EARLY PERMIAN FACIES AND PALEOGEOGRAPHY OF THE SOUTHEASTERN RUSSIAN CRATON

During the Early Permian deep-water basins existed in the southeastern part of the Russian craton. North and west of the Cis-Ural foredeep a nd the Precaspian depression (micro-ocean) carbonate platforms were fo rmed on a shallow-marine shelf during the Asselian, Sakmarian and Earl y Artinskian. Reefs developed on the margin of these platforms along t he slopes of the Cis-Ural foredeep and the Precaspian depression. The reefs shifted platformward in the eastern areas, due to the tectonic s ubsidence of the platform margin and at the same time, prograded basin ward in the south. Movements of continental blocks from the south duri ng the Late Artinskian and Kungurian caused the separation of the Earl y Permian basin of the Russian craton from the Palaeo-Tethys, followed by evaporite sedimentation in the restricted basins. The existence of source rocks (bituminous deepwater sediments), thick reservoir rocks (limestones and dolostones), evaporitic seals and strucural as well as stratigraphic traps are responsible for large productive gas and oil fields (e.g., Orenburg field), some of which are distinctly associated with reef carbonates.