The shallow-marine turbidite fans in the Upper Miocene Huangliu Formation of the Yinggehai Basin in the northwestern South China Sea (SCS) provide an excellent opportunity to understand their sedimentary processes in a shelf depositional environment. The down-slope gravity flow processes and along-slope bottom-current reworking processes of shallow-marine turbidite fans were interpreted by using seismic, well logging, core, petrographic, geochemical, and petrophysical data. Several depositional elements were identified in the shallow-marine turbidite fans, namely, channel-fill high-density turbidites (HDTs), channel-fill low-density turbidites (LDTs) and associated frontal splays, sand-rich/mud-rich lobe deposits, and bottom-current reworked channel-fill/lobe deposits. Deep U-shaped (or V-shaped) seismic reflections and low root-mean-square (RMS) amplitudes characterize the channel-fill HDTs that consist of massive fine-grained sandstones with mud clasts. The channel-fill LDTs, characterized by V-shaped or worm-shaped reflections, mostly consist of normally graded, laminated and rippled, very fine-grained sandstones. Frontal splays are generally associated with channel-fill LDTs. The sand-rich lobe deposits show continuous high-amplitude sheet-like reflections and consist of HDTs and LDTs, whereas the mud-rich lobe deposits show continuous moderate-amplitude reflections and consist of muddy debrites. The bottom-current reworked sandstones (BCRSs), which comprise well-sorted, fine-grained sandstones with traction-current structures, are usually located in the upper parts of thick sandbodies. The variability of depositional elements from large-scale channel-fill HDTs with strong basal erosion in fan-1 to small-scale channel-fill LDTs in fan-2 is closely linked with sea-level fluctuations that result in variable gravity-flow energy and sediment input. However, the reoccurrence of large-scale channel-fill HDTs in fan-3 at sea-level highstands may possibly be attributed to enhanced sediment input from the source areas. Down-slope flow transformation from turbidity flows into muddy debris flows within an individual channel-lobe complex (CLC) resulted in a dramatic increase in clay content and resultant decreasing reservoir quality from the channel-fill HDTs to the mud-rich lobe deposits, because muddy sediments are incorporated into the precursor turbidity flows and turbulence is suppressed. Additionally, it is suggested that the widely developed traction-current structures and tidal signatures (double mud layers, mud-draped ripples, discrete wavy bedding, internal truncation surface, and convex-up laminae) are the products of reworking by internal waves and -tides. During periods of sea-level highstands, the upper parts of gravity-flow sandstones would undergo bottom-current reworking, thus resulting in the retransportation of muddy fines and the formation of reworked sandstones with traction-current structures and tidal signatures. In this study, a combination of traction-current structures, tidal signatures, vertical sequences showing sharp upper contacts and non-gradational upper contacts, and trace elements is considered to be convincing diagnostic criteria in distinguishing reworked sandstones from gravity-flow sandstones. The representative bottom-current reworked sandstones should be preferable hydrocarbon targets in further exploration because of their better reservoir properties compared with gravity-flow sandstones. This research offers some insight into gravity-flow processes and bottom-current reworking processes in a shallow marine environment.

南海西北部莺歌海盆地上中新统黄流组浅海浊积扇为了解其在陆架沉积环境中的沉积过程提供了极好的机会。利用地震、测井、岩心、岩相、地球化学和岩石物理数据解释了浅海浊积扇的下坡重力流过程和沿坡底流改造过程。在浅海浊积扇中确定了几种沉积元素，即河道填充高密度浊积岩（HDTs）、河道填充低密度浊积岩（LDTs）和相关的锋片、富砂/富泥叶状沉积物，以及底部电流返工的通道填充/叶沉积物。深 U 形（或 V 形）地震反射和低均方根 (RMS) 振幅表征了通道填充 HDT，由块状细粒砂岩和碎屑组成。以 V 形或蠕虫形反射为特征的通道填充 LDTs 主要由正常分级、层状和波纹状的极细粒砂岩组成。正面张开通常与通道填充 LDT 相关。富砂叶状沉积物呈连续的高振幅片状反射，由HDTs和LDTs组成，而富泥叶状沉积物呈连续的中等振幅反射，由泥质碎屑组成。底流改造砂岩（BCRSs）由分选良好的细粒砂岩组成，具有牵引流结构，通常位于厚砂体的上部。从扇 1 中具有强烈基底侵蚀的大规模通道填充 HDT 到扇 2 中小规模通道填充 LDT 的沉积元素的变化与海平面波动密切相关，导致重力流能量和沉积物输入。然而，海平面高位扇 3 中大规模通道填充 HDT 的再次发生可能归因于源区沉积物输入的增加。在单个河道-叶复合体 (CLC) 内，从浊流到泥质碎屑流的下坡流转换导致粘土含量急剧增加，从而导致从河道填充 HDT 到富含泥浆的叶形沉积物的储层质量下​​降，因为泥质沉积物被纳入前体浊流中，湍流被抑制。此外，认为广泛发育的牵引流构造和潮汐特征（双泥层、覆泥波纹、离散波状层理、内截断面、上凸纹层）是内波和潮汐作用改造的产物。在海平面高位期间，重力流砂岩上部会发生底流改造，从而导致泥质细粉的再输送，形成具有牵引流结构和潮汐特征的改造砂岩。在这项研究中，牵引流结构、潮汐特征、显示尖锐上部接触和非渐变上部接触的垂直序列以及微量元素的组合被认为是区分再加工砂岩和重力流砂岩的令人信服的诊断标准。具有代表性的底流改造砂岩与重力流砂岩相比具有更好的储层性质，应成为进一步勘探的优选油气目标。这项研究为浅海环境中的重力流过程和底流再加工过程提供了一些见解。