Abstract

Upper Devonian-Tournaisian facies on the Russian craton’s eastern margin indicate deposition in two distinct paleomorphic environments: bathymetrically expressed basins and shallow platforms. Shallow water carbonate sedimentation persisted on the platforms, and black, thin bedded, organic-rich shales and limestones of the Domanik facies were deposited in stagnant basins that stretched more than 2,000 km from the Arctic Ocean to the Caspian Sea. Intermittently introduced clastic material and detrital carbonates fromed progradational shelves. Barrier reefs along platform edges, atolls and reef mounds on basin margins and smaller patch reefs on platforms were abundant. The basins were finally filled with Tournaisian (in the Timan-Pechora province) or basal Visean (in the Volga-Ural province) clastics. The North Caspian deep water basin survived until the end of Early Permian time when it was filled with a thick salt formation. The organic-rich Domanik facies is the major source rock in the Volga-Ural, Timan-Pechora and North Caspian petroleum provinces. About one-third of oil reserves occurs predominantly in structural traps in Middle Devonian-lower Frasnian clastics that directly underlie Domanik rocks. Most of the remaining two-thirds is found in reefs, and especially in drape structures over the reefs in Tournaisian carbonates and basal Visean clastics.