• Astronomical evidence of Cambrian millennial-scale redox cycles. • ∼4 kyr ATS dates Drumian Carbon Isotope Excursion precisely. • Semi-precession cycles modulated by Milankovitch frequencies. • Orbital forcing drives redox via ITCZ-monsoon dynamics. • Greenhouse climates can sustain high-frequency cycles. Deciphering whether and how astronomical forcing drove millennial-scale oceanic redox oscillations during the Cambrian greenhouse is crucial for understanding early Earth system dynamics. We conducted a high-resolution cyclostratigraphic and chemostratigraphic study of the Middle Cambrian Gaotai Formation in Well LT1, Sichuan Basin, South China. Based on the age of the base of the overlying Xixiangchi Formation (502.3 ± 1.9 Ma) above the Gaotai Formation, our results yield a ∼4-kyr-resolution ATS, constraining the Drumian Carbon Isotope Excursion (DICE) to (503.94–503.48) ± 1.91 Ma. The tuned series reveals significant ∼13.1–7.9 kyr semi-precession and <6.9 kyr millennial-scale cycles, whose amplitudes are modulated by short eccentricity, obliquity, and precession, confirming an astronomical origin. The geochemical proxies record a tripartite diagenetic evolution, systematically transitioning from early euxinic conditions, through an intermediate phase dominated by shifting precipitation mechanisms, and culminating in a late stage of dynamic oxygenation, in response to evolving redox conditions. We propose that the observed millennial-scale redox oscillations in tropical South China were primarily paced by precession/semi-precession through their control on Intertropical Convergence Zone migrations. This process modulated monsoon precipitation, surface productivity, and water-column stratification. Our study provides key evidence that astronomical forcing governed paleoceanographic chemistry at millennial frequencies during greenhouse climates.
Wang et al. (Fri,) studied this question.