The potential role of redox reactions for the distribution of alkyl naphthalenes and their oxygenated analogues in terrestrial organic matter of Late Palaeozoic age

Alkyl naphthalenes and phenanthrenes were abundant in all samples. The low polarity nitrogen, sulfur and oxygen compound fraction was characterised by the presence of alkyl naphthaldehydes and naphthyl ketones for the majority of the samples. The presence of naphthalene carboxylic acids and anthracene/phenanthrene carboxylic acids was restricted to samples of relatively enhanced maturity (vitrinite reflectance, Rr, 0.67-1.26%), with one exception. The correlations between the different classes of compounds based on the naphthalene skeleton led to the hypothesis that, within the maturity range investigated, aldehydes and ketones were readily formed from the corresponding aromatic hydrocarbons, while the carboxylic acids were formed at elevated maturity. For alkyl naphthalene dicarboxylic acids, two formation pathways are suggested, because of two different distribution patterns. A direct correlation of these dicarboxylic acids with the occurrence of other compounds having a naphthalene skeleton was not apparent.