Assinatura tectono-sedimentar do auge da compressão bética em Portugal: a descontinuidade sedimentar Valesiano terminal-Turoliano

An Upper Miocene important sedimentary break can be accurately recognised in the Portuguese basins and is reflected by a drastic palaeogeographic change in relation to a large-scale tectonic event of probable uppermost Vallesian-Turolian (9,5 Ma; middle Tortonian) age. The characterisation of the sedimentary record of this tectonic event, as well as its relations with interpreted active faults is made for different situations: Douro (NW border), Mondego, Lower-Tagus and Sado Tertiary basins. The sedimentary record, considered upper Tortonian-Messinian ? (uppermost Vallesian-Turolian ?) is interpreted mainly as endorheic alluvial fans (internal drainage), developed along active NNE-SSW indent-linked strike-slip faults and NE-SW reverse faults. At NE Portugal, proximal fluvial systems of an endorheic hydrographic network drained eastwards to the Spanish Duero interior Basin. The main evidences of the betic compression clímax in Portugal mainland are presented; the interpreted active tectonic structures are in accordance with an intense NNW-SSE crustal shortening, but some regional differences are also documented.

Estratigrafia e interpretação paleogeográfica do Cenozóico continental do norte de Portugal

Palaeogeographic and tectono-sedimentary interpretation of northern Portugal, in which previous studies (geomorphology, lithostratigraphy, mineralogy, sedimentology, palaeontology, etc.) were considered, is here proposed. Cenozoic shows different features according to its morphotectonic setting in the eestern region (Trás-os-Montes) or near to the Atlantic coast (western region, Minho and Douro Litoral areas). Although in the eastern region the sedimentary record is considered late Neogene, in some places Paleogene (?) was identified. This oldest record, represented by alluvial deposits, was preserved from complete erosion because of its position inside Bragança-Vilariça-Manteigas fault zone grabens. Later sedimentary episodes (upper Tortonian-Zanclean ?), represented by two allostratigraphical units, were interpreted as proximal fluvial braided systems of an endorheic hydrographic network, draining to the Spanish Duero Basin (eastwards); nowadays, they still remained in tectonic depressions and incised-valleys. Later on, eastern sedimentation becomes scarcer because Atlantic fluvial systems (e.g. the pre-Douro), successively, captured previous endorheic drainages. The proximal reaches of the allostratigraphic unit considered Placencian is recorded in Mirandela (western Trás-os-Montes) but the following fluvial episode (Gelasian-early Pleistocene ?) was already documented in east Trás-os-Montes, preserved in high platforms and in tectonic depressions. Placencian and Quaternary sedimentary records in the western coastal zone, mainly represented by terraces, are located in the Minho, Lima, Alverães, Cávado and Ave large fluvial valleys and in the Oporto littoral platform. In conclusion, northern Portugal Tertiary sedimentary episodes were mainly controlled by tectonics, but later on (Placencian-Quaternary) also by eustasy.

Estratigrafia sismica do cenozóico na plataforma continental algarvia: interpretação do controle tectónico da sedimentação

The interpretation of 64 seismic reflection profiles in the Algarve continental platform (36º 20'-37º 00' paralels and 7º 20'-8º 40' meridians) calibrated with five petroleum exploration wells, with the identification of the geometric relations between six Cenozoic seismic units (B to G) and tectonic structures, allowed the construction of sucessive time-isopach maps (twt/s) and detailed interpretation of the geologic evolution. Two major tectonic structures were identified: a) the Portimão-Monchique fracture zone (striking N-S); b) an off-shore NW-SE fault zone, probably the S. Marcos-Quarteira fault. This accident separates two tectonic domains: the western domain (with N-S and E-W predominant structures and, secondarily, NW-SE and NE-SW) and the eastern domain (dominated by WSW-ENE, NW-SE, NE-SW, NNE-SSW and NNW-SSE structures). A persistent halokinetic activity had two major moments: a) sin-C unit; b) sin- and post-E unit. An increasing flexuration of the margin was identified, with spacial and temporal variation of the subsidence. The tectonic regime is considered as generally compressive, but the interpretation of the successíve stress-fields is rendered dificult by the existence of tectonic sub-domains and evaporitic structures.