3-D Electrical Resistivity Tomography of an ancien meander (Vallon-Pont-d’Arc, France)

The present study aims to reconstruct the landscape of the Pont d’Arc meander cutoff during the Upper Paleolithic, when humans were present in the Chauvet Cave (Fig. 1). To participate to this work, I  helped to determined the subsurface morphologies of the alluvial deposits with electrical resistivity data conducted inside the cutoff meander. (More information can be found on the scientific article Genuite et al., 2021 published in Nature Scientific Reports  [download pdf]).

Figure 1. Location of the Chauvet Cave. The Chauvet Cave is in the Cirque d’Estre scarp, above the Combe d’Arc meander cutoff, which formed when the Ardèche River cut through the Pont d’Arc to form a natural arch.

For this purpose, we carried out 44 electrical resistivity profiles involving a total of 2,111 electrode , spaced at 5-m intervals (Fig. 2).

Figure 2. Electrical Resistivity Tomography survey inside the Combe d’Arc meander cutoff (yellow lines).

I used parallelized E4D code to perform a 3D inversion of the electrical resistivity data, and we selected the 10th iteration as the final electrical resistivity model (Fig. 3 and Movie 1). The low-resistivity deposits (<250 Ωm) are  clay rich sediments that form the upper part of the Combe d’Arc sediment sequence. The results of this survey enabled us to correlate sediments in the Combe d’Arc with alluvial deposits elsewhere in the Ardèche catchment.


Figure 3. 3D electrical resistivity models for the Combe d’Arc meander. (a). Topography of the mesh domain used for the 3D electrical resistivity inverse modelling inside the Combe d’Arc meander. The mesh, which is denser close to the electrodes, contains 707,953 tetrahedral elements. (b). Surface resistivity. (c). Plot of resistivity iso-values. (d). Plot of 250 Ωm resistivity isovalues. Convergence occurred very quickly, after just a few iterations, which shows that the fieldwork data was coherent across the entire meander.

Movie 1 : W-E animation of the 3-D electrical resististivity model of the meander