Planktonic foraminifera biozones and isotope stratigraphy of the Cenomanian-Turonian boundary in the western part of the Kopet-Dagh Basin, NE Iran

The carbon-isotope curves in both sections, record a negative shift values below the Aitamir-Abderaz formations boundary in Whiteinella archaeocretacea Zone, and then, a positive excursion of about 5.50‰, along with several fluctuations are well evident in both sections. The δ18O values show, from the bottom to the top, a gradual increase of averagely 2‰. Based on these results, the Cenomanian-Turonian succession in this part of the Kopet-Dagh Basin is continuous and corresponds to the siltstone and chalky limestone layers of the upper part of the Aitamir Formation and the lower part of the Abderaz Formation.