GEOCIÊNCIAS
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Percorrer GEOCIÊNCIAS por Objetivos de Desenvolvimento Sustentável (ODS) "14:Proteger a Vida Marinha"
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- Depositional environment and redox conditions of the Moncorvo Ironstone: Unveiling the evolution of ironstones under Rheic Ocean influencePublication . Urbano, Emilio Evo Magro Correa; Preto Gomes, Maria Elisa; Pinto de Meireles, Carlos Augusto; Brandão, Paulo Roberto Gomes; Hippertt, Joa Pedro T.M.; Scholz, Ricardo; Lana, CristianoABSTRACT: Ironstones, as key archives of past marine environments, provide invaluable insights into Paleozoic history. Their mineralogy may reflect the physical-chemical conditions of the environment and the nature of available sediments. This study focuses on the Moncorvo Ironstone, a Lower-Middle Ordovician deposit formed during the opening of the Rheic Ocean. Here, we use an integrated approach combining sedimentology, petrology, and geochemistry to constrain the depositional settings and the redox landscape associated with the ironstone deposition. The Moncorvo Ironstone present some unusual characteristics, such as the lack of ooids, an uncommon mineralogy, and a stratigraphic thickness that can reach over >45 m, a remarkable feature for an ironstone. Our investigation reveals that this iron-rich sequence is distributed in two distinct marine environments: an inner shelf and a middle to distal shelf. Each environment has a unique mineral assemblage. Despite the influence of metamorphism and deformation, evidence suggests that much of the mineralogy and texture of this deposit still preserve characteristics of the original sediments. Finally, our findings, alongside a careful assessment of the mineralogy of other ironstones of similar age, suggest a strong stratification of the Rheic Ocean throughout the Early and Middle Ordovician.
- Evaluating the role of physical mechanisms as possible triggers for turbidity currents in a deep ocean seamountPublication . Lebreiro, Susana M.; Peliz, Álvaro; Antón, Laura; Nave, Silvia; Reguera, M. Isabel; Lozano-Luz, Rocío; Waelbroeck, Claire; Crowhurst, Simon; Martrat, Belen; Lopez, Jordi F.; Hebert, Raphael; Lopez-Rodriguez, AlejandraABSTRACT: Turbidity currents on continental margins are often attributed to cyclic climate variability and sea-level change, while the causes of deep ocean turbidites are as yet to be tested. The Atlantic Iberian margin provides a unique setting to contrast deep ocean and continental environments, including depression features that further protect from resuspension and erosion by along-slope bottom currents. We present records of low-frequency, non-periodic, climate-independent turbidites from three deep cores covering up to 426,000 years in the Tore seamounts area. By evaluating a range of physical oceanographic mechanisms, the breaking of internal waves and mesoscale Mediterranean-eddies against unstable slopes in the seamounts area arises as the most likely triggers that precondition the recurrence pattern of the observed deep ocean turbidites.
- Evaluating the role of physical mechanisms as possible triggers for turbidity currents in a deep ocean seamount [Resumo]Publication . Lebreiro, Susana M.; Peliz, Álvaro; Antón, Laura; Nave, Silvia; Reguera, M. Isabel; Lozano-Luz, Rocío; Waelbroeck, Claire; Crowhurst, Simon; Martrat, Belen; Lopez, Jordi F.; Hebert, Raphael; Lopez-Rodriguez, AlejandraABSTRACT: Turbidity currents on continental margins are often attributed to cyclic climate variability and sea-level change, while the causes of deep ocean turbidites are as yet to be tested. The Atlantic Iberian margin provides a unique setting to contrast deep ocean and continental environments, including depression features that further protect from resuspension and erosion by along slope bottom currents. We present records of low-frequency, non-periodic, climate-independent turbidites from three exceptionally deep cores covering up to 426,000 years in the Tore seamounts area. Here we evaluate the possible role of a number of physical processes that, when combined, may induce sufficiently intense bottom boundary events and likely precondition the recurrence pattern of the observed deep ocean turbidites.
- The palynology of the Upper Triassic-Lower Jurassic in the Algarve and Lusitanian basins, PortugalPublication . Vilas Boas, Margarida; Cirilli, Simonetta; Pereira, Zélia; Duarte, Luis; Fernandes, PauloABSTRACT: High-resolution palynological analyses from the Algarve and Lusitanian basins (Portugal) provide a refined biostratigraphical framework and palaeoenvironmental reconstruction for the Late Triassic-Early Jurassic transition. In the Algarve Basin, three new palynozones (AT, SC, and CP) characterise the Silves Group from the early Carnian to early Hettangian, documenting the first Iberian occurrence of Tulesporites briscoensis and precisely delineating the Triassic-Jurassic Boundary (TJB). In the Lusitanian Basin, three palynozones (CG, IK, and Pm) constrain the Conraria and Pereiros formations to the Norian-Hettangian, with the TJB located at the base of the Pereiros Formation. Palaeoenvironmental reconstructions reveal distinct basin-specific evolutions. The Algarve Basin records an early transition from fluvial (Silves Sandstones) to marginal-marine (lagoonal and pond) settings, evidenced by abundant upper Carnian algal elements and reworked Neoproterozoic algae. Conversely, the Lusitanian Basin reflects a Norian-Hettangian marginal-marine, river-dominated setting, with microforaminiferal linings at the base of the Pereiros Formation marking the earliest marine transgression in the Lusitanian Basin. Quantitatively, both basins show a persistent dominance of xerophytic taxa, indicating a shift toward warmer, seasonally dry conditions across the TJB. Malformed sporomorphs in both records suggest environmental stress potentially linked to Central Atlantic Magmatic Province (CAMP) activity. Comparative analysis reveals that sedimentation initiated earlier in the Algarve (early Carnian) than in the Lusitanian Basin (Norian), suggesting diachronous development during Pangaea breakup. The assemblages show strong affinities with the Onslow Microflora, highlighting the Portuguese margin as a key archive for western Tethyan floral and climatic evolution.