鲁北现代洪水沉积物XRF元素扫描特征及其指示意义

2018年8月山东北部弥河流域受台风暴雨影响发生洪涝灾害，通过对洪水淹没区考察，选择弥河及其支流丹河下游新鲜洪水沉积保存完好的地点，获取两根沉积物浅钻MH1、DH2(长度分别为21.5、21 cm，下段为现代土壤)，对沉积岩芯进行X射线荧光光谱(XRF)元素连续扫描，结合粒度指标和其他研究成果，探讨现代洪水沉积物元素特征及其在古洪水事件识别中的指示意义。结果显示，Al、Ti、Si、Ca、Fe等元素具有相似的波动特征，相互之间正相关关系显著，信号强度在细粒洪水沉积层出现峰值；Rb元素信号强度与粒度相关性弱，在钻孔中的变化较为稳定，仅在沉积界面处有所降低，可能与岩芯裂隙造成的实验偏差有关；Sr、Zr两种元素显著正相关，且信号强度在洪水沉积层较低。Zr/Rb和Rb/Sr分析结果表明，两者均受控于粒度特征，风化淋溶作用对其影响有待进一步研究，其中Zr/Rb与粒度呈现较强的正相关性，Rb/Sr则与粒度负相关关系显著，且在其他区域洪水地层研究中具有一致结论。Zr/Rb峰值和Rb/Sr谷值对应黏土质洪水沉积，Zr/Rb谷值和Rb/Sr峰值对应粒度粗组分高值的粉砂质洪水沉积，可在古洪水沉积识别中作为参照指标。本研究结果将为利用XRF技术识别古洪水沉积提供有力参考。

Characteristics of X-ray fluorescence scanning element of modern flood sediments in northern Shandong Province and its geological indicative significance

In August 2018, a typhoon-storm–induced flood disaster occurred in the Mihe River Basin in the northern Shandong Province of China. By investigating the flood inundated area, the sites were selected where fresh flood deposits in the lower reaches of the Mihe River and its tributary Danhe River were well preserved, and two sediment shallow drills MH1 and DH2 (with the length of 21.5 cm and 21 cm, respectively, including the lower section of modern soil) were obtained. The Avaatech X-ray fluorescence (XRF) spectroscopy core scanner made in the Netherlands was applied for element analysis, and the characteristics of modern flood sediment elements and its significance in paleoflood layers were discussed in combination with grain size index and other research results. Results show that Al, Ti, Si, Ca, and Fe elements presented similar fluctuation characteristics, and there was a significant positive correlation between them, and the signal intensity of these chemical elements peaked in fine-grained flood sediments sections. The signal intensity of Rb element was weakly correlated with particle size, and the change through the borehole was relatively stable but decreased at sedimentary interface, which might be related to the experimental deviation caused by cracks. The two elements of Sr and Zr were significantly positively correlated, and the signal intensity of them was low in the flood sediment layer. In addition, the Zr/Rb and Rb/Sr ratios were heavily correlated with grain size properties, and the influence of weathering and leaching on them is yet to be studied further. The Zr/Rb ratio was strongly positively correlated with the grain size, while the Rb/Sr ratio was significantly negatively correlated with the grain size, which is consistent with the conclusions obtained from the studies on other regional flood formations. The maximum Zr/Rb and minimum Rb/Sr values occurred in the clayey part of flood deposits, while the minimum Zr/Rb and maximum Rb/Sr values in the silty part of flood deposits with more coarser-grain composition. Therefore, Rb/Sr and Zr/Rb ratios can be used to indicate paleoflood deposits. This study provided a good reference for the identification of paleoflood deposit by using XRF technology.