Equivalence of abrupt grain-size transitions in alluvial rivers and eolian sand seas: A hypothesis
Equivalence of abrupt grain-size transitions in alluvial rivers and eolian sand seas: A hypothesis
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DOI：
10.1130/g30922.1
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发表时间：
2010-08-01
期刊：
影响因子：
5.8
通讯作者：
Brzinski, Theodore A., III
中科院分区：
文献类型：
--
作者：
Jerolmack, Douglas J.;Brzinski, Theodore A., III
砾石河床河流组织到一个阈值状态，在该状态下，主导流动条件下的流体应力略超过临界值。这些渠道的变化相当突然，以砂为主的床，促进了在1-10毫米范围内的沉积物的匮乏。风成沉积物也是双峰;沙海往往迅速过渡顺风粉质黄土沉积。在本文中，我们假设这两个转变的结果来自相同的过程：（1）细颗粒泥沙的生产从跳跃磨损的粗颗粒，（2）分离的细和粗模式的悬浮和跳跃运输，分别。我们表明，砾石河流和风成沙丘领域的阈值运输（希尔兹应力）和碰撞动力学（斯托克斯数）是动态等效的。虽然磨蚀可能不是河流砾石下游变细的主要原因，但碰撞效率随粒径的降低设定了砾石尺寸的下限，从而导致粒度差距。碰撞效率假设可能调和的排序和岩性在下游细化的重要性相互矛盾的研究。河流和沙漠中的希尔兹和斯托克斯相似性可以用来设计适当比例的实验来检验和完善我们的假设。
Gravel-bed rivers organize to a threshold state in which the fluid stress during dominant flow conditions slightly exceeds the critical value. These channels change fairly abruptly to sand-dominated beds, facilitated by a paucity of sediment in the range of 1-10 mm. Eolian sediments are also bimodal; sand seas often transition rapidly downwind to silty loess deposits. In this paper we hypothesize that both transitions result from the same processes: (1) production of fine sediment by spallation from saltation abrasion of coarse grains, and (2) segregation of fine and coarse modes by suspension and saltation transport, respectively. We demonstrate that gravel rivers and eolian dune fields are dynamically equivalent in terms of threshold transport (Shields stress) and collision dynamics (Stokes number). While abrasion may not be the dominant cause of downstream fining of fluvial gravels, the reduction of collision efficiency with grain diameter sets a lower limit on gravel size, leading to a grain-size gap. The collision efficiency hypothesis potentially reconciles conflicting studies on the importance of sorting and lithology in downstream fining. Shields and Stokes similitude in rivers and deserts may be used to design appropriately scaled experiments to test and refine our hypothesis.