The Atlantic margin of the Norwegian, Faeroese, British and Irish sectors encompasses numerous basins which vary in character, but are related in terms of their evolution as part of a single passive margin. Lineament analysis of the margin shows a predominance of NE–SW, N–S and NW–SE trends, mainly reflecting Mesozoic–Cenozoic extensional faulting. Some major Precambrian and Caledonian structures, principally steeply-dipping shears, were opportunistically reactivated according to the prevalent stress pattern. The extensional history of the margin spanned ac.350 Ma interval between the close of the Caledonian orogeny and early Eocene break-up. Episodes of Permo-Triassic, (mainly late) Jurassic, Early Cretaceous, ‘middle’ Cretaceous and latest Cretaceous–Early Eocene age can be distinguished from one another in space and time. The anomalous length of the total period of extension prior to continental separation is partly explained by step-wise lateral offsets of the crustal thinning axes towards the line of eventual break-up. The picture is, however, complicated by some changes in extensional style and direction. These include mosaic-like fragmentation of Pangea in the Permo-Triassic, the imposition of more systematic E–W extension by Jurassic times, and the change to NW–SE extension focused on the present margin in the Early Cretaceous (probably Hauterivian). The resulting structural configuration reflects the overprinting of a complex network of Jurassic and older basins by a continuous NE–SW chain of deep Cretaceous-Cenozoic basins. An extensional pulse of latest Cretaceous to earliest Eocene age (best observed in the Norwegian Sea) with extensive basaltic volcanism led to continental break-up at approximately 53 Ma.The margin was structurally modified by some important events postdating the Early Eocene. On breakup, the background stress field changed from extension to mild SE-directed compression, and widespread inversion structures formed in the thick Cretaceous-Cenozoic depocentres. The inversions can best be explained by ridge-push from the adjacent spreading centres, but could also be linked to Tethyan closure events and changes in the North Atlantic spreading vector. Post-break-up extension of the North Atlantic passive margins has been reported in the western Barents Sea, Jan Mayen and East Greenland and (for the first time here) in the northern Vøring Basin. We propose that these areas were linked by a single extensional pulse induced by the change to a more ESE-directed relative plate motion in the Oligocene-Miocene.Major uplift and exhumation of peripheral landmasses and inboard basins took place at intervals throughout the Cenozoic. Initial uplift can be attributed to pre-break-up rifting and post-break-up compression, but the most significant event took place in the Plio-Pleistocene and was intimately associated with glacial erosion and isostatic adjustment through repeated glaciations and interglacials. The regional scale of this event and its significance for exploration is widely under-estimated.
Compressional structures of Cenozoic age are ubiquitous features of the NE Atlantic margin between the western Barents Sea and offshore western Ireland. The structural suite includes simple domes or anticlines, reverse faults and broad-scale inversions. Our analysis focuses on a recently delineated group of structures in the Norwegian Sea, although these are placed in the context of similar features on the Barents margin, West of Shetlands, on the Faroes and their surrounding shelf, and in the Rockall Trough. Some (although not all) of the compressional anticlines were formed at the sites of pre-existing Cretaceous-Palaeocene depocentres. They show a multi-phase growth history. In the Norwegian Sea, particularly important phases occurred in the middle Eocene to early Oligocene and in the Miocene. We interpret the formation of these structures as a natural outcome of the transition to sea-floor spreading that occurred in the early Eocene. From this time, extremely thick sedimentary successions that had accumulated during some 300 million years of extensional tectonics were subjected to mild compression. The overall compressive stress field can be explained in terms of spreading in the adjacent ocean (ridge push) and by the distant effects of Alpine tectonics. In a plate-wide sense these effects can be regarded as two sides of the same coin. The origin of the Norwegian Sea structures is most easily visualized in terms of ridge push. NW-SE transfer zones, characteristic of the entire margin, are strongly implicated in these tectonics. A kinematic model is described that links significant structuring with a change in the spreading direction of Oligocene-Miocene age (35-20 Ma, A13-6). The compressional structures are mainly observed by their effect on sediments and volcanics of Cretaceous and Cenozoic age. They are frequently expressed in the present-day sea-floor relief, and in the case of the Faroe islands are probably responsible for present subaerial exposure. From the point of view of hydrocarbon exploration, the Cenozoic compressive anticlines have obvious potential as fourway dip closures or as components of structural-stratigraphic traps. The NW-SE fractures, orientated parallel or sub-parallel to the maximum horizontal stress direction, were probably periodically open for fluid flow from the time of NE Atlantic opening and onwards. They may therefore have facilitated migration from deeper source rocks or remigration from pre-existing hydrocarbon accumulations.
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