Uniform basin growth over the last 500ka, North Anatolian Fault

16 Pages·2012·6.82 MB·English

by  Christopher C. Sorlien

Tectonophysics518–521(2012)1–16
ContentslistsavailableatSciVerseScienceDirect
Tectonophysics
journal homepage: www.elsevier.com/locate/tecto
Uniform basin growth over the last 500 ka, North Anatolian Fault, Marmara
Sea, Turkey
ChristopherC.Sorlien a,e,⁎,SelinD.Akhun b,Leonardo Seeber c,Michael S.Steckler c,DonnaJ.Shillington c,
Hülya Kurt d, Günay Çifçi b, Duygu Timur Poyraz d, Savaş Gürçay b, Derman Dondurur b, Caner İmren d,
Emre Perinçek d, Seda Okay b, H. Mert Küçük b, John B. Diebold c
aEarthResearchInstitute,UniversityofCaliforniaatSantaBarbara,SantaBarbara,USA
bInstituteofMarineSciencesandTechnology,DokuzEylülUniversity,Izmir,Turkey
cLamont-DohertyEarthObservatory,ColumbiaUniversity,Palisades,NY,USA
dDepartmentofGeophysics,IstanbulTechnicalUniversity,Turkey
eDepartmentofEarthScience,UniversityofMissouri,USA
a r t i c l e i n f o a b s t r a c t
Articlehistory: MuchofthenorthernstrandoftheNorthAnatoliaFaultsystemintheMarmaraSea,theMainMarmarafault,
Received25May2011 isaseismicgap,posingahighriskforIstanbul.Deepbathymetricandsedimentarybasinsarestructurallyas-
Receivedinrevisedform3October2011 sociatedwiththeMainMarmarafault.Basingrowthincludingtiltingoftheirmarginsisthuslinkedtofault
Accepted8October2011
slipthroughreleasingandrestrainingsegmentsofthisandotherbranchesoftheNorthAnatolianFaultsys-
Availableonline15October2011
tem.WhetherthissystemhasbeensteadystatethroughatleastthelasthalfoftheQuaternary,orwhether
theMainMarmarafaultmorerecentlypropagatedthroughanddeactivatedpull-apartbasinsisoneofthe
Keywords:
maincontroversies.
Transformbasins
Seismicstratigraphy Apublishedagemodelandstratigraphicframeworkforthesebasinshasbeenlacking,andtectonichistory
NorthAnatolianFault models for the Marmara Sea have relied on extrapolating present deformation rates back through time.
MarmaraSeaTurkey Over 3000km of new high-resolution multichannel seismic reflection combined with existing lower-
Evolutionstrike-slipfault resolutionseismicreflectionandmultibeambathymetricdatamakepossibleadetailedregionalstratigraphic
interpretation.Inparticular,astackofshelf-edgedeltasareimaged,andinterpretedasglacialperioddeposi-
tionduringlowsea/lakelevels.Reflectionsfromthetopsofthesedeltas,andfromunconformitieswerecor-
relatedacrossmuchofMarmaraSeabasinsandhighs,providingcriticalstratigraphiccontrol.
Wecorrelatethelow-standdeltaswithknowneustaticsealevelminimabydevelopingproxiesfortimefrom
verticalseparationofstrataacrossnormalfaults,tilts,andsedimentaryvolumes.Apreferredagemodelis
proposedatleastbacktoOxygenIsotopicstage14at536ka.Duringthistimeinterval,tiltingofbasinmar-
gins,verticalseparationacrosstheMainMarmarafaultadjacenttowesternIstanbul,andtilt-relatedslow
collapseonthesouthflankoftheÇinarcikbasinallindicatesteady-statebasingrowthandfaultslip.
©2011ElsevierB.V.Allrightsreserved.
1.Introduction ThenorthernbranchoftheNAF,alsocalledtheMainMarmaraFault
(LePichonetal,2001)isassociatedwiththree1200-m-deepbathy-
Formostofits1500-kmlength,theNorthAnatolianFault(NAF) metricbasinsintheMarmaraSea(fromwesttoeast:Tekirdağ,Central
systemisarelativelysimpleandnarrowfaultzonethatcarriesalmost andÇinarcikBasins;Fig.1)inwhichthebaseofNeogenesedimentary
all of the current and cumulative right-lateral displacement of the rockmaybeasdeepas6km(Armijoetal.,1999;Béceletal.,2010;
plateboundarybetweenEurasiaandtheAnatolian block.However, Cartonetal.,2007;Laigleetal.,2008).TheMainMarmarafaultcon-
initswesternpart,theNorthAnatolianFaultsystemsplaysintosever- nectsfromtheIzmitfaultintheeasttotheGanosfaultinthewest
albranches,eachmadeupofdiscretestrands.AtthelongitudeofIs- (Fig.1).
tanbul the splays are distributed N–S across an 80km belt (Fig. 1). GPSdataindicate23–25mmyearofdisplacementacrosstheplate
Here, in northwestern Turkey, a composite transtensional basin boundarythroughnorthwestTurkey(LePichonetal.,2003;McClusky
formedalongtheNAFsystem.TheMarmaraSeaoverliesthisbasin. etal.,2000;Meadeetal.,2002;Reilingeretal.,1997),whilepaleoseis-
micstudiessuggestaslowerHolocenerateof10mm/yr(Poloniaetal.,
2004)orlateHolocenerateof~20.5mm/yr(Kozacietal.,2007).The
⁎ Correspondingauthor. accumulatingstrainwasrelievedinpartbythe20thcenturyseries
E-mailaddress:[email protected](C.C.Sorlien). ofmajoranddeadlyearthquakesthatprogressedfromeasttowest
0040-1951/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.
doi:10.1016/j.tecto.2011.10.006
2 C.C.Sorlienetal./Tectonophysics518–521(2012)1–16
Fig.1.A:EasternMediterraneantectonics,modifiedfromOkayetal.(2000).“B”locatedbyredrectangle.NAF=NorthAnatolianfault.B:Faults,bathymetry,topographyforMar-
maraSea.Three~1200m-deepbasinsarearrayedalongtheMainMarmarafault.BathymetryfromRanginetal.(2001);Wemappedfaultsinblack;faultsinredfrompublished
sourcescompiledbyErturaç(2002);includingOkayetal(2000);Kazancietal.(1999),Kuşçuetal.,2009),Barka(1999);Cormieretal.(2006);andParkeetal.(2002).Greencircles
arelocationsofcoresfromR.V.MarionduFresne2001and2004(Becketal.,2007;LericolaisandHenry,2004).Gf=GanosFault;If=Izmitfault;M1=Marmara1well;MMf=
MainMarmarafault;T=Tekirdağbasin;Ce=CentralBasin,K=Kumburgazbasin;Ci=Çinarcikbasin;NI=Northİmralibasin;CH=CentralHigh;CMR=CentralMarmara
Ridge;WR=WesternRidge;Ii=İmraliIsland;A=ArmutluPeninsula,andK=KocasuRiverdelta.InCentralbasin:x=seafloorscarp,andy=onlap.
(Barka,1996;Steinetal.,1996;Toksozetal.,1979),leavingalongseg- continuousfault.Thisdisputeisrelevanttothepotentialforasingle
mentwithinMarmaraSeanearIstanbulasaseismicgap.Thisgaphas ruptureacrosstheentireMarmaraseismicgapvs.severalsmallerrup-
not broken since 1766 (Armijo et al., 2005; Barka, 1996; Le Pichon tures(LePichonetal.,2003;Ranginetal.,2004;Sengöretal.,2005).
etal.,2003).Furthermore,ithasbeenproposedthatpartofseismic Thesequestionshighlightthat“establishmentofagoodstratigra-
gaphasnotbrokensince1509,withashortersegmentpossiblynot phyofthesebasinsisoneofthemosturgenttaskstoprogressinthe
breakingevenin1509(AmbraseysandFinkel,1995;Ambraseysand understandingofthetectonichistory”(İmrenetal.,2001).Toaddress
Jackson,2000). thisproblem,weundertooka3-weekcruiseonboardtheR/VK.Piri
An international effort to image the sea floor and sub-bottom of Reis in 2008 with a short follow-up cruise in 2010. The high-
Marmara Seaover thelast decadewasfurthermotivatedbythede- resolution multichannel seismic (MCS) data collected images the
structive and deadly 1999 earthquakes in the easternmost Marmara upper1–2kmofthestratainsufficientresolutionforsequencestrat-
SeaintheGulfof Izmit and east of there. Istanbul isbuilt alongthe igraphicinterpretation.Thiswasfacilitatedbythediscoveryofastack
shoresofMarmaraSeaandthehazardandriskfromearthquakestoit oflowstanddeltasintheNorthİmralibasininthesouthernMarmara
and its over 13million residents overthe next decades is extremely Sea(Fig.1).Usingthesedata,thispaperdevelopsalateQuaternary
high(Hubert-Ferrarietal.,2000;Parsons,2004;Parsonsetal.,2000). (last ~800ka) stratigraphic age model for North İmrali basin), and
Modelsofandforecastsforfutureearthquakesareuncertain,however, thencorrelatesthisstratigraphytoothertransformbasinsalongthe
becauseoflargeuncertaintiespersistingonthefaultstructureandevo- MainMarmarafault.Thus,faultandbasinevolutionintheMarmara
lution.Forexample,itisuncertainwhetherthestructureofthefault Seacanbequantitativelyexaminedforthefirsttime,andtheback-
zone responsible for the basins is still active in a steady-state mode ward extrapolation of GPS velocity can be tested, rather than used
(Armijoetal.,1999,2002;Seeberetal.,2004,2010),orifithasbeen asanassumption.Ourstratigraphicmodelandcorrelationssupport
replacedinrecentgeologictimebyasimplerfaultgeometrythatcuts steady-stategrowthofbasinsandoftheverticalcomponentofmo-
through pull-apart basins and fosters pure dextral motion along a tionacrossarestrainingsegmentoftheMainMarmarafault.
C.C.Sorlienetal./Tectonophysics518–521(2012)1–16 3
2.Kinematicmodels the Western High and Central Marmara Ridge (Fig. 1). Depending
onthemodel,theseridgesareinterpretedaseitherhorsts(Aksuet
Overthepastdecades,thenumerousgeophysicalsurveys,includ- al.,2000),orcontractionalanticlines(Okayetal.,1999,2000;Rangin
ingdeepmultichannelseismicreflectionsurveys,andshallowsingle etal.,2004;Yaltirak,2002).Asaresultoftheridgesseparatingtheba-
channelchirp,andsparkerseismicreflectionsurveys,togetherwith sins, the stratigraphy within each basin has not been correlated to
multibeambathymetry,havebeenusedtomapthemajorsedimenta- otherbasins,hamperingeffortsforaglobalevolutionarymodel.
rybasinsandsurfacefaultpatternsoftheMarmaraSea.However,dif- Thethirdmodelcontrastswiththeothertwointhatitproposes
fering interpretations of the relationships of the various structures thattheMainMarmarafaultisayoungfeature,basedonidentified
have resulted in multiple models for the evolution of the Marmara offsetfeatures.TheMainMarmarafaultappearstooffsettheCentral
Sea basins and their current relationship to the NAF. Among the Marmara Ridge dextrally by 3.5km (Fig. 2; Armijo et al., 2002; Le
many models that have been proposed, the recent models can be Pichonetal.,2003).Usingarangeofslipratesof10mm/yrtothecur-
groupedintothreetypes: rentmaximumGPSdeformationrateof25mm/yronthisstrandpro-
duces an age of origin of 140,000 to 350,000years (Armijo et al.,
Steady-state1:Themajordeep-waterbasinsformedaspull-apart 2002).Inaddition,back-slippingtheMainMarmarafaultby4kmre-
basins linked by short strike-slip segments (e.g., Armijo et al, storesCentralBasintoasymmetricshape.Thisyieldsasimilarageof
1999,2002;BarkaandKadinsky-Cade,1988). formation for this strand of 200,000±100,000years (Le Pichon et
Steady-state2:TheTekirdağandÇinarcikBasins,atleast,devel- al.,2003;Ranginetal.,2004;Sengöretal.,2005).Furthermore,itis
proposedthatfollowingthisyoungformationoftheMainMarmara
oped as asymmetric basins associated with bends in the major
fault,onlypurestrike-slip,withtranspressionacrossE–Wsegments
through-going strike-slip faults (Okay et al., 1999, 2004; Seeber
of the Main Marmara fault has been occurring (Demirbağ et al.,
etal.,2004,2010). 2003;İmrenetal.,2001;LePichonetal.,2001;Ranginetal.,2004).
Youngreorganization3:Acceptsthatthebasinsdevelopedasthere- Inthesemodels,basin-boundingnormalfaultswereactive,withthe
sultoftranstensionaltectonics,butclaimsthattheMainMarmara basinsextendingandsubsiding,mainlybeforeformationoftheMain
fault has cut through and deactivated the sedimentary basins Marmara fault. Now most of the motion is focused on the almost
(İmrenetal.,2001;Kuşçu,2009;LePichonetal.,2001,2003;Rangin puretransformMainMarmaraFaultandbasingrowthisslowedto
etal.,2004;Sengöretal.,2005). stopped. Ongoing partitioned normal slip on shorter faults is inter-
pretednearaMainMarmarafaultbendinsoutheastÇinarcikbasin
Thusallmodelsagreethatextensionortranstensionisresponsible (e.g.,LePichonetal.,2003).
forformationofthethree~1200m-deepbathymetricbasins,whose In contrast, Seeber et al (2004) have interpreted a uniform and
sedimentaryfillisasdeepas6km(Armijoetal.,1999;Béceletal., rapidrateofsubsidenceandtiltaboveanon-verticalMainMarmara
2010; Cartonetal., 2007; Laigleet al., 2008). However,themodels Fault segment back to 1.4Ma in the western (Tekirdağ) basin. A
differ in the kinematics that produced the basins. Furthermore, smoothlyincreasingverticalcomponentofslipwithdepthisimaged
these three basins are separated by two NE–SW structural ridges, tothebaseof5km-deepsedimentaryfillacrosstheMainMarmara
Fig.2.Tracklinesoftheseismicreflectiondatasetsplottedascolorlines,identifiedinthelegend.Areausedforvolumesofintervalsbetweendeltahorizonsoutlined(dashed-dotted
violet);dipmeasurementlocations(dottedgreenlinesegmentslabeled“a”through“e”);heavyblacklinesindicateprofilesinotherfigures),andlightgreendottedlineindicatethe
regionalcorrelationprofileinFig.6.ThebackgroundtothisFigureisthedepthoftheGreen-6horizon.The3.5kmrightoffsetofCentralMarmaraRidge(Armijoetal.,2002)is
locatedatthepairedheavyredarrows.
4 C.C.Sorlienetal./Tectonophysics518–521(2012)1–16
FaultinCentralBasin,consistentwithsteady-statekinematicsthere across all of the deeper parts of the MarmaraSea (Le Pichon et al.,
during at least the last 1m.y. and probably several m.y. (Laigle et 2001;Ranginetal.,2001),wereimportedintotheindustryseismicre-
al.,2008).Alternatively,Armijoetal.(1999,2002),interpretcontinu- flectioninterpretationsoftware“TheKingdomSuite”.
ingpull-apartactivitywithtranstensionacrossE–Wfaultsegments.
Thelackofagecontrolearlierthan40kainthedeepbasinsmakes 4.Results
it difficult to evaluate whether or not there has been a dramatic
changeintherateofbasingrowthoverthelastfewhundredthousand Newly acquired TAMAM MCS data image structures and sedi-
years.Theproblemisexacerbatedbythelackofstratigraphiccorrela- mentsintheupper~1–2kmoftheMarmaraSeabasinsinunprece-
tionbetweenthebasins.Toaddressthisproblem,weundertookhigh- denteddetail.Inthefollowingsections,wedescribeasuccessionof
resolutionmultichannelseismicreflectionsurveystobetterimagethe low-stand deltas imaged in the North İmrali basin (Figs. 3 and 4),
basinstratigraphyandtocorrelatethatstratigraphybetweenbasins. andourcorrelationofhorizonslinkedtothedeltasthroughoutMar-
We combine these data with considerable existingdata in order to mara Sea. Following several independent analyses, we link these
searchforevidenceoftheproposedyoungreorganization. low-stand deltas to specific glacial cycles, thus constructing a delta
chronology.Thisnewagemodelisthenappliedtothedeformation
3.Data historyoftheMainMarmarafault.
Multibeambathymetrydatawererecordedacrossallofthedee- 4.1.Low-standdeltacomplex
perpartsoftheMarmaraSea,andarepubliclyavailable(LePichon
etal.,2001;Ranginetal.,2001).Severalveryhigh-resolutionchirp, Weimagedandmappedstratalgeometryinthebasinandinter-
andsparkersingle-channelsurveyshaveimagedtheshallowsubsur- veninghighs.Aparticularfocuswasastackofdeltasequencesthat
face(Aksuetal.,1999;Gökaşanetal.,2010;Smithetal.,1995). isclearlyimagedbyadensegridofMCSprofilesacrossthesoutheast
The TAMAM (Turkish American MArmara Multichannel) Project flankoftheNorthİmraliBasin(Fig.2).Thesedatarevealapreviously
undertooktwocruises(Fig.2)usingtheR/VK.PiriReis,operatedby unknown stack of four sequences of prograding reflections with
theInstituteofMarineSciencesandTechnologyofDokuzEylülUni- toplap characteristic of low-stand shelf edge deltas. Three of these
versity. During the first cruise in 2008, we acquired2700 track-km (fromtoptobottom,Blue-2,“Yellow-4”,and“Green-6”)exhibitpro-
of high-resolution 72-channel seismic reflection and chirp seismic gradationwithoutaggradationcharacteristicof“falling-stagesystems
data throughout the Sea of Marmara. In a follow-up cruise in 2010 tracts”(Figs.3and4;Pinteretal.,2003;PiperandAksu,1992;Plint
wefilledindatagapsduetoheavytrafficintheshippinglanesandcol- andNummedal,2000).Thenumbersafterhorizoncolornamesrepre-
lected targeted lines necessary for correlations between basins. senttheorderofthehorizonordeltacomplexfromtoptobottom.
TAMAM2010acquired298track-kmof240-or111-channeldata(ac- TheNorthİmraliBasinunderliesa400m-deepplatform,andissepa-
quisitionparametersaresummarizedinTable1).Theshallowtowing ratedfromthesoutherncontinentalshelfandArmutluPeninsulaby
ofthesourceandstreamerfacilitatedhigh-frequencyrecordsforim- theArmutlu–İmralifaultsystem(alsoknownastheYalovafaultor
agingthestratigraphybecausethe‘ghost’arisingfromthereflection South Boundary fault) (Fig. 2). The WNW-striking part of this fault
of the source wave off the water surface occurs at 250Hz and displaysnormalseparation,with200m-highseafloorscarps.These
187.5Hz for 3 and 4m tow depths, respectively, thus preserving a deltasarethereforepreservedduetosubsidenceonthedownthrown
largerangeofhighfrequencies.Processingofthemultichannelseis- sideofthisfault.Thestructuretowardsthemiddleofamajorarcuate
micreflection(MCS)datausedstandardstepsincludingdetailedve- bend (concave-northward) in this border fault is manifested by a
locityanalysisandpost-stacktimemigrations.Finitedifferencepost- zoneofprogressivenorthtiltthatabsorbsmostoftheverticalcompo-
stackdepthmigrationwasperformedonafewprofiles(e.g.Fig.3). nentofdeformation(thefaultismostlyblind).
ThesedataweresupplementedbyadditionalexistingMCSdatain- Thestackeddeltasliebetween400mand900mdepthonFig.4.
cluding1500kmofmigratedprofilesrecordedbyMTAin1997(İmren Theoriginallysub-horizontaltopsofeachdeltaarenowlocallypro-
etal.,2001;Okayetal.,1999,2000).Weusedthesedataasprocessed gressively tilted and folded near an ENE-striking segment of the
byParkeetal.(2003).Inaddition,graphicsfilesof948kmof12and Armutlu-İmralifault(Figs.2and3).Thedeltasthatextendsufficient-
24-fold non-migrated low resolution profiles recorded in 1972 and lyfarintothebasinflattenandaresub-horizontalthere.Eachdelta
1973(C&KPetroleum,1974)wereconvertedtoSEGYformat,plusmi- consistsofshingledofflappingstratadippinguptotendegreesrela-
grationsof83profilestotalingover2000kmofdeep-penetration,low tive to encompassing sequence boundaries. The delta terminations
resolutionSEISMARMARALeg2profileswerealsoavailableforthis are sigmoidal with sharp clinoform rollovers flattening onto gentle
study (Fig. 2; published in Carton et al, 2007). This combined data bottomsets [Fig. 3). The deltas are capped by flat-lying strata that
set,alongwitha20mgridofmultibeambathymetricdatarecorded abruptlyonlapeachdelta(Fig.4).Foresetheightsaverage40–50m.
Thusweinterprettheclinoformstorepresentprodeltaordeposition-
alshelfedgedeposits,whichmaynotcorrespondtotheshoreline.
We interpret this geometry to indicate that each delta was formed
Table1 withinoneortwotensofmetersofsealevelorlakelevel.Further-
Generalshootingandrecordingparametersforthe2008and2010TAMAMsurveys.GI: more, we interpret the most seaward clinoform rollover to have
Generator-injectorairgun. beenformedatthelowestpaleosea/lakelevelimmediatelypriorto
Parameters 2008 2010 therapidtransgressionthatcoveredthem.
Ourinterpretationoftheoriginofthedeltaisasfollows.Assea
Numberofchannels 72 111or240
level falls, the broad southern shelf becomes subaerially exposed.
Streamerlength(m) 450 750or1500
Nearoffset(m) 40or100 15or64 ThesubsidingNorthİmraliBasinbecameafocalpointforthedrain-
Faroffset(m) 493or543 760or1557 age network that developed on the exposed shelf. Presently, the
Shotinterval(m) 12.5or18.75 18.75 KocasuRiverhasbyfarthelargestdrainagebasincurrentlydraining
Groupinterval(m) 6.25 6.25 to Marmara Sea (27,600km2; Kazanci et al., 1999). Thus this and
Sampling(ms) 1 1
Recordlength(s) 4 5 other rivers draining into southeast Marmara Sea during low sea
Maximumfold 12or18 18or40 levels would have bypassed the shelf and dumped sediments into
Source 145+45in.3GIgun 145+45in.3GIgun Northİmralibasin.However,theformationofthedeltasequencesre-
Sourceandstreamertowdepth 3or4m 3m
quiresthatthewaterdepthonthesubsidinghanging-wallsideofthe
C.C.Sorlienetal./Tectonophysics518–521(2012)1–16 5
Fig.3.Depth-migratedmultichannelseismicreflectionprofileA–A′,displayedindepthwithtwotimesverticalexaggeration.ProfileislocatedonFig.2.Colorlinesontopfigure
correspondtohorizonsonotherfiguresandintext.AlargerscaleversionoftheBlue-2deltaandoftheintervalofacomplexofdeltas(Magenta-3)isshownatbottom,located
bydashedrectangle(top).Magenta-3islabeledbutnotrepresentedbyacoloredlinebecauseitdoesnothaveasingletoplapsurface.Progradingstratacharacteristicofdeltas
areimaged.Apparentdipsofdeltatopsalongthisprofileweremeasuredbeneaththedouble-headedarrow.ThesedipsareshowninFig.12as“TMdelta1–4000=e”.Stratadip
moresteeplywithdepth,indicatingprogressivetilting.M=Multiplereflections.
Armutlu–İmrali Fault was no more than a few tens of meters. The (“Red-1”;Figs.3and4)thatshowsmoundingofsedimentssuggesting
scarpiscurrently about200m-high,toolargefora sealevelfall to thatsedimentsoverflowingtheshelfedgeformedalowstandwedge,
generatedeltas.Infact,abovetheyoungestdelta,wemapahorizon butthewaterdepthwastoolargefordeltaicdeposits(westerndepo-
Fig.4.Time-migratedprofileB–B′,displayedintime,locatedonFig.2.Colorscorrespondtohorizonsonotherfiguresandintext.Progradingstratacharacteristicofdeltasareim-
aged.Clinoformrollovers,formedwithinoneortwotensofmetersofpaleo-sealevel,areindicatedbyarrowsforBlue-2,Yellow-4,andGreen-6.M=Multiplereflection.
6 C.C.Sorlienetal./Tectonophysics518–521(2012)1–16
centerinFig.5).ThissuggeststhatthewaterdepthintheİmraliBasin easternentranceofDardanellesStraight(Aksuetal.,1999;Gökaşan
hasincreased,andthatsedimentationhasnotbeenkeepingupwith etal.,2010),andshorelinesthereareuplifting(Yaltiraketal.,2002).
subsidencesincedepositionoftheBlue-2delta(Figs.3and4). Thereforeitispossiblethatpaleo-silldepthsduringpartsoflateQua-
Isochoremaps(Fig.5)indicatethatthedepocentersofthedelta ternarytimeweredifferentthanattheLastGlacialMaximum,anda
shifted within the basin from north of İmrali Island (Green-6 to marine connection could have been maintained to the Aegean
“Violet-5”)toeastoftheisland(Violet-5toBlue-2),andbacktothe throughouttheglacialcycles.
north(Blue-2toseafloor).Thisislikelyduetovariationsinthepath- Wepresumethatthedeltasareassociatedwiththe100kyrgla-
waysoflowstandriversystemsduringeachglacialcycle.Thesediver- ciaoeustaticcycles.Ifallstagesofthe100kaglacialcycleswererepre-
sionsofthelow-standriversystemsmayhavebeeninfluencedbythe sented by deltas and there were not either extra deltas deposited
growthofananticlinethatnowlinksİmraliIslandtoArmutluPeninsula within one cycle or missing cycles where no delta developed, we
andalsobychangesinlocationofthedeepestpartofthebathymetric couldjustcountdeltasandmatchthemtotheglobaloxygenisotopic
basin (similar to avulsions in deltas). The shift of deposition to the curve.However,geologyisrarelythatsimple.Forexample,oneaddi-
westafterdepositionoftheBlue-2deltaallowedpartofthesediment tional glacial period likely occurred between depositions of two of
tobecapturedbyacanyoninthatarea(Figs.1and2).Thiscontributed these deltas. We have identified a high amplitude reflection that is
tothepost-Blue-2bathymetricdeepeningsothattheshingledofflap- anerosionalunconformityonstructuralhighs,whichmaybeassociat-
pinggeometrynolongerdevelopedinNorthİmralibasinandonlya edwithprogradingstratanearwesternNorthİmralibasin(Violet-5,
lowstandwedgedevelopedforyoungerstrata. Figs.3and4).OtherhorizonsbelowGreen-6,thelowestinterpreted
WealsonotethattheMarmaraSeaisasmallbasinconnectedby deltasequence,including“Orange-7”,areassociatedwithdelta-like
narrow straits to the Black Sea (Bosphorus Strait) and the Aegean outlines and/or possible prograding strata in the western part of
Sea (Dardenelles or Çanakkale Strait). When global sealevel falls Northİmralibasin.Wealsonotethatthe“Magenta-3”complexofpro-
belowthesilldepthsofthesetwostraits,theMarmaraSeabecomes gradingstrataisnotafalling-stagesystemstract(Figs.3and4).Itis
an isolated lake whose level could be different from the global just below Blue-2 and may not represent a glacial stage separate
ocean.However,faultswithseafloorexpressionarepresentnearthe fromBlue-2;Magenta-3isfurtherdiscussedin“Section4.4”below.
Fig.5.Isochoremapsofverticalthicknessbetweengriddedhorizons.ThedepocenterhasmovedaroundNorthİmralibasinbecauseofstructuralgrowthdivertingriversystemson
theshelf,andlikelybecauseofchangesinthelocationofthedeepestpartofthepaleo-basins.TheseisochoregridswereusedforthevolumecalculationsdisplayedinFig.9.
C.C.Sorlienetal./Tectonophysics518–521(2012)1–16 7
4.2.Mappingofthedeltastratigraphy (Hughes,1985),sothe20%disagreementinTable2canbeadjusted
to10%.TheLinearVelocityEquationyieldsthefollowingformulafor
Startingfromtheareaofthedeltaswherethegeometryofthese- depthconversion:
quencesisclearlyexpressed,thetoplapboundariesofeachofthedelta
(cid:1) (cid:3)
sequencesweretracedbasinward.Standard“loop-tying”methodsfor Z¼ eC(cid:2)T=2−1 (cid:2)ðVo=CÞ ð2Þ
2Dseismicreflectiondatawereusedtoextendthecorrelation.The
correlative conformity surfaces of the sequence boundaries corre-
spondedtostrongreflectionsthatwewereabletocorrelatethrough- whereTistheintervaltwo-waytraveltime.Tocalculatetraveltime
outthegridsofseismicreflectiondata(Figs.2and3).Thedistinctive below sea floor, we converted the grid of multibeam bathymetric
patternofhighamplitudereflectionsseparatedbytransparentinter- data(Ranginetal.,2001)totwo-waytraveltime(TWTT)usingCTD
valsmadecorrelationpossibleacrosscertainfaultsorcollapse/creep water velocity information data for the deep Marmara Sea basins
folds(Shillingtonetal.,inreview;Figs.6,7,8,supplementalFigs.S1, (CTDsfromR.V.UraniaCruise,e.g.Cormieretal.,2006,providedby
S2).TAMAMstrikelinesduringthe2008cruisewerecarefullyposi- M.-H. Cormier). The horizon grids were subtracted from the sea
tionedusingexistingdataanddipprofilesastheywereacquired,so floor TWTT grid, resulting in isochron (interval TWTT) grids. The
thattheycouldbeusedforregionalstratigraphiccorrelation.Strike grids were then converted to vertical thickness (isochores) using
linesacquiredduringthe2010cruisehadtheadvantageoffullerse- Eq.(2).Waterdepthwasaddedtothicknesstoproducedepthgrids
quencestratigraphicanalysisbetweenthetwocruisesforpreciselylo- (Fig.2).Depthgridsweresubtractedfromeachothertoproducein-
catingthelines.Correlationthroughthegridsofintersectingprofiles tervalisochoregrids(Fig.5).Volumesforeachintervalwerecalculat-
providedredundancyanderrorcorrection. edusing“TheKingdomSuite”(Fig.9).
ThehorizonsweremappedthroughouttheNorthİmraliBasinand
correlatedintotheKumburgazBasinandtheÇinarcikBasin(Figs.6,8, 4.3.Stratigraphic-agemodel
Supplemental Figure S1; Kurt et al., 2011). The horizons were also
correlatedintotheCentralBasin(Fig.7).Wehavenotyetbeenable There are few stratigraphic age data from wells for Quaternary
todirectlycorrelatethehorizonstotheTekirdağBasininthewest- stratainMarmaraSea,andnoneforthedeepbasins.Hence,existing
ernmostMarmaraSea. age control is limited to about 150ka on the shelves (e.g., Çağatay
ThemappedhorizonsintheNorthİmraliBasinweregriddedand et al., 2009), to post-~40ka radiocarbon ages in the deep basins
converted to depth using the following procedure: data points for (e.g.,Becketal.,2007),TheMarmara1petroleumtestwellnearthe
eachhorizonwereexportedwithaspacingof~100malongprofiles. edge of the southern continental shelf recovered 51 to 112m of
The programSURFACEIII (KansasGeologicalSurvey) “Projectionof undifferentiated brackish Quaternary (possibly Pliocene in lower
Slopes”, usingoctantsearch and fourthpowerweighting,wasused part)sediments(Figs.1and2;MarathonPetroleumTurkeyLimited,
toproducesmooth100mgridsforeachhorizon. 1975; see also Ergun and Ozel, 1995). We correlate our sequences
Forconversiontodepth,weuseda1Dvelocitymodelfordepth to the section above 127m where we see a major unconformity.
below seafloor (linear velocity equation, Sheriff, 1973; Tolmachoff, Thispaper,usingseismicstratigraphyandtheQuaternaryglobalcli-
1993). mate record, contains the first attempt to extend the stratigraphic
age models for the basins through much of late Quaternary time
(cid:2)
VðZÞ¼VoþC Z; ð1Þ (last~800ka).Basedonthisstratigraphicanalysis,wearethenable
toexamineratesandabsolutetimingofdeformationofthetransform
whereV(Z)isvelocitybelowseafloor,Voistheintervalvelocityat basinsinMarmaraSea.
the sea floor (1514m/s) and C is a constant whose value is 0.6. The stack of shelf-edge delta sequences within the partly-filled
Table2showsacomparisonofvelocityestimatesfromEq.(1)toin- North İmrali basin forms the basis for our development of an age
dependentestimatesofintervalvelocity.Theagreementisexcellent model. The foreset/toplap geometry characteristic of these deltas
exceptforthedeepestcomparisoninÇinarcikBasinandthecompar- could not have formed in their present position basinward of the
isonusingstackingvelocitiesinNorthİmraliBasin.Intervalvelocity shelfedge,evenifthedepththeywereformedinwaslessthanthe
derived from stacking velocity is generally an overestimate of 10% current300to400m waterdepth.They mustbe associatedwitha
Fig.6.RegionalcorrelationofhorizonsfromtheareaofthedeltasinNorthİmralibasintonorthoftheMainMarmarafaultinKumburgazbasin.Correlationprofilelocatedoninset
mapbybluepolygon.FanningofdipsinbothKumburgazandNorthImralibasinrepresentstilting.Faultsandbathymetryareshownintheinsetmap.Colorscorrespondtofigures
andtextinthepaper.ThestratigraphiccorrelationisbasedonallseismicreflectiondatainFig.2andnotjustonthissinglepath.
8 C.C.Sorlienetal./Tectonophysics518–521(2012)1–16
Fig.7.Regionalcorrelationofhorizonsfrompoint“P”inthesaddlebetweenKumburgazBasinandCentralBasin.ThisprofileintersectsFig.6atpoint“P”.Itislocatedoninsetmap
bybluepolygon.Faultsandbathymetryareshownintheinsetmap.Colorscorrespondtofiguresandtextinthepaper.Thestratigraphiccorrelationisbasedonallseismicreflection
datainFig.2andthisinsetandnotjustonthissinglepath.
significantsealevelfall.Wethereforeinterpretthatsequencebound- ahighlevelcontrolledbyglobalsealevelandalowsea/lakelevelde-
arycappingthefalling-stagesystemstractsfortheBlue-2,Yellow-4, terminedbyeithertheglacialminimaortheDardanellessilldepth.
and Green-6 delta sequences, each represent a glacial interval. The To estimate the relative and then absolute age of the delta se-
mainquestionistowhichglacialcyclesdotheycorrelate?Glacialin- quences,weusethreedifferentquantitativeapproaches.Weinitially
tervals and sea level minima occurred approximately every 100ka assume relatively constant rates of structural growth and sediment
during the late Pleistocene (Lisiecki and Raymo, 2005). As a start, depositionandsubsequentlyrelaxthoseassumptions.Theseare:1).
wemakethefollowingassumptions:1)MarmaraSeahasbeencon- Dipsofdeltahorizonsonprogressively-tiltingfoldlimbsatfiveloca-
nected to global oceans during each interglacial time (Beşiktepe et tions,withfourlocationsbeingspacedfrom>10to>20kmapart;2).
al.,1994);2)thelakeshorelinethatformedat87mduringtheLast Vertical part of slip (“vertical separation” or “throw”) of each delta
GlacialMaximumwascontrolledbythedepthofapaleo-sillinthe horizon across each of four NW-striking faults within North İmrali
Dardanelles (Cormier et al., 2006); 3) Previous glacial Marmara basin, assuming constant rates of vertical separation; and 3) Total
lakesdidnotdryoutmorethantensofmeters(ifatall)belowthe corrected volumes of sedimentary rock between delta horizons for
Dardanelles paleo-sill depth; and 4) the sill depth was not greatly allofNorthİmralibasin.
shallowerthantodayoverthelastfewhundredthousandyears,and
ifsignificantlydeeperthantoday,thenglobaleustaticlowstandsrep- 4.3.1.AgeofRed-1horizon
resent the minimum elevation of Marmara Sea surfaces. Together Alloftheseapproachesproviderelativeagesandthereforerequire
theseassumptionssimplymeantheMarmaraSeaalternatedbetween an estimate for the age of one horizon in order to scale the age
Fig.8.RegionalcorrelationofhorizonsfromNorthİmraliBasintowesternÇinarcikBasin.Thismultichannelseismicreflectionprofileislocatedontheinsetmapbybluepolygon
between“M”and“N”.Faultsandbathymetryareshownintheinsetmap.Colorscorrespondtofiguresandtextinthepaper.Thestratigraphiccorrelationisbasedonallseismic
reflectiondatainFig.2andthisinsetandnotjustonthissinglepath.
C.C.Sorlienetal./Tectonophysics518–521(2012)1–16 9
Table2
ComparisonsbetweenuseofEq.(1)forvelocityagainstresultsfromrefractionseismicinCentralandCinarcikbasins,acheckshotvelocitysurveyattheMarmara1well,andin-
tervalvelocityderivedfromourstackingvelocityanalysisinNorthİmralibasin.“bsf”=belowseafloor;TWTT=two-waytraveltime;SM2=SeisMarmaraLeg2.
Location Depth/time Int.vel.(Eq.1) Comparisonreference Method Measuredvelocity
Marmara1well 115mbsf 1583m/s Marmara1well checkshot 1667m/s +5%
Nİmralibasin 0.477sTWTTbsf 1747m/s Averageof5TAMAMprofiles,59analyses, Intervalvel.Fromstackvel. 2105m/s +20%
CentralBasin(deepestpart) 1.6sTWTTbsf 2453m/s Béceletal.,2010OBSprofileSM03 Refraction 2500m/s +2%
SM2Line134 2336mbsf 2920m/s Dessaetal.,2007 Refraction 3400m/s +16%
estimatesfortheotherhorizons.Wethereforefirstestimatetheage oralmostreachedRed-1,butunfortunately,thedeeperpartsofthis
oftheyoungestinterpretedhorizon,Red-1.Red-1hasnotbeencorre- corehavenotyetbeendated(locatedonFig.1).
latedtoanimageddelta,butisahigh-amplitudereflectioncompati-
blewitha sandyinterval,and itis locallyanunconformity.Agiant 4.3.2.Relativeagesfromprogressivetilting
piston core collected with the R/V Marion Dufresne, MD01-2431, in Inordertoobtainrelativeagesofotherreflectors,weexaminethe
thesouthernCentralBasin(Fig.1)hasaradiocarbondateof16.3to dipsofsevenhorizons,includingtheseafloor,asmeasuredondepth-
17.4kaat17mbelowseafloor(bsf)(Becketal.,2007).TheRed-1 migrated seismic reflection profiles at five locations (labeled “a”
horizonclosetothatcoreisabout110mbsf.Extrapolating17kaat through“e”onFig.2).TwooftheseprofilesaredisplayedinFigs.3
17mbsfprovidesanestimateof110kafortheRed-1horizon. and11.DipsareplottedonFig.12.Weassumearelativelyflat-lying
AnimmediatequestionraisediswhetherRed-1couldcorrespond surfacehasbeenprogressivelytiltedandthatthepreservedstratare-
toOxygenIsotopeStage(OIS)6at140ka?Toaddressthisweexamine cordthisrotation.Themainlimitationswiththisapproachisthatfor
thestratigraphyassociatedwithRed-1.Seeberetal(2006)proposeda somesites,seafloordipisnon-zero,meaningthatnotallofthetilting
sedimentation-agemodelfortheMarmaraSeathatincorporatesvar- hasbeenfilledbysedimentation,andconsequentlywedonotknowif
iablesedimentsupplyinaconstantlytiltingtectonicbasin.Theypro- theinitialdipswerezero.Wethereforeconsiderthesiteswherethe
pose low sedimentation rates in basins during transgressions and surfacedipisclosetozeroasthemostreliable.Inordertocalculate
highstandsofsealevelwhensedimentisstoredontheinnershelves. theprogressivetilt,thedipattheseafloorwassubtractedfromthe
Incontrast,duringregressions,shelfsedimentsarereworkedandin- dipofeachhorizon.Thelinearityoftheincreasingdipssuggestsrela-
creasethesedimentsupplytooffshorebasins.Theresultisthatslow tiveequaltimespacingbetweenhorizonsandthusrepresentationof
interglacial sedimentation over a longer time produces strata that each~100kyglacialcycle.
showgreaterfanningofdipsinprofilethanthesamethicknessofrap-
idlydepositedglacial-periodsediment.Seeberetal.(2006)demon- 4.3.3.Relativeagesfromverticalseparationofhorizonsatfaults
strateanoverfivefoldincreaseinfanningabovethe14kalake-sea Thesecondapproachforobtainingrelativeagesinvolvesthever-
transitionintheÇinarcikBasin.Ourseismicdataimageprominentdif- ticalseparationacrossthesetofNW-strikingextensionalortransten-
ferentiallytiltedunitsineachofthreebasins.Fig.10illustratestwo sionalfaultswithinNorthİmralibasin(Fig.13).Assumingcontinuous
wedgesofonlappingreflectionswithfanningofdipsin theCentral growth should yield linearly increasing vertical separation. Separa-
BasinthatwecorrelatetoOIS5andOIS7.Theupperwedgeinthe tionforeachhorizonwasmeasuredintwo-waytraveltimeat23lo-
CentralBasinandintheotherbasinsareinterpretedasbeingtrans- cations total for the four faults where all these horizons could be
gressive and high-stand deposits from Oxygen Isotopic Stage (OIS) unequivocally identified (Fig. 14). Travel time was converted to
5eatabout125ka.Inallthreebasins,theupperprogressivelytilted depthusingEq.(2).Limitationsofthismethodarewhenfaultingex-
units occur just below Red-1. We therefore conclude that Red-1 is ceeds the rate of sedimentation, some of the throw contributes to
younger than the OIS 6 (140ka) and was deposited in the minor scarp development rather than differential sedimentation. Scarp
low-stand at 109ka (Lisiecki and Raymo, 2005). This age estimate height was measured at each location. The most reliable estimates
for Red-1 is very close to the extrapolations below the piston core areconsideredsiteswithlittletonosurfacescarp.
MD01-2431. The estimate can be tested: Core MD04-2743 reached Overall, the plot shows continuous growth in vertical separation
withthefollowingobservations.Flatslopesonthegraphsuggestthat
faults “c” and “d”, and part of “b” did not start slipping at their full
rate until after Violet-5. Similarly, fault “a” was mainly active after
Yellow-4time.Analternateexplanationwouldbethatthetimeinterval
betweenViolet-5andGreen-6isshorterthantheotherintervals.
4.3.4.Relativeagesfromsedimentvolumes
Forthethirdmethod,weusesedimentaryvolumesfortheentire
Northİmralibasinbetweeninterpretedhorizonsandtheassumption
ofsteadysedimentinputtothebasinperglacialcycle.Weusedthe
gridded horizons to estimate sediment volumes (Figs. 5 and 9). To
correct for compaction of the sediments at depth, we make use of
thevelocitymodelusedfordepthconversion.Weconvertfromveloc-
ity(vs.depth)todensityusingEq.(1)fromBrocher(2005)andthen
fromdensitytoporositybyassumingagraindensityof2680kg/m3.
Fİmigr.a9li.bVaosliunm(tersiafnorglienst)e.rTvhaelsabreetawwehenerienvteorlpurmeteesdarsetrmateigarsauprhedicihsooruiztloinnesdfoornaFlligosf.N2oarnthd Theresultingporosity-depthcurveiswellfitbyanexponentialde-
5.Colorscorrespondtothebaseofeachinterval.SF=SeaFloor;R=Red-1;B=Blue-2; creaseinporositywithdepthdownto1800m,themaximumdepth
Y=Yellow-4;V=Violet-5;G=Green-6.Squaresgivecorrected,decompactedvol- of the Green-6 horizon surface in North İmrali Basin (Fig. 2). The
umes,asdescribedintext.IfRed-1is109ka,andtherateofsedimentaccumulationis resultingequationforporosityis:
constant, then Blue-2 is 243ka, using corrected volumes. We assume that Blue-2,
Yellow-4,andGreen-6,whichcorrelatetodeltas,weredepositedduringrelativelyfall-
icnugrvseeaolfeLviesilescaknidanardeRaasysimgnoe(d2t0h0e5a).geofthemostpositivevalueoftheOxygenIsotopic Φ¼0:626(cid:2)e−0:000351Z: ð3Þ
10 C.C.Sorlienetal./Tectonophysics518–521(2012)1–16
Fig.10.MigratedprofileacrossthewesternmarginofCentralBasinlocatedonFig.1.Thearrowsatlowerleftindicatetheupperpartofablindthrustfault,barelyimagedbutsup-
portedbyfoldgeometry.The~100ka(assigned109ka)Red-1horizonisinvolvedinprogressivetilting(dipssteeperwithdepth).Dashedhorizonsarebathyalonlapsurfacesthat
formthebasesofsedimentarywedgesproposedtobedepositedduringinterglacialtimesoflowsedimentationrates(seeSeeberetal.,2006).OIS=Oxygenisotopicstage;M=
Multiplereflection.ThisyoungcontractionalfoldingonWesternRidgeisonlypresentnorthoftheMainMarmarafault.Thus,thewesternmarginofCentralbasinisnotapre-
existingstructurethatcanbeusedtoreconstructCentralbasin.
Using this equation, we estimated the decompacted volume of sedimentvolumebetweenBlue-2andRed-1tothatbetweenRed-1
sediments, i.e., the thickness of sediments if they were restored to andSeafloor,withRed-1assumedtobe109ka,resultsinanestimate
thesurfaceporosityof62.6%. of246kaforBlue-2(starinlowerpartofFig.15a).Blue-2istherefore
Fig.9presentsthecomputedsedimentvolumesandthevolumes assignedtoOIS-8at252ka.
correctedforcompaction. Thevolumesvary byup to29%fromthe WeuseBlue-2at252kaasthebasisforextrapolating theolder
mean. This is a significant amount but less than the factor of 2 horizons in order to minimize the errors inherent in extrapolation.
expectedformissedglacialcycles.Thepatternshowsanintervalvol- Extrapolatingtheagesoftheoldersequencesbasedonvolumerela-
umeincreasebetweenthedepositionofViolet-5andBlue-2,andthen tivetoBlue-2shouldoverestimatetheagebecauseofthesediment
asharperdecreaseafterdepositionofBlue-2.Thelowervolumescor- lostfromtheNorthİmraliBasin.Infact,thedecreaseinsedimentation
respond to the times when the delta depocenters are in the west volumebetweentheYellow-4andBlue-2deltasisevenmorenotable
(Fig.5).Inthisregionthereiscurrentlyacanyon,visibleintheiso- iftheBlue-2toRed-1intervalelapsedtimeintervalis143kaandthe
chores(Fig.5)andthecurrentbathymetry(Fig.1),thatbypassessed- earliertimeintervalsareclosertothe100kaglacialcyclicity.Thusthe
iment from the North İmrali Basin to the Çinarcik Basin. The starsintheupperpartofFig.15aareanupperlimitfortheagesof
decompacted volumes suggest that about 30% of the sediment is Yellow-4,Violet-5andGreen-6.Wenowturntothedipsandvertical
bypassedtotheÇinarcikBasin. separations across faults, scaled to theage estimate for Blue-2. The
verticalseparationshadtheseafloorscarpheight,ifany,subtracted
4.3.5.Absoluteageassignment from the offsets at each location. The results are plotted on the
UsingtheageassignmentforRed-1as109ka,wecanusethesed- upper part of Fig. 15a. The values show considerable scatter, as
imentvolumestoextrapolatetheageforBlue-2,asbothsetsofvol- expected,butarecenteredatvalueslowerthanthevolumeextrapo-
umesaresimilarlyaffectedbythecanyon.Scalingthedecompacted lations. Based on the extrapolations and the evidence that the
Fig.11.MigrateddepthsectionC–C′displayedwithtwotimesverticalexaggeration,locatedonFig.2.Coloredhorizonscorrespondtootherfiguresandthetext.Numbersarestruc-
turalreliefinmetersacrossandclosetothenorthernstrandoftheNorthAnatolianfault,anddipindegrees.Thesedipssuggestongoingtiltingofthebasinmarginsinceatleastthe
timeofdepositionof“orange”.ThegraphgivesstructuralreliefacrosstheMainMarmarafaultasmeasuredatthelabeledarrows.Thenearconstantrateofreliefgrowthbetween
horizons,assumingnearconstantageintervalbetweenhorizons,isconsistentwithuniformright-reverseslipontheMainMarmarafaultthroughthisrestrainingsegment.These
dipsareshownasTM25=ainFig.12.M=Multiplereflection.