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SQUID-SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle

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Date
15/04/2014
Author
Fischer, Woodward W
Fike, David A
Johnson, Jena E
Raub, Timothy D
Guan, Yunbin
Kirschvink, Joseph L
Eiler, John M
Keywords
Mass independent fractionation
MIF
Metamorphism
Metasomatism
GE Environmental Sciences
BDC
R2C
SDG 14 - Life Below Water
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Abstract
Many aspects of Earth's early sulfur cycle, from the origin of mass-anomalous fractionations to the degree of biological participation, remain poorly understood-in part due to complications from postdepositional diagenetic and metamorphic processes. Using a combination of scanning high-resolution magnetic superconducting quantum interference device (SQUID) microscopy and secondary ion mass spectrometry (SIMS) of sulfur isotopes ((32)S, (33)S, and (34)S), we examined drill core samples from slope and basinal environments adjacent to a major Late Archean (∼2.6-2.5 Ga) marine carbonate platform from South Africa. Coupled with petrography, these techniques can untangle the complex history of mineralization in samples containing diverse sulfur-bearing phases. We focused on pyrite nodules, precipitated in shallow sediments. These textures record systematic spatial differences in both mass-dependent and mass-anomalous sulfur-isotopic composition over length scales of even a few hundred microns. Petrography and magnetic imaging demonstrate that mass-anomalous fractionations were acquired before burial and compaction, but also show evidence of postdepositional alteration 500 million y after deposition. Using magnetic imaging to screen for primary phases, we observed large spatial gradients in Δ(33)S (>4‰) in nodules, pointing to substantial environmental heterogeneity and dynamic mixing of sulfur pools on geologically rapid timescales. In other nodules, large systematic radial δ(34)S gradients (>20‰) were observed, from low values near their centers increasing to high values near their rims. These fractionations support hypotheses that microbial sulfate reduction was an important metabolism in organic-rich Archean environments-even in an Archean ocean basin dominated by iron chemistry.
Citation
Fischer , W W , Fike , D A , Johnson , J E , Raub , T D , Guan , Y , Kirschvink , J L & Eiler , J M 2014 , ' SQUID-SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle ' , Proceedings of the National Academy of Sciences of the United States of America , vol. 111 , no. 15 , pp. 5468-5473 . https://doi.org/10.1073/pnas.1322577111
Publication
Proceedings of the National Academy of Sciences of the United States of America
Status
Peer reviewed
DOI
https://doi.org/10.1073/pnas.1322577111
ISSN
0027-8424
Type
Journal article
Rights
© 2014. The Authors. Freely available online through the PNAS open access option.
Description
The Agouron Institute and National Aeronautic and Space Administration Exobiology Award NNX09AM91G supported this work.
Collections
  • University of St Andrews Research
URL
http://europepmc.org/articles/PMC3992679
URI
http://hdl.handle.net/10023/5039

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