Note geomorfologiche sull’alta Valle del Sabbione e sulla Val d’Ischietto (Gruppo dell’Argentera – Alpi Marittime)

Geomorphological notes on the Upper Valle del Sabbione and the Val d’Ischietto (Argentera Group, Maritime Alps)

Abstract

Surveying of the Upper Valle del Sabbione and Val d'Ischietto has shown the typical morphogenesis of the high altitude alpine environment, together with the clear relationships between structural arrangement, land morphology and its morphoevolution. The importance of mylonitic rock outcrops was recognised, not only from a morphotectonic point of view with the production of cliff and steps in with reverse gradient, but also from a morphoselective aspect, whenever they are present in a cataclastic facies, being responsible for the distribution of some forms of erosion. Morphotectonic observations confirmed the already well-known graben structure of the Upper Valle del Sabbione and showed the importance of the alpine-age faults in conditioning the trend of the valley axis. The lack of absolute data or palynological information did not allow chronological identification of the glacial deposits, however comparison with the results obtained in surrounding areas are significant, The Valle del Sabbione shows three glacial retreat stages, of which the final two are also conserved in the Val d’Ischietto. In the Valle Fredda, right tributary of the Valle del Sabbione, there are only the first and second retreat stages. The glacial deposits consist prevalently of a massive diamict with clastic support, with a scarse matrix and isolated in pockets, with the exception of the oldest deposit, which has a matrix support and is influenced by karstic epigeal forms. The presence of rock glaciers is important, due to their paleoclimatic significance and their diffusion in the area of the Crystalline Massif of Argentera. A detailed sedimentological and morphological description of these landforms was carried out, also investigating their relationships, of superimposition and continuity of form, with the glacial deposits. Morphogenesis due to gravity and running water are responsible for the main active processes and associated landforms, as indicated by the numerous debris flows and an area influenced by bad lands forms. Observations were made of the triggering actions and the trend of the Flow routes of the debris flows, together with the sedimentological aspects of the lobes and depositional levees. As regards the bad lands forms, still in rapid evolution, genesis has been hypothesized which is in line with that for a nearby area in the French Alps.