© IPA, 2006 - Proceedings of an International Conference on Petroleum Systems ofSE Asia and Australasia, 1997

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East of the Walanae Deprdssion the Tertiary succession is mostly dominated by volcanic and volcaniclastic lithologies of the Langi, Salo Kalupang, Kalamiseng and Camba Formations (Fig. 2a, Sukamto, 1982; van Leeuwen, 1981; Yuwono et al. 1985, see Wilson et al., this volume). Carbonates of the Tacipi Formation (or Bone Formation, seen in wells in the East Sengkang Basin) unconformably overlie altered volcanic lithologies, probably of the Langi Formation (Fig. 2b; Grainge & Davies, 1985). The Tacipi Formation is overlain by volcaniclastics of the Walanae Formation. Interfingering, conformable and localised unconformable relationships are all seen at the contact betmeen these formations.

The Tertiary stratigraphic succession to the west of the Walanae Depression consists of Paleocene-Eocene volcanics of the Langi Formation and marginal marine siliciclastics, shales and coals of the Eocene Malawa Formation. These coals are the most likely source of hydrocarbons in reservoirs of the Tacipi Formation in the East Sengkang Basin (Wilson et al., this volume). These formations are overlain by a thick succession of Eocene to Miocene carbonates of the Tonasa Limestone Formation, and Mio-Plio.cene volcanics and volcaniclastics (see Wilson et al., this volume). Deposits of the Tacipi and Walanae Formations are only locally present along the eastern margin of the Walanae Depression (Fig. 1).

The study of the Tacipi Formation has involved detailed facies mapping, logging, petrography and an interpretation of seismic data. On the basis of this work, and using geomorphological comparisons, outcrops of the Tacipi Formation have been subdivided into three areas: Northern, Southern and Western Bone Regions (Fig. 3). Outcrops of the Southern Bone region border the northern margin of the Bone Mountains and consist of middle Miocene shallow water carbonates deposited in a shelfal setting. Normal faulting and the formation of an active graben system resulted in segmentation of the platform in the Southern Bone Region in late Miocene times and the contemporaneous development of shallowing- and deepening-upward sequences. The Western Bone region lies *to the west of Bone Mountains and is characterised by the occurrence of redeposited facies containing reworked upper Cretaceous sandstones, Tertiary volcanics, Miocene carbonate clasts and unlithified bioclasts.

The Northern Bone Region consists of the most northerly outcrops of the Tacipi Formation and these form the main focus of this paper (Fig. 3). This area was characterised by the development of isolated knoll-reefs surrounded by deeper-water facies (Fig. 4a). In the subsurface to the north of Northern Bone Region the lower part of the middle to late Miocene Tacipi Formation consists of interbedded limestones and calcareous mudstones (Grainge & Davies, 1985). Buildups composed of shallow water carbonates formed in localised areas and comprise the upper part of the section (Grainge & Davies, 1985). The shallow water facies consist mainly of bioclastic packstones with subordinate grainstone units. Parts of the cored interval are composed largely of corals, some of which appear to be in situ and encrusted by coralline algae, forming a framework (Mayall & Cox, 1988).

The Walanae Formation outcrops to the north of the Bone Mountains and in the Walanae Depression. It is lithologies of this formation which form the seal to subsurface reservoirs in the Tacipi Formation. This formation contains abundant volcaniclastic iaterial and consists predominantly of fight grey to grey mudstones with interbedded siltstones, lithic sandstones and occasional thin limestones and tuff beds. The thickness of this formation, on the basis of seismic data, is about 1800 m in the East Sengkang Basin and 3500 m in the West Sengkang Basin (Grainge & Davies, 1985). In the East Sengkang Basin the Walanae Formation can be divided into two parts; a lower interval made up of calcareous mudstones, and an upper interval which is more arenaceous, containing prominent sandstones intervals (Fig. 2a). Much of this material is thought to have been derived form the north (Grainge & Davies, 1985) and close to the Latimojong Mountains, conglomerates containing metamorphic and igneous clasts outcrop (Sukamto, 1982). The Walanae Formation is predominantly Pliocene in age, although the basal mudstone unit may be late Miocene in places (Sukamto, 1982).

KNOLL REEF FACES

The presence of well preserved shallow marine bioclasts and coralgal frameworks in the Tacipi Formation in the Northern Bone Region suggests that deposition occurred within the _photic zone. The shallow-water facies were deposited as isolated build-

57 1

ups which ~ e r c ~ ~ f i 0 0 . 1 1 1

sediments containing abunciant plznktonic forariiiniiera (up to 35% b j volume) were deposited Throughout the Northern Bonz Region hraolbgies of the Tacipi Forlnztion are virtually devoid of vslcaniclastic 01

lithic non-carbon& grams Isolated buildups o f thc Tac ip Formation are therefore inferred to have developed in a11 opea m m a c setting with little L 71 astic input.

The isoiittcd shailcr \ cdxmatl: b d d up$ ax; highly variable in the,; dimensions, although all ale characterised by the ocsiirrence cf coralgal frameworks a d ieef flank dcposnl s Horizontal dimensions ~ w y from 3dQ m (€3. Tanlayola;) to over 5 krn (B Sinn) The vertical thicltaess of the build-iips r a g e s f roa 30 f i ~ t,, 270111 T h t majolity of thc build- ups havr.e a ,imnded C O I ? ~ ex s h q e in veflrcal ~ e ~ t r o n and many sf these are crrcnlar to ellipsrridal II$ plan view (Fig 3 ) PO,I;PY cord a d coralline a l g a arc the principal compments of thye shallo*q 7% rlter depxns

cxilwe M d d k Miocene deposits tend to be dominated by wackestones and wackestonelpackstone @ccdsionlilly intercalated with rudstones, whereas floatstones, packstone, rudstone and framestone textures most commonly occurred in the upper Miocene

r m n a & ,flora: The carbonates in the Northern Bone Region &re dominated by Pon'fes coral (Fig. 4b), coralline algae, planktonic foraminifera and benthonic f o P am i n i f e r a ( C y c I o c l y p e u s , O p e rc u 1 i n a, A mphestigina). Echinoderm plates and sponge spicules fragments are also common in the majority of facies in the Northern Bone Region. Mollusc and I f a h edcr, although present in certain facies, generally occur in very minor amounts. The occurrence of these steriohaiine organisms in the Northern Bone P..cgizn indicates that normal marine conditions preyailed during deposition of the Tacipi Formation.

Litbologies Coralgal bioclastic rudstones, coral hoclastic floatstones, Pontes framestones, bioclastic pacl,stones and bioclastic wackestones are the dominant hthologies in the knoll reefs of the Northern Bone Area (Ascarria, 1997)

L)iqyner;& & porority development' Material, such as corals. which M: as originally composed of aragonite, ha le either been dissolved or replaced by equant s p a y ' calcite cement. In places the resulting brom nidis: pores have been partially or completely rcfiilled b? calcrtc spar. Open biomoldic pores, soinetinics Linked by fractures, are the most abundant t ipe of porosity and may form good permeability n:,ta ~ i l a s 'The riiatm-dissolution parts of the pores :r: :trcgillar iri shape, although the edges of some of t h r bugs art: smooth and relatively rounded (Fig. -LA ti) In s3ine cases matrix dissolution pores can be diffir tklt to distingmh from irregularly shaped b10mol&

Tlr, 'T'aci~i Formation in the Northern Bone Region spa15 tlnc middle Miocene (Tf2-3) to upper Mru,:t ne/lower Pliocene (Tg) There are a number of sdetmis which contain strata of middle to upper Rlrocz~ie age in the region, such as Bulu Anakdara, Bulu h4arm and Bulu Mampote (Fig 3) Other sectrirns range mostly from upper Miocene to lower Ptplii)cc:n0 (Tzg) Carbonate facies in this region can be

572

subdivided into two facies associations on the basls of time and lithologies :

Middle Miocene (Tf2-3) deep water facies with abundant planktonic foraminifera and large thin benthonic foraminifera, which are occasionally interbedded with coralgal bioclastic iudstone.

Upper Miocene-lower Pliocene (Tg) coralgal facies.

Middle Miocene (Tf2-3) deeper water facies

This sequence is composed mainly of deep water, low to moderate energy facies, such as planktonic foraminifera facies, benthonic foraminifera facies and coralgal planktonic foraminifera facies (Ascaria, 1997). These contain abundant planktonic foraminifera and thin, flat forms of large benthonic foraminifera, including Cycloclypeus, Operculina and A mphestigina. The dominant textures are mudstones, wackestones and packstones, although rudstones composed of coralgal material derived from shallow water areas are occasionally present. Textural variations occur on a scale of several metres. For example, there is a change from planktonic foraminifera to coralgal planktonic foraminifera facies, containing more diverse faunal assemblages in the lower part of the Anakdara 1 section and the upper part of the Palongki sections. In the Bulu Anakdara section a change from planktonic foraminifera facies to benthonic foraminifera also occurs over a distance of approximately 10 metres. These variations may be related to changes in water-depth caused by tectonic, autocyclic or eustatic phenomena.

Upper Miocene-lower Pliocene (Tg) codgal facies

This interval is dominated by moderate energy shallow water packstones, floatstones, rudstones and framestones. Facies present consist mainly of coralgal bioclastic facies, coralgal framestone facies and coralgal planktonic foraminifera facies (Ascaria, 1997). These contain abundant Pontes, coralline algae, echinoderm, Amphestigina and molluscs. Towards the tops of the succession, the Pontes form framestones and are commonly encrusted with coralline algae. At the top of the Bulu Mampu section, the coralgal planktonic foraminifera facies changes laterally into a coralgal bioclastic facies, which lacks planktonic foraminifera and includes a framestone texture

(Fig. 5 ) . Locally, there is evidence for subaerial expo sure.

Late Miocene lithologies laterally equivalent to shallow water deposits of the knoll reefs consist of coralgal planktonic foraminifera facies with wackestone or mudstone textures (Ascaria, 1997). These indicate that deeper water depositional environments occurred adjacent to the shallow water knoll reefs.

PALAEOREEONSTRUCIION OF THE NORTHERN BONE REGION

All of the facies in the Northern Bone Region suggest that sedimentation of the Tacipi Formation occurred within the photic zone on knoll-reefs which were surrounded by deep water depositional environments. Figure 6 shows a reconstruction of the knoll-reef build-ups in this area during the Upper Miocene.

Textural, faunal, floral and lithological data constrain the middle Miocene-upper Miocene carbonates of the Northern Bone Region to deposition in low to moderate energy environments. Abundant planktonic foraminifera in middle Miocene deposits suggest that moderately deep water,. open oceanic conditions prevailed over much of this region at this time. The knoll-reef build-ups and reef flank deposits have no preferred orientation and all facies indicate deposition in an open marine unrestricted setting.

The lower contact between carbonates of the Tacipi Formation and the underlying formations (Langi or Camba Formations) is not observed in the Northern Bone Region and precludes an understanding of the initial development of the knoll-reef. No in situ reefs were observed in middle Miocene sections examined in this area. However, the occurrence of coralgal bioclastic rudstones interbedded with planktonic foraminifera packstones of middle Miocene age in the Palongki area indicate that reefal build-ups were present in the area and detritus was reworked from these deposits into the adjacent reef flankhasinal areas. Thus, shallow water areas must have existed, prior to development of upper Miocene knoll-reefs and are probably presently buried in the central portions of some of the exhumed knoll reefs. The reworked detritus indicates that considerable penecontemporaneous erosion was occurring at this stage. The benthonic foraminifera facies is inferred to

573

have been deposited over much of the region, prior to development of the shallow water knoll reef facies. During the middle to upper Miocene, deposition in the inter knoll-reef areas changed from planktonic foraminifera packstones to planktonic foraminifera wackestones. This together with an increase in the proportion of planktonic foraminifera may reflect a further increase in water depth to below the zone of wave action where the energy regime was lower. During this period the growth of knoll-reefs was able to keep pace with the relative rise inosea level. This resulted in a dominantly aggradational system, although there was some progradation at the base of the section. Localised evidence for subaerial exposure occurs in some of the knoll-reef build-ups, although it is not clear if this was caused by emergence during the upper Miocene or later.

The later stage of knoll-reef development is better constrained, due to good exposures in several hills to the north of Anakdara (Bulu Mampu and Bulu Sailong). The sections are composed mainly of Porites and coralline algae which form patch-reefs interbedded with coralgal bioclastic facies, indicating shallow water deposition. In some knoll-reefs the reef flank deposits encircle the build-ups and produce apron deposits which are composed of coralgal bioclastic rudstones (Fig. 6). Reef flank deposits may be relatively thin and interdigitate with planktonic foraminifera mudstone/wackestones, although thicker deposits (up to 20m) also occur.

TERTIARY SUBAERIAL EXPOSURE

In the Northern Bone Region localised reddish coloured irregular surfaces and crystal silts with probable glaebules suggest Tertiary subaerial exposure of some of the shallow water knoll reefs (Bulu Mampu, Bulu Tamapole and Bulu Lanca). A number of factors may have caused subaerial exposure in this region. A utocyclicity, may result in emergence if carbonate sedimentation completely fills the available accommodation space, 'catching-up' with relative sea level; the resulting carbonates are deposited in a very shallow water setting. Alternatively, a global eustatic sea level fall might result in emergence and karstification of shallow carbonate depositional areas, or tectonics, where uplift could result in subaerial exposure.

The probable Tertiary subaerial exposure surfaces in

the Northern Bone Region are localised and cannot be accurately dated. It is unclear whether these surfaces represent one period of widespread emergence or a number of phases of emergence. It is therefore difficult to distinguish whether one or a number of factors influenced emergence of the carbonate succession. In the Southern and Western Bone Regions tectonics controlled sedimentation patterns and therefore may have influenced carbonate development in the Northern Bone Region. The localised occurrence of subaerial exposure suggests that autocyclicity or tectonics controlled emergence. However, the areas affected by emergence in the Northern Bone Region are those which were deposited in shallow water enGironments where relatively minor vertical movements would have resulted in local elevation of facies above sea level. Although the nature and timing of subaerial emergence of the knoll reefs is unclear, subaerial exposure had a strong control on porosity and permeability development and hence reservoir potential of the formation. Freshwater leaching of aragonitic bioclasts resulted in considerable biomoldic porosity (Grainge & Davies, 1985; Mayall & Cox, 1988). Fracturing of partially lithified sediment, which enhanced permeability, may have been partially triggered as a result of emergence (Grainge & Davies, 1985; Mayall & Cox, 1988).

CONTROLS ON KNOLL REEF DEVELOPMENT

The Tacipi Formation was deposited on a regional structural high to the east of the Walanae Graben (Grainge & Davies, 1985; Ascaria, 1997). The late Miocene knoll reefs developed to the north of a shallow water shelf area (Southern Bone Region) where subsidence rates were higher. Many of these shallow water knoll reefs have a north-south trend and their distribution and form may be related to antecedent topography (Grainge & Davies, 1985; Ascaria, 1997). However, the development of the knoll reefs would have been affected by a range of factors including variations in sediment accumulation rate, water circulation or accommodation space. Areas with high antecedent topography, if the conditions were suitable may have allowed the production and accumula$on of shallow water carbonates to keep pace with relative sea level rise. Areas of lower antecedent topography may have been near the base of the photic zone, where carbonate production could not keep pace with relative sea level rise, resulting in drowning and deeper water areas

574

surrounding the knoll reefs. It may be that a minor relative sea level fall allowed the production of shallow water carbonate sediments and caused initiation of knoll reef development. However, outcrop constraints in the Northern Bone Region preclude differentiation of these possible controls on sedimentation and subsequent emergence.

COMPARISON WlTH TME SUBSURFACE

Seismic and well data indicate that subsurface carbonate build-ups developed over a basement high to the east of the deep water area of the Walanae Depression (Fig. 7a; Grainge & Davies, 1985). Middle to late Miocene carbonates unconformably overlie tilted older lithologies (Fig. 7b). Seismic evidence indicates that carbonate development occurred as isolated build-ups with thicknesses reaching up to 700 m. Facies information gained from six wells across the East Sengkang Basin indicates that the lithofacies forming these buildups are comparable with those of outcrops of the knoll reefs in the Northern Bone Region. One of the wells drilled-off the flank of one of the buildups passed through rudstones containing reworked shallow water material. Therefore the buildups are inferred to have been surrounded by slope facies and deeper water depositional environments.

The main diagenetic features in shallow water carbonates from the Kampung Baru field: one of the larger buildups containing about half the hydrocarbon reserves, have been described by Grainge & Davies (1985) and Mayall & Cox (1988). These are :

(i) the extensive freshwater leaching of fossil fragments and the preservation of biomoldic pore space.

(ii) the widespread occurrence of intact micrite envelopes and lack of stylolites, indicating the limestones have not undergone compaction.

(iii) the predominance of blocky calcite cement, suggesting freshwater phreatic zone cementation.

(iv) the rare occurrence of dolomite, which only occurs as a minor replacement of micrite.

Not all of these features have been noted in knoll reefs exposed to the south in the Northern Bone

Region. Outcrop samples from the Tacipi Formation show features (i), rarely (ii) and (iii). No dolomite has been observed in the succession exposed at the surface.

Seismic information, borehole data and outcrop data suggest that during the late middle Miocene to late Miocene the depositional environments in the Northern Bone Region and the East Sengkang Basin were comparable, with the development of isolated knoll reefs surrounded by deeper water. However, in the subsurface an abrupt facies change from shallow water carbonates into deeper water marls indicates drowning of knoll reefs in the East Sengkang Basin. This probably occurred in the late Miocene. In comparison, shallow water production and accumulation of carbonates on the knoll reefs in the Northern Bone Region continued until the early Pliocene. This variation in timing of the drowning of the knoll reefs was caused by higher subsidence rates to the north (Wilson et al., this volume). The timing of 'sealing' of the knoll reefs by overlying deeper water sediments was a critical factor resulting in significant accumulation of hydrocarbons in some of the subsurface build-ups (Wilson et al., this volume).

HYDROCARBON POTENTIAL

Knoll reefs of the Tacipi Formaelon in the subsurface of the East Sengkang Basin comprise effective stratigraphic traps for hydrocarbons. Lconomically significant reserves of dry gas totalling about 0.75 TCF occur at an average depth of 700 m (Grainge & Davies, 1985). The porosity of the limestone in outcrops and subsurface is almost exclusively biomouldic, resulting from the leaching of originally aragonitic bioclasts such as corals and bivalves. Fracturing, possibly related to emergence, has also enhanced permeability. The reservoir quality of the knoll reef carbonates is therefore largely a function of the distribution and abundance of aragonitic elements, the extent to which they have been leached and the subsequent occlusion of the porosity by cementation. Cementation is extensive in certain horizons, these are mainly freshwater phreatic cements and the horizons may represent palaeowater tables (Grainge & Davies, 1983; Mayall & Cox, 1988). Extensive leaching has occurred in the coralgal bioclastic facies.

Measured porosities vary widely, ranging from 5% to 40% but most frequently 20-3r)%; permeabilities are

575

usually less than 100 md (Mayall & Cox, 1988). Porosities and permeabilities are usually best developed in the coralgal facies and reservoirs occur in packstones or rudstones. Potential reservoir lithologies are present in all the knoll reefs studied. However, the actual accumulation of economically important hydrocarbon reserves in knoll reefs of the Tacipi Formation was critically dependant on the time of sealing and hydrocarbon charge (Wilson et al., this volume) .

COMPARJSON WITH OTHER T E R m R Y CARBONATES IN SULAWESI

A thick succession of Eocene to middle Miocene carbonates of the Tonasa Limestone Formation occurs in western South Sulawesi, but no major hydrocarbon accumulations have yet been discovered in these carbonates (Wilson et al., this volume). These carbonates have been compacted under a thick volcaniclastic dominated succession and the formation of burial cements results in little primary porosity preservation. Porosity in carbonates of the Tacipi Formation was mostly secondary, caused by leaching of aragonitic bioclasts during exposure. In comparison, shallow water deposits of the Tonasa Limestone Formation were dominated by large benthonic foraminifera and few aragonitic bioclasts occur. This factor, together with only localised and short periods of emergence of the platform top, resulted in little secondary porosity development (Wilson, 1996). In direct contrast to the Tacipi Formation, shallow water deposits of the Tonasa Limestone Formation have poor reservoir potential and the best reservoir rocks are in redeposited carbonates (Wilson, 1996).

CONCLUSIONS

Carbonates of the Tacipi Formation were produced and accumulated on a relative high to the east of a major fault bounded graben (the Walanae Depression).

During the middle Miocene carbonate facies were deposited towards the base of the photic zone in the Northern Bone Region. In the late Miocene, isolated shallow water knoll-reefs, composed mainly of corals and coralline algae, developed surrounded by deeper water areas. These knoll reefs commonly have a north-south trend, perhaps controlled by antecedent topography, and are dominantly aggradational in nature. Freshwater leaching of aragonitic bioclasts

resulted in considerable biomoldic porosity.

Outcrop constraints, seismic and well data indicate that exhumed knoll reefs, exposed in the Northern Bone Region, are analogous to subsurface buildups in the East Sengkang Basin which contain significant hydrocarbon reserves. Although the depositional and diagenetic setting of the knoll reefs in these two areas are comparable, the timing of drowning varies, with buildups to the north being drowned earlier. The timing of drowning, time and nature of hydrocarbon charge were all critical factors in determining which knoll reefs formed economic hydrocarbon reservoirs. In comparison, shallow water Eocene to middle Miocene carbonates in western South Sulawesi have poor reservoir potential due to a paucity of aragonitic bioclasts, and because they were affected by only localised subaerial exposure. These studies of Tertiary carbonates in Sulawesi have implications for the exploration of hydrocarbons in other SE Asian carbonates.

ACKNOWLEDGMENTS

The authors wish to thank British Petroleum Company who funded this research and the London University SE Asia Research Group who provided additional funding.

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.

Grainge, A.M., and Davies, K.G., 1985, Reef Exploration in East Sengkang Basin, Sulawesi, Indonesian. Marine and Petroleum Geology 2, 142- 155.

Garret, P., Smith, D.L., Wilson, A.O., Patriquin, D., 1971, Physiography, ecology, and sediments of two Bermuda patch reef. Journal Geology, 79/6, 647-668.

Jordan, C.F., 1973, Carbonate facies and sedimentation of patch reefs off Bermuda, American Association of Petroleum Geologists, Bulletin, 57,42- 54.

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Mayall, M.J. and Cox, M., 1988, Deposition and diagenesis of Miocene limestones, Senkang Basin, Sulawesi, Indonesia, Sedimentary Geology, 59,77-92.

Sukamto, R. and Supriatna, S., 1982, Geologi lembar Ujung Pandang, Benteng dan Sinjai quadrangles, Sulawesi. Geological Research and Development Centre, Bandung.

Sukamto, R., 1982, Geologi lembar Pangkajene dan Watampone bagian barat, Sulawesi, Geological Research and Development Centre, Bandung.

Tucker, M.E. and Wright, V.P., 1990, Carbonate Sedimentology; Blackwell Scientific Publications, 482 p.

van Leeuwen, T.M., 1981, The geology of southwest Sulawesi with special reference to the Biru area, In Barber, A.J. and Wiryosujono, S. (eds) The Geology and Tectonics of Eastern Indonesia, Geological Research and Development Centre, Bandung, Special Publication 2, 277-304.

Wilson, J.L., 1975, Carbonate facies in geological history, Springer-Verlag, 471 p.

Wilson, M.E.J., 1996, Evolution and hydrocarbon potential of the Tertiary Tonasa Limestone Formation, Sulawesi, Indonesia, Proceedings of the Indonesian Petroleum Association, 2511 , 227-240.

Wilson, M.E.J. and Bosence, D.W.J., 1996, The Tertiary Evolution of South Sulawesi: A Record in Redeposited Carbonates of the Tonasa Limestone Formation, In Hall, R. and Blundell, D.J. (eds.), Tectonic Evolution of SE Asia. Geological Society of London Special Publication 106, 365-389.

Wilson, M.E.J., Ascaria, A., Coffield, D.Q. and Guritno, N., 1997, The Petroleum System of South Sulawesi, this volume.

Yuwono, Y.S, Bellon, H., Soeria-Atmadja, P. & Maury, R.C., 1985, Neogene and Pleistocene volcanism in South Sulawesi, Proceedings Ikatan Ahli Geologi Indonesia, 14, 169-179.

Yuwono, Y.S, Maury, R.C., Soeria-Atmadja, P. & Bellon, H., 1987, Tertiary and Quaternary geodynamic evolution of South Sulawesi: Constraints from the study of volcanic units, Geologi Indonesia, 13, (I), 32-48.

577

4'5

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FIGURE 1 - Geological map of South Sulawesi. Modified after Sukamto (1982) and Sukamto & Supriatna (1982)

5 78

A

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nd m

easu

red

sect

ion

of B

ulu

Mam

pu a

rea,

sho

win

g ve

rtica

l an

d la

tera

l fac

ies

vari

atio

ns.

onlc

fora

min

fera

mod

el o

f Bul

u M

a ---.--__I_ -_

Cw

atga

i fram

esto

ne

faci

es (p

atch

reef

)

Pla

nkto

nic f

oram

inrfe

ra fa

cres

Cor

al b

rocl

asfic

facr

es

Pat

ch re

ef c

ompl

ex

7 M

udsto

ne C

amba

For

mto

n

Cor

alga

l bio

clas

tic fa

cies

FIG

UR

E 6

- Pa

laeo

reco

nstru

ctio

n of

the

Nor

ther

n B

one

Reg

ion

in t

he u

pper

Mio

cene

, sho

win

g kn

oll-r

eefs

bui

ld-u

ps w

hich

are

sur

roun

ded

by

' de

ep w

ater

. G

ood

late

ral e

xpos

ure

of f

acie

s at

Bul

u A

nakd

ara

and

Bul

u M

ampu

allo

w d

etai

led

reco

nstru

ctio

ns o

f ind

ivid

ual b

uild

- up

s.

v1

OQ

W

LINE

B - 1

(A)

W

c/1

00

P

E

4m

l l

Y,

l

, Y50,

I ,

:OoI

,

I P

o,

, ,

tWI

, ,

Y,

l l

Pol

,

l ,

1 I

l I

, ,

, Yo

, ,

, ,

Z5O

1 I

?OoI

I

I ,

150,

,

, ,

Wes

t Sen

gkan

g B

asin

Ea

st W

alan

ae F

ault

East

Sen

gkan

g B

asin

.

__ .-

----.-

- h

~

5 km

H

OR

IZO

N ID

ENTI

FIC

ATI

ON

G - Pleistocen

elPl

ioce

ne (?

)

F P

Pl

ioce

ne (7

)

LINE

6

- 14

(B)

E - Pliocene

hppe

r Mio

cene

(?)

D _

_t

Top

Mio

cene

Lim

esto

ne (M

id-U

pper

Mio

cene

) C - Ease Mio

cene

Lim

esto

ne (M

id-U

pper

Mio

cene

)

E - lntra upp

er M

ioce

ne (?

) A - Lower M

ioce

ne (?

)

I . .. -

.

Car

bona

te b

ulld

.upe

FIG

UR

E 7a

-

The

E-W

sei

smic

sec

tion

acro

ss th

e Se

ngka

ng re

gion

sho

ws t

wo

type

s of

bas

ins.

A m

ajor

nor

mal

faul

t sep

arat

es th

e Se

ngka

ng B

asin

in

to th

e Ea

st a

nd W

est S

engk

ang

Bas

ins.

Th

e W

est

Seng

kang

Bas

in is

a d

eep

basi

n w

hich

can

be

imag

ed to

mor

e th

an 4 se

c tw

tt.

The

East

Sen

gkan

g B

asin

is r

elat

ivel

y sh

allo

w b

asin

whi

ch c

an b

e im

aged

dow

n to

abo

ut 2

sec

twtt.

FIG

UR

E 7b

-

SE-N

W s

eism

ic li

ne in

the

East

Sen

gkan

g B

asin

sho

win

g sy

n-rif

t an

d po

st-r

ift s

edim

entti

ry su

cces

sion

s. T

he p

ost-r

ift s

edim

enta

ry

rock

s ar

e ch

arac

teris

ed b

y th

e de

velo

pmen

t of

carb

onat

e bu

ild-u

ps o

f the

Tac

ipi F

orm

atio

n.