Sedimentary Facies and Evolution of Paleogene Dainan Formation in Gaoyou Sag,Subei Basin

Based on a comprehensive analysis of core,logging data and seismic survey,the sedimentary facies types of Paleogene Dainan Formation,Gaoyou Sag,Subei Basin were studied systematically,as well as their distribution and evolution.The research showed that fan delta,delta,nearshore subaqueous fan and lacustrine facies deposited in the formation,of which fan delta and nearshore subaqueous fan located along the steep south border,delta in the gently north slope and lacustrine in the central zone of the deep area and the flank of the fan delta,delta and nearshore subaqueous fan.From the margin to the depocenter of the sag,the sedimentary environments gradually changed from fan delta,delta or nearshore subaqueous fan to shore-shallow sediments and middle depth lacustrine.The palaeogeog-raphy of the Dainan Formation displayed a clear south-north zonation.The sedimentary envolution of Dainan Formation was divided into two stages,in which the sedimentary characteristics and the sedimentary facies distribution were correspondingly different.As a whole,the depth of water changed from shallow to deep,and then to shallow,sedimentary area gradually enlarged,and fan delta,delta and nearshore subaqueous fan frist retrogradated,then progradated.