Study On The Relationship Between The Elemental Geochemical Characteristics And The Pedogenetic Environment Changes At The Holocene Profiles In The Weihe Valley

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 migrate. Accordingly, the distribution of elements content and the chemical parameter all can show the variety of environment and intension of weathering in the Weihe Valley. In this study, three typical high-resolution Holocene soil profiles in the Weihe Valley were studied using element content, iron species, particle-size analysis, and measurement of magnetic susceptibility, TOC and others. The results provide new insights into pedogenic environmental evolution using geochemical means, and discuss the comparability of particle-size and chemical weathering.The main results were following: The migration apability is: Ca>Sr>Mg>Na, Fe, Al, Si, K, Ti was enrichment;the rare elements Cu, Mn, Zn, Rb, Sr and Rb/Sr ratio can indicate bio-pedogenesis, dissolving and leaching action;the content of total organic carbon(TOC)can reflect variation of climate and vegetation during soil formation, it indicated the intensity of weathering and bio-pedogenesis;six species and total contents of iron show that residual, Fe-Mn-oxide bounded and the organic mater bounded were major species, which make up 99.5 % of the total contents of iron in the loess and soil samples, whereas the other three species(soluble, exchangeable and carbonate bounded)were only 0.5 %. The chemical weathering index(CIA), K/Na ratio, eluvial coefficient(Ki)and A-CN-K diagram , can availably indicate the evolution of pedogenic environment. The A-CN-K and CIA-K/Na diagram showed that the Holocene paleosol was in the primary stage of weathering, which K-feldspar went through weak weathering and K was less leached with much leach of Ca and Na. The intensity of weathering went stronger gradually from west to east in the Weihe Valley. The new study for the content element: the bifid distributing of Ca-Sr in the XJN profile, and beeline distributing in the ETC and JYC-N , maybe cause by the difference of dissolving and leaching action in the Weihe Valley. The bifid distributing in the XJN was likely to imply the variation of environment in the early Holocene. The rareelement P was one of major migrating group in the XJN and JYC-N profile. But in the XJN ,P enriched at paleosol layer. The possible causation was that the bio-pedogenesis was stronger than dissolving and leaching action.There was stage of soil formation from the evolution of pedogenic environment in the Weihe Valley during Holocene. Soil formation showed that law of evolving from warm and wet strong soil formation period to cold and dry dust deposition (weak soil formation period) and to warm and wet strong soil formation period again. The loess-paleosol sequence was acompound soil sectional system of different kinds of soil evolution under different bio-environment and pedogenic process. The intensity of weathering, dissolving and leaching action and secondary clay action went stronger gradually from west to east in the Weihe Valley.