484 
Farther east, beneath the Kara Sea, is an offshore continuation 
of the rich West Siberian basin. The largest oil and gas fields in 
the Soviet Union are in the West Siberian basin, including such giants 
as Urengoy and Samotlor. Of the 1,077 known structures in the West 
Siberian basin which may ultimately be tested, 250 have been drilled. 
Of these only 11 were dry, hydrocarbons being found in 239.9 
Local tectonic events were prominent among the factors that deter- 
mined the extent and relationships of the alternating permeable and 
impermeable Mesozoic to Cenozoic section of the Ob-Kara basin. 
Onshore the entire Mesozoic system from the Lower Jurassic to the 
Upper Cretaceous has been shown to contain prolific reservoirs of 
oil and gas. Offshore oil and gas is expected in correlative formations 
at depths of from one to three kilometers. Lithologic facies changes 
in the northern parts of the West Siberian platform indicate that 
a considerable increase in sandstone could occur in the offshore zone 
of the Kara Sea. The increase in sandstone coupled with vast uplifts 
at shallow depts suggests that large gas and gas-condensate accumula- 
tions could occur in the offshore region.’° The Kara platform to the 
northeast offers less promise than the Ob-Kara synclinal basin, how- 
ever, local uplifts on the Kara platform could prove productive. 
The Laptev Sea has a total area of about 650,000 square kilometers 
and at the edge of the continental slope its depth is 100 to 200 
meters. In the west, it consists of the drowned margin of the West 
Siberian platform, but most of the Laptev shelf is a distinct tectonic 
unit—the Laptev block. The Laptev block is a complex unit made 
up for the most part of the Laptev uplift. The Laptev shelf consists 
of approximately five to six kilometers of Lower and Middle Paleozoic 
deposits, mostly carbonates, above a basement assumed to be Precam- 
brian in age. A thin section, less than one kilometer, of terrigenous 
Upper Cretaceous to Cenozoic rocks overlies the Paleozoic section. 
The most favorable oil and gas prospects are in the Paleozoic rocks 
of the Khatanga depression and in the southern Laptev trough." 
The East Siberian and the Chukchi Seas are shallow. The average 
depth of the East Siberian Sea is only 50 meters while the Chukchi 
(Chukotsk) Sea averages 80 meters in depth. The shelves are charac- 
terized by large folded structures. Oil and gas potential is considered 
good in the Novosibirsk synclinal basin and in the Rauchaun, South 
Wrangel, and North Wrangel depressions. The Upper Paleozoic, 
Mesozoic, and Cenozoic sedimentary deposits in these deep depres- 
sions are prospectively oil- and gas-bearing.'!2 The hydrocarbon 
deposits in northern Alaska are in zones of subsidence of the Hyper- 
borean platform, the same platform which apparently underlies the 
eastern and northern portion of the East Siberian and Chukchi Sea 
region. 
PACIFIC FAR EAST MOBILE ZONE 
_ In this region the Bering, Okhotsk, and Japan Seas are located 
in the zone of transition from continental platform to Pacific basin. 
° Meyerhoff, A. A. Soviet Arctic Oil and Gas: A Second Middle East. Professional Engineer, v. 45, 
July 1975, pp. 29-30. 
1 Eremenko, N. A., Ovanesov, G. P., and Semenovich, V. V., op. cit., p. 1716. 
'! Eremenko, N. A., Malovitskiy, Ya. P., Gramberg, I. S., and Lebedev, L. I. op. cit., p. 242. 
12 Tbid. 
