Synchrotron FTIR investigations of kerogen from Proterozoic organic-walled eukaryotic microfossils.

Fourier transform infrared spectroscopy (FTIR) provides a rapid non-destructive molecular characterization of organic and inorganic material in geological samples. Combination of qualitative and semi-quantitative approaches are routinely used in FTIR study of kerogen and coals. A diversity of descriptors provides straightforward tools to characterize kerogen type, composition and structure. However, only a few of these descriptors are applied in the chemical investigation of Precambrian organic-walled microfossils. Synchrotron radiation-based Fourier transform infrared microspectroscopy (SR-FTIR) permits high spatial resolution investigations of organic matter in a large range of applications in biology, geochemistry and cosmochemistry, but remains rarely applied in Precambrian microfossils studies. Here we show that SR-FTIR spectroscopy combined with an integrative approach of kerogen description is particularly relevant for the study of minute organic-walled microfossils of unknown biological origin. The analyses of five morphospecies from three different Proterozoic formations in northwestern Canada highlight kerogen signatures rich in aromatic, aliphatic and oxygenated moieties. This is evidenced by the combined use of spectrum qualitative descriptions (band assignments and positions) and the calculations of semi-quantitative parameters using intensities and integrated areas of absorption bands (CH2/CH3, R-3/2 , Al/C=C, C=O/C=C, A factor, C factor). Altogether, this study demonstrates the interest of an integrative approach when investigating the chemistry of organic-walled microfossils with FTIR spectroscopy.