Hypogene water-rock interaction and speleogenesis

The subject of the proposed research is hypogene karst. Unlike "normal" caves, which are carved by cold precipitation water percolating through soluble rock under the force of gravity, hypogene caves are formed by deep-seated, commonly thermal, mineralized waters ascending from depth. Besides dissolution of caves, such fluids may alter the bedrock or deposit their mineral load into the solutional voids, creating mineral or ore deposits. Although the notion of hypogene karst is not new, the knowledge about the physical and chemical conditions at which it occurs is limited. This is primarily because hypogene karst is a deep-seated process, which cannot, in most cases, be observed directly. The researchers, thus, can study fossil, presently inactive hypogene caves and cave deposits. The objective of this project is to test and develop a set of methods and techniques that allow the identification and quantification of paleowater-rock interaction in the course of hypogene speleogenesis. To this end, previously established techniques will be systematically tested and combined with novel geochemical tools, some of which were recently developed at Innsbruck University. The expected insights may have potential applications in a range of fields, including hydrogeology, paleo- hydrogeology, ore deposits and paleoclimate research.

Unlike "normal" caves, which are carved by cold precipitation water percolating through soluble rock under the force of gravity, hypogene caves are formed by deep-seated, commonly thermal, mineralized waters ascending from depth. Besides dissolution of caves, such fluids may alter the bedrock or deposit their mineral load into the solutional voids, creating mineral or ore deposits. Although the notion of hypogene karst is not new, the knowledge about the physical and chemical conditions at which it occurs is limited. This is primarily because hypogene karst is a deep-seated process, which cannot, in most cases, be observed directly. The researchers, thus, can study fossil, presently inactive hypogene caves and cave deposits.This project tested and developed a set of methods and techniques that allow the identification and to some extent also the quantification of paleo water-rock interaction in the course of hypogene speleogenesis. We studied a series of hypogene caves in Austria, Hungary and Ukraine and took drill cores from the cave wall. Their geochemical and in particular their stable isotopic composition showed different degrees of alteration by the paleofluid. Although a marked depletion in the oxygen isotopic composition of the host rock is a commonly observed feature some hypogene cave wall rocks lack such an effect. This is most likely reflecting the high dissolution rate of these apparently highly aggressive hypogene systems which outpaced the slower alteration process. Mineral deposits precipitated in hypogene caves are key to characterise the paleofluid and we found distinct fluid inclusion types and compositions in these carbonates. Among others, we explored for the first time the gas composition released from these tiny inclusions which may hold high promises for future research. Finally, we also applied laserscanning techniques to survey two hypogene caves at unprecedented detail.