Paper No. 3
Presentation Time: 2:00 PM
INFLUENCES OF MICROBIAL COMMUNITIES ON CARBONATE FABRICS IN RECENT LACUSTRINE MICROBIALITES, PAVILION LAKE, BRITISH COLUMBIA
Understanding how microbial communities influence microbialite textures is crucial for interpreting microbial evolution and ecology from ancient microbialites. Recent microbialites in Pavilion Lake, BC, are ideal for investigating how diverse microbial communities influence carbonate fabrics because they are characterized by well preserved internal microbial communities and in situ lithification. Pavilion Lake supports microbialites of various sizes and morphology, and many microbialites resemble ancient thrombolites and dendrolites. This study focuses on a suite of samples from various depths that captures the morphological variability of Pavilion microbialites. Petrographic and SEM analysis revealed that fabrics reflecting both coccoidal and filamentous microbes are defined by the distribution of dark pigments in microspar and by crystal arrangement. The spatial heterogeneity of morphologically diverse communities is preserved in carbonate fabrics in the lithified structure; both filamentous and coccoidal microbes are uniquely associated with specific spatially distinct fabrics. For example, radiating filaments form rounded hemispheres on the microbialite surface. Radiating fabrics defined by pigments are also present in dense microspar within the mineralized microbialite. However, some internal hemispheres lack a radiating fabric and consist of dense pigmented carbonate with no relict filament fabric. This texture is indistinguishable from other fabrics that do not preserve microbes. Some fabrics without preserved microbes are interpreted to have formed with coccoidal communities based on intergradation with fabrics that do preserve coccoids. These results suggest that filamentous communities produce rounded growth structures that resemble mesoclots of ancient thrombolites, and that spatially and morphologically distinct communities produce indistinguishable carbonate fabrics. Because Pavilion microbialite fabrics resemble textures in many Paleozoic thrombolites and dendrolites, they can provide insight into formation of ancient structures without preserved microbial communities.