Relief increase in the Swiss northern Alpine Foreland after the Mid-Pleistocene Transition

Abstract

Glaciations have the potential to significantly change the landscape over time. Here, we document such changes in landscape dynamics using the northern Swiss Alpine Foreland as example, and we explore how the landscape in the foreland evolved during the Early and Middle Pleistocene. Following these scopes, we investigated glaciofluvial gravels in detail at seven sites in the Mandach and Lake Constance regions situated on the northern side of the Central European Alps. Clast petrography analysis indicates that the gravels in the Mandach region were transported by the Aare, Reuss, Linth, and Rhaetian paleoglaciers from the Alps into the northern Alpine Foreland, where they were subsequently deposited by meltwaters. In contrast the sediments at Schienerberg in the Lake Constance region, situated farther to the Northeast, show that they were transported solely by the Rhaetian paleoglacier. The isochron-burial chronology at the study sites suggests that the sediments were deposited during the Middle Pleistocene within in the age range of the Möhlin Glaciation around 500 ka. Because the Early and Middle Pleistocene archives were deposited at different elevations, the chronologic record established in this paper yields information on how erosion and thus the formation of relief changed over time. In particular the ages imply that bedrock incision was accelerated from <100 m/My prior 1 Ma, to >200 m/My between 1 Ma and the onset of the Möhlin Glaciation at ca 500 ka, to <100 m/My thereafter. The timing of the relief change implies that the lowering was likely induced by the Mid-Pleistocene Transition (MPT).