Full text
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| Author(s): |
Claudia Moré de Lima
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB) |
| Defense date: | 2008-08-27 |
| Examining board members: |
Luiz Carlos Ruiz Pessenda;
Dilce de Fátima Rossetti;
Pablo Vidal Torrado
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| Advisor: | Luiz Carlos Ruiz Pessenda |
| Abstract | |
Considered the largest fluvial-marine island of the world, with approximately 48.000 km2, the Marajó Island is located in the Brazilian equatorial area, in the Pará State coast. It presents two different domains related to the geology and vegetation. In the west domain dominate soils developed on Pós Barreiras sediments (plio-pleistocenics) covered by the Amazonian Forest, while in the east domain dominate holocenic sediments derived of fluvial/estuarine environment, at present deactivated. In this sector are located the natural savanna. The objective of this work consisted of to apply the carbon isotopes (12C, 13C and 14C) of soil and sediment organic matter, in order to evaluate possible changes in the vegetation domains, in terms of C3 and C4 plants during the Late Quaternary, and inferences about their causes. The results were associated with field observations, petrographic, sedimentologic, chemical, sponge spicules and nitrogen isotope analyses and bibliography, being possible to distinguish three environmental changes related to the geology and vegetation in the eastern Marajó Island during Late Pleistocene (approximately 16.000 years BP) to the Holocene. In the central section of the Marajó Island were obtained the oldest ages of the sediment organic matter of a paleochannel. In this place, in the interval Late Pleistocene - Early Holocene, the carbon isotope data are characteristic of C3 plants, except for two points corresponding to 16.118 ± 60 years BP and approximately 13.000 years BP, with values of \'delta\' 13CPDB of -20,4 and -22,1 , respectively. The relation between the carbon and nitrogen isotopes data, indicate the presence of terrestrial plants (C4 grass) in this area, at present covered by arboreal vegetation, probably associated to a drier climate. The presence of charred wood fragments and unstable minerals to the chemical weathering as feldspar, hornblend and biotite in the sediments, confirm the hypothesis. In other points, during Middle/Late Holocene (between ~5.000 and 3.000 years BP) the carbon isotopes and charred wood fragments data, indicate that a vegetation constituted of C3 plants (trees) in the eastern sector of the island, was gradually substituted by C4 grasses, initiating the formation of savanna vegetation in the Marajó Island, associated to a drier climate. In this same period, the channels were abandoned, as indicated by the fining upward the paleochannel sediments and the color change (grey to brown orange) of the clayey sediments of the floodplain, associated to the deposition of a reducing environment to an oxidizing environment. In the reducing interval, in some profiles it was observed the formation of pirite and jarosite. Previous studies show that the channels abandonment processes is associated to tectonic Cenozoic events in the area. The more enriched isotope carbon data of soil organic matter observed in the Southwestern sector of the island, indicated in the period of ~7.000 and 3.000 years BP, an opening of the arboreal vegetation and/or the presence of C4 plants, probably associated to a drier climate. During the Late Holocene the channels were filled out and abandoned. More depleted carbon isotope data of the organic matter, indicates the implementation of the arboreal vegetation on the channels, establishing the modern conditions observed at the eastern section of the Island, with paleochannels covered by arboreal vegetation (C3 plants) and the floodplain covered by grassland vegetation (C3 and C4 plants). The sponge spicules and nitrogen isotope analysis, indicate the eastern section as a transitional deposition system (estuarine) during the Late Quaternary (AU) | |
| FAPESP's process: | 06/52173-2 - Vegetation dynamic and climatic inferences in the Late Quaternary in the region of the Ilha de Marajó, PA, using carbon isotopes (12C, 13C, 14C) of organic matter from the soils and sediments |
| Grantee: | Claudia Moré de Lima |
| Support Opportunities: | Scholarships in Brazil - Master |