The Beaufort-Chukot (Chukchi) continental margin platform is in the northeast part of the Chukchi Sea on the north of the South Chukchi downwarp. It has a Late Caledonian folded basement. Its sedimentary cover consists of Middle Paleozoic- Cenozoic rocks 3-6 km thick. Five seismic units are recognized .
The first unit with velocity of 1.7-2.1 kmps has been identified only in the western part of the platform, where it appears to be concordant on the underlying sediments. Outside this region, however, a discordance is at the base. It has a Neogene- Quaternary age. Thickness is up to 700 m.
The second unit with a velocity of 2.2-2.8 kmps (Grantz and others) is present everywhere on the platform. These sediments are Late Cretaceous in age and rest conformably on the underlying rocks. They are continental clastics and are not less than 1.8 km thick, decreasing to 250 m on the Barrow arch.
The third unit has a formation velocity of 3.0-3.3 kmps and extends to the west coast of Alaska, where it is an early Albian marine clay (Torok Formation). It appears to extend over the entire area and rests on various units. Thickness ranges from 1.5 km to 600 m.
The fourth unit has a formation velocity of 3.7-3.8 kmps and correlates with the upper part of the Ellesmere of Alaska, which is a marine clastic unit of Jurassic-Early Cretaceous age. Thickness ranges from more than 1 km to complete pinch out.
The fifth unit has a formation velocity of 4.3-4.9 kmps and has been identified only in the eastern part of the Chukot depression, where it correlates with the lower Ellesmere of Alaska. It consists of Carboniferous clastic-carbonate sediments and Permo-Triassic marine clays. This unit, however, appears to be widespread over the rest of the platform. Thickness is 680-1150 m.
The East Siberian continental margin platform is in the northern part of the Chukchi Sea west of the Beaufort-Chukot continental margin platform, from which it is separated by the Severo-Chukot fault. The platform cover consists of volcanics and sediments of Phanerozoic age more than 6 km thick. The Severo-Chukot and Vostochno-Chukot depressions, Severo-Chukot high, and Severo- Wrangel downwarp are recognized within it.
Three seismic units are recognized in the Severo-Chukot depression. These are the same as the three upper units of the Beaufort-Chukot continental margin platform. There are no data on the lower units. However, Vendian-Ordovician marine clastics up to 1 km thick are expected in the north of the platform. Then over the entire platform are expected clastic carbonates of Silurian-Devonian age about 500 m thick and of Carboniferous- Permian age 200-300 m thick, marine clastics of Triassic age more than 100 m thick and of Jurassic-Early Cretaceous age up to 500 m thick.
All the rocks of this platform are cut by numerous faults. Fault-associated synclines and anticlines extend in an east-west direction. Clay diapirs up to 2.5 km in diameter extend as far up as the sea floor.
Taken from Ya. I. Polkin,1986, one trctonic map and three
cross section; digested in Petroleum Geology, Vol. 23, No. 5/6.
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