DISLOCATED QUATERNARY DEPOSITS IN SOUTHEASTERN KATTEGAT - A GLACIAL OR GRAVITATIONAL PHENOMENON

The Quaternary deposits in the Store Middelgrund-Rodebanke area midway between the island of Anholt and Hallandsasen on the Swedish coast ar e described on the basis of reflection seismic profiles with a vertica l resolution of 5-10 m. The Quaternary rests on Upper Cretaceous limes tone, the surface of which is nearly horizontal. Three Quaternary sequ ences are defined and interpreted as: (1) Late Weichselian marine or l acustrine deposits, (2) Late Weichselian glaciogenic deposits, and (3) Late Saalian-Eemian and Early-Middle Weichselian deposits. Sequence 3 is probably comparable to the upwards-coarsening sequence known from Skaerumhede in Vendsyssel. The layers in sequence 3 are dislocated in the eastern part of the Store Middelgrund-Rodebanke area mainly by gen tle folding, but other types of deformations occur. Folding could be t he result of horizontal push from an ice sheet approaching from the ea st. Alternatively the folding is an effect of vertical, gravitational forces acting on the sediments due to an unstable density profile, as described by the Rayleigh-Taylor instability model. The zone of deform ation is located close to the northern flank of the tectonically activ e Sorgenfrei-Tornquist Zone. It is suggested that the initiation of th e folding process was facilitated by tremors from small earthquakes.