DYNAMICS OF THE ACCUMULATION OF THE MESOZ OIC-CENOZOIC SEDIMENTARY LAYER IN THE WEST-SIBERIAN BASIN

Specific character of the formation of the West-Siberian basin has bee n considered, and dynamics of the sedimentation for the last 310 Ma ha s been traced. There are three tectono-sedimentation stages recognized for this period of geological history, which account for the present- day sizes and inner structure. Orogeny stage lasted 60 Ma, from Middle Carboniferous (Moscowian age) to Late Permian (Tatarian age). Rifting stage was expressed in the Early Triassic and took 12-13 Ma (Indian, Olenekian, and Anisian ages). Plate stage is involved with the post-ri fting downwarping and accumulation of platform sediments. According to its features it is subdivided into three steps: early (Middle and Lat e Triassic, Early and Middle Jurassic), middle (Late Jurassic-Cretaceo us, Pliocene, Eocene), and late, or neotectonic (Late Eocene--Holocene ). The plate stage (200 Ma) is main, accumulation of oil- and gas-bear ing complexes being confined to it. The neotectonic step (Late Eocene to Present, about 40 Ma) is due to lithosphere plate spreading in the Arctic part of the Earth, leading to the formation of the Arctic Ocean and, as a result, to the change of the sign of vertical movement in t he north. Since the Late Eocene the northern side of the basin has ele vated, and continental regime has built up, covering the basin territo ry and transformity it into an accumulation-denudation plain.