Guanzhong Basin West Of Holocene Pedogenic Environment, High-resolution Study

With a series of global environment problems which include the greenhouse effect and global warming, desertification, environmental degradation and frequent natural disasters emerging, people are becoming more and more concerned about the change of globle climate. Being a period of rapid growth of human civilization and social economy, the Holocene is a historical period which is closely related to human beings.And study of the Holocene climate evolution has great significance to predict future climate changes and coordinate man-land relationship. Based on detailed field investigation, we choose the typical profile of the Holocene loess-palaeosol sequence in the western Guanzhong Basin, Shaanxi Province. The profile is consequent and integral.And it records the complete information of the Holocene environmental change. First we have some experiments in the lab about liang village section'environment identification such as magnetic susceptibility, content of calcium carbonate, loss-on-ignition, partical size, chemical elements, the soil micro morphological characteristics, second analyses variation and environmental significance of experiment results, and finally it comes to the main conelusion as follows:(1) Through analyzing environmental indicators such as magnetic susceptibility, content of calcium carbonate, loss-on-ignition, partical size, chemical elements, we find that these indicators have great significance to pedogenic environment.The magnetic susceptibility, clay and loss-on-ignition in palaeosol are higer than those in loess. While the content of coarse fraction and calcium carbonate in palaeosol are lower than those in loess. The elemets Ca, Na, Sr are migrated and leached during the chemical weathering progress so that they had a high value in loess.While other major and microelement contents have a high value in palaeosol and low value in loess. In addition, the geochemical parameters such as SiO2/Al2O3, eluvial coefficient, CaO/MgO and leaching coefficient have significant change in different layers. SiO2/Al2O3, CaO/MgO and leaching coefficient are low in palaeosol So and high in loess L, and loess Lo. While eluvial coefficient has the opposite variation in the profile.These Features show that during the stage of So formation, the climate was warm and humid with large precipitation, and pedogenesis and secondary clayification were stronger; and during the stage of loess accumulation, the climate turned very dry with little precipitation and pedogenesis was weakened.(2) By measuring and analyzing soil micro morphological characteristics, find that palaeosol layer had large residual clay and clay deposition, and the role of argillic were strong. Even clay deposition appeared the form of fleeting colloid. The clay was often contaminated by a small amount of amorphous iron and manganese, and the contaminations showed reddish-brown. The secondary calcite was almost all leached. The void ratio was highest in LC profile. Pore wall was smooth and the shape was regular. The loess layer was mainly residual clay without clay deposition. The clay was weakly contaminated by a small amount of amorphous iron and manganese. The secondary calcite was larger than that in palaeosol. The void ratio was lower. Pore wall was rough. The above arguments indicate during the stage of So formation, the temperature were high, rainfall were abundant, leaching were strong; during the stage of loess accumulation, rainfall were low, leaching and the role of argillic were weak.(3) CIA, Na/K ratio, Rb/Sr ratio and A-CN-K ternary diagram in LC profile indicate that paleosol (So) underwent more intense chemical weathering than loess (L0, L1) and loess Lo was higher than loess L1. When parent material and terrain were analogous, the chemical weathering differences were mainly induced by the distinction of climate condition.The results shows that during the paleosol formation, the climate was warmmer and humider than that during the stage of loess accumulation;while the climate was relatively warmmer during the stage of loess Lo accumulation than L1.(4) Many climate proxies in LC Holocene loess-palaeosol profile initially reveal the evolution of climatic environment in the western Guanzhong Basin. Pedogenetic environment in Guanzhong underwent such process:the early Holocene with dry climate, little precipitation, weak pedogenesis, weak stick and leaching deposited trasitional loess Lt; the middle Holocene with warm and humid climate, more precipitation, strong stick and leaching developed paleosoil So; the late Holocene with dry climate, intensified dust storms, weak pedogenesis deposited Holocene loess L0. As a result of human farming perturbations, a potent soil layer TS was developed.