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1、SCIENCECHINAEarthSciences?RESEARCHPAPER?January2017Vol.60No.1:80–94doi:10.1007/s11430-016-5156-yCarbonisotopecompositionandcomparisonofLowerTriassicmarinecarbonaterocksfromSouthernLongmenxiasectioninGuang’an,SichuanBasin*HUANGSiJing,HUANGKeKe,ZHONGYiJiang,LIXiaoNing,MAOXiaoDong,HUZuoWei,LIUSiBing,ZH
2、ANGMeng&WUWenHuiStateKeyLaboratoryofOil/GasReservoirGeologyandExploitation,InstituteofSedimentaryGeology,ChengduUniversityofTechnology,Chengdu610059,ChinaReceivedMay7,2016;acceptedOctober12,2016;publishedonlineNovember22,2016Abstract????TheEarlyTriassicwasaperiodofecologicalrestorationfortheearth’ss
3、ystemaftertheend-Permianmassextinction.Geochemicalrecordslinkedtothevariationsinmarineecosystemsduringthisperiodhaveattractedtheinterestofgeologistsformanyyears.Basedonpetrographicanalysisofsamplesandevaluationsoftheirreliabilityasproxiesfororiginalseawater,thisstudyinvestigatedthecarbonandoxygeniso
4、topiccompositionsof350carbonaterocksamplesfromtheLowerTriassic(andadjacentstrata)inthesouthernLongmenxiasectionofGuang’an,easternSichuanBasin.TheresultsindicatethattheTriassiccarbonaterocksfromthesouthernLongmenxiasectionfavorablypreservedtheoriginalseawater’sδ13Csignal.Furthermore,carbonandoxygenis
5、otopiccompositionsarefoundtobepoorlycorrelated,withadeterminationcoefficientaslowas0.0205andonly44rocksamplesshowresultsofMn/Sr>2and/orδ18O<-6.5‰.ThecompletecarbonisotopiccurvefortheLowerTriassicisestablishedusingthedatafromtheremaining306sampleswithMn/Sr<2and/orδ18O>-6.5‰.Thiscurvepresentsfavorable
6、comparabilityonaglobalscale,specificallyintheδ13CminimanearthePermian-Triassicboundary,atthetopoftheJia1andwithinthetheJia3,aswellasintheδ13CmaximaatthetopsoftheYe1andYe4,atthebaseoftheJia2andatthetopoftheYe3.Thepeaksandtroughscorrespondingtothesemaximaandminimaallreflectglobalsignals.Bycomparingthe
7、seresultstopreviousresearchoncoevalcarbonisotopiccurvesestablishedwithinthechronostratigraphicframework,theagesofthesecriticalevolutionpointsaredetermined.TheresultsshowthattheYe1roughlycorrespondstot
