The most complete Cretaceous succession in northern Iran can be found in Kopet-Dogh Basin. The Aitamir Formation is located in eastern Kopet-Dogh and is composed mainly of lower sandstone and upper shale. The Abderaz Formation, composed mainly of bluish gray shale and 3 to 4 chalk bands, is also one of the Late Cretaceous formations in the eastern Kopet-Dogh Basin and overlies the Aitamir Formation. Most of the previous micropaleontological studies in this area were based on foraminifera. According to these studies the boundary between the two formations is discontinuous. Hadavi & Muosazadeh (2005) studied the nannofossils in the Aitamir-Abderaz Formations in the Shoorab section, and found a transition boundary between these two formations. In the present study, 81 m of the upper Aitamir Formation and 126 m of the lower Abderaz Formation were studied in the Do-Baradar section, which is located in East Mouzdoran (East Kopet-Dogh). Nineteen samples from the upper Aitamir Formation and 28 samples from the lower Abderaz Formation were collected and prepared for biostratigraphic studies. Using a polarized microscope, 14 families, 29 genera and 48 species were identified. Based on the obtained nannofossils, the section is consistent with an age of CC12, CC16-CC22. Therefore the age of this section is Late Turonian to late Late Campanian, and according to the present study the boundary between the Aitamir-Abderaz formations is continuous.

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