Two atypical overdeepening-fills from the Lake Constance area (Southern Germany)

During the Pleistocene epoch the Alpine scenery with its surroundings was repeatedly reshaped by glacial activity. Subglacial erosion led to basin-shaped structures, so-called ‘overdeepenings’ (OD), embedded in bedrock. Their sedimentary fillings are important archives for understanding glacial history and the glacial impact on environmental transformation. Some of these infills are composed of multiple cycles representing separate glaciations.

Numerous well investigated cores in the Northern Alpine Foreland led to the recognition of typical fining-upward OD-fill sequences – characterized by glaciolacustrine deposits overlying glacially originated diamicts at the basal unconformity (e.g. Gegg & Preusser 2023, and references therein). These fining-upward sequences typically start with glacitectonites that regularly transition into coarse-grained, sand-dominated, and finally fine-grained basin fills, and can occur as several unconformably stacked units (Buechi et al. 2024).

In the ICDP-DOVE framework (Anselmetti et al. 2022), two new cored profiles were recovered north of Lake Constance (drill sites Gaisbeuren and Lichtenegg). These consist of OD-fills that are not typical for the Alpine Foreland, because they are almost entirely composed of diamictic deposits. While these deposits show some variations in concentration and size of clasts, well sorted lacustrine sediments are missing. Here we aim to start a discussion about potential reasons for the atypical character of these OD-fills.

 

 

Anselmetti, F.S., Bavec, M., Crouzet, C., Fiebig, M., Gabriel, G., Preusser, F., Ravazzi, C., DOVE scientific team, 2022. Drilling Overdeepened Alpine Valleys (ICDP-DOVE): quantifying the age, extent, and environmental impact of Alpine glaciations. Scientific Drilling, 31, 51–70. https://doi.org/10.5194/sd-31-51-2022.

Buechi, M.W., Landgraf, A., Madritsch, H., Mueller, D., Knipping, M., Nyffenegger, F., Preusser, F., Schaller, S., Schnellmann, M., Deplazes, G., 2024. Terminal glacial overdeepenings: Patterns of erosion, infilling and new constraints on the glaciation history of Northern Switzerland. Quaternary Science Reviews, 344, 108970. https://doi.org/10.1016/j.quascirev.2024.108970.

Gegg, L., Preusser, F., 2023. Comparison of overdeepened structures in formerly glaciated areas of the northern Alpine foreland and northern central Europe. E&G Quaternary Science Journal, 72, 23–36. https://doi.org/10.5194/egqsj-72-23-2023.