Riphean Depocenters and Origin of Oil Deposits of the Romashkinskoye and Yaregskoye Fields

   Interpretation of geological and geophysical data indicates an important role of Riphean strata in the formation of large and unique oil accumulations, which include the Romashkinskoye and Yaregskoye fields. Thermally immature Domanik shales in these areas could play only a supplementary role in the oil charging there. The formation of the unique oil accumulations of the Romashkinskoye field most likely was due to lateral migration of oil from the largest depocenter of Riphean sedimentation located in the Southern Urals. The huge size of the Riphean depocenter of the Southern Uralian Foredeep explains the anomalously high concentration of oil in the South Tatar arch. It is suggested that the Yaregskoye field was formed, also at least partially, by the oil charge from Riphean sediments overlain by the Timan Ridge overthrust. This fault created an extended tectonic contact between theburied oil-producing deposits and the oil accumulation zone of the Ukhta High. Transit migration of oil took place through fractured allochthonous basement rocks.