| Strong tectonic movements took place during Cenozoic in lithosphere, resulting in land and sea patterns and topography pattern changed, and therefore to a large extent caused the changes of ocean currents and weather, because of which has become the focus of global changes. Luyang Lake is located in Fuping County, Shaanxi Province which had broad water surface in historical periods and it is a saline beach now. Luyang Lake remains of Sanmen ancient lake, and Sanmen Lake is the final evolution stage of Fenwei graben in late Cenozoic. The sedimentary formations form of the famous "Sanmen Formation". Weihe basin is part of Fenwei graben, which began to develop in the Eocene and accumulated Cenozoic sedimentary to thickness of a few kilometers. The southern edge of the basin sedimentary got uplifted due to Qinling outcropping, one of representative areas of China’s Cenozoic formations. It includes the famous loess-paleosol-red clay sequence (Qinan, Baoji, Duanjiapo, etc.). Therefore, the study of Luyang Lake drilling has a very important significance to Cenozoic climate change in Weihe basin area and the late Cenozoic history of the East Asian monsoon Element geochemistry XRF core scanning element analysis is mainly used in the marine core, which has great advantages in fast, non-destructive, continuous and high resolution scanning results. According to changes in the content and representative elemental ratios to infer paleoenvironmental and ancient climate change, it helps rebuild the ancient environment and paleoclimate with a relatively high resolution analysis. The application of this method in Luyang Lake drilling has expanded the scope of application of XRF core scanning.The thesis selected representatively common elements rations like Rb/Sr, Zr/Rb, Fe/Mn and Sr/Ba and other geochemical ratios.Via comparing the relationships among Rb/Sr, Zr/Rb and median grain size and magnetic susceptibility, we has found they have good correspondence in LYH-1driling. This is consistent with previous studies that Rb/Sr of lake sediments can be indicator of the intensity of summer monsoon as well as magnetic susceptibility. In Luyang Lake area, lower Rb/Sr ratios, may indicate this area affected by the gradually increased summer monsoon, gradually increased regional precipitation and lake water level gradually increases, resulting in a relative reduction of lake sediment conditions. While Zr/Rb ratio is regarded as the geochemical indicator of grain size, which still reflect the information of original deposition of dust.It can be used to reflect the strength of the regional winter monsoon, In Luyang Lake area, the increase of Zr/Rb ratio rises may indicate a trend in the region affected by the gradually increased winter monsoon, the regional precipitation decreased gradually and reduce lake water area, resulted in lake sediments in a relatively oxidizing conditions.During the last glacial period, the record of LYH-1core corresponds well with other high-resolution records, especially with the GRIP ice core records. During which, we can find most of the D-O cycle events and recognize5Heinrich events. These phenomena indicates that those rapid climatic fluctuation events occurred in the North Atlantic region during last glaciation can also be found in the lake recorded in China hinterland.The environmental indicators of LYH-1show that there exists both primary and sub-level cycle of climate oscillations on different time scales, indicating that the climate has been driven by a number of factors together. On one hand, it shows the information synchronized with global climate change, on the other hand, it shows the obvious regional characteristics.And sometimes, the amplitude of sub-level cycle exceeds a primary cycle. The reason for this phenomenon may be mainly in the following possibilities:climate change cycles superimposed on each other’s sake; may also be the result of a nonlinear feedback system of the monsoon; additionally, some cycles may be due to the time scale of uncertainty of the distortion. |
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