TOWARD A BETTER UNDERSTANDING OF THE PALEONTOLOGICAL AFTERLIFE: A SPECTROSCOPIC CHEMICAL COMPARISON OF MODERN AND PERMINERALIZED PLANTS

The study of fossil kerogen has a long history, and is most often performed by those interested in its ability to inform about fossil fuel location and potential. But inquiries into the geochemical steps experienced during diagenesis and very low level thermal maturation are few and far between, especially those examining the detailed chemistry on a microscopic scale. This study is one such detailed inquiry, using UV resonance Raman spectroscopy (UVRR), ¹³C nuclear magnetic resonance spectroscopy (NMR), and pyrolysis-gas chromatography/mass spectrometry (pGCMS) to analyze the cell wall chemistry of an Eocene-aged, three dimensionally permineralized fossil fern (Dennstaedtiopsis aerenchymata) and its modern analogue (Dennstaedtia cicutaria), as well as isolated plant cell wall biochemicals (e.g., cellulose). Not only have these two end members (fossil and modern) been analyzed, but heating experiments have been performed to produce a series of samples (of both the ferns and biochemicals) that possess levels of thermal alteration intermediate between the modern (unaltered) and fossil fern samples. The UVRR and NMR results at first seemed contradictory. The NMR spectra show that the rate of compositional change was quite rapid at the beginning of the 250°C heating experiment and then slowed with longer periods of heating, changing from mostly polysaccharidic carbon to a mixture of mostly aromatic and aliphatic carbon. On the other hand, the UVRR spectra seem to show that very little structural change occurred even after heating at 250°C for 1000 hours. However, UVRR is much more sensitive to aromatic structures than to non-aromatic ones, such as polysaccharides, masking the presence of these non-aromatic structures in the unaltered samples and their subsequent loss or conversion in the progressively altered samples. But, though both the modern thermally altered and fossil samples are composed of aromatic structures, their UVRR spectra do not exactly match and hence, their chemical constituents are still structurally distinct. Therefore, additional heating experiments have been performed at higher temperatures and for longer periods of time to attain the level of thermal maturity seen in the fossil fern samples.