The paleoecology and significance of the Gunflint-type microbial assemblages from the Frere Formation (Early Proterozoic), Nabberu Basin, Western Australia

Abstract

Abstract Eight distinct microbial assemblages are preserved in the Frere Formation, which was deposited in the Nabberu Basin, Western Australia. These assemblages contain taxa (Animikiea, Eoastrion, Gunflintia, and Huroniospora) typical of Gunflint-type microbial assemblages, which have been described from Australia, Canada, and South Africa. Four assemblages are interpreted as primary (composed of benthic microorganisms) and four as secondary (containing components that were transported before deposition). These microbial assemblages have similar paleoecologies to other Gunflint-type microbial communities. All Gunflint-type microbial assemblages, including the Frere assemblages, were deposited in a marine subtidal environment. The apparent worldwide distribution of these similar microbial assemblages supports the hypothesis that Gunflint-type microbiotas were characteristic of the biota living in subtidal settings during the Early Proterozoic. However, this hypothesis does not account for the lack of these assemblages in post-Early Proterozoic rocks. This may be explained by the absence of primary inorganic silica precipitation in open-marine settings during the Middle and Late Proterozoic. Primary silica precipitation may be necessary for the preservation of well-preserved microbial assemblages in marine settings of normal salinity. Silica precipitation in Early Proterozoic open-marine settings is commonly associated with banded iron-formation deposition, which is confined mainly to 2500-2000 Ma ago.