Early Pleistocene complex cut-and-fill sequences in the Alps

Abstract

Cut-and-fill sequences are the result of climatically or tectonically induced alternating aggradation and incision phases of a fluvial system. A recently established cosmogenic nuclide chronology of the Cover Gravels (Deckenschotter in German) in the northern Alpine Foreland, which are the oldest Quaternary glaciofluvial gravels and comprise evidence of early Pleistocene glaciations, suggests a cut-and-fill build-up. This suggested cut-and-fill architecture challenges the morphostratigraphy. The Deckenschotter deposits represent a suitable archive for reconstructing drainage patterns, base level changes, and the landscape evolution of the northern Alpine Foreland during the early Pleistocene. In this study, we focused on the highest morphostratigraphic Deckenschotter sites: three at Irchel and one in the area around Lake Constance. Sediment analyses were performed to determine their provenance and depositional environments. The geochronology was established using isochron-burial dating. The results indicate that the sediments were transported from the Central and eastern Central Alps, as well as from the Molasse, to the foreland and deposited in a proximal glaciofluvial environment. Based on these findings, we propose that the Deckenschotter are cut-and-fill sequences that accumulated in three stages during the early Pleistocene at ca. 2.5 Ma, ca. 1.5 Ma, and ca. 1 Ma. The presence of a cut-and-fill system implies that the regional base level was relatively constant during the early Pleistocene. In addition, the ca. 2.5 Ma glaciofluvial gravels document the first evidence of glaciers in the northern Alpine Foreland. This timing is synchronous with the onset of Quaternary glaciation in the northern hemisphere at ca. 2.7 Ma.

The onset of Pliocene–Early Pleistocene fluvial aggradation in the Southeastern Alpine Foreland (Velenje Basin, Slovenia) and its paleoenvironmental implications

“…These deposits represent the highest and oldest Quaternary deposits in the Southeastern Alpine Foreland, comparable with the gravel deposits traditionally referred to as the Deckenschotter in the Northern Alpine Foreland (e.g. Graf, 1993;Ellwanger et al, 2011;Akçar et al, 2014;Claude et al, 2017;Dieleman et al, 2022).…”

An aminostratigraphy for the Quaternary of the Swiss Plateau

“…The gravels of the Irchel Plateau below the HF have also been investigated by cosmogenic dating techniques (Claude et al, 2019;Dieleman et al, 2022a). Some of the ages they have produced differ from the age for the HF proposed above based on biostratigraphy, palaeomagnetic data and the lithostratigraphic concept of Graf (1993).…”

“…The thick glacial deposits that underlie both sites may well represent the 'Möhlin Glaciation,' which seems to have been the most extensive in the Swiss Alpine foreland (Preusser et al, 2011). The glacial deposits (Bünten Till) at Möhlin might represent MIS 12 (Dieleman et al, 2022b), but this age is disputed (Norgaard et al, 2023). This period also saw a major increase in the quantity and coarseness of debris supply into the Upper Rhine Graben north of Basel (Preusser et al, 2021).…”

“…Some recent investigations using luminescence and cosmogenic dating suggest that previously proposed ages and correlations may have to be reconsidered (e.g. Gegg et al, 2022;Dieleman et al, 2022a). Additional independent evidence for the timing of depositional archives is therefore needed to improve current understanding of Quaternary landscape evolution.…”