| The most abundant natural gas resources in Sichuan Basin is in the Northeast. Naturalgas exploration has made an important breakthrough in the Changxin Formation and XujiaheFormation which deposited in marine-transitional-land depositional environment. It showsthat the good potential of oil and gas exploration in the northeast Sichuan basin.As thenorthern border of the upper Yangtze, during Changxing stage to Xujiahe stage, basin naturehas changed dramatically. Deposition of material accumulation and distribution law are verydifferent. With the progress of exploration and research, Domestic and foreign researchersand the oil exploration sector are aware of the basin with the deposition pattern in theevolution of tectonic cycles and sedimentary facies distribution law characteristics andnortheastern Sichuan periphery basin-mountain coupling. It can play a guiding role for thenext oil and gas exploration progress. Based on “structure control deposition depositionreaction construction” as the guide, Use the theory and techniques of sedimentology,sequence stratigraphy, geophysics, structural geology. And then make a systematic study ofbasin evolution of sedimentary response from Changxing stage to Xujiahe stage undercondition of a fine research on plate dynamic action and margin of the tectonic evolution ofthe background. To reveal the laws of accumulation and distribution of material in the basinevolution. The main contents and results are as follows:(1) Through analysis of Paleo-Tethys and the North Margin of Yangtze Mianlue limitedocean basin evolution,we found that late Permian Changxing stage-late Triassic Xujiahestage north Margin of Yangtze is the Paleo-Tethys ocean basin under condition of plateconvergence, subduction-the disappearance, expansion and subduction of the Yangtze blocknorth of Mian-Lue ocean experience,co-exist to the plate tectonic setting of the collisionorogenic stage.In the process of changing of tensile to compressive tectonic background,as aCratonic basins and cratonic edge of the rift basin the north of Sichuan Basin deposited carbonate sediment. Xujiahe stage of compressional tectonic filling of the foreland basin incontinental detritus-based class.(2) Based on systematic stratigraphic division and comparison of field section anddrilling，the author has recognized eight types of sequence boundary，defined sequencestratigraphic framework of Changxing-Xujiahe formation of northeastern Sichuan. Theframework is divided into four tetonic sequence which includes nine three-order sequences.Combined with different features of sequence development of carbonate rock and terrigenousclastic rock the author analyses the control factor of different types of basins.(3) From the analysis of field outcrop, rock core, well logging and seismic data, the authorhas recognized three groups of sedimentary system, which are beach-barrier sedimentarysystem, transition delta sedimentary system and lacustrine delta sedimentary system.Furthermore, beach-barrier sedimentary system consists of carbonate platform sedimentarysystem, platform-basin sedimentary system, coastal sedimentary system and shelfsedimentary system. Transition delta sedimentary system consists of marine deltasedimentary system. Lacustrine delta sedimentary system consists of alluvial fan sedimentarysystem, lake delta sedimentary system and lake sedimentary system.On the basises of allabove, further analysis for the characteristics of each sedimentary facies and sedimentarysub facies. Sedimentary facies model of marine, transitional facies and continental facies areestablished and the evolution was investigated.(4) With the third-order sequences or system tract as mapping unit, the authorsystematically compiled sequence-based lithofacies-paleogeography map of Chang Xingstage-Xu Jiahe stage in northeast Sichuan, and deep analysised paleogeography characteristicsand differences of different sequences or system tracts in these sedimentary periods. Theauthor thinks that there have the main characteristic of platform-basin sedimentary frameworkin PSQ1~PSQ2sedimentary period(Chang Xing stage), and platform margin reef distributedalong with platform margin which under controlled by platform-basin. TSQ1~TSQ2sedimentary period(Fei Xianguan stage) have experienced evolvement of sedimentaryenvironment processes of filling up and became to carbonate platform as a whole. Thedepositional environment in TSQ3~TSQ4sedimentary period(Jia Lingjiang stage) wasrestricted platform and high-energy beach sediment developed in same local area. Thedepositional environment became more restricted and became major in restricted platform andevaporation platform. The Jiangnan Xuefeng ancient land uplift and provided sediments to thestudy area, eastern and southern transformed into mixed continental shelf and tidal flat-lagoonenvironment. The depositional environment in TSQ9~TSQ11depositional period(First tothird of Xu Jiahe stage) was marine delta and had experienced the paralic stage. Thedepositional environment in TSQ12~TSQ14depositional period(Fourth to Sixth of Xu Jiahe stage) was full access to the continental sedimentary stage and main in alluvial fan–fandelta–braided river delta–shallowdepositionla system. Province in north became strengthen andQianzhong ancient land in south also provided sediments to the study area.(5) In the different basin types, different tectonic stage what are controlled by internaland external dynamic geological effect and different system tracts filling process of materialtype differences and the material quality characteristics,which reacted the characteristics ofsequence sequence structure, those are systematic summarized and elucidated.And it holds theviews as follow. The main sequence filling characteristics, which included the inner cratonicbasins and differentiation patterns of the edge of the stable carbonate platform in thebasin,are the differentiation of "carbonate factory" restricting their sequence filling structuralfeatures in the production efficiency in different facies under the influence of tectonicmovements and eustatic sea level. And the main sequence filling characteristics of forelandbasin continental margin clastic is the game relationship between accommodate space, whichis produced by the tectonic flexural subsidence, and sediment supply, which constraintssignificantly the sequence filling structure in different parts during the tectonic evolution ofthe different structural parts.(6) Based on plate tectonic background and regional tectonic evolution analysis, Thepater discussed the structural-sedimentary evolution dynamics mechanism of Changxing stage-Xu jiahe stage in the northeast of Sichuan and analyzed the structure-sedimentary evolutionprocess. The paper argues that the changxing stage-the early feixianguan stage developmentplatform of deep water deep internal sedimentary basin in the background of Southern qinlingocean pull-apart extension, especially the late Permian period the cracking and plus "crackmovement" joint action. In feixianguan1stage to the feixianguan3stage, pull activitiesdecreased. This process experienced flattened and feixianguan4stage into carbonate platformuniform of the evolution process. In the jialing river period，Pull activity become weak andtend to stop. The study area is stable limitations-evaporation carbonate platform faciessedimentary environment. In Triassic, the north China plate and the Yangtze plate from thestart of the east to the west with "scissors type" collision way and land-land collage collision，The study area into the "print a movement" evolutionary stages. The Leikoupo state of theYangtze plate slope’s overall uplift in Triassic and the peaks of the southeastern jiangnanuplift has been out of the water again and to eastern sichuan with the provenance. Theseconditions make research area appears western for restricted platform and evaporativecarbonate platform sedimentary east have barrier coast to the shelf of sedimentaryenvironment of sedimentary differentiation characteristics，the sea begin to withdraw yangtzplatform. From then on large-scale transgression in the study area basically go to end. In middle and late Triassic，The study area uplift become land in jiangnan snowy peaks andKaijiang-luzhou uplift for uplift center under the common function of southern India a plate tothe north and southeast extrusion strongly of the north west strong Chinese plot to squeeze.Leikoupo group and padang group suffered from different levels of erosion，development ofkarst water widely atmospheric phenomenon，Tong nan ba-yuan ba present a dam region inthe northeast and the northern highlands to the south western karst karst slope graduallytransition of the ancient geomorphology. Karst spinning back of the development of timescharacteristics reveal the study area at least through2to3of tectonic uplift and cause datumdecline. Northeastern sichuan area produce slow settlement in northeast sichuan formation offoreland basin, accept xujiahe deposits in the dual influence of remote effect in longmenshanthrust belt and MiCangShan-dabashan mountain thrust the pushover on load in the earth’scrust. The west study area still partially connected extensive sea in “xuxiapeng” basinformation stage, the study area development mainly Marine braided delta and gulf mudstone.the third act of Indosinian movement makes the study area to uplift the weathering anderoding of surface and suffered. Because of the west longmenshan had Completely lifted. Thestudy area development alluvial fan, fan delta, braided delta-and shallow lake sedimentarysystem from the north east to southwest and wholly gone into continental sediments stage. |
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