Reduction Of Topography Effect In Apparent Conductivity Profiles (Em38): Application On Sambaqui Site (Shell Mound) In Santa Catarina State, Brazil

Modern land developments have motivated the application of geophysical methods in archaeological investigation in order to recognize hidden patterns in poorly known areas and select suitable places for excavation. Due to quick data acquisition and interpretation, low-induction EM38 measurements (conductivity and magnetic susceptibility) have been successfully applied to map fire places, burials, and concentration of ceramic materials in many Brazilian prehistoric sites. Conductivity anomalies, however, are much affected by the soil water content, which in sites with rugged topography creates a site-scale effect that masks the expression of subtle archaeological features. Here, we apply a procedure to remove the dependence of the soil conductivity with respect to the site topography by using a linear relationship determined by cross-plotting conductivity and elevation values measured in a given site. Corrected conductivity values helped us to identify regions of archaeological interest (further confirmed by excavation), which formerly were not easily recognized from crude data. This procedure has shown proved utility as an exploration tool to study sambaqui (shell mounds) archaeological sites, at the sandy coastal plain of the Santa Catarina State, in southern Brazil.