火山地质与矿产2001，Vol.22Issue(2)：126-134,9.
川西南阿什及尔期地层中的Ce异常及其古海洋学意义
Cerium anomalies in the Ashgillian strata in southwestern Sichuan,China and their paleoceanographical significance
摘要
Abstract
The whole-rock REE abundance patterns from the Ashgillian strata in southwest Sichuan, China display regular variations in Ce anomalies: the black shales with exclusive planktic graptolites and small-sized inarticulate brachiopods and deposited apparently under anoxic bottom-water conditions possess lower Ce anomaly values (0.62～0.74); on the contrary, the non-black shales with benthic trilobites, articulate brachiopods and algae, which should have been formed under oxic bottom-water conditions, yield higher Ce anomaly values (0.92～1.32). A correlation analysis performed between Ce and other elements further shows Ce strongly correlates with Fe (r = 0.85), moderately with P (r = 0.61), weakly with Al (r = 0.29) and barely with Mn (r = 0.14) and Ca (r = -0.02). The empirical observations may suggest that, under the condition of oxidation and alkalinity in the investigated area, Ce was oxidized to Ce4＋ and incorporated into or absorbed on iron-oxyhydroxides and phosphates settling to the seafloor, causing a negative Ce anomaly in the oxic water and a less negative or positive Ce anomaly in the contemporary oxic sediments; antithetically, when a reducing and acidic environment was prevailing, Ce was concentrated as the 3+ valence state within anoxic water, resulting in a sharp negative anomaly in the coeval anoxic sediments. Our research result indicates that, with fossil bones (especially phosphatic fossil bones) removed out, fine-grained shallow marine sediments can be used for whole-rock REE analysis to obtain reliable Ce anomalies indicative of paleo-redox conditions关键词
Ce异常/阿什及尔期/川西南分类
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冯洪真,E.Wallis..川西南阿什及尔期地层中的Ce异常及其古海洋学意义[J].火山地质与矿产,2001,22(2):126-134,9.
