Straight channels are ubiquitous in deep-water settings, yet flow dynamics and sedimentation in them are far from being well understood. Stratigraphy and flow dynamics of a middle to late Miocene straight channel in Qiongdongnan Basin were quantified, in terms of angle of channel-complex-growth trajectories (Tc), stratigraphic mobility number (M), Froude number (Fr), layer-averaged flow velocity (U), flow thickness (h), and water entrainment coefficient (Ew). The documented channels are composed of three channel complexes (CC1 to CC3) all of which are all characterized by symmetrical channel cross sections without levees and by organized vertical channel-stacking patterns (represented by high mean value of Tc = 37.4° and low mean value of M = 0.038). Turbidity currents in them were estimated to have U of 1.6 to 2.0 m/s (averaging 1.8 m/s), h of 63 to 89 m (averaging 78), Fr of 0.849 to 0.999 (averaging 0.912), and Ew of 0.0003 to 0.0005. They were, in most case, subcritical over most of the channel length, and had a low degree of water entrainment and low flow height scaled to the channel depth (i.e., 0.786 to 0.81 of the channel depth), most likely inhibiting the gradual loss of sediment to form levees. With reference to modeling results of secondary flow velocity vectors of numerical straight channels with the same sinuosity, two parallel gullies seen on both sides of the interpreted channel beds are interpreted to be induced by high-velocity downward backflows produced by the negative buoyancy. Such symmetrical secondary flow structures most likely promoted symmetrical intrachannel deposition (i.e., less deposition along both channel margins but more deposition near the channel center), and thus forced individual channel complexes to progressively aggrade in a synchronous manner, forming straight-channel complexes with symmetrical channel cross sections and organized vertical channel-stacking patterns.

中文翻译：

---

南海西北部琼东南缘海底直通道海流过程与沉积

直通道在深水环境中无处不在，但远未充分了解其中的流动动力学和沉积情况。琼东南盆地中新世中晚期直通道的地层和流动动力学通过通道复杂生长轨迹的角度（Tc），地层迁移率数（M），弗洛德数（Fr），层平均流量定量速度（U），流量厚度（h）和水夹带系数（Ew）。记录的通道由三个通道复合体（CC1至CC3）组成，所有这些通道复合体均具有对称的，不带堤坝的通道横截面和有组织的垂直通道堆积模式（由Tc = 37.4°的高平均值和低平均值表示） M = 0.038）。它们中的混浊流的U值估计为1.6至2.0 m / s（平均为1.8 m / s），h为63至89 m（平均78），Fr为0.849至0.999（平均0.912），Ew为0.0003至0.0005。在大多数情况下，它们在通道的大部分长度上都处于亚临界状态，并且夹带水的程度较低，并且流量高度与通道深度成比例（即通道深度的0.786至0.81），很可能会抑制逐渐损失沉积物形成堤坝。参考具有相同波纹度的数值直通道的次级流速矢量的建模结果，在解释的通道床两侧看到的两个平行的沟壑被解释为由负浮力产生的高速向下回流引起。这种对称的二级流结构最有可能促进对称的通道内沉积（即，