南日水道“泥质”楔形沉积体特征及其成因机制探讨

根据2016年6—7月在南日水道采集的单波束测深、浅地层剖面测量以及地质钻探等数据资料,发现并确定了南日水道发育的较厚"泥质"楔形沉积体,对沉积体位置的浅地层剖面划分为4个地震单元(SU1、SU2、SU3、SU4),分析了该沉积体的分布和沉积特征。结果表明:该沉积体在南日水道中心深水区发育,沉积体中间厚、两边薄,东西宽约2 km,最大沉积厚度大于20 m;沉积体的沉积物成分在南日水道北部海域以粉砂为主,南部海域以淤泥、淤泥混砂为主;地震剖面显示沉积体内有较大面积的声学屏蔽区,推测为浅层气发育,且浅层气由北向南逐渐减少直至消失。该沉积体的形成与地形有密切联系,木兰溪的入海泥沙及沿岸小溪或冲沟向海的输沙是该沉积体的主要物质来源。通过沉积环境的分析,探讨了南日水道海域晚更新世以来经历的4个沉积阶段。

Study on the features and formation of the muddy wedge deposit in Nanri Waterway

Based on data analysis of bathymetry, sub bottom profile and cores that collected in Nanri Waterway in June and July 2016, we discovered and confirmed a thick muddy wedge deposit in the waterway. Four seismic units, SU1, SU2, SU3 and SU4 were divided according to high resolution seismic profiles on the distribution and characteristics of the sedimentary body. It shows that the sedimentary body has developed in the deep water area in the center of Nanri Waterway. It is thick in the middle, thin on both sides, about 2 km wide from east to west, and more than 20 m in thickness. The sediment composition of the wedge is mainly silty sand in the northern area of Nanri waterway, and silt mixed sand in the south. The seismic profile shows that there is a large acoustic shielding area in the sedimentary body, which is presumed to be the development of shallow gas that decreases gradually from north to south before it disappears. The formation of the sedimentary body is closely related to the terrain and the sands from Mulan stream and coastal streams or gullies to the sea are the main material sources of the sedimentary body. With results of sedimentary environment study, we also discuss the four sedimentary stages developed since the Late Pleistocene of Nanri Waterway.