Abstract The Holocene muddy infill of the valley incised by the ancient Red River during Pleistocene sea-level lowstand records a change from fluvial to estuarine and finally marine depositional conditions. Siphonichnus, a mainly vertical trace fossil produced by burrowing bivalves, documents otherwise unrecorded episodes of enhanced erosion, bypass and deposition of, on average, rapidly aggrading (> 1 m kyr−1), mainly completely bioturbated sediments within the fluvial-marine transition zone (FMTZ), supposedly within the polyhaline domain. The producers of Siphonichnus moved nearly 1 m downward or upward in response to erosional or depositional phases, respectively. The fill of Siphonichnus burrows, in addition, records erosion and/or bypass of sediment: The traces were produced in mud, but many of them are filled with coarse silt and sand that is otherwise not present in the studied intervals in distinct layers. Obviously, this material was available when Siphonichnus was produced and connected to the sediment surface. In addition to seasonal erosion and deposition during freshet and its waning stage, Siphonichnus records exceptional events that displace the sediment surface by >0.5 m. Such events occurred episodically at an estimated frequency of 1 event per several hundreds of years. The complete bioturbation of the deposits suggests apparent continuous accumulation, but in fact they represent a pile of stacked event deposits resulting from depositional phases and intermittent severe erosion.

中文翻译：

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Siphonichnus（古代红河，北部湾）记录的河口全新世切谷充填沉积物的沉积动力学

摘要 更新世海平面低位时古红河切开的河谷全新世泥质充填体记录了从河流到河口再到海相沉积条件的变化。Siphonichnus 是一种由挖洞双壳类动物产生的主要垂直痕迹化石，记录了其他未记录的侵蚀、旁路和沉积事件，这些事件平均快速加积（> 1 m kyr-1），主要是河流-海洋过渡带内完全生物扰动的沉积物（FMTZ），据说在多卤领域内。Siphonichnus 的生产者分别响应侵蚀或沉积阶段向下或向上移动近 1 m。此外，Siphonichnus 洞穴的填充物记录了侵蚀和/或沉积物绕过：痕迹是在泥浆中产生的，但其中许多都充满了粗粉砂和沙子，否则在不同层的研究间隔中是不存在的。显然，当产生 Siphonichnus 并连接到沉积物表面时，这种材料是可用的。除了在淡水及其衰落阶段的季节性侵蚀和沉积外，Siphonichnus 还记录了使沉积物表面位移 > 0.5 m 的特殊事件。此类事件以每数百年 1 次事件的估计频率偶发性发生。沉积物的完整生物扰动表明明显的连续堆积，但实际上它们代表了由沉积阶段和间歇性严重侵蚀产生的堆积事件沉积物。当 Siphonichnus 被生产并连接到沉积物表面时，这种材料就可用了。除了在淡水及其衰落阶段的季节性侵蚀和沉积外，Siphonichnus 还记录了使沉积物表面位移 >0.5 m 的特殊事件。此类事件以每数百年 1 次事件的估计频率偶发性发生。沉积物的完整生物扰动表明明显的连续堆积，但实际上它们代表了由沉积阶段和间歇性严重侵蚀产生的堆积事件沉积物。当 Siphonichnus 被生产并连接到沉积物表面时，这种材料就可用了。除了在淡水及其衰落阶段的季节性侵蚀和沉积外，Siphonichnus 还记录了使沉积物表面位移 > 0.5 m 的特殊事件。此类事件以每数百年 1 次事件的估计频率偶发性发生。沉积物的完整生物扰动表明明显的连续堆积，但实际上它们代表了由沉积阶段和间歇性严重侵蚀产生的堆积事件沉积物。此类事件以每数百年 1 次事件的估计频率偶发性发生。沉积物的完整生物扰动表明明显的连续堆积，但实际上它们代表了由沉积阶段和间歇性严重侵蚀产生的堆积事件沉积物。此类事件以每数百年 1 次事件的估计频率偶发性发生。沉积物的完整生物扰动表明明显的连续堆积，但实际上它们代表了由沉积阶段和间歇性严重侵蚀产生的堆积事件沉积物。