Calcareous nannofossils and Ammonites biostratigraphy and paleoecology of the Sarcheshmeh and Sanganeh formations in West of the Kopet-Dagh Basin, Sheikh Section

In this study, calcareous nannofossils and ammonites of the Sarcheshmeh and Sanganeh formations were investigated in the west of the Kopet Dagh Basin to determine the exact age of the strata and correlating the calcareous nannofossil and ammonite biozones. According to the index calcareous nannofossils, the first occurrences of Rucinolithus irregularis and Eprolithus floralis were recorded in the Sarcheshmeh Formation and the last occurrence of Micrantholithus spp. was recorded in the first part of the Sanganeh Formation. Regarding these data, the upper part of NC5, NC6 and the lower part of NC7A biozones were identified in the Sarcheshmeh Formation and NC7A in the first part of the Sanganeh Formation. These data confirm the age of late Barremian − early late Aptian for the Sarcheshmeh Formation and early late Aptian − ?late Aptian for the sanganeh Formation. According to the ammonite data, Deshayesites deshayesi biozone of the early Aptian was recorded in the shaly part of the Sarcheshmeh Formation and Parahoplites melchioris of the late Aptian and Leymeriella tardefurcata with the early Albian age were identified from the Sanganeh Formation. The calcareous nannofossil along with the ammonite data confirms the age of late Barremian − early Aptian for the Sarcheshmeh Formation and late Aptian − early Albian for the Sanganeh Formation. The studied assemblage suggests a shallow and neritic continental shelf environment, in terms of warm water and oligotrophic to mesotrophic conditions, with fluctuation of low oxygen condition in some parts (suboxic to dyoxic).