Laveuf,C. and Cornu,S.(2009): A review on the potentiality of Rare Earth Elements to trace pedogenetic processes. Geoderma, 154, 1-12.


 This review aims at considering the use of REEs to trace pedogenetic processes, in order to quantify the respective contribution of the successive processes on pedogenesis.
 We first consider the origins and contents of REEs in soils, to assess their natural occurrence, and tackle the common data treatment used to interpret their concentrations. We review subsequently the impact of the different pedogenetic processes on the fate of REEs in soils: from their release into a soil solution by primary mineral (heavy minerals, phosphates, silicates and carbonates) dissolution during weathering, to their fixation on- or into main REE-bearing secondary minerals (clay minerals, Fe-Mn-oxides and carbonates), then their mobilization by plant recycling and organic matter, and finally the impact of argilluviation and redox processes on their fractionation. We conclude that REEs, much more than other trace elements, can interestingly trace the considered processes that are encountered in a large diversity of non-polluted soils arising from diverse parent materials. Weathering generally fractionates REEs and accounts for a significant part of the variation in the initial REE stock of the soils. Plant recycling induces a weak mobilization of REEs and their accumulation in topsoil. Argilluviation can be traced using the MREE-enrichment and the Eu-anomaly of the clay minerals. Redox processes can be traced by the Ce-anomaly caused by the precipitation of cerium on Mn-oxides. To use REEs as tracers of pedogenetic processes, we recommend to: (i) precisely characterize the REE-bearing minerals, (ii) adapt the choice of reference(s) for normalization and (iii) perform mass balance calculations.

Keywords: Lanthanides; Lessivage; Pedological carbonates; Redox processes; Weathering』

1. Introduction
2. Contents and origins of REEs in soils
3. Normalization and anomalies
4. Impact of weathering on REE mobilization
 4.1. REEs in primary minerals
  4.1.1. Minerals with high REE concentrations
  4.1.2. REE-bearing minerals abundant in soils and parent materials
 4.2. Impact of the properties of the different REEs in the solution on their distribution within weathering profiles
 4.3. Impact of the degree of weathering on the REE distribution into weathering profiles
5. Secondary mineral formation and REE immobilization
 5.1. Clay mineral formation
 5.2. Fe-Mn-oxide formation
 5.3. Formation of pedogenetic carbonates
6. Impact of biological recycling and organic matter on REE mobilization
 6.1. Biological recycling of REEs and REE mobilization
 6.2. Complexation and mobilization of REEs by organic matter
7. Remobilization of secondary mineral by pedogenetic processes and REE mobilization
 7.1. Argilluviation
 7.2. Hydromorphy and soil degradation
8. Conclusions