Chemotaxonomic classification of fossil leaves from the Miocene Clarkia lake deposit, Idaho, USA based on n-alkyl lipid distributions and principal component analyses

Fossil leaves which show excellent preservation of lipids and other organic compounds are preserved in abundance at the Miocene Clarkia lake deposit in northwestern Idaho, USA. Eighty three fossils from nine genera which are commonly found at the site, namely Quercus, Platanus, Magnolia, Pseudofagus, Fagus, Cocculus, Taxodium, Metasequoia and Sequoia were investigated to assess whether their chemical compositions can be used in chemotaxonomic comparisons. Chromatographically separated n-alkane and n-alkanol sub-fractions were examined by GC and GC/MS to establish whether characteristic distributions were evident between fossils and distinct from the enclosing sediment. Chemotaxonomic comparisons were performed between the individual fossil specimens and six sediments using the n-alkane and n-alkanol profiles and principal component analysis (PCA). Characteristic distributions were observed for certain genera, e.g. Platanus and Quercus, which were reproducible between multiple specimens of the same genus. Concentrations of the lipids in fossils were markedly greater than in the six sediments in all of the fossils except the conifers examined. These findings demonstrate that n-alkyl lipid distributions from fossil leaves have chemotaxonomic utility, with potential for comparisons with modern taxa.