Astronomical pacing of the Ludfordian Biogeochemical event, the largest carbon cycle perturbation of the Phanerozoic

The Kosov quarry section (Prague Basin, Czech Republic) preserves one of the most complete Silurian successions spanning the Ludfordian (late Silurian) Biogeochemical Event (LBE), encompassing the mid-Ludfordian Carbon Isotope Excursion (MLCIE), the largest positive δ13Ccarb excursion of the Phanerozoic. The LBE is associated with enhanced organic carbon burial, CO₂ drawdown, redox reorganisation, climatic cooling, sea-level change, and faunal turnover, yet its tempo and driving mechanisms remain poorly constrained. Here, we establish an anchored astrochronology for the Kosov section, based on lithological induration patterns and on the estimated absolute age of the Ludfordian-Pridoli boundary. The resulting age model resolves astronomical cycles from precession to the 405-kyr eccentricity cycle, allowing us to constrain the onset of the LBE to 424.30 ± 0.61 Ma and to determine its total duration as 1.15 ± 0.26 Myr. Spectral and phase analyses reveal a strong imprint of eccentricity cycles in both the induration record and the δ13Ccarb rate-of-change record, with the latter reaching up to +0.09 ‰/kyr. The observed phase relationship indicates that the highest rates of carbon burial were synchronised with minima in astronomical eccentricity. The unusually high δ13Ccarb rates of change reflect a fundamental threshold in ocean circulation, triggered at the onset of the LBE, which reorganised the global ocean overturning system and resulted in the formation of a quasi-stable carbon reservoir that was paced by astronomical forcing. Our astrochronology thus provides the first high-resolution temporal calibration of the entire LBE and establishes a robust quantitative framework for assessing the sensitivity, pacing, and magnitude of carbon-cycle instability of Silurian δ13Ccarb excursions.