Diverse microstructures from Archaean chert from the Mount Goldsworthy-Mount Grant area, Pilbara Craton, Western Australia: Microfossils, dubiofossils, or pseudofossils?

Kenichiro Sugitani*, Kathleen Grey, Abigail Allwood, Tsutomu Nagaoka, Koichi Mimura, Masayo Minami, Craig P. Marshall, Martin J. Van Kranendonk, Malcolm R. Walter

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    101 Citations (Scopus)

    Abstract

    A diverse assemblage of indigenous carbonaceous microstructures, classified here as highly probable microfossils to pseudomicrofossils, is present in the >ca. 2.97 Ga Farrel Quartzite (Gorge Creek Group) at Mount Grant and Mount Goldsworthy, Pilbara Craton, Western Australia. The microstructures are an integral part of the primary sedimentary fabrics preserved in black chert beds. The interbedding of chert with layers of large silicified crystal pseudomorphs and fine to coarse grained volcaniclastic/clastic beds indicate deposition in a partially evaporitic basin with terrigenous clastic and volcaniclastic input. Similar associations of microstructures are present at the same stratigraphic level in outcrops more than 2 km apart. Four major microstructural types are present: thread-like, film-like, spheroidal and lenticular to spindle-like, each of which can be further subdivided into several sub-types. Most of the microstructures were deposited as part of an assemblage of chemical and clastic sediments, although there are some thread-like microstructures present for which a synsedimentary origin cannot be confirmed. Many specimens appear to have originally had flexible but breakable walls and some occur in colony-like aggregations. Size distributions for the four major types are generally narrow, a feature typical of biogenic structures. The microstructures are composed of disordered carbon (as revealed by Raman spectroscopy) and the bulk isotopic composition of the carbon is δ13C < -30 per mil, which is consistent with biological processing. The combined morphological and geological evidence suggests that the film-like structures, small spheres associated with films, large spheroids and spindle-like structures are probable to highly probable fossil remains of microorganisms. The morphological variety among the microstructures suggests that a diverse microbial ecosystem flourished in the Pilbara region during the Archaean.

    Original languageEnglish
    Pages (from-to)228-262
    Number of pages35
    JournalPrecambrian Research
    Volume158
    Issue number3-4
    DOIs
    Publication statusPublished - 5 Oct 2007

    Keywords

    • Archaean
    • Chert
    • Evaporite
    • Farrel Quartzite
    • Microfossil
    • Pilbara

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