A GEOCHEMICAL, GEOPHYSICAL, AND REMOTE SENSING-BASED APPROACH FOR THE ASSESSMENT OF THE AGE, ORIGIN, AND SUSTAINABLE UTILIZATION OF FOSSIL AQUIFERS IN SAHARAN AFRICA AND ARABIA

An integrated geochemical, field, geophysical, and remote sensing-based approach was developed to assess the origin, age, history, and groundwater potential of large fossil aquifer systems in Saharan Africa and Arabia. We used two test sites for demonstration purposes, the Nubian Sandstone Aquifer System (NSAS; area: 2×10⁶ km²) in Egypt, Sudan, Libya, and Chad and the Rub Al Khali (RAK; area: 650,000 km²) region in southern Arabian Peninsula. Geochemical (solute chemistry, O and H stable isotopes, and ²²⁶Ra activities) analyses and geochronologic (Kr-81, Cl-36, C-14) methods were used to constrain the origin, age, and history of groundwater. Digital elevation model (DEM; derived from Shuttle Radar Topography Mission [SRTM]) and subsurface data were used to extract surface and groundwater flow directions, gravity data were used to map the spatial variations in the thickness of the sedimentary cover, and temporal (01/2003-12/2012) Gravity Recovery and Climate Experiment (GRACE) and outputs of the CLM4.5 model were used to estimate depletion and recharge rates. The adopted integrated approach allowed: (1) testing of the connectivity of sub-basins within the two aquifers, (2) delineation of impediments/preferred pathways for groundwater flow, and (3) development of optimum scenarios for aquifer utilization, and (4) provides a replicable and cost-effective model for a better understanding of the hydrogeologic setting of large aquifers worldwide.