ALKYLATED PHENANTHRENE DISTRIBUTIONS AS MATURITY AND ORIGIN INDICATORS IN CRUDE OILS AND ROCK EXTRACTS

Methylphenanthrene (MP), dimethylphenanthrene (DMP), and trimethylphen anthrene (TMP) distributions have been determined in crude oils and ro ck extracts from different origins at various stages of thermal maturi ty. A methodological approach combining Correspondence Factor Analysis and Nonlinear Mapping (NLM) was used for extracting origin/maturity i nformation from these data. It allowed to benefit from the advantages of both methods. The use of such a multivariate data analysis appeared much more efficient than the use of molecular ratios that can be too restrictive and mask specific distribution patterns. This approach per formed on the set of natural samples clearly demonstrated the discrimi nation between the samples through the presence of specific methyl-, d imethyl-, and trimethylphenanthrene isomers as origin/maturity markers . Based on MP, DMP, and TMP distributions, it is possible to distingui sh the variations in organic matter type from the effects of thermal m aturation. Some substituted phenanthrenes in each isomer series appear as characteristic of the two studied systems: The Aquitaine basin as representative of a marine carbonate environment and the Mahakam delta as representative of a terrestrial environment (higher plants). These compounds could be tentatively related to natural precursors such as triterpenoids or hopanoids.