Geochemical characteristics of rare earth elements in sediments of the North China Plain: implication for sedimentation process

Rare earth elements (REE) are powerful tracers for our understanding of sedimentary provenance and depositional processes. The present study investigated geochemical characteristics of REE in 226 sediment samples collected from piedmont, central and littoral plains of the North China Plain. Results showed that average total REE concentrations exhibited a decrease trend as piedmont > central > littoral, and 82%, 70% and 67% samples had total REE concentrations higher than the value of Upper Continental Crust (UCC). The variation in REE concentrations was associated with sedimentary provenance and sediment lithology. Ternary diagrams of sandstone classification and Al2O3-CaO+Na2O-K2O reflected that sediments originated from greywackes and they have been experienced an incipient to intermediate chemical weathering with piedmont sediments to a higher degree. Average Chemical Index of Alteration values are 68, 51 and 55 in piedmont, central and littoral sediments, respectively. Sediment chondrite-normalized patterns were characterized by Light REE (LREE) enrichment over Heavy REE (HREE) and coherent negative Eu anomalies (Eu/Eu* ranging between 0.57 and 1.00). (La/Yb)CN ranged from 5.98 to 11.37, and from 7.2 to 10.42, and from 4.94 to 8.15 in three zones, indicating REE fractionation from piedmont to littoral occur over sedimentation processes. A positive correlation between (La/Yb)CN and total REE concentrations was observed in piedmont and central sediment samples, implying that LREE were preferentially enriched over HREE with an accumulation of REE. While this correlation was not found in littoral sediment samples, where a general decreasing trend along depth for REE concentrations existed. Results of present study shows implications for using REE as a tracer of sedimentary provenance from a basin scale