Lithostratigraphy, Microfacies, and Biostratigraphy of the Pabdeh Formation based on planktonic foraminifera in the Gachsaran Oil Field (Dezful Embayment, South-West Iran)

In order to study lithostratigraphy, microfacies, and biostratigraphy of the Pabdeh Formation based on the new biozonation of planktonic foraminifera in the Tethys region, 1 subsurface section in well No. 314 of Gachsaran Oil Field has been studied.The Pabdeh Formation with a thickness of 241m consists mainly of shale, calcareous shales, argillaceous limestones, and cherty limestones. The lower boundary of the Pabdeh Formation with the Gurpi Formation is unconformable and the upper boundary with the Asmari Formation is conformable.Investigation of the stratigraphic distribution of these microfossils in the subsurface section (Gachsaran well No. 314) led to the identification of 52 genera and 21 species of planktonic foraminifera and 17 biozones based on equivalent to new biozone of (Wade et al, 2011) in the global biozonation in this region. These identified biozones include 2 biozones in the Paleocene, 13 biozones in the Eocene, and 2 biozones in the Oligocene in the studied and are well correlated with some biozones in the Tethys region. Based on the foraminiferal assemblages and their biozonation, the age of the Pabdeh Formation in well No. 314 of Gachsaran Oil Field is Middle Paleocene (Selandian) – Early Oligocene (Rupelian). Defined biozones are compared with the other sections presented in the Izeh Zone (Tange Hatti, north flank of Tange Pabdeh, Chahardeh, and Lar Mountains) in the Zagros Basin.Petrography and microscopy studies of the Pabdeh Formation in section imply, these sediments are belonging to microfacies (Deep Shelf) and were deposited part of a carbonate platform.