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A hydrothermal origin for isotopically anomalous cap dolostone cements from south China

Bristow, Thomas F. and Bonifacie, Magali and Derkowski, Arkadiusz and Eiler, John M. and Grotzinger, John P. (2011) A hydrothermal origin for isotopically anomalous cap dolostone cements from south China. Nature, 474 (7349). pp. 68-71. ISSN 0028-0836.

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The release of methane into the atmosphere through destabilization of clathrates is a positive feedback mechanism capable of amplifying global warming trends that may have operated several times in the geological past. Such methane release is a hypothesized cause or amplifier for one of the most drastic global warming events in Earth history, the end of the Marinoan ‘snowball Earth’ ice age, ~635 Myr ago. A key piece of evidence supporting this hypothesis is the occurrence of exceptionally depleted carbon isotope signatures (δ^(13)C_(PDB) down to −48‰; in post-glacial cap dolostones (that is, dolostone overlying glacial deposits) from south China; these signatures have been interpreted as products of methane oxidation at the time of deposition. Here we show, on the basis of carbonate clumped isotope thermometry, ^(87)Sr/^(86)Sr isotope ratios, trace element content and clay mineral evidence, that carbonates bearing the ^(13)C-depleted signatures crystallized more than 1.6 Myr after deposition of the cap dolostone. Our results indicate that highly ^(13)C-depleted carbonate cements grew from hydrothermal fluids and suggest that their carbon isotope signatures are a consequence of thermogenic methane oxidation at depth. This finding not only negates carbon isotope evidence for methane release during Marinoan deglaciation in south China, but also eliminates the only known occurrence of a Precambrian sedimentary carbonate with highly ^(13)C-depleted signatures related to methane oxidation in a seep environment. We propose that the capacity to form highly ^(13)C-depleted seep carbonates, through biogenic anaeorobic oxidation of methane using sulphate, was limited in the Precambrian period by low sulphate concentrations in sea water. As a consequence, although clathrate destabilization may or may not have had a role in the exit from the ‘snowball’ state, it would not have left extreme carbon isotope signals in cap dolostones.

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Bristow, Thomas F.0000-0001-6725-0555
Grotzinger, John P.0000-0001-9324-1257
Additional Information:© 2011 Macmillan Publishers Limited. Received 24 August 2010. Accepted 25 March 2011. Published online 25 May 2011. We thank G. Jiang for guidance in the field and for providing samples, V. Orphan and W. Fischer for discussion and advice, M. Kennedy for supporting fieldwork and use of analytical equipment, and E. Peterman and K. Morrison for laboratory work. C. Ma and M. Anderson are thanked for analytical assistance and advice. This work was supported by an O.K. Earl Postdoctoral fellowship (to T.F.B.), by the NSF EAR and GEG programmes (to J.M.E.), and by INSU (to M.B.). Part of the work of M.B. is IPGP contribution 3138. Author Contributions: T.F.B. and J.P.G. conceived the study. M.B. carried out clumped and conventional isotope analysis and wrote part of the Supplementary Discussion. J.M.E. provided laboratory facilities for isotope work. A.D. and T.F.B. carried out clay mineral analysis. T.F.B. carried out petrographic work and trace element analysis and wrote the manuscript. All authors discussed results, planned analyses and contributed to the manuscript.
Funding AgencyGrant Number
O. K. Earl Postdoctoral FellowshipUNSPECIFIED
Institut National des Sciences de l'Univers (INSU)UNSPECIFIED
Subject Keywords:Earth science; Geology and geophysics; Climate science
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Other Numbering System NameOther Numbering System ID
IPGP Contribution3138
Issue or Number:7349
Record Number:CaltechAUTHORS:20110621-074254818
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Official Citation:Bristow, T., Bonifacie, M., Derkowski, A. et al. A hydrothermal origin for isotopically anomalous cap dolostone cements from south China. Nature 474, 68–71 (2011).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24142
Deposited By: Ruth Sustaita
Deposited On:21 Jun 2011 16:00
Last Modified:04 May 2020 18:38

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