Abstract

The anhydrite and primary dolomite sequence penetrated by wells at the Umm Shaif oil field is petrographically similar to and presumably the stratigraphic equivalent of the Hith anhydrite formation of eastern Saudi Arabia. It occurs below upper Neocomian-Aptian (lower Cretaceous) micrites but above sparites and micrites containing a fauna and flora of early Neocomian aspect; these in turn overlie upper Jurassic (Callovian-Oxfordian) beds with marked disconformity and are interpreted as basal Cretaceous transgressive deposits. On the assumption that only one anhydrite formation is represented in this part of the Mesozoic succession in the Persian Gulf region, and that the formation is isochronous throughout its lateral extent, reconsideration of the upper Jurassic age assigned to the Hith formation and its supposed equivalents in the Qatar peninsula, Iraq, and elsewhere is warranted.

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