New elements on the “Continental Intercalaire,” the most important aquifer in North Africa: joint use of seismic reflection and borehole data

The present study focused on the “Continental Intercalaire” (CI), the North Africa′’s hugest aquifer. It uses different disciplines: geology, hydrogeology, and geophysics for achieving enhanced characterization of the Tunisian “CI” in Mednine -Tataouine area (Southern Tunisia), marked by highly constrained surface water resources. Besides, this study represents a successful example of petroleum and water data joint use for hydrogeological purposes. Petroleum wells are better distributed and deeper than water boreholes. They give more complete information on the subsurface stratigraphy, whereas water boreholes furnish hydrochemistry, hydrodynamic, and hydrophysical data. Used geophysical data were composed of well logs and 2D seismic reflection profiles. Available well logs were gamma ray (GR), resistivity, and sonic (Δ T ) logs. Their analysis allowed a precise delimitation of the “CI” reservoirs, which chiefly consist of the sandstone layers of Boulouha, Douiret, Chenini, and Oum Diab members. Lithostratigraphic correlations according to different directions were established, and sixty-eight seismic reflection sections were interpreted for the reconstitution of the “CI” geometry. They highlighted that this aquifer is absent in the Jeffara domain and characterized by notable variations in depth, thickness, and lithological composition in the Dahar domain; it shows thickening (373 m), deepening (1607 m), and enrichment in clays towards the southwest, while a thinning (100 m) towards the north and a pinchout towards the northeast. This arrangement has been mainly generated by the Lower Cretaceous synsedimentary NW–SE and E-W normal faulting and the Hercynian, intra-Triassic, and Barremian to Upper Aptian compressive manifestations. The delineated geometry has an important effect on the groundwater circulation and characteristics. By generating tilted block structure of the “CI,” NW–SE normal faulting favors groundwater flow and water temperature increase towards the southwest. The present study yielded to interesting results that may contribute to a better management of groundwater resources in southern Tunisia. It can be also a reference of other scientific research dealing with the Northern Sahara Aquifer System (SASS).