HIGH-RESOLUTION SEQUENCE STRATIGRAPHY ON MILANKOVITCH CYCLES IN THE GAS HYDRATE DRILLING AREA OF SHENHU WATERS

The Quaternary sequence stratigraphic framework was established for the northern slope of the Baiyun Sag, the Pearl River Mouth Basin, based on high resolution 2D seismic profiles. The deposit is divided into three systems tracts, i.e. the LST (lowstand systems tract, LST), TST (transgressive systems tract, TST) and HST (highstand systems tract, HST). The HST could be further divided into two depositional units, HST-I and HST-Ⅱ, according to the prograding styles of the slope, the vertical stacking patterns, the change in erosion features, and the continuity of high-amplitude seismic reflectors. Under the constraints of stratigraphic framework, the natural gamma data from Well-I of the gas hydrate drilling area of the Shenhu waters have been used for spectral analysis. The Milankovitch cycles are identified by spectrum analysis, including the eccentricity cycles (95 ka), obliquity cycle (40 ka), precession cycles (22 ka, 19ka), and the sequence is mainly controlled by the eccentricity cycle (95 ka), corresponding to a thickness of 11.494 m. It is found that the number of dominant cycles controlled by the eccentricity cycles (95 ka) is about 20 after filtering of logs. The sedimentation rate in the drilling area is 12.1 cm/ka calculated with the eccentricity cycle and the corresponding thickness of the cycle. The accommodation change curves of the sequences obtained using Fischer diagram can verify the high resolution sequence stratigraphic division.