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. 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.

Let us then be up and doing, With a heart for any fate; Still achieving, still pursuing, Learn to labor and to wait. - Henry Wadsworth Longfellow