Turonian–Santonian (Upper Cretaceous) Deposits of Tersa and Karamysh Depressions, Lower Volga Region

Results of comprehensive study of the Upper Cretaceous deposits in the Miroshniki and Krasny Yar sections (Tersa depression) and Splavnukha section (Karamysh depression) are presented. The vertical distribution of benthic foraminifera is the basis for the detailed subdivision and correlation of the clay–carbonate deposits of the Bannovka and Volsk formations within the Ulyanovsk–Saratov Trough. The features of the distribution of benthic and planktonic foraminifers, inoceramides, belemnites, sea urchins, crinoids, brittlestars, and sponges in the Turonian and Coniacian sediments of the Lower Volga region are identified. The analysis of the distribution of benthic foraminifera allows the most detailed subdivision of rocks and the determination of the position of the Turonian–Coniacian boundary within a monotonous carbonate succession of the Gubkino Horizon. The differences in sequence of zonal units and their thickness are interpreted as a result of partial isolation of the studied structural zones during the formation of the northern part of the Don–Medveditsa swell.