SEDIMENTARY CHARACTERISTICS OF AN ANCIENT RIVER CHANNEL IN ZHENJIANG-JIANGDU SEGMENT OF YANGTZE RIVER DELTA

The study of a total of six drilling holes located in N-S direction in Jiangdu area,Jiangsu Province reveals that there occurred braided fluvial sediments in the Zhenjiang(Dagang)-Jiangdu segment of the Yangtze River,deposited during late Late Pleistocene including Marine Isotope Stage(MIS)3.In the last glacial maximum,the global sea level dropped dramaticly,and an incised-river channel was formed in Zhenjiang-Jiangdu area.The post-glacial transgression caused by sea level rise led to the channel filling and the formation of the sequence from the river channel to floodplain,estuary and deltaic facies in a succession upwards.Yellow gravelly sands deposited in early post-glacial stage was distributed extensively in the channel,and may be used as a marker.Furthermore,the bottom of the bed may also be used as the boundary of post-glacial and last glacial maximum stags.The continuity of the channel sequence indicates that the Yangtze River was still a running river pouring into the sea in the low stand phase of sea level change during the last glacial stage.The post-glacial transgression arrived here about 9 kaBP and the maximum transgression appeared about 6.5~7.0 kaBP when deltaic progradation started and a channel mouth bar formed synchronously.After the deltaic plain formed,the isostatic adjustment of the ancient channel happened under the influence of regional tectonic movement.The micro-geomorphologic landscape of the deltaic plain depends upon the frequent shifting of the distributaries of the Yangtze River and human activities.