Orbitally-paced climate change and organic carbon burial during the late Ordovician-early Silurian

Climate change and organic carbon burial events in the Late Ordovician-Early Silurian are well-documented, yet the mechanisms driving these events remain debated. Through high-resolution gamma-ray logging (GR) and trace element records, we establish a 12.6 Myr astronomical timescale for the Late Ordovician-Early Silurian Wufeng-Longmaxi Formation in the Sichuan Basin. Million-year-scale sea level fluctuations are reconstructed by modeling sedimentary noise in the 405 kyr-tuned GR series. Energy decomposition analysis of astronomical orbital parameters suggests that changes in land-sea water exchange, driven by enhanced tropical water vapor and heat within a ~2.1 Myr eccentricity-modulated gyre, likely served as the primary driver of seawater deposition. Maxima in total organic carbon coincides with peaks in the long-term 1.1 Myr obliquity modulation cycle, with the long-term 2.1 Myr eccentricity cycle occurring at a maximum or minimum. This long-term trajectory may have driven carbon cycle perturbations and differential organic matter enrichment by influencing various climate-related factors. During the Late Ordovician-Early Silurian, a new resonance state emerged, characterized by ~2.1 Myr eccentricity and ~1.1–1.0 Myr inclination, likely associated with long-term Earth-Mars resonance and potentially constraining the chaotic evolution of the solar system over geological timescales.