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Effect of Neotectonic Processes on Oil-Gas Potential of Barents-Kara Shelf

Internet Geology News Letter No. 24, December 20, 1999

The Barents-Kara Shelf is a vast region including the Pechora and West Siberian intra-continental platforms, extending northward to the West Arctic continental margin. Three stages are recognized in the structure. The lower consists of basement rocks of various ages. The middle is represented by Paleozoic carbonates and clastics of the platform cover. The upper is composed of clastics of the shelf basins. The latter consists of four sub-stages: Upper Permian-Triassic, Jurassic-Lower Cretaceous, Upper Cretaceous-Eocene, and Oligocene-Quaternary.

Commercial petroleum has now been found in the Paleozoic carbonate-clastic complex in the large Prirazlom oil field and Severo-Gulyayev oil-gas-condensate field. Murmansk and Severo-Kil'din gas fields are in rocks of the Upper-Permian-Triassic sub-stage. The Jurassic-Lower Cretaceous sub-stage is assessed particularly high; present there are the super-giant Shtokmanov and Ledov gas-condensate fields.

A very important change in the geologic history of the Arctic was between the Early and Late Cretaceous, when spreading began in the Norway-Greenland and Eurasian sub-basins. This was the beginning of the neotectonic stage of the region. Late Cretaceous-Danian time was characterized by extensive regional uplift and reduction of the area of the marine basins. Erosion reached the top of the Jurassic and on several highs even the Triassic. The Paleocene-Eocene epoch was marked by extension of the ocean floor.

The Oligocene-Miocene phase was characterized by fundamental change in paleo-geographic conditions. The Norway-Greenland deep-water basin took on its final form, and rifting and spreading were active in the Eurasian basin. Uplifted land areas began to form in the north of the Barents-Kara plate and became a source of detritus for basins on the intra-continental plate. Uplift in amounts of 200-1500 m took place on the West Arctic margin in the belt of the Svalbard-Severnaya Zemlya shelf-margin highs. The depressions of the Barents-North Kara mega-downwarp experienced subsidence of 400-750 m.

Recent normal, reverse, and overthrust faults fully controlled 55 percent of the oil-gas structures of the Pechora plate, and 92 percent have been neotectonically active. In West Siberia recent faulting has been important to fluid migration in the north and particularly on the shelf. It has been less important in the central and south parts. This is without doubt related to neotectonic activity on the West Arctic continental margin.

Most of the hydrocarbon accumulations on the Barents-Kara Shelf are in anticlines that formed in Late Cretaceous and Oligocene-Miocene time. Highly favorable are those areas on the continental margin and intra-continental plates where thickness of the sedimentary cover is maximum, and recent movements have been moderate (200-300 m). First among the highly favorable regions are the depressions of the Barents-Kara mega-downwarp and especially highs that lie brtween them. Assessed as favorable are the continental slopes with thick Cenozoic clinoforms.

The outer zone of the Barents-Kara Shelf along the Spitzbergen-Severnaya Zemlya continental slope experienced extensive faulting during the Late Cretaceous and Oligocene-Quaternary tectonic epochs; consequently, prospects there are assessed as low. On the whole, however, the neotectonic regime of the West Arctic continental margin was favorable for reworking and preservation of hydrocarbon pools and for moderate growth of structures (Petroleum Geology, vol. 33, no. 2, p. 107-114, 1999, from Musanov, 1997).