Genesis of a mottled horizon by Fe-depletion within a laterite cover in the Amazon Basin.

Vania Rosolen (1) , Mathieu Lamotte (2, 1) , René Boulet (1) , Jean Trichet (3) , Olivier Rouer (3) , Adolpho José Melfi (1)

1 USP - Universidade de São Paulo = University of São Paulo
2 IRD
3 ISTO - Institut des Sciences de la Terre d'Orléans

A mottled horizon in a laterite cover (without any duricrust) was studied by microscopy and quantitative chemical microanalysis. Apart from the voids, light red spots consisting of Fe-rich particles (≈2 μm) are set in clayey plasma. Dark red spots consisted of concentrations of Fe-rich particles. These patterns are inherited. On the border of structural or biological voids, where Fe-depletion features are systematic, gray or yellow spots result from dissolution of the Fe-rich particles and impregnation of the plasma by iron, respectively. The present Fe-depletion is the dominant process that explains the mottled differentiation and the absence of lateritic duricrust.

Keywords: microscopy; scanning electron microscopy; quantitative chemical microprobe; iron; plinthic Cambisol; Brazil

Domains: Geochemistry; Global Changes

Vania Rosolen, Mathieu Lamotte, René Boulet, Jean Trichet, Olivier Rouer, et al.. Genesis of a mottled horizon by Fe-depletion within a laterite cover in the Amazon Basin.. Comptes Rendus Géoscience, 2002, 334, pp.187-195. ⟨10.1016/S1631-0713(02)01721-2⟩. ⟨hal-00077598⟩