Triassic sediments. Two seismic marker horizons are present in the Triassic section: B near the top and A at the base. These sediments are present throughout the area of the Barents Sea. Depth to reflector A is 4-5 km in the Cis-Ural foredeep and 6-8 km in the Barents mega-trough. Triassic crops out on Svalbard. Seismic velocity in the Triassic rocks ranges from 2.5-2.8 kmps at the top to 4.0 kmps in the lower part. On Spitzbergen it is 4.0-4.7 kmps. In the northern part of the Barents Sea there is a predominance of argillaceous rocks, whereas in the southern part sandy rocks predominate. Thickness of the Triassic ranges up to 3.5-4.0 km in the South Barents depression.
Permian sediments of upper clastic complex. Two marker reflecting horizons are present in the section. The upper (Ia) is at the base upper clastic complex within the Lower Permian, and the lower (I-II) is at the base of the Permian. In addition, seismic horizon I at the boundary between Lower and Upper Permian is well expressed but absent in many places.
The Permian System of the Barents Sea consists of three sub-divisions: an upper continental clastic and a middle marine carbonate-clastic, these being within the upper clastic complex, and a lower carbonate unit, part of the lower carbonate complex. Velocity values in the upper clastics are generally 3.3-3.7 kmps, ranging up to 4.2 kmps. Thickness of the Permian is 400-700 m in the southeast, thinning on the highs. In the South Barents depression it increases to 2-2.5 km.
Two general characteristics of the upper clastic complex are notable. First, velocity values increase systematically with depth. Second, two types of section are present: platformal deposits 2-4 km thick on the highs, and parageosynclinal deposits 10-12 km thick in the South Barents depression and apparently in the entire Barents mega-trough due largely to a thick Permo-Triassic section.
LOWER, LARGELY CARBONATE COMPLEX. This complex is subdivided into an upper carbonate sub-complex and a lower clastic-carbonate sub-complex. Reflecting Horizon III separates these two units, and Horizon IV is the basement surface. Depth to Horizon IV is 12-14 km in the South Barents depression. Carbonate sub-complex. The presence of these rocks in the section is indicated by high velocities in the sediments beneath the upper clastic complex. Upper Devonian, Carboniferous, and Lower Permian are judged to be present on a basis of onshore drilling data. Velocity is in the 5.2-6.4 kmps range onshore in the southeast, 5.8 kmps on Spitzbergen, and 5.6-6.2 in the South Barents depression.
In the western part of Barents mega-trough in Nordkap down- warp and on the West Kola saddle there is an extensive area where seismic velocity is 4.7-5.0 kmps. This section is interpreted as having salt domes. Volcanics are also present in Carboniferous in this southern part of the Barents Sea. There is an angular unconformity at the base of the carbonate sub-complex. Thickness of this complex is in the 1-2 km range and shows no tendency to thicken in the structural lows. It thins to the north to less than 100 m on Franz Josef Land.
Clastic carbonate sub-complex. This is a relatively thin section between reflecting Horizon III and the surface of the basement (Horizon IV). Nature of the seismic signals indicates presence of a variety of lithologies. It perhaps correlates with the Silurian-Lower Devonian onshore to the southeast. Thickness varies due in part to filling of topographic irregularities in the basement surface.
Taken from Verba, 1984, one tectonic map and three cross
sections; digested in Petroleum Geology, Vol. 23, No. 5/6.
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