Applicazioni delle tecniche morfometriche al problema della distinzione dei depositi glaciali e fluvioglaciali nell’Alta Valle di Gressoney (Valle d’Aosta)

Discriminating between glacial and fluvioglacial drift in the Upper Gressoney Valley (Valle d’Aosta,Italy) by means of morphometric techniques

Abstract

Morphometric analysis has been applied to alluvial, fluvioglacial and drift material collected in the upper Gressoney Valley, in order to discriminate among the different depositional environments. Tracing the centile curve of the deposits under scrutiny, a first centile was found and an average pebble size respectively of 190 cm and 15 cm for glacial drift, 180 cm and 13 cm for fluvioglacial deposits, and 70 cm and 29 cm for the alluvial deposits. The analysis of lithofacies, carried out for the various length classes of clasts, points to the dominance, in the three different types of sediment, of kinzigites and augen gneisses, with some granites and aplites. Therefore, in order to evaluate the forms and the elaboration of clasts, gneissic clasts 40-60 mm long have been used. Bearing in mind the results of the morphometric analysis upon samples comprising 120 clasts each, collected in the alluvial, fluvioglacial and glacial drift deposits, it appears that the medians of the rounding (E), sphericity (SF), entrainment (Ω) and of the simplified form coefficient (CFS) are capable of significantly discriminating the different transport and mobilization environments.