The Core-recorded And Sedimentary Facies Of Late Pleistocene-holocene Environment Evolution,jianggang,Northern Jiangsu Coast,South Yellow Sea,Eastern China

The coast of northern Jiangsu coastal zone in adjacent to South Yellow Sea has suffer from multiple regression and transgression cycles since the late Quaternary and it formed the land-sea interaction strata.Except for sea-level change,Substance supply is the key controlling factor.The northern Jiangsu coast(also west coast of South Yellow Sea)between the coastal zone the abandoned Yellow River delta plain and the Yangtze River Delta plains,in geological history it is controlled by input sediment from the paleo-Yangtze River and the paleo-Yellow River,so the north plain of Jiangsu is formed in the process of interaction between the sea and the two major paleo-river.Quaternary strata about the South Yellow Sea and sea-level changes have many achievements,but still worthy of attention and in-depth study of scientific problems.Transgression and sea rising in oxygen isotope stage 3 is still exist many arguments,in general,most of people believed that the sea-level is lower the present mea sea level about 30-60 m,even lower up to 80m in largest scale.However,the opposite agreed that the sea-level is higher up to-10?-15 m.They claimed that the sediment dated in MIS3 may be from MIS5 for the limitation of AMS14 C dating results.Although many scientific studies have been reported in paleo-Yangtze River and incised valley in Qiantang River,the buried river valley in central of northern Jiangsu plain is limited.Quaternary in Northern South Yellow Sea continental shelf and the plains may be 8 times or 7 times transgressive and regressive,especially in regressive with the decline of sea level,river incision formed more incised valley and fluvial stratigraphy.The incised valley in south of Jianggang may be related to the migration of paleo-Yangtze River,it's flow path may disperse in the early stages,gradually southward migration in the process of evolution,and eventually moved to the position of the modern Yangtze River.Reconstruction of Late Quaternary environmental evolution may attribute to insightful explore and study the issues including the sea-level in oxygen isotope stage 3 and the process of cutting,filling and migration of paleo-Yangtze River incised valley.In the thesis,we mainly focus on the sediments from a 131m core in southern coast of Jianggang(YZ08 hole,32° 42'16.32 "E,120 0 53'7.06" N),by analysis of grain-size,magnetic susceptibility,element geochemistry,loss of ignition,identify of macrofossils and microfossils identified,combined the chronology framework of AMS 14C and OSL dating and comparison of related stratigraphy as well as sediment disruption,we recovered the evolution of sedimentary environment since the late Pleistocene in northern Jiangsu coastal zone,and we discuss the factors which controlled the development of depositional systems in the study area,all of above make a foundation for us to continue to study the sea-level issue in oxygen isotope 3 phases and development and migration of paleo-incised valley of the Yangtze River.Jianggang YZ08 core's sediments mainly consist of silt,and the content is between 0%and 93.2%,an average of 54.2%;followed by the sand content of between 0.3%and 100%,with an average of 41%;clay content in the least,content of between 0%and 15.8%,with an average of 4.7%.The average particle size of the entire core deposits between 0.445?~7.241,an average of 4.690?,sorting coefficient between 0.452?3.725,an average of 1.828,the skewness is between-0.406?0.889,an average of 0.294,kurtosis between 0.544?3.713,an average of 1.127.Magnetic susceptibility between-3.91E-04?3.66E-03,an average of 6.07E-04;Sr/Ba between 0.129?11.810,an average of 2.643;Ca/Mg between 1.019?21.488,an average of 4.547;organic matter content of 0.1%to 6.141%,with an average of 2.947%;the carbonate content of between 0.958%-16.568%,with an average of 8.586%.The sediment units of YZ08 core can be divided into six parts(U1-U6):U1 deposition unit includes the two intertidal zone to intertidal cycle,according to stratigraphic framework U1 unit OSL presented may be formed in the oxygen isotope stage 7,oriented drilling The first core transgressive sedimentary sequence,U1 unit goes south to Nantong with river sediments;U2 sedimentary units from the above phase deposition include river and floodplain,other cores are fluvial facies,thickness up to 30?40m,speculated that the unit is likely to form in the lower sea oxygen isotope stage 6,belonging to the ancient Yangtze River cut ancient river valley in northern Jiangsu plain beneath;U3 unit to a salt marsh ? shallow marine transgressive sequence,only YZ08 stomatal development,Other cores are both appear,according to the chronological framework OSL may be given oxygen isotope stage 5 product;U4 have developed floodplain and floodplain sediments from the above,the lower flood plains probably formed in oxygen isotope 4 The low sea phase,after a similar role in the formation of hard clay soil layer,and a second layer of hard clay and northern Jiangsu Yangtze River Delta region is quite plain.The upper part of the floodplain deposition phase includes the shore side of the river beaches and fine particles may be formed in the oxygen isotope stage 3,south of the river with a bulk phase transition;U5 is the iconic hard clay layer of Northern Jiangsu plain,below floodplain deposition,But U5 in CH4 and QC5,cores are change to channel facies;U6 sedimentary units from the top includes a lower shore swamp,tidal zone between shallow marine and intertidal phase.In QC5 and CH4 borehole shore swamp into fluvial deposition.CH4 intertidal zone to shallow water delta deposition phase to the hole.Sedimentary environment evolution showed relatively higher sea level during MIS7 stage,global relative sea about ten meters lower than today and northern coastal belt is submerged,the development of tidal flat deposits.With the global decline in relative sea level fluctuations MIS6 stage,the minimum sea-level lower than the last Glacial Maximum and northern coastal plain was completely exposed to the terrestrial environment,the river re-development zone in coastal plain area,this time Jianggang and the southern region of Jianggang are fluvial facies,in today's coastal and shallow water shelf to form a network of river systems,these river systems are likely to form the paleo-Yangtze cut.MIS5 stage of relative sea-level rise,gradually incised valley floodplain(Jianggang region),lake with salt marshes and shallow-marine sedimentary fill(Jianggang region)on(Nantong,Chongming Island),as well as the influx of sea level rise in the next stage,constitute a complete ancient incised valley fill sequences.About 60-70ka B.P.in MIS4 stage,the research area into the early Tamaki glacial cold climate,sea level dropped,this area deposited floodplain.In MIS3 stage,the transgression occurred in shelf of East of China Sea and South Yellow Sea,but not submerged Jianggang region,fluvial point bar and floodplain sediments,this time the main branch of the Yangtze River have been migrated to the south of Lusi.About 25kaB.P.enter into MIS2 stage study area(equivalent to late Tamaki Ice Age),where global climate cools again,with significant decline in sea level.The study area was exposed and became land completely,flood plain development phase deposition,after a soil of action,into the Yangtze River Delta and Northern Jiangsu plains iconic "hard clay." At this point,the main branch of the Yangtze River migrate to the south again.About 15 ka B.P.,after the end of the Last Glacial Maximum,The study area entered deglaciation,again warming global climate,sea level was stepped increase rapidly.Jianggang area developed shore marsh sediments in about 12.4?9.5 ka B.P.Jianggang south shore area are marsh and river environment coexist environment.Then it quickly submerged sea shore marshes and rivers,with lower research and development tide shallow sea area south of Jianggang belong estuarine environments,development estuary tidal sand ridges.Modern Yangtze Delta region development estuary to delta deposits,and see Shaba estuary accumulation.After 1128 A.D,because of the Yellow River south coast in Northern Huai river away to bring a lot of sediment in the Yellow River Mouth and rapidly developed the waste underwater delta,in the rising tide of action,most of the erosion and sediment transport in the south part were the supply of the coastal zone so quickly silt shoreline,Jianggang area by the silt shallow subtidal quickly become environmental intertidal environment until the water completely out of the area;seaborne move to another part of the sediment,so that rapid long underwater sand ridges high,it has formed scale radial sand ridges now.Acid soluble Sr/Ba,Ca/Mg,magnetic susceptibility,organic matter and carbonate content can be determined as the deposition phase auxiliary indicators.From MIS2 to MIS1 stage,acid soluble Sr/Ba ratio continues to rise,sea level rise and the trend is consistent.Magnetic susceptibility in the river under control and strong tidal tide shallow water at a high value,and in the tidal zone and flood plains on the environment at a low value,indicating strong hydrodynamic environment conducive to the enrichment of magnetic minerals so that the magnetic susceptibility values have increased.Organic matter and carbonate with simultaneous variation,they are closer to shore intertidal environment and floodplain environment has tended to increase,and these two environments were tend to concentrate the organic matter,and the financial effect caused by secondary freshwater leaching of calcium carbonate(calcium tuberculosis)elevated.Late Quaternary,Jianggang sedimentary environment is mainly controlled by global sea level and the ancient Yangtze River,Yellow River ancient material inputs.YZ08 hole revealed oxygen isotope stage 7 Jianggang region three times since undergone significant transgression,they are MIS7 stage,MIS5 stage and MIS1 stage.Jianggang in oxygen isotope stage 3 and the south area of the river depositional environment,close to the sea and did not affect the modern coastline.Low sea oxygen isotope stage 6,the ancient plains of the Yangtze River in the north(now known as the south Jianggang)net incised valley formed paleo-river,the oxygen isotope stage 5 is filled.Oxygen isotope stage 3 paleovalleys line southward migration to the south of Nantong Rudong area,oxygen isotope stage 2 is further moved to the south.