New insights from the southern margin of the Fennoscandian Ice Sheet – regional mapping of the shallow subsurface in Denmark

In southern Scandinavia, hitherto, national (and regional) scale reconstructions of glacier configuration during and after the Last Glacial Maximum/marine isotope stage 2 (LGM; MIS2) have relied heavily on data series from current onshore settings (Hughes et al., 2016; Hyttinen et al., 2020). Only few data series from marine settings have been incorporated in the reconstructions. Additionally, in-depth knowledge about the Quaternary sedimentary succession within the Exclusive Economic Zone (EEZ) of Denmark is scattered making it challenging for decisionmakers to find sites that are geologically suitable for development of offshore windfarms. To bridge the knowledge gap between marine and terrestrial archives in Denmark, several thousand kilometres of archive and newly acquired (2022 and 2023) shallow seismic data and sediment cores, across the entire Danish offshore areas, have been collected and interpreted.
The work has given new insights into the LGM ice margin position in the North Sea, ice-margin retreat patterns of the Fennoscandian Ice Sheet (FIS), the sedimentary development since the LGM in offshore Denmark and shed light on drowned palaeo-landscapes. An overall outcome of the project is thickness maps of the sedimentary succession since LGM until present and palaeo-bathymetrical maps of the glacially overridden surface as well as the base of the Holocene within the Danish EEZ.
In this talk, results and implications of the mapping in the Kattegat, a shallow gateway between the Baltic Sea and the North Sea/Atlantic, is presented. Incorporated in the work is a total of 361 radiocarbon ages from the Kattegat and adjacent (current) terrestrial areas, ranging from c. 17,300 cal. a BP to modern; 39 are new radiocarbon ages and 318 are previously published ages that we have re-calibrated with the MARINE20 and INTCAL20 calibration curves (Heaton et al., 2020; Reimer et al., 2020). Key results of the mapping in the Kattegat are the identification of not previously documented glaciotectonic complexes and retreat moraines between the islands of Læsø and Anholt, a potential post-LGM ice-marginal lake in central Kattegat, updated relative sea-level curve(s), new radiocarbon ages, and demarcation of areas that were subaerially exposed during the Early Holocene and thus are of marine-archaeological interest. We summarize our findings in a series of palaeogeographic maps.