Cryogenic ridges: a new speleothem type

Cryogenic cave carbonates have been described from several formerly or presently glaciated karst caves. In most of these occurrences, they precipitated as loose grains or aggregates with various morphologies and sizes. Here, we report on a new speleothem type (cryogenic ridges) identified in Sohodoalele Mici Cave (SW Romania) within a large chamber near the entrance shaft. This study was motivated by the presence of a network of calcite ridges over the stalactites' surface and by the observation that during winter, these speleothems are covered by a thin ice layer. The higher delta 18O (-3.5 to -1%0) and delta 13C (0 to 7%0) values found in the calcite ridges relative to delta 18O (-7.5 to -4%0) and delta 13C (-9 to -2%0) values of calcite from the inner stalactite indicate that the ridges are of cryogenic origin and formed during relatively rapid carbonate precipitation associated with evaporative cooling and freezing of the water. Four U-series ages suggest that the stalactites with ridges formed during cold winters of the Holocene, when cave air temperatures dropped below freezing.