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New data on the late Famennian miospore assemblage of the Cercal Anticline, westernmost Iberian Pyrite Belt area, Portugal
Advisor(s)
Abstract(s)
The Cercal Anticline (CA) is located in the westernmost region of the Iberian Pyrite Belt (IPB).
The exposed stratigraphic sequence includes, in ascending order, the Volcano-Sedimentary
Complex (VSC) followed by the Xistos das Abertas Fm, which passes gradually to the flysch
sequence of the Mira Formation (Carvalho, 1976). The VSC is composed from base to top by:
Felsic Volcanics (Vα), that comprehends lavas, pumice and volcaniclastic beccias with
intercalations of volcanogenic shales; diabases and intermediate/basic subvolcanics (Vβ);
jaspers and the S. Luís Formation (SL), a unit composed of shales, phyllites, siliceous shales
and volcanogenic sediments. About 500m NW of São Luís village, at the base of this last unit,
brachiopods ascribed to the late Strunian were found (Quiring, 1936). This determination led
Carvalho (1976) to assume that the volcanics of the VSC are older than the Strunian, meaning
so that this volcanism is the oldest in the Portuguese IPB.
The stratigraphic succession of the CA is still poorly constrained, in terms of lithostratigraphy
and age. In fact, three boreholes carried out in the hinge zone of the anticline by the Elf
Aquitane company, about 1km NW of São Luis village, showed that below the felsic volcanics a
thick (>250m) succession of dark shales and siltstones occur. These shales yielded very well
preserved specimens of Grandispora echinata together with Ancyrospora spp.,
Apiculiretusispora sp., Auroraspora macra, Cristicavatispora dispersa, Diducites poljessicus,
D. mucronatus, D. versabilis, Emphanisporites annulatus, Grandispora cornuta,
Punctatisporites spp., Retispora cf. macroreticulata, Retusotriletes phillipsii, R. planus, R.
triangulatus, R. rugulatus, Rugospora explicata and R. radiata. This assemblage indicates the
VH Biozone of late Famennian age. It is similar to those found in shales interbedded in felsic
volcanics in several regions of the Portuguese Pyrite Belt (Neves Corvo Mine, Albernoa
Anticline, São Domingos Mine). Palynostratigraphic research in the CA is currently still in
progress. However, these preliminary results show that the age of the CA felsic
volcanics is similar to that obtained in the northeastern branches of the Portuguese
Pyrite Belt and no prove that the volcanism migrated in time to the NW, as suggested by
Carvalho (1976), could be detected.
Description
Keywords
Palinologia Miosporos Fameniano Anticlinal do Cercal (Portugal) Faixa Piritosa Ibérica
Citation
Pereira, Zélia [et al.]. New data on the late Famennian miospore assemblage of the Cercal Anticline, westernmost Iberian Pyrite Belt area, Portugal. In: 12th International Palynological Congress, IPC-XII 2009, 8th International Organisation of Palaeobotany Conference, IOPC-VIII 2008.