Depositional environments and sequence stratigraphy of the Sarvak Formation in an oil field in the Abadan Plain, SW Iran

The late Albian-early Turonian Sarvak Formation is the most important carbonate reservoir of the Abadan Plain, SW Iran. Twelve microfacies were identified, representing six facies belts: lagoon, shoal, rudist biostrome, slope, proximal, and distal open marine. The lower and middle parts of the Sarvak Formation were deposited in a carbonate ramp, whereas the upper part is attributed to a carbonate shelf. For relative dating, biostratigraphic analysis recognized two main biozones as well as two biofacies. The biozones are Nezzazata-Alveolinids Assemblage Zone; and Nezzazatinella-Dicyclina Assemblage Zone with a Cenomanian and Turonian age, respectively. The biofacies are Rudist debris and Oligostegina facies, which involve a wide time-range and are dated based on their stratigraphic position. From the identification of sequence boundaries and maximum flooding surfaces, four third-order sequences in the Sarvak Formation were recognized. The sequence boundaries, dated as early Cenomanian, mid-Cenomanian, Cenomanian-Turonian, and mid-Turonian, are major disconformity surfaces, showing evidence of karstification, dissolution-collapse brecciation, and development of paleosols. The maximum flooding (MF) surfaces are discriminated by development of deep-marine facies and also high gamma-ray responses on the well logs. The identified sequences can be correlated with the sequence stratigraphic framework established for the Arabian Plate and Zagros Basin. The results from this study should contribute to the identification of exploration and production targets in the Abadan Plain and neighboring area.