THE UPPER EOCENE OF THE FERGANA DEPRESSION AND ADJACENT REGIONS

Abstract

Radiolarians and nannofossils have been studied in the two most complete upper Eocene sections of the Fergana depression, the classical region of the shallow-water Paleogene deposits in the southern part of the former Soviet Union (FSU). The sections display three periods of the Fergana basin deepening and its more open connections with a main aquatic region: the second half of the Rishtan time, and the Isfara and Sumsar periods. Three zones of the standard Eocene zonation are distinguished for the first time in the Fergana depression: the radiolarian Thyrsocyrtis bromia Zone in the Isfara deposits, and the nannoplankton zones NP19-NP20 in the Sumsar deposits. Two detected transgressive-regressive cycles of sedimentation comprise the late Rishtan-Khanabad and Sumsar intervals. The transgressive part of the former is correlative to the early Priabonian eustatic transgression. The second cycle comprises only transgressive deposits, and is correlated with the late Priabonian (Lattorfian) eustatic transgression.