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Sulfate availability and the geological record of cold-seep deposits

Bristow, Thomas F. and Grotzinger, John P. (2013) Sulfate availability and the geological record of cold-seep deposits. Geology, 41 (7). pp. 811-814. ISSN 0091-7613.

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Cold-seep deposits are the remnants of ancient chemosynthetic ecosystems that derive energy from microbial anaerobic oxidation of methane (AOM) using seawater sulfate. They provide a physical record of a microbial process that plays a critical role in regulating biospheric methane. Although highly ^(13)C-depleted kerogen suggests that AOM dates back 2.7 b.y., puzzlingly, the oldest reported cold seeps only appear at 635 Ma and lack carbon isotopic signals (<–30‰ Peedee belemnite) that are diagnostic of AOM in examples younger than 350 Ma. Using a one-dimensional biogeochemical reaction-transport model, we confirm that these discrepancies are an expected consequence of changes in seawater chemistry. More specifically, sub-millimolar (mM) to millimolar seawater sulfate concentrations ([SO_4^(2–)]SW) and elevated concentrations of dissolved inorganic carbon that characterized seawater through much of the Precambrian limited AOM-driven carbonate supersaturation and 13C depletion, making seep carbonates less likely to form and more challenging to identify. Moderate ^(13)C depletions observed in 420–370-m.y.-old cold-seep carbonates (independently identified by fossil assemblages and contextual and textural observations) indicate [SO_4^(2–)]SW < 5 mM in this interval. This is significant because low [SO_4^(2–)]SW has been linked to widespread ocean anoxia in the early Paleozoic, an environmental condition thought to have influenced the evolution, extinction, and recovery of early animals.

Item Type:Article
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URLURL TypeDescription
Bristow, Thomas F.0000-0001-6725-0555
Grotzinger, John P.0000-0001-9324-1257
Additional Information:© 2013 Geological Society of America. Manuscript received 26 November 2012; Revised manuscript received 28 February 2013; Manuscript accepted 5 March 2013; Published online 24 May 2013 This work was supported by a NASA Postdoctoral Fellowship to Bristow. We thank M. Alperin, K. Soetaert, and F. Meysman for discussions and several anonymous reviewers for their comments.
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NASA Postdoctoral FellowshipUNSPECIFIED
Issue or Number:7
Record Number:CaltechAUTHORS:20130924-154437448
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41516
Deposited By: Tony Diaz
Deposited On:24 Sep 2013 23:37
Last Modified:03 Oct 2019 05:49

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