Establishment of a high-resolution astronomical time scale and high-frequency sequence framework of Paleogene lacustrine fine-grained sediments using logging data: A case study from the Bohai Bay Basin, East China

Integrating geochronological and sequence stratigraphic analyses in a basin can significantly enhance the understanding of its evolution. The Paleogene Middle Sha 3 Member (Es₃^m) in the Dongying Sag is characterized by a lake-delta sedimentary system and is of particular interest due to its abundant hydrocarbon resources. However, the Es₃^m currently lacks a robust chronostratigraphic framework, and the existing sequence stratigraphic framework, primarily based on seismic data from the delta zone, exhibits relatively low resolution. In this study, a cyclostratigraphic analysis was conducted on fine-grained lacustrine sediments of the Es₃^m in the Dongying Sag, utilizing natural gamma (GR) data from three wells. The objective was to establish a high-resolution astronomical time scale (ATS) and a high-frequency sequence framework. Lake-level changes were reconstructed using lag-1 autocorrelation coefficient (ρ₁) analysis and dynamic noise after orbital tuning (DYNOT) analysis. The findings suggest that the Es₃^m spans a duration of approximately 34.7–39.2 Ma. Sedimentary accumulation rates (SARs) of lake sediments within the study area range from approximately 11 to 25 cm/kyr. Furthermore, the lake-level exhibits significant periodic variations, and 11 fourth-order sequences and 3 systems tracts (transgressive systems tract, early highstand systems tract, and late highstand systems tract) were successfully identified in the Es₃^m. This research serves as a typical case study for delineating high-frequency sequences in lacustrine fine-grained sediments and refining the geochronological framework.