The Alborz range is a part of the Alps-Himalaya fold-thrust belt, and extends for about 2000 km in the north of Iran. On the northern slope of eastern Alborz, a succession of Middle Jurassic to Late Cretaceous rocks is distinguished, which was named “northern facies” by Ghasemi (1990). Lithologically these deposits are very similar to time-equivalent sediments in the Kopet-Dogh fold belt in northeast Iran. A part of this succession is exposed at Sefidchah, where it unconformably overlies the Gorgan metamorphic complex and consists of chalky limestone and marl. In the present study, the lowermost sediments were studied at two locations; Sefidchah and the Arzak road to Sefidchah. Some foraminifera have been reported from this area, but there are no reports on the nannoplankton. Therefore, a total number of 20 samples were taken for the determination of calcareous nannofossils. The nannofossils are moderately preserved and diverse. As a result of this study, for the first time, 20 genera and 37 species of nannofossils have been identified and photographed from this area. The predominant species in both sections were Watznaueria biporta, Eprolithus floralis, Ceratolithoides longissimus and other species of Ceratolithoides. Since we found Uniplanarius trifidus in the first sample and Ceratolithoides kamptneri and Lucianorhabdus quadrifidus at the top of the sections, we conclude that the age of the studied deposits is late Late Campanian-Late Maastrichtian.

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