Browsing by Author "Goodhue, R."
Now showing 1 - 7 of 7
Results Per Page
Sort Options
- 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.
- d13Ccarbonate chemostratigraphy of the Carrapateira Outlier (Lower Kimmeridgian), Southern PortugalPublication . Borges, Marisa; Goodhue, R.; Fernandes, Paulo; Pereira, Zélia; Matos, Vasco; Rodrigues, B.The Carrapateira Outlier (CO) located 20 km north of Sagres is formed by Upper Triassic to Kimmeridgian sediments. The studied section is located at Três Angras bay and consists of approximately 50 m of limestones interbedded with marls, assigned to the Early Kimmeridgian based on corals, foraminifera and dinoflagellate cysts. The uppermost limestone beds are rich in macrofossils with well-preserved corals in life position. To compile 13C chemostratigraphy for this section, sixty five bulk carbonate samples were studied.
- New evidence concerning the thermal history of Devonian and Carboniferous rocks in the South Portuguese ZonePublication . Fernandes, Paulo; Musgrave, J. A.; Clayton, Geoff; Pereira, Zélia; Oliveira, José Tomás; Goodhue, R.; Rodrigues, B.The Late Palaeozoic rocks of southern Portugal have a complex thermal history. Vitrinite reflectance determinations from 90 samples confirm that the organic maturity of Late Palaeozoic rocks in SW Portugal is very high, mainly corresponding to meta-anthracite coal rank. The optic fabric of vitrinite in oriented coal samples from the Brejeira Formation suggests maturation under simple, non-tectonic, burial conditions with peak temperatures being attained prior to Variscan deformation. The lack of any increase in vitrinite reflectance with depth through c. 1 km of section in borehole AC-1 is not consistent with conductive heat transfer and is interpreted as the result of late synorogenic to post-orogenic advective heating. This heating episode generated temperatures sufficiently high to produce levels of maturity corresponding to metaanthracite coal rank through much of the terrane now exposed, but not high enough to result in overprinting of the pre-deformation optic fabric of vitrinite in the thin coals. The slightly lower maturity of older, platformfacies rocks in the Aljezur–Bordeira area may reflect either deposition on a basement high followed by less burial than adjacent parts of the basin, or the area being the site of a sink for descending relatively cool fluids.
- Preliminary account of the Silurian carbon isotope record (d13Corg) from the Barrancos region, Ossa Morena Zone, PortugalPublication . Lopes, Gilda; Fernandes, Paulo; Goodhue, R.; Pereira, Zélia; Piçarra, J. M.The Barrancos region provides one of the reference sections for the Silurian of the Ossa Morena Zone in Portugal. In this area the Silurian succession is condensed, with a maximum thickness of 50 m and the ages provided by graptolite faunas indicates that all the Silurian system is represented here. The lithologies are fairly homogenous throughout the succession consisting of black carbonaceous shales interbedded with black cherts, that were deposited in marine basins that developed at the northen margins of the Gondwana continent. This study is the first attempt to characterize the variation of 13Corg in this region, in order to assess well-documented Silurian climatic events. The studied section is located at Monte do Carreba, near Barrancos village, and consists of a 45 m thick succession of black shales and cherts with graptolite faunas that indicates a Llandovery to lower Ludlow age. The base of the section is faulted against Upper Ordovician greywackes and quartzites. In this section 13Corg shows a baseline of consistent low values ranging from -25.88 to -25.10%. This is interrupted by three positive excursions with maximum values of: -22.73% at the transition between the Llandovery (Telychian) and Wenlock (Sheinwoodian), -23.33% at the Homerian and -23.09% at the transition between the Wenlock and Ludlow (Gorstian). The excursions have positive shifts between +2.55 and +3.15% and are tentatively related to the three first global climatic events recognized for the Silurian (Ireviken, Mulde and Linde). Although this study is a preliminary account of 13Corg in this region, it could provide usefull data for the recognition and discussion of climatic global events in high latitude regions as was the OMZ located during Silurian times and for sections with high level of thermal maturation.
- Resultados preliminares do registo isotópico de carbono orgânico (d13C org) do Silúrico da região de Barrancos, Zona de Ossa Morena, PortugalPublication . Lopes, Gilda; Fernandes, Paulo; Goodhue, R.; Pereira, Zélia; Piçarra, J. M.A região de Barrancos apresenta uma das sessões mais complexas de Silúrico na zona da Ossa Morena.
- The thermal history and hydrocarbon source rock potential of the mid Carboniferous Quebradas Formation in SW Portugal and its correlatives in western Atlantic offshore basinsPublication . Clayton, Geoff; Fernandes, Paulo; Goodhue, R.; McCormack, Niall; Musgrave, J. A.; O'Donoghue, E. P.The mid Carboniferous Quebradas Formation of the ‘South Portuguese Zone’ (SPZ) comprises 80m of post-mature black mudrocks with a mean TOC of 2.5%. Lithostratigraphic units of similar facies and age such as the Holywell Shale, the Edale Shale and the Bowland Shale are important HC source rocks in the UK, having sourced a considerable proportion of the hydrocarbons in the East Irish Sea, East Midlands and Formby oilfields respectively. The kerogen content of the Quebradas Formation is mixed but slightly more oil-prone in its lower part. At outcrop, it is strongly post-mature with vitrinite reflectance (Rr) ca. 4%. Illite crystallinity results from the Quebradas Formation and associated units suggest lower maturity than vitrinite reflectance. Analysis of the optic fabric of very thin coal lenses within the Brejeira Formation which overlies the Quebradas Formation suggests that peak temperatures were attained before the Variscan (late Carboniferous – early Permian) deformation. Triassic rocks unconformably overlying the Carboniferous sequence are much less mature, with Rr ca. 1.2%. Although the the Quebradas Fm has no HC source potential onshore due to its high maturity, Carboniferous rocks offshore may not have experienced the same extreme thermal history as the SPZ.
- 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.