Multiple sediment sources and topographic changes controlled the depositional architecture of a palaeoslope-parallel canyon in the Qiongdongnan Basin, South China Sea
Multiple sediment sources and topographic changes controlled the depositional architecture of a palaeoslope-parallel canyon in the Qiongdongnan Basin, South China Sea
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多重沉积物源和地形变化控制南海琼东南盆地古坡平行峡谷沉积构型
DOI：
10.1016/j.marpetgeo.2019.104161
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发表时间：
2020-03
影响因子：
4.2
通讯作者：
Zhou Zhan
中科院分区：
文献类型：
--
作者：
Liang Chao;Xie Xinong;He Yunlong;Chen Hui;Yu Xiaohang;Zhang Wenyan;Mi Honggang;Lu Biyu;Tian Dongmei;Zhang Hui;Li Mingjun;Zhou Zhan
海底峡谷沉积由于其在从源到沉的分析和油气勘探方面的重要性而引起了人们的关注。利用最近在琼东南盆地乐东-陵水段采集的高分辨率二维和三维地震和探井资料，研究了有别于其他斜坡垂直峡谷的古斜坡平行中央峡谷的沉积结构。研究表明，该峡谷发育在多阶梯古地貌的海槽上，向东呈平行坡降的趋势。琼东南盆地西部海槽的位置受控于区域构造和进积斜坡床的形态。古地形延伸方向和坡度的地理变化导致了峡谷深度和宽度的变化。对峡谷填充物的分析表明，有多个泥沙来源，包括来自越南中部和海南岛西部的轴向泥沙来源和来自琼东南盆地北坡的峡谷侧来源。物源研究表明，前者提供了相对粗粒的浊积岩，后者提供了细粒物质输运沉积(MTD)。这些MTDS大多起源于盆地的北部斜坡。中央峡谷的演化可分为三个阶段。第一阶段的特点是形成峡谷的重要切口。随后或同时，峡谷中段起始处的急弯可能导致横向侵蚀，从而分别在峡谷中段和下段引发大范围和小范围的峡谷边缘破坏。随后的早期充填阶段(阶段2)指的是轴向沉积物源提供的浊积岩的沉积。然而，阶梯状坡面的形态导致了中央峡谷上段的泥沙绕行。充填晚期(阶段3)，以峡谷侧沉积物源提供的MTDS为主，并与浊积岩互层。MTDS的沉积导致峡谷容纳空间急剧减少，峡谷最深处突然向东南迈进。此外，在这一阶段，泥石流和浊流之间发生了复杂的相互作用。峡谷结构的这种变化是由多种沉积物供应和地形变化控制的。提出的峡谷充填概念模型和由此产生的地层结构可以应用于其他类似的峡谷进行油气勘探。
Submarine canyon deposits have drawn attention due to their significance on source-to-sink analysis and hydrocarbon exploration. High-resolution 2-D and 3-D seismic and exploration well data recently collected in the Ledong-Lingshui segment of the Qiongdongnan Basin are used to investigate the depositional architecture of the palaeoslope-parallel Central Canyon, which is distinct from other slope-perpendicular canyons. This study indicates that the canyon developed along the thalweg of a multiple stepped palaeotopography with a slope-parallel descending trend eastwards. The location of the thalweg is controlled by regional tectonics and progradational slope clinoforms in the western Qiongdongnan basin. Geographic changes in an extending direction and slope gradient of the palaeotopography resulted in variations in the depth and width of the canyon. Analysis of the canyon infillings indicates multiple sediment sources including an axial sediment source from the Central Vietnam and the western Hainan Island and a canyon-side source from the northern slope of the Qiongdongnan basin. Provenance study shows that the former source supplied relatively coarse-grained turbidites and the later supplied fine-grained mass transport deposits (MTD). Most of such MTDs originated from the northern slope of the basin. Evolution of the Central Canyon can be classified into three stages. Stage 1 is characterised by significant incisions that are responsible for the formation of the canyon. Subsequently or contemporaneously, the sharp bend at the beginning of the middle segment of the canyon likely resulted in lateral erosion, which triggered large-scale and small-scale canyon margin failures in the middle and lower segments of the canyon, respectively. The subsequent early filling stage (Stage 2) refers to the deposition of turbidites supplied by the axial sediment source. However, the morphology of the stepped thalweg slope resulted in sediment bypass in the upper segment of the Central Canyon. During the late filling stage (Stage 3), MTDs supplied by the canyon-side sediment source were dominated, and interbedded with turbidite deposits. The deposition of the MTDs resulted in the sharp decreases in canyon accommodation space and the abrupt southeastwards stepping of the deepest part of the canyon. Moreover, complex interactions between debris-flows and turbidity-flows occurred during this stage. Such variations in architecture of the canyon were controlled by multiple sediment supplies and topographic changes. The proposed conceptual model of canyon infilling and the resulting stratigraphic architecture could be applied in other analogous canyons for hydrocarbon exploration.
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