Preliminary Study On Environmental Geochemistry In The Paleo-sediment Of The Yellow River

In this paper, the paleosediment of Yellow River between Wuzhi and Huaxian of Henan province were selected as research object. Combined with relevant historical data and the results of previous researches, concentrations change and distribution characteristics of trace elements in the sediment was to study to discuss the respond relation between Chinese civilization development status of the Yellow River valley and the ecological environment change of the Loess Plateau in the past 4 thousand years. The results showed that:1. The trace elements in the paleosediment of Wuzhi Yellow River showed three different distribution characteristics, and the distribution characteristics of trace elements in the paleosediment of Huaxian Yellow River were basically similar to them of the second stage of Wuzhi Yellow River.2. The first stage of Wuzhi Yellow River (530cm-400cm): the mean concentration of each element was lowest, the mean value of Fe, Mn, Cu, Zn, Ni, Cr, Pb, Hg, As was 24906.50mg/kg, 190.81mg/kg, 10.39mg/kg, 200.90mg/kg, 17.68mg/kg, 30.95mg/kg, 20.23mg/kg, 0mg/kg, 54.64mg/kg, respectively. It was consistent with the results of previous researches that the Loess Plateau had thick vegetation, the climate of it was wet, the water resource of Yellow River was rich with little sediment concentration. The author suggested this stage was from Xia Dynasty to the warring states period as early as about 4000-2485 aB.P.3. The second stage of Wuzhi Yellow River (400cm-200cm): the mean concentration of each element was higher than it of the first stage, and remained at the mean, the mean value of Fe, Mn, Cu, Zn, Ni, Cr, Pb, Hg, As was 25722.60mg/kg, 207.62mg/kg, 12.84mg/kg, 249.12mg/kg, 18.03mg/kg, 34.18mg/kg, 20.80mg/kg, 0.10mg/kg, 115.25mg/kg, respectively. It was closely correlated with the climate change and increasing the intensity of human activities of the Loess Plateau. The author suggested this stage was from Qin Dynasty to Sui Dynasty as early as about 2485-1400 aB.P.4. The third stage of Wuzhi Yellow River (200cm-0cm): the mean concentration of each element was highest except Pb, and changed widely, the mean value of Fe, Mn, Cu, Zn, Ni, Cr, Pb, Hg, As was 26993.13mg/kg, 256.04mg/kg, 21.43mg/kg, 256.41mg/kg, 28.14mg/kg, 47.59mg/kg, 19.50mg/kg, 0.16mg/kg, 240.09mg/kg, respectively. It was closely correlated with the ecological environment deterioration caused by destructive agricultural development model of the Loess Plateau. The author suggested this stage was from Tang Dynasty to mid-Qing Dynasty as early as about 1400-200 aB.P.5. The distribution characteristics of trace elements in the paleosediment of Huaxian Yellow River were basically similar to them between 406cm and 143cm of Wuzhi Yellow River, the concentration of each element remained at the mean value, and changed with narrow range. Except Hg, the mean concentration of Fe, Mn, Cu, Zn, Ni, Cr, Pb, As of Huaxian Yellow River was lower than it of Wuzhi Yellow River, and the ratio was about 1/10, 9/10, 1/2, 1/5, 7/10, 1/10, 3/4, 1/7, 1/5, respectively. It was possible that the Huaxian research area may be affected by the paleosediment of Weihe basin so that the sources of paleosediment of Yellow River between Wuzhi and Huaxian were different. The author suggested this stage was about from Spring and Autumn Dynasty to South Song Dynasty as early as about 2750-800 aB.P.