Organic matter of the Upper Jurassic deposits of the Izhma shale-bearing region of the Timan-Pechora basin

The results of complex geochemical and coalpetrographic studies of the organic matter of clays and oil shales of the middle substage of the Volgian (Tithonian) stage in the Izhma shalebearing region of the Timan-Pechora basin are presented. The studied section of the Volgian deposits on the Aiyuva river is represented by alternating layers of oil shales, clays and single interlayers of clayey limestones. The deposits under consideration are characterized by an uneven distribution of organic matter across the section. The minimum content of organic carbon (C org ) is found in clayey limestone (less than 1%) and clays (2.2%), while the maximum content is found in oil shale (34%). Oil shales and clays contain immature mixed marine and terrigenous organic matter (types II and II-III kerogens), which has a high hydrocarbon potential (T max – 407-410°C, HI – 519- 600 mg of HC/g TOC). Organic matter is mainly represented by bituminite, there are inclusions of sporinite, alginite, vitrinite and inertinite. The distribution of n-alkanes and isoprenoids in the saturated fraction of bitumen also indicates the predominance of marine organic matter with a small contribution of the terrigenous component. The Volgian deposits with a high initial oil generation potential were formed in relatively shallow marine conditions with low hydrodynamics.