A deep-seated gravitational slope deformation in the Upper Bargonasco Valley (Ligurian Apennines)

Abstract

Deep-seated gravitational slope deformations (DSGSD) represent an important geomorphological feature of the Ligurian landscape, and have drawn scientific attention for the past several decades. Lithological characteristics of rock masses, tectonic movements, geomorphic and climatic factors are among the key processes generally recognized. Along the slope, which spreads between a ridge at 880 m and the Bargonasco River at 220 m a.s.l., where serpentinites and basalt outcrops connect with cherts and other sedimentary rocks along tectonic lineations, typical geomorphological evidence of DSGSD are observed, including grabens, trenches, double ridges, depressions, troughs, and counterslopes scarplets, all of which may reactivate pre-existing structural discontinuities. Within a UE program aimed at assessing the Pian del Lago wetland, which represent the top side of the DSGSD and correspond to a trench filled with lacustrine sediment, a drilling program was carried out and the stratigraphy of the area was defined. Several radiometric analyses conducted on samples of core peat demonstrated that the most ancient phase of this lacustrine basin dates from the Upper Pleistocene, featuring major climate changes. As such, it is possible that the beginning of the DSGSD occurred earlier than this, and that its formation is correlated to the various stadial-interstadial transitions that characterized the last 100 ky BP.