160 A new concept of karst development based on hydrogeology and geophysics occurs at 119.92 m, supporting the correlation. Above this surface, a bivalve-rich level—interpreted as the Gryphaea beaumonti bed—is recognized and considered to mark the base of the Aalenian. Figure 9 presents a stratigraphic synthesis of the supra-Toarcian aquifer at the HES. Figure 9 Stratigraphical synthesis of HES boreholes.
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