A regional assessment of the deglaciation history of the Swiss Plateau based on newly obtained and re-evaluated Be-10 cosmic-ray exposure ages

During marine oxygen isotope stage (MIS) 2, the Swiss Plateau temporarily hosted large piedmont lobe glaciers that retreated after their maximum advance back to the fringe of the Alps. The presence of moraines in this region indicates that overall glacier recession was punctuated by repeated phases of ice-marginal stability and re-advances. The timing of these events in the region formerly covered by the eastern lobe of the Rhône (or Valais) glacier has been controversial but remains poorly constrained due to the lack of chronological data. To fill this gap, 10Be cosmic-ray exposure (CRE) dating was applied to erratic boulders inside the assumed MIS 2 maximum extent of this piedmont lobe. Erratic boulders close to the suspected MIS 2 maximum extent gave unrealistically young CRE ages. Erratic boulders at a presumably younger ice-marginal position (Brästenberg position) yielded an average age of ~19 ka, consistent with recalibrated basal radiocarbon ages from lakes and recomputed radiocarbon ages from large Late Pleistocene mammals buried in glacio-fluvial deposits. However, several erratic boulders beyond the Brästenberg position gave internally consistent, but stratigraphically too young ages of ~17 ka. We cannot rule out that glacier recession from the Brästenberg position began no later than ~17 ka. CRE dating of a moraine of a presumably younger ice-marginal position (Solothurn position) gave unrealistically old ages and an incredibly young age (86 ka, 41 ka, and 4 ka). 14C CRE dating should be applied to check whether the boulders associated with the Solothurn and Brästenberg positions were previously exposed to cosmicradiation. Nevertheless, despite outlying ages, the presented chronological data contribute to an overall consistent and increasingly refined chronology of the last deglaciation of the Swiss Plateau when compared with 59 previously published CRE ages.