Ershov, Andrey V.1,
Maxim V. Korotaev1, Nikolay A. Malyshev2,
Mikhail P. Gudyrin2 (1) Moscow University, Moscow, Russia (2) Rosneft Oil Company,
Sedimentary record of the West Siberian basin begins with Early Triassic strata. Before this time, at mid Permian, the Ural-West Siberian orogen was located in the place of the present basin. Triassic sediments are located in the network of narrow graben-like structures interpreted as rifts. Regional platform-like subsidence in the basin started in Jurassic and was not localized in the areas of former rifts, but extended over the whole area of the Late Palaeozoic orogenic belt. Spacial pattern of the subsidence was extremely uniform over the area of more than 1000 km in lateral dimension, not typically for post-rift subsidence pattern. We propose the orogenic root detachement as a driving mechanism of this subsidence. According to this model detachement of orogenic roots occured in mid to late Permian lead to signicant uplift, erosion at the surface and thermal thinning at the base of the lithosphere. Cooling of the lithosphere lead to broad (several thousands km) and relatively uniform regional subsidence after the cessation of collision. This subsidence continued till Eocene with exponentially decreasing rate. In Oligocene the subsidence pattern was drastically changed when the region came into compressional setting. In many places subsidence was changed into uplift. Petroleum systems of the North-Eastern part of the West Siberian basin was analyzed using results of numerical modelling of subsidence and thermal histories and petroleum generation. There are several petroleum systems in the area. Their critical momemts falled within late Creataceous-Paleogene time, when most active phase of hydrocarbons generation and secondary migration took place. Oligocene to Quaternary inversions lead to destruction of some seals, formation of new ones and redistribution of hydrocarbons.