71 resultados para PLEISTOCENE


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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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The Pantanal is a Quaternary sedimentary basin located at the left margin of the Upper Paraguay River, west-central Brazil. Basin infilling was mainly by siliciclastic sediments and the stratigraphic succession exhibits an overall finingupward pattern. The depositional system tract is composed by a large meandering fluvial plain and several marginal alluvial fans, being the Taquari megafan the most striking feature. The present landscape is a complex tropical wetland, with geomorphic features derived from the present conditions and other inherited from successive Pleistocene and Holocene climates. During the Pleistocene, the sedimentary environment was dominated by braided alluvial fans, the original geometry of which is preserved as relict forms, permitting remarkable patterns of distributary paleochannels to be easily recognized in satellite images. Eolian processes were active in some abandoned lobes, contemporaneously with sedimentation in active fan lobes. Closed ponds bordered by lunette sand dunes, originally salt pans produced by eolian deflation, are relict eolian landforms in the Pantanal landscape. Eolian processes were probably more effective at the glacial maximum. Landscape has been changing in the Pantanal area since the end of the Pleistocene in adaptation to a more humid and warmer environment prevailing during Holocene. Initiation of the modern wetland has occurred during the Pleistocene / Holocene transition, with the change to a more humid climate and the individualization of lacustrine systems. The modern Pantanal wetland is a vast expanse of poorly drained lowlands that experiences annual flooding from summer to fall months. Although climatic fluctuations have occurred during all the Holocene, the alluvial fans have remained active depositional systems and lobes were formed by progradation and abandonment. Abandoned lobes were subjected... (Complete abstract click electronic address below)

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Far from the continental margin, drainage basins in Central Amazonia should be in topographic steady state; but they are not. Abandoned remnant fluvial valleys up to hundreds of square kilometers in size are observed throughout Amazonia, and are evidence of significant landscape reorganization. While major Late Miocene drainage shifts occurred due to initiation of the transcontinental Amazon River, local landscape change has remained active until today. Driven either by dynamic topography, tectonism, and/or climatic fluctuations, drainage captures in Amazonia provide a natural experiment for assessing the geomorphic response of low-slope basins to sudden, capture related base-level falls. This paper evaluates the timing of geomorphic change by examining a drainage capture event across the Baependi fault scarp involving the Cuieiras and TarumA-Mirim River basins northwest of the city of Manaus in Brazil. A system of capture-related knickpoints was generated by base-level fall following drainage capture; through numerical modeling of their initiation and propagation, the capture event is inferred to have occurred between the middle and late Pleistocene, consistent with other studies of landscape change in surrounding areas. In low-slope settings like the Amazon River basin, base-level fall can increase erosion rates by more than an order of magnitude, and moderate to large river basins can respond to episodes of base-level fall over timescales of tens to hundreds of thousands of years. Copyright (c) 2013 John Wiley & Sons, Ltd.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Pós-graduação em Genética e Melhoramento Animal - FCAV

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Pós-graduação em Geociências e Meio Ambiente - IGCE

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The roots' powder of timbo species collected in different regions of Amazonia that were tested in larvae groupings, didn't produce differential significative effects in two strains of Musca domestica. The two species with the greater number of plants used in the trial were Derris urucu and Derris nicou; the individuals from the species came from regions considered as "forestal refugies" during the Amazonian pleistocene. Among each species the plants varied since that inefficient to control, until plants lethals to the fies. This differential capacity for larvae control among plants of the same species, originated from different regions, suggests that both species had their populations isolated, during the quaternary epoch. In regions or "forestal refugies", where both species were represented, D. urucu was superior to D. nicou in the capacity to control larvae. While among plants from F region (Peruvian-East refuge) of the State of Acre, the two species had convergence in the values of damage to larvae groupings. Among the another species, Derris sp. (yellow timbo or watermelon timbo) didn't show differences in larvae control between samples from the two regions; while the species that was introduced in the Amazonia Denis elleptica showed damage in the larvae groupings similar to the most effective plants of D. nicou and D. urucu.