To understand climate changes recorded in the Luochuan loess-palaeosols, Shaanxi province, northwes- tern China, clay mineralogy was studied using X-ray diffraction （XRD）, high-resolution transmission electron micro...To understand climate changes recorded in the Luochuan loess-palaeosols, Shaanxi province, northwes- tern China, clay mineralogy was studied using X-ray diffraction （XRD）, high-resolution transmission electron microscopy （HRTEM）, and scanning electron microscopy （SEM） methods. XRD results show that clay mineral compositions in the Luochuan loess-palaeosols are dom- inantly illite, with minor chlorite, kaolinite, smectite, and illite-smectite mixed-layer clays （US）. Illite is the most abundant species in the sediments, with a content of 61%- 83%. The content of chlorite ranges from 5%-22%, and the content of kaolinite ranges from 5%-19%. Smectite （or US） occurs discontinuously along the loess profile, with a content of 0-8%. The Kfibler index of illite （IC） ranges from 0.255°-0.491°, and the illite chemical index （ICI） ranges from 0.294-0.394. The CIA values of the loess- palaeosols are 61.9-69.02, and the R3＋/（R3＋ ＋ R2＋ ＋ M＋） values are 0.508-0.589. HRTEM observations show that transformation of illite to illite-smectite has occurred in both the loess and palaeosol, suggesting that the Luochuan loess-palaeosols have experienced a certain degree of chemical weathering. The Luochuan loess-palaeosols have the same clay mineral assemblage along the profile. However, the relative contents of clay mineral species, CIA, ICI, and IC values fluctuate frequently along the profile, and all these parameters display a similar trend. Moreover, climate changes suggested by the clay index are consistent with variations in the deep-sea 6180 records and the magnetic susceptibility value, and thus, climate changes in the Luochuan region have been controlled by global climate change.展开更多
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 41272053 and 41472041）. C.W. acknowledges a postdoctoral science foundation of China （2015M582301）, Fundamental Research Funds for the Central Universities, China University of Geosciences （Wuhan）, and National Natural Science Youth Foundation of China （Grant No. 41602037）. The authors wish to thank Dr. Yu J. S. for XRD analysis, Dr. Liu X. W, for HRTEM analysis and Dr. Yang H. and Dr. Yang Q. for SEM analysis.
文摘To understand climate changes recorded in the Luochuan loess-palaeosols, Shaanxi province, northwes- tern China, clay mineralogy was studied using X-ray diffraction （XRD）, high-resolution transmission electron microscopy （HRTEM）, and scanning electron microscopy （SEM） methods. XRD results show that clay mineral compositions in the Luochuan loess-palaeosols are dom- inantly illite, with minor chlorite, kaolinite, smectite, and illite-smectite mixed-layer clays （US）. Illite is the most abundant species in the sediments, with a content of 61%- 83%. The content of chlorite ranges from 5%-22%, and the content of kaolinite ranges from 5%-19%. Smectite （or US） occurs discontinuously along the loess profile, with a content of 0-8%. The Kfibler index of illite （IC） ranges from 0.255°-0.491°, and the illite chemical index （ICI） ranges from 0.294-0.394. The CIA values of the loess- palaeosols are 61.9-69.02, and the R3＋/（R3＋ ＋ R2＋ ＋ M＋） values are 0.508-0.589. HRTEM observations show that transformation of illite to illite-smectite has occurred in both the loess and palaeosol, suggesting that the Luochuan loess-palaeosols have experienced a certain degree of chemical weathering. The Luochuan loess-palaeosols have the same clay mineral assemblage along the profile. However, the relative contents of clay mineral species, CIA, ICI, and IC values fluctuate frequently along the profile, and all these parameters display a similar trend. Moreover, climate changes suggested by the clay index are consistent with variations in the deep-sea 6180 records and the magnetic susceptibility value, and thus, climate changes in the Luochuan region have been controlled by global climate change.
