Groundwater Mounding in Fractured Fossil Aquifers in the Saharan-Arabian Desert

Understanding the role of geological structures in controlling groundwater flow in fossil aquifers is central for proper assessment of groundwater dynamics and aquifer connections. In such settings, connections between deep and shallow aquifers could potentially affect groundwater quality and availability as well as karst formation and landscape evolution. Herein, we integrate available hydrological and isotopic datasets with remote sensing data covering two aquifer units in Sinai and Qatar to indicate the occurrence of significant recharge of gaseous-rich groundwater from deep to shallow aquifers under upward hydraulic gradients along vertical/subvertical faults. Evidence include: (1) the presence of localized recharge mounds ranging from 7 to 50 m in height, in Qatar and Sinai; (2) the recharge mounds are correlated with the locations of mapped strike-slip and oblique-slip faults; and (3) isotopic composition of the groundwater in these locations indicate significant depletion (δ¹⁸O: −9.53‰ to −8.4‰; δ¹⁸O: −5.2 to −2.6‰) compared to modern precipitation (δ¹⁸O: −3.43‰; δ¹⁸O: −0.68‰) in Sinai and Qatar, respectively, which implies limited surface recharge. The mechanism of formation of these groundwater mounds and the amount of upward recharge from the deep aquifers need further investigations to be addressed.