Conference PaperPDF Available

Giraldo, C. 1999. Late Tertiary-Quaternary Structural styles: Serrania del Interior Oriental Foothills. Northeastern Venezuela, 6th Internacional Congreso of the Brazilian Geophysical Society. SBGf42899, 4 pp.

Authors:
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SBGF10099
LATETERTIARYQUATERNARY
STRUCTURALSTYLES:SERRANIA
DELINTERIORORIENTALFOOTHILLS,
NORTHEASTERNVENEZUELA
CarlosM.GiraldoCeballos
PDVSAExploraciónyProducción/Venezuela
ABSTRACT
Compressivestructureshavebeenidentified,alongtheSerraníadelInteriorOrientalRange
foothills,using2Dseismicreflexionprofiles,recordedbyPDVSA.Majortectonicelements,
shownare:Uricafault,TalaPiritalthrustsandtheMuddiapirtrend.Thrustsandassociated
rampsoccurredduringtheLateMiocenePliocene.Extensionalfeaturestotheeast,mighthave
beentriggeredduringthelast5Ma.byremobilisationoflowerMioceneshale.
INTRODUCTION
TheSerraniadelInteriorOrientalrange,representstheeasternmostbranchoftheAndeanuplift
(Figure1).ItislocatedinthenortheastcornerofVenezuela,anditcoversanareaof
aproximately6000squarekilometers.Cretaceousrocksdominatearound70%oftotaloutcrops;
theother30%,isrepresentedbypaleogeneandneogenesediments,aswellas,somesparse
pleistocenealluvialfansanderosionalterraces,acrossthemainrivers.Theexistenceofjurassic
evaporiteshavebeenproposedintheliterature;thisevaporiticsequence,wouldactasamain
detachmentlevel,associatedwiththemajorneogenecompressivecontractionalstructures.
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ThenorthernmostboundaryoftheSerraniadelInteriorOrientalrange,iscontrolledbyrightlateral
strikeslipmotion.ItincludestheElPilarFaultsystem(Figure2),amajordextralfault,
consideredtobethemaincontactbetweenCaribbeanandSouthAmericanplates;it´sdextral
movement,seemstohavestartedintheupperMiocene;currentsliprateisabout1cm/year
andtotaloffsetisaround70kms(AUDEMARDandGIRALDO,1997).Anigneous–metamorphic
belt(Caribbeanbelt),lyingtothenorthoftheElPilarfault,wasprogressivelyemplaced,against
theSouthAmericanpassivemargin(fromwesttoeast),duringtheEocene/Miocenetimes
(AUDEMARDandLUGO,1994).Towardstheeast,theSerraniadelInteriorOrientalrange,ends
upagainstaseriesofplio/pleistocenegrabens(i.e.SanJuan),relatedtoaNESWtectonic
extension.Fourseismicreflexionprofiles,recordedbyPDVSAinthelast2decades,willbe
showninthispaper.Theyhavebeenrecordedacrossmajortectonicelements,locatedalongthe
foothills:UricaFault,TalaThrust,PiritalThrustandtheMuddiapirtrend.Moreinformation,about
seismicstratigraphyandtectonics,appearsinDICROCE(1995),HUNG(1997)andYSACCIS
(1997).
URICAFAULT
TheUricafaultsystem(Figure2),islocatedatthewesternterminationoftheSerraniadelInterior
Orientalrange;thistectonicfeature,seemstobeanobliqueramp,ofthePiritalThrust.The
pliocenePirituGraben(Figure2),isalignedparalleltotheUricafault,but,notbeconsideredasit
´snorthernmostextension,aswasmentionedbyMUNROandSMITH(1984)andBLANCOand
GIRALDO(1992).
A30kmlongseismicreflexionsectionisshowninFigure3.ItisorientedNESW,orthogonalto
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A30kmlongseismicreflexionsectionisshowninFigure3.ItisorientedNESW,orthogonalto
theUricaFaultsystem,whichhasbeenmapped(ROD,1956),formorethan100km.
Sedimentarysequencesarewelldatealongthisline;theyoungestunitisthemiddleMiocene
mollasse,QuiamareFormation.TheUricafaultzonehasbeeninterpretedasanortheastdipping
ramp,havinganupperMioceneage;also,asouthwestdippingfeature,canbeinterpreted,
formingthus,atrianglezone.Thedetachmentlevel,islocatedinthelowerMiocenesequence,
knownastheCapiricualFormation;also,itcanbeinferred,thatthisshallowdetachment,has
beendeformedbyayoungeranddeeperone,developpedduringtheupperMiocene–Pliocene
(?).TheanticlineobservedunderneaththeUricafault,hasanorthwestsoutheastdirection,
extendingforaproximately10kms.
TALAPIRITALTHRUST
ThesouthernboundaryoftheSerraniadelInteriorOrientalrangeisrepresentedbythePirital
thrust,whichrunssubparalleltotherangetrend,accomodatingthus,someofthesouthward
tectonictransport.Atotalshorteningof80kmshasbeenproposedby(PARNAUDetal.,1995);
theseauthorsalsoconsideredthatpartitionningineasternVenezuelaisaccomodatedbetween
theElPilarfault(relativemotiontotheeast),andthePirital–Furrialthrustsystems(southward
tectonictransport).Figure4showsaseismicline,recordedorthogonaltotheTalathrustzone,
probablytheeasternmostextensionofthePiritalthrust(HernándezLeroy,pers.comunication).
Thetectonictransportisclearlywelldefinedtothesouth,andhasoccurredduringtheUpper
MiocenePliocene;compressivedeformation,extendstowardsthePlioPleistocene,because
theyoungestunconformityisfoldedandsubtlyfaulted.Preliminaryinterpretationshows,thata
detachmentlevel,occursalongthelowerMioceneshale.Itcanbealsointerpreted,thatyoungers
trianglezonestructure,foldedtheshallowerdetachements.TheseismicsectioninFigure5was
recordediacrossthePiritalThrustandMuddiapirtrend.Theinterpretationsuggestthat,this
"elephantlike"structure,isaconsequenceoftwoprocesses:thefirstone,beingthe
emplacementofthePiritalthrust,duringtheupperMioceneandthesecondone,arcilokinesis
developedduringthePlioPleistocene.
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MUDDIAPIRTREND
APlioPleistoceneMuddiapirtrendhasbeenwelldocumentedfromseismicsections,southof
theSerraniadelInteriorOrientalrange.TheageofremobilisedshalesislowerMiocene,andhave
beenidentifiedaspartoftheshalysectionoftheCarapitaFormation,consideredtobethemajor
sealintheeasternVenezuelabasin.Thistrendrunsparalleltothenegativegravimetricanomaly
locatedintheforedeep.Themostintensearcilokinesiseffect,liesinmediatlysoutheastofthe
SanJuangrabensystem(Figures2and6);coincidentally,thisistheareawherethegravimetric
anomalyreachesitsminimunvalue(200mgals);intensityofarcilokinesisdecreases
progressivelydisappearingtowardthewest.Mudridgesareveryconspicous,andtheyoccurred
duringPlioceneRecenttimes,causingthepinchingoutgeometryofyoungestsediments.The
upliftofmiddleMioceneisabout2.5seconds(TWT)androtatedonlapsaregoodindicatorsof
recentupliftduetoarcilokinesis;widthofdiapir´strendisabout10km.Probably,theshale
remobilisation,producesavoideffecttowardsthenorth,triggeringoracceleratingnormalfaulting
(SanJuanGraben),paralleltothemaximumhorizontalstress1.ThisMuddiapirtrend,has
beenidentifiedbyoilexplorationists,sincetheearliestdecadesofthiscentury(HEDBERG,
1950)anddocumentedfromseismiclinesbyLILIÚ(1990).
CONCLUSIONS
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CONCLUSIONS
CompressionisstillactiveineasternVenezuela,andhasbeendocumentedfromseismic
sections.Inthewesternpartofthefoothills,youngthrustspropagateunderneaththeshallowest
ones,foldingthepreviousdetachment.Towardstheeast,arcilokinesisappearsasanimportant
tectonicprocess,occurringsincePliocenetimes.However,itcanbesuggested,thatthismud
remobilisation,couldbetriggeredby,deeperactivethruststructures(FurrialThrust).Arcilokinesis
andextensionalstructuresarecontemporaneousintheeasternpartoftheSerraniadelInterior
range.Moredetailedstudiesneedtobeaccomplished,inordertohaveabetterunderstandingof
thedifferenttectonicprocesses.
SELECTEDREFERENCES
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meridionaldelaplacaCaribe,Venezuelaseptentrional,VIIICongresoGeológicoVenezolano,
Porlamar,I:101108
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Portion),Bull.Geol.Soc.America,V.61,N°11,p.11731216.
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Thesis,RiceUniversity,124pp.
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v.162,p.213215.
Passalacqua,H.,Fernández,Gou,Y.andRoureF.,1995,CrustalArchitectureandStrain
partitioningintheEasternVenezuelanRanges,inA.J.Tankard,R.SuárezS.andWelsink,H.,
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ACKNOWLEDGMENTS
IWOULDLIKETOTHANKPDVSAOIL&GASCO.FORPERMISSIONTOPUBLISHTHIS
WORK,ANDMYCOLLEAGUESOFBASINANALYSISDEPARTMENTFORHELPAND
USEFULDISCUSSIONS.
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Presentadoen:SixthInternationalCongressoftheBrazilianGeophiysicalSociety
|PáginaPrincipaldeCharlas/Presentaciones|
|CódigoGeológicodeVenezuela|EnviarComentarios|
©PDVSAIntevep,1997
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Varios modelos geodinámicos propuestos para la región caribeña invocan desplazamientos dextrales del orden de 1.000 kilómetros en el límite sur de la placa Caribe, por analogía con su frontera septentrional. No obstante, esta hipótesis parece dificilmente sustentable cuando se evalúa los desplazamientos acumulados a lo largo de cada uno de los accidentes transcurrentes mayores ubicados en territorio venezolano, que acomodan lo esencial de dicha transcurrencia (fallas de Boconó, San Sebastián, El Pilar y Oca-Ancón). Dependiendo de los autores, el valor de dichos desplazamientos, asi como el significado geodinámico de los mismos, es motivo de grandes controversias. A partir de una síntesis bibliográfica, así como de nuestra propia interpretación, consideramos que el desplazamiento dextral total acumulado es del orden de 60 km y los valores de movimiento para las distintas fallas principales que conforman esta frontera son: (a)- de unos 20 a 30 km para el sistema de falla de Boconó, (b)- inferior a 65 km y probablemente cercano a 35 km para el sistema de fallas de Oca-Ancón y (c)- inferior a 150 km y más bien del orden de 60 km para la falla de San Sebastián-El Pilar. Debemos destacar que las fallas de Oca-Ancón y Boconó se unen a nivel de Morón para proseguir hacia el Este en un único accidente dextral de orientación este-oeste (falla de San Sebastián-El Pilar), transfiriéndose sobre esta última la cinemática de las otras. En lo concerniente a la edad de activación de estas fallas transcurrentes, parece existir un consenso general en atribuirla a una fase tectónica mayor compresiva miocena superior-pliocena, aún vigente y responsable del tectonismo y orogénesis de los cinturones plegados del norte de Venezuela (Andes, Falcón, Central y Oriental).
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" , The nature of the basement underneath the Monagas foothills and the Serranía dellnterior of the Eastern Venezuela Basin is unknown. It could consist of crystalline Precambrian, Paleozoic sedimentary rocks and/or Jurassic rocks deposited in haif grabens. Alternative stiüctüial ¡nterpretat¡ons across the Monagas foothills range from basement-involved to non-basement-involved décollement tectonics. These hypotheses imply varying amounts of shortening along the Serranía to Foreland transect ranging from 15 to 115 km oblique component of the El Pilar fault. The foreland-verging thrust system appears to be "in sequenceJI. In the Monagas foothills earlier décollements at the base of the Miocene are responsible for the formation of a complex accretionary wedge. The deeper structures of the Monagas foothills involve the Mesozoic which was thrusted following the emplacement of the Carapita accretionary wedge. Apparent "out of sequenceJI are due to the interference of late deeper structures with the earlier structures of the accretionary wedge.
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