Geochemical and isotopic study of the multilayer aquifer system in the Moulares-Redayef basin, southern Tunisia

Major ion geochemistry, and water molecule isotopes (O-18, H-2) and radiogenic carbon (C-14) of dissolved inorganic carbon (DIC) were used to investigate the hydrodynamic functioning of the multilayer aquiter system in the Moulares-Redayef basin, southern Tunisia. The groundwater of different aquifer levels is characterized by sulphate to calcium sulphate water type. The major geochemical processes ill the aquifer system are evaporite mineral dissolution and mixing. The isotopic study allows two groundwater types to be identified: an old palaeoclimatic groundwater, marked by low C-14 activity and relatively depleted stable isotope (O-18 and H-2) content characterizes the shallowest aquifers of the Plio-Quaternary and Miocene formations; however, a recent groundwater, distinguished by relatively high C-14 activity and slightly enriched O-18 and H-2 content, characterizes the deep Upper Cretaceous artesian aquifer. In addition to these two water groups, other groundwaters are identified, indicating a mixing effect.