『Abstract
In geologically stable areas in the tropics, climatic changes
and geomorphic cycles give origin to polygenic soils. Polygenesis
involves new soil formation phase taking place on preweathered
materials from previous phases, resulting in soils with rather
similar chemical and mineralogical properties. Polygenetic soils
from Minas Gerais, Brazil, were investigated with the purpose
of distinguishing mineralogical aspects in relation to polygenesis.
The soil materials were studied by micromorphology and electron
microscope and analyzed by XRD. All soils are strongly weathered
and even show weathered grains of ilmenite and quartz. The soils
show two phases of kaolinite formation (pseudomorphs after mica
and precipitation from solution) and of accumulation of iron compounds.
Desilication causes gibbsite formation from kaolinite, occasionally
even in the deep saprolite. Superposed processes can be due to
progressively deeper weathering or to changes of the external
environment.
Keywords: Oxisols; Polygenesis; Soil mineralogy; Soil micromorphology;
Soil formation』
1. Introduction
2. Materials
3. Methods
4. Results and discussion
4.1. Mineralogy and weathering
4.2. Micas
4.3. Kaolinite
4.4. Gibbsite
4.5. Iron oxides
4.6. Quartz
4.7. Ilmenite and anatase
4.8. Accessory minerals
5. Conclusions
Acknowledgements
References