Abstract:

This research uses the basic end-member modeling algorithm,non-parametric estimation decomposition algorithm,and grain size-standard deviation method to evaluate the grain-size data of the Holocene sediments from core SE3 in the Hangzhou Bay area,in order to investigate the vertical distribution pattern of different grain-size end-members and their coupling relationship with environmental evolution. Results show that the basic end-member modeling algorithm acts as the best method in decomposing grain-size end-member in comparison with the other two methods. Five grain-size end-members were identified in the study area by the basic end-member modeling algorithm: EM1(clay and silt),EM2(coarse silt and very coarse silt),EM3(very coarse silt,very fine sand and fine sand),EM4(fine sand and medium sand)and EM5(medium sand and coarse sand). Their vertical distribution patterns are controlled by the evolution of sea level,depositional environment,and dynamic process. The coarse-grained end-members EM5 and EM4,representing bed load,are primarily supplied by the Qiantang River and distributed in the amalgamated fluvial channel,floodplain,and paleo-estuarine deposits. As sea levels rising,the content of proximal EM5 decreases upwards,while the content of relatively distal EM4 increases. The fine-grained end-members EM2 and EM1,representing suspended load,are distributed in the offshore shallow marine and present-day estuary stratigraphic units;they are mainly derived from the Changjiang by a combination of alongshore and tidal currents in a high sea-level setting. EM3,representing bed load with a normal distribution of grain size,is primarily distributed in the present-day estuary deposits,and probably represents the sediment transported and sorted by tidal currents and storm surges. This study sheds a new light in reconstructing the evolution history of sea level,environment,and source-to-sink processes in estuarine areas by using sensitive grain-size end-member algorithm analysis.

Key words: Holocene, Hangzhou Bay, grain-size end-member, souce-to-sink processes, environmental evolution

摘要：

本研究以杭州湾地区SE3孔全新世沉积物为研究对象,采用基本端元模型算法、非参数估计分解算法和粒级-标准偏差法对粒度数据进行分析,旨在探讨研究区沉积物粒度端元的组成特征、垂向演化规律及其与物源和沉积环境演化的耦合关系。 结果表明3种粒度端元分析方法具有良好的结果一致性,但基本端元模型算法效果更好。研究层段共识别出5个粒度端元: EM1(黏土和粉砂)、EM2(粗粉砂和极粗粉砂)、EM3(极细砂和细砂)、EM4(细砂和中砂)和EM5(中砂和粗砂)。各粒度端元的垂向展布规律受控于海平面、沉积环境和动力过程演变。粗粒的EM5和EM4端元为推移质,主要由钱塘江提供,分布在河床、河漫滩和古河口湾沉积单元内; 且随着海平面上升,代表近源的EM5端元含量逐渐减少,而代表相对远源的EM4端元含量逐渐升高。细粒的粒度端元EM2和EM1端元为悬移质,主要来自长江,分布在近岸浅海和现代河口湾沉积单元; 此时海平面较高,来自长江的沉积物可通过沿岸流和潮流搬运至钱塘江下切河谷内。EM3为推移质,分选好、粒度曲线呈正态分布,主要分布在现代河口湾沉积单元内,可能代表潮汐流和风暴潮搬运和筛选的沉积物。该研究揭示了沉积物敏感粒度端元分析在重建河口区海平面变化、环境演变以及源汇过程中的科学价值。

关键词: 全新世, 杭州湾, 粒度端元, 源汇过程, 环境演变

CLC Number: 

• P53