The Reference Section of Eocene Deposits in the Belaya River Valley, Adygea, Western Ciscaucasia

The Eocene interval of the section in the Belaya River valley is continuously exposed and is represented (from the bottom up) by green clays of the Cherkessk Formation, the marl–clayey member of the Keresta Formation, bituminous marls of the Kuma Formation, and light intensely bioturbated marls of the Belaya Glina Formation. There are gradual transitions between formations without signs of hiatuses. Eocene deposits are characterized by rich assemblages of nannoplankton, planktonic and benthic foraminifers (PF, BF), and organic-walled phytoplankton. The shallower water facies are recorded in the composition of benthos and mollusks at the boundaries of formations. The data on these groups of fossils make it possible to trace an almost complete zonal characterization of nannoplankton, dinocysts and PF and to compare these subdivisions of the middle–upper Eocene and early Oligocene both with other reference sections of the Eastern Peri-Tethys and standard zones and stages of the international stratigraphic scale. The following zones are distinguished: the upper part of the Cherkessk Formation—nannoplankton (NP15) and Acarinina bullbrooki PF zones; the Keresta Formation—nannoplankton (NP15+NP16) and Hantkenina “alabamensis” PF zones; the Kuma Formation—the nannoplankton (NP16+NP17) zones, Hantkenina “alabamensis” (at the lower boundary of the formation) and Subbotina turсmenica PF zones (above basal part), and Areosphaeridium diktyoplokum–Rhombodinium porosum dinocyst zone; the Belaya Glina Formation—nannoplankton (NP18, NP19+NP20, NP21) zones, Turborotalia centralis–Globigerinatheka tropicalis PF zone, and Charlesdowniea clathrata angulosa dinocyst zone; the lower part of the Pshekha Formation—nannoplankton (NP21) zone, Globigerina officinalis PF zone, and Phtanoperidinium amoenum dinocyst zone. These data make it possible to clearly correlate the Belaya River section with the sections studied in detail in Ciscaucasia (Kheu, Kuban, and Gubs rivers) and to reconstruct the conditions of sedimentation.