Hydrochemical Zoning and Chemical Evolution of the Deep Upper Jurassic Thermal Groundwater Reservoir Using Water Chemical and Environmental Isotope Data

A comprehensive hydrogeological understanding of the deep Upper Jurassic carbonate aquifer, which represents an important geothermal reservoir in South German Molasse Basin (SGMB), is crucial for improved and sustainable groundwater resource management. Water chemical data environmental isotope analyses ?D, ?18O 87Sr/86Sr were obtained from 24 wells coupled with a few noble gases (3He/4He, 40Ar/36Ar) gas infiltration temperatures. Hierarchical cluster analysis revealed three major water types allowed hydrochemical zoning SGMB, while exploratory factor identified processes affecting composition thermal water. 1 2 are Na-[Ca]-HCO3-Cl type, lowly mineralised have been recharged under meteoric cold climate conditions. Both show signatures, stable isotopes values calculated apparent mean residence times, suggest minor water-rock interaction within hydraulically active flow system Northeastern Southeastern Central Basin. This most likely subglacially south SGMB close proximity to Bavarian Alps delineated northwards direction. Highly type 3 (Na-Cl-HCO3 Na-Cl) occurs Eastern In contrast 2, this shows substantial terrestrial sediments increasing 40Ar/36Ar ratios, may also imply hydraulic exchange fossil formation waters overlying Tertiary sediments.