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Behavior of Sm and Nd in a lateritic soil profile

Viers, Jérôme and Wasserburg, G. J. (2004) Behavior of Sm and Nd in a lateritic soil profile. Geochimica et Cosmochimica Acta, 68 (9). pp. 2043-2054. ISSN 0016-7037. doi:10.1016/j.gca.2003.10.034.

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A study of lateritic soils and samples of ground and river waters was carried out in the Nsimi-Zoetele, a tropical watershed in the southern Cameroon. The Nd isotopic compositions and concentrations of Nd and Sm were determined. It was found that the Nd isotopic composition of the river waters was much more radiogenic than the parent rocks, and that the Nd in the waters is not homogeneous but is carried by different dissolved and complexed components that are not isotopically homogenized. The soil profile shows a regular increase in ε_(Nd) going from the parent rock (ε_(Nd) = −36) to ε_(Nd) = −18 near the top of the profile. The Nd transported in the river is thus not representative of the parent rock but reflects the results of differential weathering of constituent minerals and the redeposition of REE in phosphates and a significant contribution of radiogenic Nd from dust. The concentration of Nd in the river water is far above that found in temperate climate rivers and thus this type of tropical river may play a dominant role in the marine Nd and REE budget. It is suggested that the correlation of REE with DOC is related to DOC fixing some dissolved REE but that the REE in solution is governed by other mechanisms. No major shifts were found in Sm/Nd; however, a regular progression from the parent rock through the lateritic profile was found. The upper laterite profile shows large, almost uniform depletions in all REE below Tb and enrichment above. Complementary behavior was found in the lower part of the section. The concentration of Nd relative to the immobile elements Zr and Ti in the laterite is depleted by a factor of ∼10. Th, Nd and Sm are enriched in the lowest zone sampled and must reflect redeposition of REE from the upper part of the weathering section and is associated with phosphate formation. It is concluded that the soil evolution involves both differential dissolution of primary phases from the parent rock, significant to major input of REE from atmospheric dust from other regions, and the formation of diagenetic phases, particularly phosphates.

Item Type:Article
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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 2004 Elsevier Ltd. Received March 14, 2003; accepted in revised form October 14, 2004. This work was done during a fellowship at Caltech. Support for this work was from DOE DE-FG03-88ER13851. Caltech Division Contribution 8898(1100). The authors dedicate this small report to George Brimhall who has pioneered the study of weathering in all sorts of climates. The Nsimi-Zoetele watershed was designated since 1994 as a pilot-site for intertropical geosphere environmental studies, by the French scientific programs PEGI (Programme d’Etude de la Géosphère Intertropicale, CNRS/IRD) and DYLAT (Dynamique de la Couverture Latéritique, IRD). We thank the French “Ministère de l’Education Nationale,” the INSU/CNRS and IRD agencies for funding. The samples used in this study belong to these agencies. We would like to greatly acknowledge Henry Ngo and Jim Chen for their support in the chemistry and in the TIMS measurements. Bernard Dupré, Jean-Jacques Braun, Frederic Coppin, Rémi Freydier and Magnus Land are thanked for their helpful comments. Associate editor: G. R. Helz
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG03-88ER13851
Ministère de l’Education NationaleUNSPECIFIED
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Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences8898
Lunatic Asylum Lab1100
Issue or Number:9
Record Number:CaltechAUTHORS:20131119-074608283
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Official Citation:Jérôme Viers, G.J. Wasserburg, Behavior of Sm and Nd in a lateritic soil profile, Geochimica et Cosmochimica Acta, Volume 68, Issue 9, 1 May 2004, Pages 2043-2054, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42546
Deposited By: Ruth Sustaita
Deposited On:19 Nov 2013 16:29
Last Modified:10 Nov 2021 16:24

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