Abstract
Solar radiation and planetary gravitational interactions impose periodic constraints on Earth's climate and carbon cycle, but their role in shaping early Paleozoic marine systems remains poorly understood. Here we present high-resolution cyclostratigraphic and carbon isotope data from the middle-late Cambrian Xixiangchi Formation (Sichuan Basin, South China), revealing a robust link between long eccentricity cycles (2.4 Myr) and sea level fluctuations, carbonate sedimentation, and carbon-isotope excursions. Using gamma-ray logs, mineralogical analyses, and δ13Ccarb records, we identify Milankovitch cyclicity with periodicities of 13.1 m, 3.3 m, 1.2 m and 0.6 m, corresponding to long eccentricity, short eccentricity, obliquity, and precession cycles. Sedimentary noise modeling and orbital tuning show that sea level rise driven by 2.4 Myr eccentricity maxima correlates with positive carbon isotope excursions (up to +2 ‰), attributed to enhanced organic carbon burial in expanded epicontinental seas and increased algal productivity. Conversely, sea level lowstands coincide with negative δ13C shifts, linked to intensified weathering and organic matter oxidation. These findings establish a causal relationship between orbital forcing and Cambrian carbon cycling, highlighting the role of astronomical cycles in modulating greenhouse climate dynamics during a key interval of marine ecosystem evolution. Our results provide a template for integrating cyclostratigraphy and chemostratigraphy to decode Earth's deep-time climate archives.
Paper Information:
Wang, J., Han, Y., Hu, Z., et al. (2026). Orbitally paced sea level changes and carbon isotope fluctuations in the middle-late Cambrian Xixiangchi Formation, Sichuan Basin, South China. Global and Planetary Change, 256, 105191. https://doi.org/10.1016/j.gloplacha.2025.105191
