virtually identical to those on the northern Banda Arc islands of Buru and Seram.
The Australian-derived fragments listed above all contrast strongly with Sumba, the westernmost island in
the Outer Banda Arc Fig. 1, which resembles SW Sula- wesi. Thus, and in very simple terms, the geology of eastern
Indonesia can be summarised by three generalised associa- tions of sedimentary, metamorphic and igneous rocks, of
which two are related to the continental margins of South- east Asia Sundaland and Australasia, respectively. The
third, Banda, association is dominant in and around the Banda Sea. The stratigraphic data, while not defining the
entire history of the suture zone, can be used to constrain the range of acceptable hypotheses.
2. Sundaland Margin Association
Subduction at the Sundaland Margin can be traced back into the Cretaceous, and the exposed metamorphic rocks are
thought to represent Cretaceous accretionary complexes. Conditions changed in the Oligo-Miocene as a result of
collision with a microcontinent and many of the younger rocks record extension rather than compression.
2.1. SW Sulawesi SW Sulawesi is the end product of a series of volcanic
episodes that began in the late Mesozoic, when the block was joined to eastern Borneo, but continued after the Eocene
opening of the Macassar Straits Polve´ et al., 1997. Meta- morphic basement complexes exposed in the Barru and
Bantimala areas of SW Sulawesi Wakita et al., 1996 and farther north in the Latimojong area Bergman et al., 1996
are in thrust or depositional contact with weakly metamor- phosed deep marine clastics of the Upper Cretaceous
Balangbaru Formation. Carbonates were deposited in two main periods, in the Eocene–Oligocene and Miocene
Wilson and Bosence, 1996. Volcanogenic sediments are widely distributed, especially in the fault-bounded Walanae
depression that developed following the Late Oligocene or Early Miocene collision, which sutured western and eastern
Sulawesi. Volcanic rocks with ages ranging from 2 to 18 Ma, but concentrated around 8 Ma, were interpreted by
Bergman et al. 1996 as evidence for orogenic collapse and extension, their chemistries being consistent with partial
melting at the base of an extending, collision-thickened and possibly delaminating lithosphere. This conclusion
was endorsed by Polve´ et al. 1997, who noted the
J. Milsom Journal of Asian Earth Sciences 18 2000 761–779 762
1
122 E
o
126 E
o
130 E
o
134 E
o
2 S
o
6 S
o
10 S
o
Timor Wetar
Alor Flores
Buton Misool
Onin Peninsula
Komewa Peninsula
TBJ-1X
Buru
Tanimbar
Ridges Banda
Flores Sea Islands
BANDA
BANDA SOUTH
BASIN
BASIN BASIN
WEBER Bay
U.P. Bone
SULAWESI Seram
BIRDSHEAD Irian Jaya
Sumba Sula Is.
Banggai
Kai Aru
Obi
Ar u
T rough
Seram Trough
Tim or Tr
oug h
NOR TH WEST
SHELF
La w
an opo
Fault
7 1
1
3
3 5
400 km 200
9a 4a
5a 5b
4b
NORTH
9b 3a
3b 6a
6b 8b
8a
Fig. 1. The East Indonesia suture zone. Numbers enclosed in triangles, inverted triangles and circles refer to figure numbers for stratigraphic columns for, respectively, stratigraphies of the Australian Margin association, the Banda association and the Sundaland Margin association. The thick line with triangles on
upper plate indicates the approximate present-day location of collision suture. UP Ujung Pandang.
comparative scarcity of conventional subduction-type calc- alkaline rocks with Neogene ages. The geological evolution
of western Sulawesi is summarised by the stratigraphic column of Fig. 3a, which does not, however, include the
important but controversial Lamasi Complex. The date of emplacement of this deformed, metamorphosed and thrust
bounded ophiolite Bergman et al., 1996 is not known but the mid-Tertiary orogenic phase is an obvious possibility.
2.2. Flores Sea Islands Bouguer gravity levels indicate that the northern part of
the Flores Sea, south of Sulawesi, is underlain by thinned continental crust, but that there is oceanic crust further south
Silver et al., 1986. The small and scattered islands within the sea have been described by Guntoro 1995 as closely
related to the longitudinally corresponding areas of Sula- wesi, with acid igneous rocks in the west and more basic
igneous rocks in the east. A volcanic sequence Old Volca- nic Breccia in the western islands is equivalent to the Langi
Volcanics of SW Sulawesi, and the unconformably over- lying bioclastic limestones, reliably dated as Oligocene,
are equivalent to the upper, bioclastic, units of the Tonasa Limestone described by Wilson and Bosence 1996. Wide-
spread calc-alkaline and alkaline, granitic to rhyolitic pluto- nic and volcanic rocks have not been dated, and their
contacts with other rocks have not been seen, but they contain dioritic xenoliths interpreted as belonging to the
Old Volcanic Breccia. These suggest an age no greater than Eocene and a probable correlation with the Early to
Middle Miocene granites of SW Sulawesi.
Volcanic activity recommencing in the Pleistocene, produced the Young Volcanic Breccia, which consists of
conglomerate, volcanic tuff and volcanic breccia of andesi- tic and basaltic composition. Alkaline andesitic and basaltic
dykes and sills intrude all units except the Quaternary coral limestones. As in western Sulawesi, the combination of
calc-alkaline and alkaline chemistries suggests both subduc- tion and extension.
2.3. Sumba The Flores Sea Islands form a partial link between SW
Sulawesi and the Outer Banda Arc island of Sumba Fig. 1, which lies to the west of the region of current arc-continent
collision. The position of Sumba, and the absence there of any Australasian material, is evidence that the large islands
of the Outer Arc do not owe their existence solely to accre- tion in the course of the present-day collision.
The oldest rocks exposed on Sumba are Cretaceous open marine sediments of the Lasipu Formation, described by
Wensink 1997 as identical to the Balangbaru of SW
J. Milsom Journal of Asian Earth Sciences 18 2000 761–779 763
Tethyan Oroclines
Banda Sea
Aegean Alboran
Carpathian Tyrrhenian
500 km
Fig. 2. The Banda, Tyrrhenian, Alboran, Aegean and Carpathian oroclines, at common scale.
J. Milsom
Journal of
Asian Earth
Sciences 18
2000 761
– 779
764
EARL Y
EARL Y
CRET AC
E O
U S
CRET A
CEOUS
MESOZOIC MESOZOIC
CENOZOIC CENOZOIC
LA TE
LA TE
PLIOCENE PLIOCENE
MIO- CENE
MIO- CENE
OLIGO- CENE
OLIGO- CENE
PALEO- CENE
PALEO- CENE
EOCENE EOCENE
100 100
50 50
BALANGBARU FORMATION LASIPUFORMATION
BARRU, BANTIMALA AND LATIMOJONG COMPLEXES
LANGI VOLCANICS
JAWILA VOLCANICS
SW SULAWESI SUMBA
MALA WA FORMATION
MASU FORMATION
TONASA LIMESTONE
PAUMBAP A FORMATION
TACIPI MEMBER
QU ATERNARY REEF CAMBA
FORMATION KANANGGAR
WAIKABUBAK WALANAE
FORMATION
Tectonic melange; sandstones, shales,
cherts, basalt ultramafics and
schists Deep marine
clastic sediments Turbidites and
submarine fan deposits
Tholeiitic and calc-alkaline
volcanics Tholeiitic and
calc-alkaline volcanics
Carbonate platform with redeposited marginal facies
Shallow marine sediments including platform carbonates
Volcaniclastics Carbonate
platform Shallow marine
clastics Reef limestones
Shales Coals
? ?
? Neritic
Sediments Chalk and
reef limestones Volcaniclastics
3a 3b
Fig. 3. a Stratigraphic column for SW Sulawesi, after Bergman et al. 1996 and Wilson and Bosence 1996. b Stratigraphic column for Sumba, after Fortuin et al. 1997 and Wensink 1994. Numbers in inverted triangles refer to locations shown in Fig. 1. Vertical scale in m.y.
J. Milsom
Journal of
Asian Earth
Sciences 18
2000 761
– 779
765
BATH U R ST ISLAND GR OU P
ASHMOR E LIMESTONE
Marine siltstone and shales
Marine shales and sandstones
Marine glauconitic shales
Continental redbeds Non-marine siliciclastic
Paralic to shallow marine clastics and carbonates
Marine clastics deposited at a wide variety of depths
TR OUGHT
ON GR
OUP
TIM O R G AP IRIAN JAYA
MT. GOODWIN FOR MATION
PLOVER FOR MATION WONWOGI
SANDSTONE EKMAI
SANDSTONE
KOPAI FOR MATION
NEW GU INEA LIMESTONE
MALITA FOR MATION
CAPE LONDONDER RY FOR MATION
FLAMINGO GR OU P
TIPU MA FOR MATION
AIFAM GR OU P
KEMBELANGAN GR
OUP IMSKIN
Thickly-bedded micaceous and glauconitic orthoquartzite
Massive to thickly-bedded quartz sandstone and siltstone
Dense, well bedded calcilutite
Micaceous glauconitic and micaceous sands and silts
Argillaceous, glauconitic and calcarous quartz sandstone
and silty mudstone
Continental redbeds
Nonmarine, lacustrine and paralic sediments, some coals
Shallow water platform carbonates with isolated reefs
Sandstones and clays
STEENKOOL FOR MATION Semi-consolidated pelagic
and nanno chalks
Radiolarian chalk
MIO- CENE
OLIGO- CENE
PALEO- CENE
EOCENE
P AL
E OZ
OIC
PLIOCENE
EARL Y
CRET A
CEOUS
JURASSIC
TRIASSIC
PERMIAN ME
SO ZOI
C C
ENOZO IC
EARL Y
EARL Y
MIDDLE LA
TE
LA TE
LA TE
M L
E
100
200
300 100
200
300
MIO- CENE
OLIGO- CENE
PALEO- CENE
EOCENE
P A
L E
OZOIC
PLIOCENE
EARL Y
CRET AC
E O
U S
JURASSIC
TRIASSIC
PERMIAN MESOZOIC
CENOZOIC
EARL Y
EARL Y
MIDDLE LA
TE
LA TE
LA TE
M L
E
4 a 4 b
? ?
? ?
? ?
? ?
? ?
? ?
PINYA MU DSTONE
Fig. 4. a Stratigraphic column for the Timor Gap region of the Northwest Shelf, after Brown 1992. b Stratigraphic column for Irian Jaya, after Pieters et al. 1983. Numbers in triangles refer to locations shown in Fig. 1. Vertical scale in m.y.
J. Milsom
Journal of
Asian Earth
Sciences 18
2000 761
– 779
766
CRYSTALLINE BASEMENT
BANGGAI GRANITE
TANAMU FOR MATION
BU YA FOR MATION
Continental redbeds Paralic to shallow marine
and fluvial clastics Sandy paralic to
nearshore clastics Deepwater clays
Clays limestones on Misool
Slates, schists and
gneisses Acid to
intermediate intrusives
Calcilutitecalcarenite
? ?
? ?
?
? ?
? ?
? ?
SU LA SPUR MISOOL
MANGOLE VOLCANICS
TIPU MA FOR MATION
AIFAM GR OU P
KABAU W FOR MATION
BOBONG FOR MATION INANWATAN
POLYSEQU ENCE YEFBI
SHALE R OABIBA
POLYSEQU ENCE SEBYAR
POLYSEQU ENCE PELENG FOR MATION
PANCORAN FOR MATION SALODIC FOR MATION
Nonmarine, lacustrine and paralic sediments, some coals
FAFANLAP FOR MATION DARAM SANDSTONE
Z AAG LIMESTONE KASIM MAR LSTONE
ATKAR I LIMESTONE Fine-grained calcarenite
Calcarenite with minor oolite
FACET LIME-
STONE
BOGAL LIME-
STONE Calcarenite
and coralgal limestone
LIGU META-
MOR PH ICS Sandstone, calcareous
siltstone Siltstone
Tuff- aceous
calci- lutite
and clayey
lime- stone
Intrus iv
es Restricted shallow marine
anoxic and highly fossiliferous shales
H ighly fosilliferous pelagic limestones
Shallow water platform carbonates with isolated reefs
Shallow marine carbonates with localised reefs
Subaerial acid volcanics
Continental redbeds Paralic to shallow marine clastics
and carbonates JASS
POLYSEQU ENCE
MIO- CENE
OLIGO- CENE
PALEO- CENE
EOCENE
PA L
EOZOI C
PLIOCENE
EARL Y
CRET A
CEOUS
JURASSIC
TRIASSIC
PERMIAN M
ES OZO
IC C
EN OZO
IC
EARL Y
EARL Y
MIDDLE LA
TE
LA TE
LA TE
M L
E
MIO- CENE
OLIGO- CENE
PALEO- CENE
EOCENE
PA L
E O
Z O
I C
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
100
200
300 100
200
300
5 b 5 a
Fig. 5. a Stratigraphic column for the Sula Spur, after Garrard et al. 1988. b Misool. In the Mesozoic and Paleozoic, the formations and polysequences identified on the left are after Fraser et al. 1993. All other data from Rusmana et al. 1989. Numbers in triangles refer to locations shown in Fig. 1. Vertical scale in m.y.
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
