Recrystallization-induced oxygen isotope changes in inclusion-hosted water of speleothems - Paleoclimatological implications

Demény, A [Demény, Attila (Geokémia), author] Institute for Geological and Geochemical Research (MTA CSFK); Czuppon, G [Czuppon, György (Kőzettan-geokémia), author] Institute for Geological and Geochemical Research (MTA CSFK); Kern, Z [Kern, Zoltán (Geokémia), author] Lendület 2ka Paleoklíma Kutatócsoport (MTA CSFK / FGI); Leél-Ossy, S [Leél-Őssy, Szabolcs (Barlangtan, által...), author] ELTETTKFFI FTK Department of Physical and Appli... (ELTE / ELU FoS); Németh, A [Németh, Alexandra (paleoklimatológia), author] Institute for Geological and Geochemical Research (MTA CSFK); Szabó, M [Szabó, Máté Zoltán (gyógyszervegyészm...), author] Institute for Geological and Geochemical Research (MTA CSFK); Tóth, M [Tóth, Mária (Archeometria, XRD...), author]; Wu, C-C; Shen, C-C; Molnár, M [Molnár, Mihály (Interdiszciplináris), author] Institute for Nuclear Research; Németh, T [Németh, Tibor (Agyagásványtan), author] Institute for Geological and Geochemical Research (MTA CSFK); Németh, P [Németh, Péter (Kristálykémia, Na...), author] Plasmachemistry (MTA TTK / AKI); Óvári, M [Óvári, Mihály (Környezetkémia és...), author] Laboratory of Environmental Chemistry and Bioan... (ELTE / ELU FoS / IC)

English Scientific Article (Journal Article)
Published: QUATERNARY INTERNATIONAL 1040-6182 415 pp. 25-32 2016
  • SJR Scopus - Earth-Surface Processes: Q1
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    The issue of diagenetic alteration of carbonate deposits in caves (speleothems) has gained increasing importance in recent years, as this process has serious consequences for speleothem-based paleoclimate studies. In this study stable hydrogen and oxygen isotope data of water trapped in fluid inclusions were collected for recently forming stalagmites and flowstones in order to determine how dripwater compositions are reflected and preserved in the inclusion water compositions. Hydrogen isotope compositions were found to reflect dripwater values, whereas the oxygen isotope data were increasingly shifted from the local dripwater compositions with the time elapsed after deposition. The δ18O data are correlated with X-Ray diffraction full width at half maximum values (related to crystal domain size and lattice strain), suggesting that the oxygen isotope shift is related to recrystallization of calcite. Transmission electron microscope analyses detected the presence of nanocrystalline (<50 nm) calcite, whose crystallization to coarser-grained calcite crystals (>200 nm) may have induced re-equilibration between the carbonate and the trapped inclusion water. The Ostwald ripening process provides an explanation for unexpectedly low oxygen isotope compositions in the inclusion water. The detected diagenetic alteration and its isotopic effects should be taken into consideration during sampling strategies and data evaluation as speleothems containing nanocrystalline calcite during their deposition are prone to late-stage oxygen isotope water-carbonate re-equilibration, which may shift the oxygen isotope composition of the inclusion water to more depleted values while the hydrogen isotope composition remains intact. © 2016.
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    2020-09-30 21:11