Concurrent tectonism and aquifer evolution >100,000 years recorded in cave sediments, Dinaric Karst, Slovenia

A natural conduit that had formed along a fault was exposed in Upper Cretaceous limestones during construction of a tunnel near Postojna, Slovenia. The conduit is filled with poorly indurated clastic sediments. Slickensides found on the margin of the sediment deposit show sinistral fault motion that is consistent with regional tectonism. Analysis of the sediments revealed reversed magnetic polarity. The minimum age for latest movement on the fault, origin of the cave, and deposition of these sediments is 780 ka. Present-day tectonic stresses are concordant with the fault movement, and it is likely that the fault has been continuously active throughout growth, infilling, and hydrologic abandonment of the conduit. Based upon known and modeled growth rates for conduits, this system is recording a period of growth and abandonment that exceeds 100,000 years. The role that rock discontinuities play in groundwater flow may vary over these timescales, and it may be important to account for tectonism when evaluating the long-term evolution of aquifers

The Mineral Assemblage of Caves Within Şălitrari Mountain (Cerna Valley, SW Romania): Depositional Environment and Speleogenetic Implications

Eighteen minerals belonging to eight chemical groups were identified from three caves within Şălitrari Mountain, in the upper Cerna River basin (Romania) by means of scanning electron microscopy, electron microprobe analysis, and X-ray powder diffraction. One passage in the Great Cave from Şălitrari Mountain, the largest cave investigated, exhibits abnormal relative humidity and temperature ranges, allowing for a particular depositional environment. The cave floor is covered by alluvial sediments (ranging from cobble, sand, and clay to silt-sized material), bear bones, bat guano, and rubble. These materials reacted with percolating meteoric water and hydrogen sulfide-rich hypogene hot solutions, precipitating a variety of secondary minerals. Most of these minerals are common in caves (e.g. calcite, gypsum, brushite), however, some of them (alunite, aluminite, and darapskite) require very particular environments in order to form and persist. Cave passage morphologies suggest a complex speleogenetic history that includes changes from phreatic to vadose conditions. The latter was punctuated by a sulfuric acid dissolution/precipitation phase, partly overprinted by present-day vadose processes. The cave morphology and the secondary minerals associated with the alluvial sediments in these caves are used to unravel the region’s speleogenetic history

Guano-Derived δ\u3csup\u3e13\u3c/sup\u3eC-Based Paleo-Hydroclimate Record from Gaura cu Musca Cave, SW Romania

The δ13C values of 23 unevenly spaced guano samples from a 17-cm long clay sediment profile in Gaura cu Muscă Cave (GM), in SW Romania, made it possible to preliminarily characterize the Medieval Warm Period summer hydroclimate regime. The beginning of the sequence (AD 990) was rather wet for more than a century, before becoming progressively drier. After a brief, yet distinct wet period around AD 1170, drier conditions, with a possible shift from C3 to a mixed C3-dominated/C4 type vegetation (2 ‰ lower δ13C values), prevailed for almost half a century before the climate became colder and wetter at the onset of the Little Ice Age, when bats left the cave. The guano-inferred wet and dry intervals from the GM Cave are mirrored by changes in the color and amount of clay accumulated in the cave. They also agree well with reconstructions based on pollen and charcoal from peat bogs and δ13C and δ18O on speleothems from other Romanian sites. Overall, these results indicate that the δ13C of bat guano can provide a sensitive record of the short-term coupling between local/regional climate and the plant–insect–bat–guano system