The effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some Ancient sediments and petroleums

Abstract

The distributions of di- and trimethylnaphthalenes in two sedimentary sequences from Western Australia have been examined by capillary gas chromatography and combined gas chromatography-mass spectrometry. A general decrease was observed in the relative proportions of αα-dimethylnaphthalenes and ααβ-trimethylnaphthalenes with increasing thermal maturity. Similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories. These results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter, and the use of a number of isomer ratios is illustrated. © 1985.