The travertine of Susa and Chisone Valleys (Torino Province): Sedimentological and morphological characterization and genetic hypothesis

Abstract

The survey of Sheet 132-152-153 "Bardonecchia" of the Geological Map of Italy scale 1:50,000 determined in the Susa and Chisone Valleys numerous travertine deposits and concretionary deposits. Their study consented an outline of distribution of carbonatic precipitation process in relation to the typology of the pre-Quaternary substratum and the superficial formations. The observation of sedimentological and textural characteristics led to the recognition of five facies typologies: Breccias with travertine cement; phytohermal, stromatolitic and clastic travertines; speleothems. For every one of these typologies, a micro- and macromorphologic and textural characterisation is supplied. The overall characteristics identified, the association of facies checked and the observation of the precipitation processes still active in numerous places in Susa Valley made it possible to determine the depositional environment where bodies had developed. The picture thus defined allowed us to point out the close relationship between the precipitation of carbonate in a subaerial environment and the distribution of the main phenomena of gravitational collapse (deep-seated gravitational slope deformations and large landslide deposits) which involve extensively relieves modelled on the metasedimentary successions with main calcschists. Conditions of accentuated fracturing and disjointing of the substrate allow for the release of calcium carbonate to the meteoric waters which permeate the rocky structure. A balance of the chemical-physical parameters determine reprecipitation of carbonates at the emergency points at the surface of the fluid. Another influence hypothesised on the brittle structures are thrusts and faults, facilitating the transport of the water and conditioning the distribution of products of dissolution and reprecipitation of the calcium carbonate. Considering the relationship with other sediments, the deposition of travertine seems to have been established at the end of the Upper Pleistocene with the withdrawal of glacial masses which occupied the main valleys.