Tropical Spodosols in northeastern Amazonas State, Brazil

The white sand formation found in northeastern Amazonas State in Brazil showed three horizons—E, B, and C. The superficial horizon (E) was formed by sandy friable material of grayish to whitish colour with accumulations of organic matter in the form of wavy bands. The B horizon remained essentially sandy but showed a pale yellowish to orangish colour. The C horizon was friable with pink to creamy clayey sandy materials. In the contact zone between horizons B and C occurred an enrichment of organic matter, forming ortsteins. The profile structure, the upward increasing of quartz grains corrosion, and the predominance of quartz in the E horizon, and thus of iO2, instead of kaolinite, Al2O3, Fe2O3, and TiO2 that were more abundant in the C horizon, suggest that the white sands are the product of podzolization. Soil horizonation and accumulation of organic matter are governed by the active decomposition of the forest litter. These data also allow us to relate the Spodosols with the mottled and the saprolitic horizons of truncated lateritic profiles of the Alter do Chão Formation. This process of podzolization, which continues up to the present moment, is very aggressive since the studied profiles have developed in less than 3000 years and beneath the modern forest.