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The Barents Shear Margin separates the Svalbard and Barents Sea from the North Atlantic. It includes one northern (Hornsund Fault Zone) and a southern (Senja Fracture Zone) margin segment in which structuring was dominated by dextral shear. These segments are separated by the Vestbakken Volcanic Province that rests in a releasing bend position between the two. During the break-up of the North Atlantic the plate tectonic configuration was characterized by sequential dextral shear, extension, contraction and inversion. This generated a complex zone of deformation that contain several structural families of over-lapping and reactivated structures Although the convolute structural pattern associated with the Barents Shear Margin has been noted, it has not yet been explained in this framework. A series of crustal-scale analogue experiments, utilizing a scaled stratified sand-silicon polymer sequence, serve to study the structural evolution of the shear margin in response to shear deformation along a pre-defined boundary representing the geometry of the Barents Shear Margin and variations in kinematic boundary conditions of subsequent deformation events, i.e. direction of extension and inversion. The observations that are of particular significance for interpretating the structural configuration of the Barents Shear Margin are: 1) The experiments reproduced the geometry and positions of the major basins and relations between structural elements (fault and fold systems) as observed along and adjacent to the Barents Shear Margin. This supports the present structural model for the shear margin. 2) Several of the structural features that were initiated during the early (dextral shear) stage became overprinted and obliterated in the subsequent stages. 3) Prominent early-stage positive structural elements (e.g. folds, push-ups) interacted with younger (e.g. inversion) structures and contributed to a complex final structural pattern. 4) All master faults, pull-part basins and extensional shear duplexes initiated during the shear stage quickly became linked in the extension stage, generating a connected basin system along the entire shear margin at the stage of maximum extension. 5) The fold pattern generated during the terminal stage (contraction/inversion became dominant in the basinal areas and was characterized by fold axes with traces striking parallel to the basin margins. These folds, however, most strongly affected the shallow intra-basinal layers. This is in general agreement with observations in previous and new reflection seismic data from the Barents Shear Margin. [ABSTRACT FROM AUTHOR]

We present a crustal-scale seismic profile in the Barents Sea based on new data. Wide-angle seismic data were recorded along a 600 km long profile at 38 ocean bottom seismometer and 52 onshore station locations. The modelling uses the joint refraction/reflection tomography approach where co-located multichannel seismic reflection data constrain the sedimentary structure. Further, forward gravity modelling is based on the seismic model.We also calculate net regional erosion based on the calculated shallow velocity structure. Our model reveals a complex crustal structure of the Baltic Shield to Barents shelf transition zone, as well as strong structural variability on the shelf itself.We document large volumes of pre-Carboniferous sedimentary strata in the transition zone which reach a total thickness of 10 km. A high-velocity crustal domain found below the Varanger Peninsula likely represents an independent crustal block. Large lower crustal bodies with very high velocity and density below the Varanger Peninsula and the Fedynsky High are interpreted as underplated material that may have fed mafic dykes in the Devonian. We speculate that these lower crustal bodies are linked to the Devonian rifting processes in the East European Craton, or belonging to the integral part of the Timanides, as observed onshore in the Pechora Basin. [ABSTRACT FROM AUTHOR]

The SW Barents Sea margin experienced a pulse of extensional deformation in the Middle-Late Devonian through the Carboniferous, after the Caledonian Orogeny terminated. These events marked the initial stages of formation of major offshore basins such as the Hammerfest and Nordkapp basins. We mapped and analyzed three major fault complexes, (i) the Måsøy Fault Complex, (ii) the Rolvsøya fault, and (iii) the Troms-Finnmark Fault Complex. We discuss the formation of the Måsøy Fault Complex as a possible extensional splay of an overall NE-SW-trending, NW-dipping, basement-seated Caledonian shear zone, the Sørøya-Ingøya shear zone, which was partly inverted during the collapse of the Caledonides and accommodated top-NW normal displacement in Middle to Late Devonian-Carboniferous times. The Troms-Finnmark Fault Complex displays a zigzag-shaped pattern of NNE-SSW- and ENE-WSW-trending extensional faults before it terminates to the north as a WNW-ESE-trending, NE-dipping normal fault that separates the southwesternmost Nordkapp basin in the northeast from the western Finnmark Platform and the Gjesvær Low in the southwest. The WNW-ESE-trending, margin-oblique segment of the Troms-Finnmark Fault Complex is considered to represent the offshore prolongation of a major Neoproterozoic fault complex, the Trollfjorden-Komagelva Fault Zone, which is made of WNW-ESE-trending, subvertical faults that crop out on the island of Magerøya in NW Finnmark. Our results suggest that the Trollfjorden-Komagelva Fault Zone dies out to the northwest before reaching the western Finnmark Platform. We propose an alternative model for the origin of the WNW-ESE-trending segment of the Troms-Finnmark Fault Complex as a possible hard-linked, accommodation cross fault that developed along the Sørøy-Ingøya shear zone. This brittle fault decoupled the western Finnmark Platform from the southwesternmost Nordkapp basin and merged with the Måsøy Fault Complex in Carboniferous times. Seismic data over the Gjesvær Low and southwesternmost Nordkapp basin show that the low-gravity anomaly observed in these areas may result from the presence of Middle to Upper Devonian sedimentary units resembling those in Middle Devonian, spoon-shaped, late- to post-orogenic collapse basins in western and mid-Norway. We propose a model for the formation of the southwesternmost Nordkapp basin and its counterpart Devonian basin in the Gjesvær Low by exhumation of narrow, ENE-WSW- to NE-SW-trending basement ridges along a bowed portion of the Sørøya-Ingøya shear zone in the Middle to Late Devonian-early Carboniferous. Exhumation may have involved part of a large-scale metamorphic core complex that potentially included the Lofoten Ridge, the West Troms Basement Complex and the Norsel High. Finally, we argue that the Sørøya-Ingøya shear zone truncated and decapitated the Trollfjorden-Komagelva Fault Zone during the Caledonian Orogeny and that the western continuation of the Trollfjorden-Komagelva Fault Zone was mostly eroded and potentially partly preserved in basement highs in the SW Barents Sea. [ABSTRACT FROM AUTHOR]

The Fingerdjupet Subbasin in the southwestern Barents Sea sits in a key tectonic location between deep rifts in the west and more stable platform areas in the east. Its evolution is characterized by extensional reactivation of N-S and NNE-SSW faults with an older history of Late Permian and likely Carboniferous activity superimposed on Caledonian fabrics. Reactivations in the listric NNE-SSW Terningen Fault Complex accommodated a semi-regional rollover structure where the Fingerdjupet Subbasin developed in the hangingwall. In parallel, the Randi Fault Set developed from outer-arc extension and collapse of the rollover anticline. N-S to NNE-SSW faults and the presence of other fault trends indicate changes in the stress regime relating to tectonic activity in the North Atlantic and Arctic regions. A latest Triassic to Middle Jurassic extensional faulting event with E-W striking faults is linked to activity in the Hammerfest Basin. Cessation of extensional tectonics before the Late Jurassic in the Fingerdjupet Subbasin, however, suggests rifting became localized to the Hammerfest Basin. The Late Jurassic was a period of tectonic quiescence in the Fingerdjupet Subbasin before latest Jurassic to Hauterivian extensional faulting, which reactivated N-S and NNE-SSW faults. Barremian SE-prograding clinoforms filled the relief generated during this event before reaching the Bjarmeland Platform. High-angle NW-prograding clinoforms on the western Bjarmeland Platform are linked to Early Barremian uplift of the Loppa High. The Terningen Fault Complex and Randi Fault Set were again reactivated in the Aptian along with other major fault complexes in the SW Barents Sea, leading to subaerial exposure of local highs. This activity ceased by early Albian. Post-upper Albian strata were removed by late Cenozoic uplift and erosion, but later tectonic activity has both reactivated E-W and N-S/NNE-SSW faults and also established a NW-SE trend. [ABSTRACT FROM AUTHOR]

The Barents Sea is believed to have been influenced in most parts by Cenozoic uplift and erosion episodes. The rocks in the area are not currently at their maximum burial depth. The exhumation of the sedimentary rocks has had large effects on rock physical properties and hydrocarbon maturation and migration. The current study seeks to estimate exhumation from shale compaction and thermal maturity techniques and discuss its implications for hydrocarbon exploration in the uplifted Barents Sea area. This study uses well logs and thermal maturity data together with widely distributed shot gather data along long-offset seismic reflection lines. The use of shale compaction techniques to estimate exhumation was focused particularly on the regionally preserved Aptian-Albian (Kolmule Formation) and Paleogene (Torsk Formation) shales. Normal compaction reference curves were established for these units in areas currently at their maximum burial depth (e.g. Sørvestsnaget Basin and Vestbakken Volcanic Province). The results suggest widespread Cenozoic exhumation throughout the southwestern Barents Sea. The exhumation magnitudes increase towards east and northeast. The average exhumation estimates from the three data sources range from ∼800 to 1400 m within the Hammerfest Basin, ∼1150–1950 m on the Loppa High, ∼1200–1400 m on the Finmark Platform and ∼1250–2400 m on the Bjarmeland Platform. The marked differences in glacial erosion from mass balance and average erosion estimates from the current study suggest a significant pre-glacial uplift and erosion in the southwestern Barents Sea area. The observed stratigraphy and presence of significant volumes of Late Oligocene-Middle Miocene sediments in basins at the outer margin, and increased erosion rates at the same time in source areas suggest that maximum burial in the southwestern Barents Sea may have occurred sometime during the Oligocene, or even earlier in the Eocene. The results from this study are useful input for modelling of source rock maturation, generation, migration and trapping of hydrocarbons in the area. These results are also an important input for the prediction of more precise reservoir and seal rock properties in frontier areas away from the exploration wells and provide valuable knowledge for the use of interval velocities in the uplifted areas. [ABSTRACT FROM AUTHOR]

A series of analogue experiments utilizing sequences of sand with interlayered silicone polymer have been performed to investigate the effects of multistage extension on rock sequences of different strength, with particular reference to the Hoop Fault Complex of the Barents Sea. It was found that the width and style of the graben systems as seen in map view depend strongly on the extension velocity. Wide areas of graben formation are promoted by fast extension, whereas narrowly constrained deep-graben structures are typical of slow extension rates. Furthermore, the decoupling strata are likely to be characterized by flow rather than by distinct detachment faults. The scaled experiments produced units of contrasting fault frequencies and styles in individual sand layers positioned between layers of silicone polymer. It was also found that the fault segments developed from different levels were related to varying extents (hard-linked, soft-linked, firm-linked, unlinked). The fault configurations and the general fault pattern obtained in the experiments is similar to that observed in natural faults where salt or unconsolidated mudstone separate sequences of sand. [ABSTRACT FROM AUTHOR]

The origin of large subsidence in intracratonic basins is still under debate. We propose a new and self-consistent model for the formation of those basins, where lithospheric shortening/buckling triggers metamorphism and densification of crustal mafic heterogeneities. We use a forward thermo-mechanical finite element technique to evaluate this mechanism for the typical example of the East Barents Sea basin ( EBB) where a very large and compensated subsidence, accommodating an up to 20-km-thick sediment succession, is observed. The lower crust in the dynamic model is modelled with petrologic-consistent densities for a wet mafic gabbroic composition that depend on pressure and temperature taking into account dehydration at high PT conditions. The model successfully explains the main characteristics of the EBB, notably the large anomalous and fast subsidence during the Late Permian-Early Triassic, its present-day geometry and the absence of a significant gravity anomaly. [ABSTRACT FROM AUTHOR]

We present results from an active-source, onshore–offshore seismic reflection/refraction transect acquired as part of the PETROBAR project (Petroleum-related studies of the Barents Sea region). The 700km-long profile is oriented NW–SE, coincident with previously published multichannel seismic reflection profiles. We utilize layer-based raytracing in a Markov Chain Monte Carlo (MCMC) inversion to determine a probabilistic velocity model constraining the sedimentary rocks, crystalline crust, and uppermost mantle in a complex tectonic regime. The profile images a wide range of crustal types and ages, from Proterozoic craton to Paleozoic to early Cenozoic rift basins; and volcanics related to Eocene continental breakup with Greenland. Our analyses indicate a complex architecture of the crystalline crust along the profile, with crystalline crustal thicknesses ranging from 43km beneath the Varanger Peninsula to 12km beneath the Bjørnøya Basin. Assuming an original, post-Caledonide crustal thickness of 35km in the offshore area, we calculate the cumulative thinning (β) factors along the entire profile. The average β factor along the profile is 1.7±0.1, suggesting 211–243km of extension, consistent with the amount of overlap derived from published plate reconstructions. Local β factors approach 3, where Bjørnøya Basin reaches a depth of more than 13km. Volcanics, carbonates, salt, diagenesis and metamorphism make deep sedimentary basin fill difficult to distinguish from original, pre-rift crystalline crust, and thus actual stretching may in places exceed our estimates. [ABSTRACT FROM AUTHOR]

A sequence stratigraphic framework of the Triassic on the Norwegian Barents shelf is presented. The Triassic succession was subdivided into five second-order sequences based on facies analysis of 2D seismic data constrained by well data. The sequences were separated by maximum flooding surfaces that correlate seismically for hundreds of kilometers. The Mesozoic succession in the Barents Sea was deposited in a shallow epicontinental seaway, and shows a gradual infill of the basin throughout the Triassic, progressively prograding further west and northwest with time. The NW Barents Sea remained distal to main sediment supply until accommodation space was filled in further south, and prograding seismic clinoforms from the south and east are observed from Ladinian times. Accommodation space east of Bjørnøya–Sørkapp High was filled during the Late Triassic, sourced from the east, but possibly also from the west. The paleo-Loppa High controlled sediment distribution until early Ladinian times, with one major uplift event in latest Permian and several subsequent minor events of renewed uplift and creation of local source areas as observed from aerially restricted systems prograding from the west to the east. In the Late Triassic, paleo-Loppa High area became one of the main depocenters, responding to extension in the North Atlantic system to the west. Clinoform geometries were developed west of the high and towards the Bjørnøya Basin. Multiple clinoform units prograding from west to east was identified on top of the paleo-Loppa High in the Upper Triassic, representing a source area to the west. Within each sequence, maximum progradation and retrogradation were mapped out and discussed in terms of reservoir, seal and source rock development. Sediment accommodation space was locally controlled by salt mobilization and differential subsidence across Late Paleozoic faults. The Triassic second-order flooding surfaces are interpreted to be controlled by global and/or regional tectonics. [Copyright &y& Elsevier]

Abstract: The focus of this study is the nature of a prominent, high-velocity (S-wave) anomaly in the upper mantle below the Barents Sea–Kara Sea region and its relation to the evolution of the sedimentary basins, in particular the Permo–Triassic East Barents Sea Basin. The high-velocity anomaly exhibits a thickness of 75–100 km below the central Barents Sea and thickens considerably below the East Barents Sea Basin (150 km). The thickest part of the high-velocity anomaly follows the outline of the East Barents Sea Basin which is bended around Pai-Khoi–Novaya Zemlya Fold Belt. Density modeling of the lithosphere along a 3200 km long transect from the Barents Sea to the West Siberian Basin was used to evaluate different models for the upper mantle structure. The best fit gravity model was achieved when either assuming a 1D, horizontally- layered mantle structure, or, a forward-modeled density structure using an average Proterozoic mantle composition. The first model requires a further, compensating excess mass below the (seismic) Moho in the East Barents Sea Basin region. The latter model exhibits a higher-density dome structure below the basin. Both models indicate probable old, continental lithosphere below the central part of the transect in eastern Barents Sea/Kara Sea region. Calculated temperatures of 400–1000 °C (60–200 km depth) further support this concept. Hence, the East Barents Sea Basin developed probably as an intra-continental basin within a non-extensional setting. Such basins exhibit generally crustal inhomogeneities which contributed considerably to their subsidence history. Likely structures below the East Barents Sea Basin are Pre-Permian rifts, accumulated melts derived by the Siberian mantle plume, and/or the Late Neoproterozoic Timanide Orogen. [Copyright &y& Elsevier]

In this study we present the stratigraphic succession related to the Mjølnir impact in the Barents Sea, based on available cores, detailed sedimentological and palaeontological descriptions, as well as seismic reflection profiles. The Mjølnir impact took place in the palaeoBarents Sea, close to the Volgian - Ryazanian boundary. The epicontinental sea had a water depth of 300 - 500 m, and was characterized by anoxic to hypoxic deposition of organic rich clays, presently with kerogen of types II and I. The bolide, about 1.5 - 2.0 km in size, hit the sea/sea floor and created the 40 km wide Mjølnir crater. The Ragnarok Formation is defined as the locally derived allochthonous (mixture of re-deposited excavated material, fall back ejecta and back wash material) to parautochthonous (structurally uplifted, slumped and inverted target material from deeper levels) breccia deposits that were formed during and immediately after the Mjølnir impact. The uppermost part of the formation has been cored by a stratigraphic drilling (7329/03-U-01). It comprises siliciclastic sediments from claystones to conglomerates and consists of chaotic slump and avalanche deposits, along with different mass flow deposits. The formation is normally overlain by shales and siltstones of the uppermost part of the Hekkingen Formation (Oxfordian -Berriasian), and are succeeded by marls of the Klippfisk Formation (Berriasian-Hauterivian). On seismic reflection profiles the Ragnarok Formation can reach thicknesses of 1.3 km, including uplifted, reworked Lower Triassic fragments which originated about 3.5 km down in the crust and were structurally elevated during the impact cratering stage. The Ragnarok Formation reaches its maximum thickness in a wedge-shaped annular trough beneath the present annular crater basin, pinching out both towards the crater centre and towards the periphery. It can be recognised in seismic reflection profiles at the Mjølnir crater location and up to ∼55 km away from the crater centre, forming a wedge-shaped unit within the Mesozoic siliciclastic deposits of the Bjarmeland Platform. During the oblique Mjølnir impact event, large amounts of material were ejected and widely dispersed.Models of the impact process suggest that the ejecta were mainly spread in a north-easterly direction. The impact-related ejecta bed outside the crater boundaries varies from millimetres to a few metres in thickness and has been named the Sindre Bed. It has been recognized in core 7430/10-U-01, and in other wells of the Barents Sea. An Ir-enrichment in a time-equivalent formation at Nordvik,North Central Siberia, possibly represents a distal variety of the Sindre Bed. [ABSTRACT FROM AUTHOR]

The SW Barents Sea is an epicontinental platform consisting of N- to NNE-oriented basins separated by basement highs. The basins were formed during four distinct rift-phases in the Carboniferous, Late Permian, Late Jurassic-Early Cretaceous, and Paleocene-Eocene. Progressive rifting culminated in continental breakup and seafloor spreading along the North Atlantic axis approximately at 55 Ma. We present tectonic and thermal models of basin evolution along two seismic profiles crossing the SW Barents Sea. The thermal and isostatic history of basins is constrained through time-forward basin modelling based on an automated inverse basin reconstruction approach. We estimate the effects of continental breakup and near-margin processes (magmatic underplating and sill intrusions) on the thermal history and kerogen maturity below the Vestbakken Volcanic Province. Basin models are calibrated against well data. The results imply that both breakup and underplating alter the thermal and isostatic history of sediments along the margin. The hydrocarbon potential of source rocks modelled along the margin suggests breakup has a permanent thermal effect on the present-day sediments promoted by lateral heat flow, while heat conduction by underplating is more diffuse, inhibited to some degree by deeply-buried, low-conductivity shales and limestones. [ABSTRACT FROM AUTHOR]

In the frame of this study, we investigate the lithosphere-scale 3D physical state of the Barents Sea and Kara Sea region. Therefore, we test an existing 3D structural model against the gravitational field by considering the heterogeneous upper mantle to further assess the structural and density configuration of the continental crystalline crust. The resulting 3D density configuration of the crust is discussed in terms of its relationships with the spatial distribution of tectonically different domains. In addition, it provides the base for a lithology-controlled parameterisation of the crust with thermal properties to calculate the 3D conductive thermal field. The deeper thermal field is controlled by the depth configuration of the lithosphere–asthenosphere boundary. Accordingly, deeper isotherms such as the 450 °C isotherm deepen from below the rifted SW Barents Sea towards the intracratonic basins of the eastern Barents Sea and Kara Sea, indicating an increase of the lithospheric strength in the same direction. Temperature measurements of the upper 800 m below the SW Barents Sea reveal an increased thermal gradient which cannot be reproduced by a steady-state 3D conductive model alone. Beside fault-induced fluid flow to be active there, an alternative scenario could involve a phase of subsidence long enough to increase the temperature of the upper 800 m, followed by an uplift and erosion phase that prevented the positive thermal anomaly to propagate towards larger depths. The final lithosphere-scale 3D model is the first to integrate the geological, density and thermal configuration of the entire Barents Sea and Kara Sea region and hence provides an ideal base for future thermomechanical studies addressing, for instance, questions on the present-day, past and future relationships between lithospheric strength and deformation. [ABSTRACT FROM AUTHOR]

The age of the Cretaceous Barremian-Aptian boundary has been a long-standing problem in the geological timescale. Age suggestions range between 126 Ma and 117 Ma, making causal links between environmental crises and large-scale processes such as large igneous provinces (LIPs) problematic. New stratigraphic and radiometric data from three drillcores in Svalbard show that Barremian shelf siltstones and sandstones are overlain by Aptian shallow-marine mudstones. The organic carbon content in the mudstones is higher than 1.0 wt%, with values ranging up to 70 wt% in coal-dominated intervals. Carbon isotope measurements of the TOC show a negative δ 13 C excursion of 4.5‰ followed by a positive excursion of 6.7‰ within a 20-m interval, identified as the early Aptian Oceanic Anoxic Event 1a (OAE1a). This isotopic pattern of the excursion is in perfect agreement with excursions from lower latitude sections of the same age. A ~ 10-cm-thick zircon-bearing bentonite was discovered in the lower part of the Barremian, about 40 m below the OAE1a interval. U-Pb TIMS zircon analyses of two equivalent bentonites in adjacent boreholes gave a robust age of 123.1 ± 0.3 Ma. Based on the Barremian depositional systems, we estimate that a time interval of 1–2 Myr separates the bentonite and the OAE1a, providing an age of about 121–122 Ma for the Barremian-Aptian boundary. Our results stress that the geological timescale needs revision, and provide a benchmark test for the correlation between the OAE1a and LIPs in general. [ABSTRACT FROM AUTHOR]

Interpretation of tomography data indicates that the Barents Sea region has an asymmetric lithospheric structure characterized by a thin and hot lithosphere in the west and a thick and cold lithosphere in the east. This suggests that the lithosphere is stronger in the east than in the west. This asymmetric lithosphere strength structure may have a strong control on the lithosphere response to tectonic and surface processes. In this paper, we present computed strength and effective elastic thickness maps of the lithosphere of the Barents Sea and Kara Sea region. Those are estimated using physical parameters from a 3D lithospheric model of the Barents Sea and Kara Sea region. The lithospheric strength is computed assuming a temperature-dependent ductile and brittle rheology for sediments, crust and mantle lithosphere. Results show that lithospheric strength and elastic thickness are mostly controlled by the lithosphere thickness. The model generally predicts much larger lithospheric strength and elastic thickness for the Proterozoic parts of the East Barents Sea and Kara Sea. Locally, the thickness and lithology of the continental crust disturb this general trend. At last, the gravitational potential energy (GPE) is computed. Our results show that the difference in GPE between the Barents Sea and the Mid-Atlantic Ridge provides a net horizontal force large enough to cause contraction in the western and central Barents Sea. [ABSTRACT FROM AUTHOR]

Mafic igneous rocks of Cretaceous age (80–130 Ma) scattered around the Arctic Ocean are commonly referred to as the High Arctic Large Igneous Province (HALIP). We have mapped out the distribution of HALIP igneous rocks in the Barents Sea region over the past decade based on integrated seismic–gravity–magnetic interpretation, field work, review of publications, and analyses of new and vintage borehole and field samples. The mapping reveals abundant igneous rocks in the northern and eastern Barents Sea covering an area of ~ 900,000 km 2 with a conservative volume estimate of 100,000 to 200,000 km 3 of intrusions. The igneous province is dominated by sheet intrusions injected into Triassic and Permian sedimentary rocks. Hydrothermal vent complexes are rare, and only two potential vent complexes have been identified on seismic data in the eastern Barents Sea. We have further done extensive radiometric dating of the igneous samples in the Barents Sea region. New 40 Ar/ 39 Ar dating of thirteen samples from Svalbard reveal ages of crystallization and alteration. The large age span (60–140 Ma for the raw ages) is likely due to partial or complete overprint of the K/Ar system in plagioclase, and the age of the magma emplacement is better represented by U/Pb TIMS ages. Only one of our 40 Ar/ 39 Ar analyses of plagioclase yielded a statistically valid age that is in line with the recently published U/Pb TIMS ages of 122–125 Ma. The new data clearly document that relying on published data from the K/Ar system can lead to erroneous conclusions on the age of crystallization in this province without a careful use of additional 40 Ar/ 39 Ar degassing data (i.e., K/Ca). We propose that the magmatism on Svalbard and Franz Josef Land represents a distinct magmatic event near the Barremian/Aptian boundary (125 Ma) in the Barents Sea. This Early Cretaceous Barents Sea magmatism resulted in the formation of the BSSC (Barents Sea Sill Complex). BSSC age rocks are also present in Arctic Canada (Sverdrup Basin) and on Bennett Island (New Siberia Islands). The massive injection of hot magma into potentially organic-rich sediments in the eastern and northern Barents Basin caused rapid organic matter maturation and formation of thermogenic gas and oil in contact aureoles. We estimate that up to 20,000 Gt of carbon were potentially mobilized, corresponding to 175 trillion barrels of oil equivalent. The production rates and fate of the carbon gases are uncertain. However, we speculate that rapid release of aureole greenhouse gases (methane) may have triggered the Oceanic Anoxic Event 1a (OAE1a) and the associated negative δ 13 C excursion in the Early Aptian. Some of the methane may also be trapped in the vast hydrocarbon gas accumulations found in the east Barents Basin. [ABSTRACT FROM AUTHOR]

Lithospheric extension is proposed as one of the most common mechanism to explain the formation of intra-continental sedimentary basins. However, extension is an unlikely mechanism for the formation and preservation of certain intra-continental basins as for example the East Barents Sea basin (EBB), whose origin remains unexplained. An alternative basin-formation mechanism is buckling accompanying lithosphere shortening. Here we evaluate the conditions for lithospheric shortening/buckling as a mechanism to form deep and isostatically compensated sedimentary basins. We use a forward thermo-mechanical finite element technique to evaluate this mechanism for the EBB, where a very large and compensated subsidence is observed. The lower crust is modeled with petrologic consistent densities that depend on pressure and temperature taking into account de-hydration at high P – T conditions. Various models are tested, characterized by different compositions for the lower crust. Results show that lithospheric shortening/buckling may result in compensated ultra-deep basins like the EBB provided the presence of crustal heterogeneities such as a mafic underplate. The implications of buckling for the maturation of source rocks are evaluated. Results show that maturation of kerogen in a contractional basin takes much longer time compared to a basin formed by extension, owing to the significantly lower temperatures in the initial stages of basin formation. In the case of the EBB, buckling predicts better preservation of hydrocarbons as potential Triassic source rocks may enter the oil and gas window after deposition of Middle Jurassic reservoir rocks and formation of Late Jurassic–Early Cretaceous traps. [ABSTRACT FROM AUTHOR]