Sequence stratigraphy and microfacies of the Sarvak Formation, west of the Hendijan–Bahregansar–Nowrooz Palaeohigh

The Sarvak Formation is one of the most important oil reservoirs in southwestern Iran. The Hendijan–Bahregansar–Nowrooz strike-slip Fault (HBNF) is known as a major fault system in the northwestern of the Persian Gulf, extending for approximately 700 kilometers in a north-northeast to south-southwest direction. This fault line passes through the northwestern region of the Persian Gulf, exerting a significant influence on the geological evolution of the area. This study emphasizes on importance of the microfacies, sedimentary environments, and sequence stratigraphy of the Sarvak Formation in the western part of the Hendijan–Bahregansar–Nowrooz palaeohigh, specifically those of the Hendijan, Bahregansar, and Mahshahr oilfields in southwestern Iran. A total of 186 thin sections of rock samples was examined in terms of their petrographic, sedimentological, and stratigraphic aspects. This led to the identification of seven microfacies distributed in four facies belts of tidal flat, lagoon, shoal, and open sea. The lack of turbidites and continuous reefs indicates that carbonates of the Sarvak Formation in the studied area formed on a homoclinal ramp. Additionally, five third-order depositional sequences were identified in the strata studied northwest of the HBNF. It can be concluded that the studied area was structurally stable during the Early Cenomanian. However, starting from the Late Cenomanian, significant tectonic phases resulted in the uplift of the area along an old ridge. Furthermore, the data indicate that the uplift of the Arabian Plate during the Early Turonian had significant effects on sedimentary processes in the region. This resulted in the retreat of the sea and the occurrence of a subsequent notable erosion phase at the Cenomanian–Turonian boundary in many areas including the Bahregansar and Hendijan oilfields. The interpretation of sedimentary characteristics and depositional environments in the upper part of the Sarvak Formation in the Mahshahr Oilfield relies on seismic sections, petrophysical logs, and microfacies analysis. Based on the available information the sediments apparently accumulated in a north-northwest to south-southeast trend, forming an onlap over both sides of a palaeohigh.