Continental Margin off Norway: A Geophysical Study

Abstract

Geophysical investigations consisting of gravity, magnetic, depth sounding, seismic reflection and refraction measurements were made aboard R/V Vema on the continental margin off Norway. Utilizing these and earlier data in the area, maps showing bathymetry, free-air gravity, magnetic residual total intensity, seismic refraction results, total sediment thickness and thickness of Cenozoic sediments have been constructed. The data are also presented as profiles across the margin. The Voring Plateau is underlain by a buried escarpment; the basement is shallow on the seaward side and deep on the landward side. A similar marginal escarpment, the Faroe–Shetland, exists farther south. These escarpments mark the site of the Tertiary opening of the Norwegian Sea. Seaward, Tertiary sediments overlie a basement generated by sea-floor spreading. Landward, a thick sequence of sediments that may be as old as Paleozoic overlies a continental basement. The magnetic quiet zone on the landward side of the escarpment is attributed to the continental nature of the basement. A nearly continuous belt of positive gravity and magnetic anomalies that exists just landward of the edge of the shelf is attributed primarily to intrabasement density contrasts in rocks that are probably Precambrian in age. It extends from northwest Scotland to the Lofoten–Vesteralen islands. The continental margin off Norway formed an epicontinental sea continuous with the North Sea in which a large amount of sedimentation kept pace with subsidence—a phenomenon which perhaps started in the late Paleozoic. The thickness of pre-Cenozoic sediments exceeds 6 km in some areas, but has a relative minimum over the belt of high density rocks of Precambrian age, which presumably underwent the least relative subsidence. We suggest that the opening of the Norwegian Sea at the marginal escarpments is associated with subsidence of the continental crust between the escarpments and the shelf where the high-density belt acts as a hinge line and accounts for the existence of the shelf break. The subsided area is characterized by a regional free-air gravity low. The marginal Voring Plateau Escarpment formed at the opening of the Norwegian Sea served to dam the Tertiary sediments and develop the V0ring Plateau. The Norwegian Channel is shown not to be of tectonic origin. The Tertiary basin of the North Sea continues northward under the continental margin off Norway.