Age of the Most Extensive Glaciation in the Alps

Previous research suggested that the Alpine glaciers of the Northern Swiss Foreland reached their maximum extensive position during the Middle Pleistocene. Relict tills and glaciofluvial deposits, attributed to the Most Extensive Glaciation (MEG), have been found only beyond the extents of the Last Glacial Maximum (LGM). Traditionally, these sediments have been correlated to the Riss glaciation sensu Penck and Brückner and have been morphostratigraphically classified as the Higher Terrace (HT) deposits. The age of the MEG glaciation was originally proposed to be intermediate to the Brunhes/Matuyama transition (780 ka) and the Marine Isotope Stage 6 (191 ka). In this study, we focused on the glacial deposits in Möhlin (Canton of Aargau, Switzerland), in order to constrain the age of the MEG. The sediments from these deposits were analyzed to determine the provenance and depositional environments. We applied isochron-burial dating, with cosmogenic 10Be and 26Al, to the till layer in the Bünten gravel pit near Möhlin. Our results indicate that a glacier of Alpine origin reached its most extensive position during the Middle Pleistocene (500 ± 100 ka). The age of the MEG thus appears to be synchronous with the most extensive glaciations in the northern hemisphere.

Biophysical Determinants of Shifting Tundra Vegetation Productivity in the Beaufort Delta Region of Canada

Temperature increases across the circumpolar north have driven rapid increases in vegetation productivity, often described as ‘greening’. These changes have been widespread, but spatial variation in their pattern and magnitude suggests that biophysical factors also influence the response of tundra vegetation to climate warming. In this study, we used field sampling of soils and vegetation and random forests modeling to identify the determinants of trends in Landsat-derived Enhanced Vegetation Index, a surrogate for productivity, in the Beaufort Delta region of Canada between 1984 and 2016. This region has experienced notable change, with over 71% of the Tuktoyaktuk Coastlands and over 66% of the Yukon North Slope exhibiting statistically significant greening. Using both classification and regression random forests analyses, we show that increases in productivity have been more widespread and rapid at low-to-moderate elevations and in areas dominated by till blanket and glaciofluvial deposits, suggesting that nutrient and moisture availability mediate the impact of climate warming on tundra vegetation. Rapid greening in shrub-dominated vegetation types and observed increases in the cover of low and tall shrub cover (4.8% and 6.0%) also indicate that regional changes have been driven by shifts in the abundance of these functional groups. Our findings demonstrate the utility of random forests models for identifying regional drivers of tundra vegetation change. To obtain additional fine-grained insights on drivers of increased tundra productivity, we recommend future research combine spatially comprehensive time series satellite data (as used herein) with samples of high spatial resolution imagery and integrated field investigations.

Using stable isotopes and major ions to identify recharge characteristics of the Alpine groundwater-flow dominated Triglavska Bistrica River

Triglavska Bistrica is a typical Alpine river in the north-western part of Slovenia. Its recharge area includes some of the highest peaks in the Julian Alps. The hydrogeological conditions and flow of the river depend largely on groundwater exchange between the karstified aquifer in the carbonate rocks and the intergranular aquifer in the glaciofluvial deposits. The average volume of the river flow is up to several m3/s. In this study, water samples from different locations along the river were analysed for stable isotope ratios of oxygen and hydrogen, major ions, and concentration of tritium activity. The correlation of major ions suggests that the recharge area consists of both limestone and dolomite rocks. The δ18O and δ2H values decrease downstream, implying that the average recharge elevation increases. At the downstream sampling site V-5, located approx. 300 m upstream from the confluence of the Sava Dolinka River, the calculated mean recharge altitude is estimated to be 1,996 m.

Transport Direction and Scandinavian Source Regions of the Saalian Glacial and Glaciofluvial Deposits in a Case Study of Łubienica-Superunki (Central Poland)

The article contains detailed petrographic studies, which covered a coarse and medium-grain gravel fraction of two layers of glacial till (units ŁS II and ŁS IV) and two layers of sand-gravelly outwash deposits (units ŁS I and ŁS III) related to the Odranian Glaciation (MIS6, Saalian) in Łubienica-Superunki, North Mazovian Lowland, central Poland. Additionally, the indicator erratics were identified to indicate their Scandinavian source areas and the directions of the ice sheet transgressions. This case study is discussed against the background of similar sediments and forms from the same age but from other places in the Polish Lowlands. Regardless of the facies types and fractions, crystalline rocks dominated over all other petrographic groups in all samples. The most common were the indicator erratics derived from the Åland Islands, followed by those from the south-eastern area of Sweden (Småland) and from Dalarna in central Sweden. Amongst the erratics of limited indicative significance, the most common were Lower Palaeozoic limestones and the Jotnian red sandstones. The complex petrographic analyses point to the dipartite nature of the studied profile. This separateness was confirmed by the TBC: 59.1–59.2° N and 18.0–18.2° E for the lower units and 58.8–59.4° N and 17.3–17.9° E for the upper ones.

Geometry of glaciofluvial deposits and dynamics of the Lyonnais lobe ice front during the last glacial period (France, Northern Alps)

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 the results of several dating techniques, the age of the maximum extension of the Lyon ice lobe must have occurred during MIS 4. This result is in contrast with a consensus on the maximum extension of alpine glaciers during MIS 2. During the Last Glacial Maximum, in the western part of the Lyonnais ice lobe, glaciofluvial corridors were active during flash floods with Würmian 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 then 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 is 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 due to various glaciofluvial events. In the three corridors, the number of river terraces can be better defined by using new geomorphological analyses. A total of five 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.

Direct dating of lithic surface artefacts using luminescence and application potential in geomorphology

<p>Lithic surface artefacts are anthropogenically formed stone materials (stone tools and spall generated during knapping) resting atop or being semi-embedded into the uppermost sediment layer of a stratigraphic sequence on a given landform. Such surface artefacts lack a secure stratigraphic context are encountered worldwide and often comprise a significant proportion of the archaeological record. Yet, direct absolute dating techniques for constraining the age of lithic surface scatters are currently not available.</p><p> </p><p>Promising recent work has shown the potential of using the optically stimulated luminescence (OSL) signal from rocks to date the emplacement of gravel pavements and blocks in both, archaeological and geological contexts (e.g. Sohbati et al., 2015; Jenkins et al., 2018). We build on this work and introduce a novel way of directly dating lithic surface artefacts using OSL-rock surface burial dating. We use this approach to date a surface lithic artefact scatter site, in southern Tibet. By calculating spatially resolved OSL burial ages for slices at 1 mm increments into each artefact’s buried surface we (i) infer the timing of artefact discard by humans at the site, (ii) demonstrate that most artefacts are not in-situ but were transported downslope and/or flipped and (iii) for some samples constrain the timing and number of cycles of artefact burial and re-exhumation.</p><p> </p><p>This is the first time that the OSL signal is used to date sunlight exposure of artefacts. The method is not limited to archaeological contexts but can be applied to other surface clasts that yield a reasonable OSL signal too. OSL rock surface burial dating of surface clasts and artefacts thus holds great potential to (i) constrain manufacture and artefact discard by humans and (ii) detect and reconstruct post-depositional disturbances and transport pathways. We discuss the application potential of this approach in archaeology and geomorphology. </p><p> </p><p>References:</p><p>Jenkins, G.T.H., Duller, G.A.T., Roberts, H.M., Chiverrell, R.C., Glasser, N.F., 2018. A new approach for luminescence dating glaciofluvial deposits – High precision optical dating of cobbles. Quaternary Science Reviews 192, 263-273.</p><p>Sohbati, R., Murray, A.S., Porat, N., Jain, M., Avner, U., 2015. Age of a prehistoric Rodedian cult site constrained by sediment and rock surface luminescence dating techniques. Quaternary Geochronology 30, 90–99.</p>

A landsystems approach to understanding the evolution of ice-cored topography and distribution of retrogressive thaw slumps, western Canadian Arctic

<p>The landscape of the Tuktoyaktuk Coastlands, western Canadian Arctic is dominated by glacial and geocryological processes that have modified, imprinted and sculpted the surface, depositing surficial materials upon underlying bedrock. Climate warming continues in this region at a rate that is twice the global average, and retrogressive thaw slump (RTS) activity is increasing. Recently, RTS distribution was associated with glacial limits reached by the Laurentide Ice Sheet and corresponding morainal deposits, but RTS are common in other local terrain units. In this glacial-marginal region, permafrost existed pre-glacially, and non-glacial geomorphic processes occurred throughout the Late Quaternary. Superimposed on these conditions are the effects of thermokarst during the Holocene climatic optimum, followed by a period of cooling. Collectively, these processes and associated forms and deposits have contributed variously to preservation, development, or degradation of permafrost and ground ice. The multifaceted Late Quaternary history in this region has impeded understanding of the distributions of ice-cored topography and RTS. For example, rather than glaciogenic ice, the long reigning regional model for ice-cored topography is according to post-glacial development of intrasedimental segregation-intrusion ice. Toward better understanding the evolution of the whole landscape and the distribution of climate-sensitive terrain, we use a landsystems approach as a means to understand how the ice-cored topography developed where RTS form, through analysing the cryostratigraphy. To this end, we identify 6 RTS representing a suite of ice-cored topographic settings, including: (i) preserved basal glacial ice facies within clayey diamict that has been thrusted and folded by glacial push representing morainal deposits of the Sitidgi Stade; (ii) ice contact outwash sediments associated with the Sitidgi Stade, overlying a thermo-erosional contact with underlying basal glacial icy diamict of the Toker Point Stade; (iii) deformed basal glacial ice, eroded down by meltwater-deposited outwash sands some time between the Toker Point and Sitidgi Stades (could be ca. 12.9 kyr BP); (iv) massive, undeformed segregation-intrusion basal ice, likely formed subglacially by freezing of intrasedimental water in pre-existing Pleistocene sands into the base of the glacier, overlain by glacial diamicton;  (v) deformed basal ice facies of intermediate Toker Point – Sitidgi Stades, with an upper layer that may be supra-glacial melt-out till into which segregated ice formed; and (vi) segregation ice that formed as permafrost aggraded into glaciolacustrine clays deposited in proglacial or glacially dammed basins, that was subsequently eroded down by glaciofluvial outwash (Sitidgi Stade). To summarize, the distribution of RTS reflects primarily the distribution of icy basal glacial diamict preserved in moraines, but also basal ice and icy basal diamict that are preserved beneath glaciofluvial deposits, segregation ice in glaciolacustrine deposits, and massive segregation-intrusion ice in Pleistocene sands beneath a till plain.</p>