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- Organic maturation of the Algarve Basin (southern Portugal) and its bearing on thermal history and hydrocarbon explorationPublication . Fernandes, Paulo; Rodrigues, Bruno; Borges, Marisa; Matos, Vasco; Clayton, GeoffThe Algarve Basin, southern Portugal is under-explored in terms of petroleum geology. Organic maturation levels and the thermal history of this basin have been ascertained, together with their implications for future exploration. Maturity was determined using vitrinite reflectance and spore fluorescence/colour. The succession was extensively sampled (158 onshore samples and 20 samples from two offshore wells). Thermal history was modelled using 1D PetroMod®. A palynostratigraphic study of two offshore wells was also completed, showing thick marl–limestone sequences of Middle and Upper Jurassic age. Hiatuses were identified in the offshore wells within the Jurassic section and between the Jurassic and the Miocene sections. The Mesozoic rocks of the Algarve Basin lie within the oil window. Vitrinite reflectance ranges from 0.52–0.7%Rr in the Lower Cretaceous to 1–1.1%Rr in the Upper Triassic–Hettangian. Miocene rocks that unconformably overlie the Mesozoic strata are immature (0.42–0.47%Rr). Maturation levels increase with increasing age of the strata, indicating that burial was the main process controlling maturation. Thick marl–limestone sequences of the Middle Jurassic (Callovian) and the Upper Jurassic (Oxfordian) are the main source rock intervals. The Miocene successions of both offshore wells contains reworked vitrinite and palynomorphs with maturation levels similar to the Mesozoic rocks of the basin, suggesting exposure and erosion of these rocks during Miocene times. Palaeogeothermal gradients in the onshore Algarve Basin range from 52 °C/km to 24.7 °C/km with pre-Miocene exhumation estimated at 2000–2500 m. The probable age for the removed cover is Upper Cretaceous to Lower Palaeocene(?) and peak temperatures in the Mesozoic rocks were attained during latest Cretaceous–Early Palaeocene times. Modelled palaeotemperatures suggest that the Jurassic entered the oil-window at the beginning of the Cretaceous with peak oil generation in late Cretaceous time.
- Carbon isotope record (d13Ccarbonate) of the Middle to Late Jurassic (Callovian - Oxfordian) from the Algarve Basin, PortugalPublication . Borges, Marisa; Fernandes, Paulo; Rodrigues, Bruno; Goodhue, R.The Algarve Basin is an important Mesozoic depocentre located in southern Portugal which formed during the succesive phases of the North Atlantic rifting following the break-up of Pangea [1]. Several unconformities related to compressive episodes are observed in the stratigraphic record of the Algarve Basin. One of these episodes ocurred in the transition from Middle to Upper Jurassic times and is marked by an important tectonic episode, observed throughout Iberia [1], that caused the tilting and folding of the Middle Jurassic strata. This situation can be observed at Benaçoitão, where Oxfordian limestones rest unconformably over tilted Middle Callovian marly limestones. In this work we present !13Ccarbonate data across the Middle and Upper Jurassic rocks from the Algarve Basin at Benaçoitão.
- The thermal history of the Mesozoic Algarve Basin (South Portugal) and its implications for hydrocarbon explorationPublication . Rodrigues, Bruno; Fernandes, Paulo; Matos, Vasco; Borges, Marisa; Clayton, GeoffThe Algarve Basin is the southernmost geological province of mainland Portugal, outcropping along the entire south coast area and extending offshore, where it is recognised on seismic lines and in hydrocarbon exploration wells. It mainly comprises Jurassic and Lower Cretaceous limestones and marls making a succession over 3 km thick. This sedimentary basin belongs to a series of basins that were initiated by rifting associated with the opening of the North and Central Atlantic Ocean, following the breakup of Pangaea.
- Variação isotópicas d13C carbonatos na Sucessão da Baía de Três Angras: afloramento Mesozóico da Carrapateira (Kimeridgiano Inferior)Publication . Borges, Marisa; Goodhue, R.; Fernandes, Paulo; Pereira, Zélia; Matos, Vasco; Rodrigues, BrunoO afloramento Mesozóico da Carrapateira (AMC), localizado a 20 km a norte de Sagres é formado por sedimentos do Triássico Superior ao Kimmeridgiano. Para compilar os valores δ 13C para esta secção, sessenta e cinco amostras de carbonatos foram estudadas. Os valores δ 13C variam gradualmente ao longo da sucessão mostrando uma linha de base com uma tendência geral negativa. No entanto, a curva de δ 13C indica duas principais excursões negativas δ 13C, a primeira relacionada com a presença de um nível conglomerático, com um valor mínimo de -1,38 ‰ e uma segunda excursão com um valor mínimo de -3,10 ‰, imediatamente abaixo das camadas de calcário bioclástico do topo da sucessão. Em geral, a tendência negativa inicial está de acordo com a curva de δ 13C global, para o Kimeridgiano no Domínio Tetsiano, onde o AMC se insere. As duas excursões negativas são tendencialmente relacionadas com as perturbações no ciclo regional de carbono. Assim, ambos são interpretados como um resultado da entrada de grande quantidade de 12C para a bacia, como resultado de impulsos regressivos como sugerido pela análise sedimentológica, TOC e de palinofácies.
- Maturação Orgânica da Bacia Mesozóica Algarvia (Sul de Portugal): implicações para a exploração de hidrocarbonetosPublication . Fernandes, Paulo; Matos, Vasco; Rodrigues, Bruno; Borges, Marisa; Clayton, GeoffA Bacia Algarvia (BA) situa-se no sul de Portugale apresenta uma direção principal E - O estando a sua parte emersa representada ao longo da costa, desde o Cabo de São Vicente até ao rio Guadiana, estendendo-se também para o offshore.