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- The thermal history of the Upper Palaeozoic rocks of southern PortugalPublication . McCormack, Niall; Clayton, Geoff; Fernandes, PauloVitrinite reflectance (VR) evidence suggests that Palaeozoic rocks in the South Portuguese Zone of southwest Portugal are strongly post-mature, with mean VR (Rr) of 4.28%. Results from a thin Carboniferous coal are very similar to those from associated mudrocks, suggesting that the results from mudrocks in the region are not significantly influenced by the presence of reworked vitrinite particles. Integration of stratigraphic evidence with VR results from a field-oriented Carboniferous coal sample indicate that peak temperatures were attained post-Hercynian deformation, within the late Carboniferous–late Triassic interval. Results from the aureole of a minor Mesozoic igneous intrusion suggest that these intrusions did not significantly increase the already high maturation level of the Palaeozoic country rocks. VR (Rr) values from Triassic, Jurassic and Cretaceous sections that unconformably overlie the Palaeozoic rocks are much lower (0.87–1.14%) than those from the Palaeozoic and are fully consistent with recorded stratigraphic thicknesses and burial at geothermal gradients of 20–30 1Ckm 1. r 2007 Elsevier Ltd. All rights reserved.
- 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.
- Poder reflector da vitrinite, mineralogia das argilas e cristalinidade da ilite na Zona Sul PortuguesaPublication . McCormack, Niall; Clayton, Geoff; Fernandes, PauloO Poder Reflector Aleatório da Vitrinite (PRAV) na Zona Sul Portuguesa (ZST) varia entre 2,1% e 5,3%. O PRAV não aumenta com o aumento da idade estratigráfica e o processo de maturação é portanto, considerado como pós-deformação (pós-Vestefaliano D inferior). Amostras do Triásico e do Jurássico do Outlier da Carrapateira têm PRAV de 1,1% e 0,9% respectivamente. Isto implica que temperaturas máximas relacionadas com a maturação da ZSP foram alcançadas entre o Vestefaliano D inferior e o Triásico médio. A caulinite é o mineral das argilas dominante nas regiões ocidentais da ZSP, enquanto que as regiões localizadas a este e norte são dominadas pela clorite.