Calcareous nannofossil biostratigraphy of Valanginian ‒ Hauterivian sediments at the lower part of the Garau Formation, Arkavaz section (Kabir-Kuh anticline, SE Ilam)

Abstract The lower part of the Garau Formation with a thickness of 212 m at the southwest of the Kabirkuh anticline is investigated with regard to the calcareous nannofossils. Lithology of the studied interval is mainly consists of marl, marly limestone, black shale and limestone. 67 species from 33 genus and 13 families are recognized. Nannofossil events that are recorded from base to top of the section are as follow: the first occurrence (FO) of Calcicalathina oblongata, the last occurrence (LO) of Rucinolithus wisei, the FO of Lithraphidites bollii, the LO of Cruciellipsis cuvillieri, the first occurrence of Assipetra terebrodentarius and the last occurrence of Lithraphidites bollii. According to these index calcareous nannofossils, the studied interval is ranging from the uppermost part of CC2/NK2 biozone to the middle part of CC5b/NC5C subzone Considering these zonations, the age of the studied interval is Valanginian ‒ Hauterivian. According to the calcareous nannofossil data, the Valanginian ‒ Hauterivian boundary can’t be determined. This boundary is located at the base of the Tethyan ammonite Acanthodiscus radiatus at the leading GSSP candidate in the La Charce section of southeastern France.