MORPHOLOGICAL FEATURES AND FORMATION MECHANISM OF CENTRAL CANYON IN THE QIONGDONGNAN BASIN, NORTHERN SOUTH CHINA SEA

The Central Canyon in the Qiongdongnan basin,northern South China Sea,with an "S-shaped" geometry,trends NE across the Ledong-Lingshui,Songnan,Baodao and Changchang depressions.According to the morphology,filling and stratigraphic architectures,the Central Canyon can be divided into 4 types in shape:V U,W,and complex types,and 3 segments in area:eastern,western and transfer segments.The transfer segment that goes consistent with the tectonic transfer zone of the Qiongdongnan basin,has depression-controlling faults to the west of it strike in NE direction and those to the east of it turn into NEE or EW direction.The formation and development of the Central Canyon were a result from the tectonic activity and deep-water deposition.Eastern segment was controlled by submarine uplift,which limited the generation of Central Canyon in Huangliu Formation but formed a restricted channel for the later canyon.The western segemnt was associated with the deep-water deposition.The origin of the filling in the Central Canyon can be ascribed to the gravity sediment.At each stage,the generation of the Central Canyon was simultaneous to or a little earlier than that of synchronous slope.It can be proposed that the canyon formed initially at the east of Qiongdongnan basin and spread westwards gradually.