Nanoscale analysis of pyritized microfossils reveals differential heterotrophic consumption in the ̃1.9-Ga Gunflint chert

David Wacey*, Nicola McLoughlin, Matt R. Kilburn, Martin Saunders, John B. Cliff, Charlie Kong, Mark E. Barley, Martin D. Brasier

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

43 Citations (Scopus)

Abstract

The 1.88-Ga Gunflint biota is one of the most famous Precambrian microfossil lagerstätten and provides a key record of the biosphere at a time of changing oceanic redox structure and chemistry. Here, we report on pyritized replicas of the iconic autotrophic Gunflintia- Huroniospora microfossil assemblage from the Schreiber Locality, Canada, that help capture a view through multiple trophic levels in a Paleoproterozoic ecosystem. Nanoscale analysis of pyritic Gunflintia (sheaths) and Huroniospora (cysts) reveals differing relic carbon and nitrogen distributions caused by contrasting spectra of decay and pyritization between taxa, reflecting in part their primary organic compositions. In situ sulfur isotope measurements from individual microfossils (δ34SV-CDT +6.7% to +21.5%) show that pyritization was mediated by sulfate-reducing microbes within sediment pore waters whose sulfate ion concentrations rapidly became depleted, owing to occlusion of pore space by coeval silicification. Three-dimensional nanotomography reveals additional pyritized biomaterial, including hollow, cellular epibionts and extracellular polymeric substances, showing a preference for attachment to Gunflintia over Huroniospora and interpreted as components of a saprophytic heterotrophic, decomposing community. This work also extends the record of remarkable biological preservation in pyrite back to the Paleoproterozoic and provides criteria to assess the authenticity of even older pyritized microstructures that may represent some of the earliest evidence for life on our planet.

Original languageEnglish
Pages (from-to)8020-8024
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume110
Issue number20
DOIs
Publication statusPublished - 14 May 2013

Keywords

  • Biogeochemistry
  • Paleontology
  • Taphonomy

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