Geophysical contribution using electrical resistivity to study the Triassic sandstone aquifer, southeastern Tunisia

Abstract

A study was conducted to analyze the electrical resistivity structure of the Triassic Sandstone Aquifer in southeastern Tunisia in regions without constraints from nearby well data. The aim was to determine how the geometry, depth, thickness, and lateral extension of the aquifer within the Medenine region. Seven profiles, including two-dimensional profiles and vertical electrical soundings, were collected, with electrodes spaced between 4 and 5 m apart depending on the desired depth penetration. Geological outcrops and stratigraphic data from nearby water wells were used to constrain the final models, however these wells could only be used roughly as most of them were too far from a given profile. The models from two-dimensional inversions showed that the alluvium in the upstream region of Oued Nagueb had a maximum thickness of about 10 m, whereas in the downstream reaches, the thickness decreased to 4 m. The models indicated that the sandy clays of the alluvium may reduce the infiltration of surficial water into the Triassic Sandstone aquifer. The study area has a gradual thinning of the sedimentary cover from west to east, causing the Triassic Sandstone aquifer to deepen toward the west. The fine-grained sandstone which is characteristic of the Triassic Sandstone aquifer was detected at depths of approximately 40 m in the eastern region and more than 77 m in the western region of the study area. The electrical resistivity models imaged the Medenine fault, which may influence the structural configuration of the Triassic Sandstone aquifer. One model (ERT7) indicated that the Medenine fault acts as a water barrier and retards the groundwater movement of the aquifer. These findings provide information on the extent and depth of the aquifer for future groundwater exploration in the area and can serve as a reference model for analyzing aquifers in northeastern Tunisia.