Astronomical Calibration of the Middle–Late Cambrian Chronostratigraphy and Carbon Cycle Perturbations

The Middle–Late Cambrian records intense perturbations of the global carbon cycle, yet the poorly resolved geochronological framework hampers an in-depth understanding of the duration and causal mechanisms of these events. The Wangcun section in South China, the official auxiliary stratotype for the Guzhangian Global Boundary Stratotype Section and Point (GSSP), preserves a continuous, complete shallow-marine carbonate succession spanning the Miaolingian to Furongian Series. Here, we present high-resolution natural gamma-ray (GR) logs and carbonate carbon isotope (δ¹³Ccarb) sequences to conduct a cyclostratigraphic analysis. Robust Milankovitch cycles are clearly recorded in these sequences, including the long eccentricity (405 kyr), short eccentricity (135.66 kyr and 85.34 kyr), obliquity (30.43 kyr), and precession (21.34–19.33 kyr) cycles. An ~11.64 Myr astronomical time scale was developed by tuning the GR and carbon isotope (δ¹³Ccarb) sequences to the stable 405 kyr long eccentricity cycle, anchored at the Drumian–Guzhangian Stage boundary. The resulting time scale is biostratigraphically well-constrained, allowing correlation of global Middle–Late Cambrian Stage boundaries with the 405 kyr chronostratigraphic framework. Multiple independent statistical methods were employed to quantitatively delineate the onset and termination of major carbon cycle perturbations, thereby precisely resolving the full evolutionary trajectories, durations, and successive stages of both the Drumian Carbon Isotope Excursion (DICE) and the Steptoean Positive Carbon Isotope Excursion (SPICE) events. This study represents the first reproducible, standardized delineation of carbon cycle events constrained by cyclostratigraphic data, providing critical geochronological constraints for unraveling the causal mechanisms of these global perturbations.