珠江口盆地古近系幕式构造活动与沉积耦合关系——以长昌—鹤山凹陷为例

Coupling of Paleogene periodic rifting activity and sedimentary characteristics in Pearl River Mouth Basin: taking Changchang-Heshan Sag as an example

长昌—鹤山凹陷位于珠江口盆地,具有良好的勘探前景。通过对区域性角度不整合、断裂幕式活动、构造沉降阶段性演化以及古构造格架变化等信息的综合分析,揭示了长昌—鹤山凹陷古近纪构造具有分期异向多幕式裂陷特征,且在不同构造幕,地层沉积受断裂控制作用不同,形成的沉积体系空间展布和配置关系明显不同。主要表现在:早期裂陷幕,沉积地层完全受断层控制,断陷活动强烈,主要发育扇三角洲物源;晚期裂陷幕,断陷活动大大减弱,主要发育近源辫状河三角洲,且该时期圈闭较发育;断拗转换幕,沉积地层分层发育,早期地层完全受断层控制,主要发育浅海三角洲,晚期沉积部分受断层控制,开始接受海相沉积,陆架边缘三角洲伴随陆架不断向海迁移,陆坡的坡度逐渐变陡,开始发育重力流深水扇。

Changchang-Heshan Sag is located in the ultra-deep water basin of northern continental margin of South China Sea with good exploration prospects. Based on the comprehensive analysis of regional angular unconformities, stage evolution of tectonic subsidence, episodic activities of the fracture, and the changes of ancient tectonic frameworks, it is concluded that Changchang-Heshan Sag has the characteristic of stage incongruous multi-episodic rift. Controlled by different intensity of fault activity, the spatial distribution and configuration of depositional system are distinctive in each episode： in the early rifting episode, sedimentary process was entirely controlled by boundary fault and the fault activity was strong, which mainly developed fan delta source; in the final rifting episode, the fault activity and the scale of tectonic transformation weakened, which mainly developed shallow and braided delta; in the fault-depression stage, strata developed by layers, and the early strata were totally controlled by faults, which developed shallow-sea delta; the deposited parts were controlled by faults, which accepted marine sedimentation; shelf-margin delta migrated towards the sea constantly, and the continental slope became steeper and steeper, which developed sediment-gravity flow deep-water fan.