Contribution of isotopic techniques to the knowledge of the aquiferous system of the great Sebkha of Oran

Abstract

In the Great Sebkha Basin of Oran, water flows, both surface and subterranean, originate on the slopes and converge toward the discharging area of the salt Lake Great Sebkha of Oran (≈ 80 m above sea level). Isotopic water tracing of 2H, 18O, 14C, and 13C was carried out on the main aquifer formations to clarify the phenomena of evaporation, dissolution, mixing of different water bodies, and their residence time in the aquifer system. The data concern: the salt Lake of the Great Sebkha of Oran, the Quaternary alluvial water table of the periphery, the limestone Miocene, the Brédéah pumping station (whose waters are polluted by brackish water intrusions), deepwater tabler table of the Mio-Pliocene complex of the Plain of Maflak, the Pliocene of the Plain of Tameira, and the Thermal Complex of Hammam Bou Hadjar. The d18O levels range from −9.61 to + 4.8 ‰ V-SMOW at the salt Lake of Great Sebkha of Oran. The 2H contents range from −70 to 20. Minimum values characterize run off from the northern slopes of the Tessala. The 13C contents of dissolved total inorganic carbon (TDI) measured ranged from −10.92 to −3.9 ‰ vs PDB. The activities of the 14C are divided between 2 and 51 PMC. The highest activity in 14C (≈50 PMC) is measured on samples taken from the Miocene limestones of Djebel Murdjadjo.