An overview of the Upper Paleozoic-Mesozoic stratigraphy of the NE Atlantic region

This study describes the distribution and stratigraphic range of the Upper Paleozoic–Mesozoic succession in the NE Atlantic region, and is correlated between conjugate-margins and along the axis of the NE Atlantic rift system. The stratigraphic framework has yielded important new constraints on the timing and nature of sedimentary basin development in the NE Atlantic, with implications for rifting and the breakup of the Pangaean supercontinent. From a regional perspective, the Permian–Triassic succession records a northward transition from an arid interior to a passively-subsiding, mixed carbonate/siliciclastic shelf margin. A Late Permian–earliest Triassic rift pulse has regional expression in the stratigraphic record. A fragmentary paralic to shallow-marine Lower Jurassic succession reflects Early Jurassic thermal subsidence and mild extensional tectonism; this was interrupted by widespread Mid-Jurassic uplift and erosion, and followed by an intense phase of Late Jurassic rifting in some (but not all) parts of the NE Atlantic region. The Cretaceous succession is dominated by thick basinal-marine deposits, which accumulated within and along a broad zone of extension and subsidence between Rockall and NE Greenland. There is no evidence for a substantive and continuous rift system along the proto-NE Atlantic until the Late Cretaceous

Sequence stratigraphic analysis in deep-water, underfilled NW European passive margin basins

Sequence stratigraphic analysis is now carried out routinely on Mesozoic–Cenozoic sedimentary basins with a view to understanding their post-rift stratal geometries and predicting facies architecture. The conventional method embodies two concepts; the physical division of strata into unconformity-bounded units and their genetic interpretation on the assumption that hierarchical changes in sea-level represent the primary control on sedimentary architecture. The genetic model is reflected in a complex descriptive terminology and derives from the development of the method in shallow-water basins, where the results of analyses typically accord with geological data constraints. Applied to deep-water underfilled basins, however, the sea-level assumption yields results that are unsatisfactory and in many cases misleading, reflecting the influence of additional controls, including tectonic movements, deep-sea currents and climate (e.g. glaciation) on stratal geometries and facies architecture. This is illustrated by comparative analyses of examples from the deep-water Cenozoic basins of the NW European Atlantic passive margin, which contain a set of seismic megasequences, bounded by unconformable to conformable surfaces, correlative from shelf to slope to basinal settings. The deep-water successions contain regional, locally diachronous, submarine unconformities that were generated in response to changes in deep-water current circulation and slope processes, rather than subaerial erosion. These bound aggradational contourite drifts that include upslope accretion against basin margins. The deep-water successions interfinger at two levels with seaward-prograding shelf-slope wedges that reflect differential tectonic movements, involving coeval uplift and subsidence. The youngest wedges formed in the last 4 Ma and record seaward progradation of the margin by up to 100 km, overprinting high-amplitude variations in sea-level and coeval with changes in deep-ocean currents. Sediment supply by fluvial sources gave way in the Pleistocene to direct glacial sediment supply to the slope. In all these instances, the stratal geometries and facies architecture cannot be attributed to a simple lowering of regional sea-level, but instead reflect a complex interplay of controlling factors including tectonic movements, changes in sediment supply, deep-water current activity and climate, in addition to sea-level. Sequence stratigraphic analysis in such settings must recognise and evaluate alongslope, downslope and vertical components of sediment supply

Anomalous Cenozoic subsidence along the 'passive' continental margin from Ireland to mid-Norway

Two-dimensional flexural backstripping and thermal modelling (assuming uniform stretching and cooling) is applied to four interpreted, depth-converted seismic profiles across the Rockall, Faroe–Shetland and Vøring basins, along 1600 km of the Atlantic continental margin of NW Europe. The results reveal a significant discrepancy between the modelled palaeo-depths for the base of the Cenozoic succession and those proven by geological evidence at control points (subaerial conditions or depositional depth ranges in wells). The discrepancy is of Rm-scale, much larger than the possible range of parameter error determined by sensitivity tests (up to 0.5 km). Assuming a Cretaceous rift episode (100 Ma), the discrepancy is at least 1.7 km in the Rockall Basin, up to 2.1 km in the Faroe–Shetland Basin and at least 1 km in the Vøring Basin (which also contains evidence of kilometre-scale uplift of the inner margin). Assuming (unproven) a second rift in the early Cenozoic (60 Ma), the discrepancy remains of kilometre-scale in the Rockall and Faroe–Shetland basins. The restorations also provide evidence of uplift, both above compressive structures and across the modelled profiles as seaward rotations of palaeo-bathymetric records. The palaeo-bathymetric discrepancy corresponds to an anomaly in subsidence that is the cumulative product of all the tectonic episodes that have affected the NW European margin, and may incorporate both permanent effects of the last episode of lithospheric extension and transient responses to the interaction of the margin with mantle convective flow. Any explanation must accommodate both the large magnitude of anomalous subsidence along the margin and evidence of its episodic character

Sedimentary and oceanographic responses to early Neogene compression on the NW European margin

The lower Neogene stratigraphy of the NW European Atlantic margin, from the Vøring to the Porcupine basins, is interpreted to record a discrete phase of compressional tectonism that spanned at least 8 Ma from the earliest to the early mid-Miocene. This compressional tectonism may be coeval with a local reorganisation of the NE Atlantic plate system with the transfer of the Jan Mayen micro-plate from Greenland to Europe. The compressional tectonics has resulted in a number of stratigraphic sequences of complex character bounded by regional base Neogene and intra-Miocene unconformities. These are traceable across a range of depths and record distortion of the basin margins and changes in deep-water circulation patterns. This episode of compressional tectonics has also resulted in the creation of a number of anticlinal domes along the Norwegian, Faroese and UK Atlantic margins. The stratigraphic and structural evidence are interpreted to record two stages in the development of the margin: the first being characterised by a prolonged period of regional flexure in response to the build-up of compressive stresses; the second stage is the development of anticlinal structures that led to a rapid release of stress. In the Wyville–Thomson–Faroes region, compressional deformation influenced the creation of the present-day deep-water conduit of the Faroe Bank Channel, which is interpreted to be an early Neogene syncline. Together, the Faroe Bank and Faroe–Shetland channels represent the deepest water passageway across the Greenland–Scotland Ridge. The early Neogene development of this conduit is considered to mark the onset of deep-water exchange across this oceanic gateway

Assessing offshore geohazards: A multi-disciplinary research initiative to understand shallow landslides and their dynamics in coastal and deepwater environments, Norway

In this manuscript, we present the first results of integrated slope stability studies to investigate smaller-scale mass movement processes in different physio- graphic settings of Norway. These include coastal areas (Sørfjord, Finneidfjord), and pristine open ocean settings in intermediate (Vestera?len) and deep waters (Lofoten) on the Norwegian margin. Triggers, pre-conditioning factors and sedimentary processes associated with these landslides are currently not well constrained.The landslides occur either in clusters or isolated, and have variable geomorphologic expressions and run-out. These smaller landslides appear to be comparatively recent phenomena. However, failures likely happen repeatedly and recurrence may affect coastal communities or jeopardize offshore installations. New data indicate that the landslides developed within thin, gently-dipping sediment units that served as slip planes. Some soil samples from these units may show strain-softening behaviour, higher plasticity and higher sensitivity compared to other units. The slide-prone layers in Sørfjord can furthermore be related to specific depositional processes