| Summary: | Introduction The Kopet Dagh Sedimentary Basin is located at some parts of Turkmenistan, Afghanistan and NE of Iran (Berberian and King, 1981). This sedimentary basin formed after the closure of Paleotethys Ocean owing to the Middle Triassic Orogenic event and mainly consists of Jurassic to Tertiary deposits (Afshar-Harb, 1994). The Abderaz Formation is various in thickness and consists mainly of brown shales and chalky limestone in its type section which is located in 75 km of east of Mashhad city at Mozduran area (Afshar-Harb, 1994). It unconformably overlies the Aitamir Formation and conformably covers by the Abtalkh Formation (Afshar-Harb, 1994). There are several investigations on the Abderaz Formation biostratigraphy and stratigraphical properties such as Kalantari (1969), Vahidinia (1973), Foroughi (2004), Bakhshandeh et al. (2007, 2008), Shafiee et al. (2011, 2012), Vahidinia et al. (2014). To study the planktonic foraminifera of the Upper Cretaceous deposits in the west of the Kopet Dagh Basin, the Sheikh stratigraphic section in south flank of Sheikh syncline at north east of Bojnurd was selected and investigated. Materials and methods In order to biostratigraphic analysis of the Abderaz Formation, one stratigraphic section in south flank of Sheikh syncline were studied. The thickness of the Abderaz Formation in the studied section is 252 m and a total of 235 thin sections were prepared and analyzed. The identification of species and classification of genera follows that of Postuma (1971), Wonders (1980), Loeblich and Tappan (1988), Bolli et al. (1989), Robaszynski et al. (1984), Robaszynski and Caron (1979) and Premoli Silva and Verga (2004). Lithostratigraphy The Kalat Formation in the Sheikh section is 252 m in thickness and it conformably overlies the sandy limestones of the Aitamir Formation and conformably covers by argillaceous limestones of the Abtalkh Formation. Lithostratigraphically, the Abderaz Formation are divided into three parts. Generally, these parts are mainly composed of thick bedded ...
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