C-14 AND U-SERIES DATING OF SPELEOTHEMS IN THE BOHEMIAN PARADISE (CZECH REPUBLIC): RETREAT RATES OF SANDSTONE CAVE WALLS AND IMPLICATIONS FOR CAVE ORIGIN
Abstrakt
Speleothems in 6 sandstone caves in the Bohemian Paradise (Cesky raj) were dated by means of C-14 and U-series methods. Stable isotopes of C and O, FAAS, IR, XRD, XRF and SEM were used to characterize the carbonate material and its source.
Stable isotopes (C and O) composition of speleothems in two caves corresponds to values characteristic for cave speleothems in Central Europe. In other caves they indicate evaporation and fast carbon dioxide escape during carbonate precipitation.
The speleothems from the Krtola Cave were deposited between 8 and 13 kyr BP. Speleothems were deposited 5-8 kyr BP in the Sintrova, Mrtve Udoli and U Studanky caves.
Calcite coatings on smooth sandstone surfaces in studied caves demonstrate that cave walls did not retreat even a few mm in the last 5-8 kyr since speleothem deposition and are thus not evolving under recent climatic conditions. Most of the cave ceilings and walls are at present time indurated by hardened surfaces, which protect the sandstone from erosion.
Sandstone caves probably intensively evolved either during or at the end of the Last Glacial period. There are two different erosion mechanisms which might have formed/reshaped the caves at that time: A) In the case of permafrost conditions: Repeated freeze/melt cycles affecting sandstone pore space followed by the transport of fallen sand grains by minor temporary trickles.
We expect that heat was transmitted by air circulating between the cave and the surface; B) Seepage erosion of sandstone during the melting of permafrost, prior forming of case hardening.