【摘要】 黄土高原聚湫/淤地坝内的沉积物是黄土再侵蚀搬运的直接结果,以高堆积速率和多沉积旋回为特征,是追踪该地区小流域土壤侵蚀、认识黄土高原地球关键带过程的理想载体。如何鉴定并有效划分沉积旋回是利用沉积序列恢复小流域土壤侵蚀和生态环境变化过程的基础。本文选取靖边和合水聚湫为代表,通过典型可见沉积旋回的物理、地球化学和生物等指标综合分析,较全面地认识沉积旋回特征,进而提出划分旋回的有效地球化学指标。结果表明:沉积旋回的下部粗颗粒层主要由粗粉砂和细砂组成,以低含水量、高亮度为特征,富集石英和锆石,Si和Zr含量高;上部细颗粒层主要由黏粒和细粉砂组成,具水平层理,含水量高,亮度较低,富集方解石、白云母、伊利石、绿泥石、高岭石等轻矿物,高Al、K、Fe、Rb、Ca和Sr等造岩元素,富含孢粉、有机碳氮、磷脂脂肪酸及微生物。在此基础上,提出Rb/Zr比值是有效划分黄土高原聚湫/淤地坝沉积旋回的地球化学指标。这为深入认识黄土高原地球关键带中侵蚀风化、水文和生态环境变化等过程提供了研究载体和基础。更多还原

【Abstract】 The sediment in the landslide-dammed/check dam reservoirs on the Loess Plateau of China is the direct result of the erosion and retransfer of loess and is characterized by high deposition rate and lots of deposition couplets, thus it is an ideal object to trace erosion flux and understand the processes of the Earth’s Critical Zone. How to exactly identify and plot out the couplet is the basis for using the sediment sequence to recover soil erosion and eco-environment change within a small catchment. In this study, Jingbian(paleo) and Heshui landslide-dammed reservoirs in the north of Loess Plateau were choose as the study sites based on field investigation and documents records. Meanwhile, the physical, geochemical and biological characters of the representative couplets were analyzed in order to comprehensively understand the feature of the couplet and further put forwards the effective geochemical identification index. The results showed that the lower coarse-grained layer in the couplet was composed of coarse silts and fine sands, which was characterized by low water content and high luminance, enriched with quartz and zircon, along with high Si and Zr. On the other hand, the upper fine-grained one was characterized by high contents of clays and fine silts, high water content, low luminance and lenticular bedding, correlating well with high contents of calcite, muscovite, illite, chlorite and kaolinite, along with high Al, K, Fe, Rb, Ca, and Sr. Pollen, organic carbon and nitrogen, phospholipid fatty acids, microorganism also concentrated in this layer. Then, Rb/Zr ratios by XRF core scanning are recommended as the ideal geochemical index to identify deposition couplets within the sediment sequence. These results provide the scientific foundation on deeply realizing the processes of erosion and weathering, hydrology and eco-environment change in the Earth’s Critical Zone on the Loess Plateau.更多还原