Search

This case study from the renowned Demänová Cave System in the Carpathians of Slovakia demonstrates that the conventional methods of fluvial sedimentology, combined with an allostratigraphic mapping and speleothem U‐series isotopic dating, can give unprecedented insights into the hydrological history of underground karst conduit. The deposits studied are a relic compound sidebar ranging from gravel to mud and encapsulating the conduit's hydrological history from the middle Pleistocene to the present time. A succession of 10 allostratigraphic units, time‐constrained by speleothems, are recognized in the sidebar deposits, and the corresponding morphodynamics of an evolving cave‐floor sedimentation are reconstructed in considerable detail. The subterranean river water stages recognized from the deposits, time‐constrained by flowstone layers and stalagmites, correlate with and add to the regional record of climate changes. Two distinct episodes of flow ponding (high‐stage slackwater conditions) are recognized and attributed to the independently documented downstream cave‐roof collapses, probably triggered by the Carpathian post‐orogenic earthquakes. This multidisciplinary study may serve as a useful methodological guide for the analysis of fluviokarstic deposits in speleological research and reconstruction of their hosting cave hydrological history. [ABSTRACT FROM AUTHOR]

Detailed analyses of speleothems collected in caves of the Demänová Valley, Nízke Tatry, Slovakia, have found significant variability in uranium concentrations and initial 234U/238U activity ratios, plus correlation between these variables. They are related to the ages of samples and their differing locations in the caves. Strong variability of initial 234U/238U activity ratios is the reason for serious limitations in applying the 234U/238U Regional Uranium Best Estimate method as an age estimator for speleothems older than the range of the 230Th/234U method (500 ka). The strong variability of uranium contents in speleothems, rocks and waters and their isotopic compositions allowed us to distinguish distinct periods with changes in water circulation paths or distribution/weathering degrees of deposits in surface alimentation areas or in the epikarst zone, that result from the more ready leaching of the 234U isotope from sediments. Periods characterised with higher initial 234U/238U activity ratios are most likely associated with the deposition of "fresh" colluvial deposits and/or soil development (potential uranium source) in the alimentation area. Gradual decrease of initial 234U/238U activity values indicate prolonged stable weathering and uranium leaching conditions. The Demänová results indicate periods of intensive erosion and "fresh" sediment deposition in the alimentation areas at ~120 ka, ~80-70 ka, and during the Holocene. [ABSTRACT FROM AUTHOR]