Quaternary sequences and their relations to the pre‐Quaternary in the vicinity of Anholt, Kattegat, Scandinavia

Abstract

The stratigraphic record from a boring penetrating the 104 m thick Quaternary sequence on the island of Anholt is summarized. The spatial distribution of the pre‐Quaternary formations and the surface topography of these are described on the basis of reflection seismic profiles. It is concluded that Anholt is located in the crestal zone of a southeast–northwest trending anticline in the pre‐Quaternary. The anticline was formed during the Late Cretaceous–Early Tertiary inversion episodes and was later deeply truncated by erosion. A southeast–northwest trending erosional channel, c. 2 km wide and with a maximum depth c. 250 m below sea level, is located southeast of Anholt along the crest of the anticline. This channel is not present at the bore locality. Although no direct correlation from the boring to the seismic profiles could be achieved it is argued that a strong reflection near the base of the Quaternary outside the channel may be correlated with the Saalian–Eemian complex found in the boring. Three younger sequences of probable Early and Middle Weichselian, Late Glacial and Holocene age respectively have been recognized. The Late Glacial and Holocene sediments appear to have been deposited in erosional troughs and channels cut into a sequence of Lower and Middle Weichselian sediments. Post‐Eemian till deposits or other evidence unambiguously indicating the presence of Weichselian glaciers have not been found, either in the boring or in the seismic profiles. It is therefore assumed that the erosion of the Lower‐Middle Weichselian sequence was of fluvial origin and can be ascribed to the lowstand period of the Weichselian glacial period. The western part of Anholt can possibly be regarded as an erosional remnant of the Lower‐Middle Weichselian sequence.