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