Molluscan fossils have long been considered as an essential group for the paleoecological interpretations of the Paleogene stratigraphic successions. The distribution of bivalve and gastropod fossils in the Kopet-Dagh Mountains’ Paleogene successions, Chehelkaman and Khangiran formations, has been studied in this research. The fossil contents of the investigated intervals are categorized into four paleo-societies. They include Turriteline (gastropods of subfamily Turritellinae, by Allmon, 2011)—Pycnodonte community at the top of Chehelkaman Formation representative the terminal part of the Upper Paleocene, Flemingostrea–Ferganea community representing the lower layers of the Lower Eocene deposits and base of the Khangiran Formation, assemblages of Turkostrea spp., defining the middle part of the Early Eocene and Sokolowia community indicating the Lutetian—early Priabonian age for the upper part of the Khangiran Formation. Besides, the first appearance of Ferganea ferganensis previously had been reported only from the Upper Eocene–Oligocene deposits, is recorded from the Early Eocene, here. The faunal contents approve a shallow foreshore environment during Paleogene sequences\\\' deposition in the Kopet-Dagh Basin. Accordingly, three regressive and two transgressive phases were proposed for the Kopet-Dagh basin’s Paleogene deposits in Iran.

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