Diagenetic history of chalky-marl couplets in Ab-Deraz Formation, East Kopet-Dagh Basin

In the present study, two sections (Mozduran and Kalat sections), at the boundary between Abderaz and Abtalkh formations has been chosen and studied. After preparation, with smear-slide method, samples were photographed and counted. Taxonomical studies of calcareous nannofossils in this studied led to identification of 24 genera and 38 species in Mozduran section and 29 genera and 47 species in Kalat section. Based on identified nannofossils, 2 biozones (CC20- CC21) of Sissingh (1997) for the Mozduran section and 3 biozones (CC20- CC21- CC22) of Sissingh (1997) for the Kalat section have been suggested. According to these biozones, age of the studied sections in the Mozduran is Late Early Campanian - Early Late Campanian and in the Kalat is Late Early Campanian - Late Late Campanian. Follow these results and continuously of CC21 in the boundary, age of the boundary between Abderaz and Abtalkh formation in both sections is Early Late Campanian. On the basis of paleoecological interpretation, Abderaz and Abtalkh Formations in two sections were deposited in shallow marine environment in relatively low latitude and it is deepening from Abderaz toward Abtalkh Formations. Based on species of nannofossils that were identified, warm temperature and low productivity for this basin were suggested too.