Organic Petrology and Thermal Maturity of Dispersed Organic Matter from the Ramalhal-1 Well (Lusitanian Basin, Portugal)

Organic petrology is an important tool used to characterize dispersed organic matter (DOM) in sediments and sedimentary rocks, and to assess its thermal maturity. This study was carried out on 33 cutting samples (Middle-Upper Jurassic) from the Ramalhal-1 well to characterize the particulate organic matter and to evaluate its thermal maturity. The samples were submitted to optical petrography analysis (reflected white and blue incident lights) and the mean random reflectance was measured. Microscopic observations revealed a low DOM content, characterized by the predominance of macerals of the inertinite group (including charcoal), followed by solid bitumen. Huminite/vitrinite is usually small in size and quantity. Liptinite macerals were also present, represented by sporinite, cutinite, liptodetrinite and rare bituminite. A type III-IV kerogen was defined for the Ramalhal-1 sequence. Huminite/vitrinite mean random reflectance varied between 0.38% and 0.75%, pointing to an immature-to-mature stage of the organic matter. Multi-populations of solid bitumen occurred in almost all the samples, filling voids and fractures in the inorganic materials (mainly carbonates). The bitumen populations were quite heterogeneous, concerning both the optical characteristics and distribution, displaying different thermal maturities. No relationship between vitrinite and bitumen reflectance was established, indicating that these bitumens were not generated in situ.

Taphofacies and Petrofacies Theoretical Marine Models Applied to the Coquina of the Amaral Formation (Lusitanian Basin, Portugal)

The Amaral Formation has a wide geographic distribution within the Lusitanian Basin, at the western Iberian Margin (Portugal). The different depositional contexts for this unit enabled the distinction of three sectors: lagoon, lagoon-barrier, and marine-distal. The integration of the evolutionary taphonomic analysis of its fossil assemblages with the analysis of multiscale properties through the CAMURES methodology (Multiscale Reservoir Characterization) allowed the application of a methodology for the classification of coquina which was previously developed for the Morro do Chaves Formation (Sergipe–Alagoas Basin, Brazil). Here, it was adapted according to the complexity of the Amaral Formation deposits. The classification of ten taphofacies, in association with four lithofacies, allowed the definition of 84 petrofacies, based on the nature of the sedimentary and taphonomic processes. The relationship between the structural context, the systems tracts, the diversity of the fossil record, the classification of taphofacies and petrofacies, and the understanding of vertical and lateral variations of the sediments’ deposition within the unit support the construction of geological and theoretical models for coquina deposits. These models will allow for prediction of the spatial distribution of facies in other coquina analogous hydrocarbon reservoirs, as well as specifying the delimitation of reservoir zones for 3D geocellular modeling and flow simulation of hydrocarbon-producing reservoirs, thus improving predictive analyses.

The southernmost occurrence of <i>Ichthyosaurus</i> from the Sinemurian of Portugal

The ichthyosaur fossil record of Portugal is composed of specimens from the localities of São Pedro de Moel, Alhadas, Cadima, Murtede, Casal do Combo, Condeixa, Alvaiázere and Tomar, within the confines of the Lusitanian Basin, ranging in age from the Sinemurian to the Aalenian. We reviewed the historical ichthyosaur finds in Portugal, and in this work we focus on the specimen IST-MDT 85, from the Sinemurian of Praia de Nossa Senhora da Vitória, central west coast of Portugal. The specimen was herein ascribed to Ichthyosaurus cf. communis, based on characters of the humerus in comparison with other specimens. This is the southernmost documented occurrence of Ichthyosaurus, widening the geographical range of the genus.

The effects of the Jenkyns Event on the radiation of Early Jurassic dinoflagellate cysts

This contribution is an overview of the Early Jurassic dinoflagellate cysts of the Lusitanian Basin in Portugal, with particular emphasis on the effects of the Jenkyns Event (Toarcian Oceanic Anoxic Event - T-OAE) on the evolution of this planktonic group. We review and discuss data from 214 samples from six Lower Jurassic successions (upper Sinemurian-upper Toarcian) in the Lusitanian Basin. The late Pliensbachian radiation of dinoflagellate cysts was well recognised in this basin. The pre-Jenkyns Event interval is highly productive, with maximum abundance and species richness values. However, this palaeoenvironmental perturbation severely affected the evolution of this group for the remainder of the Early Jurassic. The prolonged recovery of the dinoflagellates in the Toarcian following the Jenkyns Event is not typical of the northern regions (Arctic and Boreal realms), where new species began to evolve earlier compared with southern European basins.