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Disentangling the influence of lithology and non-provenance factors on the geochemistry of rare earth elements: a study of fine-grained sediments from the Sava River headwaters (Slovenia, Croatia)

Purpose Rare earth elements (REE) are generally considered immobile and therefore suitable as provenance proxies. In the fluvial environment, however, several non-provenance factors may affect their content and obscure the accurate identification of sediment sources. This study, therefore, focuses on separating the lithological signal from the influence of anthropogenic activity and hydrodynamic sorting on REE geochemistry of fine-grained sediments. The study area comprises the upper catchment of the Sava River, the largest Danube tributary. Materials and methods The samples were characterised with respect to their mineralogical, granulometric and geochemical composition. The main factors governing the REE distribution were unravelled by the combined use of statistics (multidimensional scaling — MDS) and element ratios. Results and discussion Mineralogical analysis showed the dominance of carbonates in the upper reaches, while detritus, rich in aluminosilicates and quartz, predominated in other parts of the basin. Concentrations of REE ranged from 28.6 to 197 mg kg−1 in the Sava River and from 77.6 to 236 mg kg−1 in tributaries. Grain size changes due to hydrodynamic sorting influenced REE content more than lithology in the Sava River. Tributaries were more affected by the interaction between source lithology and anthropogenic activities, of which agriculture was the most important. Elemental ratios REE/Al and P/Al were found to be well- suited to estimate the influence of P- fertiliser on REE content. Conclusions This paper points out the need for detailed studies of the geochemical composition of REE in fluvial sediments and careful consideration of the influence of hydrodynamic sorting and anthropogenic activity when REE geochemistry is used as a provenance tool.

Anthropogenic impact ; Hydrodynamic sorting ; REE geochemistry ; Sediment sources ; The Sava River

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