Geology of the Madinat Zayed 1:100 000 map sheet, 100-21, United Arab Emirates

This Sheet Description describes the Quaternary and solid geology of the Madinat Zayed 1:100 000 scale geological map. 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 above the coastal sabkha in the northern part of the district. The overlying Shuwaihat Formation is characterised by red sandstones with subordinate green mudstones and grey pedogenic beds. It typically comprises a number of cyclical sequences deposited in a mixed aeolian-fluvial-sabkha environment. It is overlain by the Baynunah Formation, of which both the Barakah and Hamra members are well-developed in this area. The lower, fluvial, Barakah Member, with its characteristic basal bone bed erosively overlies the Shuwaihat Formation. The overlying Hamra Member comprises interbedded calcareous siltstones, siltstones and fine sandstones, laid down in a low-energy fluvio-lacustrine system. This is capped by reddish-brown, playa or lacustrine sandstones of the Sahil Member. These well-cemented lithologies, particularly the calcareous siltstones and limestone of the Hamra Member commonly cap low jebals and ridges in the area north of Habshan. Quaternary sediments are present throughout much of the area. The Madinat Zayed Formation overlies the Baynunah Formation and comprises a number of facies including reddish-brown, wavy and cross-bedded aeolian sandstones and light grey laminated lacustrine siltstones and rooted aeolian sands. The Ghayathi Formation, which is made up of moderately well-cemented, carbonate-dominated palaeodune sandstones, occurs as isolated areas of outcrop draping older Miocene or Madinat Zayed Formation bedrock mostly in the north and east of the district. Much of the district has a cover of unconsolidated aeolian sand either as a thin veneer or as laterally extensive 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.