Sequence stratigraphic architectures and responses to syndepositional tectonic evolution in the Paleogene Lingshui Sag, Qiongdongnan Basin, northwestern South China Sea

摘要

The syndepositional tectonic evolution and sequence stratigraphic architecture of the Paleogene Lingshui Sag, Qiongdongnan Basin, South China Sea, are investigated with seismic profiles, boreholes and well logs. First, according to the recognized sequence boundaries, the Paleogene sequence stratigraphic framework is established. Then, based on analyzing the subsidence history and paleogeomorphology evolution, the Paleogene Lingshui Sag is clarified to present episodic tectonic evolution, showing tectonic stage-I, stage-II and stage-III. From stage-I to stage-III, the major basin-marginal faults gradually lost control over the subsidence center, which moved away from the initial basin margin to the late central basin. Structural slope break belts, such as fault slope break belts and gentle slope break belts, formed through the above three tectonic stages and controlled the formation of four types of relevant distinct sequence stratigraphic architectures, namely, Types A1, A2, B1 and B2. Finally, the responses of sequence stratigraphic architectures to tectonic evolution are described, and the favorable hydrocarbon reservoirs in the different architectures are discussed, which constitute stratigraphic traps, fault traps, lenticular lithologic traps and updip wedge-out traps. This information is beneficial in prospecting for subtle traps in basins located in deepwater areas.