摘要:
在兰州黄土和下蜀黄土中粘土矿物的X衍射分析基础上,对我国不同纬度和气候带的五个黄土剖面(点)中的粘土矿物组合和空间分布进行了对比分析,并探讨了与古气候的关系。结果表明,黄土中粘土矿物组合具有明显的地带性特征。从西北到东南,随着纬度的逐渐降低,黄土中的粘土矿物组合也发生有规律的变化。主要表现为绿泥石含量的逐渐减少和蛭石含量的逐渐增多。位于温带半干旱区的兰州黄土以伊利石和绿泥石为主要粘土矿物,而位于亚热带湿润区的大港下蜀黄土则以伊利石和蛭石为主要粘土矿物。黄土中含有较多量的绿泥石可作为黄土母质堆积后干冷气候和微弱风化的标志,而蛭石和蛭石/绿泥石混层矿物含量的增加指示了风化强度的增强。因此,黄土粘土矿物组合特征不仅反映物源区古环境信息,而且指示了黄土堆积期后的生物气候环境。
Abstract:
Chinese loess, the Quaternary aeolian deposits in another term, covers a nationwide area from the east China coast to the northwest inland desert. Studies show that the origin of clayminerals bears relation to the formation and evolution of loess. To understand and exp lain the differences of loess under different climatic conditions, this paper constructs a NWW-SEE cross-section which consists of five rep resentative loess profiles (sites) in central Gansu (Lanzhou) , northern Shaanxi (Luochuan) , central Shaanxi (Baoji) , northern Henan (Jiyuan) and the lower reaches of the Yangtze river ( Zhenjiang) , respectively. Samples taken from Lanzhou loess and Zhenjiang loess, and also from the present dust-storm deposits were analyzed by using X-ray diffraction system. Preliminary conclusions can been drawn as follows: In both loess and the dust-storm deposits, a number of clay minerals were examined through X-ray diffraction. They are illite, chlorite, vermiculite, kaolinite, smectite group and mixed layerminerals. In Lanzhou loess illite and chlorite are dominant, but in Zhenjiang loess the clay mineral assemblage is illite-vermiculite type. Comparing with other loess profiles ranging between Lanzhou and Zhenjiang, it is found that the claymineral assemblage changes gradually from northwest to southeast. Along with the latitude getting lower, the content of chlorite decreases, while the content of vermiculite increases. This imp lies that clay mineral assemblage must have close reference to the climate.The dry and cold climate favors for the formation of chlorite, the warm and humid climate benefits for vermiculite.Furthermore, the content of vermiculite and its interstratified minerals can also be a proxy ofweathering intensity. To conclude, the claymineral assemblage of loess can be used to trace the source ofmothermaterial and understand the post-depositional climate conditions
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