Alkyl naphthalenes and tetralins as indicators of source and source rock lithology – Pyrolysis of a cadinane-type sesquiterpene in the presence and absence of montmorillonite

Abstract

Alkyl naphthalenes and tetralins were generated during artificial maturation process of a cadinane-type sesquiterpene in the presence and absence of montmorillonite. Tetralins, cadalene, norcadalene, and 1,6-dimethylnaphthalene were the main compounds produced without montmorillonite, whereas those generated in the presence of montmorillonite were a diverse range of alkyl naphthalenes with trace amounts of tetralins. Some alkyl naphthalenes such as ethyl naphthalenes, 1,2-, 1,4-, and 2,3-dimethylnaphthalenes and 1,2,5-trimethylnaphthalene, which are common in terrestrial oils, were trace products. The aromatization of cadinene and tetralins proceeded much faster in the presence of montmorillonite than in its absence. In addition, the presence of montmorillonite significantly influences the methyl shifts and dealkylation of alkyl naphthalenes. In the absence of montmorillonite, tetralins and norcadalene were characteristic products. Highly abundant tetralins and norcadalene in oils suggest their non-clayey source rocks such as coal, carbonate or biogenic siliceous rock. Alkyl naphthalenes and tetralins have the potential to be useful indicators of source organic matter and source rock lithology of biodegraded and highly mature oils.