Geochemical approach to the functioning of the Gafsa North deep aquifer (central Tunisia)

• Published in: Hydrological sciences journal Vol. 48; no. 1; pp. 95 - 108
• Main Authors: Yermani, M, Zouari, K, Michelot, J L, Mamou, A, Moumni, L
• Format: Journal Article
• Language: English; French
• Published: 01-02-2003
• Subjects: Tunisia
• ISSN: 0262-6667
• DOI: 10.1623/hysj.48.1.95.43482

The North Gafsa basin contains a multi-layered aquifer with three principal levels: upper Zebbag (Cenomanian-Turonian), Abiod (Maestrichian) and Mio-plio-quaternary formations. The hydrogeology of this system is largely determined by tectonics. Indeed, the basin is limited to the south by the Gafsa fault, which acts as a hydraulic sill. Chemical and isotopic data show that the different aquifer levels are recharged by flood water infiltration in the valley of wadi El Kbir, and by direct infiltration of rainwater through carbonate Cretaceous outcrops in the north of the basin. In the centre of the basin, super(14)C ages of deep groundwaters are the highest. However, the tritium concentrations show the contribution of recently recharged water coming from direct rain infiltration through sand dunes. Downstream, near the Gafsa sill, deep old groundwaters coming from the northern outcrops mix with some recent water recharged through the local Cretaceous outcrops and/or from the wadi Bayech alluvial aquifer. This mixing is marked by measurable tritium concentration, by a lowering of super(14)C ages and by a decrease of total salinity.