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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.

FaunasThe macrofaunas are composed mainlyof ammonites (Figures 4, 5), somequite large (30 cm). They are associated

with 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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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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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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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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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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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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(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.

Page 40 of 61

HALMAHERA, SERAM & BANDABerita Sedimentologi

Number 23 – March 2012

(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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Number 23 – March 2012

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.