Novel high-resolution geochemical methodologies for quantitative element maps and... - Simon V. Hohl - Video

Novel high-resolution geochemical methodologies for quantitative element maps and authigenic stable metal isotopic compositions in microbialites
Simon V. Hohl
-State Key Laboratory of Marine Geology, Tongji University, Shanghai, PR China

Microbialites are lithified remnants of microbial communities that hold the key to studying the earliest life on Earth and in extreme environments that are non-hostile to higher organisms. Various microbes can produce extracellular polymeric substances, which trap and bind ambient detrital sediment grains but also act as a substrate for carbonate nucleation. Authigenic minerals forming microbialites or stromatolites incorporate trace elements without significant fractionation from ambient fluids of neritic lacustrine and marine environments. Analysing trace element concentrations and isotopic compositions of authigenic minerals of the stromatolite geochemical archive offers the chance to directly study nutrient availability, cycling, and redox conditions in microbial habitats through deep-time. In this presentation, I will summarise recent advantages in two fields of microbialite geochemistry:
i) In-situ analyses of microbialites via laser ablation coupled to inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF-MS) and internal calibration to matrix-matching nano-powder carbonate reference materials obtain rapid high-resolution quantitative trace element maps. These maps show bio-intrinsic layering of bioactive trace metals enriched in authigenic minerals, while immobile elements are enriched in detrital coatings of microbialites. Their purpose is to understand better metal cycling between the microbial matter and ambient fluids as well as aiding in the search for regions least affected by diagenesis and detrital contamination for follow up U-Pb dating of the microbialite.
ii) Layer-specific probing and sequential leaching before novel stable metal isotope analyses are established as the gold standard for studying bio-geochemical metal cycling in microbialites. The past years have seen publications from workgroups focusing on isotopic compositions of bioactive trace metals (Ni, Cd, Ba), redox-sensitive metals (Fe, Mo, Cr, U) or carbonate nucleation (Mg). Although microbial communities' behaviour and fractionation processes are partly incompletely understood, stable metal isotope proxies have a unique potential to understand better redox conditions, metal availability and (biogenic) metal cycling processes in microbial habitats. I present insights into a few potential isotope applications, emphasising the Cd, Ba and Ni isotope systems and their future perspectives as isotope biomarkers to bridge the gap between geochemistry and microbiology and better understand the evolution of microbial life on Earth and beyond.