THE PLEISTOCENE EVOLUTION AND RECONSTRUCTION OF LGM AND LATE GLACIAL PALEOGLACIERS OF THE SILISIA VALLEY AND MOUNT RAUT (CARNIC PREALPS, NE ITALY).

Abstract

Small, peripheral mountain glaciers that remained independent from the large ice-streams throughout the Pleistocene glaciations represent an important source of paleoclimatic information in the European Alps. Here, we present new evidence on the evolution of the Silisia Valley and paleoglaciers on the northern side of Mount Raut (Carnic Prealps, NE Italy). The area is characterized by the presence of a variety of sediments and landforms, among them two generations of conglomerates and several deposits of glacigenic origin. The conglomerates are related to the infill and subsequent incision of the Silisia Valley during Plio (?)-Pleistocene times, whereas most of the glacigenic deposits can be ascribed to glacier advances during the Last Glacial Maximum (LGM) and following Late Glacial stadials. During the LGM, the glacial system extended from the headwalls of Mount Raut (2026 m a.s.l.) down to an elevation of 440 m, and had an equilibrium line altitude (ELA) of 1260 m (Accumulation-Area-Balance Ratio method - AABR). Assuming present-day amounts of precipitation, this corresponds to a mean summer air temperature (MSAT) depression of 8.5 or 9.4°C (  =±2.2°C), when compared to two recent (1960-1990) climatic records in the area. Two phasesof glacier stabilization during the Late Glacial were inferred from frontal moraine systems at higher elevations. During the first one, the glaciers had an ELA of 1590 m (corresponding to an MSAT lowering of 6.2 or 7.1°C), whereas at the second one the ELA was at 1740 m (MSAT lowering of 5.3 or 6.1°C). Our results allow to better understand the long-term Pleistocene evolution of this sector of the south-eastern Alps, probably driven by the interplay between climatic fluctuations and phases of tectonic uplift.