The sabkha sequence at Mussafah Channel (Abu Dhabi, United Arab Emirates): Facies stacking patterns, microbial-mediated dolomite and evaporite overprint

Abstract

The Mussafah Channel is a man-made canal cut perpendicular to the coastline, located to the southwest of the city of Abu Dhabi, United Arab Emirates, and is ideal for studying coastal depositional processes in an arid environment. The channel walls reveal a few meters of Pleistocene reworked dune deposits, unconformably overlain by Holocene carbonates and sabkha evaporites. The Holocene succession consists of intertidal to shallow subtidal sediments that vary significantly along depositional strike direction. Bladed gypsum crystals, gypsum rosettes, and nodular to highly contorted, discontinuous bands of classic sabkha anhydrite are present along the channel walls. Sedimentology, petrography, SEM, X-ray diffraction, and radiocarbon age-dating analyses of the sabkha sequence show the following profile from base to top: (1) non-bedded carbonate-rich sand: reworked aeolianite with an approximate (ca.) radiocarbon age in years (yrs) before present (BP) ca. 26,80014C yrs BP; (2) cross-bedded to non-bedded carbonate-rich sand: aeolianite/reworked aeolianite (ca. 24,000-23,500 14C yrs BP); (3) crinkly-laminated stromatolitic bindstone: intertidal, low-energy microbial mat (ca. 6,600-6,200 14C yrs BP); (4) lower, discontinuous and in places reworked hardground: cemented channel-lag deposits (ca. 6,40014C yrs BP); (5) peloid-skeletal packstone with rootlets or microbial-laminated peloid-skeletal packstone, laterally grading into fine- to coarse-grained, cross-bedded, cerithidrich, bioclastic packstone, grainstone, and rudstone: lowermost intertidal to shallow subtidal, low-energy, mud-rich rooted and microbial-laminated lagoonal deposits and moderate- to high-energy intertidal to shallow subtidal tidal-channel, tidal-delta, and tidal-bar deposits (ca. 6,200-5,20014C yrs BP); (6) upper discontinuous and shingled hardground: cemented beach rock (ca. 5,700 14C yrs BP); (7) cross-bedded, bioclastic rudstone/grainstone, grading laterally into intervals displaying bladed gypsum crystals and nodular to enterolithic anhydrite: intertidal to shallow subtidal, high-energy longshore beach bar and beach spit deposits; overprinted by sabkha gypsum and anhydrite (ca. 5,000 14C yrs BP).