Structural development of the continental shelf offshore Lofoten-Vesteralen, northern Norway

A striking feature of the continental shelf along the Lofoten-Vesteralen margin is the relatively thin sequence of Jurassic-Triassic sediments not only on structural highs, but also in parts of some of the sub-basins. This reflects limited sedimentation as well as periods of uplift and erosion, factors that are crucial for the hydrocarbon potential of the area. Structures in the shelf area off Lofoten-Vesteralen result primarily from major rift episodes in the Middle-Late Jurassic and Late Cretaceous-Paleocene, whereas this area appears unaffected by large faults resulting from the Late Permian-Early Triassic rift episode. This is in strong contrast to near shore and well-explored areas to the south, where large fault-bounded basins filled with thick Permo-Triassic sediments developed during and following this rift episode. At this stage of development, the Lofoten-Vesteralen archipelago and the shelf area are interpreted as parts of a huge NE-SW oriented basement high characterized by a peneplained basement relief, later progressively covered by thin Triassic to Middle Jurassic sediments. Jurassic faults in the Lofoten-Vesteralen margin segment are basement-involved, and both their orientation and listric geometry demonstrate the strong basement-governing control. A major along-strike change in structural pattern takes place across an accommodation zone at a high angle to the NNE-SSW trend of the Jurassic rift structures, and this zone acted as a rift propagation barrier during Jurassic crustal stretching. The accommodation zone reflects an E-W basement grain, and the change in dip direction of the Jurassic faults and the tilt of major fault-blocks across this zone took place without evidence of strike-slip motion. The Jurassic rift topography became overprinted by NE-SW to ENE-WSW striking faults resulting from a Campanian-Paleocene rift episode and by the overlying and NE-SW oriented Late Cretaceous Ribban Basin. A major uplift with NE-SW elongation and a maximum width of c. 70 km is located in the shelf area. The uplift is interpreted to result from tectonic compression related to the continent break-up to the NW, the main growth occurring during Oligocene-Miocene times.