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Clays and Clay Minerals; June 2007; v. 55; no. 3; p. 253-259; DOI: 10.1346/CCMN.2007.0550303
© 2007 Clay Minerals Society
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INHERITANCE VS. NEOFORMATION OF KAOLINITE DURING LATERITIC SOIL FORMATION: A CASE STUDY IN THE MIDDLE AMAZON BASIN

Etienne Balan1,2,*, Emmanuel Fritsch1,2, Thierry Allard2 and Georges Calas2

1 IRD-UMR 161 CEREGE, Europole Méditerranéen de l’Arbois BP 80, 13545 Aix-en-Provence cedex, France
2 Institut de Minéralogie et Physique des Milieux Condensés (IMPMC), UMR CNRS 7590, Université Paris VI, Université Paris VII, IPGP, 4 Place Jussieu, 75252 Paris Cedex 05, France

* E-mail address of corresponding author: Etienne.Balan{at}impmc.jussieu.fr

The tropical weathering of sedimentary kaolin deposits from the plateaux surrounding Manaus (Alter do Chao formation, Amazon basin, Brazil) leads to the in situ formation of thick kaolinitic soils. The structural changes of kaolinite have been investigated quantitatively by infrared spectroscopy and electron paramagnetic resonance. Both techniques consistently show that each sample contains two types of kaolinite in various proportions. The progressive decrease in kaolinite order from the bottom to the top of the profile results from the gradual replacement of an old population of well-ordered kaolinite, typical of the underlying sedimentary kaolin, by a more recent generation of poorly ordered soil kaolinite. The vertical pattern of kaolinite replacement differs from that of the transformation of Fe oxides and oxy-hydroxides previously observed in the same profile. The inherited fraction of well-ordered kaolinite ranges from 60% at a depth of 9 m to 30% in the upper levels of the soil. The persistence of sedimentary kaolinite in the upper horizons suggests that the rate of kaolinite transformation is relatively slow at the time scale of lateritic soil formation. Kaolinite inheritance unlocks the lateritic record of past weathering conditions.

Key Words: Disorder • EPR • Infrared • Kaolinite • Laterite




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 American MineralogistHome page
M. Blanchard, M. Lazzeri, F. Mauri, and E. Balan
First-principles calculation of the infrared spectrum of hematite
American Mineralogist, July 1, 2008; 93(7): 1019 - 1027.
[Abstract] [Full Text] [PDF]


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