The Paleogene of the Cis-Donets Monocline and Its Palynological Characteristics

The results of the palynological study of the Paleogene and the underlying Cretaceous sediments of the Cis-Donets Monocline, drilled by borehole 1238, are presented. Analysis of dinoflagellate cysts enabled the recognition of the Apectodinium hyperacanthum, Axiodinium augustum, and Ochetodinium romanum/Samlandia chlamydophora zone intervals and the Rhombodinium draco–Deflandrea spinulosa layers in the Paleogene part of the section. The age of regional formations and beds was updated: the Buzinovka Formation is dated by the early Thanetian; the Veshenskaya Formation is late Thanetian–earliest Ypresian age; the Surovikino and Osinovaya Beds are early–middle Ypresian; and the Ventsy and “Poltava” Beds are of the late Rupelian–Chattian age. Two major stratigraphic hiatuses, corresponding to the Maastrichtian–Selandian and the upper Ypresian–lower Rupelian, were recognized in the borehole 1238 section. The analysis of the quantitative fluctuations of different palynomorph groups through the section permitted to reconstruct changes in depositional environments of the Peri-Tethys Basin margin during the early and late Paleogene: the Buzinovka and Veshenskaya formations and the Surovikino and Osinovaya Beds were accumulated in an open-marine environments during the long late Paleocene–early Ypresian transgressive stage, whereas the Ventsy and “Poltava” beds were deposited in the half-landlocked basin during the Chattian.