High-resolution geochemical records of deposition couplets in a palaeolandslide-dammed reservoir on the Chinese Loess Plateau and its implication for rainstorm erosion

The sediment sequences retained by landslides and check dams on the Chinese Loess Plateau (CLP) are ideal for tracing historical catchment erosion, hydrological events and land use. This study explored a geochemical proxy to plot visible and non-visible deposition couplets in a sediment sequence from the CLP, in order to better trace soil erosion associated with historical rainstorms. An intact sediment sequence core (JB-2) was acquired in a palaeolandslide-dammed reservoir in Jingbian County, Shaanxi Province. The high-resolution elemental distribution of the entire core was generated by an Anaatech XRF Core Scanner. The water content and grain size were analysed in discrete samples of the representative core section. The Rb/Zr ratio was recommended as a high-resolution geochemical proxy for plotting the deposition couplets. Annual freeze-thaw layers among the couplets were then identified by the correlation between the Ca/Zr and Fe/Zr ratios. As a result, 41 deposition couplets and 18 annual freeze-thaw layers were identified in the JB-2 sediment sequence, indicating that 41 rainstorms occurred over 18 years during the survival of the reservoir. Furthermore, the ranges of couplet and annual specific sediment yields were 0.06-3.09 x 10(4) t km(-2) and 0.06-3.42 x 10(4) t km(-2) year(-1) in the JB-2 reservoir, respectively. High annual specific sediment yields were the combined consequence of high annual rainfall frequency and the sediment yields associated with the rainstorm intensities. This study highlights the use of high-resolution plots of deposition couplets for providing a basis for the reconstruction of recent and contemporary soil erosion records and for determining the implication of past rainstorm intensities and frequencies on the CLP.