Lanthanides in granulometric fractions of Mediterranean soils. Can they be used as fingerprints of provenance?

J M Martín‐García,J Párraga,M V Fernández‐González,J Calero,R Delgado,A Molinero‐García

doi:10.1111/ejss.12730

J M Martín‐García, J Párraga + Show 4 more

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https://doi.org/10.1111/ejss.12730

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Abstract

There is geochemical interest in the lanthanides because they behave like a group that is closely related to the parent materials during surface processes, although they also undergo fractionation as a result of supergene dynamics. We analysed lanthanide concentrations (ICPms) in the granulometric fractions fine sand, clay and free forms of clay (FFclay‐CDB and FFclay‐Ox: extracted with citrate‐dithionite‐sodium bicarbonate and with ammonium oxalate, respectively) from a soil chronosequence of Mediterranean soils. There was a relative enrichment of heavy rare earth elements (HREE) in the clay fraction and its free forms with respect to fine sand. The clay free forms behaved as scavengers of lanthanides, and oxidative scavenging of cerium (Ce) in FFclay‐CDB was also detected. Lanthanide concentrations (lanthanum to gadolinium in fine sand; terbium to lutetium in clay) varied with soil age, and chronofunctions were established. There was a strong positive collinearity between most of the lanthanide concentrations. Furthermore, the value of the correlation index (Pearson's r) of the concentrations between couples of lanthanides (rCLC) decreased significantly with increasing separation between the elements in the periodic table; this has never been described in soils. Several geochemical properties and indices in the fine sand and clay soil fractions and in the geological materials of the Guadalquivir catchment showed, on the one hand, a genetic relation between them all, enabling the lanthanides to be used as fingerprints of provenance; on the other hand, fractionation between fine sand and clay showed these are actively involved in soil lanthanide dynamics.Highlights Are lanthanides from fine sand and clay genetically related to the geological materials? Lanthanide concentrations of fine sand and clay fit chronofunctions Pearson's r of lanthanide couples decreases when separation increases in the periodic table Free forms of clay are scavengers of lanthanides and concentrate HREE and cerium

Highlights

Quantities of rare earth elements (REE) in the Earth’s crust are of the order mg kg−1, and show some characteristic periodic behaviour such as: (i) light REE (LREE), low atomic weight (Ar), are more abundant than heavy REE (HREE) (British Geological Survey, 2011) and (ii) a strong linear correlationThe chemical signatures of the parent rock assemblages in a tectonic province can persist in the daughter sediments produced, and are preserved in the corresponding sedimentary deposits (Rollinson, 1993)
The Ln patterns, where the abundance of each Ln relative to that of a chondrite or shale is plotted on a logarithmic scale against the atomic number, or the geochemical ratios between lanthanides (e.g. heavy rare earth elements (HREE)/LREE, lanthanum/ytterbium (La/Yb), samarium/ytterbium (Sm/Yb), and so on, or the cerium and europium anomalies (Ce/Ce* and Eu/Eu*, respectively)) are used for studying the provenance of geological materials and for analysing pedogenic intensity (Rollinson, 1993; Moreno et al, 2006; Mongelli et al, 2014)
The ΣLREE increased with age (P1 > P2 > P3 > P4 > P5 > point bar sediments (PM)) and profile P4 was the richest in ΣHREE and Dy

Summary

Introduction

The chemical signatures of the parent rock assemblages in a tectonic province can persist in the daughter sediments produced, and are preserved in the corresponding sedimentary deposits (Rollinson, 1993) It has been suggested (Blundy & Wood, 2003) that the trace elements (< 0.1% by weight, as in the case of lanthanides) exhibit passive behaviour during supergene processes, resulting in their being excellent tracers of the source area of sediments and soil materials. This feature can be used in paleoenvironmental studies of sedimentary origin and tectonic setting (Chen et al, 2014; Och et al, 2014), and in soil studies such as pedogenic tracers (Laveuf & Cornu, 2009). Aeolian processes are common in Mediterranean soils (Delgado et al, 2003)

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