Neotectonics, sea-level changes and biological evolution in the Fennoscandian Border Zone of the southern Kattegat Sea JØRN BO JENSEN, KAJ STRAND PETERSEN, PETER KONRADI, ANTOON KUIJPERS, OLE BENNIKE, WOLFRAM LEMKE AND RUDOLF ENDLER Jensen, J. B., Petersen, K. S., Konradi, P., Kuijpers, A., Bennike, O., Lemke, W. & Endler, R. 2002 (June): Neotectonics , sea-level changes and biological evolution in the Fennoscandia n Border Zone of the southern Kattegat Sea. Boreas , Vol. 31, pp. 133–150. Oslo. ISSN 0300-9483. Shallow seismic data and vibrocore information , sequence stratigraphi c and faunal evidence have been used for documentation of Late Weichselian reactivatio n of faulting in the south central Kattegat, southern Scandi- navia. The study area is situated on the Fennoscandian Border Zone, where tectonic activity has been recurrent since Early Palaeozoic time and still occurs, as shown by present earthquake activity. New data from the area south of the island of Anholt show that after deglaciatio n fast isostatic rebound resulted in reactivation of a NW–SE striking normal fault system. This tectonic episode is dated to a period starting shortly before 15.0 cal. ka BP and ending around 13.5 cal. ka BP, after regression had already reached a level of about 30 m b.s.l. The vertical displacement associated with the faulting was in the order of 20 m. More generally, the results support the previousl y reported late Weichselian sea-level highstand , which was followed by forced regression until the eustatic sea-level rise surpassed the rate of glacio-isostati c rebound in early Preboreal. Our ndings further imply that drainage of the Baltic Ice Lake through the Øresund at c. 15 cal. ka BP (Bergsten & Nord- berg 1992) may have been triggered by tectonic activity in this region. Jørn Bo Jensen (e-mail: jbj@geus.dk), Kaj Strand Petersen (e-mail: ksp@geus.dk), Peter Konradi (e-mail: pk@geus.dk), Antoon Kuijpers (e-mail: aku@geus.dk ) and Ole Bennike (e-mail: obe@geus.dk) , Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark; Wolfram Lemke (e-mail: wolfram.lemke@io-warnemuende.de ) and Rudolf Endler (e-mail: rudolf.endler@io-warnemuende.de) , Baltic Sea Research Institute, Seestrass e 15, DE-18119 Rostock-Warnem u ¨nde, Germany; received 2nd July 2001, accepted 30th October 2001. The southern Kattegat (Fig. 1) is relatively shallow (<50 m), and may be regarded as a drowned glacial landscape. Being situated at the entrance to the Baltic Sea, it forms a relatively protected marine basin, only little affected by tides. The water exchange between the brackish Baltic Sea and the Kattegat is through the Danish Straits, i.e. the Øresund, Storebælt and Lillebælt (see inset, Fig. 1). The major geological architecture of the southern and central Kattegat is dominated by the tectonically active Fennoscandian Border Zone, which has been recurrently tectonically active since Early Palaeozoic time (Liboriussen et al. 1987). The latest and most important event is the Late Cretaceous and Tertiary inversion of a major NW–SE trending anticli- norium, which occurred in response to right lateral wrenching. Registration of present earthquake activity along the Fennoscandian Border Zone and the relation- ship to recent geological motion proves that it still is an active zone (Gregersen et al. 1996). The pre-Quaternary stratigraphy and surface morphology have been studied by Gyldenholm et al. (1993), Lykke-Andersen et al. (1993) and Binzer & Stockmarr (1994). These studies show that the NW-dipping crystalline anticlinorium is bounded by Jurassic, Cretaceous and Tertiary sediment strata in a mainly fault-dominated structural setting. North of the anticlinorium, Middle–Late Weichselian and Holocene sediment sequences are observed with a maximum thickness of about 200 m in the Skagen boring (Knudsen et al . 1996), and about 104 m in the Anholt boring further to the south (Knudsen 1994). Because of a low seismic resolution, detailed mapping of the late- and postglacial sediments in the Kattegat has hitherto not been possible. Onshore investigations show that the southwestern margin of the receding Fenno- scandian ice sheet approximately followed the west coast of Sweden c. 17 cal. ka BP (calibrated kilo years before present) (Lagerlund & Houmark-Nielsen 1993). The highest fossil coastline is found here at about 60 m above present sea level (a.s.l.) (Sandgreen 1983) and similar palaeo-coast lines are observed in Vendsyssel, northern Denmark (Petersen 1984; Richardt 1996). Offshore mapping of Late Weichselian subaequous sediments deposited during the nal recession of the Late Weichselian ice sheet was carried out by Nielsen & Konradi (1990) and Gyldenholm et al. (1993). Late Weichselian subaequous sediments occur typi- cally as basin inll in the area north of the anti- clinorium, or in local depressions elsewhere. However, north of the Øresund, deltaic sediments point to a drainage of the Baltic Ice Lake between approximately 15 cal. ka BP and 11 cal. ka BP (Bergsten & Nordberg 1992). Detailed studies of the sediments in the delta region have yielded important information on the timing of drainage and palaeoenvironmental changes (Jiang & Klingberg 1996; Jiang et al. 1997, 1998; Majoran & Nordberg 1997). # 2002 Taylor & Francis