The Alps: glacial landforms prior to the Last Glacial Maximum

Since the establishment of Penck and Brückner's four glaciations milestone theory, glacial studies in the Alps have represented a reference for the reconstruction of Pleistocene glaciations. The widespread preservation of pre-LGM glacial landforms, in particular the end-moraine systems and the related glaciofluvial stacks, allowed reliable stratigraphic reconstructions, which have been strengthened in the last decades by the means of new dating methods. These pointed out that remarkable regional differences may be inferred from one sector to another of the Alps in terms of number of glacier advances that reflect dissimilarities in tectonic regimes (uplift vs. subsidence), accommodation space and preservation potential. Early Pleistocene glaciations are firstly identified in glaciofluvial deposits (Deckenschotter in the Swiss foreland), while the oldest moraines were identified based on reversal magnetostratigraphic polarity and ascribed to MIS22-20. Middle Pleistocene glacial landforms are bracketed between the Early Pleistocene units and the LGM. For many of them, the lack of numerical age determinations hampers the correlations with cold stages. During the Middle Pleistocene a phase of valley overdeepening occurred. The MIS 6 glaciation was dated on glaciofluvial and glaciolacustrine outcropping successions in many sectors of the Alps. The Late Pleistocene cold phases before the LGM (MIS 5d, MIS 4 and MIS 3) were formalized within the Würm glaciation in the Eastern Alps. Although paleoglacier models suggest moderate glaciers advances during these phases, the updated datasets indicate smaller glaciers in comparison to the LGM extent.