This study focuses on late Paleocene–middle Eocene planktonic and small benthic foraminiferal assemblages from the Khangiran Formation in the Kopet-Dagh Basin (NE Iran). The patterns of regional distribution of foraminiferal fauna were observed in this study, although many of the global foraminiferal index species are absent in the studied southernmost Peri-Tethys neritic section. Accordingly, this work proposes to update a regional biostratigraphic scheme and correlation with adjacent basins based on the first and last appearance of diagnostic species. Biozones correlative with Acarinina acarinata Zone, Morozovella subbotinae Zone, Morozovella aragonensis Zone, Acarinina bullbrooki Zone, and Acarinina rotundimarginata Zone of interregional zonal scheme based on planktonic foraminifera and biozones correlative with Annectina paleocenica Zone, Pseudogaudryina externa Zone, and Pseudogaudryina pseudonavarrana Zone based on small benthic foraminifera were recognized in the type section of the Khangiran Formation indicating Thanetian-middle Lutetian age. Toward the upper part of the studied section in the last phase of marine sedimentation regional oyster beds (Sokolowia spp.) point out late Lutetian-early Priabonian age. Possibly Arctic-Tethys communication systems through the early Paleogene epicontinental seas were responsible for the faunal assemblage similarities and suggest that the Kopet-Dagh Basin of Iran was connected to northern basins of Former Soviet Union and other Central Asian basins during the Paleogene.
