The Characteristics of the Organic Matter of the Upper Devonian Domanik-Type Deposits in the Northern and Central Regions of the Volga-Ural Basin According to Saturated Biomarkers Composition

Abstract

The composition of saturated biomarkers (alkanes, steranes, and triterpanes) in the Upper Devonian sediments (the Sargaev, Semiluk, and Mendym horizons, the Famennian stage) that belong to the Domanik formation, which is widespread on the territory of the Volga-Ural basin, was studied. The section elongated from N to S that covers the northern and central regions of the Volga-Ural basin was observed. A set of 21 parameters was used to characterize saturated hydrocarbons, including those rarely used in geochemical studies. For each parameter a set of mean values for the considered region as a whole and its individual parts was calculated and distribution-density plots were built. It was established that the most representative parameter for characterizing the Domanik-type deposits as a whole is a highly specific parameter, that is, the ratio of 29,30-bisnorhopane C₂₈ to hopane C₂₉. Most of the characteristics of the genetic composition demonstrate the difference between the organic matter (OM) of the vault part of the region and the Mukhanov- Erokhovsky trough. There are large differences in the parameters that characterize the maturity of OM. The characteristic values of the parameters for both the vault and the depression zone are given; two to three genetic groups of OM were determined for the majority of the parameters in both regions. A method for constructing the distribution-density graphs of the parameters is proposed that makes it possible to take their features fully into account.