Identification and division of high-frequency sequence based on Milakovitch cycle: A case of the 3rd Member of Pinghu Formation in Baoyunting Area, Pinghu Slope Zone, East China Sea Shelf Basin

Cyclical changes of climate owe its origin to cyclical changes in Earth orbit, which in turn have an effective impact on the pattern of stratigraphic sequence. During the depositional period of the Pinghu Formation, the East China Sea Continental Shelf Basin had suffered from a cold-hot alternating climate, as the records of sedimentation suggest. In this paper, we calculated the time of the variation of earth orbit parameters at the north latitude of 30°, during the time from 30~40.4Ma using the La(2004) calculation method to determine the theoretical time span of Milakovitch cycles. The 3rd Member of Pinghu Formation of the Pinghu Slope Belt is the marine sediments characterized by weak tectonic activity, stable sedimentation, similar physical properties and wide coverage. Therefore, it is selected from among others as the target layer to detect the spectrum of gamma data and analyze the one-dimensional continuous wavelet transform. Our results show that the 3rd Member of Pinghu Formation is dominated by eccentricity cycles of 405ka、131ka、99ka and a slope cycle of 52ka. A high-resolution astronomical timescale is then established according to the cyclicity of the Milakovitch cycle curve. Upon the basis, the sequence stratigraphy of high-frequency cycle in the 3rd Member of Pinghu Formation is constructed. Facts prove that the case provides a new effective approach for stratigraphic division and correlation in the Baoyunting area of the Pinghu Slope Zone.