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| Titel |
Cryogenic and non-cryogenic pool calcites indicating permafrost and non-permafrost periods: a case study from the Herbstlabyrinth-Advent Cave system (Germany) |
| VerfasserIn |
D. K. Richter, P. Meissner, A. Immenhauser, U. Schulte, I. Dorsten |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 4, no. 4 ; Nr. 4, no. 4 (2010-11-30), S.501-509 |
| Datensatznummer |
250001900
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| Publikation (Nr.) |
 copernicus.org/tc-4-501-2010.pdf |
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| Zusammenfassung |
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. |
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