长江口区晚新生代沉积物粒度特征和沉积地貌环境演变
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摘要
对长江河口区的三个晚新生代钻孔作了地层对比和粒度分析,据此探讨晚新生代长江河口的沉积地貌环境演变过程。结果表明,SG6和J18A孔上新世厚层含砾砂质沉积物粒度特征,反映了洪积扇和冲积扇相沉积环境,沉积物搬运距离短;而SG13孔缺失上新世沉积,反映古地势较高,以剥蚀为主。因此上新世长江三角洲地区古地势高差较大,侵蚀区和沉积区共存。早更新世,本区继承了上新世的冲、洪积扇沉积环境,但SG6孔泥质沉积明显变厚,J18A孔此时则以厚层含砾砂沉积为主,SG13孔也开始接受泥质沉积,反映在构造沉降作用下,冲、洪积扇体向西、南部迁移,沉积盆地范围扩大。中更新世,沉积物普遍变细且以悬浮沉积为主,显示了曲流河或曲流河冲积平原的沉积环境。晚更新世初,本区又发育含砾砂层,特别是SG13孔出现厚层含砾砂,但是粒径显著小于上新世和早更新世沉积物,反映本区再次发生显著构造沉积,河流地貌广泛发育。晚更新世中晚期和全新世沉积物以粘土和粉砂质粘土为主,悬浮沉积占优,说明本区已演变为滨、浅海沉积环境。因此在构造沉降、剥蚀和沉积的共同作用下,本区的地貌演变经历了自上新世至中更新世和自晚更新世至全新世的两次准平原化过程。
On the basis of grain size analysis of the samples from three boreholes in Changjiang Estuary,the present study discusses the sedimentary and morphologic environmental evolution throughout the late Cenozoic era.Results demonstrate that,thick layers of sand and gravelly sand dominate in the borehole sediments of Core SG6 and J18A in Pliocene,indicating quick deposition of alluvial fan system.The lack of Pliocene sedimentation in the borehole of Core SG13 indicates higher topography.Therefore obvious relief occurred in the study area with both depositional and erosion areas during Pliocene.In early Pleistocene the sedimentary environment remained as alluvial fans.But the sedimentary basin extended westward and southward due to tectonic subsidence,as evidenced by the thick layers of gravelly sand in Core J18A and initiation of deposition in Core SG13.In middle Pleistocene fine sediments accumulated generally,revealing the sedimentary environment of alluvial plain dominated by meandering river.In early late Pleistocene thick layers of sand and gravelly sand dominate in the region again,but the grain size become finer as compared with Pliocene and early Pleistocene.It reveals that rivers developed again in the region because of local tectonic subsidence.In late Pleistocene and Holocene silt and clay accumulated from still water dominate in the boreholes sediments,indicating the sedimentary environment of coastal plain and shallow sea.Hence two processes of peneplaintion occurred in the region due to the tectonic subsidence,deposition and erosion since Pliocene to middle Pleistocene and late Pleistocene to Holocene.
On the basis of grain size analysis of the samples from three boreholes in Changjiang Estuary,the present study discusses the sedimentary and morphologic environmental evolution throughout the late Cenozoic era.Results demonstrate that,thick layers of sand and gravelly sand dominate in the borehole sediments of Core SG6 and J18A in Pliocene,indicating quick deposition of alluvial fan system.The lack of Pliocene sedimentation in the borehole of Core SG13 indicates higher topography.Therefore obvious relief occurred in the study area with both depositional and erosion areas during Pliocene.In early Pleistocene the sedimentary environment remained as alluvial fans.But the sedimentary basin extended westward and southward due to tectonic subsidence,as evidenced by the thick layers of gravelly sand in Core J18A and initiation of deposition in Core SG13.In middle Pleistocene fine sediments accumulated generally,revealing the sedimentary environment of alluvial plain dominated by meandering river.In early late Pleistocene thick layers of sand and gravelly sand dominate in the region again,but the grain size become finer as compared with Pliocene and early Pleistocene.It reveals that rivers developed again in the region because of local tectonic subsidence.In late Pleistocene and Holocene silt and clay accumulated from still water dominate in the boreholes sediments,indicating the sedimentary environment of coastal plain and shallow sea.Hence two processes of peneplaintion occurred in the region due to the tectonic subsidence,deposition and erosion since Pliocene to middle Pleistocene and late Pleistocene to Holocene.
引文
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15李从先,汪品先.长江三角洲晚第四纪地层的研究[M].北京:科学出版社,1998:1-222[Li Congxian,Wang Pinxian.Study on the Late Quaternary Stratigraphic Sequence in the Changjiang RiverDelta Area[M].Beijing:Science Press,1998:1-222]
16郭玉贵,李延成,许东禹,等.黄东海大陆架及邻域大地构造演化史[J].海洋地质与第四纪地质,1997,17(1):1-11[Guo Yu-gui,Li Yancheng,Xu Dongyu,et al.Tectonic evolution of Yellow Sea,East China Sea and continental shelf and adjacent areas[J].Marine Geology&Quaternary Geology,1997,17(1):1-11]
17王张峤,陈中原,魏子新,等.长江口第四纪沉积物中构造与古气候耦合作用的探讨[J].科学通报,2005,50(14):1503-1551[Wang Zhangqiao,Chen Zhongyuan,Wei Zixin,et alCoupling con-trols of neotectonism and paleoclimate on the Quaternary sediments of the Yangtze coast[J].Chinese Science Bulletin,2005,50(14):1503-1551]
18章振铨,刘昌森,王锋.上海地区断裂活动性与地震关系初析[J].中国地震,2004,20(2):143-151[Zhang Zhenquan,Liu Changsen,Wang Feng.Preliminary study on relation of fault activity and seismicity in the Shanghai Region[J].Earthquake Research in China,2004,20(2):143-151]
19胡连英,徐学思.江苏溧阳地震孕育和发生的地质因素剖析[J].江苏地质,2001,25(1):11-16[Hu Lianying,Xu Xuesi.An anal-ysis of geological factors for the occurrence and gestation in Liyang earthquake[J].Jiangsu Geology,2001,25(1):11-16]
2韦桃源,陈中原,魏子新,等.长江河口区第四纪沉积物中的地球化学元素分布特征及其古环境意义[J].第四纪研究,2006,26(3):397-405[Wei Taoyuan,Chen Zhongyuan,Wei Zixin,et al.The distribution of geochemical trace elements in the Quaternary sediments of the Changjiang River mouth and the paleoenvironmental implications[J].Quaternary Sciences,2006,26(3):397-405]
3杨守业,李从先.长江三角洲晚新生代沉积物有机碳、总氮和碳酸盐组成及古环境意义[J].地球化学,2003,35(3):249-256[Yang Shouye,Li Congxian.Compositions of organic elements and carbonate in the late Cenozoic sediments of the Changjiang Delta:Im-plication for paleoenvironmental changes[J].Geochimica,2003,35(3):249-256]
4Wang Zhanghua,Chen Zhongyuan,Gu Jiawei,et al.Occurrence and environmental implications of magnetic iron sulfides in stiff muds from the continental shelf of the East China Sea[J].Geo-Marine Letters,2005,25(5):300-305
5Chen Zhongyuan,Stanley D J.Quaternary subsidence and river chan-nel migration in the Yangtze delta plain,eastern China[J].Journal of Coastal Research,1995,11(3):927-945
6邱金波,李晓.上海市第四纪地层与沉积环境[M].上海:上海科学技术出版社,2007:1-229[Qiu Jinbo,Li Xiao.The Quaternary Strata and Depositional Environment in Shanghai[M].Shanghai:Shanghai Scientific&Technical Publishers,2007,1-229]
7段凌云,王张华,李茂田,等.长江口沉积物210Pb分布及沉积环境解释[J].沉积学报,2005,23(3):514-522[Duan Lingyun,Wang Zhanghua,Li Maotian,et al.210Pb distribution of the Changjiang estuarine sediment and the implications to sedimentary envi-ronment[J].Acta Sedimentologica Sinica,2005,23(3):514-522]
8范代读,李从先,Yokoyama K,等.长江三角洲晚新生代地层独居石年龄与长江贯通时间研究[J].中国科学:D辑,2004,34(11):1015-1022[Fan Daidu,Li Congxian,Yokoyama K,et alMon-azite age spectra in the Late Cenozoic strata of the Changjiang delta and its implication on the Changjiang run-through time[J].Science in China:Series D,2005,48(10):1718-1727]
9陈静,王哲,王张华,等.长江三角洲东西部晚新生代地层中的重矿物差异及其物源意义[J].第四纪研究,2007,27(5):700-708[Chen Jing,Wang Zhe,Wang Zhanghua,et al.Heavy mineral distri-bution and its provenance implication in late Cenozoic sediments in western and eastern area of the Changjiang River delta[J].Quaternary Sciences,2007,27(5):700-708]
10王张华,张丹,李晓,等.长江三角洲晚新生代沉积物磁性特征和磁性矿物及其指示意义[J].中国地质,2009(待刊)[Wang Zhan-ghua,Zhang Dan,Li Xiao,et al.Magnetic properties and relevant minerals of late Cenozoic sediments,Changjiang delta area and impli-cations[J].Chinese Geology,2009(in press)]
11Chen Zhongyuan,John Rybczyk.Coastal Subsidence[C]∥Maurice L Schwartz.Encyclopedia of coastal Science.Springer Netherlands,2005:302-304
12Lowe J J,Walker M J C.Reconstructing Quaternary Environments[J].London and New York:Longman Group Limited,1984:1-446
13成都地质学院陕西队.沉积岩(物)粒度分析及其应用[M].北京:地质出版社,1978:1-147[Shannxi Team in Chengdu College of Geology.Analysis and Applications of Sedimentary Rocks(sedi-ments)Grain Size[M].Beijing:Geological Publishing House,1978:1-147]
14张家强,张桂甲,李从先.长江三角洲晚第四纪地层层序特征[J].同济大学学报,1998,26(4):438-442[Zhang Jiaqiang,Zhang Guijia,Li Congxian.Characteristics of the Late Quaternary stratigraphic sequence in the Changjiang River Delta Area[J].Jour-nal of Tongji University,1998,26(4):438-442]
15李从先,汪品先.长江三角洲晚第四纪地层的研究[M].北京:科学出版社,1998:1-222[Li Congxian,Wang Pinxian.Study on the Late Quaternary Stratigraphic Sequence in the Changjiang RiverDelta Area[M].Beijing:Science Press,1998:1-222]
16郭玉贵,李延成,许东禹,等.黄东海大陆架及邻域大地构造演化史[J].海洋地质与第四纪地质,1997,17(1):1-11[Guo Yu-gui,Li Yancheng,Xu Dongyu,et al.Tectonic evolution of Yellow Sea,East China Sea and continental shelf and adjacent areas[J].Marine Geology&Quaternary Geology,1997,17(1):1-11]
17王张峤,陈中原,魏子新,等.长江口第四纪沉积物中构造与古气候耦合作用的探讨[J].科学通报,2005,50(14):1503-1551[Wang Zhangqiao,Chen Zhongyuan,Wei Zixin,et alCoupling con-trols of neotectonism and paleoclimate on the Quaternary sediments of the Yangtze coast[J].Chinese Science Bulletin,2005,50(14):1503-1551]
18章振铨,刘昌森,王锋.上海地区断裂活动性与地震关系初析[J].中国地震,2004,20(2):143-151[Zhang Zhenquan,Liu Changsen,Wang Feng.Preliminary study on relation of fault activity and seismicity in the Shanghai Region[J].Earthquake Research in China,2004,20(2):143-151]
19胡连英,徐学思.江苏溧阳地震孕育和发生的地质因素剖析[J].江苏地质,2001,25(1):11-16[Hu Lianying,Xu Xuesi.An anal-ysis of geological factors for the occurrence and gestation in Liyang earthquake[J].Jiangsu Geology,2001,25(1):11-16]
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