Astronomical Calibration of the Sulaiy Formation (tithonian-Berriasian) in Saudi Arabia and Its Implications for the Jurassic - Cretaceous Boundary

The Jurassic–Cretaceous (J–K) transition remains one of the most challenging intervals for global stratigraphic correlation, owing to the absence of a major worldwide biotic turnover, strong provincialism of marine faunas, and reliance on regionally endemic ammonite assemblages. These issues are further complicated by widespread stratigraphic discontinuities associated with the “Purbeckian regression”, resulting in persistent uncertainties in defining the timing and environmental context of the J–K boundary. In this study, we present a high-resolution, multi-proxy dataset from the BH-02 drill core (205.13 m) from central Saudi Arabia, spanning the upper Kimmeridgian to upper Berriasian interval of the Sulaiy Formation. The dataset integrates high-resolution (1 cm) downhole gamma-ray logs, calcareous nannofossil biostratigraphy with quantitative assemblage analyses, strontium isotope stratigraphy, and stable isotope records (δ¹³C and δ¹⁸O). Together, these proxies are used to construct an astronomically calibrated cyclostratigraphic framework tied to the GTS2020 timescale. Spectral analyses, including Multi-Taper Method, Evolutive Harmonic Analysis, correlation optimization, and Average Spectral Misfit, applied to ~20,000 gamma-ray data points, reveal strong and persistent cyclicity dominated by long-eccentricity (405 kyr) forcing. Orbital tuning anchored to La2004 astronomical solutions demonstrates that sedimentation in the Sulaiy Formation was strongly paced by orbital forcing, enabling the identification of ~30 long-eccentricity cycles and the construction of a ~12.38 Myr astrochronological framework spanning the Late Kimmeridgian to Late Berriasian. Additional spectral decomposition highlights subordinate hierarchical cycles corresponding to short eccentricity (~100 kyr), obliquity (~40 kyr), and precession-scale variability. Notably, enhanced obliquity is observed in the Middle Tithonian to middle Berriasian interval, expressed through ~173 kyr amplitude modulation cycles, indicating complex astronomical-climatic coupling. This integrated astrochronological framework refines the placement of the Jurassic–Cretaceous boundary and constrains the timing of key biotic and isotopic events, including nannoconid proliferation and major carbon-isotope excursions, providing a robust temporal framework for paleoclimatic interpretation in the Southern Tethys margin.