Iron-oxidizing microbial ecosystems thrived in late Paleoproterozoic redox-stratified oceans

Noah Planavsky, Olivier Rouxel, Andrey Bekker, Russell Shapiro, Phil Fralick, Andrew Knudsen

Research output: Contribution to journalArticlepeer-review

166 Citations (Scopus)

Abstract

We conducted a geochemical and petrographic study of the 1.89 billion year old Gunflint and Biwabik iron formations, with the goal of determining the importance of microbial iron-oxidation in the formation of iron- and microfossil-rich stromatolites. We used redox-sensitive tracers, such as iron isotopes and rare earth elements, to decipher whether these ancient microbial ecosystems harbored cyanobacteria or Fe-oxidizing bacteria as primary producers. Iron-rich stromatolites contain non-significant or positive Ce anomalies, which contrast with shallow water deposits having negative Ce anomalies. This trend in Ce anomalies indicates that the stromatolites formed in low oxygen conditions, which is the ideal setting for the proliferation of Fe-oxidizing bacterial ecosystems. The stromatolites yield a large range of δ56Fe values, from -0.66 to +0.82‰, but contain predominantly positive values indicating the prevalence of partial Fe-oxidation. Based on modern analogues, Fe-oxides precipitated in cyanobacterial mats are expected to record an isotopic signature of quantitative oxidation, which in marine settings will yield negative δ56Fe values. The stromatolite iron isotope data, therefore, provide evidence for the presence of Fe-oxidizing bacteria. The stromatolites can be traced for a distance of over 100 km in these iron formations, indicating that they record a pervasive rather than localized ecosystem. Their preservation in late Paleoproterozoic successions deposited along the margins of the Superior craton suggests that there was a global expansion of iron-oxidizing bacterial communities at shallow-water redox boundaries in late Paleoproterozoic oceans.

Original languageEnglish
Pages (from-to)230-242
Number of pages13
JournalEarth and Planetary Science Letters
Volume286
Issue number1-2
DOIs
Publication statusPublished - 30 Aug 2009
Externally publishedYes

Keywords

  • Fe-isotopes
  • iron-bacteria
  • iron-formations
  • Paleoproterozoic
  • rare earth elements
  • stromatolites

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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