The alluvial architecture of a suspended sediment dominated meandering river: the Río Bermejo, Argentina
The alluvial architecture of a suspended sediment dominated meandering river: the Río Bermejo, Argentina
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DOI：
10.1111/sed.12256
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发表时间：
2016-08
期刊：
影响因子：
3.5
通讯作者：
G. S. Sambrook Smith;J. Best;Jessica Z. LeRoy;O. Orfeo
中科院分区：
文献类型：
--
作者：
G. S. Sambrook Smith;J. Best;Jessica Z. LeRoy;O. Orfeo
与砂床和砾石床河道的广泛研究相比，细粒（粉砂床）曲流河的冲积结构仍然知之甚少。这种知识的缺乏，部分原因是难以研究这样的现代河流，并从中获得类似的信息，以告知古代沉积物的相模型。本文采用了一种新的技术，参数回声测深仪，以量化的地下结构的Río Bermejo，阿根廷，这是一个主要的淤泥床河流，具有很大的悬浮泥沙负荷。这些结果表明，参数回声测深仪可以提供细粒度河流的高分辨率（分米）地下成像，相当于更常用的探地雷达，已被证明在粗粒度河流中工作良好。数据分析表明，Río Bermejo的冲积结构的特征是由点坝演化产生的大规模倾斜异石分层，以及由河道迁移产生的相关大规模冲刷面。沉积结构的小规模和中等规模结构是由垂直加积沉积物、与小沙洲、沙丘和爬升波纹相关的床组以及小横坝水道的切割和填充产生的。这种冲积结构的风格与文献中报道的其他现代细粒河流非常不同，这些河流强调斜加积的存在。Río Bermejo与其他河流不同，因为它更活跃，河岸侵蚀和河道迁移率非常高。这种高度活跃的细粒河流的现代例子在文献中很少报道，尽管古代的例子更普遍，并显示出与Río Bermejo的冲积结构相似，因此代表了对其识别和解释的有用类比。尽管细粒河流沉积学的全部谱尚未被揭示，但以侧向或斜向加积为主的曲流河可能代表了此类河道的端员，其沉积的特定样式受粒度和泥沙负荷特性控制。
The alluvial architecture of fine‐grained (silt‐bed) meandering rivers remains poorly understood in comparison to the extensive study given to sand‐bed and gravel‐bed channels. This paucity of knowledge stems, in part, from the difficulty of studying such modern rivers and deriving analogue information from which to inform facies models for ancient sediments. This paper employs a new technique, the parametric echosounder, to quantify the subsurface structure of the Río Bermejo, Argentina, which is a predominantly silt‐bed river with a large suspended sediment load. These results show that the parametric echosounder can provide high‐resolution (decimetre) subsurface imaging from fine‐grained rivers that is equivalent to the more commonly used ground‐penetrating radar that has been shown to work well in coarser‐grained rivers. Analysis of the data reveals that the alluvial architecture of the Río Bermejo is characterized by large‐scale inclined heterolithic stratification generated by point‐bar evolution, and associated large‐scale scour surfaces that result from channel migration. The small‐scale and medium‐scale structure of the sedimentary architecture is generated by vertical accretion deposits, bed sets associated with small bars, dunes and climbing ripples and the cut and fill from small cross‐bar channels. This style of alluvial architecture is very different from other modern fine‐grained rivers reported in the literature that emphasize the presence of oblique accretion. The Río Bermejo differs from these other rivers because it is much more active, with very high rates of bank erosion and channel migration. Modern examples of this type of highly active fine‐grained river have been reported rarely in the literature, although ancient examples are more prevalent and show similarities with the alluvial architecture of the Río Bermejo, which thus represents a useful analogue for their identification and interpretation. Although the full spectrum of the sedimentology of fine‐grained rivers has yet to be revealed, meandering rivers dominated by lateral or oblique accretion probably represent end members of such channels, with the specific style of sedimentation being controlled by grain size and sediment load characteristics.