Abstract: Middle to Late Paleozoic Tectonics, Stratigraphy and Hydrocarbon Potential of the West Siberia, Russia

Karl H. Fleischmann, C. Torres, V. Vysotsky, L. L. Podsosova, V. Bochkarev, Yu. Fedorov

We have synthesized an extensive database of well-log, core, seismic, geochemical and radiometric-age data to reconstruct the Paleozoic evolution of West Siberia, with emphasis on hydrocarbon potential. We interpret the basement of West Siberia to have been assembled during a protracted period of latest Precambrian through Paleozoic deformation involving the East European Platform, the Siberian Craton, and microplates which now form Kazakhstan and central West Siberia. Four Precambrian terranes, the Khanty Mansiyssk, Salekhard, Aleksandrovsky, and Kara blocks, are composed of middle to upper Proterozoic crystalline rocks and were separated from the Siberian Craton during Riphean/Vendian rifting. Following an early Paleozoic drift phase, continental convergence and deformation began du ing the Late Silurian, recorded by the addition of the Khanty Mansiysk and Aleksandrovsky microplates onto Kazakhstan between 450-420 Ma. Continued convergence between Siberia, Kazakhstan and Eastern Europe led to the destruction of a large oceanic basin during the middle Paleozoic. Collision between Siberia

and Kazakhstan may have begun south of West Siberia prior to Carboniferous time. However, metamorphic ages in both the Valerianovsky Volcanic Belt and the subsurface projection of the Chara-Irtysch-Zaisan zone suggest primarily middle to Late Carboniferous through Early Permian deformation. We interpret these to be the Kazakh-Eastern Europe and Kazakh-Siberian sutures, which merge to the north to form a single suture between Siberia and Eastern Europe.

During the wanning phases of deformation a semi-restricted basin was created between Kazakhstan, Siberia and Europe. Open to marine circulation to the north, this basin was ringed by uplifted zones of convergent deformation which shed immature sediments into the basin front on three sides. Thick accumulations of clastic sediments and coals mark the basin margins during the Early Carboniferous. Laterally, the coarse clastics give way to highly organic shales and carbonates with thicknesses locally in excess of 1 km. These appear to provide source and reservoir respectively, for Paleozoic hydrocarbons in southeastern West Siberia. In addition, production from Triassic fractured reservoirs may also reflect renewed migration of Paleozoic oils. Exploration, however, is complicated by Permi n and younger igneous intrusion which causes some areas to be overmature. In addition, Triassic and younger extensional deformation appears to have caused localized loss of seal. However, the widespread presence of both source and reservoir at relatively shallow levels may make this an attractive play in southern West Siberia.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994