High Resolution Electrical Resistivity Tomography (ERT) in a Transition Zone Environment: Application for Detailed Inter
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Marine Geophysical Researches (2005) 26:317–328 DOI 10.1007/s11001-005-3726-5
High resolution electrical resistivity tomography (ERT) in a transition zone environment: Application for detailed internal architecture and infilling processes study of a Rhoˆne River paleo-channel Gre´goire M. Maillet1,*, Enzo Rizzo2,3, Andre´ Revil3 and Claude Vella1 1
Geomorphology and Tectonics Team, CNRS-CEREGE, Universite´ Aix-Marseille 1, Aix-en-Provence, France 2 Laboratory of Geophysics, CNR-IMAA, Tito Scalo, PZ, Italy 3 Hydrogeophysics and Porous Media Team, CNRS-CEREGE, Universite´ Aix-Marseille 3, Aix-en-Provence, France *Corresponding author (Institute of Radioprotection and Nuclear Safety, DEI/SESURE/LERCM, 13115 Cadarache, France. Tel: +33-442-199-109; Fax: +33-442-199-142; E-mail: [email protected]) Received 15 January 2004; accepted 10 October 2004
Key words: channel infilling, electrical resistivity, mouth evolution model, Rhoˆne Delta
Abstract Electrical Resistivity Tomography (ERT) was applied in a sand-infilled paleo-channel located in the Rhoˆne Delta, in Southern France. The detailed pattern and sedimentological evolution of the channel fill deposits – know from both historical and geological sources – made it the ideal site to test the ERT method. A geoelectrical survey was performed, using the ABEM SAS-4000 multi-electrode array system in March 2003. Very low electrical resistivity values were obtained, ranging from 0.3 to 10 Ohm m, consistent with the high salinity measured in situ (the pore water conductivity was found to range from 0.9 to 1.2 S/m at 25 C). The electrical resistivity profiles reflect mainly salinity variations. Indeed, in this case, salinity is so high that surface conductivity associated with clay minerals can be safely neglected. ERT provided valuable high-resolution information that complemented other exiting data such as historical information, bathymetric, geological, and lithostratigraphic data, which allowed the architecture of the channel to be defined. The ERT was used to determine the infilling dynamics of the Pe´goulier Channel, which opens new perspectives in terms of paleoenvironmental reconstruction and paleodynamic studies.
Introduction Coastal and inshore areas are critical zones to study the transfer processes between continents and oceans. The evolution of these areas is of great interest to geomorphologists and sedimentologists as shown in this volume. Standard surveying techniques such as drilling, core sediment analyses, which include grain size distribution, and petrophysical measurements produce accurate details about the sediment texture and dynamics. However, these methods are expensive and timeconsuming which prevents them from being used on a large scale. Moreover, this type of data is spatially limited. On the contrary, geophysical measurements can provide a less expensive way to fill the lack of knowledge between a set of boreholes.
Electrical Resistivity Tomography (ERT) is a 2-dimensional geophysical technique to study the shallow subsurface of the Earth with
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