O01_P01

Isochron-burial dating of the oldest glaciofluvial sediments in the northern Alpine Foreland

Broś E¹, Ivy-Ochs S¹, Grischott R², Kober F³, Vockenhuber C¹, Christl M¹, Maden C⁴, Synal H¹

¹Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland, ²BTG Büro für Technische Geologie AG, Sargans, Switzerland, ³NAGRA, Wettingen, Switzerland, ⁴Geochemistry and Petrology, ETH Zurich, Zurich, Switzerland

During the Middle and Early Pleistocene, the northern Alpine Foreland was glaciated several times and witnessed numerous phases of alternating incision and deposition, shaping the landscape that can be seen today. High elevated plateaus separated by deeply incised valleys, create a topography with relief of several hundreds of meters. On top of these plateaus can be found the oldest Quaternary glaciofluvial sediments in the northern Alpine Foreland. They have traditionally been divided into two gravel units: older Höhere (Higher, HDS) and younger Tiefere (Lower, TDS) Deckenschotter. The HDS is located topographically higher by ~100-150 m than the TDS. The Deckenschotter consist mainly of glaciofluvial sediments intercalated with glacial and/or overbank deposits and form gravel terraces located up to about 250 m above the modern valley bottom. Their exact time of deposition is an important source of information for establishing erosion and incision scenarios and quantification of landscape evolution in the northern Alpine Foreland during the Middle and Early Pleistocene. Our focus is placed on similar and complementary Deckenschotter deposits outcropping in several sites across the northern Alpine Foreland. In selected six sites, we implement isochron-burial dating technique with a pair of cosmogenic nuclides ²⁶Al and ¹⁰Be, to further examine and refine the question of the age of the Deckenschotter. The first preliminary age estimates point to deposition in the latter part of the Early Pleistocene. With the aim to determine the age of these sediments, the results will also complement our understanding of landscape change during and after Deckenschotter times.