Barents Sea Basin Research Articles

Late Mesozoic-Cenozoic evolution of the south-western Barents Sea in a regional rift-shear tectonic setting

On the basis of sedimentary fill, tectonic style and crustal structure, the study area may be divided into three main geological provinces, separated by major fault zones: (1) the oceanic Lofoten Basin and the Vestbakken Volcanic Province in the west; (2) the south-western Barents Sea basin province; and (3) the eastern region which has acted as a largely stable platform since Late Palaeozoic tirnes. The seismic stratigraphy, calibrated with lithostratigraphic units in exploration wells, has provided the timing of the main tectonic events. The structural evolution of the south-western Barents Sea since Middle Jurassic times comprises two main stages: Late Mesozoic rifting and basin formation, and Early Tertiary rifting and opening of the Norwegian-Greenland Sea. The basin formation was controlled by pre-existing structural elements which were probably established in Late Palaeozoic times. The Late Mesozoic-Cenozoic evolution reflects the main plate tectonic episodes in the North Atlantic-Arctic breakup of Pangea. The Middle-Late Jurassic and Early Cretaceous structuring were characterized by regional extension accompanied by strike-slip adjustments along old structural lineaments developing the Bjørnøya, Tromsø and Harstad Basins as prominent rift basins. The Late Cretaceous development was more complex with extension still dominating west of the Senja Ridge and the Veslemøy High, while halokinesis and continued thermal subsidence prevailed in the Tromsø Basin. The Tertiary structuring was related to the two-stage opening of the Norwegian-Greenland Sea and the formation of the predominantly sheared western Barents Sea continental margin. The tectonic activity was shifted towards the west in successive phases. The south-western Barents Sea basin province developed within the De Geer Zone in a region of rift-shear interaction, having affinities to both the North Atlantic and Arctic regions; initially, as an area of oblique extension linking the Arctic and North Atlantic rift systems (Middle Jurassic-Early Cretaceous), then in a continental megashear setting (Late Cretaceous-Palaeocene), and finally a combined sheared-rifted margin setting during opening of the Norwegian-Greenland Sea (Eocene-Present).

Occurrence of Oil and Gas Fields and Source Rock Transformation in the West Siberian Basin and Barents Sea Platform

The West Siberian and Barents Sea basins contain the largest demonstrated reserves of gas in the world (more than 33 trilion m[sup 3]) and very large recoverable reserves of oil (about 19 billion tons). The main productive reservoirs are of the Jurassic and Cretaceous and are composed of marine and alluvial sandstones. Major gas fields of the West Siberian basin are located north of the Arctic Circle, from which they extend into the Yamal Peninsula and offshore into the Kara Sea. Oil fields of the basin are found mainly in the middle Ob region. Only one giant gas-condensate field has been found in the Barents Sea; however, this area has excellent potential for gas-condensate discoveries in the future. Both basins contain Kimmeridgian-Tithonian black-shale formations, which are prolific oil source rocks. In the Barents Sea basin, Kimmeridgian black shales contain 7 to 9% of organic carbon; total pyrolysis yield ranges from 5.3 to 84.2 mg HC/g rock, and hydrogen index ranges from 270 to 630 mg HC/g TOC. Our pyrolysis data and basin modeling (GALO version) indicate that the realization of the initial petroleum potential in the Shtokmanov field area has not begun because the volume of generated oil (about 8more » mg HC/g TOC) is insufficient to start expulsion (threshold of expulsion is equal to 96 mg HC/g TOC). The Bazhenov Formation shales in the central part of the West Siberian basin are characterized by extremely high values of pyrolysis measurements. The organic carbon content ranges from 10 to 25%; the residual petroleum potential varies from 50 to 190 mg HC/g rock; the maturity typically corresponds to the oil window zone; and the amount of expelled hydrocarbons ranges from 40 to 60 mg HC/g rock. The expulsion of oil commenced 90 to 35 m.y. In the northern part of the West Siberian basin, the Bazhenov shales are lean source rocks.« less

Late Mesozoic–Cenozoic evolution of the southwestern Barents Sea

Three geological provinces are recognized, separated by major fault zones: the oceanic Lofoten Basin and the Vestbakken volcanic province in the west; the southwestern Barents Sea basin province; and the eastern region which has largely acted as a stable platform since Late Paleozoic times. Since Middle Jurassic times, two structural stages are recognized in the southwestern Barents Sea: Late Mesozoic rifting and basin formation; and Early Tertiary rifting and opening of the Norwegian–Greenland Sea. This evolution reflects the main plate tectonic episodes in the North Atlantic–Arctic break-up of Pangea. Middle–Late Jurassic and Early Cretaceous structuration were characterized by regional extension accompanied by strike-slip adjustments along old structural lineaments, which developed as the Bjørnøya, Tromsø and Harstad basins. Late Cretaceous development was more complex, with extension west of the Senja Ridge and the Veslemøy High, and halokinesis in the Tromsø Basin. Tertiary structuration was related to the two-stage opening of the Norwegian–Greenland Sea and the formation of the predominantly sheared western Barents Sea continental margin. Tectonic activity shifted towards the west in successive phases. The southwestern Barents Sea basin province developed within the De Geer Zone in a region of rift-shear interaction. Initially, oblique extension linked the Arctic and North Atlantic rift systems (Middle Jurassic–Early Cretaceous). Later, a continental megashear developed (Late Cretaceous–Paleocene), and finally a sheared-rifted margin formed during the opening of the Norwegian–Greenland Sea (Eocene–Recent).

Investigation of teleseismic Lg blockage and scattering using regional arrays

Abstract Incoherent beamforming and continuous frequency-wavenumber “polar-scan” analysis have been applied to study the characteristics of P coda and Lg waves recorded at the regional arrays NORESS and ARCESS from presumed explosions on the northwestern Russian platform and at test sites of Novaya Zemlya and eastern Kazakh. Also, recordings at the Graefenburg array, near the new GERESS regional array, of Novaya Zemlya events and an eastern European platform (White Sea) event have been compared with the Norwegian array recordings of the same events. The White Sea explosion, at distances of 14° and 22° from NORESS and Graefenburg, respectively, exhibits Lg rms amplitudes on incoherent beams that exceed those of Sn . However, for explosions at Novaya Zemlya at 20° from NORESS and eastern Kazakh at 30° from ARCESS, the Lg waves have much smaller amplitudes than Sn . In the case of Novaya Zemlya, the Lg wave is almost completely blocked at both NORESS and ARCESS, but is well recorded at Graefenburg. This reduction of the Lg amplitudes relative to those from events at longer distances cannot be accounted for by anelastic attenuation and spreading. Comparison of propagation paths suggests that the reduction in amplitudes may be due to blockage and scattering of Lg in the Barents Sea. Analysis of Sn coda waves on incoherent beams and continuous frequency-wavenumber analysis “polar scans” suggests that they can result from Lg to Sn scattering from the coastline between the Barents Sea and Scandinavia. Recent geologic studies have revealed significant variations in crustal structure in the Barents Sea basin, which may cause the blockage of Lg waves from Novaya Zemlya. In the case of eastern Kazakh explosions, ARCESS incoherent beams show much reduced Lg amplitudes relative to the P coda waves compared with NORESS, even though the distance to ARCESS (31°) is less than that to NORESS (38°). This reduction in Lg amplitude at both NORESS and ARCESS is accompanied by enhancement of P and Sn coda. The timing of the coda waves and the propagation paths suggest that Lg waves may be partially blocked and scattered by the Ural Mountains and that the P and Sn coda waves may result from Lg -to- Pn , Pn -to- Sn , Sn -to- Lg , and Lg -to- Sn conversions from lateral heterogeneities in the crust beneath the Urals. The blockage is greater for the Eastern Kazakh-to-ARCESS path because it crosses the middle part of the Urals whereas the Eastern Kazakh-to-NORESS path crosses the southern part of the Urals chain. These blockage effects seem to result from sudden lateral variations in shallow crustal structure, such as variations in sediment thicknesses in the sedimentary basins of the Russian platform and adjacent to the Urals. These blockage effects can be predicted from geologic studies and need to be accounted for when using Lg amplitudes to estimate absolute yields of explosions and for event identification.

Feedback Mechanism Among Decadal Oscillations in Northern Hemisphere Atmospheric Circulation, Sea Ice, and Ocean Circulation

Decadal oscillations of the ice cover in the Barents Sea are examined for the period since 1950. They are highly correlated with atmospheric circulation when that circulation has an anomalous low pressure over the Barents Sea and Eurasian Basin, while the ice cover is weakly correlated with local air temperature. A feedback mechanism between Barents Sea ice and the atmospheric circulation is suggested; increased cyclonic wind-stress curl reduces cold Arctic flow to the Barents Sea and reduces the sea ice. The reduced ice cover encourages heat flux from the Barents Sea to the atmosphere, tending to reinforce the low pressure. This positive feedback amplifies the oscillations of the air–ice–ocean system driven by external forcing with relatively weak decadal variability. A two-level ocean model, which is driven by prescribed buoyancy flux and wind stresses, confirms that Arctic outflow to the Barents Sea decreases during a cyclonic wind stress.

Feedback Mechanism Among Decadal Oscillations in Northern Hemisphere Atmospheric Circulation, Sea Ice, and Ocean Circulation

Decadal oscillations of the ice cover in the Barents Sea are examined for the period since 1950. They are highly correlated with atmospheric circulation when that circulation has an anomalous low pressure over the Barents Sea and Eurasian Basin, while the ice cover is weakly correlated with local air temperature. A feedback mechanism between Barents Sea ice and the atmospheric circulation is suggested; increased cyclonic wind-stress curl reduces cold Arctic flow to the Barents Sea and reduces the sea ice. The reduced ice cover encourages heat flux from the Barents Sea to the atmosphere, tending to reinforce the low pressure. This positive feedback amplifies the oscillations of the air–ice–ocean system driven by external forcing with relatively weak decadal variability. A two-level ocean model, which is driven by prescribed buoyancy flux and wind stresses, confirms that Arctic outflow to the Barents Sea decreases during a cyclonic wind stress.

Palynological studies of upper cretaceous Barents Sea deposits

The age of the “Old Clays” in one of the segments of the Barents Sea Basin has been established as Late Senonian on palynological evidence.