Study On The Stratigraphy And Sedimentary Facies Of The Sinian Dengying Formation In The Western Sichuan Basin

By analysing a large number of outcrop,drilled and log wells,and comparing the predecessors' division plans of the Dengying Formation of Sinian System in the western Sichuan area and its neighboring regions.Comprehensive analysis of lithologicelectric property and paleontological characteristics of current system has been finished on the basis of characteristics of stratigraphic characteristics as a result,the Dengying Formation is divided into three sections:Deng 1?2 Memb-er,Deng 3 Member,and Deng 4 Member(for clasolite in the middle of the Dengying Formation can be compared in the whole area,so it is treated as an independent lithological section,that is the Deng 3 Member).The analysis results of stratigraphic characteristics and stratigraphy distribution of each section indicate that the Dengying Formation is dominated by microbial carbonate rocks,and the Deng 1?2(Z2dn1?2)Member is the algae-rich section and Deng 3 Member(Z2dn3)is the section of algae-rich and mud-rich,Deng 4 Member(Z2dn4)are algal-depleted and containing siliceous bands.The Dengying Formation in the main area of the western Sichuan region is remarkable in terms of relative property,and with formation continuity in vertica direction and thickness difference.In this area,the Karstification of Tongwan period caused severe erosion within the western Sichuan,and the Dengying Formation is distributed as "Finger Distribution",with the tendency of gradual thinning from south to north,and the thickest to the north.And there are thickening zones in central-southern and northern of the research area,which may be related to the underwater paleo-uplift.The paleo-uplift is conducive to the rapid construction of fungus-algae framework,and then strengthen the formation of positive lands-cape.During the tectonic uplift of Tongwan period,the Deng 2 and Deng 4 Member were under heavy erosion,and different weather-denudation further exacerbated the differences between paleo geomorphology.Therefore,under the dual influence of sedimentary structure and exposure and erosion,the pattern of the Dengying Formation in the area were formed.The Deng 3 Member and Deng 4 Member is distributed basically along the Denudation line due to the heavy erosion.The sedimentary facies of the Dengying Formation in the study area is characterized by carbonate platform and mixed platform.Containing mud mound subfacies,grain shoal subfacies,mound-shoal complex subfacies,Tidal-flat subfacies,restricted lagoon subfacies.In the Deng1?2 Member and Deng 4 Memeber,mud mound subfacies,grain shoal subfacies,mound-shoal complex subfacies are mainly developed.At the same time,due to the difference of the ancient Landform,there are Tidal-flat subfacie-s,restricted lagoon subfacies,The restricted lagoon subfacies is developed over a large area in Deng 4 Member.Ongitudinal developmental thickness and transverse continuity of the mound-shoal complex subfacies in Dengl?2 Member is better than those of Deng 4 Member..Deng 3 Member develops a mixed tidal-flat subfacies,and different regions have different distances from the ancient land,which leads to the difference of thickness in the Deng 3 Member.In order to facilitate the comparison of the whole region,Mud mound subfacies,grain shoal subfacies,mound-shoal complex subfacies are collectively referred to as the mound-shoal subfacies,which is is distributed basically along the stretching groove.Mound-shoal subfacies are most developed in central-northern area and southern of the research area takes the second place.The reservoir of Dengying Formation in the research area is mainly controlled by the sedimentary facies and karstification.The high-quality reservoirs are formed by the integration of the Mound-shoal body and karstification.The "steep ridge zone" on both sides of the stretching groove is the most favorable reservoir belts of the Dengying Formation.