High-resolution Sedimentary Records In The Yellow River Delta And Their Responses To The Mouth Migration And Human Activities

The middle and lower reaches of the Yellow River is characterized by depositionand migrate frequently. In total, eleven major shifts of the lower river courseoccurred since1855, when the mouth transformed from the Yellow Sea to the BohaiSea. In addition, they carried out a series of human activities for water diversion andflood control, such as dam-building, Project of “Artificial Regulation of the HuangheWater and Sediment” et al. As the sedimentary bodies in the estury of the YellowRiver, the Yellow River Delta can be the most sensitive response of the environmentchange in the Yellow River basion and leave a record of this. Therefore, establishthe high-resolution sedimentary records in the Yellow River Delta and study itsresponse to human activities has very important practical significance on planning andmanagement of the Yellow River basion and developing the oil and gas resources ofthe Yellow River Delta area.The granularity, gray, element geochemistry and radioisotopes of sedimentarycores from the Yellow River Delta were studied. Combining with210Pb and137Csdating system, the high-resolution sedimentary records in the Yellow River Delta hasestablished and have studide its response to human activities. The results haveshown that:The clayey silt sediments give priority to the sediments in this area. Thefrequency distribution curves show a single peak, doublet or triplet, of unimodal,bimodal, or three peaks, corresponding to different depositional environments. Mostof the average particle size is between6.5Φ~7Φ. The gray values were positivelycorrelated with grain size. The core grayscale images have played an important rolein establishing the high-resolution sedimentary records.In six short cores, Si and Na generally have positive correlation and showedpositive correlation with grain size. In contrast, although Al, Fe, Mg, Mn, K, Cu, Ni,Pb and Zn have positive correlation with each other, they showed negative correlation with grain size. P, S and Cl showed weak correlation with grain size. But in B45,all the elements showed very poor correlation with granularity. The R-type factoranalysis of those elements in B45indicates that the control factors to elementscontents in sediments are grain size, the influence of human activity, biologicalcomponents and salt remnants.The granularity and210Pb content are effective indicators of the migration of theriver. The distribution of the210Pb content in cores is different respectively, which isrelated with sedimentation closely. Under the condition of the progradation as theleading, the210Pb content decreases wite depth, while in the resuspension depositionzone, the curves of210Pb were periodicity or anti-decay form. Influenced by therunoff and sediments from the Yellow River, the estuary is dominanted by riverprogradation. When the estuary moved to another location, the original depositionzone would be erosed and transformed, and dominanted by wave action. Therefore,two different types of sediment formed: fine-single peak-positive bias-well selected(type I) and coarse-non-single peak-positive bias-bad selected (type II).The short sedimentary cores of the Yellow River Delta have recorded themigration happened in1976and1996at the Yellow River mouth. The core A11(at12.0cm) and the core A19(at14.0cm) have recorded the Yellow River to change itschannel from Qingshuigou to Qing8cha in1996. As well, the characteristics of thecore A25(at15.5cm) recorded the river to change its channel from Diaokou toQingshuigou in1976. The change of the sedimentary granularity of the core B45(at190cm) recorded the change of estuary from the Yellow Sea to the Bohai Sea for theYellow River in1855, which was almost equal to the result of isotopic dating. It isinferred that the water-sediment regulations have been recorded with the core A11atthe point2~4cm as well as the core A18at the point1.0~2.5cm, which need a furtherstudy to confirm.