THE OLIGOCENE-EARLY MIOCENE FLORAL ASSEMBLAGES FROM WESTERN SIBERIA

Abstract

The results of research show that the main geologic events Western Siberia at the end of the Eocene occurred in a succession of negative and positive tectonic movements that brought about regression of the basin. The climate cooling caused the extinction of subtropical flora and the replacement of the evergreen forests by the coniferous. In the Oligocene, the climate was the principal factor in biota evolution, and the vegetation developed in two stages. During the first stage, i.e., in the early-middle Oligocene (the Atlym-Novomikhailovskoe time), the coniferous dominated in the mixed coniferous-broad-leaved forests. In the course of the second stage, i.e., in the late Oligocene-early Miocene (the Turtass and Abrosimovka time), the Turtass flora included subtropical plants. The continental sedimentation was typical of both stages. According to paleobotanical data, there were no significant reorganizations in the vegetal biota at the late Oligocene-early Miocene interface. Consequently, the palynological data are insufficient to draw a boundary between the Turtass and Abrosimovka formations.