microbial_primary_dolomite_from_a_norian_carbonate_platform__northern_calabria_southern_italy

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1、Sedimentology(2006)53,465–480doi:10.1111/j.1365-3091.2006.00776.xMicrobialprimarydolomitefromaNoriancarbonateplatform:northernCalabria,southernItalyADELAIDEMASTANDREA*,EDOARDOPERRI*,FRANCORUSSO*,ALESSANDRASPADAFORA*andMAURICETUCKER*DipartimentodiScienzeDellaTerra,Universita`dellaCalabria,Pon

2、teBucciCubo15b–87036Rende(CS),Italy(E-mail:eperri@unical.it)DepartmentofEarthSciences,DurhamUniversity,DurhamDH13LE,UKABSTRACTTheoriginoffine-graineddolomiteinperitidalrockshasbeenthesubjectofmuchdebaterecentlyandevidenceispresentedhereforamicrobialoriginofthisdolomitetypeintheNorianDolomiaPr

3、incipaleofnorthernCalabria(southernItaly).Microbialcarbonatesthereconsistofstromatolites,thrombolites,andaphaniticdolomites.High-reliefthrombolitesandstromatolitescharacterizesub-tidalfacies,andlow-reliefandplanarstromatolites,withlocaloncoids,typifytheinter-supratidalfacies.Skeletalremainsar

4、everyrareinthelatter,whereasarelativelyrichbiotaofskeletalcyanophycea,redalgaeandforaminiferaispresentinthesub-tidalfacies.Some75%ofthesuccessionconsistsoffabric-preservingdolomite,especiallywithinthemicrobialfacies,whereastherestiscomposedofcoarsedolomitewithlittlefabricpreservation.Threeend

5、-membersofdolomitereplacementfabricaredistinguished:type1andtype2,fabricretentive,withcrystalsize<5and5–60lm,respectively;andtype3,fabricdestructive,withlargercrystals,from60toseveralhundredmicrons.Inaddition,therearedolomitecements,precipitatedinthecentralpartsofprimarycavitiesduringlaterdia

6、genesis.Microbialitetexturesinstromatolitesaregenerallycomposedofthin,darkmicriticlaminaeoftype1dolomite,alternatingwiththickerlighter-colouredlaminaeofthecoarsertype2dolomite.Thrombolitesarecomposedofdark,micriticclottedfabricswithpeloids,composedoftype1dolomite,surroundedbycoarsertype2dolom

7、ite.Marinefibrouscementcrustsarealsopresent,nowcomposedoftype2dolomite.Scanningelectronmicroscopeobservationsoftheorganic-richmicriticlaminaeandclotsoftheinter-supratidalmicrobialitesrevealthepresenceofsphericalstructureswhichareinterpretedasm