Carbonate Lab Write Up
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1) Ooids cvx e3333334 WAP‐BG Miami oolites (left) * The WAP‐BG TS, is an ooid grainstone according to Dunham’s classification, A) Modern Miami oolites demonstrate two different types of microfabrics: some have tangential and others have a random fabric of aragonite crystals. In contrast, the Carboniferous ooids primarily have a radial concentric microfabric. Also note that an intragranular fabric exists with <5% porosity. B) In addition to the differences in microfabrics, Modern day ooids are usually composed primarily of aragonite; whereas in carboniferous ooids, calcite has completed replaced the aragonite, and their original texture preserved by both blocky and sparry calcite cement as indicated on the diagram above. C) In general, the environmental significance of ooids is that they indicate formation in a high‐ energy environment where water is supersaturated in respect to calcium carbonate, which precipitates to form encrusting isopachous concentric layers. Ooids are generally formed in agitated very shallow, tropical coastal environments and are favored by either intertidal or subtidal conditions. However, ooids can form in wide variety of settings from shallow‐marine settings to lagoons, lakes, rivers, caves and even calcareous soils. Also, the microfabric of ooids can be indicative of the depositional environment. In low energy environments, such as protected lagoons or troughs between oolite bars, aragonite ooids with a loose structure predominate. In higher‐energy environments such as the crests of bars of tidal deltas the ooids outer laminae have a tangential arrangement with tightly packed crystals. Tangential aragonite
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Transcript of Carbonate Lab Write Up
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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
