Biostratigraphy of Abderaz Formation based on calcareous nannofossils in eastern Kopet-Dagh (Ghareh-Soo Section)

Abderaz Formation is studied along Ghareh-Soo stratigraphic section, in eastern part of Kopet-dagh Sedimentary Basin which measures 958 meters in thickness. Nannofossil bioevents have been utilized to biostratigraphically classify the exposed sedimentary succession based on schemes of Sissingh (1977 modified by Perch-Nielsen, 1985), Roth (1978 modified by Bralower et al., 1995) and Burnett et al. (1998) and accordingly the rocks are attributed to Late Cenomanian to Early Campanian time interval. The results of palaeoecological studies along the succession show a decrease in high fertility marker taxa like Biscutum spp., and point to warm and oligotrophic surface water conditions in the late Cenomanian sediments i.e. upper parts of Aitamir Formation. A relative increase in high fertility taxa at the base of Abderaz Formation spanning the Cenomanian-Turonian boundary interval is also distinguishable. The Turonian part of Abderaz Formation is characterized by an increase in diversity and abundance of forms belonging to family Polycylolithaceae. Appearance of cool water taxa such as Gartnerago segmentatum, Ahmuellerella octoradiata and Kamptnerius magnificus in middle part of Abderaz Formation may probably be an indication of the Late Turonian to Campanian gradual and continuous cooling.