Deciphering the weathering processes using environmental mineralogy and geochemistry: Towards an integrated model of laterite and podzol genesis in the Upper Amazon Basin

Abstract

This article reports major results from collaborative research between France and Brazil on soil and water systems, carried out in the Upper Amazon Basin. It reveals the weathering processes acting in the partly inundated, low elevation plateaus of the Basin, mostly covered by evergreen forest. Our findings are based on geochemical data and mineral spectroscopy that probe the crystal chemistry of Fe and Al in mineral phases (mainly kaolinite, Al-and Fe-(hydr)oxides) of tropical soils (laterites). These techniques reveal crystal alterations in mineral populations of different ages and changes of metal speciation associated with mineral or organic phases. These results provide an integrated model of soil formation and changes (from laterites to podzols) in distinct hydrological compartments of the Amazon landscapes and under altered water regimes.

Iron and silicon isotope behaviour accompanying weathering in Icelandic soils, and the implications for iron export from peatlands

“…6). This is consistent with observations in a tropical setting in Brazil, where Fe is leached from soils as Fe-organic complexes in lowlands characterised by poorly drained (waterlogged) organic-rich environments involving Fe reductive dissolution in anoxia Lucas et al, 1987;Fritsch et al, 2011).…”

“…Colloidal Fe exported from soils may be present as Fe oxyhydroxide nanoparticulates and/or Fe-organic complexes (Thompson et al, 2011). In the context of organic-rich soils, the contribution of Feorganic complexes transported from soils Lucas et al, 1987;Fritsch et al, 2009Fritsch et al, , 2011 to rivers is thought to explain the heavy d 57 Fe ratio of the dissolved fraction of the Rio Negro river relative to the dissolved fraction of the Amazon river, Brazil (Bergquist and Boyle, 2006;dos Santos Pinheiro et al, 2014). In Iceland, the available d 57 Fe data for H soil solutions suggests that the release of colloidal Fe from Histosols may contribute to the colloidal heavy d 57 Fe of rivers draining peat soils.…”

Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia

“…1B. Those surfaces are mainly composed of laterites developed on Paleozoic to the Archean basement and on clastic sedimentary rocks (Fritsch et al, 2011;Ishida et al, 2014;Lucas et al, 2012). A scattered patchwork of a few absolute ages is available for lateritic formations from the central Amazonia (Fig.…”

Estudo da matéria orgânica e composição elementar de solos arenosos de regiões próximas a São Gabriel da Cachoeira no Amazonas

“…A bacia amazônica é uma das maiores bacias hidrográficas da superfície emersa do planeta, com uma área total de 6,5 milhões de km 2 (Fritsch et al, 2011) ) (Fritsch et al, 2011). Contudo, esta riqueza natural vem sofrendo pressão antrópica traduzida pela exploração desordenada de madeira e expansão dos sistemas agrícolas e outras formas de uso do solo (Furtado, 1997).…”