ManuscriptreceivedNovember122004provisionalacceptanceFebruary102005revisedmanuscriptreceivedMay192005finalacceptanceJuly052005DOI10130607050504129AAPGBulletinv89no11November2005pp15 ID: 181765
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NORTHAMERICANSTRATIGRAPHICCODENorthAmericanCommissiononStratigraphicNomenclatureFOREWORDTOTHEREVISEDEDITIONBydesign,theNorthAmericanStratigraphicCodeismeanttobeanevolvingdocument,onethatrequireschangeasthefieldofearthscienceevolves.TherevisionstotheCodethatareincludedinthis2005editionencompassabroadspectrumofchanges,rangingfromacompleterevisionofthesectiononBiostratigraphicUnits(Articles48to54), ManuscriptreceivedNovember12,2004;provisionalacceptanceFebruary10,2005;revisedmanuscriptreceivedMay19,2005;finalacceptanceJuly05,2005.DOI:10.1306/07050504129AAPGBulletin,v.89,no.11(November2005),pp.15471591 strivestoincorporatethestrengthandacceptanceofestab-lishedpractice,withsuggestionsformeetingfutureneedsperceivedbyourcolleagues;itsauthorshaveattemptedtobringtogetherthegoodfromthepast,thelessonsoftheGuide,andcarefullyreasonedprovisionsfortheimmediatefuture.Participantsinpreparationofthe1983CodearelistedinAppendixI,butmanyothershelpedwiththeirsugges-tionsandcomments.Majorcontributionsweremadebythemembers,andespeciallythechairmen,ofthenamedsub-committeesandadvisorygroupsundertheguidanceoftheCodeCommittee,chairedbyStevenS.Oriel,whoalsoservedasprincipal,butnotsole,editor.Amidstthenoteworthycontributionsbymany,thoseofJamesD.Aitkenhavebeenoutstanding.TheworkwasperformedforandsupportedbytheCommission,chairedbyMalcolmP.Weissfrom1978to1982.ThisCodeistheproductofatrulyNorthAmericaneffort.ManyformerandcurrentcommissionersrepresentingnotonlythetenorganizationalmembersoftheNorthAmericanCommissiononStratigraphicNomenclature(AppendixII),butotherinstitutions,aswell,generatedtheproduct.En-dorsementbyconstituentorganizationsisanticipated,andscientificcommunicationwillbefosteredifCanadian,UnitedStates,andMexicanscientists,editors,andadministratorsconsultCoderecommendationsforguidanceinscientificre-ports.TheCommissionwillappreciatereportsofformaladoptionorendorsementoftheCode,andasksthattheybetransmittedtotheChairmanoftheCommission(c/oAmeri-canAssociationofPetroleumGeologists,Box979,Tulsa,Oklahoma74101,U.S.A.).Anycodenecessarilyrepresentsbutastageintheevo-lutionofscientificcommunication.Suggestionsforfuturechangesof,oradditionsto,theNorthAmericanStratigraphicCodearewelcome.Suggestedandadoptedmodificationswillbeannouncedtotheprofession,asinthepast,byserialNotesandReportspublishedintheAAPGBulletin.Suggestionsmaybemadetorepresentativesofyourassociationoragencywhoarecurrentcommissioners,ordirectlytotheCommis-sionitself.TheCommissionmeetsannually,duringthena-tionalmeetingsoftheGeologicalSocietyofAmerica.1982NorthAmericanCommissiononStratigraphicNomenclaturePARTI.PREAMBLE...........................................................................................................................................................1555BACKGROUND..............................................................................................................................................................1555PERSPECTIVE..............................................................................................................................................................1555SCOPE...........................................................................................................................................................................1555RELATIONOFCODESTOINTERNATIONALGUIDE...........................................................................................1556OVERVIEW.....................................................................................................................................................................1556CATEGORIESRECOGNIZED....................................................................................................................................1556MaterialCategoriesBasedonContentorPhysicalLimits..............................................................................................1557CategoriesExpressingorRelatedtoGeologicAge........................................................................................................1558PedostratigraphicTerms..............................................................................................................................................1559FORMALANDINFORMALUNITS............................................................................................................................1560CORRELATION...........................................................................................................................................................1560PARTII.ARTICLES...........................................................................................................................................................1561INTRODUCTION...........................................................................................................................................................1561Article1.Purpose......................................................................................................................................................1561Article2.Categories..................................................................................................................................................1561GENERALPROCEDURES..............................................................................................................................................1561DEFINITIONOFFORMALUNITS..............................................................................................................................1561Article3.RequirementsforFormallyNamedGeologicUnits...................................................................................1561Article4.Publication.................................................................................................................................................1561Remarks:a.Inadequatepublication.........................................................................................................................1561b.Guidebooks..........................................................................................................................................1561c.Electronicpublication..........................................................................................................................1561Article5.IntentandUtility......................................................................................................................................1561Remark:a.Demonstrationofpurposeserved........................................................................................................1561Article6.CategoryandRank....................................................................................................................................1561Remark:a.Needforspecification...........................................................................................................................1561Article7.Name.........................................................................................................................................................1561Remarks:a.Appropriategeographicterms..............................................................................................................1562b.Duplicationofnames...........................................................................................................................1562c.Priorityandpreservationofestablishednames.....................................................................................1562NorthAmericanStratigraphicCode d.Differencesofspellingandchangesinname........................................................................................e.Namesindifferentcountriesanddifferentlanguages...........................................................................1563Article8.Stratotypes................................................................................................................................................1563Remarks:a.Unitstratotype....................................................................................................................................1563b.Boundarystratotype.............................................................................................................................1563c.Typelocality........................................................................................................................................1563d.Composite-stratotype..........................................................................................................................1563e.Referencesections................................................................................................................................1563f.Stratotypedescriptions........................................................................................................................1563Article9.UnitDescription........................................................................................................................................1563Article10.Boundaries...............................................................................................................................................1563Remarks:a.Boundariesbetweenintergradationalunits..........................................................................................1563b.Overlapsandgaps...............................................................................................................................1563Article11.HistoricalBackground.............................................................................................................................1564Article12.DimensionsandRegionalRelations........................................................................................................1564Article13.Age..........................................................................................................................................................1564Remarks:a.Dating..................................................................................................................................................1564b.Calibration...........................................................................................................................................1564c.Conventionandabbreviations.............................................................................................................1564d.Expressionofageoflithodemicunits..............................................................................................1564Article14.Correlation..............................................................................................................................................1564Article15.Genesis....................................................................................................................................................1564Article16.SurfaceandSubseaUnits........................................................................................................................1564Remarks:a.Namingsubsurfaceunits......................................................................................................................1564b.Additionalrecommendations...............................................................................................................1564c.Seismostratigraphicunits.....................................................................................................................1564REVISIONANDABANDONMENTOFFORMALUNITS...........................................................................................1Article17.RequirementsforMajorChanges............................................................................................................1565Remark:a.Distinctionbetweenredefinitionandrevision.......................................................................................1565Article18.Redefinition.............................................................................................................................................1565Remarks:a.Changeinlithicdesignation................................................................................................................1565b.Originallithicdesignationinappropriate.............................................................................................1565Article19.Revision...................................................................................................................................................1565Remarks:a.Boundarychange.................................................................................................................................1565b.Changeinrank....................................................................................................................................1565c.Examplesofchangesfromareatoarea...............................................................................................1565d.Exampleofchangeinsinglearea.........................................................................................................1565e.Retentionoftypesection....................................................................................................................1565f.Differentgeographicnameforaunitanditsparts..............................................................................1565g.Undesirablerestriction.........................................................................................................................1565Article20.Abandonment..........................................................................................................................................1565Remarks:a.Reasonsforabandonment.....................................................................................................................1565b.Abandonednames...............................................................................................................................1565c.Obsoletenames...................................................................................................................................1565d.Referencetoabandonednames............................................................................................................1566e.Reinstatement......................................................................................................................................1566CODEAMENDMENT..............................................................................................................................................1566Article21.ProcedureforAmendment......................................................................................................................1566FORMALUNITSDISTINGUISHEDBYCONTENT,PROPERTIES,ORPHYSICALLIMITS....................................1566LITHOSTRATIGRAPHICUNITS.................................................................................................................................1566NatureandBoundaries................................................................................................................................................1566Article22.NatureofLithostratigraphicUnits..........................................................................................................1566Remarks:a.Basicunits............................................................................................................................................1566b.Typesectionandlocality.....................................................................................................................1566c.Typesectionneverchanged.................................................................................................................1566d.Independencefrominferredgeologichistory......................................................................................NorthAmericanCommissiononStratigraphicNomenclature e.Independencefromtimeconcepts.......................................................................................................1566f.Surfaceform........................................................................................................................................1566g.Economicallyexploitedunits...............................................................................................................1566h.Instrumentallydefinedunits................................................................................................................1566i.Zone....................................................................................................................................................1567j.Cyclothems..........................................................................................................................................1567k.Soilsandpaleosols................................................................................................................................1567l.Depositionalfacies...............................................................................................................................1567Article23.Boundaries...............................................................................................................................................1567Remarks:a.Boundaryinaverticallygradationalsequence......................................................................................1567b.Boundariesinlaterallithologicchange..................................................................................................1567c.Keybedsusedforboundaries...............................................................................................................1567d.Unconformitiesasboundaries..............................................................................................................1567e.Correspondencewithgeneticunits.......................................................................................................1567RanksofLithostratigraphicUnits.................................................................................................................................1567Article24.Formation................................................................................................................................................1567Remarks:a.Fundamentalunit.................................................................................................................................1567b.Content...............................................................................................................................................1567c.Lithiccharacteristics............................................................................................................................1567d.Mappabilityandthickness...................................................................................................................1569e.Organicreefsandcarbonatemounds....................................................................................................1569f.Interbeddedvolcanicandsedimentaryrock..........................................................................................1569g.Volcanicrock.......................................................................................................................................1569h.Metamorphicrock...............................................................................................................................1569Article25.Member...................................................................................................................................................1569Remarks:a.Mappingofmembers............................................................................................................................1569b.Lensandtongue...................................................................................................................................1569c.Organicreefsandcarbonatemounds....................................................................................................1569d.Divisionofmembers............................................................................................................................1569e.Laterallyequivalentmembers..............................................................................................................1569Article26.Bed(s)......................................................................................................................................................1569Remarks:a.Limitations...........................................................................................................................................1569b.Keyormarkerbeds.............................................................................................................................1569Article27.Flow.........................................................................................................................................................1569Article28.Group......................................................................................................................................................1569Remarks:a.Useandcontent...................................................................................................................................1569b.Changeincomponentformations.......................................................................................................1569c.Changeinrank.....................................................................................................................................1570Article29.Supergroup..............................................................................................................................................1570Remark:a.Misuseofseriesforgrouporsupergroup..........................................................................................1570LithostratigraphicNomenclature.................................................................................................................................1570Article30.CompoundCharacter..............................................................................................................................1570Remarks:a.Omissionofpartofaname...................................................................................................................1570b.Useofsimplelithicterms....................................................................................................................1570c.Groupnames.......................................................................................................................................1570d.Formationnames..................................................................................................................................1570e.Membernames....................................................................................................................................1570f.Namesofreefs......................................................................................................................................1570g.Bedandflownames.............................................................................................................................1570h.Informalunits......................................................................................................................................1570i.Informalusageofidenticalgeographicnames.......................................................................................1570j.Metamorphicrock................................................................................................................................1570k.Misuseofwell-knownname.................................................................................................................1570LITHODEMICUNITS..................................................................................................................................................1570NatureandBoundaries.................................................................................................................................................1570Article31.NatureofLithodemicUnits.....................................................................................................................1570Remarks:a.Recognitionanddefinition....................................................................................................................1570NorthAmericanStratigraphicCode b.Typeandreferencelocalities................................................................................................................1571c.Independencefrominferredgeologichistory.......................................................................................1571d.Useofzone......................................................................................................................................1571Article32.Boundaries...............................................................................................................................................1571Remark:a.Boundarieswithingradationalzones.....................................................................................................1571RanksofLithodemicUnits...........................................................................................................................................1571Article33.Lithodeme...............................................................................................................................................1571Remarks:a.Content................................................................................................................................................1571b.Lithiccharacteristics............................................................................................................................1571c.Mappability.........................................................................................................................................1572Article34.DivisionofLithodemes............................................................................................................................1572Article35.Suite........................................................................................................................................................1572Remarks:a.Purpose................................................................................................................................................1572b.Changeincomponentunits.................................................................................................................1572c.Changeinrank.....................................................................................................................................1572Article36.Supersuite................................................................................................................................................1572Article37.Complex..................................................................................................................................................1572Remarks:a.Useofcomplex................................................................................................................................1572b.Volcaniccomplex................................................................................................................................1572c.Structuralcomplex..............................................................................................................................1572d.Misuseofcomplex...........................................................................................................................1572Article38.MisuseofSeriesforSuite,Complex,orSupersuite............................................................................1572LithodemicNomenclature...........................................................................................................................................1572Article39.GeneralProvisions...................................................................................................................................1572Article40.LithodemeNames...................................................................................................................................1572Remarks:a.Lithicterm...........................................................................................................................................1572b.Intrusiveandplutonicrocks.................................................................................................................1572Article41.SuiteNames.............................................................................................................................................1573Article42.SupersuiteNames....................................................................................................................................1573MAGNETOSTRATIGRAPHICUNITS.........................................................................................................................1573NatureandBoundaries.................................................................................................................................................1573Article43.NatureofMagnetostratigraphicUnits......................................................................................................1573Remarks:a.Definition.............................................................................................................................................1573b.Contemporaneityofrockandremanentmagnetism............................................................................1573c.Designationsandscope........................................................................................................................1573Article44.DefinitionofMagnetopolarityUnit........................................................................................................1573Remarks:a.Nature.................................................................................................................................................1573b.Stratotype............................................................................................................................................1573c.Independencefrominferredhistory.....................................................................................................1573d.Relationtolithostratigraphicandbiostratigraphicunits.......................................................................15e.Relationofmagnetopolarityunitstochronostratigraphicunits............................................................1573Article45.Boundaries...............................................................................................................................................1573Remark:a.Polarity-reversalhorizonsandtransitionzones.....................................................................................1573RanksofMagnetopolarityUnits..................................................................................................................................1573Article46.FundamentalUnit...................................................................................................................................1573Remarks:a.Content................................................................................................................................................1573b.Thicknessandduration........................................................................................................................1574c.Ranks...................................................................................................................................................1574MagnetopolarityNomenclature...................................................................................................................................1574Article47.CompoundName....................................................................................................................................1574BIOSTRATIGRAPHICUNITS......................................................................................................................................1574Preamble.....................................................................................................................................................................1574Article48.FundamentalsofBiostratigraphy.............................................................................................................1574Remark:a.Uniqueness...........................................................................................................................................1574NatureandBoundaries.................................................................................................................................................1574Article49.NatureofBiostratigraphicUnits.............................................................................................................1574Remarks:a.Unfossiliferousrocks............................................................................................................................1574b.Contemporaneityofrocksandfossils..................................................................................................1574NorthAmericanCommissiononStratigraphicNomenclature c.Independencefromlithostratigraphicunits..........................................................................................1574d.Independencefromchronostratigraphicunits.....................................................................................Article50.KindsofBiostratigraphicUnits...............................................................................................................1574Remarks:a.Rangebiozone......................................................................................................................................1574b.Intervalbiozone...................................................................................................................................1574c.Lineagebiozone...................................................................................................................................1574d.Assemblagebiozone.............................................................................................................................1574e.Abundancebiozone.............................................................................................................................1574f.Hybridornewtypesofbiozones.........................................................................................................1575Article51.Boundaries...............................................................................................................................................1575Remark:a.Identificationofbiozones.....................................................................................................................1575Article52.[notused]................................................................................................................................................1576RanksofBiostratigraphicUnits....................................................................................................................................1576Article53.FundamentalUnit...................................................................................................................................1576Remarks:a.Scope...................................................................................................................................................1576b.Divisions..............................................................................................................................................1576c.Shortenedformsofexpression.............................................................................................................1576BiostratigraphicNomenclature....................................................................................................................................1576Article54.EstablishingFormalunits........................................................................................................................1576Remarks:a.Name...................................................................................................................................................1576b.Shorterdesignationsforbiozonenames...............................................................................................1576c.Revision...............................................................................................................................................1576d.Definingtaxa.......................................................................................................................................1576e.Referencesections................................................................................................................................1576PEDOSTRATIGRAPHICUNITS..................................................................................................................................1576NatureandBoundaries................................................................................................................................................1576Article55.NatureofPedostratigraphicUnits...........................................................................................................1576Remarks:a.Definition.............................................................................................................................................1577b.Recognition..........................................................................................................................................1577c.Boundariesandstratigraphicposition...................................................................................................1577d.Traceability..........................................................................................................................................1577e.Distinctionfrompedologicsoils...........................................................................................................1577f.Relationtosaproliteandotherweatheredmaterials............................................................................1577g.Distinctionfromotherstratigraphicunits.............................................................................................1577h.Independencefromtimeconcepts.......................................................................................................1578PedostratigraphicNomenclatureandUnit...................................................................................................................1578Article56.FundamentalUnit....................................................................................................................................1578Article57.Nomenclature..........................................................................................................................................1578Remarks:a.Compositegeosols................................................................................................................................1578b.Characterization..................................................................................................................................1578c.Proceduresforestablishingformalpedostratigraphicunits..................................................................1578ALLOSTRATIGRAPHICUNITS..................................................................................................................................1578NatureandBoundaries................................................................................................................................................1578Article58.NatureofAllostratigraphicUnits............................................................................................................1578Remarks:a.Purpose................................................................................................................................................1578b.Internalcharacteristics.........................................................................................................................1578c.Boundaries...........................................................................................................................................1578d.Mappability.........................................................................................................................................1578e.Typelocalityandextent.......................................................................................................................1578f.Relationtogenesis...............................................................................................................................1578g.Relationtogeomorphicsurfaces..........................................................................................................1578h.Relationtosoilsandpaleosols.............................................................................................................1578i.Relationtoinferredgeologichistory....................................................................................................1578j.Relationtotimeconcepts....................................................................................................................1578k.Extensionofallostratigraphicunits......................................................................................................1578RanksofAllostratigraphicUnits..................................................................................................................................1578Article59.Hierarchy.................................................................................................................................................1578Remarks:a.Alloformation......................................................................................................................................1578NorthAmericanStratigraphicCode b.Allomember.........................................................................................................................................1578c.Allogroup.............................................................................................................................................1578d.Changesinrank....................................................................................................................................1579AllostratigraphicNomenclature...................................................................................................................................1579Article60.Nomenclature..........................................................................................................................................1579Remark:a.Revision...............................................................................................................................................1579FORMALUNITSEXPRESSINGORRELATINGTOGEOLOGICAGE.....................................................................1579KINDSOFGEOLOGIC-TIMEUNITS.........................................................................................................................1579NatureandKinds.........................................................................................................................................................1579Article61.Kinds.......................................................................................................................................................1579UnitsBasedonMaterialReferents................................................................................................................................1580Article62.KindsBasedonReferents.........................................................................................................................1580Article63.IsochronousCategories............................................................................................................................1580Remark:a.Extent..................................................................................................................................................1580Article64.DiachronousCategories.............................................................................................................................1580Remarks:a.Diachroneity........................................................................................................................................1580b.Extent..................................................................................................................................................1581UnitsIndependentofMaterialReferents......................................................................................................................1581Article65.NumericalDivisionsofTime.....................................................................................................................1581CHRONOSTRATIGRAPHICUNITS...........................................................................................................................1581NatureandBoundaries.................................................................................................................................................1581Article66.Definition................................................................................................................................................1581Remarks:a.Purposes...............................................................................................................................................1581b.Nature.................................................................................................................................................1581c.Content...............................................................................................................................................1581Article67.Boundaries...............................................................................................................................................1581Remark:a.Emphasisonlowerboundariesofchronostratigraphicunits..................................................................1Article68.Correlation..............................................................................................................................................1581RanksofChronostratigraphicUnits.............................................................................................................................1581Article69.Hierarchy.................................................................................................................................................1581Article70.Eonothem................................................................................................................................................1581Article71.Erathem...................................................................................................................................................1581Remark:a.Names..................................................................................................................................................1581Article72.System.....................................................................................................................................................1582Remark:a.Subsystemandsupersystem..................................................................................................................1582Article73.Series.......................................................................................................................................................1582Article74.Stage........................................................................................................................................................1582Remark:a.Substage...............................................................................................................................................1582Article75.Chronozone.............................................................................................................................................1582Remarks:a.Boundariesofchronozones..................................................................................................................1582b.Scope...................................................................................................................................................1582c.Practicalutility.....................................................................................................................................1582ChronostratigraphicNomenclature.............................................................................................................................1582Article76.Requirements..........................................................................................................................................1582Article77.Nomenclature..........................................................................................................................................1582Remarks:a.Systemsandunitsofhigherrank...........................................................................................................1582b.Seriesandunitsoflowerrank..............................................................................................................1582Article78.Stratotypes...............................................................................................................................................1582Article79.RevisionofUnits......................................................................................................................................1583GEOCHRONOLOGICUNITS.....................................................................................................................................1583NatureandBoundaries.................................................................................................................................................1583Article80.DefinitionandBasis.................................................................................................................................1583RanksandNomenclatureofGeochronologicUnits......................................................................................................1583Article81.Hierarchy.................................................................................................................................................1583Article82.Nomenclature..........................................................................................................................................1583NorthAmericanCommissiononStratigraphicNomenclature POLARITY-CHRONOSTRATIGRAPHICUNITS........................................................................................................1583NatureandBoundaries.................................................................................................................................................1583Article83.Definition................................................................................................................................................1583Remarks:a.Nature..................................................................................................................................................1583b.Principalpurposes................................................................................................................................1583c.Recognition..........................................................................................................................................1583Article84.Boundaries...............................................................................................................................................1583RanksandNomenclatureofPolarity-ChronostratigraphicUnits..................................................................................1583Article85.FundamentalUnit....................................................................................................................................1583Remarks:a.Meaningofterm..................................................................................................................................1583b.Scope...................................................................................................................................................1583c.Ranks...................................................................................................................................................1583Article86.EstablishingFormalUnits.........................................................................................................................1583Article87.Name.......................................................................................................................................................1583Remarks:a.Preservationofestablishedname..........................................................................................................1583b.Expressionofdoubt.............................................................................................................................1584POLARITY-CHRONOLOGICUNITS.........................................................................................................................1584NatureandBoundaries................................................................................................................................................1584Article88.Definition................................................................................................................................................1584RanksandNomenclatureofPolarity-ChronologicUnits.............................................................................................1584Article89.FundamentalUnit...................................................................................................................................1584Remark:a.Hierarchy.............................................................................................................................................1584Article90.Nomenclature..........................................................................................................................................1584DIACHRONICUNITS..................................................................................................................................................1584NatureandBoundaries................................................................................................................................................1584Article91.Definition................................................................................................................................................1584Remarks:a.Purposes...............................................................................................................................................1584b.Scope...................................................................................................................................................1584c.Basis.....................................................................................................................................................1584d.Duration..............................................................................................................................................1584Article92.Boundaries...............................................................................................................................................1584Remark:a.Temporalrelations...............................................................................................................................1584RanksandNomenclatureofDiachronicUnits.............................................................................................................1584Article93.Ranks.......................................................................................................................................................1584Remarks:a.Diachron..............................................................................................................................................1584b.Hierarchicalorderingpermissible.........................................................................................................1584c.Episode................................................................................................................................................1584Article94.Name.......................................................................................................................................................1585Remarks:a.Formaldesignationofunits.................................................................................................................1585b.Interregionalextensionofgeographicnames......................................................................................c.Changefromgeochronologictodiachronicclassification.....................................................................1585Article95.EstablishingFormalUnits........................................................................................................................1585Remark:a.Revisionorabandonment.....................................................................................................................1585GEOCHRONOMETRICUNITS...................................................................................................................................1585NatureandBoundaries.................................................................................................................................................1585Article96.Definition................................................................................................................................................1585RanksandNomenclatureofGeochronometricUnits..................................................................................................1586Article97.Nomenclature..........................................................................................................................................1586PARTIII.ADDENDAREFERENCES.................................................................................................................................................................1586I.PARTICIPANTSANDCONFEREESINCODEREVISION..................................................................................1587II.19772002COMPOSITIONOFTHENORTHAMERICANCOMMISSIONONSTRATIGRAPHICNOMENCLATUREIII.REPORTSANDNOTESOFTHEAMERICANCOMMISSIONONSTRATIGRAPHICNOMENCLATURE....15891.Classesofunitsdefined............................................................................................................................................15572.CategoriesandranksofunitsdefinedinthisCode..................................................................................................1562NorthAmericanStratigraphicCode 1.Relationofgeologictimeunitstothekindsofrock-unitreferentsonwhichmostarebased..................................15582.Diagrammaticexamplesoflithostratigraphicboundariesandclassification.............................................................15683.Lithodemicandlithostratigraphicunits...................................................................................................................15714.Examplesofrange,lineage,andintervalbiozones....................................................................................................15755.Examplesofassemblageandabundancebiozones...................................................................................................15766.Relationbetweenpedostratigraphicunitsandpedologicprofiles..............................................................................15777.Exampleofallostratigraphicclassificationofalluvialandlacustrinedepositsinagraben........................................15798.Exampleofallostratigraphicclassificationofcontiguousdepositsofsimilarlithology..............................................15799.Exampleofallostratigraphicclassificationoflithologicallysimilar,discontinuousterracedeposits..........................158010.Comparisonofgeochronologic,chronostratigraphic,anddiachronicunits...............................................................158411.Schematicrelationofphasestoanepisode..............................................................................................................1585PARTI.PREAMBLEBACKGROUNDPERSPECTIVECodesofStratigraphicNomenclaturepreparedbytheNorthAmericanCommissiononStratigraphicNomencla-turein1983,theAmericanCommissiononStratigraphicNomenclature(ACSN,1961),anditspredecessor(Com-mitteeonStratigraphicNomenclature,1933)havebeenusedwidelyasabasisforstratigraphicterminology.Theirformu-lationwasaresponsetoneedsrecognizedduringthepastcenturybygovernmentsurveys(bothnationalandlocal)andbyeditorsofscientificjournalsforuniformstandardsandcommonproceduresindefiningandclassifyingformalrockbodies,theirfossils,andthetimespansrepresentedbythem.The1970Code(ACSN,1970)isaslightlyrevisedversionofthatpublishedin1961,incorporatingsomeminoramendmentsadoptedbytheCommissionbetween1962and1969.The2005editionofthe1983CodeincorporatesamendmentsadoptedbytheCommissionbetween1983and2003.TheCodeshaveservedtheprofessionadmirablyandhavebeendrawnuponheavilyforcodesandguidespre-paredinotherpartsoftheworld(ISSC,1976,p.104106;1994,p.143147).Theprinciplesembodiedbyanycode,however,reflectthestateofknowledgeatthetimeofitsNewconceptsandtechniquesdevelopedsince1961haverevolutionizedtheearthsciences.Moreover,increasinglyevi-denthavebeenthelimitationsofpreviouscodesinmeetingsomeneedsofPrecambrianandQuaternarygeologyandinclassificationofplutonic,high-grademetamorphic,volcanic,andintenselydeformedrockassemblages.Inaddition,theim-portantcontributionsofnumerousinternationalstratigraphicorganizationsassociatedwithboththeInternationalUnionofGeologicalSciences(IUGS)andUNESCO,includingwork-inggroupsoftheInternationalGeologicalCorrelationPro-gramme(IGCP),meritrecognitionandincorporationintoaNorthAmericancode.Fortheseandotherreasons,revisionofthe1970CodewasundertakenbycommitteesappointedbytheNorthAmeri-canCommissiononStratigraphicNomenclature(NACSN).TheCommission,foundedastheAmericanCommissiononStratigraphicNomenclaturein1946(ACSN,1947),wasrenamedtheNACSNin1978(Weiss,1979b)toemphasizethatdelegatesfromtenorganizationsinCanada,theUnitedStates,andMexicorepresentthegeologicalprofessionthrough-outNorthAmerica(AppendixII).AlthoughmanypastandcurrentmembersoftheCom-missionhelpedpreparethe1983Code,theparticipationofallinterestedgeologistswassought(forexample,Weiss,1979a).OpenforumswereheldatthenationalmeetingsofboththeGeologicalSocietyofAmericaatSanDiegoinNovember,1979,andtheAmericanAssociationofPetro-leumGeologistsatDenverinJune,1980,atwhichcom-mentsandsuggestionswereofferedbymorethan150ge-ologists.Theresultingdraftofthisreportwasprinted,throughthecourtesyoftheCanadianSocietyofPetroleumGeologists,onOctober1,1981,andadditionalcommentswereinvitedfromtheprofessionforaperiodofoneyearbeforesubmittalofthisreporttotheCommissionforadop-tion.Morethan50responseswerereceivedwithsufficientsuggestionsforimprovementtopromptmoderaterevisionoftheprinteddraft(NACSN,1981).Weareparticularlyin-debtedtoHollisD.HedbergandAmosSalvadorfortheirexhaustiveandperceptivereviewsofearlydraftsofthisCode,aswellastothosewhorespondedtotherequestforcomments.Participantsinthepreparationandrevisionsofthisreport,andconferees,arelistedinAppendixI.Recentamendmentstothe1983Codeincludeallowingelectronicpublicationofnewandrevisednamesandcorrectinginconsistenciestoimproveclarity(Ferrusqu´a-Villafrancaetal.,2001).Also,theBiostratigraphicUnitssection(Articles48to54)wasrevised(Lenzetal.,2001).SomeoftheexpensesincurredinthecourseofthisworkweredefrayedbyNationalScienceFoundationGrantEAR7919845,forwhichweexpressappreciation.Institu-tionsrepresentedbytheparticipantshavebeenespeciallygenerousintheirsupport.SCOPETheNorthAmericanStratigraphicCodeseekstodescribeexplicitpracticesforclassifyingandnamingallformallydefinedgeologicunits.Stratigraphicproceduresprinciples,althoughdevelopedinitiallytobringordertostrataandtheeventsrecordedtherein,areapplicabletoallearthmaterials,notsolelytostrata.TheypromotesystematicandNorthAmericanCommissiononStratigraphicNomenclature rigorousstudyofthecomposition,geometry,sequence,his-tory,andgenesisofrocksandunconsolidatedmaterials.TheyprovidetheframeworkwithinwhichtimeandspacerelationsamongrockbodiesthatconstitutetheEarthareorderedsys-tematically.StratigraphicproceduresareusednotonlytoreconstructthehistoryoftheEarthandofextra-terrestrialbodies,butalsotodefinethedistributionandgeometryofsomecommoditiesneededbysociety.Stratigraphicclassifica-systematicallyarrangesandpartitionsbodiesofrockorunconsolidatedmaterialsoftheEarthscrustintounitsonthebasisoftheirinherentpropertiesorattributes.stratigraphiccodeorguideisaformulationofcurrentviewsonstratigraphicprinciplesandproceduresdesignedtopromotestandardizedclassificationandformalnomencla-tureofrockmaterials.Itprovidesthebasisforformalizationofthelanguageusedtodenoterockunitsandtheirspatialandtemporalrelations.Tobeeffective,acodemustbewidelyac-ceptedandused;geologicorganizationsandjournalsmayadoptitsrecommendationsfornomenclaturalprocedure.Becauseanycodeembodiesonlycurrentconceptsandprinciples,itshouldhavetheflexibilitytoprovideforbothchangesandadditionstoimproveitsrelevancetonewscientificproblems.Anysystemofnomenclaturemustbesufficientlyex-plicittoenableuserstodistinguishobjectsthatareembracedinaclassfromthosethatarenot.Thisstratigraphiccodemakesnoattempttosystematizestructural,petrographic,paleontologic,orphysiographicterms.Termsfromtheseotherfieldsthatareusedaspartofformalstratigraphicnamesshouldbesufficientlygeneralastobeunaffectedbyrevisionsofprecisepetrographicorotherclassifications.Theobjectiveofasystemofclassificationistopromoteunambiguouscommunicationinamannernotsorestrictiveastoinhibitscientificprogress.Tominimizeambiguity,acodemustpromoterecognitionofthedistinctionbetweenobservablefeatures(reproducibledata)andinferencesorinterpretations.Moreover,itshouldbesufficientlyadaptableandflexibletopromotethefurtherdevelopmentofscience.Stratigraphicclassificationpromotesunderstandingofgeometrysequenceofrockbodies.ThedevelopmentofstratigraphyasasciencerequiredformulationoftheLawofSuperpositiontoexplainsequentialstratalrelations.Al-thoughsuperpositionisnotapplicabletomanyigneous,meta-morphic,andtectonicrockassemblages,othercriteria(suchascross-cuttingrelationsandisotopicdating)canbeusedtodeterminesequentialarrangementsamongrockbodies.Thetermstratigraphicunitmaybedefinedinseveralways.Etymologicalemphasisrequiresthatitbeastratumorassemblageofadjacentstratadistinguishedbyanyorseveralofthemanypropertiesthatrocksmaypossess(ISSC,1976,p.13;1994,p.1314).Thescopeofstratigraphicclassi-ficationandprocedures,however,suggestsabroaderdefi-nition:anaturallyoccurringbodyofrockorrockmaterialdistinguishedfromadjoiningbodiesofrockonthebasisofsomestatedpropertyorproperties.Commonlyusedprop-ertiesincludecomposition,texture,includedfossils,mag-neticsignature,radioactivity,seismicvelocity,andage.Suf-ficientcareisrequiredindefiningtheboundariesofaunittoenableotherstodistinguishthematerialbodyfromthoseadjoiningit.Unitsbasedononepropertycommonlydonotcoincidewiththosebasedonanotherand,therefore,dis-tinctivetermsareneededtoidentifythepropertyusedindefiningeachunit.Theadjectivestratigraphicisusedintwowaysintheremainderofthisreport.Indiscussionsoflithic(usedhereassynonymouswithlithologic)units,aconsciousattemptismadetorestrictthetermtolithostratigraphicorlayeredrocksandsequencesthatobeytheLawofSuperposition.Fornonstratiformrocks(ofplutonicortectonicorigin,forex-ample),thetermlithodemic(seeArticle27)isused.Thead-jectivestratigraphicisalsousedinabroadersensetorefertothoseproceduresderivedfromstratigraphythatarenowappliedtoallclassesofearthmaterials.Anassumptionmadeinthematerialthatfollowsisthatthereaderhassomedegreeoffamiliaritywithbasicprin-ciplesofstratigraphyasoutlined,forexample,byDunbarandRodgers(1957),Weller(1960),Shaw(1964),Matthews(1974),Blattetal.(1990),Boggs(2001),ortheInterna-tionalStratigraphicGuide(ISSC,1976,1994).RELATIONOFCODESTOINTERNATIONALGUIDEPublicationoftheInternationalStratigraphicGuidebytheInternationalSubcommissiononStratigraphicClassifi-cation(ISSC,1976),whichisbeingendorsedandadoptedthroughouttheworld,playedapartinpromptingexami-nationoftheAmericanStratigraphicCodeandthedecisiontoreviseit.TheInternationalGuideembodiesprinciplesandpro-ceduresthathadbeenadoptedbyseveralnationalandre-gionalstratigraphiccommitteesandcommissions.MorethantwodecadesofeffortbyH.D.HedbergandothermembersoftheSubcommission(ISSC,1976,p.VI,1,3)developedtheconsensusrequiredforpreparationoftheGuide.Al-thoughtheGuideattemptstocoverallkindsofrocksandthediversewaysofinvestigatingthem,itisnecessarilyincomplete.Mechanismsareneededtostimulateindividualinnovationstowardpromulgatingnewconcepts,principles,andpracticesthatsubsequentlymaybefoundworthyofinclusioninlatereditionsoftheGuide.Theflexibilityofnationalandregionalcommitteesorcommissionsenablesthemtoperformthisfunctionmorereadilythananinter-nationalsubcommission,evenwhiletheyadopttheGuideastheinternationalstandardofstratigraphicclassification.AguidingprincipleinpreparingthisCodehasbeentomakeitasconsistentaspossiblewiththeInternationalGuide,andatthesametimetofosterfurtherinnovationstomeettheexpandingandchangingneedsofearthscientistsontheNorthAmericancontinent.CATEGORIESRECOGNIZEDAnattemptismadetostrikeabalancebetweenservingtheneedsofthoseinevolvingspecialtiesandresistingtheproliferationofcategoriesofunits.Consequently,additionalNorthAmericanStratigraphicCode formalcategoriesarerecognizedhererelativetopreviouscodesorintheInternationalGuide(ISSC,1994).Ontheotherhand,nospecialprovisionismadeforformalizingcer-tainkindsofunits(deepoceanic,forexample)thatmaybeaccommodatedbyavailablecategories.Fourprincipalcategoriesofunitshavepreviouslybeenusedwidelyintraditionalstratigraphicwork;thesehavebeentermedlithostratigraphic,biostratigraphic,chronostratigraph-ic,andgeochronologicandaredistinguishedasfollows:1.Alithostratigraphicunitisastratumorbodyofstrata,generallybutnotinvariablylayered,generallybutnotin-variablytabular,thatconformstotheLawofSuperposi-tionandisdistinguishedanddelimitedonthebasisoflithiccharacteristicsandstratigraphicposition.Example:NavajoSandstone.2.Abiostratigraphicunitisabodyofrockdefinedandcharacterizedbyitsfossilcontent.Example:Discoastermulti-radiatusIntervalBiozone.3.Achronostratigraphicunitisabodyofrockestab-lishedtoserveasthematerialreferenceforallrocksformedduringthesamespanoftime.Example:DevonianSystem.Eachboundaryofachronostratigraphicunitissynchronous.Chronostratigraphyprovidesameansoforganizingstrataintounitsbasedontheiragerelations.Achronostratigraphicbodyalsoservesasthebasisfordefiningthespecificintervalofgeologictime,orgeochronologicunit,representedbythe4.Ageochronologicunitisadivisionoftimedistinguishedonthebasisoftherockrecordpreservedinachronostrati-graphicunit.Example:DevonianPeriod.Thefirsttwocategoriesarecomparableinthattheyconsistofmaterialunitsdefinedonthebasisofcontent.Thethirdcategorydiffersfromthefirsttwointhatitservesprimarilyasthestandardforrecognizingandisolatingma-terialsofaspecificage.Thefourth,incontrast,isnotama-terial,butratheraconceptual,unit;itisadivisionoftime.Althoughageochronologicunitisnotastratigraphicbody,itissointimatelytiedtochronostratigraphythatthetwoarediscussedproperlytogether.Propertiesandproceduresthatmaybeusedindistin-guishinggeologicunitsarebothdiverseandnumerous(ISSC,1976,p.1,96;1994,p.102103;Harland,1977,p.230),butallmaybeassignedtothefollowingprincipalclassesofcate-goriesusedinstratigraphicclassification(Table1),whicharediscussedbelow:I.Materialcategoriesbasedoncontent,inherentat-tributes,orphysicallimitsII.CategoriesexpressingorrelatedtogeologicageA.MaterialcategoriesusedtodefinetemporalspansB.Temporal(non-material)categoriesMaterialCategoriesBasedonContentorPhysicalLimitsThebasicbuildingblocksformostgeologicworkarerockbodies,definedonthebasisofcompositionandrelatedlithiccharacteristics,orontheirphysical,chemical,orbiologiccontentorproperties.Emphasisisplacedontherelativeob-jectivityandreproducibilityofdatausedindefiningunitswithineachcategory.Foremostpropertiesofrocksarecomposition,texture,fabric,structure,andcolor,whichtogetheraredesignatedlithiccharacteristics.Theseserveasthebasisfordistinguish-inganddefiningthemostfundamentalofallformalunits.Suchunitsbasedprimarilyoncompositionaredividedintotwocategories(Hendersonetal.,1980):lithostratigraphic(Article22)andlithodemic(definedhereinArticle31).AlithostratigraphicunitobeystheLawofSuperposition,whereasalithodemicunitdoesnot.Alithodemicunitisadefinedbodyofpredominantlyintrusive,highlymetamorphosed,orin-tenselydeformedrockthat,becauseitisintrusiveorhaslostprimarystructurethroughmetamorphismortectonism,generallydoesnotconformtotheLawofSuperposition.Recognitionduringthepastseveraldecadesthatrema-nentmagnetisminrocksrecordstheEarthspastmagneticcharacteristics(Cox,etal.,1963)providesapowerfulnewtoolencompassedbymagnetostratigraphy(McDougall,1977;McElhinny,1978).Magnetostratigraphy(Article43)isthestudyofremanentmagnetisminrocks;itistherecordoftheEarthsmagneticpolarity(orfieldreversals),dipole-field-poleposition(includingapparentpolarwander),thenon-dipolecomponent(secularvariation),andfieldintensi-ty.Polarityisofparticularutilityandisusedtodefineamagnetopolarityunit(Article44)asabodyofrockidenti-fiedbyitsremanentmagneticpolarity(ACSN,1976;ISSC,1979).Empiricaldemonstrationofuniformpolaritydoesnotnecessarilyhavedirecttemporalconnotationsbecausetheremanentmagnetismneednotberelatedtorockdepo-sitionorcrystallization.Nevertheless,polarityisaphysicalattributethatmaycharacterizeabodyofrock.Biologicremainscontainedin,orforming,strataareuniquelyimportantinstratigraphicpractice.First,theypro-videthemeansofdefiningandrecognizingmaterialunits Table1.ClassesofUnitsDefined*I.MATERIALCATEGORIESBASEDONCONTENTORPHYSICALLithostratigraphic(22)*Biostratigraphic(48)Pedostratigraphic(55)II.CATEGORIESEXPRESSINGORRELATEDTOGEOLOGICAGEA.MaterialCategoriesUsedtoDefineTemporalSpansChronostratigraphic(66)B.Temporal(Non-Material)CategoriesGeochronologic(80)*NumbersinparenthesesarethenumbersoftheArticleswhereunitsare**Italicizedcategoriesarethoseintroducedordevelopedsincepublicationofthepreviouscode(ACSN,1970).NorthAmericanCommissiononStratigraphicNomenclature basedonfossilcontent(biostratigraphicunits,Article48).Second,theirreversibilityoforganicevolutionmakesitpos-sibletopartitionenclosingstratatemporally.Third,biologicremainsprovideimportantdataforthereconstructionofancientenvironmentsofdeposition.Compositionalsoisimportantindistinguishingpedo-stratigraphicunits.Apedostratigraphicunitisabodyofrockthatconsistsofoneormorepedologichorizonsdevel-opedinoneormorelithicunitsnowburiedbyaformallydefinedlithostratigraphicorallostratigraphicunitorunits.Apedostratigraphicunitisthepartofaburiedsoilcharac-terizedbyoneormoreclearlydefinedsoilhorizonscontain-ingpedogenicallyformedmineralsandorganiccompounds.PedostratigraphicterminologyisdiscussedbelowandinArticle55.ManyupperCenozoic,especiallyQuaternary,depositsaredistinguishedanddelineatedonthebasisofcontent,forwhichlithostratigraphicclassificationisappropriate.How-ever,othersaredelineatedonthebasisofcriteriaotherthancontent.Tofacilitatethereconstructionofgeologichistory,somecompositionallysimilardepositsinverticalsequencemeritdistinctionasseparatestratigraphicunitsbecausetheyaretheproductsofdifferentprocesses;othersmeritdis-tinctionbecausetheyareofdemonstrablydifferentages.Lithostratigraphicclassificationoftheseunitsisimpracticalandanewapproach,allostratigraphicclassification,isintro-ducedhereandmayproveapplicabletoolderdepositsaswell.Anallostratigraphicunitisamappablebodyofrockdefinedandidentifiedonthebasisofboundingdisconti-nuities(Article58andrelatedRemarks).Geologic-Climateunits,definedinthe1970Code(ACSN,1970,p.31),wereabandonedinthe1983Codebecausetheyprovedtobeofdubiousutility.Inferencesregardingclimatearesubjectiveandtootenuousabasisforthedefinitionofformalgeologicunits.Suchinferencescommonlyarebasedondepositsassignedmoreappropriatelytolithostratigraphicorallostratigraphicunitsandmaybeexpressedintermsofdiachronicunits(definedbelow).CategoriesExpressingorRelatedtoGeologicAgeTimeisasingle,irreversiblecontinuum.Nevertheless,variouscategoriesofunitsareusedtodefineintervalsofgeo-logictime,justastermshavingdifferentbases,suchasPaleo-lithic,Renaissance,andElizabethan,areusedtodesignatespecificperiodsofhumanhistory.Differenttemporalcate-goriesareestablishedtoexpressintervalsoftimedistin-guishedindifferentways.Majorobjectivesofstratigraphicclassificationaretoprovideabasisforsystematicorderingofthetimeandspacerelationsofrockbodiesandtoestablishatimeframeworkforthediscussionofgeologichistory.Forsuchpurposes,unitsofgeologictimetraditionallyhavebeennamedtorep-resentthespanoftimeduringwhichawell-describedse-quenceofrock,orachronostratigraphicunit,wasdeposited(timeunitsbasedonmaterialreferents,Figure1).Thisprocedurecontinues,totheexclusionofotherpossibleap-proaches,tobestandardpracticeinstudiesofPhanerozoicrocks.DespiteadmonitionsinpreviousAmericancodesand Figure1.Relationofgeologictimeunitstothekindsofreferentsonwhichmostarebased.NorthAmericanStratigraphicCode theInternationalStratigraphicGuide(ISSC,1976,p.81;1994,p.87)thatsimilarproceduresshouldbeappliedtothePrecambrian,nocomparablechronostratigraphicunits,orgeochronologicunitsderivedtherefrom,proposedforthePrecambrianhaveyetbeenacceptedworldwide.Instead,theIUGSSubcommissiononPrecambrianStratigraphy(Sims,1979)anditsWorkingGroups(HarrisonandPeterman,1980)recommenddivisionofPrecambriantimeintochronometricunitshavingnomaterialreferents.Adistinctionismadethroughoutthisreportbetweenisochronoussynchronous,asurgedbyCummingetal.(1959,p.730),althoughthetermshavebeenusedsynony-mouslybymany.Isochronousmeansofequalduration;chronousmeanssimultaneous,oroccurringatthesametime.Althoughtworockbodiesofverydifferentagesmaybeformedduringequaldurationsoftime,thetermisochronousisnotappliedtothemintheearthsciences.Rather,iso-chronousbodiesarethoseboundedbysynchronoussur-facesandformedduringthesamespanoftime.incontrast,isusedforalineconnectingpointsofequalageonagraphrepresentingphysicalorchemicalphenomena;thelinerepresentsthesameorequaltime.Theadjectiveisappliedeithertoarockunitwithoneortwoboundingsurfacesthatarenotsynchronous,ortoaboundarythatisnotsynchronous(thattransgressestime).Twoclassesoftimeunitsbasedonmaterialreferents,orstratotypes,arerecognized(Figure1).Thefirstisthatofthetraditionalandconceptuallyisochronousunits,andincludesgeochronologicunits,whicharebasedonchronostratigraphicunits,andpolarity-chronologicunits.Theseisochronousunitshaveworldwideapplicabilityandmaybeusedeveninareaslackingamaterialrecordofthenamedspanoftime.Thesecondclassoftimeunits,newlydefinedinthisCode,con-sistsofdiachronicunits(Article91)thatarebasedonrockbodiesknowntobediachronous.Incontrasttoisochronousunits,adiachronictermisusedonlywhereamaterialrefer-entispresent;adiachronicunitiscoextensivewiththema-terialbodyorbodiesonwhichitisbased.chronostratigraphicunit,asdefinedaboveandinArticle66,isabodyofrockestablishedtoserveasthema-terialreferenceforallrocksformedduringthesamespanoftime;itsboundariesaresynchronous.Itisthereferentforageochronologicunit,asdefinedaboveandinArticle80.Inter-nationallyacceptedandtraditionalchronostratigraphicunitswerebasedinitiallyonthetimespansoflithostratigraphicunits,biostratigraphicunits,orotherfeaturesoftherockrecordthathavespecificdurations.Insum,theyformtheStandardGlobalChronostratigraphicScale(ISSC,1976,p.7681;1994,p.85;Harland,1978),consistingofestablishedsys-temsandseries.polarity-chronostratigraphicunitisabodyofrockthatcontainsaprimarymagnetopolarityrecordimposedwhentherockwasdepositedorcrystallized(Article83).ItservesasamaterialstandardorreferentforapartofgeologictimeduringwhichtheEarthsmagneticfieldhadacharacteristicpolarityorsequenceofpolarities;thatis,forapolarity-chronologicunit(Article88).diachronicunitcomprisestheunequalspansoftimerepresentedbyoneormorespecificdiachronousrockbodies(Article91).Suchbodiesmaybelithostratigraphic,biostrati-graphic,pedostratigraphic,allostratigraphic,oranassemblageofsuchunits.Adiachronicunitisapplicableonlywhereitsmaterialreferentispresent.geochronometric(orchronometric)isanisochro-nousdirectdivisionofgeologictimeexpressedinyears(Article96).Ithasnomaterialreferent.PedostratigraphicTermsThedefinitionandnomenclatureforpedostratigraphicunitsinthisCodedifferfromthoseforsoil-stratigraphicunitsinthe1970Code(ACSN,1970,Article18),bybeingmorespecificwithregardtocontent,boundaries,andthebasisfordeterminingstratigraphicposition.Thetermsoilhasdifferentmeaningstothegeologist,thesoilscientist,theengineer,andthelayman,andcom-monlyhasnostratigraphicsignificance.ThetermpaleosolcurrentlyusedinNorthAmericaforanysoilthatformedonalandscapeofthepast;itmaybeaburiedsoil,arelictsoil,oranexhumedsoil(Ruhe,1965;ValentineandDalrymple,1976).pedologicsoiliscomposedofoneormoresoilhorizonsAsoilhorizonisalayerwithinapedologicsoilthat(1)isapproximatelyparalleltothesoilsurface,(2)hasdistinc-tivephysical,chemical,biological,andmorphologicalprop-ertiesthatdifferfromthoseofadjacent,geneticallyrelated,soilhorizons,and(3)isdistinguishedfromothersoilhori-zonsbyobjectivecompositionalpropertiesthatcanbeob-servedormeasuredinthefield.Thephysicalboundariesofburiedpedologichorizonsareobjectivetraceableboundarieswithstratigraphicsignificance.Aburiedpedologicsoilpro-videsthematerialbasisfordefinitionofastratigraphicunitinpedostratigraphicclassification(Article55),butaburiedpedologicsoilmaybesomewhatmoreinclusivethanapedostratigraphicunit.ApedologicsoilmaycontainbothanOhorizonandtheentireChorizon(Figure6),whereastheformerisexcludedandthelatterneednotbeincludedinapedostratigraphicunit.ThedefinitionandnomenclatureforpedostratigraphicunitsinthisCodedifferfromthoseofsoilstratigraphicunitsproposedbytheInternationalUnionforQuaternaryRe-searchandInternationalSocietyofSoilScience(Parsons,1981).Thepedostratigraphicunit,geosol,alsodiffersfromtheproposedINQUA-ISSSsoil-stratigraphicunit,pedo-derm,inseveralways,themostimportantofwhicharethefollowing:(1)ageosolmaybeinanypartofthegeologiccolumn,whereasapedodermisasurficialsoil;(2)ageosolisaburiedsoil,whereasapedodermmaybeaburied,relict,orexhumedsoil;(3)theboundariesandstratigraphicpositionofageosolaredefinedanddelineatedbycriteriathatdifferfromthoseforapedoderm;and(4)ageosolmaybeeitheralloronlyapartofaburiedsoil,whereasapedodermistheentiresoil. FromGreek,,groundorsoil.Asusedinageologicalsense,aisasurfaceorline.Inpedology,however,itisabodyofmaterial,andsuchusageiscon-tinuedhere.NorthAmericanCommissiononStratigraphicNomenclature Thetermgeosol,asdefinedbyMorrison(1967,p.3),isalaterallytraceable,mappable,geologicweatheringprofilethathasaconsistentstratigraphicposition.Thetermisadoptedandredefinedhereasthefundamentalandonlyunitinformalpedostratigraphicclassification(Article56).FORMALANDINFORMALUNITSAlthoughtheCodeemphasizesformalcategoriesofgeologicunits,informalnomenclatureishighlyusefulinstratigraphicwork.Formallynamedunitsarethosethatarenamedinac-cordancewithanestablishedschemeofclassification;thefactofformalityisconveyedbycapitalizationoftheinitialletteroftheterm(forexample,MorrisonFormation).Informalunits,whoseunittermsareordinarynouns,arenotprotectedbythestabilityprovidedbyproperformalizationandrecommendedclassificationprocedures.Informaltermsaredevisedforbotheconomicandscientificreasons.For-malizationisappropriateforthoseunitsrequiringstabilityofnomenclature,particularlythoselikelytobeextendedfarbeyondthelocalityinwhichtheywerefirstrecognized.In-formaltermsareappropriateforcasuallymentionedandinnovativeunits.Also,mosteconomicunits,thosedefinedbyunconventionalcriteria,andthosethatmaybetoothintomapatusualscalesmaybeinformal.Casuallymentionedgeologicunitsnotdefinedinac-cordancewiththisCodeareinformal.Formanyofthese,theremaybeinsufficientneedorinformation,orperhapsaninappropriatebasis,forformaldesignations.Informaldes-ignationsasbedsorlithozones(thepebblybeds,theshalyzone,thirdcoal)areappropriateformanysuchunits.Mosteconomicunits,suchasaquifers,oilsands,coalbeds,quarrylayers,andore-bearingreefs,areinformal,eventhoughtheymaybenamed.Somesuchunits,however,aresosignificantscientificallyandeconomicallythattheymeritformalrecognitionasbeds,members,orformations.Innovativeapproachesinregionalstratigraphicstudieshaveresultedintherecognitionanddefinitionofunitsbestleftasinformal,atleastforthetimebeing.UnitsboundedbymajorregionalunconformitiesontheNorthAmericancratonweredesignatedsequences(example:Sauksequence)bySloss(1963).Majorunconformity-boundedunitsalsoweredesignatedsynthemsbyChang(1975),whorecom-mendedthattheybetreatedformally.Marker-definedunitsthatarecontinuousfromonelithofaciestoanotherweredesignatedformatsbyForgotson(1957).Thetermchro-nosomewasproposedbySchultz(1982)forrocksofdiversefaciescorrespondingtogeographicvariationsinsedimen-tationduringanintervalofdepositionidentifiedonthebasisofboundingstratigraphicmarkers.Successionsoffaunalzonescontainingevolutionallyrelatedforms,butboundedbynon-evolutionarybioticdiscontinuities,weretermedbiomeres(Palmer,1965).Theforegoingareonlyafewselectedexamplestodemonstratehowinformalityprovidesacontinuingavenueforinnovation.Thetermsmagnafaciesparvafacies,coinedbyCaster(1934)toemphasizethedistinctionbetweenlithostratigraphicandchronostratigraphicunitsinsequencesdisplayingmarkedfaciesvariation,haveremainedinformaldespitetheirimpactonclarifyingtheconceptsinvolved.Tephrochronologicstudiesprovideexamplesofinfor-malunitsthataretoothintomapatconventionalscalesbutyetinvaluablefordatingimportantgeologicevents.Althoughsomesuchunitsarenamedforphysiographicfeaturesandplaceswherefirstrecognized(e.g.,Guajepumicebed,whereitisnotmappedastheGuajeMemberoftheBandelierTuff),othersbearthesamenameasthevolcanicvent(e.g.,HuckleberryRidgeashbedofIzettandWilcox,1981).Informalgeologicunitsaredesignatedbyordinarynouns,adjectives,orgeographictermsandlithicorunittermsthatarenotcapitalized(chalkyformationorbeds,St.Franciscoal).Nogeologicunitshouldbeestablishedanddefined,whetherformallyorinformally,unlessitsrecognitionservesaclearpurpose.CORRELATIONCorrelationisaprocedurefordemonstratingcorrespon-dencebetweengeographicallyseparatedpartsofageologicunit.Thetermisageneralonehavingdiversemeaningsindifferentdisciplines.Demonstrationoftemporalcorre-spondenceisoneofthemostimportantobjectivesofstratig-raphy.Thetermfrequentlyismisusedtoexpresstheideathataunithasbeenidentifiedorrecognized.CorrelationisusedinthisCodeasthedemonstrationofcorrespondencebetweentwogeologicunitsinbothsomedefinedpropertyandrelativestratigraphicposition.Becausecorrespondencemaybebasedonvariousproperties,threekindsofcorrelationarebestdistinguishedbymorespecificterms.Lithocorrelationlinksunitsofsimilarlithologyandstratigraphicposition(orsequentialorgeometricrelationforlithodemicunits).Biocorrelationexpressessimilarityoffos-silcontentandbiostratigraphicposition.Chronocorrelationexpressescorrespondenceinageandinchronostratigraphicposition.Othertermsthathavebeenusedforthesimilarityofcontentandstratalsuccessionarehomotaxyandchronotaxy.Homotaxyisthesimilarityinseparateregionsoftheserialarrangementorsuccessionofstrataofcomparablecomposi-tionsorofincludedfossils.Thetermisderivedfromtaxis,proposedbyHuxley(1862,p.xlvi)toemphasizethatsimilarityinsuccessiondoesnotproveageequivalenceofcomparableunits.Thetermchronotaxyhasbeenappliedtosimilarstratigraphicsequencescomposedofunitsthatareofequivalentage(Henbest,1952,p.310).Criteriausedforascertainingtemporalandothertypesofcorrespondencearediverse(ISSC,1976,p.8693;1994,p.9297)andnewcriteriawillemergeinthefuture.Evolvingstatisticaltests,aswellasisotopicandpaleomag-netictechniques,complementthetraditionalpaleonto-logicandlithologicprocedures.BoundariesdefinedbyonesetofcriterianeednotcorrespondtothosedefinedbyNorthAmericanStratigraphicCode PARTII.ARTICLESINTRODUCTIONArticle1.Purpose.ThisCodedescribesexplicitstrati-graphicproceduresforclassifyingandnaminggeologicunitsaccordedformalstatus.Suchprocedures,ifwidelyadopted,assureconsistentanduniformusageinclassificationandtermi-nologyand,therefore,promoteunambiguouscommunication.Article2.Categories.Categoriesofformalstratigraphicunits,thoughdiverse,areofthreeclasses.Thefirstclass(IonTable1)isofrock-materialcategoriesbasedoncontent,in-herentattributes,orphysicallimits,andincludeslitho-stratigraphic,lithodemic,magnetopolarity,biostratigraphic,pedostratigraphic,andallostratigraphicunits.Thesecondclass(IIAonTable1)isofmaterialcategoriesusedasstandardsfordefiningspansofgeologictime,andincludeschronostrati-graphicandpolarity-chronostratigraphicunits.Thethirdclass(IIBonTable1)isofnon-materialtemporalcategories,andincludesgeochronologic,polarity-chronologic,diachronic,andgeochronometricunits.GENERALPROCEDURESDEFINITIONOFFORMALUNITSArticle3.RequirementsforFormallyNamedGeologicUnits.Naming,establishing,revising,redefining,andaban-doningformalgeologicunitsrequirepublicationinarecog-nizedscientificmediumofacomprehensivestatement,whichincludes(i)intenttodesignateormodifyaformalunit;(ii)designationofcategoryandrankofunit;(iii)selectionandderivationofname;(iv)specificationofstratotype(whereapplicable);(v)descriptionofunit;(vi)definitionofbound-aries;(vii)historicalbackground;(viii)dimensions,shape,andotherregionalaspects;(ix)geologicage;(x)correlations;andpossibly(xi)genesis(whereapplicable).Theserequirementsapplytosubsurfaceandoffshore,aswellasexposed,units.Article4.Publication.PublicationinarecognizedscientificmediuminconformancewiththisCodemeansthatawork,whenfirstissued,must(1)bereproducedininkonpaper;bereproducedelectronicallyonCD-ROM,ontheInternet,orbyanotherelectronicmethodwidelyacceptedbythescientificcommunity;orbereproducedbysomemethodthatassuresnumerousidenticalcopiesandwidedistribution;(2)beissuedforthepurposeofscientific,public,permanentrecord;(3)bereadilyobtainablebypurchaseorfreedistri-bution;and(4)haveundergoneadequatepeerreview.Remarks.(a)Inadequatepublication.ThefollowingdonotconstitutepublicationwithinthemeaningoftheCode:(1)dis-tributionofmicrofilms,microcards,ormatterreproducedbysimilarmethods;(2)distributiontocolleaguesorstudentsofanote,evenifprinted,inexplanationofanaccompanyingillustration;(3)dis-tributionofproofsheets;(4)open-filerelease;(5)theses,disserta-tions,anddissertationabstracts;(6)mentionatascientificorothermeeting;(7)mentioninanabstract,mapexplanation,orfigurecap-tion;(8)labelingofarockspecimeninacollection;(9)meredepositofadocumentinalibrary;(10)anonymouspublication;(11)men-tioninthepopularpressorinalegaldocument;(12)distributionbyanauthorbypostingontheInternet,orbyanotherelectronicme-dium,adocumentthathasnotundergonetheproceduresstatedbelow(Remarkc).(b)Guidebooks.Aguidebookwithdistributionlimitedtoparticipantsofafieldexcursiondoesnotmeetthetestofavailability.Someorganizationspublishanddistributewidelylargeeditionsofserialguidebooksthatincluderefereedregionalpapers;althoughthesedomeetthetestsofscientificpurposeandavailability,andthereforeconstitutevalidpublication,othermediaarepreferable.Electronicpublication.Publicationinelectronicmedium,whichhasbecomewidespreadsincedistributionoftheCodein1983,isconfinedtopublicationinajournalorotherpublicationseriesbyawidelyrecognized(1)scientificsociety,(2)governmentagency,(3)academicinstitution,or(4)otherrespectedscientificpublisher.Allversionsdistributedmustbethesame,whetherinpaperorelectronicform,withoutalteration.Otherrequirementsareasfollows:(1)archivalpracticesadequateforfutureavailability;(2)suitabletypography;(3)codingandmarkuppracticesthatad-heretoacceptedstandards;(4)databasepreparationthatincludessatisfactorysearchandretrievaltools,aswellasthecapabilityfordownloadingtoaresearcherslocalprinter;and(5)adequatecopy-editingstandards.Newstratigraphicnamescanbepublishedelectronically.Article5.IntentandUtility.Tobevalid,anewunitmustserveaclearpurposeandbedulyproposedanddulydescribed,andtheintenttoestablishitmustbespecified.Casualmentionofaunit,suchasthegraniteexposedneartheMiddlevilleschoolhouse,doesnotestablishanewfor-malunit,nordoesmereuseinatable,columnarsection,ormap.Remark.(a)Demonstrationofpurposeserved.Theinitialdefinitionorrevisionofanamedgeologicunitconstitutes,ines-sence,aproposal.Assuch,itlacksstatusuntilusebyothersdemon-stratesthataclearpurposehasbeenserved.Aunitbecomeses-tablishedthroughrepeateddemonstrationofitsutility.Thedecisionnottouseanewlyproposedoranewlyrevisedtermrequiresafulldiscussionofitsunsuitability.Article6.CategoryandRank.Thecategoryandrankofaneworrevisedunitmustbespecified.Remark.(a)Needforspecification.Manystratigraphiccon-troversieshavearisenfromconfusionormisinterpretationofthecategoryofaunit(forexample,lithostratigraphicvs.chronostrati-graphic).Specificationandunambiguousdescriptionofthecategoryisofparamountimportance.Selectionanddesignationofanappropriaterankfromthedistinctiveterminologydevelopedforeachcategoryhelpservethisfunction(Table2).Article7.Name.Thenameofaformalgeologicunitiscompound.Formostcategories,thenameofaunitshouldconsistofageographicnamecombinedwithanappropri-aterank(WasatchFormation)ordescriptiveterm(Viola ThisarticleismodifiedslightlyfromastatementbytheInter-nationalCommissionofZoologicalNomenclature(1964,p.79).Remark(c)isfromtheadviceoftheAssociationofEarthScienceNorthAmericanCommissiononStratigraphicNomenclature Limestone).Biostratigraphicunitsaredesignatedbyappro-priatebiologicforms(ExusalbusAssemblageBiozone).Worldwidechronostratigraphicunitsbearlongestablishedandgenerallyacceptednamesofdiverseorigins(TriassicSystem).Thefirstlettersofallwordsusedinthenamesofformalgeologicunitsarecapitalized(exceptforthetrivialspeciesandsubspeciestermsinthenameofabiostratigraphicRemarks.(a)Appropriategeographicterms.Geographicnamesderivedfrompermanentnaturalorartificialfeaturesatornearwhichtheunitispresentarepreferabletothosederivedfromimpermanentfeaturessuchasfarms,schools,stores,churches,crossroads,andsmallcommunities.Appropriatenamesmaybese-lectedfromthoseshownontopographic,state,provincial,county,forestservice,hydrographic,orcomparablemaps,particularlythoseshowingnamesapprovedbyanationalboardforgeographicnames.Thegenericpartofageographicname,e.g.,river,lake,village,shouldbeomittedfromnewterms,unlessrequiredtodistinguishbetweentwootherwiseidenticalnames(e.g.,RedstoneFormationandRedstoneRiverFormation).Twonamesshouldnotbederivedfromthesamegeographicfeature.Aunitshouldnotbenamedforthesourceofitscomponents;forexample,adepositinferredtohavebeenderivedfromtheKeewatinglaciationcentershouldnotbedesignatedtheKeewatinTill.(b)Duplicationofnames.Responsibilityforavoidingdu-plication,eitherinuseofthesamenamefordifferentunits(hom-onymy)orinuseofdifferentnamesforthesameunit(synonomy),restswiththeproposer.Althoughthesamegeographictermhasbeenappliedtodifferentcategoriesofunits(example:thelithostrati-graphicWordFormationandthechronostratigraphicWordianStage)nowentrenchedintheliterature,thepracticeisundesirable.TheextensivegeologicnomenclatureofNorthAmerica,includingnotonlynamesbutalsonomenclaturalhistoryofformalunits,isre-cordedincompendiamaintainedbytheCommitteeonStratigraphicNomenclatureoftheGeologicalSurveyofCanada,Ottawa,Ontario;bytheGeologicNamesCommitteeoftheUnitedStatesGeologicalSurvey,Reston,Virginia;bytheInstitutodeGeologia,CiudadUni-versitaria,Me´xico,D.F.;andbymanystateandprovincialgeologicalsurveys.Theseorganizationsrespondtoinquiriesregardingtheavail-abilityofnames,andsomearepreparedtoreservenamesforunitsthatarelikelytobedefinedinthenextyearortwo.Priorityandpreservationofestablishednames.Stabilityofnomenclatureismaintainedbyuseoftheruleofpriorityandbypreservationofwell-establishednames.Namesshouldnotbemodifiedwithoutexplainingtheneed.Priorityinpublicationistoberespected,butpriorityalonedoesnotjustifydisplacingawell-establishednamebyoneneitherwell-knownnorcommonlyused;norshouldaninadequatelyestablishednamebepreservedmerelyonthebasisofpriority.Redefinitionsinprecisetermsarepreferabletoabandonmentofthenamesofwell-establishedunitsthatmayhavebeendefinedimpreciselybutnonethelessinconformancewitholderandlessstringentstandards.Differencesofspellingandchangesinname.Thegeo-graphiccomponentofawell-establishedstratigraphicnameisnotchangedduetodifferencesinspellingorchangesinthenameofageographicfeature.ThenameBennettShale,forexample,usedforTable2.CategoriesandRanksofUnitsDefinedinThisCode* NorthAmericanStratigraphicCode morethanhalfacentury,neednotbealteredbecausethetownisnamedBennet.NorshouldtheMauchChunkFormationbechangedbecausethetownhasbeenrenamedJimThorpe.Disappearanceofanimpermanentgeographicfeature,suchasatown,doesnotaffectthenameofanestablishedgeologicunit.NamesindifferentcountriesanddifferentlanguagesForgeologicunitsthatcrosslocalandinternationalboundaries,asinglenameforeachispreferabletoseveral.Spellingofageographicnamecommonlyconformstotheusageofthecountryandlinguisticgroupinvolved.Althoughgeographicnamesarenottranslated(Cu-chilloisnottranslatedtoKnife),lithologicorranktermsare(Ed-wardsLimestone,CalizaEdwards;Formacio´nLaCasita,LaCasitaFormation).Article8.Stratotypes.Thedesignationofaunitorboundarystratotype(typesectionortypelocality)isessentialinthedefinitionofmostformalgeologicunits.Manykindsofunitsarebestdefinedbyreferencetoanaccessibleandspecificsequenceofrockthatmaybeexaminedandstudiedbyothers.Astratotypeisthestandard(originalorsubse-quentlydesignated)foranamedgeologicunitorboundaryandconstitutesthebasisfordefinitionorrecognitionofthatunitorboundary;therefore,itmustbeillustrativeandrepresentativeoftheconceptoftheunitorboundarybeingdefined.Remarks.(a)Unitstratotype.Aunitstratotypeisthetypesectionforastratiformdepositorthetypeareaforanonstratiformbodythatservesasthestandardfordefinitionandrecognitionofageologicunit.Theupperandlowerlimitsofaunitstratotypearedesignatedpointsinaspecificsequenceorlocalityandserveasthestandardsfordefinitionandrecognitionofastratigraphicunitsboundaries.(b)Boundarystratotype.Aboundarystratotypeisthetypelocalityfortheboundaryreferencepointforastratigraphicunit.Bothboundarystratotypesforanyunitneednotbeinthesamesectionorregion.Eachboundarystratotypeservesasthestandardfordefinitionandrecognitionofthebaseofastratigraphicunit.Thetopofaunitmaybedefinedbytheboundarystratotypeofthenexthigherstratigraphicunit.Typelocality.Atypelocalityisthespecifiedgeographiclocalitywherethestratotypeofaformalunitorunitboundarywasoriginallydefinedandnamed.Atypeareaisthegeographicterritoryencompassingthetypelocality.Beforetheconceptofastratotypewasdeveloped,onlytypelocalitiesandareasweredesignatedformanygeologicunitsthatarenowlong-andwell-established.Strato-types,thoughnowmandatoryindefiningmoststratiformunits,areimpracticalindefinitionsofmanylargenonstratiformrockbodieswhosediversemajorcomponentsmaybebestdisplayedatseveralreferencelocalities.Composite-stratotype.Acomposite-stratotypeconsistsofseveralreferencesections(whichmayincludeatypesection)requiredtodemonstratetherangeortotalityofastratigraphicunit.Referencesections.Referencesectionsmayserveasinvaluablestandardsindefinitionsorrevisionsofformalgeologicunits.Forthosewell-establishedstratigraphicunitsforwhichatypesectionneverwasspecified,aprincipalreferencesection(lecto-stratotypeofISSC,1976,p.26;1994,p.28)maybedesignated.Aprincipalreferencesection(neostratotypeofISSC,1976,p.26;1994,p.28)alsomaybedesignatedforthoseunitsorboundarieswhosestratotypeshavebeendestroyed,covered,orotherwisemadeinaccessible.Supplementaryreferencesectionsoftenaredesignatedtoillustratethediversityorheterogeneityofadefinedunitorsomecriticalfeaturenotevidentorexposedinthestratotype.Onceaunitorboundarystratotypesectionisdesignated,itisneverabandonedorchanged;however,ifastratotypeprovesinadequate,itmaybesupplementedbyaprincipalreferencesectionorbyseveralreferencesectionsthatmayconstituteacomposite-stratotype.(f)Stratotypedescriptions.Stratotypesshouldbedescribedbothgeographicallyandgeologically.Sufficientgeographicdetailmustbeincludedtoenableotherstofindthestratotypeinthefield,andmayconsistofmapsand/oraerialphotographsshowingloca-tionandaccess,aswellasappropriatecoordinatesorbearings.Geo-logicinformationshouldincludethickness,descriptivecriteriaap-propriatetotherecognitionoftheunitanditsboundaries,anddiscussionoftherelationoftheunittoothergeologicunitsofthearea.Acarefullymeasuredanddescribedsectionprovidesthebestfoundationfordefinitionofstratiformunits.Graphicprofiles,columnarsections,structure-sections,andphotographsareusefulsupplementstoadescription;ageologicmapoftheareaincludingthetypelocalityisessential.Article9.UnitDescription.Aunitproposedforformalstatusshouldbedescribedanddefinedsoclearlythatanysubsequentinvestigatorcanrecognizethatunitun-equivocally.Distinguishingfeaturesthatcharacterizeaunitmayincludeanyorseveralofthefollowing:composition,texture,primarystructures,structuralattitudes,biologicre-mains,readilyapparentmineralcomposition(e.g.,calcitevs.dolomite),geochemistry,geophysicalproperties(includingmagneticsignatures),geomorphicexpression,unconformableorcross-cuttingrelations,andage.Althoughalldistinguishingfeaturespertinenttotheunitcategoryshouldbedescribedsufficientlytocharacterizetheunit,thosenotpertinenttothecategory(suchasageandinferredgenesisforlithostrati-graphicunits,orlithologyforbiostratigraphicunits)shouldnotbemadepartofthedefinition.Article10.Boundaries.Thecriteriaspecifiedfortherecognitionofboundariesbetweenadjoininggeologicunitsareofparamountimportancebecausetheyprovidethebasisforscientificreproducibilityofresults.Careisrequiredinde-scribingthecriteria,whichmustbeappropriatetothecate-goryofunitinvolved.Remarks.(a)BoundariesbetweenintergradationalunitsContactsbetweenrocksofmarkedlycontrastingcompositionareappropriateboundariesoflithicunits,butsomerocksgradeinto,orintertonguewith,othersofdifferentlithology.Consequently,someboundariesarenecessarilyarbitraryas,forexample,thetopoftheuppermostlimestoneinasequenceofinterbeddedlimestoneandshale.Sucharbitraryboundariescommonlyarediachronous.(b)Overlapsandgaps.Theproblemofoverlapsandgapsbetweenlong-establishedadjacentchronostratigraphicunitsisbeingaddressedbyinternationalIUGSandIGCPworkinggroupsappointedtodealwithvariouspartsofthegeologiccolumn.TheprocedurerecommendedbytheGeologicalSocietyofLondon(Georgeetal.,1969;Hollandetal.,1978),ofdefiningonlythebasalboundariesofchronostratigraphicunits,hasbeenwidelyadopted(e.g.,McLaren,1977)toresolvetheproblem.Suchboundariesaredefinedbyacarefullyselectedandagreed-uponboundary-stratotype(marker-pointtypesectionorgoldenspike)thatbecomesthestandardforthebaseofachronostratigraphicunit.Theconceptofthemutual-boundarystratotype(ISSC,1976,p.8486),redesig-natedlower-boundarystratotype(ISSC,1994,p.90),basedontheassumptionofcontinuousdepositioninselectedsequences,alsohasbeenusedtodefinechronostratigraphicunits.NorthAmericanCommissiononStratigraphicNomenclature AlthoughinternationalchronostratigraphicunitsofseriesandhigherrankarebeingredefinedbyIUGSandIGCPworkinggroups,theremaybeacontinuingneedforsomeprovincialseries.Adoptionofthebasalboundary-stratotypeconceptisurged.Article11.HistoricalBackground.Aproposalforanewnamemustincludeanomenclatorialhistoryofcon-stituentrocksassignedtotheproposedunit,describinghowtheyweretreatedpreviouslyandbywhom(references),aswellassuchmattersaspriorities,possiblesynonymy,andotherpertinentconsiderations.Considerationofthehistori-calbackgroundofanolderunitcommonlyprovidesthebasisforjustifyingdefinitionofanewunit.Article12.DimensionsandRegionalRelations.Aper-spectiveonthemagnitudeofaunitshouldbeprovidedbysuchinformationasmaybeavailableonthegeographicex-tentofaunit;observedrangesinthickness,composition,andgeomorphicexpression;relationstootherkindsandranksofstratigraphicunits;correlationswithothernearbysequences;andthebasesforrecognizingandextendingtheunitbeyondthetypelocality.Iftheunitisnotknownanywherebutinanareaoflimitedextent,informaldesignationisrecommended.Article13..Formostformalmaterialgeologicunits,otherthanchronostratigraphicandpolarity-chronostratigraphic,inferencesregardinggeologicageplaynoproperroleintheirdefinition.Nevertheless,theage,aswellasthebasisforitsassignment,areimportantfeaturesoftheunitand,wherepos-sible,shouldbestated.Formanylithodemicunits,theageoftheprotolithshouldbedistinguishedfromthatofthemeta-morphismordeformation.Ifthebasisforassigninganageistenuous,adoubtshouldbeexpressed.Remarks.(a)Dating.Thegeochronologicorderingoftherockrecord,whetherintermsofradioactive-decayratesorotherprocesses,isgenerallycalleddating.However,theuseofthenoundatetomeanisotopicageisnotrecommended.Similarly,thetermabsoluteageshouldbesuppressedinfavorofisotopicageforanagedeterminedonthebasisofisotopicratios.Themoreinclusivetermnumericalageisrecommendedforallagesde-terminedfromisotopicratios,fissiontracks,andotherquantifi-ableage-relatedphenomena.(b)Calibration.Thedatingofchronostratigraphicbound-ariesintermsofnumericalagesisaspecialformofdatingforwhichthewordcalibrationshouldbeused.Thegeochronologictime-scalenowinusehasbeendevelopedmainlythroughsuchcalibrationofchronostratigraphicsequences.Conventionandabbreviations.Theageofastratigraphicunitorthetimeofageologicevent,ascommonlydeterminedbynumericaldatingorbyreferencetoacalibratedtime-scale,maybeexpressedinyearsbeforethepresent.Theunitoftimeisthemodernyearaspresentlyrecognizedworldwide.Recommended(butnotmandatory)abbreviationsforsuchagesareSI(InternationalSystemofUnits)multiplierscoupledwithaforannum:ka,Ma,andGaforkilo-annum(10years),Mega-annum(10years),andGiga-annum(10years),respectively.UseofthesetermsaftertheagevaluefollowstheconventionestablishedinthefieldofC-14dating.Thepresentrefersto1950AD,andsuchqualifiersasagoorbeforethepresentareomittedafterthevaluebecausemeasure-mentofthedurationfromthepresenttothepastisimplicitinthedesignation.Incontrast,thedurationofaremoteintervalofgeologictime,asanumberofyears,shouldnotbeexpressedbythesamesymbols.Abbreviationsfornumbersofyears,withoutreferencetothepresent,areinformal(e.g.,yoryrforyears;my,m.y.,orm.yr.formillionsofyears;andsoforth,aspreferencedictates).Forexample,boundariesoftheLateCretaceousEpochcurrentlyarecalibratedat65Maand99Ma,buttheintervaloftimerepresentedbythisepochis34m.y.Expressionofageoflithodemicunits.Theadjectivesearly,middle,andlateshouldbeusedwiththeappropriategeochronologictermtodesignatetheageoflithodemicunits.Forexample,agranitedatedisotopicallyat510MashouldbereferredtousingthegeochronologictermLateCambriangraniteratherthaneitherthechronostratigraphictermUpperCambriangraniteorthemorecumbersomedesignationgraniteofLateCambrianage.Article14.Correlation.Informationregardingspatialandtemporalcounterpartsofanewlydefinedunitbeyondthetypeareaprovidesreaderswithanenlargedperspective.Discussionsofcriteriausedincorrelatingaunitwiththoseinotherareasshouldmakeclearthedistinctionbetweendataandinferences.Article15.Genesis.Objectivedataareusedtodefineandclassifygeologicunitsandtoexpresstheirspatialandtemporalrelations.AlthoughmanyofthecategoriesdefinedinthisCode(e.g.,lithostratigraphicgroup,plutonicsuite)havegeneticconnotations,inferencesregardinggeologichistoryorspecificenvironmentsofformationmayplaynoproperroleinthedefinitionofaunit.However,observations,aswellasinferences,thatbearongenesisareofgreatinteresttoreadersandshouldbediscussed.Article16.SubsurfaceandSubseaUnits.Thefore-goingproceduresforestablishingformalgeologicunitsapplyalsotosubsurfaceandoffshoreorsubseaunits.Completelithologicandpaleontologicdescriptionsorlogsofthesam-plesorcoresarerequiredinwrittenorgraphicform,orboth.Boundariesanddivisions,ifany,oftheunitshouldbeindi-catedclearlywiththeirdepthsfromanestablisheddatum.Remarks.(a)Namingsubsurfaceunits.Asubsurfaceunitmaybenamedfortheborehole(EagleMillsFormation),oilfield(SmackoverLimestone),ormine,whichisintendedtoserveasthestratotype,orforanearbygeographicfeature.Theholeormineshouldbelocatedprecisely,bothwithmapandexactgeographiccoordinates,andidentifiedfully(operatororcompany,farmorleaseblock,datesdrilledormined,surfaceelevationandtotaldepth,etc.).(b)Additionalrecommendations.Inclusionofappropriateboreholegeophysicallogsisurged.Moreover,rockandfossilsam-plesandcoresandallpertinentaccompanyingmaterialsshouldbestored,andavailableforexamination,atappropriatefederal,state,provincial,university,ormuseumdepositories.Foroffshoreorsub-seaunits(ClippertonFormationofTraceyetal.,1971,p.22;ArgoSaltofMcIver,1972,p.57),thenamesoftheprojectandvessel,depthofseafloor,andpertinentregionalsamplingandgeophysicaldatashouldbeadded.Seismostratigraphicunits.High-resolutionseismicmeth-odsnowcandelineatestratalgeometryandcontinuityatalevelofconfidencenotpreviouslyattainable.Accordingly,seismicsurveyshavecometobetheprincipaladjunctofthedrillinsubsurfaceexploration.Ontheotherhand,themethodidentifiesrocktypes NotethattheinitiallettersMega-andGiga-arecapitalized,butthatofkilo-isnot,bySIconvention.NorthAmericanStratigraphicCode onlybroadlyandbyinference.Thus,formalizationofunitsknownonlyfromseismicprofilesisinappropriate.Oncethestratigraphyiscalibratedbydrilling,theseismicmethodmayprovideobjectivewell-to-wellcorrelations.REVISIONANDABANDONMENTOFFORMALUNITSArticle17.RequirementsforMajorChanges.For-mallydefinedandnamedgeologicunitsmayberedefined,revised,orabandoned,butrevisionandabandonmentrequireasmuchjustificationasestablishmentofanewunit.Remark.(a)DistinctionbetweenredefinitionandrevisionRedefinitionofaunitinvolveschangingthevieworemphasisonthecontentoftheunitwithoutchangingtheboundariesorrank,anddiffersonlyslightlyfromredescription.Neitherredefinitionnorre-descriptionisconsideredrevision.Aredescriptioncorrectsaninad-equateorinaccuratedescription,whereasaredefinitionmaychangeadescriptive(forexample,lithic)designation.Revisioninvolveseitherminorchangesinthedefinitionofoneorbothboundariesorintherankofaunit(normally,elevationtoahigherrank).Correc-tionofamisidentificationofaunitoutsideitstypeareaisneitherredefinitionnorrevision.Article18.Redefinition.Acorrectionorchangeinthedescriptivetermappliedtoastratigraphicorlithodemicunitisaredefinition,whichdoesnotrequireanewgeo-graphicterm.Remarks.(a)Changeinlithicdesignation.Priorityshouldnotpreventmoreexactlithicdesignationiftheoriginaldesignationisnoteverywhereapplicable;forexample,theNiobraraChalkchangesgraduallywestwardtoaunitinwhichshaleisprominent,forwhichthedesignationNiobraraShaleorFormationismoreappropriate.Manycarbonateformationsoriginallydesignatedlimestoneordolomitearefoundtobegeographicallyinconsis-tentastoprevailingrocktype.Theappropriatelithictermorformationisagainpreferableforsuchunits.(b)Originallithicdesignationinappropriate.Restudyofsomelong-establishedlithostratigraphicunitshasshownthattheoriginallithicdesignationwasincorrectaccordingtomoderncriteria;forexample,someshaleshavethechemicalandmineralogicalcompositionoflimestone,andsomerocksdescribedasfelsiclavasnowareunderstoodtobeweldedtuffs.Suchnewknowledgeisrecognizedbychangingthelithicdesignationoftheunit,whilere-tainingtheoriginalgeographicterm.Similarly,changesintheclas-sificationofigneousrockshaveresultedinrecognitionthatrocksoriginallydescribedasquartzmonzonitenowaremoreappropri-atelytermedgranite.Suchlithicdesignationsmaybemodernizedwhenthenewclassificationiswidelyadopted.Ifheterogeneousbodiesofplutonicrockhavebeenmisleadinglyidentifiedwithasinglecompositionalterm,suchasgabbro,theadoptionofaneutralterm,suchasintrusionorpluton,maybeadvisable.Article19.Revision.Revisioninvolveseitherminorchangesinthedefinitionofoneorbothboundariesofaunit,orintheunitsrank.Remarks.(a)Boundarychange.Revisionisjustifiableifaminorchangeinboundarywillmakeaunitmorenaturalanduseful.Ifrevisionmodifiesonlyaminorpartofthecontentofapreviouslyestablishedunit,theoriginalnamemayberetained.(b)Changeinrank.Changeinrankofastratigraphicortemporalunitrequiresneitherredefinitionofitsboundariesnoralterationofthegeographicpartofitsname.Amembermaybe-comeaformationorviceversa,aformationmaybecomeagrouporviceversa,andalithodememaybecomeasuiteorviceversa.Examplesofchangesfromareatoarea.TheConasaugaShaleisrecognizedasaformationinGeorgiaandasagroupineasternTennessee;theOsgoodFormation,LaurelLimestone,andWaldronShaleinIndianaareclassedasmembersoftheWayneFormationinapartofTennessee;theVirgelleSandstoneisafor-mationinwesternMontanaandamemberoftheEagleSandstoneincentralMontana;theSkullCreekShaleandtheNewcastleSandstoneinNorthDakotaaremembersoftheAshvilleFormationinManitoba.Exampleofchangeinsinglearea.Therankofaunitmaybechangedwithoutchangingitscontent.Forexample,theMadisonLimestoneofearlyworkinMontanalaterbecametheMadisonGroup,containingseveralformations.Retentionoftypesection.Whentherankofageologicunitischanged,theoriginaltypesectionortypelocalityisretainedforthenewlyrankedunit(seeArticle22c).(f)Differentgeographicnameforaunitanditsparts.Inchangingtherankofaunit,thesamenamemaynotbeappliedbothtotheunitasawholeandtoapartofit.Forexample,theAstoriaGroupshouldnotcontainanAstoriaSandstone,northeWashingtonFormation,aWashingtonSandstoneMember.Undesirablerestriction.Whenaunitisdividedintotwoormoreofthesamerankastheoriginal,theoriginalnameshouldnotbeusedforanyofthedivisions.Retentionoftheoldnameforoneoftheunitsprecludesuseofthenameinatermofhigherrank.Furthermore,inordertounderstandanauthorsmeaning,alaterreaderwouldhavetoknowaboutthemodificationanditsdate,andwhethertheauthorisfollowingtheoriginalorthemodifiedusage.Forthesereasons,thenormalpracticeistoraisetherankofanestablishedunitwhenunitsofthesamerankarerecognizedandmappedwithinit.Article20.Abandonment.Animproperlydefinedorobsoletestratigraphic,lithodemic,ortemporalunitmaybeformallyabandoned,providedthat(a)sufficientjustificationispresentedtodemonstrateaconcernfornomenclaturalstability,and(b)recommendationsaremadefortheclas-sificationandnomenclaturetobeusedinitsplace.Remarks.(a)Reasonsforabandonment.Aformallydefinedunitmaybeabandonedbythedemonstrationofsynonymyorhomonymy,ofassignmenttoanimpropercategory(forexample,definitionofalithostratigraphicunitinachronostratigraphicsense),orofotherdirectviolationsofastratigraphiccodeorproceduresprevailingatthetimeoftheoriginaldefinition.Disuse,orthelackofneedorusefulpurposeforaunit,maybeabasisforabandonment;so,too,maywidespreadmisuseindiversewaysthatcompoundconfusion.Aunitalsomaybeabandonedifitprovesimpracticable,neitherrecognizablenormappableelsewhere.(b)Abandonednames.Anameforalithostratigraphicorlithodemicunit,onceappliedandthenabandoned,isavailableforsomeotherunitonlyifthenamewasintroducedcasually,orifithasbeenpublishedonlyonceinthelastseveraldecadesandisnotincurrentusage,andifitsreintroductionwillcausenoconfusion.Anexplanationofthehistoryofthenameandofthenewusageshouldbeapartofthedesignation.Obsoletenames.Authorsmayrefertonationalandprovincialrecordsofstratigraphicnamestodeterminewhetheranameisobsolete(seeArticle7b).NorthAmericanCommissiononStratigraphicNomenclature Referencetoabandonednames.Whenitisusefultorefertoanobsoleteorabandonedformalname,itsstatusismadeclearbysomesuchtermasabandonedorobsolete,andbyusingaphrasesuchasLaPlataSandstoneofCross(1898).(Thesamephrasealsoisusedtoconveythatanamedunithasnotyetbeenadoptedforusagebytheorganizationinvolved.)Reinstatement.Anameabandonedforreasonsthatseemvalidatthetime,butwhichsubsequentlyarefoundtobeerroneous,maybereinstated.Example:theWashakieFormation,definedin1869,wasabandonedin1918andreinstatedin1973.CODEAMENDMENTArticle21.ProcedureforAmendment.Additionsto,orchangesof,thisCodemaybeproposedinwritingtotheCommissionbyanygeoscientistatanytime.IfacceptedforconsiderationbyamajorityvoteoftheCommission,theymaybeadoptedbyatwo-thirdsvoteoftheCommissionatanannualmeetingnotlessthanayearafterpublicationoftheproposal.FORMALUNITSDISTINGUISHEDBYCONTENT,PROPERTIES,ORPHYSICALLIMITSLITHOSTRATIGRAPHICUNITSNatureandBoundariesArticle22.NatureofLithostratigraphicUnits.Alitho-stratigraphicunitisadefinedbodyofsedimentary,extrusiveigneous,metasedimentary,ormetavolcanicstratathatisdis-tinguishedanddelimitedonthebasisoflithiccharacteristicsandstratigraphicposition.AlithostratigraphicunitgenerallyconformstotheLawofSuperpositionandcommonlyisstratifiedandtabularinform.Remarks.(a)Basicunits.Lithostratigraphicunitsarethebasicunitsofgeneralgeologicworkandserveasthefoundationfordelineatingstrata,localandregionalstructure,economicresources,andgeologichistoryinregionsofstratifiedrocks.Theyarerecog-nizedanddefinedbyobservablerockcharacteristics;boundariesmaybeplacedatclearlydistinguishedcontactsordrawnarbitrarilywithinazoneofgradation.Lithificationorcementationisnotanecessaryproperty;clay,gravel,till,andotherunconsolidatedde-positsmayconstitutevalidlithostratigraphicunits.(b)Typesectionandlocality.Thedefinitionoflithostrati-graphicunitshouldbebased,ifpossible,onastratotypeconsistingofreadilyaccessiblerocksinplace,e.g.,inoutcrops,excavations,andmines,orofrocksaccessibleonlytoremotesamplingdevices,suchasthoseindrillholesandunderwater.Evenwhereremotemethodsareused,definitionsmustbebasedonlithiccriteriaandnotonthegeophysicalcharacteristicsoftherocks,northeimpliedageoftheircontainedfossils.Definitionsmustbebasedondescriptionsofactualrockmaterial.Regionalvaliditymustbedemonstratedforallsuchunits.Inregionswherethestratigraphyhasbeenestablishedthroughstudiesofsurfaceexposures,thenamingofnewunitsinthesub-surfaceisjustifiedonlywherethesubsurfacesectiondiffersma-teriallyfromthesurfacesection,orwherethereisdoubtastotheequivalenceofasubsurfaceandasurfaceunit.Theestablishmentofsubsurfacereferencesectionsforunitsoriginallydefinedinoutcropisencouraged.Typesectionneverchanged.Thedefinitionandnameofalithostratigraphicunitareestablishedatatypesection(orlocality)that,oncespecified,mustnotbechanged.Ifthetypesectionispoorlydesignatedordelimited,itmayberedefinedsubsequently.Iftheoriginallyspecifiedstratotypeisincomplete,poorlyexposed,structurallycomplicated,orunrepresentativeoftheunit,aprincipalreferencesectionorseveralreferencesectionsmaybedesignatedtosupplement,butnottosupplant,thetypesection(Article8e).Independencefrominferredgeologichistory.Inferredgeologichistory,depositionalenvironment,andbiologicalsequencehavenoplaceinthedefinitionofalithostratigraphicunit,whichmustbebasedoncompositionandotherlithiccharacteristics;nev-ertheless,considerationsofwell-documentedgeologichistoryprop-erlymayinfluencethechoiceofverticalandlateralboundariesofanewunit.Fossilsmaybevaluableduringmappingindistinguishingbetweentwolithologicallysimilar,noncontiguouslithostratigraphicunits.Thefossilcontentofalithostratigraphicunitisalegitimatelithiccharacteristic;forexample,oyster-richsandstone,coquina,coralreef,orgraptoliticshale.Moreover,otherwisesimilarunits,suchastheFormacio´nMendezandFormacio´nVelascomudstones,maybedistinguishedonthebasisofcoarsenessofcontainedfossils(foraminifera).Independencefromtimeconcepts.Theboundariesofmostlithostratigraphicunitsaretimeindependent,butsomemaybeapproximatelysynchronous.Inferredtimespans,howevermea-sured,playnopartindifferentiatingordeterminingtheboundariesofanylithostratigraphicunit.Eitherrelativelyshortorrelativelylongintervalsoftimemayberepresentedbyasingleunit.Theaccumulationofmaterialassignedtoaparticularunitmayhavebegunorendedearlierinsomelocalitiesthaninothers;also,re-movalofrockbyerosion,eitherwithinthetimespanofdepositionoftheunitorlater,mayreducethetimespanrepresentedbytheunitlocally.Thebodyinsomeplacesmaybeentirelyyoungerthaninotherplaces.Ontheotherhand,theestablishmentofformalunitsthatstraddleknown,identifiable,regionaldisconformitiesistobeavoided,ifatallpossible.Althoughconceptsoftimeorageplaynopartindefininglithostratigraphicunitsnorindeterminingtheirboundaries,evidenceofagemayaidrecognitionofsimilarlitho-stratigraphicunitsatlocalitiesfarremovedfromthetypesectionsorareas.(f)Surfaceform.Erosionalmorphologyorsecondarysurfaceformmaybeafactorintherecognitionofalithostratigraphicunit,butproperlyshouldplayaminorpartatmostinthedefinitionofsuchunits.Becausethesurfaceexpressionoflithostratigraphicunitsisanimportantaidinmapping,itiscommonlyadvisable,whereotherfactorsdonotcountervail,todefinelithostratigraphicbound-ariessoastocoincidewithlithicchangesthatareexpressedintopography.Economicallyexploitedunits.Aquifers,oilsands,coalbeds,andquarrylayersare,ingeneral,informalunitseventhoughnamed.Somesuchunits,however,mayberecognizedformallyasbeds,members,orformationsbecausetheyareimportantintheelucidationofregionalstratigraphy.(h)Instrumentallydefinedunits.Insubsurfaceinvestiga-tions,certainbodiesofrockandtheirboundariesarewidelyrecog-nizedonboreholegeophysicallogsshowingtheirelectricalresis-tivity,radioactivity,density,orotherphysicalproperties.Suchbodiesandtheirboundariesmayormaynotcorrespondtoformallitho-stratigraphicunitsandtheirboundaries.Whereotherconsider-ationsdonotcountervail,theboundariesofsubsurfaceunitsshouldbedefinedsoastocorrespondtousefulgeophysicalmarkers;never-theless,unitsdefinedexclusivelyonthebasisofremotelysensedphysicalproperties,althoughcommonlyusefulinstratigraphicNorthAmericanStratigraphicCode analysis,standcompletelyapartfromthehierarchyofformallitho-stratigraphicunitsandareconsideredinformal.Zone.Asappliedtothedesignationoflithostratigraphicunits,thetermzoneisinformal.Examplesareproducingzone,mineralizedzone,metamorphiczone,andheavy-mineralzone.Azonemayincludeallorpartsofabed,amember,aformation,orevenagroup.(j)Cyclothems.Cyclicorrhythmicsequencesofsedimen-taryrocks,whoserepetitivedivisionshavebeennamedcyclothems,havebeenrecognizedinsedimentarybasinsaroundtheworld.Somecyclothemshavebeenidentifiedbygeographicnames,butsuchnamesareconsideredinformal.Acleardistinctionmustbemain-tainedbetweenthedivisionofastratigraphiccolumnintocyclo-themsanditsdivisionintogroups,formations,andmembers.Whereacyclothemisidentifiedbyageographicname,thewordcyclothemshouldbepartofthename,andthegeographictermshouldnotbethesameasthatofanyformalunitembracedbythecyclothem.(k)Soilsandpaleosols.Soilsandpaleosolsarelayerscom-posedofthein-situproductsofweatheringofolderrocksthatmaybeofdiversecompositionandage.Soilsandpaleosolsdifferinseveralrespectsfromlithostratigraphicunits,andshouldnotbetreatedassuch(seePedostratigraphicUnits,Articles55etseq.).Depositionalfacies.Depositionalfaciesareinformalunits,whetherobjective(conglomeratic,blackshale,graptolitic)orgeneticandenvironmental(platform,turbiditic,fluvial),evenwhenageographictermhasbeenapplied,e.g.,LantzMillsfacies.Descriptivedesignationsconveymoreinformationthangeographictermsandarepreferable.Article23..Boundariesoflithostratigraphicunitsareplacedatpositionsoflithicchange.Boundariesareplacedatdistinctcontactsormaybeselectedatsomearbi-trarylevelwithinzonesofgradation(Figure2A).Bothver-ticalandlateralboundariesarebasedonthelithiccriteriathatprovidethegreatestunityandutility.Remarks.(a)BoundaryinaverticallygradationalsequenceAnamedlithostratigraphicunitispreferablyboundedbyasinglelowerandasingleuppersurfacesothatthenamedoesnotrecurinanormalstratigraphicsuccession(seeRemarkb).Wherearockunitpassesverticallyintoanotherbyintergradingorinterfingeringoftwoormorekindsofrock,unlessthegradationalstrataaresuf-ficientlythicktowarrantdesignationofathird,independentunit,theboundaryisnecessarilyarbitraryandshouldbeselectedonthebasisofpracticality(Figure2B).Forexample,whereashaleunitoverliesaunitofinterbeddedlimestoneandshale,theboundarycommonlyisplacedatthetopofthehighestreadilytraceablelime-stonebed.Whereasandstoneunitgradesupwardintoshale,theboundarymaybesogradationalastobedifficulttoplaceevenar-bitrarily;ideallyitshouldbedrawnatthelevelwheretherockiscomposedofone-halfofeachcomponent.Becauseofcreepinout-cropsandcavinginboreholes,itisgenerallybesttodefinesucharbitraryboundariesbythehighestoccurrenceofaparticularrocktype,ratherthanthelowest.(b)Boundariesinlaterallithologicchange.Whereaunitchangeslaterallythroughgradationinto,orintertongueswith,amarkedlydifferentkindofrock,anewunitshouldbeproposedforthedifferentrocktype.Anarbitrarylateralboundarymaybeplacedbetweenthetwoequivalentunits.Wheretheareaoflateralinter-gradationorintertonguingissufficientlyextensive,atransitionalintervalofinterbeddedrocksmayconstituteathirdindependentunit(Figure2C).Wheretongues(Article25b)offormationsaremappedseparatelyorotherwisesetapartwithoutbeingformallynamed,theunmodifiedformationnameshouldnotberepeatedinanormalstratigraphicsequence,althoughthemodifiednamemayberepeatedinsuchphrasesaslowertongueofMancosShaleanduppertongueofMancosShale:Toshowtheorderofsuperpo-sitiononmapsandcrosssections,theunnamedtonguesmaybedistinguishedinformally(Figure2D)bynumber,letter,orothermeans.Suchrelationsmayalsobedealtwithinformallythroughtherecognitionofdepositionalfacies(Article22-1).Keybedsusedforboundaries.Keybeds(Article26b)maybeusedasboundariesforaformallithostratigraphicunitwheretheinternallithiccharacteristicsoftheunitremainrelativelycon-stant.Eventhoughboundingkeybedsmaybetraceablebeyondtheareaofthediagnosticoverallrocktype,geographicextensionofthelithostratigraphicunitboundedtherebyisnotnecessarilyjustified.Wheretherockbetweenkeybedsbecomesdrasticallydifferentfromthatofthetypelocality,anewnameshouldbeapplied(Figure2E),eventhoughthekeybedsarecontinuous(Article26b).Stratigraphicandsedimentologicstudiesofstratigraphicunits(usuallyinformal)boundedbykeybedsmaybeveryinformativeanduseful,especiallyinsubsurfaceworkwherethekeybedsmayberecognizedbytheirgeophysicalsignatures.Suchunits,however,maybeakindofchro-nostratigraphic,ratherthanlithostratigraphic,unit(Article75,75c),althoughothersarediachronousbecauseone,orboth,ofthekeybedsarealsodiachronous.Unconformitiesasboundaries.Unconformities,whererecognizableobjectivelyonlithiccriteria,areidealboundariesforlithostratigraphicunits.However,asequenceofsimilarrocksmayincludeanobscureunconformitysothatseparationintotwounitsmaybedesirablebutimpracticable.Ifnolithicdistinctionadequatetodefineawidelyrecognizableboundarycanbemade,onlyoneunitshouldberecognized,eventhoughitmayincluderockthatac-cumulatedindifferentepochs,periods,oreras.Correspondencewithgeneticunits.Theboundariesoflithostratigraphicunitsshouldbechosenonthebasisoflithicchangesand,wherefeasible,tocorrespondwiththeboundariesofgeneticunits,sothatsubsequentstudiesofgenesiswillnothavetodealwithunitsthatstraddleformalboundaries.RanksofLithostratigraphicUnitsArticle24.Formation.Theformationisthefunda-mentalunitinlithostratigraphicclassification.Aformationisabodyofrockidentifiedbylithiccharacteristicsandstrati-graphicposition;itisprevailinglybutnotnecessarilytabularandismappableattheEarthssurfaceortraceableinthesubsurface.Remarks.(a)Fundamentalunit.Formationsarethebasiclithostratigraphicunitsusedindescribingandinterpretingthege-ologyofaregion.Thelimitsofaformationnormallyarethosesur-facesoflithicchangethatgiveitthegreatestpracticableunityofconstitution.Aformationmayrepresentalongorshorttimein-terval,maybecomposedofmaterialsfromoneorseveralsources,andmayincludebreaksindeposition(seeArticle23d).(b)Content.Aformationshouldpossesssomedegreeofinternallithichomogeneityordistinctivelithicfeatures.Itmaycontainbetweenitsupperandlowerlimits(i)rockofonelithictype,(ii)repetitionsoftwoormorelithictypes,or(iii)extremelithicheterogeneitythatinitselfmayconstituteaformofunitywhencomparedtotheadjacentrockunits.Lithiccharacteristics.Distinctivelithiccharacteristicsin-cludechemicalandmineralogicalcomposition,texture,andsuchsup-plementaryfeaturesascolor,primarysedimentaryorvolcanicstruc-tures,fossils(viewedasrock-formingparticles),orotherorganiccontent(coal,oil-shale).AunitdistinguishableonlybythetaxonomyofitsfossilsisnotalithostratigraphicbutabiostratigraphicunitNorthAmericanCommissiononStratigraphicNomenclature Figure2.Diagrammaticexamplesoflithostratigraphicboundariesandclassification.NorthAmericanStratigraphicCode (Article48).Rocktypemaybedistinctivelyrepresentedbyelectrical,radioactive,seismic,orotherproperties(Article22h),butthesepropertiesbythemselvesdonotdescribeadequatelythelithiccharacteroftheunit.Mappabilityandthickness.Theproposalofanewformationmustbebasedontestedmappability.Well-establishedformationscommonlyaredivisibleintoseveralwidelyrecognizablelithostratigraphicunits;whereformalrecognitionofthesesmallerunitsservesausefulpurpose,theymaybeestablishedasmembersandbeds,forwhichtherequirementofmappabilityisnotman-datory.Aunitformallyrecognizedasaformationinoneareamaybetreatedelsewhereasagroup,orasamemberofanotherformation,withoutchangeofname.Example:theNiobraraismappedatdif-ferentplacesasamemberoftheMancosShale,oftheCodyShale,oroftheColoradoShale,andalsoastheNiobraraFormation,astheNiobraraLimestone,andastheNiobraraShale.Thicknessisnotadeterminingparameterindividingarocksuccessionintoformations;thethicknessofaformationmayrangefromafeatheredgeatitsdepositionalorerosionallimittothousandsofmeterselsewhere.Noformationisconsideredvalidthatcannotbedelineatedatthescaleofgeologicmappingpracticedintheregionwhentheformationisproposed.Althoughrepresentationofafor-mationonmapsandcrosssectionsbyalabeledlinemaybejustified,proliferationofsuchexceptionallythinunitsisundesirable.Themethodsofsubsurfacemappingpermitdelineationofunitsmuchthinnerthanthoseusuallypracticableforsurfacestudies;beforesuchthinunitsareformalized,considerationshouldbegiventotheeffectonsubsequentsurfaceandsubsurfacestudies.Organicreefsandcarbonatemounds.Organicreefsandcarbonatemounds(buildups)maybedistinguishedformally,ifdesirable,asformationsdistinctfromtheirsurrounding,thinner,temporalequivalents.Fortherequirementsofformalization,seeArticle30f.(f)Interbeddedvolcanicandsedimentaryrock.Sedimen-taryrockandvolcanicrockthatareinterbeddedmaybeassembledintoaformationunderonenamethatshouldindicatethepre-dominantordistinguishinglithology,suchasMindegoBasalt.Volcanicrock.Mappabledistinguishablesequencesofstratifiedvolcanicrockshouldbetreatedasformationsorlitho-stratigraphicunitsofhigherorlowerrank.Asmallintrusivecompo-nentofadominantlystratiformvolcanicassemblagemaybetreatedinformally.(h)Metamorphicrock.Formationscomposedoflow-grademetamorphicrock(definedforthispurposeasrockinwhichprimarystructuresareclearlyrecognizable)are,likesedimentaryformations,distinguishedmainlybylithiccharacteristics.Themineralfaciesmaydifferfromplacetoplace,butthesevariationsdonotrequiredefinitionofanewformation.High-grademetamor-phicrockswhoserelationtoestablishedformationsisuncertainaretreatedaslithodemicunits(seeArticles31etseq.).Article25.Member.Amemberistheformallitho-stratigraphicunitnextinrankbelowaformationandisalwaysapartofsomeformation.Itisrecognizedasanamedentitywithinaformationbecauseitpossessescharacteristicsdis-tinguishingitfromadjacentpartsoftheformation.Aforma-tionneednotbedividedintomembersunlessausefulpurposeisservedbydoingso.Someformationsmaybedividedcompletelyintomembers;othersmayhaveonlycertainpartsdesignatedasmembers;stillothersmayhavenomembers.Amembermayextendlaterallyfromoneformationtoanother.Remarks.(a)Mappingofmembers.Amemberisestab-lishedwhenitisadvantageoustorecognizeaparticularpartofaheterogeneousformation.Amember,whetherformallyorinfor-mallydesignated,neednotbemappableatthescalerequiredforformations.Evenifallmembersofaformationarelocallymappable,itdoesnotfollowthattheyshouldberaisedtoformationalrank,becauseproliferationofformationnamesmayobscureratherthanclarifyrelationswithotherareas.(b)Lensandtongue.Ageographicallyrestrictedmemberthatterminatesonallsideswithinaformationmaybecalledalens(lentil).Awedgingmemberthatextendsoutwardbeyondafor-mationorwedges(pinches)outwithinanotherformationmaybecalledatongue.Organicreefsandcarbonatemounds.Organicreefsandcarbonatemoundsmaybedistinguishedformally,ifdesirable,asmemberswithinaformation.Fortherequirementsofformalization,seeArticle30f.Divisionofmembers.Aformallyorinformallyrecog-nizeddivisionofamemberiscalledabedorbeds,exceptforvolcanicflowrocks,forwhichthesmallestformalunitisaflow.Membersmaycontainbedsorflows,butmaynevercontainothermembers.Laterallyequivalentmembers.Althoughmembersnor-mallyareinverticalsequence,laterallyequivalentpartsofafor-mationthatdifferrecognizablymayalsobeconsideredmembers.Article26.Bed(s).Abed,orbeds,isthesmallestformallithostratigraphicunitofsedimentaryrocks.Remarks.(a)Limitations.Thedesignationofabedoraunitofbedsasaformallynamedlithostratigraphicunitgenerallyshouldbelimitedtocertaindistinctivebedswhoserecognitionisparticu-larlyuseful.Coalbeds,oilsands,andotherbedsofeconomicimpor-tancecommonlyarenamed,butsuchunitsandtheirnamesusuallyarenotapartofformalstratigraphicnomenclature(Articles22gand30g).(b)Keyormarkerbeds.Akeyormarkerbedisathinbedofdistinctiverockthatiswidelydistributed.Suchbedsmaybenamed,butusuallyareconsideredinformalunits.Individualkeybedsmaybetracedbeyondthelaterallimitsofaparticularformalunit(Article23c).Article27..Aflowisthesmallestformallitho-stratigraphicunitofvolcanicflowrocks.Aflowisadiscrete,extrusive,volcanicrockbodydistinguishablebytexture,com-position,orderofsuperposition,paleomagnetism,orotherob-jectivecriteria.Itispartofamemberandthusisequiva-lentinranktoabedorbedsofsedimentary-rockclassification.Manyflowsareinformalunits.Thedesignationandnamingofflowsasformalrock-stratigraphicunitsshouldbelimitedtothosethataredistinctiveandwidespread.Article28.Group.Agroupisthelithostratigraphicunitnexthigherinranktoformation;agroupmayconsistentirelyofnamedformations,oralternatively,neednotbecomposedentirelyofnamedformations.Remarks.(a)Useandcontent.Groupsaredefinedtoexpressthenaturalrelationsofassociatedformations.Theyareusefulinsmall-scalemappingandregionalstratigraphicanalysis.Insomerecon-naissancework,thetermgrouphasbeenappliedtolithostrati-graphicunitsthatappeartobedivisibleintoformations,buthavenotyetbeensodivided.Insuchcases,formationsmaybeerectedsub-sequentlyforoneorallofthepracticaldivisionsofthegroup.(b)Changeincomponentformations.Theformationsmakingupagroupneednotnecessarilybeeverywherethesame.TheNorthAmericanCommissiononStratigraphicNomenclature RundleGroup,forexample,iswidespreadinwesternCanadaandundergoesseveralchangesinformationalcontent.InsouthwesternAlberta,itcomprisestheLivingstone,MountHead,andEtheringtonFormationsintheFrontRanges,whereasinthefoothillsandsub-surfaceoftheadjacentplains,itcomprisesthePekisko,Shunda,TurnerValley,andMountHeadFormations.However,aformationoritspartsmaynotbeassignedtotwoverticallyadjacentgroups.Changeinrank.Thewedge-outofacomponentforma-tionorformationsmayjustifythereductionofagrouptoformationrank,retainingthesamename.Whenagroupisextendedlaterallybeyondwhereitisdividedintoformations,itbecomesineffectaformation,evenifitisstillcalledagroup.Whenapreviouslyes-tablishedformationisdividedintotwoormorecomponentunitsthataregivenformalformationrank,theoldformation,withitsoldgeographicname,shouldberaisedtogroupstatus.Raisingtherankoftheunitispreferabletorestrictingtheoldnametoapartofitsformercontent,becauseachangeinrankleavesthesenseofawell-establishedunitunchanged(Articles19b,19g).Article29.Supergroup.Asupergroupisaformalassemblageofrelatedorsuperposedgroups,orofgroupsandformations.Suchunitshaveprovedusefulinregionalandprovincialsyntheses.Supergroupsshouldbenamedonlywheretheirrecognitionservesaclearpurpose.Remark.(a)MisuseofseriesforgrouporsupergroupAlthoughseriesisausefulgeneralterm,itisappliedformallyonlytoachronostratigraphicunitandshouldnotbeusedforalitho-stratigraphicunit.Thetermseriesshouldnolongerbeemployedforanassemblageofformationsoranassemblageofformationsandgroups,asithasbeen,especiallyinstudiesofthePrecambrian.Theseassemblagesaregroupsorsupergroups.LithostratigraphicNomenclatureArticle30.CompoundCharacter.Theformalnameofalithostratigraphicunitiscompound.Itconsistsofageo-graphicnamecombinedwithadescriptivelithictermorwiththeappropriaterankterm,orboth.Initiallettersofallwordsusedinformingthenamesofformalrock-stratigraphicunitsarecapitalized.Remarks.(a)Omissionofpartofaname.Wherefrequentrepetitionwouldbecumbersome,thegeographicname,thelithicterm,ortheranktermmaybeusedalone,oncethefullnamehasbeenintroduced;astheBurlington,thelimestone,ortheformation,fortheBurlingtonLimestone.(b)Useofsimplelithicterms.Thelithicpartofthenameshouldindicatethepredominantordiagnosticlithology,evenifsubordinatelithologiesareincluded.Wherealithictermisusedinthenameofalithostratigraphicunit,thesimplestgenerallyaccept-abletermisrecommended(forexample,limestone,sandstone,shale,tuff,quartzite).Compoundterms(forexample,clayshale)andtermsthatarenotincommonusage(forexample,calcirudite,orthoquartzite)shouldbeavoided.Combinedterms,suchassandandclay,shouldnotbeusedforthelithicpartofthenamesoflithostratigraphicunits,norshouldanadjectivebeusedbetweenthegeographicandthelithicterms,asChattanoogaBlackShaleandBiwabikIron-BearingFormation.Groupnames.Agroupnamecombinesageographicnamewiththetermgroup,andnolithicdesignationisincluded;forexample,SanRafaelGroup.Formationnames.Aformationnameconsistsofageographicnamefollowedbyalithicdesignationorbythewordformation.Examples:DakotaSandstone,MitchellMesaRhyolite,MonmouthFormation,HaltonTill.Membernames.Allmembernamesincludeageographictermandthewordmember;somehaveaninterveninglithicdesignation,ifuseful;forexample,WedingtonSandstoneMemberoftheFayettevilleShale.Membersdesignatedsolelybylithicchar-acter(forexample,siliceousshalemember),byposition(upper,lower),orbyletterornumber,areinformal.(f)Namesofreefs.Organicreefsidentifiedasformationsormembersareformalunitsonlywherethenamecombinesageo-graphicnamewiththeappropriaterankterm,e.g.,LeducFormation(anameappliedtotheseveralreefsenvelopedbytheIretonFor-mation),RainbowReefMember.Bedandflownames.Thenamesofbedsorflowscom-bineageographicterm,alithicterm,andthetermbedorflow;forexample,KneeHillsTuffBed,ArdmoreBentoniteBeds,NegusVarioliticFlows.(h)Informalunits.Whengeographicnamesareappliedtosuchinformalunitsasoilsands,coalbeds,mineralizedzones,andinformalmembers(seeArticles22gand26a),theunittermshouldnotbecapitalized.Anameisnotnecessarilyformalbecauseitiscapitalized,nordoesfailuretocapitalizeanamerenderitinformal.Geographicnamesshouldbecombinedwiththetermsformationorgrouponlyinformalnomenclature.Informalusageofidenticalgeographicnames.Theap-plicationofidenticalgeographicnamestoseveralminorunitsinoneverticalsequenceisconsideredinformalnomenclature(lowerMountSavagecoal,MountSavagefireclay,upperMountSavagecoal,MountSavageridercoal,andMountSavagesandstone).Theapplicationofidenticalgeographicnamestotheseverallithologicunitsconstitutingacyclothemlikewiseisconsideredinformal.(j)Metamorphicrock.Metamorphicrockrecognizedasanormalstratifiedsequence,commonlylow-grademetavolcanicormetasedimentaryrocks,shouldbeassignedtonamedgroups,for-mations,andmembers,suchastheDeceptionRhyolite,aformationoftheAshCreekGroup,ortheBonnerQuartzite,aformationoftheMissoulaGroup.High-grademetamorphicandmetasomaticrocksaretreatedaslithodemesandsuites(seeArticles31,33,35).(k)Misuseofwell-knownname.Anamethatsuggestssomewell-knownlocality,region,orpoliticaldivisionshouldnotbeappliedtoaunittypicallydevelopedinanotherlesswell-knownlocalityofthesamename.Forexample,itwouldbeinadvisabletousethenameChicagoFormationforaunitinCalifornia.LITHODEMICUNITSNatureandBoundariesArticle31.NatureofLithodemicUnits.Alithodemicunitisadefinedbodyofpredominantlyintrusive,highlyde-formed,and/orhighlymetamorphosedrock,distinguishedanddelimitedonthebasisofrockcharacteristics.Incontrasttolithostratigraphicunits,alithodemicunitgenerallydoesnotconformtotheLawofSuperposition.Itscontactswithotherrockunitsmaybesedimentary,extrusive,intrusive,tectonic,ormetamorphic(Figure3).Remarks.(a)Recognitionanddefinition.Lithodemicunitsaredefinedandrecognizedbyobservablerockcharacteristics.They FromtheGreek:livingbody,frame.NorthAmericanStratigraphicCode arethepracticalunitsofgeneralgeologicalworkinterranesinwhichrockbodiesgenerallylackprimarystratification;insuchterranestheyserveasthefoundationforstudying,describing,anddelineatinglithology,localandregionalstructure,economicresources,andgeo-logichistory.(b)Typeandreferencelocalities.Thedefinitionofalithodemicunitshouldbebasedonasfullknowledgeaspossibleofitslateralandverticalvariationsanditscontactrelations.Forpurposesofnomenclaturalstability,atypelocalityand,whereverappropriate,referencelocalitiesshouldbedesignated.Independencefrominferredgeologichistory.Conceptsbasedoninferredgeologichistoryproperlyplaynopartinthedefi-nitionofalithodemicunit.Nevertheless,wheretworockmassesarelithicallysimilarbutdisplayobjectivestructuralrelationsthatpre-cludethepossibilityoftheirbeingevenbroadlyofthesameage,theyshouldbeassignedtodifferentlithodemicunits.Useofzone.Asappliedtothedesignationoflitho-demicunits,thetermzoneisinformal.Examplesare:miner-alizedzone,contactzone,andpegmatiticzone.Article32.Boundaries.Boundariesoflithodemicunitsareplacedatpositionsoflithicchange.Theymaybeplacedatclearlydistinguishedcontactsorwithinzonesofgradation.Boundaries,bothverticalandlateral,arebasedonthelithiccriteriathatprovidethegreatestunityandprac-ticalutility.Contactswithotherlithodemicandlithostrati-graphicunitsmaybedepositional,intrusive,metamorphic,ortectonic.Remark.(a)Boundarieswithingradationalzones.Wherealithodemicunitchangesthroughgradationinto,orintertongueswith,arockmasswithmarkedlydifferentcharacteristics,itisusuallydesirabletoproposeanewunit.Itmaybenecessarytodrawanarbitraryboundarywithinthezoneofgradation.Wheretheareaofintergradationorintertonguingissufficientlyextensive,therocksofmixedcharactermayconstituteathirdunit.RanksofLithodemicUnitsArticle33.Lithodeme.Thelithodemeisthefunda-mentalunitinlithodemicclassification.Alithodemeisabodyofintrusive,pervasivelydeformed,orhighlymetamor-phosedrock,generallynon-tabularandlackingprimaryde-positionalstructures,andcharacterizedbylithichomoge-neity.ItismappableattheEarthssurfaceandtraceableinthesubsurface.Forcartographicandhierarchicalpurposes,itiscomparabletoaformation(seeTable2).Remarks.(a)Content.Alithodemeshouldpossessdistinc-tivelithicfeaturesandsomedegreeofinternallithichomogeneity.Itmayconsistof(i)rockofonetype,(ii)amixtureofrocksoftwoormoretypes,or(iii)extremeheterogeneityofcomposition,whichmayconstituteinitselfaformofunitywhencomparedtoadjoiningrock-masses(seealsocomplex,Article37).(b)Lithiccharacteristics.Distinctivelithiccharacteristicsmayincludemineralogy,texturalfeaturessuchasgrainsize,andstructural Figure3.Lithodemic(uppercase)andlithostratigraphic(lowercase)units.Alithodeme(A)containsanintrusionofdiorite(B)thatwasdeformedwiththegneiss.AandBmaybetreatedjointlyasacomplex.Ayoungergranite(C)iscutbya(D)thatiscutinturnbyunconformityI.Alltheforegoingareinfaultcontactwithastructuralcomplex(E).Avolcaniccomplex(G)isbuiltuponunconformityI,anditsfeederdikescuttheunconformity.Laterallyequivalentvolcanicstratainorderly,mappablesuccession(h)aretreatedaslithostratigraphicunits.Agabbrofeeder(G),tothevolcaniccomplex,wheresurroundedbygneissisreadilydistinguishedasaseparatelithodemeandnamedasagabbrooranintrusion.Alltheforegoingareoverlain,atunconformityII,bysedimentaryrocks(j)dividedintoformationsandmembers.NorthAmericanCommissiononStratigraphicNomenclature featuressuchasschistoseorgneissicstructure.Aunitdistinguish-ablefromitsneighborsonlybymeansofchemicalanalysisisMappability.Practicabilityofsurfaceorsubsurfacemap-pingisanessentialcharacteristicofalithodeme(seeArticle24d).Article34.DivisionofLithodemes.Unitsbelowtherankoflithodemeareinformal.Article35.Suite.Asuite(metamorphicsuite,intru-sivesuite,plutonicsuite)isthelithodemicunitnexthigherinranktolithodeme.Itcomprisestwoormoreassociatedlithodemesofthesameclass(e.g.,plutonic,metamorphic).Forcartographicandhierarchicalpurposes,suiteiscompa-rabletogroup(seeTable2).Remarks.(a)Purpose.Suitesarerecognizedforthepurposeofexpressingthenaturalrelationsofassociatedlithodemeshavingsignificantlithicfeaturesincommon,andofdepictinggeologyatcompilationscalestoosmalltoallowdelineationofindividuallitho-demes.Ideally,asuiteconsistsentirelyofnamedlithodemes,butmaycontainbothnamedandunnamedunits.(b)Changeincomponentunits.Thenamedandunnamedunitsconstitutingasuitemaychangefromplacetoplace,solongastheoriginalsenseofnaturalrelationsandofcommonlithicfeaturesisnotviolated.Changeinrank.Tracedlaterally,asuitemayloseallofitsformallynameddivisionsbutremainarecognizable,mappableentity.Undersuchcircumstances,itmaybetreatedasalithodemebutretainthesamename.Conversely,whenapreviouslyestablishedlithodemeisdividedintotwoormoremappabledivisions,itmaybedesirabletoraiseitsranktosuite,retainingtheoriginalgeographiccomponentofthename.Toavoidconfusion,theoriginalnameshouldnotberetainedforoneofthedivisionsoftheoriginalunit(seeArticle19g).Article36.Supersuite.Asupersuiteistheunitnexthigherinranktoasuite.Itcomprisestwoormoresuitesorcomplexeshavingadegreeofnaturalrelationshiptoonean-other,eitherintheverticalorthelateralsense.Forcarto-graphicandhierarchicalpurposes,supersuiteissimilarinranktosupergroup.Article37.Complex.Anassemblageormixtureofrocksoftwoormoregeneticclasses,i.e.,igneous,sedimentary,ormetamorphic,withorwithouthighlycomplicatedstruc-ture,maybenamedacomplex.Thetermcomplextakestheplaceofthelithicorrankterm(forexample,BoilMoun-tainComplex,FranciscanComplex)and,althoughunranked,commonlyiscomparabletosuiteorsupersuiteandisnamedinthesamemanner(Articles41,42).Remarks.(a)Useofcomplex.Identificationofanas-semblageofdiverserocksasacomplexisusefulwherethemappingofeachseparatelithiccomponentisimpracticalatordinarymappingscales.Complexisunrankedbutcommonlycomparabletosuiteorsupersuite;therefore,thetermmayberetainedifsubsequent,detailedmappingdistinguishessomeorallofthecomponentlitho-demesorlithostratigraphicunits.(b)Volcaniccomplex.Sitesofpersistentvolcanicactivitycommonlyarecharacterizedbyadiverseassemblageofextrusivevolcanicrocks,relatedintrusions,andtheirweatheringproducts.SuchanassemblagemaybedesignatedavolcaniccomplexStructuralcomplex.Insometerranes,tectonicprocesses(e.g.,shearing,faulting)haveproducedheterogeneousmixturesordisruptedbodiesofrockinwhichsomeindividualcomponentsaretoosmalltobemapped.Wherethereisnodoubtthatthemixingordisruptionisduetotectonicprocesses,suchamixturemaybedes-ignatedasastructuralcomplex,whetheritconsistsoftwoormoreclassesofrock,orasingleclassonly.Asimplersolutionforsomemappingpurposesistoindicateintensedeformationbyanover-printedpattern.Misuseofcomplex.Wheretherockassemblagetobeunitedunderasingle,formalnameconsistsofdiversetypesofasingleclassofrock,asinmanyterranesthatexposeavarietyofeitherintrusiveigneousorhigh-grademetamorphicrocks,thetermin-trusivesuite,plutonicsuite,ormetamorphicsuiteshouldbeused,ratherthantheunmodifiedtermcomplex.Exceptionstothisrulearethetermsstructuralcomplexandvolcaniccomplex(seeremarkscandb,above).Article38.MisuseofSeriesforSuite,Complex,orSupersuite.Thetermserieshasbeenemployedforanas-semblageoflithodemesoranassemblageoflithodemesandsuites,especiallyinstudiesofthePrecambrian.Thispracticenowisregardedasimproper;theseassemblagesaresuites,complexes,orsupersuites.Thetermseriesalsohasbeenappliedtoasequenceofrocksresultingfromasuccessionoferuptionsorintrusions.Inthesecasesadifferenttermshouldbeused;groupshouldreplaceseriesforvolcanicandlow-grademetamorphicrocks,andintrusivesuiteorplutonicsuiteshouldreplaceseriesforintrusiverocksofgrouprank.LithodemicNomenclatureArticle39.GeneralProvisions.Theformalnameofalithodemicunitiscompound.Itconsistsofageographicnamecombinedwithadescriptiveorappropriaterankterm.Theprinciplesfortheselectionofthegeographicterm,concerningsuitability,availability,priority,etc.,followthoseestablishedinArticle7,wheretherulesforcapitalizationarealsospecified.Article40.LithodemeNames.Thenameofalitho-demecombinesageographictermwithalithicordescriptiveterm,e.g.,KillarneyGranite,AdamantPluton,ManhattanSchist,SkaergaardIntrusion,DuluthGabbro.Thetermmationshouldnotbeused.Remarks.(a)Lithicterm.Thelithictermshouldbeacom-monandfamiliarterm,suchasschist,gneiss,gabbro.Specializedtermsandtermsnotwidelyused,suchaswebsteriteandjacu-pirangite,andcompoundterms,suchasgraphiticschistandaugengneiss,shouldbeavoided.(b)Intrusiveandplutonicrocks.Becausemanybodiesofintrusiverockrangeincompositionfromplacetoplaceandaredifficulttocharacterizewithasinglelithicterm,andbecausemanybodiesofplutonicrockareconsiderednottobeintrusions,latitudeisallowedinthechoiceofalithicordescriptiveterm.Thus,thedescriptivetermshouldpreferablybecompositional(e.g.,gabbro,granodiorite),butmay,ifnecessary,denoteform(e.g.,dike,sill),orbeneutral(e.g.,intrusion,pluton).Inanyevent,specialized Plutonamappablebodyofplutonicrock.NorthAmericanStratigraphicCode compositionaltermsnotwidelyusedaretobeavoided,asareformtermsthatarenotwidelyused,suchasbysmalithandchonolith.Termsimplyinggenesisshouldbeavoidedasmuchaspossible,becauseinterpretationsofgenesismaychange.Article41.SuiteNames.Thenameofasuitecombinesageographicterm,thetermsuite,andanadjectivede-notingthefundamentalcharacterofthesuite;forexample,IdahoSpringsMetamorphicSuite,TuolumneIntrusiveSuite,CassiarPlutonicSuite.Thegeographicnameofasuitemaynotbethesameasthatofacomponentlithodeme(seeArticle19f).Intrusiveassemblages,however,maysharethesamegeographicnameifanintrusivelithodemeisrepresenta-tiveofthesuite(e.g.,theMethuenPlutonicSuitemayincludetheMethuen,Deloro,AbingerandAddingtonGranites,[Eas-ton,1992].AstheMethuenGranite,alithodeme,istypicalofthesuite,theduplicationofnamesispermissible).Article42.SupersuiteNames.Thenameofasuper-suitecombinesageographictermwiththetermsupersuite.MAGNETOSTRATIGRAPHICUNITSNatureandBoundariesArticle43.NatureofMagnetostratigraphicUnitsmagnetostratigraphicunitisabodyofrockunifiedbyspec-ifiedremanent-magneticpropertiesandisdistinctfromunderlyingandoverlyingmagnetostratigraphicunitshavingdifferentmagneticproperties.Remarks.(a)Definition.Magnetostratigraphyisdefinedhereasallaspectsofstratigraphybasedonremanentmagnetism(paleomagneticsignatures).Fourbasicpaleomagneticphenomenacanbedeterminedorinferredfromremanentmagnetism:polarity,dipole-field-poleposition(includingapparentpolarwander),thenon-dipolecomponent(secularvariation),andfieldintensity.ContemporaneityofrockandremanentmagnetismManypaleomagneticsignaturesreflectearthmagnetismatthetimetherockformed.Nevertheless,somerockshavebeensubjectedsubsequentlytophysicaland/orchemicalprocessesthatalteredthemagneticproperties.Forexample,abodyofrockmaybeheatedabovetheblockingtemperatureorCuriepointforoneormoreminerals,oraferromagneticmineralmaybeproducedbylow-temperaturealterationlongaftertheenclosingrockformed,thusacquiringacomponentofremanentmagnetismreflectingthefieldatthetimeofalteration,ratherthanthetimeoforiginalrockdepo-sitionorcrystallization.Designationsandscope.Theprefixmagnetoisusedwithanappropriatetermtodesignatetheaspectofremanentmagnetismusedtodefineaunit.Thetermsmagnetointensityormagneto-secular-variationarepossibleexamples.ThisCodeconsidersonlypolarityreversals,whichnowarerecognizedwidelyasastratigraphictool.However,apparent-polar-wanderpathsofferincreasingprom-iseforcorrelationswithinPrecambrianrocks.Article44.DefinitionofMagnetopolarityUnitmagnetopolarityunitisabodyofrockunifiedbyitsrema-nentmagneticpolarityanddistinguishedfromadjacentbod-iesofrockthathavedifferentpolarity.Remarks.(a)Nature.MagnetopolarityistherecordinrocksofthepolarityhistoryoftheEarthsmagnetic-dipolefield.FrequentpastreversalsofthepolarityoftheEarthsmagneticfieldprovideabasisformagnetopolaritystratigraphy.(b)Stratotype.Astratotypeforamagnetopolarityunitshouldbedesignatedandtheboundariesdefinedintermsofrecognizedlithostratigraphicand/orbiostratigraphicunitsinthestratotype.TheformaldefinitionofamagnetopolarityunitshouldmeettheapplicablespecificrequirementsofArticles3to16.Independencefrominferredhistory.Definitionofamagnetopolarityunitdoesnotrequireknowledgeofthetimeatwhichtheunitacquireditsremanentmagnetism;itsmagnetismmaybeprimaryorsecondary.Nevertheless,theunitspresentpolarityisapropertythatmaybeascertainedandconfirmedbyothers.RelationtolithostratigraphicandbiostratigraphicunitsMagnetopolarityunitsresemblelithostratigraphicandbiostrati-graphicunitsinthattheyaredefinedonthebasisofanobjectiverecognizableproperty,butdifferfundamentallyinthatmostmag-netopolarityunitboundariesarethoughtnottobetimetransgres-sive.Theirboundariesmaycoincidewiththoseoflithostratigraphicorbiostratigraphicunits,orbeparalleltobutdisplacedfromthoseofsuchunits,orbecrossedbythem.Relationofmagnetopolarityunitstochronostratigraphicunits.Althoughtransitionsbetweenpolarityreversalsareofglobalextent,amagnetopolarityunitdoesnotcontainwithinitselfevidencethatthepolarityisprimary,orcriteriathatpermititsunequivocalrecognitioninchronocorrelativestrataofotherareas.Othercriteria,suchaspaleontologicornumericalage,arerequiredforbothcorrelationanddating.Althoughpolarityreversalsareusefulinrecognizingchronostratigraphicunits,magnetopolarityaloneisinsufficientfortheirdefinition.Article45.Boundaries.Theupperandlowerlimitsofamagnetopolarityunitaredefinedbyboundariesmarkingachangeofpolarity.Suchboundariesmayrepresenteitheradepositionaldiscontinuityoramagnetic-fieldtransition.Theboundariesareeitherpolarity-reversalhorizonsorpolaritytransitionzones,respectively.Remark.(a)Polarity-reversalhorizonsandtransitionzonesApolarity-reversalhorizoniseitherasingle,clearlydefinablesurfaceorathinbodyofstrataconstitutingatransitionalintervalacrosswhichachangeinmagneticpolarityisrecorded.Polarity-reversalhorizonsdescribetransitionalintervalsof1morless;wherethechangeinpolaritytakesplaceoverastratigraphicintervalgreaterthan1m,thetermpolaritytransitionzoneshouldbeused.Polarity-reversalhorizonsandpolaritytransitionzonesprovidetheboundariesforpolarityzones,althoughtheymayalsobecontainedwithinapolarityzonewheretheymarkaninternalchangesubsidiaryinranktothoseatitsboundaries.RanksofMagnetopolarityUnitsArticle46.FundamentalUnit.Apolarityzoneisthefundamentalunitofmagnetopolarityclassification.Apo-larityzoneisaunitofrockcharacterizedbythepolarityofitsmagneticsignature.Magnetopolarityzone,ratherthanpolarityzone,shouldbeusedwherethereisriskofcon-fusionwithotherkindsofpolarity.Remarks.(a)Content.Apolarityzoneshouldpossesssomedegreeofinternalhomogeneity.Itmaycontainrocksof(1)entirelyorpredominantlyonepolarity,or(2)mixedpolarity.NorthAmericanCommissiononStratigraphicNomenclature (b)Thicknessandduration.Thethicknessofrockofapolarityzoneortheamountoftimerepresentedshouldplaynopartinthedefinitionofthezone.Thepolaritysignatureistheessentialpropertyfordefinition.Ranks.Whencontinuedworkatthestratotypeforapolarityzone,ornewworkincorrelativerockbodieselsewhere,revealssmallerpolarityunits,thesemayberecognizedformallyaspolaritysubzones.Ifitshouldprovenecessaryordesirabletogrouppolarityzones,theseshouldbetermedpolaritysuper-zones.Therankofapolarityunitmaybechangedwhendeemedappropriate.MagnetopolarityNomenclatureArticle47.CompoundName.TheformalnameofamagnetopolarityzoneshouldconsistofageographicnameandthetermPolarityZone.ThetermmaybemodifiedbyNormal,Reversed,or(example:DeerParkReversedPolarityZone).Innamingorrevisingmagnetopolarityunits,appropriatepartsofArticles7and19apply.Theuseofin-formaldesignations,e.g.,numbersorletters,isnotprecluded.BIOSTRATIGRAPHICUNITSArticle48.Fundamentalsofbiostratigraphy.Biostra-tigraphyisthebranchofstratigraphythatdealswiththedistributionoffossilsinthestratigraphicrecordandtheclas-sificationofbodiesofrockorrockmaterialintobiostrati-graphicunitsbasedontheircontainedfossils.Remark.(a)Uniqueness.Biostratigraphicunitsaredistinctfromallotherkindsofstratigraphicunitsbecausetheircontainedfossilsrecordtheunidirectionalprocessoforganicevolution.Assuch,thestratigraphicrecordasawholecontainsanunrepeatedsequenceoffossiltaxathatmaybeusedtodeterminetherelativeageoftheirenclosingstrata.NatureandBoundariesArticle49.NatureofBiostratigraphicUnits.Abio-stratigraphicunitisabodyofrockthatisdefinedorchar-acterizedbyitsfossilcontent.Remarks.(a)Unfossiliferousrocks.Thosebodiesofrocklackingnamedfossilshavenobiostratigraphiccharacterandare,therefore,notamenabletobiostratigraphicclassification.(b)Contemporaneityofrocksandfossils.Mostfossilsarecontemporaneouswiththebodyofrockthatcontainsthem,in-cludingthosederivedfromdifferent,butcoevalsedimentaryen-vironments.Abodyofrock,however,sometimescontainsfossilsderivedfromolderoryoungerrocks.Fossilsnotcontemporaneouswiththeenclosingbodyofrockshouldnotbeusedtodefine,characterize,oridentifyabiostratigraphicunit.Independencefromlithostratigraphicunits.Biostrati-graphicunitsarebasedoncriteriathatdifferfundamentallyfromthoseusedforlithostratigraphicunits.Theirboundariesmayormaynotcoincidewiththeboundariesoflithostratigraphicunits,buttheybearnoinherentrelationtothem.Independencefromchronostratigraphicunits.Thebound-ariesofmostbiostratigraphicunits,unliketheboundariesofchro-nostratigraphicunits,arebothcharacteristicallyandconceptuallydiachronous.Theverticalandlaterallimitsofthebiostratigraphicunitrepresenttherecordedlimitsindistributionofthedefiningorcharacterizingfossilelements.Regionally,theupperandlowerboundariesofbiostratigraphicunitsarerarelysynchronoussurfaces,whereasthelateralboundariesofbiostratigraphicunitsareneversynchronoussurfaces.Nevertheless,biostratigraphicunitsareef-fectiveforinterpretingchronostratigraphicrelations.Article50.KindsofBiostratigraphicUnits.Thebio-zoneisthefundamentalbiostratigraphicunit.Fivespecifickindsofbiozonesarerecognizedherein:rangebiozone,in-tervalbiozone,lineagebiozone,assemblagebiozone,andabundancebiozone.Thesefivekindsofbiozonesarenothierarchicallyinterrelated.Thewordsrange,interval,lineage,assemblage,andabundancearemerelyde-scriptiveterms.Theyrepresentdifferentapproachesintheprocessofsettingup,andintherecognitionof,abiozone.Thekindofbiozonechosenwilldependonthenatureofthebiota,theapproachesandpreferencesoftheindividualsci-entist,andthespecificproblembeinginvestigated.Themostcommonchoiceofbiozoneisoneinwhichboththelowerboundaryandtheupperboundaryarebasedonthelowestoccurrencesofindividualtaxa;thetwotaxamayormaynothaveadirectphylogeneticlink.Therangesofthetaxawhoselowestorhighestoccurrencesormaximumabundancesde-finetheboundariesofthebiozonearenotnecessarilyre-strictedtothebiozone,norisitnecessarythattheyrangethroughtheentirebiozone.Remarks.(a)Rangebiozone.Arangebiozoneisabodyofrockrepresentingtheknownstratigraphicandgeographicrangeofoccurrenceofanyselectedelementorelementsofthechosenfossiltaxon,ortaxa,presentintherockrecord.Therearetwokindsofrangebiozones:taxon-rangebiozoneandconcurrent-rangeAtaxon-rangebiozone(Figure4A)isabodyofrockrep-resentingtheknownstratigraphicandgeographicrangeofachosentaxon.Aconcurrent-rangebiozone(Figure4B)isabodyofrockin-cludingtheconcurrent,coincident,oroverlappingpartoftherangesoftwospecifiedtaxa.(b)Intervalbiozone.Anintervalbiozoneisabodyofrockbetweentwospecifiedbiostratigraphicsurfaces(biohorizonsoftheISSC,1994,p.56).Thefeaturesonwhichbiohorizonsarecom-monlybasedincludelowestoccurrences(Figure4C),highestoc-currences(Figure4D),distinctiveoccurrences,orchangesinthecharacterofindividualtaxa(e.g.,changesinthedirectionofcoilinginforaminiferaorinnumberofseptaincorals).Lineagebiozone.Alineagebiozone(Figure4E)isabodyofrockcontainingspeciesrepresentingaspecificsegmentofanevolutionarylineage.Assemblagebiozone.Anassemblagebiozone(Figure5A)isabodyofrockcharacterizedbyauniqueassociationofthreeormoretaxa,theassociationofwhichdistinguishesitinbiostrati-graphiccharacterfromadjacentstrata.Anassemblagebiozonemaybebasedonasingletaxonomicgroup,forexample,trilobites,oronmorethanonegroup,suchasacritarchsandchitinozoans.Abundancebiozone.Anabundancebiozone(Figure5B)isabodyofrockinwhichtheabundanceofaparticulartaxonorspecifiedgroupoftaxaissignificantlygreaterthaninadjacentpartsofthesection.Abundancezonesmaybeoflimited,localutilityNorthAmericanStratigraphicCode becauseabundancesoftaxainthegeologicrecordarelargelycontrolledbypaleoecology,taphonomy,anddiagenesis.Theonlyunequivocalwaytoidentifyaparticularabundancezoneistotraceitlaterally.(f)Hybridornewkindsofbiozones.Asspecificproblemsarefaced,biostratigraphicanalysisprogresses,andnewtechnologiesappear,otherformsofbiozonesmayproveusefulandarenotprohibitedunderthisCode.Article51.Boundaries.Theboundariesofabiozonearedrawnatsurfacesthatmarkthelowestoccurrence,highestoccurrence,limit,increaseinabundance,ordecreaseinabundanceofoneormorecomponentsofthefaunaorflora.Furthermore,thebaseortopofonekindofbiozonemaynot,orneednot,coincidewiththebaseortopofan-otherkindofbiozone.Remark.(a)Identificationofbiozones.Boundariesofrangebiozonesarethehorizonsoflowestandhigheststratigraphicoccur-renceofthespecifiedtaxonortaxa.Whentwotaxaareinvolved,theconcurrent-rangebiozoneispresentonlywherebothtaxaarepresent.Boundariesofintervalbiozonesaredefinedbytwospecifiedbiostratigraphicsurfaces,inwhichcasethebaseofonebiozoneusuallydefinesthetopoftheunderlyingbiozone.Boundariesof Figure4.Examplesofrange,lineage,andinter-valbiozones.NorthAmericanCommissiononStratigraphicNomenclature lineagebiozonesaredeterminedbythebiohorizonsrepresentingthelowestoccurrence(s)ofsuccessiveelementsintheevolutionarylineageunderconsideration.Boundariesofassemblagebiozonesmaybedifficulttodefineprecisely,butsuchbiozonesarereadilychar-acterizedandidentifiedbythefullyorpartiallyoverlappingrangesofenclosedtaxaorgroupsoftaxa.Inanyonesection,however,notallcharacterizingtaxaneedbepresentinordertorecognizethebiozone,andthebiozonemaybecharacterizedoridentifiedbyothertaxa.Boundariesofabundancebiozonesaredefinedbymarkedchangesinrelativeabundanceofpreservedtaxa.Article52.notused.RanksofBiostratigraphicUnitsArticle53.FundamentalUnit.Thebiozoneisthefundamentalunitofbiostratigraphicclassification.Remarks.(a)Scope.Asinglebodyofrockmaybedividedintomorethanonekindofbiozone.Abiozonemaybebasedonasingletaxonomicgrouporonseveraldifferenttaxonomicgroups.Biozoneboundariesderivedfromonetaxonomicgroupneednot,andcommonlydonot,coincidewiththoseofanothertaxonomicgroup.Biozonesvarygreatlyintheirstratigraphicthicknessandgeographicextent,andtaxonomicrefinementorrevisionmayin-creaseordecreasetheextentofabiozone.(b)Divisions.Abiozonemaybecompletelyorpartlydi-videdintosubbiozones.Allrulesfordefiningandcharacterizingbiozonesarealsoapplicabletosubbiozones.Shortenedformsofexpression.Biozoneisacondensedexpressionforbiostratigraphiczone.Bioshouldbeusedinfrontofzonetodifferentiateitfromothertypesofzones,buttheunadornedtermzonemaybeusedonceitisclearthatthetermisasubstituteforbiozone.Furthermore,onceithasbeenmadeclearwhatkindofbiozonehasbeenemployed,thedescriptivetermisnotrequiredtobecomepartoftheformalname;forexample,theEurekaspiriferpinyonensisAssemblageBiozonecanbedesignatedsimplyastheEurekaspiriferpinyonensisBiozone.Whenabiozoneisdescribedforthefirsttime,however,thedescriptivetermshouldbecapitalized;e.g.,ExusalbusAssemblageBiozone.Similarly,sub-biozonemaybeshortenedtosubzonewhenthemeaningisclear.BiostratigraphicNomenclatureArticle54.EstablishingFormalUnits.Formalestab-lishmentofabiozonemustmeettherequirementsofArticle3andrequiresauniquename,adescriptionofitsfossilcontentandstratigraphicboundaries,andadiscussionofitsspatialRemarks.(a)Name.Thenameofabiozoneconsistsofthenameofoneormoredistinctivetaxaorparataxa(fortracefossils)foundinthebiozone,followedbythewordBiozone.(e.g.,Turbo-rotaliacerrozaulensisBiozoneorCyrtograptuslundgreni-TestograptustestisBiozone).Thenameofthespecieswhoselowestoccurrencedefinesthebaseofthezoneisthemostcommonchoiceforthebiozonename.Namesofthenominatetaxa,andhencethenamesofthebiozones,conformtotherulesoftheinternationalcodesofzoologicalorbotanicalnomenclatureor,inthecaseoftracefossils,internationallyacceptedstandardpractice.(b)Shorterdesignationsforbiozonenames.Onceaformalbiozonehasbeenestablished,anabbreviationoralpha-numericdesignationthatrepresentsthenameofthebiozonemaybeaconvenientsubstitute.Forexample,theIcrioduswoschmidtiBiozonewastermedthewoschmidtiZonebyKlapperandJohnson(1980),andtheRhombodiniumporosumAssemblageZoneintheBartonBedswastermedBAR-3byBujaketal.(1980).(c)Revision.Biozonesandsubbiozonesareestablishedempiricallyandmaybemodifiedonthebasisofnewevidence.Positionsofestablishedbiozoneorsubbiozoneboundariesmayberefinedstratigraphically,newcharacterizingtaxamayberecognized,ororiginalcharacterizingtaxamaybesuperseded.Iftheconceptofaparticularbiozoneorsubbiozoneissubstantiallymodified,anewuniquedesignationisdesirable.Definingtaxa.Whenabiozoneorsubbiozoneisformallydescribed,orlateremended,itisnecessarytodesignate,orre-designate,thedefiningorcharacterizingtaxa,and/ortodocumentthelowestandhighestoccurrencesofthetaxathatmarkthebiozoneorsubbiozoneboundaries.Referencesections.BiostratigraphicunitsdonothavestratotypesinthesenseofArticle3,item(iv),andArticle8.Nevertheless,itisdesirabletodesignateareferencesectioninwhichthebiostratigraphicunitischaracteristicallydeveloped.PEDOSTRATIGRAPHICUNITSNatureandBoundariesArticle55.NatureofPedostratigraphicUnits.Apedo-stratigraphicunitisabodyofrockthatconsistsofoneormorepedologichorizonsdevelopedinoneormorelitho-allostratigraphic,orlithodemicunits(Figure6) Figure5.Examplesofassemblageandabun-dancebiozones.NorthAmericanStratigraphicCode andisoverlainbyoneormoreformallydefinedlithostrati-graphicorallostratigraphicunits.Remarks.(a)Definition.Apedostratigraphicunitisaburied,traceable,three-dimensionalbodyofrockthatconsistsofoneormoredifferentiatedpedologichorizons.(b)Recognition.Thedistinguishingpropertyofapedostrati-graphicunitisthepresenceofoneormoredistinct,differentiated,pedologichorizons.Pedologichorizonsareproductsofsoildevel-opment(pedogenesis)thatoccurredsubsequenttoformationofthelithostratigraphic,allostratigraphic,orlithodemicunitorunitsonwhichtheburiedsoilwasformed;theseunitsaretheparentmaterialsinwhichpedogenesisoccurred.Pedologichorizonsarerecognizedinthefieldbydiagnosticfeaturessuchascolor,soilstructure,organic-matteraccumulation,texture,claycoatings,stains,orconcretions.Micromorphology,particlesize,claymineralogy,andotherproper-tiesdeterminedinthelaboratoryalsomaybeusedtoidentifyanddistinguishpedostratigraphicunits.Boundariesandstratigraphicposition.Theupperbound-aryofapedostratigraphicunitisthetopoftheuppermostpedologichorizonformedbypedogenesisinaburiedsoilprofile.Thelowerboundaryofapedostratigraphicunitisthelowestdefinitephysicalboundaryofapedologichorizonwithinaburiedsoilprofile.Thestrat-igraphicpositionofapedostratigraphicunitisdeterminedbyitsre-lationtooverlyingandunderlyingstratigraphicunits(seeRemarkd).Traceability.Practicabilityofsubsurfacetracingoftheup-perboundaryofaburiedsoilisessentialinestablishingapedostrati-graphicunitbecause(1)fewburiedsoilsareexposedcontinuouslyforgreatdistances,(2)thephysicalandchemicalpropertiesofaspecificpedostratigraphicunitmayvarygreatly,bothverticallyandlaterally,fromplacetoplace,and(3)pedostratigraphicunitsofdifferentstratigraphicsignificanceinthesameregiongenerallydonothaveuniqueidentifyingphysicalandchemicalcharacteristics.Consequently,extensionofapedostratigraphicunitisaccomplishedbylateraltrac-ingofthecontactbetweenaburiedsoilandanoverlying,formallydefinedlithostratigraphicorallostratigraphicunit,orbetweenasoilandtwoormoredemonstrablycorrelativestratigraphicunits.Distinctionfrompedologicsoils.Pedologicsoilsmayincludeorganicdeposits(e.g.,litterzones,peatdeposits,orswampdeposits)thatoverlieorgradelaterallyintodifferentiatedburiedsoils.Theorganicdepositsarenotproductsofpedogenesis,andtherefore,Ohorizonsarenotincludedinapedostratigraphicunit(Figure6);theymaybeclassifiedasbiostratigraphicorlithostrati-graphicunits.PedologicsoilsalsoincludetheentireChorizonofasoil.TheChorizoninpedologyisnotrigidlydefined;itismerelythepartofasoilprofilethatunderliestheBhorizon.ThebaseoftheChorizoninmanysoilprofilesisgradationalorunidentifiable;com-monlyitisplacedarbitrarily.Theneedforclearlydefinedandeasilyrecognizedphysicalboundariesforastratigraphicunitrequiresthatthelowerboundaryofapedostratigraphicunitbedefinedasthelowestdefinitephysicalboundaryofapedologichorizoninaburiedsoilprofile,andpartoralloftheChorizonmaybeexcludedfromapedostratigraphicunit.(f)Relationtosaproliteandotherweatheredmaterials.Amaterialderivedbyinsituweatheringoflithostratigraphic,allo-stratigraphic,and/orlithodemicunits(e.g.,saprolite,bauxite,re-siduum)maybetheparentmaterialinwhichpedologichorizonsform,butisnotapedologicsoil.Apedostratigraphicunitmaybebasedonthepedologichorizonsofaburiedsoildevelopedintheproductofin-situweathering,suchassaprolite.Theparentsofsuchapedostratigraphicunitareboththesaproliteand,indirectly,therockfromwhichitformed.Distinctionfromotherstratigraphicunits.Apedostrati-graphicunitdiffersfromotherstratigraphicunitsinthat(1)itisa Terminologyrelatedtopedostratigraphicclassificationissum-marizedonp.1559. Figure6.Relationbetweenpedostratigraphicunitsandpedologicprofiles.Thebaseofageosolisthelowestclearlydefinedphysicalboundaryofapedologichorizoninaburiedsoilprofile.InthisexampleitisthelowerboundaryoftheBhorizonbecausethebaseoftheChorizonisnotaclearlydefinedphysicalboundary.Inotherprofiles,thebasemaybethelowerboundaryofaChorizon.PedologicprofilemodifiedfromRuhe(1965)andPawluk(1978).NorthAmericanCommissiononStratigraphicNomenclature productofsurfacealterationofoneormoreoldermaterialunitsbyspecificprocesses(pedogenesis),(2)itslithologyandotherprop-ertiesdiffermarkedlyfromthoseoftheparentmaterial(s),and(3)asinglepedostratigraphicunitmaybeformedinsituinparentma-terialunitsofdiversecompositionsandages.(h)Independencefromtimeconcepts.Theboundariesofapedostratigraphicunitaretime-transgressive.Conceptsoftimespans,howevermeasured,playnopartindefiningtheboundariesofapedostratigraphicunit.Nonetheless,evidenceofage,whetherbasedonfossils,numericalages,orgeometricalorotherrelations,mayplayanimportantroleindistinguishingandidentifyingnon-contiguouspedostratigraphicunitsatlocalitiesawayfromthetypeareas.Thenameofapedostratigraphicunitshouldbechosenfromageographicfeatureinthetypearea,andnotfromatimespan.PedostratigraphicNomenclatureandUnitArticle56.FundamentalUnit.Thefundamentalandonlyunitinpedostratigraphicclassificationisageosol.Article57.Nomenclature.Theformalnameofapedostratigraphicunitconsistsofageographicnamecom-binedwiththetermgeosol.Capitalizationoftheinitialletterineachwordservestoidentifyformalusage.Thegeo-graphicnameshouldbeselectedinaccordancewithrecom-mendationsinArticle7andshouldnotduplicatethenameofanotherformalgeologicunit.Namesbasedonsubjacentandsuperjacentrockunits,forexamplethesuper-Wilcoxsub-Claibornesoil,areinformal,asarethosewithtimecon-notations(post-Wilcoxpre-Claibornesoil).Remarks.(a)Compositegeosols.Wherethehorizonsoftwoormoremergedorweldedburiedsoilscanbedistinguished,formalnamesofpedostratigraphicunitsbasedonthehorizonboundariescanberetained.Wherethehorizonboundariesoftherespectivemergedorweldedsoilscannotbedistinguished,formalpedostratigraphicclassificationisabandonedandacombinednamesuchasHallettville-Jamesvillegeosolmaybeusedinformally.(b)Characterization.Thephysicalandchemicalpropertiesofapedostratigraphicunitcommonlyvaryverticallyandlaterallythroughoutthegeographicextentoftheunit.Apedostratigraphicunitischaracterizedbytherangeofphysicalandchemicalpropertiesoftheunitinthetypearea,ratherthanbytypicalpropertiesexhibitedinatypesection.Consequently,apedostratigraphicunitischaracterizedonthebasisofacompositestratotype(Article8d).ProceduresforestablishingformalpedostratigraphicunitsAformalpedostratigraphicunitmaybeestablishedinaccordancewiththeapplicablerequirementsofArticle3.Thedefinitionshouldincludeadescriptionofmajorsoilhorizonsandtheirlateralvariations.ALLOSTRATIGRAPHICUNITSNatureandBoundariesArticle58.NatureofAllostratigraphicUnits.Anallo-stratigraphicunitisamappablebodyofrockthatisdefinedandidentifiedonthebasisofitsboundingdiscontinuities.Remarks.(a)Purpose.Formalallostratigraphicunitsmaybedefinedtodistinguishbetweendifferent(1)superposeddiscontinuity-boundeddepositsofsimilarlithology(Figures7,9),(2)contiguousdiscontinuity-boundeddepositsofsimilarlithology(Figure8),or(3)geographicallyseparateddiscontinuity-boundedunitsofsimilarli-thology(Figure9).Formalallostratigraphicunitsmayalsobedefinedtodistinguishassingleunitsdiscontinuity-boundeddepositscharac-terizedbylithicheterogeneity(units14inFigure7).Allostrati-graphicunitsaredistinguishedbyboundingdiscontinuities.Thelithologyofanallostratigraphicunitplaysnopartinitsdefinition.(b)Internalcharacteristics.Internalcharacteristics(physical,chemical,andpaleontological)mayvarylaterallyandverticallythroughouttheunit.Boundaries.Boundariesofallostratigraphicunitsarelaterallytraceablediscontinuities(Figures79).(d)Mappability.Aformalallostratigraphicunitmustbemap-pableatthescalepracticedintheregionwheretheunitisdefined.(e)Typelocalityandextent.Atypelocalityandtypeareamustbedesignated;acompositestratotypeoratypesectionandseveralreferencesectionsaredesirable.Anallostratigraphicunitmaybelaterallycontiguouswithallorpartofaformallydefinedlitho-stratigraphicunit,butasthetwokindsofunitsaredefinedbyentirelydifferentcriteria,bothkindsofunitsmaybeformallyrec-ognizedinthesamearea.(f)Relationtogenesis.Geneticinterpretationisaninap-propriatebasisfordefininganallostratigraphicunit.However,ge-neticinterpretationmayinfluencethechoiceofitsboundaries.Relationtogeomorphicsurfaces.Ageomorphicsurfacemaybeusedasaboundaryofanallostratigraphicunit,buttheunitshouldnotbegiventhegeographicnameofthesurface.(h)Relationtosoilsandpaleosols.Soilsandpaleosolsarecomposedofproductsofweatheringandpedogenesisanddifferinmanyrespectsfromallostratigraphicunits,whicharedepositionalunits(seePedostratigraphicUnits,Article55).Theupperbound-aryofasurfaceorburiedsoilmaybeusedasaboundaryofanallostratigraphicunit.Relationtoinferredgeologichistory.Inferredgeologichistoryisnotusedtodefineanallostratigraphicunit.However,well-documentedgeologichistorymayinfluencethechoiceoftheunitsboundaries.RelationtotimeconceptsInferredtimespans,howevermeasured,arenotusedtodefineanallostratigraphicunit.However,agerelationsmayinfluencethechoiceoftheunitsboundaries.(k)Extensionofallostratigraphicunits.Anallostratigraphicunitisextendedfromitstypeareabytracingtheboundarydiscontinu-itiesorbytracingormatchingthedepositsbetweenthediscontinuities.RanksofAllostratigraphicUnitsArticle59.Hierarchy.Thehierarchyofallostrati-graphicunits,inorderofdecreasingrank,isallogroupformation,andallomemberRemarks.(a)Alloformation.Thealloformationisthefun-damentalunitinallostratigraphicclassification.Analloformationmaybecompletelyoronlypartlydividedintoallomembers,ifsomeusefulpurposeisserved,oritmayhavenoallomembers.(b)Allomember.Anallomemberistheformalallostrati-graphicunitnextinrankbelowanalloformation.Allogroup.Anallogroupistheallostratigraphicunitnextinrankaboveanalloformation.Anallogroupisestablishedonlyifa FromtheGreek:other,different.Article58ewasrevisedinaccordancewithArticle21in1995.Therevisedremarkisshownhere.SeeNote60(AAPGBulletin,v.77,p.909)andNote62(AAPGBulletin,v.81,p.13421345)forfurtherdetailsontherevision.NorthAmericanStratigraphicCode unitofthatrankisessentialtoelucidationofgeologichistory.Anallogroupmayconsistentirelyofnamedalloformationsor,alter-natively,maycontainoneormorenamedalloformationsthatjointlydonotcomprisetheentireallogroup.Changesinrank.TheprinciplesandproceduresforelevationandreductioninrankofformalallostratigraphicunitsarethesameasthoseinArticles19b,19g,and28.AllostratigraphicNomenclatureArticle60.Nomenclature.Theprinciplesandproce-duresfornamingallostratigraphicunitsarethesameasthosefornamingoflithostratigraphicunits(seeArticles7,30).Remark.(a)Revision.AllostratigraphicunitsmayberevisedorotherwisemodifiedinaccordancewiththerecommendationsinArticles17to20.FORMALUNITSEXPRESSINGORRELATINGTOGEOLOGICAGEKINDSOFGEOLOGIC-TIMEUNITSNatureandKindsArticle61.Kinds.Geologic-timeunitsareconcep-tual,ratherthanmaterial,innature.Twokindsarerecog-nized:thosebasedonmaterialstandardsorreferents(specificrocksequencesorbodies),andthoseindependentofma-terialreferents(Figure1). Figure8.Exampleofallostratigraphicclassificationofcon-tiguousdepositsofsimilarlithology.Allostratigraphicunits1,2,and3arephysicalrecordsofthreeglaciations.Theyarelitho-logicallysimilar,reflectingderivationfromthesamebedrock,andconstituteasinglelithostratigraphicunit. Figure7.Exampleofallostratigraphicclassificationofalluvialandlacustrinedepositsinagraben.Thealluvialandlacustrinedepositsmaybeincludedinasingleformation,ormaybeseparatedlaterallyintoformationsdistinguishedonthebasisofcontrastingtexture(gravel,clay).Texturalchangesareabruptandsharp,bothverticallyandlaterally.Thegraveldepositsandclaydeposits,respectively,arelithologicallysimilarandthuscannotbedistinguishedasmembersofaformation.Fourallostratigraphicunits,eachincludingtwoorthreetexturalfacies,maybedefinedonthebasisoflaterallytraceablediscontinuities(buriedsoilsordisconformities).NorthAmericanCommissiononStratigraphicNomenclature UnitsBasedonMaterialReferentsArticle62.KindsBasedonReferents.Twokindsofformalgeologic-timeunitsthatarebasedonmaterialrefer-entsarerecognized:theyareisochronousanddiachronousunits.Article63.IsochronousCategories.Isochronoustimeunitsandthematerialbodiesfromwhichtheyarederivedaretwofold:geochronologicunits(Article80),whicharebasedoncorrespondingmaterialchronostratigraphicunits(Article66),andpolarity-chronologicunits(Article88),basedoncorrespondingmaterialpolarity-chronostratigraphicunits(Article83).Remark.(a)Extent.Isochronousunitsareapplicableworld-wide;theymaybereferredtoeveninareaslackingamaterialrecordofthenamedspanoftime.Thedurationofthetimemayberepresentedbyaunit-stratotypereferent.Thebeginningandendofthetimearerepresentedbypoint-boundary-stratotypeseitherinasinglestratigraphicsequenceorinseparatestratotypesections(Articles8b,10b).Article64.DiachronousCategories.Diachronicunits(Article91)aretimeunitscorrespondingtodiachronousmaterialallostratigraphicunits(Article58),pedostrati-graphicunits(Article55),andmostlithostratigraphic(Article22)andbiostratigraphic(Article48)units.Remarks.(a)Diachroneity.Somelithostratigraphicandbiostratigraphicunitsareclearlydiachronous,whereasothershaveboundariesthatarenotdemonstrablydiachronouswithintheresolvingpowerofavailabledatingmethods.Thelattercommonly Figure9.Exampleofallostratigraphicclassificationoflithologicallysimilar,discontinuousterracedeposits.A,B,C,andDareterracegravelunitsofsimilarlithologyatdifferenttopographicpositionsonavalleywall.Thedepositsmaybedefinedasseparateformalallostratigraphicunitsifsuchunitsareusefulandifboundingdiscontinuitiescanbetracedlaterally.Terracegravelsofthesameagecommonlyareseparatedgeographicallybyexposuresofolderrocks.Wheretheboundingdiscontinuitiescannotbetracedcontinuously,theymaybeextendedgeographicallyonthebasisofobjectivecorrelationofinternalpropertiesofthedepositsotherthanlithology(e.g.,fossilcontent,includedtephras),topographicposition,numericalages,orrelative-agecriteria(e.g.,soilsorotherweatheringphenomena).Thecriteriaforsuchextensionshouldbedocumented.Slopedepositsandeoliandeposits(S)thatmantleterracesurfacesmaybeofdiverseagesandarenotincludedinaterrace-gravelallostratigraphicunit.Asingleterracesurfacemaybeunderlainbymorethanoneallostratigraphicunit(unitsBandCinFigure9BandC).NorthAmericanStratigraphicCode aretreatedasisochronousandareusedforpurposesofchrono-correlation(seebiochronozone,Article75).However,theassump-tionofisochroneitymustbetestedcontinually.(b)Extent.Diachronicunitsarecoextensivewiththedia-chronousmaterialstratigraphicunitsonwhichtheyarebasedandarenotusedbeyondtheextentoftheirmaterialreferents.UnitsIndependentofMaterialReferentsArticle65.NumericalDivisionsofTime.Isochronousgeologic-timeunitsbasedonnumericaldivisionsoftimeinyearsaregeochronometricunits(Article96)andhavenomaterialreferents.CHRONOSTRATIGRAPHICUNITSNatureandBoundariesArticle66.Definition.Achronostratigraphicunitisabodyofrockestablishedtoserveasthematerialreferenceforallconstituentrocksformedduringthesamespanoftime.Eachboundaryissynchronous.Thebodyalsoservesasthebasisfordefiningthespecificintervaloftime,orgeochronologicunit(Article80),representedbythereferent.Remarks.(a)Purposes.Chronostratigraphicclassificationprovidesameansofestablishingthetemporallysequentialorderofrockbodies.Principalpurposesaretoprovideaframeworkfor(1)temporalcorrelationoftherocksinoneareawiththoseinanother,(2)placingtherocksoftheEarthscrustinasys-tematicsequenceandindicatingtheirrelativepositionandagewithrespecttoearthhistoryasawhole,and(3)constructinganinternationallyrecognizedStandardGlobalChronostratigraphic(b)Nature.Achronostratigraphicunitisamaterialunitandconsistsofabodyofstrataformedduringaspecifictimespan.Suchaunitrepresentsallrocks,andonlythoserocks,formedduringthattimespan.Content.Achronostratigraphicunitmaybebaseduponthetimespanofabiostratigraphicunit,alithicunit,amagneto-polarityunit,oranyotherfeatureoftherockrecordthathasatimerange.Oritmaybeanyarbitrarybutspecifiedsequenceofrocks,providedithaspropertiesallowingchronocorrelationwithrocksequenceselsewhere.Article67.Boundaries.Boundariesofchronostrati-graphicunitsshouldbedefinedinadesignatedstratotypeonthebasisofobservablepaleontologicalorphysicalfeaturesoftherocks.Remark.(a)Emphasisonlowerboundariesofchronostrati-graphicunits.Designationofpointboundariesforbothbaseandtopofchronostratigraphicunitsisnotrecommended,becausesub-sequentinformationonrelationsbetweensuccessiveunitsmayidentifyoverlapsorgaps.Onemeansofminimizingoreliminatingproblemsofduplicationorgapsinchronostratigraphicsucces-sionsistodefineformallyasapoint-boundarystratotypeonlythebaseoftheunit.Thus,achronostratigraphicunitwithitsbasedefinedatonelocality,willhaveitstopdefinedbythebaseofanoverlyingunitatthesame,butmorecommonlyanother,locality(Article8b).Article68.Correlation.Demonstrationoftimeequiva-lenceisrequiredforgeographicextensionofachronostrati-graphicunitfromitstypesectionorarea.Boundariesofchronostratigraphicunitscanbeextendedonlywithinthelimitsofresolutionofavailablemeansofchronocorrelation,whichcurrentlyincludepaleontology,numericaldating,re-manentmagnetism,thermoluminescence,relative-agecrite-ria(examplesaresuperpositionandcross-cuttingrelations),andsuchindirectandinferentialphysicalcriteriaasclimaticchanges,degreeofweathering,andrelationstounconfor-mities.Ideally,theboundariesofchronostratigraphicunitsareindependentoflithology,fossilcontent,orothermaterialbasesofstratigraphicdivision,but,inpractice,thecorrela-tionorgeographicextensionoftheseboundariesreliesatleastinpartonsuchfeatures.Boundariesofchronostrati-graphicunitscommonlyareintersectedbyboundariesofmostotherkindsofmaterialunits.RanksofChronostratigraphicUnitsArticle69.Hierarchy.Thehierarchyofchronostrati-graphicunits,inorderofdecreasingrank,iseonothemerathemsystemseries,andstage.Ofthese,systemistheprimaryunitofworld-widemajorrank;itsprimacyderivesfromthehistoryofdevelopmentofstratigraphicclassifica-tion.Allsystemsandunitsofhigherrankaredividedcom-pletelyintounitsofthenextlowerrank.Chronozonesarenon-hierarchicalandcommonlylower-rankchronostratigraphicunits.Stagesandchronozonesinsumdonotnecessarilyequaltheunitsofnexthigherrankandneednotbecon-tiguous.Therankandmagnitudeofchronostratigraphicunitsarerelatedtothetimeintervalrepresentedbytheunits,ratherthantothethicknessorarealextentoftherocksonwhichtheunitsarebased.Article70.Eonothem.Theunithighestinrankiseonothem.ThePhanerozoicEonothemencompassesthePaleozoic,Mesozoic,andCenozoicErathems.AlthougholderrockshavebeenassignedheretoforetothePrecambrianEonothem,theyalsohavebeenassignedrecentlytoother(ArcheanandProterozoic)eonothemsbytheIUGSPrecam-brianSubcommission.ThespanoftimecorrespondingtoaneonothemisanArticle71.Erathem.Anerathemistheformalchro-nostratigraphicunitofranknextlowertoeonothemandcon-sistsofseveraladjacentsystems.Thespanoftimecorre-spondingtoanerathemisanRemark.(a)Names.NamesgiventotraditionalPhanerozoicerathemswerebaseduponmajorstagesinthedevelopmentoflifeonEarth:Paleozoic(old),Mesozoic(intermediate),andCe-nozoic(recent)life.AlthoughsomewhatcomparabletermshavebeenappliedtoPrecambrianunits,thenamesandranksofPrecambriandivisionsarenotyetuniversallyagreeduponandareunderconsiderationbytheIUGSSubcommissiononPrecambrianStratigraphy.NorthAmericanCommissiononStratigraphicNomenclature Article72.System.Theunitofranknextlowertoerathemisthesystem.Rocksencompassedbyasystemrep-resentatimespanandanepisodeofEarthhistorysuffi-cientlygreattoserveasaworldwidechronostratigraphicref-erenceunit.ThetemporalequivalentofasystemisaperiodRemark.(a)Subsystemandsupersystem.SomesystemsinitiallyestablishedinEuropelaterweredividedorgroupedelsewhereintounitsrankedassystems.Subsystems(MississippianSubsystemoftheCarboniferousSystem)andsupersystems(KarooSupersystem)aremoreappropriate.Article73.Series.Seriesisaconventionalchronostrati-graphicunitthatranksbelowasystemandalwaysisadivisionofasystem.Aseriescommonlyconstitutesamajorunitofchronostratigraphiccorrelationwithinaprovince,betweenprovinces,orbetweencontinents.AlthoughmanyEuropeanseriesarebeingadoptedincreasinglyfordividingsystemsonothercontinents,provincialseriesofregionalscopecontinuetobeuseful.ThetemporalequivalentofaseriesisanArticle74..Astageisachronostratigraphicunitofsmallerscopeandrankthanaseries.Itismostcommonlyofgreatestuseinintra-continentalclassificationandcorre-lation,althoughithasthepotentialforworldwiderecog-nition.ThegeochronologicequivalentofastageisanRemark.(a)Substage.Stagesmaybe,butneednotbe,di-videdcompletelyintosubstages.Article75.Chronozone.Achronozoneisanon-hierarchical,butcommonlysmall,formalchronostrati-graphicunit,anditsboundariesmaybeindependentofthoserankedchronostratigraphicunitssuchasstageorseries.Althoughachronozoneisanisochronousunit,itmaybebasedonabiostratigraphicunit(example:CardiocerascordatumBiochronozone),alithostratigraphicunit(Wood-bendLithochronozone),oramagnetopolarityunit(GilbertReversed-PolarityChronozone).Modifiers(litho-,bio-,polarity)usedinformalnamesoftheunitsneednotberepeatedingeneraldiscussionswherethemeaningisevidentfromthecontext,e.g.,ExusalbusChronozone.Remarks.(a)Boundariesofchronozones.Thebaseandtopofachronozonecorrespondintheunitsstratotypetotheobserved,defining,physicalandpaleontologicalfeatures,buttheyareextendedtootherareasbyanymeansavailableforrecognitionofsynchroneity.Thetemporalequivalentofachronozoneisachron(b)Scope.Thescopeofthenon-hierarchicalchronozonemayrangemarkedly,dependinguponthepurposeforwhichitisdefinedeitherformallyorinformally.Theinformalbiochronozoneoftheammonites,forexample,representsadurationoftimewhichisenormousandexceedsthatofasystem.Incontrast,abiochronozonedefinedbyaspeciesoflimitedrange,suchastheExusalbusChronozone,mayrepresentadurationequaltoorbrieferthanthatofastage.Practicalutility.Chronozones,especiallythinandinfor-malbiochronozonesandlithochronozonesboundedbykeybedsorothermarkers,aretheunitsusedmostcommonlyinindustryinvestigationsofselectedpartsofthestratigraphyofeconomicallyfavorablebasins.Suchunitsareusefultodefinegeographicdistri-butionsoflithofaciesorbiofacies,thatprovideabasisforgeneticinterpretationsandtheselectionoftargetstodrill.ChronostratigraphicNomenclatureArticle76.Requirements.Requirementsforestab-lishingaformalchronostratigraphicunitinclude:(i)state-mentofintentiontodesignatesuchaunit;(ii)selectionofname;(iii)statementofkindandrankofunit;(iv)statementofgeneralconceptofunitincludinghistoricalbackground,synonymy,previoustreatment,andreasonsforproposedes-tablishment;(v)descriptionofcharacterizingphysicaland/orbiologicalfeatures;(vi)designationanddescriptionofboundarytypesections,stratotypes,orotherkindsofunitsonwhichitisbased;(vii)correlationandagerelations;and(vii)publicationinarecognizedscientificmediumasspeci-fiedinArticle4.Article77..Aformalchronostrati-graphicunitisgivenacompoundname,andtheinitiallet-tersofallwords,exceptfortrivialtaxonomicterms,arecapitalized.Exceptforchronozone(Article75),namespro-posedfornewchronostratigraphicunitsshouldnotdu-plicatethoseforotherstratigraphicunits.Forexample,naminganewchronostratigraphicunitsimplybyadding-anor-iantothenameofalithostratigraphicunitisRemarks.(a)Systemsandunitsofhigherrank.Namesthataregenerallyacceptedforsystemsandunitsofhigherrankhavediverseorigins,andtheyalsohavedifferentkindsofendings(Pa-leozoic,Cambrian,Cretaceous,Jurassic,Quaternary).(b)Seriesandunitsoflowerrank.Seriesandunitsoflowerrankarecommonlyknowneitherbygeographicnames(VirgilianSeries,OchoanSeries)orbynamesoftheirencompassingunitsmodifiedbythecapitalizedadjectivesUpper,Middle,andLower(LowerOrdovician).Namesofchronozonesarederivedfromtheunitonwhichtheyarebased(Article75).Forseriesandstage,ageographicnameispreferablebecauseitmayberelatedtoatypearea.Forgeographicnames,theadjectivalendings-anor-ianarerecommended(CincinnatianSeries),butitispermissibletousethegeographicnamewithoutanyspecialending,ifmoreeupho-nious.Manyseriesandstagenamesalreadyinusehavebeenbasedonlithicunits(groups,formations,andmembers)andbearthenamesoftheseunits(WolfcampianSeries,ClaibornianStage).Nevertheless,astagepreferablyshouldhaveageographicnamenotpreviouslyusedinstratigraphicnomenclature.Useofinternation-allyaccepted(mainlyEuropean)stagenamesispreferabletotheproliferationofothers.Article78.Stratotypes.Anidealstratotypeforachronostratigraphicunitisacompletelyexposedunbrokenandcontinuoussequenceoffossiliferousstratifiedrocksextendingfromawell-definedlowerboundarytothebaseofthenexthigherunit.Unfortunately,fewavailablesequencesaresufficientlycompletetodefinestagesandunitsofhigherrank,whichthereforearebestdefinedbyboundary-stratotypes(Article8b).Boundary-stratotypesformajorchronostratigraphicunitsideallyshouldbebasedoncompletesequencesofeitherfossiliferousmonofacialmarinestrataorrockswithothercriteriaforchronocorrelationtopermitwidespreadtracingofsynchronoushorizons.Extensionofsynchronoussurfacesshouldbebasedonasmanyindicatorsofageaspossible.NorthAmericanStratigraphicCode Article79.Revisionofunits.Revisionofachrono-stratigraphicunitwithoutchangingitsnameisallowablebutrequiresasmuchjustificationastheestablishmentofanewunit(Articles17,19,and76).Revisionorredefinitionofaunitofsystemorhigherrankrequiresinternationalagree-ment.Ifthedefinitionofachronostratigraphicunitisinad-equate,itmaybeclarifiedbyestablishmentofboundarystratotypesinaprincipalreferencesection.GEOCHRONOLOGICUNITSNatureandBoundariesArticle80.DefinitionandBasis.Geochronologicunitsaredivisionsoftimetraditionallydistinguishedonthebasisoftherockrecordasexpressedbychronostratigraphicunits.Ageochronologicunitisnotastratigraphicunit(i.e.,itisnotamaterialunit),butitcorrespondstothetimespanofanestablishedchronostratigraphicunit(Articles65and66),anditsbeginningandendingcorrespondstothebaseandtopofthereferent.RanksandNomenclatureofGeochronologicUnitsArticle81.Hierarchy.Thehierarchyofgeochrono-logicunitsinorderofdecreasingrankisperiodepoch,and.Chronisanon-hierarchical,butcommonlybrief,geochronologicunit.Agesinsumdonotnecessarilyequalepochsandneednotformacontinuum.Aneonisthetimerepresentedbytherocksconstitutinganeonothem;erabyanerathem;periodbyasystem;epochbyaseries;agebyastage;andchronbyachronozone.Article82.Nomenclature.Namesforperiodsandunitsoflowerrankareidenticalwiththoseofthecorrespondingchronostratigraphicunits;thenamesofsomeerasandeonsareindependentlyformed.Rulesofcapitali-zationforchronostratigraphicunits(Article77)applytogeochronologicunits.TheadjectivesEarly,Middle,andLateareusedforthegeochronologicepochsequivalenttothecorrespondingchronostratigraphicLower,Middle,andUpperseries,wheretheseareformallyestablished.POLARITY-CHRONOSTRATIGRAPHICUNITSNatureandBoundariesArticle83.Definition.Apolarity-chronostratigraphicunitisabodyofrockthatcontainstheprimarymagnetic-polarityrecordimposedwhentheconstituentrockwasdepos-ited,orcrystallized,duringaspecificintervalofgeologictime.Remarks.(a)Nature.Polarity-chronostratigraphicunitsde-pendfundamentallyfordefinitiononactualsectionsorsequences,ormeasurementsonindividualrockunits,andwithoutthesestandardstheyaremeaningless.Theyarebasedonmaterialunits,thepolarityzonesofmagnetopolarityclassification.Eachpolarity-chronostrati-graphicunitistherecordofthetimeduringwhichtherockformedandtheEarthsmagneticfieldhadadesignatedpolarity.Careshouldbetakentodefinepolarity-chronologicunitsintermsofpolarity-chronostratigraphicunits,andnotviceversa.(b)Principalpurposes.Twoprincipalpurposesareservedbypolarity-chronostratigraphicclassification:(1)correlationofrocksatoneplacewiththoseofthesameageandpolarityatotherplaces;and(2)delineationofthepolarityhistoryoftheEarthsmagneticfield.Recognition.Apolarity-chronostratigraphicunitmaybeextendedgeographicallyfromitstypelocalityonlywiththesup-portofphysicaland/orpaleontologiccriteriausedtoconfirmitsArticle84.Boundaries.Theboundariesofapolaritychronozoneareplacedatpolarity-reversalhorizonsorpo-laritytransitionzones(seeArticle45).RanksandNomenclatureofPolarity-ChronostratigraphicUnitsArticle85.FundamentalUnit.Thepolaritychrono-zoneconsistsofrocksofaspecifiedprimarypolarityandisthefundamentalunitofworldwidepolarity-chronostratigraphicclassification.Remarks.(a)Meaningofterm.Apolaritychronozoneistheworld-widebodyofrockthatiscollectivelydefinedasapolarity-chronostratigraphicunit.(b)Scope.Individualpolarityzonesarethebasicbuildingblocksofpolaritychronozones.Recognitionanddefinitionofpolaritychronozonesmaythusinvolvestep-by-stepassemblyofcarefullydatedorcorrelatedindividualpolarityzones,especiallyinworkwithrocksolderthantheoldestocean-floormagneticanoma-lies.ThisprocedureisthemethodbywhichtheBrunhes,Matu-yama,Gauss,andGilbertChronozoneswererecognized(Coxetal.,1963)anddefinedoriginally(Coxetal.,1964).Ranks.Divisionsofpolaritychronozonesaredesignatedpolaritysubchronozones.AssemblagesofpolaritychronozonesmaybetermedpolaritysuperchronozonesArticle86.EstablishingFormalUnits.Requirementsforestablishingapolarity-chronostratigraphicunitincludethosespecifiedinArticles3and4,andalso(1)definitionofboundariesoftheunit,withspecificreferencestodesignatedsectionsanddata;(2)distinguishingpolaritycharacteristics,lithologicdescriptions,andincludedfossils;and(3)corre-lationandagerelations.Article87..Aformalpolarity-chronostrati-graphicunitisgivenacompoundnamebeginningwiththatforanamedgeographicfeature;thesecondcomponentin-dicatesthenormal,reversed,ormixedpolarityoftheunit,andthethirdcomponentischronozone.Theinitialletterofeachtermiscapitalized.Ifthesamegeographicnameisusedforbothamagnetopolarityzoneandapolarity-chronostrati-graphicunit,thelattershouldbedistinguishedbyan-anor-ianending.Example:TetonianReversed-PolarityChronozone.Remarks.(a)Preservationofestablishedname.Aparticu-larlywell-establishednameshouldnotbedisplaced,eitheronthebasisofpriority,asdescribedinArticle7c,orbecauseitwasnotNorthAmericanCommissiononStratigraphicNomenclature takenfromageographicfeature.ContinueduseofBrunhes,Matuyama,Gauss,andGilbert,forexample,isendorsedsolongastheyremainvalidunits.(b)Expressionofdoubt.Doubtintheassignmentofpolarityzonestopolarity-chronostratigraphicunitsshouldbemadeexplicitifcriteriaoftimeequivalenceareinconclusive.POLARITY-CHRONOLOGICUNITSNatureandBoundariesArticle88.Definition.Polarity-chronologicunitsaredivisionsofgeologictimedistinguishedonthebasisoftherecordofmagnetopolarityasembodiedinpolarity-chronostratigraphicunits.Nospecialkindofmagnetictimeisimplied;thedesignationsusedaremeanttoconveythepartsofgeologictimeduringwhichtheEarthsmagneticfieldhadacharacteristicpolarityorsequenceofpolarities.Theseunitscorrespondtothetimespansrepresentedbypolaritychronozones,e.g.,GaussNormalPolarityChrono-zone.Theyarenotmaterialunits.RanksandNomenclatureofPolarity-ChronologicUnitsArticle89.FundamentalUnit.Thepolaritychronisthefundamentalunitofgeologictimedesignatingthetimespanofapolarity-chronozone.Remark.(a)Hierarchy.Polarity-chronologicunitsofde-creasinghierarchicalranksarepolaritysuperchronpolaritychron,andpolaritysubchronArticle90.Nomenclature.Namesforpolaritychro-nologicunitsareidenticalwiththoseofcorrespondingpolarity-chronostratigraphicunits,exceptthatthetermchron(orsuperchron,etc.)issubstitutedforchronozone(orsuper-chronozone,etc.).DIACHRONICUNITSNatureandBoundariesArticle91.Definition.Adiachronicunitcomprisestheunequalspansoftimerepresentedeitherbyaspecificlithostratigraphic,allostratigraphic,biostratigraphic,orpedo-stratigraphicunit,orbyanassemblageofsuchunits.Remarks.(a)Purposes.Diachronicclassificationprovides(1)ameansofcomparingthespansoftimerepresentedbystratigraphicunitswithdiachronousboundariesatdifferentlocalities,(2)abasisforbroadlyestablishingintimethebeginningandendingofdepositionofdiachronousstratigraphicunitsatdifferentsites,(3)abasisforinferringtherateofchangeinarealextentofdepositionalprocesses,(4)ameansofdeterminingandcomparingratesanddurationsofdepositionatdifferentlocalities,and(5)ameansofcomparingtemporalandspatialrelationsofdiachronousstratigraphicunits(WatsonandWright,1980).(b)Scope.Thescopeofadiachronicunitisrelatedto(1)therelativemagnitudeofthetransgressivedivisionoftimerepresentedbythestratigraphicunitorunitsonwhichitisbasedand(2)thearealextentofthoseunits.Adiachronicunitisnotextendedbeyondthegeographiclimitsofthestratigraphicunitorunitsonwhichitisbased.Basis.Thebasisforadiachronicunitisthediachronousreferent.Duration.Adiachronicunitmaybeofequaldurationatdifferentplacesdespitedifferencesinthetimesatwhichitbeganandendedatthoseplaces.Article92.Boundaries.Theboundariesofadia-chronicunitarethetimesrecordedbythebeginningandendofdepositionofthematerialreferentatthepointunderconsideration(Figures10,11).Remark.(a)Temporalrelations.Oneorbothofthebound-ariesofadiachronicunitaredemonstrablytime-transgressive.Thevaryingtimesignificanceoftheboundariesisdefinedbyaseriesofboundaryreferencesections(Article8b,8e).Thedurationandageofadiachronicunitdifferfromplacetoplace(Figures10,11).RanksandNomenclatureofDiachronicUnitsArticle93.Ranks.Adiachronisthefundamentalandnon-hierarchicaldiachronicunit.Ifahierarchyofdiachronicunitsisneeded,thetermsepisodephase,andclineinorderofdecreasingrank,arerecommended.Therankofahierarchicalunitisdeterminedbythescopeoftheunit(Article91b),andnotbythetimespanrepresentedbytheunitataparticularplace.Remarks.(a)Diachron.Diachronsmaydiffergreatlyinmag-nitudebecausetheyarethespansoftimerepresentedbyindividualorgroupedlithostratigraphic,allostratigraphic,biostratigraphic,and/orpedostratigraphicunits.(b)Hierarchicalorderingpermissible.Ahierarchyofdia-chronicunitsmaybedefinediftheresolutionofspatialandtem-poralrelationsofdiachronousstratigraphicunitsissufficientlyprecisetomakethehierarchyuseful(WatsonandWright,1980).Althoughallhierarchicalunitsofranklowerthanepisodearepartofaunitnexthigherinrank,notallpartsofanepisode,phase,orspanneedberepresentedbyaunitoflowerrank.Episode.Anepisodeistheunitofhighestrankandgreatestscopeinhierarchicalclassification.IftheWisconsinan Figure10.Comparisonofgeochronologic,chronostratigraphicanddiachronicunits.NorthAmericanStratigraphicCode Ageweretoberedefinedasadiachronicunit,itwouldhavetherankofepisode.Article94..Thenameforadiachronicunitshouldbecompound,consistingofageographicnamefol-lowedbythetermdiachronorahierarchicalrankterm.Bothpartsofthecompoundnamearecapitalizedtoindicatefor-malstatus.Ifthediachronicunitisdefinedbyasinglestrati-graphicunit,thegeographicnameoftheunitmaybeappliedtothediachronicunit.Otherwise,thegeographicnameofthediachronicunitshouldnotduplicatethatofanotherfor-malstratigraphicunit.Geneticterms(e.g.,alluvial,marine)orclimaticterms(e.g.,glacial,interglacial)arenotincludedinthenamesofdiachronicunits.Remarks.(a)Formaldesignationofunits.Diachronicunitsshouldbeformallydefinedandnamedonlyifsuchdefinitionisuseful.(b)Interregionalextensionofgeographicnames.Thegeographicnameofadiachronicunitmaybeextendedfromoneregiontoanotherifthestratigraphicunitsonwhichthediachronicunitisbasedextendacrosstheregions.Ifdifferentdiachronicunitsincontiguousregionseventuallyprovetobebasedonlaterallycontinuousstratigraphicunits,onenameshouldbeappliedtotheunitinbothregions.Iftwonameshavebeenapplied,onenameshouldbeabandonedandtheotherformallyextended.Rulesofpriority(Article7d)apply.Priorityinpublicationistoberespected,butpriorityalonedoesnotjustifydisplacingawell-establishednamebyonenotwell-knownorcommonlyused.Changefromgeochronologictodiachronicclassifica-tion.Lithostratigraphicunitshaveservedasthematerialbasisforwidelyacceptedchronostratigraphicandgeochronologicclassi-ficationsofQuaternarynonmarinedeposits,suchastheclassifica-tionsofFryeetal.(1968),WillmanandFrye(1970),andDreimanisandKarrow(1972).Inpractice,time-parallelhorizonshavebeenextendedfromthestratotypesonthebasisofmarkedlytime-transgressivelithostratigraphicandpedostratigraphicunitbound-aries.Thetime(geochronologic)units,definedonthebasisofthestratotypesectionsbutextendedonthebasisofdiachronousstrati-graphicboundaries,arediachronicunits.Geographicnamesestab-lishedforsuchgeochronologicunitsmaybeusedindiachronicclassificationif(1)thechronostratigraphicandgeochronologicclas-sificationsareformallyabandonedanddiachronicclassificationsareproposedtoreplacetheformergeochronologicclassifications,and(2)theunitsareredefinedasformaldiachronicunits.Preservationofwell-establishednamesinthesespecificcircumstancesretainstheintentandpurposeofthenamesandtheunits,retainsthepracticalsignificanceoftheunits,enhancescommunication,andavoidspro-liferationofnomenclature.Article95.EstablishingFormalUnits.Requirementsforestablishingaformaldiachronicunit,inadditiontothoseinArticle3,include(1)specificationofthenature,strati-graphicrelations,andgeographicorarealrelationsofthestratigraphicunitorunitsthatserveasabasisfordefinitionoftheunit,and(2)specificdesignationanddescriptionofmultiplereferencesectionsthatillustratethetemporalandspatialrelationsofthedefiningstratigraphicunitorunitsandtheboundariesoftheunitorunits.Remark.(a)Revisionorabandonment.Revisionoraban-donmentofthestratigraphicunitorunitsthatserveasthematerialbasisfordefinitionofadiachronicunitmayrequirerevisionorabandonmentofthediachronicunit.Procedureforrevisionmustfollowtherequirementsforestablishinganewdiachronicunit.GEOCHRONOMETRICUNITSNatureandBoundariesArticle96..Geochronometricunitsareunitsestablishedthroughthedirectdivisionofgeologictime,ex-pressedinyears.Likegeochronologicunits(Article80),geo-chronometricunitsareabstractions,i.e.,theyarenotmaterialunits.Unlikegeochronologicunits,geochronometricunitsarenotbasedonthetimespanofdesignatedchronostratigraphicunits(stratotypes),butaresimplytimedivisionsofconve-nientmagnitudeforthepurposeforwhichtheyareestablished Figure11.Schematicrelationofphasestoanepisode.Partsofaphasemaybedividedintospans,andspansintoclines.Formaldefinitionofspansandclinesisunnecessaryinmostdiachronicunithierarchies.NorthAmericanCommissiononStratigraphicNomenclature (e.g.,Hofmann,1990),suchasthedevelopmentofatimescaleforthePrecambrian.Theirboundariesarearbitrarilychosenoragreeduponagesinyears.RanksandNomenclatureofGeochronometricUnitsArticle97.Nomenclature.Geochronologicranktermsperiod,andchron)maybeusedforgeochronometricunitswhensuchtermsareformalized.Forexample,ArcheanEonandProterozoicEon,asrecognizedbytheIUGSSubcommissiononPrecambrianStratigraphy,areformalgeochronometricunitsinthesenseofArticle96,distinguishedonthebasisofanarbitrarilychosenboundaryat2.5Ga.Geochronometricunitsarenotdefinedby,butmayhave,correspondingchronostratigraphicunits(eonothemerathemseriesstage,andchronozonePARTIII:ADDENDAACSN(AmericanCommissiononStratigraphicNomenclature),1947,Note1OrganizationandobjectivesoftheStratigraphicCommission:AAPGBulletin,v.31,no.3,p.513518.ACSN(AmericanCommissiononStratigraphicNomenclature),1961,Codeofstratigraphicnomenclature:AAPGBulletin,v.45,no.5,p.645665.ACSN(AmericanCommissiononStratigraphicNomenclature),1970,Codeofstratigraphicnomenclature(2ded.):AmericanAssociationofPetroleumGeologists,45p.ACSN(AmericanCommissiononStratigraphicNomenclature),1976,Note44Applicationforadditiontocodeconcerningmagnetostratigraphicunits:AAPGBulletin,v.60,no.2,p.273277.Blatt,H.,W.B.N.Berry,andS.Brande,1990,Principlesofstrati-graphicanalysis:Oxford,England,BlackwellScientificPub-lications,512p.Boggs,Sam,Jr.,2001,Principlesofsedimentologyandstratigraphy,3rdedition:UpperSaddleRiver,NewJersey,PrenticeHall,726p.Bujak,J.P.,C.Downie,G.L.Eaton,andG.L.Williams,1980,DinoflagellatecystzonationoftheEocene,southernEngland,J.P.Bujak,C.Downie,G.L.Eaton,andG.L.Williams,DinoflagellatecrystsandacitarchsfromtheEoceneofsouth-ernEngland:PalaeontologicalAssociation,SpecialPapersinPalaeontology24,p.1526.Caster,K.E.,1934,Thestratigraphyandpaleontologyofnorth-westernPennsylvania,part1,stratigraphy:BulletinsofAmeri-canPaleontology,v.21,185p.Chang,K.H.,1975,Unconformity-boundedstratigraphicunits:GeologicalSocietyofAmericaBulletin,v.86,no.11,p.1544CommitteeonStratigraphicNomenclature,1933,Classificationandnomenclatureofrockunits:GeologicalSocietyofAmericaBulletin,v.44,no.2,p.423459,andAAPGBulletin,v.17,no.7,p.843868.Cox,A.V.,R.R.Doell,andG.B.Dalrymple,1963,GeomagneticpolarityepochsandPleistocenegeochronometry:Nature,v.198,p.10491051.Cox,A.V.,R.R.Doell,andG.B.Dalrymple,1964,ReversalsoftheEarthsmagneticfield:Science,v.144,no.3626,p.1537Cross,C.W.,1898,GeologyoftheTelluridearea:U.S.GeologicalSurveyl8thAnnualReport,pt.3,p.759.Cumming,A.D.,J.G.C.M.Fuller,andJ.W.Porter,1959,Separationofstrata:PaleozoiclimestonesoftheWillistonbasin:AmericanJournalofScience,v.257,no.10,p.722733.Dreimanis,A.,andP.F.Karrow,1972,GlacialhistoryoftheGreatLakesSt.Lawrenceregion,theclassificationoftheWiscon-sin(an)Stage,anditscorrelatives:InternationalGeologicCon-gress,24thSession,Montreal,1972,Section12,QuaternaryGeology,p.515.Dunbar,C.O.,andJ.Rodgers,1957,Principlesofstratigraphy:NewYork,Wiley,356p.Easton,R.M.,1992,TheGrenvilleProvinceandtheProterozoichistoryofcentralandsouthernOntario,P.C.Thurston,H.R.Williams,R.H.Sutcliffe,andG.M.Stott,eds.,GeologyofOntario:OntarioGeologicalSurvey,SpecialVolume4,pt.2,p.713904.Easton,R.M.,1996a,Sequencestratigraphicterminology:TheNACSNperspective:HoustonGeologicalSocietyBulletin,v.38,April1996,p.1516.Easton,R.M.,1996b,Lawandorderinstratigraphy:Thegood,thebadandthenewintheNorthAmericanstratigraphiccode:Sudbury,Ontario,Program,ScheduleandAbstracts,30thAssociationofEarthScienceEditorsMeeting,p.1415.Easton,R.M.,2000,Toeveryplutonicrockitsproperstratigraphicname(abs.):AssociationofEarthScienceEditors,Blueline,v.33,no.2,p.89.Easton,R.M.,D.L.Baars,andD.G.Cook,1997,Note62:RecordsofStratigraphicCommission,19921994:AAPGBulletin,v.81,p.13421345.Easton,R.M.,L.E.Edwards,andB.Wardlaw,2003,Notesongeo-chronologicandchronostratigraphicunits:Discussion:Geologi-calSocietyofAmericaBulletin,v.115,p.10161019.Edwards,L.E.,andD.E.Owen,1996,Note61:RecordsofStratigraphicCommission,19911992:AAPGBulletin,v.80,p.11561159.´a-Villafranca,I.,R.M.,Easton,L.E.Edwards,R.H.Fakundiny,andJ.O.Jones,2001,Note63:ApplicationforamendmentoftheNorthAmericanstratigraphiccodecon-cerningconsistencyandupdatingregardingelectronicpublish-ing:AAPGBulletin,v.85,p.366375.Forgotson,J.M.,Jr.,1957,Nature,usageanddefinitionofmarker-definedverticallysegregatedrockunits:AAPGBulletin,v.41,no.9,p.21082113.Frye,J.C.,H.B.Willman,M.Rubin,andR.F.Black,1968,DefinitionofWisconsinanStage:U.S.GeologicalSurveyBul-letin1274-E,22p.George,T.N.,etal.,1969,Recommendationsonstratigraphicalusage:GeologicalSocietyofLondon,Proceedingsno.1656,p.139Harland,W.B.,1977,Essayreview[of]internationalstratigraphicguide,1976:GeologicalMagazine,v.114,no.3,p.229235.Harland,W.B.,1978,Geochronologicscales,G.V.Cohee,M.F.Glaessner,andH.D.Hedberg,eds.,Contributionstothegeologictimescale:AAPGStudiesinGeology6,p.932.Harrison,J.E.,andZ.E.Peterman,1980,NorthAmericanCom-missiononStratigraphicNomenclatureNote52Aprelimi-naryproposalforachronometrictimescaleforthePrecambrian Readersareremindedoftheextensiveandnoteworthybib-liographyofcontributionstostratigraphicprinciples,classification,andterminologycitedbytheInternationalStratigraphicGuide(ISSC,1976,p.111187;1994,p.150206).NorthAmericanStratigraphicCode oftheUnitedStatesandMexico:GeologicalSocietyofAmericaBulletin,v.91,no.6,p.377380.Henbest,L.G.,1952,SignificanceofevolutionaryexplosionsfordiastrophicdivisionofEarthhistory:JournalofPaleontology,v.26,p.299318.Henderson,J.B.,W.G.E.Caldwell,andJ.E.Harrison,1980,NorthAmericanCommissiononStratigraphicNomenclature,Report8Amendmentofcodeconcerningterminologyforigneousandhigh-grademetamorphicrocks:GeologicalSocietyofAmericaBulletin,v.91,no.6,p.374376.Hofmann,H.J.,1990,Precambriantimeunitsandnomenclaturethegeonconcept:Geology,v.18,p.340341.Holland,C.H.,etal.,1978,Aguidetostratigraphicalprocedure:GeologicalSocietyofLondon,SpecialReport11,18p.Huxley,T.H.,1862,Theanniversaryaddress:GeologicalSocietyofLondon,QuarterlyJournal,v.18,p.xlliv.InternationalCommissiononZoologicalNomenclature,1964:InternationalcodeofzoologicalnomenclatureadoptedbytheXVInternationalCongressofZoology:London,Interna-tionalTrustforZoologicalNomenclature,176p.ISSC(InternationalSubcommissiononStratigraphicClassification)ofIUGSInternationalCommissiononStratigraphy,1976,Internationalstratigraphicguide([1stedition],H.D.Hedberg,ed.):NewYork,JohnWileyandSons,200p.ISSC(InternationalSubcommissiononStratigraphicClassification),1979,MagnetostratigraphypolarityunitsasupplementarychapteroftheISSCinternationalstratigraphicguide:Geology,v.7,p.578583.ISSC(InternationalSubcommissiononStratigraphicClassification)ofIUGSInternationalCommissiononStratigraphy,1994,Internationalstratigraphicguide(2dedition,AmosSalvador,ed.):Trondheim,Norway,InternationalUnionofGeologicalSciences,andBoulder,Colorado,GeologicalSocietyofAmerica,214p.Izett,G.A.,andR.E.Wilcox,1981,MapshowingthedistributionoftheHuckleberryRidge,MesaFalls,andLavaCreekvolcanicashbeds(Pearlettefamilyashbeds)ofPlioceneandPleis-toceneageinthewesternUnitedStatesandsouthernCanada:U.S.GeologicalSurveyMiscellaneousGeologicalInvestiga-tionsMapI-1325.Klapper,G.,andJ.G.Johnson,1980,EndemismanddispersalofDevonianconodonts:JournalofPaleontology,v.54,p.400Lenz,A.C.,L.E.Edwards,andB.R.Pratt,2001,Note64:Ap-plicationforrevisionofarticles4854,biostratigraphicunits,oftheNorthAmericanstratigraphiccode:AAPGBulletin,v.85,p.372375.Matthews,R.K.,1974,Dynamicstratigraphyanintroductiontosedimentationandstratigraphy:NewJersey,Prentice-Hall,370p.McDougall,I.,1977,Thepresentstatusofthegeomagneticpolaritytimescale:ResearchSchoolofEarthSciences,AustralianNationalUniversity,Publicationno.1288,34p.McElhinny,M.W.,1978,Themagneticpolaritytimescale;prospectsandpossibilitiesinmagnetostratigraphy,G.V.Cohee,M.F.Glaessner,andH.D.Hedberg,eds.,Contribu-tionstothegeologictimescale:AAPGStudiesinGeology6,p.5765.McIver,N.L.,1972,CenozoicandMesozoicstratigraphyoftheNovaScotiashelf:CanadianJournalofEarthScience,v.9,p.5470.McLaren,D.J.,1977,TheSilurian-DevonianBoundaryCommit-tee.Afinalreport,A.Martinsson,ed.,TheSilurian-Devonianboundary:IUGSSeriesA,no.5,p.134.MERQ(Ministe`redelEnergieetdesRessourcesduQuebec),1986,CodestratigraphiqueNord-Americain:DV86-02,58p.Morrison,R.B.,1967,PrinciplesofQuaternarysoilstratigraphy,R.B.MorrisonandH.E.Wright,Jr.,eds.,Quaternarysoils:Reno,Nevada,CenterforWaterResourcesResearch,DesertResearchInstitute,UniversityofNevada,p.169.NACSN(NorthAmericanCommissiononStratigraphicNomen-clature),1981,DraftNorthAmericanstratigraphiccode:Cana-dianSocietyofPetroleumGeologists,63p.Palmer,A.R.,1965,Biomereanewkindofbiostratigraphicunit:JournalofPaleontology,v.39,no.l,p.149153.Parsons,R.B.,1981,Proposedsoil-stratigraphicguide,tionalUnionforQuaternaryResearchandInternationalSocietyofSoilScience:INQUACommission6andISSSCommission5WorkingGroup,Pedology,Report,p.612.Pawluk,S.,1978,Thepedogenicprofileinthestratigraphicsection,W.C.Mahaney,ed.,Quaternarysoils:Norwich,England,GeoAbstracts,Ltd.,p.6175.Ruhe,R.V.,1965,Quaternarypaleopedology,H.E.WrightJr.andD.G.Frey,eds.,TheQuaternaryoftheUnitedStates:Princeton,PrincetonUniversityPress,p.755764.Schultz,E.H.,1982,Thechronosomeandsupersometermsproposedforlow-rankchronostratigraphicunits:CanadianPetroleumGeology,v.30,no.1,p.2933.Shaw,A.B.,1964,Timeinstratigraphy:NewYork,McGraw-Hill,365p.Sims,P.K.,1979,Precambriansubdivided:Geotimes,v.24,no.12,p.15.Sloss,L.L.,1963,SequencesinthecratonicinteriorofNorthAmerica:GeologicalSocietyofAmericaBulletin,v.74,no.2,p.94114.Tracey,J.I.,Jr.,etal.,1971,InitialreportsoftheDeepSeaDrillingProject,v.8:Washington,U.S.GovernmentPrintingOffice,1037p.Valentine,K.W.G.,andJ.B.Dalrymple,1976,Quaternaryburiedpaleosols:Acriticalreview:QuaternaryResearch,v.6,p.209Watson,R.A.,andH.E.Wright,Jr.,1980,TheendofthePleistocene:Ageneralcritiqueofchronostratigraphicclassifi-cation:Boreas,v.9,p.153163.Weiss,M.P.,1979a,CommentsandsuggestionsinvitedforrevisionofAmericanstratigraphiccode:GeologicalSocietyofAmeri-ca,NewsandInformation,v.1,no.7,p.9799.Weiss,M.P.,1979b,StratigraphicCommissionNote50ProposaltochangenameofCommission:AAPGBulletin,v.63,no.10,p.1986.Weller,J.M.,1960,Stratigraphicprinciplesandpractice:NewYork,HarperandBrothers,725p.Willman,H.B.,andJ.C.Frye,1970,PleistocenestratigraphyofIllinois:IllinoisStateGeologicalSurveyBulletin94,204p.APPENDIXI.PARTICIPANTSANDCONFEREESINCODEREVISIONCodeCommitteeStevenS.Oriel(U.S.GeologicalSurvey),chairman,HubertGabrielse(GeologicalSurveyofCanada),WilliamW.Hay(JointOceanographicInstitutions),FrankE.Kottlowski(NewMexicoBureauofMines),JohnB.Patton(IndianaGeologicalSurvey).LithostratigraphicSubcommitteeJamesD.Aitken(GeologicalSurveyofCanada),chairman,MontiLerand(GulfCanadaResources,Ltd.),MitchellW.NorthAmericanCommissiononStratigraphicNomenclature Reynolds(U.S.GeologicalSurvey),RobertJ.Weimer(Colo-radoSchoolofMines),MalcolmP.Weiss(NorthernIllinoisUniversity).BiostratigraphicSubcommitteeAllisonR.(Pete)Palmer(GeologicalSocietyofAmerica),chairman,IsmaelFerrusqu´a(UniversityofMexico),JosephE.Hazel(U.S.GeologicalSurvey),ErleG.Kauffman(UniversityofColorado),ColinMcGregor(GeologicalSurveyofCanada),MichaelA.Murphy(UniversityofCalifornia,Riverside),WalterC.Sweet(OhioStateUniversity).ChronostratigraphicSubcommitteeZellE.Peterman(U.S.GeologicalSurvey),chairman,ZoltandeCserna(SociedadGeologicaMexicana),EdwardH.Schultz(Sun-cor,Inc.,Calgary),NormanF.Sohl(U.S.GeologicalSurvey),JohnA.VanCouvering(AmericanMuseumofNaturalHistory).Plutonic-MetamorphicAdvisoryGroupJackE.Harrison(U.S.GeologicalSurvey),chairman,JohnB.Henderson(GeologicalSurveyofCanada),HaroldL.James(retired),LeonT.Silver(CaliforniaInstituteofTechnology),PaulC.Bateman(U.S.GeologicalSurvey).MagnetostratigraphicAdvisoryGroupRogerW.Macqueen(UniversityofWaterloo),chairman,G.BrentDalrymple(U.S.GeologicalSurvey),WalterF.Fahrig(Geo-logicalSurveyofCanada),J.M.Hall(DalhousieUniversity).VolcanicAdvisoryGroupRichardV.Fisher(UniversityofCalifornia,SantaBarbara),chairman,ThomasA.Steven(U.S.GeologicalSurvey),DonaldA.Swanson(U.S.GeologicalSurvey).TectonostratigraphicAdvisoryGroupDarrelS.Cowan(UniversityofWashington),chairman,ThomasW.Donnelly(StateUniversityofNewYorkatBinghamton),MichaelW.HigginsandDavidL.Jones(U.S.GeologicalSur-vey),HaroldWilliams(MemorialUniversity,Newfoundland).QuaternaryAdvisoryGroupNormanP.Lasca(UniversityofWisconsin-Milwaukee),chair-man,MarkM.Fenton(AlbertaResearchCouncil),DavidS.Fullerton(U.S.GeologicalSurvey),RobertJ.Fulton(Geolog-icalSurveyofCanada),W.HiltonJohnson(UniversityofIllinois),PaulF.Karrow(UniversityofWaterloo),GeraldM.Richmond(U.S.GeologicalSurvey).ConfereesW.G.E.Caldwell(UniversityofSaskatchewan),LucyE.Edwards(U.S.GeologicalSurvey),HenryH.Gray(In-dianaGeologicalSurvey),HollisD.Hedberg(PrincetonUniversity),LewisH.King(GeologicalSurveyofCanada),RudolphW.Kopf(U.S.GeologicalSurvey),JerryA.Line-back(RobertsonResearchU.S.),MarjorieE.MacLachlan(U.S.GeologicalSurvey),AmosSalvador(UniversityofTexas,Austin),BrianR.Shaw(SamsonResources,Inc.),OgdenTweto(U.S.GeologicalSurvey).APPENDIXII.19772003COMPOSITIONOFTHENORTHAMERICANCOMMISSIONONSTRATIGRAPHICNOMENCLATUREEachCommissionerisappointed,withfewexceptions,toservea3-yearterm(shownbysuchnumeralsas80-82for19801982)andafewarereappointed.AmericanAssociationofPetroleumGeologistsTimothyA.Anderson77-83,OrloE.Childs76-79,KennethJ.Englund74-77,SusanLongacre78-03,DonaldE.Owen79-85,87-02,GrantSteele75-78,NahumSchneidermann83-86,RobertR.Jordan85-03.AssociationofAmericanStateGeologistsLarryD.Fellows81-82,91-94,LeeC.Gerhard79-81,DonaldC.Haney80-83,WallaceB.Howe74-77,RobertR.Jordan78-84,FrankE.Kottlowski76-79,MeredithE.Ostrom77-80,JohnB.Patton75-78,RobertH.Fakundiny81-92,95-03,ErnestA.Mancini83-86,99-03,GaryB.Glass84-87,NormanC.Hester87,WilliamT.Hill86-89,ConradGazzier88-90,RobertC.Milici87-90,M.LeeAllison88-91,ThomasM.Berg90-94,JohnP.Bluemle92-02,JamesRobertson92-96,NormanHester97-02.GeologicalSocietyofAmericaClarenceA.Hall,Jr.78-81,JackE.Harrison74-77,WilliamW.Hay75-78,RobertS.Houston77-80,MichaelA.Murphy81-84,AllisonR.Palmer80-83,MalcolmP.Weiss76-82,NormanP.Lasca82-85,CharlesW.Copeland,Jr.83-86,PatrickK.Sutherland84-87,JohnM.Dennison85-88,RobertF.Lundin87-89,DonaldE.Hattin,88-90,PaulR.Seaber89-92,DonaldL.Baars88-95,PeterR.Vail90-94,GlennB.Morey91-94,LeeC.Gerhard92-96,JamesO.Jones92-97,ArdithK.Hansel98-01,W.BurleighHarris95-98,DavidT.King97-00,H.RichardLane02-03,ErnestA.Mancini96-98,WalterL.Manger02-03,ChristopherG.Maples01-03.UnitedStatesGeologicalSurveyEarlE.Brabb78-82,DavidS.Fullerton78-84,E.DaleJackson76-78,KennethL.Pierce75-78,NormanF.Sohl74-83,JoshuaI.Tracey,Jr.82-88,C.WyliePoag83-86,JohnH.Stewart84-93,LucyE.Edwards86-03,ForrestG.Poole88-94,JohnPojeta,Jr.92-96,MitchellW.Reynolds92-95,BruceR.Wardlaw95-03,RandallC.Orndorff97-03.GeologicalSurveyofCanadaJamesD.Aitken75-78,KennethD.Card80-83,DonaldG.Cook78-81,RobertJ.Fulton81-84,JohnB.Henderson74-77,LewisH.King79-82,MauriceB.Lambert77-80,ChristopherJ.Yorath76-79,AshtonF.EmbryIII82-88,R.I.Thompson83-86,AnthonyDavidson84-87,97-02,GrahamL.Williams87-89,FredW.Chandler88-91,MichaelP.Cecile88-91,LyndaDredge90-94,JohnA.Percival90-94,DonaldG.Cook92-94,BenoitBeauchamp92-97,R.J.Fulton92-96,DenisLavoie92-95,A.P.(Tony)Hamblin98-03,TerryPoulton99-01.CanadianSocietyofPetroleumGeologistsRolandF.deCaen79-85,J.RossMcWhae77-80,EdwardH.Schultz74-77,80-83,UlrichWissner76-79,TimothyR.Mar-chant83-86,C.E.Wright85-89,WayneBrideaux87-88,NorthAmericanStratigraphicCode DonaldG.Cook89-91,RaymondW.Yole91-02,BrianPratt92-03.GeologicalAssociationofCanadaW.G.E.Caldwell76-79,R.K.Jull78-79,PaulS.Karrow81-84,AlfredC.Lenz79-81,85-88,90-98,DavidE.Pearson79-81,PaulE.Schenk75-78,GrantD.Mossop82-85,JamesT.Teller84-87,JohnA.Westgate87-90,R.MichaelEaston91-03,WilliamR.Arnott98-00.Asociacio´nMexicanadeGeo´logosPetrolerosJoseCarilloBravo78-81,BaldomerroCarrasco-Velazquez,75-78,85-88,CarlosManuelCantu-Chapa98-01.SociedadGeolo´gicaMexicanaZoltandeCserna76-82,JoseCarrillo-Bravo82-85,96-01,EmilianoCampos-Madrigal98-01.InstitutodeGeologiadelaUniversidadNacionalAutono´madeMexicoIsmaelFerrusqu´aVillafranca76-81,92-03,FernandoOrtegaGutie´rrez81-90,DiegoA.Cordoba-Mendez90-92.Commissioners-at-LargeJorgeJ.Aranda-Gomez92-94,DonaldE.Hattin92-94,NormanP.Lasca92-03,DiegoA.Cordoba-Mendez92-94,PaulR.Seaber92-00.APPENDIXIII.REPORTSANDNOTESOFTHEAMERICANCOMMISSIONONSTRATIGRAPHICNOMENCLATUREReports(formaldeclarations,opinions,andrecommendations)Moore,RaymondC.,Declarationonnamingofsubsurfacestrati-graphicunits:AAPGBulletin,v.33,no.7,p.12801282,1949.Hedberg,HollisD.,Nature,usage,andnomenclatureoftime-stratigraphicandgeologic-timeunits:AAPGBulletin,v.36,no.8,p.16271638,1952.Harrison,J.M.,Nature,usage,andnomenclaturestratigraphicandgeologic-timeunitsasappliedtothePrecambrian:AAPGBulletin,v.39,no.9,p.18591861,1955.Cohee,GeorgeV.,etal.,Nature,usage,andnomenclatureofrock-stratigraphicunits:AAPGBulletin,v.40,no.8,p.20032014,1956.McKee,EdwinD.,Nature,usageandnomenclatureofbiostratigraphicunits:AAPGBulletin,v.4l,no.8,p.18771889,1957.Richmond,GeraldM.,ApplicationofstratigraphicclassificationandnomenclaturetotheQuaternary:AAPGBulletin,v.43,no.3,pt.I,p.663675,1959.Lohman,KennethE.,FunctionandjurisdictionalscopeoftheAmericanCommissiononStratigraphicNomenclature:AAPGBulletin,v.47,no.5,p.853855,1963.Henderson,JohnB.,W.G.E.Caldwell,andJackE.Harrison,Amendmentofcodeconcerningterminologyforigneousandhigh-grademetamorphicrocks:GeologicalSocietyofAmericaBulletin,pt.I,v.91,no.6,p.374376,1980.Harrison,JackE.,andZellE.Peterman,AdoptionofgeometricunitsfordivisionsofPrecambriantime:AAPGBulletin,v.66,no.6,p.801802,1982.Owen,DonaldE.,NormanP.Lasca,andEdwardH.Schultz,NewarticlesoforganizationandprocedureofNorthAmericanCommissiononStratigraphicNomenclature:AAPGBulletin,v.69,p.872873,1985.Notes(informalstatements,discussions,andoutlinesofproblems)1.Moore,RaymondC.,OrganizationandobjectivesoftheStrati-graphicCommission:AAPGBulletin,v.31,no.3,p.513518,1947.Moore,RaymondC.,Natureandclassesofstratigraphicunits:AAPGBulletin,v.31,no.3,p.519528,1947.Moore,RaymondC.,RulesofgeologicnomenclatureoftheGeologicalSurveyofCanada:AAPGBulletin,v.32,no.3,p.366367,1948.Jones,WayneV.,andRaymondC.Moore,Namingofsub-surfacestratigraphicunits:AAPGBulletin,v.32,no.3,p.367371,1948.Flint,RichardFoster,andRaymondC.Moore,Definitionandadoptionofthetermsstageandage:AAPGBulletin,v.32,no.3,p.372376,1948.Moore,RaymondC.,Discussionofnatureandclassesofstrati-graphicunits:AAPGBulletin,v.32,no.3,p.376381,1948.Moore,RaymondC.,RecordsoftheStratigraphicCommissionfor19471948:AAPGBulletin,v.33,no.7,p.12711273,1949.Moore,RaymondC.,AustralianCodeofStratigraphicalNomen-clature:AAPGBulletin,v.33,no.7,p.12731276,1949.Moore,RaymondC.,ThePliocene-Pleistoceneboundary:AAPGBulletin,v.33,no.7,p.12761280,1949.Moore,RaymondC.,Shouldadditionalcategoriesofstrati-graphicunitsberecognized?:AAPGBulletin,v.34,no.12,p.23602361,1950.Moore,RaymondC.,RecordsoftheStratigraphicCommissionfor19491950:AAPGBulletin,v.35,no.5,p.10741076,1951.Moore,RaymondC.,Divisionsofrocksandtime:AAPGBulletin,v.35,no.5,p.1076,1951.Williams,JamesSteele,andAurealT.Cross,ThirdCongressofCarboniferousStratigraphyandGeology:AAPGBulletin,v.36,no.1,p.169172,1952.OfficialreportofroundtableconferenceonstratigraphicnomenclatureatThirdCongressofCarboniferousStratigraphyandGeology,Heerlen,Netherlands,June2628,1951:AAPGBulletin,v.36,no.10,p.20442048,1952.RecordsoftheStratigraphicCommissionfor19511952:AAPGBulletin,v.37,no.5,p.10781080,1953.RecordsoftheStratigraphicCommissionfor19531954:AAPGBulletin,v.39,no.9,p.18611863,1955.Suppressionofhomonymousandobsoletestratigraphicnames:AAPGBulletin,v.40,no.12,p.29532954,1956.Gilluly,James,RecordsoftheStratigraphicCommissionfor19551956:AAPGBulletin,v.41,no.1,p.130133,1957.Richmond,GeraldM.,andJohnC.Frye,Statusofsoilsinstrati-graphicnomenclature:AAPGBulletin,v.31,no.4,p.758763,1957.Frye,JohnC.,andGeraldM.Richmond,ProblemsinapplyingstandardstratigraphicpracticeinnonmarineQuaternarydepos-its:AAPGBulletin,v.42,no.8,p.19791983,1958.21.Frye,JohnC.,PreparationofnewstratigraphiccodebyAmericanCommissiononStratigraphicNomenclature:AAPGBulletin,v.42,no.8,p.19841986,1958.NorthAmericanCommissiononStratigraphicNomenclature RecordsoftheStratigraphicCommissionfor19571958:AAPGBulletin,v.43,no.8,p.19671971,1959.Rodgers,John,andRichardB.McConnell,Needforrock-stratigraphicunitslargerthangroup:AAPGBulletin,v.43,no.8,p.19711975,1959.Wheeler,HarryE.,Unconformity-boundedunitsinstratigra-phy:AAPGBulletin,v.43,no.8,p.19751977,1959.Bell,W.Charles,MarshallKay,GroverE.Murray,HarryE.Wheeler,andJohnA.Wilson,Geochronologicandchrono-stratigraphicunits:AAPGBulletin,v.45,no.5,p.666670,1961.RecordsoftheStratigraphicCommissionfor19591960:AAPGBulletin,v.45,no.5,p.670673,1961.Frye,JohnC.,andH.B.Willman,MorphostratigraphicunitsinPleistocenestratigraphy:AAPGBulletin,v.46,no.1,p.112113,1962.Shaver,RobertH.,ApplicationtoAmericanCommissiononStratigraphicNomenclatureforanamendmentofArticle4foftheCodeofStratigraphicNomenclatureoninformalstatusofnamedaquifers,oilsands,coalbeds,andquarrylayers:AAPGBulletin,v.46,no.10,p.1935,1962.Patton,JohnB.,RecordsoftheStratigraphicCommissionfor19611962:AAPGBulletin,v.47,no.11,p.19871991,1963.Richmond,GeraldM.,andJohnG.Fyles,ApplicationtoAmericanCommissiononStratigraphicNomenclatureforanamendmentofArticle31,Remark(b)oftheCodeofStrati-graphicNomenclatureonmisuseofthetermstage:AAPGBulletin,v.48,no.5,p.710711,1964.Cohee,GeorgeV.,RecordsoftheStratigraphicCommissionfor19631964:AAPGBulletin,v.49,no.3,pt.IofII,p.296300,1965.InternationalSubcommissiononStratigraphicTerminology,HollisD.Hedberg,ed.,Definitionofgeologicsystems:AAPGBulletin,v.49,no.10,p.16941703,1965.Hedberg,HollisD.,ApplicationtoAmericanCommissiononStratigraphicNomenclatureforamendmentstoArticles29,31,and37toprovideforrecognitionoferathem,substage,andchronozoneastime-stratigraphictermsintheCodeofStrati-graphicNomenclature:AAPGBulletin,v.50,no.3,p.560561,1966.Harker,Peter,RecordsoftheStratigraphicCommissionfor19641966:AAPGBulletin,v.51,no.9,p.18621868,1967.DeFord,RonaldK.,JohnA.Wilson,andFrederickM.Swain,ApplicationtoAmericanCommissiononStratigraphicNomen-clatureforanamendmentofArticle3andArticle13,remarks(c)and(e),oftheCodeofStratigraphicNomenclaturetodisallowrecognitionofnewstratigraphicnamesthatappearonlyinabstracts,guidebooks,microfilms,newspapers,orincom-mercialortradejournals:AAPGBulletin,v.51,no.9,p.18681869,1967.Cohee,GeorgeV.,RonaldK.DeFord,andH.B.Willman,AmendmentofArticle5,remarks(a)and(e)oftheCodeofStratigraphicNomenclaturefortreatmentofgeologicnamesinagradationalorinterfingeringrelationshipofrock-stratigraphicunits:AAPGBulletin,v.53,no.9,p.20052006,1969.Kottlowski,FrankE.,RecordsoftheStratigraphicCommissionfor19661968:AAPGBulletin,v.53,no.10,p.21792186,1969.Andrews,J.,andK.JinghwaHsu,ArecommendationtotheAmericanCommissiononStratigraphicNomenclatureconcerningnomenclaturalproblemsofsubmarineformations:AAPGBulletin,v.54,no.9,p.17461747,1970.Wilson,JohnAndrew,RecordsoftheStratigraphicCommissionfor19681970:AAPGBulletin,v.55,no.10,p.18661872,1971.James,HaroldL.,SubdivisionofPrecambrian:AninterimschemetobeusedbyU.S.GeologicalSurvey:AAPGBulletin,v.56,no.6,p.11281133,1972.Oriel,StevenS.,ApplicationforamendmentofArticle8ofcode,concerningsmallestformalrock-stratigraphicunit:AAPGBulletin,v.59,no.1,p.134135,1975.Oriel,StevenS.,RecordsofStratigraphicCommissionfor19701972:AAPGBulletin,v.59,no.1,p.135139,1975.Oriel,StevenS.,andVirgilE.Barnes,RecordsofStratigraphicCommissionfor19721974:AAPGBulletin,v.59,no.10,p.20312036,1975.Oriel,StevenS.,RogerW.Macqueen,JohnA.Wilson,andG.BrentDalrymple,Applicationforadditiontocodeconcerningmagnetostratigraphicunits:AAPGBulletin,v.60,no.2,p.273277,1976.45.Sohl,NormanF.,Applicationforamendmentconcerningterminologyforigneousandhigh-grademetamorphicrocks:AAPGBulletin,v.61,no.2,p.248251,1977.Sohl,NormanF.,ApplicationforamendmentofArticles8and10ofcode,concerningsmallestformalrock-stratigraphicunit:AAPGBulletin,v.61,no.2,p.252,1977.Macqueen,RogerW.,andStevenS.Oriel,ApplicationforamendmentofArticles27and34ofstratigraphiccodetointroducepoint-boundarystratotypeconcept:AAPGBulletin,v.61,no.7,p.10831085,1977.Sohl,NormanF.,ApplicationforamendmentofCodeofStratigraphicNomenclaturetoprovideguidelinesconcerningformalterminologyforoceanicrocks:AAPGBulletin,v.62,no.7,p.11851186,1978.Caldwell,W.G.E.,andN.F.Sohl,RecordsofStratigraphicCommissionfor19741976:AAPGBulletin,v.62,no.7,p.11871192,1978.Weiss,MalcolmP.,Proposaltochangenameofcommission:AAPGBulletin,v.63,no.10,p.1986,1979.Weiss,MalcolmP.,andJamesD.Aitken,RecordsofStrati-graphicCommission,19761978:AAPGBulletin,v.64,no.1,p.136137,1980.Harrison,JackE.,andZellE.Peterman,ApreliminaryproposalforachronometrictimescaleforthePrecambrianoftheUnitedStatesandMexico:GeologicalSocietyofAmericaBulletin,pt.I,v.91,no.6,p.377380,1980.Jordan,RobertR.,RecordsofStratigraphicCommission,19781980:AAPGBulletin,v.66,no.2,p.238240,1982.Jordan,RobertR.,RecordsofStratigraphicCommission,19801982:AAPGBulletin,v.70,no.1,p.98102,1986.Owen,DonaldE.,andNormanP.Lasca,RecordsofStrati-graphicCommission,19821984:AAPGBulletin,v.71,no.3,p.353355,1987.Embry,AshtonF.,andSusanA.Longacre,RecordsofStratigraphicCommission,19841986:AAPGBulletin,v.71,no.11,p.14341443,1987.Fakundiny,RobertH.,andSusanA.Longacre,ApplicationforamendmentofNorthAmericanStratigraphicCodetoprovideforexclusiveinformaluseofmorphologicaltermssuchasBatholithIntrusion,Pluton,Stock,Plug,Dike,Sill,Diapir,andBody:AAPGBulletin,v.73,no.11,p.14521453,1989.Fakundiny,RobertH.,andRobertF.Lundin,RecordsofStratigraphicCommission,19861988:AAPGBulletin,v.75,no.7,p.12751278,1991.Chandler,FredW.,andRobertR.Jordan,RecordsofStratigraphicCommission,19881990:AAPGBulletin,v.76,no.12,p.19331934,1992.NorthAmericanStratigraphicCode 60.Edwards,LucyE.,ApplicationforamendmentofNorthAmericanStratigraphicCodetoclarifyrelationofallostrati-graphicandlithostratigraphicunits:AAPGBulletin,v.77,no.5,p.909943,1993.Edwards,LucyE.,andDonaldE.Owen,RecordsofStrati-graphicCommission,19911992:AAPGBulletin,v.80,no.7,p.11561159,1996.Easton,R.Michael,DonaldL.Baars,andDonaldG.Cook,RecordsofStratigraphicCommission,19921994:AAPGBulletin,v.81,no.8,p.13421345,1997.Ferrusqu´a-Villafranca,Ismael,R.MichaelEaston,LucyE.Edwards,RobertH.Fakundiny,andJamesO.Jones,ApplicationforamendmentoftheNorthAmericanStratigraphicCodeconcerningconsistencyandupdatingregardingelectronicpublishing:AAPGBulletin,v.85,no.2,p.366371,2001.Lenz,AlfredC.,LucyE.Edwards,andBrianR.Pratt,Appli-cationforrevisionofarticles4854,biostratigraphicunits,oftheNorthAmericanStratigraphicCode:AAPGBulletin,v.85,no.2,p.372375,2001.Easton,R.Michael,JamesO.Jones,AlfredC.Lenz,IsmaelFerrusqu´a-Villafranca,ErnestA.Mancini,BruceR.Wardlaw,LucyE.Edwards,andBrianR.Pratt,RecordsofStratigraphicCommission,19952002:AAPGBulletin,v.89,no.11,p.14591464,2005.NorthAmericanCommissiononStratigraphicNomenclature