长江三角洲ZK01孔末次盛冰期以来沉积物粒度特征及环境演化

Grain size analysis and environmental evolution indicated by the ZK01 borehole samples in the Changjiang delta since the latest glacial maximum

根据长江三角洲ZK01孔的粒度资料,从粒度参数、斜体图、概率累积曲线和频率分布曲线等对末次盛冰期以来的沉积物粒度特征进行了详细分析,并结合沉积物的岩性、沉积构造和有孔虫的分布特点,探讨了该区末次盛冰期以来的沉积环境演化。分析表明,ZK01孔末次盛冰期以来,沉积物自下而上可分为5段:河床沉积物以砂和砾质砂为主,粒度概率累积曲线为以跳跃总体为主的两段式;河漫滩相为砂质和黏土互层,概率累积曲线呈以悬浮总体为主的具过渡的两段式,频率分布曲线为双峰或多峰式;河口湾沉积物的粒度参数变化显著,在C-M图上表现为粗细分异明显的两类,对应两种两段式累积曲线,频率分布曲线亦有单峰和双峰式两类;浅海相主要为淤泥质黏土,粒度参数较稳定,概率累积曲线为一段式,几乎均为悬浮总体;三角洲沉积物以细砂和粉砂为主,概率累积曲线为以跳跃总体为主的具过渡的两段式。研究区该时期依次经历了河床、河漫滩、河口湾、浅海和三角洲等5种沉积环境。

The present paper gives a detailed description of grain size analysis on the basis of grain size parameters, C-M patterns,grain size probability accumulation curves and frequency distribution,and the environmental evolution according to lithology,sedimentary structures and foraminifera distribution in the Changjiang delta since the latest glacial maximum. The sediments herein can be divided into five segments from bottom to top. The riverbed deposits consist of sand and gravelly sand,and display the two-part grain size probability accumulation curves dominated by saltation populations. The floodplain deposits are made up of the interbeds of sand and clay, and display the two-part grain size probability accumulation curves represented by the suspension-dominated populations,and the bimodal or multimodal frequency distribution curves. The estuarine deposits display sharp changes of grain size parameters and C-M patterns,two-part grain size probability accumulation curves and unimodal or bimodal frequency distribution curves. The neritic deposits comprise muddy clay,and display one-part grain size probability accumulation curves represented by suspension populations. The delta deposits are significantly made up of fine sand and silt,and display the two-part grain size probability accumulation curves represented by saltation populations. The study area once underwent the evolution of river bed,floodsplain, estuary,shallow sea and delta sedimentary environments during the latest glacial maximum.