Caractérisation des eaux de l'aquifère turonien du bassin du Tadla (Maroc) par le rapport des concentrations molaires [formula omitted

Abstract

We present a synthesis on the meaning of the dissolved strontium concentration variations in groundwaters of the Cretaceous calcareous aquifer of the basin of Tadla in Morocco, which is some 10 000 km 2 in surface area. The geologic formations of Turonian age outcrop on the basin periphery only on the south-east boundary, which is overlapped by the High Atlas. They can be interbedded whith evaporite layers at the top or at the base. Some contaminants of the water are observed by the dissolution and by the mixing of sulphate waters with the carbonate aquifer waters. We demonstrate that the Sr 2+ Ca 2+ ratio is a way to differentiate the kind of reservoir and also the causes of hydrodynamical connections. Four geographic clusters have been recognized: a northern group which outcrops (0.8-1%), a confined aquifer (1.2-1.7%) where anhydride is associated with limestones, and two groups with sulphurous groundwaters (3–24%) separated into two parts; the first is in the northeast and is influenced by gypsiferous Cenomanian rocks (7–24%), and the second is in the south and is influenced by lagoonal Senonian sediments (top of the aquifer) and by Cenomanian deposits (base of the aquifer). We note a fifth distinct group (2.84%) of sulphurous superficial waters of wadi Oum-Er-Rbia fed by the high-sulphur waters flowing from Triassic evaporitic deposits of the Atlas mountains.