Biostratigraphy of the Cretaceous deposits based on Calcareous Nannofossils in Shushud section (North Birjand)

For biostratigraphic studies، based on calcareous nannofossils، a thickness of 480 meters of Cretaceous deposits in Shushud section (North Birjand) has been measured and sampled. The studied section is composed of shale، marl، marine sandstone and sandy limestone. The shale and marl units were more suitable for sampling. According to taxonomical studies، 10 genera and 25 species in Shushud section were identified and photographed. Based on identified calcareous nannofossils in the studied section، CC20-CC26 biozones from Sissingh (1977) biozonation were suggested، and based on determined biozones، the age of the studied sequence in this section is Late early Campanian- Late late Maastrichtian. Based on low diversity and abundance of species، it can be concluded that environmental conditions in this basin were not good for the life of the calcareous nannoplanktons، as well as digenesis caused low to medium nannofossils preservation.