Oligocene key section of South part of Eastern European Platform (North Ergeny)

The section of well 768, depth 362 m, which opened the Eocene and Maikopian deposits is comprehensively studied and can serve as a reference one for both the Northern Ergeny and the entire northern part of Paratethys. The data on lithology, mollusks, and benthic foraminifera made it possible to break up the Oligocene part of the Maikop Group into formations and subformations: Tsimlyansk, Solenovian and Kalmyk parts, compare them with neighboring and distant parts of Parathethys, with a regostage scale, restore basic sedimentation conditions. Based on nannoplankton and dinocyst composition, these units were compared with the global zonal scale (Gradstein et al., 2012), and according to the spore-pollen data, the evolution of the climate of the Parathethys northern margin was restored. The phytoplankton, foraminiferal and paleomagnetic data show a strong reduction of the section in the Eocene part, where only negatively magnetized fragments of the Keresta, Kuma and Belaya Glina formations separated by unconformity surfaces were distinguished. In the lower Oligocene part we saw the full set of biotic and paleomagnetic zones. The lower part of the Solenovian formation (50 m) is rarely complete, unlike most of the Ciscaucasian sections. The Kalmyk formation in this section is probably incomplete and responds only to the first half of the Chattian.

Lectostratotype of maikopian group – Belaya River section upstream of Maikop town (Western Ciscaucasia) in the Oligocene part

Belaya River Section of Maikop deposits is the closest to the Maikop town, typical for Western and Central Ciscaucasus, well outcropped and studied and should be considered as a type section for the Maikop Group. Here it is possible to observe a continuous transition from the underlying light marls of Belaya Glina Formation to the dark clays of Pshekha Formation at the base of the Maikop succession. Pshekha Fm is characterized by nannoplankton NP21 and NP22 zones, dinocysts Phthanoperidinium amoenum (D13) and Wetzeliella symmetrica zones, mollusk association with Pterolucina batalpashinica at the bottom and rich fish fauna. The succession shows a normal polarity chron C13n for the base of the Pshekha and revers polarity C12r above. Marl of Polbian Bed with brackish Lower Solenovian mollusks, ostracod association with Disopontocipris oligocaenica, nannoplankton of NP23 Zone and dinocysts of Wetzeliella gohtii Zone lies above with erosion contact. Overlying Lower Morozkina Balka Subformation contains from non-calcareous clays and concludes the remains of fish and dinocysts of Wetzeliella gohtii Zone. The Upper Morozkina Balka Subformation contains calcareous sublayers with nannoplankton NP23 Zone in lower part and NP24 one above, dinocysts Chiropteridium partispinatum Zone, Rhombodinium draco Subzone. Polarity pattern we interpret to correspond to C10n, C9r and C9n. Batalpashinsk Formation corresponds to the time of maximum hydrogen sulfide contamination of the Late Oligocene basin and is dated by nannoplankton NP25 Zone, and dinocysts Chiropteridium patrispinatum Zone with Rhombodinium draco Subzone in lower part and Deflandrea spinulosa (non typica) Subzone in the middle and upper parts. Septarian+Zelenchuk Fm is composed of clays with septarian concretions, and interbedded sands with the same dinocysts and foraminifera with Spiroplectammina aff. terekensis. Calcareous interlayers in the top of the formation conclude nannoplankton of NP25-NN1 Zone. Karadzhalga Formation is composed mainly “fish lithofacies” and includes dinocysts zone Labyrinthodinium truncatum (Lower Miocene) in basal part.