The chemical structure of Gloeocapsomorpha prisca microfossils: implications for their origin

Two Estonian Kukersites (Ordovician) and two samples from the Guttenberg Member (Ordovician) of the Decorah formation (North America) containing botryoidal aggregates of Gloeocapsomorpha prisca were investigated by RuO4 chemical degradation, FTIR, and flash pyrolysis-GC/MS to obtain information about the polymeric structure of these microfossils. The products formed upon oxidation by RuO4 were analysed by GC/MS and revealed the presence of a wide range of carboxyl and/or carbonyl moiety containing compounds with carbon skeletons ranging from C5 to C20. The Estonian Kukersites reveal the presence of a characteristic set of mono-, di-, and tricarboxylic acids. These compounds suggest that the Estonian Kukersites are composed of a polymer consisting of mainly C21 and C23n-alkenyl resorcinol building blocks. Similarly, although the tricarboxylic acids are not present, the RuO4 degradation product mixtures of the Guttenberg Member samples, suggest a poly(n-alkyl resorcinol) structure. The higher thermal maturity is most likely responsible for the different chemistry and morphology of the G. prisca microfossils in these samples. Because compounds like n-alkenyl resorcinols are known to polymerise under oxygenated conditions even in an aqueous environment, it is not per se necessary that these microfossils are composed of a selectively preserved biopolymeric cell wall. It is also possible that G. prisca microfossils are composed of a cell wall or sheath component that polymerised during senescence or diagenesis of the organism.