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Published November 7, 2014 | Supplemental Material
Journal Article Open

Neoarchean carbonate-associated sulfate records positive Δ³³S anomalies

Abstract

Mass-independent fractionation of sulfur isotopes (reported as Δ³³S) recorded in Archean sedimentary rocks helps to constrain the composition of Earth's early atmosphere and the timing of the rise of oxygen ~2.4 billion years ago. Although current hypotheses predict uniformly negative Δ³³S for Archean seawater sulfate, this remains untested through the vast majority of Archean time. We applied x-ray absorption spectroscopy to investigate the low sulfate content of particularly well-preserved Neoarchean carbonates and mass spectrometry to measure their Δ³³S signatures. We report unexpected, large, widespread positive Δ³³S values from stratigraphic sections capturing over 70 million years and diverse depositional environments. Combined with the pyrite record, these results show that sulfate does not carry the expected negative Δ³³S from sulfur mass-independent fractionation in the Neoarchean atmosphere.

Additional Information

© 2014 American Association for the Advancement of Science. Received for publication 2 July 2014. Accepted for publication 22 September 2014. We thank J. Johnson for help with stratigraphic sample collection and fruitful comments; N. Beukes and I. Halevy for helpful discussions; K. Bergmann for assistance with C and O analyses; and C. Ma, T. Present, and J. Johnson for assistance with scanning electron microscopy. We acknowledge support from NSF Division of Earth Sciences award no. EAR-1349858. Assistance from N. Dalleska and use of IC instrumentation in the Environmental Analysis Center at the California Institute of Technology is gratefully acknowledged. G.P. was funded by the Henry and Camille Dreyfus Postdoctoral Program in Environmental Chemistry. W.W.F. acknowledges support from the David and Lucile Packard Foundation. Drill core GKP01 was sampled with support from the Agouron Institute. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The SSRL Structural Molecular Biology Program is supported by the DOE Office of Biological and Environmental Research and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393).

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Supplemental Material - Revision1_1258211AdditionalDatatableS1.csv

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