Geochemical Features In Modern Yellow River Mouth Since Late Pleistocene

The morden Yellow River mouth area is located in the southwest coast of the Bohai sea which concerns land-ocean interaction.The change in this area are influenced by the Yellow River and coastal currents,which develops a land-ocean sediment body on the impact of sea level change and the global climate change.Thus the mud here concealed rich information on Paleoclimate change.The study of the mud elucidates the depositional characteristics and environmental evolution since late Pleistocene,and tell us the change of the depositional environment and the sediment supply.At present,some researchs of Bohai sea and the Yellow River delta was did by the way of geological drilling such as the BC-1 core,S3 core,ZKl core,ZK30 core and etc.They all carried on the research to sedimentary sequence,paleoclimate and paleoenvironment of the area where they are,but the studies are both limited and roughly,and they all default the sediment supplied by the Yellow River which is different from the result of my study.In this study,the 100-m deep geological Core KD4 and Core ZK3 are taken and sub-sampled.Analyses of Grain size,XRF element,OSL and AMS14C datings,which provides the precise record,are carried out.The core uncover the sedimentary layer since 120 ka B.P.,and on the base of the analysis of the date and surrounding geological core,the outcomes are summarized as follows:(l)The distribution of chemical composition in Core KD4 and Core ZK3 has better stratification.According to the changes of major elements and trace elements, the process of sedimentation is divided into ten periods,which are correspond to the depositional environment. In ascending order from the base, they are interpreted as L5,H5,L4,H4 deposited in the last Interglacial correspond to the MIS5,L3,H3,L2,H2 deposited in the last glaciation correspond in MIS3,L1 deposited in the Last Glacial Maximum,Hl deposited in the Holocene correspond to the marine facies in MIS1.(2)Using SPSS software for R-type cluster analysis and R-type factor analysis,the elements obtain four clusters and five main factors.The clusters of element association can tell us the geological interpretation of the elements,and the five factors,associated with grain-size, terrigenous mineral,the Yellow River,the weathering and the biological self-production,pointed out the grain size of the sediment type and terrigenous are the main factors that impact the record of sediments.(3)Since the late Pleistocene,the morden Yellow River Mouth area experienced four transgressive-regressive cycle,and the environmental evolutions can affect the distributions of elements in core.In this study,by the use of some geochemical parameters and ratios such as CIA,SiO2/Al2O3,Rb/Sr,Sr/Ba,the vertical changing, implying a close relation with the environmental evolutions is pointed out.(4) The discriminant function value of DF is used to discriminate the provenance of this area.The results show that the Yellow River is the main sediment source since the late Pleistocene,but in some period it occurred an exception. By the study of provenance index value of PI, the surrounding river flows into the sea has the most impact on its provenance in some sedimentary period such as the S4 period,S8 period and S9 period.