The biostratigraphy of calcareous nannofossils of the Cretaceous is investigated in the boundary between Abderaz and Kalat Formations through the record of species richness, diversity and distribution patterns in the west Kopet-Dagh re- gion. The Kalat Formation comprising of coarse-grained detritus limestone with subordinate sandstone intercalations and the Abderaz Formation mainly consists of limestone, Shale and Limy marl. Nannofossils of this boundary in each of studied sections are listed and figured. 21 species in Ghalehzoo section, 29 species in Sheikh section and 19 species in Jozak section have been determined. Boistratigraphy based on calcareous nannofossil allow the identification of nannofossil standard zones CC21 and CC26 in all of sections, According to these zones in all of sections, the age of the studied thickness is Early Late Campanian-Late Late Maastrichtian in these sections.

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