O01_05

Reconstructing the timing of Pleistocene glacier advances in the Swiss northern Alpine Foreland

Dieleman C¹, Christl M², Vockenhuber C², Gautschi P², Akçar N¹

¹University of Bern, Bern, Switzerland, ²ETH Zurich, Zurich, Switzerland

During the last decade, isochron-burial dating was successfully used in constraining the timing of fluvial sediment deposition. Though, its application to glacial and glaciofluvial deposits is challenging because these deposits are generally characterized by low cosmogenic nuclide concentrations due to repeated glacial erosion. The Swiss northern Alpine Foreland witnessed repeated glacier advances during the Quaternary; thirteen advances were identified yet. The records of these advances are found in, from the oldest to the youngest, Höhere Deckenschotter (HDS; Higher Cover Gravels), Tiefere Deckenschotter (TDS; Lower Cover Gravels), Hochterrasse (HT; Higher Terrace) and Niederterrasse (NT; Lower Terrace). The Deckenschotter are characterized by a succession of glaciofluvial gravel beds intercalated with glacial and/or overbank deposits and considered to be the oldest Quaternary deposits, however their chronology is still under debate, because the first cosmogenic nuclide chronology, recently established at few sites, contradicts the existing morphostratigraphy. In this study, we present a solid cosmogenic nuclide chronology for the Swiss Deckenschotter reconstructed at eighteen sites during the last decade. Based on this chronology, we revealed the timing of five Pleistocene glaciations between ca. 2.5 Ma and ca. 250 ka, whereof three occurred during the Early Pleistocene prior to the Mid-Pleistocene Revolution (MPR) and two during the Middle Pleistocene. Based on this new chronostratigraphy, we conclude that the Swiss Deckenschotter are cut-and-fill sequences. Furthermore, these ages indicate a rather constant local base level between 2.5 Ma and 1 Ma, which has likely been lowered afterwards probably induced by the MPR.