Hydrogeochemical multi-component approach to assess fluids upwelling and mixing in shallow carbonate-evaporitic aquifers (Contursi area, southern Apennines, Italy)

With the aim of deepening our understanding deep-seated fluids upwelling and mixing in large regional aquifers, we performed a hydrogeochemical study twenty-two springs Contursi area (upper Sele river valley, southern Apennines) by means measurements chemical-physical parameters, major ions, trace elements, stable radioactive isotopes. Besides, realized two updated geo-structural cross-sections order to reconstruct groundwater flowpath area. The composition, as well water temperature allow identify-three main groups groundwater: Cold Low salinity Groundwater (CLGW), Intermediate Salinity (ISGW), Thermal (TSGW). CLGW group, mostly emerging at boundary carbonate is characterized alkaline earth-bicarbonate hydrofacies. Instead, ISGW TSGW, situated inner zone show gradually evolution towards sodium-chloride type hydrofacies domain with highest value. Stable isotope (δ18O-δD) reveal local meteoric origin groundwater, while isotopic signatures TSGW associated deep inflow. hydrogeochemistry clearly related dissolution rocks. On other hand, for an additional contribution from evaporitic rocks supported saturation indices values (gypsum anhydrite) validated signature dissolved sulphate (δ34S-δ18O). application models based on tritium data (i.e., piston-flow well-mixed reservoir) attributes longer deeper flowpaths TSGW. Through geothermometric calculations (e,g., K-Mg SiO2-quartz), equilibrium reservoir also extrapolated 75–96 °C). results adopted multi-component approach allowed us propose interpretative model area, where tectonic discontinuities play significant role saline thermal shallow aquifers.