Pyritic Stromatolites from the Paleoarchean Dresser Formation, Pilbara Craton: Resolving Biogenicity and Hydrothermally Influenced Ecosystem Dynamics

This study explores the paleobiological significance of pyritic stromatolites from the 3.48 billion-year-old Dresser Formation, Pilbara Craton, by combining paleoenvironmental analyses with observations from well-preserved stromatolites in newly obtained drill cores. These structures exhibit stratiform and columnar to domal shapes with wavy to wrinkly laminations and crest thickening, hosted within facies influenced by syn-depositional hydrothermal activity. The columnar and domal stromatolites occur in strata displaying clearly distinguishable primary depositional textures. Mineralogical variability and fine-scale interference textures between the microbialites and the enclosing sediment highlight interplays between microbial and depositional processes. The examined stromatolites primarily consist of organomineralization – nanoporous pyrite and microspherulitic barite – hosting significant thermally mature organic matter (OM). This includes filamentous organic microstructures entombed within nanoporous pyrite, resembling the extracellular polymeric substance (EPS) of microbes. These findings strongly imply biogenicity and support the activity of microbial life in a volcano-sedimentary environment marked by hydrothermal activity and evaporative cycles. Coupled changes in stromatolite morphology and host facies suggest growth in diverse niches, from dynamic, hydrothermally influenced shallow-water environments to restricted brine pools strongly enriched in SO42- from seawater and hydrothermal activity. These observations, along with S stable isotope data indicating influence by S metabolisms, and accumulations of biologically significant metals and metalloids (Ni and As) within the microbialites, help constrain microbial processes. The presence of columnar to domal stromatolites in dynamic, hydrothermally influenced shallow water deposits suggests formation by microbial communities dominated by phototrophs. Stratiform pyritic structures within barite-rich strata may reflect the prevalence of chemotrophs near hydrothermal venting, where hydrothermal activity and microbial processes facilitated barite precipitation. The rapid precipitation of pyrite, a putative taphonomic process preserving microbial remnants, is attributed to microbial sulfate reduction, facilitated by reduced S sourced from hydrothermal activity. In conclusion, this research underscores the biogenicity of the Dresser stromatolites and advances our understanding of microbial ecosystems in Earth’s early history.