中国科学院南京地质古生物研究所机构知识库

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 fit 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 bioborizon 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 delta C-13 fluctuate sharply with a short period in provisional seventh stage. The onset of sharp fluctuation in the delta C-13 values begins at the proposed GSSP level, defining the base of the global seventh stage, where delta C-13 values change from a gentle trend to a sharp trend. Distinct covariant-relationships among delta C-13, delta O-18, 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 delta C-13 values.