Geological Mapping of Rates and São Félix of Laúndos Region (Northern Portugal)

Abstract

Abstract The Rates and São Félix of Laúndos region is located in the NW extension of the Valongo Anticline (Northern Portugal), comprising Palaeozoic formations with ages ranging from the Cambrian to the Carboniferous, locally overlaid by Plio-Pleistocene beach deposits and dunes. Detailed geological mapping was developed. The fieldwork allowed distinguishing different lithostratigraphic units, some of them fossiliferous. The study under optical microscope and Scanning Electron Microscope (SEM) allowed noting the presence of volcanic rocks along the Palaeozoic succession. A rhyolite in the Cambrian - Ordovician transition, a likely ignimbrite in the Upper Ordovician, and the existence of a porphyry in the Carboniferous, were for the first time identified in this region. The palaeontological study focuses on the samples collected in the field, essentially belonging to the Middle Ordovician (Valongo Formation), but also to Silurian and Carboniferous. The Devonian formations are largely covered by agricultural fields and by urbanization, not allowing the collect of fossils, so the Devonian fossils studied belong to the Stratigraphical and Palaeontological Collection of the Department of Geosciences, Environment and Spatial Planning, Faculty of Sciences, University of Porto. The geological mapping previously developed in this region goes back to the XX century. In the present work a detailed geological mapping at a scale of 1:15 000 was developed, with reinterpretation of the stratigraphic succession.