Maximum sedimentary thickness of the lower mega-complex (Riphean to Late Paleozoic in age) in the Barents-Kara mega-downwarp is 10-11 km, decreasing to 1-2 km on the paleo-highs. Facies composition is varied and controlled largely by paleo-relief. For example, mostly carbonate and carbonate-clastic sediments of the platform type collected on the paleo- highs, as found on the Pechora platform and Admiralty swell. The seismo-facies picture suggests clastics in the depressions, which appear to be rifts in nature.
At the break between Early and Late Permian time there was a marked change in the general structure associated with the beginning of ocean- formation processes. The overlying Permian-Triassic mega-complex collected against a background of rifting. Indications of these processes are both the increase in thickness of the sediments to 10-12 km as clinoforms of turbidite character and also thinning of the crust beneath these downwarps as indicated by gravity surveys. The largest structural feature of this mega-complex is the Barents Sea paleo-rift. Extending in a north-south direction for more than 1000 km, this feature broadens into north and south segments separated by a narrow (less than 100 km) zone in which sedimentary thickness is reduced to 2-3 km. This zone corresponds in modern structural plan with the Shtokmanov-Lunin mega-saddle.
Some investigators combine the north and south segments of this rift into a single north-south mega-downwarp, whereas others suggest a difference in both time and morphology of the two segments (the North and South Barents depressions).
Recent seismic surveys in vicinity of Franz Josef Land show an increase in thickness of the Permian-Triassic rift complex, whereas thickness of the Riphean-Paleozoic complex shows no change. This suggests that the north segment is younger, beginning its development only in the Permo-Triassic. The south segment inherited in great degree the east-west orientation of its Paleozoic predecessor.
Seismo-facies data and also paleogeographic reconstructions of adjacent regions indicate the presence in the north segment of this Barents Sea paleo-rift of a stable marine basin of Middle Triassic age. It opens to the north. The south limit of these seismic facies is the Barents-Kara belt of highs. Opening of this north segment appears to be due to ocean opening, one of the phases of which took place at the beginning of the Permian.
With all the differences in interpreting the structure and dynamics of the Barents Sea paleo-rift the undisputed fact remains that there was a structural bridge between the north and south segments coinciding with the Shtokmanov-Lunin mega-saddle. It is part of the east-west- trending Barents-Kara belt of highs. It is very possible that it, expressed in the basement, could have played the role of a barrier restraining penetration of the paleo-ocean trough farther south.
Taken from Gramberg, Suprumenko, and Shipel'kevich, 2001. Digested
in Petroleum Geology, vol. 36, no. 1, 2002, in preparation, three
paleo-structural maps, two cross sections, and one seismic section.
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