Establishment of astronomical time scale and high-frequency sequence stratigraphy of the Hanjiang Formation in the Xijiang Sag

This study employs cyclostratigraphic methods to investigate the Hanjiang Formation in the Xijiang Sag of the Pearl River Mouth Basin. Using natural gamma-ray logging data as a paleoclimate proxy and integrating time series analysis techniques, we identify astronomical orbital signals and extract the 405 ka long eccentricity cycle using Gaussian bandpass filtering to construct a high-precision astronomical time scale. By applying sedimentary noise models (DYNOT and ρ1 models) to reconstruct relative sea-level changes and combining lithological and logging curve characteristics, we conduct high-frequency sequence stratigraphic division of the Hanjiang Formation. The results demonstrate that the Hanjiang Formation is controlled by astronomical orbital cycles, with a depositional duration of 6.08 Ma and an optimal sedimentation rate of 20 cm/ka. Through astronomical tuning, a high-resolution astronomical time scale spanning from 16.17 Ma to 10.09 Ma was established, dividing the formation into 15 fourth-order sequences and 64 fifth-order sequences. This study highlights the critical role of sea-level fluctuations and sedimentation rates in the development of sand bodies during the Middle Miocene. The research not only provides methodological support for understanding the sedimentary facies differentiation, sequence stacking patterns, and reservoir development of the Hanjiang Formation but also confirms the significance of Milankovitch cycles in high-resolution stratigraphic studies. It offers new scientific insights and technical approaches for reservoir prediction and evaluation in the hydrocarbon exploration of the Pearl River Mouth Basin.