Cyclostratigraphy research on lower Member 3 of Shahejie Formation in Well Luo 69 in Zhanhua Sag Bohai Bay Basin

The nature gamma logging data of Well Luo 69 were chosen for a proxy, and the detailed spectra analysis and evolutional spectra analysis were conducted in the Zhanhua Sag, Bohai Bay Basin. The astronomical time scale was constructed for the Well Luo 69 in the Es3l based on the Gaussian filtering on 0.405 Ma and 0.100 Ma cycles and the anchored age was based on the magnetostratigraphic data of the lower part of Member 3 of the Shahejie Formation. The Es3l was found to have 6 long and 24 short eccentricity cycles; the 0.405 Ma long eccentricity-filtering curve could be regarded as reference curve for fourth order sequences division. It could be divided into 6 fourth-order sequences in the Es3l. The results show that the Well Luo 69 in the Es3l preserves stable Milankovitch cycles. The major cycles of 39.4, 9.74, 3.94-2.54 and 1.92-1.70 m are controlled by long eccentricity, short eccentricity, obliquity and precession, respectively. The optimum sedimentation accumulation rate(SAR) is 8.2×103 cm/Ma, and the accumulation time of the Es3l of the Well Luo 69 can be estimated at 2.38 Ma. The preservation condition controlled by long eccentricity period in the lower Es3l, and the productivity controlled by long eccentricity period in the upper Es3l can be demonstrated, which are the main factors of organic accumulation. © 2021, Central South University Press. All right reserved.