Controls on distributions of methylphenanthrenes in sedimentary rock extracts: Critical evaluation of existing geochemical data from molecular modelling

The discussed reactions are only a few of many reactions in which phenanthrene and methylphenanthrenes are potentially involved in nature to mention only biotic (biodegradation) and abiotic methylphenanthrene demethylation, and that there is no a single reaction that determines the fate of these molecules. Therefore, the commonly applied maturity index MPI-1 does not entirely reflect thermal maturity but is instead a molecular expression of complex processes and is dependent partly on catalytic effects of the mineral matrix. Analysis of the published data on methylphenanthrene abundance in rocks containing Type III kerogens indicates that there is no inversion of the MPI-1 trend above Rr = 1.35% as has been suggested previously. The maturity parameter MPR, defined as the 2-/1-MP ratio seems more closely dependant on thermal maturity than MPI-1.