西沙海域碳酸盐台地周缘水道沉积体系

高分辨率地震资料显示,南海北部西沙海域碳酸盐台地周缘广泛发育水道沉积体系。礁缘水道底界面表现出强反射特征,内部充填弱-强、连续性好的地震相,可见底部杂乱反射特征;斜坡水道在地震剖面上表现为横向上连续发育的"V"型特征,且下切深度较浅。西沙隆起与广乐隆起之间的南北向低洼地带发育大型深水水道,并且受古地貌高点影响,水道分为南北两个分支。北分支水道可分为5期,且水道迁移现象明显;南分支水道可分为4期,水道以充填强振幅、连续性好的浊流沉积体和弱振幅、杂乱的块体搬运体系(Mass Transport Deposits,MTDs)为特征,每期水道均表现出侵蚀-充填-废弃的旋回性。分析认为西沙碳酸盐台地周缘水道沉积物源来自西沙隆起和广乐隆起的碳酸盐台地和生物礁碎屑及由火成作用产生的火成岩碎屑。西沙-广乐碳酸盐台地水道相互贯通,构成台地-斜坡-深水的水道沉积体系,为碳酸盐岩、生物礁及火山碎屑向台地周缘输送提供了良好的通道。

Characteristics of periplatform channels of the Xisha area, northern South China Sea

High resolution seismic data shows that there widely exist periplatform channel system in the Xisha area, northern south China sea. Channels around reefs display strong amplitude reflections, and were filled with weak-strong and continuous reflections, chaotic seismic reflection can be found at the bottom of the channels. Small-scale channels on the slope show a serious of V-shaped reflections with incised shallow on the underlying strata. Zhongjian deep-water channel developed in the graben lying between Xisha uplift and Guangle uplift, and the channel was separated apart into two branches because of the existence of a paleo- highland. The north branch can be divided into five stages with significant migration. The south branch can be divided into four stages and with inner high amplitude, continuous reflections. Each stage of it show a erosion-infill-abandon sedimentary cycle. Paleogeography analysis shows that the channel-filled deposits compose of carbonate and reefs debris and volcaniclastic rocks. Channels in the Xisha area constitute a platform-ramp-deep water channel sedimentary system, and provide well conditions for the carbonate and reefs debris and volcaniclastic rocks transported into deep-water area. As a result, the carbonate platforms can provide carbonate clastic sediments to adjacent environment.