Ostracods and Conditions of Formation of the Plevaka Section (Southern Azov Region) in the Late Kuyalnikian (Early Pleistocene)

The upper part of the Plevaka section (Taman Peninsula, Krasnodar Region, Russia) yielded an ostracod assemblage that for the first time indicates late Kujalnikian (Gelasian) age of the deposits. The association of Cyprideis pontica–Pontoniella acuminata–Scottia tumida is described as a new biostratigraphic unit (“beds with fauna”) for the Early Pleistocene of the Kerch-Taman Region. The upper clayey member of the section is shown to accumulate in an estuary with an unstable salinity ranging around 5‰ with a decreasing trend at the top of the section. The alternation of dominant species signals two intervals of arid and warm climate and an intermediate layer accumulated in more humid and cooler conditions. Two cycles of increasing bioproductivity are indicated by the change of a dominant form from S. tumida to C. torosa. Analysis of organic carbon (C_org) content showed three peaks of increasing bioproductivity when the number of ostracods, on the contrary, decreased, which is possibly associated with a decrease in the pH of the basin, leading to the dissolution of ostracod shells.