长江远端三角洲多源沉积分异作用及其动力机制

Sedimentary Differentiation and Hydrodynamic Environment of Multi-sourced Sediment in the Changjiang Distal Delta

长江是亚洲第一大河,具有丰沛的水沙通量,其形成的长江三角洲和陆架沉积中心一直是学者的研究重点,但对受到多种物质来源供给的长江远端三角洲涉及较少。针对长江远端三角洲南部的海底表层沉积物和河流沉积物,对该地区的表层沉积物性质和分布特征等进行了分析。研究表明,该地区表层沉积物类型主要为泥、粉砂、砂质粉砂和粉砂质砂等类型,零星分布含砾沉积物,沉积物粒度自西北向东南方向逐渐变粗,与海岸带呈平行分布;该地区沉积物主体为长江源物质,近岸南北两区域主要受到闽江和瓯江河流物质混合作用,东南区域主要为台湾河流物质影响;该区沉积分异模式主要受到东海环流体系的控制影响,浙闽沿岸流与台湾暖流形成的切变锋起到“水障”作用,使长江物质主要存在于中西部地区,同时西部近岸由于受到浙闽沿岸流的季节变化,带来了近岸闽江和瓯江等中小河流物质的混合影响,而东南部则主要受到台湾暖流带来的台湾物质混合作用。该研究对研究区沉积物的物质来源和动力因素等现代过程进行了细致划分,对长江远端三角洲地质时期的形成演化具有一定的辅助作用。

The Changjiang River is the largest river in Asia in terms of its enormous amount of sediment and water discharge,which has formed a subaqueous mega-delta.Its depocenter has always been an important research area fo-cusing on high-resolution environmental evolution;however,little attention has been paid to its distal delta,which is an area in which multi-sourced sediments interact.Grain size and clay mineral data of surface sediments were ana-lyzed to determine the distribution characteristics and mechanism within the mixing zone.It was found that there are four main sediment types(mud,silt,sandy silt and silty sand)distributed parallel to the coastline and becoming coarser seawards.A provenance analysis showed that the surface sediment in the study area is primarily sourced from the Changjiang River,with four sub-zones within the study area:(i)a central sub-zone containing sediment from the Changjiang River;(ii)a northwestern sub-zone containing mixed sediment from the Oujiang River;(iii)a southwest-ern sub-zone containing mixed sediment from the Minjiang River;and(iv)a southeastern sub-zone containing mixed sediment from the Taiwan Residents River.Sediment from the different provenances is differentiated by currents in the East China Sea.The fronts and seasonal variation of the Zhejiang-Fujian Coastal Current and the Taiwan Warm Current play the key role in sediment differentiation in the study area.Knowledge of sediment differentiation and the mecha-nism of present-day sedimentary processes is helpful for understanding the evolution of the Changjiang Distal Delta since the Holocene.