32 0.57 99.25 0.82 99.84 0.88 100.58 0.99 101.34

3.21 1.57 1.53 1.46 1.48 1.44 1.67 1.64 1.52 1.53

0.099 0.112 0.110 0.090 0.096 0.091 0.106 0.103 0.110 0.106

99.73 102.34 99.88 100.84 99.27 101.13

0.68 0.93 0.95 1.08 0.94 1.05

99.05 101.41 98.93 99.76 98.33 100.08

1.57 1.48 1.44 1.39 1.51 1.46

0.101 0.099 0.090 0.089 0.100 0.090

101.05

0.93

100.12

1.50

0.098

147 The scanning microprobe, by means of which particles of relatively pure material 10-30 pm in diameter were analyzed, was used to determine the composition of the phosphatic and non-phosphatic fractions of the phosphorites. The composition of the phosphatic fraction (Table 2-24) is considerably different from the bulk composition of the concretions (Table 2-23); the contents of P,O, (24-30%), CaO (35-40%), and F (2.4-3.396) are higher. At the same time the contents of Na and Mg in the phosphatic fraction remain about the same as in the bulk samples, which apparently indicates that these elements substitute for calcium in the apatite lattice. The CaO/P, O5 and F/P, O5 ratios in the phosphatic fraction also are practically unchanged compared t o the bulk samples (Burnett, 1974). The P,O, content in the cement of the concretions ranges from 20 to 3096, in the phosphate coatings on glauconite grains from 26 to 2796, and within glauconite grains from 0.2 to 1.6%(Table 2-25, Fig. 2-52). Using the same method, schemes of distribution of the elements were plotted by area of thin-section; the relative concentration of elements on these schemes corresponds t o the density of white dots. The area illustrated in Fig. 2-53 consists of grains of quartz, alkali feldspar, and plagioclase in phosphate cement. On the scheme it is seen that the zone of occurrence of calcium is somewhat broader than that of phosphorus, which is related to the presence of plagioclase and tiny rhombohedra of dolomite in the thinsection. A thin-section area of another concretion (Fig. 2-54) consists of a plagioclase grain in phosphate cement. The concentration of calcium and phosphorus on the surface of the plagioclase grain is somewhat greater than that of the rest of the area of phosphate cement. Possibly this phenomenon represents the initial stage of formation of phosphate pellets around grains of clastic material, which act as centers of accumulation of phosphorus (Burnett, 1974). Age o f the phosphorite The phosphorite from the submerged margins of Peru and Chile has been dated by micropaleontological and radiometric methods. According to the determinations by A.P. Zhuze and V.V. Mukhina (Institute of Oceanology of the Academy of Sciences of the U.S.S.R.), the diatoms in the phosphorite of this region are Recent species. Among them there have been identified: Coscinodiscus perforatus Ehr., C. asteromphalus var. centralis Grun, C. gigas Ehr., Actinoptichus undulatus Bail, A . splendens Ralfs, Rhaphoneis wetzeli Mertz (Fig. 2-55a), Cyclotella striata (Ktz.) Grun, Thalassiosira decipiens (Fig. 2-55b) - Peru shelf, station 553, 9'13'S, 79'39'W, depth 260-340m; Chaetoceros sp., Grammatophora angulosa Ehr., Thalassiosira decipiens

TABLE 2-24

CL

Chemical composition ('70)of areas of pure phosphate in thin-sections of phosphorites from the submerged margin of Peru and Chile according to data of scanning microprobe analysis (Burnett. 1974) N

PzO, CaO

MgO

SiO:

A1203

FeO (total)

Na20

F

CI

KK-71-161 PD-12-05( a ) PD-13-15 (b) PD-15-17( a ) (b) PD-18-30 PD-19-30 PD-19-33 PD.19.37 PD-21-24 PD.21.25

2 3 2 2 3 4 3 3 2 9

23.82 26.10 29.83 27.64 29.76 30.23 27.65 25.74 29.28 30.45

1.40 0.94 1.03 1.73 1.45 0.89 1.33 1.04 1.07 1.10

15.07 3.53 7.16 7.06 6.18 6.84 3.17 16.03 4.51 2.86

4.69 1.44 1.23 1.62 1.73 3.01 0.83 3.82 0.68 1.05

2.99 0.44 0.80 1.30 2.24 0.82 0.77 1.10 1.22 0.71

1.03 1.01 1.02 0.83 0.93 1.20 0.79 1.11 0.78 1.27

2.41 2.56 3.08 2.75 3.05 2.81 2.64 2.57 3.14 3.36

0.31 0.02 0.83 0.02 0.17 0.01 0.39 0.01 0.20 0.01 0.48 0.03 0.15 0.02 0.10 0.01 0.11 0.01 0.26 0.02

35.41 39.05 43.38 42.09 44.26 44.65 44.63 38.85 46.41 46.46

La203

Ce203 Nd203

?:

CaO/PzOj F / P z O j

0.02 0.01 0.32 0.03 0.01

0.01 0.01 0.01 0.11 0.06 0.27 0.06 0.10 0.10 0.03

87.25 74.95 88.27 85.57 89.92 91.33 82.08 90.59 87.33 87.62

1.49 1.50 1.45 1.52 1.49 1.48 1.61 1.51 1.58 1.52

Y20,

Station (sample)*

0.08

0.01 0.01 0.01 0.02

0.07 0.01 0.23 0.01 0.04 0.02 0.03 0.11 0.01 0.03

0.103 0.098 0.103 0.099 0.102 0.093 0.095 0.100 0.107 0.110

N = number of determinations. * Samples: a = light parts of concretions; b = dark parts of concretions.

TABLE 2-25 Chemical composition (70)of the phosphate cement, phosphate coatings, and glauconite and plagioclase grains in thin-sections of phosphorites from the shelf Chile. according t o the data ofscanning microprobe analysis (Burnett 1974)

Y203

Of

2

AreaNo.

Materialanalyzed

P20,

CaO

MgO

SiO,

FeO*

Na20

K20 F

CI

La203

Ce203

Nd203

1** 2** 3** 4** 5** 1*** 2*** 3*** 4*** 5***

cement glauconite phosphate coating glauconite cement

19.75 1.65 27.58 0.20 28.01

28.65 0.24 43.27 0.17 41.31

0.51 2.14 1.41 3.24 1.27

29.25 14.84 7.65 49.52 14.56

7.81 3.13 2.65 3.83 2.66

0.67 50.85 2.78 28.37 1.33

1.75 0.56 0.99 0.31 0.95

1.73 1.75 0.01 3.18 7.70 0.02 2.67

0.10 0.01 0.32 0.01 0.14 0.02 0.19 0.03 0.09 0.01

0.01 0.01 0.01 0.01 0.01

0.08

0.01 0.06

0.14 0.09 0.01 0.02 0.19

90.28 85.61 89.77 93.62 93.12

glauconite plagioclase cement glauconite phosphate coating

0.79 10.70 30.38 46.33 0.22 0.24 26.48 40.02

3.59 50.61 0.10 55.96 1.01 5.65 3.17 49.97 6.60 1.28

6.52 28.15 0.81 6.79 1.69

25.12

0.34 5.19 0.91 0.53 1.13

8.10 0.07 0.38 3.53 7.48 0.02 2.32

0.59

0.06

0.01

96.38 101.36 90.00 95.93 82.77

0.56

-

* ** Total Fe. of analyzed areas is shown in Fig. 2-52a,b. *** Location Location of analyzed areas is shown in Fig. 2-52c.d.

AI,03

0.88

1.19 27.12 2.66

-

0.01 0.08

0.01

-

0.01

-

-

-

0.13 0.22 0.36

0.01 0.01 0.01

0.01 0.01 0.01

0.03 0.02 0.11

-

0.01 0.13 0.12

&

149

Fig. 2-52. Thin-sections of phosphorite from the shelf of Chile, investigated by means of the microprobe (for area numbers see Table 2-25; Burnett, 1974). (a), (b) Sample PD-1937. (c), (d) Sample PD-21-24.

(Grun.) Jorg, Trachyneis aspera (Ehr.) Cl., Coscinodiscus radiatus Ehr., Melosira sulcata (Ehr.) Ktz., Rhopalodia musculus (Ktz.) 0 .Mull., Epithemia sorex Ktz., Actinoptichus undulatus (Bail) Ralfs, Cyclotella kuetzingiana Thw., Dictiocha fibula Ehr. - Chile shelf, station 250, 2lo07'S, 7Oo21'W, depth 150 m. The absolute age of the concretions was determined radiometrically from the 234U/238Uactivity ratio as a whole and from tetravalent uranium, and

150

Fig. 2-53. Distribution of elements by area in a thin-section of a phosphorite concretion from the shelf of Peru; sample KK-71-161(Bumett, 1974).

Fig. 2-54. Distribution of elements by area in a thin-section of a phosphorite concretion from the shelf of Chile: sample PD-21-24 (Burnett, 1974).

152 from z30Th/z34U(Baturin e t al., 1972c, 1974; Burnett, 1974; Burnett and Veeh, 1977; Veeh e t al., 1973). In the phosphorites considered, the uranium content ranges within 26219 x %, thorium within 1.1-9.0 x %. Tetravalent uranium constitutes 40-7176 of the total uranium. Uranium in equilibrium was found in only one sample (from station 544, Table 2-26) from the continental slope of Peru. In the rest of the samples the 234U/238U activity ranges from 1.04 k0.03 to 1.16 kO.01 in total uranium and from 0.84 k0.03 to 1.19 k0.04 in tetravalent uranium, and the z30Th/234Uratio from 0.010 kO.001 t o 0.74 k 0.03. If it is assumed that all the ionium contained in these phosphorites was produced by decay of 234U,their maximum age, calculated from the 230Th/ 234U activity ratio, is from 1000 to 140,000 years. The age of the phosphorites calculated from the z 3 4 U / 2 3 8 Uactivity ratio of total uranium ranges from Recent to > 800,000 years, and from the activity ratio of these isotopes in tetravdent uranium, from Recent to > 150,000 years (Table 2-26).

153

Fig. 2-55. Recent diatoms in phosphorite from the Peru shelf (identified by A.P. Zhuze). (a) Rhaphoneis wetzeli Mertz; scanning microscope, x 4400. ( b ) Thalassiosira decipiens; scanning microscope x 1500.

In the latter case the age was calculated on the basis of a theoretical model according to which, as a result of radioactive decay and subsequent oxidation of 238U(IV)and 2MU(IV)in the concretions, fractionation of urkium isotopes between U(1V) and U(V1) takes place (Kolodny, 1969a; Kolodny and Kaplan, 1970a). Thus on the submerged margin of Peru and Chile, as on the shelf of southwest Africa, there occur Recent, Upper Quaternary, and apparently preQuaternary phosphorites.

LOCAL ACCUMULATIONS AND ISOLATED FINDS OF PHOSPHORITE ON THE OCEAN SHELVES

In addition to the vast phosphorite provinces, there are small phosphate outcrops and local accumulations of phosphorite on the ocean shelves, some of which have been investigated in sufficient detail.

T.\Bl.E 2.26 .\IIsoIute are

d phosphorite from the rubmereed marein

of Peru and Chile. from the aelivitv ratios of uranium and thorium isotows

total)

I'V"

Sl,Cl/

KK-71-161

5'00's. 81'25'W

eonei~tion

106(110)"

5.9

KK-71-161

5 ' 0 0 ' 5 . LI1'25'W 299-257

299-257

concretion, upper layer

103

6.7

1.09f0.01 (1.1OtO.02) 1.09t0.01

KK.71.161

5'OO'S. LIl-25'W 299-257

concretion.

10

61

1.10'0.01

77

2.0 4.7 2.2

1.16

1.07'0.01

1.16

0.40f002

l8Of45

55

-

-

0.46+0.02

180t45

66

0.62+0.03

14Of40

102

-

""&W

-

553

9 1 3 S. i9'39.W 260-340 9"46'S . ( 9= 2 3 ' W 360

i46

-

2.1

65

1.1

1.14t0.01

-

0.040f0.002

fish hone light concretion

101

n.d.

27

2.4

1.15f0.01 1.17f0.03

-

0.02OfO.001 Recent 0.050t0.002 Recent

6

dark

1021hll

3.2

concretlo" rish bone light

101

0.4

382(219)

5.5

721531

2.3

RI 150) l o o ( 103)

3.7 3.0

372(1561 IO?(i6)

9.0 3.1

544 KK-71-96 4.183 PD.12-05

67 16 118

9G 168

5.7 5 1

CO"C
PD-12-05

i ? - o s ' s . i i16'w 330-360


PD-12-05 PD-15-13

12'05's. 7 7 " 4 6 ' W 330-360 1 5 13's.i 5 ' 2 2 ' W 117-123

PD.15-13

1 5 ~ 1 3 ' s 75'22'W .

PD-1 5 . 13 PD.15-17

15'13'5. i 5 ~ 2 2 ' W 117-123 1 5 ~ 1 7 ' s75'23'W . 350-389

117-I23

2

1.16f0.01 1.06t0.02 1.OOtO.03 1.08fO.01 1.11to 01 1.15t0.01

concretton concretion

1.15t0.01 (l.14f0.01) 1.1410.01 1.15t0.01

0.02OtO 001 Recent 0.63t0.03 330t140 0.74f0.03 > 800 0.53t0.03 225f45 0.36t0.02 110235 0.021tO.001 Recent 25125

105

140 81 46 2 5 2

1.13f0.02

1.15

0.060t0.003

Recent

7

-

-

25t25

1.14t0.03

1.16

0.01OtO.001 0.029tO.001

1 3

l.lll0.01 f1.16tO.02)

1.19t0.04

1.11

0.040f0.002

25+25

5

l.lltO.O1 1.14t0.01 (1.13f0.01I 1.1210.01 1.12to.01 (1.10f0.02) 1.06t0.01 ( I .04t0.03) 1.143f0.008

1.09to.02 1.151-0 02

1.13 1.11

0.35+0.02 0.0ROf0.004

110t35 25f25

46

1 . I 1to.02 1.09t0.02

1.13

0.40f0.02 0.35f0.02

SOU0 80t30

JJ

0.71f0.03

330f65

130

Recent

COnCIetl""

Chilc s h e l l

PD-IH-30

18-30's. 7 0 " 3 6 ' W 346-423

eoncr~tion

PD-19-30 PD-19.33

19'30's. 7 0 19%' 12i-132 19'33's. 70'23'W 341-370

concretion

PD-19-37 PD.21-24

i9'3i's. io'zfi'w 4 3 0

concrptlon

2 1 ~ 2 3 'i ~O .C 1 8 ' W 4 2 0 - ~ R O

eonerction

PD-21-25

21'25'S. 7OC22'W 100

~uner~lion

9wm)

3.5

-

concrctum

250

2 1 ~ 0 7 ' s7oc21'W . 150

unconsolidated concretion

31

250

21'0i'S. ;0'21'w 150

eompactad

26

250

21'Oi'S. 70"Zl'W 150

dense

EO"C*Ctl""

12

-

-

1.146f0.010 1. I 48'0.008

ConCletlo"

** ff.

Samples from station 250 after Ralurm e l al. (1974).other samples alter Burnett (19741 and Burnett and Veeh (1977) Maximum age. In parentheses - results of repealed determinations made in investigating tefravalent Uranium

1.12

0.H4f0.03 1.34 -

Recent

I143f0.008

-

Recent

1 112f0.014

-

Recent

9 ..

46

155

Shelf o f Socotra Island Phosphorite was discovered on the shelf of Socotra in 1967 at the time of the 19th cruise of the research vessel “Mikhail Lomonosov”. According to the description by Gevork’yan and Chugunnyy (1969, 1970), the phosphorite occurs on the submerged southwest slope of the island at a depth of 210m. This sector is a bench on the shelf near the continental slope. The phosphorite occurs in depressions in the rocky basement, which is often devoid of unconsolidated sediments. In a drag-catch obtained here, 326 phosphorite pebbles 2-5mm in size were counted, very diverse in shape and in character of the surface, and chiefly dark brown in color. In microscope study it was established that the concretions consist of finely dispersed cryptocrystalline phosphate. Disseminated calcite with crystals less than 0.01 mm in size also occurs in the concretions; its amount averages 20-25%. In addition to this, the phosphorite contains carbonate detritus (foraminifera, fragments of larger shells, etc.), the amount of which ranges from a few percent to 30%. The chambers of the foraminifera are filled with pyrite, isotropic phosphate, and less often with calcite and glauconite. Finely dispersed pyrite is scattered over the whole thin-section area; less often it forms accumulations. Isolated microcrystals (possibly apatite) occasionally occur in the isotropic phosphate matrix. Some large aggregate grains of calcite and foraminifera up to 0.5 mm in size are coated with a thin layer of crystalline phosphate. In addition to calcite foraminifera tests, some completely replaced by phosphate are encountered. In some concretions a substantial amount of clastic material is observed, in the form of angular grains of quartz (up to 10%)0.05-0.20 mm in size which, like calcite, is unevenly distributed over the thin-section area. According to chemical analyses (Table 2-27), the phosphorites contain 28.58% P z 0 5 , 44% CaO, 3% SiOz, and 6% F e z 0 3 on the average. The insoluble residue of the phosphorite consists mainly of aggregates of finely dispersed clayey matter and quartz plus a little amphibole, feldspar, zircon, apatite, and chalcedony. The unconsolidated deposits on Socotra and nearby islands and banks are Meso-Cenozoic (Greenwood and Bleackley, 1967). Judging from the conditions of occurrence and rounding of the concretions, they were eroded from these deposits (Gevork’yan and Chugunnyy, 1969).

Shelf o f western Hindostan Phosphatic formations were found off the west coast of Hindostan on a

156 TABLE 2-27 Chemical composition (96) of phosphorite concretions from the shelf of Socotra Island Component

Sample

1 (Gevork’yan and Chugunnyy, 1969)

H2 Ohygr

LO1

co2 CO, c1 F Total

2 (Chugunnyy, 1972)

2.79 0.22 3.18 5.89 0.88 0.18 0.54 44.12 28.58 1.07 0.32 1.59 2.25 8.10

n.d. 2.34

3.40 0.13 1.37 5.61 1.43 0.07 1.66 43.68 27.42 0.70 0.55 2.14 1.64 8.80 0.55 0.02 1.60

101.05

100.09

cruise of the “Nauka” (Azcher NIRO*) in 1967 in the region of 8’47’S, 76”02’E,during trawling at a depth of 260-300 m (Fig. 2-56). According to the descriptions by Chugunnyy and Orlova (1970) and Chugunnyy (1972), the enclosing sediments are calcareous sands with admixed clay material. The phosphatic formations are in the form of tubes with channels running through them. The tubes are up to 35 cm long, 8-9 cm in outside diameter, and 1.8-3 cm in inside diameter. The surface of the phosphorite is rough, pustulose, and lustrous. The parts projecting above the bottom surface are bored by pholads and covered with bryozoan colonies. The structure of the rocks in thin-section is massive, the texture mainly finely crystalline, equigranular. The fine-grained material (80-90% of the rock) consists of a mixture of calcite, amorphous isotropic phosphate, and * Azov-Black Sea Scientific Research Institute of Sea Fisheries and Oceanography. (Translator.)

157

Fig. 2-56. Bathymetry of the shelf of western Hindostan. The sector where phosphorite was found is cross-hatched (Chugunnyy and Orlova, 1970).

clayey material. The sandy-silty material (10--20%) consists of fragments and concretions of calcite, quartz grains, sponge spicules, and fragments of foraminifer tests. Patchy accumulations of iron hydroxides and pyrite often are associated with the organic remains. An investigation of the insoluble residue of the rock (after treatment with HC1) showed that it consists mainly of aggregates of phosphatic-clayey matter, t o a lesser extent of quartz, tabular grains of feldspars, amphiboles, chlorite, micas, and glauconite. Three macrolayers are distinguished in the cross-section of the phosphate tubes: an outer, middle, and inner, differing in color, microstructure, and chemical composition. The outer layer (10-19 mm) is dark brown in color and discontinuously microstratified in texture with sporadic micromottling. The middle layer, which is the thickest, is gray and unstratified. The brown inner layer lines the walls of the channel through the tubes. In the body of the tubes there are radial cracks beginning from the inner channel, some of them reaching the outer layer. Apparently the cracks were formed due to dehydration of the silty-pelitic material of the rock in the course of its cementation and subsequent crystallization. The results of layer-by-layer analysis of the tubes (Table 2-28) show that the maximum P,O, content (7.60%) is in the outer layer; it is lower in the

158 TABLE 2-28 Composition (%) of tubular phosphate formations from the shelf of western Hindostan (Chugunnyy, 1972) Component

Sample

la

COG

c1 F

Total

lb

outer layer

middle layer

inner layer

15.97 0.25 4.82 12.00 2.15 0.04 9.22 23.62 7.60 0.89 0.90 1.14 3.56 16.72 1.24 0.03 0.20 --

10.07 0.22 5.60 1.61 1.44

13.75 0.18 2.94 6.41 1.79

100.26

0.00

0.00

13.90 27.22 4.90 0.70 0.80 0.46 32.00 0.48 0.06 0.15

10.30 26.46 6.20 0.78 0.70 0.76 1.49 26.60 0.92 0.07 0.50

10.46 0.19 4.05 4.32 1.43 0.06 6.77 25.87 10.27 0.60 0.55 1.11 4.20 29.04 0.53 0.09 1.05

99.54

99.64

99.83

0.00

2

11.94 0.18 5.21 13.41 0.86 0.03 5.96 25.34 8.70 0.65 0.56 1.43 5.39 18.92 0.75 0.03 1.69 100.40

inner layer (6.20%) and minimal in the middle layer (4.90%). A similar tendency is observed in the distribution of ferric and ferrous iron. The distribution of MgO content layer by layer (9.22, 13.90, 10.30%) and also of CaO and C 0 2 reflects the extent of dolomitization, which in contrast to the phosphatization, was most intensive in the middle layer. The origin of the tubular phosphate formations evidently is related to phosphatization of tracks of crustacea in the muddy sediment. Crustacean tracks of similar shape are encountered in the calcareous and sandy sedimentary rocks on land (Vyalov, 1966). Judging from the lithologic features, the phosphatic tubular formations described have been redeposited (Chugunnyy and Orlova, 1970). The approximate age of the carbonate fraction of the outer layers of the tubes, determined by the radiocarbon method, ranges from 6500 t o 33,000 years; the rate of radial growth of the tubes calculated from these results is 0.040.1 mm/1000yr, and the tentative age of the central part, of the order of 0.6 Ma (Gevork’yan e t al., 1975; Sobotovich e t al., 1972).

159

Submerged Chatham Rise The submerged Chatham Rise, topped by the island of the same name, is situated east of New Zealand, and is a structure 130 km wide and 800 km long connected to it. Phosphorite was first found in this region by a British expedition on the ship “Discovery II”, in a sample of sand brought up by trawling from a depth of 285-300 m (Reed, 1952). Later, phosphorites were found by expeditions of the New Zealand ship “Viti” and the American “Argo” at six more stations between 176”E and 175OW, at depths of 285 to 465 m (Norris, 1964), and still later at several other points, mainly in the central part of the rise (Glasby and Summerhayes, 1975; Pasho, 1976; Summerhayes, 1967; Watters, 1968). The phosphorite-bearing sediments consist of gritty sands made up of angular and slightly rounded fragments of crystalline schists, mineral grains, black phosphorite concretions, and foraminifer tests. The medium and fine sandy fractions predominate in the sands. Among the mineral grains there are products of decomposition of rhyolitic and andesitic-dacitic rocks, and also glauconite and barite. In some samples the glauconite content is more than 50%. The phosphorite concretions are irregular in shape, angular or slightly rounded, sometimes with a polished surface. They are not more than 15cm in size. There are no oolitic structures. The rocks consist of tests of foraminifera and calcareous cement, irregularly replaced by collophane. Glauconite is a usual component of the phosphorites, and pyrite is often encountered. The glauconite is present in the form of round grains, fills cracks in the concretions and cavities in foraminifera tests, and forms a coating (by replacement of collophane) on the surface of the concretions. The pyrite is disseminated in the form of tiny particles of irregular shape, replaces foraminifera tests, or fills cavities in them. Tiny (0.125-0.62mm) sharply angular grains of clastic minerals volcanic glass, quartz, feldspars, epidote, zircon, sphene, hornblende - are (Pasho, 1976). present in the phosphorites in minor amounts (up t o 1%) The phosphorites contain from 16.5 to 25.4% P, 0 5 ,averaging 20-2176 (Kams, 1974; Pasho, 1976). Their CaO content is 37-53%, SiOz 0.4--7% C 0 2 9-2196, and F 1.30-2.65% (Table 2-29). According t o the results of microprobe analyses the chemical composition of the central and peripheral parts of the phosphorite concretions is about the same (Buckenham et al., 1971). The age of the phosphorites from the Chatham Rise is pre-Quaternary, judging from the conditions of their occurrence. The foraminifera found in the enclosing sediments are Miocene species (Norris, 1964). The absolute age of the glauconite from the enclosing sediments, determined by the potassium-

TABLE 2-29 Chemical composition (%) of phosphorites from the submerged Chatham Rise Component

Sample* 1 21.8 37.5 6.9 0.1 -

1.o 9.3 2.56 -

2

3 19.51 53.31 0.50 0.45 n.d. 1.48 0.57 0.54

20.43 51.25 0.49 1.55 n.d. 2.18 0.53 0.73

0.30 2.28 21.72

0.40 2.65 20.02

100.66

100.23

4

5

6

7

19 49 4.5

25.40 42.70 tr.

19.18 47.50 tr.

18.10 44.00 tr.

tr. 1.43

tr. 2.50

1.50 4.00

20.92 1.30 0.10

0.30 4.27 19.11 1.60 5.12

87.43

91.50

92.50

-

12.40 -

-

* 1 = average of analyses of 6 samples (Reed, 1952); 2, 3 = samples CX-45 and CX-79 (Burnett, 1974); 4 = sample CX-59 (Rouse, 1969); 5-7 = after Pasho’s (1976) data.

argon method, is 3.0-5.5Ma (Cullen, 1967). The uranium isotopes in the phosphorites are in radioactive equilibrium, judging from the results of investigations on nine samples. This indicates that the age of the phosphorites is more than 0.8-1 Ma (Burnett, 1974; Kolodny, 1969a). Exploratory work done in 1968 by the company “Global Marine Incorporated” showed that reserves of up-to-standard phosphorite (- 200 million tons) occur over an area of 4600 km2 at depths of up t o 350 m. The quality of the phosphorites can be enhanced by calcination, but in agriculture they can be used as fertilizer without preliminary treatment (Karns, 1974). Phosphorites also have been found south of New Zealand, on the Campbell Plateau near the island of that name; they are phosphatized limestones coated with an iron-manganese crust (Summerhayes, 1967; Tooms et al., 1969).

Other finds of phosphorite on the shelves and continental slopes Other finds of phosphorite on the shelves and continental slopes of the ocean, which are only briefly mentioned in the literature, are known.

161 On the shelf of the Andaman Islands in the northern part of the Indian Ocean, dense black nodules of phosphatized foraminiferal limestones have been found at a depth of 180 m (Tipper, 1911). Fine platy phosphorite concretions have been brought up from a depth of 600m on the continental slope of the northeastern part of the Arabian Peninsula (Gevork’yan and Chugunnyy, 1970). Isolated finds of phosphorite off the east coast of South America, off the coast of Australia, and on the shelf of Japan have also been reported (McKelvey and Wang, 1969; Murray, 1898; Niino and Chamberlain, 1961; Von der Borch, 1970).

This Page Intentionally Left Blank

Chapter 3 PHOSPHORITE ON SEAMOUNTS Outside of the submerged margins of continents, in the pelagic zone, phosphorite occurs on seamounts, mainly in the Pacific but occasionally in the Atlantic and Indian Oceans. In most cases the seamounts on which phosphorite occurs are flat-topped (guyots). As a rule the phosphorite is non-concretionary and metasomatic, and consists of different kinds of phosphatized rocks: limestones, basalts, hyaloclastites. The phosphorite on seamounts differs from shelf phosphorite in tectonic setting, conditions of occurrence, and petrographic composition; only a few varieties of phosphatized limestone are similar to the latter.

PACIFIC OCEAN

In the pelagic zone of the Pacific Ocean phosphorite was first discovered in 1950 in the Marshall Islands region by the American Mid-Pacific expedition. Tuff breccias with fractures filled with Lower Eocene phosphatized Glo bigerina limestone and a fragment of partially phosphatized Miocene Globigerina limestone were dredged up from a depth of 1500-1900m on Sylvania guyot near Bikini atoll (Hamilton and Rex, 1959). Then Tertiary phosphatized limestones were obtained from the Horizon and Cape Johnson guyots in the Mid-Pacific mountain system (Mid-Pacific Mountains) (Hamilton, 1956), and a fragment of basalt with pores filled with phosphate from the submarine slope of the Hawaiian Islands from a depth of 1010 m (18"48'N, 157'03'W) (J.G. Moore, 1965). Subsequently Soviet, American, Japanese and New Zealand expeditions established the substantially more extensive occurrence of phosphorite and phosphatized rocks on seamounts in the northwestern, central, and southern parts of the Pacific Ocean - on numerous guyots in the Marcus-Necker Ridge system in the northwest basin, between Marcus Island and the Japan Trench, in the southern part of the Emperor Seamounts (Milwaukee Bank), on the slope of the Manihiki Plateau, on a seamount south of Rarotonga Island, and on guyots in the Tasman Sea (Bezrukov, 1971a-c; Bezrukov et al., 1969; Murdmaa e t al., 1972, Heezen et al., 1973, Shiki et al., 1974; Slater and Goodwin, 1973) (Fig. 3-1; Tables 3-1, 3-2). The depths from which phosphorite was brought up range from 300 t o 4000 m; on the Marcus-Necker Ridge phosphorite usually occurs a t depths of 1000-2500 m (Fig. 3-2), and in secondary occurrence it is found at the

164

6C

$0

5c

>O

10 :0

~

~~~

~

‘0

J996

140

160

180

160

Fig. 3-1. Distribution of phosphorite o n seamounts in the northwest part of the Pacific Ocean from data of the 43rd and 48th cruisesof the “Vityaz’ ”(Bezrukov, 1971b). Legend: 1 = stations at which phosphorite samples were obtained; 2 = areas of widespread occurrence of phosphorite and phosphate rocks.

foot of individual mounts a t depths of more than 5000m, in particular as the nuclei of iron-manganese concretions a t depths up t o 6160 m (Bezrukov, 1971a-c). The phosphorite on seamounts is related to the non-phosphatized rocks associated with it and is extremely diverse in morphology and composition. For instance, a 58 x 38 x 1 5 c m slab of dense white phosphorite; boulders and slabs (weighing up to 147 kg) of altered basalt with pores filled with phosphate, and tuff-breccias with phosphate cement; a fragment of phosphatized limestone; and iron-manganese concretions with phosphorite nuclei were brought up from depths of 1930-1970m from one of the guyots in the Mid-Pacific mountain system (20°42’N, 170’26’E). The main type of phosphorite on seamounts is phosphatized limestone. In particular, on the Marcus-Necker Ridge there are rudist, bioclastic-calcarenite, and phosphatized nannoplanktonic foraminiferal limestones, usually coated

TABLE 3-1

Phosphorite on guyots in the northwestern part of the Pacific Ocean* (Heezen et al., 1973) Guyot

Coordinates and depth

Rock type

Geologic age

Organic remains

17'47'N, 176'05'W 2250-2730 m

phosphatized chalk

Early Eocene

planktonic foraminifera

Cape Johnson

17'05'N, 177'09'W 2126-2130 m

phosphatized foraminiferal limestone

Middle Eocene

planktonic foraminifera

Shepard

19'14'N, 179'33'W 3 200-42 5 5

phosphatized chalk-like limestone with manganese crust

Cenomanian/ Turonian

planktonic foraminifera

Jacqueline

19'20'N, 176'45'E 3500-3700 m

porous lutitic phosphorite with manganese crust

Cretaceous

phosphatized coquina

Cretaceous

corals, mollusks, echinoderms

phosphatized chalk-like limestone with manganese crust

Cenomanian/ Turonian Early Cretaceous

planktonic foraminifera

-

19'19'N, 176'45'E 2057-2258 m

phosphatized rudist limestones with worm tracks and manganese crust Menard

Wilde

purple algae, mollusks, planktonic foraminifera

20°44'N, 173'27'E 1937-2000 m

phosphatized chalk-like limestone with manganese crust

Cenomanianl Turonian

planktonic foraminifera

20°47'N, 172'20'E 1421-1738 m

partially phosphatized bioclastic calcarenites

Cretaceous

stromatoporoids, mollusks, purple algae, benthic foraminifera

21°09'N, 163'22'E 1485-2630 m

partially phosphatized dense foraminiferal limestone

Middle Eocene

planktonic foraminifera

21'10'N, 163'09'E 1386-1453 m

nannoplanktonic foraminiferal limestone and lutitic phosphorite with manganese crust

Middle/Late Eocene

planktonic foraminifera

+ cn cn

c-'

Table 3-1 (continued)

Q, Q,

Guyot

Coordinates and depth

Rock type

Geologic age

Organic remains

Miami

21'43'N, 161'53'E 1535-2050 m

volcanic breccia with phosphate cement

Eocene

planktonic foraminifera

phosphatized foraminiferal limestone

Middle Eocene

planktonic foraminifera

volcanic breccia with phosphate cement

Eocene

planktonic foraminifera

partially phosphatized foraminiferal limestone

Middle Eocene

planktonic foraminifera

porous phosphatized chalklike limestone

Eocene

foraminifera and coccoliths

tuff-breccia with phosphatized chalk

Middle/Late Eocene

foraminifera

21'29'N, 159'15'E 1499-1999 m

phosphatized chalk-like limestone

Eocene

foraminifera

23'42'N, 159'33'E 2595-3200 m

porous phosphatized lutite with manganese crust

Middle Eocene

foraminifera

23'49' N, 159'26' E 1767-2004 m

phosphatized lutite

Early Eocene

foraminifera and coccoliths

phosphatized volcanic breccia

Eocene

foraminifera and coccoliths

pebbles of phosphatized foraminiferal limestone

Middle/Late Eocene

foraminifera

porous phosphorite with manganese crust

Cretaceous

casts of foraminifera

Lamont

21'29'N, 159'37'E 1640-2005 m

21'29'N, 159'32'E 1215-1275 m

Scripps

24'05'N, 159'27'E 3597-4129 m

partially phosphatized chalk with intercalations of volcanic ash phosphatized volcanic breccia

Middle Eocene

planktonic foraminifera

Late Cretaceous

planktonic foraminifera

phosphatized bioclastic arenitic limestone

Cenomanianl Turonian

29’31’.N, 153’24’E 2020-2300 m

porous bioclastic calcarenites and arenitic phosphorites

Cenomanian/ Turonian

planktonic foraminifera, echinoderms, mollusks, fish bones mollusks, benthic and planktonic foraminifera, coccoliths, fish bones

Isakov Seamount

31°33’.N, 151’13‘E 1742-1875 m

phosphatized rudist limestones

Early Cretaceous

mollusks (caprinids)

Thomas Washington

32’00’N, 149O17’E 1529-1958 m

porous phosphatized chalklike limestone

Early /Middle Eocene

planktonic foraminifera

phosphatized rudist limestones

Cenomanianl Turonian

mollusks, rudists, echinoderms

phosphatized rudist limestones

Cretaceous

rudists and other mollusks

Makarov Seamount

Winterer

29’29’N, 153’20’E 2050-2563 m

37’51’N, 148’18‘E 1677-1974 m

planktonic foraminifera

phosphatized chalk-like limestone Eiko Seamount

34’13‘N, 144’11’E 2080-3000 m

phosphatized chalk-like limestone

* Samples collected by expedition of the ship “Thomas Washington”.

Cenomanianl Late Cretaceous

planktonic foraminifera

168 TABLE 3-2 Phosphatic material from the Tasman Sea guyots (Slater and Goodwin, 1973) ~~~

~~~

Coordinates

Depth (m)

Rock type

Taupo T-1

33'10'5, 156'05'E

313

T-5

33'10'S, 156'05'E

337

T-10

33'10'S, 156'05'E

309

basaltic gravel with film of phosphate basalt with film of phosphate and coral fragments basaltic gravel with film of phosphate and sheet of limestone

Barcoo B-5

32'30's. 156'10'E

300

basaltic gravel with film of phosphate and sheet of limestone

Derwent Hunter D-9

3Oo50'S, 156O15'E

37 3

D-11

3Oo50'S, 156'15'E

309

D-19

30'50'S. 156'15'E

364

phosphatized foraminiferal limestone phosphatized foraminiferal limestone basalt with film of phosphate

Gifford G-2, 5, 6, 10, 13

26'50'S, 159'34'E

291-346

Guyot and sample no.

phosphatized foraminiferal limestones

with crusts of iron and manganese hydroxides (Bezrukov et al., 1969; Hamilton, 1956; Heezen et al., 1973). The rudist limestones consist of remains of a partially phosphatized shallowwater macrofauna including mollusks (rudists, caprinids), corals, purple coralline algae, stromatoporoids, and spines and plates of sea urchins. Sometimes only casts remain of the rudists, filled with phosphatized calcareous ooze containing whole tests of post-Cenomanian foraminifera (Globotruncana). The phosphate is chiefly amorphous; less often, when it fills cavities in the rock, it is fibrous and crystalline. The crystals of phosphate (francolite) are hexagonal and tabular, 0.5-4 pm in diameter. The bioclastic calcarenite limestones are porous rocks consisting of shell fragments cemented by calcite and a fine-grained carbonate mass. The shell fragments, 0.1-3 cm in diameter, are sorted, rounded or slightly angular, and coated with a film of carbonate cement. In those cases where the rock

169

6‘ km 6353

-

6352

6351

6350 6349 6348

6347-

-~ ~

6346

~-

E

6345 3 4 4

~

~~

~~~

6

00 -

miles

Fig. 3-2. Sublatitudinal profile of the bottom along the Marcus-Necker Ridge, on a traverse from station 6344 (1g059’N, 17Oo40‘W) to station 6369 (26O58‘N, 151°25‘E) on the 48th cruise of the “Vityaz’” (Bezrukov and Baturin, 1976). Triangles indicate sites of phosphorite finds.

is partly or wholly phosphatized, the grains and cement are replaced by phosphate t o a variable extent. The nannoplanktonic foraminiferal limestones consist of tests and fragments of tests of foraminifera (chiefly planktonic, t o a lesser extent benthic), coccoliths, and tiny grains of crystalline calcite - possibly fragments of coccoliths. Worm tracks are occasionally encountered. When phosphatized, these rocks retain the relict structure of the foraminiferal limestone (Fig. 3-3). The phosphate is mainly amorphous, occasionally crystalline. In some cases the tests of the foraminifera are preserved, in others only casts of them remain. Both hollow tests and tests filled with calcite or francolite are encountered. When the rocks are studied under the electron and scanning microscopes, aggregates of idiomorphic tabular hexagonal crystals of francolite up to 1-5pm in size, encrusting the walls of cavities, are found in them (Fig. 3-4). The virtually complete absence of detrital minerals is characteristic of phosphorite from seamounts.

170

Fig. 3-3. Phosphorite with relict organogenic structure of foraminifera1 limestone (Bezrukov et al., 1969). Station 6002-12, 20°42’N, 170’53’W;thin-section, x 6 0 , (1 nicols.

Isolated highly decomposed grains of glauconite with a brownish tinge were found in individual thin-sections of phosphorite from the Milwaukee Bank. In the phosphate core of an iron-manganese nodule from the seamount south of Milwaukee Bank (“Vityaz’ ” station 6263), a few fairly fresh, round greenish grains of glauconite were encountered, apparently formed under the usual marine conditions. Smooth fragments of concentrically layered phosphate with radial extinction which, as is known (Zanin, 1975), is typical of formations of the crust of weathering, were observed in the cement of several samples of phosphorite from various seamounts (Bezrukov et al., 1979). Blocks of tuff-breccia and basalt containing phosphate, fragments of which often constitute the nuclei of iron-manganese concretions, also occur extensively on seamounts. On the Mid-Pacific Mountains the basalts are porous and amygdaloidal; the amygdules are filled with zeolites and chlorite, sometimes with secretions of barite and cristobalite. Scoriaceous fragments of palagonitized basalt are present in the tuff-breccias. Phosphate fills the pores, fractures, and interstices between fragments and on their periphery (Fig. 3-5). Siliceous-phosphatic rocks are a relatively rare rock type on seamounts. A

171

Fig. 3-4. Crystalline phosphate in phosphatized limestone; station 6333, 12O54’S, 160’ 44’W: (a) under electron microscope, x 11,400; (b) under scanning microscope, X 11,400.

172

Fig. 3-5. Part of basalt nucleus of an iron-manganese concretion (Bezrukov et al., 1969). Fractures and pores beneath ore crust (black) on periphery of nucleus filled with phosphate (gray) with relict structure of foraminiferal ooze. Station 6002-12, 20°42‘N, 170’53‘W; thin-section, X 8, (1 nicols.

170 x 1 4 5 x 6 4 cm block of such rock, weighing more than a ton and covered with an iron-manganese crust, was brought up on the 43rd cruise of the “Vityaz’” from a depth of 3300-3800m, a t a point with the coordinates 27”51‘N, 177”lS’E (Bezrukov et al., 1969). Siliceous and phosphatic sectors alternated in the rock. The main part of the block consisted of chalcedony and quartz with patches of iron hydroxide. In the lower part of the block there were white areas with the relict structure of foraminiferal limestone. Thin bands (up to 2 mm) of pinkish white apatite occur in the ore crust, situated along the depositional surface of the ore material (Fig. 3-6). The chemical composition of the phosphorite and phosphatic rocks from seamounts reflects their diverse petrographic composition. Their P, O5 content varies widely - from 4-1176 to 32%. In dense phosphatized limestones it reaches 29-32%, in unconsolidated limestones it usually is lower (Table 3-3). In rocks with a high P,O, content the fluorine content is 3.11-3.89%, that of sesquioxides 1.04-2.10%, and the insoluble residue 0.10--1.35%. The dominant chemical components of the phosphatized basalts and hyaloclastites are the sesquioxides, and P, O5 is minor (4-1196). The siliceous parts of the block of siliceous-phosphatic rock contain 88.3%

173

Fig. 3-6. Part of nucleus of siliceous-phosphatic block from Mid-Pacific Mountains (Baturin and Bezrukov, 1971). Gray and dark gray main mass: siliceous-fenuginous rock (Si);white areas: fluorapatite with relict foraminifera tests ( F a ) .In upper left-hand part, a thin band of cryptocrystalline fluorapatite. Station 6017, 27'51'N, 177'18'E; natural size.

Si02 and 0.70% P 2 0 5 ,the phosphatic parts 31.47% P 2 0 5 (Bezrukov et al., 1969). Characteristic features of the chemical composition of phosphorite from seamounts are low contents of C, (0.09-0.33%) and uranium (0.00010.0009%), absence of pyrite sulfur, and relative enrichment of the rare earth elements contained in them in the heavy lanthanoids (Baturin, 1975a; Baturin and Kochenov, 1974, Baturin et al., 1972a). The age of the phosphatized rocks ranges from Cretaceous to Pleistocene. In the phosphorites of the MidPacific Mountains, three age assemblages of planktonic foraminifera are distinguished: Late Albian/Early Turonian ( Ticinella roberti, Clavihed bergella cf. C. simplex, Rotalipora cf. cushmani, Praeglobotruncana cf. P. helvetica, Rotalipora cf. R . greenhornensis, Hedbergella cf. H. postdownensis, Heteroelix cf. H. globulosa); Senonian/Maastrichtian (Globotruncana cf. G. lapparenti, Globotruncana cf. G . tricarinata, Globotruncana cf. G. contusa, Globo-

TABLE 3-3 Chemical c o m w s i l i o n lin 9 )or phosphorites from seamounts nn the Pacvfic Ocean IBalunn and Bezrukov. 1976. Bezrukov e l al.. 1 9 6 9 )

--

.~

Stall""

-

Coordinates IiO'S3'W

Depth ( m l

Sample

P20,

CaO

MgO

SO,

Ti02

A1201

1530

dense iiliceous phosphorite*

30Ri

4879

110

-

0.55

1.29

120

-

055

0 49

3.77

4.57

~.

6002-12

20'42'N.

6002 12s

20"12'N. 170"53'W

1930

dense white phmphonle'

31 97

44.91

6002 12127

20242'N.1 7 0 5 3 ' W

1930

unconsolidated white phosphorite*

1826

3 6 1 9 2 9 0

6002.1207

20'42'N. 1 7 0 ~ 5 S ' W 1930

6001-112

2208'N.175'2H'E

1355

slratified

6017-G-9

27'51'N. 117>1H'E

3300

dense white phosphorite from h l w k of I I I I C ~ O U S ~

basalt with phosphorite. phosphorite*

11.45

1974

2.R5

31.06

18 37

2.10

-

31.47

4907

135

160

~

Fez03

Mr.0

Na,O

iK ? O C 0 2 4.43

~

~

-

4.15

8.31

~

-

LO1

1R

320

6.92

0.41

3.44

182

6.72 1395

13.46

0 12

1.16

6.77

44.65

7.17

0.31

-

311

3.H9

1.35

14.53

0.32

-

-

0.10

1278

9.95

1.11

0.99

-

-

055

0.79

-

425

-

-

0.12

1.19

-

~

-

F

3.32

2.10

28.08

C,,,

1.40

4.87

~

~

phosphatic rock 32-17'N. 172'19'E

478-375

phosphatized coral lime-

2350

4922

26'59".

177"lR'E

2750

phosphatizrd hyaloelartite

26 10

41.44

1.20

20-35".

l79'5O'E

1650

phosphalized foraminifera1 limeslone

1 9 30

49.92

0.90

12'S4 N. 1 6 0 Q 4 4 ' W 3740-3620

mdusions of phosphatized limestone 8" luff breccia

29.12

46 4R

0.40

4.89

0.02

172

1.29

1 8 " 3 1 ' N . 175'06'W

1040-1060

phosphatized forammi feral limestone

31 60

48.72

0.60

-

0.005

0.25

0.39

0016

19 25

-

18'37'N. 171'59'E

2440

band or phorphatired lime in o m crust

30 30

1i.lfi

1.00

-

32'39'N. 160'52'E

1700-1900

dense phosphate part m hreceiform phosphorite

31.10

47.32

110

-

22'39'N. 160"S:'E

1700-1900

unconsolidated phosphatized limestone

31.60

49.2R

0.96

-

0.16

3.06

2.09

0.90

-

0.76

0.49

-

732

11.16 1.08

3.58

0.12

2.83

19.30

0.1s

-

030

350

0.18

32Q

7.12

5.30

0 15

4.90

U.25

JY7

8.38

0.13

-

0.79

1.19

0.35

4.75

0.19

389

8.42

0.33

0.75

0.6'

-

4 56

0.23

3.10

-

0.14

0.15

0.58

-

5.49

0.33

3.96

-

0.26

stone

' Phosphorites

.A

nuclei of iroi,-manganere concretions.

~

175

truncana cf. G. arca); and Eocene (Globorotalia aragonensis, Acarinina bullbrooki, A . pseudotopilensis, A . quetra, A . soldadoensis, Truncorotaloides topilensis, Glo borotalia centralis, G. cerroazulensis, Hantkenina spp.). The phosphorite of this region also contains abundant remains of coccolithopores and discoasters of Cretaceous and Paleogene age, and the phosphorite from Milwaukee Bank carries Neogene nannoplankton (Table 3-4; Figs. 3-7, 3-8). From the geologic data and results of potassium-argon dating of the rocks, the age of the basalts of the seamounts in the northern part of the Pacific Ocean ranges from Early Cretaceous (in the Marcus-Necker system) t o Oligocene (on Milwaukee Bank) (Matveyenkov and Marova, 1975; Heezen et al., 1973; Heezen and Fornari, 1976). Thus the accumulation of biogenic carbonate sediments on these seamounts began soon after they were formed. The youngest of the phosphate rocks on the seamounts of the Pacific Ocean apparently are the phosphatized limestones from the guyots in the Tasman Sea, in which Pliocene/Pleistocene foraminifera have been found Globigerina bulloides, Globigerinoides trilobis, Globorotalia inflata, Orbulina uniuersa (Slater and Goodwin, 1973). But the processes of formation of the limestones and metasomatic replacement of the calcium carbonate by phosphate apparently were separated in time, and the age gap sometimes was substantial. Moreover, phosphatization might have been initiated and broken off repeatedly. In the opinion of American investigators (Heezen et al., 1973) there were at least two stages of phosphatization on the Marcus-Necker Ridge: in Late Cretaceous time in shallow-water conditions (phosphatization of rudist limestones and bioclastic calcarenites), and in the Eocene in deep-sea conditions (phosphatization of the nannoplanktonic foraminiferal limestones). After the Eocene, phosphatization apparently was not resumed here, inasmuch as there are worm tracks in the Eocene phosphorites filled with calcareous ooze carrying a fauna of Quaternary foraminifera. Iron-manganese crusts are developed on the rocks, which also is an indication of the relative antiquity of the phosphorites. North of the Marcus-Necker Ridge, on the shallow Milwaukee Bank, and in the southern part of the Pacific Ocean on the guyots of the Tasman Sea, phosphatization of the calcareous rocks was much later, in Neogene/ Pleistocene or even at the beginning of Quaternary time. Radiochemical analysis of two samples of phosphatized limestone from Milwaukee Bank showed that their uranium, a constant companion of phosphorus in phosphorite formation, is not in equilibrium and contains an excess amount of the 234Uisotope. If it is assumed that the uranium came into these rocks from sea water at the same time as the phosphorus, then the age of the phosphatic material, calculated from the 234U/238U activity ratio, is 910,000+ 260,000 years

TABLE 3-4 CI

Coccolithophores in phosphorites from seamounts of the northwestern part of the Pacific Ocean (Baturin et al., 1977) Station

Coordinates and depth

Coccolithophores

Geologic age

6261

32O16‘N, 172O51’E 370 m

Cyclococcolithus cf. leptoporus (Murr. et Blakm.) Coccolithus pelagicus (Wallich) Discoaster cf. brouweri Tan

NeogenelQuaternary Neogene/Quatemary Neogene

6348

18’31’N, 175’06’W 1050 m

Cyclococcolithus cf. arabellus Roth Sphenolithus spp.

Paleogene/Quaternary Paleogene

6349

18030fN, 175’28’E 1050 m

Watznaueria cf. barnesae (Black) Cretarhabdus cf. crenulotus Bram. et Mart. Prediscosphaera spp.

Cretaceous Late Albian/Late Cretaceous

Watznaueria barnesae (Black) W. martelae (Noel) Cribrosphaerella ehrenbergi (Ark.) Gartnerago cf. zipperum Bukry Cretarhabdus cf. crenulatus Bram. et Mart. Zygodiscus cf. diplogrammus (Defl.)

Cretaceous

Watznaueria barnesae (Black) Bukry Cretarhabdus crenulatus crenulatus Bramlette et Martini, 1964 Chiastozygus aff. C. disgregatus Cribrosphaera aff. C. ehrenbergi Zygodiscus aff. Z. deflandrei

Turonian/Maastrichtian

6352

GDP-1-13*

18O19’N, 178’21’W 1630m

34O18’N, 143’50‘E 1420 m

* Data of Shiki et al. (1974).

Cretaceous

Late Albian/Late Cretaceous Late Cretaceous Cretaceous Cretaceous

TuroniadMaastrichtian Turonian/Maastrichtian Turonian/Maastrichtian Turonian/Maastrichtian

-3 Q,

177

Fig. 3-7. Nannoplankton in phosphorite from the Mid-Pacific Mountains; station 6352, 18’19‘N, 178’21’W (Baturin et al., 1977). (a) Watznaueria martelae (Noel), Early/Late Cretaceous, X 20,000. (b) Gartnemgo zipperum Bukry, Late Cretaceous, X 10,000.

(Baturin et al., 1974). It can be presumed that in the conditions of pelagic phosphorite formation, uranium “lags” behind phosphorus and that the age of the process of phosphatization is greater than follows from the activity ratio of the uranium isotopes. But in the old phosphorites on the is below the equilibrium ratio, shelves and on the seamounts, 234U/238U which indicates leaching of uranium after the end of phosphorite formation, rather than accumulation (Kolodny, 1969a). This fact shows that an excess of the 234Uisotope is typical only of “young” phosphorites. ATLANTIC OCEAN

Phosphorite and phosphate rocks have been found on seamounts in the Atlantic Ocean in three areas: near the Romanche fault, on the Aves Swell, and on the Jan Mayen Ridge. Near the northern boundary of the Romanche fault zone (00°24’N, 17’05‘W), fragments of phosphatized limestone with a manganese oxide

178

Fig. 3-8. Nannoplankton in phosphorite from Milwaukee Bank; station 6261, 32'16'N, 172O51'W (Baturin et al., 1977). (a) Cyclococcolithus cf. leptoporus (Murray et Blackman), NeogenefQuaternary, X 27,000. (b) Discoaster cf. brouweri Tan, Neogene, x 30,000.

crust were brought up from depths of 900-1000 and 1100-1200m (Bonatti et al., 1970, 1973). No detailed description was given for them. In the eastern part of the Caribbean Sea phosphorite was found on a guyot (13'30'N, 63OlO'W) on the Aves Swell, which consists of volcanic rocks. Phosphatized micritic limestones were brought up from a depth of 620730 and 550m, and phosphatized conglomerates from a depth of 340455 m (including the top of the guyot) (Marlowe, 1971). The phosphatized micritic limestones consist of dense and unconsolidated varieties, composed of fine-grained material with foraminifera tests and coccoliths. Rare worm tracks are filled with foraminiferal ooze. Pores and grains of carbonate material in the rock are encrusted with fibrous calcite. No minerals other than calcite and phosphate were found in the rock. The phosphate usually is crystalline; under the scanning microscope it has the form of tabular crystals of irregular shape, less often prisms. The phosphatized conglomerates consist of fragments of mollusk shells,

179 purple coralline algae, foraminifera, and pebbles of micritic limestone up to 3 cm in diameter, cemented by a micritic mass. The micritic cement is irregularly replaced by phosphate, which is intimately associated with brown iron hydroxides (probably goethite). As a rule the micritic limestone pebbles are not phosphatized. Dolomite is often encountered in the phosphatized parts, in the form of rhombohedra 0.05-0.2 mm in size. An iron-manganese crust is developed on the surface of the rock. The results of trawling and underwater photography show that the phosphorite conglomerates are overlain by non-phosphatized calcarenites, consisting of foraminifera tests and mollusk shells cemented by magnesian calcite. According to the data of chemical analyses, the phosphatized micritic limestones contain 24% P, 0 5 ,1.95%S O , , and 1.33%SO3. Atomic absorption analyses of these phosphorites showed that they are low in magnesium (0.3%), iron (0.7%),and manganese (0.057%) (Table 3-5). On the other hand, the phosphatized conglomerates are rich in magnesium (3.95%)and iron (16.4%),with a relatively low manganese content (0.34%).In the ore crusts coating the conglomerates, the iron content is 7.4%and the manganese content 10%. The age of the rocks of the seamounts is variable. Foraminifera of Oligocene/Miocene age have been found in the phosphatized micritic limestones

TABLE 3-5 Composition* (in %) of rocks from seamounts on the Aves Swell (Marlowe, 1971) Component

Micritic phosphorite

Conglomerate phosphorite

Calcarenite

Ca Mg Fe Mn A1 Si Sr Ti

31.2 fO.0 0.305 fO.0 0.71 20.20 0.057 fO.0 1.36 f0.02 1.16 f0.04 0.10 fO.00 0.00 fO.00 0.0027f0.0007 0.0229f0.0009 0.0022f0.0003 0.0099fO.0009 0.0038f0.0009

36.4 f0.4 3.95 fO.l 16.4 f0.02 0.339 fO.O1l 0.98 fO.OO1 1.04 kO.01 0.285 f0.0015 0.1 0.0125+0.001 0.0136f0.0024 0.0224f0.004 0.0268f0.0053 0.00

33.06 f2.3 3.07 f0.20 0.270f0.02 0.124f0.001

co Cr cu Ni

Pb

* From results of atomic absorption analysis.

Iron-manganese crust

32.6 fO.l 2.83 50.03 7.41 20.6 10.00 1.16 f0.08 1.04 fO.O1 0.58 f0.0015 0.053 f0.0058 < 0.1 0.0553f0.0058 0.0067f0.0017 0.0239f0.0086 0.155 f0.035 “0.0025

180

(Lepidocyclina spp.). Worm tracks and pores in this rock are filled with sediment carrying Pleistocene foraminifera. The foraminifer Globorotalia truncatulinoides is found in the phosphatized conglomerate; it is dated t o the Pleistocene and Early Holocene. The age of the calcarenites overlying the conglomerates, determined by radiocarbon, is 13,820k210 years. Judging from these data, the processes of sedimentation here went on in this order: deposition of fine-grained calcareous sediment in the Oligocene/Miocene; phosphatization of the sediment, growth of a reef, its breakup by wave action, formation of calcareous conglomerate, and possibly subsidence of the mount, in the Pleistocene/Early Holocene; phosphatization, dolomitization, and ferruginization of the cement of the conglomerate and growth of the ore crust on it; deposition of calcareous sediment and its cementation by magnesian calcite in the Holocene (Marlowe, 1971). Phosphatized mudstones and siltstones with tracks of pholads have been found on the Jan Mayen submarine ridge, which consists of alkaline basalts, trachyandesites, and trachytes (Kharin, 1974). The phosphatized mudstones are indistinctly stratified and contain 10-1596 sandy-silty material, mainly tabular and angular grains of plagioclase ( 5 0 4 0 % ) and angular and rounded grains of quartz (30-4096). Flakes of biotite (2-376) and muscovite (1-2%), isolated grains of monoclinic pyroxene, hornblende and zircon, and volcanic glass are encountered. Glauconitization of the biotite is reported. The phosphatized siltstones are similar t o the mudstones in composition but are less indurated and contain more sandy-silty material, consisting of angular and slightly rounded fragments of feldspar (60-70%), quartz (10- 15%), basalt (3-5%), volcanic glass (2-3%), and flakes of biotite and muscovite ( 4 4 % ) . Zircon and glauconite occur in the form of isolated grains. The cement of the rocks is argillaceous-phosphatic, with the inclusion of tiny phosphate globules. The refractive index of the phosphate is 1.602. Poorly preserved organic remains occasionally occur in the rocks - nuclei of foraminifera, ferruginized radiolarian tests, fragments of mollusk shells. The chemical composition of the phosphatized mudstone is as follows (in 96): Pz05 _

_

10.28

CaO _

SiOz

MgO ~

~

19.23 1.58

~

Ti02

A1203

Fez03

FeO

MnO NazO -t KzO

~

30.14 0 . 7 2

F

LO1 ~

17.8

4.62

1.33 0.17

5.52

1.16 8.46

The age of the rocks apparently is not older than Middle Miocene (Kharin, 1974). The phosphorite of the Jan Mayen Ridge is similar to shelf phosphor-

181 ites in composition and conditions of occurrence; probably its substantial depth is due either t o slumping of the sediments of the slope, or to subsidence of the ridge.

INDIAN OCEAN

Phosphorite is found on seamounts in the Indian Ocean in the area of the West Australian basin and on the Cocos Ridge. In particular, on the 54th cruise of the “Vityaz’ ”, phosphorite and fragments and blocks of limestone with lenticular intercalations of dense white and unconsolidated brownish phosphorite were obtained from an unnamed seamount (station 6754, 13’45’S, 99’56’E; depth 3689m). The P,05 content in the phosphorites ranges from 22.7 to 32.5%. The chemical composition of one of the samples is as follows (in 76):

27.8

45.35

1.40

4.66

2.29

1.39

3.55

2.58

The age of the coccoliths in the limestones of this seamount is Late Cretaceous, according t o identifications by V.V. Mukhina (Bezrukov, 1973; Bezrukov and Baturin, 1976). The samples from station 6754 are phosphatic breccias consisting either of reniform-incrusting phosphorite, or of sharp-angled phosphorite fragments of various sizes cemented by fine crystalline phosphate. In the cement and, to a lesser extent, in the fragments there are several generations of phosphate, indicating multistage formation of the breccias. In their texture they are similar to cementation breccias characteristic of phosphorites of the weathered crust (Bezrukov e t al., 1979).

ON THE ORIGIN OF THE PHOSPHORITE ON SEAMOUNTS

The wave-truncated tops of many seamounts and the presence of remains of a shallow-water fauna on them indicate that they are submerged islands. On islands now existing in the tropic zone of the Pacific, Indian, and Atlantic Oceans, there are phosphorites formed by metasomatic phosphatization of various rocks, mainly limestones, from deposits of guano that had accumulated on them in Miocene/Pleistocene time (Hutchinson, 1950; Trueman, 1965). It is possible that the phosphorites on some seamounts were formed

182

in an analogous way. It is significant that the presence of metasomatic phosphorite on Christmas Island in the Indian Ocean served as grounds for prospecting for phosphorite in the seamounts south of the island, where they actually were found (Bezrukov, 1973). The finding of phosphorite on a seamount in the Caribbean Sea (Marlowe, 1971) also reminds one of the deposits of guano present on Aves Island north of this mount (Hutchinson, 1950). But the presumption of such an origin for the phosphorites on other seamounts is not consistent with the data on submergence of the Marcus-Necker Ridge in Cretaceous time (Heezen et al., 1973), where guano could hardly have accumulated under subaerial conditions. Some investigators (Heezen et al., 1973; Marlowe, 1971) suggest that the phosphorite on seamounts was formed after their submergence, as a result of metasomatic replacement of carbonate by phosphate extracted from sea water. But if it is considered that the upper horizons of the ocean waters are poor in phosphorus and the deep waters rich in it, then the processes of phosphatization ought to have gone on more actively at greater depths than in shallow water. But that is not the case: on the Mid-Pacific Mountains (1000-4000 m) phosphatization of limestone ceased as early as Eocene, and at shallow depths (Milwaukee Bank, the Tasman Sea guyots) it evidently went on until Early Quaternary time. The hypothesis in question cannot explain what caused the extreme irregularity of phosphatization, which did not affect the many varieties of carbonate rocks of the same type and same age, both dense and unconsolidated, which occur along with the phosphate. It has been suggested that phosphorite formation was volcanogenic in nature, occurring as a result of activation of volcanic and hydrothermal activity (Kharin, 1974). That point of view has also been expressed concerning the ore crusts coating the phosphorite of the Mid-Pacific Mountains. Substantial unsystematic variations in the ratios of short-lived uranium and thorium isotopes are typical of these crusts, and this has been interpreted as evidence of their volcanic origin and geologic youth (Cherdyntsev et al., 1971). But in addition, there are numerous geological and geochemical data indicating the opposite, i.e. that volcanogenic material played an insignificant part in the formation of the ore crusts and that they are older (Strakhov et al., 1968). Therefore it must be acknowledged that there is no direct evidence for the volcanogenic nature of the concentration of phosphorus, iron, and manganese on seamounts. Thus in the present state of knowledge concerning phosphorite on seamounts, no preference can be given to any of the hypotheses enumerated; no one of them can be recognized as general. On the whole, the phosphorites of seamounts differ from those on shelves in their appearance, composition, and conditions of occurrence. They are

183 similar only to some varieties of phosphatized limestones with ferruginous cement that occur on Agulhas Bank, the Blake Plateau, and off the shores of New Zealand. It also remains unclear whether there is any similarity between the phosphatization of the limestones on seamounts and the processes of recent phosphorite formation on the shelves. Among the typical features o f the constitution and composition of the phosphorites of seamounts, which distinguish them from other oceanic phosphorites, are: the presence of sinter-like encrusting structures, the practically complete absence of clastic material and pyrite, the extreme rarity of glauconite, the low content of organic matter and uranium, the low strontium content, high fluorine content, and the unique composition of the rare earth elements. Therefore it seems to us that any hypothesis of the origin of phosphorite from seamounts should include an explanation of these features, which are unique t o them.

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Chapter 4 FACIES SETI’ING O F RECENT OCEANIC PHOSPHORITE FORMATION

The material discussed in the preceding chapter shows that definitely Recent phosphorite formation in the ocean is localized in narrow northsouth-oriented zones along the west coasts of South Africa and South America. To know the origin of Recent phosphorites it is necessary t o examine the facies setting existing in these zones, which is determined by a combination of meteorological, oceanographic, biologic, and geologic factors which have been investigated in sufficient detail by numerous oceanographic expeditions.

WINDS

The southeast Atlantic is in the region of the steady southeast trade wind. The direction of the south winds off the coast of southwest Africa is relatively constant (135-225’). The prevalence of south winds is SO%, of north winds 3%,and of west winds 1%.The wind velocity reaches 20 m/s, although for 70% of the time of observations it was between 1.5 and 1 m/s. The average velocity of the southeast trade wind for this region is 6.6+1.8 m/s. The wind system off the coast of southwest Africa is produced by the presence of a zone of high atmospheric pressure in the southeast Atlantic. The center of the anticyclone is between 26’ and 30’s. From the center the pressure gradient decreases gradually toward the north and abruptly toward the south. Anticyclones prevail around the high-pressure zone, which explains the prevalence of south and southeast winds on the southeastern periphery of the Atlantic. In the summer the anticyclone travels at a speed of 11-21 knots in the area of 30” S, in the winter its center shifts t o 26’s. The strongest winter winds (more than 16 knots) are observed in the area of 23’s (Fig. 4-1; Abramov, 1973; Komarov and Kuderskiy, 1962; Currie, 1953, 1966; Copenhagen, 1953, T.J. Hart and Currie, 1960; Jackson, 1951). In the southeastern part of the Pacific Ocean uniform steady trade winds of southerly direction prevail. The annual minimum of atmospheric pressure off the coast of Peru occurs in January to March, and in the zone of the Panama Canal in September-October. A drop in atmospheric pressure on the north corresponds to its increase on the south and vice versa (Schott, 1931,1951). According to meteorological observations made on the fourth cruise of the research vessel “Academician Kurchatov” (SeptemberNovember 1968),

186

I \ \

23'

2 5'

I

12"

1

I 14'

Fig. 4-1. Direction and velocity of wind off the coast of southwest Africa in October 1968 (Calvert and Price, 1971b). Wind velocity: 1 = 5 . 5 - 6 ; 2 = 6.5-7; 3 = 7.5-8; 4 = 8.5-9; 5 = 9.5-10; 6 = 10.5-11; 7 = 11.5-12m/s.

three north-south wind zones are distinguished in the area in question: an offshore breeze zone 30-40 miles wide, where the wind velocity does not exceed 6 m/s; 8 middle zone of open waters, 400-500 miles wide, where the winds blow with a velocity of 5-10 m/s; and an outer boundary zone where the velocity of the trade winds often exceeds 10 m/s (Fig. 4-2; Samoylenko, 1970).

187

Fig. 4-2. Direction and velocity of wind off the coast of Peru and Chile in SeptemberNovember 1968 on the course of the 4th cruise of the “Academician Kurchatov” (Samoylenko, 1970). Zones with wind velocities of: Z = up to 5 4 ; ZZ = up to 10;ZZZ = up to 13 m/s.

188 WAVES

Off the coast of southwest Africa, waves of wind-driven character prevail, with a force of 1-3 points (for 80% of the time of observation) t o 4 - 6 points (20% of the time of observation). The swell is weak and medium, from south to north (Komarov and Kuderskiy, 1962). For the Peru-Chile region a similar situation is typical. According to Schott (1931) a monotonous sea corresponds to the monotonous desert coastal belt here. Storms are not observed, at least not north of 18'S, but now and then strong surf begins when the trade winds are intensified.

CURRENTS AND WATER MASSES

In the southeast Atlantic (20-30°S), there are an oceanic and an offshore surface current separated by a line of divergence. The warm oceanic current runs westward, the cold offshore current toward the north-northwest (Fig. 4-3). Both currents are caused by the winds. The inshore Benguela current, distinguished by low temperature (13--15'C) and salinity of waters (34.95-35.20%, ),is traced for -1000 miles (from 34' t o 16--18OS), is 50-80 miles wide, does not extend beyond the shelf, and involves the upper layer of water 100 m thick. The current meanders and includes several anticyclonic circulations; in the spring the current is accelerated, in the autumn it weakens. The velocity of the Benguela current varies from 0.01 to 1knot (0.05-0.5 m/s), depending on the region and season. The origin of the water masses of the Benguela current on the whole has not been completely clarified. It consists of: central South Atlantic water, transformed intermediate Antarctic water, and the water of the Agulhas current which rounds the southern tip of Africa. In addition t o the cold surficial southern Benguela current, a warm northern bottom current of variable force, the Angola current, has been discovered off the coast of southwest Africa. The waters of this current penetrate southward to the mouth of the Orange River. Itsvelocity ranges from 3 to 2 8 cm/s. The zone of the most intensive interaction of the Benguela and Angola currents shifts within 16'30' and 20's. When the south winds slacken the Benguela current also slackens, and the Angola current intensifies and penetrates farther to the south. When the south winds intensify the opposite is observed. North of 16's the Angola current becomes predominant and the Benguela swerves t o the west and mixes with warm tropical ocean waters (Yelizarov, 1967; Komarov and Kuderskiy, 1962; Moroshkin e t al., 1970; Khovanskiy, 1962a; Clowes, 1954; Darbyshire, 1966; Defant, 1936; T.J. Hart and Currie, 1960; Schell, 1970).

-

189

Fig. 4-3. Dynamic scheme of currents off the coast of southwest Africa (T.J. Hart and Currie, 1960).

In the southeastern part of the Pacific Ocean the same system of surface currents is observed as in the southeast Atlantic. The oceanic branch of the Peru current flows northwest, the cold inshore Peru current travels northnorthwest along the coast (Fig. 4-4);its velocity is 0.2-0.37 knots (0.10.2 m/s). In addition, there also is the Peru-Chile deep countercurrent, running beneath the offshore current to the south and southeast. The inshore Peru current is traced for more than 2000 miles, from 40" to 5OS, where it swerves to the west-northwest toward the Galapagos Islands. In the zone influenced by the Peru current, three water structures differing in oceanographic characteristics are distinguished: the equatorial Pacific, the southern east-subtropical, and the Peru-Chile; in turn, the last includes

190

looo

90"

80"

70'

Fig. 4-4. Currents and temperature of the surface layer of water off the coast of Peru and Chile in the spring season (Schott, 1931).

the following water masses: surface (to 80 m), subantarctic subsurface (80200 m), subtropical subsurface (200-400 m), and antarctic intermediate (below 400 m). As in the southeast Atlantic, a direct relationship between the force of the winds of southerly bearing and the intensity of the southerly currents is observed in the southeastern part of the Pacific Ocean. In winter when the southeast trade wind is intensified the velocity of the Peru current off the

191 coast of Chile reaches 0.5-0.7 knots. In February and March, at the end of summer, the cold Peru current slackens and the temperature of the water off the coast north of 10"s rises by about 4°C (Burkov, 1971; Burkov et al., 1971; Gunther, 1936; Ryther et al., 1971; Schott, 1931; Wirtky, 1965).

UPWELLING

A typical feature of the zones of recent phosphoritization is the low temperature of inshore waters, related to the ascent of cold subsurface waters (upwelling). Present ideas concerning the mechanism of upwelling are based on the theory of Ekman (1905) on the interrelationship of winds and currents. According to this theory, in the southern hemisphere the surface drift current is deflected from the wind direction at an angle of 45' to the left, due to the force of the earth's rotation and forces of internal fluid friction. The angle of deflection increases with depth, and the force of the current decreases. Due t o wind drift, the interface between layers of a north-flowing current acquires a slope; its eastern edge rises, the western sinks. At the same time, transverse circulation to the west begins in the upper layer (Defant, 1936, 1952). In some inshore zones (in particular, off the coast of Peru), another intensive sporadic local upwelling is superposed on the quasipermanen t upwelling of climatic character; it is related to local wind conditions, and is manifested in the form of patches 5-15 miles in diameter, the hydrophysical evolution of which takes place in several days (Fedorov et al., 1975; Smith, 1971). The depth from which the ocean waters rise to the shelf usually is within 100-300m. Off the coast of Peru the salty and oxygen-poor waters of the Peru-Chile countercurrent take part in the process, and off the coast of Chile, the subantarctic subsurface waters arriving from a depth of 100-150 m (Burkov et al., 1971). The average depth from which the waters well up in the region of the Peru current is 133 m (Table 4-1). In the region of the Benguela current, upwelling occurs due to the central South Atlantic water mass. The depth from which the waters rise is not more than 200-300m, as is indicated by data on temperature and salinity: the upper layer of water (50 m) on the shelf corresponds in its main characteristics to the water layer from a depth of 200-250 m on the continental slope (Fig. 4-5). The width of the zone of upwelling in the region of the Peru current varies from 4 t o 30 miles. The belt of rising water either is close to the shore, or about 30 miles from it. At the same time the total width of the zone in-

192 TABLE 4-1 Depth from which upwelling occurs in the zone of the Peru current (Gunther, 1936) ~~~~

~

Length of zone along coast (miles)

Depth o f upwelling ( m ) min. salinity

min. temperature

max. salinity

max. temperature

Temperature o f upwelling water near shore ('C)

Area

360 196 160 130 100 180 160 100 200

200 100 150 140 280 100 160 110 200

16.83 16.50 17.38 16.00 15.73 16.61 13.79 16.57 13.93

C. Blanco (4O19'S) Punta Aguja (5O44'S) Lobos Is. (7'05's) Guaaape Is. (8'47's) Callao, August (12'29's) Callao, July (12'29'5) San Juan (15O5O'S) Arica (19O26'S) Antofagasta (23O12'S)

13.10 14.02 11.45

Caldera (27'06's) Pichidangul(32'00'S) C. Carranza (35'40's)

Subtropical water mass

110 204 128 110 155 103 152 53 47

40 126 120 130 100 40 160 80 188

40 60 80 80 80 40 90 50 90

Subantarctic water mass

56 129 83 Average

108 118 128

80 40 70

180 210 136

320 180 200

112

67

175

173

c 89

177I 133

fluenced by the upwelling cold water is much greater - u p to 100 miles (Gunther, 1936). Information on the relationships between intensity of upwelling and width of the shelf is contradictory. Off the coast of southwest Africa upwelling is weaker on the wide shelf near Walvis Bay (22'40's) than on the narrow shelf south of 25's (Khovanskiy, 1962b). Off the west coast of South America the water temperature also is lower off steep shelves than off gentle ones, according to Murphy's (1923, 1926) observations. However, according t o the data of German oceanographic expeditions, off the coast of Peru north of 13"supwelling is intensified as the shelf widens (Schott, 1931). A distinct seasonality is characteristic of upwelling in both the regions considered. In the spring and summer months (September to the beginning of February) upwelling is intensified, in the autumn and winter (February to April) it dies down (Khovanskiy, 1962a; Currie, 1953, 1966; Darbyshire, 1966; T.J. Hart and Currie, 1960).

193 Stations Sea miles

WS996

ws 997 1

W2998

w:999

W51000

WS1001

WS11002

I

Fig. 4-5. Temperature stratification of the waters of the shelf of southwest Africa on a cross-section along 26's (T.J. Hart and Currie, 1960).

In the summer off the coast of southwest Africa the centers of upwelling tend to be in the southern zone, and in the winter they shift northward due to the variable axes of the prevailing winds (Calvert and Price, 1971b). The rate of upwelling varies considerably, depending on the season and meteorological conditions. According t o McEwen (1929) it averages about 15 m/month, and according to other data, 3 0 - 6 0 mlmonth (Wooster and Reid, 1963). According to Burkov's (1971) calculations the maximum rate of upwelling in the southeastern part of the Pacific Ocean is 30 m/month. In several zones of the southeastern part of the Atlantic the rate of upwelling apparently is much greater (Bulatov et al., 1973). Upwelling is characterized by substantial inhomogeneity in space and time, but in a number of places it is observed virtually constantly. There are seven such places in the zone of the Benguela current. The most important of these are a t 16', 23-26', and 29-30's (T.J. Hart and Currie, 1960). In the zone of the Peru current four main places of upwelling are distinguished: at 25', 19-23', 1 7 O , and 5's (Schott, 1931). The absence of upwelling in the adjacent regions apparently is related t o the particulars of configuration of the shoreline: in the cases where the current is onshore, upwelling is not possible. Upwelling likewise does not occur if the angle between the direction of the current and the shoreline is too large, as surge phenomena are neutralized by a horizontal compensating

194

Fig. 4-6. Alternation of places of upwelling and downwellingof waters on theshelf of southwest Africa (Mratov, 1971). Legend: 1 = upwelling predominates all year; 2 = upwelling predominates during three seasons; 3 = downwelling predominates.

current (T.J. Hart and Currie, 1960; Schott, 1931). Places where water wells up alternate with places where it sinks (Fig. 4-6). The theoretical scheme of vertical circulation in zones of upwelling is represented as follows: on the bottom layer on the shelf the water arrives from the open ocean from depths of 100-300m and rises toward the surface, then it is carried in the opposite direction to the ocean and sinks down in the upper part of the continental slope. The boundary between the inshore and ocean water is a convection cell formed in the vertical circulation. This scheme is represented most graphically by a block diagram constructed from the data of the British expedition on the “Scoresby” (Fig. 4-7).

195

Fig. 4-7. Block diagram of horizontal and vertical circulation of waters off the shelf of southwest Africa (T.J. Hart and Currie, 1960).

The total area of the shelf zone in which upwelling occurs off the coast of southwest Africa is not more than 300,000 square miles. Off the coast of South America the corresponding area is from 24,000 (Wooster and Reid, 1963; Zuta and Guillen, 1970) t o 400,000 square miles (Cushing, 1969), according t o different estimates.

CLIMATE

A sharp contrast in climate on land and on the sea is characteristic of the inshore zone of the southeastern parts of the Atlantic and Pacific Oceans; it is explained by the contact of the continent heated by the sun and the cold inshore water, the temperature of which is 8-10°C lower than in the open ocean at the same latitudes. The amount of heat absorbed by the cold waters

196 from the lower layers of the air here is 30-40 kcal/cm2 yr (Samoylenko, 1970). Due to the influence of the Benguela current the mean annual temperature of the air a t Liideritz (26'5) is several degrees lower than at Capetown, 600 miles to the south, nearer to Antarctica. The mean monthly air temperature in the zone of the Benguela current is 18.7' in December, 17.1' in January, and 15.1'C in February (Komarov and Kuderskiy, 1962). At the same time, the sandy Namib desert, without rivers and devoid of vegetation, stretches along the coast of southwest Africa from the mouth of the Orange River (28's) t o the mouth of the Cunene (17's) (Copenhagen, 1953). A similar contrast is characteristic of the Peru-Chile region, where a substantial part of the coastal belt is occupied by the waterless Atacama desert and the shore is bathed by the cold Peru current. The moist winds reaching the shore from the open ocean d o not bring rain: when the warm moist air meets the cold inshore water the moisture condenses and hangs over the ocean in the form of fog, and the land remains in a "rain shadow". The following combination of weather conditions characterizes the coastal belt as a whole: the sun shines over the land, clouds hang over the cold inshore waters and coastal belt, and to the west is a zone of warm tropical waters (Samoylenko, 1970; Schott, 1931; Scherhag, 1937). The mean annual precipitation on the coast of southwest Africa (22-24's) is 15.2mm (US.Hydrographic Office, 1932), on the coast of Peru near Trujillo (8's) 3 5 m m , and a t Antofagasta (23's) less than 1 0 m m (Schott, 1931). HYDROCHEMISTRY OF THE WATERS

The hydrochemical composition of the waters off the coast of southwest Africa and Peru-Chile is characterized by substantial variability and variegation, which is explained by the complexity of the horizontal and vertical structure of the waters and by the diversity of water masses involved in the Benguela and Peru currents. O 2 and H 2 S . The oxygen content of the waters in the regions under consideration is related t o upwelling and the activity of phytoplankton. The cold waters arriving on the shelf are poor in oxygen, inasmuch as they come from the layer of the oxygen minimum. In the surface waters of the southeast Atlantic the oxygen content usually is 3-7 ml/l (47--124% saturation), with a minimum value of 0.33 ml/l. In the bottom waters in contact with sediments rich in organic matter the oxygen content often drops to zero and free hydrogen sulfide (up to 6.1ml/l) appears (T.J. Hart and Currie, 1960). In the waters of Walvis Bay methane also has been found (Scranton, 1977).

197 The concentration of O2 in the surface waters of the southeastern part of the Pacific Ocean is 5.1-5.5ml/l. For a water temperature of 16-20°C this corresponds t o 100--105% saturation by 0 2 ,In zones of upwelling the oxygen content is 4 ml/l, or as a function of temperature 38-70% saturated. In the layer of the oxygen minimum, which occurs a t depths of tens to 200-300m, the oxygen content drops to 0.1-0.2ml/l, and in individual cases the presence of hydrogen sulfide has been recorded (Bogoyavlenskiy and Shishkina, 1971; Vinogradov, 1975; Dugdale et al., 1977; Rowe, 1971). Active reaction (pH) and alkalinity. In the surface waters of the Benguela current the pH is -8, in the bottom waters 7.6-7.7, which is caused by the high content of carbon dioxide liberated in the decomposition of organic detritus. In the surface waters of the Peru current outside the zone of upwelling the pH is 7.9-8.2, and the partial pressure of C 0 2 is close to being in equilibrium with atmospheric (3 x atm). In the zones of upwelling the pH is 7.6-7.7 and the partial pressure of C 0 2 is three or four times greater than equilibrium. In the subsurface waters (75-120m) and in the layer of the oxygen minimum the pH is relatively stable at 7.7-7.8 (Bogoyavlenskiy and Shishkina, 1971). According to data obtained on the 3rd and 4th cruises of the research vessel “Academician Kurchatov” (1968) the alkali reserve in the zone of upwelling of the Benguela current (Walvis Bay area) varies between 2.33 and 2.41 mg-equiv/l. In the inshore surface waters of the Peru current it is 2.342.38 and in the bottom waters 2.34-2.44 mg-equiv/l. Phosphates. The distribution of phosphates in the southeast Atlantic is opposite to the distribution of oxygen: the maximum content is observed in waters poor in oxygen. In the surface layers of water in the open ocean the phosphate content ranges from 0 to 0.15pgll; in the surface waters of the shelf, arriving from depths of 200 m, it is 3 0 - 6 0 pg/1 (Fig. 4-8). In the Atlantic Ocean the minimum phosphorus content (to 90 pg/l) is typical of the Antarctic intermediate waters (Wattenberg, 1938). In some hydrological sections in the inshore zone, somewhat higher P concentrations - up to 108pg/l- are sometimes encountered, related to local accumulation of phosphorus in individual places due to decomposition of organic matter (Calvert and Price, 1971b; T.J. Hart and Currie, 1960; P.G.W. Jones, 1971). Off the coast of Peru and Chile in the zones of upwelling, two surface maximums of phosphate concentration, up to 60-75 pgP/l, are observed (Fig. 4-9). In vertical section of the inshore waters, the highest phosphate content (up to 80 pg/l) is typical of the bottom layers at depths of -100 m.

198

Fig. 4-8. Distribution of phosphates (in /.Ig-at/l) in the waters of the shelf of southwest Africa along a vertical cross-section at the latitude of Walvis Bay, 22'40's (T.J. Hart and Currie, 1960).

Beyond the shelf the minimum phosphate content in deep horizons was found in the waters of the Peru-Chile structure in the 500- to 600-m layer (less than 60pg/l) and the maximum in the waters of all structures in the 90- to 1100-m layer (up to 9Opg/l) (Bogoyavlenskiy and Shishkina, 1971; Walsh et al., 1971).

Nitrates. The nitrate content in the surface layer of inshore waters, like the phosphate content, depends substantially on upwelling. Off the coast of southwest Africa during active upwelling in October 1968 the nitrate content in the region of 25"s reached 20pg-at/l. A t the same time, in the zone of 22"S, where there was no upwelling, the nitrate content dropped to zero. In vertical section the maximum nitrate content (up to 27pg-at/l) also is observed in zones of upwelling near the shore in the bottom layer. In zones where there is no upwelling the concentration of nitrates in the bottom layer does not increase, but decreases (to 7pg-at/l), because the nitrates are partially reduced to nitrites (Calvert and Price, 1971b). In the southeastern part of the Pacific Ocean the maximum nitrate content in the upper water layers also is observed in zones of upwelling near the shore; in the subsurface water of the southern subtropical structure it reaches 20-30 pg-at/l. In vertical section the maximum concentration of nitrates (more than 40 pg-at/l) is observed within the southern subtropical structure at depths of 500-800 m (Bogoyavlenskiy and Shishkina, 1971).

Fig. 4-9. Distribution of phosphate (in pg-atll) in the surface waters off the coast ofPeruChile (Bogoyavlenskiy and Shishkina, 1971).

Nitrites. The nitrite content in the surface waters of the southeastern Atlantic ranges from <0.1 t o >0.4pg-at/l. In zones of upwelling two maximums of concentration are observed in vertical section, in the surface and bottom waters, separated by a layer with low nitrite content. In zones where there is no upwelling the surface layer is acutely impoverished in nitrites, but in the bottom layer, on the contrary, their content increases to the maximum value - more than 3 pg-at/l. The high nitrite content in the surface water is caused by the decay of nitrogen-containing organic detritus. The second nitrite maximum is also related t o reduction of nitrates, which is suggested by the inverse relation-

200 ship between these two components in the waters of the productive shelf (Calvert and Price, 1971b). In the southeastern part of the Pacific Ocean nitrites mostly occur in the surface waters only in the inshore zone. The maximum concentration of nitrites in surface waters was recorded a t 8's - 5 pg-at/l. In vertical section a second maximum of nitrite concentration (up to 8pg-atll) is observed in the subsurface waters. The formation of this second maximum is clearly recorded within the shelf, continental slope, and farther out to sea in the zone of the southern subtropical structure (Bogoyavlenskiy and Shishkina, 1971). Silica. In the southeastern Atlantic the content of silica dissolved in the surface waters ranges from 0 in the northern part of the inshore zone t o 20pg-at/l in the southern part. As in the case of other biogenic elements, such distribution is caused by the fact that silica in the surface waters is consumed by phytoplankton and is provided mainly by upwelling, which in the spring period is localized in the southern part of the region. The vertical distribution of silica is similar to the distribution of phosphates: the maximum concentration (more than 35 pg-at/l), which sometimes exceeds its content in the upwelling waters, is observed in the bottom layers, where intensive decomposition of organic detritus that has sunk from above takes place (Calvert and Price, 1971b). In the southeastern part of the Pacific Ocean the maximum content of silica in the surface layer (- 18pg-at/l) is noted in zones of upwelling in the immediate vicinity of the shore. In vertical section the silica concentration gradually increases beyond the shelf. In the subsurface (50-200 m) equatorial waters its content is -2Opg-at/l, and a t a depth of 600 m it reaches 60pg-at/l (Bogoyavlenskiy and Shishkina, 1971). Organic carbon. The content of dissolved organic carbon in the waters near the coast of southwest Africa is relatively constant and ranges between 0.65 and 1.3mgll. The content of suspended organic carbon varies much more widely - from 0.068 to 0.864 mg/l. No correlation is observed between the content of suspended and dissolved organic carbon. The predominant components in the suspended matter are phytoplankton (22-5396, rarely up to 70--90%) and detritus (30-63%), zooplankton constituting from 5 to 25% of Corg (Hobson, 1971). In the southeastern part of the Pacific Ocean the content of dissolved organic carbon in the 0- to 50-m layer near the coast of Peru ranges from 6 1 to 208mg/m2. The content of suspended Corg in the same layer ranges from 50 to 5OOpgll. Below, in the 50- to 150-m horizon, the content of

201 suspended Corg is relatively constant and usually is 25-50pg/l

(Ryther et

al., 1971).

The content of suspended hydrocarbons in the surface layer, like that of Corg, is maximal in zones of upwelling - up to 109.4 pg/l, averaging 50.5 pg/l. From the shelf toward the open ocean the content of suspended hydrocarbons decreases to 7.7 pg/l, on the average, a t the surface and t o 0.4 pg/l in the deep layers (Romankevich and Urbanovich, 1971). PRIMARY PRODUCTIVITY

Primary productivity of organic matter by phytoplankton is the basis of the biological productivity of the whole water mass from top to bottom. The factor which limits the primary productivity of the surface layer is the content of biogenic elements - phosphorus, nitrogen, and silicon. A high content of these elements in zones of upwelling is the reason why the magnitude of primary productivity off the west coasts of South Africa and South America is the highest in the World Ocean. According to the first measurements, the highest primary productivity in the Atlantic is observed in Walvis Bay on the coast of southwest Africa 3.8 g C/mZ day (Nielsen and Jensen, 1957). According t o the data of Soviet expeditions, primary productivity in the inshore surface waters of the southeastern Atlantic reaches 375-620 mg C/m3 day (Volkovinskiy et al., 1970; Koblents-Mishke e t al., 1970,1973). In the southeastern part of the Pacific Ocean the maximum productivity is characteristic of a 200-mile strip off the coast of Peru and Ecuador, and also of a 100-mile strip off the coast of Chile north of 22"s: from 25 t o 870 mg C/m3 day (averaging l o o ) , or 0.43-6.81 g C/mZ day (Vedernikov and Starodubtsev, 1971). In connection with the fact that the magnitude of primary productivity depends on the content of biogenic elements in the water, especially of phosphates, it fluctuates considerably from season to season. As an example, according t o the data of various expeditions, primary productivity in the region of 4-5"s off the coast of Peru varies within 0.470.75 g C/mZ day (Vedernikov and Starodubtsev, 1971), 1.02 g C/m2 day (Holmes e t al., 1957), 4.60-11.21 gC/m2 day (Ryther et al., 1971). On the average, primary productivity in the zones of upwelling off the coasts of Peru and Chile is 2-5 g C/m2 day (Guillen, 1971; Ryther, 1970). BIOTA

The marine biota, i.e. all living organisms collectively, includes plankton, which floats passively; nekton, which swims freely; and the benthos, the

202 bottom organisms. Marine bacteria, which occur both in the water layer and in the bottom sediments, represent a special group of organisms. Phytoplankton predominates (usually 50--100%) in the make-up of total plankton in the zone of the Benguela current both in the spring and in the autumn seasons. Diatoms dominate the composition of phytoplankton (30-99% of the total number of cells). Near the shores, species of the genus Chaetoceros predominate; the species Planctoniella sol is characteristic of the open ocean zone, and the species Thalassiosira subtilis occurs frequently in the transition zone. Next t o diatoms comes Peridinium (0-84%, usually up t o 10-4076) (T.J. Hart and Currie, 1960). The biomass of phytoplankton is maximal in zones of upwelling, where it reaches 2-3mg/l per wet weight, or up t o 0.77 mg/l recalculated to Corg (Khovanskiy, 1962a; Hobson, 1971). The concentration of phytoplankton in the zone of t h e Benguela current is 10,000 times greater on the average than in the open ocean; in net hauls at inshore stations it exceeds 100 million cells/m3 (Fig. 4-10). The volume of diatom cells varies from 1000 to 100,000pm3, of Peridinium from 10,000 to 100,000pm3 (Chyong, 1971; T.J. Hart and Currie, 1960). Diatoms also are dominant in the phytoplankton of the offshore zones of Peru and Chile; peridinia are rarer. The maximum amount of phytoplankton (up t o 1 9 5 million cells/m3 ) was found at shallow-water stations off the coast of Peru a t 9"s (Fig. 4-11). The amount of phytoplankton in this zone is 10,000 times greater, on the average, than on the equator in the region of 154'W (Semina, 1971). Zooplankton. Ciliates and copepods predominate in the composition of zooplankton in the inshore waters of southwest Africa. Most of the other representatives of zooplankton are appendicularia, foraminifera, pteropods, euphausiids, ostracodes, polychaete and mollusk larvae, and fish roe (T.J. Hart and Currie, 1960; Hobson, 1971; Iles, 1953; N.S. Jones, 1955; Morton, 1954). Suspended organic matter includes fish scales and fecal lumps, which also are counted as plankton (T.J. Hart and Currie, 1960). The distribution of zooplankton does not coincide with that of phytoplankton. In zones of upwelling the biomass of zooplankton is minimal (<0.5 mg/l per wet weight), in zones of downwelling, in the subsurface and bottom layers, it is maximal, u p to 1-3 mg/l (Komarov and Kuderskiy, 1962; Khovanskiy, 1962a), o r up to 58 pg C/1 recalculated to organic carbon (Hobson, 1971). In the waters of the southeastern part of the Pacific Ocean, according to the results of net hauls, the total deposition of plankton ranges from <0.1 cm3 /m3 in the open ocean to >1cm3 /m3 in the inshore zone (Semina,

203

Fig. 4-10. Distribution of cells of phytoplankton in net hauls on the shelf of southwest Africa (T.J. Hart and Currie, 1960). Number of cells: 1 = lo4 to lo5 ; 2 = l o 5 to l o 6 ; 3 = lo6 to 107;4= lo7 to 108;5=>108.

1971). The average content of zooplankton in the waters off the coast of Peru is 15-18cm3 /m2 (Walsh et al., 1971). fchthyofuuna. Due t o the extremely high biologic productivity and biomass of phyto- and zooplankton, the waters off the coasts of southwest Africa and Peru-Chile are characterized by maximal productivity of fish in the ocean; for the main species alone it amounts to 6-8 to 50 t/km2 yr (Marti and Martinsen, 1966; Marti and Parin, 1973). As a whole the zones of upwelling occupy only 0.1% of the area of the ocean, but they yield about half the world’s fish catch - up t o 10 million tons per year (Ryther, 1970; Ryther et al., 1971).

204

GO\ I

3

30

80

Fig. 4-11. Distribution of phytoplankton in the surface waters off the coast of Peru and Chile (Semina, 1971). Number of cells in 1 m3 : 1 = not detected; 2 = lO,OOO.

The main species of fish off the coast of southwest Africa are sardines, which feed mainly on phytoplankton (diatoms), horse mackerel, which feed on large zooplankton, and hake (Komarov, 1962; Komarov and Kuderskiy, 1962). In the inshore waters of Peru and Chile the Peruvian anchovy, which feeds mainly on diatoms and occurs in a 50-mile-wide zone along the coast

205 from 4'30' to 37'04'S, is the predominant species (R.S. Jordan, 1971; Mendiola, 1966).

Mammals. Of the mammals, mainly seals occur in the zone of the Benguela and Peru currents (Arctocephaluspusillus). On the coast of southwest Africa seal rookeries occur from Cape Cross on the north (21'40's) to Angoa Bay on the south, and also on rocky offshore islands (Rand, 1956). Sometimes whales appear in the waters of the Benguela current - blue, finback, sei, sperm (Townsend, 1925). These same species of whales, and also seals and dolphins, are encountered in the waters of the Peru current (Gunther, 1936). Birds. A vast number of fish-eating birds are present in the regions of the Benguela and Peru currents, dotting all the offshore rocks and islands. Off the coast of southwest Africa gannets, penguins, and divers predominate, off the coast of Peru and Chile, cormorants and pelicans (Coker, 1919; T.J. Hart and Currie, 1960; Murphy, 1926). In both regions guano accumulates; one bird excretes 30-120 g of it every day. On the coast of southwest Africa guano deposits occur between 22's and the Cape of Good Hope, and on islands farther north, to 12'33's; the total amount of guano deposited here every year is 20,000 tons or 440 tons of phosphorus, which is equal to its amount in 5.5 km3 of sea water (Hutchinson, 1950; T.J. Hart and Currie, 1960). In the Peru-Chile region guano deposits occur on 147 islands and a t 21 points on shore. On Chincha Island (13"39'S, 76'24'W) a layer of guano 8 c m thick is deposited annually; the total reserves of guano on this island (already exhausted) were 11 million tons (Hutchinson, 1950). Benthos. In the shelf belt washed by the Benguela current, between 18 and 24's and at depths of 50--130m, the benthic macrofauna is impoverished or absent, in connection with hydrogen sulfide contamination of the sediments. The total area of this belt is -6000 square miles. Outside of it, in the upper layer of sediments, there are annelids, benthic foraminifera, crustacea, holothurians, and mollusks (Copenhagen, 1934, 1953). In the diatomaceous oozes rich in organic matter there are developed sulfate-reducing bacteria, the concentration of which amounts t o several hundred, and when resifted, t o 10 million per gram of ooze (Butlin, 1949). The total number of micro-organisms in these oozes (including cocci, which constitute 92-96%) reaches 200 million per gram (Novozhilova and Baturin, 1973). The commonest species of the benthos on the shelves of Peru and Chile are polychaetes and ophiurans. On the continental slope large crabs, hermit

206 crabs, leather urchins, and mollusks also occur (Zenkevich and Filatova, 1971). The biomass of the benthos in the Peru region (14”30‘-16”S) varies from 2000mg/m2 near the shore to 8mg/m2 a t a depth of 300m, then increases to 5000 mg/m2 at a depth of 1000 m and again drops to 4 1 mg/m2 at a depth of 5700m, corresponding t o the distribution of oxygen in the bottom waters (Rowe, 1971) and in inverse relationship t o the distribution of organic matter in the sediments (Romankevich and Urbanovich, 1971). MASS MORTALITY OF FAUNA

The system of winds and currents characteristic of the regions under consideration is disrupted from time t o time in connection with sporadic shifts of the meteorological equator which occur in December-January. In such cases a zone of low atmospheric pressure arises in the northern part of each of these regions and the usual south and southeast winds change t o north and northwest, due t o which the warm equatorial waters penetrate far t o the south (Copenhagen, 1953; Schweigger, 1949). Disruption of the usual system of horizontal circulation of the waters leads t o the disruption of the vertical circulation also, t o slackening or complete cessation of upwelling on the shelf and the production of stagnation phenomena. Oxygen disappears from the bottom waters, being used up in oxidation of organic matter, and hydrogen sulfide appears instead, produced by bacteria in the sediments rich in organic matter. As a result, all fish die in the zone contaminated by hydrogen sulfide. Disruption of water circulation often is accompanied by mass proliferation and then dying off of some species of plankton, in particular the dinoflagellates Gymnodinium, Gonyaulax, and Glenodinium, the ciliate Mesodinium, etc. (Brongersma-Sanders, 1957), the amount of which may reach 60-100 million cells per liter (Copenhagen, 1953; Barada, 1971). At the time of the voyage of the Danish ship “Galatea”, on 2 5 December 1950 in Walvis Bay (southwest Africa) the upper layer of water ( t o 1m) was like a brownish slurry due to the enormous amount of the dinoflagellate Glenodinium (Copenhagen, 1953). When such large masses of plankton decompose, the surface waters are covered with a slimy foam over a substantial area, which also has a fatal effect on the ichthyofauna (T.J. Hart and Currie, 1960). Off the shore of southwest Africa (21-25’s) and Peru hydrogen sulfide contamination and discoloration of the water are observed in both of these areas. Off the coast of Chile only discoloration of the waters is observed, without hydrogen sulfide. Mass mortality of fauna caused by these phenomena on the shelves of the regions under consideration was recorded tens of times in the last 150 years (the so-called “red tides”).

207 At the time of mass mortality not only fish perished, but also other organisms - holothurians, birds, and mammals. Some of the dead organisms sink to the bottom, some float and are cast ashore, forming festoons and banks stretching for tens of miles (BrongersmaSanders, 1957; Copenhagen, 1953). SEDIMENTS

Zones of recent phosphorite formation are characterized by a combination of biogenic (siliceous and calcareous), clastic, and in part glauconitic sediments with a relatively persistent distribution in a north-south direction (along the shore) and sharp facies transitions in an east-west direction. Recent phosphate formation proper (formation of phosphate concretions) is localized chiefly in siliceous and slightly siliceous diatomaceous and clasticdiatomaceous sediments.

Shelf of southwest Africa On the shelf of southwest Africa diatomaceous oozes with Holocene phosphate concretions occur in a belt on the order of 20 miles wide (from 18’ to 24”s) at depths of 4 0 - 6 0 to 120-140 m; the thickness of the oozes is up to 10m. Toward the shore they are succeeded by clastic sands, toward the ocean by calcareous and clastic silty-pelitic oozes and foraminiferal sands (Fig. 4-12, see also Fig. 2-12). E

W

station 150

2042

2043

2044

2045,153 2046

152

Fig. 4-12. Facies profile of the shelf of southwest Africa along 23OS (from data of the 3rd cruise of the R.V. “Academician Kurchatov” and 26th cruise of the R.V. “Mikhail Lomonosov”. 1 = clastic sands and silts; 2 = diatomaceous oozes; 3 = foraminiferal sediments; 4 = shell sand; 5 = Holocene phosphorite concretions; 6 = pre-Holocene, including Quaternary, phosphorite concretions; 7 = erosional surface. Thickness of sediments is not to scale.

208 TABLE 4-2 Composition (%) of sandy-silty fractions of diatomaceous oozes (Yemel’yanov, 1973a) Fraction (mm)

Content of fraction (%)

Carbonates

Diatoms

Fish bones, scales

Organics

Phosphate

Clastic and volcanogenic components

Station 151, pelitic ooze

2 -0.5 0.5 -0.25 0.25-0.1 0.1 -0.05 0.05-0.01

0.2 0.7 1 .o 4.2 9.19

27.O 10.5 0.3 8.7 -

-

3.0 98.0 88.6 100

-

61.0 3.6

8.8 0.1 4.4 isol.*

-

Station 157, silty-pelitic o o z e

2 -0.5 0.5 0.5 -0.25 2.9 0.25-0.1 34.0 0.1 -0.05 6.2 0.05-0.01 13.8

2.4 14.4 -

0.5 0.3

-

40.7 93.0 94.O 50.0

80.9 7.8 isol.*

5.0

-

-

-

71.7 12.6

-

16.0 29.6 0.3

0.7 7.5 1.2 5.5 47.0

21.0 65.8 0.8

6.7 6.3 1.0 3.5 4.0

-

Station 152, silty-pelitic ooze

2 -0.5 0.5 -0.25 0.25-0.1 0.1 -0.05 0.05-0.01

0.51 0.77 7.14 12.76 14.54

0.6 2.2

-

2.2

-

-

13.1 4.2 96.4 96.0

-

-

-

94.0 -

-

-

Station 158, silly-pelitic o o z e

2 -0.5 0.5 -0.25 0.25-0.1 0.1 -0.05 0.05-0.01

1.79 0.36 8.92 18.93 11.79

0.8 3.7 id.*

-

-

0.8 77.3 90.0 98.5 86.2

49.0 6.4 isol.*

-

-

5.0

-

49.4 10.3 isoI.* isol.*

-

-

2.3 5.0 1.5 13.8

* Isolated grains. In natural form the diatomaceous oozes are dark green in color, semiliquid in consistency (moisture content 80-92%), and often contain hydrogen sulfide, with an Eh of about -200mV and pH of 7.3-7.6 in the surface layer (Baturin, 1972). As the first investigators had already established, the main components of the diataomaceous oozes are diatom valves and organic matter (Marchand, 1928, Copenhagen, 1934, 1953). Representatives of the genera Chaetoceros, Hercotheca, and Thalassionema are dominant among the diatoms; the number of diatoms per gram of sediment reaches several hundred million cells (Mukhina, 1974). The diatoms are chiefly large forms which belong to the

209 fine-sandy and silty fractions in size; the pelitic fraction consists mainly of diatom detritus, to a lesser extent of clay minerals (up t o 10-1576). Phosphate concretions, fish bones, foraminifera*, and less often embryonic gastropod shells are concentrated in the coarse-sandy fraction (Yemel’yanov, 1973b; Senin, 1971). Particles of free sulfur also are found in the diatomaceous oozes of Walvis Bay (Boukgue, 1974). Clastic material is present in insignificant amounts in all the sandy-silty fractions (Table 4-2). In the light subfraction of coarse silt, quartz and plagioclases have been identified (up to 3%).In the heavy subfraction biotite predominates (35-9276) ; monoclinic pyroxenes (4-1 5%), ilmenite and magnetite (1-25%), green hornblende (2-lo%), epidote-zoisite and isolated grains of garnet, rutile-brookite-anatase, zircon, apatite, glauconite, staurolite, sphene, tourmaline, calcite, sulfides, limonite-goethite are present (Yemel’yanov and Baturin, 1974; Soldatov et al., 1976). In the pelitic fraction illite (60-70%), montmorillonite (up t o 20%), kaolinite and chlorite (
* The total amount of planktonic and benthic foraminifera in the diatomaceous oozes reaches 1000-1300 specimens/g (Basov and Belyayeva, 1974).

210 TABLE 4-3 Chemical composition (76) of sediments of the shelf of southwest Africa* Component

Diatomaceous ooze


61.9 -88.1

9.7 -49.0

sio2 amorph sio2 total

31.62-85.0

0.12- 0.54 4.06-40.74 38.52-7 8.71 2.66- 4.71 0.25-1 5.00 0.63-10.04 0.81- 5.63 tr. - 0.02 0.02- 0.41

CaC03 Corg p2 0 5 A12 0 3

Fe2 0 3 total MnO Ti02

Shell and foraminiferal sediments

-

2.57- 8.50 3.66-20.0 0.21- 3.82 0.61- 9.64 1.08- 4.52 tr. - 0.02 tr. - 0.73

Clastic sediments

6.4 -50.4 1.0564.60 3.00-1 1.300.27-2 9.79 1.210.010.20-

9.68 6.58 8.80 3.06 4.66 0.20 1.04

* According to Baturin, 1969, 1972; Yemel’yanov, 1973a;Senin, 1970, 1971;Calvert and Price, 1970,1971a.

Among the geochemical particulars of these diatomaceous oozes is their enrichment in rare and disseminated elements, with the following maximum concentrations (in %): Ni

Zn

cu

Mo

V

co

La

Y

U

0.0455

0.0337

0.0129

0.050

0.036

0.001

0.003

0.001

0.006

Like disseminated phosphorus, the uranium, molybdenum, nickel, zinc, and copper are mainly fixed in organic matter (Baturin, 1972, 1975b; Baturin et al., 1970, 1971; Yemel’yanov, 1973b; Yemel’yanov and Senin, 1969; Calvert and Price, 1970,1971a). In cores of diatomaceous oozes (up to 2.6 m long), up to three layers can be distinguished, in each of which the granulometric composition of the sediments becomes coarser from the top to the bottom while the CaC03 content increases and the C, content decreases. Apparently such cyclic variation in granulometric, mineralogic, and chemical composition of the sediments indicates periodic changes in the facies environment, related to sea-level fluctuations in Late Quaternary time (Yemel’yanov and Baturin, 1974). The calcareous sediments adjacent to the zone of diatomaceous oozes consist of shell and foraminiferal sands, less often of coarse silts, occurring on the outer shelf and upper part of the continental slope. Their main components are biogenic carbonates (up to 75%), grains of clastic minerals (mainly

211

Fig. 4-13. Distribution of Corg in the sediments on the shelf of southwest Africa in the region of Walvis Bay (Calvert and Price, 1971a): 1 = < 5; 2 = 5-10; 3 = 10-15; 4 = 15-20; 5 = 20%.

>

quartz - up to 40%), and pelitic material (10-2096). Locally they are rich in coprolites and phosphate grains, mainly redeposited, due to which the total P, O5 content sometimes increases to 5-1596. The clastic sands and silts consist of grains of quartz, feldspars, lithic fragments, and organogenic detritus; the composition of the accessory minerals

212 is mainly the same as in the coarse silt fraction of the diatomaceous oozes. When the sands are rich in redeposited grains of phosphate or glauconite they become phosphatic or glauconitic (see Chapter 2). Submerged margin of Peru and Chile

Sediments of the following types occur on the submerged margin of Peru and Chile: (1)Clastic sands and silty pelites with an admixture of coarse clastic material in the inshore zone at depths t o 15 m. (2) Coarse and inequigranular shell sands (at depths up t o 40 m) consisting of shells and shell detritus of pelecypods and gastropods, to a lesser extent of benthic foraminifera and clastic material. In isolated cases the sands contain impurities of clay material and diatom valves and are rich in organic matter, which brings about the appearance of hydrogen sulfide in them. (3) Terrigenous-diatomaceous oozes and sands of the shelf and upper part of the continental slope occur a t depths of 50 t o 4 0 0 m and contain up to 16% S i 0 2amorph and 10% Corg. Sediments of this type are reduced (Eh to -1 95 mV), contain hydrogen sulfide, iron sulfides, and concretions, grains, and nodules of phosphorite. (4) Foraminifera1 sands and silty pelites of the lower part of the shelf and upper part of the continental shelf at depths of 250-590 m. These sediments consist of foraminifer tests with an admixture of clastic material, diatom valves and fish bones. Their Corgcontent is from 1-2% in the sands t o 6% in the silty pelites. The sediments are reduced, contain hydrogen sulfide, iron sulfides, and phosphate grains. (5) Clastic-glauconitic and glauconitic (up t o 75-9096 glauconite) sands and silts of the upper part of the continental slope at depths of 500-1800 m, with positive Eh values (120-400 mV), containing 2-396 Corg.Iron hydroxides and sometimes also sulfides are present in the sediments. The glauconite grains often are coated with collophane or bonded by phosphate cement. (6) Clastic, slightly siliceous diatomaceous-radiolarian oozes of the continental slope and bottom of the deep-sea trench a t depths of 1200-7320m contain up t o 12% SiOzamor& and 2-396 Corg; usually they have positive Eh values (Logvinenko and Romankevich, 1973; Murdmaa et al., 1976; Saidova, 1971; Burnett, 1974). On a transverse facies profile the phosphate-bearing terrigenous-diatomaceous sediments are situated between the clastic deposits of the upper part of the shelf and the clastic-glauconitic or calcareous deposits of the upper part of the continental slope (Fig. 4-14). As on the shelf of southwest Africa, enrichment of the sediments in organic matter is observed in the inshore zone (Fig. 4-15), in the terrigenous-diato-

213

- 200 t

2 5 km

-I

-300

7

-400

8 -500 rn

Fig. 4-14. Schematic facies profile of the Peru shelf (from data of the 4th cruise of the R.V. “Academician Kurchatov” and 8th cruise of the R.V. “Dmitriy Mendeleyev”): 1 = clastic sands; 2 = clastic silts; 3 = clastic-diatomaceous oozes; 4 = foraminifera1 sediments; 5 = Upper Quaternary phosphorite concretions; 6 = pre-Quaternary phosphorite concretions; 7 = glauconite; 8 = erosion surface. Thickness of sediments not to scale.

maceous and also in the calcareous sediments. But the zones of high contents of organic matter and phosphorus are offset with respect to one another (Gershanovich and Konyukhov, 1975). All three types of sediments contain fragmental (volcaniclastic), biogenic, and authigenic components. The content of clastic components in the sandy-silty fractions of the sediments is from 2 t o 56% (Table 4-4).Quartz, feldspars, fragments of volcanic glass, biotite, muscovite, chlorite, and hornblende predominate in their composition. Quartz occurs in the form of slightly rounded grains in the sand fraction and angular grains in the silt. Feldspars consist of angular and slightly rounded grains, mainly of acid plagioclase, usually weathered. Alkali feldspars - orthoclase, less often microcline - and also andesine are present in small amount. The volcanic glass has the composition of andesite-dacite and usually is represented by angular fragments, less often by drop-like particles with flow structure, sometimes with colorless inclusions of quartz and feldspar. South of 22”s glass of andesite-basalt composition also occurs. The glass fragments usually are fresh and unaltered. As a rule the micas (mainly biotite) are

214

Fig. 4-15.Distribution of Corg in sediments of the Peru-Chile region (Logvinenko and Romankevich, 1973): I = <0.5; 2 = 0.5-1; 3 = 1-2; 4 = 2-5; 5 = >5%. 6 = stations.

hydrated and glauconitized. The hornblende is the common green variety, less often the brown one, in the form of prismatic crystals and elongated slivers. The accessory minerals (0.1--0.2%of the total) are epidote, apatite, zircon, tourmaline, rutile, garnet, sphene, staurolite, magnetite, ilmenite, and monoclinic and orthorhornbic pyroxene. Lithic fragments, present in small amounts in the sand fraction of coarse-grained sediments, are represented by sandstone, siltstone, chert, and granitoids.

TABLE 4-4 Composition (%) of sandy-silty fractions of sediments on the submerged margin of Peru and Chile (Logvinenko and Romankevich, 1973) Component

Type of sediment shell

foraminiferd O-lO0S

elastic-diatomaceous, shelf

elastic-glauconitic

elastic-diatomaceous, slope

O-lO0S

10-30'5

O-lOoS

10-30°S

0-10's

10-30's

8 5 <0.2 <0.2 <0.2

10 2 <0.2 <0.2 <0.2

11-56* 5-23 <0.2 <0.2 <0.2

2-8 5-1 1 <0.2 <0.2 <0.2

2-lo* 12-45 1-7 0.3-2 <5

10-45 2-44 <10 <2 0-0.5

11-14* 28-46 1-7 <2 <4

83 <0.2 <0.2

<0.2 <0.2 5-59 <0.2 0-7 <2

0-5 1 1-57 <3 <0.2 <7

-

-

<0.2

<0.2 54 1 <0.2 <0.2 <0.2

18 3 <0.2 <0.2

1-6 0.3-1.8 <1 <0.2

7-5 1 1-19 <0.2 0-2

9-4 1 4-5 <2 <0.2

<0.2

-

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

0-10's

Quartz Feldspars Volcanic glass Hornblende Biotite, chlorite Pelecypods, gastropods Foraminifera Diatoms Radiolaria Sponge spicules Bones Spores and pollen Authigenic minerals

-

3

Eolian quartz. *** Glauconite predominates.

32

4-22

-

20-29

15 5 1

<0.2 <0.2 -

59**

-

16-78**

2-23

3-17

TABLE 4-5 Authigenic minerals ( % ) in the sand-silt fractions* o f sediments on the submerged margin of Peru and Chile (Logvinenko et al., 19'7.7) Station

Depth

No.

(m)

298

tin

285

60

272

1OG

250

150

285

200

273

200

274 289

500 590

252 253 276

650 1015 1620

* Fractions:

Type of sediment

silty clasticdiatomaceous o o z c pelitic cl-sticdiatomaceous 007t' pelitic clasticdiatomaceous o o l e fine clastic sand with foraminifera silty-pelitic ooze with diatoms and foraminifera pelitic clasticdiatomaceous ooze coarse glauconite sand silty-pelitic foraminifci II ooze glauconite sand glauconite sand elauconite sand

Iron sulfides

Phosphates

Glauconite

<1

5

10

-

-

<1

<1

3

10

-

15

10

<

1

1


!

1

1 < 1

<1

-

_

1 <1

-

5

-

15

17

-

first column of figures - >0.1 mm;second - 0.1-0.05

6

-

20

-

27 1

-

82

19

-

<1 95 '75 95

-

_

-

40

- < I - - <1 <1 <1 <1 <1 - <1 1 - <1 1 2 - - < I- - -

-

_

-

40

30 3

_

4

-

1

1

_

Iron hydroxides

Clay mineral aggregates

Organic remains


Clastic and pyroclastic material

20 30

56

15

45 5 2 56

20

10 1 2

8

45 48

85

14

5


-

86

9

20

-

-


-

8 10 A 17 20 10

m r r , third - 0.05-0.01 mm.

59

20 6 0 64

5

5

100 7 5

16

1 3 90 60

84 5 3 53
<1

9 9 8 0 10 <1 8 18 < 1 1'7 8 3 15 <1

<1

-

15 1 9 7 0 85

17 2 65 65 <1 7 5


25 50 52 70

217 On the basis of the composition of the clastic components, a northern (0--10”s) and a southern (10-32’s) clastic-mineralogic province are distinguished in the region in question. Quartz predominates among the clastic minerals in the sediments of the northern province, weathered feldspars in the southern (Logvinenko and Romankevich, 1973). Biogenic components of the sediments include calcareous shells and shell detritus of pelecypods, gastropods, foraminifera, siliceous material (remains of diatoms, radiolaria, silicoflagellates, sponge spicules), and also fish bones. The diatoms are represented mainly by spores of Chaetoceros (up to 15 species, 60% of the total of diatoms on the average), and also various species of Coscinodiscus, Cyclotella (up to 35% of the microflora), and Thalassiorisa. In the sediments near Callao (Peru shelf) and Antofagasta (Chile shelf) the number of diatoms in the sediments reaches 25-35 million, maximally 56.6 million, valves per gram. In some samples from the middle and lower part of the continental slope (more than 3000 m deep) isolated redeposited Miocene and Late Oligocene diatoms have been found. Other siliceous organisms occur in minor amount in the sediments, mostly silico-flagellates - up to 1.68 million specimens per gram (Zhuze, 1972). The authigenic minerals of the sediments on the shelf and upper part of the continental slope of Peru and Chile include phosphates, pyrite, clay minerals, and in part iron hydroxides (Table 4-5). The pyrite content in the reduced sediments is 1-3%. Mass pyritization of diatom valves and foraminifera tests (filling with pyrite globules) takes place at depths of 50-250 m, slight pyritization at depths up t o 500 m, which is related to the amount of organic matter in the planktonogenic detritus. Vertebrate bones also have undergone pyritization. The main form of occurrence of iron sulfides is globules 0.005-0.02mm in size, and aggregates of them. The globules are framboids - supermolecular colloidal aggregates. Microconcretions of pyrite, consisting of intergrowths of globules or octahedra, also have been observed in sediment cores in horizons below 150 cm. Iron monosulfides are relatively rare. Sometimes diatom valves are coated with dark blue hydrotroilite with tiny “eyes” of pyrite. In some samples iron hydroxides are preserved in the sediments along with iron sulfides and in their immediate vicinity (fractions of a centimeter), which indicates that the system is not in equilibrium physicochemically. The assemblage of authigenic minerals includes hydromicas, mixed-layer minerals, and possibly montmorillonite and subhedral chlorites. Authigenic and redeposited glauconite is common. In glauconite sands at depths of 500-800m there are sectors with phosphate cement and dense phosphate rims on glauconite grains. The glauconite sands are mainly redeposited (Logvinenko et al., 1973,1975).

218 Investigation of several sediment cores in the regon under consideration showed that the most important feature of their lithologic composition is the presence of graded bedding in the sediments on both the shelf (60200m) and continental slope (to 6000m). Probably in some cases this is related to submarine slumping, in others to abruptly changing facies conditions of sedimentation (Logvinenko and Romankevich, 1973; Zen, 1959).

Chapter 5 STAGES OF LATE QUATERNARY PHOSPHORITE FORMATION ON THE OCEAN SHELVES A review of data on the distribution, composition, and facies setting of occurrences of oceanic phosphorite together with data on the marine geochemistry of disseminated phosphorus shows that Late Quaternary phosphorite formation on the ocean shelves was caused by a favorable combination of several oceanographic, biologic, And geologic factors. Phosphorite formation is not a single-act process, but is made up of several stages succeeding one another in a certain order and providing a transition from Clarke to ore concentrations of phosphorus (Baturin, 1971a, b; Baturin and Bezrukov, 1971,1976).

SUPPLY OF PHOSPHORUS TO THE SHELF BY OCEAN WATERS

In the face of the almost total absence of river discharge and virtually complete absence of submarine hydrothermal manifestations, the only source of dissolved phosphorus in the zones of present oceanic phosphorite formation is the ocean water itself, reaching the shelf from depths of 100300 m. This water is much richer in phosphorus than the surface waters, but poorer in it than the deep waters. For an average phosphorus content of -80 mg/m3, rate of upwelling of 30m/month, and upwelling zone area of 100,000 square miles, the ocean waters supply about 1 0 million tons of dissolved phosphorus to the zone of Recent phosphorite formation each year, i.e. more by an order of magnitude than all the rivers on land bring to the World Ocean.

CONSUMPTION OF PHOSPHORUS BY ORGANISMS

Upwelling, which is a characteristic feature of the system of oceanic circulation, is of paramount importance for the biological productivity of the ocean. Owing to the continuous supply of phosphorus and other biogenic elements to the surface of the ocean, up to 10% of the primary productivity of organic matter falls t o the share of zones of coastal upwelling, which occupy less than 1%of the area of the ocean. The direct consumer of phos-

220 phorus supplied to the shelf is phytoplankton; secondary consumers are zooplankton, the benthos, fish, sea birds, and marine mammals. As a whole, in zones of upwelling phytoplankton extracts from sea water -100 million tons of dissolved inorganic phosphorus per year and produces up t o 4 billion tons of Corg,and just in the area of the shelves of southwest Africa and PeruChile, about 10 x lo6 t P and 400 x lo6 t Corg,respectively. A supply of phosphorus to the shelf in the amount of 70-80 mg/m2 day provides a primary productivity of about 3 g C/m2 day. In actuality, the amount of primary productivity in zones of upwelling reaches 11.7 g C/m2 day (Ryther et al., 1971). Thus the dissolved phosphorus reaching the surface layer of shelf waters often is not only used entirely by phytoplankton, but is used over and over during a day.

DEPOSITION OF PHOSPHORUS ON THE BOTTOM

In regions of Recent phosphorite formation, confined to zones of upwelling, phosphorus is deposited on the bottom exclusively as part of biogenic detritus - remains of phyto- and zooplankton, coprolites, bones, scales. Evidently deposition of phosphorus as part of organic matter itself plays the most important part in this, as indicated by the correlation of disseminated P and Corg(Baturin, 1972; Yemel’yanov and Senin, 1969). About 1 0 million tons of phosphorus per year take part in the process of primary productivity in these regions, but as a result of recycling of phosphorus in the water body only a small fraction of that amount is deposited on the bottom; and even less, -1-276 (100,000-200,000 t P), or up to 300 mg P/m2 yr, is buried in the sediments. With such a rate of supply of phosphorus, a sedimentation rate of about 0.5 mm/yr, and a volumetric weight of sediments of about 0.5, the phosphorus content in diatomaceous oozes on the phosphate-bearing shelves should amount to an average of 0.2-0.4%, which actually is close to the observed values. These data show that whereas only -10% of all the phosphorus involved in the biological cycle takes part in the process of primary production in zones of upwelling, apparently up to 50% of all the organic phosphorus deposited in the ocean reaches the bottom in these zones, and the greater part of this form of phosphorus buried in the oceanic sediments is confined to the zones of upwelling and the shelves. This is related to the high biologic productivity, shallow depths and high rates of biogenic sedimentation on the shelf zones of upwelling. It must also be emphasized that no chemogenic calcium phosphate is observed, either in the waters or in the suspended matter in the zones of Recent phosphorite formation.

221 DIAGENETIC REDISTRIBUTION AND CONCENTRATION OF PHOSPHORUS

In sea and Ocean sediments phosphorus occurs in clastic material, in sorbed form (on iron hydroxides, clay minerals), and also as a component of organic remains and organic matter. The phosphorus in clastic minerals is not very mobile, that in organic matter is very mobile, and sorbed phosphorus is mobile in a reducing environment. In the biogenic reduced sediments of zones of Recent phosphorite formation the main form of disseminated phosphorus is organic, which provides the possibility for its active diagenetic redistribution and concentration. The driving force of diagenetic processes is organic matter (Strakhov, 1960). The abundance of relatively fresh organic matter in the sediments of the zones of Recent phosphorite formation leads to exceptional intensity of diagenetic processes, an indication of which is the composition of the interstitial waters. The interstitial waters of the phosphatic sediments of the shelves ‘of southwest Africa and Peru-Chile differ appreciably in composition from sea waters. They are poor in sulfate ion and calcium but rich in dissolved organic matter, biogenic elements, and several trace elements (Table 5-1). As a result of decay of organic matter and sulfate reduction, hydrogen sulfide, carbonic acid ions, ammonia, silica, and phosphorus accumulate in the liquid phase of the sediments. TABLE 5-1 Composition of interstitial waters of sediments of zones of Recent and Late Quaternary phosphorite formation* Component

Southwest Africa shelf

0.0-0.2 m

0.5-2.0 m

Peru-Chile shelf

Sea water

0.0-0.2 m 19.43 2.00 -2.47 0.467-0.481 0.415-0.433 1.27 5.0 -22.2 3.9 -21.9 26 -32 10 -14 0.12 -7.7 1 -130 7.3 -7.5 to -230

20.05 -20.57 0.31 -1.17 0.549-0.556 0.109-0.286 1.23 -1.26 16.6 -46.0 13.1 -66.4 32 -42 13 -21 1.0 -8.7 13 -650 7.5 -8.0 to -200

20.1 2.0 0.47 0.30 1.30 9.9 -18 6.0 -48.2 12.8 -30.9 1.3 -6.3 0.3 -4.0

-

7.4 -8.0 to -195

19.35 2.70 0.39 0.41 1.30 2.3 0.0 -0.1 0.11-4.3 1

0.07 3 8.2 -k 400

* According to Artem’yev and Baturin, 1969;Baturin, 1972, 1975b;Romankevich and Urbanovich, 1971;Shishkina, 1971,Shishkina and Baturin, 1973.

222 Originally phosphorus passes from the solid to the fluid phase of the sediments chiefly in organic form, but then as the organic compounds decompose, inorganic phosphorus accumulates in the interstitial waters, reaching concentrations of 8-9 mg/l (Baturin, 1972). With such high concentrations of phosphorus the interstitial waters are substantially supersaturated with calcium phosphate, which begins t o precipitate out on material of different origin and composition: on the surface of diatom valves, carbonate detritus, particles of organic matter, fish bones and scales, grains of clastic minerals, or phosphate grains of previous generations. Once the process of calcium phosphate deposition begins, the phosphorus concentration in the interstitial waters drops sharply: in samples where there are no phosphorite concentrations it is maximal, and where there are it is minimal (Fig. 5-1). Possibly the “indiscrimination” of calcium phosphate with respect to the composition of the centers of deposition is caused by the presence on the surface of the particles of sediment of microcenters with high pH values due to alkalization, produced in particular by the action of bacteria including the sulfate-reducing, liberation of ammonia from organic matter, and solution of carbonates. In many pre-Quaternary oceanic phosphorites metasomatic replacement of carbonates by phosphate is observed, which can be caused by

;’

0.1

0.01

I

L 1.

a 72 20

3 0

24 4 0

7.6

7.8

ao

PH

Fig. 5-1. Phosphorus in the interstitial waters of Recent sediments on the shelf of southwest Africa (Baturin, 1972, with additions): 1 = from diatomacous oozes with phosphorite concretions; 2 = from diatomaceous oozes without concretions; 3 = from clastic and calcareous sediments; 4 = sea water. Equilibrium line for calcium phosphate in sea water after Mikhaylov (1968).

223

late diagenetic processes. Recent phosphate facies are immediately adjacent to carbonate and in places even are superposed on them, but there is no direct genetic relationship between present phosphate accumulation and carbonate accumulation. The question of the role of magnesium in phosphorite formation has not been sufficiently clarified. It has been suggested that the magnesium ion inhibits deposition of calcium phosphate from aqueous solutions, in particular from sea water, and that phosphorite formation is possible only if the Ca/Mg ratio in the interstitial waters is high due to the entrance of magnesium into the composition of dolomite and magnesian silicates sepiolite, palygorskite, nontronite, chlorite (Malone and Towe, 1970; Burnett, 1974). However, these minerals are not typical of Recent phosphatic sediments, and the magnesium content in the interstitial waters remains relatively high, in contrast to calcium (Table 5-1). The phosphate gels deposited from interstitial waters originally include various substances of the enclosing sediments and differ from them only in the higher phosphorus content (5-10% P2 O5). During subsequent lithification a substantial transformation of the composition of the phosphate concretions may occur, a self-purging of non-phosphatic components, which is accompanied by an increase in the P205content to 20-32%. A special case of this process is the formation of relatively pure phosphate grains of sandsilt size, which is caused by several factors: selective phosphatization of the organic matter of tiny coprolites and the chambers of foraminifera, formation of microconcretions or filling of cavities in large coprolites and gellike concretions, growth of layers of pure phosphate on particles of clastic minerals. In the course of diagenesis, cementation of previously formed phosphate grains and concretions by amorphous phosphate also occurs, which leads to the formation of multinucleated concretions, blocks, and sheets out of phosphate sands and gravel. The total amount of mobile phosphorus taking part in the diagenetic process of formation of the concretions is difficult to estimate, but on the whole on the shelves it apparently does not exceed 1%of its total content in the sediments. In zones of active phosphorite formation, where the sediments are rich in organic phosphorus, this percentage is much higher and reaches 20-30% (shelf of southwest Africa). REWORKING OF PHOSPHATIC SEDIMENTS

The origination and formation of phosphorite concretions on the ocean shelves occur in sediments with a high phosphorus content compared to the

TABLE 5-2 Phosphorus content in diatomaceous oozes and in sand and fine gravel fractions separated from them (Baturin, 1971b) Station

140 143 151 152 152 157 160 161 163 163

Coordinates

19'38'5, 22'26'5, 22'51'S, 22'40'5, 22'40'S, 22'28'S, 21'59'S, 21'49'5, 21'28'S, 2lo28'S,

12'35'E 13'50'E 14O12'E 14'19'E 14'19'E 14'40'E 13'51'E 13'44% 13'34'E 13'34'E

Depth (m)

120 128 110 76 76 75 91 97 100 100

Content of fraction (95)

> 0.1 mm

< 0.01 mm

0.28 1.30 1.77 8.42 8.42

79.34 70.45 84.81 64.29 64.29

-

-

8.17 5.25 9.92 9.92

75.10 80.94 61.87 61.87

Fraction involved (mm)

p2°5

in fraction

in ooze

2-0.5 4-2 0.5-0.25 2-0.5 0.5-0.25 2-0.5 2-0.5 2-0.5 2-0.5 0.5-0.25

6.52 5.80 12.36 14.30 13.91 16.10 14.47 12.90 7.05 7.60

0.40 0.84 0.56 1.35 1.35 1.25 0.44 0.32 0.30 0.80

(%)

22 5 Clarke (0.5-15’6 P20, ), but in itself this diagenetic process does not assure the formation of phosphorites proper: the concretions are ore microcomponents against a background of the main sedimentary mass, which as a whole is not ore. Originally the phosphatic sediments are chiefly semiliquid pelitic and silty-pelitic oozes with a volumetric weight of 0.5-1 in the dry state. The phosphatic material, which constitutes not more than a few percent of the sediment, is represented by the gravel, sand, and silt fractions (Table 5-2); its bulk density falls within 2-3. In the immediate vicinity of the sediments containing scattered Holocene phosphate formations on the shelf of southwest Africa and Peru-Chile, there are reworked pre-Holocene (usually pre-Quaternary) phosphorite deposits, proper, containing phosphatic material which on the whole has the same structure and composition as that in the Recent sediments. This genetic similarity is one of the signs indicating that the phosphorites were formed by reworking of originally slightly phosphatic sediments and removal of the fine, light non-phosphatic fractions by the action of currents or waves to beyond the shelf, i.e. residual concenkation of the relatively heavy phosphate fractions. Accumulation of fine-grained biogenic sediments on the shelf is possible only in a hydrodynamically quiet setting. In particular, on the shelf of southwest Africa the zone of occurrence of diatomaceous oozes coincides with the zone of minimum velocity of the Benguela current, characterized by maximum vertical stability of the waters (Yelizarov, 1967; Mratov, 1971). On

Years ago

Fig. 5.2. Fluctuations of the level of the World Ocean in Late Quaternary time (Veeh and Chappell, 1970) and absolute age of phosphorites from the shelves of Peru and Chile (indicated by arrows)(Burnett, 1974).

226

Fig. 5-3. Scheme of the process of concentration of phosphate grains and concretions by reworking of the sediments on the shelf of southwest Africa in Quaternary time (Baturi:i, 1971b). 1 = diatomaceous oozes; 2 = unconsolidated phosphate concretions; 3 = compacted phosphate concretions. Present sea level indicated by zero (0).

other parts of the shelf the currents are variable both in force and in direction, as a result of which sedimentation either is discontinuous or absent, or previously deposited sediments are being removed. The same thing occurred in the geologic past: the U-shaped longshore troughs discovered in seismic investigations of the sedimentary sequence on the submerged margin of southwest Africa could have been formed only under the influence of powerful bottom currents (Van Andel and Yalvert, 1971).

227

E

v

c c

0

m 5

10."]6

m 7

I

8

m 9

Fig. 5-4.Scheme of the process of Quaternary phosphorite formation on the ocean shelves: A = supply of phosphorus to the shelf zone by upwelling waters; B = consumption of phosphorus by organisms; C = deposition of phosphorus on the bottom in biogenic detritus and its burial in sediments; D = formation of phosphate concretions in biogenic sediments; E = reworking of sediments and concentration of phosphate concretions when sea level is low. Zones: I = zone of shallow-water clastic deposits; I Z = zone of biogenic sediments with high content of organic matter and disseminated biogenic phosphorus; I I Z = zone of reworked sediments rich in phosphate concretions; ZV = zone of carbonate sediments, locally with phosphate concretions. Legend: 1 = paths of movement of phosphorus in sea and interstitial waters; 2 = plankton; 3 = clastic sediments; 4 = biogenic siliceous, siliceous-clastic, and siliceous-carbonate sediments; 5 = carbonate sediments; 6 = unconsolidated phosphate concretions; 7 = dense phosphate concretions; 8 = glauconite; 9 = erosional surface.

Changes in sea level, which in the Pleistocene fluctuated from -200 to 4-120 m (Menard, 1966), were still more important for reworking of the shelf sediments. Due to these a substantial part of shelf sediments bear traces of reworking (Zenkovich, 1946; Leont'yev, 1963; Curray, 1964; Emery, 1969a), which in particular is true of the phosphate sands on the shelves of southern California, Georgia, the Carolinas, Morocco, and southwest Africa, described above (see Chapter 2). In the sediment wedge on the submerged margin of southwest Africa, five erosional surfaces have been established, formed when sea level stood lower. On the surface of the bottom of the shelf, seven erosion terraces 5-20 m high have been distinguished, and in the coastal belt four wave-cut terraces at heights of 2, 3, 7, and 23 m above present sea level; the lowest and youngest of these is dated as 24,000-48,000 years (Hoyt et al., 1969; Van Andel and Calvert, 1971). In many other shelf regions erosional terraces are buried beneath a layer of younger unconsolidated sediments, or are masked by the slope of the bottom (Emery, 1968). As the dating of phosphate concretions from the shelf of Peru and Chile

228 TABLE 5-3 Rough calculation of the balance of mobile phosphorus in the present ocean Index

Ocean as a whole

Phosphate-bearing and potentially phosphate-bearing shelves

Area ( lo6 km2 )

361

up t o 1-3*

Supply of dissolved phosphorus ( l o 6 t/yr)

1.5 (with river discharge)

more than 10 (due to upwelling)

Phosphorus involved in primary production (mg/m2 day) (l o 6 t / v ) Deposited phosphorus ( lo6 tlyr)

2.5-17 3 00-2 000

50-150 30-100

up to 4

up to 0.6-2

Phosphorus buried in sediments ( l o 6 t/yr)

1.5

up to 1

Phosphorus involved in formation of phosphorite concretions ( lo6 tlyr)

up to 0 . 0 1

up to 0.01

~~

~

~

* The total area of the ocean shelves is 27.5 X lo6 km2 (Poldevaart, 1957). has shown, during the last 150,000 years they were formed only when sea level was high (Fig. 5-2),which could have been a result of warming of the climate, heating of shelf waters and of the upper layer of sediments, and also of the expansion of the shelf area favorable for phosphorite formation or intensification of upwelling, biological productivity, and biogenic sedimentation. When sea level was low, owing to cooling of the climate and glaciation, only erosion of phosphatic sediments, residual concentration and accumulation of phosphorites occurred. In each cycle of phosphorite formation this process was repeated, due to migration of the surf zone twice: when sea level dropped and then when it rose (Fig. 5-3).This apparently explains the well known fact that many platform phosphorites are related to transgressive series. Thus the complete cycle of phosphorite formation on the ocean shelves includes five stages: (1)supply of phosphorus t o the shelf zone in upwelling ocean waters; (2) consumption of phosphorus by phytoplankton and other organisms; (3) deposition of phosphorus on the bottom in biogenic detritus and accumulation of sediments with a high content of mobile biogenic phosphorus; (4)formation of gel-like, gradually hardening phosphate concretions in the sediments; (5)reworking of the sediments and residual concentration of the concretions. The scheme of this cycle is depicted in Fig. 5-4. Intensive phosphorite formation on the ocean shelves is possible only with

229

an optimal combination of biogenic sedimentation and brief reworkings of the sediments, i.e. in the case of multiple repetitions of the multistage cycle described above. One of the conditions necessary for the concentration of phosphatic material in well-sorted phosphorite deposits is the “purest” possible composition of the original sediments with respect to the material not being removed, inasmuch as any coarse-grained elastic and biogenic nonphosphatic components of the sediments would be residually concentrated along with the phosphate concretions. Obviously the concretions concentrated in the deposits are far less in amount than those left scattered in the sediments. The potential rate of Recent and Late Quaternary phosphorite formation on the ocean shelves is about 10,000 t P/yr or, taking into account the area of the zones of active upwelling (300,000 km2),tenths of a millimeter per thousand years (Table 5-3). Thus if the present regime of sedimentation on the shelves of southwest Africa and Peru-Chile were maintained for one million years, phosphorite deposits a few tens of centimeters thick with total reserves of 10 billion tons of phosphorus would accumulate; this is close to the rate of formation of some pre-Quaternary phosphorite deposits.

-

This Page Intentionally Left Blank

Chapter 6 SOME FEATURES O F THE BEHAVIOR O F ELEMENTS ASSOCIATED WITH PHOSPHORUS IN THE COURSE O F OCEANIC PHOSPHORITE FORMATION Phosphorites are characterized by the presence of certain components which are constant or frequent associates of phosphorus in the biogenic and sedimentary cycles - organic matter, amorphous silica, fluorine, and several trace elements. Their behavior in the course of phosphorite formation is a component part of the geochemistry of phosphorites which is important for understanding the regularities of their composition.

ORGANIC MATTER

The functions of organic matter in the course of phosphorite formation are diverse. The main one is the fact that organic matter is a direct supplier of organic phosphorus which when mineralized forms concretions. Organic matter also plays the part of the main factor determining the pH and Eh of the environment of phosphorite formation, which correspondingly controls the deposition of calcium phosphate. Possibly the organic matter included in gel-like phosphate clots is the source of the energy used in the formation of the concretions. And finally, carbon dioxide produced in the decay of organic matter apparently is included in the composition of the molecules of carbonate-fluorapatite. Sulfate-reducing bacteria take part in the decay of organic matter in phosphatic sediments; primarily they consume the most labile compounds - proteins, carbohydrates, and organic acids, which are used as hydrogen donors in the reduction of sulfates to hydrogen sulfide (Schlegel, 1972). During phosphatization of Recent diatomaceous ooze and transformation of its phosphatized parts into concretions, the Corg content decreases 4-t o 6-fold. At the same time there is a decrease in the content of nitrogen, carbohydrates, and free lipids, calculated both as dry substance and in the composition of organic matter (Table 6-1). As relatively unstable compounds, carbohydrates are highly reactive in the course of lithification and phosphatization; their content in dry substance (in the series: ooze-unconsolidated concretions-dense concretions) decreases from 9667 to 421 pg/g, i.e. 22-fold, and recalculated to organic carbon, from 8.5 to 2.2%. Compared t o carbohydrates, the free lipids, the nitrogenous part of organic matter, and especially the bound lipids are much more conservative

to

w

to

TABLE 6-1 Composition (%) of organic matter of phosphorite concretions from the shelf of southwest Africa (Romankevich and Baturin, 1972) Components and their ratios

Enclosing diatomaceous ooze station 152

pz 0 5 SiOZ arnorph COZ Corg Norg

PZ0 5 K o r g SiOZ amorph/Corg Norg/Corg ( X 100) Cinorg K o r g Composition of organic matter (%; % of Co, in parentheses) carbohydrates free lipids bound lipids humic acids

Phosphatized diatomaceous ooze

Concretions from diatomaceous oozes unconsolidated

compacted

dense

Concretions from reworked sediments of outer shelf

station 157

1.40 38.9 1.63 4.25 0.399

1.15 53.8 1.50 5.20 0.604

8.52 30.00 2.16 3.40 0.363

23.85 7.80 5.52 1.80 0.178

29.62 4.05 5.34 1.03 0.097

32.74 0.90 6.33 0.92 0.081

21.27 0.84 3.65 0.76 0.053

0.33 9.2 9.4 0.10

0.22 10.35 11.6 0.08

2.51 8.82 10.68 0.17

13.25 4.33 9.89 0.84

28.76 3.93 9.42 1.41

35.58 0.98 8.80 1.88

27.99 1.11 6.97 1.31

0.3111 (6.91)

0.1342 (5.21) 0.1100 (8.01) 0.1250 (7.28)

0.0710 (3.09) 0.0575 (4.69) 0.0875 (5.71)

0.0421 (2.21)

0.9667 (9.10) 0.6796 (12.0) 0.1888 (2.7) 3.99 (51.6)

1.1100 (8.54) -

-

-

0.7556 (8.89) 0.4840 (10.68) 0.2600 (4.59) 3.39 (54.80)

-

-

-

-

-

Composition of carbohydrates (% of total) oligosaccharides water-soluble polysaccharides water-insoluble polysaccharides

Loss of corg* Increase of cinorg* Acinorz/Acorz

(X

100)

-

-

3.3

-

5.0

-

9.6

-

-

7.3

-

12.5

-

22.2

-

-

89.4

-

82.5

-

68.2

-

-

-

0.85 0.15 17.6

3.13 1.10 32.9

3.22 1.02 31.6

3.33 1.29 38.7

-

-

*Loss and increase compared to enclosing sediments in absolute percentage.

N

w w

234 components. In the series under consideration their content decreases from 4840 to 575pg/g (free lipids), from 0.363 to 0.08--0.053% (nitrogen), and from 2600 to 875 pg/g (fixed lipids), i.e. by about 8.5, 7, and 3 times, respectively. The amount of free lipids in the composition of organic matter decreases (from 12.8 to 5.0%), but the content of bound lipids increases (from 2.2 to 4.8-6.1%), which apparently is related to conversion of part of the free lipids t o an insoluble state. On the whole the content of lipids decreases in the series under consideration (from 1 5 to 10%of organic carbon). Thus on the basis of increasing conservatism, these classes of compounds constitute the following series: carbohydrates-free lipids-nitrogenous part of organic matter-fixed lipids. The correctness of distinguishing such a series is governed by the autochthonous syngenetic type of initial organic matter in all the substances studied. Its autochthonous nature is suggested by the systematic character of the change in composition of organic matter, in particular by the gradual decrease in ratio of free t o fixed lipids on passing from diatomaceous oozes to lithified phosphorite concretions. It should be mentioned that the nitrogenous part of organic matter in diatomaceous oozes and phosphorite concretions is much more resistant to oxidation than the analogous component of the original organic matter of the diatomaceous plankton and suspended matter. In these oozes and concretions nitrogen is part of humic acids which constitute up t o 50% of all the organic matter, while in diatomaceous plankton 70% or more of the total amount of nitrogen is included in proteins and peptides (Krey, 1958; Parsons et al., 1961). The relatively rapid decay of the most oxygen-rich organic compounds (carbohydrates) and also the substantial predominance of water-insoluble polysaccharides in the composition of the carbohydrate complex indicate the biogenic nature of the processes of oxidation of organic matter under both aerobic and anaerobic conditions (Rodionova, 1951 ; Uspenskiy, 1970). As the phosphorite concretions become lithified the content of waterinsoluble polysaccharides in the carbohydrates decreases and the content of oligosaccharides and water-soluble polysaccharides increases. These results are additional evidence that the phosphorite concretions under consideration represent one genetic series in which the content and composition of organic matter changes systematically in correspondence with the extent of lithification and age of the concretions. The most sensitive indicators in this respect are carbohydrates, to a lesser extent lipids and Norg.The proportional decrease in the concentration of carbohydrates, free lipids, and also in the total amount of organic matter and the increase in the content of phosphorus (Fig. 6-1) shows that the initial stages of the process of formation of phosphorite concretions went on continuously at a relatively constant rate (Romankevich and Baturin, 1972).

23 5

Fig. 6-1. Evolution of the composition of organic matter in Holocene phosphorite concretions (shelf of southwest Africa) as they lithify (Romankevich and Baturin, 1972). Samples: I = diatomaceous ooze; II = phosphatized ooze; III = unconsolidated concretion; I V = compacted concretion; V = dense concretion. Components: I = Corg; 2 = Cinorg; 3 = Ptotd; 4 = Si02amorph; 5 = carbohydrates; 6 = free lipids; 7 = fixed lipids; 8 = Norg.

Data on the carbon isotopic composition of lipids extracted from the phosphorites are evidence of this. In the formation and subsequent lithification of phosphorite concretions, the carbon of A lipids becomes isotopically lighter, from -20.7 to -24.2yoO, and the carbon of C lipids becomes heavier, from -24.0 to -23.0~00.This leads to an inversion of the carbon isotopic composition of the A and C lipids in the concretions relative to the enclosing sediments, where the carbon isotopes are distributed in the lipids in a directly opposite way. Apparently the observed picture is produced by the rapid biological oxidation of phospholipids, phosphorus and C 0 2 , which enter into the composition of calcium phosphate as they are liberated (Shadskiy et al., 1980).

CARBON AND OXYGEN ISOTOPES OF C02 AND PO4

Carbon and oxygen isotopes in oceanic phosphorites were investigated in

236 order to clarify the question whether C 0 2 enters into the composition of the apatite molecule. Phosphorites from the California basin, the submerged Chatham Rise, and isolated samples from other regions, including a Recent phosphatic Lingula shell, and also synthetic apatite obtained by replacement of calcite were involved in the investigations (Kolodny, 1969a; Kolodny and Kaplan, 1970b). Two parallel batches were taken from each sample, one of which was analyzed for total C 0 2 and the other for C02 fixed in apatite; for this purpose the second batch was first treated with ammonium citrate, which dissolves calcium carbonate but hardly affects apatite (Silverman et al., 1952). The C 0 2 given off was made to react with a 95% solution of phosphoric acid in a mass spectrometer with a calcite standard, taking into account a correction for the background, mixing and impurities of 1 7 0 (Craig, 1957). All the analyses were run twice. The standard deviation of the results was k0.4yoOat the 95% confidence level. The results obtained (Table 6-2) are expressed in per mil:

~ ( T O O=)

(

Rsample

standard

1

-1 x

1000, where R is the 13C/12Cor 180/170 ratio.

Carbon isotopes. In the California phosphorites no significant difference is observed in the composition of the carbon isotopes of the apatite and calcite phases. The only exception is the phosphate sand from the Baja California region (sample KP 62). In it, and also in the phosphorites of the Chatham Rise, the seamount “NI5”, Agulhas Bank, and the sample of synthetic apatite containing about 7% CaC03 unreplaced by phosphate (sample SI-6), the calcite carbon is appreciably heavier than the apatite carbon. The opposite picture is observed in the phosphatic Lingula shell and the practically pure synthetic apatite (sample SI-1). When the A13C values that are definitely different from zero and the calcite content in the investigated phosphorite samples are compared, an inverse relationship between these values is noted. Probably fractionation of carbon isotopes between the calcite and apatite phases increases as phosphatization of the carbonates progresses, due to preferential removal of the light isotopes from them in the form of HCO;. Oxygen isotopes. A similar but less clearly manifested tendency toward fractionation in proportion to phosphatization is observed in the oxygen isotope ratio. In the California phosphorites this tendency is weakly manifested. In the dark cores of samples KP 33 and KP 51, rich in organic matter, no fractionation of oxygen isotopes is observed, whereas in the light outer parts of these samples where there is little organic matter the calcite phase is markedly

TABLE 6-2 Carbon and oxygen isotopes (%,) Sample No.

Sampling site

in CO2 isolated from phosphorites (Kolodny, 1969a; Kolodny and Kaplan, 1970b) Original material

Calcite content (%)

C 0 2 in apatite

Carbon isotopes

(%)

total 6%

California region KP 1 Coronado Bank KP 2 Forty Mile Bank KP 3 Catalina Bank Catalina Bank KP 4 KP 5 Off San Clemente Is. KP 6 Off San Nicolas Is. KP 1 5 Pioneer Seamount Forty Mile Bank KP 33

KP 51

Thirty Mile Bank

KP 62

Baja California

Submerged Chathom Rise KP 9 43°20’S, 179’31’E KP 6 3 43O27‘S, 179’19’E KP 64 43O26’S 178°00’W KP 6 5 43O30‘5, 179’06‘E Other samples KP 54 Seamount NT5 26”42’S, 159O17’E (521-322m) KP 55 Agulhas Bank LH Hawaii, Kaeoha Bay ( 2 m ) SI-1

SI-6 SI-2

-

a atite 6%

Oxygen isotopes calcite 6°C

oolitic phosphorite oolitic phosphorite oolitic phosphorite oolitic phosphorite oolitic phosphorite

1.3 1.5 2.2 1.9 1.1

87 86 77 80 20

-2.2 -1.3 -1.9 -1.8 -1.4

-2.6 -1.6 -1.7 -1.8 -1.2

-1.3f5.9 -0.7f4.5 -2.5f 2.4 -1.8t2.9 -3.226.5

oolitic phosphorite oolitic phosphorite ( a ) outer part of nodule (b) core of nodule (a) outer part of nodule ( b ) core o f nodule phosphate sand

1.3 3.5 1.5

90 59 87

-2.5 -2.0 -1.3

-2.2 -2.0 -1.5

-5.Of8.2 -2.Of1.2 0.3f4.6

1.9 2.0

82 78

-1.1 -1.2

-1.5 -1.3

0.7 f 3.1 -0.6f 2.4

2.3 9.3

78 16

-1.6 -2.4

-2.1 -8.4

-0.lf 2.6 -1.3f1.3

limestone limestone limestone limestone

23.9 24.8 20.9 42.4

30 31 33 20

1.1 1.1 0.7 1.3

-0.3 -0.5 -1.4 -0.9

phosphatized limestone

41.0

23

1.9

pellet phosphorite Lingula shell

15.1 2.0

32 63.5

phosphatized phosphatized phosphatized phosphatized

synthetic apatite, replacing calcite synthetic apatite, not completely reacted original calcite

1.0 -4.4

0.3 -0.8

-2.0

1.3

89

-22.3

-20.0

6.9

58

-19.8

-22.0

100

-

-24.0

-

A~”C

-

total

a atite

calcite

6180

8 8 0

6180

-0.3

A6”O

-

-0.3 -1.7 0.3 1.3

0.2 0.1 -0.3 0.4 1.1

-3.6f4.1 -2.8f3.8 -6.1f2.3 0.122.6 2.8f6.4

-0.8 -0.2 0.9

0.2 -0.2 -0.2

-9.4f5.5 -0.2 t 1.1 8.3 f 4.2

-0.3 0.5

-0.3 -0.4

-0.3f 2.1 3.6f2.3

4.0f2.3

7.1f1.4

-0.3 -0.4

-0.5 -3.1

0.4f2.4 0.2 f 0.7

3.3f0.8

1.7f0.6 1.9t0.6 1.7f0.7 1.8t0.5

2.0f0.7 2.3f0.7 3.1f0.8 2.7f0.7

1.7 0.4 1.1 -0.2

0.8 -0.1 0.2 0.1

2.3f0.5

2.0f0.7

0.7

1.820.6 -8.6f1.5

2.6f0.7 -6.6f1.6

1.1

-40.3f47 -16.8f3.9 -24.02 0.4

-

-

-

-

5.2f3.9 -

-5.8f2.3 -

-9.6f5.5 -

8.5f4.2 -

-

2.0f0.6 0.6f0.6 1.5f0.6 -0.2?0.5

1.2f0.7 0.7f0.6 1.3f0.8

-0.5

1.1f0.5

1.6f0.7

-0.4 -5.8

1.8f0.6 -6.9f1.9

2.3? 0.7

-6.2 -12.0

-9.0

-8.4

-10.0

-12.5

-

-

-35.5f24

-6.2f 2.0 -12.5

-

-

-26.5t 24 3.8f2.0 -

N

w

238 enriched in the isotope. Possibly this was caused by secondary isotopic exchange between the phosphorite and the cold "0-enriched bottom water after the phosphatization process had ended. In the other phosphorite samples investigated, the calcite C 0 2 also is substantially enriched in the l80 isotope compared to apatite C 0 2 . There is an inverse relationship between the CaCO, content and oxygen isotope fractionation ( A 1 8 0 ) in the calcite and apatite phases. As for the Lingula shell, the 6I8O value of its apatite phase is about -6O/'&, whereas for calcite a t a corresponding water temperature (26.5'C) 6I8O would be about -2To0. Probably this indicates a difference in the isotopic composition of the COz of apatite and calcite in biogenic material, on the one hand, and the ability of Lingula to fractionate the isotopes in building its shell, on the other. The data on carbon and oxygen isotopes in oceanic phosphorites and similar results of an investigation of marine phosphorites from the Upper Cretaceous of the Near East indicate that there is a fairly clear linear correlation between 6"O and 613C values in the apatite phase of phosphorites. In general the apatite COz is enriched in the light isotopes compared t o calcite COz . The average coefficient of isotopic fractionation between the calcite and apatite phases (1+ A / l O O O ) in phosphorite samples is: 1.0031 for carbon, 1.0008 for oxygen, and together with the Near Eastern samples mentioned above, 1.0028 and 1.0021 respectively, which is confirmation of the idea that C 0 2 enters the apatite lattice (Kolodny, 1969a; Kolodny and Kaplan, 1970b).

PO4 A considerable volume of work has been done by Longinelli and his coauthors on the oxygen isotopes of phosphates in various objects in the marine environment, in the remains of organisms in sedimentary deposits and in phosphorites (Table 6-3). Through these investigations it has been established that in many organisms isotopic equilibrium is established between the phosphate oxygen of their tissues and sea water oxygen, on the basis of which several paleotemperature and paleoisotopic reconstructions are possible. At the same time the oxygen isotopic composition of phosphate in fossil biogenic carbonate formations varies unsystematically, but in phosphorites and fossil bones there is observed a tendency for the oxygen isotopic composition of the phosphate to become lighter as the age of the material increases. Apparently this indicates a change in the original oxygen isotopic composition under the influence of secondary processes, for instance coming in contact with ground water, rather than a higher temperature of the waters of the ancient oceans.

TABLE 6-3 Oxygen isotopic composition of phosphates from the marine environment ~

~~~~

Object

6' 8 0

Region

relative t o SMOW (Yo0

Number of samples

Reference

20 10

Longinelli et al., 1976 Longinelli et al., 1976

)

Sea water

Atlantic Pacific Ocean

Recent Recent

Flesh of mollusks

Tyrrhenian Sea

Recent

17.0-2 3.1

9

Longinelli et al., 1976

Flesh of fish

Atlantic and Mediterranean Sea

Recent

21.3-24.3

19

Longinelli et al., 1976

Mollusk shells

Atlantic, Tyrrhenian Sea Europe, North America*

Recent Mesozoic, Cenozoic Paleozoic

17.0-20.6 13.4-24.2 12.1-13.4

18 55 6

Longinelli, 1965, 1966 Longinelli, 1965, 1966 Longinelli, 1965, 1966

Belemnites

Europe, North America*

Jurassic/Cretaceous

16.1-24.8

33

Longinelli, 1966; Longinelli and Nuti, 1968a

Fish teeth and bones

Pacific Ocean and Atlantic

Recent Recent Recent Cenozoic

19.5-24.9 15.3-1 8.7 18.2-19.9 16.1-20.5

24 3 3 11

Cretaceous

12.8-20.1

8

England*

Paleozoic

11.6

1

Longinelli and Nuti, 1973 Gromova et al., 1976 Baturin et al., 1980a Longinelli, 1966; Longinelli and Nuti, 1968a Longinelli, 1966; Longinelli and Nuti, 1968a Longinelli, 1966; Longinelli and Nuti, 1968a

Bones of cetaceans

Pacific Ocean

Pleistocene

18.3-19.7

Phosphorites

shelves of Namibia and Chile Atlantic shelves Pacific seamounts deposits of Europe and America*

Holocene, Pleistocene Neogene Cretaceous/Pleistocene Mesozoic/Cenozoic Precambrian/Paleozoic

20.0-21 .o 17.4-24.5 14.5-22.5 15.6-23.2 8.6-1 5.5

Europe and North America*

* Data from marine sedimentary deposits on the continents.

19.4-20.0 20.1-21.2

2 3 2 10 33 16

Baturin et al., 1980a, b Baturin et al., 1980a Baturin et al., 1980a Strizhov et al., 1980 Longinelli and Nuti, 1968b Longinelli and Nuti, 1968b

240 A number of determinations of the oxygen isotopic composition of phosphate in phosphorites and bones have also been made by Soviet investigators (Gromova et al., 1976; Baturin et al., 1980a, b; Strizhov et al., 1980). According to these determinations, the range of variation of the oxygen isotopic composition of phosphate in mammal bones from the ocean floor is about the same as in the bones of Recent fish, and in phosphorites from the ocean floor the same as in phosphorites from marine sedimentary rocks on land. But in the Holocene phosphorites from the shelves of Namibia and Chile this range falls within 20-21%,, in Neogene phosphorites (from Agulhas Bank and the shelf of Namibia) within 17':4-24.5?,,, and in Cretaceous/Pleistocene phosphorites from Pacific seamounts within 14.5-22.5yoO (Table 6-3). In the brown varieties of phosphorite from seamounts, 6l8O is 18.120.9yoO, in the white varieties 22.5?,, and in quartz associated with the phosphate 19.5YoO.An attempt to interpret these data as an indication of the temperature of formation of the phosphates gave a temperature range of 18-29" to 40-50°C for the phosphates and of 110--130°C for the quartz (Strizhov et al., 1980). The complexity of the geologic environment on seamounts allows the possibility of such an interpretation, but it is hardly applicable to Recent phosphorites and bones inasmuch as the environment of their formation and deposition is characterized by a narrow temperature range. Therefore to ascertain the cause of the fluctuations in the 6 l 8 0 of phosphates in shelf phosphorites and bones from the present ocean bottom, it apparently is necessary to trace its variation in the full cycle of migration of phosphate on the paths: sea waterphytoplankton-planktonophagi-sediments-phosphorites.

AMORPHOUS SILICA

The behavior of amorphous silica in the course of phosphorite formation is of interest in connection with the fact that present phosphorite concretions are forming in siliceous diatomaceous oozes (Baturin, 1969; Burnett, 1974), and many old phosphorites are related to siliceous formations (Bushinskiy, 1966b). In zones of recent phosphorite formation amorphous silica reaches the bottom as part of diatom detritus, containing up to 77% s i o 2amo& (average 43%) (Vinogradov, 1953). The amorphous silica content of the diatomaceous oozes on the shelf of southwest Africa reaches 50-70%. In phosphatized ooze it constitutes 30-4576, in unconsolidated phosphate concretions 7-1596, in compacted and dense ones, one or two or fractions of a percent (see Chapter 2).

241 TABLE 6-4 Variation in average sioz amorph/Corgand sioz amor,,h/P ratios in the course of phosphorite formation on the shelf of southwest Africa* Material

SiOZ amorph lCorg

SiOZ amorph Ip

Diatomaceous plankton Diatomaceous ooze Phosphatized ooze Unconsolidated phosphate concretions Compacted phosphate concretions Dense phosphorite concretions Interstitial waters from diatomaceous oozes

2.5 7 13 15 4 1 1

53 150 12.5 1.3 0.3 0.06 10

* According to data of Artem’yev and Baturin, 1969; Baturin, 1969, 1972; Baturin et al., 1970; Shishkina and Baturin, 1973; Vinogradov, 1953. Thus whereas amorphous silica, organic carbon, and phosphorus migrate together in the biogenic cycle and during sedimentation in the productive shelf zones, in the diagenetic process of formation of phosphorite concretions their paths of migration may diverge, as is demonstrated by comparison of the average Si02amorph /Corgand Si02amorph /P ratios in diatomaceous plankton, diatomaceous oozes, interstitial waters, and Recent phosphorite concretions (Table 6-4). In diatomaceous plankton the Si02amorph /Corg ratio averages 2.5. When biogenic detritus is deposited the decay of organic matter goes on at a much faster rate than solution of amorphous silica, therefore the Si02amorph /Corg ratio in diatomaceous oozes is about three times greater than in diatomaceous plankton (7, on the average). During phosphatization of the oozes and formation of unconsolidated phosphate concretions this tendency is maintained, and the Si02amorph /Corg ratio doubles again (to 13-15). Subsequently, when the concretions are lithified, the most stable part of organic matter is preserved in the dense concretions, but silica is easily removed from them in the /Corg ratio gradually self-purging of phosphate, due t o which the Si02 decreases to unity. That same ratio of these components is also typical, on the whole, of interstitial waters from diatomaceous oozes (Artem’yev and Baturin, 1969; Shishkina and Baturin, 1973). The SiOzamorph /P ratio changes with much greater amplitude during phosphorite formation. In diatomaceous plankton it averages 53, in diatomaceous oozes, due t o loss of phosphorus in the deposition of biogenic detritus, it averages 150. Thus, when biogenic detritus is deposited the Si02amorph /P ratio, like the Si02amorph /Corg ratio, increases threefold. Subsequently, when the oozes are phosphatized and the phosphorite concretions are formed,

242 amorphous silica and phosphorus behave as antagonistic elements and the SiO,.,,/P ratio drops sharply - on the average to 12.5 in phosphatized ooze, to 1.3 in unconsolidated concretions, to 0.3 in compacted ones and to 0.06 in dense. In the interstitial waters the average ratio of these components is about the same as in phosphatized ooze - 10. During the formation of phosphorite concretions in diatomaceous oozes the phosphate originally adheres to the surface of diatom valves and fills pores in them (see Chapter 2). In parallel with lithification of the concretions, amorphous silica is replaced by phosphate; in dense Holocene concretions from the shelves of southwest Africa, Chile and Peru, in contrast to unconsolidated varieties, only isolated diatoms unreplaced by phosphate are observed (Baturin, 197413; Baturin and Petelin, 1972; Baturin et al., 1970). In pre-Quaternary phosphorites, in particular the Paleogene and Upper Cretaceous ones of the Nile syneclise, only rare relicts of diatoms are preserved, represented by aggregates of opal (Mikhaylov et al., 1972).

FLUORINE

In the diatomaceous oozes of the shelf of southwest Africa the fluorine content averages -0.0596, in the phosphatized ooze 0.3-0.4%. As the phosphorite concretions form and lithify, the fluorine content increases to 2-3%. Fluorine also accumulates in biogenic phosphatic material subjected to diagenetic phosphatization, the content increasing from 0.7-1.2 to 3.03.4% in scales and bones and from 1.50 to 3.82-5.48% in phosphatized coprolites (Table 6-5). In the course of phosphorite formation the fluorine content in the concretions increases by 4 orders of magnitude compared to surface waters, the phosphorus content by 6-7 orders, and the F / P 2 0 , ratio decreases by 2 orders, but rises somewhat on passing from diatomaceous ooze to lithified phosphorite concretions (Fig. 6-2). Thus the F/P,05 ratio indicates that the enclosing sediments are the immediate source of the fluorine and phosphorus concentrated in the phosphorite concretions, phosphatized bones and coprolites. The F/P, O5 ratio in interstitial waters of the sediments of the productive zones of the ocean is intermediate with respect t o the values typical of sea waters and sediments. The increase in F/P, O5 ratio in the order sediments-phosphatized sediments-unconsolidated phosphate concretions-lithified phosphorite concretions shows that accumulation of fluorine in the concretions takes place somewhat in advance of phosphorus. This apparently is caused by partial conversion of phosphate from the amorphous to the cryptocrystalline form and more intensive introduction of fluorine into the crystal lattice of apatite (Baturin and Shishkina, 1973).

243 TABLE 6-5 Content of fluorine, iodine, phosphorus and organic carbon (%) in phosphorites from the shelves of southwest Africa and Peru-Chile* Material

F

I

P

Corg

Phosphorite concretions: unconsolidated compacted dense

1.54-2.05 1.98-2.87 2.42-3.00

134-209 X 84-90 X 66 X

6.8-10.4 9.0-12.9 11.0-14.2

0.65-1.93 0.62-1.20 0.604.90

Dense phosphatized co pr olit es

3.22-5.48

13.74-14.24

0.60-0.88

82

X

Fish and mammal bones : unfossilized slightly fossilized fossilized

1.19-1.68

136-512

X

8.1-12.1

6.10-7.20

2.50-2.56 3.03-3.44

88-126 144--220

X X

12.8 12.7-16.5

4.20-4.80 1.10-1.62

Fish scales

0.70

10.0

9.17-10.12

Enclosing diatomaceous oozes**

0.02-0.28

4.3-31.9

Interstitial waters (mg/kg)

6-1 1

0.12-0.2 1

47 x 1 0 - ~ X

0.10-0.60 0.1-8.7

4 2-1 5.6 -

* According to Baturin and Shishkina, 1973; Shishkina and Pavlova, 1973; Shishkina e t al., 1972. ** Iodine c o n t e n t in diatomaceous oozes from t h e shelf of southwest Africa, rid o f salt, is (Price and Calvert, 1973). 10.9-48.3 X The F/P2O5 ratio in lithified Holocene phosphorite concretions is somewhat higher than the theoretical ratio in fluorapatite (0.089). The same thing has been observed in pre-Quaternary phosphorite concretions from the ocean floor (Dietz et al., 1942; Parker and Siesser, 1972), in phosphorite deposits on land (Bushinskiy, 1966b; Gimmel’farb, 1965) and in fossil bones (Blokh and Kochenov, 1964). This is due to the formation of ultramicroscopic secretions, grains, and veinlets of secondary fluorite (Blokh and Kochenov, 1964; Bushinskiy, 1966b; Krasil’nikova, 1963; D’Anglejan, 1967; Dietz et al., 1942). Experimental investigations of the process of take-up of fluorine from aqueous solutions by calcium phosphate showed that the final value of F/P2O5 does not exceed the theoretical value for fluorapatite; after this limit is reached, take-up of fluorine by calcium phosphate ceases (Adler and Klein, 1938). In biogenic phosphatic material - scales, bones, coprolites - the amplitude of variation in the F/P2O5 ratio as phosphatization progresses is much

244 106-

105 -

lo4lo3 ~

102 -

10

.

1

-

/‘4

Id’-

‘2O5

1

2

3

4

5

6

7

8 9

1 0 11

12 13 14 15

16 17 18

Fig. 6-2. Fluorine in the course of Recent phosphorite formation (according to Shishkina et al., 1972; Baturin and Shishkina, 1973). Open ocean: 1 = surface waters; 2 = bottom waters; 3 = interstitial waters; 4 = sediments. Productive inshore zones of the ocean: 5 = surface waters; 6 = bottom waters; 7 = interstitial waters; 8 = sediments (diatomaceous oozes); 9 = phosphatized diatomaceous ooze; 10 = unconsolidated phosphorite concretions; 1 1 = dense phosphorite concretions; 12 = fish scales; 13 = unfossilized fish bones; 1 4 = slightly fossilized fish bones; 15 = fossilized fish bones; 16 = unconsolidated coprolites; 1 7 = compacted coprolites; 18 = dense coprolites.

wider than in concretions. A very low fluorine content, 0.43% on the average (Klement, 1935), and also a very low F / P 2 0 5 ratio (-O.Ol), are typical of the bones of living marine fish. In relatively fresh fish scales from the diatomaceous oozes of the shelf of southwest Africa the F / P 2 0 5 ratio rises to 0.03, in unfossilized bones t o 0.04, in fossilized bones to 0.08-0.09, and in phosphatized coprolites to 0.16-0.18. In Holocene phosphorite concretions the F/P, 0, ratio is more stable than in bones and coprolites. Evidently this is due to the fact that the phosphorite concretions formed in diagenesis of sediments take up fluorine from the interstitial water simultaneously with phosphorus as they form, and there is relatively little subsequent enrichment in fluorine. In contrast, bone material and coprolites are originally poor in fluorine and it accumulates with greater intensity in biogenic phosphates which reach the bottom than it does in the concretions.

IODINE

The iodine content of the sediments enclosing Recent and Late Quaternary phosphorite ranges within 4.3-31.9 x (Table 6-5), which is at least 2 orders of magnitude higher than the Clarke of the earth’s crust - 4 x

245 (Vinogradov, 1959). Apparently such enrichment of the sediments in iodine is related to their high content of organic matter - up t o 10-20%. As the phosphorite concretions form and become depleted in organic matter the iodine content also decreases, averaging 172 x lo-’% in unconsolidated concretions, 87 x lo-’% in compacted concretions, 66 x lo-’% in dense concretions, and 82 x lo-’ % in dense phosphatized coprolite. In the course of fossilization of bone material iodine behaves differently: unfossilized bones of fish and marine mammals contain an average of iodine, slightly fossilized ones 107 x lo-’%, fossilized ones 383 x 167 x and relatively fresh fish scales 47 x lo-’%. In this case the ratio between I and C,, is disturbed: the scales are enriched in organic matter and poor in iodine, while the fossilized bones, which are poor in organic matter, contain more iodine than bones in the intermediate stage of fossilization. Possibly, in fossilized bones iodine is again concentrated in late diagenesis due to its extraction by the phosphatic material from interstitial waters containing 0.1-0.2 mg/kg of iodine. On the whole, during Late Quaternary phosphorite formation iodine and fluorine - the two end members of the halogen group - became separated (Shishkina and Pavlova, 1973). Among old phosphorites there are known both iodine-rich (up to 9 x - the Devonian phosphorites of Nassau, West Germany) and iodine-poor varieties (to 8 x - the Permian phosphorites of the Rocky Mountains in the U.S.A.), with no correlation of I and Corg(Bliskovskiy and Parfenskaya, 1971; Hill and Jacob, 1932).

URANIUM ISOTOPES

The uranium content in oceanic phosphorites ranges from 1t o 524 x i.e. within the same limits as in phosphorites on land (Baturin, 197513;Baturin and Kochenov, 1974). Uranium occurs in oceanic phosphorites chiefly in a dispersed state and is fixed in phosphatic material, which is demonstrated by radiographic investigation of thin sections (Burnett, 1974). In isolated cases uranium forms an independent phase in the form of ultramicroscopic segregations of uraninite crystals, discovered by V.T. Dubinchuk, in particular in the Recent phosphorite concretions from the shelf of southwest Africa. Previously a similar phenomenon was reported in pre-Quaternary phosphorites and bone detritus from marine sedimentary rocks on the continents (Kochenov e t al., 1973; Levina et al., 1976). Usually tetra- and hexavalent uranium are present in oceanic phosphorites. In Late Quaternary phosphorite concretions from the shelves of Peru and Chile

246 the relative content of tetravalent uranium is 40-7196, in the Miocene phosphorites from the California basin 38-7996, and in the Miocene phosphorites from the submerged Chatham Rise 60-8996; only hexavalent uranium has been found in the phosphorites from the Blake Plateau (Burnett, 1974; Kolodny, 1969a, b). The phosphorites from the Chatham Rise are enriched in both total (up to and tetravalent uranium (Kolodny, 1969a), but on the whole 534 x there is no correlation between U(1V) and Utotal in oceanic phosphorites (Burnett, 1974). The 234U/238Uisotope activity ratio in oceanic phosphorites ranges from 0.95k0.05 t o 1.169k0.013 in total uranium, from 0.5120.04 t o 1.19k0.04 in tetravalent uranium, and from 1.11t o 2.61 in hexavalent uranium. In Recent and Late Quaternary phosphorites these ratios are the same as in sea water on the whole - 1.14-1.16 (Tables 2-13, 2-26; Baturin e t al., 1972a,b,c, 1974; Burnett, 1974). Concerning the mechanism of accumulation of uranium in phosphorites, several hypotheses have been suggested: (a) reduction of uranium t o the tetravalent state and its replacement of calcium in the apatite structure (Altschuler et al., 1958); (b) sorption of hexavalent uranium compounds by phosphate in an oxidizing environment (Rozhkova et al., 1959); (c) introduction of hexavalent uranium into the structure of calcium phosphate during metasomatic phosphatization of carbonate rocks (Ames, 1960). Data on recent phosphorite formation show that the immediate source of g/l U), but uranium in phosphorites is not sea water (which contains 3 x the enclosing sediments, which contain up to 60 x and the interstitial waters, which contain up t o 650 x g/1 U. Despite the reducing environment in these sediments (Eh about -200 mV), uranium has a certain mobility in them and apparently occurs in the composition of metallo-organic complexes in the tetra- and hexavalent state (Baturin, 1975b). As the Recent phosphorites on the shelf of southwest Africa form, their uranium content gradually increases from unconsolidated to dense phosphatic concretions, from 3-8 t o 17-86 x A similar picture is observed in the phosphorites from the Chile shelf (Table 6-6, Fig. 6-3). Apparently when phosphate gels form in the sediments they sorb uranium-organic complexes from the interstitial waters. Subsequently, when the organic matter decays, the uranium enters into calcium phosphate both in form of an isomorphous substitution and sorptionally, inheriting the tetra- or hexavalent state from the stage of its occurrence in the interstitial waters. During formation of Recent phosphorite concretions the U/P, O5 ratio on the whole changes little in them, which indicates the syngenetic nature of concentration of uranium. Despite the fact that on the scale of the whole ocean the uranium content in phosphorites varies greatly and there is no U-P205

TABLE 6-6 Content of uranium and P2 O5 in Recent oceanic phosphorites (Baturin and Kochenov, 1974) Sample

Southwest Africa shelf Lenses of phosphatized diatomaceous ooze Unconsolidated concretions Compacted concretions Dense concretions Unconsolidated coprolites Compacted coprolite Dense coprolite Chile shelf Unconsolidated concretions Compacted concretions Dense concretions Dense black coprolite Dense gray coprolite

p2°5

u

(%)

U/P~O ( x~

range of values

average

range of values

average

range of values

average

5.10-11.54 23.85-26.53 27.88-3 1.09 31.16-32.7 7 23.69-2 7.53

8.32 25.20 29.37 32.09 25.85 31.64 32.06

3-8 9-1 9 9-80 17-86 3-52

5 14 35 53 28 68 77

0.3-0.8 0.5-0.8 0.3-3.1 0.6-2.5 0.1-1.9

0.5 0.6 1.4 1.6 1.0 2.2 2.4

15.32 20.21 25.72 30.67 32.38

7-4 5 8-4 5 9-54

28 29 34 30 40

0.5-3.0 0.4-2.2 0.4-2.2

1.8 1.5 1.5 1.0 1.3

-

14.92-1 5.73 19.78-20.64 25.10-26.45

-

-

Number of samples

,@"& /*-..*

3010-

i

1-

@/.--.--.

P*O, %

P2% %

-.

i

10.'-

2

1

2

3

4

5

6

7

8

9

1 0 1 1

12

13

-

1415

u

16

Fig. 6-3.Uranium in the course of Recent phosphorite formation (after Baturin and Kochenov, 1974, with additions). 1 = sea waters;2 = interstitial waters; 3 = diatomaceous sediments in which phosphorite concretions are forming; 4 = phosphatized diatomaceous ooze; 5 to 7 = phosphorite concretions (5 = unconsolidated; 6 = compacted; 7 = dense); 8 to 11 = coprolites ( 8 = living marine organisms; 9 = unconsolidated, from the bottom; 10, 11 = compacted and dense, from sediments); 12 to 15 = bones of fish and marine mammals ( 12 = fresh; 13 = unfossilized, from sediments; 1 4 = slightly fossilized; 15 = fossilized).

correlation, the average uranium contents in phosphorites of various shelf zones and the average U/P2 O5 ratios are relatively stable: U = 52 f25 x U / P 2 0 5 = 2.3f0.8 x (Baturin and Kochenov, 1974). The same thing has been noted in marine phosphorites from sedimentary rocks on land (Levina et al., 1976). In particular, in the phosphorites of the Russian (Baturin and Kochenov, platform the average U/P205 ratio is 3.2 x 1974), and in the phosphorites of the Phosphoria Formation it is 3.0 x (Gulbrandsen, 1966). Probably these facts indicate a similarity in the geochemical environment of phosphorite formation and in the mechanism of accumulation of uranium in them. Lithified phosphorites from the ocean floor differ from unlithified ones in greater density, lower porosity and water content, partial crystallization of the phosphate, and also formation of a dense coating on the surface

249 consisting of condensed organic matter and finely crystalline phosphate, which inhibits the process of further concentration of uranium in them. In phosphorites washed out of the enclosing sediments and in contact with oxygen-bearing bottom water for a long time, partial oxidation and loss of uranium occur. This is demonstrated by data on the content and valency of uranium in the outer and inner parts of concretions from the California basin (Kolodny and Kaplan, 1970a). In the light outer parts of the conin the dark inner part cretions the total uranium content is 6 2 - 6 7 x 71-72 x The relative content of tetravalent uranium is falling on passing from inner to outer zones from 64-70 to 44-58%. The outer zone of these concretions is depleted in the 234U isotope. The 2MU/238Uratio in tetravalent uranium is as follows: in one sample, 0.81 in the core and 0.78 in the shell of the concretion, in another 0.71 and 0.65, respectively. On the whole the data on the isotopic composition of tetra- and hexavalent uranium in pre-Quaternary oceanic phosphorites show that in an oxidizing environment, -30% of the 2 M U formed by decay of 238U(IV) is oxidized and acquires migrational mobility (Kolodny, 1969a), as in pelagic sediments (Ku, 1965). In biogenic phosphates (scales, bones of fish and mammals) occurring in the sediments of zones of Recent phosphorite formation, concentration of uranium goes on more intensively than in the concretions. Coprolites and uranium bones of living marine organisms contain no more than n x (Aten et al., 1961; Pertsov, 1964; Risik, 1973). Relatively fresh bones and %, slightly phosscales from the top layer of sediments contain 2-28 x phatized bones and scales up to 1 x and highly phosphatized bones and scales up to 7 x 5% uranium. The ability of bone material to accumulate uranium actively is due to the porous structure of bone tissue, the low degree of crystallization of bone phosphate, and the high content of organic matter in bones (Baturin et al., 1971; Baturin and Kochenov, 1974). New detailed data on the distribution and forms of uranium in oceanic phosphorites have been obtained in investigations of their ultramicroscopic structure and composition, using a combination of the methods of scanning and transmission electron microscopy, microradiography, microdiffraction and microanalysis (Baturin and Dubinchuk, 1978,1979). It has been established that the greater part of the uranium in oceanic phosphorites occurring in a reducing environment (the Recent and Upper Quaternary phosphorites on the shelves of Namibia and Peru-Chile) is present in a highly dispersed form, forming round and flocculent ultramicroscopic inclusions hundredths of a micron in a size. The relative concentration of these inclusions varies from sparse t o dense, and their distribution from even to uneven. In places the microinclusions merge into a solid field, forming aggregates of various shapes (Fig. 6-4). The microinclusions tend mainly to be

250

Fig. 6-4. Ultramicroscopic secretions of uranium, round and flocculent in shape, in phosphate with collomorphic-block structure (Baturin and Dubinchuk, 1978). Slightly cemented concretion from the shelf of Namibia, station 2048; X 32,000. In upper corner, microdiffraction pattern of the uranium secretions.

associated with amorphous phosphate, but they also are encountered in the phosphatized remains of diatoms, where they encrust the cavities of the valves, and on the surface of mineral grains, forming films on their boundaries. Another form of secretion of uranium is oval (acorn-like) and crystallomorphic isometric formations of larger size, up t o 0.3-0.5 pm. They also are restricted mainly t o amorphous phosphate and phosphatized diatom remains. In the latter case they usually fill the cavities of the valves and take on the corresponding shape (Fig. 6-5). In addition, they occur in the peripheral parts, less often in the center, of slightly crystallized phosphate globules. The largest secretions of uranium are euhedral crystals of cubic habit from fractions of a micron to 1 or 2 p m in size (Figs. 6-6, 6-7).In isolated cases the crystals have indistinct, poorly developed faces. Both isolated crystals and colonies of crystals of the same or different size are encountered. In some concretions the crystals are limited just to the microcrystalline phosphate and are absent in the amorphous, in others they also form in the

251

Fig. 6-5. Oval and crystallomorphic secretions of uranium (below) on a fragment of a valve of a diatomaceous alga included in a m a s of colloform phosphate (Baturin and Dubinchuk, 1978). Compacted concretion from the shelf of Namibia, station 2048; X 35,000. At the right, microdiffraction pattern of the uranium secretions.

amorphous phosphate. Occasionally crystals are observed on the surface of grains of clastic minerals, in particular quartz. Large crystals are sometimes associated with small ones; usually ultramicroscopic secretions of uranium, irregular in shape, are scattered on the surface of the large crystals (Fig. 6-6). In some places it is seen that small crystals or accumulations of finely dispersed uranium secretions are engulfed by a large crystal (Fig. 6-7). Each of the types of uranium secretions described is morphologically distinct, but there is no clear-cut boundary between them inasmuch as intermediate varieties are observed. The microdiffraction patterns representing areas of dense concentration of ultramicroscopic inclusions and the oval or isometric secretions and cubic crystals were similar - ring-like and corresponding to uraninite (Figs. 6-4, 6-5). On some preparates microdiffraction patterns of metallic lead, probably radiogenic, were also obtained. In pre-Quaternary phosphorites occurring in an oxidizing environment (from Agulhas Bank, the Blake Plateau and Pacific seamounts), as in the young shelf phosphorites, uranium is associated with various components in which phosphate does not always remain of foremost importance.

252

253

Fig. 6-8.Ultramicroscopic secretions of uranium in crystalline phosphate (Baturin and Dubinchuk, 1978). Phosphatized limestone from Pacific seamounts, station 6364; X 15,600.

In gel-like and collomorphic-granular phosphate the uranium is dispersed and forms round, oval or irregular secretions 0.01-0.1pm in size, rarely larger. The uranium secretions are scattered irregularly in the phosphate mass and sometimes form clumps. Ultramicroscopic secretions of uranium are similarly distributed in crystalline phosphate also, some crystals being full of them while in others they are absent (Fig. 6-8). In phosphate with block structure the ultramicroscopic secretions of uranium are concentrated mainly along the block boundaries. In those cases where the phosphate blocks are in contact with a collomorphic mass, uranium also apparently is expelled from the crystallized phosphate into the contact zone. Occasionally ultramicroscopic uranium secretions in phosphate form a semblance of crystallomorphic forms about 0.2 pm in size, and in one prepFig. 6-6(top). Crystals of uraninite in collomorphic phosphate in unconsolidated concretion from the shelf of Namibia, station 2048;X 22,500 (Baturin and Dubinchuk, 1978). Fig. 6-7(bottom). Large crystal of uraninite on fragment of the valve of a diatom, absorbing small crystals (Baturin and Dubinchuk, 1978). Compacted concretion from the shelf of Chile, station 250;X 30,000.

2 54

Fig. 6-9. Ultramicroscopic secretions of uranium on a fragment of a coccolithophore plate (Baturin and Dubinchuk, 1979). Phosphatized limestone from Pacific seamounts, station 6348; X 42,500.

arate an oval grain of uraninite, 0.3 x 0.6 pm in size, was found. Carbonate material is much poorer in uranium than the phosphate. In coccolithophore platelets only isolated, sparsely disseminated ultramicroscopic secretions of uranium were found, 0.01-0.1pm in size (Fig. 6-9); in carbonate with block structure they are as tiny, but are disseminated more evenly and somewhat more thickly. Uranium is distributed very unevenly in feldspar grains. Its usual form is sparse round or flocculent ultramicroscopic secretions, but sometimes an independent oxide mineral phase of it is encountered, in the form of irregular formations fractions of a micron in size. In quartz and flaky layered silicates, uranium usually forms a sparse irregular ultramicroscopic dissemination, sometimes with local clumps. Needle-like layer silicates are more active uranium concentrators. In cases where they come up against apatite crystals the uranium is secreted to about the same extent in both minerals. But if a carbonate mass contains flaky or needle-like silicates, the uranium is concentrated on those.

255 TABLE 6-7 Thorium isotopes in oceanic phosphorites Material

Content ( lo4

"/.I

U

Th

Southwest Africa shelf* Diatomaceous ooze 10.2-54.6 Phosphatized ooze 78.6 Pre-Quaternary concretions 1.7-158 Pre-Quaternary fish bones and teeth 139 Peru-Chile shelf ** Upper Quaternary concretions Fish bones

51-182 101 Submerged Chatham Rise** Miocene concretions 124-241 Blake Plateau** Oligocene concretions 50 California Basin** * Miocene concretions 37-73

1.1-8.1 4 1-1 8 22

Number of samples

Weight ratio U/Th

Activity ratio 230Th/234 U

7-21 78.6

0.04-0.40 0.01

7 1

7-117

1.00-1.09

3

6.6

1.04

1

1.1-9.0 11-70 0.0-0.4 252-300

0.020-0.7 1 0.010-0.020

17 2

1.1-1.3

95-219

1.01

2

4.6

11

0.99

1

4.5-43

1.7-101

0.99-1.25

10

* Veeh et al., 1974. ** Burnett, 1974. *** Kolodny and Kaplan, 1970a. When phosphate, carbonate and silicates occur together in one preparate the form and distribution of the ultramicroscopic uranium secretions may be complex in character. Therefore the relative importance of these components as concentrators of uranium (in cases where its contents are low) may vary considerably in different parts of the rock, but carbonate usually is in last place in this respect (Baturin and Dubinchuk, 1979). THORIUM ISOTOPES

The thorium content of ocean waters is n x lo-"% (Vinogradov, 1967), in pelagic sediments 5-28 x in diatomaceous oozes of the shelf of southwest Africa 1.1-8.1 x and in Recent phosphatized diatomaceous ooze 1 x (Veeh et al., 1974). The Recent and Late Quaternary phosphorites from the shelves of Peru and Chile contain 1.9-9.0 x thorium, pre-Quaternary concretions

256 from various areas 1-43 x and ,fish bones from 0.0 t o 22 x depending on the extent of fossilization (Table 6-7). The U/Th ratio in ocean water is >300, in pelagic sediments 0.1-0.5, in Recent diatomaceous oozes of the shelf of southwest Africa 7-21, in Recent and Late Quaternary phosphorites 11-78, in the Miocene phosphorites of the California basin 1.7-101, in the Miocene phosphorites from the Chatham Rise 95-219, and in fish bones from 6.6 to 300. On the whole the thorium content of oceanic phosphorites is of the same order of magnitude as in the enclosing sediments, but the U/Th ratio is higher than in the sediments but lower than in the ocean water. This indicates that the predominant part of the thorium contained in phosphorites is fixed in inclusions of clastic material. Ionium accumulates in phosphorites mainly due to decay 0f 234U contained in them. In young phosphorites the 230Th/234Uratio is much lower than the equilibrium value (0.020-0.71), in old ones it is at the equilibrium value or higher. Excess ionium can get into pre-Quaternary phosphorite concretions exposed on the eroded bottom surface both from the ionium-rich surface layer of sediments and directly from sea water, due to which the 230Th/234Uratio in some samples of Miocene phosphorites off the coast of California is increased to 1.04-1.25 (Kolodny and Kaplan, 1970a). RARE EARTH ELEMENTS

The content of rare earth elements (REE) in the waters of the World in suspended matter it is 0.001Ocean ranges from n x lo-’ to n x 0.035%,in oceanic biogenic sediments 0.007-0.014%, in red deep-sea clays up to 0.050% (Balashov and Lisitsyn, 1968; Balashov and Khitrov, 1961; Volkov and Fomina, 1967; Goldberg et al., 1963; Piper, 1974; Wildeman and Haskin, 1965). The Recent and Late Quaternary phosphorites from the shelves of southwest Africa and Peru-Chile contain 0.005-0.010% REE , pre-Quaternary phosphorites from various regions 0.010-0.098%, bones of fish and mammals from shelf sediments 0.019-0.021% and from pelagic sediments 0.2220.721%(Baturin et al., 1972a; Blokh and Kochenov, 1964). The composition of REE has been determined in pre-Quaternary oceanic phosphorites which contain at least 0.030%REE, and also in bone phosphate (Table 6-8, Fig. 6-10). The shelf phosphorites are relatively rich in elements of the cerium group and similar in REE composition t o the nodular phosphorites of the Russian platform and t o sedimentary rocks as a whole. The phosphorites from the Mid-Pacific Mountains, on the other hand, are similar to sea water in REE composition. Bone phosphate occupies an intermediate po-

TABLE 6-8 Composition of lanthanoids in phosphorites and the marine environment ZTRIO,

Content (5% of Z T R , 0 3 )

(%)

La

1. Sea water

10-8

2. Mediterranean Sea suspended matter 3. Ocean sediments

0.009

Material

4. California shelf phosphorites 5. Phosphorites of t h e southwest Africa shelf 6 . Blake Plateau phosphoritrs 7. Agulhas Bank phosphorites 8. Phosphorites of Pacific seamounts 9. Bone phosphate from ocean floor 10. Karatau bedded phosphorites 11. Nodular phosphorites, Russian platform 12. Coquina phosphorites of t h e U.S.S.R. 13. Average in sedimentary rocks

Reference

Ce

Pr

Nd

S(La-Nd)

27.4

12.2

6.0

21.6

67.2

4.1

1.0

13.5

33.7

6.7

14.8

68.7

10.0

-

0.0173

18.5

39.2

5.3

21.3

84.3

4.0

1.1

0.0435

19.8

35.8

5.0

19.4

80.0

3.6

0.066

19.3

46.4

3.9

18.2

87.8

3.5

0.040

29.1

25.0

3.5

18.0

75.6

4.6

23

0.030

36.7

38.0

-

18.8

93.5

-

2.6

0.098

28.9

9.1

5.0

23.1

66.1

5.3

1.9

0.356

15.7

28.1

2.6

27.4

73.8

13.4

-

0.080

23.7

21.4

5.2

21.3

77.6

5.0

0.06

19.7

44.7

3.9

20.9

89.2

0.100

15.0

37.1

5.0

16.7

0.024

23.4

36.8

5.8

19.0

Sm

Z(Sm-Ho)

Er

2.0

19.8

5.8

0.7

28.4

1.9

0.7

11.0

2.2

0.3

2.2

-

4.7

3.7

1.0

14.4

2.8

0.4

2.0

0.4

5.6

-

2.4

-

10.8

0.8

-

0.6

-

1.4

5.8

-

3.5

1.2

17.4

3.5

-

3.5

-

7.0

2.6

-

-

-

5.2

1.3

-

-

-

1.3

6.9

0.8

6.2

1.7

22.8

4.1

0.9

5.2

0.9

11.1

3.0

-

5.2

-

21.6

13

0.1

3.2

-

4.6

0.6

6.2

0.6

4.3

0.7

17.4

2.5

0.3

1.7

0.5

5.0

2.8

0.3

2.9

0.3

2.1

0.3

8.7

1.0

09

0.1

0.1

2.1

Baturin e t al., 1972a Baturin e t al.. 1972a Baturin e t al., 1972a Blokh and Kochenov, 1964 Bliskovskiy et al., 1969 eBliskovskiy t al.. 1969

73.8

7.7

0.5

1.5

0.8

4.1

0.5

21.1

2.1

0.3

22

0.5

5.1

Loog, 1968

85.0

4.0

1.0

3.9

0.6

-

0.8

10.3

2.1

0.3

2.0

0.3

4.7

Vinogradov,

Eu

Gd

Tb

Dy

5.8

-

6.9

10.7

-

7.0

4.5

0.7

-

0.8

4.7

0.6

1.2

3.7

Ho

Yb

Lu

X(Et-Lu)

1.2

4.9

1.1

13.0

03

0.8

-

3.0

Tu

Goldherg e t al., 1963 Balashov and Lisitsyn. 1968 Wildeman and Haskin, 1965 Goldberg e t al., 1963 Baturin e t al., 1972a

1 q5fi

258

A

3

8

Fig. 6-10. Relationship of lanthanoids in oceanic phosphorites (Baturin et al., 1972a):

Z = field of phosphorites of the Russian platform; ZZ = field of Karatau phosphorites. For numbers see Table 6-8.

sition and is similar in REE composition to the shell-limestone phosphorites of the northwestern part of the U.S.S.R. This difference apparently is caused by the fact that the composition of the REE in shelf phosphorites is controlled by the composition of the enclosing sediments, which are the direct source of the phosphorus and other elements that take part in the formation of the phosphorite concretions. The low REE content in Recent and Late Quaternary phosphorites can be explained first by their youth, and second by the composition of the enclosing diatomaceous oozes, which are poor in REE. The phosphorites from seamounts, which often are porous phosphatized limestones, have been in contact with sea water for a long geologic time, and this probably has determined the concentration and composition of the REE they contain. The high REE concentration in bones from the pelagic zone of the ocean is explained on the one hand by the spongy structure of bone tissue, and on the other by the duration of their exposure (Miocene/Pliocene) on the bottom surface (Blokh and Kochenov, 1964). In that case the source of the REE, judging from their composition, also is sea water and the en-

259

LO

Sm ELI

Tb

Yb

Lu

Fig. 6-11. Composition of REE in Recent diatomaceous oozes and phosphate concretions from the shelf of Namibia (Tambiyev et al., 1979). Normalized to average composition of REE of platform clays. 1 = diatomaceous ooze; 2 = phosphate concretions; 3 = phosphatized coprolites.

closing red deep-sea clays, rich in REE compared t o other types of ocean sediments. To ascertain the behavior of the REE in the initial and early stages of the process of phosphorite formation, a special investigation was made of a series of 30 samples of Recent and Upper Quaternary phosphorite concretions from the shelves of Namibia and Pem-Chile (Tambiyev et al., 1979). The general chemical composition of these samples is given in Tables 2-7B and 2-22. The total REE content of all the samples studied was less than 0.005% (Table 6-9). In the course of formation of the phosphate concretions on the shelf of Namibia, the concentrations of all the REE are reduced, and only slightly higher in the dense than in the compacted concretions. In phosphatized coprolites the REE content also is much lower than in the enclosing diatomaceous oozes. When the results obtained are normalized to the composition of the REE of platform clays (Balashov, 1976), it is seen that diatomaceous oozes are characterized by a relatively monotonous REE composition with slight enrichment in the light lanthanoids (Fig. 6-11). A t the same time depletion in Eu and La or an excess of Ce is observed in the phosphorites. A typical feature of the behavior of the REE during the formation of phosphate concretions is the preferential removal of the light and intermediate lanthanoids, while the heavy ones are retained in them (Fig. 6-12). The maximum rate of

to r n

0

TABLE 6-9 REE content

in Recent and Late Quaternary shelf phosphorites and in the enclosing sediments (Tamhiyev et al., 1979)

Sample

P 2 0 , (%)

La

Ce

Sm

Eu

Tb

Tm

Yb

Lu

Shelf o f Namibia (stations 2048, 2046) Diatomaceous ooze Phosphatized ooze Concretions: soft unconsolidated compacted granular compacted massive dense gray dense brown Coproli tes : unconsolidated compacted dense gray dense brown insoluble residue

1.33, 0.82 3.7, 4.16 19.0, 29.5, 28.6 29.2, 30.3, 31.9,

23.3 25.7 30.2 31.6 33.9

29.5, 26.8 29.9 30.6, 30.9 31.9, 32.4

10.5, 8.0 6.2, 3.3

23.2,16.0 9.8,10.6

1.4 n.d.

0.27, 0.21 0.03, 0.17

0.13, 0.10 0.03, 0.082

0.48 0.57,0.80

0.056 0.16, 0.059

2.1, 3.0 2.1, 2.6 2.3 2.0, 1.1 0.77,1.9 2.0, 2.2

15.5 9.8 12.2 3.3 4.1 4.1, 5.7

0.65 n.d.

0.048,0.039 0.023,0.013 n.d. 0.017 0.030,0.015 0.034,0.017

0.036 n.d. n.d. 0.053 0.030,0.082 0.027,0.091

0.32,0.23 0.22 0.49 0.18 0.21 0.18,0.25

0.038 0.087 0.059 0.033 0.047,0.039 0.044,0.039

0.051 0.038 0.053 0.026 2.21

0.15 n.d. 0.37 0.32 14

1.4 1.1 1.7, 1.5 1.0, 1.1 162

-

-

n.d. n.d. n.d.

0.053 0.054 0.040 0.065,0.037 1.9

-

0.010 n.d. 0.021 0.035 2.6

Concretions (average)

-

2.1

9.1

0.6

0.026

0.053

0.26

0.043

Coprolites (average)

-

1.3

4.9

0.23

0.022

0.042

0.28

0.050

17.1

35.8

4.0

0.91

0.29

1.6

0.37

12.8 11.1 9.4 21.3

27.7 22.0 19.5 39.1

2.4 n.d. 1.6 3.4

0.66 0.52 0.42 0.95

0.21 0.23 0.18 0.33

0.42 0.83 0.78 1.7

0.16 0.18 0.21 0.40

-

-

4.1 5.7 269

0.26 0.10 n.d. 0.34

S h e l f o f Chile (station 250) Terrigenousdiatomaceous oozes Concretions: unconsolidated compacted dense insoluble residue

0.72 16.9 21.7 28.4 -

Shelf o f P e r u (stations 546,553) Concretions : unconsolidated compacted dense

11.1 18.0 19.4

Average of Chile-Peru shelf phosphorites Andesite basalts of southern Peru* Platform clays** ~~

* Dostal et al., 1977.

** Balashov, 1976.

-

14.5 13.6 14.5

21.2 29.3 21.2

2.7 1.8 2.3

0.48 0.49 0.74

0.22 0.20 0.29

0.14 0.37 0.19

0.66 0.61 1.30

0.14 0.19 0.24

12.7

23.5

2.2

0.55

0.22

0.17

0.77

0.19

35 35.5

72 67

6.0 6.7

1.46 1.24

0.68 1.0

-

2.30 2.95

0.34 0.45

0.45

262 2 /

/

,

/

,,*'4+5

*

., 0.05Ll I La Ce

I

Eu

Tb

I

)

Yb Lu

Fig. 6-12. Behavior of REE during lithification of phosphate concretions on the shelf of Namibia (average of two stations; Tambiyev et al., 1979). Normalized to average composition of REE in enclosing diatomaceous ooze. 1 = diatomaceous ooze; 2 = phosphatized ooze; 3 to 8 = concretions ( 3 = soft, 4 = unconsolidated, 5 = compacted granular, 6 = compacted massive, 7 = dense gray, 8 = dense brown).

removal is observed for Eu and probably for La. In the initial stage of formation of phosphate concretions there is a brief increase in the contents of heavy REE as compared t o the diatomaceous oozes (Fig. 6-12). The lanthanoids behave similarly in the phosphatization of coprolites. * The REE content in Late Quaternary phosphorites from the shelves of Chile and Peru also is lower than in the enclosing sediments (Table 6-9), but substantially higher than in Holocene phosphorite concretions from the shelf of Namibia. The spectra of distribution of REE in the phosphorites from the shelves of Chile and Peru are identical (Fig. 6-13)and are characterized by a Eu maximum. When these concretions are lithified the concentrations of the light and intermediate REE decrease and simultaneously the contents of the heavy REE increase. The process of formation of Recent phosphorite concretions is accompanied by self-purification of the phosphate, which is manifested in a decrease in the concentration of biogenic (organic matter, amorphous silica) and clastic impurities in them (Baturin, 1969, 1974b). Therefore the observed decrease in REE contents can be explained by the fact that it is to those components, i.e. diatom remains and detrital minerals, that they are mainly related. In

263

i

0.5

0.3

\\

5

M I

0.2

_J

La

Ce

Sm Eu

Tb

Tm

Yb

Lu

Fig. 6-13. Composition of REE in andesites and andesite basalts of southern Peru (Dostal et al., 1977), Recent sediments of the Chile-Peru shelf (average of two stations) and phosphorite concretions from the shelf of Chile (station 250; Tambiyev et al., 1979). Normalized t o the REE composition of platform clays. I = andesites and andesite basalts; 2 = sediments, 3 = unconsolidated concretions; 4 = compacted concretions; 5 = dense concretions.

fact, the calcined insoluble (in 1.7%HC1) residue of a dense coprolite consisting of clastic material and ash of organic matter, is sharply enriched in the lanthanoids (Table 6-9). Constituting only 0.5% by weight of the original sample, it contains from 22 t o 75%of the total amount of REE. The clastic impurities in the phosphorites from the shelf of Namibia are quartz, feldspars, pyroxenes and hornblendes (Baturin e t al., 1970), i.e. minerals which do not accumulate REE (Balashov, 1976). The opal of diatom valves likewise does not concentrate trace elements (Arrhenius e t al., 1957). Therefore i t is logical to assume that most of the REE in these phosphorites is related to organic matter, which is capable of concentrating a wide range of rare and disseminated elements. It is possible that this concentration begins during the lifetime of diatomaceous phytoplankton (Volkov and Fomina, 1967), inasmuch as diatomaceous ooze is enriched in the light lanthanoids [the La/Yb ratio in rocks is 5.3, in soils 6.0, and in algae 29 (Cowgill, 1973)l. The organic matter of diatoms decomposing in the sediments additionally extracts REE from the interstitial waters, which continues during the formation of phosphate gels. Their organic matter content is almost the same as that of the enclosing oozes, but the extent of its mineralization, and the sorption capacity related to that, are appreciably higher (Romankevich and Baturin, 1972). Apparently this circumstance explains the relative increase

264 in the contents of the heavy REE in the concretions being formed, as those are stronger complex-formers than the light REE and have a greater tendency toward sorption. Upon further lithification of the concretions, the organic matter included in them undergoes more thorough decay and loss, removing the REE. In conjunction with this, the composition of the REE additionally becomes relatively heavy and there is preferential removal of Eu and La (with inhibited removal of Ce). In the highly reducing environment (Eh up to -330mV) typical of the environment of formation of the Recent phosphate concretions on the shelf of Namibia, reduction of Eu to the divalent state, its conversion t o the soluble cation group and its removal from the concretions are possible, t o which its depletion might be related. After the phosphate concretions are transformed into dense nodules the redistribution and removal of matter from them cease and apparently the process of sorption of trace elements from the interstitial waters begins to predominate, which marks a new stage in the geochemical fate of the REE not already bound in organic matter. As a result there is an increase in the content of all the REE in dense concretions compared to compacted ones. In the Late Quaternary phosphorites of the shelf of Chile-Peru the geochemistry of the REE is essentially different. Here identical spectra of the REE in the phosphorites and in the enclosing sediments are observed, which is related to the higher content of clastic impurities in the former (up to 40-60%). With Eh values up t o -100 mV, which are insufficient for the reduction of Eu3+,that element is not separated from the other REE. The observed maximum apparently is related to the fact that andesitic volcanism, the products of which are characterized by a high Eu content (Dostal e t al., 1977), is developed in this region (Gerth, 1959). During the lithification of the Late Quaternary phosphorites from the shelves of Chile and Peru the removal of light and intermediate lanthanoids is accompanied by an accumulation of the heavy ones (Fig. 6-13), the same as on the shelf of Namibia. The content of intermediate T b hardly changes. The intensity of removal of the light and intermediate REE is the same; likewise the character of the distribution of the REE in the enclosing sediments and phosphorites is the same. This is evidence of the clastic nature of the main part of the light and intermediate REE in these phosphorites, as is confirmed by analysis of the calcined residue (insoluble in 1.7% HCl) of unconsolidated and compacted concretions (Table 6-9). Amounting to 23% by weight in the original sample, the residue contains 40-6076 of the total amount of REE in them. A comparison of the balances of the distribution of REE in the Recent phosphorites on the shelf of Namibia and of the Late Quaternary phosphorites on the shelves of Chile and Peru shows that the specific concentration of

26 5 lanthanoids in the phosphate of the latter is several times higher than in the former. Thus Recent phosphorites as a whole, and especially their phosphatic matter, are depleted in REE compared to the enclosing sediments due to the strong competition of the organic matter of these sediments. In the Late Quaternary phosphorites the Clarke contents of the REE are regenerated, phosphate taking an active part. But in fact high REE contents are typical only of old phosphorites (Bliskovskiy et al., 1969). Consequently the geochemical history of the REE in phosphorites consists of several stages, and their effective concentration does not begin until the stage of late diagenesis and continues mainly in epigenesis.

IRON

The iron oxide content of oceanic phosphorites ranges from 0.1-0.6% in Recent phosphorite concretions from the shelf of southwest Africa to 50% in the ferruginous phosphatized limestones from Agulhas Bank. Most of the iron oxide is fixed in goethite, less in glauconite. Ferrous iron is present in oceanic phosphorites in amounts of 0.05-1.43%, and is fixed chiefly in pyrite. The paragenetic association of phosphate with pyrite and less often with glauconite, which forms under less reducing conditions, is characteristic of the diagenetic reducing stage of Recent phosphorite formation. The abundance of ferrous iron in some pre-Quaternary oceanic phosphorites is due to secondary ferruginization (formation of iron-manganese crusts, impregnation of phosphate with iron hydroxides from the periphery of the concretions toward the center; Bezrukov et al., 1969; Heezen et al., 1973; Pratt and Manheim, 1967; Tooms et al., 1969). But when a phosphate-goethite cement is present in phosphorites (Parker, 1971, 1975; Parker and Siesser, 1972) its formation evidently is related to joint diagenetic migration of iron and phosphorus and their subsequent deposition when reducing conditions are succeeded by oxidizing, as has repeatedly been observed in Recent sediments (Volkov and Sevast’yanov, 1968; Bonatti et al., 1971). Thus the initial stage of phosphorite formation is always accompanied by disseminated pyritization. In ocean shelf phosphorites pyrite is found practically universally. In Holocene phosphorite concretions it impregnates diatom valves, clumps into microglobules, and forms irregular secretions. Under the electron and scanning microscope it is seen that as a rule the pyrite is crystallized. The crystals are mainly octahedral and cuboctahedral but sometimes, when diatom valves are pyritized, they may take on a hexagonal habit corresponding t o the shape of the alveoli perforating the valves.

266 Usually the crystals are grouped into globular aggregates (Fig. 6-14), less often they form random accumulations. In cases where a reducing environment of initial phosphorite formation is succeeded by an oxidizing environment, the pyrite decomposes and is dissolved, which is expressed in disintegration of globules, blurring and loss of crystal form. In the lithification of Recent phosphorite concretions pyrite, along with detrital material, is expelled from them in the course of self-purging of the phosphate, which is manifested in a decrease in the concentration of total iron (see Table 6-11). RARE AND DISSEMINATED ELEMENTS

Many rare and disseminated elements have been found in oceanic phos-

26 7

Fig. 6-14. Globular aggregate of pyrite in Holocene (a) and Miocene (b) concretions from the shelf of Namibia; x 40,000 (a) and X 27,000 (b) (Baturin and Dubinchuk, 1979).

phorites. In shelf phosphorites the content of most of them often is at the limit of sensitivity of the spectral methods of determination that are used. In this connection, a t the present time only far-from-complete data can be given on the behavior of Sr, Cr, V, Ni, Co, Mo, Pb, Zn, Cu, and As in the process of phosphorite formation (Table 6-10). When data on the shelf of southwest Africa are examined it is ascertained that during their formation the Holocene phosphorite concretions are substantially depleted, compared to the enclosing sediments, in all these disseminated metals, except strontium - in chromium (from 60-140 to 3-14 x vanadium (from 30-360 t o 20 x loT4%),nickel (from 5-150 t o 2-14 x cobalt (from 10-14 to 5 x molybdenum (from 1 0 - 6 0 t o 1-3 x lead (from 1 - 6 t o 1 x zinc (from 2-70 t o 1-2 x and copper (from 5-38 t o 2-5 x lo4%). The behaviour of As is variable: in unconsolidated concretions its content is lower than in the

TABLE 6-10 Rare and disseminated elements in oceanic phosphorites* (in

Shelf o f southwest Africa Recent diatomaceous oozes Phosphatized diatomaceous ooze

Unconsolidated concretion Compacted concretion Dense concretion Phosphorite block (pre-Quaternary) Unconsolidated coprolite Dense coprolite

Chile shelf Unconsolidated concretion Compacted concretion Dense concretion Platy dense concretion Dense phosphatized coprolite

0.2-1

unless otherwise indicated)

4.5-9.3

0.002FO.01

60-140

8.52 23.85 27.70 32.74 21.27

3.59 1.27 1.03 0.92 0.75

0.08

47 16 14 3 30

100 34 20 20 21

24 16 14 2

15 15 5

1

1 1 1

15

10

18

1

25.85 29.72

3.72 0.88

3

30

12 33

2 6

5 14

2 2

1 1

15.7 20.64 25.62 26.45

0.65 0.60 -

30 30 40 200

40 40 50 30

20 30 20 30

1 1

100 20 30 20

1

0.20 0.24 0.24 0.16 0.13

0.18 0.1

0.3 0.4 0.4

30-360

5-150

10-14

1040

31 15 3

11

-

5 4

2-70

4-6 21

5-38

1

9 8

2 2

5

-

tr. v

6-14 3 6 3 10 26 9 11

6

1

4

9

20

60

50 40 40 50

-

1

200

40

-

10

10

30.67

1.39

0.5

100

10

20

Blake Plateau Concretion

20.26

0.41

0.11

100

42

30

20

4

11

3

3

15

Morocco shelf Phosphorite conglomerate

18.88

0.52

0.12

46

37

6

15

1

8

6

1

15

19.11

0.38

0.12

49

58

100

50

10

66

3

10

29

31.12

5.41-10.12

0.02-0.18

1

1

1

1

1

18-34

upto 1

4-10

18.51-27.29

3.92-6.54

0.17FO.20

1

1

1

1-3

4-10

4-10

28.61-31.64

0.44-3 03

0 . 1 3 4 22

1-19

1-9

1-48

1-36

4-43

3-120

4-79

10-40

9-15

Agulhos Bonk Phosphorite nodule Bone phosphate: bones and teeth of living fish. whales unfossilized bonen from shelves fossilized bones from shelves bones from pelagic sediments

* According to Baturin and

19.50-34.58

<1

0.10--0.32

10

3440 4 4 8

Bliskovskiy, 1974;Baturin and Petelin, 1972. Baturin et al.. 1970.

upto 1

up t o 10

1-3

u p t o 52

1-47

upto28

14-18

8-320

3-220

2-13

TABLE 6-11 Content o f P,O, (%), Fe (W),rare anddisseminated elements Oreshkin. 1977,with additions)'

in Recent phosphorite concretionsfrom the shelf of Namibia (according t o Baturin. 1974b.Tambiyev, 1978. 1979a.b.

Material

P10,

Fe

Mn

Sr

Ba

Ti

V

Co

cu

SC

Zn

Diatomaceous ooze

1.12

0.66

40

90-140 (110)

160-240 (190)

400

100-160 (124)

2.7-3.2 (2.9)

9.9-13 (11.6)

2.5-3.3 (3.0)

<20

< 10

>25

Phosphatized ooze

6.33

0.60

30

300-800 (550)

260-360 (310)

200-300 (250)

137-311 (206)

2.0-2.8 (2.4)

30-54.3 (40.4)

2.1-4.1 (3.2)

<20

< 10

>20

Concretions: soft

1200-2100 (1500) 2100-2600 (2300) 3100 2400-2900 (2700) 2700

540-2760 (960) 110-1910 (1300) 3190 130-200 (160) 230-979 (700)

65-167 (103) 12-105 (45) 10 12-16 (15) 20-40 (30) 12-27

9.2-11.4

2500-3100 (2700)

100-200 (130) 20-100 (50) 40 20-30 (23) 3040 (40) 40-0

26-43 (32) 20 16-21 (19) 23-30 (26) 25-28

(50)

(20)

(27)

10-16 (12)

0.13+.20 (0.15) 0.20--0.30 (0.25)

5.1-8.9 (6.5) 3.0 2.4-3.6 (3.0) 2.4-3.0 (2.7) 2.2-2.7 (2.5)

0.77-1.2 22 (0.96) 0.144.79 32 (0.40) <20 0.10 0.094.17 89 (0.13) 0 1 1 4 . 3 0 65 (0.20) 0.244.27 48 (0.25)

1900-2400 (2200) 2300-2700 (2400) 2600

100-150 (120) 130

10-40

7-10 (9) 10-12 (11) 12-18 (15) 27-35 (311

10-18 (13) 20-24

9-12 (11) 10

0.14-0.17 (0.15) 0.10-0.15 (0.12) 0.124.20 (0.16) 0.204.30 (0.23)

7 8-49.8 (14.9) 3.3-4.5 (3.9) 1.8-2.7 (2.4) 2.3-3.0 (2.6)

0.104.16 (0.13) 0.13-0.15 (0.14) 0.124.19 (0.16) 0.184.31 (0.23)

22.0

0.26

30

unconsolidated

27.49

0.18

10

compacted granular compacted massive

30.24

30.0

0.11 0.11

15 20

dense gray

30.74

0.10

10

dense brown

31.66

0.09 < 10

Coprolites: unconsolidated

27.98

0.07

20

compacted

30.0

0.10

40

dense gray

30.54

0.08 < 10

dense brown

30.69

0.08

* Figures in parentheses represent averages.

15

,

2200-3100 (2700)

150-280 (2201

(20)

20-30 (25)

140-510 (320) 620-3200 (1720)

4040 (50) 40-50 (43)

Cr

36-73 (52)

Ni

23-35 (30) 10-2 1 (15) 10 10

10

(22)

17-24

10

(20)

20-26 (23)

10

0.68-1.1 (0.85) 0.194.47 (0.33) 0.25 0.18--0.21 (0.20)

(10.2)

As

10 12

Cd

7.9-9.1 (9.3) 5.2-6.0 (5.6)

30 35 25

4.2 3.0-3.5 (3.3) 2.2-2.7 (2.5)

20

1.6-2.5 (2.1)

233

30

113

17

66

17

69

16

5.7-10.0 (8.0)

3.6-4.6 (4.1) 2.2-4.4 (3.2)

2.2-2.6 (2.4)

270 enclosing oozes, and in lithified concretions it increases t o the same level (10 x In contrast to the concretions, as coprolites are lithified the content of Cr, V, Ni, Co, and Cu increases. In the Upper Quaternary concretions from the shelf of Chile the content of disseminated elements, except molybdenum, is much higher than in the concretions from the shelf of southwest Africa. Pre-Quaternary concretions from other shelf areas are relatively rich in Cr, V, Ni, Pb, As, and some also in Co, Mo, and Cu. The content of disseminated elements in phosphorites is determined by several factors, the most important of which, besides the physicochemical environment, are: the crystallochemical properties of phosphate, sorption processes, composition of non-phosphatic impurities. The crystallochemical properties of phosphate encourage isomorphic substitution of several elements for calcium in the apatite lattice, in particular rare earths and uranium. The behavior of strontium is similar; its isomorphism with respect t o calcium, with similar thermodynamic properties, is governed by the ratio of concentrations of Ca2+and Sr2+ions in the environment (Bliskovskiy, 1969). If there are not enough ions of calcium it apparently can be replaced by manganese (Deer e t al., 1962), nickel, cobalt, and copper (Cruft, 1966). It is possible that vanadium and molybdenum can replace the PO:- ion, in the form of vanadates and molybdatks (Bliskovskiy, 1969; McConnell, 1973), but such substitution takes place in the oxidizing environment of the supergene zone rather than in the hydrogen sulfide environment in which authigenic phosphorite concretions are formed. The possibility of sorption of a number of disseminated elements (Cu, Zn, Pb) by phosphate in the marine environment has been verified experimentally (Krauskopf, 1963). Evidently sorption is promoted by higher contents of disseminated elements (Co, Cu, Zn, Ni, Mo) in the interstitial waters of sediments of the biologically productive zones, relative to sea water (Yemel’ yanov e t al., 1974; Pilipchuk, 1971; Brook e t al., 1968). In the interstitial waters of hydrogen sulfide sediments, rare metals occur chiefly in the form of complexes the structure of which has not yet been clarified (Presley et al., 1972). A non-phosphatic authigenic component of phosphorites which is active in geochemical respects is organic matter, genetically related to phosphorus in the enclosing sediments. Experimental data show that organic matter takes up V, Ni, Co, and Mo from sea water (Krauskopf, 1963). Diatomaceous oozes of the shelf of southwest Africa in which Recent phosphorite concretions are forming contain up to 10-25% Corg and are rich in V, Ni, Cu, Zn, and M o (Baturin e t al., 1970; Yemel’yanov, 1973b; Calvert and Price, 1970, 1971a), and the organic fraction of black marine shales, which can be considered the fossil analogs of

271

Recent sediments of the biologically productive zones, are also enriched in Co, Ag, and Sn (Degens et al., 1957). Data on the Holocene phosphorite concretions on the shelf of southwest Africa show that as they are lithified and phosphatized, there is a simultaneous decrease in the C, content on the one hand, and of V, Ni, Cu, and Mo on the other. This fact and the relationship of these elements t o C, in the enclosing sediments show that in the phosphorites also they are bound up with organic material to a certain extent. It is significant that in the Permian phosphorites of the Phosphoria Formation a direct correlation has also been established between V, Ni, Cu, Zn, Ag, and Mo and organic matter (Gulbrandsen, 1966). In the marine environment the concentrators of chalcophile and siderophile elements are sulfides and oxides of iron and manganese. Pyrite contained in phosphorites on land is rich in Cu, Zn, Mo, Pb, and Ag (Bliskovskiy, 1969). Iron-manganese concretions and crusts concentrate Ni, Co, Cu, Zn, Mo, and Pb (Strakhov et al., 1968). In the phosphorite concretions on the ocean shelves which are forming in a reducing environment, pyrite is a minor but constant constituent. Pre-Quaternary phosphorites exposed on the surface of the bottom, which occur in an oxidizing environment, are often covered with films or crusts of iron hydroxides or contain a goethite cement t o which some of these trace elements are related. The amount and composition of clastic components in phosphorites varies greatly; in the phosphorite concretions from the shelf of southwest Africa their content is not more than a few percent (mainly quartz and feldspar), but in concretions from the shelf of Chile there is up to 5 0 4 0 % (feldspar, quartz, magnetite, titanomagnetite, hornblende, etc.). Apparently the relative enrichment of the phosphorites from the Chile shelf in a number of elements (Cr, V, Pb, Cu) is in part caused by precisely this factor. A special detailed investigation of a complete series of Recent phosphorite concretions from the shelf of Namibia, carried out by the author in cooperation with S.B. Tambiyev and V.N. Oreshkin, made it possible to bring out some new features in the geochemistry of the rare and disseminated elements (Table 6-11). The analyses were made using improved methods of quantitative spectral analysis (Sr, Ba, V, Ni, Cu, Zn, As), and also by means of X-ray fluorescence (Fe, Mn, Ti), instrumental neutron activation (Sc), and atomic absorption (Cd). According to the revised data, the strontium content in the diatomaceous oozes of the shelf of Namibia (based on 1 9 samples) averages 0.016*0.014%, lower than its average content in sedimentary rocks, which according to Vinogradov (1962) is 0.045%.

272 As the phosphorite concretions produced in these oozes are formed and lithified their strontium content increases - at first t o 0.05k 0.0376, and then gradually to 0.28k 0.03%. An analogous phenomenon takes place in the formation of phosphorite on the Peru-Chile shelf: in the enclosing sediments the strontium content is 0.021 k 0.00696, in unconsolidated phosphorite concretions 0.13k 0.02%, and in dense concretions 0.01k 0.02% (Tambiyev, 1979a). It is known that due to its crystallochemical properties Sr2+isomorphously replaces Ca2+ in the structure of calcium minerals, including phosphates (Bliskovskiy et al., 1967, McConnell, 1973). During the formation of shelf phosphorites, strontium dissolved in the interstitial waters (in a concentration of 7-10 mg/l) probably is precipitated with the phosphate and then replaces the calcium in it. The Sr/Ca ratio in the phosphorites of the shelf of Namibia and in the phosphorites of the shelves of Peru and Chile is 0.77k0.11 x In the phosphorites of both regions a clear-cut Sr-P205 0.68k0.01 x correlation is observed, with a correlation coefficient of 0.82 and Sr/P2O5 ratio = 0.8k0.13. In phosphorites from seamounts and in bone phosphate from the ocean floor the strontium content is 1.5-2 times lower, and the Sr/P2O5 ratios are 0.50k 0.16 and 0.47 k 0.16, respectively (Tambiyev, 1979a). The barium content varies unevenly during the formation of Recent phosphorites, sometimes increasing, sometimes decreasing. In the enclosing diatomaceous oozes it is 0.020+ 0.004%; when the oozes are phosphatized it increases t o 0.031+0.005%, and later, in soft phosphorite concretions, to 0.054k 0.276%. After that, in unconsolidated, compacted and dense concretions, it changes in a zigzag fashion. At the same time, in the phosphatization of coprolites the barium content increases continuously, from 0.010 k'0.015 t o 0.062-0.32% (Table 6-11). In the sediments of the Peru-Chile shelf the barium content averages 0.022+ 0.010%, and in the phosphorite concretions 0.017k0.00196. In phosphorites from seamounts the barium concentration varies within extremely wide limits, from 0.005 to 1%,which is related t o the presence or absence of barite inclusions. In bone phosphate from the ocean floor the barium content is 0.010+ 0.009% (Tambiyev, 1979a). Thus despite the close similarity of the chemical properties of strontium and barium, they behave differently in the course of phosphorite formation. The strontium concentration is clearly controlled by its isomorphism with respect to calcium, and the barium concentration by a wide range of processes proceeding in different directions: accumulation in organic matter (Goldberg and Arrhenius, 1958),adsorption, coprecipitation with phosphate gels, formation of finely dispersed barite, and self-purging of the phosphate. The elements o f the iron family (Fe, Mn, Ti, V, Cr, Ni, Co, Cu, Sc) have

+

273 similar geochemical features, but they become separated during phosphorite formation. In the transition from diatomaceous ooze to phosphatized ooze the Cu, V, Ni and Cr contents increase, those of the other elements remain at the same level (Fe, Sc, Co) or decrease (Ti, Mn). With further lithification there is a decrease in the content of all the enumerated elements to a minimum in the compacted concretions, but in the dense ones their content again increases (except for copper). When coprolites are phosphatized the concentration of the elements of the iron family (except Cu, Ni and Mn) increases from unconsolidated to dense samples, but remains lower than in the enclosing diatomaceous oozes. At the same time the copper content decreases, that of nickel remains at the original level, and manganese decreases unsystematically (Table 6-11). In diatomaceous oozes and in the concretions considered, most of the elements of the iron family are related t o organic matter and clastic material. This is indicated by their high content in the insoluble residue obtained by boiling an average sample of a concretion in 1.7% HC1: Element

Fe

Content in average sample of concretions (76)

0.064

Content in insoluble residue (%)

6.6

co

sc

0.5 x 14

x

0.25 x 35

x

The increase in concentrations of Cu, V, Ni, and Cr in phosphatized clots of mud compared to the enclosing sediment is apparently related to the fact that when the organic matter contained in these clots decays, its ability to bind metals increases (Stevenson and Goh, 1971). Later, when the organic matter is expelled as the concretions are lithified, the content of these elements drops. I t also is possible that these metals are coprecipitated with phosphatic gels and then expelled from them during the crystallization of gels. In addition, some of these metals (Cu, Ni, Cr, Co) are related to iron sulfides impregnating the phosphatic material, but also are expelled from it during crystallization and self-purging of the phosphate, as is indicated by the drop in the total iron concentration (Table 6-11). In particular, the decrease in the concentrations of silica and aluminum in the central parts of dense concretions compared to their periphery, which has been established using laser emission microanalysis (Tambiyev and Zharikova, 1979), is evidence of the process of self-purging of the phosphate of clastic and other non-phosphatic impurities. In the final stage of formation of the concretions, in their densest varieties,

274

.-.a -3 -4

t-t

5

-6

1

0.03

I

Cu

Ni

V

Cr

Sc

Fe

Co

TI

29

28

23

24

21

26

27

22

Fig. 6-15. Behavior of elements of the iron family in the course of Recent oceanic phosphorite formation (after data of Tambiyev and Baturin, see Table 6-11). Content of elements normalized to enclosing diatomaceous oozes. (a) Concretion formation: 1 = diatomaceous ooze; 2 = phosphatized ooze; 3 = soft concretions; 4 = unconsolidated concretions; 5 = compacted concretions; 6 = dense concretions. (b) Lithification of phosphatized coprolites: 1 = unconsolidated coprolites; 2 = compacted coprolites; 3, 4 = dense coprolites.

the contents of most of the elements of the iron family increase somewhat, which possibly is related to their adsorption on the surface of the concretions, on which a film of condensed organic matter is formed (Baturin et al., 1970). Phosphatization of coprolites is accompanied by an increase in the concentration of most of the elements in question (Table 6-11), which apparently is related mainly to sorption processes and is promoted by the aggregate structure of the coprolites (looseness, porosity, water content). To compare the relative intensity of removal and redistribution of the elements of the iron family in phosphorites, their metal contents were normalized to diatomaceous ooze and plotted on a graph in the order of decreasing normalized concentrations in phosphatized ooze (except for manganese, in view of the low sensitivity of the method of determination). The graph (Fig. 6-15) shows that the elements with odd numbers in Mendeleyev’s periodic

275

system are removed more intensively than those with even numbers. Among the latter, chromium and nickel are most mobile. This phenomenon is probably explained by the particulars of the structure of the outer electron shells of the even- and odd-numbered elements, which is reflected in their ability to form mobile and stable organic complexes, to one extent o r other, and to be sorbed on organic matter and phosphate. Similarly, several physicochemical properties of the REE definitely depend on their atomic number, in particular, the even-numbered REE are more intensively sorbed by clay minerals than the uneven-numbered (Hesford e t al., 1959; Carnal1 et al., 1968). Zinc and arsenic, migrating together in the supergene zone and taking part in the metabolism of marine organisms, evidently reach the floor of the shelf of Namibia in the composition of diatom remains (Calvert and Price, 1970; Pilipchuk, 1974). According t o Tambiyev’s (1979b) data, when the oozes are phosphatized the zinc and arsenic contents remain a t the level of 20 x and 10 x respectively; they increase t o 89 x (Zn) and 31 x (As) in compacted concretions, and again decrease t o 48 x (Zn) and 17 x (As) in dense concretions. When coprolites are phosphatized their zinc content decreases from 250k100 t o 70k30 x and arsenic from 30 t o 16 x (Table 6-11). Thus the behavior of zinc and arsenic during Recent phosphoritization on the shelf of Namibia is the same, in general features. In the reducing environment typical of the diatomaceous oozes of the shelf of Namibia, zinc and arsenic liberated from organic matter occur in the form of easily soluble complexes: Zn(HS):, Zn(HS); and H3 A s 0 3 , as can be judged from theoretical and experimental data (Bezborodov and Zhorov, 1977; Sergeyeva et al., 1971). In the formation of phosphate concretions these elements probably are precipitated in the form of sulfides and enter into the composition of pyrite, and later are expelled from the crystallizing phosphatic matter, also in the composition of pyrite. It is also possible that in part these elements form an independent sulfide phase, inasmuch as according t o the data of laser emission microanalysis the maximum concentration of zinc is observed in the central parts of dense concretions, whereas iron is distributed relatively evenly in them (Tambiyev and Zharikova, 1979). Cadmium is one of the elements which are very mobile in the supergene zone. The marine geochemistry of cadmium is controlled by its relationship to organic matter and by coprecipitation processes (Oreshkin, 1977; Bostrom and Peterson, 1966). In the diatomaceous oozes of the shelf of Namibia the cadmium concentration is more than 25 x i.e. an order of magnitude higher than its

276 average concentration in the earth’s crust according to Vinogradov (1956). As phosphorite formation progresses the cadmium content gradually decreases t o 2-3 x %. The same thing occurs in the phosphatization of coprolites, in which the cadmium content decreases from 8 t o 2.4 x l o 4 %, on the average (Table 6-11). Earlier it was suggested that in sediments rich in calcium the latter can be replaced by cadmium due t o the similarity of their ionic radii (Goldschmidt, 1954). But that process plays no part in this case, inasmuch as Ca increases but Cd decreases as lithification progresses. It also is known that in a hydrogen-sulfide reducing environment cadmium forms difficultly soluble sulfides, which may be the reason for its concentration under natural conditions (Krauskopf, 1956). But in the formation of phosphate concretions the sulfide-sulfur content is reduced only by half (Table 2-7A), but that of cadmium by 10-15 times; thus that process likewise is not decisive in this case. Cadmium shows a definite correlation only with respect to organic matter, and quite clearly with respect t o its individual components. Passing from diatomaceous ooze t o lithified phosphorite concretions, the average C, content decreases by 5 times, that of nitrogenous substances by 6-7 times, that of carbohydrates by 14 times, and that of free lipids by 12 times but that of bound lipids by only 2-3 times (Romankevich and Baturin, 1972). Thus the dynamics of the variation of cadmium concentration during the formation and lithification of Recent phosphorite concretions is identical t o that which has been established with respect t o carbohydrates and free lipids. Probably it is these components of organic matter which are the main carriers of cadmium in phosphorites. When organic matter decays the metallo-organic complexes decompose, and cadmium is liberated and returned from the phosphate concretions t o the enclosing sediments and interstitial waters. In bone phosphate, which is a component part of oceanic phosphorites, the behavior of the rare and disseminated elements is similar to their behavior in phosphorite concretions (Baturin and Bliskovskiy, 1974). In the bones of living organisms the content of most of the elements under consideration is less than 1 x Exceptions are Sr (0.02-0.18%),As (4-10 x and Zn (18-34 x Strontium enters into the composition of bone phosphate along with calcium. Zinc evidently fulfills a biologic function in living matter; in particular, living plankton accumulates zinc from sea water selectively with respect to other disseminated elements (Presley et al., 1972). In bones of fish and mammals from shelf sediments the rare element content is higher but varies within one or two orders of magnitude; very high concentrations have been established in fossilized bones. The same picture is observed in bones from the pelagic zone of the ocean, but with greater amplitude of variations of the trace element content; the

277 maximum ocean floor concentrations of Ni, Co, Pb, Zn and Cu in bones have been established in this zone. The mechanism of concentration of rare and disseminated elements in bones, as in phosphorites as a whole, is related to their entry into the crystal lattice of apatite-like minerals, to sorption (by phosphate and organic matter), and to contamination by non-phosphatic impurities, primarily material of the enclosing sediments and iron and manganese hydroxides. The last pertains mainly to bones from the pelagic zone, with an assemblage of trace elements typical of iron-manganese nodules. It is presumed that solution of bone phosphate on the bottom in the pelagic zone of the ocean stimulates their chemical sorption of disseminated elements, with the formation of compounds less soluble than calcium phosphate (Blokh and Kochenov, 1964).

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Chapter 7

ON THE SIMILARITY OF THE PROCESSES OF RECENT AND PRE-QUATERNARY PHOSPHORITE FORMATION Phosphorites on the ocean shelves are relatively widespread formations, but they are mainly localized in a few regions with special oceanographic conditions, the most important of which is the presence of longshore currents and upwelling, and high biological productivity related to this. The phosphorites consist of grains, concretions, sheets, blocks, bones, phosphatized coprolites, made up of minerals of the apatite group, and also of various rocks and sediments of different degrees of phosphatization with a P 2 0 5 content from a few percent to 20-3375,. The age of most phosphorites on the ocean shelves is Neogene, less often Paleogene and Late Cretaceous. Recent and Upper Quaternary phosphorites have been definitely established only in two regions - on the shelves of southwest Africa and Peru-Chile, where phosphorite formation is genetically related to biogenic accumulation of silica, and to a lesser extent to accumulation of carbonate. Late Quaternary phosphorite formation is the sum of repeated cycles, each of which includes five succesive stages: (1) supply of phosphorus by upwelling; (2) its consumption by organisms; (3) deposition on the bottom as part of biogenic detritus; (4) diagenetic formation of phosphate concretions; and (5) reworking of phosphate-bearing sediments and residual concentration of phosphatic material. The present-day phosphate-bearing shelves differ in morphology, and form part of platform (southwest Africa) and geosynclinal regions (Peru-Chile). Recent phosphorite formation is controlled by a combination of facies conditions related t o upwelling, rather than by the tectonic position of the region. The role of aridity of the climate in Recent phosphorite formation is secondary and consists mainly of suppression of continental runoff as a source of elastic material that would dilute the phosphorite. Is the scheme of Recent phosphorite formation a special one, characteristic exclusively of the present stage, or is it also applicable to pre-Quaternary phosphorite formation on the ocean shelves? Apparently the latter is correct, inasmuch as the pre-Quaternary phosphorites on the ocean shelves, like the Upper Quaternary ones, occur in zones of upwelling; but Recent sedimentation and phosphate accumulation in these zones is limited or absent due to strong bottom currents which prevent deposition of phosphorus-rich biogenic detritus. Features of similarity of their morphology, structure, composition and examples of their joint occurrence in several

280 regions also are evidence of the genetic affinity of Recent and pre-Quaternary phosphorites. Also indicative are the features of geochemical similarity of Recent and ancient phosphorites - the common regularities of the behavior of their macro- and microcomponents, such as organic matter, pyrite, uranium, and the rare earth, rare and disseminated elements. Pre-Quaternary phosphorite formation on the ocean shelves took place under the influence of the same combination of factors as Recent with variations in the morphology, structure, and tectonic position of the shelf, and also in the climate and relief of the adjacent land. The main difference between pre-Quaternary and Recent oceanic phosphorite formation is the broader group of organisms (siliceous, carbonate, and soft bodied) with whose remains phosphorus reached the bottom in the case of the former, and related to this the more varied composition of the biogenic phosphatic sediments. A close spatial association of clastic, siliceous, calcareous, glauconitic, and phosphatic sediments, and also the presence of sediments of mixed composition, was characteristic of the shelves and upper part of the continental slopes in zones of oceanic phosphorite formation. Due to migration and superposition of facies caused by changes in sea level, eroded and redeposited phosphate concentrate turn up among sediments of any of the above types, regardless of the composition of the original phosphate deposits. Typical features of phosphorite formation on the ocean shelves also are its localized nature, discontinuous nature and duration. The localized nature of phosphorite formation is manifested in its selective occurrence in a limited number of regions with very active and steady upwelling inherited from the end of the Mesozoic/beginning of the Cenozoic, such as the shelves of southwest and northwest Africa, for instance. In these areas phosphorites are known from the Late Cretaceous (Morocco shelf) to Holocene (Namibia shelf), but Recent phosphorite formation is going on here in a limited area. It was the same in pre-Quaternary time: phosphorite formation did not occur simultaneously on the whole shelf, but on individual parts of it, in connection with the variability in the velocity of bottom currents and unevenness of upwelling. Discontinuity in phosphorite formation was caused by migration of the zones of biogenic sedimentation in the horizontal and vertical directions under the influence of hydrophysical phenomena and sea level fluctuations. During Late Quaternary time the formation of phosphorite concretions on the shelves occurred only when sea level was high, when biogenic sediments rich in phosphorus accumulated on the bottom. When sea level dropped these sediments were reworked and the concretions were concentrated on the eroded surface of the bottom. The duration of phosphorite accumulation is related t o the low rates of

281 supply of phosphorus to the bottom, and also t o the discontinuous nature of phosphorite formation. In the present epoch, with intensive erosion of the continents, more than 10 million tons of phosphorus reach the ocean every year with river discharge and are buried in the sediments; this includes %1.5 million tons of geochemically mobile hydrogenic phosphorus*. Out of this whole amount, not more than 10,000 tons of phosphorus, or 0.1% of the total influx, take part in the diagenetic process of formation of phosphorite concretions every year in the shelf sediments. Assuming that all the concretions formed were concentrated in ore deposits, the average rate of accumulation of phosphatic material is fractions of a millimeter in a thousand years. In reality that situation is a rare phenomenon, and most of the concretions remain scattered in the sediments. The same thing happened in the geologic past. According to a calculation by Ronov and Korzina (1960) , less than 0.01% of the amount of phosphorus disseminated in the sedimentary rocks of the earth’s crust is concentrated in sedimentary phosphorite deposits. In connection with the wide distribution of oceanic phosphorites and the ascertainment of Recent phosphorite formation on the ocean shelves, the question arises as to the extent of similarity of this process to the formation of economic phosphorite deposits in marine sedimentary rocks on the continents. Naturally, knowledge of Recent and pre-Quaternary processes is not equivalent because of the incompleteness of the geologic record, and also because of the ambiguity of interpretation of the paleogeographic environment, but it seems possible t o compare the most typical features of these processes. We will limit ourselves t o a few examples. The closest analog of Recent phosphorites on the ocean shelf apparently are the phosphorites of the Sechura deposit in Peru, the largest in South America (with reserves of % l O billion tons of ore). The phosphorite basin is a depression on the Paleozoic basement about 300 X 100 km in size, filled with Tertiary sediments up to 2700 m thick and situated about 150 km east of the present coast line. The phosphorites occur in Miocene diatomites. The producing horizons, 0.6-5 m thick, consist of phosphate grains (including phosphatized coprolites), diatom detritus, and grains of elastic minerals (mainly quartz and feldspars). The same grains are disseminated in the enclosing diatomites (Harrington e t d., 1966). Of other close analogs of Recent phosphorites, the Miocene and older phosphorites of the Coast Ranges in California, in particular the phosphorites of the Monterey Formation, can be named; they occur over an area of 650 X 150 km and are bounded on the west by the present coast line. * I n epochs of aridization of the climate the supply of phosphorus to the ocean was about an order of magnitude less.

282

The Monterey Formation consists mainly of biogenic siliceous rocks (diatomites, porcellanites, cherts), to a lesser extent of carbonate, clastic, and volcanogenic rocks. The phosphorites consist of bands of phosphate grains and concretions, usually occurring on erosion surfaces and often associated (up the section) with diatomites containing disseminated phosphatic material. Accumulation of rocks related t o the elements of the biogenic trio (Si, CorR, P) was a typical feature of sedimentation in the region of the Coast Ranges during the whole Tertiary period (Bramlette, 1946; Gower and Madsen, 1964; Page, 1966). The formation of phosphorites in both regions named took place in Tertiary time on paleoshelves of the ocean, at the same latitudes where on the present shelf, shifted to the west, there is powerful upwelling and Recent phosphorites are forming in places (shelf of Peru),which also is related to diatom-silica accumulation. Analogs of Recent phosphorites more remote in time and facies environment can be found in Mesozoic and Paleozoic deposits. They include the phosphorites of North Africa (Upper Cretaceous / Eocene) and of the Rocky Mountains of the U.S.A. (Permian), which have been described in many works. As in the present ocean, phosphorite formation in these basins occurred in biologically productive inshore zones and was related to biogenic sedimentation, as is indicated by the enrichment of the enclosing rocks and the phosphorites themselves in organic matter and the numerous organic remains, including coprolites and bones of fish and other organisms. The phosphate grains and concretions were formed in the sediments as a result of diagenetic redistribution of phosphorus; in particular, this can be judged from the similarity in morphology, structure, and composition of the phosphatic material from Recent and old deposits. The concentration and accumulation of phosphate material and formation of deposits proper occurred as a result of reworking of phosphate-bearing sediments; usually the productive layers are close to erosion surfaces (Bushinskiy, 1969; Mikhaylov et al., 1972). The make-up of the biota in the basins of North Africa and the Rocky Mountains evidently differed substantially from the present one, but the mechanism of biogenic supply of phosphorus to the bottom was the same. In their morphology the old phosphorite basins were not open ocean shelves, but seas which, however, communicated freely with the ocean. In these basins there was active circulation and upwelling of waters toward the shelf, which is demonstrated by paleogeographic reconstructions of the system of prevailing winds and currents (Sheldon, 1964). The original source of phosphorus in the process of phosphorite formation in these basins was sea water (McKelvey, 1959a), which brought to the shelf hundreds or thousands of times more phosphorus than river discharge.

283 Thus Mesozoic and Paleozoic phosphorite formation in some basins of marine type was characterized by at least some of the main features typical of Recent phosphorite formation on the ocean shelves. The main one of these features is the relationship of phosphorite formation to upwelling. Upwelling, a characteristic feature of the global system of circulation of the waters of the World Ocean, is caused by the active interaction of wind and hydrophysical fields in the inshore zone. Upwelling occurs everywhere in basins of different types - on ocean shelves, open and inland seas, and in gulfs and straits. The scale, intensity and stability of upwelling depend on factors of global, regional and local order. The global factors are the relationship, mutual positioning and morphology of the continents and oceans, vertical movements of individual crustal blocks, the overall system of circulation of air and water masses, and the earth’s rotation. Regional and local factors are the specific hydrophysical characteristics of inshore currents, the wind regime of the peripheral parts of the ocean and adjacent lands, the configuration of the shoreline, and the relief, width and slope of the shelf (Gunther, 1936; Hart and Currie, 1960; Wooster and Reid, 1963; Barton et al., 1977). Depending on the combined effect of these factors, upwelling is relatively constant (off the coasts of Peru, Chile, California, Namibia, Morocco), seasonal (Arabian Sea, Gulfs of Bengal and California) or sporadic, observed in many other regions of the ocean. The total area of manifestation of constant upwelling in the present ocean is estimated at a relatively low figure, up to 1X lo6 km2, but the zone of its influence on biological productivity is many times broader, and its effect on sedimentation processes on the submerged continental margins is of global importance, comparable to the role of river run-off. But whereas the relationship of Recent phosphorite formation to upwelling is quite obvious, the question of the existence of such a relationship in ancient water bodies, first proposed by Kazakov (1937), remains debab able. New possibilities for comparing Recent and pre-Quaternary phosphorite formation have emerged owing to the success of the new global tectonics, which permits reconstruction of the paleogeographic position of the continents and oceans (Cook and McElhinney, 1979; Baturin and Pokryshkin, 1980). It is known that the process of phosphorite formation went on unevenly in the ancient oceans. It occurred throughout the whole Late Precambrian and Phanerozoic on one scale or another, but the largest deposits, with which more than 90% of the world’s phosphorite reserves are connected, are restricted to just a few stratigraphic intervals, which usually are called epochs

284 of phosphorite formation: the Upper Proterozoic/Cambrian, Permian, Upper Senonian/Paleogene, and Neogene. In order to reconstruct the general patterns of the distribution of phosphorite basins and the paleogeographic setting of their formation during those epochs, we will use reconstructions of the position of the continents and oceans as it appears in the light of plate tectonics (Phillips and Forsyth, 1972;Dewey et al., 1973;Zonenshayn et al., 1976,Zonenshayn and Gorodnitskiy, 1977).We will also attempt to reconstruct the currents bathing the shores of the ancient continents and the upwelling related to them, on the basis of the global regularities of water circulation in the World Ocean (Kamenkovich and Monin, 1978;Stepanov, 1974) and also of the results of previous attempts at reconstruction of oceanic paleocurrents (Sheldon, 1964;Howard, 1972,Gordon, 1973;Belinko, 1977;Cooper, 1977). The Upper Proterozoic/Cambrian epoch of phosphorite formation left behind it numerous deposits of oolitic-microgranular, less often stromatolitic, phosphorite (U.S.S.R., Mongolia, South China, Viet-Nam, India, Australia, Nigeria). The lower age limit of the epoch apparently corresponds to the Middle Riphean (Bushinskiy, 1966b;I l k , 1973;Krasil’nikova, 1973). Several very large deposits are associated with the Late Riphean, Vendian and Early Cambrian: the South Chinese, Hobsogol (Mongolia), Udaipur (India), Karatau (U.S.S.R.) and Pendjari (Nigeria) basins. The upper age limit of the epoch apparently is assigned to the beginning of the Middle Cambrian (Georgina basin in Australia). Thus the oldest phosphorites were formed during a long age interval, in which several maximums of phosphorite formation alternating with a decline in this process are distinguished. The total duration of the epoch was about 200 Ma, and the proven reserves alone in the Asian, Australian and Nigerian provinces are more than 25 billion tons. But taking into account the complexity of the tectonics and depth of erosion, the paleogeographic extent of the phosphorite deposits is many hundreds of billion tons, inasmuch as it is more than 200 billion tons for the Hobsogol phosphorite basin alone (Il’in, 1973). This enables us to put the Upper Proterozoic/Cambrian epoch in first place in the history of the earth, not only in duration but also in volume of phosphate accumulation. Toward the beginning of this epoch, in the Riphean, the outlines of all the ancient continental platforms and of the main geosynclinal belts were already delineated (Ronov e t al., 1974). Phosphorite was formed in the low latitudes in miogeosynclinal zones (Hobsogol, Udaipur) and on the edges of intraplatform basins (South China, Pendjari). Due t o the particulars of the structural morphology of these tectonic elements, a series of strait- and gulf-like basins were produced, in which thick piles of carbonate (often magnesian), cherty, and phosphatic sediments accumulated.

285 In the Early Cambrian (570-550 Ma ago ) the paleotectonic setting constituted in the Late Precambrian changed but little. In the marginal parts of the Paleo-Asiatic Ocean, the phosphorite basins continued to develop or new ones arose (South Chinese, Hobsogol, Karatau). Avast ocean lay between the supercontinent of Gondwana and the relatively small continents - the Chinese, Siberian, East European and Kazakhstan. The Paleo-Asiatic Ocean was connected with the Paleo-Atlantic, which separated Gondwana from the North American continent (Fig. 7-la). With such distribution of the continents the most important feature of the oceanic circulation in the northern hemisphere, with which most of the phosphorite deposits are associated, was a vast anticyclonic system. Its very powerful southern branch, which bathed the continents and the phosphorite basins situated on their margins, was the north equatorial trade-wind current, flowing from east to west in correspondence with the general regularities of oceanic circulation (Stepanov, 1974; Kamenkovich and Monin, 1978). When this current, or flows deflected from it, approached the shelf, stable vertical movements of water masses arose, with ascending (upwelling) or descending (downwelling) components predominant, depending on local conditions. Probably the formation of the mid-ocean ridges essentially influenced water circulation. Their growth was accompanied by the subduction of lithospheric plates and transgression of epicontinental seas along wide basins. Upwelling could have been localized by the brachyform morphology of the basins on the slopes of the lithospheric plates, and stability of the basins could have been produced by a quiet tectonic regime of growth of the mid-ocean ridges and corresponding subduction of lithospheric plates. In this case the influx of detrital material from the continent was insignificant, as indicated by the limited distribution of clastic rocks in the composition of the phosphorite-bearing formations (Belinko, 1977; Cooper, 1977). In the Middle Paleozoic, the Paleo-Asiatic and Paleo-Atlantic oceans shrank considerably, which led to a weakening of water circulation and an abrupt decrease in the scale of phosphate accumulation. In the Permian epoch phosphorite formation was markedly activated. In this epoch numerous deposits of oolitic-granular phosphorites were formed in the carbonate-mudstone-cherty rocks of the Phosphoria Formation in the Rocky Mountain basin (USA.), and also several deposits in China and the Seleuk deposit on the west flank of the Urals (Gimmelfarb, 1962,1965). In the Rocky Mountain basin the lower boundary of the epoch corresponds t o the Early Permian (Meade Peak horizon), the upper to the beginning of the Late Permian (Retort horizon). The duration of the epoch was about 30 Ma, the inferred reserves of phosphorite are about 17 billion tons, and the volume of paleogeographic phosphorite deposits on the order of 600-700 billion tons (McKelvey, 1959b; Belinko, 1977).

286 N

287 By the beginning of this epoch the continents were joined into a single landmass, Pangaea, which consisted of two parts, Laurasia on the north and Gondwana on the south (Fig. 7-lb). The eastern meridional branch of the anticyclonic circulation system of the northern hemisphere bathed the northwest coast of Laurasia; its present analog is the California current, to which one of the most powerful upwellings in the Pacific Ocean is related. Permian upwelling was most active in a gulf-like part of the Paleo-Pacific shelf in a belt approximately from 3 to 15" north paleolatitude (Sheldon, 1964). In this basin, bounded on the east by a peneplaned platform landmass, sediments of a broad spectrum of facies were deposited - from normal marine t o lagoonal. Phosphatic and argillaceous siliceous sediments interbedded with carbonate were deposited in the outer open zone of this basin. The formation of the small-scale Permian deposits of South China and the west flank of the Urals could have been related to the action of branches of the south equatorial trade-wind current, which penetrated gulfs and straits of an incipient new basin, the Paleo-Tethys. During the Mesozoic the paleogeographic setting changed considerably. In the Triassic Pangaea began to break up and the continents constituting it to drift apart. The western edge of the North American continent was tectonically activated and began to rise, which caused the sea to retreat from the Rocky Mountain basin and put an end to phosphorite formation. In the south Gondwana began to break apart and the Atlantic and Indian Oceans began to form. The largest east-west-trending basin was the Tethys Ocean. In the Late Junassic/beginning of Early Cretaceous, fairly intensive phosphorite formation occurred at the northern margin of the Tethys (in the Volga and Aktyubinsk basins), culminating with the formation of deposits of nodular phosphorite. But the most favorable conditions for phosphorite formation arose later, toward the end of the Cretaceous period, on the vast shelf areas along the southern margin of the basin. The Upper Senonian/Paleogene epoch was characterized by exceptionally extensive areal distribution of numerous phosphorite deposits, particuFig.7-1. Continents and ocean basins of the main epochs of phosphorite formation (Baturin and Pokryshkin, 1980). Epochs: (a) Early Cambrian;(b) Early Permian; (c) Late Cretaceous; (d) Paleocene/Eocene; (e) Neogene. Legend: 1 = boundaries of paleocontinents; 2 = paleocontinents ( G = Gondwana, C = Chinese, S = Siberian, KZ = Kazakhstan, EE = East European, NA = North American); 3 = outlines of present continents; 4 = spreading axes; 5 = main ocean currents; 6 = phosphorite basins ( I = Pendjari, II = Udaipur, III = Georgina, I V = Karatau, V = Hobsogol, V I = South Chinese, VII = Rocky Mountains, VIII = Congo, I X = East Cordilleran, X = Moroccan, X I = East Mediterranean, X n = Aktyubinsk, XIII = Togo-Nigerian, X I V = Senegal, X V = West Saharan, X V I = Mali-Nigerian, X V I I = Algeria-Tunisian, XVIII = Central Asian, X I X = Agulhas, X X = Sechura, X X I = Californian, X X I I = Atlantic Coastal Plain); 7 = small regions of phosphate accumulation.

288 larly in the territory of the African-Arabian province. Granular phosphorites of the same age are also known in Asia (India, Soviet Central Asia), Australia and Latin America (East Cordilleran phosphorite basin of Columbia and Venezuela). The lower age limit of this epoch coincides with the boundary of the Campanian and Maastrichtian stages, with which the phosphorite deposits of Egypt, Israel, Jordan, Saudi Arabia, Syria, Turkey, the Congo, Angola, Morocco, Columbia and Venezuela are associated. Occasionally phosphorite occurs lower down (Santonian stage of Syria, the lean nodular ores of the Aktyubinsk basin in the U.S.S.R.). The upper age limit of the epoch corresponds to the Early or Middle Eocene. In the Moroccan, Algerian-Tunisian, and East Mediterranean basins phosphorite formation ended in the Early Eocene; in West Africa (MaliNigerian, Togo-Nigerian and Senegal basins) and also in the Central KyzylKums (Central Asian basin) it ended in the Middle Eocene (Pokryshkin et al., 1978). The total duration of this epoch of phosphorite formation was around 40 Ma, and the proven reserves of phosphorite related to it are more than 60 billion tons. The inferred reserves of phosphorite in the countries of Africa and the Near East are estimated at 100 billion tons. That this figure is not an absolute indication of the scale of phosphate accumulation is suggested by the active neotectonic erosional truncation of the formerly vast phosphorite basins of the marginal parts of the African-Arabian platform. The formation of phosphorite deposits on the shelves of the Tethys (Fig. 7-lc,d) occurred, as it did in the Late Proterozoic/Cambrian Ocean, under the influence of a powerful north equatorial trade-wind current flowing from east to west. The restriction of most of the large deposits precisely to the southern shelf, to paleolatitudes of 8-22'N (Sheldon, 1964),was in all probability related to strong winds blowing from the south from an arid climatic zone (like the present khamsin or sirocco), which stimulated upwelling . Other very large circulatory systems which influenced phosphorite formation in the Late Senonian/Paleogene were the northern and southern subtropical an ticyclonic circulations of the Paleo-Atlantic Ocean. The eastern marginal branches of these systems (analogs of the present Canary and Benguela currents) and the powerful stable upwelling related to them promoted the formation of a whole series of phosphorite deposits in west and northwest Africa (the Congolese, Togo-Nigerian, Senegal, West Saharan, and Moroccan basins). Under the influence of an analogous system (equivalent to the present anticyclonic subtropical circulation with its eastern branch, the Peruvian current) the East Cordilleran phosphorite basin was formed in the Paleo-Pacific Ocean.

289 The Neogene epoch of phosphorite formation was characterized by the formation of large deposits of granular diatomitic phosphorites in the basins of the Atlantic Coastal Plain (southeastern states of the U.S.A.), in California (U.S.A. and Mexico) and Sechura (Peru), and also of nodular phosphorites on the Agulhus Bank off South Africa. The beginning of this epoch apparently was in the Early Miocene (Hawthorn Formation, Florida), the maximum of phosphorite formation came in the Middle Miocene (Pungo River Formation, Lee Creek deposit in North Carolina), and the end in the Pliocene (marine gravels of the Bone Valley Formation, Florida). The total duration of the epoch was about 15 Ma. The proven reserves of phosphorite (mainly on the Atlantic Coastal Plain) are about 11.5 billion tons. At the same time the predicted reserves in the Sechura basin alone are estimated at 38 billion tons (World Survey of Phosphate Deposits, 1973). The position of the continents and oceans in the Neogene epoch of phosphorite formation was much like the present (Fig. 7-le), as was the general plan of circulation of the waters of the World Ocean. The closing of the Tethys and formation of the Mediterranean Sea entailed suppression of the east-west subequatorial current and the upwelling related to it, and along with that, of phosphorite formation. The already existing submeridional inshore branches of the anticyclonic subtropical circulations, which also have been inherited by the present ocean -the Paleo-Californian, Paleo-Peruvian and Paleo-Benguela currents - and to which the most powerful upwelling of that epoch was related, assumed the main importance for phosphorite formation. In addition, there was an upwelling in the North Atlantic which has no present analog, apparently related to an inshore branch of the Paleo-Labrador current, which bathed the northeast coast of America. Thus throughout the Late Precambrian and Phanerozoic, phosphorite formation occurred on ocean shelves in the zone of influence of powerful upwelling, related chiefly t o trade-wind subequatorial and eastern boundary currents which were the main component of anticyclonic subtropical circulatory systems, the largest in the present and in the ancient oceans, which functioned in the face of different relative positions of the continents. The stability of existence of these systems was governed by planetary regularities of the exchange of energy and matter in the atmosphere and hydrosphere, which in turn were caused by inequality in the arrival of solar energy at the earth’s surface (Kanfenkovich and Monin, 1978). In the history of circulation of the ocean waters, upwelling is as constant a factor as coastal currents. But the epochs of phosphorite formation related to upwelling are only relatively brief episodes in the history of sedimentation, separated by long intervals when there was little or no phosphorite formation.

290 Among the conditions favoring the accumulation of thick sequences of phosphate-bearing sediments are: the presence of a wide flat shelf, stagnation or feeble circulation of the bottom waters, and a quiet tectonic regime. On a steep shelf, for instance off the east coast of the Arabian peninsula, sediments are not held back, but move downslope, which leads to mineralization and dissemination of phosphorus. In the case of strong bottom currents (on the present shelf of northwest Africa) the organic matter of biogenic detritus, including the phosphorus it contains, also is washed out of the sediment and disseminated and in part consumed by the benthic fauna. In an active tectonic regime, phosphate-bearing sediments are highly diluted with detrital material (for instance, in several parts of the present shelf of Chile). In the light of these observations a relationship of the major epochs of phosphorite formation to planetary or regional transgressions seems probable. During transgressions the shelf areas widened, circulation of the bottom waters in the inshore zone apparently weakened, and the tectonic regime on the whole became quiet. Against the background of transgression there occurred transgressive-regressive cycles of lower order, causing repeated reworking of shelf sediments and the formation of phosphorite deposits proper. According to the results of lithologic investigations, tens of such microcycles occurred during the formation of the Karatau phosphorite (Smirnov, 1972). In the Tethys there were 13 transgressive-regressive cycles during the Upper Cretaceous/Paleogene epoch, each lasting 1-3 Ma (Cooper, 1977). Judging from geochronological data, in Late Quaternary time phosphorite concretions were formed on the Peru-Chile shelf only when sea level was high, whereas when it was low the sediments were reworked’and concretions accumulated there (Bumett, 1977). But in turn, planetary regressions could also create the prerequisites for phosphorite formation. Related to them are aridization and sharper northsouth contrast in climate, intensification of atmospheric and oceanic circulation, and as a result activation of upwelling (Belinko, 1977). However, the positive role of these factors for phosphorite formation apparently is cancelled out as a result of curtailment of the shelf area and intensification of bottom currents. Vast transgressions leading to a considerable expansion of the shelf areas in one or more plates were produced by such global factors as the rise of the mid-ocean ridges and the general reorganization of the paleogeographic aspect of the earth, in addition to a general warming of the climate (Sorokhtin, 1976). The epochs of phosphorite formation also bear a global character on the whole, although the maximums of phosphorite formation in each epoch might have occurred at different times in different regions. In this plan the present epoch could be linked with the Neogene, in the course of which the

291 zones of phosphorite formation repeatedly migrated within the Peru-Chile and South African phosphate provinces. f t is known that in the course of the geologic history of the earth there occurred an evolution of the sedimentary process, manifested in changes in sedimentary formations and changes in the rate of accumulation of absolute amounts of sedimentary rocks and ores, etc. Some aspects of this process (dolomite formation, formation of ferruginous quartzites) are irreversible. The evolution of lithogenesis is linked t o a general decline in the tectonomagmatic activity of the earth and relative expansion of the area of distribution of sedimentary rocks compared to magmatic (Ronov, 1972; Kholodov, 1975). Against the background of this global process there occurred a definite evolution of phosphoritization. Its main features are a probable decrease in the absolute amounts of phosphorus involved in the process of phosphorite formation from older to younger epochs, a change in the phosphoritebearing formations, and a change in the lithologic types of phosphorites. But the general scheme of the process of phosphorite formation probably has remained unchanged from the Late Precambrian to the present epoch inasmuch as, judging from a combination of paleogeographic, lithologic and oceanologic data, the supplying of phosphorus to the shelf, biogenic extraction of phosphorus from the waters on the shelf, and a three-stage process of concentration of phosphorus on the bottom (deposition, diagenesis and reworking of the sediments) are related to global regularities of the behavior of that element in lithogenesis.

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Chapter 8

CONCLUSION The discovery of Recent and Late Quaternary phosphorites on the ocean floor, the ascertaining of the facies environment of their formation, and their similarity to many pre-Quaternary phosphorites show that a type of phosphorite formation which on the whole does not fit into the framework of any one of the previously proposed hypotheses - biogenic, chemogenic, volcanogenic, or metasomatic - was widespread in the basins of the Late Phanerozoic. The chemogenic hypothesis of phosphorite formation rightly recognizes upwelling sea and ocean waters on the shelf as the immediate source of phosphorus, but at the same time postulates its chemogenic deposition from the water (Kazakov, 1937), which is not supported by the present data. The volcanogenic hypothesis suggests volcanic exhalations as the source of accumulation of phosphorus (Brodskaya, 1974; Dzotsenidze, 1969). But the concentration of phosphorus in the sediments of the ocean shelves takes place independently of volcanic processes. The biolithic hypothesis, proposed before the discovery of the phenomenon upwelling, attached paramount importance to mass mortality of fauna where cold and warm ocean currents meet. It was suggested that the remains of fauna were the main source of phosphorus which, redistributed in the sediments, was concentrated in concretions and layers of phosphorite (Murray and Renard, 1891). But phosphorite formation in the ocean is controlled mainly by seasonal dying off of plankton, a fairly universal factor, rather than by episodic mortality of fauna which are of local significance. Moreover, the biolithic hypothesis incorrectly interpreted the initial (supply of phosphorus by currents instead of upwelling) and final (diagenesis without subsequent reworking) terms of phosphatization. The more flexible and capacious biochemical hypothesis (Bushinskiy, 1963, 1966a, b) corresponds completely with the general scheme of oceanic phosphorite formation in several basic points. But categorically denying the role of upwelling, it proclaims river run-off as the source of phosphorus. This contradicts both the fact of localization of shelf phosphorites in zones of upwelling, and data on the composition of river discharge, in which suspended, and moreover disseminated and geochemically inert, phosphorus predominates. Finally, the metasomatic hypothesis (Ames, 1959; D’Anglejan, 1968) considers phosphorite formation to be replacement of limestones and carbonate sediments on the bottom by phosphate supplied by the bottom

294 water. This makes phosphorite formation directly dependent on carbonate accumulation and at the same time proposes a new version of the idea of chemogenic deposition of phosphate from ocean waters. The association of phosphate rocks and sediments with carbonates is common, but both in the ocean and in sedimentary deposits on land numerous examples are known where such association is lacking. Moreover, carbonate rocks and sediments, including those that accumulate slowly and undergo long exposure on the bottom, as a rule are characterized by low phosphorus content. Therefore the metasomatic hypothesis, which raises diagenetic phosphatization to the rank of the dominant phenomenon, is incapable of providing a universal interpretation of the process of oceanic phosphorite formation as a whole. It was shown above that the actual scheme of this process does not agree with any one of the hypotheses examined, although each of them contains elements corresponding to its most important links. Thus, river run-off and volcanic sources actually supply phosphorus to the World Ocean and maintain its overall salt balance, but their relationship to phosphorite formation is particularly indirect, via the global system of oceanic circulation. The supply of phosphorus to the phosphate-bearing shelves is accomplished by means of upwelling in accordance with the chemogenic hypothesis, but it is not followed by chemical deposition of phosphate, but rather by its consumption by organisms, deposition from the water layer as part of biogenic detritus, and redistribution during diagenesis, which is in agreement with the viewpoints of the biolithic and biochemical hypotheses. The relationship of phosphorite formation to transgressive-regressive cycles was noted earlier by many investigators, in particular Kazakov (1937), Bushinskiy (1963, 1966a, b), and Smirnov (1972). But due to the dating of the Upper Quaternary oceanic phosphorites, a fact of no little importance could be established, namely that the first stages of phosphorite formation (up t o the diagenetic) were related t o transgressions and the final stage (concentration of phosphatic material in deposits) to regressions. As we see, the hypotheses considered, however perfect and convincing they may seem, do not correspond (or only partially correspond) to the complicated picture which has been revealed by direct observations of the course of the process of oceanic phosphorite formation. To give this process a distinct name reflecting the role of all the factors taking part in it obviously is impossible. The term “biogenicdiagenetic phosphorite formation” seems most applicable inasmuch as it emphasizes the role of at least two of the factors on which it is based - the biota and diagenesis. And although their importance was pointed out earlier by the authors of one of the first (biolithic) and one of the last (biochemical) hy-

29 5 potheses, on the whole oceanic phosphorite formation has proved to be a new phenomenon which occupies an independent place in the science of phosphorite. In this connection one can be confident that the results of investigation of the distribution, composition, geochemistry, age, and conditions of formation of oceanic phosphorite not only are important for marine geology and for appraising the mineral resources of the ocean, but also carry information useful for understanding the origin of Late Phanerozoic phosphorites on the whole.

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REFERENCES

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SUBJECT INDEX Abrasion, 13, 1 7

-, coastal, 13, 1 7 Absolute age, 101, 102, 149, 154, 159, 160 - of bones, 1 5 4 - of diatomaceous oozes, 101, 102 - of glauconite, 73, 159, 1 6 0 - of phosphorites, 101, 102, 149, 154, 175 Active reaction, 197 - of water, 197 Adriatic Sea, 18 Agadir, 6 8 Agar, 3 2 Age, 64, 66, 67, 72, 100-105, 107, 109, 112, 120, 125, 147, 149, 152, 153, 155, 158, 159, 165168,173,175-177,179 - of basalt, 1 7 5 - of coccolithoforids, 6 7 j 109, 176, 177 - of diatoms, 1 0 3 - of foraminifera, 66, 73, 101, 120, 175 - of phosphorites, 64, 66, 107, 109, 112,120,125,147,152,175 - of rocks, 165, 179 Agulhas Bank, 55, 56, 58-60, 63-67, 183,257 -, geology of, 58 -, sediments of, 58 Agulhas current, 188 Aktyubinsk basin, 287, 288 Aland basin, 18 Albian, 173, 1 7 6 - coccolithoforids, 1 7 6 - foraminifera, 1 7 3 -, see also Age Algae, 25 Algeria, 288 Alkalinity, 197 Altay, 5 , 6 , 8 Aluminium, 64-66 - content in phosphorites, 64-66 Amazon, 11

Ammonia, 32, 221 Ammonium citrate, 236 Amorphous silica, 123, 124 Amphibole, 157 Amphipod, 26 Amu-Dar’ya, 11 Anadyr’ Gulf, 36 Anchovy, 29, 31, 204 Andaman Islands, 161 Andes, 1 2 6 Angoa Bay, 205 Angola, 107, 188 - current, 188 Anisotropy, 7 8 - of phosphate, 78 Annelid, 205 Antarctica, 6 Anticyclone, 1 8 5 Antofagasta, 126, 1 9 6 Antropogene factor, 19 Apatite, 42, 64, 94, 125, 141, 144, 147,172,236-238 - crust, 1 2 5 - crystals, 64 - in ore crust, 1 7 2 - phase in phosphorite, 236, 238 - substitution, 147 - synthesis, 236, 237 Appendicularia, 202 Apsheron sill, 39 Arabian Peninsula, 1 6 1 Arabian Sea, 36, 37 Aral Sea, 18, 36, 37 Arid zone, 7 5 Arsenic, 267-270, 275 Atacama desert, 196 Atacama trench, 126 Atlantic Ocean, 43, 45, 77-100, 286, 289 Atlantis I1 Deep, 14, 16 Augite, 129 Australia, 161, 284 Aves Island, 182 Aves Swell, 47, 177 Azov Sea, 18, 25,37, 4 6 , 4 9 , 51-53

330 Bacteria, 28, 29, 31, 32, 51, 205, 206,

231 - cell, 31 -, marine, 31,205 -, sulfate-reducing, 205,206,231 Bahia San Yuanico, 125 Baikal, 6 Baja California, 115,212,123-125 Baltic Sea, 18,33,36,37,45,46 Barbados, 7 Barcoo guyot, 168 Barents Sea, 18,37,46 Barite, 159,170 Barium, 269,272 Basalt, 35,170,172 -, amygdaloidal, 170 - nucleus, 172 -, palagonitized, 170 -, tholeiitic, 35 -, weathering of, 35 Bedding plane, 61 Belemnite, 239 Benguela current, 188,202,225 Benthos, 205 Bering Sea, 17,18,36-40, 46,49 Bikini atoll, 163 Biological cycle, 27,29 Biomass, 28,202,206 Biota, 201-206 Biotite, 85,180,209,213 - in phosphorites, 180 - in sediments, 209,213 Birds, 205 Birefringence, 78 Black Sea, 17, 18, 25, 36-39, 45, 46, 48,51 Blake Plateau, 108-112, 183,257 Bluegreen algae, 25 Bone, 27, 30, 42-44, 57, 59, 61, 74, 79, 86, 92-95, 98-100, 110, 117, 129, 134, 139, 142, 145, 208, 209, 217, 239, 242, 249, 276,277,282 -, absolute age of, 154 -, cetacean, 94 -, chemical composition of, 94, 95, 98,145 -,fish, 57, 59, 74, 92-94, 117, 129, 134,139,145,208 -, fluorine in, 242

-, fossilized, 93 - fragment, 79,86,139 -- in phosphorite, 139,282 -, fresh, 94 -,mammal, 57,74,92,110,117,129 -, mineralization of, 94 -, phosphatic fraction of, 100 -, phosphatized, 89,93,100 -, rare elements in, 276,277 -, thermogram of, 99 - tissue, 93,94 -, uranium in, 249 -, whale, 98,99,145 Bone Valley Formation, 111,289 Boring organism, 129 Brachiopod, 26,27,117,122,125 -, phosphatic, 122 Brine, 14 Brook, 8 Bryozoa, 26,59,68,117,156 - in phosphorite, 156 Burrowing organism, 117,132 Cadmium, 269,271,275,276 Calanus, 27 Calcarenite, 108,179,180 Calcareous algae, 25 Calcareous sediments, 42, 43, 73, 74,

75,77,78,89,127,168,210 Calcite, 32, 61, 70, 81, 85, 108, 123,

144,155,169,178-180,236

-, acicular, 61 -, fabrous, 178

-

in phosphorite, 123,144,155,236 -, magnesian, 32,179,180 -, pelitomorphic, 108 Calcium phosphate, 21-23, 34,99,222 -, precipitation of, 23,222 -, solubility of, 22,23 -, supersaturation with, 222 California, 47, 49, 115, 116, 118, 119, 121,122,281,287 - basin, 47,49,118 - current, 287 - province, 115 - syncline, 122 Callao, 217 Cambrian, 284,285 Cameron spring, 14 Campbell Plateau, 160

331 Canary current, 288 Canyon, submarine, 115, 126 Cape Agulhas, 56 Cape Cross, 205 Cape Johnson guyot, 1 6 3 Cape of Good Hope, 74 Capetown, 74 Caprinid, 168 Carbohydrate, 231, 233, 235, 276 Carbon, 65, 70, 200, 201, 209, 211, 212, 214 - dioxyde, 65, 70 -,organic, 200, 201, 209, 211, 212, 214 -, see also Phosphorite, chemical composition of Carbon-anhydrase, 3 3 Carbonate, 34, 64, 73,124,155-157 - in phosphorite, 155-157 -, phosphatization of, 34 Carbonate-apatite, 32, 35, 57 Carbonate-fluorapatite, 123, 231 Carbonate-hydroxylapatite,3 3 Cariaco basin, 47 Caribbean Sea, 47, 178 Carolina, 114 Caspian Sea, 1 2 , 18, 36, 37, 39, 40, 46,48 Catalina Bank, 237 Catchment area, 7, 8 Caucasus, 1 2 Cement, 64, 70, 73, 115, 159, 168 -, calcareous, 159 -, calcareous-phosphatic, 70 -, carbonate, 1 6 8 -, ferruginous, 1 1 5 --, microgranular, 64 -, phosphatized, 7 3 Cenomanian, 165-168 Central Africa, 107 Chaetognath, 26 Chalcedony, 1 7 2 Chatam Rise, 159, 160, 236, 237 Chert, 282 Chesapeake Bay, 47 Chile, 44, 125-154, 187-192, 196202, 204-206,212-218 China, 284, 285 Chincha Island, 205 Chitin, 27, 33

Chlorite, 7, 157, 170, 209 Chorokh, 1 0 Christmas Island, 182 Chromium, 267-270, 27 2-275 Chu, 11 Ciliate, 202, 206 Clastic material, 42, 59, 68, 81, 86, 1 1 1 , 1 5 5 , 2 0 8 , 209, 217 Clay minerals, 3 3 Climate, 1 9 5 Coagulant, 3 3 Coastal abrasion, 1 3 Coastal Plain, 289 Coast Ranges, 281, 282 Cobalt, 267-274 Coccolith, 66, 67, 108, 113, 166, 175, 176,178,181 -, age of, 1 7 6 , 1 8 1 - in phosphorite, 176, 178 COCOSRidge, 181 Coefficient, 8 , 74 - of aqueous migration, 8 - of sorting, 74 Collophane, 59-61, 64, 118, 133, 159 - cement, 61, 1 3 3 - pellet, 6 1 Columbia, 288 Concretion, 32, 59, 64, 66, 67, 78-81, 83, 84, 93, 95-98, 110, 115, 209 -, conglomeratic, 79 -,phosphatic, 32, 59, 78-81, 83, 84, 93, 95--98, 110, 209 Conglomerate, 68, 106, 107, 110, 117 -, phosphatized, 106, 107 -, ferruginized, 107 Congo, 1 0 7 , 2 8 8 Connate water, 1 5 Continental slope, 74 Copepod, 2 6 , 2 0 2 Copper, 267-274 Coprecipitation, 3 3 Coprolite, 30, 31, 33, 74, 78, 86, 8992, 94-100, 107, 132, 139, 141, 268-270,272-275, 281, 282 -, chemical composition o f , 31, 95, 9 6 , 9 8 , 145 -, phosphate of, 1 3 9 -, phosphatized, 74, 86, 94, 100, 132, 139,281

332 -,rare

elements in, 268-270, 272275 -, structure of, 97, 1 4 1 - thermogram of, 99 Coral, 26, 68, 117, 168 Coral Sea, 18 Coronado Bank, 237 Cosmic material, 1 6 Cretaceous, 74, 165-167, 176, 286, 287 -, see also Age Crinoidea, 26 Cristobalite, 170 Crust, 136,168, 1 7 2 -, iron-manganese, 168, 1 7 2 -, phosphate, 1 3 6 Crustacea, 26, 32, 158, 205 -, feces of, 32 - track, 158 Crystalline basement, 7 4 Crystallite, 88 Cunene River, 7 4 , 1 9 6 Current, 188-191, 226,283-290 -, bottom, 226 -, dynamic scheme of, 189 -, velocity of, 189 Cytoplasm, 31 Dahllite, 61 Danube, 1 0 Dating, 147, 154, 175 -, micropaleontological, 147 -, radiometric, 147, 154 -, potassium-argon, 1 7 5 Decapod, 26 Decarbonation, 100 Dehydration, 9 7 , 9 9 , 1 0 0 Deposition, 32, 3 3 Desorption, 34, 50, 5 3 Dervent Hunter guyot, 168 Detritus, 30, 42, 74, 9 3 , 1 0 8 Diagenesis, 124, 221, 223 Diatom, 25, 29, 81, 84, 85, 87, 101103, 130, 131, 133, 136, 140, 141, 147, 152, 153, 202, 208, 209, 217 - in phosphorite, 102, 103, 140, 141, 152,153 -, Miocene, 217 -, Oligocene, 217

-, Recent, 101, 103, 147 - valve, 81, 84, 85, 87, 133 Diatomaceous ooze, 32, 39, 40, 46, 81-85, 88, 90-92, 94-96, 101, 104,105,127,133,207 --, absolute age of, 1 0 1 --, phosphatized, 8 1 , 8 4 , 94-96,105 Diatomite, 282 Diffusion, 50-52 Dinoflagellate, 206 Discoaster, 175, 178 Divergence, 188 Dnieper, 9, 1 0 Dolomite, 57, 70, 81, 124, 129, 133, 144,147,179 - in phosphorite, 144, 147, 1 7 9 -, phosphatized, 57 Don, 9, 1 0 Downwelling, 194 Drainage, 9 DTA, 9 9 DTG, 97 Dune, 124 Dust, 7, 16 East Pacific Rise, 33, 34, 44 Echinoderm, 26, 59, 165 Egypt, 288 Eh, 49, 59, 208, 212, 221 Eiko Seamount, 167 Electron microscope, 72, 88, 89, 113, 141-143,169,171,265 El Jadida, 6 8 Emperor Seamounts, 1 6 3 Enzyme, 33, 5 1 Eocene, 72,165-167,175 -, see also Age Epidote, 68, 93, 124, 136, 159, 209 - in phosphorite, 136, 159 Equador, 201 Erosional surface, 74, 227, 282 Eruption, 1 6 Essaouira, 7 3 Euhedral crystal, 64 Eupelagic sediments, 4 1 Euphausiid, 26, 202 Exhalation, 1 7 Exothermal peak, 97 Facies, 185, 218

333 profile, 207, 213 Fecal pellet, 56, 57 Feces, 29, 31, 32 Feldspar, 59, 61, 63, 68, 81, 85, 88,

-

118, 124, 138, 144, 147, 157, 159,180, 213,217 - in phosphorite, 138, 144, 147, 157, 159,180 Ferruginization, 81, 265 Fertilizer, 8, 67, 160 Fish, 26, 30, 57, 74, 90, 92, 93, 101, 117,203-205 - bones, 57, 74, 90, 92, 93, 101, 117 -, phosphorus content of, 30 -, production of,30 - scales, 90 - teeth, 90 Flood, 8 Florida, 107-110, 289 Fluorapatite, 99, 107, 118, 173 Fluorcarbonate-apatite, 23, 47, 63, 64, 73,78,93,118 Fluorine, 65, 100, 124, 242-244 Fluorite, 243 Foraminifera, 41, 59, 60, 64, 66, 68, 73, 78, 93, 108, 111, 116, 120, 125, 136, 137, 155, 159, 168, 173, 175, 178-180, 202, 205, 209 -,age of, 66, 73, 116, 159, 168, 173, 175,179,180 -, benthic, 125 -- in sediments, 41, 68, 78, 81, 126, 127, 130, 159, 207, 209, 212, 213,215,216 --, phosphatized, 60, 125, 130, 155 - planktonic, 59, 125 - test, 59, 68,93, 111 Forty Mile Bank, 237 Framboid, 217 Francolite, 61, 110, 118, 168, 169 Fusiform crystal, 88

Gabon, 107 Galapagos Islands, 189 Garnet, 61, 124, 209, 214 Gastropod, 89, 97, 217 Georges Bank, 107,115 Georgia, 112 Georgina basin, 284, 286

Geyser, 1 4 Ghana, 107 Gifford guyot, 168 Glaciation, 101, 124 Glacier, 13, 17 Glauconite, 56, 58, 60, 61, 64, 68, 70, 72, 73, 75, 77, 79, 81, 90, 93, 97, 107, 108, 111, 115, 117, 125, 127, 130, 138, 141, 147, 148, 155, 159, 160, 170, 180, 209, 265 -, age of, 73, 159,160 - coating, 159 -, composition of, 148 - grain, 60, 61, 79, 80, 107, 108, 115, 117,138,159,170 - film, 97 - in foraminifera, 125, 155, 159 - in phosphorites, 97, 107, 117, 136, 138,141,159,170,180,265 - in sediments, 56, 58, 75, 77, 115, 127, 130, 131, 209, 212, 215217 -, phosphate coating on, 147, 148 -, phosphorus content of, 147, 148 - sand, 56, 58, 115, 127, 130, 212, 215,217 Glaucophane, 65 Global tectonics, 282 Globule, 64, 88, 93 Goethite, 59-61, 64, 179, 265, 271 Golden algae, 25 Gond wana, 2 85-2 8 7 Gotland basin, 1 8 Gourits River, 56 Graded bedding, 218 Granulometry of sediments, 75 Green algae, 25 Greenland basin, 37 Ground water, 1 2 Growing season, 17 Guano, 181,205 Guinea, 107 Guyot, 163,165-168

Hake, 93 Haversian canal, 79 Hawaiian Islands, 163 Hawthorn Formation, 289 Hindostan, 115

334 Hoarfrost, 6 Hobsogol, 284, 286 Holocene, 95, 101,180, 207 -, see also Age Holoturian, 205 Horizon guyot, 1 6 3 Hornblende, 68, 81, 85, 124, 134, 136, 159,180,209,213,214 Humic acid, 209, 232, 234 Humid zone, 75 Hydration, 36 Hydrocarbon, 201, 209 Hydrochemistry, 1 9 6 Hydrogen sulfide, 53, 196, 197, 206 Hydrogoethite, 107 Hydromica, 217 Hydrothermal process, 1 6 Hydrotroilite, 217 Hydroxyl ion, 99 Hydroxyl-apatite, 22, 23, 32, 9 3 Hyperstene, 124 Hypothesis of phosphorite formation, 293-295 Ichthyofauna, 203 Illite, 7, 209 Ilmenite, 209, 214 India, 157, 284 Indian Ocean, 43-45,155,157, 181 Inhibitor, 3 3 Insoluble residue (IR), 66 ' Intermediate layer, 18 Interstitial water, 32, 45-50, 221 Iodine, 243-245 Ionium, 1 2 5 , 1 5 2 Iron, 8 , 13, 16, 33, 34, 44, 49, 53, 61, 64--66, 70, 81, 84, 87, 93, 97, 108, 157, 158, 172, 179, 217, 265,266 -, colloidal, 44 - hydroxide, 33, 49, 53, 61, 70, 81, 93,108,172,217 - in phosphorite, 157, 158, 172, 179, 265,266 - -, see also Phosphorite, chemical composition of - humate, 3 3 - meteorite, 1 6 -- ore, 16 - phosphate, 3 3

- volcanogenic, 33, 34 Iron-manganese crust, 108, 109, 160, 168,172,175,179 Iron-manganese nodule, 108, 109, 164, 170 Isakov Seamount, 167 Ishim, 6 Isomorphic substitution, 270 Isomorphism, 99 Isotopic activity, 1 0 1 Isotopic composition - of carbon, 235, 236 - of oxygen, 235-240 Isotopic equilibrium, 238 Isotopic exchange, 238 Isotopic fractionation, 236, 238 Israel, 288

Jan Mayen Ridge, 1 7 7 , 1 8 0 Japan Sea, 1 6 , 1 8 Japan Trench, 1 6 3 Jacqueline guyot, 1 6 5 Java, 13, 1 4 Kamchatka, 36 Kaolinite, 7, 118, 144, 209 Kara Sea, 36, 37, 3 9 , 4 1 , 4 5 Karatau, 257, 284, 286, 290 Kawah, 1 4 Kazakhstan, 6, 8 , 285 Ket', 9, 11 . Kuban, 9 , l O Kuma, 1 0 Kunashir, 13, 1 4 Kuriles, 36 Kyzyl-Kums, 288 Labrador current, 289 Lamont guyot, 1 6 6 Landsort basin, 18 Lanthanoids, 173, 257, 259 Laurasia, 287 Leaching, 50 Lead, 251, 267, 268, 270, 271 Lee Creek, 289 Limestone, 34, 35, 57, 5 9 - 6 1 , 63-65, 72,106,124,163-179 -, arenitic, 167 -, bioclastic, 164, 167, 168 -, chalk-like, 165-167

335 -, -, --, -,

calcarenite, 164, 168, 179 foraminiferal, 164-170, 172 ferruginized, 64, 65 glauconitic, 72 -, micritic, 178, 179 -, nannoplanktonic, 164-166,169 -, phosphatized, 57, 59-61, 63-65, 72, 106, 124, 163-172, 177, 178 -, rudist, 164, 167, 168 Lingula, 26, 236-238 Lipid, 209, 231, 232, 234, 235, 276 Lobster, 26 Loire, 1 0 Los Angeles, 115 Loss o n ignition (LOI), 65, 66 Luderitz, 1 9 6 Maastrichtian, 173, 176 - coccolithophores, 176 - foraminifera, 1 7 3 Mackerel, 9 3 Magnesium, 65, 66, 70 -, see also Phosphorites, chemical composition of Magnetite, 68, 124, 134, 209, 214 Makarov Seamount, 167 Mali, 288 Mammal, 205 Manganese, 8, 33, 53, 65, 66, 116, 269, 272, 273 - hydroxide, 33, 53 - oxide, 178 - _. crust, 1 7 8 -, see a k 0 Phosphorites, chemical composition of Mangrove swamp, 124 Manihiki Plateau, 1 6 3 Marcus Island, 1 6 3 Marcus-Necker Ridge, 163, 169 Mariana Deep, 49 Marl, 57 Marshall Islands, 163 Mass mortality, 206, 207 Matrix, 81, 8 5 Meade Peak horizon, 285 Median diameter, 74 Mediterranean Sea, 16, 18, 36, 37 Medusae, 26 Menard guyot, 1 6 5

Mendeleev spring, 1 4 Mendeleev volcano, 1 3 Metasomatic replacement, 64, 293, 294 Metallo-organic complex, 276 Meteorite, 16 Methane, 196 Mexico, 1 1 5 Miami guyot, 166 Mica, 117, 141, 144, 157, 213 Micrite, 59, 61, 64, 178, 179 Microbe, 31, 32 Microdiffraction, 63, 64, 249-251 Microglobule, 79, 80, 85, 87-89, 9 2 Microorganism, 29, 32 -, see also Bacteria Microradiography, 249 Microstructure, 60, 62, 63, 72, 73, 83, 84,87-89,133,140-143 Mid-Pacific Mountains, 163, 170, 1 7 3 Milwaukee Bank, 1 6 3 , 1 7 0 , 1 7 5 Mineralization, 6, 8, 10-13, 49 - of phosphorus, 49 - of water, 6, 8, 10-13 Miocene, 66, 67, 72, 73, 101, 110-112, 1 1 6 , 1 1 8 , 1 1 9 , 1 2 4 , 289 -, see also Age Miopelagic sediment, 4 1 Mississippi, 11 Mixophyte, 25 Mobility, degree of, 8 Mohs’ scale, 84, 87, 116 Mollusk, 26, 59, 61, 165-168, 178, 205,206 Molybdenum, 267, 2 6 8 , 2 7 0 , 2 7 1 Mongolia, 284 Monohydrocalcite, 32 Monterey Formation, 281, 282 Montmorillonite, 209 Morocco, 68, 69, 72, 286-288 Mudstone, 57 Muscovite, 180, 213 Mysid, 26 Namib desert, 196 Namibia, 74 Nannoplankton, 67, 113,175-178 Nassau, 245 Neogene, 1 0 7 , 1 7 6 -, see also Age New York Bay, 51, 52

336 New Zealand, 14, 16, 159 Nickel, 267-275 Niger, 90, 288 Nigeria, 284 Nile, 11 Nitrate, 198 Nitrite, 199, 200 Nodule, 44, 45, 58, 59, 78, 82, 85-88, 108,287 -, ferromanganese, 44, 45, 108 -,phosphatic, 58, 59, 78, 82, 85-88, 97,287 -, see also Concretion, Phosphorite North Carolina, 53, 289 North Sahara, 68 Northwest Africa, 71 Norvegian fjords, 17, 18, 37 Norvegian Sea, 46 Nuclei of phosphate grains, 136, 138 Nucleic acid, 32 Ob’, 9, 10 Ocher, 107 Okhotsk, Sea of, 17, 18, 36, 37, 39, 46,49 Oligocene, 66, 67, 109, 113 -, see also Age Oligosaccharide, 233, 234 Opal, 81, 84, 1 2 3 Ophiura, 26, 205 Oolite, 115, 117, 118 Ooze, 36, 37, 46, 47, 49, 56, 58, 60, 74, 81-84, 88-93, 95, 96, 101105, 127, 207-210, 212, 216, 224, 232, 233 -,diatomaceous, 36, 37, 46, 47, 49, 56, 58, 74, 81-84, 88-93, 95, 96, 101-105, 127, 207-210, 212, 216,224,232 -, foraminiferal, 60, 216 -, see also Sediments Orange River, 74, 188, 196 Ore crust, 172 Organic carbon, 65, 200, 201, 211, 212,214,243 -, see also Organic matter, Phosphorite, chemical composition of Organic complex, 275 Organic matter, 29, 32, 49, 50, 61, 81, 122-124, 208-210,231-234

-, composition of, 209, 232-234 Ostracod, 202 Oxygen, 1 9 6 , 1 9 7 , 236-240 - content in water, 196, 197 - isotopes, 236-240 - minimum layer, 196, 197 - saturation, 197 Oyashio current, 20 Pacific Ocean, 43, 45, 47, 115-153, 163-1 78,185-206, 212-218 Paleogene, 1 7 6 -, see also Age Paleozoic, 74 -, see also Age Pamlico River, 5 3 Panama Canal, 1 8 5 Pangaea, 287 Partial pressure, 197 Pebble, 6 1 , 1 5 5 Pelagic zone, 49 Pelecypod, 217 Pellet, 75, 129 Pendjari, 284, 286 Peptide, 234 Peridinium, 25, 202 Permian, 285 Peru, 125-134,185-206, 212-218 -, see also Chile Peruvian current, 29, 31, 189 Peru-Chile countercurrent, 189 pH, 8, 19, 32, 3 5 , 4 9 , 208 Pholad, 61, 118, 156, 180 Phosphatase, 5 1 Phosphate, 17-20, 58, 60, 61, 63, 64, 67, 68, 72-74, 77-79, 81, 82, 84-90, 92-97, 99, 101, 103108, 111,112,114,115,121-125, 129, 134-136, 138-143, 147, 148, 155, 156, 164, 168-170, 178, 180, 197-199, 207, 212, 217, 223, 265, 266, 272, 273, 275 -,amorphous, 64, 73, 77, 93, 123, 135,140,141,156,168,169 -, anisotropic, 79 - block, 74 - cast, 89, 9 0 - cement, 60, 64, 1 3 5 , 1 6 4 _ _ , composition of, 148

337 - coating, 64, 147 -- on glauconite, 147 - concretion, 89, 95-97, 103-105, 129,207 - content of iron-manganese nodules, 170 - content of sea water, 197 -core, 1 7 0 - crust, 136 -, cryptocrystalline, 81, 1 5 5 -- crystal, 88 -,crystalline, 73, 77-79, 84, 86, 87, 92-94, 108, 123, 135, 136, 141, 168,178 --, crystallization of, 140-143 - distribution in sea water, 17-20, 198,199 -, fibrous, 63, 64, 93, 168 - film, 1 4 1 , 1 6 8 - finely crystalline, 139 - flake, 1 4 1 -, fusiform, 140-143 - gel, 63, 101, 223 --,glassy, 1 3 4 -, globular, 1 4 1 - globule, 140, 141, 180 - goethite cement, 265 - grain, 68, 74, 77-79, 111, 115, 122-124,129,136,212 -.-nuclei, 136, 138 - in foraminifera chamber, 1 5 5 -,isotropic, 78, 85, 90, 99, 135, 139, 156 - matrix, 1 5 5 - microcrystal, 81, 135, 140, 1 4 1 -, microcrystalline, 63, 64, 72, 8 2 , 135,143 -, microdiffraction of, 63, 64, 1 4 1 -, microglobular, 85, 93, 140, 1 4 1 -, microgranular, 63, 81, 87 - nodule, 58, 78, 82, 85-88, 97 -- pebble, 64 - pellet, 129 -, polarizing, 81, 82, 84, 1 4 1 - province, 107, 1 1 5 -, refractive index of, 136, 180 -, reserve of,67, 1 2 5 - rim, 217 - rock, 1 0 6 - sand, 68, 74, 107, 124

- sediments, 61, 111, 112, 114, 121, 122,129 -, self-purging of, 266, 272, 273, 275 - sheet, 74 -, ultramicrocrystalline, 63, 64 -, unit cell of, 1 3 5 Phosphatization, 34, 35, 64, 70, 72, 180-182 - of carbonate, 34, 64 - of cement, 1 8 0 - of limestone, 35 - of rocks, 181, 1 8 2 - of sediment, 180 -, stages of, 64 -, see also Phosphatized Phosphatized, 57, 60, 61, 63-65, 68, 72, 81-86, 95, 96, 106, 107, 110, 117, 124, 125, 129, 132, 136, 137, 139, 142, 145, 155, 158, 161, 163-169, 172-174, 177-180 - basalt, 1 7 2 - bone, 1 1 0 , 1 1 7 - breccia, 166, 167 - calcarenite, 1 6 5 - cement, 6 4 , 1 8 0 - chalk, 1 6 5 - conglomerate, 106, 107, 178-180 - coprolite, 107, 129, 132, 139, 142, 145 - coquina, 1 6 5 - diatomaceous ooze, 81-86, 95, 96 - foraminifera, 125, 136, 137, 155 - hyaloclastite, 1 7 2 - limestone, 59-61, 63-65, 68, 72, 106, 107, 110, 124, 161, 163168,172,174,177-179 - lutite, 1 6 6 - mudstone, 1 8 0 - rock, 57, 145,163, 169, 173 - sand, 6 8 - sandstone, 107, 136, 137 - silt, 137, 1 8 0 - track, 1 5 8 -, see also Phosphorite Phospholipid, 32 Phosphoprotein, 3 2 Phosphoria Formation, 248, 271 Phosphoric acid, 27 Phosphorite, 32, 55-68, 70-73, 78-

338 108, 110-113, 116-125, 129149, 152-160, 164, 165, 167183, 219--235, 245-255, 27929 1 -,absolute age of, 67, 104, 105, 125, 149,153,154,175 -,age of, 72, 100-107, 112, 120, 147, 153, 154, 173-175, 179, 180,279-291 - , arenitic, 167 - as fertilizer, 160 - - -bearing sediments, 121, 159 - breccia, 117, 181 - , brecciated, 57 -, brecciform, 61, 65, 71, 80, 174 -, calcareous-ferrugineous, 6 3 -, chemical composition of, 65, 66, 71, 80, 94, 108, 112, 118, 119, 142, 145, 146, 156, 158, 160, 172,179,180,181 -, clastic material in, 59, 61, 63, 66, 70, 78, 81, 85, 108, 117, 124, 133-138,155,157,159 -, coccolith in, 67, 113, 176-178, 254 - concretion, 56, 78, 103, 116, 117, 132,134,142,144-146, 159 - _ , lithification of, 142 - conglomerate, 68, 110, 117, 1 7 9 - conglomeratic, 57, 59, 61, 65, 68, 71,80 -, diatomic, 289 -, distribution of, 56, 57, 164 -, ferruginized, 60 -, fine-grained, 57, 61, 71, 78, 8 0 - formation, 64, 112, 124, 219-229 - -, epoch of, 284 - -, rate of, 229 -, granular, 68 -, insoluble residue of, 157 -, lithology of, 129 -, lutitic, 165 -, metasomatic, 55 -, micritic, 179 -,microstructure of, 62, 63, 72, 73, 83, 84, 87, 89, 111, 113, 122, 123, 133, 135, 137-143, 170172 -,mineralogy o f , 59-64, 68, 70, 72, 73, 78, 79, 81-93, 108, 110,

164, 117, 118, 122, 129-144, 168-173,180 -, nodular, 58, 59, 289 -, non-conglomeratic, 59 - nuclei in ferromanganese nodule, 164 -, oolithic, 284 -, organic matter in, 123, 231-235 -,organic remains in, 60, 67, 83, 84, 86, 92, 93, 103, 111, 113, 117, 120,122,137,139,152,153 --,origin of, 64, 112, 124, 181-183, 2 19-2 29 - pebble, 1 5 5 -, phosphatic fraction of, 147, 148 - province, 55 -, Recent, 32, 81-106, 147, 149, 152154,245-255 - reserve, 112, 125, 160, 229, 284, 288 - sand, 1 1 1 , 1 1 2 - sheet, 117, 136 -, sheeted, 58 -, siliceous, 174 - slab, 164 -, stromatolitic, 284 -,tubular, 158 -, ultramicrostructure of, 141-143 -, X-ray analysis of, 142, 144 -, X-ray diagram of, 134 Phosphorus -, absolute amount of, 42 - balance, 1 6 , 228 -, clastic, 42 - content, 6, 8, 9-19, 23-27, 31, 6 4 - 6 6 , 68, 69, 74, 77, 114, 115, 128,130,224 -, deposition of, 3 1 -, dissolved, 8 , 9 , 1 2 , 16-22, 31 _ - , organic, 9, 19-22 -,distribution of, 36-41, 43, 58, 69, 74-77,114,115,120,128,224 - exchange, 50 - extraction, 220 -, hydrothermal, 1 6 - in ferromanganese nodules, 45 - in interstitial waters, 221, 222 - in organisms, 24-26, 31 - in sediments, 36-41, 43, 58, 7477,114,115,120,128,224 - mineralization, 52

-, mobile, 221-223, 228

-, organic, 9, 19-22,220, 223 -, -, -, -,

recycling of, 27, 29 redistribution of, 221 residence time of, 1 9 sorbed, 5 3 -, supply o f , 220 -, suspended, 9, 1 2 , 2 3 , 3 4 Phosphorus-carbon bond, 27 Phytoplankton, 25, 28, 29, 202-204 Pioneer Seamount, 237 Plagioclase, 7, 93, 108, 129, 133, 136, 141,147,148,213 Pleistocene, 66, 120, 124, 1 7 5 -, see also Age Pliocene, 66, 72, 112, 116, 120, 124, 175 -, see also Age Podzol, 8 Point Reyes, 1 1 5 Polychaete, 26, 205 Polyphosphate, 27 Polysaccharide, 233, 234 , Porcellanite, 282 Potassium, 65, 66, 1 4 2 -, see also Phosphorites, chemical composition of Potassium-argon dating, 73, 1 7 5 Pourtales Terrace, 109, 110, 113 Precambrian, 74 Precipitate, 32 Precipitation, 5-7, 196 Pripyat’, 9, 1 0 Productivity, 28, 30, 201, 203, 220 -, fish, 203 -, primary, 30, 201, 220 Protein, 231, 234 Psammitic texture, 63 Psephitic texture, 68 Pteropod, 26, 202 Pungo River Formation, 289 Purple algae, 165, 1 7 9 Pyrite, 60, 68, 79, 81, 84-86, 90, 92, 108, 118, 133, 134, 136, 139, 141, 144, 155, 157, 159, 217, 265-267 - globule, 81, 86, 90, 217, 266, 267 - in diatom valves, 81, 84, 217 - in foraminifera chambers, 155, 159, 217

- in phosphorite, 81, 84, 134, 136, 139, 141, 144, 155, 157, 159, 265-267 - in sediments, 217 - microglobule, 84, 85, 92, 93, 136 - spherule, 1 3 3 Pyritization, 265 Pyroxene, 63, 81, 88, 93, 117, 133, 134,136,180,209,214

Quartz, 7, 59-61, 63, 64, 68, 70, 78, 81, 85, 88, 93, 97, 107, 108, 111, 114, 115, 117, 118, 129, 130, 133, 134, 136, 138, 141, 144, 147, 155, 157, 159, 172, 209,217 - grain, 60, 61, 63, 78, 81, 88, 93, 107,117,130,133,138 - gravel, 114 - in phosphorites, 59, 60, 61, 63, 64, 70, 8 1 , 85, 88, 97, 107, 108, 117, 118, 129, 133, 134, 136, 138, 141, 144, 147, 155, 157, 159,172 - in sediments, 68, 78, 93, 111, 115, 130,209,217 - sand, 5 8 , 1 1 1 , 114, 115 Quaternary, 101, 152, 153, 229 -, see also Age Rabat, 68 Rain, 6 , 8 Radiocarbon, 101, 125, 158, 175, 180 - age, 158 - analysis, 17 5 - dating, 1 8 0 - method, 125 Radiolaria, 41, 118 Rare earth elements, 173, 256-265, 275 Rare elements, 266-277 Rarotonga Island, 1 6 3 Recent, 101, 103, 105, 125, 147, 153, 229 -,see also Age; Phosphorites, age of Recycling, 27, 29 Red clay, 41-43,47 Red Sea, 1 4 , 1 6 , 4 4 Reducing environment, 53 Reducing zone, 1 2 2

340 Refractive index, 78, 81, 93, 100, 133, 136,180 Replica, 64 Replacement, 6 4 , 1 8 2 Reserve, 67, 7 3 Residue, 8, 1 3 -, dry, 1 3 -, inorganic, 8 Retort horizon, 285 Reworking, 101, 223-229 Rhone, 1 0 Rime, 6 Rioni, 1 0 Riphean, 284 River, 7-13, 1 7 - discharge, 7, 13, 17, 42 - mouth,42 - suspension, 17 - water, 8-12 Rock, 1 5 , 1 6 -, igneous, 1 5 -, ferruginous, 64 -, lunar, 1 6 -,phosphate, 57, 74, 106, 163, 169, 173 -, weathered, 15 -, see also Phosphatized rock Rocky Mountains, 245, 282, 285, 287 Romanche fault, 177 Rostov, 1 2 Rotorua, 1 4 Rudist, 164 Russian Platform, 248, 256, 257 Rutile, 209, 214 Saanich Inlet, 46 Safi, 6 8 Sahara, 68, 72, 7 3 Salinity, 19, 50 San Clemente Island, 237 Sand, 36, 37, 46, 49, 56, 58, 59, 68, 74, 77, 78, 107, 111, 112, 114, 115, 124, 127, 130, 157, 207213,215 -, bryozoan, 114 -, clastic, 211-213 -, dune, 124 -, foraminifera], 59, 114, 127, 210, 212 -, glauconitic, 58, 59, 114, 115, 127,

130, 212,216

-, gritty, 1 5 9

-, mineral composition of, 215 -,phosphatic, 68, 74, 77, 78, 111, 112,114 -, quartz, 58, 111, 114, 1 1 5 -,relict, 111 -, shell, 58, 212 Sandstone, 57, 59, 63, 68, 107 San Diego, 115 San Francisco, 115 San Nickolas Island, 237 Santorin, 1 4 , 1 6 Sardine, 9 3 Saturation, 21, 22 Saudi Arabia, 288 Saussurite, 8 5 Savanna River, 112 Scale, fish, 27 Scandium, 269,271-274 Scanning microprobe analysis, 148-151 Scanning microscope, 83, 84, 87, 141, 143, 152, 153, 169, 171, 178, 265 Scripps guyot, 1 6 6 Sea level, 101, 210, 225, 227 Sea mount, 55,56,163-183 Sea urchin, 168 Sechura, 281, 289 Secretion, 265 Sediment, 36, 37, 41-44, 46, 49, 53, 56, 58,’ 59, 61, 68, 69, 74-78, 81-83, 89-92, 95, 96, 102, 107, 111, 112, 114-116, 122, 124-130, 157, 168, 207-218, 227 -, biogenic, 41, 68, 74, 77, 90, 126, 129, 130, 207, 208, 210, 213, 215,227 -,calcareous, 42, 43, 68, 74, 75, 77, 78,90,127,168,210 -,cherty, 4 2 , 4 3 -, clastic, 42, 43, 74, 75, 77, 78, 89, 207, 210, 212, 213, 215, 216, 227 -, coccolithic, 4 1 -, diatomaceous, 74, 81-83, 91, 92, 95, 96, 102, 104, 105, 127, 129, 130, 207, 208, 210, 213, 215, 216

341 -, ethmodiscan, 4 1 -, eupelagic, 4 1 -, foraminiferal, 129, 207, 210, 212, 213,215

-, glauconitic, 44, 58, 59, 75, 77, 114, 115, 126, 127, 130, 212, 213, 216 -, hydrogoethite-chamosite, 44 -, lacustrine, 5 3 -, marine, 36-42, 5 3 -, metalliferous, 44 -, miopelagic, 4 1 -, muddy, 4 6 , 5 8 -, pelagic, 41-44 -,phosphatic, 61, 95, 96, 114, 121, 122,124,125,129 -, radiolarian, 4 1 -, relict, 115 --,sandy, 36, 37, 46, 49, 56, 58, 59, 6 8 , 7 4 , 7 7 , 7 8 , 1 0 7 , 1 1 1 , 112 --, see also Sand -, shelly, 58, 207, 212 -, siliceous, 42, 74, 75, 126, 207 _ - , see also Sediments, diatomaceous -, terrigenous, 212 Sedimentation rate, 102 Seine, 1 0 Senegal, 288 Senonian, 1 6 5 , 1 6 7 , 1 7 3 -, see also Age Serpulid, 117 Shelf -, Atlantic of U.S.A., 114 -, boundary of, 74 -, inner, 74 - island, 115 - of Angola, 107 - of Baja California, 1 2 1 - of California, 1 1 5 - of Central Africa, 107 - of Chile, 44, 52, 125-153, 185217 - of Congo, 107 - of Gabon, 107 - of Georgia, 1 1 2 - of Ghana, 107 - of Guinea, 107 - of Hindostan, 1 1 5 - ofJapan,52 - of Morocco, 55, 6 8

- of - of - of - of - of - of - of - of - of

Namibia, 52, 74 northwest Africa, 68, 71, 72 Peru, 52,125-153,185-218 Portugal, 55 Sahara, 68, 72 Socotra, 1 5 5 South Africa, 61 South America, 126 southwest Africa, 44, 55, 74, 77-80,91,96,207 Shell, 68, 72, 1 1 4 -, see also Sediment Shepard guyot, 1 6 5 Siberia, 285 Silica, 64, 66, 118, 123, 200, 240-242 -, amorphous, 123,240-242 -, see also Phosphorite, chemical composition of Siliceous-phosphatic rock, 170, 172 Silicoflagellate, 217 Silt, 36, 3 7 , 4 6 , 57, 208, 212 Silver, 271 Simushir, 1 4 Siphonophore, 26 Slumping, 218 Snow, 6 Socotra Island, 1 5 5 Sodium, 65, 66, 1 0 0 -, see also Phosphorite, chemical composition of Soil, 8, 9 Sorption, 33, 3 4 , 4 9 Sorting, 101, 124 -, coefficient of, 1 2 4 South Africa, 55, 6 1 South African Republic, 74 South America, 1 2 6 Southern California, 116 Southwest Africa, 44, 74, 76, 77 Specific gravity, 77, 94, 100, 116 Sphene, 1 2 4 , 2 0 9 , 2 1 4 Spherul, 133 -, see ~ 1 . ~Pyrite 0 Sponge, 2 6 , 1 1 7 , 1 1 8 , 1 5 6 , 2 1 7 Stagnant basin, 1 7 Stagnation, 206 Starfish, 26 Staurolite, 209, 214 Steam vent, 1 6 Stomatopod, 26

342 Straits of Florida, 107 Stratification, 193 Stream, 8 Stromatophoride, 165, 168 Strontium, 267, 269-272 Structure, 133, 172 Struvite, 32 Subcolloidal fraction, 9 Subduction, 285 Substitution, 100 Sulfur, 209 -, see also Phosphorite, chemical composition of Superphosphate, 67 Suspended matter, 7, 9-11 Sylvania guyot, 1 6 3 Syr-Dar'ya, 11 Syria, 288 Taganrog Gulf, 46 Tasman Sea, 1 6 3 , 1 6 8 , 1 7 5 Taupo guyot, 168 Tertiary, 66, 67, 74, 125, 126 -, see also Age Teterata geyser, 1 4 Tethys, 287-290 Texture, 135 TG curve, 97 Thaw, 8 Thermogram, 97-99 Thin-section, 60, 70, 86, 111, 118, 122, 123, 133, 135-139, 147151,170,172,245 Thomas Washington guyot, 167 Thorium, 152, 255 Titanium, 269, 271-274 Titanomagnetite, 134 Tjiater spring, 13, 1 4 Togo, 288 Tourmaline, 61, 209, 214 Trade wind, 185, 288, 289 Transgression, 228, 285 Tremolite, 144 Trujillo, 196 Tuff breccia, 163, 166, 1 7 0 Tunicate, 26 Tunisia, 288 Turbidity, 10, 1 2 Turkey, 288 Turonian, 173, 176

-,

see also Age Tyrrhenian Sea, 1 6

Udaipur, 284, 286 Underground discharge, 12, 13, 1 7 Unit cell, 78, 94, 97, 100, 134, 136 Upwelling, 23, 42, 52, 124, 191-207, 219, 282-289 Urals, 285 Uraninite, 245, 251, 252 Uranium, 67, 101-105, 120, 1521 5 4 , 1 7 3 , 1 7 5 , 245-255 - content, 104, 152, 173, 245, 247249, 255 - isotopes, 67, 101-105, 120, 152154,175,246,255 - leaching, 177 - tetravalent, 152, 154, 246 Urea, 32 U.S.A., 115 U.S.S.R., 284 Uzon, 1 4 Valparaiso, 126 Vanadium, 267-272, 274 Veller River, 5 1 Vendian, 284 Venezuela, 288 Venezuela basin, 47 Viet-Nam, 284 Volcanic activity, 182 Volcanic glass,'134, 159, 180, 213 Volcanics, 1 3 Volcanism, 13 Volcano, 14, 16 -, Idien, 1 4 -, T a d , 1 4 -, Santorin, 14, 1 6 Volcanogenic material, 36, 134 Volga, 9, 10, 287 Vyatka, 31 Walvis Bay, 74, 79, 192, 198, 201 Water, 5, 7, 9-11, 13-16, 19, 32, 45-50, 100, 180, 188-201, 219, 221 -, absorbed, 97, 99 -, Antarctic, 188, 197 - balance, 5, 7 -, bound, 97-100

343 -, connate, 15 content in phosphate, 100 - discharge, 7,9 -, interstitial, 32,45-50, 221 - masses, 188,190 -. runoff, 10,11 -, salinity of,19,188 - structure, 189 -, temperature of, 19,180,190,191 -,thermal, 13,14 Wave, 188 Weathering, 15,16 West Atlantic, 107 West Australian basin, 181 White Sea, 37 Wilde guyot, 165 Wind, 185-187 -

Winterer guyot, 167 Warm track, 169,175,178,180 X-ray, 78, 94, 97, 110, 118, 129, 134,

136,146

-, amorphous, 94 - analysis, 78,97,118,129,136,146 - diagram, 134 - fluorescence, 110

Yellowstone, 14 Yenisey, 11 Zeolite, 170 Zinc, 267-211, 274,275 Zircon, 61, 63, 81, 124, 159, 180,

209,214 Zooplankton, 25,28,29,31,202,203

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