Refining the Darriwilian (Middle Ordovician) Chronostratigraphy and Its Paleoclimatic and Carbon Cycling Implications

The Middle Darriwilian Carbon Isotope Excursion (MDICE) represents a major perturbation in the Paleozoic global carbon cycle. While recent studies have identified the MDICE in South China, the lack of a high-resolution temporal framework and clear driving mechanisms hinders understanding of the coupled climate–carbon cycle dynamics. Here, we investigate the Huangnitang Global Boundary Stratotype Section and Point (GSSP) in the South China, representing a critical archive along the eastern Tethyan margin. Supported by its biostratigraphic framework, a near-complete expression of the MDICE is identified in its δ13Corg record. Cyclostratigraphic analysis of Anhysteretic Remanent Magnetization (ARM) data indicates the preservation of Milankovitch cycles, including long (405 kyr) and short (~103–121 kyr) eccentricity, obliquity (27.6–30.4 kyr), and precession (16.1–18.6 kyr). Tuning to the stable 405-kyr cycle, we establish a floating astronomical time scale (ATS) that constrains the entire Darriwilian Stage to 10.9 ± 0.2 Myr and the duration of the MDICE at the Huangnitang section to at least ~4.5 Myr. Integration of obliquity amplitude modulation (AM), a relative sea-level proxy (DYNOT), and a geochronologically independent benthic biodiversity record allows for exploring coupled environmental–biotic dynamics during the Darriwilian. At the ~1.2 Myr low-frequency obliquity forcing, these proxy records exhibit coupled dynamics, with biodiversity remaining persistently in phase with AM and anti-phase with DYNOT. Our results suggest that orbitally forced sea-level fluctuations, coupled with the global cooling associated with the MDICE, served as a predominant control on marine evolutionary dynamics along this eastern Tethyan margin.