This paper presents the results of a biostratigraphic and paleoenvironmental study of the Dalichai Formation (Talu Section), eastern Alborz mountain range, northern Iran, based on calcareous nannofossils. The base of the section comprises red sandstone which is overlain by a thick layer of marl and a nodular limestone layer proceeded by alternations of sandy limestone, shale and calcareous shale in the middle part, and a layer of nodular limestone and alternations of shale and limestone on the top of the section, transitioning to the limestone of the Lar Formation. The Dalichai Formation overlies the siltstones of the Shemshak Formation. Sixty-fve samples were analyzed for calcareous nannofossils resulting in the identifcation of 9 genera and 20 species and the identifcation Berriasian to Early Barremian CC1-CC5 biozones of Sissingh (1977). The fndings of the study show that the sedimentary basin of the Dalichai Formation of the Talu Section was located in low latitudes of the Tethyan realm and was characterized by warm surface waters that represents a marine transgression upsection, and nutrient supply decreased and paleoenvironmental conditions became increasingly stable.

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