Middle/late Devonian and early Carboniferous metasedimentary sequences in the northernmost region (Porto-Espinho-Tomar) of the Ossa-Morena Zone (Portuguese Iberian Variscan Massif) contain black shales of very low to low-grade metamorphism. These metasedimentary rocks form a discrete NNW-SSE structure within a major shear zone (Porto-Tomar-Ferreira do Alentejo) and remain subparallel to the observed regional major structures (folding, thrusts or overthrusts). These black shales are overhanged and then imbricated in an upper Proterozoic metamorphic substratum. A multi-disciplinary study of these metasedimentary rocks from the Espinho-Tomar region has tectonostratigraphy, palynology, organic petrology and clay mineralogy combined methods. This approach provides new insights into the tectonic evolution and geological framework of Palaeozoic basement of the Iberian Variscides. Palaeoenvironmental and tectonostratigraphic implications on the Iberian geodynamic framework are discussed.
A l'extreme Nord (Porto-Espinho-Tomar) de la Zone d'Ossa-Morena (Massif Iberique des Variscides au Portugal), des successions d'age Devonien moyen/superieur et Carbonifere inferieur renferment des shales noirs a metamorphisme de faible a tres faible degre. Ces metasediments forment un panneau structural NNO-SSE a l'interieur de l'importante bande de cisaillement de Porto-Tomar-Ferreira do Alentejo, tout en demeurant sub-paralleles aux structures majeures regionales (plis, chevauchements, charriages). Ces shales noirs sont aujourd'hui imbriques dans un substratum metamorphique d'age Proterozoique superieur. L'etude multidisciplinaire (tectonostratigraphie, palynologie, petrologie organique, mineralogie des argiles, et petrographie metamorphique) ouvre de nouvelles perspectives sur le cadre geologique et l'evolution tectonique du socle paleozoique des Variscides Iberiques.