MGU Lecture: Amanda Oehlert

Microbialite deposits provide a long-standing archive recording the interactions of life and the environment through geological time. However, the biogenicity of ancient, laminated structures has remained a persistent subject of debate. Chemical biosignatures offer an additional and independent means of evaluating biogenicity, but their interpretation requires careful parameterization in well-constrained, actively accreting microbialite deposits. In this presentation, I will present our new conceptual model for microbialite growth and accretion and demonstrate how it improves interpretation of the chemical composition of living microbialites from Hamelin Pool in Shark Bay, Western Australia. Here, four types of surface mats accrete microbialites with a range of morphologies including microbial sediments, unlithified sheet mats, and discrete microbial buildups. New measurements of microbialite elemental composition and stable carbon isotope ratios will be contextualized by complementary analyses of sediment and seawater from Hamelin Pool. Results demonstrate the important roles of microbialite accretion mechanism, fabric, and morphology in governing microbialite composition and chemistry, providing a modern benchmark for interpreting chemical biosignatures in the ancient geological record.