Characterisation of the regional groundwater flow system in the South German Molasse Basin using apparent groundwater age distributions with 14CDOC and 81Kr

The Upper Jurassic aquifer (UJA) within the South German Molasse Basin (SGMB) is the most important exploration horizon for geothermal energy supply in Bavaria. The UJA shows a heterogeneous geology with karstic features and deep fault-zones. The result is a complex hydrogeology consisting of different groundwater types which differ significantly in their hydrochemical and isotopic composition.

Despite the great interest in the Upper Jurassic aquifer for geothermal energy supply, leading to numerous scientific studies, the exact apparent groundwater age, the infiltration area and the regional flow system remain yet unknown.

In this study we are using a multi parameter approach for the determination of apparent groundwater age distributions with the innovative ¹⁴C_DOC and ⁸¹Kr methods and combine them with hydrochemistry data and stable water isotopes (δ¹⁸O/δ²H).

Our results indicate that the UJA system consists of at least two groundwater components: an up to now unknown young meteoric water component from the Pleistocene/Holocene transition and an older Pleistocene component. The apparent ¹⁴C_DOC ages increase from south to north and show some evidence that the infiltration area of the UJA is located in the southern part of the SGMB and a groundwater flow directed to the north.