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| Titel |
First results on stable isotopes in fluid inclusions in cryogenic carbonates from Ural Mountains (Russia) |
| VerfasserIn |
Yuri Dublyansky, Mark Luetscher, Christoph Spötl, Paul Töchterle, Olga Kadebskaya |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250104631
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| Publikation (Nr.) |
 EGU/EGU2015-4061.pdf |
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| Zusammenfassung |
| Cryogenic cave carbonates (CCC) were found in a number of caves in the Ural. In
contrast to the CCC previously reported from Central Europe, the Uralian CCC
have larger sizes (up to 4-5 cm), which allows for more detailed petrographic and
geochemical studies. CCCs from Uralian caves commonly show spherulitic shapes due to
crystal splitting, supporting the model of calcite precipitating in a freezing water
pond.
δ18O values of studied CCCs are lower by 1 to 14 ‰ compared to noncryogenic
speleothems of Pleistocene and Holocene age from the same caves. δ18O and δ13C values are
inversely correlated and typically show a fractionation between the core and the rim of
individual samples. These trends are similar to those reported for CCCs from European caves
(Žák et al., 2004).
Petrographic observations performed on doubly polished, 100-150 micron-thick sections
revealed abundant fluid inclusions, trapped between fibres of the spherulites. Petrographic
relationships suggest that these inclusions are primary.
The isotopic composition of water trapped in fluid inclusions in CCCs from two caves
was analyzed following mechanical crushing at 120 ºC, cryo-trapping of released water,
pyrolysis on glassy carbon at 1400 ºC (TC/EA device; Thermo), and analysis of the evolved
gases on an isotope ratio mass spectrometer (Delta V Advantage; Thermo Fisher). The lack of
peaks on the m/z 2 trace during the heating of the loaded crushing cell attests for a good
sealing of the fluid inclusions.
The measured δD values range between -136 ‰ and -145 ‰ VSMOW. The values
measured in CCCs are more negative than the typical values of fluid inclusion water
measured in the Holocene stalagmites from central Ural (-99 to -108 ). This shift toward
more negative values is attributed to the isotopic fractionation between ice and water during
the freezing.
Reference: Žák et al., 2004, Chemical Geology, 2006, 119-136. |
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