Macromolecular composition of the dinoflagellate cyst Thalassiphora pelagica (Oligocene, SW Germany)

Abstract

Origin, composition and fate of organic particles in marine sediments are to a large extent unknown. Here we contribute to resolving this lack of information by reporting on the structural characterization (FTIR micro-spectroscopy, py/GC/MS and TMAH assisted thermochemolysis GC/MS) of hand-picked Thalassiphora pelagica dinoflagellate cysts (Oligocene). The cyst wall macromolecule is relatively condensed. It is composed of a mixture of aliphatic moieties with the linear carbon units having an average chain length of ∼12 carbon atoms. In the pyrolysate this is reflected in aliphatic series of alkanes and alkenes (both <C 23), alkan-2-ones (<C 16) and alkylbenzenes (<C 20) and a high abundance of alkylated indenes and naphthalenes (both <C 13). The relatively strong aromatic signature of the pyrolysate supports a relatively extensive cross-linking between the aliphatic moieties, which is very unlike the highly aliphatic resistant biopolymer walls of Chlorophyta and Eustigmatophyta but agrees with the sparse information on organic-walled cysts of other Dinophyta. Thermochemolysis further supports the above and further indicates that carboxylic acids have been added to the macromolecule post-mortem. Additional series of alkylated thiophenes and benzothiophenes present in the pyrolysate and thermochemolysate are considered to result from early sulphurisation of the cysts in the anoxic to suboxic setting of the depositional environment.