Figure 7. Hydrogeological model derived from the geochemical data.

The hydrogeological model presents the three steps that have been established through the geochemical data. The first stage represents the introduction of seawater in the basement through density-driven process within major faults. Seawater is introduced in the lower parts of the basement where it is mixed with freshwater. Following introduction which is spatially focused, seawater is introduced in the rock matrix (micro-porosity) through a slow diffusion process. During the second stage, permafrost breakthrough induces the introduction of cold freshwater within the same major faults. This introduction is induced by large hydrogeological loops that occur probably during a relatively short period (less than a few thousand years). The third stage represents the modern period where the hydrogeological loops are less extended towards depth which allows for the preservation of the previous signatures below 100 m depth. Figure is original and has been drawned by L.A.