长江口外陆架区埋藏古河道研究

大量高分辨率单道地震和浅地层剖面资料显示长江口外的广大海域分布着大量埋藏古河道,据区域浅层地质特征及地震相特征,可把研究区埋藏古河道断面划分为对称、不对称和复式三种类型;河道内充填的沉积物复杂多样;古河道主要存在于晚更新世晚期沉积层中。60个古河道断面串联成长180km的古长江河系以及长64km的古舟山河和长近100km的古钱塘江河两条支流河道系。长江古河道宽深比较大,盛冰期时深切81~109m,河底纵比降为0.82×10-4,平均古流量约为535.24m3/s,最大断面的古流量为20433.72m3/s。按比降-河宽法判别,当时古长江河道为辫状分汊河型。

Study of the buried ancient channels in the continental shelf area out of the mouth of the Changjiang River in China

A lot of high resolution single channel seismic data and subbottom profile data show that there are many buried channels in the continental shelf area out of the mouth of the Changjiang River. The buried ancient channel profilers of the study area can be classified into three patterns which are symmetry, asymmetry and double entry channel analyzing the characteristics of shallow geology and seismic phase. The characteristic of the filled sediment in the channels is complicated and diversified. The ancient channels mainly exist in the sedimentary layer of the Late Pleistocene epoch. Sixty profiles joined up in series to three ancient rivers which were the ancient Changjiang River system with length of 180 km, and the ancient Zhoushan River with length of 64 km and the ancient Qiantang River with length of more than 100 km. The analytical results reveal that the width to depth ratio of the ancient Changjiang River was comparatively large. In the last glacial maximum, the river used to cut a depth of 81~109 m. The longitudinal slope of the river bottom was 0.82×10-4. The ancient average flux was about 535.24 m3/s and the largest profile flux was 20 433.72 m3/s. Therefore the ancient Changjiang River was braided branched river according to the slope width method.