Upper Viséan and Serpukhovian Biostratigraphy and Lithofacies of the Southeast of the East European Platform

— This paper presents new data on the biostratigraphy and sedimentology of upper Viséan and Serpukhovian deposits (Lower Carboniferous) from boreholes in the southeast of the East European Platform around the Sol-Iletsk Swell (Orenburg oblast). Using rock lithology, sublatitudinal facies zones are recognized in the studied area. The deposits are represented by open shallow shelf facies, up to 500 m thick, in the area of the Sol-Iletsk Swell and near-side zone of the Preuralian Foredeep. To the south, at the margin of the Northern Pericaspian, their thickness sharply decreases to 36 m, and the succession is composed of carbonate-clay sediments of the relatively deep shelf. On the basis of foraminifers and conodonts, the upper Viséan and Serpukhovian are subdivided using the regional substages of the stratigraphic scheme of the East European Platform, and foraminiferal zones are recognized. The base of the Serpukhovian in the high-energy shallow-water facies of the open shelf is drawn by the entry of the foraminifers Janischewskina delicata and Endothyranopsis plana ; in lower energy facies, it is placed at the level of the first appearance of Neoarchaediscus postrugosus ; in the clay-carbonate facies of the relatively deep shelf, it is drawn according to the appearance of the conodont Lochriea ziegleri . The distribution of microfauna from five boreholes, the characteristics of the foraminiferal zonal assemblages, and the interregional correlation are discussed.