The role of the Absheron facies in the formation of the productive strata in the South Caspian Basin

   In oilfield practice, the lithofacies criterion is very often decisive for the formation of deposits of liquid and gaseous hydrocarbons. The Absheron lithofacies type of sediments (Absheron facies), enriched in quartz material, composes the reservoirs of the horizons of all large oil and gas fields in the South Caspian Basin. The genesis of the Absheron facies is closely related to the genesis of the productive stratum, there is no consensus on both issues to date. It is indisputable that the productive stratum and the Absheron facies were formed in the conditions of a closed continental basin, which arose as a result of the orogenic restructuring of the areas surrounding the Caspian Sea, the bowing of its bottom and the subsequent Pontian regression of the sea. As a result of the restructuring of the hydrographic system in the south of the Russian Platform, many paleorivers, flowing along the newly formed land, began to flow and carry a huge amount of water and precipitation into the South Caspian Basin. Deposition of the productive stratum and Absheron facies began. The greatest role in the supply of quartz-enriched sandy material belonged to the Paleovolga, which, together with other paleorivers in the north of the South Caspian Basin, formed an extensive marginal delta, from which sediments were transported far to the south, west, and east.