| 黔南—桂北地区南华系化学地层特征 |
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| 关键词:Nanhua System “cold weathering period” chemical index of alteration (CIA) potassium replacement index of compositional variability (ICV) |
| 基金项目:科技部基础工作专项(2006FY120300)和中国地质调查局项目(1212010611802-2) |
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| Chemostratigraphic Characteristics of the Nanhua System inSouthern Guizhou—Northern Guangxi Area |
| The chemical index of alteration (CIA) was first proposed as a marker to distinguish chemical weathering degrees of source rocks, and later it was used to distinguish depositional environments. The formula of the chemical index of alteration is CIA={n(Al2O3/[n(Al2O3)+n(CaO*)+n(Na2O)+n(K2O)]) x 100. Here, CaO* represents CaO in silicates, and n(CaO*)=n(CaO)?n(CO2,calcite)?0.5Xn(CO2dolomite)?10/3 x n(P2O5). It is very important to select samples for the analysis of the chemical index of alteration. The following two factors have to be considered when we perform sampling in the field: the best rocks are fine clastic rocks, and the influence of diagenetic potassium replacement should be avoided. The index of compositional variability (ICV) is used to distinguish the circulation and reformation degree of the composition of sediments. At the same time, A-CN-K diagram is used to distinguish features of source rocks and characteristics of potassium replacement and its weathering degrees. The results of the authors’ study show that the value of CIA is at 60~65 in the lower part, 70~75 in the middle part, and 65-70 in the upper part of Changan Formation of Nanhua System. CIA value is at 85~95 in Fulu Formation of Nanhua System, and CIA value is at 60~65 in the Nantuo Formation of Nanhua System. The repeated variation of the CIA value indicates separately the circle from the arid-frigid weathering environment to the warm-damp weathering environment from old to young in the Nanhua Period. Based on these results, the authors suggest a new division and correlation of the Nanhua System in the Yangtze Platform. |
| WANG Zi-giang,YIN Chong-yu,GAO Lin-zhi,TANG Feng.2009.Chemostratigraphic Characteristics of the Nanhua System inSouthern Guizhou—Northern Guangxi Area[J].Acta Geoscientica Sinica,30(4):465-474. |
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