The distribution of Baykalian (late Precambrian) to Hercynian foldbelts forming the floor of the West Siberian basin suggests active wrenching throughout the Paleozoic. Strike-slip faults also control deep, sinuous Carboniferous-Early Permian basins. During the Late Permian, a complex system of narrow grabens opened in central-eastern West Siberia. Basic igneous material filled these troughs. The continental grabens of West Siberia and of central-eastern Africa are strikingly different from oceanic rifts. One difference is the large wrenching component observed along the margins of continental grabens. Depositional trends of Early-Middle Jurassic porous clastics and organic-rich shale are clearly related to strike-slip faults. In the latest Jurassic, the West Siberian bas n was secluded from the open ocean due to wrench movements. Euxinic conditions that were thus created resulted in deposition of the Bazhenovo oil shale, the richest source rock in the province. Cretaceous and Tertiary wrenching produced low-amplitude drag folds that are the main hydrocarbon traps of West Siberia. A comprehensive wrench-tectonic approach to the structure of West Siberia should help locate new, vast oil and gas reserves.

End_Page 529------------------------