PLIOCENE SHELF MARGIN MIGRATION TRAJECTORIES IN THE QIONGDONGNAN BASIN AND ITS IMPLICATIONS FOR DEEP WATER HYDROCARBON EXPLORATION

Based on the high-precision 2D seismic data from the shelf margin of the Qiongdongnan Basin, six sequences, namely YGH-SQ1, YGH-SQ2, YGH-SQ3, YGH-SQ4, YGH-SQ5, and YGH-SQ6 from the bottom up are identified for the Pliocene Yinggehai Formation according to the typical seismic contact relationships such as local truncation, onlap, toplap, downlap and incised valley. The quantitative characterization method is adopted to follow up the trajectories of shelf edge. The Pliocene trajectories of the shelf edge of the Yinggehai Period in the Qiodngdongnan Basin can be classified into three types: negative-angle descending, low-angle gently ascending and high-angle ascending, and the vertical evolution of the Pliocene shelf edge track can be divided into six stages, with the descending and gently ascending shelf edge trajectories dominated the west and the gently ascending and ascending shelf edge trajectories dominated the east. In lateral direction the progradation is much larger in the west than that in the east, and thus the shelf slope folds formed in a pattern of “wide in the west and narrow in the east”. Based on the quantitative statistical analysis and previous work, it is clear that the vertical migration of the shelf edge tracks in the study area is mainly controlled by sea level fluctuation caused by climate change and the increase in sediment supply; while the lateral migration of the shelf edge trajectories is mainly controlled by the difference in tectonic activity and sediment supply. The sediment supply in the western part of the study area is much larger than that in the eastern part as the activity of the fracture zone is weaker than that in the eastern part, which leads to the development of the western land slope in the study area. The western part of the study area is much more abundant in sediment supply than that of the eastern part and the fault zone is less active than the eastern part, resulting in the development of the western land slope and the eastern land slope. The land slope areas and deep water fans in the deep-sea plain area are favorable exploration areas for oil and gas, which correspond to the trajectories of the negative-angle descending and low-angle slowly rising shelf edges.