MY BIOGEOCHEMICAL ROMANCE: EXPLORING RELATIONSHIPS BETWEEN MICROBIAL COMMUNITIES AND THEIR REDOX ENVIRONMENTS IN THE LATE ORDOVICIAN UTICA-POINT PLEASANT FORMATION

Here, we aim to understand the development of biogeochemical feedback mechanisms using a quantitative approach by correlating inorganic geochemical proxy data with biomarker community composition and relative abundances through the Late Ordovician Utica and Point Pleasant (U-PP) formations of the Appalachian Basin.

A section of core material from the western basin margin was logged and analyzed for Fe-speciation, major and trace elemental composition, total organic carbon contents, and biomarker composition and relative abundance. Preliminary results suggest that the U-PP can be characterized by a distinct facies progression representing a marine transgression that resulted in carbonate platform drowning and the development of a clastic-dominated foreland basin. Across the U-PP, Fe-proxy data indicate a broad transition from oxic to ferruginous (anoxic, Fe-replete) conditions, while redox-sensitive trace elements sustain near-crustal values, supporting the idea of a local control on redox. Early results from organic geochemical analyses returned abundant lipid biomarkers that suggest a dominance of eukaryotic primary producers. Intriguingly, the composition of some samples includes characteristic carotenoid biomarkers that may be indicative of photic-zone euxinia, contrasting with the Fe-speciation data.

Further analysis of the data using multivariate statistical methods and ensemble machine learning techniques will attempt to identify any significant correlations among biotic and abiotic indicators that would suggest causal relationships between microbial communities/metabolisms and the environment, especially with respect to redox. Additionally, by investigating covariation between the organic and inorganic fractions we may be able to better inform the intrinsic meaning (i.e. mechanistic basis) of Fe-speciation absolute proxy values and provide the scaffolding necessary to update the interpretive scheme beyond the current empirical thresholds.

Ultimately, understanding how controls in the geosphere (i.e., sea-level rise, sedimentation type and rate, ambient water chemistry, nutrient availability, etc.) drive adaptation and overturn in the biosphere – or vice versa – is integral to accurately interpret signals of Earth system evolution in the sedimentary record.