Biostratigraphy of the Cretaceous deposits based on ammonites in the southwest of Qayen area (Qumenjan section)

Ammonite biostratigraphy could be used in age determination and correlation of rock units in different sedimentary basins. Qumenjan section with 125 meters thickness is mainly formed by grey sandy limestone with grey and thick-bedded limestone intercalations. The study area is located in the eastern margin of the Lut Block. For a stratigraphical study of Lower–Upper Cretaceous deposits in southwestern of Qayen area, a stratigraphic section was selected and measured. Eight ammonites, including Anisoceras, Calycoceras, Hypoturrilites, Hysteroceras, Mantelliceras, Puzosia, and Scaphites genera and thirteen representative species were identified. Based on the identified assemblage fossils and comparison with international biozones, Hysteroceras orbignyi subzone for Late Albian age, Mantelliceras mantelli biozone for the lower part of Early Cenomanian age, Mantelliceras dixoni biozone for the upper part of Early Cenomanian age, and Turrilites costatus biozone for Middle Cenomanian age is suggested. According to identified genera and species a Late Albian–Middle Cenomanian age is assigned for ammonite bearing of the section. The first occurrence of Mantelliceras mantelli is taken as the base of Cenomanian. Compression of the identified ammonites with other basins shows that the east Iran basin was a part of Tethys Realm during late Albian–middle Cenomanian.