Abstract The theoretical model of turbidite bedform evolution has been verified based on laboratory tests and outcrop surveys. However, the evolution of the bedforms associated with flow regime variation within the channel–lobe transition zone (CLTZ) is poorly documented and generally extremely poorly understood. In this study, a combination of seismic sedimentological and topographic analyses, based on high-resolution 3D seismic data within the Qiongdongnan Basin of the South China Sea, was used. Continuous bedforms varied with the depositional elements within the CLTZ of the Huaguang leveed channel system along the flow direction. The depositional elements within the CLTZ change from the main channel to the distributary channels as well as to the sub-distributary channels. Numerous bifurcation and confluence points of gravity flows illustrated the complexity of the drainage network within the CLTZ. The average asymmetry index of the bedforms increased from 0.8 to 1.6, with the average wavelength increasing from 803 m to 1545 m along the thalweg of the channels. Crevasse splays at the starting reach of the CLTZ are likely to form the initial state of the new CLTZ in the future, because the slope gradient starting from the avulsion point was higher than that inside the channel. The deep scours at the bifurcation points and high steps at the confluence points demonstrate the critical roles of supercritical flows and hydraulic jumps in reworking the bedforms of the CLTZ. The high steps at confluence points were simultaneously formed along the margin and thalweg of the main channel. The acceleration mechanisms of flow velocity forming the high steps were the increase of the elevation difference along the internal slope of the main channel margin and promotion of discharge along the main channel thalweg. This paper presents newly completed deepwater observations of the present seafloor bedforms based on the turbidity currents within the CLTZ. These observations update the evolution model of local supercritical flows and hydraulic jumps under the global decreasing trend of the Froude numbers within CLTZs.

中文翻译：

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南海琼东南盆地3D地震资料揭示的华光河道-波瓣过渡带深水浊积岩床型演化

摘要 通过室内试验和露头调查，验证了浊积岩床型演化的理论模型。然而，与通道-叶片过渡区 (CLTZ) 内的流态变化相关的河床形态的演变鲜有记录，而且通常了解甚少。在这项研究中，使用了基于南海琼东南盆地高分辨率 3D 地震数据的地震沉积学和地形分析的组合。沿水流方向，华光堤水道系统CLTZ内连续床型随沉积要素变化。CLTZ 内的沉积要素由主河道转变为分流河道以及次分流河道。重力流的许多分叉点和汇合点说明了CLTZ 内排水网络的复杂性。河床平均不对称指数从 0.8 增加到 1.6，平均波长从 803 m 增加到 1545 m。由于从撕脱点开始的坡度高于河道内部，CLTZ起始段的裂隙张开很可能形成未来新CLTZ的初始状态。分岔点处的深冲刷和汇合点处的高台阶证明了超临界流动和水跃在改造CLTZ 床型中的关键作用。汇合点的高台阶沿主河道的边缘和后缘同时形成。形成高台阶的流速加速机制为增大沿主河道边缘内坡的高差和促进沿主河道低坡的泄流。本文根据 CLTZ 内的浊流介绍了最新完成的对当前海底床形态的深水观测。这些观察结果更新了 CLTZs 内 Froude 数全球下降趋势下局部超临界流动和水跃的演化模型。