The Late Oligocene Huagang Formation in the Xihu Depression, East China Sea Shelf Basin, records typical braided river delta deposits. However, the influence of astronomical forcing on sand-body distribution remains unclear. Based on core, logging, and seismic data, subaqueous distributary channels of braided river deltas were identified and multi-scale lake-level fluctuations were reconstructed. The main findings findings are: (1) The upper Huagang Formation records stable 1.2 Myr long obliquity cycles and 405 kyr long-eccentricity cycles. A 5.6 Myr floating astronomical time scale (ATS) was established using the stable 405 kyr eccentricity signal. (2) DYNOT analysis shows that both million-year and 100,000-year lake-level variations are astronomically driven. The 1.2 Myr cycle controls 3rd-order lake-level changes, influencing deltaic facies belts, while the 405 kyr cycle governs 4th-order fluctuations, affecting sand-body stacking patterns. (3) Obliquity and eccentricity cycles also jointly modulate climate. A high-obliquity, low-eccentricity mode reflects a warmer, wetter climate with lower lake levels, where sand bodies occur in tangential or superimposed patterns. A high obliquity, high eccentricity mode reflects a colder, drier climate with higher lake levels, where sand bodies are isolated. This study provides new theoretical insights for high-resolution reservoir characterization and development of braided river delta reservoirs.
Yueli et al. (Fri,) studied this question.