Subsidence and tectonics in Late Precambrian and Palaeozoic sedimentary basins of southern Norway.

Abstract

The assumption that sedimentary basins approach isotopic equilibrium provides a good foundation for modelling basin subsidence based on variables such as cooling rates (thermal contraction), crustal thinning, eustatic sea-level changes and sedimentation. The Sparagmite basin of Central Southern Norway was probably formed by crustal extention during rifting. During Cambrian and Ordovician times the Oslo Region was rather stable part of the Baltic Shield, reflected in slow epicontinental sedimentation. The Bruflat Sandstone( Uppermost Llandovery) represents the first occurence of a rapid clastic influx, reflecting a pronounced basin subsidence. This change in sedimentation is believed to be related to the emplacement of first Caledonian nappes in northern part of the Oslo Region, providing a nearby source for the sediments and resulting in subsidence due to nappe loading. The underlying Palaeozoic sequence was detached along the Cambrian Alum Shale in front of the Osen Nappe. Devonian sedimentation was characterized by vertical tectonics and some of the Devonian basins, such as the Hornelen Basin, may be related to listric faulting rather than strike-slip fractures. The Permian sediments of the Oslo Graben were probably overlain by Triassic and possibly also by Jurassic sediments during post-rift subsidence.