Glacial landscape reconstructions in the eastern Dolomites since the Last Glacial Maximum (LGM)

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Anissa Green
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1 UNIMORE PhD Course in Models and Methods for Materials and Environmental Sciences XXXII cycle Glacial landscape reconstructions in the eastern Dolomites since the Last Glacial Maximum (LGM) PhD student: Vittoria Vandelli Tutor: Prof. Mauro Soldati Co-tutor: Prof. Mauro Marchetti

g. paleoprecipitation and paleotemperature).

2 Introduction Glaciers are a natural archive of the Earth s climate. In fact, since 1970s paleoglaciers fluctuations have been used as proxy data to examine past climate changes by means of empirical relationships between glacier physical parameters (e.g. Equilibrium Line Altitude, ELA) and past climate conditions (e.g. paleoprecipitation and paleotemperature). In particular, the study of midlatitudes former glaciers fluctuations enables a higher resolution of past environmental shifts to be achieved, being mid-latitude glaciers more sensitive to climate changes. Starting from these premises, the PhD research activity is devoted to the reconstruction of the glacial evolution since the Last Glacial Maximum (LGM) in the Alta Badia valley, a region of the eastern Dolomites (Fig.1). This area, despite of the strong slope dynamics, is deeply characterized by glacial features (e.g. moraine deposits) which remain still clearly visible as witnesses of the past presence of glaciers. From a paleoglaciological point of view, despite the great interest of the area, since the 1960s no specific and systematic study has been carried out through the region. The general aim of this developing research activity is to provide further insights and to contribute in the clarification and characterization of mode and timing of last glacial cycle in the Alta Badia valley providing an update of the knowledge on the glacial history of the eastern Dolomites and new data for regional scale paleoclimate correlations relevant to the last glacial-interglacial transition. These data could provide further insights on the implications of past climate changes on mountain landscape in order to forecast those of the future. Fig.1 Location of the study area. Methods As a base step, the first year of research activity has foreseen the collection and analysis of bibliographic data regarding mode and timing of former glaciers fluctuations during the last glacial cycle in the Alta Badia valley and, for a wider perspective, in the whole Alps. The first works by Penck and Bruckner (1909), Mutschlechner (1933), Castiglioni (1940) till the more recently published works (e.g. Ghinoi and Soldati, 2017) have been examined. Together with literature data, geomorphological maps and sketches regarding former glaciers extension in the Alta Badia

3 valley and surroundings (e.g. Castiglioni, 1964; Panizza et al., 2011) have been collected and analysed. During the month of August 2017, detailed geomorphological field surveys have been carried out with the purpose of identifying and mapping glacial landforms and features, and verify origin and location of the glacial landforms reported by previous authors. The geomorphological surveys were also aimed at the identification of glacial landforms suitable to be dated with 14 C method or surface exposure dating method with 36 Cl cosmogenic nuclide (cf. Ivy Ochs and Kober, 2008) in order to constrain in a defined time frame past glaciers advances and recessions. Regarding the surface exposure dating method, the period of exposure can be calculated by measuring cosmogenic nuclide concentrations in rocks or sediment. The latter period can be approximately considered as the time since the glacier last supply sediments to the moraine, that is, the minimum age of stabilization of moraine deposit. Surface exposure dating can be applied instead of 14 C method when organic matter in deposits is absent, as often happens in former glaciated environments. Results The acquisition and analysis of bibliographic and cartographic data have let to depict a general framework regarding past glaciers fluctuations in the Alps. The output of the literature analysis was a state-of-the-art review which has been presented in May 2017, as a poster, at the Annual International Young Geomorphologists Workshop in Ammersee (Munich, Germany). The detailed geomorphological field surveys carried out in the Alta Badia Valley have led to the recognition and characterization of glacial landforms and features and to verify genesis and location of those landforms already mapped by previous authors. In addition, during the geomorphological field surveys, identification and sampling of glacial deposits to be dated with 14 C method or with surface exposure dating method (using 36 Cl cosmogenic nuclide) have been systematically carried out (Fig. 2). In particular, at La Brancia locality, in correspondence of an excavation wall, below talus deposits, massive diamicton have been observed and sampled by means of a mechanical grab. The in-situ characterization of the sample (e.g. determination of textural properties, findings of striated and iron-shaped cobbles) unable the massive diamicton to be interpreted as a glacial deposit (lodgement till) possibly dating back to the LGM. This sample has been properly collected to perform grain size analysis and to be dated with 14 C method. In addition, top surfaces of 6 erratic boulders, located on well-defined morphological units attributed to Lateglacial moraine deposits, have been sampled for exposure dating.

Fig. 2 Location of samples collected during field surveys in August 2017 in the study area. Red dot indicates the sample to be dated with 14 C method at La Brancia locality.

4 Fig. 2 Location of samples collected during field surveys in August 2017 in the study area. Red dot indicates the sample to be dated with 14 C method at La Brancia locality. Green dots indicate samples from top surfaces of erratic boulders on Lateglacial moraine deposits to be dated with surface exposure. Research perspectives The activities planned for the second year of the PhD will be aim at the definition of the time frame of glaciers fluctuations occurred in the Alta Badia valley during the last glacial cycle. To this aim, further geomorphological field surveys will be carried out in the study area, particularly along the western flank of Conturines where the abundance and the significance of erosional and depositional features require more detailed investigations. Relative age of Alta Badia glacial deposits will be defined considering the relative position of the identified glacial landforms with the support of collected literature data. In addition, absolute dating of collected samples with 14 C and surface exposure methods will be performed. As regard exposure dating, samples will be preliminary prepared at the laboratories of the University of Pisa. Further and more specific steps of samples preparation, as well as the measure of 36 Cl concentration by means of the Accelerator Mass Spectrometry, will be likely performed at the ETH in Zurich. Dating results are expected to give the approximate age of glacial deposit attribute to Lateglacial period, thus to provide quantitative information about the timing of deglaciation phases in the study area.

5 References Castiglioni B. (1940). L Italia nell'età Quaternaria. In: Touring Club Italiano (Ed.), Atlante Fisico d Italia. Milano, Map 1: Castiglioni G.B. (1964). Sul morenico stadiale delle Dolomiti. Memorie degli Istituti di Geologia e Mineralogia dell Università di Padova, XXIII, pp Ghinoi A., Soldati M. (2017). Reappraisal of Lateglacial Stadials in the Eastern Alps: the case study of Valparola (eastern Dolomites, Italy). Alpine and Mediterranean Quaternary, 30(1), Ivy-Ochs S., Kober, F. (2008). Surface exposure dating with cosmogenic nuclides. Quaternary Science Journal, 57(1-2), Mutschlechner G. (1933). Geologie des Gebietes zwischen St. Cassian und Buchenstein. (Südtiroler Dolomiten). Jahrbuch der Geologischen Bundesanstalt, 83, Penck A., Brückner E. (1909). Die Eiszeiten in den nördlichen Ostalpen, Bd.1. In: Die Alpen Im Eiszeitalter. Chr. Herm. Tauchnitz, Leipzig, pp Panizza M., Corsini A., Ghinoi A., Marchetti M., Pasuto A., Soldati M. (2011). Explanatory notes of the geomorphological map of the Alta Badia Valley (Dolomites, Italy). Geografia Fisica e Dinamica Quaternaria, 34,

Glaciology (as opposed to Glacial Geology) Why important? What are glaciers? How do they work?

Glaciology (as opposed to Glacial Geology) Why important? What are glaciers? How do they work? Glaciers are important because of their role in creating glacial landscapes (erosional and depositional features).