HAL Id: hal-02793268
https://hal.inrae.fr/hal-02793268
Submitted on 5 Jun 2020
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of
sci-entific research documents, whether they are
pub-lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
Are shallowest soil horizons suitable for U-series
soil-production rates determination?
Sophie Rihs, Alice Gontier, Eric Pelt, Damien Lemarchand, François
Chabaux, Marie-Pierre Turpault
To cite this version:
Sophie Rihs, Alice Gontier, Eric Pelt, Damien Lemarchand, François Chabaux, et al.. Are shallowest
soil horizons suitable for U-series soil-production rates determination?. Goldschmidt California 2014,
2014, Sacramento, Californie, United States. 2014. �hal-02793268�
Goldschmidt2014 Abstracts 2084
2084
Are shallowest soil horizons suitable
for U-series soil-production rates
determination?
S.RIHS*1,A.G
ONTIER1,E.PELT1,D.LEMARCHAND1, F.CHABAUX1AND M-P.TURPAULT2 1
LHyGeS/CNRS, Université de Strasbourg, France - (*correspondence: rihs@unistra.fr)
2
Laboratory of Biogeochemistry of Forest Ecosystems, INRA, Champenoux, France
Over the last decades, the U- and Th-series isotopes were successfully used to determine weathering rates in various environments. The objective of this study was to work out the origin of the complex trend often observed in the shallowest soil horizons, including the potential role of the vegetation. This study was carried out from the experimental forest site of Breuil (Morvan, France) developed by INRA-BEF, in which the native forest was partially clear-felled 37 years ago and replaced by monospecific plantations (Oak, Douglas, etc…). U-series disequilibrium were measured in four soil profiles developed on granite under the native forest, and replanted stands. Selective extractions of the Fe and Al amorphous and well crystallized oxides were performed in order to investigate the distribution of U and Th among these soil phases. A careful investigation of the lack of fractionation between U and Th isotopes during such extractions was performed, using U- and
Th-dopped synthetical oxides. The (234U/238U) and (230Th/234U)
activity ratios were measured in the amorphous oxides fraction extracted from several soil layers through one profile.
Our results demonstrate that some podzolic pedogenic processes significantly impact the shallowest soil layers (0-40cm) of this site. A significant part of U and Th is primary hold by Fe-bearing silicates, and land cover change can produce a large dissolution of these minerals, resulting in a important release of U and Th. Further pedogenic redistribution of these isotopes occurs in all the profiles,
yielding for instance to an enhance mobilization of 230Th
relative to all the other nuclides (including 232
Th). The clear
correlation between the (230Th/234U) ratios and the proportions
of amorphous and interlayer Al hydroxides suggests that in these soils the mobility of U and Th isotopes is strongly associated to Al dynamic, rather than Fe, despite the overwhelming reported control of U by Fe-oxides in oxidized environments. These pedogenic processes make the shallowest horizons of podzolic soils unsuitable for U-series dating. In contrast, a soil production rate can be deduced from the deepest soil layers which do not show such effects on the U- series nuclides.
