Some Aspects of the Diagenetic History of the Sabkha in Abu Dhabi, Persian Gulf

Abstract

Sedimentary accretion around the landward margins of coastal lagoons in Abu Dhabi has produced a low accretion plain, the “sabkha”. Concentrated sea water from the adjacent lagoon seeps into the sabkha sediments both laterally via the inter-tidal zone, and vertically through the supratidal zone during exceptional marine flooding. Aragonite and gypsum are precipitated within the sediment from both brines, increasing the Mg:Ca ratio and entraining the dolomitization of aragonitic mud.

A buried algal mat prevents the vertical penetration of brine. Where all available aragonite above this permeability barrier has been exhausted (due to dolomitization) the elevated Mg/Ca ratios resulting from the continued precipitation of gypsum lead to the formation of magnesite. Where the buried algal mat dies out, towards the inner parts of the sabkha, brines percolate into and dolomitize underlying lagoonal sediments. Nodular anhydrite forms mainly above the algal mat partly by the dehydration of pre-existing gypsum.