bacterial_fossils_and_microbial_dolomite_in_triassic_stromatolites

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1、BacterialfossilsandmicrobialdolomiteinTriassicstromatolitesEdoardoPerri*DipartimentodiScienzedellaTerra,UniversitàdellaCalabria,ViaP.Buccicubo15b,87036Rende,ItalyMauriceTucker*DepartmentofEarthSciences,DurhamUniversity,DurhamDH13LE,UKABSTRACTRESULTSTria

2、ssicstromatoliticdolomitefromItalypreservesmineralizedbacterialremains,oneofWedocumentmicrobialfossilsandorigi-thefirstunequivocalidentificationsofsuchstructuresinthegeologicalrecord.TheyconsistnalgeochemicalsignaturesfromTriassicstro-ofemptyspheroids~1.0

3、µmdiameterresemblingcoccoidbacteria,andsmaller,150–400nm,matoliticdolomites,andproposeabiological-objectsinterpretedasdwarfbacterialforms,occurringwithinandbetweensyn-sedimentarygeochemicalmodelfortheirformation.dolomitecrystals.Moreover,gentlyfoldedshe

4、ets,100–200nmthickandseveralmicrome-Stromatolitelaminationconsistsofanalter-terslong,formasub-polygonalnetworkreminiscentofEPS(extracellularpolymericsub-nationoflayersoflightgraymicrospar(planarstance).Theirgranular-texturedsurfacessuggestbacterialdegra

5、dationoforiginalorganicanhedraltosubhedralcrystals,560µm)anddarkmatter.Thesefeaturesconfirmabiologicaloriginforthestromatolites,asinmodernmicro-graymicrite(planareuhedralcrystals,<5µm).bialmats,andthepreservedoriginalgeochemicalsignaturesindicateearlypre

6、cipitationofLaminaeareusuallyisopachous,evenandsmooth,Mg-carbonatesinducedthroughmicrobialsulfate-reducingmetabolicactivities.withmicrospariticlayersvaryingfrom200to500µminthickness,andthedark-graymicriticKeywords:bacterialfossils,microbialite,dolomite,

7、stromatolite,Triassic.laminaevaryingfrom20to40µm(Fig.1).StromatoliteshaveanalmostwhollydolomiteINTRODUCTIONdominatedbymicrobialcarbonates(Perrietal.,mineralogy.Spotanalysesshowthatthe<5µmMicrobialmatsthatgeneratestromatolitesare2003;Mastandreaetal.,2006

8、).dolomitecrystalshaveanaverageof53molafeatureofmanymodernshallow-waterperi-Scanningelectronmicroscope(SEM)obser-%Ca,whereaslargercrystalshaveanexcesstidalenvironments.Severalprocessesoperatevationsoffreshsurfacesofstromatolitewe