Présentations Colloques

Oral Presentation
8.04
Session 8.04: Isotopic and residence time tracers
Khaska Mahmoud
Impact of deep saliferous Triassic deposits on groundwater mineralization in a Mediterranean costal aquifer
In the context of global climate change and the increasing pressure of water resources in the Mediterranean basin, understanding the salinization process is essential to the management of groundwater resources. The aim of this study is to investigate the hydrogeochemical evolution and the mineralization mechanisms of groundwater through the study of a major spring water in the Gulf of Lion continental. Based on an adequate set of geochemical and isotopic tracers including cosmogenic, stable and radiogenic isotopes, we have revealed complex hydrogeochemical processes that cannot be tracked with the traditional hydrochemical and isotopic tracers. The high 87Sr 86Sr ratios of the spring water associated with relatively high concentrations in trace elements (Cs, Rb, Sr, B, Li) suggest the influence either of brine from the Triass deposits containing saliferous clay or of saline fluids from the fractured basement. Contrasting with marine primary brine and current seawater, the relatively high δ+37Cl (0.22 and 0.39 ‰) of groundwater attests the non marine origin of chloride ion. 36Cl Cl shows that the spring water is issued from a mixing process between recently recharged water, lightly mineralized but significantly marked in 36Cl by the thermonuclear bomb pulse, and a saline deep end-member at 36Cl Cl secular equilibrium with the matrix. This indicates that Cl−+ in these springs are primarily derived from subsurface, non-meteoric sources. The deep saline water results from the infiltration of meteoric water into the lower Jurassic aquifer in contact with Triassic deposits and potentially basement uprising. High temperature promotes water-rock interaction enhancing leaching of saliferous Triassic deposits.
France