Middle to Late Pleistocene landscape evolution and glacial dynamics in the Eastern Alps: the Gröbminger Mitterberg record, Austria

Chapter 59 - The Pyrenees: glacial landforms from the Last Glacial Maximum

Glacial dynamics at the beginning of Termination I in the Eastern Alps and their stratigraphic implications

[1] Relatively little research has been undertaken on the use of digital elevation models to recognize the spatially variable glacial imprint of a landscape. Using theoretical topographies and a landscape evolution model, we investigate to what extent the hypsometric analysis of digital elevation models may be used to recognize the glacial signature of mountain ranges. A new morphometric parameter, which we term the hypsokyrtome (from the Greek: ipsos = elevation, kyrtoma = curvature), is derived from the gradient of the hypsometric curve. The efficacy of the hypsometric integral and hypsokyrtome is tested through the study of the Ben Ohau Range, New Zealand, whose glacial imprint has been described previously. With a numerical model we further test the geomorphic parameters in describing the morphologies of regions subject to diverse climatic and tectonic conditions. The hypsokyrtome is highly sensitive to glacial erosion, and the maps produced provide insights into the spatial distribution of glacial erosion. We use SRTM data and focus on two alternative geomorphic settings: the European Alps and the Apennines. The former has been affected by both fluvial and glacial erosion while the latter mainly exhibits a fluvially dominated morphology. The correlation between elevations with increased glacial erosion and Last Glacial Maximum (LGM) equilibrium line altitudes (ELAs) suggests the prevalence of a “glacial buzz saw” in the Alps, indicating that climate may put a limit on alpine topography.

The erosive impact of glaciers during the Last Glacial Maximum (LGM) has largely obscured evidence of earlier, less extensive glacial advances within the Alps. While Alpine paleoclimate records show that the Marine Isotope Stage (MIS) 3 was characterized by pronounced changes between stadial and interstadial conditions, similar to the Dansgaard-Oeschger (D-O) cycles observed in ice-cores from Greenland, depositional evidence of glacial extent during this period remains scarce. Here, we present new data from a sedimentary archive in the inner-alpine Bad Aussee Basin in the Austrian Eastern Alps. Located close to the main accumulation areas of the former Traun Glacier, its topographic setting suggests that down-valley glacial damming is a major factor controlling the timing of depositional phases throughout glacial-interglacial cycles. Under present interglacial conditions, fluvial incision takes place.Our investigations are focused on an 880-m-long Pleistocene sedimentary record, recovered by a drilling intended for salt exploration and later included in the ICDP (International Continental Scientific Drilling Program) project DOVE (Drilling Overdeepened Alpine Valleys). Three distinct depositional phases can be distinguished. The basal Unit A (880–580 m), dominated by glaciolacustrine deposits, can be correlated with the Penultimate Glaciation (MIS 6) based on luminescence dating and consists of locally sourced material from the Northern Calcareous Alps. In contrast, Unit B (580–67 m) records a succession of lacustrine and deltaic sediments largely derived from the Austroalpine crystalline basement to the south of the Enns Valley. Luminescence results indicate that deposition took place mainly during MIS 3. Unit B exhibits several abrupt increases in total organic carbon (TOC), which we interpret as organic productivity events, followed by a gradual decrease. This TOC pattern closely resembles the D-O cycles, allowing a tentative correlation between individual events. Unit C (67–0 m) consists of subglacial till which we attribute to the LGM, although no numerical dating results are available.Based on the sedimentological, chronological and provenance data, this study presents a reconstruction of the pre-LGM landscape evolution of the Bad Aussee Basin with particular focus on the MIS 3 stadial-interstadial cycles. Placing our results in a broader regional context, we discuss the implications for glacial dynamics and drainage evolution in the Traun and Enns valleys.

Dating the onset of LGM ice surface lowering in the High Alps

Compared with the western European Alps, the ice extent during the Last Glacial Maximum (LGM) and the subsequent deglaciation history of the eastern Alps east of the Tauern Window remain less well constrained. Also, considerable discrepancies exist between the mapped LGM ice margin and the ice extent predicted by ice‐sheet models. Here we present the first 10Be surface exposures ages from two regions east of the Tauern Window (the Gurktal and Lavantal Alps), which provide constraints on the LGM ice extent and the deglaciation history. Our results show that the deglaciation of the Gurktal Alps occurred between 16 and 14 ka, which agrees with the predictions from ice‐sheet models. In contrast, the 10Be ages from the Lavantal Alps located farther east are either LGM in age or predate the LGM, indicating that these regions were ice free or only partially covered by LGM ice. This finding suggests that ice‐sheet models may have overestimated the LGM ice extent in the easternmost Alps. In conclusion, our study highlights the need for more age data from the eastern Alps to refine the location of the LGM ice margin and the deglaciation history, which is also crucial for climate‐evolution and postglacial‐rebound models.

Glacial refugia of alpine and subnival biota have been intensively studied in the European Alps but the fate of forests and their understory species in that area remains largely unclear. In order to fill this gap, we aimed at disentangling the spatiotemporal diversification of disjunctly distributed black hellebore Helleborus niger (Ranunculaceae). We applied a set of phylogeographic analyses based on restriction-site associated DNA sequencing (RADseq) data and plastid DNA sequences to a range-wide sampling of populations. These analyses were supplemented with species distribution models generated for the present and the Last Glacial Maximum (LGM). We used exploratory analyses to delimit genomically coherent groups and then employed demographic modeling to reconstruct the history of these groups. We uncovered a deep split between two major genetic groups with western and eastern distribution within the Southern Limestone Alps, likely reflecting divergent evolution since the mid-Pleistocene in two glacial refugia situated along the unglaciated southern margin of the Alps. Long-term presence in the Southern Limestone Alps is also supported by high numbers of private alleles, elevated levels of nucleotide diversity and the species’ modeled distribution at the LGM. The deep genetic divergence, however, is not reflected in leaf shape variation, suggesting that the morphological discrimination of genetically divergent entities within H. niger is questionable. At a shallower level, populations from the Northern Limestone Alps are differentiated from those in the Southern Limestone Alps in both RADseq and plastid DNA data sets, reflecting the North-South disjunction within the Eastern Alps. The underlying split was dated to ca. 0.1 mya, which is well before the LGM. In the same line, explicit tests of demographic models consistently rejected the hypothesis that the partial distribution area in the Northern Limestone Alps is the result of postglacial colonization. Taken together, our results strongly support that forest understory species such as H. niger have survived the LGM in refugia situated along the southern, but also along the northern or northeastern periphery of the Alps. Being a slow migrator, the species has likely survived repeated glacial-interglacial circles in distributional stasis while the composition of the tree canopy changed in the meanwhile.

The European Alps were covered by a large interconnected system of valley glaciers during the Last Glacial Maximum (LGM). Many of the glaciers advanced into the Alpine Foreland leaving large latero-frontal moraine complexes suitable for (direct) exposure age dating and correlation of the ice extent at different times. In contrast to large parts of the Alps, valley glaciers flowing to the east did not reach the Alpine Foreland resulting in limited preservation of datable relicts. Fortunately, two localities at the margin of the Enns and Mur Glaciers have been found, where the requirements (quartz-rich blocks resting on latero-frontal moraine ridges) for age dating using cosmogenic 10Be and 26Al are met. The Mur Glacier occupied a W-E oriented valley located south of the Niedere Tauern mountain range in Styria. It had several outlets, one of them terminating in the very east at the village Pöls, where a roughly 400 m wide end moraine ridge is preserved. At least two-phases of ice stabilisation are indicated by two to three superimposed ridges. 1.5 m³ Pegmatite-gneiss blocks are embedded in the end moraine ridge, where we collected three samples to determine their exposure age. Age calculation using cosmogenic 10Be and 26Al yields a mean age of 19.6 ± 1.7 ka, whereby the oldest ages were obtained in the outermost part of the ridge following the expected stratigraphic sequence during ice retreat. These ages are in good agreement with other data of end moraines from LGM ice margins around the Alps. More precisely, the age range falls into a second ice re-advance, specified at other locations (especially at the southern alpine rim) but not differentiable at the Mur Glacier.At the Enns Glacier, which extended north of the Niedere Tauern mountain range, subparallel to the Mur Glacier, a multiphase moraine complex is preserved, however almost all of the  boulders are limestone or dolomite. We managed to scout few conglomerate/breccia blocks that contain 1-2 cm quartz components in a fine matrix. Three of them are embedded in the termination area and two additional boulders are located further proximal. Mean exposure ages calculated using 10Be range between 14 and 17 ka. Ages calculated from the same samples using 26Al are even more scattered. This is surprising given the similarities in location, valley orientation, geographical location, and altitude between both sample locations. Results from Enns Glacier definitely do not fall into the LGM period. But field evidence such as the location and morphological height of the ridges, strongly suggest that they were formed during the LGM and not in a Late-Glacial phase. Implementation of a snow/forest cover correction only has a minor impact on the calculated age. It is possible that the large spread in the Enns glacier exposure ages is caused by the lithological heterogenity of the sampled boulders. Large quartz clasts resist weathering for a longer duration while the matrix is continuously removed until one clast falls out and results in a discontinuous accumulation of cosmogenic radionuclides at the surface. Discussion at the conference is appreciated.

Compared to the Western European Alps, the ice extent during the Last Glacial Maximum (LGM) and the subsequent deglaciation history of the Eastern Alps east of the Tauern Window remains less well constrained. Also, considerable discrepancies exist between the mapped LGM ice margin (Ehlers and Gibbard, 2011; van Husen, 2004, 2011) and the ice extent predicted by ice-sheet models (Seguinot et al., 2018). Here we present the first 10Be surface exposures ages from two regions east of the Tauern window (Gurktal and Lavantal Alps), which provide constraints on the LGM ice extent and the deglaciation history (Wölfler et al., 2022). Our results show that the deglaciation of the Gurktal Alps occurred between 16-14 ka, which agrees with the predictions from ice-sheet models and implies that the LGM ice cover was greater than mapped. This finding also supported by our analysis of high-resolution DEMs that revealed glacially streamlined ridges and macroscale glacial striations consistent with modelled ice flow directions (Seguinot et al., 2018). In contrast, the 10Be ages from the Lavantal Alps located farther east are either LGM in age or pre-date the LGM, indicating that these regions were ice-free or only partially covered by LGM ice. Based on these results, our future investigations will aim at obtaining more age data from the Eastern Alps to refine the location of the LGM ice margin and the deglaciation history, which is also crucial for climate-evolution and postglacial-rebound models. ReferencesEhlers J, Gibbard PL, Hughes PD (2011) Quaternary glaciations - Extent and chronology. A closer look. Developments in Quaternary Science 15.Seguinot J., Ivy-Ochs S, Jouvet G, Huss M, Funk M, Preusser F. (2018) Modelling last glacial cycle ice dynamics in the Alps. The Cryosphere 12: 3265–3285.van Husen D. (2004) Quaternary glaciations in Austria. In: Quaternary Glaciations: Extent and Chronology Part I: Europe, Ehlers J, Gibbard PL (eds). Elsevier: London: 1–13.van Husen D (2011) Quaternary Glaciations in Austria. In Quaternary Glaciations – Extent and Chronology: A Closer Look, Ehlers J, Gibbard PL, Hughes PD (eds). 15: 15–28.Wölfler A, Hampel A, Dielforder A, Hetzel R, Glotzbach C (2022) LGM ice extent and deglaciation history in the Gurktal and Lavantal Alps (eastern European Alps): first constraints from 10Be surface exposure dating of glacially polished quartz veins, Journal of Quaternary Science  37: 677-687. https:// doi.org/10.1002/jqs.3399

Paleoenvironmental evolution of Picos de Europa (Spain) during marine isotopic stages 5c to 3 combining glacial reconstruction, cave sedimentology and paleontological findings

This work presents the first extensive, 1:10,000-scale field survey data concerning glacial deposits and glacigenic landforms in the Valchiavenna territory, which has an area of 578 km2. Valchiavenna is an inner Alpine valley in Northern Italy between the Lepontine and Western Rhaetian Alps.A comprehensive 1:25,000 map of deposits and landforms from the last glaciation to the present is provided, describing i) glacial trimline evidence and associated features, such as moraine ridges, erratic boulders, ice- moulded bedrock surfaces and kame terraces; ii) glacial, ice-contact, lacustrine/peat and gravity-reworked till deposits; iii) other supraglacial, marginoglacial and subglacial landforms; and iv) erratics in glacial deposits. Establishing an absolute chronology of glacier dynamics was not the objective of this work. However, a relative chronology was inferred from sedimentological and geomorphological evidence: this allowed the description of the general behaviour of glaciers in the area during and after the Last Glacial Maximum (LGM).The palaeogeography at the LGM and the palaeo-ice-flow pattern were reconstructed on the basis of field data; this data confirmed that the valleys were almost completely filled by glacier ice, covering about 88% of the study area, with only the most elevated ridges and a few nunataks emerging above the ice surface, and allowed the identification of different source areas for the erratics found on opposite sides of the main valley.The observation of stratigraphical and geomorphological relationships between glacial deposits and landforms made it possible to propose a relative chronology of glacial advances and to outline the general glacial dynamics of the area. Both at the LGM and during the deglaciation after the LGM, the valley glacier inserted offshoots in tributary valleys, thus generally blocking the advance of local glaciers. With the gradual melting of the valley glacier during the deglaciation after the LGM, tributary glaciers could deposit tills on areas previously covered by valley glacier ice and at lower altitudes than the older lateral moraines. The main outcome of this work is a rich and homogeneous database of glacial deposits and glacigenic landforms that will be useful for further local and regional studies. It can guide the planning of geochronological dating and represents a fundamental step in the identification of glacial stadials and ice mass modelling. It can also support biogeography studies and the evaluation of the effects of climate change, slope dynamics modelling and hazard prediction.

This paper presents results of the analysis of paired cosmogenic isotopes (10Be and 26Al) from eight quartz‐rich samples collected from ice‐moulded bedrock on the Aran ridge, the highest land in the British Isles south of Snowdon. On the Aran ridge, comprising the summits of Aran Fawddwy (905 m a.s.l.) and Aran Benllyn (885 m a.s.l.), 26Al and 10Be ages indicate complete ice coverage and glacial erosion at the global Last Glacial Maximum (LGM). Six samples from the summit ridge above 750–800 m a.s.l. yielded paired 10Be and 26Al ages ranging from 17.2 to 34.4 ka, respectively. Four of these samples are very close in age (10Be ages of 17.5 ± 0.6, 17.5 ± 0.7, 19.7 ± 0.8 and 20.0 ± 0.7 ka) and are interpreted as representing the exposure age of the summit ridge. Two other summit samples are much older (10Be ages of 27.5 ± 1.0 and 33.9 ± 1.2 ka) and these results may indicate nuclide inheritance. The 26Al/10Be ratios for all samples are indistinguishable within one‐sigma uncertainty from the production rate ratio line, indicating that there is no evidence for a complex exposure history. These results indicate that the last Welsh Ice Cap was thick enough to completely cover the Aran ridge and achieve glacial erosion at the LGM. However, between c. 20 and 17 ka ridge summits were exposed as nunataks at a time when glacial erosion at lower elevations (below 750–800 m a.s.l.) was achieved by large outlet glaciers in the valleys surrounding the mountains. Copyright © 2011 John Wiley & Sons, Ltd.

Stratotype for the Mérida Glaciation at Pueblo Llano in the northern Venezuelan Andes

We present marine geological and geophysical data for the Antarctic Peninsula that call for a larger ice-sheet reconstruction during the Last Glacial Maximum (LGM) than suggested by previous studies. Such glacial reconstructions are important for quantifying post-LGM sea-level rise and providing boundary conditions for general circulation models. Megascale glacial lineations on the continental shelf surrounding Antarctica provide documentation for grounded ice that was streaming. Swath bathymetry data (NBP02-01) reveal lineations in each of the major glacial troughs, except for Smith Trough, which features grooves and bedrock drumlins (0.5–3 km spacing, 1:20 elongation ratios) on crystalline bedrock. We place the maximum extent of ice at the seaward limit of the lineations, at or near ( Megascale glacial lineations imaged in this study and other areas surrounding Antarctica (including the Ross Sea, Pine Island Bay) have a consistent morphology, with elongation ratios of >80:1 and spacings of 200–600 m (mode of 300 m). In contrast, lineations (“bundles”; Canals et al., 2000) in the Gerlache-Boyd Trough exhibit larger spacing (1–5 km), and the upstream portions (∼7 km) are carved directly into bedrock rather than till, as suggested by previously unpublished air gun (∼120 Hz) seismic data. These features have yet to be dated; however, they are believed to have been active during the LGM. Radiocarbon dates in glaciomarine sediments (foraminifera and organic matter) from seven glacial troughs indicate that megascale glacial lineations were formed during the LGM. Other geomorphic features, such as the grounding zone wedge in the northwestern Weddell Sea, formed when the ice sheet was retreating. The initial retreat of the grounded ice from the outer shelf occurred by 18,500 cal yr B.P. The inner shelf was mostly ice free by 13,000 cal yr B.P. This is significantly earlier than numerical models, which suggest Antarctic deglaciation began at 12,000 cal yr B.P. This also suggests the peninsula area contributed to global sea-level rise associated with meltwater pulse (MWP) 1a.

Research Article| February 01, 2012 Subglacial carbonates constrain basal conditions and oxygen isotopic composition of the Laurentide Ice Sheet over Arctic Canada Kurt A. Refsnider; Kurt A. Refsnider 1Institute of Arctic and Alpine Research (INSTAAR) and the Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, USA Search for other works by this author on: GSW Google Scholar Gifford H. Miller; Gifford H. Miller 1Institute of Arctic and Alpine Research (INSTAAR) and the Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, USA Search for other works by this author on: GSW Google Scholar Claude Hillaire-Marcel; Claude Hillaire-Marcel 2Centre GEOTOP, Université du Québec à Montréal, Montréal, Québec H3C 3P8, Canada Search for other works by this author on: GSW Google Scholar Marilyn L. Fogel; Marilyn L. Fogel 3Geophysical Laboratory, Carnegie Institute, Washington, D.C. 20015, USA Search for other works by this author on: GSW Google Scholar Bassam Ghaleb; Bassam Ghaleb 2Centre GEOTOP, Université du Québec à Montréal, Montréal, Québec H3C 3P8, Canada Search for other works by this author on: GSW Google Scholar Roxane Bowden Roxane Bowden 3Geophysical Laboratory, Carnegie Institute, Washington, D.C. 20015, USA Search for other works by this author on: GSW Google Scholar Geology (2012) 40 (2): 135–138. https://doi.org/10.1130/G32335.1 Article history received: 08 Apr 2011 rev-recd: 13 Sep 2011 accepted: 15 Sep 2011 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kurt A. Refsnider, Gifford H. Miller, Claude Hillaire-Marcel, Marilyn L. Fogel, Bassam Ghaleb, Roxane Bowden; Subglacial carbonates constrain basal conditions and oxygen isotopic composition of the Laurentide Ice Sheet over Arctic Canada. Geology 2012;; 40 (2): 135–138. doi: https://doi.org/10.1130/G32335.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Subglacially precipitated carbonate crusts (SPCCs) formed on bedrock and till boulder surfaces adjacent to the Barnes Ice Cap (BIC), central Baffin Island, Arctic Canada, act as unique archives of Laurentide Ice Sheet basal conditions. Uranium-series dating of these features reveals that carbonate precipitation from subglacial meltwater occurred during the Last Glacial Maximum (LGM), requiring warm-based ice in the region at that time. However, the preservation of fragile SPCCs is unlikely beneath erosive warm-based ice, suggesting that the transition to subsequent cold-based conditions took place shortly after the LGM, and glacial erosion in the region occurred dominantly prior to the LGM. The oxygen isotopic composition of the meltwater from which the SPCCs precipitated is indistinguishable from that of the debris-rich BIC basal ice (δ18O –24‰ referenced to Vienna standard mean ocean water), but distinct from that of the overlying white Pleistocene ice (δ18O ∼–35‰), demonstrating that SPCCs are reliable archives of the isotopic composition of only the basal ice of past ice sheets. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.