Gild Et Al 2018.Pdf

Geomorphology 301 (2018) 39–52

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Geomorphology

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Discovery of a landscape-wide drape of late-glacial aeolian silt in the western Northern Calcareous Alps (Austria): First results and implications

Charlotte Gild a, Clemens Geitner a, Diethard Sanders b,⁎ a Institute of Geography, University of Innsbruck, A-6020 Innsbruck, Austria b Institute of Geology, University of Innsbruck, A-6020 Innsbruck, Austria article info abstract

Article history: Aeolian deposits record palaeoenvironmental conditions and may coin soil properties. Whereas periglacial loess Received 21 March 2017 is extensively investigated for ~200 years, the study of the intramontane wind-blown deposits of the Alps has just Received in revised form 24 October 2017 stuttered along. Herein, we describe a drape of polymictic siliciclastic silt interpreted as an aeolian deposit that Accepted 25 October 2017 veneers extensive areas in the western Northern Calcareous Alps (NCA), from kames terraces near valley floors Available online 27 October 2017 up to last-glacial nunataks. — — Keywords: The NCA part of the Eastern Alps mountain range consist mainly of Triassic carbonate rocks; these are over- Alps lain by deposits of the Last Glacial Maximum (LGM) and its deglacial-paraglacial aftermath (e.g., glacial tills, Loess fluvio-lacustrine successions, alluvial fans, scree slopes) — and a regional drape of polymictic silt newly described Quaternary herein. The drape is typically a few decimeters in thickness and slightly modified by soil formation; it consists Late-glacial mainly of well-sorted silt of quartz, feldspars, phyllosilicates (muscovite, chlorite, biotite), amphiboles and, rarely, calcite or dolomite. The drape is unrelated to the substrate: it overlies carbonate bedrock and — in lateral continuity — abandoned deposystems such as colluvial slopes of redeposited till, kames, alluvial fans, scree slopes, and rock avalanche deposits. The drape was spotted from near the present valley floors up to LGM nunataks, over a vertical range of some 2000 m; it is also present in catchments of the NCA that were not overridden by far-travelled ice streams and that lack metamorphic rock fragments. Two OSL quartz ages of the drape from two distinct locations (18.77 ± 1.55 ka; 17.81 ± 1.68 ka) fall into the early Alpine late-glacial interval shortly after the collapse of pleniglacial ice streams; this fits with geological and geomorphological evidence, respectively, that the drape should be of early late-glacial age, and that it accumulated during a specificinterval of time. In the NCA, localized minor deposition of aeolian dust is documented — by other authors — from plateaus deglaciated only during the late-glacial to Holocene; no evidence, however, exists for another phase of similarly widespread aeolian deposition such as that which gave rise to the described regional drape of silt. Intense aeolian transport and deposition was probably a direct consequence of the liberation of huge amounts of unsorted sediment during deglacial ice collapse, perhaps combined with climatic aridification. This provides a hitherto unappreciated element of the deglacial to paraglacial phase: intramontane dust storms. Because of its large extent and the availability to OSL dating, the aeolian drape provides an excellent geochronological marker level identified in terrestrial post-glacial successions of the Eastern Alps. Because of its fine-grained siliciclastic composition, the drape gives rise to widespread development of atypical Cambisols (on carbonate bedrocks) with comparatively high water storage capacity and nutrient supply. © 2017 Elsevier B.V. All rights reserved.

1. Introduction et al., 2001; Forman and Pierson, 2002; Little et al., 2002; Chlachula, 2003; Rutter et al., 2003; Zárate, 2003; Kehl et al., 2005; Heil et al., In the Quaternary, intervals of loess are widespread on continents 2010; Hughes et al., 2010; Ma et al., 2013; Nottebaum et al., 2014; and larger islands subject to glacial-interglacial cycles (e.g., Brunnacker, Klasen et al., 2016), and provide palaeoenvironmental information over 1974; Zhongli et al., 1992; Dearing et al., 1996; Frechen, 1999; Antoine a wide range of scales in space and time (e.g., Zhongli et al., 1992; Dearing et al., 1996; Little et al., 2002; Muhs et al., 2003; Iriondo and Kröhling, 2007; Vriend et al., 2011; Wolfe, 2013; Lehmkuhl et al., 2014; ⁎ Corresponding author. E-mail address: [email protected] (D. Sanders).

Nottebaum et al., 2014; Cremaschi et al., 2015; Stauch, 2015; Boretto change diminishes, and the regime is typically characterized by slower et al., 2017). redeposition and erosional incision (e.g., Hinderer, 2001; Ballantyne, Loess records an important component of the (palaeo-)environment: 2002; Orwin and Smart, 2004; Sanders, 2012). dust-laden storms of sufficient sediment load and/or frequency to In the Eastern Alps of Europe (Fig. 1), rapid collapse of last-glacial leave a geologically preservable interval of wind-transported sediment ice masses from ~21 ka to ~19 ka exposed trunk valleys and lower- (e.g., Koster, 1988; Frechen et al., 2003; Iriondo and Kröhling, 2007; positioned tributaries to deglacial-paraglacial sedimentation (Fig. 2) Smalley et al., 2011; Sprafke and Obreht, 2015). Because aeolian deposits (see Auer et al., 2014, for summary). Because of very high rates of sedi- are available to numerical age dating with the luminescence methods ment dispersal, no soils or other levels suited for numerical age dating they can provide, both, environmental and geochronological information accumulated. The patterns of early post-glacial intramontane sedimen- (e.g., Ding et al., 1997; Arimoto, 2001; Vriend et al., 2011; Lehmkuhl tation, and its relation to late-Glacial to Holocene land surface changes, et al., 2000, 2014; Roberts, 2008; Stauch, 2015). Except for base-level are thus hardly resolved to date. In addition, the subdivision of the changes imparted by tectonism or mass-wasting, in mountain ranges Alpine late-glacial into an orderly succession of glacial advances and subject to glacial-interglacial cycles, practically all of the sedimentation retreats — since Penck and Brückner (1909) — became controversial and erosion is directly or indirectly linked to climate. Within a mountain (see Reitner et al., 2016; Moran et al., 2016). In brief, except for range, over glacial-interglacial cycles, two major phases of sediment exposure-dated moraines, the late-glacial terrestrial record of the Alps accumulation and geomorphic change are identified: (a) proglacial is poorly resolved with respect to chronology. sedimentation, such as in valleys blocked by advancing ice streams, Over the past two years, in the western Northern Calcareous Alps and (b) deglacial to paraglacial sedimentation during to shortly after (NCA), we have systematically field targeted a polymineralic siliciclastic melting of glacial icestreams (e.g., Church and Ryder, 1972;VanHusen, drape typically a few decimeters in thickness (Figs. 1, 2 and 3). 1999; Meigs et al., 2006; Ostermann et al., 2006; Reitner, 2007; The drape veneers truncated bedrocks and — locally in exposed lateral Sanders and Ostermann, 2011; Reitner et al., 2016). Subsequent to the continuity — abandoned late-glacial deposystems such as kames, deglacial-paraglacial sedimentation pulse, the pace of geomorphic redeposited till, scree slopes, alluvial fans, and rock avalanches (see

Fig. 1. (A) Position of European Alps in Europe. (B) Gross geological subdivision into Eastern, Western, and Southern Alps, respectively. (C) Part of geological map of the central sector of the Alps (modified from Schmid et al., 2004) showing the wider environs of Innsbruck city, and the position of the Northern Calcareous Alps (NCA). White dashed area in the NCA indicates the total area of inspected locations (see also subfigure E). (D) Map of Southern and Eastern Alps during the Last Glacial Maximum (modified from Ehlers, 2011,hisFig. 2.8). The red shade shows the total area of inspected locations. C. Gild et al. / Geomorphology 301 (2018) 39–52 41

Fig. 2. Peak glacial to early Holocene climatic history of the Austrian Alps, relative to NGRIP δ18O record (modiﬁed from Auer et al., 2014). OSL quartz ages of the siliciclastic silt drape from two locations are shown with their 2 sigma standard deviation. Blue: local glacial advances (“stadials”) during the late-glacial interval in the central part of the Eastern Alps.

below) (Gild et al., 2016, 2017; Albertus, 2016). The drape was spotted striking valleys up to a few tens of kilometers in length (Fig. 3). In from near the levels of the present trunk valleys up to LGM nunatak the western NCA considered herein, the two landscape-forming plateaus (Gild et al., 2016). In the present paper the geomorphological stratigraphic units comprise: (1)theMiddletoUpperTriassic and depositional contexts as well as the sediment characteristics Wetterstein Formation, up to 1200 m in thickness, and composed (grain size distribution, mineralogy, grain shapes) of the drape are of limestones of fore-reef to tidal-flat environments, and (2) the described and interpreted. Based on two quartz OSL ages, integrated Upper Triassic Hauptdolomit unit, a succession up to N2000 m with sedimentologic-geomorphological evidence, we interpret the thick of lagoonal to tidal-flat dolostones (Tollmann, 1976). Intervals drape as a regional intramontane aeolian sediment that accumulat- with siliciclastics are thin and provided décollement levels for ed during to shortly after decay of the pleniglacial ice cover of the thrusting (Eisbacher and Brandner, 1996). Eastern Alps. This adds a new and hitherto unidentified element to During the Quaternary, the Eastern Alps were subject to at least four the palaeoclimatology of the deglacial to early paraglacial interval, major glaciations (Van Husen and Reitner, 2011). Because most of i.e., dust storms. For the post-last glacial terrestrial record of the Alps, the larger Eastern-Alpine glacial ice streams had rooted in the Central the drape provides the first ever regional land-based horizon suited Alps (Fig. 1B), in Quaternary deposits of the NCA, metamorphic rock for geochronologic dating. fragments are derived from glacial drift of ice streams. In the western NCA, the ice streams from the catchments of the Inn and Lech rivers, 2. Setting respectively, were largest. The drift of the Inn ice stream is characterized by metamorphites such as orthogneiss with greenish sericitized feld- The Eastern Alps originated during Cretaceous to Paleogene con- spar and diverse types of greenstones (Mutschlechner, 1948). The Inn vergence between the Adriatic microcontinent in the South and an ice stream had overtopped or partly invaded many valleys of the NCA; oceanic seaway and the southern margin of Meso-Europa to the in this case, the corresponding Quaternary deposits consist of NCA- North (e.g., Schmid et al., 2004). The present Eastern Alps consist of derived carbonate-rock clasts mixed with clasts of metamorphites and (a) a W-E striking northern range dominated by carbonate rocks other rocks picked up along the route of the ice stream. Larger catch- (Northern Calcareous Alps, NCA), separated by W-E to ENE-WSW ments of the NCA rooted in high-positioned groups of cirques, and striking trunk valleys from (b) the Central Alps that consist mainly catchments offstream the Inn glacier, however, are devoid of metamor- of metamorphites (Figs. 1 and 3). The trunk valleys, in turn, are phic rock fragments also in their pleniglacial deposits; in other words, linked to the orogenic crestline along the Central Alps via N-S these valleys or valley systems had their own glaciers large enough to 42 C. Gild et al. / Geomorphology 301 (2018) 39–52

Fig. 3. Overview of locations positively checked for the aeolian drape. The locations range from 595 m a.s.l. to 2592 m a.s.l. in altitude, a range of ~2000 m of topographic relief. The drape was consistently identiﬁed also on nunatak plateaus of the Last Glacial Maximum (LGM). For areas below the LGM upper ice limit, the largest lateral continuity of the drape within a single outcrop documented so far is 600 m (see Fig. 5). Samples for optically-stimulated luminescence dating of the aeolian sediment were taken at location #3 (Lab ID L012/2: 18.77 ± 1.55 ka) and from location #15 (Lab ID L012/1: 17.81 ± 1.68 ka).

block off an intrusion of far-travelled Inn ice (Mutschlechner, 1948;Van et al., 2007). All numerical ages available so far indicate that the degla- Husen, 1987; Reitner, 2011). ciation of inner-Alpine valleys was completed at ~18 ka (cf. Klasen In the Eastern Alps, the LGM lasted from ~26 ka to ~21 ka; at that et al., 2007; Ivy-Ochs et al., 2008). Subsequent to the collapse of the time, except for nunatak plateaus and crests, the entire western NCA pleniglacial ice, during the late-glacial chron (~19 ka to 11.7 ka), valley of interest herein were covered by ice (Fig. 1B). Geomorphological glaciers repeatedly advanced during relative coolings (Fig. 2). In the criteria, mapping of the presence/absence of clasts of metamorphic Eastern Alps, on from 14.6 ka b2k, when a marked warming is recorded, rocks, and glacial mass budgets together indicate peak glacial ice thick- an interstadial (Bölling-Alleröd) followed by the Younger Dryas stadial nesses of 1000–1800 m in the NCA (Van Husen, 1987). For the present are well-identifiable (Fig. 2). paper, two ice streams are pertinent, (a) the Isar-Loisach glacier, and As mentioned, during the ice collapse, huge amounts of sediment (b) the Zillertal-Inn glacier. For the Isar-Loisach glacier, 10Be exposure were liberated from both decaying ice streams and mountain flanks, ages suggest an age of terminal moraine stabilization of 17.6 ± 0.8 ka and were stored in thick scree-slope, alluvial-fan, and aggraded valley- (outer moraine) and 17.3 ± 0.7 ka (inner moraine) (Ivy-Ochs et al., bottom successions, respectively. Unfortunately, to date the pace of 2008). For the Zillertal-Inn ice stream, at the location Wasserburg shortly deglacial-paraglacial sedimentation, and a potential continuation of inboard of the terminal moraine, 14C dating of wood in fluvioglacial intense sedimentation (or phases of intensified sedimentation) farther deposits beneath the last-glacial till indicates an age of 25.7–31.2 ka into the late-glacial chron, could not be estimated quantitatively due (Habbe et al., 1996, cit. in Ivy-Ochs et al., 2008, p. 565). to the absence of time markers. The qualitative evidence from relative On from ~21 ka, the ice streams stagnated, and rapid melting started. (geomorphic) dating of landforms, and semi-quantitative evidence There is evidence for a roughly synchronous decay of the Zillertal from age-dating of diagenetic cements in post-glacial deposits, however, ice dome of the Central Alps and the piedmont glaciers in the northern indicate that most deposystems located in relatively low to intermediate foreland: while in the foreland, glacier melting started soon after 19 ka, altitude became abandoned and at least sparsely vegetated quite early for the Zillertal ice accumulation center, and exposure ages indicate a after deglaciation, and/or subject to erosion ever since (Sanders et al., start of melting at 18.6 ± 1.4 ka (Wirsig et al., 2016). The LGM ice accu- 2009; Sanders and Ostermann, 2011; Sanders, 2012). mulation centres drastically shrank within, at most, some 2000 years (Fig. 2); the rapid melting of glacial ice was probably supported by 3. Methods, definitions climatic aridification (Luetscher et al., 2015). Exposure ages further indicate that, in the Central Alps near the crestline of the orogen, rem- The aeolian drape was targeted in the field by systematic surveys. nant ice caps persisted until the start of the Bölling-Alleröd interstadial The survey is based on assessment of geological maps combined (Wirsig et al., 2016). OSL dating of proglacial deposits in the lower Inn with: (a) inspection of geomorphic features in laserscan orthoimagery valley indicates that at least this area was free of ice at ~19 ka (Klasen (https://portal.tirol.gv.at/weboffice/tirisMaps)and(b)the C. Gild et al. / Geomorphology 301 (2018) 39–52 43 reconstruction of pleniglacial ice levels and nunatak plateaus of Van subordinate fraction of sand and/or clay. In terms of slope-deposit Husen (1987). To date, a total of 32 locations distributed over the west- terminology, the aeolian drape described hereunder is part of a ern NCA have been checked positively for the drape (Fig. 3). Locations “cover bed” succession as defined by Kleber and Terhorst (2013a, ranged from 595 m a.s.l. to 2589 m a.s.l., i.e., locations with a drape 2013b,seealsoKleber, 1990, 1992), or may comprise a single cover of polymictic siliciclastic silt were identified over an altitude range of bed in itself. roughly 2000 m. Where found, the drape was excavated in order to log a vertical section and to sample the sediment. 4. Aeolian drape: description Laser diffraction granulometry: The grain-size distribution of sediments was determined by sieving and by laser diffraction. For laser 4.1. Field appearance, distribution diffraction grain size measurements, a Malvern Mastersizer 2000® was used with a detection range of 0.02–2000 μm. Approximately 1 g In the field, the drape shows as a medium-brown level that, in by of sample was stirred in 20 ml of Aqua Bidest. No difference in measure- far the most cases, is positioned directly under the vegetated organic ment results was observed with respect to time between wetting and layer (Fig. 4A–D), more or less modified by soil formation. The drape suspension and measurement; the same results were obtained for is typically between 0.2 and 0.5 m thick, but locally thickens to more 1 week, 3 days, 1 day, 2 h and 60 min of rest after suspension. Measure- than 1 m. In the field, it appears as an interval of more-or-less homoge- ments were made with a red He-Ne laser (wave length 0.632 μm) and neous well-sorted silt. To date, no primary sedimentary structures have with blue light (wave length 0.466 μm). Each sample suspension was been identified within; the drape appears unbedded and unlaminated. measured 18 times, subdivided into packages of three measurements The drape is present irrespective of its substrate, i.e., it overlies bedrock, each (=six packages in total). Each package was immediately preceded glacial till and redeposited till, alluvial deposits, scree and, in a few cases, by an ultrasonic impulse 60 s in duration, to disaggregate potential deposits of catastrophic rock avalanches (Fig. 4A–D). Where continuous clumps of fine grains. Automated calculation of the grain-size distribution outcrop or closely-spaced exposure allows us to identify it, a lateral con- was based on Fraunhofer diffraction theory. The intensity of the diffracted tinuity of the drape across several types of substrate is seen (Fig. 5) laser light was detected with 52 sensors, and with 1000 detections per (Albertus, 2016). The drape of siliciclastic silt also extensively veneers second. catchments that were not invaded by the Inn ice stream (Fig. 6)and X-ray powder diffractometry: To date, 65 samples have been analysed LGM nunatak plateaus (Figs. 3 and 4C); these areas are devoid of for bulk mineralogical composition by X-ray powder diffractometry. pebbles of metamorphic rocks. The drape has been observed in outcrops Measurements were made on a Bruker-AXS D8 diffractometer with near the floor of the Inn valley (Fig. 5) to abandoned alluvial fans and Bragg-Brentano geometry (Theta-Theta arrangement), CuKα radiation scree slopes along tributary valleys (Fig. 6) up to LGM nunatak plateaus at 40 kV/40 mA acceleration voltage, with parallel-beam optics and (Fig. 4C), over an altitude range of ~2000 m (Fig. 3). Our field searches an energy-dispersive detector. Data were recorded between 2 and progressively revealed a very large extent of the drape on deglaciated 60° 2Theta, with a step size of 0.02° 2Theta and 4 s detecting time per rock surfaces and on top of paraglacial deposystems that became step. Phase identification was done with the program Eva.Ink and the inactive soon after deglaciation, and that allowed for accumulation PDF4 database 8.0.113 of ICDD; X-ray spectra were analysed with the of silt-sized deposits. In the case of inactive deposystems, in most programs DIFFRAC PLUS (phase identification) and TOPAS (quantitative cases, lateral limitation of individual outcrops does not allow us to assessment). identify the nature — depositional or erosional — of the contact between Backscattered electron microscopy: The shapes and surfaces of sedi- underlying sediment and overlying drape. In a few cases, however, out- ment grains of selected samples were investigated using backscattered crops suggest that the drape veneers abandoned depositional surfaces electron microscopy. For inspection, a small portion of dry sediment (Fig. 4E, F) and/or surfaces of moderately deep erosional downcut was scattered onto a chip of adhesive tape, and inserted unsputtered (Figs. 5 and 6). into the SEM vacuum chamber. Electron microscopic inspection was done with a Digital Scanning Microscope JEOL JSM-5130LV in low- vacuum mode, at 25 kV acceleration voltage, a gun current of 5 μA, 4.2. Grain size distribution, autochthony, bulk mineralogy with a backscattered electron detector. OSL dating: Two samples from two different sites were chosen for From sample locations near the floors of valleys up to LGM nuntaks, optically-stimulated luminescence dating (OSL) of quartz. Samples the drape shows closely similar, unimodal grain-size distributions were taken from freshly-excavated sections by hammering a steel of well-sorted silt throughout (Fig. 7). The grain-size distribution curves tube of 4 × 4 cm inner width and 25 cm in length into the sediment. furthermore indicate a significant content of very-fine and fine-grained The samples were retrieved under careful observation and protection sand (62–250 μm); medium to coarse sand, in turn, comprises a small from light incidence, and immediately thickly wrapped with black fraction between nearly zero and b10 vol%. In addition, clay-sized parti- adhesive tape. The measurements were carried out in the Luminescence cles 4–0.4 μm in size comprise a sizeable fraction of the sediment Laboratory of the School of Geography and the Environment of the (Fig. 7). University of Oxford (Oxford Lab ID: L012/1 and Lab ID L012/2). Downward from its unsharp top that is mixed with humus, the The definition of loess has varied since the 1830s (see Smalley drape of silt may be more-or-less densely penetrated by plant roots and Leach, 1978; Pécsi, 1990; Pye, 1995; Smalley et al., 2001; Smith (Fig. 4A–D). The base of the drape in most cases is sharp relative to et al., 2002), but it is agreed that loess is an aeolian deposit mainly the underlying deposits. Notably, at none of the locations investigated of silt-sized particles (Muhs, 2013; Sprafke and Obreht, 2015). Here- so far, has any evidence for soil formation underneath the drape been in, we follow Muhs (2013, p. 149) who defines loess as an "Aeolian found. At a few locations, in particular near the toe of steep slopes, the silt thick enough to be recognizable in the field as a distinct sedimen- drape interval may contain isolated floating lithoclasts or unsharply- tary body." Note that this definition does not include statements on delimited clast layers supported by matrix; in these latter cases, (i) the chronological position (e.g., glacial or interglacial) and time redeposition of drape material and mixing with foreign materials is span of deposition, (ii) lateral extent of the deposit, and (iii) the set- indicated. At locations #2 and #19 (Fig. 3; see also Fig. 4F), together ting such as periglacial areas during glacials, or piedmont glacier with its host sediment, the drape is locally deformed into small forelands, or intramontane areas. To distinguish loess from wind- fold-like structures with an amplitude of up to a few decimeters blown sand (most grains 0.05–2 mm in size) and to aerosolic dust (Hinterwirth, 2017; Niederstrasser, 2017). Commonly, however, the (all grains smaller than 10 μm), Muhs (2013 p. 151) characterizes drape does not show evidence of intense deformation of the entire loess as consisting typically of 90–60% silt, with a potentially admixed layer, and appears to be positioned more-or-less in situ. 44 C. Gild et al. / Geomorphology 301 (2018) 39–52

Fig. 4. Details of silt drape in different settings. (A) Drape of polymictic silt (pS) directly on Triassic dolostone (Hauptdolomit unit, HD), 1242 m a.s.l., Location #6 in Fig. 3. (B) Drape of polymictic silt (pS) on 1496 m a.s.l. directly on bedrock hill of Triassic dolostone (Hauptdolomit unit, HD). Location #9 in Fig. 3. (C) Drape of brownish polymictic silt (white arrow) on LGM nunatak of Triassic limestone, 2080 m a.s.l. Inset shows that the drape here is locally nearly one meter in thickness. White dot: sample. Location #30 in Fig. 3. (D) Drape of polymictic silt (pS) directly above a rock-avalanche deposit (RD) of Triassic limestone (location on 880 m a.s.l.) An OSL quartz age from this drape yielded 18.77 ± 1.55 ka. Hu = Humus. Location #3 in Fig. 3. (E) Western part of large artificial outcrop containing the drape of polymictic silt. Redeposited LGM till [Dms(c)] is overlain by stratified and lithified redeposited till [Dms(c,l)] which, in turn, is veneered by the brownish drape of silt (pU; base stippled). The silt drape here is overlain by stratified scree that may correspond to the stratified scree Scc2 of Fig. 5. Location #15 in Fig. 3. (F) Gravel pit cut into an alluvial fan supplied from Triassic dolostones. The lower part A of the exposed succession is rich in clasts of metamorphic rocks. Part A is veneered by a drape of brownish siliciclastic silt (base stippled). The drape, in turn, is overlain by two distinct sedimentary packages B and C of younger alluvial fan deposits that are poor in clasts of metamorphites. Location #2 in Fig. 3.

The drape consists mainly of quartz, feldspars, muscovite, chlorite and vegetated early after ice collapse (Fig. 5). The OSL age from this and amphibole (Fig. 8); at a few locations near the floor of the Inn valley, location was 17.81 ± 1.68 ka (see Fig. 2). Location #3, in turn, is a significant amounts of calcite and dolomite are present, too. Inspection drape of silt directly on top of a rock avalanche deposit (Fig. 4D). For by backscattered electron microscopy shows that most grains are angu- this rock avalanche, the geomorphic context and radiocarbon dating of lar with unabraded fracture surfaces. Only a subordinate grain fraction the washed and sieved bulk organic fraction of soil levels above the shows rounded edges, or is of subrounded shape. Some of the grains rock-avalanche deposit indicated a late-glacial age of mass wasting also display irregularly-pitted and honeycomb-like surfaces. (Sanders et al., 2016); the OSL sample, in turn, indicated an age of 18.77 ± 1.55 ka (see Fig. 2)(Gild et al., 2017). 4.3. First OSL ages 4.4. Siliciclastic drape within successions At locations #15 and #3 (see Fig. 3), samples for quartz OSL dating were taken. Location #15 is positioned ~90 m above the present floor Where the drape is absent at the surface, natural or artificial of the Inn valley, i.e., a location that should have become abandoned outcrops locally expose an interval of brownish silt to fine sand within C. Gild et al. / Geomorphology 301 (2018) 39–52 45

Fig. 5. Eastern part of abandoned quarry in Triassic carbonate rocks, a few tens of meters above the bottom of the present Inn valley (location #15, Fig. 3). The Triassic rocks are overlain by subglacial till and redeposited till of the Last Glacial Maximum. The redeposited till, in turn, is locally overlain by a thin scree-slope succession SCc1; this succession is veneered by the drape of aeolian silt (pU). A younger scree-slope succession SCc2 was important to preserve the aeolian drape. Note vertical exaggeration. Figure modiﬁed from Albertus (2016).

successions of carbonate-lithic sediments (Fig. 4E and F). The mean of englacial-supraglacial till during ice collapse, it should be an grain size and composition of these “intercalated intervals” are identical extremely-poorly sorted sediment rich in pebbles to boulders (cf., to the “topping drape” directly below the topsoil (cf. Fig. 8AandE e.g., Benn and Evans, 2010) of metamorphic rocks. Ad (3): Finally, for and F); in one case, a lateral continuity from “intercalated interval” to the drape to result from colluvial winnowing of till, shallow and gentle “topping drape” can be demonstrated in the outcrop (Figs. 4E and 5) overland flows were required to leave back the coarse grain-size fraction (Albertus, 2016). The drape is absent in near-surface exposures wherever (sand to cobbles) of the till (cf., e.g., Hairsine et al., 1999; Buda, 2013; Lin deposystems are still active, or arguably were active until late-glacial to et al., 2017), to result in a sheet-like colluvial accumulation composed Holocene times (cf. Fig. 4E and F) (Niederstrasser, 2017). For instance, exclusively of silt down to more than a kilometer downslope. In view mountain flanks in the NCA may be extensively veneered by the drape; of the lateral and vertical extent of the drape, similarly extensive lags higher up along the same slope, however, fossil post-glacial rock glaciers, of glacial tills enriched in pebbles to cobbles of metamorphic rocks in contrast, are unveneered. Similar observations can be made with should always be found higher upslope; this is not the case. In addition, respect to scree slopes, alluvial fans as well as deposits of rockslides and a colluvial origin of the drape is precluded by: (i) its relatively constant rock avalanches. thickness over large lateral and vertical distances, (ii) the morphological situations it is found within, ranging from very steep slopes to the flat 5. Interpretation tops of whalebacks and plateaus below the pleniglacial ice line, and (iii) the presence of the drape — with identical granulometric and min- 5.1. Sediment eralogical characteristics — also on LGM nunataks (cf. Figs. 7 and 8). Conversely, the described geomorphological contexts, the stratigraphic The combined evidence indicates that the drape represents an associations, and the compositional and granulometric characteristics aeolian deposit (loess) that veneers large areas of the NCA. Alternative of the drape all indicate that it was initially deposited from fallout of interpretations may include: (1) the drape is a lag deposit from soil- wind-blown dust (Interpretation E in Table 1,seeFig. 9). induced chemical weathering of carbonate rocks or basal till (Interpre- The mineralogical composition of the drape indicates that at least tations A and B in Table 1), (2) the drape accumulated from meltout most of the sediment was derived from source areas with metamorphic of englacial-supraglacial till during ice collapse (Interpretation C in rocks and/or with clastic material rich in fragments of metamorphic Table 1), or (3) it is a hillslope-colluvial deposit resulting from overland rocks. Potential source areas of the dust were thus the terrains of meta- flow over pleniglacial till (Interpretation D in Table 1). Ad (1): The morphic rocks of the Central Alps (cf. Figs. 1 and 3), and valleys floored insoluble residue of carbonate rocks of the NCA is dominated by illite with scarcely vegetated to unvegetated glacio-fluvial deposits rich and smectite clays; other minerals that are common within the drape, in metamorphic rock fragments. The widespread succession from such as feldspar, chlorite and amphibole, are absent (Solar, 1964; (i) paraglacial deposystems below into (ii) the overlying aeolian drape Kralik and Schramm, 1994; Küfmann, 2008); the mineralogical compo- and organic layer above (see Fig. 4D–F, Figs. 5 and 6) suggests a specific sition, thus, contradicts chemical weathering. In addition, if the drape environmental dynamics, including: (a) abandonment or intermittent resulted from the dissolution of carbonate rocks, it should be absent inactivity of a deposystem to allow for accumulation of the silt drape, where it does not directly overlie these rocks. If the drape resulted followed by (b) vegetation and cover of the drape by soil. Because from chemical weathering of basal till, it should be rich in pebble- unvegetated areas of unsorted debris are prone to aeolian blowout, a to cobble-sized clasts of metamorphic rocks (see Section 2 above); release of sediment on a scale as large as during deglaciation might this is not the case. Ad (2): Similarly, if the drape resulted from meltout give rise to a local “autocyclic” succession from aqueous paraglacial 46 C. Gild et al. / Geomorphology 301 (2018) 39–52

Fig. 6. Section at location #19 (see Fig. 3). The lower part consists of: (i) diamicts interpreted as waterlain till and lodgement till, and (ii) an interval of carbonate silt that probably accumulated in an ice-marginal lake. Above, a package of pebbly to cobbly deposits — locally lithiﬁed in its upper part — is interpreted as a paraglacial talus fan; at least in its early stage, the talus may have been shed into the ice-marginal lake. The surface of the fan comprises the highest terrace of post-glacial deposits along the valley. A gentle erosional relief on the fan surface is draped with a layer a few decimeters in thickness of polymictic siliciclastic silt.

sedimentation (e.g., shedding of alluvial fans) to aeolian deposition. carbonate-lithic material of clay- to boulder-size grade than in meta- Two observations stand against this possibility. (1) In the NCA, the morphic rock fragments. If the aeolian drape resulted only from blow- deglacial to paraglacial deposits are overwhelmingly richer in out of local deglacial-paraglacial deposits, it should consist largely of carbonate grains; in addition, this hypothesis can hardly explain the siliciclastic-dominated composition of the “intercalated drapes” that, in some cases at least, are laterally continuous into a drape on top (Figs. 4Eand5). (2) As mentioned, the siliciclastic silt drape is present also in areas of the NCA that were not overridden by LGM ice streams and that are completely devoid of any clasts of metamorphites (except for the drape) (Fig. 6). Together, this underscores that the dust was dis- persed by larger-scale meteorological processes that overrode or blurred site-related effects. As described, at several locations, there is evidence for secondary overprint that affected the drape (e.g., folding, admixture of rock clasts). In principle, a wide spectrum of natural and human disturbances may potentially modify or obliterate the drape (Table 2). Because of the probable high age of the drape (Fig. 2), a part of the clay-sized sediment fraction may result from pedogenic processes; in addition, however small it is, it remains to be clarified how far the medium- to coarse Fig. 7. Grain-size distribution of aeolian drape from different locations, measured by laser diffractometry. Note: (a) unimodal distribution with all peaks in the silt-size range, and sand sediment fraction results from primary deposition and/or was (b) a lower but consistent content of very fine to fine sand and clay-sized particles. mixed into the sediment by secondary processes. C. Gild et al. / Geomorphology 301 (2018) 39–52 47

Fig. 8. X-ray powder diffractograms of aeolian deposits from: (a) location #15, 605 m a.s.l., (b) location #20, 1491 m a.s.l. (draping a rock avalanche), (c) location #4, 2592 m a.s.l. (LGM nunatak), (d) location #30, 2090 m a.s.l. (LGM nunatak), (e) location #2, 955 m a.s.l., (f) location #24, 907 m a.s.l. (see Fig. 3 for locations). The drape is composed of quartz, feldspars, phyllosilicates (chlorite, micas), and an accessory amount of amphibole; no signiﬁcant amount of clay minerals is identiﬁed. In addition, at location #15 (a) a low amount of calcite, and at location #2 (e) a low amount of dolomite is present, respectively. For each analysis, minerals are indicated in decreasing relative abundance. Quartz and, in most cases, phyllosilicates comprise by far the overriding fraction of the sediment.

5.2. Age 5.3. Sediment provenance and dispersal

As described, along the lower boundary of the aeolian drape, no The overall distribution of major rock types in the Eastern and evidence of soil development was identified. This suggests that the Southern Alps, respectively, leaves little doubt that most or all of the drape formed early after ice collapse, i.e., before sedimentation slowed siliciclastic material of the drape is derived from the Central Alps (part down sufficiently to allow soil to develop. This is supported by the of the Eastern Alps) (see Figs. 1 and 3). The similar relative percentages two OSL quartz ages (18.77 ± 1.55 ka; 17.81 ± 1.68 ka) that both fall of grain-size classes in sediment samples ranging from locations near into the early Alpine late-glacial (Fig. 2). Prior to the Bölling-Alleröd valley floors up to LGM nunataks (Fig. 7), as well as their similar miner- interstadial, soil development was feeble at best, perhaps confined to alogical composition (Fig. 8) indicate that the drape results from a “non- patches of sparse vegetation cover; yet only the Bölling-Alleröd local” style of aeolian sediment dispersal. The type, or types, of wind was characterized by the spread of pioneer forests (Bortenschlager, that provided the required dust transport to deposit the loess drape is 1984, 2000) and more widespread soil development. Nevertheless, as yet elusive. Katabatic winds developed over valley-glaciers can en- and in view of the few age data so far, it seems not completely excluded train and transport silt; these winds, however, typically fade within that aeolian deposition perhaps resumed during the Heinrich-1 cooling less than a kilometer when passing over non-glacierized surfaces. (=Gschnitz-Senders stadials; cf. Fig. 2) and/or during the Younger Even the very strong katabatic storms along the Greenland Dryas. The time frame for widespread aeolian deposition in the NCA and Antarctica ice sheets die out over 10–20 km beyond ice (Bullard, may thus be constrained to: (i) a short end-member (from late ice 2013). In the Eastern Alps, a common type of wind is a southerly decay to start of Heinrich-1, ca 19–17.5 ka b2k), and (ii) a long end- foehn that routinely attains strong gale to hurricane speed (e.g., Armi member (late ice decay to start of Bölling-Alleröd, ca 19–14.7 ka b2k) and Mayr, 2007); it typically occurs along the front of low-pressure (cf. Fig. 2). cells approaching from the West to Southwest (e.g., Lothon et al., 48 C. Gild et al. / Geomorphology 301 (2018) 39–52

Table 1 Decision matrix for interpretation of aeolian drape (AD). Note that, at all locations investigated so far, the only possible “local” source of siliciclastic material is from LGM glacial drift left within proglacial deposits (outwash, lacustrine deposits), till, and reworked till and outwash such as kames.

Potential interpretation Required criteria Criteria fulﬁlled Conclusion, remarks

Interpretation A (1) AD is confined to direct contacts of topsoil with (1) No; AD is present also beyond Interpretation A: rejected AD is chemical weathering underlying carbonate rocks direct contact with carbonate rock In this case, AD should consist only of clay lag of underlying carbonate minerals (mainly illites and smectites); would rocks also require dissolution of unrealistically large amounts of carbonate rocks Interpretation B (1) AD always directly overlies LGM till or (1) Rarely: yes; mostly: no Interpretation B: rejected AD accumulated from in-situ redeposited LGM till Ad (2): Where AD contains a few floating weathering of LGM till (2) AD should always contain abundant pebbles to (2) No lithoclasts, this is interpreted as a result of later cobbles creep and/or frost heave (see text) Interpretation C (1) AD always directly overlies LGM till, or (1) No Interpretation C: rejected AD is lag of fine-grained subglacially-redeposited LGM till (2) No/yes cannot be tested supraglacial/englacial drift (2) AD is overlain by all younger deposits (limited outcrop) melted out during collapse (3) AD is absent in areas where LGM till is (3) No of LGM ice stream carbonate-lithic only Interpretation D (1) AD should strongly thicken downslope (1) no Interpretation D: rejected AD accumulated from (2) AD should display layering or stratification (2) No hillslope colluvium (3) Siliciclastic source material (LGM till or (3) In a few cases: yes; mostly: no redeposited till-sourced material) must be (4) Potentially possible only under present higher upslope highly special (4) Colluvial processes transported only the conditions of prolonged, gentle silt-size sediment fraction overland flow over (5) Colluvial processes selectively winnowed the unvegetated/scarcely vegetated siliciclastic sediment fraction, clay- to silt-sized terrain; impossible in case of slopes carbonate sediment fraction was left back steeper than ~10–15° (5) No such mineralogically selective colluvial process is known Interpretation E (1) AD is of ± constant thickness over lateral scale (1) Yes Interpretation E: Accepted AD accumulated from of kilometers at least; thickness variations are (2) Yes aeolian deposition minimal relative to other deposits (3) Yes (2) AD is present over large range of altitude, present (4) Yes also on mountain ridges and LGM nunataks (5) Yes (3) Except for very steep terrain (N35–40°), AD (6) Yes presence is independent of slope dip (7) Yes (4) AD overlies bare bedrock and a host of deposits exposed during time of AD deposition (5) AD drapes — in roughly constant thickness — depositional/erosional surface morphologies of deposystems (6) AD is constantly in the silt- to fine sand grain-size range (7) AD bulk composition is roughly constant, no rapid lateral and altitudinal changes

2003). At present, the foehn can last for up to more than a month, and Frechen et al., 2003; Haase et al., 2007; Ferraro, 2009; Terhorst et al., carries siliciclastic dust from the Central Alps into the NCA (Küfmann, 2009; Frank et al., 2011; Terhorst, 2013; Cremaschi et al., 2015; 2003, 2008; Grashey-Jansen et al., 2014). Today, during foehn storms Sprafke and Obreht, 2015; Markovic et al., 2016). Inboard of the former or strong westerlies ahead of incoming fronts, gusts that rush over terminal moraines of piedmont glaciers, intervals of loess are present, ploughed acres, open gravel pits, and construction sites can stir up too, but are comparatively thin and comprise shorter time spans than dust clouds up to more than a kilometer in length (Fig. 10). These dust their periglacial counterparts (see summary in Van Husen and Reitner, clouds do not settle within a short distance, but stay afloat and pass 2011). Over the past few decades, sediment coring in northern- to west- farther over mountain flanks, where much of it may fall out; part of ern peri-Alpine lakes has revealed intervals composed of or with a high the dust, however, may be carried significantly farther. Subtracting the amount of polymineralic silt that was inferred to stem from aeolian vegetation that, today, covers valley bottoms and mountain flanks, input. Numerical age dating indicated that these intervals accumulated and taking into account that deglaciation released huge amounts of during deglacial ice collapse and shortly afterwards; conversely, no or unsorted sediments, this supports the thesis that airborne dust trans- not enough input of wind-blown dust occurred into lakes during the port should have been very intense during to shortly after ice decay Younger Dryas and later cool phases (e.g., 10.0 ka, 9.2 ka and 8.2 ka (cf. Bullard, 2013). events) to produce discrete layers (Niessen et al., 1992; Wessels, 1998; von Grafenstein et al., 1999; Girardclos et al., 2005). 6. Discussion For intramontane settings of the Alps, the potential lateral and vertical extent of terrestrial aeolian deposits that post-date the LGM is less 6.1. Loess in peri- to intramontane settings of the Alps clear. In the Valais region of the Western Alps, a cover bed containing a continuous layer of silt of presumed aeolian origin was identified in Investigation of the “classical” loess deposited in periglacial s. str. an altitude range of 1400–2200 m a.s.l.; because the silt layer overlies areas (see French, 2000, 2007, for term) started in the early 19th centu- moraines ascribed to the Daun stadial, it was assumed that the layer ry (see Smalley et al., 2001, for review). The loess of the northern and accumulated during the Younger Dryas (Vonlanthen, 2000; Veit et al., southern perimontane forelands of the Alps, in turn, has been investi- 2002; see also Kleber and Terhorst, 2013b, p. 209 f.). Numerical dating gated since the late 19th century (e.g., Sacco, 1887; Forno, 1990; of late-glacial moraines casts doubt on the traded concept of stadial gla- Frechen, 1999; Antoine et al., 2001, 2009; Zöller and Semmel, 2001; cial advances that can be time-correlated over most of the Alps (Reitner C. Gild et al. / Geomorphology 301 (2018) 39–52 49

Fig. 9. Summary of typical geomorphic and sedimentary contexts the aeolian drape (AD) is present within, mainly directly beneath organic layers. Deposystems (e.g., rock glaciers, scree slopes) that remained active until late-glacial to Holocene time, and areas of ongoing erosion (e.g., steep mountain flanks with overland flow) are devoid of the target layer (modified from Gild et al., 2016). et al., 2016; Moran et al., 2016); this implies that relative dating based the late-glacial chron (e.g., Schönhals and Poetsch, 1976; Artmann and on the altitude of terminal moraines may not be valid. In the Trentino Völkel, 1999). area of the Southern Alps, late-glacial loess is confined to relatively Radiocarbon dating of pollens in an aeolian deposit trapped in a thin lenses and discontinuous veneers; the loess locally overlies glacial karstic dolina on the Zugspitzplatt glacial plateau suggested a start of till, and may be associated with terminal Paleolithic artefacts sedimentation during the early Atlantic (7415 ± 30 a BP), shortly after (e.g., Bleich, 1980; Borsato, 2009). retreat of the glacier at site (Grüger and Jerz, 2010). In the central sector Finally, in the NCA, aeolian siliciclastic input has for a long time been of the NCA, for areas above the present timberline, Küfmann (2003, postulated by pedologists to explain the presence of cambisols on 2008) documented active siliciclastic aeolian input from the Central carbonate-rocky terrains (e.g., Schadler and Preissecker, 1937; Solar, Alps also under the present climatic conditions; the present input, how- 1964; Cech and Kilian, 1967; Schönhals and Poetsch, 1976; Wilke ever, is too low to produce a discrete layer in itself, but only comprises an et al., 1984; Biermayer and Rehfuess, 1985; Rodenkirchen, 1986; admixture to soils (Küfmann, 2008). The discussed evidence suggests Hantschel et al., 1989; Artmann and Völkel, 1999; Stahr, 2000; that siliciclastic aeolian input persisted, or nearly so, over the entire Küfmann, 2003, 2008; Grashey-Jansen et al., 2014). For the environs late-glacial to Holocene chron. Aside from local sediment traps such as of Innsbruck, perhaps the earliest mention of a post-LGM layer of the dolina mentioned above, however, the intensity of aeolian transport loess was by Kravogl (1873). Blaas (1885) pointed out that this seems to have been high enough only during the late-glacial to comprise same loess layer veneers all types of rocks as well as older sediments. a widespread discrete layer. In the long term, numerical dating of aeolian Mutschlechner (1948, p. 192 f.) later briefly mentioned a layer of cover beds is essential to solve the question of depositional age and to siliclastic sand to silt locally found in valley heads and on LGM nunataks achieve a better understanding of palaeoenvironmental dynamics of the NCA. To date, however, this layer has not been systematically (Hülle et al., 2009; Kleber and Terhorst, 2013a, 2013b). targeted over a larger area (Gild et al., 2016). The age of significant aeolian deposition was either was not discussed or tentatively placed into 6.2. Outlook

The aeolian drape described herein is strictly speaking a re-discovery Table 2 of a feature that was forgotten by the geoscientific community outside List of processes that can modify or obliterate the aeolian drape. of pedologists. We identify the drape as a recorder of specific Category Processes palaeoenvironmental conditions and — by its availability for luminescence dating — as an unprecented and widespread geochronological Gravitational Solifluction, particle creep (in underlying scree mantle) Runoff-related Downslope redeposition by overland flow and/or gully erosion, marker layer that may allow us to separate the post-LGM terrestrial illuviation into pore space of underlying deposit intramontane record into “Before” and “After”. Our future investigations Freezing-related Cryoturbation, gelifluction, frost heave will focus on: (a) the production of further luminescence ages, (b) more Snow-related Ground-hugging snow avalanches, snow shear precise determination of the provenance of wind-blown sediment by Chemical Dissolution of carbonate grains, formation of clay minerals “fi ” weathering means of heavy mineral assemblages and ngerprint minerals such Biologically Root penetration, uprooting of trees, bioturbation by as zircon and apatite, and (c) detailed documentation of the processes induced soil-inhabiting animals (e.g., annelids, arthropods, gophers), of the secondary overprint of the aeolian drape, such as rooting, biotur- excavation of ant stocks, churning by wild pigs, trampling by bation, and pedogenesis; in addition, (d) exploration of the layer in the deer and cattle eastern NCA is planned for the near future. 50 C. Gild et al. / Geomorphology 301 (2018) 39–52

Fig. 10. (A) Stir-up of dust clouds from a single open construction pit at the SE end of Innsbruck city. View to SE across Inn valley. (B) NE-ward propagation, across the valley, of dust cloud from site shown in subﬁgure A. At this stage, the cloud was nearly one kilometer in length, and did not resettle on the valley bottom. Both photos taken on March 4th, 2017, a day with a foehn wind situation.

7. Conclusions Acknowledgements

This paper is part of the PhD thesis of the first author. Financial sup- (1) In the western part of the Northern Calcareous Alps (NCA) — a port from the grant “Nachwuchsförderung der Universität Innsbruck” mountain range mainly of Triassic carbonate rocks — a (fund 2014/3/GEO-8), donated to Charlotte Gild, is gratefully acknowl- landscape-wide drape of siliciclastic silt was identified. The silt edged. The comments and suggestions of two anonymous reviewers consists mainly of quartz, phyllosilicates, feldspars and amphi- helped to shape the presentation of data and to place the described boles and, rarely, of clastic calcite or dolomite. drape into a wider context of aeolian deposition. Alois Simon, Forest (2) The silt drape is typically a few decimeters in thickness and, in Management of the federal state of Tyrol/Austria, is thanked for logisti- lateral continuity, veneers different substrates (e.g., truncated cal support. Georg Kaser and Mathias Rotach, Institute of Atmospheric carbonate rocks, glacial till, late-glacial kames terraces, alluvial and Cryospheric Sciences, and Hanns Kerschner, Institute of Geography, fans and scree slopes, mass-flow deposits); in addition, the University of Innsbruck, are thanked for discussions on potential wind drape has been identified over a vertical range of at least systems and airborne sediment dispersal. 2000 m from late-glacial stream terraces near the floors of trunk valleys up to LGM nunatak plateaus. No major change of References composition, mean grain size and sorting of the sediment was recognized among the different locations. Albertus, M., 2016. Das Quartär am Steinbruch beim Finstertalegg. Bachelor thesis. (3) At all locations investigated so far (32), the drape directly over- University of Innsbruck, Austria, p. 37. Antoine, P., Rousseau, D.-D., Zöller, L., Lang, A., Munaut, A.-V., Hatté, C., Fontugne, M., lies its local substrate of rock or sediment without evidence of 2001. High-resolution record of the Last Interglacial-Glacial cycle in the Nussloch an underlying soil. Over large areas the drape, in turn, is directly loess-paleosol sequences, Upper Rhine Area, Germany. Quat. Int. 76 (77), 211–229. overlain by vegetated organic matter. The drape is absent, how- Antoine, P., Rousseau, D.-D., Moine, O., Kunesch, S., Hatté, C., Lang, A., Tissoux, H., Zöller, L., 2009. Rapid and cyclic aeolian deposition during the Last Glacial in European loess: a ever, on top of all deposystems that are still active or that proba- high-resolution record from Nussloch, Germany. Quat. Sci. Rev. 28, 2955–2973. bly became abandoned sometime during late-glacial to Holocene Arimoto, R., 2001. Eolian dust and climate: relationships to sources, tropospheric chemistry, transport and deposition. Earth Sci. Rev. 54, 29–42. time (e.g., low-positioned scree slopes, alluvial fans, or rock Armi, L., Mayr, G.J., 2007. Continuously stratified flows across an Alpine crest with a pass: glaciers in cirques of the NCA). shallow and deep foehn. Q. J. R. Meteorol. Soc. 133, 459–477. (4) Comparative analysis with potentially competing processes Artmann, S., Völkel, J., 1999. Untersuchungen an periglazialen Deckschichten im Nationalpark Berchtesgaden, Nördliche Kalkalpen. Zeitschrift für Geomorphologie. (e.g., glacial meltout lag, chemical weathering) indicates that Neue Folge 43 (4), 463–481. the drape is an aeolian deposit. Two OSL quartz ages of the Auer, I., Foelsche, U., Böhm, R., Chimani, B., Haimberger, L., Kerschner, H., Koinig, K.A., drape from two selected locations indicate an early late-glacial Nicolussi, K., Spötl, C., 2014. Vergangene Klimaänderungen in Österreich. Austrian Panel on Climate Change (APCC) (Ed.): Österreichischer Sachstandsbericht Klimawandel age (18.77 ± 1.55 ka; 17.81 ± 1.68 ka). This fits with and can ex- 2014 (AAR14). Verlag der Österreichischen Akademie der Wissenschaften, Vienna, plain all the geological, pedological and geomorphological Austria, pp. 227–300. Ballantyne, C.K., 2002. A general model of paraglacial landscape response. The Holocene evidence the drape is associated with. Therefore, the drape 12, 371–376. records a hitherto unidentified phase of regional, intense aeolian Benn, D.I., Evans, D.J.A., 2010. Glaciers and Glaciation. Hodder Education, London, p. 802. transport including dust storms right after the collapse of the Biermayer, G., Rehfuess, K.E., 1985. Holozäne Terrae fuscae aus Carbonatgesteinen in den Nördlichen Kalkalpen. Z. Pflanzenernähr. Bodenkd. 148, 405–416. LGM ice streams in this part of the Eastern Alps. Blaas, J., 1885. Ueber die Glacialformation im Inntale. 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