The hydrochemical implications of the fossilized sandstone aquifer at Wadi Al-Kaniseh, Jordan

Understanding the geochemical evolution of the deep sandstone aquifers of Jordan is severely constrained by the limited knowledge of the mineral phases controlling the chemistry, and the inaccuracy inherent in sampling wellhead water at deep boreholes. The discovery of an exposure of the fossilized deep aquifer at Wadi Al-Kaniseh allows for a better understanding of the geochemical evolution of the deep aquifer waters. The exposure shows three secondary mineral assemblages in various forms. The presumed oldest is represented by halite present between the grains of the sandstone. The second consists of alunite associated with primary gypsum and clay minerals. This indicates that the aquifer contained low (3–4) pH water reacting with the primary minerals to produce the alunite, possibly under relatively high temperatures. The presumed youngest (third) assemblage consists of veins and concretions of carbonate as well as iron oxide (hydroxide), which reflects the mobility of iron (under the aforementioned low pH conditions connected with high dissolved CO 2 concentrations). Once the groundwater neared the surface, the pressure release caused a drop in dissolved CO 2 , a rise in pH and the deposition of the iron and carbonates. Future investigations on the deep waters of Jordan should take into account the possibility that the waters have high CO 2 concentrations and low pH, which are drivers of the geochemistry.