The Lower Oligocene exposure of the Jal Az-Zor escarpment is widely considered as a siliciclastic exposure of the Kuwait Formation (also known as the Kuwait Group) dominated by estuary complexes. These exposures are generally characterized by cyclic deposition of stacked depositional sequences composed of extensively bioturbated, poorly sorted, massive to cross bedded sandstones. Recent research suggest that each sequence is capped by a carbonate dominated layer that ranges in thickness from few centimeters to 1.5 m. The presence of such repeated layer in a clastic dominated environment will be the focus of this paper.

Field observations suggest that these carbonate layers are of microbialitic origin as a result of microbial growth patterns associated with pustular appearance. Detailed investigation of these microbial beds suggests that they are composed predominantly of thrombolites colonies.

The presence of carbonates in clastic systems is largely associated with transgression. In this scenario, the interaction between microbial and estuary complexes is directly link to periodic drops in sea level; hence, their occurrence is stratigraphically limited to the top of each depositional cycle.

Such layers extend over a wide geographic area where they have been found across the escarpment, in wells drilled in northern Kuwait, and towards the south in Al-Khafji area.

Such layers have a high potential to act as prolific reservoirs and/or source rocks that could be used as analogues for deeper Jurassic and Paleozoic reservoirs in the Arabian Gulf region.