Abstract Large-scale mass transport complex (MTC) (usually covering hundreds to thousands of km2 with a volume of tens to hundreds of km3) resulting from slope failures, can change the overall sediment dispersal pattern in deep-water canyon. However, the causal mechanisms remain enigmatic. We investigate the large-scale MTCs in the Central Canyon that are imaged in 3D by high-resolution seismic reflection data from the northwestern South China Sea. Our results indicate that a total volume of 435.3 km3 of sediments related to large-scale mass wasting processes were dumped into the Central Canyon from its side direction between 5.7 and 4.2 Ma. This led to adjustments of the geomorphology of the thalweg slope, which changed from a simply stepped slope (2 steps separated by 1 ramp) into a complexly stepped slope (3 steps separated by 2 ramps). The adjustments are argued to be caused by the thickness variations of MTCs1-4 that also ponded the axial turbidity flows at their up-dip directions. And then, the adjusted thalweg slope controlled the formation of a multi-stage submarine fan, which is proved to be an important hydrocarbon exploration target within the Central Canyon. Besides the first step in the canyon where sediments were mainly transported downslope due to the initially large velocities of turbidity flows, the following ramps were also considered as sediment bypass zones due to the further accelerated flows. Whereas, the subsequent steps became sediment deposition dominated zones as turbidity flows decelerated abruptly. Slope overstepping resulting from high sediment supply that was controlled by the East Asia summer monsoon, together with seismicity caused by the structural inversion of the Red River Fault were responsible for the occurrences of the large-scale mass wasting processes. We highlight how the large-scale mass wasting processes change the sediment dispersal pattern in the deep-water canyon for the first time. This study is of great significant to identify the locations of hydrocarbon reservoirs and evaluate the spatial variability in depositional reservoir qualities within the deep-water canyon.

中文翻译：

---

大规模消减过程在改变南海西北部深水中央峡谷沉积物扩散格局中的作用

摘要 边坡失稳引起的大规模物质传输复合体（MTC）（通常覆盖数百至数千平方公里，体积达数十至数百平方公里）可以改变深水峡谷中的整体沉积物扩散格局。然而，因果机制仍然是个谜。我们研究了通过南海西北部的高分辨率地震反射数据以 3D 方式成像的中央峡谷中的大规模 MTC。我们的研究结果表明，在 5.7 到 4.2 Ma 之间，与大规模物质浪费过程相关的总体积为 435.3 km3 的沉积物从中央峡谷的侧面倾倒到中央峡谷中。这导致了 thalweg 斜坡地貌的调整，从简单的阶梯斜坡（2 个台阶由 1 个斜坡分隔）变为复杂的阶梯斜坡（3 个台阶由 2 个斜坡分隔）。这些调整被认为是由 MTC1-4 的厚度变化引起的，MTCs1-4 的厚度变化也在其上倾方向积聚了轴向浊流。然后，调整后的thalweg坡度控制了多级海底扇的形成，被证明是中央峡谷内重要的油气勘探目标。除了在峡谷中的第一步，由于最初的浊流速度很大，沉积物主要向下坡输送，随后的斜坡也被认为是由于进一步加速流动的沉积物旁路区。然而，随着浊流突然减速，随后的步骤成为沉积物沉积主导区。由东亚夏季风控制的大量沉积物供应导致的坡度超标，加上红河断层构造反转引起的地震活动是造成大规模物质消耗过程发生的原因。我们首次强调了大规模的质量浪费过程如何改变深水峡谷中的沉积物扩散模式。该研究对于确定油气藏位置和评价深水峡谷内沉积储层质量的空间变异性具有重要意义。