GROUNDWATER HYDROCHEMISTRY AND MASS TRANSFER IN A STRATIFIED AQUIFER SYSTEM (JEFFARA-GABES BASIN, TUNISIA)

Abstract

The present work exposes the existence of a real mass transfer in the aquifer system of the Jeffara-Gabès basin. The main aquifers (Complexe Terminal) include Mio-Plio-Quaternary and Senonian sequences associated to stratified lower Cretaceous sandstone of the Continental Intercalary aquifer. Geochemical and isotopic data of groundwater aquifers needed to better understand the relationship between different stratified layers and aquifers. It indicates that Senonian aquifer has been recharged to the West of the area of study by the Continental Intercalary via the El Hamma fault network oriented N-S and NW-SE. The major elements analysis shows that water table of the Complex Terminal with low salinity fit to Ca-Na-SO4 type while waters with high total dissolved salts belong to Na-(Mg)-Ca-SO4-Cl type which characterizes the Continental Intercalary hydrochemical facies. Chemical analyses In addition to geological data and thermodynamic calculation attest the existence of an evident lateral communication between Continental Intercalary aquifer and the Jeffara aquifer system through the El Hamma active faults. Isotopic data show that Complex Terminal groundwater has been affected by a paleorecharge and indicate a mixing of Continental Intercalary and Complex Terminal groundwater. Also, the results show an upward leakage from the Senonian aquifer to the uppermost mio-plio-quaternary reservoir via NE-SW and E-W oriented faults.