BiomolecularPreservationofMioceneFossilLiquidambarfromTiantai,ChinaandClarkia,USA:ImplicationsforPalaeoenvironmentalStudy

BiomolecularcharacteristicsoffossilLiquidambarfromtheMioceneShengxianFormation,Tiantai,ZhejiangprovinceineasternChinaandMioceneClarkiasediment,Idaho,U.S.A.,areobtainedbymeansofPyrolysis-Gaschromatography-Massspectrometryanalysis(Py-GC-MS).Theirmodernequivalent(Liquidambarformosana)collectedfromNanjing,easternChina,isalsoanalyzedforcomparison.Thetotalionchromatograms(TIC)ofmodernL.formosanaleavesshowsabundantpyrolysatesoflignin,polysaccharide,aliphaticacid,andaminoacid.However,onlyonepolysaccharidemolecule,i.e.,levoglucosan,isretainedinfossilLiquidambarleavesfromthetwoMiocenesiteswiththeTiantaispecimenpossessinghigherintensity.Asexpected,someligninpyrolysatesincludingbenzene,phenol,guaiacol,vinylphenolandtheirderivatives,aredetectedinMioceneTiantaiL.miosinica.However,thelignincomponentswithlargemolecularweightotherthanbenzeneandphenolcompounds,areabsentinMioceneClarkiaL.pachyphyllum.Abundantpristeneandhomologousseriesofn-alk-1-ene/n-alkanepairswithalongretentiontimeareshowninpyrogramsofbothTiantaiandClarkiafossils.BaseduponourPy-GC-MSdata,themolecularpreservationintheseLiquidambarleafsamplescanberankedasthefollowing(fromhightolowqualityrespectively):modernsample>Tiantaisample>Clarkiasample.Vinylphenol,animportantcompound,ispresentinmodernandTiantaiLiquidambarleaves,whileabsentinClarkiasample,implyingthatvinylphenolmaybesourcedfromligninforLiquidambarleaves.Ourdatasupportthehypothesisofinsitupolymerizationfortheoriginoflong-chainhomologousseriesofn-alk-1-ene/n-alkanepairsasleafalterationproducts.Ourdatahaveimplicationsoftheimpactofleafdegradationtowardbiasesforpalaeoenvironmentalreconstructionusingstablecarbonisotopeoffossilplants,andsuggesttheimportanceofevaluatingmolecularpreservationoffossilleaftissuespriortotheapplicationofcarbonisotopecompositionsoffossilleaves.