Orbital-controlled sea-level change effects on a marginal marine coal seams deposition in Eocene

Coal-bearing strata contain important information about the environmental and depositional factors that led to their formation. The Eocene Pinghu and Baoshi formations in the Xihu Sag of the East China Sea Shelf Basin is thought to be a marginal marine environment where multiple coal seams have been found. Many studies have focused on the source rock and reservoir property in the East China Sea Shelf Basin; however, the research on the control factors of coal seams, especially the effects of sea-level changes, are still lacking. In this paper, we firstly established an astronomical age model (Eocene, ~34.5– 52.92 Ma) based on the gamma-ray logs of Well K5 and K6. Sedimentary noise analysis in both time and depth domains was processed and interpreted to reflect the relative sea-level change. We also analysed the amplitude modulation of obliquity cycles to track the ~1.2 Myr long-term cycle, which is believed to control the global sea-level change. The results show that sea-level change corresponds well to the development of coal seams in the Pinghu Formation, the coal seam accumulation layers were likely to developed in the low sea-level stage, featured by ~1.2 Myr cycle minima and high sedimentary noise (lower lag-1 and higher DYNOT value).