Abstract: Analyses of identifiable organic fossil remains of animals and plants have considerable potential to resolve conflicting models of organic matter diagenesis and kerogen formation (e.g. selective preservation versus random polymerization). Fossil cuticles of arthropods (scorpion, eurypterid) and plants .pteridosperm) from Upper Carboniferous strata of Lone Star Lake, Kansas, USA and Joggins, Nova Scotia Canada were analysed by pyrolysis gas chromatography/mass spectrometry and examined by electron microscopy. Recent Pandinus (scorpion) and Araucaria (conifer) provided a basis for comparison. Pyrolysis of Recent dewaxed scorpion cuticle yielded products derived from chitin and proteins. These products were absent in the fossil arthropod cuticles. however, which yielded an homologous series of alkanes and alkenes, together with phenolic and other aromatic constituents. Recent dewaxed plant cuticle yielded fatty acids, phenols and carbohydrate-derived compounds indicative of cutin polyester and associated lignocellulose. The pyrolysates of the fossil plant cuticles, on the other hand, were dominated by alkane-alkene doublets, with minor phenolic and other benzenoid components. There is no evidence that the preservation of these cuticles as particulate organic matter in kerogen is simply a result of selective preservation. Nonetheless, the chemistry and morphology remain characteristic of a particular taxon, thereby eliminating the possibility of incorporation of randomly repolymerized materials or the transfer of material between plant and animal residues. The aliphatic moieties in the fossil cuticles are thought to be the result of polymerization of the associated epicuticular. cuticular and/or tissue lipids during diagenesis.
Keywords: Carboniferous, arthropods. plants, cuticles, preservation.
Organic geochemical studies of sedimentary organic matter (i.e. coal, kerogen) have concentrated mainly on bulk characterization of kerogen in response to the needs of the coal, oil and gas industries. Such investigations were based on a model for the formation of kerogen in sediments that involved random repolymerization and recondensation of lipids, sugars, amino acids or other moieties (Tissot & Welte 1984). An alternative approach has focused on the chemical and structural identification of specific organisms such as algae (Largeau et al. 1990; Derenne et al. 1991), terrestrial plants (e.g. Nip et al. 1986a, b; Tegelaar et al. 1991), or soil microbes (Lichtfouse et al. 1996). This led to the development of a different model of kerogen formation involving the selective preservation of chemically resistant biomacromolecules (Nip et al. 1986a, b; Tegelaar et al. 1989b; Largeau et al. 1990; Derenne et al. 1991; de Leeuw et al. 1991). The investigation of animal remains has been largely neglected, however, based on the assumption that they are characterized by poor preservation potential, and make only a limited contribution to sedimentary organic matter. Only recently has it been shown that macromolecules derived from invertebrate tissues may be preserved in ancient sediments (Baas et al. 1995; Briggs et al. 1995; Stankiewicz et al. 1997c, cl. These preliminary investigations showed that most fossil animal cuticles have undergone diagenetic transformation, often converging towards the chemical signature of fossil plant cuticles, and that their composition cannot be explained in terms of selective preservation. This led to the suggestion that material (especially aliphatic components) might have been transferred between plant and animal remains (Baas et al. 1995)
Investigations of identifiable fossil remains clearly have considerable potential to resolve questions of organic matter diagenesis in sediments. Systematic analyses of animal and plant remains from the same strata eliminate the effects of environmental variables and allow the role of diagenetic transformations to be targeted. Animals and …