Deep electrical resistivity tomography and geothermal analysis of Bradano foredeep deposits in Venosa area (Southern Italy): first results

Geophysical surveys have been carried out to characterize the stratigraphical and structural setting and to better understand the deep water circulation system in the Venosa area (Southern Italy) located in the frontal portion of the Southern Appenninic Subduction. In this area there are some deep water wells from which a water conductivity of about 3 mS/cm and a temperature of about 35 degrees C was measured. A deep geoelectrical tomography with dipole-dipole array has been carried out along a profile of 10000 in and an investigation depth of about 900 m. Furthermore a broad band magnetotelluric profile consisting of six stations was performed to infer the resistivity distribution up to some kilometers of depth. The NIT profile was almost coincident with the geoelectrical outline. The applied methods allow to obtain a mutual control and integrated interpretation of the data. The high resolution of the data was the key to reconstruct the structural asset of buried carbonatic horst whose top is located at about 600 in depth. The final results coming from data wells, geothermal analysis and geophysical data. highlighted a horst saturated with salted water and an anomalous local gradient of 60 degrees C/km. The proposed mechanism is that of a mixing of fossil and fresh water circulation system.