Las formaciones quaternarias continentales de la Península de Setubal (al sur de Lisboa)

[Resumen] Se describen dos formaciones quaternarias atribuídas una a la base y otra al topo del Vilafranquense medio, situadas en la península de Setúbal, al sur de Lisboa. Ambas poseen facies conglomerática, sin embargo, la inferior tiene características fluviales mientras la· superior es un depósito de tipo "rafia".[Resumé] On décrit deux formations quaternaires, atribuées a la base et au sommet de Vilafranchien moyen, situées dans la Península de Setúbal, au Sud de Lisbonne. Sa facies est conglomeratique, mais l'inferieur a des caracteristiques fluviatiles tandis que la superieur est un depôt du tipe "rafia

Quaternary evolution of Vilaric.;a Graben (Trás-os-Montes, NE Portugal)

[Abstract] In Portugal, the Douro River has a first large bend, leaving it's E-W general orientation after the Spanish border and near the Coa River mouth; another infiection occurs in Pocinho, where the Douro River fills the Vilari\a tectonic depression and receives the water from the Sabor River and the Vilari\a stream. The Vilari\a stream fills a NNE-SSW fiat valley situated between Serra de Bornes and the Sabor River. Quaternary evolution of this sector of the Hesperic Massif is recognized by the valley morphology and sediments, the Serra de Bornes' uplift and tectonic displacement (horizontal and vertical) ofgranites and Paleozoic series. All these evidences are associated with the Bragan\a-Vilari\a-Manteigas NNE-SSW tectonic accident, where more sediments are being studied. Many of these sediments have in common an alluvial fan origin and ages since Paleogene are proposed. Vilari\adepositsand Pleistocene Douro terraces present identical characteristics in geomorphological position and sorne sedimentologic features like reddish color and kaolinite-illite-smectite clay association; these similar characteristics justify a Quaternary age proposal for the Vilari\adeposits. The variation ofother sedimentological characteristics along the valley suggests the presence of several alluvial fans

Aplicação dos Isótopos Radioactivos 210Pb e 137Cs na Avaliação de Taxas de Sedimentação em Planícies aluviais: o caso da Lezíria do Tejo

Este artigo visa divulgar os primeiros resultados obtidos na definição das taxas de sedimentação, no último século, numa área-amostra da planície aluvial do Tejo, com o recurso a métodos de datação radiométricos adequados a esta escala temporal (210Pb e 137Cs). O estudo baseou-se na sondagem SEV, efectuada numa área deprimida da planície aluvial, a 2,5km da margem direita do rio, a norte de Santarém, no âmbito do projecto GEOTARIF (Geology and Archaeology of the Tagus River Floodplain over Time, POCTI/CTA/39427/2001). Foram seleccionados apenas os 1,09m superficiais da sondagem, os quais foram seccionados em amostras de 1cm de espessura. A metodologia seguida para o tratamento das 109 amostras e para a análise do 210Pb seguiu o método de Sanchez-Cabeza et al (1998) e a cronologia da sedimentação foi obtida através do modelo CRS (Appleby & Oldfield, 1978; Sanchez-Cabeza et al, 2000). A taxa de sedimentação média para o século XX, obtida a partir do 210Pb (em excesso), foi de 8,8mm/ano, mas os dois aspectos essenciais são: (i) a grande variação na deposição de sedimentos ao longo do último século; (ii) a clara tendência do aumento das taxas de sedimentação, nesta área da planície aluvial, em especial a partir dos anos 60. Os dados obtidos para a deposição do 137Cs na planície aluvial do Tejo, entre 1954 e 1988, mostram uma maior contaminação dos sedimentos aluviais por este radionuclídeo, a partir da entrada em funcionamento da Central nuclear de Almaraz.info:eu-repo/semantics/publishedVersio

Quaternary evolution of Vilariça Graben (Trás-os-Montes, NE Portugal)

In Portugal, the Douro River has a first large bend, leaving it's E-W general orientation after the Spanish border and near the Coa River mouth; another infiection occurs in Pocinho, where the Douro River fills the Vilari\a tectonic depression and receives the water from the Sabor River and the Vilari\a stream. The Vilari\a stream fills a NNE-SSW fiat valley situated between Serra de Bornes and the Sabor River. Quaternary evolution of this sector of the Hesperic Massif is recognized by the valley morphology and sediments, the Serra de Bornes' uplift and tectonic displacement (horizontal and vertical) ofgranites and Paleozoic series. All these evidences are associated with the Bragan\a-Vilari\a-Manteigas NNE-SSW tectonic accident, where more sediments are being studied. Many of these sediments have in common an alluvial fan origin and ages since Paleogene are proposed. Vilari\adepositsand Pleistocene Douro terraces present identical characteristics in geomorphological position and sorne sedimentologic features like reddish color and kaolinite-illite-smectite clay association; these similar characteristics justify a Quaternary age proposal for the Vilari\adeposits. The variation ofother sedimentological characteristics along the valley suggests the presence of several alluvial fans.(undefined

As cheias na construção e evolução da Leziria do Tejo: sintese de dois projetos

This article presents a summary of the final results of two projects funded by the Foundation for Science and Technology (FCT) in the field of fluvial dynamics, specifically, the floods of the greatest Portuguese rivers and the results of which are scattered in chapters of books, articles, abstracts, conferences or have never been disclosed as a whole: IDAFRE (An Interdisciplinary Approach to Flood Risk Evaluation - Hydrology, Geomorphology and Sedimentology of the Douro, Tagus and Sado Basins) (1997-2001) and GEOTARIF (Geology and Archaeology of the Tagus Floodplain Over Time) (2002-2006), where the Tagus river was mainly studied. The methods used can be divided into three categories: 1) data research in libraries, periodical archives, topographic and geological maps, history books, newspapers and magazines and old and recent bibliography, reconstruction of the history of the Tagus through the various sources consulted, with special relevance to the changes of the river channel throughout history, elaboration of flood and degree hazard maps; 2) field work for in situ observation of flood marks and their cataloguing, carrying out both manual and mechanical cores, sampling in present-day geomorphological elements of the alluvial plain, field observation of old abandoned channels and other morphological elements, monitoring and photographing flood episodes that took place between 1997 and 2006; 3) laboratory analyses of samples from all the cores, including sedimentological, pollen, organic matter, geochemical, 137Cs and 210Pb dating analyses, and analyses of radionuclide concentrations in the sediments of the alluvial plain. This set of techniques and methodologies made possible the development of a Flood Hazard map, calculation of the return period, the development of a table of the impact indices for progressive floods, variations in channel positioning, channel bars, natural dikes and flood plain and channel infilling, the variation of sedimentation rates throughout the twentieth century, the concentration of the floodplain by the contamination by heavy metals and radionuclides. The available data also allowed evaluate the evolution of the Tagus since the last glacial maximum, where it was probably an anastomosed river that carried sandy and pebbly sediments regarding a lower sea level than the present-day one. During the Holocene, the river built an alluvial plain composed of fine sediments with large and relatively stable isles between the channels, in an anastomosed pattern. However, successive human interventions in the alluvial plain are responsible for its transformation into a single channel river with alternating bars. The building up of the Tagus alluvial plain, throughout the Holocene, depended on natural causes affecting the entire drainage basin (climatic fluctuations and sea level rise) and anthropogenic causes, manifested either in the basin or in the floodplain, markedly obvious during the Bronze Age (from 3500 cal BP), with large-scale deforestation and consequent soil erosion, leading to a huge increase in the sedimentation rates of the floodplain. The direct human intervention on the Tagus alluvial plain was felt mainly from the Roman period on and intensified at the beginning of Portuguese nationality; XIII-XIV centuries (reign of D. Dinis). These interventions were aimed at draining alluvial plains with poor drainage, protecting agricultural lands from flood destruction and making the Tagus navigable, by avoiding its silting. The results show the importance of a multidisciplinary approach, in which the combination of different data allows a clear evolution in the research of sedimentary environments as complex as the alluvial plains.info:eu-repo/semantics/publishedVersio