Abstract This paper considers the lithospheric structure and evolution of the wider Barents–Kara Sea region based on the compilation and integration of geophysical and geological data. Regional transects are constructed at both crustal and lithospheric scales based on the available data and a regional three-dimensional model. The transects, which extend onshore and into the deep oceanic basins, are used to link deep and shallow structures and processes, as well as to link offshore and onshore areas. The study area has been affected by numerous orogenic events in the Precambrian–Cambrian (Timanian), Silurian–Devonian (Caledonian), latest Devonian–earliest Carboniferous (Ellesmerian–svalbardian), Carboniferous–Permian (Uralian), Late Triassic (Taimyr, Pai Khoi and Novaya Zemlya) and Palaeogene (Spitsbergen–Eurekan). It has also been affected by at least three episodes of regional-scale magmatism, the so-called large igneous provinces: the Siberian Traps (Permian–Triassic transition), the High Arctic Large Igneous Province (Early Cretaceous) and the North Atlantic (Paleocene–Eocene transition). Additional magmatic events occurred in parts of the study area in Devonian and Late Cretaceous times. Within this geological framework, we integrate basin development with regional tectonic events and summarize the stages in basin evolution. We further discuss the timing, causes and implications of basin evolution. Fault activity is related to regional stress regimes and the reactivation of pre-existing basement structures. Regional uplift/subsidence events are discussed in a source-to-sink context and are related to their regional tectonic and palaeogeographical settings.

Abstract We perform an integrated analysis of magnetic anomalies, multichannel seismic and wide-angle seismic data across an Early Cretaceous continental large igneous province in the northern Barents Sea region. Our data show that the high-frequency and high-amplitude magnetic anomalies in this region are spatially correlated with dykes and sills observed onshore. The dykes are grouped into two conjugate swarms striking oblique to the northern Barents Sea passive margin in the regions of eastern Svalbard and Franz Josef Land, respectively. The multichannel seismic data east of Svalbard and south of Franz Josef Land indicate the presence of sills at different stratigraphic levels. The most abundant population of sills is observed in the Triassic successions of the East Barents Sea Basin. We observe near-vertical seismic column-like anomalies that cut across the entire sedimentary cover. We interpret these structures as magmatic feeder channels or dykes. In addition, the compressional seismic velocity model locally indicates near-vertical, positive finger-shaped velocity anomalies (10–15 km wide) that extend to mid-crustal depths (15–20 km) and possibly deeper. The crustal structure does not include magmatic underplating and shows no regional crustal thinning, suggesting a localized (dyking, channelized flow) rather than a pervasive mode of magma emplacement. We suggest that most of the crustal extension was taken up by brittle–plastic dilatation in shear bands. We interpret the geometry of dykes in the horizontal plane in terms of the palaeo-stress regime using a model of a thick elastoplastic plate containing a circular hole (at the plume location) and subject to combined pure shear and pressure loads. The geometry of dykes in the northern Barents Sea and Arctic Canada can be predicted by the pattern of dilatant plastic shear bands obtained in our numerical experiments assuming boundary conditions consistent with a combination of extension in the Amerasia Basin sub-parallel to the northern Barents Sea margin and a mild compression nearly orthogonal to the margin. The approach has implications for palaeo-stress analysis using the geometry of dyke swarms. Supplementary material: Details on traveltime tomography model: Resolution tests, traveltime information and ray coverage are available at https://doi.org/10.6084/m9.figshare.c.3783542

Abstract: The northern North Sea region has experienced repeated phases of post-Caledonian extension, starting with extensional reactivation of the low-angle basal Caledonian thrust zone, then the formation of Devonian extensional shear zones with 10–100 km-scale displacements, followed by brittle reactivation and the creation of a plethora of extensional faults. The North Sea Rift-related approximately east–west extension created a new set of rift-parallel faults that cut across less favourably orientated pre-rift structures. Nevertheless, fault rock dating shows that onshore faults and shear zones of different orientations were active throughout the history of rifting. Several of the reactivated major Devonian extensional structures can be extrapolated offshore into the rift, where they appear as bands of dipping reflectors. They coincide with large-scale boundaries separating 50–100 km-wide rift domains of internally uniform fault patterns. Major north–south-trending rift faults, such as the Øygarden Fault System, bend or terminate against these boundaries, clearly influenced by their presence during rifting. Hence, the North Sea is one of several examples where pre-rift basement structures oblique to the rift extension direction can significantly influence rift architecture, even if most of the rift faults are newly-formed structures.

Abstract This study focuses on Late Carboniferous-Permian tectonics and related magmatic activity in NW Europe, and specifically in the Skagerrak, Kattegat and North Sea areas. Special attention is paid to the distribution of intrusives and extrusives in relation to rift-wrench geometries. A large database consisting of seismic and well data has been assembled and analysed to constrain these objectives. The continuation of the Oslo Graben into the Skagerrak has been a starting point for this regional study. Rift structures (with characteristic half-graben geometries) and the distribution of magmatic rocks (intrusives and extrusives) were mapped using integrated analyses of seismic and potential field data. For the analysis of the Sorgenfrei-Tornquist Zone and the North Sea, seismic and well data were used. The rift structures in the Skagerrak can be linked with extensional structures in the Sorgenfrei–Tornquist Zone in which similar fault geometries have been observed. Both in the Skagerrak and in the Kattegat, lava sequences were erupted that generally parallel the underlying Lower Palaeozoic strata. This volcanic episode, therefore, pre-dates main fault movements and the development of half-grabens filled with Permian volcaniclastic material. Upper Carboniferous-Lower Permian extrusives and intrusives have also been found in wells in the Kattegat, Jutland and the North Sea (Horn and Central grabens). Especially in the latter area, the dense seismic and well coverage has allowed us to map out similar Upper Palaeozoic geometries, although the presence of salt often conceals the seismic image of the underlying strata and structures. From the results, it is assumed that the pre-Jurassic structures below large parts of the Norwegian-Danish Basin and northwards into the Stord Basin on the Horda Platform belong to the same tectonic system.

Abstract The Permo-Carboniferous evolution of the central North Sea is characterized by three main geological events: (1) the development of the West European Carboniferous Basin; (2) a period of basaltic volcanism during the Lower Rotliegend (latest Carboniferous–early Permian); and (3) the development of the Northern and Southern Permian Basins in late Permian times. The timing of the late Carboniferous–Permian basaltic volcanism in the North Sea is poorly constrained, as is the timing of extensional tectonic activity following the main phase of inversion during the Westphalian, due to the diachronous propagation of the Variscan deformation front. Results of high precision Ar-Ar dating on basalt samples taken from a core from exploration well 39/2–4 (Amerada Hess) in the UK sector of the central North Sea suggests that basaltic volcanism was active in the late Carboniferous, at c. 299 Ma. The presence of volcanics below the dated horizon suggests that the onset of Permo-Carboniferous volcanism in the central North Sea commenced earlier, probably at c. 310 Ma (Westphalian C). This is contemporaneous with other observations of tholeiitic volcanism in other parts of NW Europe, including the Oslo Graben, the NE German Basin, southern Sweden and Scotland. Interpretations of available seismic data show that main extensional faulting occurred after the volcanic activity, but the exact age of the fault activity is difficult to constrain with the data available.

Abstract This paper focuses on the Cenozoic evolution of the northern North Sea and surrounding areas, with emphasis on sediment distribution, composition and provenance, as well as on timing, amplitude and wavelength of differential vertical movements. Quantitative information about palaeo-water depth and tectonic vertical movements has been integrated with a seismic stratigraphic framework to better constrain the Cenozoic evolution. The data and modelling results support a probable tectonic control on sediment supply and on the formation of regional unconformities. The sedimentary architecture and breaks are related to tectonic uplift of surrounding clastic source areas, thus the offshore sedimentary record provides the best age constraints on Cenozoic exhumation of the adjacent onshore areas. Tectonic subsidence accelerated in Paleocene time throughout the basin, with uplifted areas to the east and west sourcing prograding wedges, which resulted in large depocentres close to the basin margins. Subsidence rates outpaced sedimentation rates along the basin axis, and water depths in excess of 600 m are indicated. In Eocene times progradation from the East Shetland Platform was dominant and major depocentres were constructed in the Viking Graben area, with deep water along the basin axis. At the Eocene-Oligocene transition, southern Norway and the eastern basin flank became uplifted. The uplift, in combination with prograding units from both the east and west, gave rise to a shallow threshold in the northern North Sea, separating deeper waters to the south and north. The uplift and shallowing continued into Miocene time when a widespread hiatus formed in the northern North Sea, as indicated by biostratigraphic data. The Pliocene basin configuration was dominated by outbuilding of thick clastic wedges from the east and south. Considerable late Cenozoic uplift of the eastern basin flank is documented by the strong angular relationship and tilting of the complete Tertiary package below the Pleistocene unconformity. Cenozoic exhumation is documented on both sides of the North Sea, but the timing is not well constrained. Two major uplift phases in early Paleogene and late Neogene times are related to rifting, magmatism and break-up in the NE Atlantic and isostatic response to glacial erosion, respectively. Additional uplift events may be related to mantle processes and the episodic behaviour of the Iceland plume.

Abstract The enormous quantity of commercial reflection seismic lines across the North SeaBasin have made the area one of the most thoroughly studied continental settings in the world.Further insight in the deep architecture of the crust is provided by c . 10000 km deep reflection seismic data. Unfortunately, these unique databases have rarely been combined systematically to constrain possible tectonic models for the area. This paper is built on a full integration of high-quality commercial lines (7s twt) and the deep (15 s twt) NSDP84–1 and –2 lines. The deep lines have been post-stack reprocessed and depth-converted. A number of deep wells have provided stratigraphic control along the lines. The overall reflective pattern in the lines divides the crust in three, with a reflective upper and lower crust separated by a less reflective middle crust. The lateral changes in reflectivity matches the observed variation in crustal thickness, where the thinnest crust coincides with the Viking Graben area with a total crustal thickness of 21–24 km, increasing to 30–36 km in the platform areas. The lower crust is seen as an undulating 4–10 km thick band with shallow dipping reflections, with a Moho that consists of reflections with variable lateral thickness and amplitude, rather than one single strong reflection. The structural analysis shows that the crust is cut by a number of large normal faults with varying geometries. It is assumed that some of these major faults are long-lived features rooted in old basement grains. The most spectacular normal faults developed during the Permo-early Triassic extensional phase, but were often reactivated during the Jurassic extensional phase, and with continued minor fault movement into the Cretaceous thermal cooling period. Integration of commercial and deep reflection seismic sections shows that three detachment levels are present within the crust. These levels, which control changes in fault geometries, are believed to represent lateral rheological interfaces combined with or intersected by long-lived zones of weaknesses. The uppermost level is represented by supra-basement low-angle normal faults controlled by gravity and/or lithological changes during extension. An intra-basement (middle crust) level between 5 and 7 s (twt) coincides with decreasing dip of the larger basin bounding faults. The lower crust is the deepest detachment level, which probably exerts control on the geometric changes of the upper-mantle shear zones and the largest crustal normal faults.

Abstract We have undertaken 2D forward modelling across the northern North Sea, based on reprocessed, interpreted and depth-converted deep reflection seismic lines NSDP84–1 and −2 (15 s twt) and refraction data. Two separate stretching phases, Permo-Triassic and Jurassic, are recognized. The cumulative stretching is consistent with the observed crustal structure and the overall basin configuration, as reproduced by forward modelling. Good agreement between observed and modelled top basement level, and crustal thickness below the platform areas are particularly emphasized. Crustal-scale modelling indicates that crustal thickness varied across the northern North Sea at the onset of the Permo-Triassic rifting, from c. 35 km in the platform areas to less than 30 km in the interior of the basin. This may be ascribed to Devonian(-Carboniferous?) crustal stretching. Thinning of the crust has progressively been narrowed, from post-Caledonian extensional collapse, to less regional Permo-Triassic basins, and finally development of the Viking Graben area in the Jurassic-early Cretaceous time. Most of the Permo-Triassic stretching occurred between the øygarden Fault Zone to the east and the Shetland Platform (southern transect) and the Hutton Fault alignment to the west. The width of the Permo-Triassic basin was c. 120 – 125 km, with calculated β mean between 1. 38 and 1. 40. Permo-Triassic β mean estimates across the present Horda Platform vary between 1. 33 and 1. 39. The Jurassic β mean estimates for the same area vary between 1. 08 and 1. 13. Across the Viking Graben, Permo-Triassic β mean varies between 1. 28 (southern transect) and 1. 41 (northern transect). This is lower than estimates for the Jurassic β mean , which amounts to 1. 53 and 1. 42. Permo-Triassic and Jurassic β mean estimates across the East Shetland Basin are 1. 29 and 1. 11, respectively. Lithospheric thermal evolution reflects the general differences between Permo-Triassic and Jurassic stretching, with a much wider thermal perturbation during the former and a focusing and lateral migration towards the east of the peak thermal elevation during the latter. There are still uncertainties related to the degree of (de)coupling between the upper crust and upper mantle during the Permo-Triassic and the Jurassic rift phases. These uncertainties are related to the interplay between age, strain rate, crustal rheology, crustal thickness and long-lived zones of weaknesses.

Abstract The Cenozoic depositional history along a regional E-W profile across the northern North Sea has been simulated using a forward process-based simulation program of dynamic-slope type. It involves a depth-dependent, dual-lithology diffusion equation that handles transport, erosion and deposition of sediments. The data used in the simulation were derived from a seismic line calibrated against wells, and from the regional literature concerning the northern North Sea. The most important of the factors used are: the initial basin form (Paleocene bathymetry), tectonic subsidence, isostatic variables, sediment supply (sand-shale), sediment compaction (porosity-depth relationships for sand-shale) and eustatic sea-level changes. The interaction between the data values extracted from the literature could not reproduce a cross-section similar to the observed cross-section from seismic data. Therefore, the subsidence pattern and the initial basin form were reconsidered. The resulting model gave an anomalous Cenozoic subsidence pattern, different from the expected post-rift thermal subsidence, with deviations corresponding to Paleocene and Late Miocene-Pliocene times. The model-derived Paleocene subsidence might have been overestimated by using an over-shallow palaeobathymetric value, although a deepening of the basin is also indicated by biostratigraphic data. The pronounced Neogene subsidence created accommodation space for a thick Pliocene sequence, derived from the uplifted eastern source area.

Abstract Deep seismic data from the Hatton-Rockall region, the mid-Norway margin and the SW Barents Sea provide images of the crustal structure that make it possible to estimate the relative amounts of crustal thinning for the Late Jurassic-Cretaceous and Maastrichtian-Paleocene NE Atlantic rift episodes. In addition, plate reconstructions illustrate the relative movements between Eurasia and Greenland back to Mid-Jurassic time. The NE Atlantic rift system developed as a result of a series of rift episodes from the Caledonian orogeny to early Tertiary time. The Late Palaeozoic rifting is poorly constrained, particularly with respect to timing. However, rifted basin geometries, inferred to be of this age, are observed at depth in seismic data on the flanks of the younger rift structures. Intra-continental rifting in Late Jurassic-Cretaceous times caused c . 50–70 km of crustal extension and subsequent Cretaceous basin subsidence from the Rockall Trough-North Sea areas in the south, to the SW Barents Sea in the north. In late Early to early Late Cretaceous times, new rifting occurred in the Rockall Trough and Labrador Sea associated with the northward propagation of North Atlantic sea-floor spreading. When sea-floor spreading was approached in the Labrador Sea the Rockall rift apparently became extinct. The final NE Atlantic rift episode was initiated near the Campanian-Maastrichtian boundary, lasted until continental separation near the Paleocene-Eocene transition, and caused c . 140 km extension. The late syn-rift and the earliest sea-floor spreading periods were affected by widespread igneous activity across a c . 300 km wide zone along the rifted plate boundary. The deep seismic data provide lower-crustal structural geometries that represent boundary conditions for a better mapping and understanding of the extensional thinning of the crust. The crustal geometries question extension estimates previously made from basin subsidence analysis, and aid in the definition of bodies of magmatic underplating beneath the outer volcanic margins.

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