水位变化对鄱阳湖三角洲分流河道沉积特征的影响

摘要

To study the impact of water level change on the sedimentary characteristics of distributary channel in Poyang Lake delta,this research applied methods of modern sedimentary investigation,mining profile,and grain size analysis to delta plain distributary channels in Ganjiang middle branch delta and Xinjiang delta front.The results suggest that there are two types of sedimentary units in the distributary channels in Ganjiang middle branch delta:lag deposit and point-bar;and three types in the distributary channels of Xinjiang delta front:tadpole-shaped sand ridge,linear low-lying sand,banded channel sand,respectively.When water level rises,sediments mainly deposit onshore back to the source in delta distributary channel;meanwhile,point bar receives sediments and develops water rising wedge-shaped sand.Sediments mainly prograde towards the basin,and delta develops at low water level.When water level declines,point bar develops water falling lateral sand.When water level rises,delta front distributary channel develops tadpole-shaped sand ridge,which is subsequently transformed into banded channel sand by waves on both sides of the river;when water level declines,delta front distributary channel develops banded channel sand.Affected by water level change,sand in the distributary channel shows a heterogeneous distribution in both the plane and vertical profiles,while sand in the delta front distributary channel has typical in plane zoning features.%选取鄱阳湖赣江中支三角洲平原分流河道和信江三角洲前缘分流河道,采用现代沉积考察、剖面挖掘、粒度分析等方法,就水位变化对分流河道沉积特征的影响进行研究.结果表明:在赣江中支三角洲平原分流河道内发育滞留沉积和边滩沉积2种沉积单元;信江三角洲前缘分流河道内发育蝌蚪状砂垄砂、长条形浅滩砂、条带状河道砂3种沉积单元;三角洲分流河道砂在水位上升期向岸溯源沉积,在低水位期向盆地进积,是三角洲发育主要时期;边滩沉积在水位上升阶段发育水位上升楔状砂,在水位下降阶段发育水位下降侧积砂;三角洲前缘分流河道在水位上升期沉积蝌蚪状砂垄,被湖浪改造后在两侧河岸形成长条形浅滩砂;水位下降期沉积条带状河道砂,受水位变化影响,分流河道类砂体在平面及剖面上的砂体组合表现出一定的分带性及储层非均质性.