Glaciofluvial Deposits Research Articles

Combined single grain and cobble luminescence dating of poorly bleached glaciofluvial deposits from the Swiss Alpine foreland

Combined single grain and cobble luminescence dating of poorly bleached glaciofluvial deposits from the Swiss Alpine foreland

A Holocene history of high bluffs, strandplains, terraces, and dunes along the southeastern margin of Lake Superior (Michigan, USA) with reference to fluctuating lake levels

The strandplains of the southeast Lake Superior coastline between Au Sable Point and Whitefish Point, Michigan, USA, record a response to Holocene lake-level variation (∼75 m), changing sediment supply, and accommodation space, and are good analogues for future shoreline behaviors associated with water-level changes along lacustrine and marine coastlines. A variety of datasets were used to explore these thick and extensive coastal deposits and to extend further back in time the available relative lake-level curve for the Lake Superior basin. Little is known about the coastal history prior to the Nipissing phase (6−2.8 ka) and what the geomorphic effect was from high rates of water-level rise (∼2−4 cm/yr) during the Nipissing transgression (ca. 8−4.5 ka). Rising and peak water levels eroded into glaciofluvial deposits, which resulted in eastward littoral transport of massive amounts of sediment that led to aggradation and basinward progradation of strandplains during the Nipissing transgression and Nipissing phase. Strandplains developed sequentially eastward as discreet littoral cells ending at the large (∼88 km2) Whitefish Point strandplain complex. High rates of sediment supply drove a shoreline behavior of depositional transgression and depositional regression. In post-Nipissing time, erosion likely continued into glaciofluvial deposits, but falling lake levels likely resulted in decreased sediment supply. With less sediment and less accommodation space, there was an increase in west-to-east longshore sediment transport that contributed to the growth of Whitefish Point during the Algoma (2.8−2.0 ka), Sault (2.0−1.0 ka), and Sub-Sault (1.0 ka to modern) phases. Lake-level rise after 1.0 ka has resulted in retrogradation (erosional transgression) along most of the shoreline between AuSable Point and Whitefish Point.

Towards a quantitative lithostratigraphy of Pleistocene glaciofluvial deposits in the southern Upper Rhine Graben

Abstract. The sediment fills of large terrestrial basins offer an opportunity to study and reconstruct regional-scale landscape history over time. An example of such a basin is the Upper Rhine Graben in central Europe, whose proximal, southern part has so far only sporadically been investigated sedimentologically. Three new drillings in close proximity have recovered the upper ∼ 40–60 m of the Quaternary sedimentary infill near the eastern graben margin north of Freiburg, Germany. Grain sizes, the rounding and shape of clasts, and the petrographic composition of the deposits have been determined and statistically analysed. The cored intervals consist of glaciofluvial gravels derived from and deposited by the Rhine system. While no consistent trends of the morphometric properties could be found, we succeeded in distinguishing two subunits within the topmost stratigraphic unit (Neuenburg Formation, Fm) based on compositional (i.e. gravel petrographic) data. An upper subunit (Hartheim Subformation, Sfm) enriched in lithologies representative of the Alpine orogen could be separated from a lower subunit (Nambsheim Sfm) that is enriched in lithologies of an outer-Alpine origin. We correlate these findings with a shift in the pattern of meltwater discharge from the Rhine glacier lobe that may have delivered more Alpine material into the study region during the last than during the penultimate glaciation and highlight the value of quantitative approaches and appropriate statistical evaluation for gravel petrographic studies.

A Cryogenian impact structure lurking in the shadows of northern Sweden

AbstractHere we report on findings for four rock samples with melt texture found in a gravel pit within a glaciofluvial deposit near the small town of Kitkiöjärvi in northernmost Sweden. The samples are comprised of granitic clasts embedded in a brown fine‐grained melt matrix. The samples all contain quartz grains and/or clasts exhibiting multiple sets of planar deformation features oriented parallel to crystallographic planes characteristic of shock metamorphism. The samples also contain Former Reidite In Granular Neoblastic (FRIGN) zircon. We therefore conclude that the investigated samples represent impact melt rock. We interpret a U‐Pb concordia age of 658.9 ± 6.9 Ma (Cryogenian) derived using secondary‐ion mass spectrometry analysis of shocked zircon, as the best estimate for the age of the impact event that formed the melt rocks. Zircon grains from two of the samples yield younger lower intercept ages, raising the possibility that the samples came from multiple impact events of different ages. Although we cannot exclude this possibility, we interpret the younger ages from the clast‐rich melt rocks to reflect non‐impact‐related Pb loss events and suggest that all samples likely came from the same structure. Analysis of the glaciofluvial history of the region, along with the relatively high frequency of finds (five in total, as one similar melt rock was found in the pit in 2018), points to a short‐distance glacial transportation of the samples from the southwest. Since there are no known impact structures in Sweden within that area and/or of similar age, we conclude that an old (the oldest known yet) impact structure in Sweden potentially is yet to be discovered somewhere in the vicinity of the gravel pit.

Proglacial sediments in High Arctic glacier foreland: A case study of Werenskioldbreen, Svalbard

The glacier environment exhibits a high sensitivity to global climate change, leading to progressive deglaciation and the exposure of previously ice-covered land. The newly exposed terrain provides a valuable opportunity to observe rapid ecosystem changes, such as the accumulation of glacial sediments, the development of soil-forming and progressive alterations in water and biogeochemical cycles. While developing hydrological and hydrogeological models for the Werenskioldbreen proglacial expanding zone, we encountered a significant problem due to insufficient data for parameterizing glacial sediments, which constitute the environment for water flow and storage. This study provides detailed insight into the physicochemical parameters of glacial sediments and classifies them in terms of grain size distribution, hydraulic conductivity, pH and the content of carbon (Corg), nitrogen (Nt) and phosphorus (Pt). We found that the marginal outwash plains of Werenskioldbreen are characterised by gravelly sand, sandy gravel and silty sand (28.6%, 23.8% and 19% of the total sample contents, respectively). The lateral moraine contains sandy clayey silt, silty sandy gravel or sandy gravelly silt (7.1%, 4.8% and 2.4 % of the total sample contents, respectively). The chemical parameters of young glaciofluvial sediments have lower values than those of moraines. Corg ranged from 0.07% to 2.70%. Nt was < 1.00 g kg−1 for 95% of the samples and < 0.5 g kg−1 for 81% of them. Pt was between 0.48 and 1.18 g kg−1. In line with the studies on this subject already published, we confirm that there is clear a relationship between the type of geomorphological form, its age, and the physicochemical parameters of glacial sediments.

Cladocerans and diatoms from an Early Pleistocene interglacial deposit at Pingorsuit, North-West Greenland

At the margin of the Pingorsuit Glacier in North-West Greenland, an organic-rich deposit that has recently emerged from the retreating ice cap was discovered in 2019 at an elevation of 480 m above sea level. Here we report on cladoceran and diatom analyses of this freshwater deposit from three samples of detritus gyttja, which occurred beneath a thin cover of till and glaciofluvial deposits. The cladoceran fauna comprises many non-Greenlandic, non-Arctic taxa, in accordance with previous studies of Coleoptera, Trichoptera and vascular plants. The fossil assemblages from the Pingorsuit beds resemble other fossil assemblages from Greenland that have been assigned an Early Pleistocene age, and a similar age has been suggested for the sediments found at the margin of the Pingorsuit Glacier. The fossil cladoceran and diatom species indicate a shallow lake with oligo- and dystrophic, circumneutral to slightly acidic waters. Their assemblages are more diverse compared to Holocene assemblages from northern Greenland, further indicating warmer summers than present.

Single-grain K-feldspar post-IR IRSL dating of glaciofluvial sediments of Guxiang Glaciation in SE Tibetan Plateau

The Guxiang Glaciation, a key reference for classifying late Quaternary glaciations on the Tibetan Plateau, has been dated to MIS 6 using cosmogenic 10Be exposure dating of two boulders. However, additional dating methods are needed to evaluate and improve its chronology. In this study, we used the post-infrared infrared stimulated luminescence (post-IR IRSL) signal at 225 °C from single K-feldspar grains to date a lateral moraine corresponding to the Guxiang Glaciation in the Bodui Zangbo Valley, southeastern Tibetan Plateau. Six samples from glaciofluvial sand lenses interbedded within the moraine were analyzed. The LnTn method was utilized for De determination to avoid truncation in De distribution and age underestimation. A common standardized growth curve (SGC) was established for all samples, and the least-squares (LS)-normalized Ln/Tn values of the brightest grains were selected for Ln/Tn and De estimation using the central age model (CAM). Using one fading-correction model, the post-IR IRSL ages (159 ± 9 ka to 181 ± 11 ka, average value of 173 ± 4 ka) fall within the expected MIS 6 interval and align with previous 10Be exposure ages. However, the ages are close to the limit of the method, and a different model for correcting fading suggests a much older age (average 308 ± 27 ka). This study reveals both the potential and challenges of single-grain K-feldspar luminescence dating as a means to establish chronological control for glaciations beyond the last glacial period on the Tibetan Plateau.

Luminescence ages of sediments from the margin of the penultimate glaciation in the north-eastern East European plain

In this study we apply optically stimulated luminescence and infra-red stimulated luminescence to the sediments from the interfluve dividing three river basins: the Pechora, the Kama and the Severnaya Dvina, hoping to gather new age data on glaciofluvial sediment. We also studied the valley of the Berezovka, a medium-scale river cutting through this interfluve. We obtained a chronology from 17 quartz and 15 feldspar ages. Sedimentological analyses and luminescence dating show that most of the sediments examined here are water-transported (gully alluvium, slopewash deposits), and their ages mark a period of accumulation during MIS 2. Some of these sediments were reworked by aeolian processes; these took place over a time span consistent with such processes in other parts of the East European Plain (19-12 ka). The Berezovka river experienced incision before ∼22 ka and another erosion event with extremely high floods at 15–16 ka. Its terrace formed in MIS 5, constraining the minimum age of the valley. In the bottom part of the sections, much older, possible MIS 8, glaciofluvial sediments were found; the apparent absence of MIS 6 sediments may argue for moving the MIS 6 ice sheet limit further to the north of the study area.

Morphodynamics and morpotectonics of the varzuga river mouth area (terskiy coast of the white sea) in the late glacial and holocene

The Late- and post-glacial history of the development of the White Sea coastal zone in the area of the Varzuga River mouth is considered as a result of the interaction of endogenous and exogenous factors of coastal morpholithogenesis. Based on geomorphological investigations, study of Holocene deposits by lithostratigraphic, diatom and radiocarbon analyses, as well as collection and analysis of published data, new results on the area’s relief development for ~13 cal ka BP have been obtained. The features of the regional hierarchical morphostructure and local post-glacial tectonics of the territory — the spatial relationships of blocks and the speed of vertical movements – were determined. The superimposed linear Nizhnevarzugskaya depression, which determined the configuration of the Varzuga River estuary in the late and postglacial time, was identified for the first time. The influence of the spatial ratio of blocks and differentiated postglacial uplift on the coastal morpholithogenesis was established. The course of changes in the relative sea level (RSL), development conditions and morphodynamics of the open coast and the estuary of the Varzuga River were reconstructed and new data on the rhythms of coastal morpholithogenesis processes (coastal, estuarine, and aeolian) obtained. Three stages of the coastal zone development were identified, corresponding to regional rhythms of changes in the relative sea level and climate: (I) Late Glacial transgression and Early Holocene regression (~12–9.8 cal ka BP), (II) Middle Holocene Tapes transgression (7.8–4.9 cal ka BP), (III) Late Holocene regression (after 4.9 cal ka BP). The upper marine boundary of the Late Glacial transgression is traced at the elevation of ~54–55 m a. s. l. to the west of the Nizhnevaruzgskaya depression, — ~39–40 m a. s. l. to the east of it, and — 22–25 m a. s. l. in the depression. The shores of lower morphostructural blocks were probably blocked by dead ice up until ~10.2–9.8 cal ka BP. During the Tapes transgression, the RSL reached a maximum (~7.8–7.6 cal ka BP; ~20 m a. s. l.), and by 4.9 cal ka BP fall to ~15 m a. s. l. The prevailing directions of sediment fluxes, winds and wave approach became similar to those of today. However, the main source of the coastal zone sedimentary supply was the erosion of glaciofluvial sediments and the input of sands from the seabed. In the interval of ~4.9–1.7 cal ka BP, the RSL decreased to ~5 m a. s. l. The sediment runoff of the Varzuga River became the main source of feeding the coastal zone.

Sediment colour as a marker of syn-depositional and early diagenetic processes in glaciofluvial sediments

The continental red beds, encompassing a broad spectrum of genetic types, can serve as important palaeoclimatological and palaeoenvironmental archives. The origin of sediment colouration is a complex process involving abiotic processes (e.g., breakdown of original and precipitation of newly-formed minerals), which, together with biogenic factors, lead to mobilisation of redox-sensitive elements and precipitation of Fe- and Mn-(oxy)hydroxides. There is still discussion about the interpretation of the continental red beds as palaeoclimatological archives or the colour patterns reflecting ancient redox gradients. The layers coloured in red, yellow or black can be found in the Quaternary glaciofluvial sediments in the Czech Republic. We are using a combination of field study with multi-spectral petrophysical, petrological and geochemical analyses to investigate the mechanism and timing of the origin of coloured coatings in glaciofluvial sediments, and causes of cycling of Fe, Mn, and other redox sensitive elements and isotopes. The results show that both syn-depositional and early diagenetic processes are responsible for the origin of colour patterns in the Quaternary glaciofluvial sediments. The stable molybdenum and iron isotope fractionation is primarily driven by the breakdown of the primary Fe and Mn-bearing silicates and the precipitation of the secondary Fe- and Mn-(oxy)hydroxides, such as goethite and birnessite. These precipitates are the main components of colouring coatings on the detrital grains and are able to bind other redox-sensitive elements, such as Cu, As, Mo, U, and REEs. The textural patterns and geochemistry suggest that the colour features were developed in the time range of decades to several thousand years after the deposition along ancient subsurface redox gradients due to changes in groundwater flow associated with primary lithology, glaciotectonics, and seasonal changes in the active layer of permafrost. The coatings show morphological features (rods, botryoids) and geochemical signatures (e.g., increased P contents) suggesting involvement of microorganisms to their precipitation.

Ice-marginal ridge relief complex in northern Kola Peninsula (NW Russia): morphology, structure, and genetic interpretation

A widely spread ridge relief complex was formed by the last ice cover in the northeastern part of the Kola Peninsula. The complex belongs to the ice-marginal formations of the ice streams of the north-eastern Fennoscandian Ice Sheet. The applied morphometric research technique (including the analysis of the digital elevation model) has allowed identifying the ridge relief complex to make a sub-longitudinal belt. The belt comprises frontal and radial ridges, ridges and hills of the distal part of the belt, and complex-shaped ridges. These landforms were studied in eight outcrops and trenches. The frontal and some complex-shaped ridges consist of basal and ablation tills and glaciofluvial deposits deformed by the east- and north-eastward advancing glacier. The radial ridges composed of glaciofluvial sediments are the eskers. Glaciofluvial deposits with a thin cover of ablation and flow tills form the ridges on the distal part of the belt. They mark the limits of glacier expansion at an individual glacial stage. Some complex-shaped ridges are composed only of the ablation melt-out till and formed in crevasses of dead ice massifs. The ridge relief complex shows morphological similarities with the Veiki moraine in North Sweden, Pulju moraine in Finland, and ridges of the “ice-walled-lake plains” in North America. The location of the moraine ridge landforms is controlled by the topography of crystalline bedrock. During the last glaciation, the glacier retreated in several stages marked by belts of the ridge landforms. Each stage was followed by a series of oscillations corresponding to chains of frontal moraine ridges. The correlation of the ice-marginal forms in other parts of the Kola and Karelia regions allows the authors to refer them to the Neva Stage (other names are Keiva I, Syamozero), which took place in the Older Dryas Stadial.

Limited Bioweathering by Cyanobacteria in Cold, Nutrient-Limited Conditions: Implications for Microbe-Mineral Interactions and Aquatic Chemistry in Cold Environments

Solute fluxes in Antarctic meltwaters indicate microbial processes influence chemical weathering. Antarctic cyanobacterial mats dominated by Leptolyngbya glacialis enhance weathering rates at 12 °C. Yet, their effects on nutrient fluxes in colder, nutrient-limited conditions, similar to the McMurdo Dry Valleys environments, are unknown. Here, we investigate biotic and abiotic weathering rates of glaciofluvial sediments at 4 °C and compare results to previous experiments at 12 °C. We also examine the effects of nutrient and salt concentrations on weathering fluxes by comparing the effects of different media concentrations (0.1X and 0.001X: 10 and 1000 times diluted) at both temperature conditions. Our results show limited evidence of biologically mediated silica release at 4 °C, yet microbe-mineral interactions still affect nutrient fluxes, particularly for Ca, Mg, Mn, P, and N. However, a higher initial salt concentration (0.1X media) increased the concentration of solutes released under abiotic conditions. These results indicate that aqueous solutes, temperature and microbial processes are all important factors controlling weathering rates and nutrient fluxes in cold settings.

Evolution of Weichselian aeolian strata on a coarse-grained substrate in a rugged piedmont topography: A case study from the foothills of the eastern Sudetes Mts., Czechia

The southern margins of the northern European loess belt on the foothills of Eastern Sudetes Mountains are less explored sedimentation zones. This study provides new data about the development of aeolian silty-sandy sediments overlying the glaciofluvial succession on the rugged topography near the village of Kolnovice. The Kolnovice sand quarry (360 × 200 m), which lies at the margin of the upland plateau, is the only active-mined outcrop on the foothills of the Eastern Sudetes and is large enough to study Pleistocene (peri-)glacial sediments. To examine the origin of these sediments, we applied lithofacies analysis (both macro-description of outcrop walls and micromorphological study of thin sections) and surface analysis of quartz grains. Periglacial structures have been identified within the sediments, allowing us to further interpret the post-sedimentary evolution of the sedimentary succession. The studied sediments resulted from colluvial redeposition of aeolian sediments, which was controlled particularly by the topography, glaciofluvial substrate, and climatic conditions. The underlying glaciofluvial sediments are the most crucial source of the studied sediments, although the fine-grained material could have been transported from more distant areas.

Evidence for ca. 1 Ga hypervelocity impact event found in northwest Greenland

There are likely many undiscovered impact structures on Earth, but several challenges prevent their detection, including possible concealment beneath large ice sheets. In recent years, geophysical, geochemical, and microphysical evidence has mounted for a ca. 58 Ma impact structure under the Hiawatha Glacier, northwest Greenland. Here, we report evidence for a second, much older hypervelocity impact event in this region, recorded in an impact melt rock sample collected from a glaciofluvial deposit in Inglefield Land. Secondary ion mass spectrometry U-Pb analyses of shock metamorphosed zircon grains yielded a previously unrecorded, Proterozoic best estimate impact age of 1039 ± 16 Ma (mean square of weighted deviates = 2.9). Based on Archean−Proterozoic target rock U-Pb ages obtained from unshocked zircon grains and the location of the melt rock sample along the ice margin, we suggest this sample was derived from a hypervelocity impact structure farther inland, concealed by the Greenland Ice Sheet. This study demonstrates the ability to uncover new impact events in some of the most inaccessible areas on Earth and the possibility of sampling multiple impact structures from one location when examining ex situ material. Our results have implications for current and future Martian and lunar returned samples that demonstrably bear complex impact histories.

Glacier dam evolution and knickpoint migration in the Yarlung Tsangpo Gorge, eastern Himalayas, since the last glacial period

The repeated cut-and-fill process induced by the late Quaternary glacial damming and catastrophic outburst events in the Yarlung Tsangpo Gorge (YTG) in the eastern Himalaya may reflect the interaction between rock uplift, climate change and river incision in the southeastern Tibetan Plateau. Here we provide the detailed reconstruction of the cut-and-fill history recorded at the entrance of the YTG, based on geomorphological, sedimentological and chronological analyses. The results reveal a catastrophic glacial-dam breach during the last deglaciation (∼18 ka), and the outburst flood eroded a ∼30–45 km long valley floor filled with glacial diamicton and glaciofluvial deposits, which was later further incised to form terrace T2 with a height of ∼350 m. The second dam failure occurred at ∼5 ka, producing a spillway, forming terrace T1 with a height of ∼100 m. The vertical incision and horizontal migration rate of the knickpoint at the glacier dams were estimated as 0.02 m/yr, and 2.5 m/yr since the last deglaciation, based on the age of the terraces and distance of the knickpoints. We consider the glacial dams to be effective in impeding headward river erosion during glacial periods. This, along with rapid river headward erosion during the last interglacial period, results in two knickpoints on the longitudinal profile due to the differences in erosion resistance. The fluvial reaches corresponding to the repeated cut-and-fill processes are confined to the center of the Namche Barwa massif, suggesting that rapid rock uplift counteracted fluvial headward erosion and maintained the stability of the bedrock knickpoint. Therefore, in comparison to glacial dams, tectonic uplift is the most important component in plateau margin stabilization.

Combined optically stimulated luminescence and radiocarbon dating of aeolian dunes in Arctic Sweden

AbstractMultiple parabolic sand dune fields formed in Arctic Sweden after the last deglaciation, facilitated by an abundance of loose glaciofluvial sediment, limited vegetation cover and strong winds. Following initial stabilisation, these dunes underwent repeated reworking after fire events, as evidenced by the presence of buried soils, charcoal layers and redeposited sands in the dune stratigraphy. These reworking events may be driven by wider climate forcing; however, to date, no chronological framework exists for this activity in Sweden. As such, here, we apply quartz optically stimulated luminescence (OSL) dating of Arctic Swedish sand dunes using two dunes at the sites of Vastakielinen and Jorggástat. Resultant double‐SAR (single aliquot regenerative dose) quartz OSL ages are in good agreement with independent ages provided by 14C dating of charcoal fragments recovered from charcoal layers within the dunes, and we conclude that the chosen protocol is generally well suited for dating aeolian reworking of dune sediments in Arctic Sweden. While feldspar contamination limits precise age assignment for initial dune movement, our results nonetheless suggest repeated and long‐lasting aeolian activity in Arctic Sweden throughout the Holocene and, although there are differences in detail, further suggest some general trends in terms of dune stability and reworking over Arctic Fennoscandia.

A marine record of Patagonian ice sheet changes over the past 140,000 years

Terrestrial glacial records from the Patagonian Andes and New Zealand Alps document quasi-synchronous Southern Hemisphere-wide glacier advances during the late Quaternary. However, these records are inherently incomplete. Here, we provide a continuous marine record of western-central Patagonian ice sheet (PIS) extent over a complete glacial-interglacial cycle back into the penultimate glacial (~140 ka). Sediment core MR16-09 PC03, located at 46°S and ~150 km offshore Chile, received high terrestrial sediment and meltwater input when the central PIS extended westward. We use biomarkers, foraminiferal oxygen isotopes, and major elemental data to reconstruct terrestrial sediment and freshwater input related to PIS variations. Our sediment record documents three intervals of general PIS marginal fluctuations, during Marine Isotope Stage (MIS) 6 (140 to 135 ka), MIS 4 (~70 to 60 ka), and late MIS 3 to MIS 2 (~40 to 18 ka). These higher terrigenous input intervals occurred during sea-level low stands, when the western PIS covered most of the Chilean fjords, which today retain glaciofluvial sediments. During these intervals, high-amplitude phases of enhanced sediment supply occur at millennial timescales, reflecting increased ice discharge most likely due to a growing PIS. We assign the late MIS 3 to MIS 2 phases and, by inference, older advances to Antarctic cold stages. We conclude that the increased sediment/meltwater release during Southern Hemisphere millennial-scale cold phases was likely related to higher precipitation caused by enhanced westerly winds at the northwestern margin of the PIS. Our records complement terrestrial archives and provide evidence for PIS climate sensitivity.

A glaciotectonic landform in the Shyok valley, Trans-Himalayan Karakoram Range, India

Abstract This study reports and discusses the first case of glaciotectonic landforms in the Shyok valley of the Trans-Himalayan Karakoram Range, Ladakh, where a large decomposed granite megablock (8.2 km2) along with underlying diamicton is thrust over the unconsolidated Quaternary glaciofluvial sediments along a fault gouge zone near the village of Khalsar. The absence of deformation signatures below the fault gouge indicates that the brittle fault acted as a décollement surface under frozen conditions along which the glaciotectonic megablock was translated. The other deformation features include slickensides, ductile shear, thrust propagation fold noses, clastic dykes and rafts of granite and slate within the diamicton sediments. These features indicate a subglacial glaciotectonic nappe origin of the landform. The presence of juxtaposed brittle to ductile deformation fabric, clastic dykes and the superimposition of deformed decomposed granite and diamicton over the undisturbed fluvial sediments indicates a permafrost glacial margin and proglacial environment under sufficient subglacial hydrodynamic conditions for the entrapment and transportation of the glaciotectonic megablock. The deformation fabric consistently shows a southeast orientation, indicating an advancing glacier motion from northwest to southeast. The Siachen Glacier which formerly flowed down the Nubra valley is the most likely cause of the Khalsar glaciotectonic landform.

Ventifacts and wind deflation surfaces in context with glaciofluvial sediment successions in southern Sweden – Their age and implication for glacial history

Recent suggestions propose that the glacial landscape in southern Sweden is primarily a relict from the Saalian glaciation (>130 ka). The arguments for this standpoint are the assertion that the majority of glaciofluvial deposits in this region are till-covered, and that wind-abraded clasts are observed at the contact between glaciofluvial sediments and till at numerous locations. Furthermore, it has been posited that this wind abrasion occurred during periglacial conditions during the Early Weichselian, preceding the Last Glacial Maximum (LGM). If this hypothesis holds true, it would necessitate a significant shift in our understanding of the Quaternary geological history for this region. To test this claim, we conducted an extensive examination of the purported stratigraphic conditions within 54 gravel pits situated south of the Middle Swedish End Moraine Zone (MSEMZ). The presence of a covering till bed on top of glaciofluvial sediments could only be confirmed in 22% of the gravel pits, and these sites were almost exclusively associated with ice-margin standstills/oscillations during the Late Weichselian deglaciation. In all other gravel pits where covering till could not be verified, ventifacts occur in several stratigraphic positions: at the contact between glaciofluvial and overlying littoral sediment, redeposited ventifacts within littoral sediment, and ventifacts at the contact between glaciofluvial or littoral sediments and overlying aeolian sediment. We conducted an extensive luminescence dating program (comprising 74 samples) in 22 of the gravel pits to determine the age of the ventification by dating underlying and overlying sediments. We conclude that wind abrasion across southern Sweden was not a single simultaneous event but rather a time-transgressive or recurrent process. It occurred in close conjunction with local deglaciation in some instances, while in others, it transpired later, extending into the Early Holocene. Notably, none of the encountered ventifact surfaces are of a pre-LGM age. For sites along the west coast, the evidence indicates a first wind abrasion event during periglacial conditions roughly between 17 and 16 ka. In upland sites, ventifact formation either occurred immediately after deglaciation, during the Bølling−Allerød interstadial complex (14.7−12.8 ka), or during the Younger Dryas. Even though the ice margin was situated far to the north of these sites during the latter event, concurrent patterned ground formation suggests a harsh climate with reduced vegetation cover, leading to sand drift and ventifact formation in both coastal and upland areas. In some locations, the sand drift and subsequent aeolian sediment deposition persisted into the Early Holocene. Based on our stratigraphic investigations and dates, we reject the idea that southern Sweden's glacial landscape was shaped primarily during the Saalian.

Coupled luminescence and cosmogenic nuclide dating of postglacial deflation surfaces and sand drift on a raised ice-contact delta at Veinge, SW Sweden

Wind-abraded cobbles (ventifacts) and aeolian sand are known from the sandy-gravelly coastal areas of south-western Sweden, especially in association with raised deltas. Ventifacts are recorded on at least two different stratigraphic levels, at some sites atop glaciofluvial sediment, at other sites atop littoral deposits, and in some places at both levels, while aeolian sand usually forms a surficial cover. The formation of ventifacts has usually been coupled to abrasion due to katabatic winds from the retreating ice sheet or with periglacial climate during the Younger Dryas stadial (12.8–11.7 ka).To determine the timing of these deflation events, we have applied a combination of dating methods to ventifacts and associated sediments on top of an ice-contact delta at Veinge, south-western Sweden. Quartz and feldspar luminescence dating as well as portable luminescence profiling has been used for littoral and aeolian sediments over- and underlying deflation surfaces, while rock surface luminescence burial dating and paired 14C–10Be cosmogenic nuclide dating were conducted on ventifacts. The results show that a first deflation event occurred c. 16.5 ka, just after deglaciation and prior to a regional transgression that peaked around 15.7 ka. At 12.4–11.4 ka, during the Younger Dryas stadial, a new set of ventifacts formed on the surface of the exposed littoral sands and gravels. Some wind abrasion also occurred in the early Holocene, but at c. 8.5 ka the surface was covered by aeolian sand, up to 2.5 m thick.The combination of different dating methods have allowed us to draw more informed conclusions on the timing and duration of these wind abrasion/transport events than would have been possible from the use of only single-method dating. It has also made it possible to infer some environmental conditions during deposition. For example, both glaciofluvial and littoral deposits show evidence of incomplete bleaching of the luminescence signal. This suggests short subaerial transport and brief reworking by waves, respectively, though bleaching conditions improved during shore regression. Rock surface burial luminescence profiles reveal that some ventifacts were repeatedly exposed, but that later event(s) were shorter in duration as indicated by quartz-feldspar age comparisons.