Imaging subsurface lithological and structural features by resistivity tomography: North Beagle Channel (Tierra del Fuego, Argentina)

Abstract

Worldwide, the study of fold and thrust belts and characterization of structures are mainly carried out through superficial geological observations and seismic reflection, as the main geophysical prospecting method. In this study we show how the resistivity method is a useful tool for identification of shallow structures (upper 80 m) when combined with the knowledge of the local geology. This is a relative low cost and easily applicable method, which can contribute to image both lithological boundaries and subsurface structures.

The Andes Fueguinos in the area of the Beagle Channel are characterized by a sequence of NNE-verging thrusts stacks of basement emplaced during the middle Cretaceous-Tertiary Andean orogenesis, combined with a strong left lateral strike-slip component. An electric resistivity survey to obtain a 2D electric resistive tomography (ERT) was carried out in the northern shore of the Beagle Channel, west of Ushuaia, in order to better understand the geometric relationships between the basement and cover units in this part of the thrust belt. The method employed, integrated with a field geological survey, allowed to differentiate the electrical signatures of different thin sheets of the thrust belt, where the major faults are recognized by a decrease in resistivity values and sharp lateral variations. Furthermore, the resistivity section shows a good spatial correspondence with a geological section of the study area, where the continuity of the tectonic boundary between the basement (Lapataia Formation) and synrift units (Lemaire Formation) could be followed at depth.