Abstract
Abstract. Weichselian cryogenic calcites collected in what is referred to as the Rätselhalle of the Herbstlabyrinth-Advent Cave system are structurally classified as rhombohedral crystals and spherulitic aggregates. The carbon and oxygen isotopic composition of these precipitates (δ13C = +0.6 to −7.3‰ δ18O = −6.9 to −18.0‰) corresponds to those of known slowly precipitated cryogenic cave calcites under conditions of isotopic equilibrium between water and ice of Central European caves. The carbon and oxygen isotopic composition varies between different caves which is attributed to the effects of cave air ventilation before the freezing started. By petrographic and geochemical comparisons of Weichselian cryogenic calcite with recent to sub-recent precipitates as well as Weichselian non-cryogenic calcites of the same locality, a model for the precipitation of these calcites is proposed. While the recent and sub-recent pool-calcites isotopically match the composition of interglacial speleothems (stalagmites, etc.), isotope ratios of Weichselian non-cryogenic pool-calcites reflect cooler conditions. Weichselian cryogenic calcites show a trend towards low δ18O values with higher carbon isotope ratios reflecting slow freezing of the precipitating solution. In essence, the isotope geochemistry of the Weichselian calcites reflects the climate history changing from overall initial permafrost conditions to permafrost-free and subsequently to renewed permafrost conditions. Judging from the data compiled here, the last permafrost stage in the Rätselhalle is followed by a warm period (interstadial and/or Holocene). During this warmer period, the cave ice melted and cryogenic and non-cryogenic Weichselian calcite precipitates were deposited on the cave ground or on fallen blocks, respectively.
Highlights
In contrast to most carbonate speleothems which precipitate from supersaturated waters above 0 ◦C (e.g. Hill and Forti 1997) cryogenic cave calcites (CCC sensu Za ́k et al, 2004) form during freezing of cave waters
Weichselian cryogenic calcites collected in what is referred to as the Ratselhalle of the HerbstlabyrinthAdvent Cave system are structurally classified as rhombohedral crystals and spherulitic aggregates
The carbon and oxygen isotopic composition varies between different caves which is attributed to the effects of cave air ventilation before the freezing started
Summary
In contrast to most carbonate speleothems (e.g. stalagmites) which precipitate from supersaturated waters above 0 ◦C (e.g. Hill and Forti 1997) cryogenic cave calcites (CCC sensu Za ́k et al, 2004) form during freezing of cave waters. Quaternary cryogenic cave calcites formed by slow growth conditions from Central European caves have been described in a series of publications (locations between Scandinavian and Alpine ice sheets; Za ́k et al, 2004, 2008, 2009; Richter and Niggemann, 2005; Richter and Riechelmann, 2008; Richter et al, 2008, 2009, 2010). The genesis of these calcite particles is essentially bound to water pools on top of ice bodies in caves during the transition periods between glacial/stadial to interglacial/interstadial.
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