Iron isotopes and the redox evolution of Ediacaran sediments

Frederic Moynier, David A. Fike, Gabrielle Menard, Woodward W. Fischer, John P. Grotzinger, Arnaud Agranier

Research output: Contribution to journalArticlepeer-review


The Ediacaran age (ca. 570 Ma) Shuram excursion, a ca. 12h depletion in δ13Ccarb, may record a dramatic oxidation of marine sediments associated with a reorganization of Earth's carbon cycle closely preceding the rise of large metazoans. However, several geochemical indicators suggest it may instead record secondary processes affecting the sediments such as post-depositional alteration. The stable isotopic composition of iron incorporated within carbonates (δ56Fecarb) reveals an anomalous 56Fe-depletion (down to -1.05h) in strata containing the Shuram excursion, while the underlying and overlying strata have crustal δ56Fecarbvalues. These depleted δ56Fecarbdata during the Shuram excursion reflect incomplete reduction of iron oxides, limited by lowambient organic carbon contents. This elevated pulse of sedimentary iron oxides would consume the majority of the limited pool of organic carbon and therefore would give rise to very low net organic carbon burial during a time of enhanced detrital delivery of oxidized iron to the sediments. These results imply a syndepositional origin for the Shuram excursion, which represents a shift in the redox composition of Earth's sedimentary shell toward more oxidizing conditions, perhaps removing a long-lived buffer on atmospheric oxygen.

Original languageEnglish
Pages (from-to)579-588
Number of pages10
JournalComptes Rendus - Geoscience
Issue number8
StatePublished - 2020


  • Ediacara
  • Fe isotopes
  • Geochemistry
  • Ocean
  • Oxygenation
  • Redox change
  • Shuram excursion


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