Seismic Features of a Submarine Mud Volcano in the Weitan Banks Area of the Northern South China Sea

Mud volcanism is often linked with hydrocarbon-bearing sedimentary basins. In the middle segment of the northern South China Sea, there sit the Cenozoic Pearl River Mouth Basin and the Mesozoic Dongsha Basin. The North and South Weitan Banks lie in their transitional zone where the petroleum geology remains poorly known and waits for discovery. Recent geophysical investigations have revealed a ~80 m high hill, the Zhongwei Hill, intra a topographic low, and a graben below in the Weitan Banks area. It is typical of an intrusion-extrusion system in view of various seismic reflection features. On the surface, the hill displays a gentle and smooth apron which is mostly buried, leaving a rimmed depression. The hill body features a chaotic reflection package. Under the package, there hung a columnar anticlinal and a few tubular fractured zones featuring foggy or weak reflections which are indicative of conduits. Downward into the graben, there appear a wide and open anticline coupling on a large diapir. By regional stratigraphic correlation with the drilling well LF35-1-1 in the Dongsha Basin, the strata of the deep anticline and diapir are comprised of the Paleogene System and thicker than 3 km Mesozoic Erathem, respectively. What is more, the hill features trivial gravity variation, meaning for its constituents of low density. All the features are supportive for the Zhongwei Hill as a mud volcano as those found over the southern Dongsha Island waters in the Dongsha Basin. The Mesozoic strata, at least 3 km thick, composing the large diapirs must be the main gas provider and of significant potential. The mud volcanism at the Zhongwei Hill poses a favorable clue for insight into the Mesozoic petroleum to the transitional zone between the Cenozoic and the Mesozoic basins.