New breakthroughs have been achieved in the exploration of the Sinian Dengying Formation natural gas in the steep slope zones at both sides of Deyang-Anyue trough in the Sichuan Basin,making it an important area for increasing reserves and production within the basin.To clarify the formation mechanisms,formation stages and new sedimentation patterns of Deyang-Anyue trough and guide the further exploration of the Dengying Formation,this paper analyzes the spatial distribution relationships between steep slopes of different ages and between the steep slope and the platform margin belt by using the latest continuous 3D seismic results and drilling data.In addition,the evolution laws of steep slopes are investigated,and the natural gas exploration direction is pointed out further.And the following research results are obtained.First,the steep slopes of the Deyang-Anyue trough generally exhibit the characteristics of erosion valleys,while the role of synsedimentary minor faults is not significant.Second,there are two steep slopes(Ⅰ and Ⅱ)in the second member of Dengying Formation(Deng 2 Member)and one in the fourth member(Deng 4 Member).These steep slopes were formed due to erosion during the Tongwan Ⅰ and Ⅱ-Ⅲ episodes and are unrelated to the platform margins of Deng 2 and Deng 4 Members.Third,during the deposition of the Deng 2 Member,controlled by the basement horst-graben background,4 or 5 rows of platform margin belts prograding from south to north were developed.These platform margin belts are distributed along northeast.Among these platform margin belts,two large ones are developed in the Penglai area,whose mound-shoal complexes were truncated by steep slopeⅡ,and superimposed with karstification processes,high-quality reservoirs were formed.In conclusion,in the Gaoshiti-Moxi area,the steep slope-type platform margin belt of Deng 4 Member is developed in the overlapping region of the steep slopes of Deng 2 and Deng 4 Members,but in the above-trough zone of Deng 4 Member,mound-shoal complexes are still developed along the northeast direction,indicating that this area is controlled by both steep slope Ⅱ and the NE paleogeomorphy.What's more,in the Penglai area,the gradient of steep slope Ⅱ decreases,resulting in a weakening and even disappearance of its controlling effect on the platform margin belt of Deng 4 Member.Instead,two rows of gently sloping platform margin belts oriented northeast,are mainly developed,namely Penglai ①and② platform margin belt.It suggests that the Penglai area can be taken as the key concerned target of natural gas exploration in the future.
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