Stratigraphic evidence of glacier interactions in the Isarco-Pusteria valley junction (Italian Alps): unraveling the Late Pleistocene landscape evolution

Giovanni Monegato^1,2, Gianfranco Fioraso¹, Federico Sciascia³, Lisa Borgatti⁴, John Menzies⁵, Gianluca Benedetti⁶ & Stefano Rodani^6
1National Research Council, Institute of Geosciences and Earth Resources, Italy.
²Istituto Nazionale di Geofisica e Vulcanologia (INGV), Roma, Italy.
³ENSER srl, Italy.
⁴Department of Civil, Chemical, Environmental and Materials Engineering, University of Bologna, Italy.
⁵Department of Earth Science, Brock University, Canada.
⁶Italferr, Italy.
Corresponding author e-mail: giovanni.monegato@igg.cnr.it

The valley junction of Isarco and Pusteria (Rienza River), located in the Bressanone area, showcases a complex stratigraphic succession that traces back to the Late Pleistocene evolution. Extensive field surveys and numerous drillings conducted between Bressanone and Varna/Sciaves have unveiled the stratigraphic architecture of the valleys. Four distinct glacier advances have been identified, with the thickest deposits attributed to the Last Glacial Maximum (LGM), characterised by a fine-grained subglacial traction till up to 30 metres thick. Additionally, two Lateglacial stadial moraines are linked to the Isarco glacier, indicating that the modern Rienza lower valley was sculpted as the ice retreated at the end of the LGM. A pre-LGM fluvial-lacustrine system, receiving contributions from both valleys, suggests that the junction was located further north than its current position. Below this deposit, an older glacigenic sediment layer consisting of coarse subglacial traction till marks a phase between two major ice advances. At the deepest point, core samples from the Isarco valley reveal fluvial deposits from the Pusteria valley catchment, highlighting the existence of a narrower lower reach across the Rienza River. This evidence indicates the long-standing presence of the river valley at the junction in the Sciaves/Varna area, well before the LGM. The discovery of a large landslide reveals notable slope dynamics due to glacial erosion, with the landslide body covered by LGM glacial deposits, whereas post-LGM slope deposits are related to small-scale slope processes.

Late Pleistocene, European Alps, Allostratigraphy, Valley junction.