A negative carbon isotope excursion defines the boundary from Cambrian Series 2 to Cambrian Series 3 on the Yangtze Platform, South China

Abstract

A globally recorded negative carbon isotope excursion characterizes the transition from Cambrian Series 2 to Cambrian Series 3. This transition is also well exposed in sedimentary successions on the Yangtze Platform, and the Wuliu–Zengjiayan section, Guizhou Province, South China has been proposed as a potential Global Stratotype Section and Point (GSSP) for this boundary. Here, we report δ 13C carb values for the Jianshan and the Wuliu–Zengjiayan sections. Both sections display a progressive decrease in δ 13C from values around + 3‰ upwards in stratigraphy to a pronounced δ 13C minimum with values as low as − 6.9‰ at the proposed boundary level, and a return to δ 13C values between 0 and + 1‰ in the upper part of the sections. The δ 13C minimum is thought to be caused by a transgressive event, flooding the shelf area with 13C depleted basinal anoxic bottom water. Our δ 13C data are in good agreement with carbon isotope profiles recorded elsewhere. These define the so called ROECE event ( Redlichiid–Oleneliid Extinction Carbon Isotope Excursion, cf. Zhu et al., 2006, 2007) and may reflect the perturbation of the global carbon cycle during the Cambrian Series 2 to Cambrian Series 3 transition.