Evolution of Carbon Isotope Composition in Potential Global Stratotype Section and Point at Luoyixi, South China, for the Base of the Unnamed Global Seventh Stage of Cambrian System |
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| Authors: | Zuo Jingxun Peng Shanchi Zhu Xuejian Qi Yuping Lin Huanling Yang Xianfeng |
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| Institution: | 1. Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences,Nanjing 210008,China;Henan Institute of Geological Survey,Zhengzhou 450001,China
2. State Key Laboratory of Palaeontology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,chinese Academy of Sciences,Nanjing,210008,china |
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| Abstract: | This work deals with the evolution of carbon isotope composition in the Luoyixi Section, a candidate of the Global Standard Stratotype-section and Point (GSSP), defining the base of the as-yet-undefined seventh stage of Cambrian System at the first appearance of the cosmopolitan agnostoid Lejopyge laevigata. This level is favored in a vote of International Subcommission on Cambrian Stratigraphy (ISCS) as the biohorizon for defining the base of a global stage. Two hundred and sixty-four samples for carbon and oxygen isotope analysis have been collected from the carbonate successions at an interval of 0.25 to 0.5 m in this section. Results of the carbon isotope data exhibit a remarkable disciplinarian trend. The pattern of the carbon isotope evolution is gently undulant with a relatively long period during the underlying Drumian Stage, and then the values of δ13C fluctuate sharply with a short period in provisional seventh stage. The onset of sharp fluctuation in the δ13C values begins at the proposed GSSP level, defining the base of the global seventh stage, where δ13C values change from a gentle trend to a sharp trend. Distinct covariant-relationships among δ13C, δ18O, and sea level fluctuations suggest that a warming change in paleoclimate took place during the early global seventh stage, which led to a positive shift in δ13C values. |
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| Keywords: | carbon isotope composition global seventh stage of Cambrian System Luoyixi Section northwestern Hunan |
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