IVANOVA N.M, SAKAULINA T.S., ROSLOV YU. V. State Company «SEVMORGEO», Russia

Since 1995 Sevmorgeo (St. Petersburg) carries out deep seismic investigations including refraction and reflection methods in complex with seismic survey CDP, seismoacoustic profiling and gravity/magnetic measurements along regional lines AR-1 and AR-2 in Barents-Kara Region.

Line AR-1 connects the superdeep hole-3 on the Kola Peninsula with the hole 1-Hayes on the Franz Joseph Land. Line AR-2 traverses the Kara Shelf - Island Novaya Zemlya - central part of the Barents Shelf. As results new data have been received about deep structures of the northern slope of the Baltic Shield, Kola-Kanin Monocline, uplifts Fedunskiy, Fersman, Vemadskiy, Demidovskiy Aulacogen, Malyginskiy Graben, North-Barents Basin. South-Kara Syneclise. Admiralteyskiy Uplift, Trough Sedova, and Novozemelskiy Fold Belt. For the all geotraverses full section of the Earth's crust with basic crust's boundaries and horizons in sedimentary cover, have been composed. Deep sections of regional lines essentially differs by age and composition of complexes of sedimentary cover, intermediate structural complex between consolidated basement and sedimentary cover, depths of heterogeneous basement and thickness of a consolidated part of Earth's crust and common thickness of earth crust in general.

The main features of the deep structure Barents-Kara Region are following: 1) a presence graben structures in the section of the sedimentary cover and basement, complicated a large faults of the listric type; 2) extremely the large thickness of sedimentary cover estimated as 15-18 km; 3) a presence in the bottom of the grabens thick high velocity (velocities up to 5.6-6.2 km/sec) series of volcanic-sedimentary rocks; 4) a presence of magnetoactive rocks, the greatest quantity of them locate in the Upper Palaeozoic and Triassic part of the section; 5) reduced thickness of the granite-gneissic complex to 3-8 km and Earth's crust to 31-36 km in grabens; 6) a presence of the mantle "domes", largest of them is fixed within Noyab'rskiy Graben and the eastern slope of the North-Barents Basin. These features are characteristic of riftogenic extension of Earth's crust. Thus new geophysical data along regional lines testify that leading process in forming of modem structure of the Barents-Kara Region is epicontinental riftogenesis accompanied by spreading, crush, dipping and possibly horizontal dislocation of Earth's crust block, earlier assumed ML. Verba (1985), Ig. S. Gramberg (1997), B.V. Senin, E.V. Shipilov, A.Yu. Yunov (1989.

For the fist time information about a deep structure of the Though Sedova has been received. Seismic data testify about its asymmetric structure. The eastern part of the Though Sedova is complicated the fault of trust type, which may represent a frontal part of the West-Novozemelskaya Zone of thrust-overfault dislocations. As result more ancient folded rocks of the Novozemelskaya Fold Belt superpose non-folded complexes of the sedimentary cover of the Trough Sedova. The sedimentary cover of the Though Sedova is presented by the Permian-Triassic terrigenous complex with thickness of 5.0-7.0 km. Confident trace of refraction boundaries with Vgr - 5.5-5.8 km/sec. (Horizon la) and V» -6.2-6.4 km/sec (Horizon I-II) allows to connect their with clay-carbonate rocks of the Lower Permian and Upper Devonian-Carboniferous, mapped on the western coast Novaya Zemlya in composition of folded complexes.

Sedimentary cover and deep structure of the marine continuation of the West-Siberian Epipaleozoic Plate have been studied more exactly in the limits of the Kara Shelf.

Sedimentary cover forms here extensive South-Kara Syneclise, in which depression with cross system of Permian- Triassic rifts in the base is located. The western margin of the Plate, adjacent to Nonozemelskiy Fold Belt, is presented by Pre-Novozemelckaya Monocline. Under plate cover there are two complexes of Riphean and Palaeozoic rocks, occurring on the consolidated ancient basement block. In the limits of Monocline both sedimentary cover and folding Upper and Middle Palaeozoic terrigenous and carbonate-terrigenous rocks and Riphean-Lower Paleozoic flyschoid and molassoid low-metamorphic complex have increasing thickness towards the east. Sedimentary cover is predominantly presented here with Jurassic and Cretaceous rocks with maximal thickness of 2.0 km. Middle and Upper Paleozoic complex is 1.0-2.0 km to 4.0-6.0 km thickness. It contours the western flange of extensive Pakhtusovskiy trough of aulacogen type. The surface of consolidated basement has clear block structure dipping towards the east by listric blocks system. It's depth is 5.0-12.0 tan.

For the first time when using seismic data, a large structural element - the Pakhtusovskiy Trough - has been identificated in the western part of the Kara shelf. It is filled with Riphean and Paleozoic deposits forming transition structural store between consolidated basement (AR-PR) and sedimentary terrigenous cover having Mesozoic age preliminary. Total thickness of Paleozoic and Riphean deposits achieves 9-12 km. The hough is limited by large faults with amplitude of displacement of 1,5 km- 2,5 km. There is the Vikulovskaya local structure, expressed in all the horizons of sedimentary Mesozoic cover, above axis fault zone.

As a whole, data analysis has shown that the Barents-Kara Region is characterized with thinner continental and sub-continental crust 37-38 km average thickness. In the area of Novaya Zemlya, the northern slope of the Baltic Shield, thickness of the Earth's crust increases up to 40-42 km that is typical for continental crust. Anomalous crust is developed in rift structures. It's thickness is 33-36 km. In the North-Barents Basin, lens of crystal-mantle mixture up to 10 km thickness is found on the base of complex interpretation of seismic. gravity/magnetic geophysical methods.

Geophysical investigations along regional profiles 1-AR, 2-AR and comparison with results of preceding surveys allow to mark several areas perspective on hydrocarbons. Taking into account rift character of main large basins and grabens, the most perspective structures are referred as a rale to the edge uplifts of the grabens, associated with large fault zones. That's why the main perspective areas along regional profiles are supposed as follows: 1 - the junction zone of the Kola-Kanin Monocline and West-Kola graben, 2 - the junction zone of the Fedynskiy uplift and Demidovskiy Aulacogen, 3 - the central zone of the Demidovskiy Aulacogen, 4 - the Fersman Uplift. 5 - the south-western flange of the North-Barents Basin, complicated by the Vernadskiy and Shatskiy highs, б - the Vilchekovskaya Monocline, 7 -the western part of South-Kara Syneclise in limits of Vikulovskaya, Geophysical and Central structures, discovered earlier by MAGE and SMNG (special attention must be paid to Central structure, located in limits of the western edge uplift of Noyabr'skiy graben), 8 - the western part of the Rusanovkiy High, where anomaly of "bright spot" type at the depth of 1800 in, above large fault zone is marked in Albian-Senomanian petroleum complex.

Reference
Verba M.L., Barents-North Kara Megabasin and its role in evolution of the West-Arctic Shelf In: Geological structure of the Barents-Kara shelf. //Leningrad, PGO
Sevmorgeologia. 1985, p. 11-28.
Gran/berg Ig. S., The Barents Pemiian-Triassic paleorift and its importance for a problem of the oil and gas potential of the Barents-Kara Plate. //DAS, 1997, v. 352, № 6, p. 789-791.
Senin B.V., Shipilov E. V., Yunov A.Ya. Tectonic of the arctic zone transition from continent to ocean. //Murmansk publishing, 1989, p. 176.

ARCTIC SHELF OIL AND GAS CONFERENCE 2004