The structural foundation and evolution of Mesozoic seaways between Europe and the Arctic

Abstract Throughout the Late Permian and Mesozoic the proto-North Atlantic seaway formed a narrow portal that, together with the linked rift systems of the North Sea, controlled marine connections between Tethys, NW Europe and the northern (Boreal) sea. Structural, stratigraphic and paleontological evidence, from offshore Norway and adjacent areas, is of key importance in understanding the seaway's evolution. The geological development of the area is described through a series of kinematically restored sedimentary/tectonic reconstructions, covering an area from the southern North Sea to the USSR Barents Sea. The plate-tectonic base maps on which the reconstructions were drawn include a first-pass attempt to incorporate Mesozoic continental extension into the kinematic model. Recognition of this effect makes for more plausible paleogeographic reconstruction and emphasizes the narrowness of the NE Atlantic seaway in the Early Mesozoic. Basement architecture inherited from the Caledonian, Variscan and Uralian orogenies was a major influence in the development of layer Mesozoic basins and seaways. A number of long-lived crustal dislocations, dating back to the Caledonian or older, exercised repeated paleogeographic control in the Late Permian and Mesozoic. Of particular importance were the Hitra Fault Alignment (More-Trondelag Fault Zone) separating the failed rift systems of the North Sea from the Atlantic rift domain, and the Senja Hornsund Alignment between the Atlantic rift and the Barents Sea, part of a much larger (ca. 4500 km) trans-Arctic lineament. Following Uralian suturing in the Late Permian and Early Triassic, the paleogeographic evolution of the area was governed by an interplay between marine transgression and a sequence of tectonic events leading to the break-up of the Pangean supercontinent. Important extensional events are recorded in the Mid-Permian, Triassic and Late Jurassic-Early Cretaceous. The Mid-Permian faulting facilitated a southwards transgression through the proto-North Atlantic rift in the Later Permian, although this marine tract did not connect to Tethys. During the Triassic, ingressions into the Atlantic rift domain were restricted by paleogeographic barriers and no direct connection existed between marine realms at the extreme north and southeast of the study area. A series of marine transgressions in the Rhaetian and Early Jurassic established an open seaway between Tethys and the Boreal Sea by Toarcian times. However, this seaway was again closed in the Middle Jurassic due to major uplift and restriction focussed on the central North Sea. Widespread rifting in the Late Jurassic and Early Cretaceous reestablished the NS amrine connection, but this seaway became increasingly restricted in Tithonian-Berriasian time as marginal and intra-basinal highs developed. Final marine unification was achieved through important transgressions in the Aptian-Albian and Late Cretaceous, associated with ocean basin development north and south of the study area. Late Cretaceous decoupling and dextral shear along the Senja-Hornsund Alignment heralded Tertiary ocean floor spreading in the North Atlantic and Arctic Oceans.