Cosmogenic burial ages reveal sediment reservoir dynamics along the Yellow River, China
Cosmogenic burial ages reveal sediment reservoir dynamics along the Yellow River, China
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DOI：
10.1130/g32030.1
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发表时间：
2011-09
期刊：
影响因子：
5.8
通讯作者：
Xiaofei Hu;E. Kirby;B. Pan;D. Granger;Huai Su
中科院分区：
文献类型：
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作者：
Xiaofei Hu;E. Kirby;B. Pan;D. Granger;Huai Su
利用宇宙成因Al-26和Be-10的埋藏年代测定是一种新兴的技术，用于建立河流沉积物的年代学，其年龄范围从约100年到约100年。0.5 5马。然而，埋藏年龄的确定需要一个假设，即沉积物是以已知的初始Al-26/Be-10比率埋藏的。利用中国兰州沿黄河沿着的一系列年代久远的河流阶地，我们证明了当上游沉积物来源包括新近纪沉积盆地时，这一假设可能会被违反。从六个阶地的河流砾石样品产生的埋藏年龄范围从约。0.83 2.81 Ma。这些结果的比较，以独立的年龄从磁地层和黄土-古土壤研究表明，在较低的三个阶地的年龄之间的高度对应。然而，在较高的阶地，埋葬年龄系统地太老，这意味着以前的埋葬历史。这些结果可以用来对阶地沉积物的物源进行定量约束。研究结果表明，晚第三纪沉积盆地的快速下切和开挖，1.7马导致低初始Al-26/Be-10比率的河流沉积物的注入。随着时间的推移，这种来源的稀释发生在切割进入上游基岩范围时。我们的研究结果表明，宇宙成因核素可以照亮的时间，长期存储和再动员的沉积物在大陆尺度的河流系统。
Burial dating using cosmogenic Al-26 and Be-10 is an emerging technique for establishing chronologies of fluvial deposits ranging in age from ca. 0.5 Ma to 5 Ma. The determination of burial age, however, requires an assumption that sediment is buried with a known initial Al-26/Be-10 ratio. Using a sequence of well-dated fluvial terraces along the Yellow River in Lanzhou, China, we demonstrate that this assumption may be violated when upstream sediment sources include Neogene sedimentary basins. Samples of fluvial gravel from six terraces yield burial ages ranging from ca. 0.83 Ma to 2.81 Ma. Comparison of these results to independent ages determined from magneto stratigraphic and loess-paleosol studies demonstrates a high degree of correspondence between ages in the lower three terraces. In the higher terraces, however, burial ages are systematically too old, implying a previous burial history. These results can be exploited to place quantitative constraints on the provenance of sediment in the terrace deposits. Our results reveal that rapid incision and excavation of late Neogene sedimentary basins ca. 1.7 Ma led to injection of fluvial sediment with low initial Al-26/Be-10 ratios. Dilution of this source through time occurred as incision progressed into upstream bedrock ranges. Our results suggest that cosmogenic nuclides can illuminate the timing of long-term storage and remobilization of sediment in continental-scale river systems.