Constraining the rise of oxygen with oxygen isotopes.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 31664027.
- Also identified by DOI 10.1038/s41467-019-12883-2 and PMC identifier 6820740.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
After permanent atmospheric oxygenation, anomalous sulfur isotope compositions were lost from sedimentary rocks, demonstrating that atmospheric chemistry ceded its control of Earth's surficial sulfur cycle to weathering. However, mixed signals of anoxia and oxygenation in the sulfur isotope record between 2.5 to 2.3 billion years (Ga) ago require independent clarification, for example via oxygen isotopes in sulfate. Here we show <2.31 Ga sedimentary barium sulfates (barites) from the Turee Creek Basin, W. Australia with positive sulfur isotope anomalies of ∆<sup>33</sup>S up to + 1.55‰ and low δ<sup>18</sup>O down to -19.5‰. The unequivocal origin of this combination of signals is sulfide oxidation in meteoric water. Geochemical and sedimentary evidence suggests that these S-isotope anomalies were transferred from the paleo-continent under an oxygenated atmosphere. Our findings indicate that incipient oxidative continental weathering, ca. 2.8-2.5 Ga or earlier, may be diagnosed with such a combination of low δ<sup>18</sup>O and high ∆<sup>33</sup>S in sulfates.