| Popis: |
The area of the West Siberian platform is about 3.3 million km 2 , the average thickness of the Mesozoic—Cenozoic platform mantle of sediments is 3 km, and the volume of sedimentary infilling is 10 million km 3 . The formation of the platform took place during a major tectonic cycle which in turn is divided into tectonic-sedimentary cycles as follows: Triassic, early-Middle Jurassic, late Jurassic, Neocomian, Aptian—Cenomanian, Turonian—Maastrichtian, Paleocene—early Oligocene and Middle Oligocene—Middle Pliocene. During the Triassic period in the arctic part of the platform large depressions were formed and continued to subside to the end of the Cretaceous. During early—Middle Jurassic part of the Triassic postorogenic shield began to subside. The late Jurassic epoch is characterized by maximum transgression and low rate of uncompensated subsidence of the basin floor. In Neocomian and Aptian—Cenomanian time, differential subsidence is sharply intensified, its rate increasing from south to north in the direction of Triassic downwarp. Turonian—Maastrichtian time is distinguished by wide transgression and reduction of subsidence rate. In Paleocene—early Oligocene the extent of the sea decreased and took the form of a submeridional gulf, the axial line of which approached the Urals. In the middle of the Oligocene epoch the sea became freshened and divided into separate basins. Eastern and northern parts of the platform were subsequently involved in the uplift. In the Neogene the region of subsidence took the form of a sublatitudinal depression extending along the southern mountain-folded margin of the platform. |
