长江口外陆架区埋藏古河道研究
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摘要
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180 km的古长江河系以及长64 km的古舟山河和长近100 km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81~109 m,河底纵比降为0.82×10-4,平均古流量约为535.24 m3/s,最大断面的古流量为20433.72 m3/s。按比降-河宽法判别,当时古长江河道为辫状分汊河型。
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.
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.
引文
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[17]李从先.冰后期海面变动和河流-河口体系发育的阶段性[J].海洋学报,1992,14(3):86—94.
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[2]寇养琦.南海北部大陆架的古河道及其工程地质评价[J].海洋地质与第四纪地质,1990,10(1):39—47.
[3]李凡,董太禄,姜秀行,等.莺歌海附近陆架区埋藏古河道及海平面变化[J].海洋与湖沼,1990,21(4):60—67.
[4]李凡,于建军,姜秀珩,等.南黄海埋藏古河系研究[J].海洋与湖沼,1991,22(6):3—10.
[5]WELLNER R W,BARTEK L R.The effect of sea level,and shelf physiography on the development of incised-valley complexes:a mod-ern example from the East China Sea[J].Journal of Sedimentary Research,2003,73(6):926—940.
[6]耿秀山.中国东部陆架的海底古河系[J].海洋科学,1981(2):22—27.
[7]叶银灿,冯应俊.东海陆架的古河系发育[G]//东海及其它陆架沉积作用国际学术讨论会论文集.北京:海洋出版社,1983:167—170.
[8]陈建文.东海某井两类河流相沉积[J].海洋地质与第四纪地质,1991,11(1):45—50.
[9]袁迎如.东海大陆架外部的晚更新世晚期长江河口[J].海洋学报,1992,14(6):87—93.
[10]刘振夏,BERNE S L ATALANTE科学考察组.东海陆架的古河谷和古三角洲[J].海洋地质与第四纪地质,2000,20(1):11—16.
[11]李广雪,刘勇,杨子赓,等.末次冰期东海陆架平原上的长江古河道[J].中国科学(D辑:地球科学),2004,35(3):284—289.
[12]唐保根,昝一平.长江水下三角洲浅孔岩芯的地层划分[J].海洋地质与第四纪地质,1986,6(2):43—54.
[13]黄庆福,苟淑名,孙维敏,等.东海DC-2孔柱状岩芯的地层划分[J].海洋地质与第四纪地质,1984,4(1):15—30.
[14]叶银灿,宋连清,陈锡土.东海海底不良工程地质现象分析[J].东海海洋,1984,2(3):30—35.
[15]黄慧珍.东海西部海域工程地质条件评价[J].海洋地质与第四纪地质,1993,13(1):47—64.
[16]任明达,王乃梁.现代沉积环境概论[M].北京:科学出版社,1981.
[17]李从先.冰后期海面变动和河流-河口体系发育的阶段性[J].海洋学报,1992,14(3):86—94.
[18]SCHUMM S A.Experimental study of channel patterns[J].Bulletin of the Geological Society of America,1972,83:1755—1770.
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