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Abstract EANA2026-99 |
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Trophic Relationships Between Ancient Microfossils in the Gunflint Formation
Introduction: The Palaeoproterozoic carbonaceous chert of the Gunflint Formation has often been cited as hosting some of the oldest well-preserved evidence for life on Earth in the form of cellular microfossils (e.g. Awramik 1983, Barghoorn et al. 1965).While the interrelationships between the microbial species present in this assemblage have not been studied in detail, both aerobic and anaerobic heterotrophy alongside sulphate-reducing pathways have been proposed based on nanoscale elemental measurements of its pyritised microfossils (Wacey et al. 2013). Using microbial consortia, it has been demonstrated that the stable carbon isotope composition of microfossils can provide insight into their trophic relationships due to the relative 13C enrichment and limited δ15N range of heterotrophic organisms (Sephton et al. 2009). Therefore, analysing the organic isotopic composition of the Gunflint chert microfossil assemblage might elucidate the trophic structure of this ancient ecosystem. Yet excluding any potential diagenetic effects would be crucial before this investigation, necessitating the use of spectroscopic analysis to establish specific geochemical signals for these organisms.
Synchrotron-based Fourier-transform infrared (FTIR) spectroscopy and Raman spectroscopy are ideal analytical techniques for use in this context due to their capacity for highly spatially specific measurements, having been applied to Proterozoic microfossils in a previous study (Loron et al. 2022). Therefore, this study will focus on the application of both techniques, coupled with high-sensitivity organic geochemical characterisation using GCMS, to the diverse cellular microfossils of the Gunflint chert as a first step towards clarifying their trophic interrelationships.
Methods: Optical microscopy has thus far been used to investigate thin sections of the Gunflint chert with a particular focus on identifying carbonaceous features and microfossils as targets for FTIR and Raman analysis.
Synchrotron-based FTIR microspectroscopy will be utilised for in situ mapping of microfossils to determine their specific organic signals. To this end, fossils will be mapped via FTIR with a beam defined by a 3 μm spatial resolution and a spectral resolution of 4 cm–1. High signal:noise point analyses will be obtained to better characterise the organic complement of individual microfossils.
Raman spectroscopy will allow the maturation level of the organics comprising the fossils to be established, thereby confirming that these structures are syngenetic to the rock and reflect diverse primary precursors.
Preliminary/Expected Results: Filamentous microfossils are identifiable within selected thin sections of the Gunflint chert. Mapping and point analyses of these and other fossils will be essential for identifying any characteristic organic signals and distinct biomolecule abundances. Differences between the signatures in different microfossil species would be an ideal indicator that the fossils have not undergone chemical replacement and are suitable for organic stable isotopic analysis and other organic geochemical studies.
References:
Awramik S.M. et al. (1983) Precambrian Research, 20, 357-374.
Barghoorn E.S. et al. (1965) Science, 148, 461–472.
Wacey D. et al. (2013) Proc Natl Acad Sci., 110(20), 8020–8024.
Sephton M.A. et al. (2009) Geology, 37(10), 875–878.
Loron C.C. et al. (2022) Vib Spectrosc. 103476.
Rasmussen B. et al. (2021) Astrobiology, 21(6)