Large rivers are characterized by large water discharges, high suspended sediment fluxes and low slope, and typically display multiple channels that are separated by large complex bars. The most common channel style found in these rivers is characterized by the alternating presence of single and multiple channel threads. Mid‐channel compound bars separate a main deeper channel from shallower secondary channels, leading to low‐order braiding and low to moderate sinuosity. Despite the importance of this type of river for global terrestrial sediment transport and the interpretation of ancient fluvial successions, integrated depositional models for large multi‐channel rivers are still not fully developed. This paper interprets the channel morphodynamics and depositional architecture of such large rivers by investigating the distinctive features of their laterally‐accreting mid‐channel bars in the Solimões–Amazonas River. This is achieved by examination of temporal series of satellite images, quantification of bedforms using multibeam echosounding surveys, analysis of shallow seismic and ground penetrating radar surveys of selected areas, and on‐site field observations and sample collections. Such mid‐channel bars produce directional variability in planform scroll bar accretion of up to 180°. As these bars – and their associated channels – evolve, they become progressively shallower, due to the bifurcation of the two channels and the resultant partitioning of discharge that leads to a gradual reduction in transport capacity within the outer channel. The preserved successions of this process in the alluvial plain are characterized by fining‐upward trends, with larger cross‐strata sets at mid‐depths and internal erosional surfaces marking distinct cycles of bar development with potentially differing palaeocurrent trends. The new depositional models proposed for these mid‐channel bars and channels constitute a basis for the recognition of large multi‐channel river deposits in the ancient rock record.

中文翻译：

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亚马逊河流域中部坝的形态动力学和沉积构造

大型河流的特点是流量大、悬沙通量高、坡度低，并且通常显示出由大型复杂坝分隔的多个河道。这些河流中最常见的河道类型的特点是交替存在单河道线和多河道线。中部河道复合坝将较深的主河道与较浅的次要河道分开，导致低阶辫状和低至中度的蜿蜒度。尽管此类河流对于全球陆地沉积物输送和古代河流序列的解释具有重要意义，但大型多河道河流的综合沉积模型仍未完全开发。本文通过研究索利莫斯-亚马逊河中横向增生的河道中部坝的独特特征，解释了此类大河的河道形态动力学和沉积结构。这是通过检查卫星图像的时间序列、使用多波束回声探测对地床形态进行量化、对选定区域的浅层地震和探地雷达勘测进行分析以及现场观测和样本收集来实现的。这种中间通道条在平面滚动条增加中产生高达 180° 的方向变化。随着这些坝及其相关通道的演变，由于两个通道的分叉以及由此产生的排放划分，导致外部通道内的运输能力逐渐减少，它们变得逐渐变浅。在冲积平原中保存下来的这一过程的演替特征是向上的细化趋势，在中深度和内部侵蚀面有较大的跨地层组，标志着不同的坝发育周期，具有潜在不同的古水流趋势。针对这些河道中部坝和河道提出的新沉积模型构成了识别古代岩石记录中大型多河道河流沉积物的基础。