| Nowdays a series of global environment problems which have never occurred before, especially global changes in climate have deep impacts on both economic development of all the coutries and survival of human beings. The Holocene which is closely related to the development of human society is an essential part of PAGES. And study of the Holocene climate change has a viallty inportmant reference value to forcasting future environment changes. Many methods were introduced into the studies and great progress was made. The loess-paleosol sequence in the Loess Plteau which is located in Northwest China was accepted as a wonderful information carrier in Quaternary research. The formative mechanism, source of loess-paleosol and history of climatic changes in the Loess Plateau was made clear through the studies of the Loess-paleosol profile.Through field exploration, systematical sampling and experimenting, we gained a lot of high-definition datum of magnetic susceptibility, partical size, chemical elements, content of calcium carbonate, loss-on-ignition and hygroscopic water which have an important indicative significance to paleoclimate evolution. The results show that the content of magnetic susceptibility, loss-on-ignition, hygroscopic water and clay in soil are higer than those in loess. But the content of calcium carbonate, coarse fraction and sand-size particles in soil are lower than those in loess. The elemet Na, Ca, Sr were obviously migrated and leached during the chemical weathering progress so that they had a high value in loess.The distribution characteristics of heavy metals (except Pb, V) and other trace elements reflect the effect of soil formation, so that they have a high value in soil and low value in loess. K2O/Na2O ratio, eluvial coefficient and Rb/Sr, as good proxy climate indexes,varied regularly in the CCY Holocene loess-soil profile, i.e. they peaked in the paleosol,and were lower in the loess,and reduced along with the intensity of pedogenesis decreasing.Whereas CaO/MgO ratio, SiO2/Al2O3 ratio and leaching coefficient went the other way in the profile,indicating that during the paleosol formation,the climate was warm and humid with abundant precipitation;while during the loess accumulation.the climate was relatively cold and arid.There is a good comparisons between these chemical parameters and magnetic susceptibility, frequency dependent susceptibility, showing that during the process of loess chemical weathering.elements seems to indirectly reflect the change of climate and pedogenic environment.The migration and enrichment of chemical elements were related to the environment changes. The Holocene loess-soil in the Loess Plateau constituted an excellent record of climate evolution, aeolian dust and soil formation. The essential of soil was that the chemical elements reset and mignation. Therefore, the distribution of elements content in soil and the chemical parameter all can show the variety of environment and intension of chemical weathering in Pengyang. In paper, the element geochemical characteristics, intensity of chemical weathering and pedogenetic environment changes were studied and discussed. The conclusions maily are as follows:(1)In relation to Malan loess layer, the major elements and trace elements in other loess layers were not obviously differentiated, which reflect the homogeneity and uniformity of loess material. But in Holocene Megatherma, the major elements and trace elements were differentiated in paleosoil (So). During the pedogenetic progress, Ca, Mg, Na were leached but Fe, Si, K were enriched. According to the migration ability, the major elements are ranked in the following order: Ca>Mg>Na>Mn>Si>Ti>Fe>K. The migration features of the macro-elements reveal that Holocene loess in Pengyang only experienced primary process of chemical weathering characterized by leaching of Ca,Na,and not reached the secondary process characterized by leaching of K.Most of the trace elements were enriched except the element Sr was obviously migrated and leached during the chemical weathering process. According to the migration ability, the major elements are ranked in the following order:Sr>Ba>V>Cu>Zn>Ni>Mn>Ti>Rb>Cr. Cu, Zn was faintly enriched in CCY profile, which indicated that the vegetation is poor during the chemical weathering progress in Pengyang.(2) CIA and A-CN-K ternary diagram indicate that intensity of chemical weathering of loess in Loess Plateau was gradually increased from northwest to southeast. In Holocene Megatherma, the Pengyang loess underwent primary chemical weathering, which is similar to that of Pingliang loess, much weaker than that of Guangzhong loess. The chemical weathering differences among the studied Aeolian-dust deposits in Loess Plateau were mainly induced by the distinction of climate condition, which imposed important influence on the geochemical environment through the mean annual temperature and annual precipitation. It seems that the annual precipitation has more important influence on the chemical weathering process in arid Loess Plateau.(3)The environmrnt proxy indicators and element geochemical characteristics in CCY Holocene loess-soil profile reveal the evolution of climatic environment. Pedogenetic environment in Pengyang underwent such process:the early Holocene with dry and cold climate deposited trasitional loess Lt, the middle Holocene with warm and humid climate developed paleosoil So, the late Holocene with dry and cold climate deposited Holocene loess Lo. Since 1500a B.P.,the climate condition had improved, and a potent soil layer TS was developed under the human farming perturbations.(4)Comparison with magnetic susceptibility, Rb/Sr, CIA of JYC profile at Guangzhong basin, these values of CCY profile was obviously lower, showing that paleosol's intensity of pedogenesis in the CCY profile was significantly weaker than that in JYC profile, precipitation was on the low side, which indicating that in relation to the subtropical climate in Guangzhong basin, Changcheng loess tableland in Pengyang may only belong to warm temperate climate in Holocene Megathermal.(5)Research in pedogenetic environment changes and correlation analysis between heavy metals and climatic index indicate that at a long-time scale particle-size distribution and content of calcium carbonate are the important factors that directly affect the distribution of heavy metals in the profile. However, these are ultimately affected by the changes in the intensity of dust storms and precipitation that controlled by monsoonal climatic changes during the Holocene. |
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