Abstract EANA2025-103

Ancient stromatolites, such as those from the Precambrian (> ~540 million years ago), provide records of early Earth’s biosphere, revealing interactions between microbial communities and environments at both local and global scales. The geochemical cycles of the Precambrian microbial biosphere may thus have influenced global oxygenation and glaciation events, as well as nutrient cycles that shaped Earth’s biodiversity. We are presently examining stromatolites from the Mbuji-Mayi Supergroup (DR Congo) with the aim of exploring the spatial distribution of light element chemical distribution and speciation, particularly carbon–oxygen bonding as this may aid in identification of organic molecule characteristics and preservation in diagenetically mature stromatolite fossils. Analyses using FTIR, optical and electron microscopy, including SEM and STEM coupled with electron energy loss spectroscopy (STEM–EELS), have provided insights into the mineralogical composition and spatial distribution of organic materials within these stromatolites, including kerogen-rich regions. Notably, EELS spectra of kerogen show well-developed C K-edge structure, including features at the pi prime transition (~285 eV) and sigma prime transition (~291 eV), collectively indicate of relatively poorly ordered amorphous carbon, as well as a small peak around 286.3 eV, which may be indicative of carbon–oxygen bonding. STXM analyses have been utlized to spatially resolve the molecular composition of functional group signatures within kerogenous regions of these stromatolites. Specifically, STXM allows spatial resolution of carbon–oxygen bonding within kerogenous material within the organosedimentary samples, while investigating the potential presence of other organic groups that were not identifiable using EELS and FTIR, such as signals from aliphatic, amide and ester bonds as evidence of diagenetic transformation of lipid fatty acids, with the aim of resolving potential hydrocarbon lipid moieties, such as carboxyl groups, within ~1 billion year old material, which would represent a significant advancement in our understanding of deep-time organic preservation. These findings aim to enhance our understanding of how early microbial ecosystems were preserved during the Precambrian, which may offer clues about environmental factors that influenced the stability of these microbial communities and their role in early Earth's biogeochemical cycles. The results have implications for the field of geobiology, particularly in reconstructing early biospheres, and could provide crucial data for broader models of Precambrian carbon cycling.