Lithostratigraphic classification and depositional history of the Permian rocks in Al Qasim Province, Saudi Arabia

Abstract

Surface and subsurface investigations on the Permian rocks (Khuff Formation) in Al Qasim Province, Saudi Arabia led to the subdivision of these rocks into two formal rock units. The lower is the Sark Formation and the upper is the Al Watah Formation. The Sark Formation consists of carbonates with interbeds of claystones and marl. Its type locality lies south of Unayzah (lat. 26° 02′ N and long.44° 00′ E). The Al Watah comprises two members, the lower is the Midhnab Shale Member and the upper is the Khartam Limestone Member. The type section of the Al Watah Formation lies at Jal Al Watah (lat. 26° 30′N and long. 44° 02′ E).

The Sark Formation exhibits facies change along the strike of the Arabian basin. Southeastwards at Al Arid, the environment was coastal marine, while at Al Mulayh the environment was quiet marine shelf, where the facies are fine-grained wackestones. In Al Qasim Province, the environment is open marine platform where the sequence consists of shallowing-upward carbonate cycles which were deposited under subtidal-supratidal conditions. The Al Watah Formation also shows gradual transition from one environment to another along southeast-northwest direction. At Al Arid, the depositional environment is coastal marine which changes northwestwards at Al Mulayh to lagoonal shelf since the facies are mostly of fine-grained dolostones. In Al Qasim Province, deeper open marine is recognized depositing the Midhnab Shale Member in low sea level and the Khartam Limestone Member in submerged platform (subtidal zone).