PRESERVATION OF QUATERNARY SEDIMENTS IN DSGSD ENVIRONMENTS: THE MONT FALLÈRE CASE STUDY (AOSTA VALLEY, NW ITALY)

Abstract

Deep seated gravitational slope deformations (DSGSD) in the Western Alps, which usually affect glacial valleys, produce strong deformation in both bedrock and Quaternary cover, generally favouring erosion. This research, which examines a DSGSD along the Mont Fallère southern slope in the Aosta Valley, suggests that DSGSD can also locally favour the formation and preservation of the Quaternary stratigraphic successions for the following reasons: - the development of transversal elongated depressions, which are essentially connected with the onset of gravitational structures (trenches, minor scarps, and counterscarps) and filled by differentiated Quaternary successions; - the occurrence of closed depressions along the slope, which originate from the gradual evolution of gravitational structures (trenches or minor scarps and associated counterscarps) and are occupied by lakes that are progressively filled by lacustrine and palustrine sequences; - the occurrence of wide, flat, irregular surfaces that are characterized by lower erosional phenomena with respect to the surrounding steep slopes and preserve various Quaternary stratigraphic successions; - the development of rounded reliefs and associated wide depressions, both of which exhibit topographic surfaces that hang over torrential incisions that are located along the main fractures; this morphology favours the preservation of glacial, outwash, lacustrine and palustrine sediments; - wide colluvial and debris cover that buries and partially preserves older Quaternary sediments; - the local occurrence of a travertine cover and cemented sediments, which preserve the older Quaternary sediments. These morphological conditions are favourable to prehistoric human settlements, resulting in archaeological mountain sites that also provide a chronological reference for the evolution of DSGSD.