Abstract: Studies on grain-size and geochemical element composition for topsoil in northwestern Shanxi Province can provide rich information on provenance, sedimentary environment and chemical weathering processes of sediments in the study area. The topsoil (0 cm, 10 cm, 20 cm to the ground surface) and the surrounding fluvial deposits were collected, and their grain-size and geochemical element composition were tested. The results indicated that:(1) the topsoil in northwestern Shanxi Province was mainly composed of clay and silt, and coarse particle contents showed an increasing tendency from the ground surface downward. (2) Major elements were mainly composed of SiO₂, Al₂O₃, CaO, Fe₂O₃, and the contents of other major elements were trace. The composition pattern of major elements suggested that the topsoil in the study region have the same source as the loess in the hinterland of Loess Plateau. The fluvial sediments of Huanghe River contributed much less to the sediments in the study area. (3) CIA values for topsoil in northwestern Shanxi Province varies between 52.70-57.89, and averages 54.06, which demonstrate that the chemical weathering degree of the sediments is very low, and in the early stage of losing Na and Ca. This can attributes to the location of the study area, which situate north of Luochuan and Lanzhou, and the annual mean temperature and precipitation are much lower than in the hinterland of Loess Plateau. The present research clearly demonstrates the composition of topsoil in the northwestern Shanxi Province, and can lay firm foundation to the controlling of potential desertification in the study area.

Key words: grain-size, geochemical element, chemical weathering, loess, northwestern Shanxi Province