lagerstätten;Metasequoia;living fossil;Py-GC-MS;SEM;diagenesis;Scanning electron microscope;Pyrolysis-gas chromatography-mass spectrometry;degradation
All rights retained by Caitlyn R. Witkowski and Bryant University
Remarkably well-preserved plants from rich fossil deposits (known as lagerstätten) provide insights into paleoenvironmental and paleoclimatic reconstructions. However, it is difficult to distinguish whether proxy signals from fossil lagerstätten represent original environmental information or modified data due to degradation. To better understand molecular and morphological changes of plant leaves over time, modern Metasequoia, a well-studied “living fossil,” was degraded to mimic early stages of diagenesis and then compared with its ancient counterpart. Two sample series were used: 1) a laboratory decay experiment with samples in a closed, controlled environment and 2) a natural decay experiment with samples collected from an open lacustrine environment. Morphological and anatomical changes during early diagenesis are evident in both decay series, as seen through SEM observations and through a new quantitative pixel-count evaluation method. The molecular and isotopic results indicate that the removal of polysaccharides collapses cellulose-based primary-walled parenchymatous cells, while cells with lignin-strengthened secondary cells walls remain intact much later in the decay process. This supports previous hypotheses that polysaccharide is significant in maintaining the three-dimensional structures found in plant fossil lagerstätten. Both modern laboratory and natural decay series show that diagenesis occurs quickly, suggesting that fossil samples must have been rapidly buried in order to avoid microbial growth. Therefore, given the overall fidelity of Metasequoia fossil lagerstätten, the approximately -24‰ δ13C values recorded in arctic Cenozoic Metasequoia fossils are likely due to physiological response to different ancient atmospheric conditions, and not due to microbial-based tissue decay during early diagenesis.