PROCEEDINGS INDONESIAN PETROLEUM ASSOCIATION Twenty Second Annual Convention, October 1993
TECTONIC AND STRATIGRAPHIC EVOLUTION OF THE KALOSI PSC AREA AND ASSOCIATED DEVELOPMENT OF A TERTIARY PETROLEUM SYSTEM, SOUTH SULAWESI, INDONESIA
D. Q. Coffield" S. C. Bergman** R. A. Garrard**
N. Guritno* N. M. Robinson*
J. Talbot**
ABSTRACT
Recent geological, geophysical, geochronological, geochemical, and remote sensing studies in the Kalosi PSC, South Sulawesi, have provided new insights into the tectonic and stratigraphic evolution of Sulawesi and the development of a Tertiary petroleum system which is responsible for several oil seeps in the area.
The most prospective hydrocarbon-bearing rocks in South Sulawesi are Cenozoic in age. Basement consists of indurated and metamorphosed Mesozoic sedimentary and ophiolitic rocks. These are unconformably overlain by Paleocene-Eocene volcanics (Van Bemmelens "Older Andesites" and associated rocks) and Eocene fluvial and lacustrine sedimentary rocks which pass conformably upwards through fluvial-deltaic clastics into widespread Upper Eocene to Middle Miocene platform carbonate deposits. The carbonates were buried during the Middle and Late Miocene to Pliocene by thick volcaniclastics and were intruded by Miocene & Pliocene plutonic complexes. These in turn are unconformably overlain by uppermost Miocene to lowermost Pliocene reef carbonates and Pliocene and younger synorogenic clastic deposits.
The rocks record a polyphase deformational history beginning in the Cretaceous with the development of an accretionary complex along the southeastern margin of Sundaland. A major Late Cretaceous to Early Eocene (mostly angular) unconformity separates the Mesozoic sequence from the overlying Tertiary section.
* Atlantic Richfield Indonesia, Inc. * * ARC0 Exploration & Production Technology Co
Subsidence, possibly associated with extension and normal faulting during the Eocene, was followed by a period of stability and quiescence from the Late Eocene to Early Miocene. Subduction beneath South Sulawesi in the Early to Middle Miocene and the obduction of oceanic crust onto the micro-continent(s) of eastern Sulawesi were followed by collision and westward vergent partial subduction of continental plate(s) derived from the Australian craton during the Middle to Late Miocene. Voluminous lithospheric melting due to lithospheric imbrication and thickening produced a widespread north-south trending bimodal alkalic to calc-alkalic volcano - plutonic belt. Continued convergence through the Pliocene formed a westward- vergent orogen in South Sulawesi, with a thin-skinned thrust system in its western half expanding into a thick skinned, basement involved thrust system in its eastern half. This new tectonic scenario departs significantly from suggestions by previous workers of oceanic subduction-related Miocene magmatism or post collisional rift-related magmatism for the region, and documents for the first time continental rocks of probable Australian cratonic affinity beneath South Sulawesi.
The Neogene orogen provided the final element in creating a working petroleum system. Eocene oil- prone fluvio-deltaic coals and associated source rocks were depressed into the oil window by deposition of a thick sequence of andesitic pyroclastic deposits and sub-sequent tectonic loading associated with thickening of the orogenic wedge. Mature oils from seeps have been typed to these Eocene source rocks. Eocene siliciclastic carrier beds provided conduits from sub- thrust kitchen areas to potential Eocene siliciclastic and Mio-Pliocene carbonate and volcaniclastic reservoirs in compressional ramp anticlines.
The aim of this paper is to integrate petrologic, isotopic, stratigraphic, structural, and geochemical data from the Kalosi PSC in South Sulawesi in order to formulate both a tectonic and a petroleum system model for the region. Sulawesi is located in a complex tectonic position at the intersection of three major lithospheric plates: the westward moving Pacific Plate, the northward moving Australian-Indian Plate, and the relatively stationary Eurasian Plate (Figure 1). Sulawesi’s present position lies at the southeast limit of the Sunda Platform crustal domain and north and west of the Australian craton and its derivative fragments now forming the islands of Irian Jaya, Sula, Buru, Seram, and the Tukang Besi Platform. The complex plate tectonic position of Sulawesi is manifested in a varied Tertiary structural and stratigraphic record (Figure 2). The south arm of Sulawesi is dominated by Miocene and younger volcanic and plutonic rocks forming a magmatic belt that has been regarded as a westward-dipping, oceanic plate subduction-related volcanic arc (Sukamto, 1978; Hamilton, 1979) and more recently as a post-collisional rift-related magmatic belt (Yuwono et al., 1985; Leterrier et al., 1990; Kalavieris et al., 1992). The present study presents evidence which demonstrates that these conventional tectonic models for the Late Cenozoic evolution of Sulawesi require modification. We propose that the Miocene to Recent tectonic framework of South Sulawesi was dominated by compressional continent collision processes which have played a key role in the development of a prospective petroleum system.
Background
The Kalosi PSC (Figure 3) is located in the central part of South Sulawesi, to the north of the South Parcel of the Onshore Sulawesi PSC where subcommercial gas reserves were discovered by British Petroleum/Gulf and Pertamina between 1976 and 1980 (Grainge and Davies, 1983). The area’s physiography ranges from subdued plains near sea level in the south to a rugged mountainous topography with peak elevations up to 3455 m in the central and eastern portions of the block. The first geological investigations in the area now encompassed by the Kalosi PSC were undertaken between 1909 and 1910 by the Dutch (Abendanon, 1915). Both coals and active oil seeps were identified at that time. Additional surface geologic mapping was conducted over the subsequent 80 years (Reyzer, 1920; Sax, 1931a, 1931b; Sung, 1948; Sukamto, 1975; Djuri and Sudjatmiko, 1974; Ratman and Atmawinata, 1988), but it was not until the award of the Kalosi -PSC in 1991 that more intensive petroleum exploration and subsurface data acquisition occurred. This recent work
has integrated diverse exploration tools such as surface geologic mapping, synthetic aperture radar (SAR) , inorganic, organic and isotopic geochemistry, geochronology , petrology, gravity, and multi-channel seismic data.
The results of the present studies have enhanced our understanding o€ the geologic evolution of the region and produced a model that better explains the petroleum system charging active oil seeps in the area. At the early stages of frontier exploration (such as in the Kalosi PSC) petroleum system models require an accurate tectonic framework, to constrain such variables as heat flow, structural geometries, and depositional facies trends. The development of such a model provides a means for integrating petroleum generation, migration and trapping into a threc- dimensional framework that explains how they may interact through time to produce potentially economic petroleum accumulations (Demaison and Huizinga, 199 1 ; Perrodon, 1992).
Regional Setting
The island of Sulawesi is located on the eastern margin of Sundaland (Figure l ) , the stable continental core of the southeast Eurasian Plate (Hutchison, 1989). The island formed along the Neogene collision zone between the Eurasian Plate and micro-continental fragments derived from the Australian-Indian Plate (Hamilton, 1970; Hutchison, 1989; Rangin et al., 1990; Daley et al., 1991). The four arms of Sulawesi form distinct megatectonic provinces. The north arm is composed of late Paleogene to Neogene subduction related volcanic arc rocks resulting from the west- dipping subduction of the Molluca Sea Plate (Jezek et al., 1981). The east and southeast arms contain a western province of metamorphic and ophiolitic rock suites which were obducted during the Miocene over an eastern province of Australian-derived Paleozoic and Mesozoic BangaiSula microcontinents (Smith and Silver, 1991; Parkinson, 1991). The south arm is dominated by Miocene and younger volcanic and plutonic rocks which form a magmatic belt that was superimposed on the eastern margin of Sundaland (Katili, 1978; Silver et al., 1983a, b).
TECTONO-STRATIGRAPHY
The stratigraphic succession of the Kalosi PSC area has been divided into four megasequences including prerift, synrift, postrift and synorogenic (Figure 2; Garrard et al., 1992). Each of these packages is separated, and disrupted internally, by thrust faults which expose successively older units in their hanging walls from west to east across the present-day orogenic belt (Figures 3, 4 and 5).
681
Prerift Sequence
The prerift sequence presently represents economic basement, and is mainly composed of indurated and metamorphosed sedimentary rocks which formed in a fore-arc environment. These rocks are grouped together in the Latimojong Complex, a Mesozoic sequence similar to the Late Cretaceous flysch of the Balangbaru and Marada Formations which overlie highly tectonized rocks of a Cretaceous accretionary and ophiolite complex in southern South Sulawesi (Sukamto, 1975; 1982; Djuri and Sudjatmiko 1974; Hassan, 1989, 1990, 1991; Hassan and Garrard, 1991). The sequence is exposed in the Latimojong Mountains (Figure 3 ) and consists of moderately metamorphosed rocks including slate, phyllite, chert, marble, quartzite, and silicified breccia with some intermediate to basic intrusions (Djuri and Sudjatmiko, 1974). Low grade metamorphic rocks (greenschist to blueshist facies) have been reported (Gisolf, 1919), together with garnet peridotites to the north in the structurally similar Palu Basement Complex (Helmers et al., 1990).
Imbricated Mesozoic continental rocks and possibly Tertiary oceanic floor assemblages form a 25 x 125 km belt east of the Latimojong Mountains, south and north of Palopo. The Mesozoic continental crustal rocks include sandstones, phyllites, quartzites, schists and gneisses whereas the ocean floor assemblage consists of illow basalts, sheared sheeted gabbros, amphibolites and red cherts of unkown age. The section represents components of an accretionary complex/forearc succession in an outer arc basin associated with a westward-dipping subduction system which was beneath the eastern margin of Sundaland in the Late Cretaceous. The previously deeply buried parts of the complex are now represented by the greenschist and blueschist facies metamorphic rocks (A. J . Barber, pers. comm.).
Basalts of probable Paleogene age also form part of the basement complex. Basaltic flow breccias from Batusindunak, north of Palopo (Figure 3 ) , are tholeiitic in composition. The geochemistry of the Batusindunak basal@ is similar to ocean floor tholeiitic basalts in major element, trace element, and 87Sr/s6Sr and ‘43Nd/ 144Nd composition (Bergman et al., 1992). These may represent obducted Paleogene or older oceanic crust or could be part of the Paleogene Langi Volcanic Formation (Van Leeuwen, 1981), or ”Older Andesites” of Van Bemmelen (1949) exposed to the south of Sengkang. We envision this eastern Latimojong imbricated complex as a mixture of Mesozoic continental rocks and probably younger oceanic rocks which were thrust onto South Sulawesi during Miocene
obduction of the Central Sulawesi ophiolite. Subsequent collapse of the orogen permitted subsidence in the intervening Bone and Tomini Bays.
Synrift Sequence
A thick succession of non-marine clastic rocks is exposed in the footwall of the thrust fault on which basement has been transported. The Middle to Late Eocene Toraja Formation is thicker than 1,250 meters and is dominated by red argillaceous claystones which were deposited in fluvial and shallow water lacustrine environments. Conglomerates and sandstones are present in channelized deposits. One marine incursion is evident in the Middle Eocene and is represented by a thin Nummulitic limestone interval.
The base of the Eocene section has not been observed in the Kalosi PSC. The lower portion of the interval is inferred to be controlled by subdued block faulting (Garrard et al., 1989), contemporaneous with extension which occurred throughout many portions of Sundaland during the Eocene (Van de Weerd and Armin, 1992; Silver et al., 1989; Cameron et al., 1980, Hutchison, 1992). The base of the section is exposed in the Balangbaru region of South Sulawesi where a quartz dominated conglomerate rests on an angular uncon formably above Late Cretaceous and older rocks (Van Leeuwen, 1981; Garrard et al., 1989).
Postcift Sequence
The upper Toraja Formation passes conformably into coastal plain and deltaic deposits with interbedded coals and carbonaceous claystones. These in turn are overlain by transgressive shoreface sandstones which represent the top of the Toraja Formation. The Makale Formation conformably overlies the sandstone unit and represents a widespread fully marine Late Eocene to Middle Miocene carbonate platform. Extension had evidently stalled and any fault-controlled relief had been buried by this time because of the widespread, lateral continuity of the transgressive interval.
Stable carbonate platform sedimentation persisted over the eastern margin of Sundaland throughout the Oligocene and in some areas continued into the Middle Miocene. The lower Makale Formation was deposited in a more restricted environment which resulted in localized (ponded) organic-rich dolomite intervals. By the Oligocene , deeper marine, outer shelf platform limestone deposition was firmly established. The Oligocene is dominated by mudstones and wackestones, with less common packstone and grainstone intervals. Large foraminifera, pelecypods and coral fragments occur throughout, although no
major reef building episodes have been identified. A succession of deep marine interbedded shales, volcanogenic turbidite sands, and fine grained carbonates, ranging in age from the Early to Middle Miocene, are exposed in a breached anticline in the Buakayu area (Figure 3). This section is informally termed the Buakayu Formation. It represents a transitional phase of sedimentation between stable carbonate conditions of the upper Makale Formation and the onset of volcanism and development of a magmatic arc. The base of the section has not been observed in this area.
Synorogenic Sequence
A volcano-plutonic complex became firmly established during Middle to Late Miocene times throughout South Sulawesi. This section is informally referred to in this paper as the Enrekang Volcanic Series. The submarine and subaerial volcanic and volcaniclastic rocks are compositionally bimodal. These include calc-alkaline, subalkaline to alkaline basalts and trachyandesites to rhyolites. Dominant volcanic lithofacies include airfall and subaqueous tuffs, tuff turbidites, lapilli tuffs, tuff breccias, and volcanic conglomerates. These form proximal stratovolcano sequences and more distal volcanic apron equivalents up to 2-5 km in thickness. Trachyandesite and trachyte domes and lavas up to 500 m thick also occur. Sills, dikes, stocks, plugs, plutons and laccoliths, ranging from several meters to 100 km in maximum plan dimension, are present in certain areas. Intrusive rocks include gabbros and biotite- and hornblende bearing granitic rocks ranging from monzonite and quartz monzonite, to quartz monzodiorite.
The mineralogy and major and trace element chemistry of the South Sulawesi Miocene magmatic rocks are typical of mildly alkalic to potassic calc-alkaline suites (classifications of Kuno, 1967; Ewart, 1979) with moderate enrichments in light rare earth elements (REE) and large-ionMhophile elements (Figure 6a and b). Major minerals include augite, andesine, sanidine, and hornblende; minor phases include olivine and leucite. Despite the presence of leucite in the suite, most range from olivine to quartz normative and contain normative hypersthene. The intrusive rocks are temporally, geochemically , and isotopically indistinguishable from the volcanic rocks in the region and both are considered members of the same cogenetic suites. These Late Miocene igneous rocks form a bimodal compositional suite, with a predominance of basaltic and silicic trachyandesitic compositional subsets, and are entirely lacking intermediate basaltic andesites (ca. 52-58 wt% silica). There are only subtle temporal-spacial-compositional trends in South
Sulawesi Miocene magmatism, such as the most shoshonitic leucite-bearing melts forming in the western portion of the belt (near Mamuju, Figure 3) and during the most recent (5-7 Ma) magmatic phase.
The bimodal magmatism was due to lithospheric thickening and resultant melting of ancient mantle peridotite and crust, respectively yielding alkaline basaltic (shoshonitic) and granitic composition melts. Lithospheric thickening was caused by a Miocene continent-continent collision involving the Australian Plate. The synorogenic phase of magmatism was not due to normal subduction of an oceanic plate beneath a continental plate (Katili, 1978), or due to rifting, as suggested by Yuwono et al. (198.51, Leterrier et al. (1990), and Kavalieris et al. (1992). In addition, no surface geologic evidence for Late Miocene rifting has been recognized within the Kalosi PSC.
Towards the end of the Miocene, compression and uplift resulted in regional subaerial exposure and erosion. Renewed subsidence and marine flooding followed during the latest Miocene to Pliocene with the deposition of the Walanae Formation ("Celebes Molasse" , Van Bemmelen, 2949). Initial deposition was carbonate dominated with widespread platform limestones and calcareous mudstones which gave way to pinnacle reef growth (Tacipi Member) as relative sea-level continued to rise (Grainge and Davies, 1983; Mayall and Cox, 1988).
During the latest Miocene, carbonate deposition ceased with the influx of clastics derived from thrust sheets in the rising orogen of the Latimojong Mountains and associated volcano-plutonic complexes. Deposition continued with calcareous mudstones, which in places interfingered with reef talus. The clastic roks coarsen upwards into siltstones, sandstone, and pebble to cobble conglomerates (particularly near the mountain fronts) and are dominated by volcanic detritus.
Geochronology and Isotope Geochemistry
Neogene igneous and volcaniclastic rocks cover more than 75% of the surface of South Sulawesi. Volcaniclastics dominate and are intimately associated with dikes, sills, stocks, plutons and laccoliths of batholithic dimensions (5100 km diameter). New geochronologic and isotopic data provide timing constraints on the stratigraphy, magmatism and tectonic history of the region. Thirty six new conventional K-Ar ages of biotite, hornblende, sanidine, and plagioclase separates from volcanic and intrusive rocks in a broad area bounded by Pare Pare, Mamasa, Palopo and Enrekang (Figure 3) are indistinguishable and range from 5 to 13 Ma, averaging 8+2 Ma. Apatite, zircon
683
and sphene fission track (FT) ages exhibit the same general relationship although apatite FT ages are slightly younger than the K-Ar ages (2-14 Ma), and average 5 f 2 Ma (Bergman et al., 1992; Bergman et al., in prep.), due to the lower blocking temperature of apatite (120+25 C) compared with feldspars, biotite, and hornblende (200-500f25 "C) (Dodson and McClelland Brown, 1985). Apatite FT analyses combined with other geochronometers indicate a two stage history consisting of an initial magmatic cooling phase at rates of 100-400 "C/m.y., followed by a second cooling phase related to compressional uplift and erosional denudation resulting in cooling rates of approximately 10-20 "C1m.y. (Figure 7). Assuming geothermal gradients of 20-30 "C/km for the most recent denudation cooling phase (heat flow data summarized in Thamrin, 1986), these cooling rates correspond to uplift rates of 200-700 m/m.y., rates typical of fold and thrust belts such as Taiwan and the Himalayan chain. These rates are confirmed by mineral equilibria geobarometry data on selected plutons, which indicate relatively shallow-level intrusion of Miocene granitic laccoliths and plutons at 3-10 km depths. Aluminum hornblende geobarometry of the Palopo and Polewali granitic plutons indicate crystallization pressures of 1-3 kbar (Bergman et al., 1992; Bergman et al., in prep.).
Initial whole-rock s7Sr/86Sr isotope ratios of Miocene volcanic and plutonic rocks overlap and range from 0.705 to 0.740 (n=23). A positive correlation between 87Sr/x6Sr and s7Rb/86Sr ratio is exhibited, indicating a possible isochron relationship (Figure 8; Bergman et al., 1992). Whole rock Rb-Sr isochrons for an individual pluton, such as Palopo (506+21 Ma) are distinct from the best fit isochron of the entire suite (306k42 Ma), yet both can be interpreted to indicate a Paleozoic "closure" or "homogenization" event of the lithospheric source region of the magmas. Whole rock 143Nd/144Nd ratios range from 0.5119 to 0.5127 and slightly correlate with Nd/Sm ratios, indicating a possible isochronal relationship with errorchron ages of 0.5-1.5 Ga (Figure 9; Bergman et al., 1992). Model ages of time since separation from depleted mantle range from 0.8-2.3 Ga.
Zircon z06PbP38U and 207Pb/235U ages of six granitic intrusive and andesitic extrusive rocks are 5-12 Ma, similar to K-Ar biotite and hornblende ages on the same rock, and reflect the Late Miocene magmatic event (Bergman et al., 1992). In contrast, zircon 207Pb/206Pb ages are grossly discordant and are in the range 88-1073 Ma, suggesting the presence of recycled ancient zircons in the Late Miocene granitic magmas derived from Proterozoic to Paleozoic lithospheric parent rocks. Since lithospheric rocks of this age and isotopic composition are uknown in Sundaland but are
characteristic of the Australian Plate, the inferred continent-continent collision must have involted the Australian Plate.
STRUCTURE/TECTONICS
The distribution of structures in the Kalosi PSC can be broadly divided into two north-south trending zones, the Majene and Kalosi Fold Belts (Figures 10 and 11), which together form part of an allochthonous westward-verging orogenic wedge thrust onto the southeastern margin of Sundaland. Magmatism is equally distributed in both the foreland and hinterland domains.
Foreland
The foreland is composed of the Majene Fold Belt and the Mamasa granitic "laccolith". The former is a thin skinned, westward verging fold and thrust belt formed by a set of thrust fault ramps which repeat the Enrekang Volcanic Series in an imbricate series of thrust sheets. The thrusts are N-S trending and laterally continuous, with tight asymmetric anticlines in their hanging walls (Figure 4). The leading edge of the fold belt is evident on seismic lines offshore in the Makassar Straits (Figure 10). Seismic Line PAC-201 illustrates a series of frontal ramps and backthrusts which cut through the Pliocene section, carrying a series of piggy-back basins in their hanging-walls. These piggy-back basins are filled With synorogenic sediments derived from growing and exposed structural highs and which subsequently were deposited in the intervening structural lows on the moving thrust sheets.
The north-south trend of the fold axes, faults and fractures changes around the perimeter of the Mamasa Granite. The north-south structural trends of the Majene Fold Belt are folded around the Mamasa Granite and become parallel to its southern margin. The granite appears to be acting as a rigid indentor, impinging into the Majene Fold Belt from the east, resulting in oroclinal folding of the fold-belt around the granite body. This implies the granite is detached from its root and is incorporated in the orogenic wedge. This in turn implies the Mamasa Granite may have been a large laccolith rather than a batholith, thereby providing a discontinuity surface along its base which subsequently acted as a detachment surface. The regional gravity field is not significantly affected by the aerial distribution of the granite, further implying it is rootless and detached.
Hinterland
A second foldbelt, the Kalosi Fold Belt, is present to the east of the Mamasa Granite. Westward-verging, north-south trending thrust faults cut deeper than in
684
the Majene Fold Belt, and expose successively older units from west to east (Figures 5 and lo), from the Miocene Enrekang Volcanic Series, to the Eocene Toraja Formation and conformably overlying Oligo- Miocene Makale Formation, to Mesozoic Basement in the core of the Latimojong Mountains. Several large breached anticlines provide windows deeper in the section, such as at Buakayu (Figure 3).
The fold belt is further complicated by a north-south trending wrench system, the Masupu Fault Zone, which is superimposed on and folds the older westward- verging thrust structures (Figure 3). The wrench system extends southwards to the Walanae Fault Zone and forms part of a major wrench system cutting through South Sulawesi (Katili, 1970; Sukamto, 1975; Tjia, 1981; Berry and Grady, 1987). This zone has been interpreted to exhibit sinistral movement which, with the Palu Fault of Central Sulawesi, is accommodating the northward movement of the Banda Sea microplate and the westward movement of the Bangai-Sula microplate(s) relative to western Indonesia (Smith and Silver, 1991). Field relationships along the Masupu Fault Zone and adjacent areas indicate the sense of movement is actually dextral. These relationships include mesoscopic strain indicators, a series of restraining bends and associated compressional structures along the trace of the fault, and the cross cutting relationships of older structures.
This dichotomy in sense of wrenching along the fault may be due to two phases of movement, the first phase consisting of sinistral movement and the second dextral movement. Evidence for this is present in the vicinity of Enrekang where a rhombic shaped structure exists which is filled with synorogenic clastics of the Pliocene Walanae Formation. This structure lies on a deflection of the fault trace and appears torepresent a small pull- apart basin consistent with initial sinistral movement. Several compressional folds in the structure trend oblique to the Masupu Fault Zone and indicate subsequent dextral movements inverted the older normal faults.
The Neogene thermal and uplift history of the hinterland is well constrained by plutonic rocks such as the Palopo pluton. Four samples from 475-1070 m elevations exhibit a range in hornblende Al contents (averaging >4.9 wt% A1,03) and predicted crystallization pressures averaging > 1 .O-1.7 kbar. Because rocks of the Cretaceous Latimojong Formation which form the contact aureole around the Palopo pluton contain abundant andalusite porphyroblasts, the intrusion pressure is limited to <3.8 kbar, the aluminosilicate triple point. The top of the pluton (1050 m elev.) crystallized at pressures of 1.OkO.S kbar
(3-4 km subsurface depths), whereas the lower-most exposed rocks (0.5 km elev.) crystallized at pressures of 1.720.5 kbar (5-6 km subsurface depths). Combining these inferences with the fission track and K-Ar geochronology data for the Palopo pluton and its contact aureole, it is possible to constrain the cooling and uplift history. The Palopo parental granitic magma was formed in the lower crust, ascended toward the surface, and intruded the Latimojong Formation at depths of 3-5 km at 6-10 Ma and rapidly cooled through 500-300 =C by 6-8 Ma. The pluton finally cooled through 60-120 = C and ascended through 2-3 km depths by 2-3 Ma, during thrust-related uplift and erosional denudation.
TECTONIC MODEL
The Eocene tectonic framework of South Sulawesi remains at this stage sketchy due to limited geologic control. On an Indonesian and broader scale, the Eocene epoch (ca. 45 Ma) was a time of worldwide plate reorganizations during which the Indian Plate collided with Eurasia (Dewey et al., 1989), the bend in the Hawaiian-Emporer seamount chain occurred, and was the time of ridge jump from the Australian Eurasian spreading center to the presently active Southeast Indian Ocean ridge spreading center (Packham, 1990). A major unconformity developed throughout In8mesia at that time (Hutchison, 1992). Although the ultimate tectonic causes of this extensional event remain uncertain, some workers have proposed that the Eocene extension was related to indentor and escape tectonics caused by the Indian plate collision (Tapponier et al., 1982, 1986). In contrast, we prefer to view Eocene extension as the result of worldwide plate reorganization.
The southeastern portion of Sundaland between South Sulawesi and Central Java contains numerous early Tertiary rift basins which have been defined both seismically and from drilling (Letouzey et al., 1989; Bransden et al., 1992; Van de Weerd and Armin, 1992). The rift basins are dominated by half grabens which contain non-marine clastics (fluvial and lacustrine) and pass upwards into paralic and shallow marine sequences. Many of these basins became inverted during the MiddleKate Miocene compressional episode to produce classic "Sunda Folds".
In contrast to the Eocene extensional framework, the Miocene plate tectonic framework of Sulawesi is more constrained, yet has been the subject of vigorous debate (eg., Sukamto, 1978; Katili, 1979; Hamilton, 1979; van Leeuwen, 1981; Hutchison, 1982, 1989; Silver et al., 1983a, b; Nishimura, 1986; Letouzey et al., 1990; Leterrier et al., 1990; Audley-Charles, 1991; Audley
685
Charles and Harris, 1991; Daly et al., 1991). Many workers envision a Miocene westward-dipping sub duction zone to produce the widespread Miocene volcanic and plutonic rocks in South Sulawesi. However, the present study indicates Paleozoic to Proterozoic lithospheric parental rocks, unlike any known in Southeast Sundaland, were melted to produce the Miocene igneous rocks (Figure 11). Such lithospheric assemblages characterize the northern Australian Plate, such as in western Irian Jaya (Pieters et al., 1983; Pigram and Pauggabean, 1984). Silurian granitic rocks form part of an Early Paleozoic continental assemblage and extensive Miocene collision of arc terranes and associated crustal melting are known along the northern margin of Northeast Australia-New Guinea (Audley-Charles, 1991). This similarity to the inferred crustal parent material for the Miocene magmatic rocks in South Sulawesi suggests that a crustal fragment derived from the northern Australian Plate was accreted on to Southeast Sundaland during Miocene times due to westward vergent motion of the ,Pacific Plate. It is also possible that the accreted crustal block was one of the allochthonous Pacific microplates (such as the Sula Block) which characterize eastern Indonesia (Hutchison, 1989a, b; Audley-Charles, 1991 ; Audley- Charles and Harris, 1991).
Early Miocene emplacement of the Central Sulawesi ophiolite marked the onset of the accretion event (Audley-Charles, 1987; Silver et al., 1983a, b; Smith and Silver, 1991; Parkinson, 1991). Continued west- vergent compression led to crustal thickening beneath the south arm of Sulawesi, culminating in Late Miocene lithospheric melting, extensive volcanism, and Late Miocene to Pliocene thin-skinned thrust faulting in a manner broadly similar (albeit of a smaller scale) to the Eocene accretion of the Indian Plate on to the Eurasian Plate and the associated development of the Himalayan orogen. The Pliocene framework was characterized by regional deformation and uplift along a 15,000 km long belt along the northern margin of Australia and in much of Indonesia. Fold and thrust belts of Alpine-Himalayan scale developed during the last 5 m.y. in New Guinea, Sulawesi, the Moluccas, and Banda arc. Interestingly, the rapid uplift inferred for South Sulawesi since 5-10 Ma on the basis of apatite fission track data is also suggested for the Papuan Fold Belt using similar data (Hill and Gleadow, 1989). Our new model for South Sulawesi is one of Neogene continental collision, in contrast to previously proposed oceanic crust subduction or rift related models.
The Pliocene structural evolution of South Sulawesi is not necessarily composed of compressive deformation alone, although the evidence for significant Pliocene to
Recent extension has not yet been recognized in the Kalosi PSC. Miocene collision-related nappe emplacement in Timor and Seram produced post collisional uplift and nappe attenuation by low and high angle normal faulting (Harris, 1989). It is possible that Neogene lower crustal extension played a role in the subsidence of the Bone and Tomini Bays.
PETROLEUM SYSTEM
A petroleum system is a means of integrating petroleum source rock, migration path, reservoir rock, seal, and trap in time and space to provide a petroleum accumulation (Magoon, 1988). All of these ingredients exist in the study area and are schematically illustrated in Figure 12.
Source Rock, Maturation and Expulsion
Coals and carbonaceous claystones deposited in fluvio- deltaic depositional environments are present in the upper portion of the Toraja Formation and are considered to be the primary source rocks in this petroleum system. The rocks contain Type II/III (Figure 13) terrestrially influenced kerogens, and have TOC values in the range 31% to 81% and HI values ranging from 158 to 578 (Garrard et al., 1992). Outcrop samples are immature to early mature for oil generation, except in the vicinity of large igneous intrusives where post-mature values result from contact metamorphism.
Numerous oil and gas seepages have now been recognized in the Kalosi PSC (Figure 14) including several new localities discovered during the recent seismic shot-hole drilling campaign. All of the oils, however, fall within the fully to late mature part of the oil window (Ro 0.60% to 0.90%). Geochemical analysis of the oils indicate they are paraffinic, low sulfur, moderately low wax to waxy oils with API gravities (where not biodegraded) of 35" to 40". Except for maturity differences, good correlation exists between the oils and the coals and carbonaceous claystones, based on GC, GC-MS, and carbon isotope data (Figure 15). All of the Eocene coals have high pristandphytane ratios (6.0-15.20) similar to or greater than the oils. During pyrolysis-GC experiments the coals generated similar waxy hydrocarbon products at maturity. The C,, carbon isotopes for the aromatic fractions are very similar (within 1 per mil) while the tricyclic, tetracyclic and pentacyclic terpane biomarker distributions are the same. The bicadinanes and steranes also both show good correlations.
The immature to early mature source rocks at outcrop implies that maturation did not occur during pre- orogenic subsidence. Optimal thermal maturity of the
686
Eocene source rocks is believed to have occurred subsequently in sub-thrust kitchens as a result of magmatic-arc related sedimentation and tectonic loading and burial beneath thrust sheets. This would place the onset of generation in the Late Miocene to Pliocene, during the development of the orogenic belt, and suggests the source kitchens are presently in the oil window. This is a key factor, as inversion structures in the Indonesion region have a tendency to be barren of oil due to major timing problems.
Migration of oil occurs along pathways of maximum permeability. Deltaic Eocene sands associated with the coal intervals provide optimum conduits for migration into the overlying transgressive shore face sands. These laterally continuous sands, sealed by the overlying carbonates of the Makale Formation, act as the primary 'plumbing' for the petroleum system. Migration is up-dip, with the actual direction controlled by the geometry of the carrier bed between the fetch area and the trap area. Neither fault nor cross-stratal migration is necessary for the petroleum system to work, although juxtaposition of porous and permeable units by faults will allow the migrating oils to enter separate thrust sheets.
Reservoir Rock, Seal, and Trap
Transgressive marine sandstones at the top of the Toraja Formation represent not only the principle hydrocarbon carrier beds, but also the primary reservoir objective. Outcrop samples of fine grained sands have porosities in the 20-2570 range and moderate permeabilities, although these have been enhanced by surface weathering. The immediately overlying muddy carbonates of the Makale Formation represent the primary seal for traps, as it did for the carrier system. Reservoir targets of secondary importance include Miocene carbonates (fractured and karsted) , Miocene volcaniclastics and Pliocene pinnacle reefs. Primary targeted traps are compressional ramp anticlines with four-way dip closure in thrust sheets which are in direct communication with down-dip kitchen areas.
Possible negative influences on Eocene reservoir quality include the provenance of Eocene sandstones, which is dominated by Mesozoic ophiolitic and metamorphic rocks. However, the Upper Eocene transgressive sandstones are depleted in lithic grains due to shallow marine processes and form the best quality reservoir targets. The limiting factor in Miocene volcaniclastic reservoir quality is the abundance of smectite.
Regional Comparisons with Southeast Kalimantan and Eastern Java Sea
The Barito Basin in southeast Kalimantan offers an analogue for exploration targets in the Kalosi PSC. The largest hydrocarbon accumulation in the basin, the Tanjung Field, has produced more than 104 MMBO through primary recovery up to the end of 1991 (IPA, 1992). Eocene coals of the Tanjung Formation provide the source for the oil while fluviodeltaic sandstones represent the primary reservoir (Kusuma et al., 1989). The trap consists of an asymmetric anticline in the hanging-wall of a thrust fault. This structure is part of a fold and thrust belt developed on the west side of the Meratus Mountains, a Late Miocene through Pliocene orogenic belt analogous to the Latimojong Mountains of Sulawesi.
Other hydrocarbon occurences of Early Tertiary affinity are located in the eastern Java Sea A R C 0 operated Kangean PSC (Phillips et al., 1991) some 510 km to the southwest of the Kalosi PSC. Apart from the JS53A oil discovery, all of the oils and condensates found to date are distinctly different from the South Sulawesi oil seeps and the Barito Basin oils, and have probably been generated from source rocks which accumulated in a different depositional setting. The Kangean PSC Sepanjang Island high wax oil and the W. Kangean Pagerungan condensates show distinctly different GC scans, carbon isotope values and GC-MS biomarker scans. Also, differences are evident in the Py-GC scans if a comparison is made between the South Sulawesi Eocene coals and the Py-GC scan obtained on the asphaltene fraction of the waxy Sepanjang Island oil.
The Kangean Sepanjang Island-1 oil and W. Kangean condensates are thought to have been generated from an Early Tertiary lacustrine shale containing a predominantly non-marine algal organic facies with only minor terrestrial input. The Pagerungan condensate may have been generated from shales/coaly shales deposited in a marginal lacustrine setting. This condensate shows similarities to the Sulawesi oils, but is still distinctly different geochemically.
So far, no organic rich "deep" water lacustrine type facies have been identified in the Early Tertiary rift basins of South Sulawesi.
SUMMARY
The stratigraphic, structural, and geochronologic record of rocks in the Kalosi PSC document the evolution of the eastern Sundaland margin from a Mesozoic accretionary complex, through an Eocene
687
extended continental margin into a Miocene active magmatic arc and finally a continent-continent collisional orogen, complete with lithospheric melting. Each phase of this evolution provided different ingredients which finally produced a working petroleum system, with the poteniial to produce economic accummulations of petroleum.
South Sulawesi extrusive and intrusive rocks form a cogenetic volcano-plutonic complex of calc-alkalic to mildly alkalic and potassic, felsic to mafic magmatic rocks which were erupted and intruded during a relatively short episode of Mid to Late Miocene (5-12 Ma) lithospheric melting. Parental material for the Miocene melts were Late Proterozoic to Paleozoic crustal and mantle lithospheric assemblages which became heated and melted due to lithospheric thickening resulting from the continent-continent collision in which west vergent lithosphere of the Australian-New Guinea plate was subducted beneath easternmost Sundaland. Regional east-west compression continued through Pliocene to Recent times and resulted in the development of a Late Neogene fold and thrust belt with ramp-related imbrication providing enhanced regional uplift rates of 300-700 m1m.y. during the last 2-5 m.y.
This study impacts exploration in the Kalosi PSC by constraining the Miocene plate tectonic framework to one dominated by accretionary events, crustal thickening, and lithospheric melting. The most important controls on hydrocarbon maturation, migration and entrapment in the Kalosi PSC are: a) Late Miocene and younger (ca. 5-13 Ma) maturation of Eocene source rocks due to rapid subsidence and burial in response to extensive regional volcanism , sedimentation, and thrust loading, b) relatively high regional Late Miocene heat flow (60-80 mW/m2) due to voluminous magmatism, and c) Late Miocene and younger structural trap development due to thin-and thick-skinned thrusting.
ACKNOWLEDGEMENTS
We thank ARCO International Oil and Gas Company and Pertamina for permission to publish this paper, particularly the support of Suherman Tisnawidjaya, John Duncan, and Dave Nicklin. The Geological Research and Development Center in Bandung contributed to the geologic mapping of the Kalosi PSC and we appreciate the efforts of Amarudin, Sukido, Supandjano, Tisna and their colleagues. We appreciate the contributions of Long Liang, Jeff Corrigan, Ron Noble and Mauri Cucci, ARCO Exploration Research and Technical Services, Piano. Sr and Nd isotope determinations were performed by Ken Foland and
Fritz Hubacher (Ohio State Univ.), fission track analyses by Shari Kelley (Southern Methodist Univ.) and Geotrack, International (Melbourne), K-Ar ages by Tom Bills (Geochron, Cambridge), and zircon U-Pb analyses by Paul Mueller (Univ. Florida). Pierre Melas and Said El Latief, TOTAL Indonesie, assisted with the review and editing of the manuscript.
REFERENCES
Abendanon, E. C., 1915. Geologische en Geographische Doorkruisingen van Midden-Celebes (1909-1910) : Leiden, E. J. Brill, v. 1, 451 p.
Audley Charles, M. G. , 1991. Tectonics of the New Guinea area. Annual Rev. Earth Planet. Sci., v. 19, p. 17-41.
Audley-Charles, M. G . , and Harris, R . A., 1991. Allochthonous terranes of the southwest Pacific and Indonesia. Phil. Trans. Royal Soc. London, v. A331, p. 115-131.
Bellon, H., Maury, R. . Soeria-Atmadja, R., Polve, M. ,Pringgoprawiro, H. , and Priadi, B., 1989.40K-40Ar chronology of the Tertiary volcanism in central Java (Indonesia): evidence for two subduction related magmatic events. C.R. Acad. Sci. Paris, v. 309, ser. 11, p. 1971-1977 (in french).
Bellon, H., and Rangin, C., 1992. Geochemistry and isotopic dating of Cenozoic volcanic arc sequences around Celebes and Sulu Seas. Proc. ODP, Sci. Results, v. 124 (in press).
Bergman, S. C., Talbot, 3 . P., and Garrard, R. A., 1992. Miocene Magmatism and Thermal History of the Kalosi Block and Adjacent S.W. Sulawesi: Evidence of Miocene Continental Collision: Unpublished Report, ARCO Oil and Gas Company, Piano, TSR 92-0038, 27p.
Bergman, S. C. , et al., in prep, Miocene Magmatism and Thermal History of the Kalosi Block and Adjacent S. W. Sulawesi. Evidence of Miocene Continental Collision.
Berry, R . F., and Grady, A. E., 1987. Mesoscopic structures produced by Plio-Pleistocene wrench faulting in South Sulawesi, Indonesia. Journal of Structural Geology, v. 9, no. 5/6, p. 563-571.
Bransden, P.J.E. , and Matthews, S.J., 1992. Structural and Stratigraphic Evolution of the East Java Sea, Indonesia. Proceedings of the Indonesian Petroleum Association, p. 417-453.
688
Brown, G.C., 1982. Calc-alkaline intrusive rocks: their diversity, evolution, and relation to volcanic arcs. In Thorpe, R.S. (ed:.) Andesites, orogenic andesites and related rocks, J. Wiley and Sons, NY, p. 437-461.
Daley, M. C., Cooper, M. A., Wilson, I., Smith, D. G., and Hooper, B. G. D. , 1991. Cenozoic Plate Tectonics and Basin Evolution in Indonesia, Marine and Petroleum Geology, v. 8, p. 2-21.
Demaison, G., and H,uizinga, B. J., 1991. Genetic Classification of Petroleum Systems. American Association of Petroleum Geologists Bulletin, v. 75, no. 10, p. 1626-1643.
Dewey, J.F., Cande, S . , and Pitman, W.C., 1989. Tectonic evolution of the India/Eurasia collision zone. Eclog. geol. Helvetic., v. 82, p. 717-734.
Djuri and Sudjatmiko, 1974. Geologic Map of Palopo- Maj ene Quadrangle, South Sulawesi. Geological Research and Development Center, Bandung, 1:250,000.
Dodson, M.H., and McClelland-Brown, E., 1985. Isotopic and paleomagnetic evidence for rates of cooling, uplift, and erosion. In Snelling,. N.J., (ed.) The chronology of the geological record, Geol. SOC. London Memoir 10, p. 315-325.
Ewart, A.J., 1982. The mineralogy and petrology of Tertiary-Recent orogenic volcanic rocks: with special reference to the andesite-basalt compositional range. In Thorpe, R.S. (ed.) ,Andesites, orogenic andesites and related rocks, J. Wiley and Sons, NY, p. 25-87.
Garrard, R. A., and Silalahi, D., 1989. Sengkang Basin, South Sulawesi, Guidebook. Indonesian Petroleum Association Post Convention Field Trip, Jakarta, 47 p.
Garrard, R.A., and Dorojatun, A., 1991. Kalosi block, S Sulawesi. A synopsis of the geology and hydrocarbon potential. Unpublished Report ARII/NV/SUL/91/06, Atlantic Richfield Indonesia, Inc., Jakarta.
Garrard, R. A., Nusatriyo G., and Coffield, D. Q., 1992. The Prospectivity of Early Tertiary Rift Sequences in the Neogene Foldbelts of South Sulawesi. Eastern Indonesian Exploration Symposium, Jakarta, 6P.
Gisolf, W. F., 1919. Lawsonite and epidote in the schists of the Latimojong Mountains, Celebes (in Dutch): Ovegedrukt uit de Handelingen van het XVIIE Nederlandsch, Natuur - en Geneeskunding Congres, gehouden op 24,25 en 26 April 1919, Leiden.
Grainge , A. M., and Davies, K. G., 1983. Reef Exploration in the East Sengkang Basin, Sulawesi. Proceedings of the Indonesian Petroleum Association, Jakarta, p. 207-227.
Hamilton, W. H., 1979. Tectonics of the Indonesian Region: United States Geological Survey Professional Paper 1078, 345 p.
Harris, R. A., 1989. Processes of allochthon emplacement, with special reference to the Brooks Range ophiolite, Alaska and Timor, Indonesia. unpubl. Ph.D. thesis, Univ. London, U.K., 514 pp.
Harris, J. R., 1992. Radar Geologic Interpretation of Kalosi Block - South Sulawesi: Unpublished Report, Atlantic Richfield Kalosi Limited, Jakarta, ARKLI Exp/Slw/92/05, 52 p.
Hassan, K., 1989. Tectonic implications of provenance studies in the Upper Cretaceous Balangbaru Formation, SW Sulawesi, Indonesia. abstract Univ. London Consortium Meeting.
Hassan, K . , 1991. The Upper Cretaceous flysch succession of the Balangbaru Formation, Southwest Sulawesi: Proceedings of the Indonesian Petroleum Association, Jakarta, p. 183-208.
Hassan, K., Garrard, R., and Mahodim, P., 1991. SW Sulawesi, Post-convention field trip guidebook, Indonesian Petroleum Association, Bandung.
Helmers, H., Maaskant, P., and Harttel, T.H.D., 1990. Garnet peridotite and associated high grade rocks from Sulawesi, Indonesia. Lithos, v. 25, p. 171-188.
Hill, K.C., and Gleadow, A.J.W., 1989. Uplift and thermal history of the Papuan fold belt, Papua New Guinea: apatite fission track analysis. Australian Jrn. Earth Sci., v. 36, p. 515-539.
Hutchison, C.S. , 1982. Indonesia: regional distribution and characteristics, In: Thorpe, R.S. (ed.), Andesites, orogenic andesites and related rocks, J. Wiley , London, p. 207-224.
Hutchison, C. S. , 1989a. Geological Evolution of South-East Asia: Oxford Monographs on Geology and Geophysics No. 13, Oxford, 368 p.
Hutchison, C. S . , 1989b. Displaced terranes of the southwest Pacific, in: Ben-Avraham, Z . (Ed.), The Evolution of the Pacific Ocean Margins, Oxford Univ. Press, p. 161-174.
689
Hutchison, C. S . , 1992. The Eocene unconformity on Southeast and East Sundaland. Geol. Soc. Malaysia Bull. 32, p. 69-88.
IPA, 1992, Indonesia - Oil and Gas Field Atlas, Volume V: Kalimantan, Indonesian Petroleum Association, Professional Division, Jakarta.
Jezek, P.A., Whitford, D.J. . and Gill, J.B., 1981. Geochemistry of recent lavas from the Sangihe- Sulawesi arc, Indonesia, In: Barber, A.J.. and Wiryosujono, S. (eds.). Geology and Tectonics of Eastern Indonesia, Geol. Res. Develop. Centre, Spec. Publ. 2, p. 383-389.
Katili, J. A., 1978. Past and Present Geotectonic Position of Sulawesi, Indonesia, Tectonophysics, v. 45, p. 289-322.
Kavalieris, I., van Leeuwen, Th.M.. and Wilson, M., 1992. Geological setting and styles of mineralization, north arm of Sulawesi. Jrn. SE Asian Earth Sci., v. 7. p. 113-129.
Kirk, H.J.C., 1968. The igneous rocks of Sarawak and Sabah. Geol. Surv. Malaysia, Borneo Region, Bull. 5.
Kuno, H . , 1968. Origin of andesite and its bearing on island arc structure. Bull. Volc., v. 32, p. 141-17.
Kusuma, I., and Darin, T., 1989. The Hydrocarbon Potential of the Lower Tanjung Formation, Barito Basin, S. E. Kalimantan. Proceedings of the Indonesian Petroleum Association,Jakarta, p. 107-1 38.
Leterrier, J . . Yuwono, Y.S., Soeria-Atmadja, R. , and Maury, R.C. , 1990. Potassic volcanism in central Java and South Sulawesi, Indonesia, Jrn. SE Asian Earth Sci., v. 4, p. 171-187.
Letouzey, J., Werner, P. , and Marty, A . , 1990. Fault reactivation and structural inversion. Backarc and intraplate compressive deformations. Example of the eastern Sunda shelf (Indonesia), Tectonophys., v. 183, p . 341-362.
Magoon, L. B., 1988. The Petroleum System - A Classification Scheme for Research, Exploration, and Resource Assessment. In L. B. Magoon (Ed.), Petroleum Systems of the United States, U.S. Geological Survey Bull., 1870, p. 2-15.
Mayall, M. J. , and Cox, M., 1988. Deposition and Diagenesis of Miocene Limestones, Senkang Basin, Sulawesi, Indonesia. Sedimentary Geolcgy, v. 59; p. 77-92.
Packham, G.H., 1990. Plate motions and Southeast Asia: some tectonic consequences for basin development. SEAPEX Proc., v. 9, p. 55-68.
Parkinson, C.D., 1991. The petrology, structure and geologic history of the metamorphic rocks of Central Sulawesi, Indonesia. PhD Thesis, University of London, London, 337 p.
Parkinson, C.D., 1991. Counterclockwise P-T-t paths from Sulawesi meta-basites: implications for subduction zone metamorphism. In Proc. Symposium Dynamics of Subduction and its Products, Res. and Dev. Centre for Geotechnology, Indonesian Unit, p. 225-226.
Perrodon, A . , 1992. Petroleum Systems: Models and Applications: Journal of Petroleum Geology, v. 15, no. 3, p. 319-326.
Phillips, T. L., Noble, R . A., and Sinartio, F. A. , 1991. Origin of Hydrocarbons, Kangean Block Northern Platform, Offshore NE Java Sea. Proceedings of the Indonesian Petroleum Association, Jakarta, p. 637-66 I .
Pieters, P. E. , Pigram, C. J., Trial, D. S . , Dow, D. B., Ratman, N . , Sukamto, R. , 1983. The stratigraphy of W Irian Jaya: Bull. Geol. Res. Dev. Centr., Bandung, Indones., v. 8, p. 14-48.
Pigram, C. J . , and Pauggabean, H., 1984. Rifting of the northern margin of the Australian continent and the origin of some microcontinents in eastern Indonesia. Tectonophysics, v. 107, p. 331-353.
Kangin, C., Jolivet, L., Pubellier, M., and 9 other members of the Tethys Pacific working group, 1990. A simple model for the tectonic evolution of southeast Asis and Indonesia region for the past 43 m.y. Bull. Soc. Geol. France, v. 8, no. 6, p. 889-905.
Ratman, N., and Atmawinata, S . , 1988. Geological report of Marnuju Quadrangle, South Sulawesi: Geologic Research and Development Center, Open File Report, Bandung, 1:250,000.
Reyzer, J . , 1920. Geologische aanteekeningen betreffende de Zuidelij ke Toraj a-landen, verzarneld uit de verslagen der mijnbouwkundige onderzoekingen in Midden-Celebes: Jaarboed v. h. Mijnwezen Nederlandsch Oost-Indie 1918, Weltevreden, Gov’t Printing Office, p. 154-209.
Sax H. G . J. , 1931a. Geological Research South West Celebes: Confidential BPM Report, Balikpapan, Indonesia.
690
Sax H. G. J., 1931b. Temporary Report of the Geological Research of the Pare-Pare and Loewoe Permits: Confidential BPM Report, Balikpapan, Indonesia.
Silver, E.A. , McCaffrey, R. , and Smith, R.B., 1983a. Collision, rotation, and the initiation of subduction in the evolution of Sulawesi, Indonesia, Jrn. Geophys. Res., v. 88, p. 9407-9418.
Silver, E. A., McCaffrey, R. , and Smith, R. B., 1983b. Ophiolite emplacement by collision between the Sula Platform and the Sulawesi island arc, Indonesia. Journal of Geophysical Research, v. 88, p. 9419-9435.
Smith, R.B., and Silver, E.A., 1991. Geology of a Miocene collision complex, Buton, eastern Indonesia. Geological Soc. America Bulletin, v. 103, p. 660-678.
Sukamto, R., 1975. Geologic map of lndonesia, Sheet VIII, Ujung Pandang. Geologic Survey of Indonesia, Bandung, 1:1,000,000.
Sukamto, R., 1978. The structure of Sulawesi in the light of plate tectonics. Proc. Reg. Conf. Geol. Min. Res. SE Asia. 1975, Jakarta, p. 121-141.
Sukamto, R., 1982. Geologic map of the Pangkajene and western part of Watampone quadrangles, South Sulawesi, scale 1:250,000. Geol. Res. and Devel. Centre, Bandung.
Sukamto, R., Simindjuntak, T.O., 1983. Tectonic relationship between geologic provinces of western Sulawesi, eastern Sulawesi, and Banggai-Sula in the light of sedimentological aspects. Bull. Geol. Res. Dev. Centre, no. 7, p. 1-12.
Sung, G. L., 1948. Samenvatting van belang-rijkere geologische gegevens over Celebes. GL. A. Raport No 22575, unpub. rept., Pertamina.
Tapponier, P., Peltzer, G., and Armijo, R . , 1986. On the mechanics of the collision between India and Asia, in Collision Tectonics (ed. M. P. Coward and A. C. Ries), Geological Society of London Special Publication 19, p. 115-157.
Tapponier, P., Peltzer, G., Le Dain, A. Y., Armijo, R., and Cobbold, P., 1982. Propogating extrusion tectonics in Asia, new insights from simple experiments with plasticene. Geology, v. 10, p. 611-616.
Thamrin, M. 1986. Terrestrial heat flow map of Indonesian basins. Proceedings of the Indonesian Petroleum Association Jakarta, p. 33-70.
Tjia, H. D. , 1981. Examples of Young Tectonism in Eastern Indonesia, in Geology and Tectonics of Eastern Indonesia (Edited by Barber, A. J . , and Wirysujono, S .). Geological Research and Development Centre, Bandung Special Publications, v. 2, p. 89-104.
Van Bemmelen, R. W., 1949. The Geology of Indonesia, Government Printing Office, The Hague, 2 vols.
Van de Weerd, A. A., and Armin, R. A., 1992. Origin and Evolution of the Tertiary Hydrocarbon Bearing Basins in Kalimantan (Borneo), Indonesia. American Association of Petroleum Geologists Bulletin, v. 76, no. 11, p. 1778-1803.
Van Leeuwen, T. M., 1981. The Geology of Southwest Sulawesi, with Special Reference to the Biru Area, in The Geology and Tectonics of Eastern Indonesia, GRDC Special Publication No. 2, p. 277-304.
Yuwono, Y.S., Priyomarsono, S., Maury,t R.C., Rampnoux, J.P., Soeria-Atmadja, R., Bellon, H., Chotin, P., 1988. Petrology of the Cretaceous magmatic rocks from Meratus Range, southeast Kalimantan. Jrn. SE Asian Earth Sci., v. 2, p. 15-22.
691
692
STRATIGRAPHY HYDRC
-1 PERIOD FORMATlON I LITHOLOGY I$ RESERVOIRS
* *
TORAJA FM ( MALAWA )
* PRIMARY * * SECONDARY
* *
?
?
U* ?
B**
:ARBON POTENTIAL SOURCE
ROCK
9- CARBONACEOUS
IUGAS PRONE)
BITUMINOUS LMST. -8-
(LOCAUSED)
* *
: PRIMARY OIL PRONE SOURCE
ECONOMIC BASEMENT
HYDROCARBON INDICATIONS
6 SUUU 6 PENlKl
A 6 PATIRASOMPA
-# E. SENGKANG GAS FIELD
6 BUAKAYUlMAJENE
6 6 A BUAKAVU
6 ( C C g t N P )
A PODO
:} PARANDEAN
A 6 PODO
(C02t Ng)
AS6TRST HIDRO/NW!
FIGURE 2 - Stratigraphic column for the Kalosi PSC.
693
(GRANITE)
LEGEND : - 04" 00' a QUATERNARY
PLIOCENE
0 M. - L. MIOCENE
L. EOCENE - M. MIOCENE
M. - L. EOCENE
AGE 7 OPHlOLlTE
3 iio. 125"
0 INDEX MAP
IN",I PRE - TERTIARY( BASEMENT)
BY: WCING DATE :APRIL 1983
I I I AslrlEoLOW AUP/APR4.
FIGURE 3 - Simplified geologic map of the Kalosi PSC.
69 4
FIGURE 4 - SAR image of Majene fold belt (above) and geologic interpretation (below). Tp: Pliocene (Walanae Formation equivalent); Tm: Middle Miocene (Enrekang Volcanic Series equivalent). See Figure 3 for location.
695
T-w ~-\~
) 0
Tm
3 KM. I
\
Q " ' . Q ~ -r "..
FIGURE 5 SAR image of Kalosi fold belt (above) and geologic interpretation (below). Q: Quaternary alluvium; Tpw: Pliocene (Walanae Formation equivalent); Tin: Middle Miocene (Enrekang Volcanic Series equivalent). See Figure 3 for location.
12
10
Na,O
8-
+ 6-
K,O L
(wt%
> 4-
2-
0-
Foid
ite
0.4
Phon
olite
w 27
(7.5
9)
Teph
r it e/
B
asan
ite
Pic
roba
sall
4
I-
5(
1.88
) = 3(
0,56
) m
t
6A(1
.11)
Bas
altic
An
desi
te
Ande
site
0.
35
Bas
alt
0.2
0.3
I I
I I
I
28(0
.22)
fa
Rhy
olite
0.
5
Dac
ite
0.4
0
16A
( 7.7
6)
40
45
50
55
60
65
70
75
80
0 S
ampl
e (F
E 203
/FE
O)
SiO
, (w
t % 1
0 In
trusi
ve R
ocks
H
Ext
rusi
ve R
ocks
FIG
UR
E 6
a A
naly
tical
rcs
ults
of
mos
tly M
ioce
ne i
gneo
us r
ocks
fro
m t
he K
alos
i PSC
are
a,
Sout
h Su
law
esk
Igne
ous
rock
tot
al
alka
lis v
ersu
s sili
ca (T
AS)
plo
t sh
owin
g th
e co
mpo
sitio
nal
nom
encl
atur
e of
co
mm
dn v
olca
nic
litho
logi
es.
697
- 9OSUL11
1 1 - 1 1
average REE abundances chondrite normalized
I I I I I I I I I I I I I I La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
FIGURK 6b - Analytical results of mostly Miocene igneous rocks from the Kalosi PSC area, South Sulawesi: Rare Earth Element (REE) "Spider Diagram".
2
20
100
200
300
400
500
2'
20
I00
200
300
400
500
AGE
(Ma)
20
15
10
5
- V v
W a
3
8 M
PMA
SA
GRA
NITE
AGE
(Ma)
2
0
15
10
5 0
01
om
U
1
I PA
REP
ARE
IGNE
OUS
R
OC
KS
2:
20
100
200
300
400
500
AGE
(Ma)
'
md
Tur
bidi
tes
A
u - D
acite
s
w a 3
Q 3 W or B E
i
4
AGE
(Ma)
2
5
20
15
10
5
0
_Qt.=
_jrE
-
'A I
6
'u
v 2 !2
om
-3
0.
E W
'W
Ei
00
*#
.
- 0 C
onta
ct P
hylll
te
Igne
ous
Roc
ks
PALO
PO
PLU
TON
AGE
(Ma)
\
1. 5
00
0 S
ands
tone
s 0
Igne
ous
Roc
ks
BUA
KAYU
EN
REKA
NG
AREA
0 S
ands
tone
s Ig
neou
s Roc
ks
FIG
UR
E 7
- T
ime-
tem
pera
ture
cool
ing
traj
ecto
ries
for m
ostly
Mio
cene
igne
ous a
nd se
dim
enta
ry
rock
s fro
m th
e Kal
osi P
SC a
rea,
Sou
th S
ulaw
esi.
0.72
5
0.72
0
0.71
5
87
~r/
“S
r
pres
ent
0.71
0 (0.709L
(0.7
07:
0.70
5
0.70
0
A ~
alo
po
lntrusives
Ext
rusi
ve
h 11
(Ext
rusi
ve)
I 1
FIG
UR
E 8
-
Plot
of s
7Rb/
86Sr
vers
us 8
7Sr/8
6Sr f
or m
ostly
Mio
cene
igne
ous r
ocks
from
the
Kal
osi
PSC
are
a, S
outh
Sul
awes
i.
700
MORBasaRs I I I I I I I
0.0 by crustal residence age - 10 - - - - - - - - - - - - - - - - - - - - - - 5 - - I - - 0 2 - c
0 u) Q
.- P - Z r) P
- - 28 c- -
- -10 - 0.5122 -
- - -
0 - - - -15 228 5.
2.0 by crustal residence age 0.51 18 1 I I I I I I
0.700 0.71 0 0.720 0.730 0.740 87sr/ 8 6 s r initial
0.51 32
z P P I /V r c
\ 0.5122 U z m P
1 I I I I
Extrusive 0 In t rus ive
0.5112 I I I
0.00 0.04 0.08 0.1 2 0.16 0.20 I I I
147sm/ 144Nd
FIGURE 9 - Miocene i eous rock isotope plots for the Kalosi PSC area, South Sulawesi: '77Sm/'44Nd versus 143Nd/'44Nd (below) and 143Nd/'44Nd versus s7Sr/86Sr initial (above).
