Extension of East Siberian oil-gas basin westward beneath West Siberian oil-gas basin
Internet Geology News Letter No. 4, August 2, 1999
The question of the boundary between the Siberian craton (East Siberian oil-gas basin) and the West Siberian platform (West Siberian oil-gas basin) has long been debated. The boundary has generally been placed at the Yenisey Ridge, a north-south-trending uplifted block of ancient rocks. Continuation of the Siberian craton westward beneath the West Siberian platform, however, was suggested in the 1940's by D. V. Nalovkin.
Three deep seismic sounding profiles were run from the West Siberian platform across the Yenisey Ridge on to the Siberian craton. These are the "Kraton", "Kimberlite", and "Batolit" (Shablinskaya and others, 1990). These profiles indicate that the pre-Mesozoic rocks west of the Yenisey Ridge are the same as those to the east. They extend westward more than 200 km to a fault designated as the Siberian suture. This zone of overlap of the West Siberian platform onto the Siberian craton has been designated as the West Marginal System of the Siberian craton and as the Near-Yenisey region of the West Siberian platform.
Distinguishing features of the East Siberian oil-gas basin are the presence of Cambrian salt and carbonate reefs, below which are clastic and carbonate rocks of Proterozoic Vendian age. In 1984 N. Ya. Kunin proposed that salt was present in the Near-Yenisey region of West Siberia. This was based on seismic, magnetic, and in particular gravity surveys. Local gravity minimums were found on a background of an otherwise low gravity field. These coincided with areas where seismic records were typical of salt (Petroleum Geology, vol. 25, no. 3/4, p. 71 and no. 11/12, p. 369, 1991). (I have not found any reference in the literature to this salt having been drilled; however, once someone on the telephone told me that he had a core sample of this salt on his desk.) The geophysical surveys also indicate presence of carbonate reefs in the Near-Yenisey region.
Seismic surveys of 1992-93 extend from the right-bank area of the Ob River eastward across the Yenisey Ridge into East Siberia. The stratigraphic identity of the reflecting horizons on these profiles has been determined in several drill holes. The pre-Mesozoic stratigraphic sections west of Yenisey Ridge appear to be identical to those of East Siberia east of the Yenisey Ridge (Petroleum Geology, vol. 31, no. 1, p 83, 1996). The Siberian craton thus appears to extend on westward beneath the West Siberian platform. Since this part of the section is host to prolific oil and gas in East Siberia, as for example at Yurubchen, the Near Yenisey region is regarded as favorable for new discoveries in Cambrian and older rocks.