Figure12.Perspectiveviewof

thetimestructuremapofthetop

ElAbraFormationhorizon.Color

onhorizonrepresentstwo-way

traveltime.

Theplatforminteriorareaisdominatedbycha-oticseismicfacies(seismicfacies6inTable2).Withintheplatforminteriorchaotic,oneotherin-tervalofhigh-amplitudemoundedreflectionscanbeobserved.Onthebasisoftheinterpretationofsimilarseismicfaciesontopoftheplatform,thisotherintervalcouldindicateanolderphaseofplat-formkarstification(seeFigures8,9,11;Figure12showsa3-DviewofthetopoftheElAbraFor-mationhorizon).ThisveryirregulartopographyisinterpretedashavingresultedfromamajorkarstFigure13.Amplitudetimesliceover

GoldenLaneplatform.Yellowline=

interpretedplatformmargin.Green

dashedline=locationofFigure11.

High-amplitudechaoticresponse(blue

circle)isinterpretedaskarstifiedtop

oftheplatform.Largereentrantsthat

scalloptheplatformmarginmighthave

beencreatedbylarge-scalecollapseor

mayresultfrompost-Albianerosion

oftheplatform.eventattheendoftheAlbian(ViniegraandCastillo-Tejero,1970;Cooganetal.,1972;Jansonetal.,2004).Seismicreflectiongeometriesindicatepossiblelarge-scaleerosionanddissolutionoftheplatformtopandmargin(Figure13).Severaldeepdepressionsinthesurfaceareinterpretedassink-holesrelatedtokarstificationoftheplatformtop.TheedgeoftheGoldenLaneplatformintheSantaAgueda3-Dseismicsurveyisnotwellde-finedeverywhere,butitwasmappedatthechangefromhigh-amplitudecontinuousreflectionsof

the

122SeismicArchitecture,SantaAguedaandPozaRicaFields,Mexico

Figure14.(A)SeismicsectionalongstrikeofGoldenLaneplatform.Yellow,green,andbluehorizons=topofMendez,topofElAbra,andtopofPimientaformations,respectively.Redandyellowboxes=locationofenlargementsshowninpanelsBandC.(B)EnlargedviewshowingtwolargeerosivechannelsthatcutthroughupperAlbianslope.(C)Inenlargedview,bluearrowspointtoreflectiongeometriesinterpretedtobeoldererosivechannelsontheslopeoftheGoldenLaneplatform.TWT=two-way

traveltime.overlyingonlappingTertiarysiliciclasticsediment

andhighlydiscontinuousreflectionsoftheplatform

top.Thischangeinreflectioncharacter,asseenon

timeslices,showsthatthemarginisnotrectilinearbutsinuous(Figure13),withseverallargereen-trants.Thesereentrantscanbeinterpretedaslarge-scalemargin-collapsefeatures(Mullinsetal.,1986;Bosellini,2001)thathavescallopedtheslope,

could

Figure15.Amplitudetime

sliceoverGoldenLaneplatform.

Yellowline=interpretedplat-

formmargin.Greendashedline=

locationofFigure11.High-

amplitudechaoticresponse(blue

circle)isinterpretedaskarstified

topoftheplatform.Orangear-

rowspointtopossiblelargecan-

yonsontheGoldenLaneplat-

formslope.

Jansonetal.123

Figure16.Threestrike-parallelsectionsacrossthePozaRicadataset.Foreachsection,theseismicsectionwithhorizonsisshown(top),alongwiththelinedrawing(bottom)oftheTamabrainterval,toillustratereflectiongeometries.PanelAisthemostlandwardsectionnearthetoeofslopeoftheGoldenLaneplatform.PanelBislocatedinthemiddleofthePozaRicafield.PanelCisthemostdistalsection.Redarrow=locationofregionaldip-parallelcrosssectionofFigures8,9.Yellowbox=positionofenlargementshowninFigure17A,B.TWT=two-waytraveltime.124SeismicArchitecture,SantaAguedaandPozaRicaFields,Mexico

Jansonetal.125

havesourcedsomeofthedebrisaccumulationob-servedinPozaRicafield,andcouldalsohaveservedaspreferentialpathsforsedimentsheddingfromtheplatformtop.

PlatformSlope

Strike-parallelverticalseismicsectionsthroughthesloperevealnumerousconcavefeaturesthattrun-cateunderlyingreflections(Figure14).Ontimeslices,thesefeaturesformindentationsontheupperbasin-facingslopebutareabsentintheplatforminterior-facingslope(Figure15).Theseerosionalfeaturesareinterpretedaserosionalchannelsthatcuttheslope.Thesizeofthesechannelsrangesfrom300to600m(984–1969ft)inwidthandbetween30and80msTWTindepth.Thistraveltimecor-respondstoadepthof60to160m(196–525ft)usingaseismicvelocityof4000m/sfortime-to-depthconversion.Thesechannelsaresometimesverticallystacked,andtheirdimensionsresemblethoseofpublishedcarbonateslopechannels(MullinsandCook,1986;Eberlietal.,2004;PhelpsandKerans,2007)andsiliciclasticslopechannels(FloodandDamuth,1987;Clarketal.,1992;Waltham,2008;WoodandMize-Spansky,2009).

NoneofthesecanyonshasthedepthorwidthrequiredtobethesinglemajorsubmarinecanyonfeedingtheentireTamabrainterval.Aregionalline-source-feedingmechanismforplatform-to-basinsedimentisthereforeprobablyassociatedwithalocalpoint-sourcefeed,suchasinthemodernBahamasslope(Mullinsetal.,1984).

PozaRicaToe-of-SlopeandBasinDepositsReflectionGeometries

ToeofSlopeandBasin:PozaRicaFieldArea

Regionaldip-orientedcrosssections(Figures8,9)showachangeinreflectioncharacterfromtheplat-formtoeofslopetothebasinalarea.Figure16il-lustratesthereflectioncharacterofthreestrikesec-tionsinvariouspositionsawayfromtheslopeintothebasin.IntheproximalpartofthePozaRicaarea(Figure16A),reflectionsshowwidemoundedfea-turesassociatedwithmultiplesmall-scalefaults.ThetoeofslopeoftheGoldenLaneplatformischar-

126acterizedbywavycontortedtochaoticreflections.Fartherbasinward,seismicfacieswithintheTamabraintervalconsistofcontortedandmoundedlow-amplitudereflections(seismicfacies3inTable1).Internalreflectiongeometrieswithinthisseismicfaciesarecomplex.ThemostdistalpartofthePozaRicaarea(Figure16C)showsmorecontinuous,undulating,high-amplitudereflections,whereasinthecentralpart(Figure16B),reflectionsareofloweramplitudeandhavemoremounded,wavy,andshingledgeometries.Figure17showsenlargeddisplaysoftheTamabrainterval,illustratingcomplexreflectiongeometriesinbothstrike(Figure17A–C)anddipdirections(Figure17D).Reflectionterminationsconsistofdownlap,onlap,toplap,andtruncation.Theshapeofreflectionsrangesfromhorizontal,inclined,andshingling,tomoundedandchannelshaped.Intheproximalpartofthedip-orientedsection(Figure17D),nearthetoeofslopeoftheGoldenLaneplatform,reflectionsareshortanddiscontin-uous.ThebaseoftheTamabraintervalshowsnu-merousshort,discontinuous,concave,andconvexreflections,whereastheupperpartoftheTamabraintervalshowsmorecontinuous,higheramplitude,convexreflections.Fartherdowndip,reflectionsaremorecontinuousandhigheramplitudeonthedip-parallelsection.Shorterreflectionsonlapontomorecontinuousconcavereflections.Anapparentgen-eralshingletothenortheastismainlycausedbytectonicupliftoftheunderlyingbasement(seefollowingparagraph).Figure17A,Bshowsanenlargementofreflec-tiongeometriesseenonthelargerstrike-parallelcrosssectioninFigure16.Similartothedip-parallelsection,thebaseoftheTamabrashowsnumerousshort,discontinuous,concavereflections,whereastheupperthirdoftheintervalshowsmorecon-tinuoushigheramplitudereflections.Afewlobate(concave-upward)packagesofreflectioncanbedis-tinguished,butoverall,thereflectionsaredifficulttofollowmorethan500m(1640ft)laterally.Themoredistalstrike-parallelsection(Figure17B)hasoverallhigheramplitudes,andmorecontinuousreflectionsareseen.Figure17Balsoshowstwoclearconcave-upwardreflectionswithlateralshingling(greenandyellowarrows)thatareapproximately1SeismicArchitecture,SantaAguedaandPozaRicaFields,Mexico

Figure18.Flattenedseismicsections.Yellow,green,orange,blue,andredhorizons=topofChicontepec,Tamabra(topAlbian4sequence),upperTamaulipas,Pimientaformations,andthebasement,respectively.(A)RegionalseismicsectionofFigure8isflattenedonthePimientaFormationhorizon.(B,C)Flatteneddip-parallelseismicsection.(D)Flattenedstrike-parallelsection.Bolddashedlineshighlightrestoredreflectiongeometriesformingshingling,mounded,andlobatereflectiongeometry.TWT=two-waytraveltime.128SeismicArchitecture,SantaAguedaandPozaRicaFields,Mexico

Jansonetal.129

130SeismicArchitecture,SantaAguedaandPozaRicaFields,Mexico

and1.7km(～0.62and1.06mi)wide,respectively.

Intheeasternpartofthesection,shorterreflections

onlapontoacontinuous,high-amplitude,faintly

convexreflection(bluearrowsonFigure17B).

ReconstructedGeometriescreatedbylateralcompensationoflobategravity-flowdeposits.InterpretationofReflectionGeometries

SothatpredeformationandtiltingoftheCreta-

ceousdepositionalsystemcanbereconstructed,