The Sedimentary Evolution Research Of Coastal Areas In Jianggang Of Jiangsu Province Since Last Glacial Epoch

The coastal sea-land interactions is one of the core program of the International Geosphere-Biosphere Programme.Chinese geological science workers target to participate in the hot topic of the international research,and disclose the basic rule of coastal sea-land interaction in China.It’s an urgent need to find the suited regions where are fit for national conditions and possess the typical characteristics of the sea-land interactions.The tidal sand ridges of Jianggang area of Jiangsu Province may belong to such typical areas.The paper investigate the evolution of sedimentary environment in the Jianggang coastal areas of Jiangsu Province since Last Glacial Epoch,based on the granularity, minerals, paleontological and AMS14C data study of two representative JC-1203 and JC-1204 cores in nearshore supratidal zone,and analyze the causes and age of the tidal sand ridge.The sediment of the two drilling cores,Yangtze River and Yellow River are compared to determine the contribution of different rivers’substance sources in Jianggang tidal sand ridges area.The 50m upper segment of the JC-1203(120°54’32.38"E,32°45’54.24"N,elevation 12.39m) core sediments is selected to analyze particle size, mineral and paleontological characteristics. Combined with sedimentary characteristics of the drilling core,the upper segment of the JC-1203 core sediments can be divided into five units named as DU1-DU5 from bottom to top.l)DU5(50.0-45.54m):it’s the sedimentary facies of the nearshore shallow sea since early MIS3.The detrital mineral association is consisted of hornblende, epidote, schistic minerals, dolomite, authigenic pyrite, and the characteristic mineral is consisted of white mica, dolomite and authigenic pyrite; 2) DU4(45.54-37.33m):it reflects the sedimentary facies of continental rivers from middle MIS3 to late MIS2.The mineral association is consisted of hornblende,epidote,schistic minerals,ilmenite,authigenic pyrite, authigenic barite,and the characteristic mineral is consisted of authigenic pyrite, authigenic barite; 3) DU3(37.33-27.39m):it’s the deposition of littoral facies since the marine transgression of early-mid MIS1. The mineral association is consisted of hornblende, epidote, magnetite, ilmenite, garnet, and the characteristic mineral is consisted of magnetite, ilmenite, garnet; 4) DU2(27.39-4.0m):it’s the inshore coastal-neritic sedimentary facies since mid-late MISI.The mineral association is consisted of hornblende, epidote, garnet, sphene, ilmenite and glauconite, and the characteristic mineral is consisted of garnet, sphene, glauconite; 5)DU1 (4.0-0m):it’s the intertidal flat sedimentary facies in the marine regression of late Holocene since 1500 years. The mineral association is consisted of schistic minerals,hematite-limonite,feldspar,calcite,and the characteristic mineral is consisted of black mica, hematite-limonite. The detrital mineral association characteristics of DU5-DU3 segments is more close to the mineral association of Yangtze River,and the substance source are mainly provided by Yangtze River.The segment of tidal sand ridges facies mainly locate in the DU2 segment(27.39-4.0m).Judging from the graph of the cumulative probability of granularity,it’s mainly composed of two different sorted saltation components.The saltation of the first components is better than the other one,and it indicate that the sediments is controlled by two tides which have different directions and different speeds.Combining sediments and detrital mineral characteristics of the drilling core to compare with the sediments of Yangtze River and Yellow River, the sedimentary substance sources of the lower part of the DU2 (27.39-6.53m) is provided by the sediments of Yangtze River.The substance sources of the superior part of the DU2(6.53-4.0m) is provided by the sedimentary substance of Yellow River and Yangtze River, and the more substance contributions are provided by Yellow River from bottom to top.The substance source of the DUI(4.0-0m) may mainly come from Yellow River.The 52.36m upper segment of the JC-1204 drilling (120°41’56.43"E,32° 45’40.90"N, elevation 11.97m)can be divided into the five unites of the DU1-DU5 from bottom to top.1) DU5(52.50-45.31m):it’s the sedimentary facies of the nearshore shallow sea since early MIS3; 2) DU4(45.31-35.50m):it’s the sedimentary facies of continental rivers since late Pleistocene; 3) DU3(35.50-20.12m):it’s the deposition of littoral facies since early MIS1 in the lower part of DU3(35.50-28.50m),and it’s the deposition of delta plain distributary channel at the wavelike rises period of sea level altitude in the superior part of the DU3(28.50-20.12m) since early-mid Holocene;4)DU2(20.12-3.0m):it’s the sedimentary facies of the nearshore shallow sea since mid-late Holocene;5) DUI(3.0-0m):it’s the intertidal flat sedimentary facies since late Holocene. The detrital mineral association characteristics of DU4,DU5 and the lower part of DU3 (35.50-28.50m) is same to the corresponding layers of JC-1203 drilling,and the substance source is mainly provided by Yangzte River.It’s the continental sedimentary environment in the superior part of DU3(28.50-20.12m), and the mineral association is consisted of the heavy minerals which have high content,such as hornblende, epidote and pyroxene.The substance source of this segment is provided by Yangtze River.The tidal sand ridges facies is located in the DU2(20.12-3.0m) segment.The sediments of the 20.12-5.55m segment is mainly provided by Yangtze River,and the sediments of the 5.55-3.0m segment is provided by Yellow River and Yangtze River.The substance source of DU1(3.0-0m)may mainly come from Yellow River.The corresponding clay mineral average content of the drilling,such as illite,montmorillonite,are respectively 65.6% and 9.8%,and the content characteristics is close to Yangtze River. The average content of tillite and montmorillonite are respectively 59.6% and 8.4%,and it show no obvious bias and indicate that the substance source of this period is provided by Yangtze River and Yellow River.12-10ka B.P.,because of global warming and global sea level rise,marine transgression occurred in East China Sea;7-8ka B.P., transgression reached to maximum range, and huge estuary which top was located in Zhenjiang, Yangzhou was formed at Yangtze River Delta region;5-6ka B.P., when the maximum transgression occurred, rivers’ sedimentary entered into the north estuary,which was affected by the tidal current field in Dongtai, and the system of the onshore tidal sand ridges which based on Changjiang delta and was affected by the convergent tidal current field began to develop.The former was the foundation of the formation of the Jianggang tidal sand ridges,and the latter was the important influencing factor; l-2ka B.P., the system of the undersea radial tidal sand ridges which top was located in Jianggang region began to develop since late Holocene epoch.