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SEDIMENTARY CHARACTERISTICS AND ENVIRONMENTAL SIGNIFICANCE OF HONGMEN COASTAL BARRIER,LIANYUNGANG,NORTHEASTERN JIANGSU PROVINCE

XU Jun1,YIN Yong1,ZHU Da-kui1,ZHU Xiao-bing1(1 The Key Laboratory of Coast & Island Development,Nanjing University,Nanjing 210093,China;2 College of Water Resources and Environment,Hehai University,Nanjing 210098,China)  
Based on core log,14C dating,grain size analysis as well as ground-penetrating radar images,genesis of Hongmen coastal barrier and the environment were discussed.Four cores are available along ground-penetrating radar transects.The cored sedimentary succession in the coastal barrier of Hongmen area can be subdivided into three units from bottom to up.The bottom unit is mainly composed of gray to dark gray clay with calcareous concretion,which is interpreted as an exposed unit formed 6 400 aBP.This unit followed by an extensive transgression clay,probably formed in a near-shore,shallow(20 m) and hyposaline(ca.30) environment in accordance with foraminifera assemblages.At about 6 000 aBP,the coastline kept steady,and in this circumstance,an increase of sandy supply or a decline of relative sea level was triggered by the development of coastal barrier in Hongmen area.The lower part of the barrier is mainly composed of coarse sandy granule,with great amounts of shell.It gradually becomes granule coarse sand into the upper part of the barrier.These sandy barriers can be chronologically correlated to the sandy barriers of north Jiangsu.After about 5 000 aBP,the sea level declined and probably retreated from the area,meanwhile the development of the sandy barriers stopped.Deposits of Hongmen coastal barrier are coarser than those of modern Haizhou Bay beach and cheniers of northern Jiangsu coastal plain.The grains are concentrated between 0~1 Φ,with a worse sorting than in modern Haizhou Bay beach sediments.It indicates that the Hongmen coastal barrier is very close to a river mouth area where flooding can carry coarse materials.The ground-penetrating radar is tentatively used to augment standard geomorphic and stratigraphic techniques.The radar images show a series of seaward oblique reflectors,which indicate a coastal progradation during barrier growth.This coastal progradation can be interpreted as having lots of material supply during that time.The results show the ground-penetrating radar is a useful technology for interpreting coastal barrier stratigraphy which can be applied to informed,sensible land use planning and environmental assessments.
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