Susceptibility measurements, optical and X-ray analysis to explain the origin of archaeological magnetic anomalies in Tavoliere lowland (Southern Italy)

Abstract

Since 2002 a non-invasive investigation integrating aerial photography and high-resolution magnetometry has been carried out for reconstructing extensive ancient settlements in Tavoliere lowland (Southern Italy). Relevant magnetic anomalies were detected in all the surveyed sites allowing a precise mapping of the buried structures over more than 150 ha. Next to this research susceptibility measurements, PXRD, XRF and optical analysis were also performed in order to explain the origin of the notable magnetization contrast between the anthropogenic structures and the embedding materials, generating the measured signals. This last study was accomplished, in 2006, in Monte S. Vincenzo site, a vast Neolithic village where the remotely sensed data were also used to guide some direct inspection. Trial archaeological excavations brought to light parts of C-shaped compounds, providing complete information on the geometry and location of the sources of magnetic signals. Profiting by the archaeological feedback, the susceptibility contrast between the soil filling the ditches and the calcareous substratum was assessed in situ. A synthetic model based on this information was created and compared with the experimental data. The infilling material was also sampled for laboratory analysis: the presence of several magnetic minerals (pyroxenes, monometric magnetite, haematite) was ascertained. Furthermore optical analyses showed different types of volcanic and igneous products such as pumices, melanite garnets and lava fragments. Geomorphological and archaeometric evidence allowed us to relate these materials to activity of the Mt. Vesuvius volcano. Eventually their possible spatial distribution was inferred from recent studies on ash transportation and deposition during explosive activity.