A new aspect in determining the age of the Cretaceous- Tertiary successtion boundary based on calcareous nannofossil in the Northwest Ilam

In this research, biostratigraphy of the Pabdeh and Gurpi Formations boundary in Northwest Ilam, Geno section was studied. The study of calcareous nannofossil led to recognition of 31 species and 25 genera. According to the first occurrence of index species and distribution fossil assemblages, zones Reinhardtites levis zone (CC24) and base of Arkhangelskiella cymbiformis zone (CC25) of Sissingh (1977) of uppermost of Gurpi Formation and Ellipsolithus macellus Zone (NP4) and Fasciculithus tympaniformis Zone (NP5) of Martini (1971) equivalent to bio zones (CP3- CP4) of Okada and Bukry (1980) of Pabdeh Formation at Geno section were identified. As a result of this study and based on the obtained bio zones, age of the Cretaceous -Tertiary successtion boundary in Northwest of Ilam, is early Late Maastrichtian to Late Danian.