Marine seismic studies in southern Kattegat, with special emphasis on longitudinal bars and their possible relationship to the drainage of the Ancylus Lake
Titel:
Marine seismic studies in southern Kattegat, with special emphasis on longitudinal bars and their possible relationship to the drainage of the Ancylus Lake
Auteur:
Novak, Bernhard Bjorck, Svante
Verschenen in:
GFF
Paginering:
Jaargang 120 (1998) nr. 3 pagina's 297-306
Jaar:
1998-09-01
Inhoud:
Forty kilometres of high-resolution subbottom- and seismic reflection profiling was undertaken in southern Kattegat. In the 3.5 kHz subbottom profiler recordings five seismic facies were recognized and they are presented in isopach maps. Two vibrocore samples constituted the stratigraphic control, and on the basis of facies analysis and core lithology, an anomalous fluvial event is proposed. The event is clearly non-cyclic and the associated gravel-sand deposit is stratigraphically situated between two units of fines. The base of the seismic facies association shows unusually deep scours, high-angled chute cuts and an unbalanced morphology. Facies 1—sheets is located at least 8 m higher than facies 5—channel—but is stratigraphically the lowermost unit. Facies 1 to 5 represent gradually lower energies. Maximum 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 water level fell rapidly. The deposits are related to the drainage and lowering of the Ancylus Lake through the Storebælt, into southern Kattegat. Instead of being a several hundred-year-long event, which has been implied earlier, this lowering seems to have occurred over a very short time. In a later and more long-lasting phase, the normal background discharge from the Baltic area dominated the flow style and the water velocity was in the order of 1 m/s.
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