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Title: Dinâmica da paisagem na porção norte da Ilha do Bananal-TO e adjacências ao longo do Quaternário tardio.
metadata.dc.creator: MENDES, Laís Aguiar da Silva
metadata.dc.contributor.advisor1: COSTA, Marcondes Lima da
Keywords: Ecótono
Dinâmica da paisagem
Quaternário tardio
Issue Date: 30-Aug-2019
Publisher: Universidade Federal do Pará
Citation: MENDES, Laís Aguiar da Silva. Dinâmica da paisagem na porção norte da Ilha do Bananal-TO e adjacências ao longo do Quaternário tardio. Orientador: Marcondes Lima da Costa. 2019. 130 f. Dissertação (Mestrado em Geologia e Geoquímica) – Instituto de Geociências, Universidade Federal do Pará, Belém, 2019. Disponível em: . Acesso em: .
Abstract: Paleoclimatic and paleoenvironmental studies aim to understand processes of global landscapes evolution, contributing to the reconstitution of the quaternary landscapes and the climatic and environmental changes to which were submitted during this period of the earth's geological history. Some studies in the Amazon, but especially those led in regions more sensitive, such as ecotones and wetlands, show that these areas underwent various paleoecological changes during the Pleistocene and Holocene. The present study was led in the Bananal Island region located in a transition area between the Amazon and Cerrado biomes. The Bananal Island, considered by many authors the largest river island in the world, occupies an area of about 20,000 km2 and is located between the middle course of the Araguaia River and its tributary by the right branch, the Javaés River, in the state of Tocantins. The northern portion of the island stands out for its complex mosaic of geomorphological features (marginal dikes, abandoned meanders, paleochannels and lakes) and contrasting geobotanical features (forests and savannas), such that reflect the intense hydrodynamic activity in this region. Seasonally it is flooded by rainwater and rising water table, so it is considered a seasonal wetland. The aim of this work is to understand the dynamics of this landscape, based on the mineralogical and chemical composition of soils and sediments and the palynological composition study of lacustrine sediments of this region. Therefore, samples of ravines exposed on the banks of Javaés and Araguaia rivers, sandy bars and lake sediments were collected. Soils and sediments were analyzed for their mineralogy by X-ray diffraction and chemistry by ICP-AES and ICPMS. The sediment cores collected in 2 distinct lakes, one located in the interior of the northern portion of Bananal Island (Quatro Veados Lake) and the other located on the surroundings of the Javaés River (Mata Verde Lake) were analyzed for their palynological content and dated by AMS 14C. The results of this research are presented in 3 articles: the first one treaties about the mineralogy and geochemistry of the soils and sediments of Bananal Island, the bars and ravines along the Javaés River. Therefore, it discusses about the diversified nature of the minerals and chemical elements that the strata and horizons of these surface covers are composed, pointing to geological provenance, as well as the geochemical processes involved in the current and past dynamics of this landscape. The second article presents the dynamics of vegetation over the last 2000 years AP in the interior of Bananal Island and discusses its relationship with local climatic and edaphic conditions. The third article, on the other hand, describes the vegetational succession occurred in the last 400 years AP, based on the pollen record of sediments from a lake located on the Bananal Island surrounds, and analyzes the modern pollen spectrum in the region. The results obtained through this work present a highly diversified landscape in terms of its geoforms, sedimentary and pedogenetic coverings and geobotanical aspects resulting from the various moments of its geological history and which even today is dynamic and intriguing. The soils and sediments of this landscape are varied as their textures (sequences of sandy and clay materials) and mineralogical and chemical compositions, where primary minerals and derivatives of varied degrees of chemical weathering coexist in the same profile, showing moments of contrasting climatic conditions. Even, nowadays it is possible to observe in situ environments with variable dynamics (erosive, sedimentary, pedogenetic, etc.), as well as, several geochemical processes, such as those of oxidation of sandy bars and ravines and also the reductive processes of these ferruginized sands (sometimes, mistakenly confused for lateritic profiles), due to contact with organic acids produced by forest cover and hydromorphic conditions such as they are subjected. Regarding vegetation changes throughout the late Holocene, climate control was observed, but especially edaphic, since this area is seasonally flooded, a fact favored by the clayey nature of the soil surface horizons, the rainfall high rates as a prolonged rainy season (on average 6 months) and extensively flat terrain. Thus, factors such as flood duration and hydromorphism conditions stemming are responsible for controlling the installation of forests and/or savannas that characterize the region. So, the regency of a drier climate with the shortening rainy seasons that causes the water table rise, may represent favorable conditions for the development and advancement of the forest. On the other hand, a wetter climate with longer rainy seasons would cause flooding, covering larger areas and the soils would remain saturated for longer periods, a fact that undermines the advancement of the forest and allows the maintenance or even expansion of savannas, especially those dominated by grasses over the region. However, as already mentioned, the climatic conditions in this region control the expansion of forest formations, but they are not the only protagonists in this process, since the presence of wetland due to low and flat topography, clay soils, soil and sediment saturation is an effective impediment to the forest installation. Another factor responsible for replacing for gallery forest by savanna’s tree, for example, is the channel abandonment, a fact that is currently observed in the region, where it is possible to tread inside these old river beds, many of these places already enriched with species such as Curatella americana and Byrsonima sp among others. The Bananal Island, which is geologically inserted in the context of the Bananal Basin and is bathed by one of the largest hydrographic basins in the Brazilian territory (Araguaia-Tocantins), sets up as an extremely important landscape for understanding the wetlands dynamics and also from the savanna-forest ecotone areas during the Quaternary, since, it fits in both situations. The northern part of the island where this research was developed still needs studies. However, in general, this research has contributed to understand the functional dynamics of this landscape in face of the region climate and environmental changes, as well as to increase the knowledge about the transition landscapes between the Amazon forest and savannas, such as the paleoenvironmental knowledge is still restricted.
Appears in Collections:Teses em Geologia e Geoquímica (Doutorado) - PPGG/IG

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