The thermal history of the Upper Palaeozoic rocks of southern Portugal

Vitrinite 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 °C km−1.