Late-glacial to Holocene sediment dynamics in high Alpine regions Insights from multimethodological approach on aeolian deposits (Sanetsch Pass, Switzerland) Elena Serra1,2, Pierre G. Valla3,1,2, Natacha Gribenski1,2, Luc Braillard4 1Institute of Geological Sciences, University of Bern, Switzerland 3Institute of Earth Sciences, CNRS - University Grenoble Alpes, France 2Oeschger Centre for Climate Change Research, University of Bern, Switzerland 4Department of Geosciences, University of Fribourg, Switzerland Email: [email protected] 5°0'E 10°0'E 15°0'E Fig. 2 Grain size distribution and sorting 7°16'E 7°18'E Clay Silt Sand GravelPebl. Bould. OSL (total counts) 100.00 (ARP and CRE). Both grain size distributions Sedimentology 48°0'N (cm) Layers Introduction and sorting indices suggest an aeolian origin Depth 0 10000 20000 30000 40000 1 1 5 8 1 75.00 of ARP and the fine layers of CRE, confirming ARP01 ARP02 ARP03 2 15 2 Widespread loess deposits accumulated the on-field logging. 3 25 3 2 35 4 Depth (cm) during the last glaciations in low-eleva- 46°0'N Arpelistock 50.00 4 5 46°21'N 40 (3036 m.s.l.) 5 8.8±1.1 ka Fig. 4 Stratigraphy, portable OSL counts and conventional tion regions of Europe and are often 25.00 3.1±0.4 ka 2.7±0.4 ka Weigth percentage (%) percentage Weigth IRSL ages of the high-elevation aeolian deposits (ARP). A com- [1, Sediments used as paleo-environmental archives 44°0'N CRE Weathered pebbles plex picture emerges from the luminescence analyses. Aeolian 0.00 Clayey silt in silty matrix 2] (2097 m.s.l.) 0.1 1 10 100 1000 10000 100000 1000000 sediments were probably deposited before or during the Younger . ARP Grain size (μm) Samples Dryas and then reworked by periglacial processes. Sanetsch Pass (2715 m.s.l.) OSL 1 Portable OSL (2252 m.s.l.) S1/C5 S3/C10 S5/C15 ARP 2015 XRD analyses High-elevation aeolian deposits occur S2/C6 S4/C12 S6/C17 ARP 2017 5 Sorting index Fig. 5 XRD analyses (ARP). The presence of also in the European Alps (Sanetsch 4.5 (Q3/Q1)1/2 ARP 01 46°20'N S1/C5 Pond Emines 46°20'N 4 albite in the aeolian sediments and its absence S2/C6 2.5 Very well sorted ARP 03 (Bertel et al., 2012) 3.5 Well sorted Pass, Switzerland, Fig. 1) where they 3 S3/C10 3.5 from the bedrock (Fig. 3) suggests an allochtho- 2.5 S4/C12 4.5 Moderately sorted 0 10 20 30 40 50 60 70 80 90 100 2 S5/C15 Poorly sorted nous origin of the ARP deposit. 1.5 S6/C17 orting index Q1 = 25th percentile; have been interpreted as result of Late- Patterned Morainic S 1 ARP 2015 Cumulative mineral percentage (%) Tsanfleuron Scree slope ground ridge 0.5 ARP 2017 Q3 = 75th percentile; [3, 4] 0 Mediane = 50th percentile glacial (19-11.6 ka) glacier retreat . glacier 1 10 100 Quartz Muscovite Clinochlore Albite Rock fall Alluvial fan River Mediane (μm) Sampling However, active geomorphic processes Glacial deposit Glacier Fig. 3 Local bedrock XRD analyses. The local bedrock is location H1 LIA glacial deposit Lake 0 0.5 1 km mainly composed of Hauterivian grey siliceous limestone (H1, and related complex sediment dynam- 7°14'E 7°16'E 7°18'E H2 46°19'N V1 H2) and Berriasian and Valenginian calcareous shales (V1, V2), Conclusions ics occurring in high Alpine regions may Fig. 1 Geomorphological map of the study area (modified from swisstopo). Among the various Quaternary deposits occur- V2 both units belonging to the Wildhorn nappe of the Helvetic ring at the Sanetsch Pass, this study focuses on a high-elevation platform covered by patterned ground (ARP, results in the light Alps. Quartz up to 20-30% occurs in both the lithologies. 0 10 20 30 40 50 60 70 80 90 · The deposit from the high-elevation platform is a prevent the direct use of high-elevation red box) and on an alluvial fan located in the fluvio-glacial plain (CRE, results in the light blue box), since aeolian sediments were Cumulative mineral percentage (%) aeolian deposits as paleo-environmen- identified in the stratigraphy of both deposits (Fig. 2). Inset: location of Sanetsch Pass within the Alps, with the Last Glacial Maxi- primary aeolian deposit with allochthonous mum ice extent[5]. Quartz Muscovite Clinochlore Calcite Dolomite tal indicators. origin, deposited before or during Younger Dryas Fig. 8 Micromorphology of Sediments Fig. 6 Stratigraphy of the CRE 01 (YD) and then reworked by cryoturbation. Sedimentology Weathered pebbles M1 xpl (cm) sediment thin sections Layers Depth Humic loam in silty matrix alluvial fan (CRE). An alter- CRE 02 1 (CRE). Three samples for mi- 10 Clayey silt Fe-precipitation nance of fine and coarse CRE 03 · After YD glacier retreat, aeolian deposits, bedrock Research questions cromorphological analyses Gravel in Mn-precipitation sediment layers was identi- CRE 04 loamy matrix were collected from the allu- fied. Samples for the differ- CRE 05 derived and glacial deposits were transported Samples vial fan in order to better un- • Which are the pre- and post-deposi- ent methodologies were CRE 06 OSL M1 Micromorphology derstand the depositional away from the slopes and deposited in the fluvio- collected in order to better CRE 07 tional histories of high-altitude aeolian Portable OSL environment of the different 2 1 XRD analyses S1 Grain size understand their origin layers. CRE 08 glacial plain, rapidly building up an alluvial fan. deposits? and the possible connec- M1 shows reworked loessic CRE 09 1 mm tivity with the ARP deposit. deposit with sub-angular CRE 10 · This study highlights the dynamic and complex • Can they be used as paleo-environ- blocky microstructure. M2 CRE 11 Quartz OSL (total counts) ppl post depositional processes experienced by aeo- M2 exhibits a well-developed CRE 12 mental archives to reconstruct paleo- 150 15000 20000 25000 30000 35000 40000 45000 50000 CRE 13 150 horizontal parallel lamina- lian sediments deposited in high elevation Alpine Fig. 7 Portable and con- CRE 14 1 tion which supports decan- climate and paleo-atmospheric circula- 3 1 CRE 15 11 ventional quartz OSL tation of the sediment in a la- settings, preventing their direct use as paleo-envi- 197 (CRE). Two populations of CRE 16 tion pattern? 2 custrine or fluviatile environ- 4 2 200 22 low and high OSL counts 0 10 20 30 40 50 60 70 80 90 100 ronmental proxies. 33 215 ment. M3 shows weathered, 5 S1 33 CRE01 44 230 can be identified within completely decarbonated, Cumulative mineral percentage (%) 44 · This study shows the importance of a multimeth- the stratigraphy, corre- lithic fragment containing Quartz Muscovite Albite Clinochlore Calcite M1 S2 55 CRE01 Multi-methodological 6 CRE02 250 55 10.0±0.9 sponding respectively to quartz grains in a fine silty 66 CRE02 odological approach to reconstruct sediment dy- 270 66 fine and coarse sediment carbonated matrix, which TC Wt% TOC Wt% TIC Wt% 7 77 77 12.3±1.2 286 layers. Conventional OSL probably derives from local 0.5 - 4.9 0.3 - 1.2 0 - 4.6 approach 88 namics and connectivity. 8 M2 290 88 9 99 1 mm bedrock or remobilization of 300 300 9 ages suggest that the fan Fig. 9 XRD, TC and TOC analyses (CRE). Fine layers con- 10 CRE03 S3 1010 slope and glacial deposits. 314 1010 was deposited rapidly Sediment stratigraphy: log, grain-size 11 11 11 CRE03 tain around 50% of quartz and 50% of micas, while calcite • 11 320 Depth (cm) 11 12 S4 27.2±2.6 soon after the Younger 330 1212 M3 xpl occur in the coarse layers (10-40%). This further demon- 13 M3 1212 336 References and micromorphological analyses 14 Dryas. The higher lumines- strates a connection between the fine layers of the fan 350 350 15 S5 1313 1313 cence signals and age [1]Muhs, D.R., 2013. The geologic records of dust in the Quaternary. Aeolian Research, 9, pp.3-48. 16 355 1414 and the aeolian deposits (Fig. 5) and between the coarse Sediment geochemistry: XRD, TC and 1414 [2]Martignier, L., Nussbaumer, M., Adatte, T., Gobat, J.M. and Verrecchia, E.P., 2015. Assessment of a • 17 S6 370 1515 CRE04 (CRE03) of the layers con- layers of the fan and the bedrock derived/glacial deposits CRE04 15 376 9.2±1.1 taining lithic fragments is locally-sourced loess system in Europe: The Swiss Jura Mountains. Aeolian Research, 18, pp.11-21. 18 (Fig. 3). [3] TOC analyses 400 probably due to partial Montandon, F., 1940. Le loess d'Evionne (Valais). Études Rhodan, 16, pp.75-103. The low TOC content demonstrates the absence of [4]Spaltenstein, H., 1985. Caractérisation de deux sols alpins minces sur calcaire dur dans le lapiaz du 418 • Sediment dating: conventional and 1616 bleaching of the quartz paleo-soils in the fan layers, further suggesting that the Sanetsch. Bulletin de la Société vaudoise des sciences naturelles, 77(367), pp.245-254. grains (Fig. 8) contained in [5 ]Ehlers, J., Gibbard, P.L., 2004. Quaternary Glaciations: Extent and Chronology: Part I: Europe. Elsevier. 19 16 alluvial fan deposition occurred rapidly. 450 portable luminescence measurements 450 the weathered clasts. 1 mm.