The sediment budget of the Northwest Sub-basin, South China Sea since the Late Miocene (11.6 Ma, average thickness > 1000 m) accounts for more than two-thirds of the total infill since the initial ocean spreading of the sub-basin (32 Ma). The sediment sources and architectural pattern of these deposits, however, are poorly known. Using high-resolution 2D reflection seismic data with age constraint from IODP boreholes, we have documented two interdigitating basin-floor fan systems that developed since the Late Miocene. These were fed by two of the largest deep-water canyon systems worldwide, from the west (the Central Canyon/Xisha Trough) and the northeast (the Pearl River Canyon), as well as from smaller headless canyons and gullies across the surrounding slopes. Based on careful analysis of seismic facies, their geometry and occurrence, we identify the principal deep-water architectural elements, including the multi-scale channels, channel-levee complexes, lobes, sheets and drapes, mass-transport deposits, volcanic intrusions, turbidity-current sediment-wave fields, and a contourite drift/terrace.

Tentative reconstructions show that the development of these Late Miocene-Quaternary basin-floor fan systems was dominated by changes of sediment supply. The Xisha fan reached its largest extent during the Late Miocene, while the Pearl River fan was most active during the Late Miocene to Quaternary. During the Late Miocene, both the conduits of the Central Canyon and the Pearl River Canyon were active with abundant sediment supply, generating the two incipient fan systems. Sediment supply from the west via the Central Canyon persisted throughout the Late Miocene, being coarser-grained than that of the Pearl River fan. With the demise of the Central Canyon during the Pliocene and consequent sharp decrease in sediment supply, the Xisha fan size reduced significantly. By contrast, supply of mud-rich sediments from the Pearl River and northern slope increased through the Pliocene and into the Quaternary, leading to the modern sedimentary pattern of interdigitating basin-floor fans. Insights into the evolution of sediment supply and fan development through time derived in this study contribute to a better understanding of how source to sink systems feed marginal oceanic basins such as the South China Sea.

自中新世末期以来，南海西北次盆地自中新世晚期以来的沉积物预算（11.6 Ma，平均厚度> 1000 m）占总充填量的三分之二以上（32）嘛）。然而，这些沉积物的沉积物来源和建筑模式知之甚少。使用受IODP井眼年龄限制的高分辨率2D反射地震数据，我们记录了自中新世以来形成的两个相互交叉的盆地-地面扇系统。这些是由世界上两个最大的深水峡谷系统提供的，它们来自西部（中央峡谷/西沙海槽）和东北（珠江峡谷），以及较小的无头峡谷和跨沟壑的沟壑。在仔细分析地震相，其几何形状和发生之后，

初步的重建表明，这些晚中新世-第四纪盆地-底扇系统的发展主要由沉积物供应的变化决定。西沙扇在中新世晚期达到最大程度，而珠江扇在中新世至第四纪晚期最为活跃。在中新世晚期，中央峡谷和珠江峡谷的导管均处于活跃状态，沉积物供应丰富，产生了两个初期扇形系统。从西部到中央峡谷的沉积物供应一直持续到整个中新世晚期，其颗粒度比珠江迷大。随着上新世时期中央峡谷的灭亡，以及随之而来的泥沙供应量的急剧减少，西沙扇的大小显着减小。相比之下，珠江和北坡富泥沉积物的供应量通过上新世进入第四纪而增加，导致现代沉积模式使盆底扇相互交错。这项研究得出的随着时间的流逝，沉积物供应和风扇发展演变的见解有助于更好地了解下沉系统的源头如何为南海等边缘海洋盆地提供营养。