Carbonate Carbon Isotope Chemostratigraphy Across the Ediacaran-Cambrian Boundary in Huize, Yunnan, China

The Ediacaran-Cambrian transition marks a pivotal era of biological evolution and geochemical cycles on Earth. Despite the continuous strata of the Yangtze Platform serving as a primary biostratigraphic reference, lateral facies heterogeneity poses a challenge for the accurate correlation of lower Cambrian units. Carbon isotope anomalies offer an effective non-biostratigraphic tool for resolving these challenges. This study focuses on the well-exposed Sujiawa and Nizheqing sections in Huize County, Yunnan Province. High-precision δ¹³C measurements (±0.06‰ VPDB) of carbonate rocks yield continuous chemostratigraphic curves. Results reveal sharp negative excursions at the Baiyanshao-Daibu boundary: from -2.27‰ to -5.23‰ (amplitude 3.0‰) in Sujiawa, and -1.63‰ to -6.40‰ (amplitude 4.8‰) in Nizheqing. Integrated with small shelly fossil biostratigraphy, comparisons with Laolin and Aijiahe sections confirm these anomalies align with the Basal Cambrian Carbon Isotope Excursion (BACE). This data fills gaps in our knowledge of the Huize region, providing chemostratigraphic constraints for lower Cambrian subdivision and correlation on the Yangtze Platform. Broader analysis with South China and global records supports the BACE as a global event, serving as an auxiliary marker for Cambrian base delineation under biostratigraphic frameworks.