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1、Sedimentology(2003)50,237–245Microbialfossilizationincarbonatesediments:aresultofthebacterialsurfaceinvolvementindolomiteprecipitation1YVONNEVANLITH,ROLFWARTHMANN,CRISOGONOVASCONCELOSandJUDITHA.MCKENZIELaboratoryofGeomicrobiology,GeologicalInstitute,SwissFederalInstituteofTechnology(ET
2、H),Sonneggstrasse5,CH-8092Zu¨rich,SwitzerlandABSTRACTRecentdolomiticsedimentsamplesfromLagoaVermelha,Brazil,wereexaminedmicroscopicallytostudytheprocessofbacterialfossilizationincarbonatesediments.Bacteria-likebodieswereintimatelyassociatedwithcarbonatemineralsurfaces,andcoatingsonthef
3、ormerdemonstratethecalcificationofsinglebacterialcells.ThebacterialfossilizationprocessinLagoaVermelhasedimentswassimulatedinthelaboratorybycultivationofmixedandpureculturesofsulphate-reducingbacteria,whichwereisolatedfromtheLagoaVermelhasediments.Theseculturesproducedcarbonatemineralst
4、hatwerestudiedtoprovideinsightintotheinitiationofthefossilizationprocess.Inmixedcultureexperiments,bacterialcoloniesbecamecalcified,whereasinpurecultureexperiments,singlebacterialcellswereassociatedwithdolomitesurfaces.Dolomitenucleatedexclusivelyinbacterialcolonies,intimatelyassociated
5、withextracellularorganicmatterandbacterialcells.Electrophoreticmobilitymeasurementsofthebacterialcellsin2+2+electrolytesolutionsdemonstratedthespecificadsorptionofCaandMgontothecellsurfaces,indicatingtheroleofthebacterialsurfaceincarbonate2+nucleationandbacterialfossilization.Theaffinity
6、ofthecellsforMgwasrelatedtothecapabilityofthestrainstomediatedolomiteformation.0Combinedwithsulphateuptake,whichdissociatesthe[MgSO4]ionpair2+2+andincreasestheMgavailability,theconcentrationofMgionsinthemicroenvironmentaroundthecells,wheretheconditionsarefavourablefordolomiteprecipitat
7、ion,maybethekeytoovercomethekineticbarriertodolomiteformation.Theseresultsdemonstratethatbacterialfossilizationisaconsequenceofthecellsurfaceinvolvementincarbonateprecipitation,implyingthatfossilizedbacterialbodiescanbeusedasatooltorecognizemicrobiallymediatedcarbonates.KeywordsBacte
