this assumption. The stratigraphic column for East Sula- wesi shown in Fig. 8a is compared with the column for
Buru, where the proportions of outcrop of metamorphic rocks and sediments are similar, although ophiolites are
absent.
4.6. Banda Association summary The Banda Association is characterised by a variety of
metamorphic rocks, some of which may represent continen- tal basement and others which may be the metamorphic
soles to ophiolite sheets, and ophiolitic rocks which are only occasionally strongly metamorphosed. The sedimen-
tary record begins in the Triassic with deposition under fluvial or marginal marine conditions. Water depths
increased, and carbonate deposition became more wide- spread, in the Early Jurassic. Sediments of this generally
conformable sequence are frequently bituminous. They are found in outcrop on Buton where they source asphalt
deposits; Davidson, 1991 and Buru, and source oil on Seram Peters et al., 1999.
A characteristic feature of the Banda Association is the presence of a major unconformity encompassing at least a
major part of the Late Jurassic and sometimes much of the Middle Jurassic and Early Cretaceous. The sediments
immediately above this unconformity are generally shales but quickly give way to condensed sequences of carbonates
with cherts, deposited in environments remote from sources of clastic sedimentation. This type of sedimentation contin-
ued into the Paleogene, when a second major unconformity developed, interpreted here as a consequence of collision
between a microcontinent and the margin of Sundaland. The subsequent history of the association can be interpreted
in terms of post-orogenic collapse and dispersal, with early molasse deposition and, in some cases, later collision with
the advancing Australian Margin around the Banda Arc.
5. Timor
Most discussions of the Outer Banda Arc begin with Timor, which is logical, since it is the largest and most
intensively studied of the islands, but unfortunate since it is probably also the most geologically complex Charlton et
al., 1991a. Moreover, at no time has it been equally easy to visit both the eastern and the western parts of the island,
which have been described rather differently even in the most recent publications Sawyer et al., 1993; Reed et al.,
1996. It is not clear whether the differences stem merely from different approaches to mapping and interpretation or
reflect real variations in geology.
It is common ground amongst all recent authors that most of the Mesozoic sediments exposed on Timor are of Austra-
lian origin see discussion in Charlton et al., 1991a. Most authors also accept the presence on Timor of a forearc,
formerly separated from Australia by an oceanic basin and referred to by Carter et al. 1976 and Barber 1981 as the
allochthon and by Harris et al. 1998 as the ‘Banda Terrane’. Seismic lines across the arc near Timor have
provided striking images of underthrusting by the thickly sedimented Australian continental margin Hughes et al.,
1996; Schlu¨ter and Fritsch, 1985 and suggest that coherent slices of the sedimentary cover have in some places been
stripped from the downgoing slab and incorporated in the overlying collision complexes. In the same terminology,
these continental shelf thrust slices constitute the parautoch- thon. Both allochthon and parautochthon are now overlain
by post-orogenic sediments of the autochthon, deposited after collision.
5.1. The allochthon Charlton et al. 1991a listed the allochthonous elements
of Timor, of which the most important were the MutisLolo- toi Complex, the Palelo Group Noni, Haulasi and Metan
Formations, the Cablac Limstone and the Ocussi Volca- nics. Many authors have drawn attention to parallels
between some of these formations and rocks on Sumba and Sulawesi. Earle 1983 and Haile et al. 1979 drew
attention to localities in Timor where Noni Formation radi- olarian cherts of Late Jurassic or Early Cretaceous age rest
directly on the metamorphics, and to similar occurrences of this globally unusual pattern in SW Sulawesi. In both cases
the environment of deposition was interpreted as a forearc basin. Elsewhere, the oldest unmetamorphosed sediments
were considered by Earle 1983 to be the tuffs and agglom- erates of the Metan Formation, but these have now been
assigned to the Upper Eocene and Oligocene Sawyer et al., 1993.. This discrepancy is some indication of the uncer-
tainty that still surrounds the Palelo Series, an uncertainty compounded by the strong similarities noted by Sawyer et
al. 1993 between some outcrops normally mapped as Palelo Group and others mapped as part of the Kolbano
Series. A distinction can, however, be made on the basis of the presence of volcanic elements throughout the Palelo,
as in similar and coeval rocks on both Sumba and SW Sulawesi.
The Palelo Group is succeeded unconformably by the Cablac Limestone and the Ocussi Volcanics. Harris 1992
considered the latter to be an upthrust part of the Late Miocene or Pliocene oceanic floor of the Savu Basin.
5.2. The parautochthon Australian shelf rocks exposed on Timor range in age
from Permian to Paleogene and have been divided into two main groups, termed the Kekneno and Kolbano series
Fig. 9a, separated by a hiatus occupying most of the Late Jurassic Sawyer et al., 1993. Three distinct Permian
Formations have been recognised, these being the Lower to Upper Permian Maubisse basalts and limestones, the
Atahoc shales, which interfinger with the Maubisse lime- stones, and the Upper Permian or possibly partly Triassic,
Reed et al., 1996 Cribas sands, silts, shales and bioclastic
J. Milsom Journal of Asian Earth Sciences 18 2000 761–779 775
limestones. The Aileu metamorphics of the north coast are now recognised as metamorphosed equivalents of some or
all of these formations. The Triassic of Timor is composed of the Niof Formation,
deposited as gravity flows in a range of water depths, and later limestones and carbonate muds of the Aitutu Forma-
tion. In western but not in eastern Timor, a massive but probably local sandstone wedge has been given formation
status Babulu Formation. The top of the Kekneno Series is represented by the Late Triassic–Jurassic Wai Luli Forma-
tion. In contrast to the other members of the Series, which are generally confined to the northern mountains, the Wai
Luli is found only in the south.
The Kolbano Series is exposed principally in thrust sheets in the Kolbano Mountains of southern West Timor. It is not
found in the north and exposures in the east are very limited. The base of the series is represented by sandstones and
conglomerates of the Lower Cretaceous Oe Baat Formation, but later sediments the Nakfunu, Menu and Ofu Forma-
tions; Fig. 9a were deposited in clastic-starved marine settings which were initially deep but became gradually
shallower in the Tertiary. The younger rocks of Timor are assigned to either the allochthon or the autochthon.
5.3. Timor controversies Four major aspects of Timor geology continue to be
controversial. One of these, concerning the relationships between the various Permian formations, interpreted by
Audley-Charles 1968 as having been deposited in widely separated areas but by many more recent authors as inter-
fingering cf. Barber, 1981, has only minor implications for later orogenic development. More significant is the question
of when orogeny actually occurred. Reed et al. 1996 iden- tified folds in East Timor which pre-dated deposition of the
Early–Middle Miocene Cablac Limestone, but Sawyer et al. 1993 considered the earliest orogenic phase in West Timor
to be Late Miocene. The timing of orogeny in Timor would have been dictated by the exact shape of the Australian
Margin and would therefore have been diachronous Harris, 1991 but the time interval suggested above seems too long
to be explained by this factor alone.
Another problem concerns the Kolbano Series, which Sawyer et al. 1993, following earlier authors, interpreted
as accreted to Timor only in the latest Miocene or Pliocene. However, paleomagnetic studies by Wensink et al. 1987
placed the site of deposition of the Lower Cretaceous Nakfunu Formation at only 208S, and thus more than
1000 km north of the Australian Margin Smith et al., 1994. If this paleomagnetic datum is correct, the Nakfunu
must have been deposited on a rifted fragment that drifted north ahead of the main continent. The fossil evidence is
ambiguous and Clowes 1997 described a radiolarian fauna of mixed Tethyan and higher latitude affinities. Given strong
J. Milsom Journal of Asian Earth Sciences 18 2000 761–779 776
1 3 0 E
o
1 3 4 E
o
2 S
o
6 S
o
1 0 S
o
Banda Sea expands
eastward
Timor allochthon moves south- east from western Sulawesi
Halmahera block moves west to collide with Sangihe Arc
Buru and Seram move east from the collision
orogen and rotate
Sumba moves south from western Sulawesi
Sula Spur collides with the East Arm of Sulawesi
W Sulawesi remnant
collision orogen
1 2 6 E
o
1 2 2 E
o
Au s t ra lia n S h e lf As s o c ia t io n
S u n d a la n d Ma rg in As s o c ia t io n
Ba n d a As s o c ia t io n
4 0 0 km 2 0 0
Fig. 10. Dispersion and amalgamation in eastern Indonesia. The convergence of all three assemblages in Timor is unproven, and not essential to the basic post orogenic extension hypothesis, but a possibility meriting further investigation.
geological resemblances and the evidence for a pre-Middle Miocene orogenic event in Timor, it seems unwise to
completely discount the possibility that the Kolbano belongs with the Banda Association as defined in this paper.
Uncertainty also surrounds the metamorphic rocks. On the basis of metamorphic grades indicating burial to depths
of more than 20 km, the Lolotoi Complex of East Timor was originally described as continental basement e.g. Audley-
Charles, 1968, although the importance of basic igneous rocks was recognised by all early workers. In West Timor
the supposedly equivalent Mutis Complex has been more intensively studied and comprehensively described, and is
now interpreted as a metamorphic sole overlain by a thrust mass of variably metamorphosed ophiolitic rocks similar to
the Lamasi Complex of west Sulawesi Sopaheluwakan et al., 1989. It is not proven that continental metamorphic
basement outcrops in either West or East Timor.
6. Discussion
