Three-dimensional gravity modelling of a Quaternary overdeepening fill in the Bern area of Switzerland discloses two stages of glacial carving

Bandou, Dimitri; Schlunegger, Fritz; Kissling, Eduard; Marti, Urs; Schwenk, Michael; Schläfli, Patrick; Douillet, Guilhem Amin; Mair, David

doi:10.1038/s41598-022-04830-x

Cited by 5 publications

(15 citation statements)

References 38 publications

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“…It is a 12 km 2 area where a large amount of drinkable water is exploited. Several glacial cycles occurred, causing a complex interwinding of glacial and interglacial deposits (Bandou et al., 2022; Graf & Burkhalter, 2016; Schorpp et al., 2022). At least two different levels of aquifer have been identified in interglacial fluvial deposits (Schorpp et al., 2022).…”

Section: Application To the Aare Valleymentioning

confidence: 99%

“…To illustrate the applicability of the proposed methodology on a real site, we used a test area in central Switzerland. The upper Aare valley is filled with Quaternary deposits, with a thickness ranging from a few meters on the sides of the valley to a few hundred in the center (Bandou et al., 2022). The investigation zone is located north of the upper Aare valley, just upstream of the city of Bern.…”

Section: Application To the Aare Valleymentioning

confidence: 99%

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A Novel Methodology for the Stochastic Integration of Geophysical and Hydrogeological Data in Geologically Consistent Models

Néven

Renard

2023

Water Resources Research

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Groundwater resources represent 99% of the total liquid fresh water on Earth and provides approximately 50% of the total volume of water withdrawn for domestic use in the world (United Nations Educational Scientific and Cultural Organization, 2022). However, because the resource is at depth below the ground surface, the interest of the general public and policy makers tends to wane due to its invisible aspect (United Nations Educational Scientific and Cultural Organization, 2022). In a changing climate, being able to understand, predict and model underground flows and resources is crucial. These questions can only be properly addressed by local to regional groundwater modeling.Another issue owing to the underground position of groundwater is the difficulty in collecting data. Data are usually sparse and often represent only a tiny fraction of the total volume of the aquifer. The data can therefore miss most of the spatial heterogeneity. Conjectures based on such groundwater models could lead to inadequate decisions. A recent paper by Adams et al. (2022) reviews the different existing remote sensing techniques (including geophysical techniques) and possible future approaches that could help fill this gap. They argue that satellite or airborne remote sensing could be key methods for understanding groundwater dynamics at various scales, which would have been impossible with classical spare in situ observations. One method mentioned in their paper is the electromagnetic induction techniques, and especially the Time Domain Electromagnetic (TEM). The TEM method is relatively inexpensive, fast and has a depth of investigation ranging from a few meters to a few hundred meters (Christiansen et al., 2009;Fitterman, 1987). Due to its inductive principle, the Electromagnetic Magnetic (EM) method will be mainly sensitive to underground electrical resistivity. Consequently, it will also be sensitive

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Section: Application To the Aare Valleymentioning

confidence: 99%

Section: Application To the Aare Valleymentioning

confidence: 99%

A Novel Methodology for the Stochastic Integration of Geophysical and Hydrogeological Data in Geologically Consistent Models

Néven

Renard

2023

Water Resources Research

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“…Such erosional troughs have particularly been identified in the European Alps (Preusser et al, 2010), where >200 m-deep and several km-long bedrock depressions beneath the modern base-level occur in the Alpine valleys as well as on foreland plateaus on either side of this mountain belt (Preusser et al, 2010;Dürst Stucki and Schlunegger, 2013;Magrani et al, 2020). Geophysical surveys (e.g., Rosselli and Raymond, 2003;Reitner et al, 2010;Stewart and Lonergan, 2011;Stewart et al, 2013;Perrouty et al, 2015;Burschil et al, 2018;Ottesen et al, 2020) in combination with drillings (Jordan, 2010;Dürst Stucki et al, 2010;Büchi et al, 2017;Gegg et al, 2021;Bandou et al, 2022;Anselmetti et al, 2022;Schwenk et al, 2022a, b;Gegg and Preusser, 2023;Schaller et al, 2023) disclosed that such overdeepenings can be several kilometers wide and tens of kilometers long and that they are generally made up of individual sub-basins separated by bedrock swells, or riegels (Cook and Swift, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Here, we summarize the results of an interdisciplinary project where we aimed at exploring the origin of tunnel valleys or overdeepenings using a combination of data collected through a gravimetry survey (Bandou et al, 2022(Bandou et al, , 2023, drillings (Reber and Schlunegger, 2016;Schwenk et al, 2022a, b) and dating (Schläfli et al, 2021;Schwenk et al, 2022a). We focus our study on the Bern area situated on the northern margin of the European Alps (Figure 3a).…”

Section: Introductionmentioning

confidence: 99%

Overdeepening or tunnel valley of the Aare glacier on the northern margin of the European Alps: Basins, riegels, and slot canyons

Schlunegger,

Kissling,

Bandou

et al. 2024

Preprint

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Abstract. This work summarizes the results of an interdisciplinary project where we aimed to explore the origin of overdeepenings or tunnel valleys through a combination of a gravimetry survey, drillings, dating and a synthesis of previously published work. To this end, we focused on the Bern area, Switzerland, situated on the northern margin of the European Alps. In this region, multiple advances of piedmont glaciers during the Quaternary glaciations resulted in the carving of the main overdeepening of the Aare River valley (referred to as Aare main overdeepening). This bedrock depression is tens of km long and up to several hundreds of meters to a few kilometers wide. We found that in the Bern area, this main overdeepening is made up of two >200 m-deep troughs that are separated by a c. 5 km-long and up to 150 m-high transverse rocky ridge, interpreted as a riegel. The basins and the riegel are overlain by a >200 m- and 100 m-thick succession of Quaternary sediments, respectively. The bedrock itself is made up of a Late Oligocene to Early Miocene suite of consolidated clastic deposits, which are part of the Molasse foreland basin, whereas the Quaternary suite comprises a middle Pleistocene to Holocene succession of glacio-lacustrine gravel, sand and mud. A synthesis of published gravimetry data revealed that the upstream stoss side of the bedrock riegel is c. 50 % flatter than the downstream lee side. In addition, information from >100 deep drillings reaching depths >50 m suggests that the bedrock riegel is dissected by an anastomosing network of slot canyons. We propose that these canyons established the hydrological connection between the upstream and downstream basins during their formation. Based on published modelling results, we interpret that the riegels and canyons were formed through incision of subglacial meltwater during a glacier’s decay state, when large volumes of meltwater were released. Such a situation has repeatedly occurred since the Middle Pleistocene Transition approximately 800 ka ago, when large and erosive piedmont glaciers began to advance far into the foreland. This resulted in the deep carving of the inner-Alpine valleys, and additionally in the formation of overdeepenings on the plateau on the northern margin of the Alps.

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“…Large amounts of Quaternary glacial deposits of a widely unknown provenance are accumulated in glacially overdeepened valleys, or so-called overdeepenings, in and around the European Alps, including the central Swiss Alps (Preusser et al, 2010). Overdeepenings are bedrock troughs with their thalwegs below the present-day base level, and they can have a U-shaped cross-sectional geometry (Bandou et al, 2022). Hence, they are thought to have formed through glacial rather than fluvial erosion (Cook and Swift, 2012).…”

Section: Introductionmentioning

confidence: 99%

Two glaciers and one sedimentary sink: the competing role of the Aare and the Valais glaciers in filling an overdeepened trough inferred from provenance analysis

Schwenk

Stütenbecker²,

Schläfli

et al. 2022

E&G Quaternary Sci. J.

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Abstract. The extent and distribution of glaciers on the Swiss Plateau during the Last Glacial Maximum (LGM) can be determined from the geological record. However, similar reconstructions for the glaciations that preceded the LGM are far more difficult to be made due to the destruction of suitable sedimentary records through recurring glaciations or due to the inaccessibility of preserved records. Here, we explored Quaternary sediments that were deposited during the Marine Isotope Stage (MIS) 8 glaciation at least around 250 ka, and which were recovered in a drilling that was sunk into an overdeepened bedrock trough west of Bern (Switzerland). We analyzed the sediment bulk chemical composition of the deposits to investigate the supply of the material to the area by either the Aare Glacier, the Saane Glacier, or the Valais Glacier, and we complement this investigation with the results of heavy mineral analyses and geochemical information from detrital garnet. The potential confluence of the Valais and the Aare glaciers in the Bern area makes this location ideal for such an analysis. We determined the sediment bulk chemical signal of the various lithological units in the central Swiss Alps where the glaciers originated, which we used as endmembers for our provenance analysis. We then combined the results of this fingerprinting with the existing information on the sedimentary succession and its deposition history. This sedimentary suite is composed of two sequences, Sequence A (lower) and Sequence B (upper), both of which comprise a basal till that is overlain by lacustrine sediments. The till at the base of Sequence A was formed by the Aare Glacier. The overlying lacustrine deposits of an ice-contact lake were mainly supplied by the Aare Glacier. The basal till in Sequence B was also formed by the Aare Glacier. For the lacustrine deposits in Sequence B, the heavy mineral and garnet geochemical data indicate that the sediment was supplied by the Aare and the Saane glaciers. We use these findings for a paleogeographic reconstruction. During the time when Sequence A and the basal till in Sequence B were deposited, the Aare Glacier dominated the area. This strongly contrasts with the situation during the LGM, when the Aare Glacier was deflected by the Valais Glacier towards the northeast. The Valais Glacier was probably less extensive during MIS 8, but it was potentially present in the area, and it could have been essential for damming a lake in which the material supplied by the Aare and the Saane glaciers accumulated. In conclusion, combining provenance with sedimentological data, we could document how sediment was supplied to the investigated overdeepened basin during the MIS 8 glacial period and how glaciers were arranged in a way that was markedly different from the LGM.

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Three-dimensional gravity modelling of a Quaternary overdeepening fill in the Bern area of Switzerland discloses two stages of glacial carving

Cited by 5 publications

References 38 publications

A Novel Methodology for the Stochastic Integration of Geophysical and Hydrogeological Data in Geologically Consistent Models

A Novel Methodology for the Stochastic Integration of Geophysical and Hydrogeological Data in Geologically Consistent Models

Overdeepening or tunnel valley of the Aare glacier on the northern margin of the European Alps: Basins, riegels, and slot canyons

Two glaciers and one sedimentary sink: the competing role of the Aare and the Valais glaciers in filling an overdeepened trough inferred from provenance analysis

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