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

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.