Evolução geomorfológica e mudanças paleo-hidrológicas na porção sul do Pantanal: a planície interleques do rio Negro e leques fluviais coalescentes
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Data
2016-12-05
Autores
Merino, Eder Renato [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O Pantanal é uma das maiores áreas alagáveis do planeta cuja dinâmica de inundação e o aporte sedimentar dos rios são os principais agentes que controlam a evolução de suas paisagens. Até o momento, as pesquisas sobre o trato deposicional moderno da Bacia do Pantanal têm se concentrado na planície tronco do rio Paraguai e nos sistemas de megaleques. Todavia, pouco tem-se realizado nas planícies interleques que são importantes áreas de captação e distribuição de águas e sedimento dos sistemas distributivos coalescentes. A planície interleque do rio Negro, limitada ao norte pelos megaleques do Taquari e do Negro e ao sul pelos megaleques do Aquidauana, Taboco e Miranda, constitui umas das principais áreas de captação da porção sul do Pantanal. A fim de compreender a evolução da planície interleques do rio Negro e sua interação com os sistemas deposicionais adjacentes foram conduzidos estudos geomorfológicos e hidrossedimentológicos a partir da integração de dados orbitais, sedimentológicos e geocronológicos. Também foram realizados estudos sobre a geomorfologia do megaleque do rio Aquidauana, um dos únicos grandes sistemas da borda sul sem estudos sistemáticos. Com isso buscou-se identificar, mapear e caracterizar de forma integrada os principais registros de mudanças paleo-hidrológicas na porção sul da bacia. Imagens de satélite e modelos digitais de elevação foram utilizados na compartimentação geomorfológica e na identificação de mudanças paleo-hidrológicas. Levantamento da descarga fluvial por ADCP (Accoustic Doppler Current Profiler) e coleta de carga sedimentar suspensa e de fundo permitiram a caracterização hidrossedimentológica dos principais rios da porção sul da bacia. Datações por luminescência opticamente estimulada (LOE) e descrição de fácies sedimentares permitiram o estabelecimento das idades das feições morfológicas bem como caracterização de descrição da arquitetura dos depósitos. A planície interleques do rio Negro foi dividida em sete compartimentos distintos: 1) planície interleques confinada; 2) lobo progradacional do rio Negro; 3) zona de alagamento permanente; 4) lobo deposicional moderno do rio Aquidauana; 5) zona de transição; 6) planície com lagoas interligadas por canais intermitentes; 7) planície em degradação por rede de canais tributários. O megaleque do rio Aquidauana foi compartimentado em três domínios: 1) lobo deposicional pleistocênico; 2) cinturão de meandros em vale inciso; e 3) lobo distributário atual. Modelo evolutivo da porção sul do Pantanal foi proposto com base no reconhecimento e estabelecimento da cronologia relativa e absoluta das principais mudanças paleo-hidrológicas ocorridas nos sistemas deposicionais desde o Pleistoceno Médio ao recente, dos quais as principais feições indicativas de mudanças foram: 1) rede de paleocanais distributários abandonados; 2) paleocinturão com mais 70 km de extensão, mapeado desde a porção central da planície interleques do rio Negro até próximo à foz do rio Miranda; 3) diferentes gerações de paleocinturões no megaleque do rio Miranda; 4) avulsão fluvial do rio Aquidauana que fez com que o rio deixasse de ser afluente do rio Negro e se tornasse afluente do rio Miranda 60 km para jusante.
The Pantanal wetland, in central-west Brazil, is one of largest seasonally flooded freshwater wetlands in the globe, with unique landscapes and a hotspot for wildlife, being rivers flood dynamics and its sediment load major agents in the landscape evolution. Until now, researches about the basin modern alluvial tract are focused on the Paraguay river trunk plain and on the megafan systems. Nonetheless, little has been done in interfan plains that are important areas of catchment and distribution of water and sediment from the coalescing distributary systems. The Negro river interfan plain, bordered to the north by the Taquari and the Negro and to the south by the Aquidauana, Taboco and Miranda, is one of the main catchment area of the Pantanal. In order to understand the evolution of the Negro rive interfan plain and its interaction with the adjacent depositional systems were performed geomorphological and hydrosedimentological studies based on the integration of orbital, sedimentological and geochronological data. Studies were also conducted on the Aquidauana megafan, one of the only major systems of the southern border without geomorphological studies. Thus, it was possible to identify, map and characterize the major records of paleohydrological changes in the southern portion of the basin in an integrated way. Satellite imagery and digital elevation models were used on the geomorphological zonation and for identifying paleohydrological changes. Survey of river discharge by ADCP (Accoustic Doppler Current Profiler), and collection of suspended and bed sediment load allowed hydrossedimentological characterization of the main rivers of the southern portion of the basin. Optically stimulated luminescence (OSL) dating and sedimentary description of facies allowed either the establishment of absolute ages of morphological features and characterization of the deposits architecture. The Negro interfan plain was divide in seven compartments: 1) confined interfan plain; 2) Negro river progradational lobe; 3) permanent flooded zone; 4) Aquidauana river modern depositional lobe; 5) transition zone; 6) plain with lakes interconnected by intermittent channels; and 7) degradational plain by tributary channels. The Aquidauana megafan was divide into three areas: 1) Pleistocene degrational lobe; 2) entrenched meander belt; and 3) modern depositional lobe originated by avulsion. Evolutional model of the southern Pantanal was proposed based on the recognition and establishment of relative and absolute chronology of major paleohydrological changes in the depositional systems from the Middle Pleistocene to recent, being the main changes: 1) network of abandoned distributary paleochannels; 2) over 70 km long paleomeander belt, mapped from the central portion of the Negro river interflan plain to near the mouth of the Miranda river; 3) different generations of paleomeander belts on the river Miranda megafan; 4) fluvial avulsion on the Aquidauana river that made the river change its mouth towards 60 km downstream in the river Miranda mouth.
The Pantanal wetland, in central-west Brazil, is one of largest seasonally flooded freshwater wetlands in the globe, with unique landscapes and a hotspot for wildlife, being rivers flood dynamics and its sediment load major agents in the landscape evolution. Until now, researches about the basin modern alluvial tract are focused on the Paraguay river trunk plain and on the megafan systems. Nonetheless, little has been done in interfan plains that are important areas of catchment and distribution of water and sediment from the coalescing distributary systems. The Negro river interfan plain, bordered to the north by the Taquari and the Negro and to the south by the Aquidauana, Taboco and Miranda, is one of the main catchment area of the Pantanal. In order to understand the evolution of the Negro rive interfan plain and its interaction with the adjacent depositional systems were performed geomorphological and hydrosedimentological studies based on the integration of orbital, sedimentological and geochronological data. Studies were also conducted on the Aquidauana megafan, one of the only major systems of the southern border without geomorphological studies. Thus, it was possible to identify, map and characterize the major records of paleohydrological changes in the southern portion of the basin in an integrated way. Satellite imagery and digital elevation models were used on the geomorphological zonation and for identifying paleohydrological changes. Survey of river discharge by ADCP (Accoustic Doppler Current Profiler), and collection of suspended and bed sediment load allowed hydrossedimentological characterization of the main rivers of the southern portion of the basin. Optically stimulated luminescence (OSL) dating and sedimentary description of facies allowed either the establishment of absolute ages of morphological features and characterization of the deposits architecture. The Negro interfan plain was divide in seven compartments: 1) confined interfan plain; 2) Negro river progradational lobe; 3) permanent flooded zone; 4) Aquidauana river modern depositional lobe; 5) transition zone; 6) plain with lakes interconnected by intermittent channels; and 7) degradational plain by tributary channels. The Aquidauana megafan was divide into three areas: 1) Pleistocene degrational lobe; 2) entrenched meander belt; and 3) modern depositional lobe originated by avulsion. Evolutional model of the southern Pantanal was proposed based on the recognition and establishment of relative and absolute chronology of major paleohydrological changes in the depositional systems from the Middle Pleistocene to recent, being the main changes: 1) network of abandoned distributary paleochannels; 2) over 70 km long paleomeander belt, mapped from the central portion of the Negro river interflan plain to near the mouth of the Miranda river; 3) different generations of paleomeander belts on the river Miranda megafan; 4) fluvial avulsion on the Aquidauana river that made the river change its mouth towards 60 km downstream in the river Miranda mouth.
Descrição
Palavras-chave
Planície interleques, Megaleques, Compartimentação geomorfológica, Hidrologia, Sensoriamento remoto, Datação LOE, Interfan plain, Megafans, Geomorphological zonation, Hydrology, Remote sensing, OSL dating