Study on the gravity flow depositional system of three sections of the Dongying Formation in the eastern slope zone of the Chengbei Low Bulge in the Bohai Bay Basin

Abstract: In order to clarify the sedimentary characteristics and spatial evolution of the deep-water gravity flow deposits of the third segment of the Dongying Formation in the eastern slope belt of the Chengbei Low Uplift, under the guidance of sedimentology and sequence stratigraphy, the sedimentary characteristics, sand body distribution, sedimentary facies distribution characteristics, and evolution rules of the study area were analyzed in depth by analyzing the seismic response characteristics of the seismic profile, the combination morphology of logging curves, and the core debris. The results show that the eastern slope belt of the Chengbei Low Uplift is divided into nearshore subaqueous fans (nearshore turbidite fans) and lakebed fans (farshore turbidite fans) under the control of material sources and paleogeography. The distribution of sedimentary facies belts, fan body distribution area, sand body extension direction, and distribution pattern on the plane are controlled by the lake level, material source supply, and paleogeomorphological changes. The steep slope zone (fault zone) controls the sedimentary body with a continuous thickness of thick sand bodies that extend forward in the direction of the source and have a band-like distribution, which is a nearshore subaqueous fan. The gentle slope zone (slope zone) gradually develops into a lakebed fan with a larger scale and thinner sand distribution. It is concluded that during the sedimentary period of the third segment of the Dongying Formation in the study area, the lake level changes control the size of the gravity flow sedimentary distribution; the size of the material source supply controls the degree of development of the deep-water gravity flow sedimentation; the orientation of the material source supply controls the deep-lake-deep water gravity flow turbidite fan sedimentation mode in the distribution area of the gravity flow sedimentation, providing a geological basis for the study of the sand body development law within the fan body and oil and gas exploration and development in the study area.

Keywords: Chengbei Low Uplift; Dongying Formation; gravity flow; sedimentary system; sand body distribution.