West, Ian M. 2013. Sabkhas, evaporites and some other desert features: an introduction. Internet Webpage. http://www.southampton.ac.uk/~imw/sabkha.htm. version: 19th December 2013.

Sedimentology of Sabkhas, Salt Lakes and Arid Environments - Introduction
Ian West,
Romsey, Hampshire

and Visiting Scientist at:
Faculty of Natural and Environmental Sciences,
Southampton University,
Webpage hosted by courtesy of iSolutions, Southampton University
Website archived at the British Library
With contributions from the work of Dr. Mokhtar Lashhab.


| Qatar - Sabkhas, Salt Lakes and Other Desert Environments | Select Bibiography of Sabkhas, Salt Lakes and Evaporites
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Windward to left horn side of a barchan, Umm Said, Qatar. Note the wind-rippled, convex surface.




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SABKHAS - INTRODUCTION

Um Said Sabkha, southeast Qatar, with large barchan dunes in the distance

Sabkha is an arabic name for a salt-flat that has come into general use in sedimentology following classic research in the United Arab Emirates of the Arabian Gulf in the 1960s and later. They are flat and very saline areas of sand or silt lying just above the water-table and often containing soft nodules and enterolithic veins of gypsum or anhydrite. A thin crust of halite and gypsum may be present in some parts. Many ancient evaporites show sedimentary feature of sabkhas, such as gypsum nodules.

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SUPRATIDAL SABKHAS - INTRODUCTION:

Arid Sabkhas with Nodular Evaporites

Soft nodules and enterolithic veins of anhydrite in muddy sand of the Recent Dukhan Sabkha, Qatar

The well-known and classic supratidal sabkhas of the Arabian Gulf with nodular anhydrite at Abu Dhabi are in this category. There is a very extensive literature and for references see the associated Sabkha Bibliography. The Abu Dhabi sabkhas are the best-described and thus most well-known type of sabkhas. Sabkhas with evaporite nodules also occur at Qatar and Kuwait in the Arabian Gulf.

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SABKHAS - INTRODUCTION:

Semi-Arid Sabkhas with Nodular Evaporites

Enterolithic veins and nodule of gypsum in a semi-vegetated sabkha, near El Alamein, northern Egypt

Militah Sabkha, northeastern Libya

It is less well-known that sabkhas with calcium sulphate nodules are well-developed on the south coast of the Mediterranean Sea in northern Egypt and northern Libya. Sabkhas with nodular gypsum, resembling the nodular anhydrite of the Arabian Gulf, are widespread on the North African Coast, from Egypt to Libya. They differ from the Arabian Gulf sabkhas in that the climate is semi-arid, rather than extremely arid. There is usually halophyte vegetation in the form of nebkhas (small mounds of blown sand or silt held by plants, such as Halocnemum).

Thus, the North African sabkhas are mostly semi-arid and semi-vegetated, with nebkhas. In terms of brines and mineralogy they are probably not very different from Arabian Gulf sabkhas. However, gypsum nodules and enterolithic veins rather than anhydrite nodules and enterolithic veins are usually found when digging a pit in a North African sabkha. Interstitial brine salinities can reach the same halite-saturation levels as in the Arabian Gulf in the summer. However, there is generally greater winter rainfall on the North African coast, and this is the reason for the survival of halophyte plants. Anhydrite is not necessarily absent from the North African coast and some details of recent anhydrite in Libya are given further below. So far anhydrite nodules do not seem to have been found in that region, but they would be expected, at least in certain parts of the Libyan coast. Insufficient pits have been investigated.

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SABKHAS - INTRODUCTION:

Sabkhas of Humid Areas (the High Salt Marsh)

The bank of a creek in a Sea Purslane (Atriplex portulacoides), middle saltmarsh, at Exbury on the Beaulieu River Estuary, Hampshire, 2006

The equivalent of a supratidal or sabkha environment of temperate humid regions contain much more vegetation than that of the semi-arid regions. This equivalent of sabkha is know as a High Salt Marsh. It usually contains salt-tolerant plants such as Atriplex portulacoides. No evaporites are normally present except for a little halite in dry summers (although a little gypsum has been found locally in special circumstances). However, with human interference they have been the major sites of salt production in England, particularly the Lymington area in historic times. The climate is semi arid only for a few months in summer, so brines were concentrated in ponds for natural evaporation during this spell and then boiled dry artificially to manufacture salt. Note that the Low Salt Marsh of temperate humid areas often has Spartina with some salt-tolerant Salicornia. This is the equivalent of the intertidal sabkha with microbial mats in arid and semi-arid regions. In humid tropical regions mangroves grow at about this level.

It should be noted that the present vegetation of saltmarshes is almost entirely of angiosperms. Thus before they evolved in the Late Cretaceous, the equivalent of what are now high salt marshes would have been barren flats, similar to supratidal sabkhas but generally without evaporites.

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SABKHAS - INTRODUCTION:

Arid Sabkhas without Nodular Evaporites

Umm Said Sabkha, Qatar

A supratidal part of a large coastal sabkha at Umm Said in Qatar. This particular area is the remains of a lagoon indirectly filled with siliciclastic sand of aeolian origin, originating from some large barchan sand dunes. The flatness is controlled by the content of capillary moisture from the water-table, which is only about half a metre (one and a half feet) down, keeping the sand damp and firm and preventing it from being blown away. Any higher dryer sand can be moved away by deflation. This particular sabkha has much granular gypsum in addition to the sand but is firm enough for a four-wheel drive vehicle where the brine is not at the surface (although it is sensible to keep only to well-used car routes and to have a mobile phone and use GPS for location).

Car in Umm Said Sabkha, Qatar

A lower part of the same sabkha where a thin halite crust is developed. The halite is empheral and easily dissolved by a rare flood of rain. The gypsum in the sand beneath is less soluble and remains. Here the water-table is almost at the surface and the sand beneath is soft with gypsum and some clay. The salt crust can sometimes support cars until they break through and rapidly rust away in the brine. The wheels and windows will eventually be the only fossil remains of this vehicle.

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NORTHERN EGYPT

SABKHAS - Beach Ridges Separating Lagoons and Sabkhas from the Coast

beachrock in Egyptian ooid beach ridge

ooid beach ridge, northern Egypt

White beach ridges of carbonate sand are often developed in arid or semi-arid regions where the sea water is warm and where evaporation is taking place. Such beach ridges may be discontinuous as in the Abu Dhabi area of the Arabian Gulf or almost continuous as on the northern Egyptian coast west of the Nile Delta. The left-hand photograph above shows the typical white sand of spherical ooid grains, but here the ridge is broken by an embayment. This is not typical for this stretch west of Alexandria and the beach is mostly continous. The ooids are of superficial type here and have nuclei that are frequently of quartz. They are probably less well-developed than in the Arabian Gulf. The oolitic sand is in some cases cemented into beachrock. This can be seen in the right-hand photograph, and the cross-bedding is probably of wind-blown sand dune origin in this upper part of the ridge. Beach cross-bedding probably occurs further down. Behind this white beach ridge are light brown sabhas of desert loess; this is blown dust from the Sahara desert which is trapped in the semi-arid, as opposed to the extremely arid, desert environment.

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PETROGRAPHY:

Lenticular Gypsum

Small lenticular crystals of gypsum in Quaternary sabkha deposits of the Northern Egypt, and similar to early gypsum in the Lower Purbeck Formation of Dorset, England

Thin-sections of lenticular gypsum from the First Depression Sabkha, between Alexandria and El-Alamein, northern Egypt

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NORTHERN EGYPT

Sulphate Lagoons of El Alamein

A gypsum-saturated lagoon with associated sabkha, at El Alamein, northern Egypt, aerial photograph

Gypsum mounds at the shoreline of a calcium sulphate saturated lagoon, El Alamein, northern Egypt

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For information on the sabkhas and other desert features of Qatar, Arabian Gulf please go to the new separate webpage:

Qatar - Sabkhas, Salt Lakes and Other Desert Environments

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SABKHAS:

Microbial-Mats (Cyanobacterial Mats)

Cyanobacterial mat, Umm Said Sabkha

Microbial mats at the margin of a small lagoon, northern part of Umm Said, Sabkha, Qatar

A microbial mat or cyanobacterial mat dug out of the intertidal sabkha of a small lagoon in Kuwait

Polygonally cracked algal-mat (more-strictly cyanobacterial mat) in hypersaline water at the intertidal margin of a lagoon near Umm Said, Qatar. This part of the lagoon seems too saline for browsing molluscs (cerithid gastropods are abundant in the intertidal zone elsewhere). Because this lagoon (unlike many ancient ones) is close to the sea and has a direct narrow connection with it true lunar tides are significant (tidal range - 0.5 to 1 m along the coast of Qatar).

Stromatolites on an old drum in Qatar

Very small stromatolites growing at the present day on an old steel drum that has sunk into a soft sabkha at Umm Said, Qatar. The iron does not seem to inhibit the cyanobacterial growth. A hard or raised surface for attachment seems favourable for stromatolite growth.

Thrombolites on three trees at the Fossil Forest, Dorset, UK

Similarly, tree stumps submerged in a hypersaline lake of the Lower Cretaceous Purbeck Formation of Dorset, UK, have provided attachment areas on which thrombolites have formed.

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SABKHAS - GYPSUM

Enterolithic Veins Soft nodules and enterolithic veins of anhydrite in muddy sand of the Recent Dukhan Sabkha, Qatar

Comparison of ancient and modern enterolithic veins

Photographs above show enterolithic veins in secondary gypsum (after anhydrite, after primary gysum) in Lower Purbeck Formation at Worbarrow Tout , Dorset, UK. With them are photographs of similar enterolithic veins forming at the present day in a sabkha of desert loess (blown wind-blown silt) between El-Alamein and Alexandria on the Mediterranean coast of Egypt, and at Dukhan Qatar where they are of anhydrite. (See - West, Ali and Hilmy, 1979.)

Early enterolithic veins now preserved in late secondary, porphyrotopic gypsum, Worbarrow Bay, Dorset Small entolithic veins showing details of growth, Purbeck, Worbarrow Bay, Dorset

Nodules, chicken-wire structure and enterolithic veins are all closely related. They are early displacive fabrics formed by continued growth of calcium sulphate from capillary water in sabkhas or salt-flats. Within them the sulphate is extremely pure because this displacive material has grown in place and contains hardly any sediment. The pure gypsum within nodules is known as alabaster and is used for carving. Enterolithic veins are over-developed displacive nodules of white soft gypsum or anhydrite which have burst out and pushed on into the associated soft sediment of a sabkha (West, 1965) . They commonly occur approximately parallel to the sediment surface, although in the Purbeck Formation there has often been a tendency towards obliquely-upward movement. Their lithification into strong but soluble rocks is the result of later diagenesis, i.e. gypsum-anhydrite-gypsum or anydrite-gypsum.



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AKROTIRI SALT LAKE, CYPRUS - Introduction

(Note: Photographs of Cyprus have been photo-edited to show clearly only geological and geomorphological features)

The Akrotiri Salt Lake, Cyprus, when dry in September, 2006

Thin salt crust on ripples, southern margin of Akrotiri Salt Lake, Cyprus

Sketch map of geomorphological features of the Akrotiri Peninsula, near Lemesos, Cyprus

The Akrotiri peninsula, showing the

The Akrotiri salt lake, in May 2005 before major precipitation and drying up in the summer; the lake is behind the Episkopi Bay Tombolo Beach. Edited image

The Akrotiri Salt Lake, Cyprus, in August 2004 when precipitating salt; the environment is a small-scale analogue for the Late Jurassic, Purbeck palaeoenvironment. Edited image

The Akrotiri Salt Lake, near Lemesos (Limassol), is one of two significant salt lakes in Cyprus, the other being at Larnaca. It is a former embayment of the sea between the Episkopi Bay Tombolo Beach, a pebble beach, on the west side and a low sand barrier beach on the east. The lake is situated in a very seasonal Mediterranean environment which has appreciable rainfall in winter but is very dry in summer. Thus it only become satured for halite in the summer season and precipitates much salt by about July or August. It usually, but not always dries completely in late summer. In Spring, before it becomes very saline the lake and associated ponds are a great nuisance as a source of numerous mosquitoes.

Old map of the Akrotiri peninsula, Cypris, showing approximately the original form of the tombola with a harbour to the east

In aerial views the relationship of the pebble beach to the original limestone island to the south is clearly visible. Old maps (see above) show that there was once a much larger body of water east of the beach. There seems to have been much natural reclamation and probably also much artificial reclamation of the original harbour or estuary.

In the aerial view notice the dry braided system of the Kouris River which has brought clasts of ultrabasic and basic igneous material from the Troodos Massif. The river mouth forms a small delta protruding seaward from the general line of the beach. On the old map a branch of this river is shown entering the salt-lake area.

The tombolo beach of Episkopi bay, Akrotiri, near Lemosos (Limassol), southern Cyprus.

Beachrock at the Shipwreck on the Episkopi Bay Tombolo Beach, Akrotiri, near Lemosos (Limassol), southern Cyprus.

The tombolo beach to the west is cemented into beachrock in places, particularly in the southern part. There is an offshore reef of beachrock which is visible in one of the aerial photographs.

Lady's Mile, the Eastern Barrier

Progradation at Lady's Mile, the low eastern barrier of the Akrotiri Salt Lake, Cyprus.

Lady's Mile, a low sand beach and the eastern barrier of the Akrotiri Salt Lake, Cyprus.

The eastern barrier of the Akrotiri Salt Lake is Lady's Mile, a publicly-accessible beach south-southwest of Lemesos or Limassol. This is a very low, prograding series of parallel sand ridges and it might well be flooded in storms. The sand is presumably able to accumulate here because there is less wave fetch and therefore less erosion on this eastern side of the peninsula. However, the source of the sand is not obvious.

Ladies Mile has little vegetation on it because the surface is so close to the salt water-table. The sabkha without vegetation, at the southern end of the beach in the picture suggests that this is a route for either flooding by seawater or by lake water escaping seaward.

Further south at Button Beach small coastal sand dunes have been developed. Here the surface is above the limit of the capillary zone and as a result this is well-vegetated. Although the vegetation is different because of the high carbonate content in Cyprus it resembles the coastal sand dunes of Studland in Dorset, England (also a prograding eastern barrier of a coastal embayment, Poole Harbour).

Button Beach, Akrotiri, Cyprus, a sand-spit and dune accumulation resembling the South Haven Peninsula, Studland

Sea-holly and grasses on sand-dunes at Button Beach, Akrotiri, Cyprus

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LIBYA - DESERT ENVIRONMENTS, SABKHAS AND ANCIENT EVAPORITES

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LIBYA

Sabkhas of the Libyan Coast
(Including Zuwarah Occurrence studied by
Mokhtar Lashhab, 1992; see also West and Lashhab, 1986)

Militah Sabkha, northeastern Libya

A small salt pan and sabkha with gypsum nodules west of Zuwarah, Libya, aerial view, for location purposes

Salt works on the coast at Zuwarah, northeast Libya

Halite crystals are growing at the sediment surface in a small salina at Zuwarah, northeast Libya

Oxygen-deficient black mud under a thin crust of halite, Zuwarah Salt Lake, Libya, 1985

Fibroradiating anhydrite in halite beneath shallow brine, small salina, Zuwara, northeast Libya, 1985

A pit through a supratidal sabkha at Zuwarah, northeast Libya

Anhydrite is well-developed as nodules or enterolithic veins in the sediment profiles of modern supratidal sabkhas of the Arabian Gulf, particularly at Abu Dhabi, Qatar and Kuwait. Photographs of such features are shown in this webpage and in the Qatar Sabkha webpage. The soft white nodules or veins are easily found, usually in the capillary zone within a metre of the surface by digging a shallow pit. With experience it is easy to recognise the best place to dig.

The areas where anhydrite is easily found usually have high-salinity groundwaters and high surface temperatures. Recent 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 usually consist of gypsum rather than anhydrite. However, it is not known whether these might have been anhydrite at some stage, since fluctuations in groundwater salinity can occur. An anhydrite to gypsum change and vice versa could happen very easily, perhaps even seasonally at some places.

In certain conditions recent anhydrite can occur on the North African coast. It is present in small quantities at Zuwarah (or Zuara) at about 33 degrees north in northeastern Libya near the Tunisian border

[It is of interest that this is a similar latitude to that at which the late Jurassic Purbeck evaporites of southern England originated. Evidence from pseudomorphs is mainly for primary gypsum though, but nodular calcium sulphate is common.]

The Zuwarah anhydrite occurs in a salina or halite pan. 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 might suggest that anhydrite is only be common here in the presence of some halite (i.e. at high groundwater salinities).

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NORTHERN LIBYA

Sedimentary Facies - Evaporites

Occurrence of the Eocene Jir Formation of gypsum, anhydrite and halite, south of the Gulf of Sirte, Libya

A simplified geological map of the Jabal Waddan area, at the southeast end of the Hun Graben, Libya

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LIBYA - DESERT:

Vanadiferous Goethite
(with acknowledgement to the detailed studies of Dr. Mokhtar Lashhab; refer to Lashhab, 1992)

Vanadiferous goethite after pyrite occurring as slightly radioactive nodules in the Eocene strata of northern Libya

Brecciated chert beneath the Eocene, Wadi Faras evaporites, margin of Hun Graben, Libya

Thin-section showing late veins of pyrite, now oxidised to goethite and associated with quartz, in a fracture vein, Wadi Rawaghah, Libya

In proximity to the evaporites of the southeastern Hun Graben of Libya there is a small but unusual occurrence of vanadiferous goethite. Slightly radioactive nodules of this mineral occur in the dolomites of the Tertiary Rawaghah Formation. They contain vanadium contents up to 3380 ppm. There is also enhanced contents of Ni and Zi.

The modes of origin is not, at present, understood. They might be the results of precipitation from vanadium and nickel porphyrins which are commonlyu associated with oil. The strata concerned are cap rocks for Libyan oil reservoirs so this seems a reasonable possibility. There has been reaction between hydrocarbon fluids and pre-existing pyrite. A peculiarity is that a chert brecca in these strata contains late pyrite veins, now oxidised. Thus there seems to have been some late occurrence of hydrogen sulphide. Vanadium precipitation can take place throught the action of hydrogen sulphide reducing V4 to V3(Wanty (1992).

Against an oil hypothesis is the fact that some of the nodules seem to resemble the typical pyrite nodules of early diagenesis. If they are of early origin, and this has not been proven, then they would seem to have been too early for diagenesis involving oil. Some other mechanism involving mineralising fluids might possibly have taken place. Volcanic rocks occur at no great distance within the Hun Graben (Jabal As Swada), so there is a fairly local source of metallic ions.

Until there has been more research and more data is available the vanadium occurrence is just a curiosity. It is not known whether it will remain only of trivial interest or might have some mineralogical significance. It seems very unlikely that as a research topic the matter will be pursued further for some time to come.

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LIBYA

Desert Environments of Hun Graben

Within the Hun Graben, Libya, where an almost flat plain is an amalgam of alluvial fans from the fault scarp of the distant graben edge

the Wadi Rawaghah area, Hun Graben, Libya, aerial photograph

A large valley or canyon at Rawaghah, southeastern margin of the Hun Graben,  Libya

A desert reg at Wadi Faras, Waddan Uplift, near Waddan, Libya, 1985

A reg or stony desert Libya that is very similar to a surface on Mars

Regs or stony deserts are very well-developed in various parts of Libya. The angular clasts usually have a coating of desert varnish, which consists of oxides of iron and manganese. The reg shown above in at Wadi Faras in northern Libya. It has a considerable resemblance to a reg on the planet Mars, although the Martian example does not seem to have desert varnish.

A hot and dry wadi at Wadi Faras, margin of the Hun Graben, Libya, with only a small amount of vegetation, 1985

Here is a dry wadi at the locality of Wadi Faras in the Hun Graben, Libya (with Ian West in 1985). In the bottom of the valley there is a limited amount of vegetation, so some moisture much be present beneath the surface. Higher on the slope there is almost nothing. Notice the extent to which the bedrock has been fracture by drastic daily temperature changes and perhaps by rare floods of water. The temperature in places in the Libyan desert can reach about 50 degrees centigrade. The implication with regard to ancient deposits is that if evidence is for extreme aridity (as in the British Permian) then signs of plants (i.e. rhizoconcretions) probably indicate the bottom of wadis. If the conditions are less extreme (as seems to be the case for the Trias of southern England) then plant evidence may be more widespread

Sunset at Wadi Faras, Tertiary evaporite locality, Libya

Uplift, wadis and alluvial vans, southeast Hun Graben, Libya, aerial view

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LIBYA - JEBEL AKHTAR REGION (NORTHEASTERN LIBYA)

Miocene Gypsum

Unusual Miocene gypsum with climbing cross ripples at a locality in Jebel Akhtar, eastern Libya

Giant crystals of Miocene gypsum, in Hawa Al Barraq Quarry, Jebel Akhtar, northeastern Libya

A close-up view of part a giant crystal of Miocene gypsum, in Hawa Al Barraq Quarry, Jebel Akhtar, northeastern Libya

Superb exposures are present in Miocene gypsum in Jebel Akhtar, not far to the east of Benghazi. Remarkable features include giant gypsum crystals. There is also, as shown above, fine-grained, primary gypsum with well-defined, climbing cross-lamination. This may be turbidite gypsum.

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Water Supply in an Arid Area

(preliminary - a section for future development)

(These photographs are intended for future discussion of some aspects of hydrogeology of a very arid region - Libya. Further material will be added later.)

We walk into the factory for the huge pipes for the Great Man-Made River, Libya

Factory for pipes for the Great Man-Made River, Libya


Pipes for the Great Man-Made River, Libya

Linking of huges pipes 
for the Great Man-Made River, Libya

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BRITISH DESERT PALAEOENVIRONMENTS

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British Desert Palaeoenvironments

A red desert deposit in the Petit Tor Member, Watcombe Formation, Permian, Oddicombe North Beach, Torquay, Devon, southern England, 2011

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ACKNOWLEDGEMENTS

My daughter Joanna Bentley, her husband Ben and my grandson Daniel were very hospitable and assisted during field work in Cyprus. I thank Tonya West for help in various ways. I am very grateful to all who assisted. I particularly thank Professor Adam El-Shahat and Dr. Yehia Ali, who worked with me on Egyptian sabkhas. Dr. Mariam Al-Yousef was extremely helpful with studies in Qatar. Professor Hilmy helped and guided at many stages of the work in Egypt. I very much appreciate the support and help of the late Professor Douglas Shearman, the well-known originator of sabkha diagenetic theories. I thank Professor Graham Evans for helpful discussion regarding sabkhas. With regard to work in Libya, I particularly thank Dr Mokhtar Lashhab who made detailed field and laboratory studies of Eocene and Recent evaporites. He greatly facilitated geological investigations in Libya. I also thank Dr. Hammid, Dr. Ibrahim Muhan and others who made it possible to study evaporites in this geologically spectacular country, some years ago. I am very grateful for the help of Al-Fatah University, Tripoli, when I was there for a time as a Visiting Professor.

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BIBLIOGRAPHY and References Please go to main reference list and biliography at:

Select Bibliography on Sabkha, Salt Lakes and Evaporites.

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SUPPLEMENT:
LIBYA - SELECTIVE REFERENCES SUPPLEMENT

This is just a small supplementary bibliography or reference list with a few selected publications regarding Libyan geology, Libyan petroleum geology and vanadiferous goethite at Jabal Waddan etc. These are mostly references not given in other associated bibliographies such as: Sabkhas and Desert Bibliography. It is here only as a convenient aide memoire.

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Garrels, R.M., Larsen, E.S., Pommer, A.M. and Coleman, R.G. 1956. Detailed mineralogical and chemical relations in two uranium-vanadium ores. United States Department of the Interior, Geological Survey, Trace Elements Investigation Report No. 635. (This report concerns work done on behalf of the Divisions of Raw Materials and Research of the U.S. Atomic Energy Commission).
Available online as a pdf file.

Abstract:
Channel samples from two mines on the Colorado Plateau have been studied in detail both mineralogically and chemically. A channel sample from the Mineral Joe Ho, 1 mine, Montrose County, Colorado., extends from unmineralized rock on one side, through a zone of variable mineralization, into only weakly mineralized rock. The unmineralized rock is a fairly clean quartz sand cemented with gypsum and contains only minor amounts of clay minerals. One boundary between unmineralized and mineralized rock is quite sharp and is nearly at right angles to the bedding. Vanadium clay minerals, chiefly mixed layered mica-montmorillonite and chlorite-montmorillonite, are abundant throughout the mineralized zone. Except in the dark "eye" of the channel sample, the vanadium clay minerals are accompanied by hewettite, carnotite, tyuyamunite, and probably unidentified vanadates. In the dark "eye," paramontroseite, pyrite, and marcasite are abundant, and bordered on each side by a zone containing abundant corvusite. Ho recognizable uranium minerals were seen in the paramontroseite zone although uranium is abundant there. Coaly material is recognizable throughout all of the channel but is most abundant in and near the dark "eye." Detailed chemical studies show a general increase in Fe, Al, U, and V, and a decrease in SOi toward the "eye" of the channel. Reducing capacity studies indicate that V(lV) and Fe(ll) are present in the clay minerals throughout the channel, "but only in and near the "eye" are other V(IV) minerals present (paramontroseite and corvusite). The uranium is sexivalent, although its state of combination is conjectural where it is associated with paramontroseite. Where the ore boundary is sharp, the boundary of introduced trace elements is equally sharp. Textural and chemical relations leave no doubt that the "eye" is a partially oxidized remnant of a former lower-valence ore, and the remainder of the channel is a much more fully oxidized remnant. A channel sample from the Virgin No. J mine, Montrose County, Colo., extends from weakly mineralised sandstone on both sides through a strongly mineralized central zone. The weakly mineralized zone is a poorly sorted sandstone with common detrital clay partings; chlorite and mixed layer mica-montmorillonite are abundant interstitial to the quartz grains. No distinct vanadium or uranium minerals are recognizable, although the clay minerals are vanadium bearing. Euhedral pyrite grains and selenian galena are present but rare* The strongly mineralized rock is separated from the weakly mineralized rock by a narrow transition zone which only approximates the bedding planes. It contains abundant vanadium-bearing clay minerals (predominantly chlorite) interstitial to the quartz grains, and apparently replacing them. Paramontroseite is common and is intergrown with the clay minerals. Pyrite and marcasite are present, chiefly in or near the abundant blebs and fragments of carbonaceous material. Selenian galena is rarely present, and generally in or near carbonaceous material. Coffinite is the only uranium mineral identified; it is extremely fine grained and was identified only in X-ray diffraction patterns of heavy separates. Distribution of trace elements is not clear; some are consistently high ... continues.
[Comment: Not necessarily very relevant to the enhanced vanadium at the Libyan locality, but it is associated with evaporites, including gypsum. The vanadium seems to be in clays.]

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Gong, J. 2004. Framework for the Exploration of Libya: An Illustrated Summary. Compiled by Jingyao Gong. Search and Discovery Article No. 10061 (2004) AAPG/Datapages, Inc., Tulsa, Oklahoma (jgong@aapg.org) Very well illustrated and very informative with very good maps.
Available online as a pdf document. Go to:
Framework for the Exploration of Libya, an Illustrated Summary.

General Statement
Recoverable reserves being produced in Libya, from more than 300 fields, exceed 50 billion barrels of oil and 40 trillion cubic feet of gas (Rusk, 2001, 2002). Even so, the Sirte (Sirt), Ghadamis, Murzuq, and Tripolitania basins (Figure 1) are yet to reach full maturity in exploration. Of the 24 giant fields, 20 were discovered prior to 1970. Deep plays are expected to be a large part of upcoming exploration efforts. Rusk (2001. 2002), in describing the petroleum potential of the centers of Libyan basins, summarized very well the petroleum systems and plays in six basin-center sectors (Figures 1, 2, 3, and 4). This compilation uses the Rusk article as the foundation for presenting several other published maps, cross-sections, and a database, as well as some images in his article; together these should add to the working tool kit for those interested in exploration of Libya....
The database of giant Libyan fields is from M.K. Horn (2003) in AAPG Memoir 78, Giant Oil and Gas Fields of the Decade 1990-1999. Other information is from various AAPG publications as well as Journal of Petroleum Geology (see Selected Bibliography).





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Hallett , D. 2002. Petroleum Geology of Libya. Elsevier Science, Ist Edition, 26th February 2011. Hardcover, 508pp. This is an important and major publication, but it costs 104 pounds sterling (from Amazon.UK). There is a Kindle Book version. Through Amazon, you can view various extracts of the book online. Go to:
Amazon.UK
and enter in the search box:
"Hallett Petroleum Libya".

Contents:

Contents List.

List of Figures

Preface.

Notes and Definitions.

Chapter 1: History of Libyan Oil Exploration and Production.
Before Independence; the fledgling Libyan oil industy; exploration activity 1956-1958; Bonanza 1959-1961; events leading to the Petroleum Law of 1965; exploration and production activity, 1962-1965; new concession awards and Joint Ventures, 1966-1969; exploration and production, 1966-1969; the Revolution and its aftermath, 1969-1974; the decline in exploration activity, 1969-1974; EPSA II and new discoveries, 1979-1986; Sanctions and EPSA III, 1986-1999; reserves; natural gas; summary.

Chapter 2: Plate Tectonic History of Libya.
Introduction; Rodinia; the break-up of Rodinia; the Pan-African Orogeny and the assembly of Gondwana; Gondwana during the Palaeozoic; Pangaea; Tethys; the development of Tethys; Tethys to Mediterranean.

Chapter 3: Stratigraphy: Precambrian and Palaeozoic.
The development of Libyan stratigraphy; Precambrian; Archaean and Proterozoic; Palaeozoic; Cambro-Ordovician; Hasawnah Formation; Ash Shabiyat Formation; Hawaz Formation; Melaz Shuqran Formation; Tasghart Formation; Mamuniyat Formation; Late Ordovician glaciation; Silurian; Iyadhar and B'ir Tlakshin Formations; Tanzuft Formation; Akakus Formation; Devonian; Tadrart Formation; Wan Kasa Formation; Awaynat Wanin Formation; local stratigraphy of the Awaynat Wanin 'Group'; south flank of the Al Qarqaf Arch; the Awaynat Wanin Formation in other areas; Tahara Formation; Carboniferous; Marar Formation; Assedjefar Formation; Dimbahah Formation; Tiguentourine Formation; Permian; Al Waryah Formation; B'ir al Jaja Formation.

Chapter 4: Stratigraphy: Mesozoic.
[This is a major section. About 100 formations are listed - not given here]

Chapter 5: Stratigraphy: Cainozoic.
[Another very large list of formations]

Chapter 6: Structure.
[A major chapter on the various basins, high, uplifts, troughs, offshore areas etc.]

Chapter 7: Petroleum Geochemistry.
[This is organised in terms of basins.]

Chapter 8: Petroleum Systems.
[This is a very large chapter divided up into the petroleum systems of the various basins, such as the Murzuq, the Ghadamis, the Western Sirt Basin, the Central Sirt Basin, the Adjabiya Trough, the Eastern Sirt Embayment, Offshore etc.]

Chapter 9: Postscript: Where are the Remaining Undiscovered Reserves?
[This is discussed in terms of basins - Murzaq Basin, Ghadamis Basin, Western Sirt Basin, Maradah Trough, Western Ajdabiya Trough, Eastern Ajdabiya Trough, Eastern Sirt Embayment, Cyrenaica, Offshore etc.]

Notes.

References.

Appendix: Glossary of Geographic Names.

Index.




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Amer, A. 2000. Processing of Egyptian boiler ash for extraction of vanadium and nickel. Physico-Chemical Problems of Mineral Processing. vol. 34, 153-171. By Ashraf Amer. "Egyptian crude oil contains considerable amount of vanadium and nickel."
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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 35 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.

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.

.

Lashhab, M.L. and West, I.M. 1997. Dolomitization of the Jir and Rawaghah Formations in Jabal al Jir and Western Sirte Basin. In: Symposium on the Geology of Libya, pp. 31-43.

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.


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Martins, A.H. 2000. Vanadium precipitation from sulphate acid solutions. Can. Met. Quarterly, vol. 39, No.1, pp. 15-22.
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Premovic, P. I. and Pavlovic, M.S. 1986. Vanadium in ancient sedimentary rocks of marine origin. Geochimica et Cosmochimica Acta, vol. 50, pp. 1923-1931. By Pavle I. Premovic and Mirjana S. Pavlovic.
Abstract:
The distribution of vanadium and vanadyl porphyrins in fractions (extractable organic, inorganic and kerogen) of the Serpiano marl and the La Luna shaly limestone have been determined by employing a variety of geochemical and spectroscopic techniques including atomic absorption, atomic emission, electronic absorption and electron spin resonance spectroscopies.
High levels of vanadium and vanadyl porphyrins were found with the major part of the total vanadium located in the kerogen fraction of both rocks. In contrast, while the kerogen of the La Luna rock also contained the major fraction of total vanadyl porphyrins (70%), the corresponding value for the Serpiano marl is only 30%. No vanadyl species wer present in the inorganic fraction of either rock.
It is suggested that the source of vanadium in these rocks is volcaniclastic materials and that the vanadyl porphyrin entities were incorporated into the kerogen structure through abiotic, geochemical modifications of biosynthetic pigment-chlorophyll.


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Wanty, R. B. 1992. Thermodynamics and kinetics of reactions involving vanadium in natural systems: Accumulation of vanadium in sedimentary rocks. Geochimica et Cosmochimica Acta, vol. 56, Issue 4, pp.1471-1483. By Richard, B. Wanty and Martin B. Goldhaber.
Abstract
A critical review of thermodynamic data for aqueous and solid V species is presented to evaluate dissolution, transport, and precipitation of V under natural conditions. Emphasis is given to results of experimental studies of V chemistry, especially those for which the experimental conditions are near those found in nature. Where possible, data are obtained for or corrected to the reference conditions of 298.15K, 1 atm (1.01325 bar) and zero ionic strength. Vanadium [IV] (V IV ) and vanadium[V] (V V ) are the most soluble forms of V in nature, and their complexes with fluoride, sulfate, and oxalate may act to increase V solubility under oxidizing conditions. Because redox behavior is of fundamental importance to understanding natural V chemistry, the kinetics of reduction of V IV to V III H2S were studied. Although H2S is predicted from thermodynamic data to be capable of reducing V IV to V III , this reaction has not been demonstrated experimentally. Experiments were carried out under conditions of temperature (45C), pH (3.6-6.8), ionic strength (0.05-0.1 m), and V concentrations (9.8-240 molar) likely to be found in nature. Because the reaction is very slow, H2S concentrations in excess of natural conditions were used (8.1 10 -4 to 0.41 atm). The results show that V IV is reduced to V III under a variety of conditions. The rate increases with increasing pH, but is not appreciably affected by ionic strength (as represented by the concentration of KCl, which was used as the supporting electrolyte in all cases). Prior to initiation of the reaction, there is an induction period, the length of which increases with increasing KCl concentration or decreasing pH. Attempts to model the reaction mechanism by numerical methods have failed to produce a satisfying fit of the results, indicating partial reaction orders, a complex mechanism, or involvement of a variety of intermediate species. The results of the thermodynamic and kinetic studies were applied to understanding the genesis of V deposits such as those commonly found on the Colorado Plateau. Vanadium in these sandstone-hosted deposits is present mostly in the reduced oxidation state, V III . Because of the insolubility of V III oxyhydroxides, it is likely that a more oxidized form of V (either [IV] or [V]) was transported to the site of mineralization, and that the V was reduced in situ and subsequently precipitated. A probable reductant is hydrogen sulfide; the presence of pyrite cogenetic with the V minerals documents the presence of H 2 S during mineralization. The experiments described here show that H 2 S could have reduced V IV to V III , and thus led to the formation of these deposits.

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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.