Ordovician-Silurian transition in the Centro-Iberian Zone; Just a stratigraphic boundary or a major element in the evolution of the Iberian Variscides?

Abstract

Although the Ordovician-Silurian transition in the Central-Iberian Zone is usually considered a normal stratigraphic one, recent studies show that often the black-shales of the Lower Silurian, control the development of shear zones subparallel to the main layers. This behavior has been observed, not only in the Marão-Alvão region, but also in other sectors such as, the synclines of S. Mamede, Mação and Buçaco. This seems to show that the Lower Silurian weak layers have been a major factor in controlling the evolution of the Iberian Variscides. Ongoing studies in the Celorico de Basto region will try to characterize and understand the evolution of these shear zones.