Browsing by Author "Santana, Paulo"
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- Chronology of the sedimentary processes during the postglacial sea level rise in two estuaries of the Algarve coast, Southern PortugalPublication . Boski, T.; Camacho, Sarita; Moura, Delminda; Fletcher, William; Wilamowski, A.; Veiga-Pires, C.; Correia, Victor; Loureiro, C.; Santana, PauloFour profiles of estuarine sediments obtained from boreholes drilled in the Algarve, Southern Portugal were studied in order to reconstruct the process of sediment accumulation driven by the postglacial sea level rise. In addition to the sedimentological analysis, the Foraminifera Index of Marine Influence (FIMI) permitted assessment of the nature and organization of sedimentary facies in the BelicheeGuadiana and Gilão-Almargem estuaries. The Beliche- Guadiana CM5 and Almargem G2 profiles accumulated in a sheltered environment, with the former presenting an almost continuous record of the sea level rise since ca 13 000 cal yr BP. The G1 and G3 profiles from the Gilão-Almargem area represent a more discontinuous record of the last 8000 years, which accumulated in the more dynamic environment of an outer estuary. The integration of all radiocarbon ages of dated levels, led to an estimate of sediment accumulation rates. Assuming a constant position of the sediment surface with respect to the tidal range and a negligible compaction of sediment, the sea level rose at the rate of 7 mm yr ^-1 in the period from 13 000 to 7500 cal yr BP. This process slowed down to ca 0.9 mm yr 1 from 7500 cal yr BP until the present. The marked historical change in the rate of sediment accumulation in these estuaries also occurred with the accumulation of organic matter and is, therefore, important data for global biogeochemical models of carbon. The main obstacle to obtain higher temporal resolution of the sedimentary processes was the intense anaerobic respiration of organic matter via sulphate reduction, which did not allow any accumulation of peat and, furthermore, led to erasure of the palaeontological record by acid formed from the subsequent oxidation of sulphides.
- Diagenese, fluxo sedimentar e subida global do nível do mar como factores de controle da geoquímica dos sedimentos estuarinosPublication . Boski, T.; Wilamowski, A.; Moura, Delminda; Correia, Victor; Veiga-Pires, C.; Santana, Paulo0 presente texto apresenta a discussão dos mais recentes resultados de estudo da geoquímica e mineralogia das sequências sedimentares acumuladas durante Plistocénico terminal e Holocénico nos dois principais estuários da Costa Sul Portuguesa, Estuário do Rio Guadiana e Estuário do Rio Arade. Em ambos, verifica-se um processo de rápida acumulação de massa sedimentar ate ca 7000 anos cal BP, sob a influência de rápida subida pós-glacial do mmm. A partir desta altura ate o presente a sedimentação nos sistemas estuarinos passa a ser sobretudo controlada pela redistribuição dos sedimentos localmente disponíveis. No estuário do Arade a proximidade entre a área alimentadora e a área de deposição reflecte-se pela abundância c diversidade dos minerais pesados erodidos do Maciço Alcalino de Monchique e da faixa vulcânica . No Estuário do Guadiana a assinatura da bacia de drenagem e menus espectacular dada a monotonia mineralógica do Flish Varisco. A sulfatoredução. oxidação dos sulfuretos e neoformação dos carbonatos são os principais processos de diagenése mineral, ligada a ciclo da matéria orgânica (MO) acumulada nos sedimentos. A taxa media de acumulação da MO que até 7000 a a calBP é aproximadamente 200 g m-2/ano-1 diminui posteriormente até aproximadamente 30% desse valor.
- Downwearing rates on shore platforms of different calcareous lithotypesPublication . Moura, Delminda; Gabriel, Selma; Ramos-Pereira, Ana; Neves, Mário; Trindade, Jorge; Viegas, José; Veiga-Pires, C.; Ferreira, Óscar; Matias, Ana; Jacob, J.; Boski, T.; Santana, PauloVertical lowering (downwearing) of shore platform surfaces is a very important mechanism in their morphological evolution albeit much remains incompletely understood. The efficacy of mechanical and chemical weathering acting on a given substrate, together with erosional processes, influences downwearing rates. In order to determine the relationship between lithotypes and downwearing rates, data collected from a Transverse Micro-erosion Meter were obtained for shore platforms of three different calcareous lithotypes (biocalcarenite, calcarenite and carbonated siltstone) along the central Algarve coast (Southern Portugal). Downwearing rates ranged between 0.096 mm year−1 and 1.676 mm year−1 in biocalcarenite and weakly cemented calcarenite, respectively. In addition, physical properties of the rocks comprising the platforms were measured, including uniaxial compressive strength (as determined by the Point Load Test), porosity, and calcium carbonate content. The results show that downwearing depends primarily on the intrinsic properties of the substrate. Porosity, in particular, acts in two ways: (i) it tends to weaken the substrate; and, (ii) it controls the downward extent of the water percolation and therefore the depth of the weathering mantle subject to erosion by waves and currents.
- Mudança do nível do mar no golfo de Cádiz durante o Plistocénico tardio e HolocénicoPublication . Boski, T.; Moura, Delminda; Mendes da Silva de Sousa, Carlos A; Gomes, Ana; Pereira, Laura; Oliveira, Sónia; Santana, PauloThe multiproxy information data set obtained from borehole sequences permitted to establish a robust chronology of events, which led to the post glacial infilling of the terminal stretches of regional river palleovaleys. The paleoecological reconstructions combined with 14C age model of Guadiana Estuary sedimentary record revealed the fast sea level rise period since ca 13.5 kyr cal BP, halted during the Younger Dryas and resuming at ca 11500 yr cal BP. The Holocene history of coastal evolution is also well documented in the Estuary of Arade and in Ria Formoza, pointing to the sea level stabilization at ca 7500 cal BP after a last jump of up to 8 meters in 700 years which corresponds to the Meltwater pulse 1c. Since then, the upwards movement of the sea surface continued at much slower pace, ie with the 1.2 mm yr-1 rate. The integration of the data embracing the period from since ca 13.5 ka cal BP, to the actuality enabled us to propose the sea-level rise curve for the SW Iberian Atlantic margin. When confronted with the current altimetric data from TOPEX/POSEIDON, Jason I and Jason II satellites, the millennial time-scale natural trend enables to estimate the anthropogenic forcing of SLR to be in order of 1.2 – 1.8 mm year.
- Postglacial sea-level rise in South Portugal as recorded in Guadiana EstuaryPublication . Boski, T.; Moura, Delminda; Camacho, Sarita; Duarte, Duarte; Scott, David; Veiga-Pires, C.; Pedro, Paulo; Santana, PauloThe Guadiana River Estuary is located in the terminal part of a deeply incised river valley, which accumulated several tens of meters of sediments during the Holocenic transgression. Five cored boreholes (see Fig.1 for localisation) that reached the pre-Holocenic substratum were drilled recently in order to recognize the architecture of sedimentary facies and to quantify the accumulation of organic carbon trapped in sediments during the valley infilling by marine waters. It was assumed that due to structural constraints imposed by Palaeozoic and Mezozoic substratum, the main estuarine channel did not change its position significantly. Consequently borehole locations were chosen in order to represent different sedimentary environments in the estuary: proximity to the main channel (CM1 and CM3), external sea facing (CM4) and lagoonal (CM2 and CM5) environments.
- Preenchimento sedimentar em três estuários do Algarve durante o HolocénicoPublication . Boski, T.; Moura, Delminda; Veiga-Pires, C.; Duarte, Duarte; Santana, Paulo; Pedro, PauloAs bacias hidrográficas são distintas quer do ponto de vista hidrológico quer na forma e àrea de captação.
- O registo de diatomáceas e foraminiferos da Ria Formosa (Sul da Península Ibérica): uma contribuição para a compreensão da evolução Holocénica do sistema lagunar.Publication . Gomes, Ana; Pereira, Laura; Boski, T.; Connor, Simon; Mendes da Silva de Sousa, Carlos A; Oliveira, Sónia; Santana, PauloAs part of a multi-proxy study to reconstruct the Holocene evolution of the Ria Formosa Lagoon, diatom and foraminifera assemblages were analyzed in a ca. 24.6-m-deep borehole, which crossed the entire infill sequence of the local paleovalley. Except in a few samples, diatom assemblages were generally poorly preserved, whereas foraminiferal assemblages were mostly well preserved. In the core depths interval from 23.5 and 3.2 m, both proxies indicate a marine environment installed during the progressive flooding of the fluvial valley during the Holocene. Above 3.2-m, both proxies