The Changjiang (i.e. the Yangtze River) debouches a huge amount of sediment to the East China Sea and exerts a significant effect on the evolution of the down-drift Qiantang River system. This study quantitatively documents the temporal change in the import of Changjiang sand and mud to the late Quaternary Qiantang River incised valley by establishing separate mixing models based on zircon U-Pb ages for the sand and trace-element compositions of the mud fraction. Results indicate that the Qiantang River provided all of the sediment to its valley before ca 8.0 cal kyr bp. However, its sediment proportion decreases upward due to the onset of export of sediment from the Changjiang after its delta had prograded sufficiently. Changjiang mud, a major component (ca 87%) of the Changjiang-derived sediment, is considered to be primarily supplied through the resuspension and landward transportation of sediment from the inner-shelf mud wedge in the East China Sea by flood-tidal currents and waves. Changjiang sand, which arrived in the Qiantang River valley later than the mud, is interpreted to be derived from the reworking of older deposits on the East China Sea shelf and along the northern margin of the Qiantang River estuary. In the later part of the valley fill, Qiantang River sediment is only ca 9% of the Changjiang contribution, although Qiantang River mud has begun to be exported recently. The Changjiang contribution to the Qiantang River system constitutes ca 50% of the total sediment load discharged by the Changjiang during the 8–6 cal kyr bp period, but <4% since 6 cal kyr bp. This study illustrates the need to exercise caution when interpreting compositional data from linked coastal-shelf sediment-dispersal systems with significant along-coast transport, and is expected to be applicable in a general way to other linked river–coastal-shelf systems.

中文翻译：

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晚第四纪钱塘江下陷河谷充填泥沙源汇分析及其对全球三角洲陆架河口扩散系统的影响

长江（即长江）向东海排放了大量泥沙，对下流的钱塘江水系演化产生了显着影响。本研究通过建立基于锆石 U-Pb 年龄的单独混合模型，定量记录了长江沙泥向晚第四纪钱塘江下切河谷输入的时间变化。结果表明，在大约8.0 cal kyr bp之前，钱塘江向其河谷提供了所有沉积物。但由于三角洲充分进积后，长江开始输出泥沙，其泥沙比重向上下降。长江泥，主要成分（约87%) 的长江沉积物被认为主要是通过潮汐流和波浪将东海内陆架泥楔沉积物的再悬浮和向陆输送提供的。晚于泥浆到达钱塘江河谷的长江沙，被解释为东海陆架和钱塘江口北缘较老沉积物的再加工。在填谷的最新部分，钱塘江泥沙只有CA长江贡献的9％，虽然钱塘江泥浆已经开始对最近被导出。钱塘江系统长江贡献构成CA由长江排出的总沉积物负载的50％时的8-6 CAL KYRbp时期，但 <4% 自 6 cal kyr bp。这项研究表明，在解释来自具有重要沿海岸运输作用的沿海-陆架沉积物扩散系统的成分数据时需要谨慎行事，并有望以一般方式适用于其他相连的河流-沿海-陆架系统。