230Th ∕ U isochron dating of cryogenic cave carbonates
-
Published:2022-09-15
Issue:2
Volume:4
Page:617-627
-
ISSN:2628-3719
-
Container-title:Geochronology
-
language:en
-
Short-container-title:Geochronology
Author:
Töchterle PaulORCID, Steidle Simon D.ORCID, Edwards R. Lawrence, Dublyansky YuriORCID, Spötl ChristophORCID, Li XiangleiORCID, Gunn John, Moseley Gina E.ORCID
Abstract
Abstract. Cryogenic cave carbonates (CCCs) are a type of
speleothem, typically dated with 230Th/U disequilibrium methods, that provide evidence of palaeo-permafrost conditions. In the field, CCCs occur as distinct patches of millimetre- to centimetre-sized loose crystals and crystal aggregates on the floors of cave chambers, so they lack a framework that would allow ages to be validated by stratigraphic order. Correction factors for the initial
230Th (230Th0) are often based on the bulk-earth-derived
initial 230Th/232Th activity ratio ((230Th/232Th)0), which is a well-established approach when
230Th0 is moderately low. For samples with elevated levels of
230Th0, however, accuracy can be improved by constraining
(230Th/232Th)0 independently. Here, we combine detailed
morphological observations from three CCC patches found in Water Icicle
Close Cavern in the Peak District (UK) with 230Th/U analyses. We find that individual CCC crystals show a range of morphologies that arise from non-crystallographic branching in response to the chemical evolution of the freezing solution. Results of 230Th/U dating indicate that samples with a large surface area relative to the sample volume are systematically more affected by contamination with 230Th0. By fitting isochrons to these results, we test whether the CCCs in a patch formed during the same freezing event, and demonstrate that (230Th/232Th)0 can deviate substantially from the bulk-earth-derived value and can also vary between the different CCC patches. Where CCCs display elevated 230Th0, isochrons are a useful tool to constrain
(230Th/232Th)0 and obtain ages with improved accuracy. Detritus absorbed to the crystal surface is shown to be the most likely
source of 230Th0. Our results suggest that some previously published CCC ages may merit re-assessment, and we provide suggestions on how to approach future dating efforts.
Publisher
Copernicus GmbH
Reference73 articles.
1. Arienzo, M. M., Swart, P. K., Pourmand, A., Broad, K., Clement, A. C.,
Murphy, L. N., Vonhof, H. B., and Kakuk, B.: Bahamian speleothem reveals
temperature decrease associated with Heinrich stadials, Earth Planet. Sc.
Lett., 430, 377–386, https://doi.org/10.1016/j.epsl.2015.08.035, 2015. 2. Beck, J. W., Richards, D. A., Lawrence, R., Edwards, R. L., Silverman, B.
W., Smart, P. L., Donahue, D. J., Hererra-Osterheld, S., Burr, G. S.,
Calsoyas, L., Timothy, A. J., Jull, and Biddulph, D.: Extremely Large
Variations of Atmospheric 14C Concentration During the Last Glacial
Period, Science, 292, 2453–2458, https://doi.org/10.1126/science.1056649, 2001. 3. Carolin, S. A., Cobb, K. M., Adkins, J. F., Clark, B., Conroy, J. L., Lejau,
S., Malang, J., and Tuen, A. A.: Varied Response of Western Pacific
Hydrology to Climate Forcings over the Last Glacial Period, Science, 340,
1564–1566, https://doi.org/10.1126/science.1233797, 2013. 4. Carolin, S. A., Cobb, K. M., Lynch-Stieglitz, J., Moerman, J. W., Partin, J.
W., Lejau, S., Malang, J., Clark, B., Tuen, A. A., and Adkins, J. F.:
Northern Borneo stalagmite records reveal West Pacific hydroclimate across
MIS 5 and 6, Earth Planet. Sc. Lett., 439, 182–193,
https://doi.org/10.1016/j.epsl.2016.01.028, 2016. 5. Chaykovskiy, I. I. and Kadebskaya, O.: Morphology of cryogenic calcite from
Rossiyskaya cave (Central Ural): Problems of mineralogy, petrography and
metallogeny, Scientific readings in memory of P.N. Chirvinsky, 18, 102–112, 2015 (in Russian).
Cited by
6 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
|
|