Element Records Of Environment Change In The Past 780ka From The No.1 Borehole Sediments Of Xinghua, Northern Jiangsu Basin, China

Northern Jiangsu basin lies in the transitional region that between the ocean and continent and its climate is dominated by the East Asian monsoon system. Using elemental geochemical studies to reconstruct the evolution history of paleoclimate in this region will provide a significant further understanding of the process, rule of the East Asian monsoon. A drilling core of 350 m at Xinghua in the basin was recovered to reconstruct its environment evolution history. We choose the upper part from 3 m to 86.5 m for elemental geochemical studies and the conclusions gained are as follows:(1) All the elements that measured can be divided into four categories based on the hierarchical cluster analysis. The R factor analysis shows that: Ti, Ga, Rb, Y, Zr, Nb, Hf, SiO₂, Al₂O₃, P, Mn, Zn, As, Br, Sr, MgO, CaO and Na₂O are mostly related to the povenance of source rocks which was directly controlled by the chemical weathering intensity; Zr, Hf, V, Co, Ni, Cu, Zn, Ga, As, Rb, Fe₂O₃, Al₂O₃, and K₂O can reflect the content of clay which is possibly related to the element redistribution in the process of diagenesis; Fe₂O₃ P and Mn can record the paleo-productivity and Fe₂O₃, MnO are usually formed under the condition of adlittoral and oxidated environment. Warm-humid and cold-dry environment can been qualitative indicated by Q factor analysis.(2) The high CaO/ ( MgO^* Al₂O₃) ratio and low Rb/Sr ratio can serve as proxies for the high temperature and high precipitation, indicating strong weathering period. High Sr/Ba ratio can reflect the water with high salinity and indicating a high chemical weathering intensity. The SiO₂/Al₂O₃ ratio is a proxy of the process of weathering and developing of paleosol. The Zr/Rb ratio is related to the content of clay. The climatic implications of the elements proxies in the Northern Jiangsu basin are different from those in the loess and lakes that located in western China.(3)Rb/Sr ratio, CaO/(MgO^*Al₂O₃) ratio, Sr/Ba ratio, SiO₂/Al₂O₃ ratio and Zr/Rb ratio in the upper part of the core not only have the same changing trend among themselves, and they also are correlated well with the lithology, susceptibility, and pollen records of the same core, which indicate that the element proxies can be used to reconstruct the environment. The geo-chemical proxies in the upper 87m depth of the core can be divided into 5 big phases and the Northern Jiangsu basin have went through a warm-humid to cold-dry period, warm period, oscillating period and two warm-humid to cold-dry periods.(4) 8 cold-warm cycles can be identified from the chemical records in the past 780ka. which are correlated well with the LR04 marineδ¹⁸O record and the granularity ratio of the loess in western China. But their differences of duration and intensity of climate variation during MIS9 to MIS11 may reflect the regional environment characteristic.(5) The strong precession cycle is found in all of the geo-chemical proxies, indicating a low latitude influence on the East Asian monsoon.