Porphyrins in Upper Jurassic source rocks and correlations with other source rock descriptors

The porphyrin content and composition in the extractable organic matter has been analysed in 13 Kimmeridge clay source rocks, spread from the north to the south of the Norwegian continental shelf. The samples are predominantly immature/early mature. The distribution of nickel and vanadyl porphyrins within the samples is markedly different. Effects of the thermal maturity on the composition of porphyrins is evaluated and compared with biomarker parameters based on sterane and hopane ratios. Maturity is modelled using partial least-squares (PLS) multivariate analysis with Tmax as a maturity indicator. Porphyrin parameters based on the total carbon number distribution of DPEP and ETIO series from the mass spectral data of the nickel and vanadyl porphyrin fractions effectively describe the Tmax of the samples with a better correlation than aliphatic biomarker ratios. Selected porphyrin and biomarker ratios were used for principal component analysis (PCA) modelling, and found to describe two types of variation that may be indicative of the prevailing depositional redox conditions.