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14 pages; International audience; Previous studies in the foreland of the French Western Alps, based on the analysis of geomorphological criteria for the internal moraine complex, show several stages of retreat or stagnation of the Lyonnais ice lobe during marine isotopic stages 4 and 2. Based on chronological data of the literature, the age of the Würmian maximum extension of the Lyon ice lobe must have occurred during MIS 4 but this result is still debated. At the Last Glacial Maximum, in the western part of the Lyonnais ice lobe, glaciofluvial corridors were active during flash floods draining glacial meltwater. Today, these corridors are dead valleys and display a series of terraces. In this paper, we analyse the sedimentary geometries and dynamics of three glaciofluvial corridors (Moidieu, Septeme and Heyrieux) located at the front of the internal moraine complex of the Lyonnais ice lobe. Upstream, the Moidieu corridor splits into three branches called North Moidieu, Central Moidieu and South Moidieu. Glaciofluvial deposits in the corridors are composed of pebbles and gravels in a sandy matrix. Sedimentary structures show mass flow events and the migration of river bars in braided channels which are characteristic of proximal glaciofluvial rivers in a proglacial environment. According to a new geomorphological map built using a high-resolution digital elevation model and an isopach map of the Quaternary deposits created from a compilation of the borehole data, we suggest that these corridors correspond to “tunnel valleys” built during the most extensive Riss glaciation. Then during the Würm maximum glacial extension, these “tunnel valleys” show complex infilling by glacio-fluvial sediments during the Würmian maximal extent. In the three corridors, the number of river terraces can be better defined by using new geomorphological analyses. A total of three Würm terraces can be observed: two in the north and three in the south. This difference between the south and north is probably a result of climatic and tectonic forcing.; Les études précédentes dans l’avant-pays des Alpes occidentales françaises, basées sur des critères géomorphologiques du complexe morainique interne, montrent de nombreux stades de recul ou de stagnation du glacier du lobe lyonnais associés aux stades isotopiques marins (MIS) 4 et 2. D’après les données chronologiques de la littérature, l’extension maximale würmienne du lobe lyonnais aurait eu lieu durant le MIS 4, mais ces résultats sont encore débattus. Pendant le dernier maximum glaciaire (LGM), dans la partie occidentale du lobe lyonnais, des couloirs fluvio-glaciaires étaient actifs pendant des crues éclairs liées aux eaux de fonte glaciaire. Aujourd’hui, ces couloirs sont des vallées mortes et présentent une série de terrasses. Dans cet article, la géomorphologie et la dynamique sédimentaire de trois couloirs fluvio-glaciaires (Moidieu, Septème et Heyrieux) situés à l’avant du complexe morainique interne du lobe lyonnais ont été analysées. Le couloir de Moidieu se ramifie en trois branches à l’amont. Une analyse sédimentologique dans plusieurs gravières a permis de reconstituer les paléoenvironnements de dépôt. Les dépôts fluvio-glaciaires des couloirs sont composés de galets et de graviers dans une matrice sableuse. Les structures sédimentaires montrent des événements d’écoulement en masse et des dépôts de barres de migration de chenaux en tresses caractéristiques des rivières fluvio-glaciaires proximales dans un environnement pro-glaciaire. La carte géomorphologique établie à l’aide d’un modèle numérique de terrain (MNT) à haute résolution et la carte isopaque du Quaternaire déduite de la compilation des données de forage suggèrent que les couloirs fluvio-glaciaires sont hérités de « vallée tunnel ». Ce processus d’érosion a probablement été actif pendant la glaciation du Riss. Les couloirs ont ensuite été remplis par les dépôts fluvio-glaciaires pendant l’extension glaciaire maximale du Würm. Dans les trois corridors, le nombre de terrasses a été défini grâce à de nouvelles analyses géomorphologiques. Au total, trois terrasses würmiennes peuvent être observées : deux au nord et trois au sud. Cette différence entre le sud et le nord est probablement le résultat d’un forçage climatique et tectonique.

The advances and retreats of ice sheets during Pleistocene significantly changed high- and mid-latitude landscapes and hydrological systems, albeit differently, in North America and Europe. On the southern margin of the Last Glacial Maximum (LGM) in the Baltic Sea basin, a specific type of valley has developed between glacial margins and upland or mountain slopes. We studied new geological data (boreholes, electrical resistivity imaging (ERI) from this geomorphic setting in Northeast Poland to understand: (1) how the landscape and river network evolved to eventually produce peat mires during the Holocene, and (2) the nature of groundwater recharge to fens in the upper Biebrza Valley. We present the results on a geological cross-section with hydrogeological interpretation. We also discuss regional geomorphology. In addition, we present the LGM extent derived from a spatial distribution of Vistulian (Weichselian) terminal moraines. These end moraines are also interpreted as Saalian kames. Thus, we additionally present another method of LGM extent delineation from a physicogeographical division. We link the steep slopes of the studied valley walls (kame terrace fronts) with thermokarst erosion in the periglacial zone. We then document the hydrogeological window (DISCONTINUITY in the till layer over the confined aquifer), which enables the outflow of groundwater into the peat bog. Although minerotrophic fen mire development in the study area is likely to be sustained in the near future through sufficient groundwater supply, the projected capture of the Biebrza River by the Neman River will not allow for sustaining peatland development.

The origin of ribbed moraines (Rogen moraine) is a long-discussed topic in the field of geomorphology. As per today, no consensus on their formation has been reached apart from a subglacial origin. This study will test the hypothesis that water presence in the form of water-saturated till or possibly a film of stagnant water under the ice sheets of the last glaciations may have caused the formation of ribbed moraines. This hypothesis, suggested in a similar form by Sollid and Sørbel (1994), has not been investigated or tested so far. The hypothesis is investigated in two steps. Firstly, ribbed moraine fields and other subglacial landform fields were mapped across the Oppland Region of Norway using new LiDAR elevation data. In a smaller area around the Langsua National Park, a detailed map and a field trip were completed to further investigate the morphology of ribbed moraines and their spatial relations to other landforms. Secondly, a model of the subglacial hydrology was constructed for the region. The model computes areas of low hydraulic gradient, possible subglacial lake positions and theoretical flow paths of subglacial streams at high resolution. High-resolution output is achieved using present-day topography data in conjunction with down-scaled ice sheet thickness data from an ice sheet reconstruction model. Mapping of subglacial landforms shows a clear continuum between ribbed moraines and hummocky bedforms across the study area, with indications for an extended continuum including glacial lineations in some locations. Glaciofluvial channels were found entering and exiting ribbed moraine fields. A widely quoted map of the ribbed moraines distribution in Southern Norway was deemed incomplete. The constructed model of subglacial hydrology was found to deliver a resolution highly suitable for interpretation with only limited and easily identifiable limitations. Modelled flow paths correspond well with flow directions interpreted from glaciofluvial traces. The modelled hydraulic gradient shows that ribbed moraine fields are consistently found in areas of low hydraulic gradient throughout the study area. This indicates that these results indicate that ribbed moraine formation is triggered by water presence at the glacial bed in the form of water-saturated till. This study suggests that water presence may facilitate instabilities at the till-ice interface, forming ribbed moraines and hummocky bedforms. Larger amounts of water are expected to have flowed at low velocity in a spread-out flow pattern between the formed ribbed moraines and hummocky bedforms during the deglaciation.

Recent studies on Neoproterozoic climate change has prompted renewed interests in Neoproterozoic glacial deposits and renewed debates over the criteria used to identify the nature of glacial influence on sedimentation. Analysis of soft sediment deformation structures have provided important clues to distinguish between competing paleoenvironmental interpretations of Quaternary glacial deposits. A similar approach is presented here in the analysis of Neoproterozoic glacial deposits of the Smalfjord Formation, northern Norway. Detailed sedimentological and structural analysis at several sites in the Varangerfjorden area reveals complex soft sediment deformation at various scales in conglomerate, sandstone and diamictite. Deformation is predominantly ductile and includes anticlinal and synclinal folding, flow noses, flame structures, recumbent folding and shear structures. The deformed sediments are predominantly associated with conglomerate and sandstone, which record glaciofluvial and deltaic depositional conditions. Some deformation can be attributed to rapid deposition and slumping, whereas others appear to record shear stress associated with overriding ice. The scale,style and range of deformation together with the coarse-grained nature of the deformed sediments and facies associations suggests these were unfrozen outwash sediments that were overridden by ice and resedimented in a dynamic ice proximal setting. Whereas recent previous studies of diamictite-bearing strata of the Smalfjord Formation had revealed no clear evidence of glacial influence on deposition, deformation structures documented here suggest that glacial conditions prevailed on the basin margin during deposition of Smalfjord Formation sediments, with sedimentary facies and deformation structures typical of temperate ice proximal settings.

Meltwater drainage systems beneath ice sheets are a poorly understood, yet fundamentally important environment for understanding glacier dynamics, which are strongly influenced by the nature and quantity of meltwater entering the subglacial system. Contemporary sub-ice sheet meltwater drainage systems are notoriously difficult to study, but we can utilise exposed beds of palaeo-ice sheets to further our understanding of subglacial drainage. In particular, eskers record deposition in glacial drainage channels and are widespread on the exposed beds of former ice sheets. This paper presents a 1:5,000,000 scale map of >20,000 large eskers (typically > 2 km long) deposited by the Laurentide Ice Sheet (LIS), mapped from Landsat imagery of Canada, in order to establish a dataset suitable for analysis of esker morphometry and drainage patterns at the ice sheet scale. Comparisons between eskers mapped from Landsat imagery and aerial photographs indicate that, in most areas, approximately 75% of eskers are detected using Landsat. The data presented in this map build on and extend previous work in providing a consistent map of an unprecedented sample of eskers for quantitative analysis. It offers an alternative perspective on the problems surrounding ice-sheet meltwater drainage and can be used for: (i) detailed investigations of esker morphometry and distribution from a large sample size; (ii), testing of numerical models of meltwater drainage routing that predict esker characteristics (e.g. channel spacing, sinuosity), (iii) assessment of the factors that control esker location and formation; and (iv), a refined understanding of ice margin configurations during retreat of the LIS.

The scientific study of quartz grains is a powerful tool in deciphering the depositional environment and mode of transportation of sediments, and ultimately the origin and classification of sediments. Surface microfeatures, angularity, chemical features, and grain-size analysis of quartz grains, collectively reveal the sedimentary and physicochemical processes that acted on the grains during different stages of their geological history. Here, we apply scanning electron microscopic (SEM) analysis to evaluating the sedimentary provenance, modes of transport, weathering characteristics, alteration, and sedimentary environment of selected detrital quartz grains from the peripheral part of two epi-shelf lakes (ESL-1 and ESL-2) of the Schirmacher Oasis of East Antarctica. Our study reveals that different styles of physical weathering, erosive signatures, and chemical precipitation variably affected these quartz grains before final deposition as lake sediments. Statistical analysis (central tendencies, sorting, skewness, and kurtosis) indicates that these quartz-bearing sediments are poorly sorted glaciofluvial sediments. Saltation and suspension seem to have been the two dominant modes of transportation, and chemical analysis of these sediments indicates a gneissic provenance.