By Dr. Ian West,
Romsey, Hampshire

and Visiting Scientist at:
Faculty of Natural and Environmental Sciences,
Southampton University,
Website hosted by courtesy of iSolutions, Southampton University

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BIBLIOGRAPHY AND REFERENCES

(This is a limited list. More will be added later.)

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Ali , Y.A. 1981. Mineralogical, Geochemical and Sedimentological Studies on Recent Sabkha Sediments West of Alexandria, Egypt, and Some Upper Jurassic Evaporites from Dorset, England. Ph.D. Thesis, Ain Shams University, Cairo, Egypt. By Dr. Yehia Abdel Hameed Ali. Supervised by Professor Ezzeldin Hilmy and Dr. Ian West at Ain Shams and Southampton University.
Abstract:
Recent sabkha of the northern coastal zone of Egypt near Alexandria and El-Alamein was investigated. This region has sufficient rainfall (16 - 19cm annually) to be almost semi-arid. The sabkha occurs in the First Depression, between a modern beach ridge (the Coastal Ridge) and a Pleistocene beach ridge (Abu Sir Ridge) to the south and in the Second Depression, south of the Pleistocene Ridge. The sabkha surface is of brown silt, sometimes salt-encrusted and with scattered small halophyte shrubs (dikaka).
The sabkha deposits consist mainly of brown carbonate and quartz silt with evaporites, including gypsum, halite and celestite. Non-evapoirte components, mostly of detrital origin, include quartz, feldspars, heavy minerals, calcite, aragonite (skeletal), dolomite and clay minerals.
Sampling was from pits and by coring. Petrographic, mineralogical and geochemical techniques were employed for the analysis of sabkha sediments, groundwater samples and extracted interstitial brines.
The sabkha sequence was sub-divided into five zones with distinctive mineralogical characteristics through the vertical profile from beneath the groundwater level to the sabkha surface. The origin of the nodules of primary gypsum in Zone IV is explained by the brine chemistry.
Groundwater brines are saturated with calcium sulphate but are only moderately hypersaline (about 60 parts per thousand). Interstitial brines move upward by capillarity through the silt of the sabkha in response to evaporation at the surface. A salinity gradient is established. They concentrated several times, becoming supersaturated with calcium sulphate at Zone IV. Precipitation causes the mMg2+/mCa2+ ration to increase to a high level (about 220).
The Second Depression, the site of a former lagoon (Lake Mareotis), contains salt lakes and sabkhas. Blister salt crusts of halite and gypsum are developed together with salt polygons and some algal blisters. Mollusc shells on the surface and in the sediments result from former lagoonal conditions. Gypsum sand crystals are developed in the sediments of this depression. A recent rise of the water table in the Second Depression, due to drainage of irrigation water, explains the lack of large gypsum nodules.
Some evaporite-bearing sequences from the Upper Jurassic Purbeck Formation of southern England were studied and sub-divided into sabkha cycles. They are interpreted as a series of semi-arid sabkha cycles and discussed in the light of the Recent model from northern Egypt.

Ali, Y.A., West, I.M. and Hilmy, M.E. 1980. Modern sabkha sediments and gypsum nodules from the Mediterranean Coast of Egypt. Second Scientific Conference of Egyptian Postgraduates Abroad, Egyptian Education Bureau, 4 Chesterfield Gardens, London, W.1, Part 4, pp. 136-151.

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Alsharhan, A.S. 1989. Petroleum geology of the United Arab Emirates. Journal of Petroleum Geology, vol. 12, 253-288.

Alsharhan, A.S. and Kendall, C.G.St.C., 1994. Depositional setting of the Upper Jurassic Hith anhydrite of the Arabian Gulf an analogue to Holocene evaporite of the United Arab Emirates and Lake Macleod of western Australia. American Association of Petroleum Geologists Bulletin, vol. 78, pp. 1075–1096.

Alsharhan, A.S. and Kendall, C.G.St.C. 1994. Depositional setting of the Upper Jurassic Hith Anhydrite of the Arabian Gulf: an analogue to Holocene evaporites of the United Arab Emirates and Lake MacLeod of Western Australia. American Association of Petroleum Geologists Bulletin, vol. 78, 1075-1096.

Alsharhan, A.S. and Kendall, C.G.St.C., 2002. Holocene carbonate/evaporites of Abu Dhabi, and their Jurassic ancient analogs. In: Barth, H.J., Boer, B.B. (Eds.), Sabkha Ecosystems. Kluwer Academic Publishers, pp. 187–202.

...

Alsharhan, A.S. and Kendall, C.G.St.C. 2003. Holocene coastal evaporites of the southern Arabian Gulf and their ancient analogues. Earth Science Reviews, vol. 61, 191-243, Elsevier. A.S. Alsharhan at Faculty of Science, United Arab Emirates University, PO Box 17551, Al-Ain, United Arab Emirates. C.G.St.C Kendal at Department of Geological Sciences, University of South Carolina, Columbia, SC 29208, USA.
This is a key paper on the Arabian Gulf evaporites and othere coastal sediments.
Abstract: The Holocene sediments of the coast of the United Arab Emirates in the southeastern Arabian Gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates, evaporites and siliciclastics throughout the geologic record. This paper is intended as a convenient single source for the description of sediments of this region, providing information on how to reach the classic localities and some of the analogs. The Holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide. The sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud, with these latter fine sediments increasing as the water deepens. The pelecypod-rich sediments also collect east of Abu Dhabi Island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons. West of Abu Dhabi Island the shallow water margin is the site of coral reefs and coralgal sands, whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands. Grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common. They are particularly common on the less protected shallow water margins of the lagoons west of Abu Dhabi Island. Pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern Abu Dhabi. Lining the inner shores of the protected lagoons of Abu Dhabi and on other islands to the west are cyano-bacterial mats and mangrove swamps. Landward of these, a prograding north facing shoreline is formed by supratidal salt flats (sabkhas), in which evaporite minerals are accumulating.
This paper describes the localities associated with (1) the mangrove swamps of the west side of the Al Dhabaiya peninsula;
(2) the indurated cemented carbonate crusts, cyanobacterial flats and sabkha evaporites on the shore of the Khor al Bazam south of Qanatir Island;
(3) the reef and oolitic sand flats on the coast just east of Jebel Dhana; and (4) the marine travertine and aragonite coats associated with the beach sediments in a small bay south of Jebel Dhana; and (5) the Sabkha Mutti between Jebel Barakah and Al Sila.
Similar sedimentological associations of carbonate and evaporites to those of the Holocene of the United Arab Emirates are to be found in the Tertiary and Mesozoic sedimentary rocks of the immediate subsurface in the Arabian Gulf. Other analogs to this setting include the Paleozoic carbonates of the western USA, Europe, and Asia, Mesozoic carbonates of the Gulf of Mexico, Europe, and Middle East and Tertiary sedimentary rocks in the Middle East. [end of Abstract].

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Alsharhan, A.S., Rizk, Z.A., Nairn, A.E.M., Bakhit, D.W. and Alhajari, S.A. 2001. Hydrogeology of an Arid Region: The Arabian Gulf and Adjoining Areas. Elsevier Science. Webpage information, including a summary of contents, and price.

[See also: Kendall and Alsharan (2011), Quaternary Carbonate and Evaporite Sedimentary Facies and their Ancient Analogues.]

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Anonymous , 1950. Development of the Dukhan Field, Qatar. Petroleum Engineer USA, 22, No.5, pp. B37-B42.
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Al-Yousef , M. 2003. Mineralogy, Geochemistry and Origin of Quaternary Sabkhas in the Qatar Peninsula, Arabian Gulf. Unpublished Ph.D. Thesis, School of Ocean and Earth Sciences, Faculty of Science, Southampton University. By Mariam Al-Yousef of Qatar University.
Abstract:
This thesis represents the first comprehensive study of Holocene sabkhas in Qatar. It presents detailed analysis of surface morphology~ recent evaporite and clastic sediments, and ground water nature and flow, for two large sabkhas: the inland Dukhan Sabkha and the coastal. Umm Said Sabkha. The fieldwork involved the taking of shallow pit and core samples, as well as brine samples from various locations within the sabkhas. In addition, sand dune samples were obtained from selected locations within and between the two sabkhas. Laboratory analyses of the mineralogy and geochemistry of the sediments included: hand specimen study, smear slide and thin section petrography, XRD, XRF, organic carbon and SEM analyses. Chemical analyses of brines were also undertaken.
The dominant sediment facies in both sabkhas are sands with variable amounts of evaporite precipitates. Of secondary importance are sandy silts, muds and algal/microbial mat deposits. Most of the evaporites occur within these detrital facies. The surface is covered with a firm duricrust of halite and gypsum. A large hypersaline lake covers part of the northeastern sector of Dukhan Sabkha. Evaporite minerals present in the sabkhas are gypsum, halite, anhydrite and a small amount of bassanite. Carbonate minerals are dolomite, calcite, Mg-calcite and aragonite. Siliciclastic minerals are quartz, K-feldspars and plagioclase, with minor heavy minerals and clays. The major oxides found in sediment samples throughout are Si02, CaO, SO3, MgO and A2O3. Of trace elements: Sr, Cr, Ba and Zr, V, Rb and Ni are high in comparison with other trace elements.
The relative abundance of gypsum and anhydrite is greater in Dukhan Sabkha than in Umm Said Sabkha, whereas halite is more abundant in Umm Said Sabkha. These differences relate primarily to the greater salinity of Umm Said Sabkha brines. The relative distribution of gypsum and halite within the upper meter of sediment is influenced both by grain size and marine flooding. The sandier sediments of Umm Said Sabkha tend to have gypsum above halite, whereas the reverse is true of the generally finer-grained Dukhan Sabkha. Anhydrite nodules are most common in the uppermost capillary zone in the salt lake area, where they are formed as a result of gypsum dehydration. Minor authigenic dolomite also occurs in this area because of high salinities and a high Mg2+:Ca2+ ratio. Elsewhere, the dolomite is of detrital origin. Clay minerals are present only in small quantities in both sabkhas, with palygorskite as the dominant clay, followed by chlorite and illite. Palygorskite is believed to be at least partly authigenic in origin. whereas the other clays are detrital. Organic carbon is only presenl in small amounts (mean 0.06-0.14%), except in few samples from the algal/microbial mats.
Gypsum crystal habits in Dukhan and Umm Said Sabkha sediments are acicular, lenticular and sublenticular, intergrown sublenticular, prismatic, pyramidal. elliptical and semielliptical. and pseudo-tetragonal shapes. Fine gypsum crystals in Dukhan Sabkha sediments are more abundant than in Umm Said Sabkha. Lenticular and sublenticular habits are dominant in Dukhan Sabkha, while prismatic crystals are dominant in Urnm Said Sabkha. The generally finer grain size of sediments in Dukhan Sabkha results in the greater variety of crystal habits observed than in Umm Said Sabkha. The crystals of both sabkhas are euhedral, simple and tabular on (010), and the cleavage (010) is very good on the crystal surface.
Most of the detrital sands throughout both sabkhas, in sand dunes across parts of the sabkha surface, as well as in other parts of Qatar, have been derived primarily as windblown sediments from an Arabian Peninsula source. Quartz sands are dominant. Carbonate minerals include calcite and dolomite. The percentage of gypsum in sand dunes in the western part of Qatar is high, whilst it is lower elsewhere. No halite is found in sand dune samples. The heavy minerals present in the sand dunes and in the surface sand from within the sabkhas are very similar. Opaque and semi-opaque grains are dominant, followed by abundant garnet, common epidote, tourmaline, hornblende, zircon and pyroxene, and a range of other minor minerals. Transport is believed to have taken place across the Gulf of Salwa from the Arabian Peninsula during the last sea-level lowstand (prior to 7-8000y BP). This would suggest that the dominant wind direction in the last glacial period was rather more northerly than the present northwesterly winds.
The sources of groundwater in Dukhan Sabkha are complex and mixed. They include: (a) fresh groundwater, particularly from the Rus and Umm Er Raduma aquifers in the north, which are above the level of Dukhan Sabkha; (b) seawaler infiltrating from the north and/or west and (c) runoff water during rainy periods. In Umm Said Sabkha. seawater forms the main source for groundwater by marine flooding and seepage reflux. There is no major barrier between sea and sabkha so that regular flooding occurs during each high tide, extending still further inland across the sabkha during exceptionally high tides and storm conditions. Freshwater provides a more minor secondary source from land aquifers and rainwater. The pH of brines in both sabkhas averages 6.8. The mean salinity of Umm Said Sabkha is higher than that of Dukhan Sabkha (mean Total Dissolved Solids 205 ppt and 113 ppt respectively).
In summary, Dukhan Sabkha is here presented as a good type example of an inland siliclastic sabkha. The topographic depression in which it occurs formed in several stages as a result of tectonic folding followed by karstic dissolution of underlying gypsum and carbonate deposits. This depression, which included one or more large inland lakes that formed sometime during the Pleistocene, was progressively infilled by detrital sand, silt and clay. Gradually Dukhan Sabkha formed and further built upwards as evaporite deposits were precipitated within the siliciclastic sediments; deposition is now kept in balance by wind deflation. The nature and distribution of sediment facies and mineralogy, the influence of climate, winds and regional setting. together with the ground water source and movement, and the brine geochemistry, as documented in this study. can be used to construct a new facies-environmental model for this type of sabkha worldwide. This is considered more appropriate than the standard model that exists for a prograding coastal sabkha with carbonate affinities. Umm Said Sabkha is more typical of a prograding coastal sabkha, although its principal difference from existing models is the dominance of siliciclastic sands of wind blown origin.
Dukhan Sabkha is seen to be increasing in size because of the death of large number of halophytes, especially in marginal zones. The margin of the sabkha has clearly moved a few meters outwards in historical times, leaving a zone of old dead halophytes. This is partly the result of increased salinity of the groundwater as a result of aquifer draw down due to excessive pumping for human use. This progressive saIinization is leading to sabkharization in Qatar. Umm Said Sabkha is also increasing in size. This is a result of seaward progradation of windblown sands, so that the increase in area is at the expense of the marine environment rather than the land.
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An Zen , E. 1965. Solubility measurements in the system CaS04, NaCl, H20 at 35°, 50° and 70° C and one atmosphere pressure. Journal of Sedimentary Petrology, vol. 6, p. 124-164.

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Bernier , P., Dalongeville,R.,Dupuis, B. and de Medwwecki,V. 1995. Holocene shoreline variations in the Persian Gulf: example of the Umm Al Qowain Lagoon, U.A.E. Quaternary International, v. 29-30, p. 95-103.
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Brankamp , R.A. and Ramirez, L.F. 1961. Geologic map of the Central Persian Gulf Quadrangle. Kingdom of Saudi Arabia. Map 1-209A. U.S. Geological Survey.
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Bush, P.R. 1970. Chloride-rich brines from sabkha sediments and their possible role in ore formation. Transactions of the Institute of Mining and Metallurgy, B, 79, B135-B144.

Bush, P.R. 1973. Some aspects of the diagenetic history of the sabkha in Abu Dhabi, Persian Gulf. Pp. 395-408 in Purser, B.H. (editor). The Persian Gulf. Springer Verlag, Berlin.
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Butler , G.P. 1969. Modern evaporite deposition and geochemistry of coexisting brines, the sabkha, Trucial Coast, Arabian Gulf. Journal of Sedimentary Petrology, vol. 39, no 1, p. 70-89.

Butler, G.P. 1970. Holocene gypsum and anhydrite of the Abu Dhabi Sabkha, Trucial Coast: an alternative explanation of origin. 3rd Symposium on Salt, Northern Ohio Geological Society, Cleveland, Ohio, 120-152.

Butler, G.P. 1973. Strontium geochemistry of modern and ancient calcium sulphate minerals. Pp. 423-453 in: Purser, B.H. (editor). The Persian Gulf. Springer Verlag, Berlin.

Butler, G.P., Kendall, C.G.St.C., Kinsman, D.J.J., Shearman, D.J. and Skipwith, A.d'E. 1964. Recent anhydrite from the Trucial Coast of the Arabian Gulf. Geological Society of London, Circular, 120, p.3.
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Cavelier , C. 1970. Geological Description of the Qatar Peninsula (Arabian Gulf). Department of Petroleum Affairs, Government of Qatar. B.R.G.M. (Bureau de Recherches Geologique et Minieres) 39pp. Explanation of the 1:100,000 geological maps of Qatar. By Claude Cavelier, Abdullah Salatt and Yves Heuze.
Example extract (p. 3):
"1 - General Geographic Situation
The Qatar peninsula covers some 10,000 km 2. It constitutes the eastern appendix to the Arabian peninsula crossed by the 25th parallel, and jutting northwards into the central zone of the Arabian Gulf.
The independent Arab state of Qatar is a Sheikdom with about 100,000 inhabitants, most of whom live in Doha, the capital. Qatar governs the offshore islands of Halul, Shra Auh, and Las Hat, of which only the first is inhabited.
Both geographically and geologically, Qatar is a quite distinct entity, the political boundaries of which are also natural ones. To thc north, west and east, the borders with Saudi Arabia, Bahrain Islands, Iran and Abu Dhabi are maritime ones. To the south, Qatar is separated from Saudi Arabia and Trucial Sheikdom of Abu Dhabi by an almost continuous belt of salt flats which, in recent times, were still marine.
Geologically, Qatar may be defined as a wide anticlinal dome gently warped and slightly folded. The general roughly elliptic configuration, with north-south main axis, is at present underlined by underlined by a wide spread outcrops of Eocene rocks, raised above younger Miocene deposits which surround them.
Several excellent works wcre published about the different gcographical aspects of Qatar by Melamid (1953) - political geography -, Johnstone and Wilkinson (1960) - history of discovery, tribes and population, glossary of arabic local topographic words - Meigs (1966) - general geographical description -. But the most complete and recent work is the book headed "Qatar 1968", published by the Government.

2. - The North of Qatar
Traditionally, Qatar is classified by geographers among desert countries. The southern half is sparsely populated but the northern region, especially the NE, is comparatively populated and agricultural development has commenced. The population is sedentary for the most part; relatively abundant water is extracted from generally shallow well; the constantly developing road network and the numerous tracks in good condition are quite frquented. In fact, it is an arid region, for there, as over the whole qatari country, the tolal volume of rainfall rainfall - essentially that of winter - is quite low.
North of the road from Doha to Dukhan, the ground is quite flat and pebbly, showing often extensive, hardly marked depressions, in which sills and muds accumulated , carrying natural pasture, in winter,on which graze camels, sheep, goats and oxen. Agriculture is constantly improving: orchards and kitchen-gardens, but also cereals (rye). Fishing is still carried out in an artisanal way.
The villages are rather numerous inland, but the small harbours along the shore-line are being deserted; the main city, however, is Khor on the eastern const.
Bctween the Doha-Dukhan and Doha-Umm Bab roads, the ground becomes more contrasted. The plateau is essentially rocky and uneven especially to the west. The depressions are generally deeper and sharper; their soil is essentially silty and muddy, but small accumulations of eolian sand, held by trees, occur especially to the west. The wells, located in important depressions, are still numerous and deeper.
To the west, along the Salwah Gulf, the rocky massive of Djebel Dukhon carries strongly marked depressions where the accumulations of eolian sand are considerable. Two important centres are implanted there: Dukhan, with the Qatar Petroleum Company (Q.P.C.) plant and Umm Bab with its cement factory. The road network which connects the numerous oil drill holes exploited in this area since 1949, is broadly developed, but generally in bad condition.
Footnote: (l) The oral tradition which reports that Qatar was formerly an Island separated from the Saudi province of Al Hasa is practically confirmed by geology. In particular by the discovery of extensive deposits of calcareous sands with a mollusc fauna comparahle to the present in the sebkha located South of Sauda Nathil."
[continues]

Cavelier, C., Salatt, A. and Heuze, Y. 1970. - Qatar Geological map. 1/100,000.
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Chowns , T.M. and Elkins, J.E. 1974. The origin of quartz geodes and cauliflower cherts through the silicification of anhydrite nodules. Journal of Sedimentary Petrology, vol. 44, No. 3, pp. 885-903.
Abstract: Quartz geodes from the dolostones of the Fort Payne and Warsaw" formations near Woodbury, Tennessee have proved to be pseudomorphs after early diagenetic anhydrite nodules. Their lithological association suggests that the anhxdrite developed in an arid tidal-flat environment by a process similar to that currently operating in the sabkhas of the Persian Gulf. Silicification took place prior to compaction and lithification of the sediments, the most likely source of silica solutions being the abundant sponge spicules which characterize the peritidal dolostones. Similar geodes from other Mississippian localities share the same lithological association and mode of origin. They help to define a recurrent sabkha facies and serve as important shoreline. indicators which may be used in the reconstruction of regional patterns of marine transgression and regression.
[These nodules have replaced nodules of anhydrite like those of the Dukhan Sabkha]
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Clarke, M.W.H. and Keij, A.J. 1973. By M.W. Hughes Clark and A.J. Keij. Organisms as producers of carbonate sediment and indicators of environment in the southern Persian Gulf. Pp. 33-56 in: Purser, B.H. (Editor) 1973. The Persian Gulf: Holocene Carbonate Sedimentation and Diagenesis in a Shallow Epicontinental Sea.. Springer-Verlag, Berlin, Heidelberg, New York. 471pp.
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Cody, R.D. 1979. Lenticular gypsum: occurrence in nature, an experimental determination of effects of soluble green plant material on its formation. Journal of Sedimentary Petrology, vol. 43, pp. 998-1011.
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Cook , J.P. 1973. Supratidal environment and geochemistry of some Recent dolomite concretions, Broad Sound, Queensland, Australia. Journal of Sedimentary Petrology, vol. 43, 998-1011.
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Cooke , R.U. and Warren, A. 1973. Geomorphology in Deserts. (Book). B.T. Batsford Ltd., 374 pp.
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Cosgrove , M.E. 1972. The Geochemistry of the Red Beds of South-West England including the Permian Volcanics. Ph.D. Thesis, Southampton University. 136pp.
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Curtis , R., Evans, G., Kinsman, D.J.J. and Shearman, D.J. 1963. Association of dolomite and anhydrite in Recent sediments of the Persian Gulf. Nature, London, 197, 697-680.

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Dean , W.E. 1978. Trace and minor elements in evaporites: in: Dean, W.E. and Schreiber, B.C. (editors). Marine Evaporites. SEPM short course No. 4., Oklahoma City, pp. 86-104.

De Cosson , A. 1935. Mareotis, being a short account of the History and Ancient Monuments of the North-Western Desert of Egypt and of Lake Mareotis. London, Country Life Ltd., 219pp. Historic information on the Lake Maryut, Alexandria to El Alamein area, west of the Nile Delta, northern Egypt.
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Durand , J.H. 1959. Les sols rouge et les croutes en Algerie. Service des Etudes Scientifiques, Algeria, Etude Generale, No.7, 188pp.

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Eardley, A.J. and Stringham, B. 1952. Selenite crystals in clays of the Great Salt Lake. Journal of Sedimentary Petrology, vol. 22, pp. 234-338. [gypsum crystals]. [Stringham - Bronson Stringham].
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El Khoriby , E.M. 2005. Origin of the gypsum-rich silica nodules, Moghra Formation, Northwest Qattara depression, Western Desert, Egypt. Sedimentary Geology, 177, 41-45. Abstract: Gypsum rich-silica nodules appear in two shale horizons of the Moghra Formation (early Miocene) northwestern Qattara Depression, Western Desert, Egypt. These nodules are gray to milky white in colour, mostly botroidal and rose-like in shape and range in diameter from 2 to 7.5 cm. The silica nodule-bearing shale is composed mainly of smectite with a little minor kaolinite. The silica nodules consist mainly of quartz and are composed of gypsum-free matrix and gypsum-rich megacrystalline quartz. The matrix consists of microflamboyant quartz (less than 36 µm in diameter) and chalcedony. The megacrystalline quartz occurs as lenticular and prismatic forms (length: 90–250 µm; width: 30–90 µm). The microprobe, petrographic and SEM examinations confirmed the occurrence of gypsum relics (diameter; 2–16 µm) within the megacrystalline quartz. The chalcedony and mosaic microcrystalline quartz occurs as pore-lining and pore-filling cements. The structure of the silica nodules begins with quartzine in its outer rim, then gypsum-free microcrystalline quartz in the middle part and ends with gypsum-rich lenticular to prismatic megaquartz in the center. Field study, petrographic examination and microprobe analysis reveal that the silica nodules were formed by silicification of precursor gypsum nodules deposited in a marginal sabkha environment under an arid climate. The silicification selectively affected the gypsum nodules rather than the surrounding shale and occurred both through gypsum replacement and void filling. Transformation of isopachous chalcedony into mosaic microcrystalline quartz also occurred. The texture of the silica minerals reflects the different physico-chemical conditions under which they crystallized. Spherical nodules grew chiefly by the diffusive supply of the silica, and elongated ones grew by pore water advection. The integrated effect of climate, pH, salinity, crack systems within the sediment and oscillation in the groundwater level and its chemical composition contributed to the formation of the nodules.
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El-Shazley , E.M., Abdel-Hady, M.A., El-Ghawaby, M.A., El-Khawasik, S.M., El-Shazly, M.M. and Sanad, S. 1975. Geologic interpretation of Landsat-satellite images from west Nile Delta area, Egypt. The Remote Sensing Project, Academy of Scientific Research and Technology, Cairo, 38p.

El-Shazley, M.M. 1964. Geology, pedology and hydrogeology of Mersa Matruh area. (Egypt) Ph.D. Thesis, Cairo University.

El Wakeel , S.K. 1964. Recent bottom sediments from the neighbourhood of Alexandria, Egypt. Marine Geology, vol. 2, pp. 137-146.

El Wakeel, S.K., Abdou, H.F. and Wahby, S.D. 1970. Foraminifera from bottom sediments of Lake Maryut and Lake Manzalah, Egypt. Bulletin of the Institute of Oceanography and Fish, Egypt. vol. 1, pp. 429-448.

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Evans, G. 1965. The recent sedimentary facies of the Persian Gulf region. Philosophical Transactions of the Royal Society, London, Series A, vol. 259, No. 1099, pp. 291-298. By Professor Graham Evans.

Evans, G. and Bush, P. 1969. Some oceanographical and sedimentological observations on a Persian Gulf lagoon. Mem. Simp. Intern. Lagunas Costeras. UNAM - UNESCO, Mexico, pp. 155-170.

Evans, G. and Kirkham, A. 2002. Part 1: Distribution of sabkhat within the Arabian Peninsula and the adjacent countries. The Abu Dhabi Sabkha. pp. 7-20 in: Barth and Boer (editors). Book: Sabkha Ecosystems, 2002. Kluwer Academic Publishers, Printed in the Netherlands.
Abstract:
The coastal plain - the sabkha - of Abu Dhabi developed by drowning of the outer parts of the deserts of Arabia during the Flandrian transgression. Subsequent deposition and progradation of an inner lagoonal shoreline protected by a chain of barrier islands, together with deflation of the adjacent desert dunefields down to the level of the water table has produced a relatively flat coastal plain. Evaporation and complex reaction between the sediment and the highly saline groundwater has produced a complex association of evaporitic minerals. Differences in elevation of microbial deposits developed and buried during the coastal progradation and the present day contemporary microbial mat suggest modem changes in the contemporary sea level are possibly recorded. This suggests that the low altitude of the present sabkha plain makes this coastal area very prone to increased inundation caused by contemporary accelerated rise in sea level and such changes need to be carefully considered during any future economic development of the coastal zone.

Evans, G., Bush, P.R. and Temple, P.H. 1980. The coastal plain and offshore islands. In: Doornkamp, J.C., Brundsden, D. and Jones, K.C. (Eds.), Geology, Geomorphology and Pedology of Bahrain. Geo Abstracts Ltd., Norwich, UK, p. 269-327.

Evans, G., Kendall, C.G., Kinsman, D.J.J., Shearman, D.J. and Skipwith, P. A. d'E. 1964. In discussion of I.M. West, 1964. Proceedings of Yorkshire Geological Society, 34 (3), p. 15.

Evans, G., Kendall, C.G.S.C. and Skipwith, A. d'E. 1964. Origin of the coastal flats, the sabkha, of the Trucial Coast, Persian Gulf. Nature, London, 202, 759-761.

Evans, G., Kirkham, A, and Carter, R.A. 2002. Quaternary Development of the United Arab Emirates Coast: New Evidence from Marawah Island, Abu Dhabi. GeoArabia, Vol. 7, No. 3, 441-457. By Graham Evans, Southampton University, Anthony Kirkham, Technoguide and Robert A. Carter, University College London
Abstract: Marawah is one of a chain of barrier islands off the coast of Abu Dhabi that separates the Khor Al Bazm lagoon from the open waters of the Arabian Gulf. The island consists of several rocky cores of Pleistocene limestone linked by areas of unconsolidated Holocene carbonates. It has the most complete Quaternary outcrop sequence in the region and the lowest exposed unit, a coralline limestone, had not been recorded previously. The Pleistocene deposits accumulated partly in a shallow-marine environment and partly under eolian conditions. The Marawah sections have revealed new data about the history of the southern Gulf in the late Pleistocene, a time interval of which little was known. The survey has shown that there were periods when sea level was close to present-day levels and other times when it was approximately 4 to 5 m higher than today. A phase of deflation and the development of a field of eolian sand dunes separated these two sealevel highstands. The unconsolidated sediments have accumulated around the Pleistocene rock cores since about 4,500 years BP to give the island its present form. Accumulation occurred because of wave action driven by the northwesterly 'Shamal' winds during periods of slightly falling or almost stationary sea level.

Evans, G., Murray, J.W., Biggs, H.E.J., Bate, R. and Bush, P.R. 1973. The oceanography, ecology, sedimentology and geomorphology of parts of the Trucial Coast barrier island complex, Persian Gulf. In: Purser, R.H. (Ed.), The Persian Gulf, Holocene Carbonate Sedimentation and Diagenesis in a Shallow Epicontinental Sea. Springer Verlag, Berlin, p. 233-277.

Evans, G., Schmidt, V., Bush, P. and Nelson, H. 1969. Stratigraphy and geologic history of the sabkha, Abu Dhabi, Persian Gulf. Sedimentology, 12, 145-159.
The sabkha of Abu Dhabi was formed during the past 7,000 years by wind erosion of pre-existing dunes and progradation of subaqueous, intertidal, and supratidal carbonate sediments. Marine transgression began in this area about 7,000 years ago and reached an apparent high about 1 m above its present level somewhat prior to 4,000 years B.P. Since then progradation of intertidal and supratidal sediments has taken place; this began 3,750 years ago. Arid conditions over the sabkha have produced large amounts of gypsum and anhydrite and lesser amounts of dolomite, magnesite, celestite and halite.

Evans, G. and Shearman, D.J. 1964. Recent celestite from the sediments of the Trucial Coast of the Persian Gulf. Nature, London, 202, 385-386.

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Goudie , A.S. and Cook, R.U. 1980. Aeolian landforms and deposits. In: Doornkamp, J.C., Brundsden, D. and Jones, K.C. (Eds.), Geology, Geomorphology and Pedology of Bahrain. Geo Abstracts Ltd., Norwich, UK, p. 269-327.

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Houbolt , J.J.H.C. 1957. Surface sediments of the Persian Gulf near the Qatar Peninsula. (Published) Thesis, Leiden, Monton and Co., Den Haag, Editor.

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Illing , L.V., Wells, A.J. and Taylor, J.C.M. 1965. Penecontemporaneous dolomite in the Persian Gulf. In, Pray, L.C. and Murray, R.C. (Eds.), Society of Economic Palaeontologists and Mineralogists Special Publication, 13, p. 89-111.

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Jauzein , A. 1972. Les donnees sur le systeme CaS0 ₄ , H ₂ 0 et leurs implications geologiques. Rev. Geogr.
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Jameson , J., Puls, D.D. and Kozar, M.G. 2009. Holocene sabkha and coastal systems of Qatar: process models for the interpretation of ancient Arabian Plate carbonate evaporite reservoirs. International Petroleum Technology Conference - 2009 . IPTC 13679. By Jeremy Jameson, David D. Puls (ExxonMobil Qatar Inc), and Michael G. Kozar (ExxonMobil Exploration Company). (also pdf). See also Puls et al. (2009), IPTC 13629 on Dukhan Sabkha.
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Johnstone , T.M. and Wilkinson, J.C. 1960. Some geographical aspects of Qatar. The Geographical Journal,126, 442-450.

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Kassler , P. 1973. The Structural and Geomorphic Evolution of the Persian Gulf. In: Purser, R.H. (Ed.), The Persian Gulf, Holocene Carbonate Sedimentation and Diagenesis in a Shallow Epicontinental Sea. Springer Verlag, Berlin, p. 11-32.
Abstract: The origin of the present-day morphology of the Persian Gulf has been studied and is summarized in figure 3. The Gulf is a tectonic basin of late Pliocene to Pleistocene age, whose morphology is greatly influenced by the tectonic style. The topography of Iran and the Iranian coastal islands is controlled by the intense folding of the Zagros orogeny, on NW-SE to E-W trends. The much more subdued relief of the Arabian side is the result of gentler tectonic movements: Plio-Pleistocene folding, faulting and salt diapirism, superimposed on older, predominantly northsouth-trending growth structures ("Arabian folds"). There is evidence over much of the Gulf of interference between Arabian and Zagros folds. This tectonically controlled morphologic pattern was subdued by sedimentation of Pleistocene limestones, but locally rejuvenated by Quarternary tectonic adjustments. The sea level fell by as much as 120 m during the Pleistocene, emptying the Gulf; river valleys were eroded down the slopes. The sea then cut a series of platforms, at its level of maximum retreat and at times of relative standstill during the post-glacial rise. However, in spite of these Pleistocene physiographic modifications, the underlying tectonic control of morphology is still apparent, and there is a partial correlation between bathymetric and structural highs and lows.
The topography controls the type and the thickness of the marine sediments. Sediment type is largely a function of the biological communities which give rise to skeletal material; these vary in vary in character from shoals to depressions. Sediment thickness is shown by sparker records to be least on topographic highs, and greatest in depressions.
The Recent unconsolidated sediments are the product of the post-glacial Flandrian transgression, which, according to Fairbridge (1961), began about 18 000 years B.P. and reached its present level about 5000 years B.P. These sediments are expected eventually to smooth out the pre-Recent topography by filling up the depressions and extending over the highs. The thickest Recent sediments are found in the Gulf axis.
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Kendall , C.G.St.C. and Skipwith, A. d'E. 1969. Geomorphology of a recent shallow water carbonate province: Khor Al Bazm, Trucial Coast, Southwest Persian Gulf. Geological Society of America Bulletin, v. 80, p. 865-892.

Kendall, C,G.St.C. and Alsharhan, A,S. (Editors) 2011. Quaternary Carbonate and Evaporite Sedimentary Facies and Their Ancient Analogues: A Tribute to Douglas James Shearman. Special Publication No. 43 of the IAS, International Association of Sedimentologists. John Wiley and Sons, 25th January 2011, 495pp. This volume commemorates the eclectic research of Douglas James Shearman into evaporites, which was initiated by his studies of the prograding UAE coastal sabkhas or salt flats that incorporate evaporite minerals which displace and replace earlier carbonate sediments. His subsequent proselytization of the study of ancient evaporites in sedimentary sections all over the world led to fundamental advances in our understanding of arid zone carbononate sedimentology. [continues]

[This large and important book is not cheap; it costs beteen about 58 to 75 pounds stirling at various book sellers, in late 2011. Extracts can be seen online at Google Books - Kendall and Alsharhan.].

...

See also: Alsharhan, A.S. and Kendall, C.G.St.C. 2003. Holocene coastal evaporites of the southern Arabian Gulf and their ancient analogues. Earth Science Reviews, vol. 61, 191-243. (and other paper by Alsharhan and Kendall).

...

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Kenig , F., Huc, A.Y., Purser, B.H. and Oudin, J.-L. 1990. Sedimentation, distribution and diagenesis of organic matter in a recent carbonate environment, Abu Dhabi, U.A.E. Organic Geochemistry, v. 16, p. 735-747.

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Khalaf, F., Literathy, V. and Anderlini, V. 1982. Vanadium as a tracer of oil pollution in the sediments of Kuwait. Hydrobiologia, Vol. 91-92, Number 1, pp. 147-154.
Abstract:
Vanadium is important as an indicator of oil pollution since oil is one of the main contributors of vanadium to the environment and because most crude oils contain relatively high concentrations of vanadium (30.6 ± 14.3 mg kg-1 were measured in nine different Kuwait crudes). If oil has settled to the bottom and biodegradation has taken place, it is obvious that enrichment of vanadium in the sediment may be observed.
More than 200 sampling sites were selected in the coastal zone of Kuwait and sediment samples were analyzed for grain size distribution, CaC03 content, heavy metals and TOC. The analytical results were normalized by taking into account the natural background levels of vanadium in different sediment fractions.
After evaluation of the results, vanadium enrichments of as much as 10 to 77 mg kg-1 were found at 15 sampling locations and of 1 to 10 mg kg-1 at many others. The areas of vanadium enrichment in the sediments were located 3–5 km from the shoreline in the areas of wastewater discharges, near oil loading piers and in the shipping 'channels'. There was no correlation between vanadium and TOC indicating that biodegradation of oils had taken place. However, high TOC values in the sediments were determined in the near shore sediments around the outlets.

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Kinsman , D.J.J. 1965. Gypsum and anhydrite of Recent age, Trucial Coast, Persian Gulf. In: Rau, L.A. (Editor), Second Symposium on Salt, 1, North Ohio Geological Society, Cleveland Ohio, pp. 302-326.

Kinsman, D.J.J. 1965. Dolomitization and evaporite development, including anhydrite in lagoonal sediments, Persian Gulf. Geological Society America Special Papers, 82, 108-109.
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Kirkham , A. 1997. Shoreline evolution, aeolian deflation and anhydrite distribution of the Holocene, Abu Dhabi. GeoArabia, v. 2, no. 4, p. 403-416.

Kirkham, A. 1998a. Pleistocene carbonate seif dunes and their role in the development of complex past and present coastlines of the U.A.E. GeoArabia, v. 3, no. 1, p. 19-32.

Kirkham, A. 1998b. A Quaternary proximal foreland ramp and its continental fringe, Arabian Gulf, U.A.E. In: V.P. Wright, V.P. and Burchette, T.P. (Eds.), Carbonate Ramps. Geological Society, London, Special Publication no. 149, p. 15-41.

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Lacroix, A. 1897. Le Gypse de Paris; et Les Mineraux qui L'Accompagnent. [The Gypsum of Paris; and the Minerals which Accompany it]. (Premiere contribution a la mineralogie du Bassin de Paris). Extrait des Nouvelles Archives du Museum, Tome IX. Paris, Masson et C., Editeurs. Libraire de L'Academie de Medecine. 120 Boulevard Saint Germain. pp. 201-296 + 15 plates. By Alfred Lacroix.
[This is a classic work, interesting and informative (and written entirely in French). The original version is preferable, of course, but a modern reprint is available from BiblioLife, LCC. This provides clear text, although the quality of the plates is not good. See also Lacroix, A. Mineralogie de la France.]

[Introduction - a loose translation (by me) of a small part, given as an example, follows: pp. 202-203:]

"In the Paris region gypsum is found in very different conditions, equally interesting from a mineralogical point of view, but also of equal importance from a geological point of view.
The Senonian (Upper Cretaceous) Chalk of Meudon has long been observed to have small crystals of gypsum and celestite. One can be sure that the gypsum is in large part the result of the reaction of the Chalk with the products of decomposition of pyrite.
At the base of the Eocene, the Plastic Clay (Sparnacian) is very rich in magnificent transparent crystals of gypsum. These are also attributed to the decomposition of pyrite and marcasite which has also given birth to numerous minerals (websterite, apatelite, siderose etc.).
A small quantity of secondary gypsum is found in the Miocene marls.
With the Middle Eocene, there appears a series of gypsiferous beds which have an origin quite different and which furnish not isolated crystals of gypsum at the surface of clays, by indeed continuous beds of gypsum; thus the Upper Eocene is of great importance both geologically and economically.
Since the end of the last century it has been known that the upper beds of the Calcaire Grossier (Upper Lutetian), designated under the name of caillasses, have curious pseudomorphs of gypsum, associated with crystals of quartz, of fluorite, and of calcite. Monsieur Munier-Chalmas has effectively used the boreholes in various parts of Paris and its surroundings, to show that the beds containing the pseudomorphs represent the strata containing beds of gypsum. They have persisted where a superficial cover has preserved them from superficial dissolution, accompanied by chemical phenomenon which will be discussed later. It seems to have been established now that the various gypsum beds of the Upper Lutetian, the same as a certain number of analogous beds in the Bartonian (Sands of Beauchamp, limestones of Saint-Ouen) have a lagoonal origin. It is the same not only for the Ludian gypsum which forms masses exploited in the Paris region, but also for that which is found as separate crystals or as continuous beds in the Lower Oligocene (the supra-gypsum marls, the green marls and the Stampian).

This hypothesis of vanished evaporites was formulated as early as 1780 by Pralon (Journal de Physique, p. 289) in a mineralogical description of Montmartre Hill, Paris, quite remarkable for that epoch. This hypothesis, adopted here, and theories on the mode of formation of the gypsum deposits and stratigraphic studies are discussed in numerous publications. These matters are not the objects of the present work and are, thus, excluded. This memoir is intended to shed light on the crystal habit of gypsum that occur in two different settings. One is direct evaporation of seawater in lagoons. The second is decomposition of pyrite and the reaction of ferrous sulphate on carbonate. In addition there are some observations on the habits which gypsum takes when deposited from water charged with calcium sulphate and circulating in gypsiferous beds after their deposition.
In each of three chapters there is a paragraph on minerals which accompany the gypsum and which have originated more or less at about the time of its deposition. I have also listed the gypsum beds which are discussed in this memoir, with an indication of their mineral content. The stratigraphic nomenclature is that of De Lapperent (1893) and Munier Chalmas (1890).
There follows a table listing Eocene and Oligocene strata with gypsum of primary depositional origin, and a table showing strata with secondary gypsum. (Gypsum has been precipitated in strata from the Upper Lutetian, through the Bartonian, Ludian of the Eocene; and then in Sannoisien and Stampian of the Oligocene. [Does its apparent absence in the Palaeocene and Lower Eocene suggest that the climate in the Paris region became semi-arid from the Middle Eocene onwards? In England minor evaporites occur only in the Upper Eocene, Priabonian, Bembridge Limestone]
[continues]

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Lambeck , K. 1996. Shoreline reconstructions for the Persian Gulf since the last glacial maximum. Earth and Planetary Science Letters, 142, p. 43-57.
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Lashhab, M. L. and West, I. M. 1992. Sedimentology and Geochemistry of the Jir Formation in Jabal al Jir and the Western Sirt Basin. Third Symposium on The Geology of Libya, held at Tripoli, September 27-30th 1987, vol. 5. Editor Salem, M.J. 1855-1869.

Abstract:
The Jir Formation of Eocene age, consists of gypsum, anhydrite, halite and dolomite. The thickest sequence is developed in the western Sirt basin in and adjacent to a major graben system. This originated in the Eocene but is parallel to the trend of the Miocene Red Sea rift. The type section of the Jir Formation is at Wadi Faras, in the Jabal al Jir area. This is a thin, basin margin exposure of porphyrotopic secondary gypsum with dolomite beds. In the subsurface of the Meulagh graben, the formation attains 1 km and consists of anhydrite and halite with dolomite. The evaporites at Wadi Faras are of shallow-water lagoonal and sabkha origin, with foraminifera-rich carbonates indicating periodic marine influx. Laminated anhydrite within the graben was probably formed in a large lagoon below wave-base. Halite was deposited in a closed salt-lake which occupied only the central part of the basin. Evaporite deposition ended in the late Eocene when marine water flooded the basin and brought in coccoliths and foraminifera. The dolomite of the Jir and the underlying Rawaghah and Bishimah Formation is similar. It is stochiometric, non-ferroan and with high Na content. Its composition and distribution indicate that the dolomite has been formed from Mg-rich brines of evaporitic origin. Diagenetic processes included the local accumulation of Sr2+ in the upper part of the evaporite sequence and the lower part of the overlying strata. Local concentrations of vanadium occur in goethite replacement of pyrite and these may have been formed by diagenetic reactions with vanadium porphyrins.

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Lashab, M.I., Daluob, H.S. and Saqer, N.H. 2004. Geological and geochemical studies on Recent sabkha of Karkurah, northeastern Libya. 7th International Conference on the Geology of the Arab World, Cairo University, Egypt, February, 2004. Pp. 1-10 with plates.
Abstract: The Karkurah salt-pan is regularly flooded by sea water from the adjacent Mediterranean Sea. It represents a back-barrier sabkha. The brine supplied the salt-pan by springs and seepage through the ridge from the sea. Sand and silt with halite deposits are the major component of the Karkurah Sabkha sediments. The sabkha around the salt-pan is a semi-vegetated with halophyte plants in nebkhahs. The major mineral as of all large evaporites, is halite. The other minerals revealed through X-ray diffraction (XRD) analysis are quartz, calcite, gypsum and clays. The salt crust consists mainly of NaCl (about 94.97%), while the presence of MgCl does not exceed 2.94%, KCl 0.39% and S0 ₃ does not exceed 5.25%. [end of abstract]

Lashhab, M.I., West, I.M. and El Manaai, M.A. 1999. Study of recent sediments at Zuwarah Salt Pan on the northwestern coast of Libya, formation of anhydrite. In: The First Earth Conference , Univ. of Ghar Yonis, Benghazi, Libya. 12pp. with three plates. (paper accepted, but not necessarily published).

Lashhab, M.I., West, I.M. and El Zarough, R. 2002. Origin and diagenesis of the evaporites in the Jir Formation, Jabal Waddan and Western Sirt Basin, Libya. 6th International Conference on the Geology of the Arab World, Cairo University, February 2002, pp. 623-632. (Written by Dr. Mokhtar Lashhab mainly on the basis of his thesis on this topic in 1992, and supervised by Ian West.)

Abstract:
The Eocene evaporites of the Jir Formation, consist of gypsum, anhydrite, halite, celestite with dolomite. The thickest sequence is developed in and adjacent to a major graben system in the western part of the Sirt Basin. The area of the Sirt Basin was open to the sea via the Sirt Gulf at the very beginning of the Eocene, and then became isolated lagoons, when the Dahra Ridge began to function as a platform or barrier bar with a lagoon to the southwest. The barrier permitted a regular influx of warm and sulphate enriched brines to maintain continuous evaporite precipitation. At the basin margin in the hills of the Jabal Waddan at Wadi Faras, the Jir Formation consists of at least 52m of secondary gypsum and dolomite. In the subsurface, in the Zalla Trough or Meulagh Graben, to the southeast, the formation comprises up to 1000 m of anhydrite and halite with dolomite. The evaporites at Wadi Faras are of shallow water lagoon and sabkha origin, with foraminifer-rich carbonates indicating the dominant marine conditions. In the Zalla Trough laminated anhydrite has been formed also in a shallow lagoon. Halite was deposited in a closed salt-lake in the central part of the basin. Celestite in the Jir Formation was formed by replacement of calcium sulphate.

INTRODUCTION
The area of study is located in the western part of the Sirt Basin, in central northern Libya (Fig. 1). The Jir Formation evaporites of Eocene age are extensively developed in the subsurface of the Zalla Trough (Meulagh Graben) in the western part of Sirt Basin and exposed at Jabal Waddan in the southeastern edge of Hun Graben (Fig. 1). During the Eocene Epoch, the palaeolatitude of the study area was between 15° and 20° N (Smith & Briden, 1977), and climate was thus probably characterized by semiarid conditions. In the Meulagh Graben, the Jir Formation is very thick and consists of anhydrite and halite with thin beds of dolomite. The evaporites of the surface and subsurface are clearly linked as one lithological unit (Lashhab & West, 1996). The mode of occurrence, rifting and depositional models and factors controlling evaporite precipitation are considered. Evaporites from the study area have been analyzed chemically, and the results used to infer the environments in which they were deposited. Trace element content can be used as a measure of the evaporation stage of the original solution, as once crystals are removed from the system there is increased segregation of trace elements either into the crystals or into the residual brine (Holser, 1979). The diagenetic minerals produced after evaporite precipitation and by the reaction between brines and sediments in the study area are similar to those of recent sabkha deposits which occur in the Abu Dhabi area (Bush, 1973), excluding the major beds of halite found in the Zalla Trough. Gypsum, celestite, anhydrite, halite and dolomite have been formed by evaporation and by brine-sediment interactions in the study area.

PETROGRAPHY AND GEOCHEMISTRY
The gypsum crystals are commonly subhedral; some are pseudomorphs after anhydrite. The crystals are well interlocked with irregular interfaces. A few irregular lenses of anhydrite occur in the Jir Formation in samples from the Wadi Faras type-section. This is an indication that the Jir Formation gypsum is secondary and is a near surface replacement of anhydrite. Most of the gypsum nodules in the Jir Formation at Wadi Faras are randomly aligned and surrounded by microcrystalline dolomite (plate 1A). The nodules are mostly small in size, ranging up to approximately 3 cm in length. Some of the gypsum nodules are composed of crystals exhibiting porphyrotopic and granotopic secondary gypsum with minor amounts of anhydrite laths. It is possible that primary gypsum nodules were converted into anhydrite by burial diagenesis and were later transformed into secondary gypsum. As erosion re-exposed the Jir Formation, rainwater and dew dissolved gypsum and reprecipitated it as the water evaporated to form gypcrete. [continues]
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Longhurst , H. 1959. Adventure in Oil: The Story of British Petroleum. Sidgwick and Jackson Ltd., London, 286 pp. By Henry Longhurst, with a Foreword by the Right Honorable Sir Winston Churchill.

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McDonald , G. J. F. 1953. Anhydrite-gypsum equilibrium relations. American Journal of Science, vol. 251, p. 884-898.
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Merritt, C.A. 1935. Gypsum crystals from Alfalfa County, Oklahoma. American Mineralogist, vol. 20, p. 674.
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Milliken , K. 1979. The silicified evaporite syndrome—two aspects of silicification history of former evaporite nodules from southern Kentucky and northern Tennessee. Journal of Sedimentary Petrology, 49 (1979), pp. 245–256
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Orti , F. Orti, Rosell, L., Salvany, J. and Ingles, M. 1997. Chert in continental evaporites of the Ebro and Calatayud basins (Spain): distribution and significance. In: A. Ruinos-Millan and M. Bustillo, Editors, Siliceous Rocks and Culture, Universidad de Granada (Spain), Monografica, Arte y Arqueologia vol. 42 (1997), pp. 78–89.
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Perthuisot, J-P. 1977. La sebkha de Doukhane (Qatar) et la transformation: gypse - anhydrite plus water. [The sabkha of Dukhan (Qatar) and the the transformation: gypsum to anhydrite plus water.] Bulletin de la Societe geologique de France, vol. 19, No. 5, 1145-1149. By Jean-Pierre Perthusiot.
Abstract: The gypsum to anhydrite transformation occurs at the present day in the Dukhan Sabkha of western Qatar. It begins within temperatures and salinity conditions clearly beyond the theoretical conditions at equilibrium, and this is because the reaction is endothermic. In addition, it is suggested that this reaction must be facilitated by the oxidising environment of the medium. [end of abstract]

[The text is in French; because this is a very useful paper I have provided an English translation of all the text - below.]

Comparison of the major ions in terms of milliequivalents for surface water of the sabkha and for that in borehole shows that Mg ²⁺ and SO ₄ ^2- are both noticeably low. This leads to comparison with the classic sabkha dolomitisation of the coasts of Arabian Gulf. Overall the origin of the salts precipitated in the basin remains hypothetical. Probably there was a mixed origin of both marine and continental brine sources.

The Profile of the Borehole:

A shallow borehole (or excavation?) was made at about 50 metres from the edge of the halite crust to a depth of almost 1.2 metres [Perthuisot's Fig 2 provides a schematic section diagram of this].

In the upper 10 cm the following succession (downward) was found:

1. A fine crust of halite of millimetre thickness.

2. A thin superficial reworked zone with a mixture of very fine quartz, some gypsum, some halite and some microcrystalline anhydrite.

3. A compact crust, 2 or 3 centimetres thick, essentially consisting of microcrystalline anhydrite forming very flattened lenticles of light colour. These were separated by streaks of dark anhydrite mixed with detrital matter (very fine quartz and clay). Locally there are some air bubbles.

4. Lenticular pockets of a mixture of water and microcrystalline anhydrite forming a soft whitish paste. It had the consistancy of chocolate mousse and with numerous bubbles. There were some crystals of gypsum present. [This may be the equivalent of the anhydrite nodules discussed below, but they are harder.]

5. Gypsum in yellowish millimetre-sized crystals. These are mostly as flattened lenticles [lenticular gypsum] with crystal faces not obvious. It may perhaps be recrystallised gypsum. Below the gypsum continues but there is a change of colour and it becomes more bluish. The water table at the time was about 10 centimetres down from the surface.

Interpretation:

The mixture - water plus anhydrite is found in pockets above the bed which is full of gypsum sediment. It is in a zone where water only occurs as a film [capillary?] on the surface of the gypsum crystals. The simplest explanation is that the lenticular pockets [equivalent of anhydrite nodules?] of anhydrite and water originated by the reaction:

gypsum -> anyhydrite + water

The distribution of the mixture as dispersed pockets results from the endothermic character of the reaction. This probably took place in temperature conditions much higher than equilibrium conditions and this could have been attained by reducing the temperature of the surrounding milieu.

Moreover, the many crystals of gypsum which exist in the whitish mixture are intact. This suggests that each crystal of gypsum remained in unaltered totality until an almost instant reaction of dehydration. Finally, the presence of the bubbles in the mixture is consistant with the imprisonment of gas which occupied the cavities between the intact gypsum crystals.

Also there exists in the upper part of the sediment profile a true "front of anhydritisation" which progressed towards the base.

The pockets of the mixture - water and anhydrite - progressively lose their water by evaporation and is incorporated in the anhydrite crust already formed.

The Conditions of Transformation

This takes place in the presence of water; the crystals of gypsum attacked by anhydritisation always occur in the humid capillary zone of the profile.
The composition of this capillary water is very similar to that of the water table, but having perhaps concentrations a little higher (see table).

The temperature of the groundwater was 24 degrees C on 31 st December, 1976. But the temperature of the ground would have attained much higher values in summer; meteorological instruments registered a soil temperature of 40 degrees C at the surface and 30 degrees C at 50 cm. depth. Butler (1969) reported some temperatures of more than 50 degrees C at the surface of the sabkha in the Trucial Coast (UAE).

Thus the conditions of temperature and salinity at the start of the reaction are clearly beyond the conditions of equilibrium. However, this reaction stops a certain time because of the lowering of the temperature and the dilution of the brine which it causes. Without doubt the lowering of the temperature and the winter rains contribute equally to this cessation.

There remains one irritating problem: it is the exclusive localisation, at least at present, of the anhydritisation of gypsum, in the conditions of the at the surface at the borders of the Arabian Gulf, even though there exist in other regions of the globe some conditions that are similar in temperature and salinity in the sabkhas of North Africa for example [there are traces of anhydrite in a coastal salt lake of Libya, but I am not aware of any significant quantities]. Now there is one marked difference between sahkhas of the two regions: most of the sahkha of North Africa have an environment that is extremely reducing, rich in organic matter and producing significant quantities of hydrogen sulphide. The sabkhas of the Arabian Gulf are in comparison much more oxygenated, lacking in odour and generally with light-coloured sediments. The intuitive hypothesis is that the transition from gypsum to anhydrite is improbable or at least more difficult to take place in a reducing medium in which S ^2- is the stable form of sulpher.

Thus the particular geochemical conditions of the region explain the localisation of the gypsum-anhydrite transition in the present-day environment of the Arabian Gulf. [end of main text]

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Powers , R.W., Ramirez, L.F., Redmond, C.D. and Elberg, E.L. Jr. 1966. Geology of the Arabian Peninsula. Sedimentary Geology of Saudi Arabia. U.S. Geol. Surv. Prof. Paper 560 D. V.S. Government Printing Office, Washington, 147 p.
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Puls , D.D., Jameson, J., Kozar, M., Hussain, A-A, LeBlanc, J. 2009. The Dukhan Sabkha: a modern analog for the Arab C carbonate reservoir, Dukhan Field, Qatar. By David D. Puls, Jeremy Jameson (ExxonMobil Qatar Inc), Mike Kozar, Al-Ansi Hussein and Jaques LeBlanc (Qatar Petroleum). International Petroleum Technology Conference - 2009. Held in Doha, Qatar, 7-9th December 2009. (also pdf). See also Jameson (2009) on sabkhas, same conference.
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Purser , B.H. (Editor) 1973. The Persian Gulf: Holocene Carbonate Sedimentation and Diagenesis in a Shallow Epicontinental Sea.. Springer-Verlag, Berlin, Heidelberg, New York. 471pp.

Purser, R.H. and Evans, G. 1973. Regional sedimentation along the Trucial Coast, SE Persian Gulf. In: Purser, R.H. (Ed.), The Persian Gulf, Holocene Carbonate Sedimentation and Diagenesis in a Shallow Epicontinental Sea. Springer Verlag, Berlin, p. 211-231.

Purser, B.H. and Seibold, E. 1973. The Principal Environmental Factors Influencing Holocene Sedimentation and Diagenesis in the Persian Gulf. In: Purser, R.H. (Ed.), The Persian Gulf, Holocene Carbonate Sedimentation and Diagenesis in a Shallow Epicontinental Sea. Springer Verlag, Berlin, p. 1-9. Abstract: The Persian Gulf is a marginal sea with an average depth of 35 m, and a maximum depth of 100 m near its narrow entrance. Its elongate bathymetric axis separates two major geological provinces - the stable Arabian Foreland and the unstable Iranian Fold Belt - which are reflected in the constrasting coastal and bathymetric morpho10gies of Arabia and Iran. The Persian Gulf has a gently inclined sea floor lacking "shelf edges" comparable with those of modern Caribbean carbonate provinces. The arid, sub-tropical climate with summer temperatures attaining 50° C, and frequent winds, stimulate the formation of evaporitic minerals and the delivery of aeo1ian dust to the basin. F1uviati1e influx is limited to the Tigris-EuphratesKarun delta and to the mountainous Iranian coast where terrigenous sediments contrast with the relatively pure carbonates forming in the shallow seas in front of the low deserts of Arabia. Excessive evaporation and partial isolation from the adjacent Indian Ocean provoke abnormal sa1inities throughout most of the basin, which attain a maximum of ca 700/00 in remote Arabian lagoons.Because the prevailing "shama1" wind blows down the axis of the gulf from the NW, most coastal environments are swept by waves and surface currents which favour the formation and dispersal of carbonate sands on the Arabian side and terrigenous material on the Iranian. Tidal currents influence sediment textures, even in the deepest parts of the gulf, while extensive rock bottoms influence the biota and skeletal composition of Ho10cene sediments. These are mixed with significant amounts of relict sediment, especially in the deeper parts of the basin.
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Sharma , V.K. 1986. Geomorphology: Earth Surface Processes and Forms. Tata McGraw-Hill Publishing Company Limited. New Delhi, 244 pp.
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Shearman , D.J. 1966. Origin of marine evaporites by diagenesis. Transactions of the Institution of Mining and Metallurgy, Section B, Applied Earth Science, vol. B75, 207-215. By the late Professor Douglas Shearman of Imperial College, London. (See also: Shearman, D.J. 1967. Report of Discussion of this paper in December 1966 at a General Meeting of the Institution of Mining and Metallurgy, published in 1977, Transactions of the Institution of Mining and Metallurgy, Section B, pp. B82-B86.) [This is an early classic and very original paper on the Abu Dhabi Sabkha, with a controversial theory of origin of the evaporites.]
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Shinn, E.A. 1969. Submarine lithification of Holocene carbonate sediments in the Persian Gulf. Sedimentology, 12, pp. 109-144.

Shinn, E.A. 1973. Sedimentary accretion along the leeward, SE coast of Qatar peninsula, Persian Gulf. Pp. 199-209 in: Purser, B.H. (Editor) 1973. The Persian Gulf: Holocene Carbonate Sedimentation and Diagenesis in a Shallow Epicontinental Sea. Springer-Verlag, Berlin, Heidelberg, New York. 471pp.
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Siedlecka A. , 1972 Length-slow chalcedony and relicts of sulphates—evidence of evaporitic environments in the Upper Carboniferous and Permian beds of Bear Island, Svalbard, Journal of Sedimentary Petrology, 42 (1972), pp. 812–816.

Siedlecka, A. 1976. Silicified Precambrian evaporite nodules from northern Norway: a preliminary report, Sedimentary Geology, 16, pp. 161–175.
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Smout , A.H. 1954. Lower Tertiary foraminifera of the Qatar Peninsula. British Museum (Natural History), London, IX + 96pp.
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Sugden ,W. 1963a. Some aspects of sedimentation in the Persian Gulf. Journal of Sedimentary Petrology, vol. 33, No.2, pp. 355-364.

Sugden, W. 1963b. The hydorology of the Persian Gulf and its significance in respect to evaporite deposition. American Journal of Science, vol. 261, pp. 741-755.
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Taylor , J.C.M. and Illing, V.C. 1969. Holocene intertidal calcium carbonate cementation, Qatar, Persian Gulf. Sedimentology, 12, pp. 69-107.
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Teller , J.T., K.W. Glennie, K.W., Lancaste, N. and Singhi, A.K. 2000. Calcareous dunes of the United Arab Emirates and Noah's Flood: the post glacial reflooding of the Persian (Arabian) Gulf. Quaternary International, 68-71, p. 297-308.
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Vogel, M.B., Marais, D.J.D., Parenteau, M.N., Jahnke, L.L., Turk, K.A and Kubo, M.D.Y. 2009 (or 2010 in print?). Biological influences on modern sulfates: Textures and composition of gypsum deposits from Guerrero Negro, Baja California Sur, Mexico. Sedimentary Geology, vol. ?, pp. ?. By Marilyn B. Vogel, David J. Des Marais, Mary N. Parenteau, Linda J. Jahnke, Kendra A. Turk and Michael D.Y. Kubo. Available online 3 December 2009.
Abstract:
Gypsum (CaSO4.2H2O) deposits from a range of sedimentary environments at Guerrero Negro, Baja California Sur, Mexico were investigated for microscale texture and composition in order to differentiate features formed under substantial microbial influence from those for which microbial effects were relatively minor or absent. Gypsum deposits were classified according to their sedimentary environment, textures, crystal habit, brine composition and other geochemical factors. The environments studied included subaqueous sediments in anchialine pools and in solar salterns, as well as subsurface sediments of mudflats and saltpans. Gypsum that developed in the apparent absence of biofilms included crystals precipitated in the water column and subsedimentary discs that precipitated from phreatic brines. Subsedimentary gypsum developed in sabkha environments exhibited a sinuous microtexture and poikilitically enclosed detrital particles. Water column precipitates had euhedral prismatic habits and extensive penetrative twinning. Gypsum deposits influenced by biofilms included bottom nucleated crusts and gypsolites developing in anchialine pools and saltern ponds. Gypsum precipitating within benthic biofilms, and in biofilms within subaerial sediment surfaces provided compelling evidence of biological influences on crystal textures and habits. This evidence included irregular, high relief surface textures, accessory minerals (S°, Ca-carbonate, Sr/Ca-sulfate and Mg-hydroxide) and distinctive crystal habits such as equant forms and crystals having distorted prism faces.
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Wells, A.J. 1962. Recent dolomite in the Persian Gulf. Nature, London, 194, 274-275.
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West , I.M. 1964. Evaporite diagenesis in the Lower Purbeck Beds of Dorset. Proceedings of the Yorkshire Geological Society, 34, 315-330. [Worbarrow evaporitic strata, lutecite, celestite, pseudomorphs etc.]

West, I.M. 1965. Macrocell structure and enterolithic veins in British Purbeck gypsum and anhydrite. Proceedings of the Yorkshire Geological Society, 35, 47- 58. [Nodular and enterolithic evaporitic structures from Worbarrow Tout and elsewhere. These were recognised as early displacive features at a time when they were not understood and they were subsequently found to be similar to evaporite structures, such as nodular anhydrite and gypsum of modern sabkhas. The word "macrocell" did not receive general use, and should be replaced now by nodular or chickenwire structure.]

[REFERENCES (for this paper only)
--- Folk, R. L. and Pittman, J. S., 1971. Length-slow chalcedony: a new testament for vanished evaporites: Journal of Sedimentary Petrology, v. 41, pp. 1045-1058.
--- Lacroix, A. 1897, Le gypse de Paris et les mineraux qui l'accompagnent: Nouvelle. Arch. Mus. Hist. Nat., Paris, vol. 9, pp. 201-296.
--- Salter, D. L. and West, I. M., 1965, Calciostrontianite in the basal Purbeck Beds of Durlston Head, Dorset: Mineralogical Magazine, vol. 35, p. 146-150.
--- Shearman, D.J. and Fuller, J.G. 1969, Anhydrite diagenesis, calcitization and organic laminites, Winnipegosis Formation, Middle Devonian, Saskatchewan: Bulletin of Canadian Petroleum Geology, vol. 17, p. 496-525.
--- West, I. M., 1964, Evaporite diagenesis in the Lower Purbeck Beds of Dorset: Proceedings of Yorkshire Geological Society, vol. 34, pp. 315-330.
--- West, I.M. 1965. Macrocell structure and enterolithic veins in British Purbeck gypsum and anhydrite. Proceedings of the Yorkshire Geological Society, vol. 35, pp. 47-58.
--- West, I.M., Brandon, A. and Smith, A. 1968 A tidal flat evaporitic facies in the Visean of Ireland. Journal of Sedimentary Petrology, vol. 38, pp. 1079-1093.
--- Zaritsky, P. V., 1961, Celestite from the Lower Permian deposits of the Donbas: Doklady, vol. 133, pp. 801-804.]

[END OF THIS PAPER]
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West, I.M. 1975 . Evaporites and associated sediments of the basal Purbeck Formation (Upper Jurassic) of Dorset. Proceedings of the Geologists' Association, London, 86, 205-225. Abstract: Four facies of limestones, each with particular contents of calcitised evaporites and of skeletal debris were recognised. They are compared with sediments of modern evaporite-depositing environments. The lowermost limestones, stromatolitic and pelletoid with foraminifera, probably originated in intertidal to shallow subtidal, moderately hypersaline, water. Overlying pelletoid limestones with algal-mats and some gypsum are products of high-intertidal flats. The main evaporite beds were originally gypsum, probably formed in supratidal to intertidal, very hypersaline, palaeoenvironments. The gypsum was converted to anhydrite and later brecciated in part, forming the Broken Beds. Extensive calcitisation produced porous unfossiliferous limestones. Ostracodal limestones above probably originated in shallow, only moderately hypersaline water. All the basal Purbeck strata were formed in and around a large shallow gulf with extensive tidal flats and with water of varying but predominantly high salinities. At times of uplift, thin soils developed on the former margins of the gulf. Forests were able to exist there because, although the area was within the semi-arid zone, it was probably very near to the boundary of the warm-temperate zone. End of Abstract. [Additional notes on topics discussed: Palaeosalinity origins of the basal Purbeck facies and lateral correlation. Mostly hypersaline to varying extents, including the stromatolite horizons. Fossil trees 'pickled' in a salt lake. Details of the basal Purbeck strata at all the main localities, studied petrographically. Depositional environments of the dirt beds and marls. Palaeoenvironmental significance of sedimentary cyles. Thickness variations of the facies. Relationship of the Broken Beds to the evaporitic facies. Local uplift. Penecontemporaneous fault movement. The Mupe Bay oil sand.] Some diagrams that are based on this paper are given below.

West, I.M. 1979a. Sedimentary Environments and Diagenesis of Purbeck Strata (Upper Jurassic - Lower Cretaceous) of Dorset, U.K. Unpublished Ph.D. Thesis, Southampton University, 181 p. Abstract: Twelve papers, notes and a contribution to a book, all either published or accepted for publication, constitute this thesis. All parts of the classic, shallow-water, schizohaline Purbeck Formation of the type area are discussed but emphasis is on Lower Purbeck evaporites. Diagenesis of these involved much conversion of initial small lenticular crystals of gypsum to anhydrite with net-texture. The anhydrite was extensively replaced by calcite and celestite in the Broken Beds, a tectonic evaporite breccia at the base of the Purbecks. Evaporites were almost completely lost in solution from this breccia leaving characteristic relics of "vanished evaporites". Elsewhere, in the more argillaceous parts of the formation the sulphate remains, mainly as porphyrotopic secondary gypsum. Nodules and enterolithic veins are abundant in both the calcium sulphate and in the replacements. The similarity to those in Holocene sabkhas of the Trucial Coast (Shearman, 1966) suggested an origin on supratidal sabkhas, but there is a lack of desert sediments and instead the evaporites are interbedded with forest soils. Analogous Carboniferous evaporites show evidence of sabkha origins but no sign of desert conditions [West, Brandon and Smith, 1968. A tidal flat evaporitic facies in the Visean of Ireland. Journal of Sedimentary Petrology, 38, 1079-1093.]. New evidence has come from sabkhas in Northern Egypt where gypsum nodules develop in partly vegetated environment, dry but not excessively so, and supports other evidence for a semi-arid origin for the Lower Purbeck evaporites [West, Ali and Hilmy. 1979. Primary gypsum nodules in a modern sabkha on the Mediterranean coast of Egypt. Geology, 7, 354-358.]. The relatively dry climate was temporary and facies of higher parts of the Purbecks seem to result from sub-humid conditions. Throughout the formation lagoonal, 'intertidal' and supratidal deposits can be recognised but in the Middle and Upper Purbecks the lagoonal sediments have abundant brackish shelly faunas and, there, 'tidal-flat' deposits consist of shell-sand with dinosaur footprints but usually without evaporites. Progressively the proportion of land-derived clastics such as kaolinite and quartz sand increases as the continental Wealden is approached and final Purbeck sediments contain debris eroded from the underlying Portland Stone Formation, then uplifted at the western margin of the basin.

West, I. 1979 . Review of evaporite diagenesis in the Purbeck Formation of southern England. Symposium on: West European Jurassic Sedimentation - "Sedimentation Jurassique W. European", A.S.F. (Association of French Sedimentologists), Special Publication No. 1, March 1979, pp. 407-416. In English with Abstracts in English and French.
Abstract (slightly enlarged and relating to fig 2, alongside): Evaporites and remains of "vanished evaporites" are widely distributed in the Purbeck Formation of southern England. Associated sediments show that these were formed in semi-arid conditions on the extensive tidal-flats of a shallow hypersaline gulf. The primary sulphate was predominantly gypsum as lenticular crystals. Fabrics developed indicate five major stages of diagenesis. There was early recrystallisation of the initial gypsum mush (Stage I) of small lenticular crystals to a less porous anhedral fabric with the small-scale "net-texture" (Stage II), a microscopic network of impurities. The coarser nodular structure, chicken wire structure and enterolithic veins developed as the sulphate was converted to anhydrite (Stage III), a process which commenced penecontemporaneously and was completed before deep burial. The anhydrite was recrystallised so that several anhydrite fabrics now exist. Hydration is a relatively recent process resulting from contact with meteoric water near the surface after uplift and erosion had taken place. This usually commenced with a Stage IV of anhydrite containing gypsum porphyroblasts or porphyrotopes. The existing porphyroblastic or porphyrotopic gypsum represents the final Stage V. Concurrent with sulphate diagenesis there was replacement of the evaporites on an appreciable scale, particularly where they were not enclosed in impermeable clays. Calcitisation of the evaporites has produced peculiar, porous, secondary limestones and limestone breccias [resembling cargneule or rauhwacke]. Associated replacement products, including the strontium minerals - celestite and calciostrontianite, euhedral quartz, the varieties of chalcedony - lutecite and quartzine, suggest an inorganic mechanism for the calcitisation [but see also the thesis of Quest on isotopic studies of Purbeck strata which suggests that there was involvement of hydrocarbons in some cases.]. Criteria are listed that may be used for the recognition of similar replaced evaporites elsewhere. [End of abstract] There follows an extract (with minor additions):
Evidence for Former Evaporites (Vanished Evaporites). An association of several points should be sought:
1. Pseudomorphs of calcite, chalcedony or quartz (or moulds or casts) after gypsum, after anhydrite or after halite.
2. Length-slow chalcedony (quartzine).
3. Spherulites of the lutecite variety of chalcedony.
4. Euhedral crystals of authigenic quartz.
5. Celestite, sometimes with calciostrontianite (occasionally barytes or barite).
6. Net-texture, a small-scale relic of gypsum with displaced impurities, now in secondary, sparry limestone, resulting from calcitisation.
7. Chicken-wire, nodular structure or spherical vugs in limestone or dolomite.
8. Coarsely crystalline (sparry) limestone, often porous, and without skeletal debris (possibly calcitised evaporites). May be massive, laminated or contorted.
9. Small contortions that are not obviously of sub-aqueous slumping or other non-evaporitic origin.
10. Minute rectangular relics of anhydrite in quartz or other minerals such as calcite (obvious in quartz because of contrasting moderate birefringence and the rectangular cleavage - but very small).
11. Oligomict limestone breccia with a carbonate matrix (possible calcitised evaporite breccia).
12. (an addition) A crumbly, brown, porous bed of carbonate and clay (like evaporitic cargneule or rauhwacke common in the Trias of the Alps and Pyrenees).
..Such evidence is likely to be found in other formations without normal marine faunas but with features such as microbial-mats, algal stromatolitic heads, caliches, abundant hypersaline ostracods or peculiar breccias. Obviously red-bed evaporites of more arid origin can provide additional criteria resulting from desert environments.

West, I.M., Ali, Y.A. and Hilmy, M.E. 1979. Primary gypsum nodules in a modern coastal sabkha on the Mediterranean coast of Egypt. Geology, 7, 354-358. Abstract: Nodules of anhydrite in Holocene sabkhas of the Arabian Gulf and Baja California have been used as analogues to interpret calcium sulphate nodules in ancient rocks to be of sabkha origin. Nodules and incipient enterolithic veins of gypsum occur in a modern sabkha in Egypt about halfway between Alexandria and El Alamein, in a depression between a modern and a Pleistocene beach ridge. The displacive gypsum is apparently being precipitated from hypersaline calcium sulphate-saturated interstitial water that increases in salinity as it rises by capillarity from the water table to the surface. Calcium and sulphate ions seem to be derived mainly from dissolution of pre-existing lagoonal gypsum beneath the water table. The nodules occur within a supratidal sand unit of a sabkha sequence capped by a gray, saline soil on which grow clumps of halophytes, separated by salt-encrusted flats. This discovery shows that calcium sulphate nodules can develop (1) within sediments of a region where the climate is almost semiarid rather than very arid, (2) as primary gypsum rather than as anhydrite, and (3) as a consequence of redistribution of calcium sulphate. End of abstract.

West, I.M., Ali, Y.A. and Hilmy, M.E. 1983 . Facies associated with primary gypsum nodules of northern Egyptian sabkhas. Sixth International Symposium on Salt, 1983, vol. 1, Salt Institute, 171-183. Abstract: Modern sabkha and lagoonal, evaporitic environments are well-developed in the Mediterranean coastal zone of Egypt between Alexandria and El Alamein. It is a semi-arid region with an annual rainfall of about 19cm. Landward of the modern, ooid beach ridge is a narrow depression. This is occupied by partially vegetated sabkhas of desert loess and some small lagoons. Those which are moderately hypersaline contain the cockle [common edible, estuarine bivalve], Cardium glaucum; very hypersaline lagoons are precipitating gypsum. The sabkhas are usually underlain by the following sequence of Holocene sediments. At the base are lagoonal shelly silts, locally with Cardium. Lagoonal gypsum follows. Then comes desert-loess, within which gypsum nodules are developing by precipitation from capillary water. These sabkha deposits are being gradually covered by ooid sand. The present marine transgression should ultimately produce a sequence in which an oolitic limestone is overlain by a cockle bed, followed by laminated gypsum, overlain, in turn, by a red bed siltstone with gypsum nodules. This would be capped by oolitic limestone. Ancient strata resembling certain of these facies include cockle beds associated with evaporites in the British late-Jurassic [or early Cretaceous, Purbeck] strata. The facies association of desert loess with gypsum nodules, halite, caliche, palygorskite and scorpions can be matched in the British Trias. End of Abstract. [The paper is partly concerned with Purbeck analogues in northern Egypt.] Extracts on analogue for the Purbeck cockle beds, such as parts of the Hard Cockle Member and Soft Cockle Member with the ancient "cockle"Protocardia purbeckensis:

"A modern, moderately hypersaline environment with Cardium glaucum is a lagoon (AL.1) east of El Alamein [ The Second World War battlefield]. The brine is of approximately 55% salinity in summer. There are other similar lagoons nearby. The bivalves here are dwarfed (Figure 4), with a mean length of 12.6mm, and are associated with turreted gastropods. Elsewhere, Cardium glaucum occurs in hypersaline lagoons of the south of France and of the Sea of Azov (Rygg, 1970). The abundant Fragum (Cardiaceae) fo hypersaline Shark Bay, Western Australia (Hagan and Logan, 1974) may be analogous. ... Perhaps the best known examples of ancient "cockle beds" with evaporites are in the lagoonal Lower Purbeck Formation (Upper Jurassic-Lower Cretaceous) of southern England (Arkell, 1947). The "cockles" are bivalves of the species Protocardia purbeckensis (Figure. 4). They occur in members known as the "Hard Cockle Beds" and the overlying "Soft Cockle Beds" (Bristow and Forbes in Damon, 1884; Clements, 1969; Ali, 1981). In the Soft Cockle Member there is secondary gypsum that has replaced anhydrite, which in turn is a replacement of primary gypsum (West, 1964). It contains well-developed nodules and enterolithic veins (West, 1965). Calcitized gypsum occurs in the Hard Cockle Member. The usual association of the small cockle Protocardia purbeckensis with evaporites suggests that the species was tolerant of hypersaline conditions. Comparison with modern analogues suggests that it might have been able to live in brine of up to about 60 parts per thousand salinity. The lack of desert sediments, the presence of coniferous forests and the characters of the insect, molluscan and ostracod faunas is evidence, however, for a climate that was semi-arid and Mediterranean type (West, 1975; 1979; Francis, 1983). This is confirmed by the palaeolatitude of about 37 degrees N (Smith and Briden, 1977).

West, I.M. and Lashhab, M. 1986. Anhydrite in a recent salt pan of northwest Libya. Desert Sediments; Ancient and Modern. A Special Scientific Meeting of the Geological Society of London, Burlington House, Piccadilly, convened by Dr. L.E. Frostick and Dr. I Reid. 20-21st May 1986. Go to webpage: Sedimentology of Sabkhas, Salt Lakes and Arid Environments, where revised notes, based on this paper and further work by Lashhab are given.
Abstract (only, there is no paper):
Anhydrite is well-developed in modern sabkhas of the Arabian Gulf, particularly at Abu Dhabi, Qatar and Kuwait. In these areas it is associated with high-salinity groundwaters and high surface temperatures. Anhydrite has rarely been reported from the cooler North African coast. Explanations usually given for this are the lower temperatures, the relatively high humidities and the higher rainfall. This accounts for the fact that the displacive, recent, calcium sulphate nodules of the sabkhas of northern Egypt, Libya and Tunisia, that are so common in the modern sabkhas, consist of gypsum rather than anhydrite.
Nevertheless, in special conditions anhydrite can occur on the North African coast. It is present in small quantities at Zuwarah (Zuara) at about 33 degrees north in northeastern Libya near the Tunisian border It occurs in a small halite pan, which exists even though the climate is Mediterranean with a rainfall of between 200 and 400mm per annum. Average January temperature here is about 15 degrees C and July temperature average temperature is 23 degrees C. Average annual humidity is between 70 and 80 percent. The vegetation associated with the coastal salt pan is of sabkha halophytes. The anhydrite occurs as small groups of fibroradiating crystals in coarsely crystalline halite under a few cm of brine, probably drying out at times. Black reduced mud and microbial mats occur beneath. Brine is presumably supplied by seepage under a beach ridge from the adjacent sea. Nodules in associated sabkhas are of gypsum. The moderate temperatures of the North African coast probably imply that in this area Recent anhydrite can only occur in the presence of halite. [end of abstract]

West, I.M., Lashhab, M.I. and Muhan, I.M. 2000 . North African sabkhas and lagoons compared to those of the Arabian Gulf. Pp. 512-530 in: Proceedings of the Sixth Mediterranean Petroleum Conference and Exhibition, November 23-25th, 1999, Tripoli, Libya (G.S.P.L.A.J.), 845 pp. Abstract: The most arid part of the southern Mediterranean coast extends from Tunisia in the west to the Sinai in the east. Here, major wave-action has produced straight coastlines with beaches. Behind these are widespread sabkhas and some lagoons. These environments and their evaporites are compared to the coastal sabkhas, lagoons and evaporites on the Arabian side of the Arabian Gulf... continues.

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Webpage - written and produced by:

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at his private address, Romsey, Hampshire, kindly supported by Southampton University,and web-hosted by courtesy of iSolutions of Southampton University. The website does not necessarily represent the views of Southampton University. The website is written privately from home in Romsey, unfunded and with no staff other than the author, but generously and freely published by Southampton University. Field trips shown in photographs do not necessarily have any connection with Southampton University and may have been private or have been run by various organisations.