GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.2 191 Case history: a magnetic and GPR prospection on a Roman rural villa in western Piedmont (Italy) L. Sambuelli 1 , D. Elia 2 , V. Meirano 2 , C. Colombero 3 1 Dipartimento di Ingegneria dell’ambiente, del Territorio e delle Infrastrutture – Politecnico di Torino, Italy 2 Dipartimento di Studi Storici – Università di Torino, Italy 3 Dipartimento di Scienze della Terra – Università di Torino, Italy Foreword. Since the half of the past century the use of geophysicalmethods for archaeological prospection has been proposed (Segre, 1958; Rees, 1962). However only in the few past decades the evolution of theory, software and instrumentation has allowed for the possibility of adopting multi methods prospection with reasonable execution times and costs. New technologies, such as ERT and GPR, have been added to the traditional ones (Pasquinucci and Trément, 2000; Gaffney and Gater, 2003). On the occasion of exploring an archaeological site in western Piedmont, we then decided to proceed to a multimethod survey using fast methods and taking also into account the information achievable after a 2D or 3D data processing and/or rendering. This choice restricted the methodologies to magnetic and GPR prospecting. The non contact resistance imaging, in our opinion, still gives too smeared results even if indicative of resistivity anomalies. We selected the magnetic prospecting because of the remarkable size of some of the walls actually excavated even if, as we explain in the geological context, the probability of collecting a significant amount of noise was high. The geological context. The village of Costigliole Saluzzo (CN) is located in north-western Italy, at the end of the Varaita Valley, at the edge between north-western Alps and the wide piedmont’s plain. The Varaita Valley elongates in WE direction from the Monviso Massif and the administrative border with France (Fig. 1). From a geological point of view, two main tectono-metamorphic units outcrop in this area: the Dora-Maira Massif, in the lower part of the valley, and the Piedmontese Zone with the Monviso Ophiolitic Massif in the upper part, from the town of Sampeyre to France. The Dora-Maira Massif is a continental crust unit mainly constituted by ercinic and pre- ercinic methamorphites (mainly gneiss and micascists). On the other hand, the upper part of the valley is characterized by oceanic lithologies (Calcescists with Green Stones, Jurassic- Cretaceous) overthrusted on the Dora-Maira Unit. The Monviso ophiolite complex is a north- trending body, 35 km long and up to 8 km wide, sandwiched structurally between the underlying Dora-Maira thrust units and the tectonically higher, dominantly metasedimentary, units of the Piedmontese Zone (Lombardo et al., 2002). Fig. 1 – On the left the geographical location of the archaeological site: the white letters refer to the surveyed area. On the right the geological map of western Alps; the black star refers to the surveyed area.