Groundwater salinization survey of the Upper Cretaceous-Miocene Complexe terminal aquifer in the Sabaa Biar area of southwestern Tunisia

• Schlumberger depth sounding method, wells and field data are used.
• The lithostratigraphy and the hydrogeology of the study area are discussed.
• The source of salinization is identified and discussed.
• The relations between the structural framework, water recharge, water exploitation and salinization are discussed.

An integrated hydrogeological study involving the Schlumberger depth sounding method, geological data and wells data was conducted at the Sabaa Biar area of southern Tunisia to elucidate the problem of increasing groundwater salinity within The “Complexe Terminal”. The “Complexe Terminal” aquifer near Sabaa Biar region is a bi-layered aquifer comprised of fractured limestones of the Cretaceous (Campanian–Maastrichtian) Berda Formation and sandstone of the Miocene Beglia Formation. The aquifer is affected by a main NW–trending fault, which is a chemical barrier that divides the study area into eastern and western blocks delivering freshwater and saline water, respectively. The salinization of groundwater within the limestone (Campanian–Maastrichtian Berda Formation) is linked mainly to the dissolution of outcropping Coniacian–Santonian gypsum along the core of the Jebel Sidi Bouhlel anticline to the east of the study area. Meteoric water dissolves salt from outcropping gypsum, flows through the fractures networks, and recharges the fractured limestone of the upper Berda Formation. The mobilization of salts stored in the salt-rich Quaternary sediment on hillslopes and inchannels contributes also to the salinization of groundwater within the sandstone (Miocene Beglia Formation) by lateral infiltration subsequent to water drainage during the wet season. The over exploitation of water from the Miocene sandstone causes an influx of saline-rich water from the underlying limestone of the Berda Formation into the sandstone of the Beglia Formation. Other sources of salinization of groundwater (such as ascension of hypersaline water from deep aquifer along faults, and the return flow of irrigation waters in the Djerid region) have been documented in this region, but are not discussed in this paper.