The sedimentary section of the South Kara basin consists of lagoonal-continental and marine sand-silt-clay deposits. The clayey types appear in the Upper Cretaceous beginning with the Santonian.
Sedimentary rocks present at greater depths are recorded by refraction surveys. These belong to a so-called intermediate stage of rocks that are probably in the greenschist facies of metamorphism. This intermediate stage is subdivided into upper and lower parts at refracting horizon II. The upper part consists of Upper Permian-Middle Triassic sedimentary and volcanic rocks 3-4 km thick, which fill grabens. The lower part is a carbonate paraplatform section, which has been dated variously from Late Proterozoic to Early Permian.
It is interesting that the Kholtogor graben, which extends north-south through most of the West Siberian platform, does not continue into the South Kara basin, being replaced there by diagonal grabens. (The Saint Anna graben far to the north is right on line with the Kholtogor graben -JC.)
The Conrad and M-discontinuities are traced clearly in the section; they have velocities of 7.0 and 8,2 kmps, respectively. Both these interfaces show a typical compensitory rise under the areas of maximum downwarping of the basement rocks.
Barents-Kara continental margin platform. The North Kara basin, which is the region north of the North Siberian sill, is part of the Barents-Kara platform, most of which is within the area of the Barents Sea. Within this basin are depressions where sedimentary thickness is up to 8-9 km and possibly more.
At the top of the section are upper Pliocene (?) and Quaternary sediments. These should be more marine in character than the sediments to the south since they are closer to the shelf margin. The Paleogene and much of the Cretaceous were removed by erosion during the uplift and regression of the late Oligocene-early Pliocene time interval.
A seismic reflection profile across the North Siberian sill suggests the presence of Jurassic and Cretaceous sediments north of the sill that have parameters similar to those to the south of the sill. Heavy mineral fractions indicate that the sill separated the North Kara and South Kara basins from one another during Early and Middle Jurassic time; these two basins had different source areas. With the maximum trans- gression of the Late Jurassic this sill ceased to exist as a barrier. The present structural state of the sill is attributed to recent uplift.
The Lower Cretaceous becomes in part volcanic on the north on approaching Franz Josef Land. The Jurassic pinched out northward toward the continental slope.
Taken from Kulakov, 1986, one structure map and one
cross section; digested in Petroleum Geology, Vol. 23, No. 5/6.
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