郑州全新世黄土的颗粒形态特征及其环境意义

Micromorphological Features of Particlesof Holocence Loess at Zhengzhou Areas,China and Their Environmental Significance

用偏光显微镜和图像处理软件对黄土颗粒形态进行观察和定量分析，用激光粒度仪测量黄土的粒度分布。结果表明：郑州地区黄土中颗粒的一般呈次圆状-圆状，具有较高的圆度和球度；矿物组合以石英和长石占绝对优势，但郑州黄土中石英／长石比值和C／F（10μm）值高于关中黄土；郑州黄土粒度峰值集中在50～80μm且曲线形态较陡，而关中黄土粒度峰值在20～40μm且曲线形态较缓。综合分析认为，郑州地区黄土可能来源于孟津以东的黄河冲积扇，应属于近源黄土。

Using the particle data obtained from the Holocene soil profile at LGT, JYC sites in the Guanzhong area and at PLG, SBLH sites in the Zhengzhou, this article attempts to illustrate the material source of Zhengzhou loess and its environmental significance. The micromorphology was observed under a petrographic microscope,and its image was quantificationally measured by NIKON NIS-ELments BR2.2 software. Particle size distribution was determined by a Malvern Mastersizer-S and with Na4P2O7 as a dispersant. Micromorphological observation of the thin sections shows that the grain-shape of Zhengzhou loess is characterized by sub-round or round, with higher length/width ratio, and that of the Guanzhong loess by sub-angular or angular, with strip, triangular and irregular shapes. Comparison with the Guanzhong loess, the coarse of Zhengzhou loess is characterized by higher Length, Area, EqDiameter, Perimeter, Elongation and Roundness, and K1, K2, K3,K4 value aremore than 1.It suggest that the particle in the Zhengzhou loess has higher roundness and sphericity and has gone through stronger hydraulic abrasion. The assemblage of minerals in both loess is mainly composed of Q and PI. However, Q ＋ P1 content, Q/P1 ratio and C/F10μm ratio are clear higher in Zhengzhou loess than in Guanzhong loess. Research result shows that particle-size of both loess falls in the same range, within particle-size range of aeloian, but peak value of particle-size of Zhengzhou loess ranges in 50-80 μm with steep particle-size curve and that of Guanzhong loess is in 20-40 μm with slow particle-size curve. All the results of this study suggest that Zhengzhou loess is aeolian, which has synchronously both aeolian and alluvium features. However its material source differs from Guanzhong loess, and it came from various loose river sediments at the Huanghe （Yellow） River alluvial fan in the east of Mengjin and transported by northeastern wind.