Astronomical Forcing of Organic Carbon Burial in the Mid-Cretaceous Lacustrine System

The lacustrine systems serve as major global reservoirs of organic carbon and play a central role in long term climate regulation and source rock formation. However, organic carbon burial in lacustrine environments is influenced by tectonic processes, productivity, geological events, and bioturbation, which complicates mechanistic interpretations and limits the quantitative evaluation of lacustrine climate feedbacks. Astronomical cycles, which link regional environmental variability to global climate evolution, provide a robust framework for assessing lacustrine organic carbon responses and feedbacks. The mid-Cretaceous lacustrine black shales from the Songliao Basin (SLB) were selected to evaluate the forcing on organic carbon burial, with emphasis on carbon and nitrogen cycling and astronomical forcing. The regulation of organic carbon burial depends fundamentally on microbially mediated biogeochemical cycles and astronomical pacing. During periods of marine transgression, primary productivity increased significantly. Simultaneously, intense precipitation driven by the East Asian summer monsoon (EASM) promoted rapid lacustrine expansion and strong water-column stratification. The ensuing bottom-water hypoxia greatly enhanced carbon sequestration. Importantly, cyclostratigraphic evidence demonstrates a transition in dominant orbital forcing from eccentricity to a 173-kyr obliquity cycle at 91.2±0.22 Ma. This transition is consistent with global correlations and aligns precisely with a decline in EASM precipitation intensity. These results confirm astronomical forcing as the principal mechanism governing periodic organic carbon burial in terrestrial systems, illustrating that continental successions preserve astronomical cycles as accurately as marine records.