Characteristics Of Iron Oxides In Loess Profiles And Indication Of Soil Environment

Our research, taken the Shanxi Provinc Wugong and Luochuan soil profile as the research object, using DXRD and DCB methods to strengthen the diffraction peak of soil iron oxides, identified different types of soil iron oxides mineral and calculated the quantity of aluminum with crystal replacement in ferric oxide mineral. We discussed the relationship between types of soil iron oxides mineral, the quantity of aluminum with crystal replacement in ferric oxide mineral and soil susceptbility, different iron forms, which mineralogical characteristics of ferric oxide could be an indicator for environment. The main results are showed below.1. The soil susceptibility of Wugong profile Loess layer(Lo), paleosoil (So), Loess layer(L0) was 163.0×10-8 SI,177.6×10-8 SI,102.3×10-8 SI respectively. There is a process of envirmental evolution in the area which formed the condition from cold and dry, warm and wet to cold and dry. The soil susceptibility values of Loess layer (Lo) from 180 to 240cm are significantly higher than others, showing that the soil environment evolution exist millennium scale and and centennial scale.2. Poor X-diffraction analysis method can effectively reduce the layer silicate clay mineral high strength of iron oxide diffraction peak at the peak of interference diffraction. In DXRD map can be observed in iron ore and hematite Shared needle 0.252 nm peak and and goethite 0.245 nm peaks. The characteristic peaks of hematite in the position of 0.269 nm 0.367 nm was observed in loess-ancient soil sequence. Meanwhile, we also observed the characteristic peaks of goethite with 0.418 nm and 0.252nm.Therefore, The DXRD is an effective method for identifing ferric oxide mineral type in the loess-ancient soil sequence, with 1.7 percent of detection limit of ferric oxide mineral type.3. Using the poor X-diffraction analysis method to identify iron oxides mineral types of Wugong profile and Luochuan profile, we found goethite and hematite with a large proportion, but some differences between the relative content. In the Wugong profile, the value of Hm/Gt in Loess is 0.37, in paleosoil is 0.24. Compared to Luochuan profile, the value of Hm/Gt in Loess 0.36, in paleo soil is 0.38.4. Compared to the curves of soil susceptibility, free iron oxide content and amorphous iron oxide content, we found that the curve of Hm/Gt was decreased continuously,showing soil evoultion process with higher precipitation intensity or precipitation occurred in the background of lowering the temperature.5. In the Wugong profile. Al-substitute in goethite in loess and paleosoil is 9.10%5.49%, respectively. In the Luochuan profiles, the amount is 4.19% and 7.16%, respectively. Regression analysis, statistics show that goethite Al-substituteis a significant positive correlation with the soil susceptibility (figure 15). In conclusion, coming into being with soil weathering, aluminum with crystal replacement quantity is also increase gradually.6. Al-substitute curve shows by low-level to surface increasing trend, with discussion of Hm/Gt curve, this paper argues that the trend indicator, after 20000a B.P. loess plateau in south-central precipitation intensity is soil development under the background of the overall increasing.