The Atlantic Margin from Norway to Ireland

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The Atlantic Marginfrom NorwaytoIreland: geologicalreviewofafrontier continentalmarginprovince

P.M.SHANNON,1 J.I.FALEIDE,2 J.R.SMALLWOOD3 andI.M.WALKER4

1 Department ofGeology,University College Dublin,Belﬁeld, Dublin4, Ireland(e-mail:[email protected]) 2 Department ofGeosciences,University ofOslo,POBox 1047Blindern,N-0316 Oslo,Norway (e-mail:[email protected]) 3 Amerada Hess Ltd, 33 Grosvenor Place, London SW1X7HY, UK (e-mail:[email protected]) 4 ConocoPhillips (UK)Ltd, RubislawHouse, Anderson Drive, AberdeenAB156FZ, UK (e-mail:[email protected])

Abstract: The deep-waterAtlantic MarginofNWEuropeisalightly explored frontierprovince.Duringthe past sixyears therehasbeenamodest levelofexploration drillingwithmixed results. However,alot ofnew geologicalandgeophysicaldatahashelped inthe understandingofthe crustalstructureandthe tectonostratigraphic development ofthe region. The 27 papers inthisthematic section illustrateacross- section ofthe newinformation andideasandhighlightremainingquestions regardingthe geologicaldevelopment andpetroleum prospectivity ofthe region. Geophysicaldataprovide evidence for depth-dependent stretching across the continental/oceanic marginandinseveralofthe deep-waterbasins. However,the associated thermal anomaliesandvolcanism arestill poorly understood.Newdrillingresults from the margins ofthe Rockall Basin provethe presence ofMesozoic andCenozoic strata.Togetherwithgeophysicaldata, well results demonstrate thatthe Cenozoic evolution wasaccompaniedbysignificant tectonism. Examplesofnewfieldsillustratethe petroleum potentialandremainingrisksinthe region. Anumberofkeyuncertaintiesandremainingquestions centreon the mechanisms ofpassivemarginbasinformation. Thesebasins,characterized bysignificant crustal thinning, appeartodifferintheirformation andintheirstructuralandsedimentary character,from low-extension, conventionalintra-platebasins. The resultant thermalhistory andplaytypesarealso different.

Keywords: Atlantic Margin,basins,crustalstructure, discoveries,outstandingquestions,stratigraphy, recent advances

The Atlantic MarginofNWEuropeextendsfrom northern the flanksandinthe axisofthe basin. Limited success wasseen Norwaytothe southwest ofIreland(Fig.1). Morphologically the alongthe flanksofthe basininthe UK sector,withthe discovery of region consists ofavery broad andcomplexcontinentalshelf, PaleocenegasbyEnterprisewell UK154/1-1. Aflankwell,drilled 300–500 kmwide, lyinglandwardsofanoceanic crustaldomain. inthe Irishsector byEnterprise/Shell reportedly foundcondensate Bathymetrically,the waterdepthsgenerally increasewestwards inthe Dooishdiscovery inwell 12/2-1. Furthersouthinthe Irish from c .100 mcloseto shoreto c .350m atthe shelfedge and sector,anumberofwells targetingthe Cenozoic succession inthe deepenrapidly to 4000 minto the oceanic domain. The westward- PorcupineBasinweredisappointingdry holes. Inaddition,frontier deepeningshelfistransected byanumberofdeep-water licencesawarded alongthe flanksofthe IrishRockall Trough in embayments such asthe PorcupineSeabight,the Rockall Trough, 1997 wereall relinquished without drilling.However,the Corrib the Faroe–ShetlandChannelandthe NorwegianBasinthatcontain GasFieldinthe SlyneBasin(Dancer etal .,thisvolume)was anumberofLatePalaeozoic to Cenozoic sedimentary basins, successfully appraised andopened up anewplayinthe region. developed withinthe broad settingofanextensional,passive Asimilarnewplaywasestablished inthe Faroe–ShetlandBasin margin. Although itcontains someofthe largest andleast explored withthe discovery ofgasinthe Eocenebywell 214/4-1.The basins inNW Europe, the geologicalevolution andpetroleum interveningyears also sawresolution ofthe UK–Faroesboundary prospectivity ofthisfrontierprovince isstill poorly constrained. issue, withthe awardofacreage inthe formerWhiteZoneinthe Lyinginaharshenvironment on the eastern marginofthe Atlantic 1st Faroeseand19thUKlicensingRounds,respectively. Anumber Ocean,exploration progress hasbeenrelatively slow inthishigh- ofwells havebeendrilled on theselicencesthat,withthe exception risk, deep-watersetting.Whiletherehavebeensomenotable ofthe Marjun discovery byFaroeswell 6004/16-1Z( Smallwood& exploration successesinthe region andpositiveindications of Kirk ,thisvolume),haveproved disappointing.InNorway, the criticalindicators ofpetroleum accumulations inmost of continued exploration ofthe deep-waterVøringandMørebasins the basins,the region still contains many uncertainties,bothin resulted inthe discovery ofthe giant OrmenLange GasFieldina terms ofits crustalandsedimentary evolution andalso inits Cenozoic domestructureatthe eastern marginofthe MøreBasin, petroleum habitat. withareservoirintervalcomprisingtwo sandunits ofMaas- Exploration results alongthe Atlantic Marginhavebeen trichtian–Danianage (Gjelberg etal .2001). Minor gasdiscoveries somewhatmixed since the last Petroleum GeologyofNorth- havealso beenmade inUpperCretaceous (NykHigh;6707/10-1) West EuropeConference in1997. Therehavebeenanumberof andTertiary (NaglfarDome;6706/6-1) sandsinthe NW Vøring wells drilled to test established andnewplays alongthe entire Basin. Oilwasfoundatthe GripHigh (6405/7-1),northofthe Atlantic Marginfrom the LofotenIslandsinnorthern Norwayto OrmenLange GasField, but thereareuncertaintieswithrespect the PorcupineBasininIreland.The UK 17thRoundsawlicensing to reservoirquality. Alarge gasdiscovery (Victoria;6506/6-1) ofacreage inthe Rockall Trough, withsubsequent drillingalong resulted inamoreoptimistic viewofthe Jurassic playofthe Halten

S HANNON,P.M.,FALEIDE,J.I.,SMALLWOOD,J.R.&WALKER,I.M.2005.The Atlantic Marginfrom NorwaytoIreland: geologicalreviewofafrontier continentalmarginprovince. In :DORE´ ,A.G.&VINING ,B.A.(eds) Petroleum Geology:North-West EuropeandGlobalPerspectives—Proceedingsofthe 6th Petroleum GeologyConference,733–737. q Petroleum GeologyConferencesLtd.Published bythe GeologicalSociety,London. Downloaded from http://pgc.lyellcollection.org/ by guest on September 25, 2021

734 P.M.SHANNON ET AL.

Fig.1. Topographyandbathymetry ofthe NW EuropeanAtlantic Margin. Datacourtesy ofNGDC.The locations ofthe maindeep-waterareas,with underlyingriftbasins,on the NW Europeanmarginareindicated. andDønnaterraces,which comprisesthe producingfieldsoff mid- include the Rockall,Faroe–Shetland, MøreandVøringbasins. Norwayatpresent. The geologyofthesebasins ispoorly constrained, withfewwells Licensingauthoritiesinmost ofthe Atlantic Margincountries andlittlepenetration ofthe deeperparts ofthe stratigraphy. In adopted innovativelicensingmethodstopromoteexploration and general,the natureandeventhe thickness,ofthe pre-Cenozoic itishoped thatthesewill slow the fallingtrendinexploration in succession islargely speculative(see below). the region. Anumberofmajor industry-sponsored drillingand The shelfregion isunderlainbycontinentalcrust. Largely seismic research programmesalongthe Atlantic Marginwithinthe unthinned beneaththe continentalmainlandsandshallow base- past fewyears havehelped to develop abetterunderstandingofthe ment banks,itistypically c .30kmthick.However,beneaththe structureandthe stratigraphyofthe frontierregion. The results of sedimentary basins itshows significant variations inthickness. someofthesearepresented inthisthematic section. Beneathmost ofthe inboardbasins crustalthicknessesare The 27 papers inthisthematic section present alot ofnew typically 20–25kmthick.Anexception isthe PorcupineBasin. information on the structuralframework, geologicaldevelopment Largerthanmost ofthe otherinboardbasins,itcontains many andpetroleum systems throughout the region andalso highlight similaritiesinsizeandshapeto the largeroutboardsediment- many ofthe geologicaluncertaintiesstill associated withthe starved basins andseems to haveacontinentalcrustalthickness Atlantic Margin. Anumberofkeygeologicalissueshaveemerged of c .6–8km,perhaps evenless ( Readman etal .,thisvolume), thathavesignificant implications for the geologicaldevelopment beneaththe centreofthe basin. Crustalthicknessesbeneaththe ofthe area.Theseissuesarealso important inthe continued largeroutboardbasins appeartobe low,reachingaminimum of c . development ofexploration plays inthe region andalso havean 5kmbeneaththe Rockall Basin. implication for the understandingofpassivecontinentalmargins Crustalthicknessesdecreaserapidly atthe outermarginofthe world-wide.The major objectivesofthispaperareto highlightthe continentalshelf, witharapid transition from thinned continental mainadvancesinthe geologicalunderstandingwithinthe past six years andto identifysomeofthe major questions thatremaintobe crust to oceanic crust. Thisboundary,west ofIreland, UK and answered.The paperdraws on someofthe recently published data Norway,ismarked byanelongatezoneofhigh-velocity material andresults and, especially,upon the newmaterialpresented atthe nearthe baseofthe crust,interpreted asanigneous underplated 6thPetroleum GeologyConference andinthe resultant papers in body. Inthisregion,volcanic strataform characteristic seaward- thisthematic section ofthe conference proceedings. The paperis dippingreflectionsinthe shallowerpart ofthe geological divided into sections dealingwiththe regionalbasinalsettingand succession. The southern continental/oceanic margin,marked by crustalstructureandwiththe stratigraphyandplays. the Charlie-GibbsFractureZone, isamorecomplexstructure, lackingthe underplated bodybut characterized bytranspressional modification ofthe boundary. Basinsettingandcrustalstructure Igneous bodiesalso occur aslavaflows,sills,dykes,igneous Ingeneralterms the Atlantic Marginregion iscomposed oftwo centresandstocks,through much ofthe Atlantic Marginregion. broad bandsofLatePalaeozoic to Cenozoic sedimentary basins Theseoccur inboththe inboardandoutboardbasins,aswell asin (Fig.1). The inner(inboard)basins consist ofasetoffault- the onshoreregions. Theyoccur asseamounts withinthe basins,as controlled, oftennarrow,elongateandstructurally segmented aseriesofvolcanic conesalongthe basinmargins andasextensive sedimentary depocentreslyingon the eastern margins ofthe sheets ofvolcanic flows andintrusivesinparts ofmany ofthe continentalshelf.Theseinclude the HaltenTerrace, the West basins. Whilemostly ofPalaeogeneage, anumberofsignificant Shetland, Hebrides,Slyne, ErrisandPorcupinebasins anda igneous centresofCretaceous age havealso beenidentified numberofsmallerperched basins lyingon the upperflanksofthe (e.g.inPorcupineandRockall basins). Theseigneous stratahave Rockall Basin. Thesebasins aretypically sediment filled. had adeleterious effectupon seismic imaginginthe basins, Outboardofthesebasins lie anumberoflarge basins,typically resultinginpoor imaginginthe sub-Cenozoic succession ofmany underlyingthe mainbathymetric embayments inthe shelf.They ofthe basins. Downloaded from http://pgc.lyellcollection.org/ by guest on September 25, 2021

ATLANTICMARGIN: GEOLOGICAL REVIEW 735

Recent advancesinregionalgeologicalsetting andthe Palaeogenemantleplume)ispresented anddebated inthe andbasindevelopment followingpapers. The ages,trendsandlocations ofsomeofthe igneous suitesthroughout the Atlantic Marginarenot easily Traditionalmodels ofcrustalthinningandconsequent sedimentary reconciled withamodelofmantleplumes sensu stricto andmaybe basinformation inthe basins ofNWEuropearebased largely on explained asthe effects ofshallowermantleconvection alongpre- the modelofMcKenzie (1978). Thesemodels assumed uniform existingcrustallineaments ( Lundin&Dore´ ,thisvolume). crustalstretching, withphasesoffault-controlled,syn-rift Major crustallineaments andbasement terranesappeartohave subsidence andpost-riftthermalsubsidence.Athemeemerging controlled andshaped the basingeometry ofthe region ( Kimbell from thisconference wasthe advocacyofdifferentialstretching etal.,thisvolume; Readman etal .,thisvolume; KeserNeish& models to explainthe observations ofanomalously thincrust and Ziska,thisvolume). Anumberofdiscretebasement and anomalously thick post-riftsection beneathlarge areasofthe Palaeozoic regions havebeendefined beneaththe Porcupineand NorthAtlantic Margin. Similarobservations werepresented atthe Rockall basins ( Naylor &Shannon,thisvolume)andappearto conference for the southern Atlantic Marginbasins byKarner etal . haveinfluenced the basinorientation through time.The overall (2003) whosuggested thatthe thickness anomaliesobserved can basinlocation anddistribution iscontrolled byarelatively be explained bydepth-dependent stretchingwithdifferentiallower complexPalaeozoic andolderstructuralandbasement template. crustalthinning. Kusznir etal .(thisvolume)presented amodelof The basins on the Atlantic Marginfollow ageneralENE–WSW differentialremovaloflowercrustalmaterialadjacent to the trend.However,anumberofindentations andstrike swingsin continent–oceanboundary anddiscussed the implications ofsuch basinorientation probably reflectchangesincrustalstructure. stretchingon temperatureandmaturation processes. Morewood Theseareinterpreted asthe responseto reactivation ofmajor etal .(thisvolume)also concur withthe pattern ofdifferential Variscan,Caledonianandpre-Caledoniandeep-seated structures, lowercrustalstretchinginareaswherecrustalseparation has togetherwithlatercross-basintransferfaults. Anumberofthe occurred, whilesuggestingdifferentialuppercrustalstretchingin structurallineaments areidentified on seismic dataaswell ason areasofattenuated but intactcrust,supportingearlierobservations gravity maps. The basement structuraltemplatefor the Atlantic made byHauser etal .(1995). However,furtherworkisneeded to Marginistypically complex,withfrequent reactivation of reconcilethe preciseage, natureandlinkagesofsuch depth- structuraltrends. For example, the orientation ofthe ENE– dependent stretching.Untilrelatively recently,much ofthe work WSW Variscantrendinthe southofIrelandisprobably controlled on deepstructuralcontrols wasmodel-driven,withrelatively few bythe strike swinginthe Caledonianfrom N–Sinthe Norwegian robust geophysicalconstraints. Thiswaslargely dueto the lack of area to NE–SWinScotlandandmuch atIreland, andto more penetration bynormal-incidence seismic reflection profiling, ENE–WSW inthe extremesouthofIreland.Inaddition,the major which imaged the upperpart (typically 2–5s) ofthe succession, effects ofplatemargindynamicscanextendaconsiderable but which failed to resolvethe deepersedimentary architecture distance from the margins,manifested, for example, inregional andthe crustalandsub-crustalstructure.Withinthe past fewyears intra-plateexhumation ( Holford etal .,thisvolume). therehasbeenanincreasinguseofwide-angleseismic Finally,severalareasalongthe Atlantic Marginhavebeen reflection/refraction profiling, usingclose-spaced OceanBottom subjected to Cenozoic compressional/transpressionaldeformation. Seismometers,alongthe Atlantic Margin,to investigatethe deep The natureandtimingofsuch deformation inthe Faroe–Shetland structure( Mjelde etal .,thisvolume). Excitingandimportant Basin,Rockall Trough andHatton Bankareashasbeen results,providingconstraints on crustalmodels andreliable investigated by Johnson etal .(thisvolume)while Løseth& constraints on velocitiesandsedimentary andcrustalthicknesses, Henriksen (thisvolume)studied similarstructuresatthe areemergingfrom alongthe lengthofthe Atlantic Margin. Three- Norwegiancontinentalmargin. dimensionalcontrol off Norwaysuggests thatlarge thickness variations withinthe lowercrust occur beneaththe samebasin. Outstandingquestions Thishasimplications for differentialverticalmotion andthermal history ofthe overlyingbasin. The results from the integrated Despitethe recent advancesinnewdataandmodels ofthe Seismic ImagingandModellingofMargins (iSIMM)project evolution ofthe region,anumberofsignificant questions remain. ( Roberts etal .,thisvolume; Smith etal .,thisvolume)andthe Hatton DeepSeismic (HADES)project(Morewood etal .,this . The relationshipbetweenthe present-dayIcelandhotspot and volume)will hopefully goalongwaytoconstrainingsomeof the igneous strataofPalaeogenetimeisstill poorly understood thesemodels. The results from projects inNorwegian,Faroese, andrequiresfurtherstudytoresolvethe disputeconcerning UK andIrishwaters arepresented inthe followingpapers. These the control on igneous strata.Aretheythe result ofoneor more results show aremarkably consistent story regardingthe gross plumesorofnon-plume(i.e.intra-mantle)thermalconvection? crustalstructureatthe outermargins ofthe Atlantic Margin. . The timingofcrustalthinningatthe continent–oceanboun- Newaspects ofthe igneous history ofthe Atlantic Marginregion dary (COB)isuncertain. Doesitoccur prior to the onsetof weredescribed anddebated inanumberofpapers inthisvolume crustalseparation or isitsynchronous withseparation? (e.g. Lundin&Dore´ ,thisvolume; Roberts etal .,thisvolume; . Isthereadifference inthe nature/depth/timingofcrustal Mjelde etal .,thisvolume; Planke etal .,thisvolume; Haughton thinningbeneaththe sedimentary basins on the Atlantic Marginshelfandthatatthe COB? etal .,thisvolume). The hitherto generally accepted originfor the Whatarethe thermalimplications ofdepth-dependent stretch- igneous activity wasassociated withthe Icelandplume/hotspot. . ingmodels? Heatmaycomefrom eitheraplumeoffrom However,whilethe mainigneous phaseappears to be ofPalaeogene shallowermantlecirculation. Doesthe thermalanomaly drive age, evidence waspresented for olderigneous stratainthe region, the observed crustaltectonicsordoesthe crustalextension especially inthe outboardbasins. The geometry andextent ofthe triggerthe thermalanomaly? Whatarethe implications for large, underplated igneous bodyatlowercrustallevels atthe thermalmaturation historiesinthe Atlantic Marginbasins? continent–oceanmarginboundary hasnow beenwell constrained andappears to be amajor feature, developed atthe timeofbreak-up, Stratigraphyandplays alongmuch ofthe margin. Ithasbeenimaged andmodelled in Norwegian,UKandIrishwaters. The precisecontrols on the igne- The stratigraphyofthe deep-waterbasins ispoorly constrained. ous activity areamatterofsomedebateanduncertainty. Evidence However,asmentioned above, sparsewell dataandmoreabundant to support the traditionalIcelandplumehypothesisandalso seismic datahavesuggested the presence ofvariablethicknessesof evidence thatcausessomeofthe tenets ofthe hypothesistobe ques- UpperPalaeozoic to Cenozoic strata.The presence ofthick tioned (e.g.the relationshipbetweenthe present Icelandhotspot DevonianandCarboniferous successions inthe shallowerinboard Downloaded from http://pgc.lyellcollection.org/ by guest on September 25, 2021

736 P.M.SHANNON ET AL. basins iswell constrained (e.g. Nichols,thisvolume). These Recent advancesinstratigraphyandplays successions offersomelimited reservoirpotential,whilethe Upper Carboniferous iscoal-bearinginanumberofbasins (e.g. Anumberofmajor advancesinthe stratigraphic understanding PorcupineBasin) andhasgaspotential. However,the distribution andplays ofthe region haverecently beendocumented andmany ofthesesuccessionsbeneaththe youngerbasins ispoorly ofthesearedescribed inthe followingpapers ofthissection. New constrained.Red-bed Permo-Triassic syn-riftstratahavebeen datahavehelped to constrainthe location anddistributions ofthe described from most ofthe inboardbasins andhavereservoir pre-Cretaceous basins andthe thickness andthe agesofthe Meso- potential(e.g.Herries etal .1999). VariablethicknessesofJurassic zoic andCenozoic stratainanumberofthe deep-waterbasins. In strataarealso known,withadegree ofdiachroneity inthe age of addition,newplays havebeendeveloped andaseriesoftechniques the major Jurassic rifting.(LateJurassic riftingoccurred inthe havehelped towardsprovidingabetterunderstandingofthe basin PorcupineBasin(Sinclair etal .1994),withMiddleJurassic rifting development andpetroleum habitatofthe Atlantic Margin. inthe SlyneandErrisbasins. Inthe west UK basins the mainphase Acommon featureofmany ofthe Atlantic Marginbasins isthe ofpre-Cretaceousriftingterminated inthe MiddleJurassic. discrepancybetweenthe observed cumulativefault throws andthe However,platereconstructions suggest the mainphaseofrifting stretchingfactors calculated from subsidence calculations and betweenEuropeandGreenlanddid not beginuntilthe lateEarly crustalthicknesses. Thisaspectwasdiscussed inpapers presented Cretaceous (Aptian–Albian) (Hooper&Walker(2003)). This atthe conference.Hooper&Walker(2003)provided one riftingestablished the Faroe–ShetlandBasinandRockall Basinas explanation bydemonstratingthatmany faults inthe region are major sedimentary depocentreswhich weresubsequently modified flat-lyingatdepth, withsubstantialportions ofbasins,such asthe locally byrelatively minor early Tertiary riftingto createtheir Faroe–ShetlandBasin,beingunderlainbyfault planes. However, present-dayform. The mainphaseofriftinginthe basins off mid- Karner etal .(2003) proposed thatsyn-riftbasins maydevelop ina NorwayandNEGreenlandisofLateJurassic–earliest Cretaceous structuralsettingdifferent to thatofthe McKenzie (1978)model age ( Hamann etal .,thisvolume; Tsikalas etal .,thisvolume). andhavelarge-scalesag morphologyratherthanafault-dominated The major oilsource rocksinthe region lie withinthe Middleand profile.Onalarge scale, animprovement inthe understandingof UpperJurassic whilereservoirrocks(Strogen etal .,thisvolume), sedimentary basindevelopment hasbeenprovided bydetailed developed influvialtodeepmarinesuccessions,arepresent within mappingandbyreverseandforwardbasinmodelling.Roberts the MiddleandUpperJurassic successions. etal .(2003) presented anexampleof3Dflexuralback-strippingof Amajor erosionalunconformity atearliest Cretaceous levelis the Norwegianmargin,calibrated byrobust palaeobathymetric developed inmost ofthe Atlantic Marginbasins andmarksthe constraints (e.g.coals),which demonstratesamarked improve- effectivetermination ofJurassic rifting.Itissucceeded by ment overmoreconventional2Dback-stripping.Withthe latter typically deepmarine, shale-pronesuccessionswithlocal modelling, major discrepanciescanresult wherethe modelled submarinefansandstonedeposits. Somereservoirpotentialis profileisnot paralleltothe mainextension direction,or where present attheselevels. Localsyn-riftdeposits arerecorded inthe therehasbeenlateralmovement out ofthe planeofthe modelled Aptian/Albianofsomeofthe basins,producingsandy,deltaic section. However,therearestill problems inremovingthe effects stratainthe PorcupineBasin. Aptian/?Albiansyn-riftdeposits are ofinversion domes,wherelithification andburialprecedes also observed atthe LofotenMarginoff Norwayandinthe SW inversion andresults inanomalously high seismic velocitiesin Barents Sea ( Tsikalas etal .,thisvolume). UpperCretaceous, the sediments. Similarproblems also occur wheremass failure chalk- or marl-dominated strataareubiquitous throughout the (e.g.the Storrega Slide)hasoccurred inthe shallow section. region,reflectingaregionalsea-levelhighstand.Severalsandbo- Anumberofperched basins havebeenmapped alongthe diesweredeposited underdeep-waterconditions inthe area margins ofsomeofthe large deep-waterbasins (Naylor etal . betweenNorwayandGreenlandduringLateCretaceous timesand 1999; 2002). Thesearetypically largely ofpre-Jurassic age andare someofthesehavebeentargeted aspossiblereservoirs inthe the preserved remnants oflargerbasins located inthe footwall of western VøringBasin(Kjennerud&Vergara ,thisvolume). the Rockall Basindueto acombination offlankupliftand The early Cenozoic succession inthe Atlantic Marginis differentialsubsidence ofalarge sediment-starved basin. New typically represented through most ofthe basins byaregressive well datafrom the eastern marginofthe Irishsector ofthe Rockall succession ofsandstonesandsiltstones,deposited inavariety of Basinhaveproved the presence ofJurassic, Cretaceous and depositionalenvironments from deltaic to submarine.Recent Cenozoic strataon the flanksofthe basin(Haughton etal .,this work, reported inthisvolume, isbeginningto identifyEast volume). The Cretaceous stratareflectashallow-watersuccession, Greenlandasaprovenance area for coarse- andfine-grained clastic withanumberofcondensed sequencesandwitharapid sediments thatarenow on the eastern side ofthe Atlantic ( Larsen& Whitham ,thisvolume; Larsen etal .,thisvolume; Jolley etal ., differentialsubsidence inlatest Eocenetime.The newwell data thisvolume). Arapid relativeriseinsea-levelinlateEocenetime demonstratethe long-standingshallow natureofthe eastern ismarked byamajor,regionalsubmarineunconformity and basinmargin. Thisisalso supported byotherregionaldata( Stoker overlainbyadeepmarinesuccession oflatePalaeogeneand etal .,thisvolume)which demonstratesamajor change inregional Neogenestrata, characterized bythe onsetandrapid development oceanographyatthistimeandaregionalchange insediment ofcontouritedriftdeposits. ProgradingsequencesofOligocene?/ distribution from predominantly downslopetransport to along- Mioceneage atboththe NorwegianandNEGreenlandmargins slopetransport atlatest Eocenetime.The differentialsubsidence in represent the first signs ofNeogeneupliftofthe hinterlands the region wassuggested to be drivenbymantleconvection. ( Løseth&Henriksen ,thisvolume; Tsikalas etal .,thisvolume). Thepresence oflocalized UpperPalaeozoic strata, with Anearly Plioceneunconformity resulted from aglobalclimate potentialsource rocks,hasbeenindicated inanumberofregions change precedingthe onsetofmajor glaciation. Thick wedgesof such asthe Irishoffshorebasins. Anewgasplaywasprovenin Plio-Pleistocenesediments reflectupliftandglacialerosion of the SlyneBasinwiththe discovery ofthe Corrib GasField major areassurroundingthe NE Atlantic. ( Dancer etal .,thisvolume),wherePermiansandstonesare Incommon withothercontinentalmargins,many ofthe chargedbygassourced fromUpperCarboniferous coals. hydrocarbon plays tested withinthe region havebeenstructural However,the regionaldistribution ofsuch strataispoorly (tilted faults blocks) andinversion domes(Keep&Harrowfield , constrained and, hence, posesamajor question for the location thisvolume),withreservoirs atJurassic andCenozoic levels. andchargingofgas-proneplays inthe basins. Stratigraphic (pinchout) plays havealso beentargeted following Reports ofafirst discovery inthe Irishsector ofthe Rockall the recognition ofanelement ofstratigraphicaltrappinginthe Basin,combined withthe newgeologicaldatafrom the basinmar- prolific PaleoceneFoinavenandSchiehallion fields. gins,provide important leadsinto possibleplays. Itisreported that Downloaded from http://pgc.lyellcollection.org/ by guest on September 25, 2021

ATLANTICMARGIN: GEOLOGICAL REVIEW 737 the discovery,inthe Dooishprospect,encountered athick Permian boundary. Thesehaveprovided well-constrained geophysicaldata sandstonereservoirwithagascondensatehydrocarbon column. supportingarguments for depth-dependent stretchingacross the Major advancesinplayanalysisinrecent years havecomeabout margin. Thecausesandimplications ofthermalanomalies, withthe widespread acquisition of3Dseismic dataand resultinginpronounced igneous activity,especially withinthe complementary seismic dataanalysistechniques,such asAVO early Cenozoic, weredebated, withcontrastingmodels ofmantle analysis. Anumberofcasehistoriesarepresented showingboth plumeandshallowermantlethermalperturbations discussed. exploration successesandalso disappointments whereanomalies Newdataarepresented on the extent ofbasins,especially the wereshowntobe the result oflithologicalchangesand pre-Cretaceous basins andsub-basins,andon the extent ofthe geophysicalartefacts ratherthanfluid factors ( Smallwood& underlyingbasement terranesandcontrollingcrustallineaments. Kirk ,thisvolume). Advancesinbasinmodellingandotherexploration techniques, bothatbasinandprospectlevel,aredocumented.Drillingresults Outstandingquestions from someofthe deep-waterbasins provide newconstraints on the agesofstratainthe region anddemonstratethatthe Cenozoic . How diagnostic ofthe tectonic settingisthe overall evolution,andespecially the Neogene, hitherto oftenregarded as sedimentary geometry? Doesa‘sag’morphologyimply beingtectonically quiescent,wasanythingbut passive.Some thermalsubsidence or canitreflectasyn-riftsuccession examplesofnewplays,newfieldsandsomenon-discovery case without major syn-sedimentary faults? Thishassignificant historiesaredocumented andserveto illustratethe petroleum implicationsfor the thermalhistoryofthe sedimentary potentialandremainingrisksinthe region. succession aswell asfor the timingoftrapformation. Anumberofkeyuncertaintiesandremainingquestions have . How canthe effects ofinversion domesandlateralmass beenidentified.Thesecentreon exploringandunderstandingsome movement (e.g.slidesandslumps) be sensibly incorporated ofthe mechanisms ofbasinformation on passivemargins. These into flexuralback-stripped modellingtechniques? Atpresent basins,characterized bysignificant crustalthinning, appearto thisimpliessignificant problems for areasofsteepslopes,such differintheirformation andintheirstructuralandsedimentary asthe margins ofthe Rockall Basin. character,from low-extension,conventionalintra-platebasins. . The provenancesofthe reservoirsandstonesinthe SlyneBasin Therearealso anumberofmajor uncertaintiesregardingsediment arereported to lie to the east andto the south( Dancer etal ., provenance andtransport routesinto the Atlantic Marginbasins. thisvolume). Thisraisesquestions concerningsedimentary provenance, especially asthe Variscansuccession insouthern Irelandispoorly constrained inthe offshoreregion but is References predominantly inamuddyfaciesonthe onshoreregion. There Gjelberg, J.G.,Enoksen,T.,Kjærnes,P.,Mangerud, G.,Martinsen,O.J., isnoobvious major known Precambriansand-pronesource to Roe, E.&Va˚gnes,E.2001. TheMaastrichtianandDanian the south.Furtherworkon provenance isrequired, for thisand depositionalsettingalongthe eastern marginofthe MøreBasin for otherreservoirsuccessions,asthereistypically alack of (mid-NorwegianShelf):implicationsfor reservoirdevelopment ofthe diagnostic lithoclasts. OrmenLange Field. In :Martinsen,O.J.&Dreyer,T.(eds) . Whatisthe distribution ofsource rockswithinthe Atlantic Sedimentary Environments OffshoreNorway–Palaeozoic to Recent. Margin? Thereisquitealot ofuncertainty regardingthe source NorwegianPetroleum Society,SpecialPublication, 10,421–440. ofdiscoveries(e.g.Carboniferous source rockswerenot Hauser,F.,O’Reilly,B.M.,Jacob, A.W.B.,Shannon,P.M.,Makris,J.& penetrated inthe Corrib GasField). Dosource rocksotherthan Vogt,U.1995.Thecrustalstructureofthe Rockall Trough: deeply buried UpperJurassic shalesoccur inthe Møreand differentialstretchingwithout underplating. JournalofGeophysical Vøringbasins? The source-rock potentialofthe Cretaceous Research, 100,4097–4116. andPaleoceneisstill unresolved. Herries,R.,Poddubiuk, R.&Wilcockson,P.1999. Solan,Strathmoreand . How doesthe distribution ofunderplated material(large the back basinplay,West ofShetland. In :Fleet,A.J.&Boldy,S.A. thickness variations withinthe samebasin) affectthe thermal R.(eds) Petroleum GeologyofNorthwest Europe: Proceedingsofthe history andsource-rock maturation inthe deepbasins ofthe 5thConference.The GeologicalSociety,London,693–712. NorthAtlantic volcanic margins (e.g.Hatton,MøreandVøring Hooper,R.J.&Walker,I.M.2003. The Mesozoic andEarly Tertiary basins)? openingofthe NorthAtlantic andits impactonthe development ofthe Faroe–Shetlandbasinsystem. 6thPetroleum GeologyConference: Summary NorthWest EuropeandGlobalPerspectives,London,Abstracts,43. Karner,G.D.,Christie-Blick, N.&Bedregal,R.P.2003. Latesyn-rift The keytofindingoilandgasliesinunderstandingthe structural regionalsubsidence across the West AfricanandBraziliancontinental andsedimentary evolution ofbasins andtheirunderlyingcrust. margins:the roleoflowerplateductileextension. 6thPetroleum Thisisparticularly important infrontierregions. The Atlantic GeologyConference: NorthWest EuropeandGlobalPerspectives, Margin,lyingwest ofNorway,UKandIrelandisoneofthe London,Abstracts,48. largest,least explored andleast understoodregions ofEurope. McKenzie, D.1978.Someremarksonthe development ofsedimentary Although exploration hasproceeded inaratherhaltingfashion basins. EarthandPlanetary Science Letters, 40 ,25–32. duringthe past fewyears,recent encouragingdrillingresults from Naylor,D.,Shannon,P.M.&Murphy,N.1999. IrishRockall Basinregion severalparts ofthe margindemonstratethe exploration potentialof –astandardstructuralnomenclaturesystem .Petroleum Affairs thisfrontierprovince.The Atlantic Marginsession,bothoraland Division,Dublin,SpecialPublication. 1/99. Naylor,D.,Shannon,P.M.&Murphy,N.2002. Porcupine–Gobanregion posterpresentations,atthe 6thPetroleum GeologyConference –astandardstructuralnomenclaturesystem .Petroleum Affairs focused largely on attemptingto understandthe various large-scale Division,Dublin,SpecialPublication. 1/02. strandsofthe structuralandsedimentary development ofthe Roberts,A.,Corfield, R.,Matthews,S.,Kusznir,N.,Hooper,R.& region. Atotalof27 ofthe 35presentations atthe conference are Gjeldvik, G.2003. Structuraldevelopment andpalaeobathymetry at included aspapers inthe followingsection ofthe Proceedings . the NorwegianAtlantic margin:revealed by3Dflexural-back- Thesecapturethe essence ofthe recent datadevelopments and stripping. 6thPetroleum GeologyConference: NorthWest Europe understandingofthe geologicalsettingofthe region andhighlight andGlobalPerspectives,London,Abstracts,46. someofthe many remaininguncertaintiesofthe region. Sinclair,I.K.,Shannon,P.M.,Williams,B.P.J.,Harker,S.D.& Much newdeepcrustaldatahavebeenacquired across the Moore, J.G.1994.Tectonic control on sedimentary evolution ofthree Atlantic Margin,bothfrom the deep-waterbasins lyingon thinned NorthAtlantic borderlandMesozoic basins. BasinResearch, 6 , continentalcrust and, morerecently,across the continent–ocean 193–218.