Dislocated Quaternary deposits in southeastern Kattegat – a glacial or gravitational phenomenon?

Abstract

The Quaternary deposits in the Store Middelgrund–Rørdebanke area midway between the island of Anholt and Hallandsåsen on the Swedish coast are described on the basis of reflection seismic profiles with a vertical resolution of 5–10 m. The Quaternary rests on Upper Cretaceous limestone, the surface of which is nearly horizontal. Three Quaternary sequences are defined and interpreted as: (1) Late Weichselian marine or lacustrine 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–Rødebanke area mainly by gentle folding, but other types of deformations occur. Folding could be the result of horizontal push from an ice sheet approaching from the east. 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 deformation is located close to the northern flank of the tectonically active Sorgenfrei–Tornquist Zone. It is suggested that the initiation of the folding process was facilitated by tremors from small earthquakes.

Absolute sea levels and isostatic changes of the eastern North Sea to central Baltic region during the last 900 years

“…In line with a tectonic interpretation of the Sorgenfrei-Tornquist Zone, high-resolution seismic surveys of Kattegat have identified a number of gentle dome structures (Vangkilde-Petersen et al 1993) in the 160-200 m thick early Weichselian to early Holocene marine clays underlying most parts of the northern Kattegat Sea (Knudsen 1986;Lykke-Andersen 1990;Gyldenholm et al 1993;Lykke-Andersen et al 1993a,b;Knudsen et al 1996Knudsen et al , 2009). The domes are comparable to Hornfiskrøn and other islets south of Laesø in terms of size and orientation.…”

“…In line with a tectonic interpretation of the Sorgenfrei‐Tornquist Zone, high‐resolution seismic surveys of Kattegat have identified a number of gentle dome structures (Vangkilde‐Petersen et al . ) in the 160–200 m thick early Weichselian to early Holocene marine clays underlying most parts of the northern Kattegat Sea (Knudsen ; Lykke‐Andersen ; Gyldenholm et al . ; Lykke‐Andersen et al .…”

“…It is likely that this gentle local updoming and tilting, which during the last 900 years has added up to 70 cm to GIA (see below), is caused by gentle, dextral strikeslip sliding and compression of the NW-SE-striking Sorgenfrei-Tornquist zone SW of Laesø (cf. Vangkilde-Petersen et al 1993;Hansen 1995;Gemmer et al 2002;T. Vangkilde-Petersen, pers.…”

The salt industry on the Danish Kattegat island of Læsø (1150–1652): Hypersaline source, climatic dependence, and environmental impact

“…This assumption is based on reflection seismic studies by Larsen et al ( 1986}, LykkeAndersen et al (1993a, Gyldenholm et al ( 1993) and Vangkilde-Petersen et al ( 1993) of the area between Lres0 and the island Anholt, southeast of Lres0. Such local deformation appears to be particularly important for the fast growth ofHorntiskr0n, Kringelmn, and Langer0n and may have been caused by clay diapirism triggered by dextral strike/slip movements in the well-known large-scale tectonic Sorgenfrei-Tornquist Zone passing through Kattegat, Skane, Bornholm, and Poland (see Mogensen & Korstgard, 2003 ).…”

Dating early Holocene palaeoseismic event(s) in the Gulf of Bothnia, Baltic Sea

“…Faults have mainly been found in northern Fennoscandia, with only a few in southern and central Fennoscandia (Kuivamäki et al 1998). In the Holocene sediments of the Baltic Sea, only a few failures related to earthquakes have been reported (Sviridov 1981;Vangkilde-Pedersen et al 1993). In a recent study (Kotilainen & Hutri 2004), ancient faults, slides and slumps recorded in high-resolution echo-sounding profiles in subaquatic Holocene Baltic Sea sediments at Olkiluoto were interpreted as indicators of early Holocene palaeoseismicity.…”