Autogenic attainment of large-scale alluvial grade with steady sea-level fall: An analog tank-flume experiment
Autogenic attainment of large-scale alluvial grade with steady sea-level fall: An analog tank-flume experiment
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DOI：
10.1130/g21923.1
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发表时间：
2006-03
期刊：
影响因子：
5.8
通讯作者：
T. Muto;J. Swenson
中科院分区：
文献类型：
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作者：
T. Muto;J. Swenson
等级河流输送泥沙时没有净淤积或侵蚀。分级状态被认为代表了冲积河流对稳定外部强迫的长期响应。我们在这里表明，冲积河流建设三角洲可以在等级作为一个自生的稳定的海平面下降的反应。考虑一个先前的级配河流剖面，其上游端由冲积层-基岩过渡组成，其下游端是一个固定的溢流，其中保持恒定的海平面。海平面上升之后，海平面下降，从而淹没了先前的递变剖面。其结果是一个新的河流剖面，终止于一个沉积在先前剖面顶部的扩张三角洲。如果海平面下降的速率是恒定的，并且先前河段的长度是足够的，则新的剖面最终会变得与先前剖面平行或准平行，并在其跨越时保持坡度。在这里报道的实验中，一系列的分级河流剖面与adverding三角洲是通过堆叠fluviodeltaic系统创建的;每个分级剖面及其相关的三角洲是堆叠在其直接的前身。对于每一个河流三角洲系统，一个分级的冲积层剖面是以任何恒定的海平面下降率获得的，前提是先行剖面有足够的长度。实验表明，这种自生的方法是更快的速度更高的海平面下降，较低的沉积物供应率，更高的水排放。
A graded river conveys its sediment load without net deposition or erosion. The graded state is thought to represent the long-term response of alluvial rivers to steady external forcing. We show here that alluvial rivers building deltas can be in grade as an autogenic response to steady sea-level fall. Consider an antecedent graded river profile, the upstream end of which consists of an alluvial-bedrock transition, and the downstream end of which is a fixed overfall where constant sea level is maintained. The antecedent graded profile is then drowned by a jump in sea level, after which sea level drops. The result is a new river profile ending in a prograding delta that deposits on top of the antecedent profile. If the rate of sea-level fall is constant and the length of the antecedent reach is sufficient, the new profile eventually becomes parallel or quasi-parallel to the antecedent profile, maintaining grade as it progrades. In the experiments reported here, series of graded river profiles with prograding deltas are created by stacking fluviodeltaic systems; each graded profile and its associated delta is stacked on its immediate predecessor. For each fluviodeltaic system, a graded alluvial profile is attained with any constant rate of sea-level fall, provided that the antecedent profile is of sufficient length. Experiments suggest that this autogenic approach to grade is more rapid for higher rates of sea-level fall, lower rates of sediment supply, and higher water discharges.