碳酸鹽巖:自生碳酸鹽礦物含量超過50%的沉積巖稱碳酸鹽巖，自生碳酸鹽礦物中若一半以上為方解石稱石灰巖或簡稱灰巖，若一半以上為白云石稱白云巖或簡稱云巖。Carbonaterocksarethoseinwhichthematrixandframeworkarecomposedofgreaterthan50%carbonateminerals(thisdefinitionexcludescement).Unlikesilicilasticsediments,wherestructuresandtexturesreflectthephysicalfactorsinthedepositionalenvironment,thestructuresandtexturesofcarbonaterockscommonlyreflectintrabasinal,biologicalfactors.Thesourceforcarbonatesedimentsisalmostexclusivelybiological.Althoughcarbonatesformincolderwaterandmorespecializedsettingssuchas'hot'springsandcaves,mostthickbuildupsrepresenthighorganicaccumulationinshallow,warmseasinareasremovedfromsignificantsiliciclasticinputTheseshallowmarineareaswherecarbonatesedimentsarecreatedbycalcareousorganismsarereferredtoasthe"carbonatefactory"

CARBONATEROCKS

Manyfeaturesofcarbonatesedimentsareanalogoustothoseinterrigenousclasticsediments,butwithsomenotabledifferences:

——Mostcarbonaterocksareintrabasinal:therocksmainlyoriginateinthebasinofsedimentationratherthanbeingtransported.——Manycarbonaterocksare"biogenic"inorigin,dueeithertobiochemically-inducedmineralprecipitationorduetohighconcentrationsofskeletalshellcomponents(biomineralization).Somecarbonaterocks,however,areabiotic(inorganic)inorigin.——Carbonaterocksgenerallylithifyveryrapidly.——Particlesizeincarbonatesdoesnotnecessarilyreflecttheenergyoftheenvironmentofdeposition.Somecoarseparticlescanformorbedepositedinlow-energyenvironments.Modern

Warm

Water

Modern

Cool

Water

Ancient

Counterpart

SedimentarycontributioncoralsNONEarchaeocyathids,corals,bryozoa,stromatoporoids,rudistidbivalves,hydrozoansthelargecomponents,ofteninplaceofreefsandmoundsbivalves,redalgae,echinodermsbivalves,redalgae,echinoderms,brachiopods,barnaclesbivalves,redalgae,brachiopods,cephalopods,trilobitesandotherarthropodsmayoccurwholeorinbrokenpeicestoformsandandgravel-sizedgrainsgastropod,benthicforaminifersgastropod,benthicforaminifersgastropod,tintinids,tentaculitids,salterellids,benthicformainifers,brachiopodssandandgravel-sizedgrainsfromedfromwholeskeletonscodiaceanalgae,spongesredalgae,bryozoanssponges,crinoids,andotherpelmatozoanssand-sizedgrainsfromedfromdisintegrationofthedeadorganismplanktonicforaminifers,coccoliths,pteropodsplanktonicforaminifers,coccoliths,pteropodsplanktonicforaminifers,coccoliths(post-Jurassic)mediumsand-sizedorsmallergrainsthatoccurinbasinaldepositsooids,peloidsNONEooids,peloidsconcentricallylaminatedormicriticsand-sizedparticlesencrustingforaminifers,bryozoans,corallinealgaeencrustingforaminifers,bryozoans,corallinealgae,serpulidwormsencrustingforaminifers,corallinealgae,phylloidalgae,reralcidsbuilduptoformthickdepositsafterencrustingonhardsubstrates,orformlimemudonseafloorcodiaceananddasycladgreenalgaeNONEcodiaceananddasycladgreenalgaedisintegratetoformlimemudcyanobacteriaandothercalcimicrobescyanobacteriaandothercalcimicrobescyanobacteriaandothercalcimicrobes(importantinpre-Ordovician)formstromatolitesandmatsbytrappingandbindingfine-grainedsediments1．石灰巖的一般特征1）形態：——海成石灰巖區域性的穩定層狀，也可與凈砂巖互層。——湖成石灰巖規模一般不大，以條帶狀出現。2） 顏色：灰白、灰、灰黑或紫紅等色。3） 成分：——方解石//其它成分常在5%以下：粘土礦物、石英粉砂、鐵質微粒、海綠石、有機質等。——砂巖過渡的灰巖中可含較多陸源碎屑，——白云石化也可使白云石含量增加。４）沉積構造：——常見泥裂、生痕、生物擾動、結核、縫合線等，特別是蟲孔、生物擾動、硅質（燧石）結核和縫合線——水平層理相對常見，——紋層狀層理（如交錯層理,顆粒性巖石，風暴或濁流石灰巖）——多見塊狀層理。——疊層構造和鳥眼構造。5）結構：——泥晶結構和各種顆粒結構為主，——生物骨架結構、粘結結構或障積結構。——結晶結構。——疊加的交代結構。6）成巖方式：壓實和膠結為主，溶蝕、交代和重結晶等作用常見。MineralogyThemainmineralsincarbonaterocksare:——Calcite:CaCO3(alsocalledlow-magnesiumcalcite)——Mg-calcite:CaCO3,butwithseveralmol%Mg(typically>4mol%)——Aragonite:CaCO3——Dolomite:CaMg(CO3)2Otherlesscommoncarbonatemineralsinclude:Ferroandolomite(Ca(MgFe)(CO3)2(alsocalledankerite);Siderite(FeCO3);Magnesite(MgCO3)Ferroandolomiteandsideritearecommonlyassociatedwithreducing(lowtozerooxygen)environments:sedimentarymagnesiteisfoundinsomesalinelakes.Calciteandaragonitearepolymorphs—theyhavethesamechemicalcomposition(althoughtheirtraceelementsaredifferent),butadifferentcrystalstructure:calciteistrigonal,whereasaragoniteisorthorhombic.Thecommoncarbonatemineralsdifferintheirsolubility.Calciteislesssoluble(i.e.morestable)thanaragoniteinmostfluidsattheearth'ssurface.ThesolubilityofMg-calcite(highmagnesiumcalcite)varieswiththeamountofMgsubstitutionforCainthecalcitecrystallattice,butMg-calciteiscommonlymoresolublethanaragonite.Mg-calcitecommonlyrecrystallizestocalciteduringdiagenesis;aragonite,beingmoresolublethecalcite(especiallyinfreshwater),maydissolvetoproducesecondaryporosityormayaltertocalciteduringdiagenesis.CalciteinskeletalgrainsTheskeletalpartsoforganismsarecommonlycomposedofcalcite,magnesiancalcite,aragoniteoropalinesilica.Thismineralogydeterminesthesusceptibilityoftheskeletalfragmenttodiageneticchangeandsoitscurrentcompositionandfabricinalimestoneordolomite.Calciteskeletalgrains,whichcontainlessthan4mole%magnesiuminthecalcite,includesomeforaminifera(有孔蟲),brachiopods（腕足類）,bryozoans苔蘚蟲類,trilobites三葉蟲,ostracodes介形蟲,calcareousnannoplankton鈣質微型浮游生物,andtintinnids纖毛蟲.Skeletalgrainsofmagnesiancalcite,thatiswith4-20mole%magnesiuminthecalcite,includethoseproducedbyechinoderms棘皮類動物,mostforaminifera有孔蟲類,andredalgae紅藻.Aragoniteskeletalgrainsareformedfromcorals珊瑚蟲,stromatoporoids層孔藻,mostmolluscs軟體動物,greenalgae綠藻,andblue-greenalgae藍綠藻.Skeletalgrainsofbiogenicopalinesilicaincludespongespicules海綿骨針andradiolarians放射蟲.Carbonatesarecomposedlargelyofbothcalciumandmagnesiumcarbonatemineralsaswellascarbondioxide.Aswell,inmostcarbonaterocks,thesilicacompositionisquitelow.Therearethreemainsedimentarycarbonateminerals:aragonite,calcite,anddolomite.Thecompositionofmostcarbonatesliessomewherebetweencalcite(CaCO3)anddolomite(CaMg(CO3)2.Forexample,mostcontainsomemagnesium,butnotasmuchaspuredolomite.Carbonatesedimentmaybeformedbybiologicalprocessesaswellasbyphysicalweatheringanderosion;however,themaincontrolontheformationofthesesedimentsischemistry.

CalciteGroup

(hexagonal)

DolomiteGroup

(hexagonal)

AragoniteGroup

(orthorhombic)

mineralformulamineralformulamineralformulaCalciteCaCO3

DolomiteCaMg(CO3)2

AragoniteCaCO3

MagnesiteMgCO3

AnkeriteCa(Mg,Fe)(CO3)2

WitheriteBaCO3

Siderite,FeCO3

KutnohoriteCaMn(CO3)2

StrontianiteSrCO3

RhodochrositeMnCO3

Thecarbonatemineralssharesomecommoncharacteristics,including:AllshowchangeofreliefwithrotationAllhaveextremebirefringence(delta=0.148to0.242),givinghigh-order,creamyorpastelinterferencecoloursTodistinguish(e.g.)first-orderwhitefromhigh-orderwhite:lookforblue-greytint,showingfirst-orderlookatthinedgesofgrains;entireinterference-coloursequencemaybepresent,makingitpossibletocountcoloursin(orsequenceofpastelsmaybevisible)insertgypsumplate;1?colourschangetoupper1?lower2?high-ordercoloursshowlittlechangeSeveralfactorsinfluencethesolubilityofCaCO3:WhatcanyougetfromaboveFig?FavourableconditionHighpHhighTLowerp(CO2)LowerpressureCarbonatedepositionalsystemsforminginthegeologicpast,andinmodernsettings,fallintothreegeneraltypes:rampmargins,rimmedmarginsisolatedplatforms.gentlysloping(<1°)platformmaybeslightshelfbreaknopronouncedreeftrend,althoughdiscontinuouscarbonatesandshoalsmaybepresentmayhavehighenergybeachandskeletal,ooliticsandshoals.斜坡的邊緣緣HIGHENERGYLOWERENERGY·pronouncedbreakinslope·presencesofnearlycontinuousrimorbarrieralongplatformedge·thebarrierisawaveresistantstructureconsistingofeitherareeforskeletal,ooliticsandshoals·landwardofrim/barrierisalowenergy"lagoonal"areaofvariablyrestrictedcirculation·lagoonalareacommonlygradeslandwardintotidalflat·"Bahamatype"-derivedfrommodernanalogywithBahamaplatform· shallowplatform10'sto100'skmwideoffshoreofshallowcontinentalshelves· surrounedbydeepwater(several100'smetrestofewkmdeep)· Mayhaveeithergentlyslopingmarginormoresteeplyslopingmargin.SedimentarystructuresandearlydiageneticfeaturesofshallowmarinecarbonatedepositsThisphotographshowsdetailofripplesonJoulter'sCayooidshoal.Notetheroundedcrestlinesandvariableplanmorphologyoftheripples.Ripplesaresuperimposedonlowdunesorientedroughlyperpendiculartoripplecrestorientation.Ripplespacingapproximately100mmLarge-scalecross-stratificationinUpperPaleozoicgrainstones.Skeletal-peloidalgrainstoneunitintheMississippianLoyalhannaLimestonefromcentralAppalachians.Clifffaceis19.5mhigh.Lower3mandupper6mmostlyflow-parallelviews.Central10mshowsflow-perpendicularandobliqueviewsoflargetroughs.Reactivationsurfaceincross-stratifiedPaleozoicgrainstones.Compositesetoflarge-scalecross-stratadevelopedinquartzsand-bearing,skeletal-peloidalgrainstones,MississippianLoyalhannaLimestone,centralAppalachians.Thefourflow-parallelsetsofcross-stratathatcomprisetheuppertwo-thirdsoftheoutcropincludemanyreactivationsurfaces,someofwhichhavesmall-scaleripplesdirecteduptheforesetslope(arrows).Flowparalleviewofwave-rippleformset(upperarrow)overlyingflowobliqueviewofwave-ripplecross-stratification(lowerarrow).Dolomitemuddrapesbothcross-stratalsets.MiddleCambrianArctomysFormation,CanadianRockyMountains,southwesternAlberta.Wavytocrinkledfinelaminaecomposedofcoupletsofgrainstonelayers(dark)anddolomiticmudstonelayers(light).UpperCambrianConococheagueLimestoneofthecentralAppalachians.Planarlaminae(greaterthan5mmthick)andthinbedsdevelopedindolomitemudstone,LowerProterozoicWittenoomDolomite,HamersleyBasin,WesternAustralia.Pocketknife,lowerleftcenter,isapproxiately80mmlong.Cross-sectionsofmudcrackfillsfromtheMiddleOrdovicianSt.PaulGroupofthecentralAppalachians.Notethatthecrackscontainseveralgenerationsofsedimentfillswithamicro-stratigraphyrelatabletooverlyinglayers.Theseobservationsdemonstratethatthesecrackswereopenatasediment-airorsediment-watersurfaceanumberoftimesandthatthesecrackscouldnothaveformedfromupward"injection"ofsediment.ConvolutefoldingincrinkledlaminatedmudstonesfromtheUpperSilurianTonolowayFormation,westernMarylandSmallstromatoliticbiohermencasedinthinbedsofcarbonatemudstonethatbendaroundthebiohermfrombothaboveandbelow.Affectedbedsthinlaterallyaboveandbelowthebiohermandshowincreasingdipsandthicknessesdownthesidesofthebioherm.Bedsasrethickestalongtheflanksofthebiohermandthinlaterallyaswell.UpperCambrianConococheagueLimestone,westernMaryland.Gypsumcastinthefloodplainlakedeposits.

Gypsumcastisformedingypsumrockby

solution.

CretaceousHasandongFm.

GyeongsangBasin.

PhotocourtesyofDr.JILeeWelldevelopedmudcracks.Mudcrackisanirregularfractureinacrudelypolygonalpattern,formedbytheshrinkageofclay,silt,ormud,generallyinthecourseofdryingunder

theinfluenceofatmosphericsurfaceconditionMiddleCambrianribbonrock.Ribbonrockis

characterizedbyasuccessionofthinlayersof

differingcompositionorcolorsshowninthis

photograph.WesternHill,ChinaOoliticgrainstone.Ooidsareobservedclearly.WesternHill,ChinaStromatolite.Stromatoliteisanorganosedimentarystructureproducedbysedimenttrapping,binding,and/orprecipitation

asaresultofthegrowthandmetabolicactivity

ofmicro-organisms,principallycyanophytes(blue-greenalgae).Ithasavariety

ofgrossforms,fromnearlyhorizontalto

markedlycolumnar,domal,orsubspherical.WesternHill,China.BeddingplaneexposureofdolomiticcolumnarstromatolitefromtheLowerProterozoicTaltheileiFormation,PetheiGroup,NorthwestTerritories.Fieldofviewapproxiately17inches.Imbricatedflat-pebbleconglomerate.Current

flewtotheright.WesternHill,China.CurrentdirectionBioturbationillustratingchurningandstirringof

sedimentbyorganismsaftersedimentation.OrdovicianMungokFm.YeongweolAreaFlat-pebbleconglomerate.Cross-section

parallelorsubparalleltothebeddingplane.OrdovicianMungokFm.

YeongweolAreaCalciteandaragoniteareprimarilyfoundinthreeforms.grains:siltsizeorlargeraggregatesofcrystals.Fivegeneraltypesofgrainsarefoundasoutlinedbelow.mud:1-4μmsizecrystals)-texturallyanalogoustosiliceousmuds.Thissizeclassiscommonlycalledmicrite泥晶spar:coarsergrainedcrystalswhichappeartranslucentinplanelight(clearotwhite),0.02-0.1mmrange.Crystalsfillporespaces,oftenduetorecrystallization–亮晶CarbonateParticlesCarbonategrainscanbedividedintonon-skeletalgrains:skeletalgrainsCarbonatePetrography(Allochems)Carbonaterocksarevolumetricallymadeupdepositionalproductsanddiageneticproducts.Thedepositionalproductsarethosefeaturesoftherock,whichresultedfromthedepositionalevent,whereasthediageneticproductsarethosefeatures,whichcameaboutduetosomepostdepositionalprocess.Thedepositionalproductsincludecarbonateallochems,non-carbonateallochems,terrigenousdetritus,micrite,andprimaryporosity.Theallochemsaredescreteandorganizedcarbonateaggregatesthatserveasthecoarserframeworkinlimestone;toparaphrasetheGlossaryofGeology.Includedinsucharebioclasts,ooids,pelloids,andintraclasts.Bioclastsarethecalciteoraragonitesecretionsofplantsandanimalsofalltypes.Excludedarenon-carbonatefossilremains.Differentorganismsproducedifferentskeletalmaterialwithdifferingmicrotextures.Eachtypeoforganismhasdistinguishingfeaturesthatallowforonetoidentifytheminthinsectionwithouttoomuchdifficulty;wellmaybealittle!Grains,a.k.a.,allochemsFivetypesofgrainsoccurincarbonaterocks:Carbonateclasts(rockfragments):Thesecanbeverydifficulttodifferentiate!!intraclasts-formed,transportedandredepositedwithinthebasinlithoclasts-formedoutsideofbasinlimeclasts-nonspecificoriginooliths:concentricallylaminatedcarbonatestrucures,including:oolites-concentricallylaminatedstructures,lessthan2mmindiameter,thoughttobeabiogenicinoriginpisolites-sameasoolites,butgreaterthan2mmindiameteroncolites-spheroidalstromatolites(>1-2cm)superficialoolites/pseudoolites-uncertainorigin3peloids:silttofinegrainedsandsizedcarbonateparticleswithnodistinctiveinternalstructure;mostthoughttobefecalpellets4compositeparticles:crystalaggregatesandcrystallinelumps.Theseareirregularlyshapedcompositeoraggregategrainswhichareboundtogetherbydark,organicrich,veryfinegrainedcalciumcarbonate.Thesegrainstendtogetdistortedduringdiagenesis-rarelyreportedinancientsediments5skeletalparticles:wholemicrofossils,wholemegafossils,brokenshellfragments.Skeletalandmudsizecarbonategrainscanbederivedfromanyorganism(cyanobacteria,algae,avarietyofinvertebratesandvertebrates)withacalcareousskeletonorbodyparts.Typesoffossilsdependentonenvironmentandgeologicage.Groupsandorganismsvariable,sizesrangefrommicriteto"boulder"Non-SkeletalGrainsOoidsaresphericalparticlesofCaCO3,usually<2mmindiameter.Theyconsistofanucleus(e.g.,sandgrain)surroundedbyconcentriclamellae.ThelamellaeconsistmainlyofCaCO3,butsomehavethindarkerlamellaecontainingorganicmatter.Ooidsforminshallowmarine(especiallytidallyinfluenced)environments,andinfreshwaterenvironments(lakes,hotsprings,cavepools).Ooliteisthesedimentaryrockcomposedmainlyofooids.Modernmarineooidsaremainlycomposedorminute(<5um)needlesofaragonite(rarelyMg-calcite)alignedtangentiallytothethesurface.Theytypicallyforminshoalsinseawaterthathasslightlyelevatedsalinityandtemperature.Althoughtheprocessesarenotfullyunderstood,ooidsformbychemicalprecipitationinseawater(agitationandCO2degassing),butmicrobes,especiallybacteria,mayplayabiochemicalroleinformingsomeofthelamellae.Infreshwater,ooidsarecomposedofeitheraragoniteorcalcite.CalcitecanprecipitateinfreshwaterbecausethelowerMg2+concentrationsdonotinhibititsgrowth.Calciteooidscommonlyhavearadialstructurewithcrystalsradiatingoutwardfromthenucleus.Mostancientooidsintherockrecordarecalcite(ordolomite).Thetexturesofancientooidshavebeenusefulindemonstratingchangesinseawatercomposition(Mg,PCO2)throughtime.Somemarineooidsshowcalcitewithradialcrystaltexturesthatmaybeprimary.Suchtextureswouldhavebeendestroyedduringdiagenesisiftheoriginalooidwascomposedofaragonite.Peloidsaresmall(<2mm)spheroidalorovoidparticlesoffine-grainedcarbonatemudthatlacksinternalstructure.Mostoriginateasfecalpelletsofarangeoforganismsthathaveingestedmud.Somepeloidsmayoriginatefrommicrobialbreakdownofotherparticles.IntraclastsarepiecesofCaCO3sedimentthathavebeenpartiallylithified,thenbrokenupandreworkedtoformaclast,thatbecomesre-incorporatedinthesediment.Acommoncaseinwhenlimemuddriesoutandcrackswithexposure,followedbyreworkingbyacurrent.Lithoclastsarepieceofoldlimestonethatbecomeincorporatedinyougersediments(e.g.,MiocenelimestonefragementsinPleistocenelimestone).Thesecanbedifficulttorecognizeunlesstheclastscontaindignosticfossilsorshowdifferentdiageneticfeatures.Thisisthemaintestforechinodermmaterial...crossthepolarizersandrotate.Sometimesyoucanactuallyseethecrystalmesh-work.Theindividualgrainswillalsofrequentlyhaverecognizableshapesinthinsection:circles,seethecrystalmesh-work.Theindividualgrainswillalsofrequentlyhaverecognizableshapesinthinsection:circles,squares,rectangles,andthe"pac-man"figure.Echnindermfragments(ossicles)whicharetheeasiestofalltoidentifyaremadeofcalcite.Theorganismproduceshundredsofcalcitecrystalstoforma3-dimensionalmesh-workwithineachossicle.Eachcalcitecrystalhasthesamecrystallographicorientationasthenexthenceallwillgoextinctundercrossedpolarizersatthesametime.CriteriafortherecognitionofcarbonatebioclastsBrachiopodssecretedcalciteasmicroscopicrodssurroundedbyanorganicsheath.Theseappearinthinsectionasveryfinelamellaethataregenerallysubparalleltotheexteriorsurfaceoftheshell.Somebrachiopodsproducedspineswhichwhenthespineiscutincrosssectionappearasadiskwiththelamellaeformingconcentricringsaroundthedisk.thataregenerallysubparalleltotheexteriorsurfaceoftheshell.Somebrachiopodsproducedspineswhichwhenthespineiscutincrosssectionappearasadiskwiththelamellaeformingconcentricringsaroundthedisk..Twotypesofmicrotexturearecommonlyobserved;a"prismatictexture"anda"cross-lamellartexture".Thearagoniticportionsareusuallyremovedbydissolutiontoformamoldicporeortheyarereplacedbythemorestablecalcite.Molluskwhichincludetheclams,oysters,cephalopods,etc.secretedbotharagoniteandcalcite.Shellmorphologycouldbeconfusedwiththatofabrachiopodhoweverthemicrotextureoftheshellisverydifferent.Themollusksgenerallyproduceamulti-layeredshellwhereinthebrachiopodsonerarelyobservesmorethanonelayer.Arthropods:whichincludetheostracoda,trilobites,andbarnacles,secretedcalciteassmallrods.Thecrystallatticeofeachrodisslightlyrotatedrelativetotheadjacentrodssuchthatwhenviewedundercrossedpolarizersoneobservesasweepingextinctionalongthelengthoftheshellasonerotatesthestage.Theostracodaarereallysmallanddelicate.Lookforthesweepingextinctionandlookforthedelicatearchshapeoftheshellandinwellpreservedsamplesonecanseeahookorhingewherethetwohalvesoftheshelljoined.Trilobitesaremuchlargerthantheostracoda.Thesweepingextinctionisverypronounced.Thetestmorphologyisfrequentlylikea"S"shape.Barnaclesaremuchmorecomplexintheirshapeanddonotalwayshaveawell-developedsweepingextinction.Coralspresentsomechallenges.PaleozoicformssecretedcalcitewhereastheCenozoicformsproducedaragonite.Startwithshaperecognitionfirst;examineanypaleontologybookforthis.Nextthechamberwallischaracteristic.Inwellpreservedspecimenslookforcrystalswhoselongaxisisnormaltothewallorsepta.Bepreparedtomissidentifytheseasbryozoaandvisa-versa.Bryozoanidentificationcanpresentachallengeastheycouldbeeasilyconfusedwithacoralorwhenfragmentalwiththatofabrachiopod.Theyproducedeitheraragoniteorcalcite,whichformedassmallrodsofthesamescaleasthatofthebrachiopods.Onedistinguishingfeaturethatmanyspecimensexhibitisthatthetesttendstobifurcateorsplitlikeatreetrunkgivingrisetonewbranches.Alotofvariationherehenceexperienceisthebestguideinidentification.Algaerecognitionisveryimportantforenvironmentofdepositiondeterminationbutunfortunatelythisgroupofcarbonateproducersisthemostdifficulttodealwith.Thisisonepointwherepicturebooksreallyhelp.Theblue-greensgenerallylooklikecryptocrystallinecalciteormicrite(seebelow)excepttheycanexhibitsomesenseoflayeringorpattern.Thegreenssometimeshavetubulesthatonecanseeespeciallywhentheyformclumps.Theredsunderhighmagnificationlooklikestacksofbricks,actuallyyouareseeingcellwalls.Foraminiferaarebestrecognizedbybecomingfamiliarwiththeirvariousshapes.Thisiswhereavisittothelibrarywillpayoff.BelowareimagesofforamsfromtheCarboniferousofUtah.ArchaeantoRecentCyanobacteria-theearliestreefbuilders(>3000Ma),stillaroundatthepresenttime.Filamentouscyanobacteriatrapfine-grainedcarbonate(andsometimesnon-carbonate,especiallyaeoliandust)sediment.Theyformgelatinoustoleatheryflexiblesheetscontainingstickyorganicmatter(mucillage),towhichsedimentsticks.Whenthematbecomescoveredinsediment,itgrowsanotherlayeroffilamentsthroughandoverthesediment,soitcancontinuetophotosynthesize.Thenanotherlayerofsedimentistrapped,buildingupinlayerswhicharealternatelyorganic-richandsediment-rich.Thiscombinationofcyanobacterialmatandsedimentisastromatolite.Microbialmatsallowfine-grainedsedimentstobedepositedinenvironmentswhoseenergywouldnormallybetoohighforsuchdeposition.ThephotosynthesisofthecyanobacteriaremovesCO2fromwaterswithinthemat,promotingtheprecipitationofCaCO3,oftenasearlycement,whichcausesthemattoharden.Modernstromatolitesarefoundmainlyinwarmclimatesandveryshallowwater.Theyoccurinshallowsubtidal,intertidalenvironments,andmayextendintothesupratidalenvironmentwheretheclimateishumid.Theyalsooccurinfreshwater.See:Favosites,aSiluriantabulatereefformerfromWenlockEdge,England.CrosssectionofmassivereefrockinaquarryintheMeusevalley,SBelgium.Thesheet-likecoloniesaremostlystromatoporoids,withsometabulatecorals(lightercolouredlens,atcentre).Inthispolished'marble'slab,theredmaterialispartofamicritemudmound,andthewhiteareaswerecavitieswiACarboniferousreef-buildingrugosecoral.Rugose&tabulatecoralsbecameextinctinthePermian.UpperCretaceousrudist'reef'fromSFrance.Therudistbivalves,ingrowthposition,indicatetheway-upofthebed.BetweenthefossilsissandstoneCutsectionthroughpartofarudist'reef'fromthesamelocalityasabove.Notegeopetalinfillsinsomeoftherudists.Cross-sectionthroughabraincoralinthePleistoceneKeyLargoLimestone,WindleyKeyQuarry,FloridaKeysModernreefatKeyLargoDryRocks,FloridaKeys.Notethelarge,massivescleractiniancoralcoloniesDiagenesisofCarbonateSediments成巖方式式：壓實實和膠結結為主，，溶蝕、、交代和和重結晶晶等作用用常見。。Diagenesisreferstothephysicalandchemicalchangeswhichtakeplaceafterthedepositionofasediment;itmayinclude:dissolutionandalterationofexistinggrainsprecipitationofnewmaterialsinporespacesduringdiagenesis:unstablemineralsmaybedestroyednewmineralsmaygrowexistingcrystalsmaybecomeenlargedCarbonatesaremuchmoresusceptibletodiagenesisthanterrigenousclasticsediments,andoriginalstructuresandtexturesareoftencompletelydestroyed.Diagenesisofcarbonatesisofgreateconomicimportance.Manyimportantoilfieldsareproducedfromcarbonatereservoirs-e.g.thegiantonshoreoilfieldsoftheMiddleEast.Diagenesiscontrolstheporosityandpermeabilityofcarbonatereservoirs.DiageneticprocessesincarbonatesCanbesummarisedas:1.solutionofmoreunstableminerals(especiallyaragonite),creatingsecondaryporosity2.pore-fillingbycements3.alterationoforiginalmineralstonewones,especiallyreplacementbyneomorphiccalcite:· hi-Mgcalcite>low-Mgcalcite· aragonite>low-Mgcalcite· fine-grained>coarse-grained(aggradingneomorphism)· dolomitization· silicificationCalciumcarbonatecementanditsrecognitionchemicallyprecipitatedmaterial,whetheranewmineral,oranadditiontoanexistingmineral,mayformacement,whichbindsthegrainsofthesedimenttogethertoformarock.Itisimportanttodistinguishbetweensparitecement(porefill)andneomorphicspar,aninsitureplacementofcalciumcarbonateinthesolidstate.Cementisdepositedinpores:thesemaybeprimary-voidsbetweenorwithingrains,ortheymaybesecondary,formedduringdiagenesisbysolution,orotherchemicalorphysicalchanges.Someofthefeatureswhichcharacterizecementsinclude:· generallyclearandcleanappearance,withwell-defined,often(butnotalways)straightcrystalboundaries;· sparbetweenthegrainswhichdoesnotpenetrateintoorcutacrossgrains;· sharpcontactsbetweensparandparticles;· micritematrixispresentbutunaltered;aragonitefragments'replaced'bycalcitecement;· thepresenceoftwoormoregenerationsofspar;· straightcrystaledgesandfrequenttriplejunctionswith180°angles(enfacialjunctions);· longaxesofcrystalsnormaltograinsurface;· increasingcrystalsizeawayfromgrainsurface.Thecompositionandcrystalhabitofcalciumcarbonatecementsarehighlydependentonvariationsinphysicalandchemicalconditions.CarbonatecementtypesThetypeofcementwhichformsdependsparticularlyonMg/Caratioandsalinityofthesolution.·InsolutionswhereMg/Caratiosarelow,calcitecancrystallisefreely,forminglarge,ratherequantcrystals.·WhereMg/Caratiosareh