Evolution patterns of seawater carbon isotope composition during the Cambrian and their stratigraphic significance

Abstract

Our current understanding of the Cambrian carbon cycle mostly comes from geologically rapid carbon isotope excursions (CIEs) of marine carbonate. In addition to carbon cycle indicators, stable carbon isotopes of marine carbonates can be used as stratigraphic correlation tools. Previous studies have recognized 10 CIEs in the Cambrian, but only 3 of them appear to have global significance. This limits the application of CIEs in chronostratigraphic correlation of Cambrian successions with the 10 successive stages. Here, we present a continuous carbon isotope record from a stratigraphically complete Cambrian section at Xiaoerbulak, Aksu region in the Tarim Basin, Xinjiang, China. Its comparison with more than 40 sections across the world shows the carbon isotope record of the Cambrian can be divided into 10 units based on the variation patterns. Each pattern has occurrences in at least two Cambrian tectonic plates, suggesting global significance. A generalized curve consisting of the 10 patterns, Carbon Isotope Pattern Curve (CIPC) has been compiled. Based on the fossil records, the 10 patterns are correlated with the 10 stages of the chronostratigraphic system of the Cambrian. The pattern Angularianis correlated with Fortunian Stage and the lower half of Stage 2, Dampingian with the upper part of Stage 2, Boxian with Stage 3, Rabbitian with Stage 4, Chairian with the lower half of Wuliuan, Zigzagian with the upper Wuliuan Stage, Stickian with the Drumian and Guzhangian stages, Towerian with the Paibian Stage and Lower Jiangshan Stage, Shelfian with Upper Jiangshan Stage and the lower half of Stage 10, and Hillian with the upper half of Stage 10.We suggest that the application of CIPC makes the chronostratigraphy of non‐fossiliferous successions realizable.