Conferences

Microbial dolomites have been fully documented in lagoonal and sabkha sediments from different parts of the world. Detailed textural characterization, using SEM coupled with Energy Dispersive X-ray (EDX), of three deep cores (down to six meters) and fifty surface samples from the intertidal and supratidal zones of the coastal sabkha of Abu Dhabi indicated that dolomites form up to 50% of the bulk sediments. This dolomite is found to form in small semi-closed pores or “micro-niches” within the carbonate sediments. Typical “micro-niches” include skeletal grains chambers, angles between mineral plates and local dissolution depressions. These “micro-niches” retains connate water for longer periods compared to the rest of the sediments; the water becomes anoxic due to the decay of organic materials by microbial activity and hence causes the precipitation of dolomite. The later spread of dolomite would depend on the presence of well-connected networks of such pores. This concept means that microbial dolomite is not restricted to the lagoonal-sabkha settings and can be found in any depositional environment at any scale because most of carbonate sediments have high porosities upon deposition.

The Upper Triassic reservoirs of the northern parts of the Arabian Plate are formed of thick dolomites of wide distribution and usually associated with microbial mats and evaporites. Thin section examination of such dolomites shows that many of these may had formed in “micro-niches” and then spread out to other parts of the rocks. Furthermore, many of the present day porous dolomite horizons were probably microbial mats rather than limestones horizons as though earlier.