长江口邻近陆架表层沉积物变化特征及成因

基于近30年长江口邻近陆架区域表层沉积物数据,对表层沉积物与流域入海泥沙特征的响应进行研究。结果表明:①沉积物表现为东粗西细,北粗南细的分布格局,砂百分比分布表现为东北向西南为减小,粉砂和黏土均表现为东北向西南增加趋势,其中整个区域黏土与粉砂百分比的比值在0.12~0.83之间;②2008~2010年与2003~2006相比,砂的百分含量表现为增加,粉砂和黏土表现为减少趋势,表层沉积物向粗化趋势发展;③砂-泥分界线在2003~2007年北侧（31°30’以北）为交替变化,2007~2010年为向西移动,南侧（31°30’以南）2003~2010年均为向西移动,长江口陆架区域表层沉积物砂泥分界线变化是综合作用的结果,砂质沉积物因海平面上升等作用再悬浮沉积在泥质区的作用将逐渐加强。④泥质区域面积在三峡水库蓄水后减小,且位置略有南偏,主要受北槽深水航道整治工程及自然因素的影响。

Surface Sediment in the Nearby Shelf of the Yangtze River:Change and Causes

The transportation to a sea of sediment with water founds the linkage mechanism of from "source" to "sink" and the response of surface sediment characteristics in the nearby shelf to factors of incoming sediment from the watershed. Take the response of the surface sediment in the offshore area of the Yangtze River to the characteristics of the incoming sediment from the watershed for example. Results showed that: ①for median grain size, it was large in the east and north while small in the west and south. Silt percentage decreased from northeast to southwest while silt and clay showed trends of increasing from northeast to southwest. And the ratio of clay percentage to silt percentage in the whole area was 0.12~0.83. ②compared to that in 2003~2006, sand percentage in 2008~2011 rose while silt and clay percentages showed trends of dropping, and surface sediment tended to be larger. ③The north part (north of 31°31') of the sand-silt boundary changed alternately during 2003~2007, shifted to the west during 2007~2010 while the south part (south of 31°31') shifted to the west for the whole period of 2003~2010. The shift of the boundary was mainly caused by the deposition of sandy sediment from sea area on argillaceous sediment, with diffusion deposition playing a secondary role. ④The argillaceous zone shrank after the impoundment of the Three Gorges and shifted slightly to the south, which was mainly influenced by the training works and natural factors.