Stratigraphic evidence for development of Aptian intrashelf basin in the Zagros area, eastern Fars Province, SW Iran


Abstract: ?The Lower Cretaceous of the Arabian Platform is renowned for the development of intrashelf basins. The study area is located in eastern Fars Province on the northeast Arabian plate and has experienced this environmental condition. The present study investigated two surface sections (Genau and Anguru) of the Dariyan Formation and compared the results with three neighboring wells in eastern Fars (eastern Zagros Fold Belt) in southern Iran to determine the development of rudist-bearing carbonates and intrashelf basin sediments. The Dariyan Formation was deposited in the Aptian as shallow-to-deep water carbonate facies. Lagoon, rudist banks/barriers, and open marine/basinal facies and six microfacies types have been distinguished. In the Genau section, the upper formation contains shallow rudistid limestone separated from the orbitolinid limestone of the lower formation by a deep pelagic unit. The pelagic sets disappear toward the Anguru section, but the rudistid unit remains. Abrupt changes were observed from shallow rudist facies to deep planktonic foraminifer facies. Comparison of the surface and subsurface sections (wells) suggests an intrashelf carbonate depositional model for the Dariyan Formation in the eastern Fars area. The term "Genau intrashelf" is proposed for this intrashelf basin surrounded by a shallow ramp. This intrashelf appears to be a northern subbasin of the Bab basin of the southern Persian Gulf. Extension of the Genau intrashelf subbasin and development of rudists around the margins of this intrashelf can be defined by tracing changes in the lateral facies of the Dariyan Formation.

Keywords: Dariyan Formation, Cretaceous, Aptian, Arabian plate, intrashelf basin, rudist

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