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

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.