Magnetic signal prospecting using multiparameter measurements: the case study of the Gallic Site of Levroux

Abstract

AbstractThe ‘magnetic signal’ that combines both the induced (Ji) and the remanent (Jr) magnetization is widely used in archaeological and pedological prospecting. Magnetic prospecting recording the lateral variations of the total magnetization is the most frequently used measurement before in‐phase magnetic susceptibility (Kph) and magnetic viscosity (Kqu) mapping. The work presented here brings together three types of prospecting technique: magnetic field survey and electromagnetic measurements with both frequency and time domain devices that measure magnetic susceptibility and viscosity respectively. The site studied, the Gallic town of Levroux (Indre, France), is particularly interesting because it includes features such as pits and ditches dug into the calcareous substratum partly filled with topsoil and with residues of different metallurgical and fire activities. The field results indicated anomalies with different types of characterization: (i) many compact features filled with magnetic, electrically conductive and minimally viscous materials; and (ii) elongated anomalies characterized by lower magnetic properties and electric conductivity but relatively higher magnetic viscosity than those of the compact features. In addition to the location of the features, the combination of the information brought by the different types of measurements allows us to evaluate the possible erosion of their upper parts by ploughing, to assess their depth (never deeper than 1.30 m) and to precise the nature of the feature's fill. Copyright © 2010 John Wiley & Sons, Ltd.