Systematic determination and diagnostic characters of Ranikothalia nuttalli in the late Paleocene–early Eocene deposits in Padagi stratigraphic section, Sefid-Abeh Basin, Sistan Suture Zone

Of the most important characteristics of the Ranikothalia genus, as large benthic foraminifera, are the existence of ornamentation in the external part of the shell especially around the central umbilicus knob, marginal mesh channels (MMC) in the marginal chord, trabeculate system with channels, V-shape plate in the floor of chambers and accumulation of septum that differentiated this genus from Nummulites genus and placing it in the Palaeonummulitinae sub-family. The Ilerdian transgression near the P5 Zone (Pelagic P5) is a stratal key surface for the determination of the Paleocene-Eocene boundary in the neritic deposits. Ranikothalia nuttalli as an index species is used for recognition of the Paleocene–Eocene boundary in the Neo-Tethys shallow water successions. This species, in the Padagi section, resembling the Pakistan Indus Basin, accompanied with Miscellanea miscella, Discocyclina sp., Discocyclina sp., Assilina sp. that indicated SBZ5/6 and suggested lower Ilerdian (earliest Eocene) age. Keywords: Ranikothalia , Ilerdian, systematic, Sistan Suture Zone Introduction Large benthic foraminifera, such as Fusulinidae, Oritoididae, Alveolinidae, Rotaliidae and Nummulitidae, are important fossil and extant forms that with respect to systematic and biostratigraphic widespread, are studied and some biozonation schemes based on them are suggested. Nummulitidae (such as Ranikothalia) are a group of large benthic foraminiferas developed in the Paleocene and Eocene of the Tethys basin. Larger benthic foraminiferas biozonation is represented by Serra-Kiel et al. (1998) which based on these group of foraminifera Paleocene and Eocene series are divided into 20 shallow benthic zones (SBZ1–SBZ20). The Paleocene–Eocene boundary is considered between SBZ4–SBZ5 (Scheibner & Speijer 2009). Ranikothalia nuttalli as an index species is used for recognition of the Paleocene–Eocene boundary in the Neo-Tethys shallow water successions. This species, in the Padagi section, resembles the Pakistan Indus Basin, accompanied with Miscellanea miscella, Discocyclina sp., Discocyclina sp., Assilina sp. that indicated SBZ5/6 and suggested the lower Ilerdian (earliest Eocene) age. The purpose of this study is to identify and introduce the Ranikothalia nuttali species and investigate its expansion in the adjacent sedimentary basin in the Neo-Tethys Ocean. Material & Method To do research and biostratigraphic investigations of the Paleocene–Eocene deposits in the Sefid-Abeh basin,