Conifer and angiosperm biomarkers in clay sediments and fossil plants from the Miocene Clarkia Formation, Idaho, USA

The aliphatic lipids and terpenoids of conifer and angiosperm macrofossils and the clay sediment from a new site (P-37) of the Miocene Clarkia Formation, Idaho, USA, were analyzed to evaluate the preservation of characteristic conifer and angiosperm biomarkers in the sediment. Series of aliphatic lipids, terpenoids and steroids similar to the biomarkers found in type locality Clarkia P-33 were the predominant compounds in the sediment and in the fossils. Long-chain aliphatic lipids were major compounds in the fossil plants and the sediment, but a differentiation of angiosperm and conifer sources is not possible due to their common distribution among all vascular plants. In addition to previously reported terpenoids, diterpenoids of a conifer origin and several angiosperm derived polar triterpenoids of the oleanane, lupane, ursane and friedelane classes are reported here for the first time from the Clarkia sediments. The conifer shoots (Taxodium, Glyptostrobus, Calocedrus) contained characteristic conifer biomarkers such as abietane type diterpenoids while characteristic angiosperm triterpenoids were predominant in the angiosperm leaves (Betula, Quercus, Lithocarpus). The biomarker compositions of the Taxodium and Glyptostrobus shoots match the terpenoid patterns previously reported from fossil seed cones of the same genera. Although conifer macrofossils contribute about 45% to the flora of site P-37, characteristic conifer biomarkers occurred in the sediment in only low amounts while the angiosperm derived triterpenoids were present in comparatively higher abundances. The results indicate that the conifers are under-represented compared to the angiosperms according to the terpenoid composition of the sediment extract. This may be due to the presence of small angiosperm derived particles (leaf detritus, wax) in the sediment and/or migration of leaf waxes from the angiosperm leaves into the sediment. In contrast, the diterpenoids are trapped in the resinous woody tissue of the conifers and are thus disseminated less into the sediment. (c) 2005 Elsevier Ltd. All rights reserved.