Distribution of rare earth elements in sediments of the North China Plain: A probe of sedimentation process

Abstract Rare earth elements (REE) are powerful tracers for our understanding of sedimentary provenance and depositional processes. This study investigated geochemical characteristics of REE in 226 sediment samples collected from the piedmont, central and littoral plains of the North China Plain. Results showed that total REE concentrations exhibited a decreasing trend as piedmont > central > littoral, and 82%, 70% and 67% samples had total REE concentrations higher than the value of upper continental crust. The REE concentrations were controlled by sedimentary provenance and sediment physicochemical properties. Ternary diagrams of sandstone classification and Al2O3–CaO + Na2O–K2O reflected that sediments originated from greywackes and they experienced an incipient to intermediate chemical weathering. Average chemical index of alteration (CIA) value was 68, 51 and 55 for sediments from piedmont, central and littoral plains, respectively. Sediment North American Shale Composite (NASC)-normalized patterns were characterized by light REE (LREE) enrichment over heavy REE (HREE) and coherent negative Eu anomaly (Eu/Eu* ranging between 0.57 and 1.00). Value of (La/Yb)NASC ranged from 0.86 to 1.15 (average 1.23), and from 1.03 to 1.49, and from 0.91 to 1.49 in three zones, respectively, indicating REE fractionation occurred from piedmont to littoral during sedimentation processes. A positive correlation between (La/Yb)NASC 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. This positive correlation was not found in littoral sediment samples, where a general decreasing trend along depth for REE concentrations existed. The findings of this study have an implication for using REE as a tracer in provenance studies from a basin scale.