SORPTION BY MINERAL SURFACES - REBIRTH OF THE CLASSICAL CONDENSATION PATHWAY FOR KEROGEN FORMATION

What are the consequences for organic matter diagenesis of the observation in two recently published articles of a strong correlation between surface area and organic content in marine sediments? The findings suggest that the typical mode of occurrence of organic matter in marine sediments is as a monolayer (or equivalent concentration) sorbed to the surface of mineral grains. This comment considers the theoretical factors which may influence adsorption and propagation of polymeric organic matter on mineral surfaces, and looks at the likely diagenetic fate of adsorbed material. Both adsorption and condensation have been suggested as possible mechanisms for the preservation of labile biopolymers, but neither process is satisfactory as a stand-alone mechanism; adsorption of monomers can merely retard their biodegradation, and condensation is not favoured in solution. However, if the two processes operate in concert, the criticisms levelled against each process considered in isolation are cancelled out, adsorption promoting condensation and condensation enhancing the strength of adsorption of the products. We suggest that the diagenetic modifications of surface adsorbed organic molecules will tend to strengthen their binding to the mineral surface, such that the geomacromolecules will evolve on the mineral surface towards strongly bound monolayers. The hypothesis overcomes many of the objections to the so-called classical condensation pathway of kerogen formation.