Astronomical forcing and sedimentary noise modeling of lake-level changes in the Middle Eocene Chezhen Sag, Bohai Bay Basin, eastern China

The pacing of the global climate system by orbital variations is clearly demonstrated in the timing of e.g. glacial-interglacial cycles. However, due to the complexity and internal nonlinearity of the Earth’s climate system, the mechanisms that translate this forcing into geoarchives and climate changes continue to be debated. A 609-m-thick, continuous lacustrine mudstone and sandstone succession in Chezhen Sag (eastern China) provides an ideal middle Eocene sedimentary record for establishing a high-resolution stratigraphic chronology framework. Based on spectrum analysis and sliding window spectrum analysis of the natural gamma (GR) logging data of well Che 271 (C271) in Chezhen Sag, the periods of 405 kyr and 40.1 kyr were filtered by a Gaussian bandpass filter, and a “floating”astrochronological time scale (ATS) was established. The total number of 405 kyr eccentricity cycles were 13.6 and 40.1 kyr obliquity cycles were 138 which recorded from the upper member 4 (Es4U) to the member 3 (Es3) of the Eocene Shahejie Formation, and the depositional duration was 5.53 Myr. Correlation Coefficient (COCO) analysis and evolutionary Correlation Coefficient (eCoCo) analysis found that the optimal sedimentary rate of different strata. Sedimentary noise simulation revealed the history of paleolake water changes in the Middle Eocene in the Chezhen Sag, according to which four sequences are divided. The study show that the lake level change of Chezhen Sag in the middle Eocene shows prominent 1.2 Myr cycles and an antiphase well-coupled relationship with obliquity modulation. Finally, we propose a model to explain the relationship between orbital cycle and lake level change in continental lake basin. When the obliquity of the earth increases, the middle and high latitudes of the earth will be closer to the sun, the direct sunlight will be higher, and the meridional sunshine will increase, thus accelerating the evaporation process of lake basin water. When the seasonal changes are obvious (Maximum period of 1.2 Myr ultra-long obliquity), this effect is more significant. Our results strengthen knowledge of the connection of Myr-scale lake-level variations to astronomically induced climate change during the middle Eocene under obliquity forcing.