Structure and evolution of the Oslo Rift in Skagerrak

ABSTRACT This thesis focuses on the structural evolution of the offshore part of the Oslo Rift, the Skagerrak Graben, with special emphasis on: • Interpretation of the main seismic sequences in the Skagerrak Graben (pre- syn- and post-rift units) • A structural analysis of the Skagerrak Graben in relation to the regional stress field. • Stratigraphic correlations to the geology onshore Norway and to Danish wells • Geological evolution of the Skagerrak area in a regional setting. Reprocessed seismic data gave a better interpretation and understanding especially of the structure of the northern graben segment, and of the distribution of the Carboniferous-Permian lavas and syn-rift sedimentary rocks. The Skagerrak Graben is divided into two graben segments; one southern segment and one northern segment. The graben segments consist of fault complexes, again consisting of smaller half graben segments. Lower and Upper Paleozoic sedimentary rocks are in both graben segments preserved in rotated fault blocks. Syn-rift sediments are present along the border faults, and along minor faults inside the southern graben segment. There is an unconformity present at the Base Triassic level covering the whole area. This unconformity covers a time span from possibly late Permian to Early Triassic. The thickest Triassic sedimentary rocks were deposited over depressions caused by differential compaction and subsidence of the syn-rift sediments, and not in the central part of the graben as predicted by the McKenzie model. This shows that a normal pure shear post-rift subsidence is not present in the Skagerrak Graben