Holocene coastal carbonates and evaporites of the southern Arabian Gulf and their ancient analogues

Abstract

The Holocene sediments of the coast of the United Arab Emirates in the southeastern Arabian Gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates, evaporites and siliciclastics throughout the geologic record. This paper is intended as a convenient single source for the description of sediments of this region, providing information on how to reach the classic localities and some of the analogs. The Holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide. The sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud, with these latter fine sediments increasing as the water deepens. The pelecypod-rich sediments also collect east of Abu Dhabi Island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons. West of Abu Dhabi Island the shallow water margin is the site of coral reefs and coralgal sands, whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands. Grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common. They are particularly common on the less protected shallow water margins of the lagoons west of Abu Dhabi Island. Pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern Abu Dhabi. Lining the inner shores of the protected lagoons of Abu Dhabi and on other islands to the west are cyano-bacterial mats and mangrove swamps. Landward of these, a prograding north facing shoreline is formed by supratidal salt flats (sabkhas), in which evaporite minerals are accumulating. This paper describes the localities associated with (1) the mangrove swamps of the west side of the Al Dhabaiya peninsula; (2) the indurated cemented carbonate crusts, cyanobacterial flats and sabkha evaporites on the shore of the Khor al Bazam south of Qanatir Island; (3) the reef and oolitic sand flats on the coast just east of Jebel Dhana; and (4) the marine travertine and aragonite coats associated with the beach sediments in a small bay south of Jebel Dhana; and (5) the Sabkha Mutti between Jebel Barakah and Al Sila. Similar sedimentological associations of carbonate and evaporites to those of the Holocene of the United Arab Emirates are to be found in the Tertiary and Mesozoic sedimentary rocks of the immediate subsurface in the Arabian Gulf. Other analogs to this setting include the Paleozoic carbonates of the western USA, Europe, and Asia, Mesozoic carbonates of the Gulf of Mexico, Europe, and Middle East and Tertiary sedimentary rocks in the Middle East.