Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 489, Issue -, Pages 1-7Publisher
ELSEVIER
DOI: 10.1016/j.epsl.2018.02.022
Keywords
banded iron formation; multiple sulfur isotopes; Neoarchean; hydrothermal; sulfur disproportionation; marine paleoenvironment
Categories
Funding
- Natural Sciences and Engineering Research Council of Canada Discovery grant
- GEOMAR - Helmholtz Centre for Ocean Research Kiel
- Society of Economic Geologists
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Neoarchean Algoma-type banded iron formations (BIFs) are widely viewed as direct chemical precipitates from proximal volcanic-hydrothermal vents. However, a systematic multiple sulfur isotope study of oxide fades BIF from a type locality in the ca. 2.74 Ga Temagami greenstone belt reveals mainly bacterial turnover of atmospheric elemental sulfur in the host basin rather than deposition of hydrothermally cycled seawater sulfate or sulfur from direct volcanic input. Trace amounts of chromium reducible sulfur that were extracted for quadruple sulfur isotope (S-32-S-33-S-34-S-36) analysis record the previously known mass-independent fractionation of volcanic SO2 in the Archean atmosphere (S-MIF) and biological sulfur cycling but only minor contributions from juvenile sulfur, despite the proximity of volcanic sources. We show that the dominant bacterial metabolisms were iron reduction and sulfur disproportionation, and not sulfate reduction, consistent with limited availability of organic matter and the abundant ferric iron deposited as Fe(OH)(3). That sulfur contained in the BIF was not a direct volcanic-hydrothermal input, as expected, changes the view of an important archive of the Neoarchean sulfur cycle in which the available sulfur pools were strongly decoupled and only species produced photochemically under anoxic atmospheric conditions were deposited in the BIF-forming environment. (C) 2018 Elsevier B.V. All rights reserved.
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