Structural evolution and its control on source-to-sink system of Panyu 27 Sag in Pearl River Mouth Basin during rifting

Sag Panyu 27 is located in the Panyu low uplift area in the middle of the central uplift zone of the Pearl River Mouth Basin. It is a Cenozoic sag developed on the basement of the Mesozoic continental margin magmatic arc, which is ‘faulted in the south and overlapped in the north’. Oil samples and extracted hydrocarbon from wells drilled in the sag can be traced back to the intermediate to deep lacustrine source rocks in the Wenchang Formation. However, none of the wells actually reached the formation, making the specific location and period for the development of source rocks still uncertain. Through the study of the controlling fault and the structural style of the sag, it is shown that the development and evolution of the sag has a ternary coupling genesis of ‘pre-existing structural constraints, dextral extension control, and magmatic underplating transformation’, which controls the structural pattern of ‘left stepping asymmetric graben-left lateral en echelon semi-graben-wide and gentle semi-graben’ in the three-stage rifting period. The differential activation of sag-controlling faults in the three stages of rifting period affects the migration of the sedimentary center, and the differential evolution of the sag architecture affects the sedimentary filling pattern of the sag. With the rifting, the sedimentary center gradually migrated from east to west, and from both ends to the middle. In the early stage of Wenchang Formation deposition, the source-to-sink sedimentary systems are mainly distributed in the central transition zone along the NW-trending axis, while in the late stage, they mainly occurred on the northern gentle slope, and a large source-to-sink sedimentary system with long provenance appeared in the northwest during deposition of the Enping Formation. As a sedimentary center for a long time, the western sub-sag is the right place for the development of high-quality source rocks. The middle stage of rifting when a large semi-graben lake basin was formed and accompanied by strong magmatic activity was the time for the development of high-quality source rocks. The long-term development of large source-to-sink sedimentary system in the northwest during the middle-late rifting stages provided favorable conditions for the formation of large Paleogene reservoirs.