Microbial dolomites from carbonate-evaporite sediments of the coastal sabkha of Abu Dhabi and their exploration implications

Detailed petrographic studies of Recent dolomites from the coastal sabkha of Abu Dhabi using SEM and Energy Dispersive X-ray (EDX) analyses indicate that most of the dolomite started to form in " micro-niches" (i.e. small isolated pore spaces) within the carbonate sediments. These micro-niches tend to retain connate waters, becoming anoxic and supporting specific microbial activity which ultimately results in the formation of dolomite. This novel concept may help to explain the origin of many dolomite types, since recently deposited carbonate sediments have high porosities (up to 60%) and the pore spaces may serve as nucleation sites or " stations" for dolomite formation. The combination of neighbouring micro-niches in a porous carbonate may result in dolomitization of an entire stratum.Six dolomite types were reported from the studied sediments in the Abu Dhabi sabkha. These were pustular and cluster dolomite; dolomites associated with clay minerals and with evaporites; and dolomites associated with microbial mats and foraminiferal tests.