Preservation of fossil leaf waxes in association with their source tissues, Clarkia, northern Idaho, USA

Abstract

An intensive study of fossil plant tissues has been undertaken at a Miocene lacustrine deposit to assess the degree of preservation of the fossil epicuticular waxes and the location of these components in the sediment relative to the leaf fossil tissues. Comparison of the preserved epicuticular wax lipids with those found on modern leaf tissues indicates that certain components have been degraded. Wax esters, aldehydes, certain sterols, and triterpenoids were not detected, whereas, n-alkanes, n-alcohols, n-acids appear to be selectively preserved. Analysis of different fossil leaves indicates that the distribution of preserved epicuticular wax components differ between species. This indicates that there is an inhomogeneous distribution of plant derived lipids within the sediment. However, comparison of lipid extracts from fossils of the same species shows a greater similarity within an individual species, than to other species or the sediment in general. This suggests that the gross characteristics of the original leaf wax are being preserved in association with fossil leaf tissues. Sampling on a submillimeter scale of sediment above and below a fossil Magnolia latahensis leaf has shown that although epicuticular lipids are found throughout the sediment, certain lipids characteristics of M. latahensis are concentrated at the surface of the fossil leaf. Therefore, components of the original epicuticular waxes appear to be located at the fossil and have not moved into the surrounding sediment. Rapid inorganic sedimentation appears to effectively dilute the background lipid signature, thus allowing the components of the preserved epicuticular wax from the fossil leaf to be distinguished from the surrounding sedimentary lipid distribution.