Swiss Journal of Geosciences最新文献

{"title":"Tectonic architecture of the northern Dora-Maira Massif (Western Alps, Italy): field and geochronological data","authors":"Francesco Nosenzo, P. Manzotti, Mikaela Krona, M. Ballèvre, M. Poujol","doi":"10.1186/s00015-024-00459-2","DOIUrl":"https://doi.org/10.1186/s00015-024-00459-2","url":null,"abstract":"","PeriodicalId":49456,"journal":{"name":"Swiss Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140677481","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Facies architecture, geochemistry and petrogenesis of Middle Triassic volcaniclastic deposits of Mt. Ivanščica (NW Croatia): evidence of bimodal volcanism in the Alpine-Dinaridic transitional zone","authors":"Duje Smirčić, Matija Vukovski, Damir Slovenec, Duje Kukoč, Branimir Šegvić, Marija Horvat, Mirko Belak, Tonći Grgasović, Luka Badurina","doi":"10.1186/s00015-024-00453-8","DOIUrl":"https://doi.org/10.1186/s00015-024-00453-8","url":null,"abstract":"During the Middle Triassic, intensive volcanic activity took place along the eastern margin of Pangea, including the Greater Adria promontory, due to the Neotethyan oceanization. This resulted in the formation of various volcanic and volcaniclastic rock types. The region of NW Croatia, acting as a transition zone between the Southern Alps and the Dinarides, showcases the outcrops of these rocks. The present study investigates the facies of volcaniclastic rocks, the distribution of those facies, formation processes, as well as the genesis of the primary magma to gain a better understanding of the complex geodynamics of this region during the Middle Triassic. Six profiles across the Vudelja quarry front were surveyed using drone imaging and samples were collected for detailed petrographic and geochemical analyses. Two groups of volcaniclastic rocks were identified—mafic and intermediate/felsic. The former is represented by (I) autoclastic effusive facies and (II) resedimented autoclastic facies, while the latter is represented by (III) secondary pyroclastic facies. Mafic volcaniclastics were generated through basaltic effusions in marine environments, fragmentation in contact with seawater, mixing with shallow marine carbonate clasts, and subsequent redeposition in deeper marine areas. The secondary pyroclastic facies (III) consists of a regionally distributed felsic Pietra Verde tuff whose deposits may be related to pyroclastic density currents and syn-eruptive resedimentation by turbidite-like currents. Geochemical data indicate that parental magmas responsible for generating the mafic volcaniclastics had a calc-alkaline composition and originated in ensialic and mature arc settings of an active continental margin. The observed chemical composition is likely inherited from older, arc-related lithologies, associated with the subduction of the Paleotethys Ocean. Parental magmas are thought to have formed during continental rifting of the passive Middle Triassic margins of the Greater Adria through (i) partial melting of the heterogeneous lithospheric mantle, which had been metasomatized during an earlier Hercynian subduction, and (ii) subordinate processes related to the melting of the upper continental crust and subsequent fractionation. Ar/Ar dating on plagioclase separates yielded an age of 244.5 ± 2.8 Ma for mafic volcaniclastics. This aligns well with biostratigraphic ages of felsic tuffs which crop out on a broader regional scale of the Dinarides, the Southern Alps, and the Transdanubian Range. The overlapping ages obtained from radiometric dating of mafic volcaniclastics and biostratigraphic ages of the felsic Pietra Verde tuffs strongly suggest that the Greater Adria region experienced concurrent bimodal volcanism during the Middle Triassic.","PeriodicalId":49456,"journal":{"name":"Swiss Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140584149","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The North Penninic Bündnerschiefer and Flysch of the Prättigau (Swiss Alps) revisited","authors":"Wilfried Winkler","doi":"10.1186/s00015-024-00454-7","DOIUrl":"https://doi.org/10.1186/s00015-024-00454-7","url":null,"abstract":"During the re-mapping of the area for the Geological Atlas of Switzerland, a significant stratigraphic unconformity was discovered in the North Penninic (Valais) Bündnerschiefer and the Flysch series of the northern Prättigau. It separates different units of the Cretaceous Bündnerschiefer from the Palaeogene Flysch. We explain this observation by a basin conversion from extension to compression, which caused the initial deformation of the Bündnerschiefer in an accretionary wedge. Interlinked return-flow has created a new heterogeneous substrate for the flysch sediments and explains the different types of unconformities. The basin conversion coincided with high-grade metamorphism in the vicinity of the the South Penninic suture and the Austroalpine units, and the increased exhumation in the Austroalpine nappe stack. Detrital zircon dating confirms also a change from European to Austroalpine detrital sources in the flysch sandstones. We discuss a palaeotectonic model leading to hP/lT metamorphism of the Bündnerschiefer in the Late Eocene (c. 42 Ma). It appears that the flysch formations were also involved, but to a lesser degree by tectonic deformation from the late Early Eocene onwards, as the pervasive folding characteristic of the Bündnerschiefer is absent. This has been followed by a phase of S-directed backfolding. During the Oligocene and Miocene, more extensive deformation occurred by SE to NW compression and finally by probable westward thrusting and folding. Our main theme is the transition from passive to active continental margins, which in Alpine plate tectonic framework corresponds to the transition to flysch sedimentation by basin conversion. Our results show that the simultaneity of the transition from extension to compression, as indicated by the accumulation of flysch, shifted in time from south to north in the Alpine Tethys.","PeriodicalId":49456,"journal":{"name":"Swiss Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140299254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Architecture and sedimentary evolution of the Ladinian Kobilji curek basin (External Dinarides, central Slovenia)","authors":"Boštjan Rožič, Anja Kocjančič, Luka Gale, Nina Zupančič, Tomislav Popit, Primož Vodnik, Tea Kolar-Jurkovšek, Rok Brajkovič, Petra Žvab Rožič","doi":"10.1186/s00015-023-00449-w","DOIUrl":"https://doi.org/10.1186/s00015-023-00449-w","url":null,"abstract":"The study area is located in cental Slovenia, and geologically located at the junction between the Alps and the Dinarides. The Middle Triassic of this region is characterised by intense rifting manifested by differential subsidence and volcanism. This led to a major paleogeographic reorganisation of the region, where three paleogeographic domains formed in the Upper Triassic: The Julian Carbonate Platform in the north, the intermediate Slovenian Basin, both parts of the Southern Alps, and the Dinaric (Adriatic, Friuli) Carbonate Platform in the south, which today is a part of the External Dinarides that host the area of investigation. Prior to the installation of the Dinaric Carbonate Platfrom, i.e. in the Ladinian, the entire area of the preset-day External Dinarides broke up into numerous tectonic blocks that were exposed to either erosion or continental, shallow-marine, and deep-marine sedimentation. In this study, we analyse at small scale a complex transitional area between a local carbonate platform and the Kobilji curek basin (depositional area dominated by deeper marine sediments), located in the Rute Plateau in central Slovenia south of Ljubljana. During enhanced subsidence, the basin was filled with volcanic material (tuffs and volcanogenic clays and subordinate extrusive material), while the adjacent platform aggraded. The slope was positioned above active paleofaults. During relative sea level lowstand, the platform prograded across the basin. The study area is divided into four major tectonic paleoblocks. The NW paleoblock experienced the most enhanced subsidence, and the platform prograded twice in this area and was submerged again by the rejuvenated subsidence and/or sea-level rise. The second and third paleoblocks subsided only during discrete major subsidence events, and the carbonates of the platform and slope were soon reinstated therein. In the fourth paleoblock to the east the platform persisted during the Ladinian. In the Carnian, the entire study area became emerged, and continental clastics were deposited. These were then replaced by a uniform shallow marine/intertidal Hauptdolomit (Dolomia Principale) formation at the onset of the Norian. This study provides the first detailed reconstruction of the sedimentary evolution of small-scale Ladinian basin and platforms system in the northern External Dinarides.","PeriodicalId":49456,"journal":{"name":"Swiss Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140070658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Christian Renggli receives the 2023 Paul Niggli Medal","authors":"","doi":"10.1186/s00015-024-00451-w","DOIUrl":"https://doi.org/10.1186/s00015-024-00451-w","url":null,"abstract":"<figure><picture><source srcset=\"//media.springernature.com/lw685/springer-static/image/art%3A10.1186%2Fs00015-024-00451-w/MediaObjects/15_2024_451_Figa_HTML.jpg?as=webp\" type=\"image/webp\"/><img alt=\"figure a\" aria-describedby=\"Figa\" height=\"590\" loading=\"lazy\" src=\"//media.springernature.com/lw685/springer-static/image/art%3A10.1186%2Fs00015-024-00451-w/MediaObjects/15_2024_451_Figa_HTML.jpg\" width=\"459\"/></picture></figure><br/><p>The Paul Niggli Medal is Switzerland’s most prestigious award for young earth scientists who made outstanding contributions in the research fields of mineralogy, geochemistry, petrology, resource geology or solid-earth geophysics. The Paul Niggli Medal honours and supports young ambassadors of Swiss geoscience, who are either Swiss citizens or obtained at least two of their academic degrees in the Swiss university system (BSc or MSc and usually their PhD).</p><p>The Board of the Paul Niggli Foundation decided, in their annual meeting of 19 June 2023, to award the Paul Niggli Medal for the year 2023 to Christian Renggli, in recognition of his outstanding research using experimental methods to understand the properties of gas-solid reactions in volcanic systems on Earth, the Moon and Mercury.</p><p><i>Maria Schönbächler (ETH Zürich)</i>.</p><p><i>On behalf of the Foundation Council of the Paul Niggli Stiftung</i>.</p><p>It is with great pleasure that I provide this citation, together with Prof. Penny King from the Australian National University. This award recognises Christian’s wide-ranging and influential contributions to the development and application of experimental and theoretical methods to study the mobility and fractionation of volatile elements in gases and low-density fluids.</p><p>Christian J. Renggli studied geology at the University of Bern and did his Masters thesis in petrology and geochemistry at the Ludwig-Maximilian University in Munich, using experiments to study magma mixing processes. He then moved down-under and began a PhD project at the Australian National University, supervised by Penny King. His research combined results from natural samples with experimental and theoretical methods, studying reactions between gases and rocks. He applied these studies to Apollo samples returned from the Moon, the Earth, and the terrestrial planets.</p><p>Perhaps it is now time to create a link to Paul Niggli, who became famous for using thermodynamic principles to address petrological and geochemical problems. Niggli published numerous influential publications and his early book “Die leichtflüchtigen Bestandteile im Magma” argues that volatile elements in magmatic and other rocks must be regarded as separate phases that affect phase relations and mineral stabilities. He was one of the first to employ both early experimental constraints and thermodynamic principles to investigate geological processes. Chris Renggli, following Niggli’s footsteps, also conducts experiments, together with thermodynamic modelling a","PeriodicalId":49456,"journal":{"name":"Swiss Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139590307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Report on an open dataset to constrain the Balmuccia peridotite body (Ivrea-Verbano Zone, Italy) through a participative gravity-modelling challenge","authors":"György Hetényi, Ludovic Baron, Matteo Scarponi, Shiba Subedi, Konstantinos Michailos, Fergus Dal, Anna Gerle, Benoît Petri, Jodok Zwahlen, Antonio Langone, Andrew Greenwood, Luca Ziberna, Mattia Pistone, Alberto Zanetti, Othmar Müntener","doi":"10.1186/s00015-023-00450-3","DOIUrl":"https://doi.org/10.1186/s00015-023-00450-3","url":null,"abstract":"The Balmuccia peridotite exposes relatively fresh mantle rocks at the Earth’s surface, and as such it is of interest for geologists and geophysicists. The outcrop is a kilometre-scale feature, yet its extent at depth is insufficiently imaged. Our aim is to provide new constraints on the shape of the density anomaly this body represents, through 3D gravity modelling. In an effort to avoid personal or methodology bias, we hereby launch an invitation and call for participative modelling. We openly provide all the necessary input data: pre-processed gravity data, geological map, in situ rock densities, and digital elevation model. The expected inversion results will be compared and jointly analysed with all participants. This approach should allow us to conclude on the shape of the Balmuccia peridotite body and the associated uncertainty. This crowd effort will contribute to the site surveys preparing a scientific borehole in the area in frame of project DIVE.","PeriodicalId":49456,"journal":{"name":"Swiss Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139582247","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Magmatic genesis, hydration, and subduction of the tholeiitic eclogite-facies Allalin gabbro (Western Alps, Switzerland).","authors":"Julia Dietrich, Jörg Hermann, Thomas Pettke","doi":"10.1186/s00015-024-00461-8","DOIUrl":"10.1186/s00015-024-00461-8","url":null,"abstract":"<p><p>The Allalin gabbro of the Zermatt-Saas meta-ophiolite consists of variably metamorphosed Mg- to Fe-Ti-gabbros, troctolites, and anorthosites, which are crosscut by basaltic dykes. Field relationships of the various rock types and petrographic studies together with bulk rock and mineral chemical composition data allow the reconstruction of the complete geological history of the Allalin gabbro. With increasing magmatic differentiation, the incompatible element content in clinopyroxene increases (e.g., REEs and Zr by a factor of 5), whereas the Mg# decreases (from 86.4 to 74.6) as do the compatible element contents (e.g., Cr and Ni by factors of 3.5 and 5, respectively). Exhumation to shallower depths led to subsolidus ductile deformation and cooling of the gabbro followed by the intrusion of fine-grained basaltic dykes, which display chilled margins. Bulk rock data of these dykes reveal strong similarities in fluid-immobile trace element patterns to tholeiitic pillow basalts of the Zermatt-Saas and nearby meta-ophiolites. The recalculated REE patterns of the melt in equilibrium with igneous clinopyroxene is very similar to the REE patterns of the mafic dykes, indicating a cogenetic origin of pillow basalts, dykes, and gabbros. Together with the previously determined Jurassic intrusion age of the gabbro, our observations demonstrate that the Allalin gabbro intruded as a tholeiitic magma in a slow spreading MOR environment of the Piemonte-Ligurian ocean of the Alpine Tethys. Subduction of the Allalin gabbro resulted in different eclogitization extents of the Mg-gabbros as a function of variable hydration degrees. Metagabbros with low extents of hydration record incomplete eclogitization; the magmatic mineralogy (olivine + clinopyroxene + plagioclase) is preserved together with disequilibrium textures in the form of reaction coronae surrounding mineral boundaries. Metagabbros with high extents of hydration are completely eclogitized and display pseudomorphic replacement textures of magmatic minerals by eclogite-facies mineral assemblages, which required significant major to trace element transport across mineral domains. The locally variable extents of hydration took place near the sea floor, as recorded by the presence of Cl-apatite (6.28 wt% Cl), and an increase in B concentrations of minerals pseudomorphically replacing olivine (e.g., chlorite with 0.20-0.31 µg/g B and omphacite with 0.22-0.25 µg/g B) compared to magmatic olivine (0.12-0.16 µg/g B). Moreover, the chemical zonation pattern of metamorphic garnet coronae is different in completely eclogitized gabbros and gabbros with relic igneous minerals, in agreement with a main hydration event prior to subduction. The Allalin gabbro therefore represents a classical example of an oceanic gabbro formed in a slow spreading setting in the mid Jurassic that experienced heterogeneous hydration near the sea floor. Paleogene subduction of the gabbro to 70-80 km depth produced variably equilibrated g","PeriodicalId":49456,"journal":{"name":"Swiss Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11186922/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141443583","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A rapid transition from subduction to Barrovian metamorphism: geochronology of mafic-ultramafic relicts of oceanic crust in the Central Alps, Switzerland.","authors":"Kim Lemke, Daniela Rubatto, Jörg Hermann","doi":"10.1186/s00015-024-00462-7","DOIUrl":"10.1186/s00015-024-00462-7","url":null,"abstract":"<p><p>Relicts of subducted oceanic lithosphere provide key information for the tectonic reconstructions of convergent margins. In the Central Alps, such relicts occur as isolated mafic-ultramafic lenses within the migmatites of the southern Adula nappe and Cima-Lunga unit. Analysis of the major-, minor-, and accessory minerals of these ophiolitic relicts, combined with zircon and rutile U-Pb ages and zircon oxygen isotopes, allows the reconstruction of different stages of their complex evolution. The mafic-ultramafic suite in Valle di Moleno consists of chlorite-harzburgites associated with metarodingites and retrogressed eclogites. Relic omphacite and kyanite in retrogressed eclogites provide evidence for subduction-related metamorphism. Increasing X_Prp in the garnet mantle towards the rim documents heating during high-pressure metamorphism up to 800-850 °C. Polyphase inclusions and chemical zoning in garnet suggest fluid-assisted melting during high-pressure metamorphism dated at 31.0 ± 0.9 Ma. In Val Cama, chlorite-harzburgites, metarodingites and calcsilicate-metasediments occur. Detrital zircon ages in the metasediment suggest a Mesozoic deposition. The metarodingite-metaperidotite-metasediment association and the low δ¹⁸O signatures of zircon (δ¹⁸O 3.0-3.7‰), inherited from seafloor metasomatism of the protoliths, show that the rocks are derived from former altered oceanic crust. Amphibolite facies metamorphism related to the Central Alps Barrovian evolution in Val Cama occurred at 28.8 ± 1.5 Ma. The combined data from Moleno and Cama indicate a rapid transition (~ 2 Ma) from subduction to collisional metamorphism with corresponding exhumation rates of 3-6 cm/year. Fast exhumation tectonics may have been favored by slab break-off or slab extraction. U-Pb dating of rutile from both localities yields ages of ~ 20 Ma, suggesting that these rocks remained at amphibolite-facies conditions for about 10 Ma and underwent a second fast exhumation of 3 cm/year associated with vertical movements along the Insubric line.</p><p><strong>Supplementary information: </strong>The online version contains supplementary material available at 10.1186/s00015-024-00462-7.</p>","PeriodicalId":49456,"journal":{"name":"Swiss Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11364590/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142114063","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"East Asian analogues for early Alpine orogenesis","authors":"John Milsom","doi":"10.1186/s00015-023-00448-x","DOIUrl":"https://doi.org/10.1186/s00015-023-00448-x","url":null,"abstract":"The Alpine orogeny is a consequence of the collision of Africa with Eurasia, which eliminated the Western Tethys Ocean. Processes similar to those that would have taken place early in that collision can today be seen operating in the islands of the Indo-Pacific gateway between Southeast Asia and Australia and have the potential to offer insights into the beginnings of orogenesis in the Alps. Studies of the gateway area emphasise the importance of the impact on subduction zones of topography on the downgoing plate, and of the effects of flows in the asthenosphere on lithosphere tectonics.","PeriodicalId":49456,"journal":{"name":"Swiss Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2023-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138561174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Overdeepenings in the Swiss plateau: U-shaped geometries underlain by inner gorges","authors":"Dimitri Bandou, Fritz Schlunegger, Edi Kissling, Urs Marti, Regina Reber, Jonathan Pfander","doi":"10.1186/s00015-023-00447-y","DOIUrl":"https://doi.org/10.1186/s00015-023-00447-y","url":null,"abstract":"We investigated the mechanisms leading to the formation of tunnel valleys in the Swiss foreland near Bern. We proceeded through producing 3D maps of the bedrock topography based on drillhole information and a new gravimetric survey combined with modelling. In this context, the combination of information about the densities of the sedimentary fill and of the bedrock, together with published borehole data and the results of gravity surveys along 11 profiles across the valleys, served as input for the application of our 3D gravity modelling software referred to as PRISMA. This ultimately allowed us to model the gravity effect of the Quaternary fill of the overdeepenings and to produce cross-sectional geometries of these troughs. The results show that 2–3 km upstream of the city of Bern, the overdeepenings are approximately 3 km wide. They are characterized by steep to oversteepened lateral flanks and a wide flat base, which we consider as a U-shaped cross-sectional geometry. There, the maximum residual gravity anomaly ranges between − 3 to − 4 mGal for the Aare valley, which is the main overdeepening of the region. Modelling shows that this corresponds to a depression, which reaches a depth of c. 300 m a.s.l. Farther downstream approaching Bern, the erosional trough narrows by c. 1 km, and the base gets shallower by c. 100 m as revealed by drillings. This is supported by the results of our gravity surveys, which disclose a lower maximum gravity effect of c. − 0.8 to − 1.3 mGal. Interestingly, in the Bern city area, these shallow troughs with maximum gravity anomalies ranging from − 1.4 to − 1.8 mGal are underlain by one or multiple inner gorges, which are at least 100 m deep (based on drilling information) and only a few tens of meters wide (disclosed by gravity modelling). At the downstream end of the Bern area, we observe that the trough widens from 2 km at the northern border of Bern to c. 4 km approximately 2 km farther downstream, while the bottom still reaches c. 300 to 200 m a.s.l. Our gravity survey implies that this change is associated with an increase in the maximum residual anomaly, reaching values of − 2.5 mGal. Interestingly, the overdeepening’s cross-sectional geometry in this area has steeply dipping flanks converging to a narrow base, which we consider as V-shaped. We attribute this shape to erosion by water either underneath or at the snout of a glacier, forming a gorge. This narrow bedrock depression was subsequently widened by glacial carving. In this context, strong glacial erosion upstream of the Bern area appears to have overprinted these traces. In contrast, beneath the city of Bern and farther downstream these V-shaped features have been preserved. Available chronological data suggest that the formation of this gorge occurred prior to MIS 8 and possibly during the aftermath of one of the largest glaciations when large fluxes of meltwater resulted in the fluvial carving into the bedrock.","PeriodicalId":49456,"journal":{"name":"Swiss Journal of Geosciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138518764","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}