Microbiostratigraphy of Cenomanian-Turonian boundary in Shurab section (east Kopet-Dagh basin)

Sedimentrary succession of Cenomanian-Turonian boundary at Shurab section is located in east Kopet-Dagh and consists of upper most layers of Aitamir Formation and lower most layers of Abderaz Formation.The lithology of this succession is mainly composed of green shale and glauconitic sandstone and alternating of grey to white shale and marl. Based on biostratigraphic studies of Foraminifera in this section, four biozones have been recognized:1- Rotalipora reicheli Total Range Zone (Late Cenomanian)2- Rotalipora cushmani Total Range Zone (Late Cenomanian)3- Whiteinella archaeocretacea Partial Range Zone (Cenomanian-Turonian)4- Marginotruncana schneegansi Interval Zone (Middle Turonian).In this study, the boundary between Aitamir Formation with Abderaz Formation considered to be within Whiteinella archaeocretacea zone. In upper part of this biozone, an intense decrease in fauna can be seen. This decreasing can be considered to be as result of biotic and paleoecologic changes that can be related to global events during this time. Therefore, most probable part of B can be considered as the base of Abderaz Formation and C/T boundary is located in this part.