Dissertations and Theses

MAGNETIC SUSCEPTIBILITY OF ARCHEOLOGICAL BLACK EARTH AMAZON

Author: Ivanildo Amorim de Oliveira

Keywords: magnetism; mineralogy, indian black earth

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Summary

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.