Suscetibilidade magnética da terra preta arqueológica amazônica
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Data
2017-04-06
Autores
Oliveira, Ivanildo Amorim de [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O trabalho fornece informações sobre a formação da Terra Preta Arqueológica e sua relação com a expressão magnética proveniente de minerais litogenênicos, pedogenéticos e influência antrópica. Os resultados da presença de minerais ferrimagnéticos nos solos de Terra Preta Arqueológica (TPA) pode ser utilizada para compreender o processo de formação destes solos ou utilizar a expressão magnética como indicador agrícola para cultivo nestes solos. O trabalho possui dois objetivos: (i) verificar as influências geológicas, pedogenéticas e antrópicas na suscetibilidade magnética (SM) da TPA e (ii) estudar o potencial da SM como indicadora agrícola e ambiental para cultivo nestes solos. Foram abertos treze perfis com TPA e um perfil de floresta (solo não antropogênico), sendo coletadas amostras por horizonte em cada perfil. Próximo de um dos perfis com TPA foi estabelecido uma malha de 70 x 70 m e coletada amostras de solos em espaçamentos regulares de 10 m na profundidade de 0,0-0,20 m. Nas amostras coletadas, realizou-se a análise textural, fertilidade e análises mineralógicas. A SM foi determinada nos solos, nas cinzas das plantas e fragmentos de cerâmica encontradas nas TPAs. Na malha, também foi determinado o fluxo de CO2 (FCO2), temparatura e umidade. Há uma grande diversidade de minerais nas TPA, entre eles destacam-se: goethitas (0,16 a 21,86 g kg-1), hematitas (0,27 a 45,14 g kg-1), e maghemita (em baixas concentrações). A SM foi maior nos horizontes antrópicos dos perfis com TPA (6,49 ˣ 10-6 m3 kg-1) diminuindo em profundidade (0,15 ˣ 10-6 m3 kg-1). Nos perfis com terra preta arqueológica, a SM é maior que em subsuperfície, sendo esse comportamento contrário no solo não antropogênico, pois estes não sofrem influência do fogo e de minerais magnéticos presentes nos fragmentos de cerâmica. O estudo de variabilidade espacial mostrou que a SM pode ser utilizada no entendimento do potencial agrícola e ambiental em TPA. Locais com maior SM (4,7 a 5,1 ˣ 10-6 m3 kg-1) apresentaram 1,2 vezes mais CTC e emitiram 1,4 vezes menos CO2 em comparação a áreas com menores valores magnéticos (3,5 a 3,9 ˣ 10-6 m3 kg-1). Os resultados das relações de causa e efeito entre mineralogia e SM encontrados neste trabalho possam ajudar tanto na compreensão de processos naturais de formação da TPA quanto em processos antrópicos.
The study provides information about the formation of archeological black earth and relation with magnetic expression from lithogenic, pedogenic and anthropogenic minerals. The results of the presence of ferrimagnetic minerals in archeological black earth (ABE) soils can be used to understand the process of formation of these soils or to use magnetic expression as an agricultural indicator for cultivation in these soils. The study has two objectives: i) to verify the geological, pedogenetic and anthropogenic influences on the magnetic susceptibility (MS) of archeoloical black earth (ii) to study the potential of MS as agricultural and environmental indicator for cultivation in these soils. Thirteen archeological black earth profiles and a forest profile (non-anthropogenic soil) were opened, and samples were collected per horizon in each profile. Next to one of the profiles with ABE a grid of 70 m x 70 m was established and soil samples were collected at regular spaced every 10 m at the depth of 0.0-0.20 m. The samples collected determine the textural, fertility and mineralogical analyzes.The MS was determined in soils, in the ashes of plants and ceramic fragments found in ABE. In the grid, the CO2 flux (FCO2), temperature and moisture was also determined. There is a hight diversity of minerals in archeological black earth, among them goethites (0.16 to 21.86 g kg-1 ), hematite (0.27 to 45.14 g kg-1 ), and maghemite (In low concentrations). The MS was higher in the anthropic horizons of the profiles with ABE (6.49 10-6 m3 kg-1 ) decreasing in depth (0.15 10-6 m3 kg-1 ). In the profiles with archeological black earth, the MS is greater than in subsurface, and this behavior is contrary to the non-anthropogenic soil, since these are not affected by the fire and the magnetic minerals present in the ceramic fragments.The study of spatial variability showed that MS can be used in understanding the agricultural and environmental potential in ABE. Sites with higher MS (4.7 to 5.1 10-6 m3 kg-1 ) presented 1.2 times more CTC and emitted 1.4 times less CO2 compared to areas with lower magnetic values (3.5 to 3.9 10-6 m3 kg-1 ). The expect the results of cause and effect relationships between mineralogy and MS found in this study can help both in understanding of natural processes of archeological black earth formation and in anthropic processes.
The study provides information about the formation of archeological black earth and relation with magnetic expression from lithogenic, pedogenic and anthropogenic minerals. The results of the presence of ferrimagnetic minerals in archeological black earth (ABE) soils can be used to understand the process of formation of these soils or to use magnetic expression as an agricultural indicator for cultivation in these soils. The study has two objectives: i) to verify the geological, pedogenetic and anthropogenic influences on the magnetic susceptibility (MS) of archeoloical black earth (ii) to study the potential of MS as agricultural and environmental indicator for cultivation in these soils. Thirteen archeological black earth profiles and a forest profile (non-anthropogenic soil) were opened, and samples were collected per horizon in each profile. Next to one of the profiles with ABE a grid of 70 m x 70 m was established and soil samples were collected at regular spaced every 10 m at the depth of 0.0-0.20 m. The samples collected determine the textural, fertility and mineralogical analyzes.The MS was determined in soils, in the ashes of plants and ceramic fragments found in ABE. In the grid, the CO2 flux (FCO2), temperature and moisture was also determined. There is a hight diversity of minerals in archeological black earth, among them goethites (0.16 to 21.86 g kg-1 ), hematite (0.27 to 45.14 g kg-1 ), and maghemite (In low concentrations). The MS was higher in the anthropic horizons of the profiles with ABE (6.49 10-6 m3 kg-1 ) decreasing in depth (0.15 10-6 m3 kg-1 ). In the profiles with archeological black earth, the MS is greater than in subsurface, and this behavior is contrary to the non-anthropogenic soil, since these are not affected by the fire and the magnetic minerals present in the ceramic fragments.The study of spatial variability showed that MS can be used in understanding the agricultural and environmental potential in ABE. Sites with higher MS (4.7 to 5.1 10-6 m3 kg-1 ) presented 1.2 times more CTC and emitted 1.4 times less CO2 compared to areas with lower magnetic values (3.5 to 3.9 10-6 m3 kg-1 ). The expect the results of cause and effect relationships between mineralogy and MS found in this study can help both in understanding of natural processes of archeological black earth formation and in anthropic processes.
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Palavras-chave
Magnetismo, Mineralogia, Terra preta de índio