fosi beritasedimentologi bs-23 march2012-libre

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Berita Sedimentologi HALMAHERA, SERAM & BANDA

Number 23 March 2012

Published byThe Indonesian Sedimentologists Forum (FOSI)The Sedimentology Commission - The Indonesian Association of Geologists (IAGI)

HHAALLMMAAHHEERRAA,, SSEERRAAMM &&BBAANNDDAA

Number 23

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HALMAHERA, SERAM & BANDA




Tectonic &Regional St ructure

of Seram & theBanda Arc

page 5

New I nsights into theGeological Evolut ion ofEastern I ndonesia from

Recent ResearchProjects by the SE Asia

Research Grouppage 21

I nterplay Betw eenSubmarine Deposit ional

Processes & RecentTectonics in the Biak

Basin, W estern Papua,Eastern I ndonesia

page 36

Number 23

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Number 2303/2012

ISBN 0853-9413

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Editorial BoardHerman DarmanChief EditorShell International Exploration and Production B.V.P.O. Box 162, 2501 AN, The Hague The NetherlandsFax: +31-70 377 4978E-mail: [email protected]

MinarwanDeputy Chief EditorPearl Oil (Thailand) Ltd.31st Floor, Shinawatra Tower 3, 1010 Viphavadi Rangsit Rd.Chatuchak, Bangkok 10900, ThailandE-mail:[email protected]

Fuad Ahmadin NasutionTotal E&P IndonesieJl. Yos Sudarso, Balikpapan 76123E-mail: [email protected]

Fatrial BahestiPT. Pertamina E&PNAD-North Sumatra AssetsStandard Chartered Building 23rd FloorJl Prof Dr Satrio No 164, Jakarta 12950 - IndonesiaE-mail: [email protected]

Wayan Ismara Heru YoungUniversity Link coordinatorLegian Kaja, Kuta, Bali 80361, IndonesiaE-mail: [email protected]

Julianta PanjaitanMembership coordinatorPT. Schlumberger Geophysics NusantaraData & Consulting ServicesJl. Mulawarman Km. 20, P.O.Box 117Balikpapan 76117, Kalimantan Timur, IndonesiaE-mail: [email protected]

Agus SuhirmantoSeruway Offshore Exploration LimitedWisma GKBI Building 37th FloorJl. Jend. Sudirman No. 28, Jakarta 10210E-mail: [email protected]

Visitasi FemantTreasurerPertamina Hulu EnergiKwarnas Building 6th FloorJl. Medan Merdeka Timur No.6, Jakarta 10110E-mail: [email protected]

Advisory BoardProf. Yahdi ZaimQuarternary GeologyInstitute of Technology, Bandung

Prof. R. P. KoesoemadinataEmeritus ProfessorInstitute of Technology, Bandung

Wartono RahardjoUniversity of Gajah Mada, Yogyakarta, Indonesia

Ukat SukantaENI Indonesia

Mohammad SyaifulExploration Think Tank Indonesia

F. Hasan SidiWoodside, Perth, Australia

International ReviewersProf. Dr. Harry DoustFaculty of Earth and Life SciencesVrije UniversiteitDe Boelelaan 10851081 HV AmsterdamThe NetherlandsE-mails: [email protected]; [email protected]

Dr. J.T. (Han) van Gorsel6516 Minola St.HOUSTON, TX 77007, USAwww.vangorselslist.comE-mail: [email protected]: www.vangorselslist.com

Dr. T.J.A. ReijersGeo-Training & TravelGevelakkers 119465TV Anderen, The NetherlandsE-mail: [email protected]

Published 3 times a year in February, June and OctoFOSI), a commission of the Indonesian Associa

Cover topics related to sedimentary geology, incl

Cover Photograph:

Bedded Cordierite-BearingDacites (Ambonites), AmbonIsland.

Taken from Watkinson et al.(BS#23, page 21)

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nd October.by the Indonesian Sedimentologists Forum (Forociation of Geologists (Ikatan Ahli Geologi Indonesia, IAGI).

y, includes their depositional processes, deformation, minerals, b

Cover Photograph:



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Forum Sedimentologiwan Indonesia,GI).

s, basin fill, etc.

Cover Photograph:



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erita Sedimentologi No. 23/2012will cover Halmahera, Seram,

Banda Arc and the northern portion ofwestern Papua. The far eastern part ofIndonesia has had more researchactivities recently due to theinvolvement of both Indonesian andforeign researchers; and alsocontributions from the oil andgas industry, who acquiredexploration acreages offered bythe government of Indonesiathrough several licensingrounds a few years ago.

The March edition of BScontains three articles on theBanda Arc and Seram Searegion and two articles on thenorthern part of western Papua.Kevin Hill will discuss thetectonic and regional structuresof the Seram and Banda Arc,while Herman Darman andPaul Reemst wrote theirobservations on seismicexpression of the geologicalfeatures in the Seram Sea. The thirdarticle on Banda Arc is written byAwang Satyana, where he discusses theorigin of the Banda Sea.

On western Papua, Claudia Bertoniand Juan lvarez Garca will discussthe interplay between tectonic activityand submarine depositional processes

in the Biak Basin; and J.T. van Gorseldiscusses nearly-forgotten paperswhere previous researchersdocumented their discoveries ofMiddle Jurassic Ammonites on thecoast of the Cendrawasih Bay. Thepresence of Ammonites within MiddleJurassic black shales in the

Cendrawasih Bay can have an impactto how explorationists see thepaleogeographic reconstruction of theregion while searching for MiddleJurassic reservoirs. We also include anarticle on new insights of the geologicalevolution of eastern Indonesia basedon recent research undertaken by SEAsia Research Group of the RoyalHolloway University of London.

We would like to welcome Dr. TomReijers, who joined us as anInternational Reviewer. Dr. Reiders is aconsultant with special interest incarbonate and deltaic sedimentologyand stratigraphy. Together with Prof.Harry Doust and Dr. Han van Gorsel,Tom will play a role in ensuring articles

published in BeritaSedimentologi to be of highscientific standard.

As of March 2012, FOSI havehad more than 410 memberswho joined our group throughLinkedIn. The statistics of ourmembers is provided in the nextpage. We hope that our articleswill be useful to all of you, ourreaders, and in the next issue, wewill still continue with a thematicissue on Timor and Arafura Sea.If you would like to contributeto BS No. 24, please get in touchwith us.

Best Regards,

MinarwanDeputy Chief Editor

I NSI DE THI S I SSUE

Tectonic and regional Structure of Seram & theBandaArcK. C. Hill 5

Middle Jurassic ammonites from theCenderawasih Bay coast and North Lenggurufoldbelt, West Papua: implications of aforgotten 1913paper J.T. (Han) van Gorsel

35Book Review : The SE Asian Getway:History and Tectonic of the Australian-Asia Collision, editor: Robert Hall et al T.J.A. Reijers

56

Origin of the Banda Arcs Collisional Orogen andthe Banda SeaA.H. Satyana 17

Interplay between submarine depositionalprocesses and Recent tectonics in the BiakBasin, Western Papua, Eastern Indonesia C.Bertoni & J.A. Garcia

42Book Review- Biodiversity,Biogeography and Nature Conservationin Wallacea and New Guinea (Volume 1),Edited byD. Telnov, Ph.D. H. Darman

58

New Insights into the Geological Evolution ofEastern Indonesia from recent ResearchProjects by the SE Asia Research Group I.M.Watkinson et. al.

21Seismic to Geological Modeling Workflow, anIntegratedApproach to determine the ReservoirQuality of a Fractured Limestone Reservoir A.K. Lopulisaet al.

47

Seismic Expression of Geological features inSeram Sea : Seram Trough, Missol-Onin Ridgeand Sedimentary BasinsH. Darman & P.Reemst

28A Guest Lecture and an AAPG Course at SultanHasanuddin University, Makassar, IndonesiaT.J.A. Reijers

53

B

Berita SedimentologiA sedimentological Journal of the Indonesia Sedimentologists Forum (FOSI),a commission of the Indonesian Association of Geologist (IAGI)From the Editor

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About FOSIhe forum was founded in 1995 asthe Indonesian Sedimentologists

Forum (FOSI). This organization is acommu-nication and discussion forumfor geologists, especially for those dealwith sedimentology and sedimentarygeology in Indonesia.

The forum was accepted as thesedimentological commission of theIndonesian Association of Geologists(IAGI) in 1996. About 300 memberswere registered in 1999, includingindustrial and academic fellows, as wellas students.

FOSI has close international relationswith the Society of SedimentaryGeology (SEPM) and the InternationalAssociation of Sedimentologists (IAS).Fellowship is open to those holding arecognized degree in geology or acognate subject and non-graduateswho have at least two years relevantexperience.

FOSI has organized 2 internationalconferences in 1999 and 2001,attended by more than 150 inter-national participants.

Most of FOSI administrative work willbe handled by the editorial team. IAGIoffice in Jakarta will help if necessary.

The official website of FOSI is:http://www.iagi.or.id/fosi/

Any person who has a background in geoscience and/or is engaged in the practising or teaching of geoscience or its relatedbusiness may apply for general membership. As the organization has just been restarted, we use(www.linkedin.com) as the main data base platform. We realize that it is not the ideal solution, and we may look for otheralternative in the near future. Having said that, for the current situation, LinkedIn is fit for purpose. International membersand students are welcome to join the organization.

Total registered members :411 a

T

FOSI Membership

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he forum was founded in 1995 asthe Indonesian Sedimentologists







Any person who has a background in geoscience and/or is engaged in the practising or teaching of geoscience or its relatedbusiness may apply for general membership. As the organization has just been restarted, we use(www.linkedin.com) as the main data base platform. We realize that it is not the ideal solution, and we may look for otheralternative in the near future. Having said that, for the current situation, LinkedIn is fit for purpose. International membersand students are welcome to join the organization.

Total registered members : as of March 2 012

T

FOSI Membership

Page 4 of 61



he forum was founded in 1995 asthe Indonesian Sedimentologists







Any person who has a background in geoscience and/or is engaged in the practising or teaching of geoscience or its relatedbusiness may apply for general membership. As the organization has just been restarted, we use LinkedI n(www.linkedin.com) as the main data base platform. We realize that it is not the ideal solution, and we may look for otheralternative in the near future. Having said that, for the current situation, LinkedIn is fit for purpose. International membersand students are welcome to join the organization.

Total registered members :

T

FOSI Membership

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Tectonic and Regional Structure of Seram andthe Banda ArcKevin C. HillOil Search Ltd., Sydney, NSW, AustraliaE-mail: [email protected]

Seram and the Banda Sea lie betweenthe passive margin tectonics ofAustralias Northwest Shelf and theactive margin tectonics of NewGuinea, both of which have played animportant role in the structure, faciesdistribution and hydrocarbonprospectivity of the area.

A restored cross section across Seramand a 3D model reconstruction of theMiocene evolution of the Banda Arcreveal the history of the area. TheProto-Banda Sea is considered to haveformed in the Permian, including amarginal basin with Permian oceaniccrust. Extension was terminated byTriassic orogenesis in New Guineasupplying vast amounts of Triassic

detritus (Kanikeh) to the stretchedBanda margins. In the Late Triassic,the sediment supply was diminished inpart due to the renewed onset ofextension along the New Guineamargin. It is notable that the Triassicorogeny was very similar to theMiocene to Recent orogeny in NewGuinea. As Triassic sediment supplywas reduced, carbonate banks werelocally built up (Manusela reservoir)surrounded by starved source rockfacies. The margin subsided in theJurassic and was starved of sedimentuntil the Tertiary when renewedtectonic activity in New Guineasupplied distal carbonates and marls,mainly in the Miocene. Around 10 Ma,the Indonesian Arc impinged on thePermian oceanic lithosphere of theProto-Banda Sea, which was thenrapidly subducted, sinking under itsown weight. The Arc advanced rapidlyeastwards towards Timor and Seram,generating a collisional margin inTimor, but a strongly transpressionalmargin in Seram. The first phase ofcollision in Seram at ~6 Ma involvedoverthrusting of an accretionary prism,largely comprising Kanikeh sediments,but also some oceanic fragments. Thesecond phase of orogenesis in Seraminvolved thrusting of the continentalmargin beneath the overthrust, creatinghighly fractured antiformal stacks inthe Manusela encased in Kanikeh sealand source rocks, as in the Oseiloilfield. To the east an imbricate thrustzone has formed in the Cretaceous andTertiary sequences which is nowimpinging on the Misool-Onin Arch.

Figure 1 . Tectonic setting of theBanda Arc and simplified geology mapof Seram, courtesy of Kufpec (Indonesia)Limited, showing the location of theregional cross section.

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I NTRODUCTI ON

Seram and the Banda Sea area liebetween the passive margin tectonicsof Australias NW Shelf and activemargin tectonics in New Guinea(Figure 1). The stratigraphy andtectonics of both areas need to betaken into account. Here, we draw onthe tectonics and stratigraphy of theBrowse Basin on the NW Shelf (Hill &Hoffman 2004; Hoffman & Hill 2004),the nearest area unaffected byMesozoic and Tertiary orogenesis, andcompare it to the tectonics andstratigraphy of New Guinea (Hill &Hall 2003). It is necessary to makecomparisons with such regions as thestratigraphy and facies variationsaround the Banda Arc are poorlyknown and there is relatively littlestructural data.

To fit the Seram stratigraphic section(Figure 2) into a regional context it wascompared to that in the Browse Basinalong Australias NW Shelf. A 500 kmlong cross-section from the BrowseBasin was balanced and restoredshowing the evolution of the marginand growth of the stratigraphicsequences (Hoffman & Hill 2004). Forthe Browse Basin region Struckmeyeret al (1998) indicated:- Upper Carboniferous to Lower

Permian extension Upper Permian to Lower Triassic

subsidence Upper Triassic to Lower Jurassic

compression and inversion Lower to Middle Jurassic extension Upper Jurassic to Paleogene

thermal subsidence Middle to Upper Miocene

inversion.

Hill & Hoffman (2004) showedsubstantial thinning of the outermargin crust (the Scott Plateau) in theMiddle Jurassic, as it stretched from 60to 120 km in length and subsidedpermanently into 2-3 km water depth.Towards the continent, this was boundby a long-lived crustal scale faultmarking a fundamental change incrustal thickness such that thecontinentward margin remained inrelatively shallow water, usually shelfaland always

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Late Devonian Tasman orogenesis(including the Birds Head), withCarboniferous strata absent

Permian extension in the west (Hillet al 2002)

Early Triassic orogenesis Middle Triassic granitic intrusions Late Triassic extension and

orogenic collapse Jurassic rifting and Cretaceous

passive margin Paleocene rifting in eastern New

Guinea and the Birds Head Neogene orogenesis, with the acme

in the Early Pliocene (e.g. Kendricket al 1995; 1997; 2003)

Pleistocene post-orogenic collapsein the Birds Head and eastern NewGuinea.

This has particular relevance to theSeram-Banda area as the margin to thenorth was in compression in the Earlyand Middle Triassic so was upliftedand eroded supplying significantvolumes of Triassic sediment.

The Neogene tectonic model used herefollows that of Hall (2002), whichshows old oceanic crust in the BandaSea consumed by subduction rollbackfrom 10 Ma to the Present. Halls(2002) model shows over 1000 km ofoceanic crust consumed in ~6 Ma,indicating very fast microplatemovements of ~10-15cm/year. Thissubduction rollback was the maindriving force for the Pliocene toRecent tectonism around the BandaArc causing rapid and changingdeformation.

Halls (2002) restoration at 10 Masymbolically shows Seram and Timoroverlying thinned continental crust andSeram is shown further away from thecontinental margin than at Present totake account of Pliocene to Recentshortening. However, the Timormargin is not similarly restored. At 10Ma the subduction zone beneath thesouthward migrating IndonesianArchipelago had just reached theBanda Sea old oceanic crust. Hall(2002) shows that the subduction zonejumped to the south from 10-8 Ma,possibly trapping a portion of the oldcrust in the overriding plate, whichends up in the Weber Deep. Thesubduction jump initiated a newsubduction zone in which the very old,

cold, thick and dense Banda Seaoceanic crust was subducted. Thiscrust then sank of its own accord andpulled the subduction zone across theBanda Sea area in a horseshoe shape.The overlying arc migrated south andeast and the northern margin waslargely a strike-slip margin. Backarcspreading occurred NW of the arc inthe present Banda Sea. Hall (2002)infers that the subduction zone andbackarc spreading ridge swept alongthe southern margin of Seram from 6-4Ma and that most of the old Banda Seaoceanic crust was consumed by 3 Ma,the time of orogeny in Timor. From 3Ma to the Present, Hall (2002) shows

movement of the Birds Head andexpansion of the Banda Sea producingcompression and shortening in Seram.

OBSERVATI ONS

A crucial observation to be tied intothe Hall (2002) model is that theoverthrust sediments in Seramcomprise a thick Triassic sequence,mostly deposited in deep water (Kemp& Mogg 1992). It is here inferred thatthis deep water Triassic section wasthrust over Seram around 6-4 Ma whenthe oceanic crust to the south wassubducted.

Figure 3 . 3D visualisation of the present tectonic setting of the Banda Arc, firstlywith the overriding plate and then with the overriding plate removed to reveal thesubducting slab.

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This is consistent with the 6-5 Macooling age on the Seram Ultramaficcomplex in SW Seram (Linthout et al.1996). Further, we suggest that theTriassic section was scraped off thedowngoing slab as an accretionaryprism and emplaced onto the adjacentmargin. Importantly, this implies thatthe underlying oceanic crust wasPermian or older. Snyder et al (1996)show subsea contours in depth on thedowngoing oceanic plate south ofSeram, based on earthquakeseismology. It is clear that the slab isbroken to the south of western Seram,consistent with the strike-slip margin.Projecting the slab upwards towardseastern Seram it meets the island at thepresent south coast (Figure 3).

Other important observations include:

1. The offshore Seram seismic data tothe north of east Seram showmultiple thrust repeats of Tertiaryto Recent sediments (Pairault et al2003a/b) indicating >50 kmshortening. This observation iscrucial to the structuralinterpretation as it indicates thin-skinned deformation and a largeamount of shortening.

2. The geological map of NE Seramshows a 3D window of Triassicoutcrop in the Nief sedimentsconsistent with an underlyingantiformal stack.

3. The Triassic to Early JurassicKanikeh sediments were regionallythrust over the deep water Niefbeds in the earliest Pliocene (e.g.Kemp & Mogg 1992). This mostlikely occurred as an accretionaryprism in deep water, similar to the

Liguride sequences in northern Italy(e.g. Hill & Hayward 1987).

4. Effective basement in the Seramarea is Permian. Along the Misool-Onin Arch, a thin Jurassic sequenceoverlies the Permian Ainimsedimentary section. To thesouthwest, a thick Triassic section ispreserved, suggesting Permianrifting.

5. Contours on the downgoing slabbeneath the Banda Arc indicate thatit projects up to the southern endof Seram Island. This is interpretedto show that the southern end ofSeram Island was a long-termcrustal and/or lithosphericboundary with stronger, thicker andmore buoyant continental crust tothe north.

6. Regional structural restoration ofthe duplex in Late Triassic to Mid

Figure 4 . Schematic regional cross-section across Seram, with a vertical exaggeration of x ~2.5. See Figure 1 for location.

Figure 5 . Schematic cross sections of the Triassic to Miocene evolution of the Seram margin (VE x 2.5).

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Jurassic Manusela beds indicatesthat prior to compression thesouthern limit of the Manuselacoincided with the southern marginof the island. There it passed intothick Triassic Kanikeh beds,suggesting a major crustal scalenormal fault along what is nowSerams southern margin.

REGI ONAL CROSS SECTI ON

The section trends 040-220O, from theMisool-Onin arch in the northeast tothe subducted crust southwest of theisland of Seram (Figure 4). The NEend of the section shows the Misool-Onin High, which was uplifted anderoded in the Late Miocene (e.g.Pairault et al 2003a/b). This area isinterpreted to lie on continental crustof normal thickness. Themorphology of the High and theregional dip into the Seram Trough areconstrained by the seismic sectionspublished by Pairault et al (2003a/b).The thin Pleistocene sediments in theSeram Trough have been mildly foldedand thrust (Pairault et al 2003a/b) asthe deformation continues to thepresent day, although this detail is notshown on the regional section.

Between the axis of the Seram Troughand the northern coast of Seram animbricate stack of Paleogene andNeogene Upper Nief beds isinterpreted. In some places theimbricate Upper Nief Beds have beencut by late stage normal faults, creatinglocal basins above it in whichPleistocene Fufa Beds were deposited.

These faults probably sole into thesame regional detachment andcontribute to toe-thrusts in the SeramTrough (Pairault et al 2003a/b). Thelate stage normal faults are notillustrated on the regional section, inorder to clearly illustrate the inferredcompressional tectonics. The regionaldetachment is interpreted to lie within

Figure 6 . Schematic cross sections of the Late Miocene to Present evolution of the Serammargin (VE x 2.5)

Figure 7 . 3D visualisation of the inferred tectonic setting of the Banda Arc at 9 Ma.

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the Jurassic and Cretaceous Kola andLower Nief beds, thin regional deep-water deposits (Figure 4).

Beneath the northern part of the islandof Seram lies the Manusela duplex.The East Nief well clearly show thatthe Manusela Limestone is overlain byconformable Late Jurassic Kola Shaleand Cretaceous Lower Nief beds andthen a few hundred metres thickimbricate zone of mixed Upper Niefand Triassic Kanikeh Beds (Kemp &Mogg 1992). This is all overlain by athick sequence of deformed TriassicKanikeh beds, usually deep-waterdeposits, but reported to contain somethin coals. The Triassic Kanikeh Bedsare here interpreted to have beenthrust over the Manusela carbonateswhen the latter were flat, resulting insome of the Upper Nief beds beingincorporated into the regional thrustzone to make the imbricate zone.Subsequently the Manusela duplexdeveloped beneath, with the imbricatezone as a roof-thrust.

The SW limit of the Manusela duplexcorresponds to a facies change to time-equivalent Kanikeh beds. Thedeformation shown in the Kanikehbeds on the cross-section is highlystylolised as it is very complex andpoorly constrained by sparse dip dataand no seismic data. Many otherinterpretations are possible, includinginvolving basement thrusts and/orophiolites. The interpretation shownhere is simply a model based on theassumption that thick Kanikeh (Ki)beds were originally deposited onthinned continental (intermediate)crust and thinner Kanikeh (Ko) bedswere deposited on Permian oceaniccrust.

TECTONI C MODEL

The tectonic model presented here isillustrated by regional schematicstructural sections shown at ~2.5:1V.E. (Figures 5 and 6) and by a seriesof block diagrams illustrating the LateMiocene to Pliocene evolution of theBanda Sea (Figures 7-12), following themodel of Hall (2002).

Perm ianRifting occurred in the area that is nowthe Banda Sea, probably by NEmovement of the Birds Head alongthe long-lived Halls Creek MobileBelt, possibly associated with clockwiserotation of the Birds Head (Norvick2003a/b, Metcalfe 1996, 2002 Charlton2001). This is interpreted to have ledto the formation of ?Middle to LatePermian oceanic crust in the Banda Seaarea. A major SW-dipping normalfault was generated along the southernmargin of the Misool-Onin High,allowing subsequent deposition of

Triassic and Jurassic sediments to thesouthwest, with no Triassic and littleJurassic on the High (e.g. TBF-1 well;Perkins & Livsey 1993). A second SW-dipping, crustal-scale normal fault wasgenerated in the area of what is nowthe southern margin of Seram withthinned continental crust to the southallowing deposition of very thickTriassic and Jurassic sediments to thesouthwest. Prior to the formation ofoceanic crust even further to the south,Permian metamorphic core complexesmay have been emplaced, probably inshallow water or emergent. At this

Figure 8 . 3D visualisation of the inferred tectonic setting of the Banda Arc at 7.5 Ma,firstly with the overriding plate and then with the overriding plate removed to reveal thesubductingslab.

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stage the margin was similar to thosealong strike to the southwest in theBrowse Basin.

TriassicThe major event in the Triassic was theorogeny along the New Guinea margincontinuing into the New Englandorogeny down the east coast ofAustralia (Hill & Hall 2003). Triassicorogenesis in New Guinea wasprobably similar to that in the LateMiocene to Pliocene that is apparenttoday. Regional compression andmountain building took place in theEarly Triassic followed by graniticintrusions in the Middle Triassic andextensional collapse in the LateTriassic.

Triassic orogenesis placed the BandaSea area into compression, inhibitingfurther subsidence and possiblycausing partial obduction of Permianoceanic crust and local inversion.However, the main effect was amassive influx of Triassic detritus fromthe mountains in New Guinea, fillingthe basins with Triassic Kanikehsediments, mainly regional turbidites(Figure 5). It is probable that aconsiderable portion of the detritusentered the basin from the east alongthe axis of the Banda Sea.

Extensional collapse in New Guinea inthe Late Triassic gradually reduced thesedimentary supply and promotedregional subsidence in the Banda Seaarea. The area that is now Seram, andits equivalents along strike to theWNW-ESE, became a shelf-edge highthat was remote from clasticsedimentation, resulting in thedevelopment of a Manusela carbonatebank 40-50 km wide (Figure 5) andperhaps hundreds of km long. It isprobable that several of these largecarbonate banks were deposited alongthe shelf margin rimming the BandaSea, such as the Bogal Limestone inMisool (Norvick 2003a/b). As themargin strikes east-west, it was possibleto have carbonate banks, like AndrossIsland, over 1000s of km in the sameclimatic zone (for instance the TriassicKuta Limestone was deposited coevally1000 km to the east in Papua NewGuinea). These banks may have beenseparated by lower areas throughwhich clastic sediments were suppliedto the deeper water offshore. There,

deposition of Kanikeh clastic detrituscontinued, sourced both from the eastand through the gaps betweencarbonate banks.

JurassicAlong Australias NW Shelf and inNew Guinea, Early Jurassic rifting ledto Middle Jurassic (Callovian) break-upand Late Jurassic regional subsidence.The regional subsidence is clearlyreflected in the sedimentary record inSeram, although it may have

commenced earlier in the Jurassic.Carbonate deposition continued in theEarly and Middle Jurassic in the area ofSeram and along strike, adjacent tostarved basins allowing deposition ofexcellent oil source rocks in the SamanSaman Formation (Figure 5). To thesouthwest, clastic deposition continuedin the Early Jurassic, sourced from theeast, but gradually dwindled due tocontinued subsidence and flooding,again facilitating deposition of sourcerocks.

Figure 9 . 3D visualisation of the inferred tectonic setting of the Banda Arc at 6 Ma,firstly with the overriding plate and then with the overriding plate removed to reveal thesubducting slab.

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In the Middle Jurassic, it is proposedthat sands were shed from theemergent Birds Head basement andwere deposited in a rim around theKemum High (e.g. Hill et al. 2002).These sands were also deposited in thenorthern Bintuni Basin forming thereservoir for the giant TangguhComplex gas fields. It is interpretedthat such sands prograded across theshallow water basin between theMisool-Onin High and the Manuselacarbonate bank. These regional sandswere deposited over the southernmargin of the carbonate bank,inhibiting its development. At thistime the Manusela carbonate bankremained high and may haveundergone karstification during timesof sea level low.

In the Late Jurassic, the entire marginunderwent regional subsidence,drowning the carbonate bank andstarving the area of sedimentsthroughout the Late Jurassic and theCretaceous, allowing deposition of acondensed sequence of Kola Shale andLower Nief Beds (Figure 5).

CretaceousThe Seram and Banda Sea area was indeep water throughout the Cretaceousand starved of sediment. The areabetween the Misool-Onin High andsouthern Seram was probably in a fewhundred metres of water, but thethinned continental crust to the southsubsided to water depths of a few kmsand the Permian oceanic crustprobably subsided to depths of ~5kms. Lower Nief deep-waterlimestone and chert condensedsequences were deposited regionally.

PaleogeneIn the latest Cretaceous to Paleogene,eastern and possibly northern NewGuinea, including part of the BirdsHead, were uplifted due to rifting (Hill& Hall 2003). Western New Guineaunderwent continued subsidenceallowing deposition of the New GuineaLimestone mainly in very shallowwater, but with deep-water limestonesand shales on the deeper part of theshelf. Thick New Guinea Limestonewas deposited on the Misool-OninArch, which became a regionaldepocentre, although always in shallowwater. The high carbonate

productivity, combined with shalederived from the Paleocene uplift,allowed deposition of deep-water toshelfal carbonate and shale (UpperNief Beds) along the Seram marginbetween the Misool-Onin High andthe southern limit of Seram (Figure 5).

MioceneCarbonate productivity and regionaldeposition of New Guinea Limestoneaccelerated along the entire northernmargin of the Australian Plate,producing prograding thick shallowwater reefs and shelf carbonates fromQueensland through New Guinea andalong Australias Northwest Shelf. Inthe Seram area this resulted in thickOpenta and Kais Limestone on theMisool-Onin High that progradedsouth into the basin towards Seramdepositing the Upper Nief Beds asshelfal carbonates. Water depthsdecreased in the Seram area as thickUpper Nief beds were deposited acrossa basin up to 150 km wide. Locally,water depths reached the photic zoneallowing deposition of reefalcarbonates similar to the KaisLimestone in the Salawati Basin.(Figure 5). These may have beenlocated above sites of local inversionassociated with the onset ofcompression in New Guinea towardsthe end of the Middle Miocene (14-12Ma), continuing through the LateMiocene. Kais reefs may be

anticipated above the Manusela shelfedge as a long-lived structural high.These would now lie in the Upper NiefImbricates along the north coast ofSeram.

Late Miocene to PresentThe compressional deformation of theBanda Arc, focussed on Seram, isshown on a series of block diagrams(Figures 3 and 7-12) and on schematicsections trending to 0400 that passesthrough the Oseil-1 well in Seram(Figure 6).

9 Ma (Figure 7)Fold and thrust deformation in theFold Belt had just commenced inmainland New Guinea, but had not yetaffected the Seram area, exceptperhaps for local inversion. Thesubduction zone beneath theIndonesian archipelago had reachedthe tip of the Birds Headmicrocontinent and the subductionzone jumped southward (Hall 2002) tothe limit of old, cold and densePermian oceanic crust that was moredense that the underlying mantle andtherefore ready to sink. The oceaniccrust captured in the overriding platemay have been Permian in age. Itbecame a forearc and now lies beneaththe Weber Deep.

At this time the Banda Sea comprisedfour main zones arranged in a


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horseshoe around the sea (Figure 7).In the middle was Permian oceaniccrust overlain by a relatively thinsequence of Triassic to Miocenepelagic sediments. Around this was abelt of Kanikeh (Ko) shallow to deep-water sediments and Jurassic toMiocene pelagic sediments overlyingPermian oceanic crust, ringed by theContinent-Ocean-Boundary (COB).The next belt comprised thick Kanikeh(Ki) sediments and thin Jurassic toMiocene deep-water sediments, inmoderate water depths, overlyingthinned and stretched (intermediate)continental crust. This zone isinterpreted to have been bound by afundamental crustal boundary fromthin to thicker continental crustmarked by major normal faults and along-lived shelf-edge, coincident withthe southern limit of Seram. The shelfedge was marked by thick Manuselacarbonates on regional highs or horstsand a thick Upper Nief sequence inrelatively shallow water (Figure 6). Atthis time, West and East Seram mayhave been separate (Hall 2002) at leastwithin the cover sequences.

7 .5 Ma (Figure 8)The old, cold and dense Permianoceanic crust had started sinking of itsown accord pulling the subductionzone into the Banda Sea area in anarcuate shape. As the overriding platemoved towards the east theTukangbesi (South Sulawesi) Spur ofthin continental crust moved with it(Hall 2002). As the oceanic crust wassubducted beneath the overriding plateadjacent to the Seram margin, theKanikeh (Ko) beds were scraped off toform a very wide and thickaccretionary prism. Along the Serammargin, motion of the overriding platerelative to the subducting plate was ofa left-lateral strike-slip nature (Figure8). Compressional thrusting within theaccretionary prism along this strike-slipzone was oblique to the wrenching,with faults striking ~ 330-3500. Theaccretionary prism was thrust over therelatively deep-water Kanikeh (Ki)sediments overlying thinnedcontinental crust. As the down-goingPermian oceanic slab was subducted ina horseshoe shape it was stretched withincreasing depth and a tear formedalong the axis close to the Serammargin (Figure 8).

At this time compressionaldeformation continued in thenortheastern Lengguru Fold Belt, andminor compressional deformation andregional inversion and erosionoccurred on the Misool-Onin High.

6 Ma (Figure 9) .Subduction of the Permian oceaniccrust continued along a curvedsubduction zone that advanced acrossthe Banda Sea. The tear in thedowngoing slab propagated to the eastand widened. This allowed upwellingof underlying magma, creating a

spreading ridge behind the volcanicarc, which developed a back-arc basin(Figure 9). The northeast end of thisbuoyant spreading ridge migrated eastalong the Seram margin subjecting themargin to sinistral transpressionalforces.

By 6 Ma, the eastward vergingaccretionary prism ahead of thesubduction zone had been thrust overthe thick Kanikeh sequence lying onthinned continental crust immediatelysouth of eastern Seram. This involvedrelative shortening of up to 100 km

Figure 11 . 3D visualisation of the inferred tectonic setting of the Banda Arc at 3 Ma,firstly with the overriding plate and then with the overriding plate removed to reveal thesubducting slab.

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and is similar to the overthrusting ofthe Liguride accretionary prism in theLate Miocene to Pliocene in theApennines, Italy (e.g. Hill & Hayward,1987). As the thick Kanikeh sequencehad previously been in deep water, it islikely that the overthrust accretionaryprism remained below sea level or justemergent (Figure 6). It is unlikely thata significant thickness of Kanikeh wasthrust up the shelf-edge and over theManusela carbonates at this time.

To the south, the subduction zone hadreached the outer limits of the Timormargin generating a thick and wideaccretionary prism that had started tothrust over the extended continentalmargin. If the model of Keep et al(2003) is correct the Timor collisionmay have started earlier due to thesubduction zone reaching a largepromontory to the west of Timorincorporating the island of Sumba,which was uplifted at ~8 Ma.

5 Ma (Figure 10) .The same processes continued from 6to 5 Ma, but the subduction zoneswept past the southern margin ofeastern Seram and the spreading ridgewas directly offshore from easternSeram, maintaining a transpressionalENE to NE-directed stress. WestSeram started moving sinistrally to joineast Seram according to Hall (2002).To the south the accretionary prismhad been thrust over Timor and truearc-continent collision commenced(Figure 10). In the Birds Head theLengguru Fold Belt had formed withmountains at least 1 km higher thantoday.

3 Ma (Figure 11) .By the Late Pliocene almost all of thePermian oceanic crust in the Banda Seahad been subducted and the Timororogeny was well underway, locking upsubduction to the south. Compressionin the Lengguru fold belt was waningand it was being eroded. The entirerim of the Banda Sea was placed intocompression, more or less radiallyaround the arc. This was probably thestart of compression within continentalcrust in Seram, probably towards 0350,resulting in structures striking to~3050. West and East Seram hadjoined and compression occurredwithin the thick Kanikeh sequenceoverlying thinned continental crust to

the south of the main shelf-edge fault(the southern margin of Seram). From3 to ~1 Ma, the Kanikeh sequence wasshortened as a duplex and theoverlying Kanikeh accretionary prismwas thrust to the NE over theManusela sequence on the shelf. Theaccretionary prism acted as a bulldozerpushing and deforming the Upper Niefsequence in front of it, initially withoutdeforming the strong, underlyingManusela carbonates. An imbricatefault zone formed, of varyingthickness, incorporating underlyingUpper Nief beds and overlyingKanikeh accretionary prism beds.During this thrusting, the Manuselacarbonates were probably buried todepths of several km for the first time(Figure 6). In the Late Pliocene theKanikeh accretionary prism was erodedsupplying sediment to the uppermostNief Beds for the first time.

The tear in the downgoing oceanic slabwidened and propagated towards eastSeram. This allowed yet moreupwelling of buoyant magma andbackarc spreading, perhaps also drivingcompression around the periphery ofthe Banda Arc. Propagation of the teartowards the east end of Seram meansthat strike-slip motion was facilitatedalong the tear, allowing varyingdeformation in Seram compared to thearea to the southeast, e.g. morecompression in Seram.

1 Ma (Figure 12)Around 2 Ma, extensional collapsecommenced in the northeasternLengguru Mountains indicating theremoval of compressional forces alongthe NE margin of the Birds Head. Tothe south, the compressional orogenyin Timor dwindled and renewedsubduction commenced towards thesouthwest. Compression continuedfrom the direction of the Banda Seatowards the northeast due to thelocking up of subduction andcontinued spreading associated withsteepening of the subduction zone andwidening of the tear within it. Hall(2002) infers that the Birds Headmoved ~100 km to the NE along theHalls Creek Mobile Zone. From 1 Mato the Present compression increasedalong the northern margin of theBanda Sea, perhaps associated withmovement back to the southeast of theBirds Head (Hall 2002) and due tosinistral movement along the Tarera-Aiduna Fault Zone.

The intensified compression occurredtowards 0400, resulting in structuresstriking 130-3100 in Seram and cross-cutting (tear) faults striking 040-2200.This compression was manifested in aduplex in the Manusela carbonateswith a roof thrust at the base of theoverlying Kanikeh accretionary prismsequence, passing northeast into thebase of the Upper Nief sequence.Consequently, there was simultaneous


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thrusting of the Manusela carbonatesand the Upper Nief sequence to thenortheast, within the Seram Trough.Compression was particularly focussedin the Oseil area forming a highlyfractured antiformal stack in theManusela carbonates. The location ofthis may be related to the offshore tearin the subducting slab and/or to anextra wide sequence of Manuselacarbonates. During formation of theManusela duplex, the adjacent oilsource rocks were deeply buried forthe first time and generated andexpelled hydrocarbons, whichcontinues to the Present.

0 Ma Present Day (Figure 3)The compressional regime present at 1Ma continued with thrusting towards0400. The thrusted Manusela andUpper Nief beds placed a considerableload on the margin of the Birds Headmicro-continent causing it to subside,creating the Seram Trough. Thebottom of the trough is the front ofthe fold and thrust belt within theUpper Nief sequence. The reliefbetween the shoreline and the bottomof the Trough has allowed minorextensional collapse within the UpperNief thrust sequence resulting in someRecent toe-thrusts.

DI SCUSSI ON

The tectonic model and cross sectionsthat have been presented indicate thatthe Seram margin has been subjectedto over 100 km of shortening withoverall shortening of the order of 50%.As the section is roughly perpendicularto the margin and the compression isinferred to have been highly oblique(sinistral transpression) the trueshortening may be considerablygreater. Much of the shortening isinferred to have been taken up byoverthrusting of the accretionaryprism, but there was also substantialshortening of the continental marginsediments, as indicated by theantiformal stack in the Manusela Bedsand the thrusting of the Upper Niefbeds to the northeast of Seram.

In the Oseil and East Nief area, theManusela carbonate reservoir porositydominantly occurs in fractures. Thestructural-tectonic model indicates twodifferent directions of thrusting, which

will have a bearing on the orientationof fractures within the Manuselacarbonates. The Early Pliocenethrusting was towards 070O+/-10O andopen fractures at that time are likely tohave been parallel to this direction.Late Pliocene to Present thrusting wastowards 040O including in theManusela carbonates, and openfractures are likely to be parallel in thesame orientation. However, a fullevaluation of the stress field throughtime is needed to predict the full range,intensity and width of fractures.

The Oseil and Bula oilfields, and theprolific seeps along Nief Gorge, whichtrends 040O, demonstrate the LateTriassic to Early Jurassic sourcesystem. The structural model suggestsrapid Pleistocene burial and heating byoverthrusting, so that the system isactive today. In terms ofhydrocarbons, it is possible that thereare more Manusela carbonate plays,but there may also be reef plays in theUpper Nief duplexes and structural-stratigraphic traps in the inferredMiddle Jurassic sandstone reservoir.

Comparing Seram to Timor, whilstthere are broad tectonic similarities dueto their positions around the BandaArc, there are structural andstratigraphic differences. As Seram layalong the northern margin of theproto-Banda Sea, it is likely that itreceived more Triassic sediment thanthe Timor margin due to Early to MidTriassic uplift and erosion in NewGuinea. In the model presented here,this would have led to a largeaccretionary prism to overthrustSeram, but less so for Timor. Inaddition, the collision in Seram washighly oblique, whilst that in Timorwas more orthogonal. This may havecaused more fracturing in Seram, butpotential carbonate plays in Timor mayhave been less buried.

A clear problem with all the modelsand hypotheses presented above is thegeneral paucity of data in the BandaArc region with which to test the ideas.Hopefully, ongoing exploration willhelp to rectify this.

ACKNOWLEDGEMENTS

This study was supported by KufpecIndonesia Limited, with particularthanks to Al Stawicki, Rob Barracloughand Nara Nilandaroe. The work wascarried out as part of the former 3d-geo partnership. Prof Robert Hall isthanked for supplying maps from hisregional tectonic reconstructions thatcould be edited to accommodate newdata. Whilst this work was carried outin collaboration with Kufpec, the viewsexpressed here are solely those of theauthor.

REFERENCES

Charlton, T.R., 2001a. Permo-Triassicevolution of Gondwanan easternIndonesia, and the final Mesozoicseparation of SE Asia fromAustralia. J. Asian Earth Sciences,19 (5), 595-617.

Hall R. 2002. Cenozoic geological andplate tectonic evolution of SE Asiaand the SW Pacific: computer-based reconstructions, model andanimations. J. Asian Earth Sciences20, 353-434.

Hill K.C. & Hall R. 2003. Mesozoic-Tertiary Evolution of AustraliasNew Guinea Margin in a WestPacific Context. In Hillis R.R. &Muller R.D. (eds) Evolution andDynamics of the Australian Plate. pp.265-290. Geological Society ofAustralia Special Publication 22and Geological Society of AmericaSpecial paper 372.

Hill K.C. & Hayward A.B. 1987.Structural constraints on the PlateTectonic evolution of Italy. Marineand Petroleum Geology. Marineand Petroleum Geology 5, 2-16.

Hill K.C. & Hoffman N. 2004.Restoration of a deepwater profilefrom the Browse Basin:implications for structural-stratigraphic evolution. Abstract,Australian Geological Congress,Hobart, Feb 2004.

Hill K.C., Hoffman N., Lunt P. & PaulR. 2002. Structure andHydrocarbons in the Sareba block,"Bird's Neck", West Papua.Proceedings of the IndonesianPetroleum Association. P. 227-249.

Hoffman N. & Hill K.C., 2004.Structural-stratigraphic evolutionand hydrocarbon prospectivity of

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the deep-water Browse Basin,North West Shelf, Australia. InEllis G.K., Baillie P.W. & MunsonT.J. (ed), Timor Sea PetroleumGeoscience. Proceedings of theTimor Sea Symposium, Darwin,Northern Territory, 19-20 June2003, p. 393-409.

Keep M., Longley I. & Jones R. 2003.Sumba and its effect on Australiasnorthwestern margin. In HillisR.R. & Muller R.D. (eds) Evolutionand Dynamics of the Australian Plate.pp. 309-318. Geological Society ofAustralia Special Publication 22and Geological Society of AmericaSpecial paper 372.

Kemp G. & Mogg W. 1992. A re-appraisal of the geology, tectonicsand prospectivity of Seram Island,Eastern Indonesia. Proceedings ofthe 21st IPA Convention, p. 521-552.

Kendrick R.D. & Hill K.C. 2002.Hydrocarbon play concepts for theIrian Jaya Fold Belt. Proceedingsof the Indonesian PetroleumAssociation. P. 353-368.

Kendrick R.D., Hill K.C., McFall S.W.,Meizarwin, Duncan A., Syafron E.,& Harahap B.H., 2003. The EastArguni Block: Hydrocarbonprospectivity in the NorthernLengguru Foldbelt, West Papua.Proceedings of the IndonesianPetroleum Association. P. 467-484.

Kendrick R.D., Hill K.C., O'SullivanP.B., Lumbanbatu K., & SaefudinI., 1997. Mesozoic to Recentthermal history and basementtectonics of the Irian Jaya FoldBelt and Arafura Platform, IrianJaya, Indonesia. In, PetroleumSystems of S.E. Asia and Australasia.IPA conference, Jakarta, May1997, p. 301-306.

Kendrick, R.D., Hill, K.C., Parris, K.,Saefudin, I., and O'Sullivan, P.B.,1995. Timing and style of Neogeneregional deformation in the IrianJaya Fold Belt, IndonesiaProceedings 24th AnnualConvention, Indonesian PetroleumAssociation, Jakarta, 1995 p. 249-262.

Linthout K, Helmers Henk, WijbransJ.R. & Van Wees J.D.A.M., 1996.40Ar/39Ar constraints onobduction of the Seram ultramaficcomplex: consequences for theevolution of the southern BandaSea in Hall R. (ed) TectonicEvolution of SE Asia. GeologicalSociety of London SpecialPublication No. 106, 455-464.Metcalfe, I., 1996. Pre-Cretaceousevolution of SE Asian terranes. In:Hall, R., & Blundell, D., (Eds).Tectonic evolution of southeastAsia. Geol. Soc. London Spec.Pub., 106, 97-122.

Metcalfe, I., 2002. Permian tectonicframework and palaeogeographyof SE Asia. J. Asian EarthSciences, 20, 551-566.

Norvick M.S., 2003a.Chronostratigraphic Sections ofThe Northern Margins of TheAustralian Plate, unpublished.

Norvick M.S., 2003b. PalaeogeographicMaps of The Northern Margins ofThe Australian Plate, unpublished.

Pairault A.A., Hall R., Elders C.F.,2003a. Structural styles andtectonic evolution of the SeramTrough, Indonesia. Marine andPetroleum Geology, 20, 1141-1160.

Pairault A.A., Hall R., Elders C.F.,2003b. Tectonic evolution of theSeram Trough, Indonesia.Proceedings of the 29th IPAConvention. P. 355-370.

Perkins T.W. & Livsey A.R. 1993.Geology of the Jurassic gasdiscoveries in Bintuni Bay, westernIrian Jaya; Proceedings 22nd IPAconvention, p. 229-261.

Sayers, J., Symonds, P.A., Direen, N.G.& Bernadel, G., 2001. Nature ofthe continent-ocean transition onthe non-volcanic rifted margin ofthe central Great Australian Bight.In Wilson, R.C.L., Whitmarsh,R.B., Taylor, B. & Froitzheim, N.(Eds) Non-volcanic rifting of continentalmargins: a comparison of evidence fromland and sea. Geological Society ofLondon Special Publication 187, 51-76.

Snyder D.B., Milsom J. & Prasetyo H.,1996. Geophyscial evidence forlocal indentor tectonics in theBanda arc east of Timor, in Hall R.(ed) Tectonic Evolution of SE Asia.Geological Society of LondonSpecial Publication No. 106, 61-73.

Struckmeyer H.I.M., Blevin J.E., SayersJ., Totterdell J.M., Baxter K. &Cathro D.L. 1998. Structuralevolution of the Browse Basin,North West Shelf: new conceptsfrom deep-seismic data. In PurcellP.G. & R.R. (eds) The SedimentaryBasins of Western Australia 2:Proceedings of PetroleumExploration Society of AustraliaSymposium, Perth, WA, 1998. p.345-368.

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Berita Sedimentologi

Origins of the Banda Arcs Collisional Orogenand the Banda SeaAw ang Harun SatyanaThe Executive Agency For Upstream Oil and Gas Business Activities (BPMIGAS) Republic of IndonesiaE-mail: [email protected] of the best examples of youngarc-continent collision are found ineastern Indonesia, where the northernmargin of Australia has been incollision throughout the Neogene witha succession of island arc systems(Charlton, 1991) (Figure 1). The BandaArc is the youngest of these collisionzones and forms the present plateboundary in this region. Behind theBanda Arcs, is the Banda Sea oceaniccrust with its debatable origin.

Origin of the Banda ArcsCollisional Orogen

The origin of Timor Island and itscollisional orogen have been matters ofdebates. Most authors describe theregion as an arccontinent collisionzone in which the Banda volcanic arccollided with Australia. Barber (1981)drew attention to the presence ofAsian continental crust within the arc.Richardson (1993) proposed that acollision between a microcontinent,forming part of an extended passivemargin and an Asian arc precededcollision of the volcanic arc and theAustralian margin. Linthout et al.(1997) proposed that severalmicrocontinental fragments collidedwith the Australian margin before thevery young arccontinent collision.(Audley Charles, 2011).

Hamilton (1979) regarded the island asa chaotic mlange. Barber (1981)interpreted Timor as collision result ofLolotoi microcontinent with Australiancontinent in Pliocene resulting insouthward overthrusts over theAustralian continental margin, or asupthrusts of Australian continentalbasement. Three main structuralmodels, resulting mainly from near-surface observations, have beenproposed for Timor:

(1) the Imbricate Model (Hamilton,1979; Audley- Charles, 2011) :Timor is interpreted as anaccumulation of chaotic materialimbricated against the hangingwall of a subduction trench, theTimor trough, and essentiallyforms a large accretionary prism,

(2) the Overthrust Model (Carter etal., 1976): Timor is interpreted interms of Alpine-style thrustsheets where allochthonous unitsof Timor overthrust theparautochthonous units of theAustralian continent.

(3) The Rebound Model(Chamalaun and Grady, 1978):the Australian continentalmargin entered a subductionzone in the vicinity of the WetarStrait. Subsequently, the oceaniclithosphere detached from thecontinental part, resulting in theuplift of Timor by isostaticrebound on steep faults.

(4) Audley- Charles (2011) saw theBanda Trench graduallyconverted into a TectonicCollision Zone progressivelyfilled by two highly deformedAustralian continental uppercrust mega-sequences that wereuplifted and raised Timor 3 kmabove sea level.

Combinations of these models havealso been proposed (e.g. Charlton,1989 and Harris, 1992) in which theparautochthon is divided into twoparts, reflecting the step-wise nature ofthe collision. The main part, theunderplated parautochthon, isthought to have accreted in the earlystages of collision by the sequentialaddition by underplating of imbricatethrust slices of the outermostAustralian continental margin to thebase of the forearc complex. A secondphase of collision is thought to havecommenced in the early Pliocene withthe addition to southern Timor of

younger parts of the Australiancontinental margin, the frontallyaccreted parautochthon. (See alsoAudey Charles 2011, Figure 6, 7, 8).

A particular controversy has also beenthe position of the suture (Hall andWilson, 2000). Audley-Charles (1986a,1988, and 2011) has advocated thatthere was a south-dipping suture in theWetar Strait. Cases can be made for allthese suggestions. The base of theBanda allochthon is the boundarybetween the former Asian Plate andunderlying deposits of the formerAustralian passive margin. The base ofthe parautochthon is the deformationfront and represents the boundarybetween completely autochthonousdeposits of the Australian margin andthose that have been displaced. Thethrust north of Wetar can beinterpreted as the new boundarybetween the Asian and Australianplates formed after subduction ceasedsouth of Timor, and perhaps inresponse to slab break-off. Audley-Charles (1986a, 2011) summarised indiagrammatic form the contrastbetween the principal models. Harris(1991) suggested that each of thedifferent models may be appropriatefor different sections through thedeveloping orogen, and each may applyat different stages in the collisionprocess.

Timor has undergone young andsevere tectonic activity. Mid-Pliocenelimestones are the youngest rockformation to be folded. The deducedmid-Pliocene tectonic event has beeninterpreted as the collision of thenorthern margin of Australia with thesubduction zone and volcanic arc(Barber, 1981). Sediments as young asearly Miocene show some evidence ofmultiple deformation. In contrast, thePliocene sediments are simply foldedwith horizontal fold axes.

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Based on deep seismic reflectionprofiles across the zone ofconvergence between Australia and theBanda arc east of Timor, Richardsonand Blundell (1996) (see Figure 2)reveal the structures formed duringlithosphere deformation in response tocontinental collision. Australiancontinental crust is bent down to thenorth to form the lower lithosphericplate. The immediately overlying upperplate is made up of a former outlier ofthe Australian continental shelf, nowsqueezed between the Australiancontinent to the south and the Bandaarc to the north. The outlier began toaccrete to the upper plate in the lateMiocene. Near the Timor Trough, atthe junction between the two plates,the upper plate to be cut by north-dipping structures interpreted asthrusts in an accretionary prismformed since the arrival of theAustralian continental shelf at thecollision zone at about 2.5 Ma.

The northern part of the collision zoneis dominated by structures dippingsouthwards, antithetic to subduction,which penetrate the lithosphere todepths of at least 50 km, dividing theupper plate into imbricate slices. Theoldest thrusts are presumably the moresoutherly ones. Since then the locus ofactivity has propagated northwards in anormal fashion until it has reached thebackarc region where thrusts are activeat the present day. Uplift is currentlycontinuing as evidenced by severalhundred meters of elevation ofPliocene coral reef of terraces on Alor,Atauro and Wetar and Sumba. In thiscollision, both oceanic and continentalmaterial is being shortened, thickenedand uplifted. The overall, large-scalecharacter of the collision zone isdominated by two sets of divergentstructures. The southern set is relatedto the subducting (lower) plate anddips in the same direction assubduction. The northern set, in theupper plate, is antithetic to this.

Origin of the Banda Sea

The Banda Sea (South Banda Basin) isan oceanic crust. The origin and age ofthe Banda Sea has long been debated.Both low heat flow values and depth ofbasement greater than 4500 meters arein agreement with a creation of theoceanic crust during Mesozoic or EarlyCenozoic time now trapped by thevolcanic and non-volcanic arcs(Lapouille et al., 1985). The hypothesisof a trapped Mesozoic origin for theBanda Sea is uncertain because thereare controversies on ages determinedfrom magnetic lineaments. The oldBanda Sea floor hypothesis waschallenged by Honthaas et al. (1998)who recovered 9.47.3 Ma backarcbasalt from fault scarp exposures ofthe basement of the North BandaBasin. They also recovered peliticmetamorphic rocks from the Sinta andTukang Besi Ridges, and LowerMiocene limestone from the RamaRidge further to the south. Other

Figure 1 . Maps and serial sections of the Banda Arc region. A) Northern Australasian region. Grey is continental crust and whiteis oceanic crust. Rectangle is area of map 1C. B) Serial cross-sections through the western Banda Arc from Savu to East Timor. C)Digital elevation model of the Banda Arc region showing active faults (yellow lines), active volcanoes (red triangles), the Sulawesiophiolite (pink area), and the many fragments embedded in oceanic crust of the Banda Sea floor. D) Location map of distribution ofcontinental and arc fragments (blue),

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dredged samples from the Luciparaand Nieuwerkerk Emperor of Chinaridges, and volcanic islands within theSouth Banda Basin, include LateMiocene to Early Pliocene backarcbasalt, and cordierite-and sillimanite-bearing andesite. The occurrence ofcordierite and sillimanite xenocrysts,and high Sr and low Nd ratios ofsamples throughout the region requirethat volcanic units are mounted on,and erupted up through continentalcrust with similar mineral assemblagesto the Banda Terrane metamorphicbasement.

These results led Honthaas et al. (1998)to also interpret the Banda Ridges asfoundered continental crust pulledfrom the edge of Sulawesi by intra-arcspreading. The arc complex is mountedon the southern edge of the detachedcontinental fragment, which wasrepeatedly pulled apart by diffusespreading and the opening of intra-arcbasins. According to this model, theeastern Sunda and western Banda Arcislands from Pantar to Damar arevolcanic constructs mounted on acontinental fragment that was riftedfrom the TukangBesi platform andBanda Ridges during the Late Mioceneto Early Pliocene opening of the SouthBanda Basin. The Wetar segment andthe Lucipara Ridge at the south andnorth of the South Banda Sea,respectively represented a singlevolcanic arc at 8-7 Ma resulted fromhigh dip subduction of the Indianoceanic lithosphere beneathcontinental blocks originated fromNew Guinea. The rifting of the South

Banda Basin at about 6 Ma separatedthe Wetar and the Lucipara volcanicarc, and intra-arc opening processesoccurred from about 6.5 to 3.5 Ma(Late Miocene-Early Pliocene) formingthe present Banda Sea. The spreadingceased at about 3 Ma due to the arc-continent collision occurred to thesouth and north of Wetar and Luciparaarc. The young age of the South BandaSea Basin is contradictory with its greatdepth. Hinschberger et al. (2001)offered three mechanisms causing thisgreat depth : rapid thermal subsidencedue to a heat loss in the small basin,induced tectonic subsidence due tocompressive tectonic setting, andincreased tectonic subsidence due todrag stress of two downgoing slabs(Banda and Seram slabs) converging atdepth.

A recent paper by Harris (2006)considered that the Banda Sea wasinitially related to subduction rollbackof the old oceanic lithosphere of theAustralian/Indian Plate. The upperplate was forced to extend, whichresulted in suprasubduction zoneseafloor spreading to form the BandaSea basin. Trench retreat eventuallybrought the southernmost rifted ridgeof Banda Terrane into collision withthe Australian continental margin. Asthe cover sequences of the Australianslope and rise stacked up in thecollision zone the Banda collisionalterrane was folded, detached, anduplifted, during accretion to the edgeof Australia. Now the southernmostpart of the Banda Terrane forms anallochthonous thrust sheet that acts as

the structural lid of the Timor fold andthrust belt. As the collision progressedit widened and the plate boundarylocalized in the thermally weakenedbackarc where the southern Banda SeaBasin underthrusts the Banda Arc.Closing of the Banda Sea basins putsthe allochthonous part of the BandaTerrane on a collision course withautochthonous Banda Terranefragments imbedded in the Banda Seafloor, and eventually with Sulawesi,where most of these fragments startedtheir journey over 50 Ma.***

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Figure 2 . Migrated seismic line from offshore south of the Kolbano fold and thrust belt shows thin-skinned thrust imbricatesoverlying a gently deformed stratigraphic sequence (Sani et al., 1995).

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Hinschberger, F., Malod, J.-A.,Dyment, J., Honthaas, C., Rehault,J., Burhanuddin, S., 2001. Magneticlineations constraints for the back-arc opening of the Late Neogenesouth Banda Basin (easternIndonesia), Tectonophysics, pp. 333,4759.

Honthaas, C., Rehault, J.-P., Maury,R.C., Bellon, H., Hemond, C.,Malod, J.-A., Cornee, J-J.,Villeneuve, M., Cotten, J.,Burhanuddin, S., Guillou, H.,Arnaud, N., 1998. A Neogene back-arc origin for the Banda Sea basins:geochemical and geochronologicalconstraints from the Banda ridges(East Indonesia), Tectonophysics, 298,pp. 297317.

Kaneko, Y., Maruyama, S.,Kadarusman, A., Ota, T., Ishikawa,M., Tsujimori, T., Ishikawa, A. andOkamoto, K., in press, On-goingorogeny in the outer arc of TimorTanimbar region, eastern Indonesia,in Santosh, M. and Maruyama, S.,eds, Island Arcs Past and Present,Gondwana Research.

Lapouille, A., Haryono, H., Larue, M.,Pramumijoyo, S., Lardy, M., 1986.Age and origin of the seafloor ofthe Banda Sea (Eastern Indonesia),Oceanological Acta, 8, pp. 379389.

Linthout, K., Helmers, H.,Sopaheluwakan, J., 1997, Late

Miocene obduction and microplatemigration around the southernBanda Sea and the closure of theIndonesian Seaway, Tectonophysics,281, pp. 1730.

Metcalfe, I.,2011. Paleozoic-Mesozoichistory of SE Asia, in: Geol. Soc ofLondon, Special Publication 355, p.7-35.

Richardson, A., 1993, Lithospherestructure and dynamics of theBanda Arc collision zone, EasternIndonesia, Bulletin of the GeologicalSociety of Malaysia, 33, pp. 105118.

Richardson, A.N. and Blundell, D.J.,1996, Continental collision in theBanda arc, in Hall, R. and Blundell,D., eds, 1996, Tectonic Evolution ofSoutheast Asia, Geological SocietySpecial Publication, no. 106, pp. 47-60.

Sani, K., Jacobson, M.I., Sigit, R., 1995,The thin-skinned thrust structuresof Timor, Proceedings IndonesianPetroleum Association 24th AnnualConvention, pp. 277-293.

Wilson, M.E.J. and Moss, S.J., 1999,Cenozoic palaeogeographicevolution of Borneo and Sulawesi,Palaeogeography, Palaeoclimatology,Palaeoecology 145, pp. 303-337.

Note: References to Audley-Charles wasadded by Tom Reijers 14/2/2012

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HALMAHERA, SERAM & BANDABerita Sedimentologi


New I nsights I nto the Geological Evolut ion ofEastern I ndonesia From Recent ResearchProjects by the SE Asia Research GroupI an M. W atkinson* , Robert Hall, Mike A. Cot tam , I nga Sevast janova, Simon Suggate,I ndra Gunaw an, Jonathan M. Pow nall, Juliane Hennig, Farid Ferdian, David Gold,Sebast ian Zimmermann, Alfend Rudyaw an & Eldert AdvocaatSE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London,Egham Surrey TW20 0EX, United KingdomE-mail: [email protected] nt roduct ion

Eastern Indonesia has a prolonged,complex tectonic history. It is wherethe Eurasian, Indo-Australian, Carolineand Philippine Sea plates converge, andwhere processes such as subduction,obduction, slab rollback, rifting,supracrustal extension, lower crustalflow and exhumation are very young orstill active (e.g. Hamilton, 1979; Silveret al., 1983; Hall, 1996; Bock et al.,2003; Spencer, 2011; Spakman & Hall,2010; Hall, 2011).

For these reasons, the SE AsiaResearch Group (SEARG) at RoyalHolloway, University of London, hasmade Eastern Indonesia one of itsmajor research themes in recent years.The SEARG has been conductinggeological research in SE Asia since1982. Work has been undertaken inIndonesia, Malaysia, Thailand, thePhilippines, Vietnam and the SouthChina Sea. In 2012 the SEARG isdirected by Professor Robert Hall, andinvolves 12 postgraduate students, 2postdoctoral researchers, a largenumber of academic staff, researchassociates and collaborators in the UKand overseas. The group is funded by aconsortium of oil companies.

Here we summarise recent andongoing SEARG projects in EasternIndonesia (Figure 1). Most of theprojects are field-based, but they allalso employ new data and techniques,such as 40Ar-39Ar, U-Pb dating(SHRIMP and LA-ICP-MS), Hfisotope dating (LA-MC-ICP-MS), U-Th/He dating, multibeam bathymetry,high quality seismic and remote sensingdata.

Sulaw esi

The SEARG is involved in severalstudies aimed at understanding theevolution of Sulawesi in the context ofEastern Indonesia.

West, central and SE SulawesiIn west, central and SE Sulawesi,metamorphic rocks (e.g. Egeler, 1947),are partly overlain by volcanic-sedimentary rocks and intruded bygranitoids as young as Pliocene (e.g.Sukamto, 1973; Sukido et al., 1993;Elburg et al., 2003; van Leeuwen &Muhardjo, 2005). Widespread uplifthas formed >3km high mountains,associated with deep intermontainebasins.

The sinistral Palu-Koro Fault (PKF)(Figure 2) bisects central Sulawesi andlinks to the North Sulawesi Trench(e.g. Silver et al., 1983; Bellier et al.,2001). Many workers also link it via theMatano/Lawanopo faults to the Tolothrust or East Sulawesi Trench in thesoutheast, forming a continuousstructure that bounds a rotating SulaBlock (e.g. Hamilton 1979; Silver et al.,1983; Bellier et al., 2006). Others linkthe Matano Fault (MF) to a Sorongfault strand that passes south of theBanggai-Sula Islands (e.g. Katili, 1975;Socquet et al., 2006).

SEARG studies of the PKF show thatstrike-slip diminishes to the south, andthe fault terminates at the northern endof Bone Bay. Similarly, the MFterminates in the west where it is

Figure 1 . Overview map of Eastern Indonesia showing geographical features,structural elements and ongoing SEARG projects (numbered). PKF: Palu-Koro Fault;MF: Matano Fault; LF: Lawanopo Fault; GF: Gorontalo Fault; BF: Balantak Fault; CF:Central fault zone of Seram.

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propagating towards, but does not yetconnect to the PKF (Watkinson, inprep.). Such a strain distribution isinconsistent with the fault bounding arotating block. Instead, we suggest thatthe PKF forms the western transformboundary of a zone of lithosphericextension, and the MF is atranstensional structure at the southernmargin of extension.

At the eastern end of the MF, recentwork by the SEARG, utilising highresolution multibeam and seismic data,suggests that the Tolo thrust is agravity-driven feature (Rudyawan,2011), and not a tectonic structure thatcould terminate a strike-slip fault.These data also show that strands ofthe

Sorong fault barely reach the Banggai-Sula Islands from the east (Ferdian etal., 2010; Rudyawan, 2011), andcertainly do not link to strike-slip faultsonshore Sulawesi (Rudyawan, 2011).

Metamorphic massifs in centralSulawesi characterised by NNW-trending corrugations may have beenformed during exhumation of ametamorphic core complex (MCC)(Spencer, 2011). Recent SEARGfieldwork in central Sulawesi tentativelysupports an interpretation of MCCexhumation during top-to-the-northshear, representing considerablelithospheric extension (Watkinson etal., in prep.).

In west and central Sulawesi, Cenozoicmagmatic rocks include older calc-alkaline/tholeiitic intrusions andyounger (including Pliocene) mafic-felsic magmas (Elburg et al., 2003). Acurrent SEARG project aims todetermine when and how granitoids inwest and central Sulawesi wereexhumed, by using low-temperature U-Th/He and 40Ar-39Arthermochronology on apatites andmicas. Of particular interest are therelationships between granitoidemplacement, cooling and uplift, toextension and exhumation of themetamorphics and strike-slip along thePKF.

Figure 2 . (A) View west across Palu Bay to mountains adjacent to the Palu-Koro Fault. (B) Sinistral Reidel shears in fault breccia of amajor Palu-Koro Fault strand south of Gimpu. (C) Damage caused by the 15-02-11 Mw 6.1 Matano Fault earthquake at Mahalona.

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Tom ini Bay

The Gorontalo Basin of Tomini Bay isa deep, enigmatic basin, containing upto 5 km of sediment (Hamilton, 1979).New field, geochemical andgeophysical studies by the SEARG arerevealing more about the basin.Cottam et al. (2011) presented a newstratigraphy for the Togian Islands, inthe centre of Tomini Bay, andinterpreted the age, character andevolution of the basin. The westernend is underlain by continental crust,the central part by Eocene to Mioceneoceanic and arc rocks, with thepossibility of Banggai-Sulamicrocontinental crust south of theTogian Islands. Field relationshipsindicate a latest Miocene to Plioceneage for inception of the basin.Volcanism in the Togian Islands is nota result of Celebes Sea subduction.Instead, it is the result of extension inthe Pliocene and Pleistocene. Modernvolcanism at Una Una may be theresult of the same process (Cottam etal., 2011).

Sulaw esis North Arm

In the western north arm, the MalinoMetamorphic Complex (MMC)

contains gneisses and schists with agreenschist carapace, and may be aMCC (Kavalieris et al., 1992; vanLeeuwen et al., 2007). The SEARG isundertaking detailed field andthermochronological investigations todetermine whether the MMC is indeeda MCC similar to those of centralSulawesi, and whether it formed/isforming during the same phase ofextension. A related project on theNeogene tectonics of the central northarm aims to understand relationshipsbetween the Gorontalo Fault,intermontaine basins and uplift east ofthe MMC. Igneous rocks, including anunexpectedly large quantity of felsicmaterial, will be used to determineemplacement ages and uplift rates.

Banggai-Sula I slands

The Banggai-Sula microcontinent haslong been considered to have beensliced from New Guinea and travelledwest along strands of the Sorong Fault(e.g. Visser & Hermes, 1962; Hamilton,1979; Silver & Smith, 1983). Collisionof the microcontinent with the eastarm of Sulawesi has been thought tohave caused deformation throughoutSulawesi (e.g. Bergman et al., 1996;

Simandjuntak & Barber, 1996; Calvert,2000; McClay et al., 2000).

Recent SEARG projects utilising newseismic and multibeam data from northand south of the islands show thatmajor continuous faults previouslyinterpreted to bound themicrocontinent, including strands ofthe Sorong Fault, do not exist (Ferdianet al., 2010; Rudyawan, 2011;Watkinson et al., 2011) (Figure 3).Gently dipping strata of the Banggai-Sula microcontinent margin can betraced north beneath younger rocks,and are not truncated by a major fault.The strike-slip Balantak Fault passesfrom the east arm of Sulawesi andterminates in a zone of dextraltranspression close to the Banggai-SulaIslands. There is no evidence that theBanggai-Sula microcontinent wastranslated along through-goingstructures, or that compressionaldeformation related to its suturing toSulawesi was widespread (Cottam et al.,2011; Watkinson et al., 2011).

Seram

Controversies surround the geologicalevolution of Seram. These include thepossibility of subduction at the Seram

Figure 3 . Map showing newly imaged faults and their deformation mechanisms. Note the absence of a through-going Sula Thrust,the Sorong Fault as a plate boundary which does not reach the surface, and the Balantak Fault and region of dextral transpressionwest of the east arm. Sources of deformation in the region are indicated by regions of colour. From Watkinson et al. (2011).

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trough (e.g. Hamilton, 1979; Karig etal., 1987); thrust sheet emplacementand ophiolite obduction (e.g. Audley-Charles et al., 1979; Linthout &Helmers, 1994); and the causes ofanatexis and cordierite-rich volcanism(Linthout & Helmers, 1994; Honthaaset al., 1999).

Recent SEARG studies in Seram areaimed at resolving these uncertainties.Peridotites crop out throughout Seram,particularly in the west, in the SE, andin the Gorong and Watubela islands tothe east. Peridotites are not associatedwith other typical ophioliticcomponents. Granites (SHRIMP U-Pbzircon age: 3 Ma, J. Decker, pers.

comm., 2011) characterised byabundant cordierite and garnet, andnumerous cordierite + spinel +sillimanite restites, are in contact withthe peridotites. Eruptive cordierite +garnet dacites (ambonites) arewidespread on nearby Ambon (Figure4) and have a similar ~3 Ma age (J.Decker, pers. comm., 2011).

There are many examples whereperidotite appears to intrude thegranites. Peridotites and granites seemto comprise a single tectonic unitexhumed along low-angle NNE-dipping detachments, not obducted bySSW-dipping thrusts as previouslythought. Serams central fault zone

incorporates thin slivers of peridotiteand may have been active at a similartime. North of the central fault zone inthe Kobipoto Complex, cordierite-granites as well as (ultra-) hightemperature granulites, with identicalmineralogy to the granite-hostedrestites, are found with peridotites andwere probably exhumed in a similarmanner to those of west Seram(Pownall et al., 2012).

West Papua

The Birds Head of New Guinea isunderlain by Australian continentalcrust and is considered to represent acoherent and little deformed domain of

Figure 4 . (A) Bedded cordierite-bearing dacites (ambonites), Ambon Island. (B) Layered peridotite, closely associated withcordierite-bearing granite. (C) Large cordierite + spinel + sillimanite restite in granite, Ambon.

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Australian affinity with a relativelycomplete Palaeozoic to Recentstratigraphy (e.g. Dow et al., 1988;AudleyCharles, 1991).

An ongoing SEARG study is focusedon the clastic sedimentation of theBirds Head. Heavy mineral analysisand zircon dating is revealing thecomposition and provenance of thesesediments. The Mesozoic TipumaFormation includes material from localsource rocks north of the formationand material from the North Australiancraton (Gunawan et al., In Press)(Figure 5). Sediments from the TipumaFormation indicate that this regionexperienced volcanic activity during theTriassic (Gunawan et al., In Press).This project has also shown that theBirds Head has a more complicatedtectonic history than previous modelssuggest.

The Biak basin, between Biak andYapen islands, is a frontier regionwhose structural and sedimentaryevolution and hydrocarbon potential ispoorly known. The relationshipbetween the Sorong Fault, subsidenceof the Biak basin and uplift of theislands is the focus of a new SEARGproject that will integrate detailed fieldstudies, offshore seismic andmultibeam data.

Banda Arc

The geodynamic evolution of theBanda Arc is a subject of great interest(e.g. Cardwell et al., 1978; McCaffrey etal., 1989; Hall, 2002). Recent workcombining seismic tomography andplate tectonic reconstructions(Spakman & Hall, 2010) has shownthat Jurassic oceanic crust of the Bandaembayment was subducted from 15Ma. Eastwards slab rollback continuedup to 2 Ma, and was associated withextensional break-up of the Sula Spur an arm of Australian crust extendingaround the north of the Banda Arc.Slab rollback and associateddelamination of the continental crustexplains many of the enigmatic featuresof the Banda Arc, such as thesynformal geometry of the subductedplate in the mantle, deep marinetroughs, and the distribution offragments of Australian crust in

Eastern Indonesia (Spakman & Hall,2010).

An ongoing SEARG study aims toprovide a detailed regional provenancefingerprint of zircons in SE Asia bycompiling a database of existing U-Pband Hf isotope analyses and acquiringnew data (e.g. samples recentlycollected from Timor). Preliminaryresults suggest that detrital zircons inthe Banda Arc (Seram), includingrecently discovered Permian-Triassicpopulation (Figure 6), were derivedfrom the Sula Spur. This confirms theexistence of an acid volcanic Permian-Triassic source in or near the Sula

Spur, si

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