Mineral Composition of Loess—Paleosol Samples from the Loess Plateau of China and Its Environmental Significance

34samples of loess-paleosol from the Luochuan and Xifeng sections in the Loess Plateau,northern China were eparated into sand,silt and clay fractions and analyzed for their mineral compositions.The results indicate that there is almost no difference between loess and paleosol in mineral composition.Major mineral species are quartz,mica,feldspar and chlorite,accounting for about 88-92% of the total;other minerals are kandite,smectite,vermiculite and a few heavy minerals.The calcite,magnetite and hematite were not taken into consideration because of their removal in the process of sample preparation.The main difference with respect to the mineral composition of samples collected from different sections and different statigraphic levels lies in the amount and grain size of minerals hosted.Comparisons between the Luochuan section and the Xifeng section,between paleosol and loess and between the upper part and the lower part of some paleosol layers show that the formers contain less feldspar but more mica and vermiculite and are finer in grain size,indicating the co-occurrence of both biochemical weathering process responsible for mineral change and physical weathering process leading to grain-size change during the soil-forming processes.This result favours such an explanation of the soil-forming mechanism that loess deposition and paleosol development occurred synchronously,though the rate of soil formation was greater than that of loess deposition,thus leading to soil development.

Mineral composition of Loess-Paleosol samples from the Loess Plateau of China and its environmental significance

34 samples of loess-paleosol from the Luochuan and Xifeng sections in the Loess Plateau, northern China were separated into sand, silt and clay fractions and analyzed for their mineral compositions. The results indicate that there is almost no difference between loess and paleosol in mineral composition. Major mineral species are quartz, mica, feldspar and chlorite, accounting for about 88–92% of the total; other minerals are kandite, smectite, vermiculite and a few heavy minerals. The calcite, magnente and hematite were not taken into consideration because of their removal in the process of sample preparation. The main difference with respect to the mineral composition of samples collected from different sections and different stratigraphic levels lies in the amount and grain size of minerals hosted. Comparisons between the Luochuan section and the Xifeng section, between paleosol and loess and between the upper part and the lower part of some paleosol layers show that the formers contain less feldspar but more mica and vermiculite and are finer in grain size, indicating the co-occurrence of both biochemical weathering process responsible for mineral change and physical weathering process leading to grain-size change during the soil-forming processes. This result favours such an explanation of the soil-forming mechanism that loess deposition and paleosol development occurred synchronously, though the rate of soil formation was greater than that of loess deposition, thus leading to soil development. This project was financially granted by the Xi’an Open Lab. for Loess and Quaternary Geology, Chinese Academy of Sciences.