长江三角洲镇江—江都河段古河谷沉积特征

江苏省江都地区南北向6个钻孔研究表明,晚更新世晚期(包括MIS3阶段)长江三角洲镇江(大港)-江都河段为辫状河道沉积,末次盛冰期由于全球性海面下降形成下切河谷。冰后期海平面上升引发的海侵造成古河谷的充填,并依次形成河床相、河漫滩相、河口湾相及三角洲相。冰后期早期的河床相黄色含砾砂层在该河段均有分布,可以作为标志层,其底板可作为冰后期-末次盛冰期的界面。古河谷中部冰后期与末次盛冰期地层具有连续沉积的特征,表明末次冰期低海面时长江仍为入海河流。冰后期海侵大约在9 kaBP到达本区;最大海侵发生在6.5~7.0 kaBP,此时三角洲已开始发生进积作用,河口沙坝也同时开始形成。三角洲平原形成以后,区域构造运动影响了河谷的均衡调整,密集的入江水道及人类活动不断改变三角洲平原的微地貌景观。

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.