3D morphology of a glacially overdeepened trough controlled by underlying bedrock geology

Gegg, Lukas; Deplazes, Gaudenz; Keller, Lorenz; Madritsch, Herfried; Spillmann, Thomas; Anselmetti, Flavio S.; Buechi, Marius W.

doi:10.1016/j.geomorph.2021.107950

Cited by 10 publications

(10 citation statements)

References 63 publications

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“…1 Location of the gravel pits at Müntschemier (MÜN) and Finsterhennen (FIH) displayed on a the Last Glacial Maximum (LGM) map (Bini et al, 2009) together with the lobes of the Valais, Saane, and Aare Glaciers (© Federal Office of Topography, swisstopo, CH-3084 Wabern) and b the geological map 2012; Dürst Stucki & Schlunegger, 2013;Magrani et al, 2020;Reber & Schlunegger, 2016). These troughs were then filled by glacio-lacustrine sediments or host modern lakes (Dehnert et al, 2012;Buechi et al, 2017;Gegg et al, 2021;Schwenk et al, 2022). The lakes and alluvial planes are bordered by drumlins and roches moutonées that are covered by a till probably of a LGM age, and that have a SW-NE extension, which parallels the flow direction of the Valais Glacier during the LGM (Dürst Stucki & Schlunegger, 2013).…”

Section: Study Sitementioning

confidence: 99%

Glaciofluvial sequences recording the Birrfeld Glaciation (MIS 5d–2) in the Bern area, Swiss Plateau

et al. 2022

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In this paper, we document that glaciofluvial gravel sequences and glacial till deposits that are exposed in the Müntschemier and Finsterhennen gravel pits (Swiss Plateau west of Bern) record three glacial advances during the Birrfeld Glaciation, which corresponds to the last glacial cycle. Sedimentological logging shows that both gravel pits expose deposits of glaciofluvial braided river systems. These sediments are overlain by a till that was deposited during the Last Glacial Maximum (LGM). The results of the provenance analysis imply that the sediments were mainly supplied by the Valais Glacier, which originated in the Central Alps. A minor contribution of the material was supplied by the Saane Glacier with sources in the northern parts of the Alps. In addition, the morphometric analysis particularly of quartzite clasts in the till deposits indicate that while some clasts (the angular ones) were eroded and transported by the Valais Glacier from the Central Alps to the depositional site, the majority of the quartzite constituents (the rounded ones) were most likely reworked from the Molasse bedrock or older gravels. This implies that a large fraction of the sediments in the Müntschemier and Finsterhennen gravel pits could represent recycled material from older fluvial gravels and conglomerates that were then reworked by the glaciers as they advanced to the foreland. Based on the sedimentological data and considering published and new optically stimulated luminescence (OSL) chronological data, we propose a landscape evolution scenario where the first glacial advance occurred during Marine Isotope Stage (MIS) 5d. The second glacier advance followed during MIS 4, while the last one during the Last Glacial Maximum (LGM), which corresponds to the MIS 2. The MIS 5d advance is recorded by the lowest unit of the Müntschemier gravel pit and consists of a fining upward sequence made up of an alternation of gravel and sand beds. The MIS 4 advance is recorded by the unit beneath the LGM till at Müntschemier and by the lowermost layer in the Finsterhennen gravel pit. It comprises an alternation of gravel and sand beds, which coarsens and thickens upwards. The LGM advance, finally, resulted in the deposition of amalgamated gravel beds at Finsterhennen, which ended with the construction of a till that is encountered on the top of both gravel pits. Sediments related to the interstadial conditions between MIS 5a and MIS 5b and MIS 3 were not encountered, which suggests that the warmer periods were characterised by non-deposition and/or erosion, which possibly resulted in the observed sedimentary hiatus. Although the chronological results are still preliminary, the available information allows us to suggest that during the Birrfeld Glaciation, the Valais lobe advanced several times to the Swiss Plateau. In addition, the facies associations imply that the eastward expansion of the Valais lobe during the MIS 5d and MIS 4 were most likely shorter than during the LGM.

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Section: Study Sitementioning

confidence: 99%

Glaciofluvial sequences recording the Birrfeld Glaciation (MIS 5d–2) in the Bern area, Swiss Plateau

et al. 2022

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“…This closed basin shape with a terminal adverse slope is today generally regarded as defining an overdeepening (Alley et al, 2019;Cook and Swift, 2012;Patton et al, 2016). Notably -but not exclusively -in Switzerland, overdeepenings have since been intensively studied based on scientific drillings (Hsü and Kelts, 1984;Preusser et al, 2005;Schlüchter, 1989;Schwenk et al, 2022), geophysical campaigns Burschil et al, 2018Burschil et al, , 2019Finckh et al, 1984;Nitsche et al, 2001;, or a combination of both (Buechi et al, 2018;Dehnert et al, 2012;Gegg et al, 2021;Pomper et al, 2017).…”

Section: History Of Recognition and State-of-the-art Researchmentioning

confidence: 99%

“…However, with increasing catchment area, basal water availability also increases towards the glacier termini. This subglacial water, pressurised by the englacial water column, is regarded as a driver of overdeepening erosion in the foreland setting (Alley et al, 1997;Dürst Stucki et al, 2010;Dürst Stucki and Schlunegger, 2013;Gegg et al, 2021), where the bedrock commonly consists of poorly consolidated Molasse-type sediments (Kühni and Pfiffner, 2001). As these deposits are generally readily eroded, the occurrence of faults does not appear to play a significant role facilitating their erosion (Dürst Stucki and Schlunegger, 2013;Gegg et al, 2021).…”

Section: Geological and Glaciological Settingsmentioning

confidence: 99%

“…This subglacial water, pressurised by the englacial water column, is regarded as a driver of overdeepening erosion in the foreland setting (Alley et al, 1997;Dürst Stucki et al, 2010;Dürst Stucki and Schlunegger, 2013;Gegg et al, 2021), where the bedrock commonly consists of poorly consolidated Molasse-type sediments (Kühni and Pfiffner, 2001). As these deposits are generally readily eroded, the occurrence of faults does not appear to play a significant role facilitating their erosion (Dürst Stucki and Schlunegger, 2013;Gegg et al, 2021). With the effect of structural preconditioning being low and ice flow being largely unconfined, the focusing of subglacial erosion may shift over time, evidenced for example by branching and off-cutting overdeepened troughs (Buechi et al, 2018;Ellwanger et al, 2011).…”

Section: Geological and Glaciological Settingsmentioning

confidence: 99%

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Comparison of overdeepened structures in formerly glaciated areas of the northern Alpine foreland and northern central Europe

Gegg

Preusser²

2023

E&G Quaternary Sci. J.

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Abstract. Overdeepened structures occur in formerly and presently glaciated regions around the earth and are usually referred to as overdeepenings or tunnel valleys. The existence of such troughs has been known for more than a century, and they have been attributed to similar formation processes where subglacial meltwater plays a decisive role. This comparison highlights that (foreland) overdeepenings and tunnel valleys further occur in similar dimensions and share many characteristics such as gently sinuous shapes in plan view, undulating long profiles with terminal adverse slopes, and varying cross-sectional morphologies. The best explored examples of overdeepened structures are situated in and around the European Alps and in the central European lowlands. Especially in the vicinity of the Alps, some individual troughs are well explored, allowing for a reconstruction of their infill history, whereas only a few detailed studies, notably such involving long drill core records, have been presented from northern central Europe. We suggest that more such studies could significantly further our understanding of subglacial erosion processes and the regional glaciation histories and aim to promote more intense exchange and discussion between the respective scientific communities.

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“…Information from these sites will be complemented by similar drilling programs in glacial overdeepenings in northwestern Switzerland (Fig. 6; QBO -Quaternary drill holes: Gegg et al, 2021;SNF-Bern: Schwenk et al, 2022), and DOVE Phase 1 will eventually comprise more than 20 sites. In addition, ICDP has indicated they will provide funding for the remaining four DOVE sites along the southern transect (DOVE Phase 2), if DOVE Phase 1 is successful and matching funds can be secured.…”

Section: Dove Approachmentioning

confidence: 99%

Drilling Overdeepened Alpine Valleys (ICDP-DOVE): quantifying the age, extent, and environmental impact of Alpine glaciations

Anselmetti

Bavec²,

Crouzet³

et al. 2022

Sci. Dril.

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Abstract. The sedimentary infill of glacially overdeepened valleys (i.e., structures eroded below the fluvial base level) is an excellent but yet underexplored archive with regard to the age, extent, and nature of past glaciations. The ICDP project DOVE (Drilling Overdeepened Alpine Valleys) Phase 1 investigates a series of drill cores from glacially overdeepened troughs at several locations along the northern front of the Alps. All sites will be investigated with regard to several aspects of environmental dynamics during the Quaternary, with focus on the glaciation, vegetation, and landscape history. Geophysical methods (e.g., seismic surveys), for example, will explore the geometry of overdeepened structures to better understand the process of overdeepening. Sedimentological analyses combined with downhole logging, analysis of biological remains, and state-of-the-art geochronological methods, will enable us to reconstruct the erosion and sedimentation history of the overdeepened troughs. This approach is expected to yield significant novel data quantifying the extent and timing of Middle and Late Pleistocene glaciations of the Alps. In a first phase, two sites were drilled in late 2021 into filled overdeepenings below the paleolobe of the Rhine Glacier, and both recovered a trough filling composed of multiphase glacial sequences. Fully cored Hole 5068_1_C reached a depth of 165 m and recovered 10 m molasse bedrock at the base. This hole will be used together with two flush holes (5068_1_A, 5068_1_B) for further geophysical cross-well experiments. Site 5068_2 reached a depth of 255 m and bottomed out near the soft rock–bedrock contact. These two sites are complemented by three legacy drill sites that previously recovered filled overdeepenings below the more eastern Alpine Isar-Loisach, Salzach, and Traun paleoglacier lobes (5068_3, 5068_4, 5068_5). All analysis and interpretations of this DOVE Phase 1 will eventually lay the ground for an upcoming Phase 2 that will complete the pan-Alpine approach. This follow-up phase will investigate overdeepenings formerly occupied by paleoglacier lobes from the western and southern Alpine margins through drilling sites in France, Italy, and Slovenia. Available geological information and infrastructure make the Alps an ideal area to study overdeepened structures; however, the expected results of this study will not be restricted to the Alps. Such features are also known from other formerly glaciated mountain ranges, which are less studied than the Alps and more problematic with regards to drilling logistics. The results of this study will serve as textbook concepts to understand a full range of geological processes relevant to formerly glaciated areas all over our planet.

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3D morphology of a glacially overdeepened trough controlled by underlying bedrock geology

Cited by 10 publications

References 63 publications

Glaciofluvial sequences recording the Birrfeld Glaciation (MIS 5d–2) in the Bern area, Swiss Plateau

Glaciofluvial sequences recording the Birrfeld Glaciation (MIS 5d–2) in the Bern area, Swiss Plateau

Comparison of overdeepened structures in formerly glaciated areas of the northern Alpine foreland and northern central Europe

Drilling Overdeepened Alpine Valleys (ICDP-DOVE): quantifying the age, extent, and environmental impact of Alpine glaciations

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