The study of Pabdeh-Asmari formations boundary based on calcareous nannofossil in one of the boreholes of Parsi Oil field, Dezful Embayment

In order to study calcareous nannofossils biostratigraphy, the upper part of Pabdeh Formation and the lower parts of Asmari Formation was selected in the one of the wells in the oil field Parsi in southwest of Iran. The study of calcareous nannofossil led to recognition of 39 species and 16 genera. According to the first occurrence of index species and distribution fossil assemblages, four biozones including Helicosphaera reticulate Zone (NP22/ Rupelian), Sphenolithus predistentus Zone (NP23/Rupelian), Sphenolithus distentus Zone (NP24/ Rupelian- Chatian) and Sphenolithus ciperoensis Zone (NP25/ Chatian), which equivalent to CP16c - CP19b was recognized at the uppermost part of Pabdeh Formation. As a result of this study and based on the identified calcareous nannofossil biozones, the age of the uppermost part of Pabdeh Formation is Rupelian-Chatian. Biozones of the calcareous nannofossil not detected in the anhydrite base of the Asmari Formation. In this study, predominant conditions of the sedimentary environmental, which is part of Neo-Tethys Basin, with the presence of index species calcareous nannofossils specified, which indicates that  basin is located in low latitude.