Microbialite morphogenesis controls arsenic incorporation as a chemical biosignature

Arsenic enrichment patterns are recognized as chemical biosignatures in microbialites, reflecting biologically mediated trace element cycling that can persist in the geological record. However, microbialites are not a uniform archive for chemical biosignatures because they exhibit a wide range of morphologies, internal fabrics, and accretion mechanisms, even within the same depositional system. How this variability in initial microbialite morphogenesis influences microbially influenced trace element incorporation and long-term preservation of associated chemical biosignatures remains largely unconstrained, limiting our ability to interpret arsenic enrichments in both modern and ancient microbialites.

Here, we investigated how microbialite morphogenesis controls arsenic enrichment patterns using actively accreting microbialites from Hamelin Pool, Shark Bay, Western Australia. We integrated petrographic characterization with sequential leaching experiments and elemental analyses to quantify arsenic concentrations of organic matter, micrite, and trapped-and-bound sedimentary fractions among microbialites with contrasting morphologies (sheet mats versus discrete buildups), fabrics (laminated versus clotted), and accretion mechanisms (micritic versus agglutinated). Our results show that arsenic enrichment patterns vary systematically with aspects of microbialite morphogenesis¹. Specific trends in arsenic enrichment patterns arise from variable contributions of microbial activity, sedimentary inputs, and seawater chemistry, the relative importance of which is controlled by microbialite morphology, fabric, and accretion mechanism.

Consequently, arsenic enrichment patterns are not universal chemical biosignatures, but context-dependent archives of biological activity shaped by microbialite morphogenesis. By explicitly linking morphology, fabric, and accretion mechanism to arsenic incorporation pathways, this study provides a framework for interpreting arsenic enrichments in modern and ancient microbialites, and for distinguishing biological signals from environmental and sedimentary contributions. More broadly, because microbialite morphogenesis governs the relative contributions of organic matter, authigenic carbonate, and trapped sediment, the same architectural controls are likely to influence the incorporation and preservation of other trace elements commonly used as chemical biosignatures through geological time.

1. Pollier, C. G. L. et al. Arsenic enrichment patterns are defined by microbialite morphology, fabric, and accretion mechanism. Nature Communications 16, 10218 (2025).