CHARACTERIZATION OF THE GROUNDWATERS OF T HE TURONIAN CATCHMENT OF TADLA (MOROCCO) BY THE CONCENTRATION RATIOS OF SR2+ CA2+/

We present a synthesis on the meaning of the dissolved strontium conce ntration variations in groundwaters of the Cretaceous calcareous aquif er of the basin of Tadla in Morocco,which is some 10 000 km(2) in surf ace 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 di ssolution and by the mixing of sulphate waters with the carbonate aqui fer waters. We demonstrate that the Sr2+/Ca2+ ratio is a way to differ entiate the kind of reservoir and also the causes of hydrodynamical co nnections. Four geographic clusters have been recognized: a northern g roup which outcrops (0.8-1 parts per thousand), a confined aquifer (1. 2-1.7 parts per thousand) where anhydride is associated with limestone s, and two groups with sulphurous groundwaters (3-24 parts per thousan d) separated into two parts; the first is in the northeast and is infl uenced by gypsiferous Cenomanian rocks (7-24 parts per thousand), and the second is in the south and is influenced by lagoonal Senonian sedi ments (top of the aquifer) and by Cenomanian deposits (base of the aqu ifer). We note a fifth distinct group (2.84 parts per thousand) of sul phurous superficial waters of wadi Oum-Er-Rbia fed by the high-sulphur waters flowing from Triassic evaporitic deposits of the Atlas mountai ns.