ALBERT

Description: The Møre and Vøring basins of the mid-Norwegian volcanic passive margin are characterized by thick accumulations of Cretaceous to Paleocene sedimentary strata. They were formed during a series of Late Mesozoic-Early Cenozoic extensional events and represent vast underexplored areas with a limited number of wells. Recently, a new generation of long-offset 2D seismic reflection lines and 3D seismic data, together with new well data, has permitted a significant improvement in the regional understanding of the Møre and Vøring basins. This has enabled much better imaging of the deep Cretaceous subbasins and sub-basalt structures. In light of this significant data improvement, we performed a regional tectonostratigraphic synthesis of the pre-breakup development of the Møre and Vøring basins. We have interpreted eight regional Cretaceous and Paleocene horizons and constructed a series of structural and thickness maps. The new interpretations allow us to examine the sequential evolution of the Cretaceous to Paleocene sedimentary infill and to discuss its relationship to the deep crustal structures and regional tectonic events. We conclude that the long and polyphased development of the Møre and Vøring basins is partly controlled by deep-seated structural highs. We show that active deposition in the Early Cretaceous was mainly focused in the Møre Basin, while the main Cenomanian and subsequent Late Cretaceous-Paleocene depocentres developed principally in the Vøring Basin and migrated sequentially west towards the present continent-ocean boundary. We argue that the outer Møre and Vøring basins are likely underlain by a relatively thick continental crust compared to the inner part of the regional sag basin. In this setting our observations do not support evidence for a large zone of exhumed upper mantle, which has previously been proposed to have formed before magmatism and breakup.

Description: Highlights • Crustal thickness of the Lofoten/Vesterålen shelf is greater than old study suggested. • Mafic lower crust of the shelf area explains observed resistance to deformation. • Four Mesozoic-Cenozoic erosion episodes are indicated by sedimentary velocities vs burial. • Extensive erosion episodes are likely to be detrimental to petroleum potential. Abstract The Norwegian continental shelf has been through several rift phases since the Caledonian orogeny. Early Cretaceous rifting created the largest sedimentary basins, and Early Cenozoic continental breakup between East Greenland and Europe affected the continental shelf to various degrees. The Lofoten/Vesterålen shelf is located off Northern Norway, bordering the epicontinental Barents Sea to the northeast, and the deep-water Lofoten Basin to the west. An ocean bottom seismometer/hydrophone (OBS) survey was conducted over the shelf and margin areas in 2003 to constrain crustal structure and margin development. This study presents Profile 8-03, located between the islands of Lofoten/Vesterålen and the shelf edge. The wide-angle seismic data were modeled using forward/inverse raytracing to build a crustal velocity-depth transect. Gravity modeling was used to resolve an ambiguity in seismic Moho identification in the southwestern part. Results show a crustal thickness of ~31 km, significantly thicker than what a vintage land station based study suggested. Profile 8-03 and other OBS profiles to the southwest show high sedimentary velocities at or near the seafloor, increasing rapidly with depth. Sedimentary velocities were compared to the velocity-depth function derived from an OBS profile at the Barents Sea margin, tied to a coincident well log, where there is little erosion. Results from this profile and the crossing Profile 6-03 (Breivik et al. 2017) indicate three major erosion episodes; Late Triassic-Early Jurassic, tentatively mid-Cretaceous, Late Cretaceous–early Cenozoic, and a minor late glacial erosion episode off Vesterålen.