以新采集的地震资料为基础,对南海北部深水西区的混合沉积作了初步研究.混合沉积在地震剖面上表现为平行-亚平行,振幅强-中,频率中等及连续性中等的反射特征.混合沉积分布在研究区地震资料覆盖范围的西北角,发育规模较大,最大长度达44.7 km,最大宽度33.2km,面积1 084km2,最大厚度为138 m,纵向上分布在中中新统梅山组.综合南海北部构造演化、地震勘探等研究成果,建立了混合沉积模式.该混合沉积分布于半深海沉积区,由其南东东方向的西沙-广乐台地提供碳酸盐岩碎屑(同时也提供部分硅质碎屑),由其西侧的中南半岛提供主要的硅质碎屑.在南海北部深水西区,控制混合沉积分布的主要因素为构造作用(包括海平面变化)、物源供给及水动力条件等三个方面,这三者之间又具有密切的内在联系.

Mixed sediments mean the mixed sedimentary carbonate clast and siliceous clast, which are common in modern and ancient sediments. Based on the new seismic data, elementary study is finished to mixed sediments in west deepwater area, Northern South China Sea. The mixed sediments have some reflection features such as parallel-subparallel, medium-strong amplitudes, medium frequency and medium continuity on seismic profiles. The according area of mixed sediments that lies in the northwest of seismic area develop in a relatively wide range with an area of 1,084km2 and up to 138m of vertical thickness in middle Miocene Meishan Formation. A model of mixed sediments is set up based on the tectonic evaluation and seismic exploration in northern South China Sea. These mixed sediments that lie in the semi-deepwater area derive from carbonate clast and parts of siliceous clast, which are provided by Xisha-Guangle Terrace on the east-southeast, and siliceous clast, which are supplied by Indochina peninsula on the west. The main factors controlling the mixed sediments are tectonic action (including changes of sea levels), source supply and hydrodynamic condition, which are closely relative each other.