Geochemical characteristics of modern flood sediment from Danhe River Basin in northern Shandong Province and its significance of paleoflood identification

The Danhe River Basin in the North of Shandong Province was affected by two typhoons, resulting in a huge flood in August 2018. Based on the investigation of flood inundation area, the short drilling depth of DH1 (21 cm, including soil layer) of modern flood sediment was obtained on the flood plain on the west side of Danhe River (tributary of Mihe River), the core was scanned by X-ray fluorescence (XRF), and the correlation statistical analysis was carried out with the particle size index. The results showed that: ① The element Fe in the borehole had the highest average signal intensity, and the signal intensity of the flood sediment layer, greatly different from that of the underlying soil layer, was not only controlled by sedimentary facies, but also strongly affected by the particle size. ② The core elements of DH1 were divided into 5 categories: the first category included Mg, Fe, Ti, Al and Si, and their signal intensity in the flood sediment layer was generally lower than that of the soil layer; Sr and Zr were in the second category; Zn, in the third category; and Ca, in the fourth category, the signal intensity of which varied completely opposite to that in the second category, and reached the peak in the flood clay sediment layer; and Rb, in the fifth category. ③ There was a significant correlation between the signal intensity and median particle size of elements in the flood sediment layer. ④ The ρ(Zr)/ρ(Rb) ratio and ρ(Rb)/ρ(Sr) ratio respectively reached the valleys and peaks in the flood clay sediment layer, but were approximate in the soil layer and flood silt layer. Therefore, there were limitations in identifying the flood sediment layer depending solely on changes in these ratios. Instead, comprehensive research and identification should be performed in conjunction with other indicators.