Depositional Filling Characteristics of Paleogene in Heshan Sag of Ultra Deepwater Area in the Northern South China Sea

Heshan Sag was located in lower continental slope of northern margin of the South China Sea , its south side was close to the NW subbasin , it had special geological conditions such as thinning crust , ductile deformation of the lithosphere and high heat flow anomalies.Therefore Heshan Sag had special characteristics of depositional filling.Sequence stratigraphy and seismic facies studies show that Wenchang , Enping and Zhuhai Formations are developed in the Paleogene of Heshan Sag , the top and base of the formation are large unconformity.Terrestrial lacustrine deposition is developed during Wenchang and Enping Formations , in which the seismic reflection characteristics of middle-deep lacustrine mudstone are similar to the source rock of Baiyun Sag , it is the main hydrocarbon source rock in Heshan Sag , the shallow marine delta deposits are developed in Zhuhai Formation with S Type of progradational reflections , delta sandstone is the main reservoir in Heshan Sag.In addition , There exist the gravity flow deepwater fan sands