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PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION ThirtyFifth Annual
Convention amp Exhibition, May SUMBA AREA DETACHED SUNDALAND TERRANE AND
PETROLEUM IMPLICATIONS
Awang Harun Satyana Margaretha E.M. Purwaningsih
ABSTRACT Sumba Island is a terrane situated in the forearc setting of the
NeogeneQuaternary SundaBanda volcanic arc. Sumba is considered a microcontinent and
its origin has been a matter of debate. There are two main competing hypotheses
provenance from NW Australia or provenance from SE/Eastern Sundaland. We studied
various considerations from previous authors and present a new interpretation and synthesis
based on multidisciplinary methods including stratigraphic succession,
geochronologygeochemistry of magmatic rocks, paleomagnetism, isotope geology, and
Eocene large foraminifera. The Paleogene stratigraphic succession of Sumba is similar to
that of Southern Sulawesi. Extruded magmas display the characteristics of typical island arc
environment at the margin of Sundaland. Paleomagnetic data of Sumba show the location of
SE/Eastern Sundaland in the Late Cretaceous and has occupied its present position since
the Early Miocene. PbNd isotope characteristics of rocks from Sumba showisotopic
signatures and affinities with rocks of Sundaland. Sumba contains typical Eocene lowlatitude
Sundaland fauna of Assilina, Pellatispira, and Biplanispira and no Eocene highlatitude
Australian fauna of Lacazinella. We present new consideration on the detachment of Sumba
from SE/Eastern Sundaland and its emplacement as continental sliver at its present position
through escape tectonics. Petroleum accumulations occur and are produced from Eastern
Indonesian foreland basins related to collision of Australoid microcontinents like the Banggai
and Bintuni Basins. However, this collisionrelated petroleum play does not typify the Sumba
microcontinent due to the absence of Australian sediments and no collision in its history.
Rifted structures, proven to be prolific in Western
BPMIGAS ConocoPhillips Indonesia
Western Indonesian basins define the Sumba petroleum potential. Geology of Sumba Island,
marine seismic and the presence ofpetroleum seeps/slicks show positive indications of a
petroleum system in Sumba area. INTRODUCTION The last publication in IPA Proceedings
discussing the Sumba Island was a paper written years ago by Burollet and Salle . In the last
years there have been studies on the geology and tectonics of the island published in various
geologic and tectonic journals or other conference proceedings. This paper examines these
studies to collect and expand the knowledge on tectonics and petroleum geology of Sumba
area. This paper deals with tectonics and petroleum implications of Sumba area. The area of
investigation in this paper covers the onshore and offshore Sumba Island and parts of the
Savu/Sawu Basin. Sumba Island is famous in Indonesian geologic literature because of its
tectonically enigmatic position. The island has been known as a detached terrane
microcontinent, a geologic block transported from its provenance and tectonically emplaced
into its current position. There have been debates on the islands provenance/origin. Previous
authors examined the origin of the island based on various methods discussed in detail in
Results section. This paper firstly will address these previous debates, examine and
synthesize them into the new interpretation covering the origin and emplacement of the
Sumba microcontinent using more comprehensive methods that have never been available
to previous researchers. Secondly, the paper will discuss petroleum implications of Sumba
area given the results of this study. There are several detached terranes in Eastern
Indonesia that are hydrocarbon productive. We will consider Sumba area similarities and
differences to other microcontinents
and present petroleum play types unique to Sumba area. METHODS This paper comprises
two parts discussion of the geology and tectonics of Sumba area Sumba Island mainly and
discussion on the petroleum implications of Sumba area. In the first step , we collected
published literature from various journals, examined them, and put them in the new
interpretation and synthesis of the origin and emplacement of the Sumba Island. A field
survey to examine the geology of Sumba Island was conducted in August . In step two , we
referred to other detached terranes, especially in Eastern Indonesia, that produce
hydrocarbons, seeking analogies with Sumba area. Special charactistics of Sumba area
compared to other microcontinents were reviewed with attention to petroleum play types of
Sumba area. Seismic lines offshore Sumba were examined for different play types.
DISCUSSION amp RESULTS Tectonic Position of the Sumba Island Sumba Island, a part of
Lesser Sunda Nusa Tenggara islands in the southern part of Central Indonesia is an island
located to the south of Quaternary volcanic islands comprising Sunda and Banda Arcs Figure
. The island is located in a forearc setting relative to the SundaBanda volcanic arcs
comprising mainly islands of BaliLombokSumbawaFloresAlorWetar. Sumba Island is
presently nonvolcanic forming one belt of nonvolcanic arcs of Banda Arc with Timor,
Tanimbar and Seram Islands. Banda Arc comprises two parallel arcs of inner volcanic
islands comprising FloresAlorWetarRomangDamarTeunNilaSeruaRozengainBanda Islands
and outer nonvolcanic islands of SumbaSavuRotiTimor Moa Sermata Babar Tanimbar
KeiWatubela Gorong Seram Buru Islands. Sumba Island is tectonically significant because it
is located at the border of the subduction zone to the west where the oceanic crust of the
Indian Ocean subducts beneath the Sunda Arc and the collision zone to the east where the
continental crust of the Australian Continent subducts beneath/underthrusts the outer Banda
Arc from Timor to Seram Figure . Sumba lies obliquely between two forearc basins, the
Lombok Basin to the west and the triangular Savu Basin to the east. Bathymetrically,
Sumba stands out as a ridge that obliquely separates the Savu forearc basin gt m depth in
the east and the Lombok forearc basin gt m depth in the west. Based on tectonic studies,
complemented by paleomagnetism and geochemistry, several researchers considered
Sumba to be a microcontinent or continental fragment/sliver Hamilton, Chamalaun and
Sunata, Wensink, , Vroon et al., SoeriaAtmadja et al., detached from its provenance and
transported to its present position as a terrane that is alien or exotic to its surrounding areas.
The island of Sumba with a Bouguer gravity anomaly of to mgal is underlain by a continental
type of crust with a thickness of km Chamalaun et al., . The exact outline of the Sumba
fragment is not fully known. The island of Sumba is some kilometers long and about
kilometers wide. Seismic profiles show that the Sumba position is unique and its features do
not extend more than km from the island Burollet and Salle, . Towards the west in the
Lombok Basin, Sumba extends below sea level for approximately km until it is cut off by a
NESW trending fault system. In the Savu ForeArc Basin east of Sumba, seismic reflections
reveal a submarine ridge, the North Savu Ridge. The ridge begins at Sumbas easternmost
end and runs to the ESE towards the island of Savu. Wensink estimated the dimension of the
Sumba crustal fragment to be km long and km wide. Geology of Sumba Island Geology of
Sumba has been investigated since the end of th century by Dutch geologists. Results of
early geological investigations on Sumba Island before World War II were synthesized by
van Bemmelen . The first investigation was conducted by Verbeek in . Several important
works on the geology of the island were all references can be found in van Bemmelen, from
Verbeek , Witkamp , , Hhnerwadel et al. , and Kinser and Dieperink . The last authors
published the geological map of the island at scale ,. After World War II, the geology of
Sumba Island was studied and mapped by the Geological Survey of Indonesia and many
other workers/scientists from various institutions. Several important works during this period
were from Effendi and Apandi , Burollet and Salle , Chamalaun et al.
, von der Borch et al. , Fortuin et al. , Fortuin et al. , Effendi and Apandi , Abdullah , Wensink
, Wensink and van Bergen , van der Werff et al. , Vroon et al. , Fortuin et al. , Rampnoux et
al. , SoeriaAtmadja et al. , Abdullah et al. , and Abdullah . A geological sketch map of Sumba
is shown in Figure . The stratigraphy of the island begins with slightly to unmetamorphosed
sediments of Mesozoic age, unconformably overlain by considerably less deformed Tertiary
and Quaternary deposits the total thickness of which is more than m van Bemmelen, . The
Quaternary coral reef terraces, which cap the seaward edge of the Neogene Sumba
Formation, are almost continuously exposed along the western, northern and eastern coasts
of Sumba. Abdullah and Abdullah et al. distinguished four sedimentary cycles in Sumba
Figure . The first cycle Late CretaceousPaleocene is represented by marine turbidites of the
Lasipu Formation. It was accompanied by two major calcalkaline magmatic episodes, the
SantonianCampanian episode Ma and the MaastrichtianThanetian episode Ma. The second
cycle Paleogene was marked by volcaniclastic and neritic sedimentation accompanied by the
third magmatic episode of LutetianRupelian age Ma EoceneOligocene, Paumbapa
Formation. The following Neogene sedimentary cycle was a period of widespread
transgression, characterized by rapid sedimentation in a deep sea environment
Kananggar/Sumba Formation Fortuin et al., , , . This syntectonic turbiditic sedimentation
containing reworked volcanic material also has been observed in neighboring Lombok and
Savu basins. The fourth cycle Quaternary was marked by the uplift of terraces, beginning Ma
ago. Pictures of these rocks from a recent field survey can be seen in Figure . The Mesozoic
sediments are typically carbonaceous siltstones with volcanogenic mudstones, sometimes
showing signs of lowgrade metamorphism in prehnitepumpellyite metagreywacke facies
Chamalaun et al. , interbedded with sandstones, conglomerates, limestones and
volcaniclastic debris. They are crosscut by Late Cretaceous intrusions which range in
composition from microgabbro to quartzdiorite, and also by granodioritic and calcalkaline
dykes of Paleogene
age. The sediments show large scale slump structures and significant fracturing. These
sediments constitute the Lasipu Formation. Microfossil assemblages in some samples
indicate Coniacian to Early Campanian ages mid to Late Cretaceous Burollet and Salle, .
The detrital material suggest either a continental origin, or an island arc environment
essentially a Mesozoic submarine fan with shallowwater deposits Von der Borch et al., or an
open marine bathyal environment Burollet and Salle , . During the Paleogene, Sumba was a
part of a magmatic arc Abdullah et al., characterized by calcalkaline volcanic rock series
Western Sumba and shallow marine fossiliferous limestones and sandstones of the
Paumbapa Formation and have an Eocene and Oligocene age Effendi and Apandi . The
corresponding deposits include tuffs, ignimbrites, greywackes, intercalations of foraminiferal
limestones, marls, microconglomerates and claystones. These rocks unconformably overlie
Mesozoic rocks and are in turn unconformably overlain by the Neogene Series. In the early
Miocene there is another period of volcanic activity Wensink, . This volcanism of the Jawila
Formation, is restricted to West Sumba. Large areas are covered with tuff, tuffagglomerates,
tuffsandstones and lahars while rather fresh basalts and basaltic andesites occur as well.
There are small exposures of the Middle Miocene Pamalar Formation with claystone and
limestone, the latter both in lagoonal and in reef facies. An enormous mass of sediments with
a thickness of at least m covers large areas on Sumba. These sediments, which slightly
unconformably overlie older rocks, belong to the Sumba Formation and have a late Miocene
to early Pliocene age Fortuin et al. . The deposits show a general shallowing from east to
west. The eastern facies of the Sumba Formation, often called Kananggar Formation,
comprises basal conglomerates, overlain by volcanoclastic turbidites, sands, gravels and
intercalated white, pelagic chalks. In East Sumba the formation contains many slumps. The
western facies is mainly shallow marine here, deposits of the Waikabubak Formation are
found with carbonate platform sediments of reef and lagoonal origins. The Quaternary is
represented by coralreef terraces which fringe the island on the west, north and east coasts.
These terraces comprise sandstones, conglomerates, marls and prominent reef limestones.
and broken by faults. . von der Borch et al. A section from south to north on Sumba shows
all formations dipping to the north.. Comparison with the Permian paleomagnetic direction of
Timor indicates that Sumba was subjected to a clockwise rotation through .. . Otofuji et al.
Vroon et al. Origin of the Sumba Island Australia. Timor. . open folds. Ma contributed to the
uplift of Sumba and created many structural features on the Australian side of the plate
boundary and partitioned the lithosphere into structural domains Keep et al.. Contrasting with
that. the geology of Timor. . . .. Sumba became detached and rotated clockwise
AudleyCharles . SoeriaAtmadja et al. rifting began some Ma ago. Fortuin et al. The main
objection to Australian provenance for Sumba is that the preTertiary and the Paleogene . . .
The outline of the geology of Sumba as given above shows that both the stratigraphy and the
tectonics of the island are rather simple. Norvick located Sumba near Australia to the west of
a SN trending fault that he called quotSumba Fracturequot. ... Sumba was either a
microcontinent or part of a larger continent within the Tethys. Nishimura and Suparka
interpreted the paleomagnetic evidence that Sumba was attached to the Australian
continental margin up to Jurassic time and rotated clockwise after separation. many authors
are in favor of a northern provenance/Sundaland/SE Asia of the Sumba fragment such as
Hamilton. Hartono and Tjokrosapoetro believed the origin of Sumba to be from northwestern
Australia. Rangin et al. Satyana. Australian origin .. . Burollet and Salle. another island of
nonvolcanic outer Banda Arc. . . Abdullah et al. The elongated dome of Sumba represents an
uplifted area of the forearc basin. Abdullah. Otofuji et al. the preTertiary sediments of the
Lasipu Formation are mildly deformed. Abdullah. . . . Other considerations are Sumba was a
fragmented Tethys isolated continent/microcontinent and Sumba was part of Timor which
escaped into its present position by the opening of Savu Basin. and Sumba was part of
Timor and escaped to its present position after the collision of TimorAustralian continent and
by the opening of the Savu Basin AudleyCharles. Rigg and Hall. . . Wensink.. . This is one of
the reasons for relating or not relating Sumba to Timor. resulting in the opening of the
Wharton Basin Falvey and Mutter. It is well known that along Australias west coast. Since the
Pliocene the uplift of Sumba amounts to approximately km. Collision of a promontory of
Australian continental lithosphere with Sumba at ca. Sumba and Timor were situated at the
Australian continental margin. Wensink and van Bergen. . Norvick. . Synsedimentary
tectonism with normal faulting and largescale slumping occurred during the Neogene. .
drifted northwards and was subsequently trapped behind the eastern Java Trench
AudleyCharles.Sumba was part of the Australian continent. . where it occupied a position
near the Scott Plateau. . Probably the prerift drift position of Sumba was at the southeastern
most part of northwest Australia compared with prebreakup positions of the other continental
fragments now occurring in eastern Indonesia. . Based on a seemingly confirmed Jurassic rift
drift event in northwestern Australia. at least until the Jurassic. There are two dominant
competing hypotheses provenance from the margin of NW Australia and provenance from
the margin of eastern Sundaland. Sumba was originally a part of the Australian Continent
which was detached when the Wharton basin was formed. Pigram and Panggabean.
exhibiting broad. . both in stratigraphy and in tectonics Hamilton.. the Sumba pole is
gradually approaching the Jurassic pole of Australia as well as Timor pole. compared
Jurassic paleomagnetic directions of Sumba and Timor. Tethys Sumba has been considered
as a microcontinent and its origin has been a matter of debate. van der Werff et al. Nishimura
and Suparka. relative to Timor since the Jurassic. a fragment broke away. The Neogene
sediments of Sumba are gently folded and or warped.In general. Hartono and
Tjokrosapoetro. In a reconstruction of Eastern Indonesia.. Rutherford et al. Along a SWNE
fracture zone at the eastern side of the Wharton Basin. . Djumhana and Rumlan. It is also
noted that more towards the southeast the breakup becomes younger. . The preTertiary
basement of Sumba reveals faulting with rifted blocks Wensink. is very complicated. This
implies that. Sumba was once part of Sundaland which drifted southwards during the
opening of the marginal seas in the eastern margin of Sundaland at present. When Sumba is
restored by a counterclockwise rotation. . which was later fragmented Chamalaun and
Sunata. .
volcaniclastic or magmatic rocks in Timor for the Late Cretaceous and Paleogene as are
present in Sumba area. . On both islands the Cretaceous members of these sequences are
regarded as characteristic of forearc deposits built on thin continental crust. Wiluba and
Cablac deposits of Timor. The composition and structure of both the Lasipu and the Sumba
sediments indicate such relationships. The rifting along Australias coasts took place in the
Jurassic and the early Cretaceous. analyzed specimens from shales in West Sumba
collected not far from the Tanadaro Granodiorite. with their own data did not provide a
straightforward answer to the question whether Sumba had an Australian or a Sundaland
origin Wensink. the geology of the island shows that it is likely that there were relationships
with other continental units. Djumhana and Rumlan suggested that Sumba was originally a
part of Timor. They assigned a Jurassic age to these shales quoting van Bemmelen . are
now assigned a Late Cretaceous age von der Borch et al. thus the referred igneous rocks of
Sumba are too young for correlation with the Australian rifting. No Paleozoic or Mesozoic
sediments are found in Sumba area as are found in Timor. meaning that Sumba did not
originate from an isolated microcontinent. Rigg and Hall suggested that the basin is underlain
by continental crust and its normal faulting in the middle Miocene and rapid subsidence to
several kilometers was driven by subduction rollback. The opening of Savu Basin by escape
tectonism of Sumba may not be the mechanism for the opening of Savu Basin since Sumba
may not be part of Timor. although they had a slight preference for a southern provenance. .
The islands of Sumba and Timor lie only some km apart. These rock sequences of Northern
Timor are considered to have a northern provenance AudleyCharles Banda Allochthon with a
Southeast Asian origin. There are no Paleozoic and Mesozoic sediments in Sumba area as
are found in NW Australia. A comparison of the stratigraphic sequences of Sumba with those
of Timor shows that there are some resemblances between the Sumba rocks and the North
Timor Palelo Series AudleyCharles . these sediments. No volcanic. separated from Timor
and rotated clockwise. However. with the present southwest part of Sumba conjoined to
northwest Timor during MesozoicOligocene time Figure . both in stratigraphy and in tectonics
Wensink. Otofuji et al. . Both islands are situated south of the SundaBanda volcanic arc and
north of the deformation front in the Java Trench and the Timor Trough. therefore it never
escaped from Timor. However. .Sumba was either an isolated microcontinent or part of a
larger continent within Tethys that was later fragmented Chamalaun and Sunata. Chamalaun
and Sunata concluded that the combination of the results of Otofuji et al. The Savu Basin
developed as an extensional basin from early Pliocene time behind the escaping Sumba
fragment. Timor origin . did not give a straightforward answer to the question whether Sumba
had an Australian or a Sundaland origin. Tethys microcontinent origin . The main objection to
Timor provenance for Sumba is similar to that of relating Sumba to NW Australia
provenance. which belong to the Lasipu Formation. the geology of Timor is very complicated.
Otofuji et al. Continental drift of Australia to the north during earlymiddle Miocene time is
believed to have caused initial movement of Sumba by transcurrent faulting that reached a
climax during middlelate Miocene time. volcaniclastic or magmatic rocks have been
discovered in NW Australia from the Late Cretaceous and Paleogene as are found in Sumba
area. The rocks may have been incorporated in the early Banda Arc and may have collided
with the Australian margin approximately Ma ago.The stratigraphy of Sumba may be
correlated with the Cretaceous to Miocene part of the Timor allochthon AudleyCharles. The
preTertiary and the Paleogene stratigraphy of Sumba are different from that of NW Australian
shelf. although they have a slight preference for a southern provenance. . There are no
volcanic. The outline of the geology of Sumba shows that both the stratigraphy and the
tectonics of the island are rather simple. In Northern Timor there are volcanics of the Metan
Formation and nummulitic limestones of Eocene age which are overlain by Oligocene reefal
limestones. .stratigraphy of Sumba differs from that of NW Australian shelf. however. The
sedimentary and eruptive rock succession in Sumba shows remarkable similarities to the
allochthonous Palelo. as well as the Paleocene volcanics of the Massu Formation. Wensink
found difficulty relating Sumba to Australian provenance due to the significant presence of
granodiorite intrusives and related rocks which have an age of approximately Ma. Sumba
moved to the southwest by escape tectonism.
Abdullah et al. The Late Cretaceous is considered to be a time of thermal doming and
plutonism. . The first tectonic phase of Sumba at the end of the Cretaceous that was
associated with Lower Paleocene dated Ma calkalkali trachyte with hypersthene and
calkalkali syenite. . initiating cratonisation of the Sunda Shield. may be compared to one of
the main tectonic phases known in East Kalimantan and Sulawesi. A set of magmatic rock
samples representing granitoid intrusions. The theory that the Sumba microcontinent
detached from SE Sundaland has been considered since Hamiltons work . . . lava flows and
subvolcanic dykes of mafic to intermediate composition from various outcrops within the
investigated area were selected for KAr dating as well as chemical analyses major and trace
elements. . Paleomagnetic data of Sumba show the location of eastern Sundaland in the
Late Cretaceous and has occupied its present position since the Early Miocene Wensink.
Lithological association of flysch slope sediments containing Globotruncana sp of Late
Cretaceous age Praikajelu Formation and the associated basaltic. Simandjuntak.
Simandjuntak considered that the detachment of Sumba Island from Sulawesi took place in
Paleogene to Neogene time. . Various methods have been used to identify the provenance
for the Sumba area. and Eocene larger foraminifera Lunt. geochronologygeochemistry of
magmatic rocks Abdullah. paleomagnetism Wensink. Late CretaceousPaleogene intrusives
of syenite. At the beginning of the Upper Eocene. Pellatispira. Origin of the Sumba Island
Sundaland Many authors are in favor of a northern provenance Sundaland/SE Asia for the
Sumba fragment/island/terrane/block. there was a nondepositional period on Sumba Island
while in SE Kalimantan sedimentation continued into the Neogene. Wensink and van
Bergen. argued that the CretaceousPaleogene geology of Sumba Island is quite similar to
the southern arm of Sulawesi and in some aspects to the southeastern part of Kalimantan
both areas are located in SE Sundaland Figure .. The Paleogene carbonate platform and
greywackes of Sumba are correlative to SE Kalimantan and the southern arm of Sulawesi
Berai and Tonasa carbonates. andesitic and rhyolitic volcanics of the Massu Formation on
Sumba Island is similar to sequences in southern arm and Central Sulawesi Latimojong
Formation and Langi Volcanics and in Southeast Kalimantan Pitap Formation. The
CretaceousPaleogene geology of the Sumba Platform correlates with the southern arm of
Sulawesi and SE Kalimantan Simandjuntak. Abdullah . Abdullah. isotope geology Vroon et
al. Based on Sumba stratigraphic succession. The island drowned in the interarc trench
during the Miocene and uplifted in the PlioQuaternary as a result of the subduction of the
front of the Australian shelf. Sumba contains typical Eocene lowlatitude Sundaland fauna of
Assilina. In Late Paleogene time. . deposition was dominated by a carbonate platform with a
break in Middle Miocene time. . showing more or less craton characteristics at the beginning
of Paleocene. respectively. on the southern arm of Sulawesi. During OligoMiocene time.
granodiorite and granite occurring in those areas are similar to the Early Paleocene
intrusives on Sumba Island. . Potential PbNd isotope characteristics of rocks from Sumba
and its expected provenances show corresponding isotopic signatures and affinities with
Sundaland Vroon et al. . Abdullah.. . Burollet and Salle provided the first comprehensive
geological study of Sumba Island that explained its geodynamic position. . Sumba represents
a borderland of the Sunda shelf..The Sumba fragment seems to have occupied its present
position at least since the early Miocene. and structural episodes. magmatic rocks. Abdullah
noted similarities in the Paleogene sedimentary facies and magmatism on Sumba and
Sulawesi and concluded that the island was originally part of a Paleogene volcanic arc that
was situated near western Sulawesi from Late Cretaceous time to the Paleogene. Abdullah
et al. . diorite. Numerous other magmatic rock samples were studied . Based on this.
including stratigraphic succession Burollet and Salle. based on regional stratigraphic
correlation. SoeriaAtmadja et al. . equivalent to a large extent to the submarine arc of the
Sunda islands. and Abdullah studied in detail the stratigraphic succession and
magmatic/volcanic rocks of Sumba and its expected provenance in SE Sundaland Figures .
and Biplanispira and no Eocene highlatitude Australian fauna of Lacazinella Lunt. Burollet
and Salle concluded that in contrast to Timor. . whose framework belongs to the Australian
foreland. Simandjuntak . andesitic and calcalkali trachyandesitic lavas that were persistent
though the Palaeogene.
Southern New Guinea has Pb/Pb of . .. siliciclastic mudstones of the Late Cretaceous
Lasipu Formation. Paleomagnetic investigation of suitable rocks can be a valuable tool for
the unraveling of tectonic problems. typical of subductionrelated magmas.... Marine
sedimentary rocks of the Late Cretaceous Lasipu Formation in Sumba were analyzed for the
PbNd isotopes. the volcanics of the Massu Formation gave a paleolatitude of .. Such affinity
is consistent with their moderately to fairly enriched incompatible element patterns showing
negative anomalies in Nb. The Birds Head area has Pb/Pb of . and indicate textural evidence
for weak metamorphism. Three periods of magmatic activity were recognized by Abdullah on
the basis of most of these data. No evidence of Neogene magmatic activity has been
recorded anywhere on Sumba. The evidence is based on a comparison of PbNd isotopic
signatures between metasedimentary or volcanic rocks from the microcontinents and
possible provenance areas. Later paleomagnetic studies of Sumba were detailed by
Wensink and van Bergen of the early Miocene Jawila volcanics followed by Wensink for the
Late Cretaceous Lasipu Formation. but with a minor southward drift.. and Pb isotopes Pb/Pb
. . Western New Guinea has low Pb/Pb . The Sumba fragment has occupied approximately
its present position since the Miocene where the island was located within the latter arc
between Sumbawa and eastern Flores. Wensink. The geology of Sumba reasonably satisfies
both conditions. The southward migration of Sumba to its present frontal arc position in the
Sunda Banda arc has occurred since Late Cretaceous Paleocene time SoeriaAtmadja et al.
Based on PbNd isotopic characteristics of sediments and volcanics. The sediments of the
Lasipu Formation revealed a paleolatitude of . between the Paleocene and early Miocene the
fragment moved in a CCW rotation of and a drift of to the south. evaluated provenances of
continental fragments in Eastern Indonesia Figure B. suggesting a typical island arc
environment. Based on a later paleomagnetic study.. volcanics of the Paleocene Massu
Formation comprising basalts and andesitic basalts.. Vroon et al... and low Nd/Nd . and
basalts from the Early Miocene Jawila Formation in West Sumba. relatively high AlO and low
TiO content. and Sumba formed one continental unit in the Late Mesozoic. Sumba performed
a counterclockwise CCW rotation of and a drift of to the south. Wensink interpreted that
Eastern Sundaland with Borneo. Sundaland has less radiogenic Pb isotopes. . and to a
lesser extent in Ti. and the volcanics of the Jawila Formation a paleolatitude of
.petrographically Abdullah et al. Since the early Miocene. and near the Southeast Kalimantan
coast Meratus Mountains Yuwono et al.. Comprehensive paleomagnetic study of Sumba
Island was first provided by Wensink . and relatively high Nd/Nd . Similarities between
Sumba and the Southwestern Sulawesi magmatic belt with respect to both the Late
CretaceousPaleocene magmatism and stratigraphy. support the idea that Sumba was part of
an Andean magmatic arc near the Western Sulawesi magmatic belt Abdullah. They display
limited variations in Nd/Nd . to determine the rotation the translation of the Sumba fragment
during transport. North Australia has very high Pb/Pb up to . . it is important that the ages of
the studied rocks are well known and the tectonics are properly understood.. Ma
MaastrichtianThanetian and Ma LutetianRupelian. In this regard. Between the Late
Cretaceous and Paleocene. Zr.. Sumba has occupied its present position. SoeriaAtmadja et
al. at ca Ma SantonianCampanian. i. Erupted magmas display the characteristics of a
predominantly calcalkaline CA and a minor potassic calcalkaline KCA series. ...e. The
Sumba microcontinent most likely became detached from eastern Sundaland soon after
deposition of the Lasipu sediments. at the margin of Asiatic Plate.. Vroon et al. It was
concluded by Wensink and van Bergen that paleomagnetic and geochemical evidence from
the early Miocene volcanics of the Jawila Formation in western Sumba constrain the final
drift stage and tectonic emplacement of the island.. they are characterized by variable KO
content. west and south Sulawesi. These paleomagnetic data have been interpreted in terms
of an original position of the Sumba fragment in the northern hemisphere in Late Cretaceous
time. Figure A. Provenance areas considered were continental margins of AustraliaNew
Guinea or Sundaland. PbNd isotopic variations in possible provenances were studied. The
lavas range from predominantly andesites to dacites. Wensink collected two hundred hand
samples from three formations dark colored. most likely attached to the Southeast Asian
mainland..
Therefore. subsequent Tertiary collision of these plates can be identified by the present
complex distribution of previously separate faunas. Detailed KAr chronology of Sumba
magmatism shows its beginning during Late Cretaceous and its vanishing in Late
EoceneEarly Oligocene.. reported and illustrated Assilina orientalis Douvill and several
species of Pellatispira from southern Sumba in the mid Eocene through Oligocene shallow
marine Tanah Roong series. and thus favor a northern rather than a southern origin. these
results constrain the . we believe that the origin/provenanse for Sumba terrane was
SE/Eastern Sundaland. Because of stratigraphic indications for a paleoposition of Sumba
near SW Sulawesi Simandjuntak. and Biplanispira hereafter abbreviated quotAPBquot
indicate a low latitude. The beginning of Sumba dispersion is various from the Late
Cretaceous Wensink. were analyzed for comparison. One of these faunal groups is
associated with the Sundaland craton. which implies a close isotopic similarity with the
Lasipu Formation.interpreted that these isotopic signatures do not correspond to the
Australian or New Guinean continental domains. and Biplanispira and no Eocene highlatitude
Australian fauna of Lacazinella shows that the provenance of Sumba Island was Sundaland.
the fauna identified by the genus Lacazinella. probably related genera Assilina. Sumba as a
fragment of Sundaland based on geological criteria. . Tectonic reconstruction for SE Asia
and SW Pacific during Cenozoic by Hall shows that Sumba was originally part of Eastern
Sundaland located between East Java and South Sulawesi. there are indications that Sumba
started to drift in the Late Cretaceous and had already arrived at or near its present position
in the Early Miocene. identified by three. Late Cretaceous flysch sedimentary rocks from the
Balangbaru Formation of SW Sulawesi Hasan. parts of Timor. The presence of two typical
Eocene lowlatitude Sundaland fauna of three APB Assilina. Pellatispira.
geochronologygeochemistry of magmatic rocks. . is thought to be a higher latitude fauna
centered on the Australian continent. including Sumba. paleomagnetism. This correlation
leads to the hypothesis that the Middle and Late Eocene Sundaland fauna. Caudri .
Detachment Terrane and Emplacement of Sumba The southward movement of Sumba took
place during preNeogene time by transcurrent/ transformal displacement and the island has
occupied its present position in the forearc basin in front of SundaBanda volcanic arc since
the early Neogene. . it is considered that Sumba originated from SE Sundaland. to Middle
Miocene Simandjuntak. Most of the authors such as Parkinson et al. Provenance of Sumba
Island can also be investigated using certain Eocene larger foraminifera. Assuming the
palaeomagnetic anomaly quotMquot.. described in Lunt. Regionally as well as
chronologically. Wensink and Wensink and van Bergen argued that based on the recent
paleomagnetic evidence.. . . The second fauna is found on the Australian Plate. . IndoPacific
Eocene carbonate sediments can be divided into two groups based on the presence of
certain larger foraminifera Lunt. Sumba has a basement of Upper Cretaceous turbidites
overlain unconformably by gently dipping Paleogene shallow water sediments and volcanic
rocks and resembles the stratigraphy of the adjacent Asian margin in SW Sulawesi and
offshore east Java Packham. Based on this. is consistent with the faunal data. They yielded
Nd/Nd of . then these fragments would have been carried north and become accreted onto
the subducting margin south of Sundaland within the Cretaceous. shallow marine fauna.
Pellatispira. and large Eocene foraminifera and earlier objections to Australian/Timor/Tethys
provenances for the Sumba terrane. suggested the Paleogene as the period of Sumba
dispersion. This faunal difference occurred at a time of maximum separation of the Sunda
and Australian plates. able to cross oceanic migration barriers but restricted from migrating
far outside the tropics Figure . isotope geology. and Pb isotopes Pb/Pb of . Many islands that
make up the Banda Arc. Based on our studies of stratigraphic succession. and the
microplate terranes have been derived from it since the Eocene. which has about the same
stratigraphic range as the APB lineage. and Seram have records of the APB fauna. This
similarity indicates that they were separate from the Australian plate and at low latitudes in
Eocene times. the geological core of western Indonesia and is also found on low latitude
Pacific islands as well as low latitude western Tethyan regions. end midJurassic riftdrift event
was the last known cause for separation of microplate fragments from the Australian margin
Veevers et al. In contrast.
rotation of the continental Southeastern Sundaland. Satyana considered the role of escape
tectonism in western Indonesia following the collision of India with Eurasia in the Paleogene
as motive for fashioning the present tectonic configuration. Volcanism along the modern
Banda Arc soon followed. Sumba formed part of a Great Indonesian Volcanic Arc system
near southeastern Eurasia. . The term tectonic escape/escape tectonics/extrusion tectonics
as . Sumba finally came to rest at its present location. related to the convergence of the
IndoAustralian. The main period of accretionary activity ended by Early Tertiary time in the
Cordillera and in northeastern Siberia. Satyana. The dispersed mass includes SW Sulawesi
through opening of the Makassar Strait. Based on the tectonostratigraphy. Eurasian and
western Pacific microplates Parkinson et al. . In Japan. The dispersion of terranes. These
rocks have suffered considerable dismemberment. Between Late Cretaceous and Early
Miocene time. The rock specimens comprise variably metamorphosed accretionary
complexes. . and thermal overprinting due to tectonic and metamorphic activity throughout
the Tertiary. This growing continent by amalgamated terranes blocked the mantle circulation
in the astenosphere. During the Late Cretaceous. tectonic and structural modification.
folding. tectonic escape due to IndiaEurasia collision and mantle delamination by upwelling
plume under Eastern Sundaland. as part of the relict arc system. after having moved km into
the forearc. Translation of these continental fragments occurred along the NS trending
protoPaternosterWalanaeSalayar fault zone between the Late Cretaceous and the early
Miocene accompanied by crustal rifting and the leftlateral fault system facilitating the
southward migration of Sumba and its counterclockwise rotation SoeriaAtmadja et al. At the
eastern margin of Sundaland. and ophiolites. was situated near the present site of Alor and
Wetar. turbidite and broken formations. southward and southeastward slivering the continent.
These accretionary episodes have been followed by a history of complex strikeslip faulting.
The history of detachment of Eastern Sundaland terrane is complicated and may involve a
number of mechanisms Satyana. The eastern margin of Sundaland is fragmented and
tectonically complicated. by either rifting or sliding. Sumba was torn from the relict arc and
began to move velocity of mm/yr in a westsouthwesterly direction. Sumba remained part of
that arc system. the accretion stopped at around Ma Middle Eocene and the accreted crust
started to detach beginning with the opening of the Makassar Straits. Postaccretionary
dispersion/detachment is a usual case in the CircumPacific region Howell et al. some of the
accreted mass of SE Sundaland rifted and drifted eastward. backarc spreading of marginal
basins of Southwest Pacific areas.. leftslip faults are smearing out and dispersing the
terranes while accretion is still occurring.. which ceased to be volcanically active by Ma.
presented another interpretation on periods of detachment and emplacement of Sumba. and
thrust faulting resulting in the breakup of some terranes. Flores Sea Islands. At Ma. Sumba.
Satyana suggesting that the uprise of buoyant metasomatized mantle in connection with the
initial opening of Makassar Strait in the Early Tertiary was responsible for the separation of
Sumba from the mainland of Sulawesi. Another mechanism of migration was movement of
the block/terrane by major strikeslip faults related to escape tectonics. Buoyant mantle
material unroofed the amalgamated terranes beginning around Ma. in the Middle Eocene.
and in eastern China.geodynamical evolution of this area during the Oligocene and Miocene.
results in the diminution of continents. backarc spreading due to subduction rollback related
to IndiaEurasia collision at Ma. During the late Miocene Ma. Sumba Island shifted to its
forearc position. and Sumba Island. as well as the islands of Doang and Salayar which now
lie to the south of Sulawesi. including crustal breakdown to the west of South Sulawesi
volcanic arc by PlioPleistocene diastrophism. . During this period. The provenance and way
of detachment of some fragments believed once part of Eastern Sundaland are also complex
and variably interpreted. By Ma. Satyana described the accretion of SE/Eastern Sundaland
by a number of terranes during the Late Jurassic to the earliest Tertiary. southern extension
related to seafloor spreading of the Sulawesi Sea. eastwest trending leftslip faults resulting
from the northeastward movement of India are fragmenting the collection of terranes in that
area. melange. Figure . imbricated terranes. Rutherford et al. This resulted in the growing of
Sundaland through amalgamated terranes and accreted mass associated with subduction
and collision Figure.
between the Paleocene and early Miocene Sumba drifted of to the south. Total drift of
Sumba from its provenance at .L. located to the east of Sumba Island has been more
explored than Sumba area. offshore Dseismic surveys . and molassic sediments in South
Sulawesi.N. . Sumba and other terranes amalgamated SE/Eastern Sundaland. Figure . or
from the Walanae depression in the south arm of Sulawesi seems to have taken place in the
middle Miocene by reactivated sinistral wrenching of the PaluKoro Fault or the Walanae
Fault prior to the development of the volcanic arcs in Lesser Sunda.N and . Strikeslip and
extensional/rifting structures accommodate the lateral motion. Sumba Island and surrounding
seas have been unexplored. During the Paleogene. It is postulated that following the collision
of India with Eurasia beginning in the Eocene. It is a transverse trending major structural
element shearing the island of Kalimantan from the Natuna Sea through to the Strait of
Makassar as long as km. Backarc spreading resulted in the southward/southeastward
migration of Sumba. refers to the lateral motion of fault bounded geological blocks following
collision indentation. After that work. The Savu Basin was explored from by International Oil
Exploration and WoodsideBurmah Oil N. the rate of movement of the Indian oceanic crust
subducting eastern Sundaland decreased. The paleolatitudes of Sumba in Late Cretaceous
and Paleocene times are . The forearc basin of the Savu Sea. The detachment of Sumba
from near Bone Bay.. Since the early Miocene the island of Sumba has been in
approximately its present position. In Kalimantan. . published their geological study of Sumba
Island in for the main purpose of gaining a better understanding of the geodynamic position
of Sumba and gathering more information to prepare a program for the offshore seismic
campaign. geologists from Total. in . The trace of this fault may also continue or attach to the
major faults in South Sulawesi such as Walanae Fault.S. During its drifting. moved as far as .
respectively. These activities included field work in Savu Island.related to indentation
tectonics. . the major strikeslip fault of AdangPaternosterWalanaeSumba Fracture resulted in
escaped terranes one of which was Sumba southeastward/southward to the free oceanic
edge which at that time was the ocean between the Sundaland and Australia. cross
latitudinal. PaluKoro Fault until the Sumba Fracture. Petroleum Implications Sumba Island
has been investigated for the possibility of petroleum accumulation since when geologists of
NPPM Nederlandsche Pacific Petroleum Maatschappij spent six months of reconnaissance
work on the island van Bemmelen. Another mechanism considered for Sumba detachment
was backarc spreading Abdullah et al. No further petroleum exploration on Sumba Island and
surrounding seas was carried out until Burollet and Salle. Sumba underwent several periods
of counterclockwise rotation. In Late Cretaceousearliest Paleogene. Simandjuntak proposed
that the northern part of Bone Bay is more likely to be the original site of the Sumba terrane
as indicated by the geological similarity and a relatively good fitting of topography of Sumba
with the northern part of the Bone Bay region. Sumba terrane detached from the rift zone
subsequent to the extensional faulting leading to the break up and formation of the Makassar
Strait during the separation of South Sulawesi from SE Kalimantan prior to the development
of the late Neogene volcanic arcs in the Lesser Sunda region. MidMiocene successions of
turbidites in Sumba are quite different to the volcanic. and Wensink and van Bergen
described the emplacement of Sumba terrane from the northern hemisphere into its present
position.N to its present position at . Simandjuntak suggested displacement of the Sumba
terrane could be kinematically related to one of the following tectonic movements Sumba
detached from SE Kalimantan and rifted southwards by transcurrenttransformal
displacement prior to the development of the late Neogene volcanic arcs in the Lesser Sunda
region. The well TD m was drilled . Satyana.L. . Satyana et al. carbonates. The motion is
away from the collision zone and towards free oceanic zone. Based on paleomagnetic
studies Wensink . Backarc spreading in SE/Eastern Sundaland caused the opening of the
Makassar Strait separating western Sulawesi from SE/Eastern Kalimantan. leading to the
generation of backarc basins and the formation of a marginal sea due to rollback movement
of the subducted plate.. major shear related to the India collision is the
LuparAdang/Paternoster Fault Satyana. and drilling of one exploration well Savu by
WoodsideBurmah Oil N. therefore Sumba drifted to the south. .
The geologic settings of Savu Basin and Sumba area are different. Donggi. its foredeep and
foldthrust belt. Transgression from the middle Oligocene to middle Miocene with fluvial
reservoirs being succeeded by the main deltaic and carbonate reservoirs occurred in the late
Oligocene to early Miocene. Recent publications on Savu Basin are from Tampubolon and
Saamena . and collision of the Luzon arc with the Asian plate at about Ma. sedimentation of
postcollision/molassic deposits. Late Miocene through Pliocene compression resulted in
structuring events and increased heat flow associated with the collision of the Australian
craton with the Asian plate. especially in Eastern Sundaland basins East Java Basin or
western Sulawesi basins. Although there are gross geological similarities between Western
Indonesia basins. Australian Mesozoic sediments were deposited as a synrift sequence in
grabens of the BanggaiSula microcontinent. there are also significant geological differences.
During the Paleogene. Sukamaju. Ma. we consider that the proven collisionrelated petroleum
play of BanggaiSula microcontinent will not typify Sumba microcontinent due to the absence
of collision in the history of Sumba tectonic transport and the absence of Australian Mesozoic
source rock and reservoirs such as Australian originated microcontinents Banggai. Recent
publication by Satyana et al. The BanggaiSula microcontinent has Australianorigin. Toothill
and Lamb and Rigg and Hall . and the Tiaka oil field sourced by Miocene lagoonal
carbonates and shales and reservoired by syndrifting Miocene reefal and platform
carbonates. the South Makassar and Bone basins show elements and processes of
petroleum systems . and Maleo Raja gas fields. it is interesting to review the petroleum
implications for Sumba area. Basically. These seismic lines will be used as the basis to
review the prospectivity of Sumba area. the analogy is made to the South Makassar and
Bone Basins. Collision and postcollision tectonic escape in the BanggaiSula collision
significantly affected basin formation due to isostatic subsidence and underthrusting of the
microcontinent. and trap formation related to collisional thrusting and postcollision wrenching.
However. Birds Head of Papua. and postcollision extension. Seram. Because the Savu Basin
is located near the prolific NW Shelf of Australia. km. should be applied in exploring Sumba
area. subsidence of the basins due to deposition of molasses and/or thrust sheet of
postcollision sequences.at the Savu Ridge. not typical of Eastern Indonesia microcontinents.
Gravity data as acquired along with both seismic surveys. These are primarily controlled by
basin position on Sundaland promontory in relation to presentday and Cenozoic subduction
of the IndoPacific plate northwards beneath Sundaland. The best examples of this are
petroleum accumulations related to the collision of the BanggaiSula microcontinent. Some
thermogenic gas seeps expected to be sourced by Mesozoic sequences occurred in this
area. Senoro. Some seismic lines of Savu Basin include the offshore areas of Sumba Island.
Gas and oil fields have been discovered in the Banggai Basin. including the main source
rocks for the majority of Western Indonesian basins. with regional seals deposited in the
Middle Miocene at maximum transgression. Considering the origin of Sumba terrane from
western Sulawesi area/Eastern Sundaland. Buton. Based on the origin of Sumba terrane.
penetrating Neogene claystones and carbonates and undifferentiated highly deformed
preNeogene section. including the Minahaki. generation of hydrocarbons in Miocene and
Mesozoic sources due to isostatic subsidence and/or burial by multiple thrust sheets.
Western Indonesian basins demonstrate gross similarities in terms of structure and
stratigraphy reflecting common regional controls throughout their Cenozoic histories
Netherwood. Matindok. new D seismic was shot in . Other petroleum plays. we consider that
play types of Sumba area will be equal with proven play types of Western Indonesian basins.
The collision of the BanggaiSula microcontinent with East Sulawesi ophiolites was
responsible for the formation of the foreland Banggai Basin. A common middle to late
Eocene timing for initial basin rifting and associated fluviolacustrine fill. Sumba area is an
exotic terrane and prospectivity review should include consideration of this matter. The well
was dry and no reservoir was encountered. . especially during the Paleogene. the rift
grabens subsided and were partly overprinted by compressional tectonics resulting in
thrusted anticlines. When collision of the microcontinent took place in the Late Miocene. As a
terrane. discusses some terranes/microcontinents in Indonesia where there are petroleum
accumulations in sedimentary basins formed by collision of these terranes. km and .
Late Miocene chalky pelagic limestones typical of bathyal environment can be seals for Late
Miocene Waingapu sandstones. woody terrigenous to marine lagoonal source rocks in
buried half grabens. slope channel fill. radiolaria and sponge spicules associated with fine
volcanic glass fragments. foraminifera. Presence of pyritous organic shale and excellent
TOC shows very goodexcellent preservation of organic matter in restrictedreduction
environments. slope channels. tilted fault blocks. first step of the transgression. cinerite.
synrift section. late synrift paralic to nearshore marine sand and early sag phase Eocene to
early Oligocene carbonate reef and sand reservoirs. Field observations and laboratory
analyses reported by Burollet and Salle provided this examination. The rocks are exposed at
the eastern part of the island. During the Upper Eocene. drape over basement highs. In the
entire series. Paleogene play types of Bone Basin are faulted anticlines. . these facies pass
progressively to greywackes with abundant planktonic foraminifera and with rare large
benthic foraminifera. and stratigraphic pinchout Sudarmono. Paleogene play types of South
Sulawesi Basin are rotated fault blocks. Botryococcus are fresh water algae species living in
restricted lacustrine environments an example of proven lacustrine kitchen is excellent
qualityOligocene Pematang source rocks from Central Sumatra Basin. thrust fold features.
Seals for reefal and coralline limestones can be provided by shaly planktonic foraminiferal
wackestonepackstone with abundant coccoliths. etc. Potential reservoirs are synrift fluvial
and paralic sands. The reefal or bioclastic limestone extends east of Waikabubak as far as
the Tanadaro mountains and seems to be there at the lower part of the carbonate series.
These greywackes correspond to the destruction of the Lower Paleocene volcanic massifs.
pyritous organic shale with a very rich fauna. The Neogene formation coarse conglomerates.
Reworked large benthonic foraminifera from Miocene were observed in several samples. etc.
excellent. Its age is indicated by calcareous nannoplankton as early Miocene to basal Middle
Miocene see Figure B. This shale is the only sample from Sumba that contains a significant
amount of organic matter with TOC . stratigraphic subcrop plays. reefal and bioclastic
limestones corals. tephra. algae. This outer shelf environment indicates a progressive
deepening which culminates in bathyal facies observed in the form of sandy shale with
abundant radiolaria and diatoms. Conglomerates are overlain by black. the mineralogy is
characterized by the . They are locally associated with Nummulitic mark. So the subsidence
of the reefal environment to deep bathyal zones is precisely located at the limit of lower to
middle Miocene analogous to East Java Basin where prolific Mudi reefs are sealed by Tuban
shales. In the Western part of the island. The existence of elements of petroleum system in
Sumba area can be examined by reviewing the related rocks in Sumba Island which may
continue into the offshore areas composing elements of the petroleum system. Elements of
the system in Sumba area. Potential source rocks are synrift Early Tertiary lacustrine.
probably deposited in a slightly shallower environment. These sandstones are interbedded
with sandy shales. locally cemented by crystalline calcite. They are dated Middle Eocene. as
analogue to South Makassar and Bone Basin can be inferred from seismic data of Sumba
area. The organic matter is a typical humic material with a lower maturation stage. and
inverted pinchouts. New seismic data around Sumba show the presence of these Paleogene
rifts and their possible play types. overlay a thick volcanodetrital series with tuff..related to
rifting. Earlymiddle Miocene limestones comprising bioclastic packstone with abundant
micritized and rolled red algae fragments and scattered quartz. Potential seals are
interbedded claystones in synrift and early sag phase deposits and interbedded hemipelagic
claystones in basinal deposits. unconformably overlies all the older formations and seems to
drape away from the PreTertiary massifs. locally microconglomeratic with boulders of
volcanic rocks. The combined presence of fresh water algae Botryococcus indicates a
restricted brackish environment. . mainly around Waikabubak and more precisely between
this town and the south coast. The rocks are exposed on the western side of Tanadaro.
Based on this. clay. Potential reservoir rocks can be referred to Eocene neritic facies littoral
to middle shelf that comprise mainly medium to coarse greywackes. Yulihanto. marls and
limestones. turbidite fans. Lower section of the Waingapu Formation late Miocene consisting
mainly of fine to coarse grained sandstones. The microfauna is characteristic of bathyal
environment and the age is middle Miocene LanghianSerravallian. it is considered that
Sumba area indicates the presence of both oilprone lacustrine and gasprone humic coal
source rocks. Potential source rocks of Sumba are Neogene rocks with abundant plant
remains coal. deformed/fractured carbonates. sandstones and limestones which covers most
of Sumba Island.
These seepages are indicative of migrating hydrocarbons. other provenances argued by
previous workers are Timor Island and Tethys Sea isolated microcontinent. The detachment
and emplacement took place during the Paleogene. cross latitudinal and several episodes of
counterclockwise rotation. . rifted structures in Sumba offshore areas with the configuration
of typical graben kitchens and traps of rifted structures as revealed by recent seismic lines.
and a number of oil seeps/slicks offshore Sumba could indicate the presence of an active
petroleum system. Sumba area has requisite characteristics for a petroleum producing
province and is worthy of . isotope geology. and fractured basement highs. southern
Makassar Straits. Tectonically. traps in synrift sections. Buton. Basically. reefal buildups over
the horst. Potential traps related to rifted structures are tilted fault blocks related to rifted
basin and drape channel sands overlying the basement high. paleomagnetism. the presence
of source. stratigraphic subcrop plays. faulted anticlines. reservoir.association
montmorillonite and mixed layers of illite/montmorillonite then by exclusive montmorillonite.
These associations are directly related to the transformation of detrital volcanic rocks in deep
water environment. In addition to these. some of the mapped slicks show clustering. and
large Eocene foraminifera. Sumba lies obliquely between two forearc basins. slope channel
fill. stratigraphic pinchout. and Sumba has no history of collision for its emplacement. like
those developed in Timor area. The movement involved southward drift of Sumba terrane as
far as . There are two main competing hypotheses Northwest Australian provenance and
SE/Eastern Sundaland provenance. which may relate to multiple vents associated with the
same geological feature. Hydrocarbon potential of the Sumba area is enhanced by the
recording of seeps on satellite images. and sealingquality rocks are exposed in Sumba
Island. Seismic lines prove the absence of structures related to collision. Figures show the
presence of rifted structures as commonly recorded in Eastern Sundaland areas Satyana.
rifted structures typical of South Sulawesi. Petroleum prospectivity of Sumba microcontinent
cannot be inferred from proven plays of other microcontinents in Eastern Indonesia
BanggaiSula. The movement of Sumba terrane to its present position may be through
regional strikeslip faults of PaternosterWalanaeSelayarSumba Fracture as a response of
escape tectonics due to the IndiaEurasia collision. turbidite fans. Figure . The origin of
Sumba terrane has been a matter of considerable debate in geologic literature. Based on
newly acquired seismic lines. geochronologygeochemistry of magmatic rocks. We examined
the possibilities of these four provenances. typical of Sundaland or South Sulawesi. and
possible elements and processes of petroleum systems in Sumba. SE/Eastern Sundaland as
the origin of the Sumba terrane is supported by examinations and interpretations of
stratigraphic succession. and believe that SE/Eastern Sundaland is the most plausible origin
for the Sumba terrane. stratigraphic succession of Sumba. the island is important since it is
located at the border between the subduction zone of Indian oceanic crust beneath Sunda
Arc to the west and the collision zone of Australian continental crust with Timor island arc to
the east. Sumba was an Asian microcontinent which means it has no Mesozoic and Upper
Paleozoic sediments which are prolific in Australian continent/microcontinents. and Bone Bay
can be analogous for petroleum plays of Sumba. many of which show good correlation with
geological features seen on seismic data Toothill and Lamb. The seeps and their strong
correlation with geological features show that a hydrocarbon system is active in the basin.
Hydrocarbon kitchens may exist in the synrift sections. Recent seismic lines in offshore
Sumba areas Toothill and Lamb. the Lombok Basin to the west and the Savu Basin to the
east. Also. Figure shows the petroleum system of South Sulawesi. CONCLUSIONS Sumba
Island is a terrane microcontinent presently located in a forearc setting of the SundaBanda
volcanic arcs. There was no foreland basin developed due to collision in Sumba area.
Detachment of Sumba terrane from SE/Eastern Sundaland could be a result of a number of
mechanisms such as mantle delamination by upwelling plume under the Eastern Sundaland
or backarc spreading due to subduction rollback related to IndiaEurasia collision at Ma.
Kepala Burung. foreland basins are proven petroleum provinces within Eastern Indonesian
microcontinents subjected to collisional tectonics. East Java.
recently acquired seismic lines show the presence of rifted structures in offshore area with
many possible traps. . Hartono. and discussions. Maury. The tectonic significance of Sumba.
Fortuin. SoeriaAtmadja.I. van Weering. . Abdullah. . D. A. Joint Prospecting for Mineral
Resources in Asian Offshore Areas CCOP. T. These characteristics are Sumba Island has
source.A. H.. . Chandra Tiranda Mitra Energy...C. W. th Annual Convention and Exhibition..
amp Apandi. and there are a number of hydrocarbon seeps/slicks offshore indicating the
presence of an active petroleum system. C. .. . P. Chamalaun. . Chalid Idham Abdullah and
Benyamin Sapiie. and Mutter. .L. p. Fortuin. . J.. Evolusi magmatisme pulau Sumba.G. Kuala
Lumpur. Dr. J. T.. A.A.M. . Th. The Sumba Fracture a major discontinuity between western
and eastern Indonesia. Effendi. BPMIGAS and ConocoPhillips Management are
acknowledged for supporting the the authors to conduct and publish this study.I.S.. . and
Hartono. . A. C. Malaysia. March . Effendi. Sumosusastro. Chamalaun. reservoir. the th
Annual Scientific Meeting. . A.H. Chamalaun. .C. unpublished data. Rampnoux. W.. . H. . C.
Indonesia AudleyCharles. Djumhana. p. and Drake.E. B. Proceedings of a Workshop. p.
unpublished. Burrolet. ITB.E. Roep. . A. .. ps. Bangkok. Sumosusastro. Dr. F.. . Thse de
Doctorat. .R.further exploration. . J.S.. Grady. von der Borch. and Salle. C. onshore and
offshore Sumba Indonesia. M.. and Sunata.. Th. A. P.G. Nusa Tenggara.. C. van der Werff.
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of Southeast Asian Earth Sciences.Cretaceous. Petrology of the Cretaceous magmatic rocks
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Figure . in front of SundaBanda volcanic arc and in between Lombok and Savu basins.
.Location of Sumba Island.
.. Sumba is bordered by major faults that could have transported the island during the
Paleogene to its present position. Blocks colored in purple in SE Kalimantan Borneo and
southern Sulawesi Celebes are argued as the origin of the Sumba terrane after Hamilton. .
The island is located in the forearc of the SundaBanda volcanic arc at the border between
Java Trench subduction zone of Indian Ocean and Timor Trough collision zone of Australian
Continent. Abdullah et al. Lombok and Savu basins are forearc basins.Figure . .Sumba
Island in regional tectonic setting of Eastern Indonesia. Burollet and Salle. .
Geological sketch map of Sumba. .Figure . Abdullah. . C are profiled in Figure Abdullah et al.
B.. . Box A.
B central.Figure . . E east is shown at Figure Abdullah et al..Stratigraphic columns/profiles of
Sumba from west to east. Area of columns as A west. Abdullah. . .
MioPliocene chalky carbonates of Waingapu Formation. showing various rocks comprising
the central part of Sumba Island.Some outcrop photographs of Central Sumba. Early
Miocenebasal middle Miocene coralline limestones of Waikabubak Formation. B. C. legends
of rock unit see Figure . brecciated of Paumbapa Formation.Figure . Field survey took place
in September . The rocks are A. and D. . Geological map is taken from Abdullah . Late
Cretaceous turbiditic interbedded sandstones and claystones of Lasipu Formation. Eocene
foraminiferal marlstone/limestone.
Figure . . detached and emplaced at its present position during MioPliocene time due to
postcollision tectonic escape relating to the collision of Australia into Timor.Schematic
diagram showing Cenozoic reconstruction for Sumba when considered as part of Timor
during the Late CretaceousPaleocene. The escape was accommodated by major strike slip
faults Djumhana and Rumlan. The Savu Basin was opened due to the escape of Sumba
from Timor. .
Figure . . indicating that Sumba shared same place with South Sulawesi before
dispersion.Stratigraphic correlation of Sumba. South Sulawesi and SE Kalimantan after
Simandjuntak. . Based on stratigraphic succession. it is obvious that Sumba is very similar to
South Sulawesi.
S. N. between the Paleocene and early Miocene the fragment moved a CCW rotation of and
a drift of to the south. Sundaland has less radiogenic Pb isotopes. Sumba has occupied its
present position.A B Figure A . the volcanics of the Massu Formation gave a paleolatitude of
. showing close relationship. . Between the Late Cretaceous and Paleocene. . N. North
Australia has very high Pb/Pb and low Nd/Nd. the volcanics of the Jawila Formation
presented a paleolatitude of . Based on paleomagnetism and isotope geology. The
sediments of the Lasipu Formation revealed a paleolatitude of . Figure B . it is concluded that
Sumba originated from SE/Eastern Sundaland. Since the early Miocene. Late Cretaceous
Lasipu Formation of Sumba displays limited variations in Nd/Nd and Pb
isotopes.Paleolatitudinal positions for the island of Sumba derived from paleomagnetic data
of three different formations Wensink. A close isotopic similarity occurs between samples
from Sulawesi and Sumba.Comparison of PbNd isotopic signatures between
metasedimentary or volcanic rocks from the microcontinents and possible provenance areas
Vroon et al. Sumba performed a counterclockwise CCW rotation of and a drift of to the south.
..
Summary of large Eocene foraminifera of Assilina/Pellatispira/Biplanispira APB and
Lacazinella faunas in the IndoPacific realm Lunt. . Lacazinella fauna in blue. whereas
Lacazinella is a high latitude Austral index.Figure A . In shallow marine carbonate facies the
APB fauna appears to dominate the tropics but can occur locally at higher latitudes. The APB
faunal group is associated with the Sundaland Craton and is also found on low latitude
Pacific islands as well as low latitude western Tethyan regions. Figure B . Note Sumba is
included into the Sundaland APB group. The Lacazinella fauna is found on the Australian
Plate. . and the microplate terrains have been derived from it since the Eocene.Middle and
Late Eocene plates and climatic zones with locations of APB fauna in red.
as well as the islands of Doang and Salayar that now lie to the south of Sulawesi Late
Cretaceous forearc basin from Hasan . Upwelling of buoyant metasomatized mantle
delaminated the upper accreted crust.Figure .Gondwanan microcontinents from Parkinson et
al.Paleotectonic reconstruction of the SE/Eastern Sundaland and its accreted crust during
the Cretaceous Satyana. . Cretaceous island arc from Hamilton . Alino Arc from Sikumbang .
The Sumba microcontinent accreted to SE/Eastern Sundaland. Presentday outlines of Java.
The accreted masses to SE/Eastern Sundaland had blocked mantle circulation. . . parts of
Sumatra and Kalimantan. resulting in initial opening of the Makassar Strait in the Early
Tertiary causing the separation of Sumba from the mainland of Sulawesi. and Sumba are
shown for reference.
. Figure .Dispersion reconstruction of eastern margin of SE Sundaland. after SoeriaAtmadja
et al. Abdullah. .Schematic Ddiagrams depicting the four main stages of tectonic evolution of
Sumba A Late CretaceousPaleocene. D Quaternary Abdullah et al. .Figure . B Paleogene. .
Sumba occupied its present position before the formation of Late Miocene arc. C Middle
MiocenePliocene... The dispersion took place in response to backarc spreading behind the
magmatic arcs of JavaWest Sulawesi and displacement by regional transform faulting.
Above the deep blue horizon. some km to the southwest. with high and low amplitude
alternating sequences probably representing sands and shales infilling the local postrift
topography. Above the light green horizon deposition becomes even more varied and in
places chaotic. as it climbs to the southeast.NWSE Seismic Section across the western
sector of the Savu Basin Toothill and Lamb. depositional patterns appear to vary laterally and
deep channels up to km across are seen at various locations. Sediment deposited after the
main rift event appears typical of that expected post rifting. Two basement highs occur in the
section and may be associated with promontories along the coast of Sumba Island. . possibly
indicating the rapid uplift of Sumba island immediately to the west and the sudden influx of
sediments associated with it. possibly associated with increasing proximity to Sumba Island.
as the line draws closer to the coast of this island. The deepest visible reflector pink horizon
shows significant faulting.Figure . The deepest sediment is deposited into rifted half grabens
that measure approximately km across. This demonstrates the development of the basin with
sedimentary section thickening towards the northwest. A thick sediment section is shown at
the northwest end of the line. In the southeast. the section crosses the western end of the
Savu Sea Basin. The section between the sage green and deep blue horizons appears
quiescent in the deeper part of the basin but. . appears to have undergone slumping. the
section thins significantly and major basement uplift is present. Situated at the northwest end
of the km seismic line. Six seismic horizons have been interpreted within the basin including
the rift event.
This is the highest point along the entire length of the section and would be a natural point of
leakage for hydrocarbons migrating along carrier beds in the sedimentary section. close to
the Island of Sumba Toothill and Lamb. The most northwesterly seep.Figure . all of which
show clustering see index map of hydrocarbon seeps/slicks light green. which in fact
comprises a cluster of five seeps. . courtesy of Mitra Energy and Directorate General of Oil
and Gas. . Seep data acquired by satellite. red. is approximately above a basement outcrop
from either side of which sedimentary section and the sea floor dips steeply away. yellow
small circles.NWSE oriented seismic line that runs along the western edge of the Savu Sea
Basin. Indonesia. Mapping have shown that a number of the identified seeps which fall
above or very close to seismic lines appear to be associated with geological features where
hydrocarbons might migrate and escape to the sea floor. A number of seeps are located
above this line shown by arrows.
Indonesia. The play types of Sumba area among others tilted fault block related to rifted
basin and draped channel sands overlying the basement high related to promontory of
Sumba Island. .Figure .Play types of Sumba offshore. Savu Basin and northwestern limit of
Australia Shelf courtesy of CGGVeritas and Directorate General of Oil and Gas.
The petroleum system for Sumba area can be referred to South Sulawesi or South
Makassar petroleum systems with similar processes of volcanism.Figure .Stratigraphic
succession between Sumba area western part. Based on the geology of the island see
discussions in the text on petroleum implications. basically similar to the central part and it
has deeper facies for eastern part of Sumba and South Sulawesi. and related sedimentation.
an expected provenance for Sumba terrane. rifting. . postrifting. reservoirs. and seals.
Sumba has potential source rocks.