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Northeastern Part
of
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.