Contribution of the resistivity method to the determination of the fault zone and the hydro-geophysical characteristics of the aquifer system in Tataouine (Southern Tunisia).

Abstract

Southern Tunisia aquifer's systems including Tataouine region has suffered since long time by over-exploitation resulting in a subsequent drop of the piezometric level. Consequently, the overexploitation of these layers poses various problems in term of quality and quantity. Therefore, to better recognize these hydraulic potentialities and evaluate their extensions in this region, a geophysical survey, using the electrical resistivity method was carried out to determine the structure, the configuration of these aquifer systems and to investigate the subsurface layering and evaluation of the aquifer characteristics. Applying the schlumberger array, a total of 335 Vertical Electrical Soundings were conducted along 4 profiles, using a maximum current electrode separation ranging between 500 and 600 m. Qualitatively and quantitively interpretation were both obtained and represents the outcomes from the study field. The qualitative interpretation is based on isoapparent resistivity maps, and the geoelectrical pseudosection analysis. It shows that Tataouine Basin is formed by alternating conductive and resistant anomalies related to the lateral and vertical variation of lithology in the study area. As well, quantitative interpretation using calibration, electrostratigrafic sections and isopach maps shows a clay-sandstone series of the Triasssic, Bathonian and Cretaceous. Theses series, with average low resistivity values, and low percentage of clay present some porosity and constitute the main aquifer unit in the study area. In addition, the carbonate unit shows in certain zone a sight fracking and high resistivity values composed of the aquifers such as; Triassic dolomite, Krachoua limestone, and marl-limestone of upper Jurassic. Furthermore, most of these aquifer units are communicating with each other through the tectonic discontinuities.