Resistant biomacromolecules as major contributors to kerogen

Abstract

Current research concerning the chemical characterization of organic macromolecules present in well-preserved fossilized materials with known morphologies revealed by (electron) microscopic studies results in the recognition of unknown, resistant biomacromolecules in a variety of organisms. It is shown that highly aliphatic, non-saponifiable biomacromolecules in cell walls of algae (algaenans) have unique structures, probably as a result of different biosynthetic pathways and that they consist of n-alkyl-, isoprenoid and tricyclic alkyl units. It is also becoming clear that algaenans are structurally different from the highly aliphatic, non-saponifiable biomacromolecules occurring in plant cuticles (cutans), periderm tissue (suberans), some sporopollenins and in tegmens of seeds of water plants. All these types of aliphatic biomacromolecules are highly resistant and therefore selectively preserved in the geosphere. In particular, Type I and II kerogens consist mainly, in some cases exclusively, of these aliphatic biomacromolecules. Polysesquiterpenoids and polyditerpenoids occur in fresh and fossil angiosperm and gymnosperm resins respectively and also show resistant behaviour in the geosphere. Some waxy crude oils contain large amounts of compounds derived from these substances after thermal cracking. A completely new polyphenol type of biomacromolecule was encountered in several fossilized outer walls of seeds (testae) of water plants. Preliminary results indicate that this phenolic biomacromolecule is an alternative source of phenolic moieties in lignites and coals. The significance of lignin as a source of phenolic moieties in subsurface organic matter (e.g. vitrinites) is probably overestimated.