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第1页共12页编号：时间：2021年x月x日书山有路勤为径，学海无涯苦作舟页码：第1页共12页CarbonisotopechemostratigraphyofaPrecambrian/CambrianboundarysectionintheThreeGorgearea,SouthExplosionTomokoIshikawaa,,,YuichiroUenob,c,TsuyoshiKomiyaa,c,YusukeSawakia,JianHand,DeganShud,YongLie,ShigenoriMaruyamaaDepartmentofEarthandPlanetaryScience,TokyoInstituteofTechnology,Meguro-ku,Tokyo152-8551,JapanbGlobalEdgeInstitute,Meguro-ku,TokyoInstituteofTechnology,Tokyo152-8551,JapancResearchCenterfortheEvolvingEarthandPlanets,TokyoInstituteofTechnology,JapandDepartmentofGeologyandKeyLaboratoryforContinentalDynamics,NorthwestUniversity,Xi’an710069,ChinaeSchoolofEarthSciencesandResourcesManagement,Chang'anUniversity,Xi'an710054,ChinafDepartmentofEnvironmentalScienceandTechnology,TokyoInstituteofTechnology,Midori-kuYokohama152-8551,JapanReceived13July2007;revised18October2007;accepted23October2007.Availableonline21November2007.AbstractCarbonisotopechemostratigraphyhasbeenusedforworldwidecorrelationofPrecambrian/Cambrian(Pc/C)boundarysections,andhaselucidatedsignificantchangeofthecarboncycleduringtherapiddiversificationofskeletalmetazoa(i.e.theCambrianExplosion).Nevertheless,thestandardbeenpoorlyestablishedmainlyduetothelackofacontinuousstratigraphicrecord.Herewereporthigh-resolutionδ13CchemostratigraphyofadrillcoresampleacrossthePc/CboundaryintheThreeGorgearea,SouthCambrianmuddylimestone(YanjiaheFm.)toamiddleEarlyCambriancalcareousblackshale(ShuijingtuoFm.).Asaresult,wehaveidentifiedtwopositiveandtwonegativeisotopeexcursionswithinthisinterval.NearthePc/Cboundary,thedramaticallydownto−7‰(negativeexcursion1:N1).Subsequently,theδ13Ccarbincreasescontinuouslyuptoabout+5‰attheupperpartoftheNemakit–Daldynianstage.Afterthispositiveexcursion,δ13Cshiftareirrespectiveoflithotype,suggestingaprimaryoriginoftherecord.Moreover,theobtainedδ13Cprofile,exceptforthesharpexcursionN2,iscomparabletorecordsofothersectionswithinandoutsideoftheYangtzePlatform.Hence,weconcludethatthegeneralfeatureofourinseawaterchemistry.Theminimumδ13CoftheN1(−7‰)isslightlylowerthancarboninputfromthemantle,thusimplyinganenhancedfluxofsubsequentδ13Criseupto+5‰(P2)indicatesanincreaseofprimaryproductivityoranenhancedrateoforganiccarbonburial,whichshouldhaveresultedinloweringshort-term,andexceptionallylowδ13C(−9‰)inN2couldhavebeenassociatedwiththereleaseofmethanefromgashydratesduetothesea-levelfall.Theinferreddramaticenvironmentalchanges(i.e.,oroccurjustbeforetheCambrianExplosion.Thismayindicatesynchronismbetweentheenvironmentalchangesandrapiddiversificationofskeletalmetazoa.Keywords:Precambrian/Cambrianboundary;Carbonisotope;EarlyCambrian;CambrianExplosion;SouthChinaArticleOutline第2页共12页第1页共12页编号：时间：2021年x月x日书山有路勤为径，学海无涯苦作舟页码：第2页共12页1.Introduction2.Geologicalsetting3.Method4.Results5.Discussion5.1.Diagenesis5.2.Characteristicsoftheδ13Ccarbprofile5.2.1.P1(positiveexcursion1)5.2.2.N1(negativeexcursion1)5.2.3.P2(positiveexcursion2)5.2.4.N2(negativeexcursion2)5.2.5.δ13CprofileabovethebasalTommotianunconformity5.3.Correlationoftheδ13Ccarbprofilewithothersections5.3.1.YangtzePlatform5.3.2.Globalcorrelation5.4.Originofthecarbonisotopeexcursions6.ConclusionAcknowledgementsReferencesFig.1.(a)GeologicalmapoftheThreeGorgearea,SouthChina.Boxindicatesthestudyarea(Fig.1b).(b)Geologicalsectionacr...