SYNTHESIS ON THE TURIN SUBSOIL STRATIGRAPHY AND HYDROGEOLOGY (NW ITALY)

Abstract

This work is a multidisciplinary synthesis of geological and hydrogeological researches on the subsoil of Turin and suburbs, summarizing the existing previous studies and also using new data specially collected, aimed at bringing together the different aspects of the subsoil in a single contribution. The stratigraphic setting of the Turin Plain, as examined through numerous boreholes (wells, piezometers and geognostic drillings) shows an erosional surface essentially shaped on the fine Villafranchian succession and locally on the Pliocene and pre-Pliocene sediments, on which the Quaternary gravelly outwash and fluvial cover rests. This cover, which is mainly fed by the Dora Riparia River, is relatively thin (thickness between 5 and 57 m) and highly variable in terms of facies and cementation degreee. The most recent excavation activities are also taken into consideration, which locally allowed the direct observation of the shallow subsoil stratigraphy. The geological literature reports that the setting of Turin subsoil is strictly conditioned by the Quaternary uplift of Turin Hill. The structural causes of this geological evolution and its relationship with seismicity are here summarized. The stratigraphy of Turin subsoil is also connected to the recent deviation of the Po River, which flowed south of Turin Hill (through the southern slope of Turin Hill and the Poirino Plateau) during the Middle-Upper Pleistocene and only recently develops at the NW foot of Turin Hill. A new reading of this Po deviation as an overflow is made, based both on a re-examination of all the existing data and new collected data. The hydrogeological features of the Turin subsoil are also reported, characterized by two superimposed main groundwater flow circuits, as well as the thermal regime of shallow groundwater and its geothermal potential. This work can help professional geologists for conducting geological, hydrogeological and geotechnical appraisals on Turin and suburbs. It can also be useful to researchers to reconstruct the geological and hydrogeological features of the Turin territory.