ORGANIC GEOCHEMICAL CHARACTERIZATION OF THE DENSITY FRACTIONS OF A PERMIAN TORBANITE

Two distinct organic components, the Botryococcus-related alginite (Re inschia) and the amorphous organic matrix, were isolated by high-resol ution density gradient centrifugation (DGC) from a Permian torbanite ( New South Wales, Australia). On the density profile, the alginite (1.0 3-1.10 g/ml) and the matrix (1.16-1.21 g/ml) appear to be two distinct peaks. With fluorescence microscopy, the alginite shows bright yellow to orange fluorescence and well-preserved algal structure, whereas th e matrix has a reddish brown fluorescence of medium intensity. The H/C and O/C atomic ratios indicate that the alginite is equivalent to a T ype I kerogen, whereas the matrix falls into the Type II kerogen categ ory. The more ''heavy'' O and S, and less ''light'' H content in the m atrix also helps in explaining the higher density of the matrix relati ve to the alginite. Flash pyrolysis-GC/MS of the CH2Cl2-extracted dens ity fractions shows that the pyrolyzates of both the alginite and the matrix are dominated by normal alk-1-enes and alkanes, which range up to C-31. However, these normal hydrocarbons are relatively more abunda nt in the alginite than in the matrix. The alginite also produced a n- alpha,omega-alkadiene series which was not detected in the matrix. Com pared to the alginite, the matrix pyrolyzate is enriched in C-19-C-31 straight-chain aliphatics and aromatic, phenolic and hopanoid compound s, suggesting that the matrix was formed through incorporation of degr aded algal material and humic matter. The higher Methylphenanthrene In dex (MPI) value of the matrix pyrolyzates relative to the alginite ind icates that the MPI is affected by organic matter type.