Structural geology and basin development of the Norwegian Sea

Abstract

The investigated area comprises the 300‒500 km-wide passive margin offshore Mid Norway as well as the 70‒40 km-wide margin northwest of the Lofoten‒Vesterålen archipelago. Following the Caledonian Orogeny, Greenland was close to Mid Norway and central-northern Norway. The orogeny climaxed with the Early Devonian continent collision with subduction of the Baltic craton beneath Laurentia, and a mountain range several kilometres high evolved. The mountain range remained a positive topographic element throughout the Late Palaeozoic and Early Mesozoic. Non-marine Carboniferous sediments were deposited onshore East Greenland, but there is no evidence of sedimentation during this period offshore Mid Norway. Three significant rift episodes, i.e., Late Permian–Early Triassic, Middle‒Late Jurassic and Campanian‒Paleocene are evident, with intervening (c. 70 Ma) periods of overall tectonic quiescence. Permo‒Triassic sediments, 4000‒6000 m in thickness, were deposited in an eastern basin area juxtaposed against basement across large normal faults close to the Norwegian mainland. The topography created by the Late Permian‒Early Triassic rift episode became levelled during the Middle Triassic, and younger sediments were deposited over a relatively flat area represented by the present Trøndelag Platform and the Halten and Dønna terraces. Due to Jurassic extension there was a change to a setting where the Halten and Dønna terraces became separate structural entities, down-faulted and with a complex basin-floor topography. Until the climax stage of the Jurassic rift episode, the Caledonian mountain range might have occupied the area between the Halten Terrace and Liverpool Land, at the east coast of Greenland. The subaerially exposed land mass was eroded and acted as an important sediment source. Middle and Lower Jurassic, but also Triassic sediments entering into the basin from the west contain conglomerates and pebbly sandstones deposited under fluvial, deltaic and marginal marine conditions, and clinoforms are recorded along the basin margin on the western Halten Terrace. The large-scale paleogeography was a central basement high, which separated the basin onshore East Greenland and the basin area offshore Mid Norway. Due to erosion and accelerated Late Jurassic rifting the basement high ceased to exist as a source area, leaving the narrow Sklinna Ridge as an easternmost remnant in the footwall of the Klakk Fault Complex. This stage of development is regarded as the first indication of a large and continuous marine basin between Mid Norway and Greenland after the Caledonian Orogeny.