Pseudofossils in relict methane seep carbonates resemble endemic microbial consortia

Jake V. Bailey, Timothy D. Raub, A. Nele Meckler, Benjamin K. Harrison, Theresa M.D. Raub, Abigail M. Green, Victoria J. Orphan

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

Pleistocene-age methane seep carbonates from the Eel River Basin, California contain aggregate-like structures composed of tightly-packed hollow spheres that morphologically resemble syntrophic archaeal-bacterial consortia known to catalyze the anaerobic oxidation of methane (AOM). Tetragonal microstructures also present in the carbonates resemble seep-endemic Methanosarcinales cell clusters. Despite morphological similarities to the seep-endemic microbes that likely mediated the authigenesis of Eel River Basin carbonates and sulfides, detailed petrographic, SEM, and magnetic microscopic imaging, remanence rock magnetism, laser Raman, and energy dispersive X-ray spectroscopy, suggest that these microstructures are not microfossils, but rather mineral structures that result from the diagenetic alteration of euhedral Fe-sulfide framboids. Electron microscopy shows that during diagenesis, reaction rims composed of Fe oxide form around framboid microcrystalites. Subsequent dissolution of greigite or pyrite crystals leaves behind hollow cell-like casings (external molds) - a transformation that occurs on timescales of ∼100 kyr or less. Despite their superficial resemblance to morphologically-distinctive extant microbes in local sediments, the presence of acellular precursor grains, as well as of partially-altered transitional forms, complicate the interpretation of these and other framboidal microstructures that have been reported from the rock record.

Original languageEnglish (US)
Pages (from-to)131-142
Number of pages12
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume285
Issue number1-2
DOIs
StatePublished - Jan 1 2010

Keywords

  • AOM
  • Archaea
  • Framboids
  • Greigite
  • Pyrite
  • Sulfate-reducing bacteria

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