Late Paleocene-Late Eocene Calcareous nannofossil biostratigraphy in the Zagros Basin (Iran), Tethyan realm

Abstract

Calcareous nannofossils are a valuable proxy commonly used in biostratigraphic and paleoenvironmental studies. A high-resolution biostratigraphic analysis of the Pabdeh Formation and transitional interval was undertaken in one of the oilfields, located in the Strait of Hormuz in Iran. The stratigraphic interval studied includes marl, argillaceous limestones and interlayers of limestone and shale. In this study, for the first time, Paleogene calcareous nannofossil assemblages comprising 67 species belonging to 28 genera were identified. The calcareous nannofossils data led to the identification of several bio-zones NP5-NP20 (CNP7-CNE20) in the Pabdeh Formation and transitional interval, these nannofossil zones allow dating the section to the Late Paleocene (Selandian) - Late Eocene (Priabonian). The biostratigraphy model, highlights the existence of relatively good continuity across the Selandian/Thanetian (S/T), Thanetian/Ypresian, Ypresian/Lutetian and Bartonian/Priabonian stage boundaries. Also, the presence of index calcareous nannofossils (e.g., Discoaster, Sphenolithus, Reticulofenestra, Dictyococcites and Helicosphaera) from the Tethyan realm and low latitude in the studied section indicates that sea level temperature has been frequently warm between the Selandian and Priabonian intervals. In addition, the calcareous nannofossils analysis indicated that their diversity and abundance changed with climate fluctuations from the Paleocene to Eocene.