关键词: 汾河源区, 不同景观带, 粒度分析, 地球化学元素, 沉积环境

Abstract: With the support of ArcGIS remote sensing image, this paper classified the landscape belts of Fenhe River headwater catchment, Shanxi Province, China into four categories including subalpine meadow belt, coniferous and deciduous forest belt, bush and grass belt and farming land belt at both shores of the river. The samples of the surface soil (0-10 cm)in different landscape belts were collected from September to October, 2012, and then preliminary analysis of its superficial deposit granularity and geochemical elements were conducted. Granularity analysis was completed through applying the Mastersizer 2000 type laser particle analyzer produced by UK Malvern Company. Specifically, 10% H₂O₂ was added to remove the organic matter and dissolvable salt; 10% HCl was added to exclude carbonate; and then distilled water was filled to keep still for over 12 h. Subsequently, the 10% sodium hexametaphosphate was put in Ultrasonic oscillators to be tested after it was fully scattered. The results prove the test error is less than 0.2%. The geochemical elements were tested as follows:firstly, the air-dried samples must be milled into below 200 meshes, then 4 g was weighed and dried at 105℃ to be put in sample preparation mold for shaping into a round test sample with the external diameter of 32 mm, finally the sequential wavelength dispersion type of x-ray fluorescence spectrometer produced by PANalytical B.V. was applied as the test instrument, for its element test error was less than 5%. Results show that the superficial deposit of Fenhe River headwater catchment is mainly composed by silt, supplemented by certain amount of extremely fine sand and clay, while the content of fine sand and medium-coarse sand is low. In general, the deposit separation is poor, showing a positively biased and extremely positively biased distribution with medium to sharp kurtosis. The deposition environment is complicated and diverse with the coexistence of eolian deposit, marine facies and fluvial deposit, which may be closely associated with the regional geological conformation movement, airborne material deposition and river development. From the analysis of geochemical elements, it is found that the superficial deposit of this area mainly contains SiO₂, Al₂O₃ and Fe₂O₃, showing significant homology with upper continental crust (UCC) and Chinese loess (CL). Active elements like Ca and Mg also present obvious vertical difference with the precipitation change influenced by altitude. The chemical weathering of the deposit basically lies in the preliminary stage of excluding Ca and Na, which belongs to the low level chemical weathering under cold and dry conditions. As the major ecological environment weak belt and environment sensitive reflection belt of the rivers sources, Fenhe River headwater catchment is taken as the typical area for exploring the current ecological environment deterioration and future environment evolution trend, which is of great academic and practical significance. As the basic link of such research, this study aims to provide theoretical basis and data support for further understanding the ecological environmental changes by utilizing the superficial deposit of different landscape belts in Fenhe River headwater catchment for preliminary granularity and geochemical analysis.

Key words: Fenhe River headwater catchment, different landscape zones, granularity analysis, geochemical elements, depositional environment