Gênese e caracterização geoquímica e mineralógica para a prospecção de argilas altamente aluminosas (Formação Marília)
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Data
2021-04-22
Autores
Coelho, Carla Vanessa de Sousa [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O estudo objetivou a prospecção e caracterização geoquímica e mineralógica das argilas altamente aluminosas na região de Uberaba, formadas sobre a Formação Marília. O trabalho foi compartimentado em três escalas de estudo com aplicações de métodos e técnicas complementares: (1) métodos cartográficos e sensoriamento remoto aéreo com o uso de VANT (Veículo Aéreo Não Tripulado); (2) descrições de campo e coletas de amostras para análises químicas e mineralógicas; e (3) ensaios geofísicos. A partir dos resultados cartográficos e do uso VANT, duas áreas foram selecionadas, a primeira uma área úmida situada no topo do platô e a segunda uma área com ligação direta com o sistema de drenagem situada na borda do platô, onde são encontrados os Latossolos e Gleissolos. Para validar o modelo da gênese das argilas altamente aluminosas, que propõe que estes materiais são formados a partir do desmantelamento de couraças ferruginosas em conseqüência ao aumento da umidade, os ensaios geoquímicos e mineralógicos foram aplicados para sete perfis de solo, duas amostras de couraça e uma de arenito, além de dois perfis previamente estudados. Os resultados mostram que a mineralogia dos materiais é composta pela associação de caulinita, gibbsita, hematita, goethita e quartzo independente do nível de hidromorfia, e que os materiais passam por processo de dessilicificação com aumento na concentração de Al. Com os resultados da tomografia de resistividade elétrica foram confeccionados modelos 2D e 3D para as duas áreas que mostrou os padrões de distribuição dos horizontes saturados em água, a elevação do nível freático acima da superfície topográfica no período de chuva cria as condições ideais para a redução do Fe que é facilmente transportado para as partes mais baixas do platô. Além dos horizontes com água, foi delimitada a superfície da couraça, reforçando a hipótese de que a formação dos materiais altamente aluminosos está associada à presença de níveis ferruginosos encouraçados. O modelado plano da chapada, sob condições climáticas adequadas e prolongadas, favoreceu a formação de cobertura encouraçada ferruginosa. Após o término da deposição sedimentar, a superfície foi truncada por longos períodos de erosão que aplainaram o relevo. Atualmente, o clima é tropical com forte sazonalidade e aumento da umidade. Esta nova condição hídrica, de saturação, somada às condições de estabilidade tectônica e vegetação exerce influência na lixiviação e na perda ferro, proporcionando a formação dos horizontes com argilas altamente aluminosas e os resultados geoquímicos, mineralógicos e geofísicos demonstram essa relação.
This study aimed the prospection and geochemical and mineralogical characterization of high alumina clays in Uberaba region, developed above the Marilia Formation. The study was compartmentalized in three work scales, applying complementary methods and techniques: (1) cartographic tools and aerial remote sensing, using with unmanned aerial vehicle (UAV); (2) field descriptions and sample collection for chemical and mineralogical analysis; and (3) geophysical testing. With the cartographic and UAV results, two areas were selected, the first a wetland located at the top of the plateau and the second an area with direct connection to the drainage system at the edge of the plateau, where Oxisols and Gleysols are found. To validate the genesis model for the high alumina clays, which suggests that these materials are developed from the dismantling of ferruginous duricrusts as a consequence of the increase in humidity, the geochemical and mineralogical tests were applied to seven soil profiles, two duricrust and one sandstone sample, as well as two previously studied profiles. The results showed that the materials mineralogy is composed by the association of kaolinite, gibbsite, hematite, goethite and quartz despite the hydromorphic degree, and that the materials go thru a desilicification process with increase of Al concentration. With the results of the electrical resistivity tomography models 2D and 3D were assembled for the two sites and it showed the distribution patterns of the horizons saturated with water, the increase of the groundwater level above the topographic surface in the rain period creates the ideal conditions for Fe reduction, which is easily transported to the lower levels of the plateau. Besides the water saturated horizons, the duricrust surface was delineated, reinforcing the hypothesis that the development of the high alumina materials is connected to the presence of the iron-rich duricrusts. The flat shaped form of the plateau, under adequate and prolonged climatic conditions favored the development of ferruginous duricruts. After the end of the sedimentary deposition, the surface was truncated by long periods of erosion that leveled the relief. Presently the climate is tropical with strong seasonality and increase of humidity. This new hydric condition, of saturation, added to the tectonic stability conditions and vegetation exerts influence in iron loss and lixiviation, allowing the formation of the high alumina clay horizons and the geochemical, mineralogical and geophysical results demonstrate this relation.
This study aimed the prospection and geochemical and mineralogical characterization of high alumina clays in Uberaba region, developed above the Marilia Formation. The study was compartmentalized in three work scales, applying complementary methods and techniques: (1) cartographic tools and aerial remote sensing, using with unmanned aerial vehicle (UAV); (2) field descriptions and sample collection for chemical and mineralogical analysis; and (3) geophysical testing. With the cartographic and UAV results, two areas were selected, the first a wetland located at the top of the plateau and the second an area with direct connection to the drainage system at the edge of the plateau, where Oxisols and Gleysols are found. To validate the genesis model for the high alumina clays, which suggests that these materials are developed from the dismantling of ferruginous duricrusts as a consequence of the increase in humidity, the geochemical and mineralogical tests were applied to seven soil profiles, two duricrust and one sandstone sample, as well as two previously studied profiles. The results showed that the materials mineralogy is composed by the association of kaolinite, gibbsite, hematite, goethite and quartz despite the hydromorphic degree, and that the materials go thru a desilicification process with increase of Al concentration. With the results of the electrical resistivity tomography models 2D and 3D were assembled for the two sites and it showed the distribution patterns of the horizons saturated with water, the increase of the groundwater level above the topographic surface in the rain period creates the ideal conditions for Fe reduction, which is easily transported to the lower levels of the plateau. Besides the water saturated horizons, the duricrust surface was delineated, reinforcing the hypothesis that the development of the high alumina materials is connected to the presence of the iron-rich duricrusts. The flat shaped form of the plateau, under adequate and prolonged climatic conditions favored the development of ferruginous duricruts. After the end of the sedimentary deposition, the surface was truncated by long periods of erosion that leveled the relief. Presently the climate is tropical with strong seasonality and increase of humidity. This new hydric condition, of saturation, added to the tectonic stability conditions and vegetation exerts influence in iron loss and lixiviation, allowing the formation of the high alumina clay horizons and the geochemical, mineralogical and geophysical results demonstrate this relation.
Descrição
Palavras-chave
Argila altamente aluminosa, Couraça ferruginosa, Latossolo, Gleissolo, Geofísica, Sensoriamento remoto, High aluminous clay, Ferruginous duricrust, Oxysol, Gleysol, Geophysics, Remote sensing