© IPA, 2006 - Cenozoic Carbonates and Petroleum Systems of South Sulawesi, 2003

The Cenozoic carbonates and petroleum systems of South Sulawesi

IPA Field Excursion

October, 2003

Moyra wilsonl and

Alit ~scaria'

1. Department of Geological Sciences, Durham University, South Road, Durham, UK, DH13LE

2.Pertamina Exploration Division, Kwarnas Pramuka Building, 1 lth floor J1. Medan Merdeka Timur no.6., Jakarta 101 10, Indonesia

Formerly of SE Asia Research Group, University of London, Geology Department, Royal Holloway, Egham, Surrey, TW20 OEX, United Kingdom

ITINERARY Day 1:

Flight to Ujung Pandang, Sulawesi Introduction to the geology and petroleum systems of South Sulawesi Eocene to middle Miocene shallow water platform carbonates of the Tonasa Formation: Depositional environment, reservoir quality, karstification, caves & waterfalls Eocene clastics of the Malawa Formation: Reservoir and source rocks Structure of South Sulawesi: the Walanae Depression and fault system Drive to, and overnight in Watampone (Bone) - traditional Bugis welcome

Day 2: Shallow water buildups of the Tacipi Formation: depositional environment & reservoir quality Volcaniclastic sealing lithologies to the Tacipi Formation Active gas seeps from carbonate buildups of the Tacipi Formation Modem lacustrine environments of Lake Tempe (source rocks of the future) Traditional Bugis meal and overnight in Sengkang

Day 3: Structure and petroleum system of western central Sulawesi Distal and proximal synorogenic clastics of the Pliocene Walanae Formation Thrusting and folding in the Latimojong Mountains Depositional environments and active oil seeps from the Eocene-Oligocene Toraja Formation Kete Kesu: a traditional Toraja village and the Oligo-Miocene carbonates of the Makale Formation

Day 4: Return to Makassar and Jakarta

CONTENTS

Itinerary Contents Acknowledgements . Fieldtrip practicalities . Introduction .

Carbonates and hydrocarbons . Introduction to South Sulawesi carbonates Tectonic Setting Petroleum Systems of South Sulawesi

The Fieldtrip . Day 1: Geology of South Sulawesi Day 2: Tacipi knoll reefs and reservoirs. Day 3: Toraja Petroleum system .

References .

Many people and organisations were involved in making this fieldtrip and guidebook possible. Moyra and Alit's PhD studies on the carbonates of South Sulawesi were undertaken at the University of London and were funded by BP and both are gratefully acknowledged. The Geological Research and Development Centre in Bandung and the Ujung Pandang office of Kanwil provided significant logistical support. Pertamina and the University of Durham are thanked for allowing us time off work to lead the fieldtrip. The 'petroleum systems' part of the trip was originally run for the IPA with Dana Coffield and Nusatriyo Gurito, both formerly of ARCO, and their substantial input is acknowledged. Atlantic Richfield Indonesia, Inc. (New Ventures), Southeast Asia Research Group (University of London), ARCO Alaska Inc., and the Indonesian Petroleum Association ( P A ) all provided logistical and financial support. Energy Equity Corporation is thanked for allowing us access to their gas processing plant, and for allowing us to use their seismic section. Richard Garrard provided material for this guidebook and, more importantly, is responsible for the development of many of the concepts presented here.

FIELDTRIP PRACTICALITIES Hammer, handlens, pen, sunhat, sunscreen, stout boots and plenty of water are all

essential. Compass clinometer, camera, notebook, sample bags and a small pair of field- glasses would be optional, but useful extras. There is no particularly strenuous fieldwork on this trip although short walks and small scrambles are required. In one locality it is necessary to cross a narrow river, which depending on the amount of rain prior to fieldwork, a short wade may be required.

South Sulawesi has an equatorial monsoonal climate. Temperatures are uniformly high, ranging from about 24°C to 34°C with an average of about 32°C and a humidity reaching 70% to 90%. It is therefore essential to be adequately protected against the sun with both sunhat and sunscreen. The high temperatures and often strong winds in South Sulawesi, can result in considerable water loss from the body and it is advisable to drink regularly throughout the day to prevent dehydration. We will carry a supply of soft drinks in the vans.

The N-S trending Western Divide Range forms an effective barrier to rainfall as it is oriented perpendicular to the prevailing wind directions. Regions on either side of this range have wet seasons at opposing times of the year, depending on the prevailing wind direction. Areas west of the Western Divide Range receive most of their rainfall between the months of November to April. East of the Western Divide Range the wet season occurs between April to November. The driest area is along the south coast of South Sulawesi, which experiences a prolonged dry season between April and November. It is unlikely to rain during fieldwork in the western part of Southern Sulawesi, however, short showers can be expected in the eastern part of South Sulawesi.

The Cenozoic carbonates and petroleum systems of South Sulawesi fieldtrip will visit the southwestern arm of Sulawesi in central Indonesia (Figs. 1.1 and 1.2). The island has been famous through history for its pivotal role in regional economics, culture and science. The island formed the staging area for the great Buginese seafarers that dominated trade in the region for centuries. The various peoples who inhabit the island have retained their unique cultures, the most famous perhaps are the mountain people of Tana Toraja in South Sulawesi. It is also Sulawesi where Asian and Australian fauna and flora interact to produce plants and animals unique to this island, and provided Alfred Wallace in the 1800's with the evidence to develop the modern theory of evolution independently of Darwin.

South Sulawesi is a frontier petroleum exploration province with proven hydrocarbon source rocks, reservoir rocks, generating kitchen areas and, most importantly, hydrocarbon accumulations. Reserves of approximately 600 bcfg have been discovered to date and these are soon to go on production for local power generation. The proven presence of all the elements required for a petroleum system analogous to the prolific systems of western Indonesia, and the presence of multiple documented kitchen areas, provides the impetus for continuing exploration in this relatively unexplored region of Indonesia (Fig. 1.3).

CARBONATES AND HYDROCARBONS Almost half the world's oil production comes from carbonate reservoirs and a

similar percentage of Indonesia's hydrocarbon production is from carbonate reservoirs (Park et al., 1995). Hydrocarbon bearing and potentially hydrocarbon bearing carbonates occur in most marine basins, excellently placed with respect to source and seal lithologies, and very definitely form worthwhile exploration targets. Figure 1.4 shows the distribution of Tertiary carbonates in SE Asia which have or may have hydrocarbon potential. However, carbonate reservoirs are notoriously fickle and unpredictable (Park et al., 1995). It is only through a knowledge of processes of carbonate sedimentation, carbonate depositional environments, the development and 'growth' of carbonate platforms, and subsequent diagenesis of carbonates that a better understanding of the inheterogeneity of carbonate reservoirs can be achieved. In this course you will have the opportunity to study a range of extremely well-exposed, shallow- and deeper-water Tertiary and modem carbonates, which were deposited in a wide variety environments. The effects different processes had on the deposition and accumulation of these carbonates, resultant facies distribution and the nature of their faunal composition will be assessed. The carbonates studied form extremely useful analogues for other SE Asian carbonates, which often form hydrocarbon rcservoirs in the subsurface

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Figure 1.2) Localities to be visited in South Sulawesi

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INTRODUCTION TO SOUTH SULAWESI CARBONATES South Sulawesi (Fig. 1.5), located on the eastern margin of Eurasia, has an almost

complete stratigraphic sequence spanning the late Cretaceous to the present day (Sukamto 1975; Hamilton 1979; van Leeuwen 1981). Carbonates were deposited throughout much of the Tertiary (Fig. 1.5) and outcrops of limestone cover large areas of South Sulawesi. The Eocene to middle Miocene Tonasa Limestone Formation outcrops over much of western South Sulawesi, whilst the middle Miocene to earliest Pliocene Tacipi Formation outcrops in the eastern part of South Sulawesi (Fig. 1.6). In addition to well-exposed Tertiary carbonates, a range of modem shallow-water carbonate depositional environments can be studied on the Spermonde Shelf, offshore Ujung Pandang or offshore Manado, in North Sulawesi. In essence, South Sulawesi provides a remarkable open air workshop in which to study Tertiary and modem carbonate sediments, depositional environments and large-scale depositional systems.

The Eocene to middle Miocene Tonasa Limestone Formation is up to 1,100 m thick and was deposited as a large syntecto~ic carbonate platform dominated by large benthic foraminifera and in some locations coralline algae. We will be study some of the shallow-water platform deposits, and the effects recent karstification had on these deposits (see Chapter 2). The Tonasa Limestone Formation occurs in the subsurface of the Makassar Straits and the possible hydrocarbon potential of this formation will be assessed.

In comparison, the middle Miocene to earliest Pliocene Tacipi Formation (see Chapter 3) has a maximum thickness of about 300 m and contains abundant coral material. We will have the chance to study knoll reefs of the Tacipi Formation, which form a gas reservoir in the subsurface (Grainge & Davies, 1983; Mayall & Cox, 1988). There will also be the opportunity to examine shallow-water shelf deposits of the Tacipi Formation, and to experience at first hand the types of porosity and permeability development within the Tacipi Formation by exploring one of the cave systems.

Sulawesi (formerly the Celebes) is located along the eastern margin of the stable cratonic area of Sundaland, in the midst of an exceedingly complex tectonic region where three major plates collide (Fig. 1.1). The geological history of Sulawesi is inextricably linked to the successive accretion from the east of oceanic and microcontinental material and to the resultant development of volcanic arcs. Sulawesi is formed of distinct north-south trending tectonic provinces (Fig. 1.7), which are thought to have been sequentially accreted onto Sundaland during the Cretaceous and Tertiary. Western Sulawesi is the eastern margin of Sundaland, the basement promontory protruding southeast from Asia, and is the site of collision with the Australian-derived microcontinents. The north arm is an active magmatic arc resulting from the northward translation of Australian crust. The east and southeast arms of Sulawesi are composed of ophiolitic and microcontinental fragments accreted onto western Sulawesi during the Cenozoic.

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Figure 1 A) Road network in South Sulawesi, and outcrops of Tertiary limestones, showing localities to be visited.

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Figure 1.7) Geology and tectonic provinces of Sulawesi

Western Sulawesi, eastern Kalimantan, the Java Sea and the Makassar Straits experienced widespread early Tertiary extensional basin formation (van de Weerd and Armin, 1992). The transgressive sequences filling these basins are commonly composed of basal non- marine clastics passing upwards into marginal-marine sediments overlain in turn by carbonates and finally deeper marine shales. Proven source rocks are found in deltaic coals associated with the early transgressive sequences. Late Tertiary magmatism and subsequent Pliocene orogenesis has resulted in the formation of multiple kitchen areas within portions of these basins adjacent to structural and stratigraphic traps capable of containing migrating hydrocarbons. Potential reservoirs are found throughout the late Tertiary section, although only Miocene-Pliocene carbonates have proven productive to date in South Sulawesi.

South Sulawesi is dominated by a west-verging Late Miocene to Pliocene collisional orogen in the north and a later (Late Pliocene) major NNW-SSE trending sinistral strike- slip fault system which has produced a pull-apart basin (Walanae Depression) with elevated rift shoulders along its margins (Western and Eastern Divide ranges) (Guritno, et al, 1996).

Outcrops in South Sulawesi occur in three broad highland areas, the two shoulders of the Walanae depression (the Western and Eastern Divide Mountains), and the Latimojong Mountains to the north (Fig. 1.8). The stratigraphies to the west of the Walanae Depression and in the Latimojong Mountains are broadly analogous, but differ considerably from that to the east of the Walanae Depression (Fig. 1.5). Each area is described separately due to differing nomenclature and certain features unique to each area.

Western South Sulawesi

Pre-Tertiary l~thologies in the western part of South Sulawesi are unconformably overlain by deposits of the Eocene Malawa Formation, which consist of non-marine siliciclastics passing transgressively upwards into marginal marine to marine siliciclastics and coals (Fig. 1.9; Sukamto, 1982; Coffield et al., 1993). The thickness of these deposits varies between less than a hundred metres to over a thousand metres (Coffield et al., 1993; Guritno et a]., 1996) and thickness variations are inferred to be controlled by block- faulting (Garrard et al., 1989). These clastics pass transgressively upwards into a shallow marine carbonate succession of the Tonasa Formation, the base of which are early to middle or late Eocene (Wilson, 1995). These carbonates are dominated by large benthic foraminifera and in some places coralline algae; no reefal buildups have been reported (Crotty & Engelhardt, 1993; Wilson, 1995). In the Tonasa and Kalosi areas thick successions of platform carbonates accumulated until the middle Miocene. However, in other areas subsidence, often related to faulting, caused drowning of the shallow marine carbonates and deep marine marls and redeposited carbonates occur (Coffield et al., 1993; Wilson & Bosence, 1995). The carbonate successions are overlain by thick sequences of middle Miocene to Pleistocene bimodal volcanic and volcaniclastic lithoiogies of the Camba and other associated formations (Yuwono et al., 1987; Bergtnan et al., 1996).

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Figure 1.8) Geological map of western central and south Sulawesi (after Sukamto, 1975; Sukamto, 1982; Sukamto & Supriatna, 1982; Djuri & Sudjatmiko, 1974; Coffield et a/, 1993)

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Figure 1.9) Stratigraphy of western and eastern South Suiawesi

This volcanic activity has been related to lithospheric thickening resulting from continent- continent collision between eastern and western Sulawesi (Coffield et al. 1993; Bergman et al. 1996).

Eastern South Sulawesi

In eastern South Sulawesi, lithologies are quite distinct from those to the west (Fig. 1.9) and are dominated by igneous lithologies (Sukamto, 1975). Palaeocene calc-alkaline volcanics of the Langi Formation occur to the east of the Walanae Depression, whereas EoceneIOligocene deposits of the Salo Kalupang Formation outcrop to the east of the Walanae Depression. These volcanics are thought to be the products of a subduction related volcanic arc (Yuwono et al., 1987). Mafic and ultramafic lithologies of the Kalamiseng and equivalent formations have been interpreted as part of an ophiolite sequence which may have been accreted or deformed in the Miocene (Yuwono et a]., 1987; Bergman et al., 1996; Barber & Simanjuntak, 1996). Eocene shallow-marine carbonates outcrop only as a fault-bounded sliver at the eastern margin of the Walanae Depression (Sukamto 1982; Wilson, 1995). Coral rich shallow water carbonates of the middle Miocene to Pliocene Tacipi Formation outcrop along the northern margin of the Bone Mountains (Ascaria, 1997) and comprise subsurface gas reservoirs in the Sengkang Basin (Grainge & Davies, 1983; Mayall & Cox, 1988). These carbonates and other older formations are unconformably overlain by late Miocene to Pliocene volcaniclastics of the Walanae Formation and equivalent, but coarser, units of the 'Celebes Molasse'. Much of this material was derived from erosion of the Latimojong Mountains, which were undergoing uplift and erosion in a compressional regime (Coffield et al., 1993).

Northern South Sulawesi The rocks exposed in the Latimojong area in northern South Sulawesi are analogous to those found in southern South Sulawesi, but the nomenclature is different (Fig. 1.10). Basement is exposed in the eastern hinterland of the orogen and are grouped together in the Latimojong complex. These are a Mesozoic low-grade metamorphic sequence similar to the Late Cretaceous flysch of the Balangbaru and Marada formations of South Sulawesi. West of the basement complex is a thick succession of non-marine clastic rocks belonging to the Toraja Formation. This sequence is analogous to the Malawa Formation to the south. It ranges in age from middle to late Eocene (a basal contact has not yet been identified, so it's lower age may be older), is dominated by red argillaceous claystones which were deposited in fluvial and shallow water lacustrine environments which are interpreted to have developed during a period of extensional tectonics. Today, the section is exposed in a westward-verging hinterland foldbelt in the footwall of the thrust system which has brought the adjacent basement to the surface.

The upper part of the Toraja Formation consists of deltaic and marginal marine deposits, and then passes conformably upwards into shallow marine carbonates. This carbonate platform, known as the Makale Formation, is equivalent to the Tonasa limestones of southern South Sulawesi. Platform, platform margin and basinal facies are present in the section; reefal buildups have not been identified.

STRATIGRAPHY HYDROCARBON POTENTIAL

RESERVOIRS SOURCE ROCK

HYDROCARBON INDICATIONS

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Figure 1 .I 0) Stratigraphy of the Kalosi Area (northern South Sulawesi)

A volcano-plutonic complex was established during the middle to late Miocene throughout South Sulawesi, with the peak in magmatism occumng 5 - 10 mya (Bergman et al., 1996). It is informally referred to in this region as the Enrekang Volcanic Series and is equivalent to the Camba Volcanics of southern South Sulawesi. The rocks were deposited in both submarine and subaerial environments. Igneous intrusive and extrusive rocks are not common, with a few notable exceptions including the Mamasa granite, a vast granitic melt that has been uplifted to the surface in the foreland of the Latimojong orogen. The bulk of the outcrop in the foreland foldbelt of the Latimojong orogen belong to the Enrekang Volcanic Series.

Towards the end of the Miocene, compression and uplift resulted in regional subaerial exposure and erosion of the orogen. Initial deposition around the margins was carbonate dominated and included reefal buildups which were laterally extensive but of limited vertical relief. These carbonates belong to Tacipi Formation, the same as the more extensive section to the south in the Sengkang basin. Carbonate sedimentation rapidly gave way to a coarsening upwards section of siliciclastics belonging to the Walanae formation. These rocks, initially dominated by calcareous mudstones but coarsening upwards to cobble conglomerates, record the unroofing of the adjacent orogen. Sediments analogous to the Walanae Formation are being deposited today around the margins of the mountains and adjacent coastal waters, with the continuing active uplift of the Latimojong mountains.

Three petroleum systems have been identified in South Sulawesi: the Eocene (.) petroleum system of the Karamar iang Basin, the Toraja (.) petroleum system of the Kalosi foldbelt, and the Malawa-Tacipi (!) petroleum system of the Sengkang Basin (Figs. 1.3 & 1.1 1). All three of these petroleum systems contain essentially the same elements and are distinguished from one another primarily by their independent kitchen areas. These petroleum systems contain the following elements (nomenclature and terminology for the described petroleum systems follow that of Magoon and Dow, 1994) :

Source - Coals and carbonaceous shales of the Eocene MalawaIToraja Formation provide potential source lithologies. The rocks contain type WIII terrestrially influenced kerogens, and have TOC values in the range of 3 1 - 81% and HI values ranging from 158 to 578. Mature oils from seeps in the Kalosi area have been typed to these Eocene source rocks.

Reservoir - Potential reservoir lithologies occur in the Eocene clastics and in overlying Tertiary carbonates. The best potential siliciclastic reservoirs are marine shoreface sandstones, with a low lithic content and 20-25% porosities and moderate permeabilities, which occur towards the top of the Malawnoraja Formations. Platform carbonates of the TonasaIMakale Formations are usually characterised by little primary or secondary porosity and low permeabilities. Redeposited facies, abutting faulted footwall

highs, contain low to moderate porosities and permeabilities and are thought to comprise the most suitable lithologies for hydrocarbon reservoirs within these formations and indeed traces of hydrocarbons do occur (Wilson, 1996). Proven thermogenic gas reservoirs are present in subsurface Miocene knoll reefs of the Tacipi Formation in the Sengkang Basin (Grainge & Davies, 1983; Mayall & Cox, 1988; Ascaria, 1997).

Conduits - Eocene deltaic sands associated with the coaly horizons are one of the primary inferred conduits for the migration of hydrocarbons. To fill potential clastic reservoirs in the Eocene section, neither fault nor cross stratal migration is required for the system to work. Faults are another possible migration pathway for hydrocarbons and outcrop examples of both oil and gas seeps along fault planes are present in the Kalosi area.

Seal - Tight clays and silts of the Walanae Formation, often rich in volcanicalstic components, comprise seal lithologies and are proven effective in the Sengkang Basin. Platform carbonates of the TonasaIMakale Formations are a potential seal for reservoirs in the underlying Eocene clastic succession.

Trap - Isolated coral rich carbonate knoll reefs comprise proven stratigraphic traps for gas accumulation in the Sengkang Basin. Compressional anticlinal traps, with four-way dip closures, are inferred in the Kalosi area where there are examples of breached anticlines with oil seeps along their crestal axes.

Timing - Known pre - Late Miocene stratigraphic thicknesses are inadequate to depress the identified source rocks into the oil window in many parts of South Sulawesi. However, in areas where Tertiary deep marine basins formed and thicker sedimentary successions accumulated, such as the Walanae Depression, source rocks are inferred to have been depressed into the oil window. Hydrocarbons were only generated in other regions possibly following Miocene magmatism and certainly during Pliocene orogenesis and thrust loading.

Aims: To provide an introduction to the geology of South Sulawesi. To understand how the different stratigraphic successions in eastern and western

South Sulawesi affect the hydrocarbon potential of the region. To study source rocks, conduits and potential reservoir rocks in the Eocene

Malawa Formation (equivalent to the Toraja Formation). To assess the role of the Eocene to middle Miocene Tonasa Limestone Formation

(equivalent to the Makale Formation) in the petroleum systems of South Sulawesi. To discuss the nature of the Walanae Depression and its influence on the

stratigraphy and petroleum system of South Sulawesi.

Introduction

During the first day of the fieldtrip we will drive east from the airport at Ujung Pandang crossing the Western Divide Mountains, the Walanae Depression and the Eastern Divide Mountains (Bone Mountains), and arrive at Watampone where we will spend the night (Fig. 1.6). On route stops will be made to study the study the stratigraphic succession in western and eastern South Sulawesi (Figs. 1.5 and 1.9); notably the Eocene coals and clastics of the Malawa Formation and the Eocene to middle Miocene and middle Miocene to earliest Pliocene carbonates of the Tonasa Limestone and Tacipi Formations respectively. We will drive through some areas of stunning scenery and there will be viewpoint stops to review the geology and structure of South Sulawesi and to access how this affects the relevant petroleum systems.

Stop 1-1) Carbonates of the Tonasa Limestone Formation: Reservoirs or Seals?

The Tonasa Limestone Formation is Eocene to middle Miocene in age and was deposited as a large scale syntectonic carbonate platform with a faulted northern margin, a gently sloping ramp type southern margin (Fig. 2.1) and areas of more complex faulting to the east and west. The platform top succession is up to 600 m thick and lithologies were dominated by large benthic foraminifera (Fig. 2.2) and in some areas coralline algae. Coral debris is rare and extensive reefal buildups have not been identified (Fig. 2.1). Depositional environments varied across the platform top from localised areas of subaerial emergence and restriction to low and high energy depositional environment with different water depths (Fig. 2.1). The resultant platform top lithologies are wackestones, packstones and packlgrainstones (Fig. 2.2).

The lack of abundant aragonitic bioclasts, from corals or green algae, together with only localised subaerial exposure, result in little porosity and permeability development in

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Fig 2.2) Larger benthic foraminifera packstone from the Tonasa Formation. Horiz. scale 5 cm

Fig 2.3) Karstic top0 raphy from the shallow-water B platform area of the onasa Formation

shallow water deposits of the Tonasa Limestone Formation. Primary porosity in high- energy grainstone units, which occur in an E-W trending facies belt in the central part of the platform, has been occluded by equant sparry calcite, probably during burial under a thick volcaniclastic pile. However, it may be that in similar deposits, which have not been affected by adverse pore occluding diagenetic processes, primary porosity may be preserved in high-energy units. In comparison, redeposited carbonate facies of the Tonasa Limestone Formation, derived from block faulted footwall areas may be both porous and permeable. This porosity and permeability is due to circum-granular stylolites and some preserved primary intergranular porosity. Although concentrations of argillaceous material around clasts in some beds may lead to reduced permeability, redeposited facies, abutting impermeable basement and platform lithologies, are thought to form the most suitable hydrocarbon reservoir within the Tonasa Limestone Formation and indeed traces of hydrocarbons do occur. Overlying marine clays may form effective seals with underlying coal deposits providing a potential source (cf. Phillips, et al., 1991; Coffield, et al., 1993).

Stop 1-2) Seismic scale geometries of the Tonasa Carbonate Platform

This stop is to view the extensive karstic outcrops of the shallow water platform deposits of the Tonasa Carbonate Platform (Fig. 2.3). These deposits were initially deposited as a well-bedded and laterally continuous platform sequence, with little depositional relief on the platform top. Uplift and subsequent karstification has resulted in the tower karst morphology seen today.

How would these outcrops appear on seismic?

Stop 1.3) Bantimurung - karstic outcrops The aims here are to view where an underground river emerges from the base of the karstic outcrops of the Tonasa Limestone Formation and to discass possible reasons for this. The implications this supply of water has for the surrounding populations and for hydrocarbon exploration is assessed. This is an area of great natural beauty, which the Indonesians have turned into a national park and no hammering is allowed. Alfred Russel Wallace spent a while here in 1847, marveling over the scenery and collecting organisms, of which butterflies were extremely abundant, unusual and beautiful. The National park at Bantimurung, and especially the waterfall, is a popular tourist attraction.

Subterranean water rises to the surface at a number of locations along the margins of the karsts of the Tonasa Limestone Formation providing a perennial supply of water (Uhlig, 1980). Villages are preferentially sited along the lines of these karstic springs (Uhlig, 1980). The spring water is channelled into imgation systems and provides sufficient water for two crops per year, rather than the more usual single annual crop in most of western South Sulawesi (Uhlig, 1980). Underground rivers may rise to the surface when they hit impermeable rock layers. This has occurred at Bantimurung where an upderground river emerges along the plane of an impermeable diorite sill (which can be clearly seen on the drive over the Western Divide Mountains towards Watarnpone) and then cascades down the eroded face of this sill. We will be able to see the waterfall at

Bantimurung, but it will not be possible to view the upstream emergence of the underground river, as this occurs some distance away. Below the waterfall at Bantimurung the river has been impounded by a weir and then channeled via concrete

canals to irrigate an area of more than 70 km2 in extent, which is capable of bearing two rice crops every year (Uhlig, 1980). Although karstic water is utilised in South Sulawesi, an improved water supply could be achieved by suitably positioned wells and the construction of cisterns (Uhlig, 1980).

What is the nature of the carbonate outcrops in this area and is this a primary or

secondary feature?

How would these outcrops appear on seismic?

What is the porosity and permeability development of these lithologies and what

factors have affected the poroperm?

Evaluate the hydrocarbon potential of this area

Stop 1-4) Padaelo and Uludaya Quam'es: Source, Reservoir and Conduits of the Eocene elastics

Here we will see the source rocks, carrier beds and potential reservoir rocks of the middle Eocene marginal marine and deltaic section of the upper portion of the Malawa Formation, as well as the potential reservoir rocks of the conformably overlying Eocene- Miocene platform carbonates belonging to the Tonasa Formation. The full stratigraphic succession of the Malawa is not exposed here (Fig. 2.4), but from this locality and others, together with borehole data we know that the succession is a trangressive one passing upwards from terrestrial to marginal marine deposits. Several distinct lithofacies can be observed here - deltaic coals and point bars, prodelta mudstones, organic rich estuarine sands, interdistributary shallow water coquina beds, and the conformabley overlying carbonate platform (Garrard et al., 1989, Crotty and Englehardt, 1993; M. Evans, pers. corn.). The following descriptions of the localities come from Garrard et al., 1989.

The Padaelo quarries expose sandstones of the upper Malawa Formation in two quarries, one above the other on a hillside. The sequence between the two quarries is believed to be continuous. The conformably overlying upper Eocene Tonasa Formation limestones cap the hills to the east and south.

The lower quarry contains a section 5-7 m thick of friable, yellowish brown to grey sandstone which dips slightly to the east. A thin (0.5 m) grey fossiliferous claystone bed is located near the top of the exposure. The sands are predominantly faintly planar to inclined planar bedded to rarely cross-bedded, fine grained, extremely well sorted, with rare burrows and occasional large concretions. Reworked smaller concretions are concentrated along some horizons. Pelecypod moulds are common. Intergranular porosity is up to 20%.

Petrography reveals the sands are dominated by subangular, volcanic-derived quartz with minor plagioclase, chert (silicified volcanics), rare mica and frequent heavy minerals (zircon, magnetite). The Malawa sandstones at this stop are barren of calcareous fossils, but are interpreted to have been deposited in a high energy transitional marine setting probably as beach foreshore to upper shoreface sandstones.

The upper quarry exposure consists of 3 to 5 m of yellowish grey to light grey frinable sandstone nearly identical to the lower quarry. This is overlain by 1.5 m of well cemented reddish brown sandy limestone which represents the contact between the Malawa and the Tonasa formations. Unlike the lower quany, the sandstones here have extensive preserved bioturbated intervals which may indicate deepening into a lower shoreface environment. Calcite and fossil content increases gradually upwards towards the limestone contact.

The overlying limestone is faintly cross-bedded, mostly fine-grained, sandy bioclastic packstonelgrainstone which was deposited in a high energy shallow marine environment, possibly as a shoal or skeletal beach. Fossil identification is hampered by heavy fragmentation. Recognizable fossils include pelecypods, gastropods and large benthic forams. In addition to rare planktonics, intraclasts, miliolids and ostracods are present. All porosity is filled by calcite cement.

Coal has been mined 5 km to the northwest at Uludaya. These coals are part of a deltaic section. Coals from the Malawa Formation that have been sampled generally show good to excellent oil and gas generating potential (Garrard et al., 1992; Coffield et al., 1993). TOC values typically range from 50.0 to 57 wt%, HI values range from 250 to 500, and pyrolysis yields of 150 to 300 mglgm, indicating good to excellent oil generating potential for this immature (Ro of 0.25-0.42) section. This data is consistent with results seen for oil prone coals elsewhere in Western Indonesia (Robinson, 1987).

Stop 1-5) The Walanae Depression and geology of eastern and western South Sulawesi

We have just driven across the Western Divide Mountains and the Walanae Depression and have stopped at the edge of the Bone Mountains. This stop allows views across these areas and is an ideal location to discuss the geology of South Sulawesi. The stratigraphy in western and eastern South Sulawesi differ considerably (Figs. 1.8 & 1.9) and only Mio- Pliocene deposits are exposed in the Walanae Depression, which separates these two regions. In western South Sulawesi the Tertiary deposits comprise a transgressive sequence of terrestrial to marginal marine clastics and coals of the Malawa Formation overlain by Eocene to middle Miocene shallow marine carbonates of the Tonasa Formation. The carbonates are in turn overlain by a thick pile of Mio-Pliocene volcaniclastics which form much of the high ground in the Western Divide Mountains. In comparison, in eastern South Sulawcsi the dominant Eocene and Oligocene lithologies are volcanics and volcaniclastics, and younger Mio-Pliocme carbonates of the Tacipi

Formation also occur. The different stratigraphy and histories of western and eastern South Sulawesi has implications for the petroleum systems in these regions.

The Walanae Depression is a present day N-S trending strike-slip system, bounded by the East and West Walanae Fault Zones (Berry and Grady, 1987). Seismic and field relationships suggest significant normal displacements along the margins of the depression. These data also suggest that the strike-slip regime was not active until the Pliocene (Grainge & Davies, 1983). Shallow-water middle to late Miocene reefal carbonates of the Tacipi Formation trend N-S along the margins of the Walanae Depression. These shallow-marine carbonates also step down towards the Walanae Depression. -Within the Walanae Depression, redeposited carbonate facies containing abundant clasts of shallow-water material and clasts from the underlying formations are interbedded with planktonic foraminifera packstones of the Tacipi Formation and clastic lithologies of the Walanae Formation.

DAY 2) GAS RESERVOIRS IN MIOCENE BUILDUPS OF THE TACIPI FORMATION

Aims: To study in detail Miocene outcrops of knoll reefs of the Tacipi Formation as an

analogue to subsurface reservoirs in the Sengkang Basin. To examine porosity and permeability of the Tacipi Formation. To analysis fine grained tuffaceous lithologies of the Pliocene Walanae Formation

which have proven effective seals for the subsurface reservoirs. To evaluate factors that resulted in the economically viable Malawa-Tacipi

petroleum system. Energy Equity Ltd. is producing gas from subsurface knoll reefs of the Tacipi Formation in the Sengkang area.

We will drive north from Watampone, stopping at Tamapole and Bulo Mampu (Figure 4.1) to study lithologies of the Walanae and Tacipi Formations which comprise the seal and reservoir rocks respectively in the subsurface to the north. The stop at Bulu Mampu will last a few hours as we walk to the top of the hill and there is also the opportunity to study macroporosity in the cave system below the hill. From Bulu Mampu we drive north to Sengkang and visit the active gas seeps from carbonate buildups. The last stop of the day involves a 'twilight' paddle on Lake Tempe to investigate a modem lacustrine depositional environment sometimes cited as a modem analogue for lacustrine source rock deposition.

Stop 2-1) Seal lithologies: Tuffaceous siltstones cf the Walanae Formation at Tamapole

The contact between late Miocene carbonates of the Tacipi Formation and Pliocene fine- grained volcaniclastics of the Walanae Formation can be studied at this location. Tamapole hill is composed of shallow-water carbonates, rich in coral and algal debris, which formed in the rniddle-upper Miocene as a shallow water knoll reef surrounded by deeper water. There will be the opportunity at the next stop to study the facies of these shallow water knoll reefs in considerable detail. During the Pliocene fine-grained volcaniclastic deposits of the Walanae Formation were deposited over and around the Miocene knoll reef deposits (Figure 4.2). It is these volcaniclastic deposits which have proven effective seals in the subsurface capping reservoirs in the Miocene carbonates. In some localities, as here, unconformable and onlapping relationships are seen, whilst in other localities interdigitating relationships have been observed between the two formations.

At this location the Walanae Formation is composed of cream to pale grey, fine to medium grained tuffaceous sandstones. The lithologies are well-bedded on a centimetre

FIGURE 4.1) Map showing the location of exposed knoll reefs and sections to be visited

Bulu Sinri

Coral framestone

@ Porites coral framestone

Bioclastic packstone

Coralgal bioclastic rudstone

Marl containing abundant planktonic toraminl(srs (Walanae Formation)

Tuffaceow sandstone (Walanae FaMlion)

sf& \ Number line -**

50 rn 0 m

c Tacipi Formation \ 1 Walanae -I Formation

No scale Intended

FIGURE 4.2) Diagrams showing the relationship between the Tacipi and Walanae Formations. A: Cross section and facies map of Bulo Sinri area showing the Walanae Formation interdigitating with the Tacipi Formation in the lower part and onlapping on the upper part. 6: A cartoon showing interdigitating relationship between the Tacipi Formation and the Walanae Formation in the Bulo Kading section.

to decimetre scale, and beds often have erosive bases, fine-upwards and contain Ta, Tb and Tc intervals of the Bouma sequence. Small scale slumping and dewatering structures can also be seen in some beds. X-Ray diffraction analysis of the fine grained fraction of these sandstones revealed the presence of zeolites, micas, mixed layer smectite-micas and smectite-chlorites, kaolinite, quartz and calcite. The zeolites, mixed layer clays, and some of the quartz are probably the products of break-down of some of the volcaniclastic material. These impermeable lithologies of the Walanae Formation are inferred to have been deposited as distal volcaniclastic turbidites in a marine setting.

Stop 2-2) Miocene knoll reefs of the Tacipi Formation at Bulu Mampu: reservoir units and stratigraphic trap

Bulu Mampu is one of a number of hills (Figure 4.4) composed of shallow water carbonates of the Tacipi Formation, which formed as isolated knoll reefs with depositional relief in the middle to late Miocene (Figure 4.3). The knoll reefs comprise stratigraphic traps for hydrocarbon in the subsurface of the Sengkang Basin to the north. Many of the knoll reefs have a north-south trend (Figure 4.1) and probably developed on slight basement highs, the location of which were controlled by pre-existing structures. These shallow water buildups are dominated by coral and coralline algal debris, and other shallow water bioclasts such as foraminifera, Halimeda and echinoid material. Shallow water facies vary from coralgal framestones and bioclastic packstonesl floatstonesl rudstones, benthic foraminifera bioclastic wacke/packstones to bioclastic packstones (Figure 4.5). During deposition these isolated knoll reefs were surrounded by deeper water, where lithologies containing abundant planktonic foraminifera were deposited. Shallow water material was reworked from the margins of the knoll reefs, and rudstones and floatstones interdigitate with lithologies rich in planktonic foraminifera on the slopes of the knoll reefs.

At this location we will walk up the exposed knoll reef at Bulu Mampu studying lithological changes up section (Figure 4.6) and discussing the reservoir quality of the different units. As well as studying poroperm development in hand specimens, there will be the opportunity to study macroporosity in the cave systems underneath Bulu Mampu. Slope deposits of coral rudstones and floatstones are interbedded with deeper water planktonic foraminifera wackelpackstones at the base of the section. A range of shallow water facies can be studied up section and at the top of the hill coral framestones can be seen. Porosity varies from intergranular, biomouldic porosity after the dissolution of aragonitic bioclasts (Figure 4.5) to large scale caverns. The best poroperm characteristics for reservoirs occur in fractured packstones or rudstones with well developed interlinked biomouldic porosity.

Stop 2-3) Active gas seeps

Immediately outside Sengkang, there are several gas seeps bubbling up through Holocene muds near the crest of the Sengkang anticline (Fig. 4.7). This antic!in~ is a transpressional structure on the margin of the kitchen beneath the Walanae trough to the

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Figure 4.5) Well developed interconnected secondary biomouldic porosity (brown areas) after leaching of aragonitic bioclasts. Horiz. scale 3 cm

EAST SENGKANG BASIN

Northern limit &I

Figure 4.7) Location of the Tacipi gas reservoirs relative to outcrops of the Tacipi Formation (modified from Grainge & Davies, 1985)

Gasseep 6 Maximum mapped

closure

Proven gas 9 I outcrop $

west, and the reservoirs in the Sengkang basin to the east (Fig. 4.8). Wet gases sampled from the Tacipi limestone are of thermogenic origin. Analyses of the gas indicates the presence of Cl-C5+ hydrocarbons. The gas composition and the iC4InC4 ratio is in the typical range for a thermogenic gas generated in the oil window. This has been substantiated with carbon isotope data. These gases are assumed to be generated from cnals and coaly shales of the Eocene Malawa formation, which is supported by the carbon isotope data.

Buildups of the Tacipi Formation form gas reservoirs in the subsurface BP discovered four separate accumulations of dry gas, totalling about 0.75 TCF in late Miocene knoll reefs of the Tacipi Formation in the Sengkang Basin (Figure 4.9, Grainge & Davies, 1983). Energy Equity Corporation is now producing gas from Karnpung Baru, the largest field which contains almost half the total reserve (Grainge & Davies, 1983). The gas treatment plant, at the KB-2 well location, will be visited.

Isolated Miocene shallow water knoll reefs of the Tacipi Formation comprise the reservoir units in the subsurface and are analogous, in terms of facies and morphology (Figure 4.9), to those outcropping at the surface along the northern margin of the Bone Mountains and studied at Bulu Mampu. Fine grained volcaniclastics of the Walanae Formation (as seen at Tamapole) unconformably overlie knoll reefs of the Tacipi Formation (Ascaria et al., 1997) and form the seals to reservoirs (Grainge & Davies, 1983). Higher rates of subsidence occurred in the northern part of the East Sengkang Basin than compared with the south, probably as a result of thrust loading in the Latimojong Mountains area. This caused the more northerly knoll reefs to be drowned and covered by volcaniclastics in the late Miocene, prior to those in the south (early Pliocene drowning; Ascaria et al., 1997). The time of sealing and migration of hydrocarbons is critical, since knoll reefs which were drowned in the late Miocene to Pliocene are not full to spill.

No potential hydrocarbon source rocks have been reported in eastern South Sulawesi. The gas in the East Sengkang Basin is of thermogenic origin and knoll reefs moving eastwards and away from the Walanae Depression contain progressively less gas and the gas becomes drier, which may indicate fractionation during migration (Grainge & Davies, 1983). The most likely source of this gas is from Eocene coals to the west, which are now deeply buried in the Walanae Depression (West Sengkang Basin). The Walanae Fault zone is thought to have formed the conduit for the migrating hydrocarbons (Grainge & Davies, 1983).

Stop 2-4) Modern lacustrine depositional environment: hydrocarbon source of the future?

Time permitting, we will rent canoes for an evening run across Lake Tempe. The lake is a shallow lake located over the deepest portions of the Walanae Depression (Fig. 1.8). The lake is the focus of drainage from the northern Western Divide Mountains and Bone Mountains to the south, and the southern margin of the Latimojong Mountains to the

north. Its position suggests the underlying graben is still subsiding, either tectonically or due to sediment compaction. In the rainy season, the lake spills and flows southeast to the Walanae River and onwards to Bone Bay.

The lake is heavily vegetated and the waters are very organic rich, as are the lake bottom muds (as you will discover if to your misfortune should you fall in). Lake Tempe is frequently cited as a modem example of a lacustrine depositional system for source rocks although no formal studies have documented this. Numerous studies (cf. Fleet et al., 1988; Katz, 1990) would suggest this is not the case here due to the very shallow water column, annual mixing of the waters, well aeriated and normal chemistry waters, and relatively low sediment influx, all of which preclude the preservation of organic matter. The shallow water allows oxidation and bioturbation of the organic rich material, allowing little to be preserved as would be the case in a deep or very rapidly subsiding basin where anoxic conditions could develop, or in a hyper-saline environment which would also limit bioturbation and reduction of organic matter.

CONCLUSIONS FROM NORTHERN OUTCROPS OF THE TACIPI FORMATION

Shallow-water, coral-dominated knoll reefs were surrounded by deeper-water

deposits.

Shallow-water knoll reefs built up from deeper-water areas, but the reasons for

there locations is unclear.

There was a great variety of organisms and depositional environments on the

knoll reefs

The porosity is mostly biomouldic after the dissolution of aragonitic bioclasts,

such as corals. There has also been some fracturing enhancing porosity and

permeability.

The reef knolls shallow upwards and were able to catch up and keep up with the

relative rise in sea level.

DAY 3) STRUCTURAL EVOLUTION, STRATIGRAPHY AND PETROLEUM SYSTEMS OF NW SOUTH SULAWESI

Aims: To view the gross geometry of the Latimojong orogen, a mountain range formed

by the collision of the Sundaland margin with Indo-Australian micro-continents. To examine synorogenic sediments of the Pliocene Walanae Formation, which

record the unroofing of the adjacent mountain range. To examine a breached anticline with oil seeps emanating from Eocene

sandstones in its core. To examine the fluvial and deltaic section of the Eocene Toraja Formation. To summarize factors that have resulted in the generation, migration and

entrapment (and subsequent exposure) of hydrocarbons in this foldbelt.

Introduction

Stop 3-1) Distal Synorogenic Walanae Formation and overview of the Latimojong Orogen

The road from the plains of the Sengkang Basin into the highlands of Tana Toraja passes initially through hilly country which is the product of uplift and folding of the adjacent orogen. The first stop will be on the flank of a syncline where fine-grained, marine sediments of the Pliocene Walanae formation are exposed on the limb of a syncline forming beneath the first emergent thrust sheets of the Latimojong orogen (Fig. 5.1). In the distance, limestones of the Tacipi Formation can be seen on the top a thrust sheet which has over-ridden the younger Walanae formation.

Stop 3-2) Proximal Synorogenic Walanae Formation and overview of the Latimojong Orogen

Roadcuts through the hills near Enrekang contain spectacular outcrops of conglomerates belonging to the Pliocene Walanae Formation. These record the erosion and unroofing of the Latimojong orogen to the north, with clasts containing lithologies of the entire underlying section, from basement through the Eocene elastics, Oligo-Miocene carbonates and Late Miocene volcanics. These rocks were deposited in fan-deltas and have been subsequently incorporated in the folding and thrusting associated with the growing orogen.

Stop 3-3) Coffee stop to view large scale folding, Mataalo River

Figure 5.1 ) Geological map of the Kalosi area with fieldtrip stops indicated (after Coffield et al, 1993)

After climbing steeply up and over the leading emergent thrust sheets of the Kalosi foldbelt, a brief stop will be made to view a large (kilometer scale), tight syncline formed in the foot-wall of a thrust fault which brings the Eocene fluvial-deltaic section of the Toraja Formation to the surface (Figs. 5.2 and 5.3). The rocks in the foreground (footwall) belong to the younger Miocene Enrekang volcanic series. The high peaks to the northwest are in the footwall of the thrust sheet forming the syncline and expose the Oligo-Miocene carbonates of the Makale Formation.

Stop 3-4) Gate to Tana Toraja, Deltaic and Estuarine facies of the Toraja Formation

The highway traversing the highlands of Tana Toraja between the towns of Kalosi and Makale provides many roadcuts which expose outcrops of the early to middle Eocene fluvial section and the overlying middle to late Eocene deltaic section of the Toraja Formation. The area is located in the Kalosi foldbelt, a hinterland foldbelt that has been extensively folded and faulted. If the skies are clear, basement can be seen to the east, forming the highest mountains in Sulawesi (3,440 m at Gunung Rantemario). These basement rocks expose the Mesozoic margin of Sundaland.

The outcrops around the gates to Tana Toraja expose deltaic and estuarine facies of the upper Toraja Formation (Figs. 5.4). The sequence comprises sub-vertical beds of calcareopus sandstones, sandy limestones and siltstones. Sandstone and limestone units are up to 2 m thick and rich in shelly mollusc detritus. Carbonaceous detritus is abundant in these lithologies and in the siltstones. Sedimentary structures are limited to parallel bedding and lamination.

The quartz sand and carbonate sand units are interpreted to represent molluscan banks deposited in shallow but quiet waters, possibly in an estuarine setting contaminated periodically by river-borne sands. A marine influence is indicated by the presence of rare foraminifera fragments.

Stop 3-5) Fluviul facies of the lower Toraja Formation

A well exposed cliff 13 m high exposes a fluvial sandstones encased within red mudstones of the lower Toraja Formation (Fig. 5.5). The sandstones are coarse grained, pebbly, lithic arenites. Sandstone components are dominantly quartz, chert and mudstone rip-up clasts, grains are sub-angular and sorting is moderate to poor. Sandstone units contain coarse conglomeratic basal lag deposits, and trough and planar cross-bedding. The most distinctive sand body is 2-3 m thick, has a sharp erosive base, a very coarse grained basal lag and a lenticular shape. The concave upward shape of the upper part of the sandstone unit may be an erosional feature prior to deposition of the overlying beds. The sandstone is interpreted as a channel point bar deposit with red siltstones forming overbank deposits within a shale-dominated floodplain succession.

Figure 5.2) Simplified geology map of the central Kalosi foldbelt with fieldtrip stops indicated

Figure 5.3) Petroleum system of the Kalosi area

I*", *LO-.. D M . Po-<- - n ' Y f I Y 7-0 l o . 1 Y O m

-(r) t r .wn;] nu. 1-

Figure 5.4) Upper Toraja Formation log through deltaiclestuarine sequence, gateway to Tana Toraja (Chamberlain et al., 1994)

~~~~~ LITHOLOGY, TEXTURE. FOSSILS. BASE SED. STRUCTURE

.- . -. - . - . - . - . - . - Om- - . - . -

CLAY AN0 SILT SAND GRAVEL

- - -

DESCRIPTION

irrlcfco~o:eo led s.llslones cnc !in@ tr. :oafre glz:ned Ltlh~c. cucm rondsloner ;o~ulof onu : fou~h crou beddlng

,%leaium lo coofre groineo I i l h ~ ~ sonarloner, hougn crou Deddlng

Sample [-I

Red sillsfones nroswe. Clockv 1ex:ute

INTERPRETATION

Flwio~ . Point Bar Geomeher

Pomt Bor

Chonnel

Figure 5.5) Logged section through fluvial deposits of the Toraja Formation (Chamberlain et al., 1994)

Stop 4-6) Ketu Kesu

A final stop will be made at Ketu Kesu where both a traditional Tana Toraja village has been preserved, as well as a spectacular example of cliff burial graveyard. The caves within the karst cliffs formed by the Oligo-Miocene Makale formation are used throughout Tana Toraja as burial chambers, with effigies of those who have passed away sitting at the cave entrances. Time permitting, we will also drive into Rantepeo, the capital of Tana Toraja, for some souvenir shopping.

PACE FOR NOTES AND SKETCHES

REFERENCES

Ascaria. N.A. 1997. Carbonate facies development and sedimentary evolution of the Miocene Tacipi Formation, South Sulawesi, Indonesia. Ph.D. Thesis, University of London, 397p.

Ascaria. N.A., N.A. Harbury & M.E.J. Wilson, 1997. Hydrocarbon Potential and development of Miocene knoll-reefs. South Sulawesi. this volume.

Barber, A.J. & Simandjuntak, T.O. 1996. Report on geological fieldwork in South Sulawesi, August - September, 1996. University of London Geological Research in Southeast Asia. Internal Report, 154.

Bergman. S.C., Coffield, D.Q., Talbot, J.P. & Garrard, R.A. 1996. Tertiary Tectonic and magmatic evolution of western Sulawesi and the Makassar Strait: evidence for a Miocene continent-continent collision. In: Hall. R. & Blundell, D.J. (eds.), Tectonic evolution of SE Asia. Geological Society of London Special Publication 106, 39 1-429.

Coffield. D.Q., Bergman, S.C., Garrard, R.A., Guritno, N., Robinson, N.M. & Talbot, J. 1993. Tectonic and stratigraphic evolution of the Kalosi PSC area and associated development of a Tertiary petroleum system, south Sulawesi, Indonesia. Proceedings of the Indonesian Petroleum Association, 22nd Annual Convention, October, 679-706.

Crotty, K.J. & Engelhardt, D.W. 1993. Larger foraminifera and palynomorphs of the upper Malawa and lower Tonasa Formations, southwestern Sulawesi Island. Indonesia. Thanasuthipitak. T. (ed.) Symposium on biostratigraphy of mainland Southeast Asia: Facies & Paleontology. 31 January - 5 February, Chiang Mai, Thailand, 7 1-82.

Djuri, M. & Sudjatmiko 1974. Geologic map of the Majene and western part of the Palopo quadrangles, South Sulawesi. (Quadrangles 171X - 1818) Scale 1:250,000. Geological Survey of Indonesia, Directorate of Mineral Resources, Geological Research and Development Centre, Bandung.

Fleet, A. J., Kelts, K., and Talbot, M. R., 1988, Lacustrine Petroleum Source Rocks: Geological Society Special Publication, No. 40, 391 p.

Garrard, R. A., Guritno, N., and Coffield. D. Q.. 1992. The prospectivity of Early Tertiary rift sequences in the Neogene foldbelts of South Sulawesi: Eastern Indonesian Exploration Symposium, Jakarta, 6 p.

Garrard. R.A., Silalahi, D., Schiller, D. & Mahodim, P. 1989. Sengkang Basin, South Sulawesi. Indonesian Petroleum Association Post Convention Field Trip, 47 p.

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, 6 p.

Grainge, A.M. & Davies, K.G. 1983. Reef exploration in the east Sengkang basin, Sulawesi, Indonesia. Proceedings of the Indonesian Petroleum Association. 12th Annual Convention, June, 207-227.

Guiitno, N., Coffield, D.Q. & Cook, R.A. 1996. Structural development of the Central South Sulawesi. Proceedings of the Indonesian Petroleum Association. 25th Annual Convention, October, 253-266.

Hamilton, W. 1979. Tectonics of the Indonesian region. United States Geological Survey Professional Paper, 1078.

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