Three-dimensional morphological and textural complexity of archean putative microfossils from the northeastern pilbara craton

Indications of biogenicity of large (>15μm) spheroidal and spindle-like structures

Kenichiro Sugitani*, Kathleen Grey, Tsutomu Nagaoka, Koichi Mimura

*Corresponding author for this work

    Research output: Contribution to journalArticle

    25 Citations (Scopus)

    Abstract

    We recently reported a diverse assemblage of carbonaceous structures (thread-like, film-like, spheroidal, and spindle-like) from chert in the ca. 3.0 Ga Farrel Quartzite of the Gorge Creek Group in the Pilbara Craton, Western Australia. Results from a rigorous examination of occurrence, composition, morphological complexity, size distributions, and taphonomy provided presumptive evidence for biogenicity. In this study, we present new data of morphological and textural complexity of large (>15μm) spheroidal and spindle-like structures, using an in-focus, 3-D image reconstruction system, which further raises the scale of credibility that these structures are microfossils. While many of the large spheroids are single-walled, and the wall is irregularly folded, a few specimens are partially blistered, double walled, or have a dimpled wall. The wall-surface texture varies from smooth and homogeneous (hyaline) to patchy, granular or reticulate. Such variation is best explained as resulting from taphonomic processes. Additionally, an inner solitary body, present in some large spheroids, is hollow and partially broken, which indicates a primary origin for this substructure. Spindle-like structures have two types of flange-like appendage; one is attached at the equatorial plane of the body, whereas the other appears to be attached peripherally. In both cases, the appendage tends to have a flat geometry, a tapering thickness, and constancy in shape, proportions, and dimensions. Spindle-wall surfaces are variously textured and heterogeneous. These morphological and textural complexities and heterogeneity refute potential abiogenic formation models for these structures, such as crystals coated with organic matter, fenestrae, and the diagenetic redistribution of carbonaceous matter. When coupled with other data from Raman spectroscopy, NanoSIMS analysis, and palynology, the evidence that these large carbonaceous structures are biogenic appears compelling, though it is still equivocal as to whether they are cells or outer envelopes of colonies of smaller cells.

    Original languageEnglish
    Pages (from-to)603-615
    Number of pages13
    JournalAstrobiology
    Volume9
    Issue number7
    DOIs
    Publication statusPublished - 1 Sep 2009

    Keywords

    • Archean
    • In-focus and 3-D images
    • Microfossil
    • Mount goldsworthy
    • Mount Grant
    • Pilbara craton

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