Miocene paleoclimate analysis of the northern South China Sea：response to cooling events based on astronomical cycles

Rich oil and gas resources occur in the northern South China Sea. To analyze the Miocene paleoclimate is of great significance to oil and gas exploration in the region. In this paper, spectrum analysis and filtering method of the Matlab software are used to process the natural gamma logging curves from 1 949.12 m to 2 020 m of the Well A in the middle of the Huilu Low Uplift of the Pearl River Mouth Basin, and the paleoclimatic events in corresponding time periods are accurately predicted and the origins of the events revealed. The results suggest that the power spectrum of the GR data series shows depositional cycles of 68.8 m, 16.99 m, 7.81 m and 3.74 m. And it is deduced that the deposition cycles of 68.8 m and 16.99 m correspond to the long eccentricity signal of 405 ka and the short eccentricity signal of 100 ka, respectively. The deposition cycle of 7.81 m corresponds to the slope periodic signal of 46 ka, and the deposition cycle of 3.74 m corresponds to the precession periodic signal of 22 ka. The deposits penetrated by the well recorded perfectly the astronomical orbital signals (eccentricity, slope, precession). According to the established astronomical chronology, the geological age of the whole Hanjiang Formation is approximately in the range of 10.2～16.5 Ma, and a cooling event may have occurred between 14 Ma and 15 Ma due to the decrease in eccentricity amplitude.