Dilution of 10Be in detrital quartz by earthquake-induced landslides: Implications for determining denudation rates and potential to provide insights into landslide sediment dynamics
Dilution of 10Be in detrital quartz by earthquake-induced landslides: Implications for determining denudation rates and potential to provide insights into landslide sediment dynamics
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DOI：
10.1016/j.epsl.2014.03.058
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发表时间：
2014-06
影响因子：
5.3
通讯作者：
A. West;R. Hetzel;Gen K. Li;Zhangdong Jin;Fei Zhang;Robert G. Hilton;A. Densmore
中科院分区：
文献类型：
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作者：
A. West;R. Hetzel;Gen K. Li;Zhangdong Jin;Fei Zhang;Robert G. Hilton;A. Densmore
来自河流沉积物的碎屑石英（10be qtz）中的10be浓度现在被广泛用于量化流域范围内的剥蚀率，但也可能对基岩滑坡输入的低10be qtz沉积物敏感。主要的山体滑坡触发事件可以为山区集水区的河流提供大量低浓度的物质，但由于此类事件而导致的河流沉积物的变化尚未被直接测量。在这里，我们研究了2008年汶川地震引发的广泛滑坡对中国四川岷江流域沉积物样品中10倍石英的影响。与汶川地震有关的滑坡沉积物物质始终低于地震前河流沉积物中的10倍石英。在同震滑坡高发区下游（即上游流域受滑坡影响面积大于~ 0.3%），由于10 Be贫化滑坡物质的输入，地震后河流沉积物10 Be qtz明显减少，而在滑坡低发区则无系统变化。河流沉积物中Be qtz浓度的变化在一级小流域中最大，但在面积为10 4 ~ 10 5 km的大流域中仍然显著。河流沉积物的时空变异性对推断构造活跃、滑坡为主的环境中具有代表性的剥蚀速率，甚至在大型盆地中也具有重要意义。虽然滑坡输入对河流沉积物中10qtz的稀释可能会使对剥蚀率的解释复杂化，但它也可能提供跟踪滑坡沉积物运输的可能机会。相关的不确定性很大，但在汶川的情况下，基于10个Be混合比例的计算表明，地震后2-3年，河流沉积物通量在0.25 - 1 mm和< 0.25 mm粒径部分分别增加了相似的数量级，分别由10个Be qtz混合计算和水文测量确定。这些资料可以提供关于沉积物转移的新见解，对与沉积物有关的次生危害和了解从山上移走的物质有影响。
The concentration of 10 Be in detrital quartz (10 Be qtz) from river sediments is now widely used to quantify catchment-wide denudation rates but may also be sensitive to inputs from bedrock landslides that deliver sediment with low 10 Be qtz. Major landslide-triggering events can provide large amounts of low-concentration material to rivers in mountain catchments, but changes in river sediment 10 Be qtz due to such events have not yet been measured directly. Here we examine the impact of widespread landslides triggered by the 2008 Wenchuan earthquake on 10 Be qtz in sediment samples from the Min Jiang river basin, in Sichuan, China. Landslide deposit material associated with the Wenchuan earthquake has consistently lower 10 Be qtz than in river sediment prior to the earthquake. River sediment 10 Be qtz decreased significantly following the earthquake downstream of areas of high coseismic landslide occurrence (ie, with greater than∼ 0.3% of the upstream catchment area affected by landslides), because of input of the 10 Be-depleted landslide material, but showed no systematic changes where landslide occurrence was low. Changes in river sediment 10 Be qtz concentration were largest in small first-order catchments but were still significant in large river basins with areas of 10 4–10 5 km 2. Spatial and temporal variability in river sediment 10 Be qtz has important implications for inferring representative denudation rates in tectonically active, landslide-dominated environments, even in large basins. Although the dilution of 10 Be qtz in river sediment by landslide inputs may complicate interpretation of denudation rates, it also may provide a possible opportunity to track the transport of landslide sediment. The associated uncertainties are large, but in the Wenchuan case, calculations based on 10 Be mixing proportions suggest that river sediment fluxes in the 2–3 years following the earthquake increased by a similar order of magnitude in the 0.25–1 mm and the< 0.25 mm size fractions, as determined from 10 Be qtz mixing calculations and hydrological gauging, respectively. Such information could provide new insight into sediment transfer, with implications for secondary sediment-related hazards and for understanding the removal of mass from mountains.