Organic geochemistry and petrography of Spanish oil shales

Four of the principal oil shale units of Spain were examined by organic geochemical and petrographic methods. The samples included three lacustrine shales (Carboniferous from Puertollano, Cretaceous from Llames and Miocene from Rubielos de Mora) and one marine shale (Lower Jurassic from Punta del Cuerno). The petrographic observations show a dominance of liptodetrinite associated with bitumen-stained mineral matter and alginite, as well as a paucity of structured terrestrial organic matter. Geochemical work shows that the soluble organic matter is a mixture of terrestrially derived and aquatic, with the lacustrine samples having the strongest land plant signatures. Low values of reflectance and fluorescence maturity parameters and the presence of thermally unstable biological markers indicate that the samples are all immature, although the Carboniferous sample is approaching the oil window. Microfluorimetric maturity assessment is optimized in immature samples if measurements are restricted to a single liptinitic component, such as Botryococcus in the Spanish lacustrine shales.