Tracing the transition from hypogene to epigene karstification in the Villány Thermal Karst area, Hungary: Linking submicron-scale cave processes with regional groundwater flow system dynamics

The geological conditions of the Villány Thermal Karst (VTK) area in southwestern Hungary provide an excellent opportunity for hydrogeological research on hypogene cave formation along the boundaries between the unconfined and adjacent confined carbonate regions. The aim of this study was to investigate the hypogene caves of the VTK area from a hydrogeological perspective to identify the effects of waters flowing upward and downward and the related speleothems. Special attention was paid to evaluating the current hydrogeological conditions and their potential for cave formation. Therefore, an in situ experiment was conducted in the largest cave situated at the karst water table. Based on these results, the karst development of the area was reconstructed, integrating the results of the regional groundwater flow system evaluation with the geological evolution history. The results showed that all the caves of the VTK region show the effects of upwelling thermal waters. However, features directly related to the infiltration of precipitation are also abundant. During the in situ experiment, microscale dissolution and significant carbonate precipitation were observed in the cave, primarily near the water table, indicating that active cave formation is not currently occurring. The development of the hypogene caves in the area was initiated by the inversion of the Pannonian Basin, during which compression-driven overpressured fluids could have interacted with the topography-driven flow systems recharged through the exhumed surfaces. However, the topography-driven flow systems have recently overwhelmed the overpressured system, and karst development is now governed by epigene processes.