Some Aspects of Formation of Oil Fields in the Productive Series, the South Caspian Basin

There exist two opposite viewpoints regarding formation of hydrocarbon (HC) accumulations in the Lower Pliocene Productive Series (PS) in the South Caspian Basin (SCB). The first states that HCs are syngenetic to this stratigraphic unit, by the second they are of epigenetic origin. This presentation is concerned with results of study of the nature of HCs in the PS based on the modern isotopic-geochemical data and recent theoretical and experimental developments. Quantitative and qualitative parameters of organic matter (OM), geochemical and temperature conditions of its conversion, maturity estimates for oil and gas and revealed vertical zonality of their formation are shown to be against counting the PS as source strata for oil. Formation of HC accumulations in the PS has been associated with Oligocene and Miocene source deposits, contribution of which was subject to variation both in space and time. In this connection subvertical migration played a dominant role, having pulsed (injection) character.