Browsing by Issue Date, starting with "2025-04"
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- Soil Classification Maps for the Lower Tagus Valley Area, Portugal, Using Seismic, Geological, and Remote Sensing DataPublication . Carvalho, João; Dias, Ruben; Borges, José Fernando; Quental, Lídia; Caldeira, BentoABSTRACT: The Lower Tagus Valley (LTV) region has the highest population density in Portugal, with over 3.7 million people living in the region. It has been struck in the past by several historical earthquakes, which caused significant economic and human losses. For a proper seismic hazard evaluation, the area needs detailed V-s30 and soil classification maps. Previously available maps are based on proxies, or an insufficient number of velocity measurements followed by coarse geological generalizations. The focus of this work is to significantly improve the available maps. For this purpose, more than 90 new S-wave seismic velocities measurements obtained from seismic refraction and seismic noise measurements, doubling the number used in previously available maps, are used to update available V-s30 and soil classification maps. The data points are also generalized to the available geological maps using local lithostratigraphic studies and, for the first time, satellite images of this area. The results indicate that lithological and thickness changes within each geological formation prevent a simple generalization of geophysical data interpretation based solely on geological mapping. The maps presented here are the first attempt to produce maps at a scale larger than 1:1,000,000 in Portugal, with direct shear wave velocity measurements. A tentative approach to produce more detailed maps using machine learning was also carried out, presenting promising results. This approach may be used in the future to reduce the number of shear wave measurements necessary to produce detailed maps at a finer scale.
- Granitos estaníferos da região de Santa Comba de Rossas, norte de PortugalPublication . Teixeira, Rui; Gomes, Maria Elisa Preto; Silva, Paulo; Pinto de Meireles, Carlos AugustoRESUMO: Na região de Santa Comba de Rossas aflora um complexo granítico (G1-G3) que se instalou durante os estágios sin-cinemáticos da Orogenia Varisca, há 317,9 ± 8,7 Ma (datação Rb-Sr de rocha total). Os granitos são intrusivos em metassedimentos de idade silúrica, do Domínio Parautóctone da Zona da Galiza – Trás-os-Montes, instalando-se no núcleo de uma antiforma NW-SE, resultante das fases de deformação D1 e D3, apresentando evidências de uma deformação em regime dúctil e frágil. Os dados geoquímicos e isotópicos sugerem que o granito G1, com biotite > moscovite e o granito G3, com biotite ≈ moscovite, correspondem a pulsos magmáticos distintos, que terão resultado da fusão parcial de materiais metassedimentares e sofrido uma diferenciação por cristalização fraccionada. Este processo foi responsável pelo aumento do teor de Sn naqueles granitos e, muito provavelmente, pela ocorrência do granito moscovítico G2, o mais rico em Sn (77 ppm), no exocontacto do plutão granítico G1.
- Effects of application of eucalyptus leaf biomass on soil quality: a field trialPublication . Teixeira, Tiago; Cachada, Anabela; Pato, Pedro; Patinha, CarlaABSTRACT: Approximately 30% of Portuguese forests are occupied by eucalyptus (Eucalyptus globulus). As this is a highly flammable invasive species, it is essential to control its proliferation. Thus, the PEST(bio) CIDE project, based on a circular economy perspective, aims to explore the phytotoxic potential of eucalyptus leaves, using its leaf biomass as an effective and environmentally safe biocide, and its use as a corrective to improve soil properties. It is also expected that the introduction of biomass into the soil will contribute to increase carbon reserves and soil fertility. Thus, it is possible to associate an economic benefit with better management of post-fire regenerated eucalyptus areas. Due to this, a field trial was carried out to test the effect of biomass application on the soil’s physico-chemical properties. The results indicate that incorporating leaves has a positive effect on some soil properties, mainly in terms of increasing organic matter and available macronutrients.
- Análogos geoquímicos portugueses de rochas e solos marcianos (S. Saturnino – Fronteira vs Cratera de Gusev e Meridiani Planum)Publication . Rocha, Carla; Alves, Eduardo IvoRESUMO: Este trabalho resulta de estudos petrográficos e geoquímicos feitos sobre afloramentos de rochas filonianas básicas na região de S. Saturnino (Fronteira, Portalegre, Portugal) como análogos de rochas e solos marcianos das regiões da cratera Gusev e de Meridiani Planum analisados nas missões dos rovers Spirit (MER-A) e Opportunity (MER-B). Mostra-se que este é o primeiro local em Portugal Continental que pode ser reconhecido como análogo dos ambientes geológico, petrográfico e geoquímico marcianos.
- Compositional heterogeneity of late to post-Variscan, mafic subvolcanic dykes from northern Portugal (Central Iberian Zone)Oliveira, António; Martins, Helena; Sant'Ovaia, H.ABSTRACT: This study is dedicated to the presentation and interpretation of whole-rock geochemical data concerning a few mafic subvolcanic dykes located in northern Portugal, related to the late to posttectonic stages of the Variscan orogeny. Overall, the analyzed rocks are reasonably fresh, ultrabasic to intermediate, metaluminous to moderately peraluminous, and calc-alkaline or alkaline. There is no evidence implying the occurrence of crustal contamination, but crystal fractionation is likely to have played either a minor or more meaningful role on the petrogenetic evolution. While most dykes were probably generated from subduction-modified, metasomatically-enriched lithospheric sources, others possibly derived from the asthenosphere. There are also important differences regarding the residual mineralogy of the sources, as well as the melting degrees.
- Geosciences research mapping for Portugal in the year 2023: standing and future challengesTavares, Alexandre; Rocha, Fernando; Dinis, Pedro; Pereira, AlcidesABSTRACT: This study carries out a mapping of research topics in geosciences within the context of Portugal for the year 2023. The data for this analysis are sourced from 11 Research Centres and 4 other entities whose missions include research as their main objective. A bibliometric analysis is performed using the SCOPUS database for a sample of 103 researchers, with data collected in May 2023. A focus group is used, qualitatively assessing advanced or specialized knowledge about geoscience research in Portugal. Future constraints and challenges were highlighted, particularly with regard to changing research priorities and access to research funding. Guidelines for research in geosciences are presented from an ex-post point of view and in accordance with the instruments and research focuses in the European Union, namely those foreseen for Horizon 2030. The discussion raises ex-ante questions for the consolidation of geosciences in research centers and the expansion of knowledge to be produced by researchers.
- Investigating the hydrothermal activity at Fogo volcano (Cape Verde) using geochemical analyses of soil samplesCandeias, Carla; Rocha, Fernando; Dumont, Stéphanie; Maineult, Alexis; Ramalho, Ricardo; Madeira, José; Antunes, JoãoABSTRACT: Characterizing hydrothermal systems at volcanoes is particularly important as they play a crucial role in controlling eruptive dynamics. On the long term, hydrothermal systems participate in the geochemical alteration of both rocks and soils, through hydrolysis, dissolution, mineral precipitation, and secondary mineralization contributing in the gradual destabilization of volcanic structures. Fogo volcano (Cape Verde) is the most active volcano in he eastern Atlantic. It features a fumarolic field and passive degassing in its summit crater. A total of 65 soil samples were collected and analyzed, 4 years after the 2014-2015 eruption, in the area surrounding the volcanic edifice including the last eruptive vent with the main objective of detecting and identifying the geochemical and mineralogical signature of hydrothermal activity. Preliminary results show that soil samples were enriched in Ca, Cu, Co, Fe, Na, P, and Ti, when compared to 2014-2015 lava flows, which is confirmed by principal component analysis. Distribution of geochemical elements clearly reflects the mineral phases and is discussed together with geophysical data to shed the light on hydrothermal processes taking place at Pico do Fogo.
- Stream sediments geochemistry in the Valongo anticline, northern Portugal: arsenic as a proxy to outline new exploration targetsCarvalho, Paula; Albuquerque, Teresa; Chambel, Luís; Silva, Manuela; Rocha, FernandoABSTRACT: The Valongo anticline is known for the occurrence of several Sb-Au and As-Au mineral deposits, many of which have been exploited since Roman times. The Sb-Au and As-Au deposits occur in brecciated quartz veins, predominantly trending NE-SW, NNW-SSE, and ENE-WSW, cutting Cambrian to Carboniferous formations. An 801-stream sediment campaign was conducted in this area. Factorial kriging was applied as an interpolation method as it enables the estimation and mapping of the individual spatial components of the variogram. Arsenic (As) was used as a proxy to outline new exploration targets. The results allow the identification of NW-SE and NE-SW alignments as preferential areas for elevated As contents. Future studies will incorporate structural information and the distribution of old mine dumps to achieve higher accuracy in target areas for mining prospection.
- Caracterização de pegadas de terópodes no Oxfordiano superior do Cabo Mondego, Bacia LusitânicaPublication . Carvalho, Ismar; Cunha, Pedro; Figueiredo, SilvérioRESUMO: São analisadas dez pegadas de dinossauros, ocorrendo em dois estratos do topo das “Camadas com Pholadomya protei” (Oxfordiano superior) do Cabo Mondego (Figueira da Foz), sector norte da Bacia Lusitânica. Trata-se de pegadas que podem ser observadas na superfície das camadas ou em seção transversal, por vezes representando estruturas que deformam muito o substrato. O material icnológico encontra-se distribuído em duas camadas sucessivas, cada uma constituída por uma base de marga arenosa e topo de arenito de grão muito fino a médio. Os depósitos destas camadas correspondem a um ambiente litoral de planície de maré, num delta.
- Heterogeneity of the mixed siliciclastic-carbonate deposits of the upper Cabo Carvoeiro formation (Lower-Middle Jurassic), Lusitanian Basin, PortugalPublication . Barata, Joao; Duarte, Luis; Azerêdo, Ana Cristina; Gomes, J.ABSTRACT: The upper CC5 member of the Cabo Carvoeiro Formation (Toarcian-Aalenian(?)) of the Lusitanian Basin is characterized by grainstone facies with quartz grains, ooids and intraclasts. These facies are observed exclusively at Peniche, contrasting with the hemipelagic marly sediments of coeval outcrop sections in the basin. A detailed facies scheme reveals the relative local heterogeneity of the succession on outcrops, while the analysed subsurface data helps to better understand its regional heterogeneity. Lateral facies variability on outcrop is observed to occur through gradation, interfingering or pinching-out geometries. Coeval sections in the analysed offshore wells are generally characterized by micritic mudstone facies, which might transition laterally into the Peniche grainstones through similar geometric relationships based on the existing conceptual model. The relative heterogeneity of this sedimentary system is defined in this study by integrating outcrop and subsurface data, allowing for its perception at different observation scales.