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- Assinaturas isotópicas de Sr em águas minerais de Portugal e suas relações com o ambiente geológicoPublication . Ribeiro, Sara; Azevedo, Maria do Rosário; Santos, José Francisco; Medina, Jorge; Costa, Augusto
- Contact metamorphism and dolomitization overprint on Cambrian carbonates from the Ossa‑Morena Zone (SW Iberian Massif): implications to Sr‑chronology of carbonate rocksPublication . Roseiro, José; Moreira, Noel; Andrade, Laura; Nogueira, Pedro; de Oliveira, Daniel Pipa Soares; Eguiluz, Luis; Mirao, Jose; Moita, Patrícia; Santos, José Francisco; Ribeiro, Sara; Pedro, J.ABSTRACT: he Cambrian Series 2 Carbonate Formation from the Alter do Chão Elvas-Cumbres Mayores unit (Ossa-Morena Zone, SW Iberian Massif) is composed of regionally metamorphosed marbles and marlstones that underwent chlorite zone metamorphism and preserve the primaeval limestone 87Sr/86Sr ratios (0.7083–0.7088). These are consistent with the established Lower Cambrian seawater curve, and therefore used for age constraints in formations lacking fossil contents. The regional mineralogical and Sr-isotopic features of the carbonate rocks are frequently overprinted by the effects of contact metamorphism induced by magmatic bodies emplaced during rift-related and synorogenic events of the Palaeozoic, as well as by post-metamorphic dolomitization processes. The development of calc-silicate minerals due to contact metamorphism is common in the rocks of the Carbonate Formation and apparently results from the interaction of the protolith with fluids of different origin: (i) internally produced fluids released by conductive heating (observed in external contact aureoles) and (ii) external intrusion-expelled fluids that, besides leading to the appearance of distinctive assemblages, also promote an influx of strontium content (observed in roof pendants). Calc-silicate mineralogy varies substantially throughout the region, likely due to the heterogeneous distribution of silicate minerals of the protolith, progression of intrusion-driven fluids, and the irregular effect of thermal gradients. Results suggest that high-grade contact metamorphism (hornblende facies or higher) and dolomitization processes imposed on the Carbonate Formation significantly influence the isotopic signatures of the carbonates, providing limitations in applying Sr-isotopic chronology.
- 87Sr/86Sr dating of the Alcácer do Sal Formation (upper Miocene, mainland Portugal)Publication . Ressurreição, Ricardo; Legoinha, Paulo; Dias, Ruben Pereira; Santos, José Francisco; Ribeiro, Sara; Patinha, Carla; Miranda, RuiThe Lower Tagus Basin was subjected to several marine transgressions along the Neogene, related to positive eustatic oscillations and also controlled by the regional tectonic activity. In the Alcácer do SalSines region, previous studies identified an episode of marine sedimentation interpreted as having occurred during the late Serravalian to early Tortonian interval, based on biostratigraphic data. This episode is represented in the Alcácer do Sal Formation. The study of the SMS-12- 01B borehole, drilled for mineral prospection purposes, located about 10 km NNE of Melides, allowed the identification of a 3 m thick layer of sediments containing marine fossils. 87Sr/86Sr determinations of oyster shells point to deposition about 11.5 Ma ago, validating previous proposals for the age of the formation. These data correspond to the first numerical ages obtained for the Alcácer do Sal Formation, allowing a solid correlation with other known marine units in the Lower Tagus and Algarve basins related to the same transgression episode
- Climate change towards more arid conditions in SW Iberia during the HolocenePublication . Ribeiro, Carlos; Terrinha, Pedro; Voelker, Antje H. L.; Candeias, António; Azevedo, Maria do Rosário; Ribeiro, Sara; Rosado, Lúcia