Milankovitch cycles and the astronomical time scale of the Zhujiang Formation in the Baiyun Sag, Pearl River Mouth Basin, China

Abstract The Zhujiang Formation in the Baiyun Sag, Pearl River Mouth Basin, China, is formed primarily in a deep-water continental slope environment. Its chronostratigraphic framework is based on biostratigraphy and sequence stratigraphy, and its geological dating is based on micropaleontological data. This makes it difficult to obtain precise absolute ages for various geological events. In this study, gamma ray (GR) well log data from Wells Y1, Y2, and Y3 were used as paleoclimate proxies, and spectral and wavelet analyses were used to conduct cyclostratigraphic research. The results show that the Milankovitch cycles were preserved in the Zhujiang Formation in the Baiyun Sag. Stratigraphic cycles controlled by 405 and 95 ka orbital eccentricity, 40.4 ka orbital obliquity, and 23.5 ka orbital precession cycles can be identified; the signal of stratigraphic cycles controlled by the 405 ka long eccentricity cycle is the strongest. The floating astronomical time scale is constructed based on 405 ka orbital eccentricity cycle tuning of the GR series. The precise durations of the Zhujiang Formation in Wells Y1, Y2, and Y3 are 7.13, 6.93, and 7.18 Ma, and the average deposition rates are 4.68, 5.91, and 5.33 cm/ka, respectively. The Zhujiang Formation was divided into 17 fourth-, 76 fifth-, and 174 sixth-order cycles using the 405, 95, and 40.4 ka orbital periods as the dividing scales, respectively. This study provides a quantitative method for high-precision isochronous stratigraphic division and correlation in deep-water sedimentary systems.