Search Results (2)

The Miocene Hanjiang Formation (HJF) is a remarkable exploration target in the Pearl River Mouth Basin (PRMB). However, challenges such as bias in current sequence stratigraphic schemes, limitations in high-resolution stratigraphic schemes, and incomplete understanding of genetic mechanisms may present obstacles for refining hydrocarbon exploration strategies. This study integrates gamma ray (GR) logging data, lithological variations, sequence stratigraphy, and cyclostratigraphy to delineate connections between sequence stratigraphy and astronomical forcing. The analysis utilizes gamma-ray logging data from boreholes LFA (1250–1960 m) and LFB (1070–1955 m) in the HJF. We constructed an absolute astronomical time scale anchored at the HJF’s top boundary (10.221 ± 0.4 Ma), identifying 6 third-order sequences through detailed analysis. Notably, 18 long-eccentricity cycles (405 kyr) and distinctive 1.2-Myr obliquity modulation signals were detected in the stratigraphic record. Our study demonstrates distinct connection between third-order sequence boundaries and the 1.2-Myr obliquity cycles, congruent with both global eustatic sea-level fluctuations and regional sea-level changes in the PRMB. The integration of cyclostratigraphic methods with sequence stratigraphic analysis proves particularly valuable for objective stratigraphic subdivision and understanding third-order sequence evolution in the divergent continental margin settings of the South China Sea. This approach enhances temporal resolution on a regional scale while revealing astronomical forcing mechanisms governing sedimentary cyclicity. Full article

This study has determined the period of sedimentation of the Lingshui Formation as the Oligocene (Rupelian-Chattian) through biostratigraphic data, including planktonic foraminifera zonation. The astronomical timescale framework for the Lingshui Formation was accurately constructed by integrating geophysical logging data and employing a multidisciplinary approach that includes time series analysis, cyclostratigraphy, astronomical dating, and Power Ratio Accumulation (PRA) methods. Sensitivity analysis of PRA has shown that natural gamma (GR) is the optimal paleoclimatic proxy, laying the foundation for subsequent analyses. The optimal sedimentation rate for the Lingshui Formation, determined by combining the coefficient of correlation (COCO) method with PRA analysis, is 5–5.4 cm/kyr. The duration of the Lingshui Formation was established at 5.02 Ma (28.52 Ma–23.5 Ma) based on time series analysis and astronomical tuning. The sediment noise model has revealed that the ~1.2 Myr obliquity modulation period has a significant impact on sea-level changes, further confirming the stratigraphic control of astronomical forcing on the sedimentation rate of the Lingshui Formation. This study establishes a high-precision astronomical timescale framework for the Lingshui Formation and provides a robust methodology, offering scientific basis for the research in astronomical chronostratigraphy and cycle stratigraphy, which has significant potential implications. Full article