Browsing by Author "Dinis, Pedro A."
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- Composition of lower cretaceous mudstones of the Algarve basin and implications for Iberian palaeoclimatesPublication . Dinis, Pedro A.; Carvalho, Joel; Callapez, Pedro M.; Mendes, Mario Miguel; Santos, Vanda F.; Manuel Carvalho Fernandes, PauloSeveral compositional features of mudstones are controlled by climate-driven weathering and have been used to approximate palaeoclimatic conditions. Mudstone composition, however, is also influenced by the geology of the source areas and diverse depositional and post-depositional processes. The present geochemical and mineralogical study of the Lower Cretaceous (upper Hauterivian to Aptian) of the Algarve Basin (Southern Portugal) was performed to investigate the main factors that control mudstone composition and extract possible climatic signals. Clay mineralogy partially reflects diverse contributions of felsic vs. mafic and recycled materials, and the geochemical weathering proxies applied to the detrital component of mudstones are differently affected by provenance and hydraulic fractionation. Despite these facts, a wide set of compositional data allows some robust climatic interpretations. Apart from the early Aptian (Burgau Formation), when climate was probably wetter, hot and dry conditions prevailed in south Iberia during the investigated interval, with minimum humidity during the late Hauterivianeearly Barremian (Salema Formation). Independent sedimentological and palaeontogical data support these interpretations. A comparison with compositional results for the Lusitanian Basin reveals substantially drier climates in southern than central and northern Iberia. Interpreted patterns of climatic evolution can be linked to shifts in air circulation from the sub-tropical high-pressure belt. (C) 2020 Elsevier Ltd. All rights reserved.
- Geochemistry and mineralogy of the Lower Cretaceous of the Lusitanian Basin (western Portugal): Deciphering palaeoclimates from weathering indices and integrated vegetational dataPublication . Dinis, Pedro A.; Dinis, Jorge L.; Mendes, Mário Miguel; Rey, Jacques; Pais, JoãoThe present study investigates the climatic influence on the geochemistry and mineralogy of the Lower Cretaceous succession of the Ericeira region (Lusitanian Basin, western Portugal). Palaeoclimatic conditions are inferred from a combination of weathering indices and independent palynological and palaeobotanical data. A composite weathering intensity index is computed from selected geochemical and mineralogical data. The concentrations of some elements (Co, Ni, Sc, Th, V, Y, Zn, Zr) indicate variable contributions of sediments from the Lusitanian Basin margin and Iberian hinterland. It is demonstrated that the weathering intensity values are largely influenced by source area geology. The increases in weathering intensity following major unconformities (Late Barremian and Late Aptian) are partially attributed to the arrival of detritus from an evolved regolith sequence in the Iberian hinterland. A combined analysis of independent proxies is found necessary to conveniently discern the roles played by distinct processes on the weathering intensity and investigate the palaeoclimatic conditions. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
- The transition from Pangea amalgamation to fragmentation: Constraints from detrital zircon geochronology on West Iberia paleogeography and sediment sourcesPublication . Dinis, Pedro A.; Fernandes, Paulo; Jorge, Raul C. G. S.; Rodrigues, Bruno; Chew, David M.; Tassinari, Colombo G.Detrital zircon U-Pb geochronology data from late Carboniferous to Triassic clastic sedimentary rocks in SW Iberia were used to investigate the regional paleogeography during the transition from Pangea amalgamation to breakup. The major U-Pb zircon age peaks are middle Devonian to Carboniferous (similar to 390-300 Ma), Cambrian Ordovician (similar to 530-440 Ma), Cryogenian-Ediacaran (similar to 750-540 Ma), Stenian-Tonian (similar to 1.2-0.9 Ga) and Paleoproterozoic (similar to 2.3-1.8 Ga). Rapid exhumation of Variscan crystalline rocks at the contact between the South Portuguese zone and Ossa Morena Zone, explains the abundance of late Paleozoic ages in the upper Carboniferous-lower Permian continental successions. The U-Pb zircon data constrain the maximum depositional age of the Santa Susana Basin to c. 304 Ma and the Viar Basin to c. 297 Ma. The Triassic sequences, despite being c. 100 Ma younger than the Variscan tectonothermal events, contain low proportions of late Paleozoic zircon. The major peaks in all zircon spectra closely resemble those found in the adjacent basement rocks, indicating small source areas, mainly located near the rift shoulders. Longer travelled fluvial systems are postulated for the eastern portions of the Algarve Basin, which was closer to the westward advancing Tethys Ocean than the rift basins of West Iberia. Sequences that contain significant proportions of similar to 1.2-0.9 Ga zircon are probably recycled from post-collisional Carboniferous-Permian continental deposits that were more extensive than those found today. (C) 2017 Elsevier B.V. All rights reserved.