RESPONSE OF TRIASSIC SEQUENCE STRATIGRAPHY OF LOWER YANGTZE TO THE COLLISION BETWEEN THE YANGTZE PLATE AND THE NORTH CHINA PLATE

ThecharacteristicsoftheTriassicsequencesdevelopedintheLowerYangtzeareadisplaysomegreatchangesinbothenvironmentandclimate.Thechangeofenvironmentwasatransitionfrommarinetocontinentviaalternatingenvironments.Thechangeofclimatewasatransitionfromtropic(torrid)towarmandwetclimateviasubtropicdryclimate.Thetypevariationsofthesequenceswerefromthemarinesequencestothecontinentalsequences,correspondingtothechangesofenvironmentsandclimates.Sequence1isatypeⅡofsequenceofmixedclasticandcarbonatesediments;sequence2isatypeⅠofsequenceofcarbonateplatform;sequence3isatypeⅠofsequenceofcarbonatetidalflat-saltlagoon,sequence4isatypeⅡofsequenceoflacustrinewithinmarinelayers,andsequence5isasequenceoflacustrine-swamp.Thedevelopment,distributionandpreservationofthosesequencesrevealthetectoniccontrolsandtheirchangesinthebackground.ThecollisionbetweentheYangtzeplateandtheNorthChinaplatewasagreatgeologicaleventinthegeologicalhistory,butthetimingofthecollisionisstilldisputed.However,thecharacteristicsofTriassicsequencestratigraphyandsealevelchangesintheLowerYangtzearearespondedtothiscoliision.ThecollisionstartedatthebeginningofmiddleTriassicandthegreatregressionintheLowerYangtzeareastarted22Maearlierthanthoseintheworld.Thetectonicconditionsoccurredbeforeandduringthecollisioncontrolledthedevelopmentofsequencesandtypechanges.