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Lecture Notes in Earth Sciences Edited by Somdev Bhattacharji, Gerald M. Friedman, Horst J. Neugebauer and Adolf Seilacher
9 I
III
III
I
I
Gisela Gerdes
Wolfgang E. Krumbein
Biolaminated Deposits I
I
I
Springer-Verlag Berlin Heidelberg NewYork London Paris Tokyo
Authors Dr. Gisela G e r d e s Prof. Dr. W o l f g a n g E. Krumbem GeomlcrobJology Division, University of Oldenburg Carl-von-Ossietzkystr. 9-11 D - 2 9 0 0 OIdenburg, West G e r m a n y
ISBN 3 - 5 4 0 - 1 7 9 3 7 - 2 Springer-Verlag Berlin Heidelberg N e w York ISBN 0 - 3 8 7 - 1 7 9 3 7 - 2 Spdnger-Verlag N e w York Berhn Heidelberg
This work is subject to copynght All rights are reserved, whether the whole or part of the material ts concerned, specifically the rights of translation, reprinting, re-use of tllustrattons, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks Duplication of this pubtlcatlon or parts thereof Is only permitted under the provisions of the German Copynght Law of September 9, 1965, in its version of June 24, 1985, and a copynght fee must always be paid, Vtolations fall under the prosecution act of the German Copyright Law, © Springer-Vedag Berlin Heidetberg 1987 Printed in Germany Pnnttng and bmding Druckhaus Beltz, Hemsbach/E,ergstr 2132/3140-543210
Petrificata parentes libus
montium calcariorum non filii
sed
sunt, cum omnis calx oriatur ab anima-
(Linnaeus,
Systema Naturae,
Ed. XII, T.
III, p. 154, 1760-1761)
PREFACE
The geological only
significance of life has long attracted mankind.
have single groups of organisms been considered,
building animals,
diatoms or "monera"
(radiolarian,
such as
Not
frame-
globigerins,
fo-
rams),
but unitarian pictures were also drawn concerned with the regu-
lation
and
pathways.
feedback The
of geochemical cycles by
enzyme-controlled
back-coupling system of
inanimate matter fascinated Vernadsky crystallographer,
interacting
metabolic living
and
(1863 - 1945), a mineralogist and
and is again stressed in Lovelock's Gaia
and Krumbein's Bioplanet or Bioid approach.
hypothesis
The role of microorganisms
in this respect is well documented in terms of disintegration of rocks, production and mineralization of organic compounds, oxidation
and reduction of metals,
ore formation. of
biomineral
catalyzation of the
formation and
biogenic
Records of stromatolites arising from the vital activity
microorganisms date back to the earliest known sedimentary environ-
ments of the Precambrian era.
The tified
aim of the work presented here is to document the in-situ straaccretion
microbes. duced the
Part
of sediments attributable to the vital I comments on terms
sedimentary structures and products. occurrence of microbial mats
activity
which relate to microbially Part II is concerned
(potential stromatolites)
in
marginal marine environments of arid and temperate coastlines. modes
of
facies
evolution in subenvironments are shown
integration of sedimentological,
microbiological
of prowith
modern Varying
through
the
and faunistic data. In
Part III structures attributed to the activity of Precambrian, and Lower Jurassic microbial communities are analyzed,
Permian
and some comple-
mentary aspects concerned with the geological potential of microbes are summarized.
Acknowledgements
(Gisela Gerdes)
P r e s e n t e d h e r e is a m o d i f i e d v e r s i o n of m y thesis w h i c h encompasses a number of individual publications. I am indebted to m a n y p e o p l e w h o a c c o m p a n i e d my way over the past years. My b e n e f a c t o r in this w o r k was W.E. Krumbein. He first introduced me to the fascinating system of microbial mats. From Gavish Sabkha and Solar Lake we went on to include the "Farbstreifen-Sandwatt" as parts of the expanding biosed i m e n t a r y system. We then turned our a t t e n t i o n to counterparts of all this in fossil records, spanning the gap b e t w e e n b i o l o g y and geology. My first encounter w i t h a c t u o p a l e o n t o l o g y was during my c o o p e r a t i o n w i t h Wo Sch~fer. His b o o k " A k t u o p a l ~ o n t o l o g i e nach Studien in der Nordsee" was the first scientific w o r k w h i c h I was able to follow through from its conception. His "Schule des Sehens", w h i c h was transformed into reality through the r e o r g a n i z a t i o n of exhibits at the Senckenberg Museum, Frankfurt, remains one of the most m e m o r a b l e imp r e s s i o n s of m y stay in that city. H.-E. Reineck p r o v i d e d support and advice in the fields of actuogeology and actuopaleontology. Our c o l l a b o r a t i o n b e g a n in "Senckenberg am Meer", Wilhelmshaven. I w o u l d like to thank h i m for the interest he shared in m y w o r k and for all his h e l p and advice. During our trips to ancient and m o d e r n d e p o s i t i o n a l environments and through our w o r k in the l a b o r a t o r y he taught me to r e c o g n i z e and understand sedimentary structures. My thanks are further extended to my other benefactor, H. K. Schminke. I am grateful also to colleagues from the G e o m i c r o b i o l o g y team and to K. Wonneberger, my former p a r t n e r at O l d e n b u r g U n i v e r s i t y marine b i o l o g y unit, Wilhelmshaven, for their d i s c u s s i o n and advice. Memories o f our w o r k together on Mellum, in the G a v i s h Sabkha, by Solar Lake and in Elat unite me w i t h Eo Holtkamp. Our stay, laboratory w o r k and accommodation on M e l l u m w e r e made p o s s i b l e b y the M e l l u m Council and in Israel by the H. Steinitz Marine B i o l o g y Laboratory, Elat and its staff. I am p a r t i c u l a r l y g r a t e f u l to F. D. Por for his advice during our stay in Israel. I would also like to thank all for a s s i s t a n c e and care in the p r e p a r a t i o n of drawings, reproductions, photographs, thin sections and checking of the manuscripts: R. Fl~gel, G., K. Oetken and H. Gerdes, W. Golletz, A. Gr~nert, E. Johnston, M. and H. M~ller, I. Raether, V. Schostak, L. Tr~nkle. I e s p e c i a l l y want to thank J. Gifford for her p a t i e n t h e l p in t r a n s f o r m i n g this m a n u s c r i p t into readable English. Finally, I am indebted to Dr. Engel and S p r i n g e r V e r l a g for p u b l i c a tion in the Lecture Notes series. I w o u l d like to thank e v e r y b o d y who made this possible.
S U M M A R Y B i o l a m i n a t e d deposits, p r o d u c e d by m i c r o b i a l communities, were studied in m o d e r n p e r i t i d a l e n v i r o n m e n t s and in the rock record. The term microbial, mat refers to modern, the t e r m s t r o m a t o l i t e to ancient analogs. The t e r m b i o l a m i n a t e d d e p o s i t s was used to e n c o m p a s s b o t h microbial m a t s and stromatolites. M i c r o b i a l mat e n v i r o n m e n t s studied are the Gavish Sabkha, the Solar Lake, b o t h h y p e r s a l i n e b a c k - b a r r i e r systems at the Gulf of Aqaba, Sinai Peninsula, and the " F a r b s t r e i f e n - S a n d w a t t " (versicolored sandy tidal flats) on Mellum, an island in the e s t u a r y e m b a y m e n t of the southern N o r t h Sea coast. Three f a c i e s - r e l e v a n t categories were distinguished: (i) the m a t - f o r m i n g microbiota, (2) e n v i r o n m e n t a l conditions controlling mat types and lithology, (3) b i o t u r b a t i o n and grazing. Cyanobacteria a c c o u n t for b i o g e n i c sediment a c c r e t i o n in all cases studied. T h r e e m a j o r groups occur: filamentous cyanobacteria, coccoid unicells w i t h b i n a r y fission and those w i t h m u l t i p l e fission. In the p r e s e n c e of these groups the following mat types evolve: (i) continuously flat (stratiform) L ~ - l a m i n a e (occur i n all environments studied); (2) translucent, v e r t i c a l l y extended L v - l a m i n a e (only Gavish Sabkha and Solar Lake); (3) n o d u l a r granules (only Gavish Sabkha). Basically, the d e v e l o p m e n t of mats is c o n t r o l l e d by moisture. Thus h i g h - l y i n g parts w h e r e the g r o u n d w a t e r table runs m o r e than 40 cm b e l o w surface are b a r e of mats. These are: The circular slope and e l e v a t e d c e n t e r of the G a v i s h Sabkha, the shorelines of the Solar Lake and the e p i s o d i c a l l y flooded upper supratidal zone of M e l l u m Island. The following situations of w a t e r supply w e r e found to stimulate mat growth: (i) Capillary m o v e m e n t of g r o u n d w a t e r to exposed surfaces, (2) shallowest calm water, b o t h r e a l i z e d in the G a v i s h Sabkha and the Solar Lake. On M e l l u m Island, mats form in the lower supratidal zone, w h i c h is flooded in the spring tide cycle and w e t t e d during low tide by capillary groundwater. S a l i n i t y is almost that of normal seawater, w h e r e a s in the Solar Lake, it ranges from 45 °/oo to 180 °/oo and in the G a v i s h Sabkha, it reaches more than 300 °/oo. S a l i n i t y increase is c o r r e l a t e d w i t h rising c o n c e n t r a t i o n s of m a g n e s i u m and sulfate ions. In the Gavish Sabkha, episodic sheetfloods cause h i g h - r a t e sedimentation w h i c h is a c c i d e n t a l to the living mats. Episodic low-rate s e d i m e n t a t i o n stimulates the mats to grow through the freshly d e p o s i t e d sediment layer. This occurs p r e d o m i n a n t l y on M e l l u m Island due to eolian transport. W i t h i n the G a v i s h Sabkha, m i n e r a l o g y of sediments, c o m m u n i t y structures, standing crops, redox p o t e n t i a l s and p H are h i g h l y c o r r e l a t i v e to the i n c r e a s i n g evenness in m o i s t u r e supply w h i c h is r e a l i z e d b y the i n c l i n a t i o n of the s y s t e m b e l o w mean sea level. These conditions bring about a lateral sequence of facies types w h i c h include (I) siliciclastic b i o l a m i n i t e s at the coastal bar base, (2) nodular to b i o l a m i noid c a r b o n a t e s at saline mud flats, (3) r e g u l a r l y stratified stromatolitic c a r b o n a t e s w i t h ooids and oncoids w i t h i n the h y p e r s a l i n e lagoon, (4) b i o l a m i n a t e d sulfate t o w a r d t h e elevated center. High-magnesium calcite in facies type 3 p r e c i p i t a t e s around d e c a y i n g organic matter and forms also the ooids and oncoids. These occur p r e d o m i n a n t l y w i t h i n h y d r o p l a s t i c L v - l a m i n a e w h i c h p r o v i d e n u m e r o u s n u c l e a t i o n centers. W i t h i n the Solar Lake, facies type 3 (stromatolitic carbonates w i t h ooids and oncoids) is m o s t important, and grows to e x t r a o r d i n a r y thickness at the lake's shelf. The regular a l t e r n a t i o n of dark and light
VJ
laminae results from seasonally o s c i l l a t i n g w a t e r depths. These conditions couple b a c k over changing light and salinity intensities t o changing dominance structures of m a t - b u i l d i n g communities. Increasing salinity correlates w i t h d e c r e a s i n g w a t e r depth and a c c o u n t s for the relative a b u n d a n c e of coccoid unicells and diatoms, b o t h active p r o d u cers of e x t r a c e l l u l a r slimes (Lv-laminae). W a t e r depths locally or temporarily i n c r e a s e d favor surface c o l o n i z a t i o n by Mic~ocoleu8 chthonoplastes (Lh-laminae). The b i o l a m i n a t e d deposits of the v e r s i c o l o r e d tidal flats on M e l l u m Island are similar to facies type 1 of the Gavish Sabkha (siliciclastic biolaminites). D i f f e r e n c e s exist in the lithology: Sediments upon or through w h i c h the mats on M e l l u m Island grow are made up of clean sand. The grains originate p r e d o m i n a n t l y from re-worked glacial sediments and are rounded to well rounded. By contrast, the strong a n g u l a r i t y of s i l i c i c l a s t i c grains in the Gavish Sabkha clearly shows their status as p r i m a r y w e a t h e r i n g products. In all environments studied, insects p l a y a s i g n i f i c a n t role. M a i n l y salt b e e t l e s c o n t r i b u t e to the l e b e n s s p u r e n spectrum. There is no indication that b u r r o w i n g and grazing beetles and dipterans are detrimental to the growing mat systems. A c c o r d i n g to the m a r i n e fauna, two distributional barriers exist: (i) p h y s i c a l and (2) b i o g e o c h e m i c a l factors. Physical b a r r i e r s are (a) h y p e r s a l i n i t y and barrier-closing, w h i c h r e s t r i c t the m a r i n e fauna in the G a v i s h Sabkha and the Solar Lake to a few species, m a i n l y m e i o f a u n a l elements such as o s t r a c o d s and copepods. Only in the Gavish Sabkha, one m a r i n e gastropod species occurs w h i c h colonizes mud flats of lower salinity. A salinity barrier of about 70 °/oo separates the g a s t r o p o d h a b i t a t s from the zones of growing mats. Under reduced salinity, the snails are able to destroy the m i c r o b i a l mats completely. (b) D e c r e a s i n g r e g u l a r i t y of flooding in the m i c r o b i a l mat e n v i r o n m e n t of M e l l u m Island excludes intertidal d e f o r m a t i v e b u r r o w e r s such as cockles and lugworms. However, locally the mats are p i e r c e d by numerous d w e l l i n g traces. These stem from small polychaetes and amphipod crustaceans w h i c h are able to spread over the i n t e r t i d a l - s u p r a t i d a l b o u n d a r y and settle up to the MHWS-Ievel. Biogeochemical b a r r i e r s are oxygen d e p l e t i o n w i t h i n the sediments, high ammonia and sulfide contents, which generate through b a c t e r i a l break-down of organic matter. W i t h i n the h i g h l y p r o d u c t i v e mats of Mic~ocoleu8 chthonoplastes on M e l l u m Island, dwelling traces of marine p o l y c h a e t e s and a m p h i p o d crustaceans d i s a p p e a r due to these conditions. Microcoleus chthonoplastes, indiThe name of the m a t - f o r m i n g species, cates its c a p a c i t y to form "soils" (Greek chthonos). While lithology is not altered, the p r e s e n c e of Mic~ocoleu8 mats leads to a h a b i t a t change which excludes t r a c e - m a k i n g "arenophile" i n v e r t e b r a t e species and favors "chthonophile" species w h i c h do not leave traces. S t r o m a t o l i t i c m i c r o s t r u c t u r e s studied in rock specimens were interpreted using m o d e r n analogs: Microcolumnar buildups in P r e c a m b r i a n stromatolites, ooids and oncoids were compared w i t h those of modern microbial mats. The nodular to b i o l a m i n o i d facies type found in the Gavish Sabkha was s u g g e s t e d to be an analog to the P l a t t e n d o l o m i t e facies of Permian Zechstein, North Poland. Studies of the Lower Jurassic ironstone of L o r r a i n e clearly indicate that fungi h a v e b e e n involved in the formation of stromatolites, ooids and oncoids. In conclusion, the comparative study of m i c r o s t r u c t u r e s in m i c r o b i a l mats and stromatolites reveals a b e t t e r u n d e r s t a n d i n g in both fields. In m a n y cases, it was g e o l o g y w h i c h first revealed the s i m i l a r i t y of recent forms to those ancient ones and c o n s e q u e n t l y e n c o u r a g e d r e s e a r c h into them.
CONTENTS
PREFACE ............................................................ ACKNOWLEDGEMENTS ................................................... SUMMARY .% . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I.
LAYERED SEDIMENT ACCRETION BY MICROBES INTRODUCTORY REMARKS .......................................... i.
2. II.
III IV V
TERMS i.i. 1.2. 1.3. THE
IN USE ............................................... Stromatolites and subsequent terms ................... Specific fabrics without direct evidence of microbes Biolaminated particles ~ ..............................
PROBLEM
OF
VERSATILITY
.
.................................
STROMATOLITE ENVIRONMENTS IN T H E P E R I T I D A L ZONE MODERN EXAMPLES ............................................... i.
THE GAVISH SABKHA A HYPERSALINE (GULF OF AQABA, SINAI PENINSULA) -
BACK-BARRIER SYSTEM ............................
.........................................
3 3 5 6 9
13
15
1.1.
Introduction
1.2.
Methods
1.3.
Locality
...........................
18
1.4.
The physical environment ............................. 1.4.1. Geomorphic relief ............................. 1.4.2. Hydrology ..................................... 1.4.3. Temperatures ..................................
18 18 22 24
1.5.
Lithological framework ........................ ....... 1.5.1. Evaporites .................................... 1.5.2. Carbonates .................................... 1.5.3. Detrital clastics ............................. 1.5.4. Internal fabrics of sheetflood deposits .......
25 25 27 27 29
1.6.
Stromatolitic facies types ........................... 1.6.1. The microbiota ................................ 1.6.2. Major mat-s%ructuring organisms ............... 1.6.3. Character and distribution of stromatolitic facies types .................................. 1.6.4. Facies type-related biogeochemistry ........... 1.6.5. Products of early diagenetic processes ........ 1.6.6. In-situ formation of ooids and oncoids ........ 1.6.7. Microbially modified surface structures .......
30 30 31 34 42 45 49 53
1.7.
Faunal 1.7.1. 1.7.2. 1.7.3. 1.7.4. 1.7.5. 1.7.6.
55 56 56 58 65 66 68
1.8.
Modes
1.9.
Summary
.............................................. and
previous
work
influence on the biolaminated deposits ........ Species composition and distribution .......... Trophic relations ............................. Systematic ichnology .......................... Environmental zonation of trace categories .... Skeletal hard parts ........................... Grazing stress (experimental approach) ........ of
stratification and
conclusions
15 16
..............................
70
..............................
72
VIII
2. T H E S O L A R L A K E - I M P O R T A N C E O F S M A L L T E C T O N I C E V E N T S (GULF OF AQABA, SINAI PENINSULA) ..........................
.
75
2.1.
Introduction
.........................................
75
2.2.
Locality
previous
76
2.3.
Bathymetric
2.4.
Sub-environments 2.4.1. The shelf 2.4.2. The slope
and facies types .................... ..................................... and bottom ..........................
78 78 84
2.5.
Lithologic and ichnologic framework .................. 2.5.1. C l a s t i c c o m p o u n d s ............................. 2.5.2. Evaporites .................................... 2.5.3. Ichnologic patterns ...........................
85 85 85 86
2.6.
Summary and conclusions .............................. 2.6.1. Occurrence of facies types compared to the Gavish Sabkha ................................. 2 . 6 . 2 . T i m e i n t e r v a l s r e c o r d e d in s t r o m a t o l i t e s ...... 2.6.3. Importance of small tectonic events ...........
87
and
zones
and
work
...........................
limnologic
cycle
...............
3. V E R S I C O L O R E D TIDAL FLATS (MELLUM ISLAND, S O U T H E R N N O R T H SEA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .........................................
77
87 89 90
93
3.1.
Introduction
3.2.
Methods
3.3.
Locality and previous work ........................... 3.3.1. Recent sedimentological history ............... 3.3.2. General setting of Mellum Island a n d s t u d y a r e a .............. . . . . . . . . . . . . . . . . . . . 3.3.3. P r e v i o u s w o r k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
95 97
3.4.
The physical environment of mat formation ............ 3.4.1. C l i m a t e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.2. F l o o d i n g f r e q u e n c y . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.3. Salinity ...................................... 3.4.4. Moisture ...................................... 3.4.5. Morphological unconformities ..................
97 97 98 98 98 99
3.5.
Sub-environments and facies .......................... 3.5.1. L o c a l d o m i n a n c e o f m a t - p r o d u c i n g s p e c i e s ...... 3.5.2. S t r a t i f i c a t i o n of living top mats ............. 3.5.3. Internal sedimentary structures ............... 3.5.4. S t a n d i n g c r o p s a n d b i o g e o c h e m i s t r y ............
i01 i01 102 105 106
3.6.
Fauna and ichnofabrics ............................... 3.6.1. Mixed marine-terrestrial composition .......... 3.6.2. Trophic types ................................. 3.6.3. Regional distribution of trophic types ........ 3.6.4. Life habits and ichnofabrics ..................
109 109 iii 114 114
3.7.
D o m i n a n c e c h a n g e a n d its i m p o r t a n c e f o r b i o t u r b a t i o n grades and patterns .................................. 118 3.7.1. Effects of increasing elevation ............... 118 3.7.2. E f f e c t s o f i n c r e a s i n g m i c r o b i a l p r o d u c t i v i t y .. 1 2 4 3.7.3 Promoting and limiting distributlonal factors 125
..............................................
93 94 94 94
IX
3.8.
Intertidal-supratidal sequence ....................... 3.8.1. Change of sedimentary internal structures ..... 3.8.2. Change of sedimentary surface forms ...........
127 128 129
3.9.
Subaerial rise of biolaminated quartz-sand (experimental approach) ..............................
132
Summary
134
3.10.
4.
III.
WHAT
THE
4.
ENVIRONMENTS
HAVE
IN C O M M O N
.......
137
4.3.
Peritidal settings ................................... 4.3.1. The "sabkha cycle" ............................ 4.3.2. Temperate humid coastlines ....................
139 139 140
THE
141
"Purpose"
BETWEEN
organisms
REMARKS
Saltbeetles:
INTRODUCTION
pioneer
- FINAL
4.2.
GAP
as
..............................
Cyanobacteria
2. M E T H O D S 3.
conclusions
4.1.
SPANNING i.
and
of
dwelling
MICROBIOLOGY
AND
...................
137
burrows
138
GEOLOGY
...........
.............
...............................................
143
....................................................
DESCRIPTION
AND
INTERPRETATION
OF
FOSSIL
MICROSTRUCTURES
144 ...
145
3.1.
Precambrian Gunflint iron formation, Ontario ......... 145 3.1.1. Provenance of rock samples and previous work .. 1 4 5 3.1.2. Microstructures ............................... 146
3.2.
Permian Zechstein Plattendolomite of North Poland (PZ3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1. Provenance of rock samples and previous work 3.2.2. Microstructures ...............................
148 .. 1 4 8 148
3.3.
Lower Jurassic ironstone, Lorraine ................... 151 3.3.1. Provenance of rock samples and previous w o r k .. 1 5 1 3.3.2. Microstructures ............................... 152
3.4.
Summary
and
conclusions
..............................
PATHWAYS INVOLVED IN M I C R O B I A L SEDIMENT ACCRETION: A COMPLEMENTARY SUMMARY ....................................
REFERENCES
.........................................................
154
157
165
PART
LAYERED
-
INTRODUCTORY
SEDIMENT
REMARKS
I
ACCRETION
ON
TERMS
BY
MICROBES
AND
PROBLEMS
-
"The
name
tions
stromatolite
with
a fine,
structure,
in c o n t r a s t
of
...
oolites
transition tion
between
the
laminated
structures
products
comment
attributable
on terms
tic b a c k g r o u n d . also
to
these
generated
The general
sedimentary
I. i. S t r o m a t o l i t e s
KALKOWSKY patterns
(Table
and
i) with
same
gene-
in use led us
of
microbially
terms
the term s t r o m a t o l i t e
only the structure
of their
aggregates
KRUMBEIN,
Subsequently,
namely
thin
structures.
used
by r e f i n e d
paleomicrobiology
the
structures
of terms
on the t e r m i n o l o g y
by o r g a n i s m s
evidenced
stromatoid
of
cover one and the
lack of d e f i n i t i o n s
produced
more
to s e d i m e n t a r y
of m i c r o o r g a n i s m s
in rocks,
1983).
to
IN USE
terms
remarks
and s u b s e q u e n t
(1908)
is also a
The transi-
from a center point."
relating
that these
introductory
formation
1908)
to the a c t i v i t y
the aim of d e m o n s t r a t i n g
ooid-bag
independance
forma-
laminated
sense there
ooid and stromatoid.
polyooid,
I. TERMS
Here we will
flat
to the c o n c e n t r i c
increasing
(E. KALKOWSKY,
to c a r b o n a t e
or less
In a c e r t a i n
from ooid,
denotes
relates
more
refer
..."
1965;
the main
to
that
(translated
suggestion
KNOLL
layered
so small
of m i c r o p a l e o n t o l o g y
& TYLER,
were
to
"have been
is p r e s e r v e d
this v i s i o n a r y
methods
(BARGHOORN
that m i c r o o r g a n i s m s
which
by
was more and merging
& AWRAMIK,
framework builders
of
into 1983),
stroma-
~olites.
The rize
term Spongiostromata
fossil
stromata
crustose
include
origin was
growth
was
structures.
stromatolites
carbonate
introduced
as well
precipitation
by PIA
According
(1927) to PIA,
as oncolites,
by crustose
algae.
to
characte-
the Spongio-
and his
theory of
TABLE 1. Terms relating to m i c r o b i a l l y g e n e r a t e d layered structures and particles
Stromatolites Spongiostromata Algal sediments Cryptalgal fabrics Algal mats B l u e - g r e e n algal bioherms Microbial mats
LAYERED STRUCTURES FOSSIL AND RECENT: SYNONYMOUS TERMS
I.
Growth b e d d i n g FABRICS W I T H O U T DIRECT EVIDENCE OF MICROORGANISMS
II.
III. PARTICLES
Subsequent intertidal
(KALKOWSKY, 1908) (PIA, 1927) (BLACK, 1933) (AITKEN, 1967) (GOLUBIC, 1976) (RICHTER et al., 1979) (BROCK, 1976; KRUMBEIN, 1986) (PETTIJOHN & POTTER, 1964)
Fenestral fabrics Thrombolitic fabrics
(TEBBUTT et al. 1965) (AITKEN, 1967)
Oncoids Ooids
(HEIM, 1916) (KALKOWSKY, 1908)
studies of crustose algae in m o d e r n shallow subtidal environments
of the tropics and subtropics have
PIA's idea that calcareous algae have built stromatolites.
Accordingly,
terms created to designate modern analogs of stromatolites were sediments" or "algal mats".
Further terms used are
and b l u e - ~ r e e n algal b i o h e r m s since
and
supported
"algal
"cryptalgal fabrics"
"blue-green algae" were o b s e r v e d to
be most c o m m o n l y involved in stromatolite formation.
The term "blue-green algae" is the traditional b o t a n i c a l assignment. However,
t a x o n o m i c a l l y they are not algae but g r a m - n e g a t i v e l y reacting,
photosynthetic
bacteria.
Thus
group is now "cyanobacteria" 1979c;
RIPPKA et al.,
the t a x o n o m i c a l l y revised name of
(STANIER & COHEN-BAZIRE,
1977;
the
KRUMBEIN,
1979).
However, we should avoid the term "cyanobacterial mats" to d e s i g n a t e m o d e r n analogs of stromatolites
for two reasons:
i. A l t h o u g h many stromatolites are in fact p r o d u c e d via p h o t o s y n t h e tic a c t i v i t y of cyanobacteria, laminated greens"
rock
structures
are
These
structures
can also originate
organotrophic al.,
it seems important to stress that
1985;
bacteria DANIELLI
1981; KRETZSCHMAR,
not e x c l u s i v e l y
(DAHANAYAKE & KRUMBEIN,
& EDINTON,
1982; KRUMBEIN,
produced
from fungi 1985;
by
"blue-
and
chemo-
DAHANAYAKE
1983; D E X T E R - D Y E R et al., 1983).
wavy
et
1984; GYGI,
2. In
the
light of studies on m o d e r n l a m i n a t e d mats w h i c h
display
very complex b i o c o e n o t i c systems including n u m e r o u s groups of and n u m e r o u s m e t a b o l i c pathways, produced
by
diverse
microbes
it is a s s u m e d that s t r o m a t o l i t e s were
microecosystems
rather than
by
"monocultures".
C y a n o b a c t e r i a l and fungal components are often well p r e s e r v e d in matolites while in
due to their e x t r a c e l l u l a r sheaths,
other a s s o c i a t e d p h o t o t r o p h s and a n a e r o b i c h e t e r o t r o p h s
evidence
however,
(AWRAMIK et al.,
regulate the
1978;
KNOLL &
AWRAMIK,
The
i m p o r t a n t for the trapping and p r e c i p i t a t i o n of
biochemical
c a l c i u m carbonate,
1979a,
which
often
bacteria
magnesium,
copper,
iron,
manganese
1972; FRIED~tAN et al.,
1980; F E R G U S O N & BURNE,
1984; E C C L E S T O N et al.,
occur in a s s o c i a t i o n
with
which
support
the s u c c e s s i o n
salts
1973; KRUMBEIN,
1981; NOVITSKY,
1985; W E S T B R O E K et al., stromatolites.
and
is
minerals
Hence
and fungi are c o n s i d e r e d to be the main p r o d u c e r s of
substrate
are
a c t i v i t y of the a s s o c i a t e d b a c t e r i a
1969; MITTERER,
b; W I L S O N et al.,
LUCAS & PREVOT,
not
These,
"physicochemistry" of a mat system and thus
fundamental.
(KITANO et al.,
are
1983).
particularly e.g.
stro-
envelopes and capsules,
subsequent
1983; 1985), cyano-
organic
biochemical
a c t i v i t y of other bacteria.
A c c o r d i n g l y the term "microbial mat" is p r e f e r e n t i a l l y used today to denote m o d e r n analogs of s t r o m a t o l i t e s 1979;
BAULD,
1984; COHEN et al.,
(BROCK,
1984).
1976;
In their u n c o n s o l i d a t e d state,
m i c r o b i a l mats of varying c o m p o s i t i o n are also termed matolites"
(KRUMBEIN,
1983).
"potential
A s a t i s f a c t o r y d e f i n i t i o n of
mats has been given r e c e n t l y by K R U M B E I N
To
K R U M B E I N et al.,
microbial
(1986a).
finish the list of terms a s s o c i a t e d w i t h s t r o m a t o l i t e s and their
m o d e r n analogs we refer to the atlas of p r i m a r y s e d i m e n t a r y of
stro-
P E T T I J O H N & P O T T E R (1964),
who included stromatolites
structures inasmuch
as
they are "a type of growth bedding".
i. 2. S p e c i f i c fabrics w i t h o u t d i r e c t e v i d e n c e of m i c r o o r g a n i s m s
Upon specific
decay,
sediments can be devoid of m i c r o b i a l cell remains
patterns
but
such as fenestral and t h r o m b o l i t i c fabrics can indi-
cate s e d i m e n t a c c r e t i o n by microbes.
F e n e s t r a l fabrics in laminated m i c r o b i a l mats commonly generate gas bubble formation,
shrinkage and d e s s i c a t i o n
(MONTY,
from
1976). The term
"fenestra"
was
suggested by TEBBUTT et al.
p e n e c o n t e m p o r a n e o u s gap in rock frame work, interstices".
(1965) for a "primary
Fenestrae were found w i t h i n laminae of u n i c e l l u l a r cyano-
b a c t e r i a w h i c h possess usually a great p l a s t i c i t y due to large ties
of gel around cell colonies.
gel-supported
If in stratified mat
quanti-
systems,
the
laminae are sandwiched b e t w e e n laminae b u i l t of filamen-
tous microorganisms,
the voids are elongated,
ding plane and d e s c r i b e a laminoid p a t t e r n & TOSCHEK,
or
larger than g r a i n - s u p p o r t e d
follow the general bed-
(LF-A-type; M U L L E R J U N G B L U T H
1969). On the other hand, more e x t e n s i v e layers d o m i n a t e d by
unicellular irregular
organisms and their e x t r a c e l l u l a r slimes can also show arrangement
sedimentary
of fenestrae
(LF-B-type).
Laminated
an
patterns,
augen structures and lensoids as well as the formation
of
oncoids
and ooids in situ can be derived p h y s i c a l l y a c c o r d i n g
to
law
p a t t e r n formation in laminae of d i f f e r e n t v i s c o s i t i e s
(D'ARCY
of
THOMPSON,
1984).
Thrombolitic ments
the
are
fabrics
due
intergrowing
(AITKEN,
1967)
in m i c r o b i a l l y p r o d u c e d
to irregular d i s t r i b u t i o n of decaying
dead
colonies or internal d i s s o l u t i o n of mineral
around colonies of m i c r o o r g a n i s m s
(MONTY,
sedi-
colonies,
precipitates
1976).
i. 3. B i o l a m i n a t e d p a r t i c l e s
The name oncoid was suggested by HEIM les
(1916) for spheroidal
partic-
w i t h n o n - c o n c e n t r i c succession of more or less concentric
laminae
(FLUGEL,
1982). PIA (1927) regarded them as a subgroup of the Spongio-
stromata, above)
and
is
his
theory
of c a r b o n a t e p r e c i p i t a t i o n by
still in use today,
algae
w h i l e HEIM's suggestion was
(see
that
the
formation of oncoids w o u l d be due to the "aggressive activity of bacterial
colonies"
environments involved; around
we should,
nuclei
empty
spaces
activity"
Whether
Oncoids appear in both the fossil record
together with m i c r o b i a l mats. however,
(bioclasts,
consider whether mineral
m i c r o b i a l clots and lumps,
w o u l d be a b e t t e r i n d i c a t i o n
of
precipitates
lithoclasts)
"aggressive
or not ooids are of b i o g e n i c origin is still a The
name
was
or
bacterial
nucleus.
matter
suggested by K A L K O W S K Y for more
spherical or ellipsoidal grains w i t h uniform, a
modern
(i. e. b a c t e r i a l decay of the organic substrate).
controversy.
ting
and
C y a n o b a c t e r i a are commonly
for
or
less
concentric laminae
coa-
The use of the t e r m ooid is rather c o m p l i c a t e d since
it
is
u n d e r s t o o d to include at least two d i f f e r e n t
(FLUGEL, ooids;
1982).
Generally,
TEICHERT,
ooids
and
oolites
kinds
of
origin
(rocks consisting
of
1970) are studied w i t h the consensus that they origi-
nate in h i g h - e n e r g y environments.
However,
several modern mat environ-
ments show h o w it b e c o m e s p o s s i b l e to o b t a i n laminated p a r t i c l e s by the interaction
of
microbial
communities with a
physical
and
chemical
environment.
LUDWIG
&
THEOBALD
(1852) o b s e r v e d the formation of
concentrically
laminated coated grains in the thermal waters of Bad N a u h e i m w h i c h w e r e called
"Erbsensteine"
and oncoid
(HEIM,
i. e.
pisoids,
the terms ooid
(KALKOWSKY,
1916) being unknown at that time.
1908)
The authors noted
c y a n o b a c t e r i a - and d i a t o m - d o m i n a t e d m i c r o b i a l mats in an o p e n - a i r thermal
w a t e r course and r e c o g n i z e d the formation of coated grains
gas
bubbles,
m e t a b o l i c a l l y derived from the
mats.
authors noted that in fall the mat was degrading, release of the "Erbensteine",
around
Furthermore,
the
which resulted in the
and their d e p o s i t i o n d o w n s t r e a m in sandy
d e p r e s s i o n s as pisolites.
These, intimate
as
well as various other studies,
imply the
existence
genetic r e l a t i o n s h i p s b e t w e e n low energy e n v i r o n m e n t s and the
formation of ooids during p a r t i t i o n of m i c r o b i a l communities 1885,
ROTHPLETZ,
MITTERER,
1892, GIESENHAGEN,
1971). F A B R I C I U S
Bahama
ooids,
slimes
of microorganisms,
the
coatings
grains.
of
noticed
and
1922; SIMONE,
(WALTHER,
1981; FLUGEL,
1982;
(1977), w h e n studying the u l t r a s t r u c t u r e of
epilithic coatings of various
particles
with
immediate p r e c i p i t a t i o n of aragonite within
finally the
genesis
of
concentrically
laminated
He concluded that m i c r o b i a l p a r t i t i o n in the genesis of coated
grains is of p r i m a r y importance, while o v e r s a t u r a t i o n of the water with calcite,
The lites the
a g i t a t i o n and even nuclei supply are of secondary importance.
recent finding of m i c r o b i a l mats b u i l d i n g real domal w i t h i n the Bahama Bank e n v i r o n m e n t strengthens the
initiation
stromato-
argument
of ooid formation w i t h i n m i c r o b i a l mats also
for
of the
Bahama Bank ooid shoals.
In summary, should
we p r o p o s e that the genetic d e f i n i t i o n of the term ooid
imply b i o g e n i c i t y rather than abiogenicity.
We p r o p o s e further
that the term ooid should be p l a c e d into the g e n e t i c a l l y linked sequence
of
laminated s e d i m e n t a r y bodies and strata w h i c h
participation
of m i c r o o r g a n i s m s
(see KALKOWSKY,
form
1908).
under
the
The term ooid
(modi-
TABLE 2. C l a s s i f i c a t i o n of b i o l a m i n a t e d deposits and p a r t i c l e s fied after D A H A N A Y A K E & KRUMBEIN, 1986)
Laminated particles
L a m i n a t e d structures Single structure
Criteria
Assemblage
Single particle
Assemblage
Single Assemp a r t i c l e blage
Stromatolite
Ooid
Oolite
Oncoid
Stromatoloid rock
Ooloid
Ooloid rock
Oncoloid Oncoloid rock
GENESIS Biogenic
Stromatoid
A b i o g e n i c Stromatoloid
Irregular rounded
Concentric discontinous
Concentric continuous
Planar to conical
LAMINAT I ON
(**)
Regular rounded
Tabular, domed or columnar
MORPHOLOGY
(*)
(*)
Oncolite
For o o i d s / o o l o i d s larger than 2 m m in diameter the terms p i s o l o i d (pisolite/pisoloid rock) may be used
(**) For o n c o i d s / o n c o l o i d s oncoid/microoncoloid used
less than 2 mm in d i a m e t e r the terms micro(microoncolite/microoncoloid rock) m a y be
w o u l d then define a regularly concentric, ly
c o n c e n t r i c coated grain.
more
the term oncoid an irregular-
Finally the term stromatoid w o u l d include
or less s t r a t i f o r m lamina types
(Lh- and L v - l a m i n a e as
in this volume), h e m i s p h e r o i d structures
described
(like the d o m a l LLH- and sepa-
rate v e r t i c a l l y stacked SH-types c l a s s i f i e d by LOGAN et al., also BATHURST,
1971).
Logically,
t h o c h t h o n o u s or allochthonous)
rocks composed of ooids
are then oolites,
lites and of stromatoids are s t r o m a t o l i t e s
to
(e. g.
gical o r i g i n is not unequivocal. ted like"
the
suffix
(ooid-like,
"-oloid"
onco-
(1981) and BUICK
geyserites)
(1984) we
deposits
or
or w h e r e the biolo-
In this case the said authors sugges-
(OEHLER,
oncoid-like)
(either au-
of oncoids are
avoid the a b o v e - m e n t i o n e d terms if l a m i n a t e d
p a r t i c l e s are clearly a b i o g e n i c
1964; see
(Table 2).
F o l l o w i n g the suggestions of BUICK et al. propose
pisoid/
1972) w h i c h means a
appearance.
advice w i t h respect to the whole sequence
"stromatolite-
We p r o p o s e to follow
(Table 2).
this
2. THE P R O B L E M OF V E R S A T I L I T Y
Fig. in
1 has b e e n c o n s t r u c t e d to illustrate the p r o b l e m of v e r s a t i l i t y
m i c r o b i a l c o m m u n i t i e s w h i c h may leave a lasting record
sediments.
Laminated
types d o m i n a t e d by d i f f e r e n t major taxa m o o r g a n o t r o p h i c bacteria;
Fig.
(cyanobacteria,
zontally,
che-
There are filamen-
for example, w h i c h arrange themselves either h o r i -
(concordant to b e d d i n g planes)
Furthermore,
so
fungi or
p l a n a r l y or r a d i a l l y and leave b e h i n d lamina o r i e n t e d either
stratiformally
allows
ancient
IA). The w e a l t h of d i f f e r e n t taxa solely
in the group of c y a n o b a c t e r i a has to be considered. tous cyanobacteria,
in
or laminoid structures can derive from c o m m u n i t y
experience
or u p w a r d l y convex.
of p r e s e n t - d a y m i c r o b i a l mat
environments
us to state that life strategies of the m i c r o b e s c o n c e r n e d
varied
that
consistency.
they are able to develop over
substrate
of
are
varying
P r e s u m a b l y w a t e r is a v a i l a b l e p e r m a n e n t l y or periodically.
It
is t h e r e f o r e i n a d v i s a b l e to restrict the formation of stromatolites
to
any one p a r t i c u l a r e n v i r o n m e n t w h i c h w o u l d imply in
f a c i e s - i n d i c a t i v e role
(Fig. IB).
general
their
In the light of the great v a r i a b i l i t y
of l a m i n a - f o r m i n g microbes,
it is e s s e n t i a l to look c a r e f u l l y at other
available
and p a l e o n t o l o g i c a l
sedimentological
facies are concerned. nor
always d e p t h - d e p e n d e n t
5tASSARI,
1980).
environmentally taxa
Dominance induced.
(JANNASCH
&
WIRSEN,
sequence
is
organisms ment
also
1981;
The b i o l o g i c a l growth h a b i t of
is also important.
MONTY,
1977;
each
sediment particles.
made p o s s i b l e w i t h o u t
single
The process of burial
S e d i m e n t a t i o n is often
and m i c r o b i a l mats act as sticky fly papers and bind a l l o c h t h o n o u s
as
structures in m i c r o b i a l mats may be m a i n l y
in turn influences the m o r p h o g e n e s i s .
re-establishment
i n f o r m a t i o n as far
S t r o m a t o l i t e s are n e i t h e r n e c e s s a r i l y intertidal
(SHINN,
and
involved,
1983) w h i c h capture
Growth of the m i c r o b i o g e n i c sedimentation
as
migrating
o v e r r i d e others in order to find the most favorable environ-
(e. g. by phototaxis).
This sort of self-burial is typical and can
be seen in b o t h lacustrine and m a r i n e l o w - e n e r g y environments.
Burial gives rise to various kinds of p e n e c o n t e m p o r a n e o u s within
the
degrees
organic s u b s t r a t e
(Fig. IC):
of b a c t e r i a l d e c a y occur;
tion
and
to
diffusion,
shrinkage,
with
varying
some p o l y s a e c h a r i d e chains and com-
plexes are more r e c a l c i t r a n t than others;
place.
Micromilieus
processes
degassing,
d i s s o l u t i o n and
gas b u b b l e forma-
precipitation
The d i f f e r e n t p l a s t i c i t y of substrates and their b e h a v i o u r
c o m p a c t i o n has to be considered.
Faunal influence c o m p l i c a t e s
take due the
10
overall
situation in so far as feeding and excretion
gration,
and the spreading of microbial
tion of thrombolitic
lead to
disinte-
colonies may support the forma-
fabrics and intraclasts.
MARINE
NON-SEDM I ENTATO IN SUBAERA I LLYEXPOSED LOWSEDM I ENTATO IN
LACUSTRN IE SUBMERSED
PERO I DC I ALLYRAPID SEDM I ENTATO IN
TERRESTRA IL
I•ERIA
FUNGI
/
/
RADA I L,HOR¢ ZONTAL / VERTC I AL / /
~
J
/
OFDF IFERENTMAJORTAXA? ~
C. PENECONT~PORANEOUS
~
~k
~
b ~
C
~
~
EARLY DA I GENESS I (DEGRADATO I N,MN I ERALPRECIPITATION) BIOTURBATIONG , RAZN IG
COMPACTO I NOFSUBSTRATESOFDF IFERENTPLASTICITY Fig. i. Schematic representation relating stromatolitic structures and parameters possibly involved in their formation and early diagenesis. The concern of this scheme is to demonstrate that the appearance of a stromatolitic structure is indicative neither of one single phylum nor of one single environment.
11
The
unifying
principle within the complexity of stromatolitic
brics is that they are products of microbes which by their physiology and
and arrangement in time and space interact with a
chemical
environment
to produce a laminated
fa-
morphology,
pattern
physical (KRUMBEIN,
1983). This basic definition is irrespective of the existence of specific growth patterns (biostromate or biohermal buildups, ticles,
and
laminoid
fenestral
laminated par-
fabrics) which may be
explained
by
biotopic and microbiocoenotic as well as by physical modifications.
A key to the recognition of biotopic and biocoenotic characteristics encoded within sedimentary structures is the study of microbial mats in modern environments. matolites
may
conditions
A limitation of the actualistic approach to stro-
be that many present-day
1980;
KNOLL,
the
strial, mats
ecological
1985a). This consequently
explain why well developed thick stromatolitic sequences are
developed in the present than in the past. to
and
do not function at the same rate and level of efficiency as
in the past (REINECK & SINGH, may
depositional
However,
present-day extension of shelf flats and some lacustrine
and deep sea environments,
less
though restricted special
present-day
witness clearly the constancy of the biolaminite
terre-
microbial
tradition.
The
following chapters deal with stromatolite environments in the peritidal zone
which
apparently include types of potential
always had world-wide distribution.
stromatolites
that
Two of our main study areas are in
the semi-arid tropics and are part of the desert coast adjacent to
the
Gulf
others
are
North
Sea
of
Aqaba
supratidal coastal dies
graben system (Sinai Peninsula) while the
flats
of offshore embankments in the
southern
region which is located in the temperate-humid zone.
describe microfacies types,
stratification microbial structures
bio- and ichnofabrics and
The stumodes
which display depositional dynamics that interfere with
activity.
Comparing
the formative
environments
of
the important role played by climate and geomorphic
becomes evident.
of
these relief
PART
STROMATOLITE
ENVIRONMENTS
-
MODERN
II
IN
THE
EXAMPLES
PERITIDAL
-
ZONE
"Alle jene Gebiete,
w e l c h e ich auf der geolo-
gischen
'Salzthon'
babe,
Karte sind
als
nichts
weiter
ausgeschieden
als
eingedampfte
L a g u n e n und m e e r e n t b l ~ s s t e r Strand." WALTHER,
i. THE G A V I S H S A B K H A
-
(JOHANNES
1888)
A H Y P E R S A L I N E B A C K - B A R R I E R SYSTEM
(GULF OF AQABA,
SINAI PENINSULA)
i. i. I n t r o d u c t i o n
Facies
is the p r o d u c t of specific d e p o s i t i o n a l and b i o t o p i c
tions acting w i t h i n a certain e n v i r o n m e n t biotopic arid
c o n d i t i o n in the Gavish Sabkha,
tropics,
remarkably even are
stable in the annual cycle.
The a v a i l a b i l i t y of
flourish in the Gavish Sabkha
The
Gavish
strong the
in subsurface contact w i t h the
sea.
e v a p o r a t i o n is c o n s t a n t l y r e c h a r g e d by seepage
moistened
is mats
Water
of
sea
by
loss
by
seawater.
Thus
is p r o v i d e d w i t h p e r m a n e n t s h a l l o w - w a t e r environments mud flats.
is
salt swamp).
Sabkha is a t o p o g r a p h i c low separated from the
but
system
water
e n v i r o n m e n t if m i c r o b i a l
(sabkha is a t r a n s l i t e r a t i o n
the arabic term sabkhat or sebkat meaning
bar-closing
1958). A specific
a coastal e n v i r o n m e n t in the
is that the h o r i z o n t a l g r a d i e n t of surface m o i s t u r e
more critical than the h y p e r s a l i n e to
(TEICHERT,
condi-
These p r e v a i l i n g conditions can
be
and
interrupted
a l t h o u g h not always p e r m a n e n t l y changed by w i n t e r flashfloods.
The purpose of this chapter is threefold: of
topographic
sedimentary tolitic
on the d e v e l o p m e n t of
microbially
produced
structures w h i c h r e p r e s e n t analogs of conspicuous
structures
1985a), provide
moisture
(i) to document the effect
(2)
in the g e o l o g i c a l record
(see for
stromaKNOLL,
framework
which
further i n f o r m a t i o n about the e n v i r o n m e n t of deposition,
(3) to
interpret
the
tO d o c u m e n t the lithological and faunal
example
mode
of s t r a t i f i c a t i o n of the sabkha deposits
as
the
16
result
of
changes b e t w e e n long-lasting
conditions
fair-weather
and
short but catastrophic sheetflooding.
i. 2. M e t h o d s
Field
work was carried out from July to October 1981 and
to March 1982. bed
It focussed on the coring and d o c u m e n t a t i o n of undistur-
sediments,
fauna,
on
February
on the sampling of m i c r o b i a l mat m a t e r i a l and
benthic
m e a s u r e m e n t s of p h y s i c o c h e m i c a l p a r a m e t e r s and on the docu-
m e n t a t i o n of surface structures.
The
Gavish
Sabkha m i c r o b i a l mats were first studied by us
early summer of 1978.
in
the
At that time the p e r m a n e n t l y w a t e r - c o v e r e d parts
of the sabkha were floored w i t h e x t r a o r d i n a r i l y m u l t i l a m i n a t e d communities at
(KRUMBEIN et al., the
end
multilaminated loads
of
of
Our next
fully
about one year after the floods.
developed
At that time
(KRUMBEIN et al.,
Data
from
ion
1985).
mineralogy mats
In summary we present in
of
which
sabkha
lished
type 3),
crops
and pH in sediments, Undisturbed long, knife,
surface
permanently water-covered
(2) data from p o s t f l o o d
studies:
sediment distribution,
is
(GAVISH studies: waters,
microbial topographic
c o m p o s i t i o n and
already
reestab-
2 and 4), vertical profiles of redox p o t e n t i a l s
faunal distribution.
sediments
were
taken w i t h plastic
50/70 mm diameter). V e r t i c a l slices
of
of m i c r o b i a l communities w h i c h were
(facies type I,
not
sediments
(I) data from p r e f l o o d
r e l a t i o n to the salinity
m o i s t u r e and salinity gradients, standing
were
we adopt data from p r e f l o o d stu-
analyses and m i n e r a l o g y
of surface sediments,
(facies
with
1979).
seawater
concentrations
the
to interpret
type
p r e s e n t e d here were also obtained during the p r e f l o o d situation et al.,
one
reestablished
Thus,
stage of the m u l t i l a m i n a t e d mat
repeatedly recorded in core segments, dies
and
studies
the benthic systems of the p r e f l o o d p e r i o d were
a l t h o u g h new initial stages had already developed. the
1980
m i c r o b i a l mats of the l a g o o n a r y b a s i n were b u r i e d
terrigenous sediments and died off.
c o n d u c t e d in 1981, all
1979). Then two strong sheetfloods occurred,
of 1979 and the other at the b e g i n n i n g of
tubes
(200/400 mm
sections were made w i t h an electric
(45 x 45 mm) were separated and frozen under
shock
in
liquid oxygen. They were s u b s e q u e n t l y dried in a d r y - f r e e z i n g apparatus
17
and
later h a r d e n e d
REINECK, pared
1970).
and
were
examined
taken
(1962).
The
from
Chips
electron
critical
gold
Sections
tions
a dissecting
Pore
core m a t e r i a l
were
(SEM-Type fixed
Stereoscan
then d e h y d r a t e d
selected
- 6 %)
dilution
the samples
905,
photographs by
HAMBLIN scanning
Instruments).
at
appropriate
series
were
HY
were pre-
for
Cambridge
(2
in e t h a n o l / H 2 0
Subsequently
X-ray
described
180,
in g l u t a r a l d e h y d e
point dried.
sections
microscope.
of the sliced
of
the sliced
distribution.
water
0.63
was
carefully
organic
recovered
geochemistry
carried
sediments) Gulton),
work
measurements
and final-
sputtered
Optical
Microbial This work,
mat
with
samples were
as well
examined
collected
a 0.5 mm sieve and
sorted,
identified
with
fixed
Temperature
and
potential)
(air,
water,
(Tastotherm,
(Ingold)
on a
refractometrically
under
millimeasured
to b u r r o w
(150 mm high,
effect
of grazing
on m i c r o b i a l
graze on mat
measurements,
(HOLTKAMP,
sections
were
1985).
Samples were
and counted.
capra)
seawater
were
To study
lab-cultured
agar
which
was
To study the
(Pi~enella conica) were
w h i c h were b r o u g h t
salinity.
passed
Specimens
25 mm in diameter). gastropods
carried
structures
and s e m i - q u a n t i t a t i v e -
(Bledius
in jelly
mats,
at 50 O / o o
and SEM microscopes.
Her data on c o m m u n i t y
of salt beetles
tubes
seawater
light
the h e l p of specialists
behavior allowed
to
samples
isotope
thermoelement
in 4 % formaldehyde.
into glass
allowed
sediment
pH and redox
i00 mm high).
filled
treated with
was
the frac-
1985).
qualitatively
(190 mm diameter,
were
and
electrodes
are included
through
burrowing
with
w i t h E. HOLTKAMP.
fauna was
corers
specimens
sediments.
of
< 0.063 mm.
mineralogical,
& KRUMBEIN,
as the p h y s i c o c h e m i c a l
concentrations
The b e n t h i c
analysis
for
Salinity
study
into the
Instruments).
out in c o l l a b o r a t i o n and p i g m e n t
mm and
a chrome/nickel
and redox p o t e n t i a l
for the
were w e t - s i e v e d
(temperature,
cored
with
(Knick Portamess).
(American
with
for water
(FRIEDMAN
out in freshly
pH
selected
0.2 - 0.063
and s u b d i v i d e d
was m e a s u r e d
voltmeter
cores w e r e
The sediments
- 0.2 mm,
taken
Physicochemical
the
thin
as
> 0.63 mm,
were
ly
F with hardener
for SEM studies.
grain-size
were
under
(Araldit
specimens,
core m a t e r i a l
was
osmolarities,
resin
the sliced
microscopy
material
ly
in an epoxy
F r o m the h a r d e n e d
to
the
lab
and
18
i. 3. L o c a l i t y and p r e v i o u s w o r k
The
Gavish
Sabkha is located in the southern coastal area
Sinai Peninsula,
o p p o s i t e the Strait of Tiran,
34020 ' east longitude, Gulf of Aqaba widely
(Figs.
the
at 28 ° north latitude,
and is a p p r o x i m a t e l y in 400 m distance 2A and 2B). Shallow h y p e r s a l i n e
surrounded by a i r - e x p o s e d saline flats
setting
of
from the
surface w a t e r is
(Fig. 2C).
The
general
describes the Gavish Sabkha as a d e p r e s s i o n w i t h i n an alluvial
fan w h i c h spreads over the coastal plain b e t w e e n the Sinai Massive
and
the
the
shoreline
sabkha, of
of the Gulf
(Fig. 2B).
Further north and south of
the fan is crossed by m a j o r wadi conducts w h i c h on the o c c a s i o n
flash floods t r a n s p o r t t e r r e s t r i a l m a t e r i a l into the coastal
area,
the Gavish Sabkha and the Gulf.
Sea-marginal by C. G. The
sabkhas of the Sinai Peninsula were already
EHRENBERG
Gavish
(HEMPRICH & EHRENBERG,
Sabkha was first recognized by
g e o l o g i s t and geochemist.
were
followed
GAVISH,
GAVISH,
investigations
1971; G A V I S H et al.,
an
Israelian
(GAriSH,
1974,
1980;
1985). These p i o n e e r i n g studies
by studies of the m i c r o b i a l systems
1979; GERDES et al., E.
E.
(1888).
After the war in 1967, he began sedimentolo-
gical, geochemical and h y d r o l o g i c a l F R I E D M A N & GARISH,
mentioned
1828) and J. W A L T H E R
(KRUMBEIN
et
al.,
1985a; E H R L I C H & DOR 1985). To h o n o r the m e m o r y of
who died in 1981, the c o m p r e h e n s i v e results of interdisci-
p l i n a r y research on sea-marginal sabkha environments using the of the G a v i s h Sabkha were compiled
(FRIEDMAN & KRUMBEIN,
example
1985).
I. 4. The p h y s i c a l e n v i r o n m e n t
I. 4. i. G e o m o r p h i c relief
GAVISH et al. tal
bar
consists
softbottom platform. uplift
its
of an u p l i f t e d reef complex and
sediments
of
the sabkha rest on
Studies conducted by F R I E D M A N
(1965,
an
that
the
underlying
present backreef
1972) indicate that such
of reefs o c c u r r e d about 2,000 - 4,000 years
G A V I S H et al. and
(1985) p r o p o s e d that the b e d r o c k underlying the coas-
ago.
Accordingly,
(1985) suggest that the unique round shape of the sabkha
location w i t h i n the alluvial p l a i n could be the result
preexisting
t o p o g r a p h i c low in the u n d e r l y i n g reef p l a t f o r m w h i c h
s u b s e q u e n t l y uplifted.
of
a was
19
N ~
' ~ LAND
."1
EVAPORITI[
~...~__
'~
/'~ F °'~51-~i'_-~' i-~°~~~Z..~ . :.~. ~.-~.;
/ /
i
BEoou,,
SEA
i
STROP1ATOLITIIZ
i
[LASTI[
I
C
Fig. 2. Map of study areas and g e n e r a l setting of the G a v i s h Sabkha° A) Sinai P e n i n s u l a w i t h l o c a t i o n s of the G a v i s h Sabkha and the Solar Lake along the Gulf of Aqaba. M o d i f i e d after F R I E D M A N & KRUMBEIN, 1985. B) A v i e w t o w a r d W showing the round d e p r e s s i o n of the G a v i s h Sabkha at the shore of the Gulf of Aqaba. F r i n g i n g reefs are v i s i b l e at the bottom, foot hills of the Sinai m o u n t a i n s at the top. After F R I E D M A N & KRUMBEIN, 1985. C) I l l u s t r a t i o n of major g e o m o r p h i c elements of the Gavish Sabkha: coastal b a r slope, rims and b a s i n of the lagoon, elevated center. B a r - d i r e c t e d s i l i c i c l a s t i c s and c e n t e r - d i r e c t e d e v a p o r i t e s interfinger w i t h m i c r o b i a l mats w h i c h form at the lower part.
20
The
p r e s e n t - d a y e n v i r o n m e n t forms a round d e p r e s s i o n about 500 m in
diameter level).
and
is at its deepest part -1.80 m b e l o w
The
m.s.l.
(mean
sea
central part of the d e p r e s s i o n is gently elevated and
is
s u r r o u n d e d by a c o n c e n t r i c channel w h i c h is p a r t i a l l y w a t e r - f i l l e d . The circular slopes rise g r a d u a l l y from the channel upwards to the alluvial p l a i n and coastal bar facing.
Three major g e o m o r p h i c elements of the G a v i s h Sabkha can be guished: The b a r r i e r slope,
The
the lagoon and the center
b a r r i e r b l o c k i n g the d e p r e s s i o n has b e e n u p h e a v e d by
d i r e c t e d currents and waves.
lying bed rock and porous sediment infilling. covered
coastline
Seawater is r e p l e n i s h e d through subsurface
conduits formed by c a r b o n a t e c e m e n t a t i o n plates,
is
distin-
(Fig. 2C).
by dry evaporite crusts.
fissures in the under-
The surface of the slope
Several gullies cut through
slope face and merge at the lower end into sandlobes
(Fig.
2C).
the Sea-
w a t e r springs rise at the sandlobe junctions. The gullies are g e n e r a l l y 0.I0 to 0.40 m deep and tend to meander. result
of
sheet floods
(GAVISH,
Gullies and sandlobes are the
1980).
A wadi conduct runs
at
the
coastal bar plateau.
The lagoon is part of the concentric channel halfmoon-shaped surrounded impondments
by
(Fig.
2C).
b a s i n w i t h w a t e r depths of up to 0.60 m. shallow and p a r t i a l l y a i r - e x p o s e d flats
occur
It forms a The basin is
where
various
(about 50 mm deep and two to three meters in
diame-
ter) w h i c h are fed from seawater springs.
The elevation of the center is about 0.50 m above the w a t e r table of the lagoon.
GAVISH p r o p o s e d that g y p s u m a c c u m u l a t i n g b e l o w the surface
caused the "swelling" of sediments and
gradually
u p h e a v e d the center.
Aerial views show three s e d i m e n t a r y plains sloping g e n t l y to NNE 2B):
(i.) The topmost part,
(2.)
the slope w i t h its e x t r e m e l y gentle incline
(Fig.
which is covered by dry evaporite crusts, towards NNE and
(3)
the rim w h i c h is s u r r o u n d e d by the c o n c e n t r i c channel. Surface m o i s t u r e g r a d u a l l y increases toward the lagoon. several and
holes,
Along the slope and the rim are
e x c a v a t e d b y fisher b e d o u i n s
in order to collect brine
to h a r v e s t the p r e c i p i t a t i n g potash and NaCI.
months
the
higher
w a t e r table of the lagoon.
sediments
of the rim are submersed due
and leaves w h i t e g y p s u m crusts.
During to
the
winter
the
slightly
In summer the w a t e r level
retreats
21
IiH
p0; 12°°
Ii Ii [L
March t982 I I
~
II
0
r-GF--~
LB
~
SMF
~ SL
~ A ? \ G U ELEVATED CENTER SW
A O0 h G N GF
~
SMF ~
GF = Gypsum Fiats LB = Lagoonery Bo.sin SMF= Satine Mud Fiats SL = Sand{obes
A
BAR h
i \ I~
~
~ ~':~~'~:,~'~'~':''! ............... .:~
m r-2
GAVISH SABKHA SURFACE WATER }ULF
SAUNITY INCREASE+
SMF
u
ION CONCENTRATIONS (ppm)
GAVISH SABKHA SURFACE WATER
I LB I
/
£ ~ B r i n e Reflux
ION RATIOS (MOLAR).
~o GF
t
~ e
LNFE[~I
SL
+-- . . . . .
SALINITY INCREASE (
GF- L8 I
S.F
i
IS
~{
3ULF ppm 20 000 10 000
4~ @
4
I
.2
t
;000 "E
I 000
3.4
so#L~
I cE! so4=
-~
.0.2 42.4
300
TOTAL SALINITY (%o]
Fig. 3. Hydrology, salinity and seawater chemistry along a horizontal transect crossing several sub-environments of mat-formation: Sand lobes (SL), saline mud flats (SMF), lagoon (LB) and gypsum flats (GF). A) Generalized horizontal transect showing the connection of the Gavish Sabkha with the Gulf. Hydrodynamic mechanisms are indicated by arrows: Seepage, evaporation and brine reflux. Salinity (upper diagram) increases towards the elevated center. B) Ion concentrations (right) and ratios (left) in surface water including Gulf water (salinity values on abcissa right from GAVISH et. al, 1985; abbreviations refer to sub-environments listed in A). Decrease in Ca and change in ion ratios take place on saline mud flats bordering the lagoon where total salinity is about 85 0/oo.
22
1. 4. 2. H y d r o l o g y
Two
m a j o r effects on the h y d r o l o g i c a l
be distinguished: physical include
(1) physical
system of the Sabkha have
to
factors o p e r a t i n g from the land and
(2)
factors o p e r a t i n g from the sea.
Those o p e r a t i n g from the sea
seawater supply and w a t e r level changes w i t h i n the sabkha
to tidal m o v e m e n t s and w e a t h e r effects re-directed against
w i n d drift,
the
coast,
(e. g.
monsoon)
outside.
w h i c h o c c a s i o n a l l y causes strong w a v e
does not affect the b a r - p r o t e c t e d Gavish
due
Onshoattack Sabkha.
Thus the h y d r o l o g i c a l p r o c e s s e s d e s c r i b e d b e l o w remain b a l a n c e d even if high energy conditions occur in the a d j a c e n t Gulf.
Tidal tidal
influence.
Gulf
range of 0.7 m.
tides are semi-diurnal w i t h a
the Gavish Sabkha at a reduced rate w i t h time delay. of
mean
pools and the b a s i n of the lagoon. is seen in
normal
(up
directly
to
The o p e r a t i o n of these t i d e - i n d u c e d
i0 cm) is common in winter.
This
phenomenon
related to the tidal m o v e m e n t but to seasonal
et al.
1985).
is
variations
communities which colonize these margins.
however,
not in
(monsoon;
Both tidal- and c l i m a t e - i n d u c e d fluctuations of
the w a t e r table do not lead to c o n s i d e r a b l e disturbances of the bial
of
A sudden rise in the w a t e r table greater than
the sea level of the Gulf as a response to climate conditions GAVISH
marginal
the shifting of w a t e r l i n e s at the m a r g i n s
the ponds and the basin.
of
Diurnal m o v e m e n t s
w a t e r levels of about 20 mm h a v e b e e n observed w i t h i n the
fluctuations
annual
This tidal m o v e m e n t affects the w a t e r level
Some faunal
micro-
elements,
w h i c h are restricted to a i r - e x p o s e d w e t l a n d habitats, have to
react by m i g r a t i n g according to the shifting water lines.
Seawater ecological of
the
seepage.
A
significance.
constant supply of seawater This is achieved by
Gavish Sabkha and (ii) the process
(sensu HSU & SIEGENTHALER,
produce
surface seawater
to
respects
salt from seawater.
of
pumping"
formerly used by hill
They c o n s i s t e d of
through gently inclined pipes into
system
greatest
"evaporative
people
a pan w i t h a
volume ratio w h i c h was s u c c e s s i v e l y fed by
running
hydrological
of
1969). The c o m b i n a t i o n of seepage and evapo-
ration is analogous w i t h the b o i l i n g - p a n s to
of
is
(i) the b a s i n m o r p h o l o g y
low the
the Gavish Sabkha differs from
rates basin.
this
in
high of The two
(i) the heat needed to evaporate the water generates from sun
irradiation
and
(ii) the natural pan of the
Gavish
Sabkha
consists
w i d e l y of exposed sediments where the w a t e r table is b e l o w the surface. In these areas "evaporative pumping"
operates
(Fig. 3A).
23
The e v a p o r a t i o n rate is about 4.6 m/year. 30
Relative h u m i d i t y averages
- 50 % w i t h a m e a n annual air t e m p e r a t u r e of 26 °C
h i g h solar irradiation. v e r t i c a l l y and sediments by
P e r c o l a £ i n g seepage seawater sinks into the
and elevates the w a t e r table, evaporation.
w h i c h is lowered s u b s e q u e n t l y
This stimulates upward m o v e m e n t
of
water
the p h r e a t i c zone by e v a p o r a t i v e p u m p i n g and results in a
stant
supply of ions n e c c e s s a r y for mineral
capillary (PURSER,
The
movement
formation.
The
in turn leads to the lateral m i g r a t i o n
vertical of
fluids
lateral m o v e m e n t induced by e v a p o r a t i v e p u m p i n g may not operate
Dhabi
sabkha
(PURSER,
G a v i s h Sabkha, however, water
1985).
as seen,
for example,
The d o w n w a r d i n c l i n a t i o n
in the of
p l a t e s e m b e d d e d in the u p h e a v e d bar
conduits sabkha
the
stimulates the lateral m o v e m e n t of i n t e r s t i t i a l
w i t h i n the s e d i m e n t a r y system as well as the lateral
supply
seepage s e a w a t e r through p e r m e a b l e sediments of the m a r i n e bar. nate
con-
1985).
w h e r e sabkha water tables rise landwards, Abu
constantly
The e v a p o r a t i o n p u m p i n g m e c h a n i s m o p e r a t e s b o t h
laterally.
capillary
within
and
(Fig.
of
Carbo-
2C) p r o b a b l y serve
as
for the seeping seawater. T h e i r gentle i n c l i n a t i o n towards the can
be seen at outcrops t e r r a s s i n g some of the
gullies
which
cross the inward slope of the coastal bar.
Besides the p r e c i p i t a t i o n of evaporite m i n e r a l s at the interfaces by evaporative pumping, posed
to
gypsum)
reflux of brines to the sea is pro-
be an important m e c h a n i s m of mineral
in deeper layers
sediment-air
(GARISH et al.,
accumulation
1985).
(mainly
Local d o l o m i t i z a t i o n
has also been suggested as an outcome of brine reflux,
a l t h o u g h several
other models have b e e n proposed.
S a l i n i t y regimes. A h o r i z o n t a l 340 °/oo,
is
established
s a l i n i t y gradient,
ranging from 50 to
along a t r a n s e c t w h i c h runs from the
slope face of the bar towards the center of the sabkha
The data in Fig.
3A were o b t a i n e d from m e a s u r e m e n t s of interstitial
water
in the gully and sandlobe sediments and of standing surface
ters.
Although
and spring 1982), of
salinity
the data r e p r e s e n t only two annual states they may n o n e t h e l e s s
zones is more or less stable t h r o u g h o u t
1980; G A V I S H et al.,
1985,
wa-
(summer 1981
indicate that the e s t a b l i s h m e n t the
year.
a s s u m p t i o n was r e i n f o r c e d by G A V I S H on several earlier visits 1975,
lower
(Fig. 3A).
see also Fig. 3B).
This
(GAVISH,
24
Short-term
oscillations
the lagoon where wind in the overall conspicuous
can flush-over
stability
change
of salinity
occur
concentrated
of the salinity
in
at the immediate
microbially
regime
produced
brine.
rim
of
This d e v i a t i o n
is r e f l e c t e d
structures
by a
(see
very
section
1.6.3).
Ion c o n c e n t r a t i o n s of
GAVISH's
dissolved SO 4
data
taken
by
(Fig.
CaSO 4
enriched
is
while
depleted
cite highly
in bulk
are enriched
(29 wt.%). reduced
with
concentrations
Mg ++
salinity
similar
a recalculation
to
of
: Ca ++ and Ca ++ measurements our
:
ob-
measurements
to the salinity
in-
lies at 80 to 90 °/oo w i t h i n
the
increase
shows
in p a r a g r a p h
so that b a c t e r i a l
sulfate
takes
a nearly
linear
of the inner
lagoonary
in high m a g n e s i u m
As is shown
is a c c o m p a n i e d
in the surface water,
sediments of the
of salinity
since
on the other hand,
the sediments
concerning
correlates
of C a + + - c o n c e n t r a t i o n s
ratio,
dy
which
Further
Ca++/SO 4 = ratio decreases,
M g + + / C a ++
lagoon,
3B).
3B shows
3A).
of C a + + - c o n c e n t r a t i o n s
flats
by the decrease the
1985)
are quite
up to a solution b a r r i e r
saline mud
ly
(Fig.
Fig.
in surface waters,
These data
later
increase
crease
et al.,
The data are c o r r e l a t e d
GAVISH.
four years
The
(GAVISH
c a l c i u m and sulfate
= ratios.
tained
in surface waters.
calcite
sulfate
of
the
Ca ++ is alrea-
(50 wt.%) these
reduction
The
increase.
shoreline
basin where
1.6.4.,
accordingover.
and
cal-
sediments
interferes
are with
CaSO4-precipitation.
Flashflood passing after
impacts.
the system rainfall
transport
for
Sabkha.
A strong of
evaporation months
in
to
sheetflood
pumping regenerate
Sabkha
in this
area
is i0 nun. Rainfall
is more or less n e g l i g i b l e mountains
freshwater.
the h y d r o l o g i c a l
the Gavish
rainfall
the adjacent
sediment-laden
quences
level
Annual
immediately
and e c o l o g i c a l
in O c t o b e r
completely
(GAVISH et al.,
run-off
sheetfloods
which
tremendous
conse-
conditions
1979 caused
of about 60 cm.
s y s t e m was
causes
Such events have
while
of the
a rise
The steady disturbed.
state It
Gavish
in the water of
took
the five
1985).
i. 4. 3 . ~ T e m p e r a t u r e s
A stable influences
zonal t e m p e r a t u r e - g r a d i e n t of wind,
irradiation
was not o b s e r v e d
and e v a p o r a t i o n
due to changing
operating
in the daily
25
cycle.
In summer,
between
day
nightly
drop
low-water tures
air t e m p e r a t u r e s
and night
temperatures
in air t e m p e r a t u r e
environments
and a n i g h t l y
ring c a p a c i t y
reach
however,
saltcrusts.
ranging
of s h a l l o w - w a t e r
range b e t w e e n
is,
and b e l o w
drop
45 °C and more
between
Data
of
GAVISH
vels. The
The
levels
which
and e v a p o r a t i v e
results
are p r e s e n t e d
g e n t l y dip to NNE
VI
graded
describe
strates
(i) the
relief
above
ration
pumping
(Fig.
different
the buffe-
calculate
4 in the course
level
le-
of a transect: of the center
IV indicates
the b o t t o m of
Sabkha.
(i.
The levels
bar
described
slope.
e. the e l e v a t i o n
of seawater
V
The
b e l o w demon-
(2) the e f f e c t i v e n e s s
recharge
the
niveau
plains
of the coastal
of g e o m o r p h o l o g y
seepage
used to
forming m i n e r a l s
table)
The
in shal-
lower daily tempera-
at d i f f e r e n t
sedimentary
elevations
the g r o u n d w a t e r and
were
part of the G a v i s h
of in-situ
influence
1985)
The
30 °C.
framework
in Fig.
4A).
and
remarkable
crusts.
(0 to -5 cm)
the three
is the deepest
distribution
annual
et al.,
sediments
I to III indicate
the lagoon w h i c h and
(GAVISH
of surface
Here,
20
6 and 8 °C indicate
1. 5. L i t h o l o g i c a l
composition
less
and d i f f e r e n c e s
of the
of
evapo-
prevailing
in
the
cycle.
i. 5. i. E v a p o r i t e s
a) H a l i t e
(Fig.
4B).
High
is over 80 %) a c c u m u l a t e ment
surfaces
other m i n e r a l s water at
(levels
indicates
(level
layer w i t h an
average
frequency
relative
height, levels
at III,
level
the
lutitic
upper
4A)
thickness
(Fig.
4C).
Anhydrite
(levels
The a s s o c i a t i o n
of g y p s u m dehydration,
1 m
It covers
(see p a r a g r a p h gradually
with
of h a l i t e while
layer
a gypsum
c
below).
decreasing the
lower
4B).
occurs
I and VI),
at
to
marine
of the h a l i t e
is 25 - 50 % while (Fig.
sedi-
of h a l i t e
of upward m o v i n g
20 cm.
decreases
frequency
unflooded
abundance
The thickness
of about
of h a l i t e
permanently
averages
B the bulk volume
dry crusts
fraction.
conditions
interface.
(the relative
relative
evaporation
IV and V it is n e g l i g i b l e
b) A n h y d r i t e in
This
the total
I in Fig.
The
of h a l i t e
at the elevated,
I and VI).
at the s e d i m e n t - a i r
the center
amounts
together
with halite
and there m a i n l y and a n h y d r i t e
the f r e q u e n c y
in
only the
may indicate
of a n h y d r i t e
in
26
HALITE
ANHYDRITE
GYPSUM
CARBONATES
DETRITAL CLASTICS
75 - D o %
~
50- 75 %
25-50 %
~
0-25%
Fig. 4. A b u n d a n c e of evaporites, c a r b o n a t e s and detrital clastics in surface sediments at d i f f e r e n t e l e v a t i o n levels of the G a v i s h Sabkha. A) Aerial view from E towards W to show e l e v a t i o n levels: I -III: Upper, m e d i a t e and lower parts of the center (white area = gypsum), IV: Lagoon, V - VI: Lower and upper parts of the coastal b a r slope. B) H a l i t e is in greatest a b u n d a n c e at the most elevated levels I and VI. C) A n h y d r i t e is g e n e r a l l y a s s o c i a t e d w i t h h a l i t e (levels I and VI). D) G y p s u m a c c u m u l a t e s at lower levels (mainly level III, see also A). E) C a r b o n a t e s make up 50 to 70 wt.% of sediments of the lagoon (mgc a l c i t e dominant, a s s o c i a t e d w i t h calcite, aragonite, dolomite). F) S a n d - s i z e d s i l i c i c l a s t s d o m i n a t e at lower parts of the coastal bar. G) F i n e r - g r a i n e d detrital clastics g e n e r a l l y occur at all levels.
27
the
lutitic
fraction indicates that it may be a p r i m a r y
precipitate.
The hot and dry climate makes both p r o c e s s e s possible.
c) Gypsu m (Fig. 4D). to
the
Here,
biological
tary
The only zone w h e r e g y p s u m rarely
b u l k volume of sediments is the lagoon
plain
contributes
(level IV in
Fig. 4D).
sulfate r e d u c t i o n is m o s t active. W i t h i n the sedimen-
III in Fig. 4D,
close to the lagoon,
w h i c h is already part of the
center
the bulk volume of g y p s u m averages nearly
but
i00 %,
thus indicating that the growth must be faster than the a c c u m u l a t i o n of clastic
sediments d e p o s i t e d by wind.
The r e l a t i v e f r e q u e n c y of g y p s u m
decreases w i t h increasing h e i g h t w h i l e in turn h a l i t e becomes more more
dominant
(compare the upward d i r e c t e d d i s t r i b u t i o n
to level I in Fig. 4B). gypsum over
B e l o w the h a l i t e crust of the e l e v a t e d center,
is the most a u t h i g e n i c mineral. 1 m,
the
(GAVISH et al.,
W i t h an average
thickness
layers reach well b e l o w the g r o u n d w a t e r table
surface
(Fig. 4E)
C a r b o n a t e s are m o s t frequent in the surface sediments of the its
(70 %),
margins. while
abundant
of
1985).
i. 5. 2. Carbonates
and
and
from level III
The
m a j o r components are
dolomite
carbonate
averages about 5 %.
c o m p o n e n t of the
clastic
calcite
and
lagoon
Mg-calcite
Aragonite,
w h i c h is
an
sediments
outside,
is
m o s t l y a minor c o m p o n e n t or c o m p l e t e l y absent w i t h i n the sabkha.
We
will
this
return to the q u e s t i o n of in-situ carbonate
highly
h y p e r s a l i n e m i l i e u w h e n referring to the
accretion
in
development
of
b i o l a m i n a t e d sediments and m i c r o b i a l habitats.
i. 5. 3. D e t r i t a l clastics
Terrigenous
clastic sediments in b u l k volumes of 0 - 25 % are mixed
w i t h the in-situ forming minerals. and
are
type).
Coarser grains are w i t h o u t
s u p p o r t e d by m a t r i c e s of g y p s u m or c a r b o n a t e mud
contact
(wackstone-
They r e p r e s e n t fragments t r a n s p o r t e d by n o r t h e r l y and s o u t h e r l y
winds w h i c h b l o w several times in the year. The p r o g r a d a t i o n a l t e n d e n c y of
the
center sloping gently to NNE
(indicated in
Fig.
4A)
m o s t l y due to successive s e d i m e n t i n f i l l i n g by s o u t h e r l y w i n d s 1985; GAVISH et al.,
1985).
may
be
(PURSER,
28
Compacted bottoms
and
sphericity,
surface
layers of terrigenous
sandlobes
4F).
The grains are
which suggests p r i m a r y provenance
from w e a t h e r i n g
cambrian granitic
(level V in Fig.
clastics occur at the gully
rocks of the adjacent Sinai Massif
(Fig.
of of
low Pre-
5A and 5B).
Fig. 5. Sheetflood deposits (thin sections from sediment cores). A) Layer of grain-flow deposits between two microbial mat generations. Scale is 1 cm. B) Texture of g r a i n - f l o w deposits showing badly sorted and rounded particles. Scale is 500 pm. C) Inverse grading of sheetflood sediments with water escape trace (or p o s s i b l y escape trace of insect larva). Scale is 1 mm. D) Sediments resulting from slow sinking deposition from suspension consist of silt, clay, plant debris and some coarser siliciclastic fragments. Scale is 250 pm. E) Sheetfloods also transport seagrasses with epiphytic forams. Scale is 1 mm.
29 Since
we carried out our field work a p p r o x i m a t e l y two years after
last strong sheetflood, exception
of
evaporites, cause and
the
the
we found all other s e d i m e n t a r y plains w i t h the
g u l l y b o t t o m s and sandlobes already
carbonate mud or m i c r o b i a l mats.
debris to flow t h r o u g h a
re-covered
That strong
by
sheetfloods
wadi system on top Of the coastal
bar
to spread over the w h o l e of the l o w e r - l y i n g region is evidenced by
several layers of c o a r s e - g r a i n e d m a t e r i a l w i t h i n the b a s i n sediments of the lagoon.
Silt/clay
fractions
(Fig. 4G)
derive from
suspension
clouds
in
freshwater w h i c h fill the d e p r e s s i o n d u r i n g sheetfloods.
1. 5. 4. I n t e r n a l fabrics of s h e e t f l o o d d e p o s i t s
a) Deposits
resulting
from debris flow:
These are
poorly
sorted
m e d i u m - to c o a r s e - s i z e d quartz sand c o n c e n t r a t i o n s w h i c h imply a gravit y - i n d u c e d lateral m o v e m e n t of debris loads in w a t e r Inverse
grading
(Fig. 5C).
is
Around
r e c o r d e d w i t h i n several the
(Figs. 5A and 5B).
siliciclastic
c i r c u l a r slope of the
sabkha
t h i c k n e s s of the debris flow deposits exceeds several dm° slope direction, central basin,
their thickness decreases. beds of debris
sequences
depression
the
In the down-
In sediment cores from the
flow range in size from a few mm to some
cm.
b) C o n c e n t r a t i o n s of silt, and
some coarser s i l i c i c l a s t i c
tions
clay, p l a n t debris, fragments
some foram skeletons
(Fig. 5D):
result from slow sinking d e p o s i t i o n
These
concentra-
from suspension.
The inter-
spersed coarser s i l i c i c l a s t i c fragments w i t h o u t contact indicate transport
in the c l a y - w a t e r fluid phase.
Haloph~la sp. of
the
forams
The intermixed plant detritus
stems from the m a n g r o v e swamps and lagoons to the
Gavish Sabkha in the order of tens (determined as So,ires
sp.
by L.
of
kilometers.
HOTTINGER)
are
t r a n s p o r t e d with seagrass leaves into the G a v i s h Sabkha
Beds
of
silt and clay are rarely d i s t r i b u t e d around
slope
but
are
c h a r a c t e r i s t i c of the sediments of the
where
the
c l a y - w a t e r fluid phase comes to
s u s p e n s i o n are a few mm to several cm thick.
rest.
The
of
north
Epiphytic
mechanically
(Fig. 5E).
the
circular
central deposits
basin from
30
i. 6. S t r o ~ t o l i t i c
facies types
i. 6. i. The m i c r o b i o t a
Various cipate
species of p r o c a r y o t i c and eucaryotic m i c r o o r g a n i s m s parti-
in forming b i o g e n i c structures in the Garish Sabkha
Since taxonomic d e t e r m i n a t i o n s are still uncertain, to the genera of the organisms found.
3).
we will refer only
Several of these genera are pre-
Oscillato~ia, echococcus, Thioc~ps~, Nitzschia, Navicula). sent w i t h more than one species
(Table
(e. g.
Spirulina,
Syn-
TABLE 3: M i c r o o r g a n i s m s in the microbial mats of the Gavish Sabkha
I.
Procaryotes A. U n i c e l l u l a r c y a n o b a c t e r i a
Gloeothece, Synechococcus, Johannesbaptistia, Gloeocapsa, Synechocystl8, Myxosarcina, Pleunocapsa, Chroococcodiopsis B. F i l a m e n t o u s C y a n o b a c t e r i a
Spirulina, oscillatoria, LPP-formsl: Microcoleus, Hydrocoleum, Phormidium, Lyngbya, Plectonema, Schizothrix C. A n o x y p h o t o b a c t e r i a
Chromatium, Thiocapsa, Ectothiorhodospira,
Chlonoflexus
D. C h e m o l i t h o a u t o t r o p h i c b a c t e r i a
Thiobacillus,
Bsggiatoa, Desulfovibrio) 2
E. C h e m o o r g a n o t r o p h i c b a c t e r i a
Pseudomonas, Spirillum, Spirochaeta, Proteus, Desulfovibrio, s°-reducing and other taxa II. P h o t o s y n t h e t i c eucaryotes Diatoms: Mastogloia, Navicula,
Amphora, Nitzschia 3
1 "LPP"-grouping refers to Rippka et al. (1979). LPP stands for the genera Lyngbya, Phormidium and Plectonema which are r e p r e s e n t a t i v s for structural and p h y s i o l o g i c a l c h a r a c t e r i s t i c s of the LPP-Group. M i c r o c o l e u s should be incorporated in LPP 2 P h y s i o l o g i c a l attributes m e n t i o n e d are only p a r t i a l l y significant 3 Only frequent forms;
for more details see Ehrlich & Dor (1985).
31
I. 6. 2. Major mat-structuring organisms
Types structure capsulated
of primary producers which give the Gavish Sabkha mats are
(i) heavily ensheathed
filamentous
their
cyanobacteria
unicellular cyanobacteria with multiple fission (3)
(2)
slime-
ensheathed cyanobacteria with binary fission.
(i) The main
ensheathed filamentous cyanobacteria present is Micro-
coleus chthonoplaste8
(Fig.
6A). It is a cosmopolitan species found in
Fig. 6. Main mat-structuring microorganisms (modified after EHRLICH & DOR, 1985). Scale is i0 pm for all presentations. A) Ensheathed filament bundles of Microcoleu8 chthonoplastes. B) Pleurocapsalean cells encased in polysaccharid capsules. C) Syneehocysti8 sp. D) Gloeothece sp. The latter both represent coccoid unicells in colloidal matrix. E) Resulting depositional structures: Colonies of M. chthonoplaste8 produce horizontally oriented laminae (Lh) , Pleurocapsalean colonies form cauliflower-shaped nodules, SynecHocystis and Gloeothece contribute to porous, slime-enriched layers containing bubbles and some diagonally to vertically oriented filamentous organisms (Lv).
32 various environments e. g. RING et al.,
1983),
al.,
Solar Lake,
1980),
streifen-Sandwatt, 1942; 3).
Laguna Mormona,
Multiple
Egypt
Australia
Mexico
(KRUMBEIN,
1985b, c; STAL,
(BAULD,
1984; SKY-
(STOLZ, 1983; M A R G U L I S et 1978;
southern North Sea coast
GERDES et al.,
which
Spencer Gulf,
COHEN,
(OERSTEDT,
1984), Farb-
1841; HOFFMANN,
1985; see also this part chapter
e n s h e a t h e d filament bundles are typical of this
are rarely if ever found in a diagonal or v e r t i c a l
species
arrangement.
M i c r o b i a l mats d o m i n a t e d by this species reveal a smooth and u n i f o r m i l y flat
microtopography.
h o r i z o n t a l l y layered, Lh-lamina
vertical sections the mat appears as
a
b e d d i n g plane c o n c o r d a n t lamina w h i c h we call
Within
a
(Fig. 6E; see facies type 1 and 3 in p a r a g r a p h 1.6.3).
(2) The most common capsulated u n i c e l l u l a r c y a n o b a c t e r i a w i t h multiple fission is Pleurocapsa sp. Pleurocapsalean cased
by
(formerly Entophys~lis sp.). Species of
form cell colonies where each individual cell
thick concentric lamellated sheaths
(Fig.
6B).
is
A
en-
crucial
d i f f e r e n c e from Microcoleus chthonoplastes is that the coccoid colonies do not form flat and b e d d i n g - p l a n e c o n c o r d a n t mats but reveal d i s c o n t i nuous,
more
sediment
or
less c o n c e n t r i c structures.
surfaces
The
microtopography
w h i c h are c o l o n i z e d by P l e u r o c a p s a l e a n
of
populations
exhibits a p u s t u l a r structure. C a u l i f l o w e r - l i k e nodules are also common at
sediment surfaces
(Fig.
6E;
see also facies type 2
in
paragraph
1.6.3). (3) The
m o s t common s l i m e - e n s h e a t h e d u n i c e l l u l a r c y a n o b a c t e r i a w i t h
b i n a r y fission are Gloeothece sp.
and Synechocysti8 sp.
(Figs. 6C and
D). These organisms account for the vast p r o d u c t i o n of p o l y s a c c h a r i d e s . Sediments
composed
of or interwoven with
sluggish and y o g h u r t - l i k e if
liquid
(e. g.
these
polysaccharides
seawater)
is
maintained,
due to the dispersal and p a r t i a l d i s s o l u t i o n of the mucilage. of
are
the organisms are i r r e g u l a r l y a r r a n g e d in the slime mass
The cells (MARTIN
&
WYATT,
1974). The species m e n t i o n e d c o n t r i b u t e p r e d o m i n a n t l y to immense
slime
layers
supported from
found in the Gavish Sabkha sediments.
coccoid
Since the
mats form v e r t i c a l l y e x t e n d e d layers
which
the flat and b e d d i n g - p l a n e c o n c o r d a n t L h - l a m i n a e of the
leus mats,
we call them L v - l a m i n a e
slimediffer
Microco-
(Fig. 6E; see also facies type 3 in
p a r a g r a p h 1.6.3). These order
unicellular
organisms
increase their
slime
production
in
to escape p h o t o t o x i c conditions when they form the surface mats.
Slime p r o d u c t i o n is also stimulated by
increase in s a l i n i t y and tempe-
33
rature
(CASTENHOLZ,
Sabkha.
1984).
Photosynthetically
All these
conditions
active populations
occur in the Gavish
of other species
(e.
g.
Mierocoleu8 ehthonoplastes) under the translucent mat benefit from
the
production
for
of large quantities
the channelling
of gel since it is an ideal m e d i u m
of light.
~
,' "~I
ELE
•
'
EVAPORITIC'
1
SEA I~
,~i,,
ULLY
~5~-~-
STROHATOLITIC ~
-
./~
•../
ELASTIE-'--'~
Cat6onates Evoporiles Detritol clastics
Lh- laminae, horizontal orientation [ ~
Lv-laminae,vertlcally extended
['~
Ooids and oncoids Pleurocopsoleon nodules
Fig. 7. Local d i s t r i b u t i o n of stromatolitic facies types. The sequence A) to D) correlates to increasing salinity. The p o s s i b i l i t y of superficial water increases from A) to C) and decreases again in type D). A) Siliciclastic biolaminites (gully bottoms and sandlobes). B) Nodular to b i o l a m i n o i d carbonates (saline mud flats). C) Stromatolitic carbonates with ooids and oncoids (lagoon). D) Biolaminated sulfate (gypsum flats).
34
i. 6. 3. C h a r a c t e r and d i s t r i b u t i o n of s t r o m a t o l i t i c facies types
A of
supply of m o i s t u r e to surface sediments where the initial microbial
Gavish
In
Sabkha m o i s t u r e at or close to the s e d i m e n t a r y surfaces
function of topography.
accumulation
(Fig. 4),
e. g. salinity
patterns
tures.
environments,
va-
An infor-
Their
are d e s c r i b e d in the following sections in
structures,
Community
a
(Fig. 3) and in-situ
o v e r v i e w of the lateral sequence is given in Fig. 7.
community
is
this g r a d i e n t will be used as the
riable to d e s c r i b e the lateral d i s t r i b u t i o n of facies types.
vidual
the
Since the t o p o g r a p h i c m o i s t u r e g r a d i e n t p a r a l -
lels other f a c i e s - r e l e v a n t factors, mineral
mal
growth
mats occurs is essential for their development.
indi-
terms
s e d i m e n t a r y textures and
of
struc-
structure is defined h e r e as the v i s u a l l y o b s e r v a b l e
p r o d u c t of species s e l e c t i o n and d o m i n a n c e at a certain place.
i__t. S i l i c i c l a s t i c b i o l a m i n i t e s
This
facies
is composed of quartz sand and
interlayered
biolami-
The b i o l a m i n i t e s characterize the Lh-type w h i c h is Microcoleus-
nites.
dominated Where
(Fig. 8 )
(Fig.
laminae
6A).
Thickness of laminae differs from 50 to 500 Nm.
are thin
(about 50 pm),
they form a
monolayered
mat.
Thicker laminae comprise several generations of mat development,
aided
by
(Fig.
sufficient surface m o i s t u r e during periods of n o n - d e p o s i t i o n
8A).
Environments slope
are the gully bottoms and sandlobes along the
(Fig. 7).
surface.
Here
Vertical
depend on
the g r o u n d w a t e r table runs -5 to -i0
barrier cm
m o v e m e n t s of the g r o u n d w a t e r table b e t w e e n 2 - 5 cm
the external tidal m o v e m e n t in the Gulf.
Sediment
surfaces
are p e r m a n e n t l y w e t t e d by c a p i l l a r y m o v e m e n t of the g r o u n d w a t e r rative
pumping).
ment-air water
Thin evaporite crusts
interfaces.
table
surfaces.
(mainly gypsum)
During w i n t e r time,
form at
(evaposedi-
o s c i l l a t i o n s of the ground-
lead o c c a s i o n a l l y to the i n u n d a t i o n
Salinity
below
of
the
of interstitial w a t e r is 45 - 60 °/oo.
sedimentary No extreme
shifts occur during the annual cycle.
Sediments are m a i n l y t e r r i g e n o u s and consist of b a d l y sorted to
g r a v e l - s i z e d s i l i c i c l a s t i c sand.
(Fig. 8B). These sediments o r i g i n a t e
The grains are of low from debris-flow.
medium
sphericity
35
Fig. 8. D o c u m e n t a t i o n of facies type i: S i l i c i c l a s t i c b i o l a m i n i t e s . A) X - r a y r a d i o g r a p h of a s e d i m e n t core showing m i c r o b i a l mats in 3 cm d e p t h and at the surface. Scale is 1 cm. B) C l o s e - u p of s i l i c i c l a s t i c sediments showing m i c r o b i a l coatings of sediment p a r t i c l e s (center). Thin section. Scale is 1 mm. C) C l o s e - u p of b i o l a m i n i t e s showing m e m b e r s of the mat community: sheathed bundles of Mic~ocoleus chthonop~as#es, diatoms and filamentous sulfur bacteria. SEM-photography. Scale is 50 pm.
community
structure
(Fig.
8C):
The b u l k of the laminae is made of
e n s h e a t h e d b u n d l e s of M~c~ocoleu8 chthonoplastes. Few u n i c e l l u l a r genera
of
c y a n o b a c t e r i a and diatoms are a s s o c i a t e d w i t h
Mic~ocoleus
the
mat. The mat d e v e l o p s -2 to -5 mm b e l o w the w a t e r surface or u n d e r n e a t h evaporite
crusts.
Both s i l i c i c l a s t i c sediments and
support l i g h t - c h a n n e l l i n g
2. N o d u l a r to b i o l a m i n o i d c a r b o n a t e s
This
term
(nodules)
granular,
cauliflower-shaped
e m b e d d e d in w i d e - s p a c e d b i o l a m i n o i d s
(a
w h i c h defines a less s i g n i f i c a n t l y laminated b u i l d - u p of b i o g e n i c
sediments). and
crusts
(Fig. 9 )
facies type is c h a r a c t e r i z e d by
microbial aggregates
evaporite
for p h o t o s y n t h e t i c activity.
The embedding m a t e r i a l consists of intermixed calcite
mucilaginous
sheaths
of
polysaccharides.
Various tubular relicts
filamentous c y a n o b a c t e r i a are visible around
the
of
mud empty
nodules
(Fig. 9A). T r a n s i t i o n a l stages towards laminoid a r r a n g e m e n t s of smaller
36
granulae exhibit facies
and
filaments can be seen (Fig. 9B)°
a mammillate mierotopography
Surfaces of
(Fig. 9C).
The p a t t e r n
the
mats
of
this
type is stimulated by constant shifts of salinity and depth
of
water.
Environment.
The n o d u l e - b i o l a m i n o i d
facies type dominates
flats just beyond and in b e t w e e n the sandlobes flats
saline mud
(Fig. 7). The saline mud
border the lagoonary basin and are p a r t i a l l y built over
by
the
37
Fig. 9. D o c u m e n t a t i o n of facies type 2: N o d u l a r to b i o l a m i n o i d carbonates (saline mud flats at the lagoon's outer rim). A) I n t r a s e d i m e n t a r y nodules e m b e d d e d in c a r b o n a t e mud. A filigrane m e s h w o r k of d i a g o n a l l y to v e r t i c a l l y o r i e n t e d filaments is visible. Dark sediments at top: reduced. Scale is 500 pm. B) I n t r a s e d i m e n t a r y t w i n - n o d u l e and b i o l a m i n o i d structures (note w a v y d i a g o n a l dark line in the right upper corner). Scale is 2 mm. C) M a m m i l l a t e surface m i c r o t o p o g r a p h y , c h a r a c t e r i s t i c of the noduleb e a r i n g zone. Scale is 1 cm. D) Larger nodules sampled at the surface of small w a t e r - f i l l e d puddles. Scale is 2 cm. E) S E M - p h o t o g r a p h y of a colony of n o d u l e - f o r m i n g c y a n o b a c t e r i a (Pleurocapsalean). Scale is 3 pm. F) S E M - p h o t o g r a p h y of nodule c o m p a r t m e n t s showing capsules of former cells. Note radial a r r a n g e m e n t of compartments. Scale is 3 pm. G) D i s s e c t e d nodule showing radial a r r a n g e m e n t of compartments, the empty center and i r o n - r i c h p i g m e n t s around the cortex. Scale is 2 mm. Figs. A, B and G thin sections from sediment cores.
elevated
sandlobe
"bars"
gullies into the lagoon.
of coarse sediment w h i c h p r o j e c t
tions and feeds the g e n t l y downwards w a t e r film. Lower s a l i n i t y at
sloping mud flats w i t h a trickling
(Ente~omo~pha
sp.). Micro-
bial mats do not d e v e l o p here. The seepage w a t e r a c c u m u l a t e s
into
and
the
drains from these e m b a y m e n t s through
central basin.
the junc-
s e a w a t e r springs b e t w e e n 50 - 70 °/oo is
m a r k e d by a thick scum of b e n t h i c m a c r o a l g a e
embayments
from
Seepage seawater merges at the sandlobe
S a l i n i t y increases w i t h
from 70 to 180 O/oo.
in shallow
narrow
passages
distance
seawater
springs
Some very shallow
(maximum
w a t e r cover i0 cm) are subject to s h o r t - t e r m
from
the
embayments
(commonly
diur-
nal) changes of w a t e r cover and air exposure due to changing conditions of
e v a p o r a t i o n and wind velocities.
observed extreme °/oo.
Short-term salinity
ranging from 70 to 150 °/oo. amplitudes
Other
HOLTKAMP
shifts
were
(1985) r e c o r d e d
ranging w i t h i n a few minutes b e t w e e n 130
more
and
embayments w i t h w a t e r levels b e t w e e n 20 and 40 cm
240
remain
w a t e r - f i l l e d during diurnal and annual cycles. The salinity ranges from 70 to 120 °/oo. Flats around the embayments are usually a i r - e x p o s e d and covered
by
thin e v a p o r a t i o n crusts.
Salinities here can reach up
to
180 °/oo.
S e d i m e n t s are m a i n l y c o m p o s e d of f i n e - g r a i n e d carbonates. G r a i n size analyses
of surface sediments show 38 wt.%
and 30 wt.% 6.3 - 20 pm. saccharides
and
<2 pm,
27 wt.%
2 - 6.3 pm
The s e d i m e n t is mixed w i t h m u c i l a g i n o u s poly-
is of a sluggish,
yoghurt-like
w a t e r - a i r interface of the embayments,
appearance.
thin and fragile
At
the
"calm skinned"
e v a p o r i t e crystals form and are i m m e d i a t e l y d i s i n t e g r a t e d by wind.
The
38
Fig. i0. Documentation of facies type 3: Stromatolitic carbonates with ooids and oncoids (lagoonary basin). A) Sequence of dark (Lh) and light laminae (Lv), growing independently from sediment transport, calcification being a p e n e c o n t e m p o r a n e o u s process (note coatings of diagonally to vertically oriented filaments within the light layer). Scale is 1 mm. B) Close-up of coated filaments w i t h i n a Lv-lamina. SEM-photography. Scale is 5 Nm. C) Ooid embedded in calcified filamentous meshwork. Scale is 500 pm. D) Cluster of coated grains within an extended light lamina. Scale is 500 ~m. E) String of coated grains captured by h o r i z o n t a l l y oriented filaments. Scale is 1 mm. F) Eye-shaped lense, formed by a discontinuous Lh-lamina. Lenses are often the m i c r o - e n v i r o n m e n t of coated grain formation. Note rigid calcification below, within and above the dark lamina. Scale is 500 ~m. G) Ooid surrounded by various intraclasts (dark spots). Scale is 500 ~m. H) View of a biohermal build-up of a mat at the lagoon's margin. The partial destruction is due to slight wind surf. Scale is 5 cm. Figs. A, C, D, E, F and G thin sections from sediment cores. fragments
sink
gypsum mush.
down
to the bottom and form
Some portions become diluted,
mucilaginous
polysaccharides
a
water-saturated
others are embedded
soft
into the
and get colonized by the microbial
commu-
nities. The
community
with multiple cellular
forms
Synechococcu8 The
colonies
(Fig.
colony (Fig.
cyanobacteria
(Fig.
9E).
The compartments
compartment 9F).
The
pigment and
scytonemine
form
cauliflower-shaped
of these
"nodules"
type changes to a more regularly
when
(Fig. 9F). The yellow-
surface m i c r o t o p o g r a p h y
the saline mud flats into the
are also
(Fig. 9A) and at the
cortex
especially the outer surface of
granular
Gloeothece,
cyanobacteria
colors the
following division of the individual of
cyanobacteria
9E, F). Other uni-
producers
and filamentous
show concentric growth around cavities
continuation facies
Figs.
9D) w h i c h occur intrasedimentarily
iron-enriched
maintained
types;
the major slime
Synechocystis)
Pleurocapsalean
sediment surface brown
is dominated by unicellular
(Pleurocapsalean
(predominantly
and
present.
dissected
structure
fission
of
the
of the
each
nodules
nodules
is
cells. With the lateral lagoonary
spaced pattern
basin,
(see next
the sec-
tion). 3. Stromatolitic
carbonates with ooids and oncoids
This facies type is characterized and dark laminae
(Fig.
10A).
(Fi 9. i0)
by regular interlayering
of
light
Both lamina types differ in the vertical
39
40
extension: light
The dark lamina is generally thin (i00 to 200 pm), while the
lamina is up to ten times thicker.
Various vertically to diago-
nally oriented filaments thread through the light layer,
demonstrating
active movements of unsheathed hormogonia and trichomes of cyanobacteria. lOB).
These
Associated
varying
with the light layers are also carbonate
diameters
layers
(Figs. 10C to 10F).
transitions
sections
show
of
light
(Fig. 10D).
(Figs. 10E and F). Some
(ooidal), others are irregularly shaped
from oval to subangular
that
grains
captured by filaments of the dark
laminae which form pockets or eye-shaped lenses grains are regularly concentric
(Fig.
Grains within thickening
show dispersed and sometimes clustered arrangements
Others appear like strings of pearls,
with
filamentous
filaments frequently show calcite coatings
forms
(oncoidal).
concentric lamination of these grains
Vertical is
common
(Fig. 10G). The
environment
seawater
is
the lagoonary basin which is
and probably artesian discharge
by
seepage
(wells) at the basin
fed
bottom.
The 70-cm-deep center of the basin slopes shallowly upwards. facies ject
to
seasonal
changes of water depth
(between i0 and
salinity ranging from 140 (winter) to 280 O/oo (summer; annual changes are performed in a long term, contrast
in
facies.
The surf
build-ups
the
attack the microbial communities tend
with
Recalculation
nodule-biolaminoid
to
of GAVISH's data (GARISH
5
wt.%.
The
form
biohermal
Communities:
al.,
(29 wt.%). consists
of
1985) high
Dolomite is sand-sized
(6 wt.%).
The matrix of this biofacies type is primarily built of
microbial biomass,
mainly of cyanobacteria.
evenness of shallow-water cover, unit
et
the most commom being
remaining portion
(I0 wt.%) and silt-sized quartz
living
in and
(Fig. 10H; see also Fig. IIA).
magnesium calcite averaging 50 wt.% and calcite
the
and
even pattern which is
the shizohaline amphibic zone of
bulk volumes o f carbonate minerals,
found
40 cm)
basin rim is subject to a slight surf caused by the wind.
Sediments: shows
said
Fig. 3). These
to the extreme short term irregularities of water supply
salinity
Under
The
type develops mainly along the shallow shelf area which is sub-
Biomass accumulates under
giving rise to a
which is clearly of stromatolitic
multilaminated
appearance.
The
dark
laminae are created by the predomination of heavily ensheathed filamentous cyanobacteria, light
mainly Mieroco~eu8 chthonoplaste8
(Lh-type).
laminae (Lv-type) are gel-supported and produced by
The
unicellular
41
Fig. ii. D o c u m e n t a t i o n of facies type 4: B i o l a m i n a t e d sulfate. A) R a i s i n - e m b e d d e d microbial mat from the lagoonary rim, laterally d i s t o r t e d b y drying cracks. The d a r k - r e d u c e d zone contains carbonates, the light o x y g e n a t e d t o p m a t i s i n t e r s p e r s e d w i t h elongated gypsum crystals. Note o x i c / a n o x i c b o u n d a r y following the l a t e r a l l y d i s t o r t e d mat surface. Left: S a l t b e e t l e b u r r o w w i t h o x y g e n a t e d halo. Scale is 1 cm. B) G y p s u m crystals growing in a m i c r o b i a l mat expand the space b e t w e e n dark Lh-laminae. Scale is 1 mm. C) F a i n t l y b i o l a m i n a t e d sulfate deposits. Scale is 1 mm. D) G y p s u m deposits, p r o t r u d i n g above the sediment surface. Pupae of the brine fly Ephydra sp. are a t t a c h e d under the crust. Scale is 2 cm. E) I n t r a s e d i m e n t a r y g y p s u m nodule, coated by a m o n o l a y e r e d microbial mat. Scale is 1 mm. Figs. B, C, E from thin sections.
42
Synechocyst~s and
Synechococcus).
Each lamina type is vertically repeated several times.
Up to I0 living
cyanobacteria strata
Gloeothece,
(mainly
thus form which harbor a multitude of oxyphotobacteria
bacteria),
anoxyphotobacteria
flexus), sulfate- and
(e. g. Thiocapsa,
sulfur-reducing
(cyano-
Ch~omatium,
chemoorganotrophic
Chlo~obacteria.
Various products of the metabolic activity of these organisms contemporaneously et al.,
penetrate the vertically structured living system
(KRUMBEIN
1979). Ranging in thickness up to 2 cm, it reflects the multi-
species nature of an organic-rich microbial environment. 4. Biolaminated sulfate Gypsum
(Fi 9. ii)
precipitation
takes place at both the
amphibious
center-oriented rims of the lagoon. As long as bacterial tion (Fig.
predominates
precipitation is restricted to
decreases
due to increasing salinity.
center-oriented rim of the lagoon (Fig. sometimes twin-shaped, above
sulfate reduc-
oxygenated
topmats
IIA). Massive gypsum banks first accumulate where the biological
activity
bial
bar- and
mats
(Fig.
the
This
occurs
at
the
7). Elongated gypsum crystals,
penetrate and fragment the interlaminated micro-
lIB).
Faintly biolaminated sulfate deposits protrude
sediment surface ranging in thickness from
several dm (Figs IIC and lID).
several
cm
to
Microbe-coated gypsum nodules also form
(Fig. lIE). Community structures.
t~8)
dominate
the
mainly Sp~ullnu, face anoxybacteria,
(mainly Synechocys-
Unicellular cyanobacteria
microbial communities.
A few
filamentous
forms,
some halobacteria and at the sulfate-sediment mainly Thiocapsu and Ch?omatium,
inter-
are also present.
This facies is the record of the gradual rise of the terrane towards the
center
and correlates also to the further increase
of
salinity.
Close to the lagoonary rim, salinity ranges between 220 and 300 °/oo in winter and between 280 and 320 °/oo in summer. A maximum of 360 °/oo is maintained
in
bedouin
boreholes which lie just
beyond
the
central
plateau.
I. 6. 4. Facies type-related bio~eochemistry This section deals with local records of standing crops and physicochemical
profiles
(Eh and pH) in sediments.
Measurements
were
made
43
within type
the facies types i),
basin
d e s c r i b e d above:
(2) the saline mud flats
(facies type 3) and
(i) the
sandlobes
(facies type 2),
(4) the sulfate flats
(facies
(3) the l a g o o n a r y
(facies
type
4).
An
informal o v e r v i e w is given in Fig. 12.
St andin ~ crops. carried large
out
by H O L T K A M P
standing
Microcoleus (e. g.
Biomass studies in the Gavish Sabkha mats have b e e n
crops
mats
(1985).
These studies reveal the
(expressed in Ng chl a per
w h i c h form the L h - l a m i n a e in both
w i t h i n the sandlobes;
form
(Fig. 12B
the
2 and 3).
endobenthic
monolayered
mats
Fig. 12B section 3). Gelatinous mats
L v - l a m i n a e are usually lower in
sections
compaction
relatively
in
Fig. 12B section i) and m u l t i l a y e r e d mats
(e. g. w i t h i n the l a g o o n a r y basin; which
cc)
chlorophyll
This can be a t t r i b u t e d to the
content different
of p h o t o s y n t h e t i c a l l y active organisms w i t h i n the
laminae.
The Microco~eu8 mat forms a h e a v i l y c o n d e n s e d network of s h e a t h - e n c a s e d filamentous o r g a n i s m s nisms
(Fig. 8D).
teristic
of
a h i g h slime to cell ratio.
swelling of the biolaminite, decreases
Studies
variations plays
carried
out by BAULD
demonstrate
to
a
cells
(1984) at Shark Bay and Spencer
s i m i l a r i l y that for any one
substantially
affect standing
the most d e c i s i v e role,
ponding
The slime contributes
h e n c e the number of p h o t o s y n t h e t i c
in relation to the total bulk volume of the Lv-lamina.
(Australia)
take
Thus a c t i v e l y p h o t o s y n t h e s i z i n g orga-
are r e l a t i v e l y more a b u n d a n t than in the gelatinous mats charac-
crops.
mat
Water
local
availability
as can be seen in Gavish Sabkha,
where
of seepage waters in the w i n t e r and d e s i c c a t i o n in the
place.
During
Mic~ocoleu8
surface
the w i n t e r p e r i o d the chlorophyll mats
Gulf
type
a
averages ten times that of the
summer
content summer
of mat
where d e s i c c a t i o n takes place.
The data of H O L T K A M P
(1985) reveal h i g h c o n c e n t r a t i o n s of p h e o p h y t i n
(the d e g r a d a t i o n a l p r o d u c t of c h l o r o p h y l l a) in almost all mat types. C o n c e n t r a t i o n s of p h e o p h y t i n a rophyll
a
up to 5 x
were found in L v mats.
p h o t o s y n t h e t i c a l l y active organisms processes. than
A
chlorophyll
g r e a t e r than those of
This indicates that the
chlo-
growth
of
is a c c o m p a n i e d by rigid d e g r a d a t i o n
a / p h e o p h y t i n ~ ratio
(C/P ratio)
1 suggests for several m i c r o b i a l mats of the Gavish
smaller
Sabkha
that
d e g r a d a t i o n of c h l o r o p h y l l a takes over a l r e a d y s i m u l t a n e o u s l y w i t h the p h o t o s y n t h e t i c a c t i v i t y in the same surface layer 3 and 4; values c a l c u l a t e d by HOLTKAMP).
(Fig. 12B sections 2,
44
A ELEVATION AND SALINITY GRADIENTS
B LIVING TOP MATS: PIGMENT CONCENTRATIONS ~ 0
20C/P
o
2o
4o
o
60 ' C/P
Chlorophyll _a
~
Pheophyfin a (pg per co)
8o 1oo/p
o
20 %o 60 %0 i00
zo ~o 6o
[/P
©
NN//,)7/IIo-71q ®
(D
®
C SEDIMENT PROFILES: REBOX POTENTIALS AND pH Eh (mY)
Eh (mV)
'-4~0 '-360 '%o'
-460 '66o '-26o '-~6o' ~' +~6o ' ...... ~,~ 6,8
O
P,,
7,~ 7,6
Eh (mY) I,,,
8
-26o '-16o'6 '+16o',26o' pH
8,~
O
0
-
E
.E
'E
6-
a
1,
'
I\ ; \ t pH
1
®
/×
I
E
14-
®
®
Fig. 12. Effects of terrane inclination and salinity increase on standing crops (data after HOLTKAMP, 1985) and p h y s i c o c h e m i s t r y . A. Schematic p r e s e n t a t i o n to show i n c l i n a t i o n and salinity increase. B: Chlorophyll a, p h e o p h y t i n a (degradational product of c h l o r o p h y l l a) and C/P ratios in surface--mats. The t e n d e n c y of m i c r o b i a l commun~ties to build m u l t i l a y e r e d mats increases w i t h the inclination of the terrane and the salinity increase. Sandlobes (I): Mats are m o n o l a y e r e d and of the Lh-type, Saline mud flats (2), lagoon (3) and gypsum flats (4): Mats consist of two or three laminae. Lowest pigment concentrations w i t h i n the g y p s u m flats (4) and Lv-tO P mats (see 2a, 3a). C/P ratios smaller one indicate that p h e o p h y t i n a takes over. Highest C/P ratios occur in L h mats (see i, 3b). C: Eh- and p H - p r o f i l e s in sediments (M-= surface mat). Reduced h o r i z o n s are dashed or shaded to show their increasing vertical extension.
45
Reduction-oxidation potentials andSterms
of
Eh
Physicochemical properties
and pH are s u m m a r i z e d in Fig. 12C w h i c h relates
to
in the
areas of standing crops d e s c r i b e d above.
Within
the s i l i c i c l a s t i c s of the sandlobes
Eh-values ching
into
sulfate Fig.
the n e g a t i v e sector indicate b u r i e d mats
reduction
prevails
12C section i).
quently
(areas of facies type I)
w e r e found m a i n l y in the p o s i t i v e sector.
reaches
(e. g.
Small peaks where
rea-
bacterial
from -4 to -6 cm b e l o w surface
The pH in p h o t o s y n t h e t i c a l l y active topmats
values a p p r o a c h i n g 9 and falls back in the
in fre-
seawater-
soaked sediments b e l o w to slightly a l k a l i n e m a r i n e conditions.
On
the
mud flats
(areas of facies type 2) only p o s i t i v e
Eh-values
are found in the surface mats. The sediments b e l o w are strongly reduced up to a depth of -12 cm under the surface.
Eh-values of up to
-400 mV
(Fig. 12C section 2) were measured.
The sediments of the lagoon
(localities of facies type 3) are
wise s t r o n g l y reduced right up to the surface Values 6.0
were b e t w e e n 7.4 and 8.2.
to 6.5 were o b s e r v e d by E.
ments
(Holtkamp,
saturated
1985).
e x t r e m e l y low values of pH
H O L T K A M P in the black anaerobic
the h i g h e r the b i o l o g i c a l activity is.
These organisms
rich sediments w h i c h are c o n s e q u e n t l y c o l o n i z e d by
of sulfate as an e l e c t r o n donor.
seepage
seawater
and
chemoorgano-
tration
(see Fig.
with
The sulfate is supplied by
c o r r e l a t e s in its c o n c e n t r a t i o n well
topographic moisture gradient
with
the the the
3). The increase in the concen-
of p h y s i o l o g i c a l l y d e r i v e d reductants within sediments of
strongly
of
form the organi-
trophic b a c t e r i a w h i c h d e c o m p o s e the dying organic material, help
sedi-
The more c o n t i n u o u s l y the sediment surface is
or covered by water,
the p h o t o s y n t h e t i c m i c r o o r g a n i s m s cally
However,
like-
(Fig. 12C section 3). pH-
h y p e r s a l i n e lagoon shows that salinity is a s e c o n d a r y
the
factor
w h i l e m o i s t u r e is of e x t r a o r d i n a r y i m p o r t a n c e for the m i c r o b i a l p r i m a r y producers.
i. 6. 5. Products o_ff early d i a g e n e t i c p r o c e s s e s
The
d e f i n i t i o n of early d i a g e n e s i s
ments after burial
(BERNER,
refers to changes
within
sedi-
1980). Besides burial by sheet flood depo-
sits,
self-burial
by vertical
successions of m i c r o b i a l mats is impor-
tant.
This is achieved by the active p o s i t i o n i n g of m i c r o b i a l
popula-
46
tions relative to their e n v i r o n m e n t a l requirements, to the light field. The rapid gliding m o t i l i t y
latoria sp.
e. g. w i t h respect
(up to 3 cm/h) of 08cil-
a common filamentous species in the Gavish Sabkha,
and its
p e n c h a n t for spreading out under optimal conditions of light and temperature
allows this species in p a r t i c u l a r to override other cyanobacte-
rial topmats
(CASTENHOLZ,
Microcoleu8
chthonoplastes is able to p e r f o r m e n v i r o n m e n t a l
induced
movement
light
conditions
forth
in
complex chomes
its
1969).
Also the filamentous
and accumulates at sediment surfaces (HOLTKAMP 1985).
interactive way
stimulus-
under
reduced
This species usually moves back and
bundled sheath and builds up h o r i z o n t a l
(and hormogonia;
cyanobacterium
(Lh-lamina type).
In crisis
bundles
in
conditions
a
tri-
short filaments of u n d i f f e r e n t i a t e d cells) move
faster and further away from the growth site.
The This
organic is
m a t t e r left b e h i n d exhibits great
evident even in the topmost layers.
The
diagenetic following
variety features
d e s c r i b e d b e l o w can be related to early d i a g e n e t i c processes:
Fig. 13. Patterns of d e h y d r a t i o n and d i s s o l u t i o n in m i c r o b i a l mats. A) S y n a e r e s i s - c r a c k running through an e x t e n d e d h y d r o p l a s t i c Lv-lamina. The dark coating may be caused by subsequent m i c r o b i a l colonization. Thin section from sediment core. Scale is 1 mm. B) Partial d i s s o l u t i o n of g y p s u m o v e r g r o w n by a m i c r o b i a l mat. Filaments of c h e m o t r o p h i c b a c t e r i a and slime threads coat the crystals. Scale is 2 ~m (B to D: SEM-photography). C) Pyrite crystals cover b a c t e r i a l slime. Scale is 3 pm. D) Partial d i s s o l u t i o n of a h a l i t e chip. Scale is 5 pm.
47
(i) Synaeresis cracks
(Fig. 13A)
S y n a e r e s i s cracks are g e n e r a l l y t h o u g h t to like m a t e r i a l
(WHITE,
1961;
BURST,
s p o n t a n e o u s d e h y d r a t i o n even in subaqueous In
the
Gavish
extended (Fig.
13A).
sediments
(PETTIJOHN,
Sabkha sediments synaeresis cracks
hydroplastic
pearance
be c h a r a c t e r i s t i c of gel-
1965) and h a v e b e e n a t t r i b u t e d to
occur
1975).
within
the
layers c o m p o s e d of e x t r a c e l l u l a r p o l y s a c c h a r i d e s
Even the m u c u l o u s clouds r e s p o n s i b l e for the viscous
ap-
of the surface w a t e r c o n t r i b u t e to these layers due to gravi-
tational displacement.
(2) D i s s o l u t i o n p a t t e r n s of evaporite m i n e r a l s
Several d i s s o l u t i o n p a t t e r n s are v i s i b l e evaporites.
on the surface of embedded
D i s s o l u t i o n of g y p s u m in b u r i e d mats
(Fig. 13B) may be m o r e
a b u n d a n t w h e r e b a c t e r i a l sulfate r e d u c t i o n occurs. g y p s u m w i t h b a c t e r i a l slime is evident.
C o m p l e t e coating of
Cobwebs of e x t r a c e l l u l a r mucus
are c o m m o n l y covered w i t h various p y r i t e rosettes as shown in Fig. 13C. In contrast,
the shape of the h a l i t e chip in Fig.
13D indicates p a r t i a l
d i s s o l u t i o n resulting from the d i f f u s i o n of salt into p o r e w a t e r
fluids
of lower concentrations.
(3) Decay centers and formation of a u t h i g e n i c m i n e r a l s
The
term
within situ
a u t h i g e n i c mineral refers to m i n e r a l species
a sediment after burial formation
of minerals,
(BERNER,
1980).
which
grow
By contrast to the in
allochems are formed e l s e w h e r e
and
are
t r a n s p o r t e d to the d e p o s i t s in q u e s t i o n w h e r e they accumulate. A causal factor
in
the formation of a u t h i g e n i c c a r b o n a t e s o c c u r i n g
in
buried
G a v i s h Sabkha mats appears to be the b a c t e r i a l d e c o m p o s i t i o n of organic material
left b e h i n d after death
(BERNER,
1980).
The sheaths of Microcoleu8 chthonoplastes w h i c h form the are
p a r t i c u l a r l y r e c a l c i t r a n t and survive decomposition.
(1985)
have
found
that the sheath m a t e r i a l consists
w h i c h are e v i d e n t l y r e s i s t a n t to m i c r o b i a l attack. after
the c y a n o b a c t e r i a l
composed (COHEN, former
Lh-laminae BOON et
of
biopolymers
The sheath
filaments have disappeared.
al.
Thus
remains
Lh-laminae
of sheaths are often retained even in deeper sediment
layers
1984). E l o n g a t e d a r r a n g e m e n t s of m i c r i t e crystals p o i n t to the p r e s e n c e of f i l a m e n t o u s o r g a n i s m s
(Figs.
14A to
formed by coccoid unicells also p o s s e s s a h i g h degree of
D).
Capsules
recalcitrance
48
while
the enclosed p r o t o p l a s t s are subject to more
resulting
honey-comb
pattern
feature of d e c a y i n g mats
A
coccoid
of h o l l o w spheres is
rapid a
early
The
(Figs. 14E and F).
colony w i t h o u t capsules
(Fig.
15A) may give rise
m i c r i t e - s u r r o u n d e d h o l l o w sphere after decomposition. showing
decay.
characteristic
stages of m i c r i t i z a t i o n are illustrated
to
a
Coccoid unicells in
Fig.
15B.
49
Fig. 14. SEM-photographs showing localized decay and carbonate precipitation in b u r i e d mats at 60 to 80 cm sediment depths (A, B, C, F) and about i cm b e l o w surface (D, E). A) Granular m g - c a l c i t e p r e c i p i t a t e around decaying trichomes of cyanobacteria. At the lower end of the left tube is its empty state visible. Scale is 5 pm. B) Continued precipitation of m i c r o c r y s t a l l i n e mg-calcite replaces g r a d u a l l y the filamentous form. Scale is 25 pm. C) Only the elongated arrangement of micrite crystals points to the former filament. Scale is I0 ~m. D) Polysaccharid capsules are more resistant to b a c t e r i a l attack than protoplasts: Degrading cell encased by the extracellular capsule. Scale is i0 pm. E) Empty capsules of cyanobacteria (probably Pleurocapsalean) surrounded by smaller eoccoids (possibly sulfur bacteria). Empty capsules later give rise to m i c r i t e - s u r r o u n d e d h o l l o w spheres. Scale is I0 pm. F) View of the decaying mat with coated filaments, diatoms and hollow spheres. Note the slightly deformed coated sphere at top. Such spheres also form around gas bubbles abundantly occurring within the decaying mat. Bubbles colonized, coated and fixed are common (see also Fig. 26). Scale is 25 pm.
Single cells appear as completely and oncoids of various records
of
calcified
shapes and sizes
carbonate p r e c i p i t a t i o n
spheres
(Figs.
(Fig.
15D,
15C).
Ooids
E and F) are also
within the buried mats
(see
next
section).
i. 6. 6. In-situ
Self-burial, ly
formation of ooids and oncoids
emphasized
in the previous
w i t h i n the facies type 3 which occurs
lagoon.
It
results
in the vertical
supported Lh- ) and light bial mats.
lations p r e d o m i n a n t l y Lh-laminae evaporites,
(unicellular
The study of thin sections
carbonate which
in the
is recorded main-
constantly
succession of
dark
grains
In sheetflood
horizontally
facies type 3, they are non-existent.
(Fig.
I0).
sediments
and v e r t i c a l l y
with
(compounds
In and the
Their close relationship with the
It is stressed that the ooids are not
in the off-shore waters nor are they found in the layers
with allochems
micro-
shows that ooid and oncoid popu-
are rare.
interfinger
submerged
(filamentous
and gel supported Lv-type)
occur within the light Lv-laminae
L v - l a m i n a e will be examined here. forming
sections,
that have been transported
into the
rich
environ-
ment).
The term ooid is applied to a rounded biogenic and continuous
laminations;
grain with concentric
it is less than 2 mm in diameter
(Table 2).
50
Fig. 15. S E M - p h o t o g r a p h s showing cells and rounded cell clusters in mats w h i c h may give rise to n u c l e a t i o n centers of ooids, compound ooids and oncoids. A) Colony of coccoid unicells p a r t i a l l y a g g l u t i n a t e d showing initial steps of calcite coatings. Scale is 2 ~m. B) M i c r o t e x t u r e of a colony of coccoid unicells during an early stage of lithification. Scale is 2 pm. C) C o m p l e t e l y calcified single cell. Scale is 5 pm. D) Sub-rounded shape of lithifying cell colony. Rod-shaped organisms at right may be c h e m o o r g a n o t r o p h i c bacteria. Scale is 2 pm. E) R e p e t i t i o n of m i c r o b i a l coating of a c o m p l e t e l y round carbonate grain. Scale is i0 pm. F) Sub-rounded grain embedded in a slime m a t r i x and c o l o n i z e d by small unicellular bacteria. Scale is 3 pm.
51
Where
the
laminations are d i s c o n t i n u o u s and irregular and the
are less rounded,
the t e r m oncoid will be applied
D A H A N A Y A K E & KRUMBEIN,
(HEIM,
1916,
grains see also
1986).
In-situ f o r m a t i o n of ooids in p a r t i c u l a r may be striking but can correlated
to
conditions already m e n t i o n e d in the
previous
be
section.
These conditions are summarized as follows:
(1) H y d r o p l a s t i c L v - l a m i n a e provide the space:
In
the vertical sequence m u c h more e x t e n s i v e L v - l a m i n a e
override shaped of
the
(Fig. 8).
gel.
The
partially vugs
thinner L h - l a m i n a e ,
w h i c h may be flat,
repeatedly
w a v y or
"eye"-
The L v - l a m i n a e are c h a r a c t e r i z e d by large q u a n t i t i e s
m u c i l a g e tends to become i r r e g u l a r l y
diluted by interstitial
d e v e l o p due to i r r e g u l a r i t i e s
seawater.
disintegrated
Small-scale
and
pockets
in the slime m a t r i x and the
and
under-
lying Lh-laminae. (2) N u c l e a t i o n centers:
On
a
microscopic
scale,
the w i d e l y spaced L v - l a m i n a e
v a r i e t y of p o s s i b l e nuclei for ooid and oncoid synthesis: bubbles,
intraclasts,
d e g r a d i n g cell clusters.
from Lh-type mats below.
contain trapped
a gas
The bubbles often come
These g e n e r a l l y h a v e a h i g h e r p r i m a r y produc-
tion rate than the L v - l a m i n a e above. The filamentous o r g a n i s m s d o m i n a n t in
Lh-laminae
conditions.
are
able to p h o t o s y n t h e s i s e even under
Metabolic products
(e. g.
reduced
light
02 , CO 2, NH 3, CH 4, H2S), b e c o m e
trapped d u r i n g upward m i g r a t i o n w i t h i n the h y d r o p h i l i c gels w h i c h lower their
diffusion
1979). laminae
The
originate
unicellular duction,
v e l o c i t y by at least the factor ten (KRUMBEIN et
intraclasts
w h i c h can be r e p e a t e d l y o b s e r v e d
from floating and/or
cyanobacteria,
tend
fragmentated
within
mats.
the
Finally,
w h i c h are m a i n l y r e s p o n s i b l e for gel pro-
to form cell clusters rather than regular
arrangements
w i t h i n the s l i m e - s u p p o r t e d layers and p r e s e n t ideal n u c l e a t i o n after death
al.,
centers
(Fig. 15).
(3) N u c l e a t i o n and c o n t i n u e d growth of ooids and oncoids:
Bubbles,
intraclasts,
organic fragments,
filaments,
single cells,
o f t e n on s u b m i c r o s c o p i c scale,
for CaCO 3 p r e c i p i t a t i o n .
cell clusters and may serve as nuclei
Initial CaCO 3 p r e c i p i t a t i o n may be due to the
52
localized
rise in c a r b o n a t e
supersaturation
due to b a c t e r i a l
tions given by B E R N E R
organic
C + CO 2
organic
N ÷ NH 3
2NH 3 + CO 2 + H20
Dissolved
bacteria.
(1980)
+
which
brine
as a result of a m m o n i a
decomposition
of proteins.
and
The
CO 2 reac-
are as follows:
2 NH4 + + CO3=
sulfate
interstitial
alkalinity
is supplied
is c o n s t a n t l y
This a d d i t i o n a l l y
in high
reduced
generates
concentrations
by
the
to sulfide by s u l f a t e - r e d u c i n g
carbonate
alkalinity:
2CH20 + S04= + H2S + 2HC03= Thus, tive is
bacterial
attack on p r o t o p l a s m
zones w i t h i n the host m a t e r i a l more
recalcitrant
commonly
of m i c r o s c o p i c
rough
measurements
6. 4.
do not p e r m i t
ments
is
to
The factors
"hard ground"
living
the c o n t i n u e d
ally
calcified
soft-bodied
ooids
colonization,
which
decomposition, This
process
and oncoids.
brine
to e m p h a s i z e
appears
production
may bring
of excess
protoplasm filled
may be analoand
calculi
to
with
external carbonate
the c o n s p i c u o u s
matrix
the coating
growth of calcareous material
result,
bubbles
layers m a y be due
again a c c e l e r a t e s
of alka-
As a
stones
i.
to disturbances.
in the surrounding
(see for example
8). Thus,
tion.
as a r e a c t i o n
are
measure-
centers
fractalized (e. g.
(kidney)
of the c o n c e n t r a t e d
Fig.
death:
bezoar
but it seems w o r t h w i l e
of m i c r o o r g a n i s m s
any given
ions
itself
centers
in section
The effect of e n c a p s u l a t i o n
of perls,
saturation
ions),
cells,
reac-
so that the rather
shown
of localized
of c o n c e n t r a t e d
growth of c o n c e n t r i c
(overall
gel which
In situ m i c r o e l e c t r o d e
the d e c o m p o s i n g
of m a c r o o r g a n i s m s
continued
scale
parameters
The effect
w i t h CO 2 or CH4).
and sulfate
quent
sediment
highly
reactive
level of CaCO 3 o v e r s a t u r a t i o n .
around
the f o r m a t i o n
found in tissues
These h i g h l y
their recognition.
and other centers
initially
generates
of e x t r a c e l l u l a r
or even s u b m i c r o s c o p i c
of general
a rise in the
CaCO 3 p r e c i p i t a t e s material
habit
decay.
can solve this problem.
linity
gous
against
material
of c o l o n i z i n g
of e x t r a c l a s t s
layers
around
to be achieved the reaction
by
in
initisubse-
chain
after
free energy and p r e c i p i t a -
about the successive
laminations
of
the
53
Finally,
the
nuclei
appears
bubbles
(Fig.
inhabitants), bring
question to be 14F
of the shape
important.
of
pre-existing
Unicellular
soft-bodied
organisms
(Fig. 15C),
shows for example the coating of a b u b b l e
and smaller lithified cell a g g r e g a t e s
(Figs.
a b o u t the c o n c e n t r i c a l l y c o n t i n u o u s ooid type
by
15A, B) may
(Fig. 15E),
the o n c o i d type is b r o u g h t about by less rounded nuclei
mat
while
(Figs. 15D
and
F). All
the
facts m e n t i o n e d above as well as other
biogeochemical COHEN et al.,
studies of m i c r o b i a l mat systems
be
1978,
and 1983;
1984) allow us to infer the p o s s i b l e syngenetic growth of
ooids and oncoids w i t h i n s t r o m a t o l i t i c not
physiological
(KRUMBEIN,
construed
sequences.
that all cases of ooid and
It should,
oncoid
however,
formations
are
c o v e r e d by these models.
i. 6. 7. M i c r o b i a ! l y m o d i f i e d surface structures
Subaerially physical
exposed and s a l t - e n c r u s t e d surfaces bearing a number of
structures such as d e s i c c a t i o n cracks and crinkle
i n c l u d e d here. The aim is to d e m o n s t r a t e h o w p h y s i c a l
marks
are
structures can be
m o d i f i e d by the p r e s e n c e of microbes.
(i) Tepee- and petee structures
The
central e l e v a t e d part of the G a v i s h Sabkha is c h a r a c t e r i z e d
d e s i c c a t i o n cracks w h i c h form polygons. FRENZEL,
1950) are common h e r e
of surface sediments
polygons
(sensu ADAM &
(Fig. 16A). These result from
l i z a t i o n p r e s s u r e in p r e c i p i t a t i n g sion
Tepee structures
(SHINN,
by
crystal-
salts, w h i c h causes a lateral expan1969;
WARREN,
1982).
Tepees
and
in the central part of the sabkha w e r e found w i t h o u t any sign
of m i c r o b i a l life.
On h i g h e r - l y i n g parts of the s e a w a r d - d i r e c t e d crobes
levels rise. For a p e r i o d of several days, les
become glued t o g e t h e r by m i c r o b i a l
During s u b s e q u e n t periods, tallization part.
slope,
however,
mi-
d e v e l o p mats e p i s o d i c a l l y after sheetfloods or w h e n g r o u n d w a t e r
pressure
According
terrigenous
sediment partic-
slime and p r e c i p i t a t i n g
the sediments dry out c o m p l e t e l y and
expands
them as on the surface of
to the m i c r o b i a l influence,
modified
w h i c h show s o m e w h a t c r i n k l e d and c o n v o l u t i o n a l patterns.
the tepees
salts. cryscentral result
In a n a l o g y to
54
Fig. 16. Physically and microbially modified sedimentary surfaces. A) Desiccation polygons and tepee structures, typical for sabkhas, are physical in origin. Elevated center of the Gavish Sabkha. B) Close-up of a tepee structure. C) Crystallization pressure and lateral expansion of surface sediments take also place where microbial slime binds surface sediments. The result is a convolutional pattern (modified tepees or "petees"). D) Sediments glued together by microbial slime form slump structures like a table cloth when moving downslope. Cracking takes place along the crests after drying. Finally "meteor-paper" results (see text). tepees
which originate under merely physical conditions,
microbially modified structures (2) Pseudo-ripples
"petees"
we call
the
(Fig. 16B),
and meteor-paper
On gently sloped,
periodically moistened surfaces,
slump structures
occur
which result from a restricted downslope movement of
glued
together by microbial
slime and precipitating
sediments,
salt (mainly
gyp-
55
sum).
The
structures
formed include small m i c r o f o l d s p e r p e n d i c u l a r to
the d i r e c t i o n of the m o v e m e n t
(Fig. 16C). After drying,
along the crests of the h o l l o w p s e u d o - r i p p l e s ,
c r a c k i n g starts
and finally
paper-like
chips d e v e l o p w h i c h can be b l o w n off by the wind.
The
p r o d u c t was first d e s c r i b e d in 1686 and was initially identified
as m e t e o r - p a p e r sky).
(organic,
p a p e r - l i k e meteorite;
i. e. fallen from the
People saved it so that about 150 years later,
C.
G. E H R E N B E R G
(1839) was able to study it again and found that it was a dried chip of microbially
glued sediments blown off by the wind
(see also
KRUMBEIN,
1986b).
i. 7. Faunal i n f l u e n c e on the b i o l a m i n a t e d d e p o s i t s
The Late P r e c a m b r i a n decline of s t r o m a t o l i t e s coincides in time with the early M e t a z o a n rise cially
of
chiopods
first by
invertebrates
1983;
step in the
increasing (for
d e c l i n e see MONTY,
PRATT,
1982).
"G~tterd~mmerung"
stromatolites
b i o t u r b a t i o n and grazing a c t i v i t y
c o n t r o v e r s a l d i s c u s s i o n of 1973; KNOLL,
the
for space.
P h a n e r o z o i c s t r o m a t o l i t e s and Recent p o t e n t i a l
Late
found in c o e x i s t e n c e w i t h i n the
usually occur in m a r g i n a l to moderate,
ronments. line,
overcome
the fact
known
diversity
or h y p e r t h e r m a l conditions.
by a marine
fauna.
of
f a u n a - p o p u l a t e d envischizoha-
These are d e s i c c a t i o n -
The Gavish Sabkha p r e s e n t s no
even more e f f e c t i v e l y r e s t r i c t e d b y
is are
M i c r o b i a l com-
and thus m a i n t a i n p h y s i o l o g i c a l b a r r i e r s w h i c h are h a r d
p a r t i c u l a r l y as the m i g r a t i o n of faunal elements is
Precambrian
Zones w h e r e they occur are often c h a r a c t e r i z e d by
hypersaline
endangered
was
benthic
stromatolites
s h a l l o w m a r i n e and intertidal b u r r o w i n g faunal habitats. munities
of
W h e t h e r there was a c o r r e l a t i o n or not,
ever
the
1985a, b, c) and the second by competi-
that
if
with
It has b e e n suggested of
tion
rarely
time
rugose and t a b u l a t e corals and articulate bra-
(KNOLL & AWRAMIK,
the
induced
1981). O r d o v i c i a n decline espe-
c a r b o n a t e shelf s t r o m a t o l i t e s coincides in
r a d i a t i o n of bryozoans,
that
(AWRAMIK 1971,
to
exception,
from the adjacent Gulf
b o t h the p h y s i o l o g i c a l
barrier
of h y p e r s a l i n i t y and by the g e o m o r p h i c b a r r i e r of bar-closing.
Nonetheless, Sabkha.
a v a r i e t y of faunal elements is p r e s e n t in the
Gavish
It is the p u r p o s e of this section to elaborate on their facies-
i n d i c a t i v e role.
56
i. 7. 1. Species c o m p o s i t i o n and d i s t r i b u t i o n
Sampling
provided
22
macrobenthic
and
i0
meiobenthic
species
(Table 4). About 80 % of all species are of terrestrial origin,
50 % (17
species) being insects.
Like
the m i c r o b i a l mats,
Sabkha
the b e n t h i c i n v e r t e b r a t e s of
Gavish
are restricted to the zones p e r i o d i c a l l y or c o n s t a n t l y supplied
by water.
While salinity is rarely a restrictive factor in the
ding of microorganisms, fauna.
According
to
strial
arthropods
(insects,
(Unit I);
gastropods,
nematodes,
ostracods,
prefer
margins
copepods,
increase
nohaline
air-exposed
turbellarians
and rotifers the
lagoon's
(3) aquatic insects w h i c h spread all over the aqua-
and w a t e r - s a t u r a t e d areas
salinity
the
(i) terre-
(2) aquatic insects, marine
seawater springs and small impondments at
(Unit II);
gradients
(Fig. 17):
spiders) w h i c h colonize
w e t l a n d s around the aquatic zones
which
sprea-
it plays a d e c i s i v e role in the d i s t r i b u t i o n of the topographic m o i s t u r e and salinity
three m a j o r species assemblages can be r e c o g n i z e d
tic
the
(Unit III).
Unit II is r e s t r i c t e d by
above 130 °/oo and thus has been defined
(GERDES et al.,
a
hyperste-
1985d) while Unit III is defined h y p e r e u r y h a -
line
b e c a u s e its members manage to p o p u l a t e the entire
dient
(Fig. 17). The remarkable evenness in spatial d i s t r i b u t i o n of the
fauna
salinity
b e t w e e n seasons documents well the stability of b i o t o p i c
tions due to the constant seawater influx
(compare Fig.
gra-
condi-
17A and B).
i. 7. 2. Trophic relations
Gut content analyses have shown that the m a j o r i t y of species
living
in the Gavish Sabkha belongs to the c a t e g o r y of p r i m a r y consumers. category
can
diatoms tous
be further split into
(i) types which p r e f e r a
and u n i c e l l u l a r cyanobacteria,
cyanobacteria
and
of
(2) types w h i c h favor filamen-
(3) types w h i c h feed on the
m a t e r i a l of m i c r o b i a l mats.
diet
This
decaying
The largest part of the p r i m a r y
organic consumers
feeds upon diatoms and u n i c e l l u l a r c y a n o b a c t e r i a w h i c h are available in abundance
in
the
Gavish Sabkha.
The h e a v i l y e n s h e a t h e d
bundles
of
Microcoleu8 are seemingly less nutritious. Only one species favors this diet
(Table 5).
the tiger beetles beetles larvae
S e c o n d a r y consumers are p s e u d o s c o r p i o n s (both larvae and imagines)
(Anacaena sp.).
Capturing prey,
and
spiders,
and larvae of h y d r o p h i l i d e
p s e u d o s c o r p i o n s and Anacaena
have been c o m m o n l y o b s e r v e d in d w e l l i n g burrows of
staphilinid
57
TABLE 4. Benthic invertebrates observed in the Gavish Sabkha MAJOR TAXA
I.INSECTA
SPECIES
Cicindelidae Georyssidae Ptiliidae Dytiscidae Hydrophilidae Hydraenidae
Blediu8 capra Bledius angustus Lophyridia aulica Georyssus sp. Actidium sp. Deronecte8 sp. Enochrus sp. Anacaena sp. Ochthebius c.f. au~atu8
L,P,A *) L,P,A L,P,A A A L,P,A L,P,A L,P,A L,P,A
exposed wet exposed wet exposed wet exposed wet exposed wet submersed submersed submersed, exp.wet submersed
Ephydra macellaria Hecamede grisescens Musca c~a88irost~is Orthellia cessation Atylotus ag.estis Bezzia sp.
L,P,A L,P,A
submersed, exp.wet submersed exposed wet exposed wet submersed submersed
DIPTERA
Ephydridae Muscidae Tabanidae Ceratopogonidae 3.INSECTA
HABITAT
COLEOPTERA
Staphilinidae
2.INSECTA
STAGES
L L L,A L,P,A
HETEROPTERA
not determined
exposed wet
4.ARACHNIDA
Pseudoscorpiones Clubionidae
Halominniza aegyptiaca not determined
J,A J,A
exposed wet exposed wet
exposed wet submersed submersed submersed submersed
5.CRUSTACEA
ISOPODA OSTRACODA
Halophiloscia sp. Cypnidei8 torosa
COPEPODA
Robertsonia salsa Nitocra sp.
J,A J,A J,A J,A J,A
Enchytraeidae, n . d . Capitellidae, n.d.
J J
exp.wet exp.wet
J,A
submersed,
exp.wet exp.wet exp.wet exp.wet
Paraeyprideinae
sp.
6.ANNELIDA
CLITELLATA POLYCHAETA 7.MOLLUSCA
GASTROPODA
Potamiidae
Pirenella conica
8.NEMATODES
Enoplus communi~ Oncholaimus fuscus Adoncholaimus oxyris
submersed, submersed, submersed,
9.ROTATORIA
Brachionu~ plicatili8
submersed
10.TURBELLARIA
Mac~ostomum
sp.
submersed
II.PROTOZOA
CILIATA
not determined
*)observed stages: L=Larvae,
P=Pupae, A=Adults,
submersed, J=Juvenile
exp.wet
58
LIIO~AL EASTERN ?AR~
"--L- ::
Fig. 17. D i s t r i b u t i o n and abundance of benthic invertebrates (selected species) along h o r i zontal gradients of w a t e r supply and salinity. A) summer B) winter situation. Unit I: W e t l a n d fauna, restricted to exposed _ flats (e. g. the sandlobes); Unit II: Aquatic fauna, salinity-restricted (hyperstenohaline), members of this group are restricted to mud flats and small impondments of the eastern (coastal bar directed) rim of the lagoon; Unit III: Aquatic fauna, n o n - r e s t r i c t e d by salini~-~ ty (hypereuryhaline). Members of i the latter group (only insects) manage to p o p u l a t e the entire salinity gradient. (Modified B after GERDES et al., 1985).
Sl,d;us
___E.%P~u_'_¢2m_m_u_"ig__
R0b.,~s0~o ,°L,0 Cyp,i~.,, L0,0.~
S,ZZ~0
~&~:=~-
beetles.
NSTRIHUTION
ANO ABUNDANCE 0~ 5£tECTE0
-
-
-
-
SPECIES
Dytiscid beetles which belong to the h y p e r s t e n o h a l i n e unit II
are p r e d a t o r s as well.
i. 7. 3. Systematic ichnology Dwelling,
crawling and feeding traces account for ichnological pat-
terns in the Gavish Sabkha.
59
A. D w e l l i n g traces:
i. Traces of the salt beetle Bledius
Description: face
and
A diagonally oriented
capra
(Staphilinidae)
"bottle neck" starts from the
converts into a v e r t i c a l l y o r i e n t e d b u r r o w
(Fig.
sur-
18A,
B).
L e n g t h of bottle neck 2 to 3 cm, of complete b u r r o w i0 to 12 cm. Diameter: b o t t l e neck about 5 mm, v e r t i c a l b u r r o w about 1 cm. At the conversion
there is a w i d e n i n g w h e r e m i c r o b i a l lumps are stored
The lower end of the v e r t i c a l b u r r o w merges where the
the beetle stores feces.
(Fig. 18C).
into one or more appendices
Female beetles
interrupt the walls
v e r t i c a l l y o r i e n t e d b u r r o w to create b r e e d i n g chambers
During
breeding
each chamber contains one egg
which
of
(Fig. 18B).
is
vertically
o r i e n t e d and stands on a sockle of s e d i m e n t grains.
Habitats:
G u l l y bottoms and sandlobes,
Trophi c relations:
Remarks: surface
The
a i r - e x p o s e d m i c r o b i a l mats.
Grazer.
beetles
rip away at the tough substrates of
mats and carry the food into the store chambers where they use
mandibles
(Fig. 18D)
Positioning
and heads to press the lumps against
wall.
S h e e t f l o o d sediments covering m u l t i l a y e r e d m i c r o b i a l
mats are well d o c u m e n t e d by b u r r o w fillings
(Fig. 18 E).
2. Traces of the salt b e e t l e Blediu8 angustu8
Description: oriented
the
the mat m a t e r i a l close to the surface enhances the chances
of p h o t o s y n t h e s i s .
Traces
consist
endobenthic
"chimneys"
burrows,
(Fig. 19A).
d i a m e t e r up to 5 mm.
(ii)
on
horizontally
wall).
(i)
vertically
oriented
feeding
(iii) v e r t i c a l l y o r i e n t e d epibenthic
of e n d o b e n t h i c burrows:
Length of epibenthic chimneys:
meter up to 1 cm (incl. precipitates
Length
(Staphilinidae)
of a c o m b i n e d system of
traces, p a r a l l e l to b e d d i n g planes
!9A).
air-exposed
up
to
up to 3 cm,
Chimneys are only present when
the surface and glues the sand grains together
5 cm, diagypsum (Fig.
L e n g t h of feeding traces about 5 cm, d i a m e t e r 5 to i0 mm, trans-
verse U-shaped.
Habitats:
Gully
e n c r u s t e d sand.
bottoms
and sandlobes c o n s i s t i n g of loose
or
salt-
60
TABLE
5.
Groups
Trophic relations of benthic i n v e r t e b r a t e s p r e s e n t G a v i s h Sabkha (after studies of gut contents)
Food type
Species Coccoid cyanobact, and diatoms
Terrestrial beetles
Aquatic beetles
Flies and mosquito larvae
X x
H. g r i s e s c e n s E. m a c e l l a r i a Muscidae B e z z i a sp. (larvae)
x x
Isopods
Halophiloscia sp.
Copepods
Detritus
R. s a l s a Nitoc~a
x x
x x x x
X x
X
Ostracods
C. t o r o s a Paracyprideinae
x x
Gastropods
P.
x
Nematodes
E. c o m m u n i 8 Adonchol a i m u s sp.
conica
Prey
x x
sp.
Turbellarians Rotatorians
Filamentous cyanobact.
x
A ~ a d a ~ n a sp. (adult) (larvae) D e r o n e c t e 8 sp. O. a u ~ a t u s Enochrus sp.
Clubionidae H. a e g y p t i a c a
the
(preference)
B. c a p r a B. a n g u e t u s G e o r y s s u 8 sp. A c t i d i u m sp. L. a u l i c a
Spiders, Pseudoscorpions
in
x
x x x
61
T r o p h i c relations:
Grazer.
Remarks:
structures
the
Feeding
endobenthic
evaporation sediment cated
microbial
run -2 to -5 mm b e l o w surface and mats of gully beds
and
sandlobes.
crusts replace tunnel roofings feeding traces
surface.
SCHWARZ
(1936) suggests
Where
furrow
that the use of
b u i l d i n g s econimizes on c o n s t r u c t i o n effort.
furrow
the
prefabri-
E v a p o r a t i o n crusts
also serve as l i g h t - c h a n n e l l i n g systems w h i c h stimulate p h o t o k i n e s i s of cyanobacteria Hence and
a
which
then colonize the furrows made
r e a c t i n g cyanobacteria,
peting
groundwater
table
beetles
three-dimensional
carcrusts
The b e e t l e s manage to survive w h e n epibenthic
cross
the
chimneys,
( r e t r a i t e - b u r r o w sensu BRO LARSEN,
support survival w h e n it falls.
access
beetles.
the latter create a dense b l u e g r e e n
rises by r e t r e a t i n g into the
w h i l e the e n d o b e n t h i c burrows
a
the
w h i c h can easily be grazed under the p r o t e c t i o n of salt
at the s e d i m e n t / a i r interface.
of
by
farming effect evolves from an interplay of b e h a v i n g
1936)
The w h o l e s y s t e m evokes the impression (Fig.
20B) w h i c h allows the
the h o r i z o n t a l l y o r i e n t e d c y a n o b a c t e r i a l
beetle
to
"garden" from both the
s u p e r s u r f i c i a l and subsurficial parts of the burrow.
The
p r e s e n c e of b o t h
piles
Blediu8 species can be recognized by the
of e x c a v a t i o n p e l l e t s they leave b e h i n d on the mat
surface r e s p e c t i v e l y
sediment
(Fig. 18F)o
3. Traces of tiger beetle larvae
Description:
or
typical
(Lophy~idia aulica~ Cicindelidae)
V e r t i c a l l y o r i e n t e d burrows,
length up to 30 cm, d i a m e t e r
up to 1.5 cm.
Habitats:
Gully embankments c o n s i s t i n g of loose,
s a n d - s i z e d sediments
w i t h a low m o i s t u r e level.
T r o p h i c relations:
Predator.
Remarks: Larvae use their h e a v y m a n d i b l e s to close entrances of burrows while
lying
in w a i t for prey.
burrow.
Excavation
burrows
(Fig.
capturing prey
20A).
pellets
M a n d i b l e s w e r e also used to clear
a c c u m u l a t e around the
Adults move freely
(mainly aquatic meiofauna).
entrances
on w a t e r - s a t u r a t e d
of
the the
sediments
62
Fig. 18. Traces of the salt beetle Bledius capra (Staphilinidae). A) The b u r r o w starts w i t h a d i a g o n a l l y o r i e n t e d "bottle neck" and merges into a vertical lower part (burrow of a male). A and B: Resin casts. B) Breeding chambers b r a n c h i n g sidewards off the main shaft characterize the b u r r o w of a female. Note also appendices filled w i t h feces. A and B: Photograph by H.-E. REINECK. C) Thin section showing storage of food (lumps of m i c r o b i a l mats) at the c o n v e r s i o n from the "bottle neck" to the v e r t i c a l shaft. Scale is 1 cm. D) S E M - p h o t o g r a p h y showing head and m o u t h parts of B. capra. Note h e a v y m a n d i b l e s w h i c h allow the beetle to dig and clear its b u r r o w and rip away at tough mat substrates for food. Scale is 250 pm. E) S h e e t f l o o d (grain-flow) sediments filling a b u r r o w of B. capra w h i c h was formed w i t h i n a m u l t i l a y e r e d m i c r o b i a l mat sequence. Thin section from sediment core. Scale is 5 mm. F) Various excavation pellets of salt beetles, i
W B. C r a w l i n g traces: G a s t r o p o d s
Description:
(Pirenell~ conica, Fig. 19C and 20C)
Bilobed crawling trails on the m u d d y w a t e r - s a t u r a t e d
sedi-
m e n t surface.
Habitats:
Seawater springs w i t h benthic m a c r o a l g a l scum
(Enteromorpha
sp., p r o b a b l y also Chaetomorpha sp.). and m e t a h a l i n e mud flats.
Trophic relations: Grazer. Remarks: M i c r o b i a l mats do not form where the snails are abundant.
C. Feeding traces: Water beetles
Description: away
at
(Fig. 19D and 20D)
Irregularly shaped holes on mat surfaces. The beetles rip
surface substrates of submerged m i c r o b i a l mats.
Diameter
of
by the small h y d r a e n i d beetle Ochthebius auratu8 are 1
to
holes
made
2 mm,
holes made by the larger species Enochrus sp.
are 5 to i0 mm in
diameter. Habitats:
Enochru8 sp.
(salinity restricted):
M a r g i n a l impondments with
soft m u c u l o u s and p a r t i a l l y floating m i c r o b i a l mats; Ochthebiu8 auratu8 (non-restricted by salinity): Whole m a t - c o v e r e d aquatic areas.
T r o p h i c relations: Grazers. Remarks: No indication that the o c c u r r e n c e of beetles is d e t r i m e n t a l to the growing mat systems.
63
64
Fig. 19. Further trace records of the Gavish Sabkha fauna. A) Epibenthic g y p s u m - e n c r u s t e d "chimneys" of the salt beetle
Blediu8
angustus. B) Feeding traces of B. angustu8 at the s e d i m e n t - g y p s u m crust interface and entrance to its e n d o b e n t h i c r e t r a i t e - b u r r o w (arrow). C) Bilobed crawling traces of g a s t r o p o d s (P. conica) on m u d d y waters a t u r a t e d flats at the lagoon's margin. D) Feeding traces in subaquous surface mats, made by w a t e r beetles (Enochru8 sp.).
65
[~
DWELLING
-~1 CRAWLING
TRACES
DOMINANT
DOMINANT
INCREASING
[ • - • C h ionmGypsum n e Crust ys ~Detrital
Olastics
FEEDING
TRACES
~
TRACES
DOMINANT
MOISTURE
~
Microbial M a t s
i/~
E-xcuvation Pellets ~ C a r b o n a t e Mud
Fig. 20. The zonation of trace categories (generalized presentation). Dwelling traces are in g r e a t e s t a b u n d a n c e at h i g h e r exposed flats, crawling traces at lower, w a t e r - s a t u r a t e d flats and feeding traces finally at submersed flats. A) B u r r o w and e x c a v a t i o n pellets of tiger b e e t l e larva. B) Burrow, e x c a v a t i o n p e l l e t s and "chimneys" of the salt b e e t l e Blediu8 angustus. C) Burrows and e x c a v a t i o n pellets of the salt beetle Bledius cap~a. D) C r a w l i n g traces of the g a s t r o p o d Pirenella conica. E) Feeding traces of w a t e r beetles on a mat surface.
i. 7. 4. E n v i r o n m e n t a l z o n a t i o n of trace cate~0ries
Dwelling around
b u r r o w s p r e d o m i n a t e on the elevated,
the saline b a s i n of the Gavish Sabkha.
observed
between
margins
t i g e r - b e e t l e larvae and the two salt beetle
B. angustu8 and B. capra, ling
air-exposed
A zonation gradient
due to increasing m o i s t u r e
species
(Fig. 20).
traces are c h a r a c t e r i s t i c of r e s t r i c t e d parts of the
is
Craw-
saline
mud
flats and feeding traces mainly p r e d o m i n a t e on the w a t e r - c o v e r e d microbial
mat surfaces
Blsdiu8
angustu8
w h i c h are,
however,
aquatic beetles.
Blediu8
cap~a
characteristic mats
(Fig. 20).
The g a r d e n i n g effect of the salt
also c o n t r i b u t e s to c h a r a c t e r i s t i c clearly d i s t i n c t i v e
feeding
beetle traces,
from the feeding traces of the
Periods of low-water levels encourage the salt beetle to m i g r a t e into d e e p e r - l y i n g areas and bottle-necked
to
burrows w i t h i n m u l t i l a m i n a t e d
form
their
microbial
(Fig. 20). These burrows clearly indicate periods of air exposure.
66
Fig. 21. Skeletal records of the Gavish Sabkha fauna. A) C o n c e n t r a t i o n of g a s t r o p o d shells w i t h i n sheetflood deposits. X-ray radiograph. Scale is 1 cm. B) G a s t r o p o d shell w i t h infillings of detrital clastics, embedded w i t h i n a m i c r o b i a l mat, indicating t r a n s p o r t by sheetfloods. Scale is 1 mm. C) D e t r i t a l clastics w i t h i n a g a s t r o p o d shell showing g e o p e t a l structures. After e m b e d d i n g w i t h i n a m i c r o b i a l mat, coating by m i c r o b e s took place. Scale is 1 mm. D) Outer and inner c o l o n i z a t i o n of a shell fragment by microbes. Note calcified filaments of c y a n o b a c t e r i a on the internal shell wall. Scale is 1 mm. E) N o d u l e - f o r m i n g P l e u r o c a p s a l e a n w i t h i n and outside a g a s t r o p o d shell. Scale is 2 mm. F) S o f t - b o d y remains of an ostracod, e n c l o s e d by its b i - v a l v e d carapax° Scale is 500 pm. G) The p o s t - m o r t e m c o l o n i z a t i o n of an empty o s t r a c o d carapax by microbes is indicated by the same filigrane network inside and outside the shell. Scale is 250 Nm. H) D i p t e r a n pupa ton in a m i c r o b i a l mat implying in-situ metamorphosis. Scale is 3 mm. (B to H: Thin sections from sediment cores.) i
W
I. 7. 5. Skeletal h a r d parts
Shells ostracod
of
g a s t r o p o d Pirenella eonica,
the
species
and
chitinous fragments of insects
almost all types of strata. most
are
above
two
common
in
zones
(Fig. 17).
The
wide
of their skeletal h a r d parts even w i t h i n places which lie
the salinity b o u n d a r i e s of the faunal p o p u l a t i o n s
lochthonous water
are
the
The animals live in the G a v i s h Sabkha, but
restricted to certain salinity
distribution
carapaxes of
transport
and sediments
which
indicate
is a c h i e v e d by the g r a v i t a t i v e
in the event of sheetfloods.
strationomic analyses are o u t l i n e d below.
The results of
The analyses
al-
flow
of bio-
focussed m a i n l y
on elaborating criteria of transport and in-situ embedding.
a) G a s t r o p o d shells: indicated by sits
showing
shells
(i) c o n c e n t r a t i o n s of shells in debris- and m u d - f l o w depocommonly a low degree
embedded
(Fig. 2 1 B ) ,
A l l o c h t h o n o u s t r a n s p o r t of g a s t r o p o d shells is
of
orientation
in m i c r o b i a l mats and filled w i t h
sometimes
also
showing g e o p e t a l
(Fig. 21A), detrital
structures
(2)
clastics
(Fig. 21C).
Shell fragments embedded in mats are c o m m o n l y c o l o n i z e d after transport by
microbes
from the mats
(Fig. 21C).
Fig.
shell fragment which are already calcified.
21D shows filaments
in
a
67
In-situ
embedding:
Sparse
numbers of juvenile snails
were
found
alive in the shallow water bodies where the nodule-forming Pleurocapsalean cyanobacteria mainly occur. interesting lean
colonies
oncoids reported 1983).
is
typical
(Fig. 21E).
(5 to 8 mm in diameter) from The
After death and in-situ embedding the
nodule formation in the coating of shells by Nuclei of
irregularly
shaped
consisting of gastropod shells are also
the lower Cretaceous of the adriatic
suggestion
Pleurocapsa-
of the author that the
region
(TISLJAR,
gastropods
represent
68
elements of a faunal community which lived under restricted corresponds well to a biotope b) Ostracods:
Fig.
21F
enclosed by its b i - v a l v e d
shows the soft body remains of an carapax.
The animal was p r o b a b l y
with the microbial mat environment the decaying organic matter. relation between bacterial which
acts
trast,
conditions
like the modern Gavish Sabkha. ostracod associated
and after death became embedded
Typical
for the embedding
decay and calcification
substrate
(see chapter
also with the soft body remains of the ostracod.
the ostracod carapax
soft
body.
Cyanobacteria
that
calcification
in Fig.
into
is the 1.6.4),
By
con-
21G does not contain parts of
the
which colonized the empty shell show
again
immediately takes place within the embedding
sedi-
ments. c) Insects: close
Embedded chitinous
fragments
to the microbial mat environments
ments of extremities
and pupae tons
of insects which live in or
include head
i. 7. 6. Grazin 9 stres s (experimental 19C
gives
conica
70 °/oo).
Possibly,
and grazing, the
The
treated
mat formation
coni~a
experiment
with
approach)
Laboratory
hypersaline
seawater
allowed to graze upon the mat section. from the joined appearance
Analyses
of filamentous
mat-forming microorganisms,
are
able
However,
(50
The typical
to survive passage
especially
enriched in unicellular
°/oo).
which Snails
structure,
was were
resulting
cyanobacteria
however,
that many of
cyanobacteria,
intestine
in mat-forming
and grazing proceeds,
colonies
shown
multilaminated
section
unicellular
through the snails'
could also p a r t i c i p a t e
as b i o t u r b a t i o n
of the gastropod
the
and unicellular
of fecal pellet contents have shown,
microorganisms
to
(Fig. 22).
the These
experiments have
was carried out with a mat
was destroyed as a result
snail (up
is hindered here due to b i o t u r b a t i o n
can completely destratify
slightly
the
zone of the Gavish Sabkha
mats can only develop and survive under
of higher salinity.
Pi~enella
mats.
in the metahaline
and m u l t i l a m i n a t e d
protection
that
for reproduction.
an impression of the high abundance of
Pi~enell~
frag-
(Fig. 21H). The pupae in p a r t i c u l a r
indicate that the insects chose the mat substrate
Fig.
capsules,
microbes
unharmed. processes.
in the vicinity
form only diffuse aggregates w h i c h are h i g h l y
types.
Consequently,
bioturbation
and grazing
69
result in a radical transformation, certain others
species,
often unicellular,
even of the c o m m u n i t y type, are favored
(mainly filamentous cyanobacteria)
to
survive,
since while
b e c o m e rarer.
Fig. 22 A). SEM m i c r o p h o t o g r a p h of the u n d i s t u r b e d surface of a m i c r o b i a l mat w h i c h was sampled to study the effect of grazing. Scale is 200 pm.
Fig. 22 B). Grazing activities conica of the snail Pirenella led to the surface d e s t r u c t i o n of the mat. Scale is 1 mm.
Fig. 22 C). As a result of continued grazing, the microbial mat section is d e s t r o y e d and its base consisting of siliciclastic sediments is visible. Scale: 200 pm.
Z0
Fig. 23. Small-scale changes in the s t r a t i f i c a t i o n of Gavish Sabkha sediments, drawn from thin sections from cores. All cores w e r e sampled at the lagoon's margins. M e c h a n i s m s r e s p o n s i b l e for the change are (I) o s c i l l a t i o n s in b i o t o p i c conditions during fair w e a t h e r periods such as p e r i o d i c exposure to w h i c h m i c r o b e s and fauna correspond (2) interruptions of the growing mat sequences by sheetfloods. For details see text.
i. 8. Modes of s t r a t i f i c a t i o n
A
well-defined
sequences
change in facies types c h a r a c t e r i z e s
of the sabkha deposits.
the
vertical
It reflects the influence of
lasting
f a i r - w e a t h e r conditions and short but c a t a s t r o p h i c
events.
A seasonal rhythmic
(varvite-stratification)
is,
long-
sheetflood however,
indicated
for the following reasons:
generally
slower a c c u m u l a t i o n prevail for most of the y e a r or
(i) F a i r - w e a t h e r conditions w i t h longer.
Sheet floods cause rapid s e d i m e n t a t i o n but only for a matter of sometimes (2)
not
after a number of several years of fair-weather
hours,
conditions.
A result of the t o p o g r a p h y is that the d e p r e s s i o n fills w i t h fresh
water
on the o c c a s i o n of stronger sheetfloods.
lishment
of fair-weather conditions,
Even
after
re-estab-
suspended loads of fine m a t e r i a l
settle until the water is e v a p o r a t e d and the conditions of seepage e v a p o r a t i v e pumping again become established, summer.
(3)
and
sometimes first in early
Climatic oscillations over several years result in
sheet
floods of varying energy levels.
The
dynamic
history
is reflected in the d i f f e r e n t
i r r e g u l a r a l t e r n a t i o n of strata types.
thickness
The trend of p o s t - e v e n t coloni-
zation of sheet flood sediments by m i c r o b i a l communities is visible, tation
for instance in core A (Fig. 23A). A further of
the
and
organic m a t e r i a l is visible in the
repeatedly
m o d e of fragmenupper
part.
Such
f r a g m e n t a t i o n is caused by shrinkage of the p r o l i f i c m i c r o b i a l mats and indicates subaerial exposure.
Burrowing of s u b a e r i a l l y exposed mats by
Blelius cap~a can also cause shrinkage cracks. of
The subaerial
exposure
the upper part of the core is also indicated by the burrows of salt
beetles w h i c h are unable to w i t h s t a n d longer periods of flooding.
Core
B
(Fig. 23)
was taken at the saline mud flat
central b a s i n of the lagoon.
from r e g u l a r l y laminated potential (present-day
bordering
The sequence shows the upward
the
transition
s t r o m a t o l i t e s with ooids and oncoids
facies type of the p e r m a n e n t l y w a t e r - c o v e r e d lagoon) to a
strata of the same type w h i c h is i n t e r s p e r s e d w i t h g y p s u m crystals,
and
71
t ~ , ~ _~
Pleurocapsaleau nodules and some
S e d i m e n t s from graln-flow
......
~ ......
o~
f i l a m e n t s in carbonate mud
_~.~:~..~ . ~~'~.~ .
Biolaminoid a r r a n g e m e n t of pleurocapsalean nodules
S e d i m e n t s from mud-flow
Salt beetle burrows. At right: Filled w i t h clastlcs
Gypsum coated
microorganisms
Synaereslscracks and some coarser clastlcs in mats
Faintly laminated sulfate
Skeletal hardparts: Top: Ostracod,
Stromatolitic carbonates with ooids and oncoids. Gypsum crystals at top
Bottom: Gastropod
G
o
oo
o,
io v,, o ~
Fo oo: oo:!
......
m °~1~;
°
°
•
r
•
•
o ,:;: L; i
° ° ° ° ° ° ° ° ° °
• -,
l'~. . . . . . . . o
oooo I
ooo
ooa
oo
o o a o o o o
o a o a
o
o o-1~,.~
o o
ao
oo
o a'-'D o Q D
N::i°~ o l P g t . , l,,e /q*o
E
t
I
i..,.l,rl.,Ol,l
. "o
I
~T
l I'M.[ E] lY: %',~ Y,I S B
shell
.NN
io~ a o o o~ o o. . . r. . . ~.
A
nodule by
C
s
o o.°
ol
72
finally to a thin bed of sheetflood deposits The
(mud with plant detritus).
nodular b i o l a m i n o i d facies of the p r e s e n t - d a y saline mud
flat
is
e s t a b l i s h e d on top of the sheetflood d e p o s i t i o n and, though also interrupted
by a thin clastic flood layer,
surface.
The
is r e - e s t a b l i s h e d again at
the
core shows that ecological conditions allowing the deve-
lopment of the regular s t r o m a t o l i t i c facies w i t h ooids and oncoids w e r e i n v a r i a b l y absent in the growing sequence.
The trend is from p e r m a n e n t
w a t e r cover to subaerial exposure.
Core
C was taken from the c e n t e r - o r i e n t e d saline mud flat which
characterized
at the surface by g y p s u m
precipitation.
The
is
following
h i s t o r y of d e p o s i t i o n can be read from the core:
Section developed
I:
A m u l t i l a m i n a t e d p o s t - e v e n t sequence of m i c r o b i a l
mats
on a thick sheetflood layer and was again b u r i e d by a sheet-
flood. Though this layer is thin it seems to have been c a t a s t r o p h i c for the
m i c r o b i a l community,
the Gavish Sabkha. on
top
p r o b a b l y due to m o v e m e n t of freshwater
During e v a p o r a t i o n a thick g y p s u m layer has
and allowed r e - c o l o n i z a t i o n by m i c r o b e s which
over formed
produced
faint
laminated structures w i t h i n the g y p s u m mush.
Section II: The same upward t r a n s i t i o n from sheetfloods to m i c r o b i a l c o l o n i z a t i o n to g y p s u m is repeated in this section.
Section III: Finally, minated
the evaporite sequence is followed by m u l t i l a -
m i c r o b i a l mats w h i c h d o c u m e n t a longer period free of
bance and with m o d e r a t e water availability. again
On the surface d i s t u r b a n c e s
occur which may be the result of climatic i r r e g u l a r i t i e s
ger e v a p o r a t i o n in summer,
distur-
(stron-
sheetfloods in winter).
i. 9. Summary and c o n c l u s i o n s
Grain sizes and m i n e r a l o g y of sediments, ding
crops,
redox
c o m m u n i t y structures,
p o t e n t i a l s and pH are h i g h l y
correlative
t e c t o n i c a l l y c h a r a c t e r i z e d terrane niveau of the Gavish Sabkha. sing
to
stanthe
Increa-
evenness in m o i s t u r e supply is realized by the inclination of the
system b e l o w mean sea level. effects c o n s e q u e n t l y follow
V a r i e d physical, (Table 6).
chemical and b i o l o g i c a l
73
Summary of interrelated facts which coincide with moisture supply in the Gavish Sabkha
TABLE 6.
increasing
INCREASING MOISTURE SUPPLY COINCIDES WITH CATEGORIES
STUDIED:
A. Seawater chemistry
increasing increasing decreasing
salinity Mg : Ca- ratios Ca : SO4-ratios
B. Microbial communities
increasing increasing increasing increasing
diversity productivity biological self-production of laminated deposits intensity in sulfate reduction
C. Physicochemistry
increasing
anoxic conditions in sediments
D. Lithology
increasing
biogenic carbonate contents (mg-calcite)
E. Stromatolitic structures
increasing
regularity in the lamination of stromatolites abundance of ooids and oncoids
increasing decreasing
F. Faunal influence
To
explain the increasing self-production of sediments by microbial
activity the
grazing and bioturbation intensities
(Table 6B) the convergence of (i) the specific
sediment-forming
undulating
character
of
response
to
microbes and (2) their migrational
environmental
factors has to be
considered.
An
organism
tends generelly to obtain the resource it needs. The individual cell or cell
chain
(sheaths, part
consists capsules,
of a large portion cysts and gels).
of the phenotype of the organism,
diately tion.
of
immobilisated
compounds
Since the immobilised matter is it has to be regenerated imme-
after the motile cell or cell chain has taken up a
new
posi-
This leads to a consequent increase of organic sediments as long
as appropriate environmental conditions are assured.
To
explain
deposits nently
the
(Table 6E), water-covered
increasing structural regularity
of
biolaminated
the evenness of seasonal shifts within the permaenvironments may be emphasized which
allow
organisms to correspond with changing gradients of environmental li,
such as light intensities,
oxidation potentials.
salinity,
moisture,
the
stimu-
pH and reduction-
74
Factors
changing
the light conditions
in the Gavish Sabkha
apart from day-night cycles - light channeling by water-cover, and particles suspended in the water. interface
and
oversedimentation
Salt crusts at the
(by eolian or
are
-
salinity
sediment/air
fluviatile
transport)
also change the light intensity. All these factors can fluctuate seasonally
or aperiodically.
populations
Qualitative change can stimulate subsurficial
to override other topmats.
Thus the variety
of
slightly
shifting environmental factors significantly determines the "depositional
dynamics" of stromatolitic growth-bedding
(sensu PETTIJOHN &
POT-
TER) in the Gavish Sabkha. The
lateral sequence of facies type 1 to 4 is actually the
expres-
sion of arid fair-weather conditions which last at least 9 to i0 months a year.
Interlayered bedding of terrigenous detrital clastics,
evapo-
rites and biogenic sediments provide clues about 1. Gavish
the
climatic
Sabkha:
setting
Long-lasting
of the depositional environment
of
the
stable arid periods without rainfall
are
suddenly interrupted by storm events, 2. sea, wards.
its geomorphic state:
depression,
no surface connection to the
gradually filled by mainland-generated
transport protruding
sea-
"Das s u b f o s s i l e jene n e g a t i v e
Riff am Strand
Bewegung
j~ngste V e r g a n g e n h e i t (JOHANNES
WALTHER,
2. THE SOLAR LAKE - I M P O R T A N C E
(GULF OF AQABA,
lehrt uns,
des Strandes hinein
in die
fortdauert."
1888)
OF SMALL T E C T O N I C
SINAI
bis
wie
EVENTS
PENINSULA)
2. i. I n t r o d u c t i o n
The 2a).
Solar
Lake
According
lies about
to a s t r a t i f i e d
strata
reach up to 65 °C. This
SZKY,
1901)
is c h a r a c t e r i z e d
cation p r e v a i l s August.
The mean
for the w a t e r
forms a basin Microbial
From
these
seepage
& COHEN,
time
Gavish
1974,
COHEN
reaching
The
et al.,
a deeper basin
and c o n s e q u e n t l y
to-depth
ratio c o m p a r e d
to the G a v i s h
of this
resulting
resulting
chapter
a sabkha-type
deposit.
in several
stratigraphic
records
stein is
(PZ3)
based
sequence
of this
1977a,
to the G a v i s h
Part),
ture about this
and
lake.
to
for n e a r l y FRIEDMAN, lagoon
below unusual pro-
2,000 years
1978).
Before to
the
subsidence
of
the
This
a w a t e r b o d y of lower
event
surface~
Sabkha.
Such
facies
a case study of stromatolitic change
(see for example
of core m a t e r i a l
can be i d e n t i f i e d Zech-
The chapter
from the Solar
(for m e t h o d s
of e x i s t i n g
changes
carbonates
in the Permian
III of this volume).
Sabkha m a t e r i a l
(2) on studies
Gulf
similar
from fault movement.
laminated
in Part
(I) on our own studies
sampled p a r a l l e l 1
mentioned
July and
of 5 m
cover the shelf
is to u n d e r t a k e
in r e g u l a r l y
overlying
between
from the a d j a c e n t
change was caused by a sudden
part of the lagoon
facies
Stratifi-
we can read that the s u n - e n e r g y
central
The p u r p o s e
in lower
(KALECSIN-
cycle:
a m a x i m u m depth
the area was a s h a l l o w b a c k - b a r r i e r
Sabkha.
(Fig.
loss by insolation.
produced
in
monomixis
inflow
mat sequences
sequences
energy"
annual
cycle of the Solar Lake has b e e n o p e r a t i n g
(KRUMBEIN that
and June,
Sabkha
temperature
of solar
by a w e l l - d e f i n e d
September
compensate
level.
thickness.
saline w a t e r body, "accumulator
takes place w h e n
Solar Lake sea
moted
between
Overturn
can no longer
200 km north of the G a v i s h
Lake,
see chapter
comprehensive
litera-
76
2. 2. L o c a l i t y and p r e v i o u s w o r k
Coastal
plains typical of the s o u t h e r n part of the Sinai
the Gulf of A q a b a are absent in the n o r t h e r n region. the
coast
Sinai rocky desert flanking the Gulf slope steeply towards
narrow
fringing reefs and frame some s e m i c i r c u l a r sandy b e a c h depressions. Solar Lake, in
w h i c h is about 140 m long and about 65 m wide,
one of these s e m i c i r c u l a r d e p r e s s i o n s
of
M o u n t a i n sides of
(Fig. 24).
The
is located
It is fed by sea-
w a t e r seeping through a c o m p l e t e l y closed gravel bar w h i c h is 60 m w i d e and 3 m above mean sea level.
The s e m i c i r c u l a r terrane, p r o t e c t e d from
wind
by
the m o u n t a i n ridges and from flood recharge and surf
bar,
recalls an a m p h i t h e a t r e on w h o s e
sun,
water
Moreover,
"stage"
by
(the sheltered
and organisms p e r f o r m their s e d i m e n t - a c c u m u l a t i n g the
ritual.
effects of flashfloods w h i c h play an important role
the u n p r o t e c t e d Gavish Sabkha are made milder,
the
center),
in
since the Solar Lake is
separated by its southern m o u n t a i n flank from a larger s h e e t f l o o d b a s i n w h e r e the most part of the s e d i m e n t - l a d e n narrow
freshwater is stored.
Only a
o v e r f l o w p a s s a g e b e t w e e n the coastal bar and the southern moun-
tain flank leads into the Solar Lake.
Fig. 24. The Solar Lake at the shore of the Gulf of Aqaba, Sinai Peninsula. The lake forms a 5-m-deep b a s i n w i t h i n a semicircular depression which is flanked by steep mountains sides. Partial e x p o s u r e of the s h a l l o w shelf of the lake indicating summer situation. Lower part: Coastline with fringing reef. (After GERDES et al., 1985.)
This
lake
may
be among the best i n v e s t i g a t e d in
l i m n o l o g y was studied by POR (1968, (1970) and COHEN et al. nic
carbonates
1978). biogenic
1969),
(1977a). F R I E D M A N et al.
w i t h i n the b i o l a m i n a t e d deposits
K R U M B E I N & COHEN
the
NEUMANN
world.
(1968),
Its
ECKSTEIN
(1973) surveyed bioge(see
(1974) and K R U M B E I N et al.
also
FRIEDMAN,
(1977) studied the
and abiogenic sediment a c c u m u l a t i o n and d e p o s i t i o n a l history.
77
COHEN
et al.
described primary dealt and
the
(1977b,
c),
K R U M B E I N & COHEN
m i c r o b i a l communities
production,
GERDES et al.
(1986).
by BOON GIANI
et
(1985) (1984), al.
studied the fauna. A I Z E N S H T A T et al.
COHEN
A H A R O N et al.
and g y p s u m p r e c i p i t a t i o n
data,
EHRLICH
(1978)
DIMENTMAN & SPIRA
(1982)
B i o g e o c h e m i c a l data were (1984) and C O H E N
(1984) studied the m e t h a n o g e n e s i s
b i o l a m i n a t e d deposits.
(1984)
physiological
mat formation and lithification.
w i t h the d i a t o m flora and POR (1975),
provided
(1977) and
in terms of
et
al.
within
the
(1977) c a l c u l a t e d isotope ratios
from e v a p o r a t i o n experiments.
2. 3. B a t h y m e t r i c zones and l i m n o l o g i c cycle
Three bottom.
bathymetric
surrounded
by
outcropping. of
zones can be
distinguished:
The shelf is a gently inclined, a
Shelf,
slope
and
20 to 25 m wide area w h i c h is with
beach-rock
The slope starts at about 1.50 m w a t e r depth.
sandy shore bare of v e g e t a t i o n and
It consists
an i n i t i a l l y gentle p a r t w h i c h merges in about 2.50 m
water
depth
into a steeper part running down toward the b o t t o m of the basin.
0m
~
0,51,0 1,5
-
2~53,0 3,5 4,0
Fig. 25. V e r t i c a l distribution of temperature, 02 and salinity w i t h i n the lake during w i n t e r s t r a t i f i c a tion (modified after Gerdes et al., 1982).
4,5~ 5~
From
September until May the lake's w a t e r b o d y is s t r a t i f i e d
(Fig.
25). Even snorkling at that time is h a r d since the m e t a l i m n i o n begins a few dm b e l o w the w a t e r surface. -2.50 m
below
w a t e r table,
In b e t w e e n a depth ranging from -i m to
t e m p e r a t u r e increases from 25
to
50 °C,
s a l i n i t y from 70 to 150 °/oo and oxygen d i m i n i s h e s to less than
1 ppm.
In the upper hypolimnion, t e m p e r a t u r e can reach 65 °C and salinity 180 O/oo. The h y p o l i m n i o n is c o m p l e t e l y anaerobic. R e l a t i v e to the
78
meta- and
hypolimnion,
the e p i l i m n i o n is cool at 20 to 25 °C.
It
is
rich in oxygen and the salt c o n c e n t r a t i o n lies b e t w e e n 70 and 80 °/oo.
Since
the
throughout seawater
w a t e r b o d y is four to five m deep and seepage
the
year,
does not lead to drying out in summer,
evaporation unstable.
and w a t e r loss,
but
salinity
In falling b e l o w the s t a b i l i t y point,
of
al.,
1977a).
the entire w a t e r b o d y lies of
with
rate
between
becomes
a sudden m i x i n g up of At this point, 160 - 180 °/oo,
27 °C prevail t h r o u g h o u t the w a t e r column
The period of h o l o m i x i s
of
increasing
the m e s o t h e r m y of the w a t e r b o d y
the p r e v i o u s l y stratified w a t e r bodies takes place.
temperatures
continues
even e v a p o r a t i o n exceeding the inflow
the and
(COHEN
et
lasts from 4 to 13 weeks, m a i n l y
b e t w e e n July and September.
2. 4. S u b - e n v i r o n m e n t s and facies types
2. 4. i. The shelf
a) Biotopic conditions On the r e l a t i v e l y flat shelf the effects of the lake's w a t e r level are considerable. a
change of 1.4 m over the year.
shelf
is exposed
(Fig. 24),
shelf is i0 to 15 cm.
seasonal fluctuations in
COHEN et al.
In late summer,
(1977a) m e a s u r e d of
the
and w a t e r depth in the lower part of
about 50 %
the
During this low-water period springs of seawater
are above the original water level.
With the r e p l e n i s h m e n t of w a t e r in
early fall, seawater springs and finally the whole shelf becomes watercovered and water depth on the lower shelf again reaches 1.50 m.
Light
intensity
oscillating ranges
and
w a t e r table.
salinity values change
b e t w e e n 50 and 80 °/oo,
summer m i x i n g period. anaerobic
with
W i t h i n the s t r a t i f i c a t i o n
the period,
seasonally salinity
w h i l e it is about 180 °/oo w i t h i n
the
Since the shelf is not supplied w i t h the hot and
b r i n e of the deeper basin,
w a t e r temperatures do not
reach
h i g h e r values than 30 °C.
b) Main m a t - b u i l d i n g organisms
The shelf mats are made up p r e d o m i n a n t l y of cyanobacteria. tous species
(oscillato~ia limnetica/Phormidium hendersoni,
Filamen-
O. 8alina,
79
Lyngbya sp.,
Mie~ocoleus chthonoplastes) and unicellular forms (mainly and Synechococcus) are abundant. Unicellu-
of the genera Synechocysti8 lar
cyanobacteria
far
less abundant,
gates
of the Pleurocapsalean
characteristic
(EHRLICH,
of the Gavish Sabkha.
the genera Nitzschia,
1978),
type
Diatoms
diatoms,
however,
With summer,
are well
reCorded
in living surface mats. The
g e n e r a l l y are not preserved
in older sections of the
increasing
light together with less or no water
unicellular
cyanobacteria
reduced
c) Mat construction
in
These organisms
and
form protective colour.
at h i g h e r w a t e r
levels and thus slightly
filamentous
(Microcoleu8 8alina) override the coc-
Osoillatoria limnetica,
c o i d / d i a t o m community.
covering
Synechocystis)
which give the surface a b r o w n - y e l l o w
light conditions,
ohthonoplastes,
(Synechococcus,
in the top layers.
(carotinoides)
In fall, winter and spring, more
are
mats.
diatoms predominate pigments
fission)
Amphora and Navicula predomina-
ting both in species and specimen abundance
microbial
(multiple
hence there is no formation of nodular cell aggre-
O.
cyanobacteria
The surface appears b l u e - g r e e n at this time. and microfacies
As in the Gavish Sabkha,
the b i o l a m i n a t e d
sediments of the shelf of
the Solar Lake consist of sets of dark L h- and light Lv-laminae , the L v usually
4 to 8 times thicker than L h (Fig. 26A).
are characterized
by a high content of extracellular
ty of irregularities bubbles). of
tion of eye-shaped
of Lh-laminae
lenses
microscopy
is common,
(Fig. 26B, D).
the light Lv-laminae.
giving rise to the forma-
voids,
probably derived
electron
from gas
(Fig. 26E).
bub-
Carbonate
takes place mainly in the light layers and the eye-shaped
together
within the
eye-shaped
lenses
particular where oolites and oncolites
devoid of a biostromate
They lie very
(Fig. 26C, D),
w i t h i n the widely spaced Lv-lamina e are more dispersed In
material
Thin section studies and scanning
show that miniscule
and
cyanobae-
The lenses enclose
lenses where ooids and oncoids occur in great abundance. close
voids
of filamentous
are initially colonized by m i c r o o r g a n i s m s
precipitation
slime and a varie-
intraclasts,
form usually condensed horizons built up
oriented ensheathed bundles
teria. The p a r t i t i o n
bles,
(decaying cell clusters,
The dark Lh-laminae
horizontally
from
The light Lv-laminae
others
(Fig. 26F).
in the fossil record
lamination which could imply in-situ
are
formation
80
of
the
indicate similar
grains, the
their close a r r a n g e m e n t w i t h i n e y e - s h a p e d lenses
formational site w h i c h had
to the Solar Lake m i c r o b i a l mats
ooids and oncoids; Fig. 43A, B and C).
formerly
a
may
microtopography
(see for example the
Minette
81
Fig. 26. Microfacies characteristics of the shelf deposits. A) Lamination including dark L h- and light Lv-laminae. Scale is 1 mm. B) Ensheathed filament bundles of the Lh-lamina forming an eye-shaped lense. The lense contains decaying organic matter and p o l y s a c c h a r i d e slimes and initial nucleation of coated grains (see also C and D). Scale is 25 pm. C) "Coated grains": Bedding plane concordant view showing the coating of ooids and oncoids by filamentous microorganisms. Scale is 50 pm. D) Vertical section showing layer with ooids and oncoids. Note arrangement of the grains within the eye-shaped lense. Similar arrangements of coated grains in rocks (compare Fig. 43C) may imply their formation in a similar microbial mat environment. Scale is 250 pm. E) A h o l l o w sphere (bubble?) within a Lv-lamina, coated by diatoms and coccoid unicells. The wall of the sphere is stabilized by polysaccharide slime (internal view). Scale: 25 pm. F) Dispersed arrangement of miniscule spheres within the decaying organic matter and mucus of a Lv-lamina. Scale: i0 pm.
d) S t r a t i f i c a t i o n
Particularly a
vertical
contains nae,
ooids
distance ranging and oncoids
cycle controls
and light laminae
succession
followed
or
tions
from 1.0 to 1.20 m.
carbonate
already described
within
increasing
Synaeresis
numbers
cracks,
the crenulated laminated
and interrupt
the varvite-like
time
time to unconformities
sequence
Sabkha.
The
alternating
the regularly
dark
laminated
sections,
grain-sized
sections
are
sequences.
of small bags,
extraclasts
summary,
form over
whole
for the Gavish
formation of
underlaid by thin strata of mud- or
which also penetrate to
The
is interrupted by more crenulated
Lv-laminae
show
deposits
facies type with L h- and Lv-lami-
a varvite-like
than within the regularly
lenses.
the b i o l a m i n a t e d
(Fig. 27). From time to time,
vertical
sediments.
extension of the shelf mats
on the lower shelf,
the stromatolitic
seasonal
thicker
and vertical
often clastic
commonly
Vertical
pockets
and
sec-
eye-shaped
and gypsum crystals
are common
the thin and fragile Lh-laminae.
formation of the shelf deposits and turns back again
to
changes the
In from
regular
microstratification.
These occurring
patterns
nal change. summers,
indicate
climate deviations
from the norm,
probably
secularly and taking place after a sequence of regular seasoThe climate deviations
are accompanied by h o t t e r and drier
consequently by higher evaporation
and light conditions, sheetfloods.
and higher rainfall
rates, in
increasing
winter,
which
salinity causes
82
Fig. 27. Deposits of the Solar Lake shelf. X-ray radiographs of sections of an o r i g i n a l l y 80 cm long core. F r o m top (section I) to b o t t o m (section IV) the sequence shows the s t r o m a t o l i t i c c a r b o n a t e facies w i t h typical l i g h t - d a r k interlaminations, ooids and oncoids. Individual constituents p r o v i d i n g clues on the e n v i r o n m e n t are listed on the next page. X - r a y radiographs by H.-E. REINECK. Scale is 2 cm for all core sections.
83
IV
g
Legend to Fig. 27 continued: Core section I: a) Intraclasts of varying size and shape, resulting from the liberation of mat fragments from the lake's deeper slope, drifting in the w a t e r and d e p o s i t i n g at the w a t e r rim on top of the s h a l l o w shelf mats. b) S h e e t f l o o d - d e r i v e d mud layers 5 to i0 m m thick. c) Burrows of the salt beetle Bledius capra in 13 to 16 cm depth indicate a former period of subaerial exposure. Section II: d) Deviations from the n o r m a l l y s t r a t i f o r m to a more c r e n u l a t e d p a t t e r n of the dark L laminae, a c c o m p a n i e d by the a g g r e g a t i o n ~f ooids and oncoids w i t h i n the "valleys". The c r e n u l a t i o n comes from m i c r o p i n n a c l e s which form at mat surfaces as a r e a c t i o n of the m a t - c o m m u n i t y to increasing light and salinity (see also Fig. 41F). Section III: e) R e g u l a r l y a l t e r n a t i n g dark and light laminae w h e r e ooids and oncoids show a chainlike a r r a n g e m e n t due to the low e x t e n s i o n of the light-colored Lv-laminae. These sequences indicate growth under a slightly higher w a t e r table and a lower impact of the seasonal change in light intensity. f) W i d e l y spaced l i g h t - c o l o r e d L v - l a m i n a e with clustered and d i s p e r s e d arrangements of ooids and oncoids. These as well as the m i c r o p i n n a c l e s indicate climate deviations from the average, a c c o m p a n i e d by increasing salinity and light conditions. Section IV: g) (sediment depth averages 75 cm at this point). C o m p o u n d ooids and oncoids m e r g i n g into c h a i n - l i k e arrangements, due to increasing c o m p a c t i o n and d e h y d r a t i o n of the l i g h t - c o l o u r e d h y d r o p l a s t i c Lv-laminae.
Light and s a l i n i t y o s c i l l a t i o n s obviously
in seasonal and also secular rhythms
are i m p o r t a n t control mechanisms.
Much more
a c c u m u l a t e under h i g h e r s a l i n i t y and irradiation, ved in the G a v i s h Sabkha and h e r e repeated. directly
polysaccharids
a fact already obser-
A n o t h e r aspect that can be
e n t a n g l e d w i t h the climatic u n c o n f o r m i t i e s
is the
morphology
84
of
the
mat surface itself.
The mats of the lower
r e s t r a t i f y themselves to m i c r o p i n n a c l e nity
and light.
Solar
Lake
formation under increasing sali-
The p i n n a c l e s are conical buildups w h i c h reach
two to three m i l l i m e t e r s upwards from the s t r a t i f o r m mat base.
M~c~o~oZ~us-dominated the pinnacles.
pinnacles.
Ooids
(Fig. 26, see also Fig.
about
Even the
in this case follow the f o r m a t i o n
In v e r t i c a l sections,
c r e n u l a t e d structure, the
Lh-lamina
shelf
of
the p i n n a c l e formation favors the
the formation of bags,
pockets and eyes b e t w e e n
and oncoids here represent
veritable
clusters
27, m a r k e d section d of core section II).
2. 4. 2. The slope and b o t t o m
a) Biotopic conditions
Effects
of
w a t e r level change are no longer
important
where
w a t e r deepens at the slope. Parts of the slope are, however, epilimnion temperature H2S.
Only
and
thus
are g r e a t l y a f f e c t e d by the steady
and salinity,
the
b e y o n d the
increase
of
the d e c r e a s e of oxygen and the increase
of
after the turnover in late summer are
these
environmental
factors m o d e r a t e d for a short period.
Fig. 28. Thin section of the crust at the Solar Lake's b o t t o m showing layered accretion of elongated g y p s u m crystals i n t e r l a m i n a t e d w i t h faint microbial mats (dark laminae). Scale is 2 cm.
85
b) M a t - b u i l d i n g o r g a n i s m s and mat c o n s t r u c t i o n
shelf.
The
mats tend to form soft flocculous fabrics w h i c h p a r t i a l l y drift in
The
initial
slope c o m m u n i t y is similar to that of the
the
w a t e r and are subject to rapid decay. W i t h increasing depth towards the bottom,
sulfur-dependent,
cyanobacteria
which
other a n o x y - p h o t o b a c t e r i a and a n a e r o b i c bac-
08cillatoria
teria increase in number.
remains common,
limnetica is the only species of even at the b o t t o m w h e r e
ratures are h i g h and c o m p l e t e l y anoxic c o n d i t i o n s mats
undergoing
bottom these
of
prevail.
rapid a n a e r o b i c d e c a y cover the lower slope
the lake
(KRUMBEIN et al.,
1977).
and
the
The internal fabric
sediments shows large g y p s u m crystals and
strata of m i c r o b i a l mats
tempe-
Flocculous
faint
of
interlaminated
(Fig. 28).
2. 5. L i t h o l o g i c and i c h n o l o g i c framework
2. 5. i. Clastic compounds
That bances
the p r e s e n t - d a y Solar Lake is nearly devoid of strong b y the wind,
from its d e p o s i t i o n a l record sediments Sabkha. between
enter Mud
(Fig.
i n t e r c a l a t e d in b i o g e n i c deposits
0.5 and 2 mm thick.
read
27). G r a i n f l o w - and m u d f l o w - d e r i v e d
the lake at less i m p o r t a n t rates than in
layers
distur-
the sea and r a i n - d e r i v e d flashfloods can be
the
Gavish
usually
range
Cores from a S - N t r a n s e c t c r o s s i n g
shelf
show that mud layers d i m i n i s h in t h i c k n e s s w i t h increasing
tance
from
the o v e r f l o w passage w h i c h is b e t w e e n the coastal bar
the s o u t h e r n m o u n t a i n flank
(KRUMBEIN & COHEN,
the disand
1974).
2. 5. 2. Evaporites
The layers, tation (1977):
almost
e n t i r e l y b i o g e n i c shelf sediments are
due to b a c t e r i a l sulfate reduction. is
reported
by K R U M B E I N & COHEN
of
gypsum
(1974) and
KRUMBEIN
et
al.
(i) A g y p s u m crust forms b e l o w a surface mat on the slope at a
d e p t h of about 2.5 m.
At this level,
seawater under a r t e s i a n p r e s s u r e
enters the lake and supplies a d d i t i o n a l oxygen. slope
free
Subaqueous gypsum p r e c i p i -
are
(2) Deeper parts of the
covered by a hard crust of g y p s u m and
carbonate,
precipi-
86
tating
from the s u p e r s a t u r a t e d brines
as
to 50 °C and minimal sulfate r e d u c t i o n at
40
concentrations
(Fig. 28).
T e m p e r a t u r e s as h i g h low
organic
matter
favor h i g h g y p s u m a c c u m u l a t i o n rates.
2. 5. 3. !chnologic p a t t e r n s
A
c o m p a r a t i v e study of the fauna of the Solar Lake and
Sabkha that
was carried out by GERDES et al. species composition,
(1985d).
the
Gavish
The study has shown
t o p o g r a p h i c m o i s t u r e - and
salinity-related
zonation in b o t h environments are similar, p a r t i c u l a r l y the p r e d o m i n a n ce of c o l e o p t e r a are
(POR,
1975).
Ichnological p a t t e r n s in the Solar Lake
m a i n l y due to the staphilinid b e e t l e Blediu8 c ~ p ~
w e t l a n d fauna). beetles
live
pockets
of
W h e n the lake's shelf is w a t e r - c o v e r e d on
(member of
the
(winter),
the
the shoreline and b u r r o w in sand-filled
the beachrock.
W h e n the w a t e r l i n e of the lake
retreat in spring or early summer,
cracks
bottle-neck
appearing
shaped
in b u r i e d strata
to
the beetles migrate along the humi-
d i t y g r a d i e n t into the g r a d u a l l y a i r - e x p o s e d shelf area and form dant
and
starts
burrows w i t h i n the
mats
(Fig. 29).
(Fig. 27) indicate that the
deposits
abunTraces have
b e e n subject to exposure.
Fig. 29. Horizontal section of a i r - e x p o s e d shelf mats of the Solar Lake showing a b u n d a n t burrows of the salt beetle Bled~u8 cap~a. Summer situation, w h e r e retreating w a t e r line attracts the beetles to migrate from the sandy shore into the m i c r o b i a l m a t - c o v e r e d shelf area. Scale is 2 cm.
87
Hydrophilid line
beetles b e l o n g i n g to b o t h stenohaline and
aquatic fauna occur in numbers in the Solar Lake and graze on the
mat
surfaces,
Gavish
leaving
Sabkha
cods,
(see Fig.
copepods,
important
feeding 19D).
nematodes,
as in the G a v i s h Sabkha; is
hypereuryha-
traces as a l r e a d y indicated
for
Meio- and m i c r o f a u n a l elements
t u r b e l l a r i a n s and protozoans)
however,
the
(ostra-
are abundant,
the g a s t r o p o d Pirenella
conica w h i c h
in the Gavish Sabkha in terms of grazing and
hard
part
supply is c o m p l e t e l y absent in the Solar Lake.
2. 6. S u m m a r y and c o n c l u s i o n s
2. 6. i. O c c u r r e n c e of facies types c o m p a r e d to the Gavish Sabkha
Grain-flow supported siliciclastic biolaminites nodular the
to b i o l a m i n o i d carbonates
G a v i s h Sabkha,
whereas
(facies type I)
(facies type 2),
both o c c u r r i n g
are absent in the p r e s e n t - d a y Solar Lake
s t r o m a t o l i t i c carbonates w i t h ooids and oncoids
are well developed.
and in
deposits
(facies type 3)
B i o l a m i n a t e d gypsum, w h i c h c h a r a c t e r i z e s the amphi-
bious
rims of the G a v i s h Sabkha lagoon
Solar
Lake
subaquatically
(facies type 4),
at the b o t t o m of the b a s i n
forms in and
the
comprises
another c o m m u n i t y type comparable to the amphibious areas of the Gavish Sabkha.
An
informal o v e r v i e w of the d i f f e r e n c e s m e n t i o n e d here is given
Table 7.
(1)
Reasons
The
Solar Lake a p p a r e n t l y does
not
provide
geomorphological
conditions
suitable to d e v e l o p facies type i.
heaved
o n - s h o r e d i r e c t e d wave energy and does not merge
by
hinterland Sabkha. the
The coastal bar is
is the case with the c i r c u l a r d e p r e s s i o n of the
of the bar and d o w n - s l o p e to form sandlobes and
Thus the h o r i z o n t a l l y
up-
with
the
Gavish
Thus s h e e t f l o o d - d e r i v e d grain flows are not able to run
plateau
mats.
as
in
for these d i f f e r e n c e s are d i s c u s s e d below:
along
to
bury
flat lh-mats s a n d w i c h e d b e t w e e n g r a i n - s i z e d
s i l i c l a s t i c sediments do not occur w i t h i n the Solar Lake area.
(2)
S u b - e n v i r o n m e n t s w h i c h favor the nodular to laminoid
facies
are
also
Gavish
Sabkha,
a p p a r e n t l y not evident in the Solar
these
are the g e n t l y
inclined,
schizohaline mudflats a d j a c e n t to the lagoon.
Lake.
carbonate In
the
water-saturated
and
The same facies type
is
88
TABLE 7. Existence Solar Lake
of
facies types
of the
Gavish
Sabkha
TYPE
i:
Lh-type blo-~-lam---inites sandwiched between siliciclastic sand-sized sediments FACIES
TYPE
TYPE
non-existent
indicating hypersaline shallow water conditions (lagoon)
indicating hypersaline shallow water conditions (shelf)
indicating hypersaline subaerial/ amphibious conditions (rims of lagoon)
indicating hypersaline/ hyperthermal subaquatic conditions (bottom of the lake)
T Y P E 4:
Biolaminated gypsum
found
indicating schizohaline conditions of water-saturated sediments (bar-oriented mudflats)
3:
Stromatolitic carbonates with ooids and oncoids
FACIES
non-existent
indicating grain-flow deposits sheetflood derived (coastal bar slope)
2:
Nodular to biolaminoid carbonates
FACIES
the
SOLAR LAKE
GAVISH SABKHA
FACIES
in
in
mudflats surrounding the Ras Muhamed pool which lies on
southernmost tip of the Sinai Peninsula
(SNEH & FRIEDMAN,
the
1985).
This
environment is very similar to the Gavish Sabkha. (3)
Though vertically more extensive,
the shelf mats of the
Solar
Lake complete the picture already painted of the Gavish Sabkha shallowwater mats. This facies type is also repeated in the permanently watercovered 1985).
shallow depression of the Ras Muhamed pool This environment,
elevation
(SNEH
as well as the Solar Lake,
&
FRIEDMAN,
lacks the central
produced by active evaporative pumping characteristic of the
Gavish Sabkha.
The development of regularly interlaminated carbonates,
ooids and oncoids in areas under the following environmental conditions is
common to all three
environments:
hypersalinity,
shallowness
of
89
water,
lowest
depth,
level energy,
and evenly o s c i l l a t i n g p a t t e r n s of w a t e r
s a l i n i t y and light t h r o u g h o u t the year.
The
d e v e l o p m e n t of s t r o m a t o l i t i c
without
any
layering in all these e n v i r o n m e n t s
o v e r s e d i m e n t a t i o n has led us to avoid the
stromatolites
as being p r o d u c t s of
sediment-fixing,
definition
sediment-binding
and/or s e d i m e n t - p r e c i p i t a t i n g activities of m i c r o o r g a n i s m s al.,
1976;
chemical
BUICK et al.,
1981),
of
(AWRAMIK
et
w h i c h w o u l d imply that p h y s i c a l and
s e d i m e n t a t i o n p r o c e s s e s are n e c c e s s a r i l y needed for stromato-
litic buildups.
2. 6. 2. Time intervals r e c o r d e d in s t r o m a t o l i t e s
Deducing
annual,
characteristic tates
seasonal
or even diurnal
millimetre-scale
periodicity
from
l a m i n a t i o n of s t r o m a t o l i t e s
the
neccessi-
some p r e c a u t i o n s even more if laminae w h i c h at first glance look
massive
are i n t e r n a l l y finely laminated
(PARK,
1976).
The
biogenic
sediments of the Solar Lake may serve as an example.
Core
material
years B.P.
at 1.20 m sediment d e p t h y i e l d e d a 14C age
(KRUMBEIN et al.,
of
2400
1977). The overall g r o w t h c a l c u l a t e d from
this
data is 0.5 m m per year including a p a i r of light and dark
nae.
These
lami-
d e v e l o p w i t h o u t the aid of s e d i m e n t a t i o n as the result
of
two d i f f e r e n t kinds of m i c r o o r g a n i s m s o v e r r i d i n g themselves in order to find
the
They
may thus r e p r e s e n t seasonal rhythmites.
biogenic
m o s t a p p r o p r i t a t e site under seasonal
lamination
changing
However,
conditions.
even the
of the Solar Lake shows some sort of
ties. The m a i n factor r e s p o n s i b l e is the climate oscillation. years
pure
irregulariSeries of
w i t h v e r y r e g u l a r l y u n d u l a t i n g e n v i r o n m e n t a l conditions are
ruptly
or
g r a d u a l l y followed by those
with
weather
ab-
unconformities,
i n c l u d i n g b r e a k s in b i o g e n i c sediment a c c r e t i o n on the one hand, h i g h e r precipitation other
hand.
rates of e v a p o r i t e s and s h e e t f l o o d s e d i m e n t a t i o n on There
remains thus a degree of u n c e r t a i n t y in using
o b v i o u s l y rhythmic lamination as a time scale. Furthermore,
a reduction
of the wet organic m a t t e r by p r o c e s s e s of b a c t e r i a l degradation, formation
to
carbonate minerals,
c o m p a c t i o n and d e h y d r a t i o n
order of about 70 % may be r e a l i s t i c to a s s u m e al., for
the the
transin
the
(PARK, 1976; K R U M B E I N et
1977). The annual a c c r e t i o n rate w o u l d then c o m p r i s e only 0.15 m m one couplet of seasonal rhythmites.
This w o u l d result in a m i c r o -
i n t e r l a y e r e d b e d d i n g r e p r e s e n t i n g 6 to 7 years w i t h i n one single m i l l i metre.
According
to these values,
regularly
biolaminated
sequences
90
developing
during a period of very r e g u l a r l y u n d u l a t i n g
conditions
may
interlayering
at
first glance look like one single
environmental layer
and
its
w i t h u n c o n f o r m i t y layers w o u l d imply p e r i o d i c i t y on
the
millimetre-scale.
2. 6. 3. Importance of small t e c t o n i c events
The chief concern of this chapter has b e e n to d e m o n s t r a t e the record of
change from a s h a l l o w - w a t e r e n v i r o n m e n t into a s u b s e q u e n t l y
basin.
deeper
In c h r o n o l o g i c a l order there have been four stages in the deve-
lopment
of the Solar Lake
(i) a stage open to the sea,
comparable
to
fjord-like embayments w h i c h occur adjacent to the Solar Lake bight,
(2)
a semi-closed stage due to the g r a d u a l l y forming coastal bar,
the
completely basin.
closed
Coring
evidence
stage and finally
and
that
(4) the
(3)
subsidence-derived
r a d i o c a r b o n dating of organic
sediments
the change from the open to the semi-closed stage
pened in the time b e t w e e n 4644 +/- 555 and 3378 +/- 172 B.P. al.,
1977a, K R U M B E I N et al.,
closing Below
may
deep
provided
have
1977; FRIEDMAN,
hap-
(COHEN et
1978). The p r o c e s s of bar-
b r o u g h t about conditions as in the
Gavish
Sabkha.
the 1.20-m-thick b i o l a m i n a t e d deposits on the Solar Lake
shelf,
carbonate mud occurs in w h i c h shells of the g a s t r o p o d Pi~enella
conica
are a b u n d a n t day
Solar
Lake
environments the
(FRIEDMAN,
1978).
This species is absent in the p r e s e n t -
area whereas it is common
along the Gulf coast,
in
various
shallow-water
including the m e t a h a l i n e parts
Gavish Sabkha and also of the Ras M u h a m m a d Pool
(SNEH &
of
FRIEDMAN,
1985). During the semi-closed stage,
the center of the lagoon w h i c h is now
just b e l o w the b o t t o m of the Solar Lake was floored by m i c r o b i a l
mats.
It was surrounded by mud flats w h e r e s l i g h t l y h y p e r s a l i n e conditions or even
normal seawater salinity allowed c o l o n i z a t i o n by
gastropod that
zone was s e p a r a t e d from the m i c r o b i a l mat
zone,
former
on the m i c r o b i a l mats.
This as well as the shallowness
s y s t e m is similar to the p r e s e n t situation of
The
indicating
a salinity b a r r i e r was e s t a b l i s h e d w h i c h h i n d e r e d the grazing
gastropods the
P. conics;
the
of of
Gavish
Sabkha and to the Ras M u h a m m a d Pool. At conlca
about
2490 +/- 155 B.P.
g r a d u a l l y disappeared,
the lagoon closed off and s h a l l o w - w a t e r
established t h r o u g h o u t the lagoon.
completely.
cyanobacterial
These conditions,
P. mats
lasting about 555
9t
SEA PRESENT- DAY WATER TABLE
X•WINTER
SHELF
MARGIN
SUMMER
\
\ \ \
\
/
'\
/
\ 0
.~. 0 ~
:
'\
ii
r-T--~ Carbonate !::i!i: cement ed " ' 'sand ~ Stromatolithic car bonates
~
#
/.
Frcgmentec ::i:i mats
/
\
#",BASIN/./
SUBSIDENCE
o
Sand and Gastropod shells
-A-~Subaqueous gypsum
PRESENT- DAY BASIN SHALLOW BASIN BEFORE SUBSIDENCE
....
Fig. 30. Schematic p r e s e n t a t i o n of facies changes caused by a fault movement which formed the deep Solar Lake b a s i n and its limnologic cycle. Shelf: R e g u l a r l y laminated m i c r o b i a l mats with ooids and oncoids overlying carbonate mud and sand with g a s t r o p o d shells (P. conica). Bottom: Subaqueous, faintly biolaminated gypsum overlying regularly laminated s t r o m a t o l i t i c c a r b o n a t e s which formed b e f o r e the subsidence. Drawings of core successions not to scale, m o d i f i e d after K R U M B E I N et al. (1977).
years, dence
came to the end due to a fault m o v e m e n t of the central
the l i m n o l o g i c a l present while
and
character
changed.
favor the shelf mats
at the b o t t o m
are a l l o w e d
part of the lagoon.
of the
lake
With
These growing
which
conditions to
caused
a deep basin
prevail
extraordinary
only a few s p e c i a l i z e d
to thrive and to i n t e r f e r e
the subsiestablished up to the thickness
microorganisms
with gypsum precipitation.
Thus
92
the change from a peritidal sabkha-type environment into a subsequently deeper
mesothermic,
sequence into
monomictic
lake is recorded within
where carbonate mud containing
regularly
"cerithid"
(i) the
shelf
gastropods
merges
laminated stromatolitic carbonates and (2) the
bottom
sequence where regularly laminated stromatolitic carbonates merge faintly biolaminated gypsum (Fig. 30).
into
That the island
is no firm land,
peak of a m i l e - l o n g the
sand
the
forces
more
3. V E R S I C O L O R E D
(MELLUM
of nature
and more
rience
(M. LUSERKE,
SOUTHERN
that thus
spectacularly
- all
this
to be a basis
SILICICLASTIC
ISLAND,
sand-drift;
here belongs
but the
to
became
of our expe-
1957).
TIDAL FLATS
NORTH
SEA)
3. i. I n t r o d u c t i o n
The the
examples
of the G a v i s h
Sabkha and the Solar Lake
aid of g e n t l y o s c i l l a t i n g
salinity,
temperature)
laminated
sediments
fication
within
internal
stability.
accidental of
borne
purely the
mat
sequences
sedimentation
described
R.
RICHTER
high
environments
studies.
(1926)
sand-drift
tide
flats
environment Early
of M e l l u m latitude
(2) their
here
is to d e s c r i b e
more of
"German
the
to
windSahara"
Island.
Island
represent
(53 ° 43' N)
lithologic
facies
data o b t a i n e d
more
the rise
than
character
(3) they are in open contact w i t h the sea.
and s e d i m e n t o l o g i c a l
the
is
owes m u c h
the i m p o r t a n c e
used the term
calci-
increase
By contrast,
chapter
at M e l l u m
of h i g h e r
Sabkha and the Solar Lake;
paper p r e s e n t e d
in this
potential,
on the other h a n d
To show p i c t o r i a l l y
the c o m m o n
siliclastic;
water
slowly g r o w i n g b i o g e n i c
deposits
"versicolored"
by e c o l o g i c a l tory
quiet
develop.
Physical
sedimentation,
Gavish
an o t h e r w i s e
show that w i t h
(water
origin
sedimentation.
microbial
stimuli
than an aid to g r o w t h of b i o l a m i n i t e s .
w h e n he d e s c r i b e d
The
within
of p u r e l y b i o g e n i c
the
biolaminated
physical
environmental
(i) the is
A i m of
and to i n t e r p r e t
it
from field and labora-
94
3. 2. Methods
Field w o r k was carried out in 1983 and 1984. from
seven
sites w h i c h were chosen to include
elevation above the m e a n h i g h w a t e r rison,
data
Samples were c o l l e c t e d different
(MHW) level.
o b t a i n e d earlier are included
degrees
of
For intertidal compa-
(GERDES & HOLTKAMP,
1980).
E l e v a t i o n of sampling sites was m e a s u r e d w i t h a theodolite.
Methods section
of sampling
preparation
parameters
(Eh,
pH,
(sediments,
temperature)
d e s c r i b e d for the Gavish Sabkha. pared
(REINECK,
sediments cores
m i c r o b i a l mats
and
and m e a s u r e m e n t s of salinity and
fauna),
were identical w i t h methods Additionally,
thin
physicochemical already
relief casts were pre-
1970), and p i g m e n t c o n c e n t r a t i o n s in the upper i0 mm of
were
d e t e r m i n e d using a corer I0 mm in
diameter.
Sediment
for nutrient c o n c e n t r a t i o n m e a s u r e m e n t s were taken w i t h a
corer
2.5 cm in diameter and 12 cm long. Pigments were extracted and m e a s u r e d using the m e t h a n e - h e x a n e e x t r a c t i o n method
(STAL et al.,
1984a). Stan-
dard m e t h o d s w e r e used for extractions of NH4+ and S 2- (PANG & 1976;
H O P N E R et al.,
eveness
(after PILOU)
1979;
DEV,
1984). D i v e r s i t y
NRIAGU,
(after SHANNON)
and
of faunal communities were determined.
3. 3. L o c a l i t y and p r e v i o u s w o r k
3. 3. i. Recen t s e d i m e n t o l o g i c a l h i s t o r y
Climatic
fluctuations in the Q u a r t e r n a r y led r e p e a t e d l y to
tions
(Elsterian,
wide
parts of the North Sea b a s i n on the one h a n d and sea level
within
of the southern coastal area
Holocene and
a c c o m p a n i e d by exposures of
interglacial periods on the other hand.
guration
1978).
Saalian and Weichselian)
glacia-
rise,
The p r e s e n t - d a y confi-
(Fig. 31A) is the result of
w h i c h is by no means c o m p l e t e d today
steps of the b a r r i e r - i s l a n d action
microbial sand
(STREIF & KOSTER,
formation,
and tide currents.
initial
b u i l t up by c o m b i n e d forces
It is h i g h l y p r o b a b l e that
of
initially
films and later mats interfered with stationary approaches of
bodies at MHW-levels.
immobilization bodies
the
L o n g s h o r e bars p a r t l y above and p a r t l y b e l o w the low w a t e r line
the formation of b a r r i e r s at MHW-levels may have been the
wave
rises
immediately
That m i c r o b i a l c o l o n i z a t i o n takes
p l a c e w i t h the
and
emergence
above MHW has been observed at stationary sand banks
sediment of
sand
presently
95
forming
in open tidal
& GERDES,
1984)
along
the
the
some
islands
ronments.
According
range
environments
is somewhat
It
of the
"German Bight",
forms
as
flats
on either
related
levels:
where
of this paper,
Intertidal:
bank
the terms
b e t w e e n mean
low w a t e r
tide
(MHW);
mean h i g h w a t e r
at spring
tide
(MHWS);
the
front
side,
longitudinal centered, tidal
ending
to tidal
slightly
range
extension of
(MLWS)
sand
intertidal
distribution
between
Island
zone
related
embayment
south-north through
and
at spring
the
supratidal
following
tide
supratidal:
and
MHW and
above MHWS.
is the strong
convexity
landwards
with
configuration
marsh
tide
(MLWS)
between
supratidal:
and wide
of
spits
protects
lower
from MLWS to M H W
to the Mean
in the lower part. zone b o u n d a r y
reaches
intertidal or above the
This
supratidal
in
environ-
31B).
recurved
31B).
a
W i t h a spring
cutting
It has a level d i f f e r e n c e
Microbial
MHW and MHWS
between
mats
which parallels
salt m a r s h
is
a
supra-
in
the
-1.80
Sea Level w h i c h
upward to the M H W S - I e v e l
tally w i t h the c e n t e r e d h i g h distance
(Fig.
upper
(MHW),
zone
Upper
have
flats.
i000 to 1200 m.
and +1.30 m
Lower
in two hooks
of the i n t e r t i d a l
intertidal-supratidal Their
of M e l l u m
inlets
cliffed
and intertidal
The
the
feature
(Fig.
envi-
mesotidal
to a m a c r o t i d a l
channels
Eider-
environments
the range of
extend w i d e l y
lie b e t w e e n
at normal
the
occur
and m a c r o t i d a l
island of the estuary
tidal
island
islands
the Jade Bay and
close
flats
mean h i g h w a t e r
A characteristic
Bank
while
flats
M e l l u m and
1975).
2 m and 4 m at springs.
tidal
which
31A),
of b a r r i e r
macrotidal
tide,
side of the islands
to sediments
(Fig.
the tidal
stages
mesotidal
is a l r e a d y
result of larger
For the p u r p o s e are
between
the most w e s t e r l y
a
(GOHREN,
(1980),
between
Island
(REINECK
sections.
fringes
Sea coast younger
represent
to DAVIES
ment.
tidal
North
of over 4 m at spring
tide of 3.40 m, M e l l u m
direction
islands w h i c h
embayment
estuary
in the f o l l o w i n g
represent
and t y p i c a l l y
and Elbe
I s l a n d and study area
"bank islands"
the e s t u a r y
staedt peninsula
tidal
and e a s t e r n
called
in
of M e l l u m
chain of b a r r i e r
smaller
development, mainly
setting
southern
other
the W e s e r
and is also d e s c r i b e d
3. 3. 2. G e n e r a l
Within
flats b e t w e e n
appear
m
crosses at
the w e s t e r n
the hook.
and m e r g e s h o r i z o n -
of the island
(Fig.
(lower and upper b o u n d a r y
31B).
of mat
The
forma-
96
tion)
is 400
points
to t h e
to 700 m. extremely
A maximum gentle
elevation
angle
500
of the
of 40 c m o v e r lower
this
supratidal
distance
zone.
m
L~'-*'.~ 5oR ~lorsh
~
Lower Supratidol Zone
~
Intedidol Zone
m
Subtidol Zone
MHW5
MHW
"
210
t ~
1
27~ Z~
~,®
]m ~o~ ~>~~
J April
Fig. 31. General setting of Mellum Island. A) L o c a t i o n of t h e i s l a n d b e t w e e n t h e Jade Bay and the Weser river. s i t u a t e d a t the b a c k B) S t u d y area, s i d e o f the w e s t e r n h o o k , between t h e m e a n h i g h w a t e r l i n e (MHW) a n d t h e m e a n h i g h w a t e r l i n e at s p r i n g tide (MHWS). Numbers refer to sampling sites. c) R a n g e s o f h i g h t i d e s a b o v e MHW, n = 706 tides from November 1981 t o O c t o b e r 1982. M H W = l o w e r b o u n dary of the versicolored flats, MHWS = upper boundary. In the a n n u a l cycle, areas between these l i n e s a r e f l o o d e d f r o m 70 % (MHW) t o 20 % (MHWS). E x t r e m e h i g h w a t e r at s p r i n g t i d e (EHWS) o c c u r s m a i n ly in w i n t e r a n d spring. During summer, periods of exposure are more extended. (A t o C w i t h p e r m i s s i o n f r o m J. S e d i m e n t . P e t r o l . , 55, 2 6 5 - 2 7 8 , 1985).
97
3. 3. 3. Previous w o r k
The
number
environments literature
of
on
have
in
be c o m p a r a t i v e l y low if one regards
However, already
biolaminations
later r e - n a m e d
a t t r a c t e d a t t e n t i o n in
preceding
Sea
ganisms,
to
microbial
h i d d e n from v i e w
(1942,
1949)
SCHULZ
1841; (1936),
tions i n s p i r e d SCHULZ
of
of
SCHULZ & M E Y E R
a North Frisian island.
the
microor-
see also KRUMBEIN,
studied the m u l t i p l e interactive
visits to Amrum,
1777),
scientists,
1986b).
(1940) and
pathways
c y a n o b a c t e r i a and a s s o c i a t e d m i c r o b e s in their s e d i m e n t a r y during
and
d e d i c a t e d their
mats in lower supratidal settings
(OERSTEDT,
lati-
At the begin-
and e m p h a s i z e d the " i s l a n d - f o r m i n g capacity"
A b o u t a h u n d r e d years later, HOFFMANN
(MULLER,
a group of S c a n d i n a v i a n natural
i n c l u d i n g H O F M A ~ N BANG, LYNGBY, O E R S T E D T and ROSENBERG,
of
tropical
centuries
"blue-green algae" and then cyanobacteria.
ning of the 19th Century,
Baltic
wealth
in tidal flats of h i g h e r
i n s p i r e d t a x o n o m i c and ecologic studies on "conferves",
observations
siliciclastic the
c a r b o n a t e s t r o m a t o l i t e s and m i c r o b i a l mats in
environments. tudes
reports on b i o l a m i n a t e d d e p o s i t s
may
of
environment
The colorful lamina-
(1936) to create the t e r m " F a r b s t r e i f e n - S a n d w a t t "
(versicolored q u a r t z - s a n d y tidal flats).
N i t r o g e n fixing by n o n - h e t e r o c y s t o u s c y a n o b a c t e r i a studied in s i l i c i c l a s t i c tidal flats & VAN GEMERDEN,
1984;
STAL et al.,
of d e p o s i t i o n a l records were given SCHWARZ et al., REINECK
&
emphasized
1975;
GEP~ES,
(STAL & KRUMBEIN,
(EVANS,
1965;
intensively
1981;
1984a, b c, 1985).
CAMERON et al.,
1984).
was
1985; STAL
Several examples
DAVIS,
1966,
1985; GERDES et al.,
1968;
1985b,
The aspect of coastal b i o - e n g i n e e r i n g
by F U H R B O T E R et al.
(1981,
1983) and M A N Z E N R I E D E R
c; was
(1984),
who noted current v e l o c i t i e s of m o r e than 12 times the n o r m needed
for
grain m o v e m e n t w h i c h w e r e made immobile t h r o u g h m i c r o b i a l colonization.
3. 4. The p h y s i c a l e n v i r o n m e n t of mat f o r m a t i o n
3. 4. I. Climate
The s o u t h e r n coast of the N o r t h Sea has a temperate, Low pressures,
w e s t e r l y winds,
p e r c e n t of the time, speeds
of
and h i g h rainfall are typical.
w i n d s come from the southwest,
6 to 15 m/s
(EISMA,
h u m i d climate.
1980).
Seventy
or n o r t h w e s t w i t h
P r e c i p i t a t i o n averages 700
to
98
750 mm
per year.
During winter,
while
in the summer
4 °C
in w i n t e r
3. 4. 2. Flooding
a yearly
MHW level,
flats
average,
but only 20 % reaches spring
only,
while
upper
the
Extreme h i g h water
several
the w a t e r
supratidal
the entire
drift
level.
lower the w a t e r
are
ice accumu-
(EHWS)
level
31C). slope
subaerially
zone
(Fig.
northwesterly level,
31C).
winds
exposed.
winds
November Wind
raise
resulting
On the other hand, dm,
the
(Fig.
Occur m o s t l y b e t w e e n
supratidal
for several
or crosses
the lower s u p r a t i d a l
zone remains
Strong
area. level
reaches
the MHWS
cross
above normal h i g h - w a t e r
tion of the supratidal south
or crosses
tides m a i n l y
at spring tide
and crosses
meters
- 95 %,
1976).
70 % of all h i g h w a t e r
the summer,
influences
During winter, (REINECK,
is 90
air t e m p e r a t u r e s
frequency
During
and April
is common
humidity
Mean annual
and 16 °C in summer.
lation on the tidal
On
the relative
it is 75 - 80 %.
also
it up to
in the inunda-
from the east or
so that even h i g h w a t e r
spring tide does not reach or cross the supratidal
at
zone.
3. 4. 3. S a l i n i t y
Salinity During measured of
in
the h i g h
rainfall
in surface waters
flood waters
time
period
found more
tide
at low tides,
drastic
of insolation, water.
deviation
is a
a minimum
(the general
lies b e t w e e n
in i n t e r s t i t i a l
flats
a maximum SCHULZ
from the normal
46 °/oo
after
described
for
salinity
regime
it may p r o b a b l y
of intense
the G a v i s h
Sabkha
does not control select
After
salinity
& MEYER
9 °/oo after a h e a v y rainfall
fluctuating
factor.
20 °/oo was
range of the o v e r a l l
30 and 32 °/oo).
measured
a period
rather
s a l i n i t y of about
of up to
(1940)
seawater
and the Solar the mat
salinity.
for special m i c r o b i a l
40 °/oo an
Lake,
an
was even
The authors
increase
However,
formation
summer-
observed
and a salinity
insolation.
salinity
a longer
of up to
as
already
oscillating
in general,
though
taxa.
3. 4. 4. M o i s t u r e
The even
sedimentary
surfaces
after a set of several
of the lower supratidal days of subaerial
zone r e m a i n
exposure
which
moist
is common
99
in the summer p e r i o d low
tides
whose
is
(see Fig.
migration
is s u p p o r t e d
1936;
HOFFMANN,
weight
determinations
sediments
31C).
The
due to the c o n t i n u o u s
1942).
by the
fine-grained
Interstitial
show values
surfade-provided
upward movement
water
comparable
(Table 8; see also GERDES
contents
at
groundwater,
sandy texture
(SCHULZ,
obtained
to contents
& HOLTKAMP,
moisture
of
of
by
dry
intertidal
1980).
TABLE 8. W e i g h t p e r c e n t a g e of i n t e r s t i t i a l fluids o b t a i n e d after sectioning of sediment cores into 1 cm thick slices, drying of the sediment p o r t i o n s and c a l c u l a t i o n of the w a t e r loss. S e d i m e n t cores were taken at sites of equate e l e v a t i o n (MHW +30 cm) of the lower supratidal slope.
08cillatoria
S e d i m e n t layers b e l o w surface 0-i 1-2 2-3 3-4 4-5
cm cm cm cm cm
TWO d i f f e r e n t supratidal
nal relief.
amount
dal-supratidal
ments.
drain
JACOBSEN such
internal
crosses
are typical (1980)
the (Fig.
flood
exposed
at low tide.
topography
area at the
relief b e c a u s e
32A).
used the term
the lower
without
the
inter-
junction b e t w e e n This area
of a
flood
has and
a ebb
and m e r g e s w i t h the intertiThe s h a l l o w
elements
"landpriel
shallows"
of sandy coasts. Both channel
and n e a r l y
of b a c k s h o r e
The
types
plains.
The p l a i n s
at MHW w h i l e
surface
This
from ebb d r a i n a g e
results
within
s e a w a r d part of
of the island.
geomorphic
the salt m a r s h h i n t e r l a n d .
subaerially
surface
junction
relief n o n c o n f o r m i t i e s
parallel-sided
even
smooth
salt m a r s h
zone b o u n d a r y
channels
can be d i s t i n g u i s h e d
is a more p r o t e c t e d
of
system which
25.8 wt.% 22.8 " 22.4 " 19.7 " 17.3 "
at the less p r o t e c t e d
has a r e l a t i v e l y
h o o k and the c e n t e r e d
channel
rize
The one,
The other
considerable
(shallows)
unconformities
sub-environments
zone.
w e s t e r n hook,
flood
variation
18.7 wt.% 18.2 " 15.0 " 18.6 " 16.7 "
3. 4. 5. M o r p h o l o g i c a l
the
Microcoleus
variation
are
filled
environ-
to characteebb
channels
bordered
by
are
flooded
at MHWS
and
water
remains
in the
channels
on the one h a n d
are
and
100
mn
0 2
6 8, 10, 12.
from of
C
small front bars on the other h a n d which build up in the v i c i n i t y the M H W - l e v e l from i n w a r d - m o v i n g sand.
characterize the h i g h e r - l y i n g plains
Dense stands of
(Fig. 32A).
halophytes
101
Fig. 32. Area and d e v e l o p m e n t of the v e r s i c o l o r e d tidal flats. Ebb channels b o r d e r A) V i e w of the area of the Mic~ocoleus variation: flood plains w i t h stands of halophytes. M i c r o b i a l mats interacting with low-rate s e d i m e n t a t i o n a~count for the e l e v a t i o n of the flood plains and make sediments rich in n u t r i e n t s thus f a c i l i t a t i n g plant growth. 08cillatoria limosa starts w i t h the mat formation, coloB) Initially, nizing and a g g l u t i n a t i n g sand grains. Scale is 200 pm. C) Mature stage of the v e r s i c o l o r e d tidal flats showing a vertical z o n a t i o n from top to b o t t o m of (i) a c y a n o b a c t e r i a l mat (usually covered w i t h a thin sand layer), (2) a n o x y g e n i c p h o t o b a c t e r i a (purple bacteria), (3) c h e m o o r g a n o t r o p h i c b a c t e r i a (sulfate-reducers). (Modified after GERDES et al., 1982). of D) Mat surface (Microcoleus) showing the densely e n t a n g l e d m e s h w o r k filaments o v e r g r o w i n g the sandy sediment. Scale is 250 pm. (oscillatoria limosa) colonize the much E) F i l a m e n t o u s cyanobacteria thicker filament of a m a c r o a l g a e (Enteromorpha sp.). Scale is 50 pm (after GERDES & KRUMBEIN, 1986). F) Forams (undetermined species) are inhabitants of the mat surfaces. Scale is 200 pm.
3. 5. S u b - e n v i r o n m e n t s and facies
3. 5. i. Local d o m i n a n c e o_~f m a t - p r o d u c i n g species
Frame genera
builders already
of the M e l l u m
mentioned
mats
are
cyanobacteria,
for the Gavish Sabkha and
the
including Solar
Lake
(Mic~ocoleus, O~cillatoria, Spi~ulina, Gloeothece, Synechococcus).
Two
species
the
of
filamentous c y a n o b a c t e r i a
share in the d o m i n a t i o n
of
lower supratidal zone: Oscillato~ia limosa and Microcoleu8 chthonoplas-
tes.
0. limosa,
within
supratidal The
zone
species
organisms
where w i n d - d r i f t e d
is d o m i n a n t
sediments settle at a
high
rate.
is capable of a rapid gliding m o t i l i t y w h i c h
aids
these
to move fast,
sedimentation zone
a very m o t i l e filamentous cyanobacterium,
the less p r o t e c t e d and less v e g e t a t e d seaward part of the lower
events.
away from the growth site in response to The t r a n s i t i o n a l part of the
lower
the
supratidal
(landpriel shallows) m e r g i n g into the c e n t e r e d saltmarsh is domi-
nated by Microcoleu8 chthonoplastes. Specific slow s e d i m e n t a t i o n conditions
c h a r a c t e r i z e e s p e c i a l l y the flood plains w h e r e dense
halophytes
(Salicornia sp.,
Spa~tina anglica,
stands
of
Limonium vulgate) occur
(Fig. 32A). These conditions provide s u f f i c i e n t shelter for the ensheathed
Microcoleu8
bundles to form mats.
d e s c r i p t i o n of the Gavish Sabkha mats,
Mic~ocoleu8
As a l r e a d y m e n t i o n e d in
the
the p e c u l i a r i t y of filaments of
chthonoplastes is to move h o r i z o n t a l l y back and forth
and
102
to
leave their sheaths only in crisis
importance of M. ~hthonoplastes (formation of Lh-laminae,
conditions.
The
geobiological
in the Gavish Sabkha and the Solar Lake
h i g h p r o d u c t i v i t y rates and sheaths which are
r e l a t i v e l y r e c a l c i t r a n t and survive decomposition) was also emphasized. The
dominance
of this species w i t h i n the p r o t e c t e d part of the
lower
supratidal zone of M e l l u m Island results in b i o l a m i n i t e s w h i c h are much more
v e r t i c a l l y e x t e n d e d than those of Oscill~toria
limosa.
seems to represent a typical o p p o r t u n i s t w h i c h colonizes freshly d e p o s i t e d sediments
predominantly
(e. g. on the flats off the shallows and in
the v i c i n i t y of the MHW-level) w h i l e M. chthonoplastes from
O. limosa
seems to b e n e f i t
the sediment stabilizing a c t i v i t y of 0. limosa and low-rate sedi-
mentation.
According species,
to
the
change of dominance and abundance of
we denote the s u b - e n v i r o n m e n t of the outer slope
variation,
these
two
08cillatoria
the t r a n s i t i o n to the centered m a r s h Micnocoleus variation.
3. 5. 2. S t r a t i f i c a t i o n o_~f living t°P mats
Osciallatoria-Variation:
Sections through the living top mat usually
show a v e r t i c a l l y structured set of three to four layers:
i. A y e l l o w - b r o w n top layer, composed of sand. Thickness ranges from 1 to 5 mm. The layer is c o l o n i z e d by diatoms
(the genera Navicula
and Diplonei8 are dominant). 2. A greenish layer underneath, ria. the
Thickness
composed of filamentous cyanobacte-
ranges from 0.5 to I mm.
dominant species
(Fig. 32B).
Oscillatoria limosa is
Also present are
bundles
of
Microcoleu8 chthonoplastes, other filamentous forms of the genera oscillatoria, Spirulina, Lyngbya, Phonmidi~m, and clusters of unicellular cyanobacteria
(Gloeocapsa, Gloeothece, Synechocystis,
Merismopedia). 3. Where
the u n d e r s i d e of layer 2 is aerated,
more than 0,2 mm thick)
a thin (usually
not
red orange h o r i z o n forms w h i c h is rich in
iron hydroxide. 4. A
layer
black w i t h iron sulfide ranging in thickness b e t w e e n
1
and 5 mm follows s u b s e q u e n t l y or in place of the iron hydroxide.
Microcoleu8 variation:
A
well-defined
microbes characterizes this variation.
change in
associations
of
The v e r t i c a l l y s t r u c t u r e d system
103
of the Microcoleus-dominated m i c r o b i a l mat
(Fig. 32C) includes four
to
five layers:
i. The
top
mat is u s u a l l y 50 - i00 pm thick
are
and
monospecifically
of b u n d l e d sheaths of Microcoleus chthonoplastes
composed
horizontal
in orientation.
number of quartz grains
This top mat contains
cyanobacteria.
o r g a n i s m s c o l o n i z e sand grains and interstices organisms
predominantly
vertical
(oscillato~ia,
Lyngbya,
in orientation.
(Fig.
layer
are
The r e p r e s e n t a t i v e s
latoria v a r i a t i o n of the outer sand flats thece, Synechocysti~, Merismopedia). third
32C).
Pho~midium)
u n i c e l l u l a r c y a n o b a c t e r i a are identical w i t h those of the
3. The
minor
c o m p l e t e l y green co-
lored by d o m i n a n c e of filamentous and u n i c e l l u l a r
Filamentous
a
(Fig. 32D);
2. B e l o w is a sandy layer, 600 to 700 pm thick,
The
which
(Gloeocapsa,
is pink from the d o m i n a n c e
of
purple
of
OscilGloeosulfur
Ch~omatium (photosynthetic a n o x y g e n i c bacteria, mainly vinosum and other n o n - i d e n t i f i e d species). Sand grains and grain-
bacteria
supported
interstices
are d e n s e l y c o l o n i z e d by
the
microorga-
nisms. The thickness of this layer ranges b e t w e e n 500 and 600 pm. 4. The
colorful v e r t i c a l z o n a t i o n merges into a fourth layer
which
is b l a c k from iron sulfide and reaches down to several cm.
The top mat is sometimes covered by a thin layer of y e l l o w i s h white, c l e a n l y w a s h e d sand.
Diatoms are not as frequently e n c o u n t e r e d in this
layer as in the Oscillatoria variation.
stage while the The Microcoleus v a r i a t i o n represents the mature 08cillatoria v a r i a t i o n may indicate the p i o n e e r stage of mat development.
The a c c u m u l a t i o n of o r g a n i c a l l y bound carbon,
and
other
the
e n r i c h m e n t of other m e t a b o l i c types.
compounds w i t h i n the n u t r i e n t - p o o r q u a r t z - s a n d
chemoorganotrophic mat.
With
which
gives
bacteria cally the
(e°
bacteria
rise to the d e v e l o p m e n t of g.
Solar Lake, The
w h i c h degrade the
primarily
aerobic
monolayered
02 becomes
anaerobic
sulfur
facilitates
I n i t i a l l y these are
the c o n s t a n t rise of organic matter,
depleted,
chemoorganotrophic
Desulfovibrio Sp.). Finally, the versicolored, verti-
s t r u c t u r e d system,
types.
nitrogen,
a l r e a d y d e s c r i b e d for the G a v i s h Sabkha
d e v e l o p s c o n s i s t i n g of a great v a r i e t y
system b e n e f i t s
of
from a setting w h i c h is p r o t e c t e d
h i g h s e d i m e n t a t i o n rates, wave attack and tidal currents.
and
metabolic against
104
105
Fig. 33. Internal s e d i m e n t a r y structures (thin sections from cores). A - E: Photographs by H.-E. REINECK. Oscillatonia variation. Dark A) Thin laminae c h a r a c t e r i s t i c of the v e r t i c a l lines are tubes of polychaets. A shell fragment is visible b e l o w the mat. Scale is 5 mm. interB) M u l t i l a m i n a t e d sequences w i t h i n the Microcoleus variation, layered w i t h light q u a r t z - s a n d deposits. Scale is 5 ram. C) A thin mat has coated a rippled surface. Scale is 5 mm. buried microbial D) Root shafts of Spa~tina anglica p i e r c i n g through mats. Note filling of root shafts at top and b o t t o m right w i t h sand. Scale is 1 cm. E) T h i n n e r laminae on top of a m u l t i l a m i n a t e d mat sequence consist of heavy mineral grains indicating the former p r e s e n c e of mats. Even w i t h o u t preservation, the captured h e a v y m i n e r a l grains may indicate the former p r e s e n c e of a mat. Scale is 5 mm. F) C l o s e - u p of the placer of h e a v y m i n e r a l s e n r i c h e d on top of a buried mat. Scale is 1 mm. (Figs. B to E with p e r m i s s i o n from J. Sediment. Petrol., 55, 265-278, 1985).
3. 5. 3. Internal s e d i m e n t a r y structures
Thin
sections
wiched
show that the sediments are almost i n v a r i a b l y
b e t w e e n layers of cleanly w a s h e d sand and
microbial
mats
organic
sand-
carbon-rich
w h i c h p r o l i f e r a t e during intervals b e t w e e n
sedimenta-
tion.
The grain-size d i s t r i b u t i o n of the sandy layers is almost w i t h intertidal sediments is
(GERDES & HOLTFu~MP,
identical
1980). The m a i n fraction
made up of f i n e - g r a i n e d sand w i t h a m e d i u m grain size of i00 ~m
(=
3.3 Phi). A fraction of m e d i u m - g r a i n e d sand is g e n e r a l l y admixed averaging
20 to 25 wt.%,
w h i l e silt and clay is not more than 3 wt.%.
lithologic c o n f o r m i t y of sediments shows that the facies are
The
modifications
m a i n l y c o n t r o l l e d by i n u n d a t i o n frequencies to w h i c h m i c r o b i a l and
faunal assemblages
(see chapter 3. 6.) correspond.
The b u r i e d mats appear as compacted, In the 08cillato~ia variation,
bands. 2 mm; mely
Fig.
between
(up to i0 mm;
sedimentation 1
mm
variation).
Light layers b e t w e e n
(Micro~oleu8 variation) and planar,
sand.
however,
It is,
Fig. 33B).
(Fig. 33C).
due
Root
(I
to
v a r i a t i o n they appear extre-
units of q u a r t z - s a n d w h i c h range in
The b i o l a m i n i t e s
predominantly
ripple
laminae are usually thin
33A), w h i l e in the Microcoleu8
thick
indicate
sharply p r o j e c t i n g i n t e r l a y e r e d
several
are m a i n l y h o r i z o n t a l to the p r e d o m i n a n c e of
cm
the
mats
thickness
(08cillatoria
in o r i e n t a t i o n
and
parallel-laminated
p o s s i b l e that a mat covers a s m a l l - s c a l e shafts of h a l o p h y t e s appear w i t h
wave
increasing
106
h e i g h t above MHW. The dense stands of h a l o p h y t e s w i t h i n the Microcoleu8 variation
(Fig. 32A)
piercing
through
are s p e c t a c u l a r l y recorded by the
the b u r i e d m i c r o b i a l mats
root
(Fig. 33D).
systems
Deposits
o r a n g e - r e d Fe(OH) 3 around the roots and filled root shafts occur 33D).
A
of
(Fig.
spectacular a r r a n g e m e n t of h e a v y mineral grains following the
morphology
of a b u r i e d mat is often visible
mineral
is
volumes
ranging b e t w e e n 0.2 to 3.5 wt.%.
mineral
(LITTLE-GADOW,
supratidal
(Fig. 33E
and
F).
c o n c e n t r a t e d in sediments around M e l l u m Island
mats
1978).
Epidot is the most
bulk
abundant
The c o n c e n t r a t i o n of grains on top
may indicate wind a c t i v i t y and
1935; G A D O W & REINECK,
Heavy
with
1969; REINECK & SINGH,
deflation
of
(TRUSHEIM,
1980).
3. 5. 4. s t a n d i n g ' crops and b i o g e o c h e m i s t r y
Standing cro~s. Pigment c o n c e n t r a t i o n s confirm the d i f f e r e n t complexity
of
both
mat types d e s c r i b e d
(Fig. 34A).
In the course
summer the c o n c e n t r a t i o n s increase in b o t h subenvironments. a contents in the 08cillator~a v a r i a t i o n
chlorophyll 50
and
(ranging
flats
(VAN DEN HOEK et al.,
Mic~ocoleus
variations
chlorophyll
a
of
are up to four
times
higher, this
and
of
upper-
1979). The c o n c e n t r a t i o n s
is m a i n t a i n e d only in samples of
the
between
170 mg x m -2) are comparable to those usually found in
intertidal
values
of
Values
in the
bacterio-
variation.
the M i c r o c o l e u s mat are almost comparable to those
The
of
the
(Fig. 34A)
can
G a v i s h Sabkha and the Solar Lake.
The
drastic increase of pigment contents
be
traced b a c k to a b l o o m of m a c r o a l g a e
by
increasing
biomass
m o i s t u r e supply (rain) in
in October
(Enteromo~pha sp.), fall.
Thus,
the
drought-
r e s i s t a n t c y a n o b a c t e r i a and prevents growth of the m a c r o a l g a e
(e. g. in
Fig.
effectively
34A).
Though
favors
microbial
the
August,
can best be estimated w h e n drier weather
initiated
their growth is ephemeral,
the m a c r o a l g a e
contribute to the biomass p r o d u c t i o n and also to the
p l e x i t y of the Microcoleus mat,
com-
since the c y a n o b a c t e r i a tend to inter-
twine w i t h the much thicker filaments of the algae
(Fig. 32E).
(mainly Entermorpha sp.) are p a r t i c u l a r l y abundant in Microcoleu8 v a r i a t i o n while almost absent in the 08cillatoria variation. Ente~omorpha species are able to use a m m o n i u m d i r e c t l y The m a c r o a l g a e
the
without
further b r e a k - d o w n to
nitrate
(RANWELL,
1972).
Hence,
the
107
OSClLLATORIA -VARIATION
l
t
NICROCOLEUS-VARIATtON
PIGMENTS m-2 1000 mg-m-2 800 600
F~
DChlorophyll e • Bacterio chbrophyll
400 200-
_ I._II ,,,I_ 4 6610 4 6810 4 5610 4 6810{month) A 4 6 510 AMMONIA AND SULFIDE S 20 0.2 0.4 0.6 0B 1 2 3 4 0 0.2 0.4 0.6 0.8 1.0 1.2 4 6 510
.
NH~0 0.2 0/. 0.6 Q8 1.0 1.2
.
.
.
.
,/__-,...-
6 d2"o~o'.6 0".8 I 2 3 4
r/
,!/
4.
12
B
REDOX POTENTIAL AND pH 7:0'72, ' 76 8:2 ' 8:6 -400 -200 0 +200 +400
'
ZO
400
' 7:4
200
' 78
0
" 8:2
200
8:6
pH
400 Eh
xq
z, "
"'"S'
T
×---x Eh ~--.o pH
,,,,,
C
Fig. 34. Substrate p a r a m e t e r s in the two v a r i a t i o n s of the v e r s i e o l o r e d 08cillatoria v a r i a t i o n (unprotected sites of the tidal flats. Left: lower supratidal slope), right: MicrocoZeu8 v a r i a t i o n (protected landpriel shallows). A) C h l o r o p h y l l a and b a c t e r i o c h l o r o p h y l l a in surface mats in the course of the summer 1983. The greater c o m p l e x i t y of Microcoleu8 mats (right) can be read from (i) chlorophyll a concentrations a b s o l u t e l y h i g h e r than of the Oscillatoria mats (left), (2) a more drastic summerly increase of c h l o r o p h y l l a and (3) the occurrence of bacteriochlorophyll a indicating the p r e s e n c e of a n o x y g e n i c photosynthetic b a c t e r i a (e~ g. purple bacteria). B) D i s t r i b u t i o n of ammonia and sulfide vs sediment depth. Both rates are increased in n e a r - s u r f a c e sediments, in p a r t i c u l a r in the Microcoleus v a r i a t i o n and less in the Oscillato~ia variation. The p r o f i l e of the Mie~ocoleu8 v a r i a t i o n indicates a site w i t h stands of macroalgae whose growth is favored by the e s p e c i a l l y high ammonia values (compare Fig. 32E). C) Redox p o t e n t i a l s and pH vs sediment depth showing p o s i t i v e Eh-values negative Ehand s l i g h t l y h i g h e r pH in the 08cillatoria variation, values and lower pH in the Microcoleu8 variation.
108
selected
growth of these species may suggest that a m m o n i u m
is high w i t h i n the sediments of the Microcoleus
A m m o n i a and sulfide concentrations. cores
production
variation.
In October 1984 we took sediment
from both s u b e n v i r o n m e n t s to study the vertical d i s t r i b u t i o n
NH4 +
and
S 2-.
variation
and
Both rates were largely increased in
concentrations
were
This
than
is
Microcoleu8
variation.
p a r t i c u l a r l y h i g h in the n e a r - s u r f a c e
d e c r e a s e d more or less rapidly w i t h depth
matter
the
08cillatoria
far less i m p o r t a n t in the
parts
consistent w i t h the p r e s e n c e of freshly
older and more resistant m a t e r i a l
The and
(Fig. 34B).
produced
organic
w h i c h is more easily degradable by c h e m o o r g a n o t r o p h i c
surface
of
(BLACKBURN,
1983).
bacteria The
near-
pool of a m m o n i u m explains why m a c r o a l g a e capable of using
the
reduced intermediate product of N - m i n e r a l i z a t i o n are a t t r a c t e d to colonize the mats. the
On the other hand, the e n r i c h m e n t of sulfide just b e l o w
surface w h i c h is a s s o c i a t e d with the b a c t e r i a l b r e a k - d o w n of
organic
m a t t e r provides a b e n e f i c i a l situation for
trophs w h i c h require light. Thus, the
aerated
purple
lized
32C).
dead photo-
the sandy sediments i m m e d i a t e l y b e l o w
mat m a i n t a i n a large and
active
population
sulfur b a c t e r i a as well as green and colorless sulfur
(compare Fig. soon
surface
anoxygenic
The g r o w t h of the sulfur b a c t e r i a is i n h i b i t e d
as oxygen penetrates b e l o w the surface mat. in the Oscillatoria
v a r i a t i o n where
of
bacteria as
This is m a i n l y
rea-
(i) physical p r o c e s s e s
such
as w a v e energy and (2) the less c o n d e n s e d fabric of the mat support the penetration
of
08cillatoria
oxygen from above into the
mat
is
system.
c h a r a c t e r i z e d by a lower
Furthermore,
productivity
rate
biomass and thus by a lower amount of dead organic m a t t e r to be down
by b a c t e r i a to ammonium.
the of
broken
This may explain why m a c r o a l g a e as well
as larger and more active a n o x y g e n i c p h o t o t r o p h s are lacking there.
Reduction-oxidation
potentia
