Lacustrine Type I kerogen characterization at different thermal maturity levels: Application to the Late Cretaceous Yacoraite Formation in the Salta Basin – Argentina
Résumé
A maturation series from the Late Cretaceous to Danian Yacoraite Formation in the Salta Basin (Argentina) was selected to investigate the evolution of organic matter properties from source rock samples mainly containing lacustrine Type I kerogen. Organic petrography determined the thermal maturity and the spatial distribution of organic matter particles. Rock-Eval analyses and kerogen isolation procedures were then applied to assess the hydrocarbon generation potential of the investigated intervals. Biomarker ratios as well as the molecular composition of organic compounds present in four immature to early-mature rock samples and their corresponding aliphatic and aromatic fractions were investigated to complete the lacustrine organic matter characterization. Based on petrographic results, immature to early-mature Yacoraite samples have a large content of yellow-brownish liptinites (alginites) whereas mature samples are characterized by abundant solid bitumen. Three kerogen samples from the Yacoraite Formation at different thermal maturity levels were also selected for analysis of bulk-kinetic parameters (e.g. activation energy distribution, frequency factor) using programmed open-system pyrolysis. In this way, bulk-kinetic parameters were calculated as a function of the thermal maturity for these three lacustrine kerogen samples. Bulk-kinetic results show both an increasing activation energy and loss of petroleum generation potential as thermal degradation proceeds. The investigated Yacoraite kerogen samples show single activation energy distributions which are typical for a Type I kerogen of lacustrine origin. Finally, it was demonstrated that the organic matter (OM) characteristics from the Yacoraite Formation (Argentina) could be compared to the typical Type I kerogen from the Green River Formation (USA), showing similar OM characteristics, petroleum potential and activation energy distributions. The novelty of the geological and geochemical information brought in this article about Yacaroite system in Argentina provides premises for further investigation.