Biostratigraphy and microfacies of the Asmari Formation in the Mansourabad Oilfield, southwest of Iran

In this research, the Asmari Formation in the Mansourabad Oilfield in the southern part of the Dezful Embayment has been studied in order to determine the age, study and identify microfacies and depositional environment. The biostratigraphy study was based on benthic foraminifera and recognition of microfacies and depositional environment carried on the thin sections prepared from core and cutting samples of two wells from the studied oilfield. The lower boundaries of this formation are conformable and gradually with the Pabdeh Formation, but sharp with the Gachsaran Formation, respectively. According to the study, four assemblage zones were identified in the Asmari Formation. Lepidocyclina-Operculina-Ditrupa zone indicates the age of Rupelian/Chattian, Archaias asmaricus-Archaias hensoni-Miogypsinoides complanatus zone indicates the age of Chattian, Indeterminat zone indicates the age of Aquitanian, and Borelis melo curdica-Borelis melo melo zone indicates the age of Burdigalian. Based on petrographic analysis nine microfacies related to tidal flat, lagoon and open marine sub-environment were identified that were deposited on a carbonate ramp environment extended from inner to outer ramp. This study led to better understanding of the stratigraphy and depositional environment of this reservoir formation.