TURNING FERNS INTO FOSSILS: BIOGEOCHEMICAL ALCHEMY
Laser-Raman spectroscopy, 13C nuclear magnetic resonance spectroscopy, and pyrolysis-gas chromatography/mass spectrometry are three such techniques. This study uses these three techniques, along with other organic geochemical methods, to analyze the structural chemistry of an Eocene-aged, three dimensionally permineralized fossil fern (Dennstaedtiopsis aerenchymata) and its modern analogue (Dennstaedtia cicutaria), as well as representative individual structural biochemicals of fern cell walls. Specimens of the modern fern and aliquots of the biochemicals were sequentially thermally altered to simulate the degradation that occurs during fossilization, and the chemical changes thus induced were tracked over the sequence to a stage of geochemical maturity comparable to that exhibited by the fossil fern.
The analyses show that there is a wealth of chemical information preserved in the fossil organic matter that is of sufficient quality to be informative about its original composition. Also, the heating experiments show that the organic matter of the modern fern can be converted into carbonaceous matter that closely resembles that of the fossil, providing new insight into the processes and products of geochemical maturation. Moreover, this study demonstrates that laser-Raman spectroscopy is a useful technique for non-destructive characterization of the structural chemical composition of modern and fossil organic matter.