MOLECULAR PRESERVATION OF THREE-DIMENSIONALLY PRESERVED CENOZOIC FOSSIL CONIFERS AT HIGH LATITUDES

We examine the molecular preservation of exceptionally-preserved conifer fossil leaves from Miocene and Pliocene deposits of the Ballast Brook Formation on Banks Island, Northwest Territories, Canada, using the Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC-MS) technology. Solvent-extracted residues from Larix, Glyptostrobus, and Pinus from a Middle Miocene site and Picea from a Pliocene site yielded abundant polysaccharide pyrolysis products such as 2-furaldehyde and levoglucosan, indicating excellent molecular preservation. A typical chromatogram from these individual plants displays three major clusters: a cluster of polysaccharides at the beginning, a polysaccharide-lignin mixture in the middle, and homologous pairs of long-chain aliphatic n-alk-1-enes/n-alkanes at the end. Comparison between pyrolysates of individual plants with bulk material from the same deposit revealed dominating plant species in these high latitude floras. Comparison with fossil conifers in fossil Lagerstätten from Ellesmere Island (Paleocene-Eocene), Axel Heiberg Island (Middle Eocene), and Clarkia in Idaho, USA (Middle Miocene) demonstrated high-quality molecular preservation in the Banks Island materials that is equivalent to other Arctic Lagerstätten and better than in the Clarkia deposit. Using relative abundance of 4-ethylphenol (m/z 122+107), vinyl phenol (m/z 91+120), and levoglucosan (m/z 60+73) as indicators of the preservation of lignin, cutin, and cellulose, we rank molecular preservation of these Lagerstätten and compare these chemical data with SEM observations. Analysis of Larix and Glyptostrobus across different geological ages (Paleocene, Eocene, Miocene, and Modern) and geographic locations suggests that the age of the sample does not correlate with its molecular preservation. Intra-genus variation of pyrolysates among conifers is attributed to different original molecular constitution and paleoenvironmental conditions for preservation. Our data provide molecular level assessment of plant fossil preservation at these high latitudinal sites and offer further information on the role of labile biomolecules in the preservation of three-dimensionally preserved morphological structures in these Arctic plant Lagerstätten.