Carbon-isotope stratigraphy of the Middle–Upper Cambrian in northwestern Yangtze Platform, China: Implications for global correlations

The Steptoean Positive Carbon Isotope Excursion (SPICE) and the Drumian Carbon Isotope Excursion (DICE) are major events in the Middle‒Late Cambrian sedimentary records, but controversially heterogeneous in their magnitudes, as well as local and global correlations. This paper presents two high-resolution δ¹³C_carb profiles from the Houtan (HT) and Qiliao (QL) sections in the northwestern Yangtze Platform (China) that span the Middle-Upper Cambrian. The investigated Xixiangchi Formation in both sections predominantly consists of thick-bedded micritic carbonates (dolomicrite) alternating with oolitic grainstone beds. A multi-technique screening proved the petrographic and geochemical preservation of the investigated micritic carbonates. In the HT section, the δ¹³C values were characterized by a mean of −0.2 ‰ and a standard deviation of 1.0 ‰ (−1.9 ‰–3.1 ‰), while the δ¹⁸O values were −9.9 ‰ ± 1.1 ‰ (−13.9 ‰ to −7.8 ‰). In the QL section, the δ¹³C values were −0.4 ‰ ± 1.3 ‰ (−2.5 ‰–3.3 ‰) and the δ¹⁸O values were −9.9 ‰ ± 1.5 ‰ (−12 ‰ to −5.9 ‰). Similarly, Mn contents in the HT section were 110 ± 89 ppm (46–524 ppm) and Sr contents were 72 ± 32 ppm (34–162 ppm), whereas in the QL section, Mn contents were 96 ± 51 ppm (35–282 ppm) and Sr contents were 290 ± 150 ppm (75–662 ppm). The δ¹³C and δ¹⁸O values exhibited insignificant correlations in both sections (HT: R² = 0.1; QL: R² = 0.1). Similarly, the δ¹³C values also show an insignificant correlation with their Mn/Sr ratio (HT: R² = 0.2; QL: R² = 0.1). These weak correlations suggest that the δ¹³C signatures are minimally affected by diagenetic processes, preserving at least their near-primary state. This preservation allows the δ¹³C values to be used for constructing high-resolution profiles and reliable global correlations, despite the lack of strong local relationships. The lower negative excursions in the HT section correlate with the global DICE and pre-SPICE events, while the upper positive excursion matches the SPICE. The middle negative and upper positive excursions in the QL section align with the pre-SPICE and the SPICE events, respectively. The findings of the current work are expected to enhance the understanding of DICE, pre-SPICE, and SPICE events by providing high-resolution δ¹³C profiles from South China. These results improve regional stratigraphic correlations within the Yangtze Platform and contribute to more reliable global chronostratigraphic frameworks.