The present study deals with molluscan accumulations of the Sokolowia horizon, which is a key-bed in the middle Eocene of the Kalateh section (Ziarat Formation, Eastern Alborz, Iran). The age of this “key horizon” is attributed to Bartonian based on presence of larger benthic foraminifera species such as Nummulites lyelli (D'Archiac & Haime), Orbitoclypeus zitteli (Checchia-Rispoli) and Asterocyclina stella stella (Gümbel) immediately below it. The paleogeographic distribution of Sokolowia occurrence from Tarim Basin in eastern Central Asia to the Transylvanian Basin in southeastern Europe indicates a middle Eocene seaway along the southern margin of an Eurasian epicontinental sea. In particular, the comparison of middle Paleogene sequences in different Central Asian regions reveals an apparent similarity between those basins pointing to their genetic relationship.
