The first major incision of the Swiss Deckenschotter landscape

Abstract

The Swiss Deckenschotter (''cover gravels'') is the oldest Quaternary units in the northern Swiss Alpine Foreland. They are a succession of glaciofluvial gravel layers intercalated with glacial and/or overbank deposits. This lithostratigraphic sequence is called Deckenschotter because it ''covers'' Molasse or Mesozoic bedrock and forms mesa-type hill-tops. Deckenschotter occurs both within and beyond the extent of the Last Glacial Maximum glaciers. The Swiss Deckenschotter consist of two subunits: Höhere (Higher) and Tiefere (Lower) Deckenschotter. Although the Höhere Deckenschotter sub-unit (HDS) is topographically higher than the Tiefere Deckenschotter, it is older. The only available age for the Swiss Deckenschotter is 2.5-1.8 Ma based on mammal remains found in HDS at the Irchel site. In this study, we present an exposure age for the topographically lowest HDS, calculated from a cosmogenic 10 Be depth-profile. Our results show that the first phase of the Deckenschotter glaciations in the Swiss Alps terminated at least 1,020 þ80 À120 ka ago, which is indicated by a significant fluvial incision. This line of evidence seems to be close to synchronous with the beginning of the Mid-Pleistocene Revolution, when the frequency of the glacial-interglacial cyclicity changed from 41 to 100 ka and the amplitude from low to high, between marine isotope stages 23 and 22.

Isochron‐burial dating of glaciofluvial deposits: First results from the Swiss Alps

“…The data from Mandach (507 m a.s.l.) suggest that incision of the HDS was already underway by 1.0 ± 0.2 Ma (Akçar et al ., ).…”

“…This range in incision rates is slightly higher than the incision rate of 0.12 mm/a determined for Stadlerberg over the last 1.9 ± 0.2 Ma (Claude et al ., ). It is also slightly higher than the bedrock incision rate of 0.1 mm/a derived for Mandach at 1.0 ± 0.2 Ma (Akçar et al ., ). Furthermore, Kuhlemann and Rahn () estimated a bedrock incision range of 0.04 to 0.13 mm/a between 2.05 and c .…”

“…(Figure ). This site is topographically slightly lower than the previously dated HDS at the Irchel (670 m a.s.l., Bolliger et al ., ) and Stadlerberg (610 m a.s.l., Claude et al ., ) sites, yet topographically higher than the HDS Mandach site (507 m a.s.l., Akçar et al ., ) (Figure ). The sampled sequence is crudely bedded and consists of poorly sorted, irregularly cemented, mainly clast‐supported cobbles and small boulders with an average size of 10–20 cm.…”

“…In addition, Akçar et al . () dated the start of incision into the Deckenschotter at Mandach (507 m a.s.l., Canton Aargau) to 1.0 ± 0.2 Ma by 10 Be depth‐profile dating.…”

Landscape evolution of the northern Alpine Foreland: constructing a temporal framework for early to middle Pleistocene glaciations

“…A second phase of gravel accumulation, the TDS at Irchel Steig and Hütz, Rechberg, Ängi and Mandach occurred at around 1 Ma, coinciding with the Mid-Pleistocene Revolution (MPR; Akçar et al, 2014;Claude et al, 2017c). At this time, sediments were eroded from both the northern Central and central Eastern Alps and brought to the Alpine Foreland by the Rheatian, Linth and Reuss paleoglaciers (Fig.…”