Linking river-flood dynamics to hyperpycnal-plume deposits: Experiments, theory, and geological implications
Linking river-flood dynamics to hyperpycnal-plume deposits: Experiments, theory, and geological implications
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DOI：
10.1130/b30125.1
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发表时间：
2010-09
影响因子：
4.9
通讯作者：
M. Lamb;B. McElroy;Bryant T Kopriva;J. Shaw;D. Mohrig
中科院分区：
文献类型：
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作者：
M. Lamb;B. McElroy;Bryant T Kopriva;J. Shaw;D. Mohrig
浑浊的河流羽流进入密度较小的海洋或湖水（即，高密度羽流）可下沉形成浊流，在陆地沉积物源和海洋沉积物汇之间提供重要联系。一个主要的假说认为，hypercnal-plume沉积准确地记录了洪水河流的上升和下降流量（在沉积物粒度分级，床形序列和存款厚度方面），如果正确的话，对解开河流动力学，水库潜力和海洋事件床的地球历史具有重要意义。在这里，我们提出了第一个实验水槽研究旨在验证这一假设。结果表明，深度平均hypercnal-plume速度可以是不相关的，甚至反相关的河流流量在某些海底位置，因为翻译的暴跌点造成的流量和泥沙浓度的时间变化，通过河流洪水的持续时间。沉降泥沙的平流长度尺度被发现是一个重要的控制hyperpycnal-plume存款，粗泥沙（砂）是最有可能记录多个流的加速和减速相关的暴跌点平移，即使是一个单峰过程线的河流洪水。相比之下，细泥沙（泥）是相对不敏感的地方暴跌点动态，最有可能保持直接上升和下降的河流流量。最后，人们发现，必要的河流泥沙浓度，形成一个暴跌羽流可以远远大于浓度通常使用假设密度等效，因为沉积上游的暴跌点。
Turbid river plumes entering ocean or lake water of lesser density (i.e., hyperpycnal plumes) can plunge to form turbidity currents providing an important link between terrestrial sediment sources and marine depositional sinks. A leading hypothesis suggests that hyperpycnal-plume deposits accurately record the rising and falling discharge of a flooding river (in terms of sediment-size grading, bedform sequence, and deposit thickness), which, if correct, has significant implications for unraveling river dynamics, reservoir potential, and Earth history from marine-event beds. Herein, we present one of the first experimental flume studies aimed at testing this hypothesis. Results indicate that depth-averaged hyperpycnal-plume velocities can be uncorrelated or even anti-correlated with river discharge at certain seabed locations because of translation of the plunge point resulting from temporal variations in discharge and sediment concentration through the duration of a river flood. An advection length scale of settling sediment is found to be an important control on hyperpycnal-plume deposits, where coarse sediment (sand) is most likely to record multiple flow accelerations and decelerations related to plunge-point translation even for a river flood with a single-peaked hydrograph. In contrast, fine sediment (mud) is relatively insensitive to local plunge-point dynamics and is most likely to preserve directly rising and falling river discharge. Finally, it was found that the necessary fluvial sediment concentration to form a plunging plume can be much larger than the concentration typically used assuming density equivalence because of deposition upstream of the plunge point.