Southwestern Barents Sea Research Articles

Caledonian basement of the western Barents Sea

Major crustal units in the western Barents Sea have been defined on the basis of depth‐converted seismic reflection data, gravity and magnetic anomaly data. The seismic data revealed three types of crustal reflectivity below the sedimentary rock units, i.e., transparency, strong lower crustal reflectivity, and thoroughly reflective. The crustal structures obtained from the seismic reflection data are supported by 2D density and magnetic modeling. Three NE‐SW‐striking crustal units have been observed south of Bjørnøya. Changes in reflectivity in southwestern Barents Sea are accompanied by gravity and/or magnetic anomalies. North of Bjørnøya, two basement provinces could be distinguished. The observed outlines of the crustal blocks in the southwestern Barents Sea match with Caledonian main thrusts onshore northern Norway. We were therefore able to outline the continuation of Scandian nappe complexes in the southwestern Barents Sea. The crustal unit to the west of the Loppa High region is supposed to be a fragment of Laurentia, since the Loppa High region aligns with the Uppermost Allochthon nappes onshore, and is therefore expected to be the collision zone between Baltica and Laurentia. The southeastern crustal unit aligns with the Lower to Upper Allochthons and their Fennoscandian basement onshore. A compilation of all known thrusts and sutures in the western Barents Sea revealed the complexity of the Iapetus closure. It challenges the concept of two Caledonian main branches (NE and N). The thrusts/sutures are fan‐shaped distributed across the western Barents Sea, resembling the structure of the Late Paleozoic–Mesozoic/Paleocene rift basins and basement highs in the southwestern Barents Sea.

Distribution of demersal fish in the south-western Barents Sea

The composition of the demersal fish fauna of the Barents Sea, and the ranges of most of the fish species, have been relatively poorly known. From 257 bottom trawl hauls distributed in a uniform grid pattern over the southwestern part of the Barents Sea in summer 2000, all fish were identified. The sampled area included the Polar Front zone where warm Atlantic water meets cold (subzero) polar water. The material was used to map the distribution of the demersal fish species, and to analyse their distribution in relation to temperature, depth and salinity. Fifty-eight species were recorded. A fauna characterized by Gadidae and Scorpaenidae was found in the warmer part of the sea, whereas a cold-water fauna of mainly Cottidae, Zoarcidae and Stichaeidae was evident from the Polar Front zone and northwards. In logistic regression analyses temperature was the most important factor associated with the distribution of species (for 26 of the 27 species analysed), but associations with salinity (19 species) and depth (15 species) were also found. The mapping considerably revised the distribution in relation to previous knowledge for 37 species, and the new and more accurate range maps provided here may serve as baseline information for future monitoring of the fish fauna in the Barents Sea.

Analysis of shallow gas and fluid migration within the Plio-Pleistocene sedimentary succession of the SW Barents Sea continental margin using 3D seismic data

Three-dimensional (3D) seismic data acquired for hydrocarbon exploration reveal that gas accumulations are common within the 2–3 km thick Plio-Pleistocene stratigraphic column of the south-western Barents Sea continental margin. The 3D seismic data have relatively low-frequency content (<40 Hz) but, due to dense spatial sampling, long source-receiver offsets, 3D migration and advanced interpretation techniques, they provide surprisingly detailed images of inferred gas accumulations and the sedimentary environments in which they occur. The presence of gas is inferred from seismic reflection segments with anomalously high amplitude and reversed phase, compared with the seafloor reflection, so-called bright spots. Fluid migration is inferred from vertical zones of acoustic masking and acoustic pipes. The 3D seismic volume allows a spatial analysis of amplitude anomalies inferred to reflect the presence of gas and fluids. At several locations, seismic attribute maps reveal detailed images of flat spots, inferred to represent gas–water interfaces. The data indicate a focused fluid migration system, where sub-vertical faults and zones of highly fractured sediments are conduits for the migration of gas-bearing fluids in Plio-Pleistocene sediments. Gas is interpreted to appear in high-porosity fan-shaped sediment lobes, channel and delta deposits, glacigenic debris flows and sediment blocks, probably sealed by low-permeability, clayey till and/or (glacio)marine sediments. Gas and fluid flow are here attributed mainly to rapid Plio-Pleistocene sedimentation that loaded large amounts of sedimentary material over lower-density, fine-grained Eocene oozes. This probably caused pore-fluid dewatering of the high-fluid content oozes through a network of polygonal faults. The study area is suggested to have experienced cycles of fluid expulsion and hydrocarbon migration associated with glacial–interglacial cycles.

Imprints of former ice streams, imaged and interpreted using industry three-dimensional seismic data from the south-western Barents Sea

Abstract Former ice-stream activity is shown from industry three-dimensional (3D) seismic data from the south-western Barents Sea. Although designed for deeper targets, the data allow, due to high spatial sample rate and three-dimensional migration techniques, construction of detailed plan view images. The integration of sea-floor geomorphology with stratigraphy documents the importance of glacial processes in the seascape evolution of this area. Fast-flowing ice streams occupying the cross-shelf troughs during the Late Weichselian glaciation caused large-scale erosion, and also left their imprints in the form of mega-scale glacial lineations on the sea floor as indicators of ice-flow direction. Various types of 3D seismic attributes, combined with detailed geomorphology and seismic stratigraphy, are used to investigate the 2–3 km of stratigraphic record that corresponds to over a million years of ice-stream activity. The appearance of mega-scale glacial lineations on various 3D seismic attribute maps indicates, together with other characteristics of ice streams, that they are formed by erosion beneath fast-flowing grounded ice. Bedform records of former ice streams may, however, be related only to the final stages of ice-streaming, immediately prior to shut down. Because we here have preserved up to several hundred metres of sediments between the buried, glacially eroded surfaces, we have the opportunity to study ice-stream imprints and associated processes covering longer time spans than just the last stages. Seismic volumetric attribute maps reveal that megablocks and rafts, often aligned in chains, commonly occur within the till units, implying that glaciotectonic erosion by fast-flowing ice streams was an important process in the transfer of sediments from the continental shelf to the Bjørnøya Trough Mouth Fan and the deep sea during the Plio-Pleistocene glaciations.

Distribution of demersal fish in the south-western Barents Sea

The composition of the demersal fish fauna of the Barents Sea, and the ranges of most of the fish species, have been relatively poorly known. From 257 bottom trawl hauls distributed in a uniform grid pattern over the southwestern part of the Barents Sea in summer 2000, all fish were identified. The sampled area included the Polar Front zone where warm Atlantic water meets cold (subzero) polar water. The material was used to map the distribution of the demersal fish species, and to analyse their distribution in relation to temperature, depth and salinity. Fifty-eight species were recorded. A fauna characterized by Gadidae and Scorpaenidae was found in the warmer part of the sea, whereas a cold-water fauna of mainly Cottidae, Zoarcidae and Stichaeidae was evident from the Polar Front zone and northwards. In logistic regression analyses temperature was the most important factor associated with the distribution of species (for 26 of the 27 species analysed), but associations with salinity (19 species) and depth (15 species) were also found. The mapping considerably revised the distribution in relation to previous knowledge for 37 species, and the new and more accurate range maps provided here may serve as baseline information for future monitoring of the fish fauna in the Barents Sea.

Severity and timing of Cenozoic exhumation in the southwestern Barents Sea

The juxtaposition of the North Atlantic rift system with the borderlands of the Eurasian Arctic shelf has resulted in an unusual basin evolution in the southwestern Barents Sea. Exploration has concentrated on the Mesozoic sandstone plays of the Hammerfest Basin. These have yielded abundant gas and very little oil. Such findings are typical of peripheral North Atlantic margin basins that have undergone Cenozoic exhumation. This is generally thought to have occurred during the Palaeocene, Oligocene–Miocene or Pleistocene. Hammerfest Basin erosion is widely estimated to be in the range of 500–1500 m. However, the relative severity of individual episodes and impact on fluid dynamics within the basin are poorly constrained. We apply basin modelling tools to establish the sensitivity of the petroleum system to three cited scenarios for Cenozoic exhumation. Vitrinite reflectance and temperature data constrain burial and thermal histories. Calibration is not possible using heat flow variations alone; erosion timing and magnitude are required to match available data. The calibrated model indicates a significant thermal disequilibrium in the Hammerfest Basin at the present day resulting from Late Cenozoic exhumation. Forward modelling of Pleistocene ice sheets allows for an estimation of pressure and temperature fluctuations in response to glacial–interglacial cycles.

Lower Cretaceous: the next target for oil exploration in the Barents Sea?

During the early days of exploration in the southwestern Barents Sea, Lower Cretaceous wedges and mounds were identified on seismic data along the margins of the Hammerfest Basin above rotated Jurassic fault blocks. They were ranked as secondary targets after the giant Jurassic closures in the central part of the basin. Drilling of the latter proved the Snøhvit area gas fields and Snøhvit’s thin oil leg. However, the majority of the wells drilled in the Hammerfest Basin have oil shows in Lower Cretaceous strata. Even the claystones in the most basinal part have oil shows, interpreted by the industry to be remnants of oil leaked from Jurassic reservoirs to the surface. Lower Cretaceous sandstones have also been drilled along the Troms–Finnmark Platform, Loppa High and Senja Ridge, where almost all wells have oil shows. Three wells drilled along the southern margin of the Loppa High have even proved small amounts of oil ranging from 31° API to 38° API and the westernmost well, 7120/1-2, is ranked as an oil discovery. Thick (123–157m) massive sandstones of Valanginian to Hauterivian age in wells 7120/1-2, 7122/2-1 and 7120/10-2 represent the reservoir analogues for a possible Lower Cretaceous oil giant. The Gamma gas discovery 7019/1-1 at the eastern margin of the Tromsø Basin could be an indication of such a giant. Lower Cretaceous sandstones were also the primary target for 7120/10-2. The reservoir sandstones were deposited as submarine fans and the drilled massive sandstones have good reservoir parameters.

Tracer-derived transit time of the waters in the eastern Nordic Seas

The spatial-temporal distribution of the anthropogenic radionuclide 137Cs originating from nuclear bomb testing and the Sellafield reprocessing plant in the Irish Sea is simulated using a global version of the Miami Isopycnic Coordinate Ocean Model (MICOM). The physical model has a horizontal resolution of about 40 km, and it is forced with daily atmospheric reanalysed fields for the period 1948 to 2002. A comparison of the temporal evolution of observed and simulated concentrations of 137Cs has been conducted for the regions east of Scotland, west of central Norway and at the entrance of the Barents Sea. It follows that the annual mean 137Cs concentration signal from the Sellafield discharge reaches the southwestern Barents Sea region in 5 yr, in accordance with available observations. To more accurately assess the age of the caesium-tagged water masses, three additional experiments were performed with an Eulerian age coupled to the evolution of the tracer concentration. It is demonstrated that the transit time depends on the duration of the tracer release history, on the dynamical ocean state and on whether the transit time is derived from the time difference between the release history and the concentration evolution downstream of the release, or as an explicit Eulerian age tracer. The Eulerian age tracer gives a transit time for a Sellafield-like discharge to reach the Barents Sea of 56 months in the 1970s, 52 months in the 1960s and 51 months in the 1980s, and that this difference is strongly governed by the ocean dynamics in the Faeroe—Scotland region.

Zooplankton biomass variation in relation to climatic conditions in the Barents Sea

Over the last two decades, there have been large changes in the zooplankton biomass in the Barents Sea. These biomass variations are mainly attributed to predation pressure and environmental factors (e.g. advective transport). When stock size of capelin (Mallotus villosus), a major planktivorous fish in the Barents Sea ecosystem, was quite low as in 1986 and 1994, the zooplankton biomass showed marked increase. However, the increase in the zooplankton biomass occurred in different water masses during 1986 and 1994. In 1986, a climatically cold year, the plankton biomass was highest in the Arctic waters of the northeastern Barents Sea. This is probably due to the increase in larger Arctic amphipod species, such as Themisto libellula. In 1994, a climatically warm year, the zooplankton biomass was high in the Atlantic waters of the southwestern Barents Sea. The large increase in zooplankton biomass in the Atlantic waters in 1994 was presumably due to the higher inflow of advected organisms, e.g. Calanus spp., as well as high temperatures, which may lead to high growth rates of zooplankton. Throughout the studied region, the plankton biomass in the "cold year" of 1986 was generally much lower than in the "warm year" of 1994.

Statoil awards sn↓hvit contract to Dragados

The Late Cretaceous foraminiferal assemblages from five wells drilled in the southwestern Barents Sea were analysed using morphogroup analysis in order to understand the palaeoenvironment and palaeobathymetry of the study area. Morphogroup analysis of assemblages in the Upper Cretaceous Kveite Formation suggests stable, possibly middle to lower bathyal, mesotrophic and relatively well-oxygenated environments in the Tromsø Basin during the Late Cretaceous. The depositional setting of Upper Cretaceous Kviting Formation in the tectonically more stable Hammerfest Basin was probably shallower, but still represents a deep-water environment similar to that of the Kveite Formation. A shallowing regional bathymetry in the southwestern Barents Sea is indicated by the general decreasing trend in the relative abundance of tubular forms and the species diversity of assemblages, which reflects the regional Late Cretaceous–Paleocene uplift prior to the break-up of the Greenland–Norwegian Sea. Changes in the relative abundance of morphogroups and in the main constituent in the cumulative length of tubular taxa from Rhizammina to Rhabdammina near the top of Kveite Formation agree with the possible existence of bottom water currents.

Polycyclic aromatic hydrocarbons (PAHs) and organochlorines (OCs) in bottom sediments of the Guba Pechenga, Barents Sea, Russia

Surface sediment samples from the Guba Pechenga and adjacent areas: Varangerfjord, Guba Malaya Volokovaya and Guba Bol'shaya Volokovaya (south-western Barents Sea) collected in March–April 1997 were analysed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated pesticides: p,p′-DDT, p,p′-DDE, p,p′-DDD, α- and γ-HCH, and hexachlorobenzene (HCB). Mean ∑PAH (sum of the two- to six-ring PAHs) concentration in sediments from the Guba Pechenga (1481 ng/g dry wt.) was significantly higher than in sediments from adjacent areas (252 ng/g dry wt.), where PAH contamination levels were similar to reported for unpolluted sediments of the northern Norway fjords and open parts of the Barents Sea. Differences between HCB levels as well as ∑HCH (sum of α- and γ-HCH) levels found in Guba Pechenga sediments and adjacent area sediments were not significant. Concentrations of these contaminants varied in ranges 0.28–1.76 and 0.05–0.68 ng/g dry wt., respectively, and were consistent with literature data on PAH levels in sediments from the northern Norway harbours, Kola Bay (Russia) and south-eastern part of the Barents Sea. Average total DDT concentration in Guba Pechenga sediments (10.5 ng/g dry wt.) was one and 2–3 orders higher than those found in sediments from the Pechora Sea and from the seas of eastern Arctic, respectively, however, it was comparable with DDT levels reported for harbours of northern Norway and Kola Bay. Significant difference between total DDT levels in Guba Pechenga and in the adjacent areas (mean 1.8 ng/g) was found. Among compounds of DDT family, p,p′-DDT isomer prevailed in all sediment samples indicating a possible local ‘fresh’ DDT source. Mean ∑PCB (sum of PCB-28, 31, 52, 101, 118, 105, 153, 138, 156, 180, 209) concentration in the Guba Pechenga sediments (12.8 ng/g dry wt.) was significantly higher than in sediments of adjacent areas (2.1 ng/g dry wt.), but it was lower in comparison with ∑PCB levels reported for the northern Norway harbours and Kola Bay sediments. The highest levels of contaminants were found in sediments collected close to the Liinakhamari harbour. The origin of both PAHs and OCs in the Guba Pechenga sediments is a combination of local sources and long-range transport from lower latitudes.

Specific Compositional Features of Sediments from the Haakon Mosby Mud Volcano, Southwestern Barents Sea

The submarine Haakon Mosby mud volcano was studied in detail during several cruises, resulting in the collection of an abundant and diverse lithological material. Comprehensive field and laboratory studies made it possible to identify different types of sediments with specific granulometric and pelite fraction (<0.005 mm) compositions, as well as the regularity of their spatial distribution relative to various morphostructural zones of the mud volcano.

Geomorphology of buried glacigenic horizons in the Barents Sea from three-dimensional seismic data

Abstract The glacigenic sequence of the southwestern Barents Sea shelf has for the first time been studied using 3-D seismic data. The close spacing of 3-D lines and powerful computer workstation interpretation techniques have allowed detailed mapping of the observed features. Several generations of subglacial lineations observed on four different palaeo-surfaces are interpreted to reflect the flow patterns of palaeo-ice sheets. To our knowledge, this is the first time that multiple levels of subglacial lineations have been observed. The lineations are 2.5–8 m in relief, 50 to 180 m wide and 0.5 to 20 km long. All four surfaces show a main lineation pattern comprising lineations with a N-S trend, suggesting that the dominant ice flow was directed northwards across the Barents Sea shelf at least four times during the last 0.8 Ma. Two of the surfaces display semi-circular to oblong depressions trending mainly in the same direction as the sub-parallel lineations. These depressions are 9–53 m in relief, 1.25–3.2 km wide and 1.9–9 km long. In contrast to the buried surfaces, the sea floor is dominated by 2.5–25 m deep cross-cutting iceberg plough-marks from the deglaciation phase of the last Barents Sea ice sheet. The 3-D seismic data are conventional industry data. Despite relatively low seismic frequencies and, hence, limited vertical resolution of seismic profiles, time slices and sub-horizontal time maps are of high spatial resolution, providing detailed images of different stages of buried Quaternary glacial geomorphology.

The Late Weichselian glaciation of the Franz Victoria Trough, northern Barents Sea: ice sheet extent and timing

High resolution seismic profiles (PARASOUND, 4 kHz) and three sediment cores from the Franz Victoria Trough and the adjacent continental slope were studied in order to constrain the timing and extent of the northern Svalbard/Barents Sea ice sheet during the Late Weichselian glaciation. Stacked debris flow lobes and layers of glacimarine diamicton on the lower continental slope indicate that large quantities of glacially derived sediments were deposited by the northern Svalbard/Barents Sea ice sheet directly onto the upper continental slope at approximately 23 14 C ka. A grounding-line advance to the shelf break is supported by the identification of diamicton, interpreted as till, in the seismic profile near the shelf break. After several ice sheet instabilities marked by significant input of ice rafted detritus to the continental margin, the disintegration of the northern Svalbard/Barents Sea ice sheet (Termination Ia) is indicated by a distinct pulse of ice rafted detritus at 15.4 14 C ka and the transition to an isotopically defined meltwater signal. The drastic change in sedimentary pattern on the upper continental slope, dated to about 13.4 14 C ka, is interpreted as grounding-line retreat from the shelf edge. A further stepwise retreat of the northern Svalbard/Barents Sea ice sheet is indicated by pulses of ice rafted detritus which appear to be contemporaneous with the onset of distinct ice rafting events in adjacent areas and pulses of glacimarine sedimentation in the southwestern Barents Sea. q 2000 Elsevier Science B.V. All rights reserved.

Lithological description of subcropping Lower and Middle Triasic rocks from the Svalis Dome, Barents Sea

Eleven shallow cores display 315 m of the >700 m thick Lower and Middle Triasic successional of the Svalis Dome, a Salt diapir in the central south-western Barents Sea. The Svalis Dome was uplifted in the late Mesozoic. and Trisassic rocks suherop below Quaternary till around the Upper Palaeozoic core of the dome. Deposition of the Triassic succession took place in deep shelf to basinal environments below storm wave base. The succession is dated by macrofossils and palynomorphs and can be assigned to four formations. The basal beds of the shaly greenish grey Havert Formation (Griesbachian) occur above Permian bioclastic carbonate. The Klappmyss Formation (Smithian) in the lower part contains gravity flow sands deposited as submarine fans pussible triggered by tectonic movements along the adjacent ault zones overlian by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe overlain by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe Formation, and was deposited in a large bight by restricted water circulation. The Snadd Formation. on top, representes a marine shelf unit deposited in front of an emerging land area in the north-east. A minimum of six higher order transgressive-regressive sequences are recognized at the Svalis Dome and these are correlated with other Arctic areas.

Lithological description of subcropping Lower and Middle Triasic rocks from the Svalis Dome, Barents Sea

Eleven shallow cores display 315 m of the >700 m thick Lower and Middle Triasic successional of the Svalis Dome, a Salt diapir in the central south-western Barents Sea. The Svalis Dome was uplifted in the late Mesozoic. and Trisassic rocks suherop below Quaternary till around the Upper Palaeozoic core of the dome. Deposition of the Triassic succession took place in deep shelf to basinal environments below storm wave base. The succession is dated by macrofossils and palynomorphs and can be assigned to four formations. The basal beds of the shaly greenish grey Havert Formation (Griesbachian) occur above Permian bioclastic carbonate. The Klappmyss Formation (Smithian) in the lower part contains gravity flow sands deposited as submarine fans pussible triggered by tectonic movements along the adjacent ault zones overlian by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe overlain by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe Formation, and was deposited in a large bight by restricted water circulation. The Snadd Formation. on top, representes a marine shelf unit deposited in front of an emerging land area in the north-east. A minimum of six higher order transgressive-regressive sequences are recognized at the Svalis Dome and these are correlated with other Arctic areas.

Southwestern Barents Sea margin: late Mesozoic sedimentary basins and crustal extension

The deep sedimentary basins of the southwestern Barents Sea were formed in response to several late Mesozoic–early Cenozoic tectonic events within the North Atlantic rift zone, which culminated with continental breakup and formation of a mainly sheared margin in early Tertiary times. Due to deteriorating data quality, the development of the margin-bordering Sørvestsnaget Basin is not well known. To improve on this, we use both seismic interpretation and gravity modelling to estimate the depth to the Middle Jurassic (MJ) sequence boundary, which marks the onset of Mesozoic rifting. The horizon represents a first-order contrast in seismic velocity and density, and the gravity field correlates well with its depth of burial. Only one seismic line enables tracing of the MJ from surrounding areas into the Sørvestsnaget Basin, down to a depth of at least 17 km in the northeastern part of the basin. The deep basin is reflected in a general thinning of the crust from 30–36 km within the Barents Sea to 20–24 km in the margin area. The gravity modelling show that the Middle Jurassic–Lower Cretaceous sequences are of comparable thicknesses in the Tromsø and Sørvestsnaget Basins. However, adjacent to the rifted margin segment the deep northern part of the Sørvestsnaget Basin is affected by additional large Late Cretaceous normal faulting and subsidence. These faults also caused additional structuring of the intrabasinal Veslemøy High. Post-Middle Jurassic crustal thinning in the southwestern Barents Sea shows maximum cumulative β-values exceeding 4 within the Tromsø and the northern Sørvestsnaget Basins. The corresponding crustal extension is estimated to 70–85 km in a west to northwest direction. There is no uniform increase in crustal thinning toward the continent–ocean boundary, which we attribute to the transform origin of the margin. However, there is a gradual migration of tectonic activity toward the incipient margin as the time of continental breakup was approached.

Inferred gas hydrate on the Barents Sea shelf -- a model for its formation and a volume estimate

On the southwestern Barents Sea shelf, sediments containing gas hydrates that overlie free gas have been inferred from multichannel seismic data. The volume of suspected gas hydrate is tentatively estimated to about 1.9×108 m3. The gas hydrate zone probably formed from thermogenic gas leaking from a deeper source. The hydrate zone may have thickened during the Neogene by including gas originally trapped as free gas below the hydrate following a significant downward migration of the isotherms caused by erosion and/or subsidence. Within the present oceanographic conditions, gas hydrate is suspected to be stable or slowly decomposing.

Late Palaeozoic structural development of the South-western Barents Sea

A regional grid of multichannel seismic reflection profiles records the Late Palaeozoic structure and tectonic development of the south-western Barents Sea. A 300 km wide rift zone, extending at least 600 km in a north-easterly direction, was formed mainly during Middle Carboniferous times. The rift zone was a direct continuation of the north-east Atlantic rift between Greenland and Norway, but a subordinate tectonic link to the Arctic rift was also established. The overall structure of the rift zone is a fan-shaped array of rift basins and intrabasinal highs with orientations ranging from north-easterly in the main rift zone to northerly at the present western continental margin. The structural style is one of interconnected and segmented basins characterized by halfgraben geometries. A less prominent north-westerly fault trend abuts against the main rift zone from the south-east. From the beginning of Late Carboniferous times, the tectonic development was dominated by regional subsidence, and the entire Barents Sea region gradually became part of a huge Permian-Triassic interior sag basin. This development was interrupted by renewed Permian-Early Triassic rifting and formation of north trending structures in the western part of the rift zone. The tectonic link between the northeast Atlantic and Arctic rifts, initiated in the Middle Carboniferous, then became the primary locus of deformation. The tectonic relationship of north-east Atlantic-Arctic rifting to the development of Late Palaeozoic basins, which dominate the structure of the eastern Barents Sea, remains poorly understood. The rapid Late Permian-Early Triassic subsidence of these earlier fault-controlled basins also affected the western Barents Sea. This suggests possible influence on rifting in the Barents Sea by active-margin processes operating at the eastern Barents Sea margin during subduction of the Uralian Ocean floor. Strong control on the Late Palaeozoic structural development by zones of weakness in the basement is interpreted to be inherited from three major compressional orogens-Baikalian, Caledonian and Innuitian-converging and partly intersecting at a major tectonic junction in the south-western Barents Sea. Local observations indicate that the Barents Sea Caledonides were affected by a Devonian phase of late-orogenic extensional collapse.

FLUCTUATIONS OF THE SVALBARD–BARENTS SEA ICE SHEET DURING THE LAST 150 000 YEARS

On Spitsbergen, western Svalbard, three major glacial advances have been identified during the Weichselian. All three reached the continental shelf west of the Svalbard archipelago. Radiocarbon, luminescence and amino acid dating of interbedded interstadial and interglacial sediments indicate that these glacial advances have Early (Isotope Stage 5d), Middle (Stage 4), and Late Weichselian ages (Stage 2). An additional, more local, advance has been dated to Isotope Stage 5b. The Late Weichselian ice sheet expanded across the entire Barents Sea. However, in the south-western Barents Sea, the Late Weichselian till is the only till above Eemian sediments, indicating that the Early- and Middle Weichselian ice advances were restricted to the Svalbard archipelago and the northern Barents Sea. A major problem with the onshore sites is the dating of events beyond the range of the radiocarbon method. To overcome this, the onshore record has been correlated with marine cores from the continental slope and the deep-sea west of Svalbard, where a chronology has been established by oxygen isotope stratigraphy. Ice rafted detritus (IRD) was used as the main monitor of glaciation. The IRD record closely mirrors the glaciation history as interpreted from the onshore sections. During the Late Weichselian, the largest IRD peak occurred during deglaciation, a pattern also postulated for the earlier events. Given this, the results from the marine cores indicate that the ages for the first glacial advances during the Weichselian were a few thousand years older than interpreted from the onshore stratigraphy.