Astronomical control on upper ordovician – lower silurian organic matter enrichment in South China

Astronomical forcing governed Late Ordovician–Early Silurian climate dynamics, yet high-resolution Astronomical Time Scales (ATS) and organic enrichment mechanisms during the end-Ordovician extinction remain poorly constrained. In this study, we integrated gamma ray (GR), δ 13 C org , and chemical index of alteration (CIA) data from the Wufeng–Longmaxi formations (Weimohani section, South China) to establish a floating ATS tuned to 405-kyr eccentricity cycles, anchored to a Hirnantian U–Pb age (444.2 ± 1.6 Ma). This ATS constrains key stage durations (Hirnantian: 1.31 Myr; 432.19–444.01 Ma span) and confirms orbital control on eustasy: 1.2-Myr obliquity paced third-order icehouse-greenhouse transitions, while 405-kyr eccentricity drove fourth-order sea-level fluctuations. The CIA records demonstrate that obliquity-modulated thermohaline circulation enhanced nutrient flux to the Yangtze Shelf, with peak organic enrichment occurring during transitional climates (δ 13 C org minima plus CIA maxima) rather than glacial extremes. These findings reveal a eustatic (orbital) dominance over tectonic controls and resolve the synergistic productivity-preservation balance governing organic matter accumulation.