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 Qiant ang 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 20433.72 m³/s.Therefore the ancient Changjiang River was braided-branched river according to the slope-width method.