Tectonic-sedimentary Response In The Key Tectonic Period Of The Sinian-cambrian In The Sichuan Basin

In recent years,a series of major breakthroughs have been made in deep-ultra-deep oil and gas exploration in the Sichuan Basin,revealing the huge exploration potential of Sinian-Cambrian carbonate reservoirs in the Sichuan Basin.The formation of oil and gas reservoirs is controlled by the original tectonic-sedimentary environment and later transformation.During this period,the formation and evolution of the Deyang-Anyue rift trough and the central Sichuan paleo-uplift respectively controlled the development of platform marginal beaches and intra-platform grain beaches,which also made the basin Important tectonic-sedimentary differentiation and evolution occurred during the Sinian-Cambrian period.This paper uses the latest drilling data,field outcrops and seismic reflection profiles,combined with previous research foundations,to carry out the study of the tectonic-sedimentary response of the Sichuan Basin during the Sinian-Cambrian key tectonic period.By identifying the main unconformities within the Sinian-Cambrian in the Sichuan Basin,analyzing their structural types and development range,combining the determination of the predecessors'stratigraphic age and the regional tectonic background,dividing the key tectonic stages,and establishing the basin's tectonic stratigraphic-chronological grid frame.Through the structural subsidence analysis of drilling and virtual wells in the basin,the nature of basin subsidence can be judged,and the structural evolution stage of the basin can be divided.On the basis of the analysis of the characteristics of the current geological structure of the basin,the use of regional stratigraphic continuous well profiles and residual strata plane distribution,combined with the study of tectonic subsidence,analyzes the paleostructural pattern of the Sichuan Basin during the Sinian-Cambrian period.Through the study of the sedimentary environment and filling characteristics in the key tectonic period,the tectonic-sedimentary evolution model is discussed.In this study,the following points of knowledge were obtained:(1)The Sinian-Cambrian of the Sichuan Basin has undergone the superimposed transformation of the Tongwan Act I,II,III and Yunan Movement.Inside,the Sinian Dengying Group Deng 3 and Deng 2(Z₂dn³/Z₂dn²),Lower Cambrian Maidiping Formation and Sinian Dengying Formation Deng 4(?₁m/Z₂dn⁴),Lower Cambrian Qiongzhusi Formation and Maidiping Formation(?₁q/?₁m),Ordovician and Han There are four major unconformities in the military system(O/?).The types of unconformities are mainly parallel unconformities,with low-angle overlying unconformities in some areas.The Tongwan movement caused a maximum time interruption of 13 Ma.Among them,Tongwan Phase II had the highest structural strength,followed by Phase III,and Phase I was the smallest.(2)The Sinian-Cambrian tectonic subsidence of the Sichuan Basin is characterized by"episodic subsidence"and"differential subsidence".Under the extensional background,the Dengying and Qiongzhusi periods showed the characteristics of rapid rifting and subsidence,and the Middle-Late Cambrian was in the stage of slowing depression and subsidence.The two periods of rapid subsidence indicate the active period of the rift trough.The tectonic subsidence center migrated from northwest Sichuan to the middle of the rift trough and southern Sichuan,indicating that the Dengying period rift trough began to develop in the north and mainly developed in the south in the Early Cambrian..The structural settlement in the northern and southern parts of the rift trough is greater than that in the middle part,and the amount of structural settlement gradually decreases from the trough area to the platform.After the middle and late Cambrian rift troughs were filled and filled,the platform was unified,structural differentiation disappeared,and the structural subsidence of each structural zone tended to be the same.(3)The Doushantuo period of the Sichuan Basin is generally characterized as an intra-platform highland with alternating platform uplifts and platform depressions.During the deposition period of the Deng 1-Deng 2 Member,the rift trough opened from the northwestern Sichuan area in a U shape,extending south to the Ziyang area,and an intra-platform rift developed in the southern Shu area.During the deposition period of the Deng 3-Deng 4 member,the rift trough penetrated the basin in a north-south direction,dividing the platform,and the structural-sedimentary differentiation intensified.In the Longwangmiao period at the end of the Early Cambrian,the western part of the basin was uplifted as a whole,and the central Sichuan appeared as an underwater paleo-uplift.The tectonic structure changed from low in the northwest and high in the southeast to high in the northwest and low in the southeast.During the deposition period of the Xixiangchi Formation in the Middle and Late Cambrian,the central Sichuan paleo-uplift was further strengthened and connected with the northern Sichuan uplift.The Wanzhou-Yibintai sag developed in the eastern Sichuan region,and the uplift pattern formed.(4)During the deposition period of the Doushantuo Formation,the Sichuan Basin appeared as an intracraton depression basin,with littoral-tidal flat-lagoon-mixed shelf deposits developed in the basin.After entering the Dengying Period,the transgression further expanded and a large-scale carbonate platform was formed.During the initial deposition of the Dengying Formation,the basin was dominated by limited platform facies deposits,shelf facies deposits developed in rift troughs,and lagoon facies developed in southern Sichuan.In the late period of the Dengying Formation,the rift trough continued to develop,connecting north to south,and mainly developed slope-basin facies and platform facies.In the Longwangmiao period of the Early Cambrian,the rift troughs were filled up and the basin developed a gentle slope sedimentary environment in a pattern of high west and low east.During the Xixiangchi period of the Middle and Late Cambrian,the basin was characterized by bordered platform deposits,and the Chongqing-Yibin platform depression developed in the eastern Sichuan Basin.The Sichuan Basin developed two sedimentary filling stages during the Sinian and Cambrian,and experienced the evolution history of the Sinian-Early Cambrian differentiated platform to the middle and late Cambrian unified platform.