GNGTS 2015 - Atti del 34° Convegno Nazionale

preferable, since data acquisition is faster. With the floating cable arrangement, exponentially spaced electrodes appear to provide the best resolution with depth (Allen and Merrick, 2007). We preliminary discuss the results of a continuous electrical resistivity survey carried out on the Po River, in a 5-km long urban sector of its flow across the city of Turin (NW Italy). The main objective of the study was to obtain a first assessment on the characterization of the riverbed sediments, in order to define nature, composition, geometry and spatial relationships of the detected bodies for further geological and hydrogeological reconstruction. The geological context. In the urban area of the city of Turin, the Po River flows at the western edge of the SW-NE-elongated reliefs of the Turin Hill (Fig. 1). The morphology of the relief is remarkably asymmetric, with the presence of a relatively steep north-western slope and a much less inclined southern slope. From a structural point of view, Turin Hill consists of a marine succession from the Upper Eocene and the Pliocene (Bortolami et al. , 1969). This Tertiary sequence lies on a Southalpine metamorphic bedrock (Mosca, 2006). The whole sedimentary succession of Turin Hill is variously deformed, forming an asymmetrical anticline with a SW–NE-oriented axis. This NW verging structure overthrusts onto the Po Plain along the Padan Frontal Thrust currently buried by the Quaternary fluvial sediments of the Po Plain (Castellarin, 1994; Festa et al. , 2009). In particular, for the hillside next to the study area (NW side), the most superficial formation, belonging to the Oligocene-Miocene succession, is the Baldissero Unit (Synthem III Langhian). This Unit consists of marl and sandstones. Arenaceous-conglomeratic bodies with clasts of ophiolite, gneiss and quartzite are present at different levels. Its extension is about several kilometers and thickness varying between 50 and 350 m (e.g. Colle Maddalena). Along the NW side of the Torino Hill, the Baldissero Unit is sometimes covered by deposits belonging to synthems of San Vito (Middle Pleistocene), Cavoretto (Upper Pleistocene) and Monte dei Cappuccini (Upper Pleistocene). These synthems are suspended stream terraces stored on N and NW slopes of the Torino Hill with thicknesses varying between 1 and 5 m and covered by aeolian deposits (Forno et al. , 2002; Boano et al. , 2004; Forno and Lucchesi, 2005). San Vito Synthem consists of sands, silts and weathered gravels and is located between 175 and 300 m above the current plain. Deposits belonging to Cavoretto Synthem consist of silt and sand weakly weathered and are located between 110 and 175 m above the plain. Monte dei Cappuccini Synthem consists of sand, silt and weakly weathered gravel and is located between 30 and 110 m above the plain. At the foot of the NW side of the Turin Hill, in the right bank of the Po River, extensive fluvial deposits of unknown thickness (Upper Pleistocene - Holocene) is found as a Fig. 1 – Structural geological model of Turin Hill and Po Plain in the area of Turin; the black bold square highlights the study area (modified from Forno and Lucchesi, 2015). GNGTS 2015 S essione 3.2 77