Unidades litoestratigráficas do Ordovícico da região de trás-os-Montes (Zona Centro-Ibérica, Portugal)

42 páginas, 17 figuras, 5 fotos.
[EN] The Ordovician System outcrops extensively in the northeastern of Portugal, in the septentrional sector of the Central-Iberian Zone. The level of lithostratigraphic knowledge about these materials is notably lower than that of identical materials in other Portuguese regions and in a comparable peleogeographic scope. In this sense, the Ordovician of Trás-os-Montes remains, in many aspects, terra incognita. Recent fieldwork focused in the Ordovician biostratigraphy of northeastern Portugal lead us to consider the conveniente of making a deeper lithostratigraphical revision of these materials. It is a much needed amendment due to the proliferation of informal units and operative divisions that exist in the region, whose significance also varies for each of the authors, and the whole totality was examined under the requirements established by the international Stratigraphic Guide. The new lithostratigraphic scheme here proposed, unified for the entire region, considers the formal definition of 19 lithostratigraphical units, most of them of siliciclastic nature. The stratigraphic succession includes one group, eight formations, seven members and three individual beds. Each unit of equal or lower range than the Formation is clearly defined regarding its lithology and boundaries at the stratotype, considering its regional aspects, subdivisions, dating, sedimentary environment and detailed revision of the synonymy, as well the thickness ascribed from the previous authors to each concrete assemblage. The stratigraphic study allowed us to characterize and contextualize several units attributed to the Upper Ordovician, scarcely or partially unknown in the region until now, as well as the detection of stratigraphic gaps with different ranges and generally with great paleogeograhic interest. The new lithostratigraphic scheme here formalized for the Ordovician of Trás-os-Montes allows a precise knowledge and correlation of this region with the remaining Portuguese Central-Iberian Zone (Valongo, Buçaco, Amêndoa-Maçâo) and in the frame of southwestern Europe.
[PT] A recente realizaçâo de trabalhos, centrados no estabelecimento da bioestratigrafia do Ordovícico do nordeste de Portugal (Zona Centro-Ibérica), conduziu a urna profunda revisiâo litoestratigáfica destes materiais, â luz dos requerimentos litoestratigráficos estabelecidos pelo Guia Estratigráfico Internacional e justificada pela grande proliferaçâo de unidades informais e divisôes operativas existentes na regiâo. Esta nova proposta, unificada para a regiâo transmontana, contempla a definiçâo formal de um total de 19 unidades litoestratigráficas, a maioria das quais de natureza siliciclástica, repartidas por um grupo, oito formaçôes, sete membros e três camadas. Este estudo permitiu caracterizar e contextualizar diversas unidades atribuídas ao Ordovícico Superior, até agora praticamente ignoradas na regiâo, assim como a detecçâo de lacunas estratigráficas de grande interesse paleogeográfico. O novo esquema litoestratigráfico, agora apresentado, permite correlacionar de forma precisa e nivelar o conhecimento relativamente à restante Zona Centro-Ibérica portuguesa (Valongo, Buçaco, Amêndoa-Maçâo) e ao restante Ordovícico do sudoeste da Europa.