Magnetic and electromagnetic data interpretation for delineating geological contacts in the Tomelilla area, Sweden

Abstract

This paper describes an application of diverse geophysical methods to detect the geological contacts in the Tomelilla area, Sweden. Airborne magnetic data and the tipper and peaker maps derived from tensor very-low-frequency electromagnetic (TVLF-EM) data are interpreted in order to indicate most geological boundaries. The inverted airborne TVLF data along adjacent profiles over each contact show the resistivity variations at depth and laterally localize the geological contacts while delineating resistive bedrocks in all cases. To control the resistivity images across these profiles, the ground-based measurements of the radio magnetotelluric data combined with controlled-source magnetotelluric data (RMT/CSMT) have been performed to plot resistivity variations with higher resolution. The obtained resistivity images are in good agreement with the ones acquired from airborne TVLF data. A relatively conductive layer with an average thickness of 20 to 30 m of the Quaternary deposits, increasing in thickness from east to the west, and a resistive basement with much higher resistivity on the granites than the shales are resolved from the geoelectric sections. This paper confirms that the combined geophysical surveys (i.e., airborne magnetometry/TVLF along with ground-based RMT/CSMT) reduce the uncertainty arising from geological mapping. It is shown that the airborne TVLF data have high capability for image resistivity variation along geological contacts in the study area while its resolution has been confirmed by the ground-based RMT/CSMT survey.