Different accretion and diagenetic patterns within the fabrics of the Permian–Triassic boundary microbialites on the Leye isolated carbonate platform, South China Block

Abstract A comprehensive study on the accretion and diagenesis of Permian–Triassic boundary microbialites is conducive to a better understanding ecological community after end-Permian mass extinction. Here we studied special microbialite sequences at Tianba section Leye isolated carbonate platform, South China Block. The are shown as small columnar stromatolites, stromatolitic thrombolites, spotted domical digitate thrombolites in an ascending order. Thin analyses, coupled with cathodoluminescence photos oxygen isotopic data, reveal that all types microbially-mediated laminae/clots partly recrystallized. Layers Polybessurus -like fossils commonly occur recrystallized fabrics laminae. However, rare quantity generally fragmentary structureless clots clots. Such taphonomic features likely interpreted early decomposition by heterotrophic bacteria oxygen-depleted microenvironment caused rapid accumulations organic matter calm water. More enrichments 13 C laminae stromatolite thrombolite than adjacent interstitial matrixes signify photosynthesis-dominated fractionation during growth microbial communities. Rare calcimicrobial structures but many calcite crystal fans were found C-depleted These phenomena indicate seawater platform was 12 C-enriched supersaturated, accelerating precipitations decompositions within community. Different preservations fossil revealed complicated microbially-dominated sedimentation post-depositional abnormal catastrophe.