This Sheet Description describes the Quaternary and solid geology of the Ghantoot 1:100 000 scale geological map. Over 400 observation points were made throughout the district. The Ghantoot district covers about 1600 km2, including a number of low offshore barrier islands, reefs and sand flats. The region has seen great anthropogenic development over the past 30 years, which has radically changed the surface geology. The underlying pre-Quaternary bedrock comprises Miocene evaporitic mudstone and siltstone of the Gachsaran Formation (Fars Group) overlain by the Baynunah Formation sandstones (not exposed at surface) and the dolomitic conglomerates, sandstones and siltstones of the Barzaman Formation. The Miocene bedrock is poorly exposed, with relatively few surface outcrops, in east-northeast to west-southwest trending inter-dune areas and in a number of temporary excavations. In many areas, the Miocene rocks are only known from boreholes. The evidence from these suggests there is a marked facies change from the coarse dolomitic conglomerates of the Barzaman Formation in the east to interbedded siltstones and sandstones of the Baynunah Formation in the far southwest of the district. The Miocene rocks are locally overlain by fluvial sandstones and channel gravels of the Hili Formation. These represent Quaternary outwash from the Hajar Mountains in the east. The gravels contain ophiolite and chert clasts ultimately derived from the UAE-Oman ophiolite to the east. Much of the region is partially covered by pale carbonate-cemented aeolianites of the Ghayathi Formation, themselves often covered in a veneer of more recent aeolian sand. These are well exposed near the coast in spectacular zeugen. Inland these paleodunes forms a series of east-northeast trending fossil linear ridges. Along the coast, some of the Ghayathi Formation zeugen have a cap of the marine deposits of the Fuwayrit Formation. More recent, modern pale carbonate-dominated low dunes drape the Ghayathi Formation and the interdune bedrock exposures inland. The coastal zone is dominated by a range of Holocene to Recent littoral and marine deposits including beach ridges, algal mats, and intertidal sediments, all contained within the Abu Dhabi Formation. The Quaternary deposits are overlain by various modern dune sands (Rub al Khali Formation), mapped as Low Dunes. Interdune areas, floored either by Miocene or Quaternary rocks typically have continental sabkha veneers and, adjacent to the dune fields, thin sand veneers. Much of the coastal strip consists of a variety of anthropogenic deposits including reclaimed ground, made ground and areas extensively landscaped for forestry and development.

Outcrop

Siltstone

Bedrock

Calcarenite

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Geology of the Abu Dhabi 1:100 000 map sheet, 100-16, United Arab Emirates

Andrew Farrant R.A. Ellison J.W. Merritt J.E. Merritt Andrew J. Newell

This Sheet Description describes the Quaternary and solid geology of the Abu Dhabi 1:100 000 scale geological map. The Abu Dhabi district covers 3620 km2 along the Arabian Gulf coast including the northern part of Saadiyat island, Abu Dhabi, part of the Mussafah district and many of the islands to the west. These include Futaisi, Bu Kesheishah, Halat al Bharaini, Al Dabiya, Bu Qumah, Bu Shara, Al Qanatir and Al Rafiq. The sheet also includes a significant part of the coastal plain southwest of Abu Dhabi between Shunayyin in the east to Borquat al Rashid in the west, and south to Maharqah, across which the main E11 coastal highway runs. In the southeast of the district, an area of higher ground is formed of Miocene rocks draped by a variable sequence of cemented and unconsolidated dune sand. The region hosts several major oilfields including the Rumaitha, Shanayel, Al Dabb’iya, Umm al Dalkh, Al Mutarib and Umm al Lulu fields. The region is dominated by a series of offshore islands, part of a chain of barrier islands that extend from north of Abu Dhabi to Marawah Island, west of the present area. These islands, along with the sea-ward margin of the coastal plain are mostly comprised of a thin sequence of intensively studied Holocene marine carbonates termed the Abu Dhabi Formation. These sediments represent a transgressive-regressive sequence, and form the classic carbonate-evaporitic ‘sabkhas’ for which the region is justly famous. The Abu Dhabi Formation includes a range of marine and supratidal facies including coastal spits, bars and beach ridges, lagoonal muds, algal mats and ooidal tidal deltas deposited over the last 10 000 years. The southern limit of the Holocene transgression is marked by a beach ridge running parallel to the coast and clearly visible on satellite imagery. The barrier islands commonly have a core of well-cemented Pleistocene carbonate dune sand (Ghayathi Formation) around which the carbonate spits, bars and ridges of the Abu Dhabi Formation were accreted. The islands have been largely deflated down to the local water-table leading to the development of extensive sabkhas. Consequently, the islands are generally flat but punctuated by small Ghayathi Formation mesas and zeugen, forming mushroom-shaped outcrops rising up to 6 m above sea-level, locally capped with marine limestones of the Late Pleistocene Fuwayrit Formation. Offshore to the north of the island, below low water, is the Great Pearl Bank, an area of reefs and coralgal sands named after the former pearling industry in the region. South of the Holocene beach ridge, much of the onshore area is an extensive, very gently sloping coastal plain, dominated by a deflated planation surface developed on either unconsolidated quartzose aeolian sand or well cemented carbonate grainstones of the Ghayathi Formation. The deflation surface is commonly marked by secondary gypsum forming a sabkha. The Ghayathi Formation palaeodunes are locally well exposed, forming spectacular wind-sculpted mesas and zeugen both on the islands and within the lagoons, but also onshore draping the Miocene rocks in the southeast of the district.

Abu dhabi

Sabkha

Coastal plain

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Fourth IGCP 348 field meeting in Northern Ethiopia and Eritrea

Journal of African Earth Sciences (1996)

R.J. Thomas

10.1016/s0899-5362(97)86883-2

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Al Wijah geological map

S.J. Price R.J. Thomas Rhiannon Smith

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Geology of the Shuwaihat 1:100 000 map sheet, 100-32 (and the Islands of Delma, Zirku, Qarnain and Arzana at 1:50 000), United Arab Emirates

R.J. Thomas R.A. Ellison Kathryn Goodenough Andrew Farrant Andrew J. Newell

This Sheet Description describes the solid and Quaternary geology of the Shuwaihat area and the salt islands of Delma, Zirku, Arzana and Qarnain (at 1:50 000 scale). The two small islands of Yasat Ali and Yasat Safli were also mapped. The mainland area shown is quite small (115 km2), but is geologically important in that it contains the Type Sections of the Miocene Shuwaihat Formation and the Barakah Member of the Baynunah Formation, on Shuwaihat Island and Jebel Barakah respectively. Some 300 observation points were made throughout the district. The oldest rocks in the area are those of the Neoproterozoic Hormuz Complex, exposed on the four salt islands included on the map. The islands are cored by salt domes with excellent outcrops of the Hormuz breccias. These were mapped at 1:25 000 scale and large clasts >100 m across have been shown on the map as igneous, sedimentary and undifferentiated megaclasts. Two metamorphic rock clasts were recorded and detrital zircons from one of these, a layered marble from Delma, constrained the maximum age of deposition of the original sediments at 590 ± 2 Ma. The island of Zirku is unique in that it contains extensive outcrops of deformed turbiditic rocks, termed the Zirku Formation, which form a semi-continuous carapace over Hormuz breccia. U-Pb dating of detrital zircons of a sandstone unit in the formation determines a depositional maximum age of 560 ± 19 Ma. U-Pb zircon dating of a felsic volcanic igneous clasts from Qarnain yielded a Neoproterozoic (Ediacaran) crystallisation age of 561 ± 16 Ma, suggesting that volcanism was penecontemporaneous with sedimentation. The salt domes are unconformably overlain by Quaternary pale cream-coloured carbonate grainstones and gravels of the Jebal Dhanna Formation, which are deposits unique to the salt domes. The salt domes were injected into Miocene strata which underlie most of the area. Recent movements of the salt diapirs are represented in numerous ‘salt blisters’ seen on many of the islands. The oldest Miocene rocks in the district, marine sedimentary rocks of the Gheweifat Member of the Dam Formation, outcrop on the two small Gulf islands of Yasat Ali and Yasat Safli. Over the rest of the area, the oldest Miocene rocks belong to the Shuwaihat Formation, which consists of highly variable sequence of fluvial, aeolian, terrestrial playa and continental sabkha red-bed siliciclastic sediments, well exposed in a number of sections on Shuwaihat Island, Jebel Barakah and on Delma. The Shuwaihat Formation is unconformably overlain by the Barakah Member of the Baynunah Formation, also well exposed in sections on Shuwaihat Island and Jebel Barakah. It comprises a sequence dominated by fluvial sandstones, with channel lag conglomerates particularly common near the base, where fossilised bone, wood and egg shells are locally abundant. The topmost few metres of strata on Jebel Barakah are made up of greyish green carbonate siltstones of the succeeding Habshan Member.

Breccia

Outcrop

Felsic

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The pre-break-up position of Haag Nunataks within Gondwana: possible correlatives in Natal and Donning Maud Land

G.H. Grantham Bryan Storey R.J. Thomas Jeffrey Bruce Jacobs

Position (finance)

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Geology of the Al Wijah1:100 000 map sheet, 100-8,United Arab Emirates

S.J. Price R.J. Thomas Richard A. Smith

This Sheet Description describes the geology of the Sweihan and Remah 1:100 000 scale geological map. The Sweihan and Remah district covers 2780 km2 east of Abu Dhabi. Over 700 observation points were made throughout the district. Pre-Quaternary bedrock comprises Miocene conglomerate of the Barzaman Formation which probably underlies the entire area. It is poorly exposed in roughly east-west trending inter-dune areas and in a number of excavations in the northwest and eastern parts of the area. Over almost the entire area, the Barzaman Formation is overlain by deposits of the Quaternary (Pleistocene) Hili Formation, which is up to at least 20 m thick in places. Three facies of the Hili Formation were mapped; coarse fluvial channel gravels, fluvial sands, and siltstones (overbank deposits). They represent a complex fluvial outwash system draining from the Hajar Mountains in the east. As such, they tend to fine distally to the southwest, where the majority of the fluvial sands and siltstone/mudstones occur. They locally contain intercalated aeolian sand beds which were blown in from the north-west. Quaternary carbonate-cemented aeolianites of the Ghayathi Formation are well-developed in the north western corner of the district. These represent fossil seif dune systems which locally form the cores to fields of modern pale carbonate-dominated low dunes. The Quaternary deposits are overlain by various modern dune sands (Rub al Khali Formation) with various morphologies, mapped as dune ridges, locally culminating in star dunes, and barchanoid low dune fields. Interdune areas, floored either by Miocene or Quaternary rocks typically have continental sabkha veneers and, adjacent to the dune fields, thin sand veneers

Bedrock

Conglomerate

Alluvial fan

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Preface to the Special Issue of IGCP 348 (Mozambique and Related Belts)

Journal of African Earth Sciences (1996)

R.J. Thomas R. SHACKLETON S. Muhongo

10.1016/s0899-5362(97)00001-8

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