DERT and Magnetotelluric Investigation of Bradano Foredeep Deposits

Geoelectrical and magnetotelluric surveys have been carried out to better understand the deep water circulation system in the Venosa area (Southern Italy) located in the frontal portion of the southern Apenninic Subduction. In this area, measurements undertaken in some deep wells give a water conductivity of 3mS/cm and a temperature of about 35°C. A deep dipole-dipole geoelectrical tomography has been carried out along a profile of 10.000m and an investigation depth of 900m. Furthermore a broad band magnetotelluric profile consisting of six station was performed in order to infer the resistivity distribution up to some kilometerers of depth. The MT profile was almost coincident to the geoelectrical outline. The applied methods allow us to obtain a mutual control and an integrated interpretation of the data. The high resolution of the data was the key to reconstruct the structural asset of buried carbonatic horst which top is located at about 600m deep. On the basis of data wells, geothermal analysis and geophysical data, it results that the horst is saturated with salted water and an anomalous local gradient of 60°C/km is present. The proposed mechanism is that of a mixing of fossil and fresh water.