Astronomically Constrained Orbital Forcing Model for Organic Matter Enrichment in the Early Cambrian Qiongzhusi Formation

【Objective】The Early Cambrian Qiongzhusi Formation in the Sichuan Basin is an important source rock interval, but whether its organic matter enrichment was driven by astronomical orbital forcing and the associated regulatory processes remains unclear. Based on cyclostratigraphic and geochemical analyses, this study utilizes natural gamma-ray logging data from wells A and B in the Deyang-Anyue taphrogenic trough of the Sichuan Basin to identify astronomical orbital cycles, establish a floating astronomical time scale, and, in combination with geochemical parameters, determine the dominant astronomical orbital cycles controlling organic matter enrichment.【Methods】Taking wells A and B as the research objects, this study employs Acycle software for cyclostratigraphic analysis to identify Milankovitch cycle signals. Sedimentation rates are estimated using the COCO (correlation coefficient) and eCOCO(evolution correlation coefficient) methods to establish a floating astronomical time scale. Relative sea-level changes are simulated through a sedimentary noise model.【Results】(1) Stable sedimentary cycles corresponding to the ~405 kyr long eccentricity and ~100 kyr short eccentricity periods are identified in the natural gamma-ray logging data from both wells. Floating astronomical time scales spanning 11.1 Myr and 11.4 Myr are established for wells A and B, respectively.(2) Integration of geochemical parameters and cyclostratigraphic analysis indicates that organic matter enrichment in the Qiongzhusi Formation was modulated by astronomical orbital cycles, exhibiting a co-evolutionary pattern: during minimum eccentricity periods, a warm and humid climate prevailed, sea level rose, marine primary productivity increased, and organic matter enrichment was enhanced. These findings suggest that under a greenhouse climate background, astronomical eccentricity cycles significantly influenced the formation of high-quality source rocks in the Early Cambrian Qiongzhusi Formation by regulating paleoclimate and sea-level changes. This study provides new astrochronological evidence for understanding the mechanisms of organic matter enrichment during greenhouse climate intervals.