Biostratigraphy of marine deposits in the upper part of the Pabdeh Formation- lower part of the Asmari Formation in the Nareh section (Fars zone, Eastern Tethys)

In this study, the deposits of the upper part of Pabdeh Formation-lower part of Asmari Formation in the stratigraphic section of Nareh with a thickness of about 236 m located in the southwest of Jahrom were studied.In the lower part of the sequence, the deposits of the upper part of Pabdeh Formation are composed of shale and interlayers of argillaceous limestone with a thickness of about 154 m. Following that, the deposits of the lower part of Asmari Formation with a thickness of about 82 m of argillaceous limestone and medium bed limestone are located. From this section, 104 samples including 68 samples from the upper part of Pabdeh Formation and 36 samples from the lower part of Asmari Formation with 1 m intervals were collected.

By preparing 104 samples of the studied sequence and preparing it by slide smear method, 33 species belonging to 16 genera from the fossil group of calcareous nanofossils were identified. The slide smear method is a quick and easy method in which nanofossils are not wasted.

Based on biological events and associated fossil assemblages, the bio-zones of Sphenolithus pseudoradians Zone (NP20), Ericsonia subdisticha Zone (NP21), Helicosphaera reticulata Zone (NP22), Sphenolithus predistentus Zone (NP23) were identified in the study sequence. The zones studied are consistent with zones CNE20, CNE21, CNO1, CNO2- CNO3 / CNO4 of Agnini et al., (2014) and zones CP15b, CP16a, CP16b, CP16c -CP17 / CP18 of Okada and Bukry (1980).

Based on the introduced bio-zones, the age of the upper part of Pabdeh Formation in the studied section of Late Eocene (Priabonian)- early Oligocene (early Rupelian) and the age of the lower part of Asmari Formation of early Oligocene (late Rupelian) are suggested. According to the present study in Nareh section, the boundary between Pabdeh Formation and Asmari Formation is continuous.