fosi beritasedimentologi bs-23 march2012

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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

Tectonic &Regional Structure

of Seram & theBanda Arc

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New Insights into theGeological Evolution of

Eastern Indonesia fromRecent Research

Projects by the SE AsiaResearch Group

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Interplay BetweenSubmarine Depositional

Processes & RecentTectonics in the Biak

Basin, Western Papua,Eastern Indonesia

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Number 2303/2012

ISBN 0853-9413

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Editorial Board

Herman 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 EnergyShinawatra 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 Board

Prof. 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 Reviewers

Prof. 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 March, July and November by the Indonesian Sedimentologists Forum (Forum Sedimentologiwan Indonesia,FOSI), a commission of the Indonesian Association of Geologists (Ikatan Ahli Geologi Indonesia, IAGI).

• Cover topics related to sedimentary geology, including their depositional processes, deformation, minerals, basin fill, etc.

Cover Photograph:

Bedded Cordierite-BearingDacites (Ambonites), AmbonIsland.

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

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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 Álvarez will discuss theinterplay between tectonic activity andsubmarine 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

INSIDE THIS ISSUE

Tectonic and regional Structure of Seram & theBanda Arc – K. C. Hill 5

Middle Jurassic ammonites from theCenderawasih Bay coast and North Lenggurufoldbelt, West Papua: implications of a'forgotten' 1913 paper – 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

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Origin of the Banda Arcs Collisional Orogen andthe Banda Sea – A.H. Satyana 17

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

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

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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, anIntegrated Approach to determine the ReservoirQuality of a Fractured Limestone Reservoir –A.K. Lapulisa et al.

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

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

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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 FOSI

he 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 LinkedIn(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 as of March 2012

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

ABSTRACT

Seram and the Banda Sea lie betweenthe passive margin tectonics ofAustralia’s 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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INTRODUCTION

Seram and the Banda Sea area liebetween the passive margin tectonicsof Australia’s 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 Australia’s 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 <500 m deep. Between theScott Plateau and Callovian oceaniccrust Hill & Hoffman (2004) showed

the presence of an outer margin higher,probably of intruded and thinnedcontinental crust. This High mayinclude metamorphic core complexesas recorded along Australia’s southernmargin along the Continent-OceanBoundary (COB) (Sayers et al. 2001).This sequence is significant as, here, weinterpret a similar crustal morphologyalong the Seram margin prior to

Pliocene compression. However, thetiming of events is not the same as inthe Browse Basin in part due to thetectonism in neighbouring NewGuinea.

For Northern and Eastern NewGuinea, Hill & Hall (2003) reported:

Figure 2. Simplified stratigraphy for Seram courtesy of Kufpec (Indonesia) Limited.

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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. Hall’s(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.

Hall’s (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.

OBSERVATIONS

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 nowSeram’s southern margin.

REGIONAL CROSS SECTION

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 Seram margin (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.

TECTONIC 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).

PermianRifting occurred in the area that is nowthe Banda Sea, probably by NEmovement of the Bird’s Head alongthe long-lived Hall’s Creek MobileBelt, possibly associated with clockwiserotation of the Bird’s 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 thesubducting slab.

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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 ‘Kanikeh’sediments, 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 1000’s 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 Australia’s 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 Bird’s 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 Bird’sHead, 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 Australia’s 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 Bird’s 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 Bird’s 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 theHall’s 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.

DISCUSSION

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 Australia’sNew 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 Australia’snorthwestern 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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HALMAHERA, SERAM & BANDA


Berita Sedimentologi

Origins of the Banda Arcs Collisional Orogenand the Banda SeaAwang Harun SatyanaThe Executive Agency For Upstream Oil and Gas Business Activities (BPMIGAS) – Republic of IndonesiaE-mail: [email protected]

Many 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 arc–continent 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 arc–continent collision.(Audley – Charles, 2011).

Hamilton (1979) regarded the island asa chaotic mélange. 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, the‘underplated 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 ‘old’Banda Sea floor hypothesis waschallenged by Honthaas et al. (1998)who recovered 9.4–7.3 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 Sulawes iophiolite (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 Tukang–Besi 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.***

REFERENCES

Audley-Charles, M.G., 1986, Timor–Tanimbar trough: the forelandbasin to the evolving Banda orogen,in Allen, P.A. and Homewood, P.,eds, Foreland Basins, InternationalAssociation of Sedimentologists,pp. 91–102.

Audley-Charles, M.G., 1988. Evolutionof the southern margin of Tethys(North Australian region) fromearly Permian to Late Cretaceous, inAudley-Charles, M.G., Hallam, A.,eds, Gondwana and Tethys, GeologicalSociety of London, SpecialPublication, 37, pp. 79–100.

Audley- Charles, M.G. 2011, Tectonicpost- cxollision processes in Timor,in; Gel. Soc. London SpecialPublication 355, p 7-35.

Barber, A.J. and Wiryosujono, S., eds,The Geology and Tectonics of EasternIndonesia, Special Publication No.2,Geological Research andDevelopment Centre, Bandung, p.183-197.

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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Carter, D.J., Audley-Charles, M.G., andBarber, A.J., 1976, Stratigraphicalanalysis of island arc-continentalmargin collision in easternIndonesia, Journal of the GeologicalSociety, London, 132, pp. 179-198.

Chamalaun, F.H. and Grady, A., 1978,The tectonic development of Timor: a new model and its implicationsfor petroleum exploration,Australian Petroleum ExplorationAssociation Journal, 18, p. 102-108.

Charlton, T.R., 1991, Postcollisionextension in arc-continent collisionzones, eastern Indonesia, Geology,vol. 19, pp. 28-31.

Hall, R, 2011, Australia-SE Asiacollision: plate tectonics and crustalflow, in Geol. Soc. LondonSopecial Publication 355, p. 75-109

Hamilton, W., 1979, Tectonics of theIndonesian Region, United StatesGeological Survey, ProfessionalPaper No. 1078, 345 ps.

Harris, R.A., 1992, Temporaldistribution of strain in the activeBanda Orogen: a reconciliation ofrival hypotheses, Journal of SE AsianEarth Sciences, 6, pp. 373-386.

Harris, R., 2006, Rise and fall of theeastern great Indonesian arcrecorded by assembly, dispersionand accretion of the Banda terrane,Timor, Gondwana Research, 10(2006), pp. 207-231.

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. 333,47–59.

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. 297–317.

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 Timor–Tanimbar 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. 379–389.

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. 17–30.

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. 105–118.

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 Insights Into the Geological Evolution ofEastern Indonesia From Recent ResearchProjects by the SE Asia Research GroupIan M. Watkinson*, Robert Hall, Mike A. Cottam, Inga Sevastjanova, Simon Suggate,Indra Gunawan, Jonathan M. Pownall, Juliane Hennig, Farid Ferdian, David Gold,Sebastian Zimmermann, Alfend Rudyawan & Eldert AdvocaatSE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London,Egham Surrey TW20 0EX, United KingdomE-mail: [email protected]

Introduction

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.

Sulawesi

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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Tomini 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).

Sulawesi’s 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 Islands

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. Seram’s 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 Bird’s 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;Audley–Charles, 1991).

An ongoing SEARG study is focusedon the clastic sedimentation of theBird’s 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 theBird’s 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, similar to that recognised for theBird’s Head area (Sevastjanova et al.,2012).

Conclusions

Recent research by the SEARG and itscollaborators shows that many long-held assumptions about the structural,magmatic, metamorphic andsedimentary evolution of EasternIndonesia require revision. Previouslyit was assumed that continuouslithospheric faults bounded continentalfragments, and deformation waspredominantly related to collision and

Figure 5. (A) CL image showing older (Precambrian ages) and Mesozoic zirconsfrom the Tipuma Formation in the Bird’s Head. (B) Bedded sandstones of the TipumaFormation, Bird’s Head. After Gunawan et al., In Press. Watkinson et al. SEARGresearch in Eastern Indonesia 7.

Figure 6. (A&B) Schematic probability density plot of detrital zircon U-Pb ages fromthe Banda Arc. (C) Cartoon showing location of Australian basement fragments (AfterHall et al., in prep.) from which these zircons were analysed. (D) Examples of zirconCL-images. Watkinson et al. SEARG research in Eastern Indonesia 8.

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extrusion tectonics. Models for thedevelopment of sedimentary basinsbuilt around these ideas have beenproven to be incorrect, and blocks aregenerally not bounded by continuousfaults. The SEARG’s research showsthat collision (e.g. India – Asiacollision, Banggai-Sula – Sulawesicollision) is not as important incontrolling intraplate deformation assubduction initiation, slab rollback,lithospheric delamination and lowercrustal flow.

Acknowledgements

The SE Asia Research group is fundedby a consortium of oil companies. Toomany individuals and organisationshave contributed to our research to listhere, but a few include: Marnie Forster,Gordon Lister, Benyamin Sapiie andstudents at Institut TeknologiBandung, Wim Spakman, Theo vanLeeuwen, TGS-NOPEC, Fugro(FMCS) and Searcher Seismic.

References

Audley–Charles, M.G. 1991. Tectonicsof the New Guinea area. Earthand Planetary Sciences, AnnualReview, 19, 17–41.

Audley-Charles, M.G., Carter, D.J.,Barber, A.J., Norvick, M.S., &Tjokrosapoetro, S. 1979.Reinterpretation of the geology ofSeram: implications for the BandaArcs and northern Australia.Journal of the Geological Society,136, 547-566.

Bellier, O., Sebrier, M., Beaudouin, T.,Villeneuve, M., Braucher, R.,Bourles, D., Siame, L., Putranto,E., & Pratomo, I. 2001. High sliprate for a low seismicity along thePalu-Koro active fault in centralSulawesi (Indonesia). Terra Nova,13, 463-470.

Bellier, O., Sebrier, M., Seward, D.,Beaudouin, T., Villeneuve, M., &Putranto, E. 2006. Fission trackand fault kinematics analyses fornew insight into the LateCenozoic tectonic regime changesin West-Central Sulawesi(Indonesia). Tectonophysics, 413,201-220.

Bergman, S.C., Coffield, D.Q., Talbot,J.P. & Garrard, R.J. 1996. Tertiarytectonic and magmatic evolution

of western Sulawesi and theMakassar Strait, Indonesia:evidence for a Miocene continent-continent collision. In: Hall, R. &Blundell, D. J. (eds.) TectonicEvolution of SE Asia. GeologicalSociety, London, SpecialPublication, 106, 391-430.

Bock, Y., Prawirodirdjo, L., Genrich,J.F., Stevens, C.W., McCaffrey, R.,Subarya, C., Puntodewo, S.S.O., &Calais, E., 2003. Crustal motion inIndonesia from GlobalPositioning Systemmeasurements. Journal ofGeophysical Research, 108, 2367.

Calvert, S.J. 2000. The CenozoicGeology of the Lariang andKarama regions, western Sulawesi,Indonesia. PhD Thesis, Universityof London.

Cardwell, R. K. & Isacks, B. L. 1978.Geometry of the subductedlithosphere beneath the Banda Seain eastern Indonesia fromseismicity and fault planesolutions. Journal of GeophysicalResearch, 83, 2825-2838.Watkinson et al. SEARG researchin Eastern Indonesia 9

Cottam, M.A., Hall, R., Forster, M.A.,& Boudagher-Fadel, M.K. 2011.Basement character and basinformation in Gorontalo Bay,Sulawesi, Indonesia: newobservations from the TogianIslands. In: Hall, R., Cottam, M.A. & Wilson, M. E. J. (eds). TheSE Asian Gateway: History andTectonics of the Australia–AsiaCollision. Geological Society,London, Special Publications,355, 177–202.

Dow, D.B., Robinson, G.P., Hartono,U., & Ratman, N. 1988. Geologyof Irian Jaya. Irian Jaya GeologicalMapping Project, GeologicalResearch and DevelopmentCenter, Indonesia, in cooperationwith the Bureau of MineralResources, Australia on behalf ofthe Department of Mines andEnergy, Indonesia and theAustralian DevelopmentAssistance Bureau, 298 p.

Egeler, C.G. 1947. Contribution to thepetrology of the metamorphicrocks of western Celebes.Geological Expedition to theIsland of Celebes, University ofAmsterdam, 185-346.

Elburg, M., van Leeuwen, T., Foden, J.,& Muhardjo. 2003. Spatial andtemporal isotopic domains ofcontrasting igneous suites inWestern and Northern Sulawesi,Indonesia. Chemical Geology,199, 243-276.

Ferdian, F., Hall, R., & Watkinson, I.2010. A structural re-evaluation ofthe north Banggai-Sula area,eastern Indonesia. IndonesianPetroleum Association,Proceedings, 34th AnnualConvention & Exhibition. IPA10-G-009.

Gunawan, I., Hall, R., & Sevastjanova,I. In Press. Age, Character andProvenance of the TipumaFormation, West Papua : NewInsights from Detrital ZirconDating. Indonesian PetroleumAssociation, Proceedings, 36thAnnual Convention & Exhibition,Jakarta, 2012.

Hall, R. 1996. Reconstructing CenozoicSE Asia. In: Hall, R. & Blundell,D. J. (eds). Tectonic Evolution ofSE Asia. Geological Society,London, Special Publication, 106,153-184.

Hall, R. 2002. Cenozoic geological andplate tectonic evolution of SEAsia and the SW Pacific:computer-based reconstructions,model and animations. Journal ofAsian Earth Sciences, 20, 353-434.

Hall, R. 2011. Australia–SE Asiacollision: plate tectonics andcrustal flow. In: Hall, R., CottamM. A., & Wilson M. E. J. (eds).The SE Asian Gateway: Historyand Tectonics of the Australia–Asia Collision. Geological Society,London, Special Publication, 355,75–109.

Hamilton, W. 1979. Tectonics of theIndonesian region. U.S.Geological Survey ProfessionalPaper, 1078, 345 pp.

Honthaas, C, Maury, RC, Priadi, B,Bellon, H & Cotten, J. 1999. ThePlio–Quaternary Ambon arc,Eastern Indonesia,Tectonophysics, 301, 261-281.

Karig, D. E., Barber, A. J., Charlton, T.R., Klemperer, S., & Hussong, D.M. 1987. Nature and distributionof deformation across the BandaArc-Australian collision zone atTimor. Geological Society ofAmerica Bulletin, 98, 18–32.

of 61



Katili, J.A. 1975. Volcanism And PlateTectonics in the IndonesianIsland Arcs. Tectonophysics, 26,165-188.

Kavalieris, I., van Leeuwen, T.M., &Wilson, M. 1992. Geologicalsetting and styles ofmineralisation, north arm ofSulawesi, Indonesia. Journal ofSoutheast Asian Earth Sciences, 7,113-130. Watkinson et al. SEARGresearch in Eastern Indonesia 10

Linthout, K., & Helmers, H. 1994,Pliocene obducted, rotated andmigrated ultramafic rocks andobduction-induced anatecticgranite, SW Seram and Ambon,Eastern Indonesia. Journal ofSoutheast Asian Earth Sciences, 9,95-109.

McCaffrey, R. 1989. Seismologicalconstraints and speculations onBanda arc tectonics. NetherlandsJournal of Sea Research, 24, 141-152.

McClay, K., Dooley, T., Ferguson, A.& Poblet, J. 2000. Tectonicevolution of the Sanga SangaBlock, Mahakam Delta,Kalimantan, Indonesia. AmericanAssociation of PetroleumGeologists Bulletin, 84, 765-786.

Pownall, J.M., Hall, R., and Watkinson,I.M., 2012. Intrusive peridotitesand granites exhumed on Seramand Ambon, eastern Indonesiaduring Banda Arc subductionrollback (abstract). TectonicStudies Group AGM, Edinburgh,Scotland.

Rudyawan, A. 2011. Tectono-stratigraphy and Structural Styleof The South Banggai – SulaBlock and NW Banda Basin,Indonesia. Unpublished MSc.Thesis, University of London,London, UK.

Sevastjanova, I., Hall, R., &Zimmermann, S. 2012. Detritalzircon provenance and insightsinto palaeogeographic recon-

structions of the Banda Arc(abstract). 1° CongressoInternacional de Geologia deTimor-Leste, Dili, Timor-Leste.

Silver, E.A. & Smith, R.B. 1983.Comparison of terrane accretionin modern Southeast Asia and theMesozoic North AmericanCordillera. Geology, 11, 198-202.

Silver, E.A., Mccaffrey, R., & Smith,R.B. 1983. Collision, rotation andthe initiation of subduction in theevolution of Sulawesi, Indonesia.Journal of Geophysical Research,88, 9407-9418.

Simandjuntak, T.O. & Barber, A.J.1996. Contrasting Tectonic Stylesin the Neogene Orogenic Belts ofIndonesia. In: Hall, R. & Blundell,D. J. (eds). Tectonic Evolution ofSE Asia. Geological Society,London, Special Publication, 106,185-201.

Socquet, A., Simons, W., Vigny, C.,McCaffrey, R., Ambrosius, B.,Spakman, W., Subarya, C. &Sarsito, D. 2006. Microblockrotations and fault coupling in SEAsia triple junction (Sulawesi,Indonesia) from GPS andearthquake slip vector data.Journal of Geophysical Research,111, doi:10.1029/2005JB003963.

Spakman, W., & Hall, R. 2010. Surfacedeformation and slab-mantleinteraction during Banda arcsubduction rollback. NatureGeoscience, 3, 562-566.

Spencer, J.E., 2011. Gently dippingnormal faults identified withSpace Shuttle radar topographydata in central Sulawesi,Indonesia, and some implicationsfor fault mechanics. Earth andPlanetary Science Letters, 308,267-276.

Sukamto, R. 1973. Reconnaissancegeologic map of Palu Area,Sulawesi - scale 1:250,000.Geological Survey of Indonesia,Directorate of Mineral Resources,

Geological Research andDevelopment Centre, Bandung.

Sukido, D., Sukarna, & Sutisna, K.1993. Geological map of thePasangkayu quadrangle, Sulawesi– scale 1:250,000. GeologicalSurvey of Indonesia, Directorateof Mineral Resources, GeologicalResearch and DevelopmentCentre, Bandung.

van Leeuwen, T.M., & Muhardjo.2005. Stratigraphy and tectonicsetting of the Cretaceous andPaleogene volcanic-sedimentarysuccessions in northwest Sulawesi,Indonesia implications for theCenozoic evolution of Westernand Northern Sulawesi. Journal ofAsian Earth Sciences, 25, 481–511. Watkinson et al. SEARGresearch in Eastern Indonesia 11

van Leeuwen, T., Allen, C.M.,Kadarusman, A., Elburg, M.,Palin, J.M., Muhardjo, &Suwijanto. 2007. Petrologic,isotopic, and radiometric ageconstraints on the origin andtectonic history of the MalinoMetamorphic Complex, NWSulawesi, Indonesia. Journal ofAsian Earth Sciences, 29, 751-777.

Visser, W.A. & Hermes, J.J. 1962.Geological results of theexploration for oil in NetherlandsNew Guinea. VerhandelingenKoninklijk NederlandsGeologisch en MijnbouwkundigGenootschap, Geologische Serie,265 pp.

Watkinson, I. M., Hall, R. & Ferdian,F. 2011. Tectonic re-interpretation of the Banggai-Sula–Molucca Sea margin,Indonesia. In: Hall, R., Cottam,M. A. & Wilson, M. E. J. (eds).The SE Asian Gateway: Historyand Tectonics of the Australia–Asia Collision. Geological Society,London, Special Publications, 355,203–224.

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Seismic Expression of Geological Features inSeram Sea: Seram Trough, Misool-Onin Ridgeand Sedimentary BasinHerman Darman & Paul ReemstShell International E & P, The Haque, Netherlands

Introduction

The Seram Sea (Figure 1) is locatedbetween Seram Island and the Bird’sHead of Papua, Eastern Indonesia.This sea extends to the east towardsBintuni Bay. Some part of the sea,between Seram and Misool are deeperthan 2000 m. The Seram Island ismountainous with altitudes reaching3000 m above sea level at the center ofthe island.

Several seismic surveys have beenconducted to understand the geologyof this region. The first seismicsections were published by Hamiltonin 1979. These seismic sections wereacquired by Western Geophysical forPhillips Petroleum. In 2000,Schlumberger published some seismiclines acquired in 1997 with animproved resolution improvement(Blunden, 2000). More higher qualityseismic lines were acquired as part ofnon-exclusive and multi-client projectsin the late 1990’s which provide abetter geological understanding of theregion and lead to several petroleumexploration opportunities.

This article discusses the seismicexpression of several geologicalfeatures in the Seram Sea vicinity basedon published seismic sections. Theoffshore seismic sections cover part ofthe imbricated complex in the north ofSeram Island, the Seram Trough, theMisool-Onin High and the sedimentarybasins the east of the Misool-OninRidge, such as the Tamaloi-MalagotBasin, the Semai-Berau Basin and theBintuni Basin (Figure 1).

Misool-Onin Ridge

The Missol-Onin Ridge is a structuralhigh located in the Seram Sea betweenthe island of Seram and the Bird’sHead of Papua. This feature is exposedabove the sea as the Misool Island in

the northwest and the Onin Peninsulain the southeast. This high is truncatedby the large Sula-Sorong Fault Systemin the north and the Terera Fault in thesouth. Both faults are interpreted assinistral lateral faults (Figure 1). Atpresent the southern flank of this highforms a steep sea bottom relieftowards the Seram Trough but thenorthern flank has been covered byyounger sediments and does not showa significant bathymetric expression.

Several wells have been drilled on theMisool-Onin Ridge. Daram Selatan-1penetrated the northern part of theMisool-Onin High and TBJ-1X wasdrilled in the south. Daram Selatan-1tested a section of more than 1000 mof Triassic age dominated bylimestones section (Wongsosantiko &Mertosono, 1996) and TBJ-1Xencountered an interval of almost 200m of Permian clastic and carbonateinterval (Fraser et al, 1993).

Figure 1. Regional Geological map of Seram Sea and vicinity, showing thestructural elements in this area, outcrops and major faults. Seismic sectionsdiscussed in this article is shown in red. Main wells are also displayed as reference.SR = Sekak Ridge; MOR = Misool-Onin Ridge; KBF = Kepala Burung Foreland Basin.

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Seismic section 1 (Figure 2) located inthe western part of the Seram Seaextends from the SW to the NE, andshows the Seram ImbricatedComplex, the Seram Trough, theKepala Burung Foredeep, the MisoolOnin Ridge and the Berau Basin. Thewestern part of the Misool-OninRidge has been penetrated by theDaram Selatan-1 well. Figure 3 showsa seismic section acquired forAmoseas and processed by Texaco in1991 (Wongsosantiko and Mertosono,1996). The structure and stratigraphyis very complex in this area and theseismic is very difficult to interpret asa result of relatively poor data quality.The two sections in figure 3 show theseismic interpretation prior to drillingof well Daram-Selatan-1 and thegeological interpretation based on welldata such as lithologies andstratigraphic data. The Top Triassicmarker was interpreted significantlyshallower and the structures are morecomplex than those in previousinterpretations.

The northern part of the Misool-OninRidge has been uplifted as indicatedby the missing Paleocene-Miocenestratigraphic section . Pliocene-Pleistocene interval covered the wholearea. The eastern uplift is also indicatedin Section 3 (Figure 4) at the centerpart of the ridge. Section 1 and 4(Figure 5) clearly show anunconformity that cuts through thePaleocene – Miocene interval. Section3 (Figure 4; Blunden, 2000), however,does not show any indication oferosion.

Based on stratigraphic reconstructionof Section 1 and 4 we identify at leasttwo major uplift events in the Misool-Onin High area. The first one is a postTriassic age and is followed by asecond event of post Cretaceous toPleistocene time. Both uplift eventsmainly took place in the northern partof the ridge (Figure 2 and 4).

Imbricate Complex at Northof Seram Island

The Imbricated Complex north ofSeram Island and south of Misool-Onin Ridge is characterized by a highlycomplex fault system that generatespoorly image seismic section. Some of

the trust faults have been interpretedby Pairault et al. (2003) in Section 1, 3,6 and 7 (Figure 2, 4 and 7). Steeplydipping thrust faults can be seen onSection 6 and 7. The fault systemgenerated a rough sea bottom and as aresult mini basins developed betweenfault blocks that accommodatePleistocene-Pliocene sediments (Figure2)Blunden (2000) published a detailseismic section of the imbricatedcomplex (Figure 4). Unfortunately thequality of the seismic is poor. Figure 8shows a higher quality seismicpublished by Searcher. The reflectorswhich cross the structures and almostparallel to the sea bottom indicatepotential hydrate layers in this area.

Seram Trough

The northwest part of the SeramTrough is relatively narrow comparedto the southeast. The deepest part ofthis trough can reach >2000 m waterdepth. Recent sediment supply ismainly accommodated thesoutheastern part of the trough,

indicated by flat sea bottom as shownin Figure 7 and 8. Bright amplitude inthe northern part of section 6 (Figure8) is interpreted as a slope failuredeposit from the Kepala BurungForeland in the north.

Differences in thickness of recentsediments deposited in the SeramTrough show that the locus ofdepocentres changed through time(Figure 8). In some areas in the southsediments are thicker than the north.This suggests active tectonism andrapid deposition in the area.

Kepala Burung Foreland

A foreland basin developed betweenthe Seram Trough and the Misool-Onin Ridge. Generally this tectonicunit covers an area with water depthsof about 200 to 2000 meters. Section 1(Figure 2) shows a structural high inwest part of the foreland (Figure 2).Further east, Section 3 shows a simpledipping foreland. Section 6 (Figure7.A) shows 3 anticlinal features whichdeveloped locally. Just south of this

Figure 2. Section 1 across Seram Sea showing the seismic expression of theimbricated comples, Seram Trough, Kepala Burung Foredeep Basin, Misool-Onin Ridgeand Bintuni Basin. CS-1X and Agung-1 well control occur in the north of the section. Thissection is modified after Pairault et al, 2003.

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section the anticlines disappear and thelargest anticline is faulted (Figure7.B).

The structural map in Figure 1 alsoshows that Section 3 is located in thenarrowest foreland area. The forelanddeveloped well in the south of OninPeninsula.

Berau Basin

The Berau Basin is located north of theMisool-Onin Ridge. Section 1, 3, 4 and5 dissect this basin. All these sectionsshow a significant unconformity as aresult of a major uplift in the southtowards the Misool-Onin Ridge andthe north. Another majorunconformity is shown in Section 1,below the Oligocene-Paleocene unit.This unconformity mainly occurs inthe south, close to the Misool-OninRidge.

Wells Agung-1 and CS-1X alongSection 1 penetrated Tertiary toPermian sedimentary formationsdeposited in the northern part of theBerau Basin. In the south of the basin,wells North Onin-1 and Gunung-1encountered a mainly Cenozoic unitbut Gunung-1 also went throughPermian clastics and carbonates sectionat the bottom of the hole (Fraser et al,1993).

Sekak Ridge

The Sekak Ridge is a large anticlinalfeature which separates the BerauBasin from the Bintuni Basin. Section5 (Figure6) shows a seismic profile ofthis ridge. The ridge has several minorhighs, that are penetrated by well TBE-1X and Kalitami-1X. Fraser et al.(1993) called the minor highsInanwatan and Puragi ridge. Both wellspenetrated a Jurassic interval at theirdeepest levels.TBE-1X found somesandstones with coal fragments andreddish color shale indicating lowterrestrial influence (Fraser et al, 1993).Kalitami-1 encountered more sands ofa similar depositional setting in aJurassic interval. The Cretaceousinterval of both wells are very shally,deposited in an open marineenvironment.

Figure 3. A detail seismic section across Daram Selatan-1 well acquired byAmoseas. Two interpretations are displayed: A) prior to the drilling result and B)after the drilling result. Note the changes of stratigraphic and structuresinterpretation (after Wongsosantiko & Mertosono, 1996).

Figure 4. Seismic section at the center of Misool-Onin Ridge acquired bySchlumberger Geco-Prakla in cooperation with the government of Indonesia in 1997(after Blunden, 2000)

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Figure 5. Section 4, modified after Pairault et al. (2003). The stratigraphic reconstruction shows a Permian paleo highand a tectonic uplift in the Misool-Onin High which caused the erosion of Tertiary section shown as unconformity in thesouth of the section.

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The northern onshore extension of theSekak Ridge was penetrated by wellsPuragi-1, Tarof-2 and Ayot-1&2.Tarof-2 and Ayot-2 wells alsoencountered Permian clastics. TheMesozoic interval of Tarof-2 well isdominated by shale, but Ayot-2 wellfound some limestone. All wellsreported the presence of a thickMiocene Kais limestone formation atshallower level.

Bintuni Basin

The sedimentary basin east of theSekak Ridge is called the Bintuni Basin.This basin contains significantpetroleum accumulation as discoveredin the Vorwata, Wiriagar, Roabiba andOfaweri fields. Towards the east, theBintuni Basin is bounded by the north-south trending Arguni Fault.

Section 5 (Figure 6) shows a seismicsection across the western part of theBintuni Basin. Several structuresdeveloped during the Mesozoic but donot continue into the Cenozoic part ofthe section.

Kepala Burung ForedeepBasin

A foredeep basin developed betweenthe Misool-Onin High and the SeramTrough. This structural unit is shownin Section 1, 3, 6 and 7. Section 1(Figure 2) in the north of this unitindicates a Miocene-Oligoceneremnant but it is not calibrated by anywell. Section 3 (Figure 4) shows arelatively steeply dipping Mesozoicinterval towards the Seram Trough.Several structures developed in thesouthern part of this foredeep basin asshown in Section 6 and 7 (Figure 7).Limestone build ups are potentiallydeveloped in the Upper Jurassicinterval and generated discontinuousstrong seismic reflectors. Tertiarydeposits in this area have thin andcontinuous reflectors typical for distalmarine deposits that are usuallydominated by fine grained clastics(Figure 8). Hydrate layers can also berecognized from the detailed seismicsection and indicated low (< 0oC)temperature, which is typical for deepwater deposits.

Well South Onin-1 drilled in this basinand reported Upper Cretaceouslimestones at bottom hole with minorshale interbeds (Fraser et al, 1993).

Slightly shallower the well encountered>500 m thick Paleogene limestone.Although there are some gas shows,

Figure 6. Section 5 across Berau Basin, Sekak Ridge and Bintuni Basin. TBE-1X islocated on Inanwatan Ridge and Kalitami-1X on Puragi Ridge. These ridges are partof larger Sekak Ridge.

Figure 7. Two seismic sections acquired by Fugro in the south of Misool-Onin Ridge,covering Kepala Burung Foldbelt system, Seram Trough and the imbricated complex insourth. Both sections are SW-NE trends. A) SM05-221 section shows 3 large anticlinesin the complex. B) SM05-222 covers a larger area of imbricated complex.

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the well is unfortunately considered asa dry well.

Seram Trough

A deep flat sea bottom characterizesthe southern part of the Seram Trough(Figure 7) indicating a recent sedimentfill. In the north, Section 1 (Figure 2)and Section 3 (Figure 4) show a narrowtrough with limited recent sedimentfill. A strong amplitude anomaly in thenorth of Section 6 (Figure 8) is anindication of slope failure debris flowdeposits came from the north slope ofthe Kepala Burung Foredeep basin.This section also shows a shift ofdepocentres as some sedimentpackages are thicker in the south andsome are in the north.

Imbricate Complex at Southof Study Area

The Imbricate Complex in the south ofthe study area is generally seismicallypoorly imaged due to intensivefaulting as shown in Figure 2, 4, 7 and8. The thrust faults are dipping to thesouth and some of them are seen onthe seismic sections, especially at thefront end of this structural unit. Figure4 and 8 show the detail of the faults.Small depositional centers developedbetween fault blocks in the southernpart, capturing recent sedimentssupplied from Seram Island (Figure 2).At the sea bottom the active faultsgenerate a rough bathymetry as seen inFigure 4a and Figure 7. Tighteranticlinal features occur as drag foldsas a result of the faulting. This impliesthat the faults are currently still active.A potential hydrate layer occurs in thisarea (Figure 8) as can be interpretedfrom a reflector parallel to the seabottom imaged in the south of thesection. Several petroleum discoverieswere made onshore Seram Island, withthe Manusela Jurassic oolithiclimestone unit as primary target (see K.Hill article in this volume).

Figure 9. Structural and depositionalreconstruction of Misool-Onin Ridge.Faults are red for normal faults, green forinverted faults and blue for reversefaults. See Figure 5 for location of thissection.

Figure 8. A detailed section of Figure 7B showing the potential hydrate layer on theleft of the section and the two major anticlines on the right. Potentially somelimestone developed in the north of the area as shown on this figure.

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Conclusion

The seismic sections reveal a complextectono-stratigraphic history of theSeram Sea. Based on the interpretationof several key seismic lines, we proposethe following sequence of events: Rift related faulting took place

over an extensive area during thePermian, followed by partial upliftin the Triassic.

During the Cenozoic, Paleogeneand Miocene limestonesdeveloped extensively during thisperiod of time.

An inversion phase in LateMiocene – Early Plioceneindicated by transpression andfolding, and reactivation of olderextensional faults. Erosionalprocess developed at the Misool-Onin Ridge during this stage.

Emplacement of the ImbricateWedge during Pliocene toQuaternary times.

Reference

Amiruddin, 2009, A Review onPermian to Triassic Active orConvergent Margin in Southeasternmost Gondwanaland: Possibility ofExploration Target for Tin andHydrocarbon Deposits in theEastern Indonesia, Jurnal GeologiIndonesia, Vol 4 No. 1, Maret 2009,p. 31-41

Blunden, T. (eds.), 2000, Indonesia2000, Reservoir OptimizationConference, Schlumberger

Fraser, T. H., Bon, J., Samuel, L., 1993,A New Dynamic MesozoicStratigraphy for the West IrianMicro-coninent Indonesia and ItsImplications, ProceedingsIndonesian Petroleum Association,22nd Annual Convention.

Hamilton, W., 1979, Tectonics of theIndonesian Region, GeologicalSurvey Professional Paper 1078, US

Government Printing Office,Washington.

Pairault A.A., Hall R., Elders C.F.,2003a. Structural styles and tectonicevolution of the Seram Trough,Indonesia. Marine and PetroleumGeology, 20, 1141-1160

Wongsosantiko, A. & Mertosono, S.,1996, Peran Teknologi EksplorasiMutakhir Sebagai Sarana PenunjangStrategi Bisnis Minyak dan GasBumi, Suatu Pengamatan danPengalaman di PT Caltex PacificIndonesia, in Kumpulan MakalahPeran Sumberdaya Geologi DalamPembangunan Jangka Panjang II,Dalam Rangka Memperingati HUTPendidikan Tinggi Teknik ke 50Yogyakarta.

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Middle Jurassic Ammonites from theCendrawasih Bay Coast and North LengguruFold-Belt, West Papua: Implications of a‘forgotten’ 1913 PaperJ.T. (Han) van GorselHouston, Texas, USA

ABSTRACT

Occurrences of Middle Jurassic bathyalshales with typical ammonite faunaswere reported from the 'Birds Neck',West Papua, in 1913 and 1927publications but these appear to belargely forgotten. They signify aneastern limit for the gas-productiveMiddle Jurassic sands of Bintuni Bayand thus have significant negativeimplications for the potential ofMesozoic hydrocarbon plays inCenderawasih Bay.

Introduction

Almost 100 years ago, in 1913,German paleontologist Georg Boehmfrom the University of Freiburg,published a paper on Middle Jurassicammonites from locations along thecoast of Cenderawasih Bay in WestPapua's 'Bird's Neck' and from nearbylocations in the North Lenggurufoldbelt. It is entitled 'UnteresCallovien und Coronaten-Schichtenzwischen MacCluer Golf undGeelvink-Bai' (translated: 'LowerCallovian and Coronatus beds betweenMacCluer Gulf and Geelvink Bay'(MacCluer Gulf= west Bintuni Bay,Geelvink Bay = Cenderawasih Bay).There is no record in the literature thatthese outcrops have ever beenrevisited, except probably by NNGPMgeologists around the 1950's (Visserand Hermes 1962; Loc. 16 on Encl. 6).

Most of the ammonites described byBoehm were collected during the 1903'Dutch scientific expedition to NewGuinea in 1903', a 9-month journeyalong the northern coastal regions ofWest Papua, led by Arthur Wichmann,professor of geology and geography atthe University of Utrecht, Netherlands.Additional, similar Middle Jurassic

ammonite material was available frommaterial collected by BPM geologist,Hirschi, around 1906 from localitiesfarther inland, west of the main divideof the northern outliers of theLengguru foldbelt. All fossil materialended up in the collections of theUniversity of Utrecht.

Boehm (1913) claimed that this paperwas the first record of ammonites fromNew Guinea Island that could bereliably dated, although Etheridge(1889) had already reported similarammonite finds at the Strickland Riverof Papua New Guinea. Similarammonite faunas were also knownfrom Taliabu and Mangoli in the Sulaislands of eastern Indonesia (Boehm1912).

A later paper by Gerth (1927) entitled'A new occurrence of the bathyalcephalopod facies of the MiddleJurassic in Netherlands New Guinea'largely confirms the Boehm results. Itdescribes a collection of MiddleJurassic ammonites collected by aDutch government official fromFakfak. Unfortunately, locationinformation is very poor, onlydescribed as Wairor River and itsWeriangki tributary, supposedly nearFak Fak. Ammonites are from geodesin hard black limestone, and species aresimilar to those from CenderawasihBay and the Sula islands.

The Boehm (1913) paper now appearsto be largely forgotten, but thepresence of Middle Jurassic openmarine black shales is an important

Figure 1. Overview map of Cenderawasih Bay (then called Geelvink Bay;Wichmann, 1917).

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control point in paleogeographicreconstructions of the region, and maybe particularly relevant to thedistribution and provenance of thepresumably age-equivalent gasreservoir sandstones of the Tangguhcomplex of Bintuni Bay.

Localities

Several localities were mentioned byBoehm (1913), but not described ingreat detail. More details can be foundin the lengthy report of the 1903 NorthNew Guinea expedition by Wichmann(1917). There are some inconsistenciesbetween the Boehm (1913) andWichmann (1917) maps of theWendesi area. We assume theWichmann maps are the more accurateones (Figures 1, 2).

The richest ammonite assemblageswere collected along the Mamapiri andPapararo and creeks, SE of the coastalvillage of Wendesi (Figure 2). TheMamapiri Creek assemblages areparticularly rich, probably belonging tomultiple horizons, and include up to 30cm large specimens of Phyllocerasmamapiricum n.sp. Most of theammonite material was not collected insitu, but as float in the riverbeds.Wichmann described the few smalloutcrops in Mamapiri creek as steeplydipping dark shales (Wichmann 1917,p. 343).

Rocks are described as black, very fine-grained, hard calcareous marl atMamapiri and as non-calcareous,slightly metamorphic shaly claystone atPapararo. Most of the ammonites arein non-calcareous black geodes. AtMamapiri the ammonites are typicallyundeformed, only a few are clearlysqueezed. At Papararo creek almost allammonites are more or less deformed.

Similar Jurassic ammonite material wascollected farther inland by BPMgeologist Hirschi, around 1906, west ofthe main divide of the northernoutliers of the Lengguru foldbelt. Thelocality is named Aramasa and wasdescribed as steeply dipping dark shalesfrom 'the western foot of the WiwiMountains, specifically from a righttributary of the upper Aramasa calledUrubate' (Figure 3). This localitydescription is rather vague and it willprobably be difficult to re-locate the

site, but it does suggest that MiddleJurassic open marine shaly facies arepresent inland near the Northerntermination of the Lengguru foldbelt aswell.

Faunas

The macrofaunas are composed mainlyof ammonites (Figures 4, 5), some

quite large (30 cm). They are associatedwith rare and poorly preservedcanaliculate belemnites, brachiopods(Rhynchonella aff. moluccana) and bivalvemollusks.

Ammonite assemblages are dominatedby species of the subfamilyMacrocephalitinae and the older, butmorphologically similar subfamilySphaeroceratinae. Dominant species

Figure 2. Map of Wendesi area, showing Mamapiri and Paporaro creeks(Wichmann, 1917).

Figure 3. Locality map of Boehm (1913), showing Wendesi area localitiesof Wichmann and upper Aramasa area, where Hirschi collected MiddleJurassic ammonites.

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are Macrocephalites keeuwensis andPhylloceras mamapiricum.

Boehm grouped many of theMacrocephalites species in informallynamed varieties of M. keeuwensis, aspecies he first described from the SulaIslands in 1912. Taxonomy of thisgroup is somewhat difficult; genus andspecies names have been revisedmultiple times (see e.g. Kruizinga 1926,Westermann and Getty 1970,Westermann and Callomon 1990).

Westermann and Callomon (1990)described a new genus and species ofSphaeroceratidae, named Satoceras satoi,which is quite abundant at theMamapiri locality (= Macrocephaliteskeeuwensis B of Boehm 1913?)

Age

Boehm (1913) recognized theCenderawasih Bay/ N Lengguruammonites as Middle Jurassic species,assigning them to the Lower Callovianand 'Coronatenschichten' (an oldGerman term for Bajocian).Westermann and Getty (1970) in theirdescription of ammonite assemblagesfrom the West Papua Central Range,revised some of the genus/ speciesnames of Boehm (1913), but essentiallyconcurred with Boehm's Bajocian toEarly-Middle Callovian ageassignments (Fig. 6).

The ammonite faunas described byGerth (1927) from the Werianki River(Fakfak District?) containMacrocephalites keeuwensis, Sphaeroceras cf.bullatum and Peltoceras, suggesting anEarly Callovian age. From the WairoriRiver two Stephonoceras species indicatea probable Bajocian age

Other localities on NewGuinea and depositional/paleotectonic position

Since the Boehm (1913) and Gerth(1927) papers, additional occurrencesof similar Middle Jurassic ammoniteassemblages were reported from theBirds Neck/ Cenderawasih region byDonovan (in Visser and Hermes, 1962;Roemberpon Island and SouthCenderawasih Bay/SE Lengguru).

Similar Middle Jurassic ammonitefaunas have subsequently beenreported from the Central Range ofNew Guinea, in both in West Papua(Gerth 1965, Westermann and Getty1970, Helmcke et al. 1978,Westermann and Callomon 1990) andin Papua New Guinea (Etheridge1889) (Fig. 7). I also observed these inriver float North of Wamena/ Tiom.Like at the Cenderawasih Baylocations, the ammonites are found innodules in black shales and aregenerally well preserved.

Depositional/ paleotectonicsetting

Observations made on the MiddleJurassic Macrocephalites shales of the'Lower Kembelangan Formation' inthe Papua Central Range foldbeltinclude:1. The outcrops are limited to thenorthernmost part of the foldbelt, wellnorth of the topographic divide, andimmediately south of the Miocenecollisional suture zone between theAustralian- New Guinea continentalplate (south) and the belts ofmetamorphics, ophiolites and Pacificoceanic and arc terranes (north);

Figure 4. Plate 2 of Boehm (1913), showing 'Phylloceras mamapiricum n.sp.' (figs.1-2; re-assigned to Holcophylloceras indicum by Westermann and Callomon 1990) and'Sphaerocers cf submicrostomata (figs. 3-4; re-assigned to Sphaeroceras boehmi byWestermann 1956).

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Age









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Age









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2. These black shales are clearly bathyalmarine facies;3. Age range shows these are a distalfacies equivalent of the widespreadMiddle Jurassic 'Plover'/Tangguhreservoir sandstones. Whether theywere deposited on a distal passivemargin or within a deepening marinerift setting that subsequently became apassive margin after oceanic break-up,is not clear;4. The ammonite shales are invariablysteeply dipping and highly deformed.They also become gradually moremetamorphic to the north, towards theophiolite belt and much of themetamorphic rock is probablymetamorphosed KembelanganFormation sediment (Visser andHermes 1962, Cloos et al. 2005,personal observation duringPertamina-Esso 1991 joint studyfieldwork). They therefore representthe outer margin of the New Guineasector of the Australian continentalmargin prior to Miocene collision withthe N-dipping subduction zone of aPacific volcanic arc system. Thecollision then caused the accretionaryprism-style deformation of sedimentsand the 'metamorphic sole' belowobducted ophiolite.

Distribution of'Macrocephalites fauna'outside New Guinea andbiogeographic significance

The classic Middle JurassicMacrocephalites-dominated ammoniteassemblages from New Guinea andSula islands are of relatively lowdiversity and are very similar across thearea. Several genera (Satoceras, Irianites)and species of this fauna are endemicto East Indonesia- New Guinea. Thistypical ammonite fauna differs fromMiddle Jurassic ammonite assemblagesfrom low-latitude Tethys regions likethe Mediterranean. Westermann andCallomon (1990) suggested they were agroup that flourished in temperate,southern latitudes, perhaps around35°-40°S or between ~30°-60° S asshown on the restoration inWestermann (2000).

The 'Macrocephalites fauna' characterizesa distinct biogeographic province,variously named 'Gondwanan-

Tethyan', 'Austral- Indo-Pacific', 'Indo-SW Pacific', 'Himalayan', etc. Thisprovince can be traced from Nepal/Tibet in the Himalayas through EastIndonesia- New Guinea and possiblyeast to New Zealand (Uhlig 1911, Enayand Cariou 1997, 1999, Westermann2000, etc.). On a Middle Jurassicrestored map all these occurrenceselegantly line up along the northern/eastern margin of Gondwana, from theNorth India margin in the west, aroundthe NW Australia- New Guinea marginand farther East (Fig. 8).Occurrences of 'Macrocephalites fauna' inEastern Indonesia outside New Guineainclude:

1. Taliabu and Mangoli, Sula Islands(Boehm 1912, Kruizinga 1925)2. Obi (Phylloceras, Stephanoceras,Macrocephalites from concretions inphyllitic shales on SW Obi Besar,indicating Bajocian–Early Callovian;Brouwer 1924)3. Rote (Roti, Rotti): rare Macrocephalitescompressus and Stephanoceras from a mudvolcano in NE Rote. (Boehm inVerbeek 1908, Krumbeck 1922) (someauthors argued that this may be part ofan allochtonous block, not necessarilypart of the present-day Australia NWShelf margin).

Figure 5. Plate IV of Boehm (1913), showing his Macrocephalites keeuwensisvarieties y (figs. 1-3) and B (figs. 4-5), species characteristic of 'North Gondwana'Early Callovian. M. keeuwensis variety B was renamed Satoceras satoi byWestermann and Callomon (1990).

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4. Babar Island: Macrocephalites faunaammonites from outcrop and mudvolcano material, dominated bySatoceras satoi (Callomon and Rose2000) (also subject to the allochtonous-autochtonous debate).

Macrocephalites faunas have never beenreported from West Indonesia(Sumatra, NW Kalimantan) or theIndochina/Malay Peninsula area (e.g.Sato 1975). Marine Middle Jurassicdeposits are present in these places, butwhether the absence of Macrocephalitesfauna reflects differentpaleogeographic positions (moreequatorial) or whether these depositsare not of exactly the right age andfacies, remains to be determined.

Macrocephalites faunas have also notbeen reported from other EastIndonesia islands with Jurassicsediments. Misool and Timor do haveMiddle Jurassic marine sediments, butprobably not in the right facies (too

shallow?). Buton, Buru and Seram havemarine Early and Late Jurassicsediments, but Middle Jurassicsediments appear to be very thin orabsent, which was interpreted as theexpression of a 'breakup unformity' byPigram and Panggabean (1984)

Conclusions/ implications ofthe Boehm (1913) paper

1. Distal continental margin setting?The Middle Jurassic ammonite-richblack shales described above from theBirds Neck/Cenderawasih Bay clearlyrepresent a relatively distal, deep andopen marine facies. They are verysimilar in lithology, fauna anddeformational history to theammonite-bearing 'KembelanganFormation' black shales in thenorthernmost part of the CentralRange fold-thrust belt and are alsosituated adjacent to a belt of youngmetamorphic rocks (Wandamen

Metamorphic complex). It is verytempting to also interpret theCenderawasih- North Lenggurulocalities as part of the outermost zoneof sediments along the JurassicAustralian-New Guinea passivemargin, which became the frontalcollision zone in the Neogene.

2. Nature of Cenderawasih Bay basementIf the Cenderawasih/North Lenggurubathyal Middle Jurassic ammoniteshales do indeed represent distalAustralia-New Guinea continentalmargin clastics, it is unlikely that thereis much, or any, Australian continentalcrust outboard of this (CenderawasihBay). The traditional view thatCenderawasih Bay is underlain byNorth New Guinea-equivalent volcanicarc and oceanic terranes that originatedin the Pacific realm, perhaps with afringe of metamorphics and ophiolites(e.g. Dow and Hartono, 1982), appearsmore likely than a floor of continentalcrust, as argued in some recent papers

Figure 6. Taxonomic revision of species described by Boehm (1913) with age interpretation by Westermann and Getty (1970).Specimens from Mamapiri placed here in Subkossmattia boehmi were originally described by Boehm (1913) as Macrocephaliteskeeuwensis var. y., then renamed Satoceras boehmi by Westermann and Callomon (1990).

Figure 6. Taxonomic revision of species described by Boehm (1913) with age interpretation by Westermann and Getty (1970).Specimens from Mamapiri placed here in Subkossmattia boehmi were originally described by Boehm (1913) as Macrocephaliteskeeuwensis var. y., then renamed Satoceras boehmi by Westermann and Callomon (1990).

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(e.g. Sapiie et al., 2010). Sula-likemicrocontinental blocks that rifted offthe New Guinea margin in Jurassic orCretaceous time may be present here,but no direct continuation of theMesozoic 'Plover' hydrocarbon playsof Bintuni Bay/ Australia-New Guineamargin should be expected here.

3. Bintuni Bay- Birds Head Middle Jurassicsandstone distribution modelsThe Bajocian- Middle Callovian agerange of the ammonite-bearing shalesappears to be of the same that of theprincipal gas reservoir sandstones inthe Tangguh field complex of BintuniBay (Roabiba Sand, etc.). Thesemarginal marine- shallow marine,quartzose sandstones arecompositionally and texturally matureand generally interpreted to be derivedfrom a cratonic source (Australia-NewGuinea). They may be compared to thewidespread Middle Jurassic sandstonesof the Australian NW Shelf, known asPlover Formation.

Decker et al (2009, Fig. 15) proposed amodel for the Early-Middle JurassicTangguh reservoir sands in BintuniBay. It shows deposition confinedwithin an extensive E-W trending'incised valley', with Early–MiddleJurassic shallow marine-non marinesand systems backstepping towards aprovenance area in the East. However,the Boehm (1913) and other papersdocument control points east of that'valley' system, where Middle Jurassic isrepresented by distal marine shales.This shows that this part of the BirdsNeck is not in the sand fairway that fedthe Bintuni Bay Tangguh sands andthat the Cenderawasih Bay-NorthLengguru area was not part of theprovenance area for these quartzosesediments in Jurassic time. Therefore,this Bintuni Bay sand distributionmodel can only be correct if somestructural discontinuity (terraneboundary or a major transcurrent fault)is invoked between the BirdsHead/Bintuni Bay block and theCenderawasih Bay-North Lengguruarea, as indeed suggested by Decker etal. (2009).

Figure 7. Outcrop localities with Middle Jurassic ammonites, New Guinea island(Westermann and Callomon 1990) (not showing all known localities)

Figure 8. Restoration at Bathonian time, showing Middle Jurassic ammonitepaleogeographic realms (Westermann 2000). Highlighted in red is the belt of theMacrocephalites-dominated 'Austral-Indo Pacific Realm', which is known from Nepal,the NW Australia- New Guinea margin and possibly New Zealand, and which restoresnicely as a continuous zone along the North/ East Gondwana margin, in temperate-latitudes.

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References

Boehm, G., 1906. Neues aus demIndo-Australischen Archipel.Geologische Mitteilungen aus demIndo-Australischen Archipel I,Neues Jahrbuch Min. Geol. Pal.,Beil. Band 22, p. 385-412.

Boehm, G., 1912. Die Sudkusten derSula-Inseln Taliabu und Mangoli. 4.Unteres Callovien.Palaeontographica, Suppl. IV, Beitr.Geologie Niederlandisch-Indien 1,p.121-179.

Boehm, G., 1913. Unteres Callovienund Coronaten-Schichten zwischenMacCluer Golf und Geelvink-Bai.Nova Guinea VI, Geologie, Brill,Leiden, 1, p. 1-20.

Callomon, J.H. and Rose, G., 2000.Middle Jurassic ammonites fromthe island of Babar in the southernMoluccan forearc, Indonesia. RevuePaleobiol., Spec. Vol. 8, p. 53-64.

Decker, J., Bergman, S.C., Teas, P.A.,Baillie, P. and Orange, D.L., 2009.Constraints on the tectonicevolution of the Bird’s Head, WestPapua, Indonesia. Proc. 33rd Ann.Conv. Indonesian PetroleumAssocation, IPA-G-139, p. 491-514.

Dow, D.B. and Hartono, U., 1982. Thenature of the crust underlyingCendrawasih (Cendrawasih) Bay,Irian Jaya. Proc. 11th Ann. Conv.Indon. Petrol. Assoc., p. 203-210.

Enay, R. and Cariou, E., 1997.Ammonite faunas andpalaeobiogeography of theHimalayan belt during the Jurassic:initiation of a Late Jurassic australammonite fauna. Palaeogeogr.,Palaeoclim., Palaeoecol. 134, p. 1-38.

Enay, R. and Cariou, E., 1999. Jurassicammonite faunas from Nepal andtheir bearing on the

palaeobiogeography of theHimalayan belt. J. Asian Earth Sci.17, 5-6, p. 829-848.

Etheridge, R., 1889. On our presentknowledge of the palaeontology ofNew Guinea. Records Geol. SurveyNew South Wales 1, 3, p. 172-179.

Gerth, H., 1927. Ein neuesVorkommen der bathyalenCephalopoden Fazies des mittlerenJura in Niederlandisch Neu Guinea.Leidsche Geol. Meded. 2, 3, p. 225-228.

Gerth, H., 1965. Ammoniten desmittleren und oberen Jura und deraltesten Kreide von Nordabhangdes Schneegebirges in Neu Guinea.Neues Jahrb. Geol. Palaeont., Abh.121, 2, p. 209-218.

Helmcke, D., Barthel, K.W. and vonHillebrandt, A., 1978. Uber Juraund Unterkreide aus demZentralgebirge Irian Jayas(Indonesian). Neues Jahrb. Geol.Palaeont., Monatshefte 1978-11, p.674-684.

Hirschi, H., 1908. Reisen in Nordwest-Neu-Guinea: Vortrag gehalten am30 November 1907. JahresberichtGeogr.-Ethnogr. Ges. in Zurich1907-1908. Von Lohbauer, Zurich1908, p. 71-106.

Kruizinga, P., 1926. Ammonieten eneenige andere fossielen uit deJurassische afzettingen der Soelaeilanden. Jaarboek MijnwezenNederl. Oost Indie 54 (1925),Verhand. 1, p. 13-85.

Pigram, C.J. and Panggabean, H., 1984.Rifting of the northern margin ofthe Australian continent and theorigin of some microcontinents inEastern Indonesia. Tectonophysics107, 3-4, p. 331-353.

Sapiie, B., Adyagharini, A.C. and Teas,P., 2010. New insight of tectonicevolution of Cendrawasih Bay andits implications for hydrocarbon

prospect, Papua, Indonesia. Proc.34th Ann. Conv. Indon. Petrol.Assoc., IPA10-G-158, 11 p.

Sato, T., 1975. Marine Jurassicformations and faunas in SoutheastAsia and New Guinea. In: T.Kobayashi & R. Toriyama (eds.)Geology and Palaeontology ofSoutheast Asia 15, University ofTokyo Press, p. 151-189.

Sukamto, R. and Westermann, G.E.G.,1992. Indonesia and Papua NewGuinea. In: G.E.G. Westermann(ed.) The Jurassic of the Circum-Pacific, Cambridge Univ. Press, p.181-193.

Uhlig, V., 1911- Die marinen Reichedes Jura und der Unterkreide. Mitt.Geol. Ges. Wien, 4, 3, p. 389-448.

Visser, W.A. and Hermes, J.J., 1962.Geological results of theexploration for oil in NetherlandsNew Guinea. Verhandy. Kon.Nederl. Geol. Mijnbouwk.Genootschap, Geol. Series 20, p. 1-265.

Westermann, G.E.G. and Callomon,J.H., 1988. The Macrocephalitinaeand associated Bathonian and earlyCallovian (Jurassic) ammonoids ofthe Sula islands and New Guinea.Palaeontographica A, 203, p. 1-90.

Westermann, G.E.G. and Getty, T.A.,1970. New Middle JurassicAmmonitina from New Guinea.Bull. Amer. Paleont. 57, 256, p.231-308.

Wichmann, A., 1917. Bericht über eineim Jahre 1903 ausgeführte Reisenach Neu-Guinea. In: A.Wichmann (ed.) Nova Guinea,Résultats de l’expéditionscientifique néerlandaise à laNouvelle Guinée en 1903, E.J. Brill,Leiden, vol. IV, 492 p.

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Interplay between Submarine DepositionalProcesses and Recent Tectonics in the BiakBasin, Western Papua, Eastern IndonesiaClaudia Bertoni & Juan ÁlvarezRepsol Exploracion SA, Madrid, Spain

ABSTRACT

The offshore Biak Basin between Biakand Yapen Islands is a transtensionalpull-apart basin. Deposition alongbasin margins is strongly influenced byactive faulting. The bathymetric map ofthe basin shows submarinedepositional processes occurred duringrelatively recent tectonic activity.

Introduction

The Biak Basin is located in EasternIndonesia, Papua Province, betweenBiak and Yapen islands. The area ischaracterised by a complex tectonichistory, being located in the obliquecollision zone between the Australianand Pacific Plates. A major strike-slipsystem, the Sorong – Yapen FaultZone, bounds the basin to the south(Figure 1).

The basin is a frontier area for oil andgas exploration and offshore data arevery limited. As a consequence, theorigin and evolution of this basin is stillpoorly known. Recently acquiredoffshore data can help constrain thehistory of this basin. In this study, weuse suite of high-resolutionbathymetric data acquired in the areaby TGS (2007). These data allowdetailed seabed imaging and thoroughmapping of the various morpho-structural surface features observed inthis tectonically active area (Figure 2).

On the seabed, fault lineaments andfold axes have been identified, togetherwith submarine depositional featuresand their generating processes. Thedeformation is dominated by thepresence of the Sorong-Yapen faultzone. Modern earthquake activityrevealed by public domain data onfocal mechanisms (Ekstrom, 2006)highlights remarkable consistencyamong earthquake mechanisms and

some of the morpho-structural featuresmapped on the seafloor.

Earthquake activity seems to befocused in the N and E flanks of thebasin, where a series of fault scarpsand associated deposits are observed.In other areas, where no earthquakeactivity has been registered (especiallyto the W and SW), deformation couldbe accommodated by plastic processes(e.g. seabed creeping). This allows us todraw conclusions on the generaltectonic setting of the area, andeventually lead to a betterunderstanding of the evolution of theBiak basin.

Submarine Depositionalprocesses

The Biak basin is a semi-enclosed basincovering an area of ca. 4000 sq km inits central part, with water depthreaching over 1100m (Figure 2). Thebasin is connected to the Yapen Straitthrough a narrow corridor to thesouth-east and to the Pacific Ocean tothe west, through a broader seaway,between the Biak and the NumforIslands (Figure 1). The basin appearsrelatively sediment-starved withdominant deep water clasticdeposition; carbonates develop on itsmargins and volcanic deposits are alsolocally observed and they outcrop onthe nearby islands. The basin marginslopes are variable and range from fewdegrees in the W and SW, to relativelysteep (5 to 15 degrees) on the NE and

Figure 1. Tectonic setting and structural elements of the West Papua area. Seabedand digital elevation model are from Gebco database (http://www.gebco.net/). Publicdomain data on earthquake focal mechanisms show recent seismic activity (fromEkstrom, 2006 http://www.globalcmt.org/). Color keys: black represents strike-slip, redand blue represent compressional and extensional mechanisms, respectively. The mainfault zones are color-coded in the same way as the earthquakes focals. Grey arrowsrepresent GPS motions relative to Australia (from Stevens et. al., 2002).

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E slopes. Sediment accumulationpatterns in the basin vary and arenormally associated with the differentslope angles. The main deposits andprocesses observed are:

Well-defined mounded bodies withlobular shape in plan view, either inisolated or coalescent configuration,located at abrupt decrease ingradient from the high angle slopesto the basin (Figures 3 and 4). Themounded bodies are interpreted asclastic lobes originated by re-sedimentation processes. Clasticlobes (Figure 3) are constructionaldepositional bodies developeddownstream of points wherelaterally confined flows from thefeeder channels expand (e.g. Stow etal., 1999). The shape and directionof the lobes suggest that they arefed from the north, where they arebounded by a series of semi-circularNW-SE scarps (Figure 3). Thescarps represent major erosionalfeatures in the basin. Erosionalactivity is also documented byincisional episodes on top of thelobes and large blocks deposited intheir most marginal parts (bluedashed lines in Figure 3).

Figure 4 shows a belt of multipleadjacent lobes, forming a linear,slope-parallel apron, 20km long andbetween 3km (lateral) to 8 km(central) wide from scarp to baseof slope. The described slope apronis directly associated with a series ofparallel linear features observed onthe seabed. Thesemorphostructures are interpreted asterraced fault scarps and representthe likely linear source for theapron. The overlapping andcoalescing series of lobescomposing the apron suggestdifferent phases of fault scarpactivity that seems to beconcentrated in the central part ofthe apron.

An aerially extensive circular crater-like structure (Figure 4) rimmed byan arcuate, crescent-moon shapefeature, open to the N and boundedat the flank by small scale circularscarps. The maximum reliefobserved at the centre of this crateris ca. 300m, and diameter reaches

nearly 10km. The typically concave-upwards subcircular shape andassociated curved scarps resemblesthat of collapse structures (e.g.Stewart, 1999). Analogous arcuate-shaped escarpments interpreted asrepeated slope failure episodes atthe edge of a carbonate platformhave been described by Ten Brinket al. (2006) offshore Puerto Rico.Possibly, this structure is associatedwith subcropping carbonate unitsand differential compaction ofoverlying deep-water sediments.Additionally, we observed a seriesof straight slope gullies, V-shaped

in section, on the slope to the westof the circular collapse structure.

A subtle wavy surface morphologyis evident on the N-NW slope ofthe basin and is associated with lowslope angles (Figure 2). Thismorphology is a typical expressionof seabed sediment creep, i.e. aprocess of slow strain due to thedownslope weight of sediment(Reading, 1999). Although creepmight be a precursor to creeprupture and slope failure, normallyit suggests the predominance ofplastic deformation.

Figure 2. Gridded multibeam data showing details of seabed morphology in the BiakBasin (data from TGS). Contour interval is 100m. Digital elevation model is from AsterGlobal Digital Elevation Model (GDEM) (http://www.gdem.aster.ersdac.or.jp/)

Toe-of-slope lobes

Canyon/Gully

Channelised body

Semi-circular scarps

Terracedfault scarp

Toe-of-slope lobes

Canyon/Gully

Channelised body

Semi-circular scarps

Terracedfault scarp

Figure 3. Details of morphostructural interpretation of seabed in the northern part ofBiak Basin (See Figure 2 for location). Note the presence of clastic lobes adjacent tosemi-circular scarps, and toe-of-slope deposits developed at the end of a channelisedbody fed from the N. Dashed lines indicate the most recent erosional episodesoverprinting the clastic lobes.

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Tectonic Setting

West Papua represents an area whereat least 3 major tectonic platesconverge, with smaller terranes actingas buffers along the edges of the mainplates (Figure 1).The Biak Basin is located within thenorthern edge of the collision zonebetween the Australian and Pacificplates, in an area which can beinterpreted as a crustal sliver boundedby the New Guinea Trench to thenorth and the Sorong-Yapen fault zoneto the south. The crustal configurationof this area is the result of the collisionand accretion of terranes of complexorigin (volcanic arcs, rotated forearcterranes, submarine plateaus, etc.) thatwere dragged by a south facingsubduction zone and collided againstthe Australian margin during Tertiary(Hill and Hall, 2003). This subductionseems to have ceased and relative platemotion is now oblique, as revealed bydominant strike-slip earthquake activityat Yapen Island along the left-lateralSorong-Yapen Fault Zone (Figure 1).

To the west of the Biak Basin, in theBird’s Head area, present dayseismicity together with GPS datasuggest that this region is moving atthe same pace as the Caroline Plate, ata rate of 7.5–8.0 cm/yr in the directionof 252° relative to northern Australia(Stevens et al., 2002; Decker et al.,2009). Considering these kinematicindicators, the Bird’s Head area isinterpreted to be a product of escapetectonics resulting from the obliquecollision between the Australian plateand the remnants of volcanic belts andaccreted terranes carried by the PacificPlate (Pubellier and Ego, 2002). Theescape movement is accommodated bytwo broad left lateral strike-slip faultzones, the Sorong-Yapen Fault Zoneto the North, and the Tarera-AidunaFault Zone to the South (Figure 1).

Based on the above tectonicframework and interpretation of highresolution multibeam bathymetry,earthquake focal mechanisms and GPSdata (Figure 5), we interpret the BiakBasin to be a transtensional pull-apartbasin which developed in an obliquedirection to the left-lateral Sorong-Yapen Fault Zone (Figure 6).

The map view of the Biak Basin showsa sigmoidal to rhomboidal geometryoriented in NW-SE direction (Figure5). Basin boundaries are analogouswith terraced oblique-slip extensionalsidewall fault systems, connectinglaterally offset principal displacementzones (PDZ) of the main strike-slipfaults. The basin floor is very flat andtends to be asymmetric where thesidewall faults join the PDZ. Thesidewall faults show changes inkinematics from dominantly dip-slipextension in their central sections tooblique slip and strike slip at either endwhere they connect with the PDZ.Another characteristic feature forinterpreting Biak Basin as a pull apart

basin lies on the typical narrow ends ofthe basin, developing in-line horst andgraben structures which broadenoutward into the basin.

The overall geometry of the basin andits bounding structures seem to becompatible with a right-lateral strike-slip displacement (Figure 7; Dooleyand McClay, 1997). Although left-lateral deformation is dominant in theSorong-Yapen, right-lateral offsetshave already been described in theRandaway Fault System (Charlton,2010), which in fact, seems to be thesouthward continuation of thesoutheastern end of the Biak basin(Figure 6).

Figure 4. Details of morphostructural interpretation of seabed in the eastern part ofBiak Basin (see Figure 2 for location). Note the multi-episode slope aprons adjacent toterraced fault scarps.

Figure 5. Details of modern earthquake activity in the Biak Basin and surroundingareas, as shown by focal mechanism data (for key to symbols, see Figure 1). Bathymetrydata s from TGS gridded multibeam merged with that of Gebco database. High resolutiontopography is from Aster GDEM database.

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Analysis of computed focalmechanisms of earthquakes(Dziewonski et al., 1981) shows thatsome of the sidewall fault systemsbounding the Biak Basin are active atpresent day and are consistent with astrike-slip motion (Figures 6 and 7).This implies therefore that thesubmarine depositional processespreviously described could becontrolled by recent strike sliptectonics.

The earthquake data also point out thatcontractional deformation to the northof the Biak Island is partitioned intostrike-slip deformation to the south,towards the Sorong-Yapen Faultsystem. In addition to the dominantstrike-slip and contractional earthquakesolutions, we also observed a fewnormal extensional earthquakes in thevicinity of Biak Island. This fact maybe due to stress perturbations causedby pre-existing structures. As thecrustal configuration of the area iscomposed of several fragments, faultblock rotations and local extensionmay exist because changes of slip ratesbetween different crustal blocks. Thesechanges in slip rates could then explainthe fact of having right-lateralstructures coexisting with a dominantlyleft-lateral strain.

Summary and Conclusions

The observations made to date on theseabed depositional and tectonicprocesses suggest that current basinaldepositional processes in the Biak

Basin are significantly controlled byseismic activity in the region.

The interplay between recent seismicactivity and deformation, erosional anddepositional patterns of the Biak Basinis illustrated by the analysis of thecircular shaped crater-like collapselocated in the southern edge of thebasin (Figure 4). This collapse is near astrike-slip focal mechanism solutionand it allows us to speculate that the

feature is controlled by recent faultactivity. A second clear example of thisinterplay is how the fault scarpsassociated with base-of-slopedepositional lobes are consistent inorientation and location with nearbystrike-slip earthquake focalmechanisms (Figures 4 and 6).

Based on these indications, we inferthat the seabed can be divided in twomain zones, based on recent tectonicactivity: seismic and aseismic zones.Seismic zones, where focalmechanisms are recorded, showsteeper slope flanks and fault scarpswith associated depositional lobes.Apron development is seen along onelinear fault scarp. The compositecharacter of the associated clastic lobesmight indicate repeated scarp activities.It is well known that instability and re-sedimentation processes are favouredby high slope angles and repeatedcyclical stress. We consider that this ismore likely to be caused by thedocumented seismic activity, ratherthan high sediment supply, in thisrelatively starved basin. Conversely, theaseismic zones correspond to areas ofabsence of earthquake activity, and arelocated to the W and SW of the basin.These areas are associated withsediment creep, typical of slow-strainand plastic deformation, and the slopesare prone to erosion by gullies.

As a general conclusion, the uplift andbending recorded in the E part of thebasin, and the scarps in the NE flank,are compatible with the basinal strike-slip tectonic setting proposed for theBiak Basin. The results presented herecan therefore be used to support abasin evolution model and providenew insights on the regional tectonicsof this highly complicated area.

Figure 6. 3 D view of the integration of earthquake focal mechanisms with structuralinterpretation on the Biak Basin and surrounding areas. PDZ = Principal DisplacementZone (for key to symbols, see Figure 1)

Figure 7. Conceptual right-lateral pull apart basin (after Dooley and McClay, 1997).

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Acknowledgements

The authors wish to thank Migas andTGS for granting permission topublish the data, and all colleaguesfrom the Indonesia and New Ventureteams in Repsol for discussions andtheir help in publishing this paper. Wealso are grateful to the editors of theBerita Sedimentologi for their supportand suggestions for improving themanuscript.

References

Charlton, T. R., 2010. The Pliocene-Recent anticlockwise rotation of theBird’s Head, the opening of the AruTrough – Cenderawasih Baysphenochasm and the closure of theBanda double arc. Proceedings ofthe Indonesian PetroleumAssociation 34, p. 203-210.

Decker, J., Bergman, S.C., Teas, P.A.,Baillie, P. and Orange, D.L., 2009.Constraints on the tectonicevolution of the Bird’s Head, WestPapua, Indonesia. Proceedings ofthe Indonesian PetroleumAssociation, 33th AnnualConvention, p. 491-514.

Dooley, T. and McClay, K.R., 1997.Analog modeling of pull-apartbasins. AAPG Bulletin 81, 1804–1826

Dziewonski, A. M., Chou, T. A., andWoodhouse, L.H., 1981.Determination of earthquakessource parameters from waveformdata for studies of global andregional seismicity. Journal ofGeophysics Research, 86, p. 2825 –2852.

Ekstrom, G., 2006. Global CMT.Accessed online athttp://www.globalcmt.org

Hill, K.C. and Hall, R., 2003.Mesozoic–Cenozoic evolution ofAustralia’s New Guinea margin in aWest Pacific context. GeologicalSociety of Australia, SpecialPublication 22 andGeologicalSociety of America Special Paper,372, p. 265–289.

Pubellier, M. and Ego, F., 2002.Anatomy of an escape tectoniczone, Western Irian Jaya(Indonesia). Tectonics, 21, 4, p. 1-16.

Reading, H.G. (Ed.), 1999,Sedimentary environments: pro-

cesses, facies and stratigraphy.Blackwell Science, Oxford,

Stow, D.A.V., Reading, H.G. andCollinson, J.D., 1999. Deep seas. In:Reading, H.G. (Ed.), Sedimentaryenvironments: processes, facies andstratigraphy. Blackwell Science,Oxford, p. 395-453.

Stevens, C.W., Mc Caffrey, R., Bock,Y., Genrich, J.F., Pubellier, M. andSubaraya, C., 2002. Evidence forblock rotations and basal shear inthe world’s fastest slippingcontinental shear zone in NW NewGuinea. In: Stein, S. andFreymeuller, J.T. (eds.), PlateBoundary Zones. AmericanGeophysical Union, GeodynamicsSeries, 20, p. 87–99.

Stewart, S.A. 1999. Seismicinterpretation of circular geologicalstructures. Petroleum Geoscience,5, 273–285.

Ten Brink, U.S., Geist, E.L., Lynett, P.,and Andrews, B., 2006. Submarineslides north of Puerto Rico andtheir tsunami potential. In:Mercado, A. and Liu, P. (eds.).Caribbean Tsunami Hazard. WorldScientific Publishers, Singapore, p.67-90.

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Acknowledgements


References














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Acknowledgements


References














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Seismic to Geological Modeling Workflow, anIntegrated Approache to Determine theReservoir Quality of a Fractured Limestone:Oseil Field ExampleArie K. Lapulisa, Roy Andrianto & Anggoro S. DradjatCITIC Seram Energy Ltd., Indonesia

Summary

Natural fractured carbonate reservoir isextremely challenging in terms ofreservoir characterization due to itshigh heterogeneity of reservoirproperty and also of its low oilrecoveries. This paper will show howthe integration of seismic data and welldata had helped significantly for thewell placement and also in the wellcompletion stage.

The datasets that are available andbeing used in this process are 3Dseismic, seismic Inversion, seismicattributes, conventional log andborehole image log. All these data arebeing utilized in an integrated way tocharacterize the fractures behavior ofthe reservoir.

Introduction

Oseil field is a naturally fracturedcarbonate heavy oil reservoir in foldedthrust belts which presents extremereservoir engineering and geologicalchallenges and opportunities. Thesetypes of reservoirs are the extremesetting for large-scale high contrast anddiscontinuous reservoir properties. Thepresences of bottom water inconjunction with high viscosity oilresult in low oil recoveries. Initialproduction stage experienced earlywater breakthrough, water cut risingand then stabilizing.

The reservoir in the Oseil field is theJurassic Manusela Formation. Skeletal,oolitic limestones, deposited as ashallow water shoal, dominate thesuccession in the Oseil-1 and Oseil-4area, and change to a muddier facies inthe Oseil-2 area. In Oseil-1, Oseil-4

and East Nief- 1, the limestones werediagenetically altered to dolomite indiscrete layers.Effective matrixporosity in all the Oseil wells is low.The Manusela Formation is however,extensively fractured on a macro andmicro scale. The macro fracturesprovide both storage capacity and

permeability. Intersection of macrofractures is required to achieve oil flowrates of hundreds of barrels per day.

The fracturing mechanism was relatedto tectonic and carbonatesmineralization (dolomite). Manuselaoolitic carbonate was developed during

Figure 1. Output screen from GMI*MohrFracs indicating the likelihood of slip onnatural fractures seen in image data collected in the Oseil-4 well

Figure 2. Manusela Depth Structure Map showing the fracture orientation of the 6exploration wells.

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basin extension, and it was followed byuplifting, (Fraser et al, 1993)mineralization and then marinetransgression of Kola shale.

In the compression phase, stressgenerated were related to Australianmovement which continue SW to NEdirection starting in the age of lateMiocene. As near surface of Manuselacarbonate contains more dolomitemineral, which means easier to breakcompared with deeper carbonate, thenear surface were fractures with lowangle fracture as the rock were folded.

Extensional normal fault weredominated during development ofSeram basin and extending to the endof Manusela sedimentation, high angleextensional fracture were developed. Incompression phase basin inversion hadhappen and all normal faultsreactivated to became reverse, createlarge high angle fractures and reopenexisting fracture.

Two fracture systems were found inOseil field, FMI log and dip meter dataindicate distinct boundary (Fig 1 Oseil-4 dip meter). 100 feet upper part ofManusela carbonate zone is the zonedominated by low angle fracture and itis also the zone with high oilsaturation. As they were low anglefracture, they created horizontalpermeability and not connected to theaquifer. The deeper part is dominatedby high angle fracture, which clearlyfound on logs and outcrops and thisfracture having larger aperture, veryhigh permeability and connects to theaquifer. As drilling the deeper part hashigh potential of hitting high anglefracture which are high risk of the wellhaving high water cut, it is thenrecommended to drill the shallow partand avoiding the deeper part.

Background & Workflow

One of the main challenges of thisfield is the fact that the matrix porosityof Manusela carbonate is very low,hence the quality of the reservoir relyheavily on the presence of fractures.On the other hand the early waterbreak-through that happened in severalwells that was mainly derived by thefractures and faults.

We need to characterize area where ithave sufficient amount of fractures butmust avoid those areas that havefractures connect to aquifers. By onlyutilizing well data, i.e conventional logsand borehole images, we are limited bya small localized area. Since theheterogeneity of this reservoir is veryhigh, then a more regional approach todefine the fractures characteristicdistribution is required.

To have a more regional understandingof the fault, we have utilized our 3Dseismic data by applying a Pre-Stack

Anisotropy Inversion to detect thedistribution of the fracture in this field.The next step is to utilize theinformation from this seismic data tosimulate the dynamic behavior of thereservoir. A dual porosity permeabilitymodel was built by generating aDiscrete Fracture Network (DFN)base on the combination of well data(mainly image interpretation) and theresult of the Pre-Stack SeismicAnisotropy.

Figure 3. Close-up whole core photographs well NUA-3 of Manusela FormationPlate 2

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The result of the seismic anisotropy,3D model building & simulation thenwas used to place new infill wells.During the testing & completion modeof the new drilled wells, all the well &seismic data are continuously beingused to monitor the performance ofthe well. One of the very useful is theAnt-Tracking Attribute that wasderived from the original 3D seismicdata.

Well Based Fracture Analysis

There are 6 wells that have completeimage data of this field. Base on theimage interpretation, it can be seen thatto the east the main orientation of thefractures is NNE-SSW while to thewest it’s tends to orient more to theNE-SW to E-W direction (Figure 2).

Core data are also available, and baseon core, the apertures of the fractureswas measured. From two wells, theaperture width of the fractures fallswithin range 0.00 mm – 5,5mm. Whilebased on image data, the range ofaperture width is between 0,00 to0.57mm (Figure 3).

From the borehole image, there areseveral types of fractures/faults thatcan be classified (figure 4).

Below are the different types offractures:1. Conductive Continues Fracture

(CCF),2. Conductive Discontinues Fracture

(CDF),3. Conductive Micro Fracture

(CMF),4. Conductive Vuggy Discontinues

Fracture,5. Stylolites,6. Vuggy Stylolites,7. Faults.

Pre-stack Seismic Anisotropyfor Fracture Detection

Studied on reservoir fractures intensityin Oseil field using pre stack 3Dseismic data are based on P-wavereflection amplitude. P-wave seismicamplitude exhibiting variableattenuation with difference fractureorientation have an anisotropyorientation, which is captured by the

seismic anisotropy as a result of thisprocess Fractures especially verticalone will generate seismic anisotropy.By analyzing the seismic anisotropy wecan detect the most possible areawhere high intensity fracture occurs.The end result of this process is aFracture Intensity cube.

There are several steps were used togenerate fracture intensity cube fromwell and 3D seismic data. Firstperformed reserved amplitudeprocessing, well and seismiccorrelation, rockphysical modeling offractured reservoir based on rock

physical studies were built to modelseismic anisotropy.

Then four azimuth seismic data setswere achieved by selecting andcombining seismic data set in the rangeof 0-2000 meters offset and 0-180degree azimuth; and calculateddifferent azimuth amplitudes andanalyzed their azimuth variations.

The next step is the spatial distributionof amplitude azimuth ellipse thatrepresents amplitude decay alongdifferent direction. This anisotropy

Figure 5. Fracture intensity correlation between wells and seismic relatively match.

Figure 4. An example image log from NUA-2 wells showing different type offractures.

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curvature attribute then finallyconverted to fracture intensity cube.

Geological Modeling

3D geological modeling is anintegrated reservoir study combiningseismic data, well data, geologicalinformation and reservoir data. Thismodel will be used later for in-placehydrocarbon volume estimation of thefield and also upscaled for simulationpurposes.

For a fractured reservoir, there isadditional step required in order togenerate a dual porosity permeability

model. A discrete fracture network(DFN) was built to create simulationproperties to predict the reservoirdynamic behavior.

A 3D fine scale geological model wasdeveloped integrating all available data.The faults from seismic were modeledin 3D after defining their interrelations.The depth converted seismic horizonswere incorporated into the 3D model,and together with the already existingfault then were used to construct thestructural framework of the 3D model.(Figure 7).

The structural framework then waspopulated by petrophyscial propertiesto define the matrix property of thereservoir. They are the porosity matrixporosity, matrix permeability and watersaturation. (Figure 8).

Figure 6. A seismic section of the fracture intensity cube along Os-1, Os-9 to Os-18, showing wells penetrating high intensity fracture zone.

Figure 7. Modeled Reservoir Top Horizons in Oseil fieldshowing the structural faremwork.

Figure 8. The matrix porosity model of the Manusela Reservoir.

Figure 9. Several fracture drivers base on different parameters.

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Prior the discrete network building,model parameters need to be definedsince they are the object that willcontrol the intensity of the fracture.This is called the fracture drivers.

Generally fracture drivers are madebase on assumption. For instancefractures are more intense along thefault zone, hence the distance to faultmodel is built. In our case, we alreadyhave the Fracture Intensity cube fromthe Pre-Stack Seismic Anisotropy. Byintegrating the fracture intensity cubein the 3D model, we can have a morereliable distribution of the fractures(Figure 9).

Discrete Fracture NetworkGeneration

A discrete fracture network (DFN) wasbuilt to create simulation properties topredict the reservoir behavior. There

are 6 wells with image interpretation.The fracture interpretation based onimage log is the main input for theDFN parameter setting. In addition tothe image interpretation, the fractureintensity cube was used as a secondaryvariable to populate the density of thefracture. A linear relationship wastaken from the intensity value fromseismic and the density of fracturefrom wells to ensure that thedistribution of fracture will honor thewell data.

Well Placement

Base on this integrated study, threedevelopment wells were proposed anddrilled in 2010-2011. The new wellsproduced oil with initial rate as much

as 300-500 bopd. It was proven thatthe study had successfullycharacterized the quality of thereservoir by detecting the high intensityfracture.

However, one of the well (Oseil-18)experienced an early water break-trough. This is quite unexpectedbecause the TD of this well isshallower 67 ft SS with the nearest wellOseil-9 with distance less than 300m(Figure 9).

Figure 10. DFN result of Oseil field using the fractureintensity cube as the distribution control.

Figure 11. Section of Manusela Depth structure from Oseil-9 toOseil-18.

Figure 12. Section of An-Track cube showing that Os-18might possibly hit a major fracture at the bottom of the well.

Figure 13. Oseil-18 Daily Average Well Test – Before/After CementPlug.

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We suspect there is sort of connectionof Os-18 to aquifer which is nothappening with nearby Os-9.

From the original seismic amplitude,no fault was interpreted so the otherpossibility is the existence of majorfracture that connects Os-18 to bottomwater.

Seismic Attribute(Ant-Tracking)

By applying the Ant-tracking workflowto the 3D seismic cube, we hadsuccessfully recognized the zone where

a vertical fracture exist and act as aconduit for the water (Figure 10).

This zone then later was plugged bycement to prevent or minimize bottomwater produced by the well. By thisapproach, the water cut was reducedfrom 95% up until 18 % (Figure 11).

Conclusion

The integration of well data andseismic data in the reservoircharacterization of a fracturedcarbonate reservoir is beneficial

especially to have a comprehensiveunderstanding of the subsurface.

Maximizing information of each datasource will enable reliable decisionmaking and adding value to the dataitself.

All the study results have beencompared with the actual drilling &production result and have shownconsistency between them.

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A Guest Lecture and An AAPG Course at SultanHasanuddin University, Makassar, IndonesiaReviewed byTom J.A. ReijersGeo-Training & Travel, Anderen, The NetherlandsE-mail : [email protected]

Mr Herman Darman (Shell, TheNetherlands) asked me to contribute apaper for a special edition of IAGI2010 (the Bulletin of the IndonesianGeological Society) at the occasion ofthe celebration of 50 years of existence.This triggered a series of follow-upactivities that are summarised here.The paper on ‘IndonesianGeotourisme and Geoparks’ was dulypublished (Berita IAGI 2010, p. 12-15),but the author felt that the courtesy ofbeing invited for a paper neededreciprocal action and discussedpossibilities with Mr. Darman. Thusthe idea was born to present a recentlypublished paper on the sedimentologyand stratigraphy of the Niger Delta(Stratigraphy and sedimentology of theNiger Delta, Geologos, 2011,17(3):133-162), and to give a shortcourse on carbonates (syllabus inEnglish by the author) at anIndonesian University during theauthor’s vacation in that country(December 2011-January 2011).In consultation with Mr MohammadSyaiful (Secretary General IndonesianGeological Association) and MrGeovani Christopher Kaeng (AAPGstudent chapter coordinator) theAAPG student chapter of the SultanHasanuddin University in Makassarwas requested to organise the event.The effective organisation of Mr EricEstrada (Vice President AAPGUNHAS SC) and in particular ofprofessor Dr A. M. Imran Oemar(Chairman of the GeologicalDepartment of Hasanuddin University)who were so kind to formally inviteme, resulted in a three day event with alecture on the Niger Delta (TuesdayJan 17th), a one-day course onCarbonate Sedimentology (WednesdayJan 18) and a field trip on Carbonate

Sedimentology in the Maros andPangkep Area in South Sulawesi(Thursday Jan 19th) (Figure 1). It was awonderful occasion with interestedstudents who - after some hesitation toexpress themselves in English - askedmany relevant questions and

demonstrated their interest and knowhow. Apparently I was the first foreignvisiting scientist at the 36 year oldGeology Department of which thefacilities are up to date, including amodern conference room. The interestfor the event was great.

Figure 1. Certificate of having given the lecture and the course. Similar certificatesfor attending the lecture, the course and participating in the fieldtrip were issued tostudents.

Figure 2. Pankep Maros karst, locally also known as ‘petrified forest’ with erosionnotches at the base.

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I benefitted personally from theinvitation by participating in thefieldtrip to the ‘hinterland’ ofMakassar, where wonderful karstscenery was already described byRussel Alfred Wallace (1869) in histravel book on the Malay Archipelago.This fascinating area is now the fieldarea for students geology andgeophysics of Hasanuddin University.We reached the Eocene-MioceneTonassa limestone - now extensivelyquarried for cement for the newmotorways - over picturesque countrylanes through well laid out dessa’sbetween fertile sawah’s. Locally,erosion remnants of tower karst‘pinnacles’ with tell-tale erosionnotches at their base, triggered adiscussion about their origin and theinterpretation of their geomorphology.Clearly, eustatic sea level rises and/ormovement of the South Sulawesilandmass have played a significant role.

The platform and slope facies of theTonassa Limestones were studied insome outcrops where also interfingering contacts were exposed withthe underlying Malawa Formation,containing some lignite beds. Thestudents geophysics were veryinterested in an explanation of apotential exploration strategy toinvestigate the areas for hydrocarbonsand many questions were asked abouthydrocarbon prospects in Sulawesi.Further courses on such matters areclearly required.

Figure 3. Negative handprints (left) and a deer ‘pushed’ (?) by negative hand prints (right) are fascinating remnants of earlyinhabitants of the Leang-Leang area in South Sulawesi.

Figure 4. Tower karst scenery around Bantimurung, South Sulawesi.

Figure 5. Colourful butterflies in the Bantimurung butterfly sanctuary, SouthSulawesi.

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Very much in line with my ownapproach if I organise and guidegeological fieldtrips, the AAPG studentchapter also took care of includingsome touristically interesting sites.Some (of more than 60) caves aroundthe dessa of Leang-Leang were visited.In many paintings of wild pigs, deerand negative handprints are presentthat have been dated by archeologistsat 6.000-30.000 years. They arecomparable to paintings in Papua andto aboriginal art in Australia, whichopens fascinating speculations on thepeople that made this art.

Not far from Leang-Leang, the dessaBantimurung was already in Wallace’stime known for the enormous varietyin colours and sizes of butterflies(Figure 5) that are diligently studied inan onsite laboratory next to the virginforestation covering the tower karstkarst cliffs (Figure 4) and that arecovered over an extensive area bynetting to keep the butterflies together.

This fascinating visit to HasanuddinUniversity clearly asks for repeats.Other geologists travelling in Indonesiashould try also to contact localuniversities in their area of travel, to

investigate possibilities to present alecture or short courses.

I was invited to return in the futureand will gladly do so, in particular ifcombinations are possible with someother universities to make the longvoyage to and from Indonesiaoptimally beneficial. Let me nowexpress my gratitude as follows:

“Saya berterima kasih untuk undanganuntuk memberikan Kuliah dan kursus diMakassar. Saya berharap untukmengunjungi Indonesia di tahun yang akandatang dan mungkin mengunjungi universitaslain dengan program yang sama.”

Tom J.A. Reijers, The Netherland

Figure 6. The core group that followed course and excursion.

Figure 6. The core group thatattended the course and the excursion.

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Book Review

The SE Asian Gateway: History and Tectonic ofthe Australia-Asia CollisionEdited byR. Hall, M. A. Cottam & M. E. J. WilsonGeological Society, London, Special Publication, 355, 2011, 381 pp. ISBN 978-1-86239-329-5.

Reviewed byTom J.A. ReijersGeo-Training & Travel, Anderen, The NetherlandsE-mail : [email protected]

The 18 papers collected here are theresult of a conference organised by theGeological Society of London inSeptember 2009 on the connectionsbetween geology and biodiversitywithin ‘The Indonesia Through flowArea’, where currents from the PacificOcean flow to the Indian Ocean. Theyhave been arranged to first explain anddiscuss the Palaeozoic and Mesozoicgeological development of the region,and then its Cenozoic history whichprovides the background to understandthe present Indonesia.

The fragmentation of Gondwana andthe assembly of these fragments in SEAsia accompany the gradual closure ofthe Paleo-, the Meso- and the Ceno-Tethys Oceans. Metcalfe’s reviewhighlights a new understanding of theSE Asia basement structurescomposed of terranes by the SouthChina-, the Indo-China-East Malayan,the Sibumasu- and the west- and theeast Borneo blocks and their sutures.The SW Borneo and/or East Java-West Sulawesi blocks are the missing‘Argoland’ that separated from NWAustralia in the Jurassic and accreted toSE Sundaland in the Cretaceous.Clements et al discuss a widespreadregional unconformity suggestingtopography at the end of thesubduction period, due to which theUpper Cretaceous-Paleocene rocks arealmost completely absent throughoutSundaland. Granath et al. show anunexpectedly thick sedimentary section

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beneath the unconformity in the JavaSea, which was deposited while thebasement block was still part of theAustralian margin. Hall interprets theNeogene collision leading to theCenozoic subduction beneathIndonesia being influenced by therifted continental margin of Australiaand by an oceanic embayment, leadingto subduction rollback into thatembayment. Such young deformationalso results from lower crustal flowenhancing the effects of sedimentloading and driving uplift of mountainranges in northern Borneo andSulawesi. Kopp, using new seismicsections, reviews subduction along theJava margin showing variations in aneast-west direction. Widiyantoro et alshow a ‘hole’ and a possible ‘tear’ inthe subducting slab beneath East Java.

Sulawesi, close to the centre ofWallacea is composed of parts of pre-Neogene Sundaland and Australiancrust, added from the Cretaceousonwards. The active strike-slip PaluKoro fault in West Sulawesi, withspectacular surface expression,seismicity and young deformation is apoorly understood hazard. Watkinsoncompares rocks on both sides anddiscusses the enigmatic wideGorontalo (Tomini) Bay with anumber of small islands including theTogian islands. The latter have recentlybeen investigated by Cottam et al tounderstand the origin of the bay and itsvolcanic history. They revealed thecollisional contact of the ophiolite withone of the micro continental fragmentsin Eastern Indonesia, possibly sliced offrom New Guinea’s ‘Birds Head’ andcarried east along the Sorong-Faultzone. This interpretation is doubted byWatkinson et al, based on recentoffshore multibeam and seismic data.Collectively these studies show thatprevious models for tectonicdevelopment of Sulawesi requiresubstantial re-evaluation.

Studies on Timor and the Banda arcgenerated many ideas andcontroversies about arc origin, natureof the crust within the arc and the ageof collision. The Savu basin north ofthe transition oceanic subduction toarc-continent collision, is discussed byRigg & Hall with the aid of newseismic. The basin is underlain byAustralian continental crust that wasincorporated in the SE Asia margin inthe Cretaceous. Subduction of part ofthe Australian continent resulted inuplift of Sumba and deformation ofdeep water deposits Audley-Charlessummarises the results of Pliocenecollision of the volcanic Banda Arcwith the Australian margin. Detachedparts of the Australian margin werestacked up beneath the leading edge ofthe fore-arc, as shown by the highestnappes of the Banda allochthon.

The last remaining equatorial gatewaybetween the Pacific and Indian oceansis the ‘Indonesian Trougflow’.Tillinger discusses the causes of thisflow, the controls on shallow and deepflow and the variations in differentpassages. The relation between themonsoons and the El Niño-SouthernOscillation is reviewed and modelled interms of restricting the through flow.The long-term history of theIndonesian Througflow, linked toglobal climate and to variations in seasurface temperatures, salinity and watermixing over the last 14ka, are studiedby Holbourn et al with benthic andplanktonic foraminifera. Terminationof deep water flow restricted theIndonesian Gateway from the EarlyMiocene, which coincided with majorchanges in the global climate system,including rapid Late Oligocenewarming followed by a brief pulse ofglaciation. The long term developmentof the Indonesian Through flow iscontrolled by the geologic history ofthe region. Von de Heydt & Dijkstradiscuss studies of control by thegeological history and analyse theeffect of increasing pressure of

atmospheric greenhouse gasses andopen tropical gateways.

Whether Pliocene plate tectonicchanges such as the northwardmovement of New Guinea causedchanges in temperature and salinitybetween the South and the NorthPacific waters was earlier reviewed andis now further assessed by Morley &Morley, based on palynological studiesfrom cores in exploration wells in theMakassar strait. They recordvegetational and climate changes overthe last 30 ka. Lelono & Morley usepalynomorph assemblages todetermine Oligocene climate changesin the East Java Sea. Finally Wilsonreviews the very diverse shallowmarine biota in the Indonesian watersof which a large proportion is relatedwith coral reefs and associated habitats.Carbonates are valuable to traceenvironmental and climatic variations,but have in the Indonesian watersbarely been studied. Wilson reviewschanges on annual, decades, centennialand millions of year’s timescales, anddiscusses the effects of terrestrialrunoff, nutrient upwelling, tectonics,volcanism and human activity.

This publication offers a great varietyof new processes, new views of thetiming of large scale plate tectonicchanges, the geological development ofspecific areas and a wealth of new ideaswith which older models can beupdated. The importance of theIndonesian Through flow and itsimpact on annual and longer-termregional and global climates are shown.The environmental history isunravelled from the biota in the rocks.In this special publication a genuinecross fertilisation takes place betweenthe regions geological,oceanographically and climatic history.Strongly recommended to anybodyinterested in the latest development ingeological and oceanographicalthinking in SE Asia.

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Book Review

Biodiversity, Biogeography and NatureConservation in Wallacea and New Guinea(Volume 1)

Edited byDmitry Telnov, Ph.D.Chairman of Coleopterology, The Entomological Society of LatviaStopinunovads, Darzaiela 10, DZIDRINAS, LV-2130, Latvia / Lettland / LettonieWebsites: http://leb.daba.lv and http://www.zin.ru/Animalia/Coleoptera/eng/telnov.htm

Reviewed byHerman DarmanShell International E & P, The Haque, Netherlands

Outcrop Photos ofMisool-Onin Ridge

Several outcrop photos are displayedon Google Map in the Misool-OninRidge area. Certainly ground-truthchecking is necessary for accuracy butfor remote sensing purposes, thesepictures give an overview of thesedimentological and lithologicalinformation of the formation. Thesephotos were taken by non-geoscientists. One of them is DmitryTelnov.Dmitry Telnov, PhD, is a coleopterist,working in taxonomy, biogeography,evolution and ecology of Anthicidae, afamily of small beetles. For researchpurposes he visits Indonesia to workon taxonomy, biogeography, ecologyand evolution of particular beetlefamilies. Dmitry is the Chairman ofColeopterology of The EntomologicalSociety of Latvia. He also has a greatscientific interest to biogeography andspeciation in the Indo-Australiantransition zone, including ‘classic’Wallacea, New Guinea and theSolomon Islands. For his work, Dmitryis travelling in areas less disturbed byhuman impact and he observes &photographs nature, particularlyinvertebrates and discovers localcultures. As a professional biologist, hehas started to collaborate withUNIPAS, Universitas Negeri Papua inManokwari, as also with KoleksiSerangga Papua in Jayapura. Previouslyhe has visited Maluku Utara (Ternate,Moti, Halmahera), Maluku tengah(Seram, Saparua, Ambon), Raja Ampat(Misool) and Indonesian New Guinea

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(several regions, among them Bird’sNeck, Bird’s Head and OninPeninsula). In February 2012 he visitedPapua Barat again. Recently, he haspublished a new book titled“Biodiversity, biogeography andnature conservation in Wallacea

and New Guinea”. During hisjourney to Eastern Indonesia, Dmitrytook a number of pictures ofsedimentary outcrops and publishedthem in Google Maps by putting acoordinate of the outcrop location.These help geologists to get an initial

idea about the geology of the area,prior to the field mapping. Althoughtravelling in Eastern Indonesia is easierthese days, in many cases it still takes awhile to get there and it may be costly.

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Number 23 – March 2012 Page 61 of 61


Number 23 – March 2012 Page 61 of 61



fosi beritasedimentologi bs-23 march2012

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