Stable isotope geochemistry of sediment-hosted groundwater from a Late Paleozoic–Early Mesozoic section in central Europe

The boron isotopic composition, in combination with oxygen, hydrogen and sulfur isotopes and hydrochemical tracers, is utilized to investigate the evolution of groundwaters from a Late Paleozoic (Permian) to Early Mesozoic (Triassic) section of the sedimentary cover in central Europe (N Switzerland–SW Germany). Four distinct groundwater types have been identified: (a) saline groundwater from Permian (Rotliegend) sediments (δ11B=+13.7 to +33.0‰, δ18O=−6.7 to −5.3‰, δD=−53.4 to −37.8‰, δ34S=+16.4 to +17.1‰); (b) brackish to saline groundwater from Lower Triassic (Buntsandstein) sediments (δ11B=+6.4 to +22.3‰, δ18O=−10.3 to −6.9‰, δD=−71.8 to −60.5‰, δ34S=+18.2 to +18.4‰); (c) fresh to saline groundwater from Middle Triassic (Muschelkalk) sediments (δ11B=−10.2 to +7.7‰, δ18O=−11.8 to −8.8‰, δD=−86.6 to −63.0‰, δ34S=+15.8 to +21.4‰); and (d) saline groundwater from Upper Triassic (Keuper) sediments (δ11B=+26.3‰, δ18O=−6.4‰, δD=−41.2‰, δ34S=+16.1‰). As evidenced by B–O–H–S stable isotope and hydrochemical (e.g. Na/Cl, Br/Cl, Ca/SO4, (Ca+Mg)/SO4, K/B, and Li/B) constraints, interactions with sedimentary host rocks and inter-aquifer mixing have contributed to the evolution of the investigated groundwaters.