The Source To Sink Processes In The Mud Area Of The Central South Yellow Sea Since The Holocene Based On Multi-Provenance Indexes

The South Yellow Sea(SYS)is a semi-closed shelf sea at the continental margin of East Asia,which is strongly influenced by the substantial sediment loads of surrounding rivers,but the dispersal patterns of these sediments,especially in the Central Yellow Sea Mud(CYSM),have not been well illustrated.In this study,the provenance and transport mechanism of the Holocene terrigenous sediments in the South Yellow Sea were studied by analyzing the grain size of the surface sediments in the South Yellow Sea and the AMS 14C dating,clay mineral,element geochemistry and Sr-Nd isotope of Core YSC-10 from the northern part of the SYS,near the western margin of the CYSMThe average Mz of surface sediments in the South Yellow Sea is 5.65 ?.Clayey silt is the most widely distributed sediment type in the South Yellow Sea.Four endmembers were isolated from the inversion of sediment grain size by endmember analysis model.The distribution of end-member 1 and end-member 2 showed an opposite trend,and the relative content of end-member 2 gradually decreased from shore to sea on the whole.The distribution of end-member 3 and end-member 4 overlaps slightly.According to the plane distribution characteristics of each endmember and the sedimentary dynamic pattern of the South Yellow Sea,end-member 1-4 were used to characterize terrigenous fine sediments,terrigenous coarser sediments,reworked sand and residual sand,respectively.Based on the hydrological characteristics of the South Yellow Sea,the provenance direction of the argillaceous area in the middle of the South Yellow Sea has two directions:north and southwest.The sedimentary records of core YSC-10 show that clay mineral assemblages mainly consist of illite(68±3%),followed by chlorite(15±2%)and kaolinite(10±2%),and scarce smectite(6±3%).The content of Al2O3 in the major elements of the sediments is high,while the content of other elements is low.Al2O3,MgO,K2O,TiO2 and Fe2O3 are positively correlated,while MnO and Al2O3 are negatively correlated.According to principal component analysis,F1 factor(45.425%)represents the element combination of K2O,P2O5,Na2O,Al2O3 and MgO.F2 factor(23.813%)represents the element combination of Fe2O3 and TiO2.The F3 factor(11.316%)represents a combination of elements CaO and MnO.Among the trace elements,Ba had the highest content with an average of 414.92 mg/kg,followed by Rb,Zr,Sr,B,V,Zn and Cr with an average content of 158.18,136.19,132.36,128.6,127.89,113.57 and 100.55 mg/kg,respectively.The average contents of Li,Ni,Cu and Pb ranged from 30 mg/kg to 80 mg/kg,the average contents of Y,Ga,Co,Nb,Sc,Cs,Th and As ranged from 10 mg/kg to 25mg/kg,and the contents of other trace elements were less than 5 mg/kg,even some were less than 1 mg/kg.The range of rare earth elements(FREE)is 172.04-199.29 mg/kg,with an average of 187.09 mg/kg.The light rare earth(LREE)content was significantly enriched(average 169.9 mg/kg),the heavy rare earth(HREE)content was low(average 17.46 mg/kg),and the fractionation of light and heavy rare earth was obvious(average LREE/HREE is 9.72).The normalized ?Eu(mean value is 0.66)of chondrites has obvious negative anomaly,while the ?Ce(mean value is 1.01)has no obvious anomaly.The ?Eu(mean of 1)and ?Ce(mean of 0.97)normalized by the upper crust have no obvious anomaly.The 87Sr/86Sr ratio varied from 0.720719 to 0.721973 with an average value of 0.721425,and the ?Nd value varied from-12.35 to-11.59 with an average value of-12.075.Combined with other published data,our results suggest the fine sediments of the CYSM are most likely a mixing product of the Huanghe(Yellow River),Changjiang(Yangtze River)and Korean Peninsula small rivers sediments with notable temporal changes.During 8.4-6.4 ka,the Huanghe sediments from the Bohai Sea flowed into the central Yellow Sea and could have played major roles in the sedimentation therein.In addition,as the modern ocean circulation pattern formed since?6 ka,the front developed along the coastal area from Shandong Peninsula to SYS,which would have prevented the dispersal of Huanghe sediments to the SYS.The Changjiang sediments delivered by the diluted water replaced those from the Huanghe as the main source of CYSM during the period of 6.4-4.2 ka.After 4.2 ka,the front weakened and moved toward the sea due to the weakening and eastward shift of the Yellow Sea Warm Current(YSWC)and the weakening and shrinking of the Yellow Sea Cold Water Mass(YSCWM),the enhanced contribution of Huanghe sediments seem to be increased and fluctuated frequently.Our study thus shows that the provenance variation of the South Yellow Sea is controlled by monsoon climate,ocean circulation(YSWC,YSCWM and coastal current)and front changes,and highlights the coastal shear front may be played critical role in the source to sink processes of the SYS.