Gravity and seismic reflection imaging of a deep aquifer in an arid region: Case history from the Jeffara basin, southeastern Tunisia

Abstract

A detailed mapping of the lateral and the vertical extension of the Upper Cretaceous units which contains aquifer bearing lithologies and may be part of the Complexe Terminal aquifer in the Jeffara basin of southeastern Tunisia using land and satellite Bouguer gravity anomaly data, eight seismic reflection profiles and two deep wells was performed. Borehole data indicated that the Upper Cretaceous unit is thickest within the Jeffara basin and thins considerably in the Dahar High. Bouguer gravity data in general confirms this result but lacks the resolution to accurately determine the thickness of the Upper Cretaceous units. Eight seismic reflection profiles constrained by borehole data indicated that the Upper Cretaceous aquifer may be present at depths greater than 500m and is up to 400m thick. The seismic reflection analysis showed that the Upper Cretaceous units contain two distinct zones. Within the northeastern portions of the Jeffara basin, the Upper Cretaceous units are influenced by horsts, grabens and tilted blocks where the Upper Cretaceous units are deeper and thicker units occur within the grabens. A second zone exits toward the basin’s southwestern section where the Upper Cretaceous units are shallower and gradually thin against the Dahar High. Structural contour maps of the top and the base of the Upper Cretaceous aquifer constructed from the seismic reflection profiles reveal the presence of fractured depressions in the northeastern part of the Jeffara basin that are favourable to the hydrogeological exploitation.