Geology of the Sahil 1:100 000 map sheet, 100-17, United Arab Emirates

This Sheet Description describes the Quaternary and solid geology of the Sahil 1:100 000 scale geological map of the UAE. The Sahil district covers 2500 km2 of the country stretching inland from the coastal sabkha. The land rises from 10 m above sea level on the coastal plain in the northwest to over 100 m in the southeast. Miocene bedrock crops out beneath the northern half of the district, forming isolated jebals up to about 30 m high within fields of low barchanoid dunes, and underlying intervening interdunes or small sabkhas. The oldest rocks in the area are the Miocene rocks of the Dam, Shuwaihat and Baynunah formations. The Dam Formation comprises pale grey, fine grained carbonates and nodular gypsum beds which crop at low elevations within and around the margins of the coastal sabkha. The overlying Shuwaihat Formation is characterised by red sandstones with subordinate green mudstones and grey pedogenic beds laid down in a mixed aeolian-fluvial-sabkha environment. It is overlain by the Baynunah Formation which has a characteristic basal bone bed with an erosive base. Above is a sequence of interbedded calcareous siltstones, siltstones and fine sandstones, laid down in a low-energy fluvio-lacustrine system (Barakah and Hamrah members), capped by reddish brown, playa or lacustrine sandstones (Sahil Member). Miocene deposits are overlain unconformably by Quaternary deposits of the Madinat Zayed Formation: quartz dominated, cross bedded aeolianite and lacustrine siltstone, and the Ghayathi Formation: moderately cemented, carbonate dominated aeolianite. Much of the district has a cover of unconsolidated aeolian sand either as a thin veneer within the interdunes and coastal sabkhas or as extensive low barchanoid dune fields, sand sheets and dune ridges. The northern part of the district includes part of the coastal sabkha, which is largely underlain by deflated unconsolidated quartzose aeolian sand and the calcareous Ghayathi Formation aeolianite.