carbonate lab write up
TRANSCRIPT
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1)Ooids
cvxe3333334
WAPBG
Miamioolites(left) *TheWAPBGTS,isanooidgrainstoneaccordingtoDunhamsclassification,A)ModernMiamioolitesdemonstratetwodifferenttypesofmicrofabrics:somehavetangentialandothershavearandomfabricofaragonitecrystals.Incontrast,theCarboniferousooidsprimarilyhavearadialconcentricmicrofabric.Alsonotethatanintragranularfabricexistswith
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ooidsarepreferentiallyfoundinareasofmaximumagitation,howeverradialooidscanformfromturbulentenvironmentsaswell.2)Peloids
AKABAHPeloids
A)Therearemanypossiblemodesoforiginofpeloids:fecalpellets,calcareousalgae,micritisedgrains,smallintraclasts,mudclastsoraprecipitateorigin.Depositfeedinganimalsproducefecalpeloids.Peloidscanalsorepresentmicritisedgrainssuchasabradedshellfragmentsorooids.Theyalsocanberemnantsoffinegrainedalgalremainsorformbythecalcificationofcyanobacteriainalgalmats.Manypeloidsaresimplysandsizedintraclastsorlithoclastsderivedfrompreexistingmicriticsubstrates.Finallytheycanalsobechemicalinoriginandrepresentcementsinwhichthepelletsaresitsofsmallcrystalsofhighmagnesiumcalcite.
B)Peloids,composedofmicrocrystallinecarbonate,areanimportantconstituteofshallowmarinecarbonatesedimentsandaretypicalofshallow,lowenergy,restrictedmarineenvironments.
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3)Intraclasts
MaynesHandSample(below)WJM608TS(above)
A)Intraclastsformedfrompoorlysortedweaklyconsolidatedsedimentthatisreworkedfromwithintheareaofdeposition.Thisprocessconsistsofdepositioninariversinterchannelarea,followedbyquicklithificationofmudandthenerosionbyfluvialaction.
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4)Pisolites
PR10HandsampleandThinsample
A)Accordingtomyobservations,thesearevadosepisolites,sincetheyarequitelargerandhaveseverallayersofisopachouscoatings,manywithstalactitictexture(duetogravity)asindicatedonthediagramabove.Tofurthersupportmyclaim,thesepisolitessharefittedlaminaeasshowninthediagramaswell.
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5)Birdseye(Fenestral)Fabric
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6)Cyanobacteria:AlgalLaminates,StromatolitesandOncolites
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A)Asshowninthediagramabove,DT20showsevidenceofalgalfilamentmolds,thesewhitecalcifiedmicrobialfilamentmoldsaregenerallynormaltobedding.B)Theselaminationsareformedbysedimentssuchassanddepositedontidalflatsandtrappedbymicrobialalgalmatswhichconsistoflayersoffilamentousandunicellularmicroorganismsmainlycyanobacteria.Thisalternatingdepositionalpatternofsandandalgaematsisthenrepeatedseveraltimes.
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C)ThealgaelaminationsofDT20andMI11probablyformedinalowenergyenvironmentsuchasarestrictedbayarea,whereastheKinbladeandrecentstromatolitesprobablyformedinthehighenergyenvironmentsuchastheintertidalzone.D)Oncolitesusuallyforminasimilarfashionascyanobacterialaminationsformexcepttheyformradiallayersaroundacentralnucleussuchasashellfragment;calciumcarbonateisprecipitatedbyencrustingmicrobes(cyanobacteria),causingalayeredsphericalgrowthstructure,facilitatedbythecyanobacteriagrowth.Oncolitesareverysimilartostromatolites,butinsteadofformingcolumnstheyformsphericalstructures.7)RedAlgae
A)Thegoniolithonredalgaealsocalledcorallinehaveadistinguishbranchingshellstructure,notethefinescalepolygonalcellularstructure.Theirmultilayeredcoaxialskeletalstructureconsistsofamedulla(centralpart)extendingupwardstothenextsegmentcomposedof
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partitionedfilamentsandperipheralcellularfilamentssurroundthemedulla.Othersamplesshowanencrustingform.B)Redalgaeareavaluablepaleoenvironmentmarker.Althoughtheyneedsunlighttocarryoutphotosynthesistheyarenotalwaysindicativeofashallowtropicalwarmwatermarineenvironment.Theyhavebeenfoundtoflourishasdeepas250meters,aslongaslightcanreachthem.Redalgaecangrowintemperateandcoldwaterclimatesaswell.Theypreferagitatedwaterenvironments,suchasintheinnerramp.Thereefframeworksandmorphologyofredalgaebranchesreflectdifferentwaterenergies.Forexample,redalgaearethedominantorganismofmostancientcarbonaterimmedshelves.8)GreenAlgae
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*AccordingtoDunhamclassification,PSMismostlyanalgalwackestonealthoughtherearesomeareasthatmaybeconsideredaalgalpackstone.A)Sincegreenalgaecanonlyexistinwarmtropicalwatersinlowlatitudestheyindicateawarmtropicalpaleoclimate.Alsotheyareunabletogrowindeepwaterandthereforeindicateashallowmarineenvironment,suchasintheouterramp.Theyarecommoninquietlagoonsbutarealsofoundinlessturbulentpartsofopenshelvesandreefswheresunlightpenetrationisabundant.3)Mollusks
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*AccordingtoDunhamsclassification,KLFIisamolluskangrainstone.A)TherearetwotypesofshellpreservationinMiamiMollusks;somearepreservedasmolds(voids)sincethearagoniteshellitselfhasdissolvedaway.Othershellsarepreservedascasts(moldfilling)thiscalcitizationpreservestherelicmicroarchitectureofthearagonite.B)Therearetwomajortypesoffabric:Thefirstisaprimarystructurethatisindicativeoftheoriginalbiogenicshell,consistingoffibrouscrystalthatareorientatedperpendiculartotheshell.Thesecondisamicriticfabric,sincethearagoniteshellsarehighlyunstableandhavebeendiageneticallyalteredbyleachingproducingmicriticenvelopes.Therearealsodifferentporositytypespresent:Thereisintragranularfabric,adiageneticstructure,theinteriorofsomeshellsisdissolvedawaybyleaching,somehavebeencompletelydissolvedcausingadiageneticmouldicfabric.TherealsoisIntergranularporosity,aprimarystructure.(IwasconfusedbythewordfabricsoIgavetwoanswers)
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10)Brachiopods
A)Thesebrachiopodshavealowanglefibrouswallstructurewhichisdifferentfromthanthehighangle(nearlyperpendicular)lamellarwallstructure(narrowbandsoflight/darkextinction)andofthemollusks.11)Echinoderms
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*AccordingtoDunhamsclassification,BURL1isaechinodermiangrainstoneinmostareasbutcanbeconsideredcoarsegrainedcrystallineinothers.A)Echinodermshavefivefoldsymmetry,singlecrystalextinctionandaholeyfabric(smallporesthatappearastinyblackspots).Asancientshellslostmagnesiumcalcite,theholesgetfilledinandthecementtakesonthesameorientationoftheechinoderms,thisiscalledsyntaxialovergrowth.12)Bryozoa
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*AccordingtoDunhamsclassification565018isabryozoanwackestone,althoughsomeareasofthethinsectioncanbeclassifiedasabryozoanpackstone.A)Themicrostructureconsistsofchamberscalledzooeciathatarearrangedineitheraradiallacypatternoranelongatedstickpattern.Notethefinelyfibrouswallstructure.
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13)Stromatoporoids
A)Thetabular,anddendroidgrowthmorphologiesarelabeledinthediagramabove.
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14)Corals
*AccordingtoDunhamsclassificationscheme,HG44,isprimarilyacoralineboundstone.A)Thecoralwallismadeoutofbundlesofaragonitethathaveanirregularextinctionpatternundercrossedpolars.Themicrostructureiscomposedofasepta(verticalcentraldarklinewithsurroundingtrabecularstructure(horizontalfibrousorbladedcrystals)anddissepiments(curvedplates).VisibleintheCKL1sampleistheradialstructureofthesepta.Onamacrostructurescale,colonialcoralshavesimilarcalcareousskeletonswithbasicskeletalelementsofaragoniteorcalcitefibers.
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15)TrilobitesandOstracodes
A)Thedistinctiveshellstructureoftrilobitesistheirlongwormlikeshapedshellthatmayormaynothavehooks.Undercrossedpolars,extinctionbandssweepacrossthegrainasthestageisrotated,thisiscalledauniformprismaticextinction.Ostracodeshaveadistincteyeshapedthinshell.B)Ostracodesaredistinguishablefrombrachiopodsorbivalvesbecausetheyassmallerinsizeandhaveahomogenousprismaticwallstructurewithcalcitecementandchitincomposition.
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16)Sponges
*AccordingtheDunhamclassification,PR610mostofthesampleisamicriticmudstonebutthemidlowersectionisspongeanboundstone.A)Whilenotingtherelationshipbetweenthespongesandtheothercomponentsoftherocksitisimportanttonoticehowthesparrycalcitefillsthespicules.Therealsoaremeanderingcanalstructuresandwellpreservedwallstructures.Somecanalsarepartlyfilledwithhematite.
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17)BenthicForaminifers
*AccordingtoDunhamsclassification,565022isaforaminiferianpackstone.A)Characteristicsofotherfossilssuchasfragmentedshellsandskeletalfragmentsin565022,andtheabundantpelletsinAAXthatalsoindicateasemirestrictedshelflagoonenvironment..
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DiageneticFeatures:19)Compaction1035TS:ChemicalCompaction:dissolutionofgrainsapparentBurl2:ChemicalCompactionsincetherearestylolitesFT88:MechanicalCompaction:grainbreakageanplasticdeformation.20)MarineCementsBAH8:Fibrousmarinecementalongroundedooliticandmicritizedgrainswithanisopachoustexture,sincethefibersarecircularandgoingallaround.ABX:Multipleisopachouslayersoffibrousmarinecementalongelongatednonsphericalgrains.TR10:columnarisopachouscementisevidentsincethelengthtowithratioisgreaterthan6:1.Theyformbladedringsaroundlargemassivecrystals.Alsosparrycalcitecementfillsvoidsandholdstherocktogether.
ABX(left)21)Beachrock**SharkBay19hasintergranularandintragranularporosity.22)MeteoricCements:VadoseCements**MiamiOolitehasthreeporositytypes,primarilyanintergranularfabricexistsbetweenooidsandalsothemeniscuscementhasintragranularporosity.Inadditionthereisaverysmallamountofmouldicporosityduetotheleachingofgrains.A)ThemeniscuscementintheMiamiOolitesampleisvadoseinorigin,evidentbythelowMgcalcitewhiskercrystalcement.Thesethin,randomlyorientatedcalcitecrystalsareproduceinthemeteoricwaters,probablyinthevadosezone.B)ThecementintheKLFIsamplealsoindicatesanorigininthevadosezoneevidentbythemicriteenvelopes,andfinelycrystallinemeniscuscement.Alsotheporesthemselvesaremoreroundedinoutlinesincethecementpreferstogrowmoreatthejunctionbetweengrains,wherewateriscaughtbycapillaryaction.Thereisalsosome,butnotmuch,evidenceofcalcitewhiskercrystalcementaswell.
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23)MeteoricCements:PhreaticCements,BlockyCalcite**Redalgaehasbothintergranularandintragranularcement.B)Intheredalgae16203sample,theblockycalcitecementsurroundstheredalgaeandoccursinbetweengrainsandalsomayreplacegrains.C)InFT88,theblockcementwasnotinplacewhenthecompactionoccurred,evidentbythefactthatthecementisnotbroken.However,cementationmustofoccurearlyandnottoolongaftercompactionforthesampletobepreservelikeso.24)MeteoriticCementsInclusionfreeCrinodfragmentscanbedistinguishedfromsyntaxialovergrowthseventhoughsyntaxialovergrowthsarecementthattakesonthesamecrystalorientationofthecrinodfragmentgrainthatitisgrowing.Thesyntaxialovergrowthsaremoremassiveandcontinuousthanthecrinoids.Also,theboundariesareevidentwhenthestageisrotatedwithcrossedpolars.BothsyntaxialovergrowthsandCrinodfragmenthaveunit(singlecrystal)extinctionthatwilloccursimultaneouslymakingthegrainseemtobeonewholegrainwhileextinct.However,inwhenrotatedoutofextinctiontheboundariesbetweencrinodfragmentandthesyntaxialovergrowthsurroundingitareclear.25)CementStratigraphy:SeeDiagrambelow:
26)NeomorphicFabricsA)Petrographicfeaturesthatdifferentiateneomorphiccalcitefromblockycalcitecementbecauseneomorphicsparhaveirregularembayedtocurvedintercrystallineboundaries,contrastingwiththecommonlyplanarintercrystallineboundariesofblockycement,andneomorphicsparalsohasandirregularcrystalsizedistributionandpatchydevelopment.Gradationalandirregularboundariestotheareasofneomorphicsparandthepresenceofskeletalandothergrainsfloatingincoarsespar,alsoofferameansoftellingonefromtheother.27)Dolomite
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**SR118hasthreeporositytypes,intercrystalline,mouldicarevisibleinthinsectionandfenestralinthehandsampleA)SW27HighdegreeofobliterationB)SR118Mediumdegreeofobliteration,originalfabricoffossilscompletelygone,butgeometryoforiginalcementthatsupportedgrainsisstillevident.C)B037HighdegreeofobliterationD)P10,notehighdegreeoffabricretentionE)GibsonTS:Highdegreeofobliteration
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LookahappyfaceintheDolomite!!!
CarbonateLabBy
GloriaGill