Fra Kridthav til Vesterhav. Nordsøbassinets udvikling vurderet ud fra seismiske hastigheder

The North Sea Chalk forms a coherent body between Scandinavia and the British Isles which were uplifted since the sea covered North-west Europe during the Cretaceous. The burial history of the North Sea Basin during the Cenozoic is thus reflected in the degree of compaction of the Chalk. Deviations from normal compaction are calculated from velocity-depth anomalies for the Chalk, the Cenozoic sequence and three Mesozoic formations based on interval velocity data from 1100 wells in the North Sea Basin. The anomalies are calculated relative to normal velocity-depth trends for the Chalk and for marine and continental shale dominated by smectite/illute and kaolin, respectively. The baselines reflect that the compaction process for these sedimentary rocks depends on their mineralogical composition. The depth anomalies vary systematically within ±1 km across the North Sea Basin for the Chalk and the lower Cenozoic sediments, whereas the upper Cenozoic sediments almost are normally compacted when the deviations for the Cenozoic sediments are calculated relative to the baseline for marine shale.