Sedimentary Characteristics and Model of Paleogene Gravity Flow in Nanpu Sag, Bohai Bay Basin

Key words: 
• Nanpu sag /
• gravity flow /
• Paleogene /
• sedimentary characteristics and model /
• Bohai Bay Basin

Abstract: Based on the microscopic description of core, macroscopic observation, 3D seismic data interpretation and previous research results, this paper studied the sedimentary characteristics, patterns and influencing factors of the gravity flow in Paleogene of Nanpu sag. Research results show that:Slump rock, Sandy debris flow, Turbidity flow is the mainly types of gravity flow deposit in Nanpu sag. Among them,the development degree of sandy debris flow is the highest. Cumulative thickness of single well drilling is 220 m, single layer thickness is up to 30 m. Cumulative grain-size distribution curve largely present two stages, C-M diagram is parallel to the QR segment,this Shows the origin of the deposited non-traction flow; Turbidity flow develops positive grading. Single layer thickness is less than 1 m but it has characteristic of multiple stage development. Incomplete BaoMa sequence can be seen in it and Tc Period is easier to see but Td Period is rare. Turbidity flow is commonly found in the outer and upper parts of sandy debris flow deposit; the size of slump rock particle is smaller, crumpled structure and convolute bedding are extremely developed, the development degree of slump rock is higher in structure 4. Shaleitian, Matouying and other uplifts, active volcano, fault activity and earthquake in Paleogene, deep water environment of Dongying Formation and Shahejie Formation, as well as slope break zone provide the conditions for gravity flow deposition. Finally, considering the various factors we establish gravity flow sedimentation model of fan delta-short steep slope type (structure 1,4) and Braided River Delta-long ramp type(structure 2,3) for Nanpu sag, and then this paper analyzes different deposition rules of them.