Marine seismic studies in southern Kattegat, with special emphasis on longitudinal bars and their possible relationship to the drainage of the Ancylus Lake

Forty kilometres of high-resolution subbottom- and seismic reflection profi ling was undertaken in southern Kattegat. In the 3.5 kHz subbottom profiler recordings five seismic facies were recognized and they are presented in i sopach maps. Two vibrocore samples constituted the stratigraphic control, a nd on the basis of facies analysis and core lithology, an anomalous fluvial event is proposed. The event is clearly non-cyclic and the associated grav el-sand deposit is stratigraphically situated between two units of fines. T he base of the seismic facies association shows unusually deep scours, high -angled chute cuts and an unbalanced morphology. Facies 1 - sheets is locat ed at least 8 m higher than facies 5 - channel - but is stratigraphically t he lowermost unit. Facies 1 to 5 represent gradually lower energies. Maximu m water velocity was calculated to be more than 8 m/s in the scours. A peak flow with a duration of a few months initiated the event, whereafter the w ater level fell rapidly. The deposits are related to the drainage and lower ing of the Ancylus Lake through the Storebaelt, into southern Kattegat. Ins tead of being a several hundred-year-long event, which has been implied ear lier, this lowering seems to have occurred over a very short time. In a lat er and more long-lasting phase, the normal background discharge from the Ba ltic area dominated the flow style and the water velocity was in the order of 1 m/s.