ABSTRACT

Naphthalene and its methyl homologs were found in Miocene to Pliocene sediments of the Shinjo basin. The total concentrations of naphthalenes ranged from 26 to 5, 700 ng g^-1 from the top to the bottom sediments of an about 1, 600 m thick sequence. Naphthalenes were mainly distributed in the Kusanagi Formation and their depth profile showed a characteristic feature, indicating a concentration peak at the onset of oil-generation layer. The ratio of 2- to 1-methylnaphthalene as well as the relative abundance of dimethylnaphthalene isomers, except for 1, 8-isomer, showed no depth dependence. Therefore, it seems that no significant isomerizations of the naphthalene homologs had occurred during the burial diagenesis around and above the oil-generating zone in the sediments. However, as to the least stable 1, 8-dimethylnaphthalene isomer, the negative logarithmic change of the relative abundance of the isomer (Alexander et al., 1984) was observed showing a trend of increasing with depth.