CARACTERIZAÇÃO DO MATERIAL ORIGINÁRIO DOS SOLOS DE PARTE DA QUADRÍCULA DE IBITIARA COMO SUBSÍDIO PARA ESTUDOS GEOQUÍMICOS

JOAQUIM JÚLIO DE OLIVEIRA, JAMES H. GALBRAITH, GASTON R. SIEFFERMANN

Resumo


The principal types of source material for soils in the western part of the Ibitiara quadrangle were determined with the objective of characterizing surface formations as an aid in geochemical prospecting. Three types of source material were differentiated in the depression of Paramirim River: aloctonous (transported), autocronous (residual) and alluvial-colluvial material. An an alysis of variance and comparison of means of data obtained from soils developed over aloctonous and autoctonous material showed significant differences between the two types for most of the studied parameters. Soils developed over aloctonous material display: a stone line over ferruginous duricrust or altered basement; weak, friable structure; a clayey-sand texture which varies to sandy-clay with depth; weak ion exchange capacity; pH near 5.0; predominantly kaolinitic clays; and low trace element content. Soils developed over autoctonous material are characterized by: high base saturation; block structure; pH above 6.0; high ion exchange capacity; predominantly montmorillonite clays; and high trace clement content. Within the two types no significant difference was found in most of the parameters with depth. Soils derived from alluvium-colluvium material show prismatic structure in the B horizon; pH greater than 6.0; high base saturation; high ion exchange capacity; and Na and Ca rich montmorillonite clays. Regional geochemical prospecting should be carried out with active stream sediment samples which will probably be a mixture of the different soil types and should register anomalies. Geophysical techniques should be used in areas where soils derived from aloctonous material is thick. Detailed geochemical prospecting may be employed with surface soil samples, but where the soils are developed from aloctonous material the anomalies will be epigenetic.

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