| 长江三角洲地区晚第四纪地层及潜在环境问题 |
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| 引用本文： | 李从先,范代读,张家强.长江三角洲地区晚第四纪地层及潜在环境问题[J].海洋地质与第四纪地质,2000,20(3):1-7. |
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| 作者姓名： | 李从先 范代读 张家强 |
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| 作者单位： | 同济大学,教育部海洋地质开放实验室,上海,200092 |
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| 基金项目： | 中国科学院资助项目，49976016， |
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| 摘 要： | 根据钻孔的沉积相序将长江三角洲分为三角洲主体、三角洲南翼和北翼等３个基本的地层分区，鉴于两翼前缘和后缘的相序具有很大差异，因而两翼均划分出前缘和后缘２个亚区。地层结构的不同决定了与沉积层有关的潜在环境问题和灾害的分布，三角洲南翼和后缘为地面沉降发育区和潜在发育区，北翼的前缘为地下海水入侵的潜在发育区，三角洲主体是污染江水的潜在渗滤区，现今河口为底辟构造潜在发育区。
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| 关 键 词： | 地层构架 环境问题 晚第四纪 长江三角洲 |
| 修稿时间： | 2000-03-15 |
LATE QUATERNARY STRATIGRAPHICAL FRAMEWORK AND POTENTIAL ENVIRONMENTAL PROBLEMS IN THE YANGTZE DELTA AREA |
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| LI Cong-xian,FAN Dai-du,ZHANG Jia-qiang.LATE QUATERNARY STRATIGRAPHICAL FRAMEWORK AND POTENTIAL ENVIRONMENTAL PROBLEMS IN THE YANGTZE DELTA AREA[J].Marine Geology & Quaternary Geology,2000,20(3):1-7. |
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| Authors: | LI Cong-xian FAN Dai-du ZHANG Jia-qiang |
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| Abstract: | Based on the analysis of drilling cores,the Yangtze Delta region can be subdivided into three basic areas by late Quaternary stratigraphical framework.They are main delta,southern and northern flanks.In both flanks there exists stiff mud as a basement of the postglacial transgressive sedimentary cycle(PTSC),which belongs to the paleosol in genesis,exposed for a long term.The PTSC thickness is varied from 3 5m to 25 28m and increased eastward.The postglacial thansgressive sedimentary cycle basically consists of muddy deposits of littoral,neritic and littoral facies in the front zone of the southern flank,and is mainly composed of sandy deposits of that in the northern flank.The PTSC in the back zone of both flanks consists of marsh lacustrine muddy deposits.There is no stiff mud in the postglacial transgressive sedimentary cycle with thickness of 60 90m in the mail delta area.The PTSC has erosional surface at the bottom and is composed of river channel sand,floodplain estuary sandy and silty clay,estuary bay soft mud and deltaic sandy clay and sand.Muddy unit thins and then punches out westward,and is completely eroded at some places,so that deltaic and river channel sandy units are superposed on each other.The upper surface of paleosol and the bottom erosional surface constitute lower boundary of the postglacial transgressive sedimentary cycle.The incised valley and associated floodplain at its both banks can be recognized in the Yangtze Delta region during last glaciation maximum,which coincides with present main delta and its both flanks respectively.These paleogeomorphological units and stratigraphical framework in the Yangtze Delta have succeeded during various transgressive cycles of Quaternary. There are some hazards and potential environmental phenomena,such as ground subsidence,underground seawater intrusion,diapiric structure,and pollution water percolation etc.which are related to sedimentary characteristics of stratigraphical units and stratigraphical framework of late Quaternary even whole Quaternary.In the area of the delta,where muddy deposits are predominated in late Quaternary strata,over pumping of groundwater usually leads to ground subsidence.The southern flank and back zone of northern flank of the Yangtze Delta have such kind of Quaternary strata and they are a area of real or potential ground subsidence,which has been found in cities of Shanghai,Suzhou,Wuxi,Changzhou etc.It will be a potential environmental problem in some places of the area with economic development and population growth.Sedimentary strata composed of sand deposits in the coastal zone provide conditions for underground seawater intrusion when the groundwater is over pumped.The front zone of northern flank in the delta has the similar stratigraphic settings and may be a potential area of underground seawater intrusion under condition of groundwater withdrawal.The present river mouth bars saw stratigraphical succession of diapiric structure development,such as Chunmin,Hunsha,Chanxin,and there was case of people death due to diapiric activity.They could be potential areas of diapiric structure distribution.The main delta may be a potential area of polluted water percolation,because of thick sandy strata and deep erosion of present Yangtze River. |
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| Keywords: | stratigraphic framework environmental problem late Quaternary Yangtze Delta |
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