Mixed, classical and hydrothermal karstification in a carbonate aquifer

In the Saida area, Algeria, a regional aquifer has formed in Jurassic carbonate rocks. Recharged by direct infiltration and swallow holes on horsts, it discharges into the Saida graben. Geochemical and isotope contents show deep groundwater flow at temperatures of around 100 °C at depth and CO 2 of deep origin, developing a hydrothermal karst interconnected with the shallow, classical karst. This particular type of karst aquifer, mixing hydrothermal karst conduits in the phreatic zone and classical karst features in the infiltration zone occurs preferably in active tectonic regions. Such a situation is favourable to productive well boring, consequently to groundwater withdrawal and deterioration of water quality. Still badly known in general, this type of complex aquifer should be studied in depth for an efficient and proper exploitation and protection of the groundwater resource.