Grain-size sorting shapes the geochemical heterogeneity of different types of dune sediments: Implications for the selection of source-tracing indicators in Kubuqi Desert, China
Description
Grain-size sorting influences the modes of occurrence and distribution of elements in sediments, thereby complicating the accurate interpretation of geochemical signals. However, the relationship between grain-size sorting and elemental fractionation across dune sediment types, as well as its implications for sediment provenance tracing, remains poorly understood. Therefore, this study investigates sediments from six dune types in the Kubuqi Desert: shrub-coppice dunes, reticulate dune chains, compound dunes, ridge-honeycomb dunes, crescen dunesand chain, and parabolic dunes. It characterizes their grain-size distributions and elemental geochemical compositions and quantifies the relative contribution of each grain-size fraction to elemental fractionation. All six dune sediment types were composed predominantly of fine- and medium-sand fractions, which together accounted for 76.56–97.83% of the total sediment. However, their grain-size parameters differed markedly among dune types. Relative to the average upper continental crust (UCC), the dune sediments were generally enriched in SiO₂ and Cr but depleted in most other major and trace elements. Partial least squares regression (PLSR) analysis indicated that the fine- and medium-sand fractions were the dominant grain-size fractions influencing elemental fractionation, with mean variable importance in projection (VIP) values of 1.151 and 1.041, respectively. The contributions of the clay- and silt-sized fractions varied significantly among dune types and were particularly pronounced in shrub-covered dunes. This study demonstrates that grain-size sorting is a key control on the elemental composition and spatial variability of dune sediments. For sediment provenance tracing, samples with relatively homogeneous grain-size distributions should be prioritized, particularly the fine- and medium-sand fractions. In dunes where sediment trapping by vegetation is pronounced, geochemical signals from the clay- and silt-sized fractions should also be incorporated. This study provides a scientific basis for understanding the mechanisms of grain size–element sorting in desert sediments and for the appropriate selection of source-tracing indicators.