Astronomical Forcing of Sea-Level Variability across the Oligocene–Miocene Transition in the Northern Persian Gulf

The Oligocene–Miocene Transition (OMT) represents a critical interval of large-scale climatic reorganization during the Cenozoic, marked by substantial changes in global ice volume, ocean circulation, and carbon cycling. Among the various proxies of climate variability, eustatic sea-level fluctuations played a fundamental role in shaping sedimentary architectures and controlling basin evolution. The northern margin of the Persian Gulf, where the Asmari Formation constitutes a major carbonate reservoir, provides an exceptional archive for investigating astronomically driven sea-level dynamics during this transitional period. This study focuses on the Asmari Formation in the Dezful Embayment, northern Persian Gulf. By integrating high-resolution cyclostratigraphic analysis with nonlinear time series methods, we systematically analyzed wireline log data and sedimentological records from two boreholes. Spectral analysis and astrochronological tuning allow us to establish a robust astronomical timescale for the studied succession. Our results constrain the depositional age of the Asmari Formation to 23.76–18.34 Ma, spanning the late Chattian to early Burdigalian, thereby significantly refining previous chronostratigraphic frameworks in the region. Based on this refined temporal framework, relative sea-level fluctuations were reconstructed using a sedimentary noise model, enabling the extraction of orbital-scale signals from stratigraphic data. Furthermore, nonlinear dynamical techniques were applied to evaluate the influence of astronomical forcing on climate–sea-level interactions. The results reveal a persistent ~1.2 Myr modulation cycle, interpreted as a long-term amplitude modulation of Earth’s obliquity signal, which exerted a dominant control on sea-level variability and depositional patterns. Notably, this modulation signal is most clearly expressed during intervals of reduced climatic variability, suggesting that astronomical forcing exerts a first-order control on the Earth system under relatively stable boundary conditions. These findings provide new insights into the mechanisms governing sea-level change during the OMT and highlight the significance of orbital forcing in carbonate platform evolution. Beyond their stratigraphic implications, our results establish a quantitative astroclimatic framework that improves predictions of reservoir distribution and heterogeneity in the Asmari Formation. This study thus bridges cyclostratigraphy, paleoclimate dynamics, and petroleum geology, offering a refined perspective on the coupling between astronomical forcing and basin evolution in low-latitude carbonate systems.