The Kara Sea is a typical continental shelf sea. Its southern boundary is ephemeral, the coast line having migrated extensively in the recent geologic past.
Two major structural features are in contact with one another beneath the waters of the Kara Sea. The North Kara Sea is part of the Barents-Kara platform, and the South Kara Sea is part of the West Siberian platform. This zone of juxtaposition is along a basement ridge called the North Siberian Sill. Thickness of the sedimentary cover above this ridge is only 1 km, whereas it is up to 7 km off its flanks. Presence of this "sill" has been confirmed by seismic surveys.
West Siberian platform. That part of the West Siberian platform beneath the Kara Sea is called the South Kara basin. Pliocene (?)-Quaternary sediments are at the top of the section. These are interpreted variously as glacial, marine, and marine-glacial. Sea floor sampling has disclosed sand and silt with admixed coarses sizes. Thickness is uneven, ranging up to 300 m.
Beneath the Pliocene-Quaternary sediments are Paleogene and Cretaceous rocks. During a late Oligocene-early Pliocene erosional break, much of the Paleogene and Cretaceous section of the eastern part of the basin was removed. An almost complete section of Paleocene, Eocene, and lower Oligocene clastics is present in the western part of the basin and in the northern onshore area.
Most of the platform cover consists of Mesozoic sedimentary rocks with an almost complete section from the Middle Triassic to the top of the Cretaceous. Seismic velocities in the Cretaceous sediments are in the 2.1-2.8 kmps range, and those in the Jurasic are 2.8-3.1 kmps. Seismic marker horizon S is in Campanian sediments; G-1 is at the top of the Cenomanian - base of the Turonian; M is in the Aptian sediments; B is in the Upper Jurassic; and B-1 is in the Lower and Middle Jurassic. Horizon G-1 is at depths up to 1.5 km; M is up to 2.0-2.5 km; and B is at 4.0-4.5 km. On a basis of these data the thickness of the Cretaceous is estimated at 3.0-3.5 km, and that of the Jurassic is 1.5-2.0 km.
The offshore seismic section is different from that onshore because permafrost is absent beneath the sea and in a narrow strip along the coast onshore. The onshore permafrost is up to 300-400 m thick, and velocities in it are as much as 3.5 kmps.
Taken from Kulakov, 1986, one structure map and one
cross section; digested in Petroleum Geology, Vol. 23, No. 5/6.
Copyright 2003 James Clarke. You are encouraged to print
out this News Letter and to forward it to others. Earlier News
Letters are available at: http://geocities.com/internetgeology
This News Letter is distributed without charge in the interest of
our science of petroleum geology. To be added to the mailing
list please send your e-mail address to: jamesclarke@erols.com
For information on the journal Petroleum Geology please telephone
703 759-4487 or FAX 703 759-3754. Vol. 37 for the year 2003
has been published, and I am well in to preparation of the material
for Vol. 38 for the year 2004. Please make provision through me or
your subscription agency for Vol. 38 so that I have a better idea as
to the size of this addition. The price is $89.00 per volume. Thank you.