Australasian Margin Association Directory UMM :Data Elmu:jurnal:J-a:Journal of Asian Earth Science:Vol18.Issue6.Dec2000:

Sulawesi. Mid-Cretaceous dinoflagellates suggest a North Tethys affinity Fortuin et al., 1997. The upper age limit of the Lasipu is uncertain, but there was widespread igneous activity in the Late Cretaceous and Paleogene. The Jawila Volcanics, originally thought to be Early Miocene, have now been dated as Late Eocene Fortuin et al., 1997 and can be regarded as part of a belt that includes the Langi Volcanics of Sulawesi and the Old Volcanic Breccia of Tanahjumpea. Also in the Eocene, a platform developed and, as with the Tonasa of SW Sulawesi, remained a site of carbonate sedimentation Paumbapa Formation into the Early Miocene Fortuin et al., 1997. The Paleogene sedi- ments are truncated by a Middle Miocene angular uncon- formity above which reef carbonates, chalks and volcanoclastic turbididites were deposited. The stratigraphy of Sumba is summarised in Fig. 3b; the similarities to SW Sulawesi are clear and are enhanced in both areas by the presence of Eocene granodioritic intrusions. Extensive paleomagnetic work Wensink, 1997 has provided additional support for a Late Mesozoic position of Sumba close to western Sulawesi, followed by detach- ment and a complicated series of rotations, the net effect of which has been some 908 of clockwise rotation. This contrasts with the mounting evidence for counter-clockwise rotation of Kalimantan and western Sulawesi Fuller et al., 1999. 2.4. Sundaland Margin summary The diagnostic features of the Sundaland Margin strati- graphy include Upper Cretaceous–Paleogene deep-water clastic sediments, volcanics which are of island arc type in the Paleogene but extensional in the Neogene, and the development of large carbonate platforms in the Eocene– Early Miocene. The type area is the South Arm of Sulawesi and, in particular, the region northeast of Ujung Pandang Fig. 1. Similar, although not always complete, Mesozoic and Paleogene sections can be recognised in the Flores Sea Islands and Sumba. Sediments above the mid-Miocene angular unconformity, which is a feature of the association, show fewer common characteristics, which is unsurprising if dispersion began during the unrecorded interval. Disper- sion, and the generation of oceanic crust in the Flores Sea, must predate the Late Neogene development of the eastern SundaBanda volcanic arc, because this lies to the north of Sumba. Since the volcanic islands from Flores to Wetar separate two Sunda-related blocks, it is possible, and perhaps even probable, that they are themselves built on Sundaland basement, although this is nowhere exposed.

3. Australasian Margin Association

Sediments were deposited along the Australian Margin under terrestrial or marginal marine conditions in the Trias- sic and Jurassic and in deeper water during and after the Cretaceous. Basement rocks in the east belong to a Late Paleozoic orogenic belt and in the west to a craton covered by Paleozoic platform sediments. Anomalously, ‘eastern’ granitic basement crops out in the Banggai Islands Fig. 1, the most northwesterly Australasian fragment. Neogene sediments vary widely due to differences in setting in rela- tion to the collision orogenies. 3.1. The Northwest Shelf During the Paleozoic, north-western Australia formed part of the interior of the Gondwana super-continent, but rifting in the Triassic and Jurassic detached India and other blocks and created new passive margins along the Northwest Shelf. Sediments deposited at these margins are almost nowhere seen in outcrop but are known from numer- ous wells. The stratigraphy of the shelf to the south of Timor has been described and compared with stratigraphies in adjacent areas by Brown 1992. Three major sedimentary groups were recognised, these being the Triassic–Jurassic Troughton Group, the Jurassic–Cretaceous Flamingo Group and the Middle and Upper Cretaceous Bathurst Island Group Fig. 4a. Troughton group sediments are predomi- nantly siliciclastic and include red beds in the Malita Forma- tion, which is of latest Triassic and earliest Jurassic age. Marine transgression followed, with deposition of the fluvio-deltaic sediments of the Jurassic Plover Formation. There are no sediments which can be unequivocally assigned to a riftbreak-up setting before the Late Jurassic when, as a result of rifting, an unconformity developed on which the sandstones and shales of the Flamingo Group were deposited under deeper marine conditions. Generally similar sediments characterise the Bathurst Group, depos- ited following an Early Cretaceous hiatus, but the sea had evidently deepened still further. Radiolarian shales were deposited in the Aptian to Early Albian and a black clays- tone with high gamma-ray signature represents a condensed sequence in the Turonian to Coniacian. Chalks were then deposited, which were dominantly radiolarian in the Late Cretaceous and foraminiferal in the Paleocene through to the Pliocene von Rad and Exon, 1983. Harris 1991 noted strong similarities between these sediments and the Lower Cretaceous Kolbano Series of Timor. 3.2. New Guinea Island arcs, which accreted to the northern margin of Australia during the Tertiary, now form mountain ranges along the north coast of New Guinea Dow, 1977. These terranes can be tentatively correlated with Halmahera, where Indonesia borders on the Pacific, but are remote from the Banda Arc and are therefore not further considered here. Southern and central New Guinea have also been inter- preted in terms of large numbers of allochthonous or ‘suspect’ terranes Struckmeyer et al., 1993, but most of the geological features of northern Australia can be traced at least as far north as the watershed in the central ranges. The western peninsula Birdshead, which forms the link J. Milsom Journal of Asian Earth Sciences 18 2000 761–779 767 between the main body of New Guinea and the smaller islands of eastern Indonesia, presents particular problems. It is widely thought to have moved independently for much of its history cf. Hamilton, 1979 and some movement relative to New Guinea continues to the present day Punto- dewo et al., 1994. The core of the peninsula is formed by the BirdsheadKemum Terrane of Struckmeyer et al. 1993, in which metamorphosed Siluro-Devonian turbidites have been intruded by Carboniferous and Permo-Triassic grani- toids and are overlain by Late Paleozoic shallow marine clastics and Triassic to Lower Jurassic continental redbeds. Marginal marine conditions were re-established in the early Middle Jurassic and continued throughout the Mesozoic and into the early Tertiary, interspersed with periods of erosion and non-deposition Dolan and Hermany, 1988. Sediments deposited during this long interval have traditionally been assigned to the ‘Kembelangan Formation’ Visser and Hermes, 1962 but the term has been used in such a variety of contexts that it has become virtually meaningless Fraser et al., 1993. The stratigraphic column of Fig. 4b is based on the more westerly of the New Guinea stratigraphies presented by Pieters et al. 1983. Shelf carbonates New Guinea Limestone, Visser and Hermes, 1962 dominate the Tertiary throughout New Guinea but deposition on the Birdshead was interrupted by a period of folding and erosion in the Late Oligocene. 3.3. The Sula Spur The Banggai and Sula Islands, which lie immediately to the north of the North Banda Basin and the northern limb of the Banda Arc, were transported from the New Guinea region to their present position by transcurrent movements along strands of the Sorong Fault System Hamilton, 1979; Pigram et al., 1985. Basement consists of poorly known metamorphics but there are also granitic rocks of assumed Paleozoic age. The Triassic is dominated by the acid Mangole Volcanics and by probably co-magmatic Permo- Triassic granites. Sedimentation, generally in marine basins with restricted circulation and water depths of less than 200 m, was almost continuous throughout the Jurassic but a ‘break-up unconformity’ Garrard et al., 1988 occupies much of the Cretaceous. Following this break, bathyal sedi- ments were deposited during the Late Cretaceous and Paleo- cene Garrard et al., 1988. A second hiatus occupied much of the Eocene but thereafter carbonate platform sedimenta- tion continued almost uninterrupted until the onset of colli- sion with East Sulawesi in the latest Miocene Davies, 1990. Davidson 1991, amongst others, has suggested correlations between the Sula Spur and Buton and the Outer Banda Arc but the statigraphic sequence described above and summarised in Fig. 5a has virtually nothing in common with either of these areas. 3.4. Kai Besar Seismic reflection surveys near the Kai islands Fig. 1 have shown that the plate suture runs between Kai Besar and Kai Kecil, rather than through the Aru Trough Milsom et al., 1996. The oldest rocks exposed on Kai Besar, on the Australian side of the suture, are Eocene flat-bedded calcilutites and marls. Shallow-water carbonates were deposited from the Oligocene almost to the present day. This stratigraphy is not significantly different from the end-Cretaceous to Late Miocene succession on the Sula Spur. 3.5. Misool–Onin–Komewa The Late Oligocene compression widely observed in the Birdshead was interpreted by Struckmeyer et al. 1993 as due to a collision with a Misool–Onin–Komewa Terrane. On Misool island a Paleozoic basement of folded and meta- morphosed turbidites is overlain by an almost complete Mesozoic passive margin sequence of Triassic turbidites, Upper Triassic shallow-water limestones and Lower Juras- sic to Upper Cretaceous bathyal clastics and carbonates Rusmana et al., 1989. Outcrop information on the geology of Misool and the related Onin and Komewa peninsulas of the New Guinea mainland Fig. 1 has been supplemented by drilling, and Fraser et al. 1993 used subsurface data from both the Misool–Onin–Komewa province and adja- cent parts of the Birdshead to develop a new scheme to replace the Kembelangan nomenclature. In this scheme the Mesozoic sediments were divided into a Lower to Middle Jurassic shallow marine to fluvial ‘Inanwatan Poly- sequence’, a Middle to Upper Jurassic paralic to nearshore ‘Roabiba Polysequence’, an Upper Jurassic–Lower Cretac- eous deepwater open marine ‘Sebyar Polysequence’and an Upper Cretaceous to Paleocene, ‘Jass Polysequence’, sepa- rated by major unconformities Fig. 5b. In the crucial TBJ- 1X well Fig. 1 off the Onin Peninsula and therefore within the Misool–Onin–Komewa Province, section is missing from the Middle Triassic to the base of the Toarcian, from the top of the Bajocian to the base of the Oxfordian, from the Lower Kimmeridgian to the mid Tithonian and from the Lower Valangian to the Cenomanian. Jass sediments have also largely been removed from the well section by erosion. Elsewhere, the Cenomanian base of the Jass is marked by a volcanic event and the overlying sediments are mainly deepwater clays, although shallow water rudists outcrop in the Misool archipelago. Fig. 5b shows that there are considerable differences between the rocks outcropping on Misool and those inter- sected in TBJ-1X. Whereas the well section fits into the pattern of the Australian Margin Association, Misool has much in common with the Banda Association described below, although it reportedly lacks the characteristic Juras- sic unconformity. Moreover, palaeomagnetic data indicates that the island was more than 1000 km north of Australia in the Cretaceous Wensink et al., 1989. There is thus a clear possibility that Misool was detached from the Australian Margin as an independent fragment in the Mesozoic and J. Milsom Journal of Asian Earth Sciences 18 2000 761–779 768 J. Milsom Journal of Asian Earth Sciences 18 2000 761 – 779 769 LAKANSAI FOR MATION TOBELO FOR MATION TOBELO FOR MATION Dark shales, limestones, occasional massive sandstone Fossiliferous red calcareous mudstone Argillaceous limestone Bathyal fine-grained limestones and argillaceous limestone Pelitic phyllite and slate with subordinate quartzose and micaceous sandstone White to pink nannofossil- microfossil pelagic limestones, some cherts Well laminated calcilutite with local clastic detritus Reef Limestone Pelagic foraminiferal marly chalk Coarse to fine grained terrigenous clastics SAMPOLAKOSA FORMATION WAPULAKA FORMATION Po s s ib le h ia tu s ? ? ? ? ? BUTON WINTO FOR MATION R U MU FOR MATION OGENA FOR MATION TONDO FORMATION H igh - very high grade schists and gneisses h i a t u s ? h i a t u s ? h i a t u s ? erosional hiatus LATE CR ETACEOU S NIEF BEDS PALAEOGENE NIEF BEDS KOBIPOTO COMPLEX TAU NU SA COMPLEX Coralli- genous limestones Chert-rich limestones, locally bioclastic Clays, shales, graywackes, some limestones Weakly metamorphosed shales, graywackes, some limestones Phyllites with graywackes, some limestones Neritic shales Argillaceous calcilutites Dense, brittle calcilututes, some cherts Cream and white calcilutites red and green marls Medium - high grade schists and gneisses. POSSIBLE GRADATIONAL CONTACT Neritic sediments Bathyal sediments Tectonite Grey argillaceous calcilututes SAKU FOR MATION TEH OR U FOR MATION NI EF B E DS EARLY NEOGENE NIEF BEDS WAHAI BEDS SALAS BLOCK CLAY SERAM KANIKEH FOR MATION SAMAN SAMAN LST EAR LY NIEF BEDS MANU SELA FOR MATION h i a t u s ? KOLA SHALE TOBELO FOR MATION FUFA FORMATION MIO- CENE OLIGO- CENE PALEO- CENE EOCENE P A L E OZOIC PLIOCENE EARL Y CRET A CEOUS JURASSIC TRIASSIC PERMIAN MESOZOIC CENOZOIC EARL Y EARL Y MIDDLE LA TE LA TE LA TE M L E MIO- CENE OLIGO- CENE PALEO- CENE EOCENE PA L EO ZOI C PLIOCENE EARL Y CRET A CEOUS JURASSIC TRIASSIC PERMIAN M ESOZO IC C EN OZ OIC EARL Y EARL Y MIDDLE LA TE LA TE LA TE M L E 100 200 300 100 200 300 6 a 6 b Fig. 6. a Stratigraphic column for Buton, after Davidson 1991. b Stratigraphic column for Seram, after Kemp and Mogg 1992. Numbers in circles refer to locations shown in Fig. 1. Vertical scale in m.y. collided with the Birdshead in the Mid-Tertiary, when the older sediments were folded. More detailed work is needed on the Mesozoic rocks, which are well exposed on the south coast of Misool and the islands immediately to the south, to clarify their role in the regional evolution. 3.6. Australian Margin summary The wide variations in Australian Margin stratigraphies are not surprising in view of the vast area covered. The type area for the association is taken to be the shelf south of Timor the ‘Timor Gap’. Western Irian Jaya, including the Birdshead, and the Sula Spur, are included in this asso- ciation but their basements of Late Paleozoic granites and associated extrusive rocks have more in common with central Papua New Guinea than the Northwest Shelf. Misool island is different again and lacks the terrestrial Triassic ‘red beds’ deposited elsewhere in the region prior to, and at the beginning, of the break-up of this part of Gondwanaland. The later Mesozoic in all areas records a steady increase in water depth, from marginal marine in the Jurassic to open water bathyal in the later Cretaceous. During the Tertiary, parts of the margin were fragmented andor involved in collisions, and Tertiary stratigraphies therefore differ considerably.

4. Banda Association