Molecular preservation of plant and insect cuticles from the Oligocene Enspel Formation, Germany: Evidence against derivation of aliphatic polymer from sediment

The 25 Ma lacustrine deposit of Enspel, Germany, is important for molecular taphonomy as weevils from this site have yielded the oldest preserved traces of chitin. These weevil cuticles show excellent morphological and ultrastructural preservation. Plant cuticle is also preserved but it is obscured or distorted by diatom impressions. Molecular analysis of dicotyledonous angiosperm leaf from the Enspel deposit revealed the presence of polysaccharide, guaiacyl and syringyl related lignin, and possibly degraded protein moieties in the insoluble macromolecular component. Analysis of fossil conifer leaf showed the same moieties, but syringyl related lignin units were absent. Py-GC/MS revealed C9-33 n-alkyl components from both types of leaf, With C-13,C-14,C-29 homologues being the most abundant n-alkanes. TMAH pyrolysis yielded a fatty acid distribution ranging in carbon number from C6-30, with the C-16,C-18,C-14 components being the most abundant. Analysis of fossil weevil cuticle also revealed the presence of an aliphatic polymer as evidenced by C9-33 n-alkyl components in the pyrolysate and C6-26 FAMEs (predominantly even-numbered C14-18 components) in the TMAH pyrolysate. Pyrolysates of the sediments contain alkanes with distributions similar to those observed in the fossils; however, TMAH pyrolysates of sediments were distinct from those of the fossils with C20-22 components being the most abundant in the conifer-bearing sediment and the even-numbered C22-26 components dominating in the weevil-bearing sediment. Thus, the aliphatic polymers in the fossils and sediment are different, apparently comprised of moieties of different chain length. This suggests that the aliphatic polymer in the plant and insect fossils is not derived from migration from the organic-rich host sediment. (c) 2006 Elsevier Ltd. All rights reserved.