PRINCIPLESOF SEQUENCE STRATIGRAPHY
SECONDEDITION
OctavianCatuneanu Professor,UniversityofAlberta,Edmonton,Alberta,Canada
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Prefacetosecondeditionvii
1.Introduction1
1.1Overviewofsequencestratigraphy 1
1.1.1Scopeofsequencestratigraphy 1
1.1.2Sequencestratigraphy a revolutioninsedimentary geology 3
1.1.3Sequencestratigraphy an integratedapproach 5
1.1.4Sequencestratigraphyvs. othertypesofstratigraphy 6
1.2Developmentofsequencestratigraphy 14
1.2.1Unconformities 16
1.2.2Unconformity-boundedunits 16
1.2.3Conceptof“sequence” 17
1.2.4Sequencemodels 20
1.2.5Standardizationofsequence stratigraphy 21
2.Datainsequencestratigraphy23
2.1Geologicaldata
2.1.1Sedimentology
2.1.2Pedology
2.1.3Bodyfossils
2.1.4Tracefossils
2.1.5Geochemistry
2.1.6Agedating
2.2Well-logdata
2.2.1Introduction
2.2.2Geologicaluncertainties
2.2.3Well-loginterpretations
2.3Seismicdata
2.3.1Introduction
2.3.2Physicalattributesofseismic
2.3.3Workflowofseismicdata
3.Controlsonsequencedevelopment93
3.1Allogenicprocesses
3.1.1Eustasy
3.4Conceptof“baselevel”
4.Stratalstackingpatterns117
4.1Stratalterminations 119
4.2Stackingpatternsindownstreamcontrolledsettings 125
4.2.1Controlsonstratalstacking patterns 127
4.2.2Geometricalvs.depositional trends 129
4.2.3Diagnosticvs.non-diagnostic stackingpatterns 131
4.2.4Shorelinetrajectories 135
4.2.5Stratigraphicscalesin downstream-controlledsettings 155
4.3Stackingpatternsinupstreamcontrolledsettings 158
4.3.1Controlsonstratalstacking patterns 158
4.3.2Depositionaltrendsin upstream-controlledsettings 161
4.3.3Typesofstackingpatterns 165
4.3.4Stratigraphicscalesin upstream-controlledsettings 166
5.Stratalunits169
5.1Depositionalsystems 169
5.1.1Definition 169
5.1.2Scaleofdepositionalsystems 170
5.2Systemstracts 176
5.2.1Definition 176
5.2.2Scaleofsystemstracts 177
5.2.3Systemstractsindownstreamcontrolledsettings 177
5.2.4Systemstractsinupstreamcontrolledsettings 221
5.2.5Nomenclatureofsystems tracts 224
5.3Stratigraphicsequences 228
5.3.1Definition 228
5.3.2Scaleofsequences 228
5.3.3Typesofsequences 231
5.4Parasequences 236
5.4.1Definition 237
5.4.2Scaleofparasequences 240
5.4.3Parasequencearchitecture 243
5.4.4Sequencesvs.parasequences 246
6.Stratigraphicsurfaces249
6.1Surfacesofsequencestratigraphy 250
6.1.1Subaerialunconformity 253
6.1.2Basalsurfaceofforced regression 259
6.1.3Correlativeconformity 261
6.1.4Maximumregressivesurface 265
6.1.5Maximumfloodingsurface 270
6.1.6Transgressivesurfaceoferosion 274
6.1.7Regressivesurfaceofmarine erosion 279
6.1.8Othersurfacesofsequence stratigraphy 283
6.2Within-trendfaciescontacts 285
6.2.1Within-trendnormal regressivesurface 286
6.2.2Within-trendforcedregressive surface 287
6.2.3Within-trendfloodingsurface 289
6.2.4Otherwithin-trendfacies contacts 291
7.Sequencestratigraphicframework295
7.1Scaleinsequencestratigraphy 295
7.1.1Stratigraphicresolution 297
7.1.2Sedimentologicalvs. stratigraphicscales 303
7.2Hierarchyinsequencestratigraphy 306
7.2.1Criteriaforstratigraphic classification 307
7.2.2Absolutevs.relative stratigraphicscales 310
7.2.3Approachestostratigraphic nomenclature 312
7.2.4Orderlyvs.variable stratigraphicpatterns 312
7.2.5Basin-specificstratigraphic frameworks 313
7.3Timeinsequencestratigraphy 316
7.3.1Referencecurvefor stratigraphicsurfaces 317
7.3.2Stratalstackingpatternsvs. bathymetrictrends 320
7.3.3Diachroneityofstratigraphic surfaces 329
7.3.4Three-dimensional stratigraphicarchitecture 333
8.Variabilityofstratigraphicsequences337
8.1Variabilitywiththetectonicsetting 337
8.1.1Sequencesintectonically “passive”basins 338
8.1.2Sequencesintectonically “active”basins 340
8.2Variabilitywiththedepositionalsetting 342
8.2.1Sequencesincontinental settings 344
8.2.2Sequencesincoastalto shallow-watersettings 350
8.2.3Sequencesindeep-water settings 371
8.3Variabilitywiththeclimaticregime 385
8.3.1Sequencesinnon-glaciated settings 386
8.3.2Sequencesinglaciatedsettings 386
9.Discussion389
9.1Architectureofthestratigraphicrecord 389
9.1.1Scale-independentstacking patterns 389
9.1.2Classificationofstratigraphic cycles 391
9.2Sequencestratigraphyandgeological time 392
9.2.1Precambrianvs.Phanerozoic sequencestratigraphy 393
9.2.2Sequencestratigraphyofthe Precambrian 394
9.3Methodologyandnomenclature 396
9.3.1Fromseismictosub-seismic scales 397
9.3.2Methodologyvs.modelingin sequencestratigraphy 400
9.3.3Standardmethodologyand nomenclature 402
9.4Workflowofsequencestratigraphy 405
9.4.1Step1:Tectonicsetting 407
9.4.2Step2:Depositionalsetting 408
9.4.3Step3:Sequencestratigraphic framework 409
10.Conclusions413
10.1Stratigraphicframework 413
10.1.1Sequences,systemstracts, anddepositionalsystems 414
10.1.2Parasequences 415
10.2Standardapproachtosequence stratigraphy 417
10.2.1Guidelinesforastandard nomenclature 417
10.2.2Guidelinesforastandard methodology 419
10.3Summaryofkeypoints 420
10.3.1Stratigraphicarchitecture 421
10.3.2Stratigraphicscales 425
10.3.3Methodologyand nomenclature 427
1 Introduction
1.1Overviewofsequencestratigraphy
1.1.1Scopeofsequencestratigraphy
Sequencestratigraphyisatypeofstratigraphythat reliesonstackingpatternsforthedefinition,nomenclature,classification,andcorrelationofstratalunitsand boundingsurfaces.Themethodexaminesthestratigraphiccyclicityandtherelatedchangesinsedimentationregimesthatcanbeobservedatthescales affordedbytheresolutionofthedataavailable.Stratal stackingpatternsareatthecoreofthesequencestratigraphicmethodology,astheyprovidethecriteriafor thedefinitionofallunitsandsurfacesofsequence
stratigraphy(Fig.1.1);i.e.,sequencestratigraphicunits arebodiesofsedimentorsedimentaryrocksdefined bystratalstackingpatternsandtheirboundingsurfaces, andsequencestratigraphicsurfacesarestratigraphic contactswhichmarkchangesinstratalstackingpattern. Thecorrelationofstratabasedontheirstackingpatterns setssequencestratigraphyapartfromothercorrelation methodsthatrelyonsimilaritiesofunitsintermsoflithology(i.e.,lithostratigraphy),fossilcontent(i.e., biostratigraphy),magneticpolarity(i.e.,magnetostratigraphy),geochemicalsignatures(i.e.,chemostratigraphy),orgeologicalage(i.e.,chronostratigraphy). Sequencestratigraphicunitsmayormaynotcoincide withothertypesofstratigraphicunits.
FIGURE1.1 Constructionofthesequencestratigraphicframework,basedontheintegrationandmutualcalibrationofindependentdatasets. Themeaningofstratalgeometriesandverticalprofilesisbestconstrainedwithinapaleo-depositionalcontext.Thereliabilityandtheresolution of theconstructedframeworkdependonthetype(s)ofdataavailable.Whereonlyseismicdataareavailable,stratalstackingpatternsareobservedat scalesabovetheseismicresolution,onthebasisofseismicreflectionterminationsandarchitecture(i.e.,seismicstratigraphy).Outcropandwell dataaffordtheconstructionofhigherresolutionsequencestratigraphicframeworksatsub-seismicscales.Agedataenhancethereliabilityof correlations,butthelackthereof(e.g.,inmostPrecambrianandmanyPhanerozoiccasestudies)doesnotpreventtheapplicationofsequence stratigraphy.Intheabsenceofagedata,physicalstratigraphicmarkers(e.g.,volcanicashbeds,regionalcoalseams,orregionalmaximumflooding surfaces)canbeusedtoaidthecorrelations.Stratalstackingpatternsprovidethebasisforthedefinitionofallunitsandsurfacesofsequence stratigraphy.
Thesequencestratigraphicmethodologyenablesthe constructionofstratigraphicframeworksbasedonthe observationofstratalstackingpatternsatscalesdefined bythepurposeofstudyorbytheresolutionofthedata available.Interpretationsinsequencestratigraphyhave differentdegreesofrelevancetothemethodology. Intrinsictothemethodistherationalizationofthesedimentaryprocessesthatgeneratetheobservedstacking patterns,byplacingthedatainthecorrecttectonicand depositionalsettings(steps1and2ofthesequencestratigraphicworkflow;detailsin Chapter9).Thisaffords predictionswithrespecttothesedimentologicalnature ofseismicfaciesorstratalunitsinareasawayfrom datacontrolpointssuchasoutcropsorwells,within thepaleogeographiccontextoflinkeddepositionalsystems.Theobservationsthataffordtheconstructionof sequencestratigraphicframeworksareindependentof theinterpretationofunderlyingcontrolsonsequence development(e.g.,therelativecontributionsoftectonism,sea-levelchanges,climate,andautogeniccontrols onstratigraphiccyclicity).Thelatterdefinesthescopeof stratigraphicmodeling(Fig.1.2).
Thecorrectunderstandingofsequencestratigraphy requiresacleardistinctionbetweentheobservational workflowofthemethodologyandtheinterpretations derivedfromstratigraphicmodeling(Fig.1.2).Case inpoint,themodelingandtestingofthepossible controlsonsequencedevelopmentcancontinueindefinitelyaftertheconstructionofasequencestratigraphic
FIGURE1.2 Methodologyvs.modelingin sequencestratigraphy.Theconstructionofa sequencestratigraphicframeworkisbasedonthe observationofstratalstackingpatterns,irrespectiveoftheinterpretationoftheunderlying controls.Incontrast,modelingteststhepossible controlsonsequencedevelopment(e.g.,the relativecontributionsoftectonism,sea/lakelevelchanges,climate,andsedimentsupply). Theobservedstackingpatternscanberationalizedintermsofdepositionalprocessesbyplacing thedataintheproperpaleogeographiccontext (seeworkflowofsequencestratigraphyin Chapter9).Indownstream-controlledsettings, diagnosticstackingpatternsrelatetoshoreline trajectories,whereasnon-diagnosticstacking patternsrefertodepositionaltrendsthatcan accompanytheformationofanysystemstract (e.g.,theaggradationoffluvialtopsets).In upstream-controlledsettings,diagnosticstacking patternsrelatetothedominantdepositionalelements(e.g.,channelsvs.floodplainsinfluvial systems),irrespectiveoffluvialstylesandthe interpretedaccommodationconditionsatsyndepositionaltime(detailsin Chapter4). Modelinghasnobearingonthemethodology, andcalibrationwithfielddataisrequiredfor realisticresults(detailsin Chapter9).
framework.Confusionbetweenthetwolinesof researchunderminestheprogressmadeinthedevelopmentofsequencestratigraphyasanobjective,datadrivenmethodology.Uncalibratednumericalmodels cangenerateunlimitedresu lts,which,intheabsence ofrealitychecks,remainanundifferentiatedmixof realisticandunrealisticstratigraphicscenarios.The methodologyrestoresthevalueofnaturalprocesses andfacts,byoutliningthefieldcriteriathatenable theidentificationofallelementsofthesequencestratigraphicframework.Theconstructionofaframeworkof sequencesandcomponentsystemstractsexplainsthe geneticrelationshipsbetweensame-agedepositional systems,whichaffordinsightsintothepatternsofsedimentdistributionacrossthebasin.
Sequencestratigraphyprovidesthemeanstorationalizethestratigraphicrelationshipsthatdevelopat differentscaleswithinsedimentarybasinsplacedin alltectonicsettings,depositionalsettings,andclimatic regimes.Whilethemethodologyisindependentof geologicalsetting,thesequencestratigraphicframeworkisvariableintermsoftiming,scales,andthe systems-tractcompositionofsequences,reflectingthe uniqueaccommodationandsedimentationconditions ofeachsedimentarybasin.Forthisreason,themethodologymustbeappliedobjectively,withoutany apriori assumptions,withthedataratherthanthemodelleadingtotheconstructionofthesequencestratigraphic framework.Thesequencestratigraphicmethodology
integratesallavailabledatasetsthatcanbederived fromsurface(e.g.,outcrops,modernenvironments) andsubsurface(e.g.,borehole,seismic)datasources, andcombinesinsightsfromallgeosciencesthat contributetobasinanalysis(e.g.,sedimentarygeology, geophysics,geomorphology,andallabsoluteand relativedatingtechniques; Fig.1.1).Thereliabilityof thesequencestratigraphic frameworkdependsonthe amountandqualityofthedataavailable.Sequence stratigraphicframeworksaretypically“workin progress”astheyareconstantlyimprovedand refinedwiththeacquisitionofmoreandhigherresolutiondata.
Seismicstratigraphy,whichistheprecursorofmodern sequencestratigraphy,settheearlystandardsforthescales andapplicationsofthemethodology(Payton,1977).Subsequently,thescopeofsequencestratigraphywasexpanded toincludeapplicationstoallscalesanddatasets(fromlowresolutionseismicstratigraphytohigh-resolution sequencestratigraphyatsub-seismicscalesaffordedby boreholeandoutcropdata;Amorosietal.,2005,2009, 2017;CatuneanuandZecchin,2013;ZecchinandCatuneanu,2013,2015,2017;Magalhaesetal.,2015;Zecchin etal.,2017a,b;detailsin Chapters2 7),depositionalsettings(fromeoliantodeep-water;KocurekandHavholm, 1993;Catuneanu,2020a;detailsin Chapter8),tectonicsettings(from“passive”to“active”basins;Bastiaetal., 2010;Martins-NetoandCatuneanu,2010;Maravelis etal.,2016,2017;detailsin Chapter8),andclimaticconditions(fromicehousetogreenhouseregimes;Bartek etal.,1991,1997;Kidwell,1997;NaishandKamp,1997; Sauletal.,1999;Fieldingetal.,2000,2001,2006,2008; Naishetal.,2001;Cantalamessaetal.,2005;2007;Di CelmaandCantalamessa,2007;Isbelletal.,2008;Csato andCatuneanu,2012;Zecchinetal.,2015;detailsin Chapter8),fromPrecambriantoPhanerozoicsuccessions (Erikssonetal.,1998;2004,2005a,b,2006,2013;CatuneanuandBiddulph,2001;Catuneanuetal.,2005;2012; Sarkaretal.,2005;detailsin Chapter9).
Beyondthefundamentalresearchofthebasin-fillarchitecture,sequencestratigraphyalsoprovidesagenetic frameworktorationalizeandpredictthedistributionof economicdepositsthatrelatetosedimentaryprocesses. Thecyclicity,geographicextent,andthephysicaland temporalrelationshipsofmineralplacers,aquifers,coal beds,andpetroleumsystemsguidetheexplorationand subsequentproductiondevelopmentofnaturalresources.Thesenatural-resourceindustriesemployand benefitfromthesequencestratigraphicmethodology. Thedevelopmentanddistributionofthevarioustypes ofmineralplacers,aquifers,petroleumreservoirs,and coalbedsdependonthesequencestratigraphicsurfaces andsystemstractswithwhichtheyareassociated(e.g., HamiltonandTadros,1994;Banerjeeetal.,1996;Bohacs andSuter,1997;Diesseletal.,2000;CatuneanuandBiddulph,2001;Ketzeretal.,2003a,b;FantiandCatuneanu,
2010).Theemphasisondepositionalprocessesalsoledto ashiftinthefocusofpetroleumexplorationfromstructuraltrapstocombinedorpurelystratigraphictraps (e.g.,Bowenetal.,1993;Brownetal.,1995;Posamentier andAllen,1999).Anentirerangeofnewtypesofpetroleumplaysthusemerged,andisnowdefinedinlight ofthesequencestratigraphicconcepts.
1.1.2Sequencestratigraphy arevolutionin sedimentarygeology
Sequencestratigraphyisthethirdofaseriesofmajor “revolutions”insedimentarygeology(Miall,1995). Eachrevolutionresultedinquantumparadigmshift thatchangedthewaygeoscientistsunderstandsedimentarystrata.Thefirstbreakthroughwasmarkedbythe developmentoftheflowregimeconceptandtheassociatedprocess/responsefaciesmodelsinthelate1950s andearly1960s(HarmsandFahnestock,1965;Simons etal.,1965).Thisfirstrevolutionprovidedaunifiedtheorytoexplain,fromahydrodynamicperspective,the genesisofsedimentarystructuresandtheirpredictable associationswithinthecontextofdepositionalsystems. Beginninginthe1960s,theincorporationofplatetectonicsandgeodynamicconceptsintotheanalysisofsedimentaryprocessesatregionalscales,markedthesecond revolutioninsedimentarygeology.Ultimately,thesefirst tworevolutionsledtothedevelopmentofBasinAnalysis inthelate1970s,whichprovidedthescientificframework forthestudyoftheoriginsanddepositionalhistoriesof sedimentarybasins.Theconceptualbreakthroughsin thefieldsofprocesssedimentologyandbasinanalysis pavedthewayfortheemergenceofsequencestratigraphyasaninterdisciplinarymethodandgenetic approachtostratigraphicanalysis.
Asthemostrecentrevolutionaryparadigminthe fieldofsedimentarygeology,sequencestratigraphy startedinthelate1970swiththepublicationofAAPG Memoir26(Payton,1977),eventhoughitsrootscanbe tracedmuchfurtherbackintimeasexplainedbelow. Theconceptsembodiedbythisdisciplinehaveresulted inafundamentalchangeingeologicalthinkingandin particular,themethodsoffaciesandstratigraphicanalyses.Overthepastfewdecades,thisapproachhas beenembracedbygeoscientistsasthepreferredstyle ofstratigraphicanalysis,whichhasservedtotie togetherobservationsfrommanydisciplines.Infact,a keyaspectofthesequencestratigraphicapproachisto encouragetheintegrationofdatasetsandresearch methods.Blendinginsightsfromarangeofdisciplines invariablyleadstomorerobustinterpretationsand, consequently,scientificprogress.Thus,thesequence stratigraphicapproachhasledtoimprovedunderstandingofhowstratigraphicunits,faciestracts,anddepositionalelementsrelatetoeachotherintimeandspace withinsedimentarybasins(Fig.1.3).Theapplications
FIGURE1.3 Sequencestratigraphyinthe contextofinterdisciplinaryresearch.Therange ofnaturalresourcesthatcanberationalizedin thecontextofsequencestratigraphyincludes hydrocarbons,water,coal,andmineraldeposits.
ofsequencestratigraphyrangewidely,frompredictive explorationfornaturalresourcestoimprovedunderstandingofEarth’sgeologicalrecordoflocaltoglobal changes.
Theconventionaldisciplinesofprocesssedimentologyandclassicalstratigraphyareparticularlyrelevanttosequencestratigraphy(Fig.1.4).The sedimentologicalcomponentemphasizesontheprocessesthatleadtotheformationoffaciesandfaciescontactswithintheconfinesofindividualdepositional systems.Someofthesecontactsrepresenteventsignificantstratigraphicsurfacesthatmarkchangesin stratalstackingpatternsandassociatedsedimentation regimes,whichareimportantforregionalcorrelation. Thestudyofstratigraphiccontactsmaynot,however, beisolatedfromthefaciesanalysisofthestratathey separate,asthelatteroftenprovidethecriteriaforthe identificationofspecificboundingsurfaces.Owingto thegeneticnatureofthesequencestratigraphic approach,processsedimentologyisanimportantprerequisitethatcannotbeseparatedfrom,andformsanintegralpartofsequencestratigraphy.Atthesmaller scalesofdepositionalsystems,sequencestratigraphy canbeusedtoresolveandexplainissuesoffacies cyclicity,faciesassociationsandrelationships,and reservoircompartmentalization,withoutnecessarily applyingthisinformationforlarger-scalecorrelations.
FIGURE1.4 Sequencestratigraphyatthelimitbetweenprocess sedimentologyandconventional stratigraphy(definitionsmodified fromBatesandJackson,1987). Sequencestratigraphymakesuseof theprinciplesandmethodsofboth processsedimentologyandconventionalstratigraphy,inadditionto whichitbringsanewelementof faciespredictability.
Theimportanceofprocesssedimentologyin sequencestratigraphybecomesevidentintheworkflowofidentificationofsequencestratigraphicsurfaces intherockrecord.Basiccriteriafortheidentificationof stratigraphicsurfacesrelatetotheconformablevs. unconformablenatureofthecontact,aswellasthe natureofthejuxtaposedfaciesacrossthecontactunder analysis.Insightsofprocesssedimentologyarecritical tounderstandingtheoriginofthevarioustypesofunconformitythatmayforminnonmarine,coastal,ormarineenvironments,aswellasthefaciescharacteristics andvariabilityacrosssystemstracts.Thestratigraphic componentofsequencestratigraphyrelatestoitsapplicabilitytocorrelations,bothwithinandbeyondthe confinesofindividualdepositionalsystems,inspite ofthelateralchangesoffaciesthatarecommonin anysedimentarybasin.Inadditiontoitssedimentologicalandstratigraphicaffinit ies,sequencestratigraphy alsobringsacomponentoffaciespredictabilitywhich isparticularlyappealingtoindustry-orientedresearch (Fig.1.4).
Thesuccessandpopularityofsequencestratigraphy followingthe1970sstemsfromitswidespreadapplicabilityinbothfrontierandmaturehydrocarbonbasins, wherelowerandhigherresolutionpredictionsoffacies developmentcanbeformulated,respectively.Thesepredictivemodelshaveproventobeparticularlyeffective
inreducinglithology-predictionrisksforhydrocarbon explorationandproduction,andhavebeensubsequentlyemployedfortheexplorationandproduction ofothernaturalresourcesaswell,includingaquifers, coalbeds,andmineralplacers.Inadditiontoitseconomicapplications,sequencestratigraphyisalso employedtoresolveissuesoffundamentalresearch relatedtotheevolutionandstratigraphicarchitecture ofsedimentarybasins.
1.1.3Sequencestratigraphy anintegrated approach
Therootsofsequencestratigraphycanbetracedfar backintheclassicprinciplesofsedimentarygeology, whichestablishedthefundamentalguidelinesofsedimentologicalandstratigraphicanalyses.These“first principles”setupthegroundrulesforthephysicsof flowandsedimentmotion,andtheprocessesofsedimentaccumulation,bypassorerosioninrelationtoa shiftingbalancebetweensedimentsupplyandtheenergyofthetransportingagent(Fig.1.5).Theseprinciples stillrepresentthescientificbackboneofsequencestratigraphy,whichallowsoldandmodernconceptstoblend
intoanewwayoflookingatthesedimentaryrockrecord.Withthisbackground,sequencestratigraphy emergedasaninterdisciplinaryapproachthatrelieson theintegrationofmultipleresearchmethodsanddatasets(Fig.1.3).Atthesametime,sequencestratigraphy alsoprovidessupportforotherlinesofresearchsuch asbasinanalysisandsource-to-sinkmodeling,which requireamultidisciplinaryapproach.
Sequencestratigraphyhasbecomeanessential componentofbasinanalysis.Inthecontextoflarger scalesource-to-sinknumericalmodels,sequencestratigraphyprovidesarealitycheckforthecalibrationof modelresultswithfielddata.Beyondthedata-based sequencestratigraphicanalysisofabasinfill,sourceto-sinkstudiesintegratetheanalysisofsedimentsourceswithinnumericalsimulationsofdrainagesystems andsedimentdeliverypatternsfromtheprovenanceto thedepocenters.Thistypeofresearchextendsthefield ofstratigraphicmodelingtolargerscales,andthereliabilityofitspredictionsdependsonthecalibrationof modelresultswithfielddata(Fig.1.2).Thedevelopment ofsource-to-sinkmodelingtechniquesdoesnotchange norreplacetheneedforsequencestratigraphicwork. Sequencestratigraphywillcontinuetoprovidethe meanstorationalizethestratigraphicrelationships
FIGURE1.5 Firstprinciplesofsedimentarygeologythatarerelevanttosequencestratigraphy(modifiedafterMiddleton,1973;Posamentier andAllen,1999).
withinabasinfill,inadata-drivenapproachthatisindependentofmodelassumptions.Theresultsofsequence stratigraphicanalysiscanbeusedtoconstrainrealistic inputparametersforthesource-to-sinkmodels.
Thecomplexityandaccuracyofgeologicalmodels devisedtoresolveacademicoreconomicissues improvedovertimeinresponsetocorrespondingadvancesinconceptsandtechnology.Classicalgeologyremainsthefoundationofeverythingweknowtoday,by providingthemeanstounderstandingthe“firstprinciples”ofsedimentarygeology(Fig.1.5).Thisdoesnot meanthatsequencestratigraphyonlypresentsoldconceptsinanewpackage,orthatitdevelopedasastandalonedisciplineinisolationfromothermethods.Dueto itsintegratedapproach(Fig.1.3),sequencestratigraphy affordsnewinsightsintothegenesisandarchitectureof sedimentarybasinfills,whichwerenotpossiblepriorto theintroductionofseismicstratigraphicconceptsinthe 1970s.Theissueoffaciespredictabilityisagood exampleofanewinsightthatwasmadepossibleby thesequencestratigraphicapproach,whichishighly significantonbothacademicandeconomicgrounds.
Technologicaladvancesinthefieldsofthreedimensionalseismicdataacquisitionandprocessing resultedinthedevelopmentofseismicgeomorphology startingwiththe1990s,inparallelwithsequencestratigraphy.AsdefinedbyPosamentier(2000,2004),seismic geomorphologydealswiththeimagingofpaleogeographicelements,suchasdepositionalsystemsandelementsthereof,usingthree-dimensionalseismicdata. Seismicgeomorphologycanbeperformedasastandalonetechnique,butitcanalsobeintegratedwith sequencestratigraphyforathree-dimensionalcontrol ofthebasinfillthatcombines2Dsection-viewinsights fromseismicstratigraphy(e.g.,reflectiongeometries andterminations,stratigraphicdiscontinuities,seismic facies)withthe3Dplan-viewimagesofseismicgeomorphology.Thisthree-dimensionalcontrolonthestratigraphicarchitectureisimportantatanystage,from frontierexplorationtoproductiondevelopment,asit providessupportandenhancestheaccuracyoffacies predictions,includingtheinterpretationofseismic faciesintermsofsedimentaryfacies.
Theresolutionofthesequencestratigraphicwork willcontinuetoimproveinparallelwithtechnological advancesindataacquisitionandprocessing.Current effortsaimatreducingtheerrormarginofstratigraphic modelsandinterpretations,duringbothstagesof explorationandproductionofnaturalresources,as wellasthecostsofexplorationandproduction.As withtheintroductionofseismicgeomorphology,technologicaladvanceswilldictatethenextcornerstone thatcanbeachieved.Forexample,boreholeimaging usingelectriclogs(microresistivitydata,whichsimulateavirtualcoringofboreholes)affordinsightsinto
processsedimentology(e.g.,thevisualizationofsedimentarystructuresandpaleoflowdirections),thus eliminatingthecostsofmechanicalcoring.Suchtechniquesanddatasetswillcontinuetobeintegrated intosequencestratigraphyinordertoadvanceour knowledgeandunderstandingoftheevolutionandarchitectureofsedimentarybasinfills,fromsedimentologicaltostratigraphicscales.
1.1.4Sequencestratigraphyvs.othertypesof stratigraphy
Sequencestratigraphyisatypeofstratigraphythatis uniquelyfocusedontheidentificationandcorrelationof stratalstackingpatternsinthesedimentaryrecord (Fig.1.6).Thisisfundamentallydifferentfromthecorrelationapproachesthatareemployedbyallothertypesof stratigraphy(Fig.1.6).Thedistinctionbetweenthe differenttypesofstratigraphyiswelldefined,andyet confusionsstillarosebetweensequencestratigraphy andothertypesofstratigraphy,notablychronostratigraphyandallostratigraphy.Someoftheseconfusionsstem fromearlymodelassumptions(e.g.,theassumptionthat sequencestratigraphicsurfacesaretimelines,hencethe confusionbetweensequencestratigraphyandchronostratigraphy)orfromfaultydefinitionsofstratalunits andboundingsurfacesintheearlydaysofsequence stratigraphy(e.g.,thedefinitionofparasequencesand floodingsurfaces,whichemployedallostratigraphic ratherthansequencestratigraphiccriteria).Although theseconfusionshavebeenaddressedandresolved, theystilloccasionallypermeatethesequencestratigraphicpracticeandliterature.
FIGURE1.6 Typesofstratigraphy,andtherockattributesthatthey useforcorrelation.Sequencestratigraphyisatypeofstratigraphy whichreliesonstackingpatternsforthedefinition,nomenclature, classification,andcorrelationofstratalunitsandboundingsurfaces. Sequencestratigraphicstudieshighlightthestratigraphiccyclicitythat developsinresponsetochangesinrelativesealevel(accommodation) andbaselevel(sedimentation).
Figs.1.7and1.8 presenttheclassicdefinitionsof sequencestratigraphyandofthemainstratalunits involvedinsequencestratigraphicanalysis.Subsequent
tothesedevelopments,theconceptof“sequence” continuedtoevolveandseveraltypesofstratigraphic sequencehavebeendefined,dependingontheselection
Definitionsofsequencestratigraphy.
FIGURE1.8
FIGURE1.7
ofthe“sequenceboundary”andthedefinitionand nomenclatureofthecomponentsystemstracts (Figs.1.9and1.10).Forthisreason,andinspiteofhavingbeenwidelyembracedbythestratigraphiccommunity,sequencestratigraphyremainedthelasttypeof stratigraphytobeendorsedwithformalguidelinesfor methodologyandnomenclaturebytheInternational CommissiononStratigraphy(Catuneanuetal.,2011). Thisformalendorsementwasmadepossiblebythe identificationofcommon-groundprinciplesthatenable astandardapplicationofthemethodinamannerthatis independentofmodel,asexplainedinthisbook.
Importanttonoteisthatthedefinitionandapplicationofsequencestratigraphicconceptsareindependent ofscale.Thereisnoreferencetoscaleinthedefinitionof concepts(Figs.1.7and1.8),andthesameterminology canbeappliedfordepositionalsystems,systemstracts, sequences,andboundingsurfacesthatdevelopat differenttemporalandphysicalscales.Sequencestratigraphythusappliestofeaturesassmallasthoseproducedinanexperimentalflume,formedinamatterof hours(e.g.,Woodetal.,1993;Kossetal.,1994;Paola, 2000;Paolaetal.,2001),aswellastothosethatarecontinentwideandformedoverperiodsofmillionsofyears. Nonethelessadistinctionmustbemadebetweenlargerandsmaller-scalesequences,systemstracts,andstratigraphicsurfaces.Thisisaddressedthroughahierarchy basedontheuseofmodifierssuchasfirst-order,second-
order,third-order,etc.,commonlyinarelativerather thananabsolutesense.Althoughthisterminologyis oftenassociatedwithspecifictimeranges(Vailetal., 1977a,b,1991;Krapez,1996),thishasnotalwaysbeen commonpracticeinthescientificliterature(seediscussionsinEmbry,1995;PosamentierandAllen,1999;Catuneanuetal.,2004,2005).Onereasonforthisisthatwe oftendonotknowthescale(especiallyduration,but alsolateralextentorthicknesschangesacrossabasin) ofthestratalunitswedealwithwithinagivenstudy area,sotheuseofspecificnamesforspecificscales maybecomequitesubjective.Anotheradvantageofusingaconsistentterminologyregardlessofscaleisthat jargoniskepttoaminimum,whichmakessequence stratigraphymoreuser-friendlyandeasiertounderstandacrossabroadspectrumofreadership.Theseissuesaretackledinmoredetailin Chapter7
Amongthekeyconceptsshownin Fig.1.8,theterm “depositionalsystem”definesthelargeststratalunitof sedimentology,andpredatesmodernsequencestratigraphy.Incontrast,“systemstract”and“depositional sequence”arespecificsequencestratigraphicterms, introducedwiththeadventofseismicstratigraphyin the1970s.Asystemstractisasumoflaterallycorrelative depositionalsystems(hence,theuseofplural:systems), whichformsduringaspecificstageofastratigraphic cycle(e.g.,a“transgressive”systemstractformsduring shorelinetransgression).Asequenceincludestwoor
FIGURE1.10 Approachestosequencestratigraphy:nomenclatureofsystemstractsandtimingofsequenceboundaries(fromCatuneanuet al.,2011).Whiletheconceptof“systemstract”wasintroducedinthe1970s(BrownandFisher,1977),itsusageinsequencestratigraphyonly startedinthe1980s(PosamentierandVail,1985).Abbreviations:CC* correlativeconformityinthesenseofPosamentieretal.(1988),herein referredtoasthe“basalsurfaceofforcedregression”;CC** correlativeconformityinthesenseofVanWagoneretal.(1988),hereinreferredtoas the“correlativeconformity”;FR forcedregression;FSST falling-stagesystemstract;HNR highstandnormalregression;HST highstand systemstract;LNR lowstandnormalregression;LST lowstandsystemstract;MFS maximumfloodingsurface;MRS maximumregressive surface;R regression;RSL relativesealevel;RST regressivesystemstract;T transgression;T R transgressive-regressive;TST transgressivesystemstract.See Fig.1.9 fortheproponentsofthedifferentmodels.
moresystemstracts,dependingonthenumberofstratal stackingpatternsthatdevelopduringastratigraphic cycle.Theactualscaleforsequencestratigraphicwork ishighlyvariable,rangingfromdepositional systemscale(alsohighlyvariable)totheentirefillofa sedimentarybasin,andbeyond.Whenappliedtothe analysisofadepositionalsystem(e.g.,anancientdelta; Fig.1.11),sequencestratigraphyismainlyusedto resolvethedetailsoffaciesrelationships.Suchstudies areoftenperformedtodescribethedegreeofreservoir compartmentalizationinthevariousstagesofoilfield explorationandproduction.Whenappliedtothescale ofdepositionalsystemassociations,theissueofstratigraphiccorrelationbecomesaprimaryobjective,and providestheframeworkforthelargerscaledistribution offacies.
Theprinciplesoutlinedaboveprovideageneralidea abouttherangeofpotentialoutcomesandobjectivesof sequencestratigraphyasafunctionofscopeandscaleof analysis.Thereisacommonmisconceptionthat sequencestratigraphyisalwaysrelatedtoregional,
continental,orevenglobalscalesofobservation(subbasins,basins,andglobalcycles).Thisdoesnotneed tobethecase,assequencestratigraphycanbeapplied virtuallytoanyscale.Agoodexampleofthisisthe studyofthe“EastCouleeDelta”(Posamentieretal., 1992a),whereanentirerangeofsequencestratigraphic elements(includingsystemstracts)havebeendocumentedatacentimetertometerscale(Fig.1.12).In recentyearstherehavebeennumerousflume-based studieswheresequenceshavebeencreatedunder controlledlaboratoryconditions(e.g.,Woodetal., 1993;Kossetal.,1994;Paola,2000;Paolaetal.,2001). Suchstudieshaveprovidedvaluableinsightastovariationsonthegeneralsequencemodel.
Almostanytypeofstudyofasedimentarybasinfill requirestheconstructionofcrosssections.Thelines wedrawonthesetwo-dimensionalrepresentationsare oftwomaintypes:(1)linesthatbuildthechronostratigraphicortimeframeworkofthestudiedinterval,and (2)linesthatillustratelateralchangesoffaciesorlithology.Thechronostratigraphicframeworkiscommonly
FIGURE1.11 Stratigraphicarchitectureofashallow-watersystem(LateCretaceous,Alberta,Canada).Followingthetransgressionofthe seaway,thelong-termregressionispunctuatedbyhigherfrequencystagesofprogradationandretrogradationwhichdelineateclinoforms separatedbytransgressiveshales.Thisisanexampleofpetroleumreservoircompartmentalizationataproductiondevelopmentscale,inwhich eachclinoformisaseparatehydrodynamicunit.Abbreviations:GR gamma-raylog;CH fluvialchannelfill;CS fluvialcrevassesplay.
FIGURE1.12 EastCouleeDelta(fromPosamentieretal.,1992a;imagecourtesyofHenry Posamentier),demonstratingtheapplicabilityof sequencestratigraphicconceptsatvirtuallyany scale.Inthisexample,thehighstandsystems tractwasincisedduringthefallinthewater level(pondevaporation),followedbytheprogradationofthelowerelevationlowstanddelta. SeePosamentieretal.(1992a)foramoredetailed interpretation.
constructedbythecorrelationofsurfacesofsequence stratigraphicsignificance,ortruetimemarkerssuchas bentonitesormagneticpolarityboundaries.Thisis wheresomeconfusioncanarise.Strictlyspeaking, sequencestratigraphicsurfacesarenottruetimelines butinfactaretosomedegreetimetransgressive,ordiachronous.However,becausetruetimelinesarenot commonlyobserved,thegeoscientistisrelegatedtousingthesesurfacesasproxiesfortimelines,beingpragmaticandacceptingthenotionthatwithintheconfines
ofmoststudyareastheyareatleastclosetobeingtime linesandtherefore,arefundamentallyuseful.Thedegreeofdiachroneityofsequencestratigraphicsurfaces, aswellasofothertypesofstratigraphicsurfaces,isdiscussedinmoredetailin Chapters6and7
Sequencestratigraphicsurfacesarenotnecessarily easiertoobservethanthemorediachronouscontacts thatmarklateralandverticalchangesoffacies.Consequentlythepractitionercanbefacedwiththedilemma ofwheretobeginastratigraphicinterpretation;inother words,whatlinesshouldgofirstonacrosssection.The sequencestratigraphicapproachyieldsageneticinterpretationofthebasinfill,whichclarifiesbytimeincrementhowabasinhasfilledwithsediment.To accomplishthis,sequencestratigraphicsurfacesare interpretedfirst,toproduceageneticframeworkwithin whichothertypesofsurfacecanberationalized.Subsequently,thesectionsbetweensequencestratigraphic surfacesareinterpretedbyrecognizingfaciescontacts. Thesetwotypesofsurfacesdefinesequencestratigraphyandlithostratigraphy,respectively(Fig.1.13).
Theinherentdifferencebetweenlithostratigraphy andsequencestratigraphyisimportanttoemphasize, asbothanalyzethesamesedimentarysuccessionbut withthefocusondifferentstratigraphicaspectsor rockproperties.Lithostratigraphydealswiththe
lithologyofstrataandwiththeirorganizationintounits basedonlithologicalcharacter(Hedberg,1976).The boundariesbetweenlithostratigraphicunitsareoften highlydiachronousfaciescontacts,inwhichcasethey developwithinthesedimentarypackagesboundedby sequencestratigraphicsurfaces(Fig.1.13).Theadvantageofthesequencestratigraphicapproachisthatcorrelationcanbecarriedoutdespitethelateralchangesof faciesthatcommonlyoccuracrossabasin,forwhich reasonsequencestratigraphicsurfacesaretypically moreextensivethanthefaciescontacts.Itisalsoimportanttonotethatfaciesanalysesleadingtotheinterpretationofpaleoenvironmentsaremuchmorecriticalfor sequencestratigraphythanforlithostratigraphy,as illustratedin Figs.1.14and1.15.Thesefiguresshow thatevenalong1Dverticalprofiles,sequencestratigraphicunitsareoftenoffsetrelativetothelithostratigraphicunitsduetotheiremphasisondifferentrock attributes.Understandingwhatconstitutesareasonable verticalandlateralrelationshipbetweenfacieswithina timeframeworkassistsincorrelatingevent-significant surfacesthatmarkchangesinstratalstackingpatterns throughvaryinglithologies.
Anexampleofasequencestratigraphic ascontrastedwithalithostratigraphic interpretationbased onthesamedatasetisillustratedin Fig.1.16.The
FIGURE1.13 Sequencestratigraphicvs.lithostratigraphicapproachestostratigraphiccorrelationandthedefinitionofstratalunits.Sequence stratigraphicsurfacesmarkchangesinstratalstackingpatterns(e.g.,fromprogradationtoretrogradationand viceversa),withorwithoutchanges inlithology.Lithostratigraphicsurfacesmarkchangesinlithology,withorwithoutchangesinstackingpattern.Astheyareindependentoflithology,sequencestratigraphicunitsandboundingsurfacesaretypicallymappableoverlargerareasdespitethelateralchangesoffacies,and thereforeprovideasuperiormethodofstratigraphiccorrelation.Faciescontactsarealsoimportanttomap after theconstructionofthesequence stratigraphicframework,astheyarebestrationalizedwithinthegeneticcontextofsystemstracts.Abbreviations:C coarseningupward;F fining upward.
FIGURE1.14 Lithostratigraphyandsequencestratigraphyofafaciessuccession(modifiedfromPosamentierandAllen,1999).Lithostratigraphydefinesrockunitsonthebasisoflithology,oftenirrespectiveofthedepositionalsystem.Sequencestratigraphydefinesrockunits basedonstratalstackingpatternsandchangesthereofacrosstheirboundingsurfaces.Lithostratigraphicandsequencestratigraphicsurfacesmay ormaynotcoincide.Themaximumfloodingsurface,whichoftenprovidesthebestdatumforstratigraphiccorrelation,iscommonlyplacedwithin undifferentiatedlithostratigraphicunits.Othersequencestratigraphicsurfacesmayalsobemissedwithinthelithostratigraphicframeworkif the faciesbelowandaboveshareasimilarlithologicalcharacter.Abbreviations:GR gamma-raylog;LST lowstandsystemstract;TST transgressivesystemstract;HST highstandsystemstract.
FIGURE1.15 Contrastbetweenlithostratigraphyandsequence stratigraphyinthedelineationofstratigraphicunits(Cretaceous, WesternCanadaSedimentaryBasin).Knowledgeofdepositionalsystemsisonlycriticaltosequencestratigraphy.Thesystemstractsof depositionalsequencesAandBincludelowerrankstratigraphiccycles.Abbreviations:SP spontaneouspotential;LST lowstandsystemstract;TST transgressivesystemstract;HST highstandsystems tract.
interpretationofsequencestratigraphicsurfacesis basedontwofundamentalobservations:thetypeof stratigraphiccontact,conformableorunconformable; andthenatureoffacies(depositionalsystems)which
areincontactacrossthestratigraphicsurface.Thereconstructionofpaleodepositionalenvironmentsiscriticalin sequencestratigraphy.Incontrast,thelithostratigraphic crosssectiondoesnotrequireknowledgeofpaleoenvironments,butonlymappingoflithologicalcontacts. Someofthesecontactsmaycoincidewithsequence stratigraphicsurfaces;othersmayonlyreflectlateral changesoffacies.Asaresult,thelithostratigraphicunits (e.g.,formationsA,B,andCin Fig.1.16)provideonly descriptiveinformationoflithologicdistribution,which insomeinstancescouldcombinetheproductsofsedimentationofvariousdepositionalenvironments.Thus asimplemapoflithologicdistributionmaygivelittle insightastothegeneralpaleogeography,andasaresult beoflittleuseinpredictinglithologiesawayfrom knowndatapoints.
Allostratigraphyisastratigraphicdisciplinewith strongaffinitytolithostratigraphy,butwithemphasis onboundingsurfacesratherthanstratalunits.The NorthAmericanCommissiononStratigraphicNomenclature(NACSN)introducedformalallostratigraphic unitsinthe1983NorthAmericanStratigraphicCode toname“discontinuity-boundedunits.”Ascurrently amended,“anallostratigraphicunitisamappable bodyofrockthatisdefinedandidentifiedonthebasis ofitsboundingdiscontinuities”(Article58).Allostratigraphicunits,inorderofdecreasingrank,areallogroup, alloformation,andallomember aterminologythat originatesandismodifiedfromlithostratigraphy.The fundamentalunitisthealloformation(NACSN,1983, Art.58).Theboundingdiscontinuitieswhichdefine theallostratigraphicapproacharerepresentedbyany mappablelithologicalcontact,withorwithouta
FIGURE1.16 Sequencestratigraphicvs.lithostratigraphicframeworks.1.Thereconstructionofdepositionalsystemsandtheobservationof thescouredvs.conformablenatureofstratigraphiccontactsareimportantstepsinthesequencestratigraphicworkflow;2.Sequencestratigraphic frameworkbasedontheobservationofstratalstackingpatterns;3.Sequencestratigraphicframeworkwithfaciescontactsanddepositional systems:A meanderingsystem;B braidedsystem;C estuary-mouthcomplex;D centralestuary;E deltaplain;F upperdeltafront; G lowerdeltafront prodelta;4.Lithostratigraphicframework(e.g.,formations):A sandstone-dominatedunit;BandC mudstonedominatedunits,withsiltyandsandyinterbeds;unitsBandCareseparatedbyunitA;additionallithostratigraphicunits(e.g.,members) maybedefinedasafunctionofvariationsinlithologyandcolor.
stratigraphichiatusassociatedwithit.Inthisapproach, alllithostratigraphicandsequencestratigraphicsurfacesthatareassociatedwithalithologicalcontrast maybeusedforallostratigraphicstudies(e.g.,BhattacharyaandWalker,1991;Plint,2000).However,notall allostratigraphicsurfacesareofsequencestratigraphic significance(e.g.,“floodingsurfaces”thatdevelopduringtransgression,withretrogradationalstackingpatternsbelowandabove,aresurfacesofallostratigraphy butnotofsequencestratigraphy;Catuneanu,2019a).
1.2Developmentofsequencestratigraphy
Modernsequencestratigraphystartedas“seismic stratigraphy”inthe1970s(Payton,1977),wherebythe methodwasappliedspecificallytoseismicdata.This evolvedintothemoregeneric“sequencestratigraphy” inthe1980sastheapplicationofthemethodwas extendedtoothertypesofdata,suchasthoseprovided bywellsandoutcrops(e.g.,Wilgusetal.,1988).Noteworthy,thedevelopmentofsequencestratigraphyasa “new”typeofstratigraphyinthe1970sand1980swas precededbythemuchearlierpublicationofseveralof itskeyconcepts(e.g.,Barrell,1917;Slossetal.,1949; Wheeler,1964, Fig.1.17).Someofthesemilestones includetheconceptsofbaselevel(Powel,1875;Gilbert, 1895;Barrell,1917),unconformity-boundedsequence (Longwell,1949;Slossetal.,1949),correlativeconformity(introducedas“continuitysurface”;Wheeler, 1964),anddepositionalsystem(FisherandMcGowan, 1967).Buildingonthisfoundation,therefinements broughtaboutbyseismicstratigraphyincludethedefinitionofsystemstracts(BrownandFisher,1977, Fig.1.8),seismic-reflectionterminations(Mitchum, 1977),arevisiontothedefinitionofa“sequence” (Mitchum,1977, Fig.1.8),andtheusageofseismic dataforageneticinterpretationofthestratigraphicarchitecture(Payton,1977).Fromhere,sequencestratigraphybloomedanddiversifiedinthe1980sandthe 1990s,withseveralmodelsbeingproposed(Figs.1.9 and1.10).
Theevolutionofsequencestratigraphyinvolvedadvancesintheunderstandingofthearrayofpossiblecontrolsonsequencedevelopment,improvementsin stratigraphicresolution,revisionstothedefinitionand classificationofsequences,andultimatelytheemergenceofastandardapproachtomethodologyand nomenclature(Figs.1.9and1.17).Themethodology improvedsignificantlysincethe1970s,fromamodeldrivenapproachunderlainbyassumptionsregarding thedominantroleofeustasyonsequencedevelopment, withconsequentassertionsofglobalcorrelations(Vail
etal.,1977a,b;Haqetal.,1987),toadata-driven approachthatpromotestheuseoflocaldatawithout anyassumptionsregardingtheunderlyingcontrolson sequencedevelopment(Miall,1986,1991,1992;Catuneanuetal.,2011).Thelatteraffordsrealisticconstructionsoflocalstratigraphicframeworks,whichproveto behighlyvariableintermsoftimingandscalesofstratigraphiccycles,notonlyfromonesedimentarybasinto anotherbutalsoamongthesub-basinsofthesamesedimentarybasin(Catuneanuetal.,1999,2000,2002;Miall etal.,2008;Menegazzoetal.,2016).Theconstructionof basin-specificstratigraphicframeworksisamajorbreakthroughanddeparturefromtheearlymodels.
Concomitantwiththeimprovementsinmethodology, refinementsinstratigraphicmodelingdrivenbyadvancesincomputingpowerenhancedtheabilityto testtheresponseofsedimentarysystemstoanycombinationsofpossiblecontrolsonsequencedevelopment. Theinsightsenabledbynumericalsimulationsare particularlyusefulwhencalibratedwithfielddata (Euzenetal.,2004;Rabineauetal.,2005,2006;Csato etal.,2013,2015;Lerouxetal.,2014;CatuneanuandZecchin,2016).Inlightoftheseadvances,acleardistinction isrequiredbetweenmethodologyandmodelingin sequencestratigraphy.Themethodologyisbasedon theobservationofstratalstackingpatternsinamanner thatisindependentoftheinterpretationoftheunderlyingcontrols.Beyondthepurposeofthemethodological workflow,themodelingandtestingofthepossiblecontrolsonsequencedevelopmentcancontinueindefinitely aftertheconstructionofasequencestratigraphicframework.Stratigraphicmodelingisanindependentlineof researchthatplaysnorolein,anditdoesnotchange theoutcomeofthemethodologicalworkflow(Catuneanu,2020b, Fig.1.2).
Mostsignificanttoitspracticalapplications,the developmentofsequencestratigraphywasaccompaniedbyagradualincreaseinstratigraphicresolution, fromtheseismicscalesofpetroleumexploration(Payton,1977)tothesub-seismicscalesofpetroleumproductiondevelopment(e.g.,VanWagoneretal.,1990; Homewoodetal.,1992;HomewoodandEberli,2000; ZecchinandCatuneanu,2013,2015;Magalhaesetal., 2015;Catuneanu,2019b).Sequencestratigraphicframeworkscanbeconstructedatdifferentscales,depending onthescopeofthestudyandtheresolutionofthedata available.Seismicdataaretypicallyusedtobuildlarger scale,lowerresolutionframeworks,whereasborehole andoutcropdataaffordtheconstructionofhigherresolutionframeworksatsub-seismicscales.Theobservationofthefullspectrumofstratigraphiccomplexity thatdevelopsatintertwiningscalesreliesontheintegrationofmultipledatasetswithdifferentresolutions.In
FIGURE1.17 Milestonesinthedevelopmentofsequencestratigraphy.Modernsequencestratigraphy,whichstartedas“seismicstratigraphy” inthe1970s(Vail,1975;Payton,1977),wasdominatedinthe1970s 1980sbytheassumptionthateustasyexertedthemaincontrolonsequence development;thisledtotheconstructionofreferenceglobal-cyclechartsforstratigraphiccyclicityandcorrelationsworldwide(Vailetal.,1977b; Haqetal.,1987,1988;Posamentieretal.,1988).Subsequentdevelopmentsinthe1990schangedtheemphasisontectonismasamajorcontrolon sequencedevelopment(e.g.,Krapez,1996:“Theimportanceofeustasyinsequencestratigraphyshouldbede-emphasized”).Thestandard methodologythatemergedinthe2000s 2010sisdecoupledfromtheinterpretationoftheunderlyingcontrols,anditisbasedontheobservation ofstratalstackingpatternsinthestratigraphicrecord.
theworkflowofhydrocarbonexploration,theconstructionofastratigraphicframeworktypicallystartswith 2Dseismictransects.Thecontextprovidedbyseismic dataenhancestheaccuracyoffaciespredictionsinsubsequenthigherresolutionstudies.
Thedevelopmentofseismicstratigraphyinthe1970s madeuseofestablishedsedimentologicalconcepts(e.g., theconceptof“depositionalsystem”asathreedimensionalassemblageoflithofacieslinkedbyacommonenvironmentofdeposition;FisherandMcGowan, 1967)todefinenewbuildingblocksofthestratigraphic
framework(e.g.,“systemstracts,”aslinkagesofcontemporaneousdepositionalsystems;BrownandFisher, 1977).Owingtothespecifictypeofdatausedtodevelop themethodology(i.e.,2Dseismictransects),seismic stratigraphyintroducedbydefaultaminimumscale fordepositionalsystems,systemstracts,andsequences, whichhadtoexceedtheverticalseismicresolution(i.e., typicallyinarangeof101 minthe1970s).Asaresult,the buildingblocksoftheseismicstratigraphicframework arecommonlyobservedatscalesof101 102 m.The perceptionthatsequencesandtheircomponentsystems
tractsanddepositionalsystemsdeveloptypicallyat scalesof101 102 misanartifactofseismicresolution, butitdominatedstratigraphicthinkingfordecades.
Therealityofsequences,systemstracts,anddepositionalsystemsatsub-seismicscaleshasbecomeevident withtheadvancesinhigh-resolutionsequencestratigraphy(e.g.,Tessonetal.,1990,2000;Loboetal.,2004; Amorosietal.,2005,2009,2017;Bassettietal.,2008, CatuneanuandZecchin,2013;Nansonetal.,2013;ZecchinandCatuneanu,2013,2015,2017;Csatoetal., 2014;Nixonetal.,2014;Magalhaesetal.,2015;Zecchin etal.,2015,2017a,b;Ainsworthetal.,2017,2018;Pellegrinietal.,2017,2018;Catuneanu,2019a,b).Improvementsinstratigraphicresolutiondemonstratedthat unconformitiesmayformoverawiderangeofscales, bothbelowandabovetheseismicresolution,andtherefore,unconformity-boundedunitsarenotrestrictedto thescalesofseismicstratigraphy(e.g.,Miall,2015; Strasser,2016,2018).Itisnowclearthatmostcommonly, thebuildingblocksofaseismicstratigraphicframework consistofhigherfrequencysequencesthatdevelopat sub-seismicscales;e.g.,seismic-scalesystemstracts (101 102 m)consisttypicallyofsequencesof100 101 mscales,whicharedifferentfromandshouldnotbe confusedwithparasequences(Catuneanu,2019a).
1.2.1Unconformities
Sequencestratigraphystartedtoemergeasamethod ofstratigraphicanalysiseversincetherecognitionofunconformitiesintherockrecord,whichallowedthesubdivisionofthesedimentarysuccessionintounits separatedbybreaksindeposition(Fig.1.17).Earlydepictionsofangularunconformitiesdateasfarbackas the17thcentury(NicolausSteno,1669),buttheirgeologicalmeaningwasonlyrealizedlateinthe18thcentury (JamesHutton,1788,1795).Huttonpresentedthe conceptofunconformityaspartoftherockcycle, althoughheneveractuallyusedtheterm“unconformity”;instead,heuseddescriptivephrasesinwhich theexpression“conjunctionofverticalandhorizontal strata”waswidelyused(Tomkeieff,1962).Theterm “unconformity”wascoinedbyRobertJamesoninthe early19thcentury(Jameson,1805),butitwasonly widelyincorporatedintothegeologicalvocabulary followingtheworkofCharlesLyellandHenryDela Beche(DelaBeche,1830;Lyell,1830).
Theterm“unconformity”wassynonymouswith whatweknowtodayas“angularunconformity”until thebeginningofthe20thcentury,whentheterm “disconformity”wasproposedforaparticulartypeof erosionalunconformitywheresedimentarystrataabove andbelowthecontactareparalleltoeachother(Grabau,
1905).Othertypesofunconformitieswererecognized subsequently,includingthecontactbetweenbasement rocksandtheoverlyingsedimentaryrocks(i.e.,known todayas“nonconformity”;Blackwelder,1909)andthe non-depositionalhiatusthatassumesagapinsedimentationwithoutnecessarilyinvolvingerosion(i.e., referredtotodayas“paraconformity”;Willis,1910). Allthesetypesofunconformityassumea“substantial” breakinthegeologicrecord(Neuendorfetal.,2005), althoughtheactualspanoftimeofwhatisconsidered tobe“substantial”(asopposedto“brief,”asinadiastem)wasneverquantified.
Thespectrumofhiatalstratigraphiccontactswas completedwiththedefinitionofthe“diastem”byBarrell(1917),essentiallyasa“minor”paraconformity. However,thedistinctionbetweenaparaconformity andadiastem,bothintermsoftemporalsignificance andphysicalexpression,remainselusivetothepresent day.Furtherdiscussionandrecommendationsontheusageofthediastemconceptarepresentedin Chapter7 Thedefinitionofthevarioustypesofstratigraphiccontactsissummarizedin Fig.1.18.
1.2.2Unconformity-boundedunits
Asearlyastheeighteenthcentury,Hutton(1788, 1795)recognizedthealternationthroughtimeofprocessesoferosionanddeposition,settingupthefoundationforwhatisknowntodayasthe“rockcycle” (Fig.1.17).Hutton’sobservationsmaybeconsideredas thefirstaccountofstratigraphiccyclicity,whereby unconformitiesprovidethebasicsubdivisionofthe rockrecordintorepetitivesuccessions.Thelinkbetween unconformitiesandbase-levelchangeswassubsequentlyexplainedbyBarrell(1917),whostatedthat “sedimentationcontrolledbybaselevelwillresultin divisionsofthestratigraphicseriesseparatedbybreaks” (Fig.1.19).
Followingtherecognitionofunconformitiesinthe rockrecord,stratigraphichiatuseshavebecomenatural candidatesforcorrelationandthesubdivisionofthestratigraphicsuccessionintounitscharacterizedbyrelatively continuoussedimentaccumulation.Thenomenclatureof unconformity-boundedunitsincludedtermssuchas “rhythms”(Barrell,1917;todescribesedimentarycycles ofvariousscales),“cyclothems”(Weller,1930;Wanless andWeller,1932;WanlessandShepard,1936;todescribe small-scaleunconformity-boundedunitsofCarboniferousageinthemid-continentalUS),“sequences”(Longwell,1949;Slossetal.,1949;Sloss,1963;todescribe continental-scaleunconformity-boundedunitsinNorth America),“depositionalcomplexes”(Frasier,1974;to describeunitsboundedbymarinestarvationsurfaces),
FIGURE1.18 Typesofstratigraphiccontacts(modifiedafterBatesandJackson,1987;Neuendorfetal.,2005;Catuneanu,2006).Thescaleindependentdefinitionofanunconformityasastratigraphichiatusofanydurationeliminatestheneedfortheconceptofdiastem.Theusageof diastemsmayberestrictedtosedimentology,orbeeliminatedaltogetherfromsedimentarygeology(seetextfordetails).
and“synthems”(Chang,1975;torenametheconceptof “sequence”ofSloss,1963).Theusageoftheterm “sequence”inastratigraphiccontextwasnotwithout controversy(e.g.,discussioninvanLoon,2000),butit eventuallyprevailed,andbecamewidelyusedfollowing thepublicationoftheseismicstratigraphicmethodology inthe1970s(Mitchumetal.,1977).
Theunconformity-boundedsequenceofSloss(1963) providedthestratigraphiccommunitywithmappable unitsthatcouldbeusedforregionalcorrelationandthe subdivisionoftherockrecordintogenetically-related packagesofstrata.Theconceptof“unconformityboundedunit”wasformalizedintheInternational StratigraphicGuidein1994.Thelimitationofthis typeofunitbecomesevidentatsmallerscales,as unconformitiesoflessermagnitudestendtobe restrictedtothebasinmargins(Fig.1.20).Insuchcases, thenumberofsequencesdecreasesinadowndipdirection,hamperingstratigraphiccorrelation.Thislimitationrequiredaconceptionalinnovationwhereby sequenceboundariescouldbeextendedbeyond
theterminationofunconformities.Thebreakthrough wastheconceptof“continuity”surface(Wheeler, 1964),whichinphysicaltermsreferredtothepaleodepositionalsurface(e.g.,seafloor)atthetimewhen theunconformityreached itsmaximumextent.The “continuity”surfaceofWheeler(1964)wassubsequentlyrebrandedasthe“correlativeconformity”in thecontextofseismicstratigraphy(Mitchum,1977). Theadvantageofthemodernsequence,boundedbya compositesurfacethatmayincludeaconformable portion,liesinitsgreaterarealextent,thuswith improvedpotentialforstratigraphicmappingandcorrelation(Fig.1.21).
1.2.3Conceptof“sequence”
Inparallelwiththedevelopmentofthe“sequence” conceptinastratigraphiccontext,sedimentologistsin the1960sand1970salsousedtheterm“sequence”to defineverticalsuccessionsoffaciesthatare“organized inacoherentandpredictableway”(Pettijohn,1975),
