Orbitally Forced Paleoclimate and Sedimentation in the Early Triassic: Evidence from the Dayulin Section, North China

The Early Triassic experienced pronounced climatic and environmental disturbances in the aftermath of the Permian–Triassic mass extinction. However, the response of continental systems to orbitally driven climate variability remains insufficiently understood, mainly because well-resolved temporal frameworks for terrestrial successions are still scarce. In this study, we investigate a Lower Triassic terrestrial succession at the Dayulin section, North China (Sunjiagou, Liujiagou, and Heshanggou formations), using time-series analyses of natural gamma-ray records together with the first principal component derived from X-ray fluorescence geochemical data. By tuning these palaeoclimate proxy series to the 405 kyr long-eccentricity cycle, we construct a floating astronomical time scale for the section. Combined with cycle-calibrated magnetostratigraphy, this framework provides a reliable basis for stratigraphic interpretation and regional correlation. Analysis of sedimentary noise in the astronomically tuned series reveals intervals of elevated noise that coincide with major facies shifts, indicating that climate instability may have played an important role in controlling depositional regime changes. In addition, we identify a ~1.2 Myr obliquity-amplitude modulation, corresponding to the Mars–Earth s₄–s₃ secular resonance, expressed in the sedimentary noise record. Recognition of this signal in a low-latitude terrestrial succession underscores the role of long-term orbital forcing in shaping continental hydroclimate and depositional stability during the Early Triassic. These results provide a new temporal framework for terrestrial astrochronology of the Early Triassic and offer geological constraints for future refinement of astronomical solutions and interbasinal correlation.