First record of paleowind-driven wave and storm activities and their controls on reservoir quality of Shahejie Formation, Liaodong Bay Depression, Bohai Bay Basin, China

Abstract

Lacustrine depositional models for wind-driven basins often inadequately represent the significant role of wave and storm processes, despite their recognition in modern analogs. This study utilizes the early Oligocene (E₂s₂) succession of the Liaodong Bay Depression (Bohai Bay Basin, China) as a critical ancient case study to address this gap. Through meticulous core analysis revealing 14 lithofacies and 5 lithofacies associations, we further conclusively identified storm events by correlating with the Paleogene ideal storm sequence in the Bohai Bay Basin. Integrating these data with logging and seismic interpretations, we propose a new depositional model: a wave-dominated clastic littoral system in the west and a fluvial-dominated braided-delta system in the east. Based on the NE-SW trend of beach bars concentrated in the northwestern study area, we infer a prevailing southeasterly wind direction—consistent with the Pacific summer monsoon that transported abundant moist air to the Liaodong Bay Basin, fostering a humid climate. This interpretation is further corroborated by palynological and oxygen isotope evidence. Furthermore, wave-reworked reservoirs are characterized by low matrix and unstable lithic fragment contents, well-sorted and highly rounded grains, and a high proportion of rigid grains. These attributes impart strong resistance to compaction and enhance dissolution, leading to superior reservoir quality. This study underscores that wave-reworked deposits should be prioritized as exploration targets in wind-driven lakes. The depositional model and reservoir formation mechanism established herein hold broad applicability for oil and gas exploration and development in other wind-driven continental lacustrine systems.