Objective There has been considerable debate about the definition of the lower boundary of Nanhua System by far.One definition is based on sedimentary sequence of different stages of basin evolution,focusing on whethe...Objective There has been considerable debate about the definition of the lower boundary of Nanhua System by far.One definition is based on sedimentary sequence of different stages of basin evolution,focusing on whether deposits of the Banxi Period should be classified as Nanhua System.Another is the onset time of Nanhua glacial period.展开更多
化学蚀变指数(chemical index of alteration)(CIA)最早作为判别源岩化学风化程度而提出,随后又应用于对沉积物沉积环境的判定。化学蚀变指数的表达式为CIA={n(Al2O3)/[n(Al2O3)+n(CaO^*)+n(Na2O)+n(K2O)]}×10...化学蚀变指数(chemical index of alteration)(CIA)最早作为判别源岩化学风化程度而提出,随后又应用于对沉积物沉积环境的判定。化学蚀变指数的表达式为CIA={n(Al2O3)/[n(Al2O3)+n(CaO^*)+n(Na2O)+n(K2O)]}×100。CaO^*代表硅酸盐中的CaO,n(CaO^*)=n(CaO)-n(CO2方解石)-n0.5×n(CO2白云石)-10/3xn(P2O5)。化学蚀变指数样品的选取极为重要,最佳岩性为细碎屑岩,并需清除成岩过程中钾交代作用的影响,以及采用成分变异指数(ICV)来判别沉积再循环作用和沉积物成分被改造的程度。使用A—CN—K三角图解判别物源区的源岩性质和样品钾交代的程度及其风化趋势。黔南-桂北地区南华系的CIA研究表明:该地区南华系下部的长安组其下部CIA值为60~65之间,中部为70~5,上部回落到65—70之间。南华系中部富禄组CIA值高,在85-95之间。南华系上部的南沱组CIA值再次回落到60—65的范围。上述CIA值的变化表明本区南华纪时期自老至新经历多次由干燥寒冷-温暖潮湿气候期的变化。本文据此提出扬子地块南华系新的划分、对比方案。展开更多
基金supported by the National Natural Science Foundation of China(grants No.41372124,41402103 and 41302091)
文摘Objective There has been considerable debate about the definition of the lower boundary of Nanhua System by far.One definition is based on sedimentary sequence of different stages of basin evolution,focusing on whether deposits of the Banxi Period should be classified as Nanhua System.Another is the onset time of Nanhua glacial period.
文摘化学蚀变指数(chemical index of alteration)(CIA)最早作为判别源岩化学风化程度而提出,随后又应用于对沉积物沉积环境的判定。化学蚀变指数的表达式为CIA={n(Al2O3)/[n(Al2O3)+n(CaO^*)+n(Na2O)+n(K2O)]}×100。CaO^*代表硅酸盐中的CaO,n(CaO^*)=n(CaO)-n(CO2方解石)-n0.5×n(CO2白云石)-10/3xn(P2O5)。化学蚀变指数样品的选取极为重要,最佳岩性为细碎屑岩,并需清除成岩过程中钾交代作用的影响,以及采用成分变异指数(ICV)来判别沉积再循环作用和沉积物成分被改造的程度。使用A—CN—K三角图解判别物源区的源岩性质和样品钾交代的程度及其风化趋势。黔南-桂北地区南华系的CIA研究表明:该地区南华系下部的长安组其下部CIA值为60~65之间,中部为70~5,上部回落到65—70之间。南华系中部富禄组CIA值高,在85-95之间。南华系上部的南沱组CIA值再次回落到60—65的范围。上述CIA值的变化表明本区南华纪时期自老至新经历多次由干燥寒冷-温暖潮湿气候期的变化。本文据此提出扬子地块南华系新的划分、对比方案。