CHARACTERISTICS OF SEDIMENTARY FACIES RESPONSE TO THE SEISMIC WAVE——AN EXAMPLE OF THE 3RD MEMBER OF SHAHEJIE FORMATION IN THE GUNAN SAG OF THE BOHAI BAY BASIN

According to the seismic waveform theories,the seismic facies have been identified and divided automatically and the plane distribution of the depositional systems have also been determined.Compared with the traditional methods,this method has the advantages of saving time,more objective and more accuracy.Using this method,the plane distribution of the depositional system of the middle part of middle submember of the 3rd member of Shahejie Formation has been studied in Gunan Sag of the Bohai Bay Basin.There is preferable relationship between the seismic facies models and the sedimentary facies,and at the same time,they are sensitive for sedimentary facies changes,therefore,can be used for microfacies division.It indicates that three depositional systems,including braided-river delta,basin floor fan and lake depositional system,were existing in the Gunan Sag at this time.The front subfacies of the braided-river delta was developed in the south slope of Gunan Sag.The basin floor fan was mainly distributed in the north of the sag,located in basal slope of the Gunan fault.In addition,the slump of the nearshore strand bar also can form basin floor fan complex.In this period,the nearshore strand sandstone bar and sheet are more abundant.