长江三角洲顶部冰后期地层的沉积特征
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摘要
钻探证实,镇江市谏壁镇长江北岸高桥镇北部埋藏硬粘土层,之上为冰后期松散沉积物。沉积物主要为粉砂、粘土质粉砂、砂泥互层,中部局部夹含细砾中细砂,顶部见淤泥质粘土;夹数十层植物炭屑层;以水平纹理为主,局部见小型交错层理、波状层理。表明冰后期以来该地处于水动力较弱的河湖环境,为多期湖沼相沉积夹汊道河流相沉积,局部有海相沉积物加入。根据碳化植物碎屑14C年龄,推测冰后期底界年龄约13 000 aBP,海侵到达该地的时间约为9 000aBP,海侵最高位时间约为6 500 aBP。冰后期平均沉积速率约为4.9 m/ka,湖沼相3.4~6 m/ka,河流相10~15 m/ka。对全新统的底界年龄和海相层的埋藏深度进行了讨论。
It is confirmed by borehole data that the sediments above the buried hard clay layer in northern Gaoqiao town,Zhenjiang city,north bank of Yangtze River,are postglacial loose sediments.Sediments are mainly silt,clayey silt and sand intercalated with mud(sand-mud);the medium-fine sand with fine gavel is found in the middle part and the puddly clay at the top.There are tens of carbonized plant fragment interbeds in sediments.The lamination types of postglacial strata are primarily horizontal lamination and locally small-scale cross lamination and wave lamination,indicating weak hydrodynamic fluviolacustrine deposition environment since postglacial period and sedimentary facies dominated by multiphase lake basin bog facies intercalated with limnetic facies and branch fluvial facies locally with marine sediments added in early stage.According to 14C ages of carbonized plant fragments,it is inferred that the boundary age between Pleistocene and postglacial strata is about 13 000 aBP,the transgression arrived at 9 000 aBP and the high est transgression position appeared at about 6 500 aBP.The deposition rate of postglacial strata is about 4.9 m/ka,that of limnetic facies about 3.4~6 m/ka and that of fluvial facies about 10~15 m/ka.The boundary age of Holocene and the buried depth of marine layer are also discussed.
It is confirmed by borehole data that the sediments above the buried hard clay layer in northern Gaoqiao town,Zhenjiang city,north bank of Yangtze River,are postglacial loose sediments.Sediments are mainly silt,clayey silt and sand intercalated with mud(sand-mud);the medium-fine sand with fine gavel is found in the middle part and the puddly clay at the top.There are tens of carbonized plant fragment interbeds in sediments.The lamination types of postglacial strata are primarily horizontal lamination and locally small-scale cross lamination and wave lamination,indicating weak hydrodynamic fluviolacustrine deposition environment since postglacial period and sedimentary facies dominated by multiphase lake basin bog facies intercalated with limnetic facies and branch fluvial facies locally with marine sediments added in early stage.According to 14C ages of carbonized plant fragments,it is inferred that the boundary age between Pleistocene and postglacial strata is about 13 000 aBP,the transgression arrived at 9 000 aBP and the high est transgression position appeared at about 6 500 aBP.The deposition rate of postglacial strata is about 4.9 m/ka,that of limnetic facies about 3.4~6 m/ka and that of fluvial facies about 10~15 m/ka.The boundary age of Holocene and the buried depth of marine layer are also discussed.
引文
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[5]Wang Pinx ian,Sun Xiang jun.Lastg lacia lmaximum in Ch ina:Com parison betw een land and sea[J].C atena,1994,(23):341-353.
[6]杨怀仁,徐馨,杨达源,等.长江中下游环境变迁与地生态系统[M].南京:河海大学出版社,1997.
[7]李萍,陈刚.长江三角洲顶部冰后期地层的沉积特征与划分[J].海洋通报,1983,2(4):67-71.
[8]陈希祥.镇江——扬州长江河谷第四系沉积演变特征[J].地层学杂志,2001,25(1):51-54.
[9]吴燕开,刘松玉,洪振舜.苏北与长江三角洲沉积环境及其土体物理性质关系探讨[J].水文地质工程地质,2005,(2):49-53.
[10]同济大学海洋地质系.全新世长江三角洲的形成和发育[J].科学通报,1978,23(6):310-313.
[11]吴标云,李从先.长江三角洲第四纪地质[M].北京:海洋出版社,1987.
[12]李从先,张桂甲.晚第四纪长江和钱塘江河口三角洲地区的层序界面和沉积间断[J].自然科学进展(国家重点实验室通讯),1996,6(4):461-469.
[13]孙顺才.长江三角洲全新世沉积特征[J].海洋学报,1981,3(1):97-112.
[14]陈庆强,李从先.长江三角洲地区晚更新世硬粘土层成因研究[J].地理科学,1998,18(1):53-58.
[15]陈报章,李从先,业治铮.长江三角洲北翼全新统底界和“硬粘土层”的讨论[J].海洋地质与第四纪地质,1991,11(2):37-46.
[16]王国庆,石学法,李从先.长江三角洲晚第四纪沉积地质学研究述评[J].海洋地质与第四纪地质,2006,26(6):131-137.
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