Facies analysis, depositional sequences and platform evolution of the Sarvak Formation (late Albian-Turonian) in the Zagros Basin, West of Iran

Abstract

The Sarvak Formation is a carbonate interval (as part of the Bangestan Group) deposited during the Cretaceous (late Albian-late Turonian), which hosts considerable hydrocarbon reserves. We logged five surface sections in the west of the Zagros Basin to depict the depositional environment and sequence stratigraphy of the Sarvak Formation. The formation comprises five 3rd order depositional sequences, including six facies belts deposited on a carbonate platform. The lower part of the formation comprises two depositional sequences (late Albian-early Cenomanian) deposited on a ramp. In contrast, the rest of the formation (Cenomanian to early Turonian), composed of three depositional sequences, were deposited on a rimmed shelf. The shift from ramp to shelf was presumably due to changes in the tectonic regime of the Arabian Plate from passive to active margin, and in part due to the obduction of the Neotethys’ ocean crust during the late Middle Cretaceous, accompanied by the development of shoal complex and rudistic reefs. This resulted in the development of some isolated carbonate platforms bordered by intrashelf basins, particularly in the Lurestan Zone. Active basement faults caused the exhumation of the platform and the development of unconformity on the Cenomanian-Turonian boundary. The five depositional sequences we studied were mainly controlled by eustatic change(s) during Albian, mid-Cenomanian to Turonian.