SEISMIC FACIES OF QUATERNARY SHELF-MARGIN DELTAS IN NORTHERN SOUTH CHINA SEA

Shelf-margin deltas have been regarded as one of the important hydrocarbon exploration targets in the world for years for its wide distribution, big thickness and well-developed reservoirs. Using high-resolution seismic data, the authors analyzed the seismic facies and sedimentary characteristics of the shelf-margin deltas of Quaternary in details located in the Panyu Low Uplift of the Pearl River Mouth Basin (PRMB), South China Sea. A shelf-margin delta is composed of three components i.e. a delta plain, a fore-delta and a delta front. The shelf-margin delta plain consists of the channel-levee complexes with frequent ravinement and deposition. The delta front usually shows a large scale of foreset seismic facies. When sea level rises and if the supply of sediment is sufficient, it moves quickly seawards, and the shelf-edge grows toward the slope. The delta front deposits are much influenced by shelf break. The depositional pattern of the fore-delta in the region is not clear to present. An integrated study of the deltaic deposits shows that the sea level changes in a cyclic manner in Quaternary. It drops slowly and rises rapidly in the research area. As the results, the deltaic deposits show a clear pattern of slow regression and fast transgression.