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Overdeepening or tunnel valley of the Aare glacier on the northern margin of the European
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Alps: Basins, riegels, and slot canyons
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Fritz Schlunegger1, Edi Kissling2, Dimitry Bandou1,3, Guilhem Douillet1, David Mair1, Urs Marti4,
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Regina Reber1, Patrick Schläfli1,5, and Michael Schwenk1,6
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1Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
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2Department of Earth Sciences, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland
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3Department of Environmental Sciences, University of Verginia, 291 McCormick Rd., Charlottesville,
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VA 22904-4123, USA
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4Landesgeologie Swisstopo, Seftigenstrasse 264, Postfach, 3084 Wabern, Switzerland
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5Institute of Plant Sciences and Oeschger Centre for Climate Change Research, Altenbergrain 21,
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3013 Bern, Switzerland
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6Bayerisches Landesamt für Umwelt, Umweltdienstleistungen, Hof, 95030 Hof Saale, Germany
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fritz.schlunegger@unibe.ch
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Abstract
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This work summarizes the results of an interdisciplinary project where we aimed to explore the origin
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of overdeepenings or tunnel valleys through a combination of a gravimetry survey, drillings, dating and
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a synthesis of previously published work. To this end, we focused on the Bern area, Switzerland,
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situated on the northern margin of the European Alps. In this region, multiple advances of piedmont
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glaciers during the Quaternary glaciations resulted in the carving of the main overdeepening of the Aare
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River valley (referred to as Aare main overdeepening). This bedrock depression is tens of km long and
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up to several hundreds of meters to a few kilometers wide. We found that in the Bern area, this main
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overdeepening is made up of two >200 m-deep troughs that are separated by a c. 5 km-long and up to
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150 m-high transverse rocky ridge, interpreted as a riegel. The basins and the riegel are overlain by a
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>200 m- and 100 m-thick succession of Quaternary sediments, respectively. The bedrock itself is made
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up of a Late Oligocene to Early Miocene suite of consolidated clastic deposits, which are part of the
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Molasse foreland basin, whereas the Quaternary suite comprises a middle Pleistocene to Holocene
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succession of glacio-lacustrine gravel, sand and mud. A synthesis of published gravimetry data revealed
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that the upstream stoss side of the bedrock riegel is c. 50% flatter than the downstream lee side. In
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addition, information from >100 deep drillings reaching depths >50 m suggests that the bedrock riegel
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is dissected by an anastomosing network of slot canyons. We propose that these canyons established
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the hydrological connection between the upstream and downstream basins during their formation.
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Based on published modelling results, we interpret that the riegels and canyons were formed through
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incision of subglacial meltwater during a glacier’s decay state, when large volumes of meltwater were
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released. Such a situation has repeatedly occurred since the Middle Pleistocene Transition
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approximately 800 ka ago, when large and erosive piedmont glaciers began to advance far into the
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foreland. This resulted in the deep carving of the inner-Alpine valleys, and additionally in the formation
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of overdeepenings on the plateau on the northern margin of the Alps.
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1 Introduction
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Overdeepenings, or tunnel valleys (e.g., Jørgensen and Sandersen, 2006; Dürst Stucki et al., 2010), are
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bedrock depressions below the current fluvial base-level (Fischer and Häberli, 2012). The downstream
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closures of these basins have adverse slopes that generally dip in the upstream direction (Häberli et al.,
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2016). Because bedrock depressions with such characteristics are commonly found in previously
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glaciated areas (Figure 1), their formation has been interpreted as resulting from the erosional work of
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glaciers with support by subglacial meltwater (Wrigth, 1973; Herman and Braun, 2008; Egholm et al.,
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2009; Kehew et al., 2012; Patton et al., 2016; Liebl et al., 2023; and many others). Overdeepenings have
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been reported for the Quaternary from beneath the Greenland and Antarctic glaciers (Ross et al., 2011;
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Patton et al., 2016), the North Sea (Moreau et al., 2012, Lohrberg et al., 2022), North America (Wright,
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1973; Lloyd et al., 2023) and northern Europe including Scandinavia (Clark and Walder, 1994;
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Piotrowski, 1997; Kron et al., 2009). In addition, numerous Paleozoic successions entailing glaciogenic
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paleovalleys were also described (e.g. Douillet et al., 2012; Dietrich et al., 2021). Such erosional troughs
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have particularly been identified in the European Alps (Preusser et al., 2010), where >200 m-deep and
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several km-long bedrock depressions beneath the modern base-level occur in the Alpine valleys as well
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as on foreland plateaus on either side of this mountain belt (Preusser et al., 2010; Dürst Stucki and
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Schlunegger, 2013; Magrani et al., 2020). Geophysical surveys (e.g., Rosselli and Raymond, 2003;
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Reitner et al., 2010; Stewart and Lonergan, 2011; Stewart et al., 2013; Perrouty et al., 2015; Burschil et
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al., 2018; 2019; Ottesen et al., 2020) in combination with drillings (Jordan, 2010; Dürst Stucki et al.,
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2010; Büchi et al., 2017; 2018; Gegg et al., 2021; Bandou et al., 2022; 2023; Anselmetti et al., 2022;
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Schwenk et al., 2022a, b; Gegg and Preusser, 2023; Schaller et al., 2023) disclosed that such
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overdeepenings can be several kilometers wide and tens of kilometers long and that they are generally
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made up of individual sub-basins separated by bedrock swells, or riegels (Cook and Swift, 2012).
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Bedrock swells or riegels that separate bedrock depressions have also been reported from modern
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landscapes. In this context, a riegel is a rock wall, which is oriented across a previous glacier’s flow
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direction.
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An ensemble consisting of a riegel separating upstream and downstream basins has been considered as
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a classical feature of a landscape, which was repeatedly sculpted by glaciers during the past glaciations
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(Brocklehurst and Whipple, 2002; Brocklehurst et al., 2008; Cook and Swift, 2012; Steinemann et al.,
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2021). Observations from modern landscapes (see Figure 2 for examples in the Swiss Alps) have
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additionally shown that such bedrock swells or riegels may be cut by slot canyons or inner gorges
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(Montgomery and Korup, 2011; Steinemann et al., 2021), establishing a hydrological link between the
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upstream and downstream basins. These features were used as key information for invoking dissection
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by meltwater as an important erosional mechanism (Carter and Anderson, 2006; Steinemann et al.,
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2021). Although bedrock swells or riegels were reported as common features in overdeepenings (Gegg
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and Preusser, 2023), the occurrence of inner gorges or slot canyons (Figure 1) have only recently been
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disclosed (Bandou et al., 2023). It is the scope of this work to document such structures in an
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overdeepening and to discuss their importance for our understanding of how such depressions were
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formed.
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Figure 1: Architecture of a landscape sculpted by piedmont glaciers during glaciations. a) Situation
immediately following a full glacial period during which a piedmont glacier, which extended far
into the foreland, started to melt. As a result, large volumes of meltwater are produced in the
ablation zone close to the glacier’s tongue. This meltwater has the potential to contribute to the
erosional downwearing of the bedrock, and it can cause the incision of canyons into bedrock
riegels, which separate two overdeepened basins. b) During interglacial time periods, the
piedmont glaciers disappear, and small ice caps may be preserved in the higher parts of a mountain
belt. During this time, the overdeepened basin will be filled by lacustrine sediments and will
eventually host a lake. Modified after Schlunegger and Garefalakis (2023).
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Here, we summarize the results of an interdisciplinary project where we aimed at exploring the origin
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of tunnel valleys or overdeepenings using a combination of data collected through a gravimetry survey
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(Bandou et al., 2022, 2023), drillings (Reber and Schlunegger, 2016; Schwenk et al., 2022a, b) and
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dating (Schläfli et al., 2021; Schwenk et al., 2022a). We focus our study on the Bern area situated on
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the northern margin of the European Alps (Figure 3a). For this region, we draw a map of the bedrock
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structure combining the results of a gravimetry survey in the region (Bandou et al., 2023) with
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information obtained through drilling. This map shows that an overdeepened trough or a tunnel valley
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system, referred to as the Aare main overdeepening (Schwenk et al., 2022), is made up of two basins
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separated by a bedrock riegel, which itself is cut by one or multiple slot canyons. This structure has a
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similar geometry as the examples reported from the Alpine valleys, which points to similar processes
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resulting in their formation.
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2 Riegels and slot canyons in the Alpine valleys, and overdeepenings in the Bern area
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Bedrock swells between neighboring basins are common features in previously glaciated landscapes
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and have been reported from various regions around the globe (Anderson et al., 2006; Alley, 2019).
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They are particularly found in the European Alps (see Figure 2, for a few examples), and they have also
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been detected underneath active glaciers (Feigel et al., 2018; Nishiyama et al., 2019). In the Alps, most
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of the bedrock swells occur at the base of valleys (Figure 2) and are dissected by inner gorges or slot
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canyons that connect the upstream with the downstream basin (Hantke and Scheidegger, 1973; Valla et
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al., 2009; Montgomery and Korup, 2011). In addition, the Alpine bedrock riegels have a geometry
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where the upstream stoss side is flatter and has thus a lower dip angle than the downstream lee side.
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This is particularly the case for the swell in (Figure 2): the Aare valley (Figure 2a; dip of stoss side and
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lee sides <5° and >6°, respectively; Hantke and Scheidegger, 1973), the Trift valley (Figure 2b; c. 30°
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versus 40°; Steinemann et al., 2021), the Maggia valley (Figure 2e; 6° versus 40°), and the downstream
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end of the Urbach valley (Figure 2f; c. 20° versus 6°). In this work, we will document that the
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overdeepening beneath the city of Bern shares the same geometric properties as the ensemble of bedrock
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riegels and slot canyons in the Alpine valleys.
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The target overdeepening near Bern was sculpted by the Aare piedmont glacier with sources in the
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Central European Alps. From there, the Aare glacier flowed onto the Swiss Plateau over a distance of
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>20 km, and it merged with the Valais glacier north of Bern, at least during the Last Glacial Maximum
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(LGM) c. 20 ka ago (Figure 3b). Upstream of the city area of Bern, two bedrock depressions, referred
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to as the Gürbe tributary channel and the Aare main overdeepening (Figure 3c), form prominent basins
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that are between c. 150 (Gürbe trough; Geotest, 1995) and >250 m deep (Aare main trough, Kellerhals
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and Häfeli, 1984) and several kilometers wide (Bandou et al., 2022). Downstream of the city of Bern,
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the Aare main overdeepening splits into several distributary branches. Among these, the Bümpliz
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channel (‘Bü’ in Figure 3c) is the most prominent one with a depth >200 m (Schwenk et al., 2022a, b).
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Figure 2: Hillshade 2 m-SwissAlti3D DEM (© swisstopo) illustrating examples in the Alpine valleys where
bedrock riegels separate overdeepened basins situated farther upstream and downstream. The
coordinates refer to the Swiss coordinate system.
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The other depressions such as the Zollikofen trough are shallower and reach a depth of <150 m (Reber
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and Schlunegger, 2016). The study region also hosts the Meikirch overdeepening (labelled as ‘Me’ on
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Figure 3c), a nearly 200 m-deep trough (Dürst Stucki et al., 2010; Dürst Stucki and Schlunegger, 2003),
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which appears to be isolated from the rest of the overdeepening system (Reber and Schlunegger, 2016).
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Because the area between the northern termination of the Aare main overdeepening and the Meikirch
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trough is made up of exposed bedrock (Gerber, 1927), a connection between both depressions was ruled
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out (Reber and Schlunegger, 2016). The Aare main overdeepening itself is the most prominent trough
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in the city area of Bern and has a maximum depth of nearly 250 m (Reber and Schlunegger, 2016).
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The bedrock in the region comprises an amalgamated suite of Early Miocene Upper Marine Molasse
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(UMM) sandstone beds south of Bern. Sedimentological analyses showed that these sediments were
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Figure 3: Local setting illustrating the a) Alpine arc (modified from Bandou et al., 2023) with latitudes and
longitudes, b) the study area during the Last Glacial Maximum (LGM; map with isohypses of the
glacier’s surfaces taken from Bini et al., 2009), and c) the surface geomorphology (2 m-
SwissAlti3D DEM © swisstopo) together with the orientation of the Aare main overdeepening,
taken from Reber and Schlunegger (2016). The figure c) shows (i) the sections along which
gravity data was collected (black lines; Bandou et al., 2022; 2023), and (ii) the sites (white circles)
where sediments in drillings (Rehhag: Schwenk et al., 2022a, b; Meikirch: Welten, 1982; Preusser
et al., 2005; Schläfli et al., 2021: Brunnenbohrung: Kellerhals and Häfeli, 1984; Zwahlen et al.,
2021) and exposures (Thalgut: Welten, 1982; 1988; Schlüchter, 1989; Preusser and Schlüchter,
2004) were either dated with various techniques, or where existing ages were reconfirmed by a
subsequent analysis. Me=Meikirch overdeepening; Bü=Bümpliz trough. The numbers along the
figure margin refer to the Swiss coordinate system (CH1903+).
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deposited in a shallow marine, mostly coastal environment (Garefalakis and Schlunegger, 2019). In the
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region north of Bern, the bedrock is made up of a Late Oligocene to Early Miocene suite of Lower
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Freshwater Molasse (LFM) sandstones and mudstones (Isenschmid, 2019). These sediments were
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originally deposited in a fluvial environment (Platt and Keller, 1992; Isenschmid, 2019). The contact
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between the UMM and the LFM gently dips towards the south (Isenschmid, 2019), with the
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consequence that south of Bern, the base of the Aare main overdeepening might consist of LFM
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deposits, while most of the upper part of the overdeepening is laterally bordered by bedrock of the
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UMM.
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3 Dataset and Methods
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3.1 Compilation of gravity data
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The bedrock topography underneath the city area of Bern was already reconstructed in 2010 and then
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updated in 2016 based on information retrieved from thousands of drillings that is available from the
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Geoportal of the Canton Bern (Dürst Stucki et al., 2010; Reber and Schlunegger, 2016). Whereas such
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information yielded highly resolved spatial information on the bedrock geometry, particularly on its
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shallower <50 m-deep part (Reber and Schlunegger, 2016), reconstructions of the details for the deeper
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and thus central part of the Aare main overdeepening have been thwarted because of a lack of drilling
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information at that time. Here, we benefit from the results of a recent gravity survey conducted in the
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city area of Bern and information of new drillings >50 m deep (Bandou et al., 2023; Figure 3c). In
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particular, Bandou et al. (2023) measured the Bouguer gravity anomalies along 10 sections (black lines
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in Figure 3c). The obtained values were then subtracted from the regional gravity field yielding a
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residual gravity anomaly value at each site where gravity data was collected. Note that the Quaternary
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deposits and thus the overdeepening fill has a lower bulk density than the Oligo-Miocene sediments
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forming the bedrock in the region (Schwenk et al., 2022a; Bandou et al., 2022). Therefore, the
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occurrence of Quaternary sediments overlying an overdeepened trough result in a negative residual
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gravity anomaly (Kissling and Schwendener, 1990). Accordingly, a larger bulk mass of Quaternary
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sediments yields a stronger (and thus a more negative residual anomaly) signal than a fill with less
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Quaternary material (Kissling and Schwendener, 1990; Bandou et al., 2022). Following this concept,
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we compiled the residual anomaly data from Bandou et al. (2023) for each gravity profile and drafted a
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contour map where each line displays the same residual anomaly value. This map (Figure 4a) was drawn
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by hand, thereby considering the a-priori information about the orientation of the Aare main
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overdeepening (Reber and Schlunegger, 2016).
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3.2 Estimating the general shape of the bedrock topography
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For a selection of 6 cross-sections along which the residual gravity anomalies were well constrained,
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Bandou et al. (2023) reconstructed the cross-sectional shape of the overdeepenings using a 3D gravity
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software referred to as PRISMA (Bandou, 2023). This program uses multiple right-handed prisms to
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predict the gravity effect of a given structure underneath a point of interest. It bases on an analytical
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solution by Nagy (1966) and Banerjee and DasGupta (1977) and was conceptualized (Bandou, 2023)
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to model the general shape of an overdeepening fill. Upon applying this model, Bandou et al. (2023)
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particularly considered geophysical and geological a-priori information such as the residual gravity
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anomalies, the density contrasts between the bedrock and the Quaternary fill, the depth of bedrock
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encountered in drillings, and the already existing bedrock topography model by Reber and Schlunegger
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(2016). Here, we used the depth of the bedrock as unraveled upon applying the PRISMA routine
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(Bandou, 2023) to reconstruct the general course of the isohypses (i.e. the lines of constant elevation)
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of the bedrock underneath the city area of Bern (Figure 4b). Upon drawing this map, we considered that
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a trend towards less negative residual anomalies points towards a shallowing of the bedrock (Kissling
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and Schwendener, 1990; Bandou et al., 2023).
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3.3 Combining the results of the gravity survey with drilling data to reconstruct the details of the
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bedrock topography
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We used the existing bedrock topography map of Reber and Schlunegger (2016) as a basis where the
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isohypses were originally drawn every 10 meters, thereby using the information of thousands of
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drillings in the region. Because these drillings mainly penetrated the entire Quaternary sequence at the
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lateral margins of the Aare main overdeepening, the reconstruction of the shallower parts of the bedrock
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trough is precise. We updated this existing map with information about the general shape of the
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overdeepening retrieved through the gravity data by Bandou et al. (2023) (Figure 4), and we additionally
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considered the information of >100 drillings that were sunk >50 m deeply into the subsurface during
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the past years (Figure 5). Similar to Reber and Schlunegger (2016), we draw the isohypses by hand
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thereby inferring that changes in the direction of the contour lines and the depths of the bedrock were
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gradual. We finally combined the map displaying the geometry of the bedrock underneath the
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overdeepening with the elevation data offered by the 2 m-SwissAlti3D DEM (based on LIDAR data of
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swisstopo) to present the shape of the bedrock topography as shaded relief. We finally used this map as
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a basis to draw the cross-sections displayed in Figures 6 and 7.
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4 Results
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4.1 Patterns of residual gravity anomalies
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Based on the results of a gravity survey, Bandou et al. (2022; 2023) showed that the Quaternary fill of
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the Aare main overdeepening results in a residual gravity anomaly signal that ranges between c. -4.0
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and -0.5 mGal. In addition, they showed that the gravity signal of the Quaternary fill has a pattern with
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a distinct change from upstream to downstream. In particular, along the Gürbe-Aare transect (Figure
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3c), which also crosses a mountain ridge (Belpberg) made up of Molasse bedrock, the corresponding
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maximum residual anomalies signal ranges from c. -2.9 mGal in the Gürbe valley to c. -4.1 mGal in the
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Aare valley (Bandou et al., 2022). Farther downstream, the signals of the overdeepening fill decreases,
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Figure 4: Residual gravity anomalies and inferred thicknesses of Quaternary sediments. a) The contour lines
of the residual gravity signals (mGal) caused by the Quaternary fill of the Aare main
overdeepening are mainly based on gravity surveys along 10 sections (red lines; Bandou et al.,
2023). Here, more negative values imply a greater gravity signal and thus a larger bulk mass of
Quaternary sediments overlying the overdeepened trough (Kissling and Schwendener, 1990;
Bandou et al., 2022). b) Spatial distribution of Quaternary sediments, here expressed by the related
thickness pattern. These are mainly based on the results of gravity modelling, where Quaternary
mass and its spatial distribution was forward modelled until a best-fit between the modelled and
observed gravity signals of the Quaternary mass overlying the overdeepened trough was reached
(Bandou, 2023; Bandou et al., 2023). Note that only the residual gravity anomalies of the Airport,
Kehrsatz, Bern4, Bern2, Bremgarten and Bümpliz sections were modelled by Bandou et al.
(2023). The grid refers to the Swiss coordinate system (CH1903+).
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and the corresponding values change from c. -3.0 mGal (Airport profile) to approximately -1.5 and
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finally c. -1.0 mGal along the Kehrsatz and Wabern2 profiles, respectively (Figure 4a). The lowest
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residual anomaly signal with values between c. -0.5 mGal and -1 mGal were reported for the Wabern1
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profile (Bandou et al., 2023; Figure 3a). Farther downstream, the gravity signal related to the Quaternary
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fill increases again and reaches values between c. -1.0 and c. -2.0 mGal along the Bern sections, and
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then approximately -2.5 mGal along the Bremgarten section c. 2 km farther downstream. The residual
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anomaly data collected along the aforementioned gravity sections thus clearly depict the course of the
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Aare main overdeepening, which strikes SE-NW in the city area of Bern (Figures 3c, 4a). Towards the
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NW margin of the study area, a second overdeepening referred to as the Bümpliz side channel (Schwenk
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et al., 2022b) strikes SW-NE and converges with the Aare main overdeepening NW of Bern. The gravity
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signal of the Bümpliz sedimentary fill is less and reaches a value of c. -1.5 mGal (Figure 4a; Bandou et
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al., 2023).
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4.2 The thickness pattern of Quaternary sediments
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The thickest Quaternary suite can be found upstream and downstream of Bern (Figure 4b), where the
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Aare main overdeepening is between 4 and 5 km wide and > 200 m deep, consistent with drilling
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information (Bandou et al., 2023). In the city area of Bern, however, the main trough tends to become
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shallower. This is indicated by the thickness of the Quaternary sediments which becomes 100 m and
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possibly less (Figure 4b). We acknowledge that further 3D-gravity modelling would be needed to
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definitely verify such a claim. Although the data cover is low in this zone, the depth versus residual
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anomaly conversion could be constrained from nearby tie points. Accordingly, the resulting map
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displaying the thickness pattern of the Quaternary sediments suggests that the bedrock is situated at
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deeper levels forming a basin on either side of Bern, and that both depressions are separated by a
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bedrock swell or a riegel that is c. 150 m high but still buried by >100 m of Quaternary sediments
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(Figure 4b). Finally, the upstream side of the bedrock riegel dips gentler than the downstream side,
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which is twice as steep: on the stoss side, the residual gravity anomalies change from <-2.5 mGal to >-
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1.0 mGal over a downstream distance of c. 4 km whereas on the lee side, the same change in the gravity
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signal occurs over only 2 km. Given that the residual gravity signal is a direct response of the bulk mass
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of Quaternary sediments overlying the Molasse bedrock, and thus their volume supposing a lower
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density than the Molasse bedrock (Bandou et al., 2022; 2023), the differences in the upstream and
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downstream gradients of the residual gravity anomaly values disclose the contrasts in the dip angles of
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the bedrock topography.
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4.3 The consideration of deep drillings discloses the occurrence of slot canyons
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The reconstructed bedrock topography of the target region reveals a complex pattern (Figure 5), which
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can be described as a bedrock riegel that is dissected by multiple, partly anastomosing slot canyons or
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inner gorges (Bandou et al., 2023). At this stage, we cannot precisely reconstruct the number of the
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inferred canyons because we lack a high-resolution database of deep drillings (Figure 5). Yet, the
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discrepancy (Figure 6) between (i) a relatively low gravity signal particularly between the Wabern2 and
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the Bern sections (Figure 4a) and (ii) several drillings that reached the bedrock at much deeper levels
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that are >200 m below the surface (Figures 5, 6) can only be resolved by invoking the occurrence of a
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plateau at shallow elevations that is dissected by one or multiple slot canyons. These gorges are up to
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150 m deep and appear to connect the overdeepened basins upstream and downstream of the city area
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of Bern. In particular, south of Bern along the Aare profile (Figures 3b and 7a), the Aare main
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overdeepening is U-shaped in cross-section and displays two levels, each of which with steep lateral
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flanks and a flat base. While the upper flat base occurs at an elevation of c. 450 m a.s.l., the lower flat
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contact to the bedrock is situated at c. 250 m a.s.l. and thus approximately 200 m deeper than the upper
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level (Bandou et al., 2022). Approximately 5 km farther downstream along the Airport section (Figures
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3b, 7b), the cross-sectional geometry of the Aare main overdeepening maintains its generally U-shaped
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geometry with a base at an elevation between 200 and 250 m a.s.l. There, the base of the overdeepening
260
appears less flat than farther upstream, but we acknowledge that the density of drillings in the region
261
(Figure 5) and the resolution of the gravity data (Figure 4a, Bandou et al., 2023) is not high enough to
262
fully support this comparison. Upon approaching the city area of Bern, the base of the bedrock becomes
263
shallower and appears to evolve towards a plateau particularly between the Kehrsatz and Bern2 sections
264
(Figures 5, 6, 7c, d and e). This plateau is situated at an elevation of c. 400 m a.s.l. (dashed lines on
265
Figure 7) and dissected by multiple slot-canyons, some of which are up to 150 m deep and too narrow
266
to be detected by the gravity survey (Bandou al., 2023). Farther to the Northwest reaching the terminal
267
part of the Aare main overdeepening (Figure 3b), the trough widens again and gives way to a relatively
268
deep basin where the deepest part occurs at an elevation of 300 m a.s.l. and possibly even deeper
269
(Figures 5, 7f). This terminal basin appears to be connected with the Bümpliz side channel farther to
270
the SW. Yet the density of drillings is too low (Figure 5) to determine whether a possible bedrock swell
271
separates the Aare main overdeepening from the Bümpliz tributary channel (Figure 3b).
272
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273
274
Figure 5: Hillshade DEM, illustrating the bedrock topography of the Bern area, together with deep drillings
that either reached the bedrock (circles) or that ended in Quaternary sediments (diamonds). The
shallow drillings (<50 m) are not displayed on this map since the number is too large (more than
1000, please see Reber and Schlunegger, 2016). The isohypses were drawn for every 10 meters.
The coordinates along the figure margin refer to the Swiss coordinate system (CH1903+). The
sections shown on this map are used to illustrate the cross-sectional geometry of the
overdeepening beneath Bern (see next figures).
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5 Discussion
275
5.1 Subglacial origin and the role of subglacial meltwater
276
It is agreed upon in the literature that the formation of overdeepened basins can be understood as the
277
response of erosion by glaciers. As summarized in Figure 1, the main arguments that have been put
278
forward are (i) the depth of the base of these depressions, which are generally located below the current
279
fluvial base-level, and (ii) the occurrence of adverse slopes in the downstream direction of these basins
280
(Preusser et al., 2010; Patton et al., 2016; Alley et al., 2019; Magrani et al., 2022; Gegg and Preusser,
281
2023). As outlined in the previous sections, such geometric features are also encountered for the Aare
282
main overdeepening beneath the city of Bern. Therefore, it is not surprising that the origin of this
283
depression has repeatedly been interpreted as the response of the erosional processes of a glacier with
284
a source in the Central Alps of Switzerland (Dürst Stucki et al., 2010; Preusser et al., 2010; Reber and
285
Schlunegger, 2016; Magrani et al., 2022; Bandou et al., 2023). Furthermore, as already outlined by
286
Bandou et al. (2023) and further detailed in this work, the overdeepening underneath Bern can
287
additionally be subdivided into a southeastern and a northwestern sub-basin. These depressions are
288
separated from each other by a bedrock riegel or swell, which itself is dissected by one or multiple slot
289
canyons establishing a hydrological link between the upstream and downstream basins (Figures 1, 5
290
and 7).
291
292
293
Using geomorphic evidence in combination with information about rates of rock uplift and fluvial
294
incision into bedrock, Montgomery and Korup (2011) argued that an ensemble of bedrock riegels and
295
slot canyons were shaped over several glacial/interglacial periods, and that they were most likely formed
296
by subglacial meltwater during the decay of the glaciers and ice caps, when large volumes of meltwater
297
were released. Such processes were particularly invoked to explain the history of inner gorge formation
298
Figure 6: Example that illustrates of how we proceeded upon reconstructing the bedrock topography
beneath Bern. We started with the general shape of the bedrock topography using the gravity
signal of the bulk Quaternary mass as a basis (red line, and Figure 4b). Information from drillings
>50 m deep (circles and diamonds: see Figure 5 for explanation of colors) allowed then to
reconstruct the course and geometry of the slot canyons (blue line). The mass of their Quaternary
fill is too low to be identified by the gravity survey. This is the case because the strength of a
gravity signal decays exponentially with depth (see also Bandou et al., 2023, for further
explanations).
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in the Landquart and the Trift valleys (Figures 6b, 6c) situated in the Swiss Alps (Montgomery and
299
Korup, 2011; Steinemann et al., 2021).
300
301
302
As further examples, erosion by subglacial meltwater was put forward to explain the occurrence of inner
303
gorges at the margin of the Fennoscandian ice sheet (based on the pattern of surface exposure ages;
304
Jansen et al., 2014) and such a mechanism was used to explain (i) the origin of the deep channels on
305
the floor of the eastern English Channel, and (ii) the breaching of the bedrock swell at the Dover strait
306
during the aftermath of the Marine Isotope Stage (MIS) 12 or a later glaciation (Gupta et al., 2007;
307
Cohen et al., 2014; Gupta et al., 2017). In this context, Jansen et al. (2014) noted that a typical field
308
evidence for inferring a subglacial meltwater control includes (i) the occurrence of anastomosing
309
Figure 7: Sections through the Bern area, where the geometry of the bedrock is taken from the DEM
illustrated in Figure 5. The Aare section is taken from Bandou et al. (2022). See Figures 3 and 5
for location and orientation of sections.
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channels, (ii) undulating valley long profiles, and (iii) a topography that apparently amplifies the
310
hydraulic potential. The resolution of our data is at a larger scale than the thalweg irregularities, but
311
sufficient to display the anastomosing patterns of the slot canyons, with channels meandering, splitting
312
and merging again (Figure 5).
313
314
5.2 Formation through erosion by subglacial meltwater inferred from theory and modelling
315
A subglacial meltwater contribution to the controls on the formation of overdeepenings was inferred
316
based on theoretical relationships between meltwater runoff and the sediment transport capacity of
317
proglacial and subglacial streams (e.g., Boultoon and Hindmarsch, 1987; Alley et al., 1997; Herman et
318
al., 2011, Beaud et al., 2016). Because sediment transport increases exponentially with both the amount
319
and seasonality of meltwater runoff, Alley et al. (1997) interpreted that subglacial and proglacial
320
streams are among the most efficient sediment-transport mechanisms on Earth. This process peaks in
321
the ablation zone of a glacier, where surface melt reaches the bed and significantly contributes to the
322
generation of subglacial runoff. Yet, subglacial meltwater appears to play a minor role in contributing
323
to a sedimentary budget if the subglacial runoff has a negligible contribution from surface melt (Alley
324
et al., 1997). Finally, Cohen et al. (2023) showed that subglacial water is able to remove the sediment
325
from the base of a glacier and to further incise into bedrock provided that the pressure of the subglacial
326
meltwater and that of the ice overburden is at least the same, as also put forward by Boulton and
327
Hindmarsch (1987). The results from the model of Cohen et al. (2023), tailored to determine the location
328
of the subglacial drainage pathways, further suggest that such conditions most likely prevailed at the
329
front of piedmont glaciers and particularly during the decay when large volumes of meltwater were
330
available. In addition, the model predicts that under such circumstances, the locations of subglacial
331
meltwater pathways are likely to coincide with segments where high rates of glacial erosion occur
332
(Cohen et al., 2023). Therefore, it is not surprising that reaches with evidence for intense erosion by
333
both water and ice occur in the same area and are hydrologically connected with each other, as is the
334
case for the ensemble of overdeepened basins and slot canyons beneath Bern. Yet besides hydrological
335
conditions, the erosional resistance of bedrock plays an important role where a bedrock swell could
336
potentially form. This aspect is elaborated in the following paragraph.
337
338
5.3 The role of bedrock strength
339
The formation of riegels and basins is consensually understood as conditioned by differences in bedrock
340
strengths. This also concerns the controls on the size of a basin itself where bedrock with a low erosional
341
resistance tends to host a larger basin than lithologies where the erosional resistance is high (e.g.,
342
Magrani et al.., 2020; Gegg and Preusser, 2023). Following this logic, swells preferentially form in
343
locations where the bedrock has a lower erodibility than the rock units farther upstream and
344
downstream. This has been documented for the riegel in the Trift valley (Figure 2a), which separates
345
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an overdeepened basin upstream from a wide valley farther downstream (Steinemann et al., 2021).
346
There, the bedrock forming the ridge is made up of a banded, biotite-rich gneiss (Erstfeld gneiss),
347
whereas the bedrock upstream and downstream of the swell is cut by multiple faults and fractures, thus
348
offering a lower resistance to erosion. As another example, the bedrock riegel downstream of the
349
confluence between the Aare and Gadmen valleys (Figure 2a) is made up of the Quinten Formation
350
(Stäger et al., 2020). These limestones tend to have a higher mechanical strength (Kühni and Piffner,
351
2001) than the sandstones-marl alternations (North Helvetic Flysch; Stäger et al., 2020) downstream of
352
the bedrock swell, and the suite of sandstones, marls and dolomite beds upstream of it (Mels- and
353
Quarten Formations; Stäger et al., 2020). In the Bern area, the inferred riegel is underlain by Late
354
Miocene shallow marine sandstone (i.e. UMM), whereas the bedrock farther downstream comprises a
355
suite of Late Oligocene fluvial sandstones (i.e. LFM) and marl interbeds (Isenschmid, 2019). It is
356
postulated that the UMM sediments have a higher erosional resistance than the underlying LFM unit,
357
based on the observation that the UMM forms a cap rock in the region (Isenschmid, 2019). Accordingly,
358
the bedrock architecture in the Bern area is comparable to the examples explained above where the
359
UMM bedrock forming the swell has a larger erosional resistance than the LFM units at least
360
downstream of the riegel (Isenschmid, 2019). It is possible that Lower Freshwater Molasse (LFM)
361
deposits with a low erosional resistance also occur at the base of the overdeepening farther upstream of
362
the swell. We infer this from the Gurten drilling on the SW margin of the Wabern1 profile (Figure 4)
363
where the LFM bedrock was encountered at a depth of >300 m a.s.l. (Garefalakis and Schlunegger,
364
2019). This is indeed shallower than the basal part of the Aare main overdeepening along e.g., the
365
Airport profile (Figure 6b).
366
Presumably more important than the contrasts in bedrock erodibility: the bedrock swell underneath Bern
367
is situated just upstream of the confluence area between the Valais and Aare glaciers (Figure 3b). As
368
such, this situation shares many similarities with the examples in the Alpine valleys where the bedrock
369
swells are situated directly upstream (Figures 2c, 2d, 2e and 2f), directly downstream (Figures 2a, b) or
370
at the confluence (Figures 2g, h) between a tributary and a trunk valley. In the same sense, Lloyd et al.
371
(2023) found that overdeepened basins and, as a consequence, the occurrence of bedrock swells farther
372
downstream, are mainly situated in the confluence area of glacial valleys. In this case, the deep carving
373
into the bedrock would be the result of an acceleration of the ice flow in response to the increase in the
374
ice flux downstream of the confluence region (Herman et al., 2015). Alternatively, a bedrock riegel
375
could also form upstream of the confluence of two glaciers as is the case in the Maggia and Urbach
376
valleys (Figure 2e, f). Such a situation most likely also prevailed in the Bern area, at least during LGM
377
times. There, the damming of the Aare glacier by the much larger Valais glacier could have caused a
378
reduction of the flow velocity of the Aare glacier (Figure 3b). Consequently, the shear velocity and thus
379
the bedrock abrasion rates would decrease, thereby facilitating the preservation of a bedrock swell.
380
381
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5.4 Differences in the geometries between the exposed riegels and basins in the Alpine valleys, and
382
the overdeepening beneath Bern
383
Despite obvious similarities, there are also major differences between the geometric properties of the
384
overdeepening system beneath Bern and the currently exposed riegels and slot canyons in the Alpine
385
valleys (Figure 2 versus Figures 5 and 7). The most striking one is the occurrence of the riegel and inner
386
gorges approximately 50-100 m below the current base-level, and the absence of an obvious
387
continuation of the thalweg NW of Bern (Figure 3c). It is indeed very unlikely that the Aare main
388
overdeepening was linked with the Meikirch depression farther to the north (Figure 3c). We base this
389
interpretation on available geological maps (Gerber, 1927) and drillings (Reber and Schlunegger, 2016),
390
showing that the northern edge of the Aare main overdeepening and the Meikirch trough are separated
391
by Molasse bedrock with no evidence for connecting channels. Accordingly, the inferred interpretation
392
where the slot canyons beneath Bern were formed by subglacial meltwater requires a mechanism where
393
the meltwater is not only capable to incise into bedrock beneath a glacier, but also to escape the
394
depression by ascending nearly 200 m from the base of the overdeepening to the surface near the
395
glacier’s snout. Using Bernoulli’s principle as a basis (e.g., Batchelor, 1967), it was proposed that such
396
an ascent of subglacial meltwater was driven by the translation of large hydrostatic pressures into
397
hydrodynamic pressures at the downstream margin of a glacier (Dürst Stucki and Schlunegger, 2013).
398
In addition, such a mechanism is most effective at work where the surface slope of a glacier is steeper
399
than the adverse slope of an overdeepening (Hooke and Pohjola, 1994), as is commonly found in the
400
frontal part of a glacier (Figure 1a). Since the ratio between the densities of ice and water is >0.9
401
(Harvey, 2007), the inferred 200 m-rise of the meltwater requires a minimum hydrostatic pressure
402
corresponding to >250 m-thick ice to allow an upward water flow, and it conditions the occurrence of
403
a hydrologically closed subglacial channel network. Such a scenario is realistic, as in the Bern area the
404
Aare glacier was several hundred m thick during the past glaciations (Bini et al., 2009; Preusser et al.,
405
2011; Figure 3b). If this hypothesis is valid, then the thickness of the piedmont glaciers sets an
406
uppermost limit to the depth at which overdeepenings can be carved into the bedrock, mainly because
407
sufficient pressures are required for the subglacial meltwater to ascend to the surface from deeper levels.
408
Yet it is possible that the large porosities of nearly 20% in the Molasse sandstones (Keller et al., 1990)
409
could have facilitated the escape of subglacial meltwater to the groundwater. This could have caused a
410
reduction in static pressures, violating the inference of a closed system. However, we consider the
411
permeabilities of the Molasse sandstone beds (<1000 md, Keller et al., 1990) as low enough to consider
412
depressurization through meltwater runoff to the groundwater as negligible.
413
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414
415
Figure 8: Development of stable isotopes and Marine Isotope Stages (MIS) within a chronological
framework (Lisiecki and Raymo, 2005; Railsback et al., 2015) and glacial periods recorded in the
Plateau of the Swiss Alps (modified after Preusser et al., 2011; 2021). The age of the Möhlin
glaciation is taken from Dieleman et al. (2022). The age of the Thalgut section is based on pollen
records (Welten, 1982; 1984) and was subsequently described by Schlüchter (1989), yielding a
Holsteinian age for the basal part of the section. The chronological framework for the upper part
of this section was then updated by Preusser and Schlüchter (2004). The Holsteinian could either
correspond to MIS 9 (according to U/Th ages established for peat layers in the type section of the
Holsteinian at Bossel, Germany; Geyh and Müller, 2005) or to MIS 11 based on 40Ar/39Ar ages of
tephra (Roger et al., 1999). Following Koutsodendris et al. (2012) we preferentially use an age
assignment to MIS 11. Ages for the Meikirch section are based on pollen assemblages (Welten,
1982) and optically stimulated luminescence (OSL) ages by Preusser et al. (2005). The pollen
assemblages of Welten (1982) were subsequently reinterpreted by Schläfli et al. (2021). The ages
of the deposits encountered in the Brunnenbohrung are based on concentrations of 14C measured
in organic material at nearly the base of the drilling (Kellerhals and Häfeli, 1984; Zwahlen et al.,
2021). The chronological framework of the Rehhag drilling was established by Schwenk et al.
(2022a) using the results of feldspar luminescence dating conducted on two samples at the top of
a section, which is exposed in a quarry next to the Rehhag drilling. Finally, the chronology of the
Niederweningen drilling and sediments encountered in the Bülach and Strassberg troughs are
based on OSL signals measured in quartz minerals (Niederweningen: Dehnert et al., 2012; Bülach
and Strassberg troughs: Büchi et al., 2018).
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5.5 Chronological framework
416
A high-resolution chronological framework (e.g., Reber et al., 2014; Kamleitner et al., 2023a) has been
417
established from deposits of the LGM that occurred c. 20 ka ago (Ivy-Ochs et al., 2008; Kamleitner et
418
al., 2023b) (Figure 7). A relatively detailed chronology is also available for the first and second glacial
419
advances during the Birrfeld glaciation (Ivy-Ochs et al., 2008; Preusser, 2004; Preusser et al., 2007;
420
2011; Pfander et al., 2022). For previous glaciations, the chronological framework is less clear. Yet,
421
Preusser et al. (2011) summarized multiple evidence for proposing that the piedmont glaciers did
422
advance into the Alpine foreland between 185 and 130 ka, i.e. the Beringen glaciation (MIS 6, Figure
423
8), and that this advance into the foreland was larger than during the LGM. The age assignments to the
424
glaciations preceding MIS 6 are still debated. While the largest extent of the north Alpine glaciers (Most
425
Extensive Glaciation of the Swiss Foreland cf. Schlüchter, 1988) was assigned to the Möhlin glaciation
426
(Preusser et al., 2011) and recently dated to 500±100 ka and thus to MIS 12 through burial dating with
427
cosmogenic 26Al and 10Be (Dieleman et al., 2022), a re-evaluation of the reported concentrations of the
428
cosmogenic nuclides yielded an age that is more consistent with MIS 6 (Nørgaard et al., 2023). Yet we
429
favour the chronology by Dieleman et al. (2022) and the assignment to a MIS 12 age because it is better
430
supported by a-priori field-based information such as the results of detailed mapping. The ages of the
431
Habsburg and Hagenholz glaciations, which occurred between the Beringen and Möhlin glaciations,
432
are the least constrained. Whereas Preusser et al. (2011) considered the Hagenholz ice advance to
433
postdate MIS 7 (Figure 8), Büchi et al. (2018) and subsequently Preusser et al. al. (2021) rather
434
considered the Hagenholz glaciation to predate MIS 7 thereby following Keller and Kryass (2010).
435
The Quaternary fill of overdeepenings can now be placed into the aforementioned chronological
436
framework of glacial advances onto the Swiss plateau during the past glaciations (Figure 8). The
437
database is sparse, but the available ages imply that the oldest backfills that have been dated so far
438
postdate the Most Extensive Glaciation (or the Möhlin glaciation), dated to MIS 12 (Figure 8). This is
439
the case for the sedimentary fill of the Are main overdeepening where the occurrence of a Holsteinian
440
interglacial lacustrine sequence (Figure 8) was reported for the basal marls of the Thalgut section, which
441
could either correspond to MIS 9 (Roger et al., 1999) or MIS 11 (see discussion in Preusser et al., 2011;
442
Koutsodendris et al., 2012; and Schwenk et al., 2022a for discussion of ages). In addition, c. 6 km
443
farther downstream from the Thalgut section, nearly the entire sedimentary sequence of the Aare main
444
overdeeepening was encountered in the Brunnenbohrung drilling (Figure 3c) and was constrained to an
445
age postdating MIS 6 (Kellerhals and Häfeli, 1984; Zwahlen et al., 2021). The related sedimentary suite
446
could thus span the entire time interval between the Beringen and Birrfeld glaciations including the
447
Holocene (Bandou et al., 2022). Farther north of Bern, the Quaternary succession overlying the bedrock
448
has an age that is MIS 8 and older (Schwenk et al., 2022a), thus corresponding to the Habsburg
449
glaciation or any other glacial period pre-dating Habsburg (Figure 8). These ages are not precise enough
450
to reconstruct in detail the history of how and particularly when the overdeepenings were formed, but
451
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they are consistent with the chronologies established for other overdeepening fills (Figure 8). In
452
particular, most published ages do support an interpretation where the deep troughs were originally
453
formed after the Middle Pleistocene Transition (Schlüchter, 2004) and thus during the same period
454
when the U-shaped Alpine valleys were carved (Häuselmann et al., 2007; Valla et al., 2011). This was
455
also the same time when the base-level in the northern margin of the Swiss Plateau lowered at the
456
highest rates (Claude et al., 2019). Apparently, the change in the frequency of glacial-interglacial cycles
457
from a 40 ka- to a 100 ka-periodicity, which occurred c. 800 ka ago, not only resulted in rapid glacial
458
erosion (Pedersen and Egholm, 2013) and in the deep glacial carving of U-shaped valleys in the Alps
459
(Häuselmann et al., 2007, Valla et al., 2011), but also in the formation of overdeepenings with complex
460
geometries including basins, riegels and slot canyons in the foreland.
461
462
6 Conclusions
463
Bedrock riegels separating upstream and downstream basins are common features in modern Alpine
464
valleys, and they are likely to be encountered in overdeepenings. In addition, we propose that these
465
riegels occur as ensembles together with slot canyons that cut through the swells and establish a
466
hydrological link between the upstream and downstream basins. We suggest this based on our
467
reconstruction of the bedrock topography of the Aare main overdeepening in the Bern area, and we
468
propose that such ensembles of basins, riegels and slot canyons also occur in other Alpine
469
overdeepenings such as the Rhone, Rhine and Inn valleys (Figure 9). We suggest that these slot canyons
470
were formed through incision by glacial meltwater during the decaying state of a glacier when large
471
volumes of meltwater were available. For the bedrock swell underneath Bern, the resolution of the
472
dataset presented in this work does not allow to locate and reconstruct the precise course of the inferred
473
slot canyons. Yet the presented reconstruction of the bedrock topography does reconcile (i) the
474
occurrence of a low residual gravity anomalies in the Bern area (Figure 4a), which implies a relatively
475
low bulk mass of Quaternary sediments, and (ii) the depth at which Quaternary sediments were
476
encountered in drillings (Figures 5, 6). In addition, in many Alpine valleys, such structures appear to be
477
preferentially formed in the confluence area between two glacial valleys and where the bedrock has a
478
relatively low erodibility. We posit this hypothesis for the overdeepening below the Bern area, where
479
such a bedrock swell appears to be situated just upstream of the confluence between the Aare and Valais
480
glaciers, at least during LGM times and possibly during previous glaciations. In addition, the inferred
481
bedrock riegel beneath Bern is located where the bedrock has a lower erodibility than downstream and
482
possibly upstream, at least in the basal part of the trough. Yet, we acknowledge that an improved
483
understanding about the origin of such structures requires more information particularly on the
484
chronology of glacial advances and the overdeepening fills.
485
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486
487
488
Acknowledgement
489
This work was financially supported by the Swiss National Science Foundation (project No.
490
200021_175555) with contributions from the Stiftung Landschaft und Kies, swisstopo and the
491
Gebäudeversicherung Bern GVB.
492
493
Data availability
494
All data used in this paper can be ordered by the Authorities of the Canton Bern and by the authors on
495
request.
496
497
Autor contributions
498
EK designed the study, together with FS and DB. DB collected the gravity data and processed them,
499
with support by UM and EK. FS wrote the paper and conducted the analyses and interpretation of the
500
Figure 9: Sections showing the patterns of overdeepenings from upstream to downstream for a) the Inn
valley, b) the Rhine valley, c) the Rhone valley and d) the Aare valley in Bern area. The examples
of the Inn, the Rhine and the Rhone valleys are taken from Hinderer (2001), whereas the section
along the Aare valley is a modified version of Bandou et al. (2023) and bases on the data presented
in Figure 5. The data from the Aare valley covers a short distance only, but it shows a striking
similarity to the riegels in the large Alpine valleys. Therefore, it is quite likely that the other riegels
are also dissected by narrow channels and that all settings share a similar origin.
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data. RB drafted the bedrock topography map. PS, MS, DM and GD contributed to the discussion. All
501
authors approved the article.
502
503
Competing interests
504
The authors declare that they have no conflict of interest.
505
506
References
507
Alley, R.B., Cuffey, K.M., Evenson, E.B., Strasser, J.C., Lawson, D.E., and Larson, G.J.: How glaciers
508
entrain and transport basal sediment: physical constraints. Quat. Sci. Rev., 16, 1017-1038, 1997.
509
Alley, R., Cuffey, K., and Zoet, L.: Glacial erosion: Status and outlook. Ann. Glaciol., 60, 1–13.
510
https://doi.org/10.1017/aog.2019.38, 2019.
511
Anderson, R.S., Molnar, P., and Kessler, M.A.: Features of glacial valley profiles simply explained. J.
512
Geophys. Res., Earth Surface, 111, F01004, doi:10.1029/2005JF000344, 2006.
513
Anselmetti, F., Bavec, M., Crouzet, C., Fiebig, M., Gabriel, G., Preusser, F., Ravazzi, C., and Dove
514
team.: Drilling Overdeepened Alpine Valleys (ICDP-DOVE): quantifying the age, extent, and
515
environmental impact of Alpine glaciations. Sci. Drill., 31, 51–70. https://doi.org/10.5194/sd-
516
31-51-2022, 2022.
517
Bandou, D.: Gravi3D: A 3D forward modelling software using gravity data to resolve the geometry of
518
subsurface objects, https://zenodo.org/doi/10.5281/zenodo.8153258, 2023.
519
Bandou, D., Schlunegger, F., Kissling, E., Marti, U., Schwenk, M., Schläfli, P., Douillet, G., and Mair,
520
D.: Three-dimensional gravity modelling of a Quaternary overdeepening fill in the Bern area of
521
Switzerland discloses two stages of glacial carving. Scientific Rep., 12, 1441,
522
https://doi.org/10.1038/s41598-022-04830-x, 2022.
523
Bandou, D., Schlunegger, F., Kissling, E., Marti, U., Reber, R., and Pfander J.: Overdeepenings in the
524
Swiss plateau: U-shaped geometries underlain by inner gorges. Swiss. J. Geosci., 116, 19,
525
https://doi.org/10.1186/s00015-023-00447-y, 2023.
526
Banerjee, B., and Gupta, S.P.: Gravitational attraction of a rectangular parallelepiped. Geophysics, 42,
527
1053–1055, 1977.
528
Batchelor, G. K.: An introduction to fluid dynamics (p. 615). Cambridge Univ. Press, 1967.
529
Beaud, F., Flowers, G.E., and Venditti, J.G.: Efficacy of bedrock erosion by subglacial water flow. Earth
530
Surf. Dyn., 4, 125-145, https://doi.org/10.5194/esurf-4-125-2016, 2016.
531
Bini, A., et al.: Die Schweiz während des letzteiszeitlichen Maximums (LGM) 1:500'000. Bundesamt
532
für Landestopografie swisstopo, Bern, Switzerland, 2009.
533
Boulton, G.S., and Hindmarsh, R.C.A.: Sediment deformation beneath glaciers: rheology and
534
geological consequences. J. Geophys. Res. 92, 9059-9082, 1987.
535
https://doi.org/10.5194/egusphere-2024-683
Preprint. Discussion started: 14 May 2024
c
Author(s) 2024. CC BY 4.0 License.
23
Brocklehurst, S.H., and Whipple, K.X.: Glacial erosion and relief production in the eastern Sierra
536
Nevada, California. Geomorphology 42, 1–24, 2002.
537
Brocklehurst, S.H., Whipple, K.X., and Foster, D.: Ice thickness and topographic relief in glaciated
538
landscapes of the western USA. Geomorphology, 97, 35-51,
539
https://doi.org/10.1016/j.geomorph.2007.02.037, 2008.
540
Büchi, M. W., Frank, S. M., Graf, H. R., Menzies, J., and Anselmetti, F. S.: Subglacial emplacement of
541
tills and meltwater deposits at the base of overdeepened bedrock troughs. Sedimentology, 64,
542
685. https://doi.org/10.1111/sed.12319, 2017.
543
Büchi, M., Graf, H.R., Haldimann, P., Lowick, S.E. and Anselmetti, F.S.: Multiple Quaternary erosion
544
and infill cycles in overdeepened basins of the northern Alpine foreland. Swiss J. Gesci., 111,
545
133-167, https://doi.org/10.1007/s00015-017-0289-9, 2018.
546
Burschil, T., Buness, H., Tanner, D.C., Wiedlandt-Schuster, U., Ellwanger, D., and Gabriel, G.: High-
547
resolution reflection seismics reveal the structure and the evolution of the Quaternay glacial
548
Tannwald Basin. Near Surf. Geophys., 16, 593-610, https://doi.org/10.1002/nsg.12011, 2018.
549
Burschil, T., Tanner, D., Reitner, J., Buness, H., and Gabriel, G.: Unravelling the complex stratigraphy
550
of an overdeepened valley with high-resolution reflection seismics: The Lienz Basin (Austria),
551
Swiss J. Geosci., 112, 341–355, https://doi.org/10.1007/s00015-019-00339-0, 2019.
552
Carter, C.L., and Anderson, R.S.: Fluvial erosion of physically modeled abrasion-dominated slot
553
canyons. Geomorphology, 81, 89-113, https://doi.org/10.1016/j.geomorph.2006.04.006, 2006.
554
Clark, P.U., and Walder, J.S. Subglacial drainage, eskers, and deforming beds beneath the Laurentide
555
and Eurasian ice sheets. Geol. Soc. Amer. Bull., 106, 304-314, https://doi.org/10.1130/0016-
556
7606(1994)106<0304:SDEADB>2.3.CO;2, 1994.
557
Claude, A., Akçar, N., Ivy-Ochs, S., Schlunegger, F., Kubik, P.W., Christl, M., Vockenhuber, C.,
558
Kuhlemann, A., Rahn, M., and Schlüchter, C.: Changes in landscape evolution patterns in the
559
northern Swiss Alpine Foreland during the mid-Pleistocene revolution. GSA Bull., 131, 2056-
560
2078, https://doi.org/10.1130/B31880.1, 2019.
561
Cohen, K. M., Gibbard, P. L., and Weerts, H. J. T.: North Sea palaeogeographical reconstructions for
562
the last 1 Ma. Neth. J. Geosci. 93, 7–29, 2014.
563
Cohen, D., Jouvet, G., Zwinger, T., Landgraf, A., and Fischer, U.H.: Subglacial hydrology from high-
564
resolution ice-flow simulaitons of the Rhine Glacier during the Last Glacial Maximum: a proxy
565
for glacial erosion. E&G Quat. Sic. J., 72, 189-201, https://doi.org/10.5194/egqsj-72-189-201,
566
2023.
567
Cook, S. J., and Swift, D. A.: Subglacial basins: Their origin and importance in glacial systems and
568
landscapes. Earth-Science Rev., 115, 332–372,
569
https://doi.org/10.1016/j.earscirev.2012.09.009, 2012.
570
https://doi.org/10.5194/egusphere-2024-683
Preprint. Discussion started: 14 May 2024
c
Author(s) 2024. CC BY 4.0 License.
24
Dehnert, A., Lowick, S.E., Preusser, F., Anselmetti, F.S., Drescher-Schneider, R., Graf, H.R., Heller,
571
F., Horstmeyer, H., Kemna, H.A., Nowaczyk, N.R., Züger, and Furrer, H.: Evolution of an
572
overdeepened trough in the northern Alpine Foreland at Niederweningen, Switzerland. Quat.
573
Sci. Rev., 34, 127-145, https://doi.org/10.1016/j.quascirev.2011.12.015, 2012.
574
Delaney, I., Anderson, L, and Herman, F.: Modelling the spatially distributed nature of subglacial
575
sediment transport and erosion. Earth Surf. Dyn., 11, 663-680, https://doi.org/10.5194/esuf-11-
576
663-2023, 2023.
577
Dieleman, C., Christl, M., Vockenhuber,C., Guatschi, P., Graf, H.R., and Akçar, N.: Age of the Most
578
Extensive Glaciation in the Alps. Geosciences, 12, 39,
579
https://doi.org/10.3390/geosciences12010039, 2022.
580
Dietrich, P., Griffis, N. P., Le Heron, D. P., Montañez, I. P., Kettler, C., Robin, C., and Guillocheau, F.:
581
Fjord network in Namibia: A snapshot into the dynamics of the late Paleozoic glaciation.
582
Geology, 49, 1521-1526, https://doi.org/10.1130/G49067.1, 2021.
583
Douillet, G., Ghienne, J. F., Géraud, Y., Abueladas, A., Diraison, M., and Al-Zoubi, A.: Late Ordovician
584
tunnel valleys in southern Jordan. Geol. Soc. London Spec. Publ., 368, 275-292,
585
https://doi.org/10.1144/sp368.4, 2012.
586
Dürst Stucki, M., Reber, R., and Schlunegger, F.: Subglacial tunnel valleys in the Alpine foreland: An
587
example from Bern, Switzerland. Swiss J. Geosci., 103, 363–374.
588
https://doi.org/10.1007/s00015-010-0042-0, 2010.
589
Dürst-Stucki, M., and Schlunegger, F.: Identification of erosional mechanisms during past glaciations
590
based on a bedrock surface model of the central European Alps. Earth Planet. Sci. Lett., 384,
591
57–70. https://doi.org/10.1016/j.epsl.2013.10.009, 2013.
592
Egholm, D.L., Nielsen, S., Pedersen, V., and Lesemann, J.: Glacial effects limiting mountain height.
593
Nature, 460, 884-887, https://doi.org/10.1038/nature08264, 2009.
594
Fischer, U., and Häberli, W.: Overdeepenings in glacial systems: Processes and uncertainties. Eos, 93,
595
35, 341-341, https://doi.org/10.1029/2012EO350010, 2012.
596
Garefalakis, P., and Schlunegger, F.: Tectonic processes, variations in sediment flux, and eustatic sea
597
level recorded by the 20 Myr old Burdigalian transgression in the Swiss Molasse basin. Solid
598
Earth, 10, 2045-2972, https://doi.org/10.5194/se-10.2045-2019, 2019.
599
Gees: Spühlbohrung Bern B1. Wasser und Energiewirtschaft des Kantons Bern, 1974.
600
Gegg, L., Deplazes, G., Keller, L., Madritsch, H., Spillmann, T., Anselmetti, F. S., and Büchi, M.W.:
601
3D morphology of a glacially overdeepened trough controlled by underlying bedrock geology.
602
Geomorphology, 394, 107950. https://doi.org/10.1016/j.geomorph.2021.107950, 2021.
603
Gegg, L., and Preusser, F.: Comparison of overdeepened structures in formerly glaciated areas of the
604
northern Alpine foreland and northern central Europa. E&G Quat. Sci. J., 72, 23–36.
605
https://doi.org/10.5194/egqsj-72-23-2023, 2023.
606
https://doi.org/10.5194/egusphere-2024-683
Preprint. Discussion started: 14 May 2024
c
Author(s) 2024. CC BY 4.0 License.
25
Geotest: Grundlagen für Schutz und Bewirtschaftung der Grundwasser des Kantons Bern.
607
Hydrogeologie Gürbetal und Stockental. Wasser- und Energiewirtschaftsamt des Kantons Bern
608
WEA, 123 pp, 1995.
609
Gerber, E.: Geologische Karte von Bern und Umgebung 1:25'000. Kümmerli und Frei, Bern, 1927.
610
Geyh, M.A., and Müller, H.: Palynological and geochronological study of the
611
Holsteinian/Hoxnian/Landos interglacial, in: The Climate of Past Interglacials, edited by:
612
Sirocko, F., Elsevier, Boston, MA, 387-396, 2007.
613
Gisler, C., Labhart, T., Spillmann, P., Herwegh, M., Della Valla, G., Trüssel, M., and Wiederkehr, M.:
614
Erläuterungen. Geologischer Altlas der Schweiz 1:25’000, 1210 Innertkirchen, Schweiz. Geol.
615
Komm., 2020.
616
Gupta, S., Collier, J.S., Palmer-Felgate, A., and Potter, G.: Catastrophic flooding origin of shelf valley
617
systems in the English Channel. Nature, 448, 342-345. https://doi.doi:10.1038/nature06018,
618
2007.
619
Gupta, S., Collier, J. S., Garcia-Moreno, D., Oggioni, F., Trentesaux, A., Vanneste, K., De Batist, M.,
620
Camelbeeck, T., Potter, G., Van Vliet-Lanoë, B., and Arthur, J. C. R.: Two-stage opening of
621
the Dover Strait and the origin of island Britain. Nat. Comm., 8, 15101.
622
https://doi.org/10.1038/ncomms15101, 2017.
623
Häberli, W., Linsbauer, A., Cochachin, A., Salazar, C., and Fischer, U.H.: On the morphological
624
characteristics of overdeepenings in high-mountain glacier beds. Earth Surf. Proc. Landf., 41,
625
1980–1990, https://doi.org/10.1002/esp.396, 2016.
626
Hantke, R., and Scheidegger, A. E.: Zur Genese der Aareschlucht (Berner Oberland, Schweiz). Geogr.
627
Helv., 48, 120–124. https://doi.org/10.5194/gh-48-120-1993, 1993.
628
Harvey, A. H.: Properties of Ice and Supercooled Water, in: CRC Handbook of Chemistry and Physics
629
(97th ed.), edited by Haynes, W. Lide, D. R. and Bruno, T., Boca Raton, FL: CRC Press., 2017.
630
Häuselmann, P., Granger, D.E., Jeannin, P.-Y., and Lauritzen, S.-E.: Abrupt glacial valley incision at
631
0.8 Ma dated from cave deposits in Switzerland. Geology, 35, 143-146,
632
https://doi.org/10.1130/G23094A, 2007.
633
Herman, F., and Braun, J.: Evolution of the glacial landscape of the Southern Alps of New Zealand:
634
insights from a glacial erosion model. J. Geophys. Res. 113, F02009,
635
https://doi.org/10.1029/2007JF000807, 2008.
636
Herman, F., Beaud, F., Champagnac, J.-D., Lemiuex, J.-M., and Sternai, P.: Glacial hydrology and
637
erosion patterns: a mechanism for carving glacial valleys. Earth Planet. Sci. Lett. 310, 498–508,
638
https://doi.org/10.1016/j.epsl.2011.08.022, 2011.
639
Herman, F., Beyssac, O., Brughelli, M., Lane, S.N., Leprince, S., Adatte, T., Lin, J.Y.Y., Avouac, J.-
640
P., and Cox, S.C.: Erosion by an Alpine glacier. Science, 350, 193-195.
641
https://doi.org/10.1126/science.aab2386.
642
https://doi.org/10.5194/egusphere-2024-683
Preprint. Discussion started: 14 May 2024
c
Author(s) 2024. CC BY 4.0 License.
26
Hinderer, M. Late Quaternary denudation of the Alps, valley and lake fillings and modern river loads.
643
Geodinamica Acta, 14, 231-263, https://doi.org/10.1080/09853111.2001.11432446, 2001.
644
Hooke, R.L., and Pohjola, V.A.: Hydrology of a segment of a glacier situated in an overdeepening,
645
Storglaciären, Sweden. J. Glaciol., 40, 140-148.
646
Isenschmid, C.: Die Grenze Untere Süsswassermolasse/Obere Meeremolasse als Schlüssel zur Tektonik
647
in der Region Bern. Mitt. Natf. Ges. Bern, 76, 108–133, 2019.
648
Ivy-Ochs, S., Kerschner, H., Reuther, A., Preusser, F., Heine, K., Maisch, M., Kubik, P. W., and
649
Schlüchter, C.: Chonology of the last glacial cycle in the European Alps. J. Quat. Sci., 23, 559–
650
573. https://doi.org/10.1002/jqs.1202, 2008.
651
Jansen, J.D., Codilean, A.T., Stroeven, A.P., Fabel, D., Hättestrand, C., Kleman, J., Harbor, J.M.,
652
Heyman, J., Kubik, P.W., and Xu, S.: Inner gorges cut by subglacial meltwater during
653
Fennoscandian ice sheet decay. Nat. Comm., 5, 3815, https://doi.org/10.1038/ncomms4815,
654
2014.
655
Jørgensen, F., and Peter B.E. Sandersen, P.B.E.: Buried and open tunnel valleys in Denmark—erosion
656
beneath multiple ice sheets. Quat. Sci. Rev., 25, 1339–1363,
657
https://doi.org/10.1016/j.quascirev.2005.11.006, 2006.
658
Jordan, P.: Analysis of overdeepened valleys using the digital elevation model of the bedrock surface
659
of northern Switzerland. Swiss J. Geosci., 103, 375–384, https://doi.org/10.1007/s00015-010-
660
0043-z, 2010.
661
Kamleitner, S., Ivy-Ochs, S., Manatschal, L., Akçar, N., Christl, M., Vockenhuber, C., Hajdas, I., Synal,
662
H.-A.: Last glacial maximum glacier fluctuations on the northern Alpine foreland:
663
Geomorphological and chronological reconstructions from the Rhine and Reuss glacier
664
systems. Geomorphology, 423, 108548. https://doi.org/10.1016/j.geomorph.2022.108548,
665
2023a.
666
Kamleitner, S., Ivy-Ochs, S., Salcher, B., and Reitner, J.M.: Reconstructing basal ice flow patterns of
667
the Last Maximum Rhine glacier (northern Alpine foreland) based on streamlined subglacial
668
landforms. Earth Surf. Proc. Landforms, 49, 746-769, https://doi.org/10.1002/esp.5733, 2023b.
669
Kehew, A.E., Piotrowski, J.A., and Jørgensen, F.: Tunnel valleys: concepts and controversies – a
670
review. Earth-Sci. Rev. 113, 33–58, https://doi.org/10.1016/j.earscirev.2012.02.002, 2012.
671
Keller, B., Bläsi, H.-R., Platt, N., Mozley, P., and Matter, A.: Sedimentäre Architektur der distalen
672
Unteren Süsswassermolasse und ihre Beziehung zur Diagenese und den petrophysikalischen
673
Eigenschaften am Beispie der Bohrungen Langenthal. NTB 90-41, Landeshydrologie und –
674
geologie, Geologische Berichte, 13, 100 pp, 1990.
675
Keller, O. and Krayss, E.: Mittel- und spätpleistozäne Stratigraphie und Morphogenese in
676
Schlüsselregionen der Nordschweiz. E&G Quat. Sci. J., 59, 88–119, 2010.
677
https://doi.org/10.5194/egusphere-2024-683
Preprint. Discussion started: 14 May 2024
c
Author(s) 2024. CC BY 4.0 License.
27
Kellerhals, P., and Häfeli, C.: Brunnenbohrung Münsingen. Geologische Dokumentation des Kantons
678
Bern, WEA-Geologie, Beilage Nr. 2, 7 pp, 1984.
679
Kissling, E., Schwendener, H.: The Quaternary sedimentary fill of some Alpine valleys by gravity
680
modeling. Eclogae Geol. Helv., 83, 311–321, 1990.
681
Koutsodendris, A., Pross, J., Müller, U. C., Brauer, A., Fletcher, W. J., Kühl, N., Kirilova, E., Verhagen,
682
F. T., Lücke, A., and Lotter, A. F.: A short-term climate oscillation during the Holsteinian
683
interglacial (MIS 11c): An analogy to the 8.2ka climatic event?, Global Planet. Chang., 92–93,
684
224–235, https://doi.org/10.1016/j.gloplacha.2012.05.011, 2012.
685
Krohn, C. F., Larsen, N. K., Kronborg, C., Nielsen, O. B., and Knudsen, K.: L. Litho- and
686
chronostratigraphy of the Late Weichselian in Vendysssel, northern Denmark, with special
687
emphasis on tunnel-valley infill in relation to a receding ice margin. Boreas, 38, 811–833,
688
https://doi.org/10.1111/j.1502-3885.2009.00104.x, 2009.
689
Kühni, A., and Pfiffner, O.A.: The relief of the Swiss Alps and adjacent areas and its relation to lithology
690
and structure: topographic analysis from a 250-m DEM. Geomorphology, 41, 285-307,
691
https://doi.org/10.1016/S0169-555X(01)00060-5, 2001.
692
Liebl, M., Robl, J., Hergarten, S., Egholm, D.L., and Stüwe, K.: Modeling large-scale landform
693
evolution with a stream power law for glacial erosin (OpenLEM v37): benchmarking
694
experiments against a more process-based description of ice flow (iSOSIA v3.4.3). Geosci.
695
Model Dev., 16, 1315-1343, https:/doi.org/10.5194/gmd-16-1315-2023, 2023.
696
Lisiecki, L.E., and Raymo, M.E.: A Plicoene-Pleistocene stack of 57 globally distributed benthic d18O
697
records. Paleoceanography, 20, PA1003, https://doi.org/10.1029/2004PA001071, 2005.
698
Lloyd, C., Clark, C.D., and Swift, D.A.: The effect of valley confluence and bedrock geology upon the
699
location and depth of glacial overdeepenings. Geogr. Ann.: Series A, Phys. Geogr.,
700
https://doi.org/10.1080/04353676.2023.2217047, 2023.
701
Lohrberg, A., Schneider von Deimling, J., Grob, H., Lenz, K.-F., and Krastel, S.: Tunnel valleys in the
702
southeastern North Sea: More data, more complexity. E&G Quat. Sci. J., 71, 267–274,
703
https://doi.org/10.5194/egqsj-71-267-2022, 2022.
704
Moreau, J., Huuse, M., Janszen, A., van der Vegt, P., Gibbard, P. L., and Moscriello, A.: The
705
glaciogenic unconformity of the southern North Sea. Geol. Soc. London Spec. Publ., 368, 99.
706
https://doi.org/10.1144/SP368.5, 2012.
707
Montgomery, D. R., and Korup, O.: Preservation of inner gorges through repeated Alpine glaciations.
708
Nat. Geosci., 4, 62-67. https://doi.org/10.1038/Ngeo1030, 2011.
709
Nagy, D.: The gravitational attraction of a right rectangular prism. Geophyscis, 31, 362–271, 1996.
710
Nishiyama, R., Ariga, A., Ariga, T., Lechmann, A., Mair, D., Pistillo, C., Scampoli, P., Valla, P.G.,
711
Vladymyrov, M., Ereditato, A., and Schlunegger, F.: Bedrock sculpting under an active alpine
712
https://doi.org/10.5194/egusphere-2024-683
Preprint. Discussion started: 14 May 2024
c
Author(s) 2024. CC BY 4.0 License.
28
glacier revealed from cosmic-ray muon radiography. Sci. Rep., 9, 6970,
713
https://doi.org/10.1038/s41598-019-43527-6, 2019.
714
Nørgaard, J., Jansen, J.D., Neuhuber, S., Ruszkiczay-Rüdiger, Z., Knudsen, M.F.: P-PINI: A
715
cosmogenic nuclide burial dating method for landscapes undergoing non-steady erosion. Quat.
716
Geochron., 74, 101420, https://doi.org/10.1016/j.quageo.2022.101420, 2023.
717
Ottesen, D., Stewart, M., Brönner, M., and Batchelor, C. L.: Tunnel valleys of the central and northern
718
North Sea (56°N to 62°N): Distribution and characteristics, Mar. Geol., 425, 106199,
719
https://doi.org/10.1016/j.margeo.2020.106199, 2020.
720
Patton, H., Swift, D. A., Clark, C. D., Livingstone, S. J., and Cook, S. J.: Distribution and characteristics
721
of overdeepenings beneath the Greenland and Antarctic ice sheets: Implications for
722
overdeepening origin and evolution. Quat. Sci. Rev., 148, 128–145,
723
https://doi.org/10.1016/j.quascirev.2016.07.012, 2016.
724
Pedersen, V.K., and Egholm, D.L.: Glaciations in response to climate variations preconditioned by
725
evolving topography. Nature, 493, 206-201, https://doi.org/10.1038/nature11786, 2013.
726
Perrouty, S., Moussirou, B., Martinod, J., Banvalot, S., Carretier, S., Gabalda, G., Monod, B., Hérail,
727
G., Regard, V., and Remy, D.: Geometry of two glacial valleys in the northern Pyrenees
728
estimated using gravity data, Comptes Rendus Geosci., 347, 13–23,
729
https://doi.org/10.1016/j.crte.2015.01.002, 2015.
730
Pfander, J., Schlunegger, F., Serra, E., Gribenski, N., Garefalakis, P., and Akçar, N.: Glaciofluvial
731
sequences recording the Birrfeld Glaciation (MSS 5d-2) in the Bern area, Swiss Plateau. Swiss
732
J. Geosci., 115, 12, https://doi.org/10.1186/s00015-022-00414-z, 2022.
733
Piotrowski, J.A.: Subglacial hydrology in north-western Germany during the last glaciation:
734
Groundwater flow, tunnel valleys and hydrological cycles. Quat. Sci. Rev., 16, 169-185,
735
https://doi.org/ 10.1016/S0277-3791(96)00046-7, 1997.
736
Preusser, F., and Schlüchter, C. Dates from an important early Late Pleistocene ice advance in the Aare
737
valley, Switzerland. Eclogae Geol. Helv., 97, 245–253. https://doi.org/10.1007/s00015-004-
738
1119-4, 2004.
739
Preusser, F., Drescher-Schneider, R., Fiebig, M., and Schlüchter, C.: Re-interpretation of the Meikirch
740
pollen record, Swiss Alpine Foreland, and implications for Middle Pleistocene
741
chronostratigraphy. J. Quat. Sci., 20., 607-620, https://doi.org/10.1002/jqs.930, 2005.
742
Preusser, F., Reitner, J. M., and Schlüchter, C.: Distribution, geometry, age and origin of overdeepened
743
valleys and basins in the Alps and their foreland. Swiss J. Geosci., 103, 407–426.
744
https://doi.org/10.1007/s00015-010-0044-y, 2010.
745
Preusser, F., Graf, H. R., Keller, O., Krayss, E., and Schlüchter, C.: Quaternary glaciation history of
746
Northern Switzerland. E&G Quat. Sci. J., 60, 282–305, https://doi.org/10.3285/eg.60.2-3.06,
747
2011.
748
https://doi.org/10.5194/egusphere-2024-683
Preprint. Discussion started: 14 May 2024
c
Author(s) 2024. CC BY 4.0 License.
29
Preusser, F., Büschelberger, M., Kemma, H.A., Miocic, J., Müller, D. and May, J.-H.: Exploring
749
possible links between Quaternary aggradation in the Upper Rhine Graben and the glaciation
750
history of northern Switzerland. Int. J. Earth Sci., 110, 1827-1846,
751
https://doi.org/10.1007/s00531-021-02043-7, 2021.
752
Railsback, L.B., Gibbard, P.L., Head, M.J., Voarintsoa, N.R.G., and Toucanne, S.: An optimized
753
scheme of lettered marine isotope substages for the last 1.0 million years, and the
754
climatostratigraphic nature of isotope stages and substages. Quat. Sci. Rev., 111, 94-106,
755
10.1016/j.quascirev.2015.01.012, 2015.
756
Reber, R., Akçar, N., Ivy-Ochs, S., Tikhomirov, D., Burkhalter, R., Zahno, C., Lüthold, A., Kubik,
757
P.W., Vockenhuber, C., and Schlüchter, C.: Timing of retreat of the Reuss Glacier
758
(Switzerland) at the end of the Last Glacial Maximum. Swiss J. Geosci., 107, 293-307,
759
https://doi.org/10.1007/s00015-014-0169-5, 2014.
760
Reber, R., and Schlunegger, F.: Unravelling the moisture sources of the Alpine glaciers using tunnel
761
valleys as constraints. Terra Nova, 28, 202–211, https://doi.org/10.1111/ter.12211, 2016.
762
Reitner, J.M., Gruber, W., Römer, A., and Morawetz, R.: Alpine overdeepenings and paleo-ice flow
763
changes: an integrated geophysical-sedimentological case study from Tyrol (Austria). Swiss J.
764
Geosci., 103, 385-405, https://doi.org/10.1007/s00015-010-0046-9, 2010.
765
Roger, S., Féraud, G., de Beaulieu, J.-L., Thouveny, N., Coulon, Ch., Choucem., J.J., Andrieu, V. and
766
Williams, T.: 40Ar/39Ar dating on tephra of the Velay maars (France): implications for the
767
Late Pleistocene proxy-climatic record. Earth Planet Sci. Lett., 170: 287–299, 1999.
768
Ross, N., Siegert, M.J., Woodward, J., Smith, A.M., Corr, H.F.J., Bentley, M.J., Hindsmarsh, R.C.A.,
769
King, E.C., and Rivera, A.: Holocene stability of the Amundsen-Weddell ice divide, West
770
Antarctica. Geology, 39, 935-938, https://doi.org/10.1130/G31920, 2011.
771
Rosselli, A., and Raymond, O. : Modélisation gravimétrique 2.5D et cartes des isohypses au 1:100’000
772
du substratum rocheux de la Vallée du Rhône entre Villeneuve et Brig (Suisse). Eclogae Geol.
773
Helv., 96, 399–423, 2003.
774
Schaller, S., Büchi, M.W., Schuster, B., and Anselmetti, F.: Drilling into a deep buried valley (ICDP
775
DOVE): a 252 m long sediment succession from a glacial overdeepening in northwestern
776
Switzerland. Sci. Drill., 32, 27-42, https://doi.org/10.5194/sd-32-27-2023, 2023.
777
Schläfli, P., Gobet, E., van Leeuwen, J.F.N., Vescovi, E., Schwenk, M.A., Bandou, D., Douillet, G.A.,
778
Schlunegger, F., and Tinner, W.: Palynological investigations reveal Eemian interglacial
779
vegetation dynamics at Spiezberg, Bernese Alps, Switzerland. Quat. Sci. Rev., 263, 106975,
780
https://doi.org/10.1016/j.quascirev.2021.106975, 2021.
781
Schlüchter, C.: The deglaciation of the Swiss-Alps: a paleoclimatic event with chronological problems.
782
Bull. l’Association française pour l’étude du Quat., 25 , 141-145, 1988.
783
https://doi.org/10.5194/egusphere-2024-683
Preprint. Discussion started: 14 May 2024
c
Author(s) 2024. CC BY 4.0 License.
30
Schlüchter, C.: Thalgut: ein umfassendes eiszeit stratigraphisches Referenzprofil im nördlichen
784
Alpenvorland. Eclogae geol. Helv., 82, 277-284, 1989.
785
Schlüchter, C. The Swiss glacial record – a schematic summary. Develop. Quat. Sci., 2, 413-418,
786
https://doi.org/10.1016/S1571-0866(04)80092-7, 2004.
787
Schlunegger, F., and Garefalakis, P.: Einführung in die Sedimentologie, Schweizerbart, Stuttgart,
788
www.schweizerbart.de/9783510655397, 2023.
789
Schwenk, M., Schläfli, P., Bandou, D., Gribenski, N., Douillet, G., and Schlunegger, F.: From glacial
790
erosion to basin overfill: A 240 m-thick overdeepening-fill sequence in Bern. Switzerland. Sci.
791
Drill., 30, 17–42, https://doi.org/10.5194/sd-30-17-2022, 2022a.
792
Schwenk, M. A., Stutenbecker, L., Schläfli, P., Bandou, D., and Schlunegger, F.: Two glaciers and one
793
sedimentary sink: The competing role of the Aare and the Valais glaciers in filling an
794
overdeepened trough inferred from provenance analysis. E&G Quat. Sci. J., 71, 163–190,
795
https://doi.org/10.5194/egqsj-71-163-2022, 2022b.
796
Steinemann, O., Ivy-Ochs, S., Hippe, K., Christl, M., Naghipour, N., and Synal, H.-A.: Glacial erosion
797
by the Trift glacier (Switzerland): Deciphering the development of riegels, rock basins and
798
gorges. Geomorphology, 375, 107533, https://doi.org/10.1016/j.geomorph.2020.107533, 2021.
799
Stewart, M.A., and Lonergan, L.: Seven glacial cycles in the middle-late Pleistocene of northwest
800
Europe: geomorphic evidence from buried tunnel valleys. Geology 39, 283-286,
801
https://doi.org/10.1130/G31631.1, 2011.
802
Stewart, M.A., Lonergan, L. and Hampson, G.: 3D seismic analysis of buried tunnel valleys in the
803
central North Sea: tunnel valley-fill sedimentary architecture, in: Glaciogenic Reservoirs and
804
Hydrocarbon Systems, edited by: Huuse, M., Redfern, J., Le Heron, D.P., Dixon, R.J., and
805
Moscariello, A.. Geol. Soc. London Spec. Publ., 368, 173-183,
806
http://dx.doi.org/10.1144/SP368.9, 2013.
807
Valla, P.G., van der Beek, P.A., and Carcaillet, J.: Dating bedrock gorge incition in the French Western
808
Alps (Ecrins-Pelvoux massif) using cosmogenic 10Be. Terra Nova, 22, 18-25,
809
https:/doi.org/10.1111/j.1365-1321.2009.00911.x, 2010.
810
Valla, P., Shuster, D.L., and van der Beek, P.A.: Significant increase in relief of the European Alps
811
during mid-Pleistocene glaciations. Nat. Geosci., 4, 688-692,
812
https://doi.org/10.1038/ngeo1242, 2011.
813
Welten, M.: Pollenanalytische Untersuchungen im jüngeren Quartär des nördlichen Alpenvorlandes der
814
Schweiz. Beitr. Geol. Karte Schweiz, 156, 174 pp., 1982.
815
Welten, M.: Neue pollenanalytische Ergebnisse über das jüngere Quartär des nördlichen
816
Alpenvorlandes der Schweiz (Mittel-und Jungpleistozän). Beitr. Geol. Karte Schweiz, 162, 9-
817
40, 1988.
818
https://doi.org/10.5194/egusphere-2024-683
Preprint. Discussion started: 14 May 2024
c
Author(s) 2024. CC BY 4.0 License.
31
Wright, H. E.: Tunnel valleys, glacial surges, and subglacial hydrology of the Superior Lobe, 340
819
Minnesota. Mem. Geol. Soc. Amer., 136, 251-276, https://doi.org/10.1130/MEM136-p251,
820
1973.
821
Zwahlen, P., Tinner, W. and Vescovi, E.: Ein neues EEM-zeitliches Umweltarchiv am Spiezberg
822
(Schweizer Alpen) im Kontext der mittel- und spätplesitozänen Landschaftsentwicklung. Mitt.
823
Naturf. Ges. Bern 78, 92–121, 2021.
824
https://doi.org/10.5194/egusphere-2024-683
Preprint. Discussion started: 14 May 2024
c
Author(s) 2024. CC BY 4.0 License.
