The Norwegian continental shelf is located between 62°N and 69°30 N. It became an area of massive sedimentary outbuilding during the late Cenozoic time when large amounts of glacial sediments were transported out into a basin where it developed into prominent prograding wedges offshore Mid-Norway. These deposits are defined today as the Naust Formation. The geographical distribution and stratigraphical and chronological data suggests that the instigatation of the wedges was related to many factors including i) tectonic uplift, ii) Late Pliocene to Pleistocene climatic deterioration which gave rise to the onset of major glaciations,iii) sediment supply which was primarily glacially derived, iv) sediment transport mechanisms and v) finally deep and shallow erosional and depositional processes.
The main objective of this study has been to further understand the Late Cenozoic outbuilding off Mid-Norway and relate this to factors such as basin morphology, eustatic sea-level, rate of sedimentation, and the dynamic behaviour of the glacial ice sheets on the shelf during the Plio-Pleistocene glacial periods. The study includes the seismic stratigraphic interpretation of six high resolution seismic lines on the shelf.
Eleven seismic sequences have been identified and mapped regionally. Two important sequence boundaries including the Regional Downlap Surface (RDS) and the Upper Regional Unconformity (URU) have also been mapped. Particular attention was paid to the internal facies character, reflector type, lateral extent and variations, trajectory patterns as well as the geological features inferred from the seismic lines. A chronostatigraphic chart has also been constructed in order to attain a better insight of the time relationships of the depositional systems, and their relationships to surfaces of non-deposition, whether it be due to erosion or condensation.
Results of the study reveal that some relief offshore Mid Norway was due to the continental break-up in the Early Eocene. Alot of other tectonic processes have probably taken place during the Oligocene to Miocene time. These processes though, are not clearly understood. Inthe Oligocene to Pliocene epoch, the deltaic system known as the Molo Formation was formed. Subsequent to this, was the onset of climatic cooling whereby glaciers developed. Ice streams in the ice sheets carried large amounts of glacial debris within it to the shelf margin.Results for the study show that the supply to the northern regions off the Mid-Norwegain margin were primarily from the Vestjorden Basin and was carried through the Trænadjupet Trough. The more central areas attained its sediment through the Sklinnadjupet Trough whilethe southern part was fed by glaciers moving from the inland areas to the flat lying Trøndelag area were they merged forming huge ice streams which fed this region.
The thick prograding packages were a result of tectonics, climate, and a high sediment supply. The more aggrading part of the system may be due to the maturation of the basin over time or it can simply be a continuation of the Late Pliocene evolution marked by more extensiveerosion.