Advances in the Stratigraphy and Geochemistry of the Organic-Rich Lower Jurassic Series of the Lusitanian Basin (Portugal)

Abstract

Here we present the main results of a study of the high-resolution stratigraphy of the Lower Jurassic organic-rich marine series in the Lusitanian Basin, Portugal. In this basin, the Lower Jurassic consists mainly of an alternating marl–limestone succession (upper Sinemurian–Toarcian), with some intervals enriched in organic matter (upper Sinemurian and Pliensbachian). These Lower Jurassic carbonate units correspond to the Coimbra, Agua de Madeiros, Vale das Fontes, Lemede, and S. Giao/Cabo Carvoeiro formations. In the last few years, these units have been the subject of a multidisciplinary and integrated stratigraphic analysis, based on the study of a range of biotic and abiotic parameters. In our study, high-resolution analysis of these units in the main reference sections of the basin have allowed seven main themes to be developed, involving sedimentological and sequential analysis, ammonite biostratigraphy, macroinvertebrate palaeontology and palaeoecology, ostracod analysis, chemostratigraphy, organic and petrographic geochemistry, and gamma-ray analysis. Besides the novel results obtained in each scientific domain, the integration of all the collected data has improved our knowledge of not only the stratigraphy and sedimentary knowledge of the Lower Jurassic carbonates but also the hydrocarbon generation potential of the different Sinemurian and Pliensbachian units.