CHARACTERISTICS OF SHELF BREAK AND SEDIMENTAION PROCESS AT THE QIONGDONGNAN BASIN, NORTHWESTERN SOUTH CHINA SEA

The shelf break zone has unique dynamic conditions and sedimentation processes. In order to reveal the origin of geomorphological features and related sedimentation, characteristics of the shelf break zone at the Qiongdongnan Basin are studied based on the bathymetry and high resolution single-channel seismic data. The results show that the water depth varies greatly in a complicated pattern along the SE-NW shelf break zone of the Qiongdongnan Basin. The west segment of the shelf break, where no gully is developed, is located at the water depth of 250 to 700 m. It is 500 m in depth, 7 km in width, with a mean slope of 2°. The middle segment of the shelf break, located at the water depth of 250 to 750 m, is 500 m in depth, 10 km in width, with a mean slope of 7°. U or V shape gullies are found at the middle segment and 5 to 6 km in length, 3 to 8 km in width, with an incision depth of 100 to 300 m. The east segment of the shelf break, located at the water depth of 400 to 1500 m, is 1100 m in water depth, 30 km in width, with a mean slope of 10°. There are many V shape gullies, which are 13 to 25 km in length, 3 to 4 km in width, with a maximum incision depth up to 500 m. The west segment of the shelf break zone is accumulative, whereas the east segment is erosional and the middle segment transitional. The results of this study could be used as the scientific base for the study of deep sea sedimentary process as well as oil and gas exploration in deep water areas.