Unstable Asia: active deformation of Siberia revealed by drainage shifts

摘要

Regional incision and lateral shifts of rivers in the West Siberian Basin and surrounding areas show the action of long wavelength surface tilting, directed away from the Urals and Central Asian mountains and towards the Siberian Craton. In the north of the basin, surface uplift of individual folds is recorded by local lateral drainage migration. Lateral slopes of river valleys vary in gradient from 0.001 to 0.0001, generally decreasing with increasing river discharge. As a result of this surface deformation significant drainage shifts are taking place in three of the longest and highest discharge river systems on Earth: the Yenisei, Ob' and Irtysh. The deformation is most plausibly caused by subtle faulting at depth, below the thick basin fill of Mesozoic and Lower Cenozoic sediments. Active deformation of western Siberia appears to represent a previously unrecognised, far-field effect of the India-Eurasia collision, up to similar to 1500 km north of the limit of major seismicity and mountain building. It adds similar to 2.5 x 10(6) km(2) to the region deformed by the collision, which is an area greater than the Himalayas and Tibet combined. It is also an analogue for the formation of low-angle unconformities in terrestrial sedimentary basins on the periphery of other orogenic belts.