Geology of the Ghantoot 1:100 000 map sheet, 100-11, United Arab Emirates

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