The Oligocene Reference Section in the South of the East European Platform (Northern Ergeni)

This work presents the results of the integrated study of the sequence of Oligocene (Maikop) and underlying Eocene deposits uncovered in borehole 768 (362 m). This section can be regarded as the reference one as for Northern Ergeni, as for the entire northern part of the Eastern Paratethys. The data obtained on lithology, mollusks, and benthic foraminifers enabled us to subdivide the Oligocene interval of the Maikop Group into formations and subformations (Tsimlyanian, Solenovian, and Kalmyk), to correlate it with adjacent and remote areas of the Paratethys and with the scale of regional stages, and to reconstruct the main sedimentation conditions. On the basis of nannoplankton and dinocysts, these subdivisions are correlated with the zonal stratigraphic scale (Gradstein et al., 2012), and according to the palynological data, the evolution of climatic conditions at the Paratethys northern margin is reconstructed. The phytoplankton, foraminiferal, and paleomagnetic data show a significant reduction of the section in its Eocene interval. The latter includes only negatively magnetized intervals of the Keresta, Kuma, and Belaya Glina formations, separated by discontinuities, as well as the complete set of biotic and paleomagnetic zones of the Lower Oligocene. The lower subformation of the Solenovian Formation (50 m), eroded in most of the sections of Ciscaucasia, is characterized by unusual completeness. It is probable that the Kalmyk Formation in this section is incomplete and is represented only by the first half of the Chattian.