Deformation And Evolution Characteristics Of Faults In Shijiutuo Uplift,Offshore Bohai Bay Basin

The Shijiutuo uplift and adjacent area experienced complex evolution,and faults have various structural styles,playing an important role in hydrocarbon migration and accumulation.The Shijiutuo uplift is composed of three parts,including the main body,the east part and the south part.The uplift is bounded by south-dipping normal faults with special shapes to the south.Based on seismic interpretation and time slice analysis,deformation and evolution characteristics of faults in the Shijiutuo uplift are addressed in this paper.Extensional faults are the most prominent in this area,and their styles involve plane,listric and ramp-flat faults in cross-section.The cross-sectional combination patterns of the extensional faults comprise of “X”,“Y”,reverse “Y”,steps and quasi-flower styles.Also,on plane view,the extensional faults assemble with each other in those ways of en echelon,feather and reverse “S” styles.The south part has similar structural attributes to the main body of the uplift,and is the extension of the Shijiutuo uplift into the Bozhong sag.The elongated east part,however,belongs the horst which is located in the lower part of “X” faults,which extends into the main body of the uplift westward.The different parts of the south boundary faults interplay with each other by different linkage styles,they have also different formation mechanisms.The evolution history of the Shijiutuo uplift can be divided into four stages,including the small uplifting stage during the deposition of the Kongdian Formation—Sha-3 member,the overall uplifting stage during the deposition of the Sha-2 and Sha-1 members,the formation stage of the east part and the inversion stage of tilting polarity of the uplift during the deposition of the Dongying Formation,and the overall sagging stage during the deposition of the Guantao Formation—Quaternary.The strong activities of the master faults happened during the deposition of the Sha-1 member—Dongying Formation and the upper member of the Minghuazhen Formation.