Evidence for a Saline Component at Shallow Depth in the Crystalline Armorican Basement (W France)

Saline fluids at shallow depth (50 – 450 m) in the Armorican basement were investigated. Fluids with salinities ranging from 80 to 900 mg/L mix with modern shallow groundwaters containing anthropogenic solutes. The most saline fluids are deeper or more isolated from mixing. These fluids reveal Br/Cl and SO4/Cl ratios that are typically marine. This work establishes the migration and the preservation of a marine end-member in a basement aquifer, and may provide keys for the understanding of such fluid circulation.