Late Quaternary glaciations and connections to the piedmont plain in the prealpine environment: The middle and lower Astico Valley (NE Italy)

This work concerns the Late Quaternary evolution of the Astico Valley, with a focus on the relations between the glacial complexes hosted in the terminal valley tract and the piedmont fans. Three distinct glacial events are considered in this paper. Remote sensing, field survey, stratigraphic measurements and reconstructions, sand petrography, radiocarbon dating and pollen analyses allowed attribution of the last one to the LGM, a previous one probably to MIS 6 and the oldest to a generic glaciation of the Middle Pleistocene. Sand petrography analyses show that all these glacial deposits contain rock fragments that reached the Astico Valley through a transfluence of the Adige glacier. During LGM, this glacial stream entered the Astico Valley from the north through the Carbonare saddle (1075 m a.s.l.), as probably happened in previous major glaciations. The chronostratigraphy of two cores drilled near the towns of Vicenza and Villaverla shows that the outwash stream changed its route to the piedmont plain at the end of LGM, as a response to rapid glacial collapse. This switch led to the deactivation of the northwestern sector of the plain (Thiene fan) in favour of the southeastern one (Sandrigo fan). The lower and middle Astico Valley preserved significant evidence of even minor glacial fluctuations during the LGM in response to subtle climatic changes, namely an early glacial withdrawal at 23e24 cal ka, which may be difficult to distinguish in major Alpine glaciers.