seismicdataneedtobeflattenedonachronostrati-

graphicallyconsistentsurfacethathasaslittlepa-

leotopographyaspossible.ThebaseoftheTamabra

Formationisalithostratigraphicchangefromgravity-

flowdepositsanddeep-watercarbonatemuddeposits

oftheupperTamaulipasFormation.Thislithostrati-

graphicsurfacecannotbeusedforflattening.The

datasetwasflattenedonthePimientaFormation

horizon,whichcorrespondstothetopofanargil-

laceousanddeep-watermudstonethatisinter-

pretedtobeaconsistentchronostratigraphicsurface

withnosignificanttopography.

Theflattenedseismicsection,whichdisplays

reflectiongeometriesthatareinterpretedtorep-

resentoveralloriginalgeometriesatthetimeof

deposition(Figure18),showswestwardthinning

oftheTamabrainterval.Inallthreedip-oriented

sections(Figure18A–C),proximalpartsofthesec-

tionsshowmorediscontinuousmoundedreflection

thandothedistalparts.Thestrike-orientedsection

(Figure18D)showsconvex-upwardreflectionge-

ometriesassociatedwithafewshinglingreflections.

Overall,theflatteningdatashowmorelobatere-

flection,withonlapofshorterreflectionontothe

lobatereflections.

Someoftheshinglingofthebasementhigh

topographyhaspreviouslybeeninterpretedasevi-

denceofshallow-watercarbonates(Horburyetal.,

2004).Ontheflattenedregionalcrosssection

(Figure18A),theirreconstructedgeometrycould

alternativelybeinterpretedasshinglingreflectionsTheblocky,discontinuous,shortreflectionsob-servedatthetoeofslopeoftheGoldenLaneplat-formareinterpretedastoe-of-slopeslumpsandcoarsedebris-flowdepositswithlargeblocks(Mullinsetal.,1986;Grammeretal.,1993;Lomandoetal.,1995;Janson,2002).SimilarreflectioncharacterisalsoobservedatthebaseoftheTamabraForma-tion,whichconsistsdominantlyofthickcarbonatebrecciainterpretedincoreandwell-loginterpre-tationasmassivedebris-flowdeposits(Figure4)(Loucksetal.,inpress).Morecontinuous,moundedtolensoid,convex-upwardreflectionsassociatedwithlateralshinglinginbothdipandstrikesectionsareinterpretedaslargefandepositsofconcen-trateddensityflowsandturbidites.Instrikesec-tion,obliquelyshingledreflectionsareinterpretedaslateralaccretionofstackedandamalgamateddebris-flowdepositsand/orconcentratedgravity-flowdeposits(Eberlietal.,2004).Indip-parallelsections,shingledreflectionsassociatedwithfandepositshavebeeninterpretedaschannel-backfilling(Betzleretal.,1999;Eberlietal.,2004;SavaryandFerry,2004).IsochoreMapAlbian1toAlbian4Sequence(TamabratoUpperTamaulipasFormations)MapFigure19Ashowsaseismic-basedisochoremapandawell-log-basedisochoremapbetweenthetopTamabrahorizonandthetopupperTamaulipashorizon.ThetwomapsshowoverallsouthwestwardthinningoftheentireTamabrasection.Thethickestintervalislocatedinthenortheastcornerofthe3-Ddataset,closetotheGoldenLaneplatform.Figure19.IsochoremapsfordifferentintervalswithintheTamabraFormationbasedoncoredata(left)andseismicdata(right).

(A)TwomapsillustratingsouthwestwardthinningoftheentireAlbianTamabraFormationinterval.PanelsBandCshowintra-Tamabraintervalthicknessvariation.(B)IsochoremapbetweentopofAlbian2sequence(topBC)andmaximumfloodingsurface(MFS)ofAlbian2sequence(topF).Thisintervalshowsthicknessvariationsinterpretedasdip-elongatedapronssuperimposedonageneralsouthwesternthinningtrend.(C)IsochoremapofAlbian3andAlbian4sequences(betweentopofTamabrahorizonandAlbian2topBChorizon).Twotopsequencescouldnotbeseparatedonseismicdata.Well-log-basedmapsontheleftshowonlytheAlbian3sequence.Whitedashedlineonseismicisochoremaps=areaofwell-log-basedmaponleft.

Jansonetal.131

Figure20.Seismicattributeslicesofthe3-DseismicdatasetflattenedonthetopTamabraFormation(topAlbian4)horizon.Slicelocationsareprogressivelydeeperlefttoright.Theuppermostslice(left)islocated12msbelowtheTamabrahorizonandcorrespondsapproximatelytotheAlbian3andAlbian4sequences.Themiddlesliceislocated44msbelowtheTamabrahorizoncorrespondsap-proximatelytotheAlbian2sequence.Thedeepestslice(right)islocated68msbelowtheTamabrahorizonandcorrespondsap-proximatelytotheAlbian1sequence(Ainterval).TheorangeareacorrespondstotheintersectionbetweenthetimesliceandtheupperTamaulipasFormationhorizon.TheAlbianintervalislocatedontherightsideoftheorangearea.(A)Slicethroughtheseismicamplitudevolume.Yellowdashedlines=lobateshape.(B–D)Slicesthroughinvertedacousticimpedancevolume,instantaneousfrequencyvolume,andcoherencevolume,respectively.Thickdashedline=lobateshapesidentifiedoneachslice,whereasthindashedline=shapeidentifiedontheseismicamplitudesliceforreference.

132SeismicArchitecture,SantaAguedaandPozaRicaFields,Mexico

Figure20.Continued.

Inthemoreproximalposition,wheretheTamabra

isthethickest,asignificantalong-strikethickness

variabilitycouldindicatethatsomepreferential

pathexistsforoff-platformsedimentsheddingand

gravity-flowdeposits.Albian2Isochore(TopF–TopBC)MapThisintervalencompassestheAlbian2TSTandAlbian2HST.Asidentifiedonthewell-log-basedisochoremap(Figure19B,left),thisintervalischar-acterizedbysouthwardthinning.Thebasal

interval

Jansonetal.133

showssignificantthicknessvariationinterpretedasdepositionalgeometriesdominatedbylobatede-posits.Inaddition,thenorthwestcornershowsthickintervalsthatareelongatedalongthenortheast-southwest.Thispatternisinterpretedaslargede-brisaprons,partlylocatedoutsidethestudyarea,separatedbydeeperchannelsatthetoeofslopeoftheGoldenLaneplatform.

Albian3andAlbian4Isochore(TopTamabra–TopBC)MapThisintervalincludesbothAlbian3andAlbian4sequences.Becauseoftheseismicresolutionofthedataset,wheretheAlbian4sequenceisrepre-sentedbyonereflection,thisisochoremaprepre-sentscombinedthicknessvariationsoftheAlbian3andAlbian4sequences(Figure19C).Theisochoremapshowsamorecomplexthicknessdistributionthantheunderlyinginterval,andtheisochoremapshowsaheterogeneousthicknessvariationsimilartothatseenontheregionalseismicsection(Figures8,

9).Southwestwardthinningisstillpresent,butitissubtler.Therapidlateralthicknessvariationscanbeinterpretedasevidenceofjuxtapositionofdif-ferentdepositionalenvironments,suchaschannelandlobes.Thethickerintervalinthiscaseislo-catedinthenortheastcornerofthedatasetandisisolatedfromtheplatformtoeofslope.Thisisolatedthickcouldbeinterpretedasalargefancomplex,suggestingachangeinthesourceofdebrisandintransportdirection.

SeismicAttributeAnalyses

The3-DseismicdatasetwasflattenedusingthetopTamabrahorizontoinvestigatethehorizontaldistributionofvariousseismicattributesinhorizon-parallelseismicslices.Foreachflattenedcubeandforeachattribute,threetimesliceswerepresentedthatintersectAlbian3andAlbian4(shallowest),Albian2,andAlbian1(deepest)sequences,respec-tively(Figure20).

FlattenedAmplitudebyrectilinearfeaturesthatcouldbeinterpretedasfansandchannels.Themiddleslice(Albian2se-quence)showsasimilarreflectioncharacterdis-tribution,butwithamuchnarrowerproximalzonewithchaoticreflections.Thelobateamplitudefeaturesseenonthetwoupperslicesareapproximately1.5to4km(～0.9–2.5mi)wide.Theirfanlikeshapeiscoherent,withsedimentcomingfromtheadjacentGoldenLane.Theuppermostslice(Albian3andAlbian4se-quences)showslobessmallerthanthoseofthemiddleslice(Albian2).TheAlbiansliceshowsmorecontinuousre-flection,withfewerlobatefeaturesandamorecha-oticamplitudedistributionthanseeninthetwoshallowerslices.Smallfanlikeseismicgeometriescanbeobservedinthenorthernarea.AcousticImpedanceInversionTheinvertedacousticimpedancedata(Figure20B)wereflattenedonthetopPimientahorizon.Timeslicesofthisflatteneddatasetshowlobatefeaturessimilartothoseseenonamplitudeslices.Thein-vertedacousticimpedancecubeisaproxyforpo-rosity.Theshallowestseismicsliceshowslargelo-bateareasoflowimpedancethatcorrespondroughlytothelobateareaontheamplitudeslice.Lowestimpedancevaluesaremostlywithinthelo-bateshapeidentifiedontheamplitudeslice.Thelowersliceshowslesslow-impedancearea.Thenorthernareasthatwereshowinglobateshapesontheamplitudedisplayconsistmostlyofhigh-impedancevaluesshowingafaintlobateshape.AgeneralincreaseinoverallimpedancevaluesandadecreaseinlateralheterogeneitiesinimpedanceseemtobeoccurringintheAlbian2slice.Frequency

Figure20Ashowsthreetimeslicesoftheflattenedseismicamplitude3-Ddataset.Theproximalpartoftheshallowestslice(Albian3andAlbian4se-quences)showsmostlychaoticreflections,whereasthemoredistalpartshowslargelobateshapescut