EARLY TRIASSIC RIFTING AND ITS EFFECT ON THE STRUCTURE AND PETROLEUM POTENTIAL OF THE WEST SIBERIAN PLATFORM

We consider the structure, depositional conditions, and subsequent development of the Koltogor-Urengoy rift system, which cuts through West Siberia in the meridional direction and has a length of 1925 km. Based on the interpretation of potential fields, the structure of the major rifts and the system of minor grabens leading to them has been defined more precisely. We have established that the Early Triassic rifting greatly influenced the geologic structure of the Mesozoic–Cenozoic sedimentary cover of the West Siberian sedimentary basin and significantly contributed to its petroleum potential. The Koltogor-Urengoy megatrough, a superorder linear depression elongated in the meridional direction and extending across the entire West Siberia, formed above the main graben-rifts of the Koltogor-Urengoy system in the structural plans of the Mesozoic reference levels. In the southern part of the basin, an active subsidence of the Koltogor-Urengoy and Tym graben-rifts in the Mesozoic and Cenozoic predetermined the occurrence of large superrift depression zones within the sedimentary succession of the Pur and Koltogor megatroughs and the Nyurolka and Tym megadepressions, which are the main oil generation zones. The positive structures of orders I and II, main zones of oil and gas accumulation, were formed above the Paleozoic basement uplifts: Severny, Nizhnevartovsk, Alexandrov, and Kaimys uplifts; and Vyngypur, Yetypur, Vasyugan, and Pudino megaswells. In the north of the basin, anticlinal traps, controlling the Aptian-Albian-Cenomanian gas accumulations, formed above the interrift blocks in the relief of the Cretaceous deposits.