Quantitativestructuralanalysisusingremotesensingdata:Kurdistan,northeastIraq

DanielReif,BernhardGrasemann,andRobertH.Faber

ABSTRACT

Theuseofremotesensingdataincreasestheefficiencyoffieldmapping,especiallyinareaswithdifficultaccessorwheregeo-logicfieldworkisexpensiveorhazardous.Thisstudypresentsanewlydevelopedsoftwaretoolforinteractivelymappingandmeasuringthespatialorientation(i.e.,dipangleanddipdi-rection)offiniteplanargeologicstructurefromdigitaleleva-tionmodels(DEMs).Theorientationsofplanardata(e.g.,sedimentarybeddingorfaultplanes)arederivedbyapproxi-matingavirtualplanetotheintersectionoftheplanarfeaturewiththeDEMtopography.ToincreasetheinformativevalueoftheDEM,satelliteimagescanbedrapedontothetopo-graphicdataset.ThesoftwaretoolwastestedintheZagrosfoldandthrustbelt,northeastofErbil(Kurdistan,northeastIraq),wherethestratigraphyhasbeendeformedintosub-cylindricalfoldtrains.Computedorientationshavebeencom-paredwithactualdipanglesanddirectionsmeasuredinthefield.Underfavorableconditions(moderatelydippingplanes,strongcompetencecontrastbetweenstratigraphicbound-aries,intersectionwitharuggedtopography,lowvegetation),statisticalcomparisonofcomputeddatawiththefieldmea-surementsdemonstratesthatthespatialdatasetcanberepro-ducedfromtheDEMwithinanaverageerrorofapproxi-mately10°.Thestrengthofthemethodisdemonstratedbyintegratingfielddatawithcomputedvaluesfrominaccessibleareas,resultinginareasonablywell-constrainedbalancedgeo-logiccrosssection.

Copyright?2011.TheAmericanAssociationofPetroleumGeologists.Allrightsreserved.

ManuscriptreceivedJune30,2010;provisionalacceptanceJuly28,2010;revisedmanuscriptreceivedSeptember13,2010;finalacceptanceNovember15,2010.DOI:10.1306/11151010112

AAPGBulletin,v.95,no.6(June2011),pp.941–956941

AUTHORS

DanielandSedimentology,Reif??DepartmentUniversityofofGeodynamicsVienna,Althanstrasse14,1090Vienna,Austria;daniel.reif@univie.ac.at

DanielReifreceivedhisM.S.degreefromtheUniversityofViennain2008,studyingneo-tectonicsandhydrogeology,focusinghisworkontheDanubeRiverBasinontheSlovakia-Austriaborder.Recently,hehasbeenworkingonhisPh.D.,dealingwithtectonicgeomor-phologyoftheZagrosfoldandthrustbelt,north-eastofErbil(Iraq).Thestudyfocusesona3-Dstructuralmodelandonthegrowthhistoryofanantiform-synformfold-trainintegratingremotesensingtechniquesandstructuralfielddata.BernhardGrasemann??DepartmentofGeodynamicsandSedimentology,UniversityofVienna,Althanstrasse14,1090Vienna,Austria;bernhard.grasemann@univie.ac.atBernhardGrasemannreceivedhisPh.D.inge-ologyfromtheUniversityofVienna.Hestud-iedinseveralinternationalprojectsthegeo-dynamicevolutionandtheactivetectonicsoftheHimalayas.Since2007,hehasbeenapro-fessoringeodynamicsandstructuralgeologyattheUniversityofVienna.Hisscientificinterestscovertheevolutionofmountainbelts,meta-morphiccorecomplexformation,andthequan-tificationofstructuralprocessesatvariousscales.RobertH.Faber??TerraMath,SPARKSCommercialBNo.23,Jl.RayaKelapaDua,GadingSerpong,15310Serpong-Tangerang,Banten,Indonesia;robert.faber@terramath.comRobertFaberreceivedhismagisterdegreeingeology(2000)anddoctorateingeology(2002)bothfromViennaUniversity,Austria.In2003,hefoundedthecompanyTerraMath.Currentprojectsincludethree-dimensionalmodelingandinterpolation,geothermalsimulations,andremotesensing(allincombinationwithsoft-waredevelopment).Hisinterestscomprisethenumericalsimulationofgeologicprocesses,re-motesensingincombinationwithstructuralgeology,softwaredevelopment,andappliedmathematics.

ACKNOWLEDGEMENTS

WethankOMVAustria,ExplorationandPro-ductionCompany,forsupportandideas,espe-ciallyGerhardMilanandDuncanLockhartaswellasDanaMawloodandAzadIbrahimfororganization,logistics,andsecurity.BernhardBretisandNikolausBartlarethankedfortheircooperationduringfieldworkinKurdistan.Fur-thermore,wethankM.Snideroandhiscol-leaguesfromtheUniversityofBarcelonafordiscussionsaboutremotesensingandH.K.A.Khamal,fromtheSulaimaniyaUniversityinIraq,forsupplyinguswiththeavailablelocalgeologicpublications.WethanktheAAPGre-viewersGarryL.ProstandSandroSerrafortheirhelpfulreviewsonthismanuscript.

TheAAPGEditorthanksthefollowingreviewersfortheirworkonthispaper:GaryL.ProstandSandroSerra.

INTRODUCTION

Dataderivedbyremotesensingtechniquescansignificantlyincreasetheefficiencyoffieldmapping,especiallyinareaswithdifficultaccess,andrepresentalow-costcomplementtogeo-logicfieldwork(RenczandRyerson,1999).Forinvestigatinglarge-scalegeologicstructuresthatcontrollandforms,geologiststraditionallyusedstereoscopicaerialphotographstocollectqualitativethree-dimensional(3-D)information.Quantitativemeasurements,especiallythespatialorientation(dipdirectionanddipangle)offeaturessuchasbeddingorfaultplanes,canbederivedfromstereoscopicaerialphotographsbymeasuringtherelativeparallax(i.e.,thedifferenceofthelocationofapointviewedfromtwodifferentlocations)ofa3-Dstructure(Colwell,1955;Tator,1960;Kraus,2007).Spatialorientationscanbedeterminedfrombestfitplanesto(atleast)threeormorein-tersectionpointsbetweenaplanarfeatureandthetopography.Computationalmethodscanincreasetheefficiencyofthistime-consumingmethodbydigitizingtheedgesofsuchafeatureinstereoscopicpairsofaerialphotographs(Bilottietal.,2000).

Withtheincreasingqualityandresolutionofdigitaleleva-tionmodels(DEMs)andwiththeenormousadvantageofthealmostglobalcoverageandfreeavailabilityofsuchdata,map-pingof3-Dinformationfromtrue-to-scale3-Dimagespro-videsanefficientandaccuratealternativetostereoscopicmap-pingusingaerialphotographsandsatelliteimages(BanerjeeandMitra,2004;Snideroetal.,2009).Recently,ithasbeendemonstratedthattheintegrationofregionaltooutcropdig-italdatacanbeusedtovisualize3-Dmultiscalestructuralgeologicmodels(Bernardinetal.,2006;Alfarhanetal.,2008;Jonesetal.,2009).

Followingtheseideas,wepresenthereapracticalapplica-tionofanewlydevelopedadd-ontool(PlaneTrace)forthesoftwareWinGeol.Thisallowsinteractivemapping,visualiza-tion,andcalculationofthespatialorientationsofplanarsur-facesfromDEMs.Thestrengthofthistoolisthatthegeologicfeatureistracedbyavirtualtransparentplane,whichallowsvisualapproximationoftheplanarstructure.TheaccuracyofthePlaneTracetoolhasbeentestedintheZagrosfoldandthrustbelt(Kurdistan,northeastIraq)bycomparingcomputedbeddingorientationwithfielddata.

REGIONALGEOLOGYOFTHESTUDYAREA

TheZagrosMountainsextendfor1800kmbetweenthecentralIranplateauinthenorth,theTaurusinTurkeytothenorthwest,

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Figure1.(A)MapofIraqandthelocationofthestudyareanortheastofthecityofErbil.(B)Mapofthestudyareawiththemajoranticlinalfoldaxes(modifiedfromBudayandJassim,1984).TheMountainFrontfaultlineseparatestheforedeepfromthehighfoldedzone.ThemainZagrosfaultistheproposedNeotethysOceansuturezonebetweentheArabianplateandEurasia.

theOmanfaultinthesoutheast,andthePersianGulfforelandtothesouthwest(Stocklin,1968;HaynesandMcQuillan,1974;TalbotandAlavi1996),formingamajorsegmentoftheAlpine-Himalayanorogen.TheorogenstartedtoformintheLateCretaceous,followingthecollisionbetweentheArabianandEurasianplatesasaresultoftheclo-sureoftheNeotethysoceanicbasin(BerberianandKing1981;SnyderandBarazangi1986;Berberian1995;TalbotandAlavi1996).TheshorteningratebetweentheArabianandEurasianplates,whichisstillontheorderof2to2.5cm/a,ispartitionedintosouth-southwest–directedfoldingandthrustingoftheTethyansedimentsandnorthwest-southeasttonorth-south–trendingdextralstrike-slipfaulting(JacksonandMcKenzie,1984;Berberian,1995;Jacksonetal.,1995;McQuarrieetal.,2003).TheZagrosfoldandthrustbelt,whichhostsmorethan5%oftheworld’shydrocarbonreserves(mostlyinanticlinaltraps),isdividedintofournorthwest-southeast–strikingtectonicunitsinIraq:theZagrossuture,theimbricatedzones,thehighfoldedzone,andthefoothillzone(figure6-1,p.72,inJassimandGoff,2006).ThelastthreezonesarebroadlyequivalenttotheHighZagrosoverthrustzone,theZagrossimplyfoldedzone,andtheZagrosforedeep,respectively,asdefinedinIran(Stocklin,1968;HaynesandMcQuillan,1974;Berberian,1995).TheboundarybetweenthehighfoldedzoneandthefoothillzoneisdefinedbytheMountainFrontfaultparalleltothegeneraltrendoftheZagrosbelt.Theboundarybetweenthesezonesalsocoincideswithadeep-seatedfaultalongthesouthwestlimboftheAqraanticline,withapproximately3000m(9843ft)displacement(JassimandGoff,2006).TheMountainFrontfaultlikelyrepresentsaforced

Reifetal.

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foldformingaboveareactivatedbasementfault(Motiei,1995;Berberian,1995).AccordingtoBudayandJassim(inJassimandGoff,2006),thehighfoldedzonehasanelevatedbasementcomparedwiththefoothillzone,withapproximately5-kmdepthdifference,estimatedfromthethicknessofthesedimentarymegasequences.

TheareausedtotestthePlaneTrace-WinGeolsoftwareliesinthehighfoldedzoneandintheimbricatedzonesoftheZagrosMountains,north-eastofErbil(Figure1).Depositionoftheapprox-imately9-to10-km(5.6-to6.2-mi)-thicksedi-mentarysequence,whichrestsonaPrecambrianpolymetamorphicbasement(JassimandGoff,2006),startedintheLatePermiantoLateTrias-sic,reflectingcontinentalriftingalongnorthwest-southeast–strikingnormalfaultsandtheopeningoftheNeotethyanOcean(Alavi,2004,andreferencescitedtherein).DuringtheCretaceous,northeast-directedsubductionofNeotethysstarted,followedbysouthwest-directedobductionofophiolitesandtheelevationoftheinnerZagrosorogen(Hooperetal.,1995).Asaresultofongoingsubduction,NeotethysclosedintheMiocene.InthePliocenetoPleistocene,continent-continentcollisionbetweentheArabianandEurasianplatesresultedinthemainphaseofZagrosorogeniccompression,withthedevelopmentofthefoldandthrustbelt(Allenetal.,2002;Homkeetal.,2004;Ziegler,2001).Locally,Permian–Triassicnormalfaultswerereac-tivatedinthebasin,leadingtoinversionoftheoverlyingsedimentarycoverinsmallbasinsandtheformationofejectiveanticlines(i.e.,compressivereactivationofolderfaultsboundinglargeelon-gatedtiltblocks(Numanetal.,1998).

OngoingdeformationinthefoldandthrustbeltinnortheastIraqisdominatedbyopentogentlefolding,withacharacteristicwavelengthbetween5and10km(3.1and6.2mi)(Figure1B),consid-erablylessthantheaveragevaluesof15to25km(9.3–15.5mi)inthesoutheasternpartsoftheZagrosfoldandthrustbelt(Mouthereauetal.,2007).Themajorcauseforthissignificantlyshorterwavelengthistheabsenceofmajorfaultingandalsotheabsenceofthicksalthorizons(e.g.,theNeo-ProterozoicHormuzsaltoverlyingthecrystallinebasementinthesoutheasternpartoftheZagros),

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Figure2.Stratigraphyofthestudiedarea.Formationsmarkedwithanasterisk(*)areincompetent,andthosemarkedwithdoubleasterisks(**)arepossiblelocaldetachmenthorizons.ThestratigraphictableissignificantlymodifiedfromBudayandJassim(1984).