Sedimentary Response Within Orogenic Movement Of Basin Edge During Late Triassic To Jurassic In Eastern And Northern Sichuan, China

Guided by sedimentology, sequence stratigraphy, paleobiology, geochemistry,geophysics, integrated researhed the outcrops, cores, logging, seismic andgeochemistry data, summarized the characteristics of tectonic uplift of NorthernLongmenshan and Dabashan. Also we researched source, sedimentary facies,sequence stratigraphy, reservoir and cover characteristics from late Triassic to Jurassic.Through the above study, we analyzed sedimentary characteristics in the process ofmountain-basin coupling between Eastern and Northern Sichuan and two orogenicbelts. Meanwhile clear about the control action of orogenic belt tectonic activities tonatural gas accumulation. The main achievements as follow were obtained:1. According to the outcrops and cores, combined with logging data and seismicfigures,6sequence typical surfaces were found, which were surface of unconformity,surface of erosion, surface of weather crust, surface of onlap,transition surface of rockcharacter and facies and flooding transgressive surface. And then6tectonic sequenceand14sedimentary sequence were recognized.2. According to the rock combination, sedimentary fabric, sedimentary sequence,biological combination and deposition mechanism, etc., in combination with previousresearch results, provenance research and physical geography method, thesedimentary facies characteristics and sedimentary microfacies distribution of eachstratums during late Triassic to Jurassic in Eastern and Northern Sichuan wereresearched in detail. The sedimentary model was established at the same time.3. According to the research of mountain-basin coupling relationship betweenorogenic belt and Eastern and Northern Sichuan Foreland basin, the evolution of basinfrom late Triassic to Jurassic is divided into four stages, which is the initial settlementperiod(T3), settlement of transition period(J1-J2early), strong settlement period(J2middle-late) and steady subsidence stage(J3). Through the multiple methods, we haveresearched uplift subsidence history and coupling relationship between the north partof Longmenshan orogenic belt and Eastern and Northern Sichuan foreland basin.4. According to the actual data of stratum, using sandstone composition statistics,gravel composition statistics, ancient flow and heavy mineral combination analysis, itresearched the source of main interval(Xujiahe formation, Zhenzhuchong segment,Qianfoya formation and Lower Shaximiao Formation). the Tectonic uplif differences of basin edge orogenic belts were discussed.5. According to the uplift history of Northern Longmenshan and Dabashan, incombination with basin evolution stages, the mountain-basin coupling process ofEastern and Northern Sichuan during Late Triassic to Jurassic would be divided into6stages. According to the characteristics of the corresponding structure-sequencelithofacies paleogeographic, the each stage of mountain-basin coupling is discussed.6. According to the sedimentary-filling graphs within tectonic sequence systemtract from late Triassic to Jurassic built up, found that:①From late Triassic toJurassic, the environment of Eastern and Northern Sichuan foreland basin wasdifferent,at the beginning,the setting was marine, then changed to transition,finallychanged to continental environment.②The tectonic movement of Longmenshan andDabashan orogenisc belts were eposide, the movement of each part of two orogeniscbelts were different form late Triassic to Jurassic, and the adjacent area’s setting wasdifferent too.So the sedimentary models built up in different place or at the differenttime was difference.③TS1is not development in study area. Only a little TS1BE iskeeped. During the stage of TS2BE, the Northern Longmenshan orogenisc belt isbeginning uplifted, which leds sedimentary structures with rapid filling charactersforming in basin edge. At this time, the Dabashan orogenisc belt is uplifted too. Thebraided river delta of sea-land transitional facies is development in basin. During thestage of TS2BW, the Longmenshan and Dabashan orogenisc belts tectonic activityintensity was reduced. When the time come to the end of TS2BW and the begin ofTS3BE, the Longmenshan orogenisc belt was uplifted rapidly due to the Anxianmovement, which brings Sichuan basin into the continental sedimentary evolutionarystages. The alluvial fan-braided river delta of continental facies are development instudy area. From TS3to TS6, the river delta-lake and alluvial fan-fan dalta-lakewere the mainly setting of western Sichuan foreland basin.④During Late Triassic toJurassi, the intensity of tectonic activity of Northern Longmenshan orogenic belt isweak to strong, strong to weak, and weak to strong again. The intensity of tectonicactivity of Dabashan orogenic belt is strong to weak, and to strong.7. From late Triassic to Jurassic, the study area has various sedimentary faciestypes in the process of marine to continental. There are mainly three sets of favorablereservoir and cover groups. The distribution of accumulation of material is conformedto the laws of structure controlling basin, basin controlling sedimentary facies,sedimentary facies controlling combination in Eastern and Northern Sichuan.