Geochemical significance of the aromatic hydrocarbon distribution in the bitumens of the Puertollano oil shales, Spain

The bituminous series of the Puertollano basin consists of three oil shale beds named PA, PB and PC from top to bottom. In this work, results from the study of the aromatic fractions of the bitumens are presented. The gas chromatographic traces are dominated by phenanthrene derivatives associated with variable contributions of arborane/fernane derivatives and benzohopanes and, overall, small amounts of chrysene derivatives and secohopanes. The compounds can be considered as part of two sub-groups: the first one consists of those compounds derived from regular hopanes such as secohopanes, benzohopanes, fully aromatized hopanes, and degradation products of hopanes such as alkylated chrysenes and naphthalenes. The second group is composed of arborane/fernane derivatives and their degradation products such as alkylated phenanthrenes and tetrahydrophenanthrenes. Both groups of compounds appear to be indicative of a strong bacterial input to the sedimentary organic matter.