21. Crustal Structures of Eastern Sundaland & petroleum implications (Satyana, 2010).pdf

Proceedings of The Bali 2010 International Geosciences Conference and Exposition, Bali, Indonesia, 19-22 July 2010

Crustal Structures of the Eastern Sundalands Rifts, Central Indonesia : Geophysical Constraints and Petroleum Implications Awang Harun Satyana (1) (1)

BPMIGAS (Executive Agency for Upstream Oil and Gas Business Activities, Republic of Indonesia) ABSTRACT

Being positioned on the active margin of southeastern Eurasian plate, Eastern Sundaland had recorded the history of subduction, accretion, and collision from oceanic plates of the Tethys Seas and Gondwanan microcontinents during the Mesozoic. The processes had grown the area of Eastern Sundaland by terrane amalgamation. Started in the middle Eocene, Eastern Sundaland dispersed through rifting due to a number of mechanisms. South and Makassar Straits, East Java Sea, Gorontalo and Bone Bays rifted forming sedimentary basins. Sediments capable to become petroleum sources, reservoirs and seals were deposited into the basin and a number of traps were formed. North and South Makassar Basins and East Java Sea Basin are the proven petroleum basins, whereas Gorontalo and Bone basins are potential basins for the occurrences of petroleum accumulation. Seismic, gravity, and magnetic data are employed to understand the origin and nature of crustal structures of Eastern Sundaland. These provide tectonic interpretation of the areas discussed and the implications for petroleum accumulation. KEY WORDS: tectonics, seismic interpretation, gravity and magnetic modeling INTRODUCTION The term Sundaland strictly defines the landmass of southeast Asia, including Sumatra, Java, Kalimantan, Malaya, and present waters around them which stood above the sea during the low sea levels of the Pleistocene epoch (Figure 1). The Sundaland represents the southeastern corner of stable Eurasian continental plate. The Sundaland was cratonized in Late Triassic times and is now generally aseismic (Hutchison, 1989). In the non-glacial Holocene epoch, the Sundaland has been flooded by sea resulting in the present Sunda Shelf. The Sunda Shelf is a present broad shallow sea

generally shallower than 100 meter between Indo-China Peninsula, Malaya, Sumatra, Java, and Kalimantan. Occupying the position of active continental margin since the Jurassic, the Sundaland had recorded the history of growing and slivering of a continent by accretion and dispersion, respectively (Satyana, 2003). In the light of terrane analysis, the Sundaland is composed of a number of terranes which came from the northern Gondwanaland (Metcalfe, 1996), drifted separately, assembled, and accreted forming the Sundaland. The terranes composing the Sundaland are : Sibumasu (formerly called Mergui and Malacca), East Malaya, Indochina, Southwest Borneo (partly called Schwaner), Semitau and Paternoster-Kangean. Later dispersion of eastern terranes broke the assembly and slivered the Sundaland. Therefore, the Sundaland records the histories of growing and slivering of a continent by accretion and dispersion, respectively. Started at around 50 Ma, in the Middle Eocene, some of the accreted mass of SE Sundaland dispersed through rifting and drifted eastward and southeastward slivering the continent, leaving rifted structures of the Eastern Sundaland presently located at the Makassar Straits, East Java Sea, Gorontalo Bay and Bone Bay (Figure 1). METHODS The goal of the paper is to show the configurations of the rifted basins in Eastern Sundaland including the Makassar Straits, East Java Sea, Gorontalo and Bone Basins. Interpreted seismic sections of these areas are keys to understand the tectonics and configurationss of crustal structures of the rifted basins. Some rifted basins may be floored by continental and/or oceanic crusts. In the absence of well penetrating the basement, gravity and magnetic modeling is applied to consider the nature of basement. Petroleum system analyses are applied mostly based on seismic characteristics.


RESULTS Dispersion and Rifting of Eastern Sundaland The history of dispersion and rifting of Eastern Sundaland is complicated and there are a number of mechanisms proposed by authors for the rifts of Eastern Sundaland (Satyana, 2003), involving: (1) crustal breakdown to the west of South Sulawesi volcanic arc by the Plio-Pleistocene diastrophism, (2) back-arc spreading of marginal basins of Southwest Pacific areas, (3) rotation of the continental Southeastern Sundaland, (4) back-arc spreading due to subduction rollback related to India-Eurasia collision at 50 Ma, (5) southern extension related to sea-floor spreading of the Sulawesi Sea, (6) tectonic escape due to India-Eurasia collision and (7) mantle delamination by upwelling plume under the Eastern Sundaland. The eastern margin of Sundaland is fragmented and tectonically very complicated. The accreted rocks comprise variably metamorphosed accretionary complexes, imbricated terranes, melange, turbidite and broken formations, and ophiolites. These rocks have suffered considerable dismemberment, tectonic and structural modification, and thermal overprinting due to tectonic and metamorphic activity throughout the Tertiary, related to the convergence of the Indo-Australian, Eurasian and western Pacific microplates (Parkinson et al, 1998). The provenance and way of dispersion of some fragments believed once parts of Eastern Sundaland are also complex and variably interpreted. Post-Accretionary Dispersion of Circum-Pacific Region Post-accretionary dispersion is a usual case in the Circum-Pacific region (Howell et al., 1985). The main period of accretionary activity ended by Early Tertiary time in the Cordillera and northeastern Siberia. These accretionary episodes have been followed by a history of complex strike-slip faulting, folding, and thrust faulting resulting in the breakup of some terranes. In North America, large-scale right-slip faults such as the San Andreas, Fairweather, and Fraser River all have minimum displacements of a few hundred kilometers, and some may have much more. The cumulative relative movement on all of these, plus innumerable subsidiary faults, must amount to several thousand

kilometers, and some may have much more. In Japan, left-slip faults are smearing out and dispersing the terranes while accretion is still occurring, and in eastern China, east-west trending left-slip faults resulting from the northeastward movement of India are fragmenting the collection of terranes in that area. At the eastern margin Sundaland, the accretion stopped at around 50 Ma (Middle Eocene) and the accreted crust started to disperse beginning with the opening of the Makassar Straits. The dispersion of terranes, by either rifting or sliding, results in the diminution of continents. Rifted Structures of the Makassar Straits East Borneo and West Sulawesi were part of a single area in the Late Mesozoic but were separated during the Cenozoic by the opening of the Makassar Straits. The Makassar Straits formed by rifting (Figure 2). There has been debate about the age of formation of the straits between Neogene and Paleogene. Eocene age for the opening is now generally accepted. Extension began in the Middle Eocene and formed graben and half-graben above which is an important unconformity of probable Late Eocene age. The unconformity marks the top of the synrift sequence. Thermal subsidence continued during the Oligocene. Flexural subsidence due to loading on the west and east sides may have deepened the straits, as inversion in eastern Kalimantan migrated east and the Mahakam delta prograded east since the Early Miocene, while folding and thrusting of western Sulawesi migrated west since the Early Pliocene. The mechanism of the opening has also been the subject of controversy (see discussion above). Most authors have favored an extensional origin for the straits. The nature of crust underlying the straits has also long been the subject of scientific debate between continental and oceanic. Most authors agree with attenuated (due to rifting) continental crust composing the South Makassar Strait, but the basement for the North Makassar Strait which is much deeper than that of the South Makassar Strait is difficult to determine. There have been much arguments arguing that the North Makassar Strait is floored by oceanic crust however, another possibility that the strait is floored by attenuated continental crust is also possible. Flexural loading model, gravity-magnetic model and seismic data show variable interpretations hence complicating the matter. This paper will not discuss the matter


any further. Further discussion on the nature of basement of North Makassar Strait can be found in recent paper by Hall et al. (2009) but, this publication can not conclude the nature of the basement of North Makassar Strait. The disagreement is likely to continue amongst those working in the area. Free-air gravity shows there is a broad gravity low beneath the central North Makassar Basin. This includes an elongated low northeast of the Paternoster Platform that follows the narrow trough connecting the North and South Makassar Basins, and an irregular low between the Mahakam delta and the Mangkalihat Peninsula. There is large gravity high beneath the Mahakam delta depocenter. In the last few years more than 10,000 km of new data have been acquired or reprocessed by TGS-NOPEC Geophysical Company during seismic surveys covering large parts of the North Makassar Straits (Figure 2). The bathymetry in the North Makassar Straits reflects some obvious features of the deeper structure. The seafloor in the central North Makassar Straits is flat and undeformed. In the north the water depth is almost 2500 m and is about 200 m less in the south. Depths decrease towards the carbonate-dominated Paternoster Platform in the south and the Mangkalihat Peninsula in the north. To the west, the seafloor rises gradually to the very shallow East Kalimantan Shelf, crossing the front of the Mahakam delta. In the east, the seafloor shallows towards western Sulawesi, rather more abruptly than on the west side, reflecting folding and thrusting of a deformed zone that is now described as the Offshore West Sulawesi Foldbelt. From south to north, the Offshore West Sulawesi Foldbelt can be divided into three provinces (Puspita et al., 2005): the Southern Structural Province (SSP), Central Structural Province (CSP) and Northern Structural Province (NSP) based on seafloor characteristics, subsurface deformation, in particular the character and position of the deformation front (Figure 2, lower section). The Cenozoic sedimentary sequence in the central part of the North Makassar Straits is undeformed and separated from the Offshore West Sulawesi Foldbelt by a change in slope at which there are folds, and blind and emergent thrusts and backthrusts. The nature of the basement to the central part of the Makassar Straits can be interpreted only indirectly, because the very thick sediment cover and the great

depth to basement means that no direct sampling is possible. The oceanic crust interpretation is favored by the great width of the extended zone and, in particular, the 200 km width of the deepest part of the straits where depths are close to 2.5 km water depth and there are several kilometers of almost undisturbed flat-lying sediments above the basement. The continental crust interpretation is favored by the observations that rifting structures can be seen below the basal unconformity. Gravity and magnetic modeling show attenuated continental crust floors northern Makassar Straits (Figure 3). Half-graben and graben are evident in places, and the pattern of faulting mapped below the basal unconformity is similar to that expected from oblique extension of a basement with a pre-existing NWSE fabric. Structures can be seen above the unconformity which could be carbonate build-ups on tilted fault blocks or volcanic edifices. Recent drillings in the North and South Makassar Straits showing the presence of both volcanic edifices above the horst (Rangkong-1, Exxon 2009) and carbonate build-up (Sultan-1, Exxon 2009). The NWSE lineaments which segment the basin are interpreted to be Cretaceous or Paleocene structures, which in places may have been reactivated. The northern margin of the Paternoster Platform is clearly a major steep fault with about 2 km of normal offset of the Eocene and the large displacement is inconsistent with an oceanic transform fault. Rifted Structures of East Java Sea The sub-basins of the East Java Sea are part of an extensive and complex basin system which has developed around the margins of the Southeastern Sundaland. Separation of West Sulawesi from Kalimantan with the opening of the Makassar Strait is considered to have rifted the basement of East Java Sea located to southwest and south of the Makassar Straits. Rifting arms of the southern Makassar Strait extended southwest- and southward into the East Java Sea segmenting its basement. Rifted structures comprising horsts and grabens trending SW-NE were resulted from, comprising (Figure 4): Karimunjawa Arch Muriah Trough Bawean Arch Pati/ Tuban/ Bawean/ Florence Trough JS 1/ Masalembo High Central/ Masalembo Deep North Madura Platform JS 5 Trough Sibaru Platform. The general characteristics of the rifted structures are as below (Manur and Barraclough, 1994).


The Muriah Trough lies between the Karimunjawa Arch and the Bawean Arch. No sedimentary rocks older than Early Oligocene (Sangka-1) have been encountered in the Muriah Trough. However, Pre-Tertiary sediment section is expected to be present in deeper parts of this trough.

The Bawean Arch separates the Muriah Trough from the Tuban-Camar Trough and is apparently of granitic composition (well H-1). The Bawean Arch remained an emergent island until Early Miocene times, when it was finally transgressed.

The Tuban-Camar Trough is situated between the Bawean Arch and the JS-1 Ridge. The underlying basement in the JS 10-1 well is Early Cretaceous metamorphics.

The JS-1 Ridge is an elongate basement high. Basement lithology is primarily basic igneous rocks of pre-Tertiary age. Transgressive deposits did not reach this ridge until the Early Oligocene.

The Central-Deep Depression runs parallel to the JS-1 Ridge. Pre-Tertiary basement in this area consists of meta-sedimentary and intrusive igneous rocks.

The Masalembo Basin is cut off from the Central-Deep by an intervening high and may have formed as an isolated sub-basin.

The North Madura Platform was a massive carbonate shelfal area during the Miocene and the Pliocene.

Another possibility for the origin of the rifted East Java Sea basement is by back-arc spreading behind the volcanic arc due to subduction roll-back mechanism of plate convergence at 50 Ma (middle Eocene) (Bransden and Matthews, 1992). The onset of rifting within the East Java Sea is broadly coincident with the collision of the Indian continent with Eurasia and the re-organisation of the Pacific Plate during the middle Eocene. The resultant reduction in convergence rate around the Southeast Sundaland, possibly resulting in subduction roll-back, is a plausible mechanism for back-arc extension around the margins of the Southeastern Sundaland. The variable rates of subduction around the arc during and after the Indian collision and Pacific Plate re-organisation are likely to be the fundamental control on stress vector variation, and hence fault movement sense, throughout the Palaeogene. A detailed understanding of the East Java Sea rift history is fundamental to the analysis of stratigraphic fill. Localized extension was

underway by early Eocene, and rifting was very widespread by late Eocene, based on interpretation of the geometry and timing of motion on major faults, which show a marked stratigraphic thickness contrast from hangingwall to footwall for time equivalent sequences. During the Neogene, the rifted structures of the East Java Sea, especially in each southern ends, subsided due to extensional stress generated from left-lateral strike-slip fault of theRembang-Madura-Kangean-Sakala Fault Zone. This fault zone deformed the areas presently located at the northern East Java from Rembang to Sakala areas. Rifted Structures of Gorontalo Basin Prior to 2005 no seismic data coverage or offshore wells existed for the Gorontalo Basin. In 2006, following encouraging interpretation of the 2005 new look deep recording 2D reconnaissance non-exclusive seismic survey, some 5800 line kilometers of 2D non-exclusive seismic data was acquired. Subsequent interpretation of this data (Jablonski et al., 2007) revealed a new geological picture that challenges pre-existing ideas about tectonic development and the hydrocarbon prospectivity of the region (Figure 5). The Gorontalo Basin is underlain by Eocene rift grabens similar in geometry to the fluvio-lacustrine source rock-rich megasequences that underlie many oil-prone petroleum systems surrounding the Sundaland. The current geological positioning of the Gorontalo Basin is the result of older, Mesozoic collisions of Australian micro-plates with Sundaland. This has been followed by the Eocene stretch of Sundaland. A relatively quiescent period of widespread carbonate platform deposition, with some intrusions associated with volcanic arc processes, ensued during the Oligocene to Middle Miocene. This depositional system was disrupted in the latest Miocene, with increased clastic deposition mostly terminating carbonate platform in eastern Indonesia. Carbonate pinnacle growth with localized deposition of clastic deltas was establisheda system that continues today. Contrary to widespread belief, the Gorontalo Basin appears to have a similar geological history to the neighboring Makassar Basin. Extensive continental crust has been identified to underlie the Gorontalo Basin. This is in contrast to the general view that a relatively young sedimentary basin is underlain by


oceanic crust. The present-day central Sulawesi Neck appears to be a relatively recent feature caused by the Pliocene to Recent compression. A pre-Eocene collision has also been identified, elucidating the break-up history of Gondwana and present-day eastern Indonesia. Despite the complexity of the onshore geology, which displays mostly compressional features, the offshore region of the Gorontalo Basin predominantly displays extensional tectonics. Large structures at multiple stratigraphic levels are similar to the Makassar and Banggai basins. , where there have been a number of significant hydrocarbon discoveries. While still classified as a frontier region, the Gorontalo Basin offers an offshore opportunity that challenges the perception of the region. Rifted Structures of Bone Basin The Gulf of Bone separates the eastern and western arcs of Sulawesi. It is thought to be the result of extension. Sudarmono (1999) interpreted that the Bone Basin is a composite basin, with its origin as a subduction complex and suture between Sundaland and Gondwana-derived micro-continents. It subsequently evolved as a submerged intra-montane basin. The basin had two major periods of development: (a) Paleogene to Early Miocene, and (b) Early Miocene to Recent. Originally, the basin probably occupied a forearc setting as part of a westward subduction complex during the Paleogene to Early Miocene. Subsequently, westerly plate convergence of Australian-derived micro-continents toward the subduction complex during the Middle to Late Miocene, dramatically changed the style of deposition, structural framework, and configuration of the basin. A Middle Miocene collision of the microcontinents with the subduction-related accretionary complex, followed by collision of the microcontinents with West Sulawesi, built orogens surrounding the Bone Basin which shed large volumes of sediment into the northern depocenter of the Bone Basin. The collision led to an eastward rotation of Southeast Sulawesi, which resulted in rifting and submergence of the southern part of the basin. The two colliding plates began to lock during the Pliocene, and the continued plate convergence was accommodated by strike-slip movements along the Walanae, Palukoro and many other faults. Subsequently the Bone Basin submerged into an

intra-montane basin setting. Clastic sediments derived from surrounding mountains to the east, north and west were deposited progradationally southward toward the depocenter of the basin. Strike-slip movements are still active, and the bathymetry of the Gulf of Bone reflects the present day tectonic activity. Recent data (2007) acquired by TGS Nopec in the Gulf of Bone (4,687 km of 2D seismic data with grid spacing 10 km to 30 km, 11,564 km of gravity and seismic) give another interpretation of the Bone Basin (Figure 6). The Bone Basin is rifted basin like rifted basins of Western Indonesia surrounding the Sundaland. Accordingly, the Bone Basin represents the basin that developed in the eastern margin of the Sundaland. There is no appearance of typical forearc basins as previously interpreted. Eocene deep, thick synrift package developed. Late Miocene potential reefal buildups grew on both basin flanks. A platform to the southeast and volcanic high to the west restrict the synrift to early post rift sediment accumulation. Numerous basement highs appear to be capped by Late Miocene carbonates / reefs. Deep synrift sections developed in north, central and south of the basin. Bone Basin may an Eocene rift basin, formed together with Makassar Straits and other Eocene rift basins in response to far-field extensional stresses. Whether the basin is an Eocene forearc or rift basin, the key difference is in the interpreted edge of Sundaland at the onset of Eocene extension. Compilation and analysis of all onshore and offshore geologic and geophysical data may resolve the issue. The nature of the basement of Bone Basin is not known. Yulihanto (2004) interpreted that the basin is floored by oceanic crust in the centre and continental crust on the flanks. Basin depocenter is restricted by the West Bone Bay Fault Zone and the East Bone Bay Fault Zone. Petroleum Implications Widespread synrift sequence across the whole or most of the Makassar Straits are potentially a greater number of exciting exploration targets in deeper water (Hall et al., 2009). If the straits are floored mainly by oceanic crust, success will depend on organic material carried into deep water and distributed through sand-rich sequences which appears a riskier system. If the floors are thinned


continental crust, there is possibility of the development of lacustrine source rocks in the rifts, with synrift reservoirs and carbonate build up growing on horst areas (Figure 2). Oil seeps in West Sulawesi onshore have been characterized geochemically and reveal the Eocene sources of lacustrine to transitional facies. This show that sources deposited in the Eocene rifts of Makassar Straits and West Sulawesi have generated oils. Eocene sourced-oils are also indicated from Ranggas oil field reservoired by Miocene Kutei turbidite fans. The Eocene sources may come from the Eocene rifts of the Makassar Straits. Eocene to Oligocene East Java Sea rifts have been proven as sites for kitchens and traps. SW-NE trending grabens formed during the Middle Eocene and were filled with alluvial clastics, lateritic clays and lacustrine shales (Figure 4). Organic rich shales in this sequence provide the source rock for hydrocarbons throughout the region. The main oil prone source potential is largely restricted to organic rich shales of the Eocene (Ngimbang) Formation which are found in the following areas: the Muriah Trough; the Camar-Tuban Trough; the Central-Deep Depression; the Masalembo Basin; and the Madura basinal area to the south of the North-Madura platform (Manur and Barraclough, 1994). The source rocks are of marginal marine, deltaic and lacustrine origin and are of varying quality. The flank of high areas of the rifts become the sites for deposition of Ngimbang synrift sandstones proven to be reservoirs. High areas of the rifts also controlled the development of Early Oligocene CD carbonates and Oligo-Miocene Kujung I carbonate build ups. The carbonates are proven reservoirs in East Java Basin. The most common traps are tilted fault blocks related to the rifting and graben formation that created the basin). Most of these hydrocarbon producing structures were formed during the early phase of active faulting in the Middle Eocene to Early Oligocene. These old pre-existing structures were present during the initial phase of hydrocarbon generation, whether it was pre-inversion or associated with the elevated heat flow during inversion. While still classified as a frontier region, the Gorontalo Basin offers an offshore opportunity that challenges the perception of the region (Jablonski et al., 2007). An active petroleum system is suggested by east-west oriented depocenters with thicknesses locally exceeding 10 kilometers, the mostly southward focused hydrocarbon migration routes,

and the presence of numerous onshore oil seeps along the southern edge of the Gorontalo Basin. Numerous Amplitude with Offset (AVO) anomalies observed on newly acquired seismic sections also suggest the presence of hydrocarbons at a variety of stratigraphic levels. The new seismic data indicate the following pre- Paleogene to Recent plays, some of which may contain stacked reservoirseal pairs sourced by several Tertiary source rocks: older rift fault blocks associated with the Australian plate rifting, and subsequent collision with Borneo in the Cretaceous; Eocene rift fault-blocks; Oligocene to Middle Miocene platform carbonates; Late Miocene to Pliocene carbonate build-ups; Late Miocene to Recent lowstand deltas and turbidites (Figure 5). In the Bone Basin, the Eocene rift interpretation implies a more favorable environment for hydrocarbon generation, and if proven could significantly reduce exploration risk in this frontier basin (Figure 6). ALF (airborne laser fluorescence) fluors have been detected in the northern and southern Bone Basin suggesting a working petroleum system. Synrift Eocene to Oligocene potential source package is up to >2.5 sec thick, areally extensive synrift package and buried by 2 3.5 seconds of postrift sediments. ALF fluors may be related to postulated hydrocarbon kitchen in very deep and mature half grabens. Traps are provided by combination of carbonate reefs, canyon fill and deep water turbidite plays. Numerous basement highs appear to be capped by Late Miocene carbonates / reefs. Play types of the Bone Basin may include: faulted anticlines, tilted fault blocks, carbonate reefs, stratigraphic subcrop plays, drape over basement highs, turbidite fans, slope channel fill, and stratigraphic pinchout. CONCLUSIONS 1. Eastern Sundaland was built by amalgamation of

terranes during Cretaceous through subduction, accretion and collision which then they were re-separated through a number of mechanisms resulting in extensional rifted structures. Identified rifted structures forming Eastern Sundaland are Makassar Straits, East Java Sea, Gorontalo Basin and Bone Basin.

2. Gravity, magnetic and seismic data show crustal structures of the rifted basins. The rifted structures are typical products of crustal extension forming horsts and grabens and ended by sagging period. Some of basements


underlying the basins are variably interpreted due to the absence of well penetrating the basements. The basements are various composed of continental, intermediate and oceanic crusts.

3. The rifted basins are proven and/or potential for petroleum implications. The grabens become the sites for synrift sources and reservoirs. The horsts become the sites of carbonate build ups which are sealed by shales deposited during the sagging period. Petroleum accumulation occurred when the traps on horsts were charged by petroleum from graben kitchens.

ACKNOWLEDGMENTS The author thanks Mr. Yunan Muzafar (Directorate General of Oil and Gas, Republic of Indonesia) for sharing seismic sections of Gorontalo and Bone basins published in this paper, and Mr.Stephen Hay (StatOil Karama) for seismic sections across the Makassar Strait. Gravity and magnetic modeling was contributed by Unocal (presently Chevron) Makassar Strait. The Management of BPMIGAS is acknowledged for giving support and permission to publish this paper. REFERENCES 1. Bransden, P.J.E. and Matthews, S.J., 1992,

Structural and stratigraphic evolution of the East Java Sea, Indonesia, Proceedings Indonesian Petroleum Association, 21st Annu. Conv., pp. 417-454.

2. Hall, R., Cloke, I.R., Nuraini, S., Puspita, S.D., Calvert, S.J., Elders, C.F., 2009, The North Makassar Straits: what lies beneath, Petroleum Geoscience, Vol. 15 2009, pp. 147-158.

3. Howell, D.G., Jones, D.L., Schermer, E.R., 1985, Tectonostratigraphic terranes of the Circum-Pacific Region in Howell, D.G., ed., Tectonostratigraphic Terranes of the Circum-Pacific Region, Circum-Pacific Council for Energy and Mineral Resources, Houston, p. 3-23.

4. Hutchison, C.S., 1989, Geological Evolution of South-east Asia, Clarendon Press, Oxford, 368 ps.

5. Jablonski, D., Priyono, R., Westlake, S., Larsen, O.A., 2007, Geology and exploration potential of the Gorontalo Basin, Central Indonesia eastern extension of the North

Makassar Basin?, Proceedings Indonesian Petroleum Association, 31st Annu. Conv., pp. 197-224.

6. Manur, H. and Barraclough, R., 1994, Structural Control on Hydrocarbon Habitat in the Bawean area, East Java Sea, Proceedings Indonesian Petroleum Association, 23rd Annu. Conv., pp. 129-144.

7. Metcalfe, I., 1996, Pre-Cretaceous evolution of SE Asian terranes, in Hall, R. and Blundell, D. (eds), Tectonic Evolution of Southeast Asia, Geological Society Spec. Publ. No. 106, pp. 97-122.

8. Parkinson, C.D., Miyazaki, K., Wakita, K., Barber, A.J., and Carswell, D.A., 1998, An overview and tectonic synthesis of the pre-Tertiary very-high-pressure metamorphic and associated rocks of Java, Sulawesi and Kalimantan, Indonesia, The Island Arc (1998) 7, pp.1-17.

9. Puspita, S.D., Hall, R., and Elders, C.F., 2005, Structural styles of the oofshore West Sulawesi fold belt, North Makassar Straits, Indonesia, Proceedings Indonesian Petroleum Association, 30th Annu. Conv., pp. 519-542.

10. Satyana, A.H., 2003, Accretion and Dispersion of Southeast Sundaland : the Growing and Slivering of a Continent, Joint Convention of Indonesian Association of Geologists (IAGI), 31st Annual Convention and Indonesian Association of Geophysicists (HAGI), 28th Annual Convention, Jakarta, December 2003.

11. Sudarmono, 2000, Tectonic and stratigraphic evolution of the Bone Basin, Indonesia: insights to the Sulawesi collision complex, Proceedings Indonesian Petroleum Association, 27th Annu. Conv., pp. 531-544.

12. Yulihanto, B., 2004, Hydrocarbon play analysis of the Bone Basin, South Sulawesi, Proceedings International Geoscience Conference on Deepwater and Frontier Exploration in Asia and Australasia, Indonesian Petroleum Association, pp. 333-348.

MakassarStraits

Sundaland GorontaloBone

EastJavaSea

Figure 1. Boxes showing study areas marking rifted basins located at Eastern Sundaland. Theareas include the Makassar Straits, East Java Basin, Gorontalo Basin and Bone Basin.

Mahakam Delta Sulawesi Fold BeltW E

100km

Top Basement

Sulawesi Fold Belt SangkulirangFZ

Sulawesi Fold BeltS N

Central High

Paternoster

100km

Top Basement

Platform

Figure 2. Seismic sections showing crustal structures of the Makassar Straits rifted basin. Uppersection trends west-east, lower section trends south-north. The sections show rifted basementresulting in horsts and grabens Synrift sediments were deposited within the rift/graben Neogeneresulting in horsts and grabens. Synrift sediments were deposited within the rift/graben. Neogenesediments of Sulawesi were tightly folded.

West East

Synrift

Mantle

AttenuatedCrustContinental

LowerCrust

Continental

Figure 3. Gravity and magnetic profiles of observed and calculated values and interpretation of thecrustal architecture The section crosses the northern Makassar Straits from west to east It is interpretedcrustal architecture. The section crosses the northern Makassar Straits from west to east. It is interpretedthat the basin is floored by attenuated (thinned) continental crust.

Figure 4. Rifted basement of East Java Sea showing the presence of a series ofhighs/arches/platforms/ridges/horsts and lows/depressions/troughs/grabens trendingSW-NE. The rifts may result from extension of southern Makassar Strait or related toback-arc spreading due to subduction roll back at middle Eocene.

Figure 5. 2006-acquired seismic section showing crustal structures of the Gorontalo rift basin and itspetroleum implications. Extension resulted in a series of horst and grabens. Very thick synrift sediments weredeposited within the grabens with capability to become kitchen generating petroleum trapped in variousplays sealed by sagging shales (seismic section courtesy of Directorate General of Oil and Gas/ Ditjen Migasand Fugro).

Figure 6. 2007-acquired seismic section showing crustal structures of the Bone rift basin. Extensionresulted in a series of horst and grabens. Thick synrift sediments were deposited within the grabens withcapability to become kitchen generating petroleum trapped in various plays formed in synrift and postriftsequences or at horst and sealed by sagging shales. ALF fluors are seeps at sea surface indicating activeq y gg g f p f gkitchens at subsurface. (seismic section courtesy of Directorate General of Oil and Gas/ Ditjen Migas andTGS Nopec).

21. Crustal Structures of Eastern Sundaland & petroleum implications (Satyana, 2010).pdf

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